Becoming a net zero greenhouse gas emission society is one of the biggest challenges mankind has ever had to face. The timeframe of 30 years set to reach this goal in order to limit the consequences of global climate change calls for resolute action by politicians and industry leaders and I am afraid also by the citizens.
But what can WE do about it?
Well, WE can analyze our own individual carbon dioxide footprint and accept that WE as well have to change our habits in order to help the economy transform from the linear “take – make – waste” system into a circular “borrow – share – return” model.
Agreed! But what does that mean in practice?
What it could mean regarding the future production and use of chemical fuels is described in our recent perspective Nature Communications paper entitled “Crowd Oil not Crude Oil”.
We propose to leave fossil oil in the ground and start building up thousands and even millions of decentralized renewable oil wells in buildings, which will transform these buildings into inhabited technical photosynthesis systems. Skyscrapers, supermarkets and eventually even individual homes will turn into chemical factories producing hydrocarbons, just as trees do with carbohydrates.
But how could this work? Well, carbon dioxide and water will be extracted from the air passing through the ventilation system and converted with renewable electrical energy or solar radiation and waste heat into a storable and easily transportable liquid. The trick is that building the extra feature of carbon dioxide capture into a ventilation system will not increase the power demand for ventilation because the limited additional pressure drop of a well-designed adsorber system is compensated by a reduced requirement for air renewal thanks to the removal of carbon dioxide from the incoming air. Another trick is that the heat needed for recovering the carbon dioxide and water from the adsorber for conversion into fuel is provided by the waste heat of the conversion reactor thanks to advanced technology enabling heat integration even at a small scale. So no extra heat is required. The system must further include an electrolyzer between the carbon dioxide capturing unit and the conversion reactor, either for generating hydrogen from water, which is then converted with carbon dioxide into synthesis gas prior to the fuel synthesis reactor, or for generating the synthesis gas directly from carbon dioxide and steam by high-temperature co-electrolysis.
Based on recent developments, it was estimated that carbon dioxide can be captured from ambient air and converted via high-temperature co-electrolysis into synthesis gas and further into Fischer-Tropsch-Fuels with a high carbon utilization of at least 90 % and approximately 50-60 % overall energy efficiency in such systems at a scale of 150 kW or larger. An experimental proof-of-concept plant including all steps at a size of 10 kW has been built recently and will soon be brought to operation and in the not too distant future integrated with a ventilation system.
To make Crowd Oil happen, much still needs to be done regarding cost-effective fabrication of components, safety, and reliable autonomous operation. Moreover, feed-in-tariff programs for the produced crowd oil or fee-and-dividend approaches for taxation of carbon dioxide emissions will be needed that will help to distribute the costs of the envisioned transformation and bring benefit to a large number of individuals of world’s societies being active contributors to the solution of climate challenge. Nevertheless, the concept seems to be very appealing, both from the technical and societal perspective.
Roland Dittmeyer, Geoffrey Ozin, Paul Kant and Michael Klumpp,
Karlsruhe Institute of Technology and University of Toronto.