Carbonization in the tube bomb leading to needle coke: I. Cocarbonization of a petroleum vacuum residue and a FCC-decant oil into better needle coke

Abstract

The cocarbonization of a Fluidized Catalytic Cracking decant oil (FCCDO) with a petroleum low sulfur vacuum residue (LSVR) was studied at a temperature range of 460 to 480°C by evaluating the qualities of coke lumps produced in a tube bomb in terms of their CTE and anisotropic development. The cocarbonization certainly improved the orientation of flow texture and CTE of the resultant coke, providing the smallest CTE as low as 0.10 × 10 −6/° C and 0.36 × 10 −6/° C at particular FCCDO/LSVR mixing ratios of 5 5 and 7 3 according to the respective carbonization temperatures of 460 and 480°C. The natures of bulk mesophase and gas evolution at the solidification stage for the axial-rearrangement of mesophase aromatic component, both of which essentially define the coke quality, are strongly influenced by the carbonization reactivities of blended feedstocks and carbonization conditions. FCCDO may moderate the carbonization progress of reactive LSVR and LSVR supply the sufficient gas evolution during the solidification, leading to excellent flow texture of axial arrangement. The formation of mosaic coke in the bottom part of the lump which may deteriolate the quality of the coke produced in a commercial coker appeared to be caused by the phase separation between the paraffin and asphaltene fractions. Such a separation at a early stage of the carbonization was found to be controlled by the blending and the carbonization conditions.