Air extraction: The feasibility of absorbing carbon dioxide directly from the atmosphere

The accumulation of anthropogenic carbon dioxide in the atmosphere may destabilize the global climate. Many strategies exist to capture carbon dioxide prior to emission and store it in a reservoir separate from the atmosphere. These methods encompass about half of the total emissions. The remainder, mainly from small and distributed sources, remains unabated. We propose a novel chemical process that removes carbon dioxide directly from the atmosphere through a wet scrubbing process. Using alkali earth metals, the carbon dioxide is dissolved into solution then precipitated out as a carbonate. The carbon dioxide is regenerated by thermal decomposition or calcination of the carbonate. The process consists of existing industrial processes combined and modified to improve energy efficiency.; The carbon dioxide is removed through absorption into a sodium hydroxide solution. This produces a mixture of sodium hydroxide and sodium carbonate, concomitant with some evaporation. The resultant solution is transferred to a causticization vessel where it is mixed with calcium hydroxide. This step, a part of the paper making process, transfers carbon dioxide from sodium to calcium canons. The solid product, calcium carbonate, precipitates out of solution. The solids are then filtered and dried to produce a powder with particles in the 1-5 micrometer range. These are heated to 900 degrees Celsius whence they decompose into lime and gaseous carbon dioxide. The carbon dioxide is then compressed and sent to storage.; The energy requirements for the process are dominated by the calcination reaction. Calcination consumes up to two thirds of the total energy. This fraction increases if a natural draft, rather than forced air, is used to contact the air with the sorbent. In industrial practice, calcination reaction has reached 90% efficiency. Additional energy is required for materials handling, oxygen production and carbon dioxide compression. The process of air extraction could benefit from a re-design of the industrial technologies to suit carbon dioxide capture. A cost analysis of the process estimates the price at 60-110 {dollar}/tonne of carbon dioxide or {dollar}0.60 to {dollar}1.12 per gallon of gasoline.