Solubility precipitation criteria

In order to investigate the conditions governing the precipitation of the particles Equations 7.6.7-7.6.9 may be used for mathematical modelling of the process. Assuming the solubility product criterion to be satisfied, that is the system is saturated with regards to the compound formed, the combined activity coefficients for the precipitated compounds may be calculated. According to Equation 7.6.8, the slope of the saturation content of... 

Rossmann, M., Braeuer, A., Dowy, S., Gallinger, T. G., Leipertz, A., Schluecker, E. (2012). Solute solubility as criterion for the appearance of amorphous particle precipitation or crystallization in the supercritical antisolvent (SAS) process. Journal of Supercritical Fluids, 66, 350-358. 

Again, as in previous chapters, the best place to investigate for determining the modes of removal is the table of solubility products constants as shown in Table 14.1. A precipitation product that has the lowest K p means that the substance is the most insoluble. As shown in the table, the phosphate ion can be precipitated using a calcium precipitant producing either Ca5(P04)3(0H)(j) or Ca3(P04)2. Of these two precipitates, Ca5(P04)3(0H)(j) has the smaller K p of 10" thus, it will be used as the criterion for the precipitation of phosphates. Ca5(P03)3(OH)(j) is also called calcium hydroxy apatite. 

The key criterion in selecting a carrier/extractant is that it and the complex formed must be soluble in the membrane phase, but not soluble in both the internal and continuous phases [46]. Further precipitation within the membrane or at the interfaces must be prevented. To ensure successful stripping, it is necessary to have a solute-complex of moderate stabihty so as to maximize the effectiveness of the stripping agent [46]. The effect of carrier concentration on the stability of ELM systems is discussed in Section 25.4.2.1. 

Methylation of hydrolyzed or methanolized copolymers. One gram samples of hydrolyzed or methanolized copolymers were suspended or dissolved in dry benzene and the mixtures were treated with diazomethane until methylation was complete. This was indicated by the complete dissolution of the copolymers and by the presence of the yellow color of diazomethane in the reaction mixtures for 8 hrs. The reaction mixtures were poured into methanol to precipitate the products, which were reprecipitated twice from benzene solution into methanol before being dried in vacuo. Completely methylated copolymers were soluble in CCli, but copolymers containing very small amounts of acid units were not. This simple test was employed routinely to ensure the completeness of methylation. The 1H-NMR spectra of the copolymers in C D6 solution were examined for the presence of carboxylic acid proton resonances at 5=11.5 ppm as an additional criterion for the completeness of methylation. 

The selectivity of the method is given first by the ability to stay dissolved in a solution containing tartrate, second by the color of the sulfide precipitate, and finally by the fact that the sulfide salt dissolves in sodium hydroxide. The first property distinguishes it from bismuth(III) and the other cations forming insoluble oxides in neutral or alkaline solutions. But since the test does not show that a precipitate is formed in pure water, which dissolves when tartrate is added, all water-soluble cations are not excluded. So it should be viewed as a trick to facilitate dissolution only and not a part of the identification. The color of the sulfide precipitate is unique, and it is the most important criterion for a positive identification if there is any doubt when judging the result, preparing a positive control would be constructive. The solubility of the sulfide salt in sodium hydroxide is a characteristic shared with, for example, the sulfide salt of arsenate, and in classic inorganic separation the sulfide precipitate solubility in hydrochloric acid or polysulfide is used instead. " ... 

Criterion 1. The dilithium initiator, 6, was soluble (0.01-0.08 mol/1) in a mixture of cyclohexane/anisole (85/15, v/v), but like most dilithium initiators [88, 89] precipitated from solution when added to the polymerization solvent, cyclohexane. Therefore, the dilithium initiator was chain extended with approximately 30 units of isoprene to generate an isoprenyldilithium oligomer which was soluble when added to cyclohexane. Since the final anisole concentration was less than 1vol. %, a high (>85%) 1,4-polyiso-prene center block was obtained (65-70% ds-1,4, 20-25% trans-1,4 and the remainder was 3,4-enchainment). 

In this chapter, further validation of the proposed differentiation criterion between precipitating and crystallizing SAS solutes based on the solute solubility is performed. Furthermore, also a study of the influence of solvent mixtures on the solute solubility will be discussed. As described before, the saturation measurements were performed in a variable volume high-pressure view ceU according to the vanishing cloud point method. 

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