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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Ultrasonic Emulsification of Liquid, Near-Critical Carbon Dioxide-Water Biphasic Mixtures for Acceleration of a Hydrolysis Reaction
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Ultrasonic Emulsification of Liquid, Near-Critical Carbon Dioxide-Water Biphasic Mixtures for Acceleration of a Hydrolysis Reaction

机译：液态，近乎临界的二氧化碳-水双相混合物的超声乳化作用，促进水解反应

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A surfactant-free method based on power ultrasound was used to emulsify biphasic mixtures of liquid, near-critical carbon dioxide and water (T=30 ℃, P=80 bar). When ultrasound above a threshold power density (roughly 0.15 W/cm~3 at 20 kHz) was applied to a biphasic system of carbon dioxide and water, emulsions were formed which remained turbid for approximately 30 min (after 2 min of continuous ultrasound). Pulsed ultrasound (20% duty of a 2.5 s cycle at 20 kHz) could be used to maintain the emulsions indefinitely. Benzoyl chloride hydrolysis was selected as a model chemical reaction because of its rapid rate in pure water and the relative insolubility of the aroyl halide in the aqueous phase as compared to the carbon dioxide phase. The kinetic rate was measured under a range of ultrasonic pulsed power densities and zero ultrasound (i.e., silently) as a control. The measured, apparent, first-order rate constant was accelerated 100-fold in the presence of ultrasound at 0.50 W/cm~3 relative to silent conditions. The accelerative effect of ultrasound saturates with increasing power beginning at 0.50 W/cm~3. These results demonstrate the use of power ultrasound to create liquid carbon dioxide-water emulsions that, without surfactants or other additives, accelerate hydrolysis of substrates with low water solubility.
机译：使用基于功率超声的无表面活性剂方法乳化液体，近临界二氧化碳和水（T = 30℃，P = 80 bar）的双相混合物。当将超过阈值功率密度（在20 kHz时约为0.15 W / cm〜3）的超声应用于二氧化碳和水的双相系统时，形成的乳液会保持浑浊约30分钟（连续超声2分钟后）。可以使用脉冲超声（20 kHz时为20秒的20％占空比）来无限期保持乳液。选择苯甲酰氯水解作为模型化学反应的模型，是因为其在纯水中的快速速率以及与二氧化碳相相比，芳酰卤在水相中的相对不溶性。在一定范围的超声脉冲功率密度和零超声（即无声）作为对照的条件下测量动力学速率。相对于无声条件，在0.50 W / cm〜3的超声波存在下，测得的表观一级速率常数被加速了100倍。从0.50 W / cm〜3开始，超声的加速作用随着功率的增加而饱和。这些结果证明了使用功率超声来产生液态二氧化碳-水乳液，该乳液无需表面活性剂或其他添加剂即可以低水溶性加速底物的水解。

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