Extractive Desulfurization

Zhang, S., Zhang, Q., Zhang, Z.C., Extractive desulfurization and denitrogena-tion of fuels using ionic liquids, Ind. Eng. Chem. Res., 43, 614-622, 2004. 

Nie, Y., Li, C., Sun, A., Meng, H., Wang, Z., Extractive desulfurization of gasoline using imidazolium-based phosphoric ionic liquids. Energy Fuels, 20, 2083-2087, 2006. 

CED [Conversion Extraction Desulfurization] A process for reducing the sulfur content of diesel fuel. Peroxyacetic acid oxidizes the organic sulfur compounds to sulfones, which are removed by solvent extraction. Developed in 2000 by Petro Star. 

The ultradeep desulfurization of the current infrastructure fuels has become a bottleneck in the production of H2 for fuel cell applications. It is urgent to develop a more efficient and environmentally friendly process and technology for the ultradeep desulfurization of the hydrocarbon fuels. Consequently, many approaches have been conducted in order to improve the conventional HDS process and to develop new alternative processes. These approaches include catalytic HDS with improved and new catalysts, reactor and/or process, adsorptive desulfurization,27 oxidative desulfurization (ODS), extractive desulfurization (EDS), and biodesulfurization (BDS) by using special bacteria and others. Some of these works were reviewed recently by Topsoe et al.,15 Whitehurst et al.,28 Kabe et al.,29 Cicero et al.,30 Babich and Moulijn,31 Dhar et al.,32 Song,33 Song and Ma,16,34 Bej et al.,35 Mochida and Choi,36 Hemandez-Maldonado and Yang,37,38 Hemandez-Maldonado et al.,39 Topsoe,40 Brunet et al.,41 Gupta et al.,42 and Ito and van Veen.43... 

The physical basis for this S5mergism in process application is based in the chemistry of the alkylated aromatic thiophenic compounds in diesel fuel feedstock those most resisitant to conversion to hydrocarbons by HDS are those most readily amenable to oxidation and extractive desulfurization. Refiners expanding their processing capacity or adjusting to the new ULSD rule may want to consider the new extractive desulfurization (EDS) alternatives to high severity HDS, including debottelnecking HDS units by feedstock pretreatment or post-treatment, or parallel operation to reduce the load on their units. 

The removal of AAT sulfur compounds from the diesel fuel feedstock by extractive desulfurization (EDS), either adsorption or solvent extraction, is a viable alternative to HDS." This approach is based on the polarity difference between the AAT family of compounds and the hydrocarbons found in the diesel fraction. Because AATs comprise several dozen different compounds, they represent a range of solvent polarities, in some cases quite similar to the aromatic compounds found in diesel fuel. The critical polarity difference between individual hydrocarbon and thiophenic compounds is therefore variable, and in some cases may be insufficient to allow a functional separation by extraction. Polarity difference can, however, be increased by oxidizing the thiophenic sulfur to the corresponding more polar mono- and dioxides, the alkylated-aryl-thiophene-sulfoxide or sulfone (AATS). This in turn facilitates the separation, and several EDS processes therefore are designed to oxidize the AAT before extraction of the sulfur." ... 

Extractive desulfurization (EDS) probably will be economically attractive as a stand-alone process in some refinery applications. However, it seems likely that many refineries also will look to employ a synergistic combination... 

There are several reasons why refinery engineers will want to consider using the new extractive desulfurization (EDS) processes. First, EDS can be considered for stand-alone desulfurization to produce ultra-low-sulfur diesel fuel (ULSD), similarly to HDS processing. Second, EDS may be considered for tandem operation with HDS, either as HDS feed pretreatment or effluent post-treatment to achieve the new ULSD specifications. In these cases EDS promises to be an alternative for very-high severity HDS processing. 

One alternative called extractive desulfurization (EDS) seems very attractive for this purpose because of its low energy cost, the elimination of hydrogen usage, the retaining of the chemical structures of fuels and no requirements of special equipment. 

Jiang, X. Nie, Y. Li, C. Wang, Z. (2008). Imidazolium-based alkylphosphate ionic liquids -A potential solvent for extractive desulfurization of fuel. Fuel 87, 79-84, ISSN 0016-2361. 

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