Desulfurization selectivity

Selective bioactivation (toxification) is illustrated in the case of the insecticide malathion (3.35). This acetylcholinesterase inhibitor is desulfurized selectively to the toxic malaoxon, but only by insect and not mammalian enzymes. Malathion is therefore relatively nontoxic to mammals (LDjg = 1500 mg/kg, rat p.o.). Higher organisms rapidly detoxify malathion by hydrolyzing one of its ester groups to the inactive acid, a process not readily available to insects. This makes the compound doubly toxic to insects since they cannot eliminate the active metabolite. 

The molecular size distributions and the size-distribution profiles for the nickel-, vanadium-, and sulfur-containing molecules in the asphaltenes and maltenes from six petroleum residua were determined using analytical and preparative scale gel permeation chromatography (GPC). The size distribution data were useful in understanding several aspects of residuum processing. A comparison of the molecular size distributions to the pore-size distribution of a small-pore desulfurization catalyst showed the importance of the catalyst pore size in efficient residuum desulfurization. In addition, differences between size distributions of the sulfur- and metal-containing molecules for the residua examined helped to explain reported variations in demetallation and desulfurization selectivities. Finally, the GPC technique also was used to monitor effects of both thermal and catalytic processing on the asphaltene size distributions. 

Table 6.18.4 Typical composition of flue gas from a coal-fired power plant before and after treatment of the flue gas by desulfurization, selective catalytic reduction of NO, and electrostatic precipitation for reduction of particulate matter (ash).

Recent regulation forces deeper hydrodesulfurization. While HDS of FCC gasoline is rather difficult without hydrogenation of olefin and aromatic components, which are major sources for high octane number, sulfur species in gasoline are reactive forms of thiols, thiophenes and benzothiophenes, which are readily desulfurized. Selective HDS without olefin hydrogenation is being extensively explored at present. ... 

Sulfur Compounds. Various gas streams are treated by molecular sieves to remove sulfur contaminants. In the desulfurization of wellhead natural gas, the unit is designed to remove sulfur compounds selectively, but not carbon dioxide, which would occur in Hquid scmbbing processes. Molecular sieve treatment offers advantages over Hquid scmbbing processes in reduced equipment size because the acid gas load is smaller in production economics because there is no gas shrinkage (leaving CO2 in the residue gas) and in the fact that the gas is also fliUy dehydrated, alleviating the need for downstream dehydration. 

Utihties that reduce emissions below the number of allowances they hold may trade emissions credits on the open market. Owners of plants affected by Phase I regulations can also petition the EPA for a two-year extension for meeting Phase I emissions if they have selected a control option capable of reducing SO2 emissions by 90% or more, such as is capable by flue-gas desulfurization. Owners of these units can receive bonus allowances for 1997—1999 if they have operated at SO2 emissions below 0.52 kg/10 kj (1.2 lb/10 Btu) of fuel heating value input. 

The addition of the lithium enolates of methyl acetate and methyl (trimelhylsilyl)acetate to ( + )-(S)-2-(4-methylphenylsulfinyl)-2-cycloalkenones gives, after desulfurization, (/ -substituted cycloalkenones. A higher level of selectivity is observed with the a-silyl ester enolate and in the cyclohexenone series13. The stereochemical outcome is rationalized by assuming attack on a ground-state conformation analogous to that in Section 1.5.3.2.1. 

Oxidative desulfuration releases active sulfur that binds to, and deactivates, P450 Selective inhibitors Specific inhibitor of lAl Specific inhibitor of 1A2 Specific inhibitor of 2A6 Specific inhibitor of 2C9 Specific inhibitor of 2D1 Specific inhibitor of 2E1... 

Roberts et al. [74] took advantage of the rapid and selective p-scissions of phosphoranyl radicals, to develop a radical chain desulfurization affording new substituted a-alkyl acrylates in good to moderate yields (Scheme 37). 

Desulfurization processes are absolutely necessary for producing clean fuels. Possible strategies to realize ultradeep suffiirization currently include adsorption, extraction, oxidation, and bioprocesses. Oxidative desulfurization (ODS) combined with extraction is considered one of the most promising of these processes [13]. Ultradeep desulfurization of diesel by selective oxidation with amphiphilic catalyst assembled in emulsion droplets has given results where the sulfur level of desulfurized diesel can be lowered from 500 ppm to about 0.1 ppm without changing the properties of the diesel [12]. 

In the context of diagenesis in recent anoxic sediments, reduced carotenoids, steroids, and hopanoids have been identified, and it has been suggested that reduction by sulhde, produced for example, by the reduction of sulfate could play an important part (Hebting et al. 2006). The partial reduction of carotenoids by sulfide has been observed as a result of the addition of sulfide to selected allylic double bonds, followed by reductive desulfurization. This is supported by the finding that the thiol in allylic thiols could be reductively removed by sulhde to produce unsaturated products from free-radical reactions (Hebting et al. 2003). 

For Burning Star SCT-SRCs, the selectivity for desulfurization is not sufficiently high, relative to those for formation of gases and insoluble residue, to make this process practicable. No other SCT-SRCs were tested. 

Samarium(II) iodide also allows the reductive coupling of sulfur-substituted aromatic lactams such as 7-166 with carbonyl compounds to afford a-hydroxyalkylated lactams 7-167 with a high anti-selectivity [74]. The substituted lactams can easily be prepared from imides 7-165. The reaction is initiated by a reductive desulfuration with samarium(ll) iodide to give a radical, which can be intercepted by the added aldehyde to give the desired products 7-167. Ketones can be used as the carbonyl moiety instead of aldehydes, with good - albeit slightly lower - yields. 

A selective enrichment strategy was pursued in developing biocatalysts for benzothio-phene desulfurization. Oldfield [119] started with contaminated soil samples and isolated two active strains, which were deposited as NUE213E and NUE213F (Accession No NCIMB 40816 and 40817, respectively, at The National Collections of Industrial and Marine Bacteria Limited). Apart from being rod-shaped and Gram positive, there was no other characterization or identification, in the patent document. This patent was published by the US PTO on July 2001 and has not yet been issued. 

In addition to DBT and BT, strain A11-2 could utilize methyl, dimethyl, and trimethyl DBTs as sulfur sources. The desulfurization of asymmetric alkylated DBTs was assessed to understand the sulfur specificity of this organism. It was shown to desulfurize several asymmetric alkyl DBTs up to C3-DBTs. It was shown that the rates of desulfurization depended on not only the position of alkyl substitution but also the number and length of alkyl substitution. An attempt was made to co-relate the data based on a molecular shape parameter. Selectivity of this organism was compared with R. erythropolis KA2-5-1 and, although clear differences were observed, the parameter fitting was not perfect. Two Paenibacillus strains, Paenibacillus sp. A11-1 and All-2, were patented [87] and were deposited as PERM BP-6025 and PERM BP-6026 in 1996 [122,123],... 

In addition to desulfurization activity, several other parameters are important in selecting the right biocatalyst for a commercial BDS application. These include solvent tolerance, substrate specificity, complete conversion to a desulfurized product (as opposed to initial consumption/removal of a sulfur substrate), catalyst stability, biosurfactant production, cell growth rate (for biocatalyst production), impact of final desulfurized oil product on separation, biocatalyst separation from oil phase (for recycle), and finally, ability to regenerate the biocatalyst. Very few studies have addressed these issues and their impact on a process in detail [155,160], even though these seem to be very important from a commercialization point of view. While parameters such as activity in solvent or oil phase and substrate specificity have been studied for biocatalysts, these have not been used as screening criteria for identifying better biocatalysts. 

Abbad-Andaloussi, S. Warzywoda, M., and Monot, F., Microbial desulfurization of diesel oils by selected bacterial strains. Oil Gas Science and Technology-Revue Institut Francais Du Petrole, 2003. 58(4) pp. 505-513. 

Castorena, G. Suarez, C. Valdez, I., et al., Sulfur-Selective Desulfurization of Dibenzothiophene and Diesel Oil by Newly Isolated Rhodococcus Sp Strains. Ferns Microbiology Letters, 2002. 215(1) pp. 157-161. 

Setti, L. Farinelli, P. Di Martino, S., et al., Developments in Destructive and Non-Destructive Pathways for Selective Desulfurizations in Oil-Biorefining Processes. Applied Microbiology and Biotechnology, 1999. 52(1) pp. 111-117. 

Maghsoudi, S. Kheirolomoom, A. Vossoughi, M., et al., Selective desulfurization of dibenzothiophene by newly isolated Corynebacterium sp strain P32C1. Biochemical Engineering Journal, 2000. 5(1) pp. 11-16. 

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