Olefin/Paraffin Separations by Membranes: Process Challenges & Opportunities
09:30 - 10:00
Light olefins (i.e. ethylene and propylene) are important building blocks in petrochemical industry. Production of olefins involves the separation of olefins from their close-boiling paraffin analogues. The separation is currently performed by distillation that requires high reflux ratios and a large number of trays. To improve the process economics, a number of membrane-distillation hybrid processes have been proposed. In this paper, using propylene/propane separation as an example, techno-economic analyses on possible process configurations for new plant and plant retrofit (e.g. cost reduction, debottlenecking) will be presented. All studies use industrially relevant conditions as the design basis, and impact of key membrane characteristics (e.g. separation properties, cost, stability) on process economics will be discussed in detail. Polyolefin plant off-gas is another source of olefin, for which cost-effective separation technologies are being sought. In such processes, paraffin in the reactor loop needs to be purged out on a constant basis, to prevent inert gas from building up in the loop. The off-gas typically contains 20-30% paraffin, with the rest being mostly olefin. Such streams are orders of magnitude smaller than those from steam crackers, and don’t offer the scale of economics for using distillation. Many streams are flared due to the lack of viable separation technologies. Compared to olefin splitters in olefin plants, olefin recovery from polyolefin plant off-gas has much less stringent targets on product purity and recovery rate, which provides a near-term opportunity for the implementation of new technologies. Correlations between process economics and membrane characteristics for this application will be discussed as well in this paper.