Abstract
The use of lignocellulosic plant biomass as an alternative to fossil feedstocks for chemistry, energy and materials often involves an intense dry comminution step, for which the energy consumed can vary significantly according to the process parameters, the particle size targeted, and the properties of the biomass. Here we studied the fine milling of maritime pine bark in an impact-mill configuration and in an attrition-mill configuration. The properties of the resulting powders (particle size distribution, particle shape, specific surface area, agglomeration level) obtained in each configuration were compared in relation to process energy consumption. Results evidenced that the agglomeration phenomena drive milling efficiency and limit the possibilities for reaching ultrafine particles. Interestingly, impact loading proved more effective at breaking down coarse particles but tended to generate high agglomeration levels, whereas attrition milling led to less agglomeration and thus to finer particles.
Highlights
Comminution is achieved by applying repeated loading constraints to a raw material in order to exceed the failure stress at particle scale
To clarify the different comminution mechanisms operating in the two media configurations, we investigated the dynamics of the jar/media system using discrete element method (DEM) simulations [23,24,25,26]
The collision points of the mobile media in the system were extracted from DEM simulation to provide information on both media motion and energy dissipation during milling
Summary
Comminution is achieved by applying repeated loading constraints to a raw material in order to exceed the failure stress at particle scale. Recent research has highlighted that high-level applications in energy, chemistry and materials fields demand ever finer biomass powders with target median sizes below 50 μm [4,5] This extreme pulverization requires huge energy input and more advanced milling technologies that are still only nascent science. The process parameters (rotation speed, mass of milling media, filling ratio, and more) and the technology employed modulate the proportion of the different mechanical loadings involved in the comminution (i.e., compression, impact, shearing, and abrasion/attrition). Media mills generally require less power input than rotor or jet mills and involve lower investment per processed mass unit For these reasons, media milling makes a good technological option for industrial-scale ultrafine comminution of lignocellulosic biomass presenting relatively low added value (for energy or materials applications)
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