Structure of toluene insoluble coal tar heavy fraction and its relevance to the coking behavior in slurry-bed hydrocracking

The hydrogenation of coal tar atmospheric residue (CTAR) was conducted in a slurry-bed hydrocracking pilot plant with a 3000mL loop reactor; the toluene insoluble (TI) fraction and coke were separated from CTAR and hydrogenation product, respectively. The properties of TI and coke were analyzed by means of element analysis, SEM, XRD, FT-IR and XPS; the relevance of TI structure to the coking behavior in the hydrogenation process was then investigated. The results show that the slurry-bed hydrocracking of CTAR has the features of high light oil yield, little coke, and almost no coke on the reactor surface. TI consists of carbonaceous, mineral particles and polycyclic aromatic hydrocarbons originated from the coal tar production process. O is the dominant heteroatom, whereas Ca, Si, Al, and Na are derived from minerals in CTAR. Furthermore, C and O are mainly present as C-C, C-H, C-O-C and C-OH, whereas N-containing groups appear as pyrrole and amine and S is mainly in the form of aliphatic sulfur. Obviously, TI has a layered stack structure, which can be easily broken to smaller carbonaceous and mineral particles (several microns) with larger specific surface area and adsorption capacity. These particles, together with the sulfurized catalyst, act as the coke centers, which are effective to adsorb macromolecular radicals and then reduce the opportunity of coking on the reactor surface.