New Preparation Method of Poly(tetrahydrofuran) 

Poly(tetrahydrofuran) is an important chemical raw material, which plays an important role in the development of various industries. The production technology and process of Poly(tetrahydrofuran) are summarized in the following, and the production status and development trend are discussed.

1.Poly(tetrahydrofuran) production technology

Poly(tetrahydrofuran) is the only polymerization method of tetrahydrofuran under cationic ring-opening polymerization. It is a white waxy solid at room temperature and a transparent colorless liquid after melting. It has been reported that polymerization reflects the reaction speed under high temperature strips, but has a low equilibrium conversion rate. However, a higher equilibrium conversion rate can be achieved in a lower temperature environment, but in this case the reaction rate will be affected. At temperatures below -20 ℃, polymerization is almost impossible. In the face of this situation, the choice and use of catalyst is the key to study Poly(tetrahydrofuran).

1.1Perfluorosulfonic acid process.

The perfluorosulfonic acid process is mainly used in the production process of Invista Company, First, PTMEA (polytetramethylene ether diester) is formed by the reaction of purified THF (tetrahydrofuran) with ACAN (acetic anhydride) and HAC (acetic acid) in polymerization reactor through polymerization process, and THF, HAC and ACAN are removed by THF separator and HAC stripper to obtain refined PTMEA. Then, in the alcoholysis process, under the action of catalyst sodium methanol, PTMEA sealed by ethyl ester was reacted with methanol to form PTMEG sealed by reaction rectification column to produce hydroxyl terminated PTMEG, and methanol was separated and recovered by methanol flash tank and methanol stripper, and methyl acetate, a by-product produced from the top of reaction rectification column, was separated and removed by azeotropic rectification column. Next, the material containing NaOMe (sodium methylate) from the alcoholysis process and 20% magnesium sulfate (MgSO4) are neutralized in the MgSO4 neutralization tank through the neutralization and catalyst process. After the reaction, the material is dried by the primary dryer and the secondary dryer to get the material containing solid particles, and the solid particles are filtered out in the high temperature filter press. Pure PTMEG was obtained. Finally, light components and low molecular weight PTMEG were removed by narrow chemical sequence. The narrow distillation process is divided into two parts: degassing and short range distillation. The role of degassing is to remove light components of PTMEG, and the task of short range distillation is to remove low molecular weight PTMEG to narrow the molecular weight distribution of the final PTMEG product. After the narrowed PTMEG is added BHT and sulfuric acid online, it is sent to the PTMEG storage tank in the finished tank farm and sold as a product.

1.2Heteropoly acid process.

Japan Asahi Kasei Company also develops and researches the process that the catalyst is heteropoly acid, but its catalytic activity must have a certain amount of water, so it is necessary. First, it is burned with water, and then at atmospheric pressure of 60℃ with tetrahydrofuran containing phosphotungstic acid catalyst (5%), after 4 hours of polymerization reaction, to flash separation of tetrahydrofuran, it is necessary to put water, tetrahydrofuran and catalyst together in the polymerization reactor, through hydrolysis, polymerization, into the flash tower for reaction. Tetrahydrofuran should return to the reaction system, the extraction tower flows into the logistics containing polytetrahydrofuran products, octane is extracted, octane is dissolved in polytetrahydrofuran, the catalyst is non-solvent, the separation requirement of catalyst and tetrahydrofuran is met, the catalyst returns to the reaction system again, tetrahydrofuran can only be removed after further distillation of the logistics containing products. The catalyst is extruded from the absorption tower of the catalyst to obtain the octane separated by entering the octane separation tower.

1.3 Clay craft.

The minerals with layered aluminosilicate structure such as kaolin, montmorillonite, medusite and soapstone are called clays. Ring-opening polymerization of tetrahydrofuran is catalyzed by acidification, a clay process used by PTG of Korea and BASF of Germany. The catalytic raw material is usually made of kaolin. To make different shapes of aluminum silicate, kaolin is burned at high temperature and activated by acidification. The ending agent of tetrahydrofuran in the polymerization process is acetic anhydride, and diester is produced in a fixed reactor at 30 ~ 55℃ under normal pressure. Diesters are catalyzed in the presence of nickel or copper-chromium. The transesterification reaction also reacts with methanol in the presence of sodium methanol to obtain the final product. The advantage of the process is that the catalyst can be reused, the process avoids water, and also avoids the corrosion of the material to the equipment. The deficiency is that the natural mineral is used as the catalyst, and its composition is unstable, and the catalyst activity is low.

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