This invention relates a process for making cyclopentadiene oligomers which are useful as high density fuels. The invention further provides a high density fuel comprising these cyclopentadiene oligomers. U.S. Patent 4,059,644 to Cannell discloses a method for producing high-energy fuels by thermal (non-catalytic) reaction of a mixture of cyclopentadiene dimer and methyl cyclopentadiene dimer at 150-220°C, and subsequent hydrogenation of the olefinic unsaturation in the oligo eric product mixture.

U.S. Patent 4,401,837 to Burdette et al. discloses a method for synthesizing cyclopentadiene trimers and higher molecular weight oligomers from cyclopentadiene dimer via thermal (non-catalytic) Diels-Alder reactions. The trimer fraction of the intermediate oligomeric product is then treated in the presence of a hydrogenation catalyst to saturate the olefinic bonds. While the initial thermal reaction produces trimers, tetramers, and pentamers, only the trimer fraction is used for the high density fuel product. After the initial reaction, the mixture is hydrogenated to saturate the olefinic bonds and distilled to recover the C ₁₅ trimer. Thus the formation of higher molecular weight oligomers (C ₂₀₊ ) represents yield loss. The trimer, after hydrogenation, is a solid at room temperature with a melting point of +49°C. This trimer is then dissolved in methylene chloride and isomerized at 0- 20°C using aluminum chloride as catalyst. The isomerized product is subsequently recovered by distillation.

These prior art processes produce a normally solid intermediate product (after hydrogenation) which must then be isomerized to form a normally liquid product. Further, the prior art processes sacrifice yield because only a portion of the oligomerized intermediate product (the trimer) is used for upgrading to the final high density

fuel product. Thus it would be desirable to provide a process which avoids the costly isomerization step. Further, it would be desirable to provide a process which enhances yield by incorporating substantially all of the oligomerized intermediate product into the final high density fuel product.

This invention comprises a two-step process for converting cyclopentadiene dimer to a high density fuel mixture comprising the steps of: (a) reacting the cyclopentadiene dimer in the presence of a solid catalyst comprising a porous crystalline material having a Constraint Index of from about 0.1 to about 12 under oligomerization/isomerization conditions to convert at least a portion of the cyclopentadiene dimer to a normally liquid intermediate product containing cyclopentadiene trimer, cyclopentadiene tetramer, and the isomerized and oligomerized products derived from the reaction of at least three cyclopentadiene monomer units; (b) catalytically hydrogenating at least a portion of the normally liquid intermediate product of step (a) to form a normally liquid high energy density fuel.

The per-pass conversion in oligomerization/isomerization step (a) is preferably controlled to less than 100%. Extremely high single pass conversions in step (a) tend to increase the yield of C ₂₀₊ constituents, thus compromising the low temperature properties (such as pour point, cloud point, and freeze point) of the resulting fuel. Accordingly, per-pass conversions of from about 20 to about 80 weight percent are preferred, and per-pass conversions of from about 40 to about 60 weight percent are more preferred.

In one preferred embodiment, the unoligomerized dicyclopentadiene is separated from the total reaction product by distillation prior to hydrogenation, and recycled to step (a) for reuse. The recycled stream is

typically enriched in non-oligomerized C ₁₀ material. The low temperature properties of the final product may be adjusted by controlling the flow of the recycle stream to step (a) . Removing and recycling a portion of the C ₁₀ material from the effluent of step (a) improves the energy density of the resulting final product, but this improvement must be balanced against the necessary low- temperature properties, which are enhanced by relatively smaller recycle ratios. The amount of non-oligomerized C ₁₀ material separated for recycle typically falls within the range of from 0 to 100%, typically from 20 to 100%, and preferably the necessary amount to achieve the desired low temperature properties. This recycle ratio may be determined for a particular product specification with a minimal amount of trial and error. In a particularly preferred embodiment, 100% of the unreacted dicyclopentadiene is recycled. The recycled C ₁₀ fraction is typically separated from the step (a) effluent stream by conventional distillation methods. In another preferred embodiment, the total effluent from the oligomerization step, containing dicyclopentadiene which has been isomerized but not oligomerized in addition to the C ₁₅ + oligomeric product, is charged directly to the hydrogenation step with no intermediate distillation step. In the subsequent hydrogenation step, this isomerized dicyclopentadiene is converted to JP-10, a current military fuel and preferred diluent used to impart improved low- temperature properties to the fuel in applications where this is desired. The crystalline materials useful as oligomerization/ isomerization catalyst components in the present process have an effective pore size of generally from about 5 to about 8 Angstroms, such as to freely sorb normal hexane. In addition, the structure must provide constrained access to larger molecules. It is sometimes possible to judge from a known crystal structure whether such constrained

access exists. For example, if the only pore windows in a crystal are formed by 8-membered rings of silicon and aluminum atoms, then access by molecules of larger cross- section than normal hexane is excluded and the zeolite is not of the desired type. Windows of 10-membered rings are preferred, although, in some instances, excessive puckering of the rings or pore blockage may render these zeolites ineffective.

Although 12-membered rings in theory would not offer sufficient constraint to produce advantageous conversions, it is noted that the puckered 12-ring structure of TMA offretite does show some constrained access. Other 12-ring structures may exist which may be operative for other reasons, and therefore, it is not the present intention to entirely judge the usefulness of the particular zeolite solely from theoretical structural considerations.

A convenient measure of the extent to which a zeolite provides control to molecules of varying sizes to its internal structure is the Constraint Index of the zeolite. The process by which the Constraint Index is determined is described in U.S. Patent Number 4,016,218. U.S. Patent Number 4,696,732 discloses Constraint Index values for typical zeolite materials and is incorporated by reference as if set forth at length herein. In a preferred embodiment, the catalyst is a zeolite having a Constraint Index of between 0.1 and 12. Examples of such zeolite catalysts include ZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35, ZSM-48, as well as MCM-22, PSH-3 , SSZ-25, and zeolite Beta. Zeolite ZSM-5 and the conventional preparation thereof are described in U.S. Patent Number 3,702,886. Other preparations for ZSM-5 are described in U.S. Patent Numbers Re. 29,948 (highly siliceous ZSM-5) ; 4,100,262 and 4,139,600. Zeolite ZSM-11 and the conventional preparation thereof are described in U.S. Patent Number 3,709,979.

Zeolite ZSM-12 and the conventional preparation thereof are

described in U.S. Patent Number 3,832,449. Zeolite ZSM-23 and the conventional preparation thereof are described in U.S. Patent Number 4,076,842. Zeolite ZSM-35 and the conventional preparation thereof are described in U.S. Patent Number 4,016,245. Another preparation of ZSM-35 is described in U.S. Patent Number 4,107,195. ZSM-48 and the conventional preparation thereof is taught by U.S. Patent 4,375,573. Zeolite Beta is taught by U.S. Patents 4,696,732, 3,308,069, 5,275,719, 5,258,114, and Re. 28,341. Gallium-containing catalysts may be used in the present invention and are disclosed in U.S. Patent No. 4,350,835 and U.S. Patent No. 4,686,312.

Zinc-containing catalysts may be used in the present invention, for example, U.S. Patent No. 4,392,989 and U.S. Patent No. 4,472,535.

Catalysts such as ZSM-5 combined with a Group VIII metal described in U.S. Patent No. 3,856,872 are also useful in the present invention.

Synthetic porous crystalline materials useful in the present invention also include the PSH-3 composition of U.S. Patent 4,439,409, the SSZ-25 composition of U.S. Patents 4,665,110 and 4,826,667, and the MCM-22 composition of U.S. Patent 4,954,325. MCM-22 is also described in U.S. Patents 4,992,615, 5,012,033, and 5,073,665. The synthetic porous crystalline material, or zeolite, catalyst preferred for use in the process of this invention, referred to herein as "zeolite MCM-22" or simply "MCM-22", appears to be related to the composition named "PSH-3" described in U.S. Patent No. 4,439,409. Zeolite MCM-22 does not appear to contain all the components apparently present in the PSH-3 compositions and is not contaminated with other crystal structures such as ZSM-12 or ZSM-5. Moreover, zeolite MCM-22 exhibits unusual sorption capacities and unique catalytic utility when

compared to the PSH-3 compositions synthesized in accordance with U.S. Patent No. 4,439,409.

Hydrogenation catalysts useful in the second step of the present process include oxides and sulfides of Groups IVA, VA, VIA, VIIA and VIIIA and mixtures thereof on an inert support such as alumina, silica-alumina, active carbon or kieselguhr. Thus, hydrogenation may be promoted by sulfides and oxides of titanium, zirconium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten and mixtures thereof. Oxides of chromium alone or in conjunction with other catalytically active species have been shown to be particularly useful in hydrogenation. Other catalytically active compounds include sulfides and oxides of manganese, iron, cobalt, rhodium, iridium, nickel, palladium, platinum and mixtures thereof.

The above-listed metals of Groups IVA, VA, VIA, VIIA and VIIIA may also be exchanged onto zeolites including those zeolites disclosed above to provide a zeolite catalyst having hydrogenation activity. Platinum has been found to be particularly useful for promoting hydrogenation over zeolite catalysts.

Process conditions useful in the oligomerization/ isomerization step of the present invention are shown below.

Catalytic Oligomerization Conversion Conditions

Useful Typical Preferred

Temperature, °C 75 to 275 100 to 250 125 to 225

Pressure, kPa 103 to 7000 103 to 5275 103 to 3550 (psig) (0 to 1000) (0 to 750) (0 to 500)

WHSV, hr.- ¹ 0.05 to 10 0.05 to 7 0.1 to 5

Process conditions useful in the hydrogenation step of the present invention are shown below.

Catalytic Hydrogenation Conditions

Useful Typical Preferred

Temperature, °C 75 to 250 75 to 200 100 to 175

Hydrogen Partial 103 to 7000 103 to 3550 103 to 1830

Pressure, kPa (0 to 1000) (0 to 500) (0 to 250)

(psig)

WHSV, hr. ^"1 0.05 to 10 0.05 to 5 0.1 to 0.3

Figure 1 shows the effect of dicyclopentadiene feed conversion (the x-axis) on the ratio of C ₁₅ oligomers to C ₂₀₊ oligomers in the reactor effluent stream. Figure 2A is a chromatogra of a dicyclopentadiene feed which has been thermally oligomerized to form a product containing cyclopentadiene trimers.

Figure 2B is a chromatogram of a dicyclopentadiene feed which has been catalytically oligomerized in the presence of a ZSM-5 catalyst to form a more complex product mixture than that produced by the thermal process of Figure 2A.

Examples Example 1 3285 grams of cyclopentadiene dimer (95% pure) were charged to an agitated one-gallon glass reactor together with 150.0 grams of ZSM-5 zeolite extrudate catalyst. The reactor was blanketed with nitrogen, heated to 150°C and the reaction allowed to proceed at 150°C for 12.2 hours at ambient pressure. The reactor was then cooled to room temperature and analysis by gas chromatography showed 48% of the cyclopentadiene dimer had been converted to cyclopentadiene oligomers having carbon numbers of C ₁₅ and higher. This reaction product was then transferred to a distillation system and the unreacted cyclopentadiene dimer removed by distillation for subsequent recycle. The total bottoms from the distillation, consisting of the C ₁₅ and higher cyclopentadiene oligomers, was a low-viscosity

liquid at room temperature having a specific gravity of 1.073, a pour point of -32°C and a net heat of combustion of 10382 kcal/1 (156,595 BTU/gallon) . After a sample was taken, the remaining C ₁₅ + oligomeric mixture was hydrogenated using a 5% Pd/Carbon catalyst at 125°C and 900 psi hydrogen pressure to reduce the olefinic unsaturation. The resulting hydrogenated product was a low-viscosity liquid at room temperature having a specific gravity of 1.044, a freezing point of -3 °C and a net heat of combustion of 10290 kcal/1 (155,213 BTU/gallon). Example 2

2053 grams of cyclopentadiene dimer (95% purity) were charged to an agitated one-gallon glass reactor together with 94.2 grams of zeolite beta extrudate catalyst. The reactor was blanketed with nitrogen, heated to 150°C and the reaction allowed to proceed at 150°C for 13 hours at ambient pressure. Analysis by gas chromatography showed 45% conversion of the cyclopentadiene dimer had been converted to cyclopentadiene oligomers having carbon numbers of C ₁₅ and higher. The reaction product was then transferred to a distillation system and the unreacted cyclopentadiene dimer removed by distillation for subsequent recycle. The total bottoms from the distillation, consisting of the C ₁₅ and higher cyclopentadiene oligomers, was a low-viscosity liquid at room temperature having a specific gravity of 1.073, a pour point of -32°C and a net heat of combustion of 10260 kcal/1 (154,741 BTU/gallon). After a sample was taken, the remaining C ₁₅ and higher oligomeric mixture was hydrogenated using a 5% Pd/Carbon catalyst at 125°C and 6200 kPa (900 psi) hydrogen pressure. The resulting hydrogenated product was a low-viscosity liquid at room temperature having a specific gravity of 1.038, a pour point of -34 °C and a net heat of combustion of 10224 kcal/1 (154,211 BTU/gallon).

Example 3

3100 grams of cyclopentadiene dimer (95% pure) were charged to an agitated one-gallon stainless steel reactor together with 150 grams of a catalyst containing zeolite Beta loaded with 0.6 wt% platinum. The reactor was blanketed with nitrogen, heated to 150°C and the reaction allowed to proceed at 150°C for 29.8 hours. Analysis by capillary GC showed 47.5% of the cyclopentadiene dimer was converted to C ₁₅ and higher polyclopentadienes. The reactor was then cooled to 125°C and pressurized with hydrogen, and the hydrogenation allowed to proceed for 28.3 hours at 125°C with 6200 kPa (700 psig) hydrogen pressure and 4 hours at 125°C with 6200 kPa (900 psig) hydrogen pressure. The hydrogenated product was a very low viscosity liquid at room temperature with a specific gravity of 1.013, a heat of combustion of 9975 kPa/1 (150,452 BTU/gallon) and a minimum cold-flow temperature (pour point) of <-54°C. Analysis by gas chromatography showed the product to contain 46.8% C ₁₅ and higher 3,4,8,9- tetrahydropolycyclopentadienes, 38.6% exo-3,4,8,9- tetrahydrodicyclopentadiene (JP-10), 8.6% endo- 2, 3 , 8, 9-tetrahydrodicyclopentadiene and 6.0% other components comprising impurities in the cyclopentadiene dimer reactant and minor reaction products.