Views: 4 Author: Site Editor Publish Time: 2023-07-04 Origin: Site
The basic refining methods for polyether polyols can be broadly classified as follows:
(1) Neutralization using inorganic or organic acids. In the polymerization reaction for the production of polyether polyol, inorganic acids are rarely used as neutralizing agents for systems using alkali metal hydroxides as catalysts (such as calcium hydroxide, barium hydroxide, strontium hydroxide, etc.). For systems using alkali metal hydroxides as catalysts, inorganic acids such as hydrochloric acid, phosphoric acid, dilute sulfuric acid, etc. are recommended as neutralizing agents.
(2) Adsorption, adsorption operation is to remove residual catalyst plasma and colored substances in polyether polyol, commonly used adsorbents are magnesium silicate, aluminum silicate, activated white clay, activated carbon, molecular sieve, diatomaceous earth, medium charcoal, etc. Therefore, the adsorption operation temperature is generally around 100 ℃.
(3) Ion exchange, in industrial production, mostly using neutralization and adsorption method, but the very demanding special polyether can also be treated by ion exchange method, the method can not only effectively remove the metal ions in polyether polyol, but also remove the colored, toxic substances in polyether.
(4) Filtration, the purpose of filtration is to remove the salt generated after the catalyst is neutralized, nowadays, advanced circular mesh filtering equipment is mostly used. In the filtration process, according to the production of polyether molecular weight size and functional degree, appropriate filtering aid should be added to reduce the viscosity of the system material, improve the filtration efficiency and reduce the amount of product residue in the filter cake.
(5) Distillation and adjustment, in order to obtain a polyether product with low impurity combination, light color and relatively narrow molecular weight distribution, it is also necessary to go through a distillation and adjustment process. The distillation of polyether is carried out at about 100 ℃ under reduced pressure, using a falling film evaporator, adding 0.05%-0.5% di-tert-butyl-p-cresol and other antioxidants, as well as butylated hydroxytoluene and amine antioxidants (such as phenothiazine, etc.) and other compounds to remove trace moisture and other impurities in polyether. At present, the industrial production of polyether polyol, generally using pretreatment - polymerization - neutralization and adsorption, filtration, dehydration, distillation and other process procedures, the production method can be divided into continuous and intermittent method. The former has a high degree of automation, stable product quality, high production efficiency and low cost, and is suitable for mass production of general-purpose polyether polyol. The latter generally adopts kettle-type reaction equipment, with less investment, faster start-up and simple production operation, but the product quality is not as stable as that produced by the continuous method, and the cost is slightly higher. For the annual production capacity of less than 20kt production plants are used intermittent production equipment.
In the production of polyether polyol, three wastes are also generated. In the advanced production process, every 1t of product will generate about 30kg of waste liquid, which is not a large amount but must be treated before discharge. The solid waste produced by filtration still contains a lot of polyether. Solvent should be used to clean and recycle, so that the organic content of the solid waste is less than 1% and then discharged. The solvent can be recycled, and the waste gas can be fed into the absorption tower to absorb the unreacted raw material gas, and then recycled and discharged into the exhaust gas treatment device that meets the environmental requirements.
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