The growing environmental concerns for global warming and climate change resulting from burning fossil fuels are reflected in the increasing number of works related to the development of more-efficient and improved processes for CO2 capture and storage. Switching completely to renewable energy technologies is of course highly desired but challenging and rob ably not realistic in western world. Fossil files are predicted to finish relatively soon. Coal is the fossil fuel that can sustainably last for another 200 years based on the current world reserves and rate of consumption. However, if we are still to use fossil fuels to satisfy our energy needs, we need to do it with careful carbon capture and storage facilities. Capturing CO2 is by far the most energy-expensive part of carbon capture and storage technologies. In this regard, physisorption of CO2 in porous solids using pressure, temperature or vacuum swing adsorption processes (PSA, TSA or VSA respectively) can decrease significantly the cost, as well as the environmental impact associated to the current used technologies involving amines.
A CO2 sorbent should satisfy the following requirements: (i) large CO2 uptake; (ii) high sorption rate; (iii) good selectivity between CO2 and other competing gases in the stream (i.e. N2); (iv) easy regeneration and (v) low-cost and high availability.
So far, numerous porous solids have been investigated, such as zeolites, metal-organic frameworks (MOFs), polymers, porous carbons including templated carbons, activated carbons and carbide-derived carbons (CDCs), or organic-inorganic hybrid materials. Among them, porous carbons stand out in terms of cost, stability, availability, large surface area, easy-to-design pore structure and low energy requirements for regeneration. More specifically, activated carbons continue being the primary choice for many adsorption-based processes based on the compromise between cost-availability and microstructure. In this regard, research on novel activation procedures which allow better controlled microstructure and pore size distribution is crucial for further development of many adsorption-based systems, such as hydrogen storage, supercapacitors or CO2 capture. However, not only the activation conditions influence the microstructure of the final material, but also the precursor used. For a large-scale sustainable production, naturally grown materials should be used as precursor. In this respect, biomass is highly attractive.
We are working on the synthesis, characterization and CO2 capture properties of algae-derived microporous carbons. Algae have very high photosynthesis efficiency and are considered a fast growing biomass, commonly doubling their biomass within a 24 h growth window which ensures quick availability of this precursor. An additional advantage of microalgae is that some species are rich in proteins and therefore have relatively high nitrogen contents, which may allow the synthesis of N-doped materials. N-containing surface functionalities grant basicity to carbon materials, which is expected to be favourable for the adsorption of acidic gases, such as CO2, SO2 or H2S.
More work on the topic includes synthesis of micro-mesoporus materials via hydrothermal carbonisation (HTC) and templating methods, such as soft templating, which offers an eco-friendly alternative to the classical activation methodology. In this way the carbon source is mixed with a soft template, such as block copolymer (Pluronic P123, F127 etc) and HTC for few hours at moderate temperatures. During the HTC the polymer forms micelles, providing a pattern for the carbon to grow on. Finally, the template is removed by pyrolysis leaving behind a porous carbon.
Some representative papers may be find below: