Method for forming carbon fibers

A process of continuously forming carbon fibers in a reactor by the steps consisting of:

• a) forming a mixture consisting essentially of a gaseous hydrocarbon, a compound decomposable to form iron nucleation sites, a gaseous sulfur-containing compound and ammonia, and flowing the mixture through the reactor at a first pressure;
• the hydrocarbon being selected from the group consisting of methane, natural gas having a methane content of at least 90 volume percent, and mixtures thereof, the hydrocarbon and the ammonia each being present in an amount sufficient to provide a ratio of carbon atoms (C) to nitrogen atoms (N) in a range of about 1:1 to about 3:1;
• b) heating the mixture in the reactor for a time and at a temperature sufficient to cause decomposition of the decomposable compound to form particles of nanometer size iron nucleation sites dispersed and entrained in the gaseous mixture which induce growth of carbon fibers and to thereby form carbon fibers having an average diameter of about 0.05 to about 0.5 micron and containing carbon and nitrogen;
• and
• c) intermittently interrupting the flow of the mixture of step (a) and, during the interruption, flowing an inert gas selected from the group consisting of helium, argon, and nitrogen through the reactor at a pressure sufficient to forcibly move at least a portion of any of the fibers plugging the reactor out of the reactor, and then flowing an oxygen-containing gas through the reactor for a time and at a temperature sufficient to oxidize at least a portion of any unreacted or partially reacted material in the reactor;
• and
• d) recovering the fibers formed in the reactor.

A process of continuously forming carbon fibers in a reactor by the steps consisting of:

• a) forming a mixture consisting essentially of a gaseous hydrocarbon, a compound decomposable to form iron nucleation sites, a gaseous sulfur-containing compound and ammonia, and flowing the mixture through the reactor at a first velocity;
• the hydrocarbon being selected from the group consisting of methane, natural gas having a methane content of at least 90 volume percent, and mixtures thereof, the hydrocarbon and the ammonia each being present in an amount sufficient to provide a ratio of carbon atoms (C) to nitrogen atoms (N) in a range of about 1:1 to about 3:1;
• b) heating the mixture in the reactor for a time and at a temperature sufficient to decompose the decomposable compound to form particles of nanometer size iron nucleation sites dispersed and entrained in the gaseous mixture which induce growth of carbon fibers and to thereby form carbon fibers having an average diameter of about 0.05 to about 0.5 micron and containing carbon and nitrogen;
• c) changing the velocity of the flowing mixture with the particles entrained therein to a second velocity less than the first velocity to enhance fiber growth on the particles;
• d) intermittently interrupting the flow of the mixture of step (a) and, during the interruption, injecting one or more pulses of air through the reactor at a pressure sufficient to forcibly move at least a portion of any of the fibers plugging the reactor out of the reactor, and for a time at a temperature sufficient to oxidize at least a portion of any unreacted or partially reacted material in the reactor;
• and
• e) recovering the fibers formed in the reactor.