阅读说明：本技术 一种延长低醇解度聚乙烯醇生产周期的方法 (Method for prolonging production period of polyvinyl alcohol with low alcoholysis degree ) 是由 肖安贺 潘友超 查从元 俞乐乐 杨萱 吴四海 乐峰莉 于 2020-07-23 设计创作，主要内容包括：本发明公开了一种延长低醇解度聚乙烯醇生产周期的方法,低醇解度聚乙烯醇是由聚醋酸乙烯的甲醇溶液经醇解、粉碎、脱液和干燥各单元过程而获得,通过对醇解单元和/或脱液单元的改进,可以延长低醇解度聚乙烯醇的生产周期。本发明的方法只需对原有生产线进行简单技改,容易实施；通过本发明的方法,可以使低醇解度聚乙烯醇生产周期极大的延长,提高了开工率、降低了生产成本,且生产稳定、容易实现生产的连续化。(The invention discloses a method for prolonging the production period of polyvinyl alcohol with low alcoholysis degree, wherein the polyvinyl alcohol with low alcoholysis degree is obtained by carrying out alcoholysis, crushing, liquid removal and drying on a methanol solution of polyvinyl acetate, and the production period of the polyvinyl alcohol with low alcoholysis degree can be prolonged by improving an alcoholysis unit and/or a liquid removal unit. The method of the invention only needs to simply technically modify the original production line, and is easy to implement; the method can greatly prolong the production period of the polyvinyl alcohol with low alcoholysis degree, improve the operating rate, reduce the production cost, realize stable production and easily realize the continuity of the production.)

1. A method for prolonging the production cycle of polyvinyl alcohol with low alcoholysis degree, which is obtained by carrying out alcoholysis, crushing, liquid removal and drying on a methanol solution of polyvinyl acetate, is characterized in that: the production period of the polyvinyl alcohol with low alcoholysis degree is prolonged by improving an alcoholysis unit and/or a liquid removal unit.

2. The method of claim 1, wherein the production cycle time of the polyvinyl alcohol with low alcoholysis degree is prolonged by: the improved method for the alcoholysis unit comprises: the quality concentration of the methanol solution of the polyvinyl acetate is improved, and alcoholysis technological parameters are controlled to improve the completeness of alcoholysis reaction, so that the production cycle of the polyvinyl alcohol with low alcoholysis degree is prolonged.

3. The method of claim 1, wherein the production cycle time of the polyvinyl alcohol with low alcoholysis degree is prolonged by: the improved method of the liquid removal unit comprises the following steps: and (3) removing liquid from the crushed material through a screw extruder, and adding clear liquid to play a role in cleaning a filter screen to prevent blockage, so that the production period of the polyvinyl alcohol with low alcoholysis degree is prolonged.

4. The method of claim 2, wherein the production cycle time of the polyvinyl alcohol with low alcoholysis degree is prolonged by: after the alcoholysis unit is improved: the mass concentration of the methanol solution of the polyvinyl acetate is not lower than 35 percent; the sodium hydroxide solution used for alcoholysis is formed by mixing a methanol solution of sodium hydroxide and water, wherein the concentration of the sodium hydroxide is 60-90 g/L, and the mass concentration of the water is 30-40%; and during alcoholysis, the molar ratio of the sodium hydroxide to the polyvinyl acetate is 0.011-0.014.

5. A method of extending the production cycle of a low alcoholysis degree polyvinyl alcohol according to claim 3 wherein: the adding amount of the clear liquid is 900-1000L/h.

6. A method for extending the production cycle of polyvinyl alcohol with a low degree of alcoholysis according to claim 3 or claim 5, wherein: the clear liquid is condensed liquid after the steam generated by the drying unit is condensed.

Technical Field

The invention relates to the production of polyvinyl alcohol, in particular to a method for prolonging the production period of polyvinyl alcohol with low alcoholysis degree.

Background

Polyvinyl alcohol (PVA) is a polymer compound with a wide range of applications, and is used in textile, food, medicine, construction, wood processing, paper making, printing, agriculture, steel, polymer chemical industry, liquid crystal displays and other industries. The production process of PVA mainly comprises the following steps: firstly, refining and polymerizing Vinyl Acetate (VAC) to obtain a methanol solution of polyvinyl acetate (PVAC); then adding a methanol solution of polyvinyl acetate (PVAC) and a methanol solution of sodium hydroxide into a static mixer for fully mixing, and then feeding the mixture into a belt alcoholysis machine for alcoholysis to obtain solidified PVA; and finally, crushing the solidified PVA, squeezing to remove the liquid, drying and removing the solvent to obtain a finished product. The performance and use of PVA are related to its degree of alcoholysis, which is achieved mainly by adjusting the amount of base added. The PVA with alcoholysis degree lower than 94 percent is called low-alcoholysis-degree PVA, which has wide application in the aspect of non-fiber, and the low-alcoholysis-degree PVA has good biodegradability and can be used as a biodegradable material.

Because the reaction of the PVA with low alcoholysis degree is incomplete, waste liquid can be further separated out in the drying process in the dryer, the drying difficulty of the dryer is large, the effect is poor, the standard reaching rate of volatile matter is only about 80%, and the load has to be reduced in production (the maximum load is only 4.5 m)³H) to achieve the volatile index. Meanwhile, the dryer needs to be frequently stopped and cleaned, so that the production cycle of the PVA with low alcoholysis degree is about 15 days,

therefore, the existing alcoholysis method for obtaining PVA with low alcoholysis degree has short production period, reduced production capacity and increased overall production cost, and leads to reduced enterprise competitiveness. How to increase the production cycle of polyvinyl alcohol with low alcoholysis degree is a big problem which has to be faced by the PVA industry.

Disclosure of Invention

Based on the defects of the prior art, the invention provides a method for prolonging the production period of polyvinyl alcohol with low alcoholysis degree, aiming at reducing the number of times of parking and cleaning a dryer and prolonging the production period of polyvinyl alcohol products with low alcoholysis degree to about 45 days.

The invention adopts the following technical scheme for solving the technical problems:

the invention discloses a method for prolonging the production cycle of polyvinyl alcohol with low alcoholysis degree, which is obtained by carrying out alcoholysis, crushing, liquid removal and drying on a methanol solution of polyvinyl acetate, and is characterized in that: the production period of the polyvinyl alcohol with low alcoholysis degree is prolonged by improving an alcoholysis unit and/or a liquid removal unit.

Further, the improved method for the alcoholysis unit comprises the following steps: the quality concentration of the methanol solution of the polyvinyl acetate is improved, and alcoholysis technological parameters are controlled to improve the completeness of alcoholysis reaction, so that the production cycle of the polyvinyl alcohol with low alcoholysis degree is prolonged.

Further, after modification of the alcoholysis unit: the mass concentration of the methanol solution of the polyvinyl acetate is not lower than 35 percent; the sodium hydroxide solution used for alcoholysis is formed by mixing a methanol solution of sodium hydroxide and water, wherein the concentration of the sodium hydroxide is 60-90 g/L, and the mass concentration of the water is 30-40%; and during alcoholysis, the molar ratio of the sodium hydroxide to the polyvinyl acetate is 0.011-0.014.

The specific mass concentration of the methanol solution of polyvinyl acetate is determined by the type of PVA to be produced. The PVA variety model consists of two parts of polymerization degree and alcoholysis degree, for example, in the 17-92(L) variety model, 17 represents that the polymerization degree is 1700, 92 represents that the alcoholysis degree is 92%, and L represents that the product is in a sheet shape. Generally, the lower the degree of polymerization of the product, the higher the control of the mass concentration of the methanol solution of polyvinyl acetate, and vice versa, as shown in the following table:

serial number	Variety and model	Concentration of
			1	04-88(L)	51±1％
2	05-88(L)	50±1％
			3	13-88(L)	39±1％
4	17-88(L)	36±1％
			5	17-92(L)	36±1％

Further, the improved method of the liquid removal unit comprises the following steps: and (3) removing liquid from the crushed material through a screw extruder, and adding clear liquid to play a role in cleaning a filter screen to prevent blockage, so that the production period of the polyvinyl alcohol with low alcoholysis degree is prolonged.

Furthermore, the adding amount of the clear liquid is 900-1000L/h.

Furthermore, the clear liquid is preferably condensed liquid obtained by condensing steam generated when the material after liquid removal is dried by a dryer (namely, a drying unit), so that the material can be fully recycled.

Compared with the prior art, the invention has the beneficial effects that:

1. the method can prolong the production cycle of the polyvinyl alcohol with low alcoholysis degree from about 15 days to about 45 days, improve the operating rate, reduce the production cost, and have stable production and easy realization of continuous production.

2. The method of the invention comprises the following steps: by adjusting alcoholysis process parameters, the mixing effect of materials can be ensured, the materials can be well formed by reaction on a belt alcoholysis machine and can smoothly pass through a crushing and screw extruder, and meanwhile, the amount of waste liquid separated out from a drying unit is effectively reduced, and the drying difficulty is reduced; through adding the clear solution when the screw extruder takes off the liquid to the material after smashing, effectively avoided the jam of filter screen, reduced the cleaning cycle of screw extruder and desiccator.

3. The method is suitable for polyvinyl alcohol with different low alcoholysis degrees, and can meet the requirements of different varieties.

4. The method of the invention does not affect the indexes of the PVA product such as volatile matter, sodium acetate, methanol content and the like.

5. The method provided by the invention has the advantages that the used raw materials and equipment are conventional raw materials and equipment, the original production line can be simply technically improved and the process is adjusted, the method is safe, environment-friendly and pollution-free, and the policy and the guideline of national green, safe and environment-friendly are met.

Detailed Description

The following examples are given for the detailed implementation and specific operation of the present invention, but the scope of the present invention is not limited to the following examples.