KR100417059B1 - Molecular Fractional Purification Method and Equipment for Polyethylene Wax - Google Patents

Abstract

The present invention relates to a method and apparatus for purifying low-density polyethylene wax produced as a by-product in a high-density polyethylene production process by slurry polymerization method by narrowing the molecular weight through a solution crystallization method to have a narrow molecular weight distribution and high purity. Mixing the raw material with a crystallization solvent having a concentration range of 1 to 95% in a firearm (S1); Raising the temperature so that the raw material reaches a uniform liquid state (S2); Cooling in a range of an overcooling temperature of 30 to 110 ° C. and a cooling rate of 0.1 to 10 ° C. per minute (S3); Step S4 for crystallizing the cooled raw material; And it is provided with a method for fractionating the molecular weight of the polyethylene wax consisting of the step of filtering the crystallized raw material (S5) and an apparatus capable of performing this more effectively. Using the crystallization method and apparatus of the present invention, it is possible to obtain purified polyethylene wax fractions having a narrow molecular weight distribution and various melting points for various average molecular weights. Available as lubricants and release agents.

Description

Molecular Fractional Purification Method and Equipment for Polyethylene Wax

The present invention relates to a method and a device for purifying low-density polyethylene wax produced as a by-product in a high-density polyethylene production process by slurry polymerization method by narrowing the molecular weight through solution crystallization method with a narrow molecular weight distribution.

Polyethylene waxes produced in the polyethylene production process by general slurry polymerization have a wide molecular weight distribution. The molecular weight of such a wide distribution is due to the radical polymerization reaction, which is essentially a polymerization condition of polyethylene. Depending on the tendency of the radicals generated in the polymerization to react, a long chain or short chain branching structure appears in the polyethylene. These branched structures ultimately broaden the molecular weight distribution of polyethylene, long chain structures affect melt properties, and short chain structures affect crystal structures. In the commercial process, after the polymerization is completed, the polyethylene is first separated into unreacted ethylene, and then centrifuged into a polyethylene low molecular weight wax containing crystalline polyethylene and a catalyst residue. In this case, the polyethylene wax produced as a by-product includes catalyst residues that adversely affect color, weather resistance, thermal stability, electrical properties, and contains a large amount of low boiling hydrocarbons. If the molecular weight distribution of the lower polyethylene wax is reduced and the catalyst residue is reduced, the lower polyethylene wax can be used as a filler for communication cables, a surfactant for printing ink or paper coating, a dispersant for a master batch, and a rubber release agent. Inherently dispersed lower polyethylene waxes are mixtures of molecules of various molecular weights, which imply that they can be useful products by changing the presence of various molecules in polyethylene with long or short chains.

As a technique for changing the existence of such chain structure, M. Dosiere's Crystallization of Polymers and P. Smith et al., 1992, published by Kluwer Academic Press. al., Macromolecules, 12 (3), 483-491 (1979), and are described using K. M. Scholesky et. al., Journal of Applied Polymer Science, 33, 2925-2934 (1987) and K. M. Scholesky et. al., Chemtech., Dec. 750-757 (1987) is known and using blending methods is described by P. Smith et. al., Macromolecules, 12 (3), 483-491 (1979) and are known using H. S. Cho et. al., Journal of Molecular Catalysis A: Chemical, 159, 203-213 (2000), E. Venema et al., Journal of Chromatography A., 765. 135-144 (1997), T. Shiono et al., Polymer , 38 (26), 6409-6411 (1997) and I. Okazaki et. al., Journal of Membrane Science, 141, 65-74 (1998), and U.S. Pat. No. 2372001, developed by RM Joyce et al. and U.S. Pat. have. If these are largely classified into methods, first, a method by polymerization, that is, a method requiring a high catalytic technology using a mixture of two to three transition metal catalysts in order to polymerize polyethylene having a narrow molecular weight distribution. Another method is a blending method that modulates molecular weight by physically or chemically treating the polymer. The above blending method may cause thermodynamic problems when physically mixing polymers having different molecular weights. And the pyrolysis method of decomposing the polymer under high temperature and atmospheric pressure of 300 ~ 500 ℃ in inert atmosphere to obtain narrow molecular weight distribution and low molecular weight polyethylene is most commonly used.However, due to the high pyrolysis temperature, energy demand is high and equipment facilities and fixed operation cost are high. There was a high issue. In addition, there is a problem in that the stability of the process or separation of the polymerization catalyst is difficult when using a catalyst or pyrolysis using hydrogen. The molecular weight control of polyethylene by supercritical fluid extraction focuses on the fact that polyethylene is a multi-molecular mixture, so that hydrocarbon molecules of low molecular weight are dissolved and removed using pentane or carbon dioxide, which can easily be supercritical. Polyethylene having a molecular weight in the range can be obtained, but there is a problem of long extraction time of 24 hours to 60 hours and high pressure and throughput of about 3 to 50 atmospheres.

In the present invention, to solve the problems of the prior art as described above, by narrowing the molecular weight by crystallization of polyethylene wax through a solution crystallization operation to increase the productivity in a short time, the polyethylene wax by-produced in the polyethylene process It is an object of the present invention to provide a method of purifying with high purity by dividing by various average molecular weights.

Still another object of the present invention is to provide a crystallization apparatus capable of fractionally controlling the molecular weight and purifying it with high purity through the solution crystallization operation of the polyethylene wax described above.

1 is a differential scanning calorie curve of a raw material polyethylene wax.

2 is an X-ray diffraction curve of polyethylene wax obtained from crystallization of raw polyethylene wax.

Figure 3 is a process chart showing the molecular weight crystallization fraction purification method of the polyethylene wax of the present invention.

Figure 4 is a process diagram of the crystallization apparatus capable of fractional molecular weight purification of the polyethylene wax of the present invention.

5 is a differential scanning calorie curve of polyethylene wax recovered by Example 1;

6 is a differential scanning calorie curve of polyethylene wax recovered by Example 2;

7 is a differential scanning calorie curve of polyethylene wax recovered by Example 3;

8 is a differential scanning calorie curve of polyethylene wax recovered in Example 4;

9 is a differential scanning calorie curve of polyethylene wax recovered by Example 5;

10 is a differential scanning calorie curve of polyethylene wax recovered in Example 6;

<Description of the symbols for the main parts of the drawings>

1: Dura-type crystallizer 2: Ventilation type stirred crystallizer

3: filter 4: stripper

In order to achieve the above object, the present invention in the method of crystallizing the lower polyethylene wax by-produced in the slurry polymerization process of polyethylene having a narrow molecular weight distribution and fractional purification by various average molecular weight,

Mixing the crystallization solvent and the raw material having a concentration range of 1 to 95% in a crystallizer (S1); Raising the temperature so that the raw material reaches a uniform liquid state (S2); Cooling in a range of an overcooling temperature of 30 to 110 ° C. and a cooling rate of 0.1 to 10 ° C. per minute (S3); Step S4 for crystallizing the cooled raw material; And filtration of the crystallized raw material (S5).

The crystallizer is characterized in that the dura-type crystallizer or ventilated crystallizer.

In addition, in the crystallizer capable of continuously operating the film-like crystallization group and the ventilated crystallization group used for the crystallization of the lower polyethylene wax produced in the slurry polymerization process of polyethylene,

A film-like crystallizer 1 equipped with a melter and a temperature control device; An aeration type stirred crystallizer (2) equipped with a stirrer and a temperature control device connected to the film-forming crystallizer (1) by a transfer pipe; A filter (3) equipped with a vacuum filtration device connected to the above-described ventilation type stirred crystallizer (2) by a transfer pipe; And a stripper 4 for removing the solvent.

Hereinafter, the present invention will be described in detail.

Polyethylene wax produced by the production of the conventional high density polyethylene wax process is composed of linear polyethylene molecules having a wide molecular weight distribution. The key to the crystallization process is to exploit the diffusion of chains of different lengths in non-uniformly present polyethylene wax, resulting in two solids with different molecular arrangements from a macroscopic perspective. That is, according to the equilibrium principle, the temperature in the crystallizer is adjusted to selectively form crystals with different melting points, that is, solids of different molecular arrangements.

The molecular weight distribution and melting point of the raw polyethylene wax and the crystallized polyethylene before crystallization used in the present invention were analyzed by Gel Permeation Chromatography (GPC) and Differential Scanning Calorimetry (DSC). Table 1 shows the physical properties of the polyethylene wax obtained in the general polyethylene slurry polymerization process. As can be seen from Table 1, the ratio of carbon (C) and hydrogen (H) is 1: 2.12, which is not completely in agreement with ethylene. As described above, it can be seen that a certain amount of low molecular weight material is contained. have. In addition, the polydispersity was 1.91 to 3.50, indicating that the polymer material and the low molecular material were mixed, and the catalyst residue content was shown to be high as 2015 to 3200 ppm.

Figure 1 shows that the melting curve is wide as a differential scanning calorie curve of the raw material polyethylene wax, it can be seen that the polymer material and the low molecular material is mixed.

FIG. 2 is an X-ray diffraction curve of polyethylene wax obtained from the raw material polyethylene wax and the crystallization, and the degree of crystallinity is calculated from the diffraction line, and the degree of crystallinity is about 28 to 30%, and a part of low molecular weight hydrocarbon is removed by crystallization. However, it can be seen that the molecular crystal structure of polyethylene wax did not change, and the tetragonal structure of polyethylene of 21.6 ° and 24.0 ° was maintained.

Figure 3 is a process chart showing the molecular weight crystallization fraction purification method of the polyethylene wax of the present invention. Mixing the crystallization solvent and the raw material having a concentration range of 1 to 95% in the crystallizer (S1); Raising the temperature so that the raw material reaches a uniform liquid state (S2); Cooling in a range of an overcooling temperature of 30 to 110 ° C. and a cooling rate of 0.1 to 10 ° C. per minute (S3); Step S4 for crystallizing the cooled raw material; And filtering the crystallized raw material (S5).

The dura-type crystallization apparatus which can be used as the above-mentioned crystallizer in the present invention comprises a tube for depositing crystals and a melter for melting polyethylene wax. In the crystallization method, polyethylene wax and a predetermined amount of solvent are put in a melter according to crystallization operation conditions and dissolved while maintaining a circulator temperature at 120 ° C. After completely dissolving the polyethylene wax, the crystallization operation is carried out by changing the working conditions in the range of a supercooling temperature of 30 to 110 ℃, a stirring speed of 200 to 400 rpm, a cooling rate of 0.1 to 10 ℃ per minute. The temperature difference between the temperature of the circulator and the thermostat causes the temperature difference necessary for crystallization, and crystals form and grow on the walls of the crystallizer. The growth rate of crystallization is controlled by the temperature of the solid-liquid interface. After the crystallization operation, the attached crystals are separated from the remaining solution to obtain a purified polyethylene wax.

In addition, in the present invention, it is possible to use a vent-type stirred crystallizer as the above-described crystallizer. The vent-type stirred crystallizer is composed of a circulator for keeping the temperature constant and a stirrer for dissolving and mixing the polyethylene wax before the crystallization operation. Depending on the crystallization conditions, polyethylene wax and a predetermined amount of solvent are added to the crystallizer and the temperature of the circulator is maintained at 120 ° C. After completely dissolving the polyethylene wax, the crystallization operation is performed by changing the temperature of the circulator according to the crystallization conditions. Unlike the duranic crystallizer, the temperature in the crystallization operation varies according to the temperature change, the stirring condition, and the cooling rate of the circulator, and the crystal is separated by filtration after the crystallization is completed. This method can be carried out stepwise and / or continuously, and it is possible to adjust the desired molecular weight distribution and melting point according to the temperature change of the circulator, the stirring conditions and the cooling rate.

4 is a flowchart of a crystallization apparatus capable of fractional molecular weight purification of the polyethylene wax of the present invention.

The crystallization apparatus used for the crystallization of the lower polyethylene wax produced in the slurry polymerization process of the polyethylene includes: a film-type crystallizer 1 having a melter and a temperature control device; An aeration type stirred crystallizer (2) equipped with a stirrer and a temperature control device connected to the film-forming crystallizer (1) by a transfer pipe; A filter (3) equipped with a vacuum filtration device connected to the above-described ventilation type stirred crystallizer (2) by a transfer pipe; And a stripper 4 for removing the solvent.

In the present invention, a method of fractionally purifying wax by molecular weight during the production of the polyethylene wax process through the crystallization apparatus of FIG. 4 is as follows.

The polyethylene wax as a raw material is first crystallized in the dura type crystallizer 1, and the high molecular weight crystalline polyethylene wax obtained here is recovered. The remaining residue is passed back into the aeration stirred crystallizer (2) where it is again crystallized and filtered through a filter (3) so that the solvent and the remaining polyethylene wax enter the stripper (4) and have a medium molecular weight. Recover the polyethylene wax. Finally, the stripper 4 recovers the solvent used for crystallization and finally produces low molecular weight crystalline polyethylene.

The molecular weight fractionation method of the polymer is closely related to the crystallization mechanism, and it is easy to control the physical properties of the polyethylene wax by changing the operating conditions of the solvent, temperature change, stirring condition, cooling rate, and crystallization device that dominate the crystallization. It is possible to fractionate the molecular weight of.

Solvents that can be used in the present invention should be capable of selectively dissolving only certain substances, have mild operating conditions, low cost, easy recovery of solvents and low deterioration and loss.

Since the polyethylene wax used in the present invention exhibits a linear molecular structure, it is possible to use aromatic hydrocarbons which are similar in molecular structure and insoluble in saturated and unsaturated aliphatic hydrocarbons which are expected to have high solubility but dissolve only certain components. Solvents with high boiling points or melting points are excluded for operating conditions or solvent recovery. The influence of the solvent on the crystallization depends on the viscosity, density, molecular weight, surface tension, etc., which are the basic physical properties of the solvent, and the operating conditions such as temperature, pressure, and concentration are combined to determine the characteristics of the crystallization process. Considering the conditions of the above solvents, solvents that can be used in the present invention include ortho xylene (o-xylene) of aromatic hydrocarbons, decane of saturated hydrocarbons, and methyl isobutyl ketone of ketones. ), Polycyclic aromatic decalin, olefin octene, acetate-based n-butyl acetate and the like can be used.

Hereinafter, the present invention will be described in more detail with reference to Examples. These examples are only for illustrating the present invention, various modifications are possible within the technical scope of the present invention, it is to those skilled in the art that the scope of the present invention is not limited to these examples. It is obvious that such modifications fall within the scope of the appended claims.

In the present invention, the subcooling temperature, the dissolution temperature, the cooling rate, the solvent, the composition and the crystallization time, and the crystallization apparatus were used as variables for the crystallization operation.

Example 1: 150 g of ortho-xylene and 68.8 g of polyethylene wax were added to a vent-type stirred crystallizer, and the circulator temperature was raised to 120 ° C. while stirring at 300 rpm to make a completely uniform liquid phase. This is followed by cooling from 120 ° C. to 30 ° C. at 1 ° C. per minute. When the mixed solution becomes cloudy, the liquid is filtered to recover the solids. The yield of polyethylene obtained at this time was 63.3%, and the catalyst residue was 71 ppm. 5 shows the differential scanning calorimetry curve for measuring the melting temperature of the recovered polyethylene wax. The melting temperature was 81.43 ° C, and the gel chromatography analysis showed that the polydispersity was 1.29 and the weight average molecular weight was 1038.

Example 2: The same conditions and methods as in Example 1 were conducted except that 74.5 g of polyethylene wax was used. The yield of polyethylene obtained at this time was 38.6%, catalyst residue content was 67ppm. Melting temperature of the recovered polyethylene wax is 80.09 ℃, Figure 6 shows the differential scanning calorie curve of the recovered polyethylene wax. Gel chromatography analysis showed that the polydispersity was 1.28 and the weight average molecular weight was 1038.

Example 3: The same conditions and methods as in Example 1 were conducted except that 45.0 g of polyethylene wax was used. The polyethylene yield was 63.2%, and the catalyst residue was 32 ppm. The melt temperature of the recovered polyethylene wax was 72.52 ° C., and FIG. 7 shows the differential scanning calorific curve of the recovered polyethylene wax. Gel chromatography analysis showed that the polydispersity was 1.12 and the weight average molecular weight was 917.

Example 4: The same conditions and methods as in Example 1 were conducted except that 154.2 g of polyethylene wax was used. The polyethylene yield was 30.4%, and the catalyst residue was 40 ppm. Melting temperature of the recovered polyethylene wax is 90.33 ° C, and Fig. 8 shows the differential scanning calorific curve of the recovered polyethylene wax. Gel chromatography analysis showed that the polydispersity was 1.35 and the weight average molecular weight was 1231.

Example 5 240 g of ortho-xylene and 160.0 g of wax polyethylene wax were added to a film crystallization unit, and the temperature was raised to 120 ° C. to make the polyethylene wax in a completely uniform liquid phase at a speed of 300 rpm. After maintaining the jacket temperature at 120 ° C., the temperature of the rod was cooled from 120 ° C. to 20 ° C. to 1 ° C. per minute to precipitate polyethylene wax. The yield of polyethylene obtained at this time was 5.0%, and the catalyst residue content was 75 ppm. The melting temperature of the recovered polyethylene wax was 94.59 ° C., and the differential scanning calorimetry curve of the recovered polyethylene wax was shown in FIG. 9. Gel chromatography analysis showed that the polydispersity was 1.51 and the weight average molecular weight was 1131.

Example 6: The same conditions and methods as in Example 5 were conducted except that 40.0 g of polyethylene wax was used. The yield of polyethylene obtained at this time was 7.4%, and the catalyst residue content was 97 ppm. The melt temperature of the recovered polyethylene wax was 100.20 ° C., and the differential scanning calorimetry curve of the recovered polyethylene wax was shown in FIG. 10. Gel chromatography analysis showed that the polydispersity was 1.36 and the weight average molecular weight was 1191.

Example 7: The same composition, conditions, and methods as in Example 1 were carried out except that the crystallization was carried out using a device capable of multi-stage and continuous operation instead of the uptake type agitated crystallizer. The polyethylene wax as a raw material is first crystallized in the dura type crystallizer 1, and the high molecular weight crystalline polyethylene wax obtained here is recovered. The remaining residue enters again the draft stirred crystallizer (2). Here again, after the crystallization operation, and filtered through the filter (3), the solvent and the remaining polyethylene wax enters the stripper (4) to recover the polyethylene wax having a medium molecular weight. Finally, the stripper recovers the solvent used for crystallization and finally produces low molecular weight crystalline polyethylene. The yield of polyethylene wax (product 1) recovered in the dura type crystallizer 1 was 9.7%, and the catalyst residue content was 85 ppm. The melt temperature of the recovered polyethylene wax was 92.98 ° C., and the gel chromatography analysis showed that the polydispersity was 1.50 and the weight average molecular weight was 1271. The yield of the polyethylene wax (product 2) recovered in the vent type stirred crystallizer (2) was 62.4%, and the catalyst residue content was 38 ppm. The melt temperature of the recovered polyethylene wax was 80.03 ℃, gel chromatography analysis showed that the polydispersity was 1.36, the weight average molecular weight was 1191. The yield of the polyethylene wax (Product 3) recovered from the stripper 4 was 27.9%, and the catalyst residue content was 70 ppm. The melt temperature of the recovered polyethylene wax was 71.33 ℃, the gel chromatography analysis showed that the polydispersity was 1.27, the weight average molecular weight was 985.

Example 8: The same conditions and methods as in Example 1 were conducted except that decane was used instead of ortho-xylene as the solvent. The yield of recovered polyethylene wax was 15%, and the catalyst residue content was 45 ppm. The melt temperature of the recovered polyethylene wax was 92.13 占 폚, and the gel chromatography analysis showed that the polydispersity was 1.30 and the weight average molecular weight was 1150.

Example 9: The same conditions and methods as in Example 1 were conducted except that methyl isobutyl ketone was used instead of ortho-xylene as the solvent. The yield of recovered polyethylene wax was 10.3%, and the catalyst residue content was 27 ppm. The melt temperature of the recovered polyethylene wax was 91.81 ° C., and the gel chromatography analysis showed that the polydispersity was 1.38 and the weight average molecular weight was 1157.

Example 10 The same procedure and procedure as in Example 1 was conducted except that decalin was used instead of ortho-xylene as the solvent. The yield of recovered polyethylene wax was 6.8%, and the catalyst residue content was 66 ppm. The melted temperature of the recovered polyethylene wax was 92.33 ° C. As a result of gel chromatography analysis, the polydispersity was 1.28 and the weight average molecular weight was 1142.

Example 11: The same conditions and methods as in Example 1 were carried out except that octene was used instead of ortho-xylene as the solvent. The yield of recovered polyethylene wax was 16.0%, and the catalyst residue content was 34 ppm. The melt temperature of the recovered polyethylene wax was 93.28 ℃, the gel chromatography analysis showed that the polydispersity was 1.30, the weight average molecular weight was 1153.

Example 12: The same conditions and methods as in Example 1 were carried out except that en-butyl acetate was used instead of ortho-xylene as the solvent. The yield of recovered polyethylene wax was 12.0%, and the catalyst residue content was 30 ppm. The melt temperature of the recovered polyethylene wax was 92.22 ° C., and the gel chromatography analysis showed that the polydispersity was 1.33 and the weight average molecular weight was 1135.

Crystallization conditions for the above Examples 1 to 12 are shown in Table 2, and the yield, catalyst residue content, melting temperature, and gel chromatography analysis results are shown in Table 3 below.

In the present invention, when the cooling rate is changed from 0.1 ° C per minute to 10 ° C, when the 1 ℃ per minute showed the optimal fractional conditions. The supercooling temperature was changed from 30 ℃ to 110 ℃ (saturation temperature was 120 ℃). As the supercooling temperature increased, the yield tended to increase 6 times due to the fast nucleation rate, but the catalyst residue content increased 1.8 times. The optimum fractionation condition was when the supercooling temperature was 90 ℃ and the catalyst residue content was less than 100ppm.

The fractionated polyethylene wax obtained according to the crystallization conditions of the present invention described above showed a catalyst residue of 100 ppm or less, a polydispersity of 1.3 or less, an average molecular weight of 900 to 1200, and a melting point of 70 to 100 ° C.

As described above, by changing the crystallization conditions using the crystallization method and apparatus of the present invention, it can be obtained by fractional purification of purified polyethylene wax having a narrow molecular weight distribution and having various melting points for various average molecular weights. The obtained polyethylene wax can also be used as a dispersant, surfactant, lubricant and release agent.

Claims (6)

In the method of crystallizing the lower polyethylene wax by-produced in the slurry polymerization process of polyethylene having a narrow molecular weight distribution and fractional purification by various average molecular weight, Mixing the crystallization solvent and the raw material having a concentration range of 1 to 95% in a crystallizer (S1); Raising the temperature so that the raw material reaches a uniform liquid state (S2); Cooling in a range of an overcooling temperature of 30 to 110 ° C. and a cooling rate of 0.1 to 10 ° C. per minute (S3); Step S4 for crystallizing the cooled raw material; And The method for filtering molecular weight crystallization fraction of polyethylene wax, characterized in that consisting of the step of filtering the crystallized raw material (S5). The method of claim 1, wherein the crystallization solvent is prepared by mixing one or two or more selected from saturated hydrocarbons, ketones, monocyclic aromatic hydrocarbons, polycyclic aromatic hydrocarbons, and olefinic hydrocarbons. The method of claim 1, wherein the crystallizer is a film-like crystallizer or a vented crystallizer. delete In the crystallizer, the crystallization solvent having a concentration range of 1 to 95% is mixed with the raw material, the temperature is raised so that the raw material reaches a uniform liquid state, a supercooling temperature of 30 to 110 ° C. and a cooling rate of 0.1 to 10 ° C. per minute Polyethylene wax produced by cooling to a range of the raw material, crystallized the cooled raw material, and filtered the crystallized raw material, the catalyst residue of 100ppm or less, polydispersity of 1.3 or less, average molecular weight of 900 to 1200 and 70 to 100 ℃ Polyethylene wax with a melting point. In a crystallization apparatus for fractional purification by various average molecular weights having a narrow molecular weight distribution by using a dissolution crystallization method of lower polyethylene wax which is by-product of slurry polymerization of polyethylene, A film-like crystallizer 1 equipped with a melter and a temperature control device; An aeration type stirred crystallizer (2) equipped with a stirrer and a temperature control device connected to the film-forming crystallizer (1) by a transfer pipe; A filter (3) equipped with a vacuum filtration device connected to the above-described ventilation type stirred crystallizer (2) by a transfer pipe; And Crystallization apparatus, characterized by consisting of a stripper (4) for removing the solvent.