Ammonium sulfate crystals

Qualitative Analysis. Nitric acid may be detected by the classical brown-ring test, the copper-turnings test, the reduction of nitrate to ammonia by active metal or alloy, or the nitrogen precipitation test. Nitrous acid or nitrites interfere with most of these tests, but such interference may be eliminated by acidifying with sulfuric acid, adding ammonium sulfate crystals, and evaporating to alow volume. 

Ammonium sulfate is produced as a caprolactam by-product from the petrochemical industry, as a coke by-product, and synthetically through reaction of ammonia with sulfuric acid. Only the third process is covered in our discussion. The reaction between anunonia and sulfuric acid produces an ammonium sulfate solution that is continuously circulated through an evaporator to thicken the solution and to produce ammonium sulfate crystals. The crystals are separated from the liquor in a centrifuge, and the liquor is returned to the evaporator. The crystals are fed either to a fluidized bed or to a rotary drum dryer and are screened before bagging or bulk loading. 

F-S [Ferrous sulfate] A process for removing ammonia, hydrogen sulfide, and hydrogen cyanide from coke-oven gas by scrubbing with aqueous ferrous sulfate solution obtained from steel pickling. A complex series of reactions in various parts of the absorption tower yield ammonium sulfate crystals and hydrogen sulfide (for conversion to sulfur or sulfuric acid) as the end products. Developed in Germany by F. J. Collin A.G. 

The experimental results reported in this paper demonstrate the ability of a flat-bottom hydrocyclone to separate the coarse fraction of ammonium sulfate crystals from a slurry which contains crystals of a wide size range. It appears that the grade efficiency curve, which predicts the probability of a particle reporting to the underflow of the cyclone as a function of size, can be adjusted by a change in the underflow diameter of the hydrocyclone. These two observations lead to the suggestion to use hydrocyclone separation to reduce the crystal size distribution which is produced in crystallisers, whilst using a variable underflow diameter as an additional input for process control. 

DOUBLE SALT. A hydrated compound resulting from crystallization ol a mixture of ions in aqueous solution. Common examples arc the alums, made by ciystallizing from solution either potassium or ammonium sulfate and aluminum sulfate Rochelle salt (potassium sodium tartrate), made from a water solution of potassium acid tartrate treated with sodium carbonate and Mohr s salt (fertous ammonium sulfate), crystallized Iruin mixed solutions of ferrous sulfate and ammonium sulfate. 

The rotary drum granulator in this process is essentially the same as was pictured for the diammonium phosphate granulation process. In early versions of the process, feed to the drum of SSP consisted of (1) crushed oversize product and fines, (2) nongranular SSP, (3) nongranular potassium chloride, (4) ammonium sulfate crystals, (5) sulfuric acid, and (6) anhydrous ammonia or an ammonia-containing nitrogen solution. 

The first three columns of Table 10.5 show sieve data for a 100-cc slurry sample containing 21.0 g of solids taken from a 20,000-gal (75-m3) mixed suspension-mixed product removal crystallizer (MSMPR) producing cubic ammonium sulfate crystals. Solids density is 1.77 g/cm3, and the density of the clear liquor leaving the crystallizer is 1.18 g/cm3. The hot feed flows to the crystallizer at 374,000 lb/h (47 kg/s). Calculate the residence time r, the crystal size distribution function n, the growth rate G, the nucleation density n°, the nucleation birth rate B°, and the area-weighted average crystal size L3 2 for the product crystals. 

Application A process to manufacture caprolactam from nitration-grade toluene. Fiber-grade flaked or molten caprolactam and white ammonium sulfate crystals are produced. 

Reactor effluent is diluted with water (5), and unconverted cyclohexane carboxylic acid is recycled to the process, while the ladam solution flows to the crystallization plant (6) where it is neutralized with ammonia. Ammonium sulfate crystallizes at bottom and the top organic layer of caproladam is recovered and purified through a two-solvent (toluene and water) extraction (7) and a continuous fractionation (8). 

For a given set of assumptions it is possible to calculate the characteristic curves for the product from the crystallizer when it is operated at various levels of fines removal as characterized by Lf. This has been done for an ammonium sulfate crystallizer in Fig. 18-63. Also shown in that figure is the actual size distribution obtained. In calculating theoretics size distributions in accordance with the Eq. (18-41), it is... 

The metal-free solution is evaporated to leave behind fertilizer grade ammonium sulfate crystals with a water-soluble nitrogen content of 21% and a sulfur content of 24%. 

Internal structure (unit cell) can be different in crystals that are chemically identical. This is called polymorphism. Polymorphs can vary substantially in physical and chemical properties such as bioavailability and solubility. They can be identified by analytical techniques such as X-ray diffraction, infrared, Raman spectro, and microscopic techniques. For the same internal structure, very small amounts of foreign substances will often completely change the crystal habit. The selective adsorption of dyes by different faces of a crystal or the change from an alkaline to an acidic environment will often produce pronounced changes in the crystal habit. The presence of other soluble anions and cations often has a similar influence. In the crystallization of ammonium sulfate, the reduction in soluble iron to below 50 ppm of ferric ion is sufficient to cause significant change in the habit of an ammonium sulfate crystal from a long, narrow form to a relatively chunky and compact form. Additional information is available in the patent literature and Table 18-4 lists some of the better-known additives and their influences. 

Figure 5.5 shows the calculated and experimental data for an ammonium sulfate crystallizer operating at a retention time of... 

The effects of perturbation of this type can be seen in the crystal size distribution for a period of 6 to 10 times the nominal retention period. For an ammonium sulfate crystallizer, for instance, operating at a retention time of 4h, the effects of an upset would not be fully dissipated until a period of 1-2 days had passed. Because of this fundamental characteristic, it is necessary that the control system of a crystallizer and the flow sheet be arranged in such a way that stable operations can be maintained for extended periods of time. Only small changes in production rate should be made within any operating shift. The following controls are typical of those required for most continuous crystallizers similar to that shown in Figure 5.16, however, no list of this type can be all inclusive. 

Figure 5.24 shows a graph indicating the equipment costs as a function of capacity for sodium sulfate crystallizers and ammonium sulfate crystallizers of the FC and the DTB type. 

A batch cooling crystallizer (Figure 10.3) was employed by Mullin and Nyvlt (1971) to study the effect of programmed cooling on the CSD of potassium sulfate and ammonium sulfate crystals. The crystallizer was a cylindrical glass vessel (4 or 301) with a round bottom provided with a discharge outlet. It was fitted with... 

While the holes in the pellicle frame are effective in preventing particles from entering the space between the pellicle and mask, they are not effective in preventing airborne molecular contaminants such as ammonia, sulfur dioxide, water vapor, etc. from reaching this space. Under DUV illumination, these contaminants react together to form ammonium sulfate crystals on the reticle, discussed in Section 13.3.4. In addition, molecular contaminants can outgas from pellicle adhesives and from degradation products of the interaction of pellicles with DUV radiation. 

Reaction pathways leading to the formation of ammonium sulfate crystals In DUV lithographic exposure tools... 

Ferric-alum indicator. Dissolve 140 g of ferric ammonium sulfate crystals in 400 mL of hot water. When cool, filter, and make up to a volume of 500 mL with dilute nitric acid. 

Growth Rate of Ammonium Sulfate Crystal In the Presence of Chromlum(III)... 

The growth rate of ammonium sulfate crystals was measured in the presence of chromium(III) in a flow cell. Chromium(III) was added as Cr.(S04)3 [the number of water of the hydrate was not indicated in the original paper]. The results are shown in Figure 5, where the growth length, AL, was directly plotted as a function of growth time for different impurity concentrations. 

As manifested in the growth of potassium sulfate (Figure 4), here also chromium(lll) is very effective in suppressing the growth rate of ammonium sulfate crystal. The unsteady state impurity action is evident at various chromium(III) concentrations. 

Fig. 5 Growth length of ammonium sulfate crystal as a function of time...

The standard procedure for the manufacture of ammonium sulfate from coal gas involves several steps. The gas is first cooled to ca. 32°C (90°F) in an appropriate condensation system. Most of the tar, which is a very troublesome contaminant of ammonium sulfate (and vice versa), condenses and, in addition, much of the water containing approximately 25% of the ammonia, primarily as ammonium salts, also condenses. This water is rendered basic (lime treatment), thereby converting the ammonium ion to ammonia, which is recovered by being stripped off in a lime still and placed back in the coal gas stream. The coal gas stream is heated to above its dew point (approximately 65°C 150°F) and the ammonia is adsorbed in 5%-10% sulfuric acid solution contained in a lead-lined saturator at a temperature of 50°C-60°C (120°F-140°F) ammonium sulfate crystals precipitate from the sulfuric acid solution. 

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