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DEHYDRATION OF ETHANOL ON ZEOLITE
BASED MEDIA USING ADSORPTION PROCESS
BY
FOUAD R. H. ABDEEN
A dissertation submitted in fulfillment of the
requirements for the degree of Master of Science in
Biotechnology Engineering
Kulliyyah of Engineering
International Islamic University
Malaysia
MAY 2012
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ABSTRACT
Continuous depletionof fossil fuels and the following increase in fuels price have
directed researchers towards producing fuel ethanol from biological materials. The
main challenge encountered in ethanol production process is the removal of large
excess amount of water within the produced ethanol. Distillation, though is an energy
extensive process, is usually used to produce ethanol up to 95% purity. Production of
higher purity ethanol is usually a major challenge due to the formation of an
azeotrope. In this study, an adsorber bed apparatus was designed, fabricated and used
to purify ethanol up to 99.5%. The apparatus consists mainly of fluid delivery system,
storage and sampling unit and adsorption column where adsorbents like zeolite can be
packed. The apparatus is designed to be packed and repacked several times and with
various types of adsorbents. 3A zeolites are used as water adsorbent materials in this
study. 3A zeolites proven to be efficient in removal of water from ethanol-water
azeotrope since their pore size is less than 0.3nm which allows only water to adsorb to
the inner large surface area of zeolite. An optimization process was performed for the
dehydration process manipulating three process parameters, namely; feed
concentration, feed flow rate and adsorption temperature. Optimum set was
determined to be at 95 % feed concentration, 200 ml/min flow rate and 25 ºC
adsorption temperature. Validation of the optimum set resulted in the production of
ethanol of 99.5% purity and with 91 % efficiency of recovery.
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APPROVAL PAGE
I certify that I have supervised and read this study and that in my opinion it conforms
to acceptable standards of scholarly presentation and is fully adequate, in scope and
quality, as a thesis for the degree of Master of Science in Biotechnology Engineering.
………...………………………….
Maizirwan Mel
Supervisor
I certify that I have read this study and that in my opinion it conforms to acceptable
standards of scholarly presentation and is fully adequate, in scope and quality, as a
thesis for the degree of Master of Science in Biotechnology Engineering.
………....………………………….
Ahmad Tariq Jameel
Internal Examiner
I certify that I have read this study and that in my opinion it conforms to acceptable
standards of scholarly presentation and is fully adequate, in scope and quality, as a
thesis for the degree of Master of Science in Biotechnology Engineering.
………....………………………….
Prof. Dato' Rusli Mohd Yunus
External Examiner
This dissertation was submitted to the Department of Biotechnology Engineering and
is accepted as a fulfillment of the requirement for the degree of Master of Science in
Biotechnology Engineering.
…………………………………….
Md Zahangir Alam
Head, Department of
Biotechnology Engineering
This thesis was submitted to the Kulliyyah of Engineering and is accepted as a
fulfillment of the requirement for the degree of Master of Science in Biotechnology
Engineering.
…………………………………….
Amir AkraminShafie
Dean, Kulliyyah of Engineering
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DECLARATION
I hereby declare that this dissertation is the result of my own investigation, except
where otherwise stated. I also declare that it has not been previously or concurrently
submitted as a whole for any other degrees at IIUM or other institutions.
Fouad R. H. Abdeen
Signature………………………………. Date…………………………
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INTERNATIONAL ISLAMIC UNIVERSITY MALAYSIA
DECLARATION OF COPYRIGHT AND
AFFIRMATION OF FAIR USE OF UNPUBLISHED
RESEARCH
Copyright © 2012 by Fouad R. H. Abdeen. All rights reserved.
DEHYDRATION OF ETHANOL ON ZEOLITE BASED MEDIA USING
ADSORPTION PROCESS
No part of this unpublished research may be reproduced, stored in a retrieval
system, or transmitted, in any form or by any means, electronic, mechanical,
photocopying, recording or otherwise without prior written permission of the
copyright holder except as provided below.
1. Any material contained in or derived from this unpublished research
may only be used by others in their writing with due
acknowledgement.
2. IIUM or its library will have the right to make transmit copies (print of
electronic) for institutional and academic purposes.
3. The IIUM library will have the right to make, store in a retrieval
system and supply copies of this unpublished research if requested by
other universities and research libraries.
Affirmed by Fouad R. H. Abdeen
…………………………….. …………………………..
Signature Date
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ACKNOWLEDGEMENTS
My utmost gratitude goes to the Almighty, Allah (swt), for He only made this study
possible, and gave me the knowledge and strength to carry it out to the best of my
knowledge and ability. And I would like to express my sincere gratefulness to my
supervisor Assoc. Prof. Dr. Maizirwan Mel for guiding me to successfully accomplish
this study, and for sharing his extensive knowledge on the subject matter. I am
thankful for having the chance to work under his supervision as he was an inspiration
for thirst for knowledge, dedication, and professionalism. I would also like to thank
my co-supervisors Assist. Prof. Dr. Maan Al-Khatib and AzlinSuhaidaAzmi for the
time and effort they spent to make this study a success.
I am exceptionally thankful to my parents, brothers, and sisters for their
continuous encouragement and support during the course of this study. Their
motivation was the fuel that kept me going, and got me through the difficulties and
hard times.
Last but not least, I would like to thank everyone who in one way or another
contributed to my study.
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TABLE OF CONTENTS
Abstract ……………………………………………………………………..... i
Abstract in Arabic …………………………………………………………..... iii
Approval Page……………………………………………………………….... iv
Declaration Page ……………………………………………………………… v
Copyright Page ……………………………………………………………….. vi
Acknowledgements …………………………………………………………… vii
List of Tables …………………………………………………………………. x
List of Figures…………………………………………………………………. xi
List of Abbreviations………………………………………………………….. xii
List of Symbols……………………………………………………………….. xiii
CHAPTER 1: INTRODUCTION…………………………………………… 1
1.1 Background………………………………………………………………... 1
1.2 Problem Statement and its Significance…………………………………… 2
1.3 Research Objectives………………………………………………………. 4
1.4 Research Scope……………………………………………………………. 4
1.5 Research Methodology……………………………………………………. 5
1.6 Dissertation Organization…………………………………………………. 8
CHAPTER 2: LITERATURE REVIEW…………………………………… 9
2.1 Introduction………………………………………………………………. 9
2.2 Overview on Ethanol………………………………………………………. 10
2.2.1 Global Production and Demand of Bio-ethanol…………………. 10
2.2.2 Bio-ethanol Production Process………………………………….. 13
2.3 Ethanol-Water Separation Techniques…………………………………….. 15
2.3.1 Distillation……………………………………………………….. 15
2.3.2 Pervaporation…………………………………………………….. 17
2.3.3 Adsorption……………………………………………………….. 18
2.4 Molecular Sieves Zeolite Technology……………………………………… 19
2.4.1 Common Industrial Zeolites……………………………………... 20
2.4.2 Zeolites for Ethanol Dehydration………………………………… 22
2.5 Fixed Bed Adsorption……………………………………………………… 23
2.5.1 Equilibrium Studies of Fixed Bed Adsorption…………………… 24
2.5.2 Kinetic Studies of Fixed Bed Adsorption………………………... 26
2.6 Apparatuses Designed as Fixed Bed Adsorbers…………………………… 28
2.7 Adsorption Process for Ethanol Dehydration………………………………. 30
2.8 Summary…………………………………...………………………………. 32
CHAPTER 3: MATERIALS AND METHODS…………………………….. 34
3.1 Introduction………………………..……………………………………….. 34
3.2 Material and Chemical Preparation……………………………………….. 34
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3.2.1 Zeolite Materials…………………………………………………. 34
3.2.2 Feed Ethanol Preparation………………………………………… 35
3.2.3 Hydrometer……………………………………………………….. 35
3.3Equations and Apparatus Design Considerations…………………………... 36
3.4Experimental Procedure…………………………………………………….. 38
3.5Data Analysis……………………………………………………………….. 41
3.6Statistical Analysis and Optimization Method……………………………… 41
3.7 Summary…………………………………...………………………………. 43
CHAPTER 4: RESULTS AND DISCUSSION……………………………… 45
4.1 Introduction………………………………………………………………… 45
4.2Adsorber Bed Apparatus Design and Fabrication…………………………... 45
4.2.1Calculations and Design Constraints……………………………… 46
4.2.2Fabrication of Adsorber Bed Apparatus…………………………... 49
4.3Ethanol Purity and Efficiency of Recovery Results………………………… 52
4.3.1 Ethanol Purity…………………………………………………….. 52
4.3.2 Efficiency of Recovery…………………………………………… 53
4.4 Statistical Analysis and Optimization Results……………………………... 56
4.4.1 Design Model and its Evaluation………………………………… 56
4.4.2 Parameters Effect on the Process Responses……..……………… 62
4.4.2.1 Parameters Effect on Ethanol Purity….……………… 62
4.4.2.2 Parameters Effect on Efficiency of Recovery………... 67
4.4.3 Optimization Results……………………………………………... 71
4.5 Validation of Optimized Parameters……………………………………….. 74
4.6 Summary…………………………………...………………………………. 75
CHAPTER 5: CONCLUSIONS AND RECOMMENDATIONS……….…. 76
5.1 Conclusion………………………………………………………………….. 76
5.2 Recommendation…………………………...………………………………. 77
BIBLIOGRAPHY……………………………………………………………..
.
78
PUBLICATIONS …………………………………………………………….. 84
APPENDIX: ABSTRACT AND FULL PAPER OF PUBLISHED WORK. 85
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LIST OF TABLES
Table No. Page No.
2.1 World Production of Bio-ethanol in 2005 and 2006
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2.2 Different Types of Adsorbents Used in Industry
20
3.1 Zeolite Properties as Provided by the Manufacturer
35
3.2 Set of Experiments Performed with Different Parameters
40
3.3 Design of Experiment for the Adsorption Process Using Design
Expert v6 Software
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4.1 Important Calculated Terms
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4.2 Ethanol Purity Results
53
4.3 Efficiency of Recovery Results
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4.4 Design Data as Keyed into Design Expert v6 Software
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4.5 ANOVA for Ethanol Purity Response Selected Model
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4.6 Statistical Terms for Ethanol Purity Response Model
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4.7 ANOVA for Efficiency of Recovery Response Selected Model
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4.8 Statistical Terms for ‘Efficiency of Recovery’ Response Model
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4.9 Parameters Effect on Ethanol Purity and Efficiency of Recovery
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4.10 Constraints Made for Optimization Process Using Design Expert
v6 Software
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4.11 Solutions Obtained from Optimization Process Using Design
Expert v6 Software
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4.12 Ethanol Purity and Efficiency of Recovery Results (Validation
Runs)
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LIST OF FIGURES
Figure No. Page No.
1.1 Flowchart that Explains the Research Methodology 7
2.1 Global Production of Bio-ethanol from 2000 to 2007 12
3.1 Adsorber Bed Column 39
4.1 Ethanol Adsorber Bed Apparatus for Ethanol Dehydration 50
4.2 Design Expert Half Normal Probability Plot for ‘Ethanol
Purity’Model
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4.3 Design Expert Half Normal Probability Plot for ‘Efficiency of
Recovery’ Model
58
4.4 Effect of feed concentration on the ethanol purity response when
flow rate is fixed at 400ml/min and adsorption temperature is
fixed at 37.5 ºC
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4.5 Interaction Graph Showing the Effect of Feed Concentration on
the Ethanol Purity Response
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4.6 Effect of flow rate on the ethanol purity response when feed
concentration is fixed at 90 % and adsorption temperature is fixed
at 50 ºC
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4.7 Interaction Graph Showing the Effect of Adsorption Temperature
on the Ethanol Purity Response
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4.8 Effect of feed concentration on the efficiency of recovery response
when flow rate is fixed at 400 ml/min and adsorption temperature
is fixed at 37.5 ºC
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4.9 Effect of flow rate on the efficiency of recovery response when
feed concentration is fixed at 90 % and adsorption temperature is
fixed at 37.5 ºc
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4.10 Effect of adsorption temperature on the efficiency of recovery
response when feed concentration is fixed at 90 % and flow rate is
fixed 400 ml/min
70
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LIST OF ABBREVIATIONS
3Å 3 Angstrom
PSA Pressure swing adsorption
TSA Temperature swind adsorption
mm millimetre
nm nanometer
𝐸𝑡𝑂𝐻 Ethanol
Kg Kilogram
kW Kilowatt
ANOVA Analysis of variance
V6 version six
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LIST OF SYMBOLS
Å Angstrom equals 10^-10 meter
q adsorbate concentration (mass basis) in the adsorbed phase
T temperature.
c concentration of the adsorbate of the liquid solution.
A adsorption surface area or coefficient of the Freundlich isotherm
equation
K Henry’s law constant
n reciprocal of the exponent of the Freundlich isotherm equation
mq value of q corresponding to complete monolayer coverage
Cadded concentration of adsorbate in the feed, expressed as gram of adsorbate
per milliliter of feed
madded mass of feed added
V added volume of feed fluid added
V liquid volume of effluent solution collected after adsorption
V medium volume of adsorbents used
M w molecular weight of water (g/mol)
V bed volume of bed adsorber (ml)
b
bed density (g/mol)
mbed mass of the zeolite used in the adsorption experiment
bed bulk density of the zeolite used in adsorption
bedV volume of the adsorption column
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C adsorber bed capacity measured as mass of water adsorbed by bed
eqC equilibrium water adsorption capacity
mf.ethanol maximum mass of ethanol-water mixture used per run
Water% percentage of water in the ethanol-water mixture used as feed
𝑉𝑑 volume of ethanol-water mixture drained from the adsorber column
(litres)
EffR efficiency of recovery measured in percentage
𝐸𝑡𝑂𝐻𝑐𝑜𝑛𝑐. concentration of feed ethanol measured in percentage
𝑉𝑐 volume of pure ethanol collected at the end of the dehydration process
(litres)
𝑉𝑓 volume of feed ethanol-water mixture (litres)
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CHAPTER 1
INTRODUCTION
1.1 BACKGROUND
Fossil fuels diminution and the following increase in fuels price have directed
researchers towards finding other sources of energy. In particular special attention has
been given to producing fuels from biological materials. Such fuels are meant to be
environmental friendly and replace the depleting fossil fuel. In fact, ethanol is being
considered as one of the major renewable fuels contributing to the reduction of
pollution impacts generated by the utilization of fossil fuels(Balatet al., 2008).
However, in the ethanol production process, ethanol is being produced with a
large excess of water. The high cost associated with the separation of ethanol from
this large amount of water is considered as a major challenge in the ethanol production
process(Cardona and Sanchez, 2007). Conventionally, ethanol is separated from water
using distillation. However, distillation cannot remove water completely due to the
presence of an azeotrope.
Hence, producingfuel grade ethanol (ethanol of purity higher than 99%) in
commercial amount has been a major challenge facing ethanol producers. Researchers
have been seeking a process that can reduce the water content in ethanol below 1%.
One of the most potential processes to be used is adsorption onzeolite molecular
sieves (PruksathornandVitidsant, 2009).
Dehydration of ethanol by adsorption process has been performed over
different types of zeolite materials.One of the most efficient zeolite materials used for
dehydrating ethanol was 3Å zeolite which has proven to be capable of producing very
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pure ethanol. The purpose of carrying out this research is to study the water adsorption
process and optimize its different parameters on 3Å zeolite materials. An adsorption
system (adsorber bed apparatus)wasdesigned and fabricated for this purpose and an
ethanol of less than 1% water content was produced.
1.2 PROBLEM STATEMENT AND ITS SIGNIFICANCE
In the industrial production of ethanol, whether by chemical or biological process
routes, the raw product is generally a dilute aqueous solution. Ethanol yield of a
biological production process is usually 5% to 10% by weight only. Further
concentration of the ethanol by traditional distillation processes usually is used to
produce an azeotrope containing about 5% water by weight (Ginderand William,
1983).
The recovery of ethanol to dryness in excess of the azeotropic composition is
normally achieved by azeotropic or extractive distillation processes. However, such
separation processes are energy intensive(Carmoet al., 2004; Sowerbyand Crittenden,
2001). Therefore, there is a high demand for non-distillation methods that
economically produce anhydrous fuel ethanol.
To produce ethanol at a high level of dryness, adsorption process on zeolite
material has proven to be of great potential. There have been several researches on
adsorption of water from ethanol-water mixture using zeolite media. Most of these
researchers studied the adsorption of ethanol in vapour phase and/or liquid phase
using some common commercialized zeolite material (Kupiec, 2003).
The effects of feed flow rate, feed concentration and adsorption temperature
are among the interesting factors that are examined. In fact, dehydration by adsorption
on 3Å zeolite is known to have the advantage that the micropores are too small to be
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penetrated by alcohol molecules. Thus, water, in the water ethanol mixture, is
adsorbed without being competed with the ethanol molecules in the liquid phase
(Simo, 2008).
Therefore, dehydration of ethanol by adsorption on 3Å zeolite requires little
energy input compared to other methods(PruksathornandVitidsant, 2009). The
aforementioned dehydration process is believed to have high adsorbent productivity
and is often capable of producing very pure product (Tianet al., 2004).
In fact several studies have emphasized the fact that 3Å zeolite is efficient in
dehydrating ethanol (PruksathornandVitidsant, 2009; Simo, 2008; Teoand Ruthven,
1986). However, only few studies have highlighted the effect of different controlling
parameters in the packed column system on the dehydration process.
Nevertheless, it is well recognized scientifically and practically that different
sets of process parameters will yield ethanol with different purities or produce pure
ethanol with different efficiencies. Hence, there is a real need for evaluating the
different performance of an adsorber apparatus using different set of controlling
parameters.
This study presents the dehydration process as an alternative to the existing
conventional methods. This study also aims to determine the actual effects of different
operating parameters on the efficiency of adsorption of water on 3Å zeolite through
experimental works system mainly in terms of product recovery and enrichment.
The significance of this study arises from the fact that reducing water content
in fuel ethanol below 1% is a crucial step in the ethanol production process. In
addition, with the absence of special researches done to compare between different
sets of parameters on the ethanol dehydration process, this study is considered of a
high importance. This study does not only compare between different sets of process
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parameters, but also sets up an adsorption system that can be packed with different
types of zeolites to dehydrate ethanol.
1.3 RESEARCH OBJECTIVES
This study aims at attaining the following objectives:
1. To design and fabricate an adsorber bed apparatus for ethanol dehydration
on zeolite based media.
2. To purify ethanol and produce final product of less than 1% water content
using the fabricated apparatus.
3. To optimize the controlling parameters in the ethanol dehydration process
using the fabricated apparatus.
1.4 RESEARCH SCOPE
Adsorption process is usually performed under different conditions based on the
controlling parameters. The combination of different parameters, of the ethanol
dehydration process on zeolite materials is expected to yield ethanol of various
purities which is worth optimizing. However, to get an optimum set of adsorption
process parameters, an adsorber bed apparatus is usually needed.
In this study an adsorber bed apparatus containing a column that can be packed
with different materials was designed and fabricated. The adsorber bed apparatus was
used for manipulating the different parameters of this process; namely, feed
concentration,feed flow rate, and adsorption temperature at a certain range. An
optimum set of these process parameters was determined for selected zeolite
materials.
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1.5 RESEARCH METHODOLOGY
The first step of conducting this research was to study the previous research work
done in this field. Based on the subject of this research work, studies concerning
azeotropic separation process, molecular sieves adsorption, zeolite adsorption,and
fixed bed adsorption system are significant for this research matter.
The second step wasdesigning a bench scale separation system following
findings and calculations based on the prior literature. This system was fabricated and
set up in the bioprocess lab in collaboration with ENK BioscienseSdn. Bhd.All
required materials like zeolite molecular sieves and ethanol of different purities were
ordered and prepared as well.Column was then placed in its correct position and
adsorbents (zeolite beads) were added slowly with the aid of a funnel.
After zeolite beads were loaded,a set of design of experiments was determined
using the Design Expertv6 software byvarying three process parameters (feed
concentration,feed flow rate, and adsorption temperature) as recommended by the
software.
After the set of experiments was completed, statistical analysis was performed
with the aid of the Design Expert v6 software. Significance of each parameter and
interactions between parameters were determined. Then the optimization was carried
out to come up with the optimum set. The optimization step was followed by
validation of the optimum set.
After all results were tabulated and analyzed, discussions,conclusions and
recommendations were made.Results analysiswas performed aftermonitoring thetwo
responses of interest in this study, namely; ethanol purity and efficiency of recovery.
Figure 1.1 shows a flow chart that clarifies the research methodology. Based on
the chart the research methodology is divided into the following main steps:
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1. Study relevant previous works done and writing literature.
2. Design and Fabrication of adsorber bed apparatus.
3. Design of experiment and preparation of all required runs varying
parameters of interests.
4. Performing the required runs using the constructed apparatus.
5. Performing statistical analysis of the results obtained of all runs. Taking
into consideration responses of interests.
6. Optimization of results and determination of optimum set.
7. Validate results by running optimum set three times.
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Figure1.1: Flowchart that Explains the Research Methodology
Design and fabrication of
adsorber bed apparatus
Statistical analysis followed by optimization using Design Expert
software
Loading the adsorber bed column with zeolites.
Validation of
optimum set
result.
Satisfactory results?
No
Yes
End
Performing set of runs varying three process parameters (feed
concentration, feed flow rate,and adsorption temperature). 8
runs were performedeach including adsorption and regeneration
step.
Literature review
Design of experiment
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1.6 DISSERTATION ORGANIZATION
The research work done in this dissertation was divided into five chapters. Chapter 1
includes mainly background information about ethanol dehydration process. It also
discusses the problem statement of this research and its significance as well as
research objectives, research scope, and research methodology.
Chapter 2 provides a review of literature concerning ethanol production
process and its global demand, ethanol water separation techniques, molecular sieves
technology, fixed bed adsorption, adsorbers design and fabrication, and different
adsorption processes used for ethanol dehydration.
Chapter 3 provides the materials and equipments used in this research as well
as methods followed. In addition, this chapter presents the equations and
considerations used in the design and fabrication of the adsorber apparatus. Moreover,
an explanation of the experimental procedure is presented in this chapter followed by
data analysis and statistical analysis methods.
Chapter 4 presents and discusses the results and findings of this research work.
A detailed discussion of the apparatus design considerations and calculations are
provided. In addition, ethanol purity and efficiency of recovery results are analyzed
and discussed in this chapter. Furthermore, this chapter presents all the results of the
statistical analysis and optimization process.
Chapter 5 includes a summary of the findings and conclusions of this research
work. Some of the recommendations for future studies are also provided in this
chapter.
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CHAPTER 2
LITERATURE REVIEW
2.1 INTRODUCTION
Ethanol bio fuel is being raised world-wide as a supplement for fossil fuels. The
production and use of ethanol as fuel has been implemented in many countries around
the world. The optimization of ethanol production and recovery is considered one of
the most potential fields to be studied by researchers.
The dehydration of ethanol has been the major challenge for ethanol producers
since the very first beginning of its production. There have been various methods to
dehydrate ethanol using different materials and apparatus. Each method has its own
pros and cons, and so, it is of great benefit to compare between these methods and
highlight their advantages and disadvantages.
The concern of this study is to dehydrate ethanol on zeolite based media using
adsorption process. Thus literature survey done in this chapter summarizes the
different methods, materials and apparatus previously used by researchers and ethanol
producers.
The following paragraphs are to give an overview on ethanol production
process, ethanol water separation techniques, Molecular sieves technology, fixed bed
adsorption, apparatuses designed as fixed bed adsorbers, and adsorption process for
ethanol dehydration.
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2.2 OVERVIEW ON ETHANOL
Ethanol or ethyl alcohol, C2H5OH, is conventionally produced by catalytic hydration
of ethylene with sulphuric acid. A process which makes ethanol regarded as a
petroleum product.However, the continuous depletion of petroleum has directed
ethanol producers towards finding other possibilities for ethanol production. The
current most potential route of producing ethanol is the microbial fermentation of
agricultural crops and/or wastes.
2.2.1 Global Production and Demand of Bio-ethanol
Ethanol (bio-ethanol) is regarded as the most bio-fuel to be used in transportation
either as a fuel or as a gasoline enhancer. When ethanol is used as an oxygenate it will
have several advantages over conventional gasoline additives. Ethanol is known to
have a high oxygen content that helps reducing the amount of oxygenate required to
be added. In addition, the high oxygen percentage leads to a better oxidation of the
gasoline hydrocarbons. Thus,carbon monoxide (CO)and aromatic
compoundsemissions are reduced.
The aforementioned advantages of using ethanol as a fuel or fuel additive have
led to an increasing demand for fuel ethanol production in several countries
worldwide. Different governmental regulations and strategies are being made by
dedicating a great concern for the production of fuel ethanol (Prasadet al., 2007).
Several countries including Brazil, United States, Canada, Japan, India, China and
Europe have been implementing strategies to increase their market use of fuel ethanol
(Mussatto, 2010).
The world leading countries in bio-ethanol production in the year 2005 and
2006 are shown in Table 2.1(Balatet al., 2009). The table shows that USA and Brazil