Why does carbon – one of the most common elements in the universe – play such a critical role in modern society? Unfortunately, its use is also associated with climate change, the greatest problem of our time.
As concepts, CCU or the capture and utilisation of carbon, and the related carbon reuse economy, are not simple or necessarily easy to grasp. CCU, a technological term used in a number of contexts, is being proposed as a solution to a range of needs.
Due to its range of applications, CCU has many champions and seems to represent many things, from the world’s salvation from climate change to new business opportunities and carbon sources. Such multiplicity also leads to confusion and misconceptions about the kinds of impacts, good or bad, which the technology’s application may have. To shed light on the issue, in this blog we try to explain what CCU and the carbon reuse economy are all about. Why should we be interested in them and how might they serve key industrial sectors in Finland, for example?
What is at stake?
CCU, or carbon capture and utilisation, refers to the separation of carbon dioxide for instance from flue gases to prevent CO2’s release into the atmosphere where it would accelerate climate change combined with use of captured carbon dioxide either as such, or as a source of carbon in other processes.
On the other hand, the carbon reuse economy refers to chemical processes and concepts using either carbon dioxide or other one-carbon molecules – such as carbon monoxide resulting from gasification or methane in biogas – as inputs.
In turn, CCS refers to the capture and storage of carbon dioxide. This could halt the rise in carbon dioxide concentrations in the atmosphere caused by the use of fossil raw materials. CCU, on the other hand, will not prove to be a long-term, overall solution if fossil resources continue to be used. It will be more of a technological solution enabling carbon-based processes in a fully sustainable system.
The ongoing energy transition is characterised by sustainability and mitigation of climate change. From this perspective, the assessment of CCU is complicated by the diversity of applications and concepts and the consequent diversity of CCU’s climate impacts, which could be anything ranging from very negative to positive; it all depends on the energy system in which CCU is applied, and the direction and speed of the systems’ transition. According to the laws of thermodynamics, energy is required when using carbon dioxide in any form other than pure carbon dioxide. For the use of carbon dioxide as a raw material to be sustainable, such energy must be produced sustainably. This ties CCU tightly into the greater use of renewable and other emission-free energy, which again highlights the system perspective.
But might there be reasons for recycling carbon dioxide, other than mitigating climate change?
Recovered carbon dioxide (CCU) is already used in many applications, for example as a protective gas or in soft drinks. It is also converted into chemicals such as urea or inorganic carbonates.
As mentioned above, the use of carbon dioxide always requires energy. Hydrogen provides the simplest way of applying energy to carbon dioxide. A key challenge in CCU and the carbon reuse economy lies in the availability of hydrogen produced using affordable, low-carbon energy. Despite the record levels of investment in low-carbon energy across the globe and the anticipated plunge in prices in forthcoming years, sustainably produced hydrogen will be the most powerful brake on CCU investments. As a result, carbon reuse economy processes can be divided into three categories according to their need for hydrogen:
- processes that do not require hydrogen;
- hybrid processes with a limited need for hydrogen and which can use other C1 gases in addition to carbon dioxide;
- processes with a significant need for hydrogen.
Processes with no requirement for hydrogen include various mineral processes for the production of inorganic carbonates. For example, VTT is studying the recovery of carbon dioxide from lime kilns and its use in the production of pure precipitated calcium carbonate. Certain organic special and fine chemicals can also be made from carbon dioxide, without using hydrogen. Hybrid processes can be used alongside biomass gasification processes, for example. The key usable components in gas from gasification are carbon monoxide and hydrogen. In addition, significant amounts of carbon dioxide are generated as a by-product, which can be converted into fuel or chemicals by using an external hydrogen source.
A range of possibilities is associated with hydrogen-based carbon dioxide conversion processes. Such possibilities tend to be based on chemical catalysis, or they are biochemical. The related processes tend to result initially in C1 intermediate products, such as methane or methanol, which can be used as a mediator and fuel, or as an intermediate product for producing other fuels and chemicals. Speciality chemicals such as acrylic acid, whose production is currently being studied by VTT, can also be directly produced via biochemical processes. Based on Fischer-Tropsch synthesis, catalytic routes can lead to the production of alkanes and alkenes instead of C1 compounds. Alkanes are potential fuel components, whereas alkenes are suitable for the production of a wide variety of chemicals.
While CCU and the carbon reuse economy are clearly technologies that would help enable a sustainable society, they are not, alone, solutions to climate change.
However, the related technologies and products could be a new growth area for Finnish industry and exports. In the short term, the greatest potential lies in technologies based on the utilisation of carbon dioxide without hydrogen, or with a limited need for it. However, as low-energy hydrogen production proliferates, hydrogen-intensive technologies will also be adopted.
CCU requires carbon dioxide as well as hydrogen sources. In the first phase, these could be major fossil-fuel-based emission sources, such as steel mills or oil refineries. However, as decarbonisation progresses, there will be a progressive transition to bio-based emission sources, such as the wood processing industry or energy production from biomass. In the case of bio-based CO2 sources, we could in some casesachieve net carbon removal from the atmosphere (bio-CCU).
The most expensive alternative would be carbon dioxide recovery from the air, but this is also a possible future option. VTT and the Lappeenranta University of Technology are currently demonstrating this concept via the Soletair project funded by Tekes. The project combines carbon dioxide captured from the air with hydrogen produced using renewable electricity; hydrocarbons suitable as fuels are obtained from these, using Fischer-Tropsch technology. The entire system consists of three production containers and a demo of their simultaneous use has been under way in Lappeenranta since June 2017.
Tell us what you think of the carbon reuse economy and CCU!
CCU is often justified on the basis of its positive effects on climate change, but other drivers might include the use of new, renewable energy as a raw material (instead of fossil fuels) in carbon-based processes, i.e., so-called indirect electrification, or simply the need for carbon dioxide in certain processes or products. Climate driver will dominate the long-term energy system change. However, favourable economic conditions for this must be in place, if companies and investors are to implement broad change. At the moment, this means incentives based on the costs of externalities (climate policy, for example) or the long-term risk management of investments.
We have tried to outline these issues in the attached discussion paper. Can you think of any aspects or applications which we have failed to account for in this?
As we produce scientific data and figures in support of the ideas outlined in this document, we would be delighted to see plenty of feedback to this paper from everyone (perhaps in the comments section below).
Juha Lehtonen, Research Professor