Effects of decompressing carbonization on the preparation of needle coke from FCC decant oil

Abstract

More efficient treatments of FCC decant oil (FDO) were developed to convert this common by-product in refineries to high-value-added carbonaceous materials, such as needle coke. The performance of the produced needle coke was determined by the properties of raw materials and the carbonization process based on the theories of carbonaceous mesophase. The preparation of needle coke can generally be divided into two stages before calcination and graphitization: liquid carbonization and solidification stage. Pressure in both stages, especially the pressure in the solidification stage, showed great effects on the properties of the products. The microstructure of semi-coke can hardly be the preferred needle structure with carbonization without decompressing operation, although the raw material satisfies the preparation requirement of needle coke. A new method for evaluating the order degree of microstructure (ODM) of semi-cokes was developed, enabling semi-cokes with preferable axial orientation to be further efficiently distinguished. The ODM value can also be used as an index to evaluate whether a semi-coke can be used as a precursor for further preparation of high-quality needle coke. The evolution of product gases can provide external force to the orientation of mesophase into the preferred needle structure in the product. This improvement can be achieved through decompressing operations in the second stage of carbonization and optimized when the pressure is at 0.5 MPa.