Escaping the Tyranny of Carbothermal Reduction: Fumed Silica from Sustainable, Green Sources without First Having to Make SiCl4

Abstract

Fumed silica is produced in 1000 tons per year quantities by combusting SiCl4 in H2/O2 flames. Given that both SiCl4 and combustion byproduct HCl are corrosive, toxic and polluting, this route to fumed silica requires extensive safeguards that may be obviated if an alternate route were found. Silica, including rice hull ash (RHA) can be directly depolymerized using hindered diols to generate distillable spirocyclic alkoxysilanes or Si(OEt)4. We report here the use of liquid‐feed flame spray pyrolysis (LF‐FSP) to combust the aforementioned precursors to produce fumed silica very similar to SiCl4‐derived products. The resulting powders are amorphous, necked, <50 nm average particle sizes, with specific surface areas (SSAs) of 140–230 m2 g−1. The LF‐FSP approach does not require the containment constraints of the SiCl4 process and given that the RHA silica source is produced in million ton per year quantities worldwide, the reported approach represents a sustainable, green and potentially lower‐cost alternative.Spirocyclic alkoxysilane, synthesized by depolymerization of rice hull ash using hindered diols, can be combusted in a controlled manner to produce fumed silica. Compared to commercial SiCl4‐derived fumed silica, no difference is noted in terms of morphologies, whereas toxic, corrosive starting material and byproduct are not present in the liquid‐feed flame spray pyrolysis (LF‐FSP) process (see scheme).