MIT: New approach suggests path to Emissions-Free Cement


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In a demonstration of the basic chemical reactions used in the new process, electrolysis takes place in neutral water. Dyes show how acid (pink) and base (purple) are produced at the positive and negative electrodes. A variation of this process can be used to convert calcium carbonate (CaCO3) into calcium hydroxide (Ca(OH)2), which can then be used to make Portland cement without producing any greenhouse gas emissions. Cement production currently causes 8 percent of global carbon emissions. Image: Felice Frankel

MIT researchers find a way to eliminate carbon emissions from cement production — a major global source of greenhouse gases.

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

A team of researchers at MIT has come up with a new way of manufacturing the material that could eliminate these emissions altogether, and could even make some other useful products in the process.

The findings are being reported today in the journal PNAS in a paper by Yet-Ming Chiang, the Kyocera Professor of Materials Science and Engineering at MIT, with postdoc Leah Ellis, graduate student Andres Badel, and others.

“About 1 kilogram of carbon dioxide is released for every kilogram of cement made today,” Chiang says. That adds up to 3 to 4 gigatons (billions of tons) of cement, and of carbon dioxide emissions, produced annually today, and that amount is projected to grow. The number of buildings worldwide is expected to double by 2060, which is equivalent to “building one new New York City every 30 days,” he says. And the commodity is now very cheap to produce: It costs only about 13 cents per kilogram, which he says makes it cheaper than bottled water.

So it’s a real challenge to find ways of reducing the material’s carbon emissions without making it too expensive. Chiang and his team have spent the last year searching for alternative approaches, and hit on 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 made by grinding up limestone and then cooking it with sand and clay at high heat, which is produced by burning coal. The process produces carbon dioxide in two different ways: from the burning of the coal, and from gases released from the limestone during the heating. Each of these produces roughly equal contributions to the total emissions. The new process would eliminate or drastically reduce both sources, Chiang says. Though they have demonstrated the basic electrochemical process in the lab, the process will require more work to scale up to industrial scale.

First of all, the new approach could eliminate the use of fossil fuels for the heating process, substituting electricity generated from clean, renewable sources. “In many geographies renewable electricity is the lowest-cost electricity we have today, and its cost is still dropping,” Chiang says. In addition, the new process produces the same cement product. The team realized that trying to gain acceptance for a new type of cement — something that many research groups have pursued in different ways — would be an uphill battle, considering how widely used the material is around the world and how reluctant builders can be to try new, relatively untested materials.

The new process centers on the use of an electrolyzer, something that many people have encountered as part of high school chemistry classes, where a battery is hooked up to two electrodes in a glass of water, producing bubbles of oxygen from one electrode and bubbles of hydrogen from the other as the electricity splits the water molecules into their constituent atoms. Importantly, the electrolyzer’s oxygen-evolving electrode produces acid, while the hydrogen-evolving electrode produces a base.

In the new process, the pulverized limestone is dissolved in the acid at one electrode and high-purity carbon dioxide is released, while calcium hydroxide, generally known as lime, precipitates out as a solid at the other. The calcium hydroxide can then be processed in another step to produce the cement, which is mostly calcium silicate.

The carbon dioxide, in the form of a pure, concentrated stream, can then be easily sequestered, harnessed to produce value-added products such as a liquid fuel to replace gasoline, or used for applications such as oil recovery or even in carbonated beverages and dry ice. The result is that no carbon dioxide is released to the environment from the entire process, Chiang says. By contrast, the carbon dioxide emitted from conventional cement plants is highly contaminated with nitrogen oxides, sulfur oxides, carbon monoxide and other material that make it impractical to “scrub” to make the carbon dioxide usable.

Calculations show that the hydrogen and oxygen also emitted in the process could be recombined, for example in a fuel cell, or burned to produce enough energy to fuel the whole rest of the process, Ellis says, producing nothing but water vapor.

In a demonstration of the basic chemical reactions used in the new process, electrolysis takes place in neutral water. Dyes show how acid (pink) and base (purple) are produced at the positive and negative electrodes. A variation of this process can be used to convert calcium carbonate (CaCO3) into calcium hydroxide (Ca(OH)2), which can then be used to make Portland cement without producing any greenhouse gas emissions. Cement production currently causes 8 percent of global carbon emissions.

In their laboratory demonstration, the team carried out the key electrochemical steps required, producing lime from the calcium carbonate, but on a small scale. The process looks a bit like shaking a snow-globe, as it produces a flurry of suspended white particles inside the glass container as the lime precipitates out of the solution.

While the technology is simple and could, in principle, be easily scaled up, a typical cement plant today produces about 700,000 tons of the material per year. “How do you penetrate an industry like that and get a foot in the door?” asks Ellis, the paper’s lead author. One approach, she says, is to try to replace just one part of the process at a time, rather than the whole system at once, and “in a stepwise fashion” gradually add other parts.

The initial proposed system the team came up with is “not because we necessarily think we have the exact strategy” for the best possible approach, Chiang says, “but to get people in the electrochemical sector to start thinking more about this,” and come up with new ideas. “It’s an important first step, but not yet a fully developed solution.”

The research was partly supported by the Skolkovo Institute of Science and Technology.

 

2 for 1: Turning Smokestack Emissions into Carbon Nanotube-Based Batteries = Clean Emissions + Clean Renewable Energy: Vanderbilt & George Washington Universities


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“Our climate change solution is two fold: To transform the greenhouse gas carbon dioxide into valuable products and to provide greenhouse gas emission-free alternatives to today’s industrial and transportation fossil fuel processes,” Stuart Licht, professor of chemistry at George Washington University

An interdisciplinary team of scientists has worked out a way to make electric vehicles that are not only carbon neutral, but carbon negative, capable of actually reducing the amount of atmospheric carbon dioxide as they operate. They have done so by demonstrating how the graphite electrodes used in the lithium-ion batteries that power electric automobiles can be replaced with carbon material recovered from the atmosphere. The recipe for converting carbon dioxide gas into batteries is described in a paper published in the March 2 issue of the journal ACS Central Science (“Carbon Nanotubes Produced from Ambient Carbon Dioxide for Environmentally Sustainable Lithium-Ion and Sodium-Ion Battery Anodes”).

Converting Carbon Dioxide into BatteriesThe Solar Thermal Electrochemical Process (STEP) converts atmospheric carbon dioxide into carbon nanotubes that can be used in advanced batteries. (Image: Julie Turner, Vanderbilt University)

“Our climate change solution is two fold: To transform the greenhouse gas carbon dioxide into valuable products and to provide greenhouse gas emission-free alternatives to today’s industrial and transportation fossil fuel processes,” Stuart Licht, professor of chemistry at George Washington University said.

“In addition to better batteries other applications for the carbon nanotubes include carbon composites for strong, lightweight construction materials, sports equipment and car, truck and airplane bodies.” The unusual pairing of carbon dioxide conversion and advanced battery technology is the result of a collaboration between Dr. Licht, and the laboratory of assistant professor of mechanical engineering Cary Pint at Vanderbilt University. Licht adapted the lab’s solar thermal electrochemical process (STEP) so that it produces carbon nanotubes from carbon dioxide and with Pint by incorporating them into both lithium-ion batteries like those used in electric vehicles and electronic devices and low-cost sodium-ion batteries under development for large-scale applications, such as the electric grid. In lithium-ion batteries, the nanotubes replace the carbon anode used in commercial batteries.

The team demonstrated that the carbon nanotubes gave a small boost to the performance, which was amplified when the battery was charged quickly. In sodium-ion batteries, the researchers found that small defects in the carbon, which can be tuned by STEP, can unlock stable storage performance over 3.5 times above that of sodium-ion batteries with graphite electrodes. Most importantly, both carbon-nanotube batteries were exposed to about 2.5 months of continuous charging and discharging and showed no sign of fatigue.

Published on Feb 25, 2016: Video interview with Cary Pint explaining this research.

Scientists from Vanderbilt and George Washington universities have worked out a way to make electric vehicles not just carbon neutral but carbon negative by demonstrating how the graphite electrodes used in the lithium-ion batteries can be replaced with carbon recovered from the atmosphere.

“This trailblazing research has achieved yet another amazing milestone with the incorporation of the carbon nanotubes produced by Stuart Licht’s STEP reduction of carbon dioxide process into batteries for electric vehicles and large scale storage,” said Michael King, chair of GW’s Department of Chemistry. “We are thrilled by this translation of basic research into potentially useful consumer products while mitigating atmospheric carbon dioxide buildup. This is a win-win for everyone!”
The researchers estimate that with a battery cost of $325 per kWh (the average cost of lithium-ion batteries reported by the Department of Energy in 2013), a kilogram of carbon dioxide has a value of about $18 as a battery material – six times more than when it is converted to methanol – a number that only increases when moving from large batteries used in electric vehicles to the smaller batteries used in electronics.

And unlike methanol, combining batteries with solar cells provides renewable power with zero greenhouse emissions, which is needed to put an end to the current carbon cycle that threatens future global sustainability.

 

Licht also proposes a modified flue system for combustion plants that incorporates this process could be self-sustaining, as exemplified by a new natural gas power plant with zero carbon dioxide emissions. That’s because the side product of the process is pure oxygen, which plants could then use for further combustion. The calculated total cost per metric tonne of CNTs would be much less expensive than current synthetic methods.

 

“This approach not only produces better batteries but it also establishes a value for carbon dioxide recovered from the atmosphere that is associated with the end-user battery cost unlike most efforts to reuse CO2 that are aimed at low-valued fuels, like methanol, that cannot justify the cost required to produce them,” said Pint.
Source: Vanderbilt University

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