Researchers demonstrate technology for producing sustainable fuels
Researchers at ETH Zürich have revealed a process technology they have developed for creating sustainable fuels. What's interesting about the technology the researchers have developed is that it can produce carbon-neutral transportation fuels using only sunlight and air. They have demonstrated the stable and reliable operation of what they call a solar mini-refinery.
The demonstration of the solar mini-refinery was conducted in real sun conditions. It demonstrated a method to create solar fuels that can be brought to market without any carbon taxes. The system was developed by a research team led by Aldo Steinfeld operated their prototype system on the roof of the Machine Laboratory in Zürich. The prototype system can produce a liquid transportation fuel, such as methanol or kerosene, utilizing sunlight and air along with a multi-stage thermochemical process.
The solar mini-refinery has been operating on the roof of the building for the last two years, and Steinfeld says he and the team have successfully demonstrated the technology's viability. In addition, the integrated system can operate stably under conditions with intermittent solar radiation and is a viable platform for future research.
The fuels created by the system are known as "drop-in fuels." That means that the fuels are synthetic alternatives for liquid hydrocarbons derived from petroleum and are fully compatible with our existing storage, distribution, and utilization infrastructure. As a result, project researchers believe their fuels can be particularly useful in sustainable long-haul aviation.
The fuels created using the system are carbon-neutral since they rely on solar energy for production. The fuels only release the amount of CO2 during combustion that was extracted from the air during their production. The lifecycle assessment for solar fuel derived from petroleum. More importantly, the lifecycle assessment indicated the process was approaching 100 percent or zero emissions when used to produce material such as steel or glass using renewable energy.
The system is based on thermodynamics with the solar refinery utilizing a trio of thermochemical conversions in series. The first of the conversion processes is the direct air capture unit responsible for extracting CO2 and H2O from the ambient air. The device then uses a solar redox unit to convert CO2 and H2O to a mixture of CO and H2, known as syngas. Finally, the third step is a gas to liquid synthesis unit converting syngas into liquid hydrocarbon.
Steinfeld says the prototype system mini-refinery operated in real field conditions without optimal solar radiation in Zürich. During a typical day's run, the amount of syngas produced was about 100 liters, which was processed into half a deciliter of pure methanol. While that's not a lot of methanol, Steinfeld was clear that components of the production chain haven't been optimized and that optimization is the next phase. Another critical aspect of the system is that it created no undesired byproducts. The team is also able to tailor syngas production to result in either methanol or kerosene. One challenge is low energy efficiency, with researchers measuring the highest efficiency value so far for the solar reactor at 5.6 percent. While optimization is ongoing, the system can be scaled up significantly for industrial use.