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Methanol synthesis as part of the circular economy of carbon and silicon

​Chemists at Iramis have proposed a new pathway for the catalytic synthesis of methanol from a formic acid derivative – a waste product of the silicon industry – whose by-products can be recycled. This is a high-yield, sustainable and environmentally friendly process that can be used for energy storage and fine chemistry!
Published on 15 July 2020

Satisfying the needs of a growing world population, anticipating the increasing scarcity of fossil carbon resources and reducing carbon emissions that cause climate change are challenges driving a paradigm shift in the energy and chemical sectors: the closing of the cycle of elementary raw materials such as carbon and silicon.

However, carbonaceous emissions (CO2 or biomass wastes) are highly oxidized by nature, and the high stability of their C-O bonds makes it difficult to recover them as chemicals or fuels. It is therefore necessary to develop efficient reduction methods that can form energy-rich C-H bonds such as those present in fossil hydrocarbons.

Methanol (CH3OH), an important precursor of industrial chemicals (such as formaldehyde, acetic acid and light olefins), is an interesting molecule that allows the storage of energy. At the industrial level, it is currently produced by the oxidation of methane (CH4) that mainly comes from oil, natural gas and shale deposits. Could it be possible for CO2, rather than methane, to give its carbon atom to a methanol precursor?

Researchers at Iramis have now shown that methanol could indeed be produced from formic acid (HCOOH) that was obtained by the electroreduction of CO2 or from biomass. In a previous study, they demonstrated that methanol can be generated from formic acid with a 50% yield, in the presence of a ruthenium-based catalyst. However, this yield was limited by a competing dehydrogenation reaction.

The same team has revealed that it is possible to avoid this secondary reaction by replacing the proton of formic acid by a silyl group (SiR3) and by using silylated formates (HCOO-SiR3), which are wastes derived from siloxanes produced by the pharmaceutical, medical, cosmetic and food industries. Their new process is based on the formation of methoxysilanes (CH3-O-SiR3) from silylated formates, which is highly efficiently catalyzed (with a yield greater than 75%) by ruthenium complexes. Methanol is then obtained by hydrolysis of methoxysilanes.

The researchers have thus proposed a new approach to methanol production derived from two wastes, while also contributing to the recycling of CO2 and silicon. In addition, the undesirable by-products of the process are easily recyclable: the ones resulting from reactions involving silicon can return silylated formates by reacting with formic acid.

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