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Title:
THE METHOD OF REDUCING POLYMER DEPOSITS ON THE SURFACES OF THE REACTOR EQUIPMENT IN THE OLEFIN OLIGOMERIZATION PROCESS
Document Type and Number:
WIPO Patent Application WO/2020/263113
Kind Code:
A1
Abstract:
The present invention relates to a method of reducing polymer deposits on the internal surfaces of a reactor equipment, wherein the polymer is a by-product of the process of olefin oligomerization or is formed during the process of olefin polymerization or copolymerization. The method of reducing polymer deposits on the surfaces of reactor equipment during the process of oligomerization or (co-polymerization of olefins involves the preliminary application of a zinc-containing coating onto the internal surfaces of the reactor equipment that are in contact with the reaction medium. Wherein, zinc metal and/or zinc compounds such as zinc oxide, zinc hydroxide, and organic zinc compounds, in particular alkylzinc, are used as the zinc-containing coating. The invention further relates to a process of oligomerization or (co-polymerization of olefins, which comprises reacting raw materials comprising -olefin, under reaction conditions, in the presence of a catalytic system, in the reactor equipment with the zinc-containing coating having been applied on the inner surfaces thereof. In addition, the invention relates to a method of applying a zinc-containing coating and a coating obtained by this method.

Inventors:
LIPSKIKH MAXIM VLADIMIROVICH (RU)
PROTSAY YURY VLADIMIROVICH (RU)
KHUSAINOV AIRAT FARITOVICH (RU)
Application Number:
PCT/RU2019/000466
Publication Date:
December 30, 2020
Filing Date:
June 26, 2019
Export Citation:
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Assignee:
SIBUR HOLDING PUBLIC JOINT STOCK CO (RU)
International Classes:
C23C2/06; C08F2/01; C08F10/00; C23C10/34; C23C22/02; C23C22/73
Domestic Patent References:
WO2005080439A22005-09-01
Foreign References:
US8088870B22012-01-03
RU2412002C12011-02-20
US5548040A1996-08-20
RU2401320C12010-10-10
US20170334734A12017-11-23
RU2073070C11997-02-10
RU2430116C12011-09-27
Attorney, Agent or Firm:
LAW FIRM "GORODISSKY & PARTNERS" LTD. (RU)
Download PDF:
Claims:
CLAIMS

1. A method for reducing polymer deposits on surfaces of a reactor equipment in the olefin oligomerization process, the method comprising preliminary application of a zinc-containing coating onto the internal surfaces of the reactor equipment which surfaces are in contact with the reaction medium.

2. The method of claim 1, wherein the zinc-containing coating comprises zinc metal and/or zinc compounds.

3. The method of claim 2, wherein a highly dispersed zinc metal powder is used as zinc metal.

4. The method of claim 2, wherein zinc oxide, zinc hydroxide and/or alkyl zinc are used as the zinc compounds.

5. The method of claim 4, wherein diethylzinc, di-(i-propyl)zinc and/or di-(i- butyl)zinc are used as the alkylzinc compounds.

6. The method according to claim 5, wherein diethylzinc is used as the alkylzinc compound.

7. The method of claim 1, wherein the zinc-containing coating is applied onto the inner surfaces of the reactor equipment by galvanizing with metallic zinc or by treating the equipment with a reaction solution comprising a zinc compound.

8. The method of claim 7, wherein the zinc-containing coating is applied onto the internal surfaces of the reactor equipment by the method of galvanizing by saturating the surface of the reactor equipment with zinc in a highly dispersed zinc powder medium at a temperature of from 290°C to 450°C.

9. The method of claim 7, wherein the zinc-containing coating is applied onto the inner surfaces of the reactor equipment by the method of galvanizing by dipping the equipment in a bath with molten zinc, preferably at a temperature of about 450-470°C.

10. The method of claim 1, wherein the zinc-containing coating is applied onto the internal surfaces of the reactor equipment comprises the following steps:

a) preparing the zinc reaction solution by mixing the zinc compound with a hydrocarbon solvent;

b) introducing the zinc reaction solution into the reactor equipment;

c) stirring the zinc reaction solution in the reactor equipment at a temperature of from 25°C to 150°C.

11. The method of claim 10, wherein the zinc reaction solution is a solution of a zinc compound in a hydrocarbon solvent.

12. The method of claim 10, wherein the entire space of the reactor equipment where the deposition of the polymer is possible is filled with a solvent prior to introducing the zinc reaction solution.

13. The method according to claim 10, wherein the amount of zinc reaction solution based on the rate of from 0.1 to 5.0 g of zinc compound calculated as zinc metal, preferably 2.0 g of zinc compound calculated as zinc metal, per one liter of the total solvent present in the reactor equipment is introduced.

14. The method of claim 10, wherein the stirring of the zinc reaction solution in the reactor equipment is carried out at a temperature of from 90°C to 100°C.

15. The method of claim 10, wherein the stirring is carried out with a gradual temperature increase from 25°C to 150°C at the rate of from 20°C to 100°C/hour, preferably at the rate of 50°C/hour.

16. The method of claim 10, wherein the stirring at the temperature of from 25°C to 150°C is carried out for the time period of 1 to 6 hours, preferably of 3 to 4 hours.

17. The method of claim 10, wherein aliphatic or cycloaliphatic hydrocarbons having from 6 to 16 carbon atoms are used as the hydrocarbon solvent for zinc compounds.

18. The method of claim 17, wherein the hydrocarbon solvent further comprises unsaturated hydrocarbons, such as olefins or aromatic compounds.

19. The method of claim 10, wherein heptane, cyclohexane, decane, undecane, iso-decane fraction, hexene- 1, Isopar™ (ExxonMobil), or the mixtures thereof are used as the hydrocarbon solvent for zinc compounds.

20. A process of olefin oligomerization comprising reacting a raw material containing a-olefin, under oligomerization conditions and in the presence of a catalytic system comprising a chromium source, a nitrogen-containing ligand and an alkylaluminum, in a reactor equipment, wherein a zinc-containing coating has been applied onto inner surfaces of the said reactor equipment that are in contact with the reaction medium.

21. The process of claim 20, wherein the zinc-containing coating comprises zinc metal and/or zinc compounds.

22. The process of claim 21, wherein a highly dispersed zinc metal powder is used as zinc metal.

23. The process of to claim 21, wherein zinc oxide, zinc hydroxide and/or alkylzinc are used as the zinc compounds.

24. The process according to claim 23, wherein diethylzinc, di-(i-propyl)zinc and/or di-(i-butyl)zinc are used as the alkylzinc compounds.

25. The process according to claim 24, wherein diethylzinc is used as the alkylzinc compound.

26. The process of claim 20, wherein ethylene (ethene), propylene (propene) and/or butylene (butene) are used as the a-olefin.

27. The process of claim 20, wherein a compound of the general formula CrXn is used as the chromium source, where X represents the same or different organic or inorganic substituents, and n is an integer from 1 to 6.

28. The process of claim 27, wherein the substituents X are organic groups having from 1 to 20 carbon atoms, and are selected from the group consisting of an alkyl group, an alkoxy group, a carboxyl group, acetylacetonate, an amino group, and an amido group.

29. The process of claim 20, wherein an organic compound comprising pyrrole ring, i.e. five-membered heteroaromatic ring with one nitrogen atom is used as the nitrogen-containing ligand.

30. The process of claim 29, wherein the nitrogen-containing ligand is selected from the group comprising pyrrole, 2,5-dimethylpyrrole, lithium pyrrolide C4H4NL1, 2- ethylpyrrole, 2-allylpyrrole, indole, 2-methylindole, 4,5,6,7-tetrahydroindole.

31. The process of claim 20, wherein an alkylaluminum compound, a halogenated alkylaluminum compound, an alkoxyalkylaluminum compound, and mixtures thereof are used as the alkylaluminum.

32. The process of claim 20, wherein the compounds used as alkylaluminum are represented by the general formulas AIR3, AlRaHal, AIRHab, AIR2OR, AIRHalOR and/or AhRsHa , where R is an alkyl group, Hal is a halogen atom.

33. The process of claim 32, wherein the alkylaluminum is selected from the group consisting of triethylaluminum, diethylaluminum chloride, tripropylaluminum, triisobutylaluminum, diethylaluminum ethoxide and/or ethylaluminum sesquichloride, and mixtures thereof.

34. The process of claim 20, wherein the molar ratio of aluminum : chromium is from 5:1 to 500:1, preferably from 10:1 to 100:1, most preferably from 20:1 to 50:1.

35. The process of claim 20, wherein the molar ratio of ligand : chromium is from 2:1 to 50:1, preferably, from 2.5:1 to 5:1.

36. The process of claim 20, wherein the catalytic system for carrying out the oligomerization reaction is obtained using microwave irradiation.

37. The process of claim 20, wherein the alkylaluminum is subjected to microwave irradiation.

38. The process of claim 36, wherein the applied microwave radiation has a frequency in the range of 0.2 to 20 GHz, preferably a frequency of 2.45 GHz.

39. The process of claim 36, wherein the applied microwave power is from 1 W to 5000 W per 1 g of alkylaluminum calculated in terms of elemental aluminum.

40. The process of claim 36, wherein the duration of the microwave irradiation is in the range of from 20 seconds to 20 minutes, preferably is 15 minutes.

41. The process of claim 20, wherein, in the oligomerization process, the pressure of the raw materials comprising olefin is in the range of from 1 to 200 atm, preferably from 10 to 60 atm, most preferably from 15 to 40 atm.

42. The process of claim 20, wherein the temperature of the oligomerization process is in the range of from 0°C to 160°C, preferably from 40°C to 130°C.

43. The process of claim 20, wherein the olefin and the catalytic system are contacted with hydrogen, which is fed to the oligomerization reactor.

44. A method for reducing polymer deposits on surfaces of a reactor equipment in the olefin polymerization or copolymerization process, the method comprising preliminary application of a zinc-containing coating on the internal surfaces of the reactor equipment which surfaces are in contact with the reaction medium.

45. The method of claim 44, wherein the zinc-containing coating comprises zinc metal and/or zinc compounds.

46. The method of claim 45, wherein a highly dispersed zinc metal powder is used as zinc metal.

47. The method of claim 45, wherein zinc oxide, zinc hydroxide and/or alkyl zinc are used as zinc compounds.

48. The method of claim 47, wherein diethylzinc, di-(i-propyl)zinc and/or di-(i- butyl)zinc are used as alkylzinc compounds.

49. The method of claim 48, wherein diethylzinc is used as the alkylzinc compound.

50. The method of claim 44, wherein the zinc-containing coating is applied onto the inner surfaces of the reactor equipment by galvanizing with metallic zinc or by treating the equipment with a reaction solution comprising zinc compound.

51. The method of claim 50, wherein the zinc-containing coating is applied onto the internal surfaces of the reactor equipment by the method of galvanizing by saturating the surface of the reactor equipment with zinc in a highly dispersed zinc powder medium at a temperature of from 290°C to 450°C.

52. The method of claim 50, wherein zinc-containing coating is applied onto the inner surfaces of the reactor equipment by the method of galvanizing by dipping the equipment in a bath with molten zinc, preferably at a temperature of about 450-470°C.

53. The method of claim 44, wherein the zinc-containing coating is applied onto the internal surface of the reactor equipment comprises the following steps:

a) preparing the zinc reaction solution by mixing the zinc compound with a hydrocarbon solvent;

b) introducing the zinc reaction solution in the reactor equipment;

c) stirring the zinc reaction solution in the reactor equipment at a temperature of from 25 °C to 150°C.

54. The method of claim 53, wherein the zinc reaction solution is a solution of a zinc compound in a hydrocarbon solvent.

55. The method of claim 53, wherein the entire space of the reactor equipment where the deposition of polymer is possible is filled with a solvent prior to introducing the zinc reaction solution.

56. The method of claim 53, wherein the amount of zinc reaction solution based on the rate of from 0.1 to 5.0 g of zinc compound calculated as zinc metal, preferably

2.0 g of zinc compound calculated as zinc metal, per 1 liter of the total solvent present in the reactor equipment is introduced.

57. The method of claim 53, wherein the stirring of the zinc solution in the reactor equipment is carried out at a temperature of from 90°C to 100°C.

58. The method of claim 53, wherein the stirring is carried out with a gradual temperature increase from 25°C to 150°C at a rate of from 20°C to 100°C/hour, preferably at a rate of 50°C/hour.

59. The method of claim 53, wherein the stirring at a temperature of from 25°C to 150°C is carried out for the time period of from 1 to 6 hours, preferably from 3 to 4 hours.

60. The method of claim 53, wherein aliphatic or cycloaliphatic hydrocarbons having from 6 to 16 carbon atoms are used as the hydrocarbon solvent for zinc compounds.

61. The method of claim 53, wherein the hydrocarbon solvent further comprises unsaturated hydrocarbons, such as olefins or aromatics.

62. The method of claim 53, wherein heptane, cyclohexane, decane, undecane, iso-decane fraction, hexene- 1, Isopar™ (ExxonMobil), or mixtures thereof are used as a hydrocarbon solvent for zinc compounds.

63. A process of olefin polymerization or copolymerization, comprising reacting a raw material comprising olefin in the presence of a catalytic system for (co- )polymerization, in the reactor equipment having inner surfaces, on which a zinc- containing coating has been applied.

64. The process of claim 63, wherein a monomer having from 2 to 6 carbon atoms, in particular ethylene, propylene or hexene- 1, is used as the olefin.

65. The process of claim 63, wherein the polymerization or copolymerization is carried out in suspension, solution or gas-phase mode.

66. The process of claim 63, wherein the polymerization or copolymerization is carried out after the completion of oligomerization, with preliminary isolation of the resulting olefin oligomer and subsequent polymerization or copolymerization thereof.

67. A method of applying a zinc-containing coating on the surface of a reactor equipment, comprising the following steps: a) preparing the zinc reaction solution by mixing the zinc compound with a hydrocarbon solvent;

b) introducing the zinc reaction solution into the reactor equipment;

c) stirring the solution of zinc in the reactor equipment at a temperature of from 25°C to 150°C.

68. The method of claim 67, wherein zinc oxide, zinc hydroxide and/or alkyl zinc are used as zinc compounds.

69. The method of claim 68, wherein diethylzinc, di-(i-propyl)zinc and/or di-(i- butyl)zinc are used as the alkylzinc compounds.

70. The method of claim 69, wherein diethylzinc is used as the alkylzinc compound.

71. The method of claim 67, wherein the zinc reaction solution is a solution of a zinc compound in a hydrocarbon solvent.

72. The method of claim 67, wherein entire space of the reactor equipment where the polymer deposition is possible is filled with a solvent prior to introducing the zinc reaction solution.

73. The method of claim 67, wherein the amount of zinc reaction solution based on the rate of from 0.1 to 5.0 g of zinc compound calculated as zinc metal, preferably 2.0 g of zinc compound calculated as zinc metal, per 1 liter of the total solvent present in the reactor equipment is introduced.

74. The method of claim 67, wherein the stirring of the zinc solution in the reactor equipment is carried out at a temperature of from 90°C to 100°C.

75. The method of claim 67, wherein stirring is carried out with a gradual temperature increase from 25°C to 150°C at the rate of from 20°C to 100°C/hour, preferably at the rate of 50°C/hour.

76. The method of claim 67, wherein the stirring at the temperature of from 25°C to 150°C is carried out for the time period of 1 to 6 hours, preferably from 3 to 4 hours.

77. The method of claim 67, wherein aliphatic or cycloaliphatic hydrocarbons having from 6 to 16 carbon atoms are used as the hydrocarbon solvent for zinc compounds.

78. The method of claim 67, wherein the hydrocarbon solvent further comprises unsaturated hydrocarbons, such as olefins or aromatics.

79. The method of claim 67, wherein heptane, cyclohexane, decane, undecane, iso-decane fraction, hexene- 1, IsoparTM (ExxonMobil), or mixtures thereof are used as the hydrocarbon solvent for zinc compounds.

80. A zinc-containing coating obtained by the method of claim 67.

Description:
THE METHOD OF REDUCING POLYMER DEPOSITS ON THE SURFACES OF THE REACTOR EQUIPMENT IN THE OLEFIN OLIGOMERIZATION

PROCESS

FIELD OF THE INVENTION.

The invention relates to the field of olefin oligomerization in order to obtain linear a-olefins, in particular hexene- 1, as well as to the field of olefin polymerization and copolymerization in order to obtain valuable polymer products such as linear low- density polyethylene, polyhexene, etc. In particular, the invention relates to a method for reducing polymer deposits on the internal surfaces of reactor equipment, where the polymer is either a by-product of the olefin oligomerization process or a desired polymer formed during the polymerization or copolymerization of olefins.

BACKGROUND OF THE INVENTION

The process of selective oligomerization of ethylene is known as an effective method of producing a-olefins of higher molecular weight, which are used as intermediates in the chemical industry or used directly as a raw material in the field of polymer chemistry. In particular, the process of ethylene trimerization is of great industrial importance, since the trimer obtained in this process, hexene- 1, is especially in demand, for example, for the production of linear polyethylene of low, medium and high density and other equally valuable products.

The main problem arising in the olefin oligomerization is the low selectivity with regard to the desired oligomer, resulting in the formation of by-products, which are other polymers and oligomers. Thus, in the process of ethylene trimerization, in addition to the target product, hexene- 1, other hexene isomers (for example, 2-hexene and 3- hexene) are usually also formed, as well as higher ethylene oligomers (for example, octene, decene and dodecene) and polyethylene.

The prior art provides various ways to solve this problem, which are mainly related to the development of an efficient catalytic system capable of increasing the selectivity to the desired a-olefin, thereby reducing, in turn, the amount of the formed by-products. However, such catalytic systems are often insufficiently effective and expensive and, despite the fact that a reduction in the by-product polymer formation is achieved, it is completely impossible to get rid of the by-product. For example, US6800702B2 claims a catalytic system for olefins oligomerization, comprising:

(a) a source of the transition metal of the VI group;

(b) a ligand corresponding to the formula (R 1 )(R 2 )X-Y-X(R 3 )(R 4 ) or X(R 1 )(R 2 )(R 3 ), wherein X is phosphorus, arsenic or antimony; Y is a connecting group; and each of R 1 , R 2 , R 3 , R 4 is independently a hydrocarbon, substituted hydrocarbon, hetero-hydrocarbon or substituted hetero-hydrocarbon group, at least one of which in each of the above structures has a polar substituent that is not a phosphane, arsan or stiban group; and (c) optionally an activator. In accordance with the embodiments of this invention, the use of the claimed catalytic system allows to achieve selectivity to hexene- 1 of more than 90%, while the purity of hexene- 1 in the hexene fraction is 99.9%.

W02003053891A1 discloses a catalytic system based on bis-(2- diethylphosphino-ethyl)-amine and a solution of CrCb in tetrahydrofuran (1 :1), wherein methylalumoxane (850 eq.) is used as an activator. Such a catalytic system allows to provide selectivity to hexene- 1 around 93.2%, however, about 2% of the by-product polymer is also formed.

The formation of polymeric by-products during the olefin oligomerization leads to negative consequences. Thus, when the process is implemented on an industrial scale, the polymer can form deposits on the inner surfaces of the oligomerization reactors and/or product lines, as well as on other equipment coming into contact with the reaction mixture and the product mixture. In this regard, it becomes necessary to remove polymer deposits formed on the surfaces of the reactor equipment in order to avoid decrease of technological process parameters.

In the prior art, the methods are known to address the problem of polymer deposition, which, for example, include washing equipment with various solutions (US3654940, RU2243830).

In particular, according to the method described in the patent RU2403991, a hot solvent with a temperature of 75°C is introduced into the reactor after the completion of the oligomerization reaction, resulting in the dissolution of the polymer deposits. The solvent used is a hydrocarbon solvent, preferably toluene. This method does not require mechanical cleaning, and the cleaning downtime of the reactor is considerably reduced, however, the use of such a method entails the need for subsequent thorough washes of the reactor equipment to remove traces of the solvent, as well as carrying out the regeneration step of the solvent used in the cleaning process.

There are also other methods of equipment washing in order to remove polymer deposits, where a mixture of 96% ethyl alcohol and acetic acid at the ratio of 1 :3 is used as a washing solution (P.P.Purygin, N.G.Cheremnykh, G.P.Zhestovsky "Industry SK", N« 8, p.lO). The method involves dismantling the equipment, placing it into a special bath with a solution, submerging it for about 12 hours and then rinsing it with water. This method can be applied only for small-sized equipment, and the use of acid can lead to equipment corrosion.

Thus, reactor washing methods known in the art often permit the removal of polymer deposits without the need for subsequent mechanical cleaning, but the use of washing solutions entails the need for their disposal. In addition, the washing of the reactor is accompanied by the downtime of the equipment operation, which is undesirable due to economic aspects.

Methods are known, where preliminary processing of the reactor surface is carried out in order to minimize roughness thereof for the purpose of reducing polymer deposits on the surface. Thus, a common method of processing equipment, in order to reduce polymer deposits on its surfaces and corrosion, is enameling (SU94008). The application of enamel is a time consuming and expensive process, especially for the surfaces of equipment of complex construction.

Thus, the methods known from the prior art to reduce or eliminate deposits of by-product polymer on equipment surface, which may include steam treatment of the polymer, treatment with water to exfoliate the polymer from equipment surfaces and physically remove the polymer, etc., are not sufficiently effective since they often entail the need for the equipment downtime or significant labor costs.

In this regard, it is important to develop a method that would reduce polymer deposits on the surface of the reactor equipment, without the need to suspend the process.

SUMMARY OF THE INVENTION The object of the present invention is to develop a method to reduce the deposition of polymer on the internal surfaces of the reactor equipment, wherein the polymer is a by-product of the process of olefin oligomerization.

The technical result resides in the reduction of deposits of a by-product polymer on the surfaces of the reactor equipment and, as a consequence, an increase in the equipment uptime. Another technical result resides in facilitating reactor equipment cleaning operation in case of need, which is achieved by reducing the number of surface sites of polymer growth on the equipment surfaces, due to which the polymer chains are not predisposed to form long fibrous structures; instead, the polymer is formed into fine globules that are easily removed from the reaction zone. Also, the technical result resides in removing residual moisture and oxygen-containing compounds toxic for the catalytic system from the reactor equipment, thereby increasing the efficiency of the used catalytic system and reducing its expenditure. The additional technical result resides in providing a method of applying a zinc-containing coating in a hydrocarbon solvent medium, which then serves as a medium for carrying out the oligomerization process without the need for the solvent replacement.

This technical problem is solved and the achievement of the technical result is ensured by pre-coating the inner surface of the reactor equipment with a zinc-containing coating, which is represented by zinc metal and/or zinc compounds. The present inventors found out that the application of the zinc-containing coating on the inner surface of the reactor equipment significantly reduces the deposition of the polymer, despite the fact that the surface of the equipment remains rough to some extent.

BRIEF DESCRIPTION OF THE DRAWINGS

To clarify the technical solutions disclosing the essence of the invention, FIG. 1 and FIG. 2 are provided.

FIG. 1 shows the tube lattice of the reactor equipment after the oligomerization process, wherein no zinc-containing coating was applied on the surface of the reactor equipment. White coat present is the deposits of the by-product polymer.

FIG. 2 shows the tube lattice of the reactor equipment after the oligomerization process, where a zinc-containing coating was preliminarily applied on the surface of the reactor equipment. The figure shows that the tube lattice is clear of the by-product polymer deposits. Invention Description

The method of reducing polymer deposits on the surfaces of the reactor equipment in the process of olefin oligomerization comprises the preliminary deposition of a zinc-containing coating onto the internal surfaces of the reactor equipment exposed to the reaction medium. The application of zinc-containing coatings on the internal surfaces of the reactor equipment is carried out by galvanizing with metallic zinc or by treating the surfaces with the reaction solution comprising zinc compounds.

As it is used in the present invention, the term "reactor equipment" means any container(s) in which the process of olefin oligomerization proceeds. The surfaces of the reactor equipment include equipment surfaces that are in contact with or can be in contact with the reaction medium, as well as other surfaces that come into contact with the reaction medium, on which polymer deposits can be formed.

Any highly dispersed zinc metal powder can be used as a source of zinc for applying onto the surface of the reactor equipment. The shape of the particles can be varied: e.g. spherical particles, or particles of a scaly, elongated, oblong shape. The process of coating the reactor equipment surfaces with metallic zinc is carried out by any method known in the art. In particular, galvanizing is used, which is known as hot or cold galvanizing, as well as diffusion galvanizing. For example, a zinc-containing coating can be deposited onto the surface of the reactor equipment by saturating the surface of the reactor equipment with zinc in the environment of highly dispersed zinc powder at a temperature of from 290°C to 450°C. (See GOST 9.316-2006: "Unified system of protection against corrosion and aging. Zinc thermal diffusion coatings. General requirements and methods of control".)

Another method of applying a zinc-containing coating is dipping of small-sized equipment into a batch with molten zinc, preferably at a temperature of about 450- 470°C (hot-dip galvanizing). More specifically, the method involves surface preparation (pre-treatment) of the reactor equipment to remove contaminants, preparing a zinc alloy by heating zinc to a temperature of 450-470°C and then immersing the equipment into a molten zinc bath. The final step is the removal of the equipment from the molten zinc bath, the removal of excess zinc by drainage, vibration, and/or centrifuging and subsequent cooling of the equipment to obtain a zinc-containing coating on its surface. (See GOST ISO 10684-2015: Fasteners. Hot dip galvanized coatings.) It should be noted that the use of dispersed metallic zinc for the zinc-containing coatings is possible primarily for the treatment of reactor equipment, the surfaces of which are smooth or are slightly curved. In the case of using of the reactor equipment of complex construction or large geometric dimensions, the most effective is the use of zinc compounds, which may be represented by zinc oxide, zinc hydroxide, organic zinc compounds, or mixtures thereof. The ratio of inorganic and organic compounds in a mixture may be, for example, about 1 :1, but the minimum content or the complete absence of inorganic zinc compounds in solution is most preferable. It is most preferable to use organic zinc compounds, in particular alkylzinc, preferably in a hydrocarbon solvent. Diethylzinc, di-i-propylzinc, di-i-butylzinc or mixtures thereof can be used as alkylzinc. The best technical result is achieved when diethyl zinc in a hydrocarbon solvent is used.

As the hydrocarbon solvent for the alkylzinc, aliphatic or cycloaliphatic hydrocarbons containing from 6 to 16 carbon atoms are used. The composition of the hydrocarbon solvent may also comprise unsaturated hydrocarbons, such as olefins or aromatic compounds. Suitable hydrocarbon solvents or solvent components are represented by heptane, cyclohexane, decane, undecane, iso-decane fraction, hexene- 1, Isopar™ (ExxonMobil), or mixtures thereof.

The process of applying a zinc-containing coating onto the internal surfaces of the reactor equipment includes the following steps:

a) preparation of a zinc reaction solution by mixing a zinc compound with a hydrocarbon solvent;

b) introducing the zinc reaction solution into the reactor equipment;

c) mixing the zinc reaction solution in the reactor equipment at a temperature of from 25°C to 150°C.

Bringing the zinc reaction solution representing a zinc compound in a hydrocarbon solvent into the contact with the reactor equipment, followed by temperature increase, contributes to the decomposition of zinc compounds and the subsequent formation of a zinc-containing coating on the surface of the reactor equipment. Besides the temperature increase, the presence of impurities such as oxygen and water may also contribute to the decomposition of zinc compounds. According to the invention, the zinc reaction solution is a zinc compound in a hydrocarbon solvent. The concentration of zinc in the hydrocarbon solvent is not limited and is determined based on the required concentration of zinc compounds in the reaction solution.

The delivery of the zinc reaction solution into the reactor equipment is carried out by any available procedure. To achieve the best technical result, all space of the reactor equipment within which polymer deposition is possible is filled with a solvent before introducing the zinc reaction solution, wherein the solvent used is any hydrocarbon solvent suitable for carrying out the oligomerization process. Then the zinc reaction solution is injected into the reactor equipment filled with a hydrocarbon solvent, wherein the amount of the zinc reaction solution is defined at a rate of from 0.1 to 5.0 g, preferably 2.0 g of zinc compound calculated as zinc metal per one liter of total solvent being found in the reactor equipment.

Stirring of the zinc reaction solution in the reactor equipment is carried out at a temperature corresponding to the decomposition temperature of the selected zinc compound. Preferably, the stirring of the zinc reaction solution in the reactor equipment is carried out at a temperature in the range of from 25°C to 150°C, most preferably from 90°C to 100°C. Wherein, an increase of the temperature up to the specified values is carried out gradually, while permanently stirring. It is preferable to carry out the gradual increase of the temperature at the rate of from 20°C to 100°C/hour, preferably at the rate of 50°C/hour. During raising the temperature of the solution to the specified temperature, it is necessary to stir the zinc reaction solution in the solvent for 1 to 6 hours, preferably for 3 to 4 hours.

After the completion of the process of applying the zinc coating, reactor equipment can be used for the oligomerization process without the need to change the solvent. Thus, in accordance with the present invention, the olefins and the components of the catalytic system are introduced directly into the reactor equipment filled with the hydrocarbon solvent.

The olefin oligomerization process according to the present invention includes reacting raw materials containing a-olefin, under oligomerization conditions and in the presence of a catalytic system comprising a chromium source, a nitrogen-containing ligand, and an alkylaluminum in the reactor equipment, the inner surfaces of which have a zinc-containing coating applied. Wherein, the process and conditions for a-olefins oligomerization can be any process and conditions known from the prior art, for example those known from WO 2011/093748.

In accordance with the present invention, the catalytic system comprises a chromium source, a nitrogen-containing ligand, and an alkylaluminum.

It is known that the catalytic system for olefin oligomerization, along with the source of chromium, nitrogen-containing ligand and alkylaluminum often contains zinc compound too, which serves as an additional activator of the catalytic site, in particular chromium.

The advantage of the method of the present invention is the reduction, up to 100%, of the diethyl zinc amount in the composition of the catalytic system. The inventors have found that carrying out the olefin oligomerization in reactor equipment having the inner surfaces with a zinc-containing coating applied thereto contributes to the efficiency increase of the catalytic system without the need to include a zinc compound thereinto. Besides, the activity of the catalytic system was found to be maintained for a long period of time, which is probably due to the neutralization of catalytic poisons, in particular water and/or oxygen, in the reactor equipment and the recycled solvent by treating the reactor equipment with a zinc reaction solution, which provides applying a zinc-containing coating onto the internal surfaces of the equipment.

Thus, using a catalytic system comprising a source of chromium, a nitrogen- containing ligand and an alkylaluminum is sufficient to achieve the desired technical result.

Wherein, the chromium source as a part of the catalytic system may be represented by organic and/or inorganic chromium compounds. The oxidation state of chromium in the compounds can vary and can be +1, +2, +3, +4, +5 and +6. In general, the chromium source is a compound of the general formula CrX n , wherein X may be the same or different organic or inorganic substituents, and n is an integer from 1 to 6. Organic substituents (X) may have from 1 to 20 carbon atoms and represent alkyl group, alkoxy group, carboxy group, acetylacetonate, amino group, amido group, etc. Suitable inorganic substituents represented by X are halides, sulfates, etc. Examples of chromium sources include: chromium (III) chloride, chromium (III) acetate, chromium (III) 2-ethylhexanoate, chromium (III) acetylacetonate, chromium (III) pyrrolide, chromium (II) acetate, chromium (IV) dioxide (CrC Cb), etc.

The nitrogen-containing ligand as a part of the catalytic system is an organic compound that includes the pyrrole ring moiety, i.e. a five-membered aromatic ring with one nitrogen atom. Suitable nitrogen-containing ligands include, but are not limited to pyrrole, 2,5-dimethylpyrrole, lithium pyrrolide C4H4NL1, 2-ethylpyrrole, 2- allylpyrrole, indole, 2-methylindole, 4,5,6,7-tetrahydroindole. Most preferably, pyrrole or 2,5-dimethylpyrrole is used.

Alkylaluminum as a part of the catalytic system can be represented by an alkylaluminum compound, as well as a halogenated alkylaluminum compound, an alkoxyalkylaluminum compound, and mixtures thereof. To increase the selectivity, it is preferable to use said compounds that were not in contact with water (non-hydrolyzed), the compounds being represented by the general formulas AIR3, AlR2Hal, AIRHab, AIR2OR, AIRHalOR and/or Ab jHab, wherein R is an alkyl group, Hal is a halogen atom. Suitable alkylaluminum compounds include, but are not limited to, triethylaluminum, diethylaluminum chloride, tripropylaluminum, triisobutylaluminum, diethylaluminum ethoxide and/or ethylaluminum sesquichloride, or mixtures thereof. Most preferred is the use of triethyl aluminum or a mixture of triethyl aluminum with diethyl aluminum chloride.

The ratios of the components of the catalytic system may vary. The aluminum to chromium molar ratio may vary from 5:1 to 500:1, preferably from 10:1 to 100:1, most preferably from 20:1 to 50:1. The ligand to chromium molar ratio may vary from 2:1 to 50:1, preferably from 2.5:1 to 5:1.

Preferably the catalytic system for carrying out the oligomerization reaction is obtained using microwave irradiation.

To increase the activity of the catalytic system, it is preferable to use microwave (UHF/SHF) irradiation of an organoaluminum compound (alkylaluminum). Preferably, the organoaluminum compound, possibly in the form of a solution in a hydrocarbon solvent, is subjected to microwave radiation, and then mixed with the chromium source and the nitrogen-containing ligand. During irradiation, it is necessary for the catalytic system components subjected to activation, to be placed in a vessel that is transparent to microwave radiation, for example, in a vessel made of glass, fluoroplastic, polypropylene.

Microwave radiation to be used can have a frequency in the range of from 0.2 to 20 GHz. It is particularly preferable to use microwave radiation having the frequency of 2.45 GHz, which does not cause radio interference and is commonly used in domestic and industrial sources of microwave radiation. The effective microwave power is from 1 W to 5,000 W per 1 g of alkylaluminum to be used calculated as elemental aluminum.

In order to achieve the best results, it is preferable that the irradiation time ranges from 20 seconds to 20 minutes, preferably 15 minutes. Irradiation duration of more than 20 minutes usually does not provide additional improvements in the properties of the resulting catalytic system. Irradiation with a duration of less than 20 seconds may be insufficient to modify significantly the properties of the components subjected to activation, which in turn will lead to an insufficient increase in the activity and/or selectivity of the resulting catalytic system.

Mixing of the alkylaluminum activated by microwave irradiation with the chromium source and the nitrogen-containing ligand is carried out in no more than 3 minutes following the completion of the irradiation, preferably no more than 1 minute following the completion of the irradiation. If the time interval between mixing the irradiated alkylaluminum with the chromium source and the nitrogen-containing ligand is 3 minutes or more, the properties of the resulting catalytic system deteriorate significantly compared to a system for which the specified time interval is less than 1 minute.

The mixing of the catalytic system components can be accomplished by any method known in the art. The mixing of the catalytic system components is carried out for the time period of from 1 minute to 30 minutes, preferably not less than 2 minutes, not less than 4 minutes, not less than 8 minutes, not less than 15 minutes, not less than 25 minutes.

Alternatively, alkylaluminum subjected to activation by microwave irradiation can be gradually fed into mixing with other components of the catalytic system directly from a tank subjected to microwave irradiation, so that the mixing time can be any suitable time, while preventing the loss of special properties acquired by the component by microwave radiation.

The components of the catalytic system can be mixed in any order. Preferably, alkylaluminum is added to the mixture of the chromium source and the nitrogen- containing ligand. The mixing of the components is carried out in a reactor equipment which could be any suitable device for carrying out oligomerization, for example, a bubble-agitated apparatus, an apparatus with a stirrer, a static mixer.

Mixing is carried out in the presence of a hydrocarbon solvent. Suitable hydrocarbon solvents include, but are not limited to hexene- 1, benzene, toluene, ethylbenzene, xylene, or mixtures thereof. Preferably, aromatic hydrocarbons are used as the solvents to increase the stability of the catalytic system and to obtain a highly active and selective catalytic system. Preferably, the aromatic hydrocarbon solvent is selected from the group comprising toluene, ethylbenzene or mixtures thereof. Ethylbenzene is the most preferred aromatic hydrocarbon. It is preferable to carry out the process of mixing the components and the subsequent oligomerization using that one solvent in which the pretreatment of the reactor equipment with zinc was carried out. However, other solvents may be used too.

After the step of mixing and obtaining the catalytic system, it is possible to remove the hydrocarbon solvent from the mixture. As it is known in the art (see RU2104088 patent), the presence of an aromatic hydrocarbon in the reaction mixture during the oligomerization process can reduce the activity of the catalytic system and increase the amount of by-products, such as polymers. Solvent removal can be carried out by any known method, for example, via applying vacuum (vacuum evaporation). However, it should be noted, that in the case of carrying out the process of olefin oligomerization at elevated temperature, the presence of an unsaturated hydrocarbon solvent, such as for example ethylbenzene, may be preferable, since under these conditions said solvent increases the stability of the catalytic system.

In addition to the catalytic systems described above, comprising a chromium source, a nitrogen-containing ligand, and an alkylaluminum, other oligomerization catalysts known from the prior art can be used to implement the present invention. The olefin oligomerization process is carried out by bringing a catalytic system diluted with a hydrocarbon solvent into a contact with raw materials, such as olefins, represented by ethylene (ethene), propylene (propene) and butylene (butene).

In the oligomerization process, the pressure of the raw materials including olefin(s) is in the range of from 1 to 200 atm. In the preferred embodiment of the process, when the oligomerization process is an ethylene trimerization process to produce 1 -hexene, the ethylene pressure can vary in the range of from 1 to 200 atm, preferably from 10 to 60 atm, most preferably from 15 to 40 atm. It is preferable to increase ethylene pressure in order to increase the rate of oligomerization.

The temperature of the oligomerization process can vary in the range of from 0°C to 160°C inclusive, preferably from 40°C to 130°C. It is most preferable to maintain the temperature in the reactor in the range of from 80°C to 120°C. At this temperature, the polymer by-product, in particular polyethylene, does not precipitate from the solution and is removed from the reactor in a form of the solution, and the catalytic system remains the most active and selective. Carrying out the oligomerization process at higher temperature (above 120°C inclusive) can lead to deactivation of the catalytic system.

According to the proposed process, the reaction time may vary. The reaction time can be defined as the residence time for the raw material and solvent in the oligomerization reaction zone. When using continuous flow reactors, the reaction time can be defined as the average residence time of the raw materials and solvent in the oligomerization reaction zone. The reaction time may vary depending on the olefin used as the raw material, the reaction temperature, the pressure, and other process parameters. In the process embodiments, the reaction time usually does not exceed 24 hours. The reaction time may be less than 12 hours, less than 6 hours, less than 3 hours, less than 2 hours, less than 1 hour, less than 30 minutes, less than 15 minutes, less than 10 minutes. The most preferred reaction time period is ranging from 30 minutes to 90 minutes.

According to the proposed method, the olefin and the catalytic system can be contacted with hydrogen, which is fed to the oligomerization reactor and used as a diluent. Hydrogen can accelerate the oligomerization reaction and/or increase the activity of the organometallic catalyst. Besides, hydrogen can reduce the amount of the produced by-product polymer and limit the deposition of the polymer on the surface of the equipment.

The olefin oligomerization process must be carried out in the absence of water and oxygen.

According to the proposed method, the effluent from the oligomerization reactor may contain organometallic compounds, the desired product (oligomer), by-products, a solvent, as well as polymers that may be formed during the oligomerization process.

The effluent from the reactor can be treated with an agent deactivating the catalytic system. Suitable deactivating agents known in the art are water, alcohols, amines, amino alcohols, or mixtures thereof, as well as various sorbents, such as silica gel, alumina, aluminosilicates, or mixtures thereof with water, alcohols, amines, amino alcohols. Preferably, alcohols or amino alcohols supported on silica gel are used as the deactivating agents.

Additionally, the effluent from the reactor can be cooled off by passing, for example, through a heat exchanger. The cooling process of the effluent coming from the reactor may comprise mixing hot effluent with cool effluent. Cooling the reactor effluent is carried out until the temperature reaches the range from 20°C to 100°C, preferably to a temperature less than 95 °C. Cooling the reactor effluent can be carried out to ambient temperature, for example, in the range of from 20°C to 25 °C. The choice of the temperature to which the effluent is cooled is determined taking into account the goal of increasing the precipitation of the polymer from the solvent.

Preferably, the effluent from the oligomerization reactor is separated from the solid phase prior to the separation of the liquid oligomerization product. The separation of the stream from the oligomerization reactor from the by-product polymer can be carried out before the step of separation of gaseous olefins (degassing stage), if such a step is present, or after the degassing step. The separation of the by-product polymer can be carried out by any known separation method, for example, by centrifugation or filtration.

After filtration and degassing (if any), the oligomerization reactor effluent is subjected to the product separation step, during which at least one olefin product is isolated. For example, if ethylene is used as the starting olefin, the main products of oligomerization, such as hexene and octene, are usually separated at the distillation stage. To increase the efficiency of the process, it is also advisable to recycle the solvent. Such separation can be done in any way, for example, by distillation.

The problem of deposition of polymers on the surfaces of the reactor equipment is associated not only with the oligomerization processes, but also with the polymerization processes. In this regard, the present inventors have also conducted experiments, which include running polymerization processes in reactor equipment, on the surface of which a zinc-containing coating has been applied. It was found that the application of a zinc-containing coating onto the surface of the reactor equipment eliminates the problem of polymer deposits for the olefin polymerization processes as well.

The process and conditions for carrying out the olefin polymerization reaction may include any process(es) and conditions known in the art, for example, a process/conditions disclosed in WO 2011/093748, RU2471813, RU2434888 documents. At this case, a monomer having from 2 to 6 carbon atoms, for example, ethylene, propylene or hexene- 1 is used as an olefin. It is possible to conduct a polymerization reaction in suspension, solution or gas-phase mode. The polymerization reaction can be carried out after completion of the oligomerization process, with the preliminary separation of the olefin oligomer produced. The oligomerization and polymerization reactions can proceed simultaneously; in this case, the copolymerization of the resulting olefin oligomer and the initial olefin monomer usually occurs.

The present invention is further described in more details, with reference to the examples below. These examples are given only to illustrate the present invention and are not limiting.

EXAMPLES

Example 1 (comparative). The process of ethylene oligomerization in the reactor equipment without zinc-containing coating

Preparation of the catalytic system

17.58 mg of chromium ethylhexanoate (Cr(CH3C(C2H5)C3H6COO)3) (63.5% solution in CIO and C12 alkanes) and 17.39 mg of 2,5-dimethylpyrrole (DMP) were placed in a 50 ml round-bottom flask. 1 ml of ethylbenzene was then added, and the flask was filled with dry nitrogen. 0.5 g of the triethylaluminum (TEA) solution in heptane at the concentration of 25 wt.% was mixed with 0.44 g of the dialuminium chloride (DEAH) solution in heptane at a concentration of 15 wt%. The resulting solution was subjected to microwave irradiation for 6 minutes with a power rating of 400 watts. Then, no later than 30 seconds after the irradiation, the resulted mixture was added to said Cr(CH3C(C 2 H 5 )C 3 H 6 COO) 3 and DMP in ethylbenzene. After 15 minutes the residue in the flask was diluted with 20 ml of cyclohexane to prepare the catalyst solution.

Ethylene oligomerization process

700 ml of cyclohexane was added to a reactor of the 2 L volume. The reactor was heated to 100°C. Ethylene was added to the reactor until the pressure reached 24 bar. The prepared solution of the catalyst in cyclohexane was added to the reactor. During the reaction, the temperature of 100°C and the pressure of 25 bar were maintained by the addition of ethylene through a flow meter, and the reaction mixture was stirred at a speed of 800 rpm. 30 minutes after the addition of the catalyst, the pressure in the reactor was reduced to the atmospheric pressure and the reactor was cooled to 0°C. The sample from the reactor contains 15.7% of 1 -hexene and 0.4% of a mixture of decenes.

Catalyst activity, g / (g Cr * h): 5800.

The total selectivity to 1 -hexene: 97.4%.

Stable operation of the reactor equipment lasted for 10-15 days. Starting of the oligomerization reaction was observed within 5-10 hours after the introduction of ethylene and the catalyst. A ramp-up to a stable operation mode was observed within the period of 8 hours to 3 days following the start of the reaction.

During the operation of the reactor equipment, pressure drops were observed, as well as a temperature difference between the reactor compartments. These effects may be associated with an inefficient heat sink due to polymer deposits on the surfacse of the reactor equipment. The termination of the oligomerization process was done extraordinarily, following the increase in pressure drop in the reactor. After the reactor had been shut down and opened, a large amount of deposits in the reactor was observed, as shown in FIG.l.

Example 2. The process of ethylene oligomerization in the reactor equipment, on the surface of which a zinc-containing coating has been applied Treating the reactor equipment with zinc reaction solution

The reactor equipment was cleaned, purged with inert gas, filled with moisture- free hydrocarbon solvent; wherein, in this particular embodiment cyclohexane was used. The total volume of the reaction zone filled with the hydrocarbon solvent and the system for applying a zinc-containing coating to the surface, together with tubes, a pump, a heat exchanger, amounted to 700 liters. A sealed container with a solution of diethyl zinc (DEZ) at the 15 wt.% concentration in the amount of 20 kg was connected to dried nitrogen tank and the prepared reactor, and then the solution was pressurized by nitrogen to enter a reaction zone filled with the solvent. As a result, the concentration of zinc was about 2.25 g per 1 liter for the total amount of solvent in the reactor equipment. Next, the solvent was mixed with the DEZ in the reactor while gradually heating the solvent to 90-100°C at the heating rate of 20°C/h, with the stirring carried out for 4 hours.

The preparation of the catalytic system was carried out according to the method described in Example 1

The process of ethylene oligomerization was carried out according to the method described in Example 1.

The reactor equipment coated with a zinc-containing coating was in operation for 60 days. Starting of the oligomerization reaction was observed within 3 hours after the delivery of ethylene and the catalyst. The ramp-up to a stable operation mode was observed within 2 to 4 hours following the start of the reaction.

During operation of the facility, the stable operation of the reactor equipment was observed. A uniform profile of temperature distribution in the reactor was observed, as well as a uniform small pressure drop associated with the ethylene consumption during the reaction. These data indirectly indicate the absence of problems associated with polymer deposits on the equipment surface, and, as a consequence, problems associated with the heat transfer.

Upon completion, the reactor equipment was shut down and opened. Reactor inspection upon opening revealed no polymer deposits on the surfaces of the reactor equipment, as shown in FIG. 2.

Example 3. The process of ethylene oligomerization in the reactor equipment, on the surface of which a zinc-containing coating has been applied Treating the reactor equipment with zinc reaction solution

The reactor equipment was cleaned, purged with inert gas, filled with moisture- free hydrocarbon solvent; wherein, in this particular embodiment cyclohexane was used. The total volume of the reaction zone filled with the hydrocarbon solvent and the system for applying a zinc-containing coating to the surface, together with tubes, a pump, a heat exchanger, amounted to 700 liters.

A sealed container with a solution of diethyl zinc (DEZ) at the 15 wt.% concentration based on zinc metal, in the amount of 20 kg was connected to dried nitrogen tank and the prepared reactor, and then the solution was pressurized by nitrogen to enter the reaction zone filled with the solvent. As a result, the concentration of zinc was about 2.25 g, calculated per 1 liter for the total amount of the solvent in the reactor equipment. Next, the solvent was mixed with the DEZ in the reactor while gradually heating the solvent to 40°C at the heating rate of 20°C/h, with the stirring carried out for 11 hours.

The preparation of the catalytic system was carried out according to the method described in Example 1

The process of oligomerization of ethylene was carried out according to the method described in Example 1.

The operation of the reactor equipment was carried out as described in Example

2.

Upon completion, the reactor equipment was shut down and opened. Reactor inspection upon opening revealed no polymer deposits on the surfaces of the reactor equipment.

Example 4. Polymerization process in the reactor equipment, on the surface of which a zinc-containing coating has been applied

Treating the reactor equipment with zinc reaction solution

A 2-liter reactor equipped with a mixer was filled with cyclohexane (1.8 liter). Diethylzinc was introduced in the amount necessary to obtain a concentration of 0.5 g of zinc metal per liter. The solution was heated to 100°C at the rate of 25°C/h while permanently stirring for 3 hours. Then, it was cooled down to 25°C, the contents were drained from the reactor and the reactor was filled with nitrogen. The preparation of the catalytic system was carried out according to the method described in Example 1.

The process of ethylene oligomerization followed by the subsequent polymerization of products

700 ml of cyclohexane was added to a 2-liter reactor. The reactor was heated to 100°C. Ethylene was added to the reactor up to the pressure of 24 bar. The prepared catalyst solution in cyclohexane was added to the reactor. During the reaction, the temperature was maintained at 100°C and the pressure was maintained at 25 bar by adding ethylene through the flow meter. The reaction mixture was stirred at 800 rpm for 30 minutes after the addition of the catalyst, then the pressure in the reactor was reduced to the atmospheric pressure and the reactor was cooled down to 0°C. The sample from the reactor contained 15.7% of 1 -hexene and 0.4% of a mixture of decenes. 10 ml of a solution of DEAH in heptane at 20% concentration and 1 ml of a catalyst suspension represented by microspheric titanium trichloride (0.48 g T1CI3/I) were added. The polymerization reaction was terminated in 2 hours by addition of 5 ml of isopropanol. The solvent was evaporated, the residue was air-dried for 7 days, then dried at 10 mbar and 50 °C for 24 hours. 53 g of elastic polymer with the average molecular weight of 9.34 x 10 6 and molecular-weight distribution of 8.2 was obtained.

At the end of the operation, the reactor equipment was shut down. No polymer deposits on the surfaces of the reactor equipment were observed.

Example 5. The process of ethylene oligomerization in the reactor equipment, on the surface of which a zinc-containing coating has been applied

Treating reactor equipment with zinc reaction solution

The reactor equipment was cleaned, purged with an inert gas, filled with the moisture-free Cs-io fraction comprising octene-1, decane and decene, as well as ethylbenzene. The total volume of the reaction zone filled with a hydrocarbon solvent, the system for applying a zinc-containing coating to the surface, the tubes, a pump, a heat exchanger, amounted to 700 liters. A sealed container with a solution of diethyl zinc (DEZ) with a concentration of 15 wt.% based on zinc metal, in the amount of 20 kg was connected to dried nitrogen tank and the prepared reactor, then the solution was pressurized by nitrogen to enter the reaction zone filled with the solvent. As a result, the concentration of zinc was about 2.25 g, calculated per 1 liter for the total amount of the solvent in the reactor equipment. Next, the solvent was mixed with the DEZ in the reactor while gradually heating the solvent to 100°C with a heating rate of 25°C/h, with stirring carried out for 4 hours, then the contents were drained, and the reactor was filled with moisture-free cyclohexane to be used in the synthesis.

The preparation of the catalytic system was carried out according to the method described in Example 1

The process of ethylene oligomerization was carried out according to the method described in Example 1.

The operation of the reactor equipment was carried out as described in Example

2.

Upon completion, the reactor equipment was shut down and opened. Reactor inspection upon opening revealed no polymer deposits on the surfaces of the reactor equipment.

Example 6. The process of ethylene oligomerization in the reactor equipment, on the surface of which a zinc-containing coating has been applied

Treating the reactor equipment with zinc reaction solution

The reactor equipment was cleaned, purged with an inert gas, filled with the moisture-free Isopar™ (ExxonMobil) (Cl 0-15 paraffins). The total volume of the reaction zone filled with the hydrocarbon solvent and the system for applying a zinc- containing coating to the surface, the tubes, a pump, a heat exchanger, amounted to 700 liters. A sealed container with a solution of diethyl zinc (DEZ) at the 15 wt.% concentration based on zinc metal, in the amount of 20 kg was connected to dried nitrogen tank and the prepared reactor, and then the solution was pressurized by nitrogen to enter a reaction zone filled with the solvent. As a result, the concentration of zinc was about 2.25 g, calculated per 1 liter for the total amount of the solvent in the reactor equipment. Next, the solvent was mixed with the D Z in the reactor while gradually heating the solvent to 130°C at the heating rate of 40°C/h, with the stirring carried out for 4 hours, then the contents were drained, and the reactor was filled with moisture-free cyclohexane to be used in synthesis.

The preparation of the catalytic system was carried out according to the method described in Example 1 The process of ethylene oligomerization was carried out according to the method described in Example 1.

The operation of the reactor equipment was carried out as described in Example

2.

Upon completion, the reactor equipment was shut down and opened. Reactor inspection upon opening revealed no polymer deposits on the surfaces of the reactor equipment.

Example 7. The process of ethylene oligomerization in the reactor equipment, on the surface of which a zinc-containing coating has been applied

Treating the reactor equipment with zinc reaction solution

The reactor equipment was cleaned, purged with inert gas, filled with moisture- free hydrocarbon solvent; wherein, in this particular embodiment cyclohexane was used. The total volume of the reaction zone filled with the hydrocarbon solvent and the system for applying a zinc-containing coating to the surface, along with the tubes, a pump, a heat exchanger, amounted to 700 liters. A sealed container with a solution of diethyl zinc (DEZ) (90 g/1), zinc oxide (30 g/1) and zinc hydroxide (40 g/1) in an amount of 20 kg was connected to dried nitrogen tank and the prepared reactor, and then the solution was pressurized by nitrogen to enter a reaction zone filled with the solvent. As a result, the concentration of zinc was about 2.95 g per 1 liter calculated for the total amount of the solvent present in the reactor equipment. Next, the solvent was mixed with the DEZ, ZnO and Zn(OH)2 in the reactor while gradually heating the solvent to 145°C at the heating rate of 50°C/h, with the stirring carried out for 4 hours.

The preparation of the catalytic system was carried out according to the method described in Example 1

The process of ethylene oligomerization was carried out according to the method described in Example 1.

The operation of the reactor equipment was carried out as described in Example

2.

Upon completion, the reactor equipment was shut down and opened. Reactor inspection upon opening revealed no polymer deposits on the surfaces of the reactor equipment. Example 8. The process of ethylene oligomerization in the reactor equipment, on the surface of which a zinc-containing coating has been applied

Operating of the galvanized pipeline

The reactor equipment was cleaned, purged with an inert gas, filled with moisture-free cyclohexane. To remove the reaction mixture from the reactor, a galvanized pipe was used.

The pipeline was galvanized by hot dip galvanizing. The pipe was submerged into a zinc melt bath at a temperature of about 460°C. Under exposing to the atmosphere, purified zinc (Zn) reacts with oxygen (O2) to form zinc oxide (ZnO), followed by the reaction with carbon dioxide (CO2) to form zinc carbonate (ZnCCb), which is gray opaque sufficiently hard substance that prevents further corrosion of the material ((UNIFORM SYSTEM OF PROTECTION AGAINST CORROSION AND AGING ZINC HOT COATINGS GENERAL REQUIREMENTS AND METHODS OF CONTROL GOST 9.307-89 (ISO 1461-89, ST CEV 4663-84; Proskurkin E.V., Gorbunov N.S., Diffusion Zinc Coatings, M., 1972; Liner V.I., Protective coatings of metals, M., 1974.).

The preparation of the catalytic system was carried out according to the method described in Example 1

The process of ethylene oligomerization was carried out according to the method described in Example 1.

The operation of the reactor equipment was carried out as described in Example

2.

Upon completion, the reactor equipment was shut down. Reactor inspection upon opening revealed no polymer deposits on the surfaces of the equipment.

Discussion of the results obtained in accordance to the examples of embodiments of the present invention is provided below.

In the examples of the embodiments of the present invention, the reactor equipment used for oligomerization process is a complex apparatus with a tube bundle. The oligomerization reaction takes place inside the tubes. It is important to eliminate the deposition of polymer formed as a by-product inside the tube space of the reactor equipment. In the case of the formation of such by-product polymer deposits on the surfaces of the reactor equipment, the deposits can lead to a decrease in the efficiency of reaction heat transfer, a decrease in the tube flow capacity and a decrease in the useful volume of the reactor. As a result, an increase in the amount of polymer deposits can lead to blockage of a significant number of tubes and the need for equipment repair. The growth of structured filiform chains of high molecular weight polyethylene formed on the“growth centers” in the solvent stream is the most critical from the point of view of the operational characteristics of the process. These chains are dense plexuses of polyethylene with a diameter of 3 to 15 mm and a length of up to 20 cm. It is these threadlike structures that, when carried away with the reaction mass from the reactor, most often lead to clogging of the reactor tubes, as well as a failure of the equipment downstream.

The inventors have shown (Examples 4-8) that the preliminary application of a zinc-containing coating onto the internal surfaces of the reactor equipment and tubing makes it possible to significantly reduce the deposition of polymer formed as a by product during the oligomerization process (Fig. 2). At the same time, realization of the oligomerization process in a conventional reactor equipment without applied zinc- containing coating is accompanied by the uprise of the large quantities of by-product polymer deposits on its surfaces, thereby entailing the need to terminate the process

(Fig- 1).

Example 3 shows that the preliminary application of the zinc-containing coating onto the surfaces of the reactor equipment makes it possible to reduce the deposition of polymers during the processes of olefins polymerization as well. High molecular weight polymers (in this case, Mw more than 9xl0 6 Da) have low solubility, and cleaning the reactor after the polymerization process takes a lot of time. However, after treating the reactor with an alkylzinc reagent, a polymer does not stick to the surface, and, as a result, the process of getting the reactor ready for a new synthesis process takes less than an hour.