Adsorption of nitrogen, oxygen and argon on polyorganosiloxanes with different functional groups

Abstract

The study presents polyorganosiloxane adsorbents containing one of the organic radicals with or without functional groups and the study of their adsorption properties based on air macrocomponents. The “sol-gel” scheme of directed copolycondensation of a mixture of reagents was chosen as the basic technique. Based on the developed synthesis technique, samples of polyorganosiloxanes with various functional groups were obtained. These samples had both four-functional (Q-links) and three-functional (T-links) fragments in the composition. In turn, the T-units had one of the organic radicals with or without functional groups.

The equilibrium capacities for nitrogen, oxygen, and argon were determined from the kinetic curves of adsorption of these gases at 25^oC and atmospheric pressure. The separation coefficient of the argon-oxygen mixture calculated as the ratio of Henry's coefficients was used as a measure of the adsorption selectivity of the samples with respect to argon.

For the description of the kinetics of sorption of nitrogen, oxygen, and argon, the model of intradiffusion kinetics of physical adsorption, pseudo first and pseudo second order models were applied. As a result of kinetic data processing, it was shown that the mechanism of adsorption of macrocomponents of air on synthesized polyorganosiloxanes has a complex character, and it was affected by both the properties of the studied gases and the type of functional group. The adsorption of argon on the obtained samples was limited by internal diffusion and was described by the model of a quasi-homogeneous porous body with a high level of reliability. The adsorption of nitrogen on polyorganosilanes was determined by the interaction with local active centres of the surface, which were silanol groups of silica. The adsorption mechanism was described with a high degree of reliability by the pseudo-second order chemical kinetics model. The rate of oxygen sorption was affected by the intradiffusion limiting, the rate of localized physical adsorption and by the type of functional group. From the presented data, it can be seen that the introduction of functional groups into polyorganosiloxanes can influence the adsorption properties of the obtained materials with respect to air macrocomponents. The highest selectivity to argon was exhibited by the sample containing the diethylaminomethyl functional group; the separation factor was 2.4