Characterization of the Products of the Catalytic Pyrolysis of Discarded COVID-19 Masks over Sepiolite

This research aims to develop a new strategy to valorize wasted COVID-19 masks based on chemical recycling by pyrolysis to convert them into useful products. First, surgical and filtering face piece masks, as defined in Europe by the EN 149 standard (FFP2), were thermally pyrolyzed at temperatures of 450, 500, and 550 degrees C, and the yields of valuable solid (biochar), liquid (biooil), and syngas products and their characteristics were determined. At low temperatures, biochar formation was favored over biooil and syngas production, while at high temperatures the syngas product yield was enhanced. The highest yield of biooil was found at a pyrolysis temperature of 500 degrees C, with both surgical and FFP2 masks achieving biooil yields of 59.08% and 58.86%, respectively. Then, the pyrolysis experiments were performed at 500 degrees C in a two-stage pyrolysis catalytic reactor using sepiolite as a catalyst. Sepiolite was characterized using nitrogen adsorption-desorption isotherms and Fourier-transform infrared spectroscopy. Results showed that the two-stage process increased the final yield of syngas product (43.89% against 39.52% for surgical masks and 50.53% against 39.41% for FFP2 masks). Furthermore, the composition of the biooils significantly changed, increasing the amount of 2,4-Dimethyl-1-heptene and other olefins, such as 3-Eicosene, (E)-, and 5-Eicosene, (E)-. Additionally, the methane and carbon dioxide content of the syngas product also increased in the two-stage experiments. Ultimately, the effect of sepiolite regeneration for its use in consecutive pyrolysis tests was examined. Characterization data showed that, the higher the use-regeneration of sepiolite, the higher the modification of textural properties, with mainly higher changes in its pore volume. The results indicated that the pyrolysis of face masks can be a good source of valuable products (especially from biooil and syngas products).