Method of removing catalyst from ethylene-alpha-olefin copolymer

Abstract: After a copolymer of ethylene and an alpha-olefin of at least 3 carbon atoms (e.g. propylene) and optionally also a non-conjugated diene has been prepared with the use of a vanadium catalyst and an organoaluminum (e.g. alkyl) compound, the residual catalyst is removed from the polymerisation reaction mixture in a hydrocarbon solvent (e.g. hexane) by (a) when the catalyst also includes a halogenated ester compound, mixing the reaction mixture with stirring into an aqueous solution of an alkaline compound (e.g. hydroxide of Li, Na or K) in an amount to give an aqueous phase pH of at least 10; or (b) the halogenated ester compound being optional, oxidising the reaction mixture with an oxidising agent (preferably O₂), e.g. to convert the vanadium to pentavalent V, in an aqueous alkaline solution as in (a). The organic phase is then separated and washed with water and the polymer is recovered therefrom. The catalyst residue is thus reduced to very low levels, so that the copolymer is not affected thereby.

Description: This invention relates to a method for purifying ethylene-α-olefin copolymers by removing therefrom catalytic ingredients. In the preparation of an ethylene-α-olefin copolymer in a hydrocarbon solvent in the presence of a catalyst comprising a vanadium compound, an organoaluminum compound, and a halogenated ester compound, if the catalytic ingredients remain or are incorporated in the copolymer as a final product, problems such as discoloration of the copolymer and deterioration in weather resistance and heat resistance of the copolymer occur. Hence, the catalytic ingredients remaining in the copolymer obtained by the polymerization reaction must be completely removed from the copolymer. Conventional methods for removing the catalytic ingredients from the ethylene-α-olefin copolymer prepared in the presence of a vanadium-based catalyst include a method wherein a large amount of water is added to a polymer solution, the mixture is mixed in a mixer, the catalyst is extracted into an aqueous phase, the aqueous phase is separated from an organic phase, and the polymer containing a reduced amount of the catalytic ingredients is recovered from the organic phase; and a method wherein water or an alcohol is added to a slurry obtained by a copolymerization reaction in a solvent which does not dissolve therein the polymer, to reduce the amount of catalytic residue in the polymer [see, Yasuharu Saeki, Polymer Production Process, published by Kogyo Chosakai (1971)]. However, these methods have some disadvantages described below. In the method wherein a polymer solution is treated with a large amount of water, it is considered that the catalytic ingredients which are solubilized in water by bringing them into contact with water are extracted with water. However, when one expects that the catalytic ingredients are more completely removed, the mixing of the polymer solution with water must be thoroughly made, and a large-size, heavy-duty mixer must be used at a high speed (at high revolution number). Hence, the costs of equipment and power are high and, therefore, the method is not industrially advantageous. In the method using an alcohol, the alcohol must be purified and reused and, hence, not only is the process complicated, but the energy consumption is increased. Thus, the method also is not industrially advantageous. As other methods, JP-A-63-275605 ("JP-A" means an unexamined published Japanese patent application) discloses a method wherein copolymers prepared in the presence of a titanium-based catalyst are washed with water containing an alkaline compound; and JP-B-43-6471 ("JP-B" means an examined Japanese patent publication) discloses a method wherein copolymers prepared in the presence of a vanadium-based catalyst are oxidized and then washed with water containing an alkaline compound. In recent years, since ethylene-α-olefin rubbery copolymers are mixed with other polymers such as polypropylene and are widely used for automobile parts and packaging materials, the requirements for weather resistance and non-discoloration of the rubbery copolymers have become more stringent. In order to meet the requirements, it is highly desirable to further reduce the amount of the catalytic ingredients remaining in the rubbery copolymer. For example, it is required that the amount of the vanadium compound in the copolymer is reduced to not higher than 1 ppm in terms of V 2 O 5 . Further, there is a problem that in addition to the metallic catalytic ingredients, halogenated ester compounds (used as activating agents for the polymerization reaction) remain in the copolymer; and this causes problems such as lowering in the quality of the copolymer so that corrosion of processing machines and coloration of the copolymers occur, and the copolymers are no longer useful as vessels and packaging materials for foods and medicines. Therefore, the conventional purification techniques described in the aforesaid patent specifications are not yet satisfactory. An object of the present invention is thus to provide a method capable of removing catalytic ingredients, to a level which could not be achieved by conventional methods, in purifying a polymerisation reaction mixture containing an ethylene-α-olefin copolymer obtained by polymerizing ethylene with an α-olefin having at least 3 carbon atoms, or ethylene with an α-olefin having at least 3 carbon atoms and a non-conjugated diene compound, in a hydrocarbon solvent in the presence of a catalyst comprising a vanadium compound, an organoaluminum compound, and a halogenated ester compound. The present invention provides a method of purifying a polymerisation reaction mixture containing an ethylene-α-olefin copolymer obtained by polymerizing ethylene with an α-olefin having at least 3 carbon atoms, or ethylene with an α-olefin having at least 3 carbon atoms and a non-conjugated diene compound, in a hydrocarbon solvent in the presence of a catalyst comprising a vanadium compound, an organo-aluminum compound, and a halogenated ester compound, the method including mixing and stirring a polymerization reaction mixture obtained by the polymerization reaction in an aqueous alkaline solution in such an amount as to give an aqueous phase having a pH of not lower than 10.0 after mixing and stirring. In the said polymerization reaction mixtures to be purified, any solvent or medium in which the copolymer is soluble or insoluble can be used as the hydrocarbon solvent or dispersant. Examples of solvents which can be suitably used include aromatic compounds such as benzene and toluene; aliphatic hydrocarbon compounds such as pentane, hexane and heptane; alicyclic hydrocarbon compounds such as cyclopentane, methylcyclopentane and cyclohexane; α-olefins such as liquefied propylene, liquefied 1-butene and 4-methylpentene-1; and mixtures thereof. Examples of the vanadium compound which can be used in the present invention include VCl 3 , VCl 4 , VOCl 3 and VO(OR) 3-m Cl m (wherein R is a straight chain or branched alkyl group, a cycloalkyl group or an aryl group, each having 1 to 10 carbon atoms; and 3 ≧ m ≧ 0), such as VO(OCH 3 )Cl 2 , VO(OCH 3 ) 2 Cl, VO(OCH 3 ) 3 , VO(OC 2 H 5 )Cl 2 , VO(OC 2 H 5 )Cl, VO(OC 2 H 5 ) 3 , VO(OC 3 H 7 )Cl 2 , VO(OC 3 H 7 ) 2 Cl, VO(OC 3 H 7 ) 3 , VO(OisoC 3 H 7 )Cl 2 , VO(OisoC 3 H 7 ) 2 Cl, VO(OisoC 3 H 7 ) 3 , V(OCH 3 ) 3 and V(OCH 2 COOCH 3 ) 3 . Examples of the organoaluminum compound which can be used include AlR′ n Cl 3-n and AlR′ n (OR′) 3 (wherein R′ is a straight chain or branched alkyl group having 1 to 8 carbon atoms; and 3 ≧ n ≧ 0), such as (C 2 H 5 ) 2 AlCl, (C 4 H 9 ) 2 AlCl, (C 6 H 13 ) 2 AlCl, (C 2 H 5 ) 1.5 AlCl 1.5 , (C 4 H 9 ) 1.5 AlCl 1.5 , (C 6 H 13 ) 1.5 AlCl 1.5 , C 2 H 5 AlCl 2 , C 4 H 9 AlCl 2 and C 6 H 13 AlCl 2 . A halogenated ester compound which can be effectively used is a compound represented by the following formula: wherein R″ represents an organic group having 1 to 20 carbon atoms, which is partially or wholly substituted by a halogen atom; and R‴ represents a hydrocarbon group having 1 to 20 carbon atoms. Compounds wherein R‴ is wholly substituted by chlorine atoms and compounds having a phenyl group and a chlorine-substituted alkyl group are preferred. More preferred are perchlorocrotonic acid esters, perchloro-3-butenoic acid esters, and phenyldichloroacetic acid esters. Specific examples of the halogenated ester compound include ethyl dichloroacetate, methyl trichloroacetate, ethyl trichloroacetate, methyl dichlorophenylacetate, ethyl dichlorophenylacetate, methyl perchlorocrotonate, ethyl perchlorocrotonate, propyl perchlorocrotonate, isopropyl perchlorocrotonate, butyl perchlorocrotonate, cyclopropyl perchlorocrotonate, phenyl perchlorocrotonate, methyl perchloro-3-butenoate, ethyl perchloro-3-butenoate, propyl perchloro-3-butenoate and butyl perchloro-3-butenoate. In addition to these catalytic ingredients, hydrogen, etc. as a molecular weight modifier may be used in the present invention. Examples of an α-olefin having at least 3 carbon atoms include propylene, 1-butene, 1-pentene, 1-hexene, 4-methylpentene-1, 1-octene and 1-decene. Examples of the non-conjugated diene compound include dicyclopentadiene, tricyclopentadiene, 5-methyl-2,5-norbornadiene, 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, 5-isopropylidene-2-norbornene, 5-isopropenyl-2-norbornene, 5-(1′-butenyl)-2-norbornene, 5-(2′-butenyl)-2-norbornene, 1,4-hexadiene, 1,6-octadiene and 6-methyl-1,5-heptadiene. There is no particular limitation with regard to other polymerization conditions than those described above. The polymerization reaction mixtures to be purified in the present invention can be obtained in the manner mentioned above. The purification methods of the present invention are now described. The method of the present invention of purifying an ethylene-α-olefin copolymer includes a step of mixing and stirring the above-described polymerization reaction mixture in an aqueous alkaline solution in such an amount as to give an aqueous phase having a pH of not lower than 10.0 after mixing and stirring. This method preferably comprises the following two steps. First step: the polymerization reaction mixture is mixed and stirred in an aqueous solution containing an alkaline compound in such an amount that an aqueous phase separated in the subsequent second step has a pH of not lower than 10.0. Second step: the mixture obtained in the first step is separated into an aqueous phase and an organic phase, and the organic phase is washed with neutral water. This method can alternatively comprise the following three steps: First step: the polymerization reaction mixture obtained by the polymerization reaction is mixed and stirred in an aqueous solution containing an alkaline compound in such an amount that an aqueous phase formed in the subsequent second step has a pH of not lower than 10.0. Second step: one part by volume of the mixture obtained in the first step is mixed with 1/5 to 10 parts by volume of neutral water. Third step: the mixture obtained in the second step is separated into an aqueous and an organic phase, and the organic phase is washed with neutral water. In a preferred manner for adding the aqueous alkaline solution in this method, an aqueous alkaline solution having a pH of not lower than 12, and preferably not lower than 13, is used, 1/1000 to 10 parts by volume of the aqueous alkaline solution is added to and mixed with one part by volume of the polymerization reaction mixture with stirring, and 1/5 to 10 parts by volume of water is additionally added thereto and mixed therewith to separate the mixture into an oily phase and an aqueous phase. As mentioned above, water must be added in an amount sufficient to extract therewith ashes (deposit) mainly formed from the catalytic ingredients and to separate the mixture into an organic phase and an aqueous phase. Specifically, the amount of water added is 1/5 to 10 parts by volume, and preferably 1/4 to 5 parts by volume, per part by volume of the polymerization reaction mixture. It is preferred that water to be added has an iron content as low as possible. When iron components are present in the water, the desired copolymer is apt to be colored. Preferably, the concentration of the iron components is not higher than 0.1 ppm. The important characteristic feature of this method resides in mixing and stirring the polymerization reaction mixture with the aqueous alkaline solution. When the halogenated ester compound is treated with an aqueous alkaline solution having a relatively high pH value, the compound is easily decomposed and extracted into the aqueous phase; but the decomposition reaction of the halogenated ester compound proceeds very slowly at a pH of not higher than 10.0 or under neutral or acidic conditions, and it is then substantially impossible to completely decompose and remove this compound. Further, the treatment with the aqueous alkaline solution does not interfere with the decomposition and extraction of the residue of the vanadium compound and organoaluminum compound-based catalyst but rather has an effect of accelerating the decomposition and extraction thereof. Accordingly, the purification method of the present invention is very effective as a method for decomposing and removing both the metallic catalyst reside and the halogenated ester compound. Examples of the alkaline compound which can be used in the method of the present invention include lithium hydroxide, sodium hydroxide, potassium hydroxide, concentrated ammonia and ammonium hydroxide. Among then, lithium hydroxide, potassium hydroxide and sodium hydroxide are particularly preferred. The alkaline compound must be used in an amount sufficient to give an aqueous phase having a pH of not lower than 10, and preferably not lower than 11, the aqueous phase being separated from the organic phase after the oxidation treatment. When the amount of the alkaline compound is insufficient, the removal of the catalytic ingredients is insufficient. It is preferred that water to be used has an iron content as low as possible. When iron components exist in water, the desired copolymer is apt to be colored. Preferably, the concentration of the iron components is not more than 0.1 ppm. In the method of the present invention the mixing and stirring or treatment of the polymerization reaction mixture with an aqueous alkaline solution or an aqueous alkaline solution containing an oxidizing agent may be carried out by using any method, so long as the catalytic ingredients can be efficiently brought into contact with these solutions so as to extract the catalytic ingredients into the aqueous phase. For example, a method using a line mixer can be used. As a method for separating the aqueous phase and the organic phase, a method using a stationary separating drum can for example be used. A step of mixing and stirring or treating the polymerization reaction mixture with the aqueous alkaline solution or the aqueous alkaline solution containing an oxidizing agent and the step of separating the aqueous and organic phases are carried out at a temperature of generally 20 to 160°C, and preferably 50 to 100°C under a pressure of 1 to 20 kg/cm 2 G, and preferably 2 to 10 kg/cm 2 G. Preferably after the phase separation is carried out, water washing is carried out several times. The thus obtained organic phase containing the desired copolymer is subjected to a conventional after-treatment stage. For example, the hydrocarbon solvent is distilled off by evaporation upon heating, and the residue is dried to obtain the desired ethylene-α-olefin copolymer. The present invention is now illustrated in greater detail by reference to the following examples. The examples show the removal of the catalytic ingredients to low levels not hitherto obtainable. EXAMPLE 1 Ethylene and propylene were copolymerized in the presence of a catalyst comprising vanadium oxytrichloride, ethylaluminum sesquichloride, and BPCC (manufactured by Marine Crott, U.S.A, n-butyl perchlorocrotonate according to a catalog of said company) by a conventional method (e.g., the method described in JP-B-44-9390) to prepare a hexane solution containing an ethylene-propylene copolymer. This uniform hexane solution (containing about 8 wt% of the copolymer) of the ethylene-propylene copolymer (ethylene content: 73 wt%) contained 47 ppm of V 2 O 5 , 560 ppm of Al 2 O 3 , 700 ppm of Cl, and about 110 ppm of BPCC, calculated as the copolymer. To 1000 ml of the hexane solution of the copolymer was added 500 ml of an aqueous sodium hydroxide solution having a pH of 13. The mixture was mixed with stirring at 60°C under atmospheric pressure in a mixer (at 10000 rpm) for 5 minutes. After the mixture was left to stand for about 10 minutes to separate an aqueous phase, the pH of the aqueous phase was measured and found to be 12.6. A 50 ml portion was sampled from the separated oily phase and poured into 50 ml of methanol with stirring to remove the copolymer. The amount of BPCC remained in the thus obtained hexane-methanol mixed solution was quantitatively determined by means of gas chromatography (measuring conditions being described below). To the remainder of the oily phase was added 500 ml of pure water. The mixture was mixed with stirring in a mixer (10000 rpm) for 5 minutes and then left to stand to separate the oily phase. Hexane was distilled off from the oily phase by heating to isolate the copolymer. The content of ashes in the copolymer was determined by means of X-ray fluorometry. The coloration of the copolymer was visually evaluated. No odor based on the halogenated ester compound, etc. was detected at all. The results are shown in Table 1. Gas chromatographic measurement conditions Type of device: Hitachi Gas Chromatograph 663-50 Column: 3 mm diameter × 3 m SE-30 Detection: FID 200°C Temperature rise condition: 100°C constant (10 min) → elevated at a heating rate of 20°C/min (for 5 min) to 200°C → 200°C constant (15 min) Retention time: BPCC: 24.5 minutes Ethyl dichlorophenylacetate: 22 minutes Methyl trichloroacetate: 7.7 minutes EXAMPLES 2 TO 5 AND COMPARATIVE EXAMPLES 1 AND 2 The procedures of Example 1 were repeated except that the type of the halogenated ester compound and the pH of the aqueous alkaline solution for use in the mixing and stirring treatment were changed. The results are shown in Table 1. EXAMPLE 6 An aqueous alkaline solution (NaOH content: 1.25 mol/ℓ, pH: at least 14) formed by dissolving 5 g of sodium hydroxide in 100 ml of water was added to 1000 ml of the hexane solution of the copolymer prepared in Example 1. The mixture was mixed with stirring at 60°C under atmospheric pressure in a mixer (10000 rpm) for 5 minutes. Subsequently, 500 ml of pure water was added thereto, and the mixture was mixed with stirring in a mixer (10000 rpm) for an additional 5 minutes. After the mixture was left to stand for about 10 minutes to separate an aqueous phase, the pH of the aqueous phase was measured and found to be 13.6. The amount of BPCC remained in the oily phase was quantitatively determined in the same manner as in Example 1. To the separated oily phase was added 500 ml of neutral pure water, and the mixture was mixed with stirring in a mixer (10000 rpm) for 5 minutes to carry out washing. Hexane was distilled off by heating, and the content of ashes was determined by means of X-ray fluorometry. The coloration of the copolymer was visually evaluated. The results are shown in Table 2. EXAMPLES 7 AND 8 AND COMPARATIVE EXAMPLE 3 The procedures of Example 6 were repeated except that the pH of the aqueous alkaline solution was changed. The results are shown in Table 2. Example Comp. Ex. 6 7 8 3 Aqueous alkaline solution Alkaline compound NaOH NaOH NaOH NaOH Concentration (mol/ℓ) 1.25 0.08 0.05 0 pH >14 12.9 12.7 7.0 Amount of aqueous alkaline solution (ml) 100 100 100 100 Amount of water additionally added (ml) 500 500 500 500 pH of aqueous phase after separation of oily phase and aqueous phase (pH) 13.6 11.4 10.5 4.3 Halogenated ester compound (1) BPCC BPCC BPCC BPCC Residual amount of halogenated ester (in hexane) ppm (2) none none none 10 Evaluation of copolymer after purifying V 2 O 5 (ppm) <1 <1 <1 13 Al 2 O 3 (ppm) 4 8 6 65 Cl (ppm) 3 5 4 48 Color white white white pale yellow Odor odorless odorless odorless slightly ester odor (1) and (2) being the same as in Table 1.

Claims: A method of purifying an ethylene-α-olefin copolymer obtained by polymerizing ethylene with an α-olefin having at least 3 carbon atoms, optionally with a non-conjugated diene compound, in a hydrocarbon solvent in the presence of a catalyst comprising a vanadium compound, an organoaluminum compound, and a halogenated ester compound, said method comprising mixing and stirring a polymerization reaction mixture obtained by the polymerization reaction in an aqueous alkaline solution in such an amount as to give an aqueous phase having a pH of not lower than 10.0 after mixing and stirring. A method as claimed in Claim 1, wherein said mixing and stirring comprises: a first step wherein the mixing and stirring of the polymerization reaction mixture obtained by the polymerization reaction is carried out in an aqueous solution containing an alkaline compound in such an amount that an aqueous phase separated in the subsequent second step has a pH of not lower than 10.0; and a second step wherein the mixture obtained in the first step is separated into an aqueous phase and an organic phase, and the organic phase is washed with neutral water. A method as claimed in Claim 2, wherein said second step comprises: (a) 1/5 to 10 parts by volume of neutral water is mixed with one part by volume of the mixture obtained in the first step; and (b) the mixture obtained in the second step is separated into an aqueous phase and an organic phase, and the organic phase is washed with neutral water. A method as claimed in any preceding claim, wherein said vanadium compound is selected from VCl 3 , VCl 4 , VOCl 3 , and VO(OR) 3-m Cl m , wherein R is a straight or branched alkyl group, a cycloalkyl group, or an aryl group, each having 1 to 10 carbon atoms; and 3 ≥ m ≥ 0. A method as claimed in any preceding claim, wherein said organoaluminum compound is selected from AlR' n Cl 3-n and AlR' n (OR') 3 , wherein R' is a straight chain or branched alkyl group having 1 to 8 carbon atoms; and 3 ≥ m ≥ 0. A method as claimed in any preceding claim, wherein said halogenated ester compound is represented by the formula: wherein R″ represents an organic group having 1 to 20 carbon atoms, which is partially or wholly substituted by a halogen atom; and R‴ represents a hydrocarbon group having 1 to 20 carbon atoms.

Inventors: INAGAKI KATSUNARI, SABA HAYATO, SUGIMORI KIYOYUKI, WAKATSUKI KIZUKU, YAMAMOTO KEISAKU, INAGAKI, KATSUNARI, SABA, HAYATO, SUGIMORI, KIYOYUKI, WAKATSUKI, KIZUKU, YAMAMOTO, KEISAKU
Applicants: SUMITOMO CHEMICAL CO, SUMITOMO CHEMICAL COMPANY, LIMITED
Application year: 1991
Main classification: C08F6
IPC codes: C08F6