Alcoholysis method in the preparation process of a kind of ethylene-vinyl alcohol copolymer

Abstract

The invention relates to an alcoholysis method in the preparation process of ethylene-vinyl alcohol copolymer. The alcoholysis raw material directly adopts the polymerization product obtained by the polymerization reaction of ethylene and vinyl acetate, which is characterized in that it is carried out according to the following steps: 1) purification and preparation of the alcoholysis raw material; 2) preparation of the catalyst solution; 3) Alcoholysis reaction: During alcoholysis, add part of the catalyst solution for pre-reaction at normal temperature to 40°C, then add the remaining catalyst solution to continue the reaction after raising the temperature, and continuously remove by-products until alcoholysis The reaction went to completion. The method can realize the effective and smooth progress of the alcoholysis reaction, reduce the yellowness of the EVOH, obviously improve the hue of the EVOH, and thereby improve the quality of the final product EVOH.

Description

technical field [0001] The invention relates to the preparation of ethylene-vinyl alcohol copolymers, in particular to an alcoholysis method in the preparation process of ethylene-vinyl alcohol copolymers. Background technique [0002] Ethylene-vinyl alcohol copolymer (EVOH), because of its special structure, combines the good processability of polyethylene and the high gas barrier property of vinyl alcohol polymer, and is a new type of barrier material. Its gas barrier property is 100 times higher than that of polyamide (PA), and 10,000 times higher than that of PE and PP. In addition, EVOH also has excellent transparency, mechanical strength, wear resistance, etc., and is one of the important products in the VAc product chain. Barrier packaging and automotive fuel tanks are the mainstream consumer markets for EVOH, especially the automotive fuel tank sector will be the fastest growing consumer segment of EVOH in the future. [0003] Normally, EVOH contains 20% to 40% mol...

AI Technical Summary

Problems solved by technology

Wherein, when carrying out alcoholysis reaction or partial alcoholysis reaction to the EVA contained in the polymerization reaction product, because the raw material of alcoholysis adopts the polymerization reaction product that directly comes from the polymerization reaction that makes, the vinyl acetate that wherein contains and very small amount of water Such impurities affect the smooth progress of the alcoholysis reaction, resulting in the uncontrollable speed of the alcoholysis reaction, and prone to side reactions, which in turn cause the coloring of the product and make the hue of the final product worse

In addition, usually during alcoholysis, a large amount of alkali used as a catalyst is directly added to the alcoholysis device and the EVA in the polymerization reaction product is subjected to alcoholysis at high temperature, and the alcoholysis reaction is a reaction that is fast first and then slow. The traditional production process is mainly aimed at the control of the reaction rate in the later stage of alcoholysis, and the control of the reaction rate in the early stage is rarely involved. At the same time, it is found that the alcoholysis reaction proceeds rapidly after the catalyst is added, and a large amount of by-product methyl acetate is generated. Methyl acetate that cannot be removed in time is easily oxidized into easily colored aldehydes, which is one of the important reasons for EVOH to have a yellowish hue, poor appearance, and affect the quality of the final product

At the same time, since sodium hydroxide is mostly used as a catalyst at present, it is inevitable to introduce residual acetate groups and sodium ions into EVOH products. However, the amount of acetate groups has a decisive effect on the barrier properties of EVOH products. The presence of sodium ions not only affects the purity and hue of the EVOH product, but also increases the ash content in the product (the ash content in EVOH prepared by traditional processes is 0.5% or higher), reduces its transparency, mechanical strength and other properties, and then It affects its application; for this reason, the current main solution is to remove sodium acetate through physical washing, but it increases the EVOH preparation process and increases the complexity of the EVOH production process

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