Inhibitor compounds to prevent reactor fouling

Abstract

The invention relates to process for producing an ethylene copolymer in a high pressure polymerization reactor (T), comprising the step of polymerizing an ethylene monomer with a vinyl based monomer (D) in presence of an inhibitor compound to obtain the ethylene copolymer, wherein the inhibitor compound is represented by the chemical formula I wherein the substituents R1 to R9 are as defined in the disclosure. The invention further relates to an ethylene copolymer obtained from the process of the present invention.

Description

24POLY0086-WO-ORD1INHIBITOR COMPOUNDS TO PREVENT REACTOR FOULINGFIELD OF INVENTION

[0001] The invention relates to a process of producing ethylene copolymers such as copolymers derived from ethylene and vinyl monomers such as 2-hydroxyethylmethacrylate (HEMA) in the presence of inhibitors. The invention further relates to the use of the inhibitors to prevent reactor fouling during the preparation of ethylene based copolymers.BACKGROUND

[0002] One of the impediments facing the industrial scale production of ethylene copolymer is that of reactor fouling due to the self-polymerization of the comonomer. For example, it was observed that during the production of ethylene copolymers using vinyl monomers such as HEMA is the self-polymerization of comonomer which may occur in the preheater sections located upstream of the polymerization reactors. Such self-polymerization typically occurs when the comonomer is exposed to elevated temperature for example temperatures of about 75 °C - 163 °C.

[0003] The self-polymerization results in a pre-polymer buildup on compressor parts and causes pre-polymer caking on the inner walls of tubing and piping leading to reduced production rates and reactor downtime.

[0004] Further, the formation of undesired prepolymer (self-polymerized product) limits heat transfer (due to fouling of the preheater surface) and consequently comonomer feed rate (e.g. HEMA feed rate) is forced to be lowered. Lowering of the monomer feed rate limits the amount of comonomer that is incorporated in the copolymer even when it is not desired to do so. For example, industry practitioners have often grappled with the issue of increasing HEMA incorporation in the ethylene-HEMA copolymer beyond 1-4 wt%.

[0005] In the past, inhibitors such as MEHQ have been used at high concentration to prevent self-polymerization of the comonomers. The use of MEHQ has had limited success in preventing or controlling self-polymerization. In addition, the use of high concentration of inhibitor such as in an amount of 500 ppm and above, is not desired as its presence beyond a certain concentration affects overall polymerization kinetics as well as cause impurity build up in the final polymer product. Further, the use of MEHQ relied on the use of molecular oxygen in combination with MEHQ. However, the presence of oxygen in certain circumstances lead to uncontrolled24POLY0086-WO-ORD2radical formation which may cause reactor fouling and further lead to plant shut down and in certain cases cause thermal run-away reactions which are operationally hazardous. In particular, the high concentration of inhibitors adversely affected the performance of the peroxide initiator and affected the conversion of ethylene in the high-pressure reactor.

[0006] Alternatively, ethylene copolymer production systems have relied on adding foulant inhibitor into the oil used to lubricate the hyper-compressor plunger used in compressing the ethylene feed. This approach is problematic. When the inhibitor is incorporated into the lubricant oil, it is difficult to control and manage the amount of inhibitor that actually reaches the areas where self-polymerization occurs.

[0007] High pressure polymerization has been described in the past such as that described in the patent W02017 / 004320 Al. However, such a patent application does not address the specific issue of self-polymerization of comonomers and reactor fouling. The patent CA2862081 Al and WO 2021 / 202278 Al describe the use of anti-foulant and inhibitors. Although the solution described in the patent applications are promising, these patent applications do not address the issue of using specific inhibitor compounds in low quantity to inhibit reactor fouling.

[0008] As a further consideration, to improve reaction kinetics, the ethylene and the comonomer streams can be mixed in the preheater. The mixing of the ethylene and the comonomer in the preheater is beneficial for several reasons. The premixing of the ethylene and the vinyl comonomer feed in the preheater allows (a) initiation temperature control - and ensures that the entire feed entering the polymerization reactor to have uniform temperature, (b) mixing in the preheater ensures uniform distribution of ethylene and comonomer and any chain transfer agents, (c) increased conversion efficiency, (d) prevention of phase separation and reduced gel formation tendency. However as noted in the patent EP4375304A1 - the presence of highly reactive comonomers increases fouling due to thermal polymerization at the tube inside wall, mainly of the comonomer, where the highest temperature is reached. The addition of conventional inhibitor typically is not solving the problem as the efficiency of the inhibitor reduces significantly at the preheating temperatures. Further, the addition of comonomers directly in the reactor may also cause reactor fouling as the reactor is generally operating at high temperature.

[0009] Accordingly, it is an objective of the present invention to provide for a process of producing ethylene copolymers with minimal reactor fouling. Yet another objective of the present24POLY0086-WO-ORD3invention is to provide for a process of producing ethylene copolymers using minimum amount of anti-fouling inhibitor and / or with minimal concentration of molecular oxygen while limiting the self-polymerization of the comonomer. It is yet another objective of the present invention to improved ethylene conversion in the polymerization reactor during the production of ethylene copolymers.DESCRIPTION

[0010] Accordingly, the one or more objectives of the present invention is achieved by a process for producing an ethylene copolymer in a high-pressure polymerization reactor (T), comprising the step of polymerizing an ethylene monomer with a vinyl-based monomer (D) in presence of an inhibitor compound to obtain the ethylene copolymer, wherein the inhibitor compound is represented by the chemical formula I:R1 R8• wherein the substituents R1to R8are each independently selected from hydrogen or a substituent selected from C1-C20 alkyl, C1-C20 alkenyl, C6-C20 aryl, C6-C20 aralkyl, C1-C20 alkoxy, C6-C20 aryloxy, halogen, nitro group, or C6-C20 alkylaryl group, with each of the substituent being optionally substituted with one or more heteroatoms; or at least any two adjacent substituent R1-R2, R2-R3, R3-R4, R5-R6, R6-R7, R7-R8may be connected to form an aliphatic ring having 5-20 carbon atoms or an aromatic ring having 5-20 carbon atoms; and R9is any one of C1-C5 alkyl or hydrogen;• wherein the substituent ‘Q’ is any one of nitrogen, oxygen or sulphur, preferably wherein the high-pressure polymerization reactor is a tubular reactor; and wherein the vinyl-based monomer (D) is selected from an acrylate based monomer (A) or an acrylate based ionomer (IA) and any combinations thereof; and24POLY0086-WO-ORD4• wherein the inhibitor compound is mixed with the vinyl based monomer (D) in an amount of > 25.0 and < 450.0 parts per million by weight, with regard to the total weight of the vinyl based monomer (D).

[0011] The term ethylene copolymer as used herein means copolymer comprising or consisting of polymeric units derived from ethylene and the vinyl-based monomer (D). The ethylene copolymer may for example consists of > 90.0 and < 99.9 wt.%, of polymeric units derived from ethylene; and > 0.1 and < 10.0 wt.%, preferably > 1.0 and < 8.0 wt.%, preferably > 1.0 and < 7.0 wt.% of polymeric units derived from the vinyl-based monomer (D). Preferably wherein the content of ethylene and vinyl-based monomer (D) is determined using13C NMR and / or1H NMR.

[0012] It is particularly, preferred that the vinyl-based monomer (D) is an acrylate-based monomer (A). In another embodiment of the invention, it is preferred that the vinyl-based monomer (D) is an acrylate-based ionomer compound (IA).

[0013] Preferably, the process for producing the ethylene copolymer in the high-pressure polymerization reactor (T), comprises the step of polymerizing the ethylene monomer with the vinyl-based monomer (D) in presence of the inhibitor compound to obtain the ethylene copolymer, wherein the inhibitor compound is represented by the chemical formula I:• wherein the substituents R1to R8are each independently selected from hydrogen or a substituent selected from Cl -CIO alkyl; and R9is any one of C1-C5 alkyl or hydrogen; • wherein the substituent ‘Q’ is any one of oxygen or sulphur, wherein the high-pressure polymerization reactor is the tubular reactor; and wherein the vinyl-based monomer (D) is selected from an acrylate based monomer (A); and24POLY0086-WO-ORD5• wherein the inhibitor compound is mixed with the vinyl-based monomer (D) in an amount of > 25.0 and < 450.0 parts per million by weight, with regard to the total weight of the vinyl based monomer (D).

[0014] Preferably, the process for producing the ethylene copolymer in the high-pressure polymerization reactor (T), comprises the step of polymerizing the ethylene monomer with the vinyl-based monomer (D) in presence of the inhibitor compound to obtain the ethylene copolymer, wherein the inhibitor compound is represented by the chemical formula I:• wherein the substituents R1to R8are each independently selected from hydrogen or a substituent selected from Cl -CIO alkyl; and R9is any one of C1-C5 alkyl or hydrogen; • wherein the substituent ‘Q’ is any one of oxygen or sulphur, wherein the high-pressure polymerization reactor is the tubular reactor; and wherein the vinyl-based monomer (D) is selected from an acrylate based monomer (A); and• wherein the inhibitor compound is mixed with the vinyl based monomer (D) in an amount of > 25.0 and < 450.0 parts per million by weight, with regard to the total weight of the vinyl based monomer (D).

[0015] In an aspect of the invention, the invention relates to a process for producing the ethylene copolymer in a high-pressure polymerization reactor (T), comprising the step of polymerizing an ethylene monomer with the vinyl-based monomer (D) in presence of the inhibitor compound to obtain the ethylene copolymer, wherein the inhibitor compound is represented by the chemical formula I:24POLY0086-WO-ORD• wherein the substituents R1to R8are each independently selected from hydrogen or a substituent selected from C1-C20 alkyl, C1-C20 alkenyl, C6-C20 aryl, C6-C20 aralkyl, C1-C20 alkoxy, C6-C20 aryloxy, halogen, nitro group, or C6-C20 alkylaryl group, with each of the substituent being optionally substituted with one or more heteroatoms; or at least any two adjacent substituent R1-R2, R2-R3, R3-R4, R5-R6, R6-R7, R7-R8may be connected to form an aliphatic ring having 5-20 carbon atoms or an aromatic ring having 5-20 carbon atoms; and R9is any one of C1-C5 alkyl or hydrogen;• wherein the substituent ‘Q’ is any one of nitrogen, oxygen or sulphur, and wherein the high-pressure polymerization reactor is a tubular reactor; and• wherein the vinyl-based monomer (D) is selected from an acrylate based monomer (A) or an acrylate based ionomer (IA) and any combinations thereof; and• wherein the inhibitor compound is mixed with the vinyl-based monomer (D) in an amount of > 25.0 and < 450.0 parts per million by weight, with regard to the total weight of the vinyl-based monomer (D).

[0016] In an aspect of the invention, the invention relates to a process for producing the ethylene copolymer in a high-pressure polymerization reactor (T), comprising the step of polymerizing an ethylene monomer with the vinyl-based monomer (D) in presence of the inhibitor compound to obtain the ethylene copolymer, wherein the inhibitor compound is represented by the chemical formula I:24POLY0086-WO-ORD• wherein the substituents R1to R8are each hydrogen; and R9is hydrogen;• wherein the substituent ‘Q’ is any one of oxygen or sulphur, and wherein the high- pressure polymerization reactor is a tubular reactor; and• wherein the vinyl-based monomer (D) is selected from an acrylate based monomer (A) or an acrylate based ionomer (IA) and any combinations thereof; and• wherein the inhibitor compound is mixed with the vinyl-based monomer (D) in an amount of > 25.0 and < 450.0 parts per million by weight, preferably > 45.0 and < 110.0 parts per million by weight with regard to the total weight of the vinyl-based monomer (D).

[0017] It is preferable that the polymerization of ethylene monomer with a vinyl-based monomer (D) is carried out in the absence of molecular oxygen.

[0018] The use of lower quantities of inhibitors of the present invention (e.g. phenoxazine) than that of traditional inhibitors (e.g. MEHQ) is particularly advantageous as the use of low amounts of inhibitors of the present invention significantly lowers presence of trace amounts of these inhibitors as impurities in the final polymer. The presence of such inhibitors as impurities in the final polymer affects the performance of the final polymer product in terms of color, mechanical stability etc. Further, if the concentration of inhibitor compound is high for example above 450 parts per million by weight, with regard to the total weight of the vinyl based monomer (D), the polymerization kinetics may be affected. On the other hand, if the concentration of inhibitor compound is too low for example below 45 parts per million by weight, the amount may not be effective for controlling the self-polymerization of the vinyl-based monomer (D).

[0019] In an aspect of the invention, the invention relates to the use of the inhibitor compound as described in the present invention for preventing reactor fouling in a process of producing ethylene copolymer.24POLY0086-WO-ORD8

[0020] In an aspect of the invention, the invention relates to an ethylene copolymer obtained by or obtainable by the process according to the present invention.

[0021] Preferably, the inhibitor compound of formula I, is at least one inhibitor compound selected from:where ‘X’ is any one of oxygen or sulfur, R4and R5are each C1-C5 alkyl group, preferably R4and R5are each methyl group; R2and R7are each independently selected from nitro group, halogen, methoxy group, tert-butyl group, a phenoxy group; orwhere ‘X’ is any one of oxygen or sulfur, preferably ‘X’ is sulfur; orwhere ‘X’ is any one of oxygen or sulfur, preferably ‘X’ is sulfur; or(iv) a phenothiazine compound represented by the formula (V)24POLY0086-WO-ORD(v) a phenoxazine compound represented by formula (VI)

[0022] For the purpose of structures (II), (III) and (IV) the variable ‘Q’ as shown in formula (I) is represented as ‘X’.

[0023] Preferably the inhibitor compound is selected from the phenothiazine compound represented by the formula (V), or the phenoxazine compound represented by formula (VI).

[0024] In an aspect of the invention, the invention relates to a process for producing the ethylene copolymer in a high-pressure polymerization reactor (T), comprising the step of polymerizing an ethylene monomer with the vinyl-based monomer (D) in presence of the inhibitor compound to obtain the ethylene copolymer, wherein the inhibitor compound is phenothiazine compound represented by the formula (V):• wherein the high-pressure polymerization reactor is a tubular reactor; and • wherein the vinyl based monomer (D) is selected from an acrylate based monomer (A) or an acrylate based ionomer (IA) and any combinations thereof; and• wherein the inhibitor compound is mixed with the vinyl-based monomer (D) in an amount of > 25.0 and < 450.0 parts per million by weight, with regard to the total weight of the vinyl based monomer (D).24POLY0086-WO-ORD10

[0025] In an aspect of the invention, the invention relates to a process for producing the ethylene copolymer in a high pressure polymerization reactor (T), comprising the step of polymerizing an ethylene monomer with the vinyl based monomer (D) in presence of the inhibitor compound to obtain the ethylene copolymer, wherein the inhibitor compound is phenothiazine compound represented by the formula (V):• wherein the high-pressure polymerization reactor is a tubular reactor; and • wherein the vinyl based monomer (D) is an acrylate based monomer (A); and • wherein the inhibitor compound is mixed with the vinyl-based monomer (D) in an amount of > 25.0 and < 450.0 parts per million by weight, with regard to the total weight of the vinyl-based monomer (D).

[0026] In an aspect of the invention, the invention relates to a process for producing the ethylene copolymer in a high-pressure polymerization reactor (T), comprising the step of polymerizing an ethylene monomer with the vinyl-based monomer (D) in presence of the inhibitor compound to obtain the ethylene copolymer, wherein the inhibitor compound is phenoxazine compound represented by formula (VI):wherein the high-pressure polymerization reactor is a tubular reactor; and24POLY0086-WO-ORD11• wherein the vinyl-based monomer (D) is selected from an acrylate based monomer (A) or an acrylate based ionomer (IA) and any combinations thereof; and• wherein the inhibitor compound is mixed with the vinyl-based monomer (D) in an amount of > 25.0 and < 450.0 parts per million by weight, with regard to the total weight of the vinyl-based monomer (D).

[0027] In an aspect of the invention, the invention relates to a process for producing the ethylene copolymer in a high-pressure polymerization reactor (T), comprising the step of polymerizing an ethylene monomer with the vinyl-based monomer (D) in presence of the inhibitor compound to obtain the ethylene copolymer, wherein the inhibitor compound is phenoxazine compound represented by formula (VI):• wherein the high-pressure polymerization reactor is a tubular reactor; and • wherein the vinyl based monomer (D) is an acrylate based monomer (A); and • wherein the inhibitor compound is mixed with the vinyl-based monomer (D) in an amount of > 25.0 and < 450.0 parts per million by weight, > 45.0 and < 110.0 parts per million by weight with regard to the total weight of the vinyl-based monomer (D).

[0028] Preferably the inhibitor compound is selected from the phenothiazine compound represented by the formula (V), or the phenoxazine compound represented by formula (VI). More preferably wherein the inhibitor compound is phenoxazine compound represented by formula (VI)24POLY0086-WO-ORD12

[0029] Preferably the inhibitor compound is selected from the phenothiazine compoundrepresented by the formulaor the phenoxazine compound represented by formulawherein the vinyl-based monomer (D) is an acrylate-based monomer (A).

[0030] Preferably the inhibitor compound is phenoxazine and the vinyl based monomer (D) is an acrylate based monomer (A) and wherein the inhibitor compound is mixed with the vinyl based monomer (D) in an amount of > 45.0 and < 110.0, preferably > 45.0 and < 80.0 parts per million by weight, with regard to the total weight of the vinyl based monomer (D).Process conditions

[0031] The reactor system for carrying out the process of the present invention may for example include an ethylene feed, a compressor (CP), a preheater (H), and a polymerization reactor (T), each component in fluid communication with, or otherwise in operative communication with, each other. The compressor (CP) may be as used herein, is a compressor that pressurizes one or more ethylene feeds to a pressure of at least 100 MPa or at least 180 MPa.

[0032] In an embodiment of the invention, the ethylene feed may for example be located upstream of the compressor (CP). In another embodiment of the invention, the reactor system may for example include (i) the ethylene feed in fluid communication with (ii) the compressor (CP), the compressor (CP) in fluid communication with (iii) the preheater (H), and the preheater (H) in fluid communication with (iv) the polymerization reactor (T). The pre-heater may for example heat the polymerization reactor (T) contents prior to injection of the free-radical initiator. The reactor system may include other components in addition to these components.24POLY0086-WO-ORD13

[0033] The compressor (CP) may for example pressurizes the ethylene feed(s) to a level sufficient to feed the polymerization reactor and produce high pressure free-radical polymerization conditions. The preheater (H) for example, receives the output from the compressor (CP) and heats this output to a temperature for high pressure free radical polymerization, or a temperature from > 55.0 °C and < 250.0 °C, preferably > 55.0 °C and < 220.0 °C, preferably > 75.0 °C and < 170.0 °C, preferably > 75.0 °C and < 150.0 °C.

[0034] In an aspect of the invention, the polymerization reactor receives the output from the preheater and increases the temperature; polymerization occurs in the polymerization reactor at a temperature from 100°C to 350°C. The term "high pressure free-radical polymerization conditions," as used herein, refers to the environment in a polymerization reactor (autoclave reactor and / or tubular reactor) with (i) a operating at a pressure of at least 100 MPa (1000 Bar), preferably at least 180 MPa (ii) and operated at a temperature from 100°C to 350°C, and (iii) the presence of a free-radical initiator.

[0035] A high-pressure reactor (T) may be any polymerization reactor for example a tubular reactor that is suitable to carry out high pressure free-radical polymerization. The high-pressure reactor (T) may for example be operated at any pressure of >180 MPa and <350 MPa, and may be operated at any temperature of >100 °C and < 350 °C.

[0036] In some embodiments of the invention, the polymerization reaction may for example can take place in a high-pressure polymerization reactor such as a tubular reactor using the high pressure CTR ™ technology as described in Chapter 7.9 of “Handbook of Petrochemicals Production Processes, 2nd Edition” (ISBN: 9781259643132).

[0037] Preferably, the process comprises the steps of:(a) mixing the inhibitor compound with the vinyl-based monomer (D) to form a comonomer mixture (M);(b) feeding the comonomer mixture (M) into a preheater unit (H) positioned upstream to the high-pressure reactor (T);(c) feeding the ethylene monomer into the preheater unit (H);(d) heating a reaction mixture (RM) comprising the ethylene monomer and the comonomer mixture (M) to form a preheated reaction mixture (R); and24POLY0086-WO-ORD14(e) introducing the preheated reaction mixture (R) into the high-pressure reactor (T) and polymerizing the ethylene monomer with the vinyl-based monomer (D) to obtain the ethylene copolymer; andwherein the reaction mixture (RM) is heated at any temperature of > 55.0 °C and < 250.0 °C, preferably > 55.0 °C and < 220.0 °C, preferably > 75.0 °C and < 170.0 °C, preferably > 75.0 °C and < 150.0 °C to obtain the preheated reaction mixture (R), preferably wherein the reaction mixture (RM) is heated in the preheater unit (H) in the absence of initiators.

[0038] Preferably, the process comprises the steps of:(a) mixing the inhibitor compound with the vinyl-based monomer (D) to form a comonomer mixture (M), wherein the inhibitor compound is a phenothiazine compound or a phenoxazine compound and wherein the vinyl-based monomer (D) is an acrylate based monomer (A); (b) feeding the comonomer mixture (M) into a preheater unit (H) positioned upstream to the high- pressure reactor (T);(c) feeding the ethylene monomer into the preheater unit (H);(d) heating a reaction mixture (RM) comprising the ethylene monomer and the comonomer mixture (M) to form a preheated reaction mixture (R); and(e) introducing the preheated reaction mixture (R) into the high-pressure reactor (T) and polymerizing the ethylene monomer with the vinyl based monomer (D) to obtain the ethylene copolymer; andwherein the reaction mixture (RM) is heated at any temperature of > 55.0 °C and < 250.0 °C, preferably > 55.0 °C and < 220.0 °C, preferably > 75.0 °C and < 170.0 °C, preferably > 75.0 °C and < 150.0 °C to obtain the preheated reaction mixture (R), preferably wherein the reaction mixture (RM) is heated in the preheater unit (H) in the absence of initiators.

[0039] In an aspect of the present invention, the polymerization of ethylene monomer with the vinyl-based monomer (D) is carried out in the absence of molecular oxygen.

[0040] The high-pressure reactor (T) can be any suitable reactor such as an autoclave reactor, a tubular reactor, or a combination of an autoclave reactor in operative communication with a tubular reactor.24POLY0086-WO-ORD15

[0041] Preferably, the inhibitor compound is mixed with a protic solvent or a non-protic solvent in a static mixer to obtain the comonomer mixture (M) and subsequently fed to the preheater (H), preferably wherein the inhibitor compound is mixed with methanol in a static mixer to obtain the comonomer mixture (M) and subsequently the comonomer mixture (M) is fed to the preheater (H).

[0042] Preferably, the process comprises the steps of compressing the ethylene monomer in one or more compressor units (CP) positioned upstream to the preheater unit (H) such that the ethylene monomer is fed into the preheater unit (H) at any pressure of >180 MPa and <280 MPa. In other words, the process of the present invention the ethylene monomer prior to being fed to the preheater unit (H) is free of the inhibitor compound.

[0043] Preferably, the polymerization of the ethylene monomer with the vinyl monomer (D) is carried out in the high pressure reactor (T) at any pressure of >180 MPa and <350 MPa, preferably > 200 MPa and <300 MPa and at any temperature of >100 °C and < 350 °C, preferably >150 °C and <310 °C, preferably >150 °C and < 260 °C, preferably >150 °C and <250 °C; and / or wherein the polymerization of ethylene monomer with the vinyl based monomer (D) is carried out in the absence of molecular oxygen.

[0044] Preferably, the polymerization of the ethylene monomer with the vinyl monomer (D) is carried out in the high pressure reactor (T) at any pressure of >180 MPa and <350 MPa, preferably > 200 MPa and <300 MPa and at any temperature of >100 °C and < 350 °C, preferably >150 °C and <310 °C, preferably >150 °C and < 260 °C, preferably >150 °C and <250 °C; and wherein the polymerization of ethylene monomer with a vinyl based monomer (D) is carried out in the absence of molecular oxygen.

[0045] Preferably, the polymerization of the ethylene monomer with the vinyl based monomer (D) is carried out in presence of initiators wherein the initiator is introduced in the high pressure reactor in an amount of > 0 ppm and < 300 ppm, preferably > 0 ppm and < 200 ppm, with regard to the total weight of the preheated reaction mixture (R); and wherein the initiator is selected from organic peroxides, azo based compounds and combinations thereof.

[0046] Advantageously, the process of the present invention involves negligible amount of self-polymerization of the comonomer. A suitable metric to evaluate self-polymerization is by evaluating the extent of conversion of the vinyl-based monomer (D) to the corresponding polyvinyl24POLY0086-WO-ORD16polymer when exposed to elevated temperature in the absence of initiator or on prolonged periods of storage.

[0047] The polyvinyl polymer may be a homopolymer comprising polymeric units derived solely from the vinyl based monomer (D). The polyvinyl polymer may also include a co-polymer comprising polymeric units derived from ethylene and the vinyl-based monomer (D) with the polymeric units derived from the vinyl monomer (D) being at least 20 wt.% and up to 90 wt.% of the polyvinyl polymer i.e a copolymer having undesirably large amounts of polymeric units derived from the vinyl monomer (D).

[0048] In other words, lower conversion in presence of the inhibitor compound is indicative of suitability of the inhibitor compound in preventing self-polymerization of the comonomer.

[0049] Preferably, the inhibitor compound is selected such that when the comonomer mixture (M) comprising the vinyl based monomer (D) and the inhibitor compound is exposed at any temperature of > 55.0 °C and < 250.0 °C, preferably > 55.0 °C and < 220.0 °C, preferably > 75.0 °C and < 210.0 °C, preferably > 150 °C and < 210 °C, the conversion of the vinyl based monomer (D) to the polyvinyl polymer ranges from 0 > and < 0.6 %, preferably 0 > and < 0.5 %, with regard to the total weight of the comonomer mixture (M).

[0050] In an embodiment of the invention, the conversion is defined as:Conversion % = ((the amount of polymeric or oligomeric products formed in the preheater) / (total amount of ethylene, HEMA monomer, and inhibitor compound fed into the preheater)) xl00%.

[0051] Accordingly, if the conversion is low in the preheater to oligomeric or polymeric products it is indicative that self-polymerization of the vinyl monomer (D) is inhibited even when exposed to high temperature.

[0052] Preferably, the inhibitor compound is mixed with the vinyl-based monomer (D) in an amount of > 25.0 and < 350.0 parts per million by weight, preferably > 25.0 and < 250.0 parts per million by weight, preferably > 45.0 and < 150.0 parts per million by weight, preferably > 45.0 and < 110.0 parts per million by weight, with regard to the total weight of the vinyl based monomer (D).24POLY0086-WO-ORD17

[0053] Preferably, the amount of comonomer mixture (M) fed to the preheater unit (H) ranges from > 0.05 and < 12.0 mole. %, with respect to the total moles of the preheated reaction mixture (R).

[0054] Preferably, the ethylene copolymer comprising with regard to the total weight of the ethylene copolymer of:(i) > 90.0 and < 99.9 wt.%, preferably > 92.0 and < 99.0 wt.%, preferably > 93.0 and < 99.0 wt.%, of polymeric units derived from ethylene; and(ii) > 0.1 and < 10.0 wt.%, preferably > 1.0 and < 8.0 wt.%, preferably > 1.0 and < 7.0 wt.% of polymeric units derived from the vinyl-based monomer (D); and preferably wherein the ethylene copolymer comprising with regard to the total weight of the ethylene copolymer of > 93.0 and < 99.0 wt.%, of polymeric units derived from ethylene; and > 1.0 and < 7.0 wt.% of polymeric units derived from the vinyl-based monomer (D).

[0055] Preferably wherein the content of ethylene and vinyl-based monomer (D) is determined using13C NMR and / or1H NMR.

[0056] Preferably, the process comprises the steps of:(a) mixing the inhibitor compound with the vinyl-based monomer (D) to form a comonomer mixture (M);(b) feeding the comonomer mixture (M) into a preheater unit (H) positioned upstream to the high-pressure reactor (T);(c) compressing the ethylene monomer (M);(d) feeding the ethylene monomer into the preheater unit (H);(e) heating the reaction mixture (RM) comprising the ethylene monomer and the comonomer mixture (M) to form the preheated reaction mixture (R); and(f) introducing the preheated reaction mixture (R) into the high-pressure reactor (T) and polymerizing the ethylene monomer with the vinyl-based monomer (D) to obtain the ethylene copolymer; and• wherein the reaction mixture (RM) is heated at any temperature of > 55.0 °C and < 250.0 °C, preferably > 55.0 °C and < 220.0 °C, preferably > 75.0 °C and < 170.0 °C, preferably >24POLY0086-WO-ORD1875.0 °C and < 150.0 °C to obtain the preheated reaction mixture (R), and wherein the reaction mixture (RM) is heated in the preheater unit (H) in the absence of initiators; • wherein the polymerization of ethylene with the vinyl based monomer (D) is carried out in absence of molecular oxygen; and• wherein the inhibitor compound and the vinyl based monomer compound is mixed with methanol in a static mixer to obtain the comonomer mixture (M) and subsequently fed to the preheater unit (H).Vinyl Monomer D

[0057] In an aspect of the invention, wherein the vinyl based monomer (D) is an acrylate based monomer (A) having a structure represented by the formula (II) or by formula (III):a) wherein the formula (II) is:• R14 is a moiety selected from the group consisting of: — CH2 —; — [CH2]x — CH(CH3) —, wherein x >1 and <10; — CH2 — CHR4-[O — CH2 — CHRa]q —, wherein q >1 and < 10, and each Ra individually is selected from CH3 or H; and — CH2 — CH(OH)— CH2—;• RIO is selected from — H or — CH3;• R11 is selected from — O —, — (CO) — (NH) — or — (CO) — O —;• n=0 or 1; and• m >1 and <10; and24POLY0086-WO-ORD19b) wherein the formula (III) is:• R16 is a moiety selected from the group consisting of: — CH2 —; — [CH2]x — CH(CH3) —, wherein x >1 and <10; — CH2 — CHR4-[O — CH2 — CHRb]q—, wherein q >1 and <10, and each Rb individually is selected from CH3 or H; and — CH2 — CH(OH) — CH2 —; • n >1 and <10; and• each R15 or R17 may individually be selected from — H or — CH3.

[0058] Preferably, the vinyl based monomer (D) is an acrylate based monomer (A) selected from the group consisting of 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 3-hydroxypropyl acrylate, 3-hydroxypropyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 2,3 -dihydroxypropyl acrylate, 2,3 -dihydroxypropyl methacrylate, 4-hydroxybutyl acrylate, 4-hydroxybutyl methacrylate, polypropylene glycol) monoacrylate, poly(propyleneglycol) monomethacrylate, poly(ethylene glycol) monoacrylate, poly(ethylene glycol) monomethacrylate, poly(ethylenepropyleneglycol) monomethacrylate and 2-hydroxyethyl vinyl ether, 1,4-butanediol dimethacrylate, hexanediol dimethacrylate, ethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, dodecanediol dimethacrylate, glycerol dimethacrylate, 1,4-butanediol diacrylate, hexanediol diacrylate, ethylene glycol diacrylate, 1,3-butylene glycol diacrylate, dodecanediol diacrylate, glycerol diacrylate, glycerol 1,3 -di glycerolate diacrylate, glycerol 1,3-diglycerolate dimethacrylate, poly(ethylene glycol) dimethacrylate, polypropylene glycol) dimethacrylate, poly thylenepropyleneglycol) dimethacrylate, 1,4-24POLY0086-WO-ORD20butanediol divinyl ether, polyethylene glycol) divinyl ether, di(ethyleneglycol) divinyl ether, 1,5-hexadiene, 1,7-octadiene, 1,9-decadiene and 1,13 -tetradecadiene.

[0059] More preferably, wherein the vinyl-based monomer (D) is an acrylate based monomer (A) selected from 2-hydroxyethyl methacrylate, 1,4-butanediol dimethacrylate and combinations thereof, preferably wherein the acrylate monomer is 2-hydroxyethyl methacrylate.

[0060] In an aspect of the invention, the vinyl-based monomer (D) is an acrylate based ionomer (IA) having any one of structure selected from:tBuAEM-AAMPSA

[0061] Preferably wherein the vinyl based monomer (D) is the acrylate based ionomer (IA) represented by the structure below and defined as MAMADAME:MAMADAME, where the ionomer MAMADAME is derived from methacrylic acid (MA) and dimethylaminoethyl methacrylic acid (MADAME).

[0062] Therefore, in an aspect of the invention, the process of the present invention comprises the step of polymerizing ethylene with 2-hydroxyethyl methacrylate to obtain the24POLY0086-WO-ORD21ethylene copolymer comprising polymeric units derived from ethylene and 2-hydroxyethyl methacrylate; wherein the polymerization is carried out in presence of a inhibitor compound selected from the phenothiazine compound represented by the formula (V) or the phenoxazine compound represented by formula (VI); wherein the inhibitor compound is present in an amount of > 45.0 and < 110.0 parts per million by weight, with regard to the total weight of 2-hydroxyethyl methacrylate.

[0063] Preferably, the process of the present invention comprises the step of polymerizing ethylene with 2-hydroxyethyl methacrylate to obtain the ethylene copolymer comprising polymeric units derived from ethylene and 2-hydroxyethyl methacrylate; wherein the polymerization is carried out in presence of a inhibitor compound is a phenothiazine compound represented by the formula (V); wherein the inhibitor compound is present in an amount of > 45.0 and < 110.0 parts per million by weight, with regard to the total weight of 2-hydroxyethyl methacrylate.

[0064] Preferably, the process of the present invention comprises the step of polymerizing ethylene with 2-hydroxyethyl methacrylate to obtain the ethylene copolymer comprising polymeric units derived from ethylene and 2-hydroxyethyl methacrylate; wherein the polymerization is carried out in presence of a inhibitor compound is a phenoxazine compound represented by formula (VI); wherein the inhibitor compound is present in an amount of > 45.0 and < 110.0 parts per million by weight, with regard to the total weight of 2-hydroxyethyl methacrylate.

[0065] Preferably, the process comprises the steps of:(a) mixing the inhibitor compound with the vinyl based monomer (D) to form a comonomer mixture (M);(b) feeding the comonomer mixture (M) into a preheater unit (H) positioned upstream to the high-pressure reactor (T);(c) feeding the ethylene monomer into the preheater unit (H);(d) heating the reaction mixture (RM) comprising the ethylene monomer and the comonomer mixture (M) to form the preheated reaction mixture (R); and24POLY0086-WO-ORD22(e) introducing the preheated reaction mixture (R) into the high-pressure reactor (T) and polymerizing the ethylene monomer with the vinyl based monomer (D) to obtain the ethylene copolymer; and• wherein the reaction mixture (RM) is heated at any temperature of > 55.0 °C and < 250.0 °C, preferably > 55.0 °C and < 220.0 °C, preferably > 75.0 °C and < 170.0 °C, preferably > 75.0 °C and < 150.0 °C to obtain the preheated reaction mixture (R), wherein the reaction mixture (RM) is heated in the preheater unit (H) in the absence of initiators;• wherein the vinyl based monomer (D) is 2-hydroxyethyl methacrylate:• wherein the inhibitor compound is present in an amount of > 45.0 and < 110.0 parts per million by weight, with regard to the total weight of 2-hydroxyethyl methacrylate;• wherein the inhibitor is compound is phenoxazine compound represented by formula (VI);• wherein the polymerization of ethylene and 2-hydroxyethyl methacrylate is carried out in absence of molecular oxygen; and• wherein the phenoxazine compound represented by formula (VI) is mixed with 2-hydroxy ethyl methacrylate in methanol in a static mixer to obtain the comonomer mixture (M) and subsequently fed to the preheater unit (H).

[0066] Preferably, the process comprises the steps of:(a) mixing the inhibitor compound with the vinyl-based monomer (D) to form a comonomer mixture (M);(b) feeding the comonomer mixture (M) into a preheater unit (H) positioned upstream to the high-pressure reactor (T);(c) feeding the ethylene monomer into the preheater unit (H);(d) heating the reaction mixture (RM) comprising the ethylene monomer and the comonomer mixture (M) to form the preheated reaction mixture (R); and(e) introducing the preheated reaction mixture (R) into the high-pressure reactor (T) and polymerizing the ethylene monomer with the vinyl based monomer (D) to obtain the ethylene copolymer;• wherein the reaction mixture (RM) is heated at any temperature of > 55.0 °C and < 250.0 °C, preferably > 55.0 °C and < 220.0 °C, preferably > 75.0 °C and < 170.0 °C, preferably >24POLY0086-WO-ORD2375.0 °C and < 150.0 °C to obtain the preheated reaction mixture (R), and wherein the reaction mixture (RM) is heated in the preheater unit (H) in the absence of initiators; • wherein the vinyl based monomer (D) is 2-hydroxyethyl methacrylate:• wherein the inhibitor compound is present in an amount of > 45.0 and < 110.0 parts per million by weight, with regard to the total weight of 2-hydroxyethyl methacrylate;• wherein the inhibitor is compound is phenothiazine compound represented by the formula (V);• wherein the polymerization of ethylene and 2-hydroxyethyl methacrylate is carried out in absence of molecular oxygen; and• wherein the phenothiazine compound represented by the formula (V) is mixed with 2-hydroxy ethyl methacrylate in methanol in a static mixer to obtain the comonomer mixture (M) and subsequently fed to the preheater unit (H).

[0067] Preferably, the process comprises the step of polymerizing ethylene with the acrylate based ionomer (IA) defined as MAMADAME to obtain the ethylene copolymer comprising polymeric units derived from ethylene and MAMADAME; wherein the polymerization is carried out in presence of a inhibitor compound selected from the phenothiazine compound represented by the formula (V) or the phenoxazine compound represented by formula (VI); wherein the inhibitor compound is present in an amount of > 85.0 and < 400.0 parts per million by weight, preferably > 100.0 and < 350.0 parts per million by weight, with regard to the total weight of MAMADAME.

[0068] Preferably, the process comprises the steps of:(a) mixing the inhibitor compound with the vinyl-based monomer (D) to form a comonomer mixture (M);(b) feeding the comonomer mixture (M) into a preheater unit (H) positioned upstream to the high-pressure reactor (T);(c) feeding the ethylene monomer into the preheater unit (H);(d) heating a reaction mixture (RM) comprising the ethylene monomer and the comonomer mixture (M) to form a preheated reaction mixture (R); and24POLY0086-WO-ORD24(e) introducing the preheated reaction mixture (R) into the high-pressure reactor (T) and polymerizing the ethylene monomer with the vinyl based monomer (D) to obtain the ethylene copolymer;• wherein the reaction mixture (RM) is heated at any temperature of > 55.0 °C and < 250.0 °C, preferably > 55.0 °C and < 220.0 °C, preferably > 75.0 °C and < 170.0 °C, preferably > 75.0 °C and < 150.0 °C to obtain the preheated reaction mixture (R), preferably wherein the reaction mixture (RM) is heated in the preheater unit (H) in the absence of initiators;• wherein the vinyl based monomer (D) is the acrylate based ionomer (IA) represented by the structure below and defined as MAMADAME:'M*MAMADAME ,where the ionomer MAMADAME is derived from methacrylic acid (MA) and dimethylaminoethyl methacrylic acid (MADAME);• wherein the inhibitor compound is present in an amount of > 85.0 and < 400.0 parts per million by weight, preferably > 100.0 and < 350.0 parts per million by weight, with regard to the total weight of MAMADAME;• wherein the inhibitor is compound is selected from the phenothiazine compound represented by the formula (V) or the phenoxazine compound represented by formula (VI).

[0069] The polymerisation process may for example be performed in the presence of an initiator. Such initiator may for example be an initiator composition comprising one or more selected from organic peroxides or azo compounds. Suitable organic peroxides may for example include diacyl peroxides, dialkyl peroxides, peroxymonocarbonates, peroxydicarbonates, peroxyketals, peroxyesters, cyclic peroxides, hydroperoxides. Suitable azo compounds may for example include 2,2'-azodi(isobutyronitrile), 2,2'-azodi(2-methylbutyronitrile), 1,1'- azodi(hexahydrobenzonitrile).

[0070] In an embodiment, the free radical initiator composition may for example comprise 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, tert-butyl peroxypivalate and / or t-butyl peroxy benzoate. Such initiators may for example be fed to the tubular reactor in a pure form or as a solution in a solvent. As solvent, for example a C2-C20 normal paraffin or C2-C20 isoparaffin may be used.24POLY0086-WO-ORD25For example, such solution may comprise >2.0% and <65.0% by weight of initiator, alternatively >5.0% and <40.0% by weight, alternatively >10.0% and <30.0% by weight, compared to the total weight of the solution.

[0071] After finishing off the polymerization, and having applied multiple cooling steps, the reaction mixture is depressurized and / or cooled and separated in a high-pressure separator (HPS). The high-pressure separator separates the reaction mixture into an ethylene rich stream, containing minor amounts of waxes and / or entrained polymer, and a polymer rich stream, which is sent for further separation to the low-pressure separator (LPS).

[0072] Ethylene stream is cooled down and cleaned in stream. Stream is a purge stream to remove impurities and / or inerts. The ethylene-based polymer separated in the LPS is further processed. The ethylene removed in the LPS is fed to the booster compressor, where during the compression condensables, like solvent, lubrication oil and other liquids, are collected and removed.

[0073] The invention will now be demonstrated with the following non-limiting examples.EXAMPLES

[0074] Purpose: To evaluate the extent of conversion of 2-hydroxyethyl methacrylate (HEMA) during the production of ethylene-HEMA copolymers in presence of phenothiazine or phenoxazine as inhibitor compounds under conditions of a preheater system. The conditions of preheater were selected to evaluate the extent of self-polymerization in the absence of initiator.

[0075] Material and process conditions: The details of the materials are provided below:Table 1Material DescriptionHigh Pressure Reactor Tubular reactorPreheater section Pressure 2000 bar (200 MPa)Vinyl based monomer (D) 2-hydroxyethyl methacrylate(HEMA (CAS No - 868-77-9))24POLY0086-WO-ORD26Protic solvent for mixing HEMA and Methanolinhibitors Phenothiazine / PhenoxazinePhenothiazine (Inhibitor as inventive 92-84-2compound)Phenoxazine (Inhibitor as inventive 135-67-1compound)MEHQ (Inhibitor as comparative) / 02 150-76-5Ethylene monomer flow rate in the 2 kg / hrpreheater sectionTemperature in the preheater As provided in Table 2Initiator No initiator was added in the preheater. Peroxide Initiator was added into the tubular reactor for polymerization.

[0076] Process Operation - For the present experiments, the inhibitor compounds were mixed with the monomer HEMA along with methanol (protic solvent) and were introduced in preheater section at a temperature as indicated below. The preheater system was positioned upstream to the polymerization reactor. The quantity of inhibitor compound was as given in the table below. The part of the product stream from the preheater was taken out for further analysis to evaluate if any polymeric or oligomeric products were formed in the preheater. The remaining stream from the preheater was subsequently passed to the tubular reactor for polymerization.

[0077] Polymerization in the tubular reactor - In a high-pressure tubular reactor, ethylene copolymers were prepared by reacting a feed mixture comprising ethylene and the HEMA monomer. In addition, a quantity of 1.40 mol % of isopropanol with regard to the molar quantity of ethylene was fed.

[0078] The reaction was performed at a pressure of 200 MPa and at a temperature of 200-210 °C. The reaction was initiated by addition of a 4.0 g / l solution of t-butyl peroxy pivalate (t-BPP) in heptane. The average residence time in the tubular reactor in all examples was 45 s. The obtained ethylene polymer was collected.24POLY0086-WO-ORD27Table 2Sample Inhibitor Quantity of Feed mol.% Temperature Conversion Conversion%Inhibitor HEMA of preheater % in the Tubular (ppm wt) (°C) preheater reactor sectionComparative 1 MEHQ / 02 500 0.1 200 0.99 Less than (CE1) 15% Comparative 2 MEHQ / 02 1750 0.1 200 0 Less than (CE2) 15% Comparative 3 MEHQ / 02 750 0.35 750 1.43 Less than (CE3) 15% Inventive 1 (IE1) Phenothiazine 50 0.1 150 0 More than 15% Inventive 2 (IE2) Phenothiazine 50 0.1 210 0.57 More than 15% Inventive 3 (IE3) Phenothiazine 100 0.1 150 0 More than 15% Inventive 4 (IE4) Phenothiazine 100 0.1 210 0 More than 15% Inventive 5 (IE5) Phenoxazine 50 0.1 150 0 More than 15% Inventive 6 (IE6) Phenoxazine 50 0.1 210 0 More than15%

[0079] The conversion in the preheater section was defined as:Conversion = ((the amount of polymeric or oligomeric products formed in the preheater) / (total amount of ethylene, HEMA monomer, and inhibitor compound fed into the preheater)) xl00%.

[0080] Results - From the data provided in the Table 2 it is evident that the conversion to polymeric or oligomeric products in the preheater is minimal for the inventive example (Inventive 1-6). A conversion of 0% or low conversion of around 0.57% at very high temperature (210 °C see Inventive example 2) is indicative of the fact that no or very minimal self-polymerization of HEMA occurred. For Inventive example 2, minimal self-polymerization occurred at high temperature even at relatively high temperature. In other words, from the results it may be24POLY0086-WO-ORD28concluded that self-polymerization of HEMA is significantly limited and almost negligible even with the use of limited amounts of phenothiazine and phenoxazine during the process of polymerization.

[0081] What is surprising is that relatively low amounts of phenothiazine or phenoxazine inhibitors were able to achieve low conversion, preferably no conversion to polymeric and oligomeric products in the preheater section. This is in contrast to conventional inhibitors such as MEHQ / 02, which required significantly higher amount of inhibitor compound. Infact, Comparative 2 had identical levels of conversion of 0% as that of Inventive Example 6. However, Comparative 2 used the inhibitor in an amount of 1750 ppm compared to 50 ppm used in Inventive Example 6.

[0082] Further, from Inventive example 6, even with a concentration of 50 ppm of phenoxazine the conversion of HEMA through self-polymerization is negligible or zero.

[0083] The lower amount of inhibitor signifies that Phenoxazine and Phenothiazine are particularly effective in preventing self-polymerization of HEMA in the preheater section. Both Phenoxazine and Phenothiazine were effective in preventing self-polymerization of HEMA in the preheater evidenced from the low conversion in the preheater. However, Phenoxazine was found to be marginally more effective than Phenothiazine as in Inventive 6, 0% conversion was achieved even at lower quantity than when Phenothiazine was used as shown in in Inventive 4.

[0084] To be able to prevent self-polymerization of HEMA when using the inhibitors in low quantities, is particularly advantageous as this helps in preventing the presence of the inhibitors in the final polymers as impurities. Further the presence of large quantities of inhibitors was found to adversely affect reaction kinetics during the polymerization. In particular, the presence of large amounts of inhibitors were found to adversely affect the functioning of the peroxide initiator in the tubular reactor and affect the conversion of ethylene. Further, for the inventive examples, IE1-IE6, the ethylene conversion to the ethylene copolymer was found to be higher than the comparative example CE1-CE3.

[0085] The content of recurring units derived from HEMA is determined via NMR, wherein the sample is dissolved in deuterated tetrachloroethane at 120° C. The NMR spectra is recorded with a Bruker Avance 500 NMR spectrometer equipped with a 10 mm diameter cryo-24POLY0086-WO-ORD29cooled probe head, operating at 125° C., to obtain both1H-NMR and13C-NMR spectra, measuring time13C-NMR 3 hrs,1H-NMR 30 min.

Claims

24POLY0086-WO-ORD30CLAIMS1. A process for producing an ethylene copolymer in a high-pressure polymerization reactor (T), comprising the step of polymerizing an ethylene monomer with a vinyl-based monomer (D) in presence of an inhibitor compound to obtain the ethylene copolymer, wherein the inhibitor compound is represented by the chemical formula I:R1 R8• wherein the substituents R1to R8are each independently selected from hydrogen or a substituent selected from C1-C20 alkyl, C1-C20 alkenyl, C6-C20 aryl, C6-C20 aralkyl, C1-C20 alkoxy, C6-C20 aryloxy, halogen, nitro group, or C6-C20 alkylaryl group, with each of the substituent being optionally substituted with one or more heteroatoms; or at least any two adjacent substituent R1-R2, R2-R3, R3-R4, R5-R6, R6-R7, R7-R8may be connected to form an aliphatic ring having 5-20 carbon atoms or an aromatic ring having 5-20 carbon atoms; and R9is any one of C1-C5 alkyl or hydrogen;• wherein the substituent ‘Q’ is any one of nitrogen, oxygen or sulphur, preferably wherein the high-pressure polymerization reactor is a tubular reactor; and wherein the vinyl based monomer (D) is selected from an acrylate based monomer (A) or an acrylate based ionomer (IA) and any combinations thereof; and• wherein the inhibitor compound is mixed with the vinyl-based monomer (D) in an amount of > 25.0 and < 450.0 parts per million by weight, with regard to the total weight of the vinyl-based monomer (D).

2. The process of claim 1, wherein the inhibitor compound of formula I, is at least one inhibitor compound selected from:24POLY0086-WO-ORD31where ‘X’ is any one of oxygen or sulfur, R4and R5are each C1-C5 alkyl group, preferably R4and R5are each methyl group; R2and R7are each independently selected from nitro group, halogen, methoxy group, tert-butyl group, a phenoxy group; orwhere ‘X’ is any one of oxygen or sulfur, preferably ‘X’ is sulfur; orwhere ‘X’ is any one of oxygen or sulfur, preferably ‘X’ is sulfur; or(iv) a phenothiazine compound represented by the formula (V)24POLY0086-WO-ORD32(v) a phenoxazine compound represented by formula (VI)H (vi),preferably wherein the inhibitor compound is selected from the phenothiazine compound represented by the formula (V), or the phenoxazine compound represented by formula (VI), more preferably wherein the inhibitor compound is phenoxazine compound represented by formula (VI).

3. The process according to any one of claims 1-2, wherein the ethylene copolymer comprising with regard to the total weight of the ethylene copolymer of:(i) > 90.0 and < 99.9 wt.%, preferably > 92.0 and < 99.0 wt.%, preferably > 93.0 and < 99.0 wt.%, of polymeric units derived from ethylene; and(ii) > 0.1 and < 10.0 wt.%, preferably > 1.0 and < 8.0 wt.%, preferably > 1.0 and < 7.0 wt.% of polymeric units derived from the vinyl-based monomer (D), preferably wherein the content of ethylene and vinyl-based monomer (D) is determined using13C NMR and / or1H NMR; andpreferably wherein the ethylene copolymer comprising with regard to the total weight of the ethylene copolymer of > 93.0 and < 99.0 wt.%, of polymeric units derived from ethylene; and > 1.0 and < 7.0 wt.% of polymeric units derived from the vinyl-based monomer (D).

4. The process according to any one of claims 1-3, wherein the process comprises the steps of:(a) mixing the inhibitor compound with the vinyl-based monomer (D) to form a comonomer mixture (M);(b) feeding the comonomer mixture (M) into a preheater unit (H) positioned upstream to the high-pressure reactor (T);(c) feeding the ethylene monomer into the preheater unit (H);24POLY0086-WO-ORD33(d) heating a reaction mixture (RM) comprising the ethylene monomer and the comonomer mixture (M) to form a preheated reaction mixture (R); and(e) introducing the preheated reaction mixture (R) into the high-pressure reactor (T) and polymerizing the ethylene monomer with the vinyl-based monomer (D) to obtain the ethylene copolymer; andwherein the reaction mixture (RM) is heated at any temperature of > 55.0 °C and < 250.0 °C, preferably > 55.0 °C and < 220.0 °C, preferably > 75.0 °C and < 170.0 °C, preferably > 75.0 °C and < 150.0 °C to obtain the preheated reaction mixture (R), preferably wherein the reaction mixture (RM) is heated in the preheater unit (H) in the absence of initiators.

5. The process according to any one of claims 1-4, wherein the inhibitor compound is mixed with a protic solvent or a non-protic solvent in a static mixer to obtain the comonomer mixture (M) and subsequently the comonomer mixture (M) is fed to the preheater (H), preferably wherein the inhibitor compound is mixed with methanol in a static mixer to obtain the comonomer mixture (M) and subsequently the comonomer mixture (M) is fed to the preheater (H).

6. The process according to any one of claims 1-5, wherein the inhibitor compound is mixed with the vinyl based monomer (D) in an amount of > 25.0 and < 350.0 parts per million by weight, preferably > 25.0 and < 250.0 parts per million by weight, preferably > 45.0 and < 150.0 parts per million by weight, preferably > 45.0 and < 110.0 parts per million, preferably > 45.0 and < 80.0 parts per million by weight by weight, with regard to the total weight of the vinyl based monomer (D).

7. The process according to any one of claims 1-6, wherein the inhibitor compound is selected such that when the comonomer mixture (M) comprising the vinyl based monomer (D) and the inhibitor compound is exposed at any temperature of > 55.0 °C and < 250.0 °C, preferably > 55.0 °C and < 220.0 °C, preferably > 75.0 °C and <210.0 °C, preferably > 150 °C and < 210 °C, the conversion of the vinyl based monomer (D) to the polyvinyl polymer24POLY0086-WO-ORD34ranges from 0 > and < 0.6 %, preferably 0 > and < 0.5 %, with regard to the total weight of the comonomer mixture (M).

8. The process according to any one of claims 1-7, wherein the process comprises the steps of compressing the ethylene monomer in one or more compressor units (CP) positioned upstream to the preheater unit (H) such that the ethylene monomer is fed into the preheater unit (H) at any pressure of >180 MPa and <280 MPa.

9. The process according to any one of claims 1-8, wherein the polymerization of the ethylene monomer with the vinyl monomer (D) is carried out in the high pressure reactor (T) at any pressure of >180 MPa and <350 MPa, preferably > 200 MPa and <300 MPa and at any temperature of >100 °C and < 350 °C, preferably >150 °C and <310 °C, preferably >150 °C and < 260 °C, preferably >150 °C and <250 °C; and / or wherein the polymerization of the ethylene monomer with the vinyl based monomer (D) is carried out in the absence of molecular oxygen.

10. The process according to anyone of claims 1-9, wherein the polymerization of the ethylene monomer with the vinyl based monomer (D) is carried out in presence of initiators wherein the initiator is introduced in the high pressure reactor in an amount of > 0 ppm and < 300 ppm, preferably > 0 ppm and < 200 ppm, with regard to the total weight of the preheated reaction mixture (R); and wherein the initiator is selected from organic peroxides, azo based compounds and combinations thereof.

11. The process according to anyone claims 1-10, wherein the inhibitor compound is selected from the phenothiazine compound represented by the formula (V)24POLY0086-WO-ORD35(V), or the phenoxazine compound represented by formula (VI)(VI); andwherein the vinyl based monomer (D) is an acrylate based monomer (A), preferably wherein the inhibitor compound is phenoxazine and the vinyl based monomer (D) is an acrylate based monomer (A) and wherein the inhibitor compound is mixed with the vinyl based monomer (D) in an amount of > 45.0 and < 110.0 parts per million by weight, preferably > 45.0 and < 80.0 parts per million by weight with regard to the total weight of the vinyl based monomer (D).

12. The process according to any one claims 1-11, wherein the vinyl based monomer (D) is an acrylate based monomer (A) selected from the group consisting of 2-hydroxy ethyl acrylate, 2-hydroxy ethyl methacrylate, 3-hydroxypropyl acrylate, 3-hydroxypropyl methacrylate, 2- hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 2,3 -dihydroxypropyl acrylate, 2,3- dihydroxypropyl methacrylate, 4-hydroxybutyl acrylate, 4-hydroxybutyl methacrylate, polypropylene glycol) monoacrylate, poly(propyleneglycol) monomethacrylate, poly(ethylene glycol) monoacrylate, poly(ethylene glycol) monomethacrylate, poly(ethylenepropyleneglycol) monomethacrylate and 2-hydroxy ethyl vinyl ether, 1,4- butanediol dimethacrylate, hexanediol dimethacrylate, ethyleneglycol dimethacrylate, 1,3- butylene glycol dimethacrylate, dodecanediol dimethacrylate, glycerol dimethacrylate, 1,4-butanediol diacrylate, hexanediol diacrylate, ethylene glycol diacrylate, 1,3 -butylene glycol diacrylate, dodecanediol diacrylate, glycerol diacrylate, glycerol 1,3-diglycerolate diacrylate, glycerol 1,3-diglycerolate dimethacrylate, poly(ethylene glycol) dimethacrylate, polypropylene glycol) dimethacrylate, poly(ethylenepropyleneglycol)24POLY0086-WO-ORD36dimethacrylate, 1,4-butanediol divinyl ether, poly(ethylene glycol) divinyl ether, di(ethyleneglycol) divinyl ether, 1,5-hexadiene, 1,7-octadiene, 1,9-decadiene and 1,13- tetradecadiene, preferably the vinyl based monomer (D) is an acrylate based monomer (A) selected from 2-hydroxy ethyl methacrylate, 1,4-butanediol dimethacrylate and combinations thereof, preferably wherein the acrylate monomer is 2-hydroxyethyl methacrylate.

13. The process according to claim 12, wherein the process comprises the step of polymerizing ethylene with 2-hydroxyethyl methacrylate to obtain the ethylene copolymer comprising polymeric units derived from ethylene and 2-hydroxyethyl methacrylate; wherein the polymerization is carried out in presence of a inhibitor compound selected from the phenothiazine compound represented by the formula (V) or the phenoxazine compound represented by formula (VI); wherein the inhibitor compound is present in an amount of > 45.0 and < 110.0 parts per million by weight, with regard to the total weight of 2- hydroxy ethyl methacrylate.

14. The process according to anyone claims 1-11, wherein the vinyl based monomer (D) is an acrylate based ionomer (IA) having any one of structure selected fromIPC MAMADAME MAMAtBu24POLY0086-WO-ORD37MADAME-AAMPSA DEAEMA-AAMPSAtBuAEM-AAMPSApreferably wherein the vinyl based monomer (D) is an acrylate based ionomer (IA) represented by the structure below and defined as MAMADAME:, where the ionomer MAMADAME is derived from methacrylic acid (MA) and dimethylaminoethyl methacrylic acid (MADAME).

15. Use of the inhibitor compound as described in any one of claims 1-14 for preventing reactor fouling in a process of forming ethylene copolymer.

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