Cane Sugar Refining - Purolite

Cane Sugar Refining with Ion Exchange Resins
Decolorization
Several techniques can be used for removing color from the sugar juice and they are
subject to continuous developments. The main ones being:
• Activated carbon: Numerous types of activated carbon are available in the
marketplace according to the precursor carbonaceous material (coal, wood,
coconut, etc.) and their size. The most common types used for sugar juice
decolorization being powdered activated carbon (usually termed as PAC) and
granular activated carbon (GAC).
• Polymeric media: This term mostly refers to synthetic ion exchange resins or
adsorbent resins (functionalized or not). There are 2 main polymeric structures
commercially available which differ by their hydrophobicity; the styrenic matrix
which tends to be more hydrophobic and the acrylic structure which is hydrophilic.
In addition to their chemical structure, polymeric adsorbents exhibit some
important porosity.
• Bone char: Pyrolyzed ground animal bones have a high surface area which adsorbs
color and remove some ash.
Evaporation
The raw sugar was melted to 72° Brix to lower the viscosity for filtration and
decolorization, but requires a much higher Brix to achieve a supersaturated sugar
concentration for crystallization in the vacuum pans which are effectively single
effect evaporators. Multiple effect evaporators are used to improve steam economy
while raising the Brix from 68° Brix (after dilution) to approximately 80° Brix.
Crystallization
Evaporative crystallization of the 98° Pol (sucrose purity) decolorized syrup occurs in a
heated vacuum pan. As the water evaporates from the syrup, the solution becomes
supersaturated. The mix is seeded with fine sucrose crystals which initiate uniform crystal
growth. As the crystals grow, most of the color bodies are excluded from the crystal.
The first strike sugar crystals will have a color approximately 1/10 th that of the pan
liquor. The massecuite is then dropped into a centrifugal where the crystals are separated
from the remaining liquor and washed with a small amount of hot water to remove
any adhering color bodies. The liquor, now at a reduced purity of 92-94° Pol is sent to
another vacuum pan for further crystallization of white sugar. The sugar produced
from the second pan is higher in color than from the first, but still meeting white sugar
specifications.
After the purity of the massequite approaches about 50° Pol, crystallization of
additional sugar becomes very energy intensive. The resulting syrup is called molasses.
It is possible to use chromatographic separation to enrich the purity of the cane molasses
to 90+° Pol where additional sugar can be recovered, but the pretreatment to remove
waxes and proteins which foul the chromatographic separation resin limits the economics
of this process.
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