Acetic acid equilibrium distribution coefficients

FIGURE 15.2-2 Equilibrium distribution coefficients For solvent extraction of acetic acid from aqueous solution into solvent mixtures containing Alamine 336. ... 

Figure 5.24 is a schematic of a water purification system. A 20 wt% mixture of acetic acid in water is to be extracted with 1-butanol. The outlet concentrations of acetic acid should be 5 wt% in the water phase and 10 wt% in the 1-butanol phase. Pure solvent is used. Find the number, N, of equilibrium stages required and the ratio, F /Fs, of water to 1-butanol. The distribution coefficient, Kd, for this system is 1.6. 

As if the low distribution coefficient does not present enough of an obstacle, extraction of acetic acid from fermentation broths is made still more unattractive by the high pH of the solutions. For the bioprocesses being evaluated, acetic acid will be produced in a solution with a pH of about 6.0. The pK of acetic acid is 4.8 and thus, at a pH of 6.0, virtually all the acetic acid produced in solution exists as an acetate ion. Current extraction/recovery schemes entail acidification (with HCl, for example) to convert the acetate ion to free acetic acid. Then the free acid can be extracted with an organic solvent. If CO2 IS used as the extractant, HCl is not required. Carbonic acid from the C02-water equilibrium will neutralize part, but not all, of the acetate ion this can be determined from a material and charge balance of species in solution. 

Acetic acid often is found in dilute solution from processes that use it as a raw material or solvenL. Fermentation processes also produce acetic acid in dilute solution. In many of these cases the solution pH is high enongh so ther the BCelic acid is iouized partially or completely. The present discussion is restricted to the recovery of un-ionized acetic acid. At a pH below the pA , all the acetic acid can be removed in ihe un-ionized lone. At a higher pH the acetate ion does not distribute into the second phase, and a large distribution coefficient is required for the un-ionized form to shift the equilibrium and obtain an attractive removal capacity. 

Equilibrium data for the system at 25°C are given below in terms of a distribution coefficient K d, where K d = AbIAc Ac = concentration of acetic acid in water, gmoles/liter and Ab = concentration of acetic acid in chloroform, gmoles/liter. 

This Appendix gives the location of the large amount of data scattered throughout the textbook, abietic acid-heptane-methylcellosolve+10% water Distribution coefficient. Table 13-3 acetic acid Adsorption isotherm on activated carbon, Table 18-2 and Problem 18.D7 acetic acid-benzene-water Distribution coefficients. Table 13-3 acetic acid-l-butanol-water Distribution coefficient. Table 13-3 acetic acid-3-heptanol-water Distribution coefficient. Problems 13.D5 and 13.D6 acetic acid-isopropyl ether-water Equilibrium data. Table 13-5 acetonaphthalene Adsorption isotherm on silica gel. Table 18-2... 

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