A method for preparing cellulose ether with high whiteness, low chromaticity and low viscosity

Abstract

This application relates to the technical field of cellulose ethers, and particularly relates to a method for preparing a cellulose ether with high whiteness, low chromaticity and low viscosity. The method for preparing a cellulose ether with high whiteness, low chromaticity and low viscosity according to this application comprises the following steps: First, a high-viscosity cellulose ether is complexed with metal ions to form a complex, then the complex undergoes an oxidative degradation reaction under the action of hydrogen peroxide to obtain a low-viscosity cellulose ether crude material, and finally impurity removal, drying and pulverization are carried out. The low-viscosity cellulose ether obtained by the above preparation method not only has a low viscosity, but also has a whiteness of 87-92 and a yellowness of less than 3. Moreover, when a catalyst is added during the oxidative degradation process, the degradation reaction rate can be further increased and the degradation reaction time can be reduced. This low-viscosity cellulose ether has good quality and processing performance and can be applied to fields such as coatings, paints, medicines, and cosmetics.

Description

Technical Field

[0001] The present application relates to the technical field of cellulose ethers, and particularly relates to a method for preparing cellulose ethers with high whiteness, low chromaticity and low viscosity. Background Art

[0002] The viscosity of cellulose ethers has a very great influence on the processing performance of cellulose ethers. Among them, the molecular chains of low-viscosity cellulose ethers are relatively short, with large solubility in water, good fluidity, and easy to disperse and mix. Therefore, they have important applications in fields such as coatings, paints, medicine, and cosmetics.

[0003] At present, there are mainly two methods for preparing low-viscosity cellulose ethers. One is to prepare them by etherification of low-molecular-weight alkaline cellulose, and the other is to degrade high-viscosity cellulose ethers. If low-molecular-weight alkaline cellulose is used for etherification preparation, the refining process is relatively difficult, and low-molecular-weight cellulose ethers may be washed out, reducing the yield of low-viscosity cellulose ethers. However, if low-viscosity cellulose ethers are obtained by degrading high-viscosity cellulose ethers, degradation is carried out after refining, and the above problems will not occur.

[0004] The viscosity reduction of high-viscosity cellulose ethers can be achieved by adding inorganic acids. However, in this method, the addition of inorganic acids and subsequent alkali neutralization during the viscosity reduction process increase the salt content of the product, and there may be a residual acid smell in the product, thus affecting the quality of the product. In addition, degradation can also be carried out by oxidation, but degradation control is difficult, and there may be more oxidation by-products, or the molecular chain lengths after degradation vary greatly, affecting the quality of low-viscosity cellulose ethers, such as a decrease in whiteness, an increase in yellowness, and uneven quality.

[0005] The patent application document with publication number CN111344308A discloses the oxidative degradation of cellulose ethers, which is to add an oxidant to a water-wet cellulose ether raw material, carry out oxidative degradation at 20 - 100 °C, then dry, and add an alkaline salt to obtain low-viscosity cellulose ethers. However, the whiteness of the obtained low-viscosity cellulose ethers is 80 - 92, and the yellowness is 3.3, with relatively low whiteness and relatively high yellowness. Summary of the Invention

[0006] In order to improve the whiteness of low-viscosity cellulose ethers and reduce the yellowness, the present application provides a method for preparing cellulose ethers with high whiteness, low chromaticity and low viscosity.

[0007] A method for preparing cellulose ethers with high whiteness, low chromaticity and low viscosity, comprising the following steps:

[0008] S1: Add high-viscosity cellulose ethers to a metal salt solution, react at 50 - 70 °C for 3 - 6 h, wash with ethanol and dry under vacuum to obtain a cellulose ether metal complex;

[0009] S2: Add the cellulose ether metal complex to a kneader, heat it up to 80 - 100 °C, spray in an aqueous hydrogen peroxide solution, continuously stir for 2 - 8 h, and discharge the material to obtain a low-viscosity cellulose ether crude product;

[0010] S3: Add the low-viscosity cellulose ether crude product to deionized water, use a cation exchange resin to remove cations, and perform vacuum drying until the mass fraction of water in the material < 4.5%, then grind it into powder to obtain the product.

[0011] In the above technical solution, there are many hydroxyl groups, ether bonds, etc. in the macromolecular chain of high-viscosity cellulose ether. Especially when the degree of substitution is low, strong intermolecular hydrogen bond interactions can form between cellulose ether molecules, resulting in relatively large intermolecular forces. Moreover, high-viscosity cellulose ether generally has a relatively high molecular weight, a long molecular chain, and the molecular chains are intertwined with each other, with a small steric hindrance. Therefore, the viscosity of high-viscosity cellulose ether is relatively large and its solubility decreases. When oxidative degradation occurs, it is difficult for oxidant molecules or generated free radicals to enter the interior of the intertwined molecular chains, but it is more conducive to attacking the ends of the molecular chains, resulting in uneven molecular chains of the degraded cellulose ether and affecting the product quality.

[0012] By forming a complex of high-viscosity cellulose ether with metal ions, the metal ions coordinate with the oxygen in the hydroxyl or ether bonds of high-viscosity cellulose ether, thereby reducing the generation of hydrogen bonds in high-viscosity cellulose ether and weakening the hydrogen bond interaction in the cellulose ether molecules. In addition, the introduction of metal ions can increase the distance between molecules, making it more conducive for small molecules such as oxidants to enter, thus causing the molecular chains of high-viscosity cellulose ether to break and form shorter molecular chains. Moreover, by adjusting the ratio of high-viscosity cellulose ether and metal ions, the number of coordination sites can be adjusted, enabling the coordination sites to be relatively evenly distributed in the high-viscosity cellulose ether molecular chain, which is conducive to obtaining relatively uniform low-molecular-weight cellulose ether chains. Also, metal ions can catalyze the decomposition of hydrogen peroxide by changing the valence state, increasing the decomposition rate of hydrogen peroxide, and thus increasing the rate of oxidative degradation.

[0013] During the oxidative degradation process, the reaction temperature, reaction time, and the addition amount of hydrogen peroxide have important effects on the degradation products. First of all, if the reaction temperature is too low, the decomposition rate of hydrogen peroxide is slow and the oxidative degradation rate is slow. If the reaction temperature is too high, hydrogen peroxide may undergo ineffective decomposition, making it impossible for high-viscosity cellulose ether to be fully oxidatively degraded. Secondly, as the reaction time prolongs, the oxidative degradation becomes more complete. However, after hydrogen peroxide is completely consumed, further prolonging the reaction time will not result in further oxidative degradation. Finally, when the concentration of hydrogen peroxide in the reaction system is too high, excessive hydrogen peroxide may become a scavenger for decomposed hydroxyl radicals, reacting with hydroxyl radicals to generate oxygen and water, resulting in a reduction in hydroxyl radicals and a slowdown in the oxidative degradation rate, making it impossible for high-viscosity cellulose to be fully degraded.

[0014] Deionized water is added to the low-viscosity cellulose ether crude material. The low-viscosity cellulose ether dissolves in water, and metal cations are removed through a cation exchange resin to reduce the impact of impurities on product quality.

[0015] Preferably, the high-viscosity cellulose ether in step S1 is one or more of carboxymethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl methyl cellulose, and hydroxyethyl cellulose.

[0016] Preferably, the viscosity of the aqueous solution prepared by the high-viscosity cellulose ether in step S1 with a mass fraction of 2% is 5000 - 50000 mPa•s.

[0017] Preferably, the metal salt in step S1 is one of iron salts, copper salts, and cobalt salts.

[0018] Preferably, in step S1, the mass ratio of the high-viscosity cellulose ether to the metal salt is 100:(10 - 30).

[0019] Preferably, in step S2, the mass ratio of the cellulose ether metal complex to hydrogen peroxide is 100:(1 - 10).

[0020] In the above technical solution, the amount of hydrogen peroxide added has a great influence on the quality of the resulting low-viscosity cellulose ether. If the amount of hydrogen peroxide added is too small, the whiteness is low, the yellowness increases, and the viscosity is on the high side, and the reaction time will also be extended. If the amount of hydrogen peroxide added is too much, hydrogen peroxide cannot be fully utilized, and the high-viscosity cellulose ether will not be fully degraded.

[0021] Further preferably, in step S2, a catalyst is also added. The preparation method of the catalyst includes the following steps:

[0022] MCM-48 molecular sieve is added to the precursor solution of the metal active component, and ultrasonic impregnation is carried out for 1 - 3 h, dried at 100 - 120 °C for 3 - 6 h, and then calcined in a muffle furnace at 450 - 650 °C for 1 - 3 h to obtain the catalyst.

[0023] In the above technical solution, the metal active component is loaded on the molecular sieve with a large surface area, so that the metal active component is evenly dispersed on the carrier, which can catalyze the decomposition of hydrogen peroxide, improve the oxidation degradation rate, reduce the generation of by-products, and improve the product quality.

[0024] Preferably, the metal active component is one or more of copper oxide, iron oxide, and cobalt oxide.

[0025] Preferably, the mass ratio of the MCM-48 molecular sieve to the precursor of the metal active component is 1:(0.1 - 0.25).

[0026] Preferably, the mass ratio of the cellulose ether metal complex to the catalyst is 100:(0.1-1).

[0027] The above technical solution of the present application has at least the following beneficial effects:

[0028] 1. In the present application, a high-viscosity cellulose ether is complexed with metal ions to form a cellulose ether metal complex having a certain number of coordination sites, which is conducive to subsequent degradation into a low-viscosity cellulose ether with relatively uniform molecular chain length, improving whiteness and reducing yellowness.

[0029] 2. In the present application, a molecular sieve is used to support a metal active component, which serves as a catalyst for hydrogen peroxide decomposition during the degradation process, improving the hydrogen peroxide decomposition rate, the degradation rate of the high-viscosity cellulose ether, and the quality of the product.

[0030] 3. The whiteness of the low-viscosity cellulose ether obtained by the preparation method of the present application is 87-92, and the yellowness <3. Description of the Drawings

[0031] Figure 1 is the viscosity of an aqueous solution prepared from a high-viscosity cellulose ether raw material and a low-viscosity cellulose ether with a mass fraction of 2%;

[0032] Figure 2 is the whiteness and yellowness of the low-viscosity cellulose ether. Detailed Embodiments

[0033] The following further describes the present application in detail with reference to embodiments.

[0034] The raw materials of the examples and comparative examples of the present application are all ordinary commercially available products unless otherwise specified.

[0035] Embodiments

[0036] Example 1

[0037] The method for preparing a high-whiteness, low-chromaticity, low-viscosity cellulose ether in this example includes the following steps:

[0038] S1: Weigh 500 g of carboxymethyl cellulose, add 5000 g of an aqueous solution of ferric chloride with a mass fraction of 1%, react at 50 °C for 6 h, wash the product with an ethanol solution with a volume fraction of 80%, and place it in a vacuum drying oven to dry at 50 °C to obtain a cellulose ether metal complex;

[0039] S2: Weigh 1 kg of the cellulose ether metal complex, add it to a kneader, start stirring, heat up to 80 °C, spray in 50 g of an aqueous hydrogen peroxide solution with a mass fraction of 20%, continuously stir for 8 h, and discharge to obtain a low-viscosity cellulose ether crude material;

[0040] S3: Dissolve the above-mentioned low-viscosity cellulose ether crude material in deionized water, use cation exchange resin to remove metal cations, conduct vacuum drying until the mass fraction of water in the material < 4.5%, and grind into powder, then it is ready.

[0041] Example 2

[0042] The method for preparing high-whiteness, low-chromaticity and low-viscosity cellulose ether in this example includes the following steps:

[0043] S1: Weigh 500 g of hydroxypropyl cellulose, add 5000 g of cobalt chloride aqueous solution with a mass fraction of 3%, react at 70 °C for 3 h, wash the product with ethanol solution with a volume fraction of 80%, put it into a vacuum drying oven, and dry at 50 °C to obtain a cellulose ether metal complex;

[0044] S2: Weigh 1 kg of the cellulose ether metal complex, add it to a kneader, start stirring, heat up to 100 °C, spray in 50 g of hydrogen peroxide aqueous solution with a mass fraction of 20%, continuously stir for 2 h, and discharge to obtain a low-viscosity cellulose ether crude material;

[0045] S3: Dissolve the above-mentioned low-viscosity cellulose ether crude material in deionized water, use cation exchange resin to remove metal cations, conduct vacuum drying until the mass fraction of water in the material < 4.5%, and grind into powder, then it is ready.

[0046] Example 3

[0047] The method for preparing high-whiteness, low-chromaticity and low-viscosity cellulose ether in this example includes the following steps:

[0048] S1: Weigh 500 g of hydroxypropyl methyl cellulose, add 5000 g of copper chloride aqueous solution with a mass fraction of 2%, react at 60 °C for 5 h, wash the product with ethanol solution with a volume fraction of 80%, put it into a vacuum drying oven, and dry at 50 °C to obtain a cellulose ether metal complex;

[0049] S2: Weigh 1 kg of the cellulose ether metal complex, add it to a kneader, start stirring, heat up to 90 °C, spray in 50 g of hydrogen peroxide aqueous solution with a mass fraction of 20%, continuously stir for 5 h, and discharge to obtain a low-viscosity cellulose ether crude material;

[0050] S3: Dissolve the above-mentioned low-viscosity cellulose ether crude material in deionized water, use cation exchange resin to remove metal cations, conduct vacuum drying until the mass fraction of water in the material < 4.5%, and grind into powder, then it is ready.

[0051] Example 4

[0052] The difference between the method for preparing high-whiteness, low-chromaticity and low-viscosity cellulose ether in this example and that in Example 3 is as follows:

[0053] S2: Weigh 100 g of the cellulose ether metal complex and 200 mL of deionized water, stir evenly, heat up to 90 °C, spray in 50 g of a 20% hydrogen peroxide aqueous solution, continuously stir for 5 h, discharge the material, and obtain the low-viscosity cellulose ether crude material;

[0054] The remaining steps are the same as those in Example 3.

[0055] Example 5

[0056] The difference between the method for preparing the high-whiteness, low-chromaticity, and low-viscosity cellulose ether in this example and that in Example 3 lies in:

[0057] S2: Weigh 100 g of the cellulose ether metal complex and 200 mL of deionized water, stir evenly, heat up to 90 °C, spray in 30 g of a 20% hydrogen peroxide aqueous solution, continuously stir for 5 h, discharge the material, and obtain the low-viscosity cellulose ether crude material;

[0058] The remaining steps are the same as those in Example 3.

[0059] Example 6

[0060] The difference between the method for preparing the high-whiteness, low-chromaticity, and low-viscosity cellulose ether in this example and that in Example 5 lies in:

[0061] S2: Weigh 1 kg of the cellulose ether metal complex and 1 g of the catalyst, add them to a kneader, start stirring, heat up to 90 °C, spray in 300 g of a 20% hydrogen peroxide aqueous solution, continuously stir for 3 h, discharge the material, and obtain the low-viscosity cellulose ether crude material;

[0062] S3: Dissolve the above low-viscosity cellulose ether crude material in deionized water, filter to remove the catalyst, use a cation exchange resin to remove metal cations, perform vacuum drying until the mass fraction of water in the material < 4.5%, and grind into powder, then it is ready;

[0063] The remaining steps are the same as those in Example 5;

[0064] The preparation method of the catalyst in this example includes the following steps:

[0065] Weigh 20 g of a 5% cobalt chloride aqueous solution, add 10 g of MCM-48 molecular sieve, perform ultrasonic impregnation for 1 h, dry at 100 °C for 6 h, and calcine in a muffle furnace at 450 °C for 3 h to obtain it.

[0066] Example 7

[0067] The difference between the method for preparing the high-whiteness, low-chromaticity, and low-viscosity cellulose ether in this example and that in Example 5 lies in:

[0068] S2: Weigh 1 kg of the cellulose ether metal complex and 10 g of the catalyst, add them to a kneader, start stirring, heat up to 90 °C, spray in 300 g of an aqueous hydrogen peroxide solution with a mass fraction of 20%, continuously stir for 3 h, discharge the material, and obtain the low-viscosity cellulose ether crude material;

[0069] S3: Dissolve the above-mentioned low-viscosity cellulose ether crude material in deionized water, filter to remove the catalyst, use a cation exchange resin to remove metal cations, perform vacuum drying until the mass fraction of water in the material < 4.5%, and grind into powder;

[0070] The remaining steps are the same as those in Example 5;

[0071] In this example, the preparation method of the catalyst includes the following steps:

[0072] Weigh 50 g of an aqueous ferric chloride solution with a mass fraction of 5%, add 10 g of MCM-48 molecular sieve, perform ultrasonic impregnation for 3 h, dry at 120 °C for 3 h, place it in a muffle furnace and calcine at 650 °C for 1 h to obtain it.

[0073] Comparative Example

[0074] Comparative Example 1

[0075] The method for preparing high-whiteness, low-chromaticity and low-viscosity cellulose ether in this comparative example includes the following steps:

[0076] Weigh 1 kg of hydroxypropyl methyl cellulose, add it to a kneader, start stirring, heat up to 90 °C, spray in 50 g of an aqueous hydrogen peroxide solution with a mass fraction of 20%, continuously stir for 5 h, perform vacuum drying until the mass fraction of water in the material < 4.5%, and grind into powder.

[0077] Performance Detection Test

[0078] 1. Viscosity Detection

[0079] Prepare aqueous solutions with a mass fraction of 2% from the high-viscosity cellulose ether raw materials and the obtained low-viscosity cellulose ether in Examples 1 - 7 and Comparative Example 1 respectively, and measure the viscosity at room temperature using a rotational viscometer. The results are as Figure 1 shown.

[0080] 2. Whiteness and Yellowness Detection

[0081] Refer to ASTM E313 standard to measure the whiteness and yellowness of the low-viscosity cellulose ether. The higher the yellowness, the more obvious the color difference and the higher the chromaticity. The results are as Figure 2 shown.

[0082] Result Analysis

[0083] From Figure 1From the data of Comparative Example 1 and the Examples, it can be seen that after the high-viscosity cellulose ether is combined with metal ions, it is more likely to degrade, with a lower viscosity. Moreover, from the data of the Examples, it can be seen that as the addition amount of hydrogen peroxide increases, the viscosity of the low-viscosity cellulose ether first decreases significantly and then basically remains unchanged. And after adding the catalyst, the viscosity of the low-viscosity cellulose ether decreases to a certain extent.

[0084] From Figure 2 the data in, it can be seen that after the high-viscosity cellulose ether is combined with metal ions, the whiteness is greatly improved and the yellowness is reduced, indicating that the quality of the obtained low-viscosity cellulose ether is better; in addition, as the addition amount of hydrogen peroxide increases, the whiteness increases and the yellowness decreases, but after reaching a certain value, it basically remains unchanged.

[0085] This specific embodiment is only an explanation of the present application and is not a limitation of the present application. Those skilled in the art can make modifications without creative contributions to this embodiment according to needs after reading this specification, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. A method for preparing high-whiteness, low-color and low-viscosity cellulose ether, characterized in that: The steps include: S1: adding high viscosity cellulose ether to a metal salt solution, reacting at 50-70°C for 3-6h, washing with ethanol, and vacuum drying to obtain a cellulose ether metal complex; S2: adding the cellulose ether metal complex into a kneader, heating to 80-100° C., spraying in an aqueous hydrogen peroxide solution, stirring continuously for 2-8 hours, discharging the material, and obtaining a low-viscosity cellulose ether crude material; S3: Add low-viscosity cellulose ether crude material into deionized water, use cation exchange resin to remove cations, vacuum dry until the mass fraction of water in the material is less than 4.5%, and grind into powder; In step S2, a catalyst is also added, and the preparation method of the catalyst comprises the following steps: Add MCM-48 molecular sieve to the precursor solution of metal active components, ultrasonically impregnate for 1-3 hours, dry at 100-120° C. for 3-6 hours, place in a muffle furnace and roast at 450-650° C. for 1-3 hours to obtain the product.

2. The method for preparing high-whiteness, low-color and low-viscosity cellulose ether according to claim 1, characterized in that: The high viscosity cellulose ether in step S1 is one or more of carboxymethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl methyl cellulose and hydroxyethyl cellulose.

3. The method for preparing high-whiteness, low-color and low-viscosity cellulose ether according to claim 1, characterized in that: The viscosity of the aqueous solution of the high viscosity cellulose ether prepared in step S1 with a mass fraction of 2% is 5000-50000 mPa•s.

4. The method for preparing high-whiteness, low-color and low-viscosity cellulose ether according to claim 1, characterized in that: The metal salt in step S1 is one of an iron salt, a copper salt and a cobalt salt.

5. The method for preparing high-whiteness, low-color and low-viscosity cellulose ether according to claim 1, characterized in that: In step S1, the mass ratio of the high viscosity cellulose ether to the metal salt is 100:(10-30).

6. The method for preparing high-whiteness, low-color and low-viscosity cellulose ether according to claim 1, characterized in that: In step S2, the mass ratio of the cellulose ether metal complex to hydrogen peroxide is 100:(1-10).

7. The method for preparing high-whiteness, low-color and low-viscosity cellulose ether according to claim 1, characterized in that: The metal active component is one or more of copper oxide, iron oxide and cobalt oxide.

8. The method for preparing high-whiteness, low-color and low-viscosity cellulose ether according to claim 1, characterized in that: The mass ratio of the MCM-48 molecular sieve to the precursor of the metal active component is 1:(0.1-0.25).

9. The method for preparing high-whiteness, low-color and low-viscosity cellulose ether according to claim 1, characterized in that: The mass ratio of the cellulose ether metal complex to the catalyst is 100:(0.1-1).

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