Enhanced self-sintering mechanical strength of carbon blocks via removal of light molecular-weight compound in green petroleum coke

Abstract

Self-sintering of green petroleum coke (GPC) offers a critical approach to prepare high performance carbon blocks owing to its remarkable homogeneity and high stability. However, the volatilization of small molecular fractions in green coke inevitably results in the formation of pores and cracks, thus severely limiting its commercial application. Herein, the GPC is divided into two soluble fractions with different molecular weight distribution, including dichloromethane-soluble (DCMS, 560.76 m/z) and dichloromethane-insoluble-toluene-soluble (DCMI-TS, 624.39 m/z), by sequential extraction with dichloromethane (CH2Cl2) and toluene based on processes of ultrasonic accompanying with continuous mechanical stirring for 4 h aging for 24 h and stirring at 130 ℃ for 4 h, respectively. All compounds extracted from GPC were further investigated via various characterizations, such as chromatography, ESR, elemental analysis, thermogravimetry, mass spectrometry, NMR, UV–Visible and FTIR, to verify their molecular weight distributions, chemical compositions, and reactivities. While DCMS contains long alkyl side chains, there are more naphthenic and oxygen-containing compounds and plasticizer species e.g. dibutyl phthalate in DCMI-TS. Thanks to the removal of volatile small molecular, when the solvent purified GPC were employed as precursor, the obtained carbon block (DCMI-C) demonstrates an apparent density of 1.48 g·cm−3, which is obviously higher than that of pristine GPC-C (1.34 g·cm−3). 1.7 times larger flexural strength, as well as 1.9 times higher compressive strength is found for DCMI-C compared to GPC-C, indicating that the DCM soluble compounds are the mainly reason for microcracks and pores generation. In addition, a much more compacted pore structure, as reflected in SEM images, is also observed in DCMI-C implying its remarkable mechanical intensity. Impressively, plasticizer species can also promote the self-sintering behavior of the green body where an enhanced mechanical property was achieved when 2 % dibutyl phthalate was added into DCMI mixtures.