Cl2 Production Research Articles

Efficient photocatalytic chlorine production on bismuth oxychloride in chloride solution

Chlorine (Cl2) one of the most important base chemicals, is manufactured conventionally by electrolysis of saturated NaCl solution in chlor-alkali process which suffers from high power consumption and economic constraints. Herein, we report the novel light-driven chlorine evolution reaction (CER) in synthetic seawater using bismuth oxychloride (BiOCl) photocatalyst, providing an economical and convenient route for Cl2 production. A superior Cl2 production rate of 19.6 μmol h−1 (about 27.79 mg L−1 h−1) is achieved, which is sufficient for methane functionalization and production of chlorine-based disinfectant. Experimental and theoretical studies reveal that the Cl− extraction from and insertion into the open structure of BiOCl contribute to the excellent performance. The lattice Cl− could be self-oxidized to form Cl2, while Cl− in solution would fill the lattice Cl− vacancies, making CER continue. This technique is also applicable to Br2 production. This work opens up prospects for halogen production based on solar energy.

Efficient Recycling of Silver and Copper from Sintering Dust by Chlorination Roasting Process

In this study, the Ag and Cu evolution in the sintering dust was extracted by chlorination roasting process, and the mechanism of the process was analyzed by atomic absorption spectroscopy, X-ray fluorescence, X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectrometry. In addition, in order to better understand the chlorination roasting process, the mechanism and thermodynamics of roasting reaction were analyzed. The recovery of Ag and Cu reached 99.05% and 59.32%, respectively, under the conditions of roasting temperature of 1423 K, holding time of 60 min, and the air flow rate of 400 L/h. Thermodynamic analysis showed that MgO and SiO2 could promote the production of Cl2 and HCl and that CuO could be chlorinated by Cl2 at 1421 K, but it was not amenable for HCl. Compared with CuO, Ag was more easily chlorinated at high temperatures. Experimental results indicate that silver and copper can be efficiently extracted, indicating that the chlorination roasting is a promising pyrometallurgical treatment for the recycling of sintering dust.

Electrochemical ammonia stripping from non-nitrified animal rendering wastewater

Electrochemical ammonia stripping (EAS) is a promising technology to remove and recover ammonium (NH4+) from wastewater with high NH4+ concentrations. In this study, we provide the proof of concept for the use of EAS for non-nitrified animal rendering wastewater. To avoid anodic chlorine (Cl2) production, a common side reaction in EAS, we evaluated the effect of electrochemical cell configuration and feeding mode. Cathode-fed operation resulted in higher NH4+ removal (83.5–99.6% removal within 1 h at a current density of 30 A/m2) compared to anode-fed operation (72 ± 2% removal within 1 h at the same current density). NH4+ removal in cathode-fed electrochemical cells that included a cation exchange membrane to separate the anode and cathode chambers had a strong dependence on the anolyte salt concentration. Although NH4+ removal in cathode-fed electrochemical cells that included an anion exchange membrane to separate the anode and the cathode did not show dependence on the anolyte salt concentration, significant anodic Cl2 production was observed (36.0 ± 13.1 mg/L of total Cl2 after 4 h at a current density of 30 A/m2). Anodic Cl2 production was the highest in anode-fed electrochemical cells (53.0 ± 0.25 mg/L of total Cl2 after 4 h at the same current density). In a cathode-fed configuration that included a trap for Cl−, no Cl2 was formed at the anode. This configuration however needed the highest applied voltage. Despite this, treating non-nitrified rendering wastewater in cathode-fed electrochemical cells with a Cl− trap provides several advantages, and presents an opportunity for scale-up of the process.

Formation of active chlorine species involving the higher oxide MOx+1 on active Ti/RuO2-IrO2 anodes: A DEMS analysis

It is accepted that the mechanism of electro-generated active chlorine (i.e. chloride oxidation on DSAs) involves water oxidation and hydroxyl radical co-electrosorption to initially form HOClads on the anode surface in a single pathway, and subsequent production of Cl2 and OCl− ions. The present study comprehensively evaluates the chloride oxidation on Ti/RuO2-IrO2 in solutions containing different NaCl concentrations and pH values. Differential Electrochemical Mass Spectroscopy (DEMS) is used to account for the in-situ surface reactions simultaneously occurring during chloride and water oxidations. It is found that HOCl does not lead the chlorine mechanism since OCl⦁ is detected in considerably larger amounts under some experimental conditions, and its onset overpotential is ~150 mV more negative than HOCl appearance at 0.2 mol L−1 NaCl. Additionally, the mass signals of OCl⦁ and HOCl are virtually similar at pH = 2 and slightly different at pH = 10, where these species should not respectively exist according to thermodynamic information. Under this premise, an extension of the reaction mechanism is proposed to consider an independent pathway producing adsorbed hypochlorite radical (OCl•ads) for electro-generated active chlorine, which could be the preferential one since RuO2 and IrO2 belong to the category of “active” anodes towards the Oxygen Evolution Reaction (OER), thus allowing the formation of the so-called higher oxide MOx(⦁O)ads (chemisorbed oxygen). Although the mechanisms involving the productions of HOClads and OCl•ads can simultaneously occur on two type of non-identified active sites, promoting the generation of both MOx(⦁OH)ads and MOx(⦁O)ads species, both strongly depend on surface pH.

Removal of micropollutants by an electrochemically driven UV/chlorine process for decentralized water treatment

The ultraviolet/chlorine (UV/Cl2) process is an emerging advanced oxidation technology for micropollutant abatement in water and wastewater treatment. However, the application of the conventional UV/Cl2 process in decentralized systems is limited by the transport and management of liquid chlorine. To overcome this limitation, this study evaluated an electrochemically driven UV/Cl2 (E-UV/Cl2) process for micropollutant abatement under conditions simulating decentralized water treatment. The E-UV/Cl2 process combines UV irradiation with in situ electrochemical Cl2 production from anodic oxidation of chloride (Cl−) in source waters. The results show that with typical Cl− concentrations present in water sources for decentralized systems (30–300 mg/L Cl−), sufficient amounts of chlorine could be quickly electrochemically produced at the anode to enable E-UV/Cl2 process for water treatment. Due to its multiple mechanisms for micropollutant abatement (direct photolysis, direct electrolysis, Cl2-mediated oxidation, as well as hydroxyl radical and reactive chlorine species oxidation), the E-UV/Cl2 process effectively eliminated all micropollutants (trimethoprim, ciprofloxacin, metoprolol, and carbamazepine) spiked in a surface water in 5 min. In contrast, at least one micropollutant with ∼20–80% residual concentrations could still be detected in the water treated by 10 min of UV irradiation, chlorination, electrolysis, and the conventional UV/Cl2 process under similar experimental conditions. The electrical energy per order (EEO) for micropollutant abatement ranged from 0.15 to 1.8 kWh/m3 for the E-UV/Cl2 process, which is generally comparable to that for the conventional UV/Cl2 process (0.14–2.7 kWh/m3). These results suggest that by in-situ generating Cl2 from anodic oxidation of Cl−, the E-UV/Cl2 process can overcome the barrier of the conventional UV/Cl2 process and thus provide a promising technology for micropollutant abatement in decentralized water treatment systems.

Integrating Nickel-Nitrogen Doped Carbon Catalyzed CO2 Electroreduction with Chlor-Alkali Process for CO, Cl2 and KHCO3 Production with Enhanced Techno-Economics

Typically, CO2 electroreduction is coupled with oxygen evolution reaction (OER), which is highly energy consuming, and also costs alkalis formed at the cathode. Here, we use chlorine evolution reaction (CER), instead of OER, to integrate with CO2 electroreduction mediated by an efficient metal-nitrogen doped carbon catalyst derived from the mixture of nickel porphyrin and commercial carbon black. The combined system was evaluated in two electrolyzer configurations that have been adopted in the chlor-alkali process to produces CO, Cl2, and KHCO3 simultaneously. To allow continuous operation, we designed a continuously operating system to collect produced KHCO3 in a precipitate tank with improved techno-economics and efficient CO2 utilization. Also, it could serve as an environmental-friendly alternative to the Solvay process for soda production. This work may provide a new strategy for the design of CO2 electrolysis systems with better economic viability.

Enhanced generation of hydrogen, power, and heat with a novel integrated photoelectrochemical system

Hydrogen is an essential component of power-to-gas technologies that are needed for a complete transition to renewable energy systems. Although hydrogen has zero GHG emissions at the end-use point, its production could become an issue if non-renewable, and pollutant energy and material resources are used in this step. Therefore, a crucial step for the fully developed hydrogen economy is to find alternative hydrogen production methods that are clean, efficient, affordable, and reliable. With this motivation, in this study, an integrated and continuous type of hydrogen production system is designed, developed, and investigated. This system has three components. There is a solar spectral splitting device (Unit I), which splits the incoming solar energy into two parts. Photons with longer wavelength is sent to the photovoltaic thermal hybrid solar collector, PV/T, (Unit II) and used for combined heat and power generation. Then the remaining part is transferred to the novel hybrid photoelectrochemical-chloralkali reactor (Unit III) for simultaneous H2, Cl2, and NaOH production. This system has only one energy input, which is the solar irradiation and five outputs, namely H2, Cl2, NaOH, heat, and electricity. Unlike most of the studies in the literature, this system does not use only PV or only a photoelectrochemical reactor. With this approach, solar energy utilization is maximized, and the wasted portion is minimized. By selecting PV/T rather than PV, the performance of the panels is maximized because recovering the by-product heat as a system output in addition to electricity, and the PV/T has less waste and higher efficiency. The present reactor does not use any additional electron donors, so the wastewater discharge is only depleted NaCl solution, which makes the system significantly cleaner than the ones available in the literature. The specific aim of this study is to demonstrate the optimum operating parameters to reach the maximum achievable production rates and efficiencies while keeping the exergy destruction as little as possible. In this study, there are four case studies, and in each case study, one decision variable is optimized to get the desired performance results. Within the selected operating parameter range, all performance criteria (except exergy destruction) are normalized and ranked for proper comparison. The maximum production rates and efficiencies with the least possible exergy destruction are observed at the operating temperature of 30 °C. At 30 °C, 4.18 g/h H2, 127.55 g/h Cl2, 151 W electricity, and 716 W heat are produced with an exergy destruction rate of 95.74 W and 78% and 30% energy and exergy efficiencies, respectively.

Multiphase Chemistry Controls Inorganic Chlorinated and Nitrogenated Compounds in Indoor Air during Bleach Cleaning.

We report elevated levels of gaseous inorganic chlorinated and nitrogenated compounds in indoor air while cleaning with a commercial bleach solution during the House Observations of Microbial and Environmental Chemistry field campaign in summer 2018. Hypochlorous acid (HOCl), chlorine (Cl2), and nitryl chloride (ClNO2) reached part-per-billion by volume levels indoors during bleach cleaning-several orders of magnitude higher than typically measured in the outdoor atmosphere. Kinetic modeling revealed that multiphase chemistry plays a central role in controlling indoor chlorine and reactive nitrogen chemistry during these periods. Cl2 production occurred via heterogeneous reactions of HOCl on indoor surfaces. ClNO2 and chloramine (NH2Cl, NHCl2, NCl3) production occurred in the applied bleach via aqueous reactions involving nitrite (NO2-) and ammonia (NH3), respectively. Aqueous-phase and surface chemistry resulted in elevated levels of gas-phase nitrogen dioxide (NO2). We predict hydroxyl (OH) and chlorine (Cl) radical production during these periods (106 and 107 molecules cm-3 s-1, respectively) driven by HOCl and Cl2 photolysis. Ventilation and photolysis accounted for <50% and <0.1% total loss of bleach-related compounds from indoor air, respectively; we conclude that uptake to indoor surfaces is an important additional loss process. Indoor HOCl and nitrogen trichloride (NCl3) mixing ratios during bleach cleaning reported herein are likely detrimental to human health.

Observational Constraints on the Formation of Cl2 From the Reactive Uptake of ClNO2 on Aerosols in the Polluted Marine Boundary Layer

AbstractWe use observations from the 2015 Wintertime Investigation of Transport, Emissions, and Reactivity (WINTER) aircraft campaign to constrain the proposed mechanism of Cl2 production from ClNO2 reaction in acidic particles. To reproduce Cl2 concentrations observed during WINTER with a chemical box model that includes ClNO2 reactive uptake to form Cl2, the model required the ClNO2 reaction probability, γ (ClNO2), to range from 6 × 10−6 to 7 × 10−5, with a mean value of 2.3 × 10−5 (±1.8 × 10−5). These field‐determined γ (ClNO2) are more than an order of magnitude lower than those determined in previous laboratory experiments on acidic surfaces, even when calculated particle pH is ≤2. We hypothesize this is because thick salt films in the laboratory enhanced the reactive uptake ClNO2 compared to that which would occur in submicron aerosol particles. Using the reacto‐diffusive length‐scale framework, we show that the field and laboratory observations can be reconciled if the net aqueous‐phase reaction rate constant for ClNO2 (aq) + Cl‐(aq) in acidic particles is on the order of 104 s−1. We show that wet particle diameter and particulate chloride mass together explain 90% of the observed variance in the box model‐derived γ (ClNO2), implying that the availability of chloride and particle volume limit the efficiency of the reaction. Despite a much lower conversion of ClNO2 into Cl2, this mechanism can still be responsible for the nocturnal formation of 10–20 pptv of Cl2 in polluted regions, yielding an atmospherically relevant concentration of Cl atoms the following morning.

Cl2 Production by Photocatalytic Oxidation of HCl over TiO2.

We studied the photocatalytic aerobic oxidation of HCl over TiO2 for producing Cl2 . Steady-state Cl2 production rates were determined with a photocatalytic fixed-bed gas-phase reactor equipped with UV light-emitting diodes (LEDs) using iodometric titration as online analytics. We found stable Cl2 production rates of up to 16 mmol h-1 m-2 for commercial anatase TiO2 Hombikat UV100. The rate increased linearly with temperature from 21 to 140 °C, indicating the acceleration of the limiting desorption rate of the coupled product water. Comparing different TiO2 polymorphs revealed that anatase possesses higher activity than rutile. The adsorption of HCl was monitored in situ by IR spectroscopy. The IR spectra indicated that HCl chemisorption chlorinates the surface of TiO2 under the reaction conditions, suggesting it to be the first step of the reaction mechanism. High stability opens up the opportunity of developing a promising photocatalytic process of HCl recycling at lower temperatures suitable for reaching full conversion.

PH-dependent production of molecular chlorine, bromine, and iodine from frozen saline surfaces

Abstract. The mechanisms of molecular halogen production from frozen saline surfaces remain incompletely understood, limiting our ability to predict atmospheric oxidation and composition in polar regions. In this laboratory study, condensed-phase hydroxyl radicals (OH) were photochemically generated in frozen saltwater solutions that mimicked the ionic composition of ocean water. These hydroxyl radicals were found to oxidize Cl−, Br−, and I−, leading to the release of Cl2, Br2, I2, and IBr. At moderately acidic pH (buffered between 4.5 and 4.8), irradiation of ice containing OH precursors (either of hydrogen peroxide or nitrite ion) produced elevated amounts of I2. Subsequent addition of O3 produced additional I2, as well as small amounts of Br2. At lower pH (1.7–2.2) and in the presence of an OH precursor, rapid dark conversion of I− to I2 occurred from reactions with hydrogen peroxide or nitrite, followed by substantial photochemical production of Br2 upon irradiation. Exposure to O3 under these low pH conditions also increased production of Br2 and I2; this likely results from direct O3 reactions with halides, as well as the production of gas-phase HOBr and HOI that subsequently diffuse to frozen solution to react with Br− and I−. Photochemical production of Cl2 was only observed when the irradiated sample was composed of high-purity NaCl and hydrogen peroxide (acting as the OH precursor) at pH = 1.8. Though condensed-phase OH was shown to produce Cl2 in this study, kinetics calculations suggest that heterogeneous recycling chemistry may be equally or more important for Cl2 production in the Arctic atmosphere. The condensed-phase OH-mediated halogen production mechanisms demonstrated here are consistent with those proposed from recent Arctic field observations of molecular halogen production from snowpacks. These reactions, even if slow, may be important for providing seed halogens to the Arctic atmosphere. Our results suggest the observed molecular halogen products are dependent on the relative concentrations of halides at the ice surface, as we only observe what diffuses to the air–surface interface.

Highly catalytic flexible RuO2 on carbon fiber cloth network for boosting chlorine evolution reaction

In this study, a novel flexible electrode consisting of homogeneous RuO2 nanoparticles (NPs) wrapped around the carbon fiber cloth (CC) is fabricated by combining the cathodic electro-deposition in the aqueous acidic RuCl3·xH2O solution and annealing in air atmosphere. The as-fabricated RuO2 NPs/CC electrode with electro-deposition duration of 10 min demonstrates a superior electrocatalytic activity with a lower overpotential of ca. 1.05 V vs. SCE and its current density reaches up to 175 mA cm−2 at 1.2 V vs. SCE for chlorine evolution reaction (CER) in 5.0 M NaCl aqueous solution, outperforming many of the reported counterparts. The as-revealed outstanding electrocatalytic activity should be attributed to several beneficial factors such as its typical integrated binder-free 3D architecture, higher usage efficiency of active RuO2 NPs, greatly decreased interfacial resistance, etc. This work paves a way to utilize the carbon fiber cloth decorated with active noble metal oxides for boosting electrochemical Cl2 production.

What is the efficiency of electro-generation of chlorine with a solid polymer electrolyte assembly?

The use of a solid polymer electrolyte (SPE) in an anode/SPE/cathode sandwich has emerged as a promising electrochemical configuration to reduce the terminal voltage and thus energy consumption during electrolysis. This study for the first time investigates and compares the efficiency of the electrochemical chlorine production process as well as estimates and compares energy consumption with and without a SPE assembly in the electrolytic cell. Results indicate that at the same current density of 12.5 mA/cm2, Cl2 production rate and instantaneous current efficiency (ICE) were higher when no SPE was used than with a functional SPE, most likely because the SPE occupied one side of the electrode surface, thus limiting the contact of Cl− with its surface to generate Cl2. However, increasing the current density to 31.25 mA/cm2 with a functional SPE resulted in an almost equal Cl2 production rate to that at 12.5 mA/cm2 without a functional SPE, and still the energy consumption per mass of produced Cl2 was the same, although lower ICE was achieved. The study also further investigated the effect of flowrate, and the influence of initial Cl− concentration and the initial pH for the system with the functional SPE.

Investigation of a unique integrated photoelectrochemical system for multigeneration purposes

This study develops, investigates and analyze a continuous type hybrid photoelectrochemical-chloralkali H2 production reactor that converts the by–products into useful industrial commodities (i.e., Cl2 and NaOH). The proposed system maximizes solar spectrum use by taking advantage of photocatalysis and PV/T. Furthermore, by using electrodes as electron donors to support the photochemical reaction, the potential risk of pollutant emissions is minimized. The final products of this novel integrated system can be listed as H2, Cl2, NaOH, heat, and electricity. In this study, the effects of operating temperature and inlet mass flow rates on H2, Cl2, heat, and electricity production, energy and exergy efficiencies, and exergy destruction rates are presented. The results of this investigation show that the proposed system is capable of producing hydrogen up to 70 L/h, chlorine up to 60 L/h, heat up to 800 W, electricity up to 160 W, with energy and exergy efficiencies up to 80% and 30%, respectively.

Demand side management and operational mode switching in chlorine production

Demand side management (DSM) gains importance due to penetration of renewable energy in energy provision. A promising candidate is the chlor‐alkali process as it is an energy‐intensive process with a high installed capacity and high penetration worldwide. In this article, we consider DSM for the purpose of chlorine production via membrane electrolysis. We allow for switching between two different operational modes with different respective electrical power demands on a per ton of produced chlorine (Cl2) basis and different modulation of production rate. Switching necessitates a cleaning procedure leading to downtimes of the Cl2 production, while a constant provision of Cl2 for downstream processes is necessary. The optimal operation of a variable and switchable chlor‐alkali process under aforementioned constraints is determined by formulation as a mixed integer linear program. The results demonstrate that oversizing, in combination with switching, leads to substantial savings, especially in future scenarios for the electricity price. © 2018 American Institute of Chemical Engineers AIChE J, 65: e16352 2019

Heterogeneous production of Cl2 from particulate chloride: Effects of composition and relative humidity

Reactions initiated by chlorine atoms can enhance the formation of ozone (O3) and secondary organic aerosol (SOA) in the troposphere. Environmental chamber experiments were conducted to quantify heterogeneous Cl2 production from NH4Cl and NaCl particles exposed to O3 and hydroxyl radicals (•OH). Observations are inconsistent with models of Cl2 production resulting solely from surface‐mediated reactions of •OH and suggest that O3 plays a significant role. The production of Cl2 increased with relative humidity and decreased in the presence of SOA or nitric oxides (NOx). Heterogeneous reactive uptake coefficients for the production of Cl2 from O3 on pure NH4Cl ( ) averaged 1.4 ± 1.0 × 10−3. Cl2 production was six times more efficient on NH4Cl aerosol than on NaCl aerosol. Model calculations under atmospheric conditions suggest this heterogeneous Cl2 production could increase peak daily O3 concentrations by over 10%. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3151–3158, 2018

Modulating Selectivity in CER and Oer through Doped RuO2

Electrochemical chlorine evolution reaction (CER) is one of the most important electrochemical reactions due to widespread importance of Cl2 as an industrial chemical. However, electrochemical CER is bridled with parallel of oxygen evolution reaction (OER) reducing the performance of anode towards Cl2 production. In this context, the guiding principles of enhancing the selectivity of CER is investigated experimentally and computationally in RuO2 doped with first-row-transition-metals. Computational studies suggest that low-valent dopant (Cu, Zn) tend to surface segregate and they tend to weaken the interaction of adsorbates with the surface. Further, doping of metals having higher d-electrons than Ru in RuO2 tend to lower the binding strength of OER intermediates (e.g. HO-, O-, HOO-) thereby increasing its overpotential . However, doping have less effect on the binding strength of monovalent CER intermediates (e.g. ClO-, Cl-) resulting in higher CER selectivity. Computational studies suggest that Cu (d9)-doped RuO2 would show maximum CER selectivity and this has been corroborated by experiments with electrodeposited doped RuO2. The electrodeposited Cu-doped RuO2 (2% dopant concentration) has been found to show 95% CER selectivity at acidic medium. However, doping of d-enriched metals also lower the bridge-oxygen vacancy formation energy which activates lattice-oxygen-vacancy aided water dissociation pathway and aid the selectivity of OER. This may result in an optimum doping concentration wherein maxima of CER selectivity is observed as in case of for Cu- and Zn-doped RuO2 electrocatalysts experimentally. The present work offers insight on catalyst design taking account of selectivity of CER and OER during electrochemical Cl2 production.

Chlorine-free alkaline seawater electrolysis for hydrogen production

A new process for chlorine-free seawater electrolysis is proposed in this study. The first step of the process is separation of Mg2+ and Ca2+ ions from seawater by nanofiltration. Next, the NF permeate is dosed into the electrochemical system. There it is completely split into hydrogen and oxygen gases and NaCl precipitate. The electrochemical system comprises an electrochemical cell operated at elevated temperatures (e.g. ≥ 50 °C) and a settling tank filled with aqueous NaOH solution (20–40 %wt) that operates at lower temperatures (e.g. 20–30 °C). High concentration of hydroxide ions in the electrolyzed solution prevents anodic chlorine evolution, while the accumulated NaCl precipitates in the settling tank. Batch electrolysis tests, performed in NaCl-saturated NaOH solutions, showed absolutely no chlorine formation on Ni200 and Ti/IrO2RuO2TiO2 anodes at [NaOH] > 100 g/kgH2O. Three long-term operations (9, 12 and 30 days) of the electrochemical system showed no Cl2 or chlorate (ClO3−) production on both electrodes operated at current densities of 93–467 mA/cm2. The Ni200 anode was corroded in the continuous operation that resulted in formation of nickel oxide on the anode surface. On the other hand, the system was successfully operated at 467 mA/cm2 with Ti/IrO2RuO2TiO2 electrodes in NaCl-saturated solution of NaOH (30 %wt) for 12 days. During this period no formation of Cl2 and ClO3− has been observed and precipitation of NaCl occurred only in the settling tank. The performance of the system was stable during the operation as indicated by the insignificant fluctuations in the applied cell potentials and measured constant concentrations of NaOH(aq) and NaCl(aq) in the electrolyte solution. During 12 days of operation at ≈ 470 mA/cm2 about 1.2 m3 of H2 and ≈150 g of solid NaCl were produced in the system. Electrical energy demand of the electrolysis cell was 5.6–6.7 kWh/m3H2 for the current density range of 187–467 mA/cm2.

A clean and membrane-free chlor-alkali process with decoupled Cl2 and H2/NaOH production

Existing chlor-alkali processes generally use asbestos, mercury or fluorine-containing ion-exchange membranes to separate the simultaneous chlorine production on the anode and hydrogen production on the cathode, and form sodium hydroxide in the electrolyte. Here, using the Na+ de-intercalation/intercalation of a Na0.44MnO2 electrode as a redox mediator, we decouple the chlor-alkali process into two independent steps: a H2 production step with the NaOH formation in the electrolyte and a Cl2 production step. The first step involves a cathodic H2 evolution reaction (H2O → H2) and an anodic Na+ de-intercalation reaction (Na0.44MnO2 → Na0.44−xMnO2), during which NaOH is produced in the electrolyte solution. The second step depends on a cathodic Na+ intercalation reaction (Na0.44−xMnO2 → Na0.44MnO2) and an anodic Cl2 production (Cl → Cl2). The cycle of the two steps provides a membrane-free process, which is potentially a promising direction for developing clean chlor-alkali technology.

Molecular Halogens Above the Arctic Snowpack: Emissions, Diurnal Variations, and Recycling Mechanisms

AbstractElevated levels of reactive bromine and chlorine species in the springtime Arctic boundary layer contribute to ozone depletion and mercury oxidation, as well as reactions with volatile organic compounds. Recent laboratory and field studies have revealed that snowpack photochemistry leads to Br2 and Cl2 production, the mechanisms of which remain poorly understood. In this work, we use a photochemical box model, with a simplified snow module, to examine the halogen chemistry occurring during the March 2012 Bromine, Ozone, and Mercury Experiment (BROMEX) near Utqiaġvik (Barrow), Alaska. Elevated daytime Br2 levels (e.g., 6–30 parts per trillion (ppt) at around local noon) reported in previous studies and in this work may be explained by Br + BrNO2/BrONO2 reactions under conditions of depleted O3 (&lt;~10 ppb) and background NO2 (10–100 ppt). Even at low background NOx levels at Utqiaġvik, ClONO2 is predicted to be important in the production of Cl2 via multiphase reaction with Cl−. In the late afternoon, photolysis alone cannot explain the rapid decrease of Cl2 observed in the Arctic boundary layer. Heterogeneous reactions of Cl2 on aerosol particles and surface snowpack are suggested to play a key role in atmospheric Cl2 removal and possible BrCl production. Given the importance of the snowpack in the multiphase chemistry of the Arctic boundary layer, future measurements should focus on vertically resolved measurements of NOx and reactive halogens, as well as simultaneous particulate and snow halide measurements, to further evaluate and isolate the halogen production and vertical propagation mechanisms through one‐dimensional modeling.