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Colourants - Formation - Carbonatation

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By Bento, Luis San Miguel
Posted on 2007-07-20    Last edited on 2009-09-19

In Carbonatation, when liquor is mixed with lime, pH increases to values higher that 11. At this alkalinity, invert sugars can be decomposed with formation of HADP. The formation of this kind of colourants was detected by GPC analysis with ELS detector (Bento, 1999). 
In order to avoid this colour formation, the contact time between lime and liquor, before gassing, must be less than 3 minutes. To achieve this goal, the mixture is done in small tanks with strong agitation or iusing static mixers in the liquor lime.

By chromatographic analysis (GPC) with ELS detector, and comparing ffination and carbonated liquor,it is observed that there is an increase of 51% on Group C compounds, with molecular weights between 2.5 kD and 10 kD  (Table; Bento and Sá, 1998). It was also observed that this formation is manifested in the second reactor (Bento, 1999). This fact can be explained by the reaction time for invert sugar destruction and molecular re-arrangement of reaction products.

Quantification of HMW Compounds using PEG as internal standard (ppm on brix)

 Group A

 Group B

Group C 

Affination Liquor

229 ppm 

490 ppm 

576 ppm 

Carbonated Liquor

211 ppm 

99 ppm 

870 ppm 

Fine Liquor

212 ppm 

--- 

896 ppm 

As it was as proved, these compounds are difficult to remove from ion exchange resins, and tend to stay irreversibly fixed to the resin. Also, these compounds remain in white sugar (Bento and Sá, 1997). Due to these facts it is very important to avoid the formation of these compounds during Carbonatatin.

A process was studied to reduce this colour formation. In this process, calcium hydroxide added to affined liquor was reduced. As part of calcium carbonate works as filter aid, this part was added to the liquor, as calcium carbonate. This calcium carbonate was prepared by making a previous carbonatation of calcium hydroxide, before be mixed with liquor (Bento, 1999). It was observed that by replacing 40% of calcium hydroxide by an equivalent quantity of calcium carbonate recently precipitated, a decolourization of 52% in carbonatation was obtained and peak C reduction, equivalent to HADP formation, was observed.

ELS___Carbonatacao

ELS diagram of liquor before an after Carbonatation

Bibliography

Bento L.S.M., 1999, Study of colour formation during Carbonatation in Cane Sugar Refining using GPC and
           ELS detector, Proc. A.V.H. Conf
Bento L.S.M., S.Sa, 1997, Application of Evaporative Light Scatering detector to study beet ans cane sugar
         colourants separated by Gel Permeation Chromatography, EuroTechlink 97 Technical Session,
         Leeds, England
Bento L.S.M., S.Sa, 1998, Study of HMW compounds in sugar liquors from carbonatation and ion exchange
         resins using GPC chromatography with an evaporative light scattering detector, Proc. S.P.R.I. Conf.,
 233-247 

E0050/60




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