Low-Temperature Co-pyrolysis of Polypropylene and Coffee Wastes to Fuels

The co-pyrolysis of coffee grounds and polypropylene was studied, at different volumetric fractions of each material, in a fixed bed, under inert flow. With a constant heating rate of 5 °C/min, a preset pyrolysis temperature, between 360 and 420 °C, was maintained for 3 h. Polymer degradation is not completed at a low temperature (360 °C), while coffee is easier to degrade, as confirmed by differential scanning calorimetry (DSC). Liquid product analysis confirms that a two-stage pyrolysis mechanism occurs, with biomass degrading first. When the pyrolysis temperature is increased, the degradation grows noticeably, doubling from 360 to 380 °C, becoming >90 wt % at 420 °C. When the fraction of polypropylene is increased, the quantity of light liquid products reduces, while the fraction of heavy condensate products rises. The presence of pyridine, phenol, C12, and C13, sometimes with hydroxyl groups, is relevant, while among the high-molecular-weight products, large quantities of hexadecanoic acid and caffein...