Effect of feedstock and pyrolysis temperature on properties of biochar governing end use efficacy

Abstract

The aim of this study was to systemically evaluate how feedstock characteristics and temperature influence biochar evolution during pyrolysis and to establish their relationships with biochar potential for soil amendments. We produced four biochar thermosequences from oak, pine, sugarcane and peanut shell at twelve temperatures (350–900 °C), and characterised them by yield, proximate analysis, elemental analysis, pH, electrical conductivity (EC) and carbon (C) functional groups using FTIR and solid-state 13C CPMAS NMR spectroscopy, along with principal component and cluster analyses. The results showed that not all biochar properties changed consistently with increasing pyrolysis temperature during slow pyrolysis. The significant increase in biochar pH with increasing pyrolysis temperature, was only observed between 350 and 500 °C (p < 0.05). Three principal components (PC) explained 88.9% of the variances in biochars. PC1 (ash, Mn, K, Fe, N, P and EC) and PC3 (Ca, Na and Mg) scores were essentially determined by feedstock type with notable influence of low pyrolysis temperatures. PC2 (O, H, C, volatile matter, fixed matter and pH) score was greatly influenced by pyrolysis temperature. Sugarcane derived biochars had high PC1 score but low PC3 score, while peanut shell derived biochars were contributed by both PC1 and PC3. The wood derived biochars had low scores of both PC1 and PC3, but the low temperature end of wood derived biochar thermosequences had significant higher PC2 scores than the high temperature end (p < 0.05). Understanding how biochar feedstock characteristics and pyrolysis temperature regulate biochar evolution will benefit tailored biochar manufacture.