DIRECT CONVERSION OF CARBOXYLATE SALTS TO CARBOXYLIC ACIDS VIA REACTIVE ...

101 Pages·2008·4.63 MB·English

DIRECT CONVERSION OF CARBOXYLATE SALTS TO CARBOXYLIC
ACIDS VIA REACTIVE EXTRACTION

A Thesis
by
XIN XU

Submitted to the Office of Graduate Studies of
Texas A&M University
in partial fulfillment of the requirements for the degree of
MASTER OF SCIENCE

August 2008

Major Subject: Chemical Engineering
DIRECT CONVERSION OF CARBOXYLATE SALTS TO CARBOXYLIC
ACIDS VIA REACTIVE EXTRACTION

A Thesis
by
XIN XU

Submitted to the Office of Graduate Studies of
Texas A&M University
in partial fulfillment of the requirements for the degree of
MASTER OF SCIENCE

Approved by:
Chair of Committee, Mark T. Holtzapple
Committee Members, Cady R. Engler
Charles J. Glover
Head of Department, Michael V. Pishko

August 2008

Major Subject: Chemical Engineering
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ABSTRACT

Direct Conversion of Carboxylate Salts to Carboxylic Acids
via Reactive Extraction. (August 2008)
Xin Xu, B.S., Jiangsu Polytechnic University, P. R. China;
M.S., Research Institute of Petroleum Processing, P. R. China
Chair of Advisory Committee: Dr. Mark T. Holtzapple

The MixAlco process, a proprietary technology owned by Texas A&M
University, converts biomass (e.g., municipal solid waste, sewage sludge, paper,
agricultural residues, and energy crops) into usable chemicals (e.g., acetic acid) and fuels
(e.g., ethanol). Historically, calcium carbonate has been used as the buffer. Recently, it
was found that using ammonium bicarbonate as the buffering agent enhances the
fermentation conversion. In this case, fermentation broth contains ammonium salts (e.g.,
ammonium acetate, propionate, butyrate, pentanoate). Therefore, the downstream
processing steps (including extraction, purification, esterification, and product
separation) must be compatible with the ammonium carboxylate salts formed in the
fermentation.
This research focuses on converting fermentation broth carboxylate salts into
their corresponding acids via “acid springing.” Reactive extraction and thermal
conversion (distillation) are crucial parts of the acid springing process.
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Because the components of the fermentation broth are over 80% ammonium
acetate and 20% other ammonium carboxylate salts (ammonium propionate, butyrate,
pentanoate, etc.), all the initial experiments in this study were performed using reagent-
grade ammonium acetate to simplify the reaction. Later, actual fermentation broth was
employed.
The primary objective of this study was to provide the optimal operating
conditions to make the downstream processing steps of the MixAlco process compatible
with ammonium carboxylate salts formed in the fermentation. The optimal initial
concentration for reactive extraction should be 150–200 g/L and the volume ratio of
aqueous phase and extractant should be 1:1. The distribution coefficient reaches the
maximum value when the concentration of TOA is 20% (vol %) in n-octanol. The batch
distillation study shows that there are two reaction stages: (1) water leaves the system at
100−106 °C and (2) the acid-amine complex decomposes at 160−180 °C.
v
DEDICATION

Not what we give,
But what we share,
For the gift
without the giver
Is bare.

— James Russell Lowell (1819-1891)

To my loving husband, Xi Ouyang.
To my lovely daughter, Emily, the little angel
came to this amazing world on May 20, 2008.
To my family and friends for their endeavor,
encouragement and enlightening.
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ACKNOWLEDGEMENTS

I would like to express my sincere gratitude to my advisor, Dr. Mark T.
Holtzapple, for his continuous academic guidance and professional training. I wouldn’t
be who I am today without his invaluable help. I would like to thank the other members
of the committee, Dr. Charles J. Glover and Dr. Cady R. Engler, for their guidance and
support throughout the course of this research.
I would like to thank my colleagues and friends: Dr. Cesar Granda, for his
tremendous guidance for my research project and thesis; Dr. Li Zhu, for her kind help
and guidance of my research; Ms. Andrea Forrest and Hema Rughoonundun, for training
me the operation of GC analysis and providing the fermentation broth for my
experiment; and Ms. Rocio Sierra and Mr. Jipeng Dong for their generous help during
setting up the laboratory equipment. Thanks also go to Towanna Hubacek and Missy
Newton for their moral help.
I am also grateful to the Chemical Engineering Department and the Graduate
School at Texas A&M University for their support through my graduation study.
Finally, my special gratitude goes to my husband, Dr. Xi Ouyang, for his
continuous love and encouragement throughout my thesis work. Indebtedness also goes
to my parents and my family for their love and support through this educational
endeavor.
vii
TABLE OF CONTENTS

Page
ABSTRACT.............................................................................................................. iii
DEDICATION.......................................................................................................... v
ACKNOWLEDGEMENTS...................................................................................... vi
TABLE OF CONTENTS ......................................................................................... vii
LIST OF FIGURES................................................................................................... ix
LIST OF TABLES.................................................................................................... xii
CHAPTER
I INTRODUCTION................................................................................ 1
Biomass Conversion to Alcohol..................................................... 2
Traditional Process......................................................................... 4
MixAlco Process............................................................................ 4
Reactive Extraction........................................................................ 8
Objective........................................................................................ 10
II EXPERIMENTAL METHODS........................................................... 12
Pretreatment and Fermentation...................................................... 12
Concentration Study....................................................................... 12
Reactive Extraction Study.............................................................. 14
Batch Distillation Study................................................................. 16
Determination of Ammonia Loss................................................... 17
Gas Chromatography...................................................................... 18
Volume and Mass Balance............................................................. 18
III EXPERIMENTAL RESULTS............................................................. 19
Concentration Study....................................................................... 19
Reactive Extraction Study.............................................................. 37
Batch Distillation Study................................................................. 52
viii
CHAPTER Page
IV CONCLUSIONS.................................................................................. 65
V RECOMMENDATIONS FOR FUTURE WORK............................... 67
REFERENCES.......................................................................................................... 68
APPENDIX A........................................................................................................... 71
APPENDIX B........................................................................................................... 73
APPENDIX C........................................................................................................... 74
APPENDIX D........................................................................................................... 75
APPENDIX E............................................................................................................ 77
APPENDIX F............................................................................................................ 80
VITA......................................................................................................................... 89
ix
LIST OF FIGURES

FIGURE Page
1-1 Schematics of biomass conversion to alcohols: (A) traditional process; (B)
MixAlco process........................................................................................ 3

1-2 Process overview........................................................................................ 6

2-1 Apparatus for determine boiling point elevation and ammonium
acetate loss.................................................................................................. 13

2-2 Apparatus for extraction of carboxylic acid from their salts...................... 15

2-3 Apparatus for batch distillation.................................................................. 16

3-1 Comparison of boiling point for the boiling artificial ammonium
acetate and calcium acetate solution.......................................................... 22

3-2 pH of the condensed fractions for the artificial
ammonium acetate solution........................................................................ 23

3-3 The relation between the concentration of the condensed fraction and
the concentration of the bottom solution for the artificial ammonium
acetate solution........................................................................................... 24

3-4 The overhead fraction recovery for the artificial
ammonium acetate solution........................................................................ 24

3-5 Total acetate loss for the boiling artificial ammonium acetate solution ... 26

3-6 The concentration of the boiling artificial ammonium acetate solution
as a function of time................................................................................... 27

3-7 The concentration of fractions as a function of time for the
artificial ammonium acetate solution ....................................................... 27

3-8 Closure study for the artificial ammonium acetate solution...................... 28

3-9 Boiling point of the boiling fermentation broth ........................................ 29

3-10 pH of condensed overhead fraction of the boiling fermentation broth ..... 30
x
FIGURE Page
3-11 The relation between concentration of overhead condensed
fractions and time for fermentation broth ................................................. 31

3-12 The relation between concentration of boiling solution and time for
fermentation broth ..................................................................................... 31

3-13 Total acid loss and concentration of boiling solution for
fermentation broth...................................................................................... 32

3-14 The concentration of NH in the overhead fraction for
3
fermentation broth...................................................................................... 33

3-15 The overhead NH to acid ratio for fermentation broth............................. 33
3

3-16 The overhead water recovery for fermentation broth................................. 34

3-17 The overhead NH recovery for fermentation broth.................................. 35
3

3-18 Closure study of fermentation broth........................................................... 36

3-19 Distribution coefficient as a function of initial acid concentration
at various mole ratios (M :M = mole solute/mole extractant).............. 41
AQ OR

3-20 The relation between distribution coefficient D and various
i
mole ratios.................................................................................................. 41

3-21 Various volume ratios and distribution coefficient D ............................... 42
i

3-22 The relation between pH and various mole ratios...................................... 44

3-23 The relation between distribution coefficient and pH................................ 45

3-24 TOA concentration in various polar diluents and distribution
coefficients................................................................................................. 46

3-25 The relation between pH and TOA concentration in various
polar diluents.............................................................................................. 47

3-26 TOA concentration in various non-polar diluents and distribution
coefficients................................................................................................. 48