(540b) Equilibrium Data Determination for Sucrose Esters Separation

Sucrose esters are biobased emulsifiers used in high value niche markets such as cosmetics and food [1]. They are produced via basic or enzymatic transesterification of sucrose and fatty acid methyl esters. With the aim of improve reactants incompatibility, traditional production processes use a large quantity of solvents (near 60%wt of reactive media) as Dimethyl Sulfoxide and Dimethyl Formamide [2]. The use of these regulated solvents in the reaction process obligates an exhaustive downstream separation process to fulfill the product specifications. The energy intensive solvent removal process is unavoidable because solvent in the product must be in the traces level [3]. For this reason, a solvent-free process using emulsifiers would be preferred [4]. Regardless the process, the sucrose ester purification is a complex task owing to the complexity of the reactive mixture.

Different purification processes to obtain commercial sucrose ester have been proposed [5–10]. Mainly, an organic solvent (non-polar) is used to extract residual fatty acid methyl esters (and the solvent if used). Then water or other solvent (polar) is used to wash the precipitated sucrose esters and to separate them from residual sucrose and catalyst. Despite this downstream processing has been described in the literature, there is a lack of information regarding the phase equilibrium of the process. This data are required for further modeling and design of the separation process.

In this work, the downstream purification of sucrose esters produced by a solvent-free reaction was studied. Taking into account that the main goal of the solvent-free process is to reduce de use of toxic solvents in the process, green solvents were selected as extracting agents in the product purification. The phase equilibria in mixtures of ethyl acetate, methyl palmitate and sucrose palmitate; and water, sucrose and sucrose palmitate have been evaluated. The solid-liquid equilibria of both systems were evaluated at different temperatures (between 5 and 30°C), and the characterization of samples was performed by HPLC method. In both cases, sucrose palmitate was a mixture of sucrose esters with different degree of substitution, so that selectivity of sucrose esters towards the extracting solvent was also evaluated. This is important since it will determine separations yields and esterification degree of final product. Obtained data was used to evaluate performance of different thermodynamic predictive methods. Results may be used in the design and optimization of purification operations for sucroesters purification.

 References

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[3] L.I. Osipow, W. Rosenblatt, S. Valley, Esterification of polyhydric compounds in the presence of transparent emulsifying agent, 3480616, 1969.

[4] 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.

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

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

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

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

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

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