design and simulation a cyclic adsorption process as the pre-refiner of a mini lng unit

Carbon dioxide separation from natural gas was investigated by pressure-temperature swing adsorption (ptsa) process as a mini-lng pre-refiner unit. the process was designed with four columns of zeolite 13x adsorbent, working in a cyclic adsorption-desorption operation at high pressure of natural gas. the ng feed composition was contained about 93.5% methane, 1% co2, and other hydrocarbons, with total flow rate of 417 kg/hr, at 62 bar pressure and 27°c temperature. the cyclic operation was designed in five main steps consisting adsorption at high pressure, depressurization, heating and cooling with the saturated steam stream in internal heat exchanger in a stepwise procedure and finally pressurization by small part of feed. heating and cooling each consist of three sub-steps. the heating of the bed consists of steps of increasing the temperature to 100, 170 and 230 ° c, respectively, and the cooling stage is performed at temperatures of 170, 100 and 27 ° c, respectively. simulation of the ptsa process was performed by aspen adsorption software. the required equilibrium isotherms and kinetic data were extracted from the literatures. after simulation and approaching to the cyclic steady-state condition, the fraction of co2 in ng product was reduced from 1% to 4.1ppmv, and the methane recovery in product was achieved about 89.8%.