We disclose a process for purification of hydrocarbons, suitable for a wide range of contexts such as refining bunker fuels to yield low-sulphur fuels, cleaning of waste engine oil (etc) to yield a usable hydrocarbon product, recovery of hydrocarbons from used tyres, recovery of hydrocarbons from thermoplastics etc, as well as the treatment of crude oils, shale oils, and the tailings remaining after fractionation and like processes. The method comprises the steps of heating the hydrocarbon thereby to release a gas phase, contacting the gas with an aqueous persulphate electrolyte within a reaction chamber, and condensing the gas to a liquid or a liquid/gas mixture and removing its aqueous component. It also comprises subjecting the reaction product to an electrical field generated by at least two opposing electrode plates between which the reaction product flows; this electrolytic step regenerates the persulphate electrolyte which can be recirculated within the process. The process is ideally applied in an environment at lower than atmospheric pressure, such as less than 1500 Pa. A wide range of hydrocarbons can be treated in this way. Used hydrocarbons such as engine oils and sulphur-contaminated fuels are prime examples, but there are a wide range of others such as hydrocarbons derived from the pyrolysis of a material having a hydrocarbon content. One such example is a mix of used rubber (such as end-of-life tyres) and used oils (such as engine oils, waste marine oils), which can be pyrolysed together to yield a hydrocarbon liquid which can be treated as above, and a residue that provides a useful solid fuel.