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US-12617876-B2 - Process for avoiding phase separation during solution polymerization of ethylene-1-butene copolymers

US12617876B2US 12617876 B2US12617876 B2US 12617876B2US-12617876-B2

Abstract

The present invention relates to a process for polymerizing ethylene-1-butene copolymers in a solution polymerization process by firstly modelling polymer systems for solution polymerization of ethylene-1-butene copolymers and then transferring pressure and temperature conditions from said modelled polymer systems to a solution polymerization process to ensure that the polymerized ethylene-1-butene copolymer is completely solved in the solvent during the polymerization process.

Inventors

  • Mohammad Al-Haj Ali
  • Noureddine Ajellal

Assignees

  • BOREALIS AG

Dates

Publication Date
20260505
Application Date
20210107
Priority Date
20200116

Claims (14)

  1. 1 . A process for polymerizing ethylene-1-butene copolymers in a solution polymerization process by firstly modelling polymer systems for solution polymerization of ethylene-1-butene copolymers and then transferring pressure and temperature conditions from said modelled polymer systems to a solution polymerization process, comprising the steps of a) determining the cloud points on the LCST curve for two or more model compositions of a specific ethylene-1-butene copolymer grade comprising ethylene monomer, 1-butene monomer, and ethylene-1-butene copolymer of a specific grade and solvent, whereby the model compositions differ in their weight amounts of at least one of ethylene monomer, 1-butene monomer, and ethylene-1-butene copolymer; b) developing a correlation for interpolating cloud points for compositions of said specific ethylene- 1 -butene copolymer grade comprising ethylene monomer, 1-butene monomer, ethylene-1-butene copolymer of said specific grade and solvent with different weight amounts of at least one of the ethylene monomer, 1-butene monomer, ethylene-1-butene copolymer of said specific grade from the cloud points determined for said model compositions; c) predicting phase separation for said specific ethylene- 1 -butene copolymer grade by interpolating the cloud points from said correlation for a composition of said specific ethylene-1-butene copolymer grade comprising ethylene monomer, 1-butene monomer, ethylene-1-butene copolymer of said specific grade with given weight amounts of at least one of ethylene monomer, 1-butene monomer, ethylene-1-butene copolymer; d) selecting pressure and temperature conditions, which in the predicted phase separation data show that the ethylene-1-butene copolymer is completely solved in the solvent; e) adjusting at least one parameter selected from the process temperature and pressure in at least one solution polymerization reactor, and optionally the first heat exchanger downstream from the at least one solution polymerization reactor, to said selected pressure and temperature conditions during a solution polymerization process of an ethylene-1-butene copolymer of said specific grade, and f) polymerizing ethylene monomer and 1-butene monomer in a solvent in said at least one solution polymerization reactor at the adjusted process temperature and/or pressure in the presence of a polymerization catalyst to obtain an ethylene-1-butene copolymer of said specific grade, which is completely solved in said solvent.
  2. 2 . The process according to claim 1 , wherein the cloud points on the LCST curve is determined by varying one of the parameters of temperature and pressure of each model composition, while keeping the other of said parameters constant and detecting phase separation.
  3. 3 . The process according to claim 1 , wherein cloud points for each model composition over a temperature span of from 150° C. to 250° C. are determined.
  4. 4 . The process according to claim 1 , wherein the amount of ethylene-1-butene copolymer in the model composition is in the range of from 10 wt % to 45 wt %, based on the total amount of the model composition.
  5. 5 . The process according to claim 1 , wherein the amount of ethylene monomer in the model composition is in the range of from 0.1 wt % to 10.0 wt %, based on the total amount of the model composition.
  6. 6 . The process according to claim 1 , wherein the amount of 1-butene monomer in the model composition is in the range of from 0.1 wt % to 20.0 wt %, based on the total amount of the model composition.
  7. 7 . The process according to claim 1 , wherein the correlation is established from models selected from free energy models, equation of state(ES) models or polynomial models.
  8. 8 . The process according to claim 1 , wherein the correlation is established from a polynomial model, which is developed from the trend lines of the determined cloud points.
  9. 9 . The process according to claim 1 , wherein the correlation is established from a polynomial model in which the cloud point pressure is given as a polynomial function of the temperature and the weight amounts of ethylene monomer, 1-butene monomer and ethylene-1-butene copolymer.
  10. 10 . The process according to claim 1 , wherein phase separation is predicted by utilizing the developed correlation for different temperatures and weight amounts of 1-butene monomer over a span of weight amounts of ethylene-1-butene copolymer of from 10 wt % to 45 wt % and a span of weight amounts of ethylene monomer of from 0.1 wt % to 10.0 wt %, each based on the total amount of the composition of said specific ethylene-1-butene copolymer grade.
  11. 11 . The process according to claim 1 , wherein the weight amount of 1-butene monomer are within the range of from 0.1 wt % to 20.0 wt %, based on the total amount of the composition of said specific ethylene-1-butene copolymer grade.
  12. 12 . The process according to claim 1 , wherein the ethylene-1-butene copolymer of said specific grade is a linear low density ethylene-1-butene copolymer.
  13. 13 . The process according to claim 1 , wherein the polymerization temperature is in the range of from higher than 100° C. to up to 250° C.
  14. 14 . The process according to claim 1 , wherein the polymerization pressure is in the range of 10 to 300 bar.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This patent application is the U.S. national phase of International Application No. PCT/EP2021/050147, filed on Jan. 7, 2021, which claims the benefit of European Patent Application No. 20152180.4, filed Jan. 16, 2020, the disclosures of which are incorporated herein by reference in their entireties for all purposes. The present invention relates to a process for polymerizing ethylene-1-butene copolymers in a solution polymerization process by firstly modelling polymer systems for solution polymerization of ethylene-1-butene copolymers and then transferring pressure and temperature conditions from said modelled polymer systems to a solution polymerization process to ensure that the polymerized ethylene-1-butene copolymer is completely solved in the solvent during the polymerization process. TECHNICAL BACKGROUND The production of linear low density polyethylene (LLDPE) is typically carried out in solution polymerization. In this type of polymerization, ethylene monomer, optional comonomers and a polymerization catalyst are dissolved in an inert hydrocarbon solvent and polymerized to form an ethylene based polymer. The polymer properties thereby are usually adapted by altering the ethylene and comonomer ratios. In solution polymerization it is important to keep the solution homogenous through the polymerization process, i.e. that through the complete polymerization process the solution is maintained a single phase liquid system in order to ensure the productivity of the process. In a two phase liquid system (L-L system) the monomers would enrich in one liquid phase and the produced ethylene based polymer would enrich in the second liquid phase. In order to maintain the polymerization process in a single phase liquid system the polymerization conditions, especially polymerization temperature and pressure, need to chosen accordingly. FIG. 1 shows a typical phase diagram with the different phases depending on the polymerization pressure and temperature. FIG. 1 is taken and adapted from FIG. 2 of EP 1 339 756 B 1. The border between the single phase liquid region and the two phase L-L region is marked by the lower critical solution temperature (LCST) curve, also identified as cloud-point curve. The LCST curve shows the p, T conditions of the transfer from the single phase liquid region to the two phase liquid region (L-L region). Thereby, the LCST curve in not only affected by the polymerization conditions but also by the monomer and comonomer ratios and the polymer concentration in the solution. During the polymerization process changes in the conditions regarding the temperature, pressure or polymer concentration inside the equipment, especially the polymerization reactor or the downstream heat exchanger, can cause phase separation, especially if these changes happen uncontrolled. These changes then can easily cause disturbances in the polymerization process. It is thus essential to understand how a change of the polymerization conditions can effect the phase system in the process and which measured need to be taken to maintain a single phase liquid system during operation. For each solution polymerization for polymerizing a low density polyethylene with a specific set of polymer properties the polymerization conditions need to be experimentally determined in order to ensure maintenance of a single phase liquid system not only in the polymerization reactor but also in the downstream processing steps, especially the downstream heat exchanger. Experimental determination of the polymerization conditions afford elaborate series experiments for each and every set of the monomer and comonomer ratios and the polymer concentration in the solution. It is therefore of interest to establish thermodynamic models or mathematical correlations which describe such polymer systems that show single phase liquid regions in the p, T phase diagrams in correlation to the monomer and comonomer ratios and the polymer concentration in the solution. Such models and correlations would significantly reduce preparatory work before establishing a solution polymerization process and thus would significantly reduce production costs, would allow for faster adaptation of solution polymerization processes and would increase production safety by reducing unexpected disturbances of the polymerization process. The present invention proposes a process for polymerizing ethylene-1-butene copolymers in a solution polymerization process by firstly modelling polymer systems for solution polymerization of ethylene-1-butene copolymers and then transferring pressure and temperature conditions from said modelled polymer systems to a solution polymerization process to ensure that the polymerized ethylene-1-butene copolymer is completely solved in the solvent during the polymerization process. SUMMARY OF THE INVENTION The present invention relates to a process for polymerizing ethylene-1-butene copolymers in a solution p