VILLALTA NESTOR GARCIA (SA)
KHAWAJI MOTAZ (SA)
XU WEI (SA)
ALMALKI FAHAD (SA)
BARMAN SAMIR (SA)
UNIV KING FAHD PET & MINERALS (SA)
ARAMCO SERVICES CO (US)
US20220168716A1 | 2022-06-02 | |||
US7297832B2 | 2007-11-20 |
CLAIMS 1. A catalyst system for tetramerizing ethylene to form 1-octene, the catalyst system comprising: a catalyst comprising a chromium compound coordinated with a ligand; and a co-catalyst comprising an organoaluminum compound, wherein: the ligand has the chemical structure: wherein: R5 is a (C1-C15) alkyl group, a (C3-C15) cyclohydrocarbyl group, a (C3-C15) cycloheterohydrocarbyl group, or a (C6-C15) aryl group, and RA, RB, RC, RD, RE, RF, RG, RH, R1, R2, R3, R4, R6, R7, R8, and R9 are independently chosen from a hydrogen atom, a (C1-C50) hydrocarbyl group, or a (C1-C50) heterohydrocarbyl group. 2. The catalyst system of claim 1, wherein R5 is an unsubstituted (C1-C15) alkyl group. 3. The catalyst system of any preceding claim, wherein R5 is a (C1-C15) linear alkyl group. 4. The catalyst system of any preceding claim, wherein R5 is penta-methylene. 5. The catalyst system of any preceding claim, wherein RA, RB, RC, RD, RE, RF, RG, and RH are independently chosen from a (C6-C50) aryl group. 6. The catalyst system of any preceding claim wherein: RA, RB, RC, RD, RE, RF, RG, and RH are each a phenyl group, and R1, R2, R3, R4, R6, R7, R8, and R9 are each a hydrogen atom. 7. The catalyst system of any preceding claim, wherein the chromium compound comprises one or more of an organic chromium salt, an inorganic chromium salt, a chromium coordination complex, and a chromium organometallic complex. 8. The catalyst system of any preceding claim, wherein the chromium compound comprises one or more of chromium trichloride tris-tetrahydrofuran complex, chromium dichloride bis- tetrahydrofuran complex, (benzene)tricarbonyl chromium, chromium (III) octanoate, chromium (III) acetylacetonoate, chromium hexacarbonyl, chromium (III) 2-ethylhexanoate, and chromium (III) 2,2,6,6-tetramethyl-3,5-heptanedionate. 9. The catalyst system of any preceding claim, wherein the catalyst comprises the ligand in an amount such that a molar ratio of the ligand to chromium is from 0.1 to 10.0. 10. The catalyst system of any preceding claim, wherein the organoaluminum compound has the structure: wherein R10, R11, and R12 are each selected from the group consisting of a hydrogen atom and an unsubstituted (C1-C20) linear or branched alkyl group. 11. The catalyst system of any of claims 1-9, wherein the organoaluminum compound comprises one or more of trimethylaluminium, triethylaluminum, tripropylaluminum, tri-iso- butylaluminum, diisobutylaluminium hydride, trihexylaluminum, tri-n-octylaluminium, methylaluminium dichloride, ethylaluminium dichloride, dimethylaluminium chloride, diethylaluminium chloride, aluminium isopropoxide, ethylaluminiumsesquichloride, methylaluminiumsesquichloride, methylaluminoxane, ethylaluminoxane, and modified methylaluminoxane. 12. The catalyst system of any preceding claim, wherein the catalyst system comprises the co- catalyst in an amount such that a molar ratio of the organoaluminum compound to the chromium compound is from 100 to 5000. 13. A method for tetramerizing ethylene to form 1-octene, the method comprising contacting ethylene with the catalyst system of claim 1 to form a product comprising 1-octene. 14. The method of claim 13, wherein the 1-octene is formed in conditions of: a reactor pressure from 2 bar to 100 bar; and a reactor temperature from 30 °C to 180 °C. 15. The method of any of claims 13 or 14, wherein ethylene is contacted with the catalyst system in the presence of a reaction medium, wherein the reaction medium comprises one or more of cyclohexane, methylcyclohexane, decahydronapthalene, chlorobenzene, toluene, xylene, heptane, and isooctane. 28277115.1 |
Chemical Structure (V) Chemical Structure (VI) Chemical Structure (VII) Chemical Structure (VIII) Chemical Structure (IX) Chemical Structure (X) Chemical Structure (XI) [0035] Referring back to Chemical Structure (I), as described herein, in one or more embodiments, R5 may be a (C1-C15) alkyl group. In embodiments, the (C1-C15) alkyl group may be a substituted or unsubstituted (C 1 -C 15 ) linear or branched alkyl group. In some embodiments, the (C1-C15) alkyl group may be an unsubstituted (C1-C15) linear alkyl group. For example, R5 may be one or more of methylene (-CH2-), di-methylene (-CH2-)2, tri-methylene (-CH2-)3, tetra- methylene (-CH 2 -) 4 , penta-methylene (-CH 2 -) 5 , hexa-methylene (-CH 2 -) 6 , hepta-methylene (- CH 2 -) 7 , octa-methylene (-CH 2 -) 8 , nona-methylene (-CH 2 -) 9 , deca-methylene (-CH 2 -) 10 . [0036] In one or more embodiments, R5 may be a (C6-C15) aryl group. In some embodiments, R5 may be a substituted or unsubstituted (C6-C15) aryl group. For example, R5 may be one or more of phenyl, benzyl, fluorenyl, tetrahydrofluorenyl, indacenyl, hexahydroindacenyl, indenyl, dihydroindenyl, naphthyl, tetrahydronaphthyl, and phenanthrenyl. In embodiments, where R5 is a (C6-C15) aryl group the two oxygen atoms connected to R5 may be connected at any position on the aryl group. For example, the two oxygen atoms may be connected in the ortho, meta, or para positions of the aryl group. [0037] In one or more embodiments, R5 may be a (C3-C15) cyclohydrocarbyl group. In some embodiments, R 5 may be a substituted or unsubstituted (C 3 -C 15 ) cyclohydrocarbyl group. For example, R 5 may be one or more of cyclopropyl, cyclobutyl, cyclopentyl, or cyclohexyl. [0038] In one or more embodiments, R5 may be a (C3-C15) cycloheterohydrocarbyl group. In some embodiments, R5 may be a substituted or unsubstituted (C3-C15) cycloheterohydrocarbyl group. [0039] Without being bound by theory, it is believed that when R5 is a (C1-C15) alkyl group, a (C3-C15) cyclohydrocarbyl group, a (C3-C15) cycloheterohydrocarbyl group, or a (C6-C15) aryl group the distance between the two N-Aryl diphosphinoamine structures of the ligand may be such that the two diphosphinoamine groups of the ligand may coordinate with the chromium compound to form a single catalytic site. It is further believed that when R5 is a greater than (C15) alkyl, cyclohydrocarbyl, cycloheterohydrocarbyl, or aryl group the two diphosphinoamine groups of the ligand may coordinate with the chromium compound to form two separate catalytic sites. It is believed that a single catalytic site with two ligand chromium coordination complexes may be more selective to the formation of 1-octene during the tetramerization of ethylene than a catalytic site with only one ligand chromium coordination complexes. [0040] In some embodiments, R1, R2, R3, R4, R6, R7, R8, and R9 may be a hydrogen atom, RA, RB, RC, RD, RE, RF, RG, and RH may be a phenyl group, and R5 may be an unsubstituted (C1- C 15 ) linear alkyl group. In an exemplary embodiment, R 1 , R 2 , R 3 , R 4 , R 6 , R 7 , R 8 , and R 9 may be a hydrogen atom, R A , R B , R C , R D , R E , R F , R G , and R H may be a phenyl group, and R 5 may be an unsubstituted (C5) linear alkyl group. [0041] In one or more embodiments, the catalyst may include the ligand in an amount such that a molar ratio of the ligand to chromium in the catalyst system is from 0.1 to 10.0. For example, the molar ratio of the ligand to chromium in the catalyst may be from 0.1 to 9.0, from 0.1 to 8.0, from 0.1 to 7.0, from 0.1 to 6.0, from 0.1 to 5.0, from 0.1 to 4.0, from 0.1 to 3.0, from 0.1 to 2.0, from 0.1 to 1.0, from 0.1 to 0.5, from 0.5 to 10.0, from 0.5 to 9.0, from 0.5 to 8.0, from 0.5 to 7.0, from 0.5 to 6.0, from 0.5 to 5.0, from 0.5 to 4.0, from 0.5 to 3.0, from 0.5 to 2.0, from 0.5 to 1.0, from 1.0 to 10.0, from 1.0 to 9.0, from 1.0 to 8.0, from 1.0 to 7.0, from 1.0 to 6.0, from 1.0 to 5.0, from 1.0 to 4.0, from 1.0 to 3.0, from 1.0 to 2.0, from 2.0 to 10.0, from 2.0 to 9.0, from 2.0 to 8.0, from 2.0 to 7.0, from 2.0 to 6.0, from 2.0 to 5.0, from 2.0 to 4.0, from 2.0 to 3.0, from 3.0 to 10.0, from 3.0 to 9.0, from 3.0 to 8.0, from 3.0 to 7.0, from 3.0 to 6.0, from 3.0 to 5.0, from 3.0 to 4.0, from 4.0 to 10.0, from 4.0 to 9.0, from 4.0 to 8.0, from 4.0 to 7.0, from 4.0 to 6.0, from 4.0 to 5.0, from 5.0 to 10.0, from 5.0 to 9.0, from 5.0 to 8.0, from 5.0 to 7.0, from 5.0 to 6.0, from 6.0 to 10.0, from 6.0 to 9.0, from 6.0 to 8.0, from 6.0 to 7.0, from 7.0 to 10.0, from 7.0 to 9.0, from 7.0 to 8.0, from 8.0 to 10.0, from 8.0 to 9.0, from 9.0 to 10.0, or any combination of these ranges. [0042] In one or more embodiments, the catalyst system also includes a co-catalyst. In some embodiments, the co-catalyst may include an organoaluminum compound. As described in the present disclosure, the term “organoaluminum compound” refers to any chemical compound that includes at least one aluminum atom and any organic moiety. It should be appreciated that the organoaluminum compound may include several chemical species, or may be a single chemical species. In some embodiments, the organoaluminum compound may be an alkyl aluminum compound. The alkyl aluminum compound may, for example, have a structure according to Chemical Structure (XII): Chemical Structure (XII) [0043] In Chemical Structure (XII), R 10 , R 11, and R 12 are each independently chosen from a hydrogen atom, a (C1-C20) hydrocarbyl group, or a (C1-C20) heterohydrocarbyl group. In embodiments, the (C1-C20) hydrocarbyl group may be a substituted or unsubstituted (C1-C20) linear or branched hydrocarbyl group. In one or more embodiments, R 10 , R 11 and R 12 may each be a hydrogen atom or a linear or branched (C 1 -C 20 ) alkyl group. In some embodiments, the alkyl aluminum compound may be an aluminoxane structure (a partial hydrolysate of a trialkylaluminum compound). For example, suitable alkyl aluminum compounds may include trimethylaluminium, triethylaluminum, tripropylaluminum, tri-iso-butylaluminum, diisobutylaluminium hydride, trihexylaluminum, tri-n-octylaluminium, methylaluminium dichloride, ethylaluminium dichloride, dimethylaluminium chloride, diethylaluminium chloride, aluminium isopropoxide, ethylaluminiumsesquichloride, methylaluminiumsesquichloride, methylaluminoxane (MAO), ethylaluminoxane (EAO), and modified alkylaluminoxanes, such as modified methylaluminoxane (MMAO). As described in the present disclosure, the term “modified alkylaluminoxane” refers to an alkylaluminoxane that includes one or more modifier groups, such as isobuytyl or n-octyl groups in addition to the alkyl groups. In one or more embodiments, the organoaluminum compound of the catalyst system may comprise, consist essentially of, or consist of any of these compounds. [0044] Without being bound by theory, it is believed that the alky aluminum compound may be operable to remove impurities, or poisons that may have a negative effect on the catalyst. Additionally, the alkyl aluminum compound may be operable to alkylate the chromium compound. Furthermore, the alkyl aluminum compound may be operable to activate the chromium compound to allow the coordination of the ethylene with the catalyst. [0045] In one or more embodiments, the catalyst system may include the co-catalyst in an amount such that a molar ratio of the organoaluminum compound to the chromium compound in the catalyst system is from 100 to 5000. For example, the molar ratio of the organoaluminum compound to the chromium compound in the catalyst system may be from 100 to 4500, from 100 to 4000, from 100 to 3500, from 100 to 3000, from 100 to 2500, from 100 to 2000, from 100 to 1500, from 100 to 1000, from 100 to 500, from 500 to 5000, from 500 to 4500, from 500 to 4000, from 500 to 3500, from 500 to 3000, from 500 to 2500, from 500 to 2000, from 500 to 1500, from 500 to 1000, from 1000 to 5000, from 1000 to 4500, from 1000 to 4000, from 1000 to 3500, from 1000 to 3000, from 1000 to 2500, from 1000 to 2000, from 1000 to 1500, from 1500 to 5000, from 1500 to 4500, from 1500 to 4000, from 1500 to 3500, from 1500 to 3000, from 1500 to 2500, from 1500 to 2000, from 2000 to 5000, from 2000 to 4500, from 2000 to 4000, from 2000 to 3500, from 2000 to 3000, from 2000 to 2500, from 2500 to 5000, from 2500 to 4500, from 2500 to 4000, from 2500 to 3500, from 2500 to 3000, from 3000 to 5000, from 3000 to 4500, from 3000 to 4000, from 3000 to 3500, from 3500 to 5000, from 3500 to 4500, from 3500 to 4000, from 4000 to 5000, from 4000 to 4500, from 4500 to 5000, or any combination of these ranges. [0046] In one or more embodiments, ethylene may be contacted with the catalyst system to form a reaction product including 1-octene. Contacting may generally include any mixing and/or combining of the reactant ethylene with the catalyst system. In some embodiments, the catalyst and co-catalyst may be separately prepared as solutions, and then combined, prior to contacting of the catalyst system with ethylene. In some embodiments, the catalyst system may be contacted with ethylene in the presence of one or more reaction mediums. Suitable reaction mediums may include, for example, cyclohexane (CyH), methylcyclohexane (MeCy), decahydronapthalene (DHN), chlorobenzene (PhCl), toluene, xylene, heptane, and isooctane, but other suitable reaction mediums are contemplated herein. In some embodiments, the ethylene may be contacted with the catalyst system in the presence of hydrogen. [0047] In one or more embodiments, the reaction may be performed as a batch reaction or as a continuous process reaction, such as a continuous stir tank reactor process. In some embodiments, the pressure of the reactor may be from 2 bar to 100 bar (such as from 10 bar to 60 bar), and the reactor temperature may be from 30 °C to 120 °C (such as from 30 °C to 100 °C). However, process conditions outside of these ranges are contemplated, especially in view of the specific design of the reactor system and concentrations of the reactants and catalyst system. [0048] It should be understood that, in one or more embodiments, similar catalyst systems that do not include the ligand of the present application may exhibit increased fouling compared to the catalyst system of the present application. In one or more embodiments, the inclusion of the ligand in a catalyst system may suppress polymer formation while not greatly reducing the yield of 1-octene. In one or more embodiments, polymer formation (fouling) may be reduced by at least 5% or higher by the use of the ligand. For example, the reaction product of the tetramerization of ethylene using the catalyst system may include less than 99 wt.% to less than 1.5 wt.% of polymer. [0049] In one or more embodiments, 1-octene production may be increased, stay the same, or may decrease by less than or equal to 100% to 5% by the inclusion of the ligand. For example, the reaction product of the tetramerization of ethylene using the catalyst system may include from greater than 5 wt.% to 100 wt.% of 1-octene. [0050] In one or more embodiments, the catalyst system may both reduce the polymer formation from 5% to 99.9% and increase, not effect, or decrease 1-octene production rate by less than or equal to 100% to 5%. Reduction in polymer formation rates and catalytic activity on a percentage basis are based on catalyst systems that include the ligand of the present disclosure as compared with catalyst systems that do not include the ligand of the present disclosure. [0051] In one or more embodiments, the catalyst system may have increased activity compared to similar catalyst systems that do not include the ligand of the present disclosure. As used in the present disclosure, the term “activity” refers to the amount of reaction product produced (in kilograms) per the amount of chromium metal used (in grams) per hour (kg.gCr -1 .h- 1 ). In some embodiments, the catalyst system may have an activity greater than 10 kg.gCr -1 .h -1 , or greater than 100 kg.g Cr -1 .h -1 to 5,000 kg.g Cr -1 .h -1 . For example, the catalyst system may have an activity from, from 100 kg·gCr -1 ·h -1 to 4000 kg·gCr -1 ·h -1 , from 100 kg·gCr -1 ·h -1 to 3000 kg·gCr -1 ·h- 1 , from 100 kg·gCr -1 ·h -1 to 2000 kg·gCr -1 ·h -1 , from 100 kg·gCr -1 ·h -1 to 1000 kg·gCr -1 ·h -1 , from 100 kg·g Cr -1 ·h -1 to 500 kg·g Cr -1 ·h -1 , from 500 kg·g Cr -1 ·h -1 to 5000 kg·g Cr -1 ·h -1 , from 500 kg·g Cr -1 ·h -1 to 4000 kg·g Cr -1 ·h -1 , from 500 kg·g Cr -1 ·h -1 to 3000 kg·g Cr -1 ·h -1 , from 500 kg·g Cr -1 ·h -1 to 2000 kg·g Cr - 1 ·h -1 , from 500 kg·gCr -1 ·h -1 to 1000 kg·gCr -1 ·h -1 , from 1000 kg·gCr -1 ·h -1 to 5000 kg·gCr -1 ·h -1 , from 1000 kg·gCr -1 ·h -1 to 4000 kg·gCr -1 ·h -1 , from 1000 kg·gCr -1 ·h -1 to 3000 kg·gCr -1 ·h -1 , from 1000 kg·g Cr -1 ·h -1 to 2000 kg·g Cr -1 ·h -1 , from 2000 kg·g Cr -1 ·h -1 to 5000 kg·g Cr -1 ·h -1 , from 2000 kg·g Cr -1 ·h- 1 to 4000 kg·gCr -1 ·h -1 , from 2000 kg·gCr -1 ·h -1 to 3000 kg·gCr -1 ·h -1 , from 3000 kg·gCr -1 ·h -1 to 5000 kg·g -1 ·h -1 , from 3000 kg -1 -1 -1 -1 -1 -1 - Cr ·gCr ·h to 4000 kg·gCr ·h , or from 4000 kg·gCr ·h to 5000 kg·gCr 1 ·h -1 . EXAMPLES [0052] The various aspects of the present disclosure will be further clarified by the following examples. The examples are illustrative in nature and should not be understood to limit the subject matter of the present disclosure. Example 1 - Preparation of m-alkoxy N-aryl bis-diphosphinoamine ligand A ligand was formed as depicted in Reaction Scheme 1: Reaction Scheme (1) [0053] First, bis amine precursor (0.465 g, 1.63 mmol), triethylamine (1.0g, 9.90 mmol), and 8 mL of dichloromethane were combined to make a solution. To the solution, chlorodiphenylphosphine (1.44 g, 6.57 mmol) was added at 0 °C. The mixture was stirred for 1 hour and allowed to warm to room temperature followed by additional stirring for 14 hours. The volatiles were removed under reduced pressure and the residue was extracted with anhydrous tetrahydrofuran (3 x 4 mL). After removing the tetrahydrofuran, the remaining solid was triturated with anhydrous acetonitrile (5 x 4 mL) followed by degassing at 50 °C to yield the desired ligand as a white solid. The yield was 63%. Example 2 – Ethylene Tetramerization Utilizing the Ligand of Example 1 [0054] Multiple ethylene tetramerization runs were performed in a magnetically stirred (1000 rotations per minute (rpm)) stainless steel reactor system (250 ml; commercially available from Buchi), which was equipped with a propeller-like stirrer and injection barrel for charging solvents and reagents. The reactor system was first heated to 110 °C, purged several times with argon and ethylene to remove air and moisture, and then cooled to the desired temperature. A solution of the co-catalyst, containing 2 mmol of modified methylaluminoxane (MMAO), was then prepared via dilution with chlorobenzene to a total volume of 95 ml. Next, a catalyst solution was prepared by dissolving 1 µmol of chromium (III) acetylacetonate (Cr(acac) 3 ) in 1 mL of chlorobenzene. The ligand synthesized in Example 1 was separately dissolved in 1 mL of chlorobenzene before being combined with the (Cr(acac)3) solution and diluted to a total volume of 5 ml. The co-catalyst and catalyst solutions had a total solution volume of 100 mL. The ratio of ligand to chromium was 1:1. The solutions were then transferred to the reactor system, which was then pressurized to 45 bar (4.5MPa) using ethylene to initiate ethylene tetramerization. The temperature of the reactor system was maintained constant at 60 °C during ethylene tetramerization by circulating relatively warm oil through a jacket of the reactor system and relatively cool liquid through a cooling coil of the reactor system as necessary. [0055] After 10 minutes, methanol (1.0 ml) was added to quench ethylene tetramerization. The reactor system was then cooled to approximately 15 °C and then was slowly depressurized using a needle valve. Next, an aliquot of the liquid inside the reaction system was collected and quantified via gas chromatography (GC) analysis. The liquid remaining in the reaction system was collected, added to 50 ml of acidic methanol (5% HCl), and stirred at room temperature for 2 hours. Polymer was then filtered from the mixture, washed with distilled water, and stirred in water (200 ml) for 1 hour. This process was repeated four times. Finally, the polymer was filtered and dried in a vacuum oven at 60 °C overnight. The results of the tetramerization reaction were reported in Table 1. [0056] As reported in Table 1, productivity refers to the amount of reaction product produced (in kilograms) per the amount of chromium metal used (in grams) per hour (kg·gCr -1 ·h- 1 ). The references to C 6, C 8 , and C 10+ refer to the amount of hydrocarbons, in weight percent of the total reaction product, with 6 total carbon atoms, 8 total carbon atoms, or with greater than 10 total carbon atoms respectively. 1-C6 and 1-C8 refer to the weight percentage of the C6 and C8 products that were 1-hexene and 1-octene respectively. PE refers to the amount of polyethylene that was formed in weight percent of the total reaction product. The production of polyethylene may be associated with fouling. Table 1 [0057] As Table 1 indicates the meta-alkoxy substituted N-Aryl bis-PNP ligand has high selectivity for both 1-hexene and 1-octene. In particular, the ligand has a selectivity of the 1-octene isomer of over 97 wt.% of the total octene produced which means over 65 wt.% of the total product produced is 1-octene. Additionally, the use of the ligand only produces a small amount of polyethylene residue (PE), less than 2 wt.%, indicating that the use of ligand is likely to significantly reduce the amount of fouling that may occur during polymerization. [0058] In a first aspect of the present disclosure, a catalyst system for tetramerizing ethylene to produce 1-octene may comprise a catalyst which comprises a chromium compound coordinated with a ligand and a co-catalyst which comprises an organoaluminum compound. The ligand has a chemical structure according to Chemical Structure (I), wherein R5 is a (C1-C15) alkyl group, a (C3-C15) cyclohydrocarbyl group, a (C3-C15) cycloheterohydrocarbyl group, or a (C1-C15) aryl group, and R A , R B , R C , R D , R E , R F , R G , R H , R 1 , R 2 , R 3 , R 4 , R 6 , R 7 , R 8 , and R 9 are independently chosen from a hydrogen atom, a (C 1 -C 50 ) hydrocarbyl group, or a (C 1 -C 50 ) heterohydrocarbyl group. [0059] A second aspect of the present disclosure may include the first aspect, where R5 is an unsubstituted (C 1 -C 15 ) alkyl group. [0060] A third aspect of the present disclosure may include the first or second aspects where R5 is a (C1-C15) linear alkyl group. [0061] A fourth aspect of the present disclosure may include the first through third aspects where R5 is penta-methylene. [0062] A fifth aspect of the present disclosure may include the first through fourth aspects where R A , R B , R C , R D , R E , R F , R G , and R H are independently chosen from a (C 6- C 50 ) aryl group. [0063] A sixth aspect of the present disclosure may include the first through fifth aspect where RA, RB, RC, RD, RE, RF, RG, and RH are each a phenyl group, and R1, R2, R3, R4, R6, R7, R8, and R9 are each a hydrogen atom. [0064] A seventh aspect of the present disclosure may include the first through sixth aspects where the chromium compound comprises one or more of an organic chromium salt, an inorganic chromium salt, a chromium coordination complex, and a chromium organometallic complex. [0065] An eighth aspect of the present disclosure may include the first through seventh aspects where the chromium compound comprises one or more of chromium trichloride tris- tetrahydrofuran complex, chromium dichloride bis-tetrahydrofuran complex, (benzene)tricarbonyl chromium, chromium (III) octanoate, chromium (III) acetylacetonoate, chromium hexacarbonyl, chromium (III) 2-ethylhexanoate, and chromium (III) 2,2,6,6- tetramethyl-3,5-heptanedionate. [0066] A ninth aspect of the present disclosure may include the first through eighth aspects where the catalyst comprises the ligand in an amount such that a molar ratio of the ligand to chromium is from 0.1 to 10.0. [0067] A tenth aspect of the present disclosure may include the first through ninth aspects where the organoaluminum compound has a structure according to Chemical Structure (XII) where R10, R11, and R12 are each selected from the group consisting of a hydrogen atom and an unsubstituted (C 1 -C 20 ) linear or branched alkyl group. [0068] An eleventh aspect of the present disclosure may include the first through tenth aspects where the organoaluminum compound comprises one or more of trimethylaluminium, triethylaluminum, tripropylaluminum, tri-iso-butylaluminum, diisobutylaluminium hydride, trihexylaluminum, tri-n-octylaluminium, methylaluminium dichloride, ethylaluminium dichloride, dimethylaluminium chloride, diethylaluminium chloride, aluminium isopropoxide, ethylaluminiumsesquichloride, methylaluminiumsesquichloride, methylaluminoxane, ethylaluminoxane, and modified methylaluminoxane. [0069] A twelfth aspect of the present may include the first through eleventh aspects where the catalyst system comprises the co-catalyst in an amount such that a molar ratio of the organoaluminum compound to the chromium compound is from 100 to 5000. [0070] A thirteenth aspect of the present disclosure may include a method for tetramerizing ethylene to form 1-octene, the method comprising contacting ethyelene with the catalyst system of the first through twelfth aspects to form a product comprising 1-octene [0071] A fourteenth aspect of the present dislcosure may include the thirteenth aspect where the 1-octene is formed in conditions of a reactor pressure of from 2 bar to 100 bar and a reactor temperature from 30 °C to 180 °C. [0072] A fifteenth aspect of the present disclosure may include the thirteenth or fourteenth aspects where ethylene is contacted with the catalyst system in the presence of a reaction medium, where the reaction medium comprises one or more of cyclohexane, methylcyclohexane, decahydronapthalene, chlorobenzene, toluene, xylene, heptane, and isooctane. [0073] [0074] The subject matter of the present disclosure has been described in detail and by reference to specific embodiments. It should be understood that any detailed description of a component or feature of an embodiment does not necessarily imply that the component or feature is essential to the particular embodiment or to any other embodiment. Further, it should be apparent to those skilled in the art that various modifications and variations can be made to the described embodiments without departing from the spirit and scope of the claimed subject matter. [0075] For the purposes of describing and defining the present disclosure it is noted that the terms “about” or “approximately” are utilized in this disclosure to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. The terms “about” and/or “approximately” are also utilized in this disclosure to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue. [0076] It is noted that one or more of the following claims utilize the term “wherein” as a transitional phrase. For the purposes of defining the present technology, it is noted that this term is introduced in the claims as an open-ended transitional phrase that is used to introduce a recitation of a series of characteristics of the structure and should be interpreted in like manner as the more commonly used open-ended preamble term “comprising.” [0077] It should be understood that where a first component is described as “comprising” a second component, it is contemplated that, in some embodiments, the first component “consists” or “consists essentially of” that second component. It should further be understood that where a first component is described as “comprising” a second component, it is contemplated that, in some embodiments, the first component comprises at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, or even at least 99% that second component (where % can be weight % or molar %). [0078] Additionally, the term “consisting essentially of” is used in this disclosure to refer to quantitative values that do not materially affect the basic and novel characteristic(s) of the disclosure. For example, a chemical composition “consisting essentially” of a particular chemical constituent or group of chemical constituents should be understood to mean that the composition includes at least about 99.5% of a that particular chemical constituent or group of chemical constituents. [0079] It should be understood that any two quantitative values assigned to a property may constitute a range of that property, and all combinations of ranges formed from all stated quantitative values of a given property are contemplated in this disclosure. It should be appreciated that compositional ranges of a chemical constituent in a composition should be appreciated as containing, in some embodiments, a mixture of isomers of that constituent. In additional embodiments, the chemical compounds may be present in alternative forms such as derivatives, salts, hydroxides, etc.