A Fluidised Bed Pyrolysis Process for Chemical Recycling of Mixed Plastic Waste

The ecological damage from plastic pollution is more evident by the day, but global manufacture and use is increasing rapidly. Even if substitutes are found in some limited cases, the unique advantages of plastic will continue to make it the material of choice in many applications. Recycling is essential and the good news is that effective processes are available now to enable this to happen. Fluidised bed pyrolysis is a leading candidate for chemical recycling to provide hydrocarbon feedstocks for reuse, but presents a number of practical problems in its implementation. This paper summarises the design and operation of a twin-fluidised bed process in which pyrolysis occurs in a bubbling bed reactor of sand-like material which is heated in a second bed by combustion of light hydrocarbon gas, with solids exchange between the two. The mixed hydrocarbon product is separated in a series of columns and clean-up stages. The process development is described, including the measurement of the pyrolysis kinetics, the design of the two fluidised beds and ancillary equipment and the overall design of an industrial scale pilot plant at Swindon, UK, which has successfully processed the equivalent of 700 tonnes/year in this way. Experience at this scale has been used in the design of a 7000 tonnes/year design. The vision is for a network of hundreds of such plants across each country distributed so as to minimise transport issues. Challenges include maximising the efficiency and availability of the process, ensuring that contaminant molecules are effectively removed and devising an industrial ecology for a circular economy which makes this approach sustainable in both environmental and economic terms.