Carbon capture has a powerful allure. The Earth is overheating because there is too much carbon dioxide in the atmosphere. So why not suck out the excess, then store it in holes deep underground — there are thousands upon thousands of old oil and gas wells just waiting for some useful purpose to come along — or use it to make biofuel, fertilizer, medicine, and biodegradable plastics? It sounds like the ideal solution to a problem that affects us all.
The MIT Breakthrough
Currently, carbon capture technologies only work in the presence of high concentrations of carbon dioxide, such as inside the smokestacks of thermal power plants. But researchers at MIT say they have invented a new process that is effective at concentrations as low as 400 parts per million, which just happens to be how much carbon dioxide is in the Earth’s atmosphere today.
In a report published recently in the journal Energy and Environmental Science, MIT postdoctoral candidate Sahag Voskian and Professor T. Alan Hatton have created a device that is essentially a large, specialized battery. It absorbs carbon dioxide from air passing over its electrodes as it is being charged up, and then releases the gas as it is discharged. The device simply alternates between charging and discharging, with ambient air blown through the system during the charging cycle and concentrated carbon dioxide blown out while discharging. Put two devices to work simultaneously, with one discharging while the other is charging, and a constant stream of carbon dioxide results.
According to MIT News, as the device charges, an electro-chemical reaction takes place on the surface of a stack of electrodes composed of carbon nanotubes coated with polyanthraquinone. “The greatest advantage of this technology over most other carbon capture or carbon absorbing technologies is the binary nature of the adsorbent’s affinity to carbon dioxide,” explains Voskian. The electrode material “has either a high affinity or no affinity whatsoever,” depending on whether it is charging or discharging.
The beauty of the MIT device is that it operates at room temperature and requires no pressurization. Other carbon capture systems require intermediate chemical processing steps or the input of significant energy such as heat or pressure differences. “All of this is at ambient conditions — there’s no need for thermal, pressure, or chemical input. It’s just these very thin sheets, with both surfaces active, that can be stacked in a box and connected to a source of electricity,” says Professor Hatton.
So far, the researchers say their device is good for about 7,000 charging-discharging cycles, with a 30% loss in efficiency over that time. They think 20,000 to 50,000 cycles are possible with further development. The plates can be manufactured using existing roll-to-roll manufacturing techniques similar to a newspaper printing press. Voskian says manufacturing costs will be on the order of tens of dollars per square meter of electrode. The process would consume about 1 gigajoule of electricity for every ton of carbon dioxide captured. A gigajoule is equivalent to 277,778 watts. Some other carbon capture systems use 10 times as much electricity.
The researchers have set up a company called Verdox to commercialize the process and hope to develop a pilot-scale plant within the next few years. The system is very easy to scale up. “If you want more capacity, you just need to make more electrodes,” Hatton says.
The Mark Jacobson Rebuttal
The idea of carbon capture is alluring, especially for fossil fuel companies. “We can still burn all our lovely coal, oil, and gas,” they argue, “then just strip the carbon emissions from the exhaust stream and bury the stuff…somewhere.” They are a little hazy about the details. If carbon capture works they way they hope it will, they would be free to monetize all their reserves and the Earth would still be the comfortable, familiar place it has always been.
Mark Z. Jacobson is a noted professor of civil and environmental engineering and director of the Atmosphere/Energy Program at Stanford University. Professor Jacobson is also a contributor to CleanTechnica. He and his colleagues have presented a plan that would bring 100% renewable energy to 139 countries around the world while creating 52 million jobs.
In a recent study also published in the journal Energy & Environmental Science, Jacobson asserts that carbon capture provides no useful reduction in total carbon emissions and may, in some cases, create more carbon emissions. While carbon capture advocates claim their technology can capture up to 90% of the carbon emitted by thermal generating plants, Jacobson says that number conveniently ignores what he calls “upstream emissions” — the carbon dioxide created by extracting fossil fuels in the first place and transporting them to where they are burned. Jacobson’s study does not take into account downstream emissions — such as leakage of the carbon dioxide after it is captured. Any gas under pressure will find a way to escape if it can and carbon dioxide is no exception.
CleanTechnica published a story recently showing that the emissions from wasted methane flared off by oil companies is equal to the exhaust emissions from 70,000,000 vehicles worldwide. Carbon capture proponents to ignore such upstream emissions, but Jacobson includes them. After doing so, he says 10 to 20% carbon capture at thermal plants is more realistic.
Then there is the problem of powering the carbon capture equipment, which consumes significant amounts of electricity. Jacobson argues that even if that electricity comes from solar or wind, it could be put to better use than operating carbon capture systems. “Even if you have 100 percent capture from the capture equipment, it is still worse, from a social cost perspective, than replacing a coal or gas plant with a wind farm because carbon capture never reduces air pollution and always has a capture equipment cost. Wind replacing fossil fuels always reduces air pollution and never has a capture equipment cost.”
“Not only does carbon capture hardly work at existing plants, but there’s no way it can actually improve to be better than replacing coal or gas with wind or solar directly,” Jacobson says. “The latter will always be better, no matter what, in terms of the social cost. You can’t just ignore health costs or climate costs.”
But surely once the world transitions to 100% renewable energy, carbon capture techniques — like the one proposed by the MIT researchers — could be used to suck carbon dioxide out of the air, couldn’t they? Jacobson suggests even then the smarter investment is in options such as reforestation and reducing halogen, nitrous oxide. and methane emissions.
“There is a lot of reliance on carbon capture in theoretical modeling, and by focusing on that as even a possibility, that diverts resources away from real solutions,” he says. “It gives people hope that you can keep fossil fuel power plants alive. It delays action. In fact, carbon capture and direct air capture are always opportunity costs.” Economists talk about opportunity costs all the time. The principle is simple. If you are doing A, by definition you cannot be doing B. You cannot simultaneously go to work and lie on a beach in Tahiti, for instance.
Stanford vs. MIT
CleanTechnica reached out to Professor Jacobson to get his reaction to the latest MIT carbon capture news and he was gracious enough to respond almost immediately.
“This technology has the exact same problem as the direct air capture technology discussed in my paper in Energy & Environmental Sciences. It requires energy and it does not reduce air pollution or mining of fossil fuels. Thus, for example, renewable electricity powering it could otherwise always be used instead more efficiently to eliminate fossil fuel power plant emissions, thereby eliminating not only CO2 (which this technology is designed for), but also air pollution and mining while not having to pay for an air capture equipment cost.
“In other words, it causes more health and climate damage than renewables replacing fossil fuels, so is an opportunity cost. If natural gas or grid electricity is used to power this new equipment, the problem is even worse because then we have even more CO2 and air pollution combustion and upstream emissions and mining of fossil fuels than if renewables were powering it. The bottom line is there is no free lunch, and no synthetic air capture is useful for helping to solve the climate problem.
“By removing CO2 from the air, direct air capture does exactly what WWS (wind-water-solar) generators, such as wind turbines and solar panels, do. This is because WWS generators replace fossil generators, preventing CO2 from getting into the air in the first place. The impact on climate of removing one molecule of CO2 from the air is the same as the impact of preventing one molecule from getting into the air in the first place.
“The differences between WWS generators and direct air capture equipment, though, are that the WWS generators also (a) eliminate non-CO2 air pollutants from fossil fuel combustion; (b) eliminate the upstream mining, transport, and refining of fossil fuels and the corresponding emissions; (c) reduce the pipeline, refinery, gas station, tanker truck, oil tanker, and coal train infrastructure of fossil fuels; (d) reduce oil spills, oil fires, gas leaks, and gas explosions; (e) substantially reduce international conflicts over energy; and (f) reduce the large-scale blackout risk associated with centralized power plants by decentralizing/distributing power.”
In other words, by focusing on carbon capture, society overlooks many more sources of pollution that also impact the quality of life on Earth. The important work involves the transition to 100% renewable energy and eliminating the generation of electricity from thermal sources, including biomass. Think of Professor Jacobson’s view as being holistic while the MIT researchers have a more limited focus. In the end, the Jacobson approach is more realistic and more likely to provide positive results for our earthly community.
Related new report from CleanTechnica: Chevron’s Fig Leaf: A Case Study of Carbon Engineering’s Direct Air Capture Plan.