KR20120134685A - A method and apparatus for manufacturing graphite oxide - Google Patents

Abstract

PURPOSE: A manufacturing method of graphite oxide and a manufacturing apparatus of the same are provided to improve dispersibility and to secure the same physical property as carbon nanotube. CONSTITUTION: A manufacturing method of graphite oxide includes the following steps: graphite slurry is prepared by mixing graphite and sulfuric acid; an oxidizer is gradually introduced into the graphite slurry to be mixed; the mixture is introduced into a tubular reactor(30) equipped in a thermostat(31) under pressure to be intermediately reacted; the intermediately resultant mixture is introduced into a continuous stirring reactor to be additionally reacted; cool water is introduced into the additionally resultant mixture to be mixed; a hydrogen peroxide solution is introduced into the water mixed product to be mixed such that oxidation is terminated; graphite oxide is washed and separated from the resultant product; and the separated graphite oxide is dried.

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing graphite oxide,

TECHNICAL FIELD The present invention relates to a process for producing graphite oxide and a process for producing graphite oxide, and more particularly, to a process for producing graphite oxide, which is an intermediate used for producing a graphene structure material, and a process for producing the same.

Andre Geim, a professor at the University of Manchester in 2004, first succeeded in mechanically removing graphene from graphite using the "Scotch tape method," and also using quantum Hall effect Research has revealed the excellent electrical conductivity of graphene. In 2008, the excellent strength of graphene was confirmed by the James Hone research team at Columbia University in the United States. In 2008, researchers at Alexander Balandin of the University of California, Riverside, USA, It was measured at 5300pW / mpK, about twice as high as the nanotubes.

Examples of the method for obtaining such graphene include a method of producing graphite oxide by peeling off by thermal shock, a method of drawing graphite like Andrejames, a surface growth method, a method of reducing graphite sheet to hydrazine, a chemical vapor deposition method, And a method of dissolving graphite in a reaction with a solution of permanganic acid are known. However, all of them except for the method of peeling off graphite oxide by thermal shock have not been able to go beyond the experimental method.

On the other hand, it has been known for a long time that a worm or accordion type expanded graphite is produced by adding an acid or the like to graphite flakes and intercalating the graphite crystals between layers and applying a thermal shock. Such worm-like expanded graphite is widely used as a filler or as an anisotropic sheet due to the compression process. However, such expanded graphite has a structure in which some layers of graphite are loosened, and the physical properties thereof are lower than that of graphene, and the size of the particles is much larger.

As a method for producing graphite oxide, there is known a Staudenmaier method for producing graphite oxide by adding sulfuric acid, fuming nitric acid and potassium perchlorate to graphite powder and reacting for several days. In addition, HUMMERS in US Pat. No. 2798878 has improved this by using sulfuric acid, sodium nitrate and potassium permanganate to shorten the reaction time.

The mixing reaction of sulfuric acid, sodium nitrate and potassium permanganate is an exothermic reaction and is generally caused by the danger of explosion at a temperature of 55 ° C or higher due to the reaction between sulfuric acid and potassium permanganate during the mixing reaction and Mn ₂ O ₇ , It is possible to produce graphite oxide only by a very small amount of batch method, which has a limitation in mass production. Therefore, there is an urgent need to develop a process capable of solving such problems and capable of mass-producing graphite oxide.

Some of the present inventors have proposed a continuous reactor of oxidized graphite in which a plurality of microchannels connected to each other having several micro-millimeters in diameter and a retention time of several minutes to several days are connected in a current patent application No. 2010-76871 There is a suggestion. However, such a long and narrow microchannel reactor is advantageous for controlling the reaction progress or the reaction temperature, but the head loss is large, so that a large number of booster pumps must be installed in the middle and a problem of having a high pressure resistant acidic microchannel reactor have. It is also not as efficient as the reactor size.

It is an object of the present invention to provide a method and apparatus for producing oxidized graphite suitable for producing nano-sized graphene structural materials.

According to an aspect of the present invention, there is provided a method for producing a graphite slurry, comprising: preparing graphite slurry by mixing graphite and sulfuric acid; Adding the oxidizing agent selected from permanganic acid, permanganate and permanganate sulfuric acid solution to the graphite slurry stepwise in a continuous batch mixer connected in a multistage manner, and mixing the graphite slurry; Pressing the mixture into a tubular reactor having a diameter of 5 mm to 50 mm packed in a thermostat to which ultrasonic waves are added, and allowing the mixture to stand for 0.2 to 5 hours to perform an intermediate reaction; Charging the intermediate reaction mixture into a continuous stirred tank reactor to perform an additional reaction; Adding and mixing water to the additional reaction mixture; Introducing an aqueous hydrogen peroxide solution into the water mixed reaction mixture and mixing to terminate the oxidation reaction; Washing and separating the oxidized graphite in the reaction mixture in which the oxidation reaction is terminated; And drying the separated graphite oxide. The present invention also provides a method for producing graphite oxide having a carbon / oxygen ratio of 1 to 5/1 by an elemental analyzer and having a maximum peak near 2θ = 12 ° by X-ray diffraction analysis .

The present invention also relates to a graphite slurry mixer for preparing a graphite slurry by mixing graphite and sulfuric acid; A continuous batch oxidizer mixer connected to the graphite slurry mixer in a cascade of two to ten stages in series; A tubular reactor having a diameter of 5 mm to 50 mm and a residence time of 0.2 hours to 5 hours charged in a thermostat to which an ultrasonic wave is added and which is subsequently connected to the oxidizer mixer to make an intermediate reaction mixture; And a continuous stirred tank reactor connected to the tubular reactor for further reaction of the intermediate reaction mixture; And a water mixer for introducing and mixing cold water into the further reaction mixture; A hydrogen peroxide mixer for introducing and mixing an aqueous hydrogen peroxide solution into the water mixture reaction mixture to terminate the oxidation reaction; A washing separator for washing and separating the oxidized graphite in the reaction mixture in which the oxidation reaction is terminated; And a dryer for drying the separated graphite oxide.

In the present invention, when the carbon / oxygen ratio of the graphite oxide is less than 1/1, graphene is finely divided and when the carbon / oxygen ratio is larger than 5/1, graphene peeling is reduced and all properties are deteriorated. Since the graphite powder as the raw material has an interlayer distance of about 3.4 Å, the oxidized graphite of the present invention is formed by forming functional groups such as a hydroxyl group, a carboxylic acid group, and an epoxy group in each layer by an oxidation reaction, , X-ray analysis shows peaks around 2? = 12.7 占 without peaks except for traces at around 2? = 26 占 characteristic of graphite powder.

The graphite slurry has a graphite: sulfuric acid weight ratio of 1:10 to 1: 100, preferably 1:30 to 1:70. If the weight ratio of graphite: sulfuric acid is too high, the viscosity of the graphite slurry becomes high and the transfer and mixing of the reactants in the tubular reactor is not smooth. On the other hand, if the weight ratio of graphite: sulfuric acid is too low, reaction efficiency is low and waste sulfuric acid by-

The graphite generally has a larger particle size, and can be used if it is 1 μm or larger. For example, graphite powder of 1 to 300 μm, preferably 1 to 100 μm, can be used. If the particle size of graphite is too low, the effect of expansion due to the weight density is low, which may cause a problem that graphene is not formed well due to peeling. Also, sulfuric acid having a concentration of 70% or more, preferably 85 to 98%, is used, and the graphite slurry can be produced by dispersing graphite powder in sulfuric acid. In the graphite slurry mixer, the mixture is maintained at a temperature of from 0 to 60 캜, preferably from 8 to 10 캜, so that the temperature is maintained in the subsequent process.

The graphite slurry is fed to a continuous batch oxidizer mixer of the same capacity connected in multiple stages and the oxidizer is charged in stages and mixed. In the oxidizer mixer, the mixing between the permanganate and the sulfuric acid should be carried out at a low temperature in the temperature range of 0 to 54 占 폚. In particular, Mn ₂ O ₇ produced by the reaction between permanganate and sulfuric acid has to be blended with permanganate or permanganate step by step in small quantities because of the danger of explosion at temperatures above 55 ° C. The temperature in the continuous batch oxidizer mixer is generally kept at a low temperature of 30 DEG C or lower, preferably 5 to 30 DEG C, most preferably 5 to 15 DEG C Keep the temperature. Oxidation reactions of less than 20% of the target value within the safe range are allowed in the continuous ash oxidizer mixer. The continuous ash oxidizer mixer is preferably connected in a multi-stage of two or more stages and ten stages or less. The oxidizing agent is selected from the group consisting of permanganic acid, permanganic acid salts and permanganic acid sulfuric acid solution.

The oxidizing agent to be added as a whole is a permanganate: sulfuric acid weight ratio of 1: 2 to 1:50, preferably 1: 5 to 1:30 based on the permanganate. The permanganate includes potassium permanganate or sodium permanganate, ammonium permanganate, calcium permanganate and the like. If the weight ratio of permanganate: sulfuric acid is less than the above range, the oxidation reaction is not smooth, whereas if it is large, the production cost may be increased due to an increase in raw material cost.

The oxidizing agent such as the permanganate is supplied to the continuous batch oxidizing agent mixer by a connected metering pump, and the amount of supplied permanganate should be strictly controlled by a quantitative method or the like. The graphite slurry to which the oxidizing agent has been added is pressed into the tubular reactor in order to prevent the risk of heat generation due to the initial oxidation and smoothly proceed the oxidation reaction. These tubular reactors are charged into a thermostat for accurate temperature control. Such a thermostat is equipped with a heat exchanger that is cooled to be controlled at a certain range of temperatures. In addition, ultrasonic waves are added to the thermostatic chamber in order to improve expansion and peeling efficiency between graphite layers and to produce good graphene by thermal expansion. The inner diameter of the tubular reactor is 5 to 50 mm, preferably 8 to 12 mm, and the residence time is 0.2 to 5 hours, preferably 1 to 3 hours. The tubular reactor has a length of 10 m to 1000 m, preferably 100 m to 300 m. At this time, the output of the ultrasonic wave is approximately 0.05 W / cm ³ to 5.0 W / cm ³ . The intermediate oxidation of graphite is accomplished in this tubular reactor. The most annoying exothermic reaction zone is to use a narrow inner diameter tube to precisely control the local temperature. If precise control of the local temperature is possible, it is advantageous to accelerate the oxidation reaction by selecting a high temperature in the range of the reaction temperature of 5 to 54 DEG C, for example in the range of 30 to 50 DEG C. In a tubular reactor, 40% to 90%, preferably 50% to 70% of the target graphite oxidation reaction is targeted based on carbon / oxygen element analysis.

The combination of oxidizer and graphite simplifies and streamlines the manufacturing process by using a continuous stirred tank reactor instead of a long tubular reactor because the latter part of the oxidation has a much reduced risk of localized heat and explosion. Since the rapid oxidation reaction is performed by the tubular reactor, the target temperature is set and controlled at a lower temperature than the tubular reactor, for example, in the range of 8 to 30 ° C, in consideration of safety. The remaining 10 to 50% of the oxidation reaction is additionally effected in this continuous stirred tank reactor. The residence time is preferably 0.5 to 5 hours.

The cold water supply unit 55 is connected to the additional reaction mixture withdrawn from the continuous stirred tank reactor 40. The remaining oxidant is diluted by adding cold water, preferably below 0 DEG C, to the reaction mixture, The supply unit 75 is connected to the hydrogen peroxide solution, and the 3% hydrogen peroxide solution is introduced into the hydrogen peroxide mixture unit 70 through the metering pump. The reaction mixture, which has been oxidized, is washed in the washing machine 80, .

Water is added to the additional reaction mixture in a water mixer to prepare for the end of the oxidation reaction. Water in the mixing water mixer is preferably graphite to water weight ratio of 1: 1 to 1: 100 on the basis of graphite, and if the weight ratio of graphite and water is out of the above range, the oxidation reaction can not be performed smoothly , A large amount of wastewater may be generated, which may result in a problem of high manufacturing cost.

The concentration of hydrogen peroxide in the aqueous hydrogen peroxide solution is not particularly limited, but it may be generally 1 to 10% by weight, preferably 2 to 7% by weight. The weight ratio of graphite: hydrogen peroxide aqueous solution is not quantitative but is 1:10 to 1: 100, preferably 1:30 to 1:70, which is similar to the graphite: sulfuric acid weight ratio based on the case where the concentration of hydrogen peroxide is 3 wt% It is possible to do so. The aqueous hydrogen peroxide solution reduces excess permanganate to terminate graphite oxidation. The excess is expensive to wash and dry, and the addition of a small amount does not terminate the reaction. The holding time after the addition of the aqueous hydrogen peroxide solution can be within several tens of minutes.

The excess permanganic acid is reduced by the addition of the aqueous hydrogen peroxide solution and the reaction mixture is terminated. The reaction mixture may be washed once more with pure water or water having an appropriate pH, for example, washing water having a pH of 5 to 6 before drying, Deg.] C or less, preferably 80 [deg.] C or less, for 96 hours or less. Such washing and drying may be carried out separately from the previous step or may be carried out continuously.

The washed oxidized graphite is separated, dried and stored in an oxidized graphite reservoir.

According to the present invention, the oxidant addition process is carried out in a multi-stage continuous ash mixer maintained at a low temperature in a stepwise manner to suppress oxidization while mixing the oxidizer, and the dangerous period of the superheat explosion during the oxidation reaction of graphite, To precisely adjust the temperature locally and to enhance the penetration effect of the oxidizer into the graphite interlayer through ultrasonic treatment and to agitate the oxidation reaction in the continuous reaction tank reactor in the additional reaction zone outside the danger zone, And it is possible to economically produce a large amount of graphite oxide.

The nano-sized graphene structure material obtained by delamination of graphite oxide has not only comparable physical properties to carbon nanotubes but also superior properties than carbon nanotubes having low dispersibility by a functional group such as a residual carboxyl or hydroxyl group A single acid can be easily obtained in the manufacturing process.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a process diagram to the intermediate oxidation step in a production apparatus for producing oxidized graphite as an embodiment of the present invention. FIG.
Fig. 2 is a process chart of Fig. 1 and subsequent figures in a production apparatus for producing graphite oxide as one embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the accompanying drawings. These drawings are scale of the pilot lot plant for the scale-up by selecting the reactor, adjusting the reaction temperature, and increasing the reaction time.

Graphite powder and 85 to 98% concentrated sulfuric acid solution are added to the graphite slurry mixer 10 having a capacity of 50 L at a weight ratio of 1:50 and mixed with 40 L of graphite slurry. The temperature in the graphite slurry mixer 10 is maintained at 8 to 10 DEG C for the next process.

The graphite slurry obtained in the graphite slurry mixer 10 is fed to a continuous batch oxidizer mixer 21 connected in a five-stage series. This oxidation reaction is an exothermic reaction and the intermediate manganese manganese (Mn ₂ O ₇ ) has a risk of explosion at temperatures above 55 ° C. Therefore, the continuous batch oxidizer mixers (21, 22, 23, 24, 25) In order to prevent explosion by overheating, permanganate, which is precisely controlled at a temperature of 8 ~ 10 ℃ and oxidant, is added to each oxidizer mixer at a small volume of 2 liters. The oxidant mixed slurry to which the oxidizing agent is added in five stages is supplied to the tubular reactor 30 of four stages of 10 mm inner diameter charged with the ultrasonic transducer 32 in the thermostatic chamber 31 equipped with the cooler 33, ). In order to reduce the head loss of the slurry to be press-fitted, three pumps (27, 28, 29) are provided in the middle to raise the pressure. The total length of the tubular reactor 30 is 200 m and the reaction residence time is 2 hours. A decompression device 36 is connected to each of the pumps 26, 27, 28, 29 to adjust the pumping pressure in accordance with the internal pressure of the tubular reactor 30.

)은 도2에 예시되어 있는 바와 같이 50ℓ 용량의 연속교반탱크 반응기(40)에서 추가 산화된다. 상기 튜브형 반응기에서 산화제의 층간 삽입이 이루어진 흑연 중간 산화물은 추가 반응에 의하여 목표 흑연산화물로 얻어진다. 체류시간은 2시간 정도이다. 산화제와 흑연의 결합으로 산화의 후반부는 국지적인 발열과 폭발의 위험이 훨씬 완화되었으므로 긴 튜브형 반응기 대신에 연속교반탱크 반응기를 사용하여 제조장치를 단순화시키고 효율화 시킨다.The graphite intermediate oxide () extruded from the tubular reactor (30)

Are further oxidized in a 50 L continuous stirred tank reactor 40 as illustrated in FIG. The intermetallic graphite oxide in which the oxidant is intercalated in the tubular reactor is obtained as a target graphite oxide by an additional reaction. The residence time is about 2 hours. The combination of oxidizer and graphite simplifies and streamlines the manufacturing process by using a continuous stirred tank reactor instead of a long tubular reactor because the latter part of the oxidation has a much reduced risk of localized heat and explosion.

The cold water supply unit 55 is connected to the additional reaction mixture withdrawn from the continuous stirred tank reactor 40, water is added to the reaction mixture to dilute the remaining oxidant, and then the hydrogen peroxide supply unit 75 is connected to the reaction mixture through a metering pump 3% hydrogen peroxide aqueous solution is added to the hydrogen peroxide mixture 70, and the reaction mixture which has been subjected to the oxidation reaction is separated and dried from the washed graphite oxide (B) drawn out from the washing machine 80 to obtain target graphite oxide. An elemental analysis of the graphite oxide obtained results are C ₁ O ₃ it was _.65 H _{2 .45.}

The oxidation graphite obtained in this way proceeds smoothly through the graphite layer under an ultrasonic irradiation, and then peeled off by thermal shock, whereby graphene having excellent physical properties can be obtained.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. Accordingly, the true scope of the present invention should be determined by the technical idea of the appended claims.

Claims (14)

Mixing graphite and sulfuric acid to prepare a graphite slurry; Adding the oxidizing agent selected from the group consisting of permanganic acid, permanganate and permanganate sulfuric acid solution to the graphite slurry in a continuous batch mixer connected in multiple stages, and mixing the graphite slurry; Pressing the mixture into a tubular reactor having a diameter of 5 mm to 50 mm packed in a thermostat to which ultrasonic waves are added, and allowing the mixture to stand for 0.2 to 5 hours to perform an intermediate reaction; Charging the intermediate reaction mixture into a continuous stirred tank reactor to perform an additional reaction; Adding cold water to the additional reaction mixture and mixing; Introducing an aqueous hydrogen peroxide solution into the water mixed reaction mixture and mixing to terminate the oxidation reaction; Washing and separating the oxidized graphite in the reaction mixture in which the oxidation reaction is terminated; And drying the separated graphite oxide, wherein the graphite oxide has a carbon / oxygen ratio of 1 to 5/1 by an elemental analyzer and has a maximum peak in the vicinity of 2? = 12 ° by X-ray diffraction analysis The graphite slurry according to claim 1, wherein the graphite slurry is a mixture of graphite and sulfuric acid at a weight ratio of 1:30 to 1:70 The graphite slurry of claim 1, wherein the graphite slurry is fed to a continuous batch oxidizer mixer of the same capacity connected in two stages to ten stages, The method for producing graphite according to claim 1, wherein the graphite powder in the graphite slurry has a particle size of 1 to 100 μm The process for producing graphite oxide according to claim 1, wherein the tubular reactor has an inner diameter of 5 to 50 mm, a residence time of 0.2 to 5 hours, and a length of 10 to 1000 m The method according to claim 1, wherein the reaction of graphite in the tubular reactor is 40% to 80% of the final graphite oxidation reaction The process according to claim 1, wherein the remaining 20 to 50% of the oxidation reaction is additionally carried out in the continuous stirred tank reactor A graphite slurry mixer for mixing graphite and sulfuric acid to prepare graphite slurry; A continuous batch oxidizer mixer connected to the graphite slurry mixer in a cascade of two to ten stages in series; A tubular reactor having a diameter of 5 mm to 50 mm, a residence time of 0.2 hours to 5 hours, and a length of 10 to 1000 m, which is connected to the oxidizer mixer and is then charged into a thermostat to which an ultrasonic wave is added to make an intermediate reaction mixture; And a continuous stirred tank reactor connected to the tubular reactor for further reaction of the intermediate reaction mixture; And a water mixer for adding and mixing cold water to the further reaction mixture; A hydrogen peroxide mixer for introducing and mixing an aqueous hydrogen peroxide solution into the water mixture reaction mixture to terminate the oxidation reaction; A washing separator for washing and separating the oxidized graphite in the reaction mixture in which the oxidation reaction is terminated; And a dryer for drying the separated graphite oxide, 9. The graphite slurry according to claim 8, wherein the graphite slurry is a mixture of graphite and sulfuric acid at a weight ratio of 1:30 to 1:70 9. The graphite according to claim 8, wherein the graphite oxide has a carbon / oxygen ratio of 1 to 5/1 as measured by an elemental analyzer and has a maximum peak in the vicinity of 2? = 12 by X-ray diffraction analysis [9] The method of claim 8, wherein the graphite powder in the graphite slurry has a particle size of 1 to 100 [ [8] The apparatus according to claim 8, wherein the tubular reactor has an inner diameter of 8 mm to 12 mm, a residence time of 1 to 3 hours, and a length of 100 to 300 m. [9] The apparatus for producing graphite according to claim 8, wherein the intermediate oxidation reaction of graphite in the tubular reactor is performed at a rate of 40% to 80% A process according to claim 8, wherein the remaining 20 to 50% of the oxidation reaction is additionally carried out in the continuous stirred tank reactor

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