Extraction of citric acid from aqueous solutions with Alamine 336: equilibrium and kinetics

Citric acid is one of the organic acids for which the world market is growing every year. This article describes equilibria and kinetic studies for the extraction of citric acid by Alamine 336 with methyl‐iso‐butylketone (MIBK) as diluent. The theory of extraction accompanied by a chemical reaction has been used to obtain the intrinsic kinetics of extraction of citric acid by Alamine 336 in MIBK. The reaction has been found to be first order in both Alamine 336 and citric acid with a rate constant of 0.013 m³ kmol^?1 s^?1. Copyright © 2004 Society of Chemical Industry     

Absorption of phosphine in aqueous solutions of sodium hypochlorite and sulphuric acid

The kinetics of absorption of phosphine in aqueous solutions of sodium hypochlorite and sulphuric acid was studied in a stirred cell and a stirred contactor. The reaction of phosphine with aqueous solutions of sodium hypochlorite was found to first order with respect to phosphine and hypochlorite. The effect of pH on the second order rate constant was also investigated. The value of the second order rate constant was found to vary from 230 to 77,000 1./g mole sec at 28°C in the pH range of 12.95-9.40.The reaction of phosphene with aqueous solutions of sulphuric acid, in the range of concentrations of 80 to 92% by weight, was also found to be first order with respect to phosphine. The value of the pseudo first order rate constant was found to be in the range of 3 × 10⁶?4 × 10' sec_?1 at 28°C. Copper sulphate was found to be an effective catalyst in sulphuric acid solutions.     

Chemical beneficiation of coal with aqueous hydrogen peroxide/sulphuric acid solutions

The removal of sulphur and ash from coal treated with aqueous hydrogen peroxide/sulphuric acid solutions has been studied at ambient temperature, under a variety of experimental conditions. Almost complete elimination of the sulphate and the pyritic sulphur was observed in most cases, as well as substantial reduction in the ash content. The other components of the organic coal matrix were not affected to a significant extent, indicating high selectivity of the $\text{H}{}_2\text{O}{}_2\text{H}{}_2\text{SO4}$ system towards sulphur oxidation. An optimal H₂SO₄ concentration was established, above which the acid was found to have an adverse effect on the oxidation of pyrite by hydrogen peroxide.     

Adsorption kinetics and mechanism of acid dye onto montmorillonite from aqueous solutions: Stopped-flow measurements

The adsorption of acid dye, namely, acid fuchsin (AF), onto sodium montmorillonite (Na⁺-Mt) from aqueous solutions was investigated. The adsorption process was very fast and attained equilibrium within 1 h, which was an economically favorable requisite. The Freundlich and Langmuir adsorption models were applied to describe the equilibrium isotherms and the isotherm constants were calculated. The experimental data fit well with Freundlich model rather than the Langmuir model. The equilibrium adsorption constant, K_c, was determined and used to calculate the enthalpy and entropy of the adsorption process. The adsorption kinetics was followed up using a stopped-flow spectrophotometer under pseudo-first-order conditions. The influence of initial dye concentrations, amount of sodium montmorillonite, and temperature on the rate of adsorption were studied. The activation energy of adsorption was calculated and indicated a chemical adsorption process. The enthalpy of adsorption confirmed an exothermic process. A proper mechanism for adsorption supported by X-ray and atomic absorption data was proposed.     

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.     

Diffusion in aqueous polymer solutions

The diffusion of Direct Blue 76 dye in aqueous dilute polymer solutions was studied using the capillary method. The polymer systems studied included dilute solution of carboxymethyl cellulose, poly(ethylene oxide), and polyacrylamide. It was found that the diffusion coefficient of Direct Blue 76 in carboxymethyl cellulose is higher than that in pure water, while in polyacrylamide and poly(ethylene oxide) solutions the value is lower than that in pure water. The diffusion coefficient of Direct Blue was found to decrease with increasing polymer concentration in case of poly(ethylene oxide) and polyacrylamide, while in case of carboxymethyl cellulose the diffusion coefficient increases with polymer concentration. The effect of temperature on the diffusion coefficient of Direct Blue 76 in the three polymers was found to obey the Arrhenius equation. The activation energy for diffusion of Direct Blue 76 in water, poly(ethylene oxide), polyacrylamide, and carboxymethyl cellulose was found to be 4.38, 7.7, 5.44, and 5 kcal, respectively, for polymer concentration of 0.25 g/l.     

Diffusion coefficients in aqueous solutions of hydrochloric acid at 298 K

Diffusion coefficients of HCl solutions at different concentrations, have been measured at 298 K using a conductimetric cell and the results are discussed on the basis of the Onsager-Fuoss theory. The cell uses the open-ended capillary method, and a conductimetric technique is used to follow the diffusion process by measuring the resistance of a solution inside the capillaries at recorded times.     

Adsorption kinetics of naphthalene onto organo-sepiolite from aqueous solutions

In this study, the adsorption kinetics of naphthalene onto organically modified-sepiolite was investigated by means of the effects of pH, contact time, adsorbent dosage and temperature. The modification of natural sepiolite was accomplished with a cationic surfactant, which is namely dodecyltrimethylammonium (DTMA) bromide. The surface characterization both natural- and modified-sepiolite were carried out by using FTIR method to observe the intercalation of DTMA between the sepiolite layers. The elemental and thermal analyses were also performed to understand the modification. The optimum pH values and the equilibrium contact time for the adsorption of naphthalene onto DTMA–sepiolite were found as 6 and 75 min, respectively. The kinetic parameters of the adsorption process were calculated from experimental data. According to these parameters, adsorption process follows the pseudo-second-order kinetic model with the high correlation coefficients (r² = 0.999). The obtained results show that modified-sepiolite is reasonably effective adsorbent for the removal of organic contaminants, which are an important source for the environmental pollutants.     

Cation exchange removal of copper from aqueous ammonia solutions

Stability constants for copper—ammine species absorbed on sulphonated polystyrene cation-exchange resin have been estimated by the method of Bjerrum. The following values are obtained; log k₁ = 4.5, log k₂ = 3.7, log k₃ = 3.1, log k₄ = 2.5, log k₅ = 1.9. There is evidence that in the resin environment the fifth coordination position on copper(ii) is equivalent to the first four, contrary to the situation in aqueous solution. Ion-exchange column experiments show that ammonia dosing of steam power plant feed-water will not affect the ability of ion-exchange condensate polishing plant to remove copper from the feed-water.     

Absorption of 2-butene and 2-methyl-2-butene in aqueous solutions of sulphuric acid

The kinetics of absorption of 2-butene in aqueous solutions of sulphuric acid was studied in a stirred cell in the range of acid concentration from 70·2 per cent w/w (11·5 g mole/l.) to 80·2 per cent w/w (14·56 g mole/l.). The absorption was found to conform to fast pseudo-first order mechanism. The pseudo-first order reaction rate constant at 28°C was found to vary from about 500 to 3·8 × 10⁶ sec^?1 over the above concentration range.The absorption of 2-methyl-2-butene (isoamylene) in aqueous solutions of sulphuric acid was also found to conform to fast psuedo-first order mechanism, in the range of acid concentration from 61·5 per cent w/w (9·395 g mole/l.) to 75 per cent w/w (12·845 g mole/l.). The pseudo-first order reaction rate constant at 30°C was found to vary from about 4·2 × 10⁵ to 2·2 × 10⁸ sec^?1 over the above concentration range.     

硫酸再生阳离子交换树脂的实践

比较硫酸再生阳离子交换树脂与盐酸再生在酸消耗量、废水排放量及生产成本方面的差异,介绍再生过程的控制要点。通过比较可知,使用硫酸再生成本较低,酸源易得,并且解决了废水中氯离子处理难的问题, 实现了废水的环保排放。     

Investigation of selective leaching and kinetics of copper from malachite ore in aqueous perchloric acid solutions

In this study, the leaching kinetics of malachite in perchloric acid solutions was investigated. The dissolution behaviors of copper, zinc, and iron in the ore matrix were determined at different acid concentrations and reaction temperatures. It was observed that the concentration of perchloric acid had a major effect on the dissolution of copper, zinc, and iron. It was determined that the effect of temperature on the dissolution of these species was not as significant as concentration impact. The results obtained shown that copper in the ore matrix was completely leached while zinc and iron were partially dissolved in perchloric acid solutions. In addition, the effects of the acid concentration, reaction temperature, stirring speed, particle size, and solid-to-liquid ratio on the leaching of malachite were researched. In these experiments, it was observed that the leaching rate of copper increased with increasing solution concentration, stirring speed, and reaction temperature, and with decreasing solid-to-liquid ratio and particle size. A kinetic analysis was performed, and it was found that the rate of leaching reaction obeyed the mixed kinetic control model in the unsteady state. The activation energy of the leaching process was calculated to be 34.69 kJ/mol.     

Dissolution mechanism of colemanite in sulphuric acid solutions

Boron compounds are very important raw materials in many branches of industry and their uses have been increasing and expanding continuously. Colemanite, one of the most common boron minerals, has a monoclinic crystal structure with a chemical formula of 2CaO·3B₂O₃·5H₂O and is used usually in the production of boric acid. The present study concerns and investigation of the dissolution mechanism of colemanite in H₂SO₄ solution and the effect of acid concentration, the effect of SO₄⁻² ion on the dissolution process, using H₂SO₄, HCI+H₂SO₄ and H₂SO₄+Na₂SO₄ solutions. The analysis of the experimental data shows that increasing H₃O⁺ acid concentration increased the dissolution rate, but increasing SO₄⁻² concentration reduced dissolution rate because of the precipitation of a solid film of CaSO₄ and CaSO₄·H₂O.     

Electrochemical removal of gallic acid from aqueous solutions

Removal of gallic acid from aqueous solutions of different concentrations has been performed by electroprecipitation using a sacrificial iron anode, by indirect electrochemical oxidation carried out via electro- and photoelectro-Fenton processes using an oxygen-diffusion cathode, and by a combination of the first two methods (peroxicoagulation process). In all cases, chromatographic analyses have shown a very quick disappearance of gallic acid and its aromatic by-products within 30-90 min of electrolysis, depending on the method. A pseudo first-order kinetic decay of gallic acid was always observed under galvanostatic conditions. A decay of TOC and COD close to 90 and 95% is observed with electroprecipitation and peroxicoagulation processes, respectively, after electrolysis time lower than 2 h. The specific charge utilised in these two processes was about half of that theoretically required for the complete direct oxidation process (mineralisation). During electrolyses some carboxylic acids have been detected as main intermediates, which completely disappear at the end of the process, except oxalic acid in the case of electro-Fenton method.     

Diffusion coefficients in strong aqueous amine solutions

Diffusion coefficients measured with a flowing junction cell and a wavefront shearing interferometer are reported. These coefficients were correlated with respect to solution concentration for three liquid systems: monoethanolamine-water, diethanolamine-water and triethanolamine-water at 25°. Equations from fundamental electrolytic theory were used as a basis for correlation.     

氨基酸在水溶液中的扩散系数

There are still limited experimental data of liquid diffusion coefficients in literature. Therefore, the experimental investigation and prediction model are of practical and theoretical significance. The diffusion coefficients of L-serine, L-threonine, L-arginine, in aqueous solution at 298. 15 K were measured respectively by holographic interferometer. The affecting factors of molecular structure and polarity were analyzed and discussed. Finally, a modified semi-empirical model for correlating the diffusion coefficients of solid organic compounds in aqueous solutions at 298. 15 K was proposed with an adjustable parameter added. The average deviation between model prediction values and experimental ones is less than 0.2%, which shows a considerably satisfactory accuracy.     

Diffusion of some dyes in aqueous polymer solutions

The diffusion of both Direct Blue 76 and acid orange dyes in aqueous dilute polymer solutions was studied using the capillary method. The polymer systems studied included dilute solutions of carboxymethyl cellulose, polyethylene oxide and polyacrylamide. It was found that the diffusion coefficients of the two dyestuffs in carboxymethyl cellulose solutions are higher than that in pure water, while in polyacrylamide solutions the values of the coefficients are lower than that in pure water. In case of polyethylene oxide solutions, the diffusion coefficient of Direct Blue 76 was found to be lower than that in pure water, whereas that of acid orange was found to be higher than that in pure water. The diffusion coefficients of both dyes were found to decrease with increasing polymer concentration in the case of polyethylene oxide and polyacrylamide, whereas in the case of carboxymethyl cellulose the diffusion coefficients increased with polymer concentration. With change of temperature, the diffusion coefficients of both dyes in the three polymer solutions were found to obey the Arrhenius equation. The activation energy for diffusion of the two dyes was calculated in pure water, as well as in the different polymer solutions.