Development of chemically activated N-enriched carbon adsorbents from urea-formaldehyde resin for CO_2 adsorption: Kinetics, isotherm, and thermodynamics

摘要

Nitrogen enriched carbon adsorbents with high surface areas were successfully prepared by carbonizing the low-cost urea formaldehyde resin, followed by KOH activation. Different characterization techniques were used to determine the structure and surface functional groups. Maximum surface area and total pore volume of 4547 m2 g−1and 4.50 cm3 g−1were found by controlling activation conditions. The optimized sample denoted as UFA-3-973 possesses a remarkable surface area, which is found to be one of the best surface areas achieved so far. Nitrogen content of this sample was found to be 22.32%. Dynamic CO2uptake capacity of the carbon adsorbents were determined thermogravimetrically at different CO2concentrations (6–100%) and adsorption temperatures (303–373 K) which have a much more relevance for the flue gas application. Highest adsorption capacity of 2.43 mmol g−1for this sample was obtained at 303 K under pure CO2flow. Complete regenerability of the adsorbent over four adsorption-desorption cycles was obtained. Fractional order kinetic model provided best description of adsorption over all adsorption temperatures and CO2concentrations. Heterogeneity of the adsorbent surface was confirmed from the Langmuir and Freundlich isotherms fits and isosteric heat of adsorption values. Exothermic, spontaneous and feasible nature of adsorption process was confirmed from thermodynamic parameter values. The combination of high surface area and large pore volume makes the adsorbent a new promising carbon material for CO2capture from power plant flue gas and for other relevant applications.