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 caffeine, arising from coffee, and hydrocarbons up to C30 were detected. Increasing the temperature shows a drop in
the amount of light liquids, while medium- and high-molecular-weight
products stabilize. Above 400 °C, co-pyrolysis allows for the
procurement of a liquid product mixture, which is comparable to fossil
fuel oil.
