Organic compounds -- part of the class 532-570 series – Organic compounds – Carbohydrates or derivatives
Reexamination Certificate
2001-11-08
2003-09-09
Barts, Samuel (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carbohydrates or derivatives
C536S102000, C536S124000, C536S123100, C423S473000, C127S071000
Reexamination Certificate
active
06617447
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of starch production. More particularly, the present invention relates to a method of starch production using continuous oxidation.
BACKGROUND OF THE INVENTION
Starch has a number of unique properties that make it useful in a variety of applications. One of starch's important properties is its ability to form a viscous fluid from aqueous slurry upon application of energy, typically in the form of heat (i.e., “cooking”). The viscous fluid can be used in food products as a thickener or applied to substances such as paper and textiles whereby it increases the stiffness and abrasion resistance of the material. Another useful property of starch is that dried starch granules are relatively free flowing and can be stored for extended time and/or easy transport to the location where the starch is to be used. Additionally, chemical modifications to the starch can be performed while it is in the granular form. After modification, it can be stored dry for extended periods.
In nature, starch is typically found in the granular form and is obtained from many different plant sources including, but not limited to corn, wheat, potato, and tapioca. Obtaining the starch granules from these plant sources requires separating the starch granules from the non-starch components such as protein, hulls, skin, germ, etc. The separation process is not 100% effective so that small amounts of non-starch material contained in the starch remain. Additionally, because it is derived from natural sources, there is an inherent variation in the concentration of starch granules and non-starch components in the source plant material. These variations can be attributed to factors such as the particular strain of plant, the growing conditions, the soil, etc.
Typically, when designing a starch separation process, a manufacturer will use a representative value for the non-starch components. However, because the concentration in the source plant material will have variations, the final starch will also have small variations in the unwanted components. While it would be possible to design a system to account for the natural variations in the feed material and which would eliminate almost all non-starch components, an appreciable amount of starch would be lost with the non-starch components. These non-starch components can be of less or greater value than the starch. Thus, the design of a starch separation system is to create a balance between eliminating as much of the non-starch components while maximizing the retention of starch components.
For some applications, the variation in concentration for non-starch components in starch will have negligible effect on the final product. These are typically applications where dried starch granules are the end product. For example, the concentration of protein in cornstarch will have only a minor effect on the starch used in body powders (provided that the protein level is relatively small). However, there are many applications where the concentrations of non-starch components will have pronounced effect on the final product. In these applications, the starch is usually cooked before its use. An example of one sensitive application is in oxidized starch. In the manufacture of oxidized starch the protein level will have a significant effect on the starch reaction and the subsequent viscosity of the cooked product made from the starch.
To further complicate the issue, in many of these sensitive starch applications, the cooked starch is required to have a specific viscosity range. A specific viscosity is needed in many applications because one wants the fluid to be thin enough that it is easily handled but not too thin that it overly penetrates the substrate or is slung from the mixer, etc. In a similar vein, one does not want to use a product that is too thick and therefore difficult to pump and spread. For example, in certain paper sizing applications one may want a low viscosity starch to promote penetration into the paper. Conversely, a paperboard manufacturer may want a high viscosity product so that starch stays close to the surface whereby it increases the stiffness of the paperboard.
A starch manufacturer can affect the viscosity of the cooked starch by treating the uncooked starch granules with chemicals. These chemicals include, but are not limited to, hydrochloric acid, sodium hypochlorite, and calcium hypochlorite. Typically, the drop in cooked starch viscosity is proportional to the amount of added chemical. For example adding a large amount of sodium hypochlorite to aqueous slurry of starch granules results in a less viscous cooked starch paste.
In the preceding paragraphs, reference is made to an “oxidized” starch. Oxidized starch is made by reacting starch with an oxidant, thereby forming carboxyl and carbonyl groups on the starch molecule. These carboxyl and carbonyl groups keep adjacent molecules in cooked starch pastes from getting into close proximity and thus hinder the tendency for the starch to coalesce into crystals. Another way to hinder the tendency for the starch to coalesce is to maintain a high cooked paste pH. For many applications, the starch crystals are unwanted because they have a detrimental effect on the cooked starch properties. In addition to forming carboxyl and carbonyl groups on the starch molecule, the oxidant can reduce the length of the starch molecule thereby lowering the viscosity of the product. A description of oxidized starch manufacture can be found in numerous publications and patents (U.S. Pat. No. 4,146,515, and Radley, J. A.,
Starch Production Technology
, Applied Science Publisher LTD, London, pg. 457-466).
Please note that in this discussion of oxidized starch production, we are only concerned with reactions involving uncooked starch granules and are not concerned with the oxidation reaction of cooked starches.
Industrially, oxidized starch is produced in a “batch” reactor, i.e., starch is placed in a vessel along with the oxidant, typically sodium hypochlorite, and then the vessel is agitated for a fixed time. At the end of this time the oxidant is neutralized, typically with a sulfite compound, and the starch is further processed by washing, drying, etc. An example of the art of producing an uncooked oxidized starch via the batch process is found on page 464 of Radley, J. A.,
Starch Production Technology
, Applied Science Publisher LTD, London. A further discussion of batch reactors can be found in Levenspiel, O.,
Chemical Reaction Engineering, Second Edition
, John Wiley and Sons, New York, 1972.
In the industrial production of oxidized starch, the amount of sodium hypochlorite added to the batch is not a fixed amount but instead varies depending on a number of factors including temperature of the reactor and the concentration of non-starch components. Typically in a production facility, they will have a “target” amount of oxidant from which the amount of oxidant to be added is adjusted based upon the results of the immediately preceding batch. This technique is known as “feedback” control. By using batch reactors, a starch producer has flexibility in his production process. This flexibility allows a starch producer to react to changes in source material and make the appropriate modifications in oxidant dosages.
As stated above, batch reactors have a number of advantages including low initial costs and flexibility of operation. However, they have a tendency to produce an inconsistent product because each batch is run under different specifications. These specifications are determined by the feedback control system earlier described. Additionally, the variation of product consistency can be attributed to such items as non-uniform temperatures in the reactor, operator error, variations in the non-starch components in the feedstock, etc.
One possible method of rectifying some of these problems is to use a continuous reactor for the production of oxidized starch. A continuous reactor is well known to provide consistent quality of the product (Levenspiel, O
Gnad Tanja
McClain James
Archer-Daniels-Midland Company
Barts Samuel
Henry Michael C.
Sterne Kessler Goldstein & Fox P.L.L.C.
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