Preparation background and overview of polytetrahydrofuran ether
Polytetrahydrofuran ether (PTMG), also known as polytetramethylene ether glycol, is a white waxy substance at room temperature. When heated and melted, it becomes a colorless and transparent liquid, which is soluble in dimethyl In polar solvents such as formamide, dimethylacetamide, dichloroethane, and tetrahydrofuran. Polytetrahydrofuran ether glycol is made from tetrahydrofuran monomer (THF) in the presence of a catalyst through cationic ring-opening polymerization to obtain crude PTMG containing hydroxyl groups at both ends, and then further refined and separated to obtain the final product. As an important chemical raw material, polytetrahydrofuran is mainly used in the field of chemical fiber to prepare spandex. In the non-fiber field, it is used to prepare elastomers, adhesives, coatings, sealants and other fields. The polyurethane products prepared with it are wear-resistant, Resistant to chemical corrosion and has good flexibility and resilience. At present, the top three uses of polytetrahydrofuran in foreign countries are polyurethane elastic fiber (49%), polyurethane elastomer (36%) and ester-ether copolymer elastomer (15%).
Preparation and application of polytetrahydrofuran ether
As far as the world is concerned, 50% of PTMG is currently used in elastomer fibers, copolyethers, etc., 40% is used in synthetic rubber elastomer materials, and 10% is used in other aspects. my country is mainly used for spandex production. PU elastomers synthesized from PTM calcium tetraborate G and diisocyanate are available in thermosetting and thermoplastic types. Their common features are high tensile strength, wear resistance, mold resistance, good steam permeability resistance, flex fatigue resistance, and low hysteresis loss. With good resilience, it has been successfully used in many fields such as metallurgy, mining, textiles, papermaking, and medical care.
For example, PT Peng type PU is widely used in ship escort materials, floating materials, large water pipes and rebound wedge gates due to its unique properties. It has good resilience; it is very important in applications involving rolling friction, such as Forklift wheels, sliding plates and rolling skates; outstanding applications of its anti-skid properties include ski boots, automobile anti-skid chains, wire sheaths and cold-resistant seals, etc.; its small hysteresis loss allows many types of wheels, rollers, etc. to take advantage of this Advantages: It has excellent bacterial resistance and can be used in industrial products such as cables; in medical applications, it can be used to make catheters, blood bags, tracheostomy tubes and various types of prostheses; its wear resistance can be used in grain transportation and mine transportation. Belts, elbows for conveying coal paddles, truck tank linings, cyclone linings, etc.
PTMG type PU elastic fiber (spandex). The production of spandex mainly relies on the sufficient supply of PTMG. Spandex fiber is also called spandex fiber. Spandex is made by reacting PTMG with excess diisocyanate. The resulting polymer is The diamines extend the chains in a solvent and are spun into fibers, which can also be processed into other products.
PTMG accounts for 80% of the final Spandex polymer molecules. Spandex raw materials are easily available and the production cost is lower than other fiber polymers such as nylon. 80% of THF in foreign developed countries is used for synthetic spandex. Underwear made of spandex is as stretchable as white and is known as the “second skin”. It is widely used in swimwear, sportswear, underwear, socks, outerwear and medical ligaments. . According to reports, there are more than 70 spandex production plants in my country, and their annual production capacity has exceeded 5,000t. If the above plan is completed, their production capacity will exceed this number. Vigorously developing the PTMG industry will drive the development of a series of chemical industries in my country.
Preparation of polytetrahydrofuran ether
The main preparation technologies for polytetrahydrofuran ether glycol are as follows: (1) perchloric acid-anhydride method; (2) fluorosulfonic acid method; (3) heteropolyacid method; (4) furfural method; ( 5) Clay method, which will be introduced in detail below.
1. Preparation of PTMG by perchloric acid-anhydride method
This method uses perchloric acid as the catalyst and acid anhydride as the end-capping agent to perform the polymerization reaction at a temperature lower than 25°C. Then, sodium hydroxide solution is added to terminate the reaction. Unreacted tetrahydrofuran and water are removed by distillation, and the polymerization is washed with water. The material is desalted, distilled and dehydrated to obtain polytetrahydrofuran ether glycol diesterate, and then methanol is added to perform transesterification reaction, and then water is added to neutralize, and excess methanol and methyl ester acid are evaporated to obtain crude PTMG, which is finally dehydrated again to obtain pure Polytetrahydrofuran ether glycol.
The advantage of this method is that the reaction conversion rate is high, which can reach more than 70%. The by-product salt is easily soluble in water and can be easily removed. The catalyst used is perchloric acid, which has high activity and can speed up the reaction rate. However, this method uses perchloric acid as a catalyst. Perchloric acid is the most acidic substance among inorganic acids. Therefore, it has higher requirements on the material of the reaction equipment. At the same time, there are many by-products, and there are many steps of water washing, evaporation and separation. , the production process is cumbersome.
2. Preparation of PTMG by fluorosulfonic acid method
This process uses fluorosulfonic acid as a catalyst. In the first step, tetrahydrofuran monomer and fluorosulfonic acid are added into the reactor together, and the reaction is carried out at normal temperature and pressure. The reaction time is about 4 hours, and the single-pass conversion rate is 60%. ~67%, a polyether intermediate with both ends blocked by fluorosulfonic acid is obtained, and then the material is transferred to the second reactor through a pump, where it is hydrolyzed at 90°C to remove unreacted tetrahydrofuran monomer to obtain Crude PTMG (its moisture content is generally less than 20%) is then mixed and neutralized in a crude PTMG:Ca(OH)2 mass ratio of 10:1. The water is removed through two stages of evaporation, and the neutralized liquid becomes containing sulfuric acid. , hydrofluoric acid and other substances.
After the above treatment, activated carbon is added to the PTMG for decolorization, and then filtered at 110°C to remove impurities such as activated carbon to obtain the final product. This method uses raw materials and generates small molecule by-products during the preparation process.It is corrosive and requires high material requirements for production equipment. At the same time, it also has problems such as the catalyst cannot be recycled, wastewater treatment is difficult, and it easily causes environmental pollution. It has been gradually eliminated and is rarely used directly.
3. Preparation of PTMG by heteropolyacid method
Heteropoly acids (Polyoxometalates) are composed of heteroatoms (such as P, SI, Fe, Co) and polyatoms (Mo, W, V, Nb, Ta, etc.) coordinated and bridged by oxygen atoms according to a certain structure. It contains a lot of oxygen, has high catalytic activity, good chemical stability, and is easily soluble in most oil solvents. Japan’s Asahi Kasei Company first used heteropoly acids as catalysts to prepare polytetrahydrofuran. The heteropoly acid used by Asahi Kasei Co., Ltd. is phosphotungstic acid. Tetrahydrofuran containing 5% heteropoly acid is polymerized at 60°C under normal pressure. The reaction time is 4 hours. After the reaction is completed, the solution is separated into layers. The top layer is polytetrahydrofuran and tetrahydrofuran monomer. The lower layer consists of polymer, tetrahydrofuran and catalyst viscous substance. Unreacted tetrahydrofuran was extracted by flash evaporation.
The upper solution is extracted from tetrahydrofuran with n-octane, and most of the solvent and trace catalyst are removed by evaporation and alumina. Finally, the residual solvent is removed by high vacuum distillation to obtain the polytetrahydrofuran ether glycol product. In this method, the catalyst can be reused through extraction, which improves product purity. At the same time, compared with the fluorosulfonic acid method, there is no water washing step, which simplifies the process. However, the disadvantage of this method is that the heteropoly acid has a small specific surface area and few active centers, which results in a low single-pass conversion rate of only 23% in the polymerization reaction. In order to improve the single-pass conversion rate of polytetrahydrofuran prepared by the heteropolyacid method, many researchers have conducted many experimental studies on the immobilization of heteropolyacid.
4. Preparation of PTMG by furfural method
The tetrahydrofuran monomer currently required to prepare polytetrahydrofuran basically comes from petrochemical cracking products. With the reduction of consumption of non-renewable resources such as petroleum, new petroleum-substitute sources of sodium carbonate are needed, especially those produced from abundant biomass in nature. The requirement to further prepare polytetrahydrofuran ether glycol from tetrahydrofuran monomer is becoming more and more urgent. Some researchers have targeted furfural. Furfural is prepared from crops such as corn cobs. As a material with rich sources and recyclable materials are attracting more and more attention.
The furfural method to prepare tetrahydrofuran monomer was first developed by DuPont. This method hydrolyzes common agricultural waste, such as corn cobs, sugarcane bagasse, etc., into pentose sugars with dilute acid solutions, and then dehydrates them into furfural. Then under the catalysis of ZnO-Cr2O3-MnO2, the carbonyl group is removed at 410°C to obtain furan, and then under the action of nickel catalyst, the tetrahydrofuran monomer is obtained under hydrogenation conditions of 100-120°C and 3-4MPa.
5. Preparation of PTMG by clay method
The clay method is to acidify clay and use it as a catalyst to cause ring-opening polymerization of tetrahydrofuran to prepare polytetrahydrofuran ether glycol. Common clays include kaolin, montmorillonite, jellyfish, etc. In this method, silicate powder is generally fired at high temperature and acidified into balls or strips. A fixed reaction bed is used, the reaction temperature is 30~50℃, and the pressure is normal. Ester anhydride is the end-capping agent, and the single-pass conversion rate of tetrahydrofuran is about 40%. The diester generated by the polymerization reaction is hydrogenated in the presence of a nickel or copper-chromium catalyst, and then transesterified with methanol in the presence of sodium methoxide to obtain a polyether glycol product with hydroxyl groups at both ends.
