Hybrid Cycles to Purify Concentrated Feeds Containing a Strongly Adsorbed Impurity with a Nonlinear Isotherm: The PSA−TSA Supercycle

Abstract

A new adsorption process is developed to remove a strongly adsorbing gaseous impurity that has a very nonlinear isotherm from a non- or weakly adsorbing gas. This process, a number of pressure-swing cycles with low purge ratios followed by thermal regeneration, is called a PSA−TSA supercycle because it consists of thermal cycles on top of PSA cycles. The PSA cycles never reach cyclic steady state by themselves, although the supercycle does reach cyclic steady state. A water/nitrogen mixture with zeolite 13X is taken as model system because water exhibits strongly nonlinear adsorption characteristics. At low feed concentrations (1000 ppm water), PSA works well and is the preferred method. At intermediate feed concentrations (4000 ppm water), TSA is the preferred method. The PSA−TSA supercycle is better than PSA and TSA in handling high solute concentrations in the feed (40 000 ppm water) and producing high-purity product (1 ppm water). PSA fails to meet this purity, and TSA has low productivity. The new hybrid cycle is promising for highly nonlinear systems with high solute concentrations in the feed.