Page 101 - Process simulation and control using Aspen

ASPEN PLUS SIMULATION OK KKACTOR MOOEI 93

2 .5 ASPEN PLUS SIMULATION OF A RPlug MODEL USING LHHW
KINETICS

Problem statement
In acetic anhydride manufacturing, the cracking of acetone produces ketene and methane
according to the following irreversible vapour-phase reaction:
CH3COCH3 -> CH2CO + CH4
acetone ketene methane
This reaction is first-order with respect to acetone. Pure acetone feed with a flow
rate of 130 kmol/hr enters a PFR at 7250C and 1.5 atm. The kinetic data for the Aspen
Plus simulation are given below.
k = 1.1 s"1
E = 28.5 x 107 J/kmol
n=0
T0 = 980 K
The unit of pre-exponential factor clearly indicates the |C ,1 basis. To use the Langmuir-
Hinshelwood-Hougen-Watson (LHHW) kinetic model, set zero for all coeficients under Term 1
f
f
and that for all coeficients except A under Term 2. Take a very large negative value for
coeficient A. The sample adiabatic PFR is 3 m in length and 0.6 m in diameter. Applying
f
the SYSOP0 base method, compute the component mole fraction in the product stream.
Simulation approach
As we select Aspen Plus User Interface, first the Aspen Plus Startup window appears,
as shown in Figure 2.60. Choose Template option and press OK.

2I=lHJ-J-Lag Pl-W i-H=J Tl I I I 'IW *l
f
f

1

1 -I
I

* *mmm*mH MM

FIGURE 2.60