Effects of Molecular Composition and Carbonization Reactivity of FCC Decant Oil and Its Derivatives on Mesophase Development

Introduction FCC decant oil is the primary feedstock to delayed coker to produce needle coke, a premium carbon precursor to synthetic graphite electrodes. Mesophase development during coking, determines the graphitizability of the needle coke product. Mesophase development, in turn, depends on the molecular composition of the feedstocks [1,2]. In a commercial delayed coking unit, liquid-phase carbonization (coking) takes place in insulated coke drums as the feed, heated in a tubular furnace, flows upward in the drums [3]. Liquid products from delayed coking are separated into light and heavy oils by distillation in a fractionator. Fresh feed (typically decant oil) is also fed to the fractionator. The furnace charge (coker feed) comes from the bottom of the fractionator that includes the heavy ends of both fresh feed and liquid products from coking. Most studies on delayed coking have used FCC decant oil as the feedstock material, although the actual coker feed may have a very different composition from that of the parent decant oil. The objective of this study is to analyze the molecular composition of the coker feeds as compared to the parent decant oils. Laboratory carbonization experiments were carried out on the decant oil and coker feed samples as well as on the bottom and top fraction (gas oil) of the decant oils separated by vacuum distillation. Samples of hydrotreated gas oil were also carbonized under comparable conditions. Semi-coke and asphaltene yields from the carbonization experiments were determined to compare the carbonization reactivity of different samples. Mesophase development was monitored by polarized-light microscopy of semi-coke samples.