Hydroxide desulfurization reactions

The desulfurization process can be carried out either, in a dedicated reactor, or within a simple storage vessel, or during transportation (in pipelines) or intermediate processing vessels. Nutrients addition, pH, and aeration are adjusted as necessary. Multiple stages can be added to the reaction to enhance the sulfur removal process and decrease the reaction time below the probable 300 h required. The produced sulfates are removed by the addition of agents such as alkaline calcium, magnesium, aluminum, barium, and metal compounds such as oxides, hydroxides, and carbonates. 

One common practice is to treat the desulfurization slag with water (Stolzenburg, ec al., 1985). This is done to generate and release acetylene gas from the unreacted calcium carbide. The other major reaction product is solid calcium hydroxide or lime. 

The reverse reaction, desulfurization, has been performed on 3-mer-capto-1,2,4-triazolo [4,3-a]pyrimidines (151) by treatment with water (59JOC787) or ammonium hydroxide (57BRP874204 60YZ1542) in the presence of Raney nickel or nitric acid (60JOC361) to give 1,2,4-tria-zolo[4,3-a]pyrimidines (152) (Scheme 61). 

Results of experiments with benzothiophene and pure NaOH serve to emphasize the difference between NaOH and KOH. Even at reaction times of 6 hours, no benzothiophene decomposition was observed with NaOH. These results not only emphasize the role of KVKOH but suggest that KVKOH is a necessary part of the hydroxide mixture for decomposition and ultimate desulfurization of thiophene-ring systems. 

Reaction of Dibenzothiophene. Dibenzothiophene was much less reactive than benzothiophene. Reactions in the standard KOH/NaOH mixture (60 40) at 375°C for 30 minutes in our laboratories demonstrated that dibenzothiophene was unreactive and quantitatively recovered. Using dibenzothiophene as a model, Maijgren and Hubner (18) observed that under similar reaction conditions (75 KOH and 25 NaOH, 370°C for 60 minutes), 81 of dibenzothiophene was recovered, but no reaction products were identified. Wallace et al. (J2) found also that dibenzothiophene was unreactive when heated at 200°C for 20 hours in a mixture of KOH and white oil. The severity of the reaction conditions in our laboratory was increased by raising the temperature to 400°C and allowing the reaction to occur for 6 hours. Under these conditions, using the standard KOH/NaOH mixture, dibenzothiophene reacted completely, producing approximately 62 o-phenylphenol and 6 biphenyl (approximately 30 of the material was unaccounted for). Apparently even dibenzothiophene will react with molten hydroxide and desulfurize if the reaction conditions are sufficiently severe. 

Metallic sodium, or sodium hydroxide and sulfur, may also be extracted from flue gas by electrolysis of molten sodium sulfide (produced in the gas desulfurization process) by application of the charging reaction of the sodium-sulfur battery. This could conceivably be converted to a power-producing system if oxygen can be reduced at the cathode without severe polarization. Again, a beta-alumina diaphragm must be used to separate the sodium sulfide from the sodium hydroxide. 

Chemical deposition from solutions of chalcogenide compound thin films finds its origin more than one century ago when for instance Emerson-Reynolds, in 1884 [1], reported that thiourea is easily desulfurated by certain metallic oxides and hydroxides (silver, mercury, lead) to form the corresponding sulfide. When the reaction proceeds in basic solutions, a specular and strongly adherent layer is formed on the sides of the vessel, in parallel with the precipitation in the volume of the solution, according to the global reaction ... 

Flue-Gas (Stack-Gas) Scrubbing. Flue-gas scrubbing is a refiner s last chance to keep NOx and SOx out of the air. In wet flue-gas desulfurization, gas streams containing SOx react with an aqueous slurry containing calcium hydroxide Ca(OH)2 and calcium carbonate CaCOs. Reaction products include calcium sulfite (CaSOs) and calcium sulfate (CaS04>, which precipitate from the solution. 

There are several reports that describe attempts to favor the formation of P- over a-D-2 -deoxynucleosides.36-39 The availability of 33a prompted us to use the chirality at C-4 to deliver the base in a stereospeciflc manner from the P side. Compound 33a was converted via the tosylate to the iododerivative 33b, which was S-alkylated with 2-thiouracil to give 34. TMS triflate-catalyzed cyclization in acetonitrile furnished the 2S,S -cyclonucleoside 35 in 65% yield. While Raney nickel desulfurization of 35 furnished 36, an unprecedented reaction took place where palladium hydroxide catalyzed a stereospecific... 

Raney nickel is a highly active, finely divided form of the metal prepared by reaction of a nickel/aluminum alloy with concentrated sodium hydroxide, which removes most of the aluminum as Na[Al(OH)4], Although active for a very wide range of reductions, it has been particularly widely used for the reduction of nitriles, and the desulfurization of thioacetals, thioethers, and dithianes (see Section 19.3.3) (Figure 23.22). The careful disposal of the catalyst after use is very important once it has dried out, the metal is highly pyrophoric. 

In a similar reaction, hydrazine has been shown to desulfurize thioacetals, cyclic and acyclic, to methylene groups (eq 5). The reaction is run in diethylene glycol in the presence of potassium hydroxide, conditions similar to the Huang-Minlon protocol. Yields are generally good (60-95%). In situations where base sensitivity is a concern, the potassium hydroxide may be omitted. Higher temperatures are then required. ... 

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