Novel mixed matrix membranes based on polymerizable room-temperature ionic liquids and SAPO-34 particles to improve CO2 separation

A mixed-matrix membrane containing three components consisting of a solid polymerized room-temperature ionic liquid (poly(RTIL)), a liquid RTIL, and a zeolite material was previously investigated. This membrane showed an improvement in CO2/CH4 separation over the neat poly(RTIL)–RTIL composite membrane without the zeolite component. It was hypothesized that the RTIL served as “wetting agent,” improving the adhesion between the poly(RTIL) (a charged organic polymer) and zeolite particles (charged inorganic particles). In this article, a detailed study of the CO2 separation performance of this 3-component MMM system is presented, along with results showing how the system can be optimized or tuned. Specifically, this study focuses on the effect of varying SAPO-34 and RTIL loadings on the separation performance of the 3-component MMMs. 3-Component MMMs containing [emim][Tf2N] and styrene-based poly(RTIL)s with various loadings of SAPO-34 and various compositions of RTILs and poly(RTIL)s were prepared. Another type of poly(RTIL), which has a longer n-alkyl substituent and a polyolefin backbone was also investigated, in addition to the initial styrene-based poly(RTIL). The single gas permeation of various compositions and types of these 3-component MMMs were investigated. The results show that increasing the amount of RTIL in the 3-component MMM increases the CO2 permeability of the composite membrane. The presence of the SAPO-34 particles in the 3-component MMM improves both the CO2/CH4 selectivity and CO2 permeability in comparison to the neat poly(RTIL)–RTIL composite membrane. For the 3-component MMMs based on the poly(RTIL) with an olefin backbone, the presence of the added liquid RTIL component is not mandatory, which may be due to the similarity of its structure compared to [emim][Tf2N]. In this paper, we also propose a potential molecular arrangement of the poly(RTIL), RTIL, and SAPO-34 particles in the 3-component MMMs.