Natural Gas sweetening by the use of a facilitated blend membrane
Advancing the chemical engineering fundamentals
Membranes and Membrane Science - I (T2-8a)
Keywords: Natural gas, CO2, membranes, separation
The sweetening of natural gas (NG) is today basically done by the use of amine solutions, requiring large columns for both absorption of the CO2 and regeneration (desorption) of the amine. A very attractive solution is the use of polymeric membranes which will selectively permeate the CO2 while the NG is being withheld on the feed side. Such membrane solutions have existed for more than 20 years, and there are several installations around in the world especially for onshore installations where the foot print area and weight are of less importance. Materials like cellulose acetate (CA) and polyimides (PI) are among these “work horses”; produced either as spiral wound membranes or hollow fibres respectively. Up until now, such membrane separation solutions have however not been the first choice; mainly because the performance of these commercial membranes do not exhibit optimum performance with respect to both flux and selectivity. Also the CH4 loss may be too high. A membrane process will additionally require pre-treatment of the gas – and this may be rather costly.
The primary goal for the membrane development for the current NG application, is increased flux and selectivity in order to design a simpler system with reduced permeation area (resulting in smaller footprint, light weight) and also reduce the loss of valuable gas. For illustration: A commercial CA membrane today may have a flux for CO2 around 0.15 m3(STP)/(m2 h bar) and a selectivity of CO2/CH4 ~15. The goal should be at least both a doubled flux and selectivity in order to be commercially atractive.
In the current work to be reported here, experimental results which meet these goals will be presented. The membrane is a blend of polymers developed within the membrane research group, Memfo, at NTNU – it is patented. The membrane contains of a facilitated transport polymer (PVAm) which selectively transport the CO2, while the other polymer component in the blend (PVA) adds mechanical strength to the membrane. The membrane is currently being tested at varying process conditions and gas mixtures. The potential for using this membrane in a natural gas sweetening process is very promising, and sample calculations for such a process will be shown in the presentation, illustrating the needed permeation area and removal of CO2 to defined specifications.
Presented Tuesday 18, 15:00 to 15:20, in session Membranes and Membrane Science - I (T2-8a).
