The invention relates to a method for producing
pyrolysis oil containing
liquid hydrocarbons from
plastic materials, preferably waste materials. The method is characterized by the use of an
energy source of preferably intermittent nature (and
variable intensity), such as, for example, solar
radiation. The plastic material enters a
pyrolysis reactor, which is heated with a
molten salt hot fluid. The
molten salt is heated by the intermittent source to a temperature that is not fixed but variable within a predetermined range. Specifically, when the availability of the
energy source is equal to or exceeds a predetermined maximum value, the temperature of the
molten salt reaches the upper end of the range. Instead, when the availability of the
energy source is equal to or lower than a predetermined minimum value, the temperature of the molten salt reaches the lower end of the range. For an intermediate availability value, the temperature may also reach an intermediate value, for example, following a linear profile. The
pyrolysis temperature follows the temperature of the molten salt. On the other hand, the pyrolysis pressure is adjusted such that when the pyrolysis temperature is lower, the pyrolysis pressure is higher (at least 2.5 bar) and when the pyrolysis temperature is higher, the pyrolysis pressure is lower (no more than 2 bar). Surprisingly, it was found that, by operating in a specified manner, the quality of the obtained
pyrolysis oil remains constant, even for considerable variations in pyrolysis temperature.