Werner's Blog — Opinion, Analysis, Commentary
Will methane cracking give natural gas an extended lease on life?

Natural gas is a fossil fuel; once burned, it turns into carbon dioxide, a greenhouse gas. To combat climate change, we need to reduce greenhouse gases, and thus it appears that natural gas has a limited future. Or perhaps not? Natural gas is cheap and cleaner than coal, and thus has much potential to help mitigate climate change by displacing coal quickly. And now it appears that methane could become useful even without producing greenhouse gases. The aim is methane decarbonization—taking the carbon out of methane.

A team of researchers from the Institute for Advanced Sustainability Studies in Potsdam, Germany, and the Karlsruhe Institute for Technology in Karlsruhe, Germany, has made great advances solving a problem that prevented turning methane into a fuel source without greenhouse gas emissions. The researchers have refined a process known as methane cracking by using a continuous reactor of molten tin to produce hydrogen and high-quality black carbon without the problematic contamination by carbon monoxide, and even better, with virtually no carbon dioxide emissions. This feat has been elusive, even though the basic principle of breaking the carbon away from the hydrogen has been known for two generations using a different chemical process.

Let's start with the basics: what is methane cracking? The endothermic chemical reaction \[ CH_4 + 74.85 \mathrm{kJ/mol} \longrightarrow C+ 2H_2 \] takes energy and methane and splits it into carbon and hydrogen. (The technical name is actually methane pyrolysis.) What looks so simple in theory is difficult in practice. An alternative method of generating hydrogen from methane involves steam reforming, a strongly endothermic two-step reaction that can be summarized as \[ CH_4 + 2H_2O + 165 \mathrm{kJ/mol} \longrightarrow CO_2+ 4H_2 \] In the first endothermic step, methane and steam are combined in the presence of a nickel catalyst, yielding carbon monoxide and hydrogen. In a second exothermic step, the carbon monoxide is combined in the presence of a copper or iron catalyst to produce a bit more hydrogen along with carbon dioxide. Steam reforming is the main commercial method to produce hydrogen in North America. The hydrogen produced for hydrogen fuel cell applications has to be free of carbon monoxide, a gas that fowls the fuel cells. It is also possible to produce hydrogen from water through electrolysis, and this remains an important competitor to benchmark against. However, electrolysis remains 3–10 times more expensive than steam reforming.

Steam reforming has two major drawbacks: it requires more energy than methane cracking, and it produces carbon dioxide. Pure methane cracking only leaves hydrogen and elemental carbon, and no carbon dioxide. Methane cracking is thus able to prevent greenhouse gas emissions, whereas steam reforming is not. To prevent greenhouse gas emissions from steam reforming, it would be necessary to capture the carbon dioxide and sequester it. This is technically possible, but expensive. It is much easier to deal with black carbon, which has the added advantage of being commercially useful; it sells for about US$ 500-1000 per metric tonne, depending on purity and application.

‘Cost-effective methane cracking could bring hydrogen into the fuel mix at last.’

The new method developed by the researchers in Germany avoids several notorious problems with the pyrolysis method. Separating the carbon from the hydrogen produced black carbon, which tended to quickly clog the reaction vessels. The way to overcome the problem involves a continuous high-temperature (1200°C) tin bath into which methane bubbles are injected. Hydrogen bubbles to the top, while the black carbon powder is transported away in the tin liquid and is separated. The continuous operation of the process ensures that the tin does not clog up with carbon. Technologically, this is a major breakthrough. Economically, the question is whether the new technology scales up and can be commercialized at a cost that can compete with steam reforming.

Early projections suggest that the new process could accomplish methane cracking at a price of about $1.5 per kilogram (kg) of hydrogen. Conveniently, one kilogram of hydrogen has an equivalence to about one gallon of gasoline (3.785 L). This compares favourable with other alternatives of hydrogen generation. Thompson et al. (2005) put the cost of hydrogen from wind-power electrolysis at about $3/kg, and more recently C. Rodriguez et al. (2014) put the potential cost for solar-power electrolysis in the $1-2/kg range. Methane cracking is an immature technology at this point, whereas solar hydrogen is getting cheaper along with the drop in cost for photo-voltaic cells. The race is on to find the cheapest way to produce hydrogen commercially!

Before getting too excited about the prospects of methane cracking, there is a cautionary note that applies: getting methane out of the ground is not without problems, and there may be significant methane leakage. New research by Schwietzke et al. (2016) suggests that methane emissions are much larger than previously thought, although industry seems to be getting better at plugging the leaks. Nevertheless, much remains to be done to further reduce methane leakage as the natural gas industry has been expanding in the wake of the fracking revolution.

Jurisdictions such as British Columbia, which sit on a wealth of natural gas, should pay close attention to this nascent technology. Combined with the technological leadership in hydrogen fuel cells by Burnaby-based company Ballard Power Systems, B.C. could find itself in a uniquely advantageous position to benefit from a cheap source of hydrogen. Methane cracking could give natural gas an extended lease of life, turning natural gas from a fossil-fuel villain into a fossil-fuel hero.

Further readings:

Posted on Sunday, October 30, 2016 at 08:30 — #Innovation | #Environment
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