Direct production of propene from the thermolysis of poly(β-hydroxybutyrate)

The transformation of biomass components into hydrocarbon fuels involves two main reactions, i.e., deoxygenation and carbon chain extension.  The potential routes for decreasing the oxygen content of biomass intermediates include dehydration, hydrodeoxygenation and decarboxylation. One route that is examined here is the conversion of polyhydroxyalkanoates (PHA) to alkenes that would be intermediates to hydrocarbon fuels. Thermal breakdown of PHA proceeds via an intermediate carboxylic acid, which can then be decarboxylated to an alkene.  Oligomerization of alkenes by well-known commercial technologies would permit production of a range of hydrocarbon fuels from a carbohydrate derived intermediate. Moreover, polyhydroxybutyrate (PHB) can be produced in Cupriavidus necator (formerly known as Ralstonia eutropha) on a variety of carbon sources including glucose, fructose and glycerol with PHB accumulation reaching 75% of dry cell mass.  We conducted thermal conversion of PHB and pure crotonic acid (CA), the intermediate carboxylic acid produced by thermal depolymerization of PHB, in a flow-through reactor. The results of initial experiments on the thermal conversion of CA showed that up to 75 mole% yields of propene could be achieved by optimizing the residence time and temperature of the reactor. Further experiments are being investigated to optimize the reactor parameters and enhance propene yields via thermal conversion of PHB.