Question

Thehormone estrogen is produced in the ovaries of females and elsewhere in the body in men and post-
menopausal women, and it is also administered in estrogen replacement therapy, a common treatment
for women who have undergone a hysterectomy. Unfortunately, it also binds to estrogen receptors in
breast tissue and can activate cells to become cancerous. Tamoxifen is a drug that also binds to estrogen
receptors but does not activate cells, in effect blocking the receptors from access to estrogen and
inhibiting the growth of breast-cancer cells.
Tamoxifen is administered in tablet form. In the manufacturing process, a finely ground powder
contains tamoxifen (tam) and two inactive fillers—lactose monohydrate (lac) and corn starch (cs). The
powder is mixed with a second stream containing water and suspended solid particles of polyvinylpyrro-
lidone (pvp) binder, which keeps the tablets from easily crumbling. The slurry leaving the mixer goes to a
dryer,inwhich94.2%ofthewaterfedtotheprocessisvaporized.Thewetpowderleavingthedryercontains
8.80wt% tam, 66.8% lac, 21.4% cs, 2.00% pvp, and 1.00% water. After some additional processing, the
powder is molded into tablets. To produce a hundred thousand tablets, 17.13kg of wet powder is required.
(a) Taking a basis of 100,000 tablets produced, draw and label a process flowchart, labeling masses of
individual components rather than total masses and component mass fractions. It is unnecessary to
label the stream between the mixer and the dryer. Carry out a degree-of-freedom analysis of the
overall two-unit process.
(b) Calculate the masses and compositions of the streams that must enter the mixer to make 100,000
tablets.
(c) Why was it unnecessary to label the stream between the mixer and the dryer? Under what
circumstances would it have been necessary?
(d) Go back to the flowchart ofPart (a). Without using the mass of the wet powder (17.13kg) or any of
the results from Part (b) in your calculations, determine the mass fractions of the stream
components in the powder fed to the mixer and verify that they match your solution to Part (b).
(Hint: Take a basis of 100kg of wet powder.)
(e) Suppose a student does Part (d) before Part (b), and re-labels the powder feed to the mixer on the
flowchart of Part (a) with an unknown total mass (m1) and the three now known mole fractions.
(Sketch the resulting flowchart.) The student then does a degree-of-freedom analysis, counts
four unknowns (the masses of the powder, pvp, and water fed to the mixer, and the mass of
water evaporated in the dryer), and six equations (five material balances for five species and the
percentage evaporation), for a net of 2 degrees of freedom. Since there are more equations than
unknowns, it should not be possible to get a unique solution for the four unknowns. Never-
theless, the student writes four equations, solves for the four unknowns, and verifies that all of the balance equations are satisfied. There must have been a mistake in the degree-of-freedom
calculation. What was it?

Answer 1