The present invention relates to a method for treating a composition comprising a liquefied-plastic oil, said composition containing at least 5 ppm by
mass of
silicon and / or at least 2 ppm by
mass of
chlorine as measured according to the ISO20884 standard, said treatment method comprising: a) a step of bringing said composition into contact, under hot conditions, with a strong base; then c) a step of washing with a polar
solvent that is immiscible with the product obtained, said polar
solvent being chosen from water and a polar
organic solvent, and mixtures thereof; then d) a step of mixing the product of the preceding step with a
petroleum product comprising at least one
petroleum distillation fraction, the mixture obtained comprising between 1% by
mass and 98% by mass of the product of the preceding step; then e) a step of catalytic hydrotreatment, in the presence of
hydrogen, of the mixture obtained in the preceding step.