Regeneration of ammonia

Scrubber liquid can be recycled to obtain a salt solution of any desired concentration prior to regeneration of ammonia from the solution. The upper limit on solution concentration presumably will be controlled by the vapor pressures of the components, ammonia and sulfur dioxide. At high pH, ammonia vapor predominates at low pH, sulfur dioxide is the dominant vapor. Therefore, optimum recycle of the scrubber liquid will be controlled at low pH and dilute solution concentration concurrent with and relative to equipment (capital) and operating costs. A solution having low pH (e.g., < 6.0) requires stainless steel or protected carbon steel to prevent corrosion. 

The relatively reactive guanidine combines with unreacted starting mate-rial to form melamine with the regeneration of ammonia. 

Industrial soda ash (sodium carbonate) is produced from natural reservoirs (e.g., in the USA) or by the Solvay process. The brutto reaction of the Solvay process is the conversion of NaCl and CaC03 into Na2C03 and CaCl2. Figure 5.2.1 shows the process scheme and the number of unit operations. The key achievement in the historic development of the process ( . Solvay) was to realize a quantitative regeneration of ammonia. This point was essential for economic success as the price of ammonia is typically higher than the prize of soda ash. 

The process synthesis suggested in this paper focuses on the use of ammonia as a recycle reagent. Regeneration of ammonia is accomplished in the absence of Ca(OH)2 used in the Solvay process as indicated in the earlier comparison. 

The mechanism of this reaction involves an activation of the ammonia and hydrogen peroxide because these compounds do not themselves react (118—121). It appears that acetamide functions as an oxygen transfer agent, possibly as the iminoperacetic acid (41) which then oxidizes the transient Schiff base formed between MEK and ammonia (40) to give the oxaziridine (42), with regeneration of acetamide ... 

The anaerobic reaction of sulfur dioxide with aqueous ammonia produces a solution of ammonium sulfite [10192-30-0]. This reaction proceeds efficientiy, even with a gas stream containing as Httie as 1 wt % sulfur dioxide. The sulfur dioxide can be regenerated at a high concentration by acidulation or by stream stripping of the ammonium sulfite solution, or the sulfite can be made to precipitate and the ammonia recovered by addition of lime (243). The process can also be modified to produce ammonium sulfate for use as fertili2er (244) (see Fertilizers). In a variant of this process, the use of electron-beam radiation cataly2es the oxidation of sulfur dioxide in the presence of ammonia to form ammonium sulfate (245). 

The ammonia-water absorption system was extensively used until the fifties when the LiBr-water combination became popular. Figure 11-103 shows a simplified ammonia-water absorption cycle. The refrigerant is ammonia, and the absorbent is dilute aqueous solution of ammonia. Ammonia-water systems differ from water-lithium bromide equipment to accommodate major differences Water (here absorbent) is also volatile, so the regeneration of weak water solution to strong water solution is a fractional distillation. Different refrigerant (ammonia) causes different, much higher pressures about 1100-2100 kPa absolute in condenser. 

Preparation. The mother liquors from strychnine manufacture are concentrated and the alkaloids precipitated as neutral oxalates. The precipitate is dried and extracted with dry alcohol in which the strychnine salt is the more soluble. The less soluble salt dissolved in water is decolorised with charcoal, the alkaloid regenerated with ammonia and purified by crystallisation as the sulphate. According to Saunders, pure brucine may be obtained by slow crystallisation from a solution of the pure hydrochloride in alcoholic ammonia. A method of separation depending on the greater solubility in water of strychnine hydriodide was employed by Shenstone, whilst others have made use of the sparing solubility of strychnine chromate for the removal of small quantities of this alkaloid from brucine. For a large scale process see Schwyzer. ... 

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... 

The ammonia stabilizes Cu11 relative to Cu1 allowing it to be regenerated in the presence of air,52 and although the reduction of Cu11 by thiosulfate is normally rapid in a pure aqueous solution, in the presence of ammonia in these systems it proceeds much more slowly,43... 

DAP-Mn Also called the Manganese Dioxide Process. A flue-gas desulfurization process using a fluidized bed of manganese dioxide, which becomes converted to manganous sulfate. The adsorbent is regenerated with ammonia. 

Photochemical addition of ammonia and primary amines to aryl olefins (equation 42) can be effected by irradiation in the presence of an electron acceptor such as dicyanoben-zene (DCNB)103-106. The proposed mechanism for the sensitised addition to the stilbene system is shown in Scheme 7. Electron transfer quenching of DCNB by t-S (or vice versa) yields the t-S cation radical (t-S)+ Nucleophilic addition of ammonia or the primary amine to (t-S)+ followed by proton and electron transfer steps yields the adduct and regenerates the electron transfer sensitizer. The reaction is a variation of the electron-transfer sensitized addition of nucleophiles to terminal arylolefins107,108. 

From a simplified scheme of reduction of the amide function it can be seen that the first stage is formation of an intermediate with oxygen and nitrogen atoms linked to an sp carbon. Such compounds tend to regenerate the original sp system by elimination of ammonia or an amine. Thus an aldehyde is formed and may be isolated, or reduced to an alcohol. Alternatively the product is an amine resulting from direct hydrogenolysis of the sp intermediate. 

Manganese dioxide can be used to absorb the initially low concentration SO2 to produce the sulphate in a Mitsubishi Process (23). In this case the absorbing phase is itself the oxidising agent. Regeneration with ammonia and air simultaneously produces ammonium sulphate which can be directly marketed as a fertiliser, thus the calcium ion problem of the dry limestone process is replaced by a plant nutrient ion -... 

When the reduction of stored NO is accomplished at 150 °C, the reaction shows a significant induction period (Figure 13.17). The decrease in the H2 concentration is accompanied by the evolution of NH3 and of minor amounts of N2 however, a time delay is observed between product evolution and H2 uptake. Therefore, the rate of reaction is low at this temperature and a critical high surface concentration of activated hydrogen species is needed for the reaction to occur. The regeneration of the catalyst is not complete, since only 80% of the stored NO could be reduced after prolonged treatment with H2 at 150 °C. Also, the calculated overall N2 selectivity is very poor, below 20%, and ammonia represents the main reaction product. 

An alternate procedure used in a few specialty applications is the cuprammonium process. This involves stabilization of cellulose in an ammonia solution of cupric oxide. Solubilization occurs by complex formation of cupric ion with ammonia and the hydroxyl groups of cellulose. Regeneration of cellulose, after formation of the desired products, is accomplished by treatment with acid. The main application of the cuprammonium process is for the synthesis of films and hollow fibers for use in artificial kidney dialysis machines. The cuprammonium process yields products with superior permeability and biocompatibility properties compared to the xanthation process. Less than 1% of all regenerated cellulose is produced by the cuprammonium process. 

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