Two-step sulfonation process for the conversion of polymer fibers to carbon fibers
Disclosed herein are processes for preparing carbon fibers, comprising: sulfonating a polymer fiber with a sulfonating agent that is fuming sulfuric acid, sulfuric acid, chlorosulfonic acid, or a combination thereof; treating the sulfonated polymer with a heated solvent, wherein the temperature of the heated solvent is at least 95° C.; and carbonizing the resulting product by heating it to a temperature of 501-3000° C. Carbon fibers prepared according to these methods are also disclosed herein.
1. Processes for preparing carbonized polymers, comprising
a) treating a polymer in a first vessel with a solution comprising a sulfonating agent that is fuming sulfuric acid, -chlorosulfonic acid, or a combination thereof at a temperature below the boiling temperature of the sulfonating agent to form a sulfonated polymer, wherein the concentration of the sulfonating agent is from 0.1 to 30 percent;
b) treating the sulfonated polymer in a second vessel with a heated solvent comprising sulfuric acid, wherein the temperature of the heated solvent is from 95° C. to 180° C.; and
c) carbonizing the resulting product by heating it to a temperature of 500-3000° C.
2. Processes according to claim 1 , wherein the sulfonating agent comprises chlorosulfonic acid.
3. Processes according to claim 1 , wherein the sulfonating agent comprises fuming sulfuric acid.
4. Processes according to claim 3 , wherein the fuming sulfuric acid is 0.1-70% fuming sulfuric acid.
5. Processes according to claim 1 , wherein the polymer consists of polyethylene or comprises a copolymer of ethylene.
6. Processes according to claim 5 , wherein the copolymer of ethylene is an ethylene/octene copolymer, an ethylene/hexene copolymer, an ethylene/butene copolymer, or a combination of two or more thereof.
7. Processes according to claim 1 , wherein the heated solvent is at a temperature of at least 100° C.
8. Processes according to claim 1 , wherein the heated solvent is sulfuric acid at 100-180° C.
9. Processes according to claim 1 , wherein the sulfonation reaction is performed at a temperature of 0-140° C.
10. Processes according to claim 1 , wherein the sulfonation is conducted while the polymer is a polymer fiber, and the polymer fiber is under a tension of 0-35.5 MPa, the treatment with a heated solvent is conducted while the polymer fiber under a tension of 0-25 MPa, or carbonization is conducted while the polymer fiber is under a tension of 0-8.8 MPa.
11. Processes according to claim 1 , wherein the sulfonation, the treatment with a heated solvent, and the carbonization are performed while the polymer is under a tension greater than 1 MPa.
12. Processes according to claim 10 , wherein the tension during the carbonization step differs from that in the sulfonation step.
13. Processes according to claim 1 , wherein the carbonization step is performed at temperatures of from 700-1,500° C.
14. Processes according to claim 1 , comprising:
a) sulfonating a polyethylene containing polymer in a first vessel with fuming sulfuric acid, wherein the sulfonation reaction is performed at a temperature of from 35-140° C. to form a sulfonated polymer;
b) treating the sulfonated polymer in a second vessel with a protic and/or polar solvent, wherein the temperature of the solvent is 100-180° C.; and
c) carbonizing the resulting product by heating it to a temperature of 500-3000° C.;
wherein at least one of steps a), b) and c) is performed while the polymer fibers are under tension.
15. Processes according to claim 14 , wherein the protic and/or polar solvent is a mineral acid.
16. Processes according to claim 14 , wherein the polyethylene containing polymers are polyethylene homopolymers or polyethylene copolymers that comprise an ethylene/octene copolymers, ethylene/hexene copolymers, ethylene/butene copolymers, ethylene/propylene copolymers, ethylene/styrene copolymers, ethylene/butadiene copolymers, a mixture of one or more homopolymers and one or more polyethylene copolymers, or a combination of two or more polyethylene homopolymers.
17. Processes according to claim 14 , wherein the protic and/or polar solvent is sulfuric acid at a temperature of 115-160° C.
18. Processes according to claim 14 , wherein steps a), b) and c) are performed while the polymer is under a tension greater than 1 MPa.
19. Processes for preparing carbonized polymers, comprising
a) treating a polymer in a first vessel with a sulfonating agent that is fuming sulfuric acid, -chlorosulfonic acid, or a combination thereof to form a sulfonated polymer;
b) treating the sulfonated polymer in a second vessel with a heated solvent consisting of sulfuric acid, wherein the temperature of the heated solvent is at least 95° C.; and
c) carbonizing the resulting product by heating it to a temperature of 500-3000° C.