Natural gas accounts for over 28 percent of US energy consumption. Its main component, methane, is a widely-used fossil fuel but also a major contributor to rising CO2 levels, and thus climate change. To address this issue, researchers from the Institute of Advanced Sustainability Studies (IASS) and Karlsruhe Institute of Technology (KIT) have developed a process that extracts the energy content of methane, in the form hydrogen, without producing carbon dioxide.
In a process called "methane cracking," the molecular components of methane – hydrogen and carbon – are separated at temperatures of over 750° C (1,382° F), without harmful emissions. The concept of methane cracking has been around for several decades, but was limited by low conversion rates and carbon clogging.
The researchers tweaked the process using a novel 1.2-meter-high (4 ft) reactor design based on liquid metal technology, and made of quartz and stainless steel. Fine methane bubbles are injected into columns of molten tin. As they rise to the surface, the carbon is separated out and deposited as powder at the top end of the reactor. Clogging is avoided due to the easily separated micro-granular carbon powder, while the reactor's design makes it resistant to corrosion.
According to Professor Thomas Wetzel of KIT, the reactor produces hydrogen with a 78 percent conversion rate at 1,200° C (2,192° F), while operating continuously for two weeks. It's this latter aspect that offers the most hope for an eventual reactor built to industrial scale, which would be powered by the produced hydrogen.
"We expect that another three years research and development could result in an industrial prototype for a modular reactor, which could be scaled by simple multiplication," researcher Stefan Stueckrad told Gizmag.
Stueckrad added that the energy efficiency of the process "has been evaluated as slightly higher than conventional steam reforming of natural gas and about 20 percent higher than coal gasification" – assuming both employ carbon capture and storage.
The team's research showed that methane cracking is comparable to water electrolysis, in regards to CO2 emissions per unit of hydrogen, and more than 50 percent cleaner than steam methane reforming technologies. Preliminary calculations reveal that the technology could achieve costs of €1.9 to €3.3 (US$2 to $3.50) per kilogram of hydrogen (at current German natural gas prices).
The next phase of the research will concentrate on optimizing aspects of the reactor design and a gradual scaling up to handle increased flow rates.