Porous CaO–MgO Nanostructures for CO₂ Capture

Abstract

Monolithic porous nanostructures of CaO−MgO composites were synthesized by a rapid self-sustained combustion reaction of molded pellets made of a mixture of nitrate salts of calcium and magnesium, urea, and starch. Urea is the fuel, and starch acts as a binder and a removable in situ template leading to porous monoliths. The synthesis is rapid, single-step, and solvent-free. In addition, the products retained a small quantity (1−2%) of carbon formed from starch. Porous monoliths were probed for high-temperature (650 °C) CO 2 capture at atmospheric pressure in a 20% CO 2 gas stream. While the pristine CaO porous nanostructure captured 76.8 mass % of CO 2 initially, it retained only a capture of 22 mass %, equivalent to 28% carbonation efficiency, after 100 carbonation−decarbonation cycles. The CaO−MgO porous nanostructures with varied amounts of MgO (10−40 mol %) exhibit CO 2 capture capacities of 67−51 mass % of the sorbent. CaO 80 −MgO 20 porous nanostructures captured 61.6 mass % of CO 2 and retained 84.6% (52.1 mass % of CO 2 ) of its initial capacity after 100 carbonation−decarbonation cycles. Thus, the hetero-oxide porous nanostructures exhibit enhanced cycle stability in addition to high CO 2 capture capacity, repressing the sintering-induced limitation of porous CaO. The high carbonation efficiency and cycling stability of the porous nanostructures as CO 2 sorbents are attributed to the synergistic combination of large surface area, a porous network, and an inert MgO stabilizer.

Calcium looping carbon capture: Progress and prospects

“…The optimum sorbent maintained an uptake capacity of 0.49 and 0.37 g/g after 50 cycles under mild (850 C under 100% N 2 ) and harsh (950 C under 100% CO 2 ) calcination conditions, respectively. In a more recent study, Rajamathi et al [171] produced CaO-based sorbents stabilized with MgO using an SCS method with urea as fuel and starch as binder. The optimum sorbent maintained an uptake capacity of 52 mass percent after 100 cycles under mild calcination conditions (700 C under 100% N 2 ).…”

“…Rajamathi et al [171] Chelating agent: citric acid or β-alanine Metal promoter: Zr Citric acid was more effective than β-alanine in producing sorbents with desirable surface properties. Sorbents maintained 0.58 and 0.27 g/g CO 2 uptake after 20 cycles under mild and harsh calcination, respectively.…”

“…In a more recent study, Rajamathi et al [ 171 ] produced CaO‐based sorbents stabilized with MgO using an SCS method with urea as fuel and starch as binder. The optimum sorbent maintained an uptake capacity of 52 mass percent after 100 cycles under mild calcination conditions (700°C under 100% N 2 ).…”

Construction of CO2 Absorption Protein Hydrogels Using MgO Nanoparticles as Cross-Linkers

“…CO 2 stemmed from fossil fuel usage has skyrocketed in recent decades, and thus, its atmospheric concentration has increased significantly, causing considerable environmental consequences, including global warming. , Recently, CO 2 capture, utilization, or storage (CCUS) technologies have received considerable attention in response to the worldwide desire to reduce CO 2 levels in the atmosphere . There is no doubt that CO 2 mineralization is one of the most effective processes for collecting and storing CO 2 from air and fuel gas streams. , CO 2 can be reacted with alkali minerals (MgO/CaO) to form solid carbonates (MgCO 3 /CaCO 3 ), achieving efficient and long-lasting CO 2 sequestration, but a high temperature (>200 °C) is usually required during this approach. , Therefore, it is of great importance to explore new ways by which absorption and conversion of CO 2 into its minerals are performed under mild conditions.…”

Directed Compartmentalization of Mg2+ and Carbonic Anhydrase by Designed Three-Dimensional Protein Crystalline Frameworks for Efficient Conversion of CO2 into Nanoparticles

“…However, solid sorbents based on alkaline-earth metal oxides such as MgO and CaO operating at high temperature (>200 °C) bring about substantial energy requirements to initiate the reactions involved due to ultrastability of CO 2 and always need a long process, organic solvents, and sophisticated equipment to prepare their corresponding colloidal nanoclusters. Although chemical catalysts may be used, poor process economics immensely limit carbon mineralization. − For large-scale carbonation to be a viable industrial process, solid carbonates must be made to occur rapidly and reliably. CO 2 exists in the form of reactive ionic CO 2 (HCO 3 – and CO 3 2– ), allowing for large-scale CO 2 capture and the generation of metal carbonates without additional energy requirements because the reaction occurs spontaneously but always is significantly hindered by relatively slow kinetics of CO 2 hydration. − Thus, enhancing the concentration of carbonate ions needed for generating solid carbonates in carbon mineralization seems to be an urgent issue to be solved at present.…”