By Bento, Luis San Miguel
Posted on 2007-07-26 Last edited on 2009-09-23
Sugar solutions contain inorganic compounds generically designed by ashes. These compounds can cause problems during sugar extraction or refining.
- Some inorganic compounds can decrease the yield of sugar crystallization (named melassigenic compounds as its presence increase the quantity of solids in mother liquors).
- Other compounds can precipitate during heating, evaporation or crystallization. This will decrease the heat transfer through calandrias or other heating surfaces increasing the evaporation/crystallization time, with increases of energy consumption, color formation and sugar destruction.
- Other compounds can decrease the filtration rate, as silica.
- Other compounds can form flocks or sediments in products using sugar, as in soft drinks.
By these reasons it is important to reduce the quantity of inorganic compounds in sugar products. The complete removal of inorganic compounds is named demineralization. To obtain a free ash sugar solution it is used, normally, ion exchange resins. The sugar solution pass though a cationic resin in H form and through an anionic resin in OH form. The resins can be used in a single column in a mixed bed form or in separate columns. In the second case it is important to consider the decrease of pH through the cationic resin. At a low pH and at a normal temperature, sucrose is hydrolyzed to glucose and fructose (inversion). To avoid these inversion sugar solutions must be cooled to temperatures lower than 15 oC . In some cases this is not inconvenient, as in production of invert liquid sugar.
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