CO2 selectivity in CO2:CH4 and CO2:N2 mixtures on carbon microfibers (CMFs) and carbon microspheres (CMSs)

• Carbon microfibers (CMFs) and carbon microspheres (CMSs) were synthesized by electrospinning. • PAN concentration and conditions in the electrospinning determine the morphology of the carbon materials. • Adsorption on CMFs and CMSs is in the order of CO 2 > CH 4 > N 2 showing a high CO 2 selectivity. • CMFs have higher microporosity and better CO 2 selectivity at low pressures compared to CMSs. • CMSs have larger BET area and better CO 2 selectivity at high pressures compared to CMFs. The CO 2 selectivity in CO 2 :CH 4 and CO 2 :N 2 mixtures has been studied in carbon materials; carbon microspheres (CMSs) and carbon microfibers (CMFs). These materials have different morphologies and textural properties but with similar chemical composition, which was demonstrated by SEM, nitrogen adsorption, and XPS techniques. The isosteric enthalpy of adsorption shows that the interaction between the CO 2 molecule and CMFs releases a higher energy than CMSs. CMSs have a higher surface area and thus superior CO 2 adsorption only at pressures above 6 bar, for example, i) at 323 K and 1 bar, 1.43 mmol CO 2 (CMFs) and 0.82 mmol CO 2 (CMSs), and ii) at 323 K and 10 bar, 3.24 mmol CO 2 (CMFs) and 3.70 mmol CO 2 (CMSs). At 1 bar, CMFs is better than CMSs, improving it by 40 %. And at 10 bar, although CMSs adsorb more than CMFs, it is only 14 % more. In addition, CMFs have a higher microporosity, which allows them to exhibit better CO 2 selectivity in CO 2 :CH 4 mixtures, even at relatively high pressures (5.4 mmol CO 2 / mmol CH 4 at 298 K and 1 bar, 4.6 mmol CO 2 / mmol CH 4 at 323 K and 10 bar). These values are like those reported in the literature for carbon materials synthesized by more complex and expensive methods.