ceng 5760 advanced physico-chemical treatment …kexhu.people.ust.hk/ceng576/576-01.pdf · ceng...

CENG 5760 Advanced Physio-Chemical Treatment Processes

Professor Xijun Hu

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CENG 5760 Advanced Physico-Chemical

Treatment Processes

Instructor: Professor Xijun Hu (Tel: 2358 7134)

Room 5579; Email: [email protected]

www page: http://ihome.ust.hk/~kexhu

Course Objectives:

to understand various waste treatment technologies at an

advanced level.

to enable students to be able to design suitable waste treatment

processes for selected pollution problems

References:

R.E. Hayes and S.T. Kolaczkowski, “Introduction to Catalytic

Combustion”, Gordon and Breach Science Publishers, 1997.

B.K. Hodnett, “Heterogeneous Catalytic Oxidation”, John Wiley

& Sons, 2000.

V.F. Kiselev and O.V. Krylov, “Adsorption and Catalysis on

Transition Metals and Their Oxides”, Springer-Verlag, 1989.

C.J. Geankoplis, “Transport Processes and Unit Operations”,

3rd ed., Prentice Hall, Englewood Cliffs, New Jersey, 1993.

Assessments: Assignments: 20%

Mid-semester test: 40%

Final Exam: 40%

mailto:[email protected]

http://home.ust.hk/~kexhu


Professor Xijun Hu

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What to do if you have questions/problems:

Email me: [email protected]

Visit me at my office: Room 5579

Encourages:

Ask & answer questions in the class

Discuss the course materials & homework after class

Preview the course materials before the class

Disciplines:

Turn off all mobile phones in the class

No talks between students in the class

Do not copy other‟s homework (both people copied &

being copied will be penalized)

Do not cheat in the examinations

mailto:[email protected]


Professor Xijun Hu

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Lecture Outlines

Week Contents

1 Introduction

1-5 Advanced Combustion

6-7 Wet air Oxidation

8 Midterm examination (21 March) 10-11 Membrane separation 12 Advanced Oxidation 14 Final examination (9 May)


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Why advanced physio-chemical treatments are needed?

The need for finding solutions to environmental problems in

Hong Kong and its region is more urgent than ever. The

problems are of increasing concern to the Hong Kong SAR

Government, the health authorities and the public. This is

true with both the aquatic and the atmospheric environments.

Conventional remediation technologies do not provide all the

solutions, particularly with regard to problems that are

regional in nature. Innovative technologies to be studied in

this course have the potential to provide supplementary

solutions.


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Air Pollutants

Aerosols

Two types of aerosols: volcanoic aerosols, a short-lived spurt in ozone depletion, ↑Cl effectiveness; propellants from pressurized container

Asbestos

Fibrous, heat resistant, ↑ airborne concentration when demolition, repair….

Carbon Monoxide (CO)

Highly toxic, replace oxygen adsorption sites in red blood cells.

Chloroflurocarbons (CFCs); Hydrochloroflurocarbons (HCFCs)

As refrigerants; Ozone-depleting substance, effects measured by ozone depletion potential (typically ranged 0.01-10), CFCs and HCFCs are around 0.01-1.0; halons is up to 10

Ozone (ground level, O3) Upper ozone (protection) and lower ozone (smog), “Good up high, bad nearby”

Hazardous Air Pollutants

187 pollutants, carcinogenic, tetratogenic

Lead (Pb) Lead accumulation, damage to liver, central nervous and peripheral systems

Mercury (Hg)

Emission from fossil-fuel driven power plants (75 tons Hg/yr by coal, 67% to air in 1999)

Nitrogen Oxides (NOx)

NOx (NO2, N2O, NO), acid rain when combined with water in atmosphere

Particulate Matter (PM)

Complex mixture of extremely small particles & liquid droplets

Sulfur Dioxide (SO2) Acid rain formation, originated from fossil fuel combustion

Volatile Organic Compounds (VOCs)

Damage to organs, such as benzene (carcinogenic), formaldehyde from paints

According to The Clean Air Act, the EPA requires to set National Ambient Air Quality

Standards (NAAQS) for six common air pollutants which are CO, NOx, SO2, PM, Pb,

and O3.

In The Clean Air Act, there are two types of national air quality standards.

- Primary standards set limits to protect public health, including the health of

“sensitive populations”.


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- Secondary standards set limits to protect public welfare, including protection

against visibility impairment, damage to animals, crops, vegetation, and

buildings.


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Review of conventional combustion

Combustion systems are designed to destroy organic

compounds of waste. By destroying the organic

fraction and converting it to carbon dioxide and water

vapor, combustion reduces the waste volume and its

threat to the environment. The heat released from

combustion can be used as energy source.

Good combustion is good oxidation of the organic

compounds - carbon and hydrogen. To achieve this,

air, which contains only 21% oxygen by volume,

must be thoroughly mixed with the carbon and

hydrogen of the fuel (waste) to produce a

stoichiometric product of carbon dioxide and water.

The 79% nitrogen in the air is inert and gets in the

way of the combustion process.

Given a completely homogeneous system (a well-

stirred reactor) which requires both Time and

Turbulence, the complete oxidation of carbon and

hydrogen should occur at some prescribed

Temperature. The three Ts of combustion affect the

reaction. Decrease one of these factors requires the

other two be increased to achieve the same degree of

combustion completeness.


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For this reason, very few combustion reactions are

complete at their minimum theoretical temperature or

amount of air. As the turbulence (mixing) of the

reactor improves, and the reaction time increases, the

amount of excess air (oxygen) needed in the reaction

decreases.

Typical combustion process reactions are C O2 N2 CO2 N2 O2 HEAT

H2 O2 N2 H2O N2 O2 HEAT

CH4 O2 N2 CO2 H2O N2 O2 HEAT

Example: A waste mixture of 30% toluene, 65%

acetone, and 5% water is to be turned in a liquid

injection type incinerator at a rate of 1000 lb/h using

20% excess air.

Compound Formula Heating value (Btu/lb)

Toluene

Acetone

Water

C6H5CH3

CH3COCH3

H2O

18,252

13,120

0

1. What is the total heat release in the incinerator?

2. What is the percent by volume of each

component in the flue gas?

Solution.

1. Toluene heat release =0.3018,252 = 5,476 Btu/lb


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Acetone heat release =0.6513,120 = 8,528 Btu/lb

Water heat release = 0 Btu/lb

Heat release

per pound of mixture =14,004 Btu/lb

Heat release in the reactor

= 1000 lb/h14,004 btu/lb = 14,004,000 Btu/h

2. C6 H5CH3 9O2 7CO2 4H 2O

The molecular weight of toluene is 92

The weight of toluene is 0.301000 lb/h=300 lb/h

300/92 = 3.26 moles/h of toluene

Constituent MW Moles/h

Toluene

O2

C O2

H2O

92

32

44

18

3.26

29.34

22.82

13.04

The oxygen in the table above is the stoichiometric

amount. An excess amount of 20% has been

specified and this excess will be in the flue gas as O2.

0.229.34 = 5.87 moles/h of O2 in addition to the above.

But air, not oxygen is used in the incinerator, and air

is 79% nitrogen, 21% oxygen. Therefore, all of the

N2 will be in the flue gas.

29.34+5.87=35.21 moles/h of O2 are required, or

79/2135.21=132.45 moles/h of N2.

Using the same approach for acetone: CH3COCH3 4O2 3CO2 3H 2O


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The molecular weight of acetone is 58

The weight of acetone is 0.651000 lb/h =650 lbs

650/58 = 11.21 moles/h of acetone

Constituent MW Moles/h

Acetone

O2

C O2

H2O

58

32

44

18

11.21

44.84

33.63

33.63

Excess O2 = 0.244.84 = 8.99 moles/h

Total O2 = 44.84+8.99 = 53.83 moles/h

Therefore N2 = 79/2153.83 = 202.5 moles/h

In addition to the above is 5% water in the waste, 50

lb/h, or 50/18 = 2.78 moles/h.

By adding the moles of flue gas generated from the

three waste components the total moles of each can

be determined.

CO2 H2O O2 N2

Toluene Acetone

Water

22.82 33.63

13.04 33.63

2.78

5.87 8.99

132.45 202.50

Totals 56.45 49.45 14.86 334.95

Total moles/h =455.71

Mole%=Vol%

Flue gas (%) is

12.39% CO2

10.85% H2O

3.26% O2

73.50% N2


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Regulations

A trial burn and a detailed report including a complete

waste analysis quantifying the hazardous constituents

in the waste to be burned, a detailed engineering

description of the incinerator must be done to obtain a

permit for the incineration facility.

The following performance standards apply to

hazardous waste incinerators in the U.S.

Emissions of particulates - 0.08 grains/dry standard

cubic foot (dscf) (180 mg/dscm) corrected to 7%

O2 in the flue gas.

Emission of HCl - 4 lb/h or 99% control.

Carbon monoxide emissions - 100 ppmv as a 60

minute rolling average corrected to 7% O2

measured on a dry basis.

Metals emissions - Emissions of ten priority metals

must meet risk based guidelines.

Destruction and Removal Efficiency (DRE) - The

incinerator must demonstrate its capability to

achieve a 99.99% DRE on one or more selected

Principle Organic Hazardous Constituents

(POHCs) during a supervised Trial Burn.


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DRE Win Wout

100% Win

where Win = Mass feed rate of a particular POHC

Wout = Mass emission rate of the POHC

Oxygen correction - Emissions are corrected to 7%

oxygen in the stack on a dry basis

P P 14

c m 21 Y

where Pc = corrected concentration Pm = measured concentration

Y = O2 concentration in stack (dry basis)

Example: The carbon monoxide (CO) concentration

in the stack from a hazardous waste incinerator is

measured at 20 ppm by volume at a temperature of

175 oF. The oxygen concentration in the stack is

measured to be 12% by volume on a wet basis. The

water content of the stack gas is 10 mole %. In

another test the particulate concentration in the stack

is measured at 20 mg/dscf at a stack oxygen

concentration of 12% measured on a dry basis at 70 oF.

1.What is the corrected CO content in the stack gas?

2.What is the corrected particulate concentration?

3.Would this meet federal regulations?


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1. The oxygen concentration in the stack on a dry

base is 12%/(1-0.1)=13.33%

P P 14

c m

corrected

21 Y

CO 20

14

21 13.33

36.52

ppm

2. The corrected particulate concentration is

20 14

21 12

31.1

mg/dscf

1098

mg/dscm

3. CO < 100 ppm OK

Particulate > 180 mg/dscm exceeds the limit

So this incinerator does not meet federal

regulations


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Example: The mixture described below is being

incinerated at 2000 oF with 50% excess air and a

residence time of 2.1 seconds. Principal Organic

Hazardous Constituents (POHCs) for this waste are

benzene, chlorobenzene, and toluene. The flow rate

of gas from the incinerator is measured at 12,500

dscfm (dry standard cubic feet per minute). The O2

concentration in the flue gas is 7.0%. Particulates out

is 7000 grains/lb.

Compound

Formula

Mol. wt.

Inlet

(lb/h)

Outlet

(lb/h)

Benzene

Chlorobenzene

Ethylbenzene

Toluene

Xylene

Hydrochloric

acid

Particulates

C6H6

C6H5Cl

C8H10

C7H8

C8H10

HCl

78.11

112.5

106.17

92.10

106.17

36.45

2015

1150

2230

637

3040

0

0.537

0.109

0.757

0.022

1.25

10.7

23.4

1.Calculate DRE for all of the organic compounds

2.Determine if this emission meets requirements for:

(a) POHCs

(b) Particulates

(c) HCl

3. Comment on the results


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Solution.

1. For benzene, DRE = [(2015-0.537)/2015]x100

=99.9733%

DREs for the other compounds are obtained in a

similar way and shown below.

2. (a) The DRE for benzene is less than 99.99%, so

this emission does not meet the regulation.

(b) The outlet particulate concentration is

(23.4 lb/h) (7000 grains/lb)

(12,500 dry std ft 3 / min)( 60 min/h)

0.218 grains/dscf

(c) Inlet HCl=(1150 lb/h)(36.45/112.5)=372.6 lb/h

The removal efficiency for HCl is

[(372.6-10.7)/372.6]x100% = 97.128%

which is less than the required 99%.


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3. The emission from this unit fail to meet any of the

three regulations listed. If these were the results of a

test burn, this unit would not pass.

Excess Air

When organic wastes are burned with a

stoichiometric amount of air (oxygen), the products

of complete combustion should not include any

oxygen. This is known as “perfect combustion”

which is not possible in commercial burners or

incinerators. Incinerators must always utilize excess

air to achieve good combustion.


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Advanced (Catalytic) Combustion

Main differences between conventional

(homogeneous) combustion and advanced

(catalytic) combustion

Conventional

combustion

Catalytic

combustion

Flame required Yes No

Operation temperature High Low

Emission of NOx

(formed at T>1500oC)

High Low

Fuel to air ratio Within the

flammability

limits

Not

constrained

Other constrains on

reactor design

More Fewer

For examples, for methane in air, the flammability

limits are between 5% and 16% methane by volume,

and therefore flames can only occur between these

two compositions. A spark or pilot flame is also

required for conventional combustion.

Temperatures within the flame often exceed the

maximum desired process temperature. The outlet

gas temperature is controlled by the addition of air in


Professor Xijun Hu

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excess of that required for complete combustion of

the fuel.

Catalytic combustion does not require the presence of

a flame, nor is it bound by flammability limits, nor is

it penalized by the severity of the conditions within a

flame.

The minimum inlet gas temperature required to

achieve complete combustion depends on the catalyst

used. The maximum temperature in a catalytic

combustion process is usually lower than 1000 oC.

At these low temperatures thermal NOx would not be

formed.

Catalytic combustion is therefore an alternate form of

combustion that provides an opportunity for a cleaner

combustion process. It also makes it possible to

design more compact furnaces and reactors and use

low calorific value fuels that cannot sustain a

conventional flame. Catalytic combustion may also

be utilized to combust volatile organic compounds

(VOC) present at low concentrations in air streams.


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Terminology and conservation equations

Homogeneous reaction – All of the species involved

in the reaction are present in a single phase.

Heterogeneous reaction – More than one phase is

involved in the reaction.

Exothermic reaction – A reaction in which heat is

release. All combustion reactions are exothermic.

Endothermic reaction – A reaction in which heat is

absorbed by the reacting mixture when it reacts.

Rate of reaction – Under specified conditions of

temperature and concentration a chemical reaction

will proceed at a certain rate. The reaction rate is

usually expressed in terms of a unit reactor volume

(mol/m3

s), a unit mass of catalyst (mol/kg s) or

catalyst surface area (mol/m2

s).

Catalyst – A catalyst is a substance which is

introduced to a mixture with the intent to increase the

rate of reaction. The catalyst does this by providing

an alternative reaction pathway that has a smaller

activation energy than the uncatalysed reaction.


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Homogeneous catalysts – the catalyst and the

reactants are in the same phase.

Heterogeneous catalyst – the catalyst is in a

different phase than the reactants.

Support – It is often desirable in heterogeneous

catalysis to have a large surface area for reaction. One

method is to spread out the active catalyst on the

surface of a porous support material. The other

benefit of using a support is that the amount of active

ingredient (usually noble metals) so the cost is

reduced. The surface area can be increased from

about 5 cm2/g (unsupported catalyst) to 10 – 1000

m2/g when porous support is used.

The pore size of the support is classified according to

the average width (or diameter):

Micropores – small pores with widths less than 2

nm,

Mesopores – intermediate pores with widths

between 2 nm and 50 nm,

Macropores – large pores with widths more than

50 nm

Diffusion – Diffusion is a mass transfer phenomenon

which occurs at the molecular level.


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F

N

Conversion – This is a measurement of the amount

of reactant that reacts. For a batch reactor,

fractional conversion of component A (XA) is

defined as

X N A0 N A

A A0

where NA0 and NA are the moles of the initial and

present after some reaction, respectively.

For a flow reactor,

fractional conversion is defined as

X FA0 FA

A A0

where FA0 and FA are the molar flow rate of the inlet

and outlet, respectively.

The moles can be replaced by concentration.


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Catalytic combustion in a single catalyst coated

channel

Let us consider a gaseous fuel (e.g. methane) and air

mixture flowing inside a circular channel, the walls of

which have been coated with a catalyst.

The oxidation of the fuel occurs on the surface of the

catalyst which in turn is usually dispersed in a high

surface area porous solid. The reaction is

heterogeneous because we have both gas and solid

phases. The role of catalyst is to provide alternative

lower-energy pathways for the reaction which result

in an increase in the rate of reaction.

Catalysts and their associated support systems operate

effectively only for a limited and well defined

temperature range. As temperature increases the

catalytic rates in the catalytic layer increase but the

overall combustion may be limited by the mass

transfer processes.


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There are five steps for the combustion to complete.

1. External or interphase mass transfer – the

reactants in the bulk gas stream must be

transported to the external surface of the catalyst.

2. Internal or intraphase mass transfer – the

reactants need to diffuse into the porous structure

that contains the dispersed catalyst.

3. Surface reactions – takes place on the catalytic

sites within the porous structure.

4. Products diffuses through the porous structure to

the external catalyst surface.

5. Products are transported to the bulk gas stream.


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Catalyst support systems

Catalysts for combustion may be supported on a

variety of materials, e.g. pellets, honeycomb

monoliths, parallel plates, fibre pads and gauze, and

sintered metals.

Pellets in a packed or fluidized bed

The pellet structure is normally highly porous

providing a large internal surface area on which the

catalyst is dispersed. Surface area can vary from 10 to

200 m2

per gram of catalyst.

As pellets are often made by compressing smaller

particles together, they contain micropores

representing the pores in the particle, and macropores

that represent the space between the compressed

particles.

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CENG 576 Advanced Physio-Chemical Treatment Processes Professor Xijun Hu

Multichannel monoliths

The monolith or honeycomb reactor is a commonly

used configuration in catalytic combustion. It

consists of a number of parallel passageways through

which the gas flows, with the catalyst being located

on the channel walls.

The monolith configuration has the following

features:

combination of a high surface-to-volume ratio

with low pressure drop.

The uniformity of the honeycomb matrix helps to

ensure an even flow distribution across the bed

with minimal „channeling‟.

If particulates are present in the gaseous stream

these can pass easily through the reactor,

provided that the diameter of the channel is

greater than that of the particles.

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'


a)

Professor Xijm Hu

.. . .

. .... ' \

( ' ' ',

' " .. .. ·.

' .......;-.

-t·...

PlATE 1.3 A ceramic catalytic monolith.

(a) End view of a 177mm diameter section, channel size approximately 1.1 mm x 1.1 mm.

(b) Magnified photograph of a cross-section that was cut through the monolith (note: in

some of the cells the washcoat has flaked from the surface -this occurred during cutting).

34

Professor X:ijrn Hu CENG 576 Advanced Physio-Cherrical Treatment Processes

a)

b)

PLATE 1.4 A metal catalytic monolith.

(a) End view of a 122 mm diameter section.

(b) Magnified photograph of an end face illustrating the shape of the cells. Approximate

cell size: height 0.9 mm; ·width 1.7 mrn.

35

CENG 576 Advanced Physio-Cherrical Treatment Processes Professor Xi.jtn1 Hu

PLATE 1.5 A magnified photograph of the end face of a monolith with hexagonal shaped

cells coated with catalyst.

PLATE 1.6 Metal monoliths can be assembled in a wide variety of shapes. Photograph

supplied courtesy of Emitec GmbH, Lohmar, Germany.

36

CENG 576 Advanced Physio-Cherrical Treatment Processes Professor Xi.jtn1 Hu

PI.ATE 1.7 Ceramic monoliths can be formed in a wide variety of shapes. Photograph

supplied comtesy of Corning Inc, New York, USA.

37

Professor Xijtm Hu CENG 576 Advanced Physio-Cherrical Treatment Processes

a)

PlATE 1.8 Scanning electron micrograph (SEM) of two types of cordierite support, sup

plied courtesy of NGK-Locke, Inc., Southfield, USA.

(a) wall porosity 35%; wall thickness 0.15 mrn.

(b) wall porosity 28%; wall thickness 0.10 mm.

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Macroscopic and microscopic structure of

heterogeneous catalysts

A mixture of hydrocarbon and oxygen passing

through a catalyst bed at elevated temperature

Heterogeneous catalytic combustion (oxidation

reaction) occurs at the gas-solid interface

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industrial reactor, meter scale

pellet (uniform particle size), mm scale

catalyst particles (1-50 m, binder may be used to

form pellet)

surface, nm scale

active site, sub-nm scale

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Catalyst dispersion

The catalyst is often dispersed in a support to create a

large number of surface metal atoms. When a catalyst

is highly dispersed the reaction rate should be higher

per unit mass of active ingredient, provided that

reactants can gain access to the catalytic sites.

Catalyst poisoning and fouling

Poisoning and fouling are two mechanisms of

catalyst deactivation: both result in the loss of active

catalyst area. Poisoning is a result of chemisorption of

species that are present in the reactor feed. The

chemisorption is so strong that the active sites

become permanently blocked (irreversible poisoning).

Fouling also blocks access to active sites due to the

physical or chemical adsorption of species formed in

the reactor from side reactions. An example is the

deposition of carbon which can result from the

cracking of methane.

Catalyst promoters

A promoter refers to an additive that enhances the

intrinsic catalytic activity.

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Steady state testing of heterogeneous catalysts

gas delivery system (gas flows are controlled by

mass flow controllers)

reactor (to accommodate 0.1 – 5 g of catalyst and

operate at 400 – 1100 K)

analytical system (comprises GC and sometimes

MS analysis)

conversion

selectivity

yield

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Transient analysis (temporal analysis of products,

TAP)

inject a gas pulse of very short duration (1 – 10

ms) into one end of reactor and continuously

evaluating the other end

the exit gas pulse (dissipated to a width of ~ 500

ms) travels as a molecular beam

the reactor effluent is analyzed by mass

spectroscopy (MS)

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TAP of propene and oxygen over Bi2Mo06

catalyst at 723 K

0 100

Time (msec) 200

Figure 2.5 TAP experiment showing the emergence of reactants and products during

the reaction of propene and oxygen over Bi2Mo06 at 723 K (Gleaves et al., 1988)

(renroduced bv nermission of Marcel Dekker);

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Safety consideration: flammability of

hydrocarbon-oxidant mixtures

Homogeneous combustible gas-air mixtures are

flammable only within a limited range of

compositions, between LFL and UFL.

LFL (LEL) – Lower flammability (explosive) limit

UFL (HEL) – Upper (higher) flammability

(explosive) limit

Generally the LFL for most hydrocarbons is 45 -50

mg/(liter air). Flammability at 298 K can be related to

the stoichiometric composition (CST).

LFL298 = 0.55CST

UFL298 = 0.48CST0.5

UFL298 = 0.65LFL2980.5

Flammability limits widen as temperature and

pressure are increased, narrow as inert gases are

added.

Let’s take an example of methane,

CH4 2O2 = CO2 2H2O

2 mol of O2 = 2/0.21 mol air

So CST = 1/(1+2/0.21) = 0.052 = 5.2%

45


Table 2.2. Summary of limits of flammability at 298 K and autoignition temperatures of

individual gases and vapours in air at atmospheripressure (Zabetakis, 1965)

Combustible Limits of jlammabilitylvol Autoignition

temperature (AIT)IK

LFL29s UFL29s

Hydrogen 4 75 673 Deuterium 4.9 75

Ammonia 15 28

Carbon monoxide 12.5 74

Methane 5 15 813 Ethane · 3 12.4 788

Ethene 2.7 36 763

Ethylene oxide · 3.6 100 -<

Acetylene 2.5 100 578.

Vinyl chloride 3.6 33

Propane 2.1 95 723

Propene 2.4 11 . 733

Acrolein 2.8 31 508 Acrylonitrile 3.0

Acetone 2.6 13 738 1,3-Butadiene 2.0 12 . 693

1-Butene 1.6 10 658

2-Butene 1.7 9.7 598 n-Butane 1.8 8.4 . 678 .

Isobutane 1.8 8.4 733

Isobutene 1.8 .. 9.6 738 Benzenea 1.3 7.9 873

Toluenea 1.2 7.1 753

n-Nonane 0.85·. - 2,2,3,3-Tetramethylpentane 0.80

0At 373 K.

478

703

46


Influence of temperature on flammability limits

LFLT/LFL298 = 1 – 0.000784 (T – 298 K)

UFLT/UFL298 = 1 + 0.000721 (T – 298 K)

47


Mixtures of combustibles

LFL298 100 / Ci / Li , Ci 100

where Li is the LFL of component i.

Example: A mixture of 60% methan, 25% ethane and

15% propane by volume has a LFL298 in air of

LFL298 100 /60 / 5 25 / 3 15 / 2.1 3.6 vol%

Influence of pressure

Autoignition temperature (AIT)

The AIT is defined as the lowest temperature at

which ignition can occur.

48


Thermodynamics

Open and closed systems

The universe is divided into a system and its

surroundings. The system is the portion of the

universe (e.g. a chemical reactor) and the remainder

of the universe is the surroundings. The system is

separated from the surroundings by the system

boundary.

In a closed system the mass of the total material in the

reactor is constant and no mass can enter or leave the

system, but heat transfer can happen.

In an open system material is allowed to cross the

system boundary.

Equation of state

The standard state for gaseous systems refers to 1

atm and the temperature of the system.

The simplest equation of state is the ideal gas law.

PV = nRT

When non-ideal gas is encountered, a compressibility

factor, Z, is used to correct the equation of state.

PV=nZRT

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M

n

Multicomponent mixtures

Let mi denote the mass of component i in a mixture

containing n components, the total system mass is: n

m mi i 1

For a mixture of volume V the mixture mass density

and the species mass density are:

m

, V

i

mi

V The mass fraction is

w mi

i i

m

Let Mi denote the malar mass of species i, the number

of moles is

n mi

i i

The molar density (or concentration) is

Ci i V

i

M i

The mole fraction of a component i in a gaseous

mixture is

50


C

Yi i C

The partial pressure of a component in an ideal gas

mixture is the product of mole fraction and the total

pressure, viz:

Pi Yi P The average molar mass of a mixture is

n

M m Yi M i i 1

Example: Calculate the molar mass for air with a

composition of 78.08 mol% N2, 20.95 mol% O2 and

0.97 mol% Ar.

28.01 x 0.7808 + 32.00 x 0.2095 + 39.9 x 0.0097

= 28.96 g/mol

The volumetric flow rate (QV) of an ideal gas is PQV FT RT

where FT is the total molar flowrate.

ceng 5760 advanced physico-chemical treatment …kexhu.people.ust.hk/ceng576/576-01.pdf · ceng...

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