Page 409 - Chemical process engineering design and economics
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Reactor Design 389
Then, for 95% conversion the reaction time,
t R = (1 / 0.02102) hi [1 / (1 - 0.95)] = 142.5 min (2.375 h)
From Equation 7.8.5, calculate the batch time, t&. Because we do not have
values for t, t, 1c, and tc for this reaction, we will have to make use of the times
F H B
given in Table 7.10 for polymerization reactions. Except for the charging time and
cooling times, select the worst case from Table 7.10. We will assume that it takes
the same time to cool the reactor as it does to heat the reactor. We have some con-
trol over the time it takes to charge the reactor. By adjusting a control valve, as-
sume that we can charge the reactor in 1.5 hours. Thus, the batch time, from
Equation 7.8.5,
t B = 1.5 + 2.0 + 2.375 + 2.0 + 1.0 = 8.875 h
Now, calculate the reaction volume from Equation 7.8.6.
3
V r = 1000 (8.875) / 56.2 = 157.9 ft 3 (1181 gal, 4.47 m )
Next, select a standard (4.54 m3) reactor size, from Equation 7.8.7. From
Table 7.3, we find that there is a 1200 gal standard reactor. To allow for some
flexibility select a 1500 gal (5.68 m3) reactor. Even if the production rate requires
1181 gal, the reactor will be filled to 1500 gal, which increases the production rate.
Now, we have to decide on how to remove the enthalpy of reaction - using a
jacket, a coil, a coil and a jacket or an external heat exchanger. First, check if a
jacket will suffice. Because the reaction is an unsteady-state process, the heat
transfer will vary with time. Initially, the reaction rate will be a maximum because
the concentration of acetylated castor oil (AO) is at its maximum value. As the
reaction proceeds, the concentration of acetylated oil will decrease, as will the
heat-transfer rate. In this problem Ah R is given. Thus, we do not need Equations
7.8.2 and 7.8.18 to 7.8.20. From Equation 7.8.4, calculate the initial rate of reac-
tion.
1 min Ib acid Ib AO Ib acid
r Ao = kc Ao = 0.02102 —— 60 —— 0.156 ——— 56.20 ———=11.06 ———
3
min h IbAO ft 3 ft -h
Now, from Equation 7.8.1 calculate Q R. The reaction volume now equals
1500 gal.
450.0 Btu 11.06 Ibacid 1500 gal 1 ft 3
Q = ______________ _____________ ___________ ________
3
1 Ibacid 1 ft -h 1 7.481 gal
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