Mercaptans desulfurization

Since the original cmde oils contain some sulfur compounds, the resulting products and gasolines also contain sulfur compounds, including hydrogen sulfide, mercaptans, sulfides, disulfides, and thiophenes. The processes used to sweeten, ie, desulfurize, the products depend on the type and amount of the sulfur compounds present and the specifications of the finished gasoline or other stocks. 

The primary reactions occurring during hydrotreating are (43) desulfurization of sulfides, polysulftdes, mercaptans, and thiophene as exemplified by... 

Sulfur in cmde oil is mainly present in organic compounds such as mercaptans (R-SH), sulfides (R-S-R ) and disulfides (R-S-S-R ), which are all relatively easy to desulfurize, and thiophene and its derivatives (Fig. 9.2). The latter require more severe conditions for desulfurization, particularly the substituted dibenzothiophenes, such as that shown in Fig. 9.2. Sulfur cannot be tolerated because it produces sulfuric add upon combustion, and it also poisons reforming catalysts in the refinery and automotive exhaust converters (particularly those for diesel-fueled cars). Moreover, sulfur compounds in fuels cause corrosion and have an unpleasant smell. 

Sweetening of petroleum products implies the removal of dissolved free sulfur and its compounds like hydrogen sulfide, and mercaptans in order that the product has no bad odour and does not tend to cause corrosion. The removal of these is accomplished by oxidation processes, solvent processes or catalytic desulfurization processes. 

As one more common example of liquid fuels present reference may be drawn to liquified petroleum gas (LPG) or bottled gas or refinery gas. This fuel is obtained as a by-product during the cracking of heavy oils or from natural gas. It is dehydrated, desulfurized and traces of odours organic sulfides (mercaptans) are added in order to identify whether a gas leak has occurred. Supply of LPG is carried out under pressure in containers under different trade names. It consists of hydrocarbons of great volatility such that they can occur in the gaseous state under atmospheric pressure, but are readily liquifiable under high pressures. The principal constituents of LPG are n-butane, iso-butane, butylene and propane,... 

Zervas48 through the catalytic reduction of 2,3,4,6-tetraacetyl-2-hydroxy-D-glucal, has recently been prepared by the reductive desulfurization of ethyl tetraacetyl-l-thio-/ -D-mannopyranoside (XL),47 a substance which has been obtained through the mercaptolysis of mannosidostreptomycin48 and may be prepared through the prolonged action of ethyl mercaptan and hydrochloric acid on D-mannose. 

Activated mercaptans undergo desulfurization to hydrocarbons using cobalt carbonyl or triiron dodecacarbonyl as the metal complex, and basic phase transfer conditions (5 ). Acidic phase transfer catalysis has been little investigated, the first example in organometallic chemistry being reported in 1983 (reduction of diarylethylenes)( ). When acidic phase transfer conditions (sodium 4-dodecylcenzenesulfo-nate as the phase transfer catalyst) were used for the desulfurization of mercaptans [Fe3(CO)] 2 the metal complex],... 

Benzyl sulfides are not desulfurized but reduced to mercaptans. From alkali salts. 

DESULFURIZATION WITH TRIALKYL PHOSPHITES Desulfurization of Mercaptans to Hydrocarbons [672]... 

Ring closure to an episulfide is a feasible reaction for thiocarbonyl ylides. In most cases, the sulfur is further extruded under the reaction conditions to afford an olefin as the final product. This cascade transformation has been utilized by Danishefsky and co-workers in their total synthesis of ( )-indolizomycin (Scheme 16)." In the Danishefsky s approach, diazo ketone 137 is treated with a catalytic amount of Rh2(OAc)4 to generate thiocarbonyl ylide 138, which cyclizes to give episulfide 139. This episulfide isomerizes to mercaptan 140, which is then desulfurized by partially deactivated W-2 Raney nickel. 

Recently it has been shown that anhydrous hydrogen fluoride exerts a selective solvent action on sulfur compounds and can be used satisfactorily for the desulfurization of kerosenes. In some respects it behaves similarly to sulfuric acid. Points of difference, however, are that it does not oxidize mercaptans to disulfides and that it can be used over a wide temperature range, 30° to 150° F., without affecting results. Hydrogen fluoride does not yet seem to have been used in full scale commercial units. 

Research is likely to continue with a view to improving methods of sweetening and removing mercaptans from all middle distillates including heater oil. It is doubtful, however, that much effort will be applied specifically toward desulfurization of heater oils except in cases where fuel instability and poor performance of equipment are due to sulfur compounds or where the treatment for stability improvement simultaneously lowers sulfur content. 

Calcium carbide desulfurization slag has a distinctive odor. Since pure acetylene is odorless, the odor must be produced by other trace constituents in the off-gases. A calcium carbide desulfurization slag sample from one ductile foundry was treated with water at a 1 1 solid-to-liquid ratio, and the gas was collected in a Tedlar bag for analysis by GC-MS. Several trace gases were identified, including arsine, divinyl sulfide (CHj-CH S, ethanethiol (ethyl mercaptan), methane, phosphine, and carbon monoxide. 

Isothiochroman undergoes simple alkylation at the sulfur to form sulfonium salts,237 is ring-opened and desulfurized with Raney nickel,244 and is ring-opened to 2-(o-tolyl)ethyl mercaptan with Ca(NH3)6.258... 

Carbonylation of mercaptans.1 Benzylic and aryl mercaptans in the presence of Co2(CO)8 undergo desulfuration and carbonylation to give esters. 

A desulfurization step is necessary in the reforming of natural gas because natural gas is odorized with a sulfur-containing substance - usually methyl mercaptan. This step will prevent damage to (i.e., deactivation of) the nickel or platinum catalysts in downstream processes. Some of these feed streams may also contain chlorides that are not only poisons to the downstream catalysts, but they may also contribute to stress corrosion in the reactors or piping. 

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