Absorption of pure oxygen into aqueous emulsions of n-heptane, n-dodecane, and n-hexadecane, respectively, has been studied at 0 to 100% oil volume fraction in a stirred tank at the stirring speed of 1000？min？1. The volumetric mass transfer coefficient, , was evaluated from the pressure decrease under isochoric and isothermal (298.2？K) conditions. The O/W emulsions of both n-dodecane and n-hexadecane show a maximum at 1-2% oil fraction as reported in several previous studies. Much stronger effects never reported before were observed at high oil fractions. Particularly, all n-heptane emulsions showed higher mass-transfer coefficients than both of the pure phases. The increase is by upto a factor of 38 as compared to pure water at 50% n-heptane. The effect is tentatively interpreted by oil spreading on the bubble surface enabled by a high spreading coefficient. In W/O emulsions of n-heptane and n-dodecane increases with the dispersed water volume fraction; the reason for this surprising trend is not clear. 1. Introduction Oxygen absorption into emulsions is encountered, for example, in fermentations with an oil as the carbon source. Most studies have been carried out at low oil volume fractions typical for this application [1, 2]. Literature data on the effect of n-alkane addition on the volumetric mass transfer coefficient for oxygen are illustrated in Figure 1. The value has been reported to increase [3, 4], decrease [5, 6], or remain unaffected [7] compared to the one in water. Da Silva et al. [8] reported that 1% n-hexadecane or n-dodecane increased in a stirred tank by factors of 1.68 and 1.36, respectively; Kundu et al. [3] found that addition of 1% n-dodecane or n-heptane could enhance oxygen transfer in a bubble column up to fourfold; Jia et al. [9] also found a fourfold increase by 2% soybean oil in an air-lift reactor. Among other factors, the oil spreading coefficient S (1) has been used to explain the differences between the oils as follows: The values of spreading coefficients S reported in the literature for the three n-alkanes used in this study, n-heptane, n-dodecane, and n-hexadecane, differ considerably (Table 1). In the present work, absorption of pure oxygen into aqueous emulsions of these n-alkanes has been studied in the full range of oil volume fraction (0 to 100%) with a barometric technique. The main advantage of the pressure technique is that it can give information on both and oxygen solubility. At high-oil volume fractions, not considered in the previous studies, the high oxygen solubilities in the oils (high driving force)
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