Christoph Gürtler studied chemistry at the University of Bonn from 1987 to 1993 and obtained his PhD at the Technical University of Berlin in 1996. After a postdoc at the Massachusetts Institute of Technology (MIT) he joined Bayer AG, Central Research department. Dr. Gürtler is currently heading a competence center in the field of process and product development dedicated to new catalytic processes.
After studying chemistry from 2004 to 2009, Annika Stute received her PhD at the University of Münster in 2013 with internships at the University of York and the University of Calgary. A postdoctoral research project at the University of Bristol followed before she joined Bayer MaterialScience in 2015 (since 9/2015 - Covestro). In her current position she focuses on strategic aspects regarding external cooperation and coordinating externally funded projects in the area of CO2 utilisation.
Global CO2 emissions are steadily rising rather than falling. Steps taken to date to curb emissions have clearly been inadequate. A contribution could be made by the chemical industry by using CO2 as a new building block for high-value plastics. Doing so would both conserve fossil resources and help the climate.
Over 30 billion metric tonnes of CO2 from buildings, cars, factories and other sources are released into the atmosphere worldwide year after year. Most experts, including the Intergovernmental Panel on Climate Change (IPCC), agree that this adds to the natural greenhouse effect. This results in long-term climate change, with increasing temperatures, melting ice and rising sea levels.
The top priority is therefore to avoid CO2 emissions – primarily by expanding renewable energies, cutting energy consumption and improving energy efficiency. Energy utilities are also working on separating off the CO2 generated by power plants and storing it permanently underground, a technology known as Carbon Capture and Storage (CCS).
A third option is also growing in importance – increased recycling of CO2 as a raw material, which the experts call Carbon Capture and Usage (CCU) or Carbon Capture and Reuse (CCR). This is a focus of governmental funding programs.
CO2 as a supplier of carbon
In times of fuel scarcity and the above mentioned funding programs, people are becoming more and more aware that CO2 is much too valuable to just be released into the atmosphere and thus worsen the greenhouse effect. The gas contains something quite valuable: the element carbon, the foundation of all life and an important building block for the chemical industry.
Of course, we have been using CO2 for a long time. As an industrial gas, CO2 provides the carbonic acid in sparkling water, is used in fire extinguishers and also serves as a coolant. In addition, it has been traditionally used as a synthetic building block in chemical reactions to make products such as fertilisers and drugs.
Substitute for petroleum
But now there is another new and promising possibility: manufacturing plastics by using CO2. Up to now plastics have been based primarily on petrochemical raw materials, meaning - essentially - petroleum. However, unlike CO2, this important carbon source has only limited availability. Furthermore, processing petroleum into chemical precursors consumes a tremendous amount of energy, leading to further CO2 emissions. The chemical industry has already made a lot of progress in implementing CO2 as a new raw material.
Using CO2 to manufacture plastics benefits the environment in two ways: firstly, CO2 is directly incorporated into polymers and partially substitutes oil as a raw material. Secondly, the amount of emitted CO2 during the manufacturing process is reduced by optimised, more environmentally-friendly processes compared to the established processes.
Naturally, this alone will not be enough to mitigate climate change. The demand for CO2 for plastics and other chemical products is much too low. Some years ago, this was estimated at 180 million metric tonnes a year, which then would have been equivalent to no more than 0.6 percent of current global CO2 emissions. However, a number of small steps together can add up to a great leap in progress.
Catalysis as the key
Why has CO2 not been used before as a polymer building block? While there were certainly many ideas on how to create valuable materials out of the waste product CO2, one problem remained: the low energetic level of CO2. No matter what products one is aiming for, it always takes huge amounts of energy to enable a reaction with CO2. Typically, this low reactivity of CO2 can be overcome by high-energy reaction partners. 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. For these reasons, only very few reactions using CO2 were suitably efficient to be used in practice for a long time. Therefore, the proper chemical utilisation of CO2 became known as the “Dream Reaction”.
Moreover, the low energetic state of CO2 often leads to a low energetic driving force of the reaction, low yields and low selectivity. One way to tackle these challenges is catalysis, a core technology for the successful and economically interesting use of CO2 as a chemical feedstock, and still one of the most sophisticated and complex research areas of modern chemistry. Catalysis is used in the production of more than 85% of all chemical industry products. Although catalysis can lower the activation energy for CO2 utilisation and improve product yields, the general energy challenge remains: since both CO2 capture and utilisation usually require substantial energy inputs, the intuitive environmental benefits cannot be taken for granted. Thus, a detailed environmental assessment is required for processes utilising CO2. For this purpose, life cycle assessment (LCA) provides a sound methodological framework. Specific guidelines for the application of LCA to CO2 utilisation have recently been developed.
Indirect CO2 utilisation
While the environmental potential of direct utilisation of CO2 for polyethercarbonate polyols has been demonstrated, CO2 can also be utilised indirectly for many intermediates in the chemical supply chain of polyurethanes. For example, it can be converted to methanol and subsequently to formaldehyde and further on to its polymer, polyoxymethylene diol, which also constitutes a potential building block for polyols. Methanol based on CO2 is the subject of many efforts in the industry, and it is already commercially available. The first material tests are showing encouraging results.
In summary, even though the field of research is hardly new, the use of CO2 as a raw material is still one of the most interesting and visionary technologies for the future. Since fossil resources are finite, using CO2 as chemical feedstock is a promising approach to global carbon management. LCA investigations show that there is a clear ecological benefit for CO2-based polymers as compared to conventional ones. This can even be improved by following the approach of the direct and indirect use of CO2. First pioneer examples already show that the chemical utilisation of CO2 for the production of polymers on an industrial scale is feasible. But establishing CO2 as an alternative raw material in the chemical industry is still in its infancy. Future endeavours will demonstrate the potential of the gas and initiate a possible image change from an environmentally harmful greenhouse gas to a useful and sustainable new raw material