Precipitants overall

The equilibrium of the overall reaction Is shifted in the direction of the condensation product by the precipitation of the p diketone as its sodium salt. 

The Biazzi continuous process is also used. The reactants are continuously fed to a series of nitrators at 15—20°C followed by separation of the PETN, water washing, solution in acetone at 50°C, neutralization with gaseous ammonia, and precipitation by dilution with water. The overall yield is more than 95%. The acetone and the spent acid are readily recovered. 

In the direct precipitation process, the seeds of iron(III) oxide are added to an iron salt solution, most often iron(II) sulfate, which is subsequendy oxidized by air. The released sulfuric acid is removed by the addition of metallic iron with which it reacts to iron(II) sulfate. The overall reaction shows that ferrous sulfate is not consumed during the process. It only helps to oxidize metallic iron to ferric oxide ... 

Other Uses. Other uses include intermediate chemical products. Overall, these uses account for 15—20% of sulfur consumption, largely in the form of sulfuric acid but also some elemental sulfur that is used directly, as in mbber vulcanization. Sulfur is also converted to sulfur trioxide and thiosulfate for use in improving the efficiency of electrostatic precipitators and limestone/lime wet flue-gas desulfurization systems at power stations (68). These miscellaneous uses, especially those involving sulfuric acid, are intimately associated with practically all elements of the industrial and chemical complexes worldwide. 

The NRC Committee s estimates of catalyst use for 1972, 1974, and 1975 were 40—80% higher than the BOM s, and the former s estimates for overall use, including ceramics, electronics, and unspecified uses, were 3—39% higher. Data pubHshed by the BOM through 1980 show a precipitous decline in total annual use from ca 311 t in 1974 to ca 82 t in 1980. The decline appears to have been caused mainly by unfavorable business conditions and conservation efforts, but part of the apparent decline may stem from incomplete collection of data. 

Many times solids are present in one or more phases of a solid-hquid system. They add a certain level of complexity in the process, especially if they tend to be a part of both phases, as they normally will do. Approximate methods need to be worked out to estimate the density of the emulsion and determine the overall velocity of the flow pattern so that proper evaluation of the suspension requirements can be made. In general, the solids will behave as though they were a fluid of a particular average density and viscosity and won t care much that there is a two-phase dispersion going on in the system. However, if solids are being dissolved or precipitated by participating in one phase and not the other, then they will be affected by which phase is dispersed or continuous, and the process will behave somewhat differently than if the solids migrate independently between the two phases within the process. 

Pedersen s preparation of dibenzo-18-crown-6 involves catechol and bis(2-chloroethyl) ether. In this procedure, sodium hydroxide is used as base and M-butanol as solvent. The reactants are heated overnight and the crude crown is obtained by precipitation from acetone in which it is almost completely insoluble. The yield range specified is 39—48% and is readily realized. The overall preparation is illustrated in Eq. (3.11). 

Using the SFM, the influence of micromixing and mesomixing on the precipitation process and properties of the precipitate can be investigated. Mass and population balances can be applied to the individual compartments and to the overall reactor accounting for different levels of supersaturation in different zones of the reactor. 

An alternative theory has been developed to model precipitation with agglomeration where, beside the overall particle size, an additional co-ordinate of crystal number within an agglomerate is introduced (Wachi and Jones, 1992). Figure 8.22 shows the concept of agglomeration and disruption respectively. 

Employing two co-ordinates of overall particle size, L, and degree of agglomeration, S (which is, of course, proportional to the mean primary particle size) to define the population density, n S, L, t), the population balance during precipitation with agglomeration is described as ... 

As the film dissolves more oxide film is formed, i.e. the metal/oxide interface progresses into the metal, and the overall rate may be low enough to be acceptable for a particular process. In other cases, the corrosion products precipitate on the surface of the oxide and either accelerate the overall rate by enhancing diffusion of ions through the porous outer layers or, when less porous layers are formed, access of hydrogen ions to the inner oxide surface is reduced thus decreasing the rate. 

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