MOF-808 as an Efficient Catalyst for Valorisation of Biodiesel Waste Production: Glycerol

Glycerol is the main residue in the biodiesel production industry; therefore, their valorisation is crucial. Acetalization of glycerol towards fuel additives as solketal (2,2-dimethyl-1,3-dioxolan-4-methanol) is of high interest, promoting circular economy since it can be added to the biodiesel or even fossil-diesel to improve their quality and efficiency. Straightforward prepared metal-organic framework (MOF) materials of MOF-808 family were applied to the valorisation of glycerol for the first time. In particular, MOF-808(Hf) revealed to be an effective heterogeneous catalyst to produce solketal under moderate conditions: small amount of the MOF material (only 4wt% of glycerol), ratio 1:6 of glycerol/acetone and temperature of 60 ºC. The high efficiency of MOF-808(Hf) was associated with the high amount of acid centres present in its structure. Furthermore, its structural characteristics such as window opening cavities size and pore diameters showed to be ideal to reuse this material during at least ten consecutive reaction cycles without losing activity (conversion > 90% and selectivity > 98%). Remarkably, it was not necessary the washing or other activation treatment of the MOF-808(Hf) catalyst between cycles (no pore blockage occurred) and it maintained structural integrity after the ten cycles, confirming to be a sustainable heterogeneous catalyst to the glycerol valorisation.