Ammonia quench

An aluminum hydride reduction of propargylic alcohol 153 to trans alkene 156 was found to proceed through retro-1,3-Brook rearrangement to vinyl silane diol 155, followed by 1,3-Brook rearrangement back again. While the final product 156 was isolated directly after longer reaction times, immediate workup following the aqueous ammonia quench revealed the formation of... 

The Ube plant consists of four complete trains of Texaco quench-type gasifiers. During normal operation, three gasifiers are on line and one is on standby. Each gasifier consumes 500 t/day of coal to generate syngas for 350 t/day of ammonia. Up to the middle of 1990 the Ube plant gasified 2.2 million t of coal and petroleum coke. 

The purified raw gas goes to a Synthol (Eischer-Tropsch) unit for catalytic conversion of CO and H2 to Hquid fuels. The tars and oils obtained from quenching the raw gas from the gasifiers go to a Phenosolvan plant to provide tar products for the refinery and ammonia for fertilizer. The Synthol plant has seven reactors, each with 1.9 x 10 m /h (1.6 x 10 ft /d) gas feed. Annual plant production is 1.5 x 10 t motor fuels, 185 x 10 t ethylene,... 

Fig. 17. (a) Kellogg vertical quench converter (b) Ammonia Casale converter basket modification. 

The route to 3-bromothiophene utilises a variation of the halogen dance technology (17). Preferably, 2,5-dibromothiophene [3141-27-3] is added to a solution of sodamide in thiophene containing the catalyst tris(2-(2-methoxyethoxy)ethyl)amine (l DA-1) (33) at temperatures marginally below reflux. On completion, quenching exothermically Hberates ammonia gas the organic phase is separated, washed, and distilled, and foremnning thiophene is recycled. Material of 97—98% purity is isolated. 

The reactor effluent is rapidly quenched with aqueous mother Hquor in specially designed equipment operating at pressures essentially equal to the reactor pressure. This operation yields an off-gas consisting of ammonia and carbon dioxide vapor and a crystalline melamine slurry saturated with ammonia and carbon dioxide. The slurry is concentrated in a cyclone mill. The mother Hquor overflow is returned to the quenching system. The concentrated slurry is redissolved in the mother Hquor of the crystallization system, and the dissolved ammonia is stripped simultaneously. 

This ammonia is recycled to the reactor via a compressor and a heater. Liquid ammonia is used as reflux on the top of the absorber. The net amount of carbon dioxide formed in the reactor is removed as bottom product from the absorber in the form of a weak ammonium carbamate solution, which is concentrated in a desorber-washing column system. The bottom product of this washing column is a concentrated ammonium carbamate solution which is reprocessed in a urea plant. The top product, pure ammonia, is Hquefted and used as reflux together with Hquid makeup ammonia. The desorber bottom product, practically pure water, is used in the quench system in addition to the recycled mother Hquor. 

FIG. 23-3 Temperature and composition profiles, a) Oxidation of SOp with intercooling and two cold shots, (h) Phosgene from GO and Gfi, activated carbon in 2-in tubes, water cooled, (c) Gumene from benzene and propylene, phosphoric acid on < uartz, with four quench zones, 260°G. (d) Mild thermal cracking of a heavy oil in a tubular furnace, hack pressure of 250 psig and sever heat fluxes, Btu/(fr-h), T in °F. (e) Vertical ammonia svi,ithesizer at 300 atm, with five cold shots and an internal exchanger. (/) Vertical methanol svi,ithesizer at 300 atm, Gr O -ZnO catalyst, with six cold shots totaling 10 to 20 percent of the fresh feed. To convert psi to kPa, multiply by 6.895 atm to kPa, multiply by 101.3. 

Fast catalytic reac tions that must be quenched rapidly are done in contac t with wire screens or thin layers of fine granules. Ammonia in a 10% concentration in air is oxidized by flowthrough a fine gauze catalyst made of 2 to 10% Rh in Pt, 10 to 30 layers, 0.075-mm (0.0030-in) diameter wire. Contact time is 0.0003 s at 750°C (1,382°F) and 7 atm (103 psi) followed by rapid quenching. Methanol is oxidized to formaldehyde in a thin layer of finely divided silver or a multilayer screen, with a contact time of 0.01 s at 450 to 600°C (842 to 1,112°F). 

Quenching Smoke, particulates (dust and mists), phenols, and ammonia Baffles and spray tower... 

An electrostatic precipitator is used to remove more tar from coke oven gas. The tar is then sent to storage. Ammonia liquor is also separated from the tar decanter and sent to wastewater treatment after ammonia recovery. Coke oven gas is further cooled in a final cooler. Naphthalene is removed in a separator on the final cooler. Light oil is then removed from the coke oven gas and is fractionated to recover benzene, toluene, and xylene. Some facilities may include an onsite tar distillation unit. The Claus process is normally used to recover sulfur from coke oven gas. During the coke quenching, handling, and screening operation, coke breeze is produced. The breeze is either reused on site (e.g., in the sinter plant) or sold offsite as a by-product. 

Toluene is a useful co-solvent in metal-ammonia reductions as first reported by Chapman and his colleagues. The author has found that a toluene-tetrahydrofuran-ammonia mixture (1 1 2) is a particularly useful medium for various metal-ammonia reductions. Procedure 8a (section V) describes the reduction of 17-ethyl-19-nortestosterone in such a system. Ethylene dibromide is used to quench excess lithium. Trituration of the total crude reduction product with methanol affords an 85% yield of 4,5a-dihydro-17-ethyl-19-nortestosterone, mp 207-213° (after sintering at 198°), reported mp 212-213°. For the same reduction using Procedure 5 (section V), Bowers et al obtained a 60% yield of crude product, mp, 196-199°, after column chromatography of the total reduction product. A similar reduction of 17-ethynyl-19-nortestosterone is described in Procedure 8b (section V). The steroid concentration in the toluene-tetrahydrofuran-ammonia system is 0.05 M whereas in the ether-dioxane-ammonia system it is 0.029 M. 

Under the conditions of the Birch reduction, IV-Boc amides such as 60 can be reductively alkylated in high yields, presumably via a dianion intermediate which is protonated by ammonia at C-5 leaving an enolate anion at C-2 <96JOC7664>. Quenching the reaction with alkyl halides or ammonium chloride then affords the 3-pyrrolines 61. 

The new process avoids these problems by gas-phase treatment using a fluidized bed of alumina particles (Figure 1.2). A mixture of air, ammonia, nitrogen, natural gas, pg (liquefied petroleum gas), and other gases are used as the fluidizing gas to carry out the heat treatment. The bed is heated by electricity or gas and quenching is also carried out in a fluidized bed.14... 

During the reductive cleavage of cyclopolyenes with potassium in liquid ammonia, the intermediate anionic species are quenched with iodine-pentane mixtures. The possibility of formation of explosive nitrogen triiodide and the need for precautions are stressed. 

The recycled hydrogen is usually employed for quenching, as explained in Section 2.2. In the case of feed pretreatment (particularly HCK), the build up of ammonia or H2S... 

Donohoe reports a novel and unprecedented reductive aldol process involving the Birch reduction of furans and pyrroles (e.g., 62) which presumably generates a dianion 63 and subsequently (after protonation at C-5 by ammonia) an enolate 64. After quenching excess... 

In the case of mono-ester substituted pyrroles (e.g., 68) wherein relatively unstable dianions likely to deprotonate ammonia might be produced, the authors instead utilized an excess of (MeOCH2CH2)2NH as a substitute for ammonia. It was felt that upon in situ formation of (MeOCH2CH2)2NLi, this base would be unable to protonate the dianion <00TL1331>. Remarkably, quenching the reduction reactions with benzoyl chloride affords P-keto esters (e.g., 69, R = COPh), a reaction that does not occur when conducted in liquid ammonia. 

Gasifiers typically produce contaminants that need to be removed before entering the fuel cell anode. These contaminants include H2S, COS, NH3, HCN, particulate, and tars, oils, and phenols. The contaminant levels are dependent upon both the fuel composition and the gasifier employed. There are two families of cleanup that can be utilized to remove the sulfur impurities hot and cold gas cleanup systems. The cold gas cleanup technology is commercial, has been proven over many years, and provides the system designer with several choices. The hot gas cleanup technology is still developmental and would likely need to be joined with low-temperature cleanup systems to remove the non-sulfur impurities in a fuel cell system. For example, tars, oils, phenols, and ammonia could all be removed in a low-temperature water quench followed by gas reheat. 

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