Affinity and Packing of Benzene, Toluene, and p-Xylene Adsorption on a Graphitic Surface and in Pores

Abstract

A grand canonical Monte Carlo simulation has been carried out at ambient temperature to investigate the adsorption of benzene, toluene, and p-xylene (BTX) on a graphite surface and in a graphitic slit and cylindrical pores. Particular emphasis has been paid to the effects of the confined space on the affinity and packing density. Simulation results for adsorption on a graphite surface were tested against the experimental data to validate the potential models used in the description of adsorption. Our extensive simulation has shown that on an open graphite surface, where there is no restriction in the packing, p-xylene has the highest affinity and adsorbed amount at a given reduced pressure and benzene has the lowest values, due to the additional interaction of the methyl groups with the surface. In a confined space, the order of the affinity remains the same, but the packing (hence the amount adsorbed per unit physical pore volume) is affected by the geometry of the space. It was found that benzene has the highest packing density, whether it is expressed in terms of moles or mass.

Methylbenzenes on graphene

“…At sparse coverages, such as here, it is favorable for the relatively flat methylbenzenes to orient the aromatic ring approximately parallel to graphene, in order to maximize the area of interaction. On the other hand, at high coverages, the total interaction with graphene and with neighboring molecules is maximized if the molecules tilt or stand up perpendicular to graphene This was shown for close to full coverage in empirical Monte Carlo simulations of benzene, toluene, and para-xylene on graphene [41], and in experiments for other flat molecules in Ref. [31].…”

“…In Ref. [41], on the other hand, Monte Carlo simulations are used to find the coverage concentration 4.30 µmol/m 2 , which corresponds to an area per molecule 38.6Å 2 . From this number, we can estimate our coverage to approximately 0.24 ML, in any case far from full coverage.…”

Involving High School Students in Computational Physics University Research: Theory Calculations of Toluene Adsorbed on Graphene

“…We estimate the coverage with the help of two sources: Ref [ 21 ] reports that the area occupied by an adsorbed toluene molecule on graphite is measured to be 46 Å 2 , of which we have one per 12.9 Å × 12.4 Å area, leading to a coverage of 46/160 ≈ 0.29 ML. Ref [ 9 ] finds from molecular dynamics calculations that the coverage concentration is 4.30 μ mol/m 2 , which means that the area per molecule is 38.6 Å 2 and which would mean that our coverage is 0.24 ML. We further know from other similar systems [ 6 ] that the adsorption energy increases with coverage, and so the adsorption energy is expected to be larger at a full monolayer coverage.…”

“…The water molecules pass through the nanopores, leaving the larger salt ions behind in a growing concentration. In this process pollutant molecules may stick to the graphene membrane [ 9 ], by which the water is then also cleaned for pollutants.…”

Comparative Study of Toluene and Hexane Adsorption on Activated Carbons From Gas and Liquid Phase. Enthalpy and Isotherms

“…There was also an effect of the structure and the size of the porosity in the adsorption process, since according to the pore size distribution the solid showed a porosity of combined slitcylinder geometry, which is quite suitable for adsorbates since toluene has a planar arrangement and hexane an elongated cylinder shape; so, what could happen in the adsorption process was that toluene, due to its molecular arrangement, could be more easily located in a slit pore while hexane in cylinder-type ones and if the pores were smaller than 10 Å (as is the case for most of the pore volume according to PSD) both adsorbates would be oriented parallel to the surface because the pores are too small to maintain another orientation (Hofmann et al, 2012;Klomkliang et al, 2012); on the other hand, when the pore size was close to 10 Å, as suggested by Diao et al (2019), toluene could be oriented perpendicular to the surface and if the pore size was >12 Å, two layers of adsorbate molecules could be generated, both with parallel orientation; while when the pore size had sizes equal to or >14 Å, it was mentioned that two layers of toluene molecules would be generated, one with a parallel orientation and the other with a perpendicular orientation (Diao et al, 2019); regarding the cylindrical pores, it was proposed that with a linear configuration of the adsorbate in small pores, a high positional ordering could be achieved inside the cylinder, where it was shown a greater adsorption for ring-like compounds than for linear ones (Cárdenas and Müller, 2019).…”