JPH0526801B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention provides improvements in obtaining purified polypropylene by washing a polypropylene slurry obtained by polymerization using a bulk polymerization method using propylene itself as a medium in a countercurrent washing tower. Concerning how it was done. BACKGROUND ART It is well known that polypropylene is polymerized by a bulk polymerization method using propylene itself as a medium, and has already been widely practiced on an industrial scale. In addition, in the polymerization of propylene, the yield per catalyst is relatively low, so there is a lot of catalyst residue, and polypropylene with low stereoregulation is produced as a by-product, which adversely affects the physical properties of the product, so the slurry is washed in countercurrent. It is also known to obtain purified polypropylene by washing in columns. For example, Tokuko Sho 41-12916
Special Publication No. 47-42379, Special Publication No. 9852-1972, Special Publication No. 24402-1977, etc. Problems to be Solved by the Invention However, since cleaning of the slurry using a countercurrent cleaning tower is performed simply by the density difference between the solid polymer particles and the diluent, the method proposed in Japanese Patent Application No. 57-93181 has been proposed. Even if the internal structure is set to a specific structure, the amount of liquid introduced into each part of the countercurrent cleaning tower,
There is a problem that the cleaning efficiency is greatly reduced due to the amount of slurry, the amount of liquid discharged, subtle changes in the amount of slurry, the concentration of slurry introduced into the countercurrent cleaning tower, and changes in temperature. For polypropylene for random copolymers or films, it is necessary to remove polypropylene with low stereoregularity as much as possible, which reduces the efficiency of the countercurrent washing tower, and reduces the polypropylene with low stereoregularity from the product (washed polypropylene). ), there was a problem that the surface of the product would become cloudy or sticky, and the commercial value would be lost. Means for Solving the Problems The present inventors have made extensive studies on methods for solving the above problems, and have developed a system in which polypropylene dispersed in liquid propylene obtained by polymerization using a bulk polymerization method using propylene itself as a medium is placed in the upper part of a countercurrent washing tower. In the method of introducing a slurry, introducing liquid propylene from the lower part to wash the slurry, and taking out the washed polypropylene from the lower part of the washing liquid from the upper part to wash the polypropylene, the temperature of the liquid propylene introduced from the lower part is adjusted to the slurry which is introduced from the upper part. Temperature of 30~90℃
Lower -30~50℃ and temperature difference 5~60℃,
Moreover, the above problem was solved by lowering the temperature in the countercurrent washing tower at a lower level. In the present invention, there are no particular limitations on the method for producing polypropylene dispersed in liquid propylene, as long as it is obtained by polymerizing propylene using a bulk polymerization method using propylene itself as a medium, as is clear from the structure of the invention. In other words, it may be obtained by polymerizing propylene by a bulk polymerization method using a known catalyst consisting of a transition metal catalyst and an organometallic compound. Specifically, a catalyst consisting of titanium trichloride and an organoaluminum, or a supported transition metal catalyst in which titanium trichloride or titanium tetrachloride is supported on a carrier such as magnesium chloride, and a catalyst consisting of an organoaluminium, and a steric catalyst as necessary. This is a highly stereoregular catalyst containing a regularity improver. In the present invention, polypropylene refers not only to propylene alone but also to random or block copolymers of propylene and ethylene, butene-1, hexene-1, etc. In the present invention, polymerization of propylene is carried out by a bulk polymerization method using propylene itself as a medium. There are no particular restrictions on the reaction conditions, and the polymerization temperature and pressure may be determined depending on the type of catalyst or to achieve a desired reaction ratio with other olefins such as ethylene, butene-1, hexene-1, etc. Room temperature ~90
℃, normal pressure to 50Kg/ ^cm2 gauge. In the present invention, the polymerization is carried out by the bulk polymerization method.
Polypropylene can be obtained at a relatively high yield per catalyst, the cleaning efficiency in the countercurrent cleaning tower is relatively high, and it is easy to separate polypropylene from the slurry extracted from the bottom of the countercurrent cleaning tower. by. In the present invention, the liquid propylene introduced into the countercurrent washing tower includes, in addition to propylene, a small amount of relatively high-boiling hydrocarbon compounds such as hexane, heptane, triene, and benzene, or low-boiling hydrocarbon compounds such as ethane, propane, and butane. It may contain boiling point hydrocarbon compounds as well as other olefins such as ethylene, propylene, butene, etc. The content of hydrocarbon compounds with relatively high boiling points is 20wt.
% or less, 30wt as a low boiling point hydrocarbon compound
% or less, because high boiling point hydrocarbon compounds are not easy to separate from polypropylene compared to propylene, and low boiling point hydrocarbon compounds make it difficult to recover and reuse propylene. . The countercurrent washing tower used in the present invention may have a structure in which the slurry to be washed is introduced from the top, the washing liquid is introduced from the bottom, and the washed slurry is extracted from the bottom after washing from the top. It has a vertically long solid cylindrical shape, and the upper part has a structure with a larger diameter to make it difficult for solids to be entrained in the cleaning liquid extracted from the top, or to improve the contact between the cleaning liquid and the slurry. It may be possible to perform gentle stirring or to improve the structure of the nozzle or the like in order to improve the dispersion of the slurry and the dispersion of the cleaning liquid. What is important in the present invention is that the temperature of the liquid propylene introduced from the lower part is -30 to 50 °C lower than the temperature of the slurry introduced from the upper part, 30 to 90 °C, and the temperature difference is 5 to 60 °C. The goal is to lower the temperature further down. A simple and preferred method for keeping the temperature inside the countercurrent washing tower lower at the bottom is to cool the countercurrent washing tower or keep it warm without heating it and separate the slurry introduced from the top and the slurry introduced from the bottom. This is done by changing the temperature of the liquid propylene. For this purpose, it is preferable to make the flow of the cleaning liquid and slurry in the countercurrent cleaning tower into a laminar flow state (for example, the method disclosed in Japanese Patent Application No. 57-93181). (Volume of liquid propylene introduced from the bottom/cross-sectional area of countercurrent washing tower) is preferably set to 1 to 0.05 cm/sec. The larger the difference in temperature between the liquid propylene introduced from the bottom and the slurry introduced from the top, the better, but considering the cost of cooling, the temperature of the slurry should be -30℃ to 50℃ for liquid propylene. 30～
90℃ and the temperature difference is 5 to 60℃, preferably 10 to 50℃
℃, a temperature difference greater than 60℃ provides little improvement. Preferably, the temperature of the liquid propylene introduced from the bottom is lower or slightly higher than the outside air temperature, and the temperature of the slurry introduced from the top is higher than the outside air temperature. The slurry is cooled by heat radiation, and even if the liquid propylene introduced from the bottom is heated by the outside temperature, the temperature inside the countercurrent washing tower can be kept lower at the bottom. Effect One of the reasons why the cleaning efficiency of the countercurrent cleaning tower is improved by the method of the present invention is that the temperature of the liquid in the cleaning tower is lower at the bottom, so a convection phenomenon occurs due to the density difference due to the temperature of the liquid. It seems that there may not be any. Therefore, the method of the present invention can be applied to countercurrent cleaning of a solid material whose density does not differ significantly from that of the solvent using a solvent having a relatively large density difference depending on temperature. Examples The present invention will be further explained with reference to Examples below. Experimental example: A countercurrent cleaning tower with an inner diameter of 10 cm in the thin part, an inner diameter of 30 cm in the thick part at the top, a length of 10 m in the thin part, and a length of 2 m in the thick part at the top, with a cleaning liquid outlet at the top. , using a countercurrent cleaning tower with a slurry inlet 1.5 m below the top, a slurry outlet at the bottom, and a liquid propylene inlet 1 m from the bottom, 1 kg of polypropylene and an organic solvent dissolved in propylene were used. aluminum compound
A slurry made by dispersing and dissolving 0.5g in 1Kg of propylene is heated at the temperature shown in the table at 30Kg/h, and propylene is added from the bottom.
The countercurrent cleaning tower is operated under conditions in which the slurry is introduced at 40 kg/h and the slurry is extracted from the upper part at 44 kg/h and the cleaning liquid at 26 kg/h from the lower part.The organic aluminum compounds in the slurry extracted from the lower part are analyzed and washed. The results of calculating the tower efficiency are shown in the table. The outside temperature is 25℃, and the countercurrent washing tower is kept warm. The cleaning tower efficiency was calculated as (1 - amount of aluminum per 1 kg of polypropylene in the slurry taken out/amount of aluminum per 1 kg of polypropylene in the introduced slurry) x 100%. Effects of the Invention As shown in the Examples, by carrying out the method of the present invention, the efficiency of the countercurrent washing tower can be extremely increased, which is industrially valuable. 【table】

Claims (1)

[Claims] 1. A polypropylene slurry dispersed in liquid propylene obtained by polymerization by bulk polymerization using propylene itself as a medium is introduced into the upper part of the countercurrent cleaning tower, and liquid propylene is introduced from the lower part to wash the slurry.
In the method of cleaning polypropylene by taking out the cleaning liquid from the upper part and the washed polypropylene from the lower part, the temperature of the liquid propylene introduced from the lower part is set to -30 to 50 °C lower than the temperature of the slurry introduced from the upper part, which is 30 to 90 °C. 5 to 60°C, and furthermore, the temperature in the countercurrent cleaning tower is lowered further below.