Evaluation of Energy Consumption and Greenhouse Gas Emissions in Preparation of Cellulose Nanofibers from Woody Biomass

Abstract

<abstract><title><italic>Abstract. </italic></title> The purpose of this study is to assess the energy consumption and greenhouse gas (GHG) emissions of a mechanochemical method for preparing cellulose nanofibers (CNF) from woody biomass using a life cycle assessment (LCA) approach. The energy requirements and GHG emissions from CNF production were compared to those of petroleum-based polymers to evaluate the environmental performance of CNF as a reinforcement of polypropylene (PP) or other petroleum-based polymers. The functional unit used in this study was 1 kg dry CNF. The background data (emission factors of industrial steam and water, wood density, grid emission factor, etc.) were collected from the Inventory Database for Environmental Analysis (IDEA) and published literature. The foreground data (power, heat, and water requirements in a CNF production plant) were obtained from pilot plant experiments. The energy requirement for preparing CNF was 11.1 to 30.2 MJ kg^-1, which was lower than that of petroleum-based polymers (63.4 to 131.0 MJ kg^-1). The GHG emissions of preparing CNF ranged from 1.2 to 3.7 kg CO₂eq kg^-1, without accounting for carbon fixation of the biomass. The water consumption for producing CNF was 17.8 to 19.4 L kg^-1, which was much lower than that of petroleum-based polymers (192.6 to 960.8 L kg^-1). When the CNF were used to produce a composite with PP, the maximum GHG reduction was 2.4 kg CO₂eq kg^-1, taking into account carbon fixation of the biomass. The results showed that the utilization of CNF prepared from woody biomass using the mechanochemical method could contribute to saving energy and mitigating GHG emissions.