JPS6411641B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for purifying unreacted monomers and/or solvents recovered from a polymer solution obtained by polymerizing a conjugated diene in the presence of a coordinating anion type catalyst or an anion type catalyst. And/or relates to a method for purifying unreacted monomers and/or solvents that does not cause a decrease in polymerization activity when the solvents are recycled. Polymerization of conjugated dienes using coordination anion type catalysts such as Ziegler type catalysts or anion type catalysts such as organolithium has been carried out industrially, but in this case, unreacted monomers and Solvents are usually purified and recycled. In such recycling use, it is essential to prevent components that inhibit polymerization activity from entering the polymerization process, and for this reason, in addition to catalyst deactivators, water, oxygen, anti-aging agents, conjugated diene oligomers, etc. A step is provided to remove the. For example, when using a water-soluble alcohol as a catalyst deactivator, the unreacted monomers and/or the water-soluble alcohol contained in the recovered solvent are first extracted into the aqueous phase by contact with water in countercurrent flow. After separation, it is generally purified and recycled to the polymerization process. This purification process usually consists of a process in which high-boiling substances such as antiaging agents and oligomers are separated by distillation, and a dehydration process. An azeotropic distillation method that utilizes azeotropy between monomers and/or solvents and water has been carried out. In any of these methods, dissolved oxygen can be removed at the same time as dehydration. Therefore, even if oxygen is dissolved in the pre-purification process, it can be removed at the same time as dehydration, resulting in polymerization due to dissolved oxygen. In the process of separating water-soluble alcohols, inexpensive industrial water containing a saturated amount of dissolved oxygen is usually used because it can prevent adverse effects on water-soluble alcohols. According to such conventional techniques, it is possible to obtain unreacted monomers and/or recovered solvents from which impurities that interfere with polymerization, such as catalyst deactivators, antioxidants, water, and oxygen, are substantially removed. However, when these unreacted monomers and recovered solvents are recycled and reused in the polymerization process, the polymerization activity often decreases, even though the impurities mentioned above are purified to the same level as fresh monomers. This has the disadvantage that it may cause the product to deteriorate or have an adverse effect on the physical properties of the product. The inventors of the present invention have carried out extensive studies to overcome these drawbacks of the prior art, and have found that such drawbacks can be improved when water with a low amount of dissolved oxygen is used in the water-soluble alcohol separation process. With this finding, we have completed the present invention. An object of the present invention is to provide a method for purifying unreacted monomers and/or solvents that does not cause a decrease in polymerization activity and does not have an adverse effect on polymerization products when the unreacted monomers and/or solvents are recycled. It is an object of the present invention to provide unreacted monomers containing a small amount of water-soluble alcohol and/or recovered from a step of polymerizing a conjugated diene in the presence of a coordinating anionic catalyst or an anionic catalyst. When a water-soluble alcohol is separated by contacting the solvent and water in countercurrent flow and then being purified and recycled for reuse in the polymerization process, unreacted monomers and/or
Alternatively, this can be achieved by bringing the recovered solvent into contact with water having a dissolved oxygen content of 2 ppm or less in a countercurrent flow to separate the water-soluble alcohol, and then purifying it. In the present invention, the unreacted monomer and/or recovered solvent to be purified are obtained by adding a water-soluble alcohol to a polymer solution derived from a step of polymerizing a conjugated diene in the shallow presence of a coordinating anion type catalyst or an anion type catalyst. After deactivating the catalyst, it contains a small amount of water-soluble alcohol, which is recovered by flash distillation, steam stripping, or other means. The conjugated diene used in the polymerization process is 1,3-
butadiene, isoprene or 1,3-pentadiene; in the polymerization process, a Ziegler type catalyst consisting essentially of an organoaluminum compound and titanium tetrahalide; a Ziegler type catalyst consisting essentially of an organoaluminum compound and a cobalt or nickel compound; Polymerization of the conjugated diene is carried out in a conventional manner using a coordinating anion type catalyst such as or an anion type catalyst such as alkyl lithium. At this time, the polymerization of conjugated dienes may be carried out by bulk polymerization, but solution polymerization is generally carried out in the presence of a solvent, and the solvents used include aliphatic hydrocarbons such as butane, pentane, hexane, heptane, etc., cyclopentane, Alicyclic hydrocarbons such as cyclohexane, aromatic hydrocarbons such as benzene, toluene, xylene, etc. are used. Examples of the water-soluble alcohol used for inactivating the catalyst include methanol, ethanol, and isopropanol. Unreacted monomers containing water-soluble alcohol and/or
Alternatively, the water-soluble alcohol is usually removed from the recovered solvent by contacting it with industrial water in a countercurrent flow, but in the present invention, the water used in the contacting countercurrent flow preferably has a dissolved oxygen content of 2 ppm or less. It is necessary to use water of 1 ppm or less, more preferably 0.2 ppm or less. At this time, if water with a dissolved oxygen content exceeding 2 ppm is used, the polymerization activity is likely to decrease when recycled and reused, even if oxygen is removed in subsequent steps.
This tendency is particularly noticeable when cis-1.4 polyisoprene rubber is produced by polymerizing isoprene in the presence of a Ziegler type catalyst consisting essentially of an organoaluminum compound and titanium tetrahalide. Such water with a low amount of dissolved oxygen can be easily obtained by bubbling industrial water with nitrogen, degassing it under reduced pressure, treating it with an oxygen scavenger such as a hyposulfite compound, or the like. The unreacted monomers and/or the water-soluble alcohol contained in the recovered solvent are extracted into water by contact with water supplied from the top of the column in countercurrent flow and separated from the bottom of the column. At this time, the amount of water used is within a range such that the amount of residual methanol is approximately 10 ppm or less, and usually 0.5 to 1.5 of the amount of unreacted monomer and/or recovered solvent.
It is double the amount (capacity ratio). On the other hand, unreacted monomers and/or recovered solvent containing water flowing out from the top of the column are then sent to a purification process to remove impurities mixed into these fractions, such as oligomers by-produced in the polymerization process and anti-aging agents. By separating the substances by distillation and then dehydrating them, they are purified to the extent that they can be used in the polymerization process. A specific example of the present invention will be explained below with reference to the drawings. In FIG. 1, a polymer solution produced in a polymerization vessel 1 is supplied to a stripping tank 4 through a pipe 2. In FIG. At this time, water-soluble alcohol is supplied from the tube 3 to stop the polymerization. A polymer slurry is discharged from the lower part of the stripping tank 4 through a pipe 5, and unreacted monomers and/or solvents containing water-soluble alcohol are discharged from the upper part through a pipe 6. After this fraction is allowed to stand still in a decanter 7, it is supplied to an extraction column 9 through a pipe 8, where it is brought into contact with water having a dissolved oxygen content of 2 ppm or less supplied from a pipe 10 in the upper part of the column. Due to this contact exchange, water containing water-soluble alcohol is discharged from the tube 11 at the bottom of the column, and unreacted monomer and/or solvent containing water is discharged from the tube 12 at the top of the column. This fraction is then fed to a distillation column 13 to remove high-boiling impurities discharged from a tube 14 at the bottom of the column.
Water is then supplied to an azeotropic distillation column 16, water is discharged from a tube 17 at the top of the column, and purified monomer and/or solvent is obtained from a tube 18 at the bottom of the column. According to the present invention, monomers and/or solvents that do not cause a decrease in polymerization activity and do not have a negative effect on polymerization products even when recycled are recovered. The present invention will be explained in more detail with reference to Examples below. Example Using a Ziegler type catalyst consisting essentially of triisobutylaluminum and titanium tetrachloride
After isobrene was polymerized in a butane solution at a monomer concentration of 20% by weight and a final conversion rate of 75%, methanol was added to stop the reaction. The resulting polymer solution is then steam-stripped, and unreacted isoprene, n
- A solution containing butane and methanol is cooled at 35°C, and this solution is mixed with water at 15°C containing variable amounts of dissolved oxygen as shown in Table 1 in a 1:1 ratio (by volume) for a contact time of 10 minutes. Methanol was removed under countercurrent contact conditions. As a result, the methanol content was reduced to about 1 ppm. Next, this solution was distilled under conditions of 45°C and 3.5 atm to remove high-boiling substances such as oligomers, and then left at room temperature for 1 day, followed by azeotropic distillation under conditions of 50°C and 3.5 atm. Water was removed from the top, and purified isoprene and n-butane were recovered from the bottom. This recovered fraction is collected regardless of the amount of dissolved oxygen in the water used for demethanolization.
In all cases, dissolved oxygen content was 0.1 ppm or less and moisture content was 10 ppm or less. A part of the recovered fraction is separated, and after adding flexible isoprene with a dissolved oxygen content of 0.1 ppm or less and a water content of 10 ppm or less to adjust the monomer concentration to 20% by weight, this solution is poured into a pressure-resistant glass tube made of No. 1 pressure-resistant glass. A Ziegler-type catalyst having a composition ratio of triisobutylaluminum/titanium tetrachloride/n-butyl ether (molar ratio) = 1/1/0.15 is added at a ratio of 0.25 mmol of titanium tetrachloride per mol of isoprene. Polymerization was carried out at 30°C for 3 hours. After the reaction was completed, methanol was added to stop the polymerization, and the yield of the obtained polyisoprene was measured. The results are shown in Table 1.

[Table] Normal industrial water contains a saturated amount of dissolved oxygen, but when such industrial water is used (Experiment No. 5), the yield decreases significantly and the amount of catalyst used must be increased. This is necessary. However, according to the method of the present invention, even if the recovered unreacted isoprene and solvent are recycled and reused, there is little adverse effect on polymerization activity, and the method is extremely effective.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet showing a specific example of the present invention. 1... Polymerization can, 4... Stripping tank, 9...
extraction column, 13... distillation column, 16... azeotropic distillation column.

Claims (1)

[Claims] 1. Contacting water with an unreacted monomer containing a small amount of water-soluble alcohol and/or a recovered solvent recovered from a step of polymerizing a conjugated diene in the presence of a coordinating anion type catalyst or an anion type catalyst. When the water-soluble alcohol is separated by countercurrent flow and then purified and recycled for reuse in the polymerization process, unreacted monomers and/or
Alternatively, a method for purifying unreacted monomers and/or recovered solvents, which comprises contacting the recovered solvent with water having a dissolved oxygen content of 2 ppm or less in countercurrent flow to separate the water-soluble alcohol, and then purifying the recovered solvent. 2. The purification method according to claim 1, wherein the polymerization catalyst is a Ziegler type catalyst consisting essentially of an organoaluminum compound and titanium tetrahalide. 3. The purification method according to claim 1, wherein the conjugated diene is isoprene.