LIGANDS FOR PRODUCTION OF 1-HEXENE IN CHROMIUM ASSISTED ETHYLENE OLIGOMERIZATION PROCESS

Abstract

Catalyst compositions and processes for the oligomerization of ethylene to 1-hexene are described. The catalyst composition includes a triamino bisphospino (NPNPN) ligand system with specific phosphorous and nitrogen ligands. The terminal nitrogen atoms include linear alkyl hydrocarbons that differ in the number of carbon atoms by 3.

Claims

1. A catalyst composition for the oligomerization of ethylene to 1-hexene, the catalyst composition comprising: a chromium (III) species; and a ligand having the formula of: ##STR00015## where R.sup.1 and R.sup.2 are the same or different and are selected from the group consisting of (i) C.sub.3 to C.sub.4 non-cyclic aliphatic groups, (ii) C.sub.5 to C.sub.7 aliphatic groups which may be cyclic or non-cyclic, linear or branched, substituted or unsubstituted, and (iii) any combination thereof; and, wherein n is 0 or 1, and m=n+3.

2. The catalyst composition of claim 1, wherein R.sup.1 and R.sup.2 are each independently a cyclic hydrocarbon group, a substituted cyclic hydrocarbon group, a linear hydrocarbon group or a branched hydrocarbon group having 1 to 10 carbon atoms.

3. The catalyst composition of claim 2, wherein R.sup.1 and R.sup.2 are each a cyclohexyl group.

4. The catalyst composition of claim 3, wherein n is 0, and the catalyst has the structure of: ##STR00016##

5. The catalyst composition of claim 3, wherein n is 1 and the catalyst has the structure of ##STR00017##

6. The catalyst composition of claim 1, wherein the composition further comprises an activator or co-catalyst.

7. The catalyst composition of claim 6, wherein the activator or co-catalyst is a methylaluminoxane compound.

8. The catalyst composition of claim 6, wherein the activator or co-catalyst is a methyl iso-butyl aluminum oxide compound.

9. The catalyst composition of claim 1, wherein the chromium (III) species is selected from the group consisting of chromium (III) acetylacetonate, Cr(2,2,6,6-tetramethyl-3,5-heptadionate).sub.3, chromium(III)2-ethylhexanoate, chromium trichloride tris-tetrahydrofuran (benzene)tricarbonyl chromium, chromium (III) octanoate and chromium (III) naphthenate.

10. The catalyst composition of claim 1, wherein one or both of R.sup.1 and R.sup.2 are selected from the group consisting of iso-propyl and tert-butyl.

11. A process to produce 1-hexene from ethylene, the process comprising contacting a reactant stream comprising an olefin source with a solution comprising the catalyst composition of claim 1 to produce a oligomer composition comprising 1-hexene.

12. The process of claim 11, wherein the solution comprises a solvent.

13. The process of claim 12, wherein the solvent is a saturated hydrocarbon.

14. The process of claim 13, wherein the solvent is n-hexane, methylcyclohexane, or a mixture thereof.

15. The process of claim 11, wherein the product stream further comprises 1-octene and a selectivity for 1-hexene is greater than 99%, and a weight ratio of 1-octene to 1-hexene is less than 0.15.

16. The process of claim 15, wherein the catalyst composition comprises ##STR00018##

17. The process of any one of claim 15, further comprising the chromium (III) species, the activator or co-catalyst.

18. The process of claim 11, wherein the catalyst composition comprises the chromium (III) species, the activator or co-catalyst and ##STR00019##

19. The process of claim 11, wherein the contacting comprises a temperature of 15° C. to 100° C.

20. The process of claim 11, wherein the contacting comprises a pressure of at least 2 MPa or 2 to 20 MPa.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Advantages of the present invention may become apparent to those skilled in the art with the benefit of the following detailed description and upon reference to the accompanying drawings.

[0033] FIG. 1 is an illustration of a schematic of a system to produce 1-hexene from the oligomerization of ethylene.

[0034] While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings. The drawings may not be to scale.

DETAILED DESCRIPTION OF THE INVENTION

[0035] A discovery has been made that provides a way to produce 1-hexene in acceptable yields, in high selectivity, and without making significant amounts of solvent insoluble material from the oligomerization of ethylene. The discovery is premised on using a NPNPN ligand system. Notably, and as illustrated in a non-limiting manner in the examples, an oligomerization product stream can include at least 80 wt. % C.sub.6 hydrocarbon, less than 10 wt. % C.sub.8 hydrocarbon, and less than 3 wt. % solvent insoluble material (e.g., polymeric materials). This is contrast to the ligands of the prior art, which produce more than 3 wt. % polymeric materials. The critical parameters include the choice of phosphorous substituents and nitrogen substituents. The phosphorous substituents include an aromatic group or an alkyl substituted aromatic group, the middle nitrogen substituent includes a methyl substituent, and the terminal nitrogen substituents include different linear alkyl hydrocarbons groups that differ in the number of carbon atoms by 3. This combination of substituents provides an elegant and simple ligand system for the production of 1-hexene in high purity and selectivity above 80 wt. %.

[0036] These and other non-limiting aspects of the present invention are discussed in further detail in the following sections.

A. Catalyst Composition

[0037] The catalyst composition can include the ligands of the present invention, a chromium (III) species, and an activator or co-catalyst. The ligands of the present invention can be prepared as described throughout the specification and in the Examples. The catalyst composition can be provided as a solution in an aliphatic or aromatic hydrocarbon solvent. Aliphatic hydrocarbon solvents can include hexane, methylcyclohexane, cyclohexane, n-heptane and the like.

[0038] The ligands of the present invention can be represented by the following formula:

##STR00011##

where R.sup.1 and R.sup.2 selected from the group consisting of (i) C.sub.3 to C.sub.4 non-cyclic aliphatic groups, (ii) C.sub.5 to C.sub.7 aliphatic groups which may be each be cyclic or non-cyclic, linear or branched, substituted or unsubstituted, and (iii) any combination thereof, and wherein n is 0 or 1, and m=n+3. The C.sub.5 to C.sub.7 aliphatic groups can substituted or unsubstituted cycloalkane groups include cyclopentyl, cyclohexyl, cycloheptyl, substituted cyclopentyl, substituted cyclohexyl, and substituted cycloheptyl. The C.sub.3 to C.sub.4 non-cyclic aliphatic groups can be iso-propyl and tert-butyl. The ligands can be (CH.sub.3)(n-C.sub.4H.sub.9)NP(R.sup.1)N(CH.sub.3)NP(R.sup.2)N(CH.sub.3)(n-C.sub.4H.sub.9) and (CH.sub.3CH.sub.2)(n-C.sub.5H.sub.11)NP(R.sup.1)N(CH.sub.3)NP(R.sup.2)N(CH.sub.2CH.sub.3)(n-C.sub.5H.sub.11) (CH.sub.3)(n-C.sub.4H.sub.9)NP(C.sub.6H.sub.11)N(CH.sub.3)NP(C.sub.6H.sub.11)N(CH.sub.3)(n-C.sub.4H.sub.9) and (CH.sub.3CH.sub.2)(n-C.sub.5H.sub.11)NP(C.sub.6HON(CH.sub.3)NP(C.sub.6HON(CH.sub.2CH.sub.3)(n-C.sub.5H.sub.11). The structure of the ligands can be illustrated as follows:

##STR00012##

where R.sub.1 and R.sub.2 represent alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, tert-butyl, and pentyl, and the like.

[0039] The NPNPN ligand system can be made by synthetic approaches known to those skilled in the art. In some embodiments, ligand (1) is accessible by reaction pathways as shown in Scheme I.

##STR00013##

[0040] where R.sup.1 and R.sup.2 are defined above, and R.sub.3 is methyl or ethyl and R.sub.4 is butyl when R.sub.3 is methyl and pentyl when R.sub.3 is ethyl.

[0041] The chromium species can be an organic salt, an inorganic salt, a coordination complex, or an organometallic complex of Cr(III). In an embodiment, the chromium species is an organometallic Cr(III) species. Non-limiting examples of the chromium species include Cr(III)acetylacetonate, Cr(III)octanoate, CrCl.sub.3(tetrahydrofuran).sub.3, Cr(III)-2-ethylhexanoate, Cr(III)chloride, or any combination thereof. The molar ligand/Cr ratio can be from about 0.5 to 50, about 0.5 to 5, about 0.8 to about 2.0, about 1.0 to 5.0, or preferably from about 1.0 to about 1.5.

[0042] The activator (also known in the art as a co-catalyst) can be an aluminum compound. Non-limiting examples of aluminum compounds include trimethylaluminum, tri ethyl aluminum, triisopropyl aluminum, triisobutyl aluminum, di ethyl aluminum chloride, ethylaluminum sesquichloride, ethylaluminum dichloride, methylaluminoxane, or a mixture thereof. In some embodiments, the activator can be a modified methylaluminoxane, more preferably MMAO-3A (CAS No. 146905-79-5), which is a modified methylaluminoxane, type 3A, available from Akzo Nobel in toluene solution containing 7% aluminum, which corresponds to an MMAO-3A concentration of about 18%. The molar Al/Cr ratio can be from about 1 to about 1000, about 10 to about 1000, about 1 to 500, about 10 to 500, about 10 to about 300, about 20 to about 300, or preferably from 50 to about 300.

[0043] The catalyst composition can further include a solvent. Non-limiting examples of solvents are straight-chain and cyclic aliphatic hydrocarbons, straight-chain olefins, ethers, aromatic hydrocarbons, and the like. A combination comprising at least one of the foregoing solvents can be used. Preferably, the solvent is n-heptane, toluene, or methylcyclohexane or any mixture thereof.

[0044] The concentration of the chromium compound in the solvent vary depending on the particular compound used and the desired reaction rate. In some embodiments, the concentration of the chromium compound is from about 0.01 to about 100 millimole per liter (mmol/l), about 0.01 to about 10 mmol/l, about 0.01 to about 1 mmol/l, about 0.1 to about 100 mmol/l, about 0.1 to about 10 mmol/l, about 0.1 to about 1 0 mmol/l, about 1 to about 10 mmol/l, and about 1 to about 100 mmol/l. Preferably, the concentration of the chromium compound is from about 0.1 to about 1.0 mmol/l.

[0045] In some embodiments, the catalyst composition includes Cr(III)acetylacetonate as the chromium compound, Et(n-pentyl)N—P(cyclohexyl)-N(Me)-P(cyclohexyl)-N(n-pentyl)Et as the NPNPN ligand, and MMAO-3A as the activator. In another embodiment, the catalyst composition includes Cr(III)acetylacetonate as the chromium compound, Me(n-butyl)N—P(cyclohexyl)-N(Me)-P(cyclohexyl)-N(n-butyl)Me as the NPNPN ligand, and MMAO-3A as the activator.

B. System for Oligomerization of Olefins to 1-Hexene

[0046] The catalyst composition of the present invention can be used in a process for the oligomerization of ethylene to 1-hexene. In an embodiment, the process encompasses contacting ethylene with the catalyst composition under ethylene oligomerization conditions effective to produce 1-hexene. Those skilled in the art will understand that oligomerization of ethylene to produce 1-hexene can be by trimerization of ethylene.

[0047] FIG. 1 depicts a schematic for a system to produce 1-hexene. The system 100 can include an inlet 102 for a reactant feed that includes ethylene, a reaction zone 104 that is configured to be in fluid communication with the inlet, and an outlet 106 configured to be in fluid communication with the reaction zone 104 and configured to remove a product stream from the reaction zone. The reactant zone 104 can include the catalyst composition of the present invention. The ethylene reactant feed can enter the reaction zone 104 via the inlet 102. In some embodiments, the ethylene reactant feed can be used to maintain a pressure in the reaction zone 104. In some embodiments, the reactant feed stream includes inert gas (e.g., nitrogen or argon). After a sufficient amount of time, the product stream can be removed from the reaction zone 104 via product outlet 106. The product stream can be sent to other processing units, stored, and/or transported.

[0048] System 100 can include one or more heating and/or cooling devices (e.g., insulation, electrical heaters, jacketed heat exchangers in the wall) or controllers (e.g., computers, flow valves, automated values, etc.) that can be used control the reaction temperature and pressure of the reaction mixture. While only one reactor is shown, it should be understood that multiple reactors can be housed in one unit or a plurality of reactors housed in one heat transfer unit.

[0049] As discussed above, the process and catalyst composition of the present invention allows for the production of 1-hexene with high selectivity with the LAO product distribution being limited to 1-hexene and 1-octene. High selectivity for 1-hexene is an advantageous feature inasmuch as it leads to higher product purity, thereby circumventing the need for additional purification steps in the separation train. Further advantageous features of the catalyst composition and process include suppression of ethylene polymerization leading to undesirable polymer formation, milder reaction conditions and, as a result, lower capital costs for equipment as well as operational and energy costs. Additionally, a relatively simple, straight-forward process design is possible. The selectivity for 1-hexene is greater than 80 wt. %, 85 wt. %, 90 wt. %, 95 wt. %, or about 100 wt. %, or any range or value therebetween. The purity for 1-hexene can be at least about 99%, or 99.1%, 99.2%, 99.3%, 99.4%, 99.5%, 99.6%, 99.7%, 99.8%, or 99.9%. A purity of at least 99.1% is preferred. In an embodiment, when 1-octene is produced, the weight ratio of 1-octene to 1-hexene can be less than 0.3, or 0 to 0.3, or 0.1, 0.15, 0.2, 0.25 or 0.3 or any range or value there between.

EXAMPLES

[0050] The present invention will be described in greater detail by way of specific examples. The following examples are offered for illustrative purposes only, and are not intended to limit the invention in any manner. Those of skill in the art will readily recognize a variety of noncritical parameters which can be changed or modified to yield essentially the same results.

Example 1

Synthesis of Ligands 2 and 3

[0051] Route A, General Procedure (See, Scheme 1). All manipulations were carried out under inert atmosphere. Bis(chlorophosphino)amine C.sub.6H.sub.11P(Cl)N(CH.sub.3)P(Cl)C.sub.6H.sub.11 (4.60 g, 14 mmol) was dissolved in 20 mL of anhydrous toluene. Appropriate secondary amine (29.4 mmol) and NEt.sub.3 (35 mmol) was mixed with 30 mL of anhydrous toluene and cooled down to −10° C. Toluene solution of bis(chlorophosphino)amine was added dropwise to the reaction mixture under inert atmosphere with vigorous stirring. Addition of the reagent resulted in precipitation of white gel-like material. With continuous stirring, solution was left to warm up to 25° C. for 3 hours, then heated to 75° C. and stirred at that temperature for additional 12 hrs. After evaporation of all volatile compounds under vacuum, the residue was taken up in anhydrous hot n-heptane and insoluble material was separated by filtration. Evaporation of the solvent led to pale yellow oil. Purity of the product was verified using .sup.1H, .sup.13C and .sup.31P NMR. If desired, the products can be recrystallized from n-hexane, cyclohexane, n-heptane or n-pentane to increase the purity.

[0052] Route B, General Procedure (See, Scheme 1). All manipulations were carried out under inert atmosphere. The appropriate secondary amine (10 mmol) was dissolved in 20 mL of anhydrous n-heptane, cooled down to −10° C. and treated with 5% mol. excess of n-BuLi in n-hexane. The solution was then stirred for 3 hrs letting the temperature raise to 25° C., forming white precipitate. Solid was separated from solution, washed with n-hexane and transferred to the flask with 30 mL of anhydrous Et.sub.2O. Resulted suspension was cooled down to −10° C. and solution of bis(chlorophosphino)amine C.sub.6H.sub.11P(Cl)N(CH.sub.3)P(Cl)C.sub.6H.sub.11 (1.61 g, 4.9 mmol) in 30 mL of anhydrous Et.sub.2O was added dropwise to the reaction mixture with vigorous stirring. After the addition, reaction mixture was continuously stirred for 12 hours letting it warm up to 25° C. During the course of the reaction, white solid was formed. Insoluble material was separated by filtration, washed with Et.sub.2O and discarded. Solution and washing liquids were combined and solvent was removed in vacuum, producing pale yellow viscous oil. Purity of the product was verified using .sup.1H, .sup.13C and .sup.31P NMR. If desired, the products can be recrystallized from n-hexane, cyclohexane, n-heptane or n-pentane to increase the purity.

[0053] Precursor (C.sub.6H.sub.11)P(Cl)N(Me)P(Cl)(C.sub.6H.sub.11) was prepared by the procedure of Jefferson et al. (J. Chem. Soc. Dalton Trans. 1973, 1414-1419).

Example 2

Catalyst Composition Preparation and Oligomerization of Ethylene

[0054] The reactor, equipped with dip tube, thermowell, mechanical paddle stirrer, cooling coil, control units for temperature, pressure and stirrer speed (all hooked up to a data acquisition system) was prepared for the catalytic run by heating to 130° C. in under vacuum for 4 hours and cooled down by venting with dry nitrogen stream to 30° C. An isobaric ethylene supply was maintained by gas dosing control unit connected to data acquisition system. Ethylene consumption was monitored via pressure loss in the feeding cylinder over time by means of a computerized data acquisition system.

[0055] Suitable amounts of the stock toluene solutions of the ligands and Cr(III)acetylacetonate as chromium precursor, at a ligand to Cr ratio of 1.20, were measured and charged to a Schlenk tube under inert atmosphere. A volume of 30 mL anhydrous n-heptane was introduced in stainless steel pressure reactor and warmed up to desired reaction temperature. After temperature of the reactor become stable, reactor was pressurized to 30 bar of ethylene and left for 30 min with continuous mechanical stirring. After that time, pressure was reduced to 0.2 bar and appropriate amount of 0.3M stock solution of MMAO-3A in anhydrous n-heptane was introduced in the reactor through the charging port, providing Al to Cr ratio of 300. Stirring was continued for 10 min. Following that, mixture of Cr and ligand solutions was introduced into the reactor through the charging port.

[0056] Immediately after introduction of the catalyst in the reactor, pressure was increased to 30 bar. Standard reaction conditions are: pressure of ethylene of 30 bar, T=45° C., stirrer speed of 450 RPM. After 1 hour catalytic run, ethylene supply was cut and reactor temperature lowered to 5° C. Ethylene from the reactor was vented to the pressure of 0.2 bar. The reaction was quenched with 0.3M HCl/iso-Propanol mixture. It should be noted that it is also possible to quench the reaction with different agents, such as Decan-1-ol, 2-EHA, 20% wt. NaOH in water. Liquid products were analyzed using gas chromatography with a known amount of toluene as internal standard. Any insoluble by-products, i.e., waxes, polyethylene, were filtered, dried, and weighed. Table 1 shows the results of ligand

##STR00014##

S12 catalyst includes the ligand is that shown as structure (2) above (having two methyl and two n-butyl substituents).

TABLE-US-00001 TABLE 1 Activity Solvent (kg/ % wt. C6 % wt. C8 Insoluble Catalyst g.sub.Cr * h) (1-hexene, %) (1-octene, %) % wt. S12 (Run 1) 56.50 85.62 (99.45)  9.69 (95.80) 2.28 S12 (Run 2) 169.00 87.99 (99.92)  5.71 (99.95) 0.53 S6 179.15 21.55 (79.20) 76.86 (99.41) 0.32 (Comparative; Structure (7)) S1 95.45 40.10 (76.78) 58.11 (96.13) 1.09 (Comparative; Structure (6))

[0057] Table 1 summarizes the results of ethylene oligomerization experimental runs performed under these standard conditions and using catalyst systems prepared with the catalyst S12 with ligand (2) and a comparative catalysts. The Table shows the respective selectivities for C6, C8, and solvent insolubles in wt. % in the liquid phase. Numbers in parentheses denote the selectivities of the respective linear alpha-olefin in the overall C6/C8 fraction. These LAO purities are generally advantageously high. The comparative catalyst differs from catalyst S12 in that catalyst S12 includes the ligands shown in Formula (2) in this specification, while the comparative catalysts include the ligands shown in Formula (6) and (7) have two phenyl groups replacing the two cyclohexyl groups in Formula (2). Two runs are shown for S12 catalyst. It was observed that a second consecutive run typically demonstrates better performance than the initial run. Although not wanting to be bound by theory, it is suspected that this quite typical behavior is likely attributable to the reactor being dried and cleaned during the first run. Notwithstanding the improvement from the first and second run, the data clearly demonstrates the different behavior in comparison to S12 and S6 species, which have aromatic groups on the two phosphorus atoms.

[0058] Although embodiments of the present application and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the embodiments as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the above disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein can be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.