Researchers have demonstrated a route for the production of major commercial C3 hydrocarbons (propane and propylene) from renewable biomass via the hydrothermal conversion of well-known fermentation end-products (butyric acid and 3-hydroxybutyrate) without the use of exogenous hydrogen. The process can potentially have high thermal efficiencies.
The two-step process first uses fermentation to produce partially deoxygenated intermediate chemicals. These intermediate chemicals are subsequently decarboxylated and/or dehydrated in hydrothermal media to produce the C3 hydrocarbons.
A paper on their work appears in the ACS journal Industrial and Engineering Chemistry Research.
Specifically, the major commercial C3 hydrocarbons, propane and propylene, can be obtained from butyric acid and 3-hydroxybutyrate (3HB) in substantial yields and industrially relevant productivities by hydrothermal decarboxylation. Butyric acid decarboxylates in supercritical water to give propane as the major product at 454 °C and 25 MPa. 3HB undergoes joint dehydration and decarboxylation in subcritical water to yield propylene at 371 °C and 25 MPa with yields of up to 48 mol %.
Although catalysts may be found that increase yields and selectivities, these processes were demonstrated without any added heterogeneous catalysts, and have the further advantage of requiring no external H2 source.—Fischer et al.
Authors Curt R. Fischer, Andrew A. Peterson, Jefferson W. Tester were originally at MIT; they are now at Ginkgo Bioworks, Stanford University, and Cornell University, respectively.
Curt R. Fischer, Andrew A. Peterson, Jefferson W. Tester (2011) Production of C3 Hydrocarbons from Biomass via Hydrothermal Carboxylate Reforming. Industrial & Engineering Chemistry doi: 10.1021/ie1023386