NAMS 2002 Workshop - ICOM 2008

absorption liquid in the pores of the membrane and leads to a reduction in the
loss of absorption liquid. Mono ethanol amine (MEA) - the traditional absorption
liquid for CO2 removal - was used as the absorption liquid. The effects of the flow
rate of the absorption liquid (72 - 315 ml/min), the feed gas pressure (1.2 - 3.5
bar) and the temperature difference between absorption and desorption
processes (T = 0 - 35°C) were investigated, and the operating window for the
membrane contactor process was identified.
Results The results of the multiple fiber contactor experiments show the effect of
the operating parameters on the CO2/CH4 separation performance of the
membrane contactor and identify the operating window for such a process. A
comparison between the porous and the asymmetric fiber modules shows
significant differences, especially concerning the pressure sensitivity. For the
porous fiber modules, an increase in the feed pressure immediately results in
increases in the permeabilities of both CO2 and - more especially - CH4, which
results in a tremendous decrease in CO2/CH4 selectivity. The asymmetric fiber
modules are more resistant to pressure fluctuations, and this thus increases the
performance and the operating window for the process significantly. Apart from
differences between the membranes types, some similar effects can be observed
for both types of membranes; for example, an increase in the temperature
difference between absorber and desorber significantly influences the process
performance. The temperature of the desorber is especially important, because
desorption is the limiting step in the process. With an increasing liquid flow rate, a
maximum in productivity can be observed. Below this maximum, the capacity of
the absorption liquid limits the process, whereas at higher flow rates mass
transport limitations determine the performance. The results of the various
experiments clearly show the influence of the different process parameters and
thus define the operating window for such a process to separate CO2 from CH4.
1. 1 IPCC Special Report on Carbon dioxide Capture and Storage;
http://www.ipcc.ch/activity/srccs/SRCCS_Chapter2.pdf.
2. B.D. Bhide, A. Voskericyan,S.A. Stern, Hybrid processes for the removal of acid gases from
natural gas, Journal of Membrane Science, 140 (1998) 27