Abstract: 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.

Abstract: Th invention provides a method of producing dialkylbiphenyls and trialkylbiphenyle efficiently using a continuous flow system. The method of continuously producing polyalkylbiphenyls comprises the following four steps: (1) a step of supplying reaction raw materials containing at least biphenyl and an olefin to a 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) a step of separating a fraction containing biphenyl and at least a part of monoalkylbiphenyls from the above reaction mixture, (3) a step of circulating the fraction separated in the step (2) to the reactor such that the ratio by weight of biphenyl to monoalkylbiphenyls is designed to be 0.