Production method of tetrahydrofuran

In the earliest industrial production, the mixture of glyoxal and steam was introduced into a reactor with zinc-chromium-manganese metal oxide (or palladium) catalyst, and the carbonyl group was removed at 400-420℃ to form furan. Then tetrahydrofuran was prepared by hydrogenation of furan with skeleton nickel as catalyst at 80- 120℃. The production of 1 ton tetrahydrofuran by this method consumes about 3 tons of polysaccharide aldehyde. There are many kinds of production methods developed later. The industrialized method is 1, 4- butanediol catalytic dehydration ring method, because butanediol is made from acetylene and formaldehyde, which is called thunder oil method (Reppe method). Tetrahydrofuran is produced by the by-product of chloroprene monomer chloroprene 1 4- dichlorobutene, which is called dichlorobutene process. A catalytic hydrogenation method using maleic anhydride as raw material was developed.

Tetrahydrofuran has five production processes:

(1) Furfural process:

Furfural is produced by decarbonylation of furfural and then hydrogenation. This is one of the earliest methods to produce tetrahydrofuran in industry. Furfural is mainly made from corncob and other agricultural and sideline products by hydrolysis. This method is seriously polluted, which is not conducive to large-scale production and has been phased out.

(2) Catalytic hydrogenation of maleic anhydride:

Maleic anhydride and hydrogen enter the reactor with nickel catalyst from the bottom, and the ratio of tetrahydrofuran to γ -butyrolactone in the product can be controlled by adjusting the operating parameters. The reaction product and raw material hydrogen are cooled to about 50℃ and enter the bottom of the washing tower to separate unreacted hydrogen from gaseous and liquid products. Unreacted hydrogen and gaseous products are recycled to the reactor after washing, and liquid products are distilled to obtain tetrahydrofuran products. The ratio of γ -butyrolactone to tetrahydrofuran can be adjusted arbitrarily in the range of 0 ~ 5:1. The conversion of maleic anhydride is 100%, the selectivity of tetrahydrofuran is 85% ~ 95%, and the product content is 99.97%. The process has the characteristics of good catalyst performance, simple process and low investment.

(3) 1, 4- butanediol dehydration cyclization method:

The process flow is as follows: add 1087kg 22% sulfuric acid aqueous solution into the reactor, and add 1 4- butanediol at the speed of 1 10kg/h at the temperature of 165438 at the top of the tower, and keep the temperature at about 80℃. After adding 50 tons 1, 4- butanediol, about 70 kg of coke was taken out of the reactor. After coke filtration, the obtained sulfuric acid aqueous solution can be reused, and the yield of tetrahydrofuran in this process can reach over 99%. Sulfuric acid is the earliest catalyst used in tetrahydrofuran industrial production, and it is also the most widely used catalyst in today's production. The process is mature and simple, with low reaction temperature and high yield of tetrahydrofuran, but sulfuric acid is easy to corrode equipment and pollute the environment.

(4) Dichlorobutene method:

Using 1, 4- dichlorobutene as raw material, butene diol was generated by hydrolysis, and then butene diol was obtained by catalytic hydrogenation. 1, 4- dichlorobutene is hydrolyzed in sodium hydroxide solution to generate butene diol at 1 10℃, and sodium chloride is removed by centrifugal separation. The filtrate is concentrated in an evaporative crystallizer to separate out alkali metal carboxylate, and then high-boiling substances are removed in a distillation column. The refined butanediol is sent into a reactor with nickel as a catalyst. At 80 ~ 120℃ and a certain pressure, butanediol is hydrogenated to produce butanediol. After distillation, it enters a cyclization reactor and generates crude tetrahydrofuran in an acidic medium of 120 ~ 140℃ at atmospheric pressure. High-purity tetrahydrofuran is obtained after distillation. The method has the advantages of simple operation, mild conditions, high yield, less catalyst consumption and continuous use.

(5) Butadiene oxidation method:

Using butadiene as raw material, furan was obtained by oxidation, and then hydrogenated. This rule has been industrialized abroad.