Reliable Absolute Vapor Pressures of Extremely Low Volatile Compounds from Fast Scanning Calorimetry
Reliable Absolute Vapor Pressures of Extremely Low Volatile Compounds from Fast Scanning Calorimetry
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DOI：
10.1007/978-3-319-31329-0_8
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发表时间：
2016
期刊：
影响因子：
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通讯作者：
M. Ahrenberg;A. Ostonen;J. Schmelzer;Martin Beck;C. Schmidt;O. Kessler;U. Kragl;S. P. Verevkin;C. Schick
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文献类型：
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作者：
M. Ahrenberg;A. Ostonen;J. Schmelzer;Martin Beck;C. Schmidt;O. Kessler;U. Kragl;S. P. Verevkin;C. Schick
使用传统技术测定极低挥发性化合物（如离子液体）的蒸汽压是具有挑战性和耗时的。特别是，离子液体在蒸汽压仍然很低的温度下就容易分解。因此，测定蒸发速率的常规方法仅限于低于分解温度的温度，在这种温度下，蒸发进行得非常缓慢。本文提出的一种测定低挥发性化合物蒸气压的新方法，能够在惰性气氛中使用差示快速扫描量热法在很短的时间尺度上克服这一限制。该方法基于纳克样品的相对快速蒸发，与传统的热重样品相比，显示出显着增强（高达104倍）的表面体积比。由于加热速率极高，样品暴露在热应力下的时间只有几毫秒。在这些条件下，即使在可能开始分解过程的温度以上，蒸发在质量损失中也占主导地位。此外，由于该方法允许非常高的加热和冷却速率（高达106K s−1），因此避免了样品在达到蒸发温度和从蒸发温度出发的过程中蒸发，因此与传统方法相比，在测量质量损失率时可以达到更高的温度。该方法使用扩散泵油Santovac®5和离子液体[EMIm][NTf2]在温度高达780 K和不同惰性气体的气氛中进行了测试。测定了几种非质子离子液体[EMIm][NTf2]、[BMIm][Br]、[BMIm][BF4]、[BMIm][PF6]、[EMIm][Cl]、[BMIm][Cl]、[EMIm][NO3]和[BMIm][NO3]的绝对蒸气压。蒸汽压符合Clarke-Glew方程。估计了离子液体的汽化焓和沸腾温度。讨论了这种测定绝对蒸气压的新方法的优点和局限性，并将结果与文献资料进行了比较。
Vapor pressure determination of extremely low volatile compounds, e.g., ionic liquids, is challenging and time-consuming using conventional techniques. Particularly, ionic liquids tend to decompose already at temperatures where the vapor pressure is still very low. Conventional methods for the determination of evaporation rates are thus limited to temperatures below the decomposition temperature where evaporation proceeds very slowly. A new method for the vapor pressure determination of low-volatile compounds, presented here, is able to overcome this limitation using differential fast scanning calorimetry on very short time scales in inert atmospheres. The method is based on the relatively fast evaporation of nanogram samples, exhibiting a significantly enhanced (up to a factor of 104) surface-to-volume ratio compared to conventional thermogravimetric samples. Due to extremely high heating rates, the sample is exposed to the thermal stress only for milliseconds. In these conditions the evaporation dominates in the mass loss even at temperatures above the possible onset of the decomposition process. In addition, since the method allows very high heating and cooling rates (up to 106K s−1) evaporation of the samples on the way to and from the evaporation temperature is avoided and thus much higher temperatures can be reached in the measurement of the mass loss rate as compared to conventional methods. This method was tested using the diffusion pump oil Santovac® 5 and the ionic liquid [EMIm][NTf2] at temperatures up to 780 K and in atmospheres of different inert gases. The absolute vapor pressures of several aprotic ionic liquids: [EMIm][NTf2], [BMIm][Br], [BMIm][BF4], [BMIm][PF6], [EMIm][Cl], [BMIm][Cl], [EMIm][NO3], and [BMIm][NO3] were measured. The vapor pressures were fitted to the Clarke–Glew equation. The vaporization enthalpies and boiling temperatures of the ionic liquids were estimated. The advantages and limitations of this new method of absolute vapor pressure determination were discussed and the results are compared with the data available in the literature.