Methanol economy

The methanol economy is a suggested future economy in which methanol replaces fossil fuels as a mean of energy storage, fuel and raw material for synthetic hydrocarbons and their products. It offers an alternative to the proposed hydrogen economy or ethanol economy.

In 2005 Nobel prize winner George A. Olah advocated the methanol economy in an essay ^[1] and in 2006 he and two co-authors published a book around this theme ^[2] In these publications, they summarize the state of our fossil fuel and alternative energy sources, their availability and limitations before suggesting a new approach in the so called methanol economy.

Methanol, is a fuel for heat engines and fuel cells. Due to its high octane rating it can be used directly as a fuel in cars (including hybrid and plug-in vehicles) using existing internal combustion engines (ICE). Methanol can also be used as a fuel in fuel cells, either directly in Direct Methanol Fuel Cells (DMFC) or indirectly after conversion into hydrogen by reforming.

Methanol is a liquid under normal conditions, allowing it to be stored, transported and dispensed easily, much like gasoline and diesel fuel nowadays. It can also be readily transformed by dehydration into dimethyl ether, an diesel fuel substitute with a cetane number of 55.

Methanol is already used today on a large scale (about 37 million tonnes per year)^[3] as a raw material to produce numerous chemical products and materials. In addition, it can be readily converted in the methanol to olefin (MTO) process into ethylene and propylene, which can be used to produce synthetic hydrocarbons and their products, currently obtained from oil and natural gas.

Methanol can be efficiently produced from a wide variety of sources including still abundant fossil fuels (natural gas, coal, oil shale, tar sands, etc.), but also agricultural products and municipal waste, wood and varied biomass. More importantly, it can also be made from chemical recycling of carbon dioxide. Initially the major source will be the CO₂ rich flue gases of fossil fuel burning power plants or exhaust of cement and other factories. In the longer range however, considering diminishing fossil fuel resources and the effect of their utilization on earth's atmosphere, even the low concentration of atmospheric CO₂ itself could be captured and recycled via methanol, thus supplementing nature’s own photosynthetic cycle. Efficient new absorbents to capture atmospheric CO₂ are being developed, mimicking plant life’s ability. Chemical recycling of CO₂ to new fuels and materials could thus become feasible, making them renewable on the human timescale.

Synthesis

The methanol needed in the methanol economy can be synthesized from a wide array of carbon sources including still available fossil fuels and biomass but also CO₂ emitted from fossil fuel burning power plants and other industries and eventually even the CO₂ contained in the air.

Today methanol is produced exclusively from syngas, a mixture of H₂, CO and CO₂ obtained by partial oxidation of fossil fuels, mainly natural gas and coal. This technology is well developed and operated on a large scale.

Although conventional natural gas resources are currently the preferred feedstock for the production of methanol, unconventional gas resources such as coalbed methane, tight sand gas and eventually the very large methane hydrate resources present under the continental shelves of the seas and Siberian and Canadian tundra could also be used. Besides methane all other conventional or unconventional (tar sands, oil shale,etc.) fossil fuels could be utilized to produce methanol.

Besides the conventional route to methanol from methane passing through syngas generation by steam reforming combined (or not) with partial oxidation, new and more efficient ways to produce methanol from methane are being developed. These include:

methane oxidation with homogeneous catalysts in sulfuric acid media
methane bromination followed by hydrolysis of the obtained bromomethane
direct oxidation of methane with oxygen
Microbial or photochemical conversion of methane

The use of methane (and other fossil fuel) for the production of methanol using all the above mentioned synthetic routes has however a major drawback of growing concern: the emission of the greenhouse gas CO₂, its accumulation in the atmosphere and detrimental effect on the climate.

To address this problem methanol will have to be made increasingly through ways minimizing the emission of CO₂. One solution is to produce it from syngas obtained by biomass gasification. For this purpose any biomass can be used including wood, wood wastes, grass, agricultural crops and their by-products, animal waste, aquatic plants and municipal waste. There is no need to use food crops as in the case of ethanol from corn, sugar cane and wheat.

More importantly, methanol can also be produced from CO₂ by catalytic hydrogenation of CO₂ with H₂ obtained from water electrolysis or through CO₂ electrochemical reduction. 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.

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.

Theoretical advantages over other energy storage media

Advantages over hydrogen

Methanol economy advantages compared to hydrogen:

efficient energy storage (by volume) and also by weight as compared with compressed hydrogen, when hydrogen pressure-confinement vessel taken into account. Methanol is considerably more efficient than liquid hydrogen, in part because of the low density of liquid hydrogen of 71 grams/liter. Hence there is actually more hydrogen in a liter of methanol (99 grams/liter) than in a liter of liquid hydrogen, and the methanol hydrogen needs no cryogenic container.
required hydrogen infrastructure would be prohibitively expensive; methanol can be directly cycled into existing gasoline infrastructure
can be blended with gasoline
user friendly (hydrogen is volatile and requires high pressure system confinement)
methanol serves as a raw material for the chemical industry