A method for preparing oxidized starch using a dual oxidizing agent and oxidized starch prepared thereby

Abstract

The application belongs to the technical field of oxidized starch production, and discloses a method for preparing oxidized starch by using double oxidants, which comprises sequentially adopting double oxidation and sodium hypochlorite to perform oxidation reaction, and after the aldehyde group of the oxidized starch by the double hydrogen peroxide is greater than or equal to 0.6%, sodium hypochlorite is adopted to perform oxidation. In the application, the hydrogen peroxide is used to first oxidize the hydroxyl group in the starch into an aldehyde group, and then the sodium hypochlorite is used to oxidize the aldehyde group into a carboxyl group. The amount of the sodium hypochlorite is greatly reduced, and the COD and salt content of the sewage formed in the production process are reduced, so that the pressure and cost of sewage treatment are reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of oxidized starch production, and particularly relates to a method for preparing oxidized starch by using double oxidants and oxidized starch prepared by the method. BACKGROUND

[0002] Starch is a renewable resource and widely exists in nature. With the development of industrial technology, the application of raw starch is limited, so people modify starch in different ways, that is, the commonly known modified starch. Oxidized starch is a kind of modified starch with a large amount of use in industry, and sodium hypochlorite oxidized starch is the most common and practical kind of oxidized starch. Compared with raw starch, the sodium hypochlorite oxidized starch has good paste transparency, low viscosity, strong adhesion and is not easy to gelatinize, and is widely used in the textile and papermaking industries.

[0003] The sodium hypochlorite oxidized starch has a wide range of applications, mainly because the oxidized starch produced has a high carboxyl content, and the carboxyl content can be bonded with fibers, so it is very popular in the papermaking and textile industries. However, in actual production, the sodium hypochlorite oxidized starch has the disadvantages of high salt content, high COD, serious environmental pollution, difficult sewage treatment and high cost in the process, which restricts the production of the sodium hypochlorite oxidized starch. The hydrogen peroxide oxidized starch has poor paste fluidity after gelatinization, the paste is not transparent, and the main product after oxidation is aldehyde group, which is limited in the downstream industry.

[0004] Therefore, it is an urgent problem for those skilled in the art to provide a preparation method of oxidized starch with good quality, less use of oxidant and less salt content of generated sewage. SUMMARY

[0005] Therefore, in order to solve the above technical problems existing in the prior art, the application provides a method for preparing oxidized starch by using double oxidants.

[0006] In order to achieve the above purpose, the application adopts the following technical scheme:

[0007] A method for preparing oxidized starch by using double oxidants, which sequentially uses double oxidation and sodium hypochlorite for oxidation reaction.

[0008] The application uses double oxidants for oxidation reaction, effectively combining the advantages of single oxidant oxidized starch. Mainly, the D-glucose group of starch molecules is oxidized to aldehyde group on the C position of the glucose unit under the action of the hydrogen peroxide oxidant, and then further oxidized to carboxyl group by sodium hypochlorite. The prepared oxidized starch has a high carboxyl content and strong adhesion, and is widely used in the papermaking and textile industries.

[0009] Preferably, after the aldehyde group of the hydrogen peroxide oxidized starch is greater than or equal to 0.6%, sodium hypochlorite is used for oxidation.

[0010] When the aldehyde group content is less than 0.6, in order to reach the viscosity value of the finished product, the subsequent need to increase the amount of sodium hypochlorite, increase the COD and salt of sewage, bring the burden to sewage treatment.

[0011] Preferably, the amount of hydrogen peroxide added is 2.6% of the mass of the starch with a concentration of 27.5%.

[0012] When the amount of hydrogen peroxide added is less than 2.6%, the aldehyde group of the oxidized starch is relatively small, the subsequent consumption of sodium hypochlorite is increased, and the COD and salt of sewage are increased. When the amount is greater than 2.6%, the aldehyde group generated by the reaction of starch is more, which reduces the whiteness of the finished product and the transparency of the paste.

[0013] Preferably, the oxidation temperature of the hydrogen peroxide is 45-50℃, and the pH value is 8.0-8.5.

[0014] When the temperature is lower than 45℃, and the pH value is lower than 8, the reaction speed is slow, which reduces the production efficiency. When the temperature is higher than 50℃, the soluble starch formed by the reaction is increased, which reduces the yield and increases the COD of sewage. When the pH value is higher than 8.5, the hydrogen peroxide is decomposed under alkaline conditions, which increases the consumption of chemicals.

[0015] Preferably, the amount of sodium hypochlorite added is 200㎏ / ton of starch with an effective content of 13% of sodium hypochlorite, and the amount of sodium hypochlorite added is determined according to the viscosity value of the starch.

[0016] Preferably, the oxidation temperature of the sodium hypochlorite is 43-45℃.

[0017] The present application limits the temperature to the optimum temperature for the reaction of sodium hypochlorite and starch. Below this temperature, the reaction speed is slow, which reduces the production efficiency. Above this temperature, the starch particles swell, which is easy to form soluble starch and increase the COD of sewage.

[0018] Preferably, the method of adding sodium hypochlorite is to adjust the pH value of the reaction solution to 7.5-7.6, and add the sodium hypochlorite at a speed of 1500-1800㎏ / h. When the pH value of the reaction solution rises to 9.5-10.00, the adding speed of the sodium hypochlorite is reduced to 500-800㎏ / h. When the pH value begins to drop, the adding speed of the sodium hypochlorite is increased to 2000-2500㎏ / h, until the sodium hypochlorite is added completely.

[0019] The adding speed of sodium hypochlorite is restricted by the pH value of the starch milk, which fully ensures that the sodium hypochlorite reacts with the aldehyde group in the starch to form carboxyl under alkaline conditions.

[0020] Preferably, the specific steps of the method are:

[0021] (1) adjust the pH value of the starch milk to 8.0-8.5, add hydrogen peroxide and heat the starch milk to 45-50℃, and detect the content of aldehyde groups in the starch milk; when the content of aldehyde groups in the starch is greater than or equal to 0.6%, cool the starch milk to 43-45℃;

[0022] (2) after adjusting the pH value of the starch milk obtained in step (1) to 7.5-7.6, add sodium hypochlorite at a speed of 1500-1800 kg / h; when the pH value of the starch milk rises to 9.50-10.00, reduce the adding speed of sodium hypochlorite to 500-800 kg / h; when the pH value of the starch milk begins to drop, increase the adding speed of sodium hypochlorite to 2000-2500 kg / h, until the sodium hypochlorite is completely added; after the reaction of sodium hypochlorite is completed, adjust the pH value to 5.5-6.5, centrifuge, wash and dry the starch milk to obtain oxidized starch.

[0023] Preferably, the starch is one or a mixture of several of corn starch, wheat starch, rye starch, oat starch, cassava starch, potato starch and waxy rice starch.

[0024] Preferably, the concentration of the starch milk in step (1) is 38-40%.

[0025] The pH value adjustment in steps (1) and (2) uses sodium hydroxide solution.

[0026] The present application uses sodium hydroxide as the pH value regulator, without adding other organic and inorganic chemical raw materials, which is convenient for sewage treatment.

[0027] Preferably, the drying in step (2) is performed until the moisture content of the finished product is less than or equal to 14%.

[0028] The oxidized starch prepared by the method described above.

[0029] As can be seen from the above technical solutions, compared with the prior art, the present application has the following advantages:

[0030] (1) The present application uses hydrogen peroxide to oxidize the hydroxyl groups in the starch into aldehyde groups, and then uses sodium hypochlorite to oxidize the aldehyde groups into carboxyl groups, which greatly reduces the amount of sodium hypochlorite used, and also reduces the COD and salt content of the sewage generated during production, thereby reducing the pressure and cost of sewage treatment.

[0031] (2) The present application uses two kinds of oxidizing agents to oxidize the starch, and the product quality can fully meet the quality of single sodium hypochlorite oxidized starch, and can fully meet the use of downstream customers.

[0032] (3) the present application in the early stage adopts hydrogen peroxide as an oxidant, and the hydrogen peroxide does not form inorganic salts in the material during the oxidation process, thereby reducing the salt content in the wastewater. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative work are within the protection scope of the present application.

[0034] Embodiment 1

[0035] A method for preparing oxidized starch by using a double oxidant, comprising the following steps:

[0036] (1) 1000 g of starch is weighed and added into water to prepare a starch milk with a concentration of 40%, and then stirred uniformly, and a 3% sodium hydroxide solution is used to adjust the pH value to 8.0, and then 2.6 wt% of hydrogen peroxide (with a concentration of 27.5%) is quickly added into the starch milk, and at the same time, the starch milk is heated to 50℃, and the content of aldehyde groups in the starch is detected, and when the content of aldehyde groups in the starch is 0.6%, the starch milk is cooled to 43℃;

[0037] (2) a 3% sodium hydroxide solution is used to adjust the pH value to 7.50, and then the addition of sodium hydroxide is stopped, and then sodium hypochlorite is added, and the amount of sodium hypochlorite is 200 kg per ton of starch (with an effective content of 13%), and the sodium hypochlorite is added at a speed of 1500 kg / h, and when the pH value of the starch milk is increased to 9.50, the addition speed of the sodium hypochlorite is reduced to 500 kg / h, and when the pH value of the whole system starts to decrease, the addition speed of the sodium hypochlorite is increased to 2500 kg / h, and the addition of the sodium hypochlorite is stopped until the end, and in the whole process, the temperature of the starch milk is maintained at 43℃, and after the complete reaction of the sodium hypochlorite is detected by using potassium iodide test paper, hydrochloric acid is added to adjust the pH value to 5.50;

[0038] (3) the product is centrifuged, washed and dried to obtain the finished oxidized starch with a moisture content of 13.8%.

[0039] Embodiment 2

[0040] A method for preparing oxidized starch by using a double oxidant, comprising the following steps:

[0041] (1) Take 1000g starch into water, prepare a starch milk with a concentration of 38%, stir it evenly, adjust the pH value to 8.50 with a 3% sodium hydroxide solution, quickly add 2.6wt% hydrogen peroxide (concentration of 27.5%) to the starch milk, and at the same time, heat the starch milk to 45℃, detect the aldehyde group content in the starch, when the aldehyde group content in the starch is 0.65%, cool the starch milk to 45℃;

[0042] (2) Adjust the pH value to 7.60 with a 3% sodium hydroxide solution, stop adding sodium hydroxide, add sodium hypochlorite, the amount of sodium hypochlorite is 200㎏ / ton of starch (effective content is 13%), add sodium hypochlorite at a speed of 1800㎏ / h, when the pH value of the starch milk rises to 10.00, reduce the speed of adding sodium hypochlorite to 800㎏ / h, when the pH value of the whole system starts to drop, increase the speed of adding sodium hypochlorite to 2000㎏ / h, until the addition of sodium hypochlorite is completed, in the whole process, keep the temperature of the starch milk at 45℃, after detecting the complete reaction of sodium hypochlorite with potassium iodide test paper, add hydrochloric acid to adjust the pH value to 6.50;

[0043] (3) Centrifuge the product, wash and dry it to obtain the finished oxidized starch with a moisture content of 13.0%.

[0044] Example 3

[0045] A method for preparing oxidized starch by using a double oxidizing agent, comprising the following steps:

[0046] (1) Take 1000g starch into water, prepare a starch milk with a concentration of 39%, stir it evenly, adjust the pH value to 8.30 with a 3% sodium hydroxide solution, quickly add 2.6wt% hydrogen peroxide (concentration of 27.5%) to the starch milk, and at the same time, heat the starch milk to 48℃, detect the aldehyde group content in the starch, when the aldehyde group content in the starch is 0.7%, cool the starch milk to 44℃;

[0047] (2) Adjust the pH value to 7.55 with a 3% sodium hydroxide solution, stop adding sodium hydroxide, add sodium hypochlorite, the amount of sodium hypochlorite is 200㎏ / ton of starch (effective content is 13%), add sodium hypochlorite at a speed of 1700㎏ / h, when the pH value of the starch milk rises to 9.70, reduce the speed of adding sodium hypochlorite to 600㎏ / h, when the pH value of the whole system starts to drop, increase the speed of adding sodium hypochlorite to 2300㎏ / h, until the addition of sodium hypochlorite is completed, in the whole process, keep the temperature of the starch milk at 44℃, after detecting the complete reaction of sodium hypochlorite with potassium iodide test paper, add hydrochloric acid to adjust the pH value to 6.00;

[0048] (3) Centrifuge the product, wash and dry it to obtain the finished oxidized starch with a moisture content of 13.2%.

[0049] Comparative Example 1 (single sodium hypochlorite oxidant)

[0050] (1) 1000 g of starch was weighed into water to prepare a starch milk having a concentration of 40%, and stirred uniformly. A 3% sodium hydroxide solution was used to adjust the pH to 7.55, and the addition of sodium hydroxide was stopped. Sodium hypochlorite was added at a rate of 400 kg / ton of starch (effective content of 13%), and the addition rate of sodium hypochlorite was reduced to 600 kg / h when the pH of the starch milk increased to 9.70. When the pH of the entire system began to decrease, the addition rate of sodium hypochlorite was increased to 2300 kg / h until the addition of sodium hypochlorite was completed. During the entire process, the temperature of the starch milk was maintained at 44°C. After the reaction of sodium hypochlorite was completed, as determined by potassium iodide paper, hydrochloric acid was added to adjust the pH to 6.00.

[0051] (2) The product was centrifuged, washed, and dried to obtain an oxidized starch product having a moisture content of 13.0%.

[0052] Comparative Example 2 (single hydrogen peroxide oxidant)

[0053] (1) 1000 g of starch was weighed into water to prepare a starch milk having a concentration of 40%, and stirred uniformly. A 3% sodium hydroxide solution was used to adjust the pH to 8.30, and 9 wt% hydrogen peroxide (concentration of 27.5%) was rapidly added to the starch milk. At the same time, the starch milk was heated to 48°C, and the viscosity of the starch was measured to be 8.4 mpa.s. The starch milk was then cooled to 43°C.

[0054] (2) The product was centrifuged, washed, and dried to obtain an oxidized starch product having a moisture content of 13.3%.

[0055] Comparative Example 3 (sodium hypochlorite oxidation followed by hydrogen peroxide oxidation)

[0056] (1) 1000 g of starch was weighed into water to prepare a starch milk having a concentration of 40%, and stirred uniformly. A 3% sodium hydroxide solution was used to adjust the pH to 7.50, and the addition of sodium hydroxide was stopped. Sodium hypochlorite was added at a rate of 200 kg / ton of starch (effective content of 13%), and the addition rate of sodium hypochlorite was reduced to 500 kg / h when the pH of the starch milk increased to 9.50. When the pH of the entire system began to decrease, the addition rate of sodium hypochlorite was increased to 2500 kg / h until the addition of sodium hypochlorite was completed. During the entire process, the temperature of the starch milk was maintained at 43°C. After the reaction of sodium hypochlorite was completed, as determined by potassium iodide paper,

[0057] (2) adjust pH value to 8.0 with 3% sodium hydroxide solution, quickly add 2.6wt% hydrogen peroxide (concentration of 27.5%) to the starch milk, and meanwhile, heat the starch milk to 50℃, detect the viscosity of the starch to be 8.0mpa.s, and then cool the starch milk to 43℃;

[0058] (3) centrifuge, wash and dry the product to obtain the finished product with 13.4% moisture.

[0059] The data of the examples and the comparative examples are compared, and the results are shown in Table 1 below,

[0060] Table 1: product and sewage detection results of examples and comparative examples

[0061] Comparative Example Carboxyl content of finished product (%) Viscosity (mpa.s) Sewage COD Sewage salinity (expressed as conductivity) (us / cm) Example 1 0.83 8.3 15500 24340 Example 2 0.84 8.2 16500 22150 Example 3 0.87 8.0 14500 23480 Comparative Example 1 0.80 8.6 30800 36630 Comparative Example 2 0.20 8.4 17500 22600 Comparative Example 3 0.45 8.0 17000 28300

[0062] From the results in Table 1, it can be seen that the viscosity of the prepared oxidized starch is the same size, the carboxyl content in Comparative Example 2 and Comparative Example 3 is low, and the carboxyl content in Example 1, Example 2, Example 3 and Comparative Example 1 is high. In addition, the COD and salt content in the sewage during the production process are lower in the examples than in Comparative Example 1. Therefore, from the overall effect comprehensive evaluation, the examples are superior to the comparative examples.

[0063] The above description of the disclosed examples enables one skilled in the art to make or use the invention. Numerous modifications to these examples will be apparent to those skilled in the art, and the general principles defined herein can be applied to other examples without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the examples shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing oxidized starch using a double oxidizing agent, characterized in that, The oxidation reaction is carried out sequentially using hydrogen peroxide and sodium hypochlorite. After the aldehyde group of starch is oxidized to 0.6-0.7% by hydrogen peroxide, sodium hypochlorite is then used for further oxidation. The hydrogen peroxide has an oxidation temperature of 45-50℃ and a pH value of 8.0-8.

5. The oxidation temperature of the sodium hypochlorite is 43-45℃.

2. The method for preparing oxidized starch using a dual oxidizing agent according to claim 1, characterized in that, The amount of hydrogen peroxide added is: 27.5% hydrogen peroxide added at 2.6% of the starch mass.

3. The method for preparing oxidized starch using a dual oxidizing agent according to claim 1, characterized in that, The amount of sodium hypochlorite added is 200 kg / ton of starch with an effective content of 13%.

4. The method for preparing oxidized starch using a dual oxidizing agent according to claim 3, characterized in that, The method for adding sodium hypochlorite is as follows: adjust the pH of the reaction solution to 7.5-7.6, add sodium hypochlorite at a rate of 1500-1800 kg / h, when the pH of the reaction solution rises to 9.5-10.00, reduce the sodium hypochlorite addition rate to 500-800 kg / h, and when the pH starts to decrease, increase the sodium hypochlorite addition rate to 2000-2500 kg / h until all the sodium hypochlorite has been added.

5. The method for preparing oxidized starch using a dual oxidizing agent according to claim 1, characterized in that, The specific steps of the method are as follows: (1) Adjust the pH of the starch milk to 8.0-8.5, add hydrogen peroxide and heat the starch milk to 45-50℃, detect the aldehyde content in the starch milk, and when the aldehyde content in the starch reaches 0.6-0.7%, cool the starch milk to 43-45℃. (2) After adjusting the pH of the starch milk obtained in step (1) to 7.5-7.6, add sodium hypochlorite at a rate of 1500-1800 kg / h. When the pH of the starch milk rises to 9.50-10.00, reduce the sodium hypochlorite addition rate to 500-800 kg / h. When the pH of the starch milk begins to decrease, increase the sodium hypochlorite addition rate to 2000-2500 kg / h until all the sodium hypochlorite has been added. After the sodium hypochlorite has reacted completely, adjust the pH to 5.5-6.5, centrifuge, wash and dry the starch milk to obtain oxidized starch.

6. The method for preparing oxidized starch using a dual oxidizing agent according to claim 5, characterized in that, The concentration of the starch milk in step (1) is 38-40%; The pH adjustment in steps (1) and (2) uses sodium hydroxide solution.