A composite adsorbent and its preparation method and application

Abstract

The invention discloses a composite adsorbent and its preparation method and application, belong to the field of adsorbent technology, the composite adsorbent includes the following raw materials by mass: 40 80 parts of amino loofah, 20 60 parts of chitosan, 4 20 parts of diatomite, 20 36 parts of halloysite, 5 20 parts of cross-linking agent. Its preparation method is first acidifying diatomite and halloysite, then adding chitosan acetic acid solution to mix, stirring and mixing after adding amino loofah, adding cross-linking agent and stirring cross-linking, stirring to colloid. After drying, crushing to obtain a composite adsorbent. The composite adsorbent provided by the present invention, due to the combination of the different porous structures of loofah, diatomite and halloysite, gives the secondary porous structure of adsorbent macroporous structure and microporous structure, enhances adsorption capacity, and utilizes the interaction of amino loofah, chitosan and halloysite with fatty acid, promotes the composite adsorbent to adsorb free fatty acids, reduces the acid value of crude oil.

Description

Technical Field

[0001] The present invention belongs to the technical field of adsorbents, and in particular relates to a composite adsorbent and a preparation method and application thereof. Background Art

[0002] Transformers are essential electrical equipment in power grids, and the key to maintaining the long-term safe and stable operation of traditional power transformers lies in the insulating oil within them. Traditional insulating oils are primarily mineral-based, with a flash point of around 160°C. Excessive temperatures within the transformer can easily cause explosions. Vegetable-based insulating oils, however, have flash points as high as 300°C and are renewable and biodegradable, making them a promising alternative to mineral-based oils. Vegetable-based insulating oils are produced from natural oil crops through processes such as pressing and refining.

[0003] Key indicators of vegetable insulating oil quality include acid value and dielectric loss factor. Acid value refers to the sum of the organic and inorganic acids in the insulating oil. Excessively high acid values ​​can not only corrode equipment but also affect the oil's insulation strength and dielectric properties, reducing insulation performance. Dielectric loss factor is a key indicator of insulating oil's insulation performance. Besides being related to the oil's moisture content, it also factors in the content of metal ions, colloids, microorganisms, organic acids, and other polar impurities.

[0004] Due to the high impurities, high acidity, and easy oxidation of crude oil, refining is required to meet the requirements of insulating oil. The refining process includes dewaxing, bleaching, deodorization, alkali refining, water washing, compounding, drying, and other processes, which are complex and tedious. The alkali refining process removes free fatty acids by adding alkaline solution for neutralization. However, this method produces a large amount of soap stock, resulting in high refining consumption and low refining yield. Adsorbent deacidification can remove free fatty acids (FFA) through adsorption and reaction. The method is simple and energy-efficient, but the commonly used deacidification adsorbents generally have the problem of high consumption. The decolorization process uses adsorbents to remove impurities such as pigments and reduce color and dielectric loss factor. However, the traditional adsorbent activated white clay used in the decolorization process has high acid residue during use. Therefore, the traditional alkali refining and decolorization process is complex and consumes a lot of adsorbent. Summary of the Invention

[0005] The object of the present invention is to provide a composite adsorbent and a preparation method and application thereof, wherein the composite adsorbent can reduce the acid value, chroma and dielectric loss factor of crude oil, thereby simplifying the refining process for preparing vegetable insulating oil.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] The present invention provides a composite adsorbent comprising the following raw materials in parts by mass:

[0008] 40-80 parts of amino-modified loofah, 20-60 parts of chitosan, 4-20 parts of diatomaceous earth, 20-36 parts of halloysite, and 5-20 parts of cross-linking agent.

[0009] Luffa, the vascular bundle within the loofah fruit, possesses a unique porous physical structure and excellent mechanical strength. The loofah is composed of interwoven ligaments, forming a macroscopic porous structure. Within the loofah, a microscopic porous structure composed of honeycomb-like tubular bundles exists. This secondary porous structure gives the loofah its lightweight and compact microstructure. As a natural material, loofah possesses low density, high strength, and high toughness. Its porous structure offers significant advantages in terms of environmental protection and sustainability.

[0010] Chitosan is a natural high molecular compound that contains a large number of hydroxyl groups (OH) and amino groups (NH3) in its molecular structure. The hydroxyl groups and amino groups of chitosan also have antioxidant properties.

[0011] Diatomaceous earth has a porous structure, which is mainly composed of mesopores and macropores, among which mesopores are the largest, followed by macropores, and micropores are relatively rare. The porous structure of diatomaceous earth gives it good adsorption properties. The surface of diatomaceous earth is covered with a large number of silicon hydroxyl groups (Si-OH). These hydroxyl groups exist not only on the surface of diatomaceous earth, but also on the inner surface of micropores.

[0012] Halloysite is a 1:1 layered silicate mineral belonging to the kaolinite family. Due to the size mismatch between silicon-oxygen tetrahedra and aluminum-oxygen octahedra, as well as the presence of interlayer water molecules, adjacent structural unit layers cannot maintain equilibrium through hydrogen bonds. As a result, the structural unit layers of halloysite curl up to form a nanotubular structure. This nanotubular structure gives halloysite a large specific surface area and rich pore structure, giving it adsorption capacity.

[0013] Further, the preparation process of described amination loofah is as follows:

[0014] Add anhydrous ethanol to a 10-30wt% sodium hydroxide solution, with the volume ratio of sodium hydroxide solution to anhydrous ethanol being 0.5-2:1, stir evenly to obtain a mixed solution, and add a 1-2cm 3 Small pieces of loofah are soaked in a solid-liquid ratio of 0.1-1:10 to the mixed liquid for 8-12 hours. After soaking, the mixture is filtered and washed with deionized water until neutral. After drying, the alkalized loofah is obtained. An aminosilane coupling agent is added to a 60-80wt% ethanol aqueous solution to prepare a solution. The concentration of the aminosilane coupling agent in the solution is 10-20wt%. The alkalized loofah is added to the solution at a mass ratio of 1-5:20. The mixture is heated to 50-70°C and stirred for reaction for 4-6 hours. After the reaction is completed, the mixture is filtered, washed until neutral, and dried to obtain the aminolated loofah.

[0015] Furthermore, the aminosilane coupling agent includes one of 3-aminopropyltrimethoxysilane and 3-aminopropyltriethoxysilane.

[0016] Furthermore, the particle size of the diatomaceous earth is 100-300 μm.

[0017] Furthermore, the diameter of the halloysite is 0.1-0.5 μm.

[0018] Furthermore, the cross-linking agent is one of glutaraldehyde and citric acid.

[0019] Furthermore, the particle size of the composite adsorbent is 0.1-1 mm.

[0020] The present invention also provides a method for preparing the composite adsorbent as described above, comprising the following steps:

[0021] Step 1, placing diatomite in a beaker and halloysite in another beaker, adding 0.1-0.5 mol / L hydrochloric acid solution to each beaker, controlling the solid-liquid mass ratio in the two beakers to be 1:5-10, stirring at room temperature and soaking for 10-16 hours, filtering and washing with deionized water until neutral, and drying to obtain acidified diatomite and acidified halloysite;

[0022] Step 2: dissolving chitosan in 2-4 wt% acetic acid solution to obtain a chitosan solution, adding acidified diatomaceous earth and acidified halloysite to the chitosan solution, and stirring uniformly to form a mixture.

[0023] Step 3: Add amino-treated loofah to the mixture, stir and mix, add cross-linking agent dropwise while stirring, continue stirring after the addition is completed to form a colloid, dry and crush to obtain a composite adsorbent.

[0024] Furthermore, the mass fraction of chitosan in the chitosan solution is 1-4%.

[0025] The present invention also provides an application of the composite adsorbent as described above, wherein the composite adsorbent can be used in an adsorption process of vegetable insulating oil.

[0026] Beneficial effects of the present invention:

[0027] (1) In the present invention, amino-modified loofah, chitosan, diatomaceous earth and halloysite are formed into a composite adsorbent under the action of a cross-linking agent. The combination of the different porous structures of loofah, diatomaceous earth and halloysite gives the composite adsorbent a secondary porous structure of macroporous structure and microporous structure, thereby increasing the specific surface area of ​​the composite adsorbent, improving its adsorption capacity, reducing the dielectric loss factor of crude oil and reducing impurities.

[0028] (2) Introducing amino groups into the loofah not only achieves cross-linking, but also allows for electrostatic bridging with the carboxyl groups of free fatty acids, thereby adsorbing free fatty acids. The amino groups of the amino-modified loofah and chitosan electrostatically bridge the free fatty acids, and the aluminum hydroxyl groups on the halloysite surface can form hydrogen bonds with the carbonyl groups of fatty acids in the oil, promoting the composite adsorbent to adsorb free fatty acids and reducing the acid value of the crude oil.

[0029] (3) The loofah in the composite adsorbent has high toughness. Its fiber network structure with interwoven ligaments enhances the bonding force of the composite adsorbent during the cross-linking process with chitosan, diatomaceous earth and halloysite. The prepared composite adsorbent is not easy to loosen during the adsorption process and is easy to recycle. DETAILED DESCRIPTION

[0030] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0031] Example 1

[0032] Preparation of amino-treated loofah:

[0033] Add anhydrous ethanol to a 30 wt% sodium hydroxide solution, with a volume ratio of 0.5:1 between the sodium hydroxide solution and the anhydrous ethanol, stir evenly to obtain a mixed solution, and add a 1-2 cm 3 Small pieces of loofah were soaked for 12 hours, with the solid-liquid mass ratio of the loofah to the mixed solution being 1:10. After soaking, the mixture was filtered, washed with deionized water until neutral, and dried to obtain alkalized loofah. 3-Aminopropyltrimethoxysilane was added to a 60wt% ethanol aqueous solution to prepare a solution, in which the concentration of aminosilane coupling agent in the solution was 10wt%. The alkalized loofah was added to the solution at a mass ratio of 1:20, heated to 50°C and stirred for reaction for 6 hours. After the reaction was completed, the mixture was filtered, washed until neutral, and dried to obtain amino loofah.

[0034] This embodiment provides a composite adsorbent, which includes the following raw materials in parts by mass:

[0035] 40 parts of amino-treated loofah, 60 parts of chitosan, 20 parts of diatomaceous earth (particle size 100-300 μm), 20 parts of halloysite (diameter 0.1-0.5 μm), and 10 parts of glutaraldehyde. The specific preparation steps are as follows:

[0036] Step 1: Place diatomite in one beaker and halloysite in another beaker, add 0.5 mol / L hydrochloric acid solution to each beaker, control the solid-liquid mass ratio in the two beakers to be 1:5, stir and soak at room temperature for 10 hours, filter and wash with deionized water until neutral, and dry to obtain acidified diatomite and acidified halloysite.

[0037] Step 2: dissolving chitosan in 4 wt % acetic acid solution to obtain a chitosan solution, wherein the mass fraction of chitosan in the chitosan solution is 3%, adding acidified diatomaceous earth and acidified halloysite to the chitosan solution, and stirring uniformly to form a mixture.

[0038] Step 3: Add amino-treated loofah to the mixture, stir and mix, add glutaraldehyde dropwise while stirring, continue stirring after the addition is complete to form a colloid, dry and crush to obtain a composite adsorbent with a particle size of 0.1-1 mm.

[0039] Soybean oil was degummed and dewaxed to obtain crude oil. The dielectric loss factor, acid value and appearance of the crude oil were tested with reference to the "DLT 1360-2014 Soybean Vegetable Transformer Oil Quality Standard". The results are shown in Table 1.

[0040] The adsorbent prepared in this example was added to the crude oil at a mass fraction of 3 wt %. The adsorption temperature was 50° C. for 2 h. The oil was cooled and filtered. The filtered soybean oil was tested for dielectric loss factor, acid value, and appearance with reference to the "DLT 1360-2014 Soybean Plant Transformer Oil Quality Standard". The results are shown in Table 1.

[0041] Example 2

[0042] The only difference from Example 1 is that the mass fraction of diatomite is adjusted to 10 parts, the mass fraction of high-quality high-white halloysite is adjusted to 30 parts, and the other steps and conditions are the same as Example 1.

[0043] The adsorbent prepared in this example was added to the crude oil at a mass fraction of 1 wt %. The adsorption temperature was 50° C. for 2 h. The oil was cooled and filtered. The filtered soybean oil was tested for dielectric loss factor, acid value, and appearance in accordance with the "DLT 1360-2014 Soybean Plant Transformer Oil Quality Standard". The results are shown in Table 1.

[0044] Example 3

[0045] The only difference from Example 1 is that the mass fraction of diatomite is adjusted to 4 parts, the mass fraction of high-quality high-white halloysite is adjusted to 36 parts, and the other steps and conditions are the same as Example 1.

[0046] The adsorbent prepared in this example was added to the crude oil at a mass fraction of 1 wt %. The adsorption temperature was 50° C. for 2 h. The oil was cooled and filtered. The filtered soybean oil was tested for dielectric loss factor, acid value, and appearance in accordance with the "DLT 1360-2014 Soybean Plant Transformer Oil Quality Standard". The results are shown in Table 1.

[0047] Example 4

[0048] The only difference from Example 2 is that the mass fraction of amino-modified loofah is adjusted to 60 parts, the mass fraction of chitosan is adjusted to 40 parts, and the other steps and conditions are the same as in Example 2.

[0049] The adsorbent prepared in this example was added to the crude oil at a mass fraction of 1 wt %. The adsorption temperature was 50° C. for 2 h. The oil was cooled and filtered. The filtered soybean oil was tested for dielectric loss factor, acid value, and appearance in accordance with the "DLT 1360-2014 Soybean Plant Transformer Oil Quality Standard". The results are shown in Table 1.

[0050] Example 5

[0051] The only difference from Example 2 is that the mass fraction of amino-modified loofah is adjusted to 80 parts, the mass fraction of chitosan is adjusted to 20 parts, and the other steps and conditions are the same as in Example 2.

[0052] The adsorbent prepared in this example was added to the crude oil at a mass fraction of 1 wt %. The adsorption temperature was 50° C. for 2 h. The oil was cooled and filtered. The filtered soybean oil was tested for dielectric loss factor, acid value, and appearance in accordance with the "DLT 1360-2014 Soybean Plant Transformer Oil Quality Standard". The results are shown in Table 1.

[0053] Comparative Example 1

[0054] Compared with Example 1, no amino-treated loofah was added to the adsorbent raw material in this comparative example, and the step of preparing the amino-treated loofah was omitted.

[0055] This comparative example provides a composite adsorbent, which comprises the following raw materials in parts by mass:

[0056] 60 parts of chitosan, 20 parts of diatomaceous earth (particle size 100-300 μm), 20 parts of halloysite (diameter 0.1-0.5 μm), and 10 parts of glutaraldehyde. The specific preparation steps are as follows:

[0057] Step 1: Place diatomite in one beaker and halloysite in another beaker, add 0.5 mol / L hydrochloric acid solution to each beaker, control the solid-liquid mass ratio in the two beakers to be 1:5, stir and soak at room temperature for 10 hours, filter and wash with deionized water until neutral, and dry to obtain acidified diatomite and acidified halloysite.

[0058] Step 2: dissolving chitosan in 4wt% acetic acid solution to obtain a chitosan solution, wherein the mass fraction of chitosan in the chitosan solution is 3%, adding acidified diatomaceous earth and acidified halloysite to the chitosan solution, stirring evenly, adding glutaraldehyde dropwise while stirring, and continuing to stir after the addition is completed to form a colloid, and then drying and crushing to obtain a composite adsorbent with a particle size of 0.1-1mm.

[0059] The specific detection steps are the same as in Example 1.

[0060] Comparative Example 2

[0061] Compared with Example 1, halloysite is not added to the adsorbent raw materials of this comparative example. This comparative example provides a composite adsorbent, which includes the following raw materials in parts by mass:

[0062] 40 parts of amino-modified loofah, 60 parts of chitosan, 20 parts of diatomaceous earth (particle size 100-300 μm), and 10 parts of glutaraldehyde. The preparation steps are as follows:

[0063] Step 1: Place diatomaceous earth in a beaker, add 0.5 mol / L hydrochloric acid solution, control the solid-liquid mass ratio in the beaker to be 1:5, stir and soak at room temperature for 10 hours, filter and wash with deionized water until neutral, and dry to obtain acidified diatomaceous earth.

[0064] Step 2: dissolving chitosan in 4 wt % acetic acid solution to obtain a chitosan solution, wherein the mass fraction of chitosan in the chitosan solution is 3%, adding acidified diatomaceous earth to the chitosan solution, and stirring uniformly to form a mixture.

[0065] Step 3: Add amino-treated loofah to the mixture, stir and mix, add glutaraldehyde dropwise while stirring, continue stirring after the addition is complete to form a colloid, dry and crush to obtain a composite adsorbent with a particle size of 0.1-1 mm.

[0066] The specific detection steps are the same as in Example 1.

[0067] Comparative Example 3

[0068] Compared with Example 1, diatomaceous earth is not added to the adsorbent raw materials of this comparative example. This comparative example provides a composite adsorbent, which includes the following raw materials in parts by mass:

[0069] 40 parts of amino-treated loofah, 60 parts of chitosan, 20 parts of halloysite (diameter 0.1-0.5 μm), and 10 parts of glutaraldehyde. The specific preparation steps are as follows:

[0070] Step 1: Place halloysite in a beaker, add 0.5 mol / L hydrochloric acid solution, control the solid-liquid mass ratio in the beaker to 1:5, stir and soak at room temperature for 10 hours, filter and wash with deionized water until neutral, and dry to obtain acidified halloysite.

[0071] Step 2: dissolving chitosan in 4 wt % acetic acid solution to obtain a chitosan solution, wherein the mass fraction of chitosan in the chitosan solution is 3%, adding acidified halloysite to the chitosan solution, and stirring uniformly to form a mixture.

[0072] Step 3: Add amino-treated loofah to the mixture, stir and mix, add glutaraldehyde dropwise while stirring, continue stirring after the addition is complete to form a colloid, dry and crush to obtain a composite adsorbent with a particle size of 0.1-1 mm.

[0073] The specific detection steps are the same as in Example 1.

[0074] .

[0075] As can be seen from Table 1, in Examples 1-3, the porous structure of the composite adsorbent was controlled by adjusting the mass fraction ratio of diatomaceous earth and halloysite. Among them, at the ratio of Example 2, the prepared composite adsorbent had a higher adsorption capacity, and the acid value and dielectric damage factor of the crude oil were significantly reduced compared with Example 1. Examples 4 and 5 increased the proportion of amino-treated loofah and reduced the proportion of chitosan on the basis of Example 2. In Example 5, due to the low proportion of chitosan, the adsorption capacity of the composite adsorbent for fatty acids was not as good as that of Example 2. The composite adsorbent of Example 4 had the best performance among the examples. The adsorbents prepared in Comparative Examples 1-3 did not add amino-treated loofah, halloysite or diatomaceous earth, and the porous structure of the adsorbent changed. Its adsorption capacity for impurities such as pigments was not as good as that of Example 1, and the dielectric loss factor was high. The visual appearance was slightly turbid.

[0076] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0077] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. An application of a composite adsorbent, characterized in that: The composite adsorbent can be used in the adsorption process of vegetable insulating oil; The composite adsorbent comprises the following raw materials in parts by mass: 40-80 parts of amino-modified loofah, 20-60 parts of chitosan, 4-20 parts of diatomaceous earth, 20-36 parts of halloysite, and 5-20 parts of a cross-linking agent; The preparation process of described amination loofah is as follows: Add anhydrous ethanol to a 10-30wt% sodium hydroxide solution, with the volume ratio of sodium hydroxide solution to anhydrous ethanol being 0.5-2:1, stir evenly to obtain a mixed solution, and add a 1-2cm 3 A small piece of loofah is prepared by soaking the loofah in a solid-liquid ratio of 0.1-1:10 to the mixed solution for 8-12 hours. After soaking, the mixture is filtered, washed with deionized water until neutral, and dried to obtain an alkalized loofah. An aminosilane coupling agent is added to a 60-80wt% ethanol aqueous solution to prepare a solution, wherein the concentration of the aminosilane coupling agent in the solution is 10-20wt%. The alkalized loofah is added to the solution at a mass ratio of 1-5:20, heated to 50-70°C, stirred, and reacted for 4-6 hours. After the reaction is completed, the mixture is filtered, washed until neutral, and dried to obtain an amino-treated loofah. The particle size of the diatomite is 100-300 μm; the halloysite is high-quality high-white halloysite with a diameter of 0.1-0.5 μm.

2. The use of a composite adsorbent according to claim 1, characterized in that: The aminosilane coupling agent includes one of 3-aminopropyltrimethoxysilane and 3-aminopropyltriethoxysilane.

3. The use of a composite adsorbent according to claim 1, characterized in that: The cross-linking agent is one of glutaraldehyde and citric acid.

4. The use of a composite adsorbent according to claim 1, characterized in that: The particle size of the composite adsorbent is 0.1-1 mm.

5. The use of a composite adsorbent according to claim 1, characterized in that: The preparation method of the composite adsorbent comprises the following steps: Step 1, placing diatomite in a beaker and halloysite in another beaker, adding 0.1-0.5 mol / L hydrochloric acid solution to each beaker, controlling the solid-liquid mass ratio in the two beakers to be 1:5-10, stirring at room temperature and soaking for 10-16 hours, filtering and washing with deionized water until neutral, and drying to obtain acidified diatomite and acidified halloysite; Step 2: dissolving chitosan in 2-4 wt% acetic acid solution to obtain a chitosan solution, adding acidified diatomaceous earth and acidified halloysite to the chitosan solution, and stirring to form a mixture; Step 3: Add amino-treated loofah to the mixture, stir and mix, add cross-linking agent dropwise while stirring, continue stirring after the addition is completed to form a colloid, dry and crush to obtain a composite adsorbent.

6. The use of a composite adsorbent according to claim 5, characterized in that: The mass fraction of chitosan in the chitosan solution is 1-4%.