(376br) Methyl Palmitate Separation from the Reaction Mixture of the Solvent-Free Transesterification to Produce Sucrose Esters

Sucrose esters are biobased emulsifiers used in high value niche markets such as cosmetics and food [1]. They are commonly produced by transesterification of sucrose and fatty acid methyl esters (FAMEs). With the aim of improve reactants incompatibility and avoid the use of toxic solvents, a solvent-free process using emulsifiers as contacting agents has been developed [2]. However, this reaction system is characterized by incomplete conversions so that the remaining reactants should be separated from the final product and recovered for recycling. However, the purification of product streams is a complex task owing to the complexity of the reactive mixture.

Different purification processes to obtain commercial sucrose ester have been reported [3–8]. Mainly, an organic non-polar solvent is used to extract residual FAMEs. Then, water or other polar solvent is used to wash the precipitated sucrose esters and to separate them from residual sucrose and catalyst. The effectiveness of this recovery process is highly dependent of the selectivity of the organic solvent for the FAMEs, its ability to enhance the color of the product, and how easily it can be removed and recycled. In the open literature there is lack on information regarding the impact of these key parameters in the process, which are required for further modeling and design of the separation process.

This work systematically studied the separation and recovery of methyl palmitate from a solvent-free sucroester production media, using different solvents. The solvents were selected among those included in the “Green Solvents Guide Selection” developed by Glaxo Smith & Kline. From this list, a screening was done using the Hansen Solubility Parameters to choose the solvents with highest affinity for the methyl ester. The resulting list was assessed considering the price, normal boiling point and solvent availability. The three chosen solvents were ethyl acetate, iso-amyl acetate and methyl isobutyl ketone. The separation performance of each solvent was evaluated by doing solid-liquid extractions using a specific solvent/solid mass ratio. After proper contact between the solvent and the solid sucroester mixture, the remaining solids were separated from the solvent by centrifugation. Quantification of FAME was done by high performance liquid chromatography (HPLC). The remaining solids were mixed with water, citric acid, sucrose and sodium chloride to precipitate the sucrose esters. Humid sucrose esters were dried in a vacuum oven at 50°C. Additionally, the recovery of the methyl palmitate extracted was performed by evaporation of the organic solvent. The yield of the recovery of the methyl palmitate and the organic solvent was calculated from the overall mass balance.

According to results ethyl acetate exhibited the best performance, in terms of FAME recovery, color enhancement, and solvent recovery straightforwardness. Then, further separation experiments were carried out with the selected solvent, under different separation temperature (5, 20 y 35°C), mass ratio of solvent to solids (2, 3, 4 and 6) and number of extraction stages (1, 2 and 3). The optimum operation conditions during the extraction process were identified, and the conceptual design of the separation process was done. Results of this work will be used in a further process design for solvent-free sucroester production.

References

[1] B.A.P. Nelen, J.M. Cooper, Sucrose esters, in: R.J. Whitehurst (Ed.), Emuls. Food Technol., Backwell Publishing Ltd, 2004: pp. 131–162.

[2] J. Fitremann, Y. Queneau, J. Maitre, A. Bouchu, Co-melting of solid sucrose and multivalent cation soaps for solvent-free synthesis of sucrose esters, Tetrahedron Lett. 48 (2007) 4111–4114. doi:10.1016/j.tetlet.2007.04.015.

[3] K. James, Purification of Sucrose Esters, US 4104464, 1978.

[4] S. Kea, C.E. Walker, Separation and purification of sugar esters synthesized from both aqueous and nonaqueous systems, US 4710567, 1987.

[5] S. Matsumoto, Y. Hatakawa, A. Nakajima, Process for purifying sucrose fatty acid esters, US 5008387, 1991.

[6] S. Matsumoto, Y. Hatakawa, A. Nakajima, Process for recovering unreacted sucrose from reaction mixture synthesis of sucrose fatty acid esters, US 4995911, 1991.

[7] S. Matsumoto, Y. Hatakawa, A. Nakajima, Method of producing powdery high hlb sugar fatty acid ester, 5144022, 1992.

[8] Y. Koyama, N. Kawase, H. Yamamoto, S. Kawata, Y. Kasori, Process for producing sucrose fatty acid ester, EP 0659760A2, 1994.