Deep desulfurization reactivity

The present review summarizes contemporary views of the problems, achievements, and prospects involved in the deep desulfurization of gas oils, including identification and reactivity of sulfur species in the feed, the reaction pathways and mechanisms, activity and selectivity of the conventional catalysts, and concerns of fluorescence color production. Process schemes and guidelines for the development of the next-generation catalysts for improved deep desulfurization technology based on these discussions are also proposed. The structure and nature of the active sites of current catalysts will not be extensively covered in this review, because several excellent reviews have been published on these subjects within the past two years (1-3). 

Besides the thermodynamic limitations of HDN, the reactivity of N-compounds is strongly influenced by their molecular structure, which interferes with the absorption of the N-atom on the active site [30]. Basic N-compounds are also the strongest inhibitors of hydrogenation sites and consequently of all reactions that may follow this pathway (e.g., HDS). Therefore, removing N-inhibitors is an essential strategy to achieve deep desulfurization of diesel fuels. 

The S content in the model oil decreased from 1000 to 8 ppm, which was superior to the solvent extraction with ILs. The reactivity of sulfur compounds in the ECODS system decreased in the order of DBT > 4,6-DMDBT > BT. The catalyst with the short alkyl chain exhibited higher catalytic activity than that with the long alkyl chain. The deep desulfurization system containing... 

A promising approach is in reactive adsorption as that mentioned in section 2.5 where the desulfurization on Z-Sorb of ConocoPhilips was addressed. The proprietary sorbent separates sulfur from thiophenic compounds, and the hydrocarbon portion is released back to the process stream. Although details about the sorbent are not disclosed it is assumed that strong reduced metal- sulfur interactions are involved [7]. A process using site-specific interactions is also under development at Pennsylvania State University. The separation occurs at ambient temperatures and formation of organoinetallic complexes with sulfur is proposed as a crucial step for deep... 

With respect to the increasing demand for practically S-free fuels (<10ppm), S-species with a very low reactivity like dibenzothiophene derivatives have to be converted (Figure 6.8.6), typically in a second deep HDS step, which leads to additional high investment and operating costs. The enormous expenses needed today for such a deep HDS of already hydrotreated (pre-desulfurized) diesel oil can be illustrated by typical industrial data [MiRO-refinery 2004 (oral communication) Wache et al. (2006)] Deep HDS reactors have a volume of up to 500 m to treat about 400 of oil per h. The feed rate of fresh H2 is about 40 m (NTP) per m oil, the recycle rate is about three, and for a typical pressure of 6 MPa the pressure drop of about 1 MPa has to be compensated by a huge recycle compressor (1 MW). 

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