NEW AIR CAPTURE TECHNIQUE COULD OFFSET OCEAN ACIDIFICATION

Tamar Hallerman
GHG Monitor
5/31/13

Researchers at Lawrence Livermore National Laboratory say they have developed a process to directly capture CO2 from the atmosphere that could also have the added side benefits of producing hydrogen and offsetting ocean acidification. In a paper published in this week’s edition of the journal Proceedings of the National Academy of Sciences, scientists at the California lab said they have demonstrated the new technique, which uses the acidity typically produced during saline water electrolysis to “accelerate silicate mineral dissolution,” at lab scale. The process involves running a current through salt water to separate out its hydrogen and oxygen while also creating an alkaline electrolyte solution that contains elevated levels of hydroxide, which is highly absorptive of atmospheric CO2, according to the paper.

The technique produces carbonates and bicarbonates from the separated CO2 that can subsequently be utilized for mitigating ocean acidification, according to the paper, in a way “similar to how an Alka Seltzer neutralizes excess acid in the stomach.” The study cautions that while more research is needed, the alkalinity of the carbonates and bicarbonates could help neutralize the excess acid being absorbed by the world’s oceans due to heightened carbon dioxide in the atmosphere. The technique also can also produce hydrogen, which can be used for fuel or as a chemical feedstock for industrial purposes. The paper argues that the generation process could also become carbon-negative if fueled by renewables. “Using non-grid or non-peak renewable electricity, optimized systems at large scale might allow relatively high-capacity, energy-efficient, and inexpensive removal of excess air CO2 with production of carbon-negative [hydrogen]. Furthermore, when added to the ocean, the produced hydroxide and/or (bi)carbonate could be useful in reducing sea-to-air CO2 emissions and in neutralizing or offsetting the effects of ongoing ocean acidification,” according to the study.

Process Doesn’t Require CO2 Concentration Prior to Capture

In an interview this week, head author Greg Rau, a visiting scientist at Lawrence Livermore and professor at the University of California-Santa Cruz, said the technique can be more efficient than other types of capture because it does not require CO2 to be concentrated from air and stored in a molecular form in order to work. “The difference between CCS and our process is that we’re not making concentrated, molecular CO2. We don’t have to go through that expensive process,” he said. “We’re storing the carbon as carbonates or bicarbonates, and as a side benefit we’re generating hydrogen as a fuel or chemical feedstock.” The paper concludes that the approach is more energy-efficient and less environmentally risky than other forms of direct air capture because it avoids the “energy inefficient base/sorbent regeneration and production of highly concentrated molecular CO2 and the need to guarantee long term sequestration of the latter volatile compound (gaseous or supercritical CO2).” He emphasized that more research must be conducted in order to determine more optimum designs and procedures.

Rau estimated that the price of separating and storing CO2 using the process could be competitive with typical CCS techniques, at about $100 per tonne of CO2. He said the cost savings come from the fact that the silicate materials used in the process are naturally abundant and relatively inexpensive and that the process does not require recycling or regenerating materials like amines, which can quickly bump up the cost of capture. “Our chemistry involves using hydroxide as the capture medium rather than amines. We also don’t regenerate CO2 in a concentrated form—we keep it as a bicarbonate or carbonate in solution and we dispose of it, or store it, as a carbonate or bicarbonate rather than involving extra energy [and cost] to regenerate the more concentrated CO2 and then having to store it safely,” Rau said.

Direct Air Capture Still Prohibitively Expensive

Rau said he hopes his team’s technique, with more research, could bring the direct capture of CO2 from the atmosphere (DAC) more within reach as a climate change mitigation tool. The field in recent years has seen a combination of political hype and sharp dissent. But DAC developers have defended their technologies, arguing that they can be cost competitive in the future, comparing such technologies to where solar and wind were decades ago, and have lobbied for continued funding.

Some politicians in recent years have looked toward the developing DAC technology—despite it being far from commercialization—as a potential last-ditch effort to halt climate change, particularly useful for emissions from small point sources like buildings and automobiles that are too expensive to capture as opposed to something like a power plant. In 2009, then-Energy Secretary Steven Chu and White House Science Advisor John Holdren both mentioned the technology as a potential mitigation method. Congress has also expressed some interest in the technology in recent years. The Senate Energy and Natural Resources Committee passed a bipartisan bill in 2011, the “Carbon Dioxide Capture Technology Prize Act,” that would have offered $10 million worth of inducement prizes to the first researchers to successfully develop bench- and demonstration-scale DAC technologies. But after clearing the energy panel, the bill was never considered by the full Senate and has not been reintroduced to date in the current 113th Congress.

Some Say DAC Technologies Could Prevent Climate Change Action

But critics of DAC technologies have been far and wide. Some have argued that such technologies—most of which are still at the small-scale and utilize the absorption or adsorption of a sorbent on collector surfaces—could enable governments to further punt action on climate change in the near term if DAC exists as a back-stop action. Others have argued that it should not be utilized until all other methods of emissions reduction and mitigation are exhausted. Meanwhile, a string of government studies have concluded that while DAC is technically feasible, the cost of such systems are likely prohibitively high and will likely play little to no role in carbon mitigation efforts in the coming decades.

A Massachusetts Institute of Technology study published in December 2011 in the journal Proceedings of the National Academy of Sciences concluded that the cost of DAC technology is often five to 10 times higher than current estimates outline, somewhere in the neighborhood of $1,000 per tonne, and that unless the systems are powered entirely by zero-emissions sources of power like solar or wind, the technology is not worth pursuing at this point barring a major technological breakthrough in the field. A May 2011 report from the American Physical Society estimated costs to be about $600 per tonne of CO2 captured. A Government Accountability Office report also from 2011 concluded that DAC is at best decades away from large-scale commercialization and that it is currently not a viable response to climate change.