SO2 Sorption Research Articles

Achieving Sub‐ppm Sensitivity in SO2 Detection with a Chemically Stable Covalent Organic Framework

We report the inaugural experimental investigation of covalent organic frameworks (COFs) to address the formidable challenge of SO2 detection. Specifically, an imine‐functionalized COF (SonoCOF‐9) demonstrated a modest and reversible SO2 sorption of 3.5 mmol g‐1 at 1 bar and 298 K. At 0.1 bar (and 298 K), the total SO2 uptake reached 0.91 mmol g‐1 with excellent reversibility for at least 50 adsorption‐desorption cycles. An isosteric enthalpy of adsorption (ΔHads) for SO2 equaled −42.3 kJ mol−1, indicating a relatively strong interaction of SO2 molecules with the COF material. Also, molecular dynamics simulations and Møller–Plesset perturbation theory calculations showed the interaction of SO2 with π density of the rings and lone pairs of the N atoms of SonoCOF‐9. The combination of experimental data and theoretical calculations corroborated the potential use of this COF for the selective detection and sensing of SO2 at the sub‐ppm level (0.0064 ppm of SO2).

Achieving Sub‐ppm Sensitivity in SO2 Detection with a Chemically Stable Covalent Organic Framework

We report the inaugural experimental investigation of covalent organic frameworks (COFs) to address the formidable challenge of SO2 detection. Specifically, an imine‐functionalized COF (SonoCOF‐9) demonstrated a modest and reversible SO2 sorption of 3.5 mmol g‐1 at 1 bar and 298 K. At 0.1 bar (and 298 K), the total SO2 uptake reached 0.91 mmol g‐1 with excellent reversibility for at least 50 adsorption‐desorption cycles. An isosteric enthalpy of adsorption (ΔHads) for SO2 equaled −42.3 kJ mol−1, indicating a relatively strong interaction of SO2 molecules with the COF material. Also, molecular dynamics simulations and Møller–Plesset perturbation theory calculations showed the interaction of SO2 with π density of the rings and lone pairs of the N atoms of SonoCOF‐9. The combination of experimental data and theoretical calculations corroborated the potential use of this COF for the selective detection and sensing of SO2 at the sub‐ppm level (0.0064 ppm of SO2).

Advancements in gas phase pollutant removal: A comprehensive study on the sorption of CO2 and SO2 on modified carbon monoliths

The synthesis of carbon monoliths using activated carbon treated with phenol-formaldehyde resin has been identified as a promising approach for the removal of pollutants from the gas phase. Monolithic adsorbents were synthesised and modified by adding silica, acid etching, and high temperature activation with CO2. Sorption capacities were determined by CO2 and SO2 adsorption tests. Preliminary findings indicated that the unmodified monoliths exhibited limited porosity. The activation process significantly altered the textural parameters, resulting in an increase in surface area and adsorption and desorption capacity. The modification yielded a monolith with a specific surface area of 598 m2/g and a pore volume of 438 mm3/g. The sorption capacity of the monoliths towards CO2 and SO2 was 1.64 mmol/g and 3.93 mmol/g, respectively. The modifications introduced developed the sorption capacity of the monoliths, enabling the regeneration process and its further use in subsequent measurement cycles.

Modulator-Dependent Dynamics Synergistically Enabled Record SO2 Uptake in Zr(IV) Metal-Organic Frameworks Based on Pyrene-Cored Molecular Quadripod Ligand.

Developing innovative porous solid sorbents for the capture and storage of toxic SO2 is crucial for energy-efficient transportation and subsequent processing. Nonetheless, the quest for high-performance SO2 sorbents, characterized by exceptional uptake capacity, minimal regeneration energy requirements, and outstanding recyclability under ambient conditions, remains a significant challenge. In this study, we present the design of a unique tertiary amine-embedded, pyrene-based quadripod-shaped ligand. This ligand is then assembled into a highly porous Zr-metal-organic framework (MOF) denoted as Zr-TPA, which exhibits a newly discovered 3,4,8-c woy net structure. Remarkably, our Zr-TPA MOF achieved an unprecedented SO2 sorption capacity of 22.7 mmol g-1 at 298 K and 1 bar, surpassing those of all previously reported solid sorbents. We elucidated the distinct SO2 sorption behaviors observed in isostructural Zr-TPA variants synthesized with different capping modulators (formate, acetate, benzoate, and trifluoroacetate, abbreviated as FA, HAc, BA, and TFA, respectively) through computational analyses. These analyses revealed unexpected SO2-induced modulator-node dynamics, resulting in transient chemisorption that enhanced synergistic SO2 sorption. Additionally, we conducted a proof-of-concept experiment demonstrating that the captured SO2 in Zr-TPA-FA can be converted in situ into a valuable pharmaceutical intermediate known as aryl N-aminosulfonamide, with a high yield and excellent recyclability. This highlights the potential of robust Zr-MOFs for storing SO2 in catalytic applications. In summary, this work contributes significantly to the development of efficient SO2 solid sorbents and advances our understanding of the molecular mechanisms underlying SO2 sorption in Zr-MOF materials.

The structural and textural characteristics of limestones and the effectiveness of SO2 sorption in fluidized bed conditions

The structural and textural characteristics of limestones and the effectiveness of SO2 sorption in fluidized bed conditions

Sorption of Polar Sorbates NH3, H2O, SO2 and CO2 on Selected Inorganic Materials.

In this paper, the sorption of NH3, H2O, SO2 and CO2 was tested for several selected inorganic materials. The tests were performed on samples belonging to two topologies of materials, faujasite (FAU) and framework-type MFI, the structures of which differ in pore size and connectivity. All sorbates are important in terms of reducing their emissions to the environment. They have different chemical nature: basic, alkaline, and acidic. They are all polar in structure and composition and two of them (ammonia and water vapor) can form hydrogen bonds. These differences result in different interactions with the surface of the adsorbents. This paper presents experimental data and proposes a mathematical description of the sorption process. The best fit of the experimental data was obtained for the Toth and GAB models. The studies showed that among the selected samples, faujasite has the best sorption capacity for ammonia and water vapor, while the best sorbent for sulfur dioxide is the MFI framework type. These materials behave like molecular sieves and can be used for quite selective adsorption of relevant gases. In addition, modification of the faujasite with organic silane resulted in a drastic reduction in the surface area of the sorbent, resulting in significantly lower sorption capacities for gases.

Efficacy and sorption of sulfur dioxide as a fumigant for control of navel orangeworm (Amyelois transitella) on stored pistachios

Sulfur dioxide (SO2) fumigation was evaluated for postharvest control of navel orangeworm (NOW), Amyelois transitella, on stored pistachios in a laboratory study. Sorption of SO2 on pistachios were measured at 5, 15, and 25 °C. Because of rapid sorption of SO2 on pistachios after SO2 injection, 3 h short fumigations were used to determine effective treatments against NOW eggs, larvae, and pupae. SO2 fumigation was effective against all of the life stages tested. However, large larvae in infested pistachios were most tolerant and eggs were most susceptible to SO2 fumigation. Smaller larvae were more susceptible to SO2 fumigation than larger larvae. Complete controls of eggs, larvae, and pupae were achieved in 3 h fumigations with 0.2, 2.0, and 1.0% SO2, respectively. Large SO2 fumigation trials each with 4.5 kg pistachios were conducted in a 19.8L chamber and complete control of 6th instar larvae were achieved in 3 h fumigation with about 1.6–1.8% SO2 at ambient temperatures of 18–21 °C. The results showed that SO2 fumigation has potential to control NOW on stored pistachios as well as to control other postharvest pests on stored products.

Magnesite as a Sorbent in Fluid Combustion Conditions—Role of Magnesium in SO2 Sorption Process

This article presents the results of research on magnesites from the Polish deposits of Szklary, Wiry and Braszowice as SO2 sorbents under the conditions of fluidized bed combustion technology. In practice, magnesites are not used as SO2 sorbents, and the role of magnesium in the desulfurization process under the conditions of fluidized bed combustion technology is evaluated differently among researchers. The literature data question the participation of magnesium in the process of SO2 capture from flue gas and prove its high reactivity. Similarly, previous studies referred to the problem of the stability of magnesium-containing desulfurization products under high temperature conditions. This paper analyzes the SO2 binding process and determines the parameters of the sorbent responsible for the efficiency of magnesite sorption. It was shown that MgO, formed as a result of thermal dissociation of magnesite, actively participates in the SO2 binding reaction to form magnesium sulfate phases (MgSO4 and CaMg2(SO4)3) stable in the temperature conditions of fluidized bed boilers. The problem of differentiated reactivity of magnesium-containing sorbents should be associated with the porosity of the sorbents. If the secondary surface of the sorbent is developed based on micropores and smaller mesopores (below 0.1 µm), the sorbent will be characterized by low sorption activity. It was shown that the SO2 binding process is then limited only to the outer part of the sorbent grains. This results in the formation of a massive, SO2-impermeable desulfurization-product layer on the sorbent grain surface. In real conditions, where the reactions of CaCO3 thermal dissociation and SO2 sorption occur almost simultaneously, the inside of the sorbent grains may remain undissociated. The results of experimental research allowed us to trace the dynamics of the SO2 binding process in relation to real conditions prevailing in fluidized bed boilers.

Adsorption of Sulfur Dioxide in Cu(II)-Carboxylate Framework Materials: The Role of Ligand Functionalization and Open Metal Sites.

The development of efficient sorbent materials for sulfur dioxide (SO2) is of key industrial interest. However, due to the corrosive nature of SO2, conventional porous materials often exhibit poor reversibility and limited uptake toward SO2 sorption. Here, we report high adsorption of SO2 in a series of Cu(II)-carboxylate-based metal–organic framework materials. We describe the impact of ligand functionalization and open metal sites on the uptake and reversibility of SO2 adsorption. Specifically, MFM-101 and MFM-190(F) show fully reversible SO2 adsorption with remarkable capacities of 18.7 and 18.3 mmol g–1, respectively, at 298 K and 1 bar; the former represents the highest reversible uptake of SO2 under ambient conditions among all porous solids reported to date. In situ neutron powder diffraction and synchrotron infrared microspectroscopy enable the direct visualization of binding domains of adsorbed SO2 molecules as well as host–guest binding dynamics. We have found that the combination of open Cu(II) sites and ligand functionalization, together with the size and geometry of metal–ligand cages, plays an integral role in the enhancement of SO2 binding.

Inclusion of CO2, NH3, SO2, Cl2 and H2S in porous N4O4-donor macrocyclic Schiff base

The removal and detection of highly toxic and environmentally harmful gases such as SO2, H2S and CO2 is a hot topic of the scientific community. Porous organic compounds, in particular, imine-based macrocycles, are promising materials for this purpose. In this paper we have used porous N4O4-donor macrocyclic Schiff base (1,6,20,25-tetraaza-2,5:8,9:17,18:21,24:27,28:36,37-hexabenzo-10,16,29,35-tetraoxa-cyclooctatriakonta-1,6,20,25-tetraen) (1) for sorption of NH3, SO2, Cl2, CO2 and H2S. Five novel inclusion compounds 1xNH3, 1xSO2, 1xCl2, 1xCO2 and 1xH2S were prepared by a single-crystal to single-crystal (SC-SC) transformation. Single-crystal X-ray diffraction (SCXRD) analysis of 1xCO2 and 1xNH3 inclusion compounds have shown that CO2 molecule resides in the plane of the macrocyclic ring connected by weak C–O … π interactions to the host, and no host-guest interactions in 1xNH3 were observed. The relative thermal stabilities of the host-guest systems (Ton – Tb parameter) is in the range from 93 (1xNH3) to 132 °C (1xH2S), indicating the formation of stable inclusion compounds. Although used gases are highly reactive and corrosive, FT-IR and powder diffraction studies indicate that the molecular and crystal structure of the host is constant upon gas sorption. The activated compound displays moderate uptake (0.35 mmol/g) of CO2 at 298 K. The relatively high thermal stability, constant molecular and crystal structure of inclusion compounds with interesting optical properties (determined by solid state UV–Vis) make this material potentially useful for the detection of toxic gases.

Zirconium and Aluminum MOFs for Low-Pressure SO2 Adsorption and Potential Separation: Elucidating the Effect of Small Pores and NH2 Groups.

Finding new adsorbents for the desulfurization of flue gases is a challenging task but is of current interest, as even low SO2 emissions impair the environment and health. Four Zr- and eight Al-MOFs (Zr-Fum, DUT-67(Zr), NU-1000, MOF-808, Al-Fum, MIL-53(Al), NH2-MIL-53(Al), MIL-53(tdc)(Al), CAU-10-H, MIL-96(Al), MIL-100(Al), NH2-MIL-101(Al)) were examined toward their SO2 sorption capability. Pore sizes in the range of about 4-8 Å are optimal for SO2 uptake in the low-pressure range (up to 0.1 bar). Pore widths that are only slightly larger than the kinetic diameter of 4.1 Å of the SO2 molecules allow for multi-side-dispersive interactions, which translate into high affinity at low pressure. Frameworks NH2-MIL-53(Al) and NH2-MIL-101(Al) with an NH2-group at the linker tend to show enhanced SO2 affinity. Moreover, from single-gas adsorption isotherms, ideal adsorbed solution theory (IAST) selectivities toward binary SO2/CO2 gas mixtures were determined with selectivity values between 35 and 53 at a molar fraction of 0.01 SO2 (10.000 ppm) and 1 bar for the frameworks Zr-Fum, MOF-808, NH2-MIL-53(Al), and Al-Fum. Stability tests with exposure to dry SO2 during ≤10 h and humid SO2 during 5 h showed full retention of crystallinity and porosity for Zr-Fum and DUT-67(Zr). However, NU-1000, MOF-808, Al-Fum, MIL-53(tdc), CAU-10-H, and MIL-100(Al) exhibited ≥50-90% retained Brunauer-Emmett-Teller (BET)-surface area and pore volume; while NH2-MIL-100(Al) and MIL-96(Al) demonstrated a major loss of porosity under dry SO2 and MIL-53(Al) and NH2-MIL-53(Al) under humid SO2. SO2 binding sites were revealed by density functional theory (DFT) simulation calculations with adsorption energies of -40 to -50 kJ·mol-1 for Zr-Fum and Al-Fum and even above -50 kJ·mol-1 for NH2-MIL-53(Al), in agreement with the isosteric heat of adsorption near zero coverage (ΔHads0). The predominant, highest binding energy noncovalent binding modes in both Zr-Fum and Al-Fum feature μ-OHδ+···δ-OSO hydrogen bonding interactions. The small pores of Al-Fum allow the interaction of two μ-OH bridges from opposite pore walls with the same SO2 molecule via OHδ+···δ-OSOδ-···δ+HO hydrogen bonds. For NH2-MIL-53(Al), the DFT high-energy binding sites involve NHδ+···δ-OS together with the also present Al-μ-OHδ+···δ-OS hydrogen bonding interactions and C6-πδ-···δ+SO2, Nδ-···δ+SO2 interactions.

Battling Chemical Weapons with Zirconium Hydroxide Nanoparticle Sorbent: Impact of Environmental Contaminants on Sarin Sequestration and Decomposition.

The promising reactive sorbent zirconium hydroxide (ZH) was challenged with common environmental contaminants (CO2, SO2, and NO2) to determine the impact on chemical warfare agent decomposition. Several environmental adsorbates rapidly formed on the ZH surface through available hydroxyl species and coordinatively unsaturated zirconium sites. ZH decontamination effectiveness was determined using a suite of instrumentation including in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) to monitor sarin (GB) decomposition in real time and at ambient pressure. Surface products were characterized by ex situ X-ray photoelectron spectroscopy (XPS). The adsorption enthalpies, entropies, and bond lengths for environmental contaminants and GB decomposition products were estimated using density functional theory (DFT). Consistent with the XPS and DRIFTS results, DFT simulations predicted the relative stabilities of molecular adsorbates and reaction products in the following order: CO2 < NO2 < GB ≈ SO2. Microbreakthrough capacity measurements on ZH showed a 7-fold increase in the sorption of NO2 vs SO2, which indicates differences in the surface reactivity of these species. GB decomposition was rapid on clean and CO2-dosed ZH and showed reduced decomposition on SO2- and NO2-predosed samples. Despite these findings, the total GB sorption capacity of clean and predosed ZH was consistent across all samples. These data provide insight into the real-world use of ZH as a reactive sorbent for chemical decontamination applications.

The Miocene Lacustrine Chalk from Lignite Bełchatów Deposit (Poland)—Structural and Textural Character and SO2 Sorption Properties in the Fluid Combustion Conditions

The Miocene lacustrine chalk in the Bełchatów lignite deposit is one of the most important accompanying minerals. It is found in three lithological varieties: white, dark and silicified. It is selectively operated and stored on anthropogenic deposits, representing the mineral resource base. The article presents the results of research on lacustrine chalk from the Szczerców mine excavation and accumulated on the anthropogenic deposit (the Szczerców field external landfill) regarding the possibility of using SO2 sorbent in the fluid combustion technology. It has been shown that primarily the structural and textural parameters of the rock, and to a lesser extent, the CaCO3 content, are responsible for the high efficiency of SO2 sorption. It has been proven that in this type of technology, the presence of carbonised plant matter only seemingly lowers the quality parameters of the raw material. It has a significant impact on the sorption properties, effectively influencing the expansion of porosity and specific surface during thermal decomposition. The expansion of the surface is mainly based on the pores on the border of mesopores and macropores, i.e., pores considered to be sorptive towards SO2. These pores, because they are formed in a lower temperature range than the calcite thermal dissociation process and are connected together to form a system, act as diffusion channels of CO2 from inside and SO2 into the inside of the sorbent grains, intensifying the decarbonisation and SO2 sorption processes.

Tuning the Structural Flexibility for Multi-Responsive Gas Sorption in Isonicotinate-Based Metal-Organic Frameworks.

Flexible metal-organic frameworks (MOFs) are of high interest as smart programmable materials for gas sorption due to their unique structural changes triggered by external stimuli. Owing to this property, which leads to opportunities such as maximizing deliverable gas capacity, flexible MOFs sometimes offer more advantages in sorption applications compared to their more rigid counterparts. Herein, we elucidate the effect of transition metal identity of a series of isonicotinate-based flexible MOFs, M(4-PyC)2 [M═Mg, Mn, and Cu; 4-PyC = 4-pyridine carboxylic acid] on the structural dynamic response to different gases (C2H4, C2H6, Xe, Kr, and SO2). Isotherms at different temperatures show that C2H4, C2H6, and Xe can form sufficiently strong interactions with both Mg(4-PyC)2 and Mn(4-PyC)2 frameworks resulting in gate-opening behavior due to the rotation of the linker's pyridine ring, while Kr cannot induce this phenomenon for the two MOFs under the measured conditions. In contrast, the gate-opening behavior occurs for Cu(4-PyC)2 solely in the presence of C2H4, and no other measured gas, due to the open metal sites of Cu centers. In comparison, SO2, a strong polar molecule, triggers the gate-opening effect in all three MOFs. Interestingly, a shape memory effect is observed for Cu(4-PyC)2 during the second SO2 sorption cycle. When comparing the different gate-opening pressures of each gas, we observed that the structural flexibility of the three frameworks is highly sensitive to the chemical hardness of the Lewis acidic metal ions (Mg2+ > Mn2+ > Cu2+). As a result, the gate opening behavior is observed at lower pressures for the MOFs containing weaker M-N bonds (harder metal ions), with the exception of Cu(4-PyC)2 toward C2H4. These observations reveal that different transition metals can be used to finely control the structural flexibility of the frameworks.

Aliphatic amine decorating metal–organic framework for durable SO2 capture from flue gas

The efficient capture of SO2 using porous adsorbents is of great significance in flue gas desulfurization (FGD) process as the reversible physical adsorption can avoid solvents/water consumption and minimize waste generation. Metal organic frameworks (MOFs) are interesting and promising candidates to sequestrate SO2 in flue gas as their high porosities, regular pore sizes and easy functionalization. However, the coordination bond nature of MOFs makes stably and persistently capture acidic SO2 gas remains a challenge in MOF. Herein, an aliphatic amine decorating strategy was introduced in a MOF (MIL-101(Cr)) with open metal sites for reversible and durable SO2 capture. The successful synthesis of N,N'-dimethylethylenediamine (mmen) decorated MIL-101(Cr) named mmen-MIL-101(Cr), was confirmed by powder X-ray diffraction (PXRD), Fourier transform-infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy-dispersive spectra (EDS) and nitrogen adsorption–desorption isotherm. Compared with chemisorption of SO2 on open Cr sites in MIL-101(Cr), the SO2 adsorption sites are transferred from Cr to N atom in mmen-MIL-101(Cr), leading to reversible SO2 adsorption and desorption. The dipole–dipole interaction between N atom and S(SO2) atom, combining with hydrogen bonding interaction between O(SO2) and H in mmen can increase the SO2 absorption capacity of mmen-MIL-101(Cr) under low SO2 partial pressure. The SO2 adsorption capacity and cycle stability properties were studied in detail by adsorption isotherm and dynamic breakthrough measurement. An unprecedented high SO2 adsorb capacity (upto 4.27 mmol·g−1) at SO2 partial pressure (0.5 mbar) is achieved in mmen-MIL-101(Cr), which is a great improvement compared to 2.92 mmol·g−1 SO2 adsorption capacity for primordial MIL-101(Cr) under the same condition. Moreover, mmen-MIL-101(Cr) manifests reversible SO2 adsorption–desorption performance while MIL-101(Cr) gradually loses its adsorption capacity during dynamic breakthrough cycles. The high SO2 sorption capacity in low partial pressure and impressive cycle stability of mmen-MIL-101(Cr) demonstrate aliphatic amine decorating strategy is an efficient way to improve MOF’s SO2 capture capability, which also can extend to other porous adsorbents for low concentration FGD process.

Deep removal of SO2 from cathode air over polyethylenimine-modified SBA-15 sorbents for fuel cells

The performance and longevity of fuel cells can be significantly degraded by the contaminants in the air, such as SO2 and NO2, which poison the cathode catalysts. The cleanup of the cathode air in a real environment may thus be required. In this work, SO2 sorption and desorption behavior over molecular basket sorbents (MBSs) consisting of polyethylenimine (PEI) and SBA-15 has been studied. The effects of temperature, PEI loading and SO2 concentration on the sorption capacity of PEI-SBA-15 sorbents were examined. The results showed that the sorption temperature and PEI loading amount greatly influence the sorption performance. The regenerability study showed that only about 10–40 % of sorption capacity was recoverable over the spent PEI-SBA-15 sorbents due to the strong chemical interaction between SO2 and amine sites. Additionally, the influence of co-existing NO2 on SO2 sorption was examined, showing a competitive sorption between SO2 and NO2 over PEI-SBA-15 sorbent. The current study demonstrates that the PEI-BA-15 sorbent could be promising for deep removal of SO2 and NO2 from the cathode air for fuel cells.

Regenerable solid molecular basket sorbents for selective SO2 capture from CO2-rich gas streams

A series of molecular basket sorbents (MBSs) consisting of SBA-15 loaded with ethylene glycol (EG) derivatives and dimethyl sulfoxide (DMSO) are developed and investigated for sulfur dioxide (SO2) capture from industrial tail gas streams. The EG derivatives and DMSO are successfully immobilized on the support via surface interaction with the silanol groups as evidenced by DRIFTS analysis. The mesoporous structure of SBA-15 is preserved after loading with different compounds, with no major morphology changes. The SO2 sorption capacity increases with decreasing the molecular weight of EG derivatives. Furthermore, changing the terminal group of EG derivatives from hydroxyl (-OH) to methoxy (-OCH3) improves SO2 sorption capacity. DMSO-based MBS exhibits much higher SO2 affinity (64 mg-SO2/g-sorb.) than EG-based sorbents (<25 mg-SO2/g-sorb.). DMSO/SBA-15 sorbents are able to selectively capture SO2 in the presence of high CO2 concentration (30 %) with a relative selectivity factor of 120. Pre-saturating the DMSO-based sorbents with water vapor does not affect SO2 sorption capacity, and the sorbents possess good stability and regenerability. Moreover, the spent DMSO/SBA-15 sorbent could be further applied for H2S removal for producing elemental sulfur via Claus reaction between H2S and the adsorbed SO2, providing an environmentally friendly and sustainable way of regenerating the spent DMSO/SBA-15 sorbents.

Metal-Organic Frameworks with Potential Application for SO2 Separation and Flue Gas Desulfurization.

Sulfur dioxide (SO2) is an acidic and toxic gas and its emission from utilizing energy from fossil fuels or in industrial processes harms human health and environment. Therefore, it is of great interest to find new materials for SO2 sorption to improve classic flue gas desulfurization. In this work, we present SO2 sorption studies for the three different metal-organic frameworks MOF-177, NH2-MIL-125(Ti), and MIL-160. MOF-177 revealed a new record high SO2 uptake (25.7 mmol·g-1 at 293 K and 1 bar). Both NH2-MIL-125(Ti) and MIL-160 show particular high SO2 uptakes at low pressures ( p < 0.01 bar) and thus are interesting candidates for the removal of remaining SO2 traces below 500 ppm from flue gas mixtures. The aluminum furandicarboxylate MOF MIL-160 is the most promising material, especially under application-orientated conditions, and features excellent ideal adsorbed solution theory selectivities (124-128 at 293 K, 1 bar; 79-95 at 353 K, 1 bar) and breakthrough performance with high onset time, combined with high stability under both humid and dry SO2 exposure. The outstanding sorption capability of MIL-160 could be explained by DFT simulation calculations and matching heat of adsorption for the binding sites Ofuran···SSO2 and OHAl-chain···OSO2 (both ∼40 kJ·mol-1) and Ofuran/carboxylate···SSO2 (∼55-60 kJ·mol-1).

Modification of fly ash produced in the process of burning fossil fuels - granulation method

The low grain size of fly ashes from the combustion of fossil fuels creates a number of ecological problems both during storage and transport, and often makes their re-use more difficult. One way to avoid this problem is to compact these materials in the granulation process. The granulation process generally requires the use of different binders, which are divided into matrix, film, and chemical type binders. Depending on the chemical composition of the fly ash and the type of the binder used, the obtained aggregate forms (granulates) find numerous applications, e.g. in the production of adhesives, zeolites and/or concrete, in manufacture of building materials, and in aggregates for road works or for ground leveling. In many applications, especially in road engineering works or in ground leveling, the basic requirements, next to the compressive strength of the granules obtained, are the leachability of sulfate ions and the pH-value of the eluates. The paper presents a research study investigating the granulation process of fly ashes produced by the combustion of hard and brown coals burned in both pulverized and fluidized furnaces, with the application of the following binders: water, calcium sulfate hemihydrate, and mixture of calcium sulfate hemihydrate and calcium hydroxide. For the resulting granulates, tests were conducted to determine compressive strength, SO2 sorption capacity, the pH-value, and the content of sulfate ions in the eluate before and after sorption tests. The obtained results show that the granulation process mostly decreases leachability of sulfate ions and the pH-value of the eluates while simultaneously providing adequate compressive strength of the obtained compacted forms (granulates).

Free energy study of H2O, N2O5, SO2, and O3 gas sorption by water droplets/slabs

Understanding gas sorption by water in the atmosphere is an active research area because the gases can significantly alter the radiation and chemical properties of the atmosphere. We attempt to elucidate the molecular details of the gas sorption of water and three common atmospheric gases (N2O5, SO2, and O3) by water droplets/slabs in molecular dynamics simulations. The system size effects are investigated, and we show that the calculated solvation free energy decreases linearly as a function of the reciprocal of the number of water molecules from 1/215 to 1/1000 in both the slab and the droplet systems. By analyzing the infinitely large system size limit by extrapolation, we find that all our droplet results are more accurate than the slab results when compared to the experimental values. We also show how the choice of restraints in umbrella sampling can affect the sampling efficiency for the droplet systems. The free energy changes were decomposed into the energetic ΔU and entropic -TΔS contributions to reveal the molecular details of the gas sorption processes. By further decomposing ΔU into Lennard-Jones and Coulombic interactions, we observe that the ΔU trends are primarily determined by local effects due to the size of the gas molecule, charge distribution, and solvation structure around the gas molecule. Moreover, we find that there is a strong correlation between the change in the entropic contribution and the mean residence time of water, which is spatially nonlocal and related to the mobility of water.