Models of Hypochlorite production in electrochemical reactors with plate and porous anodes

Pseudo two-dimensional finite element models were developed to predict the hypochlorite (chloric(I)) (HOCl + OCl⁻) production by electrolysis of near-neutral aqueous sodium chloride solution, in reactors with (a) an anode and cathode in the form of plates, and (b) a lead dioxide-coated graphite felt anode and titanium plate cathode. The model was used to investigate the feasibility of using a porous anode to achieve high single pass conversions in oxidising chloride ions. For the model reactor with planar anode, the effects of diffusion, migration and convection on the mass transport of the reacting species were considered, whereas with the porous anode, a supporting electrolyte (Na₂SO₄) was notionally present to eliminate the migrational contribution to reactant transport. For an electrolyte flow rate of 10⁻⁶ m³ s⁻¹ (Re = 10 for plate electrodes, Re _porous = 0.76 for porous anode), a cell voltage of 3.0 V and an inlet NaCl of 100 mol m⁻³, the single-pass conversion of Cl⁻ was predicted to increase from 0.45 for the reactor with a planar anode to 0.81 for the reactor with a porous anode. For the same operating conditions, the overall current efficiency was also predicted to increase from 0.71 to 0.77 by replacing the plate with the porous anode.     

A method of ranking the aggressive nature of chloride contaminated concrete

In this work, previously reported titration data obtained on cement pastes and concretes are analysed. It is postulated that the inhibitive nature of concretes may be quantified by titrating a ground suspension to the endpoint indicated by phenolphthalein while the aggressive chloride content may be determined from the soluble chloride at the endpoint of this titration. Thus, the aggressive nature of chloride contaminated concrete may be ranked using the ratio of the extracted chloride to acid neutralisation capacity. Not only is there a theoretical justification for this, but it is relatively simple to determine.     

Modelling of anodic dissolution of pure aluminium in sodium chloride

A mathematical model for simulating a passive aluminium (Al) surface with a pit in which active electrochemical metal dissolution occurs has been developed. The model includes hydrolysis products of Al and the species obtained as a result of homogeneous reactions between chloride and Al³⁺ ions and Al hydrolysis products. The model does not assume the equilibrium state in solution: all terms in homogeneous reactions are treated explicitly using kinetic constants taken from the literature. The validity of assuming reaction equilibrium has been addressed. Solution potential values and species concentrations are predicted for different dissolution current densities. The acidity in the pit is explained by the hydrolysis of Al³⁺; an analytical expression for the pH values at the pit bottom for a given dissolution current density is presented.The model is applied to a real capillary geometry used in electrochemical microcell experiments. It was found that for r_cap/r_pit < 100, where r_cap and r_pit are the capillary end and pit radii, respectively, the insulating capillary wall affects the species concentrations and the solution potential. Moreover, for r_cap/r_pit < 20, the shape of the capillary, which might not be cylindrical, should be taken into account.     

Modeling of chloride diffusivity coupled with non-linear binding capacity in sound and cracked concrete

The objective of this research is to establish a model that can predict chloride transport phenomena in sound and cracked concrete. The chloride diffusivity is formulated based on computed micro-pore structure, which considers tortuosity and constrictivity of porous network as reduction factors in terms of complex micro-pore structure and electric interaction of chloride ions and pore wall. In the real environment, concrete structures are not always crack-free, therefore chloride transport in cracked concrete is also simulated by section large void spaces in a control volume to represent the crack and by proposing a model of chloride diffusivity through the cracked region The proposed models are implemented into a finite-element computational program DuCOM, which simulates the early-age development process of cementitious materials. The calculated concentration profiles of total chloride ions are verified through a comparison with experiments results.     

Esterification of lauric acid with isopropyl alcohol by tricaprylylmethylammonium chloride as a catalyst in a liquid-liquid heterogeneous system

Experiments were performed on the esterification of lauric acid with isopropyl alcohol by tricaprylylmethylammonium chloride in a stirred vessel with a flat liquid-liquid interface. The observed initial rate of reaction was used to analyze the reaction mechanism combined with the catalyst, and to evaluate the several kinds of reaction rate constant, from which equilibrium constants were expressed as a function of reaction temperature. The analysis of reaction kinetics indicated that the reaction was between a very slow and slow reaction regime.     

The importance of SO2 and SO3 for sulphation of gaseous KCl - An experimental investigation in a biomass fired CFB boiler

This paper is based on results obtained during co-combustion of wood pellets and straw in a 12 MW circulating fluidised bed (CFB) boiler. Elemental sulphur (S) and ammonium sulphate ((NH₄)₂SO₄) were used as additives to convert the alkali chlorides (mainly KCl) to less corrosive alkali sulphates. Their performance was then evaluated using several measurement tools including, IACM (on-line measurements of gaseous alkali chlorides), a low-pressure impactor (particle size distribution and chemical composition of extracted fly ash particles), and deposit probes (chemical composition in deposits collected). The importance of the presence of either SO₂ or SO₃ for gas phase sulphation of KCl is also discussed. Ammonium sulphate performed significantly better than elemental sulphur. A more efficient sulphation of gaseous KCl was achieved with (NH₄)₂SO₄ even when the S/Cl molar ratio was less than half compared to sulphur. Thus the presence of gaseous SO₃ is of greater importance than that of SO₂ for the sulphation of gaseous KCl.     

聚合氯化铝的电化学制备及其凝聚作用

在论述聚合氯化铝的制备方法基础上，研究了它的电化学制备方法，讨论了制备原理；对制备的聚合氯化铝进行了性质分析并进行凝聚作用试验。结果表明，经电化学法制备的聚合氯化铝性能优良，凝聚作用显著，这一种制备方法很有应用价值。     

Approximate migration coefficient of percolated interfacial transition zone by using the accelerated chloride migration test

In this study, the electrochemical technique is applied to accelerate chloride ion migration in cement-based material to estimate its migration coefficient. In order to investigate the chloride migration coefficient of percolated interfacial transition zone (ITZ) on the chloride migration coefficient of specimen, specimens with cylindrical aggregates of the same height as the specimen were cast and tested. In this study, the volume fraction of aggregate is constant and the varied lateral surface area of the aggregate cylinder was obtained by using different diameters and number of aggregate. The chloride migration coefficient of cement-based material was determined experimentally as a function of the lateral surface area of aggregate. A model obtained for the migration coefficient of cement-based material and the regression analysis are used to determine the approximate chloride migration coefficient of the percolated ITZ. Based on the experimental and regression analytical results, the approximate percolated ITZ migration coefficient is 40.6, 35.5, and 37.8 times of the altered migration coefficient of matrix mortar for the water/cement (w/c) ratio of 0.35, 0.45, and 0.55, respectively.     

Influence of the alkyl chain length of HSO3-R-MCM-41 on the esterification of glycerol with fatty acids

Ordered mesoporous materials functionalized with alkyl sulfonic acid groups have been proved to be efficient catalysts for esterification. In this paper we report on the synthesis and characterization of new materials containing simultaneously alkyl groups (vinyl, chloromethyl), that have been sulfonated in a post-synthesis step, and methyl groups. Different techniques have been used to characterize the obtained materials: XRD, TEM, elemental analysis, nitrogen adsorption, TGA, ²⁹Si and ¹³C MAS NMR. Finally, the influence of the different synthesis parameters and functional groups on the behavior of the catalysts in the reaction of esterification of glycerol with lauric and oleic acids has been studied. The catalytic performance of the resulting HSO₃-ethyl-MCM-41, HSO₃-ethyl/methyl-MCM-41 and HSO₃-methyl-MCM-41 new materials is also compared to those of HSO₃-phenyl/methyl-MCM-41 and HSO₃-propyl/methyl-MCM-41 synthesized previously. It has been demonstrated that an optimum balance among parameters such as nature of the organic group which support the sulfonic acid, distance between the sulfonic group and the silica surface, average pore size of the material, etc., allows to obtain catalysts with improved activity and selectivity for these reactions.