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In a process for producing methyl-substituted biphenyl compounds, a feed comprising at least one aromatic hydrocarbon selected from the group consisting of toluene, xylene and mixtures thereof is contacted with hydrogen in the presence of a hydroalkylation catalyst under conditions effective to prod

In a process for producing methyl-substituted biphenyl compounds, a feed comprising at least one aromatic hydrocarbon selected from the group consisting of toluene, xylene and mixtures thereof is contacted with hydrogen in the presence of a hydroalkylation catalyst under conditions effective to produce a hydroalkylation reaction product comprising (methylcyclohexyl)toluenes and/or (dimethylcyclohexyl)xylenes together with dialkylated C21+ compounds. At least part of the dialkylated C21+ compounds is then removed from the hydroalkylation reaction product to produce a dehydrogenation feed; and at least part of the dehydrogenation feed is dehydrogenated in the presence of a dehydrogenation catalyst under conditions effective to produce a dehydrogenation reaction product comprising a mixture of methyl-substituted biphenyl compounds.

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1. A process for producing methyl-substituted biphenyl compounds, the process comprising: (a) contacting a feed comprising at least one aromatic hydrocarbon selected from the group consisting of toluene, xylene and mixtures thereof with hydrogen in the presence of a hydroalkylation catalyst comprisi

1. A process for producing methyl-substituted biphenyl compounds, the process comprising: (a) contacting a feed comprising at least one aromatic hydrocarbon selected from the group consisting of toluene, xylene and mixtures thereof with hydrogen in the presence of a hydroalkylation catalyst comprising a molecular sieve of the MCM-22 family under conditions effective to produce a hydroalkylation reaction product comprising (methylcyclohexyl)toluenes and/or (dimethylcyclohexyl)xylenes together with dialkylated C21+ compounds, at least 60 wt % of the 3,3, 3,4, 4,3 and 4,4-isomers of (methylcyclohexyl)toluene based on the total weight of all the (methylcyclohexyl)toluene isomers, and less than 30 wt % of methylcyclohexane;(b) removing at least part of the dialkylated C21+ compounds from the hydroalkylation reaction product to produce a dehydrogenation feed; and(c) dehydrogenating at least part of the dehydrogenation feed in the presence of a dehydrogenation catalyst under conditions effective to produce a dehydrogenation reaction product comprising a mixture of methyl-substituted biphenyl compounds. 2. The process of claim 1, wherein the dehydrogenation feed produced in (b) comprises less than 0.5 wt % of said dialkylated C21+ compounds. 3. The process of claim 1, wherein the removing (b) comprises a distillation step. 4. The process of claim 1, wherein the dehydrogenation catalyst comprises an element or compound thereof from Group 10 of the Periodic Table of Elements. 5. The process of claim 4, wherein the dehydrogenation catalyst further comprises tin or a compound thereof. 6. The process of claim 1, wherein the dehydrogenation conditions in (c) include a temperature from about 200° C. to about 600° C. and a pressure from about 100 kPa to about 3550 kPa. 7. The process of claim 1, wherein the hydroalkylation catalyst comprises a hydrogenation component selected from the group consisting of palladium, ruthenium, nickel, zinc, tin, cobalt and compounds and mixtures thereof. 8. The process of claim 1, wherein the hydroalkylation conditions in the contacting (a) include a temperature from about 100° C. to about 400° C. and a pressure from about 100 to about 7,000 kPa. 9. The process of claim 1, wherein the molar ratio of hydrogen to aromatic feed supplied to the contacting (a) is from about 0.15:1 to about 15:1. 10. The process of claim 1, wherein the aromatic hydrocarbon comprises toluene. 11. The process of claim 1, wherein the feed to step (a) further comprises benzene and/or at least one alkylbenzene different from toluene and xylene. 12. A process for producing biphenyl esters, the process comprising: (a) contacting a feed comprising at least one aromatic hydrocarbon selected from the group consisting of toluene, xylene and mixtures thereof with hydrogen in the presence of a hydroalkylation catalyst comprising a molecular sieve of the MCM-22 family under conditions effective to produce a hydroalkylation reaction product comprising (methylcyclohexyl)toluenes and/or (dimethylcyclohexyl)xylenes together with dialkylated C21+ compounds, at least 60 wt % of the 3,3, 3,4, 4,3 and 4,4-isomers of (methylcyclohexyl)toluene based on the total weight of all the (methylcyclohexyl)toluene isomers, and less than 30 wt % of methylcyclohexane;(b) removing at least part of the dialkylated C21+ compounds from the hydroalkylation reaction product to produce a dehydrogenation feed;(c) dehydrogenating at least part of the dehydrogenation feed in the presence of a dehydrogenation catalyst under conditions effective to produce a dehydrogenation reaction product comprising a mixture of methyl-substituted biphenyl compounds;(d) contacting at least part of the dehydrogenation reaction product with an oxygen source under conditions effective to convert at least part of the methyl-substituted biphenyl compounds to biphenyl carboxylic acids; and(e) reacting the biphenyl carboxylic acids with one or more C4 to C14 alcohols under conditions effective to produce biphenyl esters. 13. The process of claim 12, wherein dehydrogenation feed produced in (b) comprises less than 0.5 wt % of said dialkylated C21+ compounds. 14. The process of claim 12, wherein the removing (b) comprises a distillation step. 15. The process of claim 12, wherein the dehydrogenation catalyst comprises an element or compound thereof from Group 10 of the Periodic Table of Elements. 16. The process of claim 15, wherein the dehydrogenation catalyst further comprises tin or a compound thereof. 17. The process of claim 12, wherein the dehydrogenation conditions in (c) include a temperature from about 200° C. to about 600° C. and a pressure from about 100 kPa to about 3550 kPa (atmospheric to about 500 psig). 18. The process of claim 12, wherein the feed to step (a) further comprises benzene and/or at least one alkylbenzene different from toluene and xylene. 19. The process of claim 12, wherein the aromatic hydrocarbon comprises toluene. 20. The process of claim 1, wherein the hydroalkylation catalyst comprises a hydrogenation component comprising platinum. 21. The process of claim 1, wherein the hydroalkylation catalyst comprises a hydrogenation component comprising platinum and tin. 22. A process for producing methyl-substituted biphenyl compounds, the process comprising: (a) contacting a feed comprising at least one aromatic hydrocarbon selected from the group consisting of toluene, xylene and mixtures thereof with hydrogen in the presence of a hydroalkylation catalyst comprising MCM-22 under conditions effective to produce a hydroalkylation reaction product comprising (methylcyclohexyl)toluenes and/or (dimethylcyclohexyl)xylenes together with dialkylated C21+ compounds;(b) removing at least part of the dialkylated C21+ compounds from the hydroalkylation reaction product to produce a dehydrogenation feed; and(c) dehydrogenating at least part of the dehydrogenation feed in the presence of a dehydrogenation catalyst comprising platinum and tin under conditions effective to produce a dehydrogenation reaction product comprising a mixture of methyl-substituted biphenyl compounds. 23. The process of claim 1, wherein the hydroalkylation reaction product comprises less than 2% of dimethylbicyclohexane compounds and less than 1 wt % of dialkylated C21+ compounds. 24. The process of claim 1, wherein unreacted feed is removed from the hydroalkylation reaction effluent and recycled to the hydroalkylation reactor. 25. The process of claim 11, wherein unreacted feed is removed from the hydroalkylation reaction effluent and recycled to the hydroalkylation reactor.