From CO2 capture to the synthesis of useful chemicals: low energy consumption methods for carbon recycling

The reduction of anthropogenic CO2 emissions is an urgent challenge, and strategies must be adopted to improve the efficiency of CO2 capture and to reduce the costs of this technique. As an alternative to traditional processes, in our laboratory we developed a new concept of CO2 capture technology which combines the CO2 abatement with the production of useful compounds, in order to circumvent the energy costs of the conventional CO2 capture processes by virtue of the formation of valuable products. A process based on thermally stable and cheap absorbents that turns the captured CO2 into useful chemicals in mild conditions avoids the absorbent regeneration and the main drawbacks of the traditional capture techniques, and should be highly beneficial if the products obtained have an economic value and a commercial scale utilization. Here we present some of the processes we have devised with this unconventional approach: CO2 was efficiently captured from gas mixtures (CO2 15% v/v) using aqueous solutions of sodium carbonate, or ammonia, as sorbents. The solution containing the captured CO2 was not regenerated, but used directly to produce valuable substances of great commercial interest, such as urea or high-quality calcium carbonate, through processes with low energy impact and which involved the use of cheap industrial by-products (such as calcium chloride) or even the neutralization of environmentally hazardous wastes, such as the alkaline "red mud" coming from the aluminium production chain. Rather than treating CO2 as waste, with these procedures it can be regarded as a building block for the synthesis of other chemicals.