This discussion was supposed to be part of Green Patent Blog’s Best of 2007 post, a project that got lost amid holiday festivities.  So here it is now: 

While the important effort to reduce or eliminate greenhouse gas emissions continues, removing previously emitted greenhouse gases from the air may become necessary depending on how dire the climate change problem really is.  That’s what Columbia University physicist Klaus Lackner’s technology does.  Dr. Lackner is a named co-inventor on at least three patent applications and one issued patent relating to capturing and recovering carbon dioxide from the air. 

U.S. Application No. 2006/0051274 is directed to an apparatus for capturing CO2 called a laminar scrubber.  The laminar scrubber is a wind collector having a set of flat plates, or lamellae, arranged centimeters apart from each other.  Air is sucked through the plates by a natural pressure gradient, wind or convection.  A hydroxide based sorbent flows down the plates while a layered airflow passes through the thin spaces between the plates.  The contact between the air and the sorbent causes a chemical reaction which removes the carbon dioxide.  The patent application contemplates groups of laminar scrubber units combined in larger superstructures – what some of the press reports have called synthetic trees. (read articles here and here)

U.S. Application Pub. No. 2007/0187247 covers the next steps of the process, namely recovering the CO2-filled sorbent and separating the CO2 from the sorbent liquid.  The electrochemical methods of the application are more direct and energy efficient than prior art processes, which require transferring carbonate ions to calcium carbonate and then burning off the calcium.  Lackner’s process uses electrodialysis, in which the sorbent flows through cells having compartments separated by membranes.  At one end of the cell is a positively charged anode, at the other a negatively charged cathode.  The membranes also are charged to allow the passage of only positive ions or negative ions between compartments; a positively charged membrane traps positive ions while a negatively charged membrane traps negative ions.  Positive ions flow toward the cathode, negative ions flow toward the anode, and the ions are trapped in compartments along the way based on the type of membrane separating each compartment.  This structure separates the sorbent solution into hydroxide and CO2 by trapping and concentrating the negatively charged hydroxide ions in a compartment bounded by a negatively charged membrane.  The CO2 is released in a concentrated, pressurized stream, which can be sequestered or used for other purposes.