(398g) Study of Kinetics, Solubility, Heat of Absorption and Formation of Bicarbonate and Carbamate of Linear and Ring Diamines in CO2 Absorption Process

Study of
kinetics, solubility, heat of absorption and formation of bicarbonate and
carbamate of linear and ring diamines in CO₂ absorption process

Rui Zhang^a, Zhiwu Liang^a*, Qi Yang^b*, Xiao Luo^a

^aJoint International Center for CO₂ Capture and Storage
(iCCS), Provincial Key Laboratory for Cost-effective Utilization of Fossil Fuel
Aimed at Reducing Carbon-dioxide Emissions, College of Chemistry and Chemical
Engineering, Hunan University, Changsha, Hunan, 410082, P.R. China

^bCSIRO Manufacturing, Clayton Victoria 3168,
Australia

ABSTRACT

Climate change has caused strong concern
worldwide and excessive CO₂ emission is considered to be the main
contributor to global warming, therefore CO₂ capture and storage has
become an important research subject. Among different CO₂ capture
methods, post-combustion capture using chemical absorbents, especially amine
absorbents, is regarded as a feasible method for mitigating the CO₂
emissions from many industrial sources. The most commonly studied amine
absorbent is monoethanolamine (MEA). Aqueous solutions of other primary,
secondary and tertiary amines and amino acid salts have also been studied to
investigate their mass transfer performance, reaction kinetics and energy
consumption in absorption-desorption processes. All of these absorbents,
however, demonstrated some challenges for use in CO₂ capture
processes. For example, primary amines such as MEA have a fast reaction rate
with CO₂ during absorption but require large energy consumption
during CO₂ desorption; a tertiary amine such as
N-methyldiethanolamine (MDEA) requires less energy for CO₂
desorption but has a slow reaction rate with CO₂ during absorption.
Other challenges for CO₂ capture processes include amine
degradation, facility corrosion, and the escape of amine or other substances to
the environment. These challenges, in particular high energy consumption, result
in high CO₂ capture costs. To address these challenges, it is
important to develop better solvents and better processes.

An ideal amine absorbent for CO₂
capture should have fast reaction kinetics during CO₂ absorption,
large CO₂ cyclic capacity (the difference between rich amine CO₂
loading and lean amine CO₂ loading), and low energy consumption
during desorption. The performance of amines during CO₂ absorption
and stripping is strongly related to amine molecular structure. To design and
develop better amine absorbents for CO₂ capture, it is necessary to
understand the effect of amine molecular structure on amine performance in CO₂
capture. Yang et al. and Conway et al., have studied a number of specifically
designed amine absorbents for CO₂ capture^1,
2.
These designer amines contained two or three amino groups of different types
which were spaced by two or three carbons in the same molecules. Their results
showed that the designer amines demonstrated a significant improvement in CO₂
cyclic capacity. Especiallly the designer amines contain a ring structure in
its molecular structure, so in this work, there are 5 damines (Table 1) were
selected to investigated their CO₂ capture performance. The CO₂
equilibrium solubility, the formation of carbamate/bicarbonate, the reaction
kinetics and the heat of absorption also was investigated at the corresponding
experimental condition. The current results we obtained now shows that the ring
amine could produced more bicarbonate and less carbamate than the linear diamines
as shown in Figure 1. More bicarbonate vs. less carbamate is benefits to the CO₂
desorption performance.

The other experiments about the CO₂
absorption-desorption performance will be performed in future. Through
comparing the solubility, the heat of absorption and the reaction kinetics to
get a good understanding on the effect of the molecular structure (ring) on the
amine performance for CO₂ capture.

Table
1.
The details of each amine used in this work.

Figure 1. The profile of each
species with the CO₂ loading changes of each amine. Solid and dash
line are the fitted line for different species of each amine.

ACKNOWLEDGEMENTS

The authors are very grateful for the
CSIRO PhD student scholarship to support this research and would like to
acknowledge the research contribution to the CO₂ loaded amines test
by the CSIRO PCC team in Australia. The authors also would like to express
thanks for the financial support from the National Natural Science Foundation
of China (NSFC-Nos.21536003, U1362112 and 51521006), National Key Technology
R&D Program (MOST-No. 2014BAC18B04), Graduate Student Innovation Project of
Hunan Province (CX2016B121). China Scholarship Council and China Outstanding
Engineer Training Plan for Students of Chemical Engineering & Technology in
Hunan University (MOE-No.2011-40) are also greatly appreciated.

Reference

1.            Yang,
Q.; Puxty, G.; James, S.; Bown, M.; Feron, P.; Conway, W., Toward Intelligent CO₂
Capture Solvent Design through Experimental Solvent Development and Amine
Synthesis. Energy & Fuels 2016, 30, (9), 7503-7510.

2.            Conway,
W.; Yang, Q.; James, S.; Wei, C.-C.; Bown, M.; Feron, P.; Puxty, G., Designer
Amines for Post Combustion CO₂ Capture Processes. Energy Procedia
2014, 63, 1827-1834.