Membrane-based gas separation of ethylene/ethylene oxide mixtures for product enrichment in microreactor technology

For the off-gas product separation in an ethyleneoxide microreactor new con cepts need to be developed. Instead of using the technical process of low-t emperature distillation, the performance of gas separation through a dense polymeric membrane was investigated. Different noncrosslinked and crosslink ed 6FDA-based polyimides and copolyimides (6FDA = 4,4 ' -hexafiuoroisopropy lidene diphthalic anhydride) were screened as potential membrane materials. The polymer structure of the membrane material was found to influence the solubility of ethylene oxide and ethylene. The introduction of polar substi tuents in the polymer backbone increases the solubility selectivity drastic ally. For permeation experiments in the same pressure range, a novel setup was developed using microstructured membrane supports. With this device, di fferent polymer membranes were tested with respect to the pure gas permeabi lity of ethylene oxide and ethylene as a function of the feed pressure, so that plasticisation effects could be discussed. For different polyimides an d copolyimides, ideal ethylene oxide/ethylene selectivities between 3 and 4 .5 were found combined with permeabilities between 1.8 and 80.8 barrer.