Marine Methanol

1.2 Other production methods

The production method of methanol stands before two challenges. The first one is to make the current methods of production from fossil fuels more energy and more environmentally efficient. While the two is interconnected, they are not necessarily the same. Energy efficient is easily grasped when remembering that the current production methods require a substantial amount of heat which is usually supplied by burning a portion of the feedstock. With environmental efficiency that stands mainly for greenhouse gas emissions. With natural gas resources still vast a challenge is to utilise these but at the same time mitigate the environmental consequences.

+ Carnol process

The Brookhaven National Laboratory have developed a methane to methanol process that ideally does not contribute to CO2 emissions by using carbon capture techniques for the carbon dioxide needed for the methanol synthesis. The process relies on thermal decomposition of methane that produce the hydrogen needed for the methanol synthesis. The other product is solid coal which is easy to take care of.

- Methane therm. decomp.

- Methanol synthesis

- Overall Carnol

The main challenge for the process is to capture carbon dioxide in an economical way and to purify, concentrate and transport it to the methanol plant in an economical way. For the short term industries with large concentrated emissions is most likely the preferred route but capture from the atmosphere is a possible future route.

It should be noted that thermal decomposition from methane is an endothermic process that require external heating. The need is not as great as for steam and dry reforming and is preferably supplied from renewable sources.

The carnol process is still on the development stage but could offer a possible way to still use the natural gas sources that is available with minimal environmental effects.

+ Bi-reforming

By combining steam reforming and dry reforming Olah et. al. [6] propose a more efficient way to produce synthesis gas from natural gas. The process produces synthesis gas with the right H2/CO ratio, called metgas, in a single or two-step process.

Steam reforming (4)[2] Dry reforming (9) Bi-reforming

The big advantage with bi-reforming is that the synthesis gas has the right H2/CO ratio and thus all hydrogen can be used for methanol production. The process is though still highly endothermic and requires a substantial addition of heat. This heat is preferably supplied by renewable or even nuclear sources.

+ Direct oxidation of methane to methanol

An attractive alternative for synthesis of natural gas to methanol would be if the energy consuming step of synthesis gas could be avoidable by directly inserting an oxygen atom in the methane molecule by direct oxidation. The difficulty is that the high reactivity of the products themselves easily results in complete combustion of the methane to carbon dioxide and water.

Despite the desire of success no method has been found to achieve a high enough selectivity, productivity and catalyst stability for industrial applications [2].

+ CO2 + H2

With the advances of renewable energy as well as greater utilization of existing energy sources such as the sun and geothermal heat methanol evolves not as an energy source but as an energy carrier with great potential. While biomass and other waste materials is a possible and probable route to gradually decrease our dependence on fossil energy sources there are technologies available that allows us to produce methanol and at the same time reduce the carbon dioxide emissions in our atmosphere. The process consists of combining hydrogen and carbon dioxide to produce methanol with the only by-product being oxygen from the elect.

The idea is to produce methanol from carbon captured from the atmosphere, mainly from local emitters such as power plants and industrial facilities but with improving technologies also from the atmosphere itself. To accommodate the need for hydrogen in the synthesis process electrolysis of water is performed with electricity. Electrolysis of water is an old technology that has been used for more than a century but as the energy consumption is very high only a small part with high purity demands of the world production of hydrogen is through electrolysis. The best energy efficiency is today around 73 % with the expectancy to reach toward 85 % with current research and development programs[8].

The success of this technology relies of an abundance of energy that can come from mainly solar, wind and thermal sources that lack any efficient mean of storage in other ways. Carbon Recycling International (CRI) is currently operating one plant on Iceland that use available geothermal energy to produce 5 000 m3 methanol per year [9] and Mitsui Chemicals has announced construction of a demonstration plant capable of producing 100 tonne methanol per year from CO2.