Design and analysis of poly-3-hydroxybutyrate production processes from crude glycerol

The growing biodiesel production has generated a glycerol surplus and consequently a drop of its sale price. The development of biorefineries to convert crude glycerol to higher value products is an urgent need and an opportunity to overcome the negative impact of low glycerol prices in the biodiesel industry. Glycerol fermentation by microorganisms to useful chemicals as poly-3-hydroxybutyrate (PHB) is an interesting alternative. In this article a techno-economical analysis for PHB production from crude glycerol is presented. The glycerol fermentation process was carried out using two qualities of glycerol, either 88 or 98 wt%. Thus, the glycerol purification process was simulated and economically analyzed using Aspen Plus and Aspen Icarus, respectively. The fermentation process is carried out in two stages in which mass cell growth and PHB accumulation occurs, respectively. Also, three downstream processes to isolate and purify the PHB were considered. The process steps, namely mass cell pretreatment, PHB isolation and purification were considered in each scenario and six technological schemes were analyzed. Economical assessment results show that the most appropriate technological scheme requires purifying the crude glycerol until 98 wt%, with a downstream process involving heat pretreatment, enzymatic-alkaline digestion, centrifugation, washing, evaporation, and spray drying.