The Process Research For Produing The Glyoxal By Acetaldehyde Oxidation

Glyoxal is a kind of important chemical material and intermediate product and is widely used. Glyoxal can be producted by the oxidation of acetaldehyde or ethylene glycol in industrial process. The method of acetaldehyde oxygenation has merits of high quality and low energy consumption etc. But the traditional technic has the defects of severe pollution, low yield, and is easy to blast etc. This paper develops a new technic of glyoxal from acetaldehyde, and studies the process conditions of oxidation and separation in detail.The main influence factors of glyoxal selectivity and yield, such as the variety and amount of catalyst, reaction temperature, nitric acid concentration, the mole ratio of acetaldehyde to nitric acid and reaction time etc, have been studied by orthogonal design in this paper, and the optimum experiment condition was selected. The results show that the optimum conditions were NOx as an initiator, copper nitrate as catalyst and the amount of catalyst is0.1%(weight ratio) of acetaldehyde, the reaction temperature is about40℃, the feeding of nitric acid at the beginning is20%, which concentration is40%(weight ratio), acetaldehyde concentration is40%(weight ratio), the mole ratio of acetaldehyde to nitric acid is1:0.75, reaction time is5h. Under the above condition, the per pass yield of glyoxal can exceed50%, and the selectivity of glyoxal reaches69.72%. Comparing with the domestic level of glyoxal process, the selectivity and per pass yield of glyoxal increases10%and5%～8%, respectively.The separation of nitric acid and acetic acid with electrodialysis has been studied in this paper. When acetaldehyde is oxidized by nitric acid, the solution is made up of the product glyoxal, nitric acid without reaction, and by-product acetic acid. The experiment shows that the J-1-18(homogeneous phase) ionic exchange membrane can be used to separate nitric acid and acetic acid, and the influence separation factors were studied, too. The experiment result shows that the current efficiency of electrodialysis is86%, the electric consume is30.3×10-3kwh/L and the yield rate of glyoxal is up to98%if the depickling rate of nitric acid is90%on10voltages. The experiment results which the separation of nitric acid with electrodialysis shows that the acetic acid concentraion can decline to0.1%and the electricity consume is118.8×10-3kwh/L of this process if the membrane stack voltage is20V, the feed flow is60L/h, of pole water flow is30L/h, operation temperature is below40℃, and the electrodialysis runs22hours. If replace dense water, the time of deacidify can decline to18hours, and the yield of glyoxal is84.01%.