Introduction of preparation technology of hydroxypropyl methyl cellulose abroad

Introduction of preparation technology of hydroxypropyl methyl cellulose abroad

(1) Dow Chemical Company (Dow) Chem.Co Hydroxypropyl methyl cellulose with low hydroxypropyl content (MS = 0.05 ~ 0.2) and high methoxy content (DS = 1.4 ~ 2.1) was prepared by the reaction of alkali cellulose with a large amount of chloromethane and a small amount of propylene oxide. This is a kind of product, its 2% water solution at 20 degrees of viscosity below 30 MPa / s, gel point close to 70 degrees Celsius. The viscosity of its medium viscosity product is 40~80 MPA / s, and its gel point is about 65 degrees Celsius. The product is suitable for the polymerization of vinyl chloride, vinylidene chloride and acrylonitrile, as well as the copolymerization of vinyl chloride and vinylidene chloride, and acrylonitrile and vinylidene chloride.

(2) Henkle and CIE company of Germany has prepared hydroxypropyl methyl cellulose which is easily soluble in water for adhesive. The process also belongs to the type of low hydroxypropyl content and high methoxy content. The specific process is as follows: first add 10kg sulphurous acid refined cellulose into 35% alkali solution, press it to 2.6 times, place it at room temperature for 18h, put it into a 150L autoclave with reflux condenser, wash it with nitrogen, introduce 1 part of propylene oxide solution dissolved in 6 parts of chloromethane, heat it to 60 ℃ after 1 hour of heating, and then heat it up to 60 ℃ after 2 hours After 85 ℃, maintain the temperature for 1 h, at this time, the pressure is 2.2 MPa, stop heating, after cooling, remove the chloromethane from the kettle, wash the product with 95% hot water twice; centrifugal drying to 60% water content, after cooling, extruding and slicing, crushing by hammer crusher, and drying by air until the water content is 9%, the particle size of the product is 0.2 ~ 0.5, and the viscosity of 4% solution is 0.2 ~ 0.5 It is insoluble in water at room temperature.

(3) Kalle company in Germany uses continuous etherification to prepare cellulose ethers, such as methyl cellulose or hydroxypropyl methyl cellulose. In this process, alkali cellulose is prepared by double screw pulp press. It is connected with etherification reaction tube. Etherification liquid is forced into reaction pipe by water pressure pump. There is heating jacket outside the reaction pipe, heat exchanger regulates liquid temperature, and pumps are used for circulation. Reflux condenser is used to keep the reaction tube constant temperature, because the pressure in the reaction pipe is between 18 ~ 29 ATM. The reactant is a thick suspension, so it must have pressure relief rotating discharge equipment and rotary pump. The effluent includes cellulose ether, excess etherifying agent, dimethyl ether, sodium chloride and other by-products. After washing with hot water and centrifugation, the cellulose ether obtained is dried by conventional drying method. The etherifying agent is recycled and reused after adjusting the proportion of etherifying agent. For example, the comminuted cellulose with polymerization degree of 500 is mixed with alkali liquor in a continuous mixer with water cooling to make alkali cellulose containing 26% NaOH, 32% cellulose and 42% water. Hydroxypropyl methyl cellulose (HPMC) with 26% methylchloride, 3% carboxypropyl group and 1 pa · s viscosity (2% aqueous solution, 26 ℃) was obtained by introducing 6 times of cellulose into the reactor and discharging after 40 minutes at 80 ℃.

(4) Dow Chemical Company used aromatic organic solvents as diluents to make the reaction heat conduction uniform and easy to control the temperature. Once the reaction was completed, most of the water and side reaction organic compounds could be removed by azeotropy. For example, 3980 parts of toluene, 392 parts of solid NaOH and 145 parts of water are replaced with nitrogen to remove air, and then the mixture is heated to 80 ℃ under stirring for 1 h, and then 400 parts of crushed cellulose are added. These mixtures were protected with nitrogen and heated for 1 h, cooled to room temperature, added 594 parts of methyl chloride and 101 parts of propylene oxide, and then heated to 90 ℃ and maintained at this temperature After the reaction is completed for 4h, start the reactor, sample and analyze the residual alkali content, add sufficient formic acid to neutralize the residual sodium hydroxide, and then add water to carry out azeotropic distillation, the water amount is about 90% of the theoretical amount in the mixture, then cool the mixture to 70 ℃, add formic acid to adjust pH to 4 ~ 6, and react with Glyoxal at 70 ℃ After 30 min, the reactants were taken out from the reactor and the toluene was removed by centrifugation. The product is washed 3 times with the same amount of water at 20 ~ 25 ℃. After drying and grinding, white water insoluble powder was obtained. When the product is used, it is dissolved in water as long as the alkaline substance is added. The product contains

(5) hydroxypropyl methyl cellulose, like other cellulose ether products, can be modified by esterification into water-soluble cellulose ether ester to improve their dispersion, dissolution rate, surface activity and foam stability. For example, 110 parts of cellulose ether are mixed in 1000 parts of 70% acetone containing 3 parts of NaOH and 7.5 parts of ac2o, and heated for 5 minutes to obtain hydroxypropyl methyl cellulose acetate. After washing and impregnation purification, the cellulose ether ester with 1.2% acetyl group content is obtained. In addition, the modified HPMC can be treated with glyoxal and Na2B4O7 · 10h2o to maintain pH of 7.5 ~ 9.5, which can improve its rapid dissolution in water. The modified cellulose ether ester can also improve the impermeability of the film. For example, 100 parts of cellulose ether were reacted with 200 parts of acetic acid, 50 parts of sodium acetate and 140 parts of titanium hydride at 80 ℃ for 2 hours, then reacted with 65 ℃ for 3 hours, and then 1600 parts of water was added. The obtained hydroxypropyl methyl cellulose titanate contained tetrahydro titanium acyl 1.65/anhydrous glucose group. The film prepared by this method is impermeable to steam and can be used in medicine tablets and dye substrates.

(6) Dow Chemical Company