(239f) Solvent Free Sucrose Esters Production in Reactive Systems Containing Emulsifiers
Among biobased surfactants, fatty acid sucrose esters stand out as important additives for the food industry (food ingredient number: E473). These are generally produced by transesterification of sucrose (from sugar cane) with fatty acid methyl esters (from vegetable oils). In addition to their renewable character, sucroesters are high value added, biodegradable and biocompatible surfactants, which can also be used in specialized applications such as cosmetics, clean and care products and pharmaceuticals. Recent estimations (2) indicate that the current market of sucroesters is around than 6000 t/year, with prices around 4 to 20 USD/kg depending on the nature of the product (i.e. lipid chain, degree of substitution, etc).
Sucrose is a polyalcohol with eight hydroxyl groups (See Figure 1), so theoretically, sucrose esters could be monoesters, diesters, triesters, and, so on (up to octaesters). As a result, tuning of reaction selectivity to a specific product is a major challenge. Besides, sucroesters properties and application are heavily determined by the degree of esterification. For example, sucrose monoesters are good water-in-oil emulsifiers, while sucrose octaesters are good oil-in-water emulsifiers. In general, the degree of substitution depends of different process conditions such as temperature, reactants molar ratio, catalyst nature and concentration, and the use of other additives (e. g. solvents, emulsifiers).
In addition to controlling the degree of substitution, a major challenge of the process is the incompatibility between reactants; only 0.1 g of sucrose can be dissolved in 100g of FAME at 140Â°C (3). This reduced solubility limits the mass transfer and reduces the reaction rate and conversion. A processing alternative to overcome this problem is the use of emulsifiers, which enhance contact and solubility of sucrose in FAMEs (4â??7). Some reports indicate that fatty acid soaps (mono- and divalent), sucrose esters (the product itself), and mono- and diacylglycerols can be used as emulsifiers for the reaction. However, it is necessary to study the influence of such emulsifiers (nature and concentration) on the transesterification process (i.e. rate of reaction and esterification degree).
In this work, conversion and selectivity of transesterification reaction to produce sucroesters was experimentally evaluated using three different emulsifiers (potassium palmitate, sucrose palmitate and glyceryl monoester) at different concentrations (up to 20%w). Reactions were carried out in a 150 ml glass-jacketed reactor coupled to a methanol total condenser. The system was homogenized with an UltraturraxÂ® at 15000 rpm prior to reactions, and maintained under agitation at 600 rpm at constant temperature (110-140 Â°C) until no further evolution of methanol was observed. FAMEs consumption and sucroesters production were tracked by HPLC analysis of samples. Observed conversion were around 40% and mono substitution increased with the concentration of the emulsifying agents. Higher conversions were obtained when potassium palmitate was used as emulsifier, and reaction times were shorter when emulsifierâ??s concentration was increased. Degree of substitution of the final product was higher when a mixture mono- and diacylglycerols was used as emulsifier and lower when sucrose palmitate was used. Results of this study can be used for preliminary process design in a solvent-free production of sucrose esters with different emulsifying properties.
Figure 1. Emulsifiers used to provide contact in sucrose and fatty methyl estermixtures (Molecular structures taken from ChemSpider)
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