New insights into the formation of submicron silica particles using CO2 as anti-solvent

Abstract

A supercritical anti-solvent (SAS) process was carried out to obtain micron and submicron particles (0.35–1.78μm) of silica from a solution with a silica precursor. The effects of different parameters such as pressure (120 and 150bar), temperature (323 and 333K), CO2 flow rate (20 and 35g/min), liquid solution flow rate (4 and 8mL/min) and nozzle diameter (0.1 and 0.2μm) on the outcome of the SAS process were analyzed. The TEOS: water molar ratio (1:4–1:17) was also evaluated and seems to play a major role in the precipitation of particles, especially in terms of agglomeration and morphology in that a higher amount of water leads to lower agglomeration of particles. Higher CO2 and lower liquid solution flow rates are recommended to obtain a smaller particle size with narrow particle size distribution (0.35±0.17μm). Lower temperatures are recommended to reduce the particle size. The rest of the assayed variables did not have a significant influence on particle size and size distribution. As far as the textural properties are concerned, silica particles with low porosity (1.41–10.22m2/g) and certain hydrophilic character were generally produced.