Method for the alkalization of cellulose and derivatization under alkaline conditions
By subjecting cellulose to freeze-thaw treatment and vacuum degassing in low-concentration alkaline solution, the problems of uneven substitution degree and low efficiency in cellulose derivatization reaction are solved, realizing an efficient and simple cellulose derivatization process and reducing reagent consumption and waste liquid treatment costs.
Patent Information
- Application Number
- CN202310882784.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-07-19
- Publication Date
- 2025-11-18
- Estimated Expiration
- 2043-07-19
AI Technical Summary
Existing cellulose derivatization reactions suffer from problems such as uneven degree of substitution, low reaction efficiency, large reagent consumption, complex operation, and high safety risks, especially when carried out in high-concentration alkaline solutions.
Cellulose is subjected to freeze-thaw treatment with low-concentration alkaline solution (0.9-2.2 mol/L), and swelled after vacuum degassing. Then, cellulose derivatization reactions, including etherification, acetylation and amination, are carried out under alkaline conditions. Freeze-thaw treatment improves reaction efficiency and simplifies operation.
This method achieves good uniformity of cellulose derivative substitution, increased reaction rate, reduced reagent consumption, simplified operation, and lower waste liquid treatment costs, meeting the requirements of green synthesis.
Smart Images
Figure CN116804064B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of polymer chemistry technology, specifically relating to the alkalization and derivatization of cellulose under alkaline conditions. Technical Background
[0002] Cellulose is the most abundant renewable resource in nature, possessing advantages such as non-toxicity, good biocompatibility, renewability, and biodegradability, making it an important chemical resource. However, the numerous intramolecular and intermolecular hydrogen bonds make cellulose difficult to dissolve in water and organic solvents, allowing it to dissolve only in systems such as copper ammonia solution, lithium chloride / N,N-dimethylacetamide (LiCl-DMAC), 4-methylmorpholine-N-oxide (NMMO) / water, ionic liquid systems, and NaOH / urea / water systems, significantly limiting its applications. Derivatization of cellulose, such as hydroxypropylation, hydroxyethylation, combined hydroxypropylation and methylation, carboxymethylation, and sulfonation, can improve its solubility. Ideally, cellulose derivatization reactions should be homogeneous, under which the reaction process is easier to control, resulting in cellulose derivatives with uniform degree of substitution, which is beneficial for controllable preparation. However, the limited availability and high cost of solvents capable of dissolving cellulose, difficulties in solvent recovery, and harsh reaction conditions hinder its practical application in industrial production. Therefore, it is urgent to provide a cheap, green, and pollution-free cellulose dissolving system.
[0003] Currently, cellulose derivatization reactions mainly employ methods such as gas aeration and slurry preparation. The paper "Optimization and Exploration of Preparation Process of Low-Substitution Hydroxypropyl Cellulose" discloses a method for synthesizing low-substitution hydroxypropyl cellulose (Tan Youdan et al. Silk, 2021, 58(07):32-38.), which is as follows: 70 mL of 20% (equivalent to about 6 mol / L) NaOH solution is uniformly dispersed in 70 mL of isopropanol as an alkalizing agent. Then, 5 g of dried cotton pulp is weighed and immersed in the alkalizing agent. After uniform stirring for 2 h, alkalized cellulose is obtained. Then, it is placed in a reaction vessel, and 10 mL of propylene oxide is added into the vessel under negative pressure. The temperature is uniformly raised to 85 °C, and the reaction is completed after etherification for 2.5 h. The reactants are neutralized with acetic acid, and then repeatedly washed with deionized water above 85 °C. Finally, it is dried and pulverized to obtain L-HPC. During the research process, the inventors discovered the following problems with the above method: (1) Derivatization reaction can only occur on the surface of cellulose, and the degree of substitution is unevenly distributed; (2) The specific surface area of cellulose solid in contact with the reactants is relatively small, resulting in a slow reaction rate; (3) In order to keep the reaction system in a stirred mixed system, a large amount of diluent is required, and the amount of etherifying agent is also increased accordingly to maintain the corresponding etherifying agent concentration, thereby increasing production costs; (4) The high concentration of alkalizing reagent poses operational safety risks and high waste liquid treatment costs.
[0004] To address the aforementioned problems, this invention is proposed. Summary of the Invention
[0005] To address the problems of incomplete alkalization of cellulose, low derivatization reaction efficiency, uneven degree of substitution, large reagent consumption, and complex post-processing, this invention provides a method for alkalization and derivatization of cellulose under alkaline conditions. In a low-concentration alkaline solution, cellulose is fully swollen by freeze-thaw cycles, which improves the efficiency of the derivatization reaction. The resulting cellulose derivative has good uniformity of substitution degree, is easy to operate, requires less reagent, and has simple post-processing.
[0006] The objective of this invention is achieved through the following technical solution:
[0007] This invention provides a method for alkalizing cellulose using OH- - Cellulose raw materials are fully dispersed in an alkaline solution with a concentration of 0.9-2.2 mol / L to obtain a cellulose dispersion. The cellulose dispersion is then frozen and thawed to obtain swollen alkalized cellulose.
[0008] Furthermore, the cellulose dispersion was degassed under vacuum before freezing.
[0009] Furthermore, the cellulose feedstock is frozen in an environment below -4°C.
[0010] Furthermore, repeated freezing and thawing helps the cellulose to swell more fully.
[0011] Furthermore, methods such as filtration, pressing, or silk sieve filtration can be used to remove excess alkaline solution after swelling.
[0012] The present invention also provides a method for cellulose derivatization under alkaline conditions, wherein swollen alkaline cellulose is prepared by the above-described alkalinization method, and then the swollen alkaline cellulose is subjected to a derivatization reaction.
[0013] Cellulose derivatization under alkaline conditions includes, but is not limited to, cellulose etherification, acetylation and amination, with cellulose hydroxypropylation, hydroxyethylation and hydroxypropylation combined with methylation being preferred.
[0014] Furthermore, the etherification method is as follows: the swollen alkalized cellulose is added to a diluent, dispersed by high-speed homogenization, and an etherifying agent is added to react. After the reaction is completed, crude etherified cellulose is obtained.
[0015] Furthermore, the reaction temperature between the etherifying agent and cellulose is 20-80℃, and the reaction time is 0.5-48h.
[0016] Furthermore, the etherifying agent is propylene oxide, and hydroxypropyl cellulose is prepared.
[0017] Furthermore, the reaction temperature between hydroxypropyl cellulose and cellulose is 20-60°C. The method of this invention can prepare moderately substituted hydroxypropyl cellulose, which is suitable as a substrate for cellulase activity assays.
[0018] Further purification or refining of crude etherified cellulose: The crude etherified cellulose is washed with alcohol, and then the pH is adjusted to acidic with an acidic reagent, preferably pH 5-6, to obtain purified etherified cellulose solid. The solid is dispersed in water. If it does not dissolve, it is heated, washed, and dried to obtain etherified cellulose powder. If it dissolves, the solution is filtered, and the pH of the filtrate is adjusted to acidic with an acidic reagent, preferably pH 5-6. Then, it is dialyzed, concentrated, and dried to obtain pure etherified cellulose.
[0019] Furthermore, the alkaline solution is an aqueous solution of NaOH and / or LiOH.
[0020] Furthermore, the concentration of the alkaline solution is 1-2 mol / L.
[0021] Furthermore, the ratio of material (g) to liquid (mL) for cellulose alkalization is 1:20-1:200, and the cellulose raw material is completely submerged in the alkaline solution.
[0022] Furthermore, the diluent is one or a mixture of several of isopropanol, tert-butanol, toluene, and acetone.
[0023] Furthermore, the ratio of cellulose raw material to diluent (g) to liquid (mL) is 1:20-1:200, and the alkalized cellulose is completely and evenly dispersed in the diluent.
[0024] Furthermore, the propylene oxide is added to the cellulose solution in batches or dropwise for reaction at a temperature of 20-60°C, preferably 25-50°C, for a reaction time of 0.5-48 h, preferably 1-12 h.
[0025] In the purification of hydroxypropyl cellulose, the alcohol washing is performed using ethanol, methanol, isopropanol, etc., to remove impurities such as diluents, etherifying agents, and salts, wherein the concentration of the alcohol is above 90%.
[0026] Furthermore, the acidic reagent is hydrochloric acid, oxalic acid, nitric acid, or acetic acid.
[0027] Furthermore, adjust the pH to 5-6 using an acidic reagent.
[0028] In the refining of hydroxypropyl cellulose, dialysis or ultrafiltration is used to further remove residual diluents, etherifying agents, salts and other impurities, and to obtain hydroxypropyl cellulose with a molecular weight cutoff of 10 kDa or higher.
[0029] The present invention has the following beneficial effects:
[0030] 1. It enables cellulose to fully swell in low-concentration alkaline solutions, improving safety and reducing wastewater treatment costs.
[0031] 2. Using swollen alkalized cellulose to prepare cellulose derivatives, the swollen alkalized cellulose suspended in the diluent can significantly increase the derivatization reaction rate and shorten the reaction time.
[0032] 3. The prepared cellulose derivatives have a uniform degree of substitution and high yield.
[0033] 4. It can significantly reduce the amount of diluent and etherifying agent used, reduce the cost of waste treatment, and the operation steps are simple, meeting the requirements of green synthesis. Attached Figure Description
[0034] Figure 1 The swelling effect of cellulose raw material under different alkali concentrations is shown in Example 1.
[0035] Figure 2 The infrared images are of the hydroxypropyl cellulose prepared in Example 2 and the comparative example.
[0036] Figure 3 The above are the 1H NMR spectra of hydroxypropyl cellulose prepared in Example 2 and the comparative example.
[0037] Figure 4 The image shows the 1H NMR spectrum of the hydroxypropyl cellulose prepared in Example 3.
[0038] Figure 5 The image shows the infrared spectrum of the hydroxypropyl cellulose prepared in Example 3. Detailed Implementation
[0039] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.
[0040] The main instruments and reagents used in the following examples are as follows:
[0041] Main instruments: Nicolet IS10 Fourier Transform Infrared Chromatograph (Thermo Fisher Scientific); JNM-ECP600 Nuclear Magnetic Resonance Spectrometer (Nippon Electron Ltd.); DF-101S Thermal Collector-type Thermostatic Heating Magnetic Stirrer (Shanghai Lichen Bangxi Instrument Technology Co., Ltd.); Water Bath Thermostatic Shaker (SHZ-82 type, Changzhou Zhiborui Co., Ltd.); FE2 Laboratory pH Mettler Toledo Instruments Ltd.
[0042] Main reagents: Cotton pulp cellulose was provided by Shandong Heda Co., Ltd.; NaOH, isopropanol, anhydrous ethanol, and propylene oxide were all purchased from Sinopharm Chemical Reagent Co., Ltd.; other reagents were also purchased from Sinopharm Chemical Reagent Co., Ltd., and all were of analytical grade. Distilled water was used in the experiment.
[0043] The degree of substitution of hydroxypropyl cellulose is calculated using the following formula:
[0044]
[0045] In the formula I 2-8 For H 2-8 Peak area, I9 is the peak area of H9.
[0046] Example 1
[0047] At room temperature (25℃), cellulose was dispersed mechanically in sodium hydroxide solutions of 0.5 mol / L, 0.75 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, and 6 mol / L. After standing, no significant swelling was observed in the cellulose. When frozen and then thawed at -20℃, cellulose swelled fully at 1–2 mol / L alkali concentrations, but failed to swell fully at 3–6 mol / L alkali concentrations. Figure 1 As shown, cellulose exhibits significant swelling after freeze-thaw cycles in 1 mol / L and 2 mol / L sodium hydroxide solutions, and the swollen alkalized cellulose does not precipitate even after prolonged standing, indicating sufficient swelling. Cellulose remains in a gel state after freeze-thaw cycles in 0.5 mol / L and 0.75 mol / L sodium hydroxide solutions. Cellulose shows little swelling after freeze-thaw cycles in 3 mol / L, 4 mol / L, and 6 mol / L sodium hydroxide solutions, and the higher the sodium hydroxide concentration, the lower the degree of swelling. Comparatively, cellulose at 1–2 mol / L alkali concentrations, after vacuum degassing before freezing, shows a greater degree of swelling compared to cellulose that has not been degassed.
[0048] Example 2
[0049] Step (1), cellulose alkalization: Add 200 mL of 1 mol / L NaOH solution to 10 g of cellulose, degas under vacuum to ensure full contact between cellulose and NaOH solution, then freeze and thaw the dispersion. The cellulose will swell significantly. Filter to remove excess alkali solution and obtain swollen alkalized cellulose.
[0050] Step (2), hydroxypropylation of alkalized cellulose: 200 mL of isopropanol was added to the alkalized cellulose after the alkali solution was filtered off, and the dispersion was obtained by stirring thoroughly with a high-speed homogenizer. 60 mL of propylene oxide was added dropwise at 40 °C and 300 r / min. The reaction was carried out for 10 h. After the reaction was completed, the reaction solution was filtered off to terminate the reaction and crude hydroxypropyl cellulose was obtained.
[0051] Step (3), purification of hydroxypropyl cellulose: wash the crude hydroxypropyl cellulose obtained in step (2) with anhydrous ethanol multiple times, and adjust the pH to 5 with an acidic reagent to remove residual diluents, etherifying agents and other impurities, to obtain solid hydroxypropyl cellulose;
[0052] Step (4) Purification of hydroxypropyl cellulose: Dissolve solid hydroxypropyl cellulose in water, filter to remove residue (almost no residue), add acidic reagent to adjust pH to 5, dialyze, concentrate under reduced pressure, freeze dry to obtain pure hydroxypropyl cellulose HPC-1, as shown in Table 1.
[0053] Table 1. Substitution Degree of HPC Samples
[0054] sample <![CDATA[I1]]> <![CDATA[I 2-8 ]]> <![CDATA[I9]]> MS HPC-1 1 11.03 4.99 1.65
[0055] Comparative Example 1
[0056] Step (1), cellulose alkalization: Add 200 mL of 6 mol / L (20%) NaOH solution to 10 g of cellulose, degas under vacuum to ensure full contact between the cellulose and the NaOH solution, and alkalize at room temperature for 1 week to produce alkalized cellulose;
[0057] Other steps are as described in Example 2, and pure hydroxypropyl cellulose HPC-2 can be obtained. The degree of substitution results are shown in Table 2.
[0058] Table 2 Substitution Degree of HPC Samples
[0059] sample <![CDATA[I1]]> <![CDATA[I 2-8 ]]> <![CDATA[I9]]> MS HPC-2 1 8.88 2.29 0.69
[0060] The comparative experiment shows that when alkalizing with a 6 mol / L alkaline solution, without freezing, and alkalizing at room temperature for one week, the degree of substitution of hydroxypropyl cellulose prepared under the same etherifying agent, reaction temperature, and reaction time as in Example 2 is only 0.69, which is less than half of the degree of substitution (1.65) of hydroxypropyl cellulose prepared by alkalization with a 1 mol / L NaOH solution in Example 2. Furthermore, a large amount of filter residue was present in step (4) during the filtration process. This indicates that the hydroxypropylation reaction is more efficient under the conditions of Example 2, and the concentration of the sodium hydroxide solution and the freezing and thawing process are key steps.
[0061] Comparative Example 2
[0062] Step (1), alkalization of cellulose: 200 mL of 6 mol / L (20%) NaOH solution is added to 10 g of cellulose, vacuum degassing is performed to ensure that the cellulose and NaOH solution are fully in contact, and then the dispersion is frozen and thawed to prepare alkalized cellulose;
[0063] Other steps are as in Example 2, to obtain hydroxypropyl cellulose solid (insoluble in water). The solid is then dispersed in water according to the method in step (3) of claim 2, heated to above 85°C, thoroughly washed to remove impurities, filtered, and dried under normal pressure or vacuum to obtain hydroxypropyl cellulose powder. The degree of substitution results are shown in Table 3.
[0064] Table 3 Substitution Degree of HPC Samples
[0065] sample <![CDATA[I1]]> <![CDATA[I 2-8 ]]> <![CDATA[I9]]> MS HPC-3 1 8.25 1.59 0.40
[0066] The above experiments show that using a 6 mol / L (equivalent to 20 wt%) NaOH solution, and subjecting the alkalization solution of cellulose to low-temperature freezing and thawing according to the method in Example 2, followed by hydroxypropylation under the same etherifying agent, reaction temperature, and reaction time conditions, the degree of substitution of the resulting hydroxypropyl cellulose was only 0.40, far lower than the degree of substitution of the hydroxypropyl cellulose obtained in Example 2 (1.65), and also lower than the degree of substitution of Comparative Example 1 (0.69). This indicates that adding the "freezing and thawing" step under a 6 mol / L sodium hydroxide concentration actually reduces the efficiency of the hydroxypropylation reaction. Therefore, the sodium hydroxide concentration is a crucial factor affecting the efficiency of the hydroxypropylation reaction.
[0067] Comparative Example 3
[0068] Step (1), alkalization of cellulose: Add 200 mL of 1 mol / L NaOH solution to 10 g of cellulose, degas under vacuum, and make the cellulose fully contact with the NaOH solution to prepare alkalized cellulose;
[0069] Other steps are as in Example 2, to obtain hydroxypropyl cellulose solid (insoluble in water). The solid is then dispersed in water according to the method in step (3) of claim 2, heated to above 85°C, thoroughly washed to remove impurities, filtered, and dried under normal pressure or vacuum to obtain hydroxypropyl cellulose powder. The degree of substitution results are shown in Table 4.
[0070] Table 4 Substitution Degree of HPC Samples
[0071] sample <![CDATA[I1]]> <![CDATA[I 2-8 ]]> <![CDATA[I9]]> MS HPC-4 1 8.774 1.044 0.28
[0072] The above experiments show that using 1 mol / L sodium hydroxide as an alkalizing agent without a freeze-thaw step, the degree of substitution (0.28) of the obtained hydroxypropyl cellulose powder is only 16% of that in Example 2. Therefore, a specific range of sodium hydroxide concentration and a "freeze-thaw" step are key to improving the efficiency of the hydroxypropylation reaction, and both are indispensable.
[0073] Example 3
[0074] Step (1), cellulose alkalization: 200 mL of 1.5 mol / L NaOH solution was added to 10 g of cellulose, and vacuum degassing was performed to ensure that the cellulose and NaOH solution were in full contact. The dispersion was then frozen at -18 °C, thawed, filtered, and the alkali solution was removed to obtain alkalized cellulose.
[0075] Step (2), hydroxypropylation of alkalized cellulose: 200 mL of isopropanol was added to the alkalized cellulose after the alkali solution was filtered off, and the dispersion was obtained by stirring thoroughly with a high-speed homogenizer. 60 mL of propylene oxide was added dropwise at 40 °C and 300 r / min. The reaction was carried out for 10 h. After the reaction was completed, the reaction solution was filtered off to terminate the reaction and crude hydroxypropyl cellulose was obtained.
[0076] Step (3), purification and refining of hydroxypropyl cellulose: wash the crude hydroxypropyl cellulose obtained in step (2) multiple times with anhydrous ethanol, and adjust the pH to 4 with an acidic reagent to remove impurities such as isopropanol and propylene oxide, and obtain solid hydroxypropyl cellulose.
[0077] Step (4) Dissolve solid hydroxypropyl cellulose in water. After complete dissolution, add 2 mol / L hydrochloric acid to adjust the pH to 5, dialyze, concentrate under reduced pressure, and freeze dry to obtain pure hydroxypropyl cellulose HPC-5, as shown in Table 5.
[0078] Table 5 Substitution Degree of HPC Samples
[0079] sample <![CDATA[I1]]> <![CDATA[I 2-8 ]]> <![CDATA[I9]]> MS HPC-5 1 11.16 5.07 1.67
[0080] Example 4
[0081] Step (1), cellulose alkalization: 200 mL of 2 mol / L NaOH solution was added to 10 g of cellulose. Vacuum degassing was performed to ensure that the cellulose and NaOH solution were in full contact. The dispersion was then frozen at -20 °C and thawed. The cellulose showed obvious swelling. The solution was filtered to remove excess alkali and alkalized cellulose was obtained.
[0082] Step (2), carboxymethylation of alkalized cellulose: 100 mL of isopropanol was added to the alkalized cellulose after the alkali solution was removed by vacuum filtration. The dispersion was obtained by stirring thoroughly with a high-speed homogenizer. 50 mL of monochloroacetic acid (7.5 g) / isopropanol solution was added dropwise at 60 °C and 300 r / min. The reaction was carried out for 4 h. The reaction was terminated by vacuum filtration after the reaction was completed, and crude carboxymethyl cellulose was obtained.
[0083] Step (3), purification of carboxymethyl cellulose: wash the crude carboxymethyl cellulose obtained in step (2) with anhydrous ethanol multiple times to remove impurities such as monochloroacetic acid and isopropanol, and obtain hydroxypropyl cellulose solid;
[0084] Step (4) Refining of carboxymethyl cellulose: Dissolve solid carboxymethyl cellulose in water. After complete dissolution, dialyze, concentrate, and dry to obtain pure carboxymethyl cellulose.
[0085] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the above operations. All changes, modifications, additions or substitutions made within the scope of the present invention should be protected by the present invention.
Claims
1. A method for cellulose derivatization under alkaline conditions, characterized in that, Use OH - Cellulose is thoroughly dispersed in an alkaline solution with a concentration of 0.9-2.2 mol / L to obtain a cellulose dispersion. The cellulose dispersion is then frozen and thawed to obtain swollen alkalized cellulose. The swollen alkalized cellulose is then subjected to a derivatization reaction. The cellulose dispersion was degassed under vacuum before freezing, and the cellulose dispersion was frozen in an environment below -4°C. Under alkaline conditions, cellulose is derivatized into ethers, and the etherifying agent is propylene oxide; The etherification method is as follows: The swollen alkalized cellulose is added to a diluent, dispersed by high-speed homogenization, and then an etherifying agent is added to react. After the reaction is complete, crude etherified cellulose is obtained. The crude etherified cellulose is then purified or refined: the crude etherified cellulose is washed with alcohol, and then the pH is adjusted to acidic using an acidic reagent to obtain purified etherified cellulose solid. This solid is dispersed in water; if it does not dissolve, it is heated, washed, and dried to obtain etherified cellulose powder. If it dissolves, the solution is filtered, the filtrate is adjusted to acidic using an acidic reagent, and then dialyzed, concentrated, and dried to obtain pure etherified cellulose. The alkaline solution is an aqueous solution of NaOH and / or LiOH.
2. The method for cellulose derivatization under alkaline conditions according to claim 1, characterized in that, The alkaline solution contains OH- - The concentration is 1-2 mol / L.
3. The method for cellulose derivatization under alkaline conditions according to claim 1, characterized in that, The reaction temperature between the etherifying agent and cellulose is 20-80℃, and the reaction time is 0.5-48h.
4. The method for cellulose derivatization under alkaline conditions according to claim 1, characterized in that, The diluent is one or a mixture of several of isopropanol, tert-butanol, toluene, and acetone.