Ri.Pla.Id. concept for valorization of waste plastics into gasoline: from laboratory to pre-industrial scale

The Ri.Pla.Id. (Riconversione di Plastiche in Idrocarburi) project was started in 2017 by the Italian company Lifenergy (by Firmin), with the technical-scientific and economic-financial objective of developing a new PLASTIC TO FUEL technology. The project plans to intercept industrial plastic wastes (from collection or production facilities) and, through industrial research and experimental development, provide an alternative solution to its disposal in landfills or incineration. The technology, based on an innovative semi batch reactor design, aimed at intercepting mixtures of industrial plastic wastes (PP, PE and PS), before their disposal, and converting them into hydrocarbons. As primary objective, fuel useful for transport or oils suitable to be mixed with fossil derived fuels were targeted. The paper describes the steps done by Lifenergy in order to demonstrate the concept, moving from the basic understanding of plastic pyrolysis to the realization and startup of a pre-industrial scale plant of 5000 ton/y. Although in the literature numerous works addressed pyrolysis kinetics of the main plastic polymers as well as the properties of pyrolysis catalysts, the project had to face several technological problems. One of the initial issues encountered in the project is attributed to the variable composition of industrial plastic wastes. These wastes comprise diverse mixtures of various plastic polymers, each exhibiting decomposition within distinct temperature ranges and resulting in different products. Plastic materials have also low thermal conductivity, which impedes a fast and uniform heating within the reactor, moreover, they often contain additives (flame retardants, filler, pigments etc.) which increase the production of solid residue and may cause fouling and agglomeration. In consideration of the above-mentioned criticalities, within the project, methods for characterization as well as pre-treatments of the input mixtures have been developed, in order to facilitate selection, homogenization, handling, and feeding. The mixing and heating problems have been accounted for through a particular design of the reactor, which includes pre- and retro-mixing devices, assisted by dynamic modeling of the reactor. Selection of the reactor operating temperature was also not trivial. The project results showed that it is impossible to optimize both the oil yield and its quality. The optimal temperature for the pyrolysis of a specific plastic waste should therefore be fixed, targeting either the maximum oil productivity, or the oil quality, depending on the economic boundary conditions.