Is methane gas desirable

From methane to methanol - or how to put out the torches of waste

Methane often occurs in oil reservoirs and escapes during oil production due to its low density - just like carbon dioxide hissing up from an open beverage bottle. Because the processing, storage and transport of methane would be too expensive at today's market prices, the gas is often either burned straight away - which produces CO2 - or simply blown into the atmosphere. According to World Bank statistics, these practices, known as flaring or venting, threw 140 billion cubic meters of methane into the atmosphere of our planet worldwide in 2011. This corresponds to 30 percent of Europe's annual methane consumption and 75 percent of Russia's methane exports. From an economic point of view, the extent of wasteful use of such a valuable natural resource is enormous. The negative consequences are also of an ecological nature and include the massive deterioration in local air quality and - if the gas gets directly into the atmosphere - a considerable contribution to climate change, because methane is a much more potent greenhouse gas than carbon dioxide.

Liquid wins

Jeroen van Bokhoven, Head of the Laboratory for Catalysis and Sustainable Chemistry at the Paul Scherrer Institute PSI, has a solution to this enormous environmental and economic sin: the production of methanol from methane, directly at the source, would turn the volatile gas into an easier-to-use energy source transform. Storage and transport to consumers would be economically and technically feasible with methanol. Methanol has several advantages over methane. On the one hand, it is in a liquid state at room temperature and standard pressure. On the other hand, due to its molecular structure, methanol is more reactive than methane and thus forms a better starting material for the production of fuels and other useful chemicals. So far, however, chemists have found it hard to find efficient ways of producing methanol from methane. The conventional production methods are too complex and therefore economically unattractive.

The first step in the conventional methane conversion process is the so-called steam reforming of the methane gas. During the reforming process, hot steam is mixed with the methane - at temperatures of at least 700 degrees Celsius. This process step consumes a lot of energy. The reforming produces a mixture of carbon monoxide and hydrogen, which is known as syngas. The syngas can then be converted to methanol through further chemical reactions under high pressure.

A more direct and less energy-intensive conversion of methane to methanol would be desirable, but has proven to be a tough nut to crack for fundamental reasons. Methane is very stable due to its symmetrical molecular structure and the strength of the bonds between the single carbon atom and the hydrogen atoms surrounding it, which means that it is difficult to convert chemically. This difficulty can be avoided by using catalysts - substances that can promote and accelerate a chemical reaction without being consumed themselves. But the search for the right catalyst for methanol production remained fruitless despite decades of strenuous efforts.

The thermodynamics stand in the way

It is against the “will of nature” to produce methanol as the end product of the conversion of methane. Or in more technical terms: the laws of thermodynamics, which govern the conversion of substances in the sense of minimizing energy, tend to favor the so-called complete oxidation of methane. But this has the result of the production of carbon dioxide. In order to obtain methanol, one would have to use a trick to stop the oxidation process at the right time. To do this, chemists use a so-called selective catalysis, the substance that helps the reaction over the energetic hurdle to produce methanol, but prevents it from continuing to CO2.

It was only a few years ago that researchers succeeded in catalytically converting methane to methanol. As a catalyst they used a copper-doped zeolite, called copper mordenite - a naturally occurring, but also chemically synthesizable mineral made of aluminum, silicon and oxygen. If metal atoms are incorporated into the pores of the crystal structure of these zeolites, they function as particularly efficient selective catalytic centers. In these first experiments with copper mordenite, however, the recovery of methanol from methane was made more difficult by the fact that the methanol produced was strongly adsorbed on the surface of the zeolite interspersed with copper. After the reaction of methane and oxygen, a solvent was needed to separate out the methanol and as a result the catalytic copper centers were no longer available for further reactions. It was also observed that only a few copper atoms in the zeolite crystal actually developed a catalytic effect.

Researchers at PSI have built on this work and for the first time developed a process in which the methanol leaves the reactor as an end product without the use of solvents. You have got the problem of methanol adsorption under control and significantly increased the number of catalytically active copper centers in the zeolite. They also found a way to regularly reactivate the catalysis by flooding the reactor with oxygen after each reaction cycle. "In this way, we achieve many conversion cycles before the catalyst has to be replaced," says researcher Evalyn Mae Alayon who developed the process as part of her dissertation.

In developing and improving the new manufacturing method, PSI researchers have benefited from the excellent large-scale research infrastructure available to them at PSI. For example, they were able to demonstrate the success of their procedure through X-ray spectoscopic examinations on the SuperXAS beam line of the Swiss SLS synchrotron light source by reading their catalytic activity and thus the progress of the conversion of methane to methanol from the structural changes in the copper centers. In the future, they want to use these X-ray techniques to further improve the design of the catalytic converter. Van Bokhoven is enthusiastic about the prospects in this regard. But his success to date already fills him with pride, since the catalytic conversion of methane to methanol was long considered by chemists to be a “golden reaction” and its realization as particularly desirable. Should this one day become an industrial reality, then the end of global methane waste would be partly thanks to the efforts of the PSI scientists.