Sulfuric Acid Decomposition Research Articles

Evaluation of materials of construction for the sulfuric acid decomposition section in the sulfur–iodine (S–I) cycle for hydrogen production: Some preliminary studies on selected materials

Water splitting by Sulfur–Iodine (S–I) cycle is one of the promising thermochemical processes for hydrogen production due to its high efficiency. The decomposition of H2SO4 to produce SO2 is the reaction with the highest energy demand in the S–I cycle and it shows a large kinetic barrier. Sulfuric acid is highly corrosive and its endothermic decomposition needs elevated temperatures (>800 °C). Henceforth, before the scale-up of the process plant there is a need to explore various materials of construction under very harsh acidic environments and phase changing conditions. Corrosion studies on some of the possible materials of construction (SS-304, SS-310, SS-316, Inconel-800, Alloy-20, Inconel-600, Incoloy-800H, Hastelloy C-276) were performed in detail and the most corrosion resistant material is suggested for the construction of sulfuric acid decomposition unit. The studies were performed at low temperatures (60 °C and 120 °C) as well as at high temperatures (700 °C, 800 °C and 900 °C). The corrosion rates were determined using weight loss method at low as well as high temperature and by using electrochemical method at low temperature (80 °C). The phase changing condition was more severe and resulted in higher corrosion rate. Hastelloy C-276 showed the least corrosion rate. SYNOPSIS In order to identify the suitable materials of construction for sulfuric acid decomposition in the S–I cycle, corrosion rates of different materials were determined. Materials were exposed to the various phases of sulfuric acid. The phase changing conditions had the most adverse effect on the materials.

Cover Image, Volume 43, Issue 11

The cover image is based on the Research Article Numerical study of heat transfer and sulfuric acid decomposition in the process of hydrogen production by Qi Sun et al., https://doi.org/10.1002/er.4714.

Change of acidity of the environment in the process of decomposition of apatitis sulfuric acid

An experimental study of the decomposition process of Kovdorsky apatite with certain particle sizes, in a 1 dm3 batch reactor with stirring of the reaction mixture, initial phosphoric acid concentration 17% by weight, in the system: Apatite-H3PO4 – H2SO4-H2O. Sulfuric acid was introduced in stoichiometric amount at the beginning of the process. The process was carried out at a ratio L:S 2.5:1, at a temperature of 78– 82 °C. The process was monitored by the method of joint determination of sulfuric and phosphoric acids by titrimetric analysis of the composition of the reaction mixture in the presence of methyl orange, and then phenolphthalein. Determined the concentration of phosphoric acid, the concentration of excess or deficiency of sulfuric acid and the concentration of monocalcium phosphate gel were determined. The acidity of the reaction mixture was recorded according to the indications of a Ph-meter (pH-105 MA with a combined glass electrode – ESK-10603). In the system: Apatite-H3PO4-H2SO4-H2O, when analyzing the obtained experimental values of these parameters, it was shown that during the process the pH of the reaction mixture rises to pH 6.3 for about 30 minutes, and then decreases to pH 4.5–5. Comparison of the dependence of pH values on the concentration of sulfuric acid in an aqueous solution of phosphoric acid and the pH values of the reaction mixture with the corresponding concentrations of sulfuric and phosphoric acids shows that the pH value of the reaction mixture is determined by the presence in the mixture between weft product - monocalcium phosphate gel. The process of decomposition of apatite in the system Apatite-H3PO4-H2SO4-H2O proceeds in several stages. At the beginning, a rapid decomposition of phosphate raw materials with phosphoric acid and a corresponding change in the pH of the reaction mixture, associated with the accumulation of monocalcium phosphate in solution, takes place. Then there is a slow decomposition of monocalcium phosphate with sulfuric acid and a corresponding decrease in pH to 4.5–5. The pH value at the end of the process is determined by the physicochemical properties of phosphoric acid present in the reaction mixture. At all stages of the process there is a constant increase in the concentration of phosphoric acid associated with the decomposition of monocalcium phosphate gel.

Numerical study of heat transfer and sulfuric acid decomposition in the process of hydrogen production

Numerical study of heat transfer and sulfuric acid decomposition in the process of hydrogen production

Framework development and modeling of the thermodynamics for aqueous sulfuric acid decomposition

Experimental prediction of the thermodynamic behavior of the aqueous sulfuric acid system is complex due to its low volatility, chemical speciation of the sulfuric acid at low concentration, formation of azeotrope and decomposition of the sulfuric acid at high concentration and temperature. In this work, a chemical speciation based algorithm to estimate thermodynamic behavior of multielectrolyte system is proposed. The algorithm for chemical speciation at the known temperature and concentration of solution was solved numerically. The proposed algorithm is robust, and the results are consistent that show parity with experimental data for vapor liquid equilibrium, liquid and vapor phase speciation, excess enthalpy, degree of dissociation, pressure and activity. The effectiveness of the methodology is established using aqueous sulfuric acid solution for which phase changing compositions from pure water to pure sulfuric acid can be predicted. Moreover, the developed methodology can also predict the thermodynamic properties of the system for an extended temperature range (>Tc)

Pt stabilization on Pt/SBA-15 through surface modification using MPTMS for sulfuric acid decomposition in SI cycle to produce hydrogen

Catalysts for the sulfuric acid (SA) decomposition, one of three reactions in Sulfur–Iodine (SI) cycle to produce hydrogen, should be active and stable in wide temperature ranges of 650–850 °C. Pt based catalysts are explored for SA decomposition, but they suffered from the severe Pt loss at the high temperature of 850 °C. Uniform platinum nanoparticles (NPs) are physically trapped within mesopores of the mesoporous SBA-15 prepared in a “one pot” method (Ptx.x-NTS, x.x: loaded Pt wt%). Other Pt catalysts are prepared to stabilize Pt particles using 3-mercaptopropyletrimethoxysilane (MPTMS) as a stabilizing agent (Ptx.x-TS, x.x: loaded Pt wt%). The co-assembly method in the one pot is based on the I+M–S+ scheme in which S+ (Protonated block copolymer) and I+ (Cationic inorganic precursor) are assembled together through the M– (PtCl6-) mediator. The MPTMS containing thiol group is used to modify the cationic precursors (I+) in order to hold the Pt nanoparticles in meso-channels as the reduced platinum metal is easy to bond with thiol groups. The prepared samples are characterized by XRD, TEM, CO Chemisorption, N2 adsorption desorption, and ICP-OES techniques. The TEM images show that the small Pt NPs of an average size of 7.0 (±0.84 nm) are uniformly dispersed within the mesopores on the mesoporous SBA-15. The thiol stabilized Pt-TS catalysts display the exceptional catalytic stability for sulfuric acid decomposition at the high temperature of 850 °C for 50 h. The overall average metal loss is 67% for the Pt2.0-NTS for 50 h at 76,000 mL.gcat−1.h−1, while it is 16% for the Pt2.0-TS. The metal loss of Pt/SBA-15 is significantly suppressed by the surface functionalization using MPTMS in the catalyst preparation step.

Development of New Corrosion Test Equipment Simulating Sulfuric Acid Decomposition Gas Environment in a Thermochemical Hydrogen Production Process

Development of New Corrosion Test Equipment Simulating Sulfuric Acid Decomposition Gas Environment in a Thermochemical Hydrogen Production Process

Extraction of High-Quality Titanium Raw Materials from Leucoxene Concentrates of the Yarega Deposit

The problems of using the oil-bearing leucoxene ores of the Yarega deposit as raw materials for the production of titanium and pigment TiO2 are discussed. The results of the investigation of two variants of the technological process predicting the preparation of artificial rutile (for processing by the chloric method) and anosovite (for sulfuric acid decomposition) with the accompanying preparation of synthetic wollastonite are presented. The developed process includes reducing roasting of a leucoxene concentrate under various conditions, magnetic separation for the removal of free quartz, and chemical desiliconization of the magnesium fraction (siliceous titanium concentrate) to form the end products.

Pt encapsulated hollow mesoporous SiO2 sphere catalyst for sulfuric acid decomposition reaction in SI cycle

Sulfuric acid (SA) decomposition is one of three key reactions in sulfur Iodine (SI) cycle to produce hydrogen. The catalysts for the decomposition should be active and stable in a wide temperature range of 550–900 °C. Pt based catalysts have been explored for the application, but suffered from the Pt loss in high temperature (∼850 °C). TiO2 and Al2O3 are used as a support. They can stabilize Pt metal at higher temperature, but are degraded at the temperature lower than 700 °C. SiO2 supports with a high surface area are relatively stable in a sulfuric acid vapor stream, but the lower interaction with Pt results in high Pt sintering and Pt loss. Both Pt loss and Pt sintering at the high temperature are originated from Pt vaporization. Here, Pt metallic components are placed at the inner wall of hollow mesoporous SiO2 spheres (Pt-HMSS) to preserve Pt components even at 850 °C. PtOx vapor vaporized during the SA decomposition can be re-dispersed on the inner wall of mesoporous SiO2 shell, which can suppress the Pt loss; (1) temperature at outer wall is higher than temperature at inner wall during the endothermic reaction on Pt at the inner wall, (2) the mesoporous shell afford the long path to suppress the diffusion of PtOx vapor at the inner wall to the outer wall. Pt catalyst at the outer walls of hollow mesoporous SiO2 spheres (HMSS-Pt) is prepared and tested for clarifying the hypothesis. Additionally, TiO2-Pt catalyst, one of highly stable catalytic systems for the SA decomposition, is also prepared and compared with the Pt-HMSS catalyst.

Solar Driven Thermo-Electrochemical Hybrid Sulfur Process for Hydrogen Production

A hydrogen economy requires primary sources to provide the power required to produce hydrogen from water, fossil fuels, biomass or similar compounds. Water-splitting processes are particularly attractive, since water is abundant around the planet, the unique products from water splitting are hydrogen and oxygen and a variety of primary energy sources can be used to produce the hydrogen. External electric power can be used to produce hydrogen by conventional water electrolysis [1], but it firstly requires the production of electricity to realize the electrochemical splitting of the water molecule. A more efficient and potentially more cost effective approach is to use thermal power to drive a thermochemical water splitting process. Such cycles break the hydrogen-oxygen bounds through a series of heat-driven chemical reactions, with recirculation of intermediate substances of different type. By this approach the external heat which drives the chemical reactions is converted into chemical energy of the hydrogen produced from water splitting. Among the various water splitting processes, the thermo-electrochemical Hybrid Sulfur (HyS) is one of the most appealing cycles. It has only fluid reactants and is comprised of only two global reaction steps: a low temperature electrochemical exothermic section, operating at temperatures on the order of 100 °C, and a high temperature thermal section operating at max temperatures of about 800 °C. In the electrochemical section SO2 and H2O are combined together to produce electrochemically H2 at the electrolyzer cathode and H2SO4 at the electrolyzer anode. Sulfuric acid is recycled inside the plant, concentrated and decomposed, in the high temperature thermal section, into SO2, O2 and H2O. Oxygen is then separated from SO2 and water and extracted as byproduct of the process. Solar driven HyS process is being studied by the Greenway Energy and the University of South Carolina within the DOE HydroGEN program (part of the DOE Energy Material Network initiative) [2], partnering with the Idaho National Laboratory, the Savannah River National Laboratory and the National Renewable Energy Laboratory. The project mostly focuses on the high temperature sulfuric acid decomposition section, developing new optimized catalyst formulations (i.e. achieving higher conversion, lower performance lifetime degradation and lower costs), to be integrated in novel solar reactor systems. A new bimetallic catalyst formulation is being developed and synthesized, with the catalyst deposited on TiO2 support. Compared with the current state of the art sulfuric acid decomposition catalysts, developed by Idaho National Laboratory during the DOE Nuclear Hydrogen Initiative [3], the proposed catalyst shows the potential for higher SO3 conversion yields and very limited sintering effects. Test results, under sulfuric acid environment and operating temperatures on the order of 800 °C, will be shown and discussed. The new catalyst will be placed in a novel solar reactor, being developed within the HydroGEN project. The proposed concept is based on a solar cavity receiver system, realizing the sulfuric acid decomposition and internal heat recovery in a single unit, directly heated by the incident solar radiation. This system, along with the actual H2SO4 decomposition into SO2, allows: (1) efficient internal heat recovery from the decomposition products and (2) connections with the metallic interfaced HyS equipment (e.g. tubing, valves etc) at low temperatures. Preliminary results from detailed transport model analysis will be shown, demonstrating effective decomposition and internal heat recovery. The integration of the high temperature decomposition section with the low temperature electrochemical section of the HyS process has also been studied from a process modeling point of view. A new SO2 electrolysis concept is proposed and discussed, with a vapor SO2 mixture feeding the electrolyzer. Preliminary results show the potential to achieve high efficiencies, with actual voltage values lower than the traditional target of 600 mV and current densities higher than the target of 500 mA/cm2 [4]. A new process flowsheet, initially developed within the current HydroGEN project, will be presented and discussed, achieving thermochemical efficiencies ≥ 35%.

Numerical Modeling of a Novel Solar Driven Sulfuric Acid Decomposition Reactor

An efficient and cost-effective approach to produce hydrogen sees the direct use of thermal power to drive thermochemical water splitting processes. Such cycles break the hydrogen-oxygen bounds through a series of heat-driven chemical reactions, with recirculation of intermediate substances of different type. Among the various water splitting processes, the thermo-electrochemical Hybrid Sulfur (HyS) is one of the most appealing cycles. It has only fluid reactants and is comprised of only two global reaction steps: a low temperature electrochemical exothermic section, operating at temperatures on the order of 100 °C, and a high temperature endothermic thermal section operating at max temperatures of about 800 °C. In the electrochemical section SO2 and H2O are combined to produce electrochemically H2 at the electrolyzer cathode and H2SO4 at the electrolyzer anode. Sulfuric acid is recycled inside the plant, concentrated and decomposed, in the high temperature thermal section, into SO2, O2 and H2O. The endothermic decomposition of sulfuric acid takes place in two main reactions: H2SO4 → SO3 + H2O (1) SO3 → SO2 + 0.5 O2 (2) The required thermal power is provided by external source and by internal heat recovery from the SO2-O2 stream product of the decomposition reactions. Solar driven HyS process is being studied by the Greenway Energy and the University of South Carolina within the DOE HydroGEN program (part of the DOE Energy Material Network initiative) [1], partnering with the Idaho National Laboratory, the Savannah River National Laboratory and the National Renewable Energy Laboratory. The project focuses on the high temperature sulfuric acid decomposition section. One of the main tasks of the project is to develop and fabricate an effective and low cost high temperature solar reactor for the decomposition of the sulfuric acid into sulfur dioxide. Previous work was carried out within the DOE-NHI Initiative and resulted in identifying a reactor concept based on the bayonet heat exchanger as the baseline reactor configuration [2]. The bayonet reactor was tested both from a modeling point of view and from an experimental point of view, demonstrating the potential to achieve almost the reaction equilibrium conditions. At temperatures of about 800 °C and pressures of 14 bar, an SO2 production of approximately 19 mol fraction % was achieved, which is essentially the equilibrium value at the same operating conditions [3,2]. However, a solar driven bayonet concept presents several drawbacks, mainly relative to the need for an additional intermediate heat exchanger to transfer the solar power to the reactive sulfur mixture. The removal of the intermediate solar heat exchanger will result in increased energetic and exergetic efficiencies and decreased capital and operating costs. A novel reactor concept is proposed, described and discussed, based on a direct solar heated cavity receiver system. It realizes the solar driven sulfuric acid decomposition and internal heat recovery in a single unit, directly heated by the incident solar radiation without the presence of any intermediate heat transfer fluid. The reactor includes catalytic structures to decompose H2SO4 and foamed structures in the internal heat recovery channels to increase the overall thermal conductivity. A reactor unit, made of SiC material, and directly heated from solar radiation has preliminarily been demonstrated from a modeling point of view. A detailed transport phenomena model was developed using Finite-Volume approach and run in STAR-CCM+. The kinetics parameters reported in Reference [3] were adopted for the current simulations. Results showed excellent conversion rates and reduced temperature gradients and pressure drops inside the device, achieving better performance than the bayonet configuration. The cavity receiver-reactor also allows: (1) efficient internal heat recovery from the decomposition products and (2) connections with the metallic interfaced HyS equipment (e.g. tubing, valves, etc.) at low temperatures. Results obtained from a first conceptual scale up analysis of the reactor concept also demonstrated the actual feasibility for integration in both centralized and distributed solar tower based plants.

Investigation of the Water Treatment Process Using a Hybrid Alumosilicic Reagent

Coagulation and sorption properties of hybrid alumosilicic reagent produced by sulfuric acid decomposition of aluminosilicate raw material have been studied. The efficiency of using such reagent in the treatment of different types of model waters is shown. It was established that the use of this reagent enables us to reduce significantly (10 times and more) the residual aluminum concentration in the purified water as compared to the traditional aluminum-containing reagents. In this case, the mechanism of treatment is implemented at the expense of both the chemical interaction of reagent components (chemisorption) and the volume sorption of pollutants on self-organizing mesoporous alumosilicic structures. In addition, this study shows the efficiency of using the alumosilicic reagent as an intensifier of the clarification of waters containing coarse-dispersed and colloid pollutants. It was also established that the introduction of this reagent into Fe(III)-containing water increased the clarification rate more than 20 times, while the high degree of water clarification could be achieved just in 10 min after the reagent introduction.

Research and development on membrane IS process for hydrogen production using solar heat

Thermochemical hydrogen production has attracted considerable interest as a clean energy solution to address the challenges of climate change and environmental sustainability. The thermochemical water-splitting iodine-sulfur (IS) process uses heat from nuclear or solar power and thus is a promising next-generation thermochemical hydrogen production method that is independent of fossil fuels and can provide energy security. This paper presents the current state of research and development (R&D) of the IS process based on membrane techniques using solar energy at a medium temperature of 600 °C. Membrane design strategies have the most potential for making the IS process using solar energy highly efficient and economical and are illustrated here in detail. Three aspects of membrane design proposed herein for the IS process have led to a considerable improvement of the total thermal efficiency of the process: membrane reactors, membranes, and reaction catalysts. Experimental studies in the applications of these membrane design techniques to the Bunsen reaction, sulfuric acid decomposition, and hydrogen iodide decomposition are discussed.

Stabilization of Pt at the inner wall of hollow spherical SiO2 generated from Pt/hollow spherical SiC for sulfuric acid decomposition

Catalysts for sulfuric acid (SA) decomposition, one of three reactions in Sulfur-Iodine (SI) cycle to produce hydrogen, should be active and stable up to 800–900 °C. Here, a SiC hollow sphere supported Pt catalyst (1 wt% Pt/hSiC) is prepared, and its catalytic activity and stability are monitored in SA decomposition at 850 °C. The initial SA conversion with the Pt/hSiC catalyst is ca. 80% at 850 °C and a GHSV of 76,000 mL/gcat/h. For comparison, a core-shell SiO2 supported Pt catalyst (1 wt% Pt/SiO2@mSiO2) is prepared and tested for the reaction. The core-shell SiO2 support has the structure of a dense core and a mesoporous shell. The initial SA conversion with the Pt/SiO2@mSiO2 catalyst is ca. 54% at 850 °C and a GHSV of 76,000 mL/gcat/h. The Pt/hSiC catalyst is transformed to the SiO2 hollow sphere supported Pt catalyst (Pt/hSiO2) within 6 h reaction. CO chemisorption and TEM analysis exhibit that Pt particles on the pristine and spent catalysts, pretreated at 850 °C, are encapsulated by SiC or SiO2 on the surfaces of SiC and SiO2 supports. When the encapsulated Pt particles are in contact with sulfuric acid vapor, the Pt particles are exposed to the reactants by the removal of SiO2 encapsulating Pt during the reaction. Pt particles at the outer wall of the pristine hSiC are partly lost via PtOx evaporation, while Pt particles at the inner wall of the hollow sphere supports are stabilized without the severe Pt loss and Pt sintering. In contrast, the Pt particles on SiO2@mSiO2 with the dense SiO2 core are severely lost via PtOx evaporation during the reaction resulting in severe Pt sintering. The high stability of Pt particles at the inner wall of the hollow support is attributed to the Pt encapsulation and Pt anchoring of the small Pt particles at the inner walls and the diffusion barrier role of the shell for the migration of Pt at the inner wall to the outer wall.

Catalytic properties of dispersed iron oxides Fe2O3/MO2 (M = Zr, Ce, Ti and Si) for sulfuric acid decomposition reaction: Role of support

Supported iron oxides have been established as an important class of catalyst for high temperature sulfuric acid decomposition. With an objective to elucidate the role of support in modifying the overall catalytic properties of dispersed iron oxide catalysts, a series of supported iron oxide based catalysts, Fe2O3 (15 wt%)/MO2 (M = Zr, Ce, Ti and Si), synthesized by adsorption-equilibrium method, is investigated for sulfuric acid decomposition reaction. The structure of dispersed iron oxide phases largely depended on the nature of the support oxide as revealed by the XRD and Mössbauer studies. α-Fe2O3 is found to be present as a major phase on ZrO2 and CeO2 support while ε-Fe2O3 was the major phase on silica supported iron oxide. On the other hand, presence of mixed oxide Fe2TiO5 was revealed over TiO2 support. Strong dispersed metal oxide-support interactions inhibited the total reduction of the dispersed phase on SiO2 and TiO2 as compared to complete reduction of dispersed iron oxide on CeO2 and ZrO2 supports during temperature programmed reduction upto 1000 °C. The order of catalytic activity at a temperature of ∼750 °C is observed as Fe2O3/SiO2 > Fe2TiO5/TiO2 > Fe2O3/ZrO2 > Fe2O3/CeO2, while at higher temperatures of ∼900 °C the SO2 yield is found to be comparable for all catalysts. A relationship between the rate of sulfate decomposition and catalytic activity is established through detailed TG-DTA investigations of sulfated catalyst and support. Considerable influence of the support oxide on the composition, structure, redox properties, morphology and catalytic activities of the active iron oxide dispersed phase has been observed. Thus, the support oxides operate as a critical component in the complex supported metal oxide catalysts and these findings might influence the design and development of future high temperature sulfuric acid decomposition catalysts.

Synthesis of Pt/mesoporous SiC-15 and its catalytic performance for sulfuric acid decomposition

Sulfuric acid (SA) decomposition is one of the key reactions in the sulfur-iodine (SI) cycle to produce hydrogen. Catalysts for the SA decomposition should be active and stable in a wide temperature range of 550–850°C to absorb latent heat generated from a thermal solar heat or a very high temperature nuclear reactor. Here, mesoporous mSiC-15 is prepared using the SBA-15 template. TEM analysis shows that the morphology of the mSiC-15 has the replica structure of SBA-15. Pt/SBA-15 and Pt/mSiC-15 catalysts are prepared by impregnation and the catalytic activity is examined under the reaction condition of 650–850°C and a GHSV of 76,000mL/gcat/h. The Pt/mSiC-15 catalyst is relatively stable for 50h at 850°C, while the Pt/SBA-15 was severely deactivated. The Pt amounts on the Pt/SBA-15 and Pt/mSiC-15 catalysts decreased from 0.73 and 0.80wt% at initial reaction time to 0.39 and 0.68wt% after 12h reaction, respectively. The Pt loss during the SA reaction is main cause of deactivation, which is caused by the evaporation of Pt oxides under O2 environment produced during the SA decomposition. It is observed that the Pt particles are embedded in porous SiO2 (Pt/mSiO2), which is transformed from Pt/mSiC-15 during the SA decomposition for 6h. The Pt/mSiC-15 was relatively active and stable for the SA decomposition and the Pt loss was minimized by the structural change from Pt/mSiC-15 to Pt/mSiO2 after 6h.

PROBLEMS AND PROSPECTS OF PRODUCTION AND QUALIFICATION OF PHOSPHORIC ACID

The qualification of phosphoric acid is carried out depending on the use of phosphates of various deposits and the necessary quality of the final products. An acquisition of phosphoric acid of the required quality should be carried out taking into account three aspects: resource-energy, ecology and complex processing. Solving the problems of one aspect entails solving the problems of the other aspects. The rational use of natural resources and the reduction of environmental pollution is the determining factor in the choice of technological regimes for complex processing of raw materials with a reduction in the volume of waste of all kinds or transferring them into forms easily recyclable or specially stored. The absence of economically sound technologies for processing phosphogypsum determines its preferential warehousing. The second component that requires recycling is fluorine. In this regard, the purification of phosphoric acid from fluorine should use technologies that realize the trapping of fluorine compounds released into the gas phase. This is relevant from the point of view of the complexity of processing raw materials with the extraction of rare-earth elements. The use of mechanochemical activation makes it possible to achieve a nanoscale level. To a lesser extent, this aspect relates to the stage of sulfuric acid decomposition, proceeding with the participation of three phases: solid, liquid and gas. In turn, the surface structure of the gas-liquid layer plays the role of an energy barrier for evaporation. To establish the basic energy patterns of concentration and defluorination n the disc apparatus and to optimize the process, a thermophysical model was developed in which the range of effective parameters was determined by the joint solution of a number of equations for the desired ingredients in the phosphoric acid concentration range of 52-65%. The solution of the problem of complex purification of wet-process phosphoric acid can be carried out by adsorption methods that allow to remove to some extent almost all impurities.For citation:Smirnov N.N., Smirnova D.N., Ilyin A.P., Kochetkov S.P. Problems and prospects of production and qualification of phosphoric acid. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 7. P. 48-56.

Numerical modeling of a bayonet heat exchanger-based reactor for sulfuric acid decomposition in thermochemical hydrogen production processes

Sulfur-based thermochemical hydrogen production cycles represent one of the most appealing options to produce hydrogen from water on a large scale. The Hybrid Sulfur is one of the most advanced thermochemical cycles. The high temperature section of the process, common to all sulfur-based cycles, operates the sulfuric acid thermal decomposition reaction at temperatures on the order of 800 °C. The paper shows and discusses the modeling results obtained for a bayonet heat exchanger based high temperature reactor that decomposes the sulfur compounds into sulfur dioxide and oxygen. A detailed transport phenomena model, including suitable decomposition kinetics, has been set up using a finite volume numerical approach. A preliminary configuration of the reactor, established based on process simulation results and on the initial reactor prototype developed at Sandia National Laboratory, has been examined and simulated. Results, obtained for a reactor driven by thermal power provided by helium flow, demonstrate the effective decomposition performance at maximum temperatures on the order of 800 °C and pressures of 14 bar. For a laminar flow configuration a sulfur dioxide production yield of about 28 wt% (with sulfur trioxide reduction from 69 wt% to approximately 33 wt%) has been achieved, representing decomposition rates practically equal to the corresponding equilibrium values. Limited pressure drops of approximately 2500 Pa have also been achieved in the sulfur mixture region.

Preparation Scheme of Active Pt/SiC Catalyst and Its Phase Changes During Sulfuric Acid Decomposition to Produce Hydrogen in the SI Cycle

The Pt/SiC-AP catalyst is prepared by the polyol method using acid treated SiC for sulfuric acid (SA) decomposition, which exhibits the highest activity and stability among the Pt/SiC catalysts prepared by four different methods. In a longer-term stability test at 850 °C and a GHSV of 53,500 mL/gcat/h for 30 h, the Pt/SiC-AP catalyst shows the SA conversion of 82%. The activity loss of the Pt/SiC-AP catalyst is observed at 15 h, but the catalyst is almost stabilized at the SA conversion of ca. 78% afterwards. The Pt loss with the Pt/SiC-AP catalyst is the least among the prepared catalysts. Most of Pt loss with the Pt/SiC-AP catalyst occurs within 5 h during the phase change from Pt/SiC to Pt/SixCyOz/SiC and the Pt loss is rarely observed for 30 h thereafter. The acid treatment of the SiC support improves the catalytic stability by enhancing the interaction between Pt and SiC and the Pt/SiC catalyst with well-dispersed Pt particles is obtained by using the polyol method.

Nanostructured Fe2O3 dispersed on SiO2 as catalyst for high temperature sulfuric acid decomposition—Structural and morphological modifications on catalytic use and relevance of Fe2O3-SiO2 interactions

Through our previous studies it was established that non- precious Fe2O3 based catalyst has the potential to replace Pt based catalyst for high temperature sulfuric acid decomposition, the energy conversion step in iodine- sulfur or hybrid-sulfur thermochemical cycles for water splitting (Banerjee et al. [11] and [25]). However, issues like agglomeration and grain growth during prolonged operation still remain to be fully resolved. With an aim to develop low cost, abundant transition metal oxide catalyst with high activity and stability, Fe2O3 nanoparticles immobilized on SiO2 support is explored, anticipating that the Fe2O3-SiO2 interactions may prevent self agglomeration of Fe2O3 nanoparticles. Several catalysts with varying Fe2O3 content ranging from 5 to 20wt% were synthesized, characterized and their catalytic activity evaluated. Structural investigations by XRD and Mössbauer spectroscopy revealed that the 1000°C calcined samples contained ε-Fe2O3 as the major phase in addition to minor α and γ-Fe2O3 phases. ε-Fe2O3 were found to be dispersed as nanorods with typical width of 5nm from HRTEM images. Analysis of surface features by N2-BET surface area, pore size distribution, pore volume and XPS indicated that the majority of Fe2O3 was encapsulated within the mesoporous structure of SiO2 upto 15wt.%, beyond which Fe2O3 was deposited outside the porous network in an enhanced quantity. The surface area of Fe2O3(15wt.%)/SiO2 was found to be 99.6m2/g. Presence of Fe-O-Si linkages was confirmed by XPS, and supported by successive TPR/TPO studies. The extent of reducibility measured via TPR increased with increasing loading and was found to be maximum for the 15wt.% dispersed samples. The catalytic activity was found to increase with an increase in loading of active Fe2O3 content upto a SO2 yield of∼92% at 900°C at a WHSV of 27g acid g−1h−1, for 15wt.% and then decreased. Further evaluation of the 15wt.% sample revealed the durability (100h) and practical applicability of the composition. The surface morphology, structure and composition underwent modifications during the 100h operation in order to adapt to the reaction environment (high temperature, steam, oxides of sulfur) and the Fe2O3 (15wt.%)/SiO2 catalyst exhibited iron sulfate formation and significant surface reorganization. The high catalytic activity can be ascribed to nanoparticulate nature of Fe2O3 and stability due to its anchored structure on SiO2. These findings would inspire the design of active and stable catalyst for high temperature catalytic reactions.