Why does carbon dioxide not support combustion?

Carbon dioxide : From waste to raw material

Carbon dioxide's image is pretty bad. It has gained a certain fame as a greenhouse gas in recent years. Every year power plant chimneys, exhaust pipes and chimneys blow around 28 billion tons of it into the air. There it picks up the thermal radiation that emanates from the floor and returns some of it downwards. That drives up the global average temperature.

Researchers are therefore developing techniques to reduce greenhouse gas emissions or to separate it from industrial waste gases and dump them underground. Some also take another approach: They see carbon dioxide (CO2) not just as waste, but as a raw material, and try to convert the gas into useful materials. The Federal Ministry of Research supports such work with 100 million euros in the funding program “Technologies for Sustainability and Climate Protection - Chemical Processes and Material Use of Carbon Dioxide”.

Carbon dioxide can be processed into various substances that are useful for the chemical industry. “There are currently four important products that can be made from CO2: urea, methanol, cyclic carbonates and salicylic acid,” says Anna-Katharina Ott, head of the “Carbon Dioxide as a Polymer Building Block” project at BASF. Urea is used as a fertilizer, methanol as a raw material for plastics and as a fuel additive. Cyclic carbonates are used as solvents in the chemical industry; the drug aspirin can be made from salicylic acid.

However, all of these processes have to deal with the problem that CO2 is a very stable compound: it can hardly be made to react with other substances. “To convert carbon dioxide into other products, you have to put a lot of energy into it. That costs money and releases greenhouse gases again, ”explains Ott. The researchers are therefore looking for new catalysts, i.e. substances that make carbon dioxide more reactive. “This allows you to reduce the amount of energy required,” says Ott.

“Catalysts increase the efficiency of a chemical process and thus make some reactions economically interesting in the first place.” Various substances can be used as catalysts, such as metals, metal compounds or organic substances.

Some of the technology is quite advanced, for example in the “Dream Production” project, which is being led by Bayer MaterialScience.

Next year, a test facility is to go into operation in Leverkusen, which processes carbon dioxide into polyurethane plastics through several catalytically controlled intermediate steps. The plant is supposed to use carbon dioxide for this, which was previously separated from the flue gases of a coal-fired power plant. Polyurethane plastics can be used as insulation materials for buildings, as foams for mattresses or as lightweight components for the automotive industry.

But there are other obstacles. If you want to convert carbon dioxide with other substances in order to produce usable products, the other raw materials should also be produced sustainably. Today's processes, for example, which allow CO2 to react with hydrogen, obtain the hydrogen from fossil sources. "The gas is mainly obtained by converting natural gas," explains Oliver Scherr, the responsible project manager at the German Aerospace Center. However, natural gas is a fossil raw material and its occurrence is limited. "It doesn't make sense to use hydrogen from fossil sources to relieve the environment," says Scherr. "For this we need renewable sources."

One research project that addresses this problem is the “CO2RRECT” project, which has been running since October. The aim is to convert carbon dioxide into useful raw materials for the chemical industry with the help of renewable energies. “The problem is that renewable energy sources produce electricity very irregularly,” says Martina Peters, project coordinator at Bayer Technology Services. When the sun shines brightly or the wind blows strongly, solar systems and wind turbines provide excess energy that has not yet been used. The researchers want to change that by using the excess electricity to split water into oxygen and hydrogen. "However, today's processes for this are designed for a uniform energy supply," says Peters. "We want to adapt them so that they can cope with the fluctuating performance of renewable energy sources."

The hydrogen that is produced when water is electrically split can later be burned again, for example in fuel cells, which releases energy. But it can also be made to react with carbon dioxide, producing useful chemicals. "We focus on the second variant, we want to use the hydrogen to convert CO2 into carbon monoxide or formic acid," says Peters.

These chemicals, in turn, can be processed into polyurethane or polycarbonate plastics, which can be used to make car parts, computer cases, DVDs, tarpaulins or bags. In this way, the greenhouse gas carbon dioxide could end up in everyday mass-produced items.

However, a significant reduction in global emissions is not possible with this. "The material use of CO2 will not be able to solve the problems of climate change," emphasizes Ott. "An example: In 2012 around 59 million tons of methanol are required, which would correspond to a carbon dioxide value of 81 million tons - that is about three thousandths of the total annual emissions."

The goals of CO2RRECT lie elsewhere. "If we are successful, we kill three birds with one stone," outlines Arnold Rajathurai, press spokesman for Bayer Technology Services. “Firstly, we make the temporary surpluses of renewable energy sources usable; secondly, we show how the carbon dioxide, which is cheaply available everywhere, can be recycled. And thirdly, we are reducing our dependence on fossil raw materials. ”To achieve this, however, the cooperation between the energy industry and the chemical industry must be significantly improved. “We are only at the beginning,” says Rajathurai.

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