Desulfuration preferential

Absorption, in which a liquid solvent is used to remove certain compounds from a gas by virtue of their preferential solubility. Examples of absorption involve desulfurization of flue gases using alkaline solutions or ethanolamines,... 

NiMo and NiW formulations have succeeded in desulfurizing the sterically hindered compounds, by fully hydrogenating at least one of the lateral rings, facilitating their elimination. From this point of view, the need for a high hydrogenation activity when producing ultra-low sulfur fuel is explained. Consequently, the preferential application of a Ni-Mo(W) for the manufacture of ULS fuels can be easily understood, as well. 

Partial fluorination of 4-arylthio-l,3-dioxolan-2-ones occurs preferentially at the carbon atom adjacent to the thio group [67]. However, a remarkable solvent effect is encountered. In the more polar solvent, dimethoxyethane substitution occurs, while in the less polar dichloromethane a larger portion of the desulfurization with cleavage of the phenylthio group takes place. This is attributed to the fact that the intermediate radical cation is more stable in the polar solvent and undergoes deprotonation, while in the less polar solvent, the less stabilized radical cation dissociates into a dioxolane cation and a phenylthio radical. 

Products isolated from the thermal fragmentation of A-arylbenzamide oximes and A-arylbenzamide O-phenylsulfonyl oximes have been accounted for by invoking a free-radical mechanism which is initiated by the preferential homolysis of the N-O bond." Time-resolved IR spectroscopy has revealed that photolysis of A, A -diphenyl-l,5-dihydroxy-9,10-anthraquinone diimine affords acridine-condensed aromatic products via excited-state intramolecular proton transfer." The absolute and relative rates of thermal rearrangements of substituted benzyl isocyanides have been measured,and it has been found that the relative rates are independent of temperature and exhibit excellent Hammett correlations. Thionitrosoarene (25), thought to be generated by desulfurization of the stable A-thiosulfinylaniline (24), has been established" " as an intermediate in the formation of 3,3a-dihydro-2,l-benzisothiazole (26) from o-alkylthionitrosoarene (24). 

Inhibition by aromatic hydrocarbons is most severe for dialkyldiben-zothiophenes as these materials are preferentially desulfurized by hydrogenation of the aromatic ring prior to sulfur extraction and as aromatics are more strongly adsorbed on the hydrogenation site of Co(Ni)-Mo-S catalysts than are dibenzothiophenes. 

Patent (6) claims the desirability of intermediate pores (100-1000 A) plus channels (>1000 A) "to take up preferentially adsorbed large molecules without causing blockage, so that the smaller size pores can desulfurize smaller molecules." Patent (7) also prefers the open structure for collection of coke and metals. It specifies 0.3 cc/g of pore volume in diameters larger than 150 A and "many pores from 1,000-50,000 A."... 

Thus, it has become possible to define certain general trends that occur in the hydrodesulfurization of petroleum feedstocks. One of the more noticeable facets of the hydrodesulfurization process is that the rate of reaction declines markedly with the molecular weight of the feedstock (Figure 4-6) (Scott and Bridge, 1971). For example, examination of the thiophene portion of a (narrowboiling) feedstock and the resulting desulfurized product provides excellent evidence that benzothiophenes are removed in preference to the dibenzothiophenes and other condensed thiophenes. The sulfur compounds in heavy oils and residua are presumed to react (preferentially) in a similar manner. 

As we can see from Table III, 86% of the sulfur contained in all of the oxidation products resides in the soluble oxidation products even though this product fraction only represents 52% by weight of the combined oxidation products. This indicates that organic sulfur compounds have been preferentially depolymerized from the coal matrix and that this oxidative procedure may be a possible desulfurization process. 

Of the various heterocycles discussed in this chapter, the pyridofuroxans show the least aromatic character. In Section 7.10.5.4, subtle differences in aromaticity between the [l,2,5]thiadiazolo[3,4-c]pyridines and the [l,2,5]oxadiazolo[3,4-c]pyridines are apparent from their dissimilar reactivity towards various reducing agents. In contrast to the former where desulfurization of the thiadiazole ring or substituent reduction occur, the latter heterocycles undergo initial reduction of the C=N bond to form the 4,5-dihydro[l,2,5]oxadiazolo[3,4-c]pyridines (120) with sodium borohydride at ambient temperature (Scheme 19). However, at 80 °C, the oxadiazole moiety is preferentially reduced... 

A theoretical study of desulfurization of thiirene and methyl thiirene on the molybdenum catalysts MoS3H3 and M0S4H4 was reported to involve hydrogenation of the double bond in the first step <2003BCSE75>. The extended Huckel technique was used to determine the orientation of thiirene adsorbed on vacant sites of MoS3H3. The molecule is adsorbed preferentially in the vertical sense through the sulfur atom <2000JSOA127>. 

These factors have akeady led to a substantial investment in fuel oil-desulfurization facilities in several parts of the world, notably Japan, the Middle East, and the Caribbean. With few exceptions these facilities have been based on indirect desulfurization, i,e., vacuum distillation, desulfurization of the vacuum gas oil, and reblending. This technique has limits in a market for fuels below the 1% sulfur level because none of the heavy, high sulfur vacuum residue is processed. To some extent this can be mitigated by preferentially blending this material to bunkers and by using naturally occurring low sulfur residues as blending stocks. 

Recently, gasoline desulfurization by PV has been studied as a newly emerged technology in which sulfur components can be preferentially removed from the gasoline feed due to its higher affinity and/or quicker diffusivity in the membrane. 

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