PetroSun is one of the few biofuel companies (it also produces parts for oil refinery and drilling equipment) to advertise a “carbon negative” energy production process. This is somewhat different from the “carbon neutral” claims of other companies in that PetroSun promises to decrease overall carbon emissions through its process.
PetroSun uses a two-step process to produce ethanol (or biodiesel) and hydrogen. The process begins with burning organic matter in a kiln under low oxygen conditions to produce carbon dioxide, hydrogen, and charcoal. The CO2 is used as a feedstock for algae to produce a biofuel, the hydrogen is burnt for electricity, and the biochar is used as fertilizer. The key to the process is that charcoal from feedstock derived from plant matter that fixed CO2 will return some of that CO2 to the ground when the charcoal is used as fertilizer. The net result is a reduction in atmospheric carbon and thus it is a carbon negative process.
PetroSun built a 30 million gallon demonstration plant in Arizona in 2008. The plant was designed to test the company’s technology at a large scale and to prove the carbon-negative process was feasible.