Propylene Glycol from Biodiesel By-product

The enormous production of glycerol, a waste stream from biodiesel industries, as a low-value product has been causing a threat to both the environment and the economy. Therefore, it needs to be transformed effectively into valued products for contributing positively towards towards the biodiesel economy. In this study, propylene glycol was produced by hydrogenating glycerol with a highly selective hydrogenolysis catalyst. The effect of various reaction parameters on the product yield was evaluated. A two-step reaction process where, first, glycerol was dehydrated to form acetol, and then this acetol was hydrogenated in a further reaction step to produce propylene glycol gave higher conversion as compared to a one-step reaction process. The effects of reaction temperature and pressure on the product yield were also evaluated. Higher yields of propylene glycol were observed at higher pressures. At temperatures above 200 °C, more by-products may be formed as the selectivity on converting glycerol to propylene glycol dramatically decreased, eventhough the glycol content increased.