Process for the oligomerization of ethylene

Abstract

The present disclosure provides a process for producing one or more linear alpha-olefins by ethylene oligomerization, the process 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, and at a temperature of about 50°C to about 80°C, wherein the at least one aromatic solvent is present in an amount of about 10 wt% or less, based on the total weight of the solvent mixture; oligomerizing the ethylene to produce one or more linear alpha-olefins; and withdrawing an effluent comprising the one or more linear alpha-olefins.

Description

Technical Field

[0001] This disclosure relates to a method for producing synthetic α-olefin products by ethylene oligomerization. Background Technology

[0002] Linear olefins are a class of hydrocarbons used as feedstocks in the petrochemical industry, with linear α-olefins (unbranched olefins whose double bonds are located at the ends of the chain) forming an important subclass. Linear α-olefins can be converted to linear primary alcohols via hydroformylation. Hydroformylation can also be used to prepare aldehydes, which can then be oxidized to provide synthetic fatty acids, particularly those with an odd number of carbon atoms, used in the production of lubricants. Linear α-olefins are also used in detergents, such as in the production of linear alkylbenzene sulfonates, which are prepared by the Friedel-Crafts reaction of benzene with linear olefins followed by sulfonation. Linear α-olefins, especially 1-hexene, are also used as comonomers to manufacture high-density polyethylene (HDPE) and linear low-density polyethylene (LLDPE).

[0003] The preparation of α-olefins is primarily based on the oligomerization of ethylene, which implies that the prepared α-olefins have an even number of carbon atoms. Some oligomerization methods for ethylene utilize chromium-based organometallic complexes with ligands as catalysts in the presence of activators / co-catalysts (such as methylaluminoxane (MAO)). Typically, the effluent from reactors used for producing linear α-olefins is directed to one or more distillation columns to separate the various fractions of linear α-olefins.

[0004] Polymer materials are generated as undesirable byproducts of oligomerization reactions. The presence of polymer materials can lead to fouling within the reactor system and downstream product processing units. This fouling can cause reactor downtime and presents removal challenges. There remains a need in the art for improved techniques to address polymer fouling caused by oligomerization reactions. Summary of the Invention

[0005] Exemplary embodiments of this disclosure relate to systems and methods for reducing polymer fouling in oligomer reactors. It has been found that the choice of solvent used in the reaction system has a significant impact on catalytic activity and polymer formation. According to this disclosure, a reduction in polymer formation can be achieved by using a binary solvent system, i.e., a mixture of an aliphatic hydrocarbon solvent (e.g., n-heptane) and a relatively small amount of an aromatic solvent (e.g., xylene), instead of using only an aromatic solvent system (e.g., toluene) as is commonly seen in the art. Furthermore, it has been found that using such a binary solvent system reduces the viscosity of the polymer material generated in the reactor, making the polymer material easier to remove from the system.

[0006] This disclosure includes, but is not limited to, the following implementation schemes.

[0007] Implementation Scheme 1: A method for producing one or more linear α-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, and at a temperature of about 50°C to about 80°C, wherein 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; oligomerizing ethylene to produce one or more linear α-olefins; and extracting an effluent comprising one or more linear α-olefins.

[0008] Implementation Scheme 2: The method according to Implementation Scheme 1 further includes premixing the catalyst composition with at least one aromatic solvent to form a catalyst solution and feeding the catalyst solution into the reaction chamber.

[0009] Implementation Scheme 3: The method according to Implementation Scheme 1 or 2 further includes injecting gaseous ethylene into the reaction chamber.

[0010] Implementation Scheme 4: The method according to Implementation Scheme 3 further includes injecting hydrogen into the reaction chamber, optionally by premixing the hydrogen with gaseous ethylene before injecting it into the reaction chamber.

[0011] Implementation Scheme 5: The method according to any one of Implementation Schemes 1 to 4 includes feeding at least one aliphatic hydrocarbon solvent and at least one aromatic solvent separately into the reaction chamber.

[0012] Implementation Scheme 6: The method according to any one of Implementation Schemes 1 to 5, wherein the reaction chamber is part of a loop reactor system, the loop reactor system comprising: a 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] Implementation Scheme 7: The method according to any one of Implementation Schemes 1 to 6, wherein at least one aromatic solvent is selected from toluene, xylene, monochlorobenzene, dichlorobenzene, chlorotoluene, and combinations thereof.

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

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

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

[0017] Implementation Scheme 11: The method according to any one of Implementation Schemes 1 to 10, wherein the contact is carried out at a temperature of about 55°C to about 80°C, for example about 60°C to about 75°C or about 70°C, and optionally wherein the contact is carried out at a pressure of about 25 to about 30 bar.

[0018] Implementation Scheme 12: The method according to any one of Implementation Schemes 1 to 11, wherein the amount of polymer in the effluent is about 0.4% by weight or less, for example 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] Implementation Scheme 13: The method according to any one of Implementation Schemes 1 to 12, wherein the concentration is kg·g Cr -1 ·h -1 The catalyst activity, measured in units, is about 45 or higher, for example, about 45 to about 55 or about 48 to about 54.

[0020] Implementation Scheme 14: The method according to any one of Implementation Schemes 1 to 13, wherein the selectivity of 1-hexene is about 91% or higher, for example about 91 to about 94 or about 92 to about 93.

[0021] Implementation Scheme 15: The method according to any one of Implementation Schemes 1 to 14, wherein the catalyst composition comprises:

[0022] i) Selected from the following chromium compounds: organic or inorganic salts, coordination complexes and organometallic complexes of Cr(II) or Cr(III), such as CrCl3 (tetrahydrofuran)3, acetylacetone Cr(III), octanoic acid Cr(III), hexacarbonyl chromium, 2-ethylhexanoic acid Cr(III), benzene (tricarbonyl) chromium, Cr(III) chloride or combinations thereof.

[0023] ii) Selected from the following cocatalysts: tri(C1-C6 alkyl)aluminum, such as trimethylaluminum, triethylaluminum, triisopropylaluminum or triisobutylaluminum, ethyl sesquichloride aluminum, diethylaluminum chloride, ethyl dialuminum chloride, methylaluminoxane (MAO) and combinations thereof.

[0024] iii) Heteroatomic polydentate ligands, such as ligands with the general formula R1R2P-N(R3)-P(R4)-N(R5)-H, wherein R1, R2, R3, R4, and R5 are independently selected from halogens, amino groups, trimethylsilyl groups, C1-C4 groups, and C5-C4 groups.10 -alkyl, substituted C1-C 10 -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 the cyclic system;

[0025] iv) Modifiers selected from ammonium or phosphonium salts of type [H4E]X, [H3ER]X, [H2ER2]X, [HER3]X, or [ER4]X, wherein E is N or P, X is Cl, Br, or I, and each R is independently a C1-C22 hydrocarbon group, such as a substituted or unsubstituted C1-C16-alkyl, C2-C16-acyl, or a substituted or unsubstituted C6-C20-aryl, such as dodecyltrimethylammonium chloride, tetraphenylphosphonium chloride, tetraethylammonium chloride monohydrate, tetraethylammonium chloride, trimethyldodecylammonium chloride, isopropylamine hydrochloride, triethylamine hydrochloride, tetrapropylammonium chloride, tetra-n-butylammonium chloride, tetraethylammonium bromide, p-toluidine hydrochloride, dimethyldistearate ammonium chloride, (tri-n-butyl)-tetradecylphosphonium chloride, benzoyl chloride, acetyl chloride, and combinations thereof; or

[0026] v) A combination of two or more of the above.

[0027] These and other features, aspects, and advantages of this disclosure will become apparent from the following detailed description and reading of the accompanying drawings, which are briefly described below. This disclosure includes any combination of two, three, four, or more features or elements set forth in this disclosure, whether or not such features or elements are explicitly combined in the specific exemplary embodiments described herein or otherwise referenced. This disclosure is intended to be read as a whole, such that separable features or elements of this disclosure shall be considered composable in any of its aspects and exemplary embodiments, unless the context of this disclosure clearly provides otherwise.

[0028] Therefore, it should be understood that this invention is provided merely to summarize some exemplary embodiments in order to provide a basic understanding of some aspects of this disclosure. Consequently, it should be understood that the above exemplary embodiments are merely exemplary and should not be construed in any way as limiting the scope or spirit of this disclosure. Other exemplary embodiments, aspects, and advantages will become apparent from the following detailed description taken in conjunction with the accompanying drawings, which illustrate the principles of some of the described exemplary embodiments by way of example. Attached Figure Description

[0029] Having provided a general description of various aspects of this disclosure above, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, wherein:

[0030] Figure 1 This is a simplified schematic diagram of an exemplary ethylene oligomerization reaction system according to the present disclosure. Detailed Implementation

[0031] Some embodiments of this disclosure will now be described more fully below with reference to the accompanying drawings, which illustrate some, but not all, of the embodiments of this disclosure. Indeed, various embodiments of this disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these exemplary embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of this disclosure to those skilled in the art. The same reference numerals refer to the same elements throughout the drawings.

[0032] Unless otherwise specified or clear from the context, references to "first," "second," etc., should not be construed as implying a particular order. A feature described as situated above another feature (unless otherwise specified or clear from the context) may alternatively be situated below it, and vice versa; and similarly, a feature described as situated to the left of another feature may alternatively be situated to its right, and vice versa. Furthermore, while this document may refer to quantitative measures, values, geometric relationships, etc., any one or more of them (if not all) may be absolute or approximate to account for possible acceptable variations, such as those caused by engineering tolerances, etc., unless otherwise stated.

[0033] All ranges disclosed herein include endpoints, and endpoints can be combined independently of each other (e.g., the range “up to 25 wt%, or more specifically 5 wt%–20 wt%” includes the endpoints of the range “5 wt%–25 wt%” and all intermediate values, etc.). “Combination” includes blends, mixtures, alloys, reaction products, etc.

[0034] As used herein, unless otherwise specified or clearly stated from the context, an "OR" of a set of operands is an "inclusive OR," and therefore true if and only if one or more operands are true, not an "exclusive OR" which is false if all 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. Furthermore, the terms "a" and "an" mean "one or more" unless otherwise specified or clearly stated from the context to refer to the singular form.

[0035] The term "aliphatic" refers to organic functional groups or compounds containing carbon and hydrogen linked together by straight chains, branched chains, or non-aromatic rings.

[0036] The term "hydrocarbon group" refers to any monovalent free radical derived from hydrocarbons, 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).

[0037] The term "alkyl" refers to a linear or branched saturated hydrocarbon. Non-limiting examples of alkyl groups include methyl, ethyl, propyl, butyl, pentyl, etc.

[0038] An "aryl" group or "aromatic" group is a substituted or unsubstituted, monocyclic or polycyclic hydrocarbon having 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, halogens, hydroxyl groups, alkoxy groups, haloalkyl groups, haloalkoxy groups, carboxylic acids, esters, amines, nitro groups, amides, nitriles, acyl groups, alkylsilanes, thiols, and thioethers. 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 groups). The aryl or alkyl group can be substituted with halogens, hydroxyl groups, alkoxy groups, haloalkyl groups, haloalkoxy groups, carboxylic acids, esters, ethers, amines, nitro (-NO2), amides, nitriles (-CN), acyl groups, alkylsilanes, thiols, and thioethers. Non-limiting examples of polycyclic groups include ring systems comprising two or more conjugated rings (e.g., fused aromatic rings) and substituted conjugated rings.

[0039] solvent system

[0040] According to this disclosure, a method for producing one or more linear α-olefins by ethylene oligomerization is provided, wherein at least two solvents are used. In particular, a solvent mixture comprising at least one aromatic solvent and at least one aliphatic hydrocarbon solvent is used.

[0041] In some embodiments, the aromatic solvent is selected in part based on the solubility of the catalyst composition in the solvent. Exemplary 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 a catalyst solution, in some embodiments, the aromatic solvent is present as a minor component of the overall solvent mixture. For example, the aromatic solvent may be present in an amount of about 10% by weight or less, or 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.

[0042] Aliphatic hydrocarbon solvents are typically selected as the primary solvent in the reaction system and are therefore commonly used as the major component of the solvent mixture. For example, the solvent mixture may contain about 90% by weight or more, or about 92.5% by weight or more, such as about 93% to about 97% by weight or about 94% to about 96% by weight of an aliphatic hydrocarbon solvent, based on the total weight of the solvent mixture. Exemplary aliphatic hydrocarbon solvents include C5 to C8 cyclic or straight-chain alkanes, such as n-heptane, cycloheptane, isoheptane, n-hexane, isoheptane, cyclohexane, methylcyclohexane, and combinations thereof. In some embodiments, the aliphatic hydrocarbon solvent is n-heptane.

[0043] The solvent mixtures described above can be used in the ethylene oligomerization methods and systems described below. The relative amounts of each solvent mentioned above refer to the reaction system during the reaction, for example, as shown in the reference below. Figure 1 The relative amount of solvent present in the described reaction system.

[0044] Ethylene oligomerization methods and systems

[0045] Linear α-olefins (LAO) are those with the chemical formula C x H 2x Alkenes are distinguished from other mono-olefins with similar molecular formulas by the linearity of the hydrocarbon chain and the position of the double bonds at the primary or α-position. Linear α-olefins include a class of industrially important α-olefins, including 1-butene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, and C1-1-octadecene. 20 -C 24 C 24 -C 30 and C 20 -C 30 A more advanced mixture of olefins. Linear α-olefins are useful intermediates used in the manufacture of detergents, synthetic lubricants, copolymers, plasticizers, and many other important products.

[0046] Existing methods for producing linear α-olefins typically rely on the oligomerization of ethylene. For example, linear α-olefins can be prepared by catalytic oligomerization of ethylene in the presence of a catalyst composition, including, for example, a chromium compound, a cocatalyst, a ligand, and optional modifiers. See, for example, the catalyst composition described in US9018431 by Wöhl et al., which is incorporated herein by reference.

[0047] Exemplary chromium compounds include organic or inorganic salts, coordination complexes, and organometallic complexes of Cr(II) or Cr(III), such as CrCl3 (tetrahydrofuran)3, acetylacetone Cr(III), octanoic acid Cr(III), hexacarbonyl chromium, 2-ethylhexanoic acid Cr(III), benzene (tricarbonyl) chromium, Cr(III) chloride, or combinations thereof.

[0048] Exemplary cocatalysts include tri(C1-C6 alkyl)aluminum, such as trimethylaluminum, triethylaluminum, triisopropylaluminum or triisobutylaluminum, ethyl sesquichloride aluminum, diethylaluminum chloride, ethyl dialuminum chloride, methylaluminoxane (MAO) and combinations thereof.

[0049] A typical ligand structure is an organophosphorus compound having at least two phosphine groups covalently linked by linking groups. Exemplary ligands include compounds having any of the following skeletal structures: PNP, PNPN, PNNP, PNPNP, or NPNPN, where each P is a substituted phosphine group (typically secondary or tertiary phosphine) and each N is a substituted amino group (typically secondary or tertiary amino). Exemplary substituents for the phosphine and amino groups include optionally substituted amino, trialkylsilyl, or optionally substituted C1-C20 hydrocarbon groups (e.g., optionally substituted phenyl or optionally substituted cyclohexyl), wherein the optional substituents typically include an amino or C1-C20 hydrocarbon group. In some embodiments, the ligand skeleton structure comprises at least two N atoms (e.g., PNPN, PNNP, PNPNP, or NPNPN).

[0050] Exemplary heteroatom polydentate ligands include ligands of the general formula R1R2P-N(R3)-P(R4)-N(R5)-H, wherein R1, R2, R3, R4, and R5 are each independently selected from halogens, amino groups, trimethylsilyl groups, C1-C6 groups, and C4-C6 groups. 10 -alkyl, aryl, and substituted aryl, wherein at least one of the P or N atoms of the PNPNH unit is also optionally a member of a cyclic system. In one example, the ligand is (Ph)2P-N(iPr)-P(Ph)-N(iPr)-H, where Ph is phenyl and iPr is isopropyl.

[0051] Exemplary modifiers include ammonium or phosphonium salts of type [H4E]X, [H3ER]X, [H2ER2]X, [HER3]X, or [ER4]X, wherein E is N or P, X is Cl, Br, or I, and each R is independently a C1-C22 hydrocarbon group, such as a substituted or unsubstituted C1-C16-alkyl, C2-C16-acyl, or substituted or unsubstituted C6-C20-aryl, such as dodecyltrimethylammonium chloride, tetraphenylphosphonium chloride, tetraethylammonium chloride monohydrate, tetraethylammonium chloride, trimethyldodecylammonium chloride, isopropylamine hydrochloride, triethylamine hydrochloride, tetrapropylammonium chloride, tetra-n-butylammonium chloride, tetraethylammonium bromide, p-toluidine hydrochloride, dimethyldistearate ammonium chloride, (tri-n-butyl)-tetradecylphosphonium chloride, benzoyl chloride, acetyl chloride, and combinations thereof. In some embodiments, the modifier contains a free amino group selected from primary, secondary, or tertiary aliphatic or aromatic amines (e.g., isopropylamine).

[0052] As described above, aromatic solvents in binary solvent systems are typically used to prepare catalyst compositions. In some embodiments, a first portion of the catalyst is prepared by combining a chromium source and a ligand in an aromatic solvent to form a first solution. In some embodiments, a second portion of the catalyst is prepared by combining a co-catalyst and a modifier in an aromatic solvent to form a second solution. The first and second solutions are then premixed together, after which the catalyst solution is fed into the reaction system.

[0053] Catalyst compositions are typically prepared such that the chromium concentration is from 0.001 to 100 mmol / L, more typically from 0.1 to 10 mmol / L, based on the total catalyst composition. In some embodiments, the ligand / Cr ratio is from 0.5:1 to 50:1 mol / mol, for example from 0.8:1 to 20:1 mol / mol. The Al / Cr molar ratio is typically from 1:1 to 1000:1, for example from 10:1 to 200:1. The modifier / Cr molar ratio is typically from 0.01:1 to 100:1, for example from 1:1 to 20:1. In some embodiments, the Cr / halogen molar ratio is from 1:1 to 1:20.

[0054] Oligopolymerization can be carried out at temperatures ranging from about 10°C to about 200°C, for example, from about 20°C to about 100°C, or from about 50°C to about 80°C, or from about 55°C to about 80°C, or from about 60°C to about 75°C, or about 70°C. Operating pressures can range from 1 to 200 bar, for example, from 10 to 50 bar or from about 25 to about 30 bar. The method can be continuous, and the average residence time can range from 10 minutes to 20 hours, for example, from 30 minutes to 4 hours or from 1 to 2 hours. The residence time can be selected to achieve the desired conversion rate with high selectivity.

[0055] This method can be carried out in any reactor, such as a loop reactor, plug flow reactor, bubble column reactor, or continuous stirred tank reactor (CSTR). Ethylene oligomerization is an exothermic reaction; therefore, the reaction system may include heat exchangers for cooling. The products leaving the oligomerization reaction system may contain active catalyst and unreacted ethylene. The reaction can be terminated by extraction with an alkaline aqueous phase to remove the catalyst components from the organic phase, thus avoiding undesirable side reactions. Contact with an alkaline aqueous phase can lead to the formation of non-reactive minerals corresponding to the catalyst components.

[0056] After removal by the catalyst, the organic phase can pass through a molecular sieve adsorption bed and then be fed to a distillation column to recover dissolved ethylene. The separation sequence can be configured to separate linear α-olefins from the solvent, catalyst, and any unreacted ethylene. The recovered ethylene and solvent can be recycled back to the reaction system. The separation sequence can separate each type of linear α-olefin, for example, producing C4 streams, C6 streams, C8 streams, etc. The separation sequence can also separate linear α-olefins into certain fractions, such as C4-C6 fractions. 10distillate, C 12 -C 16 distillate, C 18 -C 20 distillate, C 20+ Fraction or any other desired fraction.

[0057] Exemplary loop reaction system 10 Figure 1 As shown, the reaction system may include a reaction chamber 12, a pump 14, and a heat exchanger 16, all of which are in fluid communication with each other within a recirculation loop 18. The reaction chamber 12 may be, for example, an autoclave suitable for mixing reactants introduced into the reaction system 10. The illustrated embodiment is in the form of a jet loop reactor, which includes a nozzle arrangement 24 that accelerates the flow of the liquid reaction mixture into the reaction chamber 12 and entrains a gaseous feed 26. The gaseous feed 26 may be ethylene gas, optionally combined with hydrogen. In some embodiments, hydrogen is added to the reaction system to reduce polymer formation. An example amount of hydrogen introduced is from about 0.1 mol% to about 10 mol%, relative to the ethylene molar concentration. The reaction chamber 12 is charged with a catalyst composition 28 dissolved in an aromatic solvent. An aliphatic hydrocarbon solvent 30 may be injected into the recirculation loop 18. An effluent stream 20 may be removed from the recirculation loop 18 and directed in a separation sequence 22, as disclosed above. Although not shown, the reaction system 10 may also include a filter for filtering polymer material circulating within the recirculation loop 18.

[0058] The type of pump 14 is not limited, 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 limited, and any heat exchanger configured to cool the reaction mixture during circulation within the recirculation loop 18 can be used.

[0059] During oligomerization, polymer fouling can occur within the reaction system. This fouling is typically detected by, for example, a decrease in effluent flow rate or a reduction in heat exchanger or pump performance. Such fouling can be treated by flushing the reaction system with a solvent. The flushing solvent, containing polymer material, can be directed into separation sequence 22.

[0060] The reaction process disclosed herein can be characterized based on the amount of polymer material produced by the reaction. In some embodiments, the effluent product stream contains about 0.4 wt% or less of polymer material, for example, about 0.1 wt% to about 0.4 wt% or about 0.2 wt% to about 0.4 wt%, based on the total weight of the effluent.

[0061] The reaction process disclosed herein can also be characterized by catalyst activity, which can be expressed as kg·g. Cr -1 ·h -1The unit is calculated as C2 consumption per hour (kg) / Cr concentration per gram. In some embodiments, it is expressed as kg·g. Cr -1 ·h -1 The catalyst activity, measured in units, is about 45 or higher, for example, about 45 to about 55 or about 48 to about 54.

[0062] The reaction process disclosed herein can also be characterized by the selectivity of 1-hexene, which can be calculated as selectivity (C0). n )=[(1C n +C n Isomer + C n(饱和) (Isomers) / Total C4 to C 20+ In some embodiments, the selectivity of 1-hexene is about 91% or higher, for example, about 91% to about 94% or about 92% to about 93%.

[0063] Generally, this disclosure may alternatively include, constitute, or substantially constitute any suitable component disclosed herein. Furthermore or alternatively, this disclosure may be formulated to be free of, or substantially free of, any component, material, ingredient, adjuvant, or class of substances used in prior art compositions, or any component, material, ingredient, adjuvant, or class of substances that is not essential to achieving the function and / or purpose of this disclosure.

[0064] experiment

[0065] Comparative Example A

[0066] Ethylene trimerization according to Scheme 1 below was carried out in a loop reactor system. Ethylene was reacted in the presence of Cr(acac)3 as a catalyst, activated with triethylaluminum (TEAL) as a co-catalyst, and in the presence of dodecyltrimethylammonium chloride (DOTRIMAC), using toluene as a solvent, an ethylene pressure of 30 bar, and a reaction temperature of 50°C. The ethylene trimerization produced 1-hexene with 90% selectivity, and other oligomers and polymer materials (polyethylene) with a polymer concentration of approximately 0.85 wt%. The polymer produced during the reaction was observed to have viscous properties and readily adhered to the reactor walls. Due to its viscosity and the relatively large amount produced, accumulation of polymer material was observed within the reaction system, eventually clogging downstream pipes, pumps, filters, and heat exchangers, necessitating reactor shutdown.

[0067]

[0068] Option 1

[0069] Example 1

[0070] To overcome the polymer formation problem, the above reaction was repeated using different solvent systems and reaction temperatures. In particular, due to the fact that not all catalyst components are completely soluble in aliphatic solvent systems, binary solvent systems were tested, using aromatic solvents to prepare the catalyst and aliphatic hydrocarbon solvents as the main reaction solvent. Xylene was more suitable as an aromatic solvent than toluene, mainly due to their boiling point difference, which made xylene easier to separate from the desired reaction products (e.g., 1-octene).

[0071] Experiments were conducted at various reaction temperatures. Theoretically, higher temperatures are believed to increase catalyst activity and performance, and to dissolve the polymer material in the reaction medium for easier removal. Tests were performed at 50°C, 70°C, and 90°C, and with 5 wt%, 10 wt%, and 15 wt% xylene in n-heptane. The data obtained are presented in Table 1 below.

[0072] Table 1

[0073]

[0074] Surprisingly, it was observed that when toluene was used alone as a solvent, the polymer material exhibited increased viscosity and became more readily adhered to components of the reaction system. While not bound by operational theory, it is thought that the high concentration of aromatic solvent in the system contributes to the observed viscosity of the polymer material, which may undesirably create greater difficulty in removing the polymer material from the system.

[0075] Surprisingly, the data above also reveal an optimal temperature range and aliphatic-to-aromatic solvent ratio for increasing catalyst activity and C6 selectivity while reducing polymer formation. Specifically, a temperature range of approximately 50°C to approximately 80°C and a maximum amount of 10% by weight of aromatic solvent (based on the total weight of the solvent mixture) yielded the best results. The optimal conditions were a reaction temperature of 70°C using 5% by weight xylene in n-heptane as the solvent system.

[0076] Many modifications and other embodiments of this disclosure will arise to those skilled in the art upon which this disclosure pertains, thanks to the foregoing description and the accompanying drawings. Therefore, it should be understood that this disclosure is not limited to the specific embodiments disclosed herein, and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terminology is used herein, it is used in a general and descriptive sense only and is not intended for limiting purposes.

Claims

1. A method for producing one or more linear α-olefins by ethylene oligomerization, the method comprising: In the presence of a solvent mixture comprising at least one aromatic solvent and at least one aliphatic hydrocarbon solvent, and at a temperature of about 50°C to about 80°C, ethylene is contacted with a catalyst composition in a reaction chamber, 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. To oligomerize ethylene to produce one or more linear α-olefins; as well as Extract the effluent containing one or more linear α-olefins.

2. The method according to 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 according to 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 the hydrogen with the gaseous ethylene prior to injection into the reaction chamber.

5. The method according to claim 1, further comprising feeding the at least one aliphatic hydrocarbon solvent and the at least one aromatic solvent separately into the reaction chamber.

6. The method of claim 1, wherein the reaction chamber is part of a loop reactor system, the loop reactor system comprising: The reaction chamber, a recirculation loop in fluid communication with the reaction chamber and configured to receive the 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.

7. The method according to any one of claims 1-6, 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 according to any one of claims 1-7, 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, isoheptane, cyclohexane, methylcyclohexane, and combinations thereof.

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

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

11. The method according to any one of claims 1-10, wherein the contact is performed at a temperature of about 55°C to about 80°C, for example about 60°C to about 75°C, or about 70°C, and optionally wherein the contact is performed at a pressure of about 25 to about 30 bar.

12. The method according to any one of claims 1-11, wherein the amount of polymer in the effluent is about 0.4% by weight or less, for example 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 according to any one of claims 1-12, wherein the weight is expressed in kg·g. Cr -1 ·h -1 The catalyst activity, measured in units, is about 45 or higher, for example, about 45 to about 55 or about 48 to about 54.

14. The method according to any one of claims 1-13, wherein the selectivity of 1-hexene is about 91% or higher, for example about 91% to about 94% or about 92% to about 93%.

15. The method according to any one of claims 1-14, wherein the catalyst composition comprises: i) Selected from the following chromium compounds: organic or inorganic salts, coordination complexes and organometallic complexes of Cr(II) or Cr(III), such as CrCl3 (tetrahydrofuran)3, acetylacetone Cr(III), octanoic acid Cr(III), hexacarbonyl chromium, 2-ethylhexanoic acid Cr(III), benzene (tricarbonyl) chromium, Cr(III) chloride or combinations thereof. ii) Selected from the following cocatalysts: tri(C1-C6 alkyl)aluminum, such as trimethylaluminum, triethylaluminum, triisopropylaluminum or triisobutylaluminum, ethyl sesquichloride aluminum, diethylaluminum chloride, ethyl dialuminum chloride, methylaluminoxane (MAO) and combinations thereof. iii) Heteroatomic polydentate ligands, such as ligands with the general formula R1R2P-N(R3)-P(R4)-N(R5)-H, wherein R1, R2, R3, R4, and R5 are independently selected from halogens, amino groups, trimethylsilyl groups, C1-C4 groups, and C5-C4 groups. 10 -alkyl, substituted C1-C 10 -alkyl, aryl and substituted aryl, wherein at least one of the P or N atoms of the PNPNH unit is also optionally a member of the cyclic system; iv) Modifiers selected from ammonium or phosphonium salts of type [H4E]X, [H3ER]X, [H2ER2]X, [HER3]X, or [ER4]X, wherein E is N or P, X is Cl, Br, or I, and each R is independently a C1-C22 hydrocarbon group, such as a substituted or unsubstituted C1-C16-alkyl, C2-C16-acyl, or a substituted or unsubstituted C6-C20-aryl, such as dodecyltrimethylammonium chloride, tetraphenylphosphonium chloride, tetraethylammonium chloride monohydrate, tetraethylammonium chloride, trimethyldodecylammonium chloride, isopropylamine hydrochloride, triethylamine hydrochloride, tetrapropylammonium chloride, tetra-n-butylammonium chloride, tetraethylammonium bromide, p-toluidine hydrochloride, dimethyldistearate ammonium chloride, (tri-n-butyl)-tetradecylphosphonium chloride, benzoyl chloride, acetyl chloride, and combinations thereof; or v) A combination of two or more of the above.

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