G. Arzamendi

Seeded semibatch emulsion polymerization of butyl acrylate : Effect of the chain-transfer agent on the kinetics and structural properties

The effect of dodecane-1-thiol on the kinetics, gel fraction, level of branches, and sol molecular weight distribution of the seeded semibatch emulsion polymerization of n-butyl acrylate carried out at 75 °C was investigated. The gel fraction was strongly affected by the content of the chain-transfer agent (CTA). The sol weight-average molecular weights decreased with increasing CTA concentration, whereas no effect on the kinetics and the level of branches was observed. The experimental data were analyzed with a mathematical model of the process that was able to catch fairly well the effect of the process variable. In addition, adhesive tests were carried out to check the effect of the gel fraction on the adhesive properties.

Multiple response optimization of vegetable oils fatty acid composition to improve biodiesel physical properties.

The effect of fatty acids chain length (LC) and its interaction with unsaturation degree (UD) on important biodiesel quality parameters was studied. Low calorific value, kinematic viscosity, flash point, cetane number and cold filter plugging point of biodiesel blends covering a wide range of fatty acids were analyzed. Analytical results were processed with statistical regression to obtain a prediction model for each property, combining LC and UD. Due to the antagonistic effects of the chemical composition over quality properties, the Derringer desirability function was proposed to allow the most suitable fatty acid composition. This target was achieved considering an average of 1.26 double bounds and 17 carbon atoms. A set of combinations of LC and UD values that provides a biodiesel that fits the European standard EN 14214 was proposed. It was found that a reduction of FAME LC allows a lower UD while keeping biodiesel specifications under the standard limits.

Dynamic optimization of semicontinuous emulsion copolymerization reactions: composition and molecular weight distribution

Abstract Iterative dynamic programming (IDP) is used to compute optimal monomer and chain transfer agent feed profiles to produce polymer with specified copolymer composition and molecular weight distribution. The approach used allows the implementation of constrained optimization procedures for systems described by complex mathematical models, as those needed for proper description of emulsion copolymerization reactors, especially when the computation of the whole molecular weight distribution is desired. The proposed approach is applied to the semicontinuous methyl methacrylate (MMA)/butyl acrylate (BuA) emulsion copolymerization in stirred tank reactors, using dodecanethiol as chain transfer agent (CTA). It is shown that this technique allows the effective computation of feed policies for the production of copolymers with constant composition and well-defined molecular weight distributions.

Dynamic optimization of non-linear emulsion copolymerization systems: Open-loop control of composition and molecular weight distribution

Time optimal monomer and chain-transfer agent feed profiles were computed and implemented experimentally for the simultaneous control of copolymer composition and molecular weight distribution in non-linear emulsion copolymerization systems. Iterative dynamic programming was used for the off-line calculation of the optimal feed policies. This approach can deal with constrained optimization of systems described by complex mathematical models, as those needed for the emulsion copolymerization kinetics, especially when the computation of the whole molecular weight distribution is included. The proposed approach was applied to the semibatch methylmethacrylate (MMA)/n-butylacrylate (n-BA) emulsion copolymerization, using n-dodecanethiol as chain-transfer agent, and allowed the production of copolymers with constant composition and with well-defined molecular weight distributions.

Influence of vegetable oils fatty acid composition on reaction temperature and glycerides conversion to biodiesel during transesterification.

Presence of unreacted glycerides in biodiesel may reduce drastically its quality. This is why conversion of raw material in biodiesel through transesterification needs to readjust reaction parameter values to complete. In the present work, monitoring of glycerides transformation in biodiesel during the transesterification of vegetable oils was carried out. To check the influence of the chemical composition on glycerides conversion, selected vegetable oils covered a wide range of fatty acid composition. Reactions were carried out under alkali-transesterification in the presence of methanol. In addition, a multiple regression model was proposed. Results showed that kinetics depends on chemical and physical properties of the oils. It was found that the optimal reaction temperature depends on both length and unsaturation degree of vegetable oils fatty acid chains. Vegetable oils with higher degree of unsaturation exhibit faster monoglycerides conversion to biodiesel. It can be concluded that fatty acid composition influences reaction parameters and glycerides conversion, hence biodiesel yield and economic viability.

Molecular weight distribution in composition controlled emulsion copolymerization

The effect of different strategies for copolymer composition control on the molecular weight distribution (MWD) and gel fraction in the emulsion copolymerization of methyl methacrylate and butyl acrylate was investigated. Starved and semistarved processes for copolymer composition control were both considered. For gel-forming systems it was found that the starved process gave more gel and lower molecular weights than the semistarved process. The feasibility of simultaneous control of the copolymer composition and the MWD was assessed.

Dynamic optimization of semicontinuous emulsion copolymerization reactions: Composition and molecular weight distribution

Iterative dynamic programming is used to compute optimal monomer and CTA feed profiles to produce polymer with pre-specified copolymer composition and MWD. This approach can deal with constrained optimizations of systems described by complex mathematical models, as those needed for the emulsion copolymerization kinetics, especially when the computation of the whole MWD is included. The proposed approach is applied to the semicontinuous MMA/BuA emulsion copolymerization, using dodecanethiol as CTA, allowing the effective computation of feed policies for the production of constant composition copolymer with well-defined MWDs.

Modeling of MWD in Emulsion Polymerization: Partial Distinction Approach

ABSTRACTA mathematical model for the calculation of the MWD in emulsion polymers is presented. The model is based on an intermediate level of description of the system, and hence is computationally more efficient than the existing detailed models, while its predictions are as accurate as those of the detailed models. The importance of the compartmentalization was assessed to determine the conditions in which there is a need to account for the compartmentalization. It was found that under many practical conditions, the predictions of models even simpler than that developed in this work are accurate enough. Only for highly compartmentalized systems, under conditions in which 0.5<n<0.7, with a strict control of the operation variables and very good GPC analysis, the differences between the models would be greater than the experimental variability. The feasibility of the on-line estimation of the MWD in seeded systems was studied. It was found that an accurate, robust and quick prediction of the MWD in seeded...

Kinetics of the seeded semicontinuous emulsion copolymerization of methyl methacrylate and butyl acrylate

The effect of a chain-transfer agent (CTA) on the kinetics and molecular weight distribution of the methyl methacrylate/butyl acrylate semicontinuous emulsion polymerization was investigated. The dodecanethiol had a slight effect on the reaction rate but significantly affected the secondary nucleation. The effect of the CTA concentration on the gel formation and the effect of the reaction conditions on the mass-transfer limitations of the CTA are discussed.

Hydrotalcites as Catalysts and Catalysts Precursors for the Synthesis of Biodiesel

This chapter aims at providing an overview of the potential of layered double hydroxides (LDHs) or hydrotalcite-like compounds (HTs) for contributing to the catalysis of the synthesis of biodiesel through the transesterification of triglycerides. First, the main methods of preparation of HTs and the most relevantfeatures of these materials are presented, with emphasis on their basic properties. Afterwards, the literature on the use of HTs as catalysts, catalysts precursors, and supports of transesterification catalysts is reviewed. HTs are promising materials for the synthesis of biodiesel from refined and waste vegetable oils, showing reasonable resistance to water and free fatty acids but an improvement of the chemical stability under the desired reaction conditions is still necessary.