Dependence of pyrolysis temperature and lignocellulosic physical-chemical properties of biochar on its wettability

Abstract

Nowadays, high attention is paid to the knowledge on wettability of biochar, which is still very complicated, since it is acknowledged that it can depend either on primary feedstock, pyrolysis conditions or on environmental factors. Until now, it is known that the main factor responsible for the production of hydrophobic biochar is aliphatic functional groups forming tar compounds which vapour only at a high temperature. High-temperature (> 500 °C) biochar types are considered as hydrophilic due to the effect of the release of pores from the tars. However, it is still not known what the relation between wettability of biochar and other physical-chemical properties of it is and, if it is possible, is there a need to predict wettability of biochar based on other available properties. The article focuses main attention on the determination of physical-chemical properties of biochar made of five different lignocellulosic feedstocks depending on the pyrolysis temperature (300–700 °C) and their relation with the water holding capacity and wettability of biochar using the multiple regression analysis. The results showed that 54% of variation of biochar wettability could be predicted by its average pore size and 77% of variation of biochar water holding capacity could be predicted according to its ash content. Relation of wettability of biochar with its average pore size can be explained by the physical capacity of biochar to adsorb water on its surface and internal pores as well as retention of water among its particles due to capillary forces.