Production and Use of Dialkylbiphenyl Isomer Mixtures

A process for producing 3,3′, 3,4′ and/or 4,4′ dimethylbiphenyl compounds, the process comprising:

• (a2) contacting toluene with hydrogen in the presence of a hydroalkylation catalyst under conditions effective to produce a hydroalkylation product comprising (methylcyclohexyl)toluenes;
• (b2) dehydrogenating at least part of the hydroalkylation product under conditions effective to produce a dehydrogenation product comprising dimethylbiphenyl isomers and unreacted (methylcyclohexyl)toluenes;
• (c2) separating the dehydrogenation product into a first fraction comprising one or more 3,3′, 3,4′ and 4,4′ dimethylbiphenyl isomers and a second fraction comprising one or more 2,X′ dimethylbiphenyl isomers (where X′ is 2, 3 or 4) and at least part of the unreacted (methylcyclohexyl)toluenes;
• (d2) contacting at least part of the second fraction with an acid catalyst under isomerization conditions effective to convert at least some of the 2,X′ dimethylbiphenyl isomers into one or more 3,3′, 3,4′ and 4,4′ dimethylbiphenyl isomers and produce an isomerization product;
• and
• (e2) recycling at least part of the isomerization product to the separating (c2).

A process for producing 3,3′, 3,4′ and/or 4,4′ dimethylbiphenyl compounds, the process comprising:

• (a3) contacting toluene with hydrogen in the presence of a hydroalkylation catalyst under conditions effective to produce a hydroalkylation product comprising (methylcyclohexyl)toluenes;
• (b3) dehydrogenating at least part of the hydroalkylation product under conditions effective to produce a dehydrogenation product comprising dimethylbiphenyl isomers and unreacted (methylcyclohexyl)toluenes;
• (c3) supplying at least part of the dehydrogenation product to a separation zone to recover a first fraction enriched in one or more 3,3′, 3,4′ and/or 4,4′ dimethylbiphenyl isomers as compared with the dehydrogenation product and a second fraction enriched in one or more of 2,X′ dimethylbiphenyl isomers (where X′ is 2′, 3′ and/or 4′) as compared with the dehydrogenation product and also containing at least part of the unreacted (methylcyclohexyl)toluenes;
• and
• (d3) supplying at least part of the second fraction as at least part of a feed to an isomerization process comprising contacting the feed comprising one or more 2,X′ dimethylbiphenyl isomers with an acid catalyst under isomerization conditions effective to convert at least some of the 2,X′ dimethylbiphenyl isomers into one or more 3,3′, 3,4′ and 4,4′ dimethylbiphenyl isomers and produce an isomerization effluent.

A process for producing 3,3′, 3,4′ and/or 4,4′ dimethylbiphenyl compounds, the process comprising:

• (a4) contacting biphenyl with a methylating agent in the presence of an alkylation catalyst under conditions effective to produce a methylation reaction product comprising a mixture of dimethyl-substituted biphenyl isomers;
• (b4) supplying at least part of the methylation reaction product to a separation zone to recover a first fraction enriched in one or more 3,3′, 3,4′ and 4,4′ dimethylbiphenyl isomers as compared with the methylation reaction product and a second fraction enriched in one or more of 2,X′ dimethylbiphenyl isomers (where X′ is 2′, 3′ and/or 4′) as compared with the methylation reaction product;
• and
• (c4) supplying at least part of the second fraction as at least part of a feed to an isomerization process comprising contacting the feed comprising one or more 2,X′ dimethylbiphenyl isomers with an acid catalyst under isomerization conditions effective to convert at least some of the 2,X′ dimethylbiphenyl isomers into one or more 3,3′, 3,4′ and 4,4′ dimethylbiphenyl isomers and produce an isomerization effluent.

A process for producing 3,3′, 3,4′ and/or 4,4′ dimethylbiphenyl compounds, the process comprising:

• (a5) contacting toluene with hydrogen in the presence of a hydroalkylation catalyst under conditions effective to produce a hydroalkylation product comprising (methylcyclohexyl)toluenes;
• (b5) dehydrogenating at least part of the hydroalkylation product under conditions effective to produce a dehydrogenation product comprising dimethylbiphenyl isomers and unreacted (methylcyclohexyl)toluenes;
• (c5) separating the dehydrogenation product into a first fraction comprising one or more 3,3′, 3,4′ and 4,4′ dimethylbiphenyl isomers and a second fraction comprising one or more 2,X′ dimethylbiphenyl isomers (where X′ is 2, 3 or 4) and at least part of the unreacted (methylcyclohexyl)toluenes;
• (d5) contacting at least part of the second fraction with an acid catalyst under isomerization conditions effective to convert at least some of the 2,X′ dimethylbiphenyl isomers into one or more 3,3′, 3,4′ and 4,4′ dimethylbiphenyl isomers and produce an isomerization product;
• (e5) recycling at least part of the isomerization product to the separating (c5);
• (f5) optionally, separating the first fraction into a third fraction enriched in one target isomer selected from 3,3′, 3,4′ and 4,4′ dimethylbiphenyl and a fourth fraction depleted in said target isomer;
• (g5) contacting at least part of the fourth fraction with an acid catalyst under isomerization conditions effective to produce an isomerization product having an increased concentration of the target isomer as compared with the fourth fraction;
• and
• (h5) recycling at least part of the isomerization product to the separating (f5).