CO2 to fuels processes - II

Recently Carbon Sciences, featured in an earlier article on this blog revealed the source of hydrogen for their CO₂ to fuels process.
"Dr. Naveed Aslam, inventor of the company's technology and chief technology advisor, commented: "Unlike other CO2 to fuel approaches, Carbon Sciences' technology does not use molecular hydrogen (H2) because the creation and reaction of H₂ is very energy intensive. Rather, the company's approach is based on a low energy biocatalytic hydrolysis process where water molecules (H₂O) are split into hydrogen atoms (H) and hydroxide ions (OH) using a biocatalyst. The hydrogen atoms (H) are immediately used in the production of hydrocarbons and the free electrons in OH are used to power the various biocatalytic processes." "Our technology is not based on photosynthetic plants where sun light is used to drive biofuel production reactions, such as in algae. Instead, it is based on natural organic chemistry processes that occur in all living organisms where carbon atoms, extracted from CO₂, and hydrogen atoms extracted from H₂O, are combined to create hydrocarbon molecules using biocatalysts and small amounts of energy. Our innovative technology allows this process to occur on a very large industrial scale through advance nano-engineering of the biocatalysts and highly efficient process design," concluded Dr. Aslam."
My opinions given below:
Understandably Carbon Sciences is justified in not fully revealing the details . However, the splitting of water to produce protons (H⁺) and hydroxide ions (OH^-) still consumes energy. All the biocatalyst does is to speed up this transformation. It cannot influence the thermodynamics (feasibility) of this reaction. Judging by what the release says, I think that there is a sacrificial oxidant (something which gets oxidized, ex: simple sugars, providing the energy to drive the splitting of water) involved.

Related links:
Opinion: CO2 to fuels processes
Carbon Sciences Announces Prototype Plan for CO2-to-Fuel Technology

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Opinion: CO2 to fuels processes

The Green Car Congress blog has an article on a CO2 to fuels process by a company called Carbon Sciences.

Important features of this process are:
1) The use of biocatalysts (enzymes?) to effect the transformations under mild conditions.
2) The use of relatively “dilute” CO2 streams, which could lower the costs for CO2 separation from power plant-flue-gas streams.
My graduate research is in a closely related area, the photocatalytic conversion of CO2 to fuels in which CO2 and water react upon light-induced electron transfer to/from a suitable photosensitizer. This reaction is not very efficient. On the other hand, the heterogeneous hydrogenation of CO2 with H2 is fairly effective (but involves high temperatures), a Japanese company, Mitsui Chemicals will begin the construction of a pilot plant this year to produce 100 T/year of methanol (CH3OH) from CO2 and solar-produced hydrogen.

My opinion:
The conversion of CO2 to fuels is a hydrogenation reaction (add hydrogen, remove oxygen). However, I could not find information on the Carbon Sciences website about their hydrogen source.
One wonders how effective the scale up of this biocatalytic process will be. The main questions for me here are the source of hydrogen, enzyme stability and costs, and the product separation and purification costs. These factors would determine if this process indeed is cheaper than the heterogeneous catalytic process (using Cu/ZnO-like catalysts).
Hat tip: Green Car Congress blog.

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