High enrichment and recovery of dilute hydrocarbons by dual-reflux pressure-swing adsorption

A twin-bed, dual (stripping and enriching)-reflux pressure-swing adsorption (DR-PSA) system utilizing an intermediate feed position in the columns was designed, constructed, and operated to study the separation and concentration of a dilute feed of ethane in nitrogen using WestVaco BAX-1500 activated carbon. Four runs were performed, changing only the stripping or enriching reflux ratios. In all the runs, the ethane was enriched between 50 and 90 times with a pressure ratio of only 8. In addition, high heavy-component recoveries were obtained, with the purity and recovery of nitrogen also being very high. The best case enriched a 0.75 vol % ethane feed to 68.4 vol % with an ethane recovery of 99.6%. The nitrogen purity was also very high containing only 30 ppm of ethane in the light product stream. This separation was markedly better than that achievable with a conventional stripping reflux PSA process, and it suggests that it should be entirely feasible to produce two very pure products from a dilute feed stream. Future work will consider this exciting possibility with DR-PSA.