Silanol-rich platelet silica modified with branched amine for efficient CO2 capture

Utilizing silica fume and synthetically produced mesoporous silicas for simulated flue gas CO2 adsorption

Carbon capture and storage (CCS) is crucial in mitigating greenhouse gas emissions. Solid adsorbents, notable for their reusability and corrosion resistance, are gaining attention in CO2 gas separation. This study uses Silica fume as an adsorbent and silica source for SiO2 and MCM-41 silica-based adsorbents. Silica was extracted via an alkaline dissolution method, and adsorbents were synthesized using a CO2-induced precipitation method, chosen for its shorter synthesis time and CO2 utilization. The effects of pore volume, average pore diameter, and specific surface area on amine loading and CO2 adsorption capacity were investigated using CTAB surfactant in SiO2 synthesis, resulting in MCM-41. The synthesized adsorbents were modified with TEPA and DEA amines due to their high affinity for CO2. After determining optimal amine loading, the impact of combining TEPA with DEA was examined. The highest CO2 adsorption capacity under simulated flue gas conditions (15% volume CO2 and 85% volume N2) was 198 milligrams per gram of adsorbent for the SiO2 adsorbent functionalized with 50% by weight amine (28% TEPA and 22% DEA). Variations in CO2 adsorption over time, the influence of adsorbent quantity on adsorption capacity, the affinity of the adsorbent for N2 adsorption, and the adsorption-desorption cycle were investigated. The 28%TEPA-22%DEA-SiO2 adsorbent emerged as the optimal choice due to its large total volume and average pore diameter, absence of a template in its structure, excellent performance in CO2 adsorption, lack of affinity for N2, and robust adsorption-desorption stability.

Synthesis and CO2 Capture of Porous Hydrogel Particles Consisting of Hyperbranched Poly(amidoamine)s

We successfully synthesized new macroporous hydrogel particles consisting of hyperbranched poly(amidoamine)s (HPAMAM) using the Oil-in-Water-in-Oil (O/W/O) suspension polymerization method at both the 50 mL flask scale and the 5 L reactor scale. The pore sizes and particle sizes were easily tuned by controlling the agitation speeds during the polymerization reaction. Since O/W/O suspension polymerization gives porous architecture to the microparticles, synthesized hydrogel particles having abundant amine groups inside polymers exhibited a high CO2 absorption capacity (104 mg/g) and a fast absorption rate in a packed-column test.

B-Doped 2D-InSe as a bifunctional catalyst for CO2/CH4 separation under the regulation of an external electric field

The separation of CO₂ or CH₄ from a CO₂/CH₄ mixture has drawn great attention in relation to solving air pollution and energy shortage issues. However, research into using bifunctional catalysts to separate CO₂ and CH₄ under different conditions is absent. We have herein designed a novel B-doped two-dimensional InSe (B@2DInSe) catalyst, which can chemically adsorb CO₂ with covalent bonds. B@2DInSe can separate CO₂ and CH₄ in different electric fields, which originates from different regulation mechanisms by an electric field (EF) on the electric properties. The hybridization states between CO₂ and B@2DInSe near the Fermi level have experienced gradual localization and eventually merged into a single narrow peak under an increased EF. As the EF further increased, the merged peak shifted towards higher energy states around the Fermi level. In contrast, the EF mainly alters the degree of hybridization between CH₄ and B@2DInSe at states far below the Fermi level, which is different from the CO₂ situation. These characteristics can also lead to perfect linear relationships between the adsorption energies of CO₂/CH₄ and the electric field, which may be beneficial for the prediction of the required EF without large volumes of calculations. Our results have not only provided novel clues for catalyst design, but they have also provided deep understanding into the mechanisms of bifunctional catalysts.

The assembly of silica species with alkylamines: Mechanism of wastewater-free synthesis and the application of gel as a catalyst

Silica species generated by the hydrolysis and condensation of tetraethyl orthosilicate (TEOS) could assemble with alkylamines to form silica gel. Herein, it was evidenced that part of the added amines, including butylamine (BA), octylamine (OA) or dodecylamine (DA), was protonated in the mixture of water and ethanol. Therefore, besides the hydrogen bonding between neutral silica species and the micelles composed of the non-protonated amines (Tanev and Pinnavaia, 1995), there existed strong electrostatic attraction between negatively charged silica species and the micelles composed of the protonated amines. This coexisting assembly mechanism could explain why the uncalcined BA- and OA-gels were millimeter-sized small blocks with large porosities and synthesized without waste water emission, while the uncalcined DA-gel was almost non-porous and formed via precipitation from its reaction medium. The uncalcined BA gel was proved to be efficient as a solid basic catalyst, replacing the commonly used ammonia solution which is easily volatilized and has a pungent smell, for the hydrolysis and condensation of TEOS to prepare silica microspheres.

Enhancement of CO2 Adsorption/Desorption Properties of Solid Sorbents Using Tetraethylenepentamine/Diethanolamine Blends

Mesocellular silica foam was impregnated with tetraethylenepentamine (TEPA), diethanolamine (DEA), and their mixtures and examined as sorbents for CO₂ capture. The sorbents were characterized by N₂ physisorption, elemental analysis, and Fourier transform infrared spectroscopy. The effects of amine blending on the CO₂ uptake, working capacity, and heat of adsorption were investigated and discussed. The experimental results showed that the heat of adsorption decreased with increasing DEA-to-TEPA ratios, but the CO₂ uptake improved by the blending of TEPA and DEA. Furthermore, the DEA/TEPA blend considerably improved the regeneration properties of the sorbents. Mesocellular silica foam loaded with a mixture of 40 wt % TEPA and 30 wt % DEA exhibited a CO₂ adsorption uptake of 5.91 mmol/g at 50 °C and 100 kPa with a heat of adsorption of 80 kJ/mol. Additionally, these sorbents demonstrated high cyclic stability and high selectivity toward CO₂/N₂ separation. In situ infrared spectroscopy investigations revealed that CO₂ adsorption occurred predominantly through the formation of carbamate species for both TEPA and DEA.

Enhancement of CO2 adsorption on biochar sorbent modified by metal incorporation

This work is scrutinizing the development of metallized biochar as a low-cost bio-sorbent for low temperature CO₂ capture with high adsorption capacity. Accordingly, single-step pyrolysis process was carried out in order to synthesize biochar from rambutan peel (RP) at different temperatures. The biochar product was then subjected to wet impregnation with several magnesium salts including magnesium nitrate, magnesium sulphate, magnesium chloride and magnesium acetate which then subsequently heat-treated with N₂. The impregnation of magnesium into the biochar structure improved the CO₂ capture performance in the sequence of magnesium nitrate > magnesium sulphate > magnesium chloride > magnesium acetate. There is an enhancement in CO₂ adsorption capacity of metallized biochar (76.80 mg g^-1) compare with pristine biochar (68.74 mg g^-1). It can be justified by the synergetic influences of physicochemical characteristics. Gas selectivity study verified the high affinity of biochar for CO₂ capture compared with other gases such as air, methane, and nitrogen. This investigation also revealed a stable performance of the metallized biochar in 25 cycles of CO₂ adsorption and desorption. Avrami kinetic model accurately predicted the dynamic CO₂ adsorption performance for pristine and metallized biochar.

Recovery of nickel ions from wastewater by precipitation approach using silica xerogel

A facile route was developed to recover nickel ions from a synthetic wastewater. It involved the use of silica xerogel containing amine in the nickel sulphate solution resulting in the formation of a greenish precipitate. It was found that this precipitate was mostly amorphous Ni(OH)₂ spherical aggregate composed of nanosheets. The pH level of the solution was monitored, and it was maintained in the range of 10-10.5 due to the steady release of amine from the xerogel into the waste solution. The prepared silica xerogel would provide a stable environment for the chemical precipitation of metal ions in wastewater during the whole precipitation process. The silica xerogel was collected and reused for two more cycles of recovery. The nickel removal efficiencies (99.34˜99.65%) kept unchanged and higher than those reported earlier. The collected precipitate that contained nickel hydroxide with some residual silica could be utilized as glass colorant.

The dynamic CO2 adsorption of polyethylene polyamine-loaded MCM-41 before and after methoxypolyethylene glycol codispersion

To reduce the cost of CO₂ capture, polyethylene polyamine (PEPA), with a high amino density and relatively low price, was loaded into MCM-41 to prepare solid sorbents for CO₂ capture from flue gases. In addition, methoxypolyethylene glycol (MPEG) was codispersed and coimpregnated with PEPA to prepare composite sorbents. The pore structures, surface functional groups, adsorption and regeneration properties for the sorbents were measured and characterized. When CO₂ concentration is 15%, for 30, 40 and 50 wt% PEPA-loaded MCM-41, the equilibrium adsorption capacities were respectively determined to be 1.15, 1.47 and 1.66 mmol g⁻¹ at 60 °C; for 30 wt% PEPA and 20 wt% MPEG, 40 wt% PEPA and 10 wt% MPEG, and 50 wt% PEPA and 5 wt% MPEG codispersed MCM-41, the equilibrium adsorption capacities were respectively determined to be 1.97, 2.22 and 2.25 mmol g⁻¹ at 60 °C; the breakthrough and equilibrium adsorption capacities for 50 wt% PEPA and 5 wt% MPEG codispersed MCM-41 respectively reached 2.01 and 2.39 mmol g⁻¹ at 50 °C, all values showed a significant increase compared to PEPA-modified MCM-41. After 10 regenerations, the equilibrium adsorption capacity for codispersed MCM-41 was reduced by 5.0%, with the regeneration performance being better than that of PEPA-loaded MCM-41, which was reduced by 7.8%. The CO₂-TPD results indicated that the mutual interactions between PEPA and MPEG might change basic sites in MCM-41, thereby facilitating active site exposure and CO₂ adsorption.

To reduce the cost of CO₂ capture, polyethylene polyamine (PEPA), with a high amino density and relatively low price, was loaded into MCM-41 to prepare solid sorbents for CO₂ capture from flue gases.