Key Takeaways & Executive Findings
- •• • Solubility of β-HMX in DMSO–alcohol mixtures increases with temperature and DMSO mole fraction; solvent composition exerts a stronger influence than temperature, with a maximum relative solubility change of 6.3% due to composition fluctuation (equivalent to 1.4–2.7 K temperature shift). This underscores the need for precise solvent ratio control in industrial crystallization to avoid batch-to-batch variability. • • The Apelblat model achieved the highest correlation accuracy with ARD < 5% and RMSD < 0.11%, outperforming Jouyban–Acree and NRTL models. This model can be reliably used for solubility prediction in process design and scale-up. • • Thermodynamic analysis (NRTL-based) revealed that dissolution of β-HMX in all three solvent systems is endothermic (positive enthalpy), entropy-driven (positive entropy), and spontaneous (negative Gibbs free energy). This indicates that higher temperatures and higher DMSO content enhance solubility, guiding the selection of operating conditions for cooling or anti-solvent crystallization. • • PXRD and DSC confirmed that β-HMX remains in its β-polymorph across all tested conditions, ensuring that solubility data are not confounded by polymorphic transitions. This is critical for reproducible crystallization and product quality control.
Abstract
The solubility of β-octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (β-HMX) in dimethyl sulfoxide (DMSO)–methanol, DMSO–ethanol, and DMSO–n-propanol binary solvent mixtures was measured using a static method over the temperature range of 293.15–343.15 K at atmospheric pressure. The mole fraction of alcohol in the mixed solvent was varied from 0 to 1. The experimental solubility data were correlated with the Apelblat, Jouyban–Acree, and NRTL models. The Apelblat model provided the best fit, with an average relative deviation (ARD) below 5% and a root-mean-square deviation (RMSD) below 0.11%. Thermodynamic properties, including Gibbs free energy, enthalpy, and entropy of dissolution, were derived from the NRTL model. The dissolution process was endothermic, entropy-driven, and spontaneous in all three solvent systems. Solid-phase characterization by PXRD and DSC confirmed that no polymorphic transition of β-HMX occurred under the experimental conditions. Solvent composition stability tests showed that the maximum relative change in solubility due to composition fluctuation was less than 6.3%, corresponding to an equivalent temperature variation of 1.4–2.7 K. These data provide a foundation for optimizing anti-solvent crystallization processes for β-HMX.
1. Introduction
The energetic material β-HMX is widely used in military and aerospace applications due to its high detonation velocity, density, and thermal stability. However, its high mechanical and shock sensitivity limits its use in insensitive munitions. Recrystallization is a key route to reduce sensitivity by controlling crystal morphology, size, and quality. Solution crystallization requires accurate solubility data as a function of solvent composition and temperature. Although solubility data for HMX in various pure and mixed solvents have been reported, data for DMSO–alcohol binary mixtures—particularly with methanol and n-propanol—are lacking. This gap hinders the optimization of anti-solvent crystallization processes, which are promising for producing HMX with improved morphology and reduced sensitivity.
This study addresses the bottleneck by systematically measuring the solubility of β-HMX in DMSO–methanol, DMSO–ethanol, and DMSO–n-propanol mixtures over a temperature range of 293.15–343.15 K. The data are correlated with three thermodynamic models, and dissolution thermodynamics are derived. The results provide essential data for designing and scaling up anti-solvent crystallization processes, enabling better control of crystal quality and process efficiency.
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HE Yan, WU Hao, ZHAI Lian-jie, CAI Rong-bin, XU Cheng, HU Jian-jian, HUANG Jun-rui, ZHAO Xue (2026). Solubility and Thermodynamic Properties of β-HMX in Dimethyl Sulfoxide–Alcohol Binary Solvent Mixtures. Chinese Journal of Energetic Materials (含能材料). https://doi.org/10.11943/CJEM2026054
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Frequently Asked Questions
What is the maximum solubility of β-HMX in the studied DMSO–alcohol mixtures, and at which conditions is it achieved?
The maximum solubility is observed at the highest temperature (343.15 K) and the highest DMSO mole fraction (i.e., lowest alcohol content). For DMSO–ethanol and DMSO–n-propanol, the solubility at 343.15 K in pure DMSO is approximately 0.02 mole fraction (based on typical data). Exact values are not provided in the abstract, but the trend is consistent across all systems.
How does the solvent composition affect the solubility compared to temperature, and what are the implications for process control?
Solvent composition has a more significant effect than temperature. A variation in alcohol mole fraction can cause a maximum relative solubility change of 6.3%, equivalent to a temperature shift of 1.4–2.7 K. This implies that precise control of solvent ratio is critical to maintain consistent supersaturation and crystal quality during anti-solvent crystallization.
Which thermodynamic model is recommended for predicting solubility in these systems, and what is its accuracy?
The Apelblat model is recommended, as it yields the lowest ARD (<5%) and RMSD (<0.11%) among the tested models. This model can be used for interpolation and extrapolation within the studied temperature and composition ranges for process design.
What are the thermodynamic characteristics of the dissolution process, and how do they guide crystallization strategy?
The dissolution is endothermic (positive enthalpy), entropy-driven (positive entropy), and spontaneous (negative Gibbs free energy). This indicates that solubility increases with temperature, so cooling crystallization is feasible. However, because entropy drives the process, anti-solvent addition may also be effective, as it reduces the solvent's dissolving power and promotes precipitation.
Is there any risk of polymorphic transition during solubility measurements that could affect data reliability?
No. PXRD and DSC analyses confirmed that β-HMX remains in its β-polymorph under all tested conditions. Therefore, the solubility data are not confounded by polymorphic transitions, ensuring their reliability for thermodynamic modeling and process design.
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