This paper deals with the development of a mathematical model for emulsion copolymerization of styrene and butyl acrylate carried out in the presence of n-dodecyl mercaptan as chain transfer agent (CTA). The model consisted of a system of differential algebraic equations in which the population balances is based on a new approach that reduces significantly the number of equations involved and the corresponding computational time. Most of the unknown kinetic and thermodynamic parameters of the model were estimated from experimental measurements using a stochastic optimization method based on a genetic algorithm. The results showed a fairly good agreement between model predictions and experiments. The model was then successfully validated through additional experiments carried out in batch and fedbatch reactors and clearly showed that the model was able to predict the time-evolution of overall conversion, amounts of each residual monomer, number and weight average molecular weights of the resulting copolymers and average diameters of the corresponding latex particles for different operating conditions, mainly CTA concentration and reaction temperature. The model was finally used to investigate and confirm the effects of CTA concentration, previously observed by several authors, on the kinetics of this polymerization process and on the main properties of the resulting macromolecules and latex particles.

International audienceBACKGROUND: The aim of this study was to assess the feasibility of coupling photocatalysis and a biological treatment for the removal of azo dyes from aqueous effluents. Biological processes do not always appear relevant for dyes removal, owing to the low or total absence of biodegradability of this class of pollutants. RESULTS: During photocatalysis pre-treatment, a decrease in the chemical oxygen demand (COD) indicated oxidation of the target compound and thus a change in the chemical structure; better biodegradability or less toxicity could then be expected. However, the concomitant decrease in dissolved organic carbon (DOC), characteristic of a high mineralization yield, led to nearly constant COD:DOC ratios, which was unfavorable for an increase in biodegradability. It was confirmed by the low values found for the ratios biological oxygen demand (BOD5) to COD, which remained in the range 0.09-0.19, namely below 0.4 after photocatalytic reaction. Moreover, toxicity increased or remained at a high level after irradiation of the azo dyes for 3 h, and decreased only for Orange II, from toxic (EC50 = 53%) to moderately toxic (EC50 = 76%). CONCLUSION: An integrated process involving photocataysis and biological treatment to treat azo dyes appeared unsuitable under the conditions tested and may only be considered for Orange II among the four dyes tested. Copyright © 2010 Society of Chemical Industr

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A B S T R A C TThe removal of Congo red dye (CR) from aqueous solutions using a novel low-cost biological adsorbent, Stipa tenassicima fibers, has been investigated in this paper. Batch experiments were conducted to examine the effect of the main parameters, such as the initial CR concentration, the pH, and the temperature on the sorption of the dye. Maximum adsorption removal was observed at pH 4 and biosorption capacity of S. tenassicima was enhanced by increasing the temperature. Rate constants of pseudo-first order, pseudo-second order, and intraparticle diffusion coefficient were calculated to analyze the dynamic of the sorption process; they showed that sorption kinetics followed an intraparticle diffusion model, while the two straight lines describing experimental data indicated that intraparticle diffusion was the limiting step for biosorption. Among the tested isotherm models, the Sips isotherm was found to be the most relevant to describe CR sorption onto S. tenassicima fibers. Thermodynamic parameters, such as changes in standard free energy, enthalpy, and entropy, were also evaluated and the results suggested that the sorption reaction was spontaneous and endothermic in nature. The potential of S. tenassicima fibers, an easily available and low-cost material, to be used as an alternative biosorbent material for the removal of a dye, CR, from aqueous solutions was therefore confirmed.