Pressure swing adsorption cycles for improved solvent vapor enrichment

A pressure swing adsorption (PSA)-solvent vapor recovery (SVR) process simulator was used to investigate new PSA cycle configurations designed for higher solvent vapor enrichment. These cycles were modifications of the four-step Skarstrom cycle used commercially for PSA-SVR and include the addition of a cocurrent blowdown step, and combinations of cocurrent blowdown and continuous/batch reflux steps. The recovery of gasoline vapor from tank filling operations was simulated with n-butane, n-heptane, and nitrogen as representatives of the light and heavy components in gasoline vapor, and carrier gas, respectively. Adding a cocurrent blowdown step increased the solvent vapor enrichment, depending mainly on the step ending pressure, not the step time. Both the continuous and batch reflux steps also increased the solvent vapor enrichment, but at the expense of an increased bed capacity factor. For similar increases in the solvent vapor enrichment, batch reflux led to significantly smaller bed capacity factors compared to continuous reflux and was thus superior for PSA-SVR. Overall PSA-SVR process performance improved markedly by adding cocurrent blowdown and batch reflux steps compared to the conventional four-step cycle.