Effects of carbon-to-zeolite ratio on layered bed H₂ PSA for coke oven gas

Effects of carbon-to-zeolite ratio on a layered bed H₂ PSA using activated carbon and zeolite 5A were studied experimentally and theoretically. Coke oven gas (56.4 vol. % H₂, 26.6 vol. % CH₄, 8.4 vol. % CO, 5.5 vol. % N₂, and 3.1 vol. % CO₂) was used as a feed gas for the seven-step two-bed PSA process incorporating a backfill step. In these experiments, the effects of three operating variables such as adsorption pressure, feed rate and purge rate on the performance of a layered bed PSA were investigated. The layered bed gave better purity than the single-adsorbent bed at the same operating condition, except at low purge rate. Since every component had its own front velocity at each layer, a carbon-to-zeolite ratio affected product purity at a given recovery or throughput. Moreover, for a high-purity H₂ product from coke oven gas, an optimum carbon-to-zeolite ratio had to be determined to control a leading wavefront of N₂. In layered bed PSA processes, the temperature variations inside the bed reflected a kind of inflection or plateau at which a roll-up phenomenon occurred and showed the dynamics of adsorption well at each step during a cycle. Simulated results of the dynamic model incorporating mass, energy and momentum balances agreed well with the PSA experimental results.