Methods to produce carbon fibers from carbon pitches

A process for preparing carbon fibers, the process comprising:

• (a) converting coal to a low-softening point carbon pitch;
• (b) extruding the pitch into carbon fibers;
• (c) adding a graphite/graphene sheath to the carbon fibers;
• and
• (d) calcining the carbon fibers;
• wherein the coal is selected from bituminous, sub-bituminous, lignite, and combinations thereof;
• wherein the pitch is an anisotropic mesophase carbon pitch;
• wherein the converting the coal to a low-softening point carbon pitch comprises air oxidation until a softening point from about 295° C. to about 350° C. is achieved, thereby yielding a low-softening point carbon pitch having a softening point from about 295° C. to about 350° C.;
• wherein the pitch is heated to a first temperature for extrusion;
• wherein the first temperature is from about 295° C. to about 345° C.;
• wherein the carbon fibers have a diameter from about 5 μm to about 10 μm;
• wherein the graphite/graphene sheath comprises a layer on the outside of the carbon fibers having a thickness from about 1 μm to about 2 μm;
• wherein the adding the graphite/graphene sheath to the carbon fibers comprises mixing graphite and/or graphene with the low-softening point carbon pitch prior to extrusion;
• and
• wherein the graphite and/or graphene is added to the low-softening point carbon pitch in a ratio equal to the thickness of the graphite/graphene layer to the desired cross-sectional area of the carbon fiber.