Verfahrenstechnische und wirtschaftliche Aspekte der Verarbeitung verdünnter SO2-Gase zu Schwefelsäure

Chemical engineering and economic aspects of converting dilute SO₂ gases into sulphuric acid. In the contact process for production of concentrated sulphuric acid the lowest limit for the autothermal processing of dilute SO₂ gases lies at around 2 vol.-% SO₂ provided that a pre-drying concentrating system is in use. Yet more dilute SO₂ gases can be processed by Ciba Geigy's nitrogen oxide/sulphuric acid process – a modern version of the well-known lead chamber process – which is already producing 70 to 75% H₂SO₄ from molybdenum disulfide roasting waste gases of ca. 1 vol.-% SO₂ on an industrial scale. The paper considers not only the specific boundary conditions, and chemical engineering characteristics of the two fundamentally different processes but considers above all the economics of processing low-concentration SO₂ gases for sulphuric acid.     

Application of diffusion dialysis in hydrometallurgical separation of nickel from spent Raney Ni catalyst

ABSTRACT

The hydrometallurgical separation of nickel from spent Raney Ni catalyst is based on the dissolution of separated nickel slurry in hot diluted sulphuric acid (H₂SO₄) with the addition of an appropriate oxidation agent. Consecutive diffusion dialysis, which was performed in a two-compartment countercurrent dialyzer with an anion-exchange membrane Neosepta-AFN at steady state, enables the removal of excess of H₂SO₄ from a solution of aluminium and nickel sulphate in H₂SO₄ and simple recycling of the isolated H₂SO₄. Next, the obtained dialysate was alkalized using excess of NaOH solution. Using this procedure, the Ni(OH)₂ contaminated with only 8.9 wt.% Al was obtained.     

Macrokinetics of toluene and benzene nitration under laminar conditions

Mononitration of toluene and benzene has been carried out in a laminar jet using aqueous mixtures of nitric and sulphuric acids. With acid mixtures containing about 30 mole % H₂SO₄, the rate data obtained are in good agreement with values predicted using a model, assuming fast reaction in a zone in the aqueous phase adjacent to the interface, in conjunction with diffusivities measured under laminar conditions. At low H₂SO₄, concentrations, the rate data fit a simple kinetic model. It is shown that the model based on mass transfer with simultaneous chemical reaction can explain previously reported results for the competitive nitration of toluene and benzene in the heterogeneous liquid phase regime.     

Reaction of iron and aluminium phosphate ores with sulphuric acid and various salts

A study has been made of the reaction of ore containing high Fe and Al phosphates (crandallite (CaAl₃(PO₄)₂OH₅·H₂O)), millisite (Na, K)CaAl₆(PO₄)₄(OH)₉·3H₂O) and minor minerals) with sulphuric acid. The products are deliquecent, poorly crystalline solids which contain polymeric aluminium phosphate. The deliquecence was greatly reduced by adding enough ammonium, potassium or sodium sulphate to form compounds of the type M(Al, -Fe)(SO₄)₂. Studies of free acid and other properties showed that two products which were still hydroscopic contained considerable amounts of inorganic polymeric phosphate. The content of phosphorus in the optimum products was too low (5.7%) for an economic fertilizer. This phosphorus level can be raised by substituting phosphoric acid for sulphuric acid or, by using ammonium sulphate followed by extraction with water. The results indicate that it may be possible to develop an economic granular fertilizer from this type of ore when competition for high grade phosphate has disappeared. However, the economic extraction of phosphoric acid from the material seem unlikely.     

Acid properties of solid acid from petroleum coke by chemical activation and sulfonation

A novel solid acid was prepared from petroleum coke by KOH chemical activation and concentrated H₂SO₄ sulfonation. The solid acid was characterized by XRD, FT-IR and solid-state NMR. The characterization results show that the chemical activation and sulfonation lead to three functional Brønsted acid sites: –OH, –COOH and –SO₃H on the solid acid. The probe molecules experimental reveal that the acid strength of the solid acid is stronger than that of SO₄²⁻ /ZrO₂, but slightly weaker than that of 100% H₂SO₄. The catalytic performance was evaluated by the esterification of oleic acid with methanol. The results indicate that this solid acid catalyst is very active, corresponding to high conversion (72%) of esterification reaction. In addition, the spent solid acid can be recovered by simple regeneration process.     

Application of bipolar electrodialysis to the recovery of acids and bases from water solutions

The studies of acid purification and base purification via bipolar electrodialysis are presented. The process of acid recovery involved spent solutions of acid (HCl or H₂SO₄) and iron salt obtained in the course of conventional electrodialysis. Bipolar electrodialysis yielded an acid solution concentrated 51-fold (in the case of hydrochloric acid) and 63-fold (in the case of sulphuric acid) as compared to the feeding solution for conventional electrodialysis. The solution of the recovered acid was only slightly contaminated with iron salt (0.12 and 0.13%). The process of base purification yielded an NaOH solution concentrated nine-fold as compared to the feeding solution for the bipolar electrodialysis process. The contamination of the recovered base varied from 1.75 to 2.50%.     

Study of Pb(II) in various H2O-H2SO4 mixtures by differential pulse polarography: solubility of lead sulphate,diffusion coefficient of Pb(II) and half-wave potential of Pb(Hg)/Pb(II)

A study of some properties of Pb(II) in solutions of sulphuric acid was carried out by means of differential pulse polarography. The range of concentrations of acid extended from 0.6 to 70 weight % of H₂SO₄ (0.06-11.5 M). Determination of the solubility of lead sulphate was found to be in good agreement with NBS's results in the range of H₂SO₄ concentrations they studied. With increasing concentration in H₂SO₄, the diffusion coefficient was found to decrease more than expected from the Stokes-Einstein equation, while the standard potential of Pb/Pb(II) related to she was found to increase. This led to a more important self-discharge of the negative electrode of the lead-acid battery.     

Coproduction of sulphuric acid and hydrogen by sulphur-assisted water electrolysis process

The addition of sulphur powder to the anode compartment of the sulphuric acid-water electrolysis cell resulted in the suppression of oxygen evolution rate; at a cell voltage of 2 V, there was an acceleration of the hydrogen production rate, and the anode reaction led to the production of sulphate ion (SO ₄ ^2? ) by the oxidation of the sulphur powder. The net equation for this sulphur-assisted water electrolysis system may be written as S + 4H₂O → H₂SO₄ + 3H₂ whose stoichiometry was proved experimentally using phosphoric acid as the electrolyte. The whole process can be rationalized if the anodic oxidation of sulphur occurs at a lower potential than oxygen evolution and hence the energy consumption is lower. Thus the addition of sulphur to the anolyte helps to improve the energy efficiency of the acidic water electrolysis system and generates, simultaneously, sulphuric acid and hydrogen.     

Utilization of spent petrochemical sulfuric acid in the production of wet‐process phosphoric acid

The possibility of the application of spent sulfuric acid from the petrochemical industry in wet‐process phosphoric acid technology was investigated. The effect of organic impurities in sulfuric acid from benzol acidic refining on the solubility of calcium sulfate hydrates is discussed. Solubility isotherms and regression equations for CaSO₄–H₃PO₄–H₂SO₄–H₂O (pure and containing impurities) systems are presented. Phase transition temperatures between dihydrate and hemihydrate calcium sulfate were determined. The difference between pure and polluted sulfuric acid systems observed is negligible over the range of typical wet‐process phosphoric acid technology parameters. It is concluded that the application of spent sulfuric acid from benzol acidic refining does not have a negative influence on the crystallization process of dihydrate calcium sulfate and therefore can be applied in wet‐process phosphoric acid technology. Copyright © 2005 Society of Chemical Industry     

Proprietes electrochimiques du titanium dans l'acide sulfurique

The electrochemical characteristics of titanium in sulphuric acid have been studied through potentiostatic and potentiodynamic methods. The range of active dissolution of titanium and the range of formation of passive films for different concentrations of H₂SO₄ have been defined by j-E curves. It has been shown that active dissolution of titanium is a complex process of charge transfer and is not controlled by diffusion, which is especially emphasized at higher concentrations of H₂SO₄. But using multiple cyclisation, the potentiodynamic measurements for various outermost anodizing potentials suggest that the passive film can be dissolved chemically in H₂SO₄. The height of the activation peak depends on the concentrations of H₂SO₄ as well as the speed of potential change.Potentiostatic measurements have confirmed that in higher concentrations of H₂SO₄ because of chemical and electrochemical dissolution, total reduction of previously made passive film is possible.     

Stoichiometry of sulphuric acid sorption by nylon 6

Sorption of sulphuric acid by Nylon 6 has been investigated. The results have been interpreted by considering the two-step dissociation of sulphuric acid in aqueous solution. Sorption occurs predominantly in the 2H⁺ + SO^2?₄ mode, but the contribution of the H⁺ + HSO^?₄ mode becomes considerable at higher concentrations. Standard affinities for both modes have been estimated.     

Effect of H2SO4 concentration in washing solution on regeneration of commercial selective catalytic reduction catalyst

Commercial SCR catalysts used in a coal-fired power plant were regenerated by H₂SO₄ solution. The characterization study of the catalysts was carried out by using various analytical techniques. Major deactivating elements for the SCR catalyst were determined and the optimal condition for regeneration of the catalyst was investigated. The catalyst regenerated with 0.5 wt% H₂SO₄ solution showed a high catalytic activity due to an increase in the polymeric vanadates and acid sites by surface sulfates. A higher H₂SO₄ concentration than 2.5 wt% in the washing solution leads to a loss of active components out of the catalyst by dissolution and a dramatic decrease in the surface area.     

Decarbonylation Kinetics of Formic Acid in Aqueous Sulphuric Acid Solutions

Decarbonylation of formic acid in 46.6–80.2% (6.5–14.1 m) sulphuric acid was studied by driving CO out of the reaction medium by an air current followed by its photometrical determination with Ag-Na-sulphamoyl-benzoate. The logarithm of the reaction rate constant increases straight with the acidity of the medium in the 6.5–12.6 M H₂SO₄ range. The data obtained argue in favour of a possible implication of a sulphuric acid molecule respectively hydrogensulphate ion in a rate controlling step.     

Kinetics of dissolution of copper(II) sulphide in aqueous sulphuric acid solutions

The rate of dissolution of synthetic cupric sulphide (CuS) which is the analogue of the naturally occurring sulphide mineral covellite, in sulphuric acid solutions of concentration range 5 × 10^?3 to 3 mole/l over the temperature range 20–65°c at atmospheric pressure was studied. Thermodynamic considerations suggested that the primary reaction taking place during the leaching is: CuS+1/2O₂ + H₂SO₄ → CuSO₄ + S+H₂O. It is proposed that up to an initial sulphuric acid concentration of 1 mole/l, the reaction rate is controlled by the diffusion of H⁺ ions through the sulphur film to the CuS/S interface. For higher sulphuric acid concentrations the oxygen dissolved in the acid decreases and the rate-determining step is believed to be diffusion of dissolved oxygen through the sulphur film to the CuS/S interface. A parabolic model is suggested for the dissolution reaction, and this model is supported by the experimental data. The activation energy for the dissolution reaction was found to be 8000±2000 cal/mole and this was independent of the H⁺ concentration and hence the nature of the diffusing species.     

Acid dissolution of manganese nodules after electric discharge

Valuable metals in manganese nodules can be rendered highly soluble in sulphuric acid by forming an electric cell with manganese nodules as a cathode active material and by discharging the cell, eliminating the need for treatment under severe conditions such as elevated temperatures and/or high pressures which is often the method for conventionally treating manganese nodules. A partial electric discharge has yielded higher metal extractions, eg nearly 95% of the Ni, Co and Cu metals contained, rather than a complete drainage of the electric current from the deep-sea nodules. Even in the latter case, however, the discharged nodules have shown a much better extractability of the metals by subsequent H₂SO₄ treatment, in comparison with the direct H₂SO₄ leaching.     

Synthesis and electrical properties of the (PVA)0.7(KI)0.3·xH2SO4 (0 ≤ x ≤ 5) polymer electrolytes and their performance in a primary Zn/MnO2 battery

Solid acid polymer electrolytes (SAPE) were synthesised using polyvinyl alcohol, potassium iodide and sulphuric acid in different molar ratios by solution cast technique. The temperature dependent nature of electrical conductivity and the impedance of the polymer electrolytes were determined along with the associated activation energy. The electrical conductivity at room temperature was found to be strongly depended on the amorphous nature of the polymers and H₂SO₄ concentration. The ac (100 Hz to 10 MHz) and dc conductivities of the polymer electrolytes with different H₂SO₄ concentrations were analyzed. A maximum dc conductivity of 1.05 × 10⁻³ S cm⁻¹ has been achieved at ambient temperature for electrolytes containing 5 M H₂SO₄. The frequency and temperature dependent dielectric and electrical modulus properties of the SAPE were studied. The charge transport in the present polymer electrolyte was obtained using Wagner's polarization technique, which demonstrated the charge transport to be mainly due to ions. Using these solid acid polymer electrolytes novel Zn/SAPE/MnO₂ solid state batteries were fabricated and their discharge capacity was calculated. An open circuit voltage of 1.758 V was obtained for 5 M H₂SO₄ based Zn/SAPE/MnO₂ battery.     

Electrolytes for methanol-air fuel cells. 11. The electro-oxidation of methanol in trifluoromethane-sulphonic acid monohydrate and aqueous solutions of trifluoromethane-sulphonic acid

Trifluoromethanesulphonic acid monohydrate CF₃SO₃H.H₂O and its aqueous solutions have been evaluated as an electrolyte for methanol electro-oxidation. The performances of conventional noble metal catalysts in the pure monohydrate are very poor compared with those in 3 M sulphuric acid. This is contrary to previously published literature data, and possible reasons for the discrepancy are given. In aqueous solutions of CF₃SO₃H at concentrations between 10 and 50%wt. considerably improved performance is obtained and at 60° C the activities of the catalysts are in most cases slightly higher than in 3 M H₂SO₄. In addition the poisoning effect of acid radicals is considerably less in CF₃SO₃H than in H₂SO₄ solutions. Above 60° C, however, the aqueous CF₃SO₃ anion decomposes to produce sulphur, which poisons the noble metal catalysts.Carbon-13 NMR studies of the CF₃SO₃H/H₂O/CH₃OH system were carried out at 20 and 37° C. From the results it was concluded that no significant ester formation occurred between CH₃OH and CF₃SO₃H.H₂O at these temperatures. Earlier published data on¹H NMR studies of these solutions had indicated that 100% of the methanol was involved in ester formation with the acid. A critical analysis of this¹H NMR work is given.Cyclic voltammetric characterization of catalysts in 10 and 25%wt. aqueous CF₃SO₃H solutions gave similar results to those in 3 M H₂SO₄; however, at concentrations of 50% wt. the acid decomposed at 0.0 V to produce a sulphur species that poisoned the catalyst.The conclusion of the work was that while aqueous CF₃SO₃H solutions produced promising catalyst performance up to 60° C the slight improvement in performance over 3 M H₂SO₄ would not offset the greater expense of the CF₃SO₃H. In addition, it was suspected that the long-term stability of the aqueous solutions even at 60° C might be poor.     

The hydrochloric acid route for phosphate rock

When phosphate rock is leached with hydrochloric acid, radium can be removed by co-precipitation with Ba_0.4Ca_0.6SO₄ and uranium by extraction with a 5% solution of tributyl phosphate in hexane or Varsol. Phosphoric acid is then separated from calcium chloride solution and other impurities by extraction with undiluted tributyl phosphate. The lanthanides can be precipitated from the raffinate by NH₃, and CaSO₄.2H₂O by H₂SO₄ to regenerate HCl for recycle. The organic phase containing H₃PO₄ can be stripped by NH₃ to yield ammonium phosphate and to regenerate the tributyl phosphate for recycle. Fluorine can be precipitated from the initial leach solution as Na₂SiF₆.     

Simultaneous removal of SO2, SO3 and H2SO4 mist from the gas after TiO2 calcining

Absorption of SO₂ and SO₃ in the solutions of waste ferrous sulfate (so-called ‘green salt’) and in the spent acid after TiO₂ hydrolysis, at H₂SO₄ concentrations ranging from 0–5 to 15 g/m³ (STP), was studied. The rate of SO₃ absorption has been found to rise linearly with increasing SO₃ concentration in the gas and to be independent on H₂SO₄ concentration in solution. The SO₂ absorption also rises linearly with increasing SO₂ content in the gas, but diminishes as H₂SO₄ concentration increases—an upper limit of 100 g H₂SO₄/kg H₂O is indicated. The initial concentration of the solution must not be higher than 40 g H₂SO₄/kg H₂O.     

Electrosynthesis of 2,3-dimethyltartaric acid from pyruvic acid in acid medium

This study reports the electrohydrodimerization of pyruvic acid to 2,3-dimethyltartaric acid in sulphuric acid medium (0.5 M H₂SO₄) on a lead cathode. The main products detected were lactic acid and 2,3-dimethyltartaric acid. The selectivity towards the formation of 2,3-dimethyltartaric acid was studied vs. pyruvic acid concentration in sulphuric acid solution, at −1.1 V vs. MSE. The best selectivity of 2,3-dimethyltartaric acid reached 69% for an initial concentration of 1.7 M pyruvic acid. The yield of pyruvic acid was 84%.