Strategy could turn CO2 emissions into useful chemicals

Capturing and using carbon emissions to make chemicals and plastics could help fight climate change, but there are a few caveats.

Harrison Tasoff-UC Santa Barbara • futurity
May 20, 2019 8 minSource

smoke stack (co2 emissions concept)

If the world can create enough renewable energy to make the effort worthwhile, there’s an opportunity to divert billions of tons of CO2 from smokestacks into the chemical supply chain, according to new research.

Chemical production emits staggering amounts of greenhouse gases via the energy it consumes and the carbon-based raw materials it uses. According to the findings, chemical production—which encompasses sectors as diverse as lubricants, paints, and plastics—accounts for over 3.3 billion metric tons of CO2 per year, or the equivalent in other greenhouse gases.

Sangwon Suh, a professor in University of California, Santa Barbara’s Bren School of Environmental Science & Management, recently released a comprehensive account of carbon emissions from plastics, in which he and his coauthor discovered that plastics alone account for the equivalent of 1.8 billion metric tons of CO2 emissions per year.

“On the one hand, this massive quantity of plastic and chemicals poses a problem,” says Suh, who researches industrial ecology, “because a huge amount of energy is needed in production and, once the products are used, a huge amount of waste will be generated.”

“On the other hand,” he continues, “this is an opportunity, because these raw materials are largely carbon-based. If we can use carbon dioxide as a carbon source for these plastics and chemicals, then we can capture and store a large quantity of CO2 in the plastics and chemicals that otherwise would have been emitted, all while creating value.”

Is it practical?

Applying carbon capture and utilization (CCU) to the chemical industry is a new idea. It would provide a renewable source of carbon compounds and has the additional benefit of pulling CO2 out of the atmosphere. CCU also produces a large quantity of pure water as a byproduct, a potential boon as water security becomes a greater issue. What’s more, putting captured carbon to use offsets some of the costs of capturing it in the first place, a major economic challenge to carbon sequestration efforts.

But the team wanted to know how practical it might be. This is new territory, so the researchers mostly had to work from scratch. They set about testing whether CCU provided a sizable opportunity to reduce greenhouse gas emissions, and found that it did. The technique could eliminate up to 3.5 billion metric tons of CO2, or the equivalent in other greenhouse gases per year.

However, this process would increase the industry’s total energy demands mainly because it also needs hydrogen, which can be produced from water through electrolysis. These demands would need to be met with renewable energy, otherwise the process would emit more carbon than simply sourcing material traditionally, via fossil fuel reserves.

The question then became: how much renewable electricity is needed to reach this 3.5 gigaton technical potential?

The answer: 126 to 222 percent of the world’s current 2030 renewable energy targets. And these targets already look very ambitious under current policies and trajectories.

“We were surprised at how much electricity is necessary in order to reduce greenhouse gas emissions through CCU,” Suh says. “Some people may think that those renewable energy generation numbers that we tested are unrealistic. Well, that’s the point.”

The threat of climate change

Many scientists became interested in CCU—as well as carbon capture and storage—as they grew more worried that various proposals and strategies for decreasing greenhouse gas emissions may come up short. LED lights and electric cars produce less greenhouse gases, but avoiding climate catastrophe requires more than just reducing emissions, Suh says.

“Scientists are starting to sense that these efforts will not be able to keep us to a 1.5 to 2 degrees Celsius global average temperature increase,” he says. These are the targets the United Nations set following the Intergovernmental Panel on Climate Change’s report in order to prevent climate disaster. Keeping within these targets requires reducing net emissions to zero by the second half of the century, says Suh, who served as a coordinating lead author on part of the panel’s 2014 report.

This leads to the concept of a carbon budget, namely a maximum total amount of greenhouse gases humans can emit and still keep warming below 2 degrees Celsius. Scientists have produced many estimates of this budget, but one of the most influential yields a figure of 763 billion metric tons of CO2, or the equivalent in other gases. Right now, we emit around 50 billion tons of CO2 per year, Suh says. That doesn’t allow much leeway to work with, or much time in which to solve the problem.

“We have to dramatically reduce our greenhouse gas emissions immediately,” Suh says.

However, he believes that holding too rosy a view of the potential of carbon capture is dangerous as well.

“Our study represents the first global assessment of the potential that CCU holds for carbon mitigation, and we found that it takes a lot for CCU to save the world,” Suh says. Humans can’t continue business as usual under the assumption that carbon capture to fix the problem even if we miss our targets.

“More than anything else, this study shows the enormous magnitude of renewable energy needed in order for CCU to make sense,” says Suh. He suspects those who read the study will balk at the requirements, saying that we cannot direct all that renewable electricity solely to CCU.

“I agree,” he says. “That’s the point.”

Weighing the benefits

If we did add the enormous amount of renewable electricity detailed in the study, it begs the question whether CCU is the best application of this additional power. So the team compared CCU with alternatives that may prove more efficient.

It turns out that CCU is not currently the most efficient use of renewable electricity for carbon mitigation. Investing this energy into heat pumps—rather than relying on natural gas for heating—would provide the biggest reduction in emissions per kilowatt-hour, followed by things like the electrification of transportation and water heaters. Only after we exhaust all these other, more efficient uses of renewable electricity would it then make sense to invest green energy into carbon capture and utilization.

However, if we generate extra capacity, CCU could prove a valuable tool in reducing greenhouse emissions, according to the scientists. The sheer tonnage of carbon-based compounds that flow through the chemical industry gives CCU the potential to have an outsized effect on curbing emissions.

“We didn’t find CCU as a savior of the global environment,” Suh says, “although it might have some local potential, where there is an excess supply of renewable electricity with no apparent uses.”

In that case, however, the bulky plastics and chemicals produced would need to be shipped to market, thereby generating more emissions. Instead, the excess electricity could go toward processing data, which is much more efficient to transmit around the globe, Suh says. He and his colleagues are now examining the role data centers and outsourced computing could have on reducing emissions by making the most efficient use of available energy sources.

The analysis appears in the Proceedings of the National Academy of Sciences.

Additional researchers from UC Santa Barbara and RWTH Aachen University in Germany contributed to the work.

Source: UC Santa Barbara

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