Production of Biochar, Bio-Oil and Synthesis Gas from Cashew Nut Shell by Slow Pyrolysis

Abstract

Cashew nut shell waste from northeast region of Brazil was characterized and slow pyrolyzed in a simple batch type reactor heated externally by liquefied petroleum gas as fuel. The experiments were performed using nitrogen or air as carrier gases. The properties of biochar, bio-oil and gases products were investigated and potential applications were proposed. Cashew nut shell showed a high heating value of 20.7 MJ kg−1 that is among the highest found for different types of biomass. Pyrolysis under nitrogen flow showed a yield of solid, liquid and gas products of about 30, 40 and 30 wt%, respectively. Under air flow an increase of gas phase (46 wt%) was observed with a decrease in the production of biochar and, mainly bio-oil. The biochars have high contents of carbon (70–75 wt%) and high heating values in the range of 25–28 MJ kg−1 presenting suitable properties for use as energy source. Biochars also contain significant quantities of K and minor amounts of Mg, Ca, Cu, Zn and Fe showing potential as fertilizer. The bio-oils showed high heating values of about 32 MJ kg−1 and are not suitable for use in pure form, but can be used in mixtures with Diesel (42.5 MJ kg−1). The gas phase revealed the predominance of CO2 and CO at temperatures lower than 400 °C and, above this temperature, there was a preferential formation of H2 resulting in synthesis gas with different compositions that could be burned to supply heat for the pyrolysis process and/or to produce organic chemicals.