Capturing atmospheric CO_2 using supported amine sorbents for microalgae cultivation

摘要

In this work, we propose, demonstrate and evaluate the concept of atmospheric CO_2 capture for enhanced algae cultivation (and horticulture), as alternative to the application of flue gas derived CO_2. A supported amine sorbent was prepared and able to capture CO_2 at atmospheric conditions and releasing it at higher pressures and purity. Adsorption capacities were determined for CO_2 concentrations from ΨCO_2 = 0.0200% to ΨCO_2 = 10% and temperatures up to 55 ℃. Regeneration was done by thermal swing. At high temperatures (above 100 ℃) high purity CO_2 can be produced at elevated pressure. However, this is not required for algae cultivation and regeneration at lower purity (e.g. ΨC0_2 = 2%) allows for lowering the regeneration temperature down to 70-80 ℃, enabling the use of low grade heat. Under these conditions the sorbent is still able to realize cyclic capacities for CO_2 of around 2 mol kg sorbent. In cultivation experiments the effect of CO_2 dosing on the growth rate of Desmodesmus sp. was investigated, showing an optimum at ΨCO_2 = 1.5%. Experiments were carried out adsorbing CO_2 from air, producing a CO_2 enriched gas and use this in the cultivation of Desmodesmus sp., thereby successfully demonstrating the concept. Finally, the concept is compared with CO_2 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 CO_2 capture a competitive, sustainable option for Algae Biorefineries.