Page 45 - Plant design and economics for chemical engineers

2 8 PLANT DESIGN AND ECONOMICS FOR CHEMICAL ENGINEERS

ALKYLATION UNIT EQUIPMENT
DESIGN AND SELECTION

Reactor Volume
Assume a 4-h cycle and operation of the alkylator at constant temperature and
pressure of 115°F and 1 atm, respectively. The volume of reactants per day (with
a 10% safety factor) is
(12,259) (26,418) (1758)(7.48)
’ = (8.34)(0.88) + (8.34)(0.7533) + (2.44)(62.4)

= 1670 + 4160 + 86 = 5916 gal/day
5916
= - = 986 gal/cycle
6
If the reactor is 75 percent full on each cycle, the volume of reactor needed is
986
VR = - = 1315 gal
0.75
Select a 1300-gal, glass-lined, stirred reactor.

HEAT OF REACTION CALCULATION
G&(,) + w-L(,) + C&b . w-bs(~,
w = AHf(C6HS.q2Hz)1 - AHf(C,H& - AHf(q2HZ4,1

The heats of formation AHf of dodecylbenzene and dodecene are evaluated
using standard thermochemistry techniques outlined in most chemical engineer-
ing thermodynamic texts, The heat formation of benzene is available in the
literature.
- 54,348 Cal/g mol
AHfc6H,.C,2HZS)I =
- 51,239 Cal/g mol
AHfWW =
AHf(C,H,Y = 11,717 Cal/g mol
Thus,
AH, = -54,348 - 11,717 + 51,239 = - 14,826 Cal/g mol
= - 26,687 Btu/lb mol

Assume heat of reaction is liberated in 3 h of the 4-h cycle (i of an operating
day):

Qr= (s)(i)(;) ,
(-26,687) = -211,500 Btu/h