Capturing atmospheric CO2 using supported amine sorbents for microalgae cultivation

In this work, we propose, demonstrate and evaluate the concept of atmospheric CO2 capture for enhanced algae cultivation (and horticulture), as alternative to the application of flue gas derived CO2. A supported amine sorbent was prepared and able to capture CO2 at atmospheric conditions and releasing it at higher pressures and purity. Adsorption capacities were determined for CO2 concentrations from φ2COφCO2 = 0.0200% to φ2COφCO2 = 10% and temperatures up to 55 °C. Regeneration was done by thermal swing. At high temperatures (above 100 °C) high purity CO2 can be produced at elevated pressure. However, this is not required for algae cultivation and regeneration at lower purity (e.g. φ2COφCO2 = 2%) allows for lowering the regeneration temperature down to 70–80 °C, enabling the use of low grade heat. Under these conditions the sorbent is still able to realize cyclic capacities for CO2 of around 2 mol kg−1 sorbent. In cultivation experiments the effect of CO2 dosing on the growth rate of Desmodesmus sp. was investigated, showing an optimum at φ2COφCO2 = 1.5%. Experiments were carried out adsorbing CO2 from air, producing a CO2 enriched gas and use this in the cultivation of Desmodesmus sp., thereby successfully demonstrating the concept. Finally, the concept is compared with CO2 dosing using fossil fuel derived flue gas. Energy costs are comparable and additional benefits, as flexibility with respect to location and scale, avoiding impurities and, above all, closing the carbon cycle makes atmospheric CO2 capture a competitive, sustainable option for Algae Biorefineries.