(382y) Anthracene-Phenanthrene-Solvent and Phenanthrene-Carbazole-Solvent Ternary Phase Diagrams and Their Applications in the Separation of Them

Anthracene (ANT), Phenanthrene (PHE) and
Carbazole (CAR) are both the common polycyclic aromatic hydrocarbons which are mainly separated from coal tar. Because of their special polycyclic molecular structures (Fig. 1), they have
been widely used to synthesize dyes,
pharmaceuticals, photoelectric materials et al. However, to obtain pure ANT, PHE or CAR is still a challenge due to the formation of solid
solution between them or other impurities.

Figure
1. Molecular structures of ANT, PHE and CAR.

As we all know, whether the
mixture
could be completely separated and how
to separate them are mainly determined by its thermodynamic equilibrium state. It has been found that ANT
and PHE formed solid solution, as well as PHE and CAR. Their
binary phase diagrams
have been reported in
the literature^1-3.However, binary phase diagram cannot
supply adequate information for the separation of ANT-PHE or PHE-CAR mixture,
since solvent is usually needed in the separation process. To study the
thermodynamic equilibrium properties of ANT-PHE and PHE-CAR mixtures in
solvents and illustrate how solvents can influence their separation processes, the
ternary phase diagrams of ANT-PHE in toluene, xylene and dimethylformamide
(DMF) and PHE-CAR in DMF, acetone, acetonitrile (MeCN) and toluene at 308.15 K and
0.1 MPa were determined by wet-residue method in our work.

ANT-PHE-Solvent ternary phase diagrams are shown in
Fig. 2. It was found that two solid solutions, ¦Á (PHE-rich) and ¦Â (ANT-rich),
respectively, formed at PHE-rich and ANT-rich ends but coexisted in the middle
section of the composition, and an invariant point existed in the liquid line.
Interestingly, for ANT-PHE-DMF phase diagram, one more invariant point appeared
in the liquid line. Furthermore, the equilibrium solid phase of ANT-PHE-toluene
phase diagram was sampled and identified by PXRD and DSC, whose result was
consistent with the phase diagram.  As a result, it can be concluded that ANT
and PHE can be purified through multiple recrystallization, but their mixture
cannot be separated completely.

Figure 2. Ternary phase diagrams of ANT-PHE in
toluene, xylene and DMF
at 308.15K and 0.1MPa.

Compared with ANT-PHE-Solvent phase
diagrams, PHE-CAR-Solvent phase diagrams (Fig. 3) only formed PHE-rich solid solution ¦Á in PHE-end,
while the other end was pure CAR. An
invariant point also existed in the liquid line. The identity of the equilibrium solid phase of PHE-CAR-DMF was also
verified through PXRD and DSC. With the guidance of phase diagram, it is obvious
that pure CAR can be separated from the mixture
through solvent crystallization. In addition,
the invariant point shifted with the change of solvent, which meant the
crystallization region of CAR changed. Therefore, a variable Ds (difference
coefficient of solubility) was defined as Ds = (S_PHE - S_CAR)/(S_PHE
+ S_CAR) to reflect how the solvent affected the separation process
of PEH-CAR mixture. Ds represents the difference of the solubilities of PHE and
CAR in the same solvent. Depending on Ds, the solvent screening for the
separation of PHE and CAR or other mixture systems could be simplified, since
only solubilities are needed to predict which solvent is more suitable. Among
the tested solvents in this work, toluene should be the most suitable solvent
for separating PHE-CAR mixture.

Figure 3. Ternary phase diagrams of PHE-CAR in
DMF, acetone, MeCN and toluene at 308.15 K and 0.1 MPa.

References:

[1] S. N. Kipot; R. M. Myasnikova;
A. I. Kitaigorodskii, Study of binary organic systems of anthracene−carbazole
and anthracene−phenanthrene. Zh. Prikl. Khim. 1976, 49, 815−820.

[2] M. Brandstätter-Kuhnert  and H. Weiß,  Monatshefte
F¨¹r  Chemie, 1957, 88(6),
1007-1016.

[3] A. Burel, N. Couvrat, S. Tisse, Y. Cartigny, P. Cardinael, and G. Coquerel,
Eur. Phys. J. Special Topics,
2017, 226(5), 869¨C880.