WO2022073805A1

WO2022073805A1 - High temperature solution process for the copolymerization of ethylene with one ore more α-Olefin comonomer(s)

Info

Publication number: WO2022073805A1
Application number: PCT/EP2021/076667
Authority: WO
Inventors: Mohammad AL-HAJ ALI; Noureddine AJELLAL
Original assignee: Borealis Ag
Priority date: 2020-10-05
Filing date: 2021-09-28
Publication date: 2022-04-14
Also published as: TW202229365A

Abstract

A process for the polymerization of a polymer from an a-olefin monomer and one or more a-olefin comonomers in the presence of a catalyst, the process having a variation of reactor temperature and monomers concentrations (VTC) higher than 0, wherein the variation of reactor temperature and monomers concentrations (VTC) fulfils the criteria of equation (I): wherein Tf, Tb and Tt are the inlet feed temperature, the reactor temperature positioned 90° or more from the feeding point and the outlet temperature, respectively. (C 8 lC 2 )in and (C 8 lC 2 )out are the ratios of the concentrations of comonomer to monomer at the inlet and outlet, respectively.

Description

High temperature solution process for the copolymerization of ethylene with one ore more a-olefin comonomer(s)

The present invention is concerned with a high temperature solution process for the copolymerization of ethylene with one or more a-olefin comonomer(s) and an ethylene copolymer obtainable by said process.

Background

High temperature solution processes for olefin polymerization in general have proven to provide improved efficiency, i.e higher throughput at lower energy consumption for separation of volatile compounds. Furthermore, fouling problems have also been decreased by utilization of such processes.

In particular in high temperature solution polymerisation processes yielding copolymers of ethylene and an a-olefin, the catalyst must fulfil a set of very strict requirements. More particularily , for achieving a production of such copolymers with a density in the area of 0.85 kg/m³ and MFR2 values of about 0.3 g/10 min with high productivity, the ability for comonomer incorporation of the catalyst, in particular the reactivity for higher comonomers must be controlled. To withstand the high temperatures in such polymerization processes, the catalyst must be thermally stable. This can be achieved e.g. by incorporation of higher weight comonomers. However, higher weight comonomers tend to be less reactive and, hence, have lower incorporation numbers than lower weight comonomer alternatives.

WO 2007/136497 A2 discloses a process for the polymerization of ethylene and optionally one or more a-olefins under continuous, solution polymerization conditions to prepare a high molecular weight polymer comprising conducting the polymerization in the presence of a catalyst composition comprising a transition metal complex and an activating cocatalyst under conditions that result in a value for the polymerization index MT However, the incorporation rates of high comonomers into the polymer still are not satisfying.

Object of the invention

It is therefore still desired to find a high temperature solution process for the copolymerisation of ethylene with one or more a-olefin comonomer(s), which offers improved incorporation of comonomers, in particular of high molecular weight comonomers, into the polymer. It is further desired to find a copolymer of ethylene obtainable by such process. Summary of the invention

It now has been surprisingly found out that above-mentioned problem is solved by a process for the polymerization of a polymer from ethylene and one or more a-olefin comonomer(s) in the presence of a catalyst, whereby the process has variation of both reactor temperature and monomers concentrations greater than 0.

Brief description of the Figures

Figure 1 shows a schematic view of the cross-section of the reactor with the inlet feeding point and the measurement point of the reactor tempterature Tb.

Definitions

The variation of reactor temperature and monomers concentrations (VTC) is defined according to equation (I):

where 0 < VTC < 0.25 wherein

Tf, is the temperature measured at the inlet feed of the reactor, in particular the inlet feed for feeding the predominate part of solvent,

Tb is the reactor temperature measured at a point at the reactor wall rotated around the center of the cross-section at the feed inlet perpendicular to the axis of the reactor about 90° or more and 180° or less from the feeding point of the inlet,

Tt is the temperature measured at the outlet of the reactor, and

(Cs/C2)in and (Cs/C2)out are the ratios of the concentrations of comonomer to monomer at the inlet and outlet

For a better understanding of the positioning of Tb, it is referred to Figure 1 . The Figure shows a cross-section of the reactor, whereas the cross-section extends through the inlet feeding point and is perpendicular to the axis of the reactor. The inlet feeding point and the center of the cross section form a line. The rotation angle referred to is the rotation angle of said line around the center of the crosssection within the plane of the cross-section. This angle should be higher than 90° and lower than 180°. At the point where the rotated line crosses the reactor wall, the reactor tempterature Tb is measured. This index (VTC) makes a statement about the temperature and monomer/comonomer concentration gradient to be found within the reactor. Furthermore, this index makes a statement about the comonomer consumption in the reactor depending on the temperature differences found in the reactor. This parameter can be used to compare the efficiency of catalysts in terms of the total fraction of monomers fed to the process, which are incorporated into the polymer even without knowing the excact monomer conversion.

Detailed description

The process of the present invention is a process for the production of a copolymer made from ethylene and an a-olefin. Preferably, the process is a solution polymerization process, more preferably, a high temperature solution polymerization process.

In solution polymerisation processes the monomer is polymerised at a temperature in which the polymer is dissolved in the solvent mixture which is present in the process.

The process includes one or more polymerisation reactors. Suitable reactors include unstirred or stirred, spherical, cylindrical and tank-like vessels and recirculating loop reactors and tubular reactors. Such reactors typically include feeding points for monomer, optional comonomer, solvent, catalyst and optional other reactants and additives and withdrawal points for polymer solutions. In addition the reactors may include heating or cooling means.

Typically the solution polymerisation process is a high temperature solution polymerisation process, using a polymerisation temperature of greater than 100 °C. Preferably the polymerisation temperature is at least 110 °C, more preferably at least 150 °C. The polymerisation temperature can be up to 250 °C. The pressure in the solution polymerisation process is preferably in a range of from 30 to 200 bar, preferably from 50 to 150 bar and more preferably from 60 to 150 bar.

The monomer used in the present process is ethylene. EA comonomer is also used in the polymerisation process. The comonomer is different from ethylene and is selected from the group consisting of linear and cyclic olefins and diolefins having from 2 to 12 carbon atoms and the mixtures thereof. More preferably, the comonomer is an a-olefin different from ethylene and selected from the group consisting of linear olefins having from 3 to 12 carbon atoms and mixtures thereof, preferably 4 to 10 carbon atoms, most preferably 1 -octene.

The polymerisation is typically conducted in the presence of an olefin polymerisation catalyst. Preferably, the olefin polymerisation catalyst is a metallocene catalyst. More preferably, the olefin polymerisation catalyst is a catalyst as defined in WO 2018/108917 A1 or WO 2018/108918 A.

In solution polymerisation process a solvent is also present. The solvent is in liquid or supercritical state in the polymerisation conditions. The solvent is typically and preferably a hydrocarbon solvent. The liquid hydrocarbon solvent used is preferably a Cs-i2-hydrocarbon which may be unsubstituted or substituted by Ci-4 alkyl group such as pentane, methyl pentane, hexane, heptane, octane, cyclohexane, methylcyclohexane and hydrogenated naphtha. More preferably unsubstituted Ce- -hydrocarbon solvents are used.

Also other components may be added into the reactor. It is known to feed hydrogen into the reactor for controlling the molecular weight of the polymer formed during the polymerisation. Also the use of different antifouling compounds is known in the art. In addition different kinds of activity boosters or activity retarders may be used for controlling the activity of the catalyst.

The process of the present invention has a variation of both reactor temperature and monomers concentrations (VTC) of higher than 0, preferably higher than 0.01 , more preferably higher than 0.05, and most preferably higher than 0.08. Preferably, the catalyst variation of both reactor temperature and monomers concentrations (VTC) is lower than 10, preferably lower than 9.

The process of the present invention preferably has a catalyst productivity between 300 and 5000 kg/g, more preferably between 310 and 4500 kg/g, and most preferably between 320 and 4000 kg/g. Moreover, the comonomer to monomer feed ratio of ther process of the present invention is preferably between 0.01 and 3.0, more preferably between 0.05 and 2.75, and most preferably between 0.1 and 2.5.

Preferably, the process of the present invention is carried out in an imperfectly mixed reactor.

Moreover, the present invention targets a polymer obtainable by a process according to any of the preceding claims. Said polymer produced in the process of the present invention preferably has a density of between 850 and 950 kg/m³, more preferably 855 and 945 kg/m³ and most preferably 860 and 940 kg/m³. Furthermore, the polymer has a FRR10/2 between 5 and 15, preferably between 6 and 12 and most preferably between 7 and 10, wherein the FRR10/2 is the flow rate ratio between the MFR10 and the MFR2. Measurement and Simulation Methods

Melt flow rate

The melt flow rate MFR10 was determined at 230 °C under a load of 10 kg, is indicated in g/10 min and measured according to ISO 1133. Likewise, the melt flow rate MFR2 was determined at 230 °C under a load of 2.16 kg, is indicated in g/10 min and measured according to ISO 1 133.

The quantity FRR (flow rate ratio) is an indication of molecular weight distribution and denotes the ratio of flow rates at different loadings. Thus, for example, FRR10/2 denotes the value of MFR10/MFR2.

Density

Density of the polymer is measured according to ISO 1183-1 method A using compression moulded samples. It is indicated in kg/m³.

Content of comonomer

Ethylene content, i.e. , the content of ethylene units in propylene polymer was measured by Fourier transmission infrared spectroscopy (FTIR). A thin film of the sample (thickness approximately 250 pm) was prepared by hot-pressing. The area of -CH2- absorption peak (800 - 650 cm’¹) was measured with Perkin Elmer FTIR 1600-spectrometer. The method was calibrated by ethylene content data measured by ¹³C NMR.

The comonomer content is herein assumed to follow the mixing rule (equation II):

C_b = w - C₁ + w₂ - C₂ (II)

Where C is the content of comonomer in weight-%, w is the weight fraction of the component in the mixture and subscripts b, 1 and 2 refer to the overall mixture, component 1 and component 2, respectively.

Catalyst productivity

The productivity of the catalyst was determined as the amount of polymer produced in the process (in kg/h) divided by the amount of catalyst fed into the process (in g/h).

Examples

The Inventive Examples IE1 to IE5 are examples of high temperature solution copolymerization processes, in which ethylene has been copolymerized with 1 - octene (Cs). 1 -octene is a high molecular weight comonomer and, hence, is less reactive than lower weight comonomers. The polymers of IE1 to IE5 have been prepared in a process as described in the following.

Ethylene and 1 -octene are absorbed in the solvent, with the removal of the heat of absorption in a deep cooling unit. From the cooler, the monomer-comonomer solutions are fed to the reactor. The catalyst is fed separately to the reactor.

The polymerization is carried out in an agitated, completely liquid-filled vessel under adiabatic conditions. The heat of reaction is absorbed by the pre-cooled reactor feed. The reactor operates at a temperature between 130 and 250 °C and a pressure between 30 and 120 bar. The residence time is less than 10 minutes. Ethylene conversion is maximum 96 percent per pass.

For these examples, the density, melt flow rate and variation of reactor temperature and monomers concentrations (VTC) (table 1 ) have been determined.

Table 1 : Densities, melt flow rates and VTC values for the inventive examples IE1 -5.

Claims

1. A process for the polymerization of a polymer from ethylene and one or more a-olefin comonomer(s) in the presence of a catalyst, the process having a variation of reactor temperature and monomers concentrations (VTC) higher than 0, wherein the variation of reactor temperature and monomers concentrations (VTC) fulfils the criteria of equation (I):

where 0 < VTC < 0.25 wherein

Tt is the temperature measured at the outlet of the reactor, and

(Cs/C2)in and (Cs/C2)out are the ratios of the concentrations of comonomer to monomer at the inlet and outlet.

2. The process according to claim 1 , wherein the variation of reactor temperature and monomers concentrations (VTC) is higher than 0.001.

3. The process according to claim 2, wherein the variation of reactor temperature and monomers concentrations (VTC) is higher than 0.002.

4. The process according to any of the preceding claims, wherein the polymer has a density of between 850 and 950 kg/m³, preferably between 855 and 945 kg/m³ and most preferably between 860 and 940 kg/m³.

5. The process according to any of the preceding claims, wherein the polymer has a FRR10/2 between 5 and 15, preferably between 6 and 12 and most preferably between 7 and 10.

6. The process according to any of the preceding claims, wherein the catalyst productivity is between 300 and 5000 kg/g, preferably between between 310 and 4500 kg/g, and most preferably between between 320 and 4000 kg/g.

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7. The process according to any of the preceding claims, wherein the comonomer to monomer feed ratio is between 0.1 and 3.0, more preferably between 0.05 and 2.75, and most preferably between 0.1 and 2.5.

8. The process according to any of the preceding claims, wherein the process is performed at a temperature of more than 100 °C, preferably of at least 110 °C, and most preferably of at least 130 °C.

9. The process according to any of the preceding claims, wherein the process is performed at a temperature of not higher than 250 °C.

10. The process according to any of the preceding claims, wherein the process is performed at a pressure of between 30 and 200 bar, preferably between 50 and 150 bar, and most preferably between 60 and 150 bar.

11. A polymer obtainable by a process according to any of the preceding claims.

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