(155f) Modification of Activated Carbons to Improve H2 PSA Performance

Hydrogen is a valuable industrial gas used in many industrial processes, such as oil refining. It is also the key to decarbonizing industrial and transportation sectors. Many hydrogen production methods, such as steam methane reforming (SMR), autothermal reforming (ATR), and partial oxidation (POX) require subsequent purification by adsorption in an H2 PSA process. The adsorbent beds usually comprise a layer of activated carbon followed by a layer of zeolite. Given the high value of H2, the PSA process has been extensively developed to maximize H2 recovery.

To explore further increasing recovery, we initiated a collaboration with teams at FAU to characterize and modify activated carbons (ACs) used for H2 PSA. The modification approach investigated was impregnation of the activated carbon with various materials (inorganic salts, Polyethylene glycol, microencapsulated phase change materials) to 1) increase the heat capacity of the activated carbon and 2) to reduce the total void fraction in the adsorption column. The increased heat capacity will limit temperature swings during PSA cycles and improve H2 productivity and recovery. The reduction in column void fraction will decrease the H2 lost on blowdown and thereby improve H2 recovery.

A detailed characterization generated the pore size distribution and heat capacities for commercial ACs. In addition, all required equilibrium and mass transfer data were collected for simulations of the PSA performance for the commercial ACs as the base case. The feed gas simulated was that from a steam methane reformer. The same data was collected for the modified ACs so that direct comparisons could be obtained.

The simulations showed that incorporation of certain inorganic salts (like barium acetate) into the activated carbon by simple aqueous impregnation could improve the H2 recovery by as much as 0.4 points, reduce temperature swings by 20% and extend cycle times.