Application of supramolecular deep-eutectic solvent in inhibition of condensation color development of lignin

Abstract

The invention relates to the technical field of high-valued utilization of cellulose raw materials, in particular to application of a supramolecular deep-eutectic solvent in inhibition of condensation and color development of lignin, and the supramolecular deep-eutectic solvent comprises a hydrogen bond acceptor, a hydrogen bond donor and polyol. Compared with a traditional fractionation system, the system disclosed by the invention can remarkably inhibit generation of color development byproducts, and cellulose with the color from cream white to white is directly obtained. Meanwhile, the method is mild in condition, the solvent can be recycled, subsequent chemical bleaching is not needed, and the obtained white cellulose can be directly used as natural functional filler of cosmetics (especially sunscreen cream). In conclusion, the invention provides a green and efficient solution for obtaining the light-color bio-based cellulose, and has wide application prospects and important popularization values in the fields of chemical products, biological materials and the like.

Description

Technical Field

[0001] This invention relates to the field of high-value utilization of cellulose raw materials, and in particular to the application of a supramolecular eutectic solvent in inhibiting lignin condensation and color development. Background Technology

[0002] Traditional industrial pulping and biomass fractionation processes, such as the sulfate process and various strong acid pretreatment technologies, are typically carried out under harsh conditions of high temperature, high pressure, and strong acid or strong alkali to achieve efficient separation of lignin and cellulose. However, these processes have long faced a significant technical bottleneck: the resulting cellulose products are dark in color, mostly dark brown or yellowish-brown. This color problem severely restricts the application of such cellulose materials in cosmetic additives, food-grade packaging, high-grade paper, and other high-end fields with stringent requirements for visual appearance and whiteness.

[0003] Studies have shown that the deep color of cellulose products does not originate from simple physical contamination, but is closely related to the profound chemical transformation of lignin during fractionation. Under acidic catalytic conditions, the hydroxyl groups (Cα-OH) at the α-position of the side chains of lignin structural units readily undergo protonation and dehydration, generating highly reactive benzyl carbocation intermediates. These intermediates, acting as strong electrophiles, attack the electron-rich aromatic rings of the lignin molecule itself, undergoing electrophilic aromatic substitution reactions to form new C-C bonds (i.e., Cα-Caryl condensation bonds) (see Li et al., Nature 2024). This disordered intermolecular condensation reaction leads to the transformation of lignin into highly cross-linked, structurally complex macromolecular polymers, accompanied by the formation of quinone structures and extended conjugated systems, resulting in a rapid darkening of the material's color, eventually turning black or dark brown. These dark-colored condensed lignin byproducts generated in situ during fractionation are difficult to remove by conventional physical methods because they are tightly bound to the surface of cellulose fibers upon formation.

[0004] To improve product color, the industry currently relies heavily on subsequent chemical bleaching processes, such as chlorine bleaching and hydrogen peroxide bleaching. However, the bleaching process itself has many drawbacks: it not only consumes a lot of energy, but may also produce toxic wastewater containing chlorinated organic compounds, putting pressure on environmental treatment; at the same time, the harsh chemical treatment may also damage the cellulose molecular chains, leading to a decrease in their degree of polymerization, which in turn affects the mechanical strength and functional properties of the final product.

[0005] Therefore, developing a green and mild fractionation technology that can avoid or effectively suppress the formation of color-developing byproducts from the reaction source, thereby directly obtaining high-quality cellulose with a light and bright color, has become a key technical challenge that urgently needs to be overcome in this field. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the present invention provides an application of supramolecular eutectic solvent in suppressing lignin condensation and color development, thereby solving the problem that the prior art is unable to balance efficiency, environmental protection and product color in the lignin fractionation process.

[0007] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: In a first aspect, the present invention provides the application of a supramolecular eutectic solvent in inhibiting lignin condensation and color development, wherein the supramolecular eutectic solvent comprises a hydrogen bond acceptor, a hydrogen bond donor, and a polyol.

[0008] Optionally, the hydrogen bond acceptor includes at least one of choline chloride, betaine, betaine hydrochloride, L-carnitine, acetylcarnitine, taurine, L-arginine, choline derivatives, proline, alanine, and glycine and their derivatives; the hydrogen bond donor includes at least one of quaternary ammonium salts (urea), polyols (glycerol, ethylene glycol), organic acids (lactic acid, citric acid), and sugars (glucose, fructose); the polyol includes at least one of aliphatic polyols or sugar alcohols containing C2-C6.

[0009] Optionally, the polyol includes at least one of ethylene glycol, 1,2-propanediol, 1,3-propanediol, glycerol, xylitol, sorbitol, mannitol, erythritol, and maltitol.

[0010] Optionally, the mass ratio of the hydrogen bond acceptor, hydrogen bond donor, and polyol is 1:9:(0-9) ~ 9:1:(0-9).

[0011] Preferably, the hydrogen bond acceptor is choline chloride or betaine and its derivatives, the hydrogen bond donor is citric acid or malic acid, and the polyol is a sugar alcohol; the mass ratio of choline chloride or betaine and its derivatives, citric acid or malic acid to sugar alcohol is 1:3:1.

[0012] Optionally, the preparation method of the supramolecular eutectic solvent includes the following steps: mixing a hydrogen bond acceptor, a hydrogen bond donor, and a polyol, heating and stirring to obtain the supramolecular eutectic solvent.

[0013] Optionally, the stirring temperature is 70-90℃ and the stirring time is 1-3 hours.

[0014] Preferably, the stirring temperature is 80°C and the stirring time is 2 hours.

[0015] A second aspect of the present invention provides a method for inhibiting lignin condensation color development using a supramolecular eutectic solvent, the method comprising the following steps: The hydrogen bond acceptor, hydrogen bond donor and polyol are mixed and heated and stirred to obtain the supramolecular eutectic solvent; The supramolecular eutectic solvent is mixed with water to obtain an aqueous supramolecular eutectic solvent. The pulverized and dried lignin raw material is mixed with the aqueous supramolecular eutectic solvent and stirred to inhibit the condensation and color development of lignin during the extraction of cellulose from cellulose biomass raw material.

[0016] Optionally, the hydrogen bond acceptor includes at least one of choline chloride, betaine, betaine hydrochloride, L-carnitine, acetylcarnitine, taurine, L-arginine, choline derivatives, proline, alanine, and glycine and their derivatives; the hydrogen bond donor includes at least one of quaternary ammonium salts (urea), polyols (glycerol, ethylene glycol), organic acids (lactic acid, citric acid), and sugars (glucose, fructose); the polyol includes at least one of aliphatic polyols or sugar alcohols containing C2-C6.

[0017] Optionally, the mass ratio of the hydrogen bond acceptor, hydrogen bond donor, and polyol is 1:3:(0-1).

[0018] Optionally, the solid-liquid mass ratio of the lignin raw material to the aqueous supramolecular eutectic solvent is 1:(5-30).

[0019] Optionally, the stirring temperature is 100-130℃ and the stirring time is 2-5 hours.

[0020] A third aspect of the present invention provides a cellulose biomass raw material treated by the processing method described above.

[0021] A fourth aspect of the present invention provides a cellulose biomass raw material as described above, for use in the cosmetics field.

[0022] Beneficial effects: This invention discloses the application of a supramolecular eutectic solvent in inhibiting lignin condensation and color development. Compared with existing technologies, it has the following significant advantages: 1. This invention achieves source-level color inhibition, innovatively proposing and verifying a new strategy of nucleophilically capturing benzyl carbocations through polyols, thereby inhibiting harmful lignin condensation and color development at the source. This strategy is a fundamental solution to the color control problem in biomass fractionation, has important scientific significance, and is a significant advantage of existing ternary supramolecular eutectic solvent pretreatment technologies, providing a revolutionary approach to obtaining cosmetic-grade white cellulose raw materials. 2. This invention eliminates the bleaching process, promoting green and clean production. By combining "fractionation" and "in-situ color inhibition" into one, the traditional high-pollution, high-energy-consumption chemical bleaching process (such as chlorine bleaching, hydrogen peroxide bleaching, etc.) is completely eliminated. This technology not only eliminates the use of toxic and harmful bleaching agents at the source, avoiding the generation of related waste gas and wastewater, but also makes the entire production process safer and more environmentally friendly, meeting the stringent requirements of sustainable development. 3. This invention significantly reduces production costs. By eliminating the need for complex bleaching and deep impurity removal units, even small- to medium-sized or simple production lines with lower investment can produce high-value-added cosmetic-grade cellulose raw materials. Simultaneously, the supramolecular eutectic solvent used is inexpensive and readily available, and the solvent can be efficiently recovered and recycled (the recovery rate can be maintained at a high level through process optimization), thereby significantly reducing raw material costs and waste disposal costs, and enhancing the overall economic viability and commercialization potential of the technology. 4. The product obtained by this invention has broad application prospects. The obtained creamy-white cellulose not only meets the color standards of high-end cosmetic raw materials, but also exhibits minimal structural damage, retaining good polymerization degree and reactivity. This cellulose can be directly added as a natural ingredient to cosmetics such as sunscreens, providing UV protection and enhancing product stability without affecting the sensory properties of the final product (such as color and texture), resulting in high market acceptance. Attached Figure Description

[0023] Figure 1 This is a schematic diagram comparing the color-inhibiting mechanism of the present invention with the blackening mechanism of a comparative example.

[0024] Figure 2 This is a schematic diagram of the process flow for the cellulose color suppression method using a ternary supramolecular eutectic solvent according to the present invention.

[0025] Figure 3 These are comparative photographs showing the colors of the reaction solutions and products after treatment with different DES systems in the embodiments and comparative examples of the present invention.

[0026] Figure 4 The color comparison shows the cellulose prepared in the embodiments and comparative examples of the present invention. Detailed Implementation

[0027] This invention provides the application of a supramolecular eutectic solvent in inhibiting lignin condensation and color development. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0028] In the field of biomass resource utilization, deep eutectic solvents (DES), as an emerging green and designable solvent system, have attracted widespread attention due to their potential in lignin fractionation. Current research primarily focuses on improving fractionation efficiency by optimizing DES composition and process conditions, such as pursuing higher lignin removal rates and cellulose retention rates, or striving for the high-value conversion and utilization of the separated lignin. However, there is a lack of systematic attention and effective control methods for the key quality indicators of the fractionated cellulose products themselves—especially their color characteristics.

[0029] In fact, efficiently separating and purifying light-colored cellulose from lignin feedstock faces significant challenges. Traditional fractionation processes are often energy-intensive and environmentally polluting, and the resulting cellulose products are generally dark brown or yellowish-brown with poor color. The root cause of this color problem lies in the fact that under acidic pretreatment conditions, lignin undergoes depolymerization, but its Cα-OH groups on the side chains are prone to protonation and dehydration, generating highly reactive benzyl carbocation intermediates. As a strong electrophile, if left uncontrolled, this intermediate will attack the aromatic ring of lignin itself, initiating irreversible intermolecular or intramolecular Cα-Caryl condensation reactions. Such condensations not only form difficult-to-degrade cross-linked network structures, but more importantly, they generate dark-colored chromophores such as quinone structures and extended conjugated systems (Li et al., Nature 2024). These chromogenic substances adhere tightly to the cellulose surface in the early stages of formation, becoming the fundamental reason for the dark color of cellulose obtained by traditional processes.

[0030] When such dark-colored cellulose is used as a functional ingredient (e.g., physical sunscreen, thickener) in high-value-added products (e.g., cosmetics), its unpleasant color severely affects the sensory quality of the final product, leading to a significant reduction in commercial value. To improve the color of cellulose, the industry typically has to introduce subsequent chemical bleaching processes, such as treatment with strong oxidants like chlorine, hydrogen peroxide, and ozone. However, this traditional approach brings a series of new problems: (i) the bleaching process may damage the cellulose molecular chains, reducing its degree of polymerization and affecting its mechanical and functional properties; (ii) it generates secondary pollutants such as chlorinated organic compounds and high chemical oxygen demand (COD) wastewater, which contradicts the principles of green chemistry and sustainable development; and (iii) it adds to the complexity of the production process, energy consumption, and overall cost.

[0031] Therefore, developing a novel solvent system and pretreatment technology that can effectively inhibit lignin color condensation at the molecular level while being green and economical is of great significance for obtaining high-quality cellulose products and promoting their high-end applications.

[0032] Based on this, embodiments of the present invention provide the application of a supramolecular eutectic solvent in inhibiting lignin condensation and color development, wherein the supramolecular eutectic solvent includes hydrogen bond acceptors, hydrogen bond donors, and polyols.

[0033] The core principle of the technical solution described in this invention's embodiments lies in "source color suppression," as detailed in [link to specific documentation]. Figure 1 In the mildly acidic environment of the fractionation process, lignin dissociates and generates a highly reactive benzyl carbocation intermediate. In this embodiment, a polyol intentionally introduced into the solvent system acts as a strong nucleophile, actively and preferentially capturing these benzyl carbocations. This nucleophilic capture reaction effectively blocks the pathway of benzyl carbocations attacking the aromatic ring of lignin by forming stable CO ether bonds, thereby inhibiting the Cα-Caryl condensation reaction that leads to the formation of dark chromophores (such as quinone structures) at the molecular level. This mechanism realizes a paradigm shift from the traditional "separation before bleaching" to "simultaneous color suppression during fractionation".

[0034] The following significant technical effects were achieved through this embodiment: 1. Directly obtaining light-colored cellulose: The resulting cellulose product is creamy white to white, with a whiteness value significantly higher than that of dark brown cellulose obtained under the same conditions using traditional acidic DES or DES without functional polyols. This proves that the technology can effectively inhibit the formation of chromogenic substances from the source. 2. Eliminating subsequent bleaching processes: Since the product's color already meets the requirements of high-end applications (such as cosmetic grade), the necessary chemical bleaching steps such as chlorine bleaching and oxygen bleaching in traditional processes are completely eliminated, thus preventing the use of toxic bleaching chemicals and the resulting environmental pollution from the source. 3. Maintaining cellulose quality: Under mild conditions, the structural integrity of cellulose is well maintained. The product has a high cellulose yield, minimal damage to the degree of polymerization, and retains its crystalline structure, providing a good material basis for its subsequent high-value applications. 4. Green and economical: The entire process does not require the addition of concentrated acid, and the solvent components used are green, low in toxicity, and recyclable, significantly reducing the burden of wastewater treatment and overall production costs, meeting the requirements of green and sustainable development.

[0035] Not all supramolecular eutectic solvents can achieve the colorimetric inhibition effect described in this invention; this effect stems solely from the functional design of specific compositions and ratios. Traditional or conventional eutectic solvents typically serve only as dissolution or fractionation media, lacking the ability to actively regulate the chemical changes of lignin in subsequent processes. The benzyl carbocation intermediate generated from lignin degradation will still uncontrollably undergo Cα-reduction. Caryl condensation leads to the formation of dark-colored byproducts. The ternary eutectic solvent system (choline chloride / citric acid / xylitol) involved in this invention is a chemical pathway regulation system with synergistic effects among its components: choline chloride provides a stable ionic environment and permeability; citric acid provides the necessary acidic conditions, catalyzing the formation of the key benzyl carbocation active intermediate; and xylitol, as the core functional component, plays the role of a highly efficient nucleophilic trapping agent with its unique molecular structure (multi-hydroxyl, straight chain, and certain rigidity), preferentially reacting with the benzyl carbocation to form C... The O-ether bond is used to "chemically cap" the lignin, fundamentally blocking the harmful condensation pathway that leads to color development. The significant effect gradient observed in the examples (xylitol → white cellulose, glycerol → light yellow, propylene glycol → yellow, no polyol → dark) conclusively demonstrates the essential differences in the capture capacity of different polyols and also confirms the irreplaceable role of xylitol in this system. Therefore, the technical effect of this invention stems from the precise molecular design targeting the lignin color development mechanism (the generation and subsequent reactions of benzyl carbocations), and is a synergistic effect produced by specific components in specific proportions.

[0036] In summary, this embodiment successfully utilizes a supramolecular eutectic solvent to inhibit the condensation and color development of lignin during the extraction of cellulose from cellulose biomass raw materials. The supramolecular eutectic solvent system demonstrates the feasibility of achieving efficient integrated "fractionation-color suppression" during lignin fractionation, providing a disruptive green solution to the long-standing problem of product color in the field of biomass refining.

[0037] In some embodiments, the hydrogen bond acceptor includes at least one of choline chloride, betaine, betaine hydrochloride, L-carnitine, acetylcarnitine, taurine, L-arginine, choline derivatives, proline, alanine, and glycine and their derivatives; the hydrogen bond donor includes at least one of quaternary ammonium salts (urea), polyols (glycerol, ethylene glycol), organic acids (lactic acid, citric acid), and sugars (glucose, fructose); the polyol includes at least one of aliphatic polyols or sugar alcohols containing C2-C6.

[0038] To achieve excellent colorimetric inhibition, the polyol is a sugar alcohol. The densely packed hydroxyl groups in the sugar alcohol molecule provide it with a stronger nucleophilic trapping ability. Its function lies not only in regulating solvent properties but also in participating in the aforementioned chemical reaction that inhibits color development.

[0039] In some embodiments, the polyol includes at least one of ethylene glycol, 1,2-propanediol, 1,3-propanediol, glycerol, xylitol, sorbitol, mannitol, erythritol, and maltitol.

[0040] In some embodiments, the mass ratio of the hydrogen bond acceptor, hydrogen bond donor, and polyol is 1:9:(0-9) ~ 9:1:(0-9).

[0041] In some preferred embodiments, the mass ratio of the hydrogen bond acceptor, hydrogen bond donor, and polyol is 1:3:(0-1). The mass ratio of the hydrogen bond acceptor, hydrogen bond donor, and polyol can be 1:3:0.1, 1:3:0.2, 1:3:0.3, 1:3:0.4, 1:3:0.5, 1:3:0.6, 1:3:0.7, 1:3:0.8, 1:3:0.9, or 1:3:1. Other specific values ​​within the above range are also possible and will not be listed here.

[0042] In the described embodiment, the mass ratio of hydrogen bond acceptor (HBA), hydrogen bond donor (HBD), and polyol (such as xylitol) is 1:3:(0-1). This specific ratio is a key parameter for achieving the synergistic effect of "fractionation-color suppression" through systematic optimization. The technical benefits, principles, and effects of deviating from this range are analyzed in detail below: Technical Benefits and Principles: ① Optimization of the Basic Solvent System (1:3): The hydrogen bond acceptor and hydrogen bond donor are combined in a 1:3 mass ratio, forming a solvent base with suitable acidity and solubility. This ratio ensures that the system can effectively break the bonds (such as ether bonds and ester bonds) between lignin and carbohydrates, achieving moderate dissolution of lignin and effective separation of cellulose, while avoiding excessive damage to the cellulose crystal structure or triggering severe side reactions of lignin itself due to excessive acidity. ② Precise Control of Functional Components (0-1): The proportion of polyols (especially xylitol) is adjustable between 0 and 1, which provides key operational flexibility for this invention. When the proportion is close to or equal to 0, the system degenerates into a traditional binary DES, mainly used for efficient fractionation, but its "source color suppression" ability is limited, suitable for applications where product color requirements are not high. When the proportion increases within the range of 0 to 1, the concentration of the nucleophilic scavenger (xylitol) in the system increases accordingly. According to the core mechanism of this invention, more xylitol molecules can more effectively capture the benzyl carbocation intermediate generated during lignin depolymerization, thereby more thoroughly blocking the Cα-Caryl condensation pathway, enhancing the color suppression effect, and significantly improving the whiteness of the final product. The upper limit is set at 1, based on the experimental equilibrium point of achieving sufficient nucleophilic dosage for adequate color suppression while ensuring fractionation efficiency. At this ratio, the system can ensure sufficient nucleophilicity to almost completely suppress colorimetric condensation while maintaining good solvent physicochemical properties and the feasibility of subsequent separation and recovery.

[0043] Effects of ratio deviations: ① Low hydrogen bond donor ratio (far less than 3): Reduced system acidity may lead to decreased lignin removal rate, incomplete fractionation, and impact on cellulose yield or purity. ② High hydrogen bond donor ratio (far greater than 3): Excessive system acidity, while potentially increasing fractionation rate, has multiple negative effects: it exacerbates hydrolysis of the amorphous and even crystalline regions of cellulose, leading to decreased polymerization degree and deteriorated mechanical properties; the excessively acidic environment itself accelerates the formation of carbocations from lignin fragments, and if the nucleophile is insufficient, it may intensify harmful condensation, producing more dark-colored byproducts, contrary to the color inhibition target; excessive acidity may increase equipment corrosion and complicate the solvent regeneration process. ③ Low polyol ratio (far less than the optimized value, such as close to 0): Insufficient nucleophilic capture ability, unable to effectively intercept all benzyl carbocations, resulting in some condensation color reactions still occurring, limited improvement in product color, and potentially requiring further bleaching. ④ Excessive polyol ratio (greater than 1): Excessive polyol has limited color-suppressing and enhancement effects, resulting in resource waste and increased raw material costs; it may alter the hydrogen bond network structure of DES, affecting its solubility selectivity for lignin, and even reducing fractionation efficiency; excessive polyol may increase the difficulty of product washing and accumulate in solvent recovery cycles, increasing purification energy consumption and costs. In summary, the 1:3:(0-1) mass ratio is an ingenious design of this invention. The 1:3 ratio lays the foundation for efficient and gentle fractionation, while the (0-1) polyol ratio provides continuously adjustable functionality, ranging from "simple fractionation" to "combined fractionation and deep color suppression." This ratio range has been proven in laboratory studies and process optimization to achieve the optimal balance between fractionation efficiency, cellulose quality protection, source color suppression effect, and process economy, which is key to achieving the objectives of this invention. Exceeding this range will adversely affect the system's performance, cost, or product quality.

[0044] In some embodiments, the hydrogen bond acceptor is choline chloride or betaine and its derivatives, the hydrogen bond donor is citric acid or malic acid, and the polyol is a sugar alcohol; the mass ratio of choline chloride or betaine and its derivatives, citric acid or malic acid to sugar alcohol is 1:3:1.

[0045] In some embodiments, the preparation method of the supramolecular eutectic solvent includes the following steps: mixing a hydrogen bond acceptor, a hydrogen bond donor, and a polyol, heating and stirring to obtain the supramolecular eutectic solvent.

[0046] The preparation method is simple and easy to operate.

[0047] In some embodiments, the stirring temperature is 70-90°C, and the stirring time is 1-3 hours. The stirring temperature can be 70°C, 72°C, 74°C, 76°C, 78°C, 80°C, 82°C, 84°C, 86°C, 88°C, or 90°C, and the stirring time can be 0.5 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours, or 3 hours. Other specific values ​​within the above ranges are also possible and will not be listed here.

[0048] In the described embodiment, stirring the hydrogen bond acceptor, hydrogen bond donor, and polyol at 70-90°C for 1-3 hours is a key process parameter for forming a supramolecular eutectic solvent with a stable, homogeneous structure and desired function. This range is set based on comprehensive optimization of reaction kinetics, component compatibility, and solvent stability. The specific technical advantages and principles are as follows: This temperature range is essential to ensure that the ternary components overcome lattice energy and spontaneously assemble into a homogeneous liquid through a hydrogen bond network. Lower temperature limit (≥70℃): Provides sufficient thermal energy to fully melt the solid hydrogen bond acceptors (such as choline chloride) and polyols (such as xylitol), and to allow them to undergo deep intermolecular interactions (mainly hydrogen bonds) with hydrogen bond donors (such as lactic acid), thereby disrupting the original crystal structures of each component and achieving the transformation from a physical mixture to a homogeneous liquid eutectic. If the temperature is too low, mixing will be incomplete, easily resulting in localized unmelted areas or phase separation, leading to inhomogeneous solvent properties and unstable pretreatment effects. Upper temperature limit (≤90℃): Ensures efficient formation of the eutectic while avoiding the negative effects of overheating. Excessively high temperatures (e.g., >90℃) may lead to: ① partial decomposition, oxidation, or intramolecular dehydration of certain heat-sensitive hydrogen bond donors (e.g., some organic acids) or polyols, altering the solvent's chemical composition and affecting its fractionation efficiency and color suppression function; ② exacerbating potential side reactions of the solvent itself, affecting its chemical stability and recyclability; ③ increasing unnecessary energy consumption.

[0049] This time range ensures the complete and thorough formation of the eutectic, reaching thermodynamic equilibrium. The lower time limit (≥1 hour) guarantees sufficient time for uniform heat transfer within the system and for molecular diffusion and hydrogen bond rearrangement to proceed fully. This is the minimum kinetic time necessary to obtain a physicochemically stable and homogeneous solvent. If the time is too short, mixing may be insufficient, resulting in uneven viscosity or poor transparency, and the pretreatment effect (especially the stability of the color-inhibiting effect) will deteriorate.

[0050] Upper time limit (≤3 hours): Prioritizing process efficiency while ensuring the formation of a stable solvent. Experiments show that at the stated temperature, 1-3 hours is sufficient for the system to reach equilibrium. Excessive stirring time (e.g., >3 hours) offers no significant benefit to improving solvent properties; instead, it reduces production efficiency, increases energy consumption, and, as mentioned earlier, may lead to unnecessary thermal degradation risks during prolonged high-temperature heating.

[0051] In summary, the combination of 70-90℃ and 1-3 hours represents an optimized window that balances the sufficient conditions for forming a homogeneous and stable eutectic solvent with the necessary constraints of avoiding component degradation and energy waste. Solvents prepared under these conditions exhibit optimal and stable viscosity, acidity, hydrogen bond network structure, and the activity of functional components (such as xylitol), providing a reliable solvent basis for subsequent efficient and stable integrated lignin fractionation and color suppression processing. Deviations from this range may lead to a decline in solvent quality, thereby affecting the yield, whiteness, and performance consistency of the final cellulose product.

[0052] In some preferred embodiments, the stirring temperature is 80°C and the stirring time is 2 hours.

[0053] This invention provides a method for treating lignin raw materials using a supramolecular eutectic solvent, the method comprising the following steps: The hydrogen bond acceptor, hydrogen bond donor and polyol are mixed and heated and stirred to obtain the supramolecular eutectic solvent; The supramolecular eutectic solvent is mixed with water to obtain an aqueous supramolecular eutectic solvent. The pulverized and dried lignin raw material is mixed with the aqueous supramolecular eutectic solvent and stirred to inhibit the condensation and color development of lignin during the extraction of cellulose from cellulose biomass raw material.

[0054] During this process, the acidic DES environment promotes the dissociation of lignin and may generate a benzyl carbocation intermediate. The specific polyols present in the system (especially xylitol) act as nucleophilic traps, preferentially reacting with the active intermediate to form a CO bond, thereby blocking the CC condensation pathway that leads to blackening.

[0055] In some embodiments, after the stirring step is completed, a product separation and purification step is further included, as follows: After the reaction is completed, the product is subjected to solid-liquid separation, and the solid residue (mainly cellulose) is collected. The product is then thoroughly washed multiple times (no less than 3 times) with a large amount of deionized water (total water volume not less than 30 times the initial volume of the reaction system) to completely remove residual DES, dissolved or modified lignin and other impurities. The washed solid is then dried at 50-60℃ to constant weight and finally pulverized to obtain light-colored to white cellulose powder.

[0056] In some embodiments, the hydrogen bond acceptor includes at least one of choline chloride, ..., ...; the hydrogen bond donor includes at least one of citric acid, ..., ...; and the polyol includes at least one of aliphatic polyols or sugar alcohols containing C2-C6.

[0057] In some embodiments, the mass ratio of the hydrogen bond acceptor, hydrogen bond donor, and polyol is 1:3:(0-1).

[0058] In some embodiments, the solid-liquid mass ratio of the lignin raw material to the aqueous supramolecular eutectic solvent is 1:(5-30). The solid-liquid mass ratio of the lignin raw material to the aqueous supramolecular eutectic solvent can be 1:5, 1:10, 1:15, 1:20, 1:25, or 1:30. Other specific values ​​within the above range are also acceptable and will not be listed here.

[0059] In this embodiment of the invention, controlling the solid-liquid mass ratio of lignin raw material to an aqueous supramolecular eutectic solvent at 1:5 to 1:30 is a key parameter optimized to achieve efficient, uniform, and economical "fractionation-color suppression" treatment. This range is based on a comprehensive balance of mass transfer efficiency, reaction kinetics, and process cost, and its technical advantages and principles are as follows: Technical Benefits: 1. Ensures thorough wetting and uniform treatment: This solid-liquid ratio range provides sufficient solvent volume, allowing the lignin raw material to be completely submerged and fully wetted. This ensures effective solvent penetration into the raw material, achieving full contact with the lignin-carbohydrate complex, thus realizing uniform fractionation and color suppression reaction. 2. Optimizes reaction mass transfer and efficiency: A suitable solid-liquid ratio helps maintain solvent fluidity, promoting the diffusion of reactants (such as hydrogen bond donors and polyols) into the raw material and the outward diffusion of dissolved lignin fragments, thereby accelerating the reaction rate and improving fractionation efficiency and color suppression effect. 3. Balances effect and economy: Avoids excessive solvent use while ensuring treatment effect. A lower solid-liquid ratio (e.g., 1:5) reduces solvent consumption and subsequent recovery costs; a higher solid-liquid ratio (e.g., 1:30) provides more sufficient reaction conditions when treating highly resistant raw materials, ensuring product whiteness and yield.

[0060] Working principle: 1. The principle of the lower limit (1:5): This ratio provides the minimum effective amount of solvent to cover the raw material. If the solvent is too little (e.g., the solid-liquid ratio is less than 1:5), the raw material cannot be fully wetted, resulting in insufficient local reaction, incomplete removal of lignin, and the inhibitor (polyol) cannot effectively capture all benzyl carbocations, thus causing uneven fractionation, darker product color, and a possible decrease in cellulose yield.

[0061] 2. The principle behind the upper limit (1:30): This ratio achieves saturation treatment while avoiding resource waste. While excess solvent (e.g., a solid-liquid ratio higher than 1:30) may further improve the fractionation effect, the benefits diminish. Furthermore, excess solvent leads to a significant increase in the unit raw material processing cost, increased energy consumption for subsequent separation and solvent recovery, and may reduce the local concentration of functional components (e.g., polyols) due to excessive dilution, which is detrimental to the efficient progress of the color inhibition reaction.

[0062] Impacts of deviations from the range: 1. When the solid-liquid ratio is less than 1:5 (too little solvent): mass transfer is limited, the reaction is uneven, resulting in low fractionation efficiency, limited improvement in product color, and the reproducibility of the treatment may be affected by excessive local solvent consumption or by-product accumulation. 2. When the solid-liquid ratio is greater than 1:30 (too much solvent): the treatment effect is not significantly improved, but the economic efficiency is greatly reduced; the solvent recovery load increases, and the amount of wastewater generated increases, which is contrary to the principles of green production.

[0063] In summary, a solid-liquid ratio range of 1:5 to 1:30 is one of the core design parameters for achieving the balance between the "efficient fractionation-source color suppression" objective of this invention and industrial economic feasibility, ensuring the stable acquisition of high-quality light-colored cellulose under mild conditions.

[0064] In some embodiments, the stirring temperature is 100-130°C, and the stirring time is 2-5 hours. The stirring temperature can be 100°C, 115°C, 120°C, 125°C, or 130°C, and the stirring time can be 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, or 5 hours. Other specific values ​​within the above range are also possible and will not be listed here.

[0065] The embodiments of the present invention provide cellulose biomass raw materials processed by the method described above.

[0066] The lignin raw material provided in this invention, especially when xylitol is used as the key component of DES, exhibits a creamy white to white color. This is because the side reactions leading to color development are effectively suppressed during fractionation, and cellulose avoids contamination by dark impurities from the source. The product possesses excellent biocompatibility, good dispersibility, and may have inherent UV absorption potential due to the retention of some lignin-related structures.

[0067] This invention provides an application of the cellulose biomass raw material described above in the cosmetics field.

[0068] This invention provides a cellulose biomass raw material prepared by the above method, and its application in high-value-added fields, particularly in cosmetic formulations. Because the cellulose biomass raw material is effectively protected during the preparation process, avoiding color contamination, it possesses excellent whiteness, biocompatibility, and functional properties, making it highly suitable as a natural physical sunscreen, thickener, stabilizer, or functional filler for use in the preparation of sunscreens, isolation lotions, skin lotions, and other cosmetic formulations.

[0069] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are merely some embodiments of the present invention, not all embodiments, and are only for illustrating the present invention and are not intended to limit the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. A schematic diagram of the color-inhibiting method process in the following embodiments is shown below. Figure 2 .

[0070] Example 1: Treatment of cellulose biomass feedstock with a ternary DES consisting of choline chloride / citric acid / xylitol Preparation of DES: Weigh 41.67 g of choline chloride, 125.00 g of citric acid, and 41.67 g of xylitol (mass ratio 1:3:1), place them in a 250 mL flask, stir the powder thoroughly with a spatula, then place the flask in an 80℃ water bath and stir magnetically for 2 hours until a uniform, transparent, colorless or pale yellow liquid is formed, thus obtaining anhydrous ternary DES.

[0071] Preparation and reaction of aqueous DES: 41.67 g of deionized water was added to the above anhydrous ternary DES and stirred until homogeneous to obtain aqueous DES (mass ratio of choline chloride:citric acid:xylitol:water = 1:3:1:1). 12.5 g of dried commercial bleached sulfate wood pulp board (cut into pieces of approximately 1.5 cm × 2 cm) was weighed and added to a 250 mL flask containing the aqueous ternary DES and a rotor (solid-liquid mass ratio 1:10). The flask was sealed with a balloon and placed in an oil bath. The mixture was stirred at 110 °C and 1500 rpm for 3 hours.

[0072] Post-processing and yield calculation of the product: After the reaction was completed, the mixture was poured into a beaker, about 3 L of pure water was added, stirred, and allowed to stand. DES was collected and recovered. This washing operation was repeated once. Subsequently, about 3 L of pure water was added again, stirred, allowed to stand, and decanted. This process was repeated twice, with the total amount of washing water exceeding 30 times the volume of the reaction system. The solid was dried in a 50°C ventilated incubator to constant weight. The mass of the dried solid was weighed, and its moisture content was measured. The cellulose yield by dry weight was calculated. The dried solid cellulose was pulverized using a pulverizer to obtain the final cellulose powder product.

[0073] DES Recovery: The supernatants collected in the washing step are combined and concentrated by evaporation in a 90°C water bath until all water is evaporated, yielding the recovered DES. The recovery rate is calculated by weighing. This recovered DES can be reformulated with the same water content and used in the next round of reaction.

[0074] Results: The ternary supramolecular DES system after the reaction was light yellow in color, and the cellulose powder product after drying and pulverizing was white powder, with a cellulose yield of 95-98%. This result indicates that the colorimetric reaction of lignin during fractionation was effectively inhibited in the presence of xylitol.

[0075] Example 2: Treatment of cellulose biomass feedstock with a ternary DES of choline chloride / citric acid / glycerol Preparation of DES: Weigh 41.67 g of choline chloride, 125.00 g of citric acid, and 41.67 g of glycerol (mass ratio of choline chloride:citric acid:glycerol = 1:3:1). Following the method in Example 1, heat and stir in an 80°C water bath for 2 hours to obtain homogeneous and transparent DES.

[0076] Reaction and post-treatment: Prepare aqueous DES (with the same amount of water as in Example 1, making the ratio of choline chloride:citric acid:glycerol:water = 1:3:1:1). Treat the same slurry raw material with the exact same reaction conditions (110°C, 3 hours, solid-liquid ratio 1:10), washing procedure, and drying conditions as in Example 1.

[0077] Results: The ternary supramolecular DES system after the reaction was pale yellow, and the cellulose product after drying and pulverizing was a white powder, slightly darker in color than the cellulose powder in Example 1. This indicates that although glycerol has some effect, its efficiency in inhibiting color development (capturing benzyl carbocations) is much lower than that of xylitol.

[0078] Example 3: Treatment of cellulosic biomass feedstock with a ternary DES of choline chloride / citric acid / propylene glycol Preparation of DES: Weigh 41.67 g of choline chloride, 125.00 g of citric acid, and 41.67 g of propylene glycol (mass ratio approximately 1:3:1, with propylene glycol replacing xylitol). Following the method in Example 1, heat and stir in an 80°C water bath for 2 hours to obtain homogeneous and transparent DES.

[0079] Reaction and post-treatment: Prepare aqueous DES (with the same amount of water as in Example 1, making the ratio of choline chloride:citric acid:propylene glycol:water = 1:3:1:1). Treat the same pulp material using the exact same reaction conditions, washing procedures, and drying conditions as in Example 1.

[0080] Results: The ternary supramolecular DES system after the reaction was pale yellow, and the cellulose product after drying and pulverizing was a white powder, which was slightly darker in color than the cellulose powder in Example 1.

[0081] Comparative Example 1: Treatment of cellulose biomass feedstock (excluding polyols) with choline chloride / citric acid binary DES. Preparation of DES: Weigh 25.00 g of choline chloride and 75.00 g of citric acid (mass ratio 1:3). Following the method in Example 1, heat and stir in an 80°C water bath for 2 hours to obtain homogeneous and transparent anhydrous binary DES.

[0082] Reaction and Post-treatment: 25.00 g of deionized water was added to anhydrous binary DES and stirred until homogeneous to obtain aqueous DES (mass ratio of choline chloride:citric acid:water = 1:3:1). 12.5 g of the same slurry raw material was weighed and added (solid-liquid mass ratio 1:10). The reaction was carried out at the same temperature (110°C), time (3 hours), and stirring conditions (1500 rpm) as in Example 1. The post-treatment washing, drying, and pulverizing steps were exactly the same as in Example 1.

[0083] See results Figure 3 The resulting binary supramolecular DES system was yellowish-brown, while the dried and pulverized cellulose product was a grayish-brown powder, the darkest color among all experimental groups. This phenomenon strongly demonstrates that, in the absence of a specific polyol (such as xylitol) as a scavenging agent, lignin underwent a violent, disordered CC condensation reaction in acidic DES, generating a large amount of dark-colored byproducts and contaminating cellulose.

[0084] Figure 4 This is a color comparison diagram of the decolorized cellulose prepared in the embodiments and comparative examples of the present invention.

[0085] In summary, this invention, through a systematic comparison of the fractionation effects of different polyol systems, confirms the irreplaceable role of xylitol in the eutectic solvent system of choline chloride / citric acid, namely, its ability to significantly inhibit the colorimetric reaction during lignin fractionation, directly yielding white cellulose. The colorimetric inhibition effects of different polyols in the examples are consistent with their ability to capture benzyl carbocations as nucleophiles, providing solid experimental support for the core mechanism of "nucleophilic capture-end-capping color inhibition." The dark-colored product reproduced in the comparative system without polyols directly reflects the problem of harmful Cα-Caryl condensation and blackening in the traditional acidic fractionation pathway, thus powerfully highlighting the advanced concept and technological innovation of this invention in actively controlling the chemical reaction pathway of lignin through carefully designed solvent composition.

[0086] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. The application of a supramolecular eutectic solvent in inhibiting lignin condensation and color development, characterized in that, The supramolecular eutectic solvent includes hydrogen bond acceptors, hydrogen bond donors, and polyols.

2. The application of the supramolecular eutectic solvent according to claim 1 in inhibiting lignin condensation and color development, characterized in that, The hydrogen bond acceptor includes at least one of choline chloride, betaine, betaine hydrochloride, L-carnitine, acetylcarnitine, taurine, L-arginine, choline derivatives, proline, alanine, and glycine and their derivatives; the hydrogen bond donor includes at least one of quaternary ammonium salts, polyols, organic acids, and sugars; the polyol includes at least one of aliphatic polyols or sugar alcohols containing C2-C6.

3. The application of the supramolecular eutectic solvent according to claim 1 in inhibiting lignin condensation and color development, characterized in that, The polyols include at least one of ethylene glycol, 1,2-propanediol, 1,3-propanediol, glycerol, xylitol, sorbitol, mannitol, erythritol, and maltitol.

4. The application of the supramolecular eutectic solvent according to claim 1 in inhibiting lignin condensation and color development, characterized in that, The mass ratio of the hydrogen bond acceptor, hydrogen bond donor, and polyol is 1:9:(0-9) ~ 9:1:(0-9).

5. The application of the supramolecular eutectic solvent according to claim 1 in inhibiting lignin condensation and color development, characterized in that, The hydrogen bond acceptor is choline chloride or betaine and its derivatives, the hydrogen bond donor is citric acid or malic acid, and the polyol is a sugar alcohol; the mass ratio of choline chloride or betaine and its derivatives, citric acid or malic acid and sugar alcohol is 1:3:

1.

6. The application of the supramolecular eutectic solvent according to claim 1 in inhibiting lignin condensation and color development, characterized in that, The preparation method of the supramolecular eutectic solvent includes the following steps: mixing hydrogen bond acceptor, hydrogen bond donor and polyol, heating and stirring to obtain the supramolecular eutectic solvent.

7. The application of the supramolecular eutectic solvent according to claim 6 in inhibiting lignin condensation and color development, characterized in that, The stirring temperature is 70-90℃, and the stirring time is 1-3 hours.

8. A method for inhibiting lignin condensation and color development using a supramolecular eutectic solvent, characterized in that, The method includes the following steps: The hydrogen bond acceptor, hydrogen bond donor and polyol are mixed and heated and stirred to obtain the supramolecular eutectic solvent; The supramolecular eutectic solvent is mixed with water to obtain an aqueous supramolecular eutectic solvent. The pulverized and dried cellulose raw material is mixed with the aqueous supramolecular eutectic solvent and stirred to inhibit the condensation and color development of lignin during the cellulose extraction process from the cellulose biomass raw material.

9. A cellulosic biomass feedstock treated using the method of claim 8.

10. The application of the cellulose biomass raw material according to claim 9 in the field of cosmetics.

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