(335d) Fructose Solubility in Water and Ethanol/Water (poster)

Fructose (C₆H₁₂O₆), also referred to as fruit sugar, is a monosaccharide widely used in sweeteners. It is a sugar of great industrial interest and it can be found in supermarkets and pharmacies. Since it's healthy, fructose is used in an extensive diversity of foods. The increase in the necessity of fructose in the past years has involved significant work in the field of preparing this monosaccharide through simple crystallization from aqueous solutions by cooling and anti-solvent addition to obtain a high purity product (MARTINEZ, 2007). This sugar presents high solubility in water, which explains why a saturated solution is highly viscous. On the other hand, a ternary solution (fructose/ethanol/water) is much less viscous, since fructose is little soluble or almost insoluble in ethanol, which decreases its solubility in the solution. The main objective of this study is to determine the solubility to obtain the optimum condition of yields and temperature for a future crystallization process, recovering the crystalline fructose in the solution. In this work, fructose solubility in aqueous solution under a temperature scale of 25 and 55°C, and solubility of the fructose/ethanol/water ternary system under temperatures between 30 and 60°C were studied. The solubility curves of fructose in aqueous solution and in ethanol/water solution were experimentally obtained and were compared to literature data. The experiments were performed in a 200 mL jacketed glass reactor attached to a thermostatic bath (to control temperature), under constant agitation performed by a propeller type agitator connected to a controller (Figure 1). The procedure used to obtain fructose solubility in water was based on the Nývlt polythermal method in which a certain mass of fructose was added to the reactor in 10g of distilled water, and the system temperature was gradually increased by 0,1 ºC until complete dissolution. The temperature in which the fructose was completely dissolved after heating was written down. When it comes to the ternary diagram, it was verified on literature and through previous tests that fructose was practically insoluble in ethanol. Therefore, the solubility of fructose in an ethanol/water mixture was chosen to be evaluated. The solubility data for temperatures from 30 to 60ºC were acquired, and the respective viscosities were measured for that mixture. The experimental data obtained for the fructose water solubility trials were plotted on Figure 2, with literature data. When both data are compared, a small deviation between them can be observed. It can be examined through the ternary diagram (Figure 3) that the greater the amount of ethanol in solution the lesser the fructose solubility. For example, by analyzing two points in the same temperature (60ºC) curve (Table 1), a solution of 1% ethanol and 88% dissolved fructose is observed, whereas for a 58% ethanol solution only 35% of the fructose is dissolved considering a fixed mass of water. The experimental data obtained for the ternary diagram were very similar to those found in literature. In addition to the solubility curves (30, 40, 50 e 60°C), the viscosity for each point of the ternary diagram was measured. It can be noticed that fructose is very soluble in water: the greater its concentration in the solution the greater the solution viscosity and the greater the amount of ethanol in the solution the lesser the solution viscosity. It can be concluded from this work that ethanol could be an interesting agent for a future fructose crystallization process through cooling and anti-solvent addition.