Highly basic solid catalysts obtained by spray drying of a NaAlO2 and boehmite suspension for the upgrading of glycerol to acetins

Abstract

In here, we present the low-cost production of NaAlO₂–Al₂O₃ catalysts, which exhibit high activity in the transesterification of methyl acetate with glycerol to obtain acetins. The catalyst preparation procedure is based on the spray drying of a colloidal boehmite suspension, supplemented with a sodium aluminate (NaAlO₂) solution using a pilot scale spray drier. Upon subsequent calcination, we obtain spherical micro particles presenting a homogeneous dispersion of sodium aluminate and featuring high basicity. The NaAlO₂ loading has a marked impact on the basicity and textural properties of the final materials. These solids are found to be efficient heterogeneous base catalysts for the upgrading of glycerol (which is essentially a waste) to glycerol acetins (which are important bio-based fuel additives). With 100 mg of the catalyst loaded with 20 wt% of NaAlO₂, a conversion of 96% is obtained after 4 h of reaction at 60 °C (10 mmol of glycerol + 100 mmol of methyl acetate). Importantly, the selectivity for triacetin is as high as 20% (the rest being 50% of diacetin and 30% of monoacetin). The catalysts act strictly in a heterogeneous way and are recyclable upon calcination.