This work deals with the determination of kinetic models for the esterification of citric acid with ethanol for the synthesis of triethyl citrate. Methanesulfonic acid (MSA) and an ion-exchange resin Amberlyst 70 (A70) were used as catalysts. Experiments were carried out under batch operation at temperatures between 345 and 393 K and at different initial reactant concentrations and catalyst loadings. The evolution of concentrations along the reaction was tracked by liquid chromatography. The proposed model corresponds to an activity-based kinetic expression, and the activity coefficients were calculated with UNIQUAC equation. The adjustment of the corresponding kinetic parameters for each catalyst was done with a genetic algorithm by minimization of the squared differences between experiments and model predictions. The obtained models exhibited good agreement with experiments and can be used for further process development. MSA exhibited around 10 times the activity of A70 under similar conditions. In the case of A70, this catalyst has not only higher temperature stability but also showed higher activity than previously reported Amberlyst 15. Both studied catalysts seem feasible alternatives for the implementation of homogenously or heterogeneously catalyzed reactive distillation processes for triethyl citrate production.
One of the most important physiological disorders of red rose cultivars is blackening of petals, it affects outer and inner ones and results in flowers of poor quality. The goal of this review is to make an approach to the blackening disorder, determining the main possible causes in order to make available to growers, academics, scientifics as well as stakeholders, the inputs that allows to unveil its origin and to optimize its handling. Symptoms of blackening are showed especially when the flowers have been harvested and stored under cold room conditions; due to high accumulation of pigments, such as anthocyanins, also could be due to stress conditions, such as high or low UV radiation, low temperatures or a nutrient imbalance in the affected tissues.The following subjects will be treated: i) calcium and boron and their interaction, ii) calcium and physiological disorders, iii) pigments involved in the petals red color, iv) role of the phenolic compounds, particularly the anthocyanins, which are responsible for most of the red, pink, purple and blue colors observed in plant parts; as well as the environmental factors that can influence the blackening on red rose.
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