SO2 Partial Pressure Research Articles

New insights into kinetics and mechanisms of acid sulphite delignification of Eucalyptus globulus wood

The kinetics of Eucalyptus globulus wood delignification in Mg-base acid sulphite pulping of dissolving pulp was studied using a pilot-scale batch digester simulating the industrial process. The behavior of lignin during impregnation, heating-up and bulk delignification at the final temperature was evaluated by the analysis of acid-insoluble lignin in wood and wood residue after pulping. The dynamics of lignin dissolution was followed by its structural analysis in solid residues and in solution by wet chemistry and 1D and 2D nuclear magnetic resonance (NMR) spectroscopy. About 30 % and 20 % of the lignin were removed in the impregnation and heating-up pulping steps, respectively. About 45 % of the lignin was removed at the final pulping temperature in bulk and 3 % in the residual delignification stages. The kinetics of bulk delignification followed a pseudo-first-order kinetics with an effective activation energy of 138.4 kJ/mol in the temperature range of 140–148 °C. Bulk delignification follows an undefined overall order in the hydrogen and bisulfite ions and depended on the partial pressure of SO2 at ca. 0.60 order within the range of combined SO2 in pulping acid of 1.14–1.66 % and total SO2 loads of 6.2–7.0 %. Minimum degree of lignin sulphonation to be dissolved in the pulping liquor was suggested to be about 0.35 sulphonic groups per one phenyl propane unit. Lignin removal during pulping showed dependence on its location in different morphological parts of the fibers and related structural characteristics, which were discussed accordingly. A role of the polysaccharide complex in the accessibility of lignin was highlighted. A noticeable cleavage of β-O-4 linkages occurred in lignin already dissolved in pulping liquor at the end of cooking.

High-efficiency recovery of valuable metals from spent lithium-ion batteries: Optimization of SO2 pressure leaching and selective extraction of trace impurities

The recovery of valuable metals from spent lithium-ion batteries (LIBs) is crucial for environmental protection and resource optimization. In the traditional recovery process of spent LIBs, the leaching of high-valence metals has the problems of high cost and limited reagent utilization, and some valuable metals are lost in the subsequent purification process of the leaching solution. To reduce the cost of reagents, this study proposes the use of low-cost SO2 as a reagent combined with pressure leaching to efficiently recover high-valence metals from delithiated materials of spent LIBs, while selective solvent extraction is used to remove trace impurities in the leaching solution to avoid the loss of valuable metals. Experimental results demonstrated that by optimizing the conditions to 0.25 MPa SO2 partial pressure and 60 min reaction time at 70 °C, the leaching efficiencies for Ni, Co, and Mn reached 99.6%, 99.3%, and 99.6%, respectively. The kinetic study indicated that the leaching process was diffusion-controlled. Furthermore, the delithiated materials were used to completely utilize the residual SO2 in the solution to obtain a high concentration Ni–Co–Mn rich solution. Subsequently, Fe and Al impurities were deeply removed through a synergistic extraction of Di-2-ethylhexyl phosphoric acid (D2EHPA) and tributyl phosphate (TBP) without loss of valuable metals, achieving a high-purity Ni–Co–Mn solution. The process developed based on this work has the characteristics of environmental friendliness, high valuable metal recovery, and high product purity, providing a reference technical method for the synergistic treatment of waste SO2 flue gas with spent LIBs and the deep purification of impurities in spent LIBs.

Nafion-Mediated Proton Transfer Facilitates the Electroreduction of SO2 to H2S.

The electrocatalytic reduction of SO2 to produce H2S is a critical approach for achieving the efficient utilization of sulfur resources. At the core of this approach for commercial applications lies the imperative need to elevate current density. However, the challenges posed by high current density manifest in the rapid depletion of protons, leading to a decrease in SO2 partial pressure, consequently hampering the generation and separation of H2S. Here, we demonstrate an effective solution to alleviate the problem of insufficient supply of protons by employing Nafion polymer as the proton conductor to modified Cu catalysts surface, creating a proton-enriched layer to boost H2S generation. It was observed that Nafion shortens the hydrogen bonds with water molecules in the electrolyte via its sulfonic acid groups, benefiting the proton transfer and consequently increasing the proton density on the electrode surface by 5-fold. With the Nafion-modified catalyst, the H2S partial current density and separation efficiency reached 205.9 mA·cm-2 (1.01 mmol·cm-2·h-1) and 87.8%, which were 1.34 and 1.22 times that on unmodified Cu, respectively. This work highlights the practicality of fabricating a proton conductor via ionic polymer for the control over product selectivity in pH-sensitive reactions under high current density.

Surface sulfurization of amorphous carbon films in the chemistry of oxygen plasma added with SO2 or OCS for high-aspect-ratio etching

Etching of oxygen-based plasmas with sulfur dioxide (SO2) or carbonyl sulfide (OCS) can form high-aspect-ratio (HAR) features of amorphous carbon films as carbon hard masks (CHM). The etched profiles showing shapes such as bowing or tapering are essentially dependent on the partial pressures of SO2 or OCS in the O2 plasma. The surface treated after the OCS-added plasma exhibited strong sulfurization by S2 and CS species in S 2p of the X-ray photoelectron spectroscopy (XPS). The gas-phase interactions in the sulfur-oxygen-carbon system generated atoms and molecules, such as O, O+, and O2+, which etched at the bottom and, conversely, SO, CO, CS, CS2, and S2, which inhibited isotropic etching at the sidewalls of the HAR features. The chemical reactions of the CS sulfurizing precursors in the gas phase were monitored by comparing their optical emission intensities at a wavelength of 257 nm with those of SO2 at approximately 320 nm. The optimization of the HAR profiles of the CHM can be controlled by sidewall sulfurization of the CHM to obtain desirable profile shapes for the HAR features.

Surpassingly efficient, selective, and reversible absorption of SO2 through pyridine based deep eutectic solvents

In this study, deep eutectic solvents (DESs) consisting of 1-ethyl-3-methylimidazolium chloride (EmimCl) and pyridine derivatives were prepared through a facile procedure. The studied DESs exhibit superb absorption behavior for SO2 at 298.15 K and 1.0 bar, of which per g EmimCl: 2-NH2Py (7: 1) could capture 1.247 g SO2, exceeding the vast majority of the previously reported DESs and ionic liquids (ILs). The factors that could affect the absorption capacity were explored orderly, like the category and molar ratio of pyridine derivatives, the absorption temperature, and SO2 partial pressure. Based on the above investigation, EmimCl: 2-NH2Py (7: 1) exhibits rapid equilibration time (<45 s), outstanding SO2/CO2 selectivity (312/1), and ultra-high recycling performance (40 times), which is far superior to the other reported DESs and ILs. In addition, the possible absorption process was studied from both experimental and theoretical aspects. The obtained data indicate that Lewis acid-base interaction and SO2···Cl- covalent interaction both exist between SO2 and DES, leading to an ideal absorption capacity and selectivity for SO2. This study might provide a novel insight to remove SO2 and other gaseous pollutants.

Facile Synthesis of Alkaline Ternary Deep Eutectic Solvents: Application for Effective and Reversible SO2 Uptake

Effective capture and recycling of SO2 are of great significance to environmental protection and high-value utilization. Herein, a promising strategy for effective and reversible capture of SO2 was proposed using alkaline ternary deep eutectic solvents (DESs) as absorbents. The absorbents consisting of choline chloride (ChCl), diethylenetriamine (DETA), and ethylene glycol (EG) with different molar ratios show a relatively lower viscosity and higher thermal stability. Here, ChCl/DETA/EG (1:1:2) could take out 0.87 g of SO2/g of solvent at 298.15 K and 1.0 bar. Surprisingly, a SO2 absorption capacity of 0.53 g/g could still be gained under a lower SO2 partial pressure (0.2 bar). Besides, the prepared absorbents also exhibit rapid equilibration time and satisfied reusability, providing a potential alternative strategy for the effective and reversible elimination of SO2.

A comprehensive kinetic investigation on sulfur deportment during nickel laterite calcination using model-free, model-fitting, and master plot approaches

The rotary kiln-electric furnace process is the most common method for ferronickel production from laterite ore. Since sulfur deteriorates the mechanical properties of ferronickel, it is essential to examine the routes through which sulfur is transferred to the nickel-containing product during the extraction process. Oxidation of fuel (e.g., coal) in the calcination kiln emits SO2, which results in sulfur transfer from the gas to the calcine. In this investigation, coal combustion atmosphere was mimicked by purging N2-CO-CO2-SO2 gas mixture in the tube furnace. A comprehensive kinetic analysis on the sulfurization of nickel laterite ore was conducted to obtain a fundamental understanding of the rate of the sulfurization reactions. The kinetic investigation was performed by three approaches: model-free, model-fitting, and master plot at various processing times, temperatures, and partial pressures of SO2. The XRD and ICP analyses were used to determine the phase composition and sulfur content of the calcine, respectively. Considering the activation energy values obtained by model-free approach, the process is divided into two steps, before and after 60 min of calcination. Contracting sphere and Avrami Erofeev are identified as the most suitable kinetic models for steps 1 and 2, respectively. Considering the small values of activation energy, 1.4–5.3 kJ/mol, the sulfurization reactions are identified as diffusion-controlled mechanism.

Control of Copper Content in Flash Smelting Slag and the Recovery of Valuable Metals from Slag—A Thermodynamic Consideration

To determine slag properties and the factors influencing these properties for optimization of operating conditions in the copper flash smelting process, the composition and microstructures of the quenched smelting and converting slags have been analyzed. Thermodynamic software FactSage 8.2 has been used to investigate the effects of matte grade, SO2 partial pressure, and the Fe/SiO2 ratio on the liquidus temperature and the copper content of the smelting slag. The possibility to recover valuable metals from the smelting and converting slags through pyrometallurgical reduction by carbon is also discussed. It was found that the flash smelting slag temperature is usually higher than its liquidus temperature and the copper (1.2% Cu) is mainly present in the slag as dissolved copper. In the copper flash smelting process, the copper content in the slag can be decreased by decreasing the Fe/SiO2 ratio and temperature. In pyrometallurgical slag reduction, most Cu, Mo, and Ni can be recovered as an alloy. The conditions of recovery such as the ratio of smelting slag to converting slag, temperature, and reduction extent have been discussed.

Ash characterisation formed under different oxy-fuel circulating fluidized bed conditions

The CO2-intensive oil shale power industry accounts for more than 70% of the Estonian energy sector, producing large amounts of ash that are mainly landfilled. Adopting oxy-fuel technology in the Estonian energy sector, in conjunction with CO2 storage, can be a critical tool for reducing carbon footprint. Nevertheless, several differences in ash formation under oxy-fuel conditions can be expected, which can lead to additional ash handling/utilization and related environmental concerns. In this context, the composition of oil shale ash was obtained from a series of combustion experiments in a 60 kWth circulating fluidized bed (CFB) test unit under both air and oxy-fuel combustion regimes studied by means of physical, chemical analysis as quantitative X-ray diffraction and element analysis for ashes from different separation ports. During the experimental work, special attention was given to understanding the impacts of the boiler temperature, recycled flue gas (RFG), and elevated oxygen concentration. As a result, the primary goal of this research is to characterise the ash produced by oxy-fuel combustion of oil shale in order to gain a better understanding of its chemical and mineral compositions, including Ca-Mg silicates and clay minerals, as well as to investigate the behaviour of the formation of free lime and anhydrite, which are the major compounds influencing potential ash utilisation routes. The results show that although the decomposition of calcium carbonates was limited during oxy-fuel combustion because of the high CO2 partial pressure, the contents of secondary silicates and anhydrite were slightly higher. The increased particle temperature and the higher SO2 partial pressure (with RFG) can explain this. The particle size distributions (PSDs) were wider under oxy combustion, and the specific surface area (SSA) in Filter ashes were much higher under elevated inlet O2% atmosphere. Oxy-fuel combustion had no significant impact on the concentration of elements in the ash. Overall, the mineralogy of the ashes formed in air and oxy-fuel combustion environments is similar, yet slight differences exist in the formation of clay minerals in the case of increased oxygen concentrations and with the application of RFG as a result of the increased residence time of the particles.

Tin Removal from Tin-Bearing Iron Concentrate with a Roasting in an Atmosphere of SO2 and CO

The tin could be volatilized and removed effectively from the tin-bearing iron concentrate while roasted in an atmosphere of SO2 and CO. The reduction of SO2 by CO occurred in preference to the SnO2 and Fe3O4, and the generated S2 could sulfurize the SnO2 to an evaporable SnS, which resulted in the tin volatilization. However, the Fe3O4 could be sulfurized simultaneously, and a phase of iron sulfide was formed, retaining in the roasted iron concentrate. It decreased the quality of the iron concentrate. In addition, the formation of Sn-Fe alloy was accelerated as the roasting temperature exceeded 1100 °C, which decreased the Sn removal ratio. An appropriate SO2 partial pressure and roasting temperature should be controlled. Under the condition of the roasting temperature of 1050 °C, SO2 partial pressure of 0.003, CO partial pressure of 0.85, and residence time of 60 min, the tin content in the roasted iron concentrate was decreased to 0.032 wt.% and the sulfur residual content was only 0.062 wt.%, which meets the standard of iron concentrate for BF ironmaking.

Efficient SO2 removal using aqueous ionic liquid at low partial pressure

The development of novel absorbents is essential for SO2 removal. In this study, a novel ionic liquid (IL, [BHEP][HSO4]) was prepared, and water was selected as the co-solvent. The density and viscosity of aqueous [BHEP][HSO4] were measured and the SO2 absorption performance was systematically investigated. Furthermore, the thermodynamic properties of SO2 in aqueous [BHEP][HSO4] were calculated. Additionally, the mechanism of SO2 absorption in aqueous [BHEP][HSO4] was confirmed using Fourier-transform infrared and nuclear magnetic resonance spectroscopy. It showed that [BHEP][HSO4] absorbed 0.302 g⋅g−1 (g SO2/g IL) at an SO2 partial pressure of 2000 μl⋅L−1 at 303.2 K, and the SO2 desorption enthalpy was −39.63 kJ⋅mol−1. The mechanistic study confirmed the chemical absorption of SO2 in aqueous [BHEP][HSO4].

Enhancement of desulfurization by hydroxyl ammonium ionic liquid supported on active carbon

Power plants emit sulfur dioxide (SO2) during combustion, which is typically removed via wet flue gas desulfurization, but this process produces numerous secondary pollutants. Ionic liquids (ILs) can potentially be used to remove SO2, but they suffer from poor mass transfer rates. Hydroxyl ammonium ILs are classical cheap ILs that contain electron-rich O and N sites that favor high absorption capacities. To accelerate mass transfer, two hydroxyl ammonium ILs, triethanolamine citrate and triethanolamine lactate, were immobilized on activated carbon (SILs) and used to capture SO2 from simulated flue gas. They exhibited excellent adsorption at low SO2 partial pressures due to the presence of a large gas-liquid interface. The molar adsorption ratios reached 7.65 and 2.40 mol/mol at 10 kPa SO2. The SILs possessed good SO2 selectivity in SO2/CO2 and SO2/O2 mixtures, because of the only 8% reduction in the total adsorption of SILs at 60 °C. And they exhibited excellent reversibility in which their total adsorption capacities were unaffected after 5 adsorption-desorption cycles. The mechanism analysis revealed that chemical adsorption was the major adsorption route, although physical adsorption also occurred. The main reactive sites included C–O and N–H groups in the ionic liquid. These SILs may potentially replace traditional chemical absorption materials for the separation of SO2 from flue gas.

Natural deep eutectic solvent-based gels with multi-site interaction mechanism for selective membrane separation of SO2 from N2 and CO2

The researches on capture of SO2 from flue gas using deep eutectic solvents (DESs) are rapidly emerging due to their unique natures, such as high efficiency and simple synthesis. However, to the best of our knowledge, DESs have not been applied to membrane separation of SO2 yet. Herein, we firstly reported novel natural deep eutectic solvent (NDES)-based gels consisting of betaine/glycerol DES (1:2) and 12-hydroxystearic acid (HSA) for selective membrane separation of SO2. Characterization of the prepared gels involving chemical structures, thermal stability and sol–gel transition temperatures were conducted. The corresponding gel membranes were facbricated and their morphology and pressure resisitance were characterized. Gas permeation test shows that the permeability of SO2 reaches 1809 barrers (0.025 bar, 40 °C) in DES + HSA 4% gel, with SO2/N2 and SO2/CO2 selectivities of 624 and 67.8, respectively. FTIR and NMR spectroscopy were used for characterize the facilitated transport of SO2, and the multisite-interaction mechanism was proposed. Surprisingly, the SO2 permeability is found to be significantly enhanced to 15,200 barrers without compromise on selectivity under humidified condition. Moreover, the effects of HSA content, SO2 partial pressure and temperature on separation performance were also investigated. Overall, this work offers an illustration of SO2 separation using DES-based gels, offering an alternative strategy for designing novel DES-based membrane materials for flue gas desulfuration.

Simultaneous fractionation of sulfur dioxide explains mass independent fractionation of sulfur isotopes in Archean sedimentary pyrites

The relationship between ∆36S and ∆33S in Archean sedimentary pyrites has been used to evaluate early geologic processes, including photochemical reactions in the anoxic atmosphere, biological activity and thermochemical alteration during sediment deposition. We have applied statistical methods to quadruple S isotope analyses of Archean sedimentary pyrites, using data compiled from the literature. Most of the best-fit lines, on plots of ∆36S against ∆33S, have Archean reference array-like ∆36S/∆33S slopes that vary between −1.5 and − 0.9. Rigorous statistical tests were conducted to calculate the probability of the best-fit lines passing through the origin. Seventeen of 23 ∆36S-∆33S regression lines, which pass our reliability filter of R2 ≥ 75% and ∆33S range ≥ 2‰, have positive intercepts on the ∆36S axis, and 13 of these have a probability of < 5% of a zero intercept on the ∆36S axis. The observed ∆36S/∆33S slopes and the non-negative intercepts, which requires at least two mass-independent fractionation source reactions to operate simultaneously, can be produced by UV radiation in the atmosphere at low SO2 partial pressures by combining collision-induced intersystem crossing in the SO2 photoexcitation band (240–340 nm), with the self-shielding effect in the SO2 photolysis band (190–220 nm). The two SO2 photochemical processes must occur simultaneously in a single atmospheric reservoir in order that the fraction contributed by the end-member process remains constant across the full range of ∆33S values. We call this process simultaneous fractionation. We applied a two-end-member model to calculate the fraction of S contributed by the SO2 photoexcitation end-member (f) needed to produce the observed ∆36S/∆33S gradients and variable intercepts on the ∆36S axis in the Archean sedimentary pyrites, when the other end-member is SO2 photolysis with the self-shielding. The simplest explanation for variations in f, and therefore variations in ∆36S/∆36S gradients, is that it is controlled by changes in the partial pressure of SO2 in the atmosphere.

Post modification of Oxo-clusters in robust Zirconium-Based metal organic framework for durable SO2 capture from flue gas

The efficient capture of SO2 after the combustion of fossil fuels is of great challenge as the low SO2 concentration (<500 ppm) and coexisting with CO2, water, O2 in flue gas. Robust zirconium-based MOFs possessing accessible polar sites usually have high SO2 adsorption capacity but poor durably in adsorption desulfurization due to the acidic sulfate deposition on the Zr-O cluster. Herein, a Zr-O cluster post-modification method was introduced in a Zr-MOF (MOF-808) to form EDTA-MOF-808 (EDTA, ethylene diaminetetraacetic acid) for selective and durable removal of SO2. The introduction of EDTA not only improve their SO2 adsorption capacity, but also sharply increase their SO2/CO2 selectivity (57.2 vs 8.9) and SO2/N2 selectivity (1915.8 vs 292.7) at low SO2 partial pressure. Moreover, the synergistic effects of dipole and hydrogen bonding interaction between SO2 and EDTA in EDTA-MOF-808 make the capture of SO2 in a reversible manner, which can prevent the formation of S(VI) species in Zr-MOF. DFT calculation confirmed that SO2 was interacted with EDTA through moderate dipole–dipole interaction (S(SO2) with N(EDTA)) and hydrogen bonds (H(–COOH) with O(SO2)). Systematic investigations including thermodynamic SO2 adsorption, dynamic breakthrough experiments, stability tests and DFT-calculations in both MOF-808 and EDTA-MOF-808 confirmed the efficient performance of post modification of Zr-O clusters with EDTA in Zr-MOFs for durable SO2 capture.

Unexpectedly promoted SO2 capture in novel ionic liquid-based eutectic solvents: The synergistic interactions

A series of novel deep eutectic solvents (DESs) composed of equimolar solid ionic compounds (EmimX and EPyY; X, Y = Cl−, Br−) were developed for SO2 absorption in this work. Effects of absorption temperature, SO2 partial pressure, gas flow rate and moisture content on SO2 absorption capacities of the DESs were investigated. These DESs exhibited an extremely high SO2 loading capacity and excellent reversibility. Concretly, the solubilities of SO2 in 1-ethyl-3-methylimidazolium chloride (EmimCl)- N-ethylpyridinium chloride (EPyCl) were 1.483 and 0.777 g SO2/g solvent under the SO2 partial pressure of 1.0 and 0.1 atm at 20 °C, respectively, which were the highest values to date under the same conditions. Furthermore, EmimCl-EPyCl exhibited a reasonable SO2 capacity of 0.193 g SO2/g solvent when the SO2 concentration in the feed gas was 2000 ppm. The absorption mechanisms based on the results of 1H NMR and DFT calculation indicated that the high SO2 absorption capacity was mainly attributed to the synergistic interactions of the two components in the DESs rather than a simple combination of the capacities of EmimCl and EPyCl.

Experimental investigation of gas-matte-spinel and gas-slag-matte-spinel equilibria in the Cu-Fe-O-S-Si system at 1200°C: effect of SO2 partial pressure

ABSTRACT Experimental measurements have been undertaken of the gas-matte-spinel and gas-slag-matte-spinel equilibria in the Cu–Fe–O–S–Si system at 1200°C and of 0.1 and 0.6 bar. The technique involved high temperature equilibration of sulfide-oxide mixtures on iron spinel support substrates, preservation of the equilibrium phases by rapid quenching, and direct compositional analysis of the phases using microanalysis techniques. The results, combined with previous data obtained at = 0.25 bar show the effects of sulphur dioxide partial pressure on the gas-matte-spinel and gas-slag-matte-spinel equilibria at fixed temperature and as a function of matte grade. For a given matte grade the concentration of dissolved copper in slag is found to decrease with increasing SO2 partial pressure.

A theoretical study on screening ionic liquids for SO2 capture under low SO2 partial pressure and high temperature

Most studies on SO2 capture using ionic liquids (ILs) have been carried out under mild conditions (e.g., about 1bar of SO2 and 20–40°C). However, these ILs only exhibit a fraction of their original SO2 uptake under harsher conditions, i.e., much lower SO2 partial pressure and evidently higher temperature (e.g., ≤0.2mbar of SO2 and ≥110°C). In this work, we screen 127 reported ILs for multi-molar SO2 absorption under the harsher conditions, covering nearly all the chemical space explored of the SO2 capturing IL. A unique cooperative anion-SO2 interaction mode with two forms (the insertion adduct and the ringed adduct) has been identified for branched anions, where SO2 acts as both acid and base to attack different reactive sites on anions. The simulated Langmuir isotherms further help screen out potential sorbents (amino-based branched singly charged anions with an Al atom as the center and carboxyl-based divalent anions) with both high overall capacity and high per-cycle absorption capacity. The energies of the reacting orbitals of the anions are linearly correlated to their SO2 binding energies. This work provides new insights for the design of task-specific ILs under harsh conditions.

SO2 absorption in highly efficient chemical solvent AChBr + Gly compared with physical solvent ChBr + Gly

Deep eutectic solvents (DESs) have been identified as optimal gas absorbents. A tertiary amine-containing task-specific DES AChBr+Gly and a conventional DES ChBr+Gly have been designed, prepared and used to capture SO2. It is found that absorption capacity of 3.74 and 2.97 mol of SO2 per mole of DES can be obtained by AChBr+Gly and ChBr+Gly, respectively, at 293.2 K and 1 bar. When SO2 partial pressure was decreased to 0.01 bar, the capacity decreased to 0.93 and 0.13 mol SO2 of per mole of AChBr+Gly and ChBr+Gly, respectively. Mechanism and thermodynamic studies show that absorption by former absorbent includes physisorption, quasi-chemisorption (a strong physisorption) and chemisorption, while absorption by later absorbent only includes physisorption and quasi-chemisorption. Two equations were first proposed for the description of SO2 absorption. In these equations, the physisorption capacity is correlated with Henry's law, and the quasi-chemisorption and chemisorption are correlated with the quasi-chemical equilibrium constant of halogen···SO2 interaction and the chemical equilibrium constant of tertiary amine···SO2 interaction, respectively. In addition, the corresponding enthalpy change, entropy change, and Gibbs energy change have been calculated and discussed.

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.