Measurements of isobaric LLV equilibria of the 1,1,4,4-tetramethyl-2-tetrazene-water binary system: novel experimental approach and modeling essays

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 + H2O binary system were studied under atmospheric pressure and in the temperature range 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 (LV) equilibria of the TMTZ + H2O system using DSC, under atmospheric pressure, highlighted the various equilibrium domains involved in the distillation step. Besides, a heteroazeotropic invariant was identified at TH = 366.3 K for x (TMTZ) = 0.254. Lastly, the thermodynamic modeling of those equilibria, using various models (Van Laar, NRTL, Wilson), enabled to improve the experimental results in order to enhance the extraction conditions leading to the production of ultra-pure TMTZ.