Asphaltenic sulfur

Feedstocks. Feedstocks are viscous aromatic hydrocarbons consisting of branched polynuclear aromatics with smaller quantities of paraffins and unsaturates. Preferred feedstocks are high in aromaticity, free of coke and other gritty materials, and contain low concentrations of asphaltenes, sulfur, and alkah metals. Other limitations are the quantities available on a long-term basis, uniformity, ease of transportation, and cost. The abiUty to handle such oils in tanks, pumps, transfer lines, and spray nozzles are also primary requirements. 

Combifining A petroleum refining process which removes asphaltenes, sulfur, and metals from residues, before further treatment. The catalyst is an activated petroleum coke in a fluidized bed, operated under hydrogen pressure at 380 to 420°C. 

Consideration of Catalyst Pore Structure and Asphaltenic Sulfur in the Desulfurization of Resids... 

Table III extends the comparison of these resids with an emphasis on reactivity, asphaltene characteristics, compound types and the refractory forms of sulfur, such as benzothiophenes and asphaltenic sulfur.

However, before considering the fate of asphaltenic sulfur at high reactor severities, some patent aspects of catalyst pore structure would be of interest. Table IV shows a divergence of opinion as to the desirability of asphaltene exclusion. 

CHANGE IN PRODUCT COMPOUND TYPE AND ASPHALTENIC SULFUR CONTENT WITH CONVERSION LEVEL... 

The removal of metals with the asphaltenic sulfur is observed in Figure 4. This response is consistent with an asphaltene model in which vanadium and nickel are buried as porphyrins or sandwich compounds (9). The slightly higher removal of vanadium reflects a general tendency for vanadium to deposit on the catalyst more readily than nickel. 

For lower conversions levels, where asphaltenic sulfur removal is not deep, refractoriness appears to be largely influenced by a large proportion of sterically hindered aromatic sulfur compounds. Substituted thiophenes, benzothiophines and di-benzothiophenes are representative compounds. 

Asphaltenic sulfur is the most refractory specie in re-sids and the removal of metals, particularly nickel, correlates well with removal of asphaltenic sulfur. 

Nevertheless, the development of general kinetic data for the hydrodesulfurization of different feedstocks is complicated by the presence of a large number of sulfur compounds each of which may react at a different rate because of structural differences as well as differences in molecular weight. This may be reflected in the appearance of a complicated kinetic picture for hydrodesulfurization in which the kinetics is not, apparently, first order (Scott and Bridge, 1971). The overall desulfurization reaction may be satisfied by a second-order kinetic expression when it can, in fact, also be considered as two competing first-order reactions. These reactions are (1) the removal of nonasphaltene sulfur and (2) the removal of asphaltene sulfur. It is the sum of these reactions that gives the second-order kinetic relationship. 

Orr W. (1986) Kerogen/asphaltene/sulfur relationships in sulfur rich Monterey oils. Org. Geochem. 10, 499-516. 

Place/country of appearance bitumen content (%) Saturated hydrocarbons (%) Aromatic hydrocarbons (%) Resins (%) Asphaltenes (%) Sulfur content (%)... 

Table 1.3 presents the elemental analysis of asphaltenes. The calculated asphaltenic sulfur content and different atomic ratios are also reported. The amount of asphaltenic sulfur follows the trend observed in the case of nickel, the heavier the crude oil the higher the amount of asphaltenic S and Ni. This trend indicates that the amount of sulfur in the crude oil mainly corresponds to that present in the asphaltenes. 

Needle Grade Coke, which is produced from highly aromatic with low asphaltenes, sulfur, and ash content feedstocks. This coke, with high strength and low coefficient of thermal expansion, is used to manufacture large electrodes for the steel industry and the production of synthetic graphite. 

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