Significantly reducing energy consumption during nanolignin production via high-solid content grinding

The production of lignin nanoparticles (LNPs) has garnered significant attention in recent decades, particularly due to its emerging industrial applications. In the context of particle size reduction during ultrafine friction grinding (UFG), energy consumption refers to the amount of energy required to break down or reduce the size of particles to a desired level. This energy is an important parameter to consider in industrial processes, as it can have significant economic and environmental implications. High energy consumption can lead to increased operating costs and may also contribute to environmental concerns, especially if the energy source is non-renewable. However, traditional UFG, used for the production of nanolignin production, usually performs at low solid concentrations of 1–2 wt%, resulting in high energy consumption and water usage. Achieving such fine particle sizes often requires high-energy input, and the efficiency of the grinding process is closely related to the energy consumption. In this study, we investigated the energy efficiency and particle size reduction of lignin at four different concentrations (1, 20, 30 and 40 wt%) during UFG. Our results show that the 20 wt% solid loading has the best energy efficiency for achieving the same lignin particle size (∼150 nm) as the 1 wt% loading; total energy consumption was reduced from ∼30 kWh per kg LNPs at 1 wt% solid loading to 3.1 kWh per kg of LNPs at 20 wt% loading. Despite the increased number of grinding cycles, higher concentrations required lower amount of energy per kg of LNPs produced. The results suggest that when the concentration of lignin particles exceeded 20 wt%, they tended to overlap, resulting in less effective size reduction during UFG. This study's significance lies in discovering concentration limits for grinding, and improving water and energy use efficiency, such that UFG could emerge as a feasible mechanical treatment and an asset for the industrialization of LNPs.