Lignin hydroxymethylation modification method
By combining ball milling with the use of grinding balls of different diameters, the problems of product uniformity and low yield during lignin hydroxymethylation were solved, achieving efficient, green, and low-cost lignin modification and promoting its large-scale application.
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 hydroxymethylation methods suffer from problems such as complex processes, high costs, poor product uniformity, and excessive waste liquid, which limit their efficient utilization.
The lignin hydroxymethylation modification was carried out by ball milling. By mixing milling balls of different diameters, the uniformity and efficiency of the reaction process were controlled, avoiding the use of water and additional temperature control devices.
This method achieves high yield and uniformity of lignin hydroxymethylation products, simplifies the operation process, reduces production costs, and promotes the large-scale application of lignin.
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Figure CN122060183A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of polymer technology, and in particular to a method for hydroxymethylation modification of lignin. 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 has been 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 of lignin.
[0003] Taking hydroxyl groups as an example, lignin contains hydroxyl groups in its structure, which can replace some polyols in the reaction with isocyanates to prepare rigid polyurethane foam. However, due to the low hydroxyl content, its activity is low, limiting its application. To increase its hydroxyl content, it is generally achieved through hydroxymethylation. Patent CN103224628A discloses a method for preparing hydroxymethylated lignin: after filtering lignin black liquor, it is reacted with formaldehyde at a certain temperature of 60-90℃ for 1-2 hours. Then, acetone is added, and the reaction continues for another 1-2 hours. After the reaction is complete, it is cooled to room temperature, and then subjected to acid precipitation, filtration, and drying to obtain hydroxymethylated lignin. This process is complex, generates a large amount of waste liquid, and has high production costs, which is not conducive to the green and efficient industrial production of hydroxymethylated lignin.
[0004] Patent CN109535441 discloses a hydrothermal method for preparing hydroxymethylated lignin: a certain amount of lignin, formaldehyde solution, and solid alkali are added to a hydrothermal reactor, stirred evenly, the reactor is sealed, and then heated to a specific temperature. After reacting for a period of time, the mixture is cooled to room temperature, and the product is washed, filtered, and dried to obtain hydroxymethylated lignin. This method effectively reduces water usage, but due to the need for homogenization operations such as stirring during the hydrothermal synthesis process, it is difficult to ensure the uniformity of the hydroxymethylated lignin modification product. Summary of the Invention
[0005] To address the shortcomings of existing technologies, this invention provides a method for lignin hydroxymethylation modification. The method utilizes ball milling to achieve uniform control of the reaction process and explores the ball milling conditions, discovering ball milling conditions that yield uniform products and high yields. The method of this invention is green and efficient.
[0006] To achieve the above-mentioned technical objectives, the technical solution of the present invention is as follows:
[0007] This invention provides a method for hydroxymethylation modification of lignin, comprising: mixing lignin, a catalyst and a formaldehyde solution, stirring, adding the mixture together with grinding balls into a ball mill jar, placing it on a ball milling device for reaction, and obtaining hydroxymethylated lignin after the reaction is completed; wherein grinding balls I and grinding balls 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.
[0008] Furthermore, the diameter of grinding ball I is 12-20 mm, and the diameter of grinding ball II is 5-10 mm.
[0009] Furthermore, in the same reaction, grinding balls of the same material are preferably added, and the addition ratio of grinding ball I and grinding ball II is 5:1-1:4 based on the weight of the grinding balls, preferably 4:1-1:3.
[0010] Furthermore, the total amount of grinding balls added is 30%-40% of the volume of the grinding jar.
[0011] Furthermore, the ball milling reaction time is 1-6 hours.
[0012] 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.
[0013] Furthermore, the ball milling device is a planetary ball mill, a drum ball mill, a stirred ball mill, or a vibratory ball mill.
[0014] Furthermore, 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.
[0015] Furthermore, the stirring is carried out using existing mixing techniques to ensure thorough mixing of the raw materials.
[0016] Furthermore, the lignin is selected from at least one of alkali lignin, lignin sulfonate, organic solvent lignin, and enzymatically hydrolyzed lignin.
[0017] Furthermore, the ratio of lignin added to the mass of the grinding ball is 1:10-1:100, preferably 1:10-1:80.
[0018] 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%.
[0019] Furthermore, the catalyst is sodium hydroxide or 4-dimethylaminopyridine (DMAP), and the amount added is 0.5%-3% of the weight of lignin.
[0020] Furthermore, after the ball milling reaction is completed, the product is also filtered, washed, and dried. The product is washed until neutral, then separated into solid and liquid phases, and the solid is dried under vacuum at 30-70°C for 2-24 hours.
[0021] Compared with the prior art, the present invention has the following advantages:
[0022] (1) This invention provides a green and efficient method for lignin modification. The hydroxymethylation modification of lignin is achieved by ball milling. It was unexpectedly discovered that by using a combination of two types of milling balls with different diameters, the consistency and yield of the product are greatly improved. The operation process is simple, avoiding the use of a large amount of water in conventional methods. After the reaction is completed, there is no need for an acid precipitation step, thus avoiding the generation of a large amount of wastewater.
[0023] (2) Compared with the hydrothermal hydroxymethylation modification method, lignin, formaldehyde, and catalyst are better dispersed and react more uniformly during ball milling. 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 ball milling jar, further promoting the occurrence of the hydroxymethylation reaction, so that the product of hydroxymethylated lignin can reach 110%, and under optimized conditions it can even reach more than 130%, and no additional temperature control device is needed.
[0024] (3) The method proposed in this invention is conducive to the large-scale application of lignin and has important economic value.
[0025] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description
[0026] Figure 1 The infrared spectra of the enzymatically hydrolyzed lignin and the prepared hydroxymethylated lignin used in Example 1 are shown. Detailed Implementation
[0027] 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.
[0028] The formulas for calculating the yield of hydroxymethylated lignin in the following examples and comparative examples are as follows:
[0029]
[0030] Example 1
[0031] 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 about 1:1) into a 250mL grinding jar and load it onto a planetary ball mill. The mass ratio of lignin to grinding balls is about 1:24.
[0032] The planetary ball mill was set to a speed of 650 rpm, and the milling reaction was carried out for 3 hours. After cooling to room temperature, the product was separated from the milling balls, washed with pure water until neutral, and then separated into solid and liquid components by vacuum filtration. The solid was dried under vacuum at 50°C for 12 hours. The yield of hydroxymethylated lignin was calculated to be 131.6%.
[0033] Figure 1 The infrared spectra of the raw material lignin hydrolyzed and the product hydroxymethylated lignin 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. (1036 cm⁻¹) -1 The absorption peak at the hydroxyl group of primary alcohol is significantly enhanced after lignin is modified with formaldehyde, and the peak is at 2849 cm⁻¹. -1 The absorption peak belongs to the methylene stretching vibration. The peak intensity of lignin increased significantly after formaldehyde modification, indicating that lignin and formaldehyde underwent a hydroxymethylation reaction, introducing hydroxymethyl functional groups into lignin.
[0034] Table 1
[0035]
[0036] Example 2
[0037] 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 well. 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.
[0038] The ball milling reaction was set at 800 rpm for 1 hour. After cooling to room temperature, the product was separated from the milling balls, washed with pure water until neutral, and then separated into solid and liquid phases by vacuum filtration. The solid was then vacuum dried at 50°C for 12 hours. The yield of hydroxymethylated lignin was calculated to be 124.5%.
[0039] Example 3
[0040] 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 to a 250mL drum 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 drum, with the weight ratio of grinding ball I to grinding ball II being approximately 4:1). The mass ratio of lignin to grinding balls is approximately 1:80.
[0041] The ball milling reaction was set at 50 rpm for 6 hours. After cooling to room temperature, the product was separated from the milling balls, washed with pure water until neutral, and then separated into solid and liquid phases by vacuum filtration. The solid was then vacuum dried at 50°C for 12 hours. The yield of hydroxymethylated lignin was calculated to be 120.3%.
[0042] Example 4
[0043] Dissolve 0.12g NaOH in 9.6g of 35% formaldehyde solution. Mix 24g of sodium lignosulfonate 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 the weight ratio of grinding ball I to grinding ball II being 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.
[0044] The vibration frequency was set to 30 Hz, and the ball milling reaction was carried out for 4 hours. After cooling to room temperature, the product was separated from the milling balls, washed with pure water until neutral, and then separated into solid and liquid components by vacuum filtration. The solid was dried under vacuum at 50 °C for 12 hours. The yield of hydroxymethylated lignin was calculated to be 110.7%.
[0045] Comparative Example 1
[0046] 0.2g NaOH was dissolved in 9g of 37% formaldehyde solution. 10g of enzymatically hydrolyzed lignin, the formaldehyde solution containing NaOH, and grinding balls (all 8mm steel balls, filling 33% of the container volume, without stirring, simply mixing the raw materials) were added to a 250mL ball mill jar. The jar was then placed on a planetary ball mill, and the milling speed was set to 650rpm. The milling reaction was carried out for 3 hours and cooled to room temperature. Upon opening the jar, it was found that large hard lumps had formed in some areas, and a lot of lignin powder had not reacted effectively. Because there were two distinct products, the product count was not performed.
[0047] Pre-mixing and stirring the raw materials can prevent the formation of large hard lumps due to localized reactions. Adding large-sized grinding balls provides stronger mechanical force, so that even if small hard lumps are formed, they can be broken down by impact, eventually forming a uniform powder.
[0048] Comparative Example 2
[0049] Except that all grinding balls are 8mm diameter steel balls, occupying 33% of the can's volume, everything else is the same as in Example 1. After opening the can, the material contained hard granules of varying sizes. Although these were smaller than the hard lumps in the comparative example, the powder was clearly uneven, and the degree of reaction was also different.
[0050] Comparative Example 3
[0051] 0.2 g of NaOH was dissolved in 9 g of 37% formaldehyde solution. 10 g of enzymatically hydrolyzed lignin was mixed with the NaOH-containing formaldehyde solution and stirred thoroughly. The mixture was then transferred to a hydrothermal reactor, and the reaction was carried out at 100°C for 3 hours. After cooling to room temperature, the product was found to be agglomerated. This agglomerated product was broken up appropriately and washed with pure water until neutral. Solid-liquid separation was achieved by vacuum filtration. The solid was then vacuum dried at 50°C for 12 hours. The final yield of hydroxymethylated lignin was 92.6%.
[0052] Since there are no mixing measures such as stirring in the hydrothermal process, the materials can only be dispersed by the initial mixing, but this is only a macroscopic dispersion, resulting in a low product yield. In contrast, the ball milling process can achieve dispersion and reaction at the molecular or atomic scale, resulting in a better reaction effect.
[0053] Comparative Example 4
[0054] 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 phases by vacuum filtration. The solid was then vacuum dried at 50°C for 12 hours. The yield of hydroxymethylated lignin was calculated to be 97.2%. Because only large-sized grinding balls were used, although the impact force was greater, the gaps between the grinding balls were larger, and some samples could not be effectively impacted, thus failing to undergo a mechanized reaction. Adding smaller grinding balls significantly improved the reaction effect and increased the final yield.
[0055] 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 lignin hydroxymethylation modification, comprising: Lignin, catalyst and formaldehyde solution are mixed and stirred, and then added to a ball mill jar along with grinding balls. The mixture is placed on a ball milling device to react. After the reaction is complete, hydroxymethylated lignin is obtained. The grinding jar contains grinding balls I and grinding balls II. Grinding ball I has a diameter greater than 10 mm, while grinding ball II has a diameter no greater than 10 mm.
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 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.
7. The method according to claim 1, characterized in that, The ball milling device is a planetary ball mill, a drum ball mill, a stirred ball mill, or a vibratory ball mill.
8. The method according to claim 7, 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.
9. 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.
10. The method according to claim 1, characterized in that, The ratio of lignin added to the mass of the grinding ball is 1:10-1:100, preferably 1:10-1:
80.
11. 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.
12. The method according to claim 1, characterized in that, The catalyst is sodium hydroxide or 4-dimethylaminopyridine, and the amount added is 0.5%-3% of the weight of lignin.
13. The method according to claim 1, characterized in that, After the ball milling reaction is completed, the steps also include filtering, washing and drying the product.