Oxygen Absorption into Stirred Emulsions of n-Alkanes

Thanh Hai Ngo,Adrian Schumpe

doi:10.1155/2012/265603

Abstract

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.

Highlights

Oxygen absorption into emulsions is encountered, for example, in fermentations with an oil as the carbon source
Much stronger effects never reported before were observed at high oil fractions
Da Silva et al [8] reported that 1% n-hexadecane or n-dodecane increased kLa in a stirred tank by factors of 1.68 and 1.36, respectively; Kundu et al [3] found that addition of 1% ndodecane or n-heptane could enhance oxygen transfer in a bubble column up to fourfold; Jia et al [9] found a fourfold increase by 2% soybean oil in an air-lift reactor

Summary

Introduction

Oxygen absorption into emulsions is encountered, for example, in fermentations with an oil as the carbon source. The values of spreading coefficients S reported in the literature for the three n-alkanes used in this study, n-heptane, ndodecane, and n-hexadecane, differ considerably (Table 1). 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. At high-oil volume fractions, not considered in the previous studies, the high oxygen solubilities in the oils (high driving force) should have a strong effect on the mass transfer characteristics

Experimental

Results and Discussion

Conclusions