The conventional gas-phase simulated moving bed (SMB) process is a promising alternative to the cryogenic distillation for the rejection of nitrogen from methane streams for small-scale applications. However, one of its biggest disadvantages is the need to separate the downstream products, in this case, methane and nitrogen, from the desorbent species that is used in the process to regenerate the adsorbent. To overcome this, one can use a combination of pressure swing adsorption (PSA) steps and displacement chromatography to remove the adsorbed phase from the solid material. This way, the desorbent gas can be removed from the process. This work presents an in-silico study of such hybrid SMB/PSA process. A parametric study was also conducted to observe the effect of different operating conditions on the performance and improve the process. This advanced technique was able to produce high purity methane and nitrogen streams, meeting stricter purity requirements for methane streams (97%) and achieving high nitrogen purity (99%). Partial recovery of the purge outlet stream as heavy product gas enables an increase in methane recovery and productivity, reaching values of up to 97.3% and 11.5 kg·m −3 ads ·h −1 , respectively. Optimising the purge flow leads to a higher nitrogen recovery and productivity. Maintaining very low desorption pressures (0.1 bar) was found necessary to achieve a good process performance, leading to higher power consumption (503.0 W·h·kg −1 CH4 ). • A hybrid SMB/PSA process was modelled for the separation of methane and nitrogen mixtures • A strategy for the determination of the optimal operating conditions of the process was defined and a parametric study was conducted • High purity, recovery and productivity values were obtained for both product streams
Dias et al. (Sun,) studied this question.