Sulfur Iodine Research Articles

Hydrogen production using thermochemical water-splitting Iodine–Sulfur process test facility made of industrial structural materials: Engineering solutions to prevent iodine precipitation

A thermochemical water-splitting iodine–sulfur process offers the potential for mass-producing hydrogen at high-efficiency levels, and it uses high-temperature heat sources, including high-temperature gas-cooled reactors, solar heat, and waste heat of industries. The raw material (H2O) is split into H2 and O2 by combining three chemical reactions using sulfur and iodine. Currently, R&D tasks are essential to confirm the integrity of the components that are made of practical structural materials and the stability of hydrogen production in harsh working conditions. A test facility for producing hydrogen was constructed from corrosion-resistant components that are developed using industrial materials. In addition, for stable hydrogen production, technical issues for instrumental improvements (i.e., stable pumping of the hydrogen iodide (HI)–I2–H2O solution without locking the shaft seal, prevention of leakage by improving the quality control of glass-lined steel, prevention of I2 precipitation using a water removal technique in a Bunsen reactor) were solved. The entire process was successfully operated for 150 h at the rate of ca. 30 L/h. The integrity of components made of practical structural materials and the operational stability of the hydrogen production facility in harsh working conditions were demonstrated.

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.

Energy and exergy analyses of a novel sulfur–iodine cycle assembled with HI–I2–H2O electrolysis for hydrogen production

A novel sulfur–iodine (SI or IS) cycle integrated with HI–I2–H2O electrolysis for hydrogen production was developed and thermodynamically analyzed in this work. HI–I2–H2O electrolysis was used to replace the conventional concentration, distillation, and decomposition processes of HI, so as to simplify the flowsheet of SI cycle. And then the new cycle was divided into Bunsen reaction, H2SO4 decomposition and HI–I2–H2O electrolysis sections. Through incorporating the user-defined module of HI–I2–H2O electrolysis with Aspen Plus, the cycle was simulated and 0.448 mol/h (10 L/h) of H2 was produced. The overall energy and exergy efficiencies of the novel SI system were estimated to be 15.3–31.0% and 32.8%, respectively. Most exergy destruction occurred in the H2SO4 decomposer and condenser for H2SO4 decomposition and Bunsen reaction sections, which accounted for 93.0% and 63.4%, respectively. A high exergy efficiency of 92.4% for HI–I2–H2O electrolysis section with less exergy destruction was determined, mostly due to the transformation of the overall electricity in electrolytic cell to exergy. Appropriate internal heat exchange and waste heat recovery will favor improving the energy and exergy efficiencies.

Improvement of HI concentration performance for hydrogen production iodine–sulfur process using crosslinked cation-exchange membrane

Cation-exchange membranes (CEMs) were developed using a radiation-grafted polymerization method to improve HI-mediated electro-electrodialysis (EED) in thermochemical water-splitting iodine-sulfur processes. The performance of the HI-mediated reaction was improved using the developed CEMs by introducing divinylbenzene (DVB) as the crosslinker. The effects of the crosslinked CEMs on performance indices such as proton conductivity, transport number, and water permeation factor were investigated. Introducing the crosslinks improved the selectivity of H+ and water transport. The permeation mechanism of the proposed EED model was investigated to determine the role of the crosslinkers in this operation. The results indicated that even though the crosslinkers had little effect on the absorption of the HIx solution and the H+ diffusion coefficient, a notable decrease was observed in the I− diffusion coefficient. The crosslinkers inhibited swelling caused by the absorption of the HIx solution that led to volume changes known to suppress H2O permeation.

Preparation and characterization of hollow carbon sphere supported catalysts (M@HCS [M=Pt, Ir, Ni]) for HI decomposition in the iodine–sulfur cycle for hydrogen production

Catalysts for HI decomposition are important in hydrogen production via the iodine–sulfur cycle. The catalysts should have a good activity, excellent thermal stability at 400 °C-500 °C, and corrosion resistance to HI and iodine. In this study, a series of hollow carbon sphere (HCS) supported mono-metallic catalysts M@HCS (M = Pt, Ir, Ni) were fabricated by coating the silica core with dopamine, carbonization, and sacrificial core technique. Active carbon-supported monometallic catalysts (M/C) were also prepared via the impregnation method. Catalytic activities of M@HCS and M/C during HI decomposition at 500 °C were compared. The composition, structure, specific surface area, morphology, and surface chemical states of M@HCS and M/C were characterized via inductively coupled plasma (ICP), X-ray diffraction (XRD), Brunauere-Emmette-Teller (BET) surface area, transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS), respectively. Results showed that the catalytic performance of M@HCS was better than that of M/C probably because of the synergistic effects between the active metals and HCSs.

Sulphonated (PVDF-co-HFP)-graphene oxide composite polymer electrolyte membrane for HI decomposition by electrolysis in thermochemical iodine-sulphur cycle for hydrogen production

In overall iodine-sulphur (I-S) cycle (Bunsen reaction), HI decomposition is a serious challenge for improvement in H2 production efficiency. Herein, we are reporting an electrochemical process for HI decomposition and simultaneous H2 and I2 production. Commercial Nafion 117 membrane has been generally utilized as a separator, which also showed huge water transport (electro-osmosis), and deterioration in conductivity due to dehydration. We report sulphonated poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) (SCP) and sulphonated graphene oxide (SGO) composite stable and efficient polymer electrolyte membrane (PEM) for HI electrolysis and H2 production. Different SCP/SGO composite PEMs were prepared and extensively characterized for water content, ion-exchange capacity (IEC), conductivity, and stabilities (mechanical, chemical, and thermal) in comparison with commercial Nafion117 membrane. Most suitable optimized SCP/SGO-30 composite PEM exhibited 6.78 × 10−2 S cm−1 conductivity in comparison with 9.60 × 10−2 S cm−1 for Nafion® 117. The electro-osmotic flux ofSCP/SGO-30 composite PEM (2.53 × 10−4 cm s−1) was also comparatively lower than Nafion® 117 membrane (2.75 × 10−4 cm s−1). For HI electrolysis experiments, SCP/SGO-30 composite PEM showed good performance such as 93.4% current efficiency (η), and 0.043 kWh/mol-H2 power consumption (Ψ). Further, intelligent architecture of SCP/SGO composite PEM, in which hydrophilic SGO was introduced between fluorinated polymer by strong hydrogen bonding, high efficiency and performance make them suitable candidate for electrochemical HI decomposition, and other diversified electrochemical processes.

Demetallized PtxNiy/C catalyst for SO2 electrochemical oxidation in the SI/HyS hydrogen production cycles

The sulfur-iodine (SI) cycle and the hybrid sulfur (HyS) cycle are considered to be promising hydrogen production methods, and the use of catalysts to reduce the overpotential of SO2 electrochemical oxidation reaction is the key to improve the cycle efficiency. In this manuscript, PtxNiy/C catalysts synthesized by the organic-sol method are demetallized with acid to form alloy catalysts with Pt-rich surface and high roughness. Compared with Pt/C catalysts, doping Ni leads to the compression of Pt lattice and the increase of valence electron vacancies, which can significantly improve the catalytic performance and Pt utilization. Pt1Ni3/C catalyst exhibits the highest catalytic activity in the high concentration H2SO4 electrolyte, and maintains a current density that is almost 80% higher than that of commercial Pt/C catalyst after 4 h of electrolysis. This work provides potential support for the extensive research and application of the SI cycle and the HyS cycle.

Pt-core silica shell nanostructure: a robust catalyst for the highly corrosive sulfuric acid decomposition reaction in sulfur iodine cycle to produce hydrogen

The platinum core silica shell catalyst has facilitated stable sulfuric acid decomposition at high-temperature which was not possible over bare Pt nanoparticles due to sintering and agglomeration.

Energy optimization of a Sulfur–Iodine thermochemical nuclear hydrogen production cycle

The use of nuclear reactors is a large studied possible solution for thermochemical water splitting cycles. Nevertheless, there are several problems that have to be solved. One of them is to increase the efficiency of the cycles. Hence, in this paper, a thermal energy optimization of a Sulfur–Iodine nuclear hydrogen production cycle was performed by means a heuristic method with the aim of minimizing the energy targets of the heat exchanger network at different minimum temperature differences. With this method, four different heat exchanger networks are proposed. A reduction of the energy requirements for cooling ranges between 58.9-59.8% and 52.6-53.3% heating, compared to the reference design with no heat exchanger network. With this reduction, the thermal efficiency of the cycle increased in about 10% in average compared to the reference efficiency. This improves the use of thermal energy of the cycle.

Review of Sulfuric Acid Decomposition Processes for Sulfur-Based Thermochemical Hydrogen Production Cycles

Thermochemical processes based on sulfur compounds are among the most developed systems to produce hydrogen through water splitting. Due to their operating conditions, sulfur cycles are suited to be coupled with either nuclear or solar plants for renewable hydrogen production. A critical review of the most promising sulfur cycles, namely the Hybrid Sulfur, the Sulfur Iodine, the Sulfur Bromine and the Sulfur Ammonia processes, is given, including the work being performed for each cycle and discussing their maturity and performance for nuclear and solar applications. Each sulfur-based process is comprised of a sulfuric acid thermal section, where sulfuric acid is concentrated and decomposed to sulfur dioxide, water and oxygen, which is then separated from the other products and extracted. A critical review of the main solutions adopted for the H2SO4 thermal section, including reactor configurations, catalytic formulations, constitutive materials and chemical process configurations, is presented.

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.

Sulfuric acid decomposition in the iodine–Sulfur cycle using heat from a very high temperature gas-cooled reactor

Using the heat of high-temperature gas-cooled reactor to drive the thermochemical iodine-sulfur cycle is an important way to produce hydrogen on a large scale. The sulfuric acid decomposition is the key reaction affecting the hydrogen production efficiency in this method, so efficient sulfuric acid decomposition is needed. The present study focuses on the temperature rise, phase change and chemical reactions of sulfuric acid in a bayonet heat exchanger. The evaporation-condensation model in a steady temperature field was used to simulate the different stages of the phase change process with the species transport model used to calculate the product proportions. Finally, the effects of two catalyst arrangements on the decomposition fraction were analyzed. The results show that the temperature in the catalytic core area reaches 1100 K which provides the heat required for the decomposition reaction. When the sulfuric acid flow rate is 0.36 kg/h, the two-phase flow section is about 0.22 m long to promote better heat transfer. The simulations show that square and circular catalysts give sulfuric acid decomposition fractions of 65% and 57%. The pressure drop of the two catalyst arrangements is almost the same, while the square catalyst has a higher decomposition fraction, which can improve the economics. This study provides a reference for optimizing catalyst selection based on the flow and heat transfer rates.

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.

Multi-tube tantalum membrane reactor for HIx processing section of IS thermochemical process

HIx processing section of Iodine-Sulphur (IS) thermochemical cycle dictates the overall efficiency of the cycle, which poses extremely corrosive HI–H2O–I2 environment, coupled with a very low equilibrium conversion (~22%) of HI to hydrogen at 450 °C. Here, we report the fabrication, characterization and operation of a 4-tube packed bed catalytic tantalum (Ta) membrane reactor (MR) for enhanced HI decomposition. Gamma coated clay-alumina tubes were used as supports for fabrication of Ta membranes. Clay-alumina base support was fabricated with 92% alumina (~8 μm particle size) and 8% clay (~10 μm particle size), sintered at a temperature of 1400 °C. An intermediate gamma alumina coating was provided with 4% polyvinyl butyral as binder for a 10% solid loading. Composite alumina tubes were coated with thin films of Ta metal of thickness <1 μm using DC magnetron sputter deposition technique. The 4-tube Ta MR assembly was designed and fabricated with integration of Pt-alumina catalyst for carrying out the HI decomposition studies, which offered >80% single-pass conversion of HI to hydrogen at 450 °C. The hydrogen throughput of the reactor was ~30 LPH at a 2 bar trans-membrane pressure, with >99.95% purity. This is the first time a muti-tube MR is reported for HIx processing section of IS process.

SO3 decomposition over β–SiC and SiO2 supported CuFe2O4: A stability and kinetic study

CuFe2O4/β–SiC and CuFe2O4/SiO2 catalysts were prepared by wet impregnation method, following the high temperature solid state route and their catalytic performance is evaluated in the SO3 decomposition reaction of the Sulfur–Iodine (S–I) cycle for hydrogen production. The synthesized catalysts are characterized by XRD, FT–IR, TGA, XPS, N2–BET, TEM, HR–TEM, FESEM–EDS and elemental mapping. CuFe2O4/β–SiC catalyst shows higher activity and stability while sintering is observed in the spent CuFe2O4/SiO2 whose activity decreased during the reaction time on stream. Kinetic studies were performed over CuFe2O4/β-SiC in the temperature range of 800–900 °C using wide range of space time, 6.54–44.40 kg h kmol−1. A heterogeneous kinetic model was developed based on the product distribution and the reaction rates determined by the model fitted well with the experimental rates at different temperatures.

Hydriodic iodide and iodine permeation characteristics of fluoropolymers as a lining material

The thermochemical water-splitting iodine–sulfur (IS) process requires corrosion-resistant materials owing to usage of corrosive fluids, such as a mixture of HI–I2–H2O. Fluoropolymers, such as PTFE and PFA, are adaptable as lining materials for protecting plant components. However, there has been a concern: PTFE and PFA have the ability to permeate various permeants. From the viewpoint of corrosion of the base material, the permeation characteristics of HI and I2 should be evaluated to improve the integrity of the IS process. In this study, permeation tests on PTFE and PFA membranes were performed to measure the permeated fluxes of HI and I2, and the effects of the operating conditions on them were investigated. The introduction of a permeability parameter could be successful for normalizing the permeated fluxes for a specific membrane thickness and a vapor pressure. Then, the empirical formula of the permeability was given as an Arrhenius-type equation to use as a plant design. Finally, based on the results, the proper conditions for design of a lining material for the inhibition of HI and I2 permeation are summarized.

Overvoltage reduction in membrane Bunsen reaction for hydrogen production by using a radiation-grafted cation exchange membrane and porous Au anode

An electrochemical membrane Bunsen reaction using a cation exchange membrane (CEM) is a key to achieving iodine-sulfur (IS) thermochemical water splitting for the mass-production of hydrogen. In this study, we prepared a radiation-grafted CEM with a high ion exchange capacity (IEC) and a highly-porous Au-electroplated anode, and then used them for the membrane Bunsen reaction to reduce cell overvoltage. The high ionic content of our CEM led to low resistivity for proton transport, while the high porosity of the electrode led to a large effective surface area for anodic SO2 oxidation. The cell overvoltage for the membrane Bunsen reaction was significantly reduced to 0.21 V at 200 mA/cm2, one-third of that achieved using a commercial CEM and non-porous anode. From the analysis of the current-voltage characteristics, the grafted CEM was demonstrated to play a dominant role in the overvoltage reduction compared to the porous Au anode.

Hydrogen production through the sulfur–iodine cycle using a steam boiler heat source for risk and techno-socio-economic cost (RSTEC) reduction

A modified sulfur-iodine cycle with a non-nuclear heat source is proposed to enhance the economics and reduce risk and damage to society in terms of cost. A modified sulfur cycle employs a steam boiler as a heat source. The modified sulfur iodine cycle is composed of fewer reactions than the original. Thermodynamic feasibility analysis, economic evaluation, risk assessment, and socio-economic analysis are carried out on both the sulfur-iodine cycle and modified sulfur-iodine cycle, and the results are compared. 50.9 kJ/mol of steam was required for the minimum entropy range without the violation of the second law. The results show that the modified process is thermodynamically feasible with a positive entropy region at operating temperatures. The capital cost and operating cost are reduced by 40% and 29% for 1 kmol/h hydrogen production, respectively. The failure rate in the modified process is reduced by 64% compared to that of the original. The social health cost in the modified cycle is reduced by 41% compared to that of the original.

Experimental study and development of an improved sulfur–iodine cycle integrated with HI electrolysis for hydrogen production

The sulfur–iodine (SI or IS) thermochemical cycle assembled with solar or nuclear energy has been proposed as a large-scale, clean and renewable hydrogen production method. In present work, an improved SI cycle integrated with HI electrolysis for hydrogen production was developed according to experiments and simulation. The mathematical models of HI electrolysis using proton exchange membrane (PEM) electrolytic cell was developed, and then the user-defined module of HI electrolysis was set up through Aspen Plus and verified by experimental data. After designing and simulating the new flowsheet of the SI cycle based on HI electrolysis, 10 L/h of H2 and 5 L/h of O2 were obtained. The theoretic thermal efficiency of flowsheet reached 25–42% in terms of the utilization of waste heat. An ideal thermal efficiency of 33.3% through the proper internal heat exchange in the flowsheet was determined. Sensitivity analyses of parameters in the system were conducted. Increasing proton transfer number of PEM electrolytic cell in HI section improved the thermal efficiency of SI cycle. The ratio of distillate to feed rate and the plate number of distillation column in H2SO4 section were the most sensitive factors to the heat duty of overall SI cycle. The proposed new flowsheet for SI cycle is competitive to the flowsheets previously proposed in the field of flowsheet simplification.

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.