SO2 Separation Research Articles

Additive-free synthesis of house-of-card NaX zeolite for supporting amine: An efficient adsorbent for SO2 removal

The efficient adsorption of sulfur dioxide (SO2) is crucial for purifying exhaust gases, and zeolites are promising adsorbents due to their low cost and excellent stability. However, developing FAU-type zeolites with high adsorption capacities and selectivities remains challenging due to their narrow pores and limited adsorption sites. Herein, an additive-free synthesis strategy is proposed to facilely obtain NaX zeolites (X-HCL) with the house-of-card-like morphology. The hierarchical structure of X-HCL not only benefits the removal of SO2 through favorable spatial diffusion, but also promotes the loading of basic adsorption sites- [caprolactam] [tetrabutylammonium bromide] (CT) ionic liquid. The obtained CT/X-HCL adsorbent demonstrates remarkable SO2 adsorption capacity (10.58 mmol/g) and cyclic stability, as well as great selectivity of SO2/N2 (1673) and SO2/CO2 (219) due to the strong affinity of CT towards SO2. Moreover, co-feeding with water vapor benefits the adsorption of SO2 on CT/X-HCL owing to the enhanced chemisorption of hydrated CT for SO2. This research provides new insights into the construction of hierarchical zeolite for efficient adsorption and separation of SO2.

Porous Organic Polymers for Efficient and Selective SO2 Capture from CO2‐rich Flue Gas

AbstractThe quest for effective technologies to reduce SO2 pollution is crucial due to its adverse effects on the environment and human health. Markedly, removing a ppm level of SO2 from CO2‐containing waste gas is a persistent challenge, and current technologies suffer from low SO2/CO2 selectivity and energy‐intensive regeneration processes. Here using the molecular building blocks approach and theoretical calculation, we constructed two porous organic polymers (POPs) encompassing pocket‐like structures with exposed imidazole groups, promoting preferential interactions with SO2 from CO2‐containing streams. Markedly, the evaluated POPs offer outstanding SO2/CO2 selectivity, high SO2 capacity, and an easy regeneration process, making it one of the best materials for SO2 capture. To gain better structural insights into the notable SO2 selectivity of the POPs, we used dynamic nuclear polarization NMR spectroscopy (DNP) and molecular modelling to probe the interactions between SO2 and POP adsorbents. The newly developed materials are poised to offer an energy‐efficient and environment‐friendly SO2 separation process while we are obliged to use fossil fuels for our energy needs.

Porous Organic Polymers for Efficient and Selective SO2 Capture from CO2-rich Flue Gas.

The quest for effective technologies to reduce SO2 pollution is crucial due to its adverse effects on the environment and human health. Markedly, removing a ppm level of SO2 from CO2-containing waste gas is a persistent challenge, and current technologies suffer from low SO2/CO2 selectivity and energy-intensive regeneration processes. Here using the molecular building blocks approach and theoretical calculation, we constructed two porous organic polymers (POPs) encompassing pocket-like structures with exposed imidazole groups, promoting preferential interactions with SO2 from CO2-containing streams. Markedly, the evaluated POPs offer outstanding SO2/CO2 selectivity, high SO2 capacity, and an easy regeneration process, making it one of the best materials for SO2 capture. To gain better structural insights into the notable SO2 selectivity of the POPs, we used dynamic nuclear polarization NMR spectroscopy (DNP) and molecular modelling to probe the interactions between SO2 and POP adsorbents. The newly developed materials are poised to offer an energy-efficient and environment-friendly SO2 separation process while we are obliged to use fossil fuels for our energy needs.

A stable Zr(IV)-MOF for efficient removal of trace SO2 from flue gas in dry and humid conditions

Obtaining suitable adsorbents for selective separation of SO2 from flue gas still remains an important issue. A stable Zr(IV)-MOF (Zr-PTBA) can be conveniently synthesized through the self-assembly of a tetracarboxylic acid ligand (H4L = 4,4',4'',4'''-(1,4-phenylenebis(azanetriyl))tetrabenzoic acid) and ZrCl4 in the presence of trace water. It exhibits a three-dimensional porous structure. The BET surface area is 1112.72 m2/g and the average pore size distribution focus on 5.9, 8.0 and 9.3 Å. Interestingly, Zr-PTBA shows selective adsorption of SO2. The maximum uptake reaches 223.21 cm3/g at ambient condition. While it exhibits lower adsorption uptake of CO2 (30.50 cm3/g) and hardly adsorbs O2 (2.57 cm3/g) and N2 (1.31 cm3/g). Higher IAST selectivities of SO2/CO2 (21.9), SO2/N2 (912.7), SO2/O2 (2269.9) and SO2/CH4 (85.0) have been obtained, which reveal its’ excellent gas separation performance. Breakthrough experiment further confirms its application for flue gas deep desulfurization both in dry and humid conditions. Furthermore, the gas adsorption results and mechanisms have also been studied by theoretical calculations.

Preparation of UiO-66-type adsorbents for the separation of SO2 from flue gas

Preparation of UiO-66-type adsorbents for the separation of SO2 from flue gas

A molecular simulation study on the adsorption and separation performance of carbon nanotubes for SO2 in flue gas

To control the emission of SO2 from flue gas into the atmosphere while considering the capture and collection of greenhouse gas CO2, the adsorption behavior of a binary mixture of SO2 and other gases in flue gas (O2/N2/H2O/CO[Formula: see text] in (10, 10) carbon nanotube (CNT) was simulated using grand canonical Monte Carlo (GCMC) simulation. The adsorption and separation performance of SO2 in CNTs with a diameter range of 0.81–1.63 nm for the five-component mixture gas was also analyzed. The findings suggest that the adsorption and separation of SO2 are primarily influenced by CO2 (reduction of adsorption capacity by about 50%, separation coefficient of SO2/CO2 is lowest) with this effect being more pronounced under high pressure. Meanwhile, it was observed that CNTs with larger pipe diameters exhibit higher SO2 adsorption capacity, but relatively lower SO2/CO2 selectivity and lower stability. On the other hand, CNTs with smaller diameters have relatively lower adsorption capacity for SO2, but exhibit good selectivity and stability (under different pressure) for SO2/CO2. Based on the statistical analysis of SO2 adsorption capacity and SO2/CO2 selectivity, it was determined that (6, 6) CNT with a diameter of 0.81[Formula: see text]nm can exhibit excellent SO2 adsorption and separation performance at atmospheric pressure, while appropriate large diameter CNTs should be selected for flue gas treatment under high pressure.

Molecular Simulation of SO2 Separation and Storage Using a Cryptophane-Based Porous Liquid.

A theoretical molecular simulation study of the encapsulation of gaseous SO2 at different temperature conditions in a type II porous liquid is presented here. The system is composed of cage cryptophane-111 molecules that are dispersed in dichloromethane, and it is described using an atomistic modelling of molecular dynamics. Gaseous SO2 tended to almost fully occupy cryptophane-111 cavities throughout the simulation. Calculations were performed at 300 K and 283 K, and some insights into the different adsorption found in each case were obtained. Simulations with different system sizes were also studied. An experimental-like approach was also employed by inserting a SO2 bubble in the simulation box. Finally, an evaluation of the radial distribution function of cryptophane-111 and gaseous SO2 was also performed. From the results obtained, the feasibility of a renewable separation and storage method for SO2 using porous liquids is mentioned.

Multiscale Co‐Assembly to Meso‐Macroporous Foamed Single‐Crystal Metal–Organic Frameworks for the Supported Capture of Sulfur Dioxide

AbstractThe introduction of enlarged and interconnected nanochannels into metal–organic frameworks (MOFs) overcome their micropore size restriction, enhances mass transportation, and improves the accessibility of anchored metal clusters. Herein, foamed Ce‐MOF single crystals (F‐Ce‐MOF‐SC‐x) designed from a multiscale co‐assembly is reported in the presence of a copolymer template and 1,3,5‐trimethylbenzene as a structural regulator. The resultant F‐Ce‐MOF‐SC‐x possessed well‐defined microporous tandem‐ordered meso‐macroporous foams with superior connectivity and versatile Ce‐defective unsaturated sites (Ce‐DUS). F‐Ce‐MOF‐SC‐x is applied as a stable carrier for anchoring polytertiary amines (PA) via coordination interactions with Ce‐DUS. Owing to the superior ability of PA to recognize SO2, the resultant F‐Ce‐MOF‐SC‐x@yPA delivers exceptional performance in terms of the high‐temperature reversible adsorption and separation of SO2, including a remarkable capacity for SO2, spectacular selectivity for SO2/CO2/N2, an ultrafast adsorption equilibrium rate, and stability for 50 cycles. These characteristics are outstanding among those of MOFs and superior to those of many reported SO2 adsorbents.

Fabrication of Pillar-Cage Fluorinated Anion Pillared Metal-Organic Frameworks via a Pillar Embedding Strategy and Efficient Separation of SO2 through Multi-Site Trapping.

Flue gas desulfurization is crucial for both human health and ecological environments. However, developing efficient SO2 adsorbents that can break the trade-off between adsorption capacity and selectivity is still challenging. In this work, a new type of fluorinated anion-pillared metal-organic frameworks (APMOFs) with a pillar-cage structure is fabricated through pillar-embedding into a highly porous and robust framework. This type of APMOFs comprises smaller tetrahedral cages and larger icosahedral cages interconnected by embedded [NbOF5]2- and [TaOF5]2- anions acting as pillars. The APMOFs exhibits high porosity and density of fluorinated anions, ensuring exceptional SO2 adsorption capacity and ultrahigh selectivity for SO2/CO2 and SO2/N2 gas mixtures. Furthermore, these two structures demonstrate excellent stability towards water, acid/alkali, and SO2 adsorption. Cycle dynamic breakthrough experiments confirm the excellent separation performance of SO2/CO2 gas mixtures and their cyclic stability. SO2-loaded single-crystal X-ray diffraction, Grand canonical Monte Carlo (GCMC) simulations combined with density functional theory (DFT) calculations reveal the preferred adsorption domains for SO2 molecules. The multiple-site host-guest and guest-guest interactions facilitate selective recognition and dense packing of SO2 in this hybrid porous material. This work will be instructive for designing porous materials for flue gas desulfurization and other gas-purification processes.

Deep eutectic solvent-based blended membranes for ultra-super selective separation of SO2

SO2 is a major atmospheric pollutant leading to acid rain and smog. As a new generation of green solvents, deep eutectic solvents (DESs) have been widely investigated for gas capture. Nevertheless, studies on DES-based membranes for SO2 separation are yet minimal. Herein, we devised polymer/DES blended membranes comprising 1-butyl-3-methyl-imidazolium bromide ([Bmim]Br)/diethylene glycol (DEG) DES and poly (vinylidene fluoride) (PVDF), and these membranes were firstly used for selective separation of SO2 from N2 and CO2. The permeability of SO2 reaches up to 17480 Barrer (0.20 bar, 40 ºC) in PVDF/DES blended membrane containing 50 wt% of [Bmim]Br/DEG (2:1), with ultrahigh SO2/N2 and SO2/CO2 selectivity of 3690 and 211 obtained, respectively, far exceeding those in the state-of-the-art membranes reported in literature. The highly-reversible multi-site interaction between SO2 and [Bmim]Br/DEG DES was revealed by spectroscopic analysis. Furthermore, the PVDF/DES blended membrane was also able to efficiently and stably separate SO2/CO2/N2 (2.5/15/82.5%) mixed gas for at least 100 h. This work demonstrates for the first time that [Bmim]Br-based DESs are very efficient media for membrane separation of SO2. The easy preparation, low cost and high performance enable polymer/DES blended membranes to be promising candidates for flue gas desulfurization.

Evaluating diethanolammonium chloride as liquid solvent for gas separation from experiments and theoretical calculations

AbstractThis study explored diethanolammonium chloride ([DEA]Cl) as a potential ionic liquid from low‐cost and commercial ones for gas separation. There are three kinds of functional sites in [DEA]Cl: acidic NH2+, hydrogen‐bond OH, and nucleophilic Cl−. The separation of NH3/N2/H2, SO2/CO2/N2, and H2S/CO2/CH4 was considered, because the three mixtures are extensively involved in many industrial processes. The experimental results demonstrated that [DEA]Cl exhibited excellent ability to separate the mixture of NH3/N2/H2. The [DEA]Cl also exhibited the proper capacity to separate SO2/CO2/N2, but the capacity of [DEA]Cl for the separation of H2S/CO2/CH4 was inferior. The theoretical calculations revealed that NH2+ and OH worked synergistically to contribute to the ability of [DEA]Cl for excellent separation of NH3 from NH3/N2/H2, with Cl− contributing to the proper separation of SO2 from SO2/CO2/N2. This study provides experimental and theoretical basis for the industrial application of [DEA]Cl in the area of gas separation.

A novel robust phosphate-functionalized metal–organic framework for deep desulfurization at wide temperature

The need to decrease environmental pollution, reduce energy consumption and produce high-purity chemicals has become an increasingly important driving force for sulfur dioxide (SO2) capture. The efficient capture of low concentrations of SO2, a highly corrosive acid gas that is not typically present in high concentrations in industrial settings, is a major challenge. Herein, a novel phosphate-functionalized metal–organic framework, ZU-801, is designed with precisely controlled pore sizes and chemical environment to achieve excellent adsorption capacity for SO2 (1.44 mmol g−1 at 0.002 bar, 2.00 mmol g−1 at 0.01 bar) and high IAST selectivities for SO2/CO2 (145), which provides great potential for selective capture of SO2. ZU-801 shows excellent stability to air, water, SO2, strong acid and strong base solutions, and it is thermally stable up to 733 K. Additionally, ZU-801 exhibits outstanding separation ability in removing SO2 from SO2/CO2 mixtures at temperature as high as 383 K or in humid environments. This work demonstrates the potential of designing ion-functionalized ultramicroporous materials with tailored pore sizes and porous chemical environments for efficient capture and separation of SO2 and sheds light on designing stable high-performance materials that operate at high temperatures.

Scalable and Depurative Zirconium Metal-Organic Framework for Deep Flue-Gas Desulfurization and SO2 Recovery.

Deep SO2 removal and recovery as industrial feedstock are of importance in flue-gas desulfurization and natural-gas purification, yet developing low-cost and scalable physisorbents with high efficiency and recyclability remains a challenge. Herein, we develop a viable synthetic protocol to produce DUT-67 with a controllable MOF structure, excellent crystallinity, adjustable shape/size, milli-to-kilogram scale, and consecutive production by recycling the solvent/modulator. Furthermore, simple HCl post-treatment affords depurated DUT-67-HCl featuring ultrahigh purity, excellent chemical stability, fully reversible SO2 uptake, high separation selectivity (SO2/CO2 and SO2/N2), greatly enhanced SO2 capture capacity, and good reusability. The SO2 binding mechanism has been elucidated by in situ X-ray diffraction/infrared spectroscopy and DFT/GCMC calculations. The single-step SO2 separation from a real quaternary N2/CO2/O2/SO2 flue gas containing trace SO2 is implementable under dry and 50% humid conditions, thus recovering 96% purity. This work may pave the way for future SO2 capture-and-recovery technology by pushing MOF syntheses toward economic cost, scale-up production, and improved physiochemical properties.

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.

Preparation of mixed matrix membrane with high efficiency SO2 separation performance by photosensitive modification and enhanced adsorption of metal–organic framework

Preparation of mixed matrix membrane with high efficiency SO2 separation performance by photosensitive modification and enhanced adsorption of metal–organic framework

Computational fluid dynamics comparison of prevalent liquid absorbents for the separation of SO2 acidic pollutant inside a membrane contactor

In recent years, the emission of detrimental acidic pollutants to the atmosphere has raised the concerns of scientists. Sulphur dioxide (SO2) is a harmful greenhouse gas, which its abnormal release to the atmosphere may cause far-ranging environmental and health effects like acid rain and respiratory problems. Therefore, finding promising techniques to alleviate the emission of this greenhouse gas may be of great urgency towards environmental protection. This paper aims to evaluate the potential of three novel absorbents (seawater (H2O), dimethyl aniline (DMA) and sodium hydroxide (NaOH) to separate SO2 acidic pollutant from SO2/air gaseous stream inside the hollow fiber membrane contactor (HFMC). To reach this goal, a CFD-based simulation was developed to predict the results. Also, a mathematical model was applied to theoretically evaluate the transport equations in different compartments of contactor. Comparison of the results has implied seawater is the most efficient liquid absorbent for separating SO2. After seawater, NaOH and DMA are placed at the second and third rank (99.36% separation using seawater > 62% separation using NaOH > 55% separation using DMA). Additionally, the influence of operational parameters (i.e., gas and liquid flow rates) and also membrane/module parameters (i.e., length of membrane module, hollow fibers’ number and porosity) on the SO2 separation percentage is investigated as another highlight of this paper.

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.

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.

COF-based MMMs with light-responsive properties generating unexpected surface segregation for efficient SO2/N2 separation

The purification of sulfur dioxide (SO2) from the flue gas is an urgent problem given its toxicity to humans and organisms and attendant environmental concerns. In this study, aiming at the separation of SO2, mixed matrix membranes (MMMs) are fabricated by incorporating covalent organic framework (COF) into Pebax 1657 polymer matrix. By strengthening the solubility-diffusion mechanism of SO2 gas molecules, SO2/N2 gas separation performance is investigated. Firstly, MMMs are fabricated by incorporating a porous framework material (TpPa-1) containing SO2 affinity groups into the Pebax 1657 matrix as a filler. Then the azo group (Azo) is introduced into the MMMs by the method of physical blending. The MMMs with light-responsive characteristic are fabricated by introducing TpPa-1 blended with pAAB into the Pebax 1657 polymer matrix. Secondly, the SO2/N2 separation performance of Pebax/TpPa-1 MMMs is improved with the increasing of filler loading. Specially, the Pebax/TpPa-1 membrane with 5 wt% exhibits the most excellent SO2/N2 separation performance with SO2 permeability of 1709 Barrer and SO2/N2 selectivity of 811. The MMMs overcome the trade-off effect and achieve enhancement of SO2 permeability and SO2/N2 selectivity simultaneously. Thirdly, both the SO2 permeabilities and SO2/N2 selectivities of Pebax/pAAB@TpPa-1-5% membrane exhibit regular and reversible changes under UV–Vis light-conversion conditions, indicating that MMMs containing Azo possesses dynamic light-responsive properties. Furthermore, TpPa-1 and pAAB repel each other in the membrane because both have negative charges, resulting in the forced surface segregation of COF in the Pebax/pAAB@TpPa-1 MMMs.