Valorization of citrus wastes by fast pyrolysis in a conical spouted bed reactor

Abstract

The fast pyrolysis of the juice squeezing derived orange waste has been carried out in a continuous pyrolysis bench-scale plant consisting of a conical spouted bed reactor (CSBR). A prior study performed in thermobalance and a kinetic model consisting of a multi-component mechanism allowed determining the contents of pectin (35 wt%), hemicellulose (16.6 wt%) and cellulose (17.1 wt%), but that of lignin could not be satisfactorily determined as its degradation curve overlapped with other compounds such as sugars, proteins and fats. In the bench scale experiments, the bio-oil yields were very high in the 425–500 °C range (close to 55 wt%) due to the suitable features of the CSBR (high heat and mass transfer rates and short residence time of the volatiles), but they are lower for higher temperatures due to the promotion of secondary cracking reactions. Compared to lignocellulosic biomasses, the orange waste produced a bio-oil with more methanol and furfural and less phenolic species, which is an encouraging fact for its stability and valorization by catalytic cracking or steam reforming. The high concentration of CO2 in the gas is a drawback for use for energy production. The char yield (33–27 wt%) was high in the whole range of temperatures studied and its high carbon content (71–73 wt%) and HHV (≈27 MJ kg−1) are suitable for use as fuel.