Sulfuric Acid Decomposition Research Articles

Effect of phosphoric acid on leaching of monazite during low-temperature sulfuric acid cyclic leaching process

To completely recover valuable elements and reduce the amount of waste, the impact of phosphoric acid on the decomposition of rare earth, fluorine and phosphorus during cyclic leaching was studied based on the characteristics of low-temperature sulfuric acid decomposition. When a single monazite was leached using 75 wt% H2SO4 solution with phosphoric acid, the size and number of monazite particles in the washing slag gradually decrease with the increase in phosphoric acid content in the leaching solution. The monazite phase can hardly be found in the slag when the phosphoric acid content reaches 70 g/L, which indicates that phosphoric acid is favorable for monazite decomposition. The mixed rare earth concentrate was leached by 75 wt% H2SO4 containing 70 g/L phosphoric acid, the mineral compositions of the washing slag are only gypsum and unwashed rare earth sulfuric acid. After cyclic leaching of 75 wt% H2SO4, the mineral compositions of the primary leaching washing slag are mainly undecomposed monazite, rare earth sulfate and calcium sulfate. However, monazite is not found in the mineral phase of the second and third leaching washing slag. The leaching rates of rare earth and phosphorus gradually increase with the increase in cyclic leaching times. In addition, the phosphoric acid content in the leaching solution increases with the increase in the number of cyclic leaching time. However, the rising trend decreases when the phosphoric acid content reaches 50 g/L by adsorption and crystallization of phosphoric acid. A small amount of water can be used to clean the leaching residue before washing to recover the more soluble phosphorus acid according to the difference of dissolution between phosphoric acid and rare earth sulfuric acid.

Application of microwave radiation for decrepitation of spodumene from the Kolmozerskoe deposit

The lithium-ion industry is experiencing a rapidly growing demand for compounds containing lithium. Spodumene is one of the primary industrial minerals used in the production of this metal. It exists in three polymorphic forms. In its natural state, it is known as α-spodumene, which possesses a high resistance to chemical attack due to its compact structure containing silicon and aluminum oxides. When subjected to microwave radiation, α-spodumene undergoes a transformation, first becoming the γ form and then transitioning to the β form. It is known that the β form can be chemically treated to extract lithium. In light of this, microwave exposure was applied to α-spodumene with the aim of decrepitation, followed by sulfuric acid decomposition of the mineral. The mineral was crushed into different sizes (1.0, 0.5, and 0.25 mm). Temperature changes, induced by both conventional and microwave heating, were analyzed. The heating process was continued for samples of various sizes until a temperature of 1200 °C was reached. Sulfation of calcined samples was carried out for 60 minutes at a temperature of 250 °C. After cooling to 22 °C, distilled water was added and mixed for 120 minutes in closed leaching vessels. To determine the recovery of valuable and associated components, leach cakes and the liquid phase were analyzed using inductively coupled plasma atomic emission spectrometry. Based on the analysis of experimental results, the feasibility of using microwave radiation for decrepitation of spodumene to extract lithium is confirmed. The influence of particle size on phase transformations and, consequently, the degree of lithium extraction from spodumene was investigated. It was found that the recovery of lithium during the microwave action and leaching process for particles smaller than 0.25 mm reached 96.82 %. Microwave heating resulted in lower recovery rates of “harmful” components, such as iron, sodium, and calcium, in the leaching process, leading to a higher purity of the resulting product.

ВЫДЕЛЕНИЕ ГИДРОПЕРОКСИДА ВТОР-БУТИЛБЕНЗОЛА ИЗ ПРОДУКТОВ ЖИДКОФАЗНОГО ОКИСЛЕНИЯ ВТОР-БУТИЛБЕНЗОЛА МЕТОДОМ ЭКСТРАКЦИИ

Hydroperoxides of alkylaromatic hydrocarbons are valuable products of organic synthesis, which are widely used as initiators of polymerization and liquid-phase oxidation of hydrocarbons, as well as an epoxidizing agent. In addition, hydroperoxides are intermediates in the production of phenol and its alkyl derivatives. In this paper, a method is proposed for the isolation of tertiary hydroperoxide of sec-butylbenzene from the products of its liquid-phase aerobic oxidation by extraction with aqueous solutions of various solvents (methanol, ethanol, isopropanol, dimethylformamide, acetone and acetonitrile). The influence of the nature of the solvent, its concentration and the initial concentration of hydroperoxide on this process has been studied. Based on the experimental data obtained, it was found that 75-80% solutions of methanol and ethanol were the most effective in the extraction process. A high distribution coefficient is observed for a 75% methanol solution and is 1.24. It has been shown that up to 60% of the hydroperoxide can be extracted by single extraction. Carrying out a five-stage extraction of products of liquid-phase oxidation of second-butylbenzene with a 75% ethanol solution makes it possible to obtain concentrated up to 95% sec-butylbenzene hydroperoxide. Its structure was confirmed by IR spectroscopy. In this case, the isolated unreacted hydrocarbon can be directed to re-oxidation while maintaining a high rate, conversion and selectivity of hydroperoxide formation. The resulting concentrated tertiary hydroperoxide of sec-butylbenzene was subjected to sulfuric acid decomposition in a methyl ethyl ketone medium. It has been established that the products of this reaction are phenol and methyl ethyl ketone. At room temperature and a catalyst content of 0.8% by weight phenol and methyl ethyl ketone with yields of 88 and 71%, respectively, were obtained from hydroperoxide loading.

INFLUENCE OF HIGH-MOLECULARS COMPOUNDS OF DIFFERENT NATURE ON THE EFFICIENCY OF PURIFICATION THE MOTHER LIQUOR OF MAGNESIUM SULFATE PRODUCTION FROM IMPURITIES Fe3+, Al3+ AND Cr3+ BY ELECTROFLOTATION

The effect of flocculants and surfactants of different nature on the process of purification of the MgSO4 mother liquor from Fe3+, Al3+ and Cr3+ impurities by electroflotation was investigated. The study is aimed at increasing the yield of magnesium sulfate by returning the purified mother liquor to the head of the process at the stage of acid decomposition of serpentinitomagnesite. In the experiments, model solutions with a concentration of MgSO4 – 100 g/l, the content ions of Fe3+ – 50 mg/l, Al3+ – 10 mg/l and Cr3+ – 10 mg/l were used. It was determined that all impurities during pH adjustment turn into slightly soluble compounds at values 6 – 7. For the MgSO4 purification process by electroflotation, the optimal current density was established, which is 0.4 A/l. The duration of the process of purification by electroflotation is 30 min. When studying the effect of surfactants of cationic, anionic, nonionic and amphoteric types on the MgSO4 purification process by electroflotation, it was found that the degree of extraction of Fe3+, Al3+ and Cr3+ impurities does not exceed 10-30%, the exception is the presence of an amphoteric surfactant, in which the degree of extraction of Fe3+ is 77 – 78%. It was found that the greatest efficiency of extraction of Fe3+, Al3+ and Cr3+ impurities from MgSO4 solution is achieved in the presence of anionic flocculant Praestol 2540. The degree of extraction for all components reaches 98-99% already at the tenth minute of the process. Thus, the purification of MgSO4 from Fe3+, Al3+ and Cr3+ impurities by electroflotation in the presence of anionic flocculant Praestol 2540 will allow the purified mother liquor to be returned to the beginning of the process at the stage of sulfuric acid decomposition of serpentinitomagnesite during the production of magnesium sulfate, which will increase the yield of the product.

O-Vacancy Mediated Partially Inverted Ferrospinels for Enhanced Activity in the Sulfuric Acid Decomposition for Hydrogen Production.

Understanding the characterization of a tailored Co3O4 spinel with Fe3+ doping poses a challenge due to the surface state complexity in bifunctional catalysts with higher cation diversity. Doping with secondary metal results in a double spinel structure (a hybrid of normal and inverted spinels). This enhances the catalytic properties by generating more active oxygen vacancies. The cobalt-rich (FeCo2O4) hybrid spinel and iron-rich (CoFe2O4) inverted spinel are synthesized using a wet impregnation method, supported over oxidized SiC (SiC-Pretrt) for an improved metal-support interaction. FeCo2O4 on pretreated SiC exhibits the highest catalytic activity (90% conversion at 1173 K) and stability (over 100 h) in sulfuric acid decomposition of the iodine-sulfur process for hydrogen production. This improved performance is attributed to the high electronegativity of Co3+, oxygen vacancies, and strong metal-support interaction. The high electronegativity of Co3+ weakens the S-O bond in M-S-O, enhancing the catalytic activity of the spinels. These results are further corroborated by detailed characterization and density functional theory calculations.

A reduced order sulfuric acid decomposition model for a nuclear-powered hybrid sulfur cycle

A reduced order model of sulfuric acid decomposition within a bayonet chemical reactor was developed to support the U. S. Department of Energy Integrated Energy System program, and address the lack of knowledge in scaling and integration for joint chemical and nuclear processes. Sulfuric acid decomposition within a bayonet reactor was modeled to provide chemical and thermodynamic data relevant to advanced nuclear reactor-driven integrated energy systems based on desired operational scale and operational conditions. The temperature range required for high-temperature advanced nuclear reactor integrated energy systems, 750-850 °C, was shown to produce reasonable agreement (within a few percent relative error) with past models and experimental data, and yielded good efficiency results for bayonet reactor operations. The results of the reduced order model agreed with previous work from Savannah River National Labs within a maximum of 3.4% error on the decomposition of sulfur trioxide, and on previous Hybrid Sulfur flowsheets from Gorensek and Summers that showed operational temperature, pressure, and composition ranges for efficiency which made the Hybrid Sulfur cycle competitive with water electrolysis. The agreement with previous high-fidelity models provided a framework for future Integrated Energy System grid evaluations with an advanced nuclear reactor and large-scale hydrogen production using a mathematical model to represent chemical operations.

Obtaining phosphate fertilizer with additional nutrients

In order to obtain phosphorus fertilizer enriched with additional nutrients, the decomposition process of apatite concentrate with sulfuric acid was carried out with an additive, in the first variant – ammonium hydrophosphate, and in the second variant - ammonium and potassium hydrophosphates. Experimental studies have studied the effect of additives on the interaction of sulfuric acid with fluorapatite, as well as X-ray phase and IR spectroscopic analyses have studied the structural composition of the resulting product. It was found that with the use of additives, the resulting phosphorus fertilizer contains, along with calcium dihydrophosphate, also ammonium dihydrophosphate. A distinctive feature is the decomposition of sulfuric acid phosphates, resulting in a poorly soluble calcium sulfate that passes into the solid phase, which has traces of its presence in the resulting fertilizer, and may also not be part of the solution. The process of decomposition of fluorapatite with sulfuric acid using an additional part (NH4)2HPO4, the optimal amount of the additional part should be considered 12-18% (by weight of sulfuric acid) additive, while the highest degree of decomposition of apatite concentrate is achieved, which is 95-97%. The conducted studies have established that the introduction of an additive - ammonium and potassium hydrophosphates - into the process of sulfuric acid decomposition of apatite concentrate also has a positive effect on the duration of the superphosphate maturation period. To clarify the structural composition of the finished product, X–ray phase studies and IR spectrometric analysis of the powdered product were carried out. Thus, mineral fertilizers obtained with the use of additives having an additional nutrient element in their composition, namely nitrogen - in the first variant, and nitrogen and potassium - in the second variant.

Selectively extracting H2WO4 of high purity from the H2SO4 decomposition product of scheelite through hydrogen peroxide coordination followed by purification using ion-exchange and solvent extraction and thermal decomposition

The discharge of ammonium-containing wastewater and saline wastewater, which are among the main sources of water pollution in China, is difficult to avoid in traditional tungsten extraction processes. Sulfuric acid decomposition of scheelite can address the issue of saline wastewater discharge, but effectively dissolving tungsten from the sulfuric acid decomposition product without causing ammonia pollution remains a challenge. To tackle these problems, this work proposes a novel process of selectively extracting tungsten from sulfuric acid decomposition products using hydrogen peroxide coordination. Under the optimum preparation conditions, 99.0% of tungsten in scheelite was transformed into tungstic acid. The extraction efficiency of tungsten from the product by hydrogen peroxide reached 99.4%, while tungsten content in residue is <1%. The conversion of tungsten from the product to peroxotungstic acid was investigated. After the purification using ion-exchange and solvent extraction, high-purity tungstic acid was obtained through thermal decomposition, with the content of each impurity element being lower than 15 mg/l. This study offers a new approach to producing high-purity tungstic acid from the sulfuric acid decomposition product of scheelite while eliminating the issues of ammonium-containing wastewater and saline wastewater.

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.

Experimental and numerical investigation of sulfuric acid decomposition for hydrogen production via iodine–sulfur cycle

In the context of global warming and the greenhouse effect, the iodine–sulfur cycle is an important method of producing hydrogen on a large scale with low carbon emissions using nuclear energy for future applications. The sulfuric acid decomposition reaction is a key step in this process. A sulfuric acid decomposer with good performance usually has the characteristics of high decomposition rate, small pressure drop loss and reasonable temperature distribution, which can ensure the efficient and stable process of sulfuric acid decomposition. Therefore, an accurate evaluation of the performance of the sulfuric acid decomposer unit and the reproducibility of the whole process is of utmost importance for designing and engineering an actual system for hydrogen generation. In this work, two sets of experimental systems were designed to measure the important kinetic parameters of sulfuric acid decomposition reaction and to determine the thermal hydraulics and chemical reaction performance indicators of the system. Then, a multi-field coupling model in which the phase change and chemical reactions were coupled by user-defined functions was developed based on the experimental kinetic parameters to account for the whole process. The thermal–hydraulic characteristics and the chemical reaction indexes predicted by the model are in good agreement with the experimental results. The maximum errors of the sulfuric acid decomposition fraction and pressure drop do not exceed 5% and 10%, respectively. Overall, this work provided a complete model for predicting the performance of the sulfuric acid decomposer.

Исследование кинетики сернокислотного разложения нефелина

The results of the study of the kinetics of sulfuric acid decomposition of nepheline are presented. Mathematical processing of experimental data has shown that the process is described with a sufficient degree of accuracy by the formal equation of the rate of transformation d(1-)/d = -k(1-)n at n = 1. It is established that the process of acid decomposition of nepheline is most accurately described by the Ginstling-Braunstein topochemical diffusion equation: 1-2/3-(1-)2/3 = k.

A Conceptual Catalytic Receiver Reactor for Solar Thermal Sulfuric Acid Decomposition

The highest‐temperature step in iodine–sulfur and hybrid–sulfur thermochemical cycles for hydrogen generation is the sulfuric acid decomposition reaction. To efficiently utilize solar energy directly to operate this step, the development of a catalytic solar receiver reactor is essential. A cavity‐type reactor coupled to a solar dish and a numerical analysis of the reactor predicting the reaction conversion as a function of the solar absorption coefficient is presented in this study. The catalytic receiver reactor consists of a double‐walled quartz cylindrical tube to form the cavity and a flat quartz plate window for entry of the concentrated solar radiation. Two catalysts, Fe1.8Cr0.2O3 and Fe2O3/SiO2, are tested in the solar catalytic receiver reactor and SO2 yields of ≈40% and 38% are observed, respectively. Numerical analysis of the reactor is performed and a reaction conversion–absorption coefficient correlation is established. For the catalytic packed bed assuming absorption coefficient of 0.65, a steady‐state temperature of 1212 K is achieved, accomplishing an approximate theoretical efficiency of ≈56%. The numerical analysis suggests that by utilizing a material of construction with high absorption coefficient, significantly enhanced sulfuric acid decomposition can be achieved by the cavity‐type solar receiver reactor.

Sulfation of Gaseous KCl by H2SO4

The sulfation of gaseous KCl by H2SO4 in the presence of O2 and H2O was investigated in a laboratory laminar flow reactor at atmospheric pressure and temperatures ranging from 873 to 1523 K. The degree of sulfation was characterized by analysis of the elemental composition (Cl, S, and K) of the submicrometer particles captured on a filter downstream of the reactor. Furthermore, concentrations of HCl and SO2 in the outlet were measured. The experimental results were interpreted in terms of a detailed chemical kinetic model for the K/S/Cl chemistry. The degree of KCl sulfation depends on the reaction temperature and the reactant concentrations. The results show that H2SO4 is effective in sulfating KCl to K2SO4 at temperatures in the range 1073–1273 K, in particular at high H2SO4/KCl ratios. At temperatures of 1373 K and above, the sulfation efficiency decreases rapidly because alkali sulfate formation is no longer thermodynamically favored. The kinetic analysis shows that reaction is initiated by decomposition of sulfuric acid: H2SO4 + H2O ⇄ SO3 + H2O + H2O. Then KCl reacts directly with SO3 to form the intermediate KSO3Cl, which is further converted via KHSO4 to gaseous K2SO4. As the gas is cooled downstream of the isothermal zone, potassium sulfate nucleates homogeneously to form an aerosol, promoting further sulfation in the gas phase. The simulations are in satisfactory agreement with the experimental results, predicting correctly the temperature window for the process. However, the model overpredicts the SO2 yield at high temperature, indicating that the K/S interactions under these conditions are not fully understood. The results are important, both for validation of models of K/Cl/S interactions in combustion and for characterization of the sulfation of KCl by sulfuric acid to evaluate the potential of the sulfur recirculation process and identify the optimum process conditions.

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.

Efficient dissolution of tungstic acid by isopolytungstate solution based on the polymerization theory of tungsten

The rare metal tungsten is a very important strategic metal. The traditional tungsten ore alkaline process has many problems, including the generation of alkali residue, ammonia‐nitrogen wastewater, and industrial wastewater during ion exchange. The feasibility of decomposing scheelite with sulfuric acid has been confirmed due to the economic and environmental pressures faced by scheelite decomposition; however, extracting tungsten from the decomposition residue is a difficult process. This study was based on the polycondensation theory of tungsten, in which tungstic acid (H2WO4) rapidly dissolves in isopolytungstate solution during the acid adjustment process of sodium tungstate solution. Taking advantage of the different polymerization morphologies, a new idea in which tungstic acid selectively enters the solution after the polycondensation reaction between tungstic acid and isopolytungstate is proposed. In this work, the dissolution of tungstic acid in isopolytungstate solution under different experimental conditions were studied. The results indicated that isopolytungstate solution can undergo polycondensation reaction with tungstic acid, and the dissolution of W reached 0.37 g/g under suitable dissolution conditions. Additionally, the residue formed in sulfuric acid decomposition had a satisfactory leaching effect of tungsten in the isopolytungstate solution with a WO3 leaching efficiency of about 98.8%. Tungsten in the hydrochloric acid decomposition residue could also be extracted efficiently in the form of an isopolytungstate solution with a WO3 leaching yield >99%. This work proposes a cleaner and more efficient idea for the selective dissolution of tungsten from the acid decomposition residue of scheelite.

Entropy generation rate minimization for sulfur trioxide decomposition membrane reactor

Sulfuric acid decomposition is the critical reaction in sulfur-iodide thermochemical cycle to produce oxygen. Sulfuric acid can decompose spontaneously into sulfur trioxide (SO3) and water, and SO3 continues to decompose into oxygen and sulfur dioxide. The application of membrane reactor can effectively improve the conversion rate of SO3 and thermal efficiency of sulfur-iodide cycle. The decomposition of SO3 requires the absorption of a large amount of heat due to its highly endothermic properties, and there are many irreversible processes such as heat transfer, mass transfer, chemical reaction and friction flow in the SO3 membrane reactor. Therefore, it is necessary to conduct thermodynamic analysis and optimization of the decomposition process to reduce the irreversible loss of the membrane reactor system. In this paper, a finite time thermodynamic model of SO3 decomposition membrane reactor is established, and the kinetic parameters of decomposition reaction are deduced and calculated based on experimental data. Firstly, the membrane reactor heated by hot helium gas is solved and used as reference reactor. Secondly, optimal control theory is used to optimize the reference reactor under fixed reactant inlet conditions and outlet conversion rate with total entropy generation rate minimization as optimization objective. The total entropy generation rate of Opt-1 reactor is reduced by 32.7% compared with the reference value. For variable reactor length, the total entropy generation rate of Opt-2 reactor is quadratic optimum at L=0.72 m, which is 34.7% less than the reference value. It is found that the reduction of total entropy generation rate in optimal reactors is mainly achieved by minimizing the entropy generation rate in heat transfer process. The distribution of local entropy generation rate is relatively uniform in the middle position, approximately consistent with the principle of equalization of entropy production rate. The conclusions obtained herein can provide guidelines for the energy-saving design of SO3 decomposition membrane reactors.

MECHANICAL PROPERTIES OF PHOSPHOGYPSUM AND TRENDS ITS UTILIZATION

Phosphogypsum is a waste obtained by binding calcium in the process of sulfuric acid decomposition of phosphate raw materials in the production of phosphorus fertilizers. The article presents the results of complex laboratory studies of more than 500 samples of calcium sulfate hemihydrate and dihydrate. Calcium sulfate dihydrate (CaSO4·2H2O) is a solid fine-crystalline substance of white or gray color with the inclusion of large aggregates. Deformability, strength properties and permeability of calcium sulfate dihydrate were determined on specially prepared samples with a relative compaction of 0.95; 0.90 and 0.80 by the methods used in engineering and geological surveys. The internal friction angle, cohesion and coefficient of permeability have values typical for silty sands and sandy loam, and the compressibility characteristics are significantly lower due to the solubility of matter. This material is characterized by subsidence and suffusion sediment characteristic of carbonate rocks (dolomite, limestone). Calcium sulfate hemihydrate (CaSO4·0.5H2O) - a loose earthy mass of white or gray color, as the process of hydration and the appearance of cementation bonds turns into a semi-rocky technogenic soil of low strength. The characteristics of calcium sulfate hemihydrate were determined on the undisturbed samples taken from the dump after 1 and 6 months, 1, 5 and 10 years after storage. These characteristics are comparable to construction gypsum materials from lower grades. It is recommended to use calcium sulfate dihydrate as ground material when carrying out water-protective measures and neutralizing the acids contained in it, the use of calcium sulfate hemihydrate is significantly limited by its setting time.

Flow of simple superphosphate using two-stage decomposition of phosphorite

The methods for producing simple superphosphate by two-stage sulfuric acid decomposition of natural phosphates are analyzed. For the first stage, the process of decomposition of high-carbonate powdered phosphorite is studied depending on the rate of sulfuric acid from stoichiometry to the formation of H3PO4, its concentration and the reaction time of the starting components. For the second stage, the process of neutralization of phosphoric acid is studied, depending on the norm of phosphate rock for the formation of Ca(H2PO4)2. The drying process of superphosphate is carried out, in which granular superphosphate is obtained, and P2O5total. - 12%, P2O5free. - 4.6%, P2O5dig : P2O5total = 90%, P2O5 water : P2O5total = 79%.

Evaluation of Goethite as a Catalyst for the Thermal Stage of the Westinghouse Process for Hydrogen Production

This work focuses on the evaluation of goethite as a catalyst for the transformation of sulfuric acid into sulfur dioxide, a reaction with great interest for the hybrid electrochemical-thermoelectrochemical Westinghouse cycle for hydrogen production. A comparison of the performance of goethite with that of CuO, Fe2O3, and SiC has been carried out. Moreover, a mixture of those catalysts was evaluated. The results demonstrate that goethite can be used as a catalyst for the thermal decomposition of sulfuric acid in the Westinghouse cycle, with an activity higher than that of SiC but lower than that of Fe2O3 and CuO. However, it does not undergo sintering during its use, but just produces small particles in its surface, which remain after the treatment. Mixtures of Fe2O3 with SiC or goethite do not produce synergism, thus operating each catalyst in an independent way.

Thermodynamic modeling of sulfuric acid decomposer integrated with 1 MW tubular SOFC stack for sulfur-based thermochemical hydrogen production

This study developed a thermodynamic model of a set of sulfuric acid decomposers for thermochemical hydrogen production. It was integrated with a 1 MW tubular-type solid oxide fuel cell (SOFC) stack. With the model, we evaluated the feasibility of the combined production of electric power, heat, and sulfur dioxide for thermochemical H2 production. The integrated reactor model consists of three parts: i) SOFC submodel, ii) sulfuric acid decomposition (SAD) submodel, and iii) sulfur trioxide decomposition (STD) submodel with the catalysts Pt/γAl2O3 and WX-1. The efficiency of the integrated system was evaluated at a low-pressure range by polarization and efficiency curves for the SOFC, as well as pinch analysis for the SAD. The highest SOFC efficiency and SO2 production were achieved at 1.25 bar, whereas the lowest fuel consumption and heat demand for SO2 production were achieved at 3.0 bar. Furthermore, WX-1 performed better in the high-temperature range, whereas Pt/γAl2O3 performed better than WX-1 under low-temperature conditions. The Pt-supported catalyst could achieve SO3 conversion of 66% and SO2 yield of 57% at a gas temperature of 1025 K using the proposed integrated reactor design.