Abstract: The present invention relates to a process for separating 2,7-DMN, characterized in that a mixture containing at least 50% by weight of 2,7-DMN and the other DMN isomers obtained by preliminarily concentrating a fraction in the range of 250.degree.-270.degree. C. of catalytically cracked petroleum oil is preliminarily adjusted to a temperature of 60.degree.-90.degree. C. to form a slurry containing the crystal of 2,7-DMN, which is placed in a tightly sealed pressure vessel, adiabatically pressurized to the range of 500-2,500 kgf/cm.sup.2 and solidified to form a state of co-existing of solid and liquid phases, liquid is then discharged under pressure from the solid-liquid co-existing system, the solid remaining in the vessel is pressed to discharge the liquid remaining between the solid particles, which are integrated to give 2,7-DMN having a purity of 98% by weight or more.

Abstract: The invention intends to separating a methyl derivative of naphthalene (2,6-dimethyl naphthalene or 2-methyl naphthalene) from a mixture material in a high purity more than 98 weight %. The starting material is preliminarily treated at a raised temperature up to 220.degree. c. at the highest and with LHSV of 0.1-6 Hr.sup.-1 in the presence of an acid catalyst usually used for olefin polymerization. The treated material is distillated to remove the polymerized impurities and to raise the naphthalene derivative content at least up to 50 weight %. And then the obtained material is subjected to the crystallization under a pressure of 500-2500 kgf/cm.sup.2 at a temperature of 80.degree.-150.degree. C. (for 2,6-DMN) or 10.degree.-35.degree. C. (for 2-MN).