Integrated hydroprocessing and microbial biotransformation of coconut oil to α,ω-diacids

Abstract

The convergence of chemical and biological technologies offers unprecedented opportunities for sustainable chemical production. Oxygenated oil-based biomass requires a chemical process to refine it into less-toxic hydrocarbons to be used for microbial biotransformation to produce value-added chemicals. This study demonstrates the transformation of hydrotreated vegetable oils, specifically coconut oil, into α,ω-diacids (DCAs), which are essential for bio-based polymer production. Through an optimized hydrodeoxygenation process in a fixed-bed reactor, bio-alkanes were produced at high yield (86.7 %) under controlled conditions (370 °C and 40 bar of H2). The recovered liquid products consisted primarily of paraffins with varying carbon chain lengths, including C12 and C11 hydrocarbons containing approximately 73 % n-paraffins and 21 % isoparaffins, as determined by GC-MS. The resulting n-alkanes (C6-C18) were non-toxic to Candida tropicalis, a biocatalyst that efficiently converted these n-alkanes into DCAs at concentrations exceeding 65 g/L, with a substrate-to-product conversion yield of approximately 80 % in a 5-L fermentation system. The carbon distribution of the resulting DCAs corresponded to that of the n-alkane substrates, with C11 and C12 chains predominating. To achieve industrial-grade purity, a robust separation and purification process was developed. Dimethyl ester mixtures, derived from DCA mixtures via reactive distillation, were subjected to simulation-based distillation, yielding crude fractions of dimethyl dodecanedioate (C12; 60.3 %) and dimethyl undecanedioate (C11; 35.6 %). Subsequent multistage distillation further increased the purity of both fractions to over 99 %. By bridging the gap between bio-based raw materials and industrial applications, this research provides a scalable model for advancing green chemistry and the production of bio-based materials.