High Temperature Sulfuric Acid Research Articles

Improvement of the technological scheme for processing zinc concentrates by hydrometallurgical method at JSC Almalyk MMC

The extraction of zinc from concentrates is carried out in pyrometallurgical and hydrometallurgical ways. Obtaining pure zinc of the highest grades is possible using the hydrometallurgical method, in which the calcined sulfide concentrate is subjected to sulfuric acid leaching, a solution of zinc sulfate and a recycled product is formed - a solid residue of the cake leaching process. After purification, the zinc sulfate solution is subjected to electrolytic refining, and the cake is processed pyroly or hydrometallurgically. At JSC "Almalyk MMC" in the process of hydrometallurgical processing of zinc concentrates, the resulting zinc cake is processed by the pyrometallurgical method - rolling. The rolling process takes place in two tubular furnaces (rolling furnaces) 50 meters long and 3.5 meters in diameter at a temperature of 1100–12000C, in the presence of a reducing agent, coke breeze and petroleum coke. As a result of the rolling process of zinc cakes, sublimates and a solid technogenic residue, clinker, containing copper, gold, and silver are formed. Clinker is processed at the plant in smelting furnaces to extract precious metals, but it is accumulating more than 450 thousand tons. In connection with this, scientific research is currently underway on the processing of zinc cakes using a hydrometallurgical method to eliminate the expensive rolling process of processing zinc cakes; high-temperature (900 C) sulfuric acid leaching of cakes with a size of 0.074 mm has been developed during leaching for 4-4.5 hours, the extraction of zinc into the solution is 98.5%; copper 92.8%; iron 75.2; cadmium 79.2.

Selective preparation of lithium carbonate from overhaul slag by high temperature sulfuric acid roasting – Water leaching

An efficient recycling process is developed to recover valuable materials from overhaul slag and reduce its harm to the ecological environment. The high temperature sulfuric acid roasting - water leaching technology is innovatively proposed to prepare Li2CO3 from overhaul slag. Under roasting conditions, fluorine volatilizes into the flue gas with HF, lithium is transformed into NaLi(SO4), aluminum is firstly transformed into NaAl(SO4)2, and then decomposed into Al2O3, so as to selective extraction of lithium. Under the optimal roasting – leaching conditions, the leaching rate of lithium and aluminum are 95.6% and 0.9%, respectively. Then the processes of impurity removal, and settling lithium are carried out. The Li2CO3 with recovery rate of 72.6% and purity of 98.6% could be obtained under the best settling lithium conditions. Compared with the traditional process, this work has short flow, high controllability, remarkable technical, economic, and environmental benefits. This comprehensive recycling technology is suitable for overhaul slag, and has great practical application potential for the disposal of other hazardous wastes in electrolytic aluminum industry.

Sol-gel mediated synthesis and characterization of hierarchically porous Fe2O3/SiO2 monolithic catalyst for high temperature sulfuric acid decomposition

To address the issues faced by microparticulate catalysts in fixed bed reactors for high temperature sulfuric acid decomposition viz. channeling and mass transfer, we report the preparation, characterization of Fe2O3/SiO2 hierarchical porous monoliths and testing of its catalytic properties. Monoliths with varying Fe2O3 amounts (5–30 wt%) are synthesized by a modified sol-gel approach and characterized by powder XRD, Mössbauer spectroscopy, SAXS, SEM-EDS and XPS. The Fe2O3(15 wt%)/SiO2 monolith exhibited a SO2 yield of ∼62% at 800 °C. The spent catalyst investigation established the dynamic nature of catalyst surface to accomplish the reaction mechanistic demands.

Corrosion Behavior of MoSi<sub>2</sub> Coated Hastelloy X Utilized in Iodine -Sulfur Cycle for Hydrogen Production Application

Molybdenum di silicide (MoSi2) has lower mismatch of coefficient of thermal expansion (CTE) with Hastelloy X as compare to silicon carbide. So, MoSi2 coatings can be a potential candidate to protect Hastelloy X against high temperature sulfuric acid. Herein, MoSi2 thin films were deposited via electron beam physical vapor deposition (EBPVD) method. Corrosion behavior of MoSi2 coated HX and bare HX was analyzed. Corrosion tests of bare Hastelloy X and coated samples was performed at different temperatures (60°C and 120°C) in 98% sulfuric acid using the weight-loss method. The morphology of pre and post corrosion test was also analyzed by using optical microscopy. Bare Hastelloy X showed a slight weight gain at 60°C and a weight loss at 120°C. The MoSi2 coated Hastelloy X showed slight weight gain at 60°C and a weight loss at 120 °C. The weight gain is the result of oxides formation whereas, weight loss may be attributed to corrosion due to H+ ions. These findings were also accompanied by optical microscopy as corroded and very rough patches were evident for bare HX, whereas, for MoSi2 coated samples, the coating was still intact.

Recycling of brass melting slag through the high-temperature oxidation-leaching process

Brass melting slag is a valuable secondary resource for the recovery of copper and zinc. The hydrometallurgical recovery process of this material is a challenge, because of its limited dissolution in sulfuric acid. The present study aimed at studying a combined pyro-hydrometallurgical treatment processes involving high temperature oxidation and sulfuric acid leaching to industrial brass melting slag to recover copper and zinc. The effect of temperature on the performance and efficiency of the high temperature oxidation process was investigated by isothermal thermogravimetry. The results revealed that by increasing the oxidation temperature, leachability improves due to the oxidation of metallic brass particles. The results obtained showed that 3 h oxidation of as-received slag at 900 °C, increased its percent leaching amount in 2 M sulfuric acid from 34 to 81%. The pregnant leach solution containing copper sulfate and zinc sulfate was subjected to the electrowining process to recover the copper as copper cathode. The zinc was also recovered as zinc sulfate via evaporation and crystallization process. Kinetic investigations showed that the 3D diffusion model has a good agreement with the isothermal oxidation results. In this model, the oxidation reaction is controlled by the outward diffusion of zinc from the brass particle. The activation energy of isothermal oxidation was obtained as 311 kJ mol− 1.

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.

Coalescence-adsorption coupling treatment instead of alkaline washing-water washing process for efficient removal of sulfuric acid and sulfates

C4 alkylate oil is an ideal blending component of automotive gasoline, and the green removal of sulfuric acid and sulfates from the high-temperature sulfuric acid alkylation reaction products (SAARP) has always been a hot issue in the field of clean alkylation production. In this paper, a novel coalescence separation-depth adsorption (CS-DA) coupling dry separation technique is introduced to efficiently separate acid-hydrocarbon emulsions, with the aim to supersede the alkaline washing-water washing (AW-WW) process in alkylation unit. Lateral line tests were conducted on the coupling treatment of the alkylation reaction products (ARP) produced in the STRATCO alkylation unit of Sinopec Tianjin Branch. The sulfur morphology analysis shows that the sulfides in the ARP mainly come from C4 feedstocks and alkylation reaction, including mercaptans, thioethers, thiophenes, trace hydrogen sulfide and sulfur dioxide. The mechanism of coalescence separation reveals that the efficient removal process of sulfuric acid by fiber coalescence separation also has a function similar to "pickling extraction" to remove sulfates. In addition, we investigated the influence of CS-DA coupling treatment on the total sulfur and sulfuric acid content in the ARP and performed the copper corrosion and water-soluble acid assays. The research findings indicated that the back sideline of the acid coalescer had the most outstanding separation effect relative to the front and rear lateral lines of the heat exchanger. The total sulfur content in the ARP after separation can be reduced to less than 5 mg/L, without water-soluble acid and copper corrosion (1a). The industrial application shows that the CS-DA coupling dry separation technique can completely replace the AW-WW process, which makes the various indicators of alkylate oil strictly controlled and the sulfur content up to the industrial standard. The novel dry separation technique provides a promising alternative for solving the difficulties in the emulsion treatment of high-temperature sulfuric acid alkylation and promoting the clean production of alkylation.

Immobilization of crystalline Fe2O3 nanoparticles over SiO2 for creating an active and stable catalyst: A demand for high temperature sulfuric acid decomposition

To address the issues of catalytic activity and stability of the promising Fe2O3/SiO2 catalyst for sulfuric acid decomposition, Fe2O3 was immobilized on SiO2 support by polyol, solvothermal and wet-impregnation methods and examined. The different methods yielded catalysts with varying crystal structure, porosity, morphology and redox properties which were investigated by XRD, Mössbauer spectroscopy, N2-BET surface area, SAXS, ED-XRF, HR-TEM, TPR/O and XPS techniques. The effect of the properties on the activity and stability was evaluated in a fixed-bed reactor and a structure-activity correlation was established. Above 750 °C the catalytic activity followed the order polyol > wet impregnation ∼ solvothermal. Stability of the sample prepared by polyol method was ascertained by 100 h experimental run at 800 °C. The higher activity and stability of the Fe2O3/SiO2 catalyst (polyol) is ascribed to the development of crystalline α-Fe2O3 dispersed phase, higher pore confinement, better support-active phase interactions and higher degree of reduction.

Kinetic modeling and simulation of catalyst pellet in the high temperature sulfuric acid decomposition section of Iodine-Sulfur process

In the iodine-sulfur (I-S) thermochemical process for hydrogen production, the most endothermic high temperature step is the sulfuric acid decomposition which is catalytic process. Here, we introduce a model-based framework to address the effect of model uncertainty on catalyst identification, designing and optimization. To investigate the kinetic parameters, the experiments are performed in the packed bed reactor under the conditions of diffusion free regime. Further, the kinetic model is implemented in a two-dimensional heterogeneous model of the catalytic packed bed reactor developed in Multiphysics software in order to investigate the effects of catalyst composition, support material, catalyst pellet shapes, sizes (i.e., diffusional length), pellet intrinsic properties (i.e., porosity and thermal conductivity) and temperature on the catalyst effectiveness factor. The 7-hole cylindrical shapes with 0.75 and 1.5 mm principle dimension at 1073 K has been found to have negligible diffusional limitation and temperature gradients across their cross sections.

Computational Fluid Dynamics Modeling of a Direct Solar Driven Sulfuric Acid Decomposition Reactor

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 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 sulfur-based cycles and in particular the thermo-electrochemical Hybrid Sulfur (HyS) is one of the most appealing cycles. This process 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 focuses on the high temperature sulfuric acid thermal decomposition section, developing new optimized catalyst formulations (i.e. achieving higher activity, lower performance degradation and lower costs), to be integrated in novel solar reactor systems. A new bimetallic catalyst formulation has been developed and synthesized, based on novel composition and 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. A novel reactive computational fluid dynamic (CFD) model is presented, integrating mass, energy and momentum balance equations. A new kinetics expression has also been developed to model the behavior of the novel catalytic formulation. The model has been developed for both the high temperature catalytic decomposition process and for the vaporization/condensation of the sulfur mixture process. A novel two-phase model has been developed with the properties of the mixtures (SO2, SO3, H2O, H2SO4, O2) extracted from process models and integrated in the CFD code using numerical modeling approximations. Results are presented and discussed.

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.

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.

Crevice Corrosion of Stainless Steels 904L, 2205, and 2507 in High-Temperature Sulfuric Acid Solution Containing Chlorides: Influence of Metal Cations

Crevice corrosion influences the integrity of materials in many industrial sectors, such as hydrometallurgy. The conditions in hydrometallurgical processes are severe, with high concentrations of sulfuric acid leachant as well as high-chloride impurity, oxygen, and metal cation contents. In this study, crevice corrosion behavior of highly-alloyed austenitic and duplex stainless steels is investigated in aerated high-temperature sulfuric acid solution with 1 g/L chlorides in the presence of three types of metal cations: Fe3+, Cu2+, and Fe2+. The experimental work contains the determination of the oxidizing capacity of the solutions, immersion crevice corrosion tests followed by characterization of the corrosion attack, and potentiodynamic polarization measurements. The results show that the alloy with the highest PREN value, grade 2507, was not susceptible to crevice corrosion under the test conditions. In the case of grades 904L and 2205 of relatively equal PREN values, the extent and nature of crevice corrosion attack was different and dependent on the ratio of activities of chlorides to sulfates and the type of metal cations. The results are presented and discussed in the light of IR drop mechanism.

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.

Erosion–corrosion resistance of various stainless steel grades in high-temperature sulfuric acid solution

Two austenitic stainless steel grades, 316L and 904L, and three duplex stainless steel grades, LDX 2101, 2205, and 2507, were erosion–corrosion tested as impeller blade materials for hydrometallurgical applications. Samples were attached to the pressure and suction sides of an impeller and were tested in 50g/l H2SO4 and 0.5g/l Fe2(SO4)3 for 72h at 80°C and 95°C in a small-scale reactor using quartz sand slurry. The results showed that under lower erosion intensity the ranking of the grades was similar to that in pure erosion. Under higher erosion intensity the ranking of the grades changed completely: lean alloys LDX 2101 and 316L suffered from the highest mass losses followed by 2205, 2507, and 904L. To clarify this behavior, the ability of the grades to repassivate was investigated with scratch tests. It was found that the ranking could be explained by the repassivation rates. The only exception was that 2507 showed a similar repassivation rate to 904L but its erosion–corrosion mass loss under higher erosion intensity was larger. One contributing factor to this was found to be the selective dissolution of the austenite phase of all the tested duplex grades. The prerequisites for the galvanic coupling between the phases that was responsible for the selective dissolution are discussed.

The influence of high-temperature sulfuric acid solution ageing on the properties of laminated vinyl-ester joints

A carbon fiber powder doped corrosion layer is used as an inner layer in large composite tanks to improve their chemical and wear resistance. In joints fabricated on site, this layer is embedded into the structure. This study evaluates the lap shear strength of specimens, simulating a laminated joint in between the corrosion layer and the inner joint laminate. Lap-shear tests were carried out for as-fabricated and aged laminates at room temperature and at elevated temperature. Ageing was carried out for half a year in a 95°C pressurized sulfuric acid solution. The tests showed that, after ageing, the room temperature shear strength remained unaltered but high-temperature shear strength was lowered. When the temperature increased, the failure location shifted from the interface between the doped layer and the joint laminate to the doped layer. Thermal analysis and microscopy were employed to clarify the reasons for the observed behavior.

Micellar mediated selective leaching of manganese nodule in high temperature sulfuric acid medium

The present study evaluates the possibility of selective leaching of manganese from complex, manganese and iron oxy-hydroxide based sea bed nodule utilising micelles in high temperature acid dissolution process. Application of surfactants during acid leaching of manganese nodules are described based on results from leaching studies. The factors that affected the sulfuric acid leaching of the manganese nodules in the presence of various surfactants were investigated. The effect of anionic (SDS-Sodium Dodecyl Sulphate), cationic (CTAB-Cetyl Trimethyl Ammonium Bromide) and nonionic (Triton-X 100) surfactant on the various metals extraction with respect to sulfuric acid concentration, temperature, type of surfactants and surfactant concentration is reported. Among them, CTAB showed highest improvement in the recovery of Cu, Ni, Co, Zn and Mn. Iron, aluminium, and silica were removed effectively through the present approach of high temperature sulfuric acid leaching route assisted by surfactant. Increasing the temperature of the medium has significant impact in the selective leaching of Mn, Cu, Ni and Co. The optimum conditions established for maximum metal extraction are: pulp density 10%, time 2h, temperature 160°C, sulfuric acid 5.0% (v/v) and at critical micellar concentration of CTAB. Under these conditions, recovery of Mn was 99% along with the (˃99%) recovery of Cu, Co, and Ni. The leached residues were analysed and their phase and morphologies were included herein. The present process may find application of separation of manganese from iron and aluminium at high temperature during various hydrometallurgical treatment of manganese based ores.

Catalytic activities of Fe2O3 and chromium doped Fe2O3 for sulfuric acid decomposition reaction in an integrated boiler, preheater, and catalytic decomposer

In our earlier work (Banerjee et al. [29]) we have reported the catalytic properties of powders of Fe2(1−x)Cr2xO3 (x=0.0, 0.1, 0.2) for sulfuric acid decomposition in a flow through quartz catalytic reactor with 2g catalyst in presence of nitrogen as a carrier gas. With a practical application approach, in this work the two screened oxides, iron oxide and 10% chromium doped iron oxide, that showed good initial promise as catalyst for sulfuric acid decomposition were prepared in granular form and evaluated for sulfuric acid decomposition reaction using an indigenously developed dual tube quartz reactor which served as an integrated acid boiler, pre-heater, and decomposer. The effect of reaction variables, e.g., temperature, time, and acid flow rate on the catalytic activity was evaluated in detail employing 20g of granular catalyst and 98wt% H2SO4 (without any carrier/diluents gas). Temperature dependent catalytic activity results revealed that at lower temperatures (<775°C) the Cr-doped sample showed much higher activity while at higher temperatures (∼825°C) the conversions levels were found to be similar on both the samples. No decrease in catalytic activity was observed for either catalysts during a 100h catalytic run at 800°C and at an acid flux of ∼0.63mlmin−1, but the chromium doped sample exhibited slightly higher activity over the entire time period. Both the catalyst exhibited a loss in catalytic activity when subjected to higher flow rates of sulfuric acid in the range 2–10mlmin−1. The catalytic activities were correlated with the structure, morphology, redox, and thermal properties of the oxides by proper characterization of the fresh and the spent catalysts by XRD, FTIR, XPS, TPR, evolved gas analysis, and SEM. From the ex situ analysis of the spent catalyst samples the most probable mechanism of the high temperature sulfuric acid decomposition reaction was also proposed, which involves metal sulfate formation and decomposition steps. The enhanced catalytic activity of Cr-doped Fe2O3 was ascribed to lower thermal stability of its sulfate and better redox properties.

Design and analysis of a high pressure and high temperature sulfuric acid experimental system

We discuss the design and analysis of a small scale sulfuric acid experimental system that can simulate a part of the hydrogen production module. Because nuclear hydrogen coupled components such as a SO3 decomposer and a sulfuric acid evaporator should be tested under high pressure and high temperature operating conditions, we developed the sulfuric acid loop to satisfy design specifications of 900°C in temperature and 1.0MPa in pressure. The components for the sulfuric acid loop were specially designed using a combination of materials with good corrosion resistance; a ceramic and Hastelloy-C276. The design feature of the loop was tested for performance in a 10h sulfuric acid experiment and optimized using Aspen+ code simulation.