Hydrogen Iodide Decomposition Research Articles

Simulation study on the catalytic decomposition of hydrogen iodide in a membrane reactor with a silica membrane for the thermochemical water-splitting IS process

Catalytic decomposition of hydrogen iodide in a membrane reactor was investigated theoretically for the application to the hydrogen production step in the thermochemical iodine–sulfur (IS) process. Characteristics of the membrane reactor were evaluated using observed permeances of H 2 and HI in a homemade silica membrane that was prepared by chemical vapor deposition (CVD) method (selectivity of H 2/HI: 650). The effect of the H 2/I 2 selectivity on the performance of the membrane reactor was evaluated by simulation since I 2 permeance through the homemade silica membrane could not be determined so far because of the difficulty of the measurements. It was found from the simulation study that the conversion of over 0.9 would be attainable using the membrane reactor with the homemade silica membrane. Design criterion of the membrane reactor was discussed using the relationships between the ratio of reaction zone volume to the membrane surface area, the dimensionless reactor length and the conversion.

Separation of hydrogen from a H2 H2 OHI gaseous mixture using a silica membrane

Hydrogen separation characteristics of silica membranes prepared by chemical-vapor deposition (CVD)-in an H{sub 2}-H{sub 2}O-HI gaseous mixture were evaluated for the application to hydrogen iodide decomposition in the thermochemical iodine-sulfur (IS) process. Porous alumina tubes with a pore size of 10 nm and different gas-permeating-portion lengths [20 mm (S membranes) and 100 mm (L membranes)] were modified by CVD using tetraethoxysilane as the Si source. Pore closure was controlled by CVD to maintain high hydrogen permeance while lowering only HI permeance. At a certain point, CVD was stopped using He/N{sub 2} selectivity as the indicator of pore closure. H{sub 2}/N{sub 2} selectivities of the modified membranes, which were measured by a single-component permeation experiment, showed 53, 9.2, 4.1, 135, and 6.6 at 600 C for S1, S2, S3, L1, and L2 membranes, respectively. Separation experiments of the H{sub 2}-H{sub 2}O-HI gaseous mixture (a molar composition of 0.09:0.78:0.13) in the modified membranes were carried out at 300--600 C. Hydrogen permeance was almost the same as the single-component permeance. The separation factors of H{sub 2}-H{sub 2}O and H{sub 2}-HI were over 3 and 150, respectively. The S3 membrane showed the highest hydrogen permeance (on the order of 10{sup {minus}7} mol/Pa.m{sup 2}s) andmore » the highest separation factor of H{sub 2}-HI (650 at 450 C).« less

Hydrogen separation in H 2–H 2O–HI gaseous mixture using the silica membrane prepared by chemical vapor deposition

Hydrogen separation in H 2–H 2O–HI gaseous mixture using the silica membrane prepared by CVD was evaluated aiming at the application for hydrogen iodide decomposition in the thermochemical IS process. Porous alumina tubes having pore size of 100 nm (M1) and 10 nm (M2) were modified by chemical vapor deposition using tetraethoxysilane as the Si source. Single-component permeance to He, H 2, and N 2 was measured at 300–600°C. Hydrogen permeance of the modified membranes at a permeation temperature of 600°C was about 6×10 −9 mol/Pa m 2 s. H 2/N 2 selectivities at 600°C were 5.2 and 160 for M1 and M2 membrane, respectively. Separation experiments of a H 2–H 2O–HI mixture using the modified membranes were carried out at 300–600°C. Hydrogen permeances were almost the same as the single-component permeances, whereas HI permeances were below 1×10 −11 mol/Pa m 2 s. The hydrogen permeances were not changed after one day exposure in a mixture of H 2–H 2O–HI with a molar composition of 0.23:0.65:0.12 at 450°C.

Dilanthanum dioxymonosulfate as a recycle reagent and recycle substrate for the sulfur dioxide-iodine thermochemical hydrogen cycle

Insoluble dilanthanum oxide-sulfite-sulfate-hydrates were prepared by reacting dilanthanum dioxymonosulfate with sulfur dioxide in aqueous media. These compositions reacted with iodine to yield sulfate in the solid phase and hydrogen iodide in the gas phase. Highest yields of hydrogen iodide were measured at 660 K for a reaction time of a few seconds. Yields also depended on the sulfite content of the hydrate compositions and were highest when the dilanthanum dioxymonosulfate was 60% neutralized. Higher yields of hydrogen iodide were obtained by a second iodine oxidation after separation of the first solid product. A water splitting thermochemical cycle using these reactions is described in which hydrogen is produced by catalytic decomposition of hydrogen iodide and oxygen results from thermal decomposition of the solid product.

Studies on a Membrane Reactor

Abstract Simulation is used to evaluate the performance of a catalytic reactor with permeable wall (membrane reactor) in shifting the equilibrium of three reversible reactions (cyclohexane dehydrogenation, hydrogen iodide decomposition, and propylene disproportionation). It is found that the preferred choice of cocurrent or countercurrent operation is dependent on the physical properties and operating conditions. Methods of enhancing conversion are suggested and temperature effects are discussed.

Thermochemical hydrogen production with the sulfur dioxide-iodine cycle by utilization of dipraseodymium dioxymonosulfate as a recycle reagent

Insoluble, dipraseodymium oxide-sulfite monosulfate hydrates were prepared by reaction of dipraseodymium dioxymonosulfate with sulfur dioxide in aqueous media at 340 K. These compositions reacted with iodine to yield sulfate in the solid phase and hydrogen iodide in the gas phase. High yields of hydrogen iodide were measured at 770 K for a reaction time of ten minutes. Yields also depended on the sulfite content of the hydrate compositions, and were highest when the dipraseodymium dioxymonosulfate was 60% neutralized with sulfurous acid. An increased yield of hydrogen iodide was obtained by a second iodine oxidation after separation of the first gaseous products. A water splitting thermochemical cycle utilizing these reactions is described in which hydrogen is produced by catalytic decomposition of hydrogen iodide, and oxygen results from thermal decomposition of the solid product, that also yields sulfur dioxide and dipraseodymium dioxymonosulfate for recycle.

Kinetics of the catalytic decomposition of hydrogen iodide in the thermochemical hydrogen production

The decomposition rates of hydrogen iodide over platinum supported γ-alumina were measured in the range from 480 to 700 K by the use of a flow method. It was found that Pt/γ-alumina catalyst was effective for the decomposition of hydrogen iodide. According to the Langmuir-Hinshelwood model, an overall rate equation was obtained on the basis of the mechanism where the rate-determining step was a surface reaction. Experimental data were well correlated with the rate equation.

Decomposition of Hydrogen Bromide or Iodide by Gas Phase Electrolysis

Abstract Gas phase electrolysis of HBr or HI was studied by using a fuel-cell-type electrolyzer provided with graphite gas diffusion electrodes and liquid film electrolyte of H3PO4. Current efficiency 100% may be achieved at decomposition voltages of 0.73 V (at 100 mA cm−2 and 150 °C) for HBr and 0.28 V (at 100 mA cm−2 and 145 °C) for HI. Both bromine and iodine produced may smoothly be evolved out of the anode in the gas or liquid form without being dissolved into the electrolyte H3PO4, causing no trouble on the separation of products. This electrolytic method may be incorporated in the bromine or iodine cycles for thermochemical hydrogen production to constitute an effective hybrid system.

The dependence of the rate constant of chemical reaction on density derived from the generalized Enskog equation for dense gases

For reaction A+A=B+C it is shown (after application of formalism similar to that used by Prigogine and Xhrouet for analysis of generalized Boltzmann equation) that the ratio k/k0 (where k and k0 are the values of rate constant in dense and dilute gas, respectively) is equal to the radial distribution function χ taken at the point of contact of reacting spheres. Comparison of theoretical results derived in this paper and experimental results due to Kistiakowsky on decomposition of hydrogen iodide is given and good agreement between those results is obtained.

Thermal efficiency of the magnesium-iodine cycle for thermochemical hydrogen production

The magnesium-iodine cycle, consisting of the redox reaction of iodine with magnesium oxide, the thermal decomposition of magnesium iodate, the hydrolysis of magnesium iodide and the thermal decomposition of hydrogen iodide, for thermochemical hydrogen production has been evaluated. The thermal efficiency of the process was calculated based on material and energy balances for three proposed flow-sheets. The three flow-sheets varied according to the method used (quenching, selective absorption of HI by magnesium oxide and the two-step chemical decomposition of HI by magnetite) to separate the products of hydrogen iodide decomposition. Values of 9–34% thermal efficiency were given as a function of the heat recovery of 65–85% for the quench method, 19–37% for the MgO method and 16–35% for the Fe 3O 4 method. In order to obtain more than 25–30% of the thermal efficiency, heat recovery must be more than 80%.

EFFICIENT PHOTOELECTROCHEMICAL CONVERSION OF SOLAR ENERGY WITH n-TYPE SILICON SEMICONDUCTOR ELECTRODES SURFACE-DOPED WITH IIIA-GROUP ELEMENTS

The stability of an n-type silicon (n-Si) electrode was remarkably improved by the doping in a thin surface layer with boron, aluminium or indium. Photoelectrochemical cells having an n-Si electrode surface-doped with boron and coated with a small amount of platinum or palladium converted light energy into either electricity or chemical energy via decomposition of hydrogen iodide into hydrogen and iodine without external bias with an outstanding high efficiency.

The Decomposition of Hydrogen Iodide and Separation of the Products by the Combination of an Adsorbent with Catalytic Activity and a Temperature-swing Method

Abstract The decomposition of hydrogen iodide and the separation of the products by the combination of a column packed with an adsorbent with catalytic activity (platinum-supported active carbon, 2.3 wt%) and a temperature-swing method (450–900 K) are carried out, and the features and the problems of the method are examined. A one-step conversion of hydrogen iodide, 70%, is obtained at 450 K, where the equilibrium conversion is 13%. It is shown that the products of the decomposition of hydrogen iodide containing water are separated from each other.

Kinetics of the Catalytic Decomposition of Hydrogen Iodide in the Magnesium–Iodine Thermochemical Cycle

Abstract The decomposition of hydrogen iodide serves as the hydrogen-evolution step in several thermochemical water-splitting cycles, including the Magnesium–Iodine cycle. A kinetic analysis of the catalytic decomposition of hydrogen iodide has been carried out by the use of a flow method at 500–700 K. The platinum-supported active carbon catalyst (1 wt%) and the active carbon catalyst which have been found effective in the research reported previously, are used as the catalysts. The contact time-conversion relationships for both the catalysts are simulated successfully on the basis of an assumed reaction scheme. The influence of water vapor on the rate and the equilibrium of the decomposition of hydrogen iodide is negligibly small. The inhibition effect of iodine on the rate of the decomposition of hydrogen iodide over the platinum-supported active carbon catalyst is remarkable below 550 K.

Thermochemical hydrogen preparation—Part V. A feasibility study of the sulfur iodine cycle

A sulfur-iodine cycle consists of the following three reactions: 2H 2O + SO 2 + I 2 → H 2SO 4 + 2HI, H 2SO 4 → H 2O + SO 2 + 1 2O 2 , 2 HI → H 2 + I 2. It was found that the first reaction can be performed as a cell reaction without the addition of external energy. The sulfuric acid and the hydriodic acid are produced separately in the anode and cathode compartments, respectively. The second and third reactions can be carried out as catalytic thermal decompositions. A process flow sheet of this cycle and its mass balance was based on experimental results, and the heat balance for this cycle was made. It was found that internal heat exchange for this cycle was very large (about 2600 kcal/mol H 2), due mainly to the low yield of the decomposition reaction of hydrogen iodide. Theoretical and experimental studies were made to improve the yield of this reaction. The following three methods seem to be promising for this purpose: (1) continuous removal of the hydrogen produced in the reaction zone; (2) performance of the reaction at low temperature (185–250°C) and high pressure (100 atml; and (3) substitution of the benzene-cyclohexane cycle (6HI − C 6H 6 → C 6H 12 + 3I 2; C 6H 12 → C 6H 6 − 3H 2) for the hydrogen iodide decomposition step.

The Kinetic Behaviour of the Decomposition of Hydrogen Iodide on the Surface of Platinum

The Kinetic Behaviour of the Decomposition of Hydrogen Iodide on the Surface of Platinum

The calcium-iodine cycle for the thermochemical decomposition of water

A new four-step thermochemical cycle based on calcium and iodine is proposed for the decomposition of water. The chemical reactions comprising the cycle are: the redox reaction of iodine with calcium hydroxide; the thermal decomposition of calcium iodate; the hydrolysis of calcium iodide; and the thermal decomposition of hydrogen iodide. Experimental verification of each of these reactions and an evaluation of the thermal efficiency of the process based on the material and energy balances for a proposed flow sheet are also presented.

Synthesis of Chrysotile Fibers with an Addition of Magnesium Iodide under a Hydrothermal-Dehydration Process

Synthesis of long chrysotile fibers was studied under hydrothermal dehydration process with an addition of magnesium iodide which had the same structure as the bromide and was found to be effective in the formation of the fibers.In this experiment free iodine appeared in the slurry by decomposition of hydrogen iodide formed by hydrolysis of magnesium iodide. When the slurry was subjected to hydrogen pressure at initial stage of the reaction, satisfactory results were obtained. The product was a layer like natural chrysotile ore bundled from fibers of the almost same length. Therefore, it was deduced that iodide contained in the intermediates was easily dissociated and the bundling of fibers was carried out at a smaller degree of disturbance as compared with the bromide.Crystal growth may be controlled by initial hydrogen pressure and dehydration velocities. The velocities were also controlled by the reactivity of metallic iron added to the outside of the slurry container.

The thermal decomposition of ethyl ether on the surface of Platinum

It is of considerable interest to compare the velocities of homogeneous and heterogeneous gas reactions. In general homogeneous bimolecular reactions tend to become unimolecular in the presence of a catalyst, and the heat of activation falls to about one-half. This has been shown to be the case in the decomposition of nitrous oxide, hydrogen iodide, and ammonia. The question arises as to what is the effect of a catalyst on a homogeneous unimolecular reaction. The decomposition of gaseous diethyl ether was chosen for investigation on account of its simplicity; and an attempt has been made to compare the heterogeneous decomposition on the surface of platinum with that of the homogeneous reaction which has been investigated by Hinshelwood.

THE RATES OF SECOND-ORDER GAS REACTIONS

It has been shown that the most accurate existing measurements of the rates of second-order gas reactions show deviations from pure exponential temperature dependence, which can be empirically represented by a linear increase of the energy of activation with temperature. It is pointed out that this requires the chance of reaction to increase with the energy of the collision in a continuous fashion. Assuming a particular form for this variation, a theory is worked out which predicts that this linear increase shall fail at temperatures only slightly higher than those yet reached in the hydrogen iodide decomposition. There is reason to believe that the numerical results of this theory are substantially correct, even though the detailed assumptions are doubtless far from right.

The Photochemical Decomposition of Hydrogen Iodide; the Mode of Optical Dissociation

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThe Photochemical Decomposition of Hydrogen Iodide; the Mode of Optical DissociationBernard LewisBernard LewisMore by Bernard LewisCite this: J. Phys. Chem. 1928, 32, 2, 270–284Publication Date (Print):February 1, 1928Publication History Published online1 May 2002Published inissue 1 February 1928https://doi.org/10.1021/j150284a010RIGHTS & PERMISSIONSArticle Views137Altmetric-Citations4LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (780 KB) Get e-Alerts