Adsorption of dimethylpolysiloxane on graphite, anthracite, and activated carbon from hexane solutions

Abstract

The article presents an analysis of the features of adsorption of high molecular substances on porous carbon adsorbents. These features include the low diffusion rate of macromolecules, the dependence of the adsorption on the porosity of the adsorbent, and the presence of the conformations in the adsorption layer that are not energetically beneficial. The conformations of the polycarboxylate macromolecule were reconstructed using individual fragments. We also obtained qualitative regularities of the distribution of the polycarbox-ylate macromolecule over the surface depending on the concentration of the 1.1-valence electrolyte at various pH-pK0. When the рН–pK0 are negative or close to zero, the degree of ionization is low and close to zero. When рН–pK0 are sufficiently high, the dissociation increases in all cases and, due to electrostatic repulsion forces between certain sections, the macromolecule unfolds, becomes more linear, and is adsorbed on the surface in this form. The amount of adsorption does not depend much on the nature of the surface, but rather depends on the conformation of the macromolecule in the solution and the root mean square radius of the degree of hydration. In our research, we also studied the adsorption of dimethylpolysiloxane (PMS-20) from solutions of the substance in hexane on graphite C-3, activated carbon B, and A grade fossil coal from the Donetsk basin (glass layer). The study determined the adsorption mechanisms and demonstrated that the ad-sorption isotherms of this type do not correspond to the Langmuir adsorption isotherms. The adsorption layer is filled more slowly on graphite, and more intensively on anthracite and activated carbon than during Lang-muir adsorption. It was suggested that during the adsorption of dimethylpolysiloxane on graphite, the glob-ules of macromolecules repel each other, while the high adsorption potential on anthracite and activated car-bon contributes to more intense filling of the adsorption layer. The study determined the maximum adsorp-tion capacity of the studied adsorbents with respect to dimethylpolysiloxane, equal to graphite, anthracite, and activated carbon to be 2, 100, and 480 mg/g respectively. The calculated values of the maximum adsorption capacity of adsorbents are 6, 130, and 768 mg/g respectively. Some parts of the porous space of anthra-cite and activated carbon are not available for adsorption of dimethylpolysiloxane macromolecules due to steric difficulties