Carbon Capture and Storage

CCS helps mitigate climate change by capturing carbon dioxide () emissions before they can reach the atmosphere or by removing historical emissions from the atmosphere.

Global CCS Institute 2 page overview PDF

Carbon emission scope types

Scope 1 | Direct emissions

Direct emissions that are owned or controlled. e.g. burning fuel in a company vehicle.

Scope 2 | Indirect emissions

Indirect emissions that are a consequence of a company’s activities but occur from sources not owned or controlled by it. Scope 2 caused indirectly from where the energy it purchases and uses is produced. e.g. use of electricity purchase from the grid to power a company building.

Scope 3 | Indirect emissions

Indirect emissions that are a consequence of a company’s activities but occur from sources not owned or controlled by it. Scope 3 covers all emissions not covered by scope 1 or 2. e.g. when a company buys, uses and disposes of products from suppliers.

removal options

Methods of removal from most to least common.

Absorption

Chemical absorption of (or other target gas) from a mixed gas stream using amine solvents that selectively absorb the is most common.

Chemical solvents are an interaction at the molecular level to break bonds and form new bonds. Common amines are MEA¹ (Monoethanolamine), DEA² (Diethanolamine), a-MDEA (Methyldiethanolamine)³.

Physical solvents dissolve a solute through intermolecular interactions and do not chemically react. Common solvents are DEPG (Dimethyl Ether of Polyethylene Glycol), methanol, NMP (N-methyl-2-pyrrolidone) and PC.

Adsorption

Adsorption of using solid sorbents like zeolites ( adheres to the surface). It can be challenging for adsorbents to selectively capture over other gases like and .

Cryogenics

Utilising low temperatures to condense and extract .

Pre-cool the containing gas stream. Compress the pre-cooled gas stream to increase the partial pressure of to improve separation efficiency. Cryogenically cool the compressed gas stream using expansion or refrigeration. Separate the high-purity liquid (~95%) using distillation at cryogenic temperatures.

Quite an energy intensive process.

Membranes

separation using membranes that allow selective permeation by taking advantage of the relative transfer rates of different gases through the membrane barrier. These are simple with no hazardous chemical or steam use, though require significant compression or vacuum capacity as a driving force.

Biological

Use of microbes or enzymes to capture via biofixation (photosynthesis in plants and algae). These use enzymes like RuBisCO. Efficiency and scalability are a challenge.

Footnotes

1. MEA is a primary amine. It is the oldest solvent used in modern Gas Sweetening plants. Gas sweetening process using MEA is in the public domain. ↩

2. This amine is a secondary amine. The processing scheme of DEA is similar to MEA processing scheme with the exception of the reclaimer which is not required. ↩

3. MDEA is a tertiary amine. It is a newcomer to the group of ethanolamines used for natural gas sweetening and has received a great deal of attention recently because of its capability for selective reaction with in the presence of . ↩