Comparison of biogas upgrading performances of different mixed matrix membranes

In this study composite membranes were manufactured by introducing zeolite 3A, 4A and 5A within polyimide (PI) and polyetherimide (PEI) in order to increase their separation performances for the gaseous mixture of CO2 and CH4 which are main components of the biogas. The effects of annealing temperatures, zeolite loadings, feed pressures and mixed gas and biogas feedings on the separation of CO2–CH4 by membranes were investigated. It has also investigated that whether there is a relation between gas sorption capacity and separation performances of membranes manufactured. Membranes were characterised DSC, TGA and SEM analysis. The pure gas permeation and the mixed gas or biogas separation experiments indicated that the mixed matrix membranes (MMMs) prepared by introducing zeolite 4A into PI is a suitable candidate for CO2/CH4 separation and/or methane enrichment from biogas. Zeolite loading into PEI increased the CO2 and CH4 permeabilities more than PI/zeolite-MMMs showed. But, the higher the zeolite loadings caused the lower the ideal CO2/CH4 selectivities for PEI/zeolite-MMMs at all the feed pressures applied. The results also showed that there is a partial relation between gas permeability and sorption capacity of membranes used.The results of biogas separation experiments showed that the CO2 content in the permeated gas increased as much as 95% at 3 bar feed pressure. The highest CO2 content in the permeated gas was obtained when PI/4A-MMM was used, and followed by PI/3A, pure PI, PI/5A, pure PEI, PEI/5A, PEI/4A and PEI/3A.

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► Annealing of membranes above solvent boiling point improves their performances.
► The effect of zeolite loadings on gas permeabilities differs for polymers.
► Partial relation exists between gas permeability and sorption capacity of membranes.
► Second component like H2O in feed gas mixture reduce the CO2 permeabilities.
► It is possible to separate CO2 from the biogas in the purity of 95% using MMMs.