Concentration solvent

Figure C2.1.18. Schematic representation of tire time dependence of tire concentration profile of a low-molecular-weight compound sorbed into a polymer for case I and case II diffusion. In botli diagrams, tire concentration profiles are calculated using a constant time increment starting from zero. The solvent concentration at tire surface of tire polymer, x = 0, is constant.

Water is continuously added to the last extraction bath and flows countercurrenfly to filament travel from bath to bath. Maximum solvent concentration of 15—30% is reached in the coagulation bath and maintained constant by continuously removing the solvent—water mixture for solvent recovery. Spinning solvent is generally recovered by a two-stage process in which the excess water is initially removed by distillation followed by transfer of cmde solvent to a second column where it is distilled and transferred for reuse in polymer manufacture. 

Solvent extraction—purification of wet-process phosphoric acid is based on preferential extraction of H PO by an organic solvent vs the cationic impurities present in the acid. Because selectivity of acid over anionic impurities is usually not sufficient, precipitation or evaporation steps are included in the purification process for removal. Cmde wet-process acid is typically concentrated and clarified prior to extraction to remove post-precipitated sludge and improve partition of the acid into the solvent. Concentration also partially eliminates fluoride by evaporation of HF and/or SiF. Chemical precipitation of sulfate (as Ba or Ca salts), fluorosiUcates (as Na salt), and arsenic (as sulfides) may also be used as a prepurification step preceding solvent extraction. 

The diglycolamine (DGA) process also allows high (up to 60 wt % DGA) solvent concentrations for reduced chculation rate and energy requhements. High solvent costs and a higher tendency to absorb heavy hydrocarbons have limited the use of this solvent. 

The solubihty of the Rhovanil vanillin in water—ethanol, water—propylene glycol, and water—glycerol solutions are shown in Eigure 1. In addition, the influence of temperature and solvent concentration are important in maximizing the vanillin concentration. 

Logarithmic-mean solvent concentration between bulk (kmol solvent)/(kmol liquid) (Ibmol solvent)/(lbmol hquid)... 

Since activity coefficients have a strong dependence on composition, the effect of the solvent on the activity coefficients is generally more pronounced. However, the magnitude and direc tion of change is highly dependent on the solvent concentration, as well as the liquid-phase interactions between the key components and the solvent. The solvent acts to lessen the nonideahties of the key component whose liquid-phase behavior is similar to the solvent, while enhancing the nonideal behavior of the dissimilar key. 

The solvent and the key component that show most similar liquid-phase behavior tend to exhibit little molecular interactions. These components form an ideal or nearly ideal liquid solution. The ac tivity coefficient of this key approaches unity, or may even show negative deviations from Raoult s law if solvating or complexing interactions occur. On the other hand, the dissimilar key and the solvent demonstrate unfavorable molecular interactions, and the activity coefficient of this key increases. The positive deviations from Raoult s law are further enhanced by the diluting effect of the high-solvent concentration, and the value of the activity coefficient of this key may approach the infinite dilution value, often aveiy large number. 

The effect of solvent concentration on the activity coefficients of the key components is shown in Fig. 13-72 for the system methanol-acetone with either water or methylisopropylketone (MIPK) as solvent. For an initial-feed mixture of 50 mol % methanol and 50 mol % acetone (no solvent present), the ratio of activity coefficients of methanol and acetone is close to unity. With water as the solvent, the activity coefficient of the similar key (methanol) rises slightly as the solvent concentration increases, while the coefficient of acetone approaches the relatively large infinite-dilution value. With methylisopropylketone as the solvent, acetone is the similar key and its activity coefficient drops toward unity as the solvent concentration increases, while the activity coefficient of the methanol increases. 

FIG. 13-72 Effect of solvent concentration on activity coefficients for acetone-methanol system, (a) water solvent, (h) MIPK solvent. 

The variable that has the most significant impact on the economics of an extractive distillation is the solvent-to-feed (S/F) ratio. For closeboiling or pinched nonazeotropic mixtures, no minimum-solvent flow rate is required to effect the separation, as the separation is always theoretically possible (if not economical) in the absence of the solvent. However, the extent of enhancement of the relative volatihty is largely determined by the solvent concentration and hence the S/F ratio. The relative volatility tends to increase as the S/F ratio increases. Thus, a given separation can be accomplished in fewer equihbrium stages. As an illustration, the total number of theoretical stages required as a function of S/F ratio is plotted in Fig. 13-75 7 for the separation of the nonazeotropic mixture of vinyl acetate and ethyl acetate using phenol as the solvent. 

The thermal quality of the solvent feed has no effect on the value of (S/F)mjn, but does affect the minimum reflux to some extent, especially as the (S/F) ratio increases. R nax occurs at higher values of the reflux ratio as the upper-feed quality decreases a subcooled upper feed provides additional refluxing capacity and less external reflux is required for the same separation. It is also sometimes advantageous to introduce the primary feed to the extractive distillation column as a vapor to help maintain a higher solvent concentration on the feed tray and the trays immediately below... 

On an XY diagram for case C the operating line will go through points Xr, Ys and Xf, with a slope of R /S similar to Fig. 15-13. When using the Kremser equation for case C, one uses the pseudo feed concentration X from Eq. (15-21) and the stripping factor from Eq. (15-22). One uses the raffinate concentration X and inlet solvent concentration Y, without modification. 

Pervaporation membranes are of two general types. Hydrophilic membranes are used to remove water from organic solutions, often from azeotropes. Hydrophobic membranes are used to remove organic compounds from water. The important operating charac teris-tics of hydrophobic and hydrophihc membranes differ. Hydrophobic membranes are usually used where the solvent concentration is about... 

Practically a more convenient way of expressing solute retention in terms of solvent concentration for a binary solvent mixture as the mobile phase is to use the inverse of equation (11), i.e.. 

Figure 10. Graph of Solvent Concentration at Elution against Program Rate...

How do the solvent concentration limits of the adsorption system compare with the solvent concentration of your waste stream ... 

Adsorbers have minimum and maximum solvent concentration limits adsorbers will not function effectively outside those solvent concentration limits. 

Give a clear indicaUon of solvent, concentration, and temperature. These parameters have a much greater effect on chemical shifts and coupling constants for fluorine than for protons. 

The rehability of these analytical methods may be questionable when chemical shift differences of derivatives are of the same magnitude as variations encountered from solvent, concentration, and temperature influences. Reported fluorine chemical shift ranges for tnfluoroacetylated alcohols (1 ppm), p-fluorobenzoylated sterols (1 ppm), and p-fluorobenzoylated ammo acids (0.5 ppm) are quite narrow, and correct interpretation of the fluonne NMR spectra of these denvatized mixmres requires strict adherence to standardized sampling procedure and NMR parameters. 

Toyopearl HW resins overcome several disadvantages of conventional gels, which do not function well at higher flow rates or pressures, are unstable to extremes of pH, salt, and organic solvent concentrations, and can leach saccharide derivatives into the process material. For process-scale SEC, Toyopearl HW resins provide the following advantages ... 

For this scheme we again obtain Eq. (5-58), because the water (solvent) concentration is essentially constant and so is absorbed into the rate constant. Thus, the rds is bimolecular, but the rate equation is first-order the role of the solvent in the transition state is not evident from the rate equation. 

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