(560at) Influence of the Stirring System in the Scaled-up Transesterification to Produce Sucrose Esters Using a Solvent-Free Mixture
Sucrose and methyl ester incompatibility is generally faced with the use of solvents (dimethylsulfoxide, (DMSO) or dimethylformamide (DMF)), in which both reactants are soluble [2,3]. However, the required solvent loading to assure complete solubility is around 60%wt of reaction mixture, so the reaction productivity is reduced. In addition, it is necessary to do an exhaustive solvent removal owing to the health concerns of DMF and DMSO, taking into account their final (cosmetics, food, pharmaceutics) [1,2,4].
An alternative process to overcome the reactants incompatibility is the use of emulsifiers as contact agents in a solvent-free process [5â8]. The solvent-free transesterification is a heterogeneous reaction affected by mass transfer limitations. Our last studies have been focused on determining the optimal particle sizes (of sucrose and catalyst), temperature, reactants ratio, catalyst concentration and contact agent (emulsifier) concentration to maximize the performance of the reaction. All experiments done before were carried out at lab scale (100mL reactor) were proper suspension of the solids was ensured. However, mass transfer effects on the reaction performance at a larger scale have never been assessed.
In this work, results of previous works were used to scale-up the reactor to carry out the solvent-free transesterification to produce sucrose ester. Two reactor configurations with different stirring configurations to reduce mass and heat transfer limitations were used; one 10 L reactor with a rotor-stator stirrer and with an anchor stirrer, and another 10L reactor with anchor stirrer only. In addition, the reactor was coupled to a falling film evaporator to improve the methanol removal from the mixture. The reaction mixture was pumped from the reactor to the evaporator and back in a closed loop. All the equipment could operate under vacuum conditions, and they were jacketed allowing to operate under controlled temperature (up to 160Â°C).
In the pilot scale experiments, the size of the solids was reduced to the optimal values obtained in the lab scale experiments. For this, sucrose was previously grinded in a ball mill and the obtained solid were sieved to determine the particle size distribution (average 100 Î¼m). The size reduction of the catalyst (K2CO3) until 10 Î¼m was performed with the rotor-stator mixer, as in the laboratory scale experiments. Experiments were carried out in order to evaluate the mass transfer effects in the up-scaled reactor. Sodium stearate was used as contact agent at the optimal concentration observed at the lab scale. Initial sucrose/FAMEs molar ratio was fixed in 0.5. The pressure of the system was varied to ensure that the methanol removal was not limiting the reaction conversion. For the quantification of the converted FAME and the produced sucrose esters, high performance liquid chromatography (HPLC) was used. Effect on reaction productivity and reaction rate was evaluated and compared with the laboratory scale results. Moreover, the homogeneity of the suspension was evaluated by taking samples of different places of the equipment and evaluating the concentration of the liquids and the particle size distribution of the solids. Results showed that the reactor using both stirring systems was better in enhancing the performance of the reaction by avoiding the heat and mass transfer limitations in the up-scaled reactor. Results of this work will be used in a further process design and for preliminary economical evaluation of the process.
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