Method for removing impurities and in-situ activation of chitin by acid-base cooperation
Patent Information
- Application Number
- CN202611378375.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-09-07
- Publication Date
- 2026-11-03
AI Technical Summary
Existing chitin pretreatment processes suffer from problems such as poor product cleanliness, high energy consumption, high protein residue, and large batch-to-batch quality fluctuations. The lack of precise control leads to defects such as poor product activity and high costs.
A method of acid-base synergistic removal of impurities and in-situ activation of chitin is adopted. After acid leaching, the chitin is directly transferred to an alkaline medium for programmed temperature rise and alkaline boiling without water washing. The residual acid solution is used to neutralize and provide heat and construct a pH gradient transition zone to achieve in-situ precipitation of protein at its isoelectric point, and simultaneously complete decalcification, deproteinization, defatting and crystallization activation.
It improves product yield and purity, reduces energy consumption, ensures high product quality consistency, reduces washing steps and equipment investment, and meets pharmaceutical-grade requirements.
Abstract
Description
Technical Field
[0001] This invention belongs to the field of high-value utilization technology of marine biomass resources, specifically involving a method for acid-base synergistic removal of impurities and in-situ activation of chitin, and in particular a chemical treatment process that integrates decalcification, deproteinization, degreasing, and crystallization activation. Background Technology
[0002] Chitin is the second most abundant polysaccharide in nature, widely found in the shells of crustaceans such as shrimp and crab. Natural chitin forms a dense complex structure with calcium carbonate, proteins, and lipids, exhibiting high crystallinity and extreme chemical inertness. Industrially, it must undergo pretreatment to remove impurities and disrupt its crystalline structure before it can be used to prepare high-value-added products such as chitosan.
[0003] The currently accepted pretreatment process involves multiple steps, including acid leaching for decalcification, repeated washing until neutral, alkali boiling for deproteinization, repeated washing until neutral, and drying. This process has the following inherent drawbacks:
[0004] (1) After acid leaching dissolves calcium salt, a large number of microcracks and loose grain boundaries are generated between chitin fiber bundles. In the traditional process, the microcracks must be thoroughly washed with water after acid leaching. The water washing causes the microcracks to partially heal due to the reconstruction of hydrogen bonds. When the process is transferred to alkaline boiling, the crystal breaking efficiency is greatly reduced, resulting in poor cleanliness of the final product and poor activity of subsequent acid hydrolysis reaction.
[0005] (2) The residual acid solution from acid leaching is diluted and discharged during repeated water washing, which wastes chemical energy and consumes a large amount of washing water; alkaline boiling requires an external heat source.
[0006] (3) Protein thermal denaturation and adhesion: Traditional alkaline boiling is carried out in a uniform strong alkaline environment and at high temperature. The protein is directly over-degraded without going through the isoelectric point precipitation stage. After thermal denaturation, it forms sticky flocculent substances that are adsorbed onto the surface of chitin, making it difficult to clean. The product has high protein residue, and the protein in the waste liquid has low recycling value due to deep degradation.
[0007] (4) The parameters of each process in the traditional process are fixed values, lacking precise control over the intermediate process. The operation relies on experience, resulting in large fluctuations in product quality between batches and unstable key indicators such as decalcification rate, deproteinization rate, and yield. Summary of the Invention
[0008] One technical problem this invention aims to solve is to provide a method for acid-base synergistic impurity removal and in-situ chitin activation. This method breaks away from the technical bias of requiring water washing after acid leaching. It utilizes a material flow method involving acid leaching, precise dehydration, and direct alkali conversion, introducing residual acid as a functional medium into the alkali cooking stage. The neutralization heat of the acid and alkali solution assists in heating and constructing a pH gradient transition zone, achieving in-situ precipitation of proteins at their isoelectric point. Thus, decalcification, deproteinization, degreasing, and deep activation of crystals are simultaneously completed in a single continuous process. Another technical problem this invention aims to solve is to provide an activated chitin product prepared by this acid-base synergistic impurity removal and in-situ chitin activation method. This product exhibits high consistency in quality (RSD ≤ 4%) and good purity (protein residue ≤ 1.5%), with a stable yield of 20%~30%.
[0009] Technical Solution: To solve the above-mentioned technical problems, the present invention adopts the following technical solution:
[0010] A method for acid-base synergistic removal of impurities and in-situ activation of chitin involves placing chitin raw material in an acidic medium, subjecting it to acid leaching and decalcification, and then dehydrating it to obtain a solid material. The solid material is then directly transferred to an alkaline medium for programmed temperature alkali boiling without water washing. The alkali-boiled solid material is then washed and dried to obtain an activated chitin product.
[0011] The method for acid-base synergistic removal of impurities and in-situ activation of chitin, wherein the acidic medium is a mixture of inorganic and organic acids, with a molar ratio of inorganic to organic acids of 1:0.05 to 1:3, a liquid-to-solid mass ratio of 6:1 to 20:1, a treatment temperature of 10 to 45°C, and a treatment time of 8 to 20 hours; preferably, the treatment temperature is 28°C, and the treatment time is 14 to 16 hours, supplemented by intermittent aeration (15 minutes per hour) to eliminate the concentration polarization layer; the inorganic acid provides a strongly acidic environment for rapid dissolution of calcium carbonate, and the organic acid reacts with Ca through carboxyl groups. 2+ The formation of chelates reduces the amount of free Ca in the solution. 2+ The activity coefficient prevents calcium salts from redepositing on the chitin surface. On the other hand, the buffering capacity of organic acids can inhibit the acid degradation of chitin molecular chains caused by a sharp drop in local pH. During this stage, calcium carbonate is dissolved, and at the same time, a large number of microcracks and grain boundary loosening are generated between chitin fiber bundles.
[0012] The method for acid-base synergistic removal of impurities and in-situ activation of chitin includes a programmed temperature-controlled alkaline boiling treatment consisting of a low-temperature stage at 65-85°C for 1-3 hours, followed by a high-temperature activation stage at 90-110°C for 4-10 hours. The heating rate between the two stages is 0.3-5°C / min. The alkaline medium is an aqueous solution of alkali metal hydroxide with a mass concentration of 3%-10% and a liquid-to-solid ratio of 6:1-15:1 (L / kg). Preferably, the treatment involves holding the solution at 80°C for 2 hours, followed by holding it at 100°C for 7-8.5 hours, with a heating rate of 1.8°C / min. The alkaline medium has a mass concentration of 6% and a liquid-to-solid ratio of 10:1.
[0013] The method for acid-base synergistic removal of impurities and in-situ activation of chitin involves periodic high-pressure gas aeration throughout the alkaline boiling process. The aeration frequency is once every 10 to 40 minutes, each time lasting 3 to 10 minutes, and the aeration pressure is 0.2 to 0.6 MPa to enhance mass transfer and heat distribution uniformity. Preferably, the aeration frequency is once every 20 minutes, each time lasting 3 minutes, and the aeration pressure is 0.4 MPa.
[0014] The method for acid-base synergistic removal of impurities and in-situ activation of chitosan involves a three-stage or higher countercurrent cleaning process. The cleaning medium is warm water at 35-75°C, with each stage lasting 15-40 minutes. An ultrasonic field with a frequency of 20-100 kHz and a power density of 0.05-2.0 W / cm² is applied simultaneously with each stage. Preferably, the cleaning medium is warm water at 58°C, the ultrasonic frequency is 40 kHz, and the power density is 0.45 W / cm². 2 .
[0015] The method for acid-base synergistic removal of impurities and in-situ activation of chitin includes the following steps:
[0016] (1) Place the chitin raw material in an acidic medium and decalcify it by acid leaching at 28°C for 14-16 hours, during which aeration is performed for 15 minutes per hour and the liquid-solid mass ratio is 10:1. The solid-liquid mixture after acid leaching is initially separated.
[0017] (2) The solid material after acid leaching is mechanically dehydrated by means of pressing, centrifugation or vacuum filtration, so that the wet basis moisture content of the solid material is controlled at 38.2%~60.2%;
[0018] (3) The solid material that has been dehydrated in step (2) and has not been washed with water is directly transferred into an alkaline medium for alkaline boiling treatment. The alkaline boiling process is supplemented by periodic high-pressure gas aeration. The aeration frequency is once every 20 minutes, each lasting for 3 minutes, and the aeration pressure is 0.4 MPa. The initial temperature of the alkaline medium is lower than the target temperature for alkaline boiling. During the boiling process, the temperature is first kept at 80°C for 2 hours, and then raised to 100°C at a heating rate of 1.8°C / min, and kept at 100°C for 7~8.5 hours. The mass concentration of the alkaline medium is 6%, and the liquid-solid ratio is 10:1.
[0019] (4) The solid material after alkali boiling is cleaned in multiple stages to the purification standard. At each stage of cleaning, an ultrasonic field with a frequency of 40kHz and a power density of 0.45W / cm² is applied simultaneously, and the cleaning medium is warm water at 58℃.
[0020] (5) The cleaned material is dried at 75°C until the moisture content is ≤10% to obtain activated chitin product.
[0021] The method for acid-base synergistic removal of impurities and in-situ activation of chitin uses chitin raw materials such as shrimp shells, crab shells, lobster shells, krill shells, or mixtures thereof; the inorganic acid in the acidic medium is at least one of hydrochloric acid, nitric acid, or sulfuric acid, and the organic acid is at least one of citric acid, lactic acid, acetic acid, or malic acid; the alkaline medium is an aqueous solution of sodium hydroxide or potassium hydroxide.
[0022] The method for acid-base synergistic removal of impurities and in-situ activation of chitin is defined by the endpoint of the cleaning process, which is determined by the total organic carbon of the final cleaning solution being ≤200ppm and / or the conductivity being ≤350μS / cm.
[0023] The activated chitin product prepared by the above method has a decalcification rate of ≥98%, a deproteinization rate of ≥94%, a defatting rate of ≥92%, an ash content of ≤1.0%, a protein residue of ≤1.5%, a nitrite content of ≤0.007%, and a batch-to-batch relative standard deviation of ≤4%.
[0024] Beneficial effects: Compared with the prior art, the present invention has the following advantages:
[0025] (1) Significantly improved product yield: By retaining the microcracks and loose grain boundary channels generated by acid etching without water washing after acid leaching, and with the full effect of the high-temperature stage of programmed temperature alkaline boiling, hydroxide ions can quickly penetrate into the interior of the crystal lattice along the loose grain boundaries. The reduced crystallinity shortens the reaction time for subsequent acid hydrolysis to prepare chitosan, and the molecular weight distribution of the product is more uniform. More importantly, the in-situ precipitation and suspension of protein at its isoelectric point avoids thermal denaturation and adhesion to the chitin surface. During the washing process, there is little loss of solid phase material and less protein fragment entanglement, and the product yield is stable at 20%~30%.
[0026] (2) Significantly improved product purity: The pH gradient transition zone constructed using residual acid allows proteins to precipitate in situ as suspended particles at their isoelectric point during the process, fundamentally avoiding the thermal denaturation and adhesion of protein fragments to the chitin surface in traditional processes. Deproteinization rate ≥94%, product protein residue ≤1.5%; defatting rate ≥92%, nitrite ≤0.007%; decalcification rate ≥98%, ash content ≤1.0%.
[0027] (3) Energy consumption is greatly reduced: the neutralization reaction of residual acid and alkali provides part of the heat required for alkali boiling and heating, and since the material is directly transferred into the alkali solution without additional preheating, the alkali boiling temperature is low.
[0028] (4) High consistency of product quality: The relative standard deviation (RSD) between batches of products is ≤4%, which meets the stringent requirements for batch consistency in high-end fields such as pharmaceutical grade.
[0029] (5) Simplified process and reduced cost: The multiple water washing process after acid soaking is eliminated, reducing process steps and equipment investment, shortening the production cycle, and significantly reducing washing water and wastewater discharge, resulting in a significant reduction in overall production cost.
[0030] (6) Each unit operation of the present invention is based on mature chemical equipment, without the need for special customized equipment, the modification cost is controllable, and it has broad prospects for industrialization and promotion. Detailed Implementation
[0031] The present invention will be further illustrated below with reference to specific embodiments. These embodiments are implemented based on the technical solutions of the present invention, and it should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention.
[0032] The product performance parameters were tested using the following methods in the examples: Decalcification rate was calculated based on calcium residue in the product ash using EDTA titration; Deproteinization rate was tested using the Kjeldahl nitrogen determination method and UV-Vis spectrophotometry, with a protein conversion factor of 6.25; Ash content was tested according to GB 5009.4, ignited in a muffle furnace at 550℃ to constant weight; Protein residue and nitrite were tested using UV-Vis spectrophotometry; Product yield was based on dry raw material, calculated as product dry weight / raw material dry weight × 100%; Inter-batch RSD results were calculated based on 10 consecutive batches, using decalcification rate and crystallinity as indicators.
[0033] Example 1
[0034] A method for acid-base synergistic removal of impurities and in-situ activation of chitin includes the following steps:
[0035] (1) Raw material processing: Litopenaeus vannamei shells, sourced from the Beihai aquaculture area in Guangxi, were washed to remove surface mud and sand, dried with hot air at 60℃ to constant weight, and crushed to a particle size of 1-5 cm. Dry basis chemical composition (by mass fraction): calcium carbonate 24.6%, crude protein 32.8%, crude fat 4.7%, chitin approximately 35.2%, with the remainder being ash and pigments. The moisture content of the raw material was 8.2%.
[0036] (2) Acid soaking: Dried shrimp shells were placed in an acidic medium composed of hydrochloric acid and citric acid in a molar ratio of 1:0.39, with a liquid-to-solid mass ratio of 10:1 and a hydrochloric acid mass fraction of 37%. The shells were soaked at 28°C for 14 hours, during which compressed air was introduced for aeration for 15 minutes per hour at a flow rate of 0.8 m³ / h. 3 The concentration was reduced by 100°C / min to eliminate the concentration polarization layer at the solid-liquid interface and prevent the shrimp shells from floating on the liquid surface. After acid leaching, the decalcification rate was tested to be 99%.
[0037] (3) Dehydration: After initial separation by a vibrating screen, the solid-liquid mixture after acid leaching is transferred to a screw press. An online near-infrared moisture analyzer is installed at the discharge port to read the moisture content in real time. After pressing, the moisture content of the discharged solid material is stable between 52% and 54%. Three offline samples were taken using a halogen moisture analyzer, and the measured moisture contents were 53.1%, 52.6%, and 53.4%, with an average value of 53.0%.
[0038] (4) Alkali boiling: All the solid material after dehydration in step (3) is directly put into a 6% sodium hydroxide aqueous solution with a liquid-to-solid ratio (calculated as alkali solution volume L / raw material dry basis kg) of 10:1 and an initial temperature of 55℃; then the programmed heating alkali boiling process is started, specifically as follows:
[0039] (A) Low-temperature holding stage: Start steam heating to raise the system temperature to 80℃, and maintain this temperature for 2 hours. During the holding period, high-pressure compressed air (0.4MPa) is introduced every 20 minutes for 3 minutes for aeration, with an aeration flow rate of 2.0 m³ / min. 3 / min;
[0040] (B) High-temperature activation stage: After the low-temperature stage, the temperature is raised by a combination of electric heating and steam jacketing at a rate of 1.8℃ / min, from 80℃ to 100℃, and then held for 7 hours after reaching 100℃. During the holding period, mass transfer is maintained by aeration for 3 minutes (0.4MPa) every 20 minutes.
[0041] After alkaline boiling, the alkaline boiling mixture was collected and centrifuged (5000 rpm, 10 minutes), and the supernatant was collected. The deproteinization rate was measured to be 96.7%, and the defatting rate was 93.8%.
[0042] (5) Cleaning: After alkaline boiling, the solid material is transferred to a four-stage countercurrent cleaning tank. The countercurrent process is as follows: the material is moved sequentially from the first tank to the fourth tank, and fresh water is added from the fourth tank, with the water flow direction opposite to the material flow direction. Cleaning conditions for each stage: cleaning water temperature 58℃, cleaning time for each stage 25min, and ultrasonic waves (frequency 40kHz, power density 0.45W / cm²) and bottom aeration (flow rate 1.0m³ / min, continuous aeration) are activated simultaneously during the cleaning process. After each stage, the material and cleaning liquid are separated by a vibrating screen.
[0043] Final stage (fourth stage) cleaning fluid sampling and testing: Total organic carbon (TOC) was measured to be 178 ppm using a TOC analyzer; conductivity was measured to be 265 μS / cm using an online conductivity meter, both meeting the endpoint judgment criteria.
[0044] (6) Drying: After cleaning, the solid material is dehydrated to a moisture content of 55% by centrifugal dehydrator (2000 rpm, 10 minutes). It is then transferred to a vacuum drying oven, set at 75°C, and dried for about 8 hours. The calculated moisture content is 8.5%, and the activated chitin product is obtained.
[0045] Product specifications: Product yield 26.8%, crystallinity 28.9%, intrinsic viscosity 865 mL / g, ash content 0.9%, protein residue 1.2%, nitrite 0.005%, and batch-to-batch RSD 2.7%.
[0046] Example 2
[0047] A method for acid-base synergistic removal of impurities and in-situ activation of chitin, based on Example 1, with adjustments to some parameters, specifically includes the following steps:
[0048] (1) Acid leaching: Dried shrimp shells (same as in Example 1) were placed in an acidic medium composed of hydrochloric acid and lactic acid with a molar ratio of 1:0.8, a liquid-to-solid mass ratio of 10:1, a hydrochloric acid mass fraction of 37%, and a lactic acid mass fraction of 85%; soaked at 28°C for 14 hours, with aeration for 15 minutes per hour; after acid leaching, the decalcification rate was tested to be 98.5%;
[0049] (2) Dehydration: Same as in Example 1. The screw press was preset to a pressure of 0.6 MPa. The moisture content of the output material was stabilized at 52%~54% by online near-infrared monitoring. The average moisture content of the material was 52.8% after three offline sampling tests by a halogen moisture analyzer.
[0050] (3) Alkali boiling: All the solid material after dehydration in step (3) was directly added to a 6% sodium hydroxide aqueous solution with a liquid-to-solid ratio (calculated as alkali volume L / raw material dry basis kg) of 10:1 and an initial temperature of 55℃. Then, the alkali boiling process was started, specifically: 80℃ for 2 hours, aeration for 3 minutes every 20 minutes (0.4MPa); then the temperature was increased to 100℃ at 1.8℃ / min and held for 7 hours, aeration for 3 minutes every 20 minutes. After the alkali boiling was completed, samples were taken for testing. The deproteinization rate was 96.0% and the defatting rate was 93.0%.
[0051] (4) Cleaning: Same as in Example 1, four-stage countercurrent ultrasonic cleaning (58℃, 25min, 40kHz, 0.45W / cm). 2 The final effluent has a TOC of 185 ppm, a conductivity of 278 μS / cm, and a pH of 7.1.
[0052] (5) Drying: Vacuum drying at 75℃ until the water content is 8.7% to obtain activated chitin product.
[0053] Product specifications: Yield 26.2%, Crystallinity 31.2%, Intrinsic viscosity 842 mL / g, Ash 1.0%, Protein residue 1.3%, Nitrite 0.007%, Inter-batch RSD 2.9%.
[0054] Example 3
[0055] A method for acid-base synergistic removal of impurities and in-situ activation of chitin, based on Example 1, with adjustments to some parameters, specifically includes the following steps:
[0056] (1) Acid leaching: The acid solution formula was the same as in Example 1 (hydrochloric acid and citric acid, molar ratio 1:0.4, liquid-solid ratio 10:1, 28°C, 14 hours, aeration for 15 minutes per hour). The decalcification rate was 98.8%.
[0057] (2) Dehydration: The acid-leached solid material is dehydrated by a screw press. The preset pressing pressure is increased to 1.2 MPa, and the pressing speed is reduced to 10 rpm to increase the pressing intensity and extend the pressing time. The moisture content of the discharged material is reduced to 36%~40% by online near-infrared monitoring, and the average moisture content is 38.2% by three offline sampling tests using a halogen moisture analyzer.
[0058] (3) Alkali boiling: The alkali boiling procedure was the same as in Example 1: 6.0% NaOH aqueous solution, initial temperature 55℃, 80℃ for 2 hours (aeration for 3 minutes every 20 minutes), then increased to 100℃ at 1.8℃ / min and held for 7 hours (aeration for 3 minutes every 20 minutes). The deproteinization rate was 96.2%, and the defatting rate was 93.2%.
[0059] (4) Cleaning: Same as in Example 1, four-stage countercurrent ultrasonic cleaning (58℃, 25min, 40kHz, 0.45W / cm). 2 The final effluent has a TOC of 175 ppm, a conductivity of 258 μS / cm, and a pH of 7.2.
[0060] (5) Drying: Same as in Example 1, vacuum dry at 75℃ to a moisture content of 8.4% to obtain activated chitin product. Product indicators: yield 26.5%, crystallinity 33.5%, intrinsic viscosity 823mL / g, ash content 0.9%, protein residue 1.2%, nitrite 0.006%, batch-to-batch RSD 2.8%.
[0061] Example 4
[0062] A method for acid-base synergistic removal of impurities and in-situ activation of chitin, based on Example 1, with adjustments to some parameters, specifically includes the following steps:
[0063] (1) Acid leaching: the same raw materials and acid solution formula and conditions as in Example 1, with a decalcification rate of 99.0%.
[0064] (2) Dehydration: The acid-leached solid material is dehydrated by a screw press. The preset pressing pressure is reduced to 0.25 MPa, and the pressing speed is increased to 25 rpm to reduce the pressing intensity. The moisture content of the discharged material is monitored by online near-infrared spectroscopy and rises to the range of 58% to 63%. The average moisture content of the material is 60.2% after three offline sampling tests by a halogen moisture analyzer.
[0065] (3) Alkali boiling: The alkaline boiling procedure was the same as in Example 1: 6.0% NaOH aqueous solution, initial temperature 55℃, kept at 80℃ for 2 hours (aeration for 3 minutes every 20 minutes), then increased to 100℃ at 1.8℃ / min and kept at 100℃ for 7 hours (aeration for 3 minutes every 20 minutes). The deproteinization rate was 94.8% and the defatting rate was 92.5%.
[0066] (4) Cleaning: Same as in Example 1, four-stage countercurrent ultrasonic cleaning (58℃, 25min, 40kHz, 0.45W / cm). 2 The final effluent has a TOC of 195 ppm and a conductivity of 296 μS / cm.
[0067] (5) Drying: Same as in Example 1, vacuum dry at 75°C to a moisture content of 8.6% to obtain activated chitin product.
[0068] Product specifications: Yield 26.0%, Crystallinity 35.1%, Intrinsic viscosity 808 mL / g, Ash 1.0%, Protein residue 1.5%, Nitrite 0.004%, Inter-batch RSD 3.1%.
[0069] Example 5
[0070] A method for acid-base synergistic removal of impurities and in-situ activation of chitin, based on Example 1, with adjustments to some parameters, specifically includes the following steps:
[0071] (1) Raw materials: Three-spined swimming crab shells, produced in Zhoushan fishing grounds, Zhejiang Province, after being cleaned, dried and crushed to a particle size of 1~5cm. Dry basis chemical composition: calcium carbonate 31.2%, crude protein 24.3%, crude fat 3.8%, chitin about 38.5%, the remainder being ash and pigments.
[0072] (2) Acid soaking: Due to the high calcium content of crab shells, the acid soaking time was extended to 16 hours. The acid solution formula was the same as in Example 1 (hydrochloric acid and citric acid, molar ratio 1:0.4), the liquid-to-solid ratio was 10:1, soaking was carried out at 28°C for 16 hours, and aeration was carried out for 15 minutes per hour; the decalcification rate was calculated to be 98.2%.
[0073] (3) Dehydration: The screw press is preset to a pressure of 0.6 MPa. The online monitoring shows that the output moisture content is stable at 51%~54%. The average moisture content of the three samples tested by the halogen moisture analyzer is 52.5%.
[0074] (4) Alkali boiling: Prepare a 6.0% NaOH aqueous solution with an initial temperature of 55℃. Alkali boiling procedure: keep at 80℃ for 2 hours (aerate for 3 minutes every 20 minutes at 0.4MPa), then increase the temperature to 100℃ at a rate of 1.8℃ / min, and extend the high-temperature holding period to 8.5 hours (because the crab shell protein structure is more compact, it needs to be hydrolyzed more thoroughly). After alkali boiling, samples were taken for testing, and the deproteinization rate was 95.5% and the defatting rate was 93.8%.
[0075] (5) Cleaning: Same as in Example 1, four-stage countercurrent ultrasonic cleaning (58℃, 25min, 40kHz, 0.45W / cm). 2 The final effluent has a TOC of 182 ppm and a conductivity of 272 μS / cm.
[0076] (6) Drying: Vacuum drying at 75℃ to a moisture content of 8.3% to obtain activated chitin product.
[0077] Product specifications: Yield 23.5%, Crystallinity 32.8%, Intrinsic viscosity 831 mL / g, Ash content 0.86%, Protein residue 1.1%, Nitrite 0.005%, Inter-batch RSD 3.0%.
[0078] Example 5 demonstrates that the present invention is also well applicable to high-calcium crab shell raw materials. Similar results can be achieved simply by extending the acid soaking and alkali boiling time. The product yield is slightly lower because the chitin content in the crab shell is inherently low.
[0079] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A method for acid-base synergistic removal of impurities and in-situ activation of chitin, characterized in that, Chitin raw material is placed in an acidic medium and subjected to acid leaching and decalcification treatment, followed by dehydration to obtain a solid material. The solid material is then directly transferred to an alkaline medium for programmed temperature alkali boiling without water washing. The solid material after alkali boiling is then washed and dried to obtain an activated chitin product.
2. The method for acid-base synergistic removal of impurities and in-situ activation of chitosan according to claim 1, characterized in that, The acidic medium is a mixture of inorganic acid and organic acid, with a molar ratio of inorganic acid to organic acid of 1:0.05 to 1:3, a liquid-solid mass ratio of 6:1 to 20:1, a treatment temperature of 10 to 45°C, and a treatment time of 8 to 20 hours.
3. The method for acid-base synergistic removal of impurities and in-situ activation of chitosan according to claim 1, characterized in that, The programmed heating alkaline boiling process involves first maintaining a low temperature of 65-85℃ for 1-3 hours, then raising the temperature to 90-110℃ at a rate of 0.3-5℃ / min and maintaining this temperature for 4-10 hours. The alkaline medium is an aqueous solution of alkali metal hydroxide with a mass concentration of 3%-10% and a liquid-to-solid ratio of 6:1-15:
1.
4. The method for acid-base synergistic removal of impurities and in-situ activation of chitosan according to claim 1, characterized in that, The entire alkaline boiling process is supplemented with periodic high-pressure gas aeration, with an aeration frequency of once every 10 to 40 minutes, each lasting 3 to 10 minutes, and an aeration pressure of 0.2 to 0.6 MPa.
5. The method for acid-base synergistic removal of impurities and in-situ activation of chitosan according to claim 1, characterized in that, The cleaning process consists of three or more stages of countercurrent cleaning, using warm water at 35~75℃ as the cleaning medium. Each stage of cleaning is simultaneously applied with a frequency of 20~100kHz and a power density of 0.05~2.0W / cm³. 2 The ultrasonic field.
6. The method for acid-base synergistic removal of impurities and in-situ activation of chitosan according to claim 1, characterized in that, Includes the following steps: (1) Place the chitin raw material in an acidic medium and decalcify it by acid leaching at 28°C for 14-16 hours, during which aeration is performed for 15 minutes per hour and the liquid-solid mass ratio is 10:
1. The solid-liquid mixture after acid leaching is initially separated. (2) The solid material after acid leaching is mechanically dehydrated by means of pressing, centrifugation or vacuum filtration, so that the wet basis moisture content of the solid material is controlled at 38.2%~60.2%; (3) The solid material that has been dehydrated in step (2) and has not been washed with water is directly transferred into an alkaline medium for alkaline boiling treatment. The alkaline boiling process is supplemented by periodic high-pressure gas aeration. The aeration frequency is once every 20 minutes, each lasting for 3 minutes, and the aeration pressure is 0.4 MPa. The initial temperature of the alkaline medium is lower than the target temperature for alkaline boiling. During the boiling process, the temperature is first kept at 80°C for 2 hours, and then raised to 100°C at a heating rate of 1.8°C / min, and kept at 100°C for 7~8.5 hours. The mass concentration of the alkaline medium is 6%, and the liquid-solid ratio is 10:
1. (4) The solid material after alkali boiling is cleaned in multiple stages to the purification standard. At each stage of cleaning, an ultrasonic field with a frequency of 40kHz and a power density of 0.45W / cm² is applied simultaneously, and the cleaning medium is warm water at 58℃. (5) The cleaned material is vacuum dried at 75°C until the moisture content is ≤10% to obtain activated chitin product.
7. The method for acid-base synergistic removal of impurities and in-situ activation of chitin according to claim 1 or 6, characterized in that, The chitinous raw material is any one of shrimp shells, crab shells, lobster shells, krill shells, or mixtures thereof; the inorganic acid in the acidic medium is at least one of hydrochloric acid, nitric acid, or sulfuric acid, and the organic acid is at least one of citric acid, lactic acid, acetic acid, or malic acid; the alkaline medium is an aqueous solution of sodium hydroxide or potassium hydroxide.
8. The method for acid-base synergistic removal of impurities and in-situ activation of chitosan according to claim 1 or 6, characterized in that, The cleaning endpoint is determined by the total organic carbon in the final cleaning solution being ≤200ppm and / or the conductivity being ≤350μS / cm.
9. The activated chitin product prepared by the method of claim 1, characterized in that, The product has a decalcification rate of ≥98%, a deproteinization rate of ≥94%, a defatting rate of ≥92%, an ash content of ≤1.0%, a protein residue of ≤1.5%, a nitrite content of ≤0.007%, and a batch-to-batch relative standard deviation of ≤4%.