Resorcinol-formaldehyde based nanostructured carbons for CO2 adsorption: kinetics, isotherm and thermodynamic studies

Silica templated nanostructured carbons were developed from a resorcinol-formaldehyde polymeric precursor by varying the carbonization temperature from 400 degrees C to 800 degrees C. The prepared carbons were characterized thoroughly for their textural, surface and chemical properties followed by dynamic CO2 capture performance at various adsorption temperatures from 30 degrees C to 100 degrees C under simulated flue gas conditions. Among the prepared carbons, carbonization at 700 degrees C resulted in the nanostructured carbon material, as indicated by XRD and TEM results, having the best textural properties i.e. specific surface area and total pore volume around 435 m(2) g(-1) and 0.22 cm(3) g(-1), respectively. The sample obtained by carbonization at the most severe conditions (>= 800 degrees C) exhibited textural properties comparable to that of RF-700 but showed lower CO2 adsorption capacity on account of reduction in surface basicity at higher temperatures. On the other hand, preparation of the carbon material by direct carbonization of the polymeric precursor, i.e. without using a template, resulted in a completely non-porous material with very low CO2 adsorption capacity. Moreover, both the textural properties and the surface chemistry had an effect on the CO2 adsorption performance of the prepared carbons. RF-700 exhibited the highest dynamic CO2 adsorption capacity of 0.761 mmol g(-1) at 30 degrees C in a binary mixture of 12.5% CO2 in N-2 attributed to a well-developed porous structure and high surface basicity of 1.93 meq g(-1). It also demonstrated high selectivity towards CO2 over N-2 and stable adsorption capacity over multiple adsorption-desorption cycles. CO2 adsorption on the prepared carbons was well described by a fractional order kinetic model. Fitting of equilibrium data of CO2 adsorption by Temkin isotherm model and variation in isosteric heat of adsorption with surface coverage indicated an energetically heterogeneous adsorbent surface. Thermodynamics of CO2 adsorption on the carbon material suggested an exothermic, random and spontaneous nature of the process. The thermal energy required for desorption of CO2 was also estimated to be around 1.9 MJ per kg CO2.