Simulation-assisted design of a catalytic hydrogenation reactor for plastic pyrolysis fuels

An enhancement of the properties of pyrolysis liquids (PL) from municipal plastic waste (mainly low-density polyethylene) by catalytic hydrotreatment is required to obtain automotive quality fuels. In this context, we report the design of a pilot catalytic hydrotreatment reactor using computational fluid dynamics (CFD). This modelling technique considered fluid flows, gas diffusion, olefin hydrogenation reactions, and heat transfer. The built model allowed the development of different sensitive analysis to evaluate the influence of spatial time, heat transfer fluid (used as a reactor coolant) and hydrogen/pyrolysis liquid ratio. Possible phase changes (from gas to liquid) were analyzed by a thermodynamic approach. The results showed that the refrigerant oil allows alleviating possible temperature gradients arising from the exothermic hydrogenation reaction. It was also found that the system can be optimized in order to minimize the energy cost by adjusting the inlet temperature of the reactive gas (H-2) and the refrigerant oil flow. Condensations in the reactive chamber could be avoided by working at intermediate pressures (40-60 bar) and/or increasing the feed of H-2. Additionally, the results obtained with the CFD 3D model together with the condensation analysis allowed to optimize the operational regime and the pilot-reactor design in terms of dimensioning and construction materials.

Automated summary

The study designed a pilot catalytic hydrotreatment reactor using computational fluid dynamics and considered factors such as fluid flows, gas diffusion, reactions, and heat transfer. The results showed that adjusting the inlet gas temperature and refrigerant oil flow can optimize the system and minimize energy costs. Working at intermediate pressures and increasing H-2 supply can also help avoid condensation in the reactive chamber.