Nanostructured MgO Sorbents Derived from Organometallic Magnesium Precursors for Post-combustion CO₂ Capture

Abstract

Nanostructured MgO sorbents show promise for intermediate-temperature CO2 capture from post-combustion flue gas stream. However, their CO2 capture behaviors can be affected by the magnesium precursors applied for sorbent synthesis. To screen potential precursors for fabricating excellent CO2 trappers, MgO nanoparticles (NPs) were synthesized by calcining several organometallic precursors, including magnesium ethoxide, magnesium acetate tetrahydrate, magnesium oxalate dehydrate, magnesium lactate dihydrate, magnesium citrate nonahydrate, and magnesium gluconate hydrate. The precursors and MgO NPs were characterized by thermogravimetric analysis, X-ray diffraction, N2 adsorption–desorption, field emission scanning electron microscopy, and CO2 temperature-programmed desorption. A fixed-bed reactor was used to evaluate the CO2 capture performances of the MgO NPs in a simulated flue gas stream. The effect of organometallic precursors on CO2 capture behaviors of the sorbents was further demonstrated. Results indicated that the different precursors would yield MgO NPs with distinct textural and surface properties, and these could further affect their CO2 capture behaviors. MgO NPs derived from magnesium oxalate dehydrate exhibited the highest CO2 uptake of 4.41 mmol of CO2/g. The excellent CO2 uptake was mainly attributed to its superlative textural properties, uniform surface morphology, and abundant base sites.

Assessment of the Effect of Process Conditions and Material Characteristics of Alkali Metal Salt Promoted MgO-Based Sorbents on Their CO2 Capture Performance

“…Extensive studies have been conducted to improve the CO 2 uptake capacity and stability of MgO-based sorbents, including optimization of the reaction temperatures, , the synthesis of highly porous MgO with specific surface areas >200 m 2 /g, − the incorporation of structural stabilizers, − and the doping with alkali metal salt (AMS). ,, The doping of MgO with AMS is considered the most effective approach; it is also relatively inexpensive and potentially suitable for large-scale production. A wide range of single AMS or a combination of various AMS (typically alkali nitrates and/or carbonates) has been used to modify MgO-based sorbents, with the main results of some selected studies summarized in Table .…”

Alkali Metal Nitrates Promoted MgO Composites with High CO2 Uptake for Thermochemical Energy Storage

“…Among various alkali/ alkaline metal-based materials, MgO shows the highest theoretical CO 2 storage capacity of 1.1 g CO 2 /g adsorbent. 31,32 Nonetheless, its practical CO 2 uptake and sorption rate could be limited due to the poor textural properties, limited basic sites, and intrinsically high lattice enthalpy. 33,34 One promising strategy to improve the CO 2 sorption capacity of MgO is doping alkaline metal nitrates/nitrites and their eutectic mixtures.…”

“…The backward carbonation allows the heat to be released and reused whenever needed (discharging). , As a result, the energy storage efficiency depends on the carbonation conversion. Among various alkali/alkaline metal-based materials, MgO shows the highest theoretical CO 2 storage capacity of 1.1 g CO 2 /g adsorbent. , Nonetheless, its practical CO 2 uptake and sorption rate could be limited due to the poor textural properties, limited basic sites, and intrinsically high lattice enthalpy. , …”

Hydrogen Direct Adsorptive Separation: Development Status and Trends

“…23 Nevertheless, the feasibility of ET-PSA is still being verified, and the adsorbents are under development, with the adsorption capacity, desorption kinetic performance, and working temperature range being in the process of improvement and optimization. 24,25 The composition of syngas is usually complex, including H 2 , CO 2 , CO, CH 4 , steam, and even N 2 and H 2 S. In both regular PSA and ET-PSA, different impurity gases are removed at several stages to obtain pure hydrogen. 26 PSA units usually contain more than four adsorption towers, because more adsorption towers mean higher separation efficiency.…”

“…Because the syngas is purified at an elevated temperature (150–450 °C), which is closer to the temperature of unpurified gases (usually above 200 °C) than that of regular PSA, heat exchange during the purification process is simpler and some gas heat can also be retained . Nevertheless, the feasibility of ET-PSA is still being verified, and the adsorbents are under development, with the adsorption capacity, desorption kinetic performance, and working temperature range being in the process of improvement and optimization. , …”