Techno-Economic\nAnalysis of a Carbon Molecular Sieve-Based\nXylene Isomer Purification Process

The separation and\npurification of xylene isomers is critical to\nthe production of polyethylene terephthalate (PET). These separations\nare complex to operate and demand tremendous amounts of energy and\nthus are an opportunity for reducing industrial energy consumption.\nMembranes provide a low-energy footprint technology with simpler operation,\nand recently, membrane materials have been developed that are capable\nof separating xylene isomers. While these materials have demonstrated\nthe ability to separate xylenes, they have yet to be commercially\ndeployed. This work conducts a techno-economic analysis (TEA) to provide\ninsight on the commercial attractiveness of a <i>p</i>-xylene\nselective carbon molecular sieve (CMS) membrane from both a cost and\nenergy standpoint. This TEA was conducted through the pairing of a\nMaxwell–Stefan transport framework for rigid microporous materials\nwith process modeling. Single-stage organic solvent reverse osmosis\n(OSRO) and pervaporation processes were used to evaluate the effects\nof recovery, selectivity, and diffusivity on the energy intensity\nand cost of the xylene separation. The final analysis used two systems,\na single pervaporation stage followed by two OSRO stages, which was\ncompared against a three-stage OSRO cascade. These were benchmarked\nagainst the commercial Parex process. We estimate that the membrane\nprocesses have the potential to enable impressive cost savings compared\nto the Parex process. While both systems outperformed the Parex process\nin terms of cost, the pervaporation/OSRO hybrid process was able to\nachieve the lowest cost of all due to its reduced membrane surface\narea compared to standalone OSRO. These findings demonstrate the potential\nof membrane systems in the field of difficult small molecule solvent\nseparations.