Application of Pressure Change

In some cases, change of pressure very much influences the location of azeotrope points and sometimes even leads to transformation of azeotropic mixture into zeotropic. That uses change of pressure for separation of azeotropic mixtures without entrainers. The example is separation of mixture acetic add(l)-water(2)-formic acid(3) at two pressures at atmospheric pressure and at 200 nun Hg pressure (Kuschner et al., 1969). 

Unfortunately, in the majority of cases, change of pressure weakly influence the location of azeotropic points, which makes this method of separation impossible or uneconomical. Possibility or impossibility of usage of two levels of pressure for separation of binary azeotropic mixtures can be easily determined by means of simulation of their phase equilibrium. 

While choosing entrainers for separation of binary azeotropic mixtures, the structure of phase equilibrium diagrams (residue curve maps) of ternary mixtures formed at the addition of entrainer is of great importance. 

The most desirable types of residue curve maps were discussed in a number of works (Doherty Caldorola, 1985 Laroche et al., 1992 Stichlmair Herguijuela, 1992). 

If entrainer - component 3 is intermediately boiling and does not form azeotropics with components of the azeotropic mixture 1,2 under separation, then ternary mixture has a residue curve map shown in Fig. 8.27. In this case. 

---

The pressure cell built by Muller et al. [37] for the terrylene sample is made of stainless steel and is equipped with quartz windows. As mentioned before, it contains both, the focusing and the collecting optics. The cell is connected to a helium gas cylinder and the pressure can be fine-tuned with a mechanical valve. This cell allows the application of pressure changes from 200 hPa to 2500 hPa. 

---