Catalytic activity of modified silica gel adsorbents under conditions of methanol conversion from water-methanol waste of natural gas

The work is devoted to the analysis of factors affecting the catalytic activity of modified silica gel adsorbents under conditions of methanol conversion to dimethyl ether. The objects of the study were the initial and modified silica gel adsorbents ASM, ASM VS, BASF KC-Trockenperlen H and BASF KC-Trockenperlen WS used in the purification of methanol from water‒methanol waste of natural gas. The purpose of this paper is to study the effect of the specific surface area, elemental and phase composition, and operating time of adsorbents on the catalytic activity of modified silica gel adsorbents under conditions of methanol conversion to dimethyl ether. The composition and structural characteristics of the samples were determined by X‒ray fluorescence, X-ray diffraction analysis and low-temperature nitrogen adsorption. Based on the results of IR‒spectrometric and thermal studies, changes in the structure of the surfaces of adsorbents during their operation by various components of organic origin were evaluated. The catalytic activity of silica gel adsorbents in methanol conversion was studied in a fixed bed reactor at atmospheric pressure in the range of 120-290°C and an optimized rate of methanol-saturated nitrogen flow of 1200 ml/min. The methanol conversion process was controlled by gas‒liquid chromatography. An increase of the catalytic activity of adsorbents in methanol conversion to dimethyl ether was found in the range of ASM VS < BASF KC-Trockenperlen WS < BASF KC-Trockenperlen H < ASM. The maximum catalytic activity at 290°C was shown by the adsorbent ASM with 4.2% aluminum oxide and an amorphous structure, which significantly reduces methanol emissions into the atmosphere. For crystalline adsorbents ASM VS with an alumina content of 13.2%, the catalytic activity was minimal. It is shown that the decrease in the catalytic activity of adsorbents in gas treatment unit during operation is associated with a decrease in the value of the specific surface area of samples with a constant content of aluminum oxide and phase state, which is associated with the possible blocking of the catalytic centers of adsorbents due to the accumulation of components of organic origin in the process of natural gas purification. The establishment of factors affecting the methanol conversion to dimethyl ether on modified silica gel adsorbents will allow managing environmental risks, as well as reducing risks to humans during transportation and disposal of water-methanol waste from natural gas purification.