CHAPTER 6 Multiphase Systems(Elementary princilples of ChemicalEngineering 4th Ed)

6.88) Serine (Ser, molecular weight=105.1g/mol) is anon-essential amino acid (seeFootnote16) produced by fermentation.As with many other fermentation products, substantial downstreamprocessing is required to meet specifications on product purity.Crystallization from an aqueous solution is useful in meeting thosespecifications. The following table shows how serine solubility inwater varies with temperature:

              

T(°C)	  5.0    10.0     15.0     20.0    25.0     30.0    35.0      45.0    50.0
Solubility17 (g Ser/100g H2O)	18.45   22.71   26.88   30.22  35.91 39.40   44.34 50.77  53.76

(a) Prepare a plot of solubility as a function of temperaturethat can be used for interpolation.

(b) An aqueous solution of serine containing 60 g Ser/100 g H2Ois pumped into a batch cooling crystallizer, and the temperature isreduced slowly to 10°C, causing the formation of crystals of themonohydrated salt Ser H2O.Using the given solubility data, estimatethe mass of crystals produced per unit mass of feed solution andthe fraction of serine fed that is recovered as crystallineproduct.

(c) The molecular structure of serine makes it much morehydrophilic than other amino acids, and therefore its solubility isabout an order of magnitude greater than that of most other aminoacids. The addition of methanol to reduce the solubility in thesolution has been suggested. Experimental data show that thesolubility of Ser as a function of methanol content is given by thecorrelation S/S₀ =exp(-4.8x_m)wherex_m is the mass fraction of methanol in a methanol–watersolvent mixture,S₀ (g/g solvent) is serine solubility inwater at a given temperature, and S is the solubility in themethanol–water solvent. In an alternative to the processing schemedescribed in Part(b), sufficient methanol is added to thecrystallizer after it has reached 10°C to produce a final solutionthat has a methanol-to-water mass ratio of 55:45, and the resultingsystem is allowed to come to equilibrium. Estimate the mass ofcrystals produced per unit mass of feed solution and the fractionof serine fed that is recovered as crystalline product.