Non-solvent-based pretreatment of poly(3-hydroxybutyrate) for improved bio-based crotonic acid production

Abstract

In this study, high purity bio-based crotonic acid was obtained by a non-solvent-based pretreatment of poly(3-hydroxybutyrate), PHB, prior to pyrolysis. PHB was produced by Cupriavidus necator KCTC 2649 utilizing heat-treated oil palm frond juice followed by mild alkaline treatment with 0.05 M NaOH. It was found that NaOH-treated PHB was highly converted to its dehydrated monomer to give bio-based crotonic acid with 89% purity; 16% higher than that produced from chloroform-treated PHB. It is believed that pretreatment of PHB with low concentration NaOH assisted in high thermal conversion of PHB into crotonic acid by producing a crotonyl chain-end and Na-binding carboxyl terminal end, which both accelerate the β-chain scission of PHB into biocrotonic acid. The initial molar mass of PHB also played a role in biocrotonic acid production. Overall, improved biocrotonic acid production with high purity is an advantage for industrial production of crotonic acid from renewable resources.