Monophenols recovery by catalytic pyrolysis of waste sawdust over activated biochar from the brown macroalgae Hizikia fusiformis: Mechanism and life-cycle assessment

Abstract

As an indispensable by-product of thermal conversion process, biochar can be modified to achieve outstanding performance in many applications. In particular, it has favorable properties for catalytic pyrolysis due to its advantageous porous structure and abundant surface functional groups. In the present study, the ecological impact of activated biochar obtained from phaeophyte Hizikia fusiformis was evaluated using life cycle assessment (LCA) approach. Subsequently, activated biochar was employed as a catalyst during pyrolysis of waste sawdust for monophenols recovery. Concretely, activated biochar was prepared from H. fusiformis in a fixed bed reactor through a two-step activation method. Results of LCA showed that employment of KOH has the highest environmental burdens in all steps for all studied impact categories. In addition, it was found that employment of KOH as an activator resulted in lower greenhouse gas emissions than other activated biochars. During catalytic pyrolysis process, the biochar-based catalyst was confirmed to facilitate the dehydration, decarbonylation, and decarboxylation reactions, resulting in more gaseous components. In addition, the content of -OH was found to decrease after catalytic process, while the content of C-O-C increased. According to GC-MS analysis, it was found that activated biochar catalyst significantly promotes the yields of monophenols (reached up to 48.99%), which were mainly ascribed to the porous structure and the surface functional groups, i.e. mesopores structure and pyridinic-N, respectively.