A hybrid simulated moving bed/pressure swing adsorption process for methane and nitrogen separation

Abstract

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 center dot m-3ads center dot 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 center dot h center dot kg- 1