The present study was carried out in the frame of the optimization of the synthesis process of 1,1,4,4-tetramethyl-2-tetrazene (TMTZ), a prospective liquid propellant. The liquid-liquid (LL) equilibria of the TMTZ + H 2 O binary system were studied under atmospheric pressure and in the range of temperature from 278.15 up to 348.15 K. These results established the conditions leading to a spontaneous demixing of TMTZ from the aqueous synthesis solutions. The experimental study of the liquid-vapor (VL) equilibria of the TMTZ + H 2 O system by DSC, under atmospheric pressure, highlighted the various equilibrium domains involved in the distillation step. Lastly, the thermodynamic modelling of those equilibria, using various models (Van Laar, NRTL, Wilson), enabled to refine the experimental results in order to enhance the extraction conditions leading to the production of ultra-pure TMTZ.