Method for recovering ethylene and vinyl-based comonomer

Abstract

The present invention relates to a method for recovering ethylene and a vinyl-comonomer that is capable of improving the rate of recovery of unreacted monomers remaining after polymerization of ethylene and a vinyl-based comonomer and increasing process efficiency through the reduction of costs. Specifically, the method for recovering ethylene and a vinyl-comonomer includes: a step of polymerizing ethylene and a vinyl-based comonomer at a pressure of 1500 bar or more; a step of depressurizing the product obtained in the polymerization step including an ethylene-vinyl-based comonomer polymer, ethylene, and a vinyl-based comonomer to 0.1 bar to 5 bar; a step of adding ethylene to the product obtained in the polymerization step under the pressure of 0.1 bar to 5 bar; and a step of separating ethylene and a vinyl-based comonomer from the product obtained in the polymerization step to which the ethylene is added.

Claims

1. A method for recovering ethylene and a vinyl-based comonomer, comprising: a polymerization step of polymerizing ethylene and a vinyl-based comonomer at a pressure of 1500 bar or more; a step of depressurizing a product obtained in the polymerization step including an ethylene-vinyl-based comonomer polymer, ethylene, and a vinyl-based comonomer to 0.1 bar to 5 bar; a step of adding ethylene to the product obtained in the polymerization step under a pressure of 0.1 bar to 5 bar; and a step of separating ethylene and vinyl-based comonomer from the product obtained in the polymerization step to which ethylene is added.

2. The method for recovering ethylene and a vinyl-based comonomer according to claim 1, wherein a content of ethylene added to the product obtained in the polymerization step is 1% to 45% by weight, based on the weight of the ethylene-vinyl-based comonomer polymer contained in the product obtained in the polymerization step.

3. The method for recovering ethylene and a vinyl-based comonomer according to claim 1, wherein a boiling point of the vinyl-based comonomer is higher than a boiling point of ethylene.

4. The method for recovering ethylene and a vinyl-based comonomer according to claim 1, wherein the vinyl-based comonomer includes one or more vinyl acetates or alpha olefins selected from the group consisting of propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-undecene, 1-dodecene, 1-tetradecene, 1-hexadecene, and 1-eicosene.

5. The method for recovering ethylene and a vinyl-based comonomer according to claim 1, wherein in the product obtained in the polymerization step to which ethylene is added, a content of ethylene is 40% to 90% by weight based on the weight of a mixture of ethylene and the vinyl-based comonomer.

6. The method for recovering ethylene and a vinyl-based comonomer according to claim 1, wherein an average boiling point of ethylene and the vinyl-based comonomer contained in the product obtained in the polymerization step to which ethylene is added is lower than an average boiling point of ethylene and the vinyl-based comonomer contained in the product obtained in the polymerization step.

7. The method for recovering ethylene and a vinyl-based comonomer according to claim 1, wherein an average boiling point of ethylene and vinyl-based comonomer contained in the product obtained in the polymerization step to which ethylene is added is 60 C. or less.

8. The method for recovering ethylene and a vinyl-based comonomer according to claim 1, wherein the step of separating ethylene and vinyl-based comonomer from the product obtained in the polymerization step to which ethylene is added is carried out at a temperature of 150 C. to 200 C.

9. The method for recovering ethylene and a vinyl-based comonomer according to claim 1, further comprising a step of pressurizing separated ethylene and vinyl-based comonomer to 1500 bar or more, after the step of separating ethylene and vinyl-based comonomer from the product obtained in the polymerization step to which ethylene is added.

10. The method for recovering ethylene and a vinyl-based comonomer according to claim 1, wherein the step of depressurizing the product obtained in the polymerization step to 0.1 bar to 5 bar includes: a first depressurization step of reducing the pressure to 200 bar to 300 bar; a second depressurization step of reducing the pressure to 40 bar to 60 bar; and a third depressurization step of reducing the pressure to 0.1 bar to 5 bar.

11. The method for recovering ethylene and a vinyl-based comonomer according to claim 10, further comprising a step of separating ethylene and vinyl-based comonomer in a gaseous state and then applying a pressure of 1500 bar or more, after the first depressurization step.

12. The method for recovering ethylene and a vinyl-based comonomer according to claim 10, further comprising a step of separating ethylene and vinyl-based comonomer in a gaseous state and then applying a pressure of 1500 bar or more, after the second depressurization step.

13. The method for recovering ethylene and a vinyl-based comonomer according to claim 1, wherein the polymerization step of polymerizing ethylene and a vinyl-based comonomer proceeds at a high pressure of 1500 bar to 2500 bar.

14. The method for recovering ethylene and a vinyl-based comonomer according to claim 1, wherein a content of ethylene and vinyl-based comonomer contained in the product obtained in the polymerization step is 0.6% by weight or less, based on the weight of ethylene and vinyl-based comonomer separated from the product obtained in the polymerization step to which ethylene is added.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The FIGURE schematically shows the apparatus and process for recovering ethylene and vinyl-based comonomer according to one embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

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

Examples 1 to 7: Recovery of Ethylene and Vinyl-Based Comonomer

(3) Referring to the FIGURE, vinyl acetate monomers from a container 1 and ethylene monomers from a container 2 were respectively charged into a reactor 3 having a temperature of about 150 C. to 250 C. and a pressure of 2000 bar to undergo a free radical polymerization reaction. After the reaction was completed, the mixture of an ethylene-vinyl acetate polymer and unreacted monomers inside the reactor 3 was transferred to a first separator 4 having a temperature of about 200 C. to 250 C. and a pressure of 250 bar.

(4) In the first separator 4, the mixture of unreacted monomers was separated in a gaseous state in the upper portion of the first separator 4, and the ethylene-vinyl acetate polymer and some mixtures of unreacted monomers were separated in a liquid phase in the lower portion of the first separator 4. The mixture of unreacted monomers separated in the upper portion of the first separator 4 was compressed to a pressure of 2000 bar through a first compressor 7 having a pressure of 250 bar and then subjected to a polymerization reaction in the reactor 3. The ethylene-vinyl acetate polymer and the mixture of unreacted monomers separated in the lower portion of the first separator 4 were transferred to a second separator 5 having a temperature of about 150 C. to 200 C. and a pressure of 50 bar.

(5) In the second separator 5, the mixture of unreacted monomers was separated in a gaseous state in the upper portion of the second separator 5, and the ethylene-vinyl acetate polymer and some mixture of unreacted monomers were separated in a liquid phase in the lower portion of the second separator 5. The mixture of unreacted monomers separated in the upper portion of the second separator 5 was transferred to a second compressor 8 having a pressure of 50 bar and compressed to a pressure of 250 bar and then allowed to undergo a polymerization reaction in the residence reactor 3 via the first compressor 7 having a pressure of 2000 bar.

(6) The ethylene-vinyl acetate polymer and the mixture of unreacted monomers separated in the lower portion of the second separator 5 were transferred to a third separator 6 having a temperature of about 150 C. to 200 C. and a pressure of 1 bar, and then an ethylene monomer was additionally charged into the third separator 6 from the container 2 containing the ethylene monomer. At this time, based on the weight of the ethylene-vinyl acetate polymer contained in the third separator 6, the charging amount of the ethylene monomer was adjusted as shown in Table 1 below.

(7) Thereafter, in the third separator 6, the mixture of unreacted monomers was separated in a gaseous state in the upper portion of the third separator 6. The mixture of unreacted monomers separated in the upper portion of the third separator 6 was transferred to a third compressor 9 having a pressure of 1 bar and compressed to a pressure of 50 bar and then compressed to a pressure of 250 bar in the second compressor 8, compressed to a pressure of 2000 bar via the first compressor 7, and then the polymerization reaction was proceeded in the reactor 3 to recover ethylene and vinyl acetate.

Comparative Example: Recovery of Ethylene and Vinyl-Based Comonomer

(8) As shown in Table 1 below, after the ethylene-vinyl acetate polymer and the mixture of unreacted monomers separated in the lower portion of the second separator 5 were transferred to the third separator 6 having a temperature of 170 C. and a pressure of 1 bar, the recovery of ethylene and vinyl acetate was carried out in the same manner as in examples above, except that the step of additionally charging the ethylene monomer from a container 2 to a third separator 6 was omitted.

(9) TABLE-US-00001 TABLE 1 Content of ethylene monomer (based on the weight of the ethylene-vinyl acetate polymer) charged in the third separator 6 Comparative Category Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example Charging 37 32 26 21 16 11 5 0 amount of ethylene mononmer (wt %)

Experimental Example: Measurement of Efficiency of the Recovery Methods of Ethylene and Vinyl-Based Comonomer of Examples and Comparative Example

(10) 1. Average Boiling Point of the Mixture of Unreacted Monomers Contained in the Third Separator

(11) In the above examples and comparative example, the content of ethylene in the mixture of unreacted monomers and the average boiling point (1 atmospheric pressure condition) of the mixture of unreacted monomers depending on the content of ethylene monomer charged in a third separator 6 in the examples and comparative example were measured through a process simulation program, and the results are shown in Table 2 below.

(12) TABLE-US-00002 TABLE 2 Average boiling point of the mixture of unreacted monomers depending on the content of ethylene monomer charged in the third separator 6 Comparative Category Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example Charging 37 32 26 21 16 11 5 0 amount of ethylene monomer (wt %) Content 81 79 76 72 68 61 51 33 of ethylene in the mixture of unreacted monomers (wt %) Average 20.6 23.7 27 31.2 36.5 43.5 54 72.6 boiling point ( C.)

(13) As shown in Table 2 above, in the case of the recovery methods of ethylene and vinyl acetate according to the examples, the average boiling point of the mixture of unreacted monomers contained in the third separator was measured to be low, whereas in the case of the comparative example, it was measured to be relatively high as compared with the examples.

(14) That is, unlike the comparative example, the above examples can charge additional ethylene monomer into the third separator 6, thereby increasing the content of ethylene in the mixture of unreacted monomers. Consequently, the average boiling point of the mixture of unreacted monomers can be lowered, thus realizing more improvement in the rate of recovery of ethylene and vinyl acetate under the same temperature and pressure conditions.

(15) 2. Content of Residual Monomers Contained in the Final Product

(16) The content of residual monomers contained in the final product depending on the content of ethylene monomers charged in the third separator 6 in the examples and comparative examples was measured, and the results are shown in Table 3 below.

(17) TABLE-US-00003 TABLE 3 Content of residual monomers (based on the weight of the final product) contained in the final product depending on the content of ethylene monomer charged in the third separator 6 Comparative Category Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example Charging 37 32 26 21 16 11 5 0 amount of ethylene monomer (wt %) Content 0.24 0.26 0.28 0.31 0.36 0.44 0.58 0.89 of residual monomer in final product (wt %)

(18) As shown in Table 3, in the case of the recovery methods of ethylene and vinyl acetate according to the examples, the content of residual monomers in the final product was measured as low as 0.24 to 0.58% by weight, and in the case of the comparative example, the content of residual monomers was 0.89% by weight, which was relatively higher than in the examples.

(19) That is, unlike the comparative example, it was confirmed that the examples charge additional ethylene monomer into the third separator 6, thereby minimizing unreacted monomers remaining in the final product and improving the rate of recovery of ethylene and vinyl acetate.

EXPLANATION OF SIGNS

(20) 1: Container containing vinyl acetate monomer

(21) 2: Container containing ethylene monomer

(22) 3: Reactor

(23) 4: First separator

(24) 5: Second separator

(25) 6: Third separator

(26) 7: First compressor

(27) 8: Second compressor

(28) 9: Third compressor