Electrosolar : Photovoltaic Energy

Electrically synthesized fuels sourced from atmospheric CO2- part 2

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Extraction of the CO2 from the air can be done chemically or physically. There are already existing chemical methods which recycle the active chemicals. These encompass alkali metal hydroxides, calcium hydroxide, sodium or potassium carbonate, or organic absorbers. Molecular-sieve materials, using temperature or pressure cycling, offer another method of extraction, which is currently used by British Oxygen to remove CO2 in their processing plants. Carbon dioxide can also be extracted from air physically using pressurisation and expansion. The ultimate efficiency of the process requires the dedicated skills of chemical and mechanical engineers, but the method chosen must be clearly energetically viable, and result in a plant size which small, but meets the throughput requirement. Alkali solutions such as sodium hydroxide appear to meet these demands. Generation of hydrogen by electrolysis has improved in efficiency, and is already at a commercial phase.

Hydrogenation of CO2 directly to methane, methanol, and even octane exists in the research and patent archives. Many researchers have demonstrated this reaction using various combinations of pressure, temperature and catalyst. Pressures of 300 bar, and temperatures of 300degC are typical. Because a lot of the energy required by this 'uphill' reaction is supplied by the mechanical work required to pressurise the reactants, the chemical reaction itself can even be slightly exothermic. A single stage process direct to hydrocarbon is possible, but a two-stage process, first to methanol, then using the well established 'Fischer-Troph' process to make a selectable molecular weight range of hydrocarbons may be the best route. To reach the ultimate efficiency of the process will require the dedicated skills of research chemists and chemical plant engineers. Careful thermodynamic design will reduce waste heat as far as possible in a large plant design.

If such a conversion process were 50% efficient, then with the electrical energy input described above for the 'large pilot plant' with a solar collection area of 10km x 10km, an output of 500,000 litres, or 3,000 'barrels' of refined petroleum-like hydrocarbon per hour could be expected.

 

 

 

It is estimated that the capital cost of globally replacing all existing oil extraction is around two trillion pounds (2000 billion). This is two years global oil revenue.

Such a broad paradigm shift away from the concept of pumping carbon fuels out of the ground, and towards synthesising them from atmospheric CO2 using solar energy, will eventually appeal to all oil companies.

When such solar fuel production plants are set up, the fuel they produce will be carbon neutral and essentially fully sustainable. Desert regions of the world will be effectively used. Aircraft will still fly, and cars will still run as they do today. Petrochemical industries can be sustained, and the oil companies can become sustainable. Atmospheric levels of CO2 can be stabilised, climate change and ocean rise averted.

The first stages in actively pursuing this target will be to set up a small research team to establish viable designs using CSP plant design and chemical engineering technology, and demonstrate on a large lab scale the viability of both the CO2 extraction, and the CO2 + H2 fuel synthesis. Expertise in oil refinery design would be a major bonus to speed up R&D in this area Once all main potential routes to the end are established, and the base level efficiency estimated, then pilot level plant design can start. Both Jordan and Egypt are already in the construction phase of suitable CSP power plants. A pilot plant with a 1 sq km solar collection area and a 100M-300M price tag would produce fuel to keep one 747-400 jetliner in service (16 hrs per day). I estimate that this form of fuel production will be economically advantageous over conventional oil well extraction when the price of oil reaches $200 per barrel in today's terms.

Other economic factors such as carbon credits, and use of the bi-products such as oxygen could improve the economic balance.

Richard Monkhouse,

Jan 2006 - Feb 2008.

Patent applied for.