(582ap) Study on the Influence of Particle Size Distribution on the Solid-Liquid Reaction to Produce Sucrose Ester
Sucrose esters are produced by basic transesterification of sucrose and fatty acid methyl esters (FAMEs) at temperatures between 90 and 180°C, and under vacuum conditions to remove the produced methanol. A main challenge of this reaction is to deal with reactants incompatibility: sucrose is highly polar solid, and FAMEs are highly non-polar liquids. Consequently, solubility of sucrose in FAMEs is very low, nearly 0.1 g of sucrose per 100g of FAME at 140°C . This reduced solubility limits mass transfer to the reactive media, reducing reaction rate and conversion.
One of the processing alternatives proposed to overcome reactants incompatibility is the use of emulsifiers to provide contact and enhance solubility of sucrose in FAME [3â6]. Main emulsifiers used are fatty acid soaps (mono- and divalent), sucrose esters (product itself), mono- and diacylglycerols. However, in this heterogeneous reaction, solid-solid-liquid interfaces are present between catalyst (usually K2CO3), sucrose and FAMEs, respectively. In this kind of reactions, particle size distribution of solid species become a major variable o the process. Reaction to produce sucrose esters should be operated at sufficient small particles to ensure that the reaction is not mass transfer limited by diffusion effects .
In this work, transesterification reaction to produce sucrose ester was performed using different particle size of sucrose and catalyst (between 30 and 1000 Î¼m) at 120 and 140Â°C. Sucrose and catalyst were grinded in a ball mill and then sieved to determine their particle size distribution. Reactions were carried out in batch reactors of 100ml of volume using potassium palmitate as emulsifier (5%wt) and K2CO3 as catalyst (5%wt). Initial sucrose/FAMEs molar ratio was 2.5. For quantification of FAME consumed and sucrose esters produced, high performance liquid chromatography (HPLC) was used. The effect of particle size distribution on the reaction productivity and the reaction rate were evaluated. Results showed that below a certain particle size of sucrose and catalyst, productivity and reaction rates achieves an optimal value. Experimental data were used to construct a kinetic model for sucroester production including the effect of particle size distribution sucrose ester production.
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