Oxalic Acid Carbon Monoxide Coupling Method
This method initially used palladium and copper salts as catalysts, and carried out a liquid-phase coupling reaction of carbon monoxide, oxygen, alcohol, and dilute nitric acid at 8–11 MPa and 90–100 °C. The reaction first produces oxalate ester, which is then hydrolyzed under heating conditions to form oxalic acid and the corresponding alcohol.
This method has a single catalyst system, high activity, good selectivity, easy recovery, high product purity, and low production pollution. However, it has high requirements for carbon monoxide purity, high consumption, expensive catalysts, and high investment.
Using Pd/C as a catalyst, carbon monoxide and nitrite ester are coupled to synthesize oxalate ester at 130 °C and atmospheric pressure, with nitric oxide as a by-product. Oxalic acid and the corresponding alcohol are obtained by hydrolyzing the oxalate ester. The separated alcohol solution is reoxidized to form nitrite ester, which can be recycled.
The Fujian Institute of Structure of Matter, Chinese Academy of Sciences, has conducted research on the ratio of raw materials and various space velocity conditions on the catalytic synthesis of dimethyl oxalate in the research of catalysts for the atmospheric pressure catalytic coupling of CO to oxalic acid, and selected suitable reaction conditions. The improved Pd (2.0%)/α-Al₂O₃ catalyst achieved a space-time yield of 999 g/L·h under the conditions of atmospheric pressure, 140 °C, CO/CH₃ONO=1.5, and space velocity of 3000/h. The institute cooperated with the Fujian Petrochemical Design Institute and Fujian Nanqing Ammonia Plant to conduct a 100 t/a pilot test of recovering CO from synthetic ammonia copper scrubbing, atmospheric pressure catalytic synthesis of dimethyl oxalate, and hydrolysis to oxalic acid.
Compared with the liquid-phase method, this method has high selectivity, simple process, high product purity, and low production cost. It can use natural gas or coal as raw materials, and can also use carbon monoxide recovered from ammonia copper scrubbing or yellow phosphorus furnace, blast furnace, and converter tail gas as the carbon monoxide gas source. At the same time, it can provide cheap raw materials for the production of ethylene glycol and the unified synthesis with oxalate ester as an intermediate.

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