SO2 Absorption Research Articles

Trace SO2 Gas Capture in Stable 3D Viologen Ionic Porous Organic Framework Microsphere.

Eliminating trace sulfur dioxide (SO2) using nanoporous adsorbents is industrially preferred yet of great challenge due to the competitive adsorption of CO2. Herein, we reported a highly stable 3D viologen porous organic framework (Viologen-POF) microsphere via one pot polymerization reaction of 4,4'-bipyridine and tetrakis(4-(bromomethyl)phenyl)methane. Compared to the previously reported irregular POF particles, viologen-POF microsphere shows better mass transfer uniformity. Owing to the intrinsic separated positive and negative electric charges center in viologen-POF microspheres, it exhibits excellent SO2 selective capture performance, which can be collaboratively confirmed by static single-component gas adsorption, time-dependent adsorption rate, and multicomponent dynamic breakthrough experiments. Viologen-POF exhibits high SO2 absorption capacity (1.45 mmol g-1) at ultralow pressure of 0.002 bar and high SO2/CO2 selectivity of 467 at 298 K and 100 kPa (SO2/CO2, 10/90, v/v). The theoretical calculations based on density functional theory (DFT) and DMol3 modules in Material Studio (MS) were also performed to elucidate the adsorption mechanism of viologen-POF toward SO2 at the molecular level. This study represents a new type of viologen porous framework microsphere for trace SO2 capture, which will pave the way on the applications of ionic POF for toxic gas adsorption and separation.

Analysis of a marine scrubber operation with a combined analytical/AI-based method

This paper describes the performances of a marine SO2 absorption scrubber installed onboard a large Ro-Ro cargo ship. The study is based on the reconstruction of an extensive dataset from one-year continuous monitoring of the scrubber’s performances and operating conditions. The dataset has been interpreted with a conventional analytical, physical-mathematical, model for absorbers' rating and its combination with an Artificial Intelligence (AI) one. First, the analytical model has been used to provide a deterministic mathematical framework for the interpretation and the prediction of the scrubber’s performances in terms of absorbed SO2 molar flow and SO2 concentration at the scrubber exit. Then, data mining and AI techniques have been applied to develop an Artificial Neural Network able to predict the error between the actual SO2 concentration at the scrubber exit and the corresponding analytical model predictions. The final result is a combined model providing superior robustness and accuracy in the prediction of the scrubber performance while preserving a rationale for process design and operation. This interesting outcome suggests that the development of combined, or hybrid, Analytical/AI models can be a reliable and cost-effective way to improve chemical engineers' ability to design and control marine scrubbers, as well as other chemical equipment.

A model for the absorption rate in electrically charged droplets

Charged droplets are produced by electrosprays or sometimes generated by natural phenomena, and nowadays their application is also investigated as a tool for process intensification in heat and mass transfer processes typical of chemical engineering. This paper analyses the absorption of slightly soluble trace gases into electrically charged droplets: it reports a new mass transfer model taking into account the electrophoretic motion of gas molecules and the possible alteration of the interfacial properties induced by the imposed electric charges. The model is successfully validated against existing experiments on the absorption of SO2 into electrified water droplets. These experiments are useful both for the robustness of data available for the SO2-air-water system and for its significance in atmospheric chemistry and physics, and chemical engineering applications.Considering the same SO2-air-water system as a case study, the model predicts that the absorption rate for a droplet produced with a conventional electrospray is up to 42% faster than that of an uncharged droplet with the same size and morphology, while the electrophoretic drift provides an improvement of the gas-side mass transfer coefficient mainly for droplets finer than 500 µm.

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.

Acetylcholine-based deep eutectic solvents for highly efficient SO2 absorption, selective separation from CO2 and their mechanism

The development of deep eutectic solvents (DESs)-based absorbents for selective uptake of SO2 from CO2 (SO2/CO2, g/g) is of interest to flue-gas desulfurization (FGD). In this work, a series of DESs are designed through acetylcholine chloride (ACC) as hydrogen bond acceptor (HBA) and ethylene glycol (EG), 1,3-propylene glycol (1, 3-PDO), glycerol (Gly), polyethylene glycol 200 (PEG200) and triethylene glycol (TG) as hydrogen bond donors (HBDs). All the DESs display good thermal stability under 150 °C and competitive capacities of SO2. ACC/PEG200 (1:1) is remarkable due to their absorption capacity of SO2 to 3.5 mol/mol (P = 1.0 bar, T = 303.2 K). All DESs show excellent selectivity separation of SO2 from CO2 more than 100, for example, up to 335 in ACC/TG (1:1). In this work, the relative mechanism reveals that DESs absorption of SO2 combining physisorption and chemisorption via a reaction equilibrium thermodynamic model and theoretical calculation. Furthermore, ACC/TG (1:1) maintains the reversible absorption capacity of SO2 after five absorption/desorption cycles. Considering high SO2 absorption capacity, desired selectivity, and excellent recyclability, DESs in this study are considered recyclable green absorbers, which can be potentially applied to SO2 capture towards CO2 mixture.

Tunable and facile preparation of chelate-based ionic liquids for highly efficient SO2 separation under low concentration in flue gas

A strategy for facile preparation of chelate-based ionic liquids (ILs) by simple chelation was developed, where a series of chelate-based ILs with tunable functionalized anions (azole), cheap ligands (PEG400), and simple metal ions (Li+, Na+, and K+) were designed for SO2 capture under 2000 ppm in flue gas. Both the anion-tunable strategy and the fine-tuned strategy were used to explore the effect of anions, ligands, and metal ions. The experimental absorptions, spectroscopic investigations, and DFT calculations indicated that the process of SO2 capture was mostly based on the nucleophilic effect of electronegative N site toward SO2. Furthermore, the tuning of alkali metal ions was proved to have little influence on SO2 absorption. The ideal IL, [Na(PEG400)][Tetz], exhibited splendid available absorption capacity of SO2 (0.57 mol/mol), excellent selectivity (63 under 2000 ppm SO2/15% CO2), and outstanding reversibility, indicating good potential for industrial application.

Experimental and modelling approach to the design of chemical absorption columns with fast gas-liquid reaction: A case-study on flue-gas desulfurization with H2O2 oxidative solutions

In this work, we propose a methodology to approach the design of chemical absorption columns with fast gas-liquid reactions by an experimental and modelling study, which accounts for thermodynamic (solubility) data, mass-transfer phenomena, and the reaction kinetics contribution. As a reference case, the SO2 absorption in aqueous solution of H2O2 at different concentrations, which oxidizes SO2 to sulfuric acid, is considered. A lab-scale fed-batch bubble column is used to evaluate SO2 solubility dataset in absorbing solutions of distilled water containing different dosages of H2O2. A thermodynamic model is developed and validated in a Thermodynamic Flash block of ASPEN PLUS®, allowing to describe the experimental results with optimum agreement. For kinetic experiments, a lab-scale falling-film absorber is used to investigate both SO2 mass-transfer rates and the fundamental kinetic aspects of an absorption process with chemical reaction. The physical contribution to the mass-transfer rate is evaluated through a set of dedicated experiments, which allowed determining gas-side (kGa) and liquid-side (kLa) coefficients in the falling-film absorber. Subsequently, the Enhancement factor (EL) of the SO2 oxidative absorption is evaluated for the oxidizing reaction (SO2 + H2O2 → H2SO4) under the explored experimental conditions, using the equilibrium dataset and the mass transfer coefficients previously obtained. Finally, EL is correlated to the Hatta number (Ha) with the Danckwerts kinetic model as a pseudo-mth-nth-order non-reversible reaction type and the model kinetic parameters are calculated.

Hybrid Modeling and Real-time Predictive Scheduling of Wet Flue Gas Desulfurization for Energy Saving and Life Extension

Sulfur dioxide (SO2) is one of the most important air pollutants emitted by power plants and ironworks. To effectively remove SO2 from flue gas, wet flue gas desulfurization (WFGD) technology is widely adopted by most of China’s coal-fired power plants. However, one of the most important issues of WFGD is the relatively high energy consumption, with the main contribution from the power consumed by circulating pumps in the absorber. In this paper, hybrid modeling and real-time predictive scheduling of a wet flue gas desulfurization (WFGD) system for energy saving and life extension are proposed. The hybrid model is based on the mechanism of the SO2 absorption process and modified based on the operation data using a particle swarm optimization (PSO) algorithm. The prediction model can describe the SO2 absorption process well, and the root-mean-square error (RMSE) of the model is 2.20 mg/m3. Effects of parameters such as the inlet SO2 concentration, pH, flue gas flow rate, and combinations of circulating pumps on the outlet SO2 concentration are further explored. The optimal combination of circulating pumps under different conditions is calculated. Finally, a real-time predictive scheduling strategy is proposed and evaluated under different parameter settings. The system shows the best performance when the upper limit, the target of outlet SO2 concentration, and the lower limit are set to 30, 15, and 10 mg/m3, respectively. The energy consumption of the system is 2564.6 kW, which is 10.6% lower than that before optimization.

The Mid-infrared Molecular Inventory toward Orion IRc2

We present the first high spectral resolution mid-infrared survey in the Orion BN/KL region, covering 7.2–28.3 μm. With SOFIA/EXES, we target the enigmatic source Orion IRc2. While this is in the most prolifically studied massive star-forming region, longer wavelengths and molecular emission lines dominated previous spectral surveys. The mid-infrared observations in this work access different components and molecular species in unprecedented detail. We unambiguously identify two new kinematic components, both chemically rich with multiple molecular absorption lines. The “blue clump” has v LSR = −7.1 ± 0.7 km s−1, and the “red clump” has 1.4 ± 0.5 km s−1. While the blue and red clumps have similar temperatures and line widths, molecular species in the blue clump have higher column densities. They are both likely linked to pure rotational H2 emission also covered by this survey. This work provides evidence for the scenario that the blue and red clumps are distinct components unrelated to the classic components in the Orion BN/KL region. Comparison to spectroscopic surveys toward other infrared targets in the region show that the blue clump is clearly extended. We analyze, compare, and present in-depth findings on the physical conditions of C2H2, 13CCH2, CH4, CS, H2O, HCN, , HNC, NH3, and SO2 absorption lines and an H2 emission line associated with the blue and red clumps. We also provide limited analysis of H2O and SiO molecular emission lines toward Orion IRc2 and the atomic forbidden transitions [Fe ii], [S i], [S iii], and [Ne ii].

Reversible sulfur dioxide capture by amino acids containing a single amino group at low sulfur dioxide concentrations.

SO2, an air pollutant, is harmful to human health and causes air pollution; therefore, numerous studies have focused on the development of SO2 control technologies. Although limestone- and ammonia-based absorbents have been widely used in wet desulfurization, they are difficult to regenerate and do not enable the recycling of SO2, which is a useful resource. Recently, amino acids have attracted attention as reversible SO2 absorbents because they are eco-friendly and have excellent reactivity with SO2, as well as high regeneration performance. Glycine, L-alanine, β-alanine, 4-aminobutyric acid, 5-aminovaleric acid, and 6-aminohexanoic acid were analyzed to investigate the relationship between SO2 absorption and the amino acid molecular structure using the simulated actual flue gas (200 ppmv SO2 + 13% CO2 in N2 balance). The SO2 absorption of amino acids (with the molecular structure of glycine and alkyl chains of various lengths) improved as the alkyl chain length increased, possibly owing to a decrease in the inductive effect in the molecular structure of the amino acid. Furthermore, 13C-nuclear magnetic resonance spectroscopy was conducted to analyze the SO2 absorption reaction mechanism (including the possible generation of irreversible species), and experiments involving a number of consecutive absorption-desorption cycles were used to confirm the reusability of the amino acids. The tested amino acids exhibited higher cyclic capacities compared to those of deep eutectic solvents and ionic liquids reported in the literature, thereby exhibiting excellent potential as SO2 absorbents. Thus, this study can guide the future design and development of eco-friendly SO2 absorbents.

Does side chain group of anion affect absorption of SO2 in amino acid ionic liquid?

1-propyl-3-methylimidazolium cation with glycinate, alaninate, valinate, leucinate, cysteinate, and serinate as amino acid anions were selected as the counter ions to study the effect of the side chain group of anions on the absorption of SO2. One can see that the enlargement of the alkyl group from glycinate to leucinate leads to a slight decrease in gas absorption interaction energy; changing the side chain group to the methyl thiol (cysteinate) and methyl alcohol (serinate), drastically changes gas nteraction energy with the same trend in absorption Gibbs energy. In addition, the charge transfer between the imidazolium-based amino acid ionic liquid and captured gas as well as the distance between anion and the absorbed SO2 gas in glycinate is the lowest which can be the main reason for being the most favorable absorbent in the present study. A deep insight into the nature of interactions sheds light on the difference in the distribution of van der Waals (vdW) interaction that plays the essential role in the SO2 capturing; in other words, vdW distribution in the glycinate system is concentrated and clear while in the other systems, this distribution is observed in a scattered manner.

Cation functional group effect on SO2 absorption in amino acid ionic liquids.

Introduction: The effect of the functional group of the cation on SO2 acidic gas absorption by some designed amino acid ionic liquids (AAILs) was studied. Methods: An isolated pair of glycinate anion and pristine imidazolium-based cation, as well as decorated cation functionalized by hydroxyl (OH), amine (NH2), carboxylic acid (COOH), methoxy (OCH3), and acetate (CH3COO) groups, were structurally optimized by density functional theory (DFT) using split-valence triple-zeta Pople basis set. Results and Discussion: The binding and Gibbs free energy (ΔGint) values of SO2 absorption show the AAIL functionalized by the COOH group is the most thermodynamically favorable green solvent and this functional group experiences the closest distance between anion and captured SO2 and vice versa in the case of cation … SO2 which may be the main reason for being the best absorbent; in addition, the highest net charge-transfer amount of SO2 is observed. Comparing the non-covalent interaction of the systems demonstrates that the strongest hydrogen bond between captured gas and anion, as well as π-hole, and van der Waals (vdW) interaction play critical roles in gas absorption; besides, the COOH functional group decreases the steric effect while the CH3COO functional group significantly increases steric effect after absorption that declines the hydrogen bond.

Study of SO2 measurement based on a dual optical path Fabry-Perot correlation spectroscopy.

This paper investigates a method for measuring SO2 concentration using Fabry-Perot interferometer correlation spectroscopy. In this method, the experimental system is designed as a separated beam, with the beam entering the F-P cavity at two incidence angles simultaneously to match the peak and valley positions of the SO2 absorption cross-section. The system achieves a 2σ detection limit of 28.2 ppm·m(15 cm) at a sampling frequency of 10 Hz. An outfield comparison experiment with the differential optical absorption spectroscopy method shows good agreement for the simultaneous measurement of SO2 concentration from sulfur combustion, with a correlation coefficient of R2 = 0.93. This study introduces a non-dispersive, highly accurate, and fast gas detection technique.

Highly Selective Absorption of Low-Concentration SO2 over CO2 in Flue Gas through Cation-Tunable Protic Ionic Liquids

A cation-tunable strategy was reported for highly selective absorption of low-concentration SO2 over CO2 in flue gas, where the cation had a significant effect on the selectivity. The absorption capacity and selectivity of low-concentration SO2 by various ionic liquids (ILs) were investigated; therein, protic IL [THEEDH][Tetz] showed the best selectivity of 80.6 (120.4) under the atmosphere of 2000 ppm of SO2 and 15% CO2. Nuclear magnetic resonance spectroscopic investigations and quantum chemical calculations indicated that the effect of the cation on the electronegativity of the anion was significant, leading to an obvious increase in selectivity. This cation-tunable IL offered a significant improvement in the selective absorption of SO2 compared to traditional ILs, indicating its potential in acid gas separation in industry.

Densities, viscosities and specific heat capacities of deep eutectic solvents composed of ethanediol + betaine and ethanediol + L-carnitine for absorbing SO2

Two types of deep eutectic solvents (DESs) based on ethanediol and betaine /L-carnitine at different molar ratios from 3:1 to 5:1 are functional for absorbing low-concentration SO2. Their densities, viscosities and specific heat capacities, which are important for their application in SO2 absorption, have been measured at temperatures from 293.2 K to 333.2 K and SO2 contents from 0 to 0.1501 g SO2/g DES. The results indicate that an increase in temperature can decrease the densities and viscosities of the DESs, but increase the specific heat capacities of the DESs. An increase in the content of SO2 absorbed in the DESs can increase the densities and viscosities of the DESs. The increase of ethanediol content in the DESs can decrease the densities and viscosities of the DESs, but increase the specific heat capacities of the DESs. The densities of the DESs were correlated using first-order empirical equations as a function of temperature and SO2 content, and the average absolute relative deviations (AARDs) of the density data from the correlations were not more than 0.08 %. The viscosities of the DESs as a function of temperature were correlated using a VFT equation, and the AARDs of the viscosity data from the correlations were not more than 0.8 %. The specific heat capacities of the DESs as a function of temperature were correlated well using a second-order empirical equation, and the AARDs of the specific heat capacities data from the correlations were not more than 0.22 %.

In Situ Photoacoustic Detection System for SO2 in High-Pressure SF6 Buffer Gas Using UV LED.

Sulfur dioxide (SO2) is a key indicator for fault diagnosis in sulfur hexafluoride (SF6) gas-insulated equipment. In this work, an in situ photoacoustic detection system using an ultraviolet (UV) LED light as the excitation source was established to detect SO2 in high-pressure SF6 buffer gas. The selection of the SO2 absorption band is discussed in detail in the UV spectral regions. Based on the result of the spectrum selection, a UV LED with a nominal wavelength of 285 nm and a bandwidth of 13 nm was selected. A photoacoustic cell, as well as a high-pressure sealed gas vessel containing it, were designed to match the output optical beam and to generate a PA signal in the high-pressure SF6 buffer gas. The performance of the proposed system was assessed in terms of linearity and detection limit. An SO2 detection limit (1σ) of 0.17 ppm was achieved. Additionally, a correction method was supplied to solve PA signal derivation induced by pressure fluctuation. The method can reduce the derivation from about 5% to 1% in the confirmation experiment.

Adsorption behavior of small molecule on monolayered SiAs and sensing application for NO2 toxic gas

Owing to the ultrahigh surface-to-volume ratio and excellent carrier transport property, two-dimensional (2D) materials are regarded as most promising candidates for gas sensor with high sensitivity. Using the first principles calculations, we have examined the adsorption behavior of typical gas molecules on the 2D SiAs monolayer. The monolayered SiAs could sensitively response physical absorption of SO2, O2, NO, and NO2 molecule due to substantial charge transfer, and these molecules have introduced various defective states around the Fermi level. Most importantly, the quantum transport calculations have shown that the I–Vb behavior is substantially enhanced due to the toxic gas absorption. Specifically, striking improvement on transport performance is induced by NO2 absorption due to remarkable charge transfer, making the SiAs monolayer a promising candidate to selectively and sensitively detect NO2 molecule. Furthermore, we have shown that the work function and the charge transfer can be manipulated by strain, allowing potential application for anisotropic electronics. Our findings could be helpful to the potential application of the NO2 toxic detection in future.

Functionalized imidazole–alkanolamine deep eutectic solvents with remarkable performance for low-concentration SO2 absorption

SO2 generated by manufacturing facilities, power plants, and ships must be removed because it adversely affects human health even at low concentrations. Flue gas desulfurization (FGD), which is a conventional method for removing SO2, causes additional environmental issues, including non-recyclable reactants and wastewater. In this study, deep eutectic solvents (DESs) functionalized to absorb SO2 at low concentrations are developed as alternatives for FGD. The physical properties, including thermal stability, of the prepared DESs were analyzed, and an enhancement in thermal stability, attributed to DES formation, was verified. Additionally, absorption capacities and reusability under 500 ppm SO2 were analyzed through experiments involving the absorption, desorption, and reabsorption cycles. The thermal stabilities of the as-prepared DESs significantly improved compared to those of the precursors. In addition, the prepared absorbents exhibited remarkable SO2 absorption performance owing to multi-site absorption, with values of 0.992, 0.684, and 0.628 g SO2/g absorbent, which are more than twice higher than those reported in previous studies. Finally, the absorption mechanism was confirmed using 1H nuclear magnetic resonance and Fourier Transform Infrared spectroscopy. Owing to the exceptional performance of the proposed absorbents, this study is expected to make a significant contribution to the alternative technology research on SO2 separation.

Desulfurization characteristics of limestone slurry with added organic acid

In this study, a desulfurization experiment was performed in a bubbling reactor to investigate the effects of adding organic acids, such as formic, acetic, propionic, lactic, oxalic and adipic acid, to limestone slurries. The limestone slurries added these organic acids were referred to as FAS, AAS, PAS, LAS, OAS, and ADS, respectively. Flue-gas desulfurization characteristics varied with the acidity of organic acid additives. The T99 of slurries increased with pKa of the organic acids because slurry pH was high in the early phase of absorption which increased the time to reach the slurry pH range (4.1–4.6) required for the T99 end. During SO2 absorption, the sulfate ion fraction was ≥0.5 in PAS, AAS, and ADS, with pKa > 4, but <0.5 in LAS and FAS with pKa < 4. PAS, AAS, and ADS supported the oxidation of sulfite ions, whereas LAS and FAS suppressed it. [H+] × [A−] increases with decreasing pKa of organic acids. Therefore, [H+]slurry and [A−]slurry in the slurry may be engaged in the oxidation of sulfite ions; consequently, increasing [H+] × [A−] inhibited the oxidation of sulfite ions. The sulfate ion fraction affected gypsum dehydration following completion of SO2 absorption. After drying at 60 °C, LAS and FAS (sulfate ion fraction < 0.5) formed only gypsum, whereas PAS, AAS, and ADS (sulfate ion fraction ≥ 0.5) formed both gypsum and anhydrite. Accelerated oxidation of sulfite ions with sulfate ion fraction ≥ 0.5 during slurry drying after reaction completion produced a sulfuric acid solution with a high sulfate ion concentration, which reduced the temperature of gypsum dehydration.

Absorption of SO2 by deep eutectic solvents composed of EmimCl and dihydric alcohols: Thermodynamic and absorption mechanism studies

As a class of green absorbents, deep eutectic solvents (DESs) show excellent application potential in the field of SO2 separation. In this work, three DESs composed of 1-ethyl-3-methylimidazolium chloride (EmimCl) and polyethylene glycol 200 (PEG 200) or tetraethylene glycol (TeEG) in a specific molar ratio are used for SO2 absorption. TeEG-EmimCl (1:2) exhibits the best SO2 adsorption capacity with up to 13.25 mol·kg−1 and good ideal selectivity of 29.9 for SO2 to CO2 at 298.2 K and 1.0 bar. To study the absorption behavior of SO2, the thermodynamic parameters of SO2 absorption, including equilibrium constant (K0), enthalpy change (ΔHm), entropy change (ΔSm), and Gibbs free energy change (ΔGm), are calculated by combining the solubility data with Henry’s law and reaction equilibrium equation (RETM). Further SO2 absorption mechanism by FTIR and NMR spectroscopy suggested that there is mainly physical interaction between SO2 and DESs, making the TeEG-EmimCl (1:2) with excellent regeneration cycle performance. These DESs reported in the current work can be used as the attractive absorbents for SO2 absorption due to their excellent absorption performance and good reversibility.