Method for removing acid value during polyester polyol synthesis process

Abstract

The invention relates to a method for removing the acid value during a polyester polyol synthesis process. According to the invention, organic dicarboxylic acid (anhydride or ester) and polyol (including diol) are molten in a reactor; nitrogen gas is introduced into the reactor; a reaction is carried out under a temperature of approximately 150 DEG C, such that water is produced; the water produced in the reaction is gradually distilled out; with the distillation of water, the temperature in the reaction kettle is gradually increased; acid value is measured during the process; under a temperature of 170-230 DEG C, when the acid value is not higher than 30mgKOH / g, 15-100ppm of organic catalyst is added, and water and low-molecular-weight polyester polyol produced in the reaction are removed by vacuuming, such that the acid value is lower than 2mgKOH / g; the temperature is reduced to 50-100 DEG C, and a certain amount of alkaline alcohol solution is dropwise added with a dropping speed of 2-200ml / min; a reaction is carried out for 0.5-3h; the temperature is increased to above 100 DEG C, and alcohol substances in the alkaline alcohol solution are distilled out, such that polyester polyol with acid value not higher than 0.5mgKOH / g is obtained. With the method, polyester polyol acid value removing is easy, cost is low, and the process is simple.

Description

technical field [0001] The invention belongs to the field of synthetic resins, and in particular relates to a method for removing acid value during the synthesis of polyester polyols. Background technique [0002] Polyester polyols are usually formed by condensation (or transesterification) of organic dicarboxylic acids (anhydrides or esters) and polyols (including diols) or by polymerization of lactones and polyols, and are mainly used as raw materials for the synthesis of polyurethane resins . The preparation process is generally produced by batch method: that is, the organic dicarboxylic acid (anhydride or ester) and polyol (including diol) are first added to the reactor to melt, and nitrogen is introduced to react at about 150 ° C to form water. , gradually evaporated, and a low-polyester mixture (low-molecular-weight polyester polyol) was generated in the kettle. With the evaporation of water, the temperature in the kettle gradually rises, and at 170-230°C, the vacuum...

AI Technical Summary

Problems solved by technology

Several important indicators for polyester polyols are hydroxyl value, acid value, moisture, viscosity, molecular weight, density and chroma, etc. Among them, the acid value has a great influence on the synthesis of polyurethane in the next step, so polyester polyols are usually required The acid value of polyols is less than 0.5mgKOH / g. To meet this acid value requirement, the general method is to add excess low-molecular-weight diols in the late stage of the reaction or finally add KOH and NaOH aqueous solution to neutralize, but in the late stage of the reaction, add excessive The low-molecular-weight diols can completely react the residual acidic substances, so a large amount of low-molecular-weight diols needs to be used, which will increase the energy consumption and loss of recovering excess low-molecular-weight diols; and finally add KOH and NaOH aqueous solution to neutralize the acid removal value, It is easy to cause saponification of polyester polyol