Process for the preparation of a lubricant base stock comprising the selective thermal decomposition of plastic polyolefin polymer

A process for the preparation of a lubricant base stock from the thermal decomposition of plastic polymer comprises the steps of: i) introducing plastic polyolefin polymer into a thermal reaction zone of a vacuum pyrolysis reactor; ii) heating the plastic polyolefin polymer at sub-atmospheric pressure, wherein the temperature in the thermal reaction zone of the reactor is from 500 °C to 750 °C, to induce thermal decomposition of the plastic polyolefin polymer and to form a thermal decomposition product effluent which comprises a major portion by weight of a C20 to C60 wax fraction; iii) condensing a vapour component of the thermal decomposition product effluent from the vacuum pyrolysis reactor; and iv) subjecting the C20 to C60 wax fraction of the thermal decomposition product to catalytic hydroisomerization in a hydroisomerization reactor in the presence of hydrogen to form the lubricant base stock; wherein the plastic polyolefin polymer comprises polyethylene and polypropylene in a polyethylene to polypropylene weight ratio of from 60:40 to 90:10. The lubricant base stock may be used in internal combustion engines or turbine bearings.