A molecular model for adsorption of water on activated carbon: Comparison of simulation and experiment

Experimental and molecular simulation results are presented for the adsorpt ion of water onto activated carbons. The pore size distribution for the car bon studied was determined from nitrogen adsorption data using density func tional theory, and the density of acidic and basic surface sites was found using Boehm and potentiometric titration. The total surface site density wa s 0.675 site/nm(2). Water adsorption was measured for relative pressures P/ P-0 down to 10(-3). A new molecular model for the water/activated carbon sy stem is presented, which we term the effective single group model, and gran d canonical Monte Carlo simulations are reported for the range of pressures covered in the experiments. A comparison of these simulations with the exp eriments show generally good agreement, although some discrepancies are not ed at very low pressures and also at high relative pressures. The differenc es at low pressure are attributed to the simplification of using a single s urface group species, while those at high pressure are believed to arise fr om uncertainties in the pore size distribution. The simulation results thro w new light on the adsorption mechanism for water at low pressures. The inf luence of varying both the density of surface sites and the size of the gra phite microcrystals is studied using molecular simulation.