Influence of sodium and potassium proportion on the adsorption of methanol and water on LTA zeolites at high temperature

Abstract

Catalytic hydrogenation of CO2 or CO, obtained from biomass gasification, is the most used technology to produce renewable methanol. The main problem is that the reactions are controlled by equilibrium, achieving low conversions to methanol, leading to high purification costs and reagent recirculation rates. At 250 °C and 50 bar, the equilibrium conversion of CO2 is around 25%, and methanol selectivity is about 64%. The process can be improved by a sorption-enhanced reaction process (SERP), removing the reaction products in situ and overcoming the equilibrium. To carry out the process, adsorbents with high affinity to the products at high temperatures, like LTA zeolites, are required. Experimental data on methanol and water adsorption at reaction temperatures is quite scarce in the literature, and it is usually assumed that methanol is not adsorbed onto 4A and 3A zeolites. This information is required to design a SERP process with this adsorbent. In this work, the influence of sodium and potassium proportion on the adsorption of methanol and water on LTA zeolites is studied by measuring Henry's adsorption equilibrium constants and reciprocal diffusion time constants. Sodium LTA zeolites (4A) strongly adsorb water and methanol. Potassium-rich LTA zeolites (3A) have higher water/methanol selectivity than sodium-rich LTA zeolites.