CO2 Capture with E. coli

Tyler Hamilton of Clean Break has an article in Technology Review about a Canadian company called CO2 Solution (CDNX: CST.V), who has developed a bioreactor for capturing CO2 from the exhaust from power plants and industrial facilities.

The bioreactor contains packing that has an enzyme, extracted from genetically engineered E. coli,  attached to it, that can absorb CO2 and convert it into bicarbonate, which is an environmentally safe product. Water flows counter current to the CO2 rich gas, the bicarbonate-rich solution is then removed.

The bicarbonate ions can be extracted for making everything from baking powder (sodium bicarbonate) to calcium carbonate (limestone) or the CO2 can be taken out of the solution and sequestered.

Quoting from Technology Review is this more detailed process description:

The bioreactor is a long cylinder containing a packing material that acts as a solid support for the enzyme. The surface of this material has been chemically modified so that the enzymes attach securely. At the top of the cylinder, a water solution is pumped in and flows around the packing material, while gases from a smokestack enter the bottom of the cylinder and bubble up through the solution. The carbon dioxide is absorbed into the solution and then interacts with the enzymes, which convert the greenhouse gas into bicarbonate ions. To end the process, cleaned up air escapes from the top while the bicarbonate solution is extracted [from the bottom] for further processing--either back into pure carbon dioxide for long-term geological storage or into a carbonate compound, such as limestone, that can be used by industry.

This process differs from other systems of capturing CO2 from smokestacks, the others capturing it by growing algae, which can be converted to biodiesel or dried and burned.

The process has already been tested on a small municipal incinerator and an Alcoa aluminum smelter. In small-scale tests at Alcoa the system removed 80% of the CO2. They are now working with Babcock and Wilcox (B & W) to adapt the technology to a coal-fired power plant. B & W believes that the technology is better than the algae systems because it takes less land.

Current work is aimed at improving the system efficiency, scaling up the reactor for use in power plants and producing the enzyme in large quantities

Comments

[Wayne Bond]

O.K. but! You don't have a usable product and the plants to produce a usable product will take more land. Bio fuels have a growing market and will continue to have a growing market. The economics are not mentioned. Pilot plant biodiesel is being produced for about $80 a barrel; close to being a cost effective product.

[Tony]

This is a new version of existing technology. The problem of removing carbon dioxide from calcium carbonate remains. Calcining (cooking the gas from) lime is very energy intensive. Certain amines are already better. Novel ionic solvents and carbon dioxide selective membranes may offer the only acceptably energy efficient solutions. The chief obstacle to cyrogenic separation from air is the dilution of carbon dioxide in air. In flue gas this problem is lessened but not eliminated.

[Tim]

The problem with this is that to turn one atom of carbon into calcium carbonate, it takes one calcium atom and 3 oxygen atoms. So sequestering 1 ton or coal requites 3.3 tons of calcium and creates 8.3 tons of calcium carbonate.

I think the US uses over 1 billion tons of coal per year. That requires 3.3 billion tons of calcium and creates 8.3 billion tons of calium arbonate, more than an order of magnatude more than the world consumption of calcium carbonate.

Also only large scale way to produce calcium (actually lime) creates more co2 than than the calcium is going to sequester.

[Casey C]

Doesn't it take energy to convert CO2 to bicarbonate? Where is the energy coming from? And how much energy is that? Is the bicarbonate going to be a solid? How long can you store bicarb outside before it goes back to CO2? Thank you.

[*_*]

To everyone discussing CaCO3 - this articles does *not* say that this process is making CaCO3. It only mentions that that could be the subsequent step. The technology only absorbs CO2 into aqueous phase (likely just uses a method of enhancing the equilibrium of that happening since it is a carbonate-deficient solution when it has been flowed out - I would be interested to know how they do this) and the enzyme converts it to an aqueous solution of bicarbonate (HCO3-) ions for use in subsequent processes such as reacting with Ca or Na or possibly other more useful things.

[Paul Dietz]

The technology only absorbs CO2 into aqueous phase (likely just uses a method of enhancing the equilibrium[...]

There are two issues here. The first is the equilibrium concentration of carbon in the solution. The enzyme can't change this (but it can be tailored by controlling the pH of the solution). The second is the rate at which CO2 is absorbed into or released from the solution when it isn't in equilibrium. The enzyme speeds this up dramatically.

Carbonic anhydrases drastically accelerate the reaction H2O + CO2 <--> H2CO3 <--> H+ + HCO3-, increasing the reaction rate up to six orders of magnitude. As I understand it, to get this reaction to go quickly without the enzyme requires a high pH (so the CO2 reacts with OH- ions).

[Dentist Los Angeles]

I have always though of E-coli negatively... guess this is one way to turn around it's reputation.