One-pot production of hydrocarbon oil from poly(3-hydroxybutyrate)

Abstract

Poly(3-hydroxybutyrate) (PHB) is an energy storage material of many microbial species, and has been found to be an effective feedstock for production of renewable hydrocarbon oils. A high oil yield (up to 38.2 wt%) was obtained in a phosphoric acid (H₃PO₄) solution at mild temperatures (165–240 °C). PHB and crotonic acid (C₄H₆O₂), a dominant thermal degradation product of PHB, were deoxygenated mainly via decarboxylation, generating similar liquid and gaseous products. Carbon dioxide and propylene were the major products in gas phase with little CO formation. The hydrocarbon oil (C4–C16) is a mixture of alkanes, alkenes, benzenes and naphthalenes. Aromatics (C10–C15) were the major hydrocarbons in a 100 wt% H₃PO₄ solution, while alkenes and alkanes (C4–C9) were favored in diluted solutions (50 wt% to 85 wt% H₃PO₄). The concentration of H₃PO₄ was a key factor that affected the oil composition and yield. A highly efficient decarboxylation of crotonic acid at 220 °C for 3 hours resulted in 70.8 wt% of oxygen being removed as CO₂ and 57.0 wt% of carbon being recovered as hydrocarbon oil. The H₃PO₄ solution can be repeatedly used for high yield oil production. This work shows that a type of new biological feedstock can be used to produce renewable hydrocarbon oil in an efficient one-pot reaction.