Evaporation rates and vapor pressures of the even-nunibered C8-C18 monocarboxylic acids
Evaporation rates and vapor pressures of the even-nunibered C8-C18 monocarboxylic acids
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DOI：
10.1021/jp710586m
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发表时间：
2008-05-01
影响因子：
2.9
通讯作者：
Ravishankara, A. R.
中科院分区：
文献类型：
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作者：
Cappa, Christopher D.;Lovejoy, Edward R.;Ravishankara, A. R.
用程序升温解吸法（TPD）测定了C-8-C-18中奇数烷烃单酸的温度依赖蒸汽压。在TPD中，直接测量样品的蒸发速率，然后根据Hertz-Knudsen方程确定蒸汽压。我们的测量结果表明，从碳-8到碳-18，固体偶数烷烃酸的蒸汽压随碳数的增加而单调降低，减小幅度大于6个数量级。升华焓随碳数的增加而单调增加，从大约110 M/mol增加到205 M/mol。测定了C-18烯酸油酸的液相蒸气压。与相应的C-18烷烃酸的液相蒸汽压的估算值进行比较表明，这两种化合物的液相蒸汽压是相同的。我们测量的C-14和更大的烷烃酸的固相蒸汽压比以前的研究要低。我们将这些差异归因于残余溶剂分子对先前测量的影响，这导致测量的蒸汽压过大。
Temperature-dependent vapor pressures of the even-numbered alkanoic monoacids from C-8-C-18 were measured using temperature-programmed desorption (TPD). In TPD, the evaporation rates from the samples are directly measured and the vapor pressures are subsequently determined from the Hertz-Knudsen equation. Our measurements indicate that the vapor pressures of the solid even-numbered alkanoic acids decrease monotonically with increasing carbon number by more than 6 orders of magnitude going from C-8 to C-18. The enthalpies of sublimation increase monotonically with carbon number, from similar to 110 to 205 M/mol. The liquid-phase vapor pressure was measured for oleic acid, a C-18 alkenoic acid. Comparison to the estimated liquidphase vapor pressure for the corresponding C-18 alkanoic acid indicates that the liquid-phase vapor pressures of these two compounds are identical. Our measured solid-phase vapor pressures for the C-14 and larger alkanoic acids are lower than in previous studies. We attribute these differences to the influence of residual solvent molecules on the previous measurements, Which cause the measured vapor pressures to be too large.