EFFECT OF THE FEED GAS MIXTURE COMPOSITION AT METHANOL DEHYDROGENATION TO FORMALDEHYDE ON SUPPORTED OXIDE CATALYSTS

Abstract

The article presents the results of a study of the activity of deposited oxide catalysts in the process of obtaining formaldehyde from methanol. Model catalysts were prepared by impregnation of finely porous silica gel with nitrate solutions of zinc, copper, silver, sodium, followed by heat treatment. The catalytic properties of the samples were studied in the reaction of methanol dehydrogenation in the flow mode on a fine fraction of the catalyst. With the complication of the composition of the feed gas mixture, part of argon was replaced with hydrogen, mono- and carbon dioxide. The reaction mixture was analyzed by gas chromatography, IR spectroscopy and photocolorimetry. At a temperature of ~350 °C, a noticeable formation of formaldehyde begins, upon reaching a temperature of 500 °C in the reactor, methanol processing begins to decrease, while the concentration of formaldehyde changes insignificantly. Along with formaldehyde, dimethyl ether, methane and carbon dioxide are fixed in the reaction products. At the end of the tests on the surface of the catalyst, carbon, oxygen and hydrogen are quantified using elemental analysis methods, the ratio between which corresponds to the formula (-COH-)n. That is, along with the target reaction, methanol is consumed for the formation of surface hydrocarbons. Oxymethylene oligomers can decompose along two competing routes to form formaldehyde or carbon and CO2. The addition of carbon dioxide to the feed gas mixture after the catalyst enters the stationary mode leads to a significant increase in its formaldehyde yield. It is obvious that the route with the formation of carbon dioxide is associated with the target reaction of formaldehyde production, where the catalytic reaction maintains a certain concentration of active centers. Thus, it can be assumed that carbon dioxide as a product of decomposition of surface oxymethylene compounds affects the rate of the catalytic reaction by maintaining a certain concentration of surface hydrocarbons, which are necessary as an element of the active catalytic center. For citation: Morozov L.N., Vorobyov A.S., Kunin A.V., Egorov N.A., Timoshin E.S. Effect of the feed gas mixture composition at methanol dehydrogenation to formaldehyde on supported oxide catalysts. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 7. P. 88-95. DOI: 10.6060/ivkkt.20246707.7003.