Sugar – starch – and carbohydrates – Processes – Carbohydrate manufacture and refining
Reexamination Certificate
2000-06-23
2002-11-26
Brunsman, David (Department: 1755)
Sugar, starch, and carbohydrates
Processes
Carbohydrate manufacture and refining
C127S048000
Reexamination Certificate
active
06485574
ABSTRACT:
FIELD OF THE INVENTION
The present invention concerns the field of refined low colored sugar manufactured from a colored aqueous sugar solution.
BACKGROUND OF THE INVENTION
In the beet sugar production, a beet refined granulated sugar with 20-30 ICUMSA color units (abbreviated I.C.U. hereafter) is usually crystallized from a standard feed liquor of about 3000 I.C.U. and 94% sugar purity. For example, a beet standard liquor of 2864 I.C.U. gives a sugar of 29 I.C.U.
However, a cane refined sugar with 20-40 I.C.U. is generally produced from standard feed liquor of 200 to 300 I.C.U. and 99% sugar purity.
Thus, it appears that the occlusion (adsorption/absorption) of colorants into refined sugar crystals is considerably greater for cane refined sugar production. Therefore, for production of cane refined sugar, extracted sucrose from sugar cane is first produced in the form of cane raw sugar with a color ranging from 1500 to 6000 I.C.U. in a raw sugar mill. The cane raw sugar is then further refined into final refined sugar product, with a color ranging from 20 to 50 I.C.U. in a sugar refinery.
The refining process primarily is a decolorization process using (a) mechanical separation (affination); (b) chemical color separation (carbonation or phosphatation); (c) physical separation (ion exchange resin, granulated activated carbon bone char process, etc.); and (d) final crystallization, which also transforms sucrose into soluble solid granulated sugar. Steps (a) and (b) can be classified as “primary decolorization”. Step (c) can be classified as secondary decolorization.
The above refining process is extremely cost intensive in both capital investment and operation cost, particularly in energy requirement and plant maintenance. If a carbonation or phosphatation process is used, disposal of carbonate cake or phosphate scum is increasingly an environmental problem. If a cane refined sugar with a color of 30 to 70 I.C.U. could be crystallized from a standard cane liquor of 3000 I.C.U. color, as it is the case of beet sugar production, then the entire refinery decolorization steps, e.g. affination, carbonation/phosphatation, ion exchange resin, all can be eliminated resulting in a tremendous saving in both capital, operation and disposal cost. Furthermore, if cane refined sugar of 30 to 60 I.C.U. could be crystallized from a cane raw sugar mill's evaporated syrup with a color ranging from 5000 to 10,000 I.C.U., refined sugar could be produced in raw sugar mills. At any rate, if cane refined sugar could be crystallized from a standard liquor having a color anywhere between 500 to 10,000 I.C.U., selective refining process step could be eliminated resulting in considerable saving in refined sugar production.
The distinct difference in occlusion characteristics, thereafter termed as “occlusion index”, between beet sugar and cane sugar colorants has been a subject of speculation and postulation for many years. That “occlusion index” is defined as the color ratio between the color of the sugar and the color of the crystallization liquor: O.I.=100×col. Sugar / col. Syrup.
Because of the inability of the researchers in the field to adequately explain it, with some degree of technical and scientific certainty, the obvious difference in occlusion between beet and cane colorants are generally attributed to the nature of the colorants which have been studied by Lionnet, G. R. E. [(1987), Impurity transfer during A-massecuite boiling, Proc. S. African Sugar Technol. Assoc., p. 70 and Shore, M., Broughton, N.W. et al. (1984), Factors affecting white sugar color, Sugar Technology Review. 12:1-99].
Recent studies, Godshall, M. A. and Clarke, M. A., [“High molecular weight color in refineries”,
Proc. Conf Sugar Process. Research
, pp. 75-95, (1988)] indicated that the high molecular weight colorants are preferentially occluded. Donovan, M. and Williams, J. C., [“The factors influencing the transfer of colour to sugar crystals”,
Proc. Conf. Sugar Process. Research
, pp. 31-48, (1992)], in a study on color transfer, also seem to have a similar finding. Although the findings of these studies are subject to speculation, they pointed to the need to search for the cause of preferential occlusion in crystals in order to find a solution to reduce “the occlusion index” of feed liquor colorant.
The so-called NAP process developed by APPLEXION (U.S. Pat. No. 5,554,227 and U.S. Pat. No. 5,902,409) showed that, by using a system as tight as a filtration membrane, due to the removal of high molecular weight molecules, the color of the sugar is drastically reduced with respect to the direct decolorization of the juice. With such a NAP process, a decreasing of the occlusion index is observed; moreover, approximately 40 to 50% of color and ash reduction is observed on crystalized sugar.
Carpenter, F. and Deitz, V. R. (Technical report, NBS report 7750, Bone char Research Project, Inc., NBS project 1502-20-15122, 19-69, 1962) clearly showed that adsorption of colorants by bone char is greatly diminished in the presence of an excess polyvalent anions. This indicates that comparatively small changes in the ionic composition of a liquor/syrup may cause a large change in the effluent liquor, i.e. color is not “picked-up” by the bone char. In other words, an excess of polyvalent anions in a sugar solution containing colorants, will reduce the adsorption/absorption of said colorants on bone char, resulting in a poor decolorization by the bone char. However, if the colorant molecular weight is high enough, adsorption by granular carbon can be anticipated.
The present invention is based on the hypothesis that occlusion (adsorption/absorption) of colorants into sugar crystals during a crystallization process, could follow the same rules as adsorption on bone char.
This hypothesis has been thoroughly studied by the inventors.
DESCRIPTION OF THE INVENTION
Therefore, in one aspect, the present invention concerns a process for decreasing the occlusion of colorants in sugar crystals during the crystallization step of an aqueous sugar solution containing colorants, polyvalent cations such as Ca
2+
and Mg
2+
ions and possibly polyvalent anions, said process being characterized in that it comprises the step of treating said solution so as to increase the number of polyvalent anion equivalents with regard to the number of polyvalent cation equivalents.
In a further aspect, the present invention concerns a process for manufacturing crystallized sugar from an aqueous sugar solution containing colorants, polyvalent cations such as Ca
2+
and Mg
2+
ions and possibly polyvalent anions, said process comprising the step of submitting said solution to a crystallization procedure to obtain a crystallized sugar, the process being characterized in that, in order to decrease the occlusion of colorants in the crystals of said crystallized sugar, it further comprises the step of treating said solution so as to increase the number of polyvalent anion equivalents with regard to the number of polyvalent cation equivalents.
According to this invention, it is possible to reduce the occlusion of colorants in the sugar crystals, that is to reduce the above-defined occlusion index and, hence, to obtain less colored sugar crystals.
Advantageously, the treating step according to the present invention comprises the step of adding a source of polyvalent anions to said solution.
The treating step in the above processes may lead to a solution containing an excess of polyvalent anion equivalents with regard to the polyvalent cation equivalents.
Having in mind that a beet or cane sugar solution usually contains mainly chloride as monovalent anions and Ca
2+
and Mg
2+
as polyvalent cations, such an excess of polyvalent anion equivalents (EPA) for such a sugar solution may generally be expressed as follows:
EPA=TA−Cl
−
−Ca
2+
−Mg
2−
wherein TA=total anion equivalents, and
TA−Cl
−
=polyvalent anions equivalents.
The sour
Chou Chung-Chi
Gao Da-Wei
Min Ya-Guang
Theoleyre Marc-Andre
Brunsman David
Roylance Abrams Berdo & Goodman L.L.P.
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