Decomposition Of Iodide Research Articles

Gaseous diffusion coefficients of methyl bromide and methyl iodide into air, nitrogen, and oxygen

AbstractThe gaseous diffusion coefficients of methyl bromide (CH3Br) and methyl iodide (CH3I) into dry air, nitrogen, and oxygen have been measured in the temperature range 303–453 K and at atmospheric pressure via the Taylor dispersion method. Both for methyl bromide and methyl iodide, the diffusion coefficients do not vary in practice on substituting pure nitrogen or oxygen for dry air. The diffusion coefficients for methyl iodide are systematically smaller than those for methyl bromide by about 11%. For the methyl iodide‐oxygen system, the effect of the thermal decomposition of methyl iodide has been observed at 453 K. The present results can be reproduced well by the functional form D = ATB, where D (cm2s−1) is the diffusion coefficient at 101 325 Pa (1 atm) and T (K) is the absolute temperature. The constants A and B are as follows: methyl bromide‐(air, nitrogen, oxygen), A = 5.57 × 10−6, B = 1.76; methyl iodide‐(air, nitrogen, oxygen), A = 5.26 × 10−6, B = 1.75. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20255

Characterization of Sonochemical Reactor for Physicochemical Transformations

Complete knowledge of the pressure field distribution in a sonochemical reactor should be known for an efficient utilization of acoustic energy emitted by the transducers for targeted physicochemical transformations using cavitation phenomena. This work deals with the identification of the active and passive regions in the sonochemical reactor based on the measured pressure field intensities. Iodine liberation experiments based on the decomposition of aqueous potassium iodide (KI) as a representative of cavitationally induced chemical transformation were carried out at various locations in the bath type reactor and compared with the measured pressure intensities in the reactor. Similarly, extraction of natural dye from the bark of Pterocarpus marsupium tree has also been carried out as a representative of cavitationally induced physical transformation (extraction) and compared with the measured pressure intensities. Both the transformations indicate a similar trend of variation in the degree of transformation when correlated with the local pressure and indicated the existence of an optima, which is at a plane (≈3λ/2) away from the transducer surface.

Ceria as a catalyst for hydrogen iodide decomposition in sulfur–iodine cycle for hydrogen production

Abstract In this work, ceria (CeO 2 ) prepared with different methods and at various calcination temperatures have been tested to evaluate their effect on hydrogen iodide (HI) decomposition in sulfur–iodine (SI) cycle at various temperatures. The CeO 2 catalysts' strongly enhance the HI decomposition by comparison with blank test, especially gel CeO 2 300. TG–FTIR, BET, XRD, TEM and TPR were performed for catalysts' characterization. The results show that the CeO 2 catalyst synthesized by citric-aided sol–gel method and calcined at low temperature ( 3+ and oxygen vacancy, play the dominant role in surface reactions of HI decomposition. A new reaction mechanism for HI catalytic decomposition over CeO 2 catalyst is proposed.

Use of metallic Ni for H 2 production in S–I thermochemical cycle: Experimental and theoretical analysis

Abstract The gaseous hydrogen iodide decomposition is a thermodynamically limited reaction and subsequently a considerable energy expense for the separation and recirculation of the unreacted species is required. In addition the homogeneous gas phase decomposition of hydrogen iodide has a very low rate and the use of a catalytic system, which is generally highly expensive, is necessary. Hence, with the aim of overcoming the bottleneck represented by the hydrogen releasing step of the Sulphur–Iodine (S–I) cycle in terms of costs and process efficiency, in the present work an alternative version of the HI decomposition section (HIx section) is proposed. In that alternative configuration the addition of metallic nickel into the heavy phase coming from Bunsen reaction is conceived in order to quantitatively obtain hydrogen at low temperature. A theoretical and experimental investigation has been performed, a new cycle has been conceived and the resulting energy demand assessed.

G0801-1-6 オープンサイクル熱化学IS法における水素生成反応器の性能向上(動力エネルギー部門一般(1))

Merits of open-cycle thermochemical processes are characterized -as compared with closed-cycle thermochemi-cal processes to make water-splitting- by unnecessity of high-temperature equipments, acceptable low thermal efficiency than water electrolysis to produce hydrogen, and conversions of unwanted materials into valuable ma-terials. This study focuses a open cycle process to produce hydrogen and sulfuric acid from water and sulfur dioxide which is obtained from sulfur of general industry wastes. Improvement of hydrogen iodide decomposition rate by absorptions of reactant of iodine into active carbon was adapted to measure thermal burden on hydrogen production section and to utilize low temperature waste heat ranged 200-400℃. A heat requirement to drive a hydrogen production reactor with active carbon was estimated to be 194 kJ/mol-H_2, thereby heat input of total process was reduced from 6380 without active carbon to 1480 kJ/mol-H_2 with that.

Effect of preparation methods on Pt/alumina catalysts for the hydrogen iodide catalytic decomposition

Three kinds of Pt/alumina catalysts were prepared by impregnation-hydrogen reduction, impregnation-hydrazine reduction and electroless plating methods. Their differences in the structures, specific areas and particle sizes were characterized by XRD, BET and TEM, respectively. Furthermore, their catalytic activities for the hydrogen iodide (HI) decomposition were evaluated in a fixed bed reactor. The results show that the catalyst 5%Pt/Al2O3 prepared by the electroless plating has the optimum catalytic properties for HI decomposition owing to the high dispersion of the platinum nano-particles (<5 nm) on the alumina supports.

Decomposition of hydrogen iodide in the S–I thermochemical cycle over Ni catalyst systems

Abstract The sulphur–iodine thermochemical cycle for hydrogen production has been investigated by ENEA (Agency of New Technologies, Energy and Environment, Italy) over the last 5 years, with a particular focus on chemical aspects. Regarding the hydrogen iodide decomposition, four γ-alumina-supported nickel catalysts were produced and characterized, and then tested in terms of catalytic activity and stability by means of a tubular quartz reactor. In particular, the relationship between catalytic activity and preparation procedure was investigated. From the experimental data acquired, it can be concluded that three of the four catalysts tested demonstrated high catalytic activity, since hydrogen iodide conversion was almost coincident with the theoretical equilibrium value. On the other hand, for all the catalysts, a gradual but considerable deactivation phenomenon was observed at 500 °C, while at a temperature higher than 650 °C the catalytic activity was recovered.

Decrease the rate of recycling agents in the sulfur–iodine cycle by solid phase separation

A modification of the conventional Sulfur–Iodine (S–I) thermochemical water-splitting cycle (TWSC) by means of double exchange reactions (metathesis) is presented. In conventional S–I TWSC an excess of water and iodine has to be used for phase separation and a large amount of heat is requested for water and iodine evaporation. To reduce the amount of these chemicals we propose the formation of solid phases obtained by using lead as the precipitating agent. The obtained solid can be easily separated from the liquid by filtration avoiding evaporation processes. The formation of anhydrous gases allows to minimize corrosion problems and to reduce heat demand during hydrogen iodide decomposition.

Hydrogen iodide decomposition over nickel–ceria catalysts for hydrogen production in the sulfur–iodine cycle

Abstract In this work, pure CeO2 and three nickel–ceria catalysts prepared by different methods have been tested to evaluate their effect on hydrogen iodide (HI) decomposition in the sulfur–iodine (SI or IS) cycle at various temperatures. BET, XRD, HRTEM and TPR were performed for catalysts characterization. Indeed, the pure CeO2 also strongly enhance the decomposition of HI to H2 by comparison with blank yield. Nickel–ceria catalysts show better catalytic activity, especially Ni-doping-G sample. It is found that, through the sol-gel method, the Ni2+ ions have dissolved into the ceria lattice instead of the Ce4+ ions during the synthesis process of Ni-doping-G sample. Oxygen vacancies are formed because of the charge imbalance and lattice distortion in CeO2. The presence of Ni during the CeO2 synthesis process of Ni-doping-G also causes smaller average particle size, larger surface area, better thermal stability and better Ni dispersion than the Ni-loading samples. These provide nickel–ceria catalyst with a potential to be used in the SI cycle for HI decomposition.

Influence of the oxidative/reductive treatments on Pt/CeO 2 catalyst for hydrogen iodide decomposition in sulfur–iodine cycle

Abstract A Pt/CeO 2 catalyst was prepared by sol–gel method. The as-received sample was successively oxidized, reduced and re-oxidized. The samples were characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS) and hydrogen iodide (HI) catalytic decomposition activity evaluation for the sulfur–iodine cycle. The oxidative/reductive atmosphere affected the structure and performance of the catalyst by the strong metal-support interaction (SMSI). It was suggested that a migration of Ce 4+ from the bulk to the surface occurred during the reductive treatment. The diffusion process was reversed when the atmosphere was changed to an oxidative one. The decoration or encapsulation of Pt by ceria support changed with the atmosphere, and affected the activity of the catalyst. At temperature below 400 °C, the reduced sample exhibited the best activity. After then the activity of the reduced and re-oxidized samples tends to be the similar, but still better than the as-received and oxidized samples. The surface and interfacial Pt 0 sites were both considered as the effective factors. Models were constructed to describe the diffusion of Ce 4+ and oxygen vacancies as well as the possible shell-core structure of Pt crystallites and the decoration/encapsulation by ceria support.

Catalytic Thermal Decomposition of Hydrogen Iodide in Sulfur−Iodine Cycle for Hydrogen Production

In this work, the Pt/CeO2 catalysts with different calcination temperatures have been tested to evaluate their effect on hydrogen iodide (HI) decomposition in the sulfur−iodine cycle at various temperatures. The Pt/CeO2 catalysts strongly enhance the decomposition of HI to H2 by comparison with blank yield, especially the catalysts calcinated at high temperature. TG-FTIR, BET, XRD, TEM, and TPR were performed for catalysts characterization. Platinum was introduced into ceria to form the Pt/CeO2 catalysts by sol–gel. It was found that, through the sol–gel method, the Pt ions could be inserted into the ceria lattice. This brought about a different synergistic effect between the Pt and Ce components, such as increase of the oxygen mobility in ceria support and improvement of the thermal stability of catalyst. According to a so-called “self-regeneration” model and the results of XRD and TPR, a similar mechanism is supposed to exist in the Pt/CeO2 catalysts synthesized by sol–gel at high calcination temperatur...

Homogeneous Phase Polymerization of Vinylidene Fluoride in Supercritical CO2: Surfactant Free Synthesis and Kinetics

AbstractSummary: Vinylidene fluoride (VDF) polymerizations were carried out in homogeneous phase with supercritical carbon dioxide (scCO2) at 120 °C and 1500 bar. To control molecular weight perfluorohexyl iodide was used. Molecular weight analysis by size‐exclusion chromatography indicates that polymers of low polydispersities ranging from 1.5 to 1.2 at the highest iodide concentration of 0.25 mol · L−1 were obtained. In addition, polymer molecular weight increases linearly with reaction time, indicating that living conditions were established. The “livingness” is based on the labile C‐I bond. The weakness of the C‐I bond is associated with a fast decomposition of the original hexyl iodide, thus, contributing to initiation and to a significant increase in the initiation rate in the initial phase of the polymerization.

Effect of preparation method on platinum–ceria catalysts for hydrogen iodide decomposition in sulfur–iodine cycle

Abstract In this work, three catalysts, Ce 0.99 Pt 0.01 O 2 called the Pt-doping sample, Pt / CeO 2 called the Pt-loading sample and pure CeO 2 , have been tested to evaluate their effect on hydrogen iodide (HI) decomposition in sulfur–iodine (SI or IS) cycle at various temperatures. BET, XRD, TPR and TEM were performed for catalysts characterization. Platinum was introduced into ceria to form the Pt-doping sample by sol–gel. It was found that, through sol–gel method, the Pt ions could be inserted into the ceria lattice. This brought about a different synergistic effect between the Pt and Ce components in the Pt-doping sample by comparison with the Pt-loading sample prepared by traditional impregnation, such as increase of the oxygen mobility in ceria support and improvement of the thermal stability of catalyst. Indeed, the pure CeO 2 also strongly enhances the decomposition of HI to H 2 by comparison with blank yield, and the Pt-doping and Pt-loading samples show better catalytic activity, especially the Pt-doping sample. These provide this material with a potential to be used in SI cycle for hydrogen iodide decomposition.

Detailed kinetic modeling and sensitivity analysis of hydrogen iodide decomposition in sulfur–iodine cycle for hydrogen production

A new detailed kinetic modeling was developed for homogeneous decomposition of hydrogen iodide (HI) in the sulfur–iodine cycle. Results show the HI decomposition reaction is sensitive to temperature, and the response time of reaction reduces from 1 s to 10 ms as temperature increases from 500 to 800 ∘ C . The decomposition is also improved as pressure increased. Kinetic calculations are also compared with the experimental data, and all trends of the experiment can be reproduced by the model. Sensitivity analysis shows that the reactions of HI with HI, H and I play a major role in the hydrogen production process and the hydrogen consumption occurs primarily by reaction of H with I 2 and reaction of I with H 2 to form HI. As temperature increases, different reactions play a dominant role in HI decomposition process. Based on the detailed kinetic modeling and sensitivity analysis results, the HI decomposition reaction path diagram was constructed in this paper.

The decomposition of normal hexyl radicals

Abstract Normal hexyl radicals generated from the decomposition of n-hexyl iodide have been decomposed in single pulse shock tube experiments. All the products arising from the decomposition of 1-hexyl (the initial reactant) and 2-hexyl and 3-hexyl (isomerization products) have been detected in the temperature range 890–1020 K and 1.5–5 bar pressures. We find that k ( C 6 H 13 - 3 = > C 2 H 5 + 1 - C 4 H 8 ) / k ( C 6 H 13 - 3 = > CH 3 + 1 - C 5 H 10 ) = 3.4 ± 0.1 when this is combined with literature values of the beta bond scission reactions of hexyl radicals we find the following high pressure rate expressions for the isomerization processes; k ( C 6 H 13 - 1 = > C 6 H 13 - 2 ) = 1.83 × 10 2 T 2.55 exp ( - 5516 / T ) s - 1 k ( C 6 H 13 - 1 = > C 6 H 13 - 3 ) = 6.98 × T 3.2 exp ( - 8333 / T ) s - 1 with an uncertainty of a factor of 1.5 in the rate constants and 5 kJ/mol in the activation energy. They are compatible with low as well as the high temperature results. The effects of energy transfer have been deduced from a master equation RRKM analysis covering the pressure range of 0.1–100 bar, 500–1900 K. The low reaction thresholds and multichannel nature of the process leads to special problems. These include a non-monotonic decrease in rate constants from high pressure values with increasing temperature and rate constants in the “fall-off” region that are dependent on the initial isomer. Overall effects are minimal in the 100 bar region. Maximum deviation from high pressure behavior is approximately an order of magnitude near 1000 K for reactions in the 1 bar region.

Flowsheet study of the thermochemical water-splitting iodine–sulfur process for effective hydrogen production

Abstract The Japan Atomic Energy Agency (JAEA) is performing research and development on the thermochemical water-splitting iodine–sulfur (IS) process for hydrogen production with the use of heat (temperatures close to 1000 °C) from a nuclear reactor process plant. Such temperatures can be supplied by a High Temperature Gas-cooled Reactor (HTGR) process. JAEA's activity covers the control of the process for continuous hydrogen production, processing procedures for hydrogen iodide (HI) decomposition, and a preliminary screening of corrosion resistant process materials. The present status of the R&D program is reported herein, with particular attention to flowsheet studies of the process using membranes for the HI processing.

TG-FTIR, DSC, and Quantum-Chemical Studies on the Thermal Decomposition of Quaternary Ethylammonium Halides

The thermal decomposition of quaternary ethylammonium chloride, bromide, and iodide has been studied using the experimental techniques of thermal gravimetry coupled to Fourier transform infrared spectroscopy (TG-FTIR) and differential scanning calorimetry (DSC) as well as the density functional theory (DFT) and MP2 quantum-chemical methods. These compounds decompose in a one-step process, and the almost perfect agreement between the experimental IR spectra and those predicted at the B3LYP/6-311G(d,p) level demonstrates for the first time that decomposition produces an equimolar mixture of triethylamine and a haloethane. The respective experimental enthalpies of dissociation of the chloride, bromide, and iodide are 158, 181, and 195 kJ/mol. These values correlate well with the calculated enthalpies of dissociation based on crystal lattice energies and quantum-chemical thermodynamic barriers. The experimental activation barriers were derived from the least-squares fit of the F1 kinetic model (first-order process) to thermogravimetric traces. These estimates are 184, 286, and 387 kJ/mol for chloride, bromide, and iodide, respectively, and agree well with the theoretical calculations. It has been demonstrated that the theoretical approach assumed in this work is capable of predicting the relevant characteristics of the thermal decomposition of solids with experimental accuracy. DFT methodology is recommended for the quantum-chemical part of the model: B3LYP for evaluating the thermodynamic barriers and MPW1K for assessing the activation characteristics. These quantum-chemical data then have to be combined with crystal lattice energies. The latter should be calculated using both electrostatic and repulsion-dispersion terms.

Applied Thermodynamics in Chemical Technology: Current Practice and Future Challenges

AbstractFor Abstract see ChemInform Abstract in Full Text.

Shock Wave Study on the Thermal Unimolecular Decomposition of Allyl Radicals

We present the first direct study on the thermal unimolecular decomposition of allyl radicals. Experiments have been performed behind shock waves, and the experimental conditions covered temperatures ranging from 1125 K up to 1570 K and pressures between 0.25 and 4.5 bar. Allyl radicals have been generated by thermal decomposition of allyl iodide, and H-atom resonance absorption spectroscopy has been used to monitor the reaction progress. A marked pressure dependence of the rate constant has been observed which is in agreement with the results from a master equation analysis. However, our experimental results as well as our Rice-Ramsperger-Kassel-Marcus calculations seem to contradict the results of Deyerl et al. (J. Chem. Phys. 1999, 110, 1450) who investigated the unimolecular decomposition of allyl radicals upon photoexcitation and tried to deduce specific rate constants for the unimolecular dissociation in the electronic ground state. At pressures around 1 bar we extracted the following rate equation: k(T) = 5.3 x 10(79)(T/K)(-19.29) exp[(-398.9 kJ/mol)/RT] s(-1). The uncertainty of the rate constant calculated from this equation is estimated to be 30%.

Determination of the rate coefficient for the C 3H 3 + C 3H 3 reaction at high temperatures by shock-tube investigations

The kinetics of the C3H3 + C3H3 reaction was investigated behind incident shock waves at temperatures ranging from 995 to 1440 K and at pressures between 600 and 1000 mbar with argon as bath gas. The C3H3 radicals were generated by thermal decomposition of propargyl iodide with initial concentrations between 3 × 1015 and 6 × 1015 cm−3 corresponding to initial mole fractions between 750 and 800 ppm. Measurement of the UV absorption at 332.5 nm was used to monitor the C3H3 concentration, and the rate coefficients for the C3H3 + C3H3 reaction were determined by fitting a second-order rate law to the absorption–time profiles. Values between 2 × 10−11 cm3 s−1 near 1000 K and 7.5 × 10−12 cm3 s−1 near 1400 K were obtained with no significant pressure dependence. The negative temperature dependence can be expressed in the form k1 = 5.8 × 10−13 exp (3534 K/T) cm3 s−1 with an estimated maximum error of ±30% in k1. The reaction channel leading to C6H5 + H is estimated to contribute with less than 10% to the overall reaction at temperatures between 1000 and 1300 K and, pressures ranging from 80 to 500 mbar.