Method of continuous production of polyalkylbiphenyls
A method of continuously producing polyalkylbiphenyls involves reacting biphenyl and an olefin in the presence of a solid acid catalyst to obtain a reaction mixture containing monoalkylbiphenyls and dialkylbiphenyls, separating a fraction containing biphenyl and at least a part of the monoalkylbiphenyls, circulating the separated fraction to the reactor such that the ratio of biphenyls to monoalkylbiphenyls is designed to be 0.1 or more and is designed to be less than the soluability of biphenyl to monoalkylbiphenyl at a circulation temperature, and recovering polyalkylbiphenyls.
1. A method of continuously producing polyalkylbiphenyls, comprising the steps of:
(1) supplying reaction raw materials containing at least biphenyl, dialkylbiphenyl and an olefin to a fixed-bed flow system reactor wherein the mol ratio of olefin/biphenyl is 0.3 to 3 at the inlet of the reactor and reacting the raw materials in the presence of a solid acid catalyst to obtain a reaction mixture containing monoalkylbiphenyls and dialkylbiphenyls;
(2) separating a fraction containing biphenyl and at least a part of monoalkylbiphenyls from said reaction mixture, wherein the concentration of dialkylbiphenyls in the fraction separated in said step (2) is made to be 15% by mass or less and the amount of dialkylbiphenyls in the fraction separated in said step (2) is made to be 30% by mass or less of the amount of dialkylbiphenyls produced in said step (1);
(3) circulating the fraction separated in said step (2) to said reactor such that the ratio by weight of biphenyl to monoalkylbiphenyls is designed to be 0.1 or more and is designed to be less than the soluability of biphenyl to monoalkylbiphenyl at a circulation temperature; and
(4) recovering polyalkylbiphenyls containing at least one of 3,3′-dialkylbiphenyl, 3,4′-dialkylbiphenyl, 4,4′-dialkylbiphenyl and 3,5′-dialkylbiphenyl from the reaction mixture through said step (2), whereby no precipitation of 4,4′-dialkylbiphenyl crystal is observed at −10° C.
2. A method of continuously producing polyalkylbiphenyls according to claim 1 , wherein the olefin has 2 to 6 carbon atoms.
3. A method of continuously producing polyalkylbiphenyls according to claim 2 , wherein the dialkylbiphenyl reaction raw material is a 3,3′-, 3,4′- , 4,4′- or 3,5-dialkylbiphenyl, the olefin is propylene, 1-butene, 2-butene or isobutene and the acid catalyst is silica alumina, arid wherein the mol ratio of olefin/biphenyl is 0.5–1.5 at the inlet of the reactor.
4. A method of continuously producing polyalkylbiphenyls according to claim 3 , wherein the fraction separated in step 2 contains up to 10 mass percent of dialkylbiphenyl and is made to be 20 mass percent or less of the amount of dialkylbiphenyls produced in said step (1).