Study On Structure And Composition Of Coke On Spent Catalysts Of Commercial Fixed-bed Residue Hydrotreating Unit

At present, as one of the most important processing methods, fixed-bed hydrotreating united processing residue has significant impression both on increasing yield of light oil and reducing air pollution. A lot of asphaltene and polycyclic aromatic compounds deposited coke on the catalyst with polymerization, deactivating catalysts seriously. There will be nothing more important than the coke which deposited on catalysts can lead catalysts inactivation. To research of construction and component of coke on spent catalysts will be benefit for learning deactived reasons, choosing and improving reaction materials and optimizing operational conditions.In order to study structure and composition of coke on spent catalysts used for fixed-bed hydrotreating unit processing residue, many kinds of advanced instrumental analysis methods are used, such as element analysis（EA）, thermogravimetry（TG）, X-ray photoelectron spectroscopy（XPS）, fourier transform infrared spectroscopy（FTIR） and 13 C solid nuclear magnetic resonance(¹³C NMR). Among them, 13 C NMR has a great outstanding contribution in studying chemical structure of the solids.The EA experiment of a series of hydrotreating catalysts found that nonmetal element N have a stable content while element S have a relatively high content and don’t show any regulation. This result refers to the coke on spent catalysts used for fixed-bed hydrotreating unit processing residue is the substance which has a relatively stationary structure, composition and origin. As for the high content of element S, it is because that the presulfurization is an essential process before hydrotreating catalysts used, in order to improve reactivity of them. Experiments of TG-DTG can show us the relatively composition of coke. Catalysts HDM have three obvious degradation stages while catalysts HDS, HDN and HG only have two. This situation is caused by the content of hard coke; HDM has a great deal of hard coke content and the coke on other three spent catalysts is mainly soft coke.It can conclude that catalysts HDM have the highest content of graphitized carbon by studying C1 s XPS of all kinds of catalysts. This conclusion can consistent with the study of TG-DTG. Meanwhile, the relative contents of C-S and C-N in XPS spectrograms are in line with EA experiments. FTIR is the most efficient and convenient method so it can be used in analyzing the structure and composition of coke. The FTIR spectrograms show that the coke on this series of spent catalysts share the similarity in functional group; the same wavenumber can attribute to the same functional group.¹³C NMR has great advantage in analyzing chemical structure of the solids. We can obtaine the relative contents of different structural units of coke by using NMR software to overlap peak resolve of NMR spectrograms, and then we can speculate the chemical structure of coke based on these data. The other computer software g NMR can calculate and stimulate theoretical NMR spectrogram and compare with the experiment ones, owing to this technology, chemical structure of coke can be revised and its accuracy can be improved. The coke on spent catalysts contains a large quantity of aromatic hydrocarbon and little aliphatic hydrocarbon. Among these four kinds of catalysts, HDM has the highest polymerization degree; this may be caused by the large content of hard coke in HDM and this conclusion agrees with TG-DTG.