The concentration of CO₂ in our atmosphere continues to rise – despite a temporary reduction during the COVID-19 pandemic – and reached a record high last month. The world’s oldest continuous CO₂ monitoring station Mauna Loa Observatory in Hawaii continues to break record after record each year, with a new record-breaking monthly average in April. Never before since the measurements began in 1958 did scientists calculate a daily average of 420 parts per million in our atmosphere.

A sad trend, Chemical Engineering PhD candidate Francesco Sabatino says. We really need to take action now if we want to limit global temperature rise to well below 2 degrees Celsius; we still haven’t managed to structurally decrease CO₂ emissions. One thing we can do is purify the air to reduce CO₂ concentration. And that’s precisely what Sabatino has been focusing on at TU/e during the past four years. In collaboration with Utrecht University and oil company Shell, Sabatino developed a technique for removing CO₂ from air; on top of that, his fellow PhD candidate from Utrecht tried to optimize CO₂ capture from ocean water.

CO₂ vacuum cleaner

“Perhaps you’ve heard of the wall of extractor fans put up by Climeworks in Iceland, the world’s first large-scale project for capturing CO₂ from air?” Sabatino shows a picture of rows of giant fans placed amid snowy mountain tops. “It’s really a kind of vacuum cleaner that sucks in the air and binds the concentration of CO₂ with a filter. What makes things extra complicated, however, is the fact that emitted CO₂ is quickly diluted in outdoor air, to only 0.04 percent by volume. You need millions of these vacuum cleaners if you want to achieve any kind of climate effect. A very costly affair, not just in terms of money, but also in terms of energy use.”

Sabatino wondered how he could reduce the costs of this CO₂ capture technique, and decided to take a thorough look at Direct Air Capture (DAC) technology. He developed models to optimize the capture process and realized that there were still some significant improvements to be made by focusing on the filters. “You want a filter that binds CO₂ in an efficient manner without using too much energy when you start to remove that CO₂ for reuse. In our search for the right balance, we saw that amines combined with porous filter material worked really well.”

More sustainable air travel

Hoping to develop a sustainable, circular technology, Sabatini examined the possibility of using the captured CO₂ as raw material for renewable fuel. “We need to focus on smart combinations if we want to reduce the costs of CO₂ capture. During the process of converting CO₂ into methane, for example, heat is released, which can be used to remove the absorbed CO₂ from the filters. It’s possible to produce methane with hydrogen produced with wind and solar power. Over the past five years or so, there has been a growing interest in this so-called Power-to-X technology. This technology makes it possible to convert renewable energy (power) into fuels (X) in a very efficient way. During this process, the captured CO₂ replaces the fossil carbon materials.”

Power-to-X technology could be an interesting application, in particular to sectors that continue to need liquid fuels in the long run, such as the aviation industry. “Electric flying is still a long way off, but this definitely offers a chance to make the transportation sector more sustainable.”

No magic wand

Because we need to take action now if we want to contain climate change, Sabatino stresses once again. “This Power-to-X technology won’t solve all our problems either, like some sort of magic wand. We will need to apply a broad range of technologies, and every additional technology that contributes to a reduction of CO₂ concentration in our atmosphere is welcome.” Sabatino will certainly do his share. He recently started working on an exciting challenge at Climeworks – that’s right, the Swiss company responsible for that wall of fans.