Sulfur Iodine Thermochemical Water-splitting Cycle Research Articles

Energy and exergy analysis of a novel solar-hydrogen production system with S–I thermochemical cycle

A novel hydrogen production system based on a sulfur-iodine (S–I) thermochemical water-splitting cycle driven by 100% solar energy is proposed in this paper. A solar power tower (SPT) with thermal energy storage (TES) is used to supply heat stably. Considering the large heat recovery potential in the S–I cycle, a supercritical carbon dioxide (S–CO2) Brayton cycle is used to improve the system performance. A complete thermodynamic model and detailed description of the energy and exergy flow from the sun to SPT, TES, S–I cycle, S–CO2 Brayton cycle and hydrogen is obtained. The system performance in the base case and actual weather conditions are obtained. The influence of major parameters on the system performance is investigated. The results show that the hydrogen production rate is 3.52 mol s−1 in the base case. Using the S–CO2 Brayton cycle, the overall energy and exergy efficiency can be increased from 10.6%, 11.1% to 30.5%, 32.4%, respectively. The solar part accounts for 48.2% of the total energy loss and 76.1% of the exergy destruction. In addition, increasing DNI, the maximum reaction temperature, the regeneration ratio of the S–CO2 Brayton cycle (RR) can improve the system performance, and the system efficiency is more sensitive to RR.

Thermodynamics and Kinetic Modeling of the ZnSO4·H2O Thermal Decomposition in the Presence of a Pd/Al2O3 Catalyst

The sulfur–iodine thermochemical water-splitting cycle is a promising route proposed for hydrogen production. The decomposition temperature remains a challenge in the process. Catalysts, such as Pd supported on Al2O3, are being considered to decrease reaction temperatures. However, little is known regarding the kinetic behavior of such systems. In this work, zinc sulfate thermal decomposition was studied through non-isothermal thermogravimetric analysis to understand the effect of a catalyst within the sulfur–iodine reaction system context. The findings of this analysis were also related to a thermodynamic assessment. It was observed that the presence of Pd/Al2O3 modified the reaction mechanism, possibly with some intermediate reactions that were suppressed or remarkably accelerated. The proposed model suggests that zinc sulfate transformation occurred in two sequential stages without the Pd-based material. Activation energy values of 238 and 368 kJ·mol−1 were calculated. In the presence of Pd/Al2O3, an activation energy value of 204 kJ·mol−1 was calculated, which is lower than observed previously.

SO3 decomposition over silica-modified β-SiC supported CuFe2O4 catalyst: characterization, performance, and atomistic insights.

The sulfur-iodine (S-I) thermochemical water-splitting cycle is one of the potential ways to produce hydrogen on a large scale. CuFe2O4 was dispersed over modified silica or treated β-SiC and untreated β-SiC using the wet impregnation method for SO3 decomposition, which is the most endothermic reaction of the S-I cycle. Various state-of-the-art techniques such as XRD, FT-IR, BET, XPS, TEM, HR-TEM, FESEM-EDS and elemental mapping were employed to characterize both the synthesized catalysts. CuFe2O4 catalyst supported on silica-modified β-SiC resulted in enhanced catalytic activity and stability due to better metal-support interaction. In order to get a better insight into the reaction mechanism over this bimetallic catalyst, the first principles based simulation under the framework of density functional theory was performed. We have found that the presence of Cu gives rise to an improved charge localization at the O-vacancy site alongside favourable reaction kinetics, which results in an enhanced catalytic activity for the CuFe2O4 nano-cluster compared to that of a single metallic catalyst containing Fe2O3 nano-cluster.

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.

Computational model of a sulfur-iodine thermochemical water splitting system coupled to a VHTR for nuclear hydrogen production

Sulfur-Iodine thermochemical water splitting cycle coupled is one of the most promising methods for hydrogen production using a nuclear reactor as the primary energy source. However, there are not references in the scientific publications of a test facility that allow to evaluate the efficiency of the overall process. A computational model for the evaluation and optimization of the sulfur-iodine cycle coupled to a very high temperature reactor for nuclear hydrogen production was developed using a chemical process simulator Aspen HYSYS®. Some operational and design parameters of the cycle sections can be optimized in order to obtain the maximum hydrogen production and higher efficiency. The optimized sections of the flowsheet are coupled to a very high temperature nuclear system (TADSEA) through a Brayton gas cycle for power cogeneration. It is proposed a closed flowsheet for the sulfur-iodine thermochemical water splitting cycle coupled to an accelerator driven system, considering a Brayton cycle for the energy production. It is obtained an acceptable value of global efficiency for the initial operating condition. Several parametric studies are conducted using the flowsheet proposed to evaluate important operating parameters in the overall process efficiency.

Ni 기반 촉매를 이용한 HI 분해 반응 특성

HI decomposition reaction requires a catalyst for the efficient production of hydrogen as a key reaction for hydrogen production in sulfur-iodine thermochemical water-splitting (SI) cycle. As a catalyst used in the reaction, the performance of platinum catalyst is excellent. While, the platinum catalyst is not economical. Therefore, studies of a nickel catalyst that could replace platinum have been carried out. In this study, the characteristics of the catalytic HI decomposition on the amount of loaded nickel (Ni = 0.1, 0.5, 1, 3, 5, 10 wt%) were investigated. As the supported Ni amount increased up to 3 wt%, HI decomposition was found to increase in linear proportion. However, the conversion of <TEX>$Ni/Al_2O_3$</TEX> catalyst loaded above 3 wt% was not linear. It was thought that the different HI decomposition characteristics was caused in the size and metal dispersion of Ni particles of catalyst. The physical property of catalyst before and after HI decomposition reaction was characterized by BET, chemisorption, XRD and SEM analysis.

Hydrogen production by HI decomposition over nickel–ceria–zirconia catalysts via the sulfur–iodine thermochemical water-splitting cycle

Effects of Ni/Ce0.8Zr0.2O2 catalysts with different calcination temperatures were investigated for HI decomposition in the sulfur–iodine cycle. Calcination temperature affected the properties and performance of the catalysts. The catalytic activity of Ni/Ce0.8Zr0.2O2 catalysts was higher than that of catalysts based on pure ceria. The Ni/Ce–Zr300 demonstrated the best catalytic activity for temperature below 425°C, while the Ni/Ce–Zr700 demonstrated the best catalytic activity above 450°C. The Ni/Ce0.8Zr0.2O2 catalysts were formed with Zr4+ replacing Ce4+ in the ceria lattice and the Ni2+ ions dissolved into the ceria lattice. The NiO species are highly dispersed in Ni/Ce–Zr300, Ni/Ce–Zr500 and Ni/Ce–Zr700, but the sintering and agglomeration occurred obviously in Ni/Ce–Zr900. Interfacial NiO sites that strongly interacted with ceria and oxygen vacancy were regarded as the main active sites in HI catalytic decomposition. The incorporation of Zr improved the catalytic performance, textual features, thermal resistance and oxygen storage/transport properties of Ce–ZrO2 mixed oxides and the corresponding catalysts.

Commercial activated carbon for the catalytic production of hydrogen via the sulfur–Iodine thermochemical water splitting cycle

Eight commercial activated carbon catalysts were examined for their catalytic activity to decompose hydroiodic acid (HI) to produce hydrogen; a key reaction in the sulfur–iodine (S–I) thermochemical water splitting cycle. Activity was examined under a temperature ramp from 473 to 773 K. No statistically significant correlation was found between the measured catalyst sample properties and catalytic activity. Four of the eight samples were examined for one week of continuous operation at 723 K. All samples appeared to be stable over the period of examination.

HI extraction by H3PO4 in the Sulfur–Iodine thermochemical water splitting cycle: Composition optimization of the HI/H2O/H3PO4/I2 biphasic quaternary system

Abstract Iodine excess separation from hydriodic acid (HI) is one of the most challenging steps of the Sulfur–Iodine thermochemical water splitting cycle. One promising method is the extraction of HI by using phosphoric acid (H 3 PO 4 ), with the subsequent separation of gaseous hydriodic acid from water and H 3 PO 4 by a distillation step. The aim of the present work is to provide new experimental liquid–liquid equilibrium data for the biphasic HI/I 2 /H 2 O/H 3 PO 4 quaternary system, varying both temperature and solution composition in order to optimize the excess of anhydrous phosphoric acid to be added. Two temperature levels were tested, i.e. 100 °C and 120 °C, and the H 3 PO 4 amount was varied in the feed mixture from 7.7% wt to 38% wt while the [I 2 ]/[HI] and [H 2 O]/[HI] molar ratios were kept constant at, respectively, a value of 3.7 and 5.6. A temperature level of 120 °C, with an H 3 PO 4 initial concentration of about 29% wt leads to the lowest amount of water against HI, which minimizes energy costs in the phosphoric acid reconcentration step, the most energy consuming part in this separation process.

CFD modeling and experimental validation of sulfur trioxide decomposition in bayonet type heat exchanger and chemical decomposer for different packed bed designs

The growth of global energy demand during the 21st century, combined with the necessity to master greenhouse gas emissions has lead to the introduction of a new and universal energy carrier: hydrogen. The Department of Energy (DOE) Nuclear Hydrogen Initiative was investigating thermochemical cycles for hydrogen production using high-temperature heat exchangers. In this study a three-dimensional computational model of high-temperature heat exchanger and decomposer for decomposition of sulfur trioxide by the sulfur–iodine thermochemical water-splitting cycle with different packed bed designs has been done. The decomposer region of the bayonet heat exchanger also called as silicon carbide integrated decomposer (SID) is designed as the packed bed region. Cylindrical, spherical, cubical and hollow cylindrical pellets have been arranged inside the packed bed. The engineering design of the packed bed was very much influenced by the structure of the packing matrix, which was governed by the shape, dimension and the loading of the constituent particles. Staggered and regular packing methods are used for packing the pellets in the packed bed region. The numerical model is created using GAMBIT and fluid, thermal and chemical analyses were performed using FLUENT. The decomposition percentage of sulfur trioxide is found for the packed bed region with different pellets and the numerical results obtained is compared with the experimental results. A comparison is made for the decomposition percentage of SO3 for the packed bed approach and the porous media approach.

Survey of Bunsen reaction routes to improve the sulfur–iodine thermochemical water-splitting cycle

A large excess of water and iodine is typically employed in the Bunsen reaction step of the sulfur–iodine thermochemical cycle in order to induce liquid–liquid phase separation of the two acid products. This paper presents an overview of some alternative routes for carrying out the Bunsen reaction. The use of a reaction solvent other than water is first discussed, and experimental results obtained with tributylphosphate are presented. Another approach is separation of the product acids by selective precipitation of insoluble salts, and the addition of lead sulfate as the precipitating agent is discussed in detail. Finally, the electrochemical Bunsen reaction route is investigated. All of these methods have the potential to reduce the iodine and/or water requirement of the sulfur–iodine cycle.

A study on the dynamic behavior of a sulfur trioxide decomposer for a nuclear hydrogen production

The sulfur–iodine thermochemical water-splitting cycle (S–I cycle) is one of the most promising technologies for mass H 2 production. The S–I cycle is generally divided into three sections, one of which involves a H 2SO 4 concentration and decomposition. In the sulfuric acid processing section (Section 2), H 2SO 4 is decomposed into H 2O and SO 3, and then the produced SO 3 is further decomposed into SO 2 and O 2, which takes place in a H 2SO 4 decomposer and a SO 3 decomposer, respectively. The SO 3 decomposition requires heat of a high temperature and this suggests a heat-exchanger type reactor. To understand the temperature profiles and chemical reactions through a SO 3 decomposer, a dynamic model was developed by considering the heat and material balances in partial differential forms. A model was used to size the decomposer to a proposed design basis and it was also applied to simulate the responses corresponding to the changes of the operation conditions such as increased or decreased flow rates.

Activated carbon catalysts for the production of hydrogen via the sulfur–iodine thermochemical water splitting cycle

Abstract Seven activated carbon catalysts obtained from a variety of raw material sources and preparation methods were examined for their catalytic activity to decompose hydrogen iodide (HI) to produce hydrogen, a key reaction in the sulfur–iodine (S–I) thermochemical water splitting cycle. Activity was examined under a temperature ramp from 473 to 773 K. Within the group of lignocellulosic steam-activated carbon catalysts, activity increased with surface area. However, both a mineral-based steam-activated carbon and a lignocellulosic chemically activated carbon displayed activities lower than expected based on their higher surface areas. In general, ash content was detrimental to catalytic activity while total acid sites, as determined by Boehm's titrations, seemed to favor higher catalytic activity within the group of steam-activated carbons. These results suggest that activated carbon raw materials and preparation methods may have played a significant role in the development of surface characteristics that eventually dictated catalyst activity and stability as well.

Experimental study of two phase separation in the Bunsen section of the sulfur–iodine thermochemical cycle

The Bunsen reaction for the production of hydriodic and sulfuric acids from water, iodine and sulfur dioxide, has been studied with the evaluation of the effect of some operative parameters on product phase behavior. Results show that operative temperature has a minor effect on the phase behavior. In contrast, both iodine and water loads can be adjusted to enhance the downstream operations of the sulfur–iodine thermochemical water-splitting cycle: the effect of iodine and water excess on resulting phases purity, side reaction occurrence and acid concentration was studied and, then, the most favorable operative conditions defined.

Preliminary results from bench-scale testing of a sulfur-iodine thermochemical water-splitting cycle

Portions of a bench-scale model of a sulfur-iodine thermochemical water-splitting cycle have been operated at General Atomic Company as part of a comprehensive program to demonstrate the technology for hydrogen production from non-fossil sources. The bench-scale model consists of three subunits which can be operated separately or together and is capable of producing as much as 4 l/min −1 (6.7 × 10 −5 m 3 s −1) at standard conditions of gaseous hydrogen. One subunit (main solution reaction) reacts liquid water, liquid iodine (I 2) and gaseous sulfur dioxide (SO 2) to form two separable liquid phases: 50 wt % sulfuric acid (H 2SO 4) and a solution of iodine in hydroiodic acid (HI x ). Another subunit (H 2SO 4 concentration and decomposition) concentrates the H 2SO 4 phase to the azeotropic composition, then decomposes it at high temperature over a catalyst to form gaseous SO 2 and oxygen. The third subunit (HI separation and decomposition) separates the HI from water and I 2 by extractive distillation with phosphoric acid (H 3PO 4) and decomposes the HI in the vapor phase over a catalyst to form I 2 and product hydrogen. This paper presents the results of ongoing parametric studies to determine the operating characteristics, performance, and capacity limitations of major components.