Study on Mechanism of Formation and Quality Improvement of Petroleum-based Needle Coke.

Abstract

Needle coke which has been the best filler of graphite electrodes need to be upgraded because the quality of graphite electrodes for electric arc furnace is improved with progress of steel making technique.The role of respective feedstock based on mechanism of formation of needle coke is overviewed in terms of pretreatment of the feedstocks, such as modification of FCC decant oil (FCCDO), solvent deasphaltene process, and heat treatment of low sulfur vacuum residue (LSVR), to improve the characteristics of the needle coke.The mechanism of formation of needle coke is traced through the observation of the carbonization process using tube bomb which can provide nearly the same condition as delayed coker. Coefficient of thermal expansion (CTE), which is the most important property of needle coke, is strongly influenced by uni-axial orientation of flow texture in the coke. Gas evolution of solidification, therefore, is important for production of low CTE coke as well as formation of bulk mesophase. The carbonization condition, especially pressure and temperature, influences the above important factor. Furthermore, the cocarbonization of LSVR with FCCDO produced excellent needle coke of low CTE because formation of bulk mesophase and gas evolution at solidification were improved. As the amount of mosaic coke of high CTE affects the CTE of needle coke, in the present study, the modification of FCCDO and LSVR was studied to eliminate the formation of mosaic coke.Addition of high aromatic pitch, dewaxing and heat treatment were highly effective for elimination of mosaic coke by modification of FCCDO. On the other hand, elimination of asphaltene by solvent extraction and heat treatment with hydrogen donor were highly effective as modification of LSVR.