Study of the system CaO---SiO2---CO2---H2O in relation to scawtite under hydrothermal conditions

Hydrothermal studies showed the location of scawtite in the narrow internal tetrahedronfoshagite-xonotlite-CO₂---H₂O of the system CaO---SiO₂---CO₂---H₂O and its compatibility with the calcium silicate hydrates in the 4-phase assemlages. The phase assemblages in this region involve scawtite, foshagite, xonotlite, tobermorite, hillebrandite, calcite and silica. The carbonation series of the 4-phase assemblages were determined in the sections C₄S₃---CO₂---H₂O (C₄S₃ = 4CaO · 3SiO₂), C₇S₆---CO₂---H₂O and C₆S₆---CO₂---H₂O at 473 K and saturated steam pressure in dependence on the CO₂ content. The carbonating influence of CO₂ takes place in the volume of the CaO---SiO₂---CO₂---H₂O system up to the CO₂ concentration limited by the calcite-silica-H₂O triangle. Above this CO₂ content, carbon dioxide appears in a gaseous form together with gaseous H₂O in the 4-phase assemblage calcite-silica-CO₂H₂O. The instability of scawtite under the CO₂ excess (CO₂/C₇S₆ > 1) is influenced by its structural arrangement. The present channels enable penetration of CO₂ molecules into the structure and formation of carbonated phases.     

Modelling formation and growth of H2SO4-H2O aerosols: Uncertainty analysis and experimental evaluation

An aerosol dynamics model, AERO2, is presented, which describes the formation of H₂SO₄-H₂O aerosol in a smog chamber. The model is used to analyse how the uncertainties on four input parameters are propagated through an aerosol dynamics model. The input parameters are: the rate of the reaction between SO₂ and OH (k₁), the ratio between the nucleation rate used in AERO2 and that derived from classical nucleation theory (t_n), the H₂SO₄ mass accommodation coefficient () and a measure of the turbulence intensity in the reactor (k_e). Uncertainties for these parameters are taken from the literature. One of the results of the analysis is that AERO2 and aerosol dynamics models in general can only predict upper bounds for the total number (N_tot) and total volume (V_tot) concentrations of the particles. The uncertainties on N_tot and V_tot are mainly due to the uncertainties on k₁, and t_n. An uncertainty factor of 20–100 still remains when the uncertainty on k₁, is reduced to ±5%. Aerosol measurements from three smog chamber experiments have therefore been used, in an attempt to reduce the uncertainty on k₁ and t_n. Values for k₁ are obtained in the reduced range 7.8 × 10⁻¹³ to 1.0 × 10⁻¹² cm³ s⁻¹, which is within the range found in the literature. For t_n, values in the range 10⁴–10⁷ are obtained, which is close to the upper bound of the range in literature. These values for t_n are in marked contrast with a recent set of experiments on nucleation in H₂SO₄-H₂O mixtures, which suggests a value for t_n of at most 10⁻⁵.     

四元体系LiCl-LiBO2-Li2SO4-H2O在298.15K时的相平衡

采用等温溶解平衡法开展了四元体系LiCl-LiBO₂-Li₂SO₄-H₂O在298.15 K时相平衡实验研究,测定体系溶解度和平衡溶液的折光率、密度、pH和电导率。根据实验数据,分别绘制该四元体系的干基图、水图以及相对应的物化性质-组成图。研究结果表明:在该四元体系298.15 K相图中,有2个无变度共饱点分别为相称共饱点(Li₂SO₄·H₂O + LiCl·H₂O + LiBO₂·2H₂O)和不相称共饱点(Li₂SO₄·H₂O + LiBO₂·2H₂O + LiBO₂·8H₂O)、5条溶解度曲线和4个单盐结晶相区(Li₂SO₄·H₂O、LiCl·H₂O、LiBO₂·8H₂O和LiBO₂·2H₂O),无复盐和固溶体产生,属于简单四元体系水合物Ⅱ型相图。实验研究中,发现2种偏硼酸锂水合矿物存在(LiBO₂·8H₂O和LiBO₂·2H₂O),LiCl对Li₂SO₄的盐析效应显著;四元体系平衡溶液物化性质随着溶液中氯化锂浓度的变化呈现规律性的变化。     

四元体系Rb+, Cs+, Mg2+ // SO42- - H2O 298.2 K相平衡研究

采用等温溶解平衡法研究了298.2 K下四元体系Rb⁺, Cs⁺, Mg²⁺ // SO₄^2- - H₂O的相平衡关系,测定了该体系的溶解度、密度以及折射率,并绘制了相应的稳定相图、水图、密度-组成图和折射率-组成图。研究表明：298.2 K下,该四元体系为复杂四元体系,有复盐Cs₂SO₄·MgSO₄·6H₂O和Rb₂SO₄·MgSO₄·6H₂O以及固溶体[(Rb, Cs）₂SO₄]生成。其稳定相图由4个四元共饱点、9条单变量曲线以及6个结晶区组成。四元共饱点中E₁、E₂、E₃为相称共饱点,E₄为不相称共饱点。6个结晶相区分别对应3种单盐Rb₂SO₄、MgSO₄·7H₂O、Cs₂SO₄,2种复盐Cs₂SO₄·MgSO₄·6H₂O、Rb₂SO₄·MgSO₄·6H₂O和1种固溶体[(Rb,Cs）₂SO₄]。其中,复盐Rb₂SO₄·MgSO₄·6H₂O结晶区最大,表明其在该体系中最易结晶析出;Cs₂SO₄结晶区最小。平衡液相的密度和折射率随着溶液中Cs₂SO₄含量变化呈规律性变化。该体系稳定相图将为硫酸镁亚型盐湖卤水中的铷、铯等资源开发利用提供理论依据。     

Some experimental observations of aerosol formation in the photo-oxidation of sulphur dioxide

The formation of particles in the u.v. photolysis of ppm concentrations of SO₂ in pure nitrogen and in nitrogen-oxygen mixtures has been studied in a flow system. Both the number of particles and the mass of the H₂SO₄ aerosol produced was determined over a range of SO₂ and water vapour concentrations.

In the near u.v. (λ = 290–400nm) the mass conversion of SO₂ to H₂SO₄ was too small to be measured, but particles were detected on a condensation nucleus counter above a threshold SO₂ concentration when the H₂SO₄ formation rate was sufficient to achieve an appreciable nucleation rate. The number of stable particles formed increased with water vapour concentration at a given H₂SO₄ production rate. These experimental data agree reasonably well with recent theoretical calculations of aerosol nucleation and growth rate in the H₂SO₄/H₂O system.

At short wavelengths (λ = 185 nm) a much higher H₂SO₄ formation rate was achieved. Although nucleation occurred at < 1 per cent r.h. the aerosol growth process was slow at low water vapour concentrations. A r.h. of 30 per cent was required for the incorporation of the bulk of the H₂SO₄ into the aerosol phase.     

Resistance of sodium polyphosphate-modified fly ash/calcium aluminate blend cements to hot H2SO4 solution

Sodium polyphosphate-modified Class F fly ash/calcium aluminate blend (SFCB) cements were prepared at room temperature and their resistance to hot acid erosion was evaluated by submerging them in H₂SO₄ solution (pH 1.6) at 90°C. Sodium polyphosphate preferentially reacted with calcium aluminate cement (CAC) to form amorphous Ca(HPO₄).xH₂O and Al₂O₃.xH₂O gel, rather than fly ash. These amorphous reaction products, which bound the partially reacted and unreacted CAC and fly ash particles into a coherent mass, were responsible for strengthening and densifying the SFCB specimens at room temperature, playing an essential role in mitigating their acid erosion. In these cements, the extent of acid erosion depended primarily on the ratio of fly ash/CAC; namely, those with a higher ratio underwent a severe erosion. This effect was due to the formation of a porous structure, which allowed acid to permeate the cement easily, diminishing the protective activity of Ca(HPO₄).xH₂O and Al₂O₃.xH₂O gel against H₂SO₄.     

PRECIPITATION IN THE Mg+2-Na+-SO3-2-SO4-2 AQUEOUS SYSTEM

Spontaneous precipitation in the aqueous system Mg₊₂-Na₊-SO₃^-2-SO₄^-2 affected by mixing solutions of MgSO₄ and Na₂SO₃, together was studied for temperature varying from 40 to 80°C and for pH from 5,5 to 9. The initial composition of a precipitating system was 0·67 and 1·17 mol of MgSO₃ and Na₂SO₄ per liter and 0·82 mol of MgSO₃ and Na₂SO₄ together with 0·83 mol of MgSO₄ per liter, respectively. Depending on the prevailing reaction conditions, solid phase consisting of MgSO₃ 6H₂O, MgSO₃ 3H₂O, Mg₂NaOH(SO₃)₂ H₂O or their mixture is formed. Each solid phase forms crystals of typical size and shape. The precipitation diagrams drawn in the temperature and pH coordinates for three different initial composition of the studied system are presented.     

Catalytic combustion of natural gas as the role of on-site heat supply in rapid catalytic CO2---H2O reforming of methane

Development in highly active catalysts for the reforming of methane with H₂O, CO₂, and H₂O+CO₂, and partial oxidation of methane was conducted to produce hydrogen with high reaction rates. A Ni-based three-component catalyst such as Ni---La₂O₃---Ru or Ni---Ce₂O₃---Pt supported on alumina wash-coated ceramic fiber in a plate shape was very suitable for both reactions. The catalyst composition was set at 10 wt.-% Ni, 5.6 wt.-% La₂0₃, and 0.57 wt.-% Ru for example, or molar ratios of these components were 1:0.2:0.03. Even with such a low concentration, the precious metal enhanced the reaction rate markedly, and this synergistic effect was ascribed to the hydrogen spillover effect through the part of precious metal and it resulted in a more reduced surface of the main catalyst component. In particular, a marked enhancement in the reaction rate of CO₂-reforming of methane was observed by the modification of a low concentration Rh to the Ni---Ce₂0₃---Pt catalyst. Very high space-time yields of H₂ (i.e., 8300 mol/1 h in partial oxidation of methane at 600°C with a methane conversion of 37.5%, and 3585 mol/1 h in CO₂reforming of methane at 600°C with a methane conversion of 58%) were realized in those reactions. By combining the catalytic combustion reaction, methane conversion to syngas was markedly enhanced, and even with a very short contact time (10 ms) the conversion of methane increased more than that at 50 ms. The space-time yield of hydrogen amounted to 2,780 mol/1 h with a methane conversion of 90% at 700°C. Furthermore, in a reaction of CH₄---CO₂---H₂O---O₂ on the four components catalyst, an extraordinarily high space-time yield of hydrogen, 12 190 mol/1 h, could be realized under the conditions of very high space velocity (5 ms).     

新型纳米SO42-/TiO2催化剂制备及催化合成醋酸丁酯

采用高压水热法合成纳米锐钛矿相TiO₂前驱体,通过H₂SO₄溶液浸渍制备系列新型SO₄^2-/TiO₂催化剂,采用XRD、TG-DTG和TEM对其结构和形貌进行表征,并用于催化醋酸与正丁醇的酯化反应,考察H₂SO₄溶液浓度、浸渍时间和反应时间对酯化率的影响。结果表明,在H₂SO₄浓度1 mol·L^-1、浸渍时间12 h和反应时间180 min条件下,酯化率高达99.2%,催化剂具有优异的催化性能和较佳的重复使用性。     

AgBr/Zn3(OH)2V2O7·2H2O可见光催化降解亚甲基蓝溶液

采用水热和沉淀两步合成法制备AgBr/Zn₃(OH)₂V₂O₇·2H₂O催化剂,研究其在可见光下降解亚甲基蓝溶液的性能,并考察催化剂用量、亚甲基蓝溶液初始浓度、pH值以及盐浓度对光催化性能的影响,评价AgBr/Zn₃(OH)₂V₂O₇·2H₂O催化剂的重复使用性能。结果表明,在前驱液pH为10、120 ℃水热10 h、Ag与Br物质的量比为0.20条件下制备的复合催化剂在可见光下反应120 min后,1.0 g·L^-1的催化剂对10 mg·L^-1的亚甲基蓝溶液脱色率达到85.2%。NaCl对亚甲基蓝的降解起抑制作用,Na₂SO₄对亚甲基蓝的降解起促进作用。催化剂重复使用4次后,光照120 min后的亚甲基蓝溶液脱色率可达66.4%。催化剂对不同初始浓度亚甲基蓝溶液的光催化降解符合一级动力学模型。     

Inhibition effect of H2O on V2O5/AC catalyst for catalytic reduction of NO with NH3 at low temperature

The inhibition effect of H₂O on V₂O₅/AC catalyst for NO reduction with NH₃ is studied at temperatures up to 250 °C through TPD, elemental analyses, temperature-programmed surface reaction (TPSR) and FT-IR analyses. The results show that H₂O does not reduce NO and NH₃ adsorption on V₂O₅/AC catalyst surface, but promotes NH₃ adsorption due to increases in Brønsted acid sites. Many kinds of NH₃ forms present on the catalyst surface, but only NH₄⁺ on Brønsted acid sites and a small portion of NH₃ on Lewis acid sites are reactive with NO at 250 °C or below, and most of the NH₃ on Lewis acid sites does not react with NO, regardless the presence of H₂O in the feed gas. H₂O inhibits the SCR reaction between the NH₃ on the Lewis acid sites and NO, and the inhibition effect increases with increasing H₂O content. The inhibition effect is reversible and H₂O does not poison the V₂O₅/AC catalyst.     

Combined effect of H2O and SO2 on V2O5/AC catalysts for NO reduction with ammonia at lower temperatures

Combined effect of H₂O and SO₂ on V₂O₅/AC the activity of catalyst for selective catalytic reduction (SCR) of NO with NH₃ at lower temperatures was studied. In the absence of SO₂, H₂O inhibits the catalytic activity, which may be attributed to competitive adsorption of H₂O and reactants (NO and/or NH₃). Although SO₂ promotes the SCR activity of the V₂O₅/AC catalyst in the absence of H₂O, it speeds the deactivation of the catalyst in the presence of H₂O. The dual effect of SO₂ is attributed to the SO₄²⁻ formed on the catalyst surface, which stays as ammonium-sulfate salts on the catalyst surface. In the absence of H₂O, a small amount of ammonium-sulfate salts deposits on the surface of the catalyst, which promote the SCR activity; in the presence of H₂O, however, the deposition rate of ammonium-sulfate salts is much greater, which results in blocking of the catalyst pores and deactivates the catalyst. Decreasing V₂O₅ loading decreases the deactivation rate of the catalyst. The catalyst can be used stably at a space velocity of 9000 h⁻¹ and temperature of 250 °C.     

Hydrothermal transformation of the calcium aluminum oxide hydrates CaAl2O4·10H2O and Ca2Al2O5·8H2O to Ca3Al2(OH)12 investigated by in situ synchrotron X-ray powder diffraction

The hydrothermal transformation of calcium aluminate hydrates were investigated by in situ synchrotron X-ray powder diffraction in the temperature range 25 to 170 °C. This technique allowed the study of the detailed reaction mechanism and identification of intermediate phases. The material CaAl₂O₄·10H₂O converted to Ca₃Al₂(OH)₁₂ and amorphous aluminum hydroxide. Ca₂Al₂O₅·8H₂O transformed via the intermediate phase Ca₄Al₂O₇·13H₂O to Ca₃Al₂(OH)₁₂ and gibbsite, Al(OH)₃. The phase Ca₄Al₂O₇·19H₂O reacted via the same intermediate phase to Ca₃Al₂(OH)₁₂ and mainly amorphous aluminum hydroxide. The powder pattern of the intermediate phase is reported.     

Oxidative leaching kinetics of molybdenum-uranium ore in H2SO4 using H2O2 as an oxidizing agent

The processing of molybdenum-uranium ore in a sulfuric acid solution using hydrogen peroxide as an oxidant has been investigated. The leaching temperature, hydrogen peroxide concentration, sulfuric acid concentration, leaching time, particle size, liquid-to-solid ratio and agitation speed all have significant effects on the process. The optimum process operating parameters were: temperature: 95°C; H₂O₂ concentration: 0.5 M; sulfuric acid concentration: 2.5 M; time: 2 h; particle size: 74 μm, liquid-to-solid ratio: 14 ∶ 1 and agitation speed: 600 rpm. Under these experimental conditions, the extraction efficiency of molybdenum was about 98.4%, and the uranium extraction efficiency was about 98.7%. The leaching kinetics of molybdenum showed that the reaction rate of the leaching process is controlled by the chemical reaction at the particle surface. The leaching process follows the kinetic model 1 ? (1?X)^1/3 = kt with an apparent activation energy of 40.40 kJ/mole. The temperature, concentrations of H₂O₂ and H₂SO₄ and the mesh size are the main factors that influence the leaching rate. The reaction order in H₂SO₄ was 1.0012 and in H₂O₂ it was 1.2544.     

Thermodynamic investigation of the CaO---Al2O3---CaSO4---H2O system at 50°C and 85°C

The CaO---Al₂O₃---CaSO₄---H₂O system has been investigated at 50°C and 85°C, by calculations of the equilibrium solubility surfaces of AH₃, C₃AH₆, CH, ettringite, monosulphoaluminate and gypsum. The results indicate that monosulphoaluminate becomes a stable phase at elevated temperature. Since ettringite also remains stable at 85°C, new invariant points are created, for which calculated aqueous phase compositions are given.     

A STUDY OF H2SO4 FORMATION IN THE PROCESS OF SIMULTANEOUS SORPTION OF SO2, O2 AND H2O ONTO A SINGLE CARBON PARTICLE

A mathematical model to describe simultaneous sorption of SO₂, O₂ and H₂O in an activated carbon particle is presented in this paper. The competition for active sites of these species is taken into account by a modified Langmuir-type isotherm, which incorporates the competition of the immobile reaction product phase, H₂SO₄. Simulations of the model are presented in terms of transient micropore filling of reactant species and product H₂SO₄. The simulation results show that the multicomponent interactions play an important role in the sorption process. Fast diffusing species like O₂ and H₂O instantaneously adsorb in the micropore volume of the sorbent. In the course of simultaneous adsorption and reaction of all species in the micropore, a rollup phenomenon on the transient behavior of fast diffusing species could occur, i.e. the micropore loading of these gaseous species can overshoot the final equilibrium level. The simulation results of H₂SO₄ micropore loading are found to agree reasonably well with the experimental data.     

-15℃下Na+, K+, Mg2+// Cl-, SO4-2-H2O体系相平衡

采用等温溶解平衡法,研究了Na⁺, K⁺, Mg²⁺//Cl^-, SO₄^-2-H₂O, 五元水盐体系在-15℃下NaCl·2H₂O饱和时的相平衡关系,测定了溶解度和密度,并绘制出相应的相图。研究结果表明:该五元体系平衡相图中有3个四盐共饱点,7条单变量溶解度曲线及5个两盐结晶区,5个两盐结晶区分别对应于KCl+NaCl·2H₂O、Na₂SO₄·10H₂O+ NaCl·2H₂O、MgSO₄·7H₂O+NaCl·2H₂O、MgCl₂·8H₂O+NaCl·2H₂O、KCl·MgCl₂·6H₂O+ NaCl·2H₂O;所 得-15℃相图和25℃下相图相比,相图结构大为简化:K₂SO₄·MgSO₄·4H₂O、KCl·MgSO₄·3H₂O、Na₂SO₄·3K₂SO₄、Na₂SO₄·MgSO₄·4H₂O、MgSO₄·(4～6)H₂O、K₂SO₄·MgSO₄·6H₂O结晶区均消失,Na₂SO₄结晶区转变为Na₂SO₄·10H₂O且结晶区扩大,KCl、MgSO₄·7H₂O、KCl·MgCl₂·6H₂O结晶区缩小,MgCl₂·6H₂O结晶区转变为MgCl₂·8H₂O。在此基础上研究了不同组成的盐湖卤水在降温过程中的结晶规律,为低温盐田工艺的开发提供了理论依据。     

Catalytic decomposition of N2O over CeO2 promoted Co3O4 spinel catalyst

A series of CeO₂ promoted cobalt spinel catalysts were prepared by the co-precipitation method and tested for the decomposition of nitrous oxide (N₂O). Addition of CeO₂ to Co₃O₄ led to an improvement in the catalytic activity for N₂O decomposition. The catalyst was most active when the molar ratio of Ce/Co was around 0.05. Complete N₂O conversion could be attained over the CoCe0.05 catalyst below 400 °C even in the presence of O₂, H₂O or NO. Methods of XRD, FE-SEM, BET, XPS, H₂-TPR and O₂-TPD were used to characterize these catalysts. The analytical results indicated that the addition of CeO₂ could increase the surface area of Co₃O₄, and then improve the reduction of Co³⁺ to Co²⁺ by facilitating the desorption of adsorbed oxygen species, which is the rate-determining step of the N₂O decomposition over cobalt spinel catalyst. We conclude that these effects, caused by the addition of CeO₂, are responsible for the enhancement of catalytic activity of Co₃O₄.     

Decomposition of nitric oxide over perovskite oxide catalysts: effect of CO2, H2O and CH4

Direct nitric oxide decomposition over perovskites is fairly slow and complex, its mechanism changing dramatically with temperature. Previous kinetic study for three representative compositions (La_0.87Sr_0.13Mn_0.2Ni_0.8O_3−δ, La_0.66Sr_0.34Ni_0.3Co_0.7O_3−δ and La_0.8Sr_0.2Cu_0.15Fe_0.85O_3−δ) has shown that depending on the temperature range, the inhibition effect of oxygen either increases or decreases with temperature. This paper deals with the effect of CO₂, H₂O and CH₄ on the nitric oxide decomposition over the same perovskites studied at a steady-state in a plug-flow reactor with 1 g catalyst and total flowrates of 50 or 100 ml/min of 2 or 5% NO. The effect of carbon dioxide (0.5–10%) was evaluated between 873 and 923 K, whereas that of H₂O vapor (1.6 or 2.5%) from 723 to 923 K. Both CO₂ and H₂O inhibit the NO decomposition, but inhibition by CO₂ is considerably stronger. For all three catalysts, these effects increase with temperature. Kinetic parameters for the inhibiting effects of CO₂ and H₂O over the three perovskites were determined. Addition of methane to the feed (NO/CH₄=4) increases conversion of NO to N₂ about two to four times, depending on the initial NO concentration and on temperature. This, however, is still much too low for practical applications. Furthermore, the rates of methane oxidation by nitric oxide over perovskites are substantially slower than those of methane oxidation by oxygen. Thus, perovskites do not seem to be suitable for catalytic selective NO reduction with methane.