Deep desulfurization

Due to the increasing restrictions on allowable automobile emissions, deep desulfurization will be needed in future. If we consider a normal crude oil feed, with 1% wt sulfur, the reduction down to 50 ppm requires an increase in conversion of 99.5% that will be increased to 99.9% if the reduction to 10 ppm for 2010 is finally approved. The increase in conversion could be achieved by three strategies  

This strategy is the simplest in the short term, but it is also very expensive, as it would require new production units able to work at pressures double those currently used. This method would also considerably increase consumption of hydrogen, the availability of which is limited. 

One possibility to enhance the activity for HDS of resistant molecules is to favour the hydrogenation pathway, by doping the catalyst with small amounts of Pt or Rh. Another possibility is to use molybdenum carbide, which has a higher hydrogenating activity than the sulfide. 

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As we have shown previously, obtaining both good cold operation characteristics and sufficient cetane numbers constitutes the principal objective for the refiner in the formulation of diesel fuel. To this is added the need for deep desulfurization and, perhaps in the future, limitations placed on the chemical nature of the components themselves, e.g., aromatics content. 

The discussion that follows will show the effects of several operating variables on product inspections. The effects of the variables are illustrated best by deep desulfurization of heavier gas oils. 

Some other processes are based on a severe hydrotreatment followed by a stage for octane recovery. Octgain from ExxonMobil [57] and ISAL from UOP-Intevep [58], Deep desulfurization is achieved by an increase in severity, causing lost in octane by olefins saturation. In the first case, in a second reactor octane number is recovered by a combination of cracking and isomerization reactions. In the latter case, the catalyst employed during desulfurization possess isomerization capabilities inhibiting an excessive octane lost. Other mentioned functionalities of the catalyst include dealkylation and conversion. 

ExxonMobil extended the Hydrofining technology to produce a 200 ppm diesel, with the Diesel Oil Deep Desulfurization technology, DODD. The reactor is packed with multiple beds of different catalysts. A preceding history of commercial experience provided data to build a model for deep HDS and pave the way to a new technology, MAK Fining. 

Song, C., an Overview of New Approaches to Deep Desulfurization for Ultra-Clean Gasoline, Diesel Fuel and Jet Fuel. Catal. Today, 2003. 86 pp. 211-263. 

Song, C., and Ma, X., New design approaches to ultra-clean diesel fuels by deep desulfurization and deep dearomatization. 

The treatment of hydrotreated diesel oil (250 ppm sulfur) to achieve deep desulfurization by CYKS1 was also reported [192], Sulfur reduction to 61 ppm was reported within 20 hours using 18.6 g/L biocatalyst concentration and water/oil ratio of 10. A rate of 10.6 mmol/kg dcw/h was reported for first four hours however, the rate was significantly reduced thereafter. 

Villasenor, F. Loera, O. Campero, A., and Viniegra-Gonzalez, G., Oxidation of dibenzothiophene by laccase or hydrogen peroxide and deep desulfurization of diesel fuel by the later. Fuel Processing Technology, 2004. 86(1) pp. 49-59. 

Monticello, D. J., Multistage System for Deep Desulfurization of Fossil Fuels Patent No. WO9216602. 1992, Oct. 01. 

Guobin, S. Jianmin, X. Huaiying, Z., and Huizhou, L., Deep desulfurization of hydrodesul-furized diesel oil by Pseudomonas delafieldii R-8. J. Chem. Tech. Biotechnol., 2005. 80 pp. 420 124. 

Deep desulfurization method of fossil fuels, comprising a first step of HDS and a BDS step for the removal of HDS sulfur refractory compounds, using an effective amount of a biocatalyst. The fuel is incubated in the presence of one or more BDS-active microorganisms, which converts the organic sulfur compounds into water-soluble inorganic sulfur. Then, in a separation stage, the products of the incubation are separated into a deeply desulfurized liquid fossil fuel, and the water-soluble inorganic sulfur. 

Multi-stage system for deep desulfurization of fossil fuels [30-33],... 

DODD A process for the deep desulfurization of middle petroleum distillates. Introduced by Exxon in 1989. 

Bosmann, A., Datsevich, L., Jess, A., Lauter, A., Schmitz, C., Wasserscheid, P, Deep desulfurization of diesel fuel by extraction with ionic liquids, Chem. Commun., 2494-2495, 2001. 

Much of the sulfur contained in a crude oil remains with the tar, asphalt or coke after refining. As crude prices rise, even this residuum becomes valuable as a feedstock for cracking to make lighter products. This involves deep desulfurization. Whether the coke is burned as a fuel or used for anodes, desulfurization will take place before or after combustion or processing. Sulfur removal from coke plants is a currently feasible process. 

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). 

Some major problems associated with deep desulfurization of gas oil are as follows ... 

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