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International audience; The ability to couple membrane processes and crystallization operations, in order to develop efficient crystallization technologies, is increasingly reported. The main features of membrane crystallization systems are (1) to control and limit the maximum level of supersaturation due to defined mass transfer across the membrane; (2) to act as a support able to activate heterogeneous nucleation; (3) to control solid features such as size, shape, polymorphic form, and purity; and (4) to reduce energy consumption. To achieve these goals, several membrane techniques are used: reverse osmosis, membrane distillation, membrane contactor, and membrane templates. This review describes briefly the principles, applications, and advantages and drawbacks of each technique for crystallization operations.

This paper presents numerical simulations and experimental data on the iodide–iodate reaction in a hollow fiber membrane device. The principle of reactive mixing in a membrane device is the following. Component A flows through the inlet of the lumen side and component B comes from the membrane pores (shell side). Components A and B then mix and react inside the lumen side. Experimental measurements of the segregation index were carried out under various experimental conditions and for two different hollow fiber devices. The numerical and experimental segregation indexes, X S , were found in the range 10 −2 –10 −3 , indicating effective mixing. The numerical simulations showed that I 3 − ions were produced mainly in the first part of the lumen side of the hollow fiber. This confirmed our previous results on precipitation which showed that high supersaturation data and experimental fouling were obtained in this part of the hollow fibers.

International audience; in this second of two papers, we investigated the influence of process parameters on BaSO(4) particle precipitation in a hollow fiber membrane device. The solution of barium chloride was passed tangentially over the membrane surface and reacted with a solution of K(2)SO(4) introduced through the membrane pores. The resulting supersaturation induced nucleation and particle growth on the lumen side of the hollow fibers. A specific technique was developed to measure crystal size directly at the outlet of the hollow fiber device by using EDTA as a neutralizing agent of crystal nucleation and growth. Concentrations of barium chloride and potassium sulphate were shown to influence mainly the CSD, the effect of inlet flow rates on the lumen and shell sides being less pronounced. The chemical conversions measured were between 3.7% and 20.5%. We propose improvements in the design of hollow fiber devices in order to give higher chemical conversions.

International audience; Particle formation by precipitation is an important unit operation for the production of fine solids such as catalysts, pigments, and pharmaceuticals. It is the decisive step for determining properties such as particle size, shape, and purity, which in turn determine the quality of the end product. in this study, we investigated the precipitation of BaSO(4) particles in a. hollow fiber membrane device. A solution of BaCl(2), was passed tangentially over a membrane surface and reacted with a solution of K(2)SO(4) introduced through the membrane pores. The resulting supersaturation induced nucleation and particles grew on the lumen side of the hollow fibers. Particulate fouling was observed using X-ray images with BaSO(4) as a radiocontrast agent. It was shown that this fouling was attributed primarily to fiber blockage by newly formed crystals rather than to pore blockage. Moreover, a larger inner diameter of hollow fiber was shown to slow down considerably the fouling of the device. A numerical simulation was developed to calculate the supersaturation inside a hollow fiber, and the results of the simulation were compared with experimental data.

International audience; Liquid-liquid phase membrane contactors are increasingly being used for mixing and reaction. The principle is the following: component A flows through the membrane device inlet to mix/react with component B which comes from the membrane pores. This study presents a numerical simulation using computational fluid dynamics (CFD) of momentum and mass transfer in a tubular membrane contactor for laminar flow conditions. The velocity and concentration profiles of components A-C are obtained by resolution of the Navier-Stokes and convection-diffusion equations. The numerical simulations show that mixing between A and B is obtained by diffusion along the streamlines separating both components. The mixing/reaction zone width is within the region of a few hundred of microns, and depends on the diffusion coefficients of A and B. Hollow fiber membrane devices are found to be of particular interest because their inner diameter is close to the mixing zone width.