New approach suggests a path to zero-emission cement



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<div data-thumb = "https://scx1.b-cdn.net/csz/news/tmb/2019/newapproachs.gif" data-src = "https://scx2.b-cdn.net/gfx/ news / 2019 / newapproachs.gif "data-sub-html =" In a demonstration of the basic chemical reactions used in the new process, the electrolysis takes place in a neutral water.The dyes show how the acid (pink) and base (violet) are produced at positive and negative electrodes. A variant of this process can be used to convert calcium carbonate (CaCO3) calcium hydroxide (Ca (OH)2), which can then be used to make Portland cement without emitting greenhouse gases. Cement production is currently responsible for 8% of global carbon emissions. Credit: Mbadachusetts Institute of Technology ">

<img src = "https://scx1.b-cdn.net/csz/news/800/2019/newapproachs.gif" alt = "** A new approach suggests a path to emissions-free cement" title = "In a demonstration Electrolysis is one of the basic chemical reactions used in neutral water The dyes show how acid (pink) and base (violet) are produced at the positive and negative electrodes A variant of this process can be used to convert calcium carbonate (CaCO3) calcium hydroxide (Ca (OH)2), which can then be used to make Portland cement without emitting greenhouse gases. Cement production is currently responsible for 8% of global carbon emissions. Credit: Mbadachusetts Institute of Technology "/>
In a demonstration of the basic chemical reactions used in the new process, the electrolysis takes place in neutral water. The dyes show how acid (pink) and base (purple) are produced at positive and negative electrodes. A variant of this process can be used to convert calcium carbonate (CaCO3) calcium hydroxide (Ca (OH)2), which can then be used to make Portland cement without emitting greenhouse gases. Cement production is currently responsible for 8% of global carbon emissions. Credit: Mbadachusetts Institute of Technology

It is well known that cement production, the world's leading construction material, is a major source of greenhouse gas emissions, accounting for about 8% of all releases. If cement production were a country, it would be the third largest emitter in the world.


A team of MIT researchers has developed a new material manufacturing method that could totally eliminate these emissions and could even create other useful products.

The results are reported today in the journal PNAS in an article by Yet-Ming Chiang, Kyocera Professor of Materials Science and Engineering at MIT, with post-doc Leah Ellis, graduate student Andres Badel, and others .

"About 1 kilogram of carbon dioxide is released for every kilogram of cement manufactured today," Chiang said. This represents 3 to 4 gigatonnes (billion tonnes) of cement and carbon dioxide emissions, produced every year today, and this amount is expected to increase. The number of buildings in the world is expected to double by 2060, which equates to "building a new New York every 30 days," he said. And the merchandise is now very inexpensive to produce: it costs only 13 cents per kilo, which, according to him, makes it cheaper than bottled water.

It is therefore difficult to find ways to reduce the carbon emissions of the material without making it too expensive. Over the past year, Chiang and his team have been looking for alternative approaches and have had the idea of ​​using an electrochemical process to replace the current fossil fuel dependent system.

Ordinary Portland cement, the most widely used standard variety, is obtained by grinding limestone and then baking it with sand and clay over high heat, obtained by burning coal. The process produces carbon dioxide in two different ways: from burning coal and from gases released by limestone during heating. Each of these produces contributions roughly equal to total emissions. The new process would eliminate or significantly reduce both sources, says Chiang. Although they have demonstrated the basic electrochemical process in the laboratory, the process will require more work to be developed on an industrial scale.

First, the new approach could eliminate the use of fossil fuels for the heating process, replacing the electricity generated by clean, renewable sources. "In many geographic areas, renewable electricity is the least expensive electricity we have today, and its cost is still going down," Chiang said. In addition, the new process produces the same cement product. The team realized that trying to get a new type of cement accepted – which many research groups have undertaken in different ways – would be a difficult battle, given the importance of the use of the material in the world and the rigor with which the builders can be tempted. new materials, relatively untested.

The new process focuses on the use of an electrolyser, a phenomenon encountered by many people in high school chemistry clbades. A battery is connected to two electrodes in a glbad of water, producing oxygen bubbles from one electrode and hydrogen bubbles from the other when electricity divides the molecules of water in their constituent atoms. It is important to note that the electrode releasing oxygen from the electrolyzer produces an acid, while the hydrogen-generating electrode forms a base.

In the new process, the pulverized limestone is dissolved in the acid at a high purity electrode and carbon dioxide is released, while calcium hydroxide, usually called lime, precipitates. in solid form to each other. The calcium hydroxide can then be processed in another step to produce the cement, which is mainly calcium silicate.

Carbon dioxide, in the form of a pure and concentrated stream, can then be easily sequestered, exploited to produce value-added products, such as liquid fuels replacing gasoline, or used for applications such as recovery. oil or even in soft drinks and soft drinks. dry ice. The result is that no carbon dioxide is released into the environment by the whole process, says Chiang. On the other hand, the carbon dioxide emitted by conventional cement plants is heavily contaminated by nitrogen oxides, sulfur oxides, carbon monoxide and other materials that prevent the "cleaning up" of carbon dioxide into a carbon dioxide. practical use.

Calculations show that the hydrogen and oxygen emitted in the process could also be recombined, for example in a fuel cell, or burned in order to produce enough energy to power the rest of the process, explains Ellis, producing only steam.

During their laboratory demonstration, the team performed the key electrochemical steps required, producing lime from calcium carbonate, but on a small scale. The process looks a bit like shaking a snow globe because it produces a multitude of white particles hanging inside the glbad container when lime escapes from the solution.

Although the technology is simple and can, in principle, be easily scaled, a typical cement plant now produces around 700,000 tonnes of material per year. "How do you enter an industry of this type and open the door?" Ellis asks, the main author of the newspaper. According to her, one approach is to try to replace part of the process at a time, rather than the entire system at a time, and gradually add other parties.

The system originally proposed by the team is "not because we necessarily think we have the exact strategy" for the best possible approach, says Chiang, "but to get people from the electrochemical sector to start thinking more about it. subject "and coming up with new ideas. "It's an important first step, but not yet a fully developed solution."


Reduction of carbon dioxide emissions at the horizon for cement


More information:
Leah D. Ellis et al. Towards the Electrochemical Synthesis of Cement – An Electrolyser-based Process for the Decarbonation of CaCO3 While Producing Useful Gas Flows, Proceedings of the National Academy of Sciences (2019). DOI: 10.1073 / pnas.1821673116

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