METHOD FOR PURIFYING POLYALKYLENE CARBONATE

Abstract

The present invention relates to a method for purifying polyalkylene carbonate. More specifically, a method for purifying polyalkylene carbonate is provided, which uses a multistage extraction column having the number of stages of at least 10 stages, using water for effectively removing by-products such as alkylene carbonate generated in a process for producing polyalkylene carbonate resin, thereby controlling the content of by-products to a certain level or less through a continuous operation, particularly, the extraction is performed at room temperature, thereby easily removing by-products in the resin without a high temperature volatilization.

Claims

1. A method for purifying polyalkylene carbonate comprising the steps of: providing a polymerization solution of polyalkylene carbonate including a polyalkylene carbonate, a by-product, and a solvent; and continuously removing the by-product from the polymerization solution by a multistage extraction method using water at room temperature, wherein the multistage extraction method is performed in a multistage extraction column having at least 10 stages and equipped with a stirrer so as to maintain a feed linear velocity of 0.1 to 1 cm/s, wherein the rotating speed of the stirrer is 100 to 200 rpm, and wherein a ratio between water and the polymerization solution of polyalkylene carbonate (S/F ratio) (Solvent/Feed ratio) is 1:1 to 5:1.

2. The method for purifying polyalkylene carbonate according to claim 1, wherein the ratio between water and a polymerization solution of polyalkylene carbonate (S/F ratio) (Solvent/Feed ratio) is 1:1 to 3:1.

3. The method for purifying polyalkylene carbonate according to claim 1, wherein the viscosity of the polymerization solution of polyalkylene carbonate is 50 to 300 cP.

4. The method for purifying polyalkylene carbonate according to claim 1, wherein, based on the total weight of a final polyalkylene carbonate resin, the by-product content in the resin is 2% by weight or less.

5. The method for purifying polyalkylene carbonate according to claim 1, wherein the multistage extraction column includes a multistage countercurrent extraction column for liquid-liquid extraction which is partitioned into at least ten or more plural stages by perforated plates and has an extraction unit having at least one baffle plate.

6. The method for purifying polyalkylene carbonate according to claim 5, wherein the extraction unit is partitioned into 10 to 150 stages, and the total length is 1 to 50 m.

7. The method for purifying polyalkylene carbonate according to claim 1, wherein the multistage extraction column includes a Karr-type column, a rotating disc contactor column, a Scheibel column, or a pulsed column.

8. The method for purifying polyalkylene carbonate according to claim 1, wherein the polymerization solution of polyalkylene carbonate is provided through polymerization of a monomer containing an epoxide compound and carbon dioxide in the presence of a catalyst and the solvent.

9. The method for purifying polyalkylene carbonate according to claim 8, wherein the catalyst is a zinc-based catalyst.

10. The method for purifying polyalkylene carbonate according to claim 8, wherein the epoxide compound is at least one selected from the group consisting of: an alkylene oxide having 2 to 20 carbon atoms which is unsubstituted or substituted with a halogen or an alkyl group having 1 to 5 carbon atoms; a cycloalkylene oxide having 4 to 20 carbon atoms which is unsubstituted or substituted with a halogen or an alkyl group having 1 to 5 carbon atoms; and a styrene oxide having 8 to 20 carbon atoms which is unsubstituted or substituted with a halogen or an alkyl group having 1 to 5 carbon atoms, and wherein the solvent is methylene chloride or ethylene dichloride.

11. The method for purifying polyalkylene carbonate according to claim 1, wherein the by-product includes an alkylene carbonate having 2 to 5 carbon atoms.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0072] FIG. 1 shows the configuration of a multistage countercurrent extraction column according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0073] Hereinafter, preferred examples of the present invention will be described in detail. It is to be understood, however, that these examples are for illustrative purposes only and are not to be construed as limiting the scope of the present invention.

Preparation Example 1

[0074] Polyethylene carbonate resin was continuously produced after connecting and installing a polymerization reactor, a water feed tank for removing by-products, a centrifugal dryer, an extruder for pelletization, and a pellet recovery device.

[0075] As the polymerization reactor, an autoclave reactor equipped with a stirrer was used, and a dry diethyl-zinc catalyst, a solvent, ethylene oxide (EO), and carbon dioxide were charged in this reactor. Solution polymerization was performed under the conditions shown in Table 1 below to prepare polyethylene carbonate. At this time, ethylene oxide (EO), carbon dioxide, and the solvent were purified before polymerization and maintained so that the water content was less than 10 ppm.

TABLE-US-00001 TABLE 1 Example 1 Cat.amt (g) 8 EO (g) 180 Solvent (MC) (g) 900 EO/cat. 99.8 CO.sub.2 (bar) 40 Temperature ( C.) 70 Time (h) 4 Yield (g) 90.5 Yield (g/g-cat) 11 Activity (g/g-cat.h) 2.83 Conversion ratio of (%) 25 EO TOF (mol/mol-cat.h) 6.28

Reference Example 1

[0076] Using the polymerization solution containing MC and polyethylene carbonate obtained under the conditions of Preparation Example 1, a stepwise extraction experiment was carried out as follows.

[0077] (1) One Stage Extraction Experiment

[0078] A polymer polymerization solution obtained by polymerization and water were mixed at a weight ratio of 1:1, placed in a beaker, mixed vigorously for 30 minutes, and then left until layer separation occurred. Then, the solvent of the organic solvent layer was removed, and the content of EC was analyzed by NMR. The content of EC before extraction was 14.68%, and the content of EC after extraction was lowered to 10.53%. (Hereinafter, % may mean wt % of EC in the polymer resin).

[0079] (2) One Stage Extraction Experiment (Time Change)

[0080] An extraction experiment was carried out in the same manner as in the above (1), except that the mixing time of the polymer solution and water was set low, to 10 minutes from 30 minutes.

[0081] As a result, the content of EC before extraction was 14.68%, and the content of EC after extraction was lowered to 10.28%. It can be seen that there is no significant difference in the extraction results of 10 minutes and 30 minutes.

Reference Example 2

[0082] Multistage Extraction Experiment of Number of 3 Times

[0083] The polymerization solution obtained by polymerization of polyethylene carbonate and water were mixed at a weight ratio of 1:1, placed in a beaker, mixed vigorously for 10 minutes, and left until layer separation occurred. For analysis, after obtaining a small amount of sample in the organic solvent layer, the content of EC was analyzed and all water was carefully removed from the remaining organic solvent layer. Then, the same amount of fresh water was charged in a beaker containing the organic solvent layer, followed by vigorous mixing for 10 minutes. The content of EC in the organic solvent layer was analyzed in the same manner. This method was then repeated one more time.

[0084] As a result, the content of EC before extraction was 14.68%, and it was found that the content of EC was 10.28% after the first extraction, 6.41% after the second extraction, and 4.26% after the third extraction.

Reference Example 3

[0085] Multistage Extraction Experiment of Number of 10 Times

[0086] The extraction experiment was performed in the same manner as in Reference Example 2, but was performed up to 10 times. As a result, the final EC content was shown to be 0.95%.

Example 1

[0087] <Method for Purifying Polyethylene Carbonate Using Multistage Extraction Column>

[0088] Multistage Extraction of Number of 3 Times

[0089] By using the Karr type of multistage extraction column of FIG. 1 under the following conditions, a continuous extraction test was performed on the polymerization solution of Preparation Example 1 to remove by-products.

[0090] Controllable Parameters

[0091] 1. Linear velocity/flow velocity: 0.3 cm/s or 0.6 cm/s, determined by the system

[0092] 2. Rotating speed: 150 to 180 rpm (affects dispersion degree and droplet size)

[0093] 3. Ratio of injecting water in a polymerization solution (solvent to feed ratio, S/F): 1 or 2

[0094] 4. Polymer solution injection viscosity (Feed viscosity): 200 cP or 60 cP

[0095] Fixed Parameters

[0096] 1. Number of stages: 50

[0097] A. Top (larger in diameter): 6 stages

[0098] B. Bottom (smaller in diameter): 44 stages

[0099] 2. Spacing among plates

[0100] Plate geometry: the top plate had a free open space of about 54.9% through feed droplets, and the bottom plate had a free open space of about 34.7%.

[0101] A sample in which the content of EC in the polymerization solution was 21.36 wt % was used as a feed, and was fed to the feed inlet 110 on the upper part of the multistage extraction column of FIG. 1. Then, water was fed to the solvent inlet 210 of the multistage extraction column, and the multistage extraction was continuously performed in the extraction unit 200 through mechanical stirring.

[0102] In this case, TSC (Total Solid Content) was 10 wt %, and the viscosity of the polymerization solution fed to the feed inlet was 180 cP (measured by a Brookfield viscometer). The weight average molecular weight of the resin was 216 kg/mol. The extraction results are shown in Table 2 below.

TABLE-US-00002 TABLE 2 Extraction condition Linear NMR data velocity Speed EC content in (cm/s) (rpm) S/F Operability resin (wt %) Raffinate 0.3 165 1 Ok 6.56 1-1 Raffinate 1- 0.3 180 1 Ok 7.04 2 Raffinate 1- 0.3 150 1 Ok 6.88 3

[0103] According to the present invention as shown in Table 2, when the EC content in the polymerization solution was 21.36 wt % through continuous operation using the multistage extraction column of FIG. 1 together with the conditions where the linear velocity, the stirrer velocity, and the S/F were specified, it was confirmed that the content was removed to 6.56 to 7.04 wt %, thereby controlling the by-product content to a certain level or less.

Example 2

[0104] Multistage Extraction of Number of 4 Times

[0105] A sample in which the content of EC in the polymerization solution was 6.35 wt % was used as a feed, and was fed to the feed inlet 110 on the upper part of the multistage extraction column of FIG. 1. Then, water was fed to the solvent inlet 210 of the multistage extraction column, and the multistage extraction was continuously performed in the extraction unit 200 through mechanical stirring. The operation parameter conditions of the multistage extraction column are the same as in Example 1.

[0106] In this case, TSC was 9.53 wt %, and the viscosity of the polymerization solution fed to the feed inlet was 55 cP (measured by a Brookfield viscometer). The weight average molecular weight of the resin was 187 kg/mol. The extraction results are shown in Table 3 below.

TABLE-US-00003 TABLE 3 Extraction condition NMR data Linear EC content velocity Speed in the resin (cm/s) (rpm) S/F Operability (wt %) Raffinate 2-1 0.3 180 1 OK 1.81 Raffinate 2-2 0.3 165 1 OK 2.06 Raffinate 2-3 0.6 150 2 OK 0.75 Raffinate 2-4 0.3 160 2 OK 0.72

[0107] According to the present invention as shown in Table 3, when the EC content in the polymerization solution was 6.35 wt % through continuous operation using the multistage extraction column of FIG. 1 together with the conditions where the linear velocity, the stirrer velocity, and the S/F were specified, it was confirmed that the content could be removed to a range of 0.72 to 2.02 wt %.

[0108] While the present invention has been specifically described with reference to particular embodiments thereof, it will be apparent to those skilled in the art that this specific description is merely a preferred embodiment and that the scope of the invention is not limited thereby. It is therefore intended that the substantial scope of the invention be defined by the appended claims and their equivalents.

EXPLANATION OF SIGN

[0109] 100: upper fixing part [0110] 110: Feed inlet [0111] 120: Extraction phase outlet [0112] 130: Drive assembly [0113] 200: Extraction unit [0114] 210: Solvent inlet [0115] 220: Raffinate [0116] 230: Interface between a heavy phase and a light phase [0117] 240: interface control unit [0118] 300: Lower fixing part