Supercritical fluid process for producing graphene from coke or coal

1. A process for producing isolated graphene sheets from a supply of coke or coal powder containing therein domains of hexagonal carbon atoms and/or hexagonal carbon atomic interlayers with an interlayer spacing, said process comprising: (a) exposing said supply of coke or coal powder to a supercritical fluid at a first temperature and a first pressure for a first period of time in a pressure vessel and then (b) rapidly depressurizing said supercritical fluid at a fluid release rate sufficient for effecting exfoliation and separation of said coke or coal powder to produce said isolated graphene sheets; wherein said coke or coal powder is selected from the group consisting of petroleum coke, coal-derived coke, meso-phase coke, synthetic coke, leonardite, anthracite, lignite coal, bituminous coal, natural coal mineral powder, and a combination thereof wherein said coke or coal powder has never been previously intercalated or oxidized prior to step (a).

2. The process of claim 1 , wherein said supercritical fluid comprises a fluid selected from carbon dioxide, water, hydrogen peroxide (H 2 O 2 ), methanol, ethanol, acetone, methane, ethane, propane, ethylene, propylene, nitrous oxide (N 2 O), ozone, sulfonic group (SO 3 ), or a combination thereof.

3. The process of claim 1 wherein said depressurizing step is followed by a mechanical shearing treatment selected from air milling, air jet milling, wet milling, ball milling, rotating blade shearing, ultrasonication, or a combination thereof.

4. The process of claim 1 , further comprising a procedure of essentially repeating step (a) and step (b) that includes (i) subjecting said isolated graphene sheets to a supercritical fluid at a second temperature and a second pressure for a second period of time in a pressure vessel and then (ii) rapidly depressurizing said fluid at a fluid release rate sufficient for effecting further exfoliation and separation of graphene sheets.

5. The process of claim 4 , wherein said second temperature differs from said first temperature or said second pressure differs from said first pressure.

6. The process of claim 1 , wherein said supercritical fluid contains a surfactant or dispersing agent dissolved therein.

7. The process of claim 1 , wherein said pressure vessel further comprises a surfactant or dispersing agent selected from the group consisting of anionic surfactants, nonionic surfactants, cationic surfactants, amphoteric surfactants, silicone surfactants, fluoro-surfactants, polymeric surfactants, sodium hexametaphosphate, sodium lignosulphonate, poly (sodium 4-styrene sulfonate), sodium dodecylsulfate, sodium sulfate, sodium phosphate, sodium sulfonate, and combinations thereof.

8. The process of claim 1 , wherein said pressure vessel further comprises a surfactant or dispersing agent selected from melamine, ammonium sulfate, sodium dodecyl sulfate, sodium (ethylenediamine), tetraalkyammonium, ammonia, carbamide, hexamethylenetetramine, organic amine, pyrene, 1-pyrenecarboxylic acid, 1-pyrenebutyric acid, 1-pyrenamine, poly(sodium-4-styrene sulfonate), or a combination thereof.

9. The process of claim 1 , wherein said supercritical fluid comprises therein an organic solvent, a monomer, an oligomer, a polymer solution, or a combination thereof.

10. The process of claim 1 wherein said supercritical fluid further comprises a monomer or an oligomer dispersed in said fluid and said step (b) is followed by polymerization of said monomer or oligomer to form a polymer.

11. The process of claim 1 wherein said supercritical fluid comprises a coating agent dissolved therein.

12. The process of claim 11 , wherein said coating agent comprises a monomer, a prepolymer or oligomer, a polymer, a resin, a curing agent, or a combination thereof.

13. The process of claim 1 , wherein said supercritical fluid comprises a curing agent dissolved therein and the process further comprises mixing said isolated graphene sheets with a thermosetting resin to form a resin-graphene mixture.

14. The process of claim 13 , further comprising a step of curing said resin-graphene mixture into a composite material.

15. The process of claim 1 , wherein said supercritical fluid comprises a reactive chemical group and said step (a) imparts said reactive chemical group to said isolated graphene sheets.

16. The process of claim 1 , wherein said process is conducted intermittently or continuously and said supply of coke or coal powder and supercritical liquid are provided into said pressure vessel intermittently or continuously.

17. A process for producing isolated graphene sheets from a supply of coke or coal powder containing therein domains of hexagonal carbon atoms and/or hexagonal carbon atomic interlayers with an interlayer spacing, said process comprising: (a) exposing said supply of coke or coal powder to a supercritical fluid at a first temperature and a first pressure for a first period of time in a pressure vessel and then (b) rapidly depressurizing said supercritical fluid at a fluid release rate sufficient for effecting exfoliation and separation of said coke or coal powder to produce said isolated graphene sheets; wherein said coke or coal powder is selected from the group consisting of petroleum coke, coal-derived coke, needle coke, synthetic coke, leonardite, anthracite, lignite coal, bituminous coal, natural coal mineral powder, and a combination thereof, wherein said step (a) is conducted under the influence of ultrasonic waves.

18. The process of claim 17 , wherein said supercritical fluid comprises a fluid selected from carbon dioxide, water, hydrogen peroxide (H 2 O 2 ), methanol, ethanol, acetone, methane, ethane, propane, ethylene, propylene, nitrous oxide (N 2 O), ozone, sulfonic group (SO 3 ), or a combination thereof.

19. The process of claim 17 , wherein said pressure vessel further comprises a surfactant or dispersing agent selected from the group consisting of anionic surfactants, nonionic surfactants, cationic surfactants, amphoteric surfactants, silicone surfactants, fluoro-surfactants, polymeric surfactants, sodium hexametaphosphate, sodium lignosulphonate, poly (sodium 4-styrene sulfonate), sodium dodecylsulfate, sodium sulfate, sodium phosphate, sodium sulfonate, melamine, ammonium sulfate, sodium dodecyl sulfate, sodium (ethylenediamine), tetraalkyammonium, ammonia, carbamide, hexamethylenetetramine, organic amine, pyrene, 1-pyrenecarboxylic acid, 1-pyrenebutyric acid, 1-pyrenamine, poly(sodium-4-styrene sulfonate), and combinations thereof.

20. The process of claim 17 , wherein said supercritical fluid further comprises an organic solvent, a monomer, a prepolymer, an oligomer, a polymer solution, a resin, a curing agent, or a combination thereof.

21. The process of claim 17 , wherein said supercritical fluid comprises a reactive chemical group and said step (a) imparts said reactive chemical group to said isolated graphene sheets.