Torrefaction of olive pomace with low-density polyethylene (LDPE) plastic and its interactive effects

Abstract

Olive Pomace (OP) biomass has a high potential for biofuel production. Dry torrefaction of OP was carried out at 200–290 °C in an inert environment in a tubular reactor. Low-Density Polyethylene (LDPE) is the most common plastic seen in landfills. Therefore, the blends of Olive Pomace with LDPE were torrefied at different ratios. The product yield and characteristics of torrefied OP were studied. As the temperature increased, the torrefied OP's mass yield decreased while the HHV increased. In the case of OP-LDPE blends, mass yield and HHV increased with the increase in LDPE content. Results showed that mass yield ranged between 59.2–82.6% for torrefied olive pomace depending on torrefaction temperature. 12% increase in mass yield was noticed when 30 wt% LDPE was blended with OP as compared to the OP at 240 °C. As for fuel properties, torrefaction enhanced HHV from 19.8 to 24.2 and 25.5 MJ/kg for OP at 290 °C and OP-LDPE blend of 30% plastic at 240 °C, respectively. Additionally, the fuel ratio rose to 0.4; the combustibility index reduced to 63.5 MJ/kg for torrefied biomass at 240 °C. The fuel ratio drastically dropped when LDPE was blended with olive pomace, reaching 0.09 with a combustibility index of 284.55 MJ/kg. Thermogravimetric analysis (TGA) revealed that hemicellulose decomposed at the specified temperature range (>200 °C), while cellulose and lignin partially decomposed. TGA showed that plastic breaks down at one stage at temperatures greater than 400 °C. According to Fourier Transform Infrared Spectroscopy (FTIR), adding LDPE replaced alkenyl groups with ketones and aldehydes. FESEM analysis showed that adding plastic clogged biomass pores resulted in higher mass yield.