Method and system for capturing carbon dioxide from the air

A method for separating and recovering carbon dioxide from ambient air, comprising continuously performing the following steps:

• a) bringing ambient air into contact with a basic aqueous solution of at least one alkaline metal or alkaline earth metal cation to absorb the carbon dioxide into the solution to form the hydrogencarbonate or carbonate of the at least one metal;
• b) electrodialysis of the solution with absorbed carbon dioxide using a combination of bipolar and anion-selective ion exchange membranes to obtain one solution enriched in hydrogencarbonate and/or carbonate ions and one solution depleted thereof, each having a pH>7, the solution depleted in hydrogencarbonate and/or carbonate ions being recycled to step a);
• c) separating carbon dioxide from the solution enriched in hydrogencarbonate and/or carbonate ions to obtain a CO2-depleted solution which is recycled to step b);
• and
• (d) optionally drying and purifying the separated carbon dioxide;
• wherein:
• A) the absorption of step a) is performed
• Ai) in at least one absorber (01a);
• or
• Aii) in at least one open basin (01c);
• or
• Aiii) in a combination of at least one absorber (01a) and at least one open basin (01c);
• and/or
• B) separating the carbon dioxide from the solution enriched in hydrogencarbonate and/or carbonate ions in step c) is performed
• Bi) by thermal desorption of the carbon dioxide by steam stripping to obtain a carbon dioxide/steam mixture;
• and/or
• Bii) by chemical reaction of the hydrogencarbonate and/or carbonate ions, in which the CO2 contained is converted into a water-insoluble salt or gas and thereby removed from solution;
• and/or
• C) the pH of either solution obtained in step b) by means of electrodialysis is measured prior to recycling to step a) or prior to separating carbon dioxide in step c), respectively, and is in each case adjusted to a predetermined value;
• with the proviso that, if the absorption is not carried out according to Aiii) in a combination of at least one absorber (01a) and at least one basin (01c), but the separation of carbon dioxide is carried out according to Bi) by thermal desorption of the carbon dioxide by means of steam stripping, the pH is measured and adjusted according to C).