Microstructure effect of carbon materials on the low-concentration methane adsorption separation from its mixture with nitrogen

Due to the weak polarities of CH4 and N2 and their similar physicochemical properties, the microporous adsorbents have a little amount of adsorption capacity for the low-concentration methane, and the separation of CH4/N2 is also very difficult to accomplish by the adsorption-based process. Microstructure of carbon materials plays a decisive role for CH4/N2 effective separation and CH4 enrichment from the low-concentration methane gas mixed with nitrogen. This work focuses on the research of carbon material microstructure, including the selection of raw material or precursor for the carbon skeleton formation, effect of the specific surface area of carbon material on the low-concentration methane adsorption amount, the relationship between micropore size distribution of carbon material and CH4/N2 adsorption separation mechanism, and effect of different activator on the weak polar methane adsorption capacity. According to the microstructure analysis, the granular activated carbons (GACs) are prepared in lab-scale with the optimal preparation conditions, raw coconut shell carbonization for 2 h at 1073 K under N2 atmosphere and KOH activation for 1 h at 1073 K under N2 atmosphere with the KOH to carbonized material ratio of 3:1. And then, the home-made GACs (about 200 g) were packed in a column. A four-step one-bed vacuum pressure swing adsorption (VPSA) process was adopted to evaluate the low-concentration methane adsorption separation performance from its mixture with nitrogen.