Method for purifying a pyrolysis oil in order to upgrade it by steam-cracking

A method for purifying a pyrolysis oil originating from the pyrolysis of waste containing plastics, comprising:

• providing a pyrolysis oil containing saturated and unsaturated hydrocarbon compounds and polar compounds comprising at least one heteroatom selected from the group consisting of oxygen, sulphur, nitrogen, a transition metal, an alkali metal, an alkaline-earth metal and a halogen, the pyrolysis oil provided being a liquid organic phase or a mixture of liquid organic phases resulting from the pyrolysis of plastic waste and at least one other waste which comprises biomass, optionally in mixture with another waste which is an elastomer,
• contacting the pyrolysis oil with a polar extraction solvent immiscible with the pyrolysis oil,
• recovering an extract and a raffinate which are immiscible with each other, the extract containing the extraction solvent and at least one part of the polar compounds, and optionally at least one part of the unsaturated hydrocarbon compounds, initially contained in the pyrolysis oil, the raffinate containing a treated pyrolysis oil with a reduced content of polar compounds and optionally of unsaturated hydrocarbon compounds,
• wherein the polar extraction solvent immiscible with the pyrolysis oil is selected from the group consisting of water having an acidic, basic or neutral pH, glycol ethers, dialkyl formamides in which the alkyl group comprises from 1 to 8 carbon atoms, dialkyl sulphoxides in which the alkyl group comprises from 1 to 8 carbon atoms, compounds comprising a furan ring, cyclic carbonate esters comprising from 3 to 8 carbon atoms, and mixtures thereof, and is a solvent for which a recovery rate greater than or equal to 0.95 is obtained, this recovery rate being defined as the ratio of the volume of an extract to a volume of initial solvent, and this extract is a phase containing the solvent, immiscible with the pyrolysis oil, recovered after agitation and then decanting a mixture of one part by volume of solvent with twenty-five parts by volume of the pyrolysis oil at atmospheric pressure and at a temperature of 20° C.