The main purpose of this work is the numerical investigation of PEBX membrane performance for natural gas sweeting. Hence, a single-stage process for PEBX membrane was considered in various flow patterns, namely, cocurrent, cross flow and countercurrent to separate a typical natural gas mixture. To this target, a black box numerical model was extended for the ASPEN HYSYS commercial package and also its validation was realized by litterature experimental data. The validation results indicated a good agreement between thoritical results and experimental data. After model validation, the effect of the some significant operating parameters (pressure gradient, stage cut and membrane area) on the performance of PEBX membrane was analysed in terms of acid gases removal percentage. The simulation results presented a noticeable performance of PEBX membrane to produce high purity CH 4 . In particular, concerning the stage cut effect, it was found that the CO 2 and H 2 S compositions in the permeate side were decreased through the enhancment of stage cut from 0.005 to 0.03, whereas the CH 4 composition increased for whole the flow patterns. Moreover, a similar effect was achived for membrane surface area. On the other hand, the transmembrane pressure effect was positive on the PEBX membrane performance during natural gas sweeting.