A continuous approach to the emulsion gelation method for the production of aerogel micro-particle

Abstract

Aerogel micro-particles have a wide range of applications demonstrated at lab-scale in numerous publications, but material in a larger amount needs to be produced to allow for industrial tests and prototyping. In this work, we propose a continuous emulsion-gelation process able to produce gel micro-particles in sizeable quantities, demonstrating the industrial relevance of such approach. Alginate is taken as a model gelling system and two gelation mechanisms are demonstrated. Alginate solution and oil are pumped together through a progressive cavity pump and fed to a colloid mill to produce alginate in oil emulsion in one pass. The gelation in emulsion is then carried in-line via a controlled injection of a gelation trigger (acetic acid or calcium chloride). The gel microparticles are separated from the oil via sedimentation or centrifugation and partitioning into an ethanol solution. Further solvent exchange to ethanol and supercritical drying with CO2 yielded aerogel microparticles with large specific surface area. The size of the emulsion droplets is directly related to the final aerogel particles size. The influence of the emulsification parameters on the droplet size is thus discussed and assessed using critical capillary number values from the literature. To complete this task, the dynamic interfacial tension of the alginate-paraffin oil-Span80 system was measured and the rheology of the alginate solution and of the emulsion assessed.