Hydroprocessing severity, conversion

Figure 7. Polar asphaltenes conversion as a function of hydroprocessing severity o Harshaw 618X, (A) Amocat IB, (V) Mobil HCL12, ( O) HDS-1443...

The cracking of the BMO gave a poor result mainly due to the low H/C-ratio (see Table III). Hemler and Wilcox (29,30) catalytically cracked coal liquids, hydroprocessed at different severities, and found that the conversion increased and the selectivity improved with increasing severity of hydroprocessing. Hydroprocessing the BMO at more severe conditions should improve the cracking properties of this oil. 

The chemical character of the unconverted asphaltenes is also a function of processing. Both the H/C and O/C atomic ratios declined in a regular manner as conversion progressed. In some cases, the oxygen content was reduced to that typically found for pentane-soluble oils (about 2%). At the same time, the atomic H/C ratio of the residual asphaltenes was reduced to values considerably lower (<0.7) than that of the coal. The relative oxygen content may be used as a crude indicator of the severity of hydroprocessing experienced by a particular asphaltene. 

In the past few years the residue hydrodesulfiirization process has gone through a number of changes. Deeper desulfurization and more conversion to mid-distillate have become a primary target for several units. At the same time, heavier residues are being processed. To address these and other questions, Nippon Ketjen has developed a new series of resid catalysts, viz. the KFR series. The two most common modes of resid hydroprocessing applied on commercial scale, are illustrated with pilot plant test data and data from commercial units. 

Sulfur Sulfur is present in all lube plant feedstocks fractionated from crude oil and its content may be up to several percentage points. Solvent refining removes some but not all, therefore such stocks with no further treatment can contain up to several mass percent of sulfur. Hydrofinishing of solvent refined stocks can reduce this level substantially. Base stocks from conversion processes will have sulfur levels in the low parts per million (ppm) range since sulfur is relatively easily removed in severe hydroprocessing. 

Because several hydroprocessing reactors operate in the pulse regime, we need experience in the application of the above-mentioned models in this range. The same is true for the modeling of nonisothermal gas/liquid catalytic reactors, where the chemical conversion is accompanied by the evolution of a considerable amount of heat, causing either a heat flux to reactor walls or the evaporation of an important part of the liquid phase. 

The combination of extraction and hydroprocessing is a very efficient route to basestocks needed for GF-3 quality. Extraction alone is inappropriate because of an inability to selectively remove multiring naphthenes (these tend to be split evenly between the raffinate and extract phases). Yields by extraction to the same basestock property levels may be less than half of that achieved by RHC . Also, VGO hydrocracking, i.e. with no pre-extraction step, requires more severe conditions and has potentially lower yields than RHC because of the higher conversion needed to offset the highly negative VI characteristics of refiiactory multi-ring species present in the distillate feed. 

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