Microalgae: Potential precursors of CO2 adsorbents

With faster growth rates and higher photosynthetic efficiencies than other terrestrial plants, microalgae biomass could be considered as a green, low-cost, alternative carbon source. This paper explores the potential use of various species of microalgae as activated carbon precursors. Chlorella and Spirulina were evaluated both as freeze-dried microalgae and in fresh paste form, while Acutodesmus Obliquus and Coelastrella sp. were studied only as paste. Activated carbons were produced using the selected species of microalgae as well as mixtures of pine sawdust and microalgae. Two different preparation routes were compared: with and without hydrothermal carbonization pretreatment before physical activation with CO2 in a single step. All samples were conformed into pellets prior to CO2 activation. The CO2 adsorption capacity of the microalgae derived carbons was assessed in conditions representative of a flue gas (10.5 vol.% CO2 at atmospheric pressure and 50 °C). Significant differences in terms of CO2 adsorption capacity, carbon yield and pellet density were obtained among the species studied. These preliminary results showed that activated carbons produced from microalgae mixed with pine sawdust and directly activated with CO2 are among the most promising adsorbents to capture CO2 from flue gas.