Toshihiro Tomita

Natural gas purification with a DDR zeolite membrane; permeation modelling with maxwell-stefan equations

Abstract The permeation of CO 2 , N 2 and CH 4 and their mixtures through a DDR membrane has been investigated over a wide range of temperatures and pressures. The synthesized DDR membrane exhibits a very high selectivity for CO 2 and a moderate selectivity for N 2 over CH 4 with good permeances. At a total pressure of 101 kPa and temperature of 225 K, the selectivity for CO 2 was found to be over 3000 and 40 for N 2 in a 50/50 feed mixture with CH 4 , both decrease with temperature. The N 2 /CH 4 selectivity remains constant with pressure, while that for CO 2 /CH 4 decreases. An engineering model, based on the generalized Maxwell-Stefan equations, has been used to interpret the transport phenomena in the membrane. The diffusivity of these permanent gases is strongly dependent on the loading in the membrane, severely complicating modelling work. A model developed by Reed and Ehrlich [ 1 ] could describe this phenomenon well for both the unary as the binary permeances. The feasibility of DDR membranes as applied to CO 2 and N 2 removal from natural gas is anticipated.

Separation of CO2 and CH4 by a DDR membrane

The permeation of CO2 and CH4 and their binary mixtures through a DDR membrane has been investigated over a wide range of temperatures and pressures. The synthesized DDR membrane exhibits a high permeance and maintains a very high selectivity for CO2. At a total pressure of 101 kPa, the highest selectivity for CO2 in a 50∶50 feed mixture was found to be over 4000 at 225 K. This is ascribed to the higher adsorption affinity, as well as to the higher mobility for the smaller CO2 molecules in the zeolite, preventing the bypassing of the CH4 through the membrane. An engineering model, based on the generalized Maxwell-Stefan equations, has been used to interpret the transport phenomena in the membrane. The feasibility of DDR membranes as applied to CO2 removal from natural gas or biogas is anticipated.