Integrated study of fermentation and downstream processing in a miniplant significantly improved the microbial 1,3-propanediol production from raw glycerol.

ABSTRACT

In this work, an integrated and optimized production process for 99 % pure 1,3-propanediol (PDO) from raw glycerol is presented. Glycerol fermentation is carried out applying a newly isolated strain Clostridium pasteurianum K1 under non-sterile conditions without any complex ingredients in the fermentation media. In this environment over 55 g/L PDO, yields of 0.52 g/g and space time yields over 2.3 g/(Lh) were achieved in up to 1 m(3) pilot scale. The downstream process for PDO purification consists of an ultrafiltration for biomass and protein separation, an evaporation step for concentration of PDO and a two-step rectification for final purification. For a proof of concept, process optimization and especially investigation of interactions of individual steps, the downstream process was performed in miniplant scale. A minimum salt input into the downstream process was shown to be important to overcome precipitation in evaporation as well as rectification. Thus, raw glycerol is desalinated before fermentation and the fermentation medium was minimized and complex nutrients, such as yeast extract, were avoided totally to prevent furthermore dark color formation. Furthermore, by titration of fermentation with ammonia instead of sodium hydroxide, the later separation of the major by-products, organic acids, in the evaporation step was significantly enhanced.