(74f) Evaluating Pyrolysis Gas from Waste Plastics As a Fuel for Portable Power Generation

Chemical recycling technologies, including pyrolysis, have gained recent popularity in the past decade to help close material flows in plastics recycling. These technologies seek to breakdown waste plastics into monomers, liquid fuels, or other useful chemicals. During fast pyrolysis, the plastic thermally degrades in an inert atmosphere at 500-600 °C and short vapor residence time (2-5 sec), creating three main products: wax, liquid, and gas. While the wax and liquid products have commercial markets, the pyrolysis gas is typically consumed internally for process heat. This product, which is composed of a mixture of C1-C6 alkanes and alkenes, has a lower heating value (LHV) equivalent to that of propane. To the best of our knowledge, no one has previously evaluated pyrolysis gas as a fuel source, nor measured the emissions of its combustion in portable power generation.

In this work, pyrolysis gas was generated from a novel liquid-pyrolysis process using military waste PE and PP feedstock. The composition of the pyrolysis gas was determined to be 25 wt% methane, 6 wt% ethylene, 29 wt% propylene, 24 wt% butene, 11 wt% pentene, and 4 wt% hexene using GC-MS and GC-FID. The collected pyrolysis gas was compressed into a receiving tank up to 300 PSIG and then used to fuel a portable power generator. Due to the complex nature of the fuel, a vapor-liquid equilibrium model was created using the Peng-Robinson equation of state and Rachford-Rice equation to model the changing composition in the receiving tank as a function of filling/draining cycles. We found that the heavier compounds in the fuel slowly accumulate in the liquid phase of the tank over several filling/draining cycles. Despite this change in composition, the LHV of the fuel was found to remain constant across 100 filling/drying cycles. In addition, emissions data (including CO, CO₂, O₂, Total Hydrocarbons, NOx) is reported from the combustion of the pyrolysis gas to evaluate the fuel quality. Finally, overall generator efficiencies were found to range from 20-25%, equivalent to commercial propane fuel.