Interaction of derivatives of cellulose and lignin in co-HTC, co-pyrolysis and co-activation

Abstract

Cellulose and lignin co-exist in agroforestry biomasses and their distinct structures lead to the formation of varied derivatives in their thermal conversions. This might induce interaction of these derivatives and shape the properties of resulting products. In this study, potential interaction of the derivatives from cellulose and lignin was investigated in three scenarios: hydrothermal carbonization (HTC) at 250 °C, pyrolysis at 550 °C and activation with CO2 at 800 °C. The results indicated interactions among volatiles and between volatiles and char, influencing properties of varied chars. The co-HTC of cellulose/lignin reduced the yield of hydrochar, due to the enhanced depolymerization of feedstocks and heavy organics with the aid of carboxylic acids derived from cellulose. In converse, cross-polymerization reaction between volatiles and biochar in pyrolysis/activation formed additional carbonaceous solids, increasing the yield of biochar (by 5.5%) and activated carbon (by 12.4%) as well as large π-conjugated organics in the bio-oils. Aromatization reaction was enhanced during the co-pyrolysis of lignin/cellulose, making the biochar thermally more stable, while co-activation of mixture significantly increased the specific surface area of resulting activated carbon (889.0 m2g−1 versus 691.5 m2g−1 in theoretical average), as the volatiles of varied origins involved in activation of the biochar. Additionally, the co-HTC, co-pyrolysis and co-activation also significantly affected evolution of functionalities, hydrophobicity and morphologies of the hydrochar/biochar/activated carbon.