(152t) Performance Assessment of Dense and Asymmetric Polymeric Membranes with Metal Organic Framework As Fillers for Biogas Enrichment

Enrichment of biogas is an important industrial process that increases its calorific value so that it can be used in place of non-renewable fuels, like, natural gas or LPG. The use of MOFs has been known to enhance the performance of pure polymeric membranes but most of the literature focuses on pure gas studies with either the dense or asymmetric structure. This study is focused on highlighting the difference in membrane performance with respect to structure as well as the feed gas composition. Towards this end, we have synthesized dense and asymmetric polysulfone/MOF MMMs with different filler loadings, 0.5 wt.%-5 wt.% and subjected to pure gas and mixed gases. ZIF-8 has been used as the filler. Pure gases CO₂ and CH₄, artificial mixed gas in different proportions of CH₄:CO₂, i.e., 50:50, 60:40, 70:30 and 90:10 and raw biogas mixture that contains O₂,N₂ and H₂S along with CO₂ and CH₄ have been used.

For permeation of pure gases through dense membranes, a highest increase of 59% in CO₂ permeability was recorded with the MOF loading of 1wt.% whereas an increase of 36% in ideal CO₂/CH₄ selectivity was observed for 5wt.% loading. The membranes showed better performance than pure polysulfone membranes only till loading of 0.75 wt.% where an increment of 51.3% and 5.5% was observed in CO₂ permeance and CO₂/CH₄ selectivity respectively. The decreased selectivity and increased permeance at higher loadings arise due to thin selective layer of asymmetric membranes that is susceptible to formation of non-selective channels due to agglomeration of the filler particles that leads to. However, in case of dense membranes agglomerated particle only tend reduce the surface available for sorption of gas thereby reducing permeability and not the selectivity.

An analysis of membrane effectiveness in case of artificial mixtures and biogas was also done. It was found that artificial mixture and biogas with similar composition had different values of permeability and hence the selectivity. For dense membranes with 0.75 wt.% loading of MOF, a difference of 20% in CO₂ permeability and 30.8% in CO₂/CH₄ selectivity was observed between the two compositions. Similar observation was found in case of asymmetric membranes where the difference in CO₂ permeance and CO₂/CH₄ selectivity was 23% and 29% respectively.

The observations have been rationalised on the basis of the dual mode sorption theory, and the effect of the filler has been explained on the basis of the structural arguments based on Maxwell’s equation and related developments.