CN107814953B - Hydroxypropyl chitosan microspheres, preparation method thereof and application thereof in reducing dielectric loss of vegetable oil - Google Patents
Hydroxypropyl chitosan microspheres, preparation method thereof and application thereof in reducing dielectric loss of vegetable oil Download PDFInfo
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Abstract
The invention provides hydroxypropyl chitosan microspheres, a preparation method thereof and application thereof in reducing dielectric loss of vegetable oil, and belongs to the field of chitosan modification. The preparation method of the hydroxypropyl chitosan microspheres comprises the following steps: mixing chitosan with the viscosity of 0.25-0.65 Pa.s, isopropanol and a first sodium hydroxide solution, adding tetramethyl ammonium hydroxide, dripping propylene oxide for reaction, cooling, adjusting the pH value to 7, dispersing in acetone or water, stirring, filtering, washing with absolute ethyl alcohol, drying in vacuum to obtain hydroxypropyl chitosan, preparing a hydroxypropyl chitosan solution, spraying the hydroxypropyl chitosan solution into sodium polyphosphate, performing ultrasonic treatment for crosslinking, 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 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 chitosan modification, and particularly relates to hydroxypropyl chitosan microspheres, 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 the dielectric loss rise of the transformer and a processing method thereof, volume 46, No. 6 of the transformer), besides the internal pollution of the transformer, the pollution of the transformer oil from external pollutants can also be included, and the pollutants such as acidic oxidation products, microorganisms, metal oxides, colloid insoluble matters and the like have great influence on the generation of the dielectric loss value of the transformer oil; on the other hand, the research of Wangcongling et al (analysis of the cause of the increase of dielectric loss of transformer oil and regeneration treatment. high voltage technology 1997 No. 3) shows that the dielectric loss value of the transformer oil in operation is increased, and the main causes 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 sludge acidThe products of the sexual oxidation corrode the metal, which in turn increases the metal content of the oil and accelerates the oxidation of the oil.
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 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 obtains 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 hydroxypropyl chitosan microspheres, which has the advantages of simple process and convenient operation, and is suitable for large-scale production and preparation of hydroxypropyl chitosan microspheres.
The invention also provides the hydroxypropyl chitosan microsphere prepared by the preparation method, and the hydroxypropyl chitosan microsphere has the advantages of uniform particle size, stable structure, good adsorption effect, no toxicity, safety, environmental protection and the like.
The invention also provides application of the hydroxypropyl chitosan microspheres in reducing the dielectric loss of vegetable oil, and the hydroxypropyl chitosan microspheres can effectively reduce the dielectric loss of the vegetable oil.
The invention is realized by the following steps:
a preparation method of hydroxypropyl chitosan microspheres comprises the following steps:
adding chitosan with the viscosity of 0.25-0.65 Pa.s and isopropanol into a first sodium hydroxide solution, mixing and stirring uniformly to obtain a solution, adding tetramethylammonium hydroxide into the solution, then dripping propylene oxide into the solution to react to obtain a reaction solution, cooling the reaction solution, adjusting the pH value to 7 by using hydrochloric acid, dispersing the reaction solution into acetone or water, stirring, carrying out suction filtration, washing by using absolute ethyl alcohol, and carrying out vacuum drying to obtain hydroxypropyl chitosan;
dissolving the hydroxypropyl chitosan in water, spraying the solution into a sodium polyphosphate water solution, and performing crosslinking reaction under ultrasonic treatment to obtain a primarily crosslinked hydroxypropyl chitosan microsphere;
washing the hydroxypropyl chitosan microspheres with water, filtering, draining, adding the hydroxypropyl chitosan microspheres into a second sodium hydroxide solution, stirring, and adding glutaraldehyde for reaction to obtain secondary cross-linked hydroxypropyl chitosan microspheres;
washing the hydroxypropyl chitosan microspheres subjected to secondary crosslinking 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 first sodium hydroxide solution has a mass concentration of 10 to 20%, and the mass ratio of the chitosan, the isopropyl alcohol, and the propylene oxide is 1 to 2: 10-25: 10 to 20.
In a preferred embodiment of the present invention, the chitosan and the isopropanol are added into the first sodium hydroxide solution, and mixed and stirred at 25 to 35 ℃ for 0.5 to 1.5 hours.
In a preferred embodiment of the present invention, the reaction solution is obtained by dropping the propylene oxide into the solution and then stirring and reacting at 55-65 ℃ for 4-6 hours.
In a preferred embodiment of the present invention, the hydroxypropyl chitosan is dissolved in water to form 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.
In a preferred embodiment of the present invention, the hydroxypropyl 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 secondary cross-linked hydroxypropyl chitosan microspheres, wherein the dosage ratio of the chitosan to 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 hydroxypropyl chitosan microspheres, which are prepared by the preparation method of the hydroxypropyl chitosan microspheres.
The invention also provides application of the hydroxypropyl chitosan microspheres in reducing dielectric loss of vegetable oil.
In a preferred embodiment of the invention, vegetable oil is circulated through hydroxypropyl chitosan microspheres, and the mass ratio of the hydroxypropyl chitosan microspheres to the vegetable oil is 1-20: 1000.
the invention has the beneficial effects that: the preparation method of the hydroxypropyl chitosan microspheres provided by the invention comprises the following steps: mixing chitosan with the viscosity of 0.25-0.65 Pa.s, isopropanol and a first sodium hydroxide solution, adding tetramethyl ammonium hydroxide, dripping propylene oxide for reaction, cooling, adjusting the pH value to 7 by using hydrochloric acid, dispersing in acetone or water, stirring, carrying out suction filtration, washing by using absolute ethyl alcohol, carrying out vacuum drying to obtain hydroxypropyl chitosan, preparing a hydroxypropyl chitosan solution, spraying the hydroxypropyl chitosan solution into sodium polyphosphate, carrying out crosslinking reaction under ultrasonic treatment, washing by using 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 be used for preparing hydroxypropyl chitosan microspheres on a large scale. The hydroxypropyl 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 hydroxypropyl 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 microscope photograph of hydroxypropyl chitosan microspheres prepared in example 3 of the present invention;
FIG. 3 is an electron microscope photograph of hydroxypropyl chitosan microspheres prepared in comparison group 1 of the present invention;
fig. 4 is an electron microscope photograph of hydroxypropyl chitosan microspheres prepared in the control group 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 hydroxypropyl chitosan microspheres, a preparation method thereof and application thereof in reducing dielectric loss of vegetable oil.
The embodiment provides a preparation method of hydroxypropyl chitosan microspheres, which comprises the following steps:
s1, adding chitosan and isopropanol with the viscosity of 0.25-0.65 Pa.s into a first sodium hydroxide solution, mixing and stirring uniformly to obtain a solution, adding tetramethylammonium hydroxide into the solution, then dripping propylene oxide into the solution to react to obtain a reaction solution, cooling the reaction solution, adjusting the pH value to 7 by using hydrochloric acid, dispersing the reaction solution into acetone or water, stirring, carrying out suction filtration, washing by using absolute ethyl alcohol, and carrying out vacuum drying to obtain hydroxypropyl chitosan; preferably, the mass concentration of the first sodium hydroxide solution is 10-20%, and the mass ratio of chitosan to isopropanol to propylene oxide is 1-2: 10-25: 10-20, putting chitosan and isopropanol into the first sodium hydroxide solution, and mixing and stirring for 0.5-1.5 h at the temperature of 25-35 ℃; preferably, the solution is dripped with propylene oxide and then stirred for reaction for 4-6 h at the temperature of 55-65 ℃ to obtain a reaction solution.
S2, dissolving hydroxypropyl chitosan in water, spraying the solution into sodium polyphosphate water solution, and performing crosslinking reaction under ultrasonic treatment to obtain primarily crosslinked hydroxypropyl chitosan microspheres; preferably, hydroxypropyl chitosan is dissolved in water to prepare a water solution with the mass concentration of 0.5-3%, and then the water solution is sprayed into a sodium polyphosphate water solution with the mass fraction of 1-5% to perform a crosslinking reaction; the ultrasonic treatment is preferably carried out for 5-30 min under the ultrasonic frequency of 40-120 KHz; preferably, the hydroxypropyl chitosan aqueous solution is atomized by using compressed air of 0.6-1.0 MPa through a nozzle of a compressed air machine, and then sprayed into the sodium polyphosphate aqueous solution for cross-linking reaction and sprayed into the sodium polyphosphate aqueous solution.
S3, washing the hydroxypropyl chitosan microspheres with water, filtering, draining, adding the hydroxypropyl chitosan microspheres into a second sodium hydroxide solution, stirring, and adding glutaraldehyde for reaction to obtain secondary cross-linked hydroxypropyl chitosan microspheres; preferably, the hydroxypropyl chitosan microspheres are added into a second sodium hydroxide solution with the mass fraction of 2-8% and stirred, and then glutaraldehyde is added for reaction for 2-5 hours to obtain secondary cross-linked hydroxypropyl chitosan microspheres, wherein the dosage ratio of chitosan to glutaraldehyde is 1-2 g: 5-20 ml.
S4, washing the hydroxypropyl chitosan microspheres subjected to secondary crosslinking with water, filtering, draining, performing gradient dehydration and leaching by organic solvents with the volume fractions of 21-29%, 41-49%, 61-69% and 85-89%, and then 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 hydroxypropyl chitosan microspheres provided by the embodiment of the invention comprises the following steps of mixing chitosan and isopropanol according to the ratio of 1-2: 10-25, adding the mixture into a first sodium hydroxide solution with the mass fraction of 10-20%, mixing and stirring for 0.5-1.5 h at 25-35 ℃ for reaction, adding a catalyst of tetramethylammonium hydroxide, then, dripping propylene oxide into the mixture, stirring and reacting for 4-6 h at 55-65 ℃ to obtain a reaction solution, wherein the mass ratio of chitosan to propylene oxide is 1-2: and 10-20, cooling the reaction liquid, adjusting the pH value to 7 by using hydrochloric acid, dispersing the reaction liquid in acetone or water, stirring, carrying out suction filtration, washing by using absolute ethyl alcohol, and carrying out vacuum drying to obtain hydroxypropyl chitosan. Wherein, chitosan with the viscosity of 0.25-0.65 Pa.s is selected as a raw material, so that the formed hydroxypropyl chitosan microspheres have proper particle size to stabilize the 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 chitosan used is too small, the mechanical strength of the finally formed microspheres is insufficient.
Preparing hydroxypropyl chitosan into an aqueous solution with the mass concentration of 0.5-3%, atomizing by using 0.6-1.0 MPa 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 through 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 prepared by 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 uniformly distributed 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 the hydroxypropyl chitosan microspheres subjected to primary crosslinking reaction with water, filtering, draining, adding the hydroxypropyl chitosan microspheres into a second sodium hydroxide solution with the mass fraction of 2-8%, stirring, adding 5-20 ml of glutaraldehyde, reacting for 2-5 hours to obtain the hydroxypropyl chitosan microspheres subjected to secondary crosslinking, adopting a step-by-step crosslinking method to facilitate forming and curing of the hydroxypropyl chitosan microspheres, sequentially adopting 21-29%, 41-49%, 61-69% and 85-89% of organic solvents to perform gradient dehydration leaching on the hydroxypropyl chitosan microspheres, gradually performing the dehydration process of the hydroxypropyl chitosan microspheres according to a proportion, avoiding the swelling and cracking phenomena of the microspheres in the dehydration process, preferably sequentially performing gradient dehydration leaching on the chitosan microspheres with the volume fractions of 23-26%, 43-47%, 63-66% and 86-88%, and ensuring uniform removal of water in the chitosan microspheres, the method avoids breakage of the chitosan microspheres and reduction of the breakage rate of the chitosan microspheres, and finally adopts a freeze-drying method for drying, so that conditions of microsphere internal shrinkage, hole collapse and the like caused by thermal drying are avoided, and the hydroxypropyl chitosan microspheres with uniform particle size, complete structure, large specific surface area and good adsorption effect are obtained.
The invention also provides a hydroxypropyl chitosan microsphere which is prepared by the preparation method of the hydroxypropyl chitosan microsphere, the diameter of the hydroxypropyl chitosan microsphere is 5-15 mu m, and the hydroxypropyl 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 application of the hydroxypropyl chitosan microspheres in reducing dielectric loss of vegetable oil. The hydroxypropyl chitosan microspheres can effectively reduce dielectric loss in oil products, the dielectric loss of waste oil after adsorption treatment reaches the national standard, and the adsorption effect of the hydroxypropyl chitosan microspheres is obviously superior to 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 a hydroxypropyl chitosan microsphere, and the specific preparation method comprises the following steps:
s101, preparing hydroxypropyl chitosan solution with the mass fraction of 0.5%; mixing chitosan and isopropanol according to the proportion of 1: 15 into a first sodium hydroxide solution with the mass concentration of 10%, mixing and stirring for 1h at 30 ℃ to obtain a solution, adding tetramethylammonium hydroxide into the solution, then dripping propylene oxide into the solution, stirring and reacting for 5h at 60 ℃ to obtain a reaction solution, wherein the mass ratio of chitosan to propylene oxide is 1: cooling the reaction liquid, adjusting the pH value to 7 by using hydrochloric acid, dispersing the reaction liquid in acetone or water, stirring, carrying out suction filtration, washing by using absolute ethyl alcohol, and carrying out vacuum drying to obtain hydroxypropyl chitosan; dissolving hydroxypropyl chitosan in water to prepare a hydroxypropyl chitosan solution with the mass fraction of 0.5%; wherein the viscosity of the chitosan is 0.48 pas;
s102, atomizing a hydroxypropyl 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 hydroxypropyl 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 primary crosslinking reaction, washing the hydroxypropyl chitosan microspheres subjected to primary crosslinking with distilled water, filtering and draining the washed hydroxypropyl chitosan microspheres, adding the filtered hydroxypropyl chitosan microspheres into a sodium hydroxide solution with the mass concentration of 5%, stirring the solution, adding 15ml of glutaraldehyde solution serving as a crosslinking agent, and performing secondary crosslinking reaction at the temperature of 25 ℃ for 2h to obtain secondary crosslinked hydroxypropyl chitosan microspheres;
s103, washing and filtering the secondary cross-linked hydroxypropyl 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 hydroxypropyl chitosan microspheres.
The prepared hydroxypropyl chitosan microspheres are filled into a cloth bag, after the cloth bag is sealed, the cloth bag is fixed in the middle of an adsorption filter plate of a transformer insulating oil regeneration multilayer adsorption tank with the patent application number of 201420078137.4, as shown in figure 1, devices such as a heater, a vacuum oil filter and the like are started, so that the plant insulating oil is continuously filtered through the adsorption filter plate at the temperature of 55 ℃, wherein the mass ratio of the hydroxypropyl 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 a hydroxypropyl chitosan microsphere, and the specific preparation method comprises the following steps:
s201, preparing hydroxypropyl chitosan solution with the mass fraction of 2%; mixing chitosan and isopropanol according to the proportion of 1: 20, adding the mixture into a first sodium hydroxide solution with the mass concentration of 15%, mixing and stirring the mixture for 1h at 25 ℃ to obtain a solution, adding tetramethyl ammonium hydroxide into the solution, then dripping propylene oxide into the solution, stirring and reacting the mixture for 5h at 55 ℃ to obtain a reaction solution, wherein the mass ratio of chitosan to propylene oxide is 1: 15, cooling the reaction liquid, adjusting the pH value to 7 by using hydrochloric acid, dispersing the reaction liquid in acetone or water, stirring, carrying out suction filtration, washing by using absolute ethyl alcohol, and carrying out vacuum drying to obtain hydroxypropyl chitosan; dissolving hydroxypropyl chitosan in water to prepare hydroxypropyl chitosan solution with the mass fraction of 2%; wherein the viscosity of the chitosan is 0.54 pas;
s202, atomizing a hydroxypropyl 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 hydroxypropyl chitosan aqueous solution into a sodium polyphosphate aqueous solution with the mass fraction of 3%, treating the mixture for 20min at an ultrasonic frequency of 75KHz, reacting the mixture at 25 ℃ for 3h to perform a primary crosslinking reaction, washing the hydroxypropyl chitosan microspheres subjected to primary crosslinking with distilled water, filtering and draining the washed hydroxypropyl chitosan microspheres, adding the filtered hydroxypropyl chitosan microspheres into a sodium hydroxide solution with the mass concentration of 7%, stirring the solution, adding 10ml of glutaraldehyde as a crosslinking agent, and performing a secondary crosslinking reaction at 25 ℃ for 4h to obtain secondary crosslinked hydroxypropyl chitosan microspheres;
s203, washing and filtering the hydroxypropyl chitosan microspheres subjected to secondary crosslinking with distilled water, then sequentially performing gradient dehydration and leaching with methanol aqueous 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 hydroxypropyl chitosan microspheres.
The prepared hydroxypropyl chitosan microspheres are filled into a cloth bag, after the cloth bag is sealed, the cloth bag is fixed in the middle of an adsorption filter plate of a transformer insulating oil regeneration multilayer adsorption tank with the patent application number of 201420078137.4, as shown in figure 1, devices such as a heater, a vacuum oil filter and the like are started, so that the plant insulating oil is continuously filtered through the adsorption filter plate at the temperature of 60 ℃, wherein the mass ratio of the hydroxypropyl 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 a hydroxypropyl chitosan microsphere, and the specific preparation method comprises the following steps:
s301, preparing a hydroxypropyl chitosan solution with the mass fraction of 3%; mixing chitosan and isopropanol according to the proportion of 1: 25 into a first sodium hydroxide solution with the mass concentration of 20%, mixing and stirring for 1h at 30 ℃ to obtain a solution, adding tetramethylammonium hydroxide into the solution, then dripping propylene oxide into the solution, stirring and reacting for 4h at 65 ℃ to obtain a reaction solution, wherein the mass ratio of chitosan to propylene oxide is 1: 20, cooling the reaction liquid, adjusting the pH value to 7 by using hydrochloric acid, dispersing the reaction liquid in acetone or water, stirring, carrying out suction filtration, washing by using absolute ethyl alcohol, and carrying out vacuum drying to obtain hydroxypropyl chitosan; dissolving hydroxypropyl chitosan in water to prepare a hydroxypropyl chitosan solution with the mass fraction of 3%; wherein the viscosity of the chitosan is 0.65 Pa.s;
s302, atomizing a hydroxypropyl chitosan aqueous solution with the mass fraction of 3% by using 1Mpa compressed air through a nozzle system of a compressed air machine, dispersing the atomized hydroxypropyl chitosan aqueous solution into a sodium polyphosphate aqueous solution with the mass fraction of 5%, treating the mixture for 10min at the ultrasonic frequency of 100KHz, reacting the mixture at 25 ℃ for 5h to perform primary crosslinking reaction, washing the hydroxypropyl chitosan microspheres subjected to primary crosslinking with distilled water, filtering and draining the obtained product, adding the obtained product into a sodium hydroxide solution with the mass concentration of 3%, stirring the obtained product, adding 6ml of glutaraldehyde as a crosslinking agent, and performing secondary crosslinking reaction at 25 ℃ for 5h to obtain secondary crosslinked hydroxypropyl chitosan microspheres;
s303, washing and filtering the hydroxypropyl chitosan microspheres subjected to secondary crosslinking with distilled water, then sequentially carrying out gradient dehydration and leaching with acetone aqueous solutions with volume concentrations of 29%, 49%, 69% and 88%, draining, freezing, and treating for 24 hours with a freeze dryer to obtain the dried hydroxypropyl chitosan microspheres.
The prepared hydroxypropyl chitosan microspheres are filled into a cloth bag, after the cloth bag is sealed, the cloth bag is fixed in the middle of an adsorption filter plate of a transformer insulating oil regeneration multilayer adsorption tank with the patent application number of 201420078137.4, as shown in figure 1, devices such as a heater, a vacuum oil filter and the like are started, so that the plant insulating oil is continuously filtered through the adsorption filter plate at the temperature of 65 ℃, wherein the mass ratio of the hydroxypropyl 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 hydroxypropyl chitosan microspheres used in the control group 1 is similar to that in the example 3, but the control group 1 does not adopt a gradient dehydration and leaching process, the hydroxypropyl chitosan microspheres subjected to secondary crosslinking are directly drained and then frozen, and then the obtained product is processed for 24 hours by using a freeze dryer to obtain the dried hydroxypropyl chitosan microspheres.
Control group 2
The preparation method of the hydroxypropyl chitosan microspheres used in the control group 2 is similar to that in the example 3, but the control group 2 adopts gradient dehydration leaching and draining of the hydroxypropyl chitosan microspheres subjected to secondary crosslinking treatment, and then adopts a heat drying method instead of a freeze drying method to obtain the dried hydroxypropyl chitosan microspheres.
Control group 3
Activated carbon was used as control 3.
Control group 4
Activated clay was used as control 4.
Transformer vegetable insulating oil was treated at 55 ℃ using the hydroxypropyl chitosan microspheres prepared in example 1, transformer vegetable insulating oil was treated at 60 ℃ using the hydroxypropyl chitosan microspheres prepared in example 2, transformer vegetable insulating oil was treated at 65 ℃ using the hydroxypropyl chitosan microspheres prepared in example 3, and dielectric loss factors of transformer vegetable insulating oil before and after treatment and at different treatment times were respectively determined, and the results are shown in table 1.
TABLE 1 dielectric loss Change of hydroxypropyl 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 hydroxypropyl chitosan microspheres provided in embodiments 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 hydroxypropyl chitosan microspheres provided in this embodiment can effectively reduce the dielectric loss of the transformer vegetable oil.
After the transformer plant insulating oil was treated for 48 hours by using the hydroxypropyl 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 plant 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 hydroxypropyl chitosan microspheres, activated carbon, activated clay treatment of vegetable oils
As can be seen from table 2, the acid value, the content of metal elements, the number of particles and the average dielectric loss of the transformer plant insulating oil treated by using the hydroxypropyl chitosan microspheres provided in examples 1, 2 and 3 of the present invention are significantly reduced, and the adsorption effect of the hydroxypropyl chitosan microspheres provided in examples 1, 2 and 3 is significantly better than that of the hydroxypropyl chitosan microspheres provided in control group 1 and 2, the activated carbon provided in control group 3 and the activated clay provided in control group 4.
The hydroxypropyl 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, fig. 3 and fig. 4. As shown in fig. 2, the hydroxypropyl chitosan microspheres prepared by the method of the present invention have the advantages of complete microstructure and uniform particle size; as shown in fig. 3, by adopting the preparation method of the control group 1, the hydroxypropyl 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 action of water molecules and chitosan, the integrity of the microsphere is damaged when water molecules escape from micropores in the freeze drying process of the microsphere, so that the sphere is cracked, and the structural strength and the adsorption effect of chitosan are reduced; as shown in fig. 4, by using the preparation method of the control group 2, collapse and shrinkage of the hydroxypropyl chitosan microsphere sphere obtained by a hot drying method instead of a freeze-drying process are caused, so that oil molecules are difficult to diffuse in the microsphere, the actual contact area of chitosan and oil is reduced, and the adsorption effect is reduced.
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 (7)
1. A preparation method of hydroxypropyl chitosan microspheres is characterized by comprising the following steps:
adding chitosan with the viscosity of 0.25-0.65 Pa.s and isopropanol into a first sodium hydroxide solution, mixing and stirring uniformly to obtain a solution, adding tetramethylammonium hydroxide into the solution, then dripping propylene oxide into the solution to react to obtain a reaction solution, cooling the reaction solution, adjusting the pH value to 7 by using hydrochloric acid, dispersing the reaction solution into acetone or water, stirring, carrying out suction filtration, washing by using absolute ethyl alcohol, and carrying out vacuum drying to obtain hydroxypropyl chitosan;
dissolving the hydroxypropyl chitosan in water, spraying the solution into a sodium polyphosphate water solution, and performing crosslinking reaction under ultrasonic treatment to obtain a primarily crosslinked hydroxypropyl chitosan microsphere;
washing the hydroxypropyl chitosan microspheres with water, filtering, draining, adding the hydroxypropyl chitosan microspheres into a second sodium hydroxide solution, stirring, and adding glutaraldehyde for reaction to obtain secondary cross-linked hydroxypropyl chitosan microspheres;
washing the hydroxypropyl chitosan microspheres subjected to secondary crosslinking with water, filtering, draining, sequentially performing gradient dehydration and leaching by using organic solvents with the volume fractions of 21-29%, 41-49%, 61-69% and 85-89%, and then performing freeze drying.
2. The preparation method of hydroxypropyl chitosan microspheres according to claim 1, wherein the mass concentration of the first sodium hydroxide solution is 10-20%, and the mass ratio of chitosan, isopropanol and propylene oxide is 1-2: 10-25: 10 to 20.
3. The preparation method of hydroxypropyl chitosan microspheres according to claim 1, wherein the chitosan and the isopropanol are added into the first sodium hydroxide solution, mixed and stirred at 25-35 ℃ for 0.5-1.5 h.
4. The preparation method of hydroxypropyl chitosan microspheres according to claim 1, wherein the reaction solution is obtained by dropping the propylene oxide into the solution and then stirring and reacting at 55-65 ℃ for 4-6 hours.
5. The preparation method of the hydroxypropyl chitosan microspheres according to claim 1, wherein the hydroxypropyl 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 preparation method of the hydroxypropyl chitosan microspheres according to claim 1, wherein the hydroxypropyl chitosan microspheres are added into a second sodium hydroxide solution with the mass fraction of 2-8% and stirred, and then glutaraldehyde is added to react for 2-5 hours to obtain the secondary cross-linked hydroxypropyl chitosan microspheres, wherein the dosage ratio of chitosan to glutaraldehyde is 1-2 g: 5-20 m L.
7. The preparation method of hydroxypropyl chitosan microspheres according to claim 1, wherein the organic solvent comprises one of methanol, ethanol, and acetone.
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