Giant wind parks far away at sea and huge solar farms in the Sahara are places to generate tons of renewable energy efficiently – and without bothering a soul. Unfortunately, there isn’t too much demand for electricity at sea or in the desert. Some way or another, it will have to be transported to populated areas. And that’s not easy, as the experts at distribution network Alliander know. When transporting electricity a lot is lost, and to get the electricity generated by a field of solar panels in the Sahara to Europe, you’d need a cable duct that’s two kilometers wide.

It would make sense, then, to use existing infrastructure for gas transportation. In part of the Netherlands (including Eindhoven) that grid is managed by Alliander. Two pipes would suffice to connect Europe to the Sahara, and the elaborate grid under the Netherlands allows for large amounts of gas to be stored (the equivalent of 100 TWh, about the amount of electricity the Netherlands uses in a year). It’s impossible to store such large amounts of energy as electricity for an extended period of time.

The challenge is to secure solar energy or wind energy in an energy-rich gas like methane – the main component of natural gas, which is currently flowing through the pipes. We can already make methane with electricity, but that requires an extra step where water is separated with an electric current (electrolysis) and that’s a rather laborious and expensive process.

There is another way, too: using plasma, CO₂ can be converted into CO, which in turn can react with water to form methane. Renewable electrical energy is used to power a microwave-type machine that generates the plasma, and so, using a detour, the solar/wind energy is indirectly stored in methane.

A promising technique, as far as funding agent STW was concerned, so it decided to set up the Plasma Conversion of CO₂ program with financial support of Alliander. Last summer, the program accepted three projects, and each project features TU/e researchers.

"My first reaction was: that's impossible!"

Dr.ir. Jan van Dijk, researcher at Elementary Processes in Gas Discharges (EPG) and his colleague dr.ir. Kim Peerenboom are involved in even two of the projects, along with colleagues of the DIFFER Institute and Twente University. Initially, Van Dijk was surprised to hear of the STW program, he admits. “My first reaction was: that’s impossible. But then I heard Alliander was funding part of the project, I figured it had to be a serious idea.” After deliberating he and Peerenboom – who graduated with honors at EPG last year, and who will soon return on a WISE tenure track from Brussels, where she’s currently gaining postdoc experience at the Université Libre – decided to take a head-on approach to this socially relevant challenge.

“In both projects, the objective is to produce methane with plasmas from recycled CO₂”, says Van Dijk. “The main difference is the moment water vapor is added.” The essence of the suggested plasma technique is to separate CO₂ into carbon monoxide (CO) and oxygen. Because the CO₂ molecules collide with the rapidly moving plasma electrons, the former collect enough internal energy to release an oxygen atom. “It’s a reverse combustion process, in a way”, the plasma physicist explains. “Which is why it’s important the oxygen is removed quickly, before the CO combusts and turns back into CO₂. To that end we intend to use membranes, and that’s where Twente University comes in.”

When producing CO, the idea is to lose as little energy as possible. “And for that you need a plasma with perfect characteristics”, says Van Dijk. To determine those perfect conditions, the TU/e researchers will compare computer simulations with experiments that will be conducted by their colleagues at DIFFER (that will move to TU/e campus next year). “There are so many variables, so many switches to turn, that you really need the interplay between simulations and actual experiments to give direction to the project.”

Eventually, the method is to be implemented on a large scale, and that limits the possibilities for the researchers. “We have to keep in mind the entire chain. It’s no use working in conditions where a huge amount of CO is released, but where there’s no way of extracting the oxygen. Regular meetings with all parties involved are therefore imperative – and those include intended end users like Alliander.”

“The interaction between plasma and catalyst hasn’t been researched properly yet”

The third STW project is a TU/e exclusive, and has a slightly different approach. The plan of dr. Qi Wang (Micro Flow Chemistry & Process Technology) doesn’t involve the creation of methane, but rather the liquid fuel methanol. The first step is the same, however: converting recycled CO₂ into CO. “For that we use technology from our industrial partner Evonik”, says Wang. “The idea is to add hydrogen, too. Combined with the right catalyst, we should be able to create methanol quite efficiently.”

The plan to convert CO₂ into methanol using plasma technology isn’t entirely new, the Chinese researcher explains, but the process hasn’t been researched widely, and profits are still very modest. “Profits depend on the synergy between plasma and catalyst, and that hasn’t been researched properly yet. Besides, nobody has figured out how to expand this process to an industrial level.”

Wang does intend to figure that out over the next few years, and to do so she’ll be working closely with catalyst expert prof.dr. Emile Hensen, and flow expert prof.dr. Federico Toschi. She’ll get additional input from an elaborate user panel that was put together by prof.dr. Volkel Hessel: the main applicant of the STW grant. Wang will probably be exchanging her findings with Jan van Dijk and his colleagues at Applied Physics every now and then. “We have to, since this project requires a multidisciplinary approach. We’ve been in touch already. I’d love to learn more about the physics part, and the physicists in turn were interested in my knowledge of chemical engineering. I’m positive we can teach each other many useful things.”