Influence of Nanoporous Carbon Structures on High-Pressure Adsorption Separation of Light Hydrocarbons

摘要

Four activated carbons (ACs) prepared from polymers (PMB, P- 300), wood waste (S-1), and silicon carbide (AUK) by chemical and physical activation were investigated as potential adsorbents for ethane/methane mixture separation. Their textural properties were compared by performing scanning electron microscopy, X-ray, and CHNS/O elemental analysis. N_2 and CO_2 adsorption interpreted in terms of the theory of volume filling of micropores, non-local density functional theory (NLDFT), and Brunauer-Emmett-Teller (BET) models revealed very different porosity features of these ACs. The adsorption of pure ethane and methane onto all of the ACs was measured at pressures up to 50 bar and temperatures of 303-333 K in order to evaluate their adsorption selectivity for a methane/ethane mixture using the IAST method. The calculations indicated that ACs with the largest mean pore sizes, P-300 and PBM, are least suitable for adsorption-based separation of the ethane/methane mixture since they demonstrated a relatively strong dependence of selectivity coefficient (SF) on pressure and temperature. AUK showed the highest value of SF for ethane at low pressures (up to 5 bar), reaching 18 at 303 K for the mixture 95/5% CH_4/C_2H_6. Finally, S-l was found to be the most efficient adsorbent for the ethane/methane separation since it demonstrated a relatively high separation performance in a pressure range of 2-50 bar with almost no reduction in separation performance. In general, the SF value of ACs for ethane correlated with the difference between the initial differential isosteric heats of ethane and methane adsorption as well as with the presence of high-energy adsorption centers as narrow micropores with size less than 1 nm and heteroatoms (N,O). Molecular dynamics simulations of the adsorption of the methane/ethane mixture onto the model carbon adsorbents also indicated the influence of pore width on selective capacity.