Gas permeation applied to biogas upgrading using cellulose acetate and polydimethylsiloxane membranes

Membrane gas permeation has great potential for the biogas upgrading. The present work evaluates the performance of membranes made of two different polymers aiming at the carbon dioxide (CO2) removal: cellulose acetate and polydimethylsiloxane (PDMS). The results indicated that CO2 caused membrane plasticization, which led to lower separation factors in tests with gas mixtures, in comparison to the pure gas experiments. Based on experimental results, a simplified model was developed which considered the permeability variation with the CO2 partial pressure in the gas feed. The modeling approach for a single stage process pursued a compromise between methane (CH4) purity and recovery. For a given purity, the highest recoveries were obtained for the cellulose acetate membrane, due to its higher selectivity. For this membrane, a CH4 purity of 97% led to a recovery of 86.8%, while the PDMS membrane presented a CH4 recovery of only 19.8%, considering the same CH4 content. A multiple stage design improved methane recovery considerably in comparison to the single stage process for both membranes, making it possible to attain 99.6% CH4 purity associated with 99.8% CH4 recovery for the cellulose acetate membrane. (C) 2018 Elsevier Ltd. All rights reserved.