Effect of the Heat Treatment of Pyrolysis Fuel Oil on the Naphthalene Yield and Quality

Abstract— Pyrolysis fuel oil was heat-treated for 6–8 h at 250–270°C in a stirred autoclave, after which it was separated into the distillate and bottoms by atmospheric and vacuum distillation. The distillate was distilled again to obtain close-cut fractions: prenaphthalene (s.b.–200°C), naphthalene (200–230°C), methylnaphthalene (230–245°C), and residual (245–340°C). The heat treatment led to an increase in the yield and naphthalene content of the naphthalene fraction with a simultaneous decrease in the concentration of unsaturated compounds: mono- and bicyclic alkenes and dienes, vinylaromatic hydrocarbons, indene and its homologs, and dihydronaphthalenes. Naphthalene was isolated from the naphthalene fraction by crystallization and was purified by recrystallization from ethanol. As a result of the heat treatment of the tar, the yield of the purified naphthalene increased by a factor of 2, its melting point increased by 0.4–0.7°C, and the color index on the iodine scale decreased by 18–19 units. After the heat treatment, naphthalene crystallized not only from the close-cut naphthalene fraction but also from the broad distillate taken in the course of primary distillation of pyrolysis fuel oil. In this case, the yield of purified naphthalene was lower by 11.3–27.7 rel %, but its melting point was 0.3–0.6°C higher compared to the isolation from the naphthalene fraction. The highest levels of the naphthalene yield and quality were reached after the heat treatment of the tar at 260°C for 7 h.