Process for avoiding phase separation during solution polymerization of ethylene-1-butene copolymers
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.
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 . 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 . 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 . 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 . 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 . 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 . 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 . 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 . 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 . 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 . 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 . 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 . 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 . The process according to claim 1 , wherein the polymerization pressure is in the range of 10 to 300 bar.