Catalytic Pyrolysis of a Model Plastic Mixture with a Montmorillonite Clay Catalyst and Upgrading via Distillation

Plastic recycling has become a focal point in the field of sustainability and circular economy, where pyrolysis is an emerging technology to handle a mixture of different types of plastics to be converted into simpler compounds. However, pyrolysis does not come without challenges, particurly due to the wide product distribution, where waxes, oil, and light hydrocarbons are produced. Moreover, pyrolysis is seldom sufficient in generating a liquid that meets the end-product specifications, requiring subsequent processing steps. In this work, the objective was to investigate the effect of a montmorillonite catalyst in a fluidized-bed reactor to avoid wax formation without the compromise of liquid yield. The feedstock was a model plastic mixture that simulated the share of different polyolefins (LDPE, HDPE, PP, PS) in the MSW (Municipal Solid Waste). Among the five tested temperature levels, the optimal pyrolysis temperature (525 °C) was found with no formation of detectable wax. The reuse of the spent catalyst was tested by regeneration, and the experiment was repeated. The regenerated catalyst resulted a similar liquid yield, but with deviating aromatic content which was hypothesized to be associated with reduced activity, resulting in more styrene from PS. The produced pyrolysis liquid was upgraded by distillation to separate the light (BP < 200 °C) and heavy (BP > 200 °C) fractions. A clear difference between bottom and distillate fractions was observed; aliphatics concentrated to the bottom fraction and aromatics to the distillate fraction. The results demonstrated that the montmorillonite catalyst excludes the formation of wax in a fluidized-bed reactor with a relatively high liquid yield (75% of dry feed) and that regeneration of the catalyst is possible without compromising the liquid yield. In addition, distillation proved to be a potential choice as a downstream step as the product can be refined to be better suited for the petrochemical industry. The use of a montmorillonite catalyst could be an industrially tempting choice due to the cost-effectiveness and the potential for continuous regeneration.