Sugar – starch – and carbohydrates – Processes – Carbohydrate manufacture and refining
Reexamination Certificate
2000-06-30
2001-05-08
Brunsman, David (Department: 1755)
Sugar, starch, and carbohydrates
Processes
Carbohydrate manufacture and refining
C127S042000, C127S046200, C127S055000, C127S058000, C127S063000, C210S660000, C210S687000
Reexamination Certificate
active
06228178
ABSTRACT:
This invention pertains to an improved method for producing white sugar.
Sugar cane juice contains both sucrose and other components. Refined white cane sugar is primarily sucrose, with most polysaccharides and other non-sucrose compounds removed. The color of refined sugar should be less than about 25 ICUMSA units (“IU,” a standard measure of color in the sugar industry). In the conventional method of producing refined cane sugar, initially a raw sugar is produced at the mill by crystallization from cane juice, with only rudimentary clarification. Raw sugar typically includes polysaccharides and other compounds in addition to sucrose, and has a color in the range of 1,000 to 5,000 IU. The raw sugar is later refined, usually at an off-site refinery. The raw sugar is washed or affined; “melted” (i.e., dissolved in hot water); and then clarified to remove polysaccharides and colloids. Conventional clarification is usually performed by liming, carbonatation, and phosphatation. The clarified syrup is decolorized, typically by adsorption of impurities onto activated carbon, charcoal, or ion exchange resins. A conventionally decolorized syrup should have no more than 800 IU color for successful refining to white sugar having a color below 25 IU; for some uses, a color as high as 50 IU can be acceptable. Traditional refining methods suffer from high energy costs, high chemical reagent costs, and high waste disposal costs.
Ceramic ultrafiltration membranes with pore sizes ranging between 0.05 to 0.2 &mgr;m (500 to 2,000 Å) have been used to clarify cane juice, i.e., to remove turbidity and colloidal particles from the juice. Ceramic ultrafiltration membranes can be made, for example, in the form of single- or multi-channel tubes formed of a thin TiO
2
, ZrO
2
, or Al
2
O
3
coating on an Al
2
O
3
, silicate, or carbon support. See R. J. Kwok, “Ultrafiltration/Softening of Clarified Juice at HC&S Puunene Mill,” 53rd Annual Conference of Hawaiian Sugar Technologists (October 1994); and X. Lancrenon et al., “Mineral membranes for the sugar industry,” Sugar y Azucar (May 1993). Clarification by ultrafiltration allows several modifications to be made to the traditional process, such as juice softening with ion exchange resins, production of very-low-color sugar (VLC), and desugarization of B or C molasses.
Based on the size (or molecular weight) of the targeted particles, membranes used in filtration are usually classified as reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF), or microfiltration (MF) filters. UF filters usually have a pore size in the range from about 80 Å to about 2,000 Å, and a molecular weight cut-off (for saccharide-type molecules) in the range from about 20,000 to about 400,000. NF filters usually have a pore size in the range from about 10 Å to about 80 Å, and a molecular weight cut-off in the range from about 200 to about 20,000. “Molecular weight cut-off,” an approximate measure of membrane pore size, is usually defined as the molecular weight of a compound that is rejected by the membrane at more than 90%.
R. J. Kwok et al., “Process of manufacturing crystal sugar from an aqueous sugar juice such as cane juice or sugar beet juice,” U.S. patent application Ser. No. 08/151,383, filed Nov. 12, 1993, discloses a process for removing turbidity from clarified juice by tangential microfiltration, ultrafiltration, or nanofiltration. The disclosure states that the molecular weight cut-off should be at least 1,000, and that good results were obtained with a membrane having a molecular weight cut-off of 300,000, with a pore diameter of 0.1 &mgr;m (i.e., 1,000 Å). An intermediate crystallized raw sugar of color not more than 300 IU is first produced, and then remelted and decolorized on an adsorbent in a decolorization column; or in a variant, decolorization of the remelted 300 IU syrup can be effected by tangential ultrafiltration or nanofiltration of the syrup.
M. Saska et al., “Concentration and Decolorization of Dilute Products from Cane Molasses Desugarization with Reverse Osmosis and Nanofiltration Membranes,” paper presented at Sugar Industry Technologists Meeting (Honolulu, May 1994) discloses the processing of the “invert” and “raffinate” liquid fractions that are byproducts of the desugarization of cane molasses. Reverse osmosis of both the invert and raffinate fractions was used to concentrate the non-aqueous components of those fractions; i.e., to remove water from the retentate. In a separate process, nanofiltration of the invert fraction was used to decolorize the sugars of the invert syrup. The sugars in the invert syrup are primarily glucose and fructose, with smaller amounts of sucrose and other carbohydrates. Because glucose and fructose do not crystallize easily, the decolorized invert syrup would be useful primarily as a liquid sweetener.
D. Herve et al., “Production of Refined Sugar at the Cane Sugar Mill,” Sugar y Azucar (May 1995) discloses the use of ultrafiltration to remove turbidity from sugar juice, including macromolecules such as waxes, dextrans, and gums. The resulting filtrate was decolorized by an ion-exchange process.
Cameco Industries et al., “A.B.C. Process,” paper distributed at 22nd I.S.S.C.T. Congress in Colombia (Sept. 1995) discloses the use of ultrafiltration to remove particulate matter larger than 0.2 microns, followed by decolorization by adsorption on a macroporous styrene divinylbenzene sorbent with a specific amount of a weak base anion functionality.
A new, direct route has been discovered for the production of crystalline white cane sugar, a route that requires no intermediate steps of crystallizing and subsequently remelting a raw sugar. It has been discovered that nanofiltration of a solution such as a clarified cane sugar juice or syrup through a membrane with pore size on the order of 20 to 50 Å not only decolorizes the solution, but also produces a permeate having enhanced crystallization properties. The feed can have a color as high as about 25,000 IU. The decolonized permeate can have a color as high as about 3,000, and even at this high level of color may be used for the direct crystallization of white sugar without further processing. No intermediate crystallization of a raw sugar is needed. This novel method can be used to replace, modify, or supplement conventional sugar-refining techniques. The novel technique reduces costs, nearly eliminates the need to purchase chemical reagents, and greatly reduces waste liquid discharge.
The degree of decolorization achieved to date with the novel technique has ranged from 50% to 85%, which is less than the decolorization attained by traditional recrystallization or adsorbent treatments. However, despite the numerically smaller decolorization effect, the crystallization properties of the permeate were superior as compared to a conventionally decolorized syrup. White sugar with color from 10 to 50 IU has been crystallized directly from nanofiltered permeate of color as high as 2,000 to 3,000 IU. These values are substantially higher than the approximate maximum 800 IU color that a traditional refinery liquor may have for crystallizing white sugar.
Membrane filtration preferably uses cross-flow (or tangential flow) of the liquid feed over the membrane, allowing continuous cleaning and high filtration rates, at the expense of having a somewhat larger volume of the reject (final retentate) stream. Periodic cleaning with caustic, acids or a combination of treatments is required only infrequently in the novel process, and when needed usually restores membrane performance easily.
Preferred configurations for the membranes are spiral-wound and hollow fiber configurations for the polymeric membranes used in the nanofiltration, and a tubular, multi-channel design for the ceramic membranes used in the initial clarification step. In a spiral-wound membrane, several flat membrane sheets are wound around a central (permeate) tube, and are separated from each other by a polymeric mesh spacer.
Polymeric nanofiltration membranes suitable f
Board of Supervisors of Louisiana State University and Agricultu
Brunsman David
Runnels John H.
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