FIELD OF THE INVENTION

This invention is an acid catalyzed process for producing 2,6- dimethyldecalin from cyclohexyl compounds and naphthenic compounds or naphthenic compound precursors such as cyclohexane or methylcyclopentane.

BACKGROUND OF THE INVENTION

Thermotropic liquid crystal polymers ("LCP's") are high molecular weight materials which can exist in a so-called "liquid crystalline state" where the material has some of the properties of a liquid (in that it can flow) but retains the long range molecular order of a crystal. The term "thermotropic" refers to the class of LCP's which are formed by temperature adjustment. LCP's may be prepared from p.p'-dihydroxy-aromatics or dicarboxy-aromatics. Although these LCP's are easily molded, these polymers retain the necessary interpolymer attraction at room temperature to act as high strength plastic artifacts such as fibers or films. The p.p'-dihydroxy- and dicarboxy-aromatics desirably contain polynuclear aromatic moieties such as those based on biphenyl and naphthalene. These monomers are, however, difficult to synthesize. They may be made using the corresponding p.p'-dialkyl-poiynuclear aromatic compounds. However, these compounds are also difficult to synthesize. A suitable route to those dialkylates from biphenyl and naphthalene using direct alkylation is shown in WO 90/03961 t Fellmann et al. (published April 19, 1990). Fellmann .sLaJ. shows a process for selective diisopropyiation of naphthyl compounds using certain acidic molecular sieve catalysts. A less selective process for the production of p,p'-aromatic dialkylates is shown in EP 0,317,907 to Lee el_aj.

U.S. Patent No. 4,795,847 to Weitkamp elaj. similarly shows a process for the production of 2,6-dialkylnaphthalenes by alkylating naphthalenes or ø-alkyl- naphthalenes with alcohols, alkyl ethers, or alkylchlorides using a zeolite such as

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ZS -5. This process exhibits low conversion and a low selectivity based on the alcohol alkylating agent. There are a few known processes for making p,p'- polyπuclear aromatic dialkylates which do not involve the direct alkylation of the polynuclear aromatic core. These processes are generally classified in two groups. One group involves the acylation or alkylation of toluene or xylenes with various uπsaturated hydrocarbons. An example of this synthesis route is the process shown in U.S. Pat. Nos. 3,244,758 and 4,740,647, in which 2,6-dimethyl naphthalene is produced from o-xyfene and butadiene, using the following steps:

1. catalytic carbionic addition of butadiene to o-xyleπe to yield 5-(o- tolyl)-2-pentene;

2. cyclizatϊon of 5-(o-tolyl)-2-pentene to 1,5-dimethyltetraliπ;

3. dehydrogenation of 1,5-dimethyltetraliπ to 1,5-dimethylnaphthalene; 4. isomerizatioπ of 1,5-dimethyfπaphthalene to 2,6-dimethylnaphthalene.

Another process developed by Mitsubishi and shown in European Patent 362,507, involves the acylation of toluene with 1-butene and carbon monoxide to produce p-tolyl sec-butyl ketone. The carbonyl group of the p-tolyl sec-butyl ketone is then hydrogenated to yield p-tolyl sec-butyl carbinol. The p-tolyl sec- butyl carbinol can undergo either dehydrogenation and cyclization to yield 2,6- dimethylπaphthalene directiylor ddehydration first to give 2-methyl-(p-tolyl)-butene with subseqent dehydrogenation and cyclization to yield 2,6-dimethylnaphthalene. Japanese patent 296,540, also assigned to Mitsubishi, shows a process in which m-xylene, propylene, and carbon monoxide are subjected to an acylation reaction to produce 2,4-dimethyl-isobutyrophenone, followed by hydrogenation of its carbonyl group, dehydrogenation, and cyclization to yield 2,6- dimethylnaphthalene.

These processes suffer from the afflictions of expensive feedstocks, large recycle streams, and costly catalytic steps.

The other process group involves the synthesis of dimethyldecalins and

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their subsequent dehydrogenation to dimethylnaphthalenes.

In making use of this latter method, a source of dimethyldecalin is required. For example, U.S. Patent No. 3,243,469 to Schneider discloses a method for the preparation of 2,6-dimethyldecaiin by isomerization of a dicyclic naphthene of twelve carbon atoms utilizing a catalyst system of aluminum halide and hydrogen halide at a temperature of -10 ^* C to 60 ^* C. The isomerization product is an equilibrium mixture of dimethyldecalins and the 2,6-isomer is separated from the equilibrium mixture by fractional crystallization at a temperature below -10'C. The other isomers are recycled to the isomerization step for further equilibration, ultimately to convert the original dicyclic naphthenes to 2,6-dimethyldecalin. Another patent to Schneider, U.S. Patent No. 3,346,656, discloses a method for preparing dimethyldecalins from naphthenes of six carbon atoms in which a naphthene of six carbon atoms or a mixture of such naphthenes is contacted at a temperature in the range of -20* C to 80* C with a preformed liquid catalyst complex obtained by reacting a paraffin hydrocarbon having at least seven carbon atoms per molecule with AICI ₃ -HCI or AIBr ₃ -HBr. Under such conditions, the naphthene precursor of six carbon atoms dimerizes to form a dicyclic naphthene of twelve carbon atoms which isomerizes to an equilibrium mixture of dimethyldecalins. A further patent to Schneider, U.S. Patent No. 3,219,718, discloses a method for the preparation of decalins by the rearrangement of uncondensed dicyclic naphthenes having two cyclohexyl rings with an aluminum halide- hydrogen halide catalyst. This patent discloses that any uncondensed dicyclic naphthene having twelve to 20 carbon atoms and two cyclohexyl rings in the presence of such catalyst at a temperature in the range of -20 ^* C to 70' C will rearrange to form decalins having the same empirical formulas as the dicyclic naphthene. The decalin mixture formed when relatively long reaction times are used is an equilibrium mixture of isomers having the same number of carbon atoms per molecule as the dicyclic naphthene used as the starting material. U.S. Patent No. 3,200,161 to Suld et al. discloses another method in which a dicyclic naphthene containing twelve carbon atoms is isomerized to a mixture of

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dimethyldecalins. The naphthene rings of the starting material may be either condensed or noncondensed. Any alkyl substituent or substituents on the rings may result in the naphthene having twelve carbon atoms. Disclosed sources of such starting materials include those prepared by separation from suitable petroleum fractions, hydrogenation of coal tar fractions, and dimerization of methylcyclopentane and/or cyclohexane. In the disclosed method, the dicyclic naphthene is contacted with a catalyst containing hydrogen fluoride, a promoter, and an initiator at a temperature in the range of -10'C to -60 ^* C. The promoter may be either boron trifluoride or an antimony pentafluoride. The initiator can be an olefiπ, alcohol, ether, or alkyl halide containing not more than five carbon atoms. Within a short time interval after isomerization commences, 2,6- dimethyfdecalin begins to precipitate. Thereafter, isomerization and precipitation occur simultaneously and continue until over 50 weight percent of the starting material has been recovered as solid 2,6-dimethyldecaliπ. A method disclosed in abandoned patent application Serial No. 69,798 filed

November 17, 1960, was reported in the aforesaid U.S. Patent No. 3,200,161 to Suld et al. That process involves isomeriziπg dicyclic naphthene containing twelve carbon atoms to an equilibrium mixture of dimethyldecalins in which 2,6- dimethyldecalin occurs in relatively high proportion. The dicyclic naphthene is contacted with an aluminum bromide-hydrogen bromide catalyst at a temperature in the range of from about 10'C to 60 'C. The 2,6-dimethyldecalin is separated from the resulting equilibrium mixture by cooling the mixture to about -20 'C to - 40 'C since the 2,6-isomer selectively crystallizes within that temperature range leaving the other isomers in the liquid phase. U.S. Patent No. 3,509,223 to Bushick et al. discloses a method for dimerizing monocyclic naphthenes in the presence of a catalyst system and a suitable hydrogen acceptor. Naphthenes containing six carbon atoms are suitable as a charge stock in such method. The catalyst system employed for the dimerization consists of hydrogen fluoride, a boron trifluoride, and a hydride acceptor-chain initiator. The hydride acceptor-initiator is an organic compound containing less than six carbon atoms, specifically an olefin or an alkyl halide,

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although alcohols and ethers are also functional. The naphthene or a mixture of such naphthenes is contacted with the catalyst system at a temperature in the range of -20 ^* C to 80' C. Under these conditions, the naphthene dimerizes to form a dicyclic naphthene containing twelve carbon atoms which then isomerizes to form an equilibrium mixture of dimethyldecalins. The equilibrium mixture contains approximately 30% each of 2,6- and 2,7-dimethyldecalins.

Two Japanese Kokai (49-1548 and 49-1549) describe a process for the production of 2,6-dimethyldecaliπ by contacting six carbon naphthenic hydrocarbons with a catalyst of HF and BF ₃ at a temperature between -20 ^* C and 120'C. A branched alkane (four to eleven carbon atoms), such as isohexane, is used as the reaction initiator in the earlier Kokai. An olefin of two to five carbon atoms is the initiator in the latter Kokai. Obviously, the reaction involves the dimerization of the feedstock to produce the 2,6-dimethyldecalin.

Two documents showing the non-initiated production of 2,6-dimethyldecalin are U.S. Patent No. 4,300,008 to McCauiay and Vol'pin, New Journal of

Chemistry, Vol. 13, p. 771 (1989). McCauiay shows a method in which a catalyst system of a hydrogen fluoride solution of tantalum and/or niobium pentafluoride is used both to synthesize 2,6-dimethyldecalin from a twelve carbon dicyclic naphthenic isomer and a mixture of 2,6-dimethyldecalin of twelve carbon dicyclic naphthenic isomer from methylcyclopentane and/or cyclohexane. McCauiay does not suggest the use of an initiator although the presence of hydrogen during the reaction seems to affect the dimerization reaction.

Vol'pin suggests the use of AIBr^acetyl halide catalyst in the production of dimethyldecalins utilizing free hexane or methylcyclopentane. The process is very inefficient since the acetyl halide also reacts with hexane and methylcyclopentane. None of these suggest an acid catalyzed process using both cyclohexyl compounds (such as cyclohexene or cyclohexyl halides) and inexpensive materials such as naphthenic materials or precursors such as cyclohexane or methylcyclopentane to prepare dimethyldecalins.

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SUMMARY OF THE INVENTION This invention is a process for producing dimethyldecalins, particulary 2,6- dimethyldecalin,. from streams containing cyclohexyl compounds such as cyciohexene or cyclohexylhaiide and streams containing naphthenic materials or naphthenic precursors such as the cyclic aikanes, e.g., cyclohexane and methylcyclopentane. The process uses an acid catalyst such as H ₂ S0 ₄ , HF, HCI, HBr, BF ₃ , TiCI ₃ , TiCl ₄ , AICI ₃ , and the like.

The 2,6-dimethyldecalins product stream may be separated using processes such as crystallization or adsorptive separation, then hydrogenated to 2,6-dimethylnaphthaleπe, and further reacted to 2,6-dihydroxynaphthalene or 2,6- dicarboxynaphthalene.

DETAILED DESCRIPTION OF THE INVENTION As noted above, this is an add catalyzed process for coupling naphthenic materials or cyclo-alkanes (preferably cyclohexane) using cyclohexyl compounds, typically as reactants. The desired products are dimethyldecalins, preferably 2,6- dimethyldecalin. The dimethyldecalin may be dehydrogenated to dimethyinaphthalene, again preferably to 2,6-dimethylnaphthalene:

EQUATION

Cyclo-alkanes + cyclohexyl compounds + acid catalyst ? dimethyldecalin

Feedstock

There are two feedstocks used in this process: the coupling material stream and the cyclohexyl stream.

Coupling Material Stream The coupling material stream comprises one or more naphthenic materails or naphthenic precursors.

If the coupling material is a naphthenic precursor, it is nominally a cydic C _β stream. These compounds may be cydohexane, methyicydopentane, dimethylcydobutane, ethylcydobutane, and mixtures thereof. The most desireable

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components are cyclohexane, methylcyclopentane, and mixtures. Other cyclic and linear alkanes, aromatics, and olefins may be present in the stream without particular harm to the operation of the process but the presence of certain components, e.g., benzene, xylenes, and diolefinic materials, could be viewed as undesirable because of the byproducts made. The liquid linear alkanes, e.g., C ₅ - C ₁₂ , are essentially unreactive in this reaction system and may be used if a diluent is needed.

Cyclohexyl Stream The cyclohexyl stream contains at least one of cyclohexene and cyclohexyl halides, preferably cyclohexyl chloride. Methylcyclopentyi halides are also acceptable cyclohexyl stream stream components.

Naphthenic Materials We have found that certain higher molecular weight naphtheinc materials may be used in lieu of or in addition to the naphthenic precursors noted above.

We have also found that our process tends to maximize the amount of C ₁₂ 's present in the dimethyldecalin product stream leaving the coupling step. The equilibrium concentration of 2,6-dimethyldecalin appears to be about 30% at the typical operating conditions we designate below. This approach to equilibrium appears to occur without regard to the C ₁₂ cyclic olefiπ or alkane material fed to the coupling step. Consequently, certain feeds containing C ₁₀ - C^ naphthenic materials may be used as feedstocks to the coupling step. These supplemental feeds may be a recycle feeds coming from the hydrogenation of dimethylnaphthalene produced as described below. The C ₁₂ source may be other than a recycle stream. For instance, streams from a fluid catalytic cracking unit known as a light cat cycle oils ("LCCO") or light gas oils ("LGO") contain significan amounts of C ₁₂ aromatics. These streams may be hydrogenated to naphthenics using known technology and introduced into the coupling step. The C ₁₂ 's in the stream are isomerized to the equilibrium mixture and non-C ₁₂ 's are cracked to form cyclohexane and methylcyclopentane which eventually form dimethyldecalins.

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Another suitable stream for introduction into the coupling step is one containing bicyclohexyl (or bicyclohexane). These may be obtained by the coupling of benzene or from the bottoms of a hydrodealkylation unit (after an additional dehydrogenation step). Although this latter stream contains only about 50% biphenyl, the stream may be hydrogenated using known hydrogenation technology and introduced into the coupling step.

The streams containing C^-C^ naphtheπics (containing one or more rings) may be introduced equally effectively into the coupling step with or without the introduction of cyclic alkanes into the coupling step.

Catalyst

The catalyst of this process is acidic and comprises one or more Lewis or Bronsted depending upon the selected operational conditions.

A Lewis acid is a molecule which can form another molecule or an ion by forming a complex in which it accepts two electrons from a second molecule or

* ion. Typical acceptable strong Lewis acids include mineral adds such as H ₂ S0 ₄ ,

HCI, HF, H ₃ P0 ₄ , and the like; boron halides such as BF ₃ , BCI ₃ , BBr ₃ , and Bl ₃ ; antimony pentachloride (SbF^; aluminum halides (AICI ₃ and AIBr^; titanium halides such as TiBr _4> TiCI ₄ , and TiCI ₃ ; zirconium tetrachloride (ZrCI ₄ ); phosphorus pentafluoride (PF^; iron halides such as FeCI ₃ and FeBr ₃ ; and the like. Weaker Lewis acids such as tin, indium, bismuth, zinc, or mercury halides are also acceptable. Preferred Lewis acids are SbF ₅ , AICI ₃ , and BF ₃ ; most preferred is BF ₃ . Certain Lewis add mixtures are known to provide desireable results: AIX ₃ -HX (where X is Cl or Br), HF-BF ₃ , and HF-MF _β (where M = Ta or Nb). Supported Lewis adds, such as AICI ₃ on chlorinated alumina, BF ₃ on transition aluminas or silica, platinum chloride on alumina or silica, and BF ₃ on zeolites. Most of these catalyst have the ability to cause the isomerization of n-butanβ to isobutane or n- pentane to isopentane under mild conditions. (See. Pines, H., Advances in Catalysis, volume I, page 201, 1948.) A Bronsted add is a material which is capable of donating a proton to another material. Such materials include addic clays such as montmorillonite and

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attapulgite and acidic aluminosilicates such as zeolites X, Y, L, ZSM-5, and the like.

We have found that certain catalysts work best with certain cyclohexyl streams. For instance, cyclohexyl chloride works quite well with AICI ₃ but does not typically work well with H ₂ S0 ₄ . Consequently, some selection of catalyst is necessary prior to initial operation of the process. The catalysts are usually included at a rate of between 1:10 and 10:1 moles of acid equivalent per mole of feed. Preferably the ratio of acid to catalyst is betweeen 1:1.5 and 1.5:1.

Coupling Step Process Conditions

The cyclohexyl compounds and cyclic alkanes, along with any ancillary naphthenic materials and catalysts, are introduced into the coupling step at the concentration and feed to catalyst ratios specified above.

The reaction is carried out in one or more liquid phases. Multiple phases may occur where the catalyst is immiscible with the feedstocks or products. The reaction may be carried out in a mixed solid/liquid phase where the catalyst is a solid; if a gaseous Lewis acid such as BF ₃ , the reaction is carried out in a mixed gas/liquid medium.

Conducting the reaction in a well mixed reactor so to mix thoroughly the various phases is desirable. Countercurrent highly dispersed mixer reactors, e.g., jet reactors, are suitable. Where the catalysts are solid, fixed, or moving beds of catalyst are acceptable although fixed beds are preferred from the viewpoint of ease of operation.

The temperature of reaction may be between about 0 ^* C and the boiling point of the liquid. The temperature is not particularly critical to the operation of the coupling reaction. Ambient temperature is acceptable provided the feeds and products remain in the liquid phase but higher temperatures within the range are preferred.

Similarly, the pressure at which the reaction is carried out is not critical.

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Separation

The product stream leaving the coupling step is first subjected to a catalyst stripping step if the catalyst is either paniculate, gaseous, or a dissimilar phase. For instance, particulate catalysts may be removed by filtration or by centrifuge; gaseous catalysts such as BF ₃ may be removed by stripping with an inert gas such as N ₂ ; and a non-miscible liquid such as a strong acid may be separated using coalescing devices such as horizontal separators containing gauze packing. Once separated, the catalysts may be recycled. These are all known technologies and are subject to the usual choices of the process designer. Because of the highly acidic nature of the preferred catalysts, it may be desirable to subject the product stream to a neutralization or wash step after the catalyst separation step to minimize corrosion problems with equipment used in the steps which follow.

The separation steps typically would include those shown in Figure 1. There the cyclohexyl steam (10), catalyst (11) and cyclic alkane stream (12) are fed to the coupling reactor (14). The product stream (16) from the coupling reactor is fed to optional catalyst separation step (18) and to optional neutralization or water wash step (20). The clean product steam may then be distilled in light ends tower (22). Light ends tower (22) may be a known type of distillation tower suitable for removing components generally having a carbon content lower than dimethyldecalin. In an optimum operation, this stream would contain excess cyclic alkanes and cyclohexyl materials. If cracking of ancillary materials (24) such as bicydohexyl occurs, the gaseous products will be found in the light ends separator (22) overhead (26). After gas separation (a removal of any materials which have a carbon content less than about C ₅ ) the stream may be recycled to the coupling reactor (14).

After the product stream has been stripped of lighter ends, the product steam is then passed to a heavy ends separation unit (28). Materials having a carbon content greater than C ₁₂ are separated, typically using distillation so that the resulting middle cut may be processed further. The heavy ends separation unit (28) bottoms stream (30) normally contains C _l3 -C ₁₈ cyclic alkanes and may be

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recycled to the coupling unit (14) where it is isomerized and cracked ultimately to form dimethyldecalins.

The overhead stream (32) from the heavy ends separator unit (28) may then be primarily dimethyldecalins. These dimethyldecalins may be used in a variety of ways. If the intent is to produce 2,6-dimethylπaphthalene, a variety of process schemes will be apparent but two are considered most appropriate. The first process scheme is shown in the remainder of Figure 1. The dimethyldecalin stream (32) is dehydrogenated in dehydrogenation unit (34) using, for instance, a Group VIII noble metal dehydrogenation catalyst comprising platinum or palladium, to produce a stream containing primarily dimethylnaphthalenes. The dimethylnaphthalene stream (36) may be subjected to a crystallization step (38) to produce a reasonably pure 2,6-dimethylnaphthalene stream (40). The 2,6-dimethynaphthalene stream may optionally be oxidized to produce a 2,6-dicarboxynaphthalene stream (44) suitable for polymerization to various polyester materials.

The crystal liquor stream (46) may be used for other purposes or may be hydrogenated in hydrogenation unit (48) to produce dimethyldecalins and the resulting stream recycled to coupling unit (14) for further reaction.

An addition to the process shown in Figure 1 is the separation of at least a portion of the crystal liquor stream (46) coming from the crystallizer (38) into a stream containing 1,5- and 1,6-dimethylnaphthaienes (52) using a suitable separation process (54) and subjecting the 1,5- and 1,6-dimethylnaphthalenes to an isomerization step (54) as is found in U.S. Patent No. 4,783,569. In such a step, 1,5-dimethyinaphthalene and 1,6-dimethylnaphthalene are diminished again to form an equilibrium mixture stream (56) having a larger amount of 2,6- dimethylnaphthalenes; which stream may be recycled to the crystallization unit for recovery of additional 2,6-dimethyinaphthaIene. The other stream from the 1,5- and 1,6-dimethylnaphthalene separation unit may be hydrogenated in hydrogenation unit (48) and recycled to the coupling unit (14) much in the same way the process is operated without the isomerization unit.

Figure 2 shows an alternative separation process in which 2,6-

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dimethyldecaiin is separated and alone is hydrogenated to form 2,6- dimethylπaphthalene.

As with the process shown in Figure 1, the cyclohexyl stream (10), catalyst (11), and cyclic alkane stream (12) are fed to the coupling unit (14) along with any ancillary naphthenic materials (24), if present. The coupling reaction takes place to produce a product stream (16) which may be subjected to an optional catalyst separation step (18) and neutralization step (20). The stream may then be subjected to a light ends separation step in light ends unit (22) and a separation step in light ends separation unit (28). The overhead (26) of light ends separation unit containing C ₅ ^' materials may be recycled to the coupling unit (14). The bottoms from of the light ends separation unit (27) is sent to the heavy ends separation unit (28) where the C ₁₃ ⁺ stream (30) is separated and returned to the coupling unit (14). The overhead stream (32) is then sent to a 2,6-dimethyldecalϊn separation unit, which may be a cryogenic crystallizer, where the 2,6- dimethyldecalin is separated from the other materials in the stream. The other materials are recycled in a stream (72) to the coupling unit (74). The 2,6- dimethyldecaliπ stream (74) may be dehydrogenated in dehydrogenation unit (76) and recovered directly or may be oxidized in an oxidation unit (78) to produce a 2,6-dicarboxynaphthaleπe stream. Other procedures for separating the 2,6-dimethyldecalin from the other materials in the product stream leaving the coupling unit will be apparent to a skilled worker in this art. However, the procedures outlined above are considered to be desirable from the aspects of good economics and simplicity of operation. The following examples are provided to show the demonstration of the inventive process but are not intended in any way to limit the scope of the invention later daimed.

EXAMPLES Example 1 This example shows a series of repetitive processes used as laboratory screens in which various acid catalysts and feedstocks were utilized to show the

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efficiency (or lack thereof) of these catalysts and feedstocks.

In run nos. 1-3, cyclohexane was first mixed with the respective catalysts in a 1000ml. flask at ambient temperature and pressure. Cyclohexylchloride or cyclohexane was then added dropwise while the whole mixture was stirred using a magnetic stirring bar. The flask was immersed in a temperature controlled bath for the time noted. At the end of the reaction period, the stirring was stopped and the mixture separated into two layers. The upper layer, after separation, was washed with water and 10% NaOH solution to neutralize the acidity and then dried over anhydrous potassium carbonate. The products were analyzed using gas chromatography.

In run nos. 4-7, cyclohexane or dicyclohexyl were first mixed with the Al ₂ 0 ₃ catalyst in a in a 500 ml. Fisher-Porter bottle. The bottle was then purged with N ₂ and pressured with BF ₃ to 30 psig. The BF ₃ pressure was maintained by a back pressure regulator. Upon initiation of stirring, cyclohexene was pumped into the bottle at a rate of 2 ml/min. At the end of the reaction period, a sample was taken from the bottle into a pressurized vial containing a small amount of NaOH to neutralize the acidity. The product was analyzed using gas chromatography. The reaction parameters and results are shown in the following table:

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Tablβ I

Run No. 1 shows the successful production of dimethyldecalins using AlCI ₃ as the catalyst cydohexane as the cyclic alkane, and cyclohexyl chloride as the cyclohexyl compound. Run No. 2 shows the production of a trace amount of methylcyclopentane when H ₂ S0 ₄ is the acid catalyst. The compound methylcyclopentane is an intermediate to dimethyldecalin. Similarly, when the cyclohexyl initiator is cydohexene (Run No. 3), a small amount of methylcyclopentane is produced as is a trace of dimethyldecalin. Similarly, in Run

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Nos. 5 and 6, the use of Al ₂ 0 ₃ /BF ₃ as the catalyst, cyclohexane as the cyclic alkane, and cyclohexene as the cyclohexyl compound produce a trace of methylcyclopentane. In Run No. 4, only cyclohexane was introduced into the reactor with A _g /BF _g as catalyst to determine whether cyclohexane would dimerize alone. Clearly neither methylcyclopentane nor dimethyldecalin is found; the initiator cyclohexyl compound is required for coupling. Similarly, when dicyclohexyl is introduced alone, no reaction takes place.

This screening reaction shows that the cyclohexyl compound must be added with the cyclic alkane compound (in the presence of the acid catalyst) in order to produce the dimethyldecalin, or its intermediate methylcyclopentane. The highest conversion is seen with AICI ₃ as catalyst.

Example 2

This example shows the results of five runs using AICI ₃ and investigated the use of cyclohexane as the cyclic alkane with various cyclohexyl initiators at different reaction conditions. In each run cyclohexane was mixed with AICI ₃ in a 1000ml three-necked flask at room temperature. Cyclohexyl chloride or cyclohexene was then added drop-wise to the stirred mixture at room temperature over a period of one hour. For the experiments at approximately 80 ^* C, an ethylene glycol bath was used to maintain the temperature and the glass reactor was equipped with a condenser. The reaction product had two layers. The upper hydrocarbon layer (after separation) was washed once with 100ml of water and twice with 100ml of 10% by weight NaOH solution to neutralize the add and then dried with 10g of anhydrous potassium carbonate. Product composition was obtained by gas chromatographic analysis.

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Ta le II

This data clearly shows the superiority of using cydohexyi chloride instead of cyclohexene with AICI ₃ . However, each produces some amount of the desired product.

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Examole 3

This example shows the effect of various ratios of cyclohexylchloride to cyclohexane on the composition of the product stream.

Table I

In Run No. 2, the catalyst had been recycled from Run No. 1 to demonstrate that the catalyst could be recycled with similar conversions. The highest cyclohexyl group conversion (shown by the percentage of dimethyldecalin in the product stream) was found at a cyclohexylchloride/cyclohexane ratio of 1:1. The methylcyclopentane production appeared to increase as the ratio of cyclohexylchloride/cyclohexane decreased. Since methylcyclopentane is an intermediate to dimethyldecalin, the residence time in the reactor would likely need be longer to achieve the same production or yield of dimethyldecalin. The production of "other" materials is minimized with the lower cyclohexylchloride/cyclohexane ratios.

Example 4

This example shows that for the coupling reaction, methylcyclopentane is the equivalent of cyclohexane as a cyclic alkane.

This experiment was run in the same way as was Example 3 with the exception that 150 g of methylcyclopentane, 40 g of AICI ₃ , and 106 g of

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cydohexylchloride were added to the reaction mixture. The reaction was carried out at 80 ^* C for two hours. The results were as follows:

Table IV

Cydohexylchloride/methytcydopentane ratio: 1:1

Example 5

This example shows the feasibility of isomerizing a C ₁₂ saturated feed containing no 2,6-dimethyldecalin to produce an equilibrium mixture of dimethyldecalins in the coupling unit. The first run used dicydohexyl and the second used a mixture of 10% by weight 1,7-dimethyldecalin in decaliπ. The dimethyldecalin-in-decaiin feed was obtained by hydrogenating a 10% by weight 1,7-dimethylnaphthaIene/decalin mixture with 4g of 5% (wt) platinum on carbon catalyst in an autoclave at 125* C and 750 psig hydrogen pressure for two hours. Both isomerization runs were carried out at 50 ^* C and ambient pressure in a glass reactor. The feed was first mixed with AICI ₃ catalyst and the temperature of the stirred mixture was raised to 50 'C. The gaseous effluent from a cydohexyi coupling reaction (100g of cyclohexane and 55g of AICI ₃ with 150g of cyclohexyl chloride being added drop-wise at room temperature), containing HCI, was then added by bubbling it through the mixture over a period of three hours. The product was separated, washed, and dried as in the cydohexyi coupling reactions shown in the Examples above. The following table shows that both feeds were converted to a mixture of dimethyldecalins with over 90% selectivity. A blank test under these reaction conditions using only decalin produced no dimethyldecalins.

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The products from the Run Nos. 1 and 2 of this example were then dehydrogenated using a platiπum/Si0 ₂ catalyst at 350 ^* C. This catalyst was reduced in situ with flowing hydrogen at 400 ^* C for an hour before feed was introduced to the reactor. The product streams were analyzed using a gas chromatograph. The results of this hydrogenation are as follows:

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The amount of 2,6-dimethylnaphthalene was near the equilibrium composition of 30% to 32% 2,6-dimethylnaphthalene in each case showing the practicality of recycling dehydrogenated dimethyldecalins or other C ₁₂ 's to do the coupling reaction step.

Example 6

This example shows the. dehydrogenation of a dimethyldecalin stream (Run Nos. 3 and 5 of Example 2) using a fixed bed of a platiπum/Si0 ₂ catalyst The dehydrogenation procedure was that used in Example 5 above. The following table shows the results of the dehydrogenation:

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Table Vπ

The dehydrogenation reaction proceeded readily and to high conversion. The remaining cydohexane was largely converted to benzene. In an actual process the unreacted cyclohexane and methyicydopentane would likely be separated and recycled with the dimethyldecalins prior to dehydrogenation.

The isomer distribution of dimethylnaphthalenes showed the 2,6-isomer to be the predominant isomer at 29%. Thermodynamic calculations reveal that the percent 2,6- in the dialkylates is largely independent of temperature and is

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approximately 10% to 12%. This suggests that the isomer distribution of the dimethyldecalins is rich in the 2,6-isomer relative to dimethylnaphthalene distribution.

Example 7

This example shows that the hydrogenation of dimethylπaphthalenes proceeds easily to dimethyldecalins without significant conversion to other products. In the first experiment,^ 7-dimethylnaphthalene was converted to 2,7- dimethyldecalin with cyclohexane as the solvent. In the other experiment 1 ,7- dimethylnaphthalene was converted to 1,7-dimethyldecalin in decalin. Both runs were conducted by first mixing the dimethylnaphthalene, solvent, and the platinum on carbon in an autoclave. The mixture was then heated to the reaction temperature in an hour under high hydrogen pressure and rapid agitation. Gas chromotographic analysis of both reaction products showed complete conversion of dimethylnaphthalene to dimethyldecalin.

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This invention has been shown by description and by example. As noted above, the examples are only examples and are not to be used to limit the scope of the appended claims. It will also be recognized that those having ordinary skill in this art will be able to devise equivalent procedures to those found in the claims but will be within the spirit of the invention.

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