Chapter 4, Problem 4.39P

The hormone estrogen is produced in the ovaries of females and elsewhere in the body in men and postmenopausal women, and it is also administered in estrogen replacement therapy, a common treatment for w omen 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 com starch (cs). The powder is mixed w ith a second stream containing w ater and suspended solid particles of polyvinylpyrrolidone (pvp) binder, w hich keeps the tablets from easily crumbling. The slurry leaving the mixer goes to a dryer, in w hich 94.2% of the water fed to the process is vaporized. The w et pow der leasing the dryer contains 8.80 wt% tam. 66.8% lac. 21.4% cs, 2.00% pvp. and 1.00% water. After some additional processing, the pow der is molded into tablets. To produce a hundred thousand tablets, 17.13 kg of w et pow der is required.

1. 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. Cany out a degree-of-freedom analysis of the overall two-unit process.
2. Calculate the masses and compositions of the streams that must enter the mixer to make 100,(MX) tablets.

Why was it unnecessary' to label the stream between the mixer and the dryer? Under what circumstances would it have been necessary?

Go back to the flow chart of Part (a). Without using the mass of the wet powder (17.13 kg) 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 100 kg of wet powder.)

Suppose a student does Part (d) before Part (b), and re-labels the pow der feed to the mixer on the flowchart of Part (a, with an unknown total mass (nq) 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. Nevertheless, the student w rites four equations, solves for the four unknow ns, 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?