Fine control of NaCl crystal size and particle size in percrystallisation by tuning the morphology of carbonised sucrose membranes

Mesoporous SiC-Based Photocatalytic Membranes and Coatings for Water Treatment

Photocatalytically active silicon carbide (SiC)-based mesoporous layers (pore sizes between 5 and 30 nm) were synthesized from preceramic polymers (polymer-derived ceramic route) on the surface and inside the pores of conventional macroporous α-alumina supports. The hybrid membrane system obtained, coupling the separation and photocatalytical properties of SiC thin films, was characterized by different static and dynamic techniques, including gas and liquid permeation measurements. The photocatalytic activity was evaluated by considering the degradation efficiency of a model organic pollutant (methylene blue, MB) under UV light irradiation in both diffusion and permeation modes using SiC-coated macroporous supports. Specific degradation rates of 1.58 × 10^-8 mol s^-1 m^-2 and 7.5 × 10^-9 mol s^-1 m^-2 were obtained in diffusion and permeation modes, respectively. The performance of the new SiC/α-Al₂O₃ materials compares favorably to conventional TiO₂-based photocatalytic membranes, taking advantage of the attractive physicochemical properties of SiC. The developed synthesis strategy yielded original photocatalytic SiC/α-Al₂O₃ composites with the possibility to couple the ultrafiltration SiC membrane top-layer with the SiC-functionalized (photocatalytic) macroporous support. Such SiC-based materials and their rational associations on porous supports offer promising potential for the development of efficient photocatalytic membrane reactors and contactors for the continuous treatment of polluted waters.

Evaluation of percrystallization coupled with electrodialysis for zero liquid discharge in the pulping industry

We evaluated percrystallization at laboratory scale to determine its suitability as core technology for achieving Zero Liquid Discharge (ZLD) in a Kraft effluent desalination process. Compared with conventional evaporation/crystallization techniques, percrystallization allows to operate at room temperature and with barely pressurized fluids, using relatively unexpensive membranes and vacuum to allow evaporation of aqueous brine solutions. For further comprehension of the technology before experimentation, a computational fluid dynamics model was developed, showing how temperature affects the performance of percrystallization in terms of transmembrane flux. Additionally, we performed experiments with single and double salt solutions (NaCl and NaCl/Na₂SO₄) and concentrated industrial effluent from a Kraft pulp mill (brine from the effluent desalination with electrodialysis). Percrystallization of the concentrated industrial effluent was successfully achieved at laboratory scale, showing no signs of fouling on the membrane surface. However, high energy consumptions (above 3000 kWh/ton of evaporated water) were measured. Theoretical power consumptions of an optimized industrial percrystallization system were therefore computed. Percrystallization showed a more efficient performance compared with similar membrane systems, such as vacuum membrane distillation, but higher energy consumptions than conventional ZLD technologies (mechanical vapor compression), having an estimated energy consumption of around 110-150 kWh/ton of removed water, depending on the feed fluid temperature. Nevertheless, percrystallization could be suitable for ZLD applications where low-cost heating (e.g., solar) is available, since the vacuum energy demand is only 32-140 kWh/ton. Alternatively, it could be applied to low scale processes where the temperature of the solution must remain low (e.g., less than 40 °C).