Evolution Of Hydrogen Chloride Research Articles

Global Mapping of HCl on Mars by IRTF/iSHELL

Hydrogen chloride (HCl)—a key marker of the chlorine cycle on Mars—has been recently discovered in the Martian atmosphere by the ExoMars/TGO mission. In-orbit data indicate that this molecule appears in the atmosphere only in a limited time period and specifically in the southern summer season. A snapshot global mapping of HCl is indispensable to examine its sources and sinks, but such observations are not currently possible from any orbiters. Here, we present the first spatially resolved map of HCl obtained with the ground-based NASA InfraRed Telescope Facility. We find clear features of HCl, demonstrating that HCl is present close to the surface. HCl is detected in the equatorial region for the first time, revealing that HCl is widely distributed on Mars. However, the spatial distribution of HCl is not uniform, and it is enhanced in the southern polar region. Interestingly, this nonuniform spatial distribution of HCl column abundance is strikingly similar to that of water vapor column abundance. This highlights the important role of water vapor in the evolution of HCl through the atmosphere, as previously noted, and suggests its potential involvement in the atmospheric chlorine source processes.

A New Perspective on Hydrogen Chloride Scavenging at High Temperatures for Reducing the Smoke Acidity of PVC Cables in Fires V: Comparison between EN 60754-1 and EN 60754-2

Regulation (EU) No 305/2011 lays down harmonized conditions for marketing construction products in the European Union. One of its consequences has been the introduction of the product standard EN 50575 and standard EN 130501-6, concerning power, control, and communication cables permanently installed in buildings to prevent the risk of a fire and its consequences. EN 13501-6 provides the reaction to fire classifications for cables, the test methods to be performed, the requirements to meet a specific reaction to fire, and additional classifications for smoke production, flaming droplets, and acidity. It requires EN 60754-2 as the technical standard to assess acidity, and it defines three classes: a1, a2, and a3 (the less performant). Due to the release of hydrogen chloride during the combustion, acidity is the weak point of PVC cables, which are not yet capable of achieving the a1 or a2 classes required for specific locations according to fire risk assessments. EN 13501-6 does not include EN 60754-1, used in harmonized standards outside the scope of Regulation (EU) No 305/2011. EN 60754-1 and EN 60754-2 are common standards for determining halogen gas content, and acidity/conductivity, respectively. While they involve the same type of test apparatus, they differ in heating regimes, final temperatures, and detection methods. In particular, EN 60754-2 requires testing at temperatures between 935–965 °C in the tube furnace, where the sample burns, the smoke is collected in bubblers, and pH and conductivity are measured as an indirect assessment of acidity. On the other hand, the temperature regime of EN 60754-1 is a gradual heating run, followed by isothermal heating at 800 °C. The paper shows that when potent acid scavengers are used in PVC compounds, performing EN 60754-2 with the thermal profile of EN 60754-1 or at 500 °C in isothermal conditions, the evolution of hydrogen chloride changes significantly up to 10 times less than the test performed in isothermal at 950 °C. The reason lies behind the kinetic of hydrogen chloride release during the combustion of PVC compounds: the higher the temperature or faster the heat release, the quicker hydrogen chloride evolution and the lower the probability for the acid scavenger to trap it. Thus, these findings emphasize the “fragility” of EN 60754-2 as a tool for assessing risks associated with the release of hydrogen chloride during fires.

Oxygen effects on the evolution of hydrogen chloride and chlorine gas during combustion of PVC-CaCO3 based cable

This paper investigates the migration and evolution of chlorinated (Cl-) chemicals during the combustion of polyvinyl chloride-calcium carbonate (PVC-CaCO3) composite cable outer sheath under different oxygen (O2) concentrations. Previous studies have mainly focused on the combustion of cables and subsequent generation of gaseous products under ambient air, and there is limited knowledge on the combustion behavior when the O2 concentration of the combustion air varies, especially at elevated, above ambient level. In this paper, the variations of Cl-contents in the remaining solid residues and Cl-gaseous products were studied under different O2 concentrations and external heat fluxes. The results show that when the O2 concentration increases from 12 to 18 %, the increased surface temperature enhances the pyrolysis rate and the hydrogen chloride (HCl) yield which increases from ∼0.15–0.18 g/g. Over 18–24 % O2 concentration, the HCl yield diminishes sharply and continuously, from ∼0.18–0.13 g/g with increasing O2 concentration. By 30 % O2 concentration, HCl yield has reduced by more than 40 %. Under O2-rich combustion, a large amount of chlorine gas (Cl2) is presence in the combustion products following the reduction in HCl yield, where over 75 % converted HCl was oxidized to form Cl2. HCl competes for O2 which is also required for carbon monoxide (CO) oxidation, and the O2 consumed for HCl oxidation is approximately 3 times that of CO oxidation. Under 12–18 % O2 concentration, the presence of high HCl yield inhibits CO oxidation, resulting in an increase in CO yield with intensified pyrolysis.

Oxygen Effects on the Evolution of Hydrogen Chloride and Chlorine Gas During Combustion of Pvc-Caco3 Based Cable

Oxygen Effects on the Evolution of Hydrogen Chloride and Chlorine Gas During Combustion of Pvc-Caco3 Based Cable

Thermal Stability of Nanosilica-Modified Poly(vinyl chloride).

The thermal stability of PVC with 1 wt % of spherical porous nanosilica, prepared by roll milling at processing time varied from 1 to 20 min, was investigated by means of visual color changes, Congo red, and thermogravimetric tests (TGA and DTG), as a function of rolling time and composition of PVC matrix. The melt flow rate (MFR) measurements were realized to identify the degradation-induced changes of processing properties. A high level of gelation of the PVC matrix for all samples was verified by DSC (differential scanning calorimetry). It was found that the addition of porous nanosilica to absorb a certain volume of HCl, produced by dehydrochlorination reaction, leads to an improvement of thermal stability, an effect observed in a form of minor color changes of the samples, lower evolution of gas hydrogen chloride, and slight changes of the MFR value. It was demonstrated that the TGA measurements are not sufficiently sensible to detect the degradation of PVC at the processing conditions, i.e., at the temperature equal to 220 °C and below this temperature.

A Continuous Flow Sulfuryl Chloride-Based Reaction-Synthesis of a Key Intermediate in a New Route toward Emtricitabine and Lamivudine.

We demonstrate a continuous two-step sequence in which sulfenyl chloride is formed, trapped by vinyl acetate, and chlorinated further via a Pummerer rearrangement. These reactions produce a key intermediate in our new approach to the oxathiolane core used to prepare the antiretroviral medicines emtricitabine and lamivudine. During batch scale-up to tens of grams, we found that the sequence featured a strong exotherm and evolution of hydrogen chloride and sulfur dioxide. Keeping gaseous byproducts in solution and controlling the temperature led to better outcomes. These reactions are ideal candidates for implementation in a continuous mesoscale system for the sake of superior control. In addition, we found that fast reagent additions at controlled temperatures decreased byproduct formation. Herein we discuss the flow implementation and the final reactor design that led to a system with a 141 g/h throughput.

The effect of magnesium hydroxide, hydromagnesite and layered double hydroxide on the heat stability and fire performance of plasticized poly(vinyl chloride)

Emulsion grade poly(vinyl chloride) was plasticized with 100 phr of diisononyl phthalate and filled with 30 phr of different hydrated filler-type flame-retardant additives. Static heat stabilities were determined at 200°C by following the time dependence of hydrogen chloride evolution. Fire-retardant performance was studied with a cone calorimeter at a radiant flux of 35 kW m−2. The layered double hydroxide outperformed the other fillers with regard to improving static heat stability and also with respect to most fire-retardant performance indices.

Catalytic ring-opening addition of thiols to epoxides in the gas-phase over molecular rhenium sulfide cluster complexes [Re6S8X6] (X = Cl, OH, H2O) with retention of their octahedral metal frameworks

A series of molecular rhenium sulfide clusters K4[Re6S8Cl6] (1), K4[Re6S8(OH)6], and [Re6S8(H2O)6]SO4 supported on silica gel catalyze ring-opening addition of thiols to epoxides to yield β-hydroxy sulfides in a stream of hydrogen at temperatures ranging from 175 to 250°C. The thermal activation mechanisms of 1 is studied. Powder X-ray diffraction analyses and Raman spectrometry reveal the retention of integrity of the octahedral cluster framework up to 500°C. Thermogravimetry and elemental analyses of the silica gel-supported 1 show the loss of chlorido ligands, and evolution of hydrogen chloride is observed on activation. No coordinatively unsaturated metal site is observed by CO titration. Titration of the activated cluster shows the appearance of weak Brønsted acid sites with H0≈1.8. The catalytically active site of the silica gel-supported 1 is a hydroxo ligand that is formed by reaction with silanol groups.

Heat stabilising flexible PVC with layered double hydroxide derivatives

The layered double hydroxide ([Mg0.667Al0.333(OH)2](CO3)0.167·mH2O) (LDH) has found application as a heat stabiliser for PVC. Derivatives of this compound were synthesised using a hydrothermal method. Emulsion grade PVC was plasticised with 100 phr diisononyl phthalate and stabilised with 30 phr of the LDH filler additives. Heat stabilities were determined at 200 °C. The dynamic heat stability tests were performed on the plastisols using the torque rheometer method. Static heat stability was evaluated on the fused compounds. It was evaluated from discoloration profiles of strips exposed for various lengths of time to heat in a Metrastat oven. The time dependence of hydrogen chloride evolution was followed with a Metrohm Thermomat instrument. The conventional LDH provided the best dynamic heat stability. However, partial replacement of the magnesium with copper significantly delayed the release of volatile HCl. If instead the replacement was done using zinc, better colour retention was achieved.

Technical Note: SWIFT – a fast semi-empirical model for polar stratospheric ozone loss

Abstract. An extremely fast model to estimate the degree of stratospheric ozone depletion during polar winters is described. It is based on a set of coupled differential equations that simulate the seasonal evolution of vortex-averaged hydrogen chloride (HCl), nitric acid (HNO3), chlorine nitrate (ClONO2), active forms of chlorine (ClOx = Cl + ClO + 2 ClOOCl) and ozone (O3) on isentropic levels within the polar vortices. Terms in these equations account for the chemical and physical processes driving the time rate of change of these species. Eight empirical fit coefficients associated with these terms are derived by iteratively fitting the equations to vortex-averaged satellite-based measurements of HCl, HNO3 and ClONO2 and observationally derived ozone loss rates. The system of differential equations is not stiff and can be solved with a time step of one day, allowing many years to be processed per second on a standard PC. The inputs required are the daily fractions of the vortex area covered by polar stratospheric clouds and the fractions of the vortex area exposed to sunlight. The resultant model, SWIFT (Semi-empirical Weighted Iterative Fit Technique), provides a fast yet accurate method to simulate ozone loss rates in polar regions. SWIFT's capabilities are demonstrated by comparing measured and modeled total ozone loss outside of the training period.

The Solvation and Dissociation of 4-Benzylaniline Hydrochloride in Chlorobenzene

A reaction scheme is proposed to account for the liberation of 4-benzylaniline from 4-benzylaniline hydrochloride, using chlorobenzene as a solvent at a temperature of 373 K. Two operational regimes are explored: “closed” reaction conditions correspond to the retention of evolved hydrogen chloride gas within the reaction medium, whereas an “open” system permits gaseous hydrogen chloride to be released from the reaction medium. The solution phase chemistry is analyzed by 1H NMR spectroscopy. Complete liberation of solvated 4-benzylaniline from solid 4-benzylaniline hydrochloride is possible under “open” conditions, with the entropically favored conversion of solvated hydrogen chloride to the gaseous phase thought to be the thermodynamic driver that effectively controls a series of interconnecting equilibria. A kinetic model is proposed to account for the observations of the open system.

Systematic Study to Convert Polyvinyl Chloride Waste into Commercial Chemicals

Polyvinyl chloride (PVC) waste is considered one of the environmentally hazardous plastic materials accumulating in huge quantities in landfills. This work was conducted for the purpose of using green chemistry techniques to convert the PVC waste into other chemicals that could be used for commercial purposes. Pyrolysis process of the PVC waste was carried out under inert atmospheric condition. The effect of grain size, temperature and heating time on the amount of evolved hydrogen chloride gas (HCl) was investigated. More than 95% of theoretical calculated amount of HCl was evolved before any emission of any other organic fumes. The evolved HCl was trapped and converted into concentrated hydrochloric acid (11.22 M) and then to a highly pure sodium chloride salt. The residual black material was heated further to remove and trap oily organic fumes. About 14% of initial PVC weight was found to be as heavy metals free oil and may be used as fuel. Finally, 27.74% of the degraded PVC remained as carbon black. The carbon black was grounded and acid digested to remove and determine heavy metal ions content.

Evolution of Hydrogen Chloride and Change in the Chlorine Functionality during Pyrolysis of Argonne Premium Coal Samples

In order to understand chlorine chemistry in coal pyrolysis, the dynamics of HCl evolution and changes in chlorine functional forms during temperature-programmed pyrolysis of eight Argonne premium coal samples have been examined with an online HCl-monitoring technique and by the Cl 2p X-ray photoelectron spectroscopy (XPS) method. The rate profiles of HCl evolved show at least three distinct peaks at 390, 520, and 600 °C, and the presence of these peaks depends strongly on the type of coal. The HCl peak at 390 °C appears with four coals alone and becomes considerably small by water washing, whereas the high-temperature peaks above 450 °C observed with almost all of the coals do not change significantly after washing. Yields of HCl up to 1000 °C are in the range of 50–90% in many cases, and the yield tends to decrease with increasing atomic Ca/Cl ratio in coal. The chlorine XPS analyses show that the chlorine in each coal is enriched at the surface and composed of inorganic and organic functional forms. The extent of the enrichment and proportion of organic chloride species increase after pyrolysis at 450 °C, whereas they decrease at high temperatures of 800 and 1000 °C. Some model experiments followed by the chlorine XPS measurements show that the reaction of HCl with carbon active sites proceeds readily at 500 °C to produce organic C–Cl forms, which release HCl again above 500 °C upon reheating in an inert gas. On the basis of the above-mentioned results, it is possible that HCl evolved below 450 °C in coal pyrolysis comes predominantly from water-soluble chlorine functional groups in coal, whereas HCl formation above 450 °C originates mainly from organic chlorides, which could be present inherently in coal and/or may be formed by secondary reactions of HCl evolved at a lower temperature with carbon active sites in the nascent char.

Effect of cyanoguanidine‐metal and urea‐metal complexes on the thermal degradation of poly(vinyl chloride)

AbstractTin, nickel, cobalt, zinc, and copper complexes of cyanoguanidine and urea were synthesized and investigated as thermal stabilizers for rigid poly(vinyl chloride) at 180°C in air. Their stabilizing efficiencies were evaluated by measuring the induction period (the period during which no evolved hydrogen chloride could be detected) and the rate of dehydrochlorination as determined by continuous potentiometric measurements, in addition to the extent of discoloration. The results clearly revealed the greater efficiency of all of the investigated metal complexes as compared to those of well‐recognized reference stabilizers. The tin complex always exhibited the highest efficiency irrespective of the type of ligand used. The nickel and cobalt complexes also possessed high stabilizing efficiencies. The order of the stabilizing potency of the various metal complexes was Sn ⋙ Co, Ni ≫ Zn, Cu. Combining the ligand itself with dimethyltin‐s,s′‐bis (isooctyl thioglycolate), as a reference stabilizer containing a tin atom, led to a true synergism. This synergistic effect might be attributed to the formation in situ of a complex between the ligand and the tin atom. J. VINYL ADDIT. TECHNOL., 2010. © 2010 Society of Plastics Engineers

Inhibition of the thermal degradation of rigid poly(vinyl chloride) using poly(N-[4-(N′-phenyl amino carbonyl)phenyl]maleimide)

Poly(N-[4-(N′-phenyl amino carbonyl)phenyl]maleimide), poly(PhPM), has been investigated for the inhibition of the thermal degradation of rigid poly(vinyl chloride) (PVC) in air, at 180°C. Its stabilizing efficiency was evaluated by measuring the length of the induction period, the period during which no detectable amounts of hydrogen chloride gas could be observed, and also from the rate of dehydrochlorination as measured by continuous potentiometric determination, and the extent of discoloration of the degraded polymer. The results have proved the greater stabilizing efficiency of poly(PhPM) relative to that of the DBLC commercial stabilizer. This is well demonstrated by the longer induction period values and by the lower rates both of dehydrochlorination and discoloration of the polymer during degradation relative to those of the DBLC reference stabilizer. The greater stabilizing efficiency of the poly(PhPM) is most probably attributed not only to its possession of various centers of reactivity that can act as traps for radical species resulting during the degradation process, and replacement of labile chlorine atoms on PVC chains by relatively more thermally stable poly(PhPM) moieties, but also due to the ability of its fragmentation products to react with the evolved hydrogen chloride gas. A radical mechanism is suggested to account for the stabilizing action of this polymeric stabilizer. A synergistic effect is achieved when the poly(PhPM) was blended in various weight ratios with DBLC. This synergism attains its maximum when poly(PhPM) and DBLC are taken at 3 : 1 weight ratio. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Material properties of nanoclay PVC composites

Nanocomposites of poly(vinyl chloride) have been prepared using both hectorite- and bentonite-based organically-modified clays. The organic modification used is tallow-triethanol-ammonium ion. The morphology of the systems was investigated using X-ray diffraction and transmission electron microscopy and these systems show that true nanocomposites, both intercalated and exfoliated systems, are produced. The mechanical properties have been evaluated and the modulus increases upon nanocomposite formation without a significant decrease in tensile strength or elongation at break. Thermal analysis studies using thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis were conducted. Thermal stability of the PVC systems was assessed using a standard thermal process evaluating the evolution of hydrogen chloride and by color development through the yellowness index. Cone calorimetry was used to measure the fire properties and especially to evaluate smoke evolution. The addition of an appropriately-modified bentonite or hectorite nanoclay leads to both a reduction in the total smoke that is evolved, and an increase in the length of time over which smoke is evolved. Along with this, a reduction in the peak heat release rate is seen. It is likely that the presence of the clay in some way interferes with the cyclization of the conjugated system formed upon HCl loss.

Thermal degradation behaviour of poly(vinyl chloride) in the presence of poly( N′-acryloyl benzhydrazide)

The thermal degradation behaviour of poly(vinyl chloride), PVC, in the presence of poly( N′-acryloyl benzhydrazide), PABH, has been studied using continuous potentiometric determination of the evolved hydrogen chloride gas from the degradation and by measuring the extent of discoloration of the degraded samples. Blending this polymeric additive with dibasic lead carbonate, DBLC, reference stabilizer in different ratios had synergistic effects on both the thermal stability and the extent of discoloration of PVC.

Flame‐retardant properties of magnesium hydroxystannate and strontium hydroxystannate coated calcium carbonate on soft poly(vinyl chloride)

AbstractThe flame‐retardant and smoke‐suppressant properties of soft poly(vinyl chloride) (PVC) treated with zinc hydroxystannate (ZHS), calcium carbonate (CaCO3), magnesium hydroxystannate [MgSn(OH)6], strontium hydroxystannate [SrSn(OH)6], ZHS–MgSn(OH)6, ZHS–SrSn(OH)6, MgSn(OH)6‐coated CaCO3, SrSn(OH)6‐coated CaCO3, ZHS–MgSn(OH)6‐coated CaCO3, and ZHS–SrSn(OH)6‐coated CaCO3 were studied with the limited oxygen index, char yield, and smoke density rating methods; the mechanical properties were also studied. The results showed that, with the equivalent addition of the corresponding hydroxystannate, the soft PVC treated with hydroxystannate‐coated CaCO3 had a higher limited oxygen index than the corresponding hydroxystannate, and the soft PVC treated with the agents containing magnesium had a higher limited oxygen index than the soft PVC treated with the agents containing strontium, except for ZHS–MgSn(OH)6‐coated CaCO3. The improvement in the char formation of the hydroxystannate‐coated CaCO3 was better than that of the corresponding hydroxystannate in most cases, and the aforementioned agents reduced the smoke density rating, decreased the tensile strength, and increased the elongation and impact strength basically. Thermal analysis showed that the additives promoted the evolution of hydrogen chloride, early crosslinking, and rapid charring through the strong catalyzing effect of Lewis acids. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Copolymerization of vinyl chloride with 1-vinyl-4,5,6,7-tetrahydroindole and 2-methyl-5-vinylpyridine

The radical copolymerization of vinyl chloride with 2-methyl-5-vinylpyridine and 1-vinyl-4,5,6,7-tetrahydroindole is accompanied by dehydrochlorination. In the vinyl chloride-2-methyl-5-vinylpyridine system, the evolved hydrogen chloride interacts with a pyridine hydrogen atom to give charged units of a heterocycle. In the vinyl chloride-1-vinyl-4,5,6,7-tetrahydroindole system, the hydrogen chloride being formed initiates the cationic dimerization of a nitrogen-containing monomer. The synthesized copolymers based on vinyl chloride surpass the commercial poly(vinyl chloride) in terms of thermal stability and solubility in organic solvents.

Inhibition of the thermal degradation of rigid poly(vinyl chloride) by dienophilic compounds

AbstractN‐(N′‐Arylamino)maleimide derivatives N‐(N′‐RPh)AMI (R = H, 2‐NO2, 4‐NO2, 2,4‐di‐NO2) were investigated as organic thermal stabilizers and costabilizers for rigid poly(vinyl chloride) (PVC) at 180°C in air. Their stabilizing efficiencies were evaluated by measuring the induction period (Ts, the period during which no evolved hydrogen chloride could be detected) and the dehydrochlorination rate as measured by continuous potentiometric determination, as well as the extent of discoloration. The stabilizing efficiencies were compared with those of some industrially used stabilizers. The results clearly revealed the greater efficiency of all of the investigated derivatives except the unsubstituted N‐(N′‐Ph)AMI, which was found to possess efficiency comparable with those of the reference stabilizers. The dinitro aminomaleimide [2,4‐di(NO2)AMI] exhibited the highest efficiency. The stabilizing efficiencies of the AMIs are attributed to the replacement of the labile chlorine atoms on the PVC chains by more thermally stable stabilizer moieties. An ionic mechanism is proposed that explains the stabilizing action. Mixing the investigated stabilizers with cyanoguanidine, which is known to act as an HCl absorber, led to a true synergistic effect. The effect of the degradation process of adding small amounts of K2CO3 to PVC stabilized with the materials under investigation also is discussed. J. VINYL ADDIT. TECHNOL., 2008. © 2008 Society of Plastics Engineers