The production of propionic acid, propanol and propylene via sugar fermentation: an industrial perspective on the progress, technical challenges and future outlook

Propionic acid, n-propanol and propylene are chemicals in a variety of markets ranging from plastics to food preservatives. Propylene is an important commodity monomer and precursor to many chemical products, while propionic acid and n-propanol are smaller volume chemicals with growth potential. In place of petrochemicals, carbohydrates are a possible feedstock to all three by fermentative production of propionic acid followed by synthetic derivation of n-propanol and propylene through chemical reductions. There are few studies that directly assess the industrial practicality of this process despite five decades of scientific literature describing propionic acid fermentation with Propionibacterium. The work herein describes a sugar fermentation process evaluation for propionic acid production that achieved productivities at commercial levels, reaching yields of 0.55 g g(-1) and reducing media costs to less than $1.00 per kg. Industrial scalability was explored via modeling fermentor size, raw material costs and capital, in order to compete with a conventional petrochemical route. Extra attention was given to separations, as aqueous acid separation is energy intensive and has frequently rendered biological processes non-competitive. Economic analysis and conceptual process evaluation of each of these experimentally supported steps combined resulted in targets to produce a cost competitive route to biologically derived propionic acid and subsequent n-propanol and propylene derivatives. Product yield from sugar was shown to be a key component of any successful propionic acid with a 0.6 g g(-1) yield being immediately competitive. These findings prescribe and prioritize remaining parameters for subsequent research seeking to develop a cost-competitive bio-chemical route to C3 materials.