Researchers propose using AC and ventilation systems for decentralized production of carbon-neutral synthetic fuels
Researchers at the Karlsruhe Institute of Technology (KIT) and the University of Toronto have proposed a method enabling air conditioning and ventilation systems to produce synthetic fuels from CO2 and water from the ambient air. Compact plants are to separate CO2 from the ambient air directly in buildings and produce synthetic hydrocarbons which can then be used as renewable synthetic oil. The team presents this “crowd oil” concept in Nature Communications.
Due to the low CO2 concentration in the ambient air—today, the proportion is 0.038%—large quantities of air have to be treated in large filter systems in order to produce significant quantities of synthetic energy sources.
A research team led by Professor Roland Dittmeyer from the Institute for Micro Process Engineering (IMVT) at KIT and Professor Geoffrey Ozin from the University of Toronto (UoT) in Canada proposes to decentralize the production of synthetic energy sources in the future and to link them to existing ventilation and air conditioning systems in buildings.
Envisioned modular, on-site renewable hydrocarbon synthesis
system based on CO2 capture from thin air. Counterclockwise from top: Powered by renewable electricity, using modified A/C and ventilation
systems CO2 and water can be captured from ambient air. Via electro-,
photo- or thermocatalytic processes, synthesis gas is generated which is
further converted to hydrocarbon fuels by miniaturized chemical processes
such as the Fischer-Tropsch synthesis plus integrated upgrading processes
(e.g. hydrocracking) allowing to further increase product yield and quality.
The synthesized hydrocarbon fuels can be stored and/or transported for further utilization. In case of combustion for mobility or power generation, in this scenario the CO2 emitted is again captured, finally allowing for a closed, net zero carbon cycle, thus, enabling a circular CO2 economy based on hundreds, thousands, and ultimately millions of modular plants. When stored without further utilization even negative emissions can be realized. Dittmeyer et al.
According to Professor Dittmeyer, the necessary technologies are essentially available, and the thermal and material integration of the individual process stages is expected to enable a high level of carbon utilization and a high energy efficiency.
We want to use the synergies between ventilation and air-conditioning technology on the one hand and energy and heating technology on the other to reduce the costs and energy losses in synthesis. In addition, ‘crowd oil’ could mobilize many new actors for the energy transition. Private photovoltaic systems have shown how well this can work.—Professor Dittmeyer
However, the conversion of CO2 would require large amounts of electrical power to produce hydrogen or synthesis gas. This electricity must be CO2-free, i.e. it must not come from fossil sources. An accelerated expansion of renewable power generation, including through building-integrated photovoltaics, is therefore necessary, says Dittmeyer.
The researchers use quantitative analyses of office buildings, supermarkets and energy-saving houses to demonstrate the CO2 saving potential of their vision of decentralized conversion plants coupled to building infrastructure. They reckon that a significant proportion of the fossil fuels used for mobility in Germany could be replaced by “crowd oil”.
According to the team’s calculations, for example, the amount of CO2 that could potentially be captured in the ventilation systems of the approximately 25,000 supermarkets of Germany’s three largest food retailers alone would be sufficient to cover about 30% of Germany’s kerosene demand or about 8% of its diesel demand. In addition, the energy sources produced could be used in the chemical industry as universal synthesis building blocks.
The team relies on preliminary investigations of the individual process steps and process simulations from, among others, the Kopernikus project P2X of the Federal Ministry of Education and Research. On this basis, the scientists expect an energy efficiency—i.e. the proportion of electrical energy used that can be converted into chemical energy—of around 50 to 60 percent.
In addition, they expect carbon efficiency—i.e. the proportion of spent carbon atoms found in the fuel produced—to range from around 90 to almost 100 percent. In order to confirm these simulation results, IMVT researchers and project partners are currently building up the fully integrated process at KIT, with a planned CO2 turnover of 1.25 kilograms per hour.
At the same time, however, the scientists have found that the proposed concept—even if it were introduced all over Germany—would not be able to fully meet today’s demand for crude oil products. Reducing the demand for liquid fuels, for example through new mobility concepts and the expansion of local public transport, remains a necessity.
Although the components of the proposed technology, such as the plants for CO2 capture and the synthesis of energy sources, are already commercially available in some cases, the researchers believe that major research and development efforts and an adaptation of the legal and social framework conditions are still required in order to put this vision into practice.
Roland Dittmeyer, Michael Klumpp, Paul Kant, Geoffrey Ozin (2019) “Crowd oil not crude oil” Nature Communications doi: 10.1038/s41467-019-09685-x