Thermochemical Iodine Sulfur Research Articles

Experimental Study of the Characteristics of HI Distillation in the Thermochemical Iodine–Sulfur Cycle for Hydrogen Production

Experimental Study of the Characteristics of HI Distillation in the Thermochemical Iodine–Sulfur Cycle for Hydrogen Production

Process modelling and assessment of thermochemical sulfur-iodine cycle for hydrogen production considering Bunsen reaction kinetics

Thermochemical sulfur-iodine (SI) cycle is one of the large-scale, clean, and efficient hydrogen production routes. The Bunsen reaction process is always simulated by a stoichiometric reaction, without considering the realistic Bunsen reaction kinetic process. Herein, a user-defined Fortran module concerning Bunsen reaction kinetics was developed and embedded into a continuous stirred tank reactor (RCSTR), and then a SI flowsheet with 100 L/h hydrogen production was modeled. The key parameter optimization, mass and energy balance were analyzed, the internal heat exchange network was created using the pinch point temperature difference analysis and the principle of energy cascade utilization, along with thermal efficiency evaluation. Bunsen reaction process reaches equilibrium after a period, which is consistent with experiments. The increase of H2SO4 decomposition ratio is beneficial to reduce the energy consumption of system. Increase in temperature has less effect on increasing the equilibrium decomposition ratio of HI. The theoretical thermal efficiency of system reaches 14.0–57.4 % considering the recovery of exothermic heat. This work provides a theoretical basis for the optimization of SI cycle.

A review on the development of supported non-noble metal catalysts for the endothermic high temperature sulfuric acid decomposition step in the Iodine–Sulfur cycle for hydrogen production

The decomposition of sulfuric acid to sulfur dioxide is an important reaction section in both the thermochemical Iodine–Sulfur (IS) cycle and the Hybrid (Hybs) cycle for hydrogen production. This decomposition reaction is a high temperature, highly endothermic reaction whose activation barrier needs to be reduced by a highly active catalyst. The catalysts reported in this reaction are either exorbitantly expensive, synthesized using noble metals, or exhibiting low activity and stability. Hence, the development of non-noble active and stable catalysts in this reaction is a significant challenge. This review comprehensively discusses the recent developments and activity trends of supported non-noble catalysts including their synthesis, activity & stability trends, mechanistic and kinetic aspects. The catalytic activity of nano-catalysts in sulfuric acid decomposition is largely affected by the size of the metal nanoparticles, dispersion, oxygen vacancies, and metal-support interaction. Herein, we report an in-depth theoretical and experimental understanding of the catalytic challenges and solutions that leads to designing a cost-effective, efficient and stable catalyst in this reaction. The role of catalyst support modification for long run stability is also discussed. Further, literature considering reaction kinetics over various catalysts is also reviewed.

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.

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.

Design of 24/7 continuous hydrogen production system employing the solar-powered thermochemical S–I cycle

We propose a system design for continuous and emission-free hydrogen production using the thermochemical Sulfur–Iodine cycle. Process heat required for the sulfuric acid decomposition is exclusively generated by a combination of concentrating solar thermal parabolic trough and solar tower systems, which are operated during the daytime only. The proposed design relies on the decoupling of the high temperature section from the rest of the process through material and energy storage for continuous operation. We conceptually design the whole process via steady-state simulation and assess its thermal efficiency and economics. We reveal that the proposed system is comparable to its alternatives in terms of the heat-to-hydrogen efficiency (38.0%) and the levelized cost of hydrogen 10.4$/kgH2. Since the levelized cost is primarily attributed to the capital investment, enlarging the proposed system will lead to significant cost reduction due to economies-of-scale.

Reliability improvements of corrosion-resistant equipment for thermochemical water splitting hydrogen production iodine-sulfur process

Japan Atomic Energy Agency (JAEA) has been conducting R&D on the thermochemical iodine-sulfur (IS) process for nuclear-powered hydrogen production. The IS process is one of the promising candidates of heat application of the high-temperature gas-cooled reactors. JAEA achieved continuous hydrogen production for one week with a hydrogen production rate of 30 NL/h by using a test apparatus made of glass and fluororesin material. Subsequently, JAEA fabricated main chemical reactors made of industrial structural materials and confirmed their integrity in practical corrosive environments in the IS process. Based on the results, JAEA has fabricated a 100 NL/h-H2-scale test facility made of industrial structural materials; one of the important materials is the glass-lined steel for corrosion resistant components such as vessels, pipes and protective sheaths of sensors. This report will present technical matters to improve reliability of the glass-lined protective sheaths of thermocouple. In addition, results of quality confirmation will be presented, which are stress analyses for the glass layer by FEM, tests for heat cycle, bending load and corrosion.

Development of strength evaluation method of ceramic reactor for iodine-sulfur process and hydrogen production test in Japan Atomic Energy Agency

Japan Atomic Energy Agency (JAEA) has been conducting R&D on the thermochemical iodine–sulfur (IS) process for nuclear-powered hydrogen production. The IS process is one of the promising candidates of heat application of the high-temperature gas-cooled reactors. JAEA achieved continuous hydrogen production for one week with a hydrogen production rate of approximately 20 NL/h by using a test apparatus made of glass and fluororesin material. Subsequently, as a next step, JAEA fabricated main chemical reactors made of industrial structural materials and confirmed their integrity in practical corrosive environments in the IS process. Based on the results of these confirmation tests, JAEA has constructed a 100 NL/h-H2-scale test facility made of industrial structural materials. This paper presents an outline and results of hydrogen production tests by using the test facility and reliability improvements by developing a strength estimation method for heat-resistant and corrosion-resistant ceramics components made of silicon carbide.

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...

Analyses of the Efficiency of a High-Temperature Gas-Cooled Nuclear Reactor Cogeneration System Generating Heat for the Sulfur–Iodine Cycle

The paper presents the possibilities of the use of a high-temperature gas-cooled nuclear reactor for energy purposes in the hydrogen and electricity production process. The system provides heat for a thermochemical sulfur–iodine cycle producing hydrogen and generates electricity. Its structure and electricity generation capacity are conditioned by the demand for heat and the levels of temperature required at the sulfur–iodine cycle individual stages. In the three structures under analysis, electricity is generated in a gas turbine system and steam systems (steam, low-boiling fluids). The impact of helium parameters in a two-stage compression system with interstage cooling on power efficiency of the analyzed structures of cogeneration systems and on total power efficiency of the systems is investigated assuming that both hydrogen and electricity are produced. Thermodynamic analyses are conducted using the EBSILON Professional program. The aim of the analyses is to determine the optimum structure of the system and parameters of the mediums in terms of power efficiency.

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.

Kinetic analysis of Bunsen reaction with HI existence in the thermochemical sulfur–iodine cycle for hydrogen production

The sulfur–iodine (SI) cycle is considered as a promising method for large-scale and high-efficiency hydrogen production. The Bunsen reaction in the cycle dominates the following HI and H2SO4 decomposition section and even the whole SI flowsheet. In this work, the detailed kinetics of the Bunsen reaction at practical condition with HI recycled was studied. The effects of operating temperature and initial HI concentration on the overall reaction rate were explored. A SO42- production rate model was proposed based on three elementary reactions, and well described the kinetic process of Bunsen reaction. Both theoretical and experimental results indicated that increasing the initial HI concentration (0–3.08mol/kgH2O) or operating temperature (303–358K) enhanced the reaction rate, including the earlier appearance of liquid separation and thermodynamic equilibrium. But the recycled HI should be controlled within 6.17mol/kgH2O, so as to make the separation of H2SO4 and HIx phase possible. The calculated apparent activation energy for kinetics-controlled reactions (4) and (5) were 8.536 and 21.516kJ/mol, respectively. These results may contribute to the further optimization and reactor design of the Bunsen reaction in the SI cycle.

Apparent kinetics of the Bunsen reaction in I2/HI solution for the iodine–sulfur hydrogen production process

Massive hydrogen production featuring high efficiency, CO2 free, and cost effectiveness is a crucial challenge for the hydrogen economy. Nuclear hydrogen production through thermochemical iodine–sulfur (IS) process is a potential candidate for this purpose. Chemical reaction kinetics data are indispensable for developing a high-performance reactor as well as the scaling up of the process. The apparent kinetics of the reaction under simulated recycling conditions of IS closed cycle operation was studied by initial rate method. The effects of key parameters, including agitation speed, SO2 partial pressure, I2 concentration, and reaction temperature, on reaction rate, were systematically investigated by measuring the variation in SO2 pressure with reaction time. Initial rate analysis method indicated that the Bunsen reaction rates were 0.23 ± 0.01 and 0.77 ± 0.01 order with respect to SO2 pressure and I2 concentration. The apparent activation energy was 5.86 ± 0.21 kJ/mol. Based on these results, an exponential rate expression of the Bunsen reaction was established. In addition, a simplified method for calculation of kinetics parameters was proposed and compared with conventional techniques. Experimental results provide theoretical basis for design and development of Bunsen reactors and for elucidating the reaction process.

Progress of the IAHE Nuclear Hydrogen Division on international hydrogen production programs

This paper presents recent activities of the IAHE Nuclear Hydrogen Division and associated research advances in Canada, China, France, Germany, Poland, and Romania on programs and major initiatives on large-scale hydrogen production and utilization. Germany and France have made significant advances in high temperature steam electrolysis (HTSE). Germany is going to demonstrate a 3-kW steam electrolyzer and 100-kW Hybrid Sulfur Cycle powered by solar energy soon. France operated several HTSE 25-cell stacks at various operating points. Recently, a HTSE packaged system has been built, containing this 25-cell stack and other Balance of Plant components. At 700 °C, this system produces 1.2 Nm3/h of H2 with a total electrical consumption of 3.9 kWh/Nm3, achieving 92% of efficiency (electrical consumption of the system vs HHV of the produced hydrogen). It demonstrates that a 150 °C heat source temperature is sufficient for the steam generation, and that a slightly exothermic operating mode of the stack is sufficient to preheat the inlet gas up to 700 °C and compensate the heat losses of the system. China has also made significant progress in developing the HTSE process at a hydrogen production rate of 105 dm3/h and the thermochemical Sulfur–Iodine (SI) cycle at the rate of 60 dm3/h, which already achieved the goal of China's HTR-PM Demonstration Nuclear Power Plant Project. The components and facilities were developed and tested in Tsinghua University. Romania is collaborating with Canada on nuclear hydrogen production with the thermochemical Cu–Cl cycle. The individual unit operations of the Cu–Cl cycle have been verified experimentally. Research on integration of a laboratory scale system to produce 3 kg of hydrogen per day is underway at the University of Ontario Institute of Technology in Oshawa, Ontario. Poland has developed advanced simulation capabilities for Solid Oxide Fuel/Electrolysis Cells for hydrogen peak energy storage as well as laboratory scale experiments focused on solid oxide and molten carbonate fuel cells. This paper presents a review of activities of members of the IAHE Nuclear Hydrogen Division in these six countries.

Study of effect of high pressures and elevated temperatures on Bunsen reaction of Iodine–Sulfur thermo-chemical process

Hydrogen production by water splitting method is one of the promising solutions for the future energy systems. Among all hydrogen production processes, thermo-chemical Iodine–Sulfur process is one of the efficient and environmentally attractive methods. Iodine–Sulfur process consists of three chemical reactions: (i) Bunsen reaction, which is the acid production step, (ii) sulfuric acid decomposition to produce oxygen and (iii) hydrogen iodide decomposition to produce hydrogen. A detailed parametric study of Bunsen reaction has been carried out through semi-batch experiments. Experiments are carried out in a metallic tubular Bunsen reactor at different pressure and temperature with pure sulfur dioxide (SO2). It has been observed that the overall reaction rate increases with increase in pressure and decreases with increase in temperature. Further studies have been carried out with nitrogen in SO2, to understand the effect of gas film resistance on the overall reaction rate and conversion.

Nuclear Systems for Hydrogen Production: State of Art and Perspectives in Transport Sector

A technologically feasible transition towards a realistic and sustainable hydrogen economy (i.e. on large scale and without carbon dioxide emissions) could be made through the use of nuclear energy. In fact, nowadays hydrogen production methods without the employment of fossil fuel represent only a low share of the total production; but the use on large scale of hydrogen produced by “carbon-based” sources is neither environmentally nor economically meaningful.In the present paper, besides a deep evaluation of the state of art of hydrogen production methods via nuclear source, it has been proposed an energy scenario analysis (based on the hydrogen produced by the thermo-chemical Iodine-Sulfur process fed by High Temperature Gas Reactor (HTGR) included in a symbiotic nuclear fuel cycle), focused on the China region, that would meet the sustainability criteria in both the energy and environmental domains for transport sector.

Experimental Investigation on Multiphase Bunsen Reaction in the Thermochemical Sulfur–Iodine Cycle

The effects of SO2 flow rate, SO2 mole fraction, iodine content and water content on the Bunsen reaction were experimentally studied for the thermochemical iodine–sulfur cycle for hydrogen production. One multistage reaction mechanism on the Bunsen reaction has been hypothesized, considering the kinetic characteristics. The appearance of a liquid–liquid equilibrium (LLE) phase separation was in the range of 20–40 min in the apparatus we chose. An increase in iodine content and a decrease in water content improved LLE separation characteristics to the H2SO4 phase and HIx phase. The H2S formation side reaction easily occurred with the increase in water content and decrease in iodine content. The optimal operating condition that the inlet SO2 mole fraction exceeds 0.12 coupled with initial I2/H2O molar ratio exceeding 0.284 has been proposed based on the experimental results, for the criteria of improving the separation characteristics and preventing side reactions.

Boiling heat transfer characteristics of a sulfuric-acid flow in thermochemical iodine–sulfur cycle

The Japan Atomic Energy Agency has been conducting research and development on the thermo-chemical iodine–sulfur (IS) process, which is one of the most attractive water-splitting hydrogen production methods that uses nuclear thermal energy. The sulfuric acid decomposer is one of the key components of the IS process. The boiling heat transfer coefficients of sulfuric acid solutions are required to design the sulfuric acid decomposer. These coefficients were measured in aqueous solutions where the mole fraction of H2O ranged from 0.17 to 0.37 (heat flux range from 16.9kW/m2 to 5.6kW/m2) and compared with the empirical correlations formulated for binary mixtures. A combination of the Stephan–Körner correlation, using the empirical constant A0=2.00, and the Nishikawa–Fujita correlation was used to predict the experimental results with an accuracy of ±10%.

Components development for sulfuric acid processing in the IS process

The Japan Atomic Energy Agency (JAEA) has been conducting research and development on a thermochemical iodine–sulfur (IS) process, one of most attractive water-splitting hydrogen production methods, that uses the nuclear heat of a high-temperature gas-cooled reactor (HTGR). An examination is planned to verify the integrity of the components in the sulfuric acid decomposition section. A bayonet-type sulfuric acid decomposer made of SiC ceramics, a key component in the section, was test-fabricated. In parallel, a direct-contact heat exchanger (DCHX) is contemplated for use in the sulfuric acid decomposition section to simplify the process. The application of the DCHX makes it possible to perform heat recovery and separate undecomposed sulfuric acid from the decomposed gaseous mixture in one reactor. Although the concept is very attractive, little is known about the heat and mass transfer behavior in the DCHX. Therefore, a test apparatus was constructed to measure the gas-phase mass transfer coefficients required for the optimal design of the DCHX. These coefficients of water were acquired and compared with an empirical correlation. The experimental data were in good agreement with those obtained from empirical correlation, and thus, the apparatus was confirmed to be reasonable.

Prediction of phase equilibria of HIx system using artificial neural network: Experimental verification

Thermochemical sulfur–iodine (SI) cycle is one of the promising technologies investigated for hydrogen production using solar and nuclear energy. The development and validation of a reliable thermodynamic model for the HIx mixture (HI–H2O–I2) encountered in the SI cycle have been identified as a central research issue to provide estimations on the HIx section energy demand.In this contribution, we develop an artificial neural network (ANN) model to predict the real time phase equilibrium behavior. For the binary HI–H2O system, the ANN model is constructed for a pressure up to 84 bar, while for the ternary HI–H2O–I2 system, the model describes the equilibrium behavior for a pressure up to 53 bar. The proposed models show their potential with a maximum relative deviation (RD) of about 2.5% and a root mean square percentage error (RMSPE) of within 0.9% for binary, and a maximum RD of 3.6% along with an RMSPE of 0.64% for ternary systems.