Equilibrium Theory for Pressure Swing Adsorption. 3. Separation and Purification in Two-Component Adsorption

Abstract

The periodic behavior of an adsorption bed that is alternatively fed with a binary mixture in inert gas and purged countercurrently, but incompletely, with pure inert gas is analyzed using local equilibrium theory. The bed is isothermal with the two adsorbable components present in trace amounts and adsorption equilibrium described by a binary Langmuir isotherm. The purge step ends as soon as one of the components has been completely removed from the bed. For this nonlinear system, the periodic state is found analytically, without iteration, and feed and purge times are obtained directly. Both separation and purification problems are analyzed. A system is completely defined by three parameters: the constant separation factor for each component and the ratio of partition ratios of the components as pure feeds. Different combinations of these parameters yield wave interactions among simple waves and shocks, which are resolved numerically, and corresponding bed profiles that are quite dissimilar.

Advances in Pressure Swing Adsorption for Gas Separation

“…This equilibrium establishes the thermodynamic limit of the adsorbent loading for a given fluid phase composition, temperature, and pressure [3]. Information about the adsorption equilibrium of the different species is vital to design and model adsorption processes [19][20][21][22][23][24][25][26][27]. The time required to achieve the equilibrium state may be also important, particularly when the size of the pores of the adsorbent are close to the size of the molecules to be separated [28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43].…”

Equilibrium Theory for Pressure-Swing Adsorption. 4. Optimizations for Trace Separation and Purification in Two-Component Adsorption

“…For purifications, recovery of mixed solvents used in spraying, coating, and drying operations can be accomplished by pressure-swing adsorption. For separations of components in carrier gas, pressure-swing adsorption can be employed as shown in our previous paper (Pigorini and LeVan, 1997). Economically viable systems are expected to be those in which the components are originally present in the vapor phase or those for which distillation is difficult because of low relative volatilities (e.g., mixed xylenes) or true azeotropic mixtures.…”

“…In part 3 of this series (Pigorini and LeVan, 1997) we analyzed separation and purification problems in pressure-swing adsorption for a system of two adsorbable components present in trace amounts in an inert carrier gas. For the separation problem the light component breaks through and is present in the product during much of the feed step.…”

Heat and Mass Transport Characteristics of Pressure Swing Adsorption for the Removal of High-Level Moisture along with CO2 from Air

“…LeVan analytically determined the cyclic steady state of a PSA system for both favorable and unfavorable isotherms based on an isothermal and local equilibrium model. Pigorini and LeVan − serially investigated PSA for purification and enrichment in layered beds for two-trace-component separation and purification and related optimizations and for multicomponent adsorption with equilibrium theory. They derived periodic concentration profiles and discussed the effects of isotherm shapes, bed layering, and operating conditions on the periodic state.…”