The industrial production methods of oxalic acid include sodium formate method, oxidation method, carbonyl synthesis method, ethylene glycol oxidation method, propylene oxidation method and carbon monoxide coupling method.

1. Carbon monoxide purified by sodium formate reacts with sodium hydroxide under pressure to produce sodium formate, then dehydrogenates at high temperature to produce sodium oxalate, which is then prepared by lead (or calcification), acidification, crystallization, dehydration and drying. The synthesis pressure of carbon monoxide and sodium hydroxide is generally 1.8-2.0 MPa. The dehydrogenation temperature is 400 C.

2. Oxalic acid was synthesized by oxidation of starch or mother liquor of glucose with nitric acid-sulfuric acid in the presence of alum catalyst. Nitrogen oxide in waste gas is recycled to form dilute nitric acid in the absorption tower.

3. Carbonyl synthesis of carbon monoxide after purification to more than 90%, in the presence of palladium catalyst and butanol carbonylation reaction, the formation of dibutyl oxalate, and then hydrolysis to oxalic acid, this method is divided into liquid phase method and gas phase method, the reaction conditions are low, the reaction pressure is 300-400 kPa. The liquid phase reaction pressure is 13.0-15.0 MPa.

4. Ethylene glycol oxidation is obtained from ethylene glycol by air oxidation in the presence of nitric acid and sulfuric acid.

5. Propylene oxidation process is carried out in two steps. In the first step, propylene is oxidized by nitric acid to form a-nitrolactic acid, and then oxalic acid is obtained by further catalytic oxidation. In the second step, mixed acid can also be used as oxidant. Propylene oxidation process is used to produce industrial-grade oxalic acid dihydrate. The total yield of propylene is more than 90%.

Material consumption quota: coke (84%) 510kg/t, sulfuric acid (100%) 950kg/t, caustic soda (100%) 920kg/t.

Oxalic acid in nature usually exists in many plant cell membranes in the form of salt. In the past, sawdust and strong alkali were used to melt together at 240 - 250 C in industry. Oxalate was first prepared and then oxalic acid was obtained by acidification. Later, oxalic acid was produced by dehydrogenation of sodium formate. In industry, carbon monoxide (such as tail gas from yellow phosphorus production) is absorbed by caustic sodium to produce sodium formate. The latter is dehydrogenated to sodium oxalate at 380 C, then treated with lime and sulfuric acid to produce oxalic acid.