Chlorine Chemistry Research Articles

Sustainable synthesis of fine chemicals and polymers using industrial chlorine chemistry.

To achieve sustainable resource circulation, preparation of reactive species from stable compounds is unavoidable. Chlorine chemistry is an eco-friendly methodology to address this demand. Chlorine is industrially produced from sodium chloride (NaCl), an abundant natural resource in oceans. Chlorine provides various chemical products, including polymers, through chlorination and subsequent conversion reactions. In these reactions, the byproducts are usually hydrogen chloride, which is commercially utilized as hydrochloric acid and is finally neutralized to NaCl after use. Therefore, chlorine chemistry enables fine chemical production from NaCl with almost no wastage. This review provides an overview of the synthesis of fine chemicals and polymers using chlorine chemistry and discusses them from the perspective of sustainability.

Constructing Ru-Co2P Lewis Acid-Base Pairs to Prompt Hydrogen Evolution Reaction in Alkaline Seawater Electrolyte.

Seawater electrolysis is an ideal approach to generating green hydrogen. Nevertheless, the sluggish kinetics of water dissociation and the detrimental chlorine chemistry environment are serious obstructions for industrial applications. Herein, constructing unique (Co) Lewis acid and (Ru-P) base pair sites in Ru-Co2P decorated on nitrogen and phosphorus co-doped carbon (Ru-Co2P/NPC) significantly optimizes the energy barrier of water dissociation and enhances the anti-corrosive ability for alkaline seawater splitting. As expected, the optimal Ru-Co2P/NPC-2 exhibits exceptional hydrogen evolution reaction (HER) performances with overpotentials as low as 22.0 and 26.0mV to derive 10 mAcm-2 and operate steadily (@ 50 mAcm-2) over 30 h in alkaline and alkaline seawater electrolytes. The experimental and theoretical results elucidate that Co acting as Lewis acid sites prompts the water adsorption and breakage of the H─O bond, whereas Ru-P as Lewis base sites facilitates the hydrogen desorption in alkaline media. Furthermore, modulated chemical microenvironments can be beneficial to hinder chloride corrosion on the active sites of catalysts. This work sheds light on the rational construction of a highly efficient electrocatalyst for alkaline HER in seawater.

Interfacial engineering to create ionically bonded heterostructures for ampere-level chlorine-free anodic reactions in seawater

Production of hydrogen directly from seawater can be a sustainable method; however, corrosive and competitive chlorine chemistry at the anode interfere with the oxygen evolution reaction (OER). Special materials need to be designed to avoid chlorine chemistry; hence, a two-dimensional metal-organic framework@WO3.B2O3 (MOF@WB) heterostructure with ionic bonds was engineered, which can deliver ~10x better performance and is ~65% more economical than commercial IrO2 for OER. Our system is stable in alkaline seawater for over 1000h without chlorine evolution and remains functional even after sitting idle for 5 days, making it integrable with renewable power sources. The catalyst also operated stably at the industrial-scale current density of 1.58Acm-2 for over 100h with 99% performance retention in alkaline seawater. Theoretical calculations reveal that B assists in the adsorption of the MOF on the WO3 substrate via the creation of ionic bonds, resulting in optimized surface geometries for selective reactions, which safeguard against chlorine chemistry. B2O3 helps modulate the B-OH sites at the interface via B-O-B bond hydrolysis, activating the OER kinetics, hence providing an ideal platform for effective direct seawater catalysis to produce low-cost hydrogen.

Contrasting Chlorine Chemistry on Volcanic and Wildfire Aerosols in the Southern Mid‐Latitude Lower Stratosphere

Contrasting Chlorine Chemistry on Volcanic and Wildfire Aerosols in the Southern Mid‐Latitude Lower Stratosphere

Significant chlorine emissions from biomass burning affect the long-term atmospheric chemistry in Asia.

Biomass burning (BB) is a major source of trace gases and particles in the atmosphere, influencing air quality, radiative balance, and climate. Previous studies have mainly focused on the BB emissions of carbon and nitrogen species with less attention on chlorine. Reactive chlorine chemistry has significant effects on atmospheric chemistry and air quality. However, quantitative information on chlorine emissions from BB, particularly the long-term trend and associated atmospheric impacts, is limited both on regional and global scales. Here, we report a long-term (2001-2018) high-resolution BB emission inventory for the major chlorine-containing compounds (HCl, chloride, and CH3Cl) in Asia based on satellite observations. We estimate an average of 730 Gg yr-1 chlorine emitted from BB activity in Asia, with China contributing the largest share at 24.2% (177 Gg yr-1), followed by Myanmar at 18.7% and India at 18.3%. Distinct seasonal patterns and significant spatial and interannual variability are observed, mainly driven by human-mediated changes in agricultural activity. By incorporating the newly developed chlorine emission inventory into a global chemistry-climate model (CAM-Chem), we find that the BB-chlorine emissions lead to elevated levels of HCl and CH3Cl (monthly average up to 2062 and 1421 parts per trillion by volume (pptv), respectively), subsequently resulting in noticeable changes in oxidants (up to 3.1% in O3 and 17% in OH radicals). The results demonstrate that BB is not only a significant source of air pollutants but also of oxidants, suggesting a larger role of BB emissions in the atmospheric chemistry and oxidation process than previously appreciated. In light of the projected increase in BB activity toward the end of the century and the extensive control of anthropogenic emissions worldwide, the contribution of BB emissions may become fundamental to air quality composition in the future.

Potential environmental impact of the chlorine-containing disinfectants usage during the COVID-19

Chlorine radicals (Cl) play a crucial role in atmospheric chemistry. The COVID-19 (coronavirus disease 2019) pandemic significantly increased the use of chlorine-containing disinfectants in China, leading to enhanced emissions of chlorine gas (Cl2) and hypochlorous acid (HOCl). In this study, we use the Community Multiscale Air Quality (CMAQ) model with updated chlorine chemistry to evaluate the potential air quality impact of chlorine emissions from disinfectant usage during February 2020, a month with a large outbreak of COVID-19 in mainland China. Results indicate that during the pandemic, there was a sharp increase of reactive chlorine emissions, with Cl2 and HOCl emissions reaching 773.9 t and 5913.1 t, making 3 times increase. The emissions of chlorine enhanced atmospheric oxidation capacity (AOC) through the oxidation of VOC by Cl and OH, with the average enhancement in Shanghai, Beijing and Wuhan areas reaching 4.6% ± 1.8%, 10.3% ± 6.6% and 7.4% ± 4.6%, respectively. Consequently, the use of chlorine-containing disinfectants may have contributed to observed increases in the monthly average of the maximum daily 8-h average ozone (MDA8 O3) and fine particulate matter (PM2.5) concentrations by up to 1.5 ppbv (5%) and 1.7 μg/m3 (1%), respectively. Especially, the maximum hourly increase values of O3 and PM2.5 concentrations were 4.8 ppbv and 11.4 μg/m³, 2.5 ppbv and 4.5 μg/m³ in Beijing and Wuhan, respectively. These results indicate that chlorine emissions from the widespread use of disinfectants have had a significant impact on air quality in certain regions (Beijing and Wuhan) and during specific periods (9:00∼12:00).

Persistent Organochlorine Pollutants in High-Moor Peats of the Arkhangelsk Region

The results of a study of the contamination of a peat deposit of a representative oligotrophic bog complex (Primorsky district of the Arkhangelsk region) with persistent organic pollutants of polychlorobenzenes and pentachlorophenol are presented. Data on the quantitative content, composition and depth distribution of organochlorine pollutants have been obtained. The maximum amounts of polychlorobenzenes, pentachlorophenol and other chlorinated phenols in the upper 40-centimeter aerated layer of the peat deposit, the formation of which coincides with the period of “chlorine chemistry”, have been established. In addition, the presence of polychlorobenzenes and pentachlorophenol was revealed in all horizons of the upper meter layer of the peat deposit, which indicates their vertical migration in the peat body.

Energy-saving hydrogen production by seawater electrolysis coupling tip-enhanced electric field promoted electrocatalytic sulfion oxidation

Hydrogen production by seawater electrolysis is significantly hindered by high energy costs and undesirable detrimental chlorine chemistry in seawater. In this work, energy-saving hydrogen production is reported by chlorine-free seawater splitting coupling tip-enhanced electric field promoted electrocatalytic sulfion oxidation reaction. We present a bifunctional needle-like Co3S4 catalyst grown on nickel foam with a unique tip structure that enhances the kinetic rate by improving the current density in the tip region. The assembled hybrid seawater electrolyzer combines thermodynamically favorable sulfion oxidation and cathodic seawater reduction can enable sustainable hydrogen production at a current density of 100 mA cm−2 for up to 504 h. The hybrid seawater electrolyzer has the potential for scale-up industrial implementation of hydrogen production by seawater electrolysis, which is promising to achieve high economic efficiency and environmental remediation.

Sandmeyer Chlorosulfonylation of (Hetero)Aromatic Amines Using DABSO as an SO2 Surrogate.

Sulfonyl chlorides not only play a crucial role in protecting group chemistry but also are important starting materials in the synthesis of sulfonamides, which are in-demand motifs in drug discovery chemistry. Despite their importance, the number of different synthetic approaches to sulfonyl chlorides is limited, and most of them rely on traditional oxidative chlorination chemistry from thiol precursors. In this report, we disclose a novel Sandmeyer-type sulfonyl chloride synthesis from feedstock anilines and DABSO, used as a stable SO2 surrogate, in the presence of HCl and a Cu catalyst. The method works on a wide range of anilines and allows for the isolation of the sulfonyl chloride after aqueous workup or its direct conversion into the sulfonamide by simple addition of an amine after the completion of the Sandmeyer reaction. The scalability of this method was demonstrated on a 20 g scale, and the corresponding heterocyclic sulfonyl chloride was isolated in 80% yield and excellent purity.

Impact of Molecular Chlorine Production from Aerosol Iron Photochemistry on Atmospheric Oxidative Capacity in North China.

Elevated levels of atmospheric molecular chlorine (Cl2) have been observed during the daytime in recent field studies in China but could not be explained by the current chlorine chemistry mechanisms in models. Here, we propose a Cl2 formation mechanism initiated by aerosol iron photochemistry to explain daytime Cl2 formation. We implement this mechanism into the GEOS-Chem chemical transport model and investigate its impacts on the atmospheric composition in wintertime North China where high levels of Cl2 as well as aerosol chloride and iron were observed. The new mechanism accounts for more than 90% of surface air Cl2 production in North China and consequently increases the surface air Cl2 abundances by an order of magnitude, improving the model's agreement with observed Cl2. The presence of high Cl2 significantly alters the oxidative capacity of the atmosphere, with a factor of 20-40 increase in the chlorine radical concentration and a 20-40% increase in the hydroxyl radical concentration in regions with high aerosol chloride and iron loadings. This results in an increase in surface air ozone by about 10%. This new Cl2 formation mechanism will improve the model simulation capability for reactive chlorine abundances in the regions with high emissions of chlorine and iron.

Rovibrational Transitions in HCl due to Collisions with H2: Spin-free and Hyperfine-resolved Transitions

Hydrogen chloride (HCl) is a key repository of chlorine in the interstellar medium. Accurate determinations of its abundance are critical to assessing the chlorine elemental abundance and constraining stellar nucleosynthesis models. To aid in modeling recent and future observations of HCl rovibrational spectra, we present cross sections and rate coefficients for collisions between HCl and molecular hydrogen. Transitions between rovibrational states of HCl are considered for temperatures ranging from 10 to 3000 K. Cross sections are computed using a full dimensional quantum close-coupling (CC) method and a reduced dimensionality coupled-states (CS) approach. The CS results, benchmarked against the CC results, are used with a recoupling approach to calculate hyperfine-resolved rate coefficients for rovibrational transitions of HCl induced by H2. The rate coefficients will allow for a better determination of the HCl abundance in the interstellar medium and an improved understanding of interstellar chlorine chemistry. We demonstrate the utility of the new rate coefficients in a nonthermodynamic equilibrium radiative transfer model applied to observations of HCl rovibrational transitions in a circumstellar shell.

Sulfur and phosphorus co-doped FeCoNiCrMn high-entropy alloys as efficient sulfion oxidation reaction catalysts enabling self-powered asymmetric seawater electrolysis

Seawater electrolysis (SWE) represents a promising approach to green hydrogen (H2) production but currently faces substantial challenges such as the interference of chlorine chemistry and high energy consumption. In this work, we demonstrate that by replacing the energy-demanding oxygen evolution reaction (OER) with the sulfion oxidation reaction (SOR) and by implementing the concept of bipolar membrane (BPM) electrolysis in an acid-base dual electrolyte system, not only can the notorious chlorine evolution reaction (CER) be completely circumvented, but the energy consumption of SWE be significantly reduced. To do so, we develop a sulfur and phosphorus co-doped FeCoNiCrMn high entropy alloy (HEA-SP) catalyst, which shows good electrocatalytic performance for the SOR in alkaline-saline water. This can be attributed to the abundant lattice defects and strains in HEA-SP, leading to a high density of active sites and an optimized electronic structure favorable for the SOR. Moreover, density functional theory calculations and in situ Raman spectroscopy characterization reveal the crucial role of imperfect sulfur coverage on the HEA in facilitating the formation of Sx clusters during the SOR. Using the HEA-SP as anode catalysts, the SOR-assisted SWE only needs electrical energy of 0.253 kWh to produce one cubic meter of H2 at 100 mA cm−2, in the presence of a BPM. Impressively, chlorine-free H2 production from seawater and upgrading of sulfions to valuable sulfur can occur simultaneously and spontaneously at 10 mA cm−2, highlighting the great potential of the HEA-SP catalysts and the asymmetric cell design to enable energy- and cost-effective seawater electrolysis.

In Situ Phase Separation-Induced Self-Healing Catalyst for Efficient Direct Seawater Electrolysis.

Direct seawater electrolysis technology for sustainable hydrogen production has garnered significant attention, owing to its abundant resource supply and economic potential. However, the complex composition and high chloride concentration of seawater have hindered its practical implementation. In this study, we report an in situ-synthesized dual-phase electrocatalyst (HPS-NiMo), comprising an amorphous phosphide protective outer phase and a crystalline alloy inner phase with supplementary sulfur active sites, to improve the kinetics of direct seawater electrolysis. The HPS-NiMo exhibits long-term stability, remaining stable for periods exceeding 120 h at 200 mA cm-2; moreover, it lowers the required operating voltage to ∼1.8 V in natural seawater. The chlorine chemistry, corrosion during direct natural seawater electrolysis, and mechanism behind the high-performing catalysts are discussed. We also investigated the possibility of recovering the anode precipitates, which inevitably occurs during seawater electrolysis.

Isotopic effects on the rotational (de-)excitation rate coefficients of ortho-CH3Cl colliding with He

Chloromethane, CH3Cl, is the first organohalogen molecule to be detected in the interstellar medium. Using the recently generated accurate three-dimensional potential energy surface (3D-PES) for the weakly bound CH335Cl–He complex, we deduced that of CH337Cl–He. Both 3D-PESs were incorporated later into dynamical computations code for nuclear motions treatments of each isotopologue colliding with He. We determined the state-to-state (de-)excitation cross sections for transitions among the 105 lowest rotational levels of both ortho-CH335Cl and ortho-CH337Cl (up to jkɛ = 206±). For total energies up to 100 cm−1, we used the quantum close-coupling methodology, and we adopted the coupled state approach for higher energies (up to 2500 cm−1). Rate coefficients for temperatures ranging from 5 to 150 K are then deduced after averaging these cross sections over a Maxwell–Boltzmann velocity distribution. Computations show that isotopic effects are weak, validating the use of collision rates of ortho-CH335Cl for ortho-CH337Cl and vice-versa. However, we expect that our results will be helpful to accurately determine the abundances of these isotopologues in the interstellar medium and, more generally, for understanding the complex and still not fully elucidated chemistry of chlorine containing molecular species there.

Metallic Cu-incorporated NiFe layered double hydroxide nanosheets enabling energy-saving hydrogen generation from chlorine-free seawater electrolysis coupled with sulfion upcycling

Development of multifunctional non-noble electrocatalysts for seawater electrolysis is imperative but still challenging for scale-up hydrogen production to avoid harmful chlorine chemistry. Herein, the metallic Cu-incorporated NiFe layered double hydroxide (LDH) nanosheets are prepared by a facile consecutive corrosion strategy using iron foam (IF) as a reactive substrate, which enable the corrosion-resistant and chlorine-free seawater electrolysis combined with anodic sulfion oxidation for energy-efficient hydrogen production at ultralow electricity consumption. The NiFe-LDH/Cu-IF exhibits excellent electrocatalytic activities for hydrogen evolution reaction (HER) and sulfion oxidation reaction (SOR), achieving low potentials of 0.203 and 0.310 V (vs RHE) at 100 mA cm−2 in alkaline seawater, respectively. The assembled hybrid HER||SOR seawater electrolyzer realizes the ultra-low cell voltage of 0.619 V and power consumption of 1.48 kWh/m3 H2 at 50 mA cm−2, cutting energy consumption over 67 % compared to conventional seawater electrolysis.

Reconciling Modeled and Observed Δ17O(NO3−) in Beijing Winter Haze With Heterogeneous Chlorine Chemistry

AbstractThe fine particulate matter (PM2.5) in Chinese megacities has declined significantly after the implementation of strict mitigation strategies since 2013. However, the concentration of wintertime nitrate in PM2.5 (p‐NO3‐) has only changed slightly and became the dominant inorganic component despite considerable precursor emission reductions. Discerning chemical mechanisms leading to nitrate growth during haze events is critical to implementing effective pollution mitigation policies. The oxygen isotope anomaly of nitrate (Δ17O(NO3−)) is a powerful means to distinguish nitrate formation mechanisms. Nevertheless, the observed high Δ17O(NO3−) values were significantly underestimated by chemical transport models during extreme haze events (PM2.5 > 225 μg m−3) in Beijing, indicating an incomplete understanding of nitrate chemistry. To reconcile this model‐observation discrepancy, we compiled reported Δ17O(NO3−) data in Beijing haze along with relevant observational parameters (e.g., hydroxyl (OH) reactivity, peroxyl radical concentrations), then tested assumptions on Δ17O of key precursors (e.g., OH and nitrogen dioxide (NO2)), recalculated Δ17O(NO3−) and compared them with observations. Our results indicate that considering heterogeneous dinitrogen pentoxide reactions on chlorine‐containing aerosols (N2O5 + Cl− chemistry) with a nitryl chloride (ClNO2) yield of ∼0.75 can explain the observed high Δ17O(NO3−) during extreme haze events. According to the Δ17O(NO3−) data, on average this heterogeneous N2O5 + Cl− chemistry can explain ∼60% of nighttime nitrate production and make daytime and nocturnal pathways equally important in winter Beijing haze (PM2.5 > 75 μg m−3). Our results highlight the critical role of reactive chlorine chemistry in air pollution/chemistry in inland cities.

High-temperature reaction chemistry of chromium and chlorine over Fe2O3 within sludge-incinerated fly ash

Fe2O3 is one of the main compositions of sludge-incinerated fly ash and shows reactivity for chromium removal from flue gas in the incinerator. Experiments and density functional theory (DFT) calculations were performed to investigate the high-temperature reaction chemistry of chromium and chlorine over Fe2O3 within fly ash. Fe2O3 exhibits outstanding chromium removal efficiency of 86.29 % in N2 atmosphere. The presence of HCl obviously inhibits chromium removal, the inhibition effect increases with increasing HCl concentration. Fe-Cr composite oxides are the main products of chromium-Fe2O3 high-temperature reaction. Chromium within the reaction products in N2 or HCl-containing atmosphere mainly exists in the form of Cr3+. O2 addition leads to the formation of a small amount of Cr6+. Fe2O3 exhibits excellent inhibition performance of chromium oxidation. DFT calculations suggest that CrCl3 and CrO2Cl2 are chemically adsorbed on Fe2O3 surface. Both O and Fe atoms of Fe2O3 surface serve as active sites for chromium adsorption. HCl is dissociatively adsorbed on the Fe2O3 surface, and reacted with chromium to form CrCl3. CrCl3 formation on the Fe2O3 surface is dominated by a four-step reaction pathway: Cr(ads) → CrCl(ads) → CrCl2(ads) → CrCl3(ads) → CrCl3. CrCl formation is the rate-determining step with the energy barrier of 39.51 kJ/mol.

Rotational excitation and de-excitation of interstellar chloronium cation in collisions with helium atoms

Abstract Chloronium, H2Cl+, is detected in astrophysical media. It is key chemical intermediate for understanding of the physical chemistry of chlorine species there. At present, we compute the collision rates for the rotational excitation and de-excitation of ortho- and para-H2Cl+ colliding with He for T ≤ 150 K, relevant for the interstellar medium (ISM) conditions. Prior to that, we generated the 3D interaction potential of the weakly bound H2Cl+-He complex along the Jacobi coordinates. For electronic structure computations, we used a post-Hartree-Fock explicitly correlated method at the CCSD(T)-F12/aug-cc-pVTZ level. The analytical expansion of this potential was incorporated into close coupling computations of the cross-sections for the rotational excitation and de-excitation of ortho- and para-H2Cl+ colliding with He and for collision kinetic energies Ek ≤ 1000 cm−1. The rates were obtained after averaging these cross-sections over a Maxwell–Boltzmann distribution of kinetic energies. Our data show that the ∆j=∆ka=∆kc=−1 de-excitation transitions exhibit the largest values, in particular those used to identify this cation in the surveys. Besides, our results should help for determining more accurate abundances of H2Cl+ in the ISM and thus better modelling the chlorine chemistry there.

Fe/P dual-doping NiMoO4 with hollow structure for efficient hydrazine oxidation-assisted hydrogen generation in alkaline seawater

Electrosynthesis of hydrogen straightforwardly from seawater represents a potential solution towards carbon-neutral economy. However, with the sluggish oxygen evolution reaction (OER) at anode, the sustainable and cost-effective application is greatly hindered by extra energy consumption and serious chlorine chemistry in seawater. Herein, based on the advanced hydrazine-assisted electrolysis strategy, we reported a trifunctional Fe, P dual-doping NiMoO4 nanorods with a hollow structure for highly active hydrogen evolution reaction (HER) (23 mV @ 10 mA cm−2) and OER (213 mV @ 10 mA cm−2) activity, which also significantly decreased the cell voltage (activity variation for ∼1.40 V) in two-electrode system by replacing OER with thermodynamically beneficial hydrazine oxidation reaction (HzOR). Notably, a record low electricity expense of 2.3 kW h m−3 was obtained among commercial reactor in alkaline seawater/0.5 M N2H4. Meanwhile, the corrosion resistance of catalyst allows stable catalytic performance in seawater without any ClO- generation. Density functional theory calculations showed that Fe/P co-doping effectively endowed optimized electronic structure and modulated d-band centre for intermediates adsorption/desorption.

Enhanced Sulfate Formation through Synergistic Effects of Chlorine Chemistry and Photosensitization in Atmospheric Particles

Enhanced Sulfate Formation through Synergistic Effects of Chlorine Chemistry and Photosensitization in Atmospheric Particles