Ab initio vibrational calculations for H2SO4 and H2SO4 x H2O: spectroscopy and the nature of the anharmonic couplings

Vibrational frequencies for fundamental, overtone, and combination excitations of sulfuric acid (H2SO4) and of sulfuric acid monohydrate cluster (H2SO4 x H2O) are computed directly from ab initio MP2/TZP potential surface points using the correlation-corrected vibrational self-consistent field (CC-VSCF) method, which includes anharmonic effects. The results are compared with experiment. The computed transitions show in nearly all cases good agreement with experimental data and consistent improvement over the harmonic approximation. The CC-VSCF improvements over the harmonic approximation are largest for the overtone and combination excitations and for the OH stretching fundamental. The agreement between the calculations and experiment also supports the validity of the MP2/TZP potential surfaces. Anharmonic coupling between different vibrational modes is found to significantly affect the vibrational frequencies. Analysis of the mean magnitude of the anharmonic coupling interactions between different pairs of normal modes is carried out. The results suggest possible mechanisms for the internal flow of vibrational energy in H2SO4 and H2SO4 x H2O.     

Experimental determination of the H2SO4/(NH4)2SO4/H2O phase diagram

We have experimentally investigated the water and sulfuric acid-rich regions of the H2SO4/(NH4)2SO4/H2O ternary liquid/solid phase diagram using differential scanning calorimetry (DSC) and infrared spectroscopy of thin films. We present the liquid/solid ternary phase diagram for temperatures below 373 K and H2SO4 concentrations below 60 wt %. We have determined two ternary eutectics and two tributary reaction points for this system in the regions studied. It is also seen that sulfuric acid tetrahydrate (SAT) forms as a metastable solid over a large concentration range. Two true binary systems have been identified: ice/letovicite and SAT/ammonium bisulfate. Finally, we have compared our results to the predictions of the aerosol inorganics model and have found significant differences both in the final melting points and in the location of some of the phase boundaries including a significant discrepancy in the invariant points predicted versus those observed.     

Anion-exchange behaviour of 12 elements in H2SO4 and HF−H2SO4 medium

Anion-exchange data have been obtained for the elements As, Hf, Mo, Nb, Pa, Re, Sb, Sn, Ta, Tc, W, and Zr in 0.1 to 10M H₂SO₄ and in HF–H₂SO₄ mixtures of combination extending from 0.1 to 10M HF and from 0.1 to 10M H₂SO₄. The distribution ratios for mixed solutions are presented in form of adsorption contour lines.     

Dynamics of vibrational overtone excitations of H2SO4, H2SO4-H2O: hydrogen-hopping and photodissociation processes

Photochemical processes of sulfuric acid (H2SO4) and sulfuric acid monohydrate (H2SO4-H2O) following overtone excitation of the OH stretching mode are studied by classical trajectory simulations using the semiempirical PM3 potential suface in "on the fly" calculations. The main results are the following: (1) In the excitation of H2SO4 to the fifth OH-stretch overtone, hopping of the H atom between oxygen atoms is found to take place in 22% of the trajectories, only once during simulations of 400 ps. (2) All the trajectories for H2SO4 show a rapid cis-trans isomerization. (3) The photolysis of H2SO4 into SO3 + H2O takes place in 5% of the trajectories on a time scale of approximately 9 ps. (4) Only low overtone levels of H2SO4-H2O have sufficiently long lifetimes to be spectroscopically relevant. Excitation to these OH stretching overtones is found to result in the dissociation of the cluster. H hopping or dissociation of H2SO4 does not take place.     

Kinetic stability of tetrazaporphin in binary H2SO4-AcOH and H2SO4-DMSO solutions

The state and kinetic stability of tetrazaporphin (I) in acetic acid and in dimethyl sulfoxide (DMSO) in the presence of H₂SO₄ were investigated. Partial protonatiqn of I to give I-AcOH₂ associates occurs in acetic acid. The kinetic parameters of the reaction involving the destruction of tetrazaporphin in the presence of H₂SO₄ in acetic acid and DMSO solutions were determined. The mechanism of the destruction is discussed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 932–936, July, 1984.     

Study on electrochemical performance of activated carbon in aqueous Li2SO4, Na2SO4 and K2SO4 electrolytes

The electrochemical performances of activated carbon (AC) in 0.5 mol/l Li₂SO₄, Na₂SO₄ and K₂SO₄ aqueous electrolytes were investigated. The cyclic voltammetric results at different scan rates show that the rate behaviors of AC in the three electrolytes improve in the order of Li₂SO₄ < Na₂SO₄ < K₂SO₄. This improvement can be mainly ascribed to the following two reasons: (1) the decreasing equivalent series resistance in the order of Li₂SO₄ > Na₂SO₄ > K₂SO₄, which is the main factor influencing the maximum output power, and (2) the increasing migration speed of hydrated ions in the bulk electrolyte and in the inner pores of AC electrode in the order of Li⁺ < Na⁺ < K⁺. Their cycling behaviors do not show any differences in capacitive fading. The above results provide valuable information to explore new hybrid supercapacitors.     

Contact Deposition of Copper Powders onto Zinc in H2SO4-CuSO4 and H2SO4-CuSO4-ZnSO4 Solutions and Their Morphology

The contact extraction of copper in the form of dispersed powders onto compact zinc from H₂SO₄-CuSO₄ and H₂SO₄-CuSO₄-ZnSO₄ solutions was studied. The influence exerted by acidity and temperature of the solution on the rate and time of cementation, specific consumption of metallic zinc, and morphology of copper deposits was investigated.     

Excess Gibbs energy of mixing of the systems H2O-LiCl-Na2SO4 and H2O-CsCl-Na2SO4 at 25°C

The osmotic coefficients of aqueous solutions of lithium chloride+sodium sulfate and cesium chloride+sodium sulfate at 25°C have been measured. Interaction coefficients have been calculated and also the excess Gibbs energy of mixing. A correlation is found between the binary interaction coefficients and the Pauling cation radius of the alkali halide component.     

Oxidization of SO2 by Reactive Oxygen Species for Flue Gas Desulfurization and H2SO4 Production

A strong ionization dielectric barrier discharge was used to produce a high concentration of reactive oxygen species that were then injected into a simulated flue gas in a duct to remove SO₂ by oxidation. Sulfuric acid (H₂SO₄) was produced through the following two reactions: (1) O₃ oxidation of SO₂–SO₃, which then reacted with H₂O to produce H₂SO₄; and (2) reaction of O₂ ⁺ with H₂O to produce ·OH radicals, which then rapidly and non-selectively oxidized SO₂–H₂SO₄. When the molar ratio of reactive oxygen species to SO₂ was 4:1, the SO₂ removal efficiency was 94.6%, the energy consumption per cubic meter of flue gas was 13.3 Wh/m³, the concentration of recovered H₂SO₄ was 4.53 g/l, and the H₂SO₄ recovery efficiency was 28.8%. The H₂O volume fraction in the simulated flue gas affected the SO₂ removal efficiency, whereas the O₂ and CO₂ volume fractions did not. These results prove that oxidation by reactive oxygen species is a feasible method for flue gas desulfurization.     

H2O2—H2SO4体系电化学振荡行为的研究

Ｈ２Ｏ２参与的电化学振荡反应长期以来倍受人们的关注［１,２,３］,文献［１］报道了Ａｇ电极在Ｈ２Ｏ２－ＨＣｌＯ４水溶液中的电势振荡现象;文献［２］报道了Ｐｔ电极Ｈ２Ｏ２－Ｈ２ＳＯ４体系在控电流条件下的电势振荡,其实验的Ｈ２Ｏ２浓度范围为０．０２～０．...     

Gas phase dissociation of H2SO4: A computational study

The decomposition of gaseous sulfuric acid has been investigated computationally. In particular the role of the hydrated gaseous coordination adducts of SO₃(g) and H₂SO₄(g) in the (dissociation + decomposition) process has been evaluated. A first principles study of the gaseous coordination complexes SO₃(H₂O)_n (n = 1 to 3) and H₂SO₄(H₂O)_m (m = 1 to 2) has been carried out deriving equilibrium ground state structures, vibrational frequencies and energetic stabilities by the Moller–Plesset perturbation approximation. These results have been used to derive the enthalpy of formation at 0 K and the Gibbs energy functions of these molecules. A new thermodynamic modeling of the decomposition of H₂SO₄(g) has been therefore performed considering the effect of temperature, pressure and initial composition of the gas (hydration conditions).     

Combined use of H2SO4 and SO2 impregnation for steam pretreatment of spruce in ethanol production

Fuel ethanol can be produced from softwood through hydrolysis in an enzymatic process. Prior to enzymatic hydrolysis of the softwood, pretreatment is necessary. In this study, two-step steam pretreatment employing dilute H₂SO₄ impregnation in the first step and SO₂ impregnation in the second step, to improve the overall sugar and ethanol yield, was investigated. The first pretreatment step was performed under conditions of low severity (180°C, 10 min, 0.5% H₂SO₄) to optimize the amount of hydrolyzed hemicellulose. In the second step, the washed solid material from the first pretreatment step was impregnated with SO₂ and pretreated under conditions of higher severity to make the cellulose more accessible to enzymatic attack, as well as to hydrolyze a portion of the cellulose. A wide range of conditions was used in the second step to determine the most favorable combination. The temperatures investigated were between 190 and 230°C, the residence times were 2, 5, and 10 min; and the SO₂ concentration was 3%. The effect of pretreatment was assessed by both enzymatic hydrolysis of the solids and by simultaneous saccharification and fermentation (SSF) of the whole slurry, after the second pretreatment step. For each set of pretreatment conditions, the liquid fraction was also fermented to determine any inhibitory effects. Ethanol yield using the SSF configuration reached 66% of the theoretical value for pretreatment conditions in the second step of 210°C and 5 min. The sugar yield using the separate hydrolysis and fermentation configuration reached 71% for pretreatment conditions of 220°C and 5 min.     

Quasi-unary homogeneous nucleation of H2SO4-H2O

We show that the binary homogeneous nucleation (BHN) of H2SO4-H2O can be treated as quasi-unary nucleation of H2SO4 in equilibrium with H2O vapor. A scheme to calculate the evaporation coefficient of H2SO4 molecules from H2SO4-H2O clusters is presented and a kinetic model to simulate the quasi-unary nucleation of H2SO4-H2O is developed. In the kinetic model, the growth and evaporation of sulfuric acid clusters of various sizes are explicitly simulated. The kinetic quasi-unary nucleation model does not have two well-recognized problems associated with the classical BHN theory (violation of the mass action law and mismatch of the cluster distribution for monomers) and is appropriate for the situations where the assumption of equilibrium cluster distribution is invalid. The nucleation rates predicted with our quasi-unary kinetic model are consistent with recent experimental nucleation experiments in all the cases studied, while the most recent version of the classical BHN model systematically overpredicts the nucleation rates. The hydration of sulfuric acid clusters, which is not considered in the classical model but is accounted for implicitly in our kinetic quasi-unary model, is likely to be one of physical mechanisms that lead to lower nucleation rates. Further investigation is needed to understand exactly what cause the difference between the kinetic quasi-unary model and the classical BHN model.     

Medicago sativa as a green corrosion inhibitor for 1018 carbon steel in 0.5 M H2SO4 solution

A study on the use of the methanol extract of Medicago sativa as a green corrosion inhibitor for 1018 carbon steel in 0.5?M of sulfuric acid has been carried out by using potentiodynamic polarization curves, electrochemical impedance spectroscopy and gravimetric tests. Testing temperatures were 25°C, 40°C and 60°C. Results showed that M. sativa is a good corrosion inhibitor, with its efficiency increasing with its concentration and with time, but decreasing with the temperature. M. sativa forms a passive film on top of the steel with a passive current density and pitting potential values lower than that for uninhibited solution, and remained on the steel for 8–12?h. This film formed by iron ions and heteroatoms present in OH^? and amine groups from the extract are adsorbed on the steel and form a protective film on to the steel.     

Adsorption of NH3 onto activated carbon prepared from palm shells impregnated with H2SO4

Adsorption of ammonia (NH3) onto activated carbons prepared from palm shells impregnated with sulfuric acid (H2SO4) was investigated. The effects of activation temperature and acid concentration on pore surface area development were studied. The relatively large micropore surface areas of the palm-shell activated carbons prepared by H2SO4 activation suggest their potential applications in gas adsorption. Adsorption experiments at a fixed temperature showed that the amounts of NH3 adsorbed onto the chemically activated carbons, unlike those prepared by CO2 thermal activation, were not solely dependent on the specific pore surface areas of the adsorbents. Further adsorption tests for a wide range of temperatures suggested combined physisorption and chemisorption of NH3. Desorption tests at the same temperature as adsorption and at an elevated temperature were carried out to confirm the occurrence of chemisorption due to the interaction between NH3 and some oxygen functional groups via hydrogen bonding. The surface functional groups on the adsorbent surface were detected by Fourier transform infrared spectroscopy. The amounts of NH3 adsorbed by chemisorption were correlated with the contents of elemental oxygen present in the adsorbents. Mechanisms for chemical activation and adsorption processes are proposed based on the observed phenomena.     

二甲氧基甲烷在硫酸溶液中的电化学行为

电化学反应;直接甲醇燃料电池;燃料电池;二甲氧基甲烷在硫酸溶液中的电化学行为     

The protonation of Co(C5Me4Et)(C2H4)2

Reversible protonation of the bis-ethylene complex, Co(C₅Me₄Et)(C₂H₄)₂ yields [Co(C₅Me₄Et)(C₂H₄)₂H][BF₄], which readily exchanges its hydridic and olefinic protons stereospecifically at low temperatures; subsequent protonation at room temperature yields cobalt(III) complexes, C₂H₄ and C₂H₆.     

The crystallization kinetics of Zn(Met)SO4·H2O in mixed solvent of water with acetone

Journal of Thermal Analysis and Calorimetry -