DIRECT CARBON CONVERSION

Direct carbon conversion is any chemical process that changes one form of carbon into another form with a concurrent production of energy, usu­ally as electricity. Fuel cells have been built on the principle of direct car­bon conversion into energy by generating a flow of electrons that convey an electrical current. Innovations in direct carbon conversion have now been proposed that would convert much larger amounts of atmospheric carbon into a usable form.

Fossil fuels, biomass, synthetic fuels, and biodiesel all work as fuels because they contain carbon compounds that release energy during com­bustion. Energy held within chemical bonds between carbon and other elements, usually hydrogen, serve as the energy-storage form in these
fuels. When considering all of the combustion engines in use today and the fact that all living things cannot exist without carbon compounds, it seems as if carbon chemistry truly powers the planet.

Reliance on carbon fuels has caused an accumulation of carbon- containing by-products in the atmosphere in the form of CO2 and meth­ane. Most people know that these greenhouse gases cause global warming by holding excess heat in the Earth’s atmosphere. Less understood is the time that the gases stay in the atmosphere. The Time magazine reporter Robert Kunzig warned in 2008, “Once we stop burning fossil fuels, it could take as long as 100,000 years for the CO2 we’ve been pouring into the atmosphere to be gone.” The Earth’s plants, water, and soil soak up a considerable quantity of carbon, but carbon emissions outpace carbon consumption. Photosynthetic organisms absorb CO2. Some of the carbon also settles in soil or in sediments under the ocean and begins a slow inex­orable return to fossil fuel. But Kunzig warned that scientists have found that the ocean and land do not soak up as much CO2 as they once did, perhaps because humanity’s carbon emissions have begun to overload the Earth’s natural carbon cycling.

Most atmospheric CO2 returns to the Earth by absorption into ocean phytoplankton, tiny plant organisms that serve as food for millions of other organisms. Phytoplankton levels have decreased in parts of the world’s oceans, due to pollution, climate change, and other factors in damaged ocean ecosystems. Some scientists have wondered if technology can find a way to restore the ocean’s absorptive ability or even increase it to control atmospheric carbon. The San Francisco company Climos has undertaken a plan to add nutrients to ocean waters to reinvigorate phytoplankton. In this method called iron-seeding, ships will pour iron-rich mixtures into the sea—about 20 pounds of iron per square mile (3.5 kg/km2). The chief science officer of Climos Margaret Leinen told Time, “We’re not think­ing of this as solving the problem. We’re looking at this as one of a whole portfolio of techniques.” This ambitious plan has yet to be proven as a way to reduce CO2 in the atmosphere, but climate experts have learned to wel­come any innovation to slow global warming.

Other scientists have investigated similar ideas for pulling carbon out of the atmosphere and converting it back into useful fuels. A Harvard graduate student Kurt House has developed a scheme for changing the ocean’s chemistry so that it can again absorb very large amounts of CO2. House’s plan involves the following steps:

1. Pump seawater into facilities that split the salt (sodium chloride) into positively charged sodium and negatively charged chloride molecules.

2. Remove the chloride, which would turn the water more basic.

3. Return acid-depleted water to the ocean.

4. The ocean acts to regain its acid-base balance by absorbing more CO2 from the air.

Allen Wright of Global Research Technologies in Arizona has pro­posed a third approach in carbon conversion. Wright and physicist Klaus Lackner of Columbia University have built scrubbers to remove CO2 directly from the air. Their prototype scrubbers each contain about 30 plastic sheets measuring about 9 feet (2.7 m) high. As air moves through the sheets in the scrubber, the CO2 sticks to the specially formulated plas­tic. The scientists envision much larger scrubbers and sheets distributed throughout the continents to remove carbon emissions from the atmo­sphere. Wright remarked in 2008 to the reporter Robert Kunzig, “If we built one [a scrubber] the size of the Great Wall of China, and removed 100 percent of the CO2 that went through it, it would capture half of all the emissions in the world.” Like House and the scientists at Climos, scrub­ber technology seeks to take on the problem of global warming on an extremely large scale.

The examples of carbon conversion described here have plausibility in laboratory experiments, but no one has implemented them on a grand scale to truly affect climate change. Changing the planet’s ocean chemis­try represents a monumental job, and the impact of adding large quanti­ties of iron or altered seawater on ecosystems is unknown. Some of the methods also produce large amounts of material that must be managed; House’s technique of turning seawater more basic results in large amounts of acid on land that require disposal. For the present, no one has proposed a good solution for managing the excess acid.

But what if these ideas work? Wright has suggested that the CO2 exit­ing his scrubbers can be combined with hydrogen to make a new batch of hydrocarbon fuels for cars. Though cars would release more emissions, the scrubbers would simply remove the emissions again and again to cre­ate a sustainable carbon loop.

image132,image133,image134

These methods may not come about in the near future, but they show that innovative thinkers have not been afraid to tackle the environment on a massive scale. Direct carbon conversion such as the scrubber-to-fuel concept might become one of the next-next-generation technologies in sustainability.

Leave a reply

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>