Waste-derived low-grade glycerol purification and recovery from biorefineries: an experimental investigation

A combination of different physio-chemical treatment steps was applied to purify industrially derived crude glycerol at laboratory scale. The full process included acid–base treatments, phase separation, and adsorption, and the glycerol purity and recovery were optimized by varying the pH during saponification and acidification, the solvent-to-glycerol ratio, and type of base used in the process to enhance both. The testing campaign resulted in a final purity of up to 87% wt starting from a very low-quality ‘end-of-life’ waste glycerol sampled from different refineries. The net glycerol recovery at laboratory scale reached 42% of the initial glycerol in the feedstock and the maximum ash removal exceeded 90% given the low quality of the feedstock and high content of impurities and the attempt to achieve high glycerol recovery. The experiment showed that mild operations such as saponification with KOH (pH of 8), acidification with H₃PO₄ (pH of 6), an ideal 2-propanol to glycerol volume ratio equal to 3 and potassium hydroxide as a base for the neutralisation step were the optimum conditions despite the differences between samples. The sequence of the processes proposed was therefore considered a viable option to treat any kind of crude glycerol to make it profitable for fuel and chemical applications.