Molecular simulation study of water–methanol mixtures in activated carbon pores

Abstract

We report a theoretical study of the adsorption behavior of water–methanol mixtures in slit activated carbon micropores. The adsorption isotherms are obtained for a pore of width 2 nm at a temperature of 298 K from grand canonical ensemble Monte Carlo simulations. The water molecules are modeled using the four point transferable intermolecular potential functions (TIP4P) and methanol by the optimized potentials for liquid simulations (OPLS). Carboxyl (COOH) groups are used as active sites on a structured carbon surface. The effect of the relative contributions from dispersion and hydrogen bonding interactions of adsorbates, and of the chemical activation of adsorbents on adsorption behavior is investigated. The adsorption of the mixture components in activated carbon pores occurs by continuous filling, without the sharp capillary condensation observed in graphite pores. Water is preferentially adsorbed over methanol in activated carbon pores for a wide range of pressures, except at lower pressures. The hydrophilic nature of activated carbon pores results in the complexation of both water and methanol molecules with the active sites on the surfaces, leading to bulklike water behavior over the entire pore width. Solvation forces are also calculated as a function of pore size. The negative values found for the solvation force for all pore sizes reflect the hydrophilic interactions of the mixtures with the activated carbon surfaces.

Description of a Polar Molecular Liquid in a Disordered Microporous Material With Activating Chemical Groups by a Replica Rism Theory

“…The matrix density is adjusted accordingly to keep the porosity value of p = 0.80. The mean density of -COOH groups per surface area of matrix chains is about 0.0035Å −2 , which is of the order of typical surface density of carboxylic groups in activated carbons as studied in experiment [65] and simulations [63]. Inclusion of activating groups induces neutralizing charges on matrix grafting "carbons", which brings about additional repulsion between them.…”

“…Same values are assigned to the LJ size and energy of the hydrogen site entering into the OH chemical bond in -COOH activating groups of the matrix in the second model. The LJ parameters of "carbon" particles constituting the matrix in the two models are the same as for carbon atoms of microporous carbon solids in simulations [63]. The geometry of the -COOH group is taken as that [64] of acetic acid (CH 3 COOH), with the methyl group replaced by the matrix "carbon" atom to which the activating group is grafted.…”

“…The geometry of the -COOH group is taken as that [64] of acetic acid (CH 3 COOH), with the methyl group replaced by the matrix "carbon" atom to which the activating group is grafted. Their site charges and LJ parameters are taken from the simulation [63]; a small neutralizing charge is assigned to a grafting "carbon" atom of the matrix.…”

Molecular Description of Electrolyte Solution in a Carbon Aerogel Electrode

“…Rovere et al [21] performed molecular dynamics simulations for the structure of water confined in a cylindrical nanopore of Vycor glass. Shevade et al [22] employed grand canonical Monte Carlo (GCMC) simulations to determine the structure and the adsorption isotherms of water-methanol mixture in a slit activated carbon micropore with carboxyl groups periodically grafted to its surface. Cascarini de Torre and Bot-tani obtained the isotherms of adsorption of nitrogen [23] and ethylene fluid [24] on a heterogeneous solid surface exhibiting the adsorption properties similar to real carbonaceous materials.…”

Molecular dynamics study of selective adsorption of PCB on activated carbon

“…To the best of our knowledge, all previous simulations involving activated carbon employed zero partial atomic charges [25,26]. This approach is quite reasonable for a uniform surface such as the top layer of a graphite sheet, but the influence of pore corners, sheet edges, and other irregularities may lead to polarization and thus non-neutral carbons.…”