Information Technology Reference
In-Depth Information
Figure 2.12 Tabular results for analysis PT-2.
the critical temperature, is given by
N k (tck) 2
0 . 584 + 0 . 965
k
N k (tck)
1
T c (K) = T b
(2.3)
k
where tck are structural group contribution values and N k are the number of appear-
ances of that group in the molecule. Note that the critical temperature is directly
proportional to the boiling point modified by group contribution functions.
Equations of state provide the means for estimating many other properties, such
as the effect of pressure on enthalpy at constant pressure. Since the equation-of-state
parameters are composed primarily of critical properties and in many cases the acentric
factor (derived from vapor pressure), experimental values for the boiling point and
vapor pressure data are very important.
The property constant estimations system within Aspen Plus, sometimes referred to
as PCES, is initiated by the same methods as in Chapter One, except that the Run type
Property Estimation is entered. This function is used when a user-defined component
is required. The component should not be entered into the component list, but rather,
the new component wizard, shown in Figure 2.13, should be employed. Aspen Plus
prompts for any available basic data and molecular structure, as shown in Figure 2.14
followed by Figure 2.15 for additional data. It is imperative that the radio button to
estimate properties by the Aspen Plus system be selected. Methyl vinyl ketone (MVK)
is an example of a user-defined component. The molecule's structure is
CH 3 -CO-CH = CH 2
Search WWH ::




Custom Search