Page 364 - Chemical engineering design

DESIGN INFORMATION AND DATA
8.15. ENTHALPY OF REACTION AND ENTHALPY
OF FORMATION 339
Enthalpies of reaction (heats of reaction) for the reactions used in the production of
commercial chemicals can usually be found in the literature. Stephenson (1966) gives
values for most of the production processes he describes in his book.
Heats of reaction can be calculated from the heats of formation of the reactants
and products, as described in Chapter 3, Section 3.11. Values of the standard heats of
formation for the more common chemicals are given in various handbooks; see also
Appendix C. A useful source of data on heats of formation, and combustion, is the critical
review of the literature by Domalski (1972).
Benson has developed a detailed group contribution method for the estimation of heats
of formation; see Benson (1976) and Benson et al. (1968). He estimates the accuracy
of the method to be from š2.0 kJ/mol for simple compounds, to about š12 kJ/mol for
highly substituted compounds. Benson’s method, and other group contribution methods
for the estimation of heats of formation, are described by Reid et al. (1987).

8.16. PHASE EQUILIBRIUM DATA
Phase equilibrium data are needed for the design of all separation processes that depend
on differences in concentration between phases.

8.16.1. Experimental data
Experimental data have been published for several thousand binary and many multicom-
ponent systems. Virtually all the published experimental data has been collected together in
the volumes comprising the DECHEMA vapour-liquid and liquid-liquid data collection,
DECHEMA (1977). The books by Chu et al. (1956), Hala et al. (1968, 1973), Hirata
et al. (1975) and Ohe (1989, 1990) are also useful sources.

8.16.2. Phase equilibria
The criterion for thermodynamic equilibrium between two phases of a multicomponent
mixture is that for every component, i:

v
f D f L 8.28
i i
L

where f is the vapour-phase fugacity and f the liquid-phase fugacity of component i:
i i

f D
i y i 8.29
i
and
L OL
f D f i x i 8.30
i i
where
D total systems pressure
i D vapour fugacity coefficient
y i D concentration of component i in the vapour phase