Adsorption characteristics of hydrogen mixtures in a layered bed: Binary, ternary, and five-component mixtures

Adsorption characteristics in a layered bed packed with activated carbon and zeolite 5A were studied experimentally and theoretically through the breakthrough experiments of binary (H₂/CO, H₂/CH₄, H₂/CO₂), ternary (H₂/CH₄/CO), and five-component (H₂/CH₄/CO/N₂/CO₂) systems. The effects of adsorption pressure, feed flow rate, and carbon-to-zeolite ratio on the breakthrough curve in a layered bed were observed. Breakthrough curves in all of the mixtures showed tailing due to temperature variance in the bed by the heat of adsorption. In the layered bed, each mixture showed the specific characteristics of concentration and temperature wave fronts in each layer. Although the amount of impurity in a ternary mixture is larger than that in a binary mixture, the breakthrough time and elongation depending on the adsorption pressure and flow rate showed an intermediate value between the results of the H₂/CO and H₂/CH₄ mixtures, and the tailing was not much different from those in these binary systems. Also, the roll-up phenomenon of CO breakthrough curves occurred because of the breakthrough of CH₄. Also, because the wave propagation velocity was changed in the layer interface, the concentration wave fronts could become crossover in layered bed. The breakthrough behavior of the major impurities (CH₄ and CO) in the five-component system was very similar to the results for the ternary system with the same carbon-to-zeolite ratio, and the most weakly adsorbed impurity (N₂) was the leading wave front in all cases. As a result, in the breakthrough study, the most weakly adsorbed impurity in the mixture should be included in the design of the optimum layered bed for the PSA process.