超临界CO_2GAS沉析HMX过程的颗粒形貌控制

Crystal Morphology of HMX and Its Control with Supercritical CO_2 Anti-solvent Precipitation

文章研究了超临界CO2GAS沉析HMX丙酮溶液过程的颗粒形貌控制。研究结果表明,GAS过程中不同的膨胀方式,可以得到不同的沉析颗粒大小和尺寸分布。当溶液持续膨胀时,得到多种粒度尺寸的颗粒,尺寸分布宽;当溶液从开始到5.0MPa,维持20s后再上升到10.0MPa分段膨胀时,得到平均粒度在3.1μm和9.5μm分段的颗粒尺寸和分布。快速膨胀溶液,可以在短时间内产生高过饱和度,根据吉普斯自由能理论,当溶液的过饱和度主要消耗在成核过程时,可以得到平均颗粒度为5.2μm、粒度分布比较窄的HMX颗粒,降低溶液初始浓度,可得到更小的颗粒。溶液的初始浓度增加,在相同膨胀度的情况下,单位体积内新相颗粒密度增加,使颗粒增长比较明显。GAS过程中,温度对过饱和度的影响相对比较小,与传统的结晶过程一样,温度是影响晶形的主要因素,当操作温度超过50℃或增压膨胀、沉析结晶放热引起的局部温度过高时,都会产生α HMX,适当搅拌可以防止局部过热以防止α HMX产生。

The particle size and crystal morphology control of precipitated 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane (HMX) in acetone solution using supercritical CO_2 anti-solvent were studied. The results show that the different particle size and size distribution can be obtained by changing the way of solution expansion. When the solution is expanded continuously, the wide particle size distribution is obtained, and the average particle size of 3.1μm and 9.5μm with narrow size distribution can be obtained when solution expansion by alternate gas injection pressure rises to 5.0MPa, holds 20 seconds, then rises to 10.0MPa. The high supersaturation ratio can be obtained within a few seconds using supercritical CO_2 anti-solvent and when the high supersaturation is mainly consumed by nuclei, according to Gibbs free energy theory, we can expect small particle size with narrow size distribution. HMX, for example, we can obtain 5.2μm β-HMX and even smaller particle size we can expect by decreasing the original solute concentration in solvent. Increasing the original solute concentration in solvent will cause crystal growth quickly at the same expansion conditions. The effect of temperature on particle size is much smaller than that of pressure. When the experimental temperature is more than 50℃ or partial superheat caused by rapidly exothermic crystallization, by pressure process etc., α-HMX will be formed, and some measures to prevent α-HMX can be taken.