Demineralization of Liquid Sucrose
When highly refined liquid sucrose is desired by customers instead of dry sugar, there are a few options for producing a non-inverted liquid sucrose product using various configurations and forms of ion exchange resin technology.
Weak Acid Cation Mixed Bed
One process for producing liquid sugar involves passing the high Brix, moderate temperature liquid sucrose through a mixed bed containing a high pK weak acid cation resin (H+ form) and strong base anion resin (OH- form). This process produces a liquid sucrose with < 0.2% invert and color < 20 ICUMSA.
Pressure Drop of Mixed Bed
1/3 C115EC (H+ form)
2/3 PFA440S (OH- form)
67° Brix Sucrose, 60 °C, 1.85 ft bed depth
y = 2.045X + 0.3617
Strong Base Anion / Weak Acid Cation Two Bed
The sucrose solution can be decolorized and demineralized by passing through a bed of strong base anions (OH- form) to convert all the salts to base, then passing through a separate bed of high pK weak acid cation resin which will exchange the cations and neutralize the base. The weak acid cation effluent pH will be approximately 4.0 and must be blended with a sidestream of syrup to bring the pH up to avoid inversion.
In order to avoid precipitation of Mg(OH)2 or CaCO3 in the resin bed, either a cation resin can be used to soften the syrup, or the anion can be run in the HCO3- form which will produce more highly soluble bicarbonate salts. Conductivity reduction and color removal will be somewhat less in the HCO3- form.
Low Temperature, Strong Acid Cation / Weak Base Anion Two Bed
The liquid sucrose can be treated through a macroporous cation resin (H+ form), followed by weak base anion resin (free base form) for removal of salts and color below liquid sugar standards. This process requires a treatment temperature less than 10 °C (50 °F) to avoid sucrose inversion.
To be able to operate at this low temperature without high viscosity, (causing pressure drop and kinetic problems) the syrup concentration must be below 50 °Brix. The liquid sucrose must then be evaporated back up to 68 °Brix prior to storage and shipment to avoid bacteria growth.
Powdered Resin - Decolorization and Demineralization
Decolorization
Ion exchange resin can be ground into fine 50-100 micron-sized pieces which are added as a body feed to the syrup and filtered out with a pressure filter. The finely ground resin has rapid kinetics and a greater surface area than the same amount of bead resin.
The powdered resin can be mixed with an inert fiber to assist in achieving high filtration rate with a low pressure drop. The powdered resin is used on a once-through basis and discarded. The advantage of powdered resin is the simple equipment required and the lack of regeneration chemicals used. Powdered resin can be cost-effective at low color levels, reducing 50-100 IU sugar to 20-35 IU.
Demineralization
The same strong base anion and weak acid cation resins used in bead form in a column are available in a powdered resin form as well, which can be used to produce high purity sugar when melting white sugar. A 35 IU white sugar can be melted and purified to < 20 IU.
A powdered strong acid cation and strong base anion mix (including fiber) is also used to polish low color syrup. The low dosage of the powdered mix prevents significant inversion from occurring.
