Hydrogen Iodide Decomposition Research Articles

Experimental investigations of hydrogen iodide (HI) decomposition process for different catalysts and various temperature conditions

This article presents the results of experimental work carried out at the Institute of Power Engineering on the process of thermal decomposition of hydrogen iodide. This process is one of the three key steps taking place in sulfur-iodine (S-I) thermochemical hydrogen production technology. For this purpose, a laboratory test rig equipped with an electrically heated chemical reactor was constructed, enabling the study of hydrogen iodide decomposition under controlled conditions. The research was carried out using various catalytic substances, as well as different temperature conditions. The process of hydrogen iodide decomposition required keeping the temperature of the reactor above 300°C and continuous analysis of the concentration of hydrogen formed over time. The results of the study will make it possible to determine the kinetics of the hydrogen iodide decomposition reaction under selected conditions of the process, allowing for future optimization of the process with the use of numerical methods.

Directional introduction of pyridine nitrogen functional groups in activated carbon catalysts for the catalytic production of hydrogen: An experimental and DFT calculation

With the increase in global energy consumption, it has become difficult for traditional energy (re)sources to meet our basic needs. Hydrogen energy is an important component of a low-carbon or carbon-free energy strategy, and the thermochemical sulfur-iodine cycle is considered to be one of the most promising methods for hydrogen production. Nitrogen-doped activated carbon catalysts (NACCs) can improve the decomposition efficiency of hydrogen iodide (HI). However, the investigation of the active nitrogen-containing functional group (NFG) is still in progress. In this study, results from experiments and density functional theory (DFT) calculations were combined to achieve a pyridine nitrogen targeted modification, with the idea that pyridine nitrogen is the catalytically active center.Using ammonia-carbon dioxide co-activation, the samples contained a maximum of 7.79 % N content, and 77.28 % pyridine nitrogen content. An increase in the pyridine nitrogen content resulted in an increase in the catalytic decomposition efficiency. Bipyridine was used to increase the pyridine nitrogen content to complement the nitrogen-modulation mechanism. The N-6 content reached a maximum when the bipyridine solution concentration was in the range of 0.3–0.35 g/L; this resulted in the highest catalytic efficiency. The transition state and reaction path energies were calculated at the B3LYP/def2-TZVP level and combined with thermodynamic enthalpy correction quantities to improve accuracy. According to the DFT calculations, the models for pyridine nitrogen substitution all reduced the activation energy of HI decomposition reaction compared to the other models.

Integration of neural network-based prediction for enhanced process controllability: application in hydrogen iodide decomposer for hydrogen production via water splitting process

Sulfur-Iodine Thermochemical cycle (SITC) process can be broken down into 3 sections. Based on the literature, there is limited study on the third section which is hydrogen iodide (HI) decomposition. In this work, a study to develop a model and controller of the HI decomposition is carried out. The goal of this work is to address this important gap, and more specifically to focus on the controllability of the HI decomposition section. Before the control and simulation study can be performed, a dynamic model of a HI decomposer is first established to obtain the baseline for the necessary data to be fed into the Artificial Neural Network for training to predict the correct outcome accordingly. The proposed controller is a Multi-Scale Control (MSC) integrated into an Artificial Neural Network (ANN) model (ANN-MSC-based-PID). It is worth highlighting that; the proposed model-based control strategy has proven to effectively control the HI decomposition reactor.

Fabrication, permeation, and corrosion stability measurements of silica membranes for HI decomposition in the thermochemical iodine–sulfur process

In this study, a corrosion-stable silica membrane was developed to be used in H2 purification during the hydrogen iodide decomposition (2HI → H2 + I2), which is a new application of the silica membranes. From a practical perspective, the membrane separation length was enlarged up to 400 mm and one end of the membrane tubes was closed to avoid any thermal variation along the membrane length and sealing issues. The silica membranes consisted of a three-layer structure comprising a porous α-Al2O3 ceramic support, an intermediate layer, and a top silica layer. The intermediate layer was composed of γ-Al2O3 or silica, and the top silica layer that is H2 selective was prepared via counter-diffusion chemical vapor deposition of a hexyltrimethoxysilane.To the best of our knowledge, this is the first report of 400-mm-long closed-end silica membranes supported on Si-formed α-Al2O3 tubes produced via chemical vapor deposition method. A 400-mm-long closed-end membrane using a Si-formed α-Al2O3 tube exhibited a higher H2/SF6 selectivity of 1240 but lower H2 permeance of 1.4 × 10−7 mol Pa−1 m−2 s−1 with compared with the membrane using a γ-Al2O3-formed α-Al2O3 tube (907 and 5.6 × 10−7 mol Pa−1 m−2 s−1, respectively). The membrane using the Si-formed α-Al2O3 tube was more stable in corrosive HI gas than a membrane with a γ-Al2O3-formed α-Al2O3 tube after 300 h of stability tests. In conclusion, the developed silica membranes using the Si-formed α-Al2O3 tubes seem suitable for membrane reactors that produce H2 on large scale using HI decomposition in the thermochemical iodine–sulfur process.

Performance analysis of hydrogen iodide decomposition membrane reactor under different sweep modes

Hydrogen iodide decomposition is the core hydrogen production step in the sulfur-iodine thermochemical cycle, which determines the hydrogen production rate and thermal efficiency of the device. The conventional decomposition reactor is limited by equilibrium conditions, so the hydrogen iodide conversion rate is low at normal reaction temperature, and membrane reactor technology can break the limit of equilibrium condition and greatly improve the conversion rate. Most of the previous hydrogen iodide membrane reactor models were built under isothermal conditions and did not consider the influence of different sweep modes. In this paper, a one-dimensional non-isothermal hydrogen iodide decomposition membrane reactor mathematical model in co-current and countercurrent sweep modes is established, and the effects of reactor parameter on hydrogen iodide conversion and hydrogen recovery rate are analyzed under the two sweep modes. The results show that the countercurrent mode can obtain higher hydrogen iodide conversion rate than the co-current mode under larger sweep flow rate, inlet pressure of reaction and permeation zone, reactor length; the maximum recovery rate of hydrogen in countercurrent mode is close to 100%. A modified membrane reactor structure combining the traditional reactor and membrane reactor is proposed, which could effectively increase the hydrogen permeation flux per unit membrane surface. In engineering application, the reasonable design of the modified membrane reactor can effectively reduce the investment cost of the membrane reactor on the premise of satisfying the hydrogen production rate.

Development of a membrane reactor with a closed-end silica membrane for nuclear-heated hydrogen production

Hydrogen production from nuclear energy has attracted considerable interest as a clean energy solution to address the challenges of climate change and environmental sustainability. With respect to the large-scale and economical production of hydrogen using nuclear energy, the thermochemical water-splitting iodine-sulfur (IS) process is a promising method. The IS process uses sulfur and iodine compounds to decompose water into its elemental constituents, hydrogen and oxygen, by using three coupled chemical reactions: the Bunsen reaction; sulfuric acid decomposition; and hydrogen iodide (HI) decomposition. The decomposition of HI is the efficiency-determining step of the process. In this work, a membrane reactor with a silica membrane closed on one end was designed, and its potential for hydrogen production from HI decomposition was explored. In the reactor-module design, only one end of the membrane tube was fixed, while the closed-end of the tube was freely suspended to avoid thermal expansion effects. The closed-end silica membranes were prepared for the first time by a counter-diffusion chemical vapor deposition of hexyltrimethoxysilane. In application, HI conversion of greater than 0.60 was achieved at a decomposition temperature of 400 °C, which is three times greater than the equilibrium conversion (0.20). Thus, the membrane reactor with closed-end silica membrane was shown to produce a successful equilibrium shift in the production of hydrogen via HI decomposition in the thermochemical IS process.

Exploring the relationship between the physical properties of activated carbon catalysts and their efficiency in catalyzing hydrogen iodide decomposition to produce hydrogen

Using simple and efficient methods to synthesize biological activated carbon catalysts (ACCs) with the decomposition of hydrogen iodide (HI) in the sulfur-iodine cycle as a typical reaction is urgently needed for the commercialization of hydrogen energy production and development. In this study, a series of ACCs with different specific surface areas (SSAs) and pore structures are prepared by comparing and controlling the changes in carbonization and activation methods of activated carbon (AC) preparation process. Hierarchical porous AC with larger SSA has higher HI decomposition efficiency. The representative samples H240H1h and H240C4h are hierarchical porous ACCs with 48.96% and 46.88% micropores, respectively, and have the highest catalytic activity in the entire series. The nitrogen adsorption and desorption curve is combined with pore size distribution data and analyzed using the capillary aggregation (Kelvin) and monolayer adsorption (Langmuir) theories. And ACC pore grading coefficient—which can improve data visualization—is introduced.

Minimization of Entropy Generation Rate in Hydrogen Iodide Decomposition Reactor Heated by High-Temperature Helium.

The thermochemical sulfur-iodine cycle is a potential method for hydrogen production, and the hydrogen iodide (HI) decomposition is the key step to determine the efficiency of hydrogen production in the cycle. To further reduce the irreversibility of various transmission processes in the HI decomposition reaction, a one-dimensional plug flow model of HI decomposition tubular reactor is established, and performance optimization with entropy generate rate minimization (EGRM) in the decomposition reaction system as an optimization goal based on finite-time thermodynamics is carried out. The reference reactor is heated counter-currently by high-temperature helium gas, the optimal reactor and the modified reactor are designed based on the reference reactor design parameters. With the EGRM as the optimization goal, the optimal control method is used to solve the optimal configuration of the reactor under the condition that both the reactant inlet state and hydrogen production rate are fixed, and the optimal value of total EGR in the reactor is reduced by 13.3% compared with the reference value. The reference reactor is improved on the basis of the total EGR in the optimal reactor, two modified reactors with increased length are designed under the condition of changing the helium inlet state. The total EGR of the two modified reactors are the same as that of the optimal reactor, which are realized by decreasing the helium inlet temperature and helium inlet flow rate, respectively. The results show that the EGR of heat transfer accounts for a large proportion, and the decrease of total EGR is mainly caused by reducing heat transfer irreversibility. The local total EGR of the optimal reactor distribution is more uniform, which approximately confirms the principle of equipartition of entropy production. The EGR distributions of the modified reactors are similar to that of the reference reactor, but the reactor length increases significantly, bringing a relatively large pressure drop. The research results have certain guiding significance to the optimum design of HI decomposition reactors.

Dynamic Simulation of Hydrogen Iodide Decomposition in Catalytic Multi-Tubular Reactor

Sulfur-Iodine thermochemical cycle process has been considered a promising method to generate hydrogen from water. One of the main limitations of this process lies in the hydrogen iodide decomposer section, which requires substantial amount of heat at high temperature. The present study analyses the heat transfer limitation effect on the performance of hydrogen iodide decomposition in a multi-tubular catalytic reactor by means of dynamic simulation. The extensive numerical simulation shows that the inlet temperature heating medium (Helium gas) should be at least 700°C so to enable at least 90% conversion when the inlet molar fraction of hydrogen iodide is 0.6. Lowering the inlet heating medium will require the reduction in the inlet molar fraction of hydrogen iodide in order to keep the conversion at 90% and above.

Modeling and simulation of non-isothermal packed-bed membrane reactor for decomposition of hydrogen iodide

HI decomposition using a membrane reactor is one of the important steps in hydrogen production by the thermal splitting of water using the Sulfur–Iodine cycle. Though, this reaction is endothermic. The mathematical model available to study the performance of such a reactor is an isothermal model. In this study, a non-isothermal mathematical model is developed by microscopic material and energy balance across the length of the membrane reactor. Experimental results from the literature are used for validation of the developed model. Comparing the simulations from the developed model and already reported isothermal model showed significant differences, which endorses the importance of the developed model. Later, the effects of different operating and design parameters were analyzed. Higher feed temperature (950–1000 K), lower feed pressure (100,000–150,000 Pa), lower feed flow rate (<200 ml/min), lower permeate pressure (<2500 Pa) and low to moderate N 2 /HI ratio (0.3–0.4) were found to be the optimum operating conditions. Similarly, the conversion also increased with increasing reactor length, membrane area, and membrane permeance but eventually became constant. Reactor length around 0.4 m, membrane area around 0.008 m 2 and membrane permeance around 2 × 10 −7 mol m 2 Pa −1 s −1 were estimated to be the optimum design conditions for the maximum HI decomposition. • A non-isothermal model for HI decomposition using membrane reactor is developed. • Developed model is validated using experimental results. • Performances of developed model are significantly different from isothermal model. • Operating and design parameters are optimize using developed model.

Minimization of entropy generation rate during hydrogen iodide decomposition reaction process

Minimization of entropy generation rate during hydrogen iodide decomposition reaction process

Effect of N-doping on the catalytic decomposition of hydrogen iodide over activated carbon: Experimental and DFT studies

A series of N-doped activated carbon (NAC) with varying N contents were prepared to study the effect of N-doping on hydrogen iodide (HI) decomposition over activated carbon in sulfur-iodine (SI) cycle for hydrogen production. Element analysis, XPS and N2 adsorption were performed for samples’ characterization. The HI conversion was proportional to the N content and the sample with 6.006% N content gave the highest HI conversion of 22.84%. Density functional theory (DFT) calculations confirmed the experimental results and elucidated the influence mechanism. The increase of N contents was favor to the decomposition of HI by enhancing the chemisorption of HI molecule on carbon structure. The role of N-doping was to remodel the local electronic density and charge distribution on the carbon surface. In addition, the effect of types of N-containing functional groups on HI decomposition was calculated. Results showed that the N-6 structure was conducive to the chemisorption of HI but N-5 and N-Q structures had a reverse effect. However, when the three N-containing functional groups exist simultaneously, the overall chemisorption of HI was enhanced, which, in turn, enhanced the decomposition of HI. This study can provide underlying guidance for preparing highly efficient NAC for HI decomposition.

Comparison of experimental and simulation results on catalytic HI decomposition in a silica-based ceramic membrane reactor

In this study, the catalytic decomposition of hydrogen iodide was theoretically and experimentally investigated in a silica-based ceramic membrane reactor to assess the reactor's suitability for thermochemical hydrogen production. The silica membranes were fabricated by depositing a thin silica layer onto the surface of porous alumina ceramic support tubes via counter-diffusion chemical vapor deposition of hexyltrimethoxysilane. The performance of the silica-based ceramic membrane reactor was evaluated by exploring important operating parameters such as the flow rates of the hydrogen iodide feed and the nitrogen sweep gas. The influence of the flow rates on the hydrogen iodide decomposition conversion was investigated in the lower range of the investigated feed flow rates and in the higher range of the sweep-gas flow rates. The experimental data agreed with the simulation results reasonably well, and both highlighted the possibility of achieving a conversion greater than 0.70 at decomposition temperature of 400 °C. Therefore, the developed silica-based ceramic membrane reactor could enhance the total thermal efficiency of the thermochemical process.

Module design of silica membrane reactor for hydrogen production via thermochemical IS process

The potential of the silica membrane reactors for use in the decomposition of hydrogen iodide (HI) was investigated by simulation with the aim of producing CO2-free hydrogen via the thermochemical water-splitting iodine-sulfur process. Simulation model validation was done using the data derived from an experimental membrane reactor. The simulated results showed good agreement with the experimental findings. The important process parameters determining the performance of the membrane reactor used for HI decomposition, namely, reaction temperature, total pressures on both the feed side and the permeate side, and HI feed flow rate were investigated theoritically by means of a simulation. It was found that the conversion of HI decomposition can be improved by up to four times (80%) or greater than the equilibrium conversion (20%) at 400 °C by employing a membrane reactor equipped with a tubular silica membrane. The features to design the membrane reactor module for HI decomposition of the thermochemical iodine-sulfur process were discussed under a wide range of operation conditions by evaluating the relationship between HI conversion and number of membrane tubes.

H2SO4 poisoning of Ru-based and Ni-based catalysts for HI decomposition in Sulfur[sbnd]Iodine cycle for hydrogen production

The sulfur–iodine (SI) cycle is deemed to be one of the most promising alternative methods for large-scale hydrogen production by water splitting, free of CO2 emissions. Decomposition of hydrogen iodide is a pivotal reaction that produces hydrogen. The homogeneous conversion of hydrogen iodide is only 2.2% even at 773 K [1]. A suitable catalyst should be selected to reduce the decomposition temperature of HI and attain reaction yields approaching to the thermodynamic equilibrium conversion. However, residual H2SO4 could not be avoided in the SI cycle because of incomplete purification. The H2SO4 present in the HI feeding stream may lead to the poisoning of HI decomposition catalysts. In this study, the activity and sulfur poisoning of Ru and Ni catalysts loaded on carbon and alumina, respectively, were investigated at 773 K. HI conversion efficiency markedly decreased from 21% to 10% with H2SO4 (3000 ppm) present, which was reversible when H2SO4 was withdrawn in the case of Ru/C. In the case of Ru/C and Ni/Al2O3, catalyst deactivation depends on the concentration of H2SO4; the higher the concentration of H2SO4, the greater the severity of deactivation. Catalysts before and after sulfur poisoning were characterized by transmission electron microscopy (TEM), energy-dispersive X-Ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). Experimental results and characterization of poisoned and fresh catalysts indicate that the catalyst deactivation could be ascribed to the competitive adsorption of sulfur species and change in its surface properties.

Corrosion Resistance of Nickel-Based Alloy to Gaseous Hydrogen Iodide Decomposition Environment in Thermochemical Water-Splitting Iodine-Sulfur Process

Corrosion Resistance of Nickel-Based Alloy to Gaseous Hydrogen Iodide Decomposition Environment in Thermochemical Water-Splitting Iodine-Sulfur Process

Synthesis, Characterization and Catalytic Activity of CeO2 and Ir-doped CeO2 Nanoparticles for Hydrogen Iodide Decomposition

Ceria (CeO2) and Ir-doped CeO2 nanoparticles are tested for catalytic hydrogen-iodide decomposition in a thermochemical sulfur-iodine (SI) cycle. Ir-doped CeO2 strongly increases the hydrogen-iodid...

Catalytic performance of semi-coke on hydrogen iodide decomposition in sulfur-iodine thermochemical cycle for carbon dioxide-free hydrogen production

Sulfur-iodine thermochemical water splitting cycle is a promising and carbon dioxide-free method for hydrogen production. Among the reactions in this cycle, hydrogen iodide catalytic decomposition is the rate-determining step. In this study, catalytic reactivity test combined with characterizations of nitrogen physisorption, X-Ray diffraction, and Raman spectroscopy provide evidences that hydrofluoric acid modified semi-coke is a promising catalyst candidate for hydrogen iodide decomposition because of its high active and low cost. The raw semi-coke enhanced the hydrogen iodide conversion rate. After modification of hydrofluoric acid, the catalytic activity of semi-coke increased largely. Semi-coke modified by 40 wt% hydrofluoric acid showed better performance than commercial activated carbon catalyst. Combine the characterization results and catalytic reactivity, the graphitic edge carbon atoms in semi-coke are the active sites for hydrogen iodide decomposition. This finding pointed out the direction of carbon material catalyst design for hydrogen iodide decomposition.

Thermochemical production of hydrogen from hydrogen sulfide with iodine thermochemical cycles

With the goal of eventually developing a replacement for the Claus process that also produces H2, we have explored the possibility of decomposing hydrogen sulfide through a thermochemical cycle involving iodine. The thermochemical cycle under investigation leverages differences in temperature and reaction conditions to accomplish the unfavorable hydrogen sulfide decomposition to H2 and elemental sulfur over two reaction steps, creating and then decomposing hydroiodic acid. This proposed process is similar to ideas put forth in the 1980s and 1990s by Kalina, Chakma, and Oosawa, but makes use of thermochemical hydrogen iodide decomposition methods and catalysts rather than electrochemical or photoelectrochemical methods.Process models describing a potential implementation of this thermochemical cycle were created. Motivated by the process model results, experimentation showed the possibility of using alternative solvents to dramatically decrease the energy requirements for the process. Further process modeling incorporated these alternative solvents and suggests that this theoretical hydrogen sulfide processing unit has favorable economic and environmental properties.

Catalytic performance of carbon nanotubes supported palladium catalyst for hydrogen production from hydrogen iodide decomposition in thermochemical sulfur iodine cycle

Abstract The current work presents the synthesis of carbon nanotubes supported palladium catalyst for hydrogen production from hydrogen-iodide decomposition in thermochemical water-splitting sulfur-iodine (SI) cycle. XRD results showed that the Pd nanoparticles were highly dispersed on the CNT support. Raman results showed that Pd(3%) possessed the highest quantity of defects than other loaded Pd samples and CNT support. The order of catalytic activity for hydrogen-iodide decomposition is: Pd(3%)/CNT > Pd(5%)/CNT > Pd(1%)/CNT > CNT. This is due to high degree of defects present in Pd(3%)/CNT as compared to others. Pd(3%)/CNT also showed an excellent stability of 100 h for the reaction. The post-characterizations (BET, ICP-AES, XRD and TEM) of spent-Pd(3%)/CNT after 100 h were carried out in order to find out the changes in the specific surface area, elemental analysis, structure and particle size. No changes were observed in the specific surface area, elemental analysis, particle size, and structure of the spent catalyst as compared to the fresh one. This shows the Pd/CNT has a lot of potential of generating hydrogen in the thermochemical SI cycle.