Influence of pyrolysis temperature and bio-waste composition on biochar characteristics

Abstract

The aim of this work was to analyse the influence of the pyrolysis temperature and feedstock composition on biochar yield and physicochemical properties. The raw materials to be pyrolyzed were characterized, and an experimental design was applied to carry out a statistical study. Three operating temperatures (673, 773 and 873 K) and two bio-wastes (nut and almond shells) were used. Several correlations linking the values of different physicochemical properties of the biochar with the two variables were proposed. On the basis of these correlations, it was found that almost all physicochemical characteristics of both almond and nut shell-based biochars depended on both the pyrolysis temperature and bio-waste composition, and an interaction of the two variables was observed in our experiments. Only the biochar yield did not exhibit an interaction between these two variables. The biochars presented H/C and O/C ratios and higher heating values similar to those of bituminous coal, confirming their potential as solid bio-fuels. They also presented high K and Ca contents. The obtained values for the aromaticity factor, stable C mass fraction and recalcitrance potential, indicated that the biochars could also be used for soil amendments, especially as acidic or basic compounds, according to their pH values.