Degradation of desiccants in temperature swing adsorption processes: The temperature dependent degradation of zeolites 4A, 13X and silica gels

Many raw and treated natural gas streams are dehydrated using temperature swing adsorption with molecular sieves. These systems are designed to operate for years at a time, with adsorbent materials subjected to thousands of cycles. Despite all the efforts in adsorption research, there is very little open literature on the degradation of these materials over prolonged cycling. In this work, we investigated the degradation rates of zeolite 4A, zeolite 13X and three different pore size silica gels using a rapid cycling thermal swing adsorption apparatus. Zeolite 13X was found to lose 31 %, 51 % and 68 % of its adsorption capacity after 5,000 temperature swing adsorption cycles at regeneration temperatures of T = 150, 200 and 250 ℃, respectively. It is noted that all tested materials had a higher capacity loss at a higher regeneration temperature. At a regeneration temperature of T = 250 ℃ zeolite 4A, 22 Å pore size silica, 30 Å pore size silica and 60 Å pore size silica were observed to lose 6 %, 52 %, 33 % and 19 % adsorption capacity, respectively, after 5,000 temperature swing adsorption cycles. Interestingly, all five materials showed lower degradation rates when water was included in the regenerating gas stream, indicating that a wet gas regeneration can mitigate the degradation of the desiccants.