World Resource Review Vol. 16 No.2 CAPTURING CARBON DIOXIDE DIRECTLY FROM THE ATMOSPHERE

The increasing concern over rising CO2 levels in the atmosphere and their potential climate effects is fuelling research aimed at carbon management. One area of research focuses on capturing the CO2 after combustion and sequestering it underground. Capture schemes would operate at the site of generation taking advantage of the elevated concentrations of CO2 in the effluent. Here, however, we propose an indirect method of carbon capture that removes CO2 from the atmosphere. This process combines existing technologies with recent technological innovations into a novel carbon capture concept ermed air extraction. The process uses dissolved sodium hydroxide to remove the CO2 from ambient air. The resultant sodium carbonate solution is causticized using calcium hydroxide to regenerate the sodium hydroxide solution and precipitate calcite. The calcite is then thermally decomposed to produce lime and CO2. The lime is hydrated to complete the process. These latter stages are used routinely in the paper industry and the calcination of limestone is central to the cement industry. This paper reviews the process and highlights pertinent research to develop a likely cost-effective process. It is shown that the proposed process is well defmed and technically feasible. The wide parameter space and potential for improvements suggest hat further efficiency improvements are attainable. The most significant improvements will be derived from efficient heat management.