Activated carbon induced hydrothermal carbonization for the treatment of cotton pulp black liquor

Powdered activated carbon (PAC) was introduced into hydrothermal carbonization (HTC) as a catalyst for treatment of cotton pulp black liquor (CPBL) in the present work. The influence of main operating parameters on treatment efficiency in hydrothermal carbonization catalyzed by PAC (PAC-HTC) and changes of PAC due to hydrochar formation on PAC surfaces were studied. Experimental results showed that high temperature and sufficient carbonization time were crucial for HTC of CPBL. The presence of PAC in HTC resulted in significant improvement for CPBL decontamination for 6 h of reaction at 300 °C. Removals of chemical oxygen demand (COD), UV254 and lignin reached 89.59%, 99.71% and 99.79%, respectively. PAC can not only adsorb small molecule organics, but also promote the decomposition and carbonation of biomass macromolecules such as lignin. PAC showed outstanding reusability in the PAC-HTC process, as organics adsorbed on the surface of PAC participated in HTC reactions to realize in-situ regeneration. The PAC-HTC process developed in this work may provide a new alternative for CPBL treatment.