NL1010660C2 - Method for oxidizing starch. - Google Patents

Description

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Method for oxidizing starch

The invention relates to a method for reducing the viscosity of carbohydrates by oxidative degradation.

Before it can be used industrially, starch must undergo a viscosity-lowering treatment. For this purpose, the starch is generally treated oxidatively at an elevated temperature (40-60 ° C) in a basic medium. Using, for example, hypochlorite as an oxidizing agent at 40 ° C, the reaction lasts 4-15 hours. A disadvantage of this method is the amount of salt formed and the extensive degradation of starch, accompanied by the incorporation of chlorine. According to DE-738909, practically 10 dry potato starch can be gelled by treatment with hydrogen peroxide at 45 ° C for 6 hours. Such a treatment is suitable for the preparation of pudding, but for other applications the viscosity is too high and not stable.

Another method uses hydrogen peroxide with a transition metal as the catalyst. However, the usually toxic catalyst is difficult to remove afterwards, even using compounds such as EDTA. A further drawback is the discoloration of the product.

US-A-5,362,868 discloses a method according to which the viscosity of (hydroxyethyl) starch is reduced by oxidation with a peracid. The peracid used is, for example, pcroxosulfuric acid (H2S05) or peracetic acid. The peroxosulfuric acid 20 must be prepared on site from hydrogen peroxide and sulfuric acid. The reactivity of peracetic acid is lower and leads to longer reaction times. US-A-5,362,868 also describes that reaction with hydrogen peroxide leads to unacceptable reaction times.

According to WO 97/31951, the viscosity of starch and other carbohydrates can be reduced by treatment with hydrogen peroxide in the presence of an acylated carbohydrate.

The object of the invention is to provide a method for reducing the viscosity of starch and other carbohydrates with simple means, without the use of heavy metals and salt-forming agents, and without organic by-products. In addition, it is desirable that a stable viscosity is achieved, i.e. a stability that no longer increases at ambient temperature.

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This object is achieved by a process in which the carbohydrate is oxidized with hydrogen peroxide in the presence of a catalyst, and the carbohydrate, after contacting it with the hydrogen peroxide, is dried at a temperature below 60 ° C and then at a temperature of 80 -140 ° C is treated.

The method according to the invention is an inexpensive method with short reaction times and with a low consumption of hydrogen peroxide, about 5 times lower than the method according to WO 97/31951. There is also no significant salt load or other waste stream. The process leads in high yield and with little loss to a soluble or dispersible carbohydrate, the solution or dispersion of which has a low and stable viscosity.

As the carbohydrate that can be treated according to the method according to the invention, any wholly or partly water-soluble polysaccharide is suitable. This primarily includes starch and fractions and derivatives thereof, such as amylose, ethoxylated starch and carboxymethyl starch. Furthermore, the solubility of cellulose and chitin and derivatives thereof can be improved or the viscosity thereof reduced by the process of the invention.

The amount of hydrogen peroxide to be used depends entirely on the desired degree of oxidation. Due to the higher efficiency of the method according to the invention, a limited amount of hydrogen peroxide is sufficient. Generally, a solution of 0.1-20 wt.% Hydrogen peroxide, preferably 1-10 wt.%, Is used. Preferably, such an amount and concentration of hydrogen peroxide is used that the carbohydrate does not dissolve appreciably and, in the case of starch, remains in granular form. The catalyst can be an organic acid such as acetic acid, formic acid, propionic acid, lactic acid, oxalic acid, citric acid, tartaric acid or an anhydride such as acetic anhydride, and in particular a cyclic anhydride of a dicarboxylic acid such as succinic anhydride, maleic anhydride or citraconic anhydride. Phosphoric acid can also be used. The amount of the catalyst is, for example, 0.1-4% by weight, in particular 0.5-2% by weight, relative to the carbohydrate.

After hydrogen peroxide and catalyst are added and mixed, the undissolved carbohydrate is optionally filtered off and then dried. Drying. J 3% 3 is effected at a temperature of at most 60, in particular below 55 ° C, for example at ambient temperature, up to a water content of at most 25% by weight, in particular of 15-20% by weight, relative to the carbohydrate. In the case of starch, drying must take place under such conditions that the starch 5 does not or hardly gelatinises. Tumble dryers can be used for large-scale drying.

Then, the dried carbohydrate is kept at a temperature above 80 ° C, especially above 100 ° C, up to about 140 ° C for at least 10 minutes, especially for 1-10 hours, the actual oxidation taking place . At higher temperatures, for example 120 ° C, use can be made of fluidized beds, microwave ovens and the like. It is important that an open reactor is used, so that any residual water released can be easily removed. If the residual water is not drained sufficiently, the carbohydrate, in the case of starch, can still gelatinize.

The viscosity of the viscosity-reduced carbohydrate obtained by the method according to the invention can be measured with a Brabender viscometer. According to the measurement method, a 25 wt% solution or suspension is heated from 40 ° C at a rate of 1.5 ° C / min; during this heating the viscosity initially increases to a maximum (top viscosity); with further heating the viscosity drops again; at 90 ° C the temperature is not increased further and the viscosity reaches a minimum (trough viscosity); after 30 min at 90 ° C, cooling is continued at a rate of 1.5 ° C / min, to a final temperature of 40 ° C; the viscosity at this end point is called final viscosity. The product according to the invention preferably has a top, trough and end viscosity of resp. 4000, 200 and 2000, most preferably from resp. 2000, 100 and 500 Brabender units, with minimal molecular weight reduction. The viscosity-reduced product can serve as the basis for various applications. An important application is in papermaking, where it can be used to increase the initial wet strength of the paper, improved printability, better adhesion of cationic agents and improved pastability.

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Examples

An amount of potato starch (100-1000 g) is suspended in a solution of 5% or 2.5% hydrogen peroxide in water. Acetic acid or maleic anhydride is optionally added. After filtration, the filtered material contains 30-40% water; the hydrogen peroxide content is therefore around 1% by weight at 2.5% H 2 O 2. The filter cake is air-dried for three days. Alternatively, drying can take place under an air flow of about 50 ° C for several hours. The resulting powder is then kept in an oven at 120 ° C for several hours (reaction time). The resulting material is white and has retained its grain structure. The number of carbon-10 acid groups is about 1 per 57 anhydroglucose units. Brabender curves of the materials (25% in water) are included at pH 7.0. The results are summarized in the table below.

Table 1 reaction time catalyst H202 viscosity 15 (h) type 1% 2% 2 top off end 3 AZ 1 5 320 40 100 3 - - 2.5 5480 300 7080 3 AZ 1 - x3 oc3 3 AZ 1 2.5 3760 148 3400 20 4 AZ 1 2.5 3160 132 2680 3 AZ + MZA 1 + 1 2.5 32 32 32 3 MZA 0.5 2.5 1010 40 984 35 MZA 0.5 2.5 850 64 104 AZ = acetic acid; MZA = maleic anhydride 25 2: weight percentage in water 3: viscosity too high to be measured 4: after 30 minutes at 40 ° C: 108 5: wheat starch

Claims (10)

Process for reducing the viscosity of polymeric carbohydrates by treatment with hydrogen peroxide in the presence of a catalyst, characterized in that the carbohydrate is contacted with the hydrogen peroxide and the catalyst, and then dried at a temperature below 60 ° C , and treat the dried carbohydrate at a temperature of 80-140 ° C. 2. Process according to claim 1, wherein the carbohydrate is contacted with a solution of 0.1-20 wt.%, In particular 1-10 wt.% Hydrogen peroxide. 3. Process according to claim 1 or 2, wherein the catalyst is an organic acid, an organic acid anhydride or phosphoric acid. The method of claim 3, wherein the catalyst is an anhydride of an organic dicarboxylic acid. 5. Process according to any one of claims 1-4, wherein the carbohydrate is dried to a water content of at most 25% by weight, in particular of 10-20% by weight, relative to the carbohydrate. A method according to any one of claims 1 to 5, wherein drying is carried out at a temperature of 20-55 ° C and then treatment at a temperature of 100-130 ° C. A method according to any one of claims 1-6, wherein the carbohydrate is starch. The method of claim 7, wherein the average molecular weight is 0.2-1 20 MDa. A method according to claim 7 or 8, wherein the final viscosity increases by less than 100%, in particular by less than 50% (in Brabender units), within 1 hour after the end of gelatinization at 40 ° C. 1 0 1 0 6 6 0 COOPERATION TREATY (PCT) REPORT ON NEWNESS RESEARCH OF INTERNATIONAL TYPE IDENTIFICATION OF NATIONAL APPLICATION Characteristic of the applicant or of the authorized representative ~ | NO 41985 EE Dutch application no. Filing date 1010660 November 26, 1998 Priority date invoked Applicant INname) AGROTECHNOLOGICAL RESEARCH INSTITUTE {ATO-DLO) Date of request for an international type investigation By the International Research Authority (ISA) to the application No. SN 32338 EN I. FOR AN INQUIRY OF INTERNATIONAL TYPE. I. CLASSIFICATION OF THE SUBJECT (bi) application of different classifications, indicate all classification symbols. 18, C 08 B 37/00 II FIELDS OF TECHNIQUE Researched Minimum Documentation Classification System Classification Symbols IC 6 C 08 B Documentation examined other than the minimum documentation to the extent that such documents are included in the areas examined Hl EXAMINATION FOR CERTAIN CONCLUSIONS comments on supplement sheet IV | LACK OF UNITY OF INVENTION (comments on supplement sheet) ^ orm P * CT / fSA / 20T («ï 07.1979