An investigation on dissolution kinetics of single sodium carbonate particle with image analysis method

Dissolution kinetics of sodium carbonate is investigated with the image analysis method at the approach of single particle. The dissolution experiments are carried out in an aqueous solution under a series of controlled temper-ature and pH. The selected sodium carbonate particles are al spherical with the same mass and diameter. The dissolution process is quantified with the measurement of particle diameter from dissolution images. The concentration of dissolved sodium carbonate in solvent is calculated with the measured diameter of particle. Both surface reaction model and mass transport model are implemented to determine the dissolution mecha-nism and quantify the dissolution rate constant at each experimental condition. According to the fitting results with both two models, it is clarified that the dissolution process at the increasing temperature is controlled by the mass transport of dissolved sodium carbonate travelling from particle surface into solvent. The dissolution process at the increasing pH is control ed by the chemical reaction on particle surface. Furthermore, the dissolution rate constant for each single spherical sodium carbonate particle is quantified and the results show that the disso-lution rate constant of single spherical sodium carbonate increases significantly with the rising of temperature, but decreases with the increasing of pH conversely.     

Effect of carboxymethyl cellulose on dissolution kinetics of carboxymethyl cellulose-sodium carbonate two-component tablet

Sodium carbonate and carboxymethyl cellulose powders are compressed into two-component tablets with three mass ratios, 97%:3%, 95%:5% and 93%:7%. The dissolution tests for two-component tablets and reference pure sodium carbonate tablets are carried out at various temperatures. The dissolution process of each tablet is measured by electrical conductivity tracking method and the concentration of dissolved sodium carbonate is quantified with calibrated conductivity-concentration converting equation of sodium carbonate. The quantified dissolution data is fitted with both surface reaction model and diffusion layer model and the results clearly show that surface reaction model is suggested as the appropriate dissolution model for all measured tablets. Therefore, it is determined that carboxymethyl cellulose is a stable element to remain the dissolution mechanism of tablet unchanged. The dissolution rate constant quantified with surface reaction model presents that carboxymethyl cellulose-sodium carbonate two-component tablets obtain significant higher dissolution rate constant than pure sodium carbonate tablet and higher proportion of carboxymethyl cellulose leads to apparent higher dissolution rate constant. The results prove for the usage of carboxymethyl cellulose in most practical applications at a relative low-level, the effect of carboxymethyl cellulose is effective and positive for two-component tablet to enhance the dissolution process and improve dissolution rate constant and this effect is speculated coming from its dynamic physical transforming process in water including dilation and conglutination.     

The electrochemical behaviour of polycrystalline nickel electrodes in different carbonate-bicarbonate ion-containing solutions

The dissolution and passivation of polycrystalline nickel in carbonate-bicarbonate ion-containing solutions covering wide ranges of pH and electrolyte concentration were investigated by employing voltammetric, galvanostatic and potentiostatic transient techniques. Results obtained with a rotating disc electrode allow the competing reactions related to the active-passive transition to be distinguished through the influence of the potential sweep rate and the rotation speed on the electrochemical behaviour of the system at fixed concentrations of either carbonate or bicarbonate ion. The first oxidation level of nickel corresponds mainly to Ni(OH)₂ formation, the chemical dissolution of the surface layer and the precipitation of NiCO₃ and Ni(OH)₂. The partial removal of the prepassive layer is predominantly assisted by both the bicarbonate ion concentration and the electrode rotation. In the presence of chloride ions the formation of soluble Ni(II) species and NiCo₃ in the potential range of the first oxidation level appears to be enhanced. This effect can be interpreted by taking into account competitive adsorption processes at the base metal between Cl^– and OH^– ions.     

碳酸锂在碳酸钠溶液中的溶解度与热力学

采用等温溶解平衡法开展碳酸锂在碳酸钠溶液中(278.15～358.15 K)的溶解平衡实验研究,测定平衡体系碳酸锂溶解度和平衡溶液密度,利用E-DH方程对碳酸锂溶解度实验数据进行关联,标准偏差小于0.01;利用Connaughton方程对液相密度数据进行关联,标准偏差小于2×10^-3。实验和计算研究结果表明：在同离子和盐效应协同影响下,碳酸锂在Na₂CO₃-H₂O体系中溶解度随碳酸钠浓度增加先降低后降低趋势变缓,在278.15～358.15 K温度范围内,溶解度转变折点为碳酸钠浓度约为0.1 mol·kg^-1;通过溶解热力学计算,得到碳酸锂在碳酸钠中的溶解焓变(ΔH_d)、熵变(ΔS_d)和Gibbs自由能变(ΔG_d),结果表明溶解过程为放热、熵减的非自发过程,溶解焓变和熵变随着碳酸钠浓度增加而增加,Gibbs自由能变在0.6 mol·kg^-1出现最大值,且溶解过程为熵控制过程。研究结果将为卤水提锂碳化沉锂过程设计提供基础数据。     

THE USE OF THE PENETRATION MODEL FOR THE DISSOLUTION OF LIMESTONE IN THE CO2-WATER SYSTEM

The penetration model was implemented for the dissolution of limestone in the CO₂-water system. The model includes the acid-base reactions of the carbonate species as well as the autoprotolysis of water. It was also assumed that there is no surface resistance to the dissolution of the solid. This assumption restricts the use of the model to those conditions where the dissolution rate is limited by the rate of mass transfer. When using the model, only the hydrodynamics of the water solution need to be experimentally determined and put in terms of the model's hydrodynamic parameter. All other model inputs are either physical constants or known bulk concentrations. Dissolution experiments, performed on a rotating cylinder system, were used to test the ability of the model to predict the dissolution rate of limestone in an aqueous solution. Of special significance was the ability of the model to predict the dissolution rate at different pH-values, CO₂ partial pressures, temperatures and hydrodynamic conditions. An explicit finite differences method was used to deal with the system of non-linear partial differential and algebraic equations, which arose from the implementation of the penetration model. This investigation has shown that the limestone dissolution process in the mass transfer controlled region, can be modelled and described by the penetration model. The penetration model accurately describes the effects of all parameters investigated, including the enhancement effect from CO₂ (up to a factor of 10 compared with dissolution in a CO₂-free atmosphere) and temperature. The penetration model has also been compared with the film theory model. The comparison of the two models shows that the penetration model yields a better correlation to the experimental data in a CO, atmosphere. In a CO₂-free atmosphere the models are almost identical. However, the penetration model is computationally more difficult. A numerical procedure for solving the penetration model has been designed. This procedure includes a method of dealing with the unusual boundary conditions at the surface.     

Effect of an added base on (4-cyanopentanoic acid)-4-dithiobenzoate mediated RAFT polymerization in water

The effect of an added base on the aqueous reversible addition-fragmentation chain transfer polymerization of a methacrylic glycomonomer with (4-cyanopentanoic acid)-4-dithiobenzoate was investigated. When sodium carbonate or sodium bicarbonate were used to dissolve the RAFT agent in aqueous solution at room temperature, an inhibition period of 60-90 min was observed at the beginning of the polymerization together with a marked decrease in the overall polymerization rate. Also, experimental M_n values were much higher than the calculated ones in both cases. When sodium carbonate was used, control over the polymerization process was lost within 43% conversion. Better results were obtained with sodium bicarbonate, in which case the molecular weight distribution remained narrow and unimodal up to 81% conversion. At that point, a higher molecular weight shoulder developed that kept growing in intensity at the proceeding of the reaction. Dramatically improved results were obtained by adding circa 10% ethanol to the polymerization mixture to facilitate the dissolution of (4-cyanopentanoic acid)-4-dithiobenzoate. Following this protocol, narrow polydispersity poly(methyl 6-O-methacryloyl-α-d-glucoside) was obtained possessing a molecular weight close to the predicted value.     

Observer based nonlinear quadratic dynamic matrix control for state space and input/output models

An observer based nonlinear Quadratic Dynamic Matrix Control (QDMC) algorithm is developed for use with nonlinear input-output (I/O) and state space models. It generalizes and extends previously published nonlinear QDMC algorithms. The extension to I/O models is particularly important due to the increased use of neural networks and other types of nonlinear black box models in the chemical industry. Disturbance rejection and offset free tracking is addressed in a general setting utilizing concepts from filtering theory. Various kinds of disturbance models can be incorporated in the formulation. Even though nonlinear models are utilized for model prediction, the on-line optimization is formulated as a single Quadratic Program, thus preserving the computational advantages of nonlinear QDMC as compared to Model Predictive Control algorithms based on nonlinear programming techniques. The examples illustrate parameter tuning for open-loop unstable and stable processes and point out both benefits and shortcomings of the algorithm.     

Mathematical Model of the Dissolution Stage in Cooling Batch Crystallization

Abstract

Experiments were performed in a cooling batch crystallizer to develop a phenomenological model that represents the dissolution stage in crystallization. Two models were used: a theoretical and a black box, comparing their results with the experimental ones through the simulation of these models (use the mean and the standard deviation of crystal size like comparative means). The theoretical model was obtained by population's balance, mass and energy balances, and constitutive relations (decrease speed and production‐reduction speed). The black box model consisted of a set of equations, which are functions of the mean, standard deviation, agitation speed and time.     

基于神经网络和过程机理的热流体系统仿真

构建了一种基于复合神经网络和过程机理特性的热流体系统仿真模型 .该模型在形式上为一种复合人工神经网络模型 ,保证了模型具有十分理想的仿真速度 ;在网络模型设计上较好地考虑了系统输入与输出间的物理基础 ,网络模型在一定程度上由常规的黑箱模型转化为“灰箱模型” ,网络的训练除了具有常规的输入、输出间的纯数值映射关系学习功能之外较好地体现了对象输入与输出间的物理机理学习 ,保证了网络模型具有良好的联想能力、外推能力和时间递推能力 .     

磷酸装置转盘式过滤机板网改进及运用

云峰分公司磷酸厂转盘式过滤机板网孔眼及滤盒内结垢堵塞严重,液相穿透性能差,导致过滤系统非计划停车频繁,过滤装置出现硫酸消耗、滤布消耗、水溶磷含量高,磷收率、洗涤率和滤布再生效果低的三高三低现象。经分析发现,过滤机板网和滤盒本身设备结构不合理,滤板透气性能差是结垢的主要原因。通过采取针对性的解决措施,降低了过滤机板网及滤盒内结垢速率,磷收率由96.84%提高至97.31%,实现了过滤机清理检修周期与滤布更换周期同步。     

Modeling and Optimization of Anode‐Supported Solid Oxide Fuel Cells on Cell Parameters via Artificial Neural Network and Genetic Algorithm

An artificial neural network (ANN) and a genetic algorithm (GA) are employed to model and optimize cell parameters to improve the performance of singular, intermediate‐temperature, solid oxide fuel cells (IT‐SOFCs). The ANN model uses a feed‐forward neural network with an error back‐propagation algorithm. The ANN is trained using experimental data as a black‐box without using physical models. The developed model is able to predict the performance of the SOFC. An optimization algorithm is utilized to select the optimal SOFC parameters. The optimal values of four cell parameters (anode support thickness, anode support porosity, electrolyte thickness, and functional layer cathode thickness) are determined by using the GA under different conditions. The results show that these optimum cell parameters deliver the highest maximum power density under different constraints on the anode support thickness, porosity, and electrolyte thickness.     

Kinetics of non-congruent dissolution of E-glass fiber in saturated calcium hydroxide solution

The kinetics of non-congruent dissolution of long E-glass fiber in saturated calcium hydroxide solution has been investigated at 25°C in a closed reactor adopting the rotating disc method for the sample holder. The fiber dissolution rate (), measured from the relative loss weight of the fiber after selective dissolution of the attack layer in acetic acid, is a linear function of time, what implies an interfacial dissolution process. However, the kinetics does not stay regular for a long time due to local detachment of the attack layer. The comparison between = f (t) and ′ = f (t) curves, where ′ is the formation rate of the attack layer, shows that the formation of the layer does not only imply the deposit of a bad-crystalline hydrated calcium silicate but the nucleation and growth of solid calcium hydroxide and calcium carbonate resulting from the transfert, to the interface, of ions coming from the liquid phase. This phenomenon was precedently observed by some other authors in the case of glass-fiber reinforced cement matrix.     

Dissolution kinetics of calcined ulexite in ammonium carbonate solutions

The leaching kinetics of calcined ulexite in ammonium carbonate was studied in this work. The effect of parameters of ammonium carbonate concentration, solid/liquid ratio, stirring speed, calcination temperature and reaction temperature was determined in the experiments. It was found that the conversion rate increased with increasing ammonium carbonate concentration, reaction temperature and decreasing solid/liquid ratio. However, the effect of stirring speed on the conversion rate was insignificant. The experimental data practised the heterogeneous and homogeneous models, and an acceptable model for the conversion rates of ulexite was determined to be a first-order pseudohomogeneous reaction model. The activation energy of dissolution process was determined to be 35.3 kJ/mol.     

酯交换法合成碳酸二甲酯的催化精馏过程研究

在催化精馏实验装置中 ,以等体积浸渍法负载于是碳分子筛上的 12 磷钨酸为催化剂 ,通过碳酸丙烯酯和甲醇之间的酯交换反应合成碳酸二甲酯。通过实验考察了原料配比、操作压力、回流比、处理量等工艺参数对催化精馏过程的影响。采用神经网络与遗传算法相结合的方法 ,用黑箱模型计算催化精馏过程 ,并进行了全局优化 ;以动力学模型为基础 ,借助ASPEN软件用平衡级模型进行了催化精馏过程的模拟与预测。     

The anodic dissolution of SIMFUEL (UO2) in slightly alkaline sodium carbonate/bicarbonate solutions

The corrosion of nuclear fuel under waste disposal conditions is likely to be influenced by the bicarbonate/carbonate content of the groundwater since it increases the solubility of the U^VI corrosion product, [UO₂]²⁺. As one of the half reactions involved in the corrosion process, the anodic dissolution of SIMFUEL (UO₂) has been studied in bicarbonate/carbonate solutions (pH 9.8) using voltammetric and potentiostatic techniques and electrochemical impedance spectroscopy. The reaction proceeds by two consecutive one electron transfer reactions (U^IV → U^V → U^VI). At low potentials (≤250 mV (vs. SCE) the rate of the first electron transfer reaction is rate determining irrespective of the total carbonate concentration. At potentials >250 mV (vs. SCE) the formation of a U^VIO₂CO₃ surface layer begins to inhibit the dissolution rate and the current becomes independent of potential indicating rate control by the chemical dissolution of this layer.     

HYBRID NEURAL APPROACHES FOR MODELLING DRYING PROCESSES FOR PARTICULATE SOLIDS

ABSTRACT

This work presents methods for synthesizing drying process models for particulate solids that combine prior knowledge with artificial neural networks. The inclusion of prior knowledge is investigated by developing two applications with the data from two indirect rotary steam dryers. The first application consisted in the modelling of the drying process of soya meal in a batch indirect rotary dryer, The external and internal mass transfer resistances were associated in the hidden layer of the network to linear and sigmoidal nodes, respectively. The second application consisted in the modelling of the drying process of soya meal in a continuos indirect rotary dryer. The model was constructed using the Semi-parametric Design Approach. The model predicts the evolution of solid moisture content and temperature as a function of the solid position in the dryer. The results show that the hybrid model performs better than the pure “ black box” neural network and default models. They also shows that prior knowledge enhances the extrapolation capabilities of a neural network model,     

Eutectic freeze crystallization from the ternary Na2CO3–NaHCO3–H2O system: A novel scraped wall crystallizer for the recovery of soda from an industrial aqueous stream

Eutectic freeze crystallization was tested in a scaled up version of a scraped cooled wall crystallizer on an industrial aqueous sodium carbonate–sodium bicarbonate waste stream containing traces of molybdenum. A heat transfer rate of 5 kW m⁻² was maintained in the crystallizer. Sodium carbonate decahydrate with molybdenum content below 1 ppm and pure ice were produced by continuous crystallization at −3.8 °C by operating within the metastable zone width of bicarbonate. At −4.0 °C bicarbonate started to co-crystallize. The bimodal size distribution of the mixture resulted in poor filtration and purity of the salt product.     

COD fractionation and biodegradation kinetics of segregated domestic wastewater: black and grey water fractions

BACKGROUND: Household wastewater was segregated to grey and black water components as part of a recent approach aiming to separate wastewater fractions for more efficient treatment and reuse. Chemical oxygen demand (COD) fractionation and biodegradation characteristics of black and grey water were determined by means of model calibration of the oxygen uptake rate profiles. An ASM1 type of model modified for endogenous respiration was selected for this purpose. RESULTS: Calibration identified, aside from the readily biodegradable COD, two hydrolysable COD fractions in the black water, and only a single, slowly biodegradable COD fraction, in the grey water. The relative magnitude of the readily biodegradable COD fraction was high compared with typical domestic sewage, especially for grey water, and the level of particulate inert COD fraction, was relatively low. Biodegradation of soluble COD fractions in both wastewaters approximated typical rates observed for domestic sewage. However, the hydrolysis rate of the slowly biodegradable COD was quite low, reflecting the characteristics and impact of settleable organic matter. CONCLUSION: Based on the process rates obtained, aerobic biodegradation was equally effective for black and grey water fractions, both for the removal of soluble COD and the stabilization of particulate COD. Copyright © 2010 Society of Chemical Industry     

Electrooxidation of stainless steel AISI 304 in carbonate aqueous solution at pH 8

The electrochemical behaviour of stainless steel AISI 304 (SS304) has been investigated in deaerated 0.1–1 m NaHCO₃ solutions at pH 8 using a rotating disc electrode. The polarization curves are characterized by a broad range of passivity at low potentials (–0.8 to 0.3 V), a depassivation region at 0.4 V vs SCE and, at high potentials (0.5 to 0.85 V), a passive region before oxygen evolution. In the low potential range, the SS304 electrode behaves like a Cr-rich metallic phase, and the dissolution of Fe²⁺ ions into the solution is hindered by the formation of a Cr₂O₃ layer. As the potential reaches 0.4V, the oxidation-dissolution of Cr(iii) oxide/hydroxide to CrO₄ ² ions occurs, with the participation of bicarbonate/carbonate as a catalyst in the dissolution reaction. Since the chromium oxide/hydroxide dissolution and subsequent surface enrichment of iron oxides occur, the applied potential, exposure time and oxidation charge have a considerable effect on the passive film properties. At high potentials, the presence of a passive film of iron oxides/hydroxides or oxyhydroxides plays a key role in the SS304 passivity with the presence of Fe(vi) species incorporated or adsorbed into the passive films. Colouration of the SS304 surface is observed in the second passive region. A film of a uniform gold colour formed on SS304, mild steel 1024 and iron in carbonate and borate solutions at pH 8. The colour of the electrode surfaces remain unchanged in air and in solutions at positive potential but it disappears at open-circuit potential or is easily reduced in the first negative-going potential scan.     

Indole and 5-chloroindole as inhibitors of anodic dissolution and cathodic deposition of copper in acidic chloride solutions

The effect of indole, IN, and 5-chloroindole, Cl-IN, on the anodic dissolution of copper in acidic sodium chloride solutions was studied using voltammetry on a rotating disc electrode (RDE). Both compounds used at 10^–3 M concentration act as strong inhibitors on the copper dissolution, but indole exhibits better inhibiting properties. The inhibitory action substantially increases with decreasing solution pH. The influence of these organic additives on the electrodeposition of copper on platinum was also investigated using RDE and electrochemical quartz crystal microbalance (EQCM) techniques. The EQCM measurements show that a sparingly soluble layer of the inhibitor is responsible for the protective effects observed in chloride solutions.