Two-step salting-out extraction of 1,3-propanediol and lactic acid from the fermentation broth of Klebsiella pneumoniae on biodiesel-derived crude glycerol

摘要

Crude glycerol is a primary by-product in the biodiesel production process and its large surplus blocks the development of the biodiesel industry. In this study, crude glycerol was used as a substrate to co-produce 1,3-propanediol (1,3-PD) and lactic acid through fermentation of Klebsiella pneumoniae. The final concentrations of 1,3-PD and lactic acid were 62.6 and 33.4 g/L, respectively, and the total mass conversion yield was 55.7%. The two-step salting-out extraction method was adopted for the separation of 1,3-PD and lactic acid from the fermentation broth. In the first step of extraction, the maximal partition coefficient and recovery of 1,3-PD reached 9.81 and 92.4% under the optimal conditions of 30% isopropanol and 30% potassium carbonate. Subsequently, 28% ethanol was added into the salt phase to perform the second salting-out extraction at pH 6.5. The partition coefficient and recovery of lactic acid reached 1.27 and 73.8%, respectively. All cells and most of the proteins (98.5%) were finally removed. The results suggest that crude glycerol can be used as a promising feedstock to co-produce 1,3-PD and lactic acid from fermentation broths, and this could not only reduce the production cost but also promote the further development of the biodiesel industry.