WO2013162573A1

WO2013162573A1 - Diesel and jet fuels based on the oligomerization of butene

Info

Publication number: WO2013162573A1
Application number: PCT/US2012/035184
Authority: WO
Inventors: Michael E. Wright; Benjamin G. HARVEY; Roxanne L. QUINTANA
Original assignee: The Government Of The Usa As Represented By The Secretary Of The Navy
Priority date: 2012-04-26
Filing date: 2012-04-26
Publication date: 2013-10-31

Abstract

A renewable biofuel is based on a highly efficient batch catalysis methodology for conversion of 1-butene to a new class of potential jet fuel blends. By tuning the catalyst and then using the dimer produced, the carbon use can be about 95% or greater. This is particularly useful where the source of raw materials (i.e., biomass/biofeedstock) is limited. The batch catalysis approach disclosed requires a minimal input of energy and hydrogen to make fuels that possess useful flash points, coldflow properties, and solution density/energy content. This new process affords a saturated hydrocarbon fuel that has a high solution density and thus possesses a higher calculated power density (per volume) than similar fuels made by the GTL Fischer-Tropsch processes.

Description

DIESEL AND JET FUELS BASED ON THE

OL1GOMERIZATION OF BUTENE

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] A renewable biofuel for turbine engines based on a highly efficient batch catalysis methodology for conversion of 1 -butene to a new class of fuels.

BACKGROUND OF THE INVENTION

[0003] Demonstrated herein is that that the quantitative conversion of 1-butene to a Schultz-Flory distribution of oligomers can be accomplished by use of Group 4 transition-metal catalysts in the presence of methylaluminoxane (MAO). The oligomerization reaction can be carried out at ambient temperature (up to 70°C, such as 0-70°C or 10-50°C) in a sealed reaction vessel with complete conversion of 1 -butene at catalyst turnover numbers greater than 17,000. The combination of high catalyst activity without concomitant production of high polymer can lead to a highly efficient method for production of new hydrocarbon jet fuel candidates. The reaction proceeds with high regioselectivity; however, because achiral catalysts were used, several diastereoisomeric structures were produced and observed in the gas chromatography- mass spectrometry (GC-MS) chromatograms. The single and specific dimer formed in the reaction, 2-ethyl-1-hexene, was easily removed by distillation and then was itself dimerized using acid catalysis to yield a mixture of mono-unsaturated Ci6 compounds. Changes in the oligomerization catalyst led to production of fuels with excellent cold- flow viscosity without the need for a high-temperature distillation. Thus, removal of the dimer followed by catalytic hydrogenation (PtO₂) led to a 100% saturated hydrocarbon fuel with a density of 0.78 g/mL, a viscosity of 12.5 cSt at -20 °C (ASTM 445), and a calculated heat of combustion of 44+ MJ/kg. By back-addition of hydrogenated dimer in varying amounts (e.g., 6.6, 11.5, and 17 wt %), it is possible to tailor the viscosity of the fuel (8.5, 7, and 6.5 cSt, respectively).

[0004] There exist several commercial and research programs around the world aimed at creating full-performance jet fuels based on alternative feedstocks. Traditionally, jet propulsion (JP) fuels contain a complicated array of saturated and aromatic hydrocarbons that are highly refined to meet fuel specifications for a particular application. For instance, the Navy's JP-5 has a significantly higher flash point (60 °C) in comparison to the Air Force JP-8 and commercial jet fuel (about 38 °C). (Corporan, E.; DeWitt, M. J.; Belovich, V.; Pawlik, R.; Lynch, A. C; Gord, J. R.; Meyer, T. R. Energy Fuels 2007, 21, 2615-2626) (Chang, P. H.; Colbert, J. E.; Hardy, D. R.; Leonard, J. T. Prepr. Pap. Am Chem. Soc, Div. Pet. Chem. 2004, 49, 414). Syntroleum and Sasol have independently produced JP-5 and JP-8 equivalents based on gas-to-liquid (GTL) Fischer-Tropsch processes. (Feerks, R. L.; Muzzell, P. A. Prepr. Pap. Am Chem. Soc, Div. Pet. Chem 2004, 49, 407-410) (Muzzell, P. A.; Feerks, R. L.; Baltrus, J. P.; Link, D. D. Prepr. Pap. Am Chem. Soc, Div. Pet. Chem. 2004, 49, 41 1-413) and (Lamprecht, D. Energy Fuels 2007, 21, 1448-1453). One of the most challenging aspects to making a jet fuel using Fischer-Tropsch chemistry (Fischer, F.; Tropsch, H. Brennst. Chem. 1923, 4, 276) has been to meet the required coldflow properties. To date, this has required significant postprocessing or "reforming" of the fuel to increase the iso/normal paraffin product ratio. Typically, the Chevron isocracking technology produces a predominance of methyl branching at the 2 position of a hydrocarbon chain; however, the chemical product distribution is quite complicated.

[0005] Conversion of propene and butylenes to dimers/oligomers was one of the first commercial processes in the petroleum industry. (Schmerling, L.; Ipatieff, V. N. Adv. Catal. 1950, 21, 2). Some more recent approaches have looked at using mesoporous catalysts and newly designed large-pore acidic zeolite catalysts. (Catani, R.; Mandreoli, M.; Rossini, S.; Vaccari, A. Catal. Today 2002, 75, 125-131 ) (Schmidt, R.; Welch, M. B.; Randolph, B. B. Energy Fuels 2008, 22 (2), 1148-1155). Transition-metal catalysts (homo- and heterogeneous), generally grouped into the category of Ziegler-Natta (ZN), have enjoyed a successful history for converting olefins, in particular, ethylene and propene, into oligomeric and polymeric materials. (Natta, G. J. Polym. Sci. 1955, 16, 143) (Natta, G.; Pino, P.; Corradti, P.; Danusso, F.; Mantica, E.; Mazzanti, G.; Moraglio, G. J. Am. Chem. Soc. 1955, 77, 1708) (Natta, G. Angew. Chem. 1956, 12, 393. Ziegler, K. Angew. Chem. 1952, 64, 323) (Ziegler, K.; Holzkamp, E.; Breil, H.; Martin, H. Angew. Chem. 1955, 67, 541 ) (Janiak, C. Coord. Chem. ReV. 2006, 250, 66-94) (Belov, G. P. Petrol. Chem. 1994, 34, 105). Studies using 1 -butene can involve a co-polymerization reaction with more reactive olefins, such as ethylene or propene. (Janiak, C; Blank, F. Macromol. Symp. 2006, 236, 14-22). A study by Kaminsky explored the oligomerization of 1 -butene using selected chiral Group 4 transition-metal catalysts and methylaluminoxane (MAO). (Kaminsky, W. Macromol. Symp. 1995, 89, 203-219). In general, the catalysts studied required elevated reaction temperatures and typically led to incomplete conversion of the 1 -butene. A study by Christoffers and Bergman reported that using an aluminum/zirconium ratio of 1/1 and with a nearly stoichiometric amount of zirconium "catalyst" that 1 -butene could be converted selectively to dimer (2-ethyl-1 - hexene). (Christoffers, J.; Bergman, R. G. Inorg. Chim. Acta 1998, 270, 20).

[0006] i one exemplary embodiment, the method facilitates creating a full- performance JP-5/tactical biojet fuel that can be derived from a fully renewable and sustainable source of reduced carbon. Carbon dioxide is initially reduced via photosynthesis (e.g., cellulose and triglyceride oils). Further reduction can occur in a second fermentation or microbial treatment to afford an alternative biofuel and/or biofeedstock. (Wright, M. E.; Harvey, B. G.; Quintana, R. Prepr. Pap. Am. Chem. Soc, Fuel Div. 2008, 53 (1 ), 252-253.)

[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.

SUMMARY

[0008] In one aspect, a process for conversion of 1 -butene to butene oligomers includes activating a bis(cyclopentadienyl)zirconium dichloride pre-catalyst with methylaluminoxane in an aromatic solvent. The solvent may be removed, to form an activated catalyst. A C4-C10 alkane is mixed with the activated catalyst to form a slurry. Dried 1 -butene is added to the slurry to form a mixture. The mixture to allow contact of 1 -butene with the activated catalyst at ambient temperature in a gas tight vessel until reaction is complete to form a first mixture of butene oligomers.

[0009] The organic solvent can be an aromatic solvent which is without heteroatoms.

[0010] The process can include distilling the first mixture of butene oligomers to remove the C4-C10 alkane forming a second mixture of butene oligomers.

[0011] The second mixture of butene oligomers can be hydrogenated to form a first mixture of hydrogenated oligomers.

[0012] The first mixture of hydrogenated oligomers can be formulated with 3-methyl heptane as the C4-C10 alkane to form a fuel having a viscosity at -20 °C of from 6.0 cSt to 12.5 cSt, a density of from 0.75 g/mL to 0.80 g/mL, and a flash point of at least 59 °C or at least 61 °C.

[0013] The first mixture of hydrogenated oligomers can be formulated with 3-methyl heptane to form a fuel suitable for turbine engines.

[0014] The C4-C10 alkane can include 3-methyl heptane, e.g., be at least 20 wt. % or at least 50, or 60, or 70, or 90 or 100 wt, % 3-methyl heptane.

[0015] The stirring of the mixture can be performed at an ambient temperature of up to 70°C, or at least 10°C, or at least 15°C, and can be up to 60°C or up to 50°C or up to 40°C.

[0016] The butane oligomers can include Ci₆ oligomers.

[0017] The first reaction mixture can include 2-ethyl-1 -hexene, and the process include distilling the first reaction mixture to recover the 2-ethyl-1 -hexene, mixing the 2- ethyl-1 -hexene with concentrated sulfuric acid to form a heterogeneous mixture, stirring the heterogeneous mixture to allow contact of reactants at ambient temperature until reaction is complete to form a reaction mixture, separating the organic phase from the aqueous phase of the reaction mixture, and isolating butene oligomers from the organic phase. The C4-C10 alkane can be 3-methyl heptane.

[0018] The slurry can further include an aromatic solvent, which is without heteroatoms, with the C₄-Ci₀ alkane and activated catalyst.

[0019] In another aspect of the invention, a catalytic agent is produced by mixing bis(cyclopentadienyl)zirconium dichloride with methylaluminoxane in a solvent, removing the solvent to form a residue, and adding dried 1 -butene to slurry to form a mixture, stirring the mixture to allow contact of reactants at ambient temperature in a gas tight vessel until reaction is complete to form a first mixture of butane oligomers. The catalytic agent solvent can be an aromatic solvent without heteroatoms.

[0020] In another aspect of the invention, a process for converting 1-butene to C₁₆ butene oligomers includes mixing bis(cyclopentadienyl)zirconium dichloride with methylaluminoxane in a solvent, removing the solvent to form an activated catalyst, mixing 3-methyl heptane with the activated catalyst to form a slurry, adding dried 1 - butene to the slurry to form a mixture, stirring the mixture to allow contact of reactants at ambient temperature in a gas tight vessel until substantially all 1-butene has been reacted to form a first reaction mixture containing 2-ethyl-1 -hexene, distilling the first reaction mixture to recover 2-ethyl-1-hexene, mixing the 2-ethyl-1 -hexene with concentrated sulfuric acid to form a heterogeneous mixture, stirring the heterogeneous mixture to allow contact of reactants at ambient temperature until reaction is complete to form a second reaction mixture comprising an organic phase and an aqueous phase, separating the organic phase from the aqueous phase of the second reaction mixture, and isolating butene C-ie oligomers from the organic phase.

[0021] The butene C-ιβ oligomers can be hydrogenated to form a turbine engine fuel mixture. The solvent can be an aromatic solvent without heteroatoms.

[0022] In another aspect, a process includes activating a bis(cyclopentadienyl)zirconium dichloride pre-catalyst with methylaluminoxane in an organic solvent, removing the solvent from the activated catalyst, mixing aromatic solvent, which is without heteroatoms, with the activated catalyst to form a slurry, adding dried 1 -butene to the slurry, and allowing contact of the activated catalyst with 1 - butene in a gas tight vessel to form a mixture of butene oligomers.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 of the drawings is a plot of GC-MS total ion chromatogram for the oligomers produced from 1-butene.

[0024] Figure 2 of the drawings is a graph of relative area integration for each of the oligomers by carbon number for the GC-MS chromatogram of Figure 1 above.

[0025] Figure 3 of the drawings is an ¹H NMR spectrum of butene oligomers.

[0026] Figure 4 of the drawings is an ¹H NMR spectrum of hydrogentated butene oligomers. [0027] Figure 5 of the drawings is a Gas Chromatogram of hydrogenated butene oligomers.

[0028] Figure 6 of the drawings is a Gas Chromatogram of distilled fuel.

[0029] Figure 7 of the drawings is a ¹H (top) and ¹³C (bottom) NMR spectra of the product mixture from sulfuric acid dimerization of 2-ethyl-1-hexene.

[0030] 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 THE INVENTION

[0031] Recent advances have been made in the conversion of starch (Ramey, D. E. U.S. Patent 5,753,474) and cellulosic biomass to biobutanol (Qureshi, N.; Sahaa, B. C; Hector, R. E.; Hughes, S. R.; Cotta, M. A. Biomass Bioenergy 2008, 32 (2), 168-175. Qureshi, N.; Sahaa, B. C; Cotta, M. A. Biomass Bioenergy 2008, 32 (2), 176-183). In aspects of the invention described herein, this C4 alcohol can be used as a pivotal and versatile starting point for the creation of new fuels. Because both butyl ether and 1- butene can be easily derived from -butanol (Berteau, P.; Delmon, B.; Dallons, J. L; Vangysel, A. Appl. Catal. 1991 , 70 (2), 307-323. Bautista, F. M.; Delmon, B. Appl. Catal., A 1995, 130 (1 ), 47-65), use of these chemicals was investigated as precursors to biojet fuels that will meet the required energy content and key performance specifications of JP-5 jet fuel. Disclosed herein are methods for converting 1 -butene into butene oligomers (dimers, trimers, etc. derived from butene) to provide a variety of useful saturated hydrocarbon fuels using a highly efficient batch-catalysis process. The new approach affords a product that is composed of 100% iso-paraffins, retains good fuel density, possesses attractive cold-flow properties, and can be easily tailored to have a high flash point.

[0032] In aspects of the embodiments described herein, synthetic fuel experiments were initiated using the commercially available precatalyst bis(cyclopentadienyl)zirconium dichloride. The precatalyst is activated by treatment with a solvent (e.g. toluene) solution of MAO followed by removal of the toluene under reduced pressure. The MAO may also be prepared in a solution of any aromatic solvent able to solvate the MAO and the precatalyst such as, without limitation, for example xylene, cumene, and mesitylene. In general, coordinating solvents with heteroatoms are not appropriate. These are solvents which contain an atom other than carbon and hydrogen, in particular, one or more atoms of sulfur, oxygen, and/or nitrogen, in the chain or ring. Removal of solvent after catalyst activation also removes any residual trimethylaluminum, creating "dried" MAO. The "dried" MAO has been shown to have a significant affect on catalyst activity for olefin oligomerization/polymerization reactions for several non-metallocene catalysts. (Hasan, T.; loku, A.; Nishii, K.; Shiono, T.; Ikeda, T. Macromolecules 2001 , 34 (10), 3142-3145) ( Hagimoto, H.; Shiono, T.; Ikeda, T. Macromol. Rapid Commun. 2002, 23, 73) ( Furayama, R,; Saito, J.; Ishii, S.; Mitani, M.; Matsui, S.; Tohi, Y.; Makio, H.; Matsukawa, N.; Tanaka, H.; Fujita, T. J. Mol. Catal. A: Chem. 2003, 200, 31 ) (Long, R. J.; Gibson, V. C; White, A. J. P. Organometallics 2008, 27 (2), 235-245). The catalyst may be consistently prepared using an aluminum/zirconium ratio of 100 (mol/mol). It may be noted that here the MAO is an oligomer of formula [CH₃AIO]_n and there is one mole of aluminum for every mole of MAO repeat unit. Similarly, there is one mole of Zr per mole of Cp₂ZrCI₂. Conveniently, both the molar ratio of MAO/Cp₂ZrCI₂ and Al/Zr is 100:1. It may be noted as well, that the turnover number (TON) here is at least about 17,000 and may be pushed to as high as on the order of 10⁷ whereas the TON utilized by Christoffers and Berg was only about 10 or less. It is well known that use of very high Al/M ratios on the order of 10,000:1 results in the production of polymers, whereas significantly lower ratios leads to oligomeric mixtures. Use of the Al/M ratio of 100:1 (M being a metal such as Zr) is an approximate first optimization of the system based upon previous observations.

[0033] In one exemplary method, the 1 -butene (375 ml_, about 240 g) is condensed onto CaH₂ and then transferred over the course of 3 h to a chilled (dry ice bath) pressure reaction vessel containing the "activated" catalyst. Reactions were performed in a Parr steel pressure reaction vessel lined with a glass insert and stirring was accomplished using a Teflon coated stirring bar. The 1 -butene [Specialty Gas Concepts, Lancaster, CA, 98% Chemically Pure (CP) grade] was transferred after drying (over CaH₂) to the chilled reaction vessel through Tygon tubing. Once the pressure vessel was charged, the port was sealed, the cooling bath was removed, and the reaction was run for 16 h. The reaction vessel is sealed and allowed to react with stirring at ambient temperature for 16 h (Scheme 1 ). At completion of the reaction, a partial vacuum exists in the reaction vessel. This observation is consistent with complete consumption of the 1 -butene (bp -6.3 °C). Gas chromatography-mass spectrometry (GC-MS) analysis indicates a Schultz-Flory distribution of products consisting primarily of C8, C12, and C16 oligomers with small amounts of heavier oligomers. GC-MS analyses were performed using an Agilent 6890 gas chromatography (GC) system equipped with a Restek RTX-5MS 30 m column coupled to an Agilent 5973 mass selective detector system. After quenching as described herein below, a distillation using a vigreux column is used to remove the C₈ dimer, which accounts for about 25 wt % of the product mixture. Roughly 90% of the butene oligomer mixture consists of Ce dimer and Ci₂, C-ie, C20, and C₂₄ oligomers, and there are essentially no oligomers larger than C3₂. After removing the C₈ dimer, hydrogenation (about 0.08 wt % PtO₂/H₂, 2 psig) of the remaining oligomers yields a potential diesel fuel that has a flash point (ASTM D93) of 59 °C, viscosity of 103 cSt (ASTM D445 at -20 °C), and a lubricity value of 0.45 mm [ASTM 6079, high frequency reciprocating rig (HFRR)]. All ASTM tests herein were performed at the Southwest Research Institute, San Antonio, TX 78238 (www.swri.org). Interestingly, this fuel does not show any sign of freezing (or cloudiness) when cooled to -60 °C. When this fuel blend is subjected to a second high-temperature distillation, a colorless viscous oil residue is left behind that accounts for about 1 1 % of the total fuel production. It is this oil fraction that leads to the good lubricity value for the fuel. It is important to note that incremental jumps are made in 4-carbon units, the reaction is highly regioselective based on GC-MS data, and the fuels generated in this process are 100% iso-paraffinic. The branching is quite distinctive in that ethyl groups are located at regular positions along the carbon main chain of the oligomer. Furthermore, not only does this fuel have extensive branching, it contains a mixture of diastereoisomers that are produced as a consequence of the chiral carbon centers (marked with an asterisk in Scheme 1 ) generated at the branch points. The diastereoisomers have different physical properties (e.g., boiling point) and can be clearly observed in both the nuclear magnetic resonance (NMR) spectra and GC-MS chromatograms. For example, the hydrogenated tetramer has three chiral centers. Using the standard formula of 2n (where n is the number of chirai centers) will have 8 possible stereoisomers. This consists of 4 pairs of enantiomers and 4 different diastereoisomers.

[0034] Hence, after hydrogenation of the trimer and generation of a second chirai center, two major peaks in the GC-MS chromatogram are observed. This observation is consistent with the structures shown in Scheme 1 and the regiochemistry anticipated from the earlier work of Kaminsky (above) on the ZN-catalyzed reactions of 1-butene.

Scheme 1

Cp₂ZrC!₂

MAO

dimer Irimer

[0035] By making a change in catalyst preparation, it is possible to produce a significant change in the resulting oligomer distribution toward lighter oligomers; however and importantly, the complete, or near complete, conversion of 1 -butene remains unchanged. The catalyst is first formed in solution, then dried under vacuum and suspended in a small volume of hydrogenated butene dimer (3-methyl-heptane) derived from a previous run. This allows for reaction in which the solvent is primarily the reactant, 1 -butene, without the need for addition of other solvent. This approach results in a mostly heterogeneous catalyst (i.e., the catalyst is dispersed in the solvent, but is not in solution, or is present in solution in only very low concentration). Using this heterogeneous, unsupported catalyst in the reaction results in a remarkable product distribution consisting primarily of dimer, trimer, and tetramer, but without production of heavy oligomers and polymer. This metallocene based unsupported heterogeneous catalyst method is a novel approach that results in a unique product distribution. Thus, it is shown herein that if, after removal of the toluene, the aluminum/zirconium catalyst is slurried in hydrogenated dimer and then delivered to the reactor, the surprising result is: (1 ) complete, or essentially complete, conversion of 1 -butene to oligomers as evidenced by a partial vacuum after completion of the reaction and the yield of oligomers obtained from the initial reactants; (2) an about 12 wt % increase in 2-ethyl-1 -hexene dimer produced; and, (3) a decrease of high-molecular-weight oligomer generated, with the distribution defined by Mr\ about 176, Mw about 21 1 , and Mw/Mn about 1 .2, where, Mn is number average molecular weight, Mw is weight average molecular weight, and Mw/Mn is the polydispersity (Figure 1 ). This distribution can be observed in Figure 1 which is a plot of a GC-MS total ion chromatogram for the oligomers produced from 1 - butene (Al/Zr: 100) using the catalyst made by removal of the toluene and delivering the zirconium/MAO as a slurry in hydrogenated dimer (in this example, 3-methyl heptane). It will be understood by one of ordinary skill in the art that any lower molecular weight C₄ to about Cio alkane may be used in place of 3-methyl-heptane, such as for example, butane, pentane, hexane, heptane, octane, and branched chain alkanes. Figure 2 is a relative area integration for each of the oligomers by carbon number for the GC-MS chromatogram of Figure 1. The relative abundance areas are derived from the total ion count for the peaks of that particular set of oligomers (e.g., C₂₄). Typically yields of 98% or more are obtained with some loss of product due to filtration, handling and transfer. This advantageously also enables the entire procedure to be performed using simple Schlenk techniques while avoiding using a glovebox. While the exact chemical differences/changes in the new active catalyst are not defined; the results are very consistent from run to run for this new catalyst preparation. In general, distillation is used to remove the 2-ethyl-1 -hexene dimer, and the resulting fuel blend of oligomers minus the dimer is subjected to hydrogenation. Using the new catalyst formulation, a significant decrease in viscosity is observed, down to 12.5 cSt, (entry 1 in Table 1) compared to products prepared using other catalyst formulations. It is possible to further tailor the cold-flow viscosity by back-addition of hydrogenated Ce dimer. Thus, by adding 6.6 wt % (entry 2 in Table 1) of the dimer, the viscosity decreases to 8.5 cSt, which is quite close to JP-8 (8.0 cSt) and does meet the JP-5 (8.5 cSt) specification.

Table 1. Viscosity Data (ASTM D445, -20 °C) for Fuel Blendsa

a Catalyst delivered as a slurry in hydrogenated dimer.

[0036] Further dilution with the C₈ dimer brings the viscosity down to an impressive 6.0 cSt at -20 °C (entry 4 in Table 1 ). As anticipated, there is a decrease in fuel density as the dimer concentration increases. Carrying out a high-temperature distillation to 313 °C leaves a colorless pot residue of less than 1 wt % and physically/experimentally confirms the decrease in high-molecular-weight oligomer content. For the fuel blend of entry 1 in Table 1 , elemental analysis indicates 85% carbon and 15 wt % hydrogen, which is consistent with a fully saturated hydrocarbon. It follows that the calculated heat of combustion is greater than 44+ MJ/kg or 34.3+ MJ/L. The heat of combustion is calculated for the stoichiometric reaction with oxygen to form carbon dioxide and water using an average formula of Ci₆H₃4. The elemental analysis was performed at Atlantic Microlab, Inc., Atlanta, GA.

[0037] Although demonstrating an overall efficient use of the reduced-carbon source (i.e., 1 -butene), a means of taking the olefinic dimer and converting it to a higher boiling material [e.g., Ci6 compound(s)] is also desirable. The latter could then be blended with little negative effect on the flash point of the fuel. Thus, treatment of 2-ethyl-1 -hexene with concentrated sulfuric acid leads to rapid conversion to a complex mixture of monounsaturated Ci₆ alkenes (Scheme 2). The proton and carbon NMR spectral data for the product mixture are quite complicated, as is shown in Figure 3 for an ¹ H NMR spectrum of butene oligomers and in Figure 4 for an ¹ H NMR spectrum of hydrogenated butene oligomers. However, the GC-MS data, as is shown in Figure 5 for a gas chromatogram of hydrogenated butene oligomers, in Figure 6 for a gas chromatogram of distilled fuel, and Figure 7 for an ¹ H (top frame) and ¹³C (bottom frame) NMR spectra of the product mixture from sulfuric acid dimerization of 2-ethyl-1 -hexene, is consistent with an elution time that is expected for Ci6 isomers, and most importantly, a molecular ion peak of 224 is observed for each peak in the GC-MS chromatogram, with very small amounts of 238 molecular ions (C₁₇ alkenes) indicated.

[0038] The mixture of Ci6-alkene isomers has a measured density of about 0.80 g/mL that is similar to pure linear n-hexadecane (0.773 g/mL). One of the unique and useful features for these 1 -butene derived fuels is the high degree of branching (100%) yet a good overall retention of fuel density. It is noted that although for jet fuels cetane rating is not specified nor directly related to any performance parameter, there is interest to further evaluate these fuels for their respective cetane and octane ratings. Extensive and regular ethyl branching is not typically found in fuel blends; therefore, an appropriate model for predicting a cetane rating is not presently available. Fuel density is an important parameter that contributes to meeting fuel performance requirements and may ultimately determine if a biojet version of JP-5/JP-8 can indeed meet or exceed mission critical Department of Defense (DoD) requirements.

Experimental

[0039] General Methods. All organometallic manipulations were carried out using standard Schlenk techniques under an atmosphere of purified nitrogen or in a glovebox. 1 -butene (CP grade) was purchased from Specialty Gas Concepts, stirred over CaH₂, and degassed prior to use. MAO (10% in toluene) and PtO₂ were purchased from Aldrich and used as received. Cp₂ZrCI₂ was purchased from Strem and used as received. Butene oligomerization reactions were conducted in a 750 mL stainless steel Parr reactor fitted with a glass insert. ¹H and ¹³C NMR spectra were collected on a Bruker Avance II 300 MHz spectrometer in CDCI₃ and referenced to the residual solvent peaks (¹H, _ 7.27; ¹³C, _ 77.16). Fuel samples were analyzed for viscosity (ASTM D445 at -20 °C), lubricity (ASTM D6069, HFRR), and flashpoint (ASTM D93) at Southwest Research Institute.

[0040] GC/MS Analysis Methods. 0.5 mg of oligomer mixture was dissolved in 1.0 mL of methylene chloride. 1 ί of sample was injected into an Agilent 6890 gas chromatography (GC) system equipped with a Restek RTX-5MS 30-meter column. The GC inlet temperature was 250 °C, the initial column temperature was 40 °C held at 3 min, and the temperature was increased at 10° C/min up to a final temperature of 350 °C. An Agilent mass selective detector 5973 system was used to identify the sample components.

[0041] Synthesis of Butene Oligomers (Method A). Utilizing Schlenk techniques, Cp₂ZrCI₂ (70 mg, 0.24 mmol) was dissolved in MAO solution (16.5 mL, 25 mmol) to yield a pale yellow solution which was stirred at ambient temperature for 1 h. The resulting golden colored solution was then stripped of solvent under reduced pressure (0.1 mm Hg) to give a yellow solid. The flask was taken into a glovebox and the solid transferred to a bomb. The bomb was then removed from the glovebox and packed in dry ice. 1 - butene (375 mL, 4.22 mol) was condensed into the bomb which was sealed, placed on a stir plate, allowed to warm to room temperature, and allowed to react for 16 h with stirring. A port on top of the bomb was opened (with a nitrogen purge) and this released a significant partial vacuum due to the complete_conversion of butene to oligomers. The catalyst was quenched with distilled water (1 mL) and the mixture was stirred for 1 h. The top portion of the bomb was completely removed to reveal a white heterogeneous mixture smelling strongly of olefins. This mixture was filtered through a short plug of basic alumina (2 cm) and glass wool to yield 230 g (97%) of butene oligomers.

[0042] Synthesis of Butene Oligomers (Method B). The activated catalyst solution was prepared as above. The solvent was removed under reduced pressure (0.1 mm Hg) and dry 3-methyl heptane (10 mL), was added to the flask with vigorous stirring to form a pale yellow slurry that was then transferred via a syringe into the bomb. The oligomerization reaction was then carried out as above. Yields were similar to Method A.

[0043] Hydrogenation of Butene Oligomers. Butene oligomers (400 g) were placed in a 3-neck flask with a gas outlet. The solution was degassed and the atmosphere was replaced with nitrogen. PtO₂ (400 mg, 1.76 mmol) was added and the mixture was placed under a continuous hydrogen pressure of 2 psig. One of ordinary skill in the art will understand that butene oligomers may also readily be hydrogenated under pressure using nickel catalysts. The reaction could be conveniently monitored by NMR spectroscopy, but flocculation of the catalyst occurred upon completion of the reaction and was subsequently used to determine the end point. After 24 h the reaction mixture was filtered through glass wool to give a quantitative yield of colorless liquid.

[0044] Dimerization of 2-ethyl-1-hexene. A flask was charged with sulfuric acid (98%, 0.3 mL) and 2-ethyl-1-hexene (4.45 g, 40 mmol) in that order. There was an initial exotherm upon mixing. The heterogenous mixture was allowed to react with stirring at ambient temperature for a period of 16 h. The colorless organic layer was separated and washed with aqueous Na₂CO₃ solutions (3x3 mL), followed by distilled water (3 mL) and analyzed by GC/MS, ¹H and ¹³C NMR spectroscopy. Most of the peaks observed by GC/MS have molecular ion peaks of 224 and eluted in the range of 15-17 min, suggesting that primarily dimerization had taken place without a significant amount of cracking. The NMR spectra of the mixture were complex due to the formation of several isomers, yet the ratio of aliphatic protons to olefinic protons determined by NMR spectroscopy was consistent with an average formulation of ΟιβΗ₃₂ based on the assumption that primarily tri-substituted olefins were formed by the acid catalysis.

[0045] By tuning the catalyst and then using the dimer produced, the carbon use can be brought to about 95% or greater. This latter point will be particularly important in the future, where the source of raw materials (i.e., biomass/biofeedstock) is limited. Also noteworthy, the batch catalysis approach herein requires a minimal input of energy and hydrogen to make fuels that possess useful flash points, coldflow properties, and solution density/energy content. This new process affords a saturated hydrocarbon fuel that has a higher solution density and thus possesses a higher calculated power density (per volume) than similar fuels made by the GTL Fischer-Tropsch processes.

Claims

CLAIMS What is claimed is:

1. A process for conversion of 1 -butene to butene oligomers characterized by: activating a bis(cyclopentadienyl)zirconium dichloride pre-catalyst with methylaluminoxane in an organic solvent;

optionally, removing the solvent to form an activated catalyst;

mixing a C4-C10 alkane with the activated catalyst to form a slurry;

adding dried 1 -butene to the slurry to form a mixture; and

stirring the mixture to allow contact of 1 -butene with the activated catalyst at ambient temperature in a gas tight vessel until reaction is complete to form a first mixture of butene oligomers.

2. The process of claim 1 further characterized by said solvent being an aromatic solvent and is without heteroatoms.

3. The process of claim 1 or 2 further characterized by:

distilling the first mixture of butene oligomers to remove the C4-C10 alkane forming a second mixture of butene oligomers.

4. The process of claim 3 further characterized by:

hydrogenating the second mixture of butene oligomers to form a first mixture of hydrogenated oligomers.

5. The process of claim 4 further characterized by:

formulating the first mixture of hydrogenated oligomers with 3-methyl heptane as the C4-C10 alkane to form a fuel having a viscosity at -20 °C of from 6.0 cSt to 12.5 cSt, a density of from 0.75 g/mL to 0.80 g/mL, and a flash point of at least 59 °C.

6. The process of claim 4 further characterized by the flash point being at least

61 °C:

7. The process of claim 4 further characterized by: formulating the first mixture of hydrogenated oligomers with 3-methyl heptane to form a fuel suitable for turbine engines.

8. The process of claim 1 , further characterized by the C4-C10 alkane comprising 3-methyl heptane.

9. The process of claim 1 further characterized by the stirring the mixture to allow contact of 1-butene with the activated catalyst is performed at an ambient temperature of up to 70°C.

10. The process of claim 1 further characterized by the butane oligomers comprising de oligomers.

11. The process of claim 1 further characterized by: the first reaction mixture comprising 2-ethyl-1-hexene, distilling the first reaction mixture to recover the 2-ethyl-1- hexene, mixing the 2-ethyl-1 -hexene with concentrated sulfuric acid to form a heterogeneous mixture; stirring the heterogeneous mixture to allow contact of reactants at ambient temperature until reaction is complete to form a reaction mixture; separating the organic phase from the aqueous phase of the reaction mixture; and isolating butene oligomers from the organic phase.

12. The process of claim 11 further characterized by the C₄-Ci₀ alkane comprising 3-methyl heptane.

13. The process of claim 1 further characterized by the forming of the slurry further comprising including an aromatic solvent, which is without heteroatoms, with the C₄- C-10 alkane and activated catalyst.

14. A catalytic agent produced by the steps comprising:

mixing bis(cyclopentadienyl)zirconium dichloride with methylaluminoxane in a solvent; removing the solvent to form a residue; and

adding dried 1-butene to slurry to form a mixture stirring the mixture to allow contact of reactants at ambient temperature in a gas tight vessel until reaction is complete to form a first mixture of butane oligomers.

15. The catalytic agent of claim 14 further characterized by said solvent being an aromatic solvent without heteroatoms.

16. A process for converting 1 -butene to C-ie butene oligomers characterized by: mixing bis(cyclopentadienyl)zirconium dichloride with methylaluminoxane in a solvent for the methylaluminoxane;

removing the solvent to form an activated catalyst;

mixing 3-methyl heptane with the activated catalyst to form a slurry;

adding dried 1-butene to the slurry to form a mixture;

stirring the mixture to allow contact of reactants at ambient temperature in a gas tight vessel until substantially all 1 -butene has been reacted to form a first reaction mixture containing 2-ethyl-1 -hexene;

distilling the first reaction mixture to recover 2-ethyl-1 -hexene;

mixing the 2-ethyl-1 -hexene with concentrated sulfuric acid to form a heterogeneous mixture;

stirring the heterogeneous mixture to allow contact of reactants at ambient temperature until reaction is complete to form a second reaction mixture comprising an organic phase and an aqueous phase;

separating the organic phase from the aqueous phase of the second reaction mixture; isolating butene Cie oligomers from the organic phase.

17. The process of claim 16 further characterized by said butene C₁₆ oligomers being hydrogenated to form a turbine engine fuel mixture.

18. The process of claim 16 further characterized by said solvent being an aromatic solvent without heteroatoms.

19. A process characterized by:

activating a bis(cyclopentadienyl)zirconium dichloride pre-catalyst with methylaluminoxane in asolvent;

removing the solvent from the activated catalyst;

mixing aromatic solvent, which is without heteroatoms, with the activated catalyst to form a slurry; adding dried 1-butene to the slurry; and

allowing contact of the activated catalyst with 1-butene in a gas tight vessel to form a mixture of butene oligomers.