Method for improving esterification grafting rate of lignin
By modifying lignin with hydroxymethylation using a mechanochemical method and utilizing ball milling reactions with grinding balls of different diameters, the problems of low esterification rate and complex operation in existing lignin modification methods have been solved. This method achieves efficient and low-cost lignin esterification modification, which is suitable for large-scale applications.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHINA PETROLEUM & CHEMICAL CORP
- Filing Date
- 2024-11-18
- Publication Date
- 2026-05-19
AI Technical Summary
Existing lignin modification methods involve the use of large amounts of reagents or solvents, are complex to operate, costly, and have difficulty in improving the lignin esterification rate.
The lignin was first modified by hydroxymethylation using a mechanochemical method to give it more aliphatic hydroxyl groups. Then, it was esterified with a compound containing carboxyl functional groups. The esterification grafting rate was improved by using grinding balls of different diameters to perform the ball milling reaction.
It achieves an increased lignin esterification grafting rate, simplifies the operation process, reduces costs, is suitable for large-scale applications, and does not require additional temperature control devices, with a yield of up to 131.6%.
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Figure CN122060184A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of polymer technology, and more particularly to a method for modifying lignin, specifically a method for increasing the esterification grafting rate to obtain lignin with a higher grafting rate. Background Technology
[0002] Lignin is a natural polymer material with a three-dimensional network structure. Its structure contains numerous functional groups, such as hydroxyl, carbonyl, carboxyl, methoxy, conjugated double bonds, aromatic groups, and carbon-carbon double bonds, providing a theoretical basis for further functionalization. However, it is reported that over 100 million tons of industrial lignin are produced globally annually from pulp and paper production and biorefining, but only about 10% is effectively utilized. This is mainly due to the limited number of functional groups and complex network structure of lignin, which greatly restricts its reactivity and accessibility, thus hindering the development of high-value-added applications. Graft modification of lignin using maleic anhydride and other materials is one of the effective ways to achieve high-value and efficient utilization of lignin.
[0003] Kühnel et al. (Synthesis of lignin polyols via oxyalkylation with propylenecarbonate, Holzforschung 2015; 69(5):531–538) prepared maleic anhydride-modified lignin by reacting it overnight at 50°C in 1,4-dioxane using organic solvent lignin and maleic anhydride as raw materials and 1-methylimidazole as catalyst. They then used this modified lignin to prepare high-quality lignin polyols with polycarbonate. Su Shengpei et al. (Research on the Preparation of Lignin Maleate, Fine Chemical Intermediates, 2019, 49(2):36-39) provided a method for preparing lignin maleate: using alkali lignin and maleic anhydride as raw materials, they successfully prepared lignin maleate through a reflux reaction in ethylene glycol dimethyl ether medium. The optimized conditions were a reaction temperature of 85°C, a reaction time of 6 h, and the amount of maleic anhydride being 40% of the lignin. Chen Mingqing et al. (Effect of maleic anhydride-modified lignin on the properties of polylactic acid / epoxidized soybean oil, Polymer Materials Science and Engineering, 2019, 35(10):61-67) studied the effect of maleic anhydride-modified lignin on the properties of polylactic acid / epoxidized soybean oil, and mentioned the lignin modification method: 8g of lignin was weighed and added to a 25mL DMF flask, stirred evenly, and 10g of maleic anhydride (MA) and 18mg of DMAP (1% of monomer mass fraction) were added to the mixture, and the temperature was raised to 80℃ and reacted for 12h. After multiple washings and drying, maleic anhydride-modified lignin was obtained.
[0004] The methods described above can achieve chemical modification of lignin, but the modification process uses a large amount of modifying reagents or solvents, the operation procedure is complex, and the cost of modified lignin is high, making it difficult to apply on a large scale. Developing green, efficient, and low-cost lignin modification technologies is imperative.
[0005] Patent CN105111461 discloses a method for preparing lignin esters via mechanically activated solid-phase reaction, comprising the following steps: weighing the reactants according to the ratio of lignin: acylation agent: catalyst = 15g: 0.08-0.6mol: 0.15-6.7g, placing the reactants in a ball mill, and carrying out an acylation reaction for 0.5-4h under constant temperature water bath at 50-90℃ and low speed stirring at 100-500r / min. After the reaction, crude lignin ester is obtained, which is then separated and washed to obtain the final lignin ester product. This method achieves lignin chemical modification under solvent-free conditions through mechanically activated solid-phase reaction, and the operation is simpler. However, due to the limited number of hydroxyl functional groups in lignin itself, the esterification rate of the obtained lignin ester is difficult to further improve. Summary of the Invention
[0006] To address the shortcomings of existing technologies, this invention provides a method for improving the esterification grafting rate of lignin. The method involves first modifying lignin with hydroxymethylation using a mechanochemical method to give it more aliphatic hydroxyl groups, and then subjecting it to an esterification reaction with a compound containing carboxyl functional groups, thereby achieving efficient esterification modification of lignin.
[0007] To achieve the above-mentioned technical objectives, the technical solution of the present invention is as follows:
[0008] This invention provides a method for improving the lignin esterification grafting rate, comprising:
[0009] (1) Hydroxymethylated modified lignin: lignin, catalyst and formaldehyde solution are mixed and stirred, and added to a ball mill jar along with grinding balls. The mixture is placed on a ball milling device for reaction. Grinding balls I and II are placed in the ball mill jar. The diameter of grinding ball I is greater than 10 mm and the diameter of grinding ball II is not greater than 10 mm.
[0010] (2) Esterification grafting modification: Add acylation reagent and catalyst to the solution after reaction (1), continue to react on a ball mill, cool, separate the product, and obtain esterified lignin.
[0011] Furthermore, the diameter of grinding ball I is 12-20 mm, and the diameter of grinding ball II is 5-10 mm.
[0012] Furthermore, in the same reaction, grinding balls of the same material are added. The ratio of grinding ball I to grinding ball II, based on the weight of the grinding balls, is 5:1-1:4, preferably 4:1-1:3.
[0013] Furthermore, the total amount of grinding balls added is 30%-40% of the volume of the grinding jar.
[0014] Furthermore, the ball milling reaction time in step (1) is 1-6 hours.
[0015] Furthermore, the grinding balls are steel balls or ZrO2 balls, and the grinding jar is a stainless steel jar or a zirconium oxide jar, used in accordance with the material of the grinding balls.
[0016] Furthermore, the ball milling device is a planetary ball mill, a drum ball mill, a stirred ball mill, or a vibratory ball mill.
[0017] Furthermore, the reaction conditions of the ball milling device in step (1) are: the rotation speed of the planetary ball mill is 500-800 rpm, the rotation speed of the stirred ball mill is 500-900 rpm, the rotation speed of the drum ball mill is 30-60 rpm, and the frequency of the vibrating ball mill is 20-35 Hz.
[0018] Furthermore, the stirring is carried out using existing mixing techniques to ensure thorough mixing of the raw materials.
[0019] Furthermore, the lignin is selected from at least one of alkali lignin, lignin sulfonate, organic solvent lignin, and enzymatically hydrolyzed lignin.
[0020] Furthermore, the ratio of lignin added to the mass of the grinding ball is 1:10-1:100, preferably 1:10-1:80.
[0021] Furthermore, the formaldehyde solution concentration is 35-40%, and the amount of formaldehyde solution added is 20%-100% of the weight of lignin, preferably 40%-90%.
[0022] Furthermore, the catalyst mentioned in step (1) is sodium hydroxide or 4-dimethylaminopyridine (DMAP), and the amount added is 0.5%-3% of the weight of lignin.
[0023] Further, the acylation reagent in step (2) is selected from at least one of an acid, an anhydride, and an acyl chloride; wherein the acid is selected from at least one of formic acid, acetic acid, propionic acid, and butyric acid; the anhydride is selected from at least one of acetic anhydride, propionic anhydride, butyric anhydride, succinic anhydride, maleic anhydride, methacrylic anhydride, valeric anhydride, hexanoic anhydride, lauric anhydride, and stearic anhydride; and the acyl chloride is selected from at least one of octanoyl chloride, lauroyl chloride, myristoyl chloride, palmitoyl chloride, and stearoyl chloride. The amount added is 10-60% of the weight of the lignin, preferably 20-40%.
[0024] Furthermore, the catalyst mentioned in step (2) is at least one of sodium hydroxide and 4-dimethylaminopyridine (DMAP), and the amount added is 0.1%-3% of the lignin content.
[0025] Furthermore, the ball milling reaction time in step (2) is 1-6 hours.
[0026] Furthermore, the reaction conditions of the ball milling device in step (2) are: the rotation speed of the planetary ball mill is 500-800 rpm, the rotation speed of the stirred ball mill is 500-900 rpm, the rotation speed of the drum ball mill is 30-60 rpm, and the frequency of the vibrating ball mill is 20-35 Hz.
[0027] Furthermore, after the reaction in step (2) is completed, the product is also filtered, washed, and dried. The product is washed until neutral, and then separated into solid and liquid phases. The solid is then dried under vacuum at 30-70°C for 2-24 hours.
[0028] Compared with the prior art, the present invention has the following advantages:
[0029] (1) In the method of the present invention, the hydroxymethylation modification of lignin reaction process is first achieved by ball milling reaction. Through the exploration of ball milling conditions, it was unexpectedly discovered that by using a mixture of milling balls of two different diameters, the consistency of the product and the product yield can be greatly improved, so that the lignin has more aliphatic hydroxyl groups, which is beneficial to further esterification grafting efficiency.
[0030] (2) Compared with the hydrothermal hydroxymethylation modification method, lignin, formaldehyde, and catalyst are better dispersed and react more uniformly during ball milling due to the action of the milling balls. During ball milling, not only do the active hydrogens adjacent to the phenolic hydroxyl groups participate in the reaction, but the mechanical force of the impact between the milling balls also causes lignin to break bonds, and the new bonds react with formaldehyde to provide more alcohol hydroxyl groups. At the same time, the mechanical force of ball milling will increase the temperature of the milling jar, further promoting the occurrence of the hydroxymethylation reaction, so that the yield of hydroxymethylated lignin can reach 131.6%, and no additional temperature control device is required.
[0031] (3) After hydroxylation modification of lignin in step (1), the content of alcohol hydroxyl groups on lignin that can participate in esterification reaction is greatly increased. Then, esterification graft modification of lignin is carried out, which is conducive to grafting more carboxyl functional group compounds onto lignin. A higher degree of esterification can be achieved with a low dose of carboxyl functional group compounds. The weight of the modified lignin increases significantly, and under optimized conditions, the weight increases by more than 60%.
[0032] (4) The method of the present invention is simple to operate and avoids the use of a large amount of water in conventional methods. After the reaction in step (1) is completed, there is no need for acid precipitation step, and the next reaction can be carried out directly, which avoids the generation of a large amount of wastewater, which is conducive to the large-scale application of lignin and has important economic value.
[0033] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description
[0034] Figure 1 Infrared spectra of the enzymatically hydrolyzed lignin used in Example 1, the hydroxymethylated lignin prepared in step (1), and the maleic anhydride esterified lignin. Detailed Implementation
[0035] The following non-limiting embodiments are intended to enable those skilled in the art to more fully understand the invention, but do not limit the invention in any way.
[0036] In the following examples and comparative examples, the modified lignin yield was used to characterize the reaction effect, and the following formula was used for calculation:
[0037]
[0038] Example 1
[0039] (1) Dissolve 0.2g NaOH in 9g of 37% formaldehyde solution. Mix 10g of enzymatically hydrolyzed lignin with the formaldehyde solution containing NaOH and stir well. Then add the mixture along with grinding balls (4 steel balls with a diameter of 20mm, and the rest supplemented with steel balls with a diameter of 8mm, so that the grinding balls occupy 33% of the volume of the grinding jar, and the weight ratio of grinding ball I to grinding ball II is approximately 1:1) into a 250mL grinding jar. Load the jar onto a planetary ball mill. The mass ratio of lignin to grinding balls is approximately 1:24. Set the speed of the planetary ball mill to 650rpm and mill for 3 hours. Cool to room temperature.
[0040] (2) Add 4g of maleic anhydride and 0.1g of DMAP to the tank, and continue ball milling at 650rpm for 2h. After cooling to room temperature, separate the product from the milling balls, wash the product with pure water until neutral, and achieve solid-liquid separation by vacuum filtration. Dry the solid under vacuum at 50℃ for 12h. The yield of modified lignin was calculated to be 165.2%.
[0041] In addition, the product yield of step (1) was calculated. Using the same materials and reaction conditions, after the ball milling reaction in step (1) was completed, the product was cooled to room temperature and then separated from the milling balls. The product was washed with pure water until neutral, and solid-liquid separation was achieved by vacuum filtration. The solid was dried under vacuum at 50°C for 12 hours. 13.11 g of hydroxylated lignin was obtained, and the product weight increased by 31.1%.
[0042] Figure 1 Infrared spectra of lignin hydrolyzed from raw material, hydroxymethylated lignin (product of step (1), and esterified lignin (product of step (2)) were obtained. To compare the relative amounts of functional groups, the baseline of the spectral data was first calibrated, and then a 1514 cm⁻¹ spectral depth was selected. -1 Using the characteristic absorption peaks of the aromatic ring skeleton as a reference, the intensities of each peak were read, and the results are shown in Table 1. As can be seen from the figure: 1694 cm⁻¹ -1 The peak at 1694 cm⁻¹ belongs to the conjugated carbonyl group. This peak disappears after formaldehyde modification of lignin, indicating that formaldehyde reacts with the conjugated carbonyl group. Further esterification results in a peak at 1694 cm⁻¹. -1 Another absorption peak appeared nearby, but it shifted to 1707 cm⁻¹. -1 This is due to the introduction of ester groups by maleic anhydride esterification, indicating that a significant esterification reaction has occurred.
[0043] Table 1
[0044]
[0045] Example 2
[0046] (1) Dissolve 0.45g NaOH in 10.5g of 37% formaldehyde solution. Mix 15g of organic solvent lignin with the formaldehyde solution containing NaOH and stir until homogeneous. Then, add the mixture along with grinding balls (6 15mm zirconia balls, supplemented with 10mm and 8mm balls, so that the grinding balls occupy 35% of the jar volume, with a weight ratio of grinding ball I to grinding ball II of approximately 1:3) into a 250mL ball mill jar. Load the jar onto a stirred ball mill. The mass ratio of lignin to grinding balls is approximately 1:13. Set the rotation speed to 800rpm and mill for 1 hour. Cool to room temperature.
[0047] (2) Add 2g of octanoyl chloride and 0.015g of DMAP to the tank, and continue ball milling at 800rpm for 6h. After cooling to room temperature, separate the product from the milling balls, wash the product with pure water until neutral, and separate the solid and liquid by vacuum filtration. Dry the solid under vacuum at 50℃ for 12h. The yield of modified lignin was calculated to be 125.6%.
[0048] Example 3
[0049] (1) Dissolve 0.04g NaOH in 2.4g of 40% formaldehyde solution. Mix 4g of alkali lignin with the formaldehyde solution containing NaOH and stir well. Then add the mixture, along with grinding balls (6 20mm steel balls, supplemented with 10mm and 6mm balls, so that the grinding balls occupy 40% of the volume of the container; the weight ratio of grinding ball I to grinding ball II is approximately 4:1), into a 250mL drum. The mass ratio of lignin to grinding balls is approximately 1:80. Set the rotation speed to 50rpm and ball mill for 6 hours. Cool to room temperature.
[0050] (2) Add 2.4 g of succinic anhydride and 0.08 g of DMAP to the tank, and continue ball milling at 50 rpm for 3 h. After cooling to room temperature, separate the product from the milling balls, wash the product with pure water until neutral, and achieve solid-liquid separation by vacuum filtration. Dry the solid under vacuum at 50 °C for 12 h. The yield of modified lignin was calculated to be 160.7%.
[0051] Example 4
[0052] (1) Dissolve 0.12g NaOH in 9.6g of 35% formaldehyde solution. Mix 24g of sodium lignin sulfonate with the formaldehyde solution containing NaOH and stir well. Then add the mixture along with grinding balls (3 20mm steel balls, supplemented with 10mm and 8mm balls, so that the grinding balls occupy 30% of the jar volume, with a weight ratio of grinding ball I to grinding ball II of approximately 1:1.5) into a 250mL ball mill jar. Load the jar onto a vibratory ball mill. The mass ratio of lignin to grinding balls is approximately 1:10. Set the vibration frequency to 30Hz and ball mill for 4 hours. Cool to room temperature.
[0053] (2) Add 2.4 g of acetic acid and 0.72 g of DMAP to the tank, and continue ball milling at a vibration frequency of 30 Hz for 4 h. After cooling to room temperature, separate the product from the milling balls, wash the product with pure water until neutral, and achieve solid-liquid separation by vacuum filtration. Dry the solid under vacuum at 50 ℃ for 12 h. The yield of modified lignin was calculated to be 118.5%.
[0054] Comparative Example 1
[0055] Direct modification of lignin with maleic anhydride, without the hydroxymethylation step:
[0056] 10g of enzymatically hydrolyzed lignin, 4g of maleic anhydride, and 0.1g of DMAP were added to a 250mL ball mill jar and stirred thoroughly. Then, grinding balls (four 20mm steel balls, supplemented with 8mm balls, filling the jar to 33% of its volume) were added and the jar was loaded onto a planetary ball mill. The milling speed was set to 650rpm, and the reaction was carried out for 5 hours. After cooling to room temperature, the product was separated from the grinding balls. The product was washed with pure water until neutral, and solid-liquid separation was achieved by vacuum filtration. The solid was then vacuum dried at 50℃ for 12 hours. The final yield of modified lignin was 93.2%. This indicates that the yield of lignin without hydroxymethylation modification is low. The main reasons are: firstly, lignin itself has relatively few hydroxyl groups suitable for esterification, resulting in less maleic acid that can react; secondly, a small amount of enzymatically hydrolyzed lignin dissolves in the aqueous solution containing maleic acid during the washing process, causing a loss and thus reducing the yield to less than 100%. Compared to the method of this invention, the yield is significantly reduced.
[0057] Comparative Example 2
[0058] In step (1), large-diameter grinding balls are not used; only 8mm diameter steel balls are used, making the grinding balls occupy 33% of the can's volume. All other steps and operations are the same as in Example 1. After opening the can, the material contains hard granules of varying sizes. Although smaller than the hard lumps in the comparative example, the powder is clearly uneven, and the degree of reaction is also different. Performing esterification on this basis will result in only surface esterification of the particles, failing to guarantee a uniform esterification effect.
[0059] Comparative Example 3
[0060] Except that all grinding balls were 20mm diameter steel balls, occupying 33% of the tank volume, everything else was the same as in Example 1. After opening the tank, the product was separated from the grinding balls, washed with water until neutral, and then separated into solid and liquid components by vacuum filtration. The solid was then vacuum dried at 50°C for 12 hours. The yield of hydroxymethylated lignin was calculated to be 108.7%. Because only large-sized grinding balls were used, although the impact force was greater, the gaps between the grinding balls were also larger, preventing some samples from effectively colliding and thus avoiding mechanized reactions. This resulted in a yield difference of more than 50% compared to Example 1. Adding smaller grinding balls significantly improved the reaction effect and increased the final yield.
[0061] The above embodiments are used to explain and illustrate the present invention, but not to limit the present invention. Any modifications and changes made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.
Claims
1. A method for improving the lignin esterification grafting rate, comprising: (1) Hydroxymethylated modified lignin: lignin, catalyst and formaldehyde solution are mixed and stirred, and added to a ball mill jar along with grinding balls. The mixture is placed on a ball milling device for reaction. Grinding balls I and II are placed in the ball mill jar. The diameter of grinding ball I is greater than 10 mm and the diameter of grinding ball II is not greater than 10 mm. (2) Esterification grafting modification: Add acylation reagent and catalyst to the solution after reaction (1), continue to react on a ball mill, cool, separate the product, and obtain esterified lignin.
2. The method according to claim 1, characterized in that, The diameter of grinding ball I is 12-20mm, and the diameter of grinding ball II is 5-10mm.
3. The method according to claim 1, characterized in that, In the same reaction, grinding balls of the same material are added, and the ratio of grinding ball I to grinding ball II is 5:1 to 1:4 based on the weight of the grinding balls.
4. The method according to claim 1, characterized in that, The total amount of grinding balls added is 30%-40% of the volume of the grinding jar.
5. The method according to claim 1, characterized in that, The ball milling reaction time in step (1) is 1-6 hours.
6. The method according to claim 1, characterized in that, The grinding balls are steel balls or ZrO2 balls, and the grinding jar is a stainless steel jar or a zirconium oxide jar; the grinding device is a planetary ball mill, a drum ball mill, a stirred ball mill, or a vibratory ball mill.
7. The method according to claim 6, characterized in that, The planetary ball mill has a rotational speed of 500-800 rpm, the stirred ball mill has a rotational speed of 500-900 rpm, the drum ball mill has a rotational speed of 30-60 rpm, and the vibrating ball mill has a frequency of 20-35 Hz.
8. The method according to claim 1, characterized in that, The lignin is selected from at least one of alkali lignin, lignin sulfonate, organic solvent lignin, and enzymatically hydrolyzed lignin.
9. The method according to claim 1, characterized in that, The ratio of lignin added to the mass of the grinding ball is 1:10 to 1:
100.
10. The method according to claim 1, characterized in that, The formaldehyde solution concentration is 35-40%, and the amount of formaldehyde solution added is 20%-100% of the weight of lignin.
11. The method according to claim 1, characterized in that, The catalyst mentioned in step (1) is sodium hydroxide or 4-dimethylaminopyridine, and the amount added is 0.5%-3% of the weight of lignin.
12. The method according to claim 1, characterized in that, The catalyst mentioned in step (2) is sodium hydroxide or 4-dimethylaminopyridine, and the amount added is 0.1%-3% of the weight of lignin.
13. The method according to claim 1, characterized in that, The acylation reagent in step (2) is selected from at least one of acid, acid anhydride and acyl chloride.
14. The method according to claim 13, characterized in that, The acid is selected from at least one of formic acid, acetic acid, propionic acid, and butyric acid; the anhydride is selected from at least one of acetic anhydride, propionic anhydride, butyric anhydride, succinic anhydride, maleic anhydride, methacrylic anhydride, valeric anhydride, hexanoic anhydride, lauric anhydride, and stearic anhydride; the acyl chloride is selected from at least one of octanoyl chloride, lauroyl chloride, myristoyl chloride, palmitoyl chloride, and stearoyl chloride.
15. The method according to claim 1, characterized in that, The amount of the acylation reagent added is 10-60% of the weight of lignin.
16. The method according to claim 6, characterized in that, The ball milling reaction time in step (2) is 1-6 hours. The reaction conditions of the ball milling device in step (2) are: the rotation speed of the planetary ball mill is 500-800 rpm, the rotation speed of the stirred ball mill is 500-900 rpm, the rotation speed of the drum ball mill is 30-60 rpm, and the frequency of the vibrating ball mill is 20-35 Hz.
17. The method according to claim 1, characterized in that, After the reaction in step (2) is completed, the product is also filtered, washed and dried.