Graphite processing improvements

Abstract

Improvements in graphite processing. A method for processing graphite in a flow reactor, the method comprising the steps of: (i) providing a flow reactor comprising: (a) a vessel for receiving a reaction mixture comprising natural graphite and water; (b) an activator for imparting rotational motion to the reaction mixture; and (c) at least one input channel for introducing the reaction mixture into the vessel, the activator being rotatably mounted to a hollow tube providing the input channel; (ii) introducing the reaction mixture into the vessel; (iii) operating the activator to process the reaction mixture; obtaining the treated reaction mixture from the vessel; and, optionally, repeating steps (ii) through (iv) one or more times with the treated reaction mixture. 1. A flow reactor for use in the purification of graphite, comprising: (a) a vessel for receiving a reaction mixture comprising natural graphite and water, (b) an activator for imparting rotational motion to the reaction mixture, and (c) at least one input channel for introducing the reaction mixture into the vessel, the activator being rotatably mounted to a hollow tube providing the at least one input channel. 2. An electrically conductive composition comprising graphite having a carbon content of at least 97.5%, wherein the electrically conductive composition has an electrical conductivity greater than 60,000 S / m, and wherein the graphite is substantially free of added impurities.

Description

[Technical field]

[0001] The present invention relates to a hydrodynamic method for treating natural graphite in a flow reactor, a flow reactor for use in the method, and a conductive composition that is substantially free of additional impurities due to purification processes. [Background technology]

[0002] Graphite is an allotrope of carbon with a crystalline structure. Graphite is a mineral that is a type of coal. Graphite has a lattice structure composed of graphene sheets separated by a distance of about 0.335 nm. The scientific definition of graphene refers to a single graphene sheet obtained from graphite, although commercially available graphene may consist of multiple sheets or layers. Graphene layers are very strong and conduct heat and electricity efficiently.

[0003] Graphene is useful for many applications, such as electromagnetic shielding and far-infrared heating solutions. However, it is expensive to produce and purchase, and alternative sources of conductive materials with similar properties to graphene have been sought.

[0004] The purity of mined graphite is typically about 80-85% by weight (calculated as the weight of carbon relative to the total weight). Known methods for purifying graphite include flotation purification with hydrohalic acids such as hydrogen fluoride or hydrogen chloride, or calcination of the graphite. Flotation-purified graphite obtained by such methods is typically about 94% pure by weight, but contains hydrohalic acid residues. Such flotation-purified graphite is typically valued at about US$800 per ton. To obtain graphene with a purity of 95-97% by weight, high electrical conductivity, and low number of layers, flotation-purified graphite must be subjected to further expensive processing. Such graphene is typically valued at about US$1200 per ton. Summary of the Invention [Problem to be solved by the invention]

[0005] Methods to remedy these problems have been sought. [Means for solving the problem]

[0006] According to the present invention, there is provided a method for treating graphite in a flow reactor, the method comprising the steps of:

[0007] (i) providing a flow reactor comprising: (a) a vessel for receiving a reaction mixture comprising natural graphite and water; (b) an activator for imparting rotational motion to the reaction mixture; and (c) at least one input channel for introducing the reaction mixture into the vessel, the activator being rotatably mounted to a hollow tube providing the input channel.

[0008] (ii) introducing said reaction mixture into said vessel;

[0009] (iii) operating said activator to treat said reaction mixture.

[0010] (iv) obtaining the treated reaction mixture from the vessel, and, optionally, repeating steps (ii) through (iv) one or more times with the treated reaction mixture.

[0011] There is also provided in accordance with the present invention a flow reactor for use in the purification of graphite, the flow reactor comprising: (a) a vessel for receiving a reaction mixture comprising natural graphite and water; (b) an activator for imparting rotational motion to the reaction mixture; and (c) at least one input channel for introducing the reaction mixture into the vessel, the activator being rotatably mounted to a hollow tube providing the at least one input channel.

[0012] According to the present invention there is further provided an electrically conductive composition comprising graphite, the composition having a carbon content of at least 96%, the composition having an electrical conductivity of greater than 60,000 S / m, and the graphite being substantially free of added impurities.

[0013] Advantages of the present invention include providing a new method for treating and cleaning graphite with significantly higher efficiency and environmental safety than other known methods for cleaning graphite. In particular, the method uses water to purify the graphite, so that the resulting purified graphite is not contaminated with impurities. The method allows natural graphite to be removed from impurities and further processed to obtain a conductive composition. Furthermore, the method is less energy intensive and does not require grinding of the graphite. One advantage of avoiding the use of grinding is that the risk of metal impurities being contaminated in the purified graphite product is greatly reduced. Purifying the graphite with water instead of chemicals such as hydrohalic acid reduces or avoids the need for further purification steps, reducing the time and cost of processing. The electrical conductivity of the conductive composition according to the present invention is comparable to that of graphite with a purity of 97-99.9% by weight, but at a much lower cost than that required to process the purified graphite.

[0014] Further advantages of the present invention are:

[0015] The electrical conductivity of natural graphite treated by the method of the present invention is significantly increased. The increase in electrical conductivity of the treated graphite is believed to be the result of a significant reduction in contaminants on the surfaces and edges of the graphite particles. The electrical conductivity of the dried conductive composition can be increased up to 69,000 S / m.

[0016] The extent of the conversion of graphite to graphene can be controlled by the selection of the treatment time.

[0017] In some embodiments, the activator may have one or more arms or paddles, for example, between 2 and 12 paddles, for example, 4 or 6 paddles.

[0018] In some embodiments, the activator can impart centrifugal motion to the reaction mixture. In some embodiments, step (iii) of the method of the present invention comprises operating the activator to rotate at a minimum rotational speed of about 1000 rpm. In some embodiments, the minimum rotational speed of the activator can be about 2000 rpm. In some embodiments, the maximum rotational speed of the activator can be about 5000 rpm. In some embodiments, the maximum rotational speed of the activator can be about 3500 rpm. In some embodiments, the rotational speed of the activator can be about 3000 rpm.

[0019] In some embodiments, step (ii) may include introducing the reaction mixture at a minimum flow rate of about 50 liters per minute. In some embodiments, the minimum flow rate may be about 100 liters per minute. In some embodiments, the minimum flow rate may be about 200 liters per minute. In some embodiments, the minimum flow rate may be about 300 liters per minute. In some embodiments, step (ii) may include introducing the reaction mixture at a maximum flow rate of about 800 liters per minute. In some embodiments, the maximum flow rate may be about 600 liters per minute. In some embodiments, the maximum flow rate may be about 400 liters per minute.

[0020] In some embodiments, step (iii) may be performed over a period of time within a single cycle, referred to herein as the processing time. In some embodiments, step (ii) may be performed simultaneously with step (iii), and the total processing time may be the total time it takes to perform steps (ii) and (iii) in one cycle. In some embodiments, the minimum processing time may be 1 minute. In some embodiments, the minimum processing time may be 2 minutes. In some embodiments, the minimum processing time may be 3 minutes. In some embodiments, the minimum processing time may be 4 minutes. In some embodiments, the maximum processing time may be 20 minutes. In some embodiments, the maximum processing time may be 15 minutes. In some embodiments, the maximum processing time may be 10 minutes. In some embodiments, the maximum processing time may be 15 minutes.

[0021] In some embodiments, the reaction vessel may be a pressurized reaction vessel. In some embodiments, step (iii) of the method of the present invention may be performed after step (ii) to pressurize the reaction vessel. In some embodiments, step (iii) of the method of the present invention may be performed simultaneously with step (ii) where the reaction vessel is pressurized and the source of reaction mixture is a source of pressurized reactants. In some embodiments, the minimum pressure of the reaction vessel and / or the pressurized reactant source may be about 150 kPa. In some embodiments, the minimum pressure may be about 200 kPa. In some embodiments, the minimum pressure may be about 250 kPa. In some embodiments, the minimum pressure may be about 300 kPa. In some embodiments, the maximum pressure of the reaction vessel and / or the pressurized reactant source may be about 600 kPa. In some embodiments, the maximum pressure may be about 500 kPa. In some embodiments, the maximum pressure may be about 400 kPa. In some embodiments, steps (ii) and (iii) of the method of the present invention may include the use of a graphite processing mode to select one or more process parameters. In some embodiments, the graphite processing mode may depend on process parameters such as the processing time of a single cycle, the rotation speed of the activator, the pressure of the reaction vessel, the pressure source of the reactants, the graphite content in the reaction mixture, and / or the flow rate of the reaction mixture to the reaction vessel, etc. For example, the rotation speed is 2500 rpm, the flow rate is 400 liters per minute, the reactor pressure is 300 kPa (3 bar), the graphite content in the reaction mixture is 7 wt%, and the single cycle processing time is about 2 minutes.

[0022] In some embodiments, the flow reactor may comprise at least two activators in a vessel. In some embodiments, the two activators may be counter-rotating activators arranged to rotate in opposite directions. In some embodiments, the two activators may be coaxial. In some embodiments, the or each activator may be rotatably mounted in a hollow tube that provides an input channel. The advantage of counter-rotating activators is that the interaction of the activators generates sound waves, the frequency of which depends on the profile of the activators and the rotational speed of the activators. In some embodiments, step (iii) may include the use of one or more sound waves to improve the efficiency of the process.

[0023] In some embodiments, the reaction vessel may be connected to a resonator of acoustic vibrations through which the reaction mixture can pass. Benefits of including a resonator in the flow reactor include increasing the efficiency of the method by increasing the power of the acoustic waves. In some embodiments, the flow reactor may include a resonator that aids in the formation of one or more acoustic waves. In some embodiments, the acoustic waves may result from cavitation. In some embodiments, the resonator may be connected to the vessel of the flow reactor by an adapter. In some embodiments, the resonator may be a substantially spherical resonator. In some embodiments, the size of the resonator and / or the length and / or diameter of the adapter may be selected to optimize the acoustic resonance frequency to aid in the processing of the reaction mixture. In some embodiments, the resonator may be a Helmholtz resonator. In some embodiments, the rotation speed of the activator may be determined as a function of the resonant frequency of the resonator. In some embodiments, the resonant frequency of the resonator may be calculated using the following formula: fo=V / 2d where fo represents the fundamental or resonant frequency, V represents the speed of sound in the reaction mixture, and d represents the dimensions of the resonator (usually the length, width, and / or height). In some embodiments, the resonant frequency of the acoustic resonator is between 70 and 300 Hz. Advantages of using sonic waves include the ability to increase the purity of graphite in the reaction mixture to up to 99 wt% (by carbon content).

[0024] In some embodiments, the flow reactor vessel may have a circular cross-sectional shape. In some embodiments, the vessel has a circular side having a radius, and the width of the vessel between the circular sides is less than the radius, such that the vessel has the shape of a flattened spheroid. In some embodiments, the vessel may have a circular side, and the or each activator may be arranged to rotate in a plane substantially parallel to the circular side. In some embodiments, the or each activator may have a length that is about 75%-95% of the length of the circular side.

[0025] In some embodiments, the flow reactor includes two activators, and the input channel can have an inner end directed between the two activators. Advantages of introducing the reaction mixture between at least two activators include exposing the reaction mixture to maximum laminar flow of the mixture during processing. In some embodiments, the or each activator can have a rotatable activator support. In some embodiments, when there are two activators, each with a rotatable activator support, the rotatable activator supports can be coaxial.

[0026] In some embodiments, the reaction mixture can include natural graphite and water in a minimum weight ratio of about 1:40. In some embodiments, the reaction mixture can include natural graphite and water in a minimum weight ratio of about 1:100. In some embodiments, the reaction mixture can include natural graphite and water in a maximum weight ratio of about 1:300. In some embodiments, the reaction mixture can include natural graphite and water in a maximum weight ratio of about 1:200. In some embodiments, the reaction mixture can consist of natural graphite and water.

[0027] In some embodiments, the natural graphite may be mined graphite. In some embodiments, the natural graphite may be unprocessed graphite, e.g., unmilled graphite. In some embodiments, the minimum purity (or carbon content) of the natural graphite may be about 75% by weight. In some embodiments, the minimum purity of the natural graphite may be about 80% by weight. In some embodiments, the minimum purity of the natural graphite may be about 85% by weight. In some embodiments, the maximum purity of the natural graphite may be about 95% by weight. In some embodiments, the maximum purity of the natural graphite may be about 90% by weight.

[0028] In some embodiments, the conductive composition may include a mixture of graphite and graphene.

[0029] In some embodiments, the conductive composition may include graphite particles and up to 10 layer graphene particles. In some embodiments, the conductive composition may have a minimum of about 0.1% graphene by weight. In some embodiments, the conductive composition may have a minimum of about 0.5% graphene by weight. In some embodiments, the conductive composition may have a minimum of about 1% graphene by weight. In some embodiments, the conductive composition may have a maximum of about 5% graphene by weight. In some embodiments, the conductive composition may have a maximum of about 4% graphene by weight. In some embodiments, the conductive composition may have a maximum of about 3% graphene by weight. In some embodiments, the conductive composition may have a maximum of about 2% graphene by weight. As known to those skilled in the art, there are various methods for measuring or estimating graphene content, including using an optical microscope to count the number of graphene particles in a sample of purified graphite.

[0030] In some embodiments, the additional impurities may be impurities introduced into the conductive composition or natural graphite during processing, hi some embodiments, the additional impurities may be metal impurities or hydrohalic acid impurities.

[0031] In some embodiments, the conductive composition comprises graphite and graphene. In some embodiments, the graphene in the conductive composition may comprise up to 10 layers. In some embodiments, the graphite of the conductive composition of the present invention may have a carbon content of at least 96%. In some embodiments, the conductive composition (or the graphite of the conductive composition according to the present invention) may have a minimum carbon content of about 97.5% by weight. In some embodiments, the conductive composition (or the graphite of the conductive composition according to the present invention) may have a maximum carbon content of about 99.4% by weight. As known to those skilled in the art, the carbon content of the conductive composition (or the graphite of the conductive composition according to the present invention) can be measured by the loss on ignition method, in which the graphite is subjected to high temperatures (e.g., 450° C.) to determine its mineral residue content (see Dr. Gregory B. Pasternack, “Watershed Hydrology, Geomorphology, and Ecohydraulics: Loss-On-Ignition Protocol´´; pasternack.ucdavis.edu). Alternatively, the carbon content of the graphite can be measured by XRF screening of powdered graphite and measuring its electrical conductivity.

[0032] In some embodiments, compositions according to the invention may have a maximum electrical conductivity of 69,000 S / m. As will be appreciated by those skilled in the art, the electrical conductivity of compositions according to the invention may be measured using the method described in Celzard et al., "Electrical conductivity of carbonaceous powders": Carbon 40 (2002) 2801-2815, in which purified graphite powder is pressed between two copper contacts at a pressure of at least 3 MPa and a micro-ohmmeter is used to measure the value of the electrical resistance between the copper contacts. The present invention will now be described with reference to the accompanying drawings, which are not intended to limit the scope of the claimed invention. [Brief description of the drawings]

[0033] [Figure 1] FIG. 1 shows a schematic cross-sectional view of a flow reactor according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] A reactor according to the invention is shown diagrammatically at 10 in FIG. 1. The reactor 10 is for processing natural graphite. The reactor 10 comprises a circular vessel 5, tubes 1, 2, activators 3, 4 mounted on the tubes 1, 2, a spherical resonator 7 connected to the circular vessel 5 by a first adapter 6, and a second adapter 8 connected to the spherical resonator 7. The circular vessel 5 has the shape of a flattened spheroid (or flattened sphere or disk), with substantially flat disk-shaped sides 16, 18 and a curved circumferential side 20. The volume of the circular vessel 5 is about 1000 liters. The circular vessel 5 is arranged so that its disk-shaped sides 16, 18 are substantially vertical.

[0035] A tube 1, 2 is provided at the center of each of the disk-shaped sides 16, 18 of the circular vessel 5. Each tube 1, 2 has the dual function of a rotatable activator support and an input channel. The tubes 1, 2 are arranged coaxially. The tubes 1, 2 extend into the circular vessel 5. Each tube 1, 2 forms an input channel 12, 14 for receiving reactants to be inserted into the circular vessel 5, as indicated by the input arrow 22. Each tube 1, 2 is a rotatable activator support with an activator 3, 4 at its inner end 28, 30. Each tube 1, 2 is rotatable, as indicated by the rotation arrows 24, 26, with the direction of rotation 26 of tube 2 being opposite to the direction of rotation 24 of tube 1, and the activators 3, 4 rotating counter-rotate. Each activator 3,4 is in the form of a vane with one or more arms 34 (or paddles 34) configured to impart a rotational force 24,26 to a liquid medium (usually water) in a circular vessel 5. The length of each arm 34 is selected so that the length of the activator is approximately 80% of the length of the substantially flat, disc-shaped sides 16,18.

[0036] The spherical resonator 7 is connected to the side 20 of the circular vessel 5 by a first adapter 6. The size of the spherical resonator 7 and the length and / or diameter of the first adapter 6 are selected to optimize the acoustic resonance frequency to aid in the processing of natural graphite. The spherical resonator 7 has a second adapter 8 disposed opposite the first adapter 6. The second adapter 8 has a filter 32 for separating the solid graphite / graphene reaction products from the liquid reaction products. The reactants in the space 36 in the center of the circular vessel 5 between the activators 3, 4 are subjected to acoustic resonance and rotational shear forces from the counter-rotating activators 3, 4, and the reactants flow through the circular vessel 5 as indicated by the radial reactant flow arrows 38 and the first rotational flow arrow 40, and through the spherical resonator 7 as indicated by the second rotational flow arrow 42. At the end of the reaction, the rotation of the tubes 1, 2 is stopped and the contents of the circular vessel 5 and the spherical resonator 7 are pumped out 40 through the second adapter 8, and the filter 32 separates the liquid from the graphite particles. In another embodiment, the input channels 12, 14 are provided by separate input tubes provided in the curved side 20 of the circular vessel 5, with the inner ends of each input tube being located within the central reaction space 36, and the tubes 1, 2 can be solid. In another embodiment, the circular vessel 10 can have a single input channel 12.

[0037] In use, a reaction mixture of water and natural graphite is introduced into the circular vessel 5 through the hollow tubes 1, 2. The tubes 1, 2 are then rotated in opposite directions as indicated by arrows 24, 26. The first adapter 6 is opened and the spherical resonator 7 generates acoustic resonance. The reactor 10 is operated to process the reaction mixture for a preselected time. The rotation of the tubes 1, 2 is then stopped and the reaction mixture is pumped out of the reactor 10 through the filter 32 in the second adapter 8 (44) and the water is separated from the graphite / graphene particles.

[0038] The treatment of the water and graphite reaction mixture in reactor 10 may be for two or more cycles. The number of cycles may be selected depending on the product requirements of the resulting graphite product.

[0039] The present invention is illustrated by the following examples, which are not intended to limit the scope of the invention as claimed.

[0040] Working Example

[0041] A mixture of natural graphite with a carbon content of 92% and water in a weight ratio of 1:60 in an amount of 1000 liters was introduced into the circular vessel 5 of the reactor 10 at a rate of 250 liters per minute. The rotation frequency of the activators 3, 4 was 2900 rpm. The total treatment time 20 of the entire amount of mixture was 10 minutes. The entire amount of mixture was treated in the reactor 10 for 3 cycles.

[0042] The conductive composition containing graphite obtained by the method of this example had a carbon content of 92% and an electrical conductivity increased from 46,000 S / m to 65,000 S / m compared to dry graphite powder.

[0043] The graphite-containing conductive composition obtained by the method of this example was examined by optical microscopy and the graphene content was estimated to be 0.1 wt % to 2 wt % of the weight of the composition.

Claims

1. 1. A method for treating graphite in a flow reactor, comprising: (i) providing a flow reactor comprising: (a) a vessel for receiving a reaction mixture comprising natural graphite and water; (b) an activator for imparting rotational motion to the reaction mixture; and (c) at least one input channel for introducing the reaction mixture into the vessel, the activator being rotatably mounted to a hollow tube providing the input channel; (ii) introducing the reaction mixture into the vessel; (iii) operating the activator to treat the reaction mixture; (iv) obtaining the treated reaction mixture from the vessel, and optionally repeating steps (ii) through (iv) one or more times with the treated reaction mixture.

2. 10. The method of claim 1, wherein the activator comprises one or more arms or paddles, preferably the activator comprises 2 to 12 paddles.

3. 3. The method of claim 1 or 2, wherein the activator imparts centrifugal motion to the reaction mixture.

4. 3. The method according to claim 1 or 2, wherein the rotation speed of the activator is between 1000 rpm and 5000 rpm.

5. 3. The method of claim 1 or 2, wherein the flow reactor comprises at least two of the activators within the vessel, preferably the flow reactor comprises two activators, and the input channel has an inner end directed between the two activators.

6. The method of claim 5 , wherein the two activators are coaxial.

7. 6. The method of claim 5, wherein the two activators are counter-rotating activators.

8. 3. The method of claim 1 or 2, wherein the flow reactor comprises a resonator that aids in the formation of one or more acoustic waves.

9. 9. The method of claim 8, wherein the resonator is connected to the vessel of the flow reactor by an adapter.

10. 3. The method of claim 1 or 2, wherein the vessel of the flow reactor has a circular cross-sectional shape, preferably the vessel has circular sides with a radius, and the width of the vessel between the circular sides is less than the radius.

11. 3. The method of claim 1 or 2, wherein the container has a circular side and the activator is arranged to rotate in a plane substantially parallel to the circular side.

12. 3. The method of claim 1 or 2, wherein step (iii) comprises using one or more sonic waves to improve processing efficiency.

13. 3. The method according to claim 1 or 2, wherein the reaction mixture comprises the natural graphite and water in a weight ratio of 1:40 to 1:

300.

14. 3. The method of claim 1 or 2, wherein the reaction mixture consists of the natural graphite and the water.

15. 3. The method of claim 1 or 2, wherein the natural graphite is mined graphite, preferably the natural graphite is untreated graphite, preferably the natural graphite is uncrushed graphite, preferably the natural graphite has a carbon content of 75% to 95% by weight.

16. 1. A flow reactor for use in the purification of graphite, comprising: (a) a vessel for receiving a reaction mixture comprising natural graphite and water; (b) an activator that imparts rotational motion to the reaction mixture; (c) at least one input channel for introducing the reaction mixture into the vessel, the activator being rotatably mounted to a hollow tube providing the at least one input channel; A flow reactor comprising:

17. 17. The flow reactor of claim 16, further comprising one or more of the features of claim 2.

18. 1. An electrically conductive composition comprising graphite having a carbon content of at least 97.5%, wherein the conductive composition has an electrical conductivity greater than 60,000 S / m, and wherein the graphite is substantially free of added impurities.

19. 19. The conductive composition according to claim 18, wherein the carbon content of the graphite is 97.5 to 99.4 wt %.

20. 20. The conductive composition according to claim 18 or 19, comprising a mixture of graphite and graphene, preferably the conductive composition comprising up to 10 layers of graphite particles and graphene particles.

21. 20. The conductive composition according to claim 18 or 19, wherein the additional impurities are impurities introduced into the conductive composition or natural graphite during processing, preferably the additional impurities are metal impurities or hydrohalic acid impurities.

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