Dissecting the cohesiveness among aromatics, saturates and structural features of aromatics towards needle coke generation in DCU from clarified oil by analytical techniques

Abstract A comprehensive study relating structural parameters of carbonaceous feedstock with quality of produced needle coke in delayed coker unit (DCU) has been carried out. The used feedstock, clarified oil (CLO), was studied by various analytical techniques; the results of which was then correlated with needle coke properties. The average structural parameters of CLO as determined by q-1H and q-13C NMR, class-wise distribution of aromatics by HPLC-PDA-ELSD and molecular weight distribution (MWD)-cum-estimation of individual components possessing high needle coke potential from HRMS provided in-depth understanding about the science of maintaining balance between reactivity and fluidity during needle coke production. It was observed that presence of an optimal amount of saturates and all of mono-, di-, tri-, tetra-, penta- aromatics in an optimum ratio help producing good quality needle coke. The study also reveals that while the presence of methyl-substituted aromatics and multimodal MWD are desirable, presence of long chain-substituted aromatics, heteroatoms, non-linear polyaromatics with high bay regions and uniformity in MWD are detrimental to a better mesophase formation and uni-axial rearrangement of molecules during delayed coking process. The quality of needle coke was determined, in addition to CTE values, by crystallinity index using XRD and SEM analysis. Few compositional features of CLO that appears to be critical in determining needle coke character are listed to rate them for their needle coke potential.