Sugar crystallization is a principal process in sugar processing, and sugar recovery and quality through crystallization greatly depend on the kind and the amount of impurities contained in the sugar solution. It is known that invert sugar and inorganic salts in the sugar solution hinder the crystallization of sucrose and increase the volume of molasses. In general, most impurities enhance the solubility of sucrose at higher concentration and at higher temperature; the impurities that increase the solubility are referred to as melassigenic. Different kinds of impurities have different levels of influence on the formation of molasses and "melassigenic coefficients" of a number of individual impurities were determined by Z. A. Siline. Many formulas are in use for calculating "available sugar" under consideration of pol or purity in cane sugar factories and in beet sugar factories. In the refinery, "rendement" which is the formula for calculating the yield of refined sugar under consideration of pol and contents of invert sugar and ash is used Thus the influence of the low molecular weight impurities on the crystallization of sucrose has been discussed. However, it has been hardly been reported how high molecular weight impurities (HM) in the sugar solution affect on the crystallization. Ultrafiltration (UF), electrodialysis (ED) and chromatographic separation (CS) are rather modern techniques in the sugar industry and several companies adopted these. By these techniques industrial sugar solution can be clarified more effectively than by the traditional methods. Through ED or CS, the purity in the sugar solution is enhanced and the yield of sugar is increased. Through UF, HM and turbid substances are exhaustively eliminated but the purity is only a little increased because the content of HM in sugar solution is low. It is reported that light color sugar is recovered from the sugar solution clarified through UF. UF is validly applicable to eliminate HM, while the elimination through the traditional clarification is not sufficient. The effect of clarification of sugar solution by UF on crystallizing sucrose was studied and also it was discussed how UF improves the physical properties of the sugar solution which has an influence on handling of pan boiling.
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