Multi-factorial central composite and complete mixing model for optimizing industrial biogas valorization

Abstract

There is an increasing interest to use CO2 selective membrane to purify methane from natural or biogas because of the ease of access to this membrane configuration. The use of this membrane, however imposed an additional strain on the system because there was H2S contamination in the enriched product stream and requirement of high CO2/CH4 selectivity. To address this issue, an empirically validated complete mixing model integrated with a multi-factorial central composite design was applied to optimize the membrane process in methane enrichment from biogas containing H2S. The optimization resulted in 100% methane purity and 91.51% recovery using a methane selective membrane at 837.43 CH4/CO2 selectivity, 35.00 bar feed pressure, and 0.643 stage cut, without H2S contamination in the product stream. For comparison with CO2 selective membrane, methane purity of 91.74% and 90.26% recovery were achieved using CO2/CH4 selectivity of 1086.87, 31.82 bar feed pressure, and 0.310 stage cut. Methane selective membrane was performed better than CO2 selective membrane on four fronts, namely lower selectivity, higher CH4 recovery, higher CO2 recovery, higher CH4 purity, and the product stream was H2S free. CO2 selective membrane was superior in other aspects, namely higher CO2 purity, lower stage cut and feed pressure.