Method of purifying polyolefin

Abstract

Provided is a method of purifying polyolefin, the method including the step of contacting linear low-density polyethylene synthesized by a gas phase polymerization reaction with a purge gas containing an ethylene gas and an inert gas in a purge bin. According to this purification method, residual alkene monomers with high carbon numbers may be removed in a simpler and more efficient manner.

Claims

1. A method of purifying polyolefin, the method comprising the step of contacting a linear low-density polyethylene including residual monomers with a purge gas containing an ethylene gas and an inert gas in a purge bin, wherein the linear low-density polyethylene is synthesized by a gas phase polymerization reaction, wherein the amount of the residual monomers is 0.01 to 5% by weight based on the total weight of the linear low-density polyethylene, wherein the residual monomers include ethylene and 1-octene, and wherein the step of contacting the linear low-density polyethylene with the purge gas is performed at a temperature of 25 to 100° C. and a pressure of 1 to 50 kgf/cm.sup.2.

2. The method of claim 1, wherein the linear low-density polyethylene is formed by a gas phase polymerization reaction of ethylene and alkene having 3 to 10 carbon atoms.

3. The method of claim 1, wherein the linear low-density polyethylene has a density of 0.500 to 1.000 g/ml.

4. The method of claim 1, wherein the linear low-density polyethylene has a melt index of 0.1 to 100 g/10 min.

5. The method of claim 1, wherein a volume ratio of the ethylene gas and the inert gas in the purge gas is 1:99 to 70:30.

6. The method of claim 1, wherein the purge gas has a temperature of 25 to 100° C.

7. The method of claim 1, wherein the purge gas has a pressure of 1 to 50 kgf/cm2.

8. The method of claim 1, wherein the step of contacting the linear low-density polyethylene with the purge gas is performed for 10 minutes to 12 hours.

9. The method of claim 1, further comprising the step of separating a gas which is produced by contacting the linear low-density polyethylene with the purge gas.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic illustration of a purge bin for a method of purifying polyolefin of an embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(2) Hereinafter, the present invention will be described in more detail with reference to the following Examples. However, the following Examples are for illustrative purposes only, and the invention is not intended to be limited by these Examples.

Examples 1 to 3

(3) Residual monomers in linear low density polyolefin, which were introduced into a purge bin, were determined as ethylene (C2) and 1-octene (C8), and an ethylene gas and a nitrogen gas were injected as a carrier gas and a purge gas, and then the monomers and gases were mixed and maintained. Then, it was examined whether the residual monomers were vaporized and separated from products. As a computer simulation, an Aspen Plus simulation program was used. Temperature and pressure, and feed amounts of individual components specified by the computer simulation are given in the following Table 1. The computer simulation results under respective conditions are given in the following Table 1.

Comparative Example 1

(4) A computer simulation was performed under the same computer simulation conditions as in Example 1, except that ethylene gas was not introduced as a carrier gas and a purge gas, and the results are given in the following Table 1.

Comparative Example 2

(5) A computer simulation was performed under the same computer simulation conditions as in Example 2, except that ethylene gas was not introduced as a carrier gas and a purge gas, and the results are given in the following Table 1.

Comparative Example 3

(6) A computer simulation was performed under the same computer simulation conditions as in Example 3, except that ethylene gas was not introduced as a carrier gas and a purge gas, and the results are given in the following Table 1.

(7) TABLE-US-00001 TABLE 1 Comparative Comparative Comparative Example Example Example Example Example Example Section 1 2 3 1 2 3 Temperature (° C.) 85 95 60 85 95 60 Pressure (kgf/cm.sup.2) 22 35 5 22 35 5 Feeding 1 Ethylene (kg/hr) 3.0 13.9 13.9 3.0 13.9 13.9 1-Octene (kg/hr) 5.0 2.4 2.9 5.0 2.4 2.9 2 Ethylene (kg/hr) 40 19.2 2 — — — Nitrogen (kg/hr) 50.0 19.2 19.2 50.0 19.2 19.2 Discharging 3 Ethylene (kg/hr) 43.0 33.1 15.9 3.0 13.9 13.9 1-Octene (kg/hr) 5.0 2.4 2.9 3.0 1.6 2.8 Nitrogen (kg/hr) 50.0 19.2 19.2 50.0 19.2 19.2 4 Ethylene (kg/hr) — — — Less About Less than 0.1% than 0.1% 0.1% 1-Octene (kg/hr) — — — 2.0 0.8 0.1 Nitrogen (kg/hr) — — — Less Less Less than than than 0.1% 0.1% 0.1%

(8) A feed line and a discharge line of 1 to 4 in Table 1 are as follows:

(9) 1. Residual monomers discharged from the reactor

(10) 2. Nitrogen gas and ethylene gas for transferring and purging

(11) 3. Vaporized monomers separated from products and inert gas

(12) 4. Liquid-state monomers remaining in products and inert gas

(13) As shown in Table 1, the computer simulation results of Example 1 show that all of the monomers introduced as reactants were vaporized and separated, but the results of Comparative Example 1 show that some of 1-octene passed through the purge bin remained in a liquid state, indicating incomplete separation of the monomers from the products, even though there is no difference except that no ethylene was introduced, compared to corresponding Example.

(14) According to the results, the same phenomenon was also observed, when Examples 2 and 3 performed in the same structure as in Example 1 but under different conditions of temperature, pressure, and composition of introduced monomers were compared to corresponding Comparative Examples 2 and 3, suggesting that the ethylene gas as well as nitrogen gas may be additionally used as the carrier gas and the purge gas to vaporize and separate alkene monomers with high carbon numbers, such as 1-octene.