Low-temperature partial oxidation of ethanol on Ni/ZnO catalyst

The paper investigates the partial oxidation of ethanol process in a quartz microreactor at atmospheric pressure in the temperature range 300–450 °C on a nickel catalyst (20 wt%) deposited on zinc oxide. Rectified ethanol (an azeotropic mixture of 95.6 wt.% ethanol and 4.4 wt.% water) is fed into the reactor at a rate of 0.4–1.3 g / hour by a peristaltic pump, first into the evaporator, and then as a gas phase into the reactor. Air is used as a source of oxygen which is supplied by an air pump to the reactor and its flow is controlled by a rotameter so that the oxygen-ethanol molar ratio varied between 0.45 and 2.0. The nickel catalyst is prepared by impregnating industrial zinc oxide powder with nickel nitrate, followed by calcination and reduction of nickel oxide to metallic nickel. Analysis of gaseous products is performed on a Tsvet-500 gas chromatograph. The detector is a katharometer.

A catalyst Ni/ZnO developed earlier is shown to have high efficiency in the partial oxidation of ethanol at low temperatures. The main products of this process are hydrogen, methane, carbon monoxide and dioxide. With an increase in the oxygen-ethanol molar ratio, the hydrogen content in the products of the process decreases (from 60 to 25 vol.%), carbon dioxide, on the contrary, increases (26 to 65 vol.%). The hydrogen yield is 1 mol per 1 mol of ethanol at a temperature of 450 °C.

Carbon monoxide is observed with a low ratio of oxygen-ethanol (up to 0.85). With a higher ratio, carbon monoxide is absent in the entire temperature range studied. The conversion of ethanol proceeds intensively and already at a temperature of 450 °C ethanol is converted almost completely. A high methane content (20–30% vol.%) in reforming products indicates that the initial stage of the process is the oxidation of ethanol followed by decomposition of the resulting acetaldehyde into methane and carbon monoxide.

The insignificant water content in the supply mixture leads to an almost complete absence of a shift reaction. Carbon monoxide is then oxidized with oxygen to carbon dioxide. The reduced methane content in comparison with the process of water-steam ethanol reforming can be explained by its partial oxidation to carbon dioxide, which explains the high content of the latter in reforming products. 

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