Decarbonisation Technology - February 2023

Life cycle analysis confirms the environmental benefits of CCM

CO lean ue gas

Oxygen

The environmental impact or benefit of a process can be confirmed using a technique known as life cycle analysis, or LCA. For the Airovation mineralisation process, the main input is the alkali feedstock, and the main output is the mineral. Also, CO2 emissions are avoided due to capture and mineralisation of the flue gas. If the mineral is subsequently used, for example when baking soda is used for baking bread and the CO2 is released into the dough, the full life cycle environmental benefit of the capture process is somewhat neutralised. On the other hand, the avoidance of CO2 emissions from alternative production processes to make the baking soda must be considered. In this respect, the Airovation process scores highly in the LCA. As an example, soda ash is a major ingredient in glassmaking. When it is combined with sand and melts during the glass-forming process, CO2 is liberated. However, using Na 2CO3 from the mineralisation of flue gas CO2 consumes no CO2 and CO2 emissions are avoided. On the other hand, the conventional Bayer synthetic Na2CO3 process liberates many kilograms of CO2 per tonne of soda ash produced – avoiding these emissions boosts the environmental benefit of the Airovation CCM process when valuable commercial products are generated. Natural soda ash is produced from Trona mineral ore in the US, Turkey, and from some African Trona deposits. Whilst this route to natural Na2CO3 is slightly less CO2 intensive than the Bayer process, the energy requirement to crush and refine the Trona ore is large and significant CO2 emissions result. These emissions are avoided in the LCA for the Airovation Technologies CCM process when valuable mineral products at marketable specifications are produced.

HO 2(aq)

NaOH or KOH

HO 2(aq)

NaOH or KOH

(aq)

CO rich ue gas

Pure CO

NaCO , KCO or other minerals (aq)

removal of CO and CO2 from flue gas streams with capture rates exceeding 95%. The carbon capture reaction consumes either NaOH or KOH as a strongly alkaline aqueous solution used as the contact medium through which the flue gas is passed. Hydrogen peroxide (H2O2) is consumed to generate the superoxide radicals that catalyse the carbonation reactions. Hydrogen peroxide is purchased as a standard high-strength solution in water and is dosed continuously to the process at a rate according to the mineralisation product requirement and the associated stoichiometry. The hydrogen peroxide is consumed rapidly in the reaction pathway, and residual concentration in the reactor is low. CO2 capture rates of 98% have been achieved using KOH and up to 100% using NaOH, and it compares favourably with conventional CO2 capture technologies, which tend to operate between 90 and 95% capture rates. Uniquely, in the CCM process, both CO2 and CO are removed from the flue gas, with capture efficiencies of more than 99% for both gases. CCM process parameters and economics The process flowsheet for the Airovation process involves two gas/liquid contactors. They are both extremely compact due to the rapid reaction kinetics and concentrated solutions used in the process. The feedstocks, NaOH (or KOH) and H2O2, flow counter-current to the flue gas through the two contactors to ensure high capture rates of CO2 within the compact process equipment (see Figure 7 ). Figure 6 Airovation mineralisation processes for CO2 capture and utilisation using alkalis and the superoxide radical

Chemistry behind the CCM process Airovation has innovated a proprietary

chemical oxidation process based on the in-situ generation of highly concentrated superoxide radicals in an aqueous environment (Stoin, Barnea, & Sasson, 2014). The superoxide radical is extremely reactive and rapidly catalyses the