Method for producing carbon fiber

A method for producing a carbon fiber, comprising:

• mixing a copolymer solution of acrylonitrile copolymer consisting of an acrylonitrile monomer, a comonomer, an initiator and a solvent, and performing a polymerization, so as to obtain an acrylonitrile copolymer, wherein the acrylonitrile monomer includes impurities comprising water, methylpropenenitrile, propionylnitrile, oxazole, 4-methoxyphenol, butenone, iron, copper and (meth)acrylic acid alkyl ester, based on a weight of the acrylonitrile monomer as 100 weight percent (wt. %), a content of the acrylonitrile is more than 99.93 wt. %, and based on the content of the acrylonitrile monomer as 1×106 ppm, a content of the water is more than or equal to 48 ppm and less than 70 ppm, a content of the methylpropenenitrile is less than 2 ppm, a content of the propionylnitrile is less than 1 ppm, a content of the oxazole is less than 2 ppm, a content of the 4-methoxyphenol is less than 40 ppm, a content of the butenone is less than 2 ppm, a content of the iron is less than 0.001 ppm, a content of the copper is less than 0.002 ppm, and a content of the (meth)acrylic acid alkyl ester is less than 1 ppm;
• and based on a total weight of the acrylonitrile monomer and the comonomer as 100 wt. %, a content of the comonomer is 0.2 wt. % to 2.0 wt. %, and a content of the initiator is not more than 0.1 wt. %;
• performing a spinning operation on the acrylonitrile copolymer, so as to obtain a raw filament of the acrylonitrile copolymer, wherein a falling-ball viscosity of the acrylonitrile copolymer is 620 seconds to 650 seconds, and a molecular weight distribution of the acrylonitrile copolymer is less than 2.2;
• performing a stretching operation on the raw filament of the acrylonitrile copolymer, so as to obtain a carbon fiber precursor;
• performing an oxidation treatment on the carbon fiber precursor, so as to obtain an oxidized fiber;
• and
• performing a carbonization treatment on the oxidized fiber, so as to obtain the carbon fiber.