The Azimuth Project
Methanol economy (Rev #5)

Idea

Carbon dioxide is recycled naturally though photosynthesis, using the sun’s energy. But new fossile fuels can only be formed after sufficient geological time. In contrast, carbon dioxide can be chemically recyled to methanol, and a carbon cycle based on methanol (instead of fossile fuels) allows much shorter recycling times. Therefore, an economy based on methanol instead of fossile fuels as an energy carrier could be renewable at the shorter time scales necessary for human economics.

Methanol is advantageous to hydrogen as an energy carrier because the latter is potentially explosive and highly volatile. In addition, methanol can be used as a starting material for synthetic hydrocarbons. The advantage of methanol to biofuels is that the former does not require shifting valuable food resources to fuel production.

The chemical recycling of carbon dioxide to ethanol involves two steps: carbon dioxide capture and successive hydrogenation. In theory, the energy needed for the production of methanol would be supplied by renewable energy sources.

How much energy would be needed to support the recycling of methanol, if all fossile fuels were replaced by ethanol?

Fuels: methanol and dimethyl-ether (DME)

Methanol is already a prime material for the chemical industry. It has excellent combustion characteristics (average octane number of 100). Dimethyl-ether is derived from methanol (presently produced by the bimolecular dehydration of methanol) and it is superior compared to methanol to replace diesel in internal combustion engines because of its higher cetane number (55-60).

Manufacture of methanol

From fossil fuel syngas

Methanol is presently exclusively produced from fossil fuel based syngas (a mixture of CO and H 2H_2), about 40 million tonnes annually. This process generates large amounts of carbon dioxide.

From CO 2CO_2 to methanol

Even the small concentration of carbon dioxide in the air can be separated and chemically recycled to methanol ( check this claim from JOC 74(2):487 ). The most studied route is the catalytic regenerative conversion of carbon dioxide with hydrogen.

(1)CO 2+3H 2CH 3OH+H 2Ohspace5mmΔH 298K=11,9kcal/mol CO_2 + 3 H_2 \leftrightarrow CH_3OH + H_2O \hspace{5mm} \Delta H_{298K}= -11,9 kcal/mol

The synthesis of methanol has been demonstrated on a pilot scale in Japan.

The first commercial recycling plant (using geothermal energy) has been built in Iceland by Carbon Recycling International. In Japan, a pilot plant is being built by Mitsui chemicals.

From methane

Carnol process

(2)3CH 4+2CO 22CH 3OH+2H 2O+3C 3 CH_4 + 2 CO_2 \rightarrow 2 CH_3OH + 2 H_2O + 3 C

Bireforming

(3)3CH 4+2H 2O+CO 224CH 3OH 3 CH_4 + 2 H_2O + CO_2 \rightarrow 2 4 CH_3OH

Additional information

From:

More importantly, methanol can also be produced from CO2 by catalytic hydrogenation of CO2 with H2 where the hydrogen has been obtained from water electrolysis. Methanol may also be produced through CO2 electrochemical reduction, if electrical power is available. The energy needed for these reactions in order to be carbon neutral would come form renewable energy sources such as wind, hydroelectricity and solar as well as nuclear power. In effect, all of them allow free energy to be stored in easily transportable methanol, which is made immediately from hydrogen and carbon dioxide, rather than attempting to store energy in free hydrogen.

CO2 + 3H2 → CH3OH + H2O

CO2 +2H2O + electrons → CO + 2H2 (+ 3/2 O2) → CH3OH

The necessary CO2 would be captured from fossil fuel burning power plants and other industrial flue gases including cement factories. With diminishing fossil fuel resources and therefore CO2 emissions, the CO2 content in the air could also be used. Considering the low concentration of CO2 in air (0.037%) improved and economically viable technologies to absorb CO2 will have to be developed. This would allow the chemical recycling of CO2, thus mimicking nature’s photosynthesis.

For more details, see:

  • George A. Olah, Alain Goeppert and G. K. Surya Prakash, Chemical recycling of carbon dioxide to methanol and dimethyl ether: From greenhouse gas to renewable, environmentally carbon neutral fuels and synthetic hydrocarbons, Journal of Organic Chemistry, 74 (2009), 487–498.

Also see the Wikipedia references:

There is a bit more about the methanol economy here:

category: energy, carbon