Page 353 - Elements of Chemical Reaction Engineering Ebook

324 Multiple Reactions Chap. 6

and subsequent elimination can be modeled as a series reaction. The rate of
absorption from the gastrointestinal tract into the bloodstream and body is a
first-order reaction with a specific reaction rate constant of 10 h-l . The rate at
which ethanol is broken down in the bloodstream is limited by regeneration of
a coenzyme. Consequently, the process may be modeled as a zero-order reac-
tion with a specific reaction rate of 0.192 g/h.L of body fluid. How long
would a person have to wait (a) in the United States; (b) in Sweden; and (c) in
Russia if they drank two tall martinis immediately after arriving at a party?
How would your answer change if (d) the drinks were taken h apart; (e) the
two drinks were consumed at a uniform rate during the first hour? (f) Suppose
that one went to a party, had one and a half tall martinis right away, and then
received a phone call saying an emergency had come up and they needed to
drive home immediately. How many minutes would they have to reach home
before he/she became legally intoxicated, assuming that the person had noth-
ing further to drink? (g) How would your answers be different for a thin per-
son? A heavy person? For each case make a plot of concentration as a function
of time. (Hint: Base all ethanol concentrations on the volume of body fluid.
Plot the concentration of ethanol in the blood as a function of time.) What
generalizations can you make? What is the point of this problem?
Additional information:
Ethanol in a tall martini: 40 g
Volume of body fluid: 40 L (SADD-MADD problem)
P6-88 (Pharmacokinetics) Tarzlon is a liquid antibiotic that is taken orally to treat
infections of the spleen. It is effective only if it can maintain a concentration
in the blood-stream (based on volume of body fluid) above 0.4 mg per dm3 of
body fluid. Ideally, a concentration of 1.0 mg/dm3 in the blood would like to
be realized. However, if the concentration in the blood exceeds 1.5 mg/dm3,
harmful side effects can occur. Once the Tarzlon reaches the stomach it can
proceed in two pathways, both of which are first order: (1) It can be absorbed
into the bloodstream through the stomach walls; (2) it can pass out through
the gastrointestinal tract and not be absorbed into the blood. Both these pro-
cesses are first order in Tarzlon concentration in the stomach. Once in the
bloodstream, Tarzlon attacks bacterial cells and is subsequently degraded by a
zero-order process. Tarzlon can also be removed from the blood and excreted
in urine through a first-order process within the kidneys. In the stomach:
Absorption into blood kl = 0.15 h-l
Elimination through gastrointestine k, = 0.6 h-'
In the bloodstream:
Degradation of Tarzlon k, = 0.1 mg/dm3. h
Elimination through urine k, = 0.2 h-l
(a) Plot the concentration of Tarzlon in the blood as a function of time when
1 dose (i.e. one liquid capsule) of Tarzlon is taken.
(b) How should the Tarzlon be administered (dosage and frequency) over a
48-h period to be most effective?
(c) Comment on the dose concentrations and potential hazards.
(d) How would your answers change if the drug were taken on a full or
empty stomach?
One dose of Tarzlon is 250 mg. in liquid form: Volume of body fluid = 40 dm3