De Q. Vu

Mixed matrix membranes using carbon molecular sieves: II. Modeling permeation behavior

Abstract Mixed matrix membranes have been formed from flat-sheet solution casting of carbon molecular sieves (CMS) dispersed within two different polymer matrices. In a preceding paper (Part I), the performance of these mixed matrix membrane films has been demonstrated for gas separations. It was shown that the CMS particles produced a mixed matrix or heterogeneous membrane having significantly enhanced effective permselectivities (CO 2 /CH 4 and O 2 /N 2 ) and fast-gas permeabilities (CO 2 and O 2 ) over the intrinsic properties of the pure polymer matrix phase alone. For the CO 2 /CH 4 separation, enhancements by as much as 45% in CO 2 /CH 4 permselectivity and 200% in CO 2 permeability over the corresponding intrinsic permeation properties of the pure polymer matrix phases were observed. These performance enhancements increased incrementally as the loading of CMS particles (up to 35% by weight) being dispersed within the two polymer matrices (Matrimid ® 5218 and Ultem ® 1000) increased. In this paper, these experimental findings are compared with two theoretical mixed matrix models, the Maxwell and the Bruggeman Models. In general, the Bruggeman Model was observed to consistently predict both higher permeabilities and permselectivities than the Maxwell Model. For the Ultem ® -CMS mixed matrix films, the Bruggeman Model reasonably predicted the experimental permeability data, while the Maxwell Model underpredicted the gas permeabilities. Both models, however, gave permselectivity predictions that compared reasonably well with experimental values for the Ultem ® -CMS mixed matrix films. For the Matrimid ® -CMS mixed matrix films, both models significantly overpredicted the observed gas permeabilities and permselectivities. A matrix rigidification phenomenon in Matrimid ® was postulated to be occurring in the region or zone near the CMS surface. An ad hoc adaptation to the Maxwell Model was employed to account for this phenomenon. Predictions from this modified approach gave better agreement with experimental values for the Matrimid ® -CMS mixed matrix films.

Mixed Matrix Membrane Materials: An Answer to the Challenges Faced by Membrane Based Gas Separations Today?

The current status and the limitations faced by available membrane materials used or gas separations are reviewed. One of the biggest challenges that emerges from this survey is the need for materials with enhanced permselectivity with at least equivalent productivity compared to current materials. So called “mixed matrix” materials comprising molecular sieving entities such as zeolites dispersed in conventional polymer materials are possibly attractive solutions to this challenge. These materials ideally offer the excellent transport properties of molecular sieving materials with the processability of polymers, offering a cost effective solution to the need for economical high selectivity membrane materials. The potential impact of mixed matrix materials on the current applications is considered and the status of mixed matrix materials is presented in this paper.

Mixed matrix membrane technology : enhancing gas separations with polymer/molecular sieve composites

Abstract There is increased interest in membranes with high selectivity and productivity for a number of gas separations of interest to the petroleum and chemical industries. While glassy, polymeric membranes have provided efficient performance to date, getting significant improvements over current technology will likely require novel materials. This has led researchers to study molecular sieve membranes, including carbon molecular sieve and zeolitic materials. While these membranes offer very attractive properties, their cost, difficulty of commercial scale manufacture and brittleness remain major challenges. This paper will review the development and status of a new technology based on composite membranes of polymer matrices in which molecular sieves are dispersed to give enhanced separation properties compared to membranes of the polymer alone, with results reported for the separation of CO 2 from natural gas.