Denitrogenation of waste plastic pyrolysis oil using dihydrolevoglucosenone as a green solvent

Recycling of plastic waste employing pyrolysis yields a valuable liquid product called plastic pyrolysis oil (PPO). This PPO could then be used in industrial steam crackers to produce monomers for new plastic materials, facilitating a closed-loop economy. However, the pyrolysis product is not pure enough to be fed to the industrial steam crackers. One limitation is the nitrogen-containing compounds in the PPO, whose removal currently requires harsh conditions and expensive catalysts. This study explored liquid – liquid extraction (LLX) for the removal of such compounds using dihydrolevoglucosenone (Cyrene) as a green solvent at mild conditions. Nitrogen content was reduced from 1504 ppm to below 100 ppm, which is deemed necessary for the safe operation of industrial steam crackers. Then, model systems were studied to deepen the understanding of underlying thermodynamics, which is paramount for the design of separation processes. The monomer of Nylon-6, called ε-caprolactam, was chosen as one of the model components. ε-Caprolactam is industrially relevant and contains a nitrogen atom, making it a viable choice for a model component. Phase equilibria of binary and ternary model systems were measured experimentally and modelled with universal quasi-chemical functional group activity coefficients – Dortmund modified (UNIFAC-Dortmund), nonrandom, two-liquid (NRTL), and Conductor-like screening MOdel for realistic solvents (COSMO-RS). Finally, interactions of the solvent with some important compounds present in plastic pyrolysis oil were discussed.