(254f) The Experimental and Simulated Investigation on Carbon Dioxide Absorption into Aqueous Alkanoamines Aqueous Solution in the Hollow Fiber Membrane Contactor

The experimental and simulated investigation on carbon
dioxide absorption into aqueous alkanoamines aqueous solution in the hollow
fiber membrane contactor

Fan Cao^a, Ge Gao^a, Wichitpan Wong, Zhiwu Liang^a,b*,
Raphael Idem^a,band Paitoon Tontiwachwuthikul^a,b
aJoint International Center for CO₂
Capture and Storage (iCCS), ProvincialHunan Key Laboratory for Cost-effective
Utilization of Fossil Fuel Aimed at Reducing CO₂ Emissions, College
of Chemistry and Chemical Engineering, Hunan University, Changsha 410082, PR
China

^bClean Energy Technologies
Research Institute (CETRI), Faculty of Engineering and Applied Science

University of Regina, Regina, Saskatchewan, S4S 0A2,
Canada

* Tel.: +86-13618481627; fax:
+86-731-88573033; E-mail address: zwliang@hnu.edu.cn

Key Words:CO₂ absorption; Amine
solution; Hollow fiber membrane contactor; wetting  phenomenon; Membrane separation

Either nowadays or in the next decades, fossil fuels still play
very important roles in energy consumption worldwide. Ahuge number of carbon
dioxide (CO₂) was discharged into atmosphere with combustion of
fossil fuels, which was considered to be one of dominating greenhouse gas
responsible for global warming. Accordingly, given that when confronted with
increasingly severe situation of CO₂ emission, it is extremely
urgent for human to take effective measures to capture CO₂ released
from industrial processes, especially from coal fired power plant.

Current major research efforts for mitigating CO₂
emission have been focusing on the development of novel CO₂
separation techniques. Generally, the most common method for CO₂ capture
is applied by amine-based absorption in various gas-liquid contactors including
packed, bubble, and spray columns. However, aforementioned conventional mass
transfer equipments usually are exposed to their inherent drawbacks
considerably weakening mass transfer performance in operation process such as entrainment,
foaming, flooding and channeling. What¡¯s worse, an enormous capital and
operation costs will also impose restrictions on a large-scale application. In
order to overcome these problems, researchers have already proposed several
alternatives. Amongst varieties of alternatives, the application of hollow
fiber membrane contactors (HFMCs) employed for chemical absorption into aqueous
alkanolamines has been proved to be a promising alternative on account of
distinguished advantages over conventional gas-liquid contactor. HFMCs are a
hybrid process combing chemical absorption with membrane contactors. Porous-structured
property in HFMCs guarantees a higher gas-liquid contacting area so as to improve mass transfer performance remarkably compared with
conventional contactors. In addition, it is flexible for HFMCs to scale-up and
save space to meet actual requirements in terms of modularity and compactness
respectively. Regardless of advantages above, It is generally known that the
disadvantage of membrane contactors is membrane wetting phenomenon due to the intrusion
of liquid absorbent into membrane pores, which causes a sharp decline in gas
absorption process due to great contribution of resistance to mass transfer within
membrane to resistance to total mass transfer. Hence, numerous researchers have
been devoting themselves to wetting problem of hydrophobic membrane micropores
in HFMCs^[1-5].

    This paper mainly investigates
CO₂ absorption performance into aqueous solutions of monoethanolamine
(MEA), methyldiethanolamine (MDEA) Diethylaminoethanol (DEEA) and
their blends using a commercial micro-porous poly(tetrafluoroethylene) (PTFE)
hollow fiber membrane contactor. CO₂ absorption performance with
various operational parameters inclusive of liquid flow rate, gas flow rate, CO₂
concentration, composition of solution, gas-liquid flow orientation as well as CO₂
loading was performed under non-wetted and partially wetted mode. A 2D mathematical
model on the basis of finite element method was established for the CO₂
capture in the flue gas by employing COMSOL Multiphysics. The model can present
concentration profiles and flux vectors of transferred species existing in the
tube side, membrane, shell side respectively. When it comes to real operating
conditions, the wetting phenomenon (partially wetted mode) was taken into
consideration for ensuring the accuracy of the model. The experimental results
revealed that the order of decarburization performance is DEEA>MDEA, the
impact of the gas phase parameters on CO₂ capture and mass transfer
performance is more significant than that of liquid phase parameters. The
simulated results indicated the membrane pores were partially wetted in the
process of gas absorption. which makes the mass transfer performance of hollow
fiber membrane contactor suffer from enormous losses. Even though a very small
region of membrane pore is wetted, the CO₂ absorption flux will drop
significantly compared with non-wetted mode,

Fig.1 Scheme of Hollow Fiber

Acknowledgments

The financial supports from the National Natural Science
Foundation of China (Nos. 21376067, U1362112 and 21476064), Innovative Research
Team Development Plan-Ministry of Education of China(No. IRT1238), National Key
Technology R&D Program (Nos. 2012BAC 26B01 and 2014BAC18B04), Specialized
Research Fund for the Doctoral Program of Higher Education (No.
20130161110025), Key Project of International & Regional Scientific and
Technological Cooperation of Hunan Provincial Science and Technology Plan
(2014WK2037), and China¡¯s State ¡°Project 985¡± in Hunan University ¨C Novel
Technology Research & Development for CO₂ capture are all
gratefully acknowledged.

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