Liquid to capture acid gases

A reusable organic liquid that can pull harmful gases such as carbon dioxide or sulphur dioxide out of industrial emissions from power plants has been developed by US researchers.

The process developed at the US Department of Energy's Pacific Northwest National Laboratory (PNNL) could directly replace current methods.

The technology, which can be retrofitted to power plants, could capture double the amount of harmful gases in a way that uses no water and less energy and saves money.

Harmful gases such as carbon dioxide or sulphur dioxide are called ‘acid gases’. The scrubbing process uses acid gas-binding organic liquids that contain no water and appear similar to oily compounds.

These liquids capture the acid gases at near room temperature. Scientists then heat the liquid to recover and dispose of the acid gases properly.

It is claimed these recyclable liquids require much less energy to heat but can hold two times more harmful gases by weight than the current leading liquid absorbent used in power plants. It is a combination of water and monoethanolamine - a basic organic molecule that grabs the carbon dioxide.

‘Current methods used to capture and release carbon dioxide emissions from power plants use a lot of energy because they pump and heat an excess of water during the process,’ said David Heldebrant, PNNL's lead research scientist for the project.

He added the monoethanolamine component is too corrosive to be used without the excess water.

In PNNL's process, called ‘Reversible Acid Gas Capture’, the molecules that grab onto the acid gases are already in liquid form and do not contain water. The acid gas-binding organic liquids require less heat than water does to release the captured gases.

Heldebrant and his colleagues demonstrated the process in previous work with a carbon-dioxide-binding organic liquid called CO₂BOL. In this process, scientists mix the CO₂BOL solution into a holding tank with emissions that contain carbon dioxide. The CO₂BOL chemically binds with the carbon dioxide to form a liquid salt solution.

In another tank, scientists reheat the salt solution to strip out the carbon dioxide. Non-hazardous gases such as nitrogen would not be captured and are released back into the atmosphere. The toxic compounds are captured separately for storage. At that point, the CO₂BOL solution is back in its original state and ready for reuse.

Heldebrant and his colleagues have also developed organic liquid systems that bind sulphur dioxide, carbonyl sulphide and carbon disulfide, which are acid gases that are also found in emissions.