Preparation of pitch-based carbon fiber from medium coal tar pitch refined by wash oil

Abstract

The composition and structure of spinnable pitch was always the key issue of pitch-based carbon fiber preparation, with the foundation step of coal tar pitch purifying. In this work, wash oil was chosen as refining solvent due to its aromatic properties, compared with tetrahydrofuran (THF). Two isotropic spinnable pitches (WO-SP and THF-SP) were prepared by air-blowing of refined pitches, with similar elementary compositions, soften points (250 ℃) and aromaticity, but WO-SP displayed a slower descent of viscosity with temperature rising, which was related to the molecular weight distribution and aromatic structure. The main aromatic components of pitches/spinnable pitches were determined by using fluorescence excitation-emission spectroscopy with parallel factor analysis (EEM-PARAFAC), combined with a stepwise extraction and mass spectrometry analysis. Difference between WO-SP and THF-SP mainly lied in 9.16 wt% more proportion of components with molecular weight > 600 Da in the THF-soluble fraction of WO-SP, forming less pyrene-like structure (four fused rings) and more structure bigger than benzo[g,h,i]perylene (six fused rings). Meanwhile, WO-SP had 9.6 wt% more content of large quinoline-soluble components than THF-SP, with little aromatic structures smaller than five fused rings. These characteristics made carbon fiber from WO-SP with a better tensile strength of 790 ± 37 MPa and a tensile modulus of 40.8 ± 3.2 GPa, than that from THF-SP. Therefore, wash oil could be a promising refining solvent, and increasing the content and large aromatic structure of high molecular weight component in spinnable pitch was beneficial for improvement of carbon fiber performance.