Determination of Henry's law constants by equilibrium partitioning in a closed system using a new in situ optical absorbance method

Abstract

A new method for measurement of thermodynamic Henry's law constants (H) is reported. In this method, the optical absorbance of a dilute aqueous solution containing an organic compound is followed with time as the compound partitions into the air above the solution in a sealed vessel. The change in optical absorbance (i.e., change in concentration) and the vapor to liquid volume ratio of the vessel are then used to calculate the value for H. The concentration of the organic compound in the aqueous and vapor phases need not be known. This method allows the approach to equilibrium to be observed in real time so that attainment of equilibrium is readily apparent. This method works particularly well for water‐soluble compounds having low vapor pressures. The applicability of this method is limited to compounds that exhibit significant optical absorbance in the ultraviolet and visible regions of the electromagnetic spectrum. Values for H and their temperature dependencies measured using this new method are reported for methacrolein, methyl vinyl ketone, benzaldehyde, and acetophenone. Values for H are also reported for benzene, toluene, and ethylbenzene at 298 K. All reported H data are compared with previously reported values.

Using an internal standard method to determine Henry's law constants

“…Figure 1 shows the UV‐vis spectra of methyl vinyl ketone in deionized water and dry acetonitrile, which indicate that methyl vinyl ketone undergoes hydration in water. The values of H * likely were measured by the literature method [10], which should give results higher than the data reported herein.…”

“…For methyl vinyl ketone, however, some discrepancies in H were observed when compared with the reported numbers. At 25°C, the literature H (1.9 × 10 −3 ) [10] is rather higher than that determined by the internal standard method (1.52 × 10 −3 ). It can be noted in Allen et al [10] that the values of H measured by the in situ optical absorbance method for benzaldehyde (1.25 × 10 −3 ) and acetophenone (0.43 × 10 −3 ) also are higher than the previously reported data (1.09 × 10 −3 and 0.37 × 10 −3 , respectively) at 25°C.…”

“…The values of H determined experimentally by the internal standard method are values of the apparent H . Comparatively, the reported approach [10] employed UV‐vis spectrometry to monitor the change in optical absorbance for the aqueous solution of methyl vinyl ketone to calculate the value of H . Figure 1 shows the UV‐vis spectra of methyl vinyl ketone in deionized water and dry acetonitrile, which indicate that methyl vinyl ketone undergoes hydration in water.…”

Thermodynamic properties of five biofuel-relevant compounds at infinite dilution in water

“…While for furans no literature data are available and data for furfural [14,15] and allyl alcohol [18] are rather scarce (two and three c 1 1 data points, respectively), for methyl vinyl ketone more numerous K aw values were reported at several temperatures in two studies [16,17]. Unfortunately, these literature data for methyl vinyl ketone differ greatly (in some cases even by a factor of two) both each other and when compared to our K aw measurements, the literature K aw ðTÞ dependences being in addition inconsistent with calorimetric data obtained in this work.…”

Rate constants and activation energies for ozonolysis of isoprene methacrolein and methyl-vinyl-ketone in aqueous solution: Significance to the in-cloud ozonation of isoprene

“…McAucliffe [4] and Mackay and Shiu [5]) is rather small (1.30 ϫ 10 Ϫ2 M atm Ϫ1 ), supposedly making its reactivity in cloud water less important, the same might not be the case for the isoprene daughters, which have 2 -3 orders of magnitude larger Henry's law constants: 4.29 M atm Ϫ1 for MAC and 21.5 M atm Ϫ1 for MVK (Allen et al [6]). The same is true for the third product of ozonation of isoprene, formaldehyde, which was studied in aqueous solution in reaction with OH, by Marcovic and Sehested [7] and Bothe and Schulte-Frohlinde [8].…”