LU506480B1 - Method for oligomerization of ethylene - Google Patents

Abstract

The disclosure provides a method of producing one or more linear alpha olefins by ethylene oligomerization, the method including contacting ethylene with a catalyst composition in a reaction chamber in the presence of a solvent mixture including at least one aromatic solvent and at least one aliphatic hydrocarbon solvent, wherein the at least one aromatic solvent is present in an amount of about 10% by weight or less, based on the total weight of the solvent mixture, and at a temperature of about 50 °C to about 80 °C; oligomerizing the ethylene to produce one or more linear alpha olefins; and withdrawing an effluent comprising the one or more linear alpha olefins.

Description

METHOD FOR OLIGOMERIZATION OF ETHYLENE

TECHNOLOGICAL FIELD

[0001] The present disclosure relates to methods for producing linear alpha olefin products through oligomerization of ethylene.

BACKGROUND

[0002] Linear olefins are a class of hydrocarbons useful as raw materials in the petrochemical industry and among these the linear alpha olefins, unbranched olefins whose double bond is located at a terminus of the chain, form an important subclass. Linear alpha olefins can be converted to linear primary alcohols by hydroformylation. Hydroformylation can also be used to prepare aldehydes, which in turn can be oxidized to afford synthetic fatty acids, especially those with an odd carbon number, useful in the production of lubricants. Linear alpha olefins are also used in the production of detergents, such as linear alkylbenzenesulfonates, which are prepared by Friedel-Crafts reaction of benzene with linear olefins followed by sulfonation. Linear alpha olefins, particularly 1-hexene, are also used as a co-monomer to make high-density polyethylene (HDPE) and linear low-density polyethylene (LLDPE).

[0003] Preparation of alpha olefins is based largely on oligomerization of ethylene, which has a corollary that the alpha-olefins produced have an even number of carbon atoms. Certain oligomerization processes for ethylene utilize chromium-based metal-organic complexes with ligands as catalysts in the presence of an activator/co-catalyst such as methyl aluminoxane (MAO). Typically, the effluent from the reactor used to produce the linear alpha olefins is directed to one or more distillation columns to separate the various fractions of linear alpha olefins.

[0004] Polymeric material is produced as an undesirable side product of the oligomerization reaction. The presence of polymeric material can lead to equipment fouling both within the reactor system and in downstream product processing units. Such fouling can lead to reactor shutdowns and cause removal challenges. There remains a need in the art for improved techniques to address polymer fouling resulting from the oligomerization reaction. -1-

BRIEF SUMMARY

[0005] Example implementations of the present disclosure are directed to systems and processes for reducing polymer fouling in an oligomerization reactor. It has been discovered that choice of solvent used in the reaction system has a marked effect on catalytic activity and polymer formation. According to the present disclosure, reduction in polymer formation can be accomplished by employing a binary solvent system; namely, a mixture of an aliphatic hydrocarbon solvent (e.g., n-heptane) and a relatively small amount of aromatic solvent (e.g., xylene), rather than using a solely aromatic solvent system, such as toluene, as typically seen in the art. In addition, it has been discovered that use of such a binary solvent system can reduce the tackiness of polymeric material produced in the reactor, rendering the polymeric material easier to remove from the system.

[0006] The present disclosure includes, without limitation, the following embodiments.

[0007] Embodiment 1: A method of producing one or more linear alpha olefins by ethylene oligomerization, the method comprising: contacting ethylene with a catalyst composition in a reaction chamber in the presence of a solvent mixture comprising at least one aromatic solvent and at least one aliphatic hydrocarbon solvent, wherein the at least one aromatic solvent 1s present in an amount of about 10% by weight or less, based on the total weight of the solvent mixture, and at a temperature of about 50 °C to about 80 °C; oligomerizing the ethylene to produce one or more linear alpha olefins; and withdrawing an effluent comprising the one or more linear alpha olefins.

[0008] Embodiment 2: The method of Embodiment 1, further comprising premixing the catalyst composition with the at least one aromatic solvent to form a catalyst solution and feeding the catalyst solution into the reaction chamber.

[0009] Embodiment 3: The method of Embodiment 1 or 2, further comprising injecting gaseous ethylene into the reaction chamber.

[0010] Embodiment 4: The method of Embodiment 3, further comprising injecting hydrogen into the reaction chamber, optionally by premixing hydrogen with the gaseous ethylene prior to injection into the reaction chamber.

[0011] Embodiment 5: The method of any one of Embodiments 1 to 4, comprising feeding the at least one aliphatic hydrocarbon solvent to the reaction chamber separately from the at least one aromatic solvent. 2-

[0012] Embodiment 6: The method of any one of Embodiments 1 to 5, wherein the reaction chamber 1s part of a loop reactor system comprising the reaction chamber, a recirculation loop in fluid communication with the reaction chamber and configured to receive a reaction mixture from the reaction chamber and return the reaction mixture to the reaction chamber, a pump configured to pump the reaction mixture through the recirculation loop, and a heat exchanger configured to cool the reaction mixture during circulation within the recirculation loop.

[0013] Embodiment 7: The method of any one of Embodiments 1 to 6, wherein the at least one aromatic solvent is selected from the group consisting of toluene, xylene, monochlorobenzene, dichlorobenzene, chlorotoluene, and combinations thereof.

[0014] Embodiment 8: The method of any one of Embodiments 1 to 7, wherein the at least one aliphatic hydrocarbon solvent is a C5 to C8 cyclic or straight chain alkane, such as n- heptane, cycloheptane, isoheptane, n-hexane, isohexane, cyclohexane, methylcyclohexane, and combinations thereof.

[0015] Embodiment 9: The method of any one of Embodiments 1 to 8, wherein the at least one aromatic solvent is xylene and the at least one aliphatic hydrocarbon solvent is n-heptane.

[0016] Embodiment 10: The method of any one of Embodiments 1 to 9, wherein the at least one aromatic solvent is present in an amount of about 7.5% by weight or less, such as about 3 to about 7% by weight or about 4 to about 6% by weight, based on the total weight of the solvent mixture.

[0017] Embodiment 11: The method of any one of Embodiments 1 to 10, wherein the contacting is conducted at a temperature of about 55 °C to about 80 °C, such as about 60 °C to about 75 °C, or about 70 °C, and optionally wherein the contacting is conducted at a pressure of about 25 to about 30 bar.

[0018] Embodiment 12: The method of any one of Embodiments 1 to 11, wherein the amount of polymer within the effluent is about 0.4% by weight or less, such as about 0.1% by weight to about 0.4% by weight or about 0.2% by weight to about 0.4% by weight, based on the total weight of the effluent.

[0019] Embodiment 13: The method of any one of Embodiments 1 to 12, wherein a catalyst activity in units of kg-gcr +h! is about 45 or higher, such as about 45 to about 55 or about 48 to about 54. 3-

[0020] Embodiment 14: The method of any one of Embodiments 1 to 13, wherein a selectivity for 1-hexene is about 91% or higher, such as about 91 to about 94 or about 92 to about 93.

[0021] Embodiment 15: The method of any one of Embodiments 1 to 14, wherein the catalyst composition comprises: 1) a chromium compound selected from organic or inorganic salts, coordination complexes and organometallic complexes of Cr(IT) or Cr(IIT), such as

CrCls(tetrahydrofuran)s, Cr(IIT) acetylacetonate, Cr(IIT) octanoate, chromium hexacarbonyl, Cr(IIT)-2-ethylhexanoate, benzene(tricarbonyl)-chromium,

Cr(IID)chloride, or combinations thereof; 11) a co-catalyst selected from the group consisting of a tri(C1-C6 alkyl) aluminum such as trimethyl aluminum, triethyl aluminum, triisopropyl aluminum, or triisobutyl aluminum, ethyl aluminum sesquichloride, diethyl aluminum chloride, ethyl aluminum dichloride, methyl aluminoxane (MAO), and combinations thereof; 111) a heteroatomic multidentate ligand, such as a ligand of the general structure

R1R2P—N(R3)—P(R4)—N(Rs)—H, wherein Rı, Ra, R3, R4and Rs are independently selected from halogen, amino, trimethylsilyl, C1-C10-alkyl, substituted C1-C10-alkyl, aryl and substituted aryl, wherein at least one of the P or

N atoms of the PNPNH-unit is optionally also a member of a ring system; iv) a modifier selected from ammonium or phosphonium salts of the type [H4E]X, [H3FR]X, [H:ER2]X, [HER3]X or [ER4]X, wherein E is N or P, X is Cl, Br or I, and each R is independently C1-C22 hydrocarbyl, such as a substituted or unsubstituted C1-C16-alkyl, C2-C16-acyl, or substituted or unsubstituted C6-

C20-aryl, such as dodecyl trimethyl ammonium chloride, tetraphenyl phosphonium chloride, tetraethyl ammonium chloride monohydrate, tetraethyl ammonium chloride, trimethyl dodecyl ammonium chloride, isopropylamine hydrochloride, triethylamine hydrochloride, tetrapropyl ammonium chloride, tetra-n-butyl ammonium chloride, tetraethyl ammonium bromide, p-toluidine hydrochloride, dimethyl distearyl ammonium chloride, (tri-n-butyl)-n-tetradecyl -4-

phosphonium chloride, benzoyl chloride, acetyl chloride, and combinations thereof; or

Vv) a combination of two or more of the above.

[0022] These and other features, aspects, and advantages of the present disclosure will be apparent from a reading of the following detailed description together with the accompanying figures, which are briefly described below. The present disclosure includes any combination of two, three, four or more features or elements set forth in this disclosure, regardless of whether such features or elements are expressly combined or otherwise recited in a specific example implementation described herein. This disclosure is intended to be read holistically such that any separable features or elements of the disclosure, in any of its aspects and example implementations, should be viewed as combinable, unless the context of the disclosure clearly dictates otherwise.

[0023] It will therefore be appreciated that this Brief Summary is provided merely for purposes of summarizing some example implementations so as to provide a basic understanding of some aspects of the disclosure. Accordingly, it will be appreciated that the above described example implementations are merely examples and should not be construed to narrow the scope or spirit of the disclosure in any way. Other example implementations, aspects and advantages will become apparent from the following detailed description taken in conjunction with the accompanying figures which illustrate, by way of example, the principles of some described example implementations.

BRIEF DESCRIPTION OF THE FIGURES

[0024] Having thus described aspects of the disclosure in the foregoing general terms, reference will now be made to the accompanying figure, which is not necessarily drawn to scale, and wherein:

[0025] FIG. 1 is a simplified schematic diagram of an example ethylene oligomerization reaction system in accordance with the present disclosure.

DETAILED DESCRIPTION

[0026] Some implementations of the present disclosure will now be described more fully hereinafter with reference to the accompanying figures, in which some, but not all -5-

implementations of the disclosure are shown. Indeed, various implementations of the disclosure may be embodied in many different forms and should not be construed as limited to the implementations set forth herein; rather, these example implementations are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Like reference numerals refer to like elements throughout.

[0027] Unless specified otherwise or clear from context, references to first, second or the like should not be construed to imply a particular order. À feature described as being above another feature (unless specified otherwise or clear from context) may instead be below, and vice versa; and similarly, features described as being to the left of another feature else may instead be to the right, and vice versa. Also, while reference may be made herein to quantitative measures, values, geometric relationships or the like, unless otherwise stated, any one or more 1f not all of these may be absolute or approximate to account for acceptable variations that may occur, such as those due to engineering tolerances or the like.

[0028] All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other (e.g., ranges of “up to 25 wt. %, or, more specifically, wt. % to 20 wt. %”, is inclusive of the endpoints and all intermediate values of the ranges of “5 wt. % to 25 wt. %,” etc.). “Combination” is inclusive of blends, mixtures, alloys, reaction products, and the like.

[0029] As used herein, unless specified otherwise or clear from context, the “or” of a set of operands is the “inclusive or” and thereby true if and only if one or more of the operands is true, as opposed to the “exclusive or” which is false when all of the operands are true. Thus, for example, “[A] or [B]” is true if [A] is true, or if [B] is true, or if both [A] and [B] are true.

Further, the articles “a” and “an” mean “one or more,” unless specified otherwise or clear from context to be directed to a singular form.

[0030] The term “aliphatic” means an organic functional group or compound containing carbon and hydrogen joined together in straight chains, branched chains, or non-aromatic rings.

[0031] The term “hydrocarbyl” refers to any univalent radical derived from a hydrocarbon, such as any aliphatic group (e.g., alkyl groups such as methyl or cycloalkyl groups such as cyclohexyl) or any aryl group (e.g., phenyl).

[0032] The term “alkyl” refers to a linear or a branched saturated hydrocarbon. Non limiting examples of alkyl groups include methyl, ethyl, propyl, butyl, pentyl, etc. -6-

[0033] An “aryl” group or an “aromatic” group 1s a substituted or substituted, mono- or polycyclic hydrocarbon with alternating single and double bonds within each ring structure, such as a phenyl group. Non-limiting examples of aryl group substituents include alkyl, substituted alkyl groups, linear or branched alkyl groups, linear or branched unsaturated hydrocarbons, halogen, hydroxyl, alkoxy, haloalkyl, haloalkoxy, carboxylic acid, ester, amine, nitro, amide, nitrile, acyl, alkyl silane, thiol and thioether substituents. Non-limiting examples of alkyl groups include linear and branched C1 to C5 hydrocarbons. Non-limiting examples of unsaturated hydrocarbons include C2 to C5 hydrocarbons containing at least one double bond (e.g., vinyl).

The aryl or alkyl group can be substituted with the halogen, hydroxyl, alkoxy, haloalkyl, haloalkoxy, carboxylic acid, ester, ether, amine, nitro (-NO»), amide, nitrile (-CN), acyl, alkylsilane, thiol and thioether substituents. Non-limiting examples of polycyclic groups include ring systems that include 2 or more conjugated rings (e.g., fused aromatic rings) and substituted conjugated rings.

Solvent System

[0034] According to the present disclosure a method of producing one or more linear alpha olefins by ethylene oligomerization is provided, wherein at least two solvents are utilized. In particular, a solvent mixture comprising at least one aromatic solvent and at least one aliphatic hydrocarbon solvent is utilized.

[0035] In some embodiments, the aromatic solvent is selected in part based on solubility of the catalyst composition within the solvent. Example aromatic solvents include toluene, xylene, monochlorobenzene, dichlorobenzene, chlorotoluene, and combinations thereof. In some embodiments, the aromatic solvent is xylene. Since the primary purpose of the aromatic solvent is to form the catalyst solution, in some embodiments, the aromatic solvent is present as a minor component of the overall solvent mixture. For example, the aromatic solvent can be present in an amount of about 10% by weight or less or an amount of about 7.5% by weight or less, such as about 3 to about 7% by weight or about 4 to about 6% by weight, based on the total weight of the solvent mixture.

[0036] The aliphatic hydrocarbon solvent is typically selected as the primary solvent in the reaction system, and is therefore typically used as the major component of the solvent mixture.

For example, the solvent mixture can contain about 90% by weight or more of aliphatic hydrocarbon solvent or about 92.5% or more, such as about 93 to about 97% by weight or about 7-

94 to about 96% by weight, based on the total weight of the solvent mixture. Example aliphatic hydrocarbon solvents include CS to C8 cyclic or straight chain alkanes, such as n-heptane, cycloheptane, isoheptane, n-hexane, isohexane, cyclohexane, methylcyclohexane, and combinations thereof. In some embodiments, the aliphatic hydrocarbon solvent is n-heptane.

[0037] The above-noted solvent mixture can be utilized in an ethylene oligomerization process and system as set forth below. The relative amounts of each solvent noted above are the relative amounts of solvent present in the reaction system during the reaction, such as the reaction system described below with reference to FIG. 1.

Ethylene Oligomerization Process and System

[0038] Linear alpha olefins (LAOs) are olefins with a chemical formula CxH2x, distinguished from other mono-olefins with a similar molecular formula by linearity of the hydrocarbon chain and the position of the double bond at the primary or alpha position. Linear alpha olefins comprise a class of industrially important alpha-olefins, including 1-butene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, and higher blends of C20-C24,

C24-C30, and C20-Czo olefins. Linear alpha olefins are useful intermediates for the manufacture of detergents, synthetic lubricants, copolymers, plasticizers, and many other important products.

[0039] Existing processes for the production of linear alpha olefins typically rely on the oligomerization of ethylene. For example, linear alpha olefins can be prepared by the catalytic oligomerization of ethylene in the presence of a catalyst composition including, for example, a chromium compound, a co-catalyst, a ligand, and optionally a modifier. See, for example, the catalyst compositions set forth in US9018431 to Wohl et al., which is incorporated by reference herein.

[0040] Example chromium compounds include organic or inorganic salts, coordination complexes and organometallic complexes of Cr(II) or Cr(IIT), such as CrCla(tetrahydrofuran)s,

Cr(IID) acetylacetonate, Cr(III) octanoate, chromium hexacarbonyl, Cr(III)-2-ethylhexanoate, benzene(tricarbonyl)-chromium, Cr(IID)chloride, or combinations thereof.

[0041] Example co-catalysts include a tri(C1-C6 alkyl) aluminum such as trimethyl aluminum, triethyl aluminum, triisopropyl aluminum, or triisobutyl aluminum, ethyl aluminum sesquichloride, diethyl aluminum chloride, ethyl aluminum dichloride, methyl aluminoxane (MAO), and combinations thereof. -8-

[0042] Typical ligand structures are organophosphorus compounds with at least two phosphino groups covalently linked through a linkage. Example ligands include compounds with any of the following backbone structures: PNP, PNPN, PNNP, PNPNP, or NPNPN, wherein each

P 1s a substituted phosphino group (typically a secondary or tertiary phosphino group) and each

N is a substituted amino group (typically a secondary or tertiary amino group), with example substituents for both the phosphino and amino groups including optionally substituted amino, trialkylsilyl, or optionally substituted C1-C20 hydrocarbyl (e.g., optionally substituted phenyl or optionally substituted cyclohexyl), with the optional substituents typically including amino or

C1-C20 hydrocarbyl. In certain embodiments, the ligand backbone structure includes at least two

N atoms (e.g., PNPN, PNNP, PNPNP, or NPNPN).

[0043] Example heteroatomic multidentate ligands include ligands of the general structure

R1R2P—N(R3)—P(R4)—N(Rs)—H, wherein R1, Ra, R3, R4and Rs are independently selected from halogen, amino, trimethylsilyl, Ci-Cio-alkyl, aryl, and substituted aryl, wherein at least one of the P or N atoms of the PNPNH-unit is optionally also a member of a ring system. In one example, the ligand is (Ph))P—N(1Pr)-P(Ph)-N(iPr)-H, wherein Ph is phenyl, and 1Pr is isopropyl.

[0044] Example modifiers include ammonium or phosphonium salts of the type [H4F]X, [H3ER]X, [H:ER2]X, [HER3]X or [ER4]X, wherein E is Nor P, X is CI, Br or I, and each R is independently C1-C22 hydrocarbyl, such as a substituted or unsubstituted C1-C16-alkyl, C2-

C16-acyl, or substituted or unsubstituted C6-C20-aryl, such as dodecyl trimethyl ammonium chloride, tetraphenyl phosphonium chloride, tetraethyl ammonium chloride monohydrate, tetraethyl ammonium chloride, trimethyl dodecyl ammonium chloride, isopropylamine hydrochloride, triethylamine hydrochloride, tetrapropyl ammonium chloride, tetra-n-butyl ammonium chloride, tetraethyl ammonium bromide, p-toluidine hydrochloride, dimethyl distearyl ammonium chloride, (tri-n-butyl)-n-tetradecyl phosphonium chloride, benzoyl chloride, acetyl chloride, and combinations thereof. In some embodiments, the modifier contains a free amine group selected from primary, secondary or tertiary aliphatic or aromatic amine (e.g., isopropylamine).

[0045] As noted above, the catalyst composition 1s typically prepared using the aromatic solvent of the binary solvent system. In some embodiments, a first portion of the catalyst 1s prepared by combining the chromium source and the ligand in the aromatic solvent to form a -9-

first solution. In some embodiments, a second portion of the catalyst is prepared by combining the co-catalyst and the modifier in the aromatic solvent to form a second solution. The first and second solutions are then premixed together prior to feeding the catalyst solution into the reaction system.

[0046] The catalyst composition 1s typically prepared such that the chromium concentration is 0.001 to 100 mmol/1, based on the total catalyst composition, more typically between 0.1 and mmol/1. In some embodiments, the ligand/Cr ratio is 0.5:1 to 50:1 mol/mol, such as from 0.8:1 to 20:1 mol/mol. The molar Al/Cr ratio is typically from 1:1 to 1000:1, such as from 10:1 to 200:1. The molar modifier/Cr ratio is typically from 0.01:1 to 100:1, such as from 1:1 to 20:1. In some embodiments, the molar ratio of Cr/halide is from 1:1 and 1:20.

[0047] Oligomerization can occur at temperatures of about 10 to about 200 °C, such as about to about 100 °C, or about 50 to about 80 °C, or about 55 °C to about 80 °C, or about 60 °C to about 75 °C, or about 70 °C. Operating pressures can be 1 to 200 bar, such as 10 to 50 bar or about 25 to about 30 bar. The process can be continuous and mean residence times can be 10 minutes to 20 hours, for example 30 minutes to 4 hours or 1 to 2 hours. Residence times can be chosen so as to achieve the desired conversion at high selectivity.

[0048] The process can be carried out in any reactor, such as a loop reactor, a plug-flow reactor, a bubble column reactor, or a continuous stirred tank reactor (CSTR). Oligomerization of ethylene is an exothermic reaction and, thus, the reaction system can include a heat exchanger for cooling. A product leaving the oligomerization reaction system can contain the active catalyst and unreacted ethylene. The reaction can be terminated to avoid undesirable side reactions by removing catalyst components from the organic phase through extraction with a caustic aqueous phase. Contact with the caustic aqueous phase can result in formation of nonreactive minerals corresponding to the catalyst components.

[0049] The organic phase, after passage through the catalyst removal system, can pass through a molecular sieve absorption bed and can then be fed to a distillation column to recover dissolved ethylene. The separation train can be configured to separate the linear alpha olefins from the solvent, catalyst, and any unreacted ethylene. Recovered ethylene and solvent can be recycled to the reaction system. The separation train can separate each linear alpha olefin, for example, yielding a C4 stream, Cs stream, Cs stream, and so on. The separation train can also -10-

separate the linear alpha olefins into certain fractions, such as C4-C10 fraction, C12-C16 fraction,

Ci8-Coo fraction, C20+ fractions, or any other desired fraction.

[0050] An example loop reaction system 10 1s set forth in FIG. 1. As shown, the reaction system can include a reaction chamber 12, a pump 14, and a heat exchanger 16, all in fluid communication with each other within a recirculation loop 18. The reaction chamber 12 can be, for example, an autoclave adapted for mixing of the reagents introduced into the reaction system 10. The illustrated embodiment is in the form of a jet loop reactor that includes a nozzle arrangement 24 that accelerates the flow of liquid reaction mixture into the reaction chamber 12 and entrains the gaseous feed 26 therein. The gaseous feed 26 can be ethylene gas, optionally in combination with hydrogen gas. In some embodiments, hydrogen gas is added to the reaction system to reduce polymer formation. An example amount of hydrogen introduced is between about 0.1 and about 10 mol% with respect to the ethylene molar concentration. The reaction chamber 12 is charged with the catalyst composition 28 dissolved in the aromatic solvent. The aliphatic hydrocarbon solvent 30 can be injected into the recirculation loop 18. A discharge stream 20 can be removed from the recirculation loop 18 and directed into a separation train 22 as disclosed above. Although not shown, the reaction system 10 can also include a filter for filtering polymeric material circulating within the recirculation loop 18.

[0051] The type of pump 14 is not limiting, and any pump capable of pumping the reaction mixture through the recirculation loop 18 can be used. The type of heat exchanger 16 is not limiting, and any heat exchanger configured to cool the reaction mixture during circulation within the recirculation loop 18 can be used.

[0052] Polymer fouling within the reaction system can occur during the oligomerization reaction process. Such fouling is typically detected by, for example, reduced effluent flow rate or reduced heat exchanger or pump performance. Such fouling can be treated by flushing the reaction system with a solvent. The flushing solvent comprising the polymeric material can be directed into a separation train 22.

[0053] The reaction process of the present disclosure can be characterized by the amount of polymer material produced by the reaction. In some embodiments, the effluent product stream contains about 0.4% polymer material by weight or less, such as about 0.1% by weight to about 0.4% by weight or about 0.2% by weight to about 0.4% by weight, based on the total weight of the effluent. -11-

[0054] The reaction process of the present disclosure also can be characterized by catalyst activity, which can be calculated in units of kg'gc-"-h" as C2 consumption in kg per hour/ Cr concentration per gm. In some embodiments, the catalyst activity in units of kg‘ger!*h"! is about or higher, such as about 45 to about 55 or about 48 to about 54.

[0055] The reaction process of the present disclosure also can be characterized by selectivity for 1-hexene, which can be calculated as Selectivity (Cn) = [(1Cn + Ch isomers + Cr(saturated) isomers) / total C4 to C20+]. In some embodiments, the selectivity for 1-hexene is about 91% or higher, such as about 91 to about 94 or about 92 to about 93.

[0056] In general, the present disclosure may alternately comprise, consist of, or consist essentially of, any appropriate components herein disclosed. The disclosure may additionally, or alternatively, be formulated so as to be devoid, or substantially free, of any components, materials, ingredients, adjuvants or species used in the prior art compositions or that are otherwise not necessary to the achievement of the function and/or objectives of the present disclosure.

EXPERIMENTAL

Comparative Example A

[0057] An ethylene trimerization reaction per Scheme 1 below was conducted in a loop reaction system. Ethylene was reacted in the presence of Cr(acac)3 as catalyst, activated by a co- catalyst triethyl aluminum (TEAL) and in the presence of dodecyl trimethyl ammonium chloride (DOTRIMAC), using toluene as a solvent and an ethylene pressure of 30 bar and a reaction temperature of 50 °C. The ethylene was trimerized to give 1-hexene with 90% selectivity, along with other oligomers and polymer material (polyethylene) at a polymer concentration of about 0.85 wt%. The polymer produced during the reaction was observed to be tacky in nature and was prone to sticking to the reactor walls. Due to its tackiness and the relative amount produced, the accumulation of polymeric material within the reaction system was observed, with the eventual clogging of downstream pipes, pump, filters and heat exchangers, requiring reactor shutdown.

Cr(acac),, TEAL, Toluene

CH=CH, —0M8M MM >» ANN + Other oligomers + Polymer

Ligand, DOTRIMAC, 30 Bar, 50°C 1-hexene -12-

Scheme 1

Example 1

[0058] To overcome polymer formation issues, the above reaction was repeated using different solvent systems and different reaction temperatures. In particular, binary solvent systems were tested using an aromatic solvent for catalyst preparation and an aliphatic hydrocarbon solvent as the primary reaction solvent due to the fact that all catalyst components are not fully soluble in an aliphatic solvent system. Xylene was favored over toluene as the aromatic solvent mainly due to their boiling point difference, which makes xylene easier to separate from the desired reaction products, such as 1-octene.

[0059] The experiments were conducted at various reaction temperatures. It was theorized that higher temperatures could increase catalyst activity and performance, as well as keep the polymeric material solubilized in the reaction media for easier removal. Testing was performed at °C, 70°C and 90°C, as well as at 5%, 10% and 15% by weight of xylene in n-heptane. The resulting data is set forth in Table 1 below.

Table 1

Temp Activity i 0 Solvent Polymer wt% 4,4 C6 selectivity | 1- C6 purity (in °C) (kg gcr_h”) 90 [s%xyleneinn-heptane |. 069 | 248 | 89.60% | 98.30% 90 |10% xylene in n-heptane 89.30% 98.10% 90 |15% xylene in n-heptane | 0.96 | 215 | 89.30% | 98.10% 5% xylene in n-heptane 92.30% | 99.40% 10%xylene in n-heptane 92.00% | 99.10% 15% xylene in n-heptane 91.90% | 99.00% 5% xylene in n-heptane 92.10% | 99.20% 10%xylene in n-heptane 91.90% | 99.00% 15% xylene in n-heptane 91.90% | 99.00% 90 [Toluene | 11 | 196 | 88.60% 98.20% 70 rolene | 09% | 469 | 90.00% | 98.70% 90.50% | 99.00%

[0060] Surprisingly, it was observed that the polymeric material had an increased tackiness and was more prone to sticking to components of the reaction system when toluene was used as the sole solvent. Although not bound by a theory of operation, it is believed that aromatic solvents at high concentrations in the system lead to the observed stickiness of the polymer material, which can undesirably create greater difficulty in removing the polymeric material from the system. -13-

[0061] It is also surprisingly apparent from the data above that there is an optimal temperature range and ratio of aliphatic to aromatic solvent in terms of increasing catalyst activity and C6 selectivity, and reducing polymer formation. In particular, a temperature range of about 50 °C to about 80 °C and a maximum amount of aromatic solvent of 10% by weight, based on the total weight of the solvent mixture produced the best results. The most optimized condition was a reaction temperature of 70 °C using 5% xylene in n-heptane as the solvent system.

[0062] Many modifications and other implementations of the disclosure will come to mind to one skilled in the art to which this disclosure pertains having the benefit of the teachings presented in the foregoing descriptions and the associated figures. Therefore, it is to be understood that the disclosure is not to be limited to the specific implementations disclosed herein and that modifications and other implementations are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. -14-

Claims (15)

1. CLAIMS:

   1. A method of producing one or more linear alpha olefins by ethylene oligomerization, the method comprising: contacting ethylene with a catalyst composition in a reaction chamber in the presence of a solvent mixture comprising at least one aromatic solvent and at least one aliphatic hydrocarbon solvent, wherein the at least one aromatic solvent is present in an amount of about 10% by weight or less, based on the total weight of the solvent mixture, and at a temperature of about 50 °C to about 80 °C: oligomerizing the ethylene to produce one or more linear alpha olefins; and withdrawing an effluent comprising the one or more linear alpha olefins.

   2. The method of claim 1, further comprising premixing the catalyst composition with the at least one aromatic solvent to form a catalyst solution and feeding the catalyst solution into the reaction chamber.

   3. The method of claim 1, further comprising injecting gaseous ethylene into the reaction chamber.

   4. The method of claim 3, further comprising injecting hydrogen into the reaction chamber, optionally by premixing hydrogen with the gaseous ethylene prior to injection into the reaction chamber.

   5. The method of claim 1, comprising feeding the at least one aliphatic hydrocarbon solvent to the reaction chamber separately from the at least one aromatic solvent.

   6. The method of claim 1, wherein the reaction chamber is part of a loop reactor system comprising the reaction chamber, a recirculation loop in fluid communication with the reaction chamber and configured to receive a reaction mixture from the reaction chamber and return the reaction mixture to the reaction chamber, a pump configured to pump the reaction mixture through the recirculation loop, and a heat exchanger configured to cool the reaction mixture during circulation within the recirculation loop. -15-

   7. The method of any one of claims 1 to 6, wherein the at least one aromatic solvent is selected from the group consisting of toluene, xylene, monochlorobenzene, dichlorobenzene, chlorotoluene, and combinations thereof.

   8. The method of any one of claims 1 to 7, wherein the at least one aliphatic hydrocarbon solvent is a C5 to C8 cyclic or straight chain alkane, such as n-heptane, cycloheptane, isoheptane, n-hexane, isohexane, cyclohexane, methylcyclohexane, and combinations thereof.

   9. The method of any one of claims 1 to 6, wherein the at least one aromatic solvent is xylene and the at least one aliphatic hydrocarbon solvent is n-heptane.

   10. The method of any one of claims 1 to 9, wherein the at least one aromatic solvent is present in an amount of about 7.5% by weight or less, such as about 3 to about 7% by weight or about 4 to about 6% by weight, based on the total weight of the solvent mixture.

   11. The method of any one of claims 1 to 10, wherein the contacting is conducted at a temperature of about 55 °C to about 80 °C, such as about 60 °C to about 75 °C, or about 70 °C, and optionally wherein the contacting is conducted at a pressure of about 25 to about 30 bar.

   12. The method of any one of claims 1 to 11, wherein the amount of polymer within the effluent 1s about 0.4% by weight or less, such as about 0.1% by weight to about 0.4% by weight or about 0.2% by weight to about 0.4% by weight, based on the total weight of the effluent.

   13. The method of any one of claims 1 to 12, wherein a catalyst activity in units of kg‘ger!-h"! is about 45 or higher, such as about 45 to about 55 or about 48 to about 54.

   14. The method of any one of claims 1 to 13, wherein a selectivity for 1-hexene 1s about 91% or higher, such as about 91 to about 94 or about 92 to about 93.

   15. The method of any one of claims 1 to 14, wherein the catalyst composition comprises: 1) a chromium compound selected from organic or inorganic salts, coordination complexes and organometallic complexes of Cr(IT) or Cr(IIT), such as -16-

   CrCls(tetrahydrofuran)s, Cr(IIT) acetylacetonate, Cr(IIT) octanoate, chromium hexacarbonyl, Cr(IIT)-2-ethylhexanoate, benzene(tricarbonyl)-chromium, Cr(IID)chloride, or combinations thereof;

   11) a co-catalyst selected from the group consisting of a tri(C1-C6 alkyl) aluminum such as trimethyl aluminum, triethyl aluminum, triisopropyl aluminum, or triisobutyl aluminum, ethyl aluminum sesquichloride, diethyl aluminum chloride, ethyl aluminum dichloride, methyl aluminoxane (MAO), and combinations thereof;

   111) a heteroatomic multidentate ligand, such as a ligand of the general structure R1R2P—N(R3)—P(R4)—N(Rs)—H, wherein Rı, Ra, R3, R4and Rs are independently selected from halogen, amino, trimethylsilyl, C1-C10-alkyl, substituted C1-C10-alkyl, aryl and substituted aryl, wherein at least one of the P or N atoms of the PNPNH-unit is optionally also a member of a ring system;

   iv) a modifier selected from ammonium or phosphonium salts of the type [H4E]X, [H3ER]X, [H:ER2]X, [HER3]X or [ER4]X, wherein E is N or P, X is CI, Br or I, and each R is independently C1-C22 hydrocarbyl, such as a substituted or unsubstituted C1-C16-alkyl, C2-C16-acyl, or substituted or unsubstituted C6- C20-aryl, such as dodecyl trimethyl ammonium chloride, tetraphenyl phosphonium chloride, tetraethyl ammonium chloride monohydrate, tetraethyl ammonium chloride, trimethyl dodecyl ammonium chloride, isopropylamine hydrochloride, triethylamine hydrochloride, tetrapropyl ammonium chloride, tetra-n-butyl ammonium chloride, tetraethyl ammonium bromide, p-toluidine hydrochloride, dimethyl distearyl ammonium chloride, (tri-n-butyl)-n-tetradecyl phosphonium chloride, benzoyl chloride, acetyl chloride, and combinations thereof’ or

   Vv) a combination of two or more of the above.

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