Sugar – starch – and carbohydrates – Processes – Carbohydrate manufacture and refining
Reexamination Certificate
2001-04-06
2004-03-23
Wood, Elizabeth D. (Department: 1755)
Sugar, starch, and carbohydrates
Processes
Carbohydrate manufacture and refining
C127S055000, C127S058000, C210S656000, C210S687000, C210S705000
Reexamination Certificate
active
06709527
ABSTRACT:
THIS INVENTION relates to the treatment of sugar juice. It relates in particular to a process for treating impure cane-derived sugar juice, typically raw juice which has been subjected to conventional preclarification by heating, liming and settling.
According to the invention, there is provided a process for treating impure cane-derived sugar juice, which process comprises
subjecting, in a clarification stage, impure cane-derived sugar juice to microfiltration/ultrafiltration to decrease the levels of suspended solids, organic non-sugar impurities and/or colour therein;
sequentially passing the resultant clarified sugar juice through at least one ion exchange stage by bringing the clarified sugar juice into contact with a strong acid cation ion exchange resin in the hydrogen form, and thereafter into contact with an anion ion exchange resin in the hydroxide form;
withdrawing a purified sugar solution from the ion exchange stage;
concentrating the purified sugar solution, to produce a syrup;
subjecting the syrup to primary crystallization in at least one primary crystallization stage, to produce refined white sugar and primary mother liquor or molasses;
subjecting the primary mother liquor to secondary crystallization in at least one secondary crystallization stage, to produce impure crystallized sugar and secondary mother liquor or white strap molasses.
The impure cane-derived sugar juice typically is that obtained by preparing sugarcane stalks, eg disintegrating or breaking up the stalks; removing sugar juice from the prepared stalks by diffusion and/or milling, using imbibition water, thereby to obtain mixed juice; heating and liming the mixed juice; and subjecting it to primary clarification, to obtain clear juice, ie to obtain the impure cane-derived sugar juice which constitutes the feedstock to the process of the invention. Instead, however, the clear juice or impure cane-derived sugar juice which is used as feedstock can be that obtained by any other suitable preparation process.
The impure cane-derived juice is typically at an elevated temperature, eg a temperature above 90° C. Thus, the microfiltration/ultrafiltration will also be effected at elevated temperature; however, since ion exchange normally takes place at a lower temperature, eg at a temperature below 60° C., such as at about 10° C., the juice will normally be cooled before ion exchange.
The impure sugar juice as obtained from sugar cane stalks as hereinbefore described, has a low sugar or sucrose concentration, typically less than 15% (m/m), for example in the order of 10% to 15% (m/m). This low concentration impure sugar juice is suitable as a feedstock for the process of the present invention; however, it is believed that it will be advantageous to use a higher concentration impure sugar juice as feedstock, eg to reduce the cost of the capital equipment required to treat the same amount of sugar or sucrose. Thus, the process may include concentrating, eg by means of evaporation, the impure sugar juice before it enters the clarification stage. It may be concentrated to a sugar or sucrose concentration of at least 20% (m/m), preferably from 20% to 40% (m/m), typically about 25% (m/m).
The impure cane-derived sugar juice will thus normally, during preparation thereof, have been subjected to initial or primary clarification; the treatment in the clarification stage of the process of the invention thus constitutes secondary clarification of the sugar juice. In the secondary clarification stage, sufficient suspended solids, organic non-sugar impurities and colour are removed to render the sugar amenable to subsequent treatment in the ion exchange stage. During the secondary clarification, the sugar juice may be passed through a membrane in the size range 15000 Dalton to 300000 Dalton or 200 Angstrom to 0,2 micron. The Applicant has found that microfiltration/ultrafiltration prior to ion exchange is important in order to inhibit rapid fouling of the ion exchange resins, and to ensure that the refined white sugar product meets the required turbidity specifications.
In the ion exchange stage, de-ashing or demineralization and further colour removal takes place. The contacting of the clarified sugar juice with resins is effected in such a manner that inversion, ie breakdown of sucrose to glucose and fructose is kept as low as possible, and resin use is optimized.
In certain circumstances, strong acid cation resins can catalyze the inversion reaction of sucrose. To inhibit sucrose inversion in such cases, the ion exchange, or a portion of the ion exchange, can be effected at sugar juice temperatures below 30° C. The process may thus include, when necessary, reducing the impure sugar juice temperature to below 30° C., ahead of or during its passage through the ion exchange stage. For example, the sugar juice temperature can be reduced to about 10° C., eg by using a refrigeration plant, to ensure minimal sucrose inversion.
The ion exchange stage may be provided by a simulated moving bed arrangement or system, eg by a continuous fluid-solid contacting apparatus such as that described in U.S. Pat. No. 5,676,826; by a separation train system such as that described in U.S. Pat. No. 5,122,275; or the like.
The process may include subjecting the clarified sugar juice to a first pass through the ion exchange stage, to obtain a partially purified sugar solution, and thereafter subjecting the partially purified sugar solution to at least one further pass through the ion exchange stage, to obtain the purified sugar solution.
The process includes regenerating the resins from time to time, as required. Thus, the strong acid cation resin may be regenerated by contacting it with a strong acid, such as hydrochloric acid or nitric acid, with an acid stream rich in potassium salts thereby being obtained. This component is suitable for use as a fertilizer feedstock. The anion resin may be regenerated by contacting it with a strong or weak base such as sodium hydroxide, potassium hydroxide, ammonium hydroxide, or a combination of sodium or potassium hydroxide and ammonium hydroxide, with an alkaline stream which is rich in nitrogen being obtained. This component is also suitable for use as a fertilizer feedstock.
As indicated hereinbefore, de-ashing or demineralization (cations and anions) and colour removal are effected simultaneously in the ion exchange stage. However, the Applicant has found that it is not always the most efficient route to remove all colour during passage of the sugar juice through the ion exchange stage. Some colour may thus, if desired, be removed in the ion exchange stage, with the remaining colour then being removed by further treatment of the sugar juice.
Thus, in one embodiment of the invention, the process may include subjecting the purified sugar solution from the ion exchange stage, or the partially purified sugar solution of the ion exchange stage, to further decolourizing in a decolourizing stage.
The decolourizing stage may comprise an anion resin, in particular an anion resin in hydroxide or chloride form; an absorption resin; activated carbon; or another absorption medium.
When the decolourizing stage includes an anion resin in the chloride form, the partially purified sugar solution, after the first pass thereof through the ion exchange stage, may be brought into contact with the anion resin in the chloride form in the further ion exchange stage, and thereafter subjected to a second pass through the ion exchange stage.
When the decolourizing stage includes an anion resin in the hydroxide form, an absorption resin, activated carbon, or another absorption medium, the purified sugar solution from the ion exchange stage may be brought into contact with the anion resin, the absorption resin, the activated carbon or the other absorption medium.
The concentration of the purified sugar solution into the syrup may be effected by means of evaporation. The resultant syrup may have a sucrose or sugar concentration of about 65% (m/m).
The primary crystallization may be effected in a plurality of sequential prima
Brewer Peter A.
Fechter Wolfgang L.
Smith Ian A.
Van De Pypekamp Gerrit
Brinks Hofer Gilson & Lione
Hailey Patricia L.
Ufion (Pty) Limited
Wood Elizabeth D.
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