Ammonium sulfate formation

The vanadium content of some fuels presents an interesting problem. When the vanadium leaves the burner it may condense on the surface of the heat exchanger in the power plant. As vanadia is a good catalyst for oxidizing SO2 this reaction may occur prior to the SCR reactor. This is clearly seen in Fig. 10.13, which shows SO2 conversion by wall deposits in a power plant that has used vanadium-containing Orimulsion as a fuel. The presence of potassium actually increases this premature oxidation of SO2. The problem arises when ammonia is added, since SO3 and NH3 react to form ammonium sulfate, which condenses and gives rise to deposits that block the monoliths. Note that ammonium sulfate formation also becomes a problem when ammonia slips through the SCR reactor and reacts downstream with SO3. 

Equilibrium Constant for Ammonium Sulfate Formation Let us determine the equilibrium constant for the following reaction ... 

A lower temperature limit will be set at 300°C. Using urea injection at lower temperatures, polymerisation products can be formed. Furthermore, at these temperatures ammonium sulfate formation will block most SCR activity. The temperature range in which the catalyst will have to work is consequently from about 300°C to 550°C. 

In this paper much attention is paid to an effect which is typical for diesel engine exhaust the implications of the presence of sulfur in diesel fuel with regard to using catalysts. These implication can roughly be divided into two parts the effect on the particulate emission and the effect on SCR activity. The sulfur in diesel fuel is mainly converted to SO2. An increase in particulate emission would be caused by catal>4ic oxidation of SO2 to SO3 over the SCR catalyst. Since SO3 forms aerosols, this is being detected as particulates. The second effect is deactivation of the SCR catalyst by poisoning (p.e. ammonium sulfate formation). 

In Figure 3 the DeNOx performance of the vanadium catalyst is also given. It should be noted that comparison with the zeolite type catalysts is somewhat complicated because the vanadium catalyst is already put on a monolith carrier. However, what can be seen is the characteristic behaviour of a vanadium catalyst it starts to work well above 300°C (also because of ammonium sulfate formation) and shows an activity decline at 450°C because of ammonia oxidation. 

The sulfate production of this type of catalysts, Fi e 5, follows the same trend as depicted in Figure 2 at about 400°C the vanadium type catalyst and Cu-MOR start producing sulfates whereas Ce-MOR does not produce any sulfates. One might expect no ammonium sulfate formation when the catalyst does not oxidize SO2. However, the deactivation in a diesel exhaust or in model gases occurs at a much lower temperature than when SO2 oxidation is observed. 

Figure 13.16 Ammonium sulfate formation mechanism in ArF lithographic exposure tools.

Therefore, only 0.5 mol of ammonium sulfate per mol of hydroxylamine is then produced in the subsequent neutralization with ammonia. This is half as much as in the Raschig process. Complete elimination of ammonium sulfate formation characterizes a process introduced in 1970 by Stamicarbon [118,119]. This process involves catalytic hydrogenation of nitrate ions on Pd-C in a phosphoric acid ammonium hydrogen phosphate buffering system ... 

In 1974, SNIA revealed a further modification of this process that resulted in eliminating ammonium sulfate formation [129]. In this modified process, the product of the reaction between cyclohexane carboxylic acid and nitrosyl sulfuric acid is slightly diluted with water and treated with an alkylphenol to extract the caprolactam, which is then purified by distillation. The sulfuric acid is mixed with a fuel and thermally cracked to sulfur dioxide, which is recycled into the process. 

Important side reactions are the formation of ether and addition of alcohol to the acrylate to give 3-alkoxypropionates. In addition to high raw material costs, this route is unattractive because of large amounts of sulfuric acid—ammonium sulfate wastes. 

Coproductioa of ammonium sulfate is a disadvantage of the formamide route, and it has largely been supplanted by processes based on the direct hydrolysis of methyl formate. If the methanol is recycled to the carbonylation step the stoichiometry corresponds to the production of formic acid by hydration of carbon monoxide, a reaction which is too thermodynamicaHy unfavorable to be carried out directly on an iadustrial scale. 

The reaction is mn for several hours at temperatures typically below 100°C under a pressure of carbon monoxide to minimise formamide decomposition (73). Conversions of a-hydroxyisobutyramide are near 65% with selectivities to methyl a-hydroxyisobutyrate and formamide in excess of 99%. It is this step that is responsible for the elimination of the acid sludge stream characteristic of the conventional H2SO4—ACH processes. Because methyl formate, and not methanol, is used as the methylating agent, formamide is the co-product instead of ammonium sulfate. Formamide can be dehydrated to recover HCN for recycle to ACH generation. 

Ammonium chloride [12125-02-9], ammonium sulfate [7783-20-2], and diammonium phosphate [7708-28-0] have also been used for shale stabilization (102,103). Ammonium ions have essentially the same effect on shales as potassium ions but use of ammonium salts is often objectionable because of the alkaline nature of the mud. In the North Sea and northern Europe, where magnesium-bearing salt formations ate encountered, magnesium chloride [7786-30-3] is used, but in the United States it is used only on a small scale. 

The ammonium sulfate and sodium chloride are simultaneously dissolved, preferably ia a heel of ammonium chloride solution. The sodium chloride is typically ia excess of about 5%. The pasty mixture is kept hot and agitated vigorously. When the mixture is separated by vacuum filtration, the filter and all connections are heated to avoid cmst formation. The crystalline sodium sulfate is washed to remove essentially all of the ammonium chloride and the washings recycled to the process. The ammonium chloride filtrate is transferred to acid resistant crystallising pans, concentrated, and cooled to effect crystallisation. The crystalline NH Cl is washed with water to remove sulfate and dried to yield a product of high purity. No attempt is made to recover ammonium chloride remaining ia solution. The mother Hquor remaining after crystallisation is reused as a heel. 

The formation of oxime and rearrangement to caprolactam are conventional. The rearrangement produces 1.5 kg of the total 2.4 kg by-product ammonium sulfate per kilogram of caprolactam. Purification is accompHshed by vacuum distillation. A similar caprolactam process is offered by Inventa (11). 

Minisci reactions have also been applied to these compounds. formation by exposure to w-CPBA and O-methylation with Meerwein s reagent converted 54 into 55. Nucleophilic attack of the hydroxymethyl radical, generated with ammonium sulfate, provides an alternate route to 2-hydroxymethyl pyridines 56. 

A liquid absorption process for the removal of SO2 involves the absorption of the S02 into a solution of ammonia and water with resultant formation of ammonium sulfide. The liquid is then sent to an oxidizing unit to form ammonium sulfate, which can be sold as a by-product or reacted with milk of line to regenerate the ammonia and produce gypsum.28... 

Gould and coworkers have extensively studied the biosyntheses of the kinamycins, and this work was recently reviewed [5a]. Feeding studies established that the carbo-cyclic skeletons of the kinamycins are constructed from 10 equivalents of 5-acetyl coenzyme A, and the pathway shown in Scheme 3.4 was proposed. The pathway begins with formation of the natural product dehydrorabelomycin (29). A novel ring contraction then occurs to form the cyclopentadienone 30. Feeding studies with /V-15-ammonium sulfate established that the diazo functional group is then installed... 

In addition there is other evidence pointing to the fact that the same enzyme is involved in reactions with both D-fructose and L-arabinose. First, the relative rates of reaction with D-fructose and L-arabinose, respectively, remain constant after partial inactivation of the enzyme by heat. Second, the enzyme catalyzing both reactions is produced to a marked extent when sucrose is used as substrate for the growth of the organisms, but not when D-glucose or L-arabinose is used sucrose phos-phorylase is an adaptive enzyme. Third, on fractionation of the enzyme preparation with various concentrations of ammonium sulfate, the relative activities of the fractions are the same for both sugars. These observations indicate not only that the same enzyme is involved in both reactions but also that no additional enzyme is required for the formation of D-glucosyl-L-arabinose. 

Formation of ammonium sulfate gradient by its removal from the extraliposome medium... 

In some scrub and strip circuits, the crud is mainly composed of silica, as well as inorganic sulfates. Also, if poor pH control is used in the uranium stripping circuits with ammonium sulfate, then uranium is a major constituent [33,46]. Such crud may be treated with dilute sulfuric acid, and recirculation through a pump results in the crud breaking down. There is evidence, in at least a few uranium circuits, that the presence of humic acids may be a possible cause of the crud problem [34,47]. Lignin appears to be another cause of crud formation [33,46]. Humic acids contained in the feed solution have also been implicated in the formation of waxy cruds in plants extracting uranium from phosphoric acid. 

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