Hydroxypropyl methyl cellulose as well as preparation method and application thereof
By etherifying the surfactant, monohalogenated methane and alkylene oxide with alkalized cellulose solution under a protective gas atmosphere, the problems of complex process and high risk in the prior art are solved, and high efficiency and low-cost preparation of hydroxypropyl methyl cellulose is achieved, which is suitable for pharmaceutical excipients and other fields.
Patent Information
- Application Number
- CN202411801354.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-09
- Publication Date
- 2025-03-04
AI Technical Summary
The existing hydroxypropyl methylcellulose synthesis process has problems such as long process, complex operation, high risk and high synthesis cost.
Hydroxypropylmethylcellulose is prepared by adding surfactant, monohalogenated methane and alkylene oxide to the alkalized cellulose solution under a protective gas atmosphere. Preferred surfactants include polyquaternary ammonium salt-7, cetylpyridine bromide or polypropylene glycol.
The preparation method of hydroxypropyl methyl cellulose with simple process, short process, low risk coefficient and low synthesis cost is realized. The products obtained have high substitution and high viscosity, and are suitable for pharmaceutical excipients and other fields.
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Figure CN119552276A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of cellulose preparation and relates to hydroxypropyl methylcellulose and a preparation method and application thereof. Background Art
[0002] Hydroxypropyl methylcellulose (also known as hydroxypropyl methylcellulose, referred to as HPMC) is a non-ionic water-soluble cellulose mixed ether, and its structure is shown in the following formula I, where R=CH3 or CH2CH(OH)CH3; n is the degree of substitution. Hydroxypropyl methylcellulose is widely used in many fields such as coatings, polymerization reactions, building materials, oil drilling and mining, textiles, food, medicine, daily ceramics, electronic devices and agricultural seeds. It is an indispensable chemical additive in industry. The viscosity range of hydroxypropyl methylcellulose varies depending on its degree of substitution and is suitable for different fields. For example, hydroxypropyl methylcellulose with a high degree of substitution has a higher viscosity and is mainly used as a pharmaceutical excipient; while hydroxypropyl methylcellulose with a low degree of substitution is suitable for food and cosmetics.
[0003]
[0004] Formula Ⅰ.
[0005] In the existing synthesis process of hydroxypropyl methylcellulose, an inert organic diluent is often required to be added to achieve the effect of diluting and diffusing the etherifying agent. In the subsequent treatment process, the organic reagent needs to be heated and evaporated for recycling. This process has the disadvantages of long process, complex operation, high risk and high synthesis cost. Summary of the invention
[0006] In view of the deficiencies in the prior art, the present invention provides a method for preparing hydroxypropyl methylcellulose with a simple process, a short flow, a relatively low risk factor and a low synthesis cost. Furthermore, the hydroxypropyl methylcellulose prepared above can be applied to pharmaceutical excipients.
[0007] In order to achieve the above-mentioned object of the invention, the embodiment of the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing hydroxypropyl methylcellulose, the method comprising the following steps: Under a protective gas atmosphere, a surfactant, a methyl halide and an alkylene oxide are added to an alkalized cellulose solution to carry out an etherification reaction to obtain hydroxypropyl methylcellulose; Wherein, the surfactant comprises at least one of polyquaternium-7, cetylpyridinium bromide or polypropylene glycol; The alkalized cellulose solution is prepared by an alkalization reaction between a cellulose raw material and a strong alkali solution; The mass ratio of the surfactant to the cellulose raw material is 1:4100-1:8000.
[0008] The preparation method of hydroxypropyl methylcellulose provided by the present invention uses natural cellulose as raw material, first reacts with a strong alkaline solution to alkalize the cellulose, and then etherifies the alkalized cellulose with a halogenated methyl and an alkylene oxide under the action of a surfactant to prepare hydroxypropyl methylcellulose. Among them, the preferred surfactant (polyquaternium-7, cetylpyridinium bromide, polypropylene glycol) of the present invention can significantly improve the solubility of the halogenated methyl and the alkylene oxide in water, so as to promote the etherification reaction in the preparation method.
[0009] The preparation method of hydroxypropyl methylcellulose provided by the present invention has the advantages of simple operation, short process flow, relatively low risk factor and low synthesis cost. The prepared hydroxypropyl methylcellulose has high degree of substitution and viscosity, wherein the methoxy content is 28.8% to 29.6%, the hydroxypropoxy content is 7.7% to 8.5%, and the viscosity can reach 15.3 mPa·s, and has broad application prospects.
[0010] Preferably, the method for preparing the alkalized cellulose solution comprises the following steps: in a protective gas atmosphere, the cellulose raw material and the strong alkaline solution are subjected to an alkalization reaction at a temperature of 10° C. to 20° C. for 3 h to 5 h to obtain the alkalized cellulose solution.
[0011] Preferably, the protective gas includes at least one of nitrogen, argon or helium. Based on practicality, the present invention uses high-purity nitrogen as an example for illustration in the embodiments, and other inert gases or rare gases can also achieve similar effects.
[0012] The cellulose raw material includes short cotton linter cellulose, which is crushed to 50-500 meshes when used; The strong alkaline solution includes sodium hydroxide solution or potassium hydroxide solution.
[0013] Preferably, the mass ratio of the cellulose raw material to the strong alkaline solution is 1:2.5 to 1:3.0; Wherein, the concentration of the strong alkaline solution is 30%~70%.
[0014] Preferably, the monohalomethane comprises methyl chloride; The alkylene oxide includes propylene oxide.
[0015] After adding the preferred surfactant of the present invention, the solubility of methyl chloride and propylene oxide in the reaction system can be significantly improved, which is beneficial to the positive progress of the etherification reaction.
[0016] In the preparation method provided by the present invention, the reaction process is specifically as follows: .
[0017] Preferably, the mass ratio of the cellulose raw material, the monohalogenated methyl ethane and the alkylene oxide is 1:0.8~1.2:0.25~0.50.
[0018] Preferably, the reaction temperature of the etherification reaction is 80° C. to 100° C., the reaction time is 3 h to 5 h, and the reaction pressure is 0.3 MPa to 0.5 MPa.
[0019] Preferably, after the etherification reaction is completed, the pH of the reaction solution is adjusted and then purified to obtain pure hydroxypropyl methylcellulose. The specific steps include: after the etherification reaction is completed, hydrochloric acid or acetic acid is added to adjust the pH of the reaction solution to 6.8-7.2, the temperature is raised to 50°C-60°C to solidify the cellulose ether in the reaction solution, and a solid filtrate is obtained by filtering; The solid filtrate is dissolved in low-temperature purified water, kept at 10°C to 20°C for 25min to 40min, heated to 50°C to 60°C again, filtered, and the solid is collected to obtain the hydroxypropyl methylcellulose.
[0020] In a second aspect, the present invention provides hydroxypropyl methylcellulose, which is prepared by the preparation method of hydroxypropyl methylcellulose provided in the first aspect.
[0021] The hydroxypropyl methylcellulose prepared by the invention has high substitution degree and viscosity, wherein the methoxy content is 28.9%-29.6%, the hydroxypropoxy content is 7.7%-8.5%, and the viscosity can reach 15 mPa·s, and has broad application prospects.
[0022] In a third aspect, in view of the properties of the hydroxypropyl methylcellulose provided in the second aspect of the present invention, it can be used as a pharmaceutical excipient and further applied in the field of biomedicine. BRIEF DESCRIPTION OF THE DRAWINGS
[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.
[0024] Figure 1 This is a gas chromatogram of the determination of the methoxyl content and hydroxypropoxyl content in hydroxypropyl methylcellulose in Example 1 of the present invention. DETAILED DESCRIPTION
[0025] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with the examples. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. The raw materials and reagents used in the present invention, unless otherwise specified, are conventional commercial products; the methods used in the present invention, unless otherwise specified, are conventional methods in the art.
[0026] In order to better explain the present invention, the following two aspects are described here.
[0027] 1. Effect of preferred surfactants on the solubility of methyl chloride and propylene oxide At room temperature and pressure (25°C, 101KPa), the present invention investigates the effect of surfactants (polyquaternium salt-7, cetylpyridinium bromide, polypropylene glycol) on the solubility of methyl chloride and propylene oxide in water. The specific contents are as follows: The present invention uses the micro Karl Fischer method and the turbidity point method to determine the solubility of methyl chloride in water; uses a solubility tester to accurately measure the solubility of propylene oxide in water by controlling temperature and pressure conditions. The results are shown in the following tables 1-2.
[0028] Table 1 Effect of different surfactants on the solubility of methyl chloride
[0029] Table 2 Effect of different surfactants on the solubility of propylene oxide
[0030] At room temperature and pressure, the solubility of methyl chloride in water is 4.2 g / L, and the solubility of propylene oxide in water (mass fraction) is 40.5%. As shown in Table 1-2, within the experimental range of the present invention, after adding the preferred surfactant-polyquaternium salt-7, cetylpyridinium bromide, and polypropylene glycol, the solubility of methyl chloride can reach more than 31.29 g / L, and the solubility of propylene oxide can reach more than 78.3%. Therefore, after adding the preferred surfactant of the present invention, the solubility of methyl chloride and propylene oxide in the reaction system can be significantly improved, which is conducive to the forward progress of the etherification reaction.
[0031] 2. Determination of Degree of Substitution In the present invention, the methoxy content and hydroxypropoxy content in hydroxypropyl methylcellulose are determined according to the first method (gas chromatography) of the methoxy, ethoxy and hydroxypropoxy determination method of Part IV 0712 of the 2020 edition of the Chinese Pharmacopoeia.
[0032] Example 1 This embodiment provides a method for preparing hydroxypropyl methylcellulose, which comprises the following steps: (1) Alkalization reaction 50 g of natural short cotton linter cellulose crushed to 50 mesh and 125 g of 30% sodium hydroxide solution at room temperature were placed in an autoclave, and the reaction system was reacted at 15° C. for 4 hours under a nitrogen atmosphere to obtain an alkalized cellulose solution; (2) Etherification reaction To the above alkalized cellulose solution, add 6.25 mg of polyquaternium-7, 40 g of monochloromethane and 20 g of propylene oxide, and react for 4 hours under a nitrogen atmosphere at a pressure of 0.4 MPa and a temperature of 90° C. to obtain a reaction solution after etherification.
[0033] (3) Refining After the etherification reaction is completed, the pH is adjusted to 7.0 with acetic acid, and then the reaction solution is heated to 55°C to solidify the cellulose ether, and filtered to obtain a solid filtrate (filter cake), which is placed in 10°C low-temperature purified water and stirred to fully dissolve the cellulose ether. The mixture is stirred for 30 minutes at a temperature of 55°C and then heated to 55°C to solidify the cellulose ether again. The cellulose ether is filtered to obtain 50.15 g of a refined filter cake, namely, hydroxypropyl methylcellulose.
[0034] The methoxy content of the hydroxypropyl methylcellulose prepared in this embodiment was determined to be 29.3%, and the hydroxypropoxy content was 7.7%. The gas chromatogram for determining the methoxy content and hydroxypropoxy content of the hydroxypropyl methylcellulose is shown in FIG. Figure 1 shown.
[0035] The viscosity of the obtained hydroxypropyl methylcellulose was measured by rotational viscosity measurement method and was found to be 15 mPa·s.
[0036] Example 2 This embodiment provides a method for preparing hydroxypropyl methylcellulose, which comprises the following steps: (1) Alkalization reaction 50 g of natural short cotton linter cellulose crushed to 100 mesh and 125 g of 50% potassium hydroxide solution were placed in an autoclave, and the reaction system was reacted at 10° C. for 5 hours under a nitrogen atmosphere to obtain an alkalized cellulose solution; (2) Etherification reaction To the above alkalized cellulose solution, add 7.50 mg of polyquaternium-7, 45 g of monochloromethane and 20 g of propylene oxide, and react for 5 hours under a nitrogen atmosphere at a pressure of 0.5 MPa and a temperature of 80°C to obtain a reaction solution after etherification.
[0037] (3) Refining After the etherification reaction is completed, the pH is adjusted to 7.2 with hydrochloric acid, and then the reaction solution is heated to 50°C to solidify the cellulose ether, and filtered to obtain a solid filtrate (filter cake), which is placed in 15°C low-temperature purified water and stirred to fully dissolve the cellulose ether. The mixture is stirred at this temperature for 40 minutes, and the temperature is raised to 50°C again to solidify the cellulose ether again, and filtered to obtain 50.09 g of a refined filter cake, namely, hydroxypropyl methylcellulose.
[0038] It was determined that the methoxy content of the hydroxypropyl methylcellulose prepared in this example was 28.9%, and the hydroxypropoxy content was 7.8%.
[0039] The viscosity of the obtained hydroxypropyl methylcellulose was measured by rotational viscosity measurement method and was found to be 15.3 mPa·s.
[0040] Example 3 This embodiment provides a method for preparing hydroxypropyl methylcellulose, which comprises the following steps: (1) Alkalization reaction 50 g of natural short cotton cellulose crushed to 500 mesh and 140 g of 70% potassium hydroxide solution were placed in an autoclave, and the reaction system was reacted at 20° C. for 3 hours under a nitrogen atmosphere to obtain an alkalized cellulose solution; (2) Etherification reaction To the above alkalized cellulose solution, 11.20 mg of polypropylene glycol, 50 g of methyl chloride and 22.5 g of propylene oxide were added, and the mixture was reacted for 3 h under the conditions of a pressure of 0.3 MPa and a temperature of 100° C. in a nitrogen atmosphere to obtain a reaction solution after etherification.
[0041] (3) Refining After the etherification reaction is completed, the pH is adjusted to 6.8 with hydrochloric acid, and then the reaction solution is heated to 55°C to solidify the cellulose ether, and filtered to obtain a solid filtrate (filter cake), which is placed in 20°C low-temperature purified water and stirred to fully dissolve the cellulose ether. The mixture is stirred for 30 minutes at a temperature of 55°C and then heated to 55°C to solidify the cellulose ether again. The cellulose ether is filtered to obtain 50.17 g of a refined filter cake, namely, hydroxypropyl methylcellulose.
[0042] It was determined that the methoxy content of the hydroxypropyl methylcellulose prepared in this example was 29.6%, and the hydroxypropoxy content was 8.5%.
[0043] The viscosity of the obtained hydroxypropyl methylcellulose was measured by rotational viscosity measurement method and was found to be 15.1 mPa·s.
[0044] Example 4 This embodiment provides a method for preparing hydroxypropyl methylcellulose, which comprises the following steps: (1) Alkalization reaction 50 g of natural short cotton linter cellulose crushed to 200 mesh and 150 g of 30% sodium hydroxide solution were placed in an autoclave, and the reaction system was reacted at 15° C. for 4 hours under a nitrogen atmosphere to obtain an alkalized cellulose solution; (2) Etherification reaction To the above alkalized cellulose solution, 12.0 mg of cetylpyridine, 50 g of methyl chloride and 25 g of propylene oxide were added, and the mixture was reacted for 4 h at a pressure of 0.4 MPa and a temperature of 90° C. in a nitrogen atmosphere to obtain an etherified reaction solution.
[0045] (3) Refining After the etherification reaction is completed, the pH is adjusted to 7.0 with hydrochloric acid, and then the reaction solution is heated to 60°C to solidify the cellulose ether, and filtered to obtain a solid filtrate (filter cake), which is placed in 15°C low-temperature purified water and stirred to fully dissolve the cellulose ether. The mixture is stirred for 30 minutes at a temperature of 40°C and heated to 60°C again to solidify the cellulose ether again. The filtrate is filtered to obtain 50.21 g of a refined filter cake, namely, hydroxypropyl methylcellulose.
[0046] It was determined that the methoxy content of the hydroxypropyl methylcellulose prepared in this example was 29.2%, and the hydroxypropoxy content was 8.0%.
[0047] The viscosity of the obtained hydroxypropyl methylcellulose was measured by rotational viscosity measurement method and was found to be 14.5 mPa·s.
[0048] Example 5 The hydroxypropyl methylcellulose prepared in Examples 1 to 4 has a high degree of substitution and viscosity, wherein the methoxy content is 28.8% to 29.6%, the hydroxypropoxy content is 7.7% to 8.5%, and the viscosity is 14.5 mPa·s to 15.3 mPa·s. In view of the properties of the hydroxypropyl methylcellulose prepared in the present invention, it can be used as a pharmaceutical excipient.
[0049] Comparative Example 1 This comparative example provides a method for preparing hydroxypropyl methylcellulose. The preparation method provided in this comparative example is basically the same as that in Example 1, except that the "30% sodium hydroxide solution" in step (1) is replaced by an equal amount of "30% sodium bicarbonate solution", and the remaining conditions and parameters are the same as those in Example 1 and are not described in detail.
[0050] According to the method provided in this comparative example, 50.01 g of hydroxypropyl methylcellulose was prepared. According to the measurement, the methoxy content of the hydroxypropyl methylcellulose prepared in this comparative example was 13.4%, the hydroxypropoxy content was 4.3%, and the viscosity was 5.1 mPa·s.
[0051] In this comparative example, the alkaline solution used in the alkalization process is a 30% sodium bicarbonate solution, which is a weak alkaline solution and has a relatively low concentration. It is unable to fully swell the cellulose molecules to expand the surface area to produce sufficient reaction activity. The lower concentration of the alkaline solution also affects the progress of the etherification reaction, resulting in lower methoxy and hydroxypropoxy contents of the obtained hydroxypropyl methylcellulose.
[0052] Comparative Example 2 This comparative example provides a method for preparing hydroxypropyl methylcellulose. The preparation method provided in this comparative example is basically the same as that in Example 1, except that no surfactant is added during the etherification reaction in step (2). The remaining conditions and parameters are the same as those in Example 1 and are not described in detail.
[0053] According to the method provided in this comparative example, 50.10 g of hydroxypropyl methylcellulose was obtained. According to the measurement, the methoxy content of the hydroxypropyl methylcellulose prepared in this comparative example was 9.4%, the hydroxypropoxy content was 3.1%, and the viscosity was 4.0 mPa·s.
[0054] In this comparative example, no preferred surfactant is added during the etherification reaction, which will cause the solubility of methyl chloride and propylene oxide in the reaction solution to be significantly lower than that in Example 1, thereby affecting the etherification reaction and causing the methoxy and hydroxypropoxy contents to be lower. The viscosity range of hydroxypropyl methylcellulose varies due to its different substitution degrees, and hydroxypropyl methylcellulose with a low degree of substitution has a lower viscosity. The contents of methoxy and hydroxypropoxy in the product obtained in this comparative example are significantly lower than those in Example 1, thereby causing the viscosity of the product obtained in this comparative example to be significantly lower than that in Example 1.
[0055] Comparative Example 3 This comparative example provides a method for preparing hydroxypropyl methylcellulose. The preparation method provided in this comparative example is basically the same as that in Example 1, the only difference is that during the etherification reaction in step (2), "polyquaternium-7" is replaced by an equal amount of "sodium dodecyl sulfate", and the remaining conditions and parameters are the same as those in Example 1 and will not be repeated here.
[0056] According to the method provided in this comparative example, 50.0 g of hydroxypropyl methylcellulose was prepared. According to the measurement, the methoxy content of the hydroxypropyl methylcellulose prepared in this comparative example was 15.5%, the hydroxypropoxy content was 5.2%, and the viscosity was 6.9 mPa·s.
[0057] Comparative Example 4 This comparative example provides a method for preparing hydroxypropyl methylcellulose. The preparation method provided in this comparative example is basically the same as that in Example 1, the only difference is that in step (2) the etherification reaction, "polyquaternium-7 6.25 mg" is replaced by "polyquaternium-7 2.5 mg", and the other conditions and parameters are the same as those in Example 1 and are not repeated here.
[0058] According to the method provided in this comparative example, 50.14 g of hydroxypropyl methylcellulose was obtained. According to the measurement, the methoxy content of the hydroxypropyl methylcellulose prepared in this comparative example was 14.8%, the hydroxypropoxy content was 5.3%, and the viscosity was 7.1 mPa·s.
[0059] Comparative Example 5 This comparative example provides a method for preparing hydroxypropyl methylcellulose. The preparation method provided in this comparative example is basically the same as that in Example 1, the only difference is that during the etherification reaction in step (2), no surfactant is added, 500 g of toluene (10 times the mass of natural short cotton linter cellulose) is added to achieve the effect of dilution and diffusion of the etherifying agent, and the toluene is evaporated after the etherification is completed; the remaining conditions and parameters are the same as those in Example 1 and are not repeated here.
[0060] According to the method provided in this comparative example, 50.11 g of hydroxypropyl methylcellulose was prepared. It was determined that the methoxy content of the hydroxypropyl methylcellulose prepared in this comparative example was 28.1%, the hydroxypropoxy content was 7.0%, and the viscosity was 14 mPa·s. Adding a corresponding amount of organic solvent (toluene) in this comparative example can achieve the effect of diluting and diffusing the etherifying agent and improving the solubility of the etherifying agent, and under the action of toluene, the etherification reaction can also be promoted to proceed in the positive direction. Compared with the preparation method of hydroxypropyl methylcellulose provided by the present invention, the preparation method provided in comparative example 5 has the disadvantages of cumbersome operation, relatively dangerous preparation process, long process and high cost. However, in terms of the performance of the obtained product, the hydroxypropyl methylcellulose prepared in the embodiment of the present invention is equivalent to the hydroxypropyl methylcellulose obtained in comparative example 5 in terms of degree of substitution and viscosity, and is even slightly better than comparative example 5.
[0061] In summary, the hydroxypropyl methylcellulose obtained by the preparation method provided in Examples 1 to 4 has a methoxy content of 28.8% to 29.6%, a hydroxypropoxy content of 7.7% to 8.5%, and a viscosity of 14.5 mPa·s to 15.3 mPa·s, which meets the relevant requirements of hydroxypropyl methylcellulose as a pharmaceutical excipient. In addition, compared with the conventional preparation method of hydroxypropyl methylcellulose, the preparation method provided by the present invention has the advantages of being simple, efficient, relatively low in risk factor, and low in synthesis cost.
[0062] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent substitution or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims
1. A method for preparing hydroxypropyl methylcellulose, characterized in that: The preparation method comprises the following steps: Under a protective gas atmosphere, a surfactant, a methyl halide and an alkylene oxide are added to an alkalized cellulose solution to carry out an etherification reaction to obtain hydroxypropyl methylcellulose; Wherein, the surfactant comprises at least one of polyquaternium-7, cetylpyridinium bromide or polypropylene glycol; The alkalized cellulose solution is prepared by an alkalization reaction between a cellulose raw material and a strong alkali solution; The mass ratio of the surfactant to the cellulose raw material is 1:4100-1:8000.
2. The method for preparing hydroxypropyl methylcellulose according to claim 1, wherein: The preparation method of the alkalized cellulose solution comprises the following steps: under a protective gas atmosphere, the cellulose raw material reacts with a strong alkaline solution at a temperature of 10° C. to 20° C. for 3 h to 5 h to obtain the alkalized cellulose solution.
3. The method for preparing hydroxypropyl methylcellulose according to claim 1 or 2, characterized in that: The protective gas comprises at least one of nitrogen, argon or helium; and / or The cellulose raw material comprises short cotton linter cellulose; and / or The strong alkaline solution includes sodium hydroxide solution or potassium hydroxide solution.
4. The method for preparing hydroxypropyl methylcellulose according to claim 2, wherein: The mass ratio of the cellulose raw material to the strong alkaline solution is 1:2.5-1:3.0; wherein the concentration of the strong alkaline solution is 30%-70%.
5. The method for preparing hydroxypropyl methylcellulose according to claim 1, wherein: The monohalomethane comprises monochloromethane; and / or The alkylene oxide includes propylene oxide.
6. The method for preparing hydroxypropyl methylcellulose according to claim 1, wherein: The mass ratio of the cellulose raw material, monohalomethane and alkylene oxide is 1:0.8-1.2:0.25-0.
50.
7. The method for preparing hydroxypropyl methylcellulose according to claim 1, wherein: The reaction temperature of the etherification reaction is 80° C. to 100° C., the reaction time is 3 h to 5 h, and the reaction pressure is 0.3 MPa to 0.5 MPa.
8. The method for preparing hydroxypropyl methylcellulose according to claim 1, wherein: After the etherification reaction is completed, the method further comprises: adjusting the pH of the reaction solution to 6.8-7.2, heating the reaction solution to 50°C-60°C, filtering the solid filtrate to obtain a primary solid filtrate, dissolving the solid filtrate in water, keeping the solid filtrate at 10°C-20°C for 25min-40min, heating the reaction solution to 50°C-60°C again, filtering the solid filtrate to obtain the hydroxypropyl methylcellulose.
9. A hydroxypropyl methylcellulose, characterized in that: Prepared by the preparation method of hydroxypropyl methylcellulose according to any one of claims 1 to 8.
10. Use of the hydroxypropyl methylcellulose as claimed in claim 9 in pharmaceutical excipients.