Sulfuric Acid Decomposition Research Articles

Sulfuric acid decomposition on Pt/SiC-coated-alumina catalysts for SI cycle hydrogen production

Sulfuric acid decomposition was conducted at atmospheric pressure and a GHSV of 72,000mL/gcath in the temperature ranges from 650 to 850°C. The Pt–Al (1wt% Pt/Al2O3) and and Pt–SiC–Al (1wt% Pt/SiC-coated-Al2O3) catalysts were prepared by an impregnation method. The Pt–Al catalyst rapidly deactivated at 650 and 700°C, but was stable at 750 and 850°C. The aluminum sulfate was observed on the spent Pt–Al catalyst by an FT-IR, an X-ray spectroscopy and a TGA/DSC analyzer, which was suggested to be a cause of the deactivation at lower reaction temperature. The alumina support was coated with SiC by a CVD method with methyltrichlorosilane (MTS) to get a non-corrosive support (SiC–Al) with high surface areas. The thermal analysis of the spent Pt–SiC–Al showed that the aluminum sulfate formation was suppressed during the sulfuric acid decomposition. The Pt–SiC–Al catalyst was not only active higher than the Pt–Al catalyst, but was also stable at all the tested reaction temperature.

Stability and kinetics of powder-type and pellet-type iron (III) oxide catalysts for sulfuric acid decomposition in practical Iodine–Sulfur cycle

The efficiency of sulfuric trioxide decomposition strongly affects to the overall efficiency of the Iodine–Sulfur (IS) cycle, because the decomposition process is highly endothermic and most energy-consuming process. Therefore, we carefully selected iron (III) oxide (Fe2O3) for high temperature decomposition on the assumption of commercialization considering its proper activity, stability and price. This study starts with collecting the very basic empirical data as well as considering practical implications for actual design. Experimental results of stability test with Fe2O3 powder showed that over 65% of SO3 conversion was secured during 110 h operation. We experimentally investigated the effects related to the weight hourly space velocity (WHSV) and gas inlet composition to SO3 conversion with pellet-type catalyst in the temperature range of 730–910 °C. Reaction order of SO3 decomposition was empirically verified as first-order reaction. The activation energy was also obtained as 141.4 kJ/mol under four different WHSV values.

A study of the effect of nepheline acid processing conditions on structural-surface properties of silica products formed

A study of the physicochemical properties of silica products formed in acid processing of the nepheline concentrate is reported. It was found that amorphous silica produced in precipitation of silicon dioxide from solutions obtained in sulfuric acid decomposition of nepheline occupies an intermediate position between white carbon and silica gel, whereas silica produced from gelatinized silica-containing solutions close in properties to silica gel. The morphology of silicon dioxide samples formed by various methods was studied and a comparative analysis of their structural-surface properties was made.

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 of a Compact Ceramic High-Temperature Heat Exchanger and Chemical Decomposer for Hydrogen Production

This article describes a compact silicon carbide ceramic, high-temperature heat exchanger for hydrogen production in the sulfur iodine thermochemical cycle, and in particular, to be used as the sulfuric acid decomposer. In this cycle, hot helium from a nuclear reactor is used to heat the SI (sulfuric acid) feed components (H2O, H2SO4, SO3) to obtain appropriate conditions for the SI decomposition reaction. The inner walls of the SI decomposer channels are coated with platinum to catalytically decompose sulfur trioxide into sulfur dioxide and oxygen. Hydrodynamic, thermal, and the sulfur trioxide decomposition reaction were coupled for numerical modeling. Thermal results of this analysis are exported to perform a probabilistic mechanical failure analysis. This article presents the approach used in modeling the chemical decomposition of sulfur trioxide. Stress analysis of the design is also presented. The second part of the article shows the results of parametric study of the baseline design (linear channels). Several alternate designs of the chemical decomposer channels are also explored. The current study summarizes the results of the parametric calculations whose objective is to maximize the sulfur trioxide decomposition by using various channel geometries within the decomposer. Based on these results, a discussion of the possibilities for improving the productivity of the design is also given.

Transient simulation of an endothermic chemical process facility coupled to a high temperature reactor: Model development and validation

Abstract A high temperature reactor (HTR) is a candidate to drive high temperature water-splitting using process heat. While both high temperature nuclear reactors and hydrogen generation plants have high individual degrees of development, study of the coupled plant is lacking. Particularly absent are considerations of the transient behavior of the coupled plant, as well as studies of the safety of the overall plant. The aim of this document is to contribute knowledge to the effort of nuclear hydrogen generation. In particular, this study regards identification of safety issues in the coupled plant and the transient modeling of some leading candidates for implementation in the Nuclear Hydrogen Initiative (NHI). The Sulfur Iodine (SI) and Hybrid Sulfur (HyS) cycles are considered as candidate hydrogen generation schemes. Three thermodynamically derived chemical reaction chamber models are coupled to a well-known reference design of a high temperature nuclear reactor. These chemical reaction chamber models have several dimensions of validation, including detailed steady state flowsheets, integrated loop test data, and bench scale chemical kinetics. The models and coupling scheme are presented here, as well as a transient test case initiated within the chemical plant. The 50% feed flow failure within the chemical plant results in a slow loss-of-heat sink (LOHS) accident in the nuclear reactor. Due to the temperature feedback within the reactor core the nuclear reactor partially shuts down over 1500 s. Two distinct regions are identified within the coupled plant response: (1) immediate LOHS due to the loss of the sulfuric acid decomposition section and (2) continuing slow LOHS due to the chemical species cascade throughout the plant.

Influence of HTR Core Inlet and Outlet Temperatures on Hydrogen Generation Efficiency Using the Sulfur-Iodine Water-Splitting Cycle

The performance of hydrogen production via thermochemical cycles is typically evaluated using thermal efficiency. In this study, the sulfur-iodine cycle with heat supplied by a high-temperature reactor (HTR) is analyzed. Two cases are examined: one flow sheet designed by General Atomics in the United States, the other by Commissariat à l’énergie atomique et aux énergies alternatives in France. In each case, HTR helium inlet and outlet temperatures are specified. Differences in these temperature specifications lead to process variations between the flow sheets and in how the hydrogen processes interface with the nuclear heat source. Two principal conclusions result from the analysis. First, the thermal efficiency tends to plateau above a certain outlet helium temperature. This is a characteristic effect of the method of Öztürk et al. for sulfuric acid decomposition. Second, it is clear that it is impractical to discuss efficiencies for the hydrogen process that are independent of defined operating parameters of the HTR.

Hydrogen production via sulfur-based thermochemical cycles: Part 3: Durability and post-characterization of silicon carbide honeycomb substrates coated with metal oxide-based candidate catalysts for the sulfuric acid decomposition step

This work is a follow-up of previous efforts reported on the synthesis of various single and mixed oxide materials and their evaluation as catalysts for the sulfuric acid dissociation reaction for the production of SO2 and O2. The current work concerns the comparative assessment of Fe2O3, CuO, Cu–Fe, Fe–Cr, Cu–Al and Cu–Fe–Al mixed oxides coated as catalysts on silicon carbide monolithic honeycomb structures, with respect to sulfuric acid decomposition reaction conditions for 100h at 850°C and ambient pressure, as well as their ex-situ characterization after such operation. The exposure conditions are representative to a potential future real application. The exposure time, although of relatively short-term, is adequate to extract safe conclusions on the stability and therefore to a large extent also on the suitability of the candidate oxide-based catalysts. All catalytic systems tested exhibited high SO3 conversions reaching or exceeding 70%, for space velocities in the range of 5–35h−1. For some of the samples, the relatively high initial activity decreased by about 5–10 percentage points in the course of the 100h testing, reaching stable mean values. It was concluded that Fe2O3, CuO and Fe–Cr mixed oxide retained their chemical and structural stability after exposure to reaction conditions, while the other three mixed oxides studied suffered from significant phase decomposition phenomena. Based on the fact that the initial catalytic activity of the Fe–Cr mixed oxide, as identified in a previous comparative study among several materials, was found higher than the ones of Fe2O3 and CuO and relatively close to the one of the highly active but costly Pt/Al2O3 catalyst, the particular mixed oxide is considered a promising catalyst for the SO3 dissociation reaction.

Preparation of TiO2 from ilmenite using sulfuric acid decomposition of the titania residue combined with separation of Fe3+ with EDTA during hydrolysis

A new process of “mechanical activation–hydrochloric acid leaching–concentrated sulfuric acid decomposition–water leaching–separation of Fe3+ with EDTA during hydrolysis” was proposed to prepare high-purity TiO2 from Panzhihua ilmenite. The hydrolyzed titania residue prepared from mechanically activated Panzhihua ilmenite leached by hydrochloric acid was decomposed by concentrated sulfuric acid and subsequently dissolved in water yielding titanium sulfate solution. In order to improve the purity of the precursor during the hydrolysis of TiO2+, EDTA was investigated as an additive to restrain the hydrolysis of Fe3+. The effects of sulfuric acid concentration, acid-to-titania residue mass ratio in the process of acid digestion and the significant effects of water leaching time, leaching temperature and liquid-to-solid mass ratios on the recovery of Ti from the residue were studied in this paper. The recovery of Ti was above 98% under optimal conditions. Well-crystallized anatase TiO2 and rutile TiO2 could be obtained through calcining at different temperatures and no impurity can be detected by EDS in titanium dioxide. The results demonstrated that the process is inexpensive, environment friendly and promising in preparing high-purity TiO2 from ilmenite with a high content of gangues like Panzhihua ilmenite.

Macroporous Supported Cu–V Oxide as a Promising Substitute of the Pt Catalyst for Sulfuric Acid Decomposition in Solar Thermochemical Hydrogen Production

The macroporous supported Cu–V oxide prepared by a novel dissolution–reprecipitation process was found to be the first example of a promising substitute of Pt catalysts for sulfuric acid decomposit...

Methodology for Thermal Analysis of Bayonet Reactor

Whether green house gas emissions are mainly responsible for global warming or not, the truth is that they have to be reduced in order to improve air quality and to be able to face many problems which span from environmental issues to economical and political ones. Nuclear hydrogen production (NHP), defined as those processes that obtain energy from nuclear reactors to drive the chemical plants in which hydrogen is produced, have been studied since the early 70's as an effective way to provide clean fuels to the automotive and electricity industry. In the past, this concept was really far from industrial application; however, recent advances in nuclear and chemical technology are bringing these plants closer to reality. Two of the most promising NHP technologies have an important step in common: sulfuric acid decomposition, this part of the process is the most energy demanding and the one which operates at the highest temperature; therefore if some improvements in energy usage can be done in this section they will have a strong and positive impact on the whole process efficiency. In the present study, a very simple but realistic methodology is presented to simulate and analyze this important section, validation is achieved through direct comparison with experimental data and a thermal optimization is performed. A 4% reduction in energy consumption is achieved by varying the reactor's outlet temperature.

A Hybrid-Sulfur Flowsheet Using an Ionic Liquid Absorbent to Separate Sulfur Dioxide from Oxygen

A hybrid sulfur (HyS) flowsheet using an ionic liquid absorbent to separate SO2 from oxygen has been developed. The key chemical reactors in the HyS flowsheet are a sulfuric acid distillation column, a sulfuric acid vaporization and decomposition reactor, a knock-out drum to separate SO2/O2-mixed gas from the SO3/H2O-recombined and condensed aqueous phase, a separation part of SO2, and a SO2-depolarized electrolysis cell. The separation part of SO2 consists of SO2 absorption and desorption columns adopting a temperature swing methodology. The hydrogen production thermal efficiency of 39% can be expected by this HyS process.

Formic Acid Catalyzed Gas‐Phase Reaction of H2O with SO3 and the Reverse Reaction: A Theoretical Study

The formic acid catalyzed gas-phase reaction between H(2)O and SO(3) and its reverse reaction are respectively investigated by means of quantum chemical calculations at the CCSD(T)//B3LYP/cc-pv(T+d)z and CCSD(T)//MP2/aug-cc-pv(T+d)z levels of theory. Remarkably, the activation energy relative to the reactants for the reaction of H(2)O with SO(3) is lowered through formic acid catalysis from 15.97 kcal mol(-1) to -15.12 and -14.83 kcal mol(-1) for the formed H(2)O⋅⋅⋅SO(3) complex plus HCOOH and the formed H(2)O⋅⋅⋅HCOOH complex plus SO(3), respectively, at the CCSD(T)//MP2/aug-cc-pv(T+d)z level. For the reverse reaction, the energy barrier for decomposition of sulfuric acid is reduced to -3.07 kcal mol(-1) from 35.82 kcal mol(-1) with the aid of formic acid. The results show that formic acid plays a strong catalytic role in facilitating the formation and decomposition of sulfuric acid. The rate constant of the SO(3)+H(2)O reaction with formic acid is 10(5) times greater than that of the corresponding reaction with water dimer. The calculated rate constant for the HCOOH+H(2)SO(4) reaction is about 10(-13) cm(3) molecule(-1) s(-1) in the temperature range 200-280 K. The results of the present investigation show that formic acid plays a crucial role in the cycle between SO(3) and H(2)SO(4) in atmospheric chemistry.

ChemInform Abstract: Efficient Catalytic Decomposition of Sulfuric Acid with Copper Vanadates as an Oxygen‐Generating Reaction for Solar Thermochemical Water Splitting Cycles.

AbstractCu2V2O7 is found to be a highly efficient catalyst for decomposition of sulfuric acid to evolve O2 at moderate temperatures around 650 °C, where most of the conventional oxide catalysts are much less active and less stable.

Synthesis of graphitic carbon nitride by directly heating sulfuric acid treated melamine for enhanced photocatalytic H 2 production from water under visible light

Herein we report the synthesis of graphitic carbon nitride (g-C 3N 4) by directly heating sulfuric acid treated melamine precursor. Thermoanalytical methods (TG-DSC) in combination with XRD, XPS and elemental analysis were used to characterize the condensation steps of the precursor. The TG-DSC curves clearly show significant difference in thermal behavior between the treated and untreated melamine. The sublimation of melamine during condensation was significantly suppressed by treating melamine with sulfuric acid. The decomposition of melamine sulfuric acid and the condensation of melamine occur simultaneously. The N/C ratio of the prepared carbon nitride (1.53) is slight higher than that of the ideal crystal g-C 3N 4 (1.33), indicating the incomplete condensation of amino groups in the material. The XPS and elemental analysis show that there is no sulfur residue in the final product. The sample synthesized from sulfuric acid treated melamine shows relatively higher BET surface area. The photocatalytic performance of the as prepared carbon nitride was evaluated under visible light irradiation ( λ > 420 nm). The photocatalytic H 2 production rate on sample synthesized from sulfuric acid treated melamine is 2 times higher than that on sample synthesized from untreated melamine.

Solar hydrogen production by the Hybrid Sulfur process

A conceptual design and economic analysis are presented for a hydrogen production plant based on the use of thermochemical water splitting combined with a solar central receiver. The reference design consists of a Hybrid Sulfur thermochemical process coupled to a solar plant, based on the particle receiver concept, for a yearly average hydrogen production rate of 100 tons per day. The Hybrid Sulfur plant has been designed on the basis of results obtained from a new flowsheet ASPEN Plus ® simulation, carrying out specific evaluations for the Sulfur dioxide Depolarized Electrolyzer, being developed and constructed at Savannah River National Laboratory, and for the sulfuric acid decomposition bayonet-based reactor, investigated at Sandia National Laboratory. Solar hydrogen production costs have been estimated considering two different scenarios in the medium to long term period, assuming the financing and economic guidelines from DOE’s H2A model and performing ad hoc detailed evaluations for unconventional equipment. A minimum hydrogen production specific cost of 3.19 $/kg (2005 US $) has been assessed for the long term period. The costs, so obtained, are strongly affected by some quantities, parameters and assumptions, influence of which has also been investigated and discussed.

Kinetic studies of sulfuric acid decomposition over Al–Fe2O3 catalyst in the sulfur-iodine cycle for hydrogen production

The decomposition of H2SO4 to produce SO2 is the reaction with the highest energy demand in the sulfur-iodine cycle and it shows a large kinetic barrier. In the present study, alumina supported iron (III) oxide has been chosen for a detailed kinetic study. Experiments were carried out in the temperature range of 1023 K–1173 K using space hour velocities in the range of 0.146–0.731 kmol/kg-h in a quartz tube double stage continuous flow fixed bed reactor with 98% sulfuric acid feed over alumina supported Fe2O3 catalyst, nitrogen as inert carrier gas. From the homogeneous kinetic analysis, the apparent activation energy (EA) was found to be 138.6 kJ/mol. This high activation energy indicates that the experiments were conducted in a kinetic controlled regime. The catalyst was well characterized by XRD, BET, TPR/TPO, SEM and FT-IR before and after reaction.

Catalytic decomposition of sulfuric acid on composite oxides and Pt/SiC

Thermochemical iodine–sulfur (IS) cycle is one of the most promising massive hydrogen production methods with its high efficient and CO 2 free credits. The decomposition reaction of sulfuric acid, one of the three reactions of which IS cycle is composed, is kinetically very slow and needs to proceed in the presence of catalyst. In this work, copper chromite (CuCr 2O 4) and copper ferrite (CuFe 2O 4) were prepared and employed as the catalysts for sulfuric acid decomposition, their activities were tested at various space velocities and temperatures, and their lifetimes were tested. To overcome the shortcoming of instability in long-time operation of Pt/Al 2O 3, Pt was loaded on SiC and its activity and lifetime were evaluated and compared with those of CuCr 2O 4 and CuFe 2O 4. Results showed that CuCr 2O 4 has the highest catalytic activity at higher temperature, while Pt/SiC presented the best stability. In addition, the reasons for the deactivation of these catalysts were explored. It was proposed that the deactivation was attributed to formation of sulfate, agglomeration and specific area decreasing.

Numerical analysis of operation conditions and design aspects of a sulfur trioxide decomposer for solar energy conversion

A basic concept for a receiver-reactor for solar sulfuric acid decomposition as the key step of the Hybrid Sulfur Cycle for hydrogen production has been developed and realized. A prototype reactor has been built and is specialized for the second part of the reaction, the decomposition of sulfur trioxide. For a detailed understanding of the operational behaviour of the developed reactor type a mathematical model was developed. The reactor model was validated using experimental data from the test operation with a prototype reactor. The present work deals with the optimization of process and design parameters and the evaluation of the achievable performance of the reactor type. Furthermore the reactor model is used for numerical simulations to predict specific operational points of the prototype reactor and the performance of a large-scale reactor on a solar tower. Influences of operational parameters like absorber temperature, feed mass flow, residence time, and initial concentration of the acid are analyzed. In many cases those analyses reveal the existence of an optimum of reactor efficiency. When varying the absorber temperature an optimum of reactor efficiency emerges due to two compensating effects: chemical conversion increases with temperature, whereas re-radiation losses increase disproportionately at the same time. This matches the experimental findings very well. A large scale tower-receiver-reactor consisting of several individual modules is modelled and simulated. The main differences to the prototype system are the reduced gradients of solar flux distribution on the receiver front face and the reduced thermal conduction losses due to the presence of several neighbor modules at a comparable temperature level. This leads to higher chemical conversions and better efficiencies. Reactor efficiencies up to 75 % are predicted.

Hydrogen production via sulfur-based thermochemical cycles: Part 2: Performance evaluation of Fe 2O 3-based catalysts for the sulfuric acid decomposition step

The sulfuric acid dissociation reaction, via which the production of SO 2 and O 2 is achieved, is the most energy intensive step of the so-called sulfur-based thermochemical cycles for the production of hydrogen. Efforts are focused on the feasibility and effectiveness of performing this reaction with the aid of a high-temperature energy/heat source like the sun. Such coupling can be achieved either directly in a solar reactor by concentrated solar radiation, or indirectly by means of a heat-exchanger/decomposer reactor using a suitable heat transfer fluid. Since a very limited amount of work regarding the potential formulations and sizing of such suitable reactors has been performed so far, the present work addresses further steps necessary for the efficient design, manufacture and operation of such reactors for sulfuric acid decomposition. In this respect, parametric studies on the SO 3 decomposition with iron(III) oxide-based catalysts were performed investigating the effect of temperature, pressure and space velocity on SO 3 conversion. Based on these results, an empirical kinetic law suitable for the reactor design was developed. In parallel, siliconised silicon carbide honeycombs coated with iron(III) oxide were prepared and tested in structured laboratory-scale reactors to evaluate their durability (i.e. activity vs. time) during SO 3 decomposition, with the result of satisfactory and stable performance for up to 100 h of operation. The results in combination with characterization results of “aged” materials can provide valuable input for the design of prototype reactors for sulfuric acid decomposition.