Development of ceramic membranes for resource recovery from brine through percrystallization

Availability of efficient methods to fractionate a solution into its solid and liquid components is the key to recycling and reuse of industrial effluents. Percrystallization is a novel membrane process where a thin film of warm permeate present at the membrane surface is evaporated through vacuum to crystalize the soluble compounds. Thus, the process separates a solution into crystalline solute and solvent in a single-step and can partly be operated with sustainable sources of energy such as solar and geothermal heat. Since the process is at early stage of exploration, there is no sufficient knowledge about the suitable membrane features for the percrystallization which hampers its further development and potential progress towards commercialization. This work performs a systematic and groundbreaking investigation to identify and develop suitable membranes for percrystallization applications. The study has been carried out by using silicon carbide (Si-C) and polymeric membranes with different porosities and thicknesses. The effect of pore size and surface hydrophobicity on the process operation was investigated by coating the surface of Si-C membranes with methylated silica particles of different sizes. Inherent hydrophobicity of the polymeric membranes was also modified to test their suitability for the percrystallization applications. All the membranes were tested for separation of NaCl crystals from solution by using different concentrations (3.5, 10 and 17.5 wt%) of NaCl at operating temperatures of 50 °C, 55 °C and 60 °C. It was observed that the membranes with the rate of permeation comparable with the rate of evaporation under the applied vacuum are crucial to operate the process. Thus, only less porous and thick Si-C membranes with liquid entry pressure approaching to 1 bar were suitable for percrystallization. The developed membranes yielded water and NaCl flux in the range of 9.43±2 and 1.2 kg/m2.h, respectively. The process outperformed state-of-the-art membrane processes in terms of productivity and simplicity.