NOVELTY - A process for purifying organic residues such as plastics, used oil or biomass, in one separation stage using a reactor (1), before conversion into oil by thermolysis, involves melting the material by heating under inert gas in a closed reactor (1), taking off volatile impurities such as halogen compounds, sulfur compounds, plasticisers and/or water together with the inert gas under reduced pressure, removing the impurities and recycling the inert gas in pulses for further stripping of the melt.    USE - For purifying organic residues such as plastics, used oil or biomass before conversion into oil by thermolysis.    ADVANTAGE - Enables the effective purification of organic residues such as plastics, used oil or biomass to remove interfering substances such as halogen compounds, sulfur compounds, plasticisers, water and higher-density impurities before thermolytic conversion into oil. This is greatly assisted by improved mass transfer between the stripping gas and the melt due to the pulsed injection of gas.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for a system for performing the process described above, comprising a closed, stirred reactor (1) with an internal tubular heater (2) and a feed inlet (M, 3) for the organic residue, a bottom outlet (4) for higher-density impurities, a connecting pipe (5) for transferring molten material to the thermolysis reactor, an inert gas inlet pipe (6) in the gas space and a gas take-off pipe (7) for applying reduced pressure to strip off the inert gas; this pipe (7) is connected to an inert gas injector (12) in the lower part of the reactor (for stripping the melt) via at least one purification stage (8, 9) for separating the volatile impurities from the inert gas and also via a compressor (10).    DESCRIPTION OF DRAWING(S) - The drawing shows a diagram of a system according to the invention, for purifying organic residues before thermolytic olefaction.    closed, stirred reactor in the form of a pressure vessel (1)    heat exchanger coils (2)    feeder system for residues (M, 3)    outlet for impurities (4)    connecting line to thermolysis reactor (5)    inlet pipe for inert gas blanket (6)    gas take-off line (7, 18)    purification stages 1 and 2 (8, 9)    compressor (10)    first pulsator (11)    stripping gas injector (12)    take-off pipes for impurity groups 1 and 2 (13, 14)    excess gas outlet (15)    condenser (16)    second pulsator. (17)