Investigation of the Effect of Acid Modification of AG-3 Activated Carbon on the Process of Acetone Vapor Adsorption

Abstract

Air purification from volatile organic compounds (VOCs) remains a serious problem of maintaining public health and environmental safety due to their toxic properties and widespread use in various fields of industrial production. In the presented work, the kinetic patterns of acetone vapor adsorption processes with commercially activated carbon AG-3 and its nitric acid–modified analogues were studied. To obtain modified adsorbent samples, the initial activated carbon AG-3 was treated with 2 M, 4 M, and 6 M aqueous solutions of nitric acid at a temperature of 100°C for 2 h. The reaction mixture was then cooled to room temperature and washed with distilled water until the neutral pH of the filtrate was reached. The obtained samples were dried at 110°C until a constant mass was obtained. To evaluate the acidic properties of the surface of semiconductor adsorbents, the adsorption of pyridine from its solutions in octane was studied using UV spectrometry. The results showed that the sorbent samples obtained by treatment of the initial industrial activated carbon AG-3 with a 2 M aqueous solution of nitric acid had the highest acidity. A further increase in the concentration of nitric acid led to a decrease in the acidic properties of the adsorbent and the specific surface area of the modified samples. The processes of acetone vapor adsorption were studied at room temperature and atmospheric pressure using the gravimetric method. The kinetic data obtained was analyzed using the Yelovich and Morris–Weber pseudo-first and pseudo-second order models. It was found that acid modification of the adsorbent significantly increased its capacitance characteristics, but it had little effect on the rate of acetone vapor adsorption. At the same time, the activated carbon image modified with a 2 M HNO₃ solution also showed the best results. Kinetic investigation has shown that, in all cases, the process of acetone vapor absorption under consideration was best described by a pseudo-second-order model, which indicated the limiting nature of the stage of chemisorption of adsorbate molecules on the adsorbent surface. At the same time, the use of the Morris–Weber model also showed a good agreement between experimental and calculated results, which indicated the possible influence of diffusion processes on the rate of acetone vapor adsorption as the number of free centers on the adsorbent surface decreased. The results obtained indicate that it is impossible to control the conditions of acid modification of carbon adsorbents in order to increase the effectiveness of their practical application.