A circular economy of carbon dioxide

For most people, carbon dioxide is a transparent gas that causes the earth’s temperature to rise. It is a product of many industries, our mobility and even our breathing. Currently, there are ideas, concepts and technologies that remove CO2 from the atmosphere and use it to synthesize valuable fuels and products. Not only would that make our flights to holiday destinations CO2-neutral, we could also counteract climate change and revolutionize the chemical industry and energy sector.

How do we get CO2 from the air?

Extracting the most prominent greenhouse gas from the atmosphere and using it to synthesize raw materials for the chemical industry? That sounds utopian, but the technology has existed for some years now. Climeworks1, Carbon Engineering2 and Global Thermostat3 are three companies that use cyclical processes to directly obtain CO2 from the air. With the help of a filter material that bonds to CO2 at room temperature and releases it at a higher temperature, CO2 can be cyclically filtered out of the air and turned into stone4,5 or used as fertilizer or raw material for fuels6 and chemical products7. This process is known as Direct Air Capture, the capturing of CO2 from the atmosphere whereby CO2 is available in low concentration, around 420 ppm. Another process is post-combustion carbon capture, where CO2 is filtered from exhaust gasses from burning8. From a kinetic standpoint, it is easier to obtain CO2 from exhaust gasses because here there is a higher concentration of CO2, around 15%. The disadvantage is that other gasses and particles can damage the filter. 

Flying without shame to a holiday destination

The first idea behind this is that we can finally lower the rising CO2 concentration. We will most likely not be able to prevent an increase of global temperatures of 1.5°C, the goal stated in Paris in 20159, even if we were to stop emitting CO2 tomorrow10. By removing CO2 from the atmosphere, we not only create negative emissions but could also revolutionize the chemical industry and the mobility sector. 

Next to batteries and hydrogen for cars, trucks and trains, synthetic fuels made from CO2 from the air could be a solution for sustainable mobility. Even though the energy density of batteries will increase11, and the price of hydrogen fuel cells will decrease, these alternatives do not seem achievable for the shipping and aviation sector at the moment. We will have to continue using the conventional combustion engine for a while in these areas. Is there no alternative without ‘flying shame’?

We will have to accept the nitrogen oxides and particles that are released during combustion and the low efficiency of combustion engines, but the fuel can be made CO2 neutral. These CO2-neutral fuels are called synthetic fuels and can be made from biomass for example. Another possibility is the conversion of carbon dioxide and water to carbon monoxide and hydrogen with the help of renewable energy. This can be done with electrolysis12, an electrochemical conversion13, or with a direct conversion at high pressure and high temperature, that can be achieved using solar energy. The mixture of carbon monoxide and hydrogen is called syngas and is an important gas in the chemical industry. It is the starting product for a few synthetic processes and also for synthetic fuels and plastics. The hydrogen would also be produced in a sustainable manner, whereas today around 95% of hydrogen is produced from natural gas14. The sustainable production of hydrogen from water using electrolysis is not yet executed on a large scale. 

Thinking big: Power-to-X

Through combining Direct Air Capture with the conversion of carbon dioxide to valuable products, the carbon cycle can be closed and fuels and plastics can be made in a CO2-neutral way15. Different sectors would become linked. This concept is known as Power-to-X16. The X in this name can refer to hydrogen, fuel, methane or a different chemical or physical energetically valuable product. An important sector, which you will see change more and more over the next few years, is the energy sector. If the share of renewable energy increases, the fluctuations in the production of energy will also increase, since the sun does not always shine, nor does the wind blow at a constant speed. In moments where a lot of electricity is produced, this excess can be converted into other forms, such as hydrogen, synthetic fuels or methane for the mobility sector or the chemical industry.

An economic analysis of CO2 from Direct Air Capture for the mobility sector. 

These are a few innovative technologies to slow, or even counteract climate change. The extent to which they will grow in the next few years is very dependent on political conditions. Currently the cost of capturing one ton of CO2 is around 500 euros17. That means that for one liter of diesel, for which 3 kg of CO2 are necessary, 1.5 euros are necessary, and this is only the cost of carbon source for the fuel. De costs of the process to synthesize the fuel is not included in that price. Since the price for one liter of diesel is currently around 1 euro, this way towards synthetic processes is not yet profitable. Carbon capture is still a very young technology, so there is a real chance that this price will drop18, but politics could support this technology by, for example, introducing a carbon tax. As a result, the price of traditional fuels would rise, and it would create an economic stimulus for synthetic fuels.

Can we as people tinker with the climate? 

The acceptance of society will also have a large impact on the evolution of these technologies. Direct Air Capture is part of geo-engineering, the large-scale intervention in the climate to counteract climate change19. The ethical philosophical question is: ‘Can we as humans play with the climate?’. If the answer to this question is yes, then it is clear that Carbon Capture can only have a (positive) influence on the climate when it is done on a large-scale. Not everyone is convinced that these “CO2 vacuums”, as they are also called, will be the solution because they also require raw materials, energy and ground. Despite the fact that these global consequences as a result of Carbon Capture are not fully known, the IPCC (Intergovernmental Panel on Climate Change) came to the conclusion in 2018 that technologies that create negative CO2 emissions will be necessary to reach the goal of a maximum of 1.5°C warming10

So, there really are solutions to tackle the climate problem and it is clear that reducing CO2 emissions alone will not be enough to achieve our climate goals. As to how far Carbon Capture and synthetic fuels will contribute to a circular carbon economy and lead to a Power-to-X system is unclear and will depend on political conditions, the economical development of these technologies and the motivations of society, so on all of us.  

Original article in Dutch available on yera.be, translated by Karen Aerts.