Co-production of bio-oil and propylene through the hydrothermal liquefaction of polyhydroxybutyrate producing cyanobacteria

In this investigation, PHB producing cyanobacteria were converted through hydrothermal liquefaction (HTL) into propylene and a bio-oil suitable for advanced biofuel production. HTL of model compounds demonstrated that in contrast to proteins and carbohydrates, which react to produce a range of alternative intermediates, no synergistic effects were detected when converting PHB in the presence of algal biomass. Subsequently, Synechocystis cf. salina, which had accumulated 7.5 wt% PHB was converted via HTL (15 % dry weight loading at 340 °C). The reaction gave an overall propylene yield of 2.6 %, higher than that obtained from the analogous model compounds, in addition to a bio-oil with a low total nitrogen content of 4.6 %. No propylene was recovered from the alternative non-PHB producing cyanobacterial strains, Anabaena, Spirulina or Synechococcus, suggesting that PHB is the sole source of propylene. PHB producing microorganisms could therefore be used as a feedstock for a biorefinery to produce polypropylene and advanced biofuels, with the level of propylene being directly proportional to the accumulated amount of PHB.