(447b) Fermentation-Based Propionic Acid Production: An Industrial Perspective on the Progress, Technical Challenges and Future Outlook

Propionic acid is an important commodity chemical with a rapidly growing demand in a variety of markets.  Propionic acid has significant value as a food preservative, but it can also serve as feedstock for high-volume commodity products such as propanol and propylene.  Currently, the majority of propionic acid is manufactured through petrochemical routes which can be tied to increasing prices and volatility due to difficultly in forecasting demand and feedstock availability.  A renewable, fermentation based approach to manufacture propionic acid would increase sustainability and enable production in new geographies. As with many fermentation processes, the challenges to developing an economically viable propionic acid process include productivity, titer and product yield. Over five decades of research has shown that propionic acid can be produced by fermentation of Propionibacterium at relatively high amounts.    However, this work has not led to commercialized processes because propionic acid is highly inhibitory to Propionibacterium limiting titers to below commercially feasible levels and product yield is redox constrained due to the stoichiometry of the native biochemical pathways.  Recently, product yield has become an even bigger factor in achieving an economically viable fermentation process because of increases in feedstock cost.  This work summarizes the research advancements made towards developing an industrially feasible propionic acid fermentation process.  Improvements in titer were made through classical organism selection and screening.  Fermentation productivity was improved more than three-fold to exceed 2 g/L/h by densifying the fermentation inoculum source.  Byproduct levels, particularly lactic acid and succinic acid, were reduced significantly by optimizing fermentor headspace pressure and agitation shear. In addition to the process advancements, a novel medium recipe was developed to improve product yield and reduce manufacturing costs to economically competitive levels.  The optimized fermentation process achieved a manufacturing cost of less than 1 USD per kilogram of propionic acid and is expected to become economically competitive with incumbent petrochemical processes within the next 10 years.