Systematic experiment on adsorption, separation and regeneration of X zeolites for LNG production with different regeneration strategies: vacuum, purging, heating and hybrid combinations

Abstract

This work experimentally investigated the adsorption, separation and regeneration properties of two X zeolites for natural gas deep decarbonization in liquified natural gas (LNG) production. The regeneration properties of JLOX500 and 13X were compared with relation to regeneration efficiency, energy consumption, desorption and adsorption rate of CO2, and other factors in different pathways: vacuum, purging, heating, and hybrid combinations. The results demonstrated that fresh JLOX500 with more cations and less binders had significantly greater CO2 adsorption capacities and larger separation factor (CO2/CH4) than those of fresh 13X, because of its larger micro-porosity and higher CO2 isosteric heat. Due to higher partial pressure, the adversely significant effect of CH4 competing adsorption against CO2 on adsorbent regeneration is confirmed. The flow rate increases of purge gas had no effects on regeneration efficiency for 13X when the CO2 concentration of desorbed gas reached to zero. Because of a greater cumulative pore volume, JLOX500 after sufficient regeneration has a larger CO2 adsorption capacity and a higher desorption rate of CO2 than 13X, which also makes it more efficient with regards to purge gas and energy consumption utilization. With 150 mL/min of purge gas, the energy consumptions for 13X and JLOX500 regenerated at 150 °C were 4.20 and 2.89 MJ/kg-CO2, respectively. The CH4 recovery relied on the regeneration efficiency of adsorbents, duration of adsorption, and the amount of purge gas used. Both X zeolites regenerated by purging (150 mL/min) or vacuuming at 1 kPa at 150°C could purify the feed to the CO2 content less than 50 ppm, but JLOX500 is more efficient with regards to the overall performance.