Enhanced ammonia adsorption performance of MgCl2-loaded activated carbon in pressure swing adsorption

Abstract

Ammonia, which decomposes to N2 and H2, is considered an excellent hydrogen storage material because of its high capacity. However, undecomposed ammonia can cause corrosion and catalyst poisoning, thereby necessitating its removal from the effluent stream. One of the methods used to separate H2, N2, and residual NH3 gases after ammonia decomposition is pressure swing adsorption (PSA). In this study, activated carbon (AC) loaded with MgCl2 was used as an adsorbent for PSA. High-pressure adsorption and breakthrough experiments showed that the optimum Mg loading amount is 4 wt% Mg and the optimum operating temperature is 40 °C. Under these conditions, a balance between the adsorption and desorption performance (in terms of adsorption capacity and desorption time, respectively) was achieved. The optimal MgCl2-loaded AC had an average adsorption capacity of 6.48 mmol NH3/g, which was higher than that of AC by 93%. This adsorbent maintained its high adsorption capacity throughout 15 cycles of adsorption–desorption and performed well in breakthrough experiments simulating either the removal or enrichment of ammonia. Thus, MgCl2-loaded AC is a promising adsorbent that can be potentially applied for both ammonia removal and enrichment in industrial PSA processes for hydrogen extraction.