THE OLIGOMERIZATION OF OLEFINS IN ALIPHATIC- HYDROCARBON SOLVENTS

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0001 ] The invention described herein may be manufactured and used by or for the government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

FIELD OF THE INVENTION

[0002] The invention generally relates to an approach that permits continuous batch conversion of alpha-olefins and internal olefins to oligomeric materials without fouling the reaction vessel and provides a simple and highly efficient method for making very cost effective catalyst systems based on Group 4 metallocenes. Embodiments of the invention create synthetic iso-paraffinic kersosenes with high flashpoints suitable for use gas, diesel, and turbine engines.

SUMMARY

[0003] A process for preparing an Activated Homogeneous Metal locene Catalyst (AHMC) includes contacting a metallocene precatalyst of the formula (I):

L'L ² MX'X ² (I)

with an alkylaluminoxane of formula (II):

[0004] The precatalyst, alkylaluminoxane and/or their combination is combined with at least one saturated hydrocarbon solvent. M is Ti, Zr, or Hf. X ¹ and X ² are independently at least one of i halogen, hydrogen, alkyl, and a mixture thereof. L and L~ are independently at least one π-ligand selected from the group consisting of cyclopentadienyl, indenyl, fluorenyl, and derivatives thereof, n is an integer of at least 3. R is a C ₁ -C30 alkyl. The at least one saturated hydrocarbon solvent can be selected from the group consisting of cycloalkanes, normal alkanes, iso-alkanes, and combinations thereof.

[0005] In another aspect, a process for oligomerizing an a-olefin can be performed by contacting an olefin feedstock with the Activated Homogeneous Metallocene Catalyst to form an olefinic-oligomer product, the olefin feedstock including at least one olefin, such as an a-olefin.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] FLG. 1 is a photograph of a beaker removed directly from SS-bomb showing a typical homogeneous oligomeric mixture from 1-butene that contains the Cp2ZrCl ₂ /MAO catalyst system prepared in cyclohexane, according to embodiments of the invention.

[0007] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not to be viewed as being restrictive of the invention, as claimed. Further advantages of this invention will be apparent after a review of the following detailed description of the disclosed embodiments, which are illustrated schematically in the accompanying drawings and in the appended claims.

DETAILED DESCRIPTION OF EMBODIMENTS OFTHE INVENTION

[0008] The invention generally relates to an approach that permits continuous batch conversion of alpha-olefin and internal-olefins to oligomeric materials without fouling the reaction vessel and provides a simple and highly efficient method for making very cost effective catalyst systems based on Group 4 metallocenes.

[0009] Currently no homogeneous Ziegler Natta (ZN) catalyst can be used in the absence of aromatic solvents. Aspects of the exemplary embodiments disclosed herein provide a versatile and inexpensive means for creating and using highly active catalysts for the oligomerization of alpha- olefins, like 1-butene. Hence, the method is very valuable for turning 1-butene (made from bio-1- butanol) to oligomers suitable for use in creating diesel and jet fuels with flashpoints over 61 deg C. Furthermore, by addition of a homogeneous isomerization catalyst mixtures of alpha-oleflns and internal-olefins can be converted to high flashpoint diesel and jet fuels using a homogeneous ZN catalyst prepared as disclosed herein. The exemplary activated catalyst can be used in oligomerization and/or dimerization of olefins in the absence of any aromatic solvents (i.e., where aromatic solvents make up less than 5 wt.% or less than 1 wt. % of the liquid reaction mixture).

[0010] In various aspects, an activated catalyst, a method for making it and a method for using it to oligomerize/dimerize an olefin are disclosed.

[0011] One aspect of the invention includes a fuel(s). The fuel(s) can be produced from oligomerization and/or dimerization processes including at least one alpha-olefin and/or internal olefins, at least one homogenous Ziegler-Natta catalyst and at least one homogenous activating co- catalyst (e.g., together forming the exemplary activated catalyst), and at least one or mixture hydrocarbon solvent, where the fuel has a flashpoint of 61 to 100 °C. Embodiments of the invention further include at least one olefin-isomerization catalyst. Other embodiments of the invention include the Ziegler-Natta catalyst being group four (4) metallocene catalyst. In other embodiments, the co-catalyst is an alkylaluminoxane (AAO). Yet in other embodiments, the catalyst is prepared by contacting a metallocene precatalyst with an aliphatic hydrocarbon solution containing an alkylaluminoxane (AAO). In still yet other embodiments, the aliphatic hydrocarbon solution is derived from a fuel.

[0012] Embodiments of the invention include the activated catalyst being prepared by dissolving trialkylalane in an aliphatic-hydrocarbon solvent (e.g., a fuel) and being treated with one mol-equivalent of water and then contacted with a metallocene precatalyst and filtered. In embodiments, the trialkylalanes are selected from the group consisting of trimethylalane, triethylalane, tributylalane, and tri(iso-butyl)alane (TIBA). In other embodiments, the aliphatic hydrocarbon solvents (which can be fuels) are selected from the group consisting of straight chain alkanes including hexane, heptane, octane, nonane, decane, and alkanes having greater than 10 carbons. In yet other embodiments, the aliphatic hydrocarbon solvents are C6 to C16 hydrocarbons and may be selected from the group consisting of, but not limited to, branched-aliphatic- hydrocarbons including 3-methylheptane, 2-methyloctane, and the like. Still yet in other embodiments, the aliphatic hydrocarbon solvents are selected from the group consisting of, but not limited to, cyclic aliphatic-hydrocarbons including cyclohexanes, methylcyclohexanes, dimethylcyclohexanes, tetralins, pinanes, and other mono- and bicyclic aliphatic-hydrocarbons.

[0013] Another aspect of the invention includes a process for preparing a saturated hydrocarbon fuel including contacting an olefin feedstock with an Activated Homogeneous Metallocene Catalyst (AHMC) for use in the dimerization and oligomerization of olefins, such as neat a-oleflns, where the AHMC can be prepared by contacting a metallocene precatalyst of the formula (I) with an alkylaluminoxane of formula (II), where the latter is prepared in and/or the resulting activated catalyst mixed with a saturated hydrocarbon solvent:

L'L ² MX'X ² (I)

[0014] In formula ((I), M is Ti, Zr, or Hf, X ¹ and X ² is at least one halogen, hydrogen, alkyl, or a mixture thereof, L and L are comprised of π-ligands selected from the group consisting of cyclopentadienyl, indenyl, fluorenyl and derivatives thereof. In the derivatives, substituents are attached to the ligands, the attachments includes ansa-linkages that bind the two rings, with at least one carbon or silicon atoms each bearing hydrogen or alkyl radicals. In formula (II), n is an integer of at least 3, and R can be a C ₁ -C30 alkyl, which can be linear, branched, or a combination thereof. The at least one saturated hydrocarbon solvent can be selected from the group consisting of cycloalkanes, normal-alkanes, and/or iso-alkanes.

[0015] The Al/M molar ratio can be about 1 to 100. In other embodiments, the Al/M molar ratio is 10 to 20. Embodiments of the invention include the product being prepared by placing the activated catalyst in contact with a neat solution having at least one a-olefin during a period of 1 to 24 h and forms the a-olefinic-oligomer (III) in 98-100% conversion based on starting a-olefins:

[0016] In formula (III) each R can be independently as described for formula (II).

[0017] Embodiments of the invention include the AHMC being introduced in one portion, in discrete aliquots, or through a continual addition process directly to the neat (undiluted) a-olefin feedstock. Embodiments of the invention include the ratio of metallocene precatalyst (g of M) to a- olefinic-oligomer product (Kg) being about 5 to 40. In other embodiments, the entire a-olefinic- oligomer product (III) is transferred to quench vessel, treated with water, and then filtered to remove solids. In other embodiments, the a-olefinic-oligomer product (III) is passed through an alumina or other metal oxide filter material to remove M and Al species from the product solution. Other embodiments, the α-olefinic-oligomer product (III) is treated with a stabilizing agent selected from either a hydroquinone or phenol family of stabilizers, e.g., with butylated hydroxytoluene (BHT) and at concentrations of 10-300 ppm.

[0018] Embodiments of the invention include the process lowering the boiling fraction of the a- olefinic-oligomer products (III) between 50 °C and 150 °C, including between 70 °C and 130 °C, and are removed by flash distillation. Embodiments of the invention include the process having a low boiling fraction from about 25 to 45 wt. % of the total α-olefinic-oligomer product, or comprises about 30-40 wt. % of the total α-olefinic-oligomer. In embodiments, the process includes a light boiling fraction subjected to select! ve-dimerization chemistries to create a mixture of mono- olefinic hydrocarbon products having a boiling point greater than 200 °C but less than 300 °C at atmospheric pressure. Embodiments of the invention include the process having a high boiling fraction subjected to catalytic hydrogenation over heterogeneous metal catalysts having palladium, platinum, and/or nickel (or any combination thereof). Embodiments of the invention include the process having a hydrogen pressure in the range of about 30-3000 psig (approximately 300-20800 kpa), or a pressure between 50 and 100 psig (approximately 440-790 kpa). Embodiments of the invention the reaction temperature used is in the range of about 20 to 100 °C with ambient or 40 °C temperature range.

[0019] Embodiments of the invention further include the product being subjected to hydrogenation over heterogeneous metal catalysts which includes palladium, platinum, and/or nickel; hydrogen pressure is performed in the range of about 30-3000 psig, or a pressure between 1000 and 2000 psig. In embodiments, the temperature is in the range of 20 to 100 °C or 60 °C to 80 °C temperature range. In embodiments, the products are combined and distilled at atmospheric pressure. In other embodiments, the products obtained are combined and distilled at reduced pressure. Embodiments of the invention a collection of hydrocarbon, a completely 100% synthetic iso-paraffinic kerosene (SiPK) product, starting at 150 °C and finishing at 280 °C affords a fuel mixture that meets Jet-A/JP-8 and diesel #1 flashpoint requirements (>38 °C). Embodiments of the invention the SiPK jet diesel fuel produced has a derived Cetane index of 40-55 or 50 Cetane index. In other embodiments, the SiPK jet diesl fuel produced has a maximum cold flow viscosity of 8 cSt as measured at -20 °C (ASTM 445LT).

[0020] Embodiments of the invention include the collection of product starting at 170 °C and finishing at 280 °C yields a SiPK jet/diesel that meets military JP-5 and diesel #2 flashpoint requirements with a flashpoint >61 °C. Embodiments of the invention include the SiPK jet diesel fuel produced has a derived Cetane index of 40-55 or 50 Cetane index. Embodiments of the invention include SiPK jet/diesl fuel produced has a maximum cold flow viscosity of 8.5 cSt as measured at -20 °C (ASTM 445LT).

[0021 ] The α-olefins can be selected from the group consisting of, but not limited to, 1 -propene, 1-butene, 1-pentene, and 1-hexene, with neat 1-butene or a mixture of 1-butene and 1 -propene (3:1, mokmol, respectively).

[0022] In embodiments of the invention the π-ligands can be cyclopentadienyl, R is methyl, and the aliphatic hydrocarbon solvent is cyclohexane or methylcyclohexane. Embodiments of the inventions include the π-ligands are cyclopentadienyl rings having at least one alkyl group attached, R is methyl, and the aliphatic hydrocarbon solvent is selected from the group consisting of cyclic, acyclic linear and branched hydrocarbon solvent that include jet and diesel fuels prepared. Embodiments of the invention include the π-ligands being cyclopentadienyl, R is at least three carbons, and the aliphatic hydrocarbon solvent is selected from acyclic linear and/or branched hydrocarbon solvent.

[0023] Embodiments of the invention include the trialkylalane compound being prepared by direct reaction of one mole of trialkylalane with one mole-equivalent of water in an SiPK. Other embodiments of the invention include the trialkylalane is selected from the group consisting of, but not limited to, trimethyl, triethylalane, tripropylalane, tri-isopropylalane, tributylalane, and tri- isobutylalane, and tri-isobutylalane. Still yet in other embodiments the π-ligands are cyclopentadienyl rings having at least two alkyl groups attached, R is methyl, and the aliphatic hydrocarbon solvent is selected from the group consisting of cyclic, acyclic linear, branched hydrocarbon solvents, solutions thereof, and jet and diesel fuels previously prepared. Embodiments of the invention include a fuel having a flashpoint of about 61 to about 100. Embodiments of the invention further include an isomerization catalyst having a range from about 0.1 ppm to about 0.1 weight %, relative to the total olefin component.

[0024] Oligomers, suitable for conversion and use as jet and diesel fuels, are prepared from alpha-olefins using highly active purely homogeneous Ziegler-Natta catalysts, a homogeneous co- catalyst, and in pure aliphatic hydrocarbon solvent. The oligomerization can be conducted controlled without the use of hydrogen and produce an ideal molecular distribution of oligomers for use in preparing diesel and jet fuels. This method creates fuels that do not require any subsequent hydrocracking or reforming yet retain outstanding cold flow properties and exceptionally high gravimetric densities.

[0025] The homogeneous catalyst of embodiments of the invention is prepared as shown in Scheme 1 by contacting a metallocene precatalyst with a solution of an alkylaluminoxane (AAO). Typically, R and R ^" can independently be hydrogen or any combination of Ci-C ₃₀ alkyl chains. The R and R substituents(s) are linear or branched chains and/or a combination thereof. The alkylaluminoxane can be prepared using methods that are familiar to people skilled in the art, e.g., from a trialkylalane A1(R ₃ ) ₃ where R is typically a Ci-C ₃₀ alkyl group, although larger chains can be employed. Branching in the alkyl group can be used to increase solubility although is not required herein. When the AAO is prepared in an aromatic solvent, the metallocene precatalyst is combined and the aromatic solvent is removed under reduced pressure and the solids redissolved in the desired aliphatic-hydrocarbon solvent or fuel, filtered if necessary, and then transferred to the reaction vessel that contains the mixture of alpha-olefin and internal-olefins. These activated homogeneous catalyst solutions are stable and suitable for storage. Typical alpha-olefins can include R ⁴ being a Cj-Cio alkyl group that can be a linear chain or contain branching at various places in the carbon chain. The internal olefin is any olefin-isomer where the double-bond has chemically migrated internally along the carbon chain. The homogeneous isomerization catalyst takes the internal-olefin and isomerizes the bond so as to create the corresponding alpha-olefin. Pre-Catalyst

Activated Homogeneous Metallocene

Oligomerization Catalyst

Filter and add Aliphatic- Hydrocarbon Solution to neat

alpha-olefin(s)

Scheme 1

[0026] Another embodiment of the chemical process for preparing the homogeneous metallocene catalyst in pure aliphatic-hydrocarbon solvent is illustrated in Scheme 2: A tnalkylalane is dissolved in an aliphatic-hydrocarbon solvent and treated with one mol-equivalent of water, this solution is then placed in contact with a metallocene precatalyst. The molar ratio of alane/metallocene can be varied from 1 : 1 to 100:1, respectively, depending on the desired catalytic process and outcome. The final solutions may be filtered to remove any impurities or undesired products resulting from the controlled hydrolysis of the alane and subsequent reaction with the metallocene pre-catalyst. The final solutions are typically light yellow in color and crystal clear to the eye. Typical concentrations of the active homogeneous catalysts are in the range of 0.1 M to 0.01M, with lower concentrations possible with equal catalytic activity. These latter solutions can be stored for long periods or immediately transferred to reaction vessels using common techniques that include Teflon® diaphragm pumps or by simple polypropylene syringes, all with equal success and retention of catalyst activity.

[0027] Typical trialkylalanes can be trimethylalane, triethylalane, tripropylalane, tributylalane, and tri(isobutyl)alane (TIBA), which are all commercially available. Alanes containing longer alkyl chains can be prepared by existing methods familiar to those in the art by simple reaction of an alkyl Grignard with aluminum trichloride. For the methylaluminoxane, toluene solutions can be utilized from commercial sources to prepare the active metallocene catalyst followed by removal and recycling of the toluene. Then the active metallocene/MAO catalyst can be dissolved in the desired aliphatic-hydrocarbon solvent. Use of MAO in this invention it is found preferable to utilize a metallocene precatalyst that has alkyl substitution on one or more of the cyclopentadienyl rings, although this is not required if certain aliphatic hydrocarbon solvents are used. In general, alkyl- substitution of the metallocene rings provides enhanced solubility over a range of aliphatic- hydrocarbons and can be used to increase the activated metallocene catalyst concentration when desired.

1. Aliphatic- Hydrocarbon

Solvent

AI(R ³ ) ₃

2. H ₂ 0

neat trialkylalane

AAO Aliphatic-

For example: Hydrocarbon Solution

Scheme 2

[0028] Typical aliphatic-hydrocarbon solvents useful in this invention include straight chain alkanes such as hexane, heptanes, octane, nonane, and decane. Branched-aliphatic-hydrocarbons such as 3-methylheptane, 2-methylheptane, and 2-methyloctane work well in this invention as well as other branched aliphatic hydrocarbons containing from 6 to 16 carbons. In particular, C12 to CI 6 staturated synthetic iso-parafflnic kerosenes are suitable for use in this embodiment. Cyclic aliphatic-hydrocarbons can be used that include cyclohexane, methylcyclohexane, dimethylcyclohexanes, tetralin, pinane, and other mono- and bicyclic aliphatic-hydrocarbons.

[0029] Useful metallocene pre-catalysts for this invention can be prepared by several methods, some found in the open literature covering nearly four decades of group metallocene synthetic procedures [Y. Qian et al, Chem. Rev., 103(7), pp 2633-2690 (2003); R. Halterman, Chem. Rev., 92(5), pp 965-994 (1992)]. In addition, two patents describe the synthesis of simple bis(n- alkylcyclopentadienyl)MCl ₂ (where M = Group 4 transition metal) [J.-S. Oh et al. US6214953 Bl (2001) and J. M. Sullivan et al. US6175027 Bl (2001)]. Oh and co-workers describe the use of alkyl-metallocenes for preparing supported ZN-catalysts and Sullivan and coworkers do not report any catalytic chemistry or solubility properties for the metallocene compounds prepared.

[0030] By way of example, unsubstituted and all alkyl and multiple-alkyl substituted metallocenes, ansa-metallocenes, indenyl, fluorocenyl, and related metallocenes can be used in the present invention when combined with the appropriate aliphatic-hydrocarbon solvent and AAO, all affording highly active and selective oligomerization ZN-catalysts. Examples of the precatalyst (I) include formulas (IV)-(VII) below.

(IV) (V) (VI0) (VII)

[0031] Olefmic monomers that can be used in the current invention include a-olefins (including ethane), mono- and bicyclic olefins, dienes, vinyl-aromatics and the like. Examples include ethene, 1-propene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, cyclopentene, cyclopentadiene, norbornene, styrene, and the like. The olefin monomer can be copolymerized with one or more other monomers. Internal-olefins including 2-hexene, 2-pentene, 2-butene can be used in the invention by introduction of a homogeneous group 8 transition metal complex/isomerization catalyst, with nickel being another embodiment of a transition metal.

EXAMPLE 1: Preparation of the Homogeneous Zn-Catalyst in an Aliphatic-Hydrocarbon Solvent

[0032] A Schlenk flask is charged with Cp ₂ ZrCl ₂ (0.080 g, 0.274 mmol) and 10 mL of a toluene MAO solution (8.0 wt. % active MAO). Cp=cyclopentadiene. The toluene was removed under reduced pressure to afford a yellow solid. To this mixture was added cyclohexane (15 mL) and heated briefly with stirring to dissolve the activated catalyst. The solution was allowed to settle and clear yellow solution was collected by syringe (~10 mL) and used directly or stored for future use.

EXAMPLE 2: Oligomerization of an Alpha-Olefin Using a Homogeneous ZN-Catalyst Delivered in an Aliphatic Hydrocarbon-Solvent

[0033] 1 -Butene (-390 g, ~ 500 mL, CP grade) was condensed over calcium hydride inside a Schlenk flask maintained at -70 °C and re-evaporated and passed through a column of activated alumina in route to being condensed inside a dried 0.7L capacity PARR SS bomb. A 500 mL beaker was placed inside the bomb to simulate a glass lined reaction vessel. Once the 1 -butene was condensed inside the SS bomb the sample was subjected to five evacuation/backfill cycles to remove residual amounts of oxygen. The homogeneous aliphatic-hydrocarbon solution containing the active catalyst was added to the mixture and 3 addition evacuation/backfill cycles were performed. The SS bomb was sealed and allowed to react for 8 h. Shorter times could be used if the SS bomb was warmed by external heat. Typically after ~1 h the bomb reached a maximum pressure of 80 psig and approached 60 °C in temperature. At completion of the reaction little or no pressure remained in the vessel and the when removed from the SS bomb the beaker contained a clear light yellow solution of oligomers (see Figure 1). Quenching the mixture with 0.5 mL of water and then drying over potassium carbonate (~3 g) afforded ~380 g of an oligomeric mixture suitable for use in making diesel and jet fuels with flash points over 61 deg C.

[0034] Figure 1 shows a beaker removed directly from SS-bomb showing a typical homogeneous oligomeric mixture from 1 -butene that contains the Cp ₂ ZrCl ₂ MAO catalyst system prepared in cyclohexane. The sample contains no aromatic hydrocarbons. It is a clear solution.

[0035] Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limits of that range is also specifically disclosed. Each smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in that stated range is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range, and each range where either, neither or both limits are included in the smaller ranges is also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the invention.