Waste glycerol conversion on pilot scale continuous process by Al-modified mesoporous SiO2 catalysts

Abstract

This work describes the conversion of the waste glycerol (as generated in the biodiesel industry, supplied by Petrobras) to valuable chemicals (such as formic acid, diglycerol, and dioxanes). The reactions were evaluated in batch and continuous-flow fixed-bed reactors (PBR) on a pilot scale using high porosity mesoporous silica (≈ 1500 m2 g−1) and Al-modified silica catalysts (SiAl = 15/1 and 5/1). The Al addition increased the acidity of the catalysts and reduced their surface areas (698 m2 g−1 in SiAl = 5). High glycerol conversion (80%) was reached for 15 Si/Al and 5 Si/Al whereas SiO2 tends to deactivate in a continuous-flow fixed-bed reactor (PBR). Furthermore, the catalysts exhibited different selectivity: SiO2 produced mainly formic acid (≈ 65% average) in the liquid phase whereas the Al-modified catalysts generated a large amount of diglycerol, possibly due to the different acidity of the catalysts. This study indicates the potential industrial use of the catalysts and contributes to increasing the sustainability of the biodiesel industry.