(A) study on pressure swing adsorption process for the production of more strongly adsorbed component ($N_2$-PAS, $CO_2$-PSA)

Abstract

High purity $N_2$ PSA (pressure swing adsorption) and $CO_2$ PSA using zeolite molecular sieve as an adsorbent are selected to study the PSA process for the production of more strongly adsorbed component based on equilibrium controlled separation. The PSA air separation process to produce a high purity nitrogen product using zeolite-X (W-A) is studied experimentally and theoretically. Adsorption equilibrium data of $N_2$, $O_2$, and Ar on a zeolite-X (W-A) were measured at temperature between 0 and 40℃ and pressure ranging from 0 to 4 atm. Breakthrough experiments were performed to obtain the appropriate mass transfer coefficients. The $N_2$ PSA process is composed of two pretreatment beds (50 cm in length, 5.45 cm in I.D.) to remove moisture and carbon dioxide from atmospheric air, and following three separation beds (150 cm in length, 5.45 cm in I.D.) to recover nitrogen from the purified air. The cycle of the separation beds consists of six steps: pressurization with air, adsorption, recovery, null, high pressure purge with product nitrogen, and evacuation. The product is obtained by evacuation up to 100 mmHg with a vacuum pump. The range of adsorption pressure and reflux ratio are 800-1200 mmHg and 0.3-0.9, respectively. In a typical run, the productivity was 2.8 NI/(kg.min) and the recovery was 55% at the nitrogen purity of 99.99% and the adsorption pressure of 800mmHg. The product purity of $N_2$ increased rapidly and then slowly with increasing the reflux ratio. The reflux ratio of the turning point was around 0.6. In the range of the reflux ratio above 0.6, the lower the adsorption pressure became, the higher the product purity was obtained. The recovery of nitrogen decreased gradually with increasing the reflux ratio. The productivity for a given product purity increased as the adsorption pressure increased below the nitrogen purity of 99.95%(0.05% $O_2$) and the tendency was reversed in the other region. An isothermal model with a linear driving f...