Membrane Organic Separations: An Overview

The rapid increase in global industrialization necessitates technology shifts in energy production, manufacturing, and carbon management techniques.  Large energy costs in refineries, power plants, and manufacturing facilities using traditional separation techniques are currently a major opportunity for innovation.  Approximately 10% of global energy use can be attributed to separation processes, with the vast majority of separations being “thermal” in nature (e.g., distillation). Significant energy and cost savings can be realized using advanced separation techniques such as membranes and sorbents. One of the major barriers to acceptance of these techniques remains linking engineering materials to actual processes that are effective in the presence of aggressive industrial feeds (Sholl and Lively, 2016).

We created free-standing carbon molecular sieve membranes that translate the advantages of reverse osmosis for aqueous separations to the separation of organic liquids (Lively and Sholl, 2017). High-performance membranes derived from carbon materials have shown excellent chemical resistance, high molecular selectivity and fast mass transport across the membrane. Carbon molecular sieve (CMS) membranes with tailored ultramicropore and micropore dimensions show both high processability of polymeric membrane and the high selectivity of inorganic membranes. CMS membranes have been proven to be effective in a variety of gas separation processes such as olefin/paraffin separation, natural gas separation and air separations. However, the low fluxes observed in CMS hollow fibers (due to porous substructure collapse during pyrolysis) hinder scale-up of CMS membranes for industrial separation applications. The performance of carbon molecular sieve separation membranes, which exploit the effect of mass transport across a selective diffusion barrier to separate molecules, can be improved by reducing the thickness of the membrane. We discuss methods to create hollow fiber membranes with thin CMS skin layers. We show that these membranes operate in “organic solvent reverse osmosis” (OSRO) separation modalities and purify p-xylene at room temperature without requiring any phase change (Koh et al., 2016).

References

“Seven chemical separations to change the world”, DS Sholl, RP Lively, Nature 2016, 532, 435-437.

“From water to organics: revolutionizing membrane separations”, RP Lively, DS Sholl, Nature Mater. 2017, 16, 276-279.

“Reverse osmosis molecular differentiation of organic liquids using carbon molecular sieve membranes,” DY Koh, BA McCool, HW Deckman, RP Lively, Science 2016, 353(6301), 804-807.