Evaluation of Hollow Fiber DD3R Zeolite Membrane Module for CO₂ 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%.