Amine Oxidation in CO2 Capture Processes

286 Pages·2008·7.18 MB·English

Copyright
by
Andrew James Sexton
2008
The Dissertation Committee for Andrew James Sexton
certifies that this is the approved version of the following dissertation:

Amine Oxidation in CO Capture Processes

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Committee:

______________________________
Gary T. Rochelle, Supervisor

______________________________
David T. Allen

______________________________
Nicholas A. Peppas

______________________________
Eric V. Anslyn

______________________________
James E. Critchfield
Amine Oxidation in CO Capture Processes

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by

Andrew James Sexton, B. S.; M. Eng.

Dissertation
Presented to the Faculty of the Graduate School of
The University of Texas at Austin
in Partial Fulfillment
of the Requirements
for the Degree of
Doctor of Philosophy

The University of Texas at Austin
December 2008
To my loving parents,
Joe and Carol Sexton
Your support and encouragement has guided me and I am forever grateful.
Acknowledgements
First and foremost, I would like to thank my research advisor Dr. Gary Rochelle.
I was initially drawn to Dr. Rochelle’s group solely by the enthusiasm and excitement he
exhibited when discussing his research. Upon joining his group, I quickly learned that
Dr. Rochelle’s initial impression was not just a sales pitch to attract new graduate
students; he brings that eagerness to teach – and to learn – with him every single day.
The door to his office is always open, literally and figuratively, to any graduate or
undergraduate student – even those he does not supervise or teach. While Dr. Rochelle
and I did not always agree on everything during our weekly meetings, I always felt like I
left each meeting having learned at least one thing I did not know before I stepped in his
office. If given the opportunity to rewind the clock four years and pick another research
advisor, I would make the same decision without hesitation. Dr. Rochelle has been a
great mentor and I truly appreciate everything he has done for me.
The Rochelle research group has doubled in size since I joined, yet Dr. Rochelle
has always been accessible and things run as efficiently as ever in the group. For this I
thank Dr. Rochelle’s assistants during my time here – Jody Lester, Lane Salgado and
Maeve Cooney. The three of you were always available meet any last-second requests
from this self-proclaimed procrastinator when conference or quarterly report time came
around. And to Jody – I am still slowly working my way through the list of restaurants
you compiled for me; I have yet to be disappointed by a single one.
I would also like to acknowledge all the Rochelle group members that I have
gotten to know during my time at The University of Texas: Tim Cullinane, Akin
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Alawode, Chuck Okoye, Babatunde Oyenekan, Marcus Hilliard, Jennifer Lu, Fred
Closmann, Thu Nguyen, Qing Xu, Xi Chen, Jorge Plaza, Sepideh Ziaii, David Van
Wagener, Stephanie Freeman, Eric Chen and George Goff. I extend my gratitude to all
senior group members who I could always call upon for advice while I was learning the
ropes, especially George Goff. Even while writing your dissertation, you never hesitated
to stop and answer a question, share your knowledge of Aspen or stay at the lab until
4AM demonstrating high gas flow experiments. You will make a great professor
someday.
I think it speaks volumes that a majority of the members of the Rochelle group get
along with one another and interact quite often outside of the laboratory environment. To
those Rochelle group members I have befriended (John McLees, Ross Dugas, Jason
Davis, and Bob Tsai), I would like to say that I have many great memories from
conferences, parties, tailgates and The Posse. It was refreshing to be surrounded a
number of intelligent and hard-working individuals who knew how to let loose and enjoy
themselves after quitting time. It is now up to you to continue the traditions of burrito
Thursday and Friday happy hour.
I have also been fortunate to have made a number of friends in the department
since I moved to Austin, Texas (keep in mind that I do not use the term friend lightly).
Terry Farmer, Jason Cantor, Luke Henderson, Saul Lee, Mikey Lin, Ryan Fitzpatrick and
Danielle Smith are all people I will keep in touch with long after I have left the 40 Acres.
To all those except Mikey and Terry, enjoy the rest of your time at UT. It will be over
before you know it. Special thanks are reserved for Jason and John McLees as well – you
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two had to live with me as your roommate for four years. I also want to mention those
close friends of mine I met outside the College of Engineering (yes, it does happen
sometimes). Paul Anderson, Paul Norwine, Greg Beatty, Jesse Sultzer, Melody Lee,
Brian Talarico and Adam Johnson have all helped me retain my sanity during time spent
outside of CPE.
Sometimes there are not enough hours in the day to accomplish everything; in that
case you either pick it up the next day or you hire some good help. Along those lines, I
would like to thank the undergraduate research assistants I have collaborated with:
Humera Rafique, Dan Ellenberger, Jon Mellin, Ellie Doh, and Jang Lee. Without your
assistance, I would probably be graduating in December 2009 instead of 2008.
The members of my committee – Drs. Jim Critchfield, David Allen, Nicholas
Peppas, and Eric Anslyn – have been extremely helpful as this project has progressed.
Dr. Anslyn has done an excellent job in providing this chemical engineer with a refresher
in organic chemistry. Dr. Critchfield has been an invaluable resource over the past four
years. Being a Rochelle group graduate himself, Dr. Critchfield has almost served as a
second advisor. He has been able to call on his experience from grad school and provide
an industry perspective on this research project. His suggestions and critiques have led to
a couple of important discoveries.
I like to think of myself as a capable troubleshooter. I have taken the IC and
FTIR apart so many times I think I have their internals etched into my brain. However,
there were certain times where I would just have to throw my hands up and call in the
professionals. Fortunately, Randy West and Donnie Lummus at Dionex and Mark
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Nelson at Air Quality Analytical, Inc. always came through. They would even forgo
guaranteed future business by explaining to me the underlying problem and the solution
in case it ever happened again.
I do not think I would be at this point in my life without the love and support of
my family. From an early age, my parents recognized my talents and encouraged me to
use them. At the time, I didn’t understand why I was getting up at 8AM on Saturday
morning to work with a gifted children specialist, taking middle school math classes in 4th
grade, or attending community college as high school freshman. Now I realize that my
parents just wanted what any parent wants for their child, no matter the situation. They
have raised four well-mannered and successful children who have graduated from college
and started their professional careers; that is quite an accomplishment. And don’t worry
– I promise that I will be in Australia for only six months.
The final – and most important – thank you is reserved for my fiancée, Melissa.
You have endured long hours spent in the lab and countless complaints about broken
equipment and experiments gone awry. You have seen the best and the worst of me over
the past three and a half years, yet you are still standing by my side. I am excited about
spending the rest of my life with my best friend.
Without the financial support of our generous research sponsors – the U. S.
Department of Energy, the Separations Research Program, the Industrial Associates
Program for CO Capture and the Luminant Carbon Management Program – this project
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would not have been possible.

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Amine Oxidation in CO Capture Processes
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Publication No. ________

Andrew James Sexton, Ph.D.
The University of Texas at Austin, 2008

Supervisor: Gary T. Rochelle

Aqueous amine solutions were batch loaded into 500 mL glass jacketed reactors
and subjected to oxidative degradation at both low and high gas rates. Solutions at low
gas were degraded with 100 mL/min of 98%O /2%CO with mass transfer achieved by
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vortexing. Samples were drawn from the reactor during the course of the experiment and
analyzed for degradation using ion chromatography and HPLC with evaporative light
scattering detecion. In a parallel apparatus 7.5 L/min of 15%O /2%CO was sparged
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through 350 mL of solution; additional mass transfer was achieved by vortexing. A
Fourier Transform Infrared Analyzer collected continuous gas-phase data on amine
volatility and volatile degradation products.
Hydroxyethyl-formamide (HEF), hydroxyethylimidazole (HEI) and formate are
the major carbon containing monoethanolamine (MEA) oxidation products; HEF, HEI
and ammonia are the major nitrogen containing products. In terms of catalyst oxidation
potential, Cu > Cr/Ni (combined) > Fe > V. The oxygen stoichiometry (ν) ranges from
1.5 mol MEA degraded/mol O consumed for Cu and Fe catalyzed systems to 1.0 for V
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catalyzed systems. Estimation of rates from an industrial absorber show degradation
costs to range from $1.17 / metric ton (MT) CO captured for a system controlled by the
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solubility of O to $2.22 / MT CO for a mass transfer controlled system.
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Inhibitors A and B (reaction mechanism inhibitors) and EDTA (a chelating agent)
were established as effective MEA oxidation inhibitors. EDTA and Inhibitor A were
successful inhibitors at 100 mM, while 7.5 mM Inhibitor B successfully inhibited
degradation. Sodium sulfite and reaction intermediates formaldehyde and formate
(expected oxygen scavengers) were unsuccessful at inhibiting MEA oxidation.
Cu catalyzes concentrated PZ oxidation, while Fe has no effect on PZ oxidation
even at high catalyst concentration. MEA/PZ blends were more susceptible to oxidation
than any other amine system investigated. It is believed that free radicals formed in the
MEA oxidation process serve to accelerate the degradation of the PZ structure. All MEA
analogs (glycine, ethylenediamine and ethylene glycol) and secondary/hindered amines
(diethanolamine, diglycolamine and 2-amino-2-methyl-1-propanol) were resistant to
oxidation in the presence of Fe or Cu, except for diethanolamine.

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