Initial solution

As the reservoir pressure drops from the initial reservoir pressure towards the bubble point pressure (PJ, the oil expands slightly according to its compressibility. However, once the pressure of the oil drops below the bubble point, gas is liberated from the oil, and the remaining oil occupies a smaller volume. The gas dissolved in the oil is called the solution gas, and the ratio of the volume gas dissolved per volume of oil is called the solution gas oil ratio (Rg, measured in scf/stb of sm /stm ). Above the bubble point, Rg is constant and is known as the initial solution gas oil ratio (Rgj), but as the pressure falls below the bubble point and solution gas is liberated, Rg decreases. The volume of gas liberated is (Rg - Rg) scf/stb. 

Bromophenol blue 2, 7 -DichIorofluorescein Eosin, tetrabromofluorescein Fluorescein Potassium rhodizonate, C404(0K)2 Rhodamine 6G Sodium 3-aIizarinsuIfonate Thorin Dissolve 0.1 g of the acid in 200 mL 95% ethanol. Dissolve 0.1 g of the acid in 100 mL 70% ethanol. Use 1 mL for 100 mL of initial solution. See Dichlorofluorescein. Dissolve 0.4 g of the acid in 200 mL 70% ethanol. Use 10 drops. Prepare fresh as required by dissolving 15 mg in 5 mL of water. Use 10 drops for each titration. Dissolve 0.1 g in 200 mL 70% ethanol. Prepare a 0.2% aqueous solution. Use 5 drops per 120 mL endpoint volume. Prepare a 0.025% aqueous solution. Use 5 drops. 

Chloride is determined by titrating with Hg(N03)2, forming soluble HgCb-The sample is acidified to within the pH range of 2.3-3.8 where diphenylcarbazone, which forms a colored complex with excess Hg +, serves as the visual indicator. Xylene cyanol FF is added as a pH indicator to ensure that the pH is within the desired range. The initial solution is a greenish blue, and the titration is carried out to a purple end point. 

In preparing the sample for analysis the initial solution is filtered. Why is it not necessary to collect the entire filtrate before proceeding ... 

After being formed as a spray, many of the droplets contain some excess positive (or negative) electric charge. Solvent (S) evaporates from the droplets to form smaller ones until, eventually, ions (MH+, SH+) from the sample M and solvent begins to evaporate to leave even smaller drops and clusters (S H+ n = I, 2, 3, etc,). Later, collisions between ions and molecules (Cl) leave [M + H]" ions, which proceed on into the mass analyzer. Ion yield can be enhanced by including a volatile ionic compound (e.g., ammonium acetate) in the initial solution before it reaches the spraying zone. 

The physical process of Hquid—Hquid extraction separates a dissolved component from its solvent by transfer to a second solvent, immiscible with the first but having a higher affinity for the transferred component. The latter is sometimes called the consolute component. Liquid—Hquid extraction can purify a consolute component with respect to dissolved components which are not soluble in the second solvent, and often the extract solution contains a higher concentration of the consolute component than the initial solution. In the process of fractional extraction, two or more consolute components can be extracted and also separated if these have different distribution ratios between the two solvents. 

Physical Equilibria and Solvent Selection. In order for two separate Hquid phases to exist in equiHbrium, there must be a considerable degree of thermodynamically nonideal behavior. If the Gibbs free energy, G, of a mixture of two solutions exceeds the energies of the initial solutions, mixing does not occur and the system remains in two phases. Eor the binary system containing only components A and B, the condition (22) for the formation of two phases is... 

Quantitative Analysis of All llithium Initiator Solutions. Solutions of alkyUithium compounds frequentiy show turbidity associated with the formation of lithium alkoxides by oxidation reactions or lithium hydroxide by reaction with moisture. Although these species contribute to the total basicity of the solution as determined by simple acid titration, they do not react with allyhc and henzylic chlorides or ethylene dibromide rapidly in ether solvents. This difference is the basis for the double titration method of determining the amount of active carbon-bound lithium reagent in a given sample (55,56). Thus the amount of carbon-bound lithium is calculated from the difference between the total amount of base determined by acid titration and the amount of base remaining after the solution reacts with either benzyl chloride, allyl chloride, or ethylene dibromide. 

HMnO 2H20 [24653-70-1] decomposes at 18°C. Aqueous solutions of permanganic acid below a concentration of 3 wt % are stable over time, whereas in the concentration range of 5—15% HMnO, the decomposition rate increases with increasing initial solution concentration at room temperature (103). 

Control of a batch ciystaUizer is almost always the most difficult part and veiy often is not practiced except to permit homogeneous nucleation to take place when the system becomes supersaturated. If control is practiced, it is necessary to have some means for determining when the initial solution is supersaturated so that seed of the appropriate size, quantity, and habit may be introduced into the batch. Following seeding, it is necessaiy to limit the coohng or evaporation in... 

Like simulated annealing, tabu search is a technique designed to avoid the problem of becoming trapped in local optima. The procedure is basically hill-climbing, which commences at an initial solution and searches the neighbourhood for a better solution. However, the process will recognize, and avoid areas of the solution space that it has already encountered, thus making these areas tabu . The tabu moves are kept in a finite list, which is updated as the search proceeds. 

The initial solution to this problem was to install an exhaust channel on the opening tor the films, as in Fig. 12. 8. Laboratory experiments show that the principle is inexpedient and it is possible only to obtain a capture efficiency of 70% at a flow rate of 100 m- h"L... 

The reactor is loaded with a solution of emulsifier in an organic solvent and the aqueous monomer solution (20-60%) is dispersed in the organic phase by stirring. The obtained emulsion is deoxygenated by purging dry nitrogen or by multiple evacuation and thermostated at 30-60°C. Then, an initiator solution is introduced in the reaction mixture and the process is carried out at 30-60°C for 3-6 h, after which the reaction mixture is aged for 1-5 h. 

The last definition has widespread use in the volumetric analysis of solutions. If a fixed amount of reagent is present in a solution, it can be diluted to any desired normality by application of the general dilution formula V,N, = V N. Here, subscripts 1 and 2 refer to the initial solution and the final (diluted) solution, respectively V denotes the solution volume (in milliliters) and N the solution normality. The product VjN, expresses the amount of the reagent in gram-milliequivalents present in a volume V, ml of a solution of normality N,. Numerically, it represents the volume of a one normal (IN) solution chemically equivalent to the original solution of volume V, and of normality N,. The same equation V N, = V N is also applicable in a different context, in problems involving acid-base neutralization, oxidation-reduction, precipitation, or other types of titration reactions. The justification for this formula relies on the fact that substances always react in titrations, in chemically equivalent amounts. 

Precipitation of fluoride compounds from solutions of hydrofluoric acid, HF, is performed by the addition of certain soluble compounds to solutions containing niobium or tantalum. Initial solutions can be prepared by dissolving metals or oxides of tantalum or niobium in HF solution. Naturally, a higher concentration of HF leads to a higher dissolution rate, but it is recommended to use a commercial 40-48% HF acid. A 70% HF solution is also available, but it is usually heavily contaminated by H2SiF6 and other impurities, and the handling of such solutions is extremely dangerous. 

Two kinds of tantalum-containing initial solutions were chosen according to their ionic complex structure. The first one contained mostly TaF6 ions (Ta F = 1 18) while the second was characterized predominantly by TaF72 ions (Ta F = 1 6.5). The ionic composition of the solutions was determined by Raman spectroscopy. 

Three kinds of niobium-containing initial solutions were used, with different Nb F ratios 1 9, 1 18 and 1 6. The first two initial solutions contained mostly NbF6" ions, whereas the third was composed primarily of NbOF52 ions. Table 5 presents the composition of the compounds that were precipitated following the addition of certain alkali fluorides to the initial solutions. 

An increase in the Me F ratio leads to an increase in the acidity of the initial solution, whereas the acidity of alkali metals increases according to their molecular weight, from Li to Cs. Therefore the additives of fluorides of alkali metals having higher atomic weight provide formation of complex fluorides with lower coordination number of tantalum or niobium. 

An initial solution was prepared by dissolving metallic niobium powder in 40% hydrofluoric acid. The dissolution was performed at elevated temperature with the addition of a small amount of nitric acid, HN03, to accelerate the process. The completeness of niobium oxidation was verified by UV absorption spectroscopy [21]. The prepared solution was evaporated to obtain a small amount of precipitate, which was separated from the solution by filtration. A saturated solution, containing Nb - 7.01 mol/1, HF - 42.63 mol/1, and corresponding to a molar ratio F Nb = 6.08, was prepared by the above method. The density of the solution at ambient temperature was p = 2.0 g/cc. Concentrations needed for the measurements were obtained by diluting the saturated solution with water or hydrofluoric acid. 

Fig. 48. Raman spectra of initial solution (1) and following additions of (expressed as molar ratios) NH4F Nb=l l (2) NH4F Nb=4 l (3) KF Nb=l l (4) RbF Nb=0.5 l. Reproducedfrom [291], D. V. Tsikaeva, S. D. Nikitina, A. I. Agulyansky, V. T. Kalinnikov, Zh. Obschei. Khim. 57 (1987) 974, Copyright 1987, with permission of Nauka (Russian Academy of Sciences) publishing.

The tantalum dissolution process takes longer compared to the preparation of the corresponding niobium solution, therefore the solution is heated and a small amount of nitric acid is added. A grey precipitate indicates saturation of the solution. The prepared solution is separated from the precipitate by filtration and used as the initial solution. 

Another point is related to the high acidity level of the final solution, which leads to certain limitations in the subsequent technological steps. Specifically, the high acidity of the initial solution eliminates any possibility for selective extraction, i.e. sequential separation of tantalum and then of niobium. Due to the high concentration of acids, only collective extraction (of tantalum and niobium together) can be performed, at least at the first step. In addition, extraction from a highly acidic solution might cause additional contamination of the final products with antimony and other related impurities. In order to reduce the level of contaminants in the initial solution, some special additives are applied prior to the liquid-liquid extraction. For instance, some mineral acids and base metals are added to the solution at certain temperatures to cause the precipitation of antimony [455 - 457]. 

Two main schemes exist for the separation and purification of tantalum and niobium using liquid-liquid extraction. The first is based on the collective extraction of tantalum and niobium from an initial solution into an organic phase so as to separate them from impurities that remain in the aqueous media, the raffinate. The separation of tantalum and niobium is subsequently performed by fractional stripping into two different aqueous solutions. In this case, stripping of niobium is performed using relatively weak acids prior to the stripping of tantalum. Fig. 125 presents a flow chart of the process. 

The second process of selective extraction is more effective and leads to better separation of tantalum and niobium and to more effective purification. Its performance, however, requires the initial solution to be of relatively low acidity. 

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