(582ap) Study on the Influence of Particle Size Distribution on the Solid-Liquid Reaction to Produce Sucrose Ester

Biobased surfactants are chemicals produced from renewable raw materials, which reduces environmental impact compared with traditional petroleum based surfactants. Fatty acid sucrose esters (emulsifier food ingredient E473) is a value added entirely biobased surfactant used in niche applications such as food, cosmetics and pharmaceuticals. These are produced from sucrose and fatty acid methyl esters, and they have interesting properties as green chemical such as rapid biodegradability, biocompatibility, and biocide potential for certain microorganisms [1]

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 [2]. 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 [3–6]. 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 [7].

In this work, transesterification reaction to produce sucrose ester was performed using different particle size of sucrose and catalyst (between 30 and 1000 μm) at 120 and 140°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.

References

[1] N. Otomo, Basic properties of sucrose fatty acid esters and their applications, in: D.G. Hayes, D. Kitamoto, D.K.Y. Solaiman, R.D. Ashby (Eds.), Biobased Surfactants Deterg., AOCS Press, Urbana, Illinois, 2009.

[2] R. Zhao, Z. Chang, Q. Jin, W. Li, B. Dong, X. Miao, Heterogeneous base catalytic transesterification synthesis of sucrose ester and parallel reaction control, Int. J. Food Sci. Technol. 49 (2014) 854–860. doi:10.1111/ijfs.12376.

[3] K.J. Parker, K. James, J. Hurford, Sucrose Ester Surfactants — A Solventless Process and the Products Thereof, in: J.L. Hickson (Ed.), Sucrochemistry, American Chemical Society, Washington, DC, 1977: pp. 97–114.

[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] H.R. Galleymore, K. James, H.F. Jones, C.L. Bhardwaj, Process for the production of a surfactant containing sucrose esters, 4298730, 1981.

[6] G.P. Rizzi, H.M. Taylor, Synthesis of higher polyol fatty acid polyesters, 3963699, 1976.

[7] H.S. Fogler, Elements of Chemical Reaction Engineering, 4th. ed., Pearson Education Inc., 2006.