JPS62161B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is a novel method for purifying polyolefin, and is particularly aimed at removing halogen remaining in polyolefin obtained using a halogen-containing catalyst and avoiding deterioration and alteration of polyolefin caused by this. When producing polyolefins from olefins such as ethylene, propylene, butene-1, etc., catalysts prepared mainly from halides of transition metals such as titanium and vanadium, and organometallic compounds such as alkyl aluminum halides and alkylaluminums are used. (So-called Ziegler-Natsuta catalyst) is generally used, and such a catalyst remains in the obtained polyolefin at the end of polymerization. However, the halogen contained in the remaining catalyst becomes one of the causes of thermal deterioration of the polyolefin when the polyolefin is heated and molded, and furthermore, it becomes a cause of corrosion of the equipment. Therefore, a technique is required to remove or deactivate the residual catalyst from polyolefin. The most common techniques for removing catalysts are:
A method of washing polyolefin with a lower aliphatic alcohol such as methanol or isopropanol has been used. However, although such a method can be applied to a polyolefin slurry without any disadvantage, when applied to a dried powder, the process becomes complicated and is not advantageous in terms of cost. As a result of various studies on these problems, the present inventors removed the halogen contained in the catalyst remaining in the polyolefin by treating it with a specific compound,
We have found a method to stabilize polyolefin and solve the problems of thermal deterioration and equipment corrosion during molding or heat treatment. That is, the present invention provides at least one method of polymerizing a polyolefin obtained by polymerizing using a halogen-containing catalyst in the absence of substantially water at a temperature equal to or lower than the melting point of the polyolefin.

This is a method for purifying polyolefin, which is characterized by treating it with a compound having a structure represented by the following formula. To explain the present invention in more detail, the polyolefin referred to in the present invention includes ethylene, propylene,
Polymerization or copolymerization of olefins such as butene-1 in the presence of a so-called Ziegler-Natsuta catalyst, which is a catalyst system consisting of a halide of a transition polymetal of group ~ group of the periodic table and an organometallic compound of group ~ group of the periodic table. It is a polyolefin obtained by At least for use in the present invention

Compounds having the structure represented by [Formula] basically belong to the group of carboxylic acid anhydrides, and specifically include acetic anhydride, succinic anhydride, propionic anhydride, isolactic anhydride, etc. be able to. These are hereinafter referred to as carboxylic acid anhydrides. In the present invention, derivatives of these compounds are not excluded as long as they have the specific structure defined in the claims, and even mixtures thereof do not impede the effects of the present invention. In the present invention, a specific method for treating a polyolefin with such a carboxylic acid anhydride is to bring the polyolefin to be treated and the carboxylic acid anhydride into contact in a container. It is assumed that when the treated polyolefin is separated using a separator such as a cyclone, the halogen contained in the polyolefin reacts with carboxylic acid anhydrides and is removed from the polyolefin as a relatively volatile substance. be done. The amount of the carboxylic acid anhydride used in the method of the present invention is preferably 0.1 to 200 times, particularly 1 to 100 times, by mole, relative to the amount of halogen in the polyolefin to be treated. Also, the contact temperature is generally 30~
The temperature is 150°C, preferably 60-130°C. The contact treatment time can be appropriately selected depending on the treatment temperature and the amount of carboxylic acid anhydride added, and is usually 1 minute to 5 hours, preferably 2 minutes to 2 hours. The reason for choosing a state in which substantially no water is present in the present invention is that, as is well known, carboxylic acid anhydrides easily react with water to produce carboxylic acids, which significantly inhibits the expression of the desired effects of the present invention. This is because it will hinder you. The reason for limiting the treatment to temperatures below the melting point is that it is easier to handle polyolefins in powder form than in molten form, and temperatures above 30°C are particularly preferred because the reaction product is volatile. This is because room temperature or higher is advantageous for this purpose, and on the other hand, if this temperature is low, the odor of carboxylic acid anhydrides tends to remain in the polyolefin. Furthermore, the reason why carboxylic acid anhydrides are particularly preferably made to have 4 to 8 carbon atoms is because of the trade-off between ease of handling and the effects of the present invention. This is because there is no difficulty in handling and the reaction appears to be easily carried out. The polyolefin purification method of the present invention has the advantage that even if the carboxylic acid anhydrides used and the compounds produced thereby remain in the polyolefin, they do not affect the polyolefin. Therefore, for polyolefins in which only a small amount of catalyst remains, such as polyolefins obtained using highly active catalysts, the purification method of the present invention is applied, and the harmful halogens are removed from the polyolefins as volatile substances. Furthermore, metals to which halogens are bonded, such as magnesium, also form stable compounds, making it possible to obtain polyolefin products that are of sufficient practical value. Examples 1 to 3 Polypropylene (chlorine content: 140 ppm) obtained by polymerization using a Ziegler catalyst containing titanium supported on magnesium chloride was subjected to contact treatment in an autoclave using the compounds and methods shown in Table 1. The residual chlorine content was measured. The results are also shown in Table 1. Example _{4 Polypropylene} (chlorine content
300ppm) was subjected to contact treatment with acetic anhydride shown in Table 1 and the treatment method in that case, and the residual chlorine content was measured.

[Table] Comparative Example 2 Polypropylene powder was treated in the same manner as in Example 1, except that acetic acid was used instead of carboxylic anhydride. The chlorine content after treatment was 85 ppm. The reason is not clear, but residual chlorine is increasing. Comparative Example 3 Polypropylene powder was treated in the same manner as in Example 1, except that 0.2 g of benzoic anhydride was used as the carboxylic anhydride. Chlorine after treatment
It was 92ppm.

Claims (1)

[Scope of Claims] 1. A polyolefin obtained by polymerizing using a halogen-containing catalyst is polymerized at a temperature below the melting point of the polyolefin in substantially the absence of water, at least a structure represented by the formula 1. A method for purifying a polyolefin, comprising treating it with a compound having the following. 2. The purification method according to claim 1, wherein the compound having at least the structure represented by [Formula] is an anhydride of a carboxylic acid having 4 to 8 carbon atoms, or a derivative of this compound. . 3. The purification method according to claim 1 or 2, wherein the temperature below the melting point is 30°C or higher.