Salt-out temperature

Nitrogen solutions are usually produced from urea, ammonium nitrate, and water. They usually contain a corrosion inhibitor and can be stored and used in mild steel (carbon steel) equipment. Solutions usually sold in the United States have three concentrations 32%, 30%, and 28% N. Their salt-out temperatures vary directly with their plant nutrient concentrations. Some of the physical and chemical characteristics of the three nonpressure solutions are shown in Table 10.4 [5[. 

The concentration and the solidification of ammonium nitrate and urea solutions to form solid fertilizers require considerable expenditure of energy and processing expense so it is attractive to use the solutions in the formulation of liquid fertilizers, without processing them into solid form. However, neither ammonium nitrate nor urea alone is sufficiently soluble at ambient temperatures to be attractive for direct use as liquid fertilizer. With either compound alone, a solution with a salting-out temperature of 32°F would contain only about 18 percent nitrogen. Fortunately, however, the joint solubility of the two compounds in water is much more favorable than this so the liquid nitrogen solutions marketed for fertilizer use almost invariably are joint solutions of ammonium nitrate and urea. Typical commercial solutions contain 28 to 32 percent nitrogen, with compositions and characteristics as shown in Table 11.2. 

Trichloro- and dichloromethane, ether, dioxane, benzene, toluene, chlorobenzene, acetonitrile, or even pyridine itself has been employed to carry out the one-pot syntheses. Tliese solvents allow straightforward preparation of the salts. The temperature range between 0° and 20°C is usually employed and the salts formed are sufficiently soluble. In the case of slow reactions, selection of a solvent with a higher boiling point is prohtable since thermal instability of the A -(l-haloalkyl)heteroarylium halides has not been reported. Addition of water or an aqueous solution of sodium acetate does not cause a rapid decomposition of the salts so that this constitutes a useful step in the optimization of some procedures. 

Where is the initial analyte concentration in the liquid phase, C( the concentration of analyte in the gas phase, K the gas-liquid partition coefficient for the analyte at the analysis temperature, V, the volume of liquid phase, and V, the volume of gas phase (318-321,324,325). From equation (8.3) it can be seen that the concentration of the analyte in the headspace above a liquid in equilibrium with a vapor phase will depend on the volume ratio of the geis and liquid phases and the compound-specific partition coefficient which, in turn, is matrix dependent. The sensitivity 1 of the headspace sampling method can be increased in some instances adjusting the pH, salting out or raising the... 

Two basic methods are used for SPME direct immersion of the fibre into the sample and headspace sampling. Experimental parameters comprise the polarity of the sample matrix and coating material, solvent and salting-out. Other parameters for optimisation of SPME conditions include desorption time, injector port temperature and initial oven temperature. 

Bouvier, C. Cote, G. Cierpiszewski, R. Szymanowski, J. Influence of salting-out effects temperature and the chemical structure of the extractant on the rate of copper(II) extraction from chloride media with dialkyl pyridine dicarboxylates. Solvent Extr. Ion Exch. 1998, 16, 1465-1492. 

For most organic chemicals the solubility is reported at a defined temperature in distilled water. For substances which dissociate (e.g., phenols, carboxylic acids and amines) it is essential to report the pH of the determination because the extent of dissociation affects the solubility. It is common to maintain the desired pH by buffering with an appropriate electrolyte mixture. This raises the complication that the presence of electrolytes modifies the water structure and changes the solubility. The effect is usually salting-out. For example, many hydrocarbons have solubilities in seawater about 75% of their solubilities in distilled water. Care must thus be taken to interpret and use reported data properly when electrolytes are present. 

Effect of Temperature on Salting-Out Coefficients. Long and McDevit (23) point out that on differentiation of their equation with respect to temperature, several terms are obtained of which the dVg/dT one is dominant, and the predicted temperature coefficient is approximated by the equation ... 

To apply the correlation of Figure 10 for prediction of the salting out of carbon dioxide by ammonium hydrosulfide and bicarbonate solutions we need to correct for the differences of their partial molar volumes from that of sodium chloride. Partial molar volumes were obtained from Ellis and McFadden(53). Volume change of the hydrosulfide and bicarbonate are equal within 0.2 cm3/mol at temperatures up to 100 C and differ very little at still higher temperatures thus, we assume that the changes with temperature of the salting-out coefficients of the two salts are equal up to... 

Table VIII. EFFECT OF TEMPERATURE ON SALTING-OUT OF CARBON DIOXIDE BY SODIUM CHLORIDE AND CALCIUM CHLORIDE SOLUTIONS... 

Data on the effect of temperature on salting out of ammonia are even less satisfactory than those for carbon dioxide. Perman obtained some data on a potassium sulfate solution at temperatures of 40° to 59°C and on two ammonium chloride solutions at temperatures from 19° to 58°C.(54). His ammonia concentrations were in the range of 5 to 13 molal. His data indicate only small changes in the salting-out coefficient, but the coefficient for ammonium chloride increases with temperature, which is contrary to the effect found with carbon dioxide. 

Figure 11. Effect of temperature on salting out of ammonia (coefficient source (O) at 25°C (28), at 60°C, 155,561 salts LiCl, KOH, NaOH, KCl, NaCl, KNO, ...

The partial molar volume of hydrogen sulfide is nearly equal to that of carbon dioxide (Table 1), and we tentatively assume that changes in its salting-out coefficients with temperature are the same as those of carbon dioxide. 

Coefficient expressing the effect of concentration of gas on its activity coefficient, kg H20/mole Coefficient expressing the effect of change of partial molal volume of electrolyte (with temperature) on the salting-out coefficient, kg H20/cm3. Salt concentration, mol/2. 

Clever, H.L. Holland, C.J. "Solubility of Argon Gas in Aqueous Alkali Halide Solutions — Temperature Coefficient of the Salting Out Parameter," J. Chem. Eng. Data, 1968, 13, 411-14. 

Due to very limited experimental data, ion-ion interaction-parameters had to be assumed to be independent of temperature. Ion-molecule interaction parameters 0 iy were estimated from experimental results on salting-out effects, while 0were set equal zero. 

The addition of an amino acid to mixed solvents at selected temperatures can be a means to compensate even partially for the decrease of dielectric constant due to the solvent addition. Limitations are imposed by the solubility of the amino acid in such mixtures for instance, there is a salting-out effect in methanol-water 50 50 at 25°C when the concentration of glycine is about 0.5 Af (8 20). 

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