Much "to do" with CO2
As a fossil derived greenhouse gas (GHG), carbon dioxide (CO2) is a major problem and widespread efforts are being made to curtail its accumulation in the atmosphere. Parallel to source emission reduction policies and technologies, a new strand of research is rapidly emerging under the umbrella term “carbon (dioxide) capture and utilisation” (CCU). The focus is on looking at the world’s perhaps most frowned upon gas as a resource instead.
Held in Essen, Germany under the patronage of Svenja Schulze, Minister of Innovation, Science and Research in the German State of North Rhine-Westphalia, the 4th Conference on Carbon Dioxide as Feedstock for Fuels, Chemistry and Polymers attracted some 170 academic and industrial experts from 25 countries. The two-day conference was organised at the end of September by nova-Institute, a private independent research and consultancy focused on the biobased and carbon dioxide (CO₂) based economy.
CO2 usage today
With the exception of urea, aspirin and carbonates the industrial utilisation of CO₂ as a chemical feedstock is limited by thermodynamic and kinetic constraints. In contrast it is the properties that these constraints give rise to – inert, stable and heavier than air – that makes it a major commercial product for fire extinguishing systems, refrigerants and the food and beverage industry. Recent advances in carbon capture and utilisation (CCU) technologies, so-called “power-to-x” pathways where x is a product, presented during the event suggest that CO₂ could become an industrial-scale feedstock for synthetic fuels and other key chemicals sooner not later.
– The complete needs of energy sources and platform chemicals could be sustainable and covered with renewable energies and CCU technologies, stated Michael Carus, physicist and Managing Director of nova-Institute and conference organiser in his opening address.
Carus highlighted that in 2050, 5-10 percent of the world’s desert area would be enough to cover both the global energy demand and the carbon needs of the chemical and polymer industry with solar power, even taking into account grid and storage construction. The cost to “solarise the world” he suggested would only be 5-10 years worth of the annual global spend of US$ 1 300 billion on arms and defence.
– This implies that it is primarily a question of the right political guidance and of investments, whether we will have raw material shortage in the future or not, said Carus stressing the need and importance “to show society and politicians a positive vision, to encourage them to break new ground.”
Katy Armstrong from the international CO2Chem network and the European research project Smart CO₂ Transformation (SCOT) cautioned against exaggerated expectations.
– Much would be achieved if a pilot project could provide a local population with wind power and CCU fuels, remarked Armstrong, bringing to mind lessons learnt from talk of potentials and hype in other sectors such as cellulosic biofuels.
Dr Markus Friedl, Professor and Head of Institute for Energy Technology Hochschule für Technik Rapperswil, Switzerland reminded the audience that power-to-gas only makes sense if using the methane produced has less negative impact on the environment than using fossil derived methane. First Life Cycle Assessments (LCA) for Switzerland suggest that this is only the case, if the following two conditions are fulfilled: the power used for the electrolyser is renewable and the CO₂ used in the methanation is of biological nature or its production is “unavoidable”.
– Unavoidable means CO₂ that is released as part of a necessary process other than combustion of fossil fuels, explained Friedl, adding that 18 percent of Swiss man-made, unavoidable CO₂ emissions are concentrated in 36 locations and candidates for power-to-methane plants.
Delegates called upon politicians to create market incentives to facilitate bringing new CCU technologies to the market. The European Commission (EC) took a first step in this direction with the reform of the “Renewable Energy Directive (RED)”, partially equating CCU fuels with biofuels, as Andreas Pilzecker, DG Climate, reported.
A particularly intense discussion ensued on whether a mandatory blend of CCU based kerosene in aviation fuel would be a good route to develop market and capacity as CCU fuels and platform chemicals remain around a factor of 2-3 times more expensive than their fossil counterparts, yet show really low carbon footprints after first life cycle assessments, clearly less than even the best biofuels.
Hydrogen (H₂) is a key component for most CCU-technologies as it is used to reduce the CO₂. However conventional H₂ production, such as by electrolysis of water, is energy intensive and, as pointed out by Dr Friedl, may defeat the purpose. Several speakers remarked that H₂ production represents over 80 percent of the costs for CO₂ based fuels and chemicals. Lowering the cost of H₂ production is a critical factor and the research race is on.
Well-developed CCU technologies on the cusp of industrial-scale commercialisation were presented as well as those still in laboratory or pilot scale. Icelandic company International Carbon Recycling (ICR) is an example of the former with its 4 000 tonne-per-annum renewable methanol plant in Iceland making it the largest CCU plant of its kind.
Another pathway has been demonstrated by American company, Joule Fuels Unlimited, with its continuous flow “reverse combustion” CO₂-to-fuel production platform. According to Kees van de Kerk the pilot plant in New Mexico uses sunlight, non-potable water and engineered cyanobacteria that function as living catalysts to produce specific products, ethanol or hydrocarbon fuels that are “inherently compatible” with existing infrastructure.
Thomas Heller with MicrobEnergy, owned by Viessmann Group, presented a novel microbiological process set up as a demonstration power-to-gas at a biogas plant in Allendorf (Eder), Germany. The project is part of the German BioPower2Gas subsidy programme. The process combines hydrogen from an external source with the CO₂ generated during fermentation in a biogas plant converting it into methane. A PEM electrolyser built by Carbotech, another Viessmann company, is used to produce hydrogen.
– Specialised microorganisms perform the actual methanisation. They absorb the carbon dioxide and the hydrogen in liquid form through their cell walls, ’digesting’ and converting them into methane. The only thing left over after this process is water. Biological methanation impresses due to its optimum flexibility, making it eminently suitable to absorb fluctuating quantities of power produced by wind or solar power, said Heller.
Leading in the usage of CO₂ for production of CO₂ based polymers is Covestro, formerly Bayer Material Science and one of the world’s largest polymer producers, which will be the first to produce CO₂ based polyurethane foams in Dormagen, Germany next year.
– This should be the start for a new product family based on CO₂ based polyols and polymers, said Dr Christoph Gürtler from Covestro.
Also in an advanced state of pre-commercial deployment are CCU systems that combine electrolysis of water and then from the hydrogen plus CO₂ produce a variety of synthetic fuels and platform chemicals via Fischer-Tropsch processes. This includes for example the technologies from the German company sunfire and the Israeli company NewCO₂Fuels.
Dr Dunwei Wang, Professor from Boston College, US presented the latest update on work to develop cheap low-cost metallic catalysts, which may enable artificial photosynthesis with high efficiency.
– The promise held by solar water splitting, however, cannot be materialised unless the process can be carried out using earth-abundant, low-cost materials, said Wang.
Wang’s research involves using hematite (alpha phase iron oxide) and addressing the key problems shared by low-cost materials.
– Many of these issues are addressable and collectively our improvement strategies demonstrate that the performance of hematite can be improved dramatically, enabling complete solar water splitting without the need for external power input other than the presence of a silicon-based photocathode. These results open up new opportunities toward practical low-cost solar hydrogen generation, said Wang.
– The design of highly efficient, non-biological, molecular-level energy conversion “machines” that generate fuels directly from sunlight, water, and carbon dioxide is both a formidable challenge and an opportunity that, if realised, could have a revolutionary impact on our energy system, said Dr Nathan Lewis, Professor at the California Institute of Technology and US Department of Energy Energy Innovation Hub, Joint Center for Artificial Photosynthesis (JCAP).
Lewis presented a bold example of mimicry. His research thus far has developed so-called “silicon microwires”, which can split water directly into hydrogen and oxygen with the use of sunlight. These “polymer mats” can be rolled out like a carpet and produce hydrogen from sunlight and humidity.
– Basic research has already provided enormous advances in our understanding of the subtle and complex photochemistry behind the natural photosynthetic system, and in the use of inorganic photo-catalytic methods to split water or reduce carbon dioxide – key steps in photosynthesis, Lewis said.
In a second step these could be designed to produce synthetic fuels using CO₂ from the air. In other words solar energy could be tapped and transformed into high energy density synthetic fuels and stored in decentralised locations.
When could such technologies appear on the market? The next edition of the event, slated to be held in December 2016, is a good place to find out.