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The isolation of crystalline regions from fibers cellulose via the hydrolysis route generally requires corrosive chemicals, high-energy demands, and long reaction times, resulting in high economic costs and environmental impact. From this basis, this work seeks to develop environment-friendly processes for the production of Bacterial Cellulose Nanocrystals (BC-NC). To overcome the aforementioned issues, this study proposes a fast, highly-efficient and eco-friendly method for the isolation of cellulose nanocrystals from Bacterial Cellulose, BC. A two-step processes is considered: (1) partial depolymerization of Bacterial Cellulose (DP-BC) under ultrasonic conditions; (2) extraction of crystalline regions (BC-NC) by treatment with diluted HCl catalyzed by metal chlorides (MnCl2 and FeCl3.6H2O) under microwave irradiation. The effect of ultrasonic time and reactant and catalyst concentrations on the index crystallinity (CrI), chemical structure, thermal properties, and surface morphology of DP-BC and BC-NC were evaluated. The results indicated that the ultrasonic treatment induced depolymerization of BC characterized by an increase of the CrI. The microwave assisted by MnCl2-catalyzed mild acid hydrolysis enhanced the removal of the amorphous regions, yielding BC-NC. A chemical structure analysis demonstrated that the chemical structures of DP-BC and BC-NC remained unchanged after the ultrasonic treatment and MnCl2-catalyzed acid hydrolysis process.

Abstract. The combined computational fluid dynamics and discrete element method (CFD-DEM) has been extended and used in recent years to study heat transfer between bed and an immersed cylinder in fluidized beds at the particle scale. The previous models usually assume the gas flow to be two-dimensional. This does not fully represent the reality in which both the gas motions and particle-gas interactions naturally have more than six degrees of freedom. Here, a full 3DCFD-DEM model is developed to study the heat transfer in 3D gas-fluidized beds with immersed cylinders. For the purpose of the model validation, the simulations are conducted first for a single cylinder under different superficial gas velocities. It is shown that the predicted heat transfer coefficients between the cylinder and bed as a function of superficial gas velocity qualitatively agree with the measurements reported in the literature. The v-shaped curve is also reproduced. Then the simulations are conducted for a fluidized bed with cylinder banks (inline and staggered configurations) at a moderate superficial gas velocity. It is also shown that there is no significant difference in the averaged heat transfer coefficient between inline and staggered arrangements at a moderate superficial gas velocity. This work demonstrates that the developed 3D CFD-DEM approach could be a useful tool to study the coupled flow phenomena and heat transfer in such complex systems.