In Example 8.19, the % extraction of lysozyme is high (95.2%), but the % purity of the lysozyme in the total extracted proteins is low (15.1%). The Kremser plot of Figure 5.9 suggests that by reducing the amount of solvent and increasing the number of stages, the % purity can be increased. To verify this, repeat the calculations of Example 8.19 by reducing the flow rate of PEG 3000 by a factor of 10 to 40.6 kg/h and re-solving Eqs. (1) to (6) to obtain a new, muchlower water flow rate in the solvent, and new protein-free top and bottom phase equilibrium compositions that satisfy the tie line given in Example 8.19. Then, as a function of the number of countercurrent equilibrium stages from 1 to 5, calculate the % extraction of lysozyme and the other proteins, and the % purity of lysozyme in the extracted proteins.

Data From Example 8.19

Lysozyme is an enzyme of the innate immune system, lacking from the diet of children who are fed infant formula, increasing their susceptibility to pathogens like Salmonella or E. coli. Balasubramaniam et al. [108] discuss genetically engineering tobacco, a ubiquitous gene host, to produce large quantities of recombinant lysozyme. A clarified tobacco broth contains 800 kg/h of water, 5 kg/h of lysozyme (L), and 40 kg/h of other proteins (OP). The lysozyme is to be extracted by ATPE using the PEG 3000–water–Na2SO4 (salt) system at 20C. A phase diagram for this system, similar to Figure 8.44, has been measured by Hammer et al. [109]. One tie line for this system, in terms of wt% for PEG, salt, and water shows a top-phase composition of 40, 1, and 59, with a bottom-phase composition of 0.6, 18, and 81.4. The partition coefficients based on mass ratios K' _L and K'_OP have been measured with the system to be 20 and 2, where K0 i is defined as (kg i in top phase/kg protein-free top phase)/(kg i in bottom phase/kg protein-free bottom phase). If 190 kg/h of salt is added to the broth and if equilibrium is achieved n a single extraction stage, determine: 

(a) The flow rate of the water in the aqueous PEG solvent if it is to contain 406 kg/h of PEG, and if the overall composition of PEG–water–salt for the extraction system is to lie on the aforementioned tie line; 

(b) The compositions in wt% on a protein-free basis of the equilibrium top phase and bottom phase; 

(c) The percent of lysozyme and of other proteins extracted to the top phase; and 

(d) The % purity of the lysozyme in the total extracted protein.

 

Transcribed Image Text:

(KA)D = (XA)/(XA) = (YA)¹/(YA)" (8-1)