Patent Description:
Graphite electrode scrap is a residue in the steelmaking process. Indeed, Graphite electrodes scrap are used in electric arc furnaces (EAF). EAF is a furnace comprising the graphite electrodes that heats charged material, i.e. scraps, by means of an electric arc. After charging the EAF with scraps, the electrodes are lowered onto the scrap, an arc is struck and the electrodes are then set to bore into the layer of shred at the top of the furnace. Once the electrodes have reached the heavy melt at the base of the furnace and the arcs are shielded by the scrap, the voltage can be increased and the electrodes raised slightly, lengthening the arcs and increasing power to the melt.

The electrodes can be used several times but their life time is short. Usually, waste graphite electrodes scrap are open-air stored.

It is known to use the waste graphite electrodes are used to synthesize Graphene. Graphene is a single layer of Graphite consisting of carbons that are bonded together in a hexagonal honeycomb lattice. In other terms, it is an allotrope of carbon in the structure of a plane of sp<NUM> bonded atoms.

The patent <CIT> discloses a mechanical Exfoliation process. In this patent, the method for preparing graphene using a waste graphite electrode comprises following steps:.

However, the method for the manufacture of graphene comprises a multitude of steps. In particular, the pretreatment, purification and liquid phase stripping strengthening of the waste graphite electrode (step <NUM>) includes a multitude of sub-steps extending significantly the method duration. Indeed, the method pulverizing the surface layer into graphite powder with a particle size of <NUM> to <NUM>, and placing the graphite powder in a liquid phase purification stripping solution containing an aluminum ion salt formulated and added in a mass ratio of aluminum element to graphite powder of <NUM>:<NUM> to <NUM>:<NUM> to perform purification and stripping strengthening treatment, controlling the pH of the liquid phase purification stripping solution at <NUM> to <NUM> during the treatment process, after finishing the treatment, allowing the solution to stand and stratify, resulting in the upper layer which is a graphene-containing cloudy solution and the lower layer which is coarse graphite and insoluble impurity particles, and separating the upper layer and the lower layer to obtain the graphene-containing cloudy solution ready for use; to prepare graphene. Then, a centrifugation is performed. Finally, an intercalation step is performed using sodium, aluminum and fluorine as an intercalation reagent to intercalate the graphite. Thus, Graphite can be exfoliated to obtain graphene. This method, especially the pretreatment, purification and liquid phase stripping strengthening step, is very difficult to handle at industrial scale. Moreover, by applying this method, it is only possible to obtain graphene, no other materials such as graphene oxide since these compounds are completely different. The methods for producing graphene cannot be transposed to the method for manufacturing graphene oxide.

Graphene oxide is composed of one or few layers of graphene sheets containing oxygen functional groups. Thanks to its interesting properties such as a high thermal conductivity and a high electrical conductivity, graphene oxide has many applications as mentioned above. Moreover, the presence of oxygen functional groups make it hydrophilic and therefore it can be easily dispersed in water.

It is known to produce graphene oxide from Kish graphite. Kish graphite comprises a high amount of carbon, usually above <NUM>% by weight, it is a good candidate to produce graphene based materials.

The patent <CIT> discloses a method of manufacturing graphene oxide, comprising:.

In this Korean patent, the pre-treatment of Kish graphite comprises: a flushing process, a process of purification using a chemical pretreatment composition and a mechanical separation process (separation by size). After the process of purification, the purified Kish graphite is separated by size, the Kish graphite having a particle size of <NUM> mesh or less, i.e. <NUM> or less, is kept for the manufacture of graphene oxide.

However, the pretreatment of Kish graphite comprises <NUM> steps using a chemical composition: the flushing step and the process of purification step. In the Example of <CIT>, the flushing step is performed with an aqueous solution comprising water, hydrochloric acid and nitric acid. Then, the process of purification is performed with a pretreatment composition comprising a chelating agent, an iron oxide remover, a surfactant, an anionic and nonionic polymer dispersant and distilled water. At industrial scale, two chemical treatments are difficult to manage since a lot of chemical waste has to be treated and the stability of such composition is difficult to control.

Moreover, the pretreatment composition needs a long time preparation. The productivity is therefore slowed. Additionally, the pre-treatment of Kish graphite including the process of purification using the pretreatment composition is not environmentally friendly.

It is also known from the paper "<NPL>, that highly-oriented pyrolytic graphite, natural flake graphite, Kish graphite, flake graphite powder or artificial graphite can be oxidized by the Hummer method, expanded to form thermally expanded graphite oxide and then reduced in graphene.

Thus, there is a need to produce graphene oxide by an environmentally friendly method in a short time to increase the productivity compared to conventional methods.

Therefore, the purpose of the invention is to provide a less polluting method for the manufacture of graphene oxide compared to the conventional methods. Additionally, the object is to provide an industrial method to obtain graphene oxide having good quality in the shortest time possible.

This is achieved by providing a method according to claim <NUM>. The method can also comprise any characteristics of claims <NUM> to <NUM> taken alone or in combination.

To illustrate the invention, various embodiments and trials of non-limiting examples will be described, particularly with reference to the following Figures:.

The present invention relates to a method for the manufacture of graphene oxide from graphite electrode scrap comprising:.

Without willing to be bound by any theory, it seems that with the method according to the present invention, it is possible to produce graphene oxide from graphite electrode scrap without a long time preparation step of the graphite electrode. Indeed, the grinding (step B) followed by the chemical oxidation of the electrode allows for a more environmentally friendly method compared to the method of the prior art in a short time increasing the productivity of graphene oxide.

Preferably, in step B), the grinding is performed to obtain grinded graphite electrode having a size less than <NUM>, more preferably less than <NUM> and advantageously between <NUM> and <NUM>. Without willing to be bound by any theory, it is believed that when the grinded graphite electrode has the above size, the method productivity is further improved since the grinded graphite electrode is completely oxidize in a shorter time. Indeed, it seems that the grinded graphite electrode size can also have an impact on the method productivity, especially on the oxidation time, because the oxidizing agent can easily navigate between the graphite having the above size. So to obtain graphene oxide having a high oxygen percentage, there is a risk to increase the oxidation time when the electrode graphite size is outside the above range.

Preferably, in step C. i), the salt nitrate is chosen from: NaNOs, NH<NUM>NO<NUM>, KNO<NUM>, Ni(NO<NUM>)<NUM>, Cu(NO<NUM>)<NUM>, Zn(NO<NUM>)<NUM>, Al(NO<NUM>)<NUM> or a mixture thereof. More preferably, the salt nitrate is chosen from NaNO<NUM> and NH<NUM>NO<NUM>.

i), the acid is chosen from: H<NUM>SO<NUM>, HCl, HNO<NUM>, H3PO4, C2H2Cl2O2 (dichloroacetic acid), HSO2OH (alkylsulfonic acid) or a mixture thereof.

ii), the oxidizing agent is chosen from: potassium permanganate (KMnO<NUM>), H<NUM>O<NUM>, O<NUM>, H<NUM>S<NUM>O<NUM>, H<NUM>SO<NUM>, KNO<NUM>, NaClO or a mixture thereof. In a preferred embodiment, the oxidizing agent is potassium permanganate.

Preferably, the reaction is realized at a temperature below <NUM> or at room temperature.

Then, in step C. iii), when the targeted level of oxidation is reached, a chemical element is added to stop the oxidation. The targeted level of oxidation depends on the oxidation degree of graphene oxide, i.e. having at least <NUM>% by weight of oxygen groups according to the present invention. The level of oxidation of graphene oxide can be analyzed by scanning electron microscopy (SEM), X ray diffraction spectroscopy (XRD), Transmission electron microscopy (TEM), LECO analysis and/or Raman spectroscopy over time during the oxidation.

Then, in step C. iii), the chemical element used to stop the oxidation reaction is chosen from: an acid, non-deionized water, deionized water, H<NUM>O<NUM> or a mixture thereof.

In a preferred embodiment, when at least two elements are used to stop the reaction, they are used successively or simultaneously. Preferably, deionized water is used to stop the reaction and then H<NUM>O<NUM> is used to eliminate the rest of the oxidizing agent. In another preferred embodiment, H<NUM>O<NUM> is used to stop the reaction and eliminate the rest of the oxidizing agent. In another preferred embodiment, H<NUM>O<NUM> is used to stop the reaction by this following reaction:.

2KMnO<NUM> + <NUM><NUM>O<NUM> = 2MnO<NUM> + 3O<NUM> + 2KOH + <NUM><NUM>O.

Then, to eliminate MnO<NUM>, an acid can be used. For example, HCl is added to the mixture so that the following reaction happens:.

MnO<NUM> + 2HCl = MnCl<NUM> (soluble in water) + H<NUM>O.

Without willing to be bound by any theory, it seems that when the element to stop the reaction is added into the mixture, there is a risk that this addition is too exothermic resulting in explosion or splashing. Thus, preferably in step C. iii), the element used to stop the reaction is slowly added into the mixture obtained in step C. More preferably, the mixture obtained in step C. ii) is gradually pumped into the element used to stop the oxidation reaction. For example, the mixture obtained in step C. ii) is gradually pumped into deionized water to stop the reaction.

Optionally in step C. iv), graphite oxide is separated from the mixture obtained in step C. Preferably, the graphite oxide is separated by centrifugation, by decantation or filtration.

Preferably, in step C. v), the exfoliation is performed by using ultrasound, by mechanical agitator, by sieve shaker or thermal exfoliation. Preferably, the mixture obtained in step C. iii) is exfoliated by using ultrasound into one or a few layers of graphene oxide. Preferably, the lateral size of the graphene oxide is below <NUM>, preferably below <NUM>.

The obtained graphene oxide has good quality since it is produced from grinded graphite electrode scrap. The percentage of oxygen functionalities is high. Thus, the graphene oxide is easy dispersible in water and other organic solvents.

By applying the method according to the present invention, Graphene oxide comprising at least <NUM>% by weight of oxygen functional groups and having an average lateral size between up to <NUM> comprising at least one layer sheet is obtained.

<FIG> illustrates an example of one layer of graphene oxide according to the present invention. The lateral size means the highest length of the layer through the X axis, the thickness means the height of the layer through the Z axis and the width of the nanoplatelet is illustrated through the Y axis.

<FIG> illustrates an example of a few layers of graphene oxide according to the present invention. The lateral size means the highest length of the layer through the X axis, the thickness means the height of the layer through the Z axis and the width of the nanoplatelet is illustrated through the Y axis.

Preferably, graphene oxide is deposited on metallic substrate steel to improve some properties such as corrosion resistance of a metallic substrate.

In another preferred embodiment, graphene oxide is used as cooling reagent. Indeed, graphene oxide can be added to a cooling fluid. Preferably, the cooling fluid can be chosen from among: water, ethylene glycol, ethanol, oil, methanol, silicone, propylene glycol, alkylated aromatics, liquid Ga, liquid In, liquid Sn, potassium formate and a mixture thereof. In this embodiment, the cooling fluid be used to cool down a metallic substrate.

For example, the metallic substrate is selected from among: aluminum, stainless steel, copper, iron, copper alloys, titanium, cobalt, metal composite, nickel.

The invention will now be explained in trials carried out for information only. They are not limiting.

Trials <NUM> and <NUM> were prepared by providing graphite electrode scrap from steelmaking plant. Trials <NUM> and <NUM> were respectively grinded to have a size less than <NUM> and less than <NUM>.

After, Trials <NUM> and <NUM> were mixed with sodium nitrate and sulfuric acid. Potassium permanganate was slowly added into Trials <NUM> and <NUM>. The mixture was kept at around <NUM> using a cooling system. Then, the cooling process was stopped and the mixtures were heated until reaching <NUM> to oxidize the graphite electrode scrap. After the oxidation, Trials <NUM> and <NUM> were gradually pumped into deionized water.

Then, the heat was removed and H<NUM>O<NUM> in aqueous solution was added until there was no gas producing. MnO<NUM> was produced. HCl was added to the mixture to eliminate MnO<NUM>.

Then, graphite oxide was washed and separated from the mixture by decantation. Then, it was exfoliated using ultrasound in order to obtain one or two layer(s) of graphene oxide.

Finally, graphene oxide of was separated from the mixture by centrifugation, washed with water and dried with air.

Trial <NUM> is the disclosed Example prepared according to the method of the Korean patent <CIT>.

Results are shown in the following Table <NUM>:.

Claim 1:
Method for the manufacture of graphene oxide from graphite electrode scrap comprising:
A. The provision of scrap of graphite electrode used in electric arc furnaces,
B. The grinding of electrode graphite scrap to obtain grinded graphite electrode,
C. An oxidation step of the grinded graphite electrode to obtain graphene oxide comprising the following successive sub-steps:
i. The preparation of a mixture comprising the grinded graphite electrode, an acid and a nitrate salt, the mixture being kept at a temperature below <NUM>, the acid being chosen from: H<NUM>SO<NUM>, HCl, HNO<NUM>, H<NUM>PO<NUM>, C<NUM>H<NUM>Cl<NUM>O<NUM> (dichloroacetic acid), HSO<NUM>OH (alkylsulfonic acid) or a mixture thereof,
ii. The addition of an oxidizing agent, chosen from: potassium permanganate, H<NUM>O<NUM>, O<NUM>, H<NUM>S<NUM>O<NUM>, H<NUM>SO<NUM>, KNO<NUM>, NaClO or a mixture thereof, into the mixture obtained in step C.i) to obtain graphite oxide,
iii. After the targeted level of oxidation of at least <NUM>% by weight of oxygen functional groups is reached, the addition of a chemical element to stop the oxidation reaction, the chemical element being chosen from: an acid, non-deionized water, deionized water, H<NUM>O<NUM> or a mixture thereof,
iv. the separation of graphite oxide from the mixture obtained in step C.iii),
v. The exfoliation of graphite oxide into graphene oxide.