Mild pyrolysis of P3HB/switchgrass blends for the production of bio-oil enriched with crotonic acid

• Switchgrass and polyhydroxybutyrate (P3HB) were co-pyrolyzed.
• Switchgrass pyrolysis oil, bio-char and crotonic acid were produced at 375 °C.
• Maximum crotonic acid yield was about 45% of input P3HB.
• Crotonic acid may be present as both gas and aerosol in the pyrolysis vapor stream.

The mild pyrolysis of switchgrass/poly-3-hydroxybutyrate (P3HB) blends that mimic P3HB-producing switchgrass lines was studied in a pilot scale fluidized bed reactor with the goal of simultaneously producing crotonic acid, a switchgrass-based bio-oil, and bio-char. Factors such as pyrolysis temperature, reactor residence time, flow rate and particle size of the P3HB were studied to determine their effects on the recovery of crotonic acid as a component of the pyrolysis oil produced from the mixture. Crotonic acid yields were maximized at 45 wt% of the input P3HB by using small P3HB particles and a pyrolysis temperature of 375 °C. The remaining components of the liquid product were similar to those produced via fast pyrolysis of switchgrass alone. Fractional collection within the condensation system of the pyrolysis process development unit (PDU) did not significantly fractionate crotonic acid more than the total liquids collected. Concentrations of 6 to 10 wt% crotonic acid in the liquids were found in all fractions and crotonic acid was effectively collected by both condensation and electrostatic precipitation suggesting that pyrolysis of P3HB produces crotonic acid in both gas and aerosol phases.