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Cooperative Research Centre for Contamination Assessment and Remediation of the Environment

Adsorbed organic species on respirable alumina particles

Final reportPrepared for:Department of Environment and ConservationLocked Bag 104Bentley Delivery CentreBentley, WA 6983

By:ChemCentre, Resources and Chemistry PrecinctSouth Wing, Building 500Manning Road,Bentley, WA 6102

CRC CARE Pty LtdBuilding X, University of South AustraliaMawson Lakes, SA 5095

2009

Important NoticeThis proposal is confidential and was prepared exclusively for the client(s) named above for the purpose to which it refers. It is not intended for, nor do we accept any responsibility for its use by, any third party and neither the whole of the document nor any part or reference thereto may be published neither in any document, circular or statement nor in any communication with third parties without our prior written consent.

CRC CARE PROJECT 1-1-01-05/06

Adsorbed Organic Species on Respirable Alumina Particles

Anita D’Angelo, Dave Fleming, Steve Wilkinson, Ewald Swinny, Sasha Kazemi

and Neil Rothnie

ChemCentre

Final Report

Prepared for

CRC CARE Pty Ltd

PO Box 486, Salisbury South, South Australia

2009

Copy for

Department of Environment and Conservation

Locked Bag 104, Bentley Delivery Centre, Bentley, WA, 6983

i

Sponsors

The work described herein has been conducted for:

1. CRC CARE Pty Ltd

PO Box 486,

Salisbury South, SA, 5106

Prof Ravi Naidu

Phone: 08 8302 5041

Fax: 08 8302 3124

e-mail: [email protected]

2. Department of Environment and Conservation

Locked Bag 104,

Bentley Delivery Centre

Bentley, WA, 6983

Mr. John Sutton

Phone: 0417919415 / 08 93337450


ii

Contact Information

Any queries related to the work described herein should be directed to either:

Dr. Steve Wilkinson

Science Business Manager

Emergency Response Section, Investigative Chemistry Laboratory

ChemCentre, Resources and Chemistry Precinct

South Wing, Building 500

Manning Road,

BENTLEY, WA, 6102

Phone: 08 9422 9930

Fax: 08 9422 9801


or

Dr. Neil Rothnie

Chief

Investigative Chemistry Laboratory

ChemCentre, Resources and Chemistry Precinct

South Wing, Building 500

Manning Road,

BENTLEY, WA, 6102

Phone: 08 9422 9892

Fax: 08 9422 9801


Authorising signatures:

Dr Steve Wilkinson Dr Neil Rothnie

iii

Contents

Sponsors i

Contact Information ii

Contents iii

Acknowledgments vi

Publications vii

Project Objectives viii

Executive Summary ix

List of Abbreviations xi

1.0 Background 1

2.0 Materials and Methods 6

2.1 Characterisation of Alumina 6

2.1.1 X-Ray Diffraction 6

2.1.2 Fourier Transform Infrared (FTIR) Analysis 6

2.1.3 Scanning Electron Microscopy (SEM) Analysis 6

2.1.4 Surface Area Analysis 7

2.1.5 Particle Size Distribution and conversion of γ-Alumina from Gibbsite for Adsorption and Desorption Experiments

7

2.2 Development of Methodology to Generate and Contain Dust Clouds of γ-Alumina Particles

8

2.2.1 Design of Dust Chamber 8

2.3 Investigation of the Adsorption and Desorption Properties of γ-Alumina 9

2.3.1 Volatile Organic Compound Gas Standards for Adsorption Experiments

9

2.3.2 Adsorption Experiments 10

2.3.3 Desorption Experiments 11

2.4 Development of Analytical Methodology to Determine Identity and Concentrations of Organic Compounds Adsorbed on and Desorbed from γ-Alumina

11

2.4.1 Thermal Desorption Gas Chromatography Mass Spectrometry (TD-GCMS) Analysis

11

2.4.1.1 Analytical Sample Preparation 11

iv

2.4.1.2 Calibration Standards 12

2.4.1.3 Thermal Desorption Gas Chromatography Mass Spectrometry (TD-GCMS) Analysis

13

2.4.2 Liquid Chromatography Mass Spectrometry (LCMS) Analysis 14

2.4.2.1 DNPH Derivatisation 14

2.4.2.2 Carbonyl-DNPH mixed standard 15

2.4.2.3 LCMS Analysis 16

2.5 Reactions of Polar Volatile Organic Compounds adsorbed onto γ-Alumina 16

2.5.1 Reaction of Benzaldehyde on γ-Alumina 16

2.5.2 Reaction of Acetaldehyde on γ-Alumina 17

2.5.3 Reaction of Propionaldehyde on γ-Alumina 17

2.5.4 Reaction of Benzyl Alcohol on γ-Alumina 17

2.5.5 Reaction of Acetone on γ-Alumina 18

2.6 Investigate the Photochemistry of Selected VOCs adsorbed on γ-Alumina 18

2.6.1 Measurement of Solar Irradiance 18

2.6.2 Determination of the Optimum Distance of the UV Sensors from UV Lamps

18

2.6.3 Reaction of Acetaldehyde on γ-Alumina in the presence of UV radiation

19

2.6.4 Reaction of Acetone on γ-Alumina in the presence of UV radiation 19

3.0 Results and Discussion 20

3.1 Characterisation of Alumina 20

3.1.1 X-Ray Diffraction 20

3.1.2 Fourier Transform Infrared (FTIR) Analysis 21

3.1.3 Scanning Electron Microscopy (SEM) Analysis 21

3.1.4 Surface Area Analysis 22

3.1.5 Particle Size Distribution and Preparation of γ-Alumina from Gibbsite for Adsorption and Desorption Experiments

22

3.2 Development of Dust Chamber 23

3.2.1 Influence of Water Vapour on Dust Cloud 24

3.2.2 Influence of Water Vapour on Adsorption 25

3.2.3 Optimization of Equilibration Time of the Dust Chamber 26

3.3 Investigation of the Adsorption and Desorption Properties of γ-Alumina 26

v

3.3.1 Adsorption and Desorption of Non-Polar VOC’s 26

3.3.1.1 n-Hexane 27

3.3.1.2-Hexene 29

3.3.1.3 Benzene 31

3.3.1.4 Toluene 32

3.3.1.5 o-Xylene 34

3.3.1.6 m-Xylene 35

3.3.1.7 p-Xylene 36

3.3.2 Adsorption and Desorption of Polar VOCs 39

3.3.2.1 Trans-2-Hexenal 40

3.3.2.2 2-Butanone 40

3.3.2.3 Acetophenone 42

3.3.2.4 Acetone 43

3.4 Investigation of reactions of selected polar organic compounds adsorbed on γ-Alumina

45

3.4.1 Benzaldehyde 46

3.4.2 Acetaldehyde 47

3.4.3 TD-GCMS Analysis Versus LCMS Analysis 54

3.4.4 Propionaldehyde 55

3.4.5 Benzyl Alcohol 57

3.4.6 Acetone 58

3.5 The Photochemistry of Selected Polar organic compounds adsorbed on γ-Alumina

60

3.5.1 Measurement of Solar Irradiance 61

3.5.2 Determination of Optimum Distance of the UV sensors from UV lamps

61

3.5.3 Acetaldehyde 63

3.5.4 Acetone 66

4.0 References 73

vi

Acknowledgments

• Our project partner, Department of Environment and Conservation.

• The Emergency Response Section within ChemCentre for providing help and support

throughout the duration of the project.

• The Racing Chemistry Section within ChemCentre for providing analytical advice,

training and access to their LC-MS ion trap.

vii

Publications

1. D’Angelo, A. 2008, Adsorbed Organic Species on Inhalable γ-Alumina Particles.

Submitted as a dissertation in part fulfillment of the requirements for the BSc

Honours degree in Chemistry, Curtin University of Technology, Bentley, Perth.

2. D’Angelo, A., Fleming, D., Wilkinson, S. 2009, Adsorbed Organic Species on Inhalable

γ-Alumina Particles, CASANZ Conference, Perth Convention Centre, WA.

3. Fleming, D., D’Angelo, A., Wilkinson, S. Adsorbed Non-Polar Organic Species on

Inhalable -Alumina Particles. Reviewed by CRC. Submission to Journal on hold

pending project final report review.

4. Fleming, D., D’Angelo, A., Wilkinson, S. Adsorbed Polar Organic Species on Inhalable

-Alumina Particles. In preparation.

5. D’Angelo, A., Fleming, D., Wilkinson, S., Swinny, E., Kazemi, S., Rothnie, N. Reactions

and Photochemistry of Adsorbed Polar Organic Species on -Alumina Particles.

Preparation of short communication pending.

viii

Project Objectives

The project proposal is appended to this report as Appendix 5.1.

The project task timelines are described in Appendix 5.2 which is an extract of the IMAP

project management software.

The objectives of the project are listed below:

1. To characterise alumina dust.

2. To develop methodology to generate and contain dust clouds of dispersed -alumina

particles (dust chamber).

3. To develop analytical methodology for determining identities and concentrations of

organic compounds adsorbed on and desorbed from -alumina dust under controlled

laboratory conditions.

4. To investigate the adsorption and desorption properties of alumina by exposing

dispersed -alumina particles in the dust chamber to selected polar and non-polar

organic compounds, and desorption of these compounds from the alumina particles.

5. To investigate whether selected polar and non-polar organic compounds adsorbed on

-alumina are transformed into new products via surface catalytic reactions.

6. To investigate the photochemistry of selected polar and non-polar organic

compounds adsorbed on -alumina.

ix

Executive Summary

The presence of organic compounds and particulate matter in the atmosphere is

ubiquitous and their health effects in and around industrialised areas of the world are

well documented. The health guidelines of airborne particulate matter are usually based

on the size, quantity and type of substrate, with little or no consideration of organic

and/or inorganic species that may be adsorbed on the surface of the particle. It has been

shown that certain pollutants can become concentrated on airborne particles and

consequently alter the surface chemistry of dust particles. Thus information regarding the

types and concentrations of organic species adsorbed on to particles is important to the

understanding of the mechanisms behind related health problems.

Alumina refining is a multi-billion dollar industry in Western Australia (WA). During the

processing of alumina, numerous volatile organic compounds (VOCs) are produced which

may adsorb onto the alumina surface. Typically, alumina refinery emission levels are

measured separately as either gaseous or particulate matter concentrations and this

exercise does not consider the probability that the emissions may consist of a

combination of both components, whereby these organics may be adsorbed onto the

particulates.

This project characterised the alumina and this was followed by exposing γ-alumina, the

major alumina phase, in a custom designed dust chamber to a range of VOCs for specified

times. Analysis was conducted by thermal desorption gas chromatography (TDGC) and

high performance liquid chromatography (HPLC), both equipped with mass spectrometric

detection (MS). From this work the adsorptive capacity of the alumina particles was

determined under ambient temperature and pressure with VOCs known to be typically

produced by alumina refineries. The VOCs selected included n-hexane, 1-hexene,

benzene, toluene, o-, m- and p-xylene, trans-2-hexenal, 2-butanone, acetophenone,

benzaldehyde, propionaldehyde, benzyl alcohol, acetaldehyde and acetone.

x

Results of the adsorption and desorption studies with n-hexane, 1-hexene, benzene,

toluene, o-, m- and p-xylene, trans-2-hexenal, 2-butanone, acetophenone, benzaldehyde,

propionaldehyde, benzyl alcohol, and acetaldehyde and acetone showed that these VOCs

were adsorbed and retained by γ-alumina for up to 120 minutes.

The reactions of selected polar VOC’s adsorbed on γ-alumina particles were investigated.

Condensation and oxidation products were found to form during the adsorption of benzyl

alcohol, propionaldehyde, acetone and acetaldehyde. The influence of UV light (254 nm

irradiation) on the reactions of acetaldehyde and acetone adsorbed on to γ-alumina was

investigated. The level of the acetaldehyde aldol condensation products appeared to

increase in the presence of UV light. However, project time constraints did not allow for

optimisation of the reaction mixture and product derivatisation techniques, hence the

extraction recoveries were low. Therefore the results of the reaction experiments are at

best qualitative and semi-quantitative.

The results of the experiments done under controlled laboratory conditions clearly

indicated that the organic compounds studied were adsorbed onto γ-alumina.

Additionally it was shown that organic compounds such as benzaldehyde, acetaldehyde,

propionaldehyde, acetone and benzyl alcohol when adsorbed on γ-alumina were

converted into other products. These results provide an opportunity to correlate these

laboratory observations with real-life conditions. It would be reasonable to expect that

under the influence of environmental stimuli such as UV radiation and elevated

temperatures a host of reaction products including mixed condensation products could

be produced.

Further long-term research, including in-source and ambient toxicological studies, will be

necessary before conclusions about human health can be drawn.

xi

List of Abbreviations

α-Al2O3 Alpha alumina

γ-Al2O3 Gamma alumina

θ-Al2O3 Theta alumina

χ-Al2O3 Chi alumina

α-AlO(OH) Disapore

γ-Al(OH)3 Gibbsite polymorph

γ-AlO(OH) Boehmite

H3PO4 Phosphoric acid

HCl Hydrochloric acid

FTIR Fourier Transform infrared red

GCMS Gas chromatography mass spectrometry

HPLC High pressure liquid chromatography

LCMS Liquid chromatography mass spectrometry

MS Mass spectrometry

SEM Scanning electron microscopy

TD Thermal desorption

TD-GCMS Thermal desorption gas chromatography mass spectrometry

VOC Volatile organic compound

UHP Ultra high purity

USEPA United States Environmental Protection Agency

XRD X-ray diffraction

1

1.0 Background

The presence of organic compounds and particulate matter in the atmosphere is

ubiquitous and their health effects in and around industrialised areas of the world are

well documented (Arden Pope III et al 2002; Mazzarella et al 2007). As a consequence,

Health and Environmental Authorities set limits on industrial emissions, focussing

primarily on the quantities of particulate matter and organic compounds released into

the atmosphere. The prescribed limits are derived from the health effects of individual

components.

Apart from the research carried out on diesel and gasoline exhaust emissions (Mazzarella

et al 2007; Parent et al 2007; Reed et al 2008), most work concerning measurements of

hazardous gas and vapour concentrations in the atmosphere has been conducted

independently of airborne particulate matter. This has been the usual approach because

the National Exposure Standards (National Exposure Standards 1995) and Environmental

Standards are largely expressed in this manner. Even with this traditional approach,

airborne particulate matter has often been associated with asthma, bronchitis, chronic

cough, respiratory illness and lung cancer (Arden Pope III et al 2002; Kelly 2003; Bai et al

2007). Several published articles, however, have indicated that significant health effects

can be attributable to toxic organic compounds adsorbed on other particulate matter

apart from those from diesel emissions (Al-Yakoob 1993; Hildemann, Markowski & Cass

1993; Cotham & Bidleman 1995).

As it is now known that the concentration of toxic components on particulate emissions

may exceed those in the gas phase (Ho et al 2009), the potential to adversely affect

human and animal health, and possibly plant life, may be far greater than currently

known. Published literature has shown that in the emissions from many industries organic

species adsorbed on respirable particles affect human health (Mazzarella et al 2007).

Alumina refining is a multi-billion dollar industry in Western Australia (WA). Health

complaints received from the community in areas surrounding certain refineries cannot

2

be explained by data obtained in monitoring programs. Stack emission levels are shown

to be within recommended limits (Environment and Public Affairs Committee 2004;

Coffey et al 2005). Data present in the 2002 Wagerup Refinery Air Emissions Inventory is

evaluated against a time weighted average (TWA) which is defined as the amount a

worker can be exposed to daily without adverse effects (Department of Education,

Employment and Workplace Relations 1995). These TWAs are for exposure over an eight

hour and five day week and cannot be accurately used for evaluation of community

exposure. Stack emission levels are also measured separately as either gaseous or

particulate matter concentrations which do not include the combination of both such as

organics adsorbed onto particulates. One of the main alumina products emitted from the

alumina refinery stacks consists of γ-alumina particulate matter that is produced from

bauxite.

Bauxite is the most common ore of aluminium and is comprised of aluminium hydroxides

of gibbsite polymorph (γ-Al(OH)3), boehmite γ-AlO(OH), disapore α-AlO(OH) and various

other minerals and organics (Wefers & Misra 1987; Kloprogge et al 2006). The gibbsite

polymorph and boehmite are the major constituents of bauxite. Deposits of bauxite

(alumina-rich laterite) in Western Australia are mined at Jarrahdale, Huntly, Willowdale

and Boddington in the Darling Ranges. Seven alumina refineries are currently operated in

Australia with four located in the south west of Western Australia. Refineries are located

in Kwinana, Pinjarra, Wagerup (Coffey & Ioppolo-Armanios 2004) and Worsley, 13

kilometres North West of Collie. In 2006, Western Australia produced 11.6 million tonnes

of alumina accounting for 17 % of global production (Department of Industry and

Resources 2008). The gibbsite polymorph is the major aluminium hydroxide constituent

of bauxite mined in Western Australia.

Gibbsite dehydrates to form aluminium oxide or alumina (Al2O3). Little work has been

done to characterise the dehydration pathway of gibbsite despite it being the primary

product in Western Australia Bayer process refineries. Whittington and Ilievski (2004)

determined the dehydration pathway to occur through χ-Al2O3 using gibbsite (91 µm)

similar to that produced in Bayer process plants as below:

3

γ-Al(OH)3 → χ-Al2O3 → γ-Al2O3 → θ-Al2O3 → α-Al2O3

Adsorption is defined by the International Union of Pure and Applied Chemistry (IUPAC)

as “an increase in the concentration of a dissolved substance at the interface of a

condensed and a liquid phase due to the operation of surface forces. Adsorption can also

occur at the interface of a condensed and a gaseous phase” (McNaught & Wilkinson

1997). Molecules adsorb on a surface via either a physisorption or chemisorption process

and the processes by which adsorption occurs depend on the adsorbing molecule.

Molecules which readily adsorb to the γ-alumina surface are present in alumina refinery

emissions.

Stack emissions from the alumina production process are comprised of particulate

matter, alcohols, aromatics, carbonyl and volatile organic compounds. The 2002 Wagerup

refinery air emissions inventory monitoring program list these compounds to include

toluene, benzene, isomers of xylene, acetaldehyde, acetone, benzaldehyde and

particulate matter sizes ranging from less than 2.5 µm and less than 10 µm (Coffey et al

2005). Many of the compounds in the emissions, including particulate matter, are harmful

if inhaled into the lung.

Numerous studies have shown an increase in cardiovascular disease, decreased lung

function, lung cancer and cardiopulmonary mortality associated with air pollution

particulate matter (Arden Pope III et al 2002; Kelly 2003; Bai et al 2007). In the study by

Arden Pope III et al (2002), exposure to particulate matter less than 2.5 μm showed an

increase of 6 % and 8 % in cardiopulmonary and lung cancer mortality respectively. This

was observed for each 10 μg/m3 increase in particulate matter after taking into account

lifestyle effects such as weight and cigarette smoking.

Particle surface area and hence diameter has also been shown to have a greater effect on

the degree of inflammation, dust translocation and particle clearance from the lung in

comparison to particle solubility or toxicity (Cullen et al 2000). The larger surface area of

4

smaller sized particulate matter results in greater interaction with lung alveoli (Bai et al

2007). Scientific literature suggests that there is a strong association between respirable

size particulate matter with adsorbed organic compounds, and respiratory disease.

Airborne particles of diameter (10 m and less) penetrate into the respiratory system and

whatever chemicals the particles have adsorbed, at their source or from ambient air, are

transported into the body. A greater adverse health effect may occur through the

presence of organics which readily adsorb to particle surfaces. This project aims to

investigate the potential of respirable size alumina particles to adsorb selected organic

chemical species from a gaseous environment and the subsequent desorption of those

compounds.

Particulate matter in the lung may have increased adverse health effects from the

presence of adsorbed organics (Mazzarella et al 2007). Limited work has been carried out

in the area of adsorption of organic species onto mineral dusts, including alumina, where

the literature focuses on the adsorption of trace atmospheric compounds such as SO2

(Fellner et al 2006), NO2 (Lisachenko et al 2007) and ozone (Thomas et al 1997). As trace

atmospheric volatile organic compounds are known to adsorb onto the surface of mineral

dusts (Usher, Michel & Grassian 2003), this may well apply to alumina particles.

Health complaints received around refineries may be correlated to the detection of

refinery odours or enhanced sensitivity of some community members to refinery

chemicals (Donoghue & Cullen 2007). An individual’s sensitivity and response has been

linked to their perception of the chemical hazard and variables such as age, gender or

exposure history (Dalton 2003). Luginaah et al (2002) observed a strong relationship

between the reporting of adverse health effects and odour perception. The reporting of

adverse health effects was also linked to an individual’s annoyance at refinery emissions

believed to cause adverse health effects.

Little work has been conducted on absorbed organic species on respirable alumina

particles and this project has the potential to address this knowledge gap. For

experimental reasons the size fraction 38 – 52 µm was used in this study rather than size

5

fraction 10 µm. With the development of new techniques we recommend that there is

scope for similar work done in this study to be repeated using the 10 µm size fraction.

6

2.0 Materials and Methods

2.1 Characterisation of Alumina

Gibbsite (C33 alumina hydrate) was sourced from the Alcoa World Alumina Australia

Wagerup refinery in Western Australia. Characterisation of alumina was achieved by XRD,

FTIR and surface area analysis. Images of the γ-alumina particles were obtained by SEM.

2.1.1 X-Ray Diffraction

Samples were prepared for analysis using the ‘backpack’ method. Alumina samples (3 g)

were ground with acetone (Honeywell Burdick and Jackson, > 99.99 %) three times and

heated (100 °C) to remove acetone. The dried samples were assembled into backpack

discs for analysis on a Philips Generator (PW 1830) using instrument method ‘SCAN’.

2.1.2 Fourier Transform Infrared (FTIR) Analysis

Samples of gibbsite, γ-alumina (gibbsite heated to 900 °C) and α-alumina (gibbsite heated

to 1200 °C) were analyzed on a BIORAD Excalibur Series (FTS 3000MX) with a DTGS

(deuterated triglycine sulphate) detector using the transmission accessory. The resolution

was 4 cm-1 with 16 scans obtained. Samples were mixed with KBr and pressed to form a

disk for analysis. Sample spectra were consistent with literature spectra (Wefers & Misra

1987).

2.1.3 Scanning Electron Microscopy (SEM) Analysis

Particles were deposited on an aluminium stub using carbon tape and carbon coated

before placement in a CamScan CS3200LV SEM coupled to an Oxford INCAx-sight x-ray

detector (model 7788). Images were taken of a ‘typical’ γ-alumina particle with the

secondary electron detector and beam acceleration voltage of 25 kV using thermionic

emission.

2.1.4 Surface Area Analysis

Surface area analysis was carried out by CSIRO Division of Minerals Particle Analysis

Service, Waterford, Western Australia. The 38 – 52 µm fraction of gibbsite was thermally

converted to χ-alumina, γ-alumina, and α-alumina. A sample of α-alumina (product no.

7

342726, Sigma-Aldrich) was purchased and this together with the final thermally

produced alumina products described above (obtained from Alcoa World Alumina,

Wagerup) were analysed by CSIRO (Division of Minerals, Particle Analysis Service,

Waterford Western Australia) for surface area analysis using the BET (Brunauer, Emmett

and Teller) method. The surface areas of the samples were obtained on a TriStar 3000

using nitrogen and an analysis bath temperature of 77.35K.

2.1.5 Particle Size Distribution and conversion of γ-Alumina from Gibbsite for

Adsorption and Desorption Experiments

It was initially envisaged that an alumina particle size range averaging 10 m in diameter

(PM10) would be used for the adsorption and desorption experiments because this

particle size represents the upper end of the respirable range. The reasoning for this was

that deposition of PM10 is known to occur in the tracheobronchial and alveolar regions of

the lower respiratory system. The larger surface area of smaller sized particulate matter

results in greater interaction with lung alveoli (Bai et al 2007). Additionally, it was decided

that uniformity of particle size would be preferred, as opposed to using a range of particle

sizes, as this would remove one variable parameter in the study. To isolate PM10,

sedimentation trials were carried out to initially separate different sized particles.

Gibbsite (2 g) was added to deionised water (100 mL). After 10 minutes the suspension

was confirmed, using optical microscopy, to contain particles < 10 m in diameter. The

suspension was discarded and the sediment was found to contain particles greater than

or equal to 10 m in diameter. It was concluded that sedimentation would be a viable

technique if required.

Sieving (10 m and 20 m) trails were also carried out using a woven (nylon, Milipore)

filter with water washing. These were successful. In addition, sieving with water was

found to not change the surface characteristics of the alumina (C. Armanis [Alcoa World

Alumina] pers. comm., 19 June 2006).

Another separation trial was conducted using a glass column with nitrogen blown in

through the bottom. Particles were separated however this technique had poor and

variable yields.

8

Eventually the gibbsite was dry sieved using sieves 38, 53, 63 and 75 µm. The range 38 –

52 µm was chosen for adsorption and desorption experiments as this represented the

smallest size that could be accurately sieved. The sieved gibbsite was converted to γ-

alumina by heating to 900 °C. This γ-alumina was used for the adsorption and desorption

experiments.

2.2 Development of Methodology to Generate and Contain Dust Clouds of γ-Alumina

Particles

The method development in this part involved the design and manufacture of a suitable

dust chamber that could be used to expose the alumina dust clouds to the polar and non-

polar organic compounds. This chamber was modified for the UV experiments. Other

parameters which were taken into account included the effect of water vapour on the

dust cloud and the consequent influence on adsorption and desorption.

2.2.1 Design of Dust Chamber

A dust chamber was successfully designed, prepared and tested for the generation of a

suspended dust cloud. The dust chamber was designed to replicate exposure of

particulate matter to a VOC atmosphere in a manner analogous to that which may occur

in areas surrounding alumina refineries. The design enabled γ-alumina particles (38 – 52

µm) to be exposed equally to a vapour of selected VOC and permitted adsorption to occur

whilst particles were airborne.

The glass dust chamber was connected to a dynamic dilution instrument (Entech

Instruments dynamic diluter, model 4600A) that delivered sufficient gas flow to generate

a stable cloud of γ-alumina particles (38 – 52 µm). In addition, the dynamic diluter

allowed VOC standards (100 ppm) to be diluted with humidified UHP nitrogen (99.999 %,

BOC Sydney Australia) before entry into the dust chamber at a known concentration (3

ppm).

To achieve a stable dust cloud, a number of devices necessary for the satisfactory

introduction and delivery of γ-alumina particles to the dust chamber were tried. The most

9

successful type was in the form of a glass “U” tube having a partial bore constriction at

the bottom of the “U” section. Before adsorption and desorption experiments

commenced, γ-alumina was placed in the constricted channel of the U-bend. When the

line from the dynamic diluter was connected, a dust cloud of alumina was created and

this cloud was exposed to the VOC vapour.

This device allowed an amount of γ-alumina (38 - 52µm) sample (0.3g) to be efficiently

transformed into a dust cloud when the delivery gas from the dynamic diluter to the dust

chamber was turned on (at 1.5 L/min). The dust chamber was considered to be an

efficient dust generator because no settling or agglomeration of particles was observed

during generation of the dust cloud. Humidification was considered necessary to avoid

particles adhering to the sides of the dust chamber as a result of electrostatic effects.

2.3 Investigation of the Adsorption and Desorption Properties of Alumina

2.3.1 Volatile Organic Compound Gas Standards for Adsorption Experiments

The VOCs selected were those known to be present in typical refinery stack emissions and

the concentrations selected for use were based on typical stack emission measurements

(Coffey et al 2005). NATA certified gas standards of n-hexane (103 ppm ± 2 ppm),

benzene (101 ppm ± 2 ppm) and toluene (97.2 ppm ± 1.9 ppm) with ultra high purity

(UHP) nitrogen (99.999 %) make up gas were purchased from BOC Scientific (Sydney,

Australia). Liquid o-xylene (98 %, Sigma), m-xylene (> 99 %, Sigma), p-xylene (≥ 99 %,

Sigma), propionaldehyde (97 %, Aldrich), 2-butanone (99 %, Lancaster), benzaldehyde (≥

99 %, Merck), acetophenone (≥ 98 %, Merck), benzyl alcohol (≥ 97 %, Unilab), trans-2-

hexenal (98 %, Aldrich), 1-hexene (99 %, Sigma-Aldrich), acetone (Honeywell Burdick and

Jackson, > 99.99 %) and acetaldehyde (Fluka, ≥ 99.5 %) were used to produce gas

standards of compounds not obtainable as gas standards from BOC Scientific. These gas

standards were prepared from the liquid compounds by injecting approximately 18 µL of

the liquid compound into a 104 L cylinder and pressurising it to approximately 600 psi

with UHP nitrogen. Accurate concentrations of o-xylene, m-xylene and p-xylene standards

prepared were determined by GCMS according to USEPA method TO14A with

propionaldehyde, 2-butanone and benzaldehyde determined by HPLC according to USEPA

10

method TO11A (US EPA 1999). VOC gas standards were used in both adsorption and

desorption experiments.

2.3.2 Adsorption Experiments

The γ-alumina (0.3 g) was exposed in a dust chamber (figure 1) to an atmosphere of VOC

gas standard for time intervals of 2, 5, 10, 30, 60 and 120 minutes in the presence of

water vapour. VOC gas standard concentrations were prepared at approximately 100

ppm in UHP nitrogen and further diluted to approximately 3 ppm using an Entech

Instruments dynamic diluter, model 4600A. All results were normalised to 3 ppm.

The average concentration of water vapour delivered by the dynamic diluter was

determined by measurement with a photoacoustic multi-gas analyser (Filter SB 0527,

Brüel & Kjær type 1302) and was found to be an average of 4000 ppm between 20 – 24°C.

The average laboratory temperature in which all experiments were undertaken was 22 °C.

Diluent (N 2 )

Dynamic Diluter

Dust Chamber

VOC

Figure 1: Schematic of dust chamber used in adsorption and

desorption experiments.

11

2.3.3 Desorption Experiments

Organic compounds were adsorbed onto γ-alumina (2.4 g) by exposure to a VOC

atmosphere for 15 minutes in the absence of water vapour to maximise the amount of

VOC adsorbed. A portion (0.3 g) of this γ-alumina was added to the dust chamber and

adsorbed VOCs were desorbed with UHP nitrogen in the presence of water vapour (4000

ppm) for time intervals similar to those in adsorption experiments.

2.4 Development of Analytical Methodology to Determine the Identity and

Concentrations of Organic Compounds Adsorbed on and Desorbed from Alumina

Thermal desorption gas chromatography mass spectrometry (TDGCMS) and liquid

chromatography mass spectrometry (LCMS) analytical methods were developed to

identify and quantify the VOCs adsorbed on the γ-alumina. These methods are described

below.

2.4.1 Thermal Desorption Gas Chromatography Mass Spectrometry (TD-GCMS) Analysis

2.4.1.1 Analytical Sample Preparation

Glass thermal desorption TD tubes were packed in-house with Tenax TA (80/100 mesh,

Grace Division Discovery Sciences) between two sections of glass wool (silanised). A metal

‘alpha’ clip was used at one end of the TD tube to ensure contents did not shift during the

analytical desorption step. In initial trials, to transfer alumina exposed to organics to the

TD tube, one section of the glass wool was removed and the alumina (0.1 g) added.

Losses of the adsorbed organics through desorption were observed. A modified design

involved transferring the alumina sample to the TD tube after removing one section of

the glass wool and approximately half of the Tenax TA. The portion of the Tenax TA that

was removed was added back into the TD tube followed by the glass wool. Alumina

packed in between two sections of Tenax TA ensured desorbing organics were trapped by

the Tenax TA. The Tenax TA segment in the tube was found to be necessary as it

prevented loss of adsorbed organic compounds from the alumina during an initial

nitrogen purge prior to the thermal analysis segment of the method. Eventually the

optimised procedure involved the following preliminary steps. Prior to use, 50 mg of

Tenax TA (80/100 mesh, Grace Division Discovery Sciences), cleaned using methanol (≥

12

99.7 %, Ajax Finechem) in a Soxhlet apparatus (5 hr), was added to a 0.6 cm O.D. × 8.9 cm

length glass TD tube (Supelco, part no. 25084). Prior to use TD tubes were cleaned by

thermal desorption and weighed.

After exposure to the VOC vapour in the dust chamber, the γ-alumina (0.01 g) was added

to a TD tube between two sections of Tenax TA. Three sample TD tubes were prepared

for each time interval. TD tubes were then weighed to determine the amount of γ-

alumina added. For each set of adsorption and desorption experiments, five calibration

standard TD tubes were prepared and analysed. To prepare the TD tube calibration

standard, a tube was injected with 3 µL of one of the five liquid working standards (1A to

5A). This was repeated with the remaining standards. Each TD tube containing a γ-

alumina sample was injected with 3 µL of the prepared internal standard. VOCs present

on the γ-alumina from adsorption and desorption studies were quantified using TD-

GCMS.

2.4.1.2 Calibration Standards

For each non polar VOC used in adsorption and desorption studies five stock standards (1

to 5) of approximately 5, 50, 130, 260 and 520 ng/µL were prepared in methanol (≥ 99.7

%, Ajax Finechem). Polar VOC standards were prepared in higher concentrations than

those used for the non polar VOCs as they adsorbed at higher levels to the γ-alumina. For

each polar VOC, stock standards (1 to 5) of approximately 50, 130, 260, 520 and 1050

ng/µL were prepared in methanol.

Five working non polar VOC standards (1A to 5A) were prepared from each of the five non

polar VOC stock standards where, 1 g of non polar VOC stock standard (1 to 5) was added

to 1 g of deuterated toluene (toluene-d8) (Toluene-d8 was purchased from Aldrich, catalog

no. 26958-9) and 1 g methanol (table 1). The toluene-d8 was used as an internal standard

and was prepared at a concentration of 25 ng/µL in methanol.

13

Table 1: Non polar and polar VOC stock standard concentrations and working VOC standard preparation

Non Polar VOC Standard

Stock Standard Number

1 2 3 4 5

Concentration (ng/µL)

5 50 130 260 520

Added to 1g of Each Non Polar VOC Standard

1 g toluene-d8(25 ng/µL in methanol)

1 g methanol

Working Non Polar VOC Standard

1A 2A 3A 4A 5A

Polar VOC Standard

Stock Standard Number

1 2 3 4 5

Concentration (ng/µL)

50 130 260 520 1050

Added to 1g of Each Polar VOC Standard

1 g toluene-d8(25 ng/µL in methanol)

1 g methanol

Working Polar VOC Standard

1A 2A 3A 4A 5A

Five working polar VOC standards (1A to 5A) were prepared from each of the five polar

VOC stock standards where, 1 g of polar VOC stock standard (1 to 5) was added to 1 g of

deuterated toluene and 1 g methanol. As the concentration of the compounds in the

working standard are diluted by three from the addition of toluene-d8 and methanol,

when 3 µL of one of the five working standards (1A to 5A) was injected onto a TD tube,

the amount on the TD tube was equal to that of the initial stock standard (standard 1 to

5). An internal standard was prepared with 1 g of toluene-d8(25 ng/µL in methanol) and 2

g methanol so that when 3 µL was injected onto a TD tube, the amount on the TD tube

was 25 ng.

2.4.1.3 Thermal Desorption Gas Chromatography Mass Spectrometry (TD-GCMS)

Analysis

Samples were injected onto the column using a Perkin Elmer ATD 400 thermal desorber.

TD tubes were dry purged for 1 minute. Desorption was achieved at a pressure of 35 kPa

with a valve temperature of 200 °C. Tubes were primary desorbed at 270 °C at a flow of

50 mL/min for 10 minutes into a secondary trap held for 10 minutes at a temperature of -

10 °C. On completion of the primary desorption the secondary trap was heated to 270 °C

14

to transfer the sample onto the GCMS via a transfer line at 220 °C. No inlet split was

utilised.

Gas chromatographic mass spectrometric (GCMS) analyses were performed using a

Varian Saturn 2000 MS/MS interfaced to a Varian CP3800 gas chromatograph. A Zebron

Phenonemex 30 m × 0.25 mm i.d. fused silica capillary column coated with a 0.5 µm, 5 %

phenyl – 95 % dimethylpolysiloxane (ZB-5MSi) stationary phase (part no. 7HG-G018-17)

was used to carry out the separation. The oven was programmed from 30 °C to 250 °C at

10 °C/min with an initial and final hold time of 5 minutes. Helium was used as the carrier

gas with a column pressure of 15 psi.

2.4.2 Liquid Chromatography Mass Spectrometry (LCMS) Analysis

2.4.2.1 DNPH Derivatisation

Several attempts were made at derivatising using various derivatisation techniques

including DNPH Sep-Pak cartridges. Eventually it was decided to employ a modification of

a method previously published in the literature (Saczk et al 2005).Development of this

modification started with a first phase trial without γ-alumina. An acetaldehyde standard

(1510 µg/mL) was prepared in methanol (≥ 99.7 %, Ajax Finechem) and injected into

DNPH solution (900 µL, 0.4 % in acetonitrile). Phosphoric acid,H3PO4 (50 µL, 1 mol/L) was

added and the samples were sonicated (20 min) before analysis by LCMS (APCI).

Recoveries were acceptable (table 2).

Table 2: Acetaldehyde derivatisation recoveries (no γ-alumina) using published method (Saczk et al 2005).

Sample No. Description Recovery

(%)

/001 500 µL inject 90

/002 400 µL inject 100

/003 200 µL inject 111

/004 100 µL inject 109

/005 50 µL inject 111 /006 10 µL inject 106 /007 5 µL inject 113

15

γ-Alumina was then incorporated into the next stage of the derivatisation method

development. This derivatisation method was used for all trials hereafter. The

acetaldehyde standard (1510 µg/mL) was injected onto γ-alumina (approx. 0.1 g), DNPH

solution was added followed by H3PO4. Samples were sonicated (30 min) before passing

through a C18 Sep-Pak. C18 Sep-Paks were pre-conditioned (10 mL) with acetonitrile (10

mL) and eluted with acetonitrile (10 mL). The filtrate was evaporated to dryness and

reconstituted with acetonitrile (1 mL) before filtration through a nylon filter (0.45 µm,

Alltech) for analysis by LCMS (APCI).

Recoveries were low (table 3) and attributed to prolonged sample handling. Due to

project time constraints it was not possible to continue with efforts to optimise this

method and it was decided to use this method for the work-up of the reaction mixture in

the adsorption and desorption experiments of acetaldehyde and acetone and the UV

studies.

Table 3: Recovery of acetaldehyde after extraction, derivatisation and C18 Sep-Pak filtration

Sample No. Description Recovery

(%)

/001 500 µL inject 31

/001 500 µL inject repeat 40

/002 400 µL inject 28

/003 200 µL inject 47

/004 100 µL inject 41

/005 50 µL inject 38



/008 DNPH Blank < 1

2.4.2.2 Carbonyl-DNPH mixed standard

For identification and quantification of the acetaldehyde and crotonaldehyde derivatives

a carbonyl-DNPH mixed standard (Supleco, part no. 47672-U) was purchased and this

contained derivatised acetaldehyde and crotonaldehyde as analysed by LCMS.

16

2.4.2.3 LCMS Analysis

Separations were performed on a Zorbax SB-C18 RRHT 4.6 × 150 mm × 1.8 µm (PN

829975-902) analytical column at a flow rate of 1 mL/min from 65 % acetonitrile/35 %

ammonium formate (10 mmol, pH 3) which was initially held for 6 minutes then increased

to 100 % acetonitrile within 1 minute. An ion trap system (Agilent 1100 LC/MSD Trap) was

used in atmospheric pressure chemical ionisation mode. Negative ions were detected

(APCI(-)). Samples were introduced into the MS using a nebuliser pressure of 60 psi and a

drying gas flow of 5 L/min at 350 °C. The APCI vaporiser temperature was 400 °C with a

corona current of 20 000 nA and capillary voltage of 3500 V.

2.5 Reactions of Polar Volatile Organic Compounds Adsorbed onto Alumina

The reactions of benzaldehyde, acetaldehyde, propionaldehdye, benzyl alcohol and

acetone on alumina were investigated. All these compounds, except benzyl alcohol, are

carbonyl compounds and can be derivatised with DNPH. Additionally the corresponding

aldol condensation carbonyl products may also be derivatised with DNPH. It was

predicted that it was likely that benzyl alcohol would be converted to benzaldehyde and

this could be derivatised with DNPH.

2.5.1 Reaction of Benzaldehyde on Alumina

γ-Alumina (2 g, 38 – 52 µm) was exposed in a dust chamber to an atmosphere of

benzaldehyde for 60 minutes in the presence of water vapour (4000 ppm). A

benzaldehyde concentration was prepared at 100 ppm in instrument air (BOC, Australia)

and further diluted to 10 ppm using a dynamic diluter, model 4600A. After exposure to

the benzaldehyde , carbonyls adsorbed on γ-alumina were derivatised with DNPH.

The γ-alumina (1 g) exposed to the benzaldehyde was added to DNPH solution (20 mL)

and sonicated (30 min). Derivatised carbonyls that were present were extracted three

times (10 mL) with 70:30 % hexane (≥ 99.5 %, Mallinckrodt Chemicals)/dicloromethane (≥

99.9 %, Burdick and Jackson), and evaporated to dryness. Derivatised carbonyls were

reconstituted in acetonitrile (2 mL) and filtered (0.45 um, nylon) before analysis.

17

2.5.2 Reaction of Acetaldehyde on Alumina

The γ-alumina (0.3 g) was exposed in a dust chamber to an atmosphere of acetaldehyde

for time intervals of 2, 5, 10, 30, 60 and 120 minutes in the presence of water vapour. An

acetaldehyde concentration was prepared at approximately 100 ppm in UHP nitrogen and

further diluted to approximately 3 ppm using a dynamic diluter. All results were

normalised to 3 ppm. After exposure to the acetaldehyde , carbonyls adsorbed on γ-

alumina were derivatised with DNPH solution and this was followed by LCMS analysis.

2.5.3 Reaction of Propionaldehyde on Alumina

When investigating the adsorption characteristics for propionaldehyde, γ-alumina (0.3 g)

was exposed in a dust chamber to an atmosphere of propionaldehyde for time intervals

of 2, 5, 10, 30, 60 and 120 minutes in the presence of water vapour. A propionaldehyde

concentration was prepared at approximately 100 ppm in UHP nitrogen and further

diluted to approximately 3 ppm using a dynamic diluter. Samples were analysed by TD-

GCMS and all results were normalised to 3 ppm. These results were primarily used to

determine the adsorption profile of propionaldehyde. At a later stage of the project, the

TDGCMS chromatograms were re-examined. An extracted ion chromatogram showed the

presence of a peak and the mass spectrum indicated that this peak represented the

propionaldehyde aldol condensation product, 2-methyl-2-pentanal. The identity of this

peak was confirmed to be 2-methyl-2-pentanal by comparison against an authentic

standard. Because this compound was only noticed at a later stage of the project, this

product was not quantified. Time constraints did not allow repeat of the adsorption

experiments.

2.5.4 Reaction of Benzyl Alcohol on Alumina

The γ-alumina (0.3 g) was exposed in a dust chamber to an atmosphere of benzyl alcohol

for time intervals of 2, 5, 10, 30, 60 and 120 minutes in the presence of water vapour. A

benzyl alcohol concentration was prepared at approximately 100 ppm in UHP nitrogen

and further diluted to approximately 3 ppm using a dynamic diluter. Samples were

analysed by TD-GCMS and all results were normalised to 3 ppm.

18

2.5.5 Reaction of Acetone on Alumina

The γ-alumina (0.3 g) was exposed in a dust chamber to an atmosphere of acetone for

time intervals of 2, 5, 10, 30, 60 and 120 minutes in the presence of water vapour. An

acetone concentration was prepared at approximately 100 ppm in UHP nitrogen and


normalised to 3 ppm. Acetone and the corresponding aldol condensation products

diacetone alcohol (4-hydroxy-4-methyl-2-pentanone, 99 %, Aldrich) and mesityl oxide (>

97 %, Merck) were purchased from Sigma Aldrich.

2.6 Investigation of the Photochemistry of selected VOCs adsorbed on Alumina

In preparation for photochemistry studies of organics adsorbed to γ-alumina particulate

matter, experiments were undertaken in order to determine the optimum placement of

the UV lamps relative to the dust chamber. The first experiment included the initial

determination of irradiance generated by the sun at 254 nm, 310 nm and 365 nm. This

was followed by attempting to replicate the results in the laboratory through changing

the distance between the respective ultraviolet (UV) sensors (254 nm, 310 nm, 365 nm)

and UV lamps (254 nm, 302 nm, 365 nm).

2.6.1 Measurement of Solar Irradiance

The solar irradiance at 254 nm, 310 nm and 365 nm was measured outside the

Emergency Response Section at ChemCentre, East Perth on the 2nd December 2008. The

temperature was approximately 31 °C with no cloud cover. For measurements, each

sensor was initially zeroed and the irradiance measured at the range switch position 200

μW/cm2. Irradiance was too great to be measured in this range and was then measured

at the range switch position 2000 μW/cm2 or 20 mW/cm2. Measurements were made

where the sensor was placed both inside and outside of the quartz dust chamber.


The distances between each of the UV sensors to the UV lamps were adjusted to mirror

the initial solar irradiance readings recorded previously. The results obtained were used

to determine the distance between the UV lamps and the dust chamber. All

19

measurements were taken in a fume hood modified with a poly-cover to prevent any light

leakage either internally or externally. Each UV sensor at 254 nm, 310 nm and 365 nm

was individually placed at measured distances from its respective UV lamp emitting at

254 nm, 302 nm, and 365 nm until the measured UV irradiance mirrored the initial solar

readings.

2.6.3 Reaction of Acetaldehyde on γ-Alumina in the presence of UV radiation

The γ-alumina (0.3 g) was exposed in a dust chamber, in the presence of UV radiation, to

an atmosphere of acetaldehyde for 120 minutes in the presence of water vapour. An



normalised to 3 ppm. After exposure to the acetaldehyde, carbonyls adsorbed on γ-

alumina were derivatised with DNPH and this was followed by LCMS analysis. A similar

experiment was done in the absence of UV.

2.6.4 Reaction of Acetone on γ-Alumina in the presence of UV radiation

The γ-alumina (0.3 g) was exposed in a dust chamber, in the presence of UV radiation, to

an atmosphere of acetone for 120 minutes in the presence of water vapour. An



normalised to 3 ppm. After exposure to the acetone , carbonyls adsorbed on γ-alumina

were derivatised with DNPH and this was followed by LCMS analysis. A similar experiment

was done in the absence of UV.

20

3.0 Results and Discussion

3.1 Characterisation of Alumina

3.1.1 X-Ray Diffraction

XRD analysis confirmed that the sample was gibbsite polymorph (γ-Al(OH)3) as shown in

figure 2. XRD analysis of the gibbsite showed the presence of a dominant phase of γ-

alumina and a minor α-alumina phase. Heating the sample to 400 °C produced boehmite

and heating to 900 °C produced γ-alumina as shown in figure 3 and 4 respectively.

Figure 2: XRD pattern of gibbsite (C33) obtained from Alcoa World Alumina, Wagerup.

Figure 3: XRD pattern of gibbsite heated to 400 °C (boehmite).

21

Figure 4: XRD pattern of gibbsite heated to 900 °C (γ-alumina).

3.1.2 Fourier Transform Infrared (FTIR) Analysis

Gibbsite spectra were consistent with literature spectra (D. Fleming [Department of

Petroleum and Mines] pers. comm., 27 April 2010), Wefers & Misra 1987).

3.1.3 Scanning Electron Microscopy (SEM) Analysis

Fig 9 shows a ‘typical’ γ-alumina particle used in this study for both adsorption and

desorption work that was obtained through gibbsite (C33)1 dehydration. The particle is

shown to have an approximate diameter of 50 μm and is an aggregate of smaller flat,

tablet and hexagonal-shaped particles that increase the γ-alumina surface area to which

organics adsorb.

Figure 5: SEM image of 'typical' γ-alumina particle.

1 Reference standard used by Alcoa World Alumina.

22

3.1.4 Surface Area Analysis

The results obtained from surface analysis of the various phases are listed in table 4

below.

Table 4: Summary of the surface area of various alumina phases obtained using the BET method (CSIRO).

Phase Surface Area (m2/g)

Gibbsite 0.31 ± 0.00

Boehmite 252.88 ± 5.70

χ-Alumina 171.70 ± 1.56

γ-Alumina 38.00 ± 0.36

α-Alumina 0.24 ± 0.00

α-Alumina Purchased 0.2581 ± 0.0005

Final Product 63.05 ± 0.50

3.1.5 Particle Size Distribution and Preparation of γ-Alumina from Gibbsite for

Adsorption and Desorption Experiments

In the early stage of this work, an investigation was done to establish the particle size

distribution of the γ-alumina that could be produced by conversion of the gibbsite to γ-

alumina. To do this a portion of gibbsite was converted to γ-alumina (by heating) and a

particle size distribution was obtained by weighing the different fractions obtained by

sieving the γ-alumina. This particle size distribution is shown below in figure 6. Following

these observations it was decided to sieve the gibbsite first to a 38 – 52 µm size and then

convert this fraction to γ-alumina. This was then used in adsorption and desorption

experiments.This represented the smallest size that could be accurately sieved.

23

0

5

10

15

20

25

30

35

40

45

50

200 150 100 60 40 < 38

We

igh

t (%

of

Tota

l)

Fraction Diameter (μm)

Figure 6: γ-Alumina particle size distribution.

Various transition phases including γ-alumina are known to form through heating gibbsite

(Levin, Gemming & Brandon 1998; Paglia et al 2004). To obtain γ-alumina, the gibbsite (20

g, 50 μm) was heated to a range of temperatures between 400 °C and 1000 °C. XRD

analysis of gibbsite heated to 400 °C showed it was converted to boehmite (γ-AlO(OH)).

Heating to 600 °C produced χ-alumina, 900 °C formed γ-alumina and temperatures

greater than 1000 °C formed α-alumina. In addition, it was found that heating was found

did not change the surface characteristics of the alumina (C. Armanis [Alcoa World

Alumina] pers. comm., 19 June 2006). For the purposes of our experiments in this study,

Gibbsite was converted to γ-alumina by heating to 900 °C. This γ-alumina was used for

the adsorption and desorption experiments.

3.2 Development of Dust Chamber

A dust chamber was successfully developed and this was used to conduct the adsorption

and desorption experiments. Figure 7 shows a picture of the dust chamber connected to

U-bend that in turn was connected to the dynamic diluter.

24

Figure 7: Dust chamber containing alumina used in adsorption and desorption experiments.

3.2.1 Influence of Water Vapour on Dust Cloud

Initial dust creation trials were carried out without the presence of water vapour in the

dust chamber. γ-Alumina (200 µm) was placed in the U-bend constriction of the dust

chamber and UHP nitrogen passed through at a rate of 1 – 2 mL/min. Significant

electrostatic problems arose as particles adhered to the inner surface of the dust

chamber. In a subsequent attempt γ-alumina (200 µm) was placed in the U-bend

constriction of the dust chamber and UHP nitrogen was passed through a humidifier

attached to the dynamic diluter. This solved the problem as particles did not adhere to

the inner surface of the dust chamber. Smaller particle diameter γ-alumina (20 µm) were

then trialled in the dust chamber using humidified UHP nitrogen and some particles

(approx. < 1 %) were found to adhere. These though were removed if the dust chamber

was lightly tapped and it was concluded that they would have an insignificant effect on

future experiments.

25

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

0 5 10 15 20 25 30

Wat

er

Vap

ou

r C

on

cen

trat

ion

(p

pm

)

Temperature (°C)

Figure 8: Concentration of water vapour delivered by the dynamic diluter as a function of temperature.

Water vapour levels delivered by the dynamic diluter varied as a function of temperature.

The concentration of water vapour delivered by the dynamic diluter was measured in the

range of 0 – 25 °C using a photoacoustic multi-gas analyser (Filter SB 0527, Brüel & Kjær

type 1302) as shown in figure 8.

3.2.2 Influence of Water Vapour on Adsorption

It was hypothesized that adsorption of VOCs on γ-alumina would be influenced by the

concentration of water vapour delivered by the dynamic diluter to the dust chamber

(figure 9). To investigate this toluene (3 ppm) was adsorbed on γ-alumina for 8 minutes in

the presence of both 4000 ppm and 1000 ppm water vapour. At 4000 ppm, 3 ng/mg

toluene adsorbed and at 1000 ppm, 5 ng/mg toluene adsorbed. Adsorbed toluene levels

were 42 ng/mg when water vapour levels were < 1 ppm however there was adherence to

the inner surface of the dust chamber due to electrostatics.

26

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

0 2 4 6 8 10

Tolu

en

e A

dso

rbe

d (

ng/

mg)

Time (min)

Humidifier - 22 C

No Humidifier - 22 C

Humidifier - 10 C

Humidifier - 0 C

Figure 9: Variation of toluene (3 ppm) adsorption to γ-alumina with change in water vapour

concentration (a function of temperature).

3.2.3 Optimisation of Equilibration Time of the dust chamber

The time taken for n-hexane (5 ppm) and toluene (5 ppm) to reach equilibrium conditions

in the dust chamber was established. Each gas was delivered into the dust chamber as

described for the adsorption experiments. The times taken for equilibrium to be reached

were 1 minute and 6 minutes respectively. Equilibrium times were also found to vary with

the concentration of compound used. A longer equilibration time was required for lower

concentrations.

3.3 Investigation of the Adsorption and Desorption Properties of γ-Alumina

3.3.1 Adsorption and Desorption of Non-Polar VOC’s

Adsorption and desorption levels of non polar VOCs n-hexane, 1-hexene, benzene,

toluene, o-xylene, m-xylene and p-xylene on γ-alumina were measured after 2, 5, 10, 30,

60 and 120 minutes and these results (ng VOC adsorbed/mg γ-alumina) are presented in

figures 10 to 23. A summary of the data is presented in figure 24 and 25 as well as tables

5 and 6.

Generally for all non polar VOCs, adsorption profiles exhibited a sharp decrease followed

by a plateau in the curve. Alumina samples were not collected before the second minute

27

of the adsorption experiments hence no analytical data were available to assess the

immediate initial adsorption characteristics. It is thought that the rate of adsorption of

the VOC’s was initially fast and adsorption of the VOC reached a maximum during the first

two minutes. We hypothesise that the sharp decrease in the adsorption curve after two

minutes is an indication of the competition between water vapour molecules (from the

humidifier) and the VOC for adsorption sites on the γ-alumina. A comparison among the

VOC’s of the amount adsorbed at different times showed that at two minutes the highest

levels were observed for p-xylene (18 ng/mg) followed by m-xylene (12 ng/mg), o-xylene

(10 ng/mg), toluene (3.3 ng/mg), benzene (2.2 ng/mg) and n-hexane (0.6 ng/mg). After

120 minutes, the same adsorption trend occurred, whereby the highest level of VOC

adsorbed after 120 minutes was p-xylene (14 ng/mg) followed by m-xylene (12 ng/mg), o-

xylene (8.4 ng/mg), toluene (2.9 ng/mg), benzene (1.0 ng/mg) and n-hexane (0.4 ng/mg).

Generally in the desorption experiments, a comparison among the VOC’s of the amounts

remaining on the γ-alumina after 2 minutes desorption showed that the highest levels

were those of 1-hexene (1.0 ng/mg) followed by n-hexane (0.8 ng/mg), benzene and

toluene (0.4 ng/mg), p-xylene (0.5 ng/mg) and m-xylene (0.3 mg/mg) and o-xylene (0.2

ng/mg). The greatest amount of residual VOC present after 120 minutes desorption was

shown by 1-hexene (4.0 ng/mg) and n-hexane (0.3 ng/mg) followed by toluene and

benzene (0.1 ng/mg), o-xylene (0.02 ng/mg) and p-xylene and m-xylene (0.01 ng/mg). 1-

Hexene, n-hexane, benzene and toluene were slowly desorbed from the γ-alumina with

the maximum amount of VOC desorption occurring after 60 minutes (4.0, 0.1, 0.3, 0.1

ng/mg respectively). o-Xylene, m-xylene and p-xylene exhibited a sharp decrease with

little residual present after 10 minutes. Residual p-xylene after 10 minutes was 0.03

ng/mg while residual o-xylene and m-xylene were both 0.02 ng/mg.

3.3.1.1 n-Hexane

The limited adsorption of n-hexane is an indication of a weak interaction with the γ-

alumina surface in comparison to the other non polar VOCs. n-Hexane has little affinity

for both nucleophiles and electrophiles, hence a similarly low affinity for the γ-alumina

surface oxygen bridges or Lewis acid sites would be expected. The affinity would be

28

expected to be less than that expected for aromatic non polar VOCs since adsorption of

aromatics is favoured by van der Waals forces. It is thought that the decrease in the

adsorption profile curve of n-hexane in this experiment was primarily due to the

competition with water vapour molecules. n-Hexane cannot compete with water vapour

for adsorption sites and is readily displaced (Ruiz, Bilbao & Murillo 1998).

The ready desorption of n-hexane as shown by the sharp curve in the desorption profile is

possibly an indication that the surface-adsorbed n-hexane is readily displaced by water

vapour molecules. Although n-hexane adsorbed the least of all the non polar VOCs onto

γ-alumina, the desorption study showed that n-hexane residuals were greater than those

of the other non polar VOCs. It is proposed that this reluctance for complete desorption is

due to the inability of the water vapour molecules to compete with n-hexane that may be

adsorbed within the γ-alumina pores. The linear geometry and small kinetic diameter of

n-hexane (4.30 nm) probably allows for accommodation in the slit shaped lamellae pores

thereby enabling adsorption in the pore structure with limited repulsion. Short range

repulsion between two n-hexane molecules adsorbing adjacent to each other in a pore

would most likely be reduced as n-hexane is not branched and possesses C-H atoms with

similar electronegativities. Also, diffusion into the pore network is predicted to be fastest

for n-hexane due to its neutral charge distribution and linear geometry. Both of these

factors would also likely permit easier packing of n-hexane molecules in a pore so the

number of molecules in an individual pore could increase.

29

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 20 40 60 80 100 120 140

Org

anic

s A

dso

rbe

d (

ng/

mg)

Time (min)

Figure 10: Adsorption of n-hexane on γ-alumina.

0

1

2

3

4

5

6

7

8

0 20 40 60 80 100 120 140

Re

sid

ual

Org

anic

s (n

g/m

g)

Time (min)

Figure 11: Residual n-Hexane on γ-Alumina after desorption.

3.3.1 2-Hexene

1-Hexene showed a slightly higher capacity than hexane to adsorb and be retained on γ-

alumina. In an investigation (Cai & Sohlberg, 2006) of the adsorption of 1-hexene on the

γ-alumina surface using semi-empirical cluster calculations, it was found that on the Al-O

terminated surface, H-abstraction to surface oxygen from the hexene allylic position was

the most favourable reaction and was facilitated by C-Al interaction. It was found that

30

hexene interactions with surface aluminium atoms were purely repulsive. It was

concluded that except for H-abstraction, chemisorptions occurs through interactions of C

and H with surface oxygen atoms. This was typically an endothermic process that was

most favourable when an H was abstracted from the hexene allylic position accompanied

by the formation of a C-O bond, and this process became exothermic when there was an

associated transfer of surface H. These workers stated that on the oxygen-terminated

surface different types of H atoms on hexene could be abstracted by surface oxygen

when they came sufficiently close to the surface and these reactions were exothermic.

The energy barriers for the various H-abstraction steps were comparable but were slightly

lower for the dehydrogenation of a terminal H beyond the double bond or an allylic H

than from other positions.

0.86

0.88

0.90

0.92

0.94

0.96

0.98

1.00

1.02

1.04

0 20 40 60 80 100 120 140

Org

anic

s A

dso

rbe

d (

ng/

mg)

Time (min)

Figure 11: Adsorption of 1-hexene on γ-alumina.

0

1

2

3

4

5

6

0 20 40 60 80 100 120 140

Re

sid

ual

Org

anic

s (n

g/m

g)

Time (min)

Figure 12: Residual 1-hexene on γ-alumina after desorption.

31

3.3.1.3 Benzene

Results showed that the levels of all the aromatic non polar VOCs (benzene, toluene, o-

xylene, m-xylene and p-xylene) adsorbed on γ-alumina were higher than those of n-

hexane and 1-hexene. The aromatic non polar VOCs interactions with the γ-alumina

surface possibly occurred through van der Waals forces. The adsorption profiles showed

that adsorption increased with increasing molecular weight and polarisability resulting in

the trend; xylene isomers (106.17 g/mol-1) > toluene (92.14 g/mol-1) > benzene (78.11

g/mol-1). It may also be that specific interactions might have occurred through the VOC

aromatic ring delocalised π electrons. For the benzene and toluene molecules these

interactions might have formed between the Lewis acid sites of the γ-alumina and the

nucleophilic π electrons above and below the plane of the VOC aromatic ring. Zaitan et al

(2008) however suggested that interactions between the γ-alumina surface and o-xylene

may occur between the γ-alumina surface and o-xylene molecule or o-xylene methyl

group and γ-alumina Lewis acid sites. Suggestions that interactions with the γ-alumina

surface occur through the methyl group of the o-xylenes and not through the aromatic

group may be a result of the two adjacent methyl group electron clouds strengthening

the interaction more than interactions with the aromatic ring. This may also be possible

for m-xylene. In addition, for p-xylene, steric effects from the methyl groups would hinder

aromatic ring interactions with the γ-alumina Lewis acid sites.

The results of the desorption studies showed that the overall levels of residual VOC’s

present after 120 minutes desorption were lower than those of n-hexane and 1-hexene.

Unlike n-hexane, the majority of non polar aromatics interact more readily with the

surface thereby increasing the capacity to adsorb and it may be that the number of

molecules entering the pore network was lower. It is thought that only these molecules

adsorbed to the surface, and not those adsorbed in the pores, were removed by water

vapour molecules.

32

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

0 20 40 60 80 100 120 140

Org

anic

s A

dso

rbe

d (

ng/

mg)

Time (min)

Figure 14: Adsorption of benzene on γ-alumina.

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0 20 40 60 80 100 120 140

Re

sid

ual

Org

anic

s (n

g/m

g)

Time (min)

Figure 15: Residual benzene on γ-Alumina after desorption.

3.3.1.4 Toluene

The desorption studies showed that residual toluene was still present on the γ-alumina

after 120 minutes. We hypothesise that toluene was able to enter the γ-alumina surface

pores. The adsorption of toluene in surface pores is less than n-hexane and has been

attributed to its larger molecular size (Van Bavel et al 2005). Aromatic non polar

molecules have a rigid structure which is also not easily accommodated around other

aromatic non polar molecules in a pore. The close proximity of one molecule next to

33

another in a pore may have a short range repulsion effect from the aromatic ring π

electrons which inhibits adsorption to a pore surface. Repulsion between the pore walls

and the electron cloud of the toluene and xylene methyl substitutes can also occur

(Mukti, Jentys & Lercher 2007).

While toluene might have been able to enter pores and adsorb, it may also have

adsorbed to the γ-alumina surface through the interaction of the aromatic ring. The

benzene desorption study showed lower loss of residuals compared to toluene and this

would be expected because it does not have the added size, geometry and repulsion

effects provided by the methyl group of toluene.

2.8

3.0

3.2

3.4

0 20 40 60 80 100 120 140

Org

anic

s A

dso

rbe

d (

ng/

mg)

Time (min)

Figure 16: Adsorption of toluene on γ-alumina.

0

2

4

6

8

10

12

14

16

0 20 40 60 80 100 120 140

Re

sid

ual

Org

anic

s (n

g/m

g)

Time (min)

Figure 17: Residual toluene on γ-alumina after desorption.

34

3.3.1.5 o-Xylene

Desorption profiles show that all isomers of xylene were rapidly desorbed from γ-alumina

in the presence of water vapour whereas n-hexane, benzene and toluene were desorbed

gradually. In the desorption studies the amounts of residual xylene (o-, m-, p-) on the γ-

alumina after the desorption experiment were lower than those obtained for all the other

VOCs (non polar and polar), with almost all xylene being completely desorbed. The larger

sized xylene isomers may not be able to enter surface pores so the molecule only adsorbs

to the γ-alumina surface through strong interactions with the γ-alumina surface. Water

may be able to more readily compete for interaction with the γ-alumina surface resulting

in desorption of xylene.

8.3

8.4

8.5

8.6

8.7

8.8

8.9

9

9.1

9.2

9.3

9.4

0 20 40 60 80 100 120 140

Org

anic

s A

dso

rbe

d (

ng/

mg)

Time (min)

Figure 18: Adsorption of o-xylene on γ-alumina.

-5

0

5

10

15

20

0 20 40 60 80 100 120 140

Re

sid

ual

Org

anic

s (n

g/m

g)

Time (min)

Figure 19: Residual o-xylene on γ-alumina after desorption.

35

3.3.1.6 m-Xylene

If xylene molecules are able enter surface pores, their large molecular size and electron

cloud would possibly slow diffusion into the pores. Their size would also limit the ability of

the number of other xylene and water molecules to enter the pores. Repulsion effects

inside the pore would also exist between xylene molecules as they have an electron cloud

larger than the other non polar VOCs. Adsorption onto the γ-alumina surface would be

favoured and, in turn, xylene would be more accessible to water vapour molecule

competition. Comparing the desorption profiles of individual xylene isomers after two

minutes desorption, the higher residual levels were shown by p-xylene. The planar

geometry may have an influence. The presence of two methyl substitutes may reduce the

number of molecules able to enter the pore network. Diffusion of o- and m-xylene

molecules may be slower than p-xylene due to their larger kinetic diameter (both 6.80

nm) arising from the position of the two methyl substitutes. The smaller kinetic diameter

of p-xylene (5.85 nm) could possibly allow the molecule to enter surface pores whereas

the o- and m-xylene isomers might not be able to enter the pore network at all.

11.5

11.6

11.7

11.8

11.9

12

12.1

12.2

0 20 40 60 80 100 120 140

Org

anic

s A

dso

rbe

d (

ng/

mg)

Time (min)

Figure 20: Adsorption of m-xylene on γ-alumina.

36

-10

0

10

20

30

40

50

60

70

80

0 20 40 60 80 100 120 140

Re

sid

ual

Org

anic

s (n

g/m

g)

Time (min)

Figure 21: Residual m-xylene on γ-alumina after desorption.

3.3.1.7 p-Xylene

The results obtained in our study suggest that adsorption is affected by steric factors

resulting from the arrangement of the two methyl groups on the aromatic ring. Unlike p-

xylene, methyl substituents on o-xylene are sterically hindered because of their close

proximity to each other. It is possible that steric constraints may inhibit adsorption as the

separation distance between the adsorbing molecule and the γ-alumina surface is

increased. Steric effects were found to have an effect on adsorption in a study by Díaz et

al (2004). Their work showed cyclohexane and cycloheptane inhibited adsorption on

Zeolite 5A compared to adsorption of n-hexane and heptane respectively. It may be that

symmetrical molecules such as p-xylene have a greater affinity for the γ-alumina surface

than a less symmetrical molecule such as o-xylene or m-xylene. This would result from a

lower loss of rotational and translational freedom during adsorption (Reitmeier et al

2008). Differences in the adsorption profiles in this study might also have been due to the

VOCs ability to enter surface pores.

37

0

2

4

6

8

10

12

14

16

18

20

0 20 40 60 80 100 120 140

Org

anic

s A

dso

rbe

d (

ng/

mg)

Time (min)

Figure 22: Adsorption of p-xylene on γ-alumina.

-10

0

10

20

30

40

50

60

70

80

0 20 40 60 80 100 120 140

Re

sid

ual

Org

anic

s (n

g/m

g)

Time (min)

Figure 23: Residual p-xylene on γ-alumina after desorption.

In summary, displacement of VOC molecules by water may be possible because VOCs

physisorb to the γ-alumina surface through weaker van der Waal forces than those of the

water molecules. Although VOCs are displaced (particularly non polar VOCs), adsorption is

increased from interactions of the presence of an aromatic ring and entry into the surface

pore network.

38

Table 5: Summary of n-hexane, 1-hexene, benzene, toluene, o-, m- and p-xylene adsorption data

Contact Time

n-Hexane 1-Hexene Benzene Toluene o-Xylene m-Xylene p-Xylene

(min) (ng/mg) (ng/mg) (ng/mg) (ng/mg) (ng/mg) (ng/mg) (ng/mg)

2 0.6 1.0 2.2 3.3 10 12 18

5 0.5 1.0 1.8 3.1 9.3 12 15

10 0.4 0.9 1.6 3.0 9.0 12 14

30 0.4 0.9 1.3 3.0 8.7 12 14

60 0.4 0.9 1.2 3.0 8.5 12 14

120 0.4 0.9 1.0 2.9 8.4 12 14

Figure 24: Summary of adsorbed organics on γ-alumina data.

Table 6: Summary of residual organics on γ-alumina after desorption.

Contact Time

n-Hexane 1-Hexene Benzene Toluene o-Xylene m-Xylene p-Xylene

(min) (ng/mg) (ng/mg) (ng/mg) (ng/mg) (ng/mg) (ng/mg) (ng/mg)

2 0.8 4.3 0.4 0.4 0.02 0.03 0.05

5 0.7 4.1 0.3 0.3 0.02 0.02 0.04

10 0.6 4.1 0.3 0.2 0.02 0.02 0.03

30 0.5 4.0 0.3 0.2 0.02 0.02 0.03

60 0.3 4.0 0.1 0.1 0.02 0.02 0.03

120 0.3 4.0 0.1 0.1 0.02 0.01 0.01

39

Figure 25: Summary of residual organics on γ-alumina after desorption.

3.3.2 Adsorption and Desorption of Polar VOCs

The adsorption and desorption levels of polar VOCs trans-2-hexenal, 2-butanone,

acetophenone and acetone on γ-alumina was measured after 2, 5, 10, 30, 60 and 120

minutes and these results are presented in figures 26 to 34. Adsorption curves of the

polar compounds vary depending on the properties of the adsorbing VOC. Both the

curves of 2-butanone and benzaldehyde exhibit a rapid increase in initial adsorption

followed by a slower continuous increase. This initial increase might have occurred from

these VOCs chemisorbing to the surface. Unlike non polar compounds, it may be possible

that polar molecules with carbonyl groups adsorb onto a surface through strong dipole-

dipole interactions between the carbonyl group and the surface. This may lead to

chemisorbed species rather than physisorbed. Also, as polar compounds form stronger

interactions with the surface, multilayer adsorption may occur.

40

3.3.2.1 Trans-2-Hexenal

0

20

40

60

80

100

120

140

0 20 40 60 80 100 120 140

Org

anic

s A

dso

rbe

d (

ng/

mg)

Time (min)

Figure 26: Adsorption of trans-2-hexenal on γ-alumina.

0

0.5

1

1.5

2

2.5

3

0 20 40 60 80 100 120 140

Re

sid

ual

Org

anic

s (n

g/m

g)

Time (min)

Figure 27: Residual trans-2-hexenal on γ-alumina after desorption

3.3.2.2 2-Butanone

The levels of adsorption after 120 minutes were lower than those of the other polar VOCs

but higher than those of the non polar VOCs studied. Levels of adsorption for 2-butanone

was less than the levels of adsorption for benzaldehyde. The lower electronegativity of

41

the ketone functional group compared to that of the aldehyde functional group may be a

factor. 2-butanone also lacks the interactions that would arise from an aromatic ring.

The adsorption profile of 2-butanone showed no initial decrease in adsorption as

observed with the adsorption profiles of the non polar VOC’s. Both water vapour and 2-

butanone compete for Lewis acid sites. If both water and polar VOCs form chemisorbed

species they would be competing directly for the alumina surface, meaning the

concentration of both species would increase over time with the favoured species

dominating at longer times.

40

41

42

43

44

45

46

47

48

0 20 40 60 80 100 120 140

Org

anic

s A

dso

rbe

d (

ng/

mg)

Time (min)

Figure 28: Adsorption of 2-butanone on γ-alumina.

0

5

10

15

20

25

30

35

40

45

50

0 20 40 60 80 100 120 140

Re

sid

ual

Org

anic

s (n

g/m

g)

Time (min)

Figure 29: Residual 2-butanone on γ-alumina after desorption.

42

3.3.2.3 Acetophenone

The adsorption profile of acetophenone did not resemble that of the other non polar or

other polar VOCs studied. Adsorption increased linearly with increasing adsorption time.

The indication is that acetophenone had a strong affinity for γ-alumina and is not easily

desorbed. This is apparent from the gradual desorption as shown by the desorption

curve. It may also be that acetophenone might have adsorbed in multilayers. Desorption

of acetophenone from γ-alumina was carried out with initial adsorption times of 15, 30

and 60 minutes and results are shown in figure 32.

0

50

100

150

200

250

0 20 40 60 80 100 120 140

Org

anic

s A

dso

rbe

d (

ng/

mg)

Time (min)

Figure 30: Adsorption of acetophenone on γ-alumina.

0

50

100

150

200

250

0 20 40 60 80 100 120 140

Org

anic

s A

dso

rbe

d (

ng/

mg)

Time (min)

Aug-08

Nov-08

Figure 31: Repeat adsorption of acetophenone on γ-alumina.

43

0

10

20

30

40

50

60

70

80

90

0 20 40 60 80 100 120 140

Re

sid

ual

Org

anic

s (n

g/m

g)

Time (min)

30 Minutes

60 Minutes

15 Minutes

Figure 32: Desorption of acetophenone from γ-alumina with varying initial adsorption times.

3.3.2.4 Acetone

Adsorption of acetone (3 ppm) on γ-alumina was measured after 2, 5, 10, 30, 60 and 120

minutes. The results are presented in figure 33 and table 7.

0

2

4

6

8

10

12

14

16

0 20 40 60 80 100 120 140

Org

anic

s A

dso

rbe

d (

ng/

mg)

Time (min)

Figure 33: Adsorption of acetone on γ-alumina.

44

Table 7: Adsorption of acetone on alumina.

Contact Time Acetone

(min) (ng/mg)

2 13

5 13

10 14

30 11

60 13

120 11

Desorption of acetone (3 ppm acetone in the gas phase with 4000 ppm water vapour)

from γ-alumina (38 – 52 μm diameter) was carried out. Results are shown in figure 34 and

table 8.

0

10

20

30

40

50

60

70

80

90

0 20 40 60 80 100 120 140

Re

sid

ual

Ace

ton

e (

ng/

mg)

Time (min)

Figure 34: Residual acetone present after desorption from γ-alumina.

Table 8: Residual acetone present after desorption

from alumina.

Contact Time Acetone

(min) (ng/mg)

2 2.3

5 2.3

10 2.3

30 2.3

60 2.3

120 2.3

45

3.4 Investigation of reactions of selected polar organic compounds adsorbed on alumina

The reactions of benzaldehyde, acetaldehyde, propanal, benzyl alcohol, and acetone

adsorbed on alumina were investigated. It was predicted that the strongly alkaline

environment (NaOH from the Baeyer process) of the alumina surface would encourage

some of these compounds to participate in condensation reactions.

Aldehydes that do not have α-hydrogens participate in the Cannizarro reaction to form a

carboxylic acid and an alcohol. Benzaldehyde in particular is known to form benzoic acid

and benzyl alcohol via the Cannizaro reaction.

It is well known that acetaldehdye and aldehydes in general, with α-hydrogens, readily

react with aqueous hydroxide at room temperature to form aldol condensation products

(Bruce 2004). Acetaldehyde forms 3-hydroxybutanal that in turn readily dehydrates to

crotonaldehyde (2-butenal), a process that is facilitated by heating. Aldol reactions are

also reversible in excess base and water. The formation of aldol condensation products of

acetaldehyde and acetone is shown in figure 35. Ketones, such as acetone, do not

participate in aldol reactions as readily as aldehydes. The equilibrium to the right is not

favoured.

Figure 35: Possible aldol Condensation product pathways of acetone and acetaldehyde (Li et al 2001).

46

5 10 15 20 25 minutes

0

1

2

3

4

5 MCounts 2 hour adsorption sample.SMS TIC

45:300

Figure 36: TD-GCMS chromatogram of benzyl

alcohol (13.850 min) and benzaldehyde (14.462

min) in 2 hour adsorption sample.

50 100 150 200 250 300 m/z

0%

25%

50%

75%

100%

51.0

77.0

105.0

106.0

Spectrum 1A BP: 105.0

Figure 37: Mass spectrum of benzaldehyde

(14.462 minutes) in 2 hour adsorption sample.

3.4.1 Benzaldehyde

The γ-alumina (0.3 g) was exposed in a dust chamber to an atmosphere of benzaldehyde

for time intervals of 2, 5, 10, 30, 60 and 120 minutes in the presence of water vapour.

TD-GCMS analysis showed the presence of benzyl alcohol (figure 36 and 37). We believe

that the formation of benzyl alcohol was via a Cannizzaro mechanism. This mechanism

predicts that benzoic acid would also be formed however this was not detected by TD-

GCMS. It is suspected that the benzoate might have been adsorbed to the alumina and

not easily volatilised. At this stage of the project no attempts were made to extract the

benzoate (by acidification) for subsequent analysis by LCMS

51.0

63.0

77.0

78.0

79.0

91.0

92.0

108.0


Figure 38: Mass spectrum of benzyl alcohol

peak at 13.850 minutes.

50 100 150 200 250 300 m/z 0%

25%

50%

75%

100%

47

3.4.2 Acetaldehyde

The γ-alumina (0.3 g) was exposed in a dust chamber to an atmosphere of VOC standard

for time intervals of 2, 5, 10, 30, 60 and 120 minutes in the presence of water vapour.

Adsorbed organics were extracted, derivatised, filtered using a C18 Sep-Pak and analysed

using LCMS as described in section 2.4.2.1 and 2.4.2.3. The adsorption profile is described

in figure 39 and table 9.

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

0 20 40 60 80 100 120 140

Ad

sorb

ed

Ace

tald

eh

yde

(n

g/m

g)

Time (min)

Figure 39: Adsorption of acetaldehyde on γ-alumina.

Table 9: Acetaldehyde adsorption on γ-alumina

Time ng/mg

2 3.0 5 3.3

10 3.2 30 3.5 60 4.2

120 4.3

Acetaldehyde is known to react via the aldol condensation reaction in the presence of an

oxide surface with acidic or basic properties. The alumina used in this project was alkaline

due to the presence of NaOH impurities from the Bayer process. Aldol condensation

reactions occur through the formation of an enol. Acetaldehyde may produce 3-

hydroxybutanal. This can dehydrate to form crotonaldehyde.

48

In the above adsorption experiment crotonaldehyde (figure 42 and table 10) and 2-

hydroxybutanal (figure 43 and table 10) were found to be present. Typically the two hour

acetaldehyde (m/z223) adsorption sample LCMS chromatogram showed the presence of

the aldol condensation product 3-hydroxybutanal (m/z267) and crotonaldehyde (m/z249)

(figure 40).

3

055-3001.D: EIC 223 -All MS

4

055-3001.D: EIC 249 -All MS

1

2

055-3001.D: EIC 267 -All MS

0

2

4

5x10

Intens.

0.0

0.5

1.0

1.5

2.0

5x10

0.0

0.5

1.0

1.5

2.0

6x10

2 4 6 8 10 12 Time [min]

162.9

182.8 196.9 222.9267.0

-MS, 1.2min #153

162.9

182.8 222.9 267.0

-MS, 1.4min #179

150.9

162.9

182.8

222.9

-MS, 2.4min #310

162.9

182.8

248.9-MS, 4.6min #560

0

1

6x10

Intens.

0.0

0.5

6x10

0

1

5x10

0

2

4

4x10

100 150 200 250 300 350 m/z

Figure 40: Two hour acetaldehyde (m/z 223) adsorption sample with the aldol condensation products 3-

hydroxybutanal (m/z 267) and crotonaldehyde (m/z 249) ions extracted.

For quantification a DNPH standard mix was used and a typical LCMS chromatogram of

the DNPH standard mix is shown below (figure 41). Derivatised acetaldehyde was

detected at a retention time of 2.4 minutes with a m/z223 fragment. Derivatised

crotonaldehyde, an acetaldehyde aldol condensation product eluted at 4.5 minutes and

detected as m/z249.

49

0 2 4 6 8 10 12 Time [min]

0.0

0.2

0.4

0.6

0.8

1.0

7x10

Intens.

007-0701.D: TIC -All MS

162.9 178.8

222.9-MS, 2.4min #241

206.9

236.9-MS, 3.3min #344

248.9-MS, 4.5min #480

0.0

0.5

6x10

Intens.

0.0

0.5

1.0

6x10

0

1

6x10

100 150 200 250 300 350 m/z

Figure 41: Carbonyl-DNPH mixed standard (10 µg/mL) analysed using LCMS showing acetaldehyde elution

at 2.4 minutes (m/z223), acetone at 3.3 minutes (m/z237) and crotonaldehyde at 4.5 minutes (m/z249).

The levels of crotonaldehyde and 3-hydroxybutanal are described below.

50

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0 20 40 60 80 100 120 140

Ad

sorb

ed

Cro

ton

ald

eh

yde

(n

g/m

g)

Time (min)

Figure 42: Crotonaldehyde present after adsorption of acetaldehyde on γ-alumina.

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

0 20 40 60 80 100 120 140

Ad

sorb

ed

3-H

ydro

xyb

uta

nal

(n

g/m

g)

Time (min)

Figure 43: 3-Hydroxybutanal present after adsorption of acetaldehyde on γ-alumina.

Table 10: Crotonaldehyde and 3-hydroxybutanal present after adsorption of acetaldehyde on γ-alumina.

Contact Time Crotonaldehyde 3-Hydroxybutanal

(min) (ng/mg) (ng/mg)

2 0.2 0.2

5 0.2 0.2

10 0.2 0.8

30 0.5 2.6

60 0.7 2.4

120 1.9 8.5

51

The amount of adsorbed 3-hydroxybutanal (commercial standard was not available) was

quantified as crotonaldehyde equivalents. Hydroxy refers to 3-hydroxybutanal or the

analyte concentration to be estimated. Croton referes to crotonaldehyde.

As a measure of the desorption characteristics of the condensation products, a

desorption experiment with acetaldehyde and alumina was carried out. It was hoped that

this would give an indication of how readily 3-hydroxybutanal and crotonaldehyde would

desorb from the alumina.

In a separate experiment to investigate the desorption characteristics of acetaldehyde

and its condensation products, acetaldehyde was first adsorbed to alumina using the

method previously described. Then desorption of acetaldehyde, with water vapour from

γ-alumina was carried out. The derivatised reaction mixtures were analysed by LCMS .

52

The LCMS chromatogram for the two hour desorption sample is shown below in figure 44.

2

029-2901.D: EIC 249 -All MS

1

029-2901.D: EIC 223 -All MS

029-2901.D: EIC 267 -All MS

0.0

0.5

1.0

1.5

2.0

4x10

Intens.

0

1

2

3

44x10

0

1

2

3

4x10

2 4 6 8 10 12 Time [min]

162.9

182.8222.9 331.0 363.0

-MS, 2.5min #305

137.9

162.9

182.9208.9

248.9

-MS, 4.6min #5310.0

0.2

0.4

0.6

0.8

5x10

Intens.

0.0

0.5

1.0

1.5

4x10

100 150 200 250 300 350 m/z

Figure 44: Two hour acetaldehyde (m/z223) desorption sample with the aldol condensation products 3-

hydroxybutanal (m/z267) and crotonaldehyde (m/z249) ions extracted. No 3-hydroxybutanal is present.

The levels for acetaldehyde and crotonaldehyde are shown below in figures 45 and 46 as

well as table 11. 3-Hydroxybutanal was not identified in the two hour desorption samples.

53

-0.1

0.1

0.3

0.5

0.7

0.9

1.1

1.3

1.5

0 20 40 60 80 100 120 140

Re

sid

ual

Ace

tald

eh

yde

(n

g/m

g)

Time (min)

Figure 45: Residual acetaldehyde present on γ-alumina.

Table 11: Residual acetaldehyde and crotonaldehyde present on γ-alumina.

Contact Time Acetaldehyde Crotonaldehyde

(min) (ng/mg) (ng/mg)

2 0.5 0.7

5 0.1 0.2

10 < 0.1 0.1

30 < 0.1 0.1

60 < 0.1 0.1

120 < 0.1 0.1

.

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0 20 40 60 80 100 120 140

Re

sid

ual

Cro

ton

ald

eh

yde

(n

g/m

g)

Time (min)

Figure 46: Residual crotonaldehyde present after desorption of acetaldehyde from γ-alumina.

54

Regarding the recoveries obtained with derivatisation, preliminary investigations involved

developing and improving the DNPH derivatising method. An acetaldehyde solution was

injected onto γ-alumina. The crotonaldehyde derivative was identified (4.5 min, m/z 249)

as well as acetaldehyde derivative (2.5 min, m/z 223) in the LCMS chromatograms. As the

crotonaldehyde derivative was present in the DNPH standard mix (Supelco, catalogue no.

47672-U) it was possible to quantify this compound. The results are listed in table 12.

Table 12: Crotonaldehyde levels

Sample No. Description Concentration

(ng/mg)

/001 500 µL inject 10

/002 500 µL inject repeat 14

/003 400 µL inject 8.5

/004 200 µL inject 0.2

/005 100 µL inject 0.1

/006 50 µL inject < 0.1

/007 10 µL inject 0.1

/008 5 µL inject 1.2

/009 DNPH Blank < 0.1

We believe that there is further scope to optimize the derivatisation method however

project time constraints did not allow for this. Therefore the results described above

should at best be treated as qualitative and semi-quantitative.

3.4.3 TD-GCMS Analysis Versus LCMS Analysis

Due to recovery issues with extraction of derivatised carbonyls from particles and

subsequent analysis by LCMS, adsorption experiments were repeated and quantification

was carried out using TD-GCMS. A 3-hydroxybutanal standard was not commercially

available. Delivery of an underivatised crotonaldehyde standard was also not possible

before the expected project completion date.

Acetaldehyde was not expected to be present in chromatograms due to its polarity and

molecular weight resulting in a low breakthrough volume on Tenax TA. This was

confirmed when no acetaldehyde was detected by TDGCMS of a TD tube that had an

55

injection of acetaldehyde on the Tenax TA. 3-Hydroxybutanal (m/z 70, m/z 45) was also

not detected. A peak suspected to be crotonaldehyde (m/z 70) was detected after 30

minutes adsorption eluting at 3.58 minutes as shown below. This peak increased in

counts as time increased to 2 hours.

3.6.4 Propionaldehyde

In the first part of this project where the adsorption characteristics of propionaldehyde

on γ-alumina adsorption were investigated, this aldehyde was not clearly detected in the

TD-GCMS chromatograms (figure 51 and 52). Due to the poor response propionaldehyde

was not quantified. This poor response was suspected to be due to the low affinity of

propionaldehdye for Tenax TA. Propionaldehyde’s volatility requires a low volume of gas

to elute it from the Tenax TA, i.e. breakthrough volume. In a study by Rothweiler, Wäger

and Schlatter (1991) the recovery of propionaldehyde from a TD tube containing 155

milligrams of Tenax TA after 1 litre of air had passed through was 85.2 % compared to

93.8 % for toluene. When 5 litres was passed through the recovery was 37.8 % and 99.7 %

for propionaldehyde and toluene respectively.

Figure 47: Suspected crotonaldehyde peak present

in acetaldehyde two hour adsorption on γ-alumina

sample.

Figure 48: Mass spectra of suspected

crotonaldehyde peak present in acetaldehyde two

hour adsorption on γ-alumina sample.

56

At a later stage of the project when investigating the reactions of the VOCs on γ-alumina,

the propionaldehyde adsorption experiment chromatograms were re-examined. These

chromatograms showed the presence of 2-methyl-2-pentenal. It is known that aldehydes

may adsorb and react readily on metal oxide surfaces by undergoing conversion via aldol

condensation. For example the saturated propionaldehyde molecule may self couple to

form higher molecular weight unsaturated compounds. Adsorption of propionaldehyde

on α-alumina was shown to form 2-methyl 2-pentenal (Li et al 2001). In the

propionaldehyde adsorption chromatograms 2-methyl-2-pentenal was identified as

shown in figures 49 and 50. The identity of the peak in the chromatogram was confirmed

against the chromatogram and mass spectrum of an authentic sample of 2-methyl-2-

pentenal standard. 2-Methyl-2-pentenal was present in all chromatograms associated

with each adsorption time.

Figure 49: TD-GCMS chromatogram of 2-methyl-2-

pentenal (8.152 min) in 2 hour propionaldehyde

adsorption sample.

Figure 50: Mass spectrum of 2-methyl-2-pentenal

(8.152 min) in 2 hour propionaldehyde adsorption

sample.

57

3.4.5 Benzyl Alcohol

When benzyl alcohol (m/z108, 91) was injected onto a Tenax TA tube it was readily

detected using TD-GCMS as shown in figure 53 and 54.

However during the adsorption studies where benzyl alcohol was exposed to γ-alumina,

benzyl alcohol was not observed. Examination of the chromatogram showed the presence

of benzaldehyde (m/z105, 77) and a trace amount of benzoic acid (figure 55 and 56).

5 10 15 20 25 minutes

0.0

0.5

1.0

1.5

2.0

MCounts 1050 ng/µL Standard.SMS TIC 45:300

Figure 53: TD-GCMS chromatogram of benzyl alcohol 1050 ng/μL standard injected onto Tenax TA only.

50 100 150 200 250 300 m/z 0%

25%

50%

75%

100%

51.0

63.0

77.0

78.0

79.0

91.0

92.0

108.0


Figure 51: TD-GCMS chromatogram of

propionaldehyde (1.345 min) after 2 hour

adsorption.

Figure 52: Mass spectrum of propionaldehyde

(1.345 min) after 2 hour adsorption.

Figure 54: Mass spectrum of benzyl alcohol


58

5 10 15 20 25 minutes

0

1

2

3

4

5 MCounts 2 hour adsorption sample.SMS TIC

45:300

Figure 55: TD-GCMS chromatogram of benzyl

alcohol (13.850 min) and benzaldehyde (14.462

min) in 2 hour adsorption sample.

50 100 150 200 250 300 m/z

0%

25%

50%

75%

100%

51.0

77.0

105.0

106.0


Figure 56: Mass spectrum of benzaldehyde

(14.462 minutes) in 2 hour adsorption sample.

Benzaldehyde has been shown to be a product of benzyl alcohol oxidation over an

alumina catalyst where the amount of benzaldehyde increased with increasing reaction

temperature (Jayamani & Pillai 1983). Oxidation of alcohols with a catalyst yields its

corresponding aldehyde which may further oxidise to form the corresponding carboxylic

acid.

3.4.6 Acetone

Acetone is known to react via the aldol condensation reaction in the presence of an oxide

surface with acidic or basic properties. The alumina used in this project was alkaline from

the presence of NaOH impurities from the Bayer process. Aldol condensation reactions

occur through the formation of an enol. Typically acetone would produce diacetone

alcohol. This can dehydrate to form mesityl oxide.

59

Examination of the adsorption chromatograms showed the presence of diacetone alcohol

and a signal indicating a trace of mesityl oxide. Diacetone alcohol was present in

chromatograms for all adsorption samples including 30 minutes, one hour and two hour

samples (figure 59 and 60). The signal that was suspected to represent mesityl oxide was

was indistinct and too weak to confirm the identification of mesityl oxide.

Figure 59: TD-GCMS chromatogram of diactone

alcohol (9.759 min) in 2 hour adsorption sample.

Figure 58: Mass spectrum of acetone (1.726 min)

in 2 hour adsorption sample.

Figure 57: TD-GCMS chromatogram of acetone

(1.726 min) in 2 hour adsorption sample.

Figure 60: Mass spectrum of diacetone alcohol

(9.759 min) in 2 hour adsorption sample.

60

The identity of the acetone and the condensation product diacetone alcohol was

confirmed by comparison against authentic standards. The chromatograms and spectra

are shown in figure 61 and 62.

In order to obtain a quantitative description of the products a separate adsorption and

desorption experiment were carried out for a continuous period of two hours only. The

samples were analysed immediately to avoid any possible losses from diffusion through

Tenax TA. The adsorption was performed in duplicate and the amount of acetone

adsorbed after 120 minutes was 17 ng/mg for both sample sets. Residual acetone from

the desorption repeat was < 2.3 ng/mg.

3.5 The Photochemistry of Selected Polar and Non-Polar organic compounds adsorbed

on alumina

To investigate the effect of UV light on the organic compounds adsorbed on alumina

adsorption experiments were carried out in the presence of UV radiation. Only

acetaldehyde and acetone were selected for this study. Preliminary work involved

measurement of typical solar irradiance and the determining the optimum distance

between the UV lamps and the dust chamber in order to replicate solar irradiance.

Figure 61: 1000 ng/μL diacetone alcohol standard. Figure 62: Mass spectrum of diacetone alcohol


61

3.5.1 Measurement of Solar Irradiance

Measurements were made where the sensor was placed both inside (table 13) and

outside (table 14) of the quartz dust chamber and the results are given below.

Table 13: Sensor inside quartz tube

Time of Measurement Sensor Average Irradiance

14:51 254 nm 289 μW/cm2

14:44 310 nm 1840 μW/cm2

14:26 365 nm 2.93 mW/cm2

Table 14: Sensor ouside quartz tube

Time of Measurement Sensor Average Irradiance

14.53 254 nm 320 μW/cm2

14:42 310 nm 1970 μW/cm2

14:24 365 nm 3.1 mW/cm2


The distances between each of the UV sensors to the UV lamps were optimised to mirror

the initial solar irradiance readings recorded in section 3.5.1. The results obtained here

were used to determine the distance between the UV lamps and the dust chamber during

the adsorption experiments carried out in the presence of UV radiation. The optimum

distance was determined to be 50-54cm.

Table 15: Target irradiance levels for each sensor

Sensor Target Irradiance

254 nm 320 µW/cm2

310 nm 1970 µW/cm2

365 nm 3.1 mW/cm2

0

100

200

300

400

500

600

700

30 40 50 60 70

Irra

dia

nce

(µ

W/c

m2)

Sensor Distance from Lamp (cm)

Figure 63: Irradiance variation recorded using a 254 nm probe (320 μW/cm2

target) as a function of

distance from 254 nm lamp.

62

0

500

1000

1500

2000

2500

10 15 20 25 30 35 40

Irra

dia

nce

(µ

W/c

m2

)


Figure 64: Irradiance variation recorded using a 310 nm probe (1970 μW/cm2 target) as a function of


0

0.5

1

1.5

2

2.5

3

3.5

4

7.5 8 8.5 9 9.5 10 10.5 11

Irra

dia

nce

(m

W/c

m2)


Figure 65: Irradiance variation recorded using a 365 nm probe (3.1 mW/cm2 target) as a function of


A summary of the target irradiance and distance between individual sensors and lamps is

presented in table 16.

63

Table 16: Summary of optimum distance between each probe and UV lamp to mirror the solar irradiance

levels as measured in experiment 1.

Sensor Lamp Target Irradiance Distance Between Sensor and Lamp

Measured Irradiance

254 nm 254 nm 320 μW/cm2 54.5 cm 321 μW/cm

2

310 nm 302 nm 1970 μW/cm2 17.3 cm 2.00 mW/cm

2

365 nm 365 nm 3.1 mW/cm2 10 cm 3.16 mW/cm

2

3.5.3 Acetaldehyde

In this work acetaldehyde was exposed to γ-alumina in the dust chamber for 2 hours

under UV radiation. LCMS analysis of the DNPH derivatised reaction mixture showed the

presence of derivatised aldol condensation products which were 3-hydroxybutanal and

crotonaldehyde.

Table 17 below shows the results of the analysis of the reaction mixture done in triplicate.

Average levels of acetaldehyde present in the two hour adsorption samples were

4.1ng/mg. The data from the two hour adsorption carried out before the two hour

adsorption with UV (average 4.1 ng/mg) correlates well (< 5 % difference) with the

previously obtained acetaldehyde two hour adsorption data (average 4.3 ng/mg). Average

levels of acetaldehyde after exposure to UV were 3.2 ng/mg. Although there is a greater

amount of variability (difference between 1.2 ng/mg and 6.2 ng/mg is 20 %) sample 004

and 005 were expected to have more error than sample 006 due to workup errors. The

concentration for sample 006 was assumed to be closer to the actual than sample 004

and 005.

Table 17: Acetaldehyde present after adsorption on γ-alumina with and without the presence of 254 nm

UV light

Sample No. Description

Concentration

(ng/mg)

/001 2 hr 3.4

/002 2 hr 4.3

/003 2 hr 4.8

/004 2 hr + UV 1.2

/005 2 hr + UV 2.2

/006 2 hr + UV 6.2

64

3-Hydroxybutanal was also detected and quantified, the results of which are summarised

in table 18. Average levels of 3-hydroxybutanal present in the two hour adsorption

samples were 6.4 ng/mg. Average levels of 3-hydroxybutanal when the adsorption was

done in the presence of UV radiation were 13.9 ng/mg.

The 3-hydroxybutanal dehydration product crotonaldehyde was detected and quantified,

the results of which are summarised in table 18. Average levels of crotonaldehyde

present in the two hour adsorption samples were 0.6 ng/mg. Average levels of

crotonaldehyde when the adsorption was done in the presence of UV radiation were 1.2

ng/mg. The amounts of the two acetaldehyde aldol condensation products with and

without the presence of UV light are further summarised in figure 66.

Table 18: 3-Hydroxybutanal and crotonaldehyde present after acetaldehyde adsorption on γ-alumina

with and without the presence of 254 nm UV light.


3-Hydroxybutanal Concentration

(ng/mg)

Crotonaldehyde Concentration

(ng/mg)

/001 2 hr 5.8 0.6

/002 2 hr 6.0 0.9

/003 2 hr 7.5 0.4

/004 2 hr + UV 9.9 1.2

/005 2 hr + UV 12 1.9

/006 2 hr + UV 20 0.5

Figure 66: Summary of LCMS analysis of acetaldehyde, 3-hydroxybutanal and crotonaldehyde in

adsorption and adsorption with UV light.

65

Due to quantification issues associated with the low extraction recoveries after DNPH

derivatisation, a separate adsorption experiment was carried out and samples were

analyzed by TD-GCMS. However GCMS did not give satisfactory results. 3-Hydroxybutanal

was not detected in the chromatograms. A peak suspected to be crotonaldehyde (m/z 70)

was present in the chromatograms of the two hour adsorption samples (with exposure to

UV radiation) as shown in figure 67 and figure 68. The identification of this peak was

based solely on the mass spectrum and comparison against a NIST library as no authentic

standard was available.

To establish that the acetaldehyde aldol condensation reactions observed in the UV

exposed adsorption samples were due to the presence of γ-alumina, acetaldehyde (3

ppm) was exposed to 254 nm for 2 hours in a quartz reaction chamber with a gas tight tap

on each end. To enable sampling from the closed reaction chamber a Tedlar Bag (3 L)

containing ultra high purity (UHP) nitrogen (99.999 %, BOC Australia) was attached to one

tap of the reaction chamber. The taps were opened simultaneously with the Tedlar bag

and the pump turned on. The gaseous sample was drawn through a thermal desorption

(TD) tube (100 mL/min for 15 minutes) to capture any possible products. The TD tube was

analysed by TD-GCMS. The analysis showed no signs of 3-hydroxybutanal or

crotonaldehyde.

Figure 68: Mass spectrum of Suspected

crotonaldehyde peak present in acetaldehyde

two hour adsorption on γ-alumina sample with

exposure to 254 nm UV.

Figure 67: Crotonaldehyde peak present in

acetaldehyde two hour adsorption on γ-alumina

sample with exposure to 254 nm UV.

66

3.5.4 Acetone

In this work acetone was exposed to γ-alumina in the dust chamber for 2 hours in the

presence of UV radiation. LCMS analysis of the DNPH derivatised reaction mixture

showed the presence of derivatised aldol condensation products diacetone alcohol and a

trace of mesityl oxide. This is shown in figure 69.

4

016-1601.D: EIC 237 -All MS

1

2

016-1601.D: EIC 295 -All MS

016-1601.D: EIC 277 -All MS

0.0

0.5

1.0

6x10

Intens.

0.00

0.25

0.50

0.75

1.005x10

0.0

0.5

1.0

1.5

4x10

2 4 6 8 10 12 Time [min]

162.9 206.9

236.9-MS, 3.3min #399

162.9

182.8 196.9 236.9295.0

350.1

-MS, 2.0min #253

162.9

182.8 196.9 236.9295.0

-MS, 2.9min #362

0

2

5x10

Intens.

0.0

0.5

1.0

5x10

0

2

4

4x10

100 150 200 250 300 350 m/z

Figure 69: Diacetone alcohol present in 2 hour acetone adsorption only sample. No mesityl oxide was

detected.

The identification of diacetone alcohol and mesityl oxide was confirmed through the

analysis of the DNPH derivatives of authentic standards as shown in figure 70 and 71.

67

060-1701.D: TIC -All MS

1

2

060-1701.D: EIC 295 -All MS

0.0

0.5

1.0

1.5

2.0

2.5

7x10

Intens.

0

1

2

3

4

6x10

2 4 6 8 10 Time [min]

162.9

237.0

277.0

295.1 -MS, 2.2min #276

162.9

236.9

277.0

295.1

-MS, 3.1min #3920

2

4

6

8

5x10

Intens.

0

1

2

3

4

5

5x10

100 150 200 250 300 350 m/z

Figure 70: Diacetone alcohol (5.9 µg/mL) analysed using LCMS showing elution as two peaks (isomers) at

2.2 minutes and 3.1 minutes (m/z 295).

68

058-1501.D: TIC -All MS

1

2

3

058-1501.D: EIC 277 -All MS

0.0

0.5

1.0

1.5

2.0

2.5

7x10

Intens.

0

1

2

3

4

5

6x10

2 4 6 8 10 12 Time [min]

137.9162.9 178.8 231.9 265.0

277.8

-MS, 7.6min #858

162.9232.0

277.8

-MS, 7.8min #886

231.9

277.8

311.2 325.2 339.2

-MS, 8.0min #901

0

2

4

6

4x10

Intens.

0.0

0.5

1.0

5x10

0

1

2

3

5x10

100 150 200 250 300 350 m/z

Figure 71: Mesityl oxide (5.3 µg/mL) analysed using LCMS showing elution as three peaks (m/z 277) at 7.6

minutes, 7.8 minutes and 8.0 minutes.

Table 19 and 20 below shows the analysis of the reaction mixture done in triplicate.

Diacetone alcohol (m/z 295) (table 20) was quantified by summing two peaks and levels

were expressed as acetone equivalents. Average two hour adsorption levels were

obtained from sample 001 and 002 only. Average levels of diacetone alcohol present in

the two hour adsorption samples were 1.4 ng/mg. Average levels obtained of the two

hour adsorption experiments with exposure to UV were obtained from sample 005 and

006 only. Average levels of diacetone alcohol obtained, with exposure to UV, were 1.4

ng/mg suggesting that UV did not affect the conversion of acetone to diacetone alcohol.

69

Table 19: Acetone adsorbed on alumina after exposure to UV.


Concentration

(ng/mg)

/001 2 hr 29

/002 2 hr 24

/003 2 hr 12

/004 2 hr + UV 15

/005 2 hr + UV 30

/006 2 hr + UV 21

Table 20: Diacetone alcohol adsorbed on alumina.


Concentration

(ng/mg)

/001 2 hr 1.5

/002 2 hr 1.4

/003 2 hr < 0.5

/004 2 hr + UV < 0.5

/005 2 hr + UV 2.2

/006 2 hr + UV 0.6

Traces of mesityl oxide were detected in adsorption samples from experiments done in

the absence of UV radiation and samples from experiments done in the presence of UV

radiation. The amounts of the two acetone aldol condensation products with and without

the presence of UV light are summarised in figure 72.

Figure 72: Summary of acetone, diacetone alcohol and mesityl oxide in adsorption and adsorption with

UV light.

70

Due to recovery issues with extraction of the carbonyls from the alumina particles,

subsequent derivatisation and analysis by LCMS, an attempt was made at quantification

using TD-GCMS.

In a separate experiment, adsorption of acetone on alumina in the presence of UV

radiation showed the presence of mesityl oxide, diacetone alcohol as well as acetone. The

chromatograms and mass spectra of diacetone alcohol and mesityl oxide present in the

adsorption samples after exposure to 254 nm UV light are shown in figure 73, 74 and 75,

76 respectively. The chromatogram and mass spectrum of a mesityl oxide standard is

shown in figures 77 and 78. Reliable quantification was not successful due to internal

standard errors and project time constraints did not permit a repeat experiment.

Figure 74: Mass spectra of diacetone alcohol (9.681

min) in 2 hour acetone adsorption sample with

exposure to 254 nm UV light.

Figure 73: TD-GCMS chromatogram of diacetone

alcohol (9.681 min) in 2 hour acetone adsorption

sample with exposure to 254 nm UV light.

71

As with the acetaldehyde photochemistry experiments, an experiment was done to

confirm that γ-alumina was the agent of transformation of acetone to diacetone alcohol

and mesityl oxide. In this exposure of ultraviolet radiation to acetone was conducted

Figure 75: TD-GCMS chromatogram of mesityl

oxide (8.499 min) in 2 hour acetone adsorption

sample with exposure to 254 nm UV light.

Figure 76: Mass spectra of mesityl oxide (8.499

min) in 2 hour acetone adsorption sample with

exposure to 254 nm UV light.

Figure 77: 1040 ng/μL mesityl oxide standard. Figure 78: Mass spectrum of mesityl oxide peak at

8.450 minutes.

72

without the presence of γ-alumina. Diacetone alcohol and mesityl oxide were not

detected and this confirmed that γ-alumina was the agent of transformation.

73

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