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Method for producing polyester polyol

2019-08-13 03:08:32 admin Read 608

A method of industrially producing polyester polyols. 1. Generally, it is produced by batch method: firstly, the carboxylic acid and the diol are added to the reactor for melting, and nitrogen gas is introduced to form water at about 150 ° C, which is gradually distilled off, and a low-polyester mixture is formed in the kettle (low Molecular weight polyester polyol). With the evaporation of water, the temperature in the kettle gradually increases. At 170-230 ° C, the vacuum gradually decreases to 500 Pa, and an excess of diol and a small amount of side reaction products (low molecular polyester, aldehyde and ketone) are reacted to form The residual water is distilled together. 2. An inert gas, (nitrogen, carbon dioxide) can also be bubbled through the mixture of carboxylic acid and glycol to remove water, but the loss of monohydric alcohol is higher than direct vacuum distillation. 3. It is also possible to reflux the water using an inert solvent such as toluene or xylene. The method is carried out at a relatively low temperature (145 to 190 ° C) at normal pressure, and the reaction conditions of this method are mild, but industrially less popular than the first two. 4. Production control. The production of polyester polyols requires strict monitoring of acid values, hydroxyl values, and viscosity changes to ensure the production of acceptable polyester polyols. The polyester polyol used in the polyurethane adhesive is of high quality, and the acid value is particularly important in addition to the molecular weight (hydroxyl value) because it is a measure of the residual terminal carboxyl group. The terminal carboxyl group reacts with the isocyanate to form an amide and emits carbon dioxide, which not only causes the chain to terminate, but also forms an objectionable bubble. This acylamino group can also react with an isocyanate to form a ureide group. The residual acid in the polyester also catalyzes the polyurethane reaction, causing undesirable effects and reducing the hydrolytic stability of the polyurethane. Therefore, it is generally required that the acid value is less than 1 mg KOH/g, and even less than 0.5 g: KOH/g is often required; however, the acid value is too low (< KOH> causes the reaction to form a polyurethane resin too fast and affects the operation, and the acid value is 0.3-0.5mg KOH/g is the most suitable. The preparation of the polyester polyol can shorten the polycondensation reaction time by adding the catalyst: but the catalyst is not easy to remove, which has a bad influence on the next polyurethane reaction, and the dosage is not affected. The inorganic catalyst has The mixture of zinc acetate and antimony trioxide or zinc acetate and antimony trioxide is added in an amount of 100 to 300 ppm; and the organic catalyst is tetrabutyl titanate or tetraisopropyl titanate, and the amount thereof is 15 to 100 ppm.