Production of Porous Silica Microparticles by Membrane Emulsification

A method for the production of near-monodispersed spherical silica particles with controllable porosity based on the formation of uniform emulsion droplets using membrane emulsification is described. A hydrophobic metal membrane with a 15 mu m pore size and 200 mu m pore spacing was used to produce near-monodispersed droplets, with a mean size that could be controlled between 65 and 240 mu m containing acidified sodium silicate solution (with 4 and 6 wt % SiO2) in kerosene. After drying and shrinking, the final silica particles had a mean size in the range between 30 and 70 mu m. The coefficient of variation for both the droplets and the particles did not exceed 35%. The most uniform particles had a mean diameter of 40 mu m and coefficient of variation of 17%. By altering the pH of the sodium silicate solution and aging the gel particles in water or acetone, the internal structure of the silica particles was successfully modified, and both micro- and mesoporous near-monodispersed spherical particles were produced with an average internal pore size between 1 and 6 nm and an average surface area between 360 and 750 m(2) g(-1). A material balance and particle size analysis provided identical values for the internal voidage of the particles, when compared to the voidage as determined by BET analysis.