S63: Bio-based adipic acid from renewable fats and oils

Adipic acid is an important chemical building block used to make Nylon 6,6 and polyurethane resins with a global market over $6 billion.  It is currently produced by nitric acid catalyzed oxidation of cyclohexane derived from benzene in a process that generates nitric and nitrous oxides, VOCs and up to 4 tons CO₂ per ton of adipic acid. A cost-competitive bio-based adipic acid would offer a sustainable alternative to benzene price swings and allow the production of completely renewable nylon 6,6 and polyurethanes with a substantially smaller environmental footprint. To this end, we have engineered an industrial yeast strain to produce adipic acid from renewable vegetable oils. The parental strain can normally grow on alkanes or fatty acids as the sole carbon source via cyclic degradation through its beta-oxidation pathway. A strain in which this pathway has been completely blocked can convert these substrates at high yield and selectivity to the corresponding dicarboxylic acids via the omega-oxidation pathway, producing diacids with a chain-length distribution that precisely mimics the feedstock. We have since engineered this yeast to enable selective production of bio-based adipic acid from any plant-based oil, regardless of its fatty acid composition. We have scaled-up the fermentation and down-stream purification process to produce polymer-grade bio-based adipic acid, and have demonstrated its use for synthesis of nylon 6,6 fibers and chips.