Graphene oil slurry, its preparation method and application

Abstract

The application discloses a graphene oily slurry, a preparation method and application thereof. The preparation method comprises the following steps: mixing expanded graphite and a switching microemulsion, performing dispersion and first grinding treatment, adding a first switching substance, and switching the switching microemulsion to a water phase system through a switching reaction to generate precipitated particles, continuing to perform grinding and homogenization treatment, performing solid-liquid separation, removing the precipitated particles in the solid phase system, and obtaining a graphene aqueous concentrated slurry; finally, mixing and stirring the graphene aqueous concentrated slurry with an oily dispersant and base oil, simultaneously performing vacuum water removal and second grinding treatment, and obtaining the graphene oily slurry. The preparation method uses the switching microemulsion as a dispersion medium, does not need an additional dispersant, can realize mechanical peeling preparation and good dispersion of the graphene, the switching operation of the switching microemulsion can realize rapid separation of the graphene and the liquid phase, and the product graphene oily slurry has good anti-wear and friction-reducing effects and dispersion stability when applied to lubricating oil.

Description

Technical Field

[0001] This invention relates to a method for preparing graphene oily slurry, and more particularly to a method for preparing graphene and graphene oily slurry based on a switch-type microemulsion. The obtained graphene oily slurry and its application in lubricating oil belong to the fields of nanomaterials and lubricating additives. Background Technology

[0002] In existing technologies, graphene is typically added as a powder when used as an additive in lubricating oils. However, graphene powder exhibits soft agglomeration, hindering its dispersion in the oil phase. Improving the dispersion stability of powdered graphene requires modifications to the lubricating oil production line, necessitating the addition of extra dispersion equipment, significantly increasing production costs and complexity. Furthermore, the dispersion process of graphene powder inevitably involves intense shearing, which can negatively impact lubricating oil performance (e.g., decreased viscosity, reduced oxidation stability, and shortened service life). Additionally, dust pollution is generated during the powder addition process.

[0003] To address the aforementioned issues, a method for preparing a graphene slurry is proposed, ensuring that the graphene is in a well-dispersed state. When added to lubricating oil, it can be uniformly mixed through simple dispersion, maintaining a good dispersion of graphene. This solves the problems of difficult graphene powder addition, poor dispersion, and decreased oil performance during the production of graphene lubricating oil. Existing graphene slurries are typically aqueous or oil-based. Oil-based slurries use organic solvents with good compatibility with graphene, such as NMP (N-methylpyrrolidone), DMF (N,N-dimethylformamide), and ethyl acetate, as the medium, with NMP slurry being the most common. However, existing lubricant standards, such as the API (American Petroleum Institute) standard, require automotive engine oils to have a water content of less than 0.2%, and the ISO 6743 / 18 standard specifies that industrial lubricants should have a water content of less than 0.05%. Therefore, using water-based graphene slurries in lubricants would lead to excessive water content. Furthermore, water-based graphene slurries typically contain dispersants, which are generally water-soluble and unsuitable for lubricants. As for NMP slurries, NMP is not a permitted component in lubricants; its addition would degrade the lubricant's performance, such as viscosity, flash point, and rubber compatibility. Therefore, the application of graphene slurries in lubricants using existing technologies is limited. Summary of the Invention

[0004] The main objective of this invention is to provide a method for preparing graphene oily slurry to overcome the shortcomings of the prior art.

[0005] Another object of the present invention is to provide a graphene oily slurry and its application in lubricating oils.

[0006] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0007] This invention provides a method for preparing a graphene oily slurry, comprising:

[0008] A switchable microemulsion is provided, comprising a carboxylic acid as an oily solvent, a surfactant, an alkanolamine as a first co-surfactant, a small molecule organic acid as a second co-surfactant, oxalates and / or bicarbonates, and water.

[0009] Expanded graphite is mixed evenly with the switch-type microemulsion, and then dispersed and ground in sequence. A first switching substance is then added, which can react with the switch-type microemulsion to form a switching reaction. Grinding continues, followed by homogenization to obtain a mixture. During the switching reaction, carboxylic acids in the switch-type microemulsion become water-soluble, and the switch-type microemulsion is transformed into an aqueous phase system. At the same time, oxalate and / or bicarbonate form precipitated microparticles.

[0010] The mixture is subjected to solid-liquid separation to obtain a solid-phase system and a liquid-phase system containing at least graphene and precipitated microparticles;

[0011] After removing the precipitated particles from the solid-phase system, a graphene-containing concentrated slurry is obtained.

[0012] The graphene aqueous concentrate, oily dispersant, and base oil are mixed and stirred, while being dehydrated under vacuum. Finally, a second grinding process is performed to obtain the graphene oily slurry.

[0013] This invention also provides a graphene oily slurry prepared by the aforementioned method, which comprises at least a base oil and graphene uniformly dispersed in the base oil.

[0014] This invention also provides the application of the graphene oily slurry in the field of lubricating oil.

[0015] Accordingly, embodiments of the present invention also provide a lubricating oil additive, which includes the aforementioned graphene oily slurry.

[0016] Compared with the prior art, the beneficial effects of the present invention include at least the following:

[0017] 1) The method for preparing graphene oily slurry provided by the present invention uses a switch-type microemulsion as a dispersion medium. By utilizing the amphiphilic nature of the switch-type microemulsion, the mechanical exfoliation and good dispersion of graphene can be achieved without additional dispersants. At the same time, the cationic surfactant of the switch-type microemulsion can be used as an intercalating agent for graphene preparation to promote graphene exfoliation.

[0018] 2) This invention enables rapid separation of graphene from the liquid phase through the switching operation of a switchable microemulsion. Simultaneously, the precipitates such as calcium oxalate or calcium bicarbonate microparticles generated during the switching process can serve as auxiliary abrasives to promote graphene exfoliation. Furthermore, the separated liquid phase can also be regenerated through the switching operation to achieve the purpose of recycling.

[0019] 3) The graphene oily slurry prepared in this invention does not undergo a graphene powdering process, which can avoid graphene agglomeration; the resulting graphene oily slurry, when applied to lubricating oil, has good anti-wear and friction-reducing effects and dispersion stability. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a SEM image of graphene powder obtained after drying the graphene concentrated slurry prepared in step S2 of Example 1 of the present invention.

[0022] Figure 2 This is a SEM image of graphene powder obtained after drying the graphene concentrated slurry prepared in step S2 of Comparative Example 1 of the present invention.

[0023] Figure 3 This is a SEM image of the graphene powder obtained after drying the graphene concentrated slurry prepared in step S2 of Comparative Example 2 of this invention. Detailed Implementation

[0024] In view of the deficiencies in the prior art, the inventors of this invention, through long-term research and extensive practice, have proposed the technical solution of this invention, which mainly uses a switchable microemulsion as a dispersion medium to achieve the mechanical exfoliation preparation and good dispersion of graphene. At the same time, some components of the switchable microemulsion can act as intercalating agents for graphene preparation, promoting graphene exfoliation.

[0025] The following will further explain the technical solution, its implementation process, and its principles. However, it should be understood that within the scope of this invention, the above-mentioned technical features of this invention and the technical features specifically described below (in embodiments) can be combined with each other to form new or preferred technical solutions. Due to space limitations, they will not be described in detail here.

[0026] As one aspect of the technical solution of this invention, a method for preparing a graphene oily slurry includes:

[0027] A switchable microemulsion is provided, comprising a carboxylic acid as an oily solvent, a surfactant, an alkanolamine as a first co-surfactant, a small molecule organic acid as a second co-surfactant, oxalates and / or bicarbonates, and water.

[0028] Expanded graphite is mixed evenly with the switch-type microemulsion, and then dispersed and ground in sequence. A first switching substance is then added, which can react with the switch-type microemulsion to form a switching reaction. Grinding continues, followed by homogenization to obtain a mixture. During the switching reaction, carboxylic acids in the switch-type microemulsion become water-soluble, and the switch-type microemulsion is transformed into an aqueous phase system. At the same time, oxalate and / or bicarbonate form precipitated microparticles.

[0029] The mixture is subjected to solid-liquid separation to obtain a solid-phase system and a liquid-phase system containing at least graphene and precipitated microparticles;

[0030] After removing the precipitated particles from the solid-phase system, a graphene-containing concentrated slurry is obtained.

[0031] The graphene aqueous concentrate, oily dispersant, and base oil are mixed and stirred, while being dehydrated under vacuum. Finally, a second grinding process is performed to obtain the graphene oily slurry.

[0032] Specifically, the reaction process and mechanism of this invention are explained as follows: A switchable microemulsion is selected as the reaction medium. The switchable microemulsion is amphiphilic and can effectively disperse expanded graphite before mechanical exfoliation, promoting the occurrence of mechanical exfoliation and achieving efficient preparation of graphene. At the same time, due to the amphiphilic nature of the switchable microemulsion, it can also effectively disperse graphene, and the expanded graphite / graphene maintains a good dispersion state throughout the mechanical exfoliation process. After the graphene preparation is completed, utilizing the reaction and phase switching characteristics between the switchable microemulsion and the switchable substance, a first switchable substance (taking calcium hydroxide as an example) is added to cause a switch reaction with the switchable microemulsion. The hydroxide ions in calcium hydroxide react with carboxylic acid substances, and the carboxylic acid substances become water-soluble carboxylate ions. The switchable microemulsion is transformed into an aqueous phase system. Simultaneously, calcium ions react with oxalate, bicarbonate, etc., to generate calcium oxalate and / or calcium bicarbonate precipitates.

[0033] In some embodiments, the mass ratio of the expanded graphite to the sum of the components other than water in the switchable microemulsion is 1:(2-4).

[0034] In some embodiments, the dispersion treatment is performed at a rotation speed of 6000 rpm to 10000 rpm for 2 h to 4 h. During the dispersion treatment, surfactants and oxalates and / or bicarbonates, etc., act as intercalating agents into the expanded graphite sheets.

[0035] In some embodiments, the first grinding process uses a rotation speed of 2000 rpm to 3000 rpm and a time of 2 h to 4 h. During the first grinding process, with the assistance of an intercalating agent, the initial exfoliation of graphene can be achieved.

[0036] In some implementations, the first switching substance may include calcium hydroxide, calcium oxide, etc., but is not limited to these.

[0037] In some preferred embodiments, the preparation method specifically includes: slowly adding a first switching substance to the material after the first grinding treatment to initiate a switching reaction, controlling the addition to be completed within 0.5 to 1 hour, adjusting the pH value of the material to 7.5 to 8.5, and then continuing grinding for 2 to 4 hours. During the switching process, the first switching substance reacts with oxalate, bicarbonate, etc., to generate calcium oxalate and / or calcium bicarbonate precipitates in the graphite layers, which can play an auxiliary grinding role, promoting rapid graphene exfoliation. The precipitates act as both auxiliary grinding agents and further aid in exfoliation.

[0038] Furthermore, the homogenization process is carried out at a pressure of 80 MPa to 100 MPa, and the number of homogenization processes is 4 to 6. The main purpose of this homogenization process is to reduce the size of the graphene and further reduce the number of graphene sheets.

[0039] In some embodiments, the preparation method specifically includes: adding an acidic substance or a complexing agent to the solid system to remove precipitated particles from the solid system, and then washing the remaining solid phase with water and centrifuging to obtain a graphene aqueous concentrated slurry.

[0040] Furthermore, the acidic substance may be hydrochloric acid, but is not limited to this.

[0041] Furthermore, the complexing agent may be EDTA, but is not limited to this.

[0042] In some embodiments, the preparation method further includes: adding a second switching substance to the liquid phase system obtained from solid-liquid separation, adjusting the pH value to 5.6–6.6, regenerating the switching microemulsion, and enabling recycling. When reused, a portion of the concentrated switching microemulsion is added to maintain the ratio of expanded graphite to the portion of the switching microemulsion excluding water within a mass ratio of 1:2–4.

[0043] Furthermore, the second switching substance can be oxalic acid, carbonic acid, etc., but is not limited to these.

[0044] In some embodiments, the oily dispersant may include one or more of polyisobutylene succinimide, boronized polyisobutylene succinimide, isopropyl titanate, sorbitan oleate, polyether, stearic acid, oleic acid, tallow amine, tallow amine polyoxyethylene ether, etc., but is not limited thereto.

[0045] In some implementations, the base oil may include one or more of Group II base oils, Group III base oils, Group IV base oils, Group V base oils, etc., but is not limited to this.

[0046] In some embodiments, the mass ratio of graphene, oily dispersant and base oil in the graphene aqueous concentrate is 1:(5-20):(20-50).

[0047] Furthermore, the stirring process is a planetary stirring process, with a temperature of 80℃~100℃ and a time of 2h~4h.

[0048] Furthermore, the second grinding process employs a three-roll mill for 2 to 4 grinding cycles. The purpose of this second grinding process is to uniformly disperse the graphene in the oily slurry and reduce its fineness.

[0049] In some embodiments, the carboxylic acid substances in the switchable microemulsion may be lower fatty acids and / or cycloalkanoic acids, preferably cycloalkanoic acids.

[0050] In some preferred embodiments, the lower fatty acids are fatty acids with no more than 10 carbon atoms in their carbon chains and which are liquid at room temperature.

[0051] Furthermore, the lower fatty acid may be one or more of hexanoic acid, heptanoic acid, octanoic acid, isooctanoic acid, nonanoic acid, isononanoic acid, decanoic acid, and neodecanoic acid, but is not limited thereto.

[0052] In some embodiments, both alkanolamines and small-molecule organic acids are added to the switch-type microemulsion; neither can be omitted, otherwise the microemulsion cannot be formed.

[0053] In some embodiments, the alkanolamine may include one or more combinations of monoethanolamine, diethanolamine, triethanolamine, N-(2-hydroxyethyl)ethylenediamine, N,N′-bis(2-hydroxyethyl)ethylenediamine, N,N,N′,N′-tetra(2-hydroxyethyl)ethylenediamine, etc., but is not limited thereto.

[0054] In some embodiments, the small molecule organic acid may include one or more combinations of dicarboxylic acids, maleic acid, citric acid, malic acid, tartaric acid, etc., but is not limited to these.

[0055] Furthermore, the dicarboxylic acid can be one or more of oxalic acid, malonic acid, succinic acid, etc.

[0056] In some embodiments, the oxalate or bicarbonate may be one or more of soluble ammonium salts, sodium salts, potassium salts, etc., but is not limited thereto.

[0057] Furthermore, the oxalate can be obtained by neutralizing oxalic acid with a base.

[0058] In some preferred embodiments, the oxalate may include one or more combinations of ammonium oxalate, sodium oxalate, potassium oxalate, etc., but is not limited thereto.

[0059] In some embodiments, the surfactant is a cationic surfactant, preferably including one or more combinations of dodecyltrimethylammonium chloride, dodecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide, octadecyltrimethylammonium chloride, octadecyltrimethylammonium bromide, dodecyl dimethylbenzylammonium chloride, dodecyl dimethylbenzylammonium bromide, hexadecyl dimethylbenzylammonium chloride, hexadecyl dimethylbenzylammonium bromide, octadecyl dimethylbenzylammonium chloride, octadecyl dimethylbenzylammonium bromide, etc., but not limited thereto.

[0060] In some embodiments, the ratio of carboxylate ions in the carboxylic acid substances, carboxylate ions in the small molecule organic acids, and amino groups in the alkanolamine substances to oxalates and / or bicarbonates is calculated by molar ratio as 1:(0.95-1.05):(1-1.1):(1-1.05). That is, from another perspective, calculated by molar ratio, 1 part of carboxylic acid substances (based on the number of carboxylate ions) corresponds to 0.95-1.05 parts of small molecule organic acids (based on the number of carboxylate ions), 1-1.1 parts of alkanolamine substances (based on the number of amino groups), and 1-1.05 parts of oxalates and / or bicarbonates.

[0061] In some embodiments, the mass ratio of the carboxylic acid to the surfactant is 1:(0.2 to 0.5), that is, in other words, by mass, 1 part of carboxylic acid corresponds to 0.2 to 0.5 parts of surfactant.

[0062] In some embodiments, the water comprises 60% to 80% of the total mass of the switchable microemulsion.

[0063] As another aspect of the technical solution of the present invention, it also relates to a method for preparing the switchable microemulsion, which includes: adding a surfactant, an alcohol amine, an oxalate and / or a bicarbonate to water, adding a carboxylic acid to cause an acid-base neutralization reaction with the amino group on the alcohol amine, and then adding a small molecule organic acid to regenerate the carboxylic acid to form the switchable microemulsion.

[0064] In some preferred embodiments, the preparation method of the switchable microemulsion specifically includes: dissolving cationic surfactants, alkanolamines, oxalates and / or bicarbonates in water, adding carboxylic acids while stirring to allow them to undergo an acid-base neutralization reaction with the amino groups on the alkanolamines, adding small molecule organic acids to regenerate the carboxylic acids and form a switchable microemulsion, and adjusting the pH value to 5.6-6.6.

[0065] In some preferred embodiments, a method for preparing a graphene oily slurry includes the following steps:

[0066] (1) The expanded graphite and the switch-type microemulsion are mixed evenly (the mass ratio of the expanded graphite to the sum of the other components in the switch-type microemulsion except water is 1:(2~4)).

[0067] (2) Disperser treatment (speed 6000rpm~10000rpm, time 2h~4h), sand mill treatment (speed 2000rpm~3000rpm, grinding time 2h~4h), slowly add calcium hydroxide, adjust the pH value to 7.5~8.5, the addition process lasts 0.5h~1h, then continue grinding for 2h~4h, homogenize 4~6 times;

[0068] (3) Centrifuge, separate solid and liquid, collect the liquid phase system, add oxalic acid, adjust the pH value to 5.6-6.6 to realize the regeneration of the switch-type microemulsion, which can be recycled. When using it again, add some of the concentrated liquid of the switch-type microemulsion to keep the ratio of expanded graphite to the part of the switch-type microemulsion except water in the mass ratio range of 1:2-4 (because the addition of oxalic acid will produce water in the reaction, which will continuously dilute the switch-type microemulsion during the recycling process).

[0069] (4) Add an acidic substance (such as hydrochloric acid) or a complexing agent (such as EDTA) to the solid phase system obtained by solid-liquid separation to dissolve calcium oxalate, wash several times with deionized water, centrifuge, and obtain a concentrated graphene slurry containing water.

[0070] (5) Add oily dispersant and base oil (the mass ratio of graphene, oily dispersant and base oil is 1:(5~20):(20~50)) to the graphene aqueous concentrated slurry, and perform planetary stirring treatment (time is 2h~4h, temperature is 80℃~100℃), while vacuum dehydration, and process with a three-roll mill 2~4 times to obtain graphene oily slurry.

[0071] As another aspect of the technical solution of the present invention, it also relates to a graphene oily slurry prepared by the aforementioned preparation method, wherein the graphene oily slurry comprises at least a base oil and graphene uniformly dispersed in the base oil.

[0072] Furthermore, the graphene sheet diameter is 2μm to 10μm.

[0073] Furthermore, the specific surface area of ​​the graphene is 50 m². 2 / g~100m2 / g.

[0074] Furthermore, the number of graphene sheets is less than 30.

[0075] As another aspect of the technical solution of the present invention, it also relates to the application of the aforementioned graphene oily slurry in the field of lubricating oil.

[0076] Correspondingly, another aspect of the technical solution of the present invention also provides a lubricating oil additive, which includes the aforementioned graphene oily slurry.

[0077] The technical solution of the present invention will be further described in detail below with reference to several preferred embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. It should be noted that the following embodiments are intended to facilitate the understanding of the present invention, and do not constitute any limitation thereof. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or according to the conditions recommended by the manufacturer. The naphthenic acids used in the following embodiments were all purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0078] Example 1

[0079] S1. Preparation of the switch-type microemulsion. 28.84 g of dodecyltrimethylammonium bromide, 110 g of triethanolamine, and 88.2 g of sodium oxalate were dissolved in 1696.16 g of water. 144.2 g of naphthenic acid was added and stirred until homogeneous. Then, 49.4 g of maleic acid was added, and stirring was continued until the maleic acid was completely dissolved, yielding the switch-type microemulsion. The pH of the switch-type microemulsion at this point was 6.0.

[0080] S2. Preparation of graphene concentrated slurry. 1 part by mass of expanded graphite and 4 parts by mass of switch-type microemulsion (based on the portion after removing water) were mixed and treated in a disperser at 10,000 rpm for 2 hours. Then, the mixture was transferred to a sand mill at 3,000 rpm for 2 hours. Calcium hydroxide was slowly added over 1 hour, and the pH was adjusted to 8.0. The mixture was then ground for another 4 hours. The mixture was then transferred to a homogenizer and treated four times. Centrifugation was used to separate the solid and liquid phases. Oxalic acid was added to the liquid phase, and the pH was adjusted to 6.0 to regenerate the switch-type microemulsion. The solid phase was then treated with hydrochloric acid to dissolve the calcium oxalate, and washed multiple times with deionized water until the pH reached 7.0, simultaneously removing soluble substances to obtain a graphene aqueous concentrated slurry.

[0081] S3. Preparation of graphene oily slurry. Graphene aqueous concentrate containing 1 part by mass of graphene, 5 parts by mass of tallow amine polyoxyethylene ether, and 50 parts by mass of Group IV base oil PAO were added to a planetary mixer and treated at 100℃ for 2 hours while simultaneously removing water under vacuum. The mixture was then transferred to a three-roll mill and processed twice to obtain graphene oily slurry #1.

[0082] Example 2

[0083] S1. Preparation of the switch-type microemulsion. Dissolve 36.05g of cetyltrimethylammonium bromide, 70.47g of diethanolamine, and 104.2g of potassium oxalate in 922.27g of water. Add 144.2g of naphthenic acid and stir until homogeneous. Then add 42.36g of oxalic acid and continue stirring until the oxalic acid is completely dissolved to obtain the switch-type microemulsion. The pH value of the switch-type microemulsion at this time is 6.1.

[0084] S2. Preparation of graphene concentrated slurry. 1 part by mass of expanded graphite and 3 parts by mass of switch-type microemulsion (based on the portion after removing water) were mixed and treated in a disperser at 6000 rpm for 4 hours. Then, the mixture was transferred to a sand mill at 2500 rpm for 3 hours. Calcium hydroxide was slowly added over 1 hour, and the pH was adjusted to 7.9. The mixture was then ground for another 3 hours. The mixture was then transferred to a homogenizer and treated 6 times. Centrifugation was used to separate the solid and liquid phases. Oxalic acid was added to the liquid phase, and the pH was adjusted to 6.1 to regenerate the switch-type microemulsion. The solid phase was then treated with hydrochloric acid to dissolve the calcium oxalate, and washed multiple times with deionized water until the pH reached 7.0, simultaneously removing soluble substances to obtain a graphene aqueous concentrated slurry.

[0085] S3. Preparation of graphene oily slurry. Graphene aqueous concentrate containing 1 part by mass of graphene, 10 parts by mass of isopropyl titanate, and 40 parts by mass of Group III base oil GTL were added to a planetary mixer and treated at 90℃ for 3 hours while simultaneously removing water under vacuum. The mixture was then transferred to a three-roll mill and processed three times to obtain graphene oily slurry #2.

[0086] Example 3

[0087] S1. Preparation of the switch-type microemulsion. 72.1 g of octadecyltrimethylammonium chloride, 79.2 g of N,N,N′,N′-tetra(2-hydroxyethyl)ethylenediamine, and 77.79 g of ammonium oxalate were dissolved in 629.87 g of water. 144.2 g of naphthenic acid was added and stirred until homogeneous. Then, 46.62 g of malonic acid was added, and stirring was maintained until the malonic acid was completely dissolved, yielding the switch-type microemulsion. The pH of the switch-type microemulsion at this point was 6.3.

[0088] S2. Preparation of graphene concentrated slurry. 1 part by mass of expanded graphite and 2 parts by mass of switch-type microemulsion (based on the portion excluding water) were mixed and treated in a disperser at 8000 rpm for 3 hours. Then, the mixture was transferred to a sand mill at 2000 rpm for 4 hours. Calcium hydroxide was slowly added over 1 hour, and the pH was adjusted to 8.1. Grinding continued for 2 hours. The mixture was then transferred to a homogenizer and treated five times. Centrifugation was used to separate the solid and liquid phases. Oxalic acid was added to the liquid phase, and the pH was adjusted to 6.3 to regenerate the switch-type microemulsion. The solid phase was collected, and hydrochloric acid was added to dissolve the calcium oxalate. The mixture was then washed multiple times with deionized water until the pH reached 7.0, simultaneously removing soluble substances to obtain a graphene aqueous concentrated slurry.

[0089] S3. Preparation of graphene oily slurry. Graphene aqueous concentrated slurry containing 1 part by mass of graphene, 20 parts by mass of tallow amine polyoxyethylene ether, and 20 parts by mass of Class V base oil oil-soluble polyether OSP were added to a planetary mixer and treated at 80℃ for 4 hours while simultaneously removing water under vacuum. The mixture was then transferred to a three-roll mill and processed four times to obtain graphene oily slurry #3.

[0090] Comparative Example 1: Graphene prepared using sodium hydroxide (specific surface area decreased, particle size increased).

[0091] S1. Preparation of the switch-type microemulsion. 28.84 g of dodecyltrimethylammonium bromide, 110 g of triethanolamine, and 88.2 g of sodium oxalate were dissolved in 1696.16 g of water. 144.2 g of naphthenic acid was added and stirred until homogeneous. Then, 49.4 g of maleic acid was added, and stirring was continued until the maleic acid was completely dissolved, yielding the switch-type microemulsion. The pH of the switch-type microemulsion at this point was 6.0.

[0092] S2. Preparation of graphene concentrated slurry. 1 part by mass of expanded graphite and 4 parts by mass of switch-type microemulsion (based on the portion excluding water) were mixed and treated in a disperser at 10,000 rpm for 2 hours. Then, the mixture was transferred to a sand mill at 3,000 rpm for 2 hours. Sodium hydroxide was slowly added over 1 hour to adjust the pH to 8.0, and grinding continued for 4 hours. The mixture was then transferred to a homogenizer and treated four times. Centrifugation was used to separate the solid and liquid phases. Oxalic acid was added to the liquid phase to adjust the pH to 6.0, regenerating the switch-type microemulsion. The solid phase was treated with hydrochloric acid to dissolve calcium oxalate, and then washed multiple times with deionized water until the pH reached 7.0, simultaneously removing soluble substances to obtain a graphene aqueous concentrated slurry.

[0093] S3. Preparation of graphene oily slurry. 1 part by mass of graphene-containing aqueous concentrated slurry, 5 parts by mass of tallow amine polyoxyethylene ether, and 50 parts by mass of Group IV base oil PAO were added to a planetary mixer and treated at 100℃ for 2 hours while simultaneously removing water under vacuum. Then, the mixture was transferred to a three-roll mill and processed twice to obtain graphene oily slurry #4.

[0094] Comparative Example 2 used anionic surfactants (resulting in a decrease in specific surface area and an increase in particle size).

[0095] S1. Preparation of the switch-type microemulsion. 28.84 g of dodecyltrimethylammonium bromide, 110 g of triethanolamine, and 88.2 g of sodium oxalate were dissolved in 1696.16 g of water. 144.2 g of naphthenic acid was added and stirred until homogeneous. Then, 49.4 g of maleic acid was added, and stirring was continued until the maleic acid was completely dissolved, yielding the switch-type microemulsion. The pH of the switch-type microemulsion at this point was 6.0.

[0096] S2. Preparation of graphene concentrated slurry. 1 part by mass of expanded graphite and 4 parts by mass of switch-type microemulsion (based on the portion after removing water) were mixed and treated in a disperser at 10,000 rpm for 2 hours. Then, the mixture was transferred to a sand mill at 3,000 rpm for 2 hours. Calcium hydroxide was slowly added over 1 hour, and the pH was adjusted to 8.0. The mixture was then ground for another 4 hours. The mixture was then transferred to a homogenizer and treated four times. Centrifugation was used to separate the solid and liquid phases. Oxalic acid was added to the liquid phase, and the pH was adjusted to 6.0 to regenerate the switch-type microemulsion. The solid phase was then treated with hydrochloric acid to dissolve the calcium oxalate, and washed multiple times with deionized water until the pH reached 7.0, simultaneously removing soluble substances to obtain a graphene aqueous concentrated slurry.

[0097] S3. Preparation of graphene oily slurry. Graphene aqueous concentrate containing 1 part by mass of graphene, 5 parts by mass of tallow amine polyoxyethylene ether, and 50 parts by mass of Group IV base oil PAO were added to a planetary mixer and treated at 100℃ for 2 hours while simultaneously removing water under vacuum. The mixture was then transferred to a three-roll mill and processed twice to obtain graphene oily slurry #5.

[0098] Test Example 1: SEM Test

[0099] The inventors of this case conducted SEM tests on the graphene powder obtained after drying the graphene concentrated slurry prepared in step S2 of Example 1, Comparative Example 1, and Comparative Example 2, respectively. The results are as follows: Figure 1 , Figure 2 and Figure 3 As shown, the graphene sheet diameter prepared in Example 1 is significantly smaller than that in Comparative Examples 1 and 2.

[0100] Test Example 2: Particle Size and Specific Surface Area Test

[0101] The inventors of this case dried the graphene concentrated slurry prepared in step S2 of Examples 1-3, Comparative Examples 1 and 2 to obtain graphene powder, and tested its specific surface area. The graphene powder was dispersed in NMP to test the particle size. The particle size was obtained by laser particle size analyzer, and the specific surface area was obtained by BET method. The test results are shown in Table 1.

[0102] Table 1 Comparison of particle size and specific surface area test results

[0103] sample <![CDATA[D 50 / μm]]> <![CDATA[Specific surface area / m 2 / g]]> Example 1 (Graphene Oily Slurry #1) 5.2 65.7 Example 2 (Graphene Oily Slurry #2) 4.9 71.3 Example 3 (Graphene Oily Slurry #3) 4.7 74.2 Comparative Example 1 (Graphene Oily Slurry #4) 10.3 34.2 Comparative Example 2 (Graphene Oily Slurry #5) 9.4 31.4

[0104] As shown in Table 1, calcium oxalate as an auxiliary grinding agent and cationic surfactant as an intercalating agent can both reduce the graphene sheet diameter and increase the specific surface area (i.e., reduce the number of sheets).

[0105] Test Example 3: Dispersion Stability Test

[0106] The graphene oily slurry 1#, graphene oily slurry 2#, graphene oily slurry 3# prepared in Examples 1-3, the graphene oily slurry 4# prepared in Comparative Example 1, and the graphene oily slurry 5# prepared in Comparative Example 2 were added to the finished lubricating oil Merbühne GL-585W-140 at a graphene weight ratio of 100 ppm, and were simply dispersed by manual stirring.

[0107] Centrifuge at 1440g (1440 times the acceleration of gravity) for 30 minutes (approximately equivalent to one month of natural settling), pause for 30 minutes, then centrifuge again for 30 minutes, repeating this process for a total of 3 hours. The test results are shown in Table 2.

[0108] Table 2 Dispersion stability test results

[0109]

[0110] As shown in Table 2, the graphene oily slurry prepared by the present invention has good dispersion stability in lubricating oil. Among them, the graphene prepared in Examples 1-3 has the best effect due to its smaller particle size and larger specific surface area (lower number of sheets).

[0111] Test Example 4: Friction and Wear Performance Test

[0112] The graphene oily slurry 1#, graphene oily slurry 2#, graphene oily slurry 3# prepared in Examples 1-3, the graphene oily slurry 4# prepared in Comparative Example 1, and the graphene oily slurry 5# prepared in Comparative Example 2 were used as additives and added to the finished lubricating oil Merrenz SP 0W-30 at a graphene weight ratio of 10 ppm. The friction and wear performance of the lubricating oil, including the coefficient of friction and the wear scar diameter, was tested.

[0113] The oil samples and finished lubricating oils obtained by compounding graphene oily slurries 1#, 2#, and 3# prepared in Examples 1-3, graphene oily slurries 4# prepared in Comparative Example 1, and graphene oily slurries 5# prepared in Comparative Example 2 were evaluated using a four-ball friction testing machine to test their friction-reducing and anti-wear properties (industry standard SH / TO189-92). The test conditions included: GCr15 steel balls, a rotation speed of 1200 r / min, an oil temperature of 75℃, a long grinding time of 60 min, and a load of 392 N. The data provided by the four-ball friction testing machine included the wear scar diameter and the coefficient of friction. The smaller the wear scar diameter, the higher the anti-wear ability; the smaller the coefficient of friction, the better the friction-reducing performance. The results are shown in Table 3.

[0114] Table 3. Tribological and Wear Properties of Lubricating Oils

[0115]

[0116]

[0117] As shown in Table 3, the graphene oily slurry prepared by the present invention has good anti-wear and friction reduction effects. Among them, the graphene in Examples 1-3 has better effects due to its smaller particle size and larger specific surface area (lower number of sheets).

[0118] In addition, the inventors of this case also conducted experiments with other raw materials, process operations and process conditions described in this specification, referring to the foregoing embodiments. For example, the naphthenic acid in the switch-type microemulsion in the above embodiments was replaced with other lower fatty acids such as hexanoic acid, heptanoic acid, octanoic acid, isooctanoic acid, nonanoic acid, isononanoic acid, decanoic acid, neodecanoic acid, etc., and relatively ideal results were obtained in all cases.

[0119] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a graphene oily slurry, characterized in that, include: A switchable microemulsion is provided, comprising a carboxylic acid as an oily solvent, a surfactant, an alkanolamine as a first co-surfactant, a small-molecule organic acid as a second co-surfactant, oxalate and / or bicarbonate, and water. The surfactant is a cationic surfactant. The molar ratio of the carboxyl group in the carboxylic acid, the carboxyl group in the small-molecule organic acid, the amino group in the alkanolamine, and the oxalate and / or bicarbonate is 1:(0.95~1.05):(1~1.1):(1~1.05); the mass ratio of the carboxylic acid to the surfactant is 1:(0.2~0.5); and the water constitutes 60%~80% of the total mass of the switchable microemulsion. The expanded graphite is mixed evenly with the switch-type microemulsion, and then dispersed and ground sequentially. A first switching substance is slowly added to the material after the first grinding to initiate a switching reaction, with the addition completed within 0.5-1 hour. The pH of the material is adjusted to 7.5-8.5, followed by further grinding for 2-4 hours, and then homogenization to obtain a mixture. The first switching substance is calcium hydroxide, which can react with the switch-type microemulsion. The mass ratio of the expanded graphite to the sum of all components in the switch-type microemulsion except water is 1:(2-4). The dispersion process is carried out at 6000-10000 rpm for 2-4 hours, the first grinding process at 2000-3000 rpm for 2-4 hours, and the homogenization process at a pressure of 80... MPa~100MPa, homogenization treatment times are 4~6; during the switching reaction, carboxylic acids in the switching microemulsion become water-soluble, the switching microemulsion is transformed into an aqueous phase system, and oxalate and / or bicarbonate precipitate particles are generated. The mixture is subjected to solid-liquid separation to obtain a solid-phase system and a liquid-phase system containing at least graphene and precipitated microparticles; After removing the precipitated particles from the solid-phase system, a graphene-containing concentrated slurry is obtained. The graphene aqueous concentrate, oily dispersant, and base oil are mixed and stirred, while being vacuum dehydrated. Finally, a second grinding process is performed to obtain the graphene oily slurry. The mass ratio of graphene, oily dispersant, and base oil in the graphene aqueous concentrate is 1:(5~20):(20~50).

2. The preparation method according to claim 1, characterized in that, include: An acidic substance or complexing agent is added to the solid system to remove the precipitated particles. The remaining solid phase is then washed with water and centrifuged to obtain a concentrated graphene slurry.

3. The preparation method according to claim 2, characterized in that: The acidic substance is hydrochloric acid.

4. The preparation method according to claim 2, characterized in that: The complexing agent is EDTA.

5. The preparation method according to claim 1, characterized in that: The oily dispersant includes one or more of the following: polyisobutylene succinimide, boronized polyisobutylene succinimide, isopropyl titanate, sorbitan oleate, polyether, stearic acid, oleic acid, tallow amine, and tallow amine polyoxyethylene ether. And / or, the base oil includes one or more combinations of Group II base oil, Group III base oil, Group IV base oil, and Group V base oil; And / or, the stirring treatment is carried out at a temperature of 80℃~100℃ for a time of 2h~4h; And / or, the second grinding process is performed using a three-roll mill, with the number of processing cycles being 2 to 4.

6. The preparation method according to claim 1, characterized in that: The carboxylic acids include lower fatty acids and / or cycloalkanoic acids.

7. The preparation method according to claim 6, characterized in that: The lower fatty acids include fatty acids with no more than 10 carbon atoms in their carbon chains and which are liquid at room temperature.

8. The preparation method according to claim 7, characterized in that: The lower fatty acids include one or more combinations of hexanoic acid, heptanoic acid, octanoic acid, isooctanoic acid, isononanoic acid, nonanoic acid, and neodecanoic acid.

9. The preparation method according to claim 1, characterized in that: The alkanolamines include one or more combinations of monoethanolamine, diethanolamine, triethanolamine, N-(2-hydroxyethyl)ethylenediamine, N,N'-bis(2-hydroxyethyl)ethylenediamine, and N,N,N',N'-tetra(2-hydroxyethyl)ethylenediamine; And / or, the small molecule organic acid substances include one or more combinations of oxalic acid, malonic acid, succinic acid, maleic acid, citric acid, malic acid, and tartaric acid.

10. The preparation method according to claim 1, characterized in that: The oxalate or bicarbonate includes one or more combinations of soluble ammonium, sodium, and potassium salts.

11. The preparation method according to claim 10, characterized in that: The oxalate is obtained by neutralizing oxalic acid with a base.

12. The preparation method according to claim 11, characterized in that: The oxalate includes one or more combinations of ammonium oxalate, sodium oxalate, and potassium oxalate.

13. The preparation method according to claim 1, characterized in that: The surfactant comprises one or more of the following: dodecyltrimethylammonium chloride, dodecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide, octadecyltrimethylammonium chloride, octadecyltrimethylammonium bromide, dodecyl dimethylbenzylammonium chloride, dodecyl dimethylbenzylammonium bromide, hexadecyl dimethylbenzylammonium chloride, hexadecyl dimethylbenzylammonium bromide, octadecyl dimethylbenzylammonium chloride, and octadecyl dimethylbenzylammonium bromide.

14. The preparation method according to claim 1, characterized in that, Also includes: A second switching substance is added to the liquid phase system obtained from solid-liquid separation, and the pH value is adjusted to 5.6~6.6 to regenerate the switching microemulsion.

15. The preparation method according to claim 14, characterized in that: The second switching substance includes one or a combination of two of oxalic acid and carbonic acid.

16. A graphene oily slurry prepared by any one of the preparation methods of claims 1-15, wherein the graphene oily slurry comprises at least a base oil and graphene uniformly dispersed in the base oil.

17. The graphene oily slurry according to claim 16, characterized in that: The graphene sheets have a diameter of 2 μm to 10 μm.

18. The graphene oily slurry according to claim 16, characterized in that: The specific surface area of ​​the graphene is 50 m². 2 / g~100 m 2 / g.

19. The graphene oily slurry according to claim 16, characterized in that: The number of graphene sheets is less than 30.

20. The application of the graphene oily slurry of claim 16 in the field of lubricating oil.

21. A lubricating oil additive, characterized in that, Includes the graphene oily slurry as described in claim 16.

Images