1Research background
By 2050, 700 GtCO2 needs to be reduced and to meet the International Energy Agency’s 2°C scenario (IEA 2DS), which aims to reduce anthropogenic CO2 emissions and achieve a net-zero society. Carbon capture and storage (CCS) is a sound climate action, while carbon capture and utilization (CCU) is an attractive pathway to reduce costs associated with emissions reductions and encourage new industrial investment. For example, CO2 is captured from the atmosphere by direct air capture (DAC), which involves the physical or chemical absorption of CO2 by alkaline solutions based on sodium hydroxide or ammonia. Although simple, it has limited absorptive capacity, is water intensive, and has limited success rates. On the other hand, the weathering of rocks and soils associated with agricultural fields rich in carbonates, silicates and magnesia represents a sustainable agricultural strategy. However, large amounts of land resources are required. Alternative technologies, relying on the high selectivity and catalytic activity of metal oxides or activated carbon, display high CO2 specific absorption capacity per available surface area. With network chemistry, such as using MOFs, the highest retention rate reported was 1.47 gCO2 g-1. Although some progress has been made in natural gas upgrading and wet flue gas CO2 capture, high cost, high energy consumption, and poor scalability limit the applicability of MOFs on an industrial scale.
Simple methods, such as direct carbon dioxide mineralization, are highly efficient and easy to scale. Additionally, industrial alkaline and solids streams are cost-effective and maximize carbon economies. In particular, alkaline industrial streams from the cement and paper industries are more attractive for direct mineralization capture of CO2, converting to 2100 and 187 Mt CO2 yr-1 respectively (~6.8% reduction in total global anthropogenic CO2 emissions). This is profitable for the cement industry (considering only CO2 mineralization, €32 per ton). In addition, considering the multiple synergies between cement materials and cellulose fibers in the pulp and paper industry, it is reasonable to expect new opportunities for building materials to achieve better CO2 emission reduction effects. We note that pathways involving additional chemicals may reduce CO2 emissions but have limited removal potential. In contrast, building materials can both utilize and remove CO2. cellulose mineralization provides unprecedented opportunities for CO2 removal and storage.
Cellulose is a biopolymer obtained from plant and biomass residues and has been reported for use in advanced materials and energy-efficient buildings . Importantly, using mineralized cellulose as a building matrix may add new functions and properties to materials such as cement, ceramic materials and even coral reefs, which are the subject of current research.
2 Research results
Current carbon capture and utilization (CCU) technologies require high energy input and expensive catalysts. In view of this, Guillermo Reyes and Orlando J. Rojas of Aalto University in Finland collaborated to report an industrially relevant direct air capture strategy using highly active alkali cellulose solutions as CO2 absorption media. Mineralized cellulose material (MCM) is formed by adjusting the ratio of cellulose to minerals, forming an organic-inorganic viscous system (viscosity 102-107 mPa s, storage modulus 10-105 Pa) . CO2 is absorbed and converted into calcium carbonate and related minerals, with a maximum absorption of 6.5 gCO2 gcellulose-1, which is inversely proportional to the cellulose loading.
Cellulose thin gel is easily converted into a dry powder and is a functional ingredient in ceramic glazes and cement-based composites. At the same time, the cellulose-rich gel is moldable and squeezable, creating stone-like structures that can serve as artificial substrates for coral reef restoration. Life Cycle Assessment (LCA) offers new CCU opportunities for construction materials, as shown in underwater deployments for coral reef ecosystem restoration.
Relevant research work was published in the top international journal "Advanced Materials" under the title "Direct CO2 capture by alkali-dissolved cellulose and sequestration in building materials and artificial reef structures".
3 Graphic Express
In this study, CO2 gas was used to produce MCM under controlled atmosphere, alkaline conditions. After dissolution, the mineralization process is carried out at room temperature with continuous stirring until the CO2 solution absorption capacity (saturation or constant weight) is reached. The study found that the CO2 absorption capacity is inversely proportional to the cellulose concentration, reaching a maximum value of 6.5 gCO2 gcellulose-1 (61 mgCO2 gsolution-1) at 1 wt%. This dilute cellulose MCM precursor (MCMl) produces a solid powder that can be used as a flux material for ceramic glaze , improving glaze viscosity and reducing glaze cracking.
used the same formula in a cement slurry, showing workability and a dense microstructure, indicating great promise in building materials. By increasing the cellulose loading (7 wt% cellulose), a moldable/printable paste (high cellulose content MCMh) was prepared, which solidified into a tough stone-like material, reaching a maximum compressive strength of 31MPa at 30% strain. The material is being used as a replacement for Gulf of Mexico coral stone, allowing the implantation of three coral species that will grow healthily for at least nine months.
LCA analysis shows that MCM has a global warming potential (GWP) of -0.74 gCO2eq g-1. The results show that further GWP is between 0.9 and 7.2gCO2eq g-1, including the cellulose dissolution process (upstream stage), representing a reduction of up to 62% in the environmental impact produced during the dissolution stage. In conclusion, the use of MCM as a building material brings new opportunities for residual alkaline flow, expanding the prospects of cellulose to reduce CO2 emissions and achieve marine coral reef ecosystem restoration.
Figure 1. Mineralized materials with low cellulose content (MCMl) and high cellulose content (MCMh) and their structural characteristics
Figure 2. Crystal structures and compositions of MCM samples
Figure 3. Applications of MCM in ceramic glazes and grouts
Figure 4. MCM application for coral stone (CS) production and testing
Figure 5. Boundary and Life Cycle Impact Assessment (LCA) of MCM Production (S0/S7)
4 Conclusion and Outlook
Mineralized cellulose materials (MCM) are a platform for the development of structures with a variety of mechanical properties and applications. The LCA results show that global warming effects caused by the cement industry are expected to be addressed through MCM production. Furthermore, low cellulose materials show suitable properties as additives in ceramic and cement formulations. At the same time, the high cellulose content allowed the production of moldable and printable artificial coral stones that housed three species of coral within 7 months. Currently, ongoing research aims to produce ceramic/cement/MCM hybrid materials that synergize the properties of the different components, such as proper control of ions (essential during coral growth) and extend the life of the material in the marine environment.
Literature link:
https://doi.org/10.1002/adma.202209327
