CN107778379B - N-trimethyl chitosan microspheres, preparation method thereof and application thereof in reducing dielectric loss of vegetable oil - Google Patents
N-trimethyl chitosan microspheres, preparation method thereof and application thereof in reducing dielectric loss of vegetable oil Download PDFInfo
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- C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
- C08B37/00—Preparation of polysaccharides not provided for in groups C08B1/00 - C08B35/00; Derivatives thereof
- C08B37/0006—Homoglycans, i.e. polysaccharides having a main chain consisting of one single sugar, e.g. colominic acid
- C08B37/0024—Homoglycans, i.e. polysaccharides having a main chain consisting of one single sugar, e.g. colominic acid beta-D-Glucans; (beta-1,3)-D-Glucans, e.g. paramylon, coriolan, sclerotan, pachyman, callose, scleroglucan, schizophyllan, laminaran, lentinan or curdlan; (beta-1,6)-D-Glucans, e.g. pustulan; (beta-1,4)-D-Glucans; (beta-1,3)(beta-1,4)-D-Glucans, e.g. lichenan; Derivatives thereof
- C08B37/0027—2-Acetamido-2-deoxy-beta-glucans; Derivatives thereof
- C08B37/003—Chitin, i.e. 2-acetamido-2-deoxy-(beta-1,4)-D-glucan or N-acetyl-beta-1,4-D-glucosamine; Chitosan, i.e. deacetylated product of chitin or (beta-1,4)-D-glucosamine; Derivatives thereof
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- C11—ANIMAL OR VEGETABLE OILS, FATS, FATTY SUBSTANCES OR WAXES; FATTY ACIDS THEREFROM; DETERGENTS; CANDLES
- C11B—PRODUCING, e.g. BY PRESSING RAW MATERIALS OR BY EXTRACTION FROM WASTE MATERIALS, REFINING OR PRESERVING FATS, FATTY SUBSTANCES, e.g. LANOLIN, FATTY OILS OR WAXES; ESSENTIAL OILS; PERFUMES
- C11B3/00—Refining fats or fatty oils
- C11B3/10—Refining fats or fatty oils by adsorption
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Abstract
The invention provides an N-trimethyl chitosan microsphere, a preparation method thereof and application thereof in reducing dielectric loss of vegetable oil, belonging to the field of modified chitosan. The preparation method of the N-trimethyl chitosan microsphere comprises the following steps: mixing chitosan with the viscosity of 0.25-0.65 Pa.s, sodium iodide and N-methyl-2-pyrrolidone for reaction, adding sodium hydroxide and methyl iodide for reaction, then precipitating with ethanol, separating, freeze-drying to obtain N-trimethyl chitosan with the quaternization substitution degree of 10-20%, preparing a solution of the N-trimethyl chitosan, spraying the solution into sodium polyphosphate for reaction, washing with water, adding the solution into a sodium hydroxide solution, stirring, adding glutaraldehyde, and reacting to obtain microspheres; washing the microspheres with water, and then sequentially leaching and freeze-drying the microspheres with 21-29%, 41-49%, 61-69% and 85-89% of organic solvent by volume fraction. The modified chitosan prepared by the method can reduce dielectric loss of vegetable oil.
Description
Technical Field
The invention relates to the field of modified chitosan, and particularly relates to an N-trimethyl chitosan microsphere, a preparation method thereof and application thereof in reducing dielectric loss of vegetable oil.
Background
The transformer oil is insulating oil of a natural hydrocarbon mixture obtained by refining petroleum, is used as a main insulating and cooling medium for oil-filled high-voltage electrical appliances, and is widely applied to equipment such as transformers and circuit breakers. The protocol simplified inspection of transformer oil includes the following items: appearance, flash point, pressure resistance, water-soluble acid (pH value), acid value, micro-water, chromatogram, gas content in oil, dielectric loss factor and the like, wherein the unqualified reasons of the transformer oil mainly comprise: 1. the oil micro-water exceeds the standard, and the oil pressure resistance can not meet the requirement in serious cases; 2. the oil chromatography test result shows that the oil contains C2H2Or deviation of total oil gas content; 3. oil loss out of specification (>4%). The former two defects are obvious in forming reason and easy to treat, potential safety hazards can be effectively eliminated through heating circulation of a vacuum oil filter, and the 3 rd oil is difficult to eliminate by a conventional oil filtering treatment method when dielectric loss exceeds the standard. Research shows that the dielectric loss factor (hereinafter referred to as dielectric loss) of the transformer oil can reflect the quality of the insulating property of the transformer oil, the aging degree of the transformer oil under the action of an electric field, oxidation, high temperature and the like, and the pollution degree of polar impurities, charged colloid and the like in the oil. In the actual use process, the reasons that the dielectric loss of the transformer oil exceeds the standard are found in Liu Bohai Hua and the like (the influence of cleanliness on dielectric loss rise of the transformer oil and a processing method thereof, volume 46, No. 6 of a transformer), besides the internal pollution of the transformer, the transformer oil can also contain the pollution from external pollutants, and the pollutants such as acidic oxidation products, microorganisms, metal oxides, colloid insoluble matters and the like have great influence on the dielectric loss value of the transformer oil; on the other hand, the researches of Wangcong and the like (analysis of the cause of the increase of dielectric loss of the transformer oil and regeneration treatment. high voltage technology No. 3 in 1997) show that the medium loss value of the transformer oil in operation is increased, and the main reasons are the oxidation of the oil and the catalytic action of metal elements on the oxidation of oil products, so that the oil generates acidic oxidation products and oil sludge acidic oxidation products to corrode metals, the metal content in the oil is increased, and the oxidation of the oil is accelerated.
The chitosan is a derivative formed by deacetylating chitin under an alkaline condition, the deacetylation degree of the chitosan is generally between 65% and 90%, and the chitosan is the only basic polysaccharide existing in large quantity in nature. Chitosan is a natural high molecular compound, and the molecular weight varies from hundreds of thousands to millions according to the difference of raw materials and preparation methods. The chitosan is formed by connecting D-glucosamine and N-acetyl-D-glucosamine by glycosidic bonds, and has the advantages of no toxicity, biodegradability, strong flocculation, good precipitability and the like, so that the chitosan becomes an ideal environment-friendly adsorbent and can overcome the defects that the traditional adsorbent is difficult to treat harmlessly and is easy to cause secondary pollution. The adsorption mechanism of chitosan is mainly three, namely three functions of chelating, charge neutralization and adsorption bridging, but the adsorption effect of chitosan is not single but mainly one mechanism and the result of combined action of other mechanisms for different colloidal particles, suspended particles and different systems. The chelating adsorption is that chitosan forms cage-shaped molecules with a similar net structure through contained free amino groups through hydrogen bonds or salt bonds, and the chitosan and metal particles have a chelating effect; the charge neutralization adsorption is that chitosan adsorbs colloid with opposite electric property through the charge carried by the chitosan, so that charged particles in the liquid are removed; the bridging adsorption function is that the chitosan adsorbs colloidal particles at different parts of a long chain through the long chain structure of the chitosan, and the colloidal particles are connected by the long chain like a bridge, so that the colloidal particles in the liquid are effectively removed;
one of the main factors causing the dielectric loss of the transformer oil to exceed the standard is the generation of acidic substances, the impurities are mostly in a colloid or suspension state, most of the impurities are negatively charged, and chitosan is a cationic polymer adsorbent. Therefore, when chitosan with positive charges approaches, the negative charges of the colloidal particles are partially neutralized, the potential is reduced, the colloid is destabilized, and floccules with larger volume are formed after combination and then settle. Therefore, chitosan exhibits good adsorption properties in acidic liquid treatment. A series of researches show that chitosan has strong adsorption effect on acid dye and has better effect in the treatment of acid dye waste liquid.
The study of chitosan and its derivatives for the adsorption treatment of waste oils is known from the prior art. The Master research paper 'research on the deacidification effect of chitosan and modified products thereof on waste lubricating oil' (2016, Chongqing university of Industrial and commercial sciences) tests the deacidification effect of chitosan and two modified products thereof on waste lubricating oil, and researches show that the chitosan and the modified products thereof have good deacidification effect on the waste lubricating oil and the chitosan and the modified products thereof have feasibility for treating the deacidification regeneration of the waste lubricating oil. However, the above cited prior art documents show significant disadvantages for chitosan adsorbent in transformer oil regeneration applications, and the prior art documents utilize stirring and blending of chitosan and oil products, resulting in that flocculent chitosan is dispersed in lubricating oil products with low viscosity, and although the purpose of reducing acid value through flocculation is achieved, the separation difficulty of suspended adsorbent and oil products is large, which is not favorable for practical production and application, and in addition, the hydrogen bonding force of chitosan itself can agglomerate molecular chains, thereby reducing the actual contact area with oil products, and reducing the chelating, electrical neutralization and adsorption bridging effects thereof.
Therefore, a modified chitosan with strong structural stability, large specific surface, uniform particle size and good adsorption effect is needed.
Disclosure of Invention
The invention provides a preparation method of N-trimethyl chitosan microspheres, which has simple process and convenient operation and is suitable for large-scale production and preparation of the N-trimethyl chitosan microspheres.
The invention also provides the N-trimethyl chitosan microsphere prepared by the preparation method, and the N-trimethyl chitosan microsphere has the advantages of uniform particle size, stable structure, good adsorption effect, no toxicity, safety, environmental friendliness and the like.
The invention also provides application of the N-trimethyl chitosan microspheres in reducing the dielectric loss of the vegetable oil, and the N-trimethyl chitosan microspheres can effectively reduce the dielectric loss of the vegetable oil.
The invention is realized by the following steps:
a preparation method of N-trimethyl chitosan microspheres comprises the following steps:
mixing chitosan with the viscosity of 0.25-0.65 Pa.s, sodium iodide and N-methyl-2-pyrrolidone, then carrying out a light-shielding reaction to obtain a reaction solution, adding a first sodium hydroxide solution and methyl iodide into the reaction solution, carrying out a light-shielding reaction to obtain a solution, and then precipitating, separating and drying the solution by using ethanol to obtain N-trimethyl chitosan; wherein the quaternization substitution degree of the N-trimethyl chitosan is 10-20%;
dissolving N-trimethyl chitosan in water, spraying the solution into sodium polyphosphate water solution, and performing crosslinking reaction under ultrasonic treatment to obtain preliminarily crosslinked N-trimethyl chitosan microspheres;
washing the N-trimethyl chitosan microspheres with water, filtering, draining, adding the washed N-trimethyl chitosan microspheres into a second sodium hydroxide solution, stirring, and adding glutaraldehyde for reaction to obtain secondary cross-linked N-trimethyl chitosan microspheres;
washing the secondarily crosslinked N-trimethyl chitosan microspheres with water, filtering, draining, sequentially performing gradient dehydration leaching by using organic solvents with the volume fractions of 21-29%, 41-49%, 61-69% and 85-89%, and then freeze-drying.
In a preferred embodiment of the present invention, the ratio of the chitosan, sodium iodide and N-methyl-2-pyrrolidone is 1-2: 3-4: 30-40 mass ratio mixing reaction.
In a preferred embodiment of the present invention, the chitosan, sodium iodide and N-methyl-2-pyrrolidone are mixed and reacted at 50-70 ℃ in a dark place for 0.5-2 h to obtain a reaction solution.
In a preferred embodiment of the present invention, 5 to 20 mass% of the first sodium hydroxide solution and methyl iodide are added to the reaction solution to react for 1 to 2 hours to obtain a solution, wherein the ratio of the chitosan to the first sodium hydroxide solution to the methyl iodide is 1 to 2 g: 15-30 ml: 10 to 25 ml.
In a preferred embodiment of the present invention, the N-trimethyl chitosan is dissolved in water to form an aqueous solution with a mass concentration of 0.5-3%, and then sprayed into an aqueous solution of sodium polyphosphate with a mass fraction of 1-5% to perform a crosslinking reaction.
In a preferred embodiment of the present invention, the N-trimethyl chitosan microspheres are added into a second sodium hydroxide solution with a mass fraction of 2-8%, and stirred, and then glutaraldehyde is added to react for 2-5 hours to obtain the twice-crosslinked N-trimethyl chitosan microspheres, wherein the ratio of the amount of the N-trimethyl chitosan microspheres to the amount of the glutaraldehyde is 1-2 g: 5-20 ml.
In a preferred embodiment of the present invention, the organic solvent includes one of methanol, ethanol and acetone.
The invention also provides the N-trimethyl chitosan microsphere which is prepared by the preparation method of the N-trimethyl chitosan microsphere.
The invention also provides application of the N-trimethyl chitosan microspheres in reducing dielectric loss of vegetable oil.
In a preferred embodiment of the invention, the vegetable oil is circulated through the N-trimethyl chitosan microspheres, and the mass ratio of the N-trimethyl chitosan microspheres to the vegetable oil is 1-20: 1000.
the invention has the beneficial effects that: the preparation method of the N-trimethyl chitosan microsphere provided by the invention comprises the following steps: mixing chitosan with the viscosity of 0.25-0.65 Pa.s, sodium iodide and N-methyl-2-pyrrolidone for reaction, adding sodium hydroxide and methyl iodide for reaction, then precipitating with ethanol, separating and drying to obtain N-trimethyl chitosan with the quaternization substitution degree of 10-20%, then spraying the N-trimethyl chitosan into sodium polyphosphate, performing crosslinking reaction under ultrasonic treatment, washing with water, filtering, adding into a sodium hydroxide solution, stirring, adding glutaraldehyde, and reacting to obtain microspheres; washing the microspheres with water, and then sequentially leaching and freeze-drying the microspheres by using 21-29%, 41-49%, 61-69% and 85-89% of organic solvents in volume fraction. The preparation method has simple process and convenient operation, and can prepare the N-trimethyl chitosan microspheres on a large scale. The N-trimethyl chitosan microsphere prepared by the preparation method has the advantages of stable and reliable structure, large specific surface area, no pollution hazard, safety and environmental protection. The invention also provides application of the N-trimethyl chitosan microspheres in reducing dielectric loss of vegetable oil.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.
FIG. 1 is a schematic flow chart of the adsorption treatment of vegetable oil by an adsorbent;
FIG. 2 is an electron micrograph of N-trimethyl chitosan microspheres prepared in example 3 of the present invention;
FIG. 3 is an electron micrograph of N-trimethyl chitosan microspheres prepared according to control 1 of the present invention;
FIG. 4 is an electron micrograph of N-trimethyl chitosan microspheres prepared according to control 2 of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.
The following specifically describes embodiments of the present invention.
The embodiment provides a preparation method of N-trimethyl chitosan microspheres, which comprises the following steps:
s1, mixing chitosan with the viscosity of 0.25-0.65 Pa & S, sodium iodide and N-methyl-2-pyrrolidone, reacting in a dark place to obtain a reaction liquid, adding a first sodium hydroxide solution and methyl iodide into the reaction liquid, reacting in a dark place to obtain a solution, and then precipitating, separating and drying the solution by using ethanol to obtain N-trimethyl chitosan; wherein the quaternization substitution degree of the N-trimethyl chitosan is 10-20%; preferably, the chitosan, the sodium iodide and the N-methyl-2-pyrrolidone are mixed according to the weight ratio of 1-2: 3-4: 30-40, and reacting at 50-70 ℃ in a dark place for 0.5-2 h to obtain a reaction solution. Preferably, a first sodium hydroxide solution with the mass fraction of 5-20% and methyl iodide are added into the reaction solution to react for 1-2 hours to obtain a solution, wherein the dosage ratio of chitosan to the first sodium hydroxide solution to the methyl iodide is 1-2 g: 15-30 ml: 10 to 25 ml.
S2, dissolving N-trimethyl chitosan in water, spraying the solution into sodium polyphosphate water solution, and performing crosslinking reaction under ultrasonic treatment to obtain preliminarily crosslinked N-trimethyl chitosan microspheres; preferably, the N-trimethyl chitosan is dissolved in water to prepare an aqueous solution with the mass concentration of 0.5-3%, and then the aqueous solution is sprayed into a sodium polyphosphate aqueous solution with the mass fraction of 1-5% to carry out a crosslinking reaction; the ultrasonic treatment is preferably carried out for 5-30 min under the ultrasonic frequency of 40-120 KHz; further preferably, the N-trimethyl chitosan aqueous solution is atomized by using a nozzle of a compressed air machine and using 0.6-1.0 MPa of compressed air, and then sprayed into the sodium polyphosphate aqueous solution for crosslinking reaction.
S3, washing the N-trimethyl chitosan microspheres with water, filtering, draining, adding the washed N-trimethyl chitosan microspheres into a second sodium hydroxide solution, stirring, and adding glutaraldehyde for reaction to obtain secondary cross-linked N-trimethyl chitosan microspheres; preferably, adding the N-trimethyl chitosan microspheres into a second sodium hydroxide solution with the mass fraction of 2-8%, stirring, and then adding glutaraldehyde to react for 2-5 hours to obtain secondary cross-linked N-trimethyl chitosan microspheres, wherein the dosage ratio of the N-trimethyl chitosan microspheres to the glutaraldehyde is 1-2 g: 5-20 ml.
S4, washing the secondarily crosslinked N-trimethyl chitosan microspheres with water, filtering, draining, sequentially performing gradient dehydration leaching by using organic solvents with the volume fractions of 21-29%, 41-49%, 61-69% and 85-89%, and then performing freeze drying; the organic solvent preferably comprises one of methanol, ethanol and acetone; preferably, the chitosan microspheres subjected to secondary crosslinking are sequentially subjected to gradient dehydration leaching by organic solvents with the volume fractions of 23-26%, 43-47%, 63-66% and 86-88%.
The preparation method of the N-trimethyl chitosan microspheres provided by the embodiment of the invention comprises the following steps of mixing chitosan, sodium iodide and N-methyl-2-pyrrolidone according to the ratio of 1-2: 3-4: 30-40 parts by mass of the raw materials are mixed and reacted for 0.5-2 hours in a dark place at 50-70 ℃ to obtain a reaction liquid, then 15-30 ml of a first sodium hydroxide solution with the mass fraction of 5-20% and 10-25 ml of methyl iodide are added into the reaction liquid to react for 1-2 hours to obtain a brown liquid, finally ethanol is used for precipitation and separation, the product is dissolved in deionized water for dialysis and drying to obtain white spongy solid N-trimethyl chitosan, and the quaternization substitution degree of the white spongy solid N-trimethyl chitosan is controlled to be 10-20%. The chitosan with the viscosity of 0.25-0.65 Pa.s is selected as a raw material, so that the formed N-trimethyl chitosan microspheres have proper particle size to form a stable structure, and if the molecular weight of the adopted chitosan is too large, a nozzle is easy to block, and the cross-linking operation is difficult to complete; if the molecular weight of the adopted chitosan is too small, the mechanical strength of the finally formed microspheres is insufficient; in addition, the quaternization substitution degree of 10-20% can ensure that the N-trimethyl chitosan has certain structural stability, and the problem that the N-trimethyl chitosan is difficult to crosslink and form in a sodium polyphosphate aqueous solution due to excessive water solubility is avoided.
Preparing N-trimethyl chitosan into an aqueous solution with the mass concentration of 0.5-3%, atomizing by using 0.6-1.0 MPa of compressed air, pressing into an aqueous solution of sodium polyphosphate with the mass fraction of 1-5% through a nozzle, and carrying out primary crosslinking reaction under ultrasonic treatment, atomizing the chitosan dissolved in water by using compressed air by using a nozzle system of a compressed air machine, and spraying the atomized chitosan into the aqueous solution of sodium polyphosphate for crosslinking operation, so that the cost is low, the large-scale industrial production is facilitated, the number of the prepared microspheres in unit time is far larger than that of the microspheres in a common manual needle dropping method, and the size of the prepared microspheres can be controlled by changing the air pressure and the sectional area of the nozzle, so that the microspheres with uniform granularity are obtained; the chitosan microspheres which are preliminarily crosslinked can keep a good dispersion state in a solution by adopting ultrasonic treatment, and the aggregation and reunion of the microspheres are avoided, so that the microspheres can keep a uniform and complete spherical shape; washing N-trimethyl chitosan microspheres subjected to preliminary crosslinking reaction with water, filtering, draining, adding the washed N-trimethyl chitosan microspheres into a sodium hydroxide solution with the mass fraction of 2-8%, stirring, adding 5-20 ml of glutaraldehyde into each 1g of N-trimethyl chitosan microspheres, reacting for 2-5 hours to obtain secondary crosslinked N-trimethyl chitosan microspheres, performing gradient dehydration on the N-trimethyl chitosan microspheres by sequentially adopting 21-29%, 41-49%, 61-69% and 85-89% of organic solvents by adopting a step-by-step crosslinking method to facilitate forming and curing of the N-trimethyl chitosan microspheres, and performing gradient elution on the N-trimethyl chitosan microspheres by sequentially adopting 21-29%, 41-49%, 61-69% and 85-89% of organic solvents to ensure that the dehydration process of the N-trimethyl chitosan microspheres is gradually performed according to a proportion, so that the swelling and cracking phenomena of the microspheres in the dehydration process are avoided, preferably, and sequentially passing the secondary crosslinked chitosan microspheres through a volume fraction of 23-26, Carrying out gradient dehydration and leaching on 43-47%, 63-66% and 86-88% of organic solvent, so that the moisture contained in the chitosan microspheres can be uniformly removed, and the breakage rate of the chitosan microspheres is prevented from being reduced due to breakage; and finally, the N-trimethyl chitosan microspheres are dried by adopting a freeze drying method, so that the conditions of microsphere internal shrinkage, hole collapse and the like caused by thermal drying are avoided, and the N-trimethyl chitosan microspheres with uniform particle size, complete structure, large specific surface area and good adsorption effect are obtained.
The invention also provides the N-trimethyl chitosan microsphere which is prepared by using the preparation method of the N-trimethyl chitosan microsphere, wherein the diameter of the N-trimethyl chitosan microsphere is 5-15 mu m, and the N-trimethyl chitosan microsphere has the characteristics of uniform and controllable particle size, stable structure, good adsorption effect, no toxicity, safety, environmental protection and the like.
The invention also provides the application of the N-trimethyl chitosan microspheres in reducing the dielectric loss of vegetable oil, the N-trimethyl chitosan microspheres can effectively reduce the dielectric loss of oil products, the dielectric loss of waste oil after adsorption treatment reaches the national standard, and the adsorption effect of the N-trimethyl chitosan microspheres is obviously better than that of industrial adsorption materials such as activated carbon, activated clay and the like.
The features and properties of the process of the invention are described in further detail below with reference to examples.
Example 1
The embodiment provides an N-trimethyl chitosan microsphere, which is prepared by the following specific steps:
s101, preparing an N-trimethyl chitosan solution with the mass fraction of 0.5% (the quaternization substitution degree is 14.6%); mixing chitosan, sodium iodide and N-methyl-2-pyrrolidone according to the weight ratio of 2: 4: 40, reacting for 1 hour at 60 ℃ in a dark place to obtain a reaction solution, adding 20ml of a first sodium hydroxide solution with the mass fraction of 10% and 20ml of methyl iodide into the reaction solution to react for 1-2 hours to obtain a solution, then precipitating, separating and drying the solution by using ethanol to obtain N-trimethyl chitosan, and dissolving the N-trimethyl chitosan in water to prepare an N-trimethyl chitosan solution with the mass fraction of 0.5%; wherein the viscosity of the chitosan is 0.48 pas;
s102, atomizing an N-trimethyl chitosan solution with the mass fraction of 0.5% by using compressed air with the pressure of 0.8Mpa through a nozzle system of a compressed air machine, dispersing the atomized N-trimethyl chitosan solution into a sodium polyphosphate water solution with the mass fraction of 1%, treating the solution for 25min at the ultrasonic frequency of 60KHz, reacting the solution at the temperature of 25 ℃ for 2h to perform a primary crosslinking reaction, washing the primarily crosslinked N-trimethyl chitosan microspheres with distilled water, filtering and draining the microspheres, adding the microspheres into a sodium hydroxide solution with the mass concentration of 5%, stirring the solution, adding 15ml of glutaraldehyde serving as a crosslinking agent into each 1g of N-trimethyl chitosan microspheres, and performing a secondary crosslinking reaction at the temperature of 25 ℃ for 2h to obtain secondarily crosslinked N-trimethyl chitosan microspheres;
s103, washing and filtering the secondarily crosslinked N-trimethyl chitosan microspheres with distilled water, then sequentially carrying out gradient dehydration and leaching with ethanol water solutions with volume concentrations of 21%, 41%, 61% and 88%, draining, freezing, and treating for 24 hours with a freeze dryer to obtain the dried N-trimethyl chitosan microspheres.
Filling the prepared N-trimethyl chitosan microspheres into a cloth bag, sealing, fixing the cloth bag in the middle of an adsorption filter plate of a multilayer transformer insulating oil regeneration adsorption tank with the patent application number of 201420078137.4, starting a heater, a vacuum oil filter and other devices as shown in figure 1, and continuously filtering the plant insulating oil at the temperature of 55 ℃ through the adsorption filter plate, wherein the mass ratio of the N-trimethyl chitosan microspheres to the plant insulating oil is 5: and 1000, sampling and detecting the medium loss factor at different time periods, wherein the test standard is in accordance with GB/T5654-2007.
Example 2
The embodiment provides an N-trimethyl chitosan microsphere, which is prepared by the following specific steps:
s201, preparing an N-trimethyl chitosan solution with the mass fraction of 2% (the quaternization substitution degree is 14.6%); mixing chitosan, sodium iodide and N-methyl-2-pyrrolidone according to the weight ratio of 2: 4: 40, reacting for 1 hour at 60 ℃ in a dark place to obtain a reaction solution, adding 20ml of a first sodium hydroxide solution with the mass fraction of 10% and 20ml of methyl iodide into the reaction solution to react for 1-2 hours to obtain a solution, then precipitating, separating and drying the solution by using ethanol to obtain N-trimethyl chitosan, and dissolving the N-trimethyl chitosan in water to prepare an N-trimethyl chitosan solution with the mass fraction of 2%; wherein the viscosity of the chitosan is 0.54 pas;
s202, atomizing an N-trimethyl chitosan aqueous solution with the mass fraction of 2% by using compressed air of 0.9Mpa through a nozzle system of a compressed air machine, dispersing the atomized N-trimethyl chitosan aqueous solution into a sodium polyphosphate aqueous solution with the mass fraction of 3%, treating the solution for 20min at an ultrasonic frequency of 75KHz, reacting the solution at 25 ℃ for 3h to perform a primary crosslinking reaction, washing the primarily crosslinked N-trimethyl chitosan microspheres with distilled water, filtering and draining the washed microspheres, adding the filtered microspheres into a sodium hydroxide solution with the mass concentration of 7%, stirring the solution, adding 10ml of glutaraldehyde serving as a crosslinking agent into each 1g of N-trimethyl chitosan microspheres, and performing a secondary crosslinking reaction at 25 ℃ for 4h to obtain secondary crosslinked N-trimethyl chitosan microspheres;
s203, washing and filtering the secondarily crosslinked N-trimethyl chitosan microspheres with distilled water, then sequentially carrying out gradient dehydration and leaching with methanol water solutions with volume concentrations of 25%, 45%, 65% and 85%, draining, freezing, and treating for 24 hours with a freeze dryer to obtain the dried N-trimethyl chitosan microspheres.
Filling the prepared N-trimethyl chitosan microspheres into a cloth bag, sealing, fixing the cloth bag in the middle of an adsorption filter plate of a multilayer transformer insulating oil regeneration adsorption tank with the patent application number of 201420078137.4, starting a heater, a vacuum oil filter and other devices as shown in figure 1, and continuously filtering the plant insulating oil at the temperature of 60 ℃ through the adsorption filter plate, wherein the mass ratio of the N-trimethyl chitosan microspheres to the plant insulating oil is 5: and 1000, sampling and detecting the medium loss factor at different time periods, wherein the test standard is in accordance with GB/T5654-2007.
Example 3
The embodiment provides an N-trimethyl chitosan microsphere, which is prepared by the following specific steps:
s301, preparing an N-trimethyl chitosan solution with the mass fraction of 3% (the quaternization substitution degree is 12.8%); mixing chitosan, sodium iodide and N-methyl-2-pyrrolidone according to the weight ratio of 2: 3.5: 40, reacting for 2 hours in a dark place at 55 ℃ to obtain a reaction solution, adding 30ml of a first sodium hydroxide solution with the mass fraction of 12% and 20ml of methyl iodide into the reaction solution to react for 2 hours to obtain a solution, then precipitating, separating and drying the solution by using ethanol to obtain N-trimethyl chitosan, and dissolving the N-trimethyl chitosan in water to prepare an N-trimethyl chitosan solution with the mass fraction of 3%; wherein the viscosity of the chitosan is 0.65 Pa.s;
s302, atomizing an N-trimethyl chitosan aqueous solution with the mass fraction of 3% by using compressed air of 1Mpa through a nozzle system of a compressed air machine, dispersing the atomized N-trimethyl chitosan aqueous solution into a sodium polyphosphate aqueous solution with the mass fraction of 5%, treating the solution for 10min at the ultrasonic frequency of 100KHz, reacting the solution at 25 ℃ for 5h to perform a primary crosslinking reaction, washing the primarily crosslinked N-trimethyl chitosan microspheres with distilled water, filtering and draining the washed microspheres, adding the microspheres into a sodium hydroxide solution with the mass concentration of 3%, stirring the solution, adding 6ml of glutaraldehyde serving as a crosslinking agent into each 1g of N-trimethyl chitosan microspheres, and performing a secondary crosslinking reaction at 25 ℃ for 5h to obtain secondarily crosslinked N-trimethyl chitosan microspheres;
s303, washing and filtering the secondarily crosslinked N-trimethyl chitosan microspheres with distilled water, then sequentially carrying out gradient dehydration leaching with 29%, 49%, 69% and 88% acetone aqueous solution by volume concentration, draining, freezing, and treating for 24 hours by using a freeze dryer to obtain the dried N-trimethyl chitosan microspheres.
Filling the prepared N-trimethyl chitosan microspheres into a cloth bag, sealing, fixing the cloth bag in the middle of an adsorption filter plate of a multilayer transformer insulating oil regeneration adsorption tank with the patent application number of 201420078137.4, starting a heater, a vacuum oil filter and other devices as shown in figure 1, and continuously filtering the plant insulating oil at the temperature of 65 ℃ through the adsorption filter plate, wherein the mass ratio of the N-trimethyl chitosan microspheres to the plant insulating oil is 5: and 1000, sampling and detecting the medium loss factor at different time periods, wherein the test standard is in accordance with GB/T5654-2007.
Control group 1
The preparation method of the N-trimethyl chitosan microspheres used in the control group 1 is similar to that in the example 3, but the control group 1 does not adopt the gradient dehydration and elution process, and the secondarily crosslinked N-trimethyl chitosan microspheres are directly drained and then frozen, and then are treated for 24 hours by using a freeze dryer to obtain the dried N-trimethyl chitosan microspheres.
Control group 2
The preparation method of the N-trimethyl chitosan microspheres used in the control group 2 is similar to that in the example 3, but the control group 2 adopts the gradient dehydration leaching and draining of the N-trimethyl chitosan microspheres subjected to the secondary crosslinking treatment, and then adopts a heat drying method instead of a freeze drying method to obtain the dried N-trimethyl chitosan microspheres.
Control group 3
Activated carbon was used as control 3.
Control group 4
Activated clay was used as control 4.
The transformer vegetable insulating oil was treated at 55 c using the N-trimethyl chitosan microspheres prepared in example 1, at 60 c using the N-trimethyl chitosan microspheres prepared in example 2, and at 65 c using the N-trimethyl chitosan microspheres prepared in example 3, and the dielectric loss factors of the transformer vegetable insulating oil before and after the treatment and at different treatment times were measured, respectively, and the results are shown in table 1.
TABLE 1 dielectric loss Change of N-trimethyl chitosan-treated vegetable insulating oil of this example
As can be seen from table 1, the dielectric loss of the transformer vegetable insulating oil treated by using the N-trimethyl chitosan microspheres provided in examples 1, 2 and 3 of the present invention is significantly reduced, and the longer the treatment time is, the more the dielectric loss is reduced, which indicates that the N-trimethyl chitosan microspheres provided in this example can effectively reduce the dielectric loss of the transformer vegetable oil.
After the transformer vegetable insulating oil was treated for 48 hours using the N-trimethyl chitosan microspheres provided in the above examples 1, 2, 3, control 1 and 2, the activated carbon provided in the control 3 and the activated clay provided in the control 4, the acid value of the transformer vegetable insulating oil before and after the treatment was measured according to GB/T5530-2005; testing the dielectric loss factor of the plant insulating oil of the transformer before and after treatment according to GB/T5654-2007 test standard; measuring the content of metal elements in the transformer plant insulating oil by adopting an inductive coupling plasma emission spectrometry, and taking the content of three metal elements of iron, copper and aluminum as comparison values; the number and distribution of the particle sizes in the vegetable insulating oil of the transformer were measured by a particle size counter, and the results are shown in Table 2.
TABLE 2 results of treatment of vegetable oils with N-trimethyl chitosan microspheres, activated carbon, activated clay
As can be seen from table 2, the acid value, the metal element content, the number of particles and the dielectric loss of the transformer plant insulating oil treated by the N-trimethyl chitosan microspheres provided in examples 1, 2 and 3 of the present invention are significantly reduced, and the adsorption effect of the N-trimethyl chitosan microspheres provided in examples 1, 2 and 3 is significantly better than that of the N-trimethyl chitosan microspheres provided in control 1 and 2, the activated carbon provided in control 3 and the activated clay provided in control 4.
The N-trimethyl chitosan microspheres provided in example 3, control 1 and control 2 were subjected to electron microscope scanning, and the results are shown in fig. 2, 3 and 4. As shown in FIG. 2, the N-trimethyl chitosan microsphere prepared by the method of the invention has complete microstructure and uniform granularity; as shown in fig. 3, by using the preparation method of the control group 1, the N-trimethyl chitosan microsphere sphere obtained without the gradient dehydration leaching process is cracked, and the sphere mostly shows an irregular shape, because of the hydrogen bond interaction between water molecules and chitosan, in the freeze drying process of the microsphere, the integrity of the microsphere is damaged when the water molecules escape from micropores, so that the sphere is cracked, and the structural strength and the adsorption effect of the chitosan are reduced; as shown in fig. 4, by using the preparation method of the control group 2, collapse and shrinkage of the N-trimethyl chitosan microsphere sphere obtained by the hot drying method instead of the freeze-drying process occurred, which made it difficult to diffuse oil molecules in the microsphere, reduced the actual contact area between chitosan and oil product, and reduced the adsorption effect.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. A preparation method of N-trimethyl chitosan microspheres is characterized by comprising the following steps:
mixing chitosan with the viscosity of 0.25-0.65 Pa.s, sodium iodide and N-methyl-2-pyrrolidone, then carrying out a light-shielding reaction to obtain a reaction solution, adding a first sodium hydroxide solution and methyl iodide into the reaction solution, carrying out a light-shielding reaction to obtain a solution, and then carrying out precipitation, separation and drying on the solution by using ethanol to obtain N-trimethyl chitosan; wherein the quaternization substitution degree of the N-trimethyl chitosan is 10-20%;
dissolving the N-trimethyl chitosan in water, spraying the solution into sodium polyphosphate water solution, and performing crosslinking reaction under ultrasonic treatment to obtain preliminarily crosslinked N-trimethyl chitosan microspheres;
washing the N-trimethyl chitosan microspheres with water, filtering, draining, adding the washed N-trimethyl chitosan microspheres into a second sodium hydroxide solution, stirring, and adding glutaraldehyde for reaction to obtain secondary cross-linked N-trimethyl chitosan microspheres;
washing the secondarily crosslinked N-trimethyl chitosan microspheres with water, filtering, draining, sequentially performing gradient dehydration leaching by using organic solvents with the volume fractions of 21-29%, 41-49%, 61-69% and 85-89%, and then freeze-drying.
2. The method for preparing N-trimethyl chitosan microspheres according to claim 1, wherein the ratio of the chitosan, the sodium iodide and the N-methyl-2-pyrrolidone is 1-2: 3-4: 30-40 mass ratio mixing reaction.
3. The method for preparing N-trimethyl chitosan microspheres according to claim 2, wherein the reaction solution is obtained by mixing chitosan, sodium iodide and N-methyl-2-pyrrolidone, and reacting at 50-70 ℃ in the dark for 0.5-2 h.
4. The preparation method of N-trimethyl chitosan microspheres according to claim 1, wherein a first sodium hydroxide solution with a mass fraction of 5-20% and methyl iodide are added into the reaction solution to react for 1-2 h to obtain the solution, wherein the dosage ratio of the chitosan to the first sodium hydroxide solution to the methyl iodide is 1-2 g: 15-30 mL: 10-25 mL.
5. The method for preparing N-trimethyl chitosan microspheres according to claim 1, wherein the N-trimethyl chitosan is dissolved in water to prepare an aqueous solution with a mass concentration of 0.5-3%, and then the aqueous solution is sprayed into an aqueous solution of sodium polyphosphate with a mass fraction of 1-5% to perform a crosslinking reaction.
6. The method for preparing N-trimethyl chitosan microspheres according to claim 1, wherein the N-trimethyl chitosan microspheres are added into a second sodium hydroxide solution with a mass fraction of 2-8%, stirred, and then added with glutaraldehyde, and reacted for 2-5 hours to obtain the secondary cross-linked N-trimethyl chitosan microspheres, wherein the ratio of the amount of the N-trimethyl chitosan microspheres to the amount of the glutaraldehyde is 1-2 g: 5-20 mL.
7. The method of claim 1, wherein the organic solvent comprises one of methanol, ethanol, and acetone.
8. N-trimethyl chitosan microspheres prepared by the method for preparing N-trimethyl chitosan microspheres according to any one of claims 1 to 7.
9. Use of N-trimethyl chitosan microspheres according to claim 8 for reducing vegetable oil dielectric loss.
10. Use of N-trimethyl chitosan microspheres according to claim 9, wherein the vegetable oil is circulated through said N-trimethyl chitosan microspheres, wherein the mass ratio of said N-trimethyl chitosan microspheres to said vegetable oil is 1-20: 1000.
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| CN104525071A (en) * | 2014-11-24 | 2015-04-22 | 张家港保税区鑫和成国际贸易有限公司 | Chitosan microsphere preparation method |
| CN105374518A (en) * | 2015-11-29 | 2016-03-02 | 国网吉林省电力有限公司电力科学研究院 | Elimination method for microorganisms in transformer oil |
| CN107094765A (en) * | 2017-03-20 | 2017-08-29 | 浙江工商大学 | A kind of quaternary ammonium salt-modified chitosan microball and its preparation method and application |
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| BRPI0702090A2 (en) * | 2007-07-23 | 2009-03-17 | Padetec | chitosan films, membranes and microspheres containing dead cells of the bacterium staphylococcus saprophyticus lami001 for use as a bioemulsifier, oil biocoagulant and for the removal of trace metals in natural, domestic and industrial environments. |
| CN104525071A (en) * | 2014-11-24 | 2015-04-22 | 张家港保税区鑫和成国际贸易有限公司 | Chitosan microsphere preparation method |
| CN105374518A (en) * | 2015-11-29 | 2016-03-02 | 国网吉林省电力有限公司电力科学研究院 | Elimination method for microorganisms in transformer oil |
| CN107094765A (en) * | 2017-03-20 | 2017-08-29 | 浙江工商大学 | A kind of quaternary ammonium salt-modified chitosan microball and its preparation method and application |
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