Generation of biochars for gas separation upon cellulose pyrolysis: A reactive molecular dynamics study

The pyrolysis of cellulose via reactive molecular dynamic simulation to obtain an adsorbent for CO 2 separation is the main goal of the present study. Biochars with six different densities ranging from 0.160-0.987 g/cm 3 were produced and adsorption of pure CO 2 , CH 4 , N 2 and mixtures of CO 2 (0.05)/CH 4 (0.95) and CO 2 (0.2)/N 2 (0.8) at 300 K was investigated as a function of pressure by Grand Canonical Monte Carlo simulations. Dual-site Langmuir (DSL) model was adjusted to the isothermal adsorption data with very good accuracy. Thermodynamic quantities were calculated based on the DSL parameters which showed that the amount of adsorbed CH 4 and N 2 decreases as the density of biochar increases. Adsorption isotherms, selectivity, and isosteric heat were calculated, which revealed that the biochar with 0.351 g/cm 3 density had the highest selective adsorption of CO 2 . The higher Gibbs free energy and surface potential of pure CO 2 indicated that CO 2 adsorption on biochars is more favorable and spontaneous than CH 4 and N 2 . Henry's constant for CH 4 and N 2 was smaller than that of CO 2 , which indicates that their affinity for biochar surfaces was weaker than CO 2 . The higher entropy changes of CO 2 adsorption of pure gases and binary gas mixtures showed that CO 2 molecules constitute a much more stable rearrangement than CH 4 and N 2 . We may conclude that pyrolysis of cellulose, as a cheap and available material, can be used to make an economic structure with high ability for CO 2 separation.