Evaluation of Hollow Fiber DD3R Zeolite Membrane Module for CO_<b>2</b> Removal from Natural Gas at Industrially Relevant Conditions

Decadodecasil 3R (DD3R) zeolite membranes with a pore size of 0.36 nm × 0.44 nm and an all-silica structure are highly desired for CO2/CH4 separation. A large-area DD3R zeolite membrane module (membrane area: 811 cm2) with a uniform membrane thickness was horizontally synthesized and employed to evaluate the performance of CO2 removal from natural gas at industrially relevant conditions. Increasing feed pressure improved the CO2 flux but simultaneously reduced the CO2/CH4 selectivity, which resulted in more CH4 loss at the same retentate CO2 concentration. When the permeate pressure shifted from atmospheric to vacuum, not only was the CO2 flux enhanced but also the CH4 loss was reduced, which resulted in lower natural gas upgrading cost. The CO2 content in the gas mixture was lowered from 50% to 3.0%, while the corresponding CH4 loss was 9.2% by one-stage separation using the membrane module. In the case of 10% feed CO2 content, the CO2 content was lowered to 2.3%, while the CH4 loss was 3.0%. The energy consumption of the one-stage zeolite membrane process was estimated, and it is significantly less than that of the two-stage polymeric membrane process. The effect of concentration polarization became more serious at high feed pressure and high stage-cut, which led to large CH4 loss. At a high feed pressure of 4 MPaG, the CH4 loss was restrained to 3.0% when the stage-cut was below 35%.