CO2Capture and Ca2+Exchange Using Zeolite A and 13X Prepared from Power Plant Fly Ash

Effect of Water on CO2 Adsorption on CaNaY Zeolite: Formation of Ca2+(H2O)(CO2), Ca2+(H2O)(CO2)2 and Ca2+(H2O)2(CO2) Complexes

Efficient CO2 capture materials must possess a high adsorption capacity, suitable CO2 adsorption enthalpy and resistance to water vapor. We have recently reported that Ca2+ cations exchanged in FAU zeolite can attach up to three CO2 molecules. Here we report the effect of water on the adsorption of CO2. Formation of Ca2+(H2O)(CO2), Ca2+(H2O)(CO2)2 and Ca2+(H2O)2(CO2) mixed ligand complexes were established. The Ca2+(H2O)(CO2) species are readily formed even at ambient temperature and are characterized by ν(12CO2) and ν(13CO2) infrared bands at 2358 and 2293 cm-1, respectively. The Ca2+(H2O)(CO2)2 species are produced at low temperature and are identified by a ν(13CO2) band at 2291 cm-1. In the presence of large amounts of water, Ca2+(H2O)2(CO2) complexes were also evidenced by ν(12CO2) and ν(13CO2) bands at 2348 and 2283 cm-1, respectively. The results demonstrate that, although it has a negative effect on CO2 adsorption uptake, water in moderate amounts does not block CO2 adsorption sites.

A green and multi-win strategy for coal fly ash disposal by CO2 fixation and mesoporous silica synthesis

Coal combustion provides plenty of energy, along with enormous coal fly ash (CFA) and CO₂ emission. CFA could be recycled for mesoporous silica synthesis, but expensive templates are usually needed. In this work, we proposed a multi-win strategy using CO₂ as the precipitator and template. Mesoporous silica powders, with a maximum specific surface area of 355.45 m²/g, a pore volume of 0.73 cm³/g, and an average pore size of around 7.67 nm, were synthesized. The influences of silicon concentration, CO₂ flow rate, and ultrasound were investigated. In addition, the Na₂CO₃ by-product was produced with a purity of over 92 %. By averagely calculating, 1 ton CFA could generate 285 kg mesoporous silica and 1.02 t crude Na₂CO₃. Around 433 kg of CO₂ could be absorbed. Therefore, multi-goals of CFA disposal, CO₂ storage, and valuable silica materials production were realized, and the study could pave the way for large-scale industrial applications.

Process optimization for enhanced carbon capture and cyclic stability using adsorbents derived from coal fly ash

Zeolites and metal-organic frameworks (MOFs) are popular adsorbents when it comes to capturing CO₂ from the gaseous feed stream. In this study, a hybrid of zeolite and ZIF-8 adsorbent was synthesized from coal fly ash via fusion-hydrothermal process and then in-situ aqueous ZIF-8 synthesis technique. This technique of in-situ synthesis is highly cost-effective as it is done at room temperature. The hybrid adsorbent showed an enhanced microporosity as compared to zeolites synthesized from coal fly ash due to the in-situ synthesis of ZIF-8 upon coal fly ash zeolite. It was designated as CFAZ/ZIF-8. At 298 K, a maximum CO₂ uptake value of 2.83 mmol/g was observed with a constant decrease with an increase in temperature. BET surface area value of 426 m²/g was obtained for this adsorbent. Kinetics fit for the best uptake value was performed with the Avrami model kinetics, describing the adsorption well at an R² value of 0.997 for the fit. The adsorbent also showed impressive cyclic stability after five cycles of carbonation and decarbonation. The cyclic stability studies show that the as-synthesized hybrid adsorbent shows promise in CO₂ uptake studies.

Zeolite greenly synthesized from fly ash and its resource utilization: A review

Fly ash is an incineration byproduct of thermal power plants. Due to the complex composition of fly ash, improper disposal will seriously harm the ecological environment. Therefore, how to effectively use fly ash to safely and environmentally replace landfills is a worldwide concern. Considering the high silicon and aluminum contents in fly ash, it has the potential to synthesize zeolite, which has a wide range of applications in sewage treatment, gas adsorption, etc. Therefore, the synthesis of zeolites from fly ash is consistent with the theme of sustainable development. The synthesis mechanism of zeolite, various synthetic methods of zeolite from fly ash and their advantages and disadvantages was introduced in detail. In addition, combined with the current research hotspots, the application of synthetic zeolite from fly ash in the fields of sewage treatment and gas adsorption was introduced. Finally, the future development prospects and research directions of synthetic zeolite from fly ash to improve the utilization rate of fly ash were considered.

High performance CO2 capture at elevated temperatures by using cenospheres prepared from solid waste, fly ash

Cenospheres (CS) are spherical shaped inorganic frameworks present in with fly ash which is generated from coal-fired thermal power plants. These spherical structures were functionalized with imidazole and amine moieties to capture CO₂ selectively from flue gases at elevated temperature. The functionalized CS have shown a high selectivity for CO₂ adsorption (4.68 mmol g^-1) over N₂ (0.46 mmol g^-1) at 333 K/1 bar from a simulated flue gas (0.15 CO₂ and 0.85 N₂, v%) composition of thermal power plants. When the moisture content reached to 30 vol% the adsorption capacity of CS materials was reduced to 20 vol% as compared to dry flue gas. The functionalized CS can be used repeatedly for 50 cycles without losing its adsorption capacity. The cost estimate for CO₂ capture by using the proposed adsorption system would be $12.01/ton of CO₂ which is lower as compared to amine absorption system and zeolite-based adsorption system reported in the literature. The CS materials are prepared from solid wastes reduce the cost of production and their large scale manufacturing is technically feasible to capture CO₂ from industrial flue gases efficiently in near future.

Fly Ash, from Recycling to Potential Raw Material for Mesoporous Silica Synthesis

In order to meet the increasing energy demand and to decrease the dependency on coal, environmentally friendly methods for fly ash utilization are required. In this respect, the priority is to identify the fly ash properties and to consider its potential as raw material in the obtaining of high-value materials. The physico-chemical and structural characteristics of the fly ash coming from various worldwide power plants are briefly presented. The fly ash was sampled from power plants where the combustion of lignite and hard coal in pulverized-fuel boilers (PC) and circulating fluidized bed (CFB) boilers was applied. The fly ash has high silica content. Due to this, the fly ash can be considered a potential raw material for the synthesis of nanoporous materials, such as zeolites or mesoporous silica. The samples with the highest content of SiO₂ can be used to obtain mesoporous silica materials, such as MCM-41 or SBA-15. The resulting mesoporous silica can be used for removing/capture of CO₂ from emissions or for wastewater treatment. The synthesis of various porous materials using wastes would allow a high level of recycling for a sustainable society with low environmental impact.