Carbon Dioxide Solubility and Mass Transfer in Aqueous Amines for Carbon Capture.

578 Pages·2015·6.27 MB·English

Copyright
by
Le Li
2015
The Dissertation Committee for Le Li Certifies that this is the approved version of
the following dissertation:

Carbon Dioxide Solubility and Mass Transfer in Aqueous Amines for
Carbon Capture

Committee:

Gary T. Rochelle, Supervisor
Benny D. Freeman
Isaac C. Sanchez
Hallvard F. Svendsen
Ross E. Dugas
Carbon Dioxide Solubility and Mass Transfer in Aqueous Amines for
Carbon Capture

by
Le Li, B.S.E.

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
August 2015
Dedication

to my mother,
for teaching me how to think, and how to enjoy life.
Acknowledgements

First and foremost, I would like to thank my advisor, Dr. Gary Rochelle, for his
guidance and mentorship during the past six years. His (often outrageously creative)
ideas and his patience with me made this work possible. Dr. Rochelle’s enthusiasm
about research and his scientific curiosity has been an inspiration for me to find joy and
value in my own work. His dedication to his family and community taught me the
importance of work-life balance. Most importantly, his love for teaching and generosity
for his students are values I hope to carry on in my career and in my life. Beyond the
technical expertise and scientific knowledge I have learned, I also treasure the memories
from the extra-curricular activities organized by Dr. Rochelle, such as: backpacking trips
in the mountains, descending into caves, and exploring in exotic foreign cities. Joining
his research group was one of the easiest and best decisions I have made.
This work and my graduate studies were supported financially by the Luminant
Carbon Management Program, and later the Texas Carbon Management Program. I
received additional financial assistance from the Thrust Fellowship through the Cockrell
School of Engineering at UT Austin. I am very grateful to these programs as they
allowed me to not only survive, but enjoy my life during the past six years in Austin.
I would like to thank Prof. Benny Freeman, Prof. Issac Sanchez, Prof. Hallvard
Svedsen, and Dr. Ross Dugas for offering their time and professional expertise as
members of my dissertation committee. I’m especially grateful to Dr. Svendsen’s extra
efforts in his participation from very far away. Moreover, Dr. Svendsen and his
research group at NTNU gave me important alternative perspectives on the science of
amine scrubbing, which were very valuable in the development of my research ideas.
v
The faculty and staff at the McKetta Department of Chemical Engineering at The
University of Texas in Austin offered invaluable support for this work and my learning.
Prof. Michael Baldea offered important assistance to my MATLAB modeling activity in
this work. I also enjoyed working with Prof. Hal Alper in the organization of the
Graduate Seminar class. I am thankful to Prof. Keith Freidman for letting me regularly
use the rheometer under his care for my viscosity measurements.
I greatly appreciate our administrative assistance, Maeve Cooney, for her hard
work to take care of the many important logistics during my time in the research group.
I must thank her especially for putting up with me missing the deadline for many
quarterly reports. The graduate program coordinators at the department, T Stockman
and Kate Baird, provided assistance during my enrollment, through my preliminary
exams, and most importantly with my graduation paperwork and logistics. Jim
Smitherman and Butch Cunningham, along with the machine shop, was a great resource
for hardware problems in the lab. Eddie Ibarra and Kevin Haynes helped with my many
purchase orders and deliveries of chemicals and equipments. Randy Rife and Patrick
Danielewski helped me with several computer software related issues. Carrie Brown
and Kay Costales-Swift provided numerous assistance with arranging meeting rooms and
other administrative matters.
The cryogenic lab operated by the Department of Physics offered a convenient
source of liquid nitrogen, which was crucial to the mass transfer experiments. On
several occasion, the glass shop in the Department of Chemistry and the glass technician
Mike Ronalter provided efficient support for the glassware that was used in this work.
During the past six years I received daily support and inspirations from my
colleagues in the Rochelle group. I am especially thankful for the detailed and patient
mentorship offered by Dr. Xi Chen, with whom I learned to operate the wetted wall
vi
column. I really appreciate Dr. Fred Closmann and Dr. Stephanie Freeman for training
me on the basics in the lab, as well as for maintaining several shared apparatus in the lab
during their time in the group. Their work ethics, thoroughness, and dedication to
excellence set an important example for me. I very much value the experience of
working closely with Dr. Qing Xu, Dr. Alex Voice, Steven Fulk, Humera Rafique, Dr.
Nathan Fine, and Yang Du. I’m also thankful for the support and friendship of Dr.
David Van Wagner, Dr. Jorge Plaza, Dr. Peter Frailie, Dr. Omkar Namjoshi, Darshan
Sachde, Tarun Madan, Brent Sherman, Matt Walters, Yu-Jeng Lin, Di Song, Kent
Fischer, and our exchange scholar Dr. Han Li from Tsinghua University.
I was fortunate to have had excellent help from my undergraduate assistants:
Trang Nguyen, Joseph Ming-Han Lee, and Nina Salta.
I would like to thank my mother, who provided constant support, guidance, as
well as home cooked deliciousness during my graduate studies. Her firm belief in the
value and importance of graduate education and her faith in me are what kept me going
through my challenges and doubts. I would like to also thank her husband Victor Pol,
for his understanding and many helps with my apartment and life in Austin. I am very
thankful for the love and support from my grandparents, aunt, uncle, and cousins (Lei and
Chen) in China. I also appreciate the support and thoughts from my father.
Through the Department of Chemical Engineering I am honored to have met great
friends including Dr. Nathan Crook, Dr. Erwan Chabert, Dr. Zach Frye, Peach Kasamset,
Dr. Avni Jain, Dr. Sunmi Lee, Dr. Kate Curran, Dr. Jie Sun, Dr. Jong Suk Kim, Dr.
Leqian Liu, Dr. Wenzong Li, Dr. Bo Lu, Joseph Cheng, and Jorge Vasquez. During my
time at UT, I also became close friends with Dr. Man Liang and (soon to be Dr.) Beatrice
Mabrey. The times shared and support I received from these friendships I will always
treasure.
vii
Last but not least I would like to thank Brent Sherman, for his love and company
during the last few years. Our relationship, much like the experience of this Ph.D. work,
has been very challenging and rewarding at the same time. The writing of this
dissertation would’ve been much more painful without his encouragement and support
along the way.
viii
Carbon Dioxide Solubility and Mass Transfer in Aqueous Amines for Carbon Capture

Le Li, Ph.D.
The University of Texas at Austin, 2015

Supervisor: Gary T. Rochelle

Amine scrubbing is the state of the art technology for CO capture, and solvent
2
selection can significantly reduce the capital and energy cost of the process. This work
presents rigorous CO mass transfer and solubility data at expected process conditions for
2
more than 20 aqueous amines and amino acid salts.
Amino acid salts are generally not competitive with aqueous amines as solvents
for CO capture, particularly from coal fired power plants. The capacity of amino acid
2
salts is intrinsically low (0.2 – 0.35 mol/mol alkalinity).
Piperazine (PZ) blends have good overall performance. 3.5 m PZ/3.5 m 2-
amino-2-hydroxymethyl-propane-1,3-diol (Tris) shows good absorption rates, good
capacity, and low solvent viscosity. 6 m PZ/2 m hexamethylenediamine (HMDA) has
moderate absorption rates, capacity, and a high viscosity.
High solvent viscosity has been shown to reduce CO absorption rate and increase
2
sensible heat cost.
A simplified speciation model (SSM) was developed in MATLAB to represent
CO VLE in a mono-amine solvent using only four adjustable parameters. The model
2
can also predict liquid phase speciation. Primary and secondary amines were shown to
have different CO VLE dependence on amine pK . At pK higher than 8, secondary
2 a a
ix
amines have lower carbamate stability than primary amines. A correlation was
developed to predict the SSM parameters based on the amine type and amine pK .
a
The third order overall reaction kinetic expression better explains the mass
transfer data at process conditions than the more widely applied second order overall
expression. A new Bronsted correlation was developed to represent the third order
concentration based kinetic constant at 40 °C for primary and secondary amines:
𝑙𝑜𝑔 (𝑘 ∗) = −11.728+1.113∙𝑝𝐾 .
10 𝑐−3 𝑎𝑎𝑚𝑖𝑛𝑒
This work shows the absorption rate of CO at process conditions do not always
2
increase with amine pK . As the reaction rate constant increases with amine pK , the
a a
free amine available for CO absorption decreases. As the result, for primary and
2
secondary mono-amines, the optimum amine pK for the best mass transfer performance
a
is around 8.7 (at 40 °C).

x