(527g) Insight into the Role of Piperazine in the Thermodynamics and Nucleation Kinetic of Triethylenediamine - Methyl Tertiary Butyl Ether System

Recently,
additives have been taken into consideration in order to improve solubility,
stability, and crystal habit. Besides the additive, a certain impurity
originating from solvent or a by-product from former reaction also has an
influence on the crystallization process and crystal product. In this work, we
explore the role of piperazine, a major by-product from former reaction, in the
nucleation behavior of triethylenediamine (referred as TEDA below) - Methyl tertiary butyl ether
(referred as MTBE below) system. Different amounts of piperazine (1%, 3%, 5%),
which is close to the crude material, are considered to investigate how it
affects the thermodynamic and nucleation behavior of the crystallization of
TEDA-MTBE system. The solubility of TEDA in MTBE in the presence of piperazine is
analyzed to describe thermodynamic behavior. It is found that the solubility of
TEDA in MTBE increases with increasing the amount of piperazine. Then, radial
distribution function (RDF) analysis is used to uncover the interactions
between piperazine, TEDA and MTBE by Materials Studio. As expected, the
interaction between the solute and the solvent becomes stronger in the presence
of piperazine, thus improving the solubility of TEDA in MTBE. Meanwhile, data of
supercooling ¦¤T_max,
a measure of metastable zone width (MSZWs), as a function of saturated
temperature T₀, cooling rate R, and the content of piperazine are
analyzed to describe the role of piperazine in the nucleation kinetics of
TEDA-MTBE system. It is found that piperazine can significantly promote the
nucleation rate of TEDA-MTBE system. Furthermore, based on
our previous work, modified Sangwal¡¯s theory is employed to take further insight into the role
of impurity in the nucleation behavior of TEDA-MTBE system. In the CNT framework, it
shows that the critical Gibbs free energy is lower in the presence of piperazine,
as a result it is easier to form nuclei and narrow the MSZWs. At last, the
effect of piperazine on the crystal size distribution (CSD) of TEDA product is
also investigated and discussed.