Hidden Value - If one thinks about coal-fired power plants, what is it that comes first into one's mind? The picture of high-value starting materials or rather the picture of low value carbon dioxide (CO₂) emissions? Most people will probably end up with the latter one. However, the utilization of CO₂ as a valuable raw material is not as devious as one would expect: Advanced research shows that it could be used as new source of carbon - thus replacing at least partially crude oil from which the element is normally extracted.

At present, the chemical industry is mainly dependent on petroleum, both as a feedstock and energy source - roughly 6-7% of the annual oil production is consumed by this sector. To become more independent in terms of energy, renewable resources and energy storage options are a matter of current research all over the industry.

Realistic Alternatives

Replacing petroleum as product feedstock is also part of the ongoing research. The chemical industry is looking for realistic alternatives, for example biomass, coal or gas. Coal and gas on the one hand both offer interesting options to become major carbon sources. However, their exploitation is energy intensive, and this inevitably leads to an increase in CO₂ emissions - something one would like to avoid in the age of sustainability and climate protection. Biomass, on the other hand, also has pros and cons which are intensively discussed. Is there any other option? How about CO₂?

In the chemical literature, researchers have been discussing for decades to use carbon dioxide directly as a chemical feedstock. All over the world, attempts to make use of this waste product have emerged in regular cycles. Currently, there are various research activities dealing with the utilization of CO₂ as chemical building block. In Germany for example, the Federal Ministry of Education and Research (BMBF) is heavily investing into this research area.

But there is one technical obstacle that makes this appealing idea very challenging: the low energetic level of CO₂. No matter what product one strives for, it will always be necessary to invest huge amounts of energy to enable a reaction with CO₂. Consequently, new CO₂ emissions will be the result.

Advances In Technology

Surely, there are already different possibilities to overcome the low reactivity of CO₂, for example using high-energy reaction partners such as hydrogen, unsaturated compounds or strained cyclic molecules. However, when evaluating the overall energy balance and efficiency of the process, the energy used to generate these high-energy materials has to be taken into account, which is especially relevant regarding hydrogen. For a long time there were only very few reactions using CO₂ that were efficient enough to be used in practice and the chemical utilization of carbon dioxide became known as the "dream reaction."

A core technology for the successful and economically interesting use of CO₂ as a chemical feedstock is catalysis, one of the most sophisticated and complex research areas of modern chemistry. Catalysis is used in the production of more than 85% of all products of the chemical industry, and the catalyst by its nature strongly determines the outcome of the reaction and the final product formation.

Finding The Right Catalyst

In order to find the right catalyst, Bayer initiated the project "Dream Reactions" in 2009, partly funded by the BMBF. Here, the company and numerous well-known academic partners have been investigating the preconditions of using CO₂ as building block for polyurethanes - a class of polymers widely used in every-day life, e.g. in mattresses, car seats, and as insulation materials. Polyurethanes are the reaction product of two components, isocyanates and polyols. The chemical nature of polyols gives them considerable potential for incorporating CO₂. Consequently the possibilities of using it as building block for a new kind of polyols, so called polyether-polycarbonate polyols, have been investigated within the "Dream Reactions" project. A broad catalyst screening helped to identify promising candidates, which were then optimized in terms of activity and selectivity towards the desired product.

Finally, Bayer researchers succeeded in finding the one suitable catalyst for this special reaction - a scientific breakthrough after decades of fruitless research. Consequently, Bayer thought about going one step further: Within the energy industry, strategies for capturing CO₂ from flue gases out of coal-fired power plants are discussed, yielding relatively pure CO₂ in vast quantities. Why not combine the chemical industry with the energy sector and turn the "Dream Reaction" into a "Dream Production"?

A Consortium for ‘Dream Production'

Thus, another consortium was established, consisting of Bayer, German energy provider RWE Power and researchers from RWTH Aachen University. The project "Dream Production" is again partly funded by the German Federal Ministry of Education and Research within their strategy to enhance the utilization of CO₂ as chemical building block. The consortium depictures the total value chain of CO₂ utilization in a very unique way - from source to final product.
The overall goal is to make the discoveries from "Dream Reaction" become reality, i.e. to design and develop a technical process able to produce CO₂-based polyether polycarbonate polyols on a larger scale. As a first major step, a pilot facility for the chemical treatment of carbon dioxide from the energy industry was opened at the Bayer Chempark Leverkusen in February 2011. Since then, the CO₂ delivered from RWE Power is converted into the already mentioned polyether-polycarbonate polyols. These are then subsequently transformed into polyurethane samples tested for their material properties and competitiveness. The first results are encouraging. Though having a higher viscosity, the new polyols show similar properties as products already on the market and can be processed in conventional plants as well.

In parallel, the eco-efficiency of the new process is being compared with existing alternatives. Initial research, conducted by an independent team of scientists at RWTH Aachen University, seems to underpin the hypothesis that in the end real CO₂ savings are reached. But the examination is very complex and will still last for a while. If progress continues, "Dream Production" will start bringing CO₂-based products to market at 2015 earliest. The first application could be soft foam matrasses.

In summary, even though the field of research is hardly new, the use of CO₂ as a raw material is one of the most interesting and visionary technologies for the future. Since fossil resources are finite, using CO₂ as a chemical feedstock is a promising approach to global carbon management, helping to pave the way to alternative sources of raw materials. And next time when people are asked to think about coal-fired power plants, the picture that comes into their minds might be just a bit different than before.