Hydrogen Bromide Concentration Research Articles

ELECTROCHEMICAL DISSOLUTION OF TITANIUM ELECTRODES POLARIZED BY ALTERNATING CURRENT IN A HYDROBROMIC ACID AQUEOUS SOLUTION

The work shows the patterns of electrochemical dissolution of titanium electrodes polarized by alternating current in an aqueous solution of hydrogen bromide. The current density (200-1200 A/m2), hydrogen bromide concentration (1.0-5.0 M), electrolysis duration (0.25-2.0 hours), and electrolyte temperature depend on the current rate of the titanium electrode in the alternating current source (20°C-80°C) were considered. The maximum value of current yield was obtained at a current density of 400 A/m2 when titanium electrodes were polarized by an alternating current and it was recorded that the current yield is reduced at a high current density. It is shown that the current output for titanium increases directly proportional to the concentration of hydrogen bromide, i.e., hydrogen ion content. The order of the reaction which occurs during the electrolysis of hydrogen bromide is determined. It is proved that the current efficiency of dissolving titanium in the alternating current source decreases when the electrolysis time is increased, as the electrolysis products in the electrolyte settle down on the electrode surface. It is shown that as the temperature of the electrolyte solution is increased, the current output value for dissolving titanium rises to 48%. The activation energy determined according to the temperature-kinetic regime was 17.76 kJ/mol, the process was carried out according to the diffusion-kinetic regime. It was shown that titanium is dissolved in hydrogen bromide aqueous solution to form titanium (III) ions. The influence of the main parameters on the electrochemical dissolution of a polarized alternating current titanium electrode in hydrochloric acid is investigated and effective ways of titanium dissolution are considered. The results of the research can be used to propose a new method of titanium waste recycling and increase the potential of titanium electrode usage in production.

Inhibition effect of amine compounds derived from hardening agents on the extraction of hydrogen bromide by water from the pyrolysis oil of brominated printed circuit boards

The pyrolysis oil of waste printed circuit boards (PCBs) obtained through industrially feasible methods commonly contains high concentrations of hydrogen bromide (HBr). This HBr must be further eliminated if the oil is intended to be used in commercial applications. For this purpose, a conventional liquid-liquid extraction process was explored using water as the extracting solvent. It was shown that the extraction efficiency decreases with the concentration of HBr in oil, reaching a limiting concentration below which HBr can hardly be removed. This finding was explained by considering the presence of amines in oil that result from the decomposition of amine-hardening agents in epoxy boards. In connection with these results, the distribution equilibria of HBr in a phenolic model oil–aqueous biphasic system was theoretically and experimentally analysed. The results revealed that the presence of amines in concentrations as low as 0.1 wt% of nitrogen was sufficient to inhibit the removal of HBr below the 1000 ppm level. The dissociation constant of HBr in oil and the partition coefficient of bromine ions between the two phases were evaluated, obtaining 0.088 mol dm−3 and 2.6 × 10−4, respectively. The findings of this work are fundamental for the optimal production of bromine-free oils from waste PCBs.

Core-shell Cu@Au nanoparticles as an optical probe for ultrasensitive detection of chromium(VI) via an etching effect

Under normal circumstances, chromate ions cannot oxidize core-shell Cu-Au nanoparticles (NPs) because the standard redox potential of the Cr(VI)/Cr(III) system is lower than that of Au(I)/Au. However, in the presence of a certain concentration of hydrogen bromide, the Nernst potential becomes higher than that of Au(I)/Au and Cu(II)/Cu (as calculated by the Nernst equation). Based on this finding, a colorimetric method was developed that is based on oxidative etching of Cu@Au NPs by chromate. The Cu-Au NPs have a light red color in the presence of 5 mM HBr. On addition of Cr(VI), the gold shell is rapidly etched from the surface of the Cu-Au NPs, and this is accompanied by a color change to blue. The color changes were characterized by UV-vis spectroscopy. The absorbance at 526 nm changes in the 0.4 nM to 1 μM chromate concentration range, and the detection limit is 0.21 nM.

Destruction of the flame retardant hexabromocyclododecane in a full-scale municipal solid waste incinerator.

Hexabromocyclododecane containing polystyrene foam obtained from the building and construction market has been co-incinerated in a full-scale waste incineration plant. The co-feeding of 1 and 2 wt% of polystyrene foam had no influence on the operation of the plant. The bromine content increased the raw gas hydrogen bromide concentration slightly. The air emission, including that of dioxins and bromine, was not altered and so was the quality of the solid residues. The hexabromocyclododecane concentrations in the solid residues were almost identical, regardless of whether or not and how much polystyrene foam was added. The obtained destruction efficiency was >99.999% independent of the amount of added polystyrene foam. This finding indicates a virtually total destruction of hexabromocyclododecane.

Selective hydrobromination of metallurgical-grade silicon in a flow reactor system

Reactions of metallurgical-grade silicon (MG-Si) with gaseous hydrogen bromide (HBr) has been monitored by means of online gas chromatography in a flow reactor system. The formation of tri-bromosilane started to occur at 380 °C, accompanied by the consumption of HBr. The conversion of HBr into bromosilanes increased with an increase in reaction temperature and reached a maximum at 440 °C. An increase of the HBr concentration in a HBr-N2 mixed gas led to an increase in the consumption of MG-Si, while it reduced the selectivity of the tri-bromosilane formation. An increase in total flow rate of the reaction gas caused a dramatic decrease in the HBr conversion and enhanced the selectivity of the tri-bromosilane formation. The rate constant for overall bromination reaction at 400 °C was measured to be 0.46 s−1. Concentrations of impurities in the product were much less than those in MG-Si. Moreover, kerf loss silicon was subjected to the bromination reaction under the optimized conditions.

Stratospheric HBr concentration profile obtained from far‐infrared emission spectroscopy

Hydrogen bromide (HBr) is the principal bromine sink species for the ozone loss chemistry induced by bromine‐containing gases in the stratosphere. We report a 1994 balloon‐based measurement of the daytime stratospheric HBr profile between 20 and 36.5 km altitude. The average concentration result of 1.31±0.39 parts per trillion in volume (pptv) and an analysis for the concentration versus altitude profile are consistent with previously reported measurements. These results strengthen the evidence for a significantly higher HBr concentration than that predicted by current photochemical models which, on the basis of recent kinetics results, do not include significant HBr production by the reaction branch, BrO + HO2 → HBr + O3.

Kinetics; of Hydrogen Oxidation Part 5. Inhibition and Catalysis at Low Pressures

Abstract The switching of inhibition to catalysis at low pressures is analysed. It occurs at a certain concentration of hydrogen bromide, which depends on temperature and pressure. Catalysis is caused by very fine balancing of the processes H + HBr ⇌2H2+ Br. Other elementary processes can cause either inhibition or catalysis depending on the kinetic scheme in which they are involved.

Hydrocarbon cool flames and the influence of hydrogen bromide

Small amounts of hydrogen bromide added ton-pentane + 1.33 O2mixtures lower both the limiting pressure for the onset of two-stage ignition and also, to a smaller extent, that for the appearance of cool flames. The induction period preceding the first cool flame, ז1, is shown to be related to the initial pressure,P0, by a relation of the form ז1=kP-n0+c, wherek,nandcare constants for a given set of initial conditions. The results show that c ≠ 0 and that the addition of hydrogen bromide reduces both ז1andc. However, since ז1≽candcis always finite, it is clear that, even at temperatures above the ignition profiles, ignition continues to take place as a two-stage process. Plots of lg ז1against reciprocal temper­ature are invariably characterized by a well-defined change in slope and the temperature at which this occurs decreases with increasing concentration of hydrogen bromide, eventually reaching a limiting value ofca. 270 °C. Above this temperature the slopes of the plots are more or less independent of hydrogen bromide and correspond to an overall activation energy of 82 kJ mol-1. Below this temperature the apparent energy of activation decreases from 206 to 113 kJ mol-1as the concentration of hydrogen bromide is increased. Similarly there is a limiting concentration of the additive above which the pressure change accompanying the first cool flame is not appreciably increased except at low temperatures. In systems which exhibit multiple cool flames, the second and fourth cool flames are generally too indistinct for their characteristics to be measured with any accuracy. However, the third cool flame appears as a well-defined but relatively weak pressure pulse. In striking contrast to the behaviour of the first cool flame, neither the third cool flame nor the induction period preceding it is appreciably affected by the presence of hydrogen bromide. It thus appears that, although the halogen compound is pre­sumably involved in the chemical reactions leading to the first cool flame, the third cool flame is propagated by intermediates whose mode of forma­tion is independent of the additive.

The catalysed thermal decomposition of organic acids. Part I. The catalysed decomposition of cyclohexanecarboxylic acid by hydrogen bromide

Hydrogen bromide catalyses the thermal decomposition of cyclohexanecarboxylic acid into essentially cyclohexene, carbon monoxide, and water in the temperature range 642–703 K in a seasoned Pyrex reaction vessel. The first-order rate constants are proportional to the hydrogen bromide concentration. The reaction is homogeneous and predominantly molecular. The Arrhenius equation is k2/cm3 mol–1 s–1= 1013·562 exp (–34,480/RT).

Synthesis of isoprene from propylene—IV. Decomposition of 2-methylpent-2-ene in the presence of HBr

1. 1. A study has been made of the effect of temperature, contact time and hydrogen bromide concentration on isoprene yield and of the composition of decomposition products of 2-methylpent-2-ene in the presence of HBr at atmospheric pressure in vacuo.

The Effect of Catalyst Containing Bromine in Liquid Phase Air Oxidation I

The liquid phase oxidation of p-xylene was carried out in the presence or absence of solvents (fatty acids) using cobaltous stearate, organic bromine compounds, hydrogen bromide and their mixtures as catalyst. The reaction temperature and the oxygen partial pressure were varied in the range of 130∼230°C and 1∼16atm., respectively. p-Toluic acid was also oxidized in the same manner in di-tert-butyl benzene. The following results were obtained.1) By use of bromine compounds other than hydrogen bromide as catalyst, p-xylene always yielded larger amount of p-toluic acid than p-tolualdehyde. However, aldehyde predominated when hydrogen bromide was used as catalyst and the yield of aldehyde increased with an increase in the concentration of hydrogen bromide.2) In the case of p-xylene oxidation in the fatty acid solvent, the yield of aldehyde using bromine compounds with cobaltous salt as catalyst was higher than when using cobaltous salt alone. It seems, therefore, that hydrogen bromide participates to some extent in this reaction.3) In the cases of p-xylene oxidation in the acidic solvent and p-toluic acid oxidation in inert solvent under the condition of high temperatures and high pressures, synergism of cobaltous salt with bromine compounds was noticed.4) It is concluded from the above that an addition of bromine compounds in the reaction mixture is more effective to the toluic acid→terephthalic acid stage than to the xylene→toluic acid stage.

Hot Atom Reactions in Organic Bromides

Summary The yields of parent bromide from neutron irradiation of bromoethane, 1:1 -dibromoethane and 1:1:2:2- tetrabromoethane have been measured as a function of either bromine or hydrogen bromide concentration. The results appear to be consistent with those predicted by the "billiard-ball" replacement mechanism.