Ethane adsorption on microporous carbon adsorbent with a wide pore size distribution

Abstract

A microporous carbon adsorbent MPU-007 with a wide pore size distribution (specific micropore volume W₀ calculated within the framework of the theory of micropore volume filling is 1.44 cm³ g⁻¹; first-mode micropore diameter X₀₁ is 1.5 nm; second-mode micropore diameter X₀₂ is 3.5 nm; specific surface area S_BET is 2520 m² g⁻¹) was prepared by chemical activation of a mixture of corn dextrin, ethylene glycol, and phenol formaldehyde resin. Adsorption of ethane on this adsorbent was studied at pressures up to 4 MPa at T = 303, 313, 323, and 333 K. The maximum ethane adsorption value attained in the experiments was 25 mmol g⁻¹ or 75 wt%. The adsorption isosteres plotted in the ln P–1/T coordinates using the data obtained can be well approximated by linear functions at constant adsorption values. The dependences of the differential molar isosteric heats of adsorption of ethane on MPU-007 on the amount adsorbed in the temperature range of 303–333 K were calculated. The heat of adsorption of ethane equal to 23 kJ mol⁻¹ remained constant throughout the initial range of micropore fillings up to ∼7 mmol g⁻¹ and then gradually decreased to 8 kJ mol⁻¹ at an uptake of 24 mmol g⁻¹ at 333 K. Such a pattern of the dependence of the heat of adsorption can be due to a wide pore size distribution and to the formation of associates in the adsorbate.