Refining and reforming of fossil feedstock produces indispensable materials

chemicals and fuels

but releasing a substantial amount of carbon dioxide (CO2). Bio-refineries of renewable biomass produce bio-based products of low carbon footprint. The biomass feedstock originates from CO2

water and sunlight

but relies on limited natural resources including arable land. This paper illustrates a green refinery that directly uses CO2

water and solar energy as the feedstock. A laboratory facility was set up and operated for verification

including a photovoltaic assembly

a membrane water electrolyzer

and a novel bioreactor in which an autotrophic hydrogen-oxidizing bacterium fixed CO2. Hydrogen was the only source of reducing agents and biological energy in microbial CO2 fixation

and obtained from water electrolysis with solar electricity. The reduced carbon was stored in bacterial biomass (CH1.74O0.46N0.19) and polyhydroxybutyrate (PHB

C4H6O2). PHB is a thermoplastic that can find a variety of applications because of its genuine biodegradability and similar material properties to that of polypropylene. It is also a platform material from which C3—C4 chemicals and aromatic compounds can be derived. Under catalysis of phosphoric acid

PHB was reformed into a gasoline-like transportation fuel. In addition

the residual bacterial mass can be also liquefied under thermal hydrolysis conditions and separated into a hydrophobic bio-oil and hydrophilic nutrient-rich hydrolysates. The former has a higher heating value than bio-oils from lignocellulose

and the latter can be reused in the microbial CO2 fixation as nutrients. A bioreactor of high mass transfer rate is the key to the technology because of the very low solubility of the gaseous substrates in the aqueous solution. A novel bioreactor was tested

exhibiting a high mass transfer rate even at a low gas feeding rate. The dry cell mass productivity reached 0.18 g·L-1·h-1 and the PHB content was about 50% (mass).