Method for one-step extraction of small molecule chitin by ternary eutectic solvent system

Abstract

The application discloses a method for extracting small-molecule chitin by using a ternary eutectic solvent system, and belongs to the technical field of chitin extraction. The method comprises the following steps: adding shrimp and crab shell powder into the ternary eutectic solvent system, heating and reacting, cooling and filtering the mixture, adding a precipitant into the filtrate, and separating insoluble substances. The ternary eutectic solvent system comprises choline chloride, a pH regulator, and a weak acid with pKa>3. The pH regulator is a strong acid and / or a medium-strong acid. The amount of the pH regulator is less than the amount of the weak acid. The ternary eutectic solvent system has good chitin dissolving capacity and extraction efficiency, and the extraction period is greatly reduced. The extraction process is simple and convenient to operate, and is suitable for large-scale production. The extracted chitin has low molecular weight, good water solubility and biological activity. The extraction process avoids using only a large amount of strong acid and strong base, reduces environmental pollution, and the solvent can be recycled. The raw material is cheap and widely available compared with the enzymatic method.

Description

Technical Field

[0001] This invention relates to a one-step method for extracting small molecule chitin using a ternary eutectic solvent system, belonging to the field of chitin extraction technology. Background Technology

[0002] Chitin is the second most abundant polysaccharide in nature, widely found in shrimp and crab shells. Traditional extraction of small-molecule chitin requires two core steps: extraction and degradation. The main extraction methods include acid-base methods and enzymatic hydrolysis, both of which have significant drawbacks, as detailed below: The acid-base method is currently the most widely used industrial method for chitin extraction. Its core principle is to use strong acids to remove minerals from shrimp and crab shells, and then use strong alkalis to remove proteins, thereby obtaining chitin. However, this method has many prominent problems. The extraction process requires large amounts of strong acids and alkalis, and the reaction generates a large amount of highly polluting wastewater, which has a serious impact on the ecological environment. Moreover, the chitin extracted by this method has a large molecular weight, poor solubility, and low biological activity, making it difficult to meet the needs of high-end applications. At the same time, the extraction process is cumbersome, each step is time-consuming, and the overall extraction efficiency is low, which is not conducive to large-scale industrial production.

[0003] Enzymatic hydrolysis is a relatively green and environmentally friendly method for extracting chitin. Its principle is to break down the proteins in shrimp and crab shells with enzymes to separate chitin. However, this method also has many shortcomings. The enzymes used are expensive, which significantly increases the extraction cost of small molecule chitin. In addition, the enzymatic hydrolysis reaction rate is slow and the extraction cycle is long, making it difficult to improve the overall extraction efficiency. At the same time, the quality of the extracted chitin is affected by a variety of factors such as enzyme activity, reaction temperature, and pH value, resulting in large fluctuations and making it difficult to ensure product uniformity.

[0004] Furthermore, the degradation of chitin also presents numerous challenges, making it difficult to achieve efficient and stable small-molecule transformation. Currently, the main methods for chitin degradation include enzymatic degradation, acid degradation, and oxidative degradation, each with significant drawbacks: enzymatic degradation requires specific degrading enzymes, which are expensive, require stringent storage conditions, have low degradation efficiency, long reaction cycles, and are highly susceptible to temperature and pH fluctuations, easily leading to incomplete or excessive degradation; acid degradation requires large amounts of strong acid reagents, not only generating substantial amounts of highly polluting wastewater but also damaging the active structure of chitin in a strong acid environment, resulting in a decline in product quality; while oxidative degradation has a faster reaction rate, the reaction conditions are difficult to control, easily generating byproducts that reduce the purity of small-molecule chitin, and the oxidizing reagents used are often toxic, making subsequent treatment difficult and costly. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention provides a one-step method for extracting small molecule chitin using a ternary eutectic solvent system, which can directly obtain small molecule chitin more efficiently and at a lower cost.

[0006] The technical solution adopted by this invention to solve its technical problem is: A method for one-step extraction of small molecule chitin using a ternary eutectic solvent system includes the following steps: adding at least one of shrimp shell powder and crab shell powder to the ternary eutectic solvent system, heating and reacting, cooling and filtering the mixture after the reaction, adding a precipitant to the filtrate, separating the insoluble matter, and obtaining small molecule chitin. The ternary eutectic solvent system includes choline chloride, a pH adjuster, and a weak acid with pKa > 3; the pH adjuster is at least one of a strong acid and a moderately strong acid; the mass amount of the pH adjuster is less than the mass amount of the weak acid.

[0007] The method for one-step extraction of small molecule chitin using a ternary eutectic solvent system provided in this application is simple to operate, can extract low molecular weight chitin in one step, and has high extraction efficiency and good product quality.

[0008] Preferably, the mass amount of the pH adjuster is less than one-fifth of the mass amount of the weak acid.

[0009] Furthermore, the pH adjuster is selected from at least one of hydrochloric acid, phosphoric acid, sulfuric acid, sulfurous acid, and oxalic acid. Adjusting the pH promotes the degradation of chitin, yielding small molecule chitin.

[0010] Furthermore, the weak acid is an organic acid. Choline chloride acts as a hydrogen bond acceptor, the organic acid acts as a hydrogen bond donor, and the pH is adjusted using a pH adjuster, which can improve the solubility and extraction efficiency of the eutectic solvent, thus achieving the controlled degradation of chitin.

[0011] Furthermore, the weak acid is selected from at least one of lactic acid, citric acid, acetic acid, formic acid, and malic acid. Different organic acids have different hydrogen bond donor capabilities and solubilities, which significantly affect the extraction effect.

[0012] Furthermore, the precipitant is selected from at least one of ethanol, methanol, acetone, and isopropanol.

[0013] Furthermore, the mass ratio of the choline chloride, the weak acid, and the pH adjuster is 1:1~5:0.1~2. By optimizing the composition and ratio of the ternary eutectic solvent system, the solvent's solubility and extraction efficiency can be improved, while the molecular weight of the product can be controlled.

[0014] Furthermore, in the step of adding at least one of shrimp shell powder and crab shell powder to the ternary eutectic solvent system, the solid-liquid mass ratio is 1:5~30.

[0015] Furthermore, the temperature of the heating reaction is 60℃~120℃.

[0016] Furthermore, the heating reaction time is 1h to 8h.

[0017] By optimizing the extraction reaction conditions, efficient extraction of small molecule chitin and improvement of product quality can be achieved.

[0018] Further, the steps for obtaining the shrimp shell powder include: washing the shrimp shells, drying them, and then crushing them to obtain the shrimp shell powder; The steps to obtain the crab shell powder include: washing the crab shells, drying them, and then crushing them to obtain the crab shell powder.

[0019] This pretreatment helps remove impurities from shrimp and crab shells, improving extraction efficiency.

[0020] Furthermore, the step of separating the insoluble matter includes: centrifugation, followed by washing and drying. The washing liquid can be a precipitant.

[0021] The beneficial effects of this invention are: the invention uses a ternary eutectic solvent system, which has good chitin solubility and extraction efficiency, and significantly reduces the extraction cycle; the extraction process is simple, easy to operate, and suitable for large-scale production; the extracted chitin has a low molecular weight and good water solubility and biological activity; the extraction process avoids the use of large amounts of strong acids and bases, reducing environmental pollution, and the solvent can be recycled; the raw materials are cheaper and more widely available than those for enzymatic hydrolysis. Attached Figure Description

[0022] Figure 1 These are chitin molecular weight distribution diagrams for each embodiment and comparative product. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure are described clearly and completely below. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the described embodiments of this disclosure without creative effort are within the scope of protection of this invention.

[0024] It should be understood that, without conflict, any and all embodiments of the present invention can be combined with technical features of any other embodiment or multiple other embodiments to obtain other embodiments. The present invention includes such combinations to obtain other embodiments.

[0025] Unless otherwise specified, all technical and scientific terms used herein have the standard meaning in the field to which the claimed subject matter pertains. Where multiple definitions exist for a term, the definition herein shall prevail.

[0026] This application provides a method for one-step extraction of small molecule chitin using a ternary eutectic solvent system. The steps include: adding at least one of shrimp shell powder and crab shell powder to the ternary eutectic solvent system, heating and reacting, cooling and filtering the mixture after the reaction, adding a precipitant to the filtrate, separating the insoluble matter, and obtaining small molecule chitin.

[0027] The ternary eutectic solvent system includes choline chloride, a pH adjuster, and a weak acid with pKa > 3; the pH adjuster is at least one of a strong acid and a moderately strong acid; the mass amount of the pH adjuster is less than the mass amount of the weak acid.

[0028] This method combines the two core steps of chitin extraction and degradation, which are typically performed in separate steps, into a single reaction by constructing a ternary eutectic solvent system consisting of choline chloride, a weak acid, and a small amount of strong and / or moderately strong acid. Choline chloride acts as a hydrogen bond acceptor, forming a hydrogen bond network with the weak acid to create a highly dissolving eutectic solvent environment. The weak acid not only acts as a hydrogen bond donor in this system, but its pKa greater than 3 ensures a mildly acidic environment. Introducing a small amount of pH adjuster regulates the proton activity of the eutectic solvent system, catalyzing the cleavage of glycosidic bonds and achieving the degradation of chitin from large molecules to smaller molecules. The entire process eliminates the need for high-concentration strong acid and strong alkali treatments found in acid-base methods, as well as the expensive enzymes and stringent reaction conditions required in enzymatic hydrolysis. Demineralization, deproteinization, and molecular chain degradation are completed simultaneously in a single reactor, significantly shortening the process and reducing wastewater generation.

[0029] Specifically, the pH adjuster is selected from at least one of hydrochloric acid, phosphoric acid, sulfuric acid, sulfurous acid, and oxalic acid. These strong or moderately strong acids all have high acid dissociation constants, which can provide sufficient free protons in the eutectic solvent system to catalyze the hydrolysis and cleavage of chitin glycosidic bonds. Among them, hydrochloric acid is a volatile strong acid, which can be partially removed by heating or reducing pressure after the reaction, reducing the amount of residual acid in the product and facilitating subsequent purification; phosphoric acid is a moderately strong acid, and its tertiary ionization characteristics give it a certain buffering capacity in the system, which can work with the weak acid to maintain the relative stability of the pH of the reaction system and avoid the degradation process from getting out of control due to drastic fluctuations in proton concentration; oxalic acid is a binary moderately strong acid, and both carboxyl groups in its molecule can participate in the construction of hydrogen bond networks, forming richer interactions with choline chloride and weak acids, enhancing the system's chelation ability for calcium ions in minerals, thereby improving the demineralization efficiency.

[0030] Weak acids are specifically organic acids. The carboxyl group in organic acid molecules can act as a hydrogen bond donor, forming stable hydrogen bonds with the chloride ions of choline chloride to jointly construct a eutectic solvent system. They can also provide a mild acidic environment through proton dissociation of the carboxyl group. Compared to inorganic weak acids, the structural diversity of organic acids gives the system greater tunability. Organic acid molecules typically contain multiple carboxyl or hydroxyl groups. These polar groups can form multiple hydrogen bond interactions with the acetylamino and hydroxyl groups on the chitin molecular chain, effectively weakening the original intramolecular and intermolecular hydrogen bond network of chitin, making chitin easier to swell and disperse in solvent systems.

[0031] When a strong acid ionizes to release a large number of protons, organic acid anions can capture excess protons to form undissociated organic acid molecules. When local protons are consumed too quickly, the stored organic acid molecules can dissociate and release protons, maintaining the dynamic balance of proton concentration in the system.

[0032] The weak acid is specifically selected from at least one of lactic acid, citric acid, acetic acid, formic acid, and malic acid. These organic acids are mostly natural metabolites with good biocompatibility. The eutectic solvent system composed of organic acids and choline chloride itself has good biodegradability, further reducing the environmental impact of the process. Compared with the high-concentration inorganic strong acids used in acid-base methods and the expensive specialized enzymes in enzymatic hydrolysis, this scheme uses organic acids as the main solvent component, which significantly reduces raw material costs and post-processing difficulty while ensuring extraction and degradation efficiency.

[0033] The precipitant is selected from at least one of ethanol, methanol, acetone, and isopropanol. These precipitants differ significantly from small-molecule chitin in terms of polarity and solubility parameters. After the reaction, the small-molecule chitin dissolves in a ternary eutectic solvent system. Ethanol, methanol, acetone, or isopropanol is added to the filtrate. These precipitants have good miscibility with the eutectic solvent system and can rapidly disrupt the hydrogen bond interactions between choline chloride, weak acids, residual strong acids, and small-molecule chitin. Due to its poor solubility in pure organic solvents, the small-molecule chitin precipitates, forming a precipitate, thus achieving separation of the product from the solvent system.

[0034] The filtrate obtained after precipitation contains choline chloride, a weak acid, a small amount of a strong acid, and a precipitant, which can be separated and recovered by distillation and other methods to achieve solvent recycling.

[0035] Preferably, the mass ratio of choline chloride, weak acid, and pH adjuster is 1:1~5:0.1~2, and the ternary eutectic solvent contains no other additives. This ratio range ensures the homogeneity and fluidity of the reaction system. After choline chloride and weak acid form a eutectic solvent, the viscosity is usually high. Adding an appropriate amount of pH adjuster can reduce the viscosity of the system and improve mass transfer. The ions generated by the ionization of strong or moderately strong acids in the pH adjuster can further disrupt the hydrogen bonds between chitin molecules.

[0036] Specifically, in the step of adding shrimp or crab shell powder to the ternary eutectic solvent system, the solid-liquid mass ratio is 1:5~30. From a mass transfer perspective, the minerals and proteins in the shrimp and crab shell powder are encapsulated by a chitin fiber network, and the solvent needs to penetrate into the interior of the particles for an effective reaction. A suitable solid-liquid ratio ensures that the solvent can fully wet the solid particles, allowing the choline chloride-weak acid-strong acid (or moderately strong acid) ternary eutectic solvent system to act uniformly on all parts of the raw material. This solid-liquid ratio range ensures reaction efficiency while also providing a suitable material concentration for subsequent separation operations such as filtration and precipitation.

[0037] Preferably, the heating reaction temperature is 60℃~120℃, and the time is 1h~8h. The viscosity of the eutectic solvent system formed by choline chloride and the weak acid decreases significantly above 60℃, and the molecular mobility is enhanced, which is beneficial for the penetration and diffusion of solvent molecules into the shrimp and crab shell powder. When the temperature rises to 120℃, the thermal motion of molecules in the reaction system intensifies, the activation energy for glycosidic bond breaking is more easily crossed, and the degradation reaction rate increases. However, when the temperature exceeds 120℃, the organic acid may undergo thermal decomposition, and choline chloride may also degrade. Simultaneously, small molecule chitin may undergo further condensation or other side reactions at high temperatures.

[0038] Example 1 1. Shrimp shell pretreatment: Wash, dry and crush the shrimp shells to obtain shrimp shell powder with a particle size of 200 mesh.

[0039] 2. Preparation of a ternary eutectic solvent system: Choline chloride, lactic acid and hydrochloric acid were mixed in a mass ratio of 1:3:0.5, heated to 80°C and stirred until completely dissolved to obtain a ternary eutectic solvent system.

[0040] 3. Extraction reaction: Add 100g of shrimp shell powder to a ternary eutectic solvent system with a solid-liquid ratio of 1:20 and react at 100℃ for 3 hours.

[0041] 4. Post-processing: After the reaction is complete, the mixture is cooled to room temperature, filtered, and the filtrate is obtained. Two volumes of anhydrous ethanol are added to the filtrate to precipitate small molecule chitin. The precipitate is then separated by centrifugation, washed, and dried to obtain the small molecule chitin product.

[0042] Example 2 1. Shrimp shell pretreatment: Wash, dry and crush the shrimp shells to obtain shrimp shell powder with a particle size of 200 mesh.

[0043] 2. Preparation of ternary eutectic solvent system: Choline chloride, citric acid and phosphoric acid are mixed in a mass ratio of 1:4:0.8, heated to 90℃ and stirred until completely dissolved to obtain ternary eutectic solvent system.

[0044] 3. Extraction reaction: Add 100g of shrimp shell powder to a ternary eutectic solvent system with a solid-liquid ratio of 1:25 and react at 110℃ for 4 hours.

[0045] 4. Post-processing: After the reaction is complete, the mixture is cooled to room temperature, filtered, and the filtrate is obtained. Three times the volume of acetone is added to the filtrate to precipitate chitin. The precipitate is then separated by centrifugation, washed, and dried to obtain the small molecule chitin product.

[0046] Example 3 1. Shrimp shell pretreatment: The shrimp shell mixture is washed, dried and crushed to obtain shrimp shell powder with a particle size of 200 mesh.

[0047] 2. Preparation of a ternary eutectic solvent system: Choline chloride, acetic acid and sulfuric acid were mixed in a mass ratio of 1:2:0.3, heated to 70°C and stirred until completely dissolved to obtain a ternary eutectic solvent system.

[0048] 3. Extraction reaction: Add 100g of shrimp shell powder to a ternary eutectic solvent system with a solid-liquid ratio of 1:15 and react at 90℃ for 2 hours.

[0049] 4. Post-processing: After the reaction is complete, the mixture is cooled to room temperature, filtered, and the filtrate is obtained. Isopropanol with 1.5 times its volume is added to the filtrate to precipitate chitin. The chitin is then separated by centrifugation, washed, and dried to obtain the small molecule chitin product.

[0050] Comparative Example 1 1. Shrimp shell pretreatment: The shrimp shell mixture is washed, dried and crushed to obtain shrimp shell powder with a particle size of 200 mesh.

[0051] 2. Preparation of binary system: Choline chloride and lactic acid are mixed at a mass ratio of 1:3, heated to 80°C, and stirred until completely dissolved to obtain a binary eutectic solvent system.

[0052] 3. Extraction reaction: Add 100g of shrimp shell powder to a binary eutectic solvent system with a solid-liquid ratio of 1:20, and react at 100℃ for 3 hours.

[0053] 4. Post-processing: After the reaction is complete, the mixture is cooled to room temperature and filtered to obtain the filtrate. Two volumes of anhydrous ethanol are added to the filtrate to precipitate chitin and obtain the chitin product of Comparative Example 1. Since the obtained chitin product is insoluble in water, in order to determine the molecular weight of the product, a deacetylation reaction is carried out using 10 times the mass of 40% sodium hydroxide, and the molecular weight of the corresponding product is determined.

[0054] Comparative Example 2 1. Shrimp shell pretreatment: The shrimp shell mixture is washed, dried and crushed to obtain shrimp shell powder with a particle size of 200 mesh.

[0055] 2. Extraction reaction: After heating concentrated hydrochloric acid to 80°C, shrimp shell powder is added to the concentrated hydrochloric acid at a solid-liquid ratio of 1:20, and the reaction is carried out at 100°C for 3 hours.

[0056] 3. Post-processing: After the reaction is complete, the mixture is cooled to room temperature, filtered, and the filtrate is obtained. Two volumes of anhydrous ethanol are added to the filtrate to precipitate chitin. The chitin is then separated by centrifugation, washed, and dried to obtain the chitin product, which is the chitin product of Comparative Example 2.

[0057] Comparative Example 3 (Traditional method for extracting chitin) 1. Shrimp and crab shell pretreatment: The shrimp and crab shell mixture is washed, dried, and crushed to obtain shrimp and crab shell powder with a particle size of 200 mesh.

[0058] 2. Extraction reaction: Chitosan was added to 10 times its mass of 1% hydrochloric acid solution and treated at room temperature for 8 hours. This was repeated twice. Then, it was treated twice with 4% sodium hydroxide solution at 80°C. The solid-liquid ratio was 1:10. After each treatment, the mixture was washed with water until neutral.

[0059] 3. Post-processing: The obtained chitin was dried in an oven at 60℃ to obtain the chitin product of Comparative Example 3. The chitin product obtained by this method is insoluble in water, and its molecular weight was determined after deacetylation reaction using 10 times its mass of 40% sodium hydroxide.

[0060] The extraction rates of each example and comparative example were calculated, the molecular weight and degree of deacetylation of each example and comparative example product were tested, and the water solubility of each example and comparative example product was observed. The results are shown in Table 1 below.

[0061]

[0062] Table 1 Examples 1, 2, and 3 show that the ternary eutectic solvent can effectively extract low-molecular-weight chitin, with yields all greater than 29%, which is higher than the yield of the traditional acid-base method. Comparative Example 1 shows that the binary eutectic solvent, composed only of choline chloride and organic acid, has a very low yield of low-molecular-weight chitin. Chitin has a large molecular weight and is water-insoluble, which is due to the limited solubility of chitin in the binary eutectic solvent. Even heating cannot effectively degrade chitin, and the filtrate contains only a small amount of small-molecule chitin. Comparative Example 2 shows that acid reagents alone can also degrade chitin, but the yield of small-molecule chitin obtained is low.

[0063] The chitin molecular weight distribution of each embodiment and comparative product is as follows: Figure 1 As shown, Figure 1 In the diagram, the cyan line corresponds to Example 3, the green line to Example 1, the magenta line to Example 3, the red line to Example 1, the blue line to Example 2, and the black line to Example 2. From...Figure 1 It can be seen that the products obtained in Comparative Examples 1 and 3 have larger molecular weights and wider distributions; while the products obtained in Examples 1, 2, and 3 have smaller molecular weights and more concentrated distributions.

[0064] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0065] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A method for one-step extraction of small molecule chitin using a ternary eutectic solvent system, characterized in that the steps include... include: At least one of shrimp shell powder and crab shell powder is added to a ternary eutectic solvent system, heated to react, and the mixture is cooled and filtered after the reaction. A precipitant is added to the filtrate to separate the insoluble matter and obtain small molecule chitin. The ternary eutectic solvent system includes choline chloride, a pH adjuster, and a weak acid with pKa > 3; the pH adjuster is at least one of a strong acid and a moderately strong acid; the mass amount of the pH adjuster is less than the mass amount of the weak acid.

2. The method for one-step extraction of small molecule chitin using a ternary eutectic solvent system according to claim 1, characterized in that, The pH adjuster is selected from at least one of hydrochloric acid, phosphoric acid, sulfuric acid, sulfurous acid, and oxalic acid.

3. The method for one-step extraction of small molecule chitin using a ternary eutectic solvent system according to claim 1, characterized in that, The weak acid is an organic acid.

4. The method for one-step extraction of small molecule chitin using a ternary eutectic solvent system according to claim 3, characterized in that, The weak acid is selected from at least one of lactic acid, citric acid, acetic acid, formic acid, and malic acid.

5. The method for one-step extraction of small molecule chitin using a ternary eutectic solvent system according to claim 1, characterized in that, The precipitant is selected from at least one of ethanol, methanol, acetone, and isopropanol.

6. The method for one-step extraction of small molecule chitin using a ternary eutectic solvent system according to claim 1, characterized in that, The mass ratio of the choline chloride, the weak acid, and the pH adjuster is 1:1~5:0.1~2.

7. The method for one-step extraction of small molecule chitin using a ternary eutectic solvent system according to claim 6, characterized in that, In the step of adding at least one of shrimp shell powder and crab shell powder to the ternary eutectic solvent system, the solid-liquid mass ratio is 1:5~30.

8. The method for one-step extraction of small molecule chitin using a ternary eutectic solvent system according to claim 6, characterized in that, The temperature of the heating reaction is 60℃~120℃.

9. The method for one-step extraction of small molecule chitin using a ternary eutectic solvent system according to claim 8, characterized in that, The heating reaction time is 1 hour to 8 hours.

10. The method for one-step extraction of small molecule chitin using a ternary eutectic solvent system according to claim 1, characterized in that, The steps to obtain the shrimp shell powder include: washing the shrimp shells, drying them, and then crushing them to obtain the shrimp shell powder; The steps to obtain the crab shell powder include: washing the crab shells, drying them, and then crushing them to obtain the crab shell powder.

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