Preparation of isotropic spinnable pitch and carbon fiber by the bromination–dehydrobromination of biotar and ethylene bottom oil mixture

An isotropic pitch which has a relatively high softening point and an excellent spinnability for general performance carbon fiber was successfully prepared through the low-temperature co-carbonization with ethylene bottom oil (EO). The special bromination and dehydrobromination reaction of the mixed biotar and EO was adapted at a relatively low temperature for minimizing the phase separation of the two raw materials. The optimized reaction conditions for bromination and dehydrobromination were the heat treatments at 110 °C for 1 h with 20 wt% of Br2 addition and at 320 °C for 3 h under N2 atmosphere, respectively. After removal of volatile matters by thin layer evaporation at 350 °C, the target spinnable isotropic pitch, which has a relatively softening point of 205 °C and excellent spinnability, was successfully obtained with high synthetic yield of 45 wt%. The carbon fiber fabricated using the obtained isotropic pitch precursor showed an enormous tensile strength of 1200 MPa by heat treatment alone at 800 °C for 5 min.