Plastic reduces the greenhouse effect

CO2, which is known to be a pollutant that is bad for the climate, is now becoming a material of potentially high value: the chemical industry has had its eye on carbon dioxide as a possible source of carbon for quite a long time now, but separating the different elements has been considered difficult, energy-intensive and, as a result, uneconomic up to now. A new era is beginning now: research scientists from Bayer Technology Services have discovered catalysts that incorporate carbon dioxide in the molecular structure of plastics in an economically viable and environmentally sound way. Thanks to the “dream reaction” that has now become reality, use can be made of CO2 obtained from the emissions of brown coal power plants, e.g. for manufacturing polyurethane (PUR) in what is being called a “dream production” process. This is good for the atmosphere – helping to reduce not only the anthropogenic greenhouse effect but also and not least of all the consumption of crude oil, which is a finite resource. A pilot plant in Leverkusen operated by Bayer MaterialScience is supposed to develop the process so that it is ready to go to market by 2015. The participants in the project for which funding is being provided by the German Ministry of Education and Research include not just Bayer but also Aachen Technical University (RWTH) and RWE Power AG.

Anthropogenic emissions of the greenhouse gas carbon dioxide attributable to energy generation climbed to a new record level in 2010. More than 33 billion tonnes (33 gigatonnes), almost six per cent more than in 2009, demonstrate that the international community has failed to take effective action against impending climate collapse. More than half of global CO2 emissions are attributable to China, the USA, India and Russia (see photo gallery:List of environmental polluters). If emissions are related to population, the emerging countries among the four biggest environmental polluters are not performing quite as badly as it might seem: considerably fewer tonnes of CO2 are still being emitted per capita in China and India than in most of the industrialised European states (see photo gallery: National per capita CO2 emission in selected countries), including Germany. Although we are considered to be good examples, because we have succeeded in cutting annual CO2 emissions by almost 30 per cent over the all-time national high, we are still in what is a not very flattering sixth place by volume in the current global table (see photo gallery: List of environmental polluters ). The CO2 performance at EU level is patchy too: although the European Union is likely to reach its climate target of undercutting the level of 1990 by 20 per cent by 2020 without any difficulty – with respect to other gases that are bad for the climate as well, incidentally – many feel that this is not ambitious enough in the meantime. The coalition government agreement concluded by the Conservative and Liberal Parties in Germany already talks about 40 per cent instead of only 20 per cent, for example. The Intergovernmental Panel on Climate Change (IPCC) set up by the industrialised countries recommends a CO2 reduction of this order by 2020 to limit global warming and even suggests that a reduction of at least 80 per cent is necessary by 2050. The international Climate Change Conference in Durban, South Africa, that just ended did not specify any such target at all, however, and critics think that there is a risk as a result that the average temperature on earth will be increasing by even more than the two degrees currently feared.

So action to reduce CO2 emissions is needed more urgently than ever before. And any measures taken should neither be cancelled out by nor hamper ongoing economic growth. Up to now, it has seemed to be impossible to resolve this conflict – in the past, whenever CO2 emissions decreased significantly, this was due to economic recession. The conflict could, however, be resolved if a way could be found to make successful use of CO2, an industrial waste product, because of the carbon it contains – on the condition that this was done without having any adverse impact on the environment.

So far, industrial use of CO2 has been restricted to such applications as carbonated drinks, dry ice in laboratory and food contexts, fire extinguishers that produce carbon dioxide snow (link: Brief portrait of CO2) or CO2 lasers. The chemical industry needs the gas to manufacture such carbonates as soda and potash too. Carbon dioxide is also involved when fog is produced artificially on nightclub dancefloors. While it creates better conditions for plants to grow in greenhouses (photosynthesis is the process promoted here – it is not unusual for natural gas to be burned specially for this purpose). It goes without saying that these applications are not climate-neutral – so that CO2 cannot get into the atmosphere, it would have to be processed in such a way that it is “frozen” in the final product, i.e. stays locked away for ever, as it were. An obvious solution would then even be to obtain the raw material from the exhaust gases of power plants or from the atmosphere itself.

Trials carried out by the Bayer material research staff to take advantage of CO2 as a source of carbon and to incorporate the substance into the molecular structure of plastics have produced successful results in this context. Up to now, crude oil has provided the carbon needed; the fossil raw material could now be replaced by carbon dioxide, at least to some extent. Using CO2 in the production of polymers is not a new idea, but it has remained a theoretical possibility for decades because it poses tremendous technical challenges. Carbon dioxide molecules are very stable and are therefore slow to react, i.e. they are very reluctant to form compounds with other substances. The bond between one carbon atom and two oxygen atoms is so strong that it can only be separated by force, i.e. via activation energy, in order to make reactions with other chemical elements possible. Energy which has an immense quantum and the production of which releases new CO2 – a solution that cannot be viable. For this reason, research scientists for a long time considered the transformation of carbon dioxide into a raw material for the production of plastic to be a “dream reaction” – a reaction that probably only exists in the dream world. It almost turned into a nightmare for many research scientists, because their experiments failed again and again. Now the dream is becoming reality, however: after completing years of testing, chemists from the “Reaction Engineering & Catalysis” centre of excellence at Bayer Technology Services have found a catalyst that persuades stubborn carbon dioxide to combine with other substances. Catalysis, currently the most important interdisciplinary technology for the chemical industry, enables reactions that would never take place on their own to take place with only minimal activation energy.

As long ago as the end of the 60s, Japanese research scientists had indicated the road that needed to be followed and had succeeded in demonstrating that CO2 can in principle be activated with the help of catalysts; the reaction speed was disappointing, however. In their attempts to optimise the process, Bayer research scientists achieved a breakthrough in 2008. The team headed by the chemist Aurel Wolf combined carbon dioxide and propylene oxide in about 200 test series using a different catalyst each time, with the subsequent application of heat. What is created in this context is polyether polycarbonate polyol (PPP), a viscous, colourless substance that acts as the basic material for the production of polyurethane (PUR). It is a substance of great use to chemists, because PUR – as is generally known – is a foam material of low weight that can be used universally to produce lightweight components – to an increasing extent in vehicle manufacturing as well – and that is particularly popular as an insulation material: polyurethanes that protect buildings against cold save about 70 times more energy than is consumed in their production.

But to get back to our story: following application of the catalysts and completion of a specific reaction time, the Bayer research scientists determined how much PPP was produced in each case and how much CO2 had actually been incorporated in the polymer molecule. A maximum of 43 per cent by weight is possible without sacrificing quality. This is far more than the results achieved at the beginning of the tests. In 2009, the search for an improved catalyst was continued in the context of the “Dream Reactions” project with funding from the German Ministry of Education and Research and in co-operation with the Catalytic Centre at Aachen Technical University (RWTH), with the aim of getting the CO2 content of the PPP as close as possible to the above-mentioned level of 43 per cent.

What has worked at the laboratory level is now to be confirmed in testing under industrial conditions so that the process can be launched on the market: “dream reactions” are being turned into “dream production”. Since February 2011, a pilot plant set up in Leverkusen has been producing sample batches of PPP that are supplied to Bayer MaterialScience, which processes them into polyurethane (the company manufactures 1.4 million tonnes of the plastic every year). RWE Power AG, Germany’s biggest power generator, is involved as the CO2 supplier. The environmental pollutant is extracted from the flue gas flow at the RWE brown coal power plant in Niederaußem in the first CO2 scrubbing system installed in Germany. The CO2 is then cleaned, liquefied and filled in containers for delivery.

The process is to be fine-tuned in Leverkusen for at least four more years, not least of all in order to develop the optimum formulations: polyurethanes need to be versatile; soft foam is required for mattresses sometimes, while rigid insulation material for construction applications is needed in other cases. “We intend to be in a position to produce the ingredients for CO2-based polyurethanes from 2015 onwards. And they will then contain 10 to 40 per cent carbon dioxide”, says Project Manager Dr Christoph Gürtler, a chemist at Bayer MaterialScience. Another plan is to integrate carbon dioxide in other plastics, e.g. polycarbonates, as well in future - and possibly even in medical drugs that Bayer also manufactures.

Whether and when the new process is ready to be marketed will be determined not least of all by its environmental efficiency; RWTH Aachen has been commissioned to complete the necessary analyses about this. Among the points that need to be settled is whether less overall energy is needed than in the past to produce PPP by using CO2. Dr Gürtler emphasises that the process is not at any rate a universal solution to the climate change problem and that this is not what Bayer was aiming to achieve anyway. At the present time, only 0.3 per cent of carbon dioxide emissions in Germany is made use of for industrial purposes. Experts estimate that this figure could be ten per cent by the end of the decade, if the potential for using CO2 to store excess power is included – something that is becoming increasingly important with the increase in renewable energy sources. So 90 per cent would still be unused even then – there is simply too much of the greenhouse gas around. All the same: Bayer and RWE have estimated that CO2 emissions could be reduced by five to ten million tonnes every year in future by using carbon dioxide in plastics production. Not much compared with the 33 billion tonnes that are released into the atmosphere around the world, but a step in the right direction – particularly in view of the fact that dependence on crude oil will be decreased quite considerably into the bargain: “About a third of the oil needed can be eliminated by using carbon dioxide”, explains Dr Gürtler. At the present time, more than half a billion litres of crude oil are processed into plastics around the world – every day! So it is no surprise that the “Dream Production” co-operation between Bayer AG, RWTH Aachen and RWE Power AG was one of the three finalists in the category “Germany’s most sustainable projects in 2011” when the German Sustainability Awards were presented in Düsseldorf in early November. The jury was impressed by the commitment to “energy-efficient, resource-minimising and environmentally sound use of CO2” and concluded that there were “excellent chances of success”.

Guido Deußing
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