GEL REDUCTION IN HIGH CIS-1,4-POLYBUTADIENE PRODUCTION PROCESS

Abstract: A process for the production of cis-1,4-polybutadiene having a low level of gel content is described. The process comprises polymerizing 1,3-butadiene in the presence of a catalyst and a polymerization diluent. The polymerization diluent comprises an organic solvent and water particles having a median particle size less than or equal to about 10 mu m. By controlling the mean particle size of the water present in the diluent, the level of gel content in the polymer product may be reduced.

Description: GEL REDUCTION IN HIGH CIS-1.4 POLYBUTADIENE PRODUCTION PROCESS TECHNICAL FIELD The present invention relates to an improved process for the production of poly butadiene having a high cis-1,4 content and a reduced gel content. BACKGROUND ART Processes for the production of polybutadiene having a high cis-1,4 content, generally known cis-l,4-polybutadiene, are well known. Such processes include the polymerization of 1 ,3-butadiene in an inert polymerization diluent using as catalyst a mixture of a transition metal salt, such as a cobalt salt, an aluminum alkyl halide or a mixture aluminum alkyl halides and water. During such processes, same gel is produced, such gel being essentially insoluble particles containing cross-linked polybutadiene. The gel is not a desirable component due to the problems it can cause to equipment used for the production of the polymer and due to the problems it can cause relating to the quality of the cis-l,4-polybutadiene. It is thus desirable to minimize and reduce to the lowest level possible the extent of gel formation during the polymerization process. United States patent 3,094,514 teaches a process for the production of a cis-l,4-polybutadiene, having a cis-l,4-content greater than 90 per cent. Generally, the process comprises polymerization of 1,3 -butadiene in a hydrocarbon diluent in the presence as catalyst of an anhydrous dihalide diluent cobalt salt, a monoalkyl aluminum, and dialkyl aluminum monohalide. A similar type of process is described in United States patent 3,135,725. United States patent 3,646,001 teaches that cis-1-4- polybutadiene may be produced by polymerizing 1,3-butadiene in the presence of cobalt octoate and diethyl aluminum chloride which have been reacted with benzene containing water. United States patent 4,224,426 teaches the polymerization of 1,3-butadiene to produce cis-l,4-polybutadiene in the presence of a cobalt compound, at least one organo-aluminum chloride and water, the polymerization diluent being a mixture of C 5 -C 8 cycloalkane, a saturated aliphatic hydrocarbon or an -monoolefin, and an alkyl substituted benzene having 1 to 4 alkyl substituents. United States patent 5,397,851 teaches a process for the production of a cis-l,4-poly butadiene by the polymerization of 1,3-butadiene in an inert hydrocarbon diluent in the presence as catalyst of a diluent cobalt salt, an alkyl aluminum chloride, a tri-alkyl aluminum compound and water. DISCLOSURE OF THE INVENTION An objective of this invention is a process for the production of a high cis-l,4-poly butadiene having a very low level of gel content. Accordingly, in one of its aspects, the present invention provides a process for the production of cis-1 ,4-polybutadiene having a low level of gel content, the process comprising the step of polymerizing 1,3 butadiene in the presence of a catalyst and a polymerization diluent, the polymerization diluent comprising an organic solvent and water particles having a median particle size less than or equal to about 10 μm. In one of its preferred embodiments, the present invention provides a process for the preparation of an essentially linear cis-1, 4-polybutadiene having a very low level of gel content, the process comprising polymerizing 1,3-butadiene in the presence of a cobalt salt-organo aluminum halide- water catalyst system, the improvement being that the polymerization is carried out in the presence as polymerization diluent of a mixture of a C 5 -C 6 cycloalkane and butene-1, a cobalt salt of an organic acid having 6 to 12 carbon atoms in the organic acid, an organo aluminum halide selected from (I) a mixture of (a) an alkyl aluminum chloride selected from diethyl aluminum chloride and ethyl aluminum sesqui chloride and (b) an organo aluminum or formula R 3 Al wherein R is an alkyl group having 8 to 12 carbon atoms and (II) an alkyl aluminum chloride wherein the alkyl group has 8 to 12 carbon atoms, a polymerization modifier selected from 1 ,2-butadiene and 1,3-cyclo octadiene, and water, said water having been mixed with at least a portion of said polymerization diluent such that the water is present in said polymerization diluent as particles having a median particle size less than or equal to about 10 μm. Thus, the present inventor has discovered that controlling the median particle size of the water used in the diluent surprisingly and unexpectedly results in the production of high cis-1, 4-polybutadiene having a relatively low level of gel content. Thus, the median diameter of the water particles used in the polymerization diluent is less than or equal to about 10 μm. Preferably, the water is present in said polymerization diluent as particles having a median particle size in the range of from about 0.5 μm to about 8 μm, more preferably from about 0.5 μm to about 6 μm, most preferably from about 1 μm to about 5 μm. The median particle size of the water particles may be determined in a conventional manner, for example, using a Master sizer™ particle size measuring system commercially available from Malvern Instruments Inc. BEST MODE FOR CARRYING OUT THE INVENTION Thus, the present process relates to the use of a polymerization diluent comprising an organic solvent and water particles. Preferably, the organic solvent is selected from the group comprising an aliphatic compound, an aromatic compound and mixtures thereof. The aliphatic compound may be selected from a saturated hydrocarbon, an unsaturated hydrocarbon and mixtures thereof. Preferred saturated hydrocarbons may be selected from the group comprising C 4 -C 10 aliphatic hydrocarbon, a C 5 -C 10 cyclic aliphatic hydrocarbon, a C 6 -C 9 aromatic hydrocarbon, a C 2 -C 10 monoolefinic hydrocarbon and mixtures thereof. Non-limiting examples of a suitable C 4 -C, 0 aliphatic hydrocarbon may be selected from the group comprising butane, pentane, hexane, heptane, octane and mixtures thereof. Non-limiting examples of a suitable C 2 -C 10 monoolefinic hydrocarbon may selected from the group comprising butene-1, pentene-1, hexene-1 and mixtures thereof. Non-limiting examples of a suitable C 5 -C ]0 cyclic aliphatic hydrocarbon may be selected from the group comprising unsubstituted cycloalkanes, methyl substituted cycloalkanes, ethyl substituted cycloalkanes and mixtures thereof. Non-limiting examples of a suitable C 5 -C 10 cyclic aliphatic hydrocarbon is selected from the group comprising cylcopentane, cyclohexane, cyclooctane and mixtures thereof. Non-limiting examples of a suitable a C 6 -C 9 aromatic hydrocarbon may be selected from the group comprising benzene, toluene, xylene and mixtures thereof. The most preferred organic solvent for use in the present process comprises a mixtures of cyclohexane and butene-1. Preferably, the polymerization diluent further comprises a polymerization modifier. The use of such a modifier allows for controlling the molecular weight of the polymer product. Illustrative examples of useful polymerization modifiers for use in the present process may selected from the group comprising C 2 -C lg non-conjugated dienes, C 6 -C 12 cyclic dienes and mixtures thereof. Non-limiting examples of suitable polymerization modifiers may be selected from the group comprising 1,2-butadiene, 1 ,3- cyclooctadiene, 1,5-cyclooctadiene and mixtures thereof. The amount of polymerization modifier may be from about 1.6 to about 3.5, preferably from about 1.95 to about 3.0, millimols per mole of 1,3-butadiene in the polymerization mixture. The choice catalyst that is employed in butadiene polymerization art are well known. Preferably, the catalyst comprises a substantially anhydrous cobalt salt and an organo-aluminum halide compound. The substantially anhydrous cobalt salt may comprise a compound having the formula CoA m , wherein A is selected from a monovalent anion and a divalent anion, and m is 1 or 2. Preferably, the anion is derived from a C 6 -C 12 organic acid. Thus, non-limiting examples of usefully such anions may be selected from the group comprising an acetylacetonate, an acetate, a hexanoate, an octoate, an oxalate, a tartrate, a stearate, a sorbate, an adipate and a naphthenate. The most preferred substantially anhydrous cobalt salt for use in the present process is cobalt octoate. Preferably, the organo-aluminum halide compound comprises a compound having the formula: R p ALX q wherein: R is a C 2 -C 12 alkyl group, X is a halogen and p+q is 3. More preferably, the organo-aluminum halide compound is selected from the group comprising a dialkyl aluminum chloride compound, an alkyl aluminum sesquichoride compound and mixtures thereof. Even more preferably, the organo-aluminum halide compound is selected from: (I) a mixture of: (a) an alkyl aluminum chloride selected from diethyl aluminum chloride and ethyl aluminum sesquichloride (this may be achieve by a mixture containing approximately equimolar amounts of diethyl aluminum chloride and ethyl aluminum dichloride), and (b) an organo aluminum compound of formula R 3 A1 wherein R is C 8 -C 12 alkyl group (e.g. , trioctyl aluminum, tridecyl aluminum and the like); and (II) an alkyl aluminum chloride wherein the alkyl group has 8 to 12 carbon atoms (e.g., dioctyl aluminum chloride, didecyl aluminum chloride and the like). Embodiment (I) is more preferred. In this preferred embodiment, it is especially preferred to use the organo aluminum compound of formula R 3 A1 is present in an amount of 0 to 1 percent by weight of the mixture of (I) and (II). The preferred organo aluminum compound of formula R 3 A1 comprises tri-octyl aluminum. The preferred catalyst system for use in the present process comprises a cobalt salt selected from cobalt octoate and cobalt naphthenate, and an organo aluminum halide compound selected from: (i) a mixture of diethyl aluminum chloride and one or more of trioctyl aluminum, tridecyl aluminum and tridodecyl aluminum, and (ii) one or more of dioctyl aluminum chloride, didecyl aluminum chloride and didodecyl aluminum chloride. In a preferred process, using cyclohexane and butene-1 as the diluent the weight ratio of butene-1 in the cyclohexane-butene-1 mixture may be from about 24 to about 40, preferably from about 24 to about 38 and most preferably from about 34 to about 36, weight percent. A preferred catalyst cobalt octoate which is used with a preferred organo aluminum halide compound which is a mixture of diethyl aluminum chloride and trioctyl aluminum, wherein the molar ratio of cobalt octoate to the total of the diethyl aluminum chloride plus trioctyl aluminum is from about 1: 15 to about 1:30, preferably from about 1: 15 to about 1 :20 and wherein the molar ratio of chlorine in the diethyl aluminum chloride to the total aluminum in the diethyl aluminum chloride plus trioctyl aluminum is from about 0.7: 1 to about 0.95: 1, preferably from about 0.8: 1 to about 0.9: 1. The amount of 1,3-butadiene in the 1.3-butadiene plus diluent mixture may be from about 15 to about 35, preferably from about 25 to about 35, weight percent. The polymerization mixture also contains water. The amount of water is from about 0.3 to about 0.8, preferably from about 0.5 to about 0.65, millimols per millimol of the alkyl aluminum chloride used. The water is mixed with at least a portion of the polymerization diluent. Accordingly, in the preferred diluent comprising cycloalkane and butene-1, the water may be mixed with cycloalkane alone, or, preferably with cycloalkane and butene-1 mixture. The mixing of the water with the polymerization diluent is such that the water as present in the polymerization diluent as particles having a median particle size equal to or less than 10 μm. Because of the very low solubility of water in hydrocarbons, including the polymerization diluents, and because of the long time to achieve a solution of water in such hydrocarbons, it is desirable for the present polymerization system to disperse the water in the polymerization diluent as very small particles to provide as high as possible a surface area to weight ratio for the particles so that interaction with the aluminum compound(s) is as efficiently as possible - this is believed to be important in reducing the amount of gel in the polybutadiene produced. The dispersion of water in the polymerization diluent may be achieved by various means such as, but not limited to, mechanical methods and sonic treatment. The improvement of the present invention is not dependent on the method used to obtain the dispersion of water in the polymerization diluent and is only dependent on the median diameter of the water particles used in the polymerization diluent being less than or equal to about 10 μm. Preferably, the water is present in said polymerization diluent as particles having a median particle size in the range of from about 0.5 μm to about 8 μm, more preferably from about 0.5 μm to about 6 μm, most preferably from about 1 μm to about 5 μm. The polymerization may be undertaken at a temperature of from about -10°C to abut 50°C, preferably from about 5°C to about 40°C and most preferably from about 15 °C to about 35 °C. The polymerization process may be carried out in a batch process or in a continuous process, the continuous process being preferred. The reaction time for the polymer ization may be from about 20 to about 90 minutes, preferably from about 25 to about 60 minutes. However, the reaction time is not a critical aspect of the process and may be affected by the desired conversion of the 1,3-butadiene to polymer which may range from about 40 to about 90 percent. The gel content of the polymer may be determined by a method in which the gel is separated from a solution of the polymer in styrene and weighed. In detail, approximately 50 g of polymer, accurately weighed, is dissolved in pure, filtered styrene to produce an approximately 4 weight percent by volume solution. The polymer-styrene mixture is shaken for 4 to 5 hours, then allowed to stand for 10 minutes and then filtered through a previously weighed filtration screen of 400 mesh. The filtration screen is then weighed again and the amount of wet gel is calculated as parts per million by weight based on the original weight of polymer used. Gel contents of less than about 250 ppm are desirable and less than about 150 ppm are more desirable and less than about 100 ppm are most desirable. In order to provide the greatest accuracy to the gel content of the polymer, normally at least three and up to 5 samples of the polymer are used to provide the corresponding number of gel content measurements. In the following examples, the 1,3-butadiene was obtained from Union Carbide, the cyclohexane and butene-1 was Phillips pure grade and all three were passed through a column containing 4A molecular sieves followed by passage through a column containing 13X molecular sieves before use in polymerization. The 1,3-cyclooctadiene was used as a 20 weight percent solution in cyclohexane from Aldrich Chemical Company. Diethyl aluminum chloride in hexane as a 1 molar solution was from Albemarle Corporation and Akzo Nobel. Tri-octyl aluminum in heptane (20% wt.) was obtained from Albemarle Corporation as a 25.3 wt. % solution. Cobalt octoate was obtained from Mooney Chemical Inc. and used as a 6% cobalt solution in cyclohexane. Diethyl aluminum chloride was mixed with trioctyl aluminum in sealed bottles under an inert gas in such ratios as to provide a solution having an average composition of Et, 8 Oct 03 Al j Cl 09 in cyclohexane which was used in all examples and is referred to as M-DEAC. Polymerization was undertaken in sealed 1 litre polymerization bottles at a temperature of 27 °C for 40 minutes at the end of which time the polymerization was stopped by the injection of 5 ml of ethanol containing required amount of stabilizer and the polymer was recovered by steam coagulation. Embodiments of the present invention will be illustrated with reference to the following Examples which should not be used to limit or construe the scope of the invention. EXAMPLE 1 Using 1 liter glass bottles capped with gasketted crown caps, 110 g of cyclohexane, 80 g of 1,3-butadiene, 60 g of butene-1, 1.8 mL of a 20% solution of 1,3-octadiene in cyclohexane, 0.01 mL of pure distilled water, 0.54 mL of a 25 % solution of M-DEAC and 0.19 mL of a 0.25 % solution of cobalt octoate in cyclohexane were charged to the glass bottles. When the cobalt octoate was added, the glass bottles were placed in an agitated polymerization bath maintained at 27 °C for 40 minutes, followed by addition of ethanol to stop polymerization. The polymer was recovered and dried and samples used to measure the gel content, with the results shown in Table 1. With reference to Table 1, Experiment #1 is a control in which the cyclohexane plus water was shaken for 5 minutes which produced clearly visible particles (median much greater than 10 μm) of water in the cyclohexane. The other components were added after the shaking. In Experiment #2, the cyclohexane and water was subjected to sonification for 5 minutes in a Branson™ ultrasonic cleaner which produced a mixture of water particles in cyclohexane in which the water particles had a median particle size of less than 10 μm. The other components were added after completion of the ultrasonic mixing. In Experiment #3, the cyclohexane, 1,3-butadiene, butene-1 and water were subjected to sonification as described above; the water particles had a median particle size of less than 10 μm. The other components were added on completion of the ultrasonic mixing. In Experiment #4, the cyclohexane, 1,3-butadiene, butene-1 and water were subjected to shaking for 48 hours producing water particles having a median particle size of less than 10 μm. The other components were added on completion of the shaking. The gel data provided in Table 1 clearly show that the presence of water particles having a median particle size of less than 10 μm resulted in the production of polymers having significantly reduced gel contents. TABLE 1 EXAMPLE 2 Using the procedure and components described in Example 1 , polymerizations were undertaken in which the cyclohexane, 1,3-butadiene, butene-1, water and M-DEAC were mixed by shaking for a period ranging from 0 to 30 minutes. The other components were added on completion of the shaking. The gel results shown in Table 2 show that when the median particle size is reduced less than 10 μm, the gel content of the polymer is significantly reduced. TABLE 2 EXAMPLE 3 Using the procedure described in Example 1 , the following experiments were undertaken. 110 g of cyclohexane and 0.011 mL of water was subjected to sonification for 5 minutes producing a mixture containing particles of water having a median particle size of less than 10 μm. Following this, 80 g of 1,3-butadiene, 2.0 mL of a 20% solution of 1:3 cyclooctadiene in cyclohexane, 60 g of butene-1, 1.25 mL of a 12% solution of diethyl aluminum chloride in cyclohexane and 0.2 mL of a 0.25% solution of cobalt octoate in cyclohexane were added and the contents immersed in an agitated water bath at 27 °C for 40 minutes. After stopping the polymerization, the polymer was recovered and the gel content was determined to be 120 ppm. In a control experiment, the same procedure was followed except that instead of being sonified, the cyclohexane and water was mixed by shaking. The water particles were found to have a median particle size of greater than 10 μm. The resulting polymer was found to have a gel content of greater than 3000 ppm. All publications, patents and patent applications referred to herein are incorporated by reference in their entirety to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated by reference in its entirety.

Claims: What is claimed is: 1. A process for the production of cis-1, 4-poly butadiene having a low level of gel content, the process comprising the step of polymerizing 1,3 butadiene in the presence of a catalyst and a polymerization diluent, the polymerization diluent comprising an organic solvent and water particles having a median particle size less than or equal to about 10 μm. 2. The process defined in claim 1, wherein the water is present in said polymerization diluent as particles having a median particle size in the range of from about 0.5 μm to about 8 μm. 3. The process defined in claim 1, wherein the water is present in said polymerization diluent as particles having a median particle size in the range of from about 0.5 μm to about 6 μm. 4. The process defined in claim 1, wherein the water is present in said polymerization diluent as particles having a median particle size in the range of from about 1 μm to about 5 μm. 5. The process defined in any one of claims 1-4, wherein the organic solvent is selected from the group comprising an aliphatic compound, an aromatic compound and mixtures thereof. 6. The process defined in claim 5, wherein the aliphatic compound is selected from a saturated hydrocarbon, an unsaturated hydrocarbon and mixtures thereof. 7. The process defined in claim 6, wherein the saturated hydrocarbon is selected from the group comprising C 4 -C 10 aliphatic hydrocarbon, a C 5 -C ]0 cyclic aliphatic hydrocarbon, a C 6 -C 9 aromatic hydrocarbon, a C 2 -C 10 monoolefmic hydrocarbon and mixtures thereof. 8. The process defined in claim 7, wherein the C 4 -C 10 aliphatic hydrocarbon is selected from the group comprising butane, pentane, hexane, heptane, octane and mixtures thereof. 9. The process defined in claim 7, wherein the C 2 -C 10 monoolefmic hydrocarbon is selected from the group comprising butene-1, pentene-1, hexene-1 and mixtures thereof. 10. The process defined in claim 7, wherein the C 5 -C 10 cyclic aliphatic hydrocarbon is selected from the group comprising unsubstituted cycloalkanes, methyl substituted cycloalkanes, ethyl substituted cycloalkanes and mixtures thereof. 11. The process defined in claim 7, wherein the C 5 -C 10 cyclic aliphatic hydrocarbon is selected from the group comprising cylcopentane, cyclohexane, cyclooctane and mixtures thereof. 12. The process defined in claim 7, wherein the a C 6 -C 9 aromatic hydrocarbon is selected from the group comprising benzene, toluene, xylene and mixtures thereof. 13. The process defined in any one of claims 1-4, wherein the organic solvent comprises a mixtures of cyclohexane and butene-1. 14. The process defined in any one of claims 1-13, wherein polymerization diluent further comprises a polymerization modifier selected from the group comprising C 2 -C 18 non-conjugated dienes, C 6 -C 12 cyclic dienes and mixtures thereof. 15. The process defined in claim 14, wherein the polymerization modifier is selected from the group comprising 1,2-butadiene, 1,3-cyclooctadiene, 1,5-cyclooctadiene and mixtures thereof. 16. The process defined in any one of claims 1-15, wherein the catalyst comprises a substantially anhydrous cobalt salt and an organo-aluminum halide compound. 17. The process defined in claim 16, wherein the substantially anhydrous cobalt salt comprises a compound having the formula CoA m , wherein A is selected from a monovalent anion and a divalent anion, and m is 1 or 2. 18. The process defined in claim 17, wherein the anion is derived from a C 6 -C 12 organic acid. 19. The process defined in claim 17, wherein the anion is selected from the group comprising an acetylacetonate, an acetate, a hexanoate, an octoate, an oxalate, a tartrate, a stearate, a sorbate, an adipate and a naphthenate. 20. The process defined in claim 16, wherein the substantially anhydrous cobalt salt comprises cobalt octoate. 21. The process defined in any one of claims 16-20, wherein the organo- aluminum halide compound comprises a compound having the formula: R p AlX q wherein: R is a C 2 -C 12 alkyl group, X is a halogen and p+q is 3. 22. The process defined in any one of claims 16-20, wherein organo- aluminum halide compound is selected from the group comprising a dialkyl aluminum chloride compound, an alkyl aluminum sesquichoride compound and mixtures thereof. 23. The process defined in any one of claims 16-20, wherein the organo- aluminum halide compound is selected from: (I) a mixture of: (a) an alkyl aluminum chloride selected from diethyl aluminum chloride and ethyl aluminum sesquichloride and (b) an organo aluminum compound of formula R 3 A1 wherein R is C 8 -C 12 alkyl group; and (II) an alkyl aluminum chloride wherein the alkyl group has 8 to 12 carbon atoms. 24. The process defined in any one of claims 16-20, wherein the organo aluminum halide comprises a mixture of: (a) an alkyl aluminum chloride selected from diethyl aluminum chloride and ethyl aluminum sesquichloride and (b) an organo aluminum compound of formula R 3 A1 wherein R is C 8 -C 12 alkyl group. 25. The process defined in any one of claims 23-24, wherein the organo aluminum compound of formula R 3 A1 is present in an amount of 0 to 1 percent by weight of the mixture. 26. The process defined in any one of claims 23-24, wherein the organo aluminum compound of formula R 3 A1 comprises tri-octyl aluminum. 27. The process defined in claim 16, wherein the substantially anhydrous cobalt salt comprises cobalt octoate and the organo-aluminum halide compound comprises a mixture of diethyl aluminum chloride and tri-octyl aluminum 28. The process defined in claim 27, wherein the molar ratio of cobalt octoate to the total of diethyl aluminum chloride plus tri-octyl aluminum is from about 1: 15 to about 1:30. 29. The process defined in claim 27, wherein the molar ratio of chlorine in diethyl aluminum chloride to the total aluminum in diethyl aluminum chloride plus tri-octyl aluminum is from about 0.7: 1 to about 0.95: 1. 30. The process defined in any one of claims 1-29, wherein the water is mixed with the polymerization diluent by a mechanical method. 31. The process defined in any one of claims 1-29, wherein the water is mixed with the polymerization diluent by sonic treatment. 32. The process defined in any one of claims 1-31, wherein the polymerization temperature is in the range of from about 5° to about 40 °C.

Inventors: BARSAN FLORIN, OSMAN AKHTAR, BARSAN, FLORIN, OSMAN, AKHTAR
Applicants: BARSAN FLORIN, BAYER INC, OSMAN AKHTAR, BARSAN, FLORIN, BAYER INC., OSMAN, AKHTAR
Application year: 1999
Main classification: C08F136
IPC codes: C08F4, C08F36, C08F136, C08F236