Process for the Production of a Catalyst Component for Use in the Polymerization of .Alpha.-Olefins

This invention relates to an improvement in a catalyst component for use in the polymerization of .alpha.-olefins (which will hereinafter be referred to as "catalyst component") and more particularly, to a process for the production of a catalyst component capable of producing polymer of low particle size distribution whereby in the stereoregular polymerization of .alpha.-olefins such as propylene, in particular, not only the stereoregularity is improved but also the polymerization speed is markedly increased.

As a method of producing a crystalline polyolefin on a commercial scale, it has been widely known to use a polymerization catalyst comprising, in combination, a catalyst component consisting of a low valence transition metal halide, and an organo metal halide compound. In particular, a titanium trichloride composition has been used as the low valence metal halide.

A known method of preparing a titanium trichloride composition consists in reducing titanium tetrachloride by metallic aluminum at a high temperature and then grinding the product for activation. The catalyst component prepared in this way is ordinarily called Grade AA titanium trichloride, which contains, in addition to titanium trichloride, aluminum chloride in an eutectic form, but has the disadvantage that when used as a polymerization catalyst, the polymerization speed and the stereoregularity of the product are unsatisfactory and, on a commercial scale, a large amount of the expensive catalyst is necessary while a great cost is simultaneously required for the treatment of non-crystalline polymers produced as byproduct.

Many efforts have been made to overcome these disadvantages. For example, some of the catalytic components have been removed to improve somewhat the polymerizaton speed or stereoregularity by extracting with a solvent (Soga et al.: "Shokubai (Catalysts)" vol. 11, page 75 (1969)), reacting with an ether compound followed by washing (Japanese Patent Application (OPI) No. 34281/1973) or grinding together with various materials followed by solvent extraction (Japanese Patent Publication No. 26376/1972). In these methods, however, the particle size distribution of the catalytic component has not been sufficiently improved, so that a polymer obtained using this catalyst component may also have a wide particle size distribution, resulting in trouble in handling this polymer powder.

Another known method of preparing a titanium trichloride composition consists in reducing titanium tetrachloride with diethylaluminum chloride in a proportion substantially equimolar or less to the titanium atom present at low temperature, as disclosed in, for example, Japanese Patent Publication Nos. 10415/1971, 21575/1972 and 11807/1972. This method has the advantage that a catalytic component with a relatively even particle size can be obtained, but, on the other hand, the titanium trichloride composition obtained by this method is a brown .beta.-type titanium trichloride composition whose polymerization capacity is very inferior. Therefore, it is necessary to subject this composition to a heat activation treatment to convert it into a violet titanium trichloride composition. In this case, however the polymerization speed and stereoregularity when used as a polymerization catalyst are not superior to those in the case of using the above described Grade AA titanium trichloride. The alkylaluminum dihalide byproduct of the reduction in the above described method is regarded as a harmful material to the catalytic component and, as described in the above publications, for example, Japanese Patent Publication No. 10415/1971, therefore, it is recommended to process it with a complexing agent such as ether compounds. Even if this processing is carried out when the reduced solid is subjected to a heating and activating treatment, the catalytic activity of the resulting component is deficient.

As a further method of preparing a titanium trichloride composition, it has been proposed to obtain a catalyst component capable of giving a relatively high polymerization speed, high stereoregularity and excellent particle size distribution by reducing titanium tetrachloride by diethylaluminum chloride at a low temperature to form a .beta.-type titanium trichloride composition and then treating it with a complexing agent and titanium tetrachloride to convert into a violet .delta.-type catalyst solid, as disclosed in Japanese Patent Application (OPI) No. 34478/1972 (Published on Nov. 21, 1972). However, this method has the disadvantage that when using a complexing agent other than diisoamyl ether, the titanium trichloride composition is not substantially improved and further it is necessary to use a reagent having a concentration of 15% by volume or more, preferably 30 to 40% by volume when treating titanium tetrachloride. Since diisoamyl ether is an expensive reagent which is 10 to 20 times more expensive than other organic ether compounds or about 1 times more expensive than the marketed Grade AA titanium trichloride, the above described method has the disadvantage that the production cost of the catalyst component on a commericial scale is high even though the product exhibits excellent properties as a catalyst.

In accordance with the present invention, it has been found that a catalyst component for use in the polymerization of .alpha.-olefins, excellent in polymerization activity, and capable of producing polymer high in stereoregularity and narrow in particle size distribution, can be obtained by reducing titanium tetrachloride with an organo aluminum compound, removing aluminum compounds contained in the resulting reduced solid by any suitable method and then treating this solid with a complex consisting of titanium tetrachloride and diisoamyl ether or a mixture thereof.

Thus, the present invention provides a process for the production of a catalyst component for use in the polymerization of .alpha.-olefins, which comprises reducing titanium tetrachloride with an organo aluminum compound represented by the general formula AlR.sub.n X.sub.3-n wherein R represents a hydrocarbon group having 1 to 18 carbon atoms, X represents a halogen atom and n represents a number expressed as 0<<n.ltoreq. 3, to thus obtain a reduced solid, then removing aluminum compounds contained in the reduced solid and further activating with a complex consisting a diisoamyl ether and titanium tetrachloride or a mixture of diisoamyl ether and titanium tetrachloride.

It is a feature of the present invention that aluminum compounds contained in the reduced solid are removed and then the reduced solid is subjected to an activation treatment using a particular complex or mixture as described above. Even in the combination of the prior art methods, that is, for removing aluminum compounds with a heating and activating treatment, the catalyst component obtained is not improved much, whilst according to the present invention, a great advantage is obtained by the use of a small amount of a complex consisting of diisoamyl ether and titanium tetrachloride or a mixture thereof.

It is another feature of the present invention that the method of removing aluminum compounds contained in the reduced solid is not limited to treatment with a specific complexing agent, but that any of several methods can effectively be used. The prior art method has hitherto succeeded in obtaining a relatively large improvement by the combination of the method of removing aluminum compounds comprising treating the reduced solid with a complexing agent followed by an activation treatment with titanium tetrachloride, but, on the other hand, it has the disadvantage that a large improvement cannot be obtained when another complexing agent than diisoamyl ether is used. In fact, according to our tracing experiments, the improvement is very unsatisfactory even when the reduced solid is treated with, for example, di-n-butyl ether and then activated by titanium tetrachloride only, as shown in thefollowing Comparative Examples.

According to the present invention, on the contrary, the removal of aluminum compounds can be carried out not only by the use of a specific compound such as diisoamyl ether but also by the application of known techniques, so long as the activation is carried out using a complex or mixture of titanium tetrachloride and diisoamyl ether.

It is very difficult to explain why a complex or mixture of titanium tetrachloride and diisoamyl ether has a particular action in the final processing step of the catalyst component in the present invention, but it is true that there is a difference as to the object of using diisoamyl ether between the present invention and the above described known method, since the quantity of diisoamyl ether used in the former is small while the quantity of diisoamyl ether used in the latter is very large, that is, 0.8 to 1 mol per 1 mol of titanium. This is possibly due to the fact that diisoamyl is used for the particular activation action in the present invention, while diisoamyl ether is used for the purpose of removing aluminum compounds present in a large quantity in the known method.

A further feature of the invention consists in the quantity of complexing agent and diisoamyl ether present in the finaly processed solid. That is to say, in the present invention, there remain in the final catalyst solid a considerable quantity of complexing agent and diisoamyl ether even after the reduced solid is treated with the complexing agent to remove aluminum compounds, subjected to activation with a complex or mixture of diisoamyl ether and titanium tetrachloride, washed several times with fresh solvent and then dried. It is a well known fact in the art that if there are large amounts of such compounds in the catalyst solid, the polymerization properties, and especially the stereoregularity of the product, are markedly lowered and it is confirmed as shown in the following Comparative Example that the stereoregularity is markedly reduced if the polymerization is carried out with addition of a complexing agent corresponding, in variety and quantity, to titanium trichloride. Therefore it is surprising that the catalyst solid of the present invention is capable of yielding a product having a high degree of stereoregularity in spite of the fact that it contains large amounts of a complexing agent together with diisoamyl ether and it will clearly be understood from this that diisoamyl ether used in the present invention is an essential condition for producing a catalyst solid capable of giving a polymer with a high degree of stereoregularity.

The catalyst component produced by the process of the invention having the above described features is excellent in activity and produces polymer having a narrow particle size distribution as is apparent from the following Examples, and furthermore, the process of the invention is economical because diisoamyl ether is used in small quantities.

The reducing reaction of the invention is carried out by contacting titanium tetrachloride with a reducing agent represented by the general formula AlR.sub.n X.sub.3-n in an inert diluent. In this formula, R represents a hydrocarbon group having 1 to 18 carbon atoms, preferably 1 to 12 carbon atoms, more preferably, an alkyl group having 2 to 6 carbon atoms; X represents a halogen atom selected from fluorine, chlorine, bromine and iodine, chlorine being used with best results; and n represents a suitable number expressed as 0< n.ltoreq.3, preferably 1<n.ltoreq.2.5.

As diluents for the reducing reaction, C.sub.4 to C.sub.12 aliphatic hydrocarbons substantially free of aromatic hydrocarbons or alicyclic hydrocarbons may be mentioned. The temperature of the reducing reaction is relatively important for the properties of the final product and should be adjusted within a range of -50.degree. to +30.degree. C. The reaction is begun by contacting titanium tetrachloride with the reducing agent while agitating the mixture, resulting in deposition of the reduced solid, insoluble in the inert diluent. Contacting is carried out by adding dropwise either a solution of titanium tetrachloride or a solution of reducing agent to the other. All the solutions are preferably mixed for 1 hour or more, in particular, 3 hours or more, during which time the reaction system should be kept at the above described temperature. It is desirable to control the concentration of the reagent throughout the reaction time so that the slurry concentration of the resulting titanium trichloride may be 150 to 800 g/l, preferably 300 to 500 g/l. After both the solutions are completely mixed, the mixture is kept at the same temperature for at least 10 minutes, preferably, 1 hour or more, then gradually heated and kept for 15 minutes or more at a constant temperature between 20.degree. and 120.degree., preferably 60.degree. and 100.degree. C. with continuous agitation. The reduced solid obtained in this way should be thoroughly washed with a fresh solvent.

The aluminum compounds contained in the thus resulting reduced solid can be removed by known techniques, for example, subjecting the solid to a high vacuum to sublimate the aluminum compounds or by treating the reduced solid with a compound capable of forming a complex compound with the aluminum compounds (i.e., complexing agent) and then extracting with a solvent. As the complexing agent (generally a Lewis base), there are used, for example, ethers, thioethers, thiols, organo phosphorus compounds organo nitrogen compounds, ketones or esters.

Examples of ether complexing agents are diethyl ether, diisopropyl ether, di-n-nutyl ether, diisobutyl ether, diisoamyl ether di-2-ethylhexyl ether, di-2-ethylheptyl ether, allyl ethyl ether allyl butyl ether, anisole, phenetole, chloroanisole, bromoanisole and dimethoxybenzene.

Examples of thioether complexing agents are diethyl thioether, di-n-propyl thioether, dicyclohexyl thioether, diphenol thioether, ditolyl thioether, ethyl phenyl thioether, propyl phenyl thioether and diallyl thioether.

Examples of the organo phosphorus complexing agents are tri-n-butylphosphine, triphenylphosphine, triethyl phosphite and tributyl phosphite. Examples of the organo nitrogen compounds are diethylamine, triethylamine, n-propylamine, di-n-propylamine, and dimethylaniline.

Ethers, in particular, having 4 to 16 carbon atoms are preferable as complexing agents. The extraction can be carried out by any known methods, for example, by stirring the reduced solid with an ether compound in an inert medium and separating into a liquid phase and solid phase. Such a medium may be the same as that used in the reducing reaction. The extraction is ordinarily carried out at a constant temperature between 0.degree. C. for 5 minutes or more, for example, 30 minutes to 2 hours. The quantity of complexing agent used is ordinarily 0.1 to 2.5 mols, preferably 0.4 to 1.0 mol per 1 mol of titanium atom in the reduced solid.

The solid obtained by the above described treatment is then subjected to an activation treatment with a complex consisting of diisoamyl ether and titanium tetrachloride or a mixture of diisoamyl ether and titanium tetrachloride. Preparation of such a complex consisting of diisoamyl ether and titanium tetrachloride can be carried out by contacting both the compounds in equimolar amounts as it is or in a hydrocarbon solvent at room temperature or with heating. This complex is a green plate crystal, complex compound of equimolar diisoamyl ether and titanium tetrachloride which can be confirmed by analysis after purification, for example, by recrystallization using a hydrocarbon solvent. In the activation treatment with a complex according to the present invention, the thus prepared complex is used. The treatment of the solid with a mixture of diisoamyl ether and titanium tetrachloride can be carried out by mixing the solid with diisoamyl ether and titanium tetrachloride but it is preferable to mix both previously before use thereof. The quantity of diisoamyl ether used in the activation treatment should be 0.1 mol or more per 1 mol of titanium trichloride in the solid whether the complex or mixture is used. If less than this range of ether is used, the resulting catalyst component is unsatisfactory in polymerization activity and stereoregularity and if more is used, the particle size distribution of the catalyst component treated is broadened resulting in an increase of the proportion of fine powder in the product, in addition to poor economy, i.e. use of an excess of an expensive reagent. Therefore, in fact, the quantity of diisoamyl ether is preferably 0.1 to 0.6 mol per 1 mol of titanium trichloride. On the other hand, the quantity of titanium tetrachloride is so adjusted that the concentration thereof may be 1% by volume or more, preferably, 5% by volume or more of the whole liquid phase throughout the treatment. This activation treatment is carried out using a hydrocarbon solvent such as pentane, hexane, heptane, octane, cyclohexane, cyclopentane, etc. in such a manner that the solid concentration in the treating system be 50 to 800 g/l, preferably, 200 to 600 g/l. The temperature of the activation treatment is ordinarily within a range of -30.degree. to 100.degree. C., preferably 40.degree. to 80.degree. C., and the time required for the activation is sufficiently 30 minutes but should be 1 to 3 hours so as to obtain good results with a high reproducibility. Then the thus treated solid should thoroughly be washed with the hydrocarbon solvent used in the above described treatment.

The thus obtained catalyst component is used for the polymerization together with a co-catalyst component. As the co-catalyst, organometallic compounds of Group I, II and III elements of the Periodic Table are used. In particular, organic aluminum compounds are preferably used and, above all, triethylaluminum and diethylaluminum chloride are most suitable for the polymerization of propylene. Any polymerization methods known in the art can be used. For example, as an economical method, a liquid monomer may be used as a polymerization medium without using a polymerization diluent or a gaseous monomer may be used similarly.

The present invention will be illustrated in detail by the following Examples.

700 ml of purified heptane and 250 ml of titanium tetrachloride were charged in a 2000 ml flask equipped with a stirrer and kept at 0.degree. C. in a bath. 315 ml of diethylaluminum chloride (1.1 mol of titanium tetrachloride) was dissolved in 400 ml of heptane and added dropwise from a dropping funnel. The dropping was continued for a period of time of about 3 hours and, during the same time, the reaction system was kept at 0.degree. C. After the dropwise addition, the reaction mixture was gradually heated for 1 hour to 65.degree. C. with agitation. The reaction was further continued at the same temperature for another 1 hour. After completion of the reaction, the reaction mixture was allowed to stand to separate the solid formed and the solid was washed three times with 700 ml of purified heptane, followed by drying at 65.degree. C. for 30 minutes under reduced pressure. The thus reduced solid was black brown and, according to X-ray diffraction, there was contained therein a large quantity of .beta.-type crystal. The particle size distribution was very narrow and there was 1% or less of fine particles of 5 microns or less. The molar Al/Ti ratio in the reduced solid was 0.43.

150 g of the reduced solid was suspended in 1850 ml of purified heptane, to which 127 ml (equimolar to the titanium in the reduced solid) of di-n-butyl ether (referred hereinafter to as "NBE") was dropwise added for 10 minutes with agitation at room temperature, and the mixture was reacted at 35.degree. C. for 1 hour. After the reaction, the reduced solid was washed three times with 500 ml of purified heptane to remove aluminum compounds present in the solid, followed by drying at 65.degree. C. for 30 minutes under reduced pressure.

30 g of the resulting solid, from which the aluminum compounds had substantially been removed by the above described treatment, were again suspended in 53 ml of purified heptane, to which 47.6 ml of a heptane solution of an equimolar complex of titanium tetrachloride and diisoamyl ether (referred hereinafter to as "IAE"), adjusted previously to a concentration of 2 mols/l, was added, and the mixture was reacted at 65.degree. C. for 2 hours. The molar ratio of IAE to titanium trichloride was 0.6 and the proportion of titanium tetrachloride in the whole liquid phase was 10% by volume. After the reaction, the solid was washed three times with 100 ml of purified heptane, followed by drying at 65.degree. C. for 30 minutes under reduced pressure.

The catalyst solid obtained in this way also had a narrow particle size distribution and there was only 2% of fine powder of 5 microns or less size. Moreover the catalyst solid contained NBE and IAE amounting to 0.10 mol and 0.14 mol respectively per 1 mol of the titanium in spite of repeated washing and drying. The molar Al/Ti ratio in the solid was 0.015.

100 mg of the catalyst solid was charged in an autoclave of 1000 ml, to which 180 mg of diethylaluminum chloride as co-catalyst, 600 ml (Standard State) of hydrogen as a molecular weight regulator and 800 ml of liquid propylene were added. The polymerization was carried out at a temperature of 68.degree. C. for 30 minutes and the unreacted propylene was removed by flashing, thus obtaining 150 g of polypropylene powder. Thus the polymer yield per 1 g of the catalyst solid (catalyst efficiency, referred hereinafter to as "E") was 1530. This polymer had a melt flow rate of 4.5 (Melt Flow Rate -ASTM D 1238- referred to as "MFR") and a heptane-insoluble content of 97% (referred hereinafter to as "HI"), which was measured by extracting with heptane for 5 hours by means of a Soxhlet extractor.

The results are shown in Table 1.

The procedure of Example 1 was repeated except that the activation treatment with the complex consisting of titanium tetrachloride and IAE was not carried out and the polymerization test was immediately carried out, thus obtaining results as shown in Table 1.

It is apparent from these results that the activation treatment with the complex is essential.

The procedure of Example 1 was repeated except that the activation treatment with the complex consisting of titanium tetrachloride and IAE was not carried out and instead of heating and activating treatment was carried out at 150.degree. C. for 1 hour, thus obtaining results shown in Table 1.

It is apparent from these results that a marked improvement cannot be expected by an activation treatment by heating even after removing aluminum compounds.

The procedure of Example 1 was repeated except that, in place of the activation treatment with the complex consisting of titanium tetrachloride and IAE, an activation treatment with titanium tetrachloride having the same concentration was carried out, thus obtaining results shown in Table 1.

It is apparent from these results that a marked improvement cannot be expected by activating with titanium tetrachloride alone after aluminum compounds are removed and it is thus essential to add IAE at the time of treatment with titanium tetrachloride.

The procedure of Example 1 was repeated except that, in place of the NBE treatment, a treatment with a mixture of 0.5 mol of NBE and 0.5 mol of IAE per 1 mol of titanium trichloride was carried out to remove aluminum compounds and then an activation treatment was carried out with a solution of titanium tetrachloride having the same concentration. The molar ratio of Al/Ti in the resulting catalyst solid was 0.021. The polymerization results were E = 950, HI = 95 and MFR = 6.0.

It is apparent from these results that the use of a small amount of IAE at the time of removing aluminum compounds is not so effective for the activation and, that is to say, it is essential to use the same when effecting the activation by titanium tetrachloride.

Using titanium trichloride of Grade AA manufactured by Toyo Stauffer Co., a polymerization test was carried out (Comparative Example 5),. On the other hand, another polymerization test was carried out with addition of an ether compound in the same quantity as that remaining in the catalyst solid obtained in Example 1 (Comparative Example 6).

The results are shown in Table 2, from which it is evident that the catalyst obtained by the present invention is very excellent in activity, HI and particle size distribution and capable of giving excellent properties in spite of that there remains a large quantity of an ether compound in the catalyst solid. This is a very interesting phenomenon.

The procedure of Example 1 was repeated except the quantity of the equimolar complex of IAE and titanium tetrachloride was varied, thus obtaining results as shown in Table 3.

The procedure of Example 1 was repeated except that, in place of the complex consisting of titanium tetrachloride and IAE, titanium tetrachloride and IAE were separately added to the processed solid to activate it, thus obtaining results shown in Table 3.

The procedure of Example 1 was repeated except that mixtures of IAE and titanium tetrachloride in various proportions, previously prepared were used in place of the complex consisting of titanium tetrachloride and IAE, thus obtaining results as shown in Table 4.

The procedure of Comparative Example 3 was repeated except varying the concentration of titanium tetrachloride in the whole liquid phase, thus obtaining results as shown in Table 5. It is apparent from these results that the activation treatment using the complex or mixture of the present invention is very effective.

The procedure of Example 1 or Example 9 was repeated except the quantity of NBE used was varied thus obtaining results shown in Table 6. It is apparent from these results that the effect of the quantity of NBE necessary for removing aluminum compounds is not so large within the examined range.

The procedure of Example 1 was repeated except using IAE in a quantity equimolar to the titanium in the reduced solid instead of NBE used for removing aluminum compounds in the reduced solid. Consequently, the quantity of particles of 5 microns or less in the catalyst solid was 3%, the quantity of ether remaining was 0.19 mol and the molar Al/Ti ratio was 0.018. E=1520, HI=97 and MFR=3.9.

In Examples 9 to 12, IAE was used in an equimolar quantity to Ti in place of NBE to remove aluminum compounds and the activation of the reduced solid was carried out by adding 40% by volume of titanium tetrachloride and 0.3 mol of IAE based on Ti. Consequently, the quantity of particles of 5 microns or less in the catalyst solid was 6% and the molar Al/Ti ratio was 0.017. E=1520, HI=97 and MFR=5.3

The procedure of Example 1 was repeated except that various complexing agents were used in an equimolar quantity to titanium trichloride in place of NBE used for removing aluminum compounds, thus obtaining the results shown in Table 7.

For comparison, the same complexing agents were used and thereafter an activation treatment with titanium tetrachloride was only carried out in place of the activation treatment with the complex consisting of titanium tetrachloride and IAE, thus obtaining results as shown in Table 7.

It is apparent from these results that various compounds can be used to remove aluminum compounds and it is essential to add IAE in the subsequent activation treatment.

In Comparative Example 13, the procedure of Example 9 to 12 was repeated except using IAE in an equimolar quantity to Ti to remove aluminum compounds and then using titanium tetrachloride in a quantity of 40% by volume for the activation. In Comparative Example 14, the quantity of IAE used was decreased to 0.5 mol per 1 mol of Ti. The results are shown in Table 8.

It will be clearly understood from these experimental results that the catalyst of the present invention has an activity similar to or the same as the catalysts produced by the prior art method in spite of the fact that the quantity of IAE used is small in the former and the performance of the catalyst is markedly lowered if the quantity of IAE is decreased in the prior art method.