JPS5910684B2 - Polypropylene purification method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for purifying polypropylene.

In propylene polymerization using a so-called Ziegler-type catalyst, a highly active catalyst is prepared by using a titanium halide supported on magnesium halide as one component, to which an organoaluminum compound and preferably an electron donor such as a carboxylic acid ester are added. When used, the yield of polypropylene per transition metal can be sufficiently increased, and as a result, the titanium content contained in the polypropylene after polymerization is extremely small, and the titanium content is at a low level that can be practically used without any treatment (
As titanium, it is located below the IOP ostium.

However, it contains relatively large amounts of catalyst residues based on magnesium halides and organic aluminum (e.g. diethylaluminium monochloride) used in the carrier, and if such polypropylene is used without purification, it may remain during molding. It has been found that halogen-based molding machines cause rust. If the catalyst is not removed at all, the ash content will be high, so it will not be suitable for fields such as insulating films that require a low ash content product (ash content of 5 Oppa or less). However, there are disadvantages such as some remaining residue and odor on the product. As a simple method for purifying polypropylene, JP-A-52-6948
No. 8 proposes a method in which a catalyst residue-containing polymer is brought into contact with an aromatic carboxylic acid or an oxycarboxylic acid. Although this method reduces residual chlorine in the product, the catalyst residue remains as ash, resulting in a brownish hue and inferior weather resistance and heat aging resistance compared to commercially available polymers. Furthermore, JP-A-52-65591 discloses that a hydroxyether having an HLB of 8.0 or less is reacted with a polyolefin containing catalyst residue obtained by using a transition metal compound supported on magnesium halide as a catalyst component. A method has been proposed in which the material is then washed with water.

However, in the above method, in the water washing step after hydroxyether treatment, the polymer becomes hydrophilic due to the action of the reaction product between the hydroxyether and the catalyst, making it difficult to separate the polymer slurry from water. It becomes necessary to discharge the waste water (washing water) containing the water out of the system, and the weight of the hydroxy ether used is 0.0% relative to the polymer.
It is relatively large at 2 to 2.0% by weight, and has disadvantages such as being expensive to make disposable. As a result of various studies on decomposition methods to improve the above-mentioned problems, the present inventors removed the catalyst by treating polypropylene containing catalyst residue with glycol monoether as a decomposer for a short time, and then washing it in countercurrent with propylene. The present invention was achieved with the aim of improving this. The feature of the present invention is that when refining crystalline polypropylene produced using a magnesium halide carrier catalyst, the polypropylene is purified by the general formula R(C2H4O)M.
OH (R is a hydrocarbon residue, especially an alkyl group, an alkenyl group, an aryl group, an aralkyl group, or an alkaryl group, and m is an integer from 1 to 4) for a short time to treat the catalyst component. The purpose is to render the catalyst inert and soluble in lower hydrocarbons and then to remove catalyst residues by countercurrent washing with propylene.

The method of the present invention is superior to known methods in the following points. (1) There is less catalyst residue in the product polypropylene,
The color is improved and no odor is generated. (2) No wastewater is produced as the treatment is performed in a non-aqueous system. (3) Propylene is easily separated from propylene due to the boiling point of the decomposer.
It can be reused for polymerization by simply evaporating it. (4
) Requires less amount of decomposer. (5) Since the decomposition time is short, the decomposer can be made smaller, making it an extremely useful method industrially. In the present invention, polypropylene refers to a homopolymer of propylene and a copolymer of propylene with an α-olefin such as ethylene, butene-1, hexene-1, etc., and as a solid under the conditions in which the method of the present invention is applied. It is fine as long as it exists.

In the present invention, the catalyst used in the production of polypropylene is a titanium halide supported on magnesium halide, and oxygen-containing compounds such as esters, ethers, and alcohols, or nitrogen-containing compounds such as amines and amides. It is preferable that they coexist. The catalyst is usually used for the polymerization of propylene using an organometallic compound such as an organoaluminum compound as a cocatalyst, but it is preferable that the oxygen-containing compound or nitrogen-containing compound mentioned above be present at that time. General formula R(0C2H4)MOH (where R
Specifically, the glycol monoether represented by C2H4OC2H4OH, (CH3
)2CH0C2H40H,C4H,0C2H40H,C
6H5CH20CH2CH20H, CH3(0C2H4
)20H,C2H5(0C2H020H,(CH3)2
CH(0C2H4)20H,C4H9(0C2H4)2
0H, CH3 (0C2H4), 0H, C2H5 (0C2
H4) 30H9C3H7 (0C2H4) 30H2p-C
, H, , C6H4O(CH2CH2O)2H, and the like.

These may be used alone or in combination. In order to cause these glycol monoethers to act on polypropylene, the glycol monoethers may be directly added to the polymer slurry for treatment. The amount of glycol monoether used can be effective even if it is very small, for example, 1 mole of magnesium halide in polypropylene.
About 8 mol is used. Of course, there is no problem in using a large amount, but it is not economical due to problems such as collection. The treatment temperature is generally room temperature to 100°C, preferably 50 to 90°C.
The treatment may be carried out for 1 minute to 2 hours, particularly 5 minutes to 30 minutes.

The slurry containing the catalyst residue solubilized in the hydrocarbon solvent is then countercurrently washed with fresh propylene.

This fresh propylene means propylene that does not contain large amounts of catalyst residues and soluble low molecular weight polymers, as long as it contains small amounts of ethane, ethylene, propane, butane, butene, pentane, hexane, heptane, etc. It is also possible to use propylene recovered by an appropriate method for cleaning without adversely affecting the cleaning effect, for example, as proposed in Japanese Patent Publication No. 47-42.

A propylene solution containing excess decomposer, catalyst residue and soluble low molecular weight polymer is withdrawn from the top of the vertical washing tower, and purified polypropylene is removed from the bottom as a thick suspension of propylene. Washing temperature ranges from room temperature to 80℃
is appropriate. According to the method of the present invention, a rate of rise of the cleaning liquid in the countercurrent cleaning tower of 0.05 to 0.5 cTn/sec is sufficient. The solid polymer with reduced ash content is extracted from the lower part of the washing tower together with the washing solvent propylene and dried to form a product. In some cases, it is further pelletized using a thermoplastic extruder. The catalyst residue of highly crystalline polypropylene treated according to the present invention is 1/3 to 1/10 of that before treatment.
The pellets do not have any color or odor, and hardly any harmful hydrogen chloride is generated even when heated, so they can be used for textiles, films, etc.
It is useful in a wide range of fields as it is formed into pipes, containers, etc.

Next, the method of the present invention will be explained in more detail with reference to Examples.

Example 1 To a titanium catalyst 209 obtained by adding and co-pulverizing magnesium chloride 3009, aluminum chloride 849 and ethyl benzoate 827ne to support titanium tetrachloride, diethylaluminium monochloride 469 and triisobutylaluminum 579 were added as co-catalysts. Further, using ethyl benzoate 309 as a third component, propylene was bulk polymerized at 70° C. in the presence of hydrogen.

Ethylene glycol monoisopropyl ether 1001 was added to the thus obtained polymer slurry consisting of polypropylene 100K7 and propylene 120K7 at 70°C.
for 15 minutes. The slurry was then fed to the top of a washing tower having a diameter of 3 inches and a height of 5 m for 5 hours. Fresh propylene was fed from the bottom of the washing tower at a rate of 31 Kf/hr, and overflow liquid was withdrawn from the top of the tower at a rate of 41 Kf/hr. Additionally, an effluent consisting of 20 Kf of polypropylene and 14 Kf of propylene was taken out from the bottom of the tower every hour. The ash content in the polypropylene powder obtained by evaporating the solvent is 48P, the Ti content is 0.8PP1, and the chlorine content is 3
It was 5PF1. The powder was extruded at 240° C. to form pellets, yielding a colorless product. The pellets were heated at 280° C. for 12 hours by being sandwiched between well-polished iron plates, but the surface of the iron plates did not lose its luster. Comparative example
1 Except that ethylene glycol monoisopropyl ether was not used, the powder obtained by processing in the same manner as in Example 1 had an ash content of 240 PIU, a chlorine content of 160 PF, a titanium content of 5 PF1, and the color of the powder was colorless. The powder was similar to the powder of Example 1, but when it was pelletized at 240°C, it turned light yellowish brown in color and had a sweet aroma.

As a result of a heating test conducted between iron plates in the same manner as in Example 1, speckled areas that had lost their luster were observed on the iron plate surface. Examples 2 to 8 Polymerization was carried out in the same manner as in Example 1, and the catalyst was decomposed by changing the type and amount of glycol monoether used. Table 1 shows the results of treatment in the same manner as in Example 1.

The amount of the decomposer used was expressed as the number of 9 glycol monoethers per 19 titanium catalysts produced in Example 1. Example 9 A polymerization reaction was carried out in the same manner as in Example 1 except that ethylene was allowed to coexist during the polymerization to produce a propylene-ethylene copolymer containing 5.1% by weight of ethylene, and the resulting polypropylene 100K9 and propylene 120Kf, ethylene 0
．． Example 1 except that diethylene glycol monoisopropyl ether was added to the polymer slurry consisting of 5K9 and treated at 70°C for 15 minutes, and then propylene containing 12% ethylene was used as the propylene charged from the bottom of the washing tower.
It was purified in the same manner.

Claims (1)

[Claims] 1. In the production of polypropylene, polypropylene containing catalyst residue obtained by using titanium halide supported on magnesium halide as a catalyst component is used with the general formula R (OC_2H_4)_mOH (R is a hydrocarbon residue and m is 1. A method for purifying polypropylene, which comprises treating it with a glycol monoether (an integer from 1 to 4), followed by countercurrent washing with propylene.