Patent Description:
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 Fiedel-Crafts reaction of benzene with linear olefins followed by sulfonation. Another important use of linear alpha olefins relates to production of linear low-density polyethylene (LLDPE) through catalytic co-polymerization with ethylene.

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. Oligomerization processes utilize a variety of different catalyst systems. In certain embodiments, the catalyst system comprises a chromium compound and a ligand having phosphorus and nitrogen atoms in its backbone, such as the catalyst composition set forth in <CIT> <CIT> discloses the oligomerization of ethylene in the presence of a PNP ligand, a chromium compound and MAO in decalin as sole solvent.

One of the main challenges of any oligomerization process is undesirable polymer formation, which leads to fouling in the reactor that requires periodic flushing or tedious mechanical cleaning to remove. Traditional ways to increase activity of the catalyst include increasing the reaction temperature or increasing the amount of co-catalyst used in the process. Both ways lead not only to larger quantities of target oligomers, but also to increases in the amount of polymer formed during the reaction. Increasing the amount of co-catalyst also makes the process significantly more expensive due to the typically high price of co-catalyst. There remains a need in the art for improving catalyst activity in oligomerization reactions without significantly increasing polymer formation.

Example implementations of the present disclosure are directed to methods for forming a linear alpha olefin through ethylene oligomerization and catalyst compositions for use in such methods, where the catalyst is combined with a mixture of solvents including a relatively minor amount of decalin. It has been surprisingly discovered that the presence of a minor amount of decalin can enhance catalyst activity without a significant increase in polymer formation or a significant loss of target oligomer selectivity.

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 figure, which is 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.

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 figure which illustrates, by way of example, the principles of some described example implementations.

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:
<FIG> is a simplified schematic diagram of an example ethylene oligomerization reactor in accordance with the present disclosure.

Some implementations of the present disclosure will now be described more fully hereinafter with reference to the accompanying figure, in which some, but not all 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.

Unless specified otherwise or clear from context, references to first, second or the like should not be construed to imply a particular order. A 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 if 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.

All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other (e.g., ranges of "up to <NUM> wt. %, or, more specifically, <NUM> wt. % to <NUM> wt. %", is inclusive of the endpoints and all intermediate values of the ranges of "<NUM> wt. % to <NUM> wt. "Combination" is inclusive of blends, mixtures, alloys, reaction products, and the like.

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.

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).

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.

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..

An "aryl" group or an "aromatic" group is 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<NUM>), amide, nitrile (-CN), acyl, alkylsilane, thiol and thioether substituents. Non-limiting examples of polycyclic groups include ring systems that include <NUM> or more conjugated rings (e.g., fused aromatic rings) and substituted conjugated rings.

A "cyclohexyl" group is a substituted or unsubstituted, cyclic hydrocarbon group containing <NUM> carbon atoms. When fully saturated with hydrogen and having the formula C<NUM>H<NUM>, the cyclohexyl group is an unsubstituted cyclohexyl group. When at least one of the hydrogen atoms is replaced by another atom or functional group, the cyclohexyl group is a substituted cyclohexyl group.

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 <NUM>-butene, <NUM>-hexene, <NUM>-octene, <NUM>-decene, <NUM>-dodecene, <NUM>-tetradecene, <NUM>-hexadecene, <NUM>-octadecene, and higher blends of C<NUM>-C<NUM>, C<NUM>-C<NUM>, and C<NUM>-C<NUM> olefins. Linear alpha olefins are useful intermediates for the manufacture of detergents, synthetic lubricants, copolymers, plasticizers, and many other important products.

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 various catalyst systems.

The catalyst composition of the present disclosure typically includes a ligand having a backbone with at least one phosphorus atom and at least one nitrogen atom, a chromium compound, and a co-catalyst.

Typical ligand structures are organophosphorus compounds with 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 is 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).

In certain embodiments, the ligand has an NPNPN structure, such as ligands of the formula I: (R<NUM>)(R<NUM>)N-P(R<NUM>)-N(R<NUM>)-P(R<NUM>)-N(R<NUM>)(R<NUM>), wherein R<NUM>, R<NUM>, R<NUM>, R<NUM>, R<NUM>, R<NUM>, and R<NUM> can be each independently hydrogen, optionally substituted amino, trialkylsilyl (e.g., trimethylsilyl or triethylsilyl), or optionally substituted C<NUM>-C<NUM> hydrocarbyl. Examples of the C<NUM>-C<NUM> hydrocarbyl groups include straight-chain or branched C<NUM>-C<NUM> alkyl, C<NUM>-C<NUM> cycloalkyl (e.g., cyclohexyl), C<NUM>-C<NUM> aryl (e.g., phenyl), and C<NUM>-C<NUM> alkyl-substituted C<NUM>-C<NUM> aryl. In certain embodiments, each R<NUM>, R<NUM>, R<NUM>, R<NUM>, R<NUM>, R<NUM>, and R<NUM> is independently hydrogen, methyl, ethyl, isopropyl, tert-butyl, n-hexyl, cyclohexyl, or phenyl. In some embodiments, R<NUM> is methyl, R<NUM> and R<NUM> are each independently selected C<NUM>-C<NUM> aryl (e.g., phenyl) or C<NUM>-C<NUM> aliphatic groups (e.g., cyclohexyl), which may be cyclic or non-cyclic, linear or branched, substituted or unsubstituted, and R<NUM>, R<NUM>, R<NUM>, and R<NUM> are each independently selected C<NUM>-C<NUM> alkyl (e.g., C<NUM>-C5 alkyl).

In certain embodiments of the above NPNPN formula, R<NUM> and R<NUM> are each independently a cyclic hydrocarbon group, a substituted cyclic hydrocarbon group, a linear hydrocarbon group or a branched hydrocarbon group having <NUM> to <NUM> carbon atoms including, isopropyl, tert-butyl, and substituted or unsubstituted cycloalkyl groups including cyclopentyl, cyclohexyl, cycloheptyl, substituted cyclopentyl, substituted cyclohexyl, and substituted cycloheptyl. In other embodiments, R<NUM> and R<NUM> are each independently an aromatic group or a substituted aromatic group, such as a phenyl group, a substituted phenyl group, or an aromatic group including two or more conjugated rings.

A subset of ligands of Formula I is shown below as Formula Ia:
<CHM>
wherein R<NUM> and R<NUM> are independently cyclohexyl or phenyl, optionally substituted with one or more C1-C10 alkyl, such as C1-C5 alkyl, and R<NUM> is C1-C4 alkyl (e.g., methyl, ethyl, isopropyl, or butyl).

Table <NUM> below includes specific examples of ligands suitable for use in the present disclosure:
<IMG>.

Optionally, the ligand can be a cyclic derivative wherein at least one of the P or N atoms of the ligand is a member of a ring system, or any cyclic derivative thereof wherein at least one of the P or N atoms of the NPNPN ligand is a member of a ring system. The ring system can be formed from one or more constituent compounds of the NPNPN ligand by substitution, i.e., by formally eliminating per constituent compound either two whole groups R<NUM>-R<NUM> (as defined), one atom from each of two groups R<NUM>-R<NUM> (as defined) or a whole group R<NUM>-R<NUM> (as defined) and an atom from another group R<NUM>-R<NUM> (as defined), and joining the formally so-created valence-unsaturated sites by one covalent bond per constituent compound to provide the same valence as initially present at a given site.

The ligands for use in the present disclosure can be made by synthetic approaches known to those skilled in the art, such as synthetic methods set forth in <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; and <NPL>, each of which is incorporated by reference herein.

The chromium compound is an organic salt, an inorganic salt, a coordination complex, or an organometallic complex of Cr(II) or Cr(III). In certain embodiments, the chromium compound is an organometallic complex, preferably of Cr(II) or Cr(III). Examples of the chromium compound include Cr(III)acetylacetonate, Cr(III)octanoate, Cr(III)Cl<NUM>(tetrahydrofuran)<NUM>, Cr(III)-<NUM>-ethylhexanoate, Cr(III)chloride, Cr(III)-naphthenate, and Cr(III) tris(<NUM>,<NUM>,<NUM>,<NUM>-tetramethyl-<NUM>,<NUM>-heptanedionate). A combination comprising at least one of the foregoing chromium compounds can be used.

The concentration of the chromium compound can vary depending on the particular compound used and the desired reaction rate. In some embodiments, the concentration of the chromium compound is from about <NUM> to about <NUM> millimole per liter (mmol/<NUM>), about <NUM> to about <NUM> mmol/l, about <NUM> to about <NUM> mmol/l, about <NUM> to about <NUM> mmol/l, about <NUM> to about <NUM> mmol/l, about <NUM> to about <NUM> mmol/l, and about <NUM> to about <NUM> mmol/l. In one example embodiment, the concentration of the chromium compound is from about <NUM> to about <NUM> mmol/l.

The activator (also known in the art as a co-catalyst) is typically an aluminum compound, for example trimethylaluminum, triethylaluminum, triisopropylaluminum, triisobutylaluminum, diethylaluminum chloride, ethylaluminum sesquichloride, ethylaluminum dichloride, methylaluminoxane, or modified methylaluminoxane. A combination of different aluminum compounds can be used.

In some embodiments, the activator is a modified methylaluminoxane ("MMAO"), which refers to methylaluminoxanes containing alkyl substituents derived from C<NUM> or higher alkyl ligands in addition to methyl ligands, typically as a result of, for example, tetraalkyldialuminoxane and/or polyalkylaluminoxane reagents reacted with trimethylaluminum during preparation of the MMAO. One example MMAO is MMAO-3A (<NPL>), which is a modified methylaluminoxane, type 3A, available from Akzo Nobel in toluene solution containing <NUM>% aluminum, which corresponds to an MMAO-3A concentration of about <NUM>%.

The molar ligand/Cr ratio can be from about <NUM> to <NUM>, about <NUM> to <NUM>, about <NUM> to about <NUM>, about <NUM> to <NUM>, or from about <NUM> to about <NUM>.

The molar Al/Cr ratio can be from about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to <NUM>, about <NUM> to <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, or from <NUM> to about <NUM>.

The catalyst composition disclosed herein can be used in a process for the oligomerization of ethylene. In an embodiment, the process encompasses contacting ethylene with the catalyst composition under ethylene oligomerization conditions effective to produce target linear alpha olefins, such as <NUM>-butene, <NUM>-hexene, or <NUM>-octene. It will be understood that other olefins, including branched olefins, can be produced as side products in this reaction.

The oligomerization of ethylene can be carried out at a pressure of from about <NUM> to about <NUM> bar, about <NUM> to about <NUM> bar, about <NUM> to about <NUM> bar, about <NUM> to about <NUM> bar, and about <NUM> to <NUM> bar. In certain embodiments, the oligomerization is carried out at a pressure from about <NUM> to about <NUM> bar.

The oligomerization of ethylene can also be performed at a temperature of from about <NUM> to about <NUM>° C, about <NUM> to about <NUM>° C, about <NUM> to about <NUM>° C, about <NUM> to about <NUM>° C, about <NUM> to about <NUM>° C, or about <NUM> to about <NUM>° C.

The oligomerization process can be carried out continuously, semi-continuously or discontinuously. In one embodiment, the process can be continuous and mean residence times can be <NUM> minutes to <NUM> hours, such as <NUM> minutes to <NUM> hours or <NUM> to <NUM> hours. Residence times can be chosen so as to achieve the desired conversion at high selectivity.

The process can be conducted in solution using an inert solvent mixture, which is advantageously non-reactive with the catalyst composition. The solvent mixture includes decalin and at least one additional solvent. Decalin (i.e., decahydronaphthalene also known as bicyclo[<NUM>. <NUM>]decane) is a bicyclic organic compound, and its structure is shown below.

The additional solvent utilized with decalin can include, but is not limited to, saturated or unsaturated linear or branched hydrocarbons, ethers, aromatic hydrocarbons which can be unsubstituted or substituted with halogens, halogenated alkanes, and combinations thereof. Specific examples include toluene, benzene, xylene, monochlorobenzene, dichlorobenzene, chlorotoluene, pentane, hexane, heptane, octane, nonane, decane, cyclohexane, methylcyclohexane, dichloroethane, dichlorobutane, or a combination thereof.

It has been surprisingly discovered that using decalin as a minority component of a solvent mixture, in combination with the catalyst system of this disclosure, results in enhanced catalyst activity without significant loss of oligomer selectivity or significant increase in polymer formation. In particular, using decalin in an amount of less than <NUM> wt. %, based on the total weight of the solvent mixture, is advantageous. According to the invention, the decalin is present in an amount of about <NUM> to <NUM> wt. %, based on the total weight of the solvent mixture. In certain embodiments, the decalin is present in an amount of about <NUM> to about <NUM> wt. %, based on the total weight of the solvent mixture, such as about <NUM> to about <NUM> wt. The remainder of the solvent mixture can include one or more additional solvents, such as those set forth above. Due to its high boiling point, use of decalin does not present any additional difficulties in separation of the target products by distillation.

In certain embodiments, the solvent mixture is substantially or completely free of perhydroindane, or contains relatively minor amounts of perhydroindane. For example, the solvent mixture can be characterized as comprising about <NUM> wt. % of perhydroindane or less, such as about <NUM> wt. % or less or about <NUM> wt. % or less or about <NUM>% or less. In certain embodiments, the content of perhydroindane is about <NUM> wt. % or less or about <NUM> wt. % or less or about <NUM> wt. % or less or about <NUM> wt. Example ranges for perhydroindane contain include <NUM> wt. % to about <NUM> wt. % or about <NUM> wt. % to about <NUM> wt. In certain embodiments, the solvent mixture contains no detectable perhydroindane.

In certain embodiments, use of the solvent mixture of the present disclosure can increase catalyst activity as determined by ethylene consumption per weight of chromium compound during one hour of reaction time using units kg ethylene / gCr * h. In some embodiments, the catalyst activity can be greater than <NUM> / gCr * h, such as greater than <NUM> / gCr * h, greater than <NUM> / gCr * h, greater than <NUM> / gCr * h, greater than <NUM> / gCr * h, greater than <NUM> / gCr * h, or greater than <NUM> / gCr * h (e.g., about <NUM> to about <NUM> / gCr * h or about <NUM> to about <NUM> / gCr * h).

In certain embodiments, use of the solvent mixture of the present disclosure boosts the catalyst activity while retaining the olefin selectivity without increase in unwanted polymer formation. For example, polymer content in the product stream can be about <NUM> wt. % or less, about <NUM> wt. % or less, about <NUM> wt. % or less, about <NUM> wt. % or less, about <NUM> wt. % or less, or about <NUM> wt. % or less (e.g., about <NUM> wt. % to about <NUM> wt. % or about <NUM> wt. % to about <NUM> wt. % or about <NUM> wt. % to about <NUM> wt. %), based on the total weight of the product stream. Unwanted polymer species are defined as polymer species having a molecular weight of at least <NUM> Da, and typically include species that are insoluble in the reactor media and needed to be filtered or otherwise removed.

The process can be carried out in any reactor, such as a loop reactor, a plug-flow reactor, or a bubble column reactor. Oligomerization of ethylene is an exothermic reaction that can be cooled by a surplus flow of ethylene. The gases leaving at a top portion of the reactor can be cooled using a series of external coolers and condensers. The gas phase, after further cooling, can be recycled.

A bottom stream leaving the oligomerization reactor from a bottom portion 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.

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. Recovered ethylene can be recycled via an ethylene recycle loop while the product is fed to an intermediate vessel, after which the product can be fed to a separation section. In certain embodiments, the linear alpha olefins produced from the reactor can be directed into a separation train.

In an embodiment, the oligomerization process can be carried out in a bubble column reactor. <FIG> depicts an example bubble column reactor <NUM> for use in the present disclosure. Ethylene can be introduced using feed stream <NUM> to the reactor <NUM> via a gas distribution system attached to a bottom section of the bubble column reactor, which typically includes one or both of a gas sparger plate <NUM> and a gas bubbler <NUM>. The gas distribution system disperses the gaseous ethylene evenly throughout the reactor <NUM>. Gaseous ethylene rises up through a liquid composition <NUM> within the reactor <NUM>, which typically includes linear alpha olefins and reaction byproducts, the solvent mixture described herein, and a catalyst composition. For example, catalyst can enter the reactor <NUM> through a catalyst injection stream <NUM>. Solvent can enter the reactor <NUM> through solvent injection stream <NUM>. An oligomerization reaction can occur as the gaseous ethylene interacts with the liquid composition, producing reaction products that can include polymer droplets and linear alpha olefin droplets.

The liquid heavy linear alpha olefins, together with the solvent and the catalyst, can be withdrawn from the bottom section of the reactor <NUM> via bottom effluent stream <NUM>. A portion of the formed linear alpha olefins, which are gaseous under reaction conditions, can be condensed at a top portion of the reactor using an internal condenser <NUM> and can serve as reflux for cooling purposes, taking advantage of the respective heat of evaporation. Gaseous ethylene and light linear alpha olefins can be removed at the top of the bubble column reactor via top effluent stream <NUM>. One or both effluent streams can be further treated using additional downstream processing units, such as condensers, heat exchangers, distillation columns, and the like.

Catalyst performance in the presence of various solvent compositions was evaluated through ethylene oligomerization reaction carried out in a stainless steel pressure reactor at <NUM>. Dry n-heptane and decalin were used in various solvent combinations, MMAO-3A was used as a co-catalyst, and Cr(III)acetylacetonate was used as a chromium compound. A ligand of Formula Ia was used, where R<NUM> and R<NUM> are phenyl and R<NUM> is methyl.

Results summary is presented in Table <NUM> below. Product distribution was evaluated by GC-MS analysis and activity of the catalyst activity was calculated based on ethylene consumption during one hour of reaction time. The table provides the yield of <NUM>-hexene (C6 total) as well as the % wt. of <NUM>-hexene within all C6 olefins separated. The same information is provided for <NUM>-octene. Amount of polymer formed is also provided.

As shown in Table <NUM>, use of solvent mixtures containing minor amounts of decalin, such as <NUM>-<NUM> wt. %, can increase catalyst activity as compared to use of n-heptane alone. Alternatively, the data above show that the addition of decalin will allow lowering the catalyst to co-catalyst ratio while preserving the same catalyst performance characteristics. The presence of minor amounts of decalin does not have detrimental impact on selectivity of the reaction for desired oligomers, such as C6 or C8 oligomers, and does not significantly increase polymer formation. Indeed, at <NUM>-<NUM> wt. % decalin, polymer formation is reduced as compared to n-heptane alone. Use of decalin as the sole solvent results in greatly reduced catalyst activity and increased polymer formation, as compared to use of n-heptane alone.

Although not bound by a theory of operation, these experimental results may be explained by an increase in ethylene solubility in the reaction solvent, making ethylene more readily available to the activated catalyst. Activation of chromium species by aluminum alkyl co-catalyst leads to the formation of extremely reactive species. If ethylene is not readily available in solution, such species undergoes a decomposition with the formation of different chromium compounds. Such compounds promote polymerization instead of oligomerization activity.

However, addition of larger amounts of decalin to the reaction mixture appears to detrimentally impact catalyst performance, lowering overall catalyst activity. This could be explained by a decrease of the solubility of the active catalytic species in the reaction solvent when decalin concentration exceeds a certain percentage. Increase of viscosity of the solvent with greater addition of decalin might also cause ethylene mass transfer limitations, leading to decrease in catalytic activity.

In general, the invention may alternately comprise, consist of, or consist essentially of, any appropriate components herein disclosed. The invention 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 invention.

Claim 1:
A catalyst reaction mixture comprising a ligand having a backbone with at least one phosphorus atom and at least one nitrogen atom, a chromium compound, and a solvent mixture comprising decalin and at least one additional solvent, wherein the solvent mixture comprises decalin in an amount of about <NUM> to <NUM> wt. % and, optionally, perhydroindane in an amount of <NUM> wt. % or less, based on the total weight of the solvent mixture.