Cane Sugar Refining - Purolite

Cane Sugar Refining with Ion Exchange Resins
Cane Sugar Refinery
Sugar Receiving
Some refineries are attached to cane mills while others are stand alone facilities. In a
stand alone sugar refinery, raw sugar will arrive in bulk by barge, rail or trucks for
unloading into the raw sugar warehouse. The raw sugar will undergo metal and
debris removal and large lumps will be crushed prior to transfer to the mingler to
begin remelting and refining.
Affination
The raw sugar is mingled with hot affination syrup which melts just the outermost
layer of the raw sugar crystal. This outer layer contains the largest concentration of
color. The resulting syrup from melting of the outer layer, is separated from the sugar
crystals in a centrifuge. The bulk of the colorants are removed during the affination step
(about 50% of raw sugar color) and then during the clarification step (about 40% of
melt liquor color).
Melter
The affinated sugar is dissolved with hot condensate to a liquid concentration of
approximately 72º Brix at 75ºC prior to defecation.
Defecation/Clarification
Approximately 40% of the remaining colorants are removed in the clarification step.
There are two alternative types of defecation processes in use in cane refineries,
carbonatation and phosphatation:
Carbonatation, also called carbonation, involves adding lime (CaO) to the melt liquor and
then passing this juice through a carbonation vessel where carbon dioxide (CO 2 ) is bubbled
up through the juice. The reaction of the carbon dioxide with the lime produces a calcium
carbonate precipitate. Color bodies are entrapped in the precipitate and are removed during
filtration of the solids. Another action occurring in the limed melt liquor is destruction of
invert sugars at the high pH produced by the lime. Polymers are added to the juice to assist
in the formation of a precipitate floc which is more easily settled and filtered.
Phosphatation involves addition of lime (CaO) and phosphoric acid (H 3 PO 4 or P 2 O 5 )
to the melt liquor which results in formation of a calcium phosphate precipitate. Color
bodies adsorb onto the calcium phosphate precipitate and are removed during the
subsequent clarification and filtration. Polymers are added to aid in the formation of a
precipitate floc which is more easily filtered.
Filtration
The clarified juice from carbonatation or phosphatation contains suspended solids which
would plug the interstitial spaces and blind the pores of decolorization resin, bone char
or carbon. Precoat vacuum filters, precoat pressure filters, deep bed multimedia filters or
some combination of these are used to produce a filtered syrup which will flow through
the decolorization columns without causing a pressure buildup.
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