Decomposition Of Sulphuric Acid Research Articles

Catalytic decomposition of sulphuric acid in Iodine-Sulphur and Hybrid-Sulphur processes for Hydrogen production: Estimation of effectiveness factor of catalyst

High endothermic heat of SO3 decomposition reaction (ΔHR∼+98 kJ mol−1) can lead to significant thermal gradients (lower temperatures) inside the catalyst particle, depending up on mass diffusion, heat conduction and intrinsic reaction kinetics in the particle. The lower catalyst effectiveness (due to thermal gradients) leads to lower decomposition conversions in Packed Bed Reactors (PBR), which has to be maximized. In this study, a multi-scale model (Double Porosity Model, DPM) is used for the estimation of non-isothermal effectiveness factor (η) of Cr-Fe2O3 catalyst types; less porous pellet and porous foam types. η obtained using DPM (foam∼0.249 and pellet∼0.147) are found to be in good agreement with experimental data and also with the results of derived model (Weisz model). Further, effect of porosity and size/diameter on η are studied and obtained the optimum porosity required for maximum η. The present study is useful for estimation and optimization of non-isothermal η of catalysts.

Experimentation, modeling and optimisation studies of an integrated-packed bed reactor (PBR) for the decomposition of sulphuric acid

Decomposition of sulphur trioxide (SO3) is highly endothermic, catalytic and overall rate-controlling step, in three-step decomposition of sulphuric acid. SO3 decomposition in Packed Bed Reactor (PBR) involves transport resistances in two (multi) scales; macro-voids and micro-pores together with surface reaction. Objective of the present study is to develop a double porosity (multi-scale) model, DPM for the catalytic decomposition of SO3 in a heat recuperated (integrated)-PBR and also to maximize SO3 conversion. DPM and simulation studies are carried out using COMSOL® and the model is validated with experimental studies. Experiments are performed at different flow rates, wall temperature, feed concentration and with two catalyst loadings, where chromium doped iron oxide ‘foam’ type (porous particle) catalyst is used. Simulation study shows, increase in conversion with decrease in particle size, annular gap and with increase in porosity, thermal conductivity of catalyst. Catalyst size is found to be an insignificant parameter, for porosity >0.2 and thermal conductivity is found to be a significant parameter. A conversion close to isothermal conversion has been obtained with the tuned parameters.

Sulphuric acid decomposition using Cr–Fe2O3 catalyst in a tubular Packed Bed Reactor (PBR): Modeling and experimental studies

Catalytic decomposition of sulphur trioxide (SO3), is the rate-controlling and high temperature-endothermic reaction step in three-step decomposition of sulphuric acid. In this work, formulation of one dimensional (1-D) model, detailed transport modeling and experimental studies have been carried out for a non-isothermal, non-adiabatic, tubular-Packed Bed Reactor (PBR). This is to study the effect of heat and mass transfer resistances, in the catalyst bed and also within the catalyst particle, for the decomposition of SO3. 1-D model consists of set of coupled Differential Algebraic Equations (DAEs), which are numerically solved for axial profiles (Temperature, Flow, Pressure) with plug flow reactor assumption. Further, a double-porosity modeling of the reactor has been carried out for the detailed transport study using COMSOL MULTIPHYSICS® simulation software. Here transport equations with the rate law are solved for two different porosities (domains); micro pores inside the catalyst particle (ε) and macro pores (void fraction-φ) in the packing. Models are validated with experimental studies and the molar conversion of SO3 obtained using the models are compared with conversion of an isothermal PBR. Chromium doped iron oxide (Cr–Fe2O3) catalyst; a ‘pellet’ type catalyst is used in this experimental study. Experiments are carried out at different flow (liquid) rates (160–315 ml h−1), wall temperature (973–1243 K) and with two different catalyst bed lengths (catalyst loading of 555 g and 288 g). Double-porosity (COMSOL) model predictions are better close to the experimental data. A multi-scale analysis of the system has been carried out using the double-porosity model, in order to get an insight of concentration drops in the particle (pore diffusion resistance) and fluid film (film resistance) at various locations inside the reactor. Film resistance is found to be negligible when compared with the pore diffusion resistance, in the studied experimental conditions. Modeling of transport (heat and mass transfer) resistances together with kinetics of SO3-decomposition, in two different porous-domains in a PBR, is the novelty of present work. The developed models are useful for maximizing the conversion of SO3 (by tuning the model parameters) in a PBR by minimizing the heat and mass transfer resistances.

Kinetic study and modeling of sulphuric acid decomposition using Cr–Fe2O3 catalyst for sulphur based water splitting processes

Sulphuric acid decomposition is the high temperature (850–900 °C) reaction step of sulphur based water splitting processes (Iodine–Sulphur and Hybrid-Sulphur processes) for hydrogen production. In this work, reaction kinetics and mass transfer data are generated experimentally, for sulphuric acid decomposition using chromium doped iron oxide, Cr–Fe2O3, catalyst in a packed bed reactor (PBR). Experiments are performed using catalyst powder, less porous catalyst particle (pellet) and high porous catalyst particle (foam), between 700 and 850 °C and 0.1–10 ml min−1 liquid feed flow rate. Activation energy and frequency factor of Cr–Fe2O3 catalyst obtained from the powder catalyst study are 74 kJ mol−1 and 183 m3 kg−1 s−1. Internal effectiveness factor (η) of pellet and foam, two industry types of Cr–Fe2O3 catalyst (5 mm size) are calculated from the experimental studies performed at external mass transfer resistance free regime. Internal effectiveness factor of pellet and foam obtained are 0.12 and 0.26 respectively, which shows strong pore diffusion resistance in these catalyst types. Overall effectiveness factor (Ω) for both the catalyst types (pellet and foam) are also obtained for the investigated range of temperatures and flow rates. Further, catalyst particle (pellet and foam) is modeled in COMSOL MULTIPHYSICS® simulation software to get an insight into concentration and temperature profiles. Significant concentration drop and smaller temperature drop are seen in less porous pellet. Small concentration drop and significant temperature drop are observed in porous foam, through simulation studies. Focus of future R&D is to optimise the size and porosity of Cr–Fe2O3 catalyst, for maximum effectiveness factor and thereby maximizing the reaction rate and conversion.

SiC mesoporous membranes for sulfuric acid decomposition at high temperatures in the iodine-sulfur process.

Inorganic microporous materials have shown promise for the fabrication of membranes with chemical stability and resistance to high temperatures. Silicon-carbide (SiC) has been widely studied due to its outstanding mechanical stability under high temperatures and its resistance to corrosion and oxidation. This study is the first to prepare mesoporous SiC membranes for use in sulphuric acid decomposition to achieve thermochemical water splitting in the iodine–sulfur process. Single-gas permeation was carried out to confirm the stability of this mesoporous membrane under exposure to steam and H2SO4 vapor. Benefiting from the excellent chemical stability of the α-Al2O3 membrane support and the SiC particle layer, the SiC membrane exhibited stable gas permeance without significant degradation under H2SO4 vapor treatment at 600 °C. Additionally, with extraction, the membrane reactor exhibited an increased conversion from 25 to 41% for H2SO4 decomposition at 600 °C. The high performance combined with outstanding stability under acidic conditions suggests the developed SiC membrane is a promising candidate for H2SO4 decomposition in a catalytic membrane reactor.

Maximum production rate optimization for sulphuric acid decomposition process in tubular plug-flow reactor

A sulphuric acid decomposition process in a tubular plug-flow reactor with fixed inlet flow rate and completely controllable exterior wall temperature profile and reactants pressure profile is studied in this paper by using finite-time thermodynamics. The maximum production rate of the aimed product SO2 and the optimal exterior wall temperature profile and reactants pressure profile are obtained by using nonlinear programming method. Then the optimal reactor with the maximum production rate is compared with the reference reactor with linear exterior wall temperature profile and the optimal reactor with minimum entropy generation rate. The result shows that the production rate of SO2 of optimal reactor with the maximum production rate has an increase of more than 7%. The optimization of temperature profile has little influence on the production rate while the optimization of reactants pressure profile can significantly increase the production rate. The results obtained may provide some guidelines for the design of real tubular reactors.

Study of Bunsen reaction in agitated reactor operating in counter current mode for iodine-sulphur thermo-chemical process

The iodine-sulphur (IS) thermo-chemical process is being studied as a potential process for production of hydrogen by water splitting. It consists of three chemical reactions: 1) Bunsen reaction, which is the acid production step, 2) sulphuric acid decomposition to produce oxygen; 3) hydrogen iodide decomposition to produce hydrogen. In this work, a detailed parametric study of the Bunsen reaction is presented, which was carried out in agitated reactor (ABR) in counter current mode of operation. Experiments have been carried out in the reactor at different temperatures by varying the sulphur dioxide (SO2) flow rate and partial pressure of SO2. Bunsen reaction rate and SO2 conversion are calculated experimentally from feed rate and scrubbing rate of SO2. It has been observed that the reaction rate and SO2 conversion increase with increase in SO2 flow, increase in SO2 partial pressure and decrease in temperature. 'Tanks-in-series' model, one of the non-ideal reactor models, has been proposed to describe the ABR reaction system. The model has been validated with experimental results. This approach can be useful for the design and scaling up of the agitated reactor.

Sulphur based thermochemical cycles: Development and assessment of key components of the process

HycycleS was a cooperation of nine European partners and further non-European partners and aimed at the qualification and enhancement of materials and components for key steps of solar and nuclear powered thermochemical cycles for hydrogen generation from water. The focus of HycycleS was the decomposition of sulphuric acid (H2SO4) which is the central step of the sulphur-based family of those processes. Emphasis was put on materials and components for H2SO4 evaporation, decomposition, and sulphur dioxide separation. The suitability of materials and components was demonstrated by decomposing H2SO4 and separating its decomposition products in scalable prototypes. Silicon Carbide (SiC) turned out as the material of choice for the components facing the most corrosive environment of the process: the sulphuric acid evaporator and decomposer. Candidate catalysts for the high temperature reduction of sulphur trioxide have been screened and analysed. Cr–Fe mixed oxide (Fe0.7Cr1.3O3) was the most promising material among the ones examined. Based on the use of the highlighted construction and catalyst materials prototype decomposers have been developed and tested. The successful fabrication and testing of a large size heat exchanger/reactor prototype composed of SiC plates shows promise with respect to its use for H2SO4 decomposition in the SI and HyS cycle. A solar specific decomposer prototype was developed, realised and successfully tested on sun in a solar furnace. A novel approach of using dense oxygen transport membranes, made from complex ceramics, for oxygen removal from the H2SO4 decomposition product in order to shift the equilibrium in favour of increased decomposition was investigated. The membranes stability and suitability for carrying out this separation was investigated experimentally. Parallel to this, a conventional oxygen separator, a low-temperature wet scrubbing system, was investigated as well. Scale-up scenarios of components and of the process were addressed.

Electrochemical method for sulphur dioxide removal from flue gases: Application on sulphuric acid plant in Tunisia

Abstract This article presents an electrochemical method for sulphur dioxide removal; the idea consists to couple the phenomenon of electrolysis upstream to the sulphuric acid plant. Otherwise, this proposition consists in modifying the hybrid cycle Westinghouse by the elimination of the sulphuric acid decomposition stage, which corresponds to 61% of the energy distribution of this cycle. The step of the decomposition is replaced by the exploitation of the quantity of sulphur dioxide emissions SO2 stemming from the process of sulphuric acid H2SO4 production. The industrial complex of Gabes in South Tunisia is selected to be the case study complex. In fact, most industries are chemical oriented, the fast growing numbers of H2SO4 factories have resulted in fairly serious air pollution, especially sulphur dioxide SO2 pollution. To confirm the efficiency of this process, a mass balance study was made on the sulphuric acid plant, which used a double contact/double absorption process; this study demonstrates that this new method can treat 8 t d−1 of sulphur dioxide, recover 12 t d−1 of sulphuric acid of title 50% and produce 6889 m3 d−1 of the hydrogen. This idea can achieve economical and environmental benefits. It is concluded that the usage of this electrochemical process can significantly reduce the SO2 air pollution in Gabes (South Tunisia) by the elimination of 46.94 t d−1 of SO2. The results obtained are ambitious for future application of the new process, which can succeed in the realisation of 3.92 million dollars of gain every day.

Development and test of a solar reactor for decomposition of sulphuric acid in thermochemical hydrogen production

Abstract Decomposition of sulphuric acid is a key step of sulphur based thermochemical cycles for hydrogen production by thermal splitting of water. The Hybrid Sulphur Cycle (HyS) consisting of two reaction steps is considered as one of the most promising cycles: firstly, sulphuric acid is decomposed by high temperature heat of 800–1200 °C forming sulphur dioxide, which in a second step is used to electrochemically split water. Compared to conventional water electrolysis only about a tenth of the theoretical voltage is required making the HyS one of the most efficient processes to produce hydrogen by concentrated solar radiation. As a result, this thermochemical cycle has the potential to significantly reduce the amount of energy required for water splitting and to efficiently generate hydrogen free of carbon dioxide emissions. The European research project HycycleS aims at a technical realisation of the HyS. One objective of the project is to develop and qualify a solar interface, meaning a device to couple concentrated solar radiation into the endothermal steps of the chemical process. Therefore, a test reactor for decomposition of sulphuric acid by concentrated solar radiation was developed and tested in the solar furnace of DLR in Cologne. Tests in concentrated solar radiation were carried out for temperatures of the honeycomb up to 950 °C decomposing sulphuric acid of 50 and 96 weight-percent. Mass and energy flow of the process were calculated in order to determine energy efficiency and chemical conversion. The influence of process parameters like temperature, flow rates and space velocity on chemical conversion and reactor efficiency was analysed in detail. If catalysts like iron oxide (Fe2O3) and mixed oxides (i.e. CuFe2O4) were used a conversion of SO3 to SO2 of more than 80% at a thermal efficiency of over 25% could be reached.

Iodine compounds speciation in HI–I2 aqueous solutions by Raman spectroscopy

The Sulphur–Iodine (S–I) thermochemical cycle for hydrogen production from water is one of the widest investigated cycles in the world. The S–I cycle is composed of three main sections which correspond to its three main reactions: the Bunsen reaction, the hydriodic acid (HI) decomposition and the sulphuric acid decomposition. The investigation, comprehension and modelling of the complex electrolytic chemistry of the HI solutions is crucial for the process optimization. In particular, the analysis of chemical speciation in the HI solutions is a key factor for the full understanding of the chemical equilibria involved at varying I2:HI ratio in the mixtures. The aim of the present study is to use Raman spectroscopy for characterizing the chemical speciation of iodine compounds existing in the mixtures that pertain to the S–I process. For this purpose, Raman spectra of solutions with known HI and I2 concentration have been recorded. It has been found that the chemistry of these solutions is highly dependent on I2:HI molar ratio. Up to 1:1 ratio, I3− and its corresponding ion pair HI3* are the dominant iodine compounds. At higher values, the formation of higher polyiodine and polyiodides compounds has been suggested.

High temperature oxygen separation for the sulphur family of thermochemical cycles - part I: Membrane selection and flux testing

This work investigates the feasibility of applying high temperature oxygen separation to the sulphuric acid decomposition process, a common step in the Sulphur Iodine and Hybrid Sulphur thermochemical cycles for massive scale hydrogen production. Process simulations indicate that the decomposition yield can be increased from 62.3% to 90.1% by using a catalytic membrane reactor. Equilibrium calculations show yttria-stabilised zirconia (YSZ), combined with platinum electrodes, to be a candidate membrane for the separation process. Bespoke experimental apparatus was designed and commissioned in order to investigate the oxygen flux through YSZ membranes in the presence of sulphur dioxide, during external voltage application. Results from an experiment at 900 °C show that oxygen permeation through YSZ membranes occurs under these conditions. X-ray diffraction and impedance spectroscopy are used to investigate the reason for the oxygen flux decrease with time.

Measurements of the solubility of sulphur dioxide in water for the sulphur family of thermochemical cycles

In recent years, the Hybrid Sulphur (HyS) and Sulphur Iodine (SI) cycles have emerged as promising routes for the massive scale thermochemical production of Hydrogen from water. Common to these two cycles is a high temperature stage involving the decomposition of sulphuric acid to sulphur dioxide, water and oxygen. The work considered here focuses on the oxygen separation stage of the process where, in order for a science based design approach to be taken, thermodynamic data are required for multicomponent phase equilibrium relationships between the decomposition products; H 2O–SO 2–O 2. A method of making flash calculations, useful in the separation equipment design, has been proposed and coded into Mathematica ®. Further, a vapour–liquid equilibrium still has been designed and built to make measurements of the multicomponent solubility of sulphur dioxide and oxygen in water. The experiments presented here concentrate on the binary SO 2–H 2O system, covering a wider range of pressures than that found in the literature. Solubility, expressed in molality, was obtained at 25 and 40 °C and pressures ranging from 0.2 to 3.6 atm. Good agreement is seen between the experimental data and the model at lower pressures, however improvements are needed at higher pressure. Preliminary data for the ternary system at 40 °C is presented, showing good agreement with the multicomponent model. Future work will focus on the three component system.

Preparation of mesostructured barium sulfate with high surface area by dispersion method and its characterization

The spherical and cubic mesoporous BaSO 4 particles with high surface area were successfully produced via one-step process through precipitation reaction in aqueous solution of Ba(OH) 2 and H 2SO 4 with ethylene glycol ( n-HOCH 2CH 2OH) as a modifying agent. The BaSO 4 nanomaterial revealed that the high surface area and the mesoporous was stable up to 400 °C. Agglomerate mesoporous barium sulfate nanomaterials were obtained by the reaction of Ba 2+ and SO 2− 4 with ethylene glycol aqueous solution. The ethylene glycol was used to control the BaSO 4 particle size and to modify the surface property of the particles produced from the precipitation. The dried and calcined mesoporous BaSO 4 nanomaterials were characterized by X-ray diffraction (XRD), BET surface area and N 2 adsorption–desorption isotherm, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared resonance (FTIR) and thermogravimetric analysis (TGA). The as-prepared mesoporous dried BaSO 4 possesses a high BET surface area of 91.56 m 2 g −1, pore volume of 0.188 cm 3 g −1 ( P / P 0 = 0.9849 ) and pore size of 8.22 nm. The SEM indicates that the morphology of BaSO 4 nanomaterial shows shell like particles up to 400 °C, after that there is drastically change in the material due to agglomeration. Synthesis of mesoporous BaSO 4 nanomaterial is of significant importance for both sulphuric acid decomposition and oxidation of methane to methanol.

Catalytic thermal decomposition of sulphuric acid in sulphur–iodine cycle for hydrogen production

Zero emission energy production systems are the main goal of engineering and research efforts. The use of hydrogen is the most suitable option, and hydrogen production by water using renewable energy power supply could be the final solution. In this study the sulphur–iodine cycle for hydrogen production by a water-splitting reaction has been investigated and new experimental results on thermal dissociation of sulphuric acid has been discussed. The decomposition of H 2 SO 4 to produce SO 2 is the reaction with the highest energy demand in the S–I cycle and it shows a large kinetic barrier. In this work, two catalysts, a Pd–Ag alloy and ferric oxide ( Fe 2 O 3 ) , have been tested to evaluate their effect on dissociation efficiency at various temperatures. For both catalysts a large onset temperature decrease for the activation of this reaction has been achieved. In the case of the intermetallic alloy Ag–Pd it may be suggested that the metal oxide PdO could be the active catalytic species.

The present state of sulphuric acid thermal decomposition

Interconnected alternative variants for thermal decomposition of sulphuric acid with the formation of sulphur dioxide by a combined sulphuric acid thermoelectrochemical process are proposed. These alternative variants make it possible to obtain hydrogen and sulphuric acid or liquid sulphur dioxide using the same equipment both with the heat from a high temperature source (HTGR) and without an external heat source. The process equipment to be used, the results of experimental tests and a preliminary economic feasibility study are given.

Suitability of nitric—sulphuric acid decomposition for the determination of tungsten and molybdenum in geochemical exploration

A mixture of nitric and sulphuric acids is used for the decomposition of geochemical samples for the estimation of tungsten. In the resulting sample solution tungsten is determined colorimetrically by the dithiol method. The decomposition procedure suggested works well for scheelite mineral. However wolframite is only partially decomposed. The same sample solution is used for estimation of molybdenum by the thiocyanate method. The method is suitable for batch analysis and results in a high throughput.

Exergetic and engineering analyses of sulphuric acid decomposition process

AbstractThe purpose of this study was to evaluate the exergetic efficiency of the sulphuric acid decomposition process, which occurs in hydrogen producing thermochemical cycles and chemical energy storage systems. It is a process in which sulphuric acid is decomposed to a gaseous mixture consisting of water, sulphur dioxide and oxygen, using high temperature thermal energy, oxygen as a vector and mostly adiabatic equipment. Parts of the basic process with excessive exergy losses have been identified and a modified flow sheet has been developed and analyzed from thermodynamic and engineering points of view. Thermodynamic analysis of the modified flow sheet indicates that the overall exergetic efficiency of the decomposition process is 79.86%, which represents an improvement of 14.17% over the basic process. Engineering analysis of a plant producing 106 mol of SO2 per hour shows that the typical levelized cost of chemical exergy production was $ 2.25/GJ exergy from the basic process and $ 1.79/GJ exergy from the modified process.

A study of fluospar properties affecting the hydrogen fluoride formation mechanism

Sulphuric acid decomposition of a fluorite flotation concentrate can be intensified by AC excitation, by additives diminishing the sulphuric acid viscosity and surface tension, as well as by air calcination, thus activating the fluorite flotation concentrate. Research carried out has determined that calcination in ambient air containing 23.1–50.0% of oxygen proceeds in several series-parallel stages. At the first stage, at 240–530 °C dehydration, the organic flotation reagents are removed and a partial sulphides decomposition take place. At the second stage, at 560–650 °C the sulphides get reoxidized and the carbonates are thermally decomposed. Studies on the sulphuric acid decomposition of calcined fluorite flotation concentrate have shown that the decomposition process proceeds in two stages at 45–192 °C and at 158–280 °C. It is noteworthy that in the case of uncalcined fluorite decomposed with sulphuric acid, the mass of hydrogen fluoride generated in both the first and second stages is about equal, and in the case of calcinated fluorite the hydrogen fluoride generated at the first stage amounts to 60–75%. The kinetic data have shown that the preliminary calcination of fluorite facilitated the transition from the diffusion area to the kinetic one: the observed reaction order at the first stage increases from 0.58 to 0.93–1.03, and the apparent activation energy from 71.5 to 91.8–124.7 kJ/mol.

Selection and evaluation of materials for the construction of a pre-pilot plant for thermal decomposition of sulphuric acid

The selection of containment materials for the decomposition of sulphuric acid, by direct heating with air (CRISTINA process) was made by using information from the literature or by experimental investigation. Commercial materials having a reasonable corrosion resistance were identified for each process step and an allowance for the effect of corrosion was made in the design of the plant built at the JRC-Ispra (CHRIS plant). After dismantling of the CHRIS plant, the materials used were examined visually and by the use of metallographic and X-ray diffraction techniques. The results of this exercise are critically reviewed with the aim of facilitating the choice of materials for a pilot plant.