Transport phenomena and crystal growth in novel multifunctional inorganic membrane reactor percrystallization

This work shows that novel membrane reactor percrystallization is a multifunctional process. Percrystallization means permeation + crystallization in a single-step process. Fundamental to percrystallization is the membrane structure, predominantly carbon-base coating on alpha-alumina substrates. A unique feature of percrystallization is the wet-thin film interface at the permeate side of the membrane. Under vacuum pressure conditions, solvents evaporate very quickly aiding mass transfer of the solute to fast nucleation and crystallization. At the wet-thin film interface, all solute available forms crystals (100% reaction completion) and simultaneously fully separated from the solvent (100% crystal/solvent separation). Prior understanding of the solvent and crystal fluxes reported that the driving force was a function of pressure gradient. Analysis of the transport phenomena data suggest that permeation is a function of the solvent’s vapour pressure and viscosity of solutions. In addition, this work proposes for the first time that crystal growth is a function of the residence time of the solute in the wet-thin film. Lower solvent evaporation rate allows for a higher residence time for the solute’s mass transfer thus forming large particles and vice-versa. For instance, the NaCl crystal growth Rg = 0.78 is linear and proportional to the residence time and four orders of magnitude faster than evaporative crystallizers. Membrane reactor percrystallization proved to be flexible to process a number of solutes in water (NaCl, KCl, NiCl2, Li compounds, NiSO4, Vitamin C and oxalic acid) and in ethanol (paracetamol) with potential applications in mineral processing, food and pharmaceutical industries.