Kinetics of the transesterification of methyl palmitate and sucrose using surfactants

Abstract

This work studied the synthesis of sucroesters via transesterification of sucrose and methyl palmitate in a solvent-free process. The kinetic experiments were carried out under slight vacuum (80 kPa) to ensure an irreversible reaction, with K2CO3 as catalyst, and using a variety of surfactants (potassium palmitate, sucrose palmitate and glyceryl monostearate) with different Hydrophilic-Lipophilic Balance (HLB) as contacting agents. Reaction samples were analyzed with a novel isocratic HPLC method using a refraction index detector. The kinetic effects of temperature (369–409 K) and surfactant type and concentration (5–15%wt) were assessed. Results revealed that the reaction exhibited a lag period, consistent with a limiting sucrose activation step, followed by faster transesterification to monoester. Also, the different substitution steps on the sucrose backbone showed strong temperature dependence, and the corresponding large energies of activation. According to the product distribution, the reaction proceeded mostly to mono, di and tri substituted sucroesters. Particularly, potassium palmitate exhibited synergic contact-enhancing and catalytic effects, delivering a sucrose ester productivity of 55 g SE/h kg and a selectivity to monoesters in the range of 52–67%. It was observed that high HLB surfactants promoted a higher selectivity for monosubstituted sucroesters. The reaction kinetics was modeled as a set of steps involving sucrose activation, monoester formation, and lumped oligoester synthesis. The kinetic parameters were regressed for each surfactant, and the model showed good agreement with experiments. Obtained models can be used for further process analysis and design.