The carbon dioxide required for CCU technologies can be extracted from various sources, each of which incur different environmental impacts and costs. In some chemical processes, for example, fermentation or ammonia production, extremely pure CO2 is created as a by-product. Commercially available recovery technologies can be used to isolate this carbon dioxide and render it suitable for use in a highly pure form. Carbon dioxide can also be filtered from flue gases at power plants or other industrial point sources using carbon capture technologies and then made available for further use or storage.
The choice of technology for the capture of CO2 is determined to a large degree by the concentration of carbon dioxide at a given source. As a rule, the technical challenges arising in the extraction of carbon dioxide from a given source are relative to its concentration in the available gas mixture. To put it in a nutshell: the higher the concentration, the easier it is. There are numerous potential industrial sources of carbon dioxide, ranging from smaller industrial smoke stacks to large power plants. Using existing methods, these sources could already provide large quantities of carbon dioxide in different purity grades. However, low demand and the high cost of capturing carbon dioxide have slowed the uptake of these technologies to date.
The atmosphere is another available source of carbon dioxide. One method that is not yet commercially feasible attempts to filter previously emitted carbon dioxide from the atmosphere using chemical engineering. Such Direct Air Capture processes are energy intensive and accordingly costly. Nevertheless, they are already being tested at pilot plant scale by several firms, including Climeworks Engineering in Switzerland and Carbon Engineering in Canada. However, significant advances in relevant technologies, including new materials that can be used as absorbers (see carbon capture technologies), will be required before technologies of this kind become economically viable at scale. Even then, these technologies will always be at a disadvantage to higher concentrated CO2 point sources. In order to minimise their carbon footprint, direct capture facilities would need to utilise renewable sources of energy.
In the case of both direct air capture technologies and carbon capture from industrial sources, the technologies could have undesirable and as yet poorly understood environmental impacts depending on the materials used.
IASS, Mario Mensch