from first principles PP-I-1

PP-III-72Conversion of Methanol to Formaldehyde on Supported Copper-ZincCatalysts in Synthesis-Gas MediumMorozov L.N., Popov M.S., Smirnov A.I.Ivanovo State University of Chemistry and Technology, Ivanovo, Russiamorozov@isuct.ruProduction of formaldehyde by methanol dehydrogenation is considered to be more advancedprocess as compared to its partial oxidation as hydrogen evolved in the reaction returns into thestage of methanol synthesis, which reduces drastically raw material consumption.In the paper presented, methanol dehydrogenation to formaldehyde was carried out on supportedcopper-zinc catalysts, with porous silica gel being used as a carrier. The surface of the latter hasbeen modified with carbonate and silicate compounds of potassium, which enables the activity ofthe catalysts concerned to considerably increase. The effect of the reaction medium simulating thecomposition of synthesis-gas of methanol production has been studied by varying the compositionof the initial gaseous mixture by altering carbon monoxide, carbon dioxide and hydrogen ratio,with the concentration of methanol remaining constant.The raise of carbon monoxide partial pressure increases the efficiency of copper catalysts fordehydrogenation reaction. In this case, it takes a long time for the system to reach steady stateoperating condition, and the process is accompanied by a change in the selectivity ofhydrogenation reaction from methyl-formate to formaldehyde.Along with the main reaction, there takes place the formation of dimethyl ether, methane aswell as methanol decomposition accompanied by isolation of carbon. The catalysts with zincoxide only are less susceptible to the presence of a gaseous mixture of carbon oxides. Nomethyl-formate is formed in this case, and in the presence of hydrogen the reaction route offree carbon allocation is markedly depressed. Copper-zinc applied catalysts are more activetowards formaldehyde, but the increase in hydrogen concentration in a reaction mixturedeactivates the catalysts at high temperature (~500 0C) and minimizes the effect of copper.Hence, it is the right choice of the applied components ratio that is responsible for activity andstability of a catalyst performance.The process of reaching catalyst steady state consists both in reducing oxide copper compoundsand the formation of hydrocarbon species on its surface. Mutual influence ofreducing agents - hydrogen and carbon monoxide, leads to an increase in the degree ofreduction of oxide compounds, and changes in reaction selectivity as to the reaction products:methyl formate - formaldehyde.227