FIELD OF THE DISCLOSURE

The present disclosure relates to polymerization process, and especially to a solution polymerization process.

BACKGROUND OF THE DISCLOSURE

Document WO 2014/058663 A1 discloses a polymerization process of producing ethylene- alpha-olefin polymer. The polymerization process comprises supplying at a feed temperature a feed containing ethylene, at least one alpha-olefin and optionally, a diene in a solvent, the solvent is supplied at a solvent feed rate; supplying at a catalyst feed rate a catalyst to a reactor, and contacting the feed with the catalyst to produce a reaction mixture containing the polymer. The document also relates to processes for improving the energy utilization of polymerization processes, wherein the process comprises decreasing the feed temperature, decreasing the solvent feed rate, and decreasing the catalyst feed rate.

Document WO 2010/027491 A1 discloses a process for feeding ethylene into a polymerization system operating in a liquid phase or supercritical phase, including providing a low -pressure ethylene stream, one or more low-pressure C3 to C20 monomer streams, an optional low-pressure inert solvent/diluent stream, and one or more reactors, metering and mixing the streams together to form an ethylene-carrying low-pressure blended liquid feed stream, pressurizing the ethylene-carrying low-pressure blended liquid feed stream to the polymerization system pressure with one or more high-pressure pumps to form an ethylene-carrying high-pressure blended reactor feed stream, and feeding the ethylene- carrying high-pressure blended reactor feed stream to the one or more reactors. The monomer recycle stream may also be optionally blended with the ethylene feed stream and the C3 to C20 higher olefin before being pressurized to the reactor pressure.

Document WO 201 1/087728 A2 discloses a plant for the continuous solution polymerization of one or more monomers in a solvent, e.g., a hydrocarbon solvent. In one aspect, the plant comprises a high-pressure pump and at least one heat exchanger downstream of the pump. In another aspect, a feed is cooled by three heat exchangers, which are refrigerated by means of a common three-stage compressor. In another aspect, the plant comprises a primary reactor and a secondary reactor arranged to operate in parallel, in which the ratio of volume of the primary reactor to the secondary reactor is in the range of 60:40 to 95:5. In another aspect, a method of defouling a heat exchanger is provided in which the level of liquid refrigerant in the heat exchanger is temporarily lowered.

In current solution alpha-olefin polymerization processes, the control of the reactor temperature is usually done by feeding low temperature stream of hydrocarbons, i.e. solvent, monomer and comonomer. The cool hydrocarbons absorb the heat produced by the polymerization reaction. Generally, the feeding temperature is kept very low, preferably < -30 °C, to ensure having enough capacity to produce the required amount of polymer while still keeping the required polymer concentration inside the reactor. Moreover, to ensure having high-quality products, it is important to remove as much as possible hydrocarbons in the separators downstream of the reactor. Therefore, the product stream is heated up before being fed to the separator.

A problem with the known polymerization processes is that the cooling of the hydrocarbons before feeding them to the reactor and the heating of the product stream requires a lot of energy.

BRIEF DESCRIPTION OF THE DISCLOSURE

An object of the present disclosure is to provide a polymerization process to solve the above problem.

The object of the disclosure is achieved by a polymerization process, which is characterized by what is stated in the independent claim. The preferred embodiments of the disclosure are disclosed in the dependent claims.

The disclosure is based on the idea of providing an alpha-olefin monomer, at least one alpha-olefin comonomer and a hydrocarbon solvent at a temperature of greater than -30 °C to less than 10 °C, and polymerizing the alpha-olefin monomer and the alpha- olefin comonomer in the presence of a polymerization catalyst in the polymerization reactor.

An advantage of the polymerization process of the disclosure is that the need for initial cooling of the hydrocarbons before feeding them to the polymerization reactor is reduced or even prevented, thus reducing the amount of energy needed for cooling the hydrocarbons. Another advantage is that because the temperature of the hydrocarbons fed into the polymerization reactor is higher, the temperature of the product stream of the polymerization reactor is also higher. This reduces the need for heating up the outlet stream for a subsequent separation step, thus reducing the amount of energy needed for heating up the outlet stream. The reduction of energy needed for cooling the hydrocarbons or for heating up the outlet stream is obtained while still producing the same grades, i.e. while maintaining the same product. The polymerization process of the disclosure is usable with one, two or more reactors, in series or in parallel.

DETAILED DESCRIPTION OF THE DISCLOSURE

Polymerization

The disclosure relates to a polymerization process. The polymerization may be conducted in one or more polymerization reactors arranged in parallel or in series. It is obvious that where the text refers to one polymerization reactor it can be equally applied to more than one polymerization reactor, and in specific to any one of the polymerization reactors. In addition, where a reference to more than one polymerization reactor has been made it can equally be applied to one polymerization reactor.

In the polymerization reactors, olefin monomers, one or more polymerization catalysts, one or more comonomers, optionally one or more chain transfer agents, and one or more solvents are used for conducting a polymerization.

The polymerization process comprises providing a monomer stream. The monomer stream comprises alpha-olefin monomer. According to an embodiment, the alpha-olefin monomer is selected from the group of ethylene and propylene.

The polymerization process comprises passing the monomer stream having a temperature in the range of greater than -30 °C to less than 10 °C into a polymerization reactor. According to an embodiment of the disclosure, the monomer stream has a temperature of at least -29 °C, typically -29 °C to less than 10 °C, preferably at least -28 °C, typically -28 °C to less than 10 °C, more preferably at least -27 °C, typically -27 °C to less than 10 °C and most preferably at least -26 °C, typically -26 °C to less than 10 °C, such as at least -25 °C, typically -25 °C to less than 10 °C, when passed into the polymerization reactor. According to an embodiment of the disclosure, the monomer stream has a temperature of at most 9 °C, preferably at most 7 °C, more preferably at most 5 °C and most preferably at most 0 °C, such as at most -5 °C, when passed into the polymerization reactor.

The polymerization process comprises providing a comonomer stream. The comonomer stream comprises at least one alpha-olefin comonomer. According to an embodiment, the at least one alpha-olefin comonomer is selected from the group of propene, 1 -butene, 1-pentene, 1-hexene, 1-heptene and 1-octene, or mixtures thereof. The polymerization process comprises passing the comonomer stream having a temperature in the range of greater than -30 °C to less than 10 °C into the polymerization reactor. According to an embodiment of the disclosure, the comonomer stream has a temperature of at least -29 °C, typically -29 °C to less than 10 °C, preferably at least -28 °C, typically -28 °C to less than 10 °C, more preferably at least -27 °C, typically -27 °C to less than 10 °C and most preferably at least -26 °C, typically -26 °C to less than 10 °C, such as at least -25 °C, typically -25 °C to less than 10 °C, when passed into the polymerization reactor. According to an embodiment of the disclosure, the comonomer stream has a temperature of at most 9 °C, preferably at most 7 °C, more preferably at most 5 °C and most preferably at most 0 °C, such as at most -5 °C, when passed into the polymerization reactor.

The polymerization process comprises providing a hydrocarbon solvent stream. The hydrocarbon solvent stream comprises a hydrocarbon solvent capable of dissolving the alpha-olefin monomer and the alpha-olefin comonomer in polymerization conditions. The solvent may be any suitable straight-chain or branched alkyl having from 3 to 20 carbon atoms, a cyclic alkyl, optionally having alkyl substituents, having from 5 to 20 carbon atoms, or an aryl, optionally having alkyl substituents, having from 6 to 20 carbon atoms, or a mixture of two or more of the above-listed compounds. The hydrocarbon solvent must be inert towards the polymerization catalyst and the monomers. The hydrocarbon solvent should be stable in the polymerization conditions. According to an embodiment, the polymerization conditions include a temperature of 120 °C to 250 °C and a pressure of 50 to 300 bar. According to an embodiment, the hydrocarbon solvent is mixture of hydrocarbons with major components having a number of carbon atoms between 4 and 9; i.e. C4— C9.

The polymerization process comprises passing the hydrocarbon solvent stream having a temperature in the range of greater than -30 °C to less than 10 °C into the polymerization reactor. According to an embodiment of the disclosure, the hydrocarbon solvent stream has a temperature of at least -29 °C, typically -29 °C to less than 10 °C, preferably at least -28 °C, typically -28 °C to less than 10 °C, more preferably at least -27 °C, typically -27 °C to 40 °C and most preferably at least -26 °C, typically -26 °C to less than 10 °C, such as at least -25 °C, typically -25 °C to less than 10 °C, when passed into the polymerization reactor. According to an embodiment of the disclosure, the hydrocarbon solvent stream has a temperature of at most 9 °C, preferably at most 7 °C, more preferably at most 5 °C and most preferably at most 0 °C, such as at most -5 °C, when passed into the polymerization reactor. According to an embodiment, the polymerization process comprises combining at least two of the monomer stream, the comonomer stream and the hydrocarbon solvent stream before passing them into a polymerization reactor. According to another embodiment, the monomer stream, the comonomer stream and the hydrocarbon solvent stream are passed into the polymerization reactor separately.

The polymerization process may comprise using a chain transfer agent for controlling the molecular weight and molecular weight distribution (broadening) of the polymer, as it is known in the art. A suitable chain transfer agent is, for instance, hydrogen.

The polymerization process may also comprise using a scavenger.

The polymerization process comprises providing an activated catalyst stream. The polymerization process comprises passing the activated catalyst stream into the polymerization reactor. According to an embodiment, the activated catalyst stream is produced by contacting a polymerization catalyst, i.e. one or more catalysts, and an activator, i.e. one or more activators, for activating the polymerization catalyst. Polymerization catalyst and the activator can be contacted upstream of the polymerization reactor or in the polymerization reactor. The polymerization catalyst is preferably provided as a catalyst stream. The activator is preferably provided as an activator stream.

The polymerization process comprises contacting the monomer stream, the comonomer stream, the hydrocarbon solvent stream, the activated catalyst stream, the optional chain transfer agent and the optional scavenger in the polymerization reactor to form a reaction mixture comprising an alpha-olefin polymer. The reaction mixture also comprises the hydrocarbon solvent, unreacted alpha-olefin monomer, unreacted alpha-olefin comonomer and the optional chain transfer agent.

Preferably, the polymerization process is continuous, and thus the monomer stream, the comonomer stream, the hydrocarbon solvent stream and the activated catalyst stream are passed into the polymerization reactor continuously.

The temperature and the pressure in the polymerization reactor is such that the alpha- olefin polymer formed in the polymerization reaction is completely dissolved in the reaction mixture. The temperature in the polymerization reactor is suitably greater than the melting temperature of the alpha-olefin polymer. Thus, the temperature is suitably from 120 °C to 240 °C, depending on the content of comonomer units in the polymer.

The pressure in the polymerization reactor depends on the temperature, on one hand, and on the amount of the monomer and the comonomer in the reaction mixture, on the other hand. The pressure is suitably from 50 to 300 bar, preferably from 50 to 250 bar and more preferably from 70 to 200 bar. For example, the residence time in the polymerization reactor is 1 to 30 minutes.

The polymerization process comprises withdrawing a first product stream from the polymerization reactor. The first product stream comprises hydrocarbon solvent and alpha- olefin polymer dissolved in the hydrocarbon solvent. According to an embodiment, the first product stream further comprises unreacted alpha-olefin monomer and unreacted alpha- olefin comonomer. The first product stream may also comprise the chain transfer agent.

In continuous polymerization process, the first product stream is withdrawn continuously from the polymerization reactor.

According to an embodiment, the polymerization process is conducted adiabatically. Heating

Before feeding the first product stream from the polymerization reactor to a separation step, the stream is usually preheated in at least one heating step, preferably in two heating stages including a pre-heating stage and a final-heating stage.

Typically, the temperature of first product stream before entering the pre-heating stage is from 120 °C to 240 °C, preferably from 140 °C to 220 °C, most preferably from 150 °C to 200 °C, when the polymer is a homo or copolymer of ethylene. Typically, the temperature of the first product stream before entering the pre-heating stage is from 120 °C to 250 °C, preferably from 140 °C to 235 °C. most preferably from 150 °C to 225 °C, when the polymer is a homo- or copolymer of propylene.

The temperature of the first product stream immediately downstream of the pre-heating stage is typically from 160 °C to 240 °C and preferably from 170 °C to 220 °C, most preferably from 180 °C to 200 °C, when the polymer is a homo- or copolymer of ethylene. The temperature of the first product stream immediately downstream of the pre-heating stage is typically from 200 °C to 250 °C and preferably from 210 °C to 250 °C, most preferably from 220 °C to 250 °C, when the polymer is a homo- or copolymer of propylene.

It is preferred that the pressure of the first product stream is not substantially affected by the pre-heating stage. The pressure is suitably from 50 to 300 bar, preferably from 50 to 250 bar and more preferably from 70 to 200 bar.

The first product stream is passed from the polymerization reactor to the pre-heating stage. The purpose of the pre-heating stage is to preheat the first product stream before it enters the separation step. The pre-heating is usually effected by a heat exchanger. For instance, the first product stream is distributed in a number of tubes and a heating fluid is passed to contact the tubes thereby heating the solution flowing therein.

The purpose of the pre-heating step is to recover heat from the process streams thereby improving the economy of the process.

The heating fluid may be any process fluid, which contains recoverable heat. Preferably, a third product stream recovered from the separation step as described below is used as the heating fluid. During the process, the heating fluid, e.g. the third product stream, is cooled. It is preferred to withdraw so much heat from the third product stream that at least a part of the third product stream condenses in the pre-heating stage.

When the pre-heating is effected by a heat exchanger transferring heat from the third product stream withdrawn from the separating step on the first product stream from the polymerization reactor, the third product stream cooled in the heat exchanger is preferably at least partially condensed.

Preferably, the pre-heating is effected by a heat exchanger transferring heat from the separation on the first product stream from the polymerization reactor, whereby the stream cooled in the heat exchanger is at least partially condensed.

When the unreduced reactor effluents stream from the polymerization reactor is heated in two stages including a pre-heating stage and a final heating stage, the final heating stage preferably includes heating of the stream to at least 200 °C.

Preferably, the final-heating stage includes heating of the first product stream to preferably at least at 180 °C, more preferably at least at 200 °C and most preferably at least 210 °C.

The purpose of the final heating stage is to heat the first product stream to a required temperature for the separation step. The final heating stage may be required because the recoverable heat in the heating medium in the pre-heating stage may be insufficient for reaching the desired temperature of the first product stream.

The final heating stage may be conducted by using similar principles as in the pre-heating stage. However, the temperature of the heating fluid used in the final heating stage is suitably controlled to a temperature, which allows heating of the first product stream to the desired temperature. Thereby it is preferred that the stream of the heating fluid used in the final heating stage is heated to a desired temperature prior to introducing it into the final heating stage. According to one embodiment of the disclosure, the temperature of the first product stream is measured downstream of the pre-heating stage and the flow rate of the heating fluid used in the final heating stage is adjusted based on the difference between the measured temperature and the desired temperature of the first product stream.

The temperature of the unreduced reactor effluents stream downstream of the final heating stage is typically from 200 °C to 300 °C, preferably from 210 °C to 260 °C and more preferably from 210 °C to 230 °C, when the polymer is a homo- or copolymer of ethylene. The temperature of the first product stream downstream of the final heating step is typically from 200 °C to 300 °C, preferably from 210 °C to 270 °C and more preferably from 220 °C to 250 °C, when the polymer is a homo- or copolymer of propylene.

It is preferred that the pressure of the unreduced reactor effluents stream is not substantially affected by the final heating step. The pressure is suitably from 50 to 300 bar, preferably from 60 to 250 bar and more preferably from 70 to 200 bar.

Separation step

The polymerization process comprises a separation step for separating a second product stream and a third product stream from the first product stream. The second product stream comprises majority of the alpha-olefin polymer present in the first product stream. In other words, the second product stream comprises more than 50 % by weight of the alpha-olefin polymer present in the first product stream. According to an embodiment, the third product stream comprises majority of the solvent, unreacted alpha-olefin monomer and unreacted alpha-olefin comonomer present in the first product stream. In other words, the third product stream comprises more than 50 % by weight of the solvent, unreacted alpha-olefin monomer and unreacted alpha-olefin comonomer present in the first product stream. The third product stream may also comprise a minor amount, such as at most 5 % by weight of the hourly production rate, of the alpha-olefin polymer.

The separation step can be performed in any process step where volatile compounds can be withdrawn from the first product stream. Typically, such a process step involves pressure reduction and preferably heating of the solution. One typical example of such a process step is flashing.

According to an embodiment, the separation step is performed in a separator arranged in combination with the polymerization reactor.

In the separation step, the first product stream is for example, passed along a pipe to a receiving vessel, which is operated at a pressure, which is substantially lower than the pressure in the polymerization reactor. Thereby a part of the fluid contained in the first product stream evaporates and is withdrawn as the third product stream. The part remaining in the solution with the polymer forms the second product stream.

According to an embodiment, the separation step is a flashing step. Thereby a liquid phase and a vapour phase are present in the separation step. The flashing step is suitably conducted in a flash vessel which is a vertical vessel preferably having a generally cylindrical shape. Thereby the flash vessel has a section, which has approximately a circular cross-section.

Preferably, the flash vessel has a cylindrical section, which has a shape of a circular cylinder. In addition to the cylindrical section, the flash vessel may have additional sections, such as a bottom section, which may be conical, and a top section, which may be hemispherical.

Alternatively, the flash vessel may also have a generally conical shape.

The temperature in the flash vessel is typically from 120 to 240 °C. The temperature should be sufficiently high to keep the viscosity of the solution at a suitable level but less than the temperature where the polymer is degraded. The pressure in the flash vessel is typically from 15 bar to atmospheric, or even less than atmospheric.

The first product stream enters the flash vessel at the top. The first product stream travels downwards in the flash vessel, while the gases, which evaporate from the first product stream, travel upwards. According to this preferred embodiment, the polymer solution forms a thin film, which falls downwards in the flash vessel. This facilitates the removal of hydrocarbons from the polymer solution. The gases are typically withdrawn from the top of the flash vessel while the solution is withdrawn from the bottom.

The polymer content in the second product stream withdrawn from the first flashing stage is typically from 40 to 90 % by weight of the first product stream. In other words, the second product stream withdrawn from the first flashing stage contains from 10 to 60 % by weight of residual hydrocarbons.

When viewed from a different angle, the third product stream withdrawn from the flash vessel is from 35 to 80 % by weight from the total of the second product stream and the third product stream withdrawn from the flash vessel. The third product stream typically comprises unreacted alpha-olefin monomer, hydrocarbon solvent and unreacted alpha- olefin comonomer. By using the flash as described above, it is possible to achieve high separation efficiency. For instance, separation efficiency for hydrocarbons containing 6 carbon atoms is at least 75 % and preferably at least 80 %. Additionally still, separation efficiency for hydrocarbons containing 8 carbon atoms is at least 60 % and preferably at least 65 %. The separation efficiency is defined as the mass flow of the component withdrawn in the vapour stream divided by the (theoretical) mass flow rate of the component in the vapour stream in equilibrium conditions.

The second product stream contains the polymer, dissolved in solvent and unreacted alpha-olefin comonomer. It may also contain residual monomer, which remains in the solution. Typically, the polymer concentration in the second product stream is from 25 % by weight to 70 % by weight greater than the polymer concentration in the first product stream. The second product stream is then typically in liquid phase. The second product stream may however, contain a minor amount of vapour, such as vapour bubbles. The amount of vapour in the second product stream is typically not more than 40 % by volume, preferably not more than 30 % by volume and especially preferably not more than 20 % by volume, such as not more than 10 % by volume or not more than 5 % by volume.

The third product stream contains unreacted alpha-olefin monomer and other volatile compounds, such as hydrogen. The third product stream also contains some of the solvent and comonomer. Typically, the third product stream is a vapour stream, optionally comprising a small amount of liquid droplets. The amount of such droplets is typically not more than 40 % by volume, preferably not more than 30 % by volume and especially preferably not more than 20 % by volume.

Further separation steps

After the separation step, the second product stream may still comprise solvent and unreacted alpha-olefin monomer. The polymerization process may contain one or more further separation steps for separating a) the alpha-olefin polymer and b) solvent and unreacted alpha-olefin monomer from the second product stream. For example, the one or more further separation steps is performed in a similar manner as the separation step described above.

Polymerization catalyst

The polymerization catalyst may be any catalyst known in the art, which is capable of polymerising the monomer and the optional comonomer. Thus, the polymerization catalyst may be a Ziegler-Natta catalyst as disclosed in EP-A-280352, EP-A-280353 and EP-A- 286148, or it may be a metallocene catalyst as disclosed in WO-A- 1993025590, US-A- 5001205, WO-A 1987003604 and US-A-5001244, or it may be a combination of these. Other suitable catalysts, such as late transition metal catalysts, can also be used.

Preferably, the polymerization catalyst is a metallocene catalyst.

According to an embodiment, the polymerization catalyst is

(i) at least one metallocene complex of formula (I)

wherein

Mt1 is Hf,

X is a sigma-donor ligand,

R1 , R2, R3 are the same or different from each other and can be hydrogen or a saturated linear or branched C1-C10 alkyl, whereby the alkyl group can optionally contain up to 2 heteroatoms belonging to groups 14-16 of the periodic table, or R1 and R2 or R2 and R3 can form a ring having 4 to 6 C-atoms and 1 to 3 double bonds,

R4 and R5 are the same or different from each other and can be saturated linear or branched C1-C10 alkyl, C5-C10 aryl, C6-C20 alkylaryl or C6-C20 arylalkyl groups, which can optionally contain up to 2 heteroatoms belonging to groups 14-16 of the periodic table,

n can be 1 to 5,

Ar is a C6-C20-aryl or -heteroarylgroup, which can be unsubstituted or substituted by 1 to 5 linear or branched C1- C10 alkyl group(s),

and

(ii) an aluminoxane cocatalyst and

(iii) optionally an aluminium alkyl compound AI(R7)3, with R7 being a linear or branched C2-C8-alkyl group. This kind of catalyst has been described in more detail in document WO 2018/178151 A1 , contents of which has been incorporated herein by reference.

According to an embodiment, the polymerization catalyst is

(i) at least one metallocene complex of formula (II)

wherein

Mt1 is Hf,

X is a sigma-donor ligand,

R1 , R2, R3 are the same or different from each other and can be hydrogen or a saturated linear or branched C1-C10 alkyl, whereby the alkyl group can optionally contain up to 2 heteroatoms belonging to groups 14-16 of the periodic table, or R1 and R2 or R2 and R3 can form a ring having 4 to 6 C-atoms and 1 to 3 double bonds,

R4 and R5 are the same or different from each other and can be saturated linear or branched C1-C10 alkyl, C5-C10 aryl, C6-C20 alkylaryl or C6-C20 arylalkyl groups, which can optionally contain up to 2 heteroatoms belonging to groups 14-16 of the periodic table,

n can be 1 to 5,

Ar is a C6-C20-aryl or -heteroarylgroup, which can be unsubstituted or substituted by 1 to 5 linear or branched C1- C10 alkyl group(s),

and

(ii) a boron containing cocatalyst.

This kind of catalyst has been described in more detail in document WO 2018/178152 A1 , contents of which has been incorporated herein by reference. According to an embodiment, the polymerization catalyst is

(i) a metallocene complex of formula (III)

wherein

M is Hf or a mixture with Zr, provided that more than 50% by moles of the complex of Formula I has M = Hf,

X is a sigma ligand,

R are the same or different from each other and can be saturated linear or branched C1-C10 alkyl, C5-C10 aryl, C6-C20 alkylaryl or C6-C20 arylalkyl groups, which can optionally contain up to 2 heteroatoms or silicon atoms,

R1 is a C6-C20-aryl, which can be unsubstituted or substituted by one or up to 5 linear or branched C1- C10 alkyl group(s),

R2 is a saturated linear or cyclic C3 - C20 alkyl group or a branched CR3R4R5 group, wherein R3 is hydrogen or a C1 - C20 alkyl group and R4 and R5 are the same or are different and can be an C1 - C20 alkyl group

and

(ii) a boron containing cocatalyst.

This kind of catalyst has been described in more detail in document WO 2018/108917 A1 , contents of which has been incorporated herein by reference. According to an embodiment, the polymerization catalyst is

(i) a metallocene complex of formula (IV)

wherein

M is Hf or a mixture with Zr, provided that more than 50% by moles of the complex of Formula I has M = Hf

X is a sigma ligand

R are the same or different from each other and can be saturated linear or branched C1-C10 alkyl, C6-C10 aryl, C4-C10 heteroaryl, C6-C20 alkylaryl or C6-C20 arylalkyl groups, which can optionally contain up to 2 heteroatoms or silicon atoms

R1 is a C6-C10 aryl or C6-C20 alkylaryl group optionally containing up to 2 heteroatoms or silicon atoms or a C4-C10 heteroaryl group

R2 is a C4-C20 cycloalkyl group, optionally carrying alkyl substituents in beta- positions, of formula (V)

in which R’ can be the same or can be different from each other and can be hydrogen or is defined as R and n is 1 to 17

and

(ii) a boron containing cocatalyst This kind of catalyst has been described in more detail in document WO 2018/108918 A1 , contents of which has been incorporated herein by reference.

EXAMPLES

Comparative example 1

Ethylene is copolymerized with 1-octene using (phenyl)(cyclohexyl)methylene-

(cyclopentadienyl)(2,7-di-te/f-butylfluoren-9-yl)hafnium dimethyl as a catalyst in a process described above to produce a grade with a density of 857 kg/m ³ and melt index of 0.2. A method for obtaining the catalyst has been described in WO 2018/108918 A1. The production conditions for such grade are summarized in Table 1.

Table 1

The reactor inlet consists of ethylene as monomer, 1-octene as a comonomer and hexane as a solvent. Reactor outlet comprises dissolved ethylene- 1-octene polymer, hexane and unreacted ethylene and 1-octene.

Inventive example 2

The polymerization temperature of Example 1 is modified so that the inlet temperature to the reactor increases to -12 °C, resulting in an increase of the temperature of the reactor outlet by 20 °C, i.e. to 165 °C. The outlet temperature of the heat exchanger upstream of the separator is kept constant. As a result, the amount of energy consumed in the deep cooling of the reactor inlet decreases by 24 % and in the heating before the separation step by 19 %.