Page 474 - Elements of Chemical Reaction Engineering Ebook

Sec. 8.3 Nonisothermal Continuous-Flow Reactors 445

You are feeding 2500 lb/h (43.04 lb mol/h) of propylene oxide (P.O.) to the
' reactor. The feed stream consists of (1) an equivolumetric mixture of propylene
oxide (46.62 ft3/h) and methanol (46.62 ft3/h), and (2) water containing 0.1 wt %
H,SO,. The volumetric flow rate of water is 233.1 ft3/h, which is 2.5 times the
methanol-P.O. flow rate. The corresponding molar feed rates of methanol and water
are 71.87 and 802.8 lb mol/h, respectively. The water-propylene oxide-methanol
mixture undergoes a slight decrease in volume upon mixing (approximately 3%),
but you neglect this decrease in your calculations. The temperature of both feed
strani is 58°F prior to mixing, but there is an immediate 17OF- temperature rise
upon mixing of the two feed streams caused by the heat of mixing. The entering
temperature of all feed streams is thus taken to be 75°F (Figure E8-4.1).

Furosawa et a1.S state that under conditions similar to those at which you are
operating, the reaction is first-order in propylene oxide concentration and apparent
zero-order in excess of water with the specific reaction rate

k = Ae-EIRT = 16.96 X 1012(e-32,400/RT) h-1

The units of E are Btu/lb mol.
There is an important constraint on your operation. Propylene oxide: is a
rather low-boiling substance (b.p. at 1 atm, 93.7"F). With the mixture you are lasing,
you feel that you cannot exceed an operating temperature of 125"F, or you will lose
too much oxide by vaporization through the vent system.
Can you use the idle CSTR as a replacement for the leaking one if it will be
opeirated adiabatically? If so, what will be the conversion of oxide to glycol?

Solution
(All data used in this problem were qbtained from the Handbook of Chemistry and
Physics unless otherwise noted.) Let the reaction be represented by

A+B --+ C
where

T. Fuiusawa, H. Nishimura, and T. Miyauchi, j. Chem. Eng. Jpn., 2, 95 (1969).