HYDROTHERMAL PRE-TREATMENT OF BIOMASS FOR HIGH SURFACE AREA MESOPOROUS ACTIVATED CARBONS

Abstract

As candidate precursors for synthesis of mesoporous activated carbons, the characteristics of lignocellulosic biomass-derived-hydrochar have been investigated in this thesis. Hydrothermal pre-treatment of biomass (coconut shell) in the presence of a chemical activating agent (ZnCl2) is shown to be a highly desirable step in the synthesis since it enhances the presence of oxygenated functional groups (OFGs) which facilitate efficient activation. Hydrothermal processing conditions were used as parameters to tune the properties of the hydrochar and a working range for the processing conditions that considers energy requirement (hydrothermal treatment temperature) and resource usage (ZnCl2:shell ratio) to obtain improved mesoporosity have been identified. Apart from the temperature and ZnCl2:shell ratio, concentration of both biomass and the activating agent were important parameters that influenced mesopore formation. The effect of the process conditions was identified to be due to the conflicting effects of ZnCl2 diffusion in the biomass and its solubility in the aqueous phase. Mesopore area of the activated carbon strongly correlated with the OFG content in the hydrochar, thereby leading to the inference that the OFG content in the latter is an excellent indicator of the characteristics of the final carbon product. The mesoporous activated carbons were employed in environmental/ energy storage applications such as immobilization of horseradish peroxidase (HRP), removal of several dyes from wastewater and as a cathode material in Li-ion hybrid electrochemical capacitors (Li-HEC).