An experimental investigation into the rate-limited solubilization of liquid organic compounds in micellar surfactant solutions.

The effectiveness and efficiency of surfactant-enhanced aquifer remediation (SEAR) technologies will be largely controlled by the extent and rates of solubilization mass transfer. This study examines the influence of surfactant and organic liquid properties on the solubilization rates of octane, decane, and dodecane in micellar solutions of purified dodecyl alcohol ethoxylates (with average ethoxylate chain lengths of 8, 12, 17, and 30) and the commercial surfactants Witconol SN-120 \rm(C\sb{10-12}H\sb{21-25}(OCH\sb2CH\sb2)\sb9OH) and Witconol 2722 \rm(C\sb{18}H\sb{34}O\sb2C\sb6H\sb{10}O\sb4(OCH\sb2CH \sb2)\sb{20}). Two types of experimental systems are used to quantify solubilization rates: completely mixed batch reactor and segregated-phase flow reactor. Concentration-time data from the batch reactor experiments reveal that the time to reach equilibrium increases with an increase in ethoxylate chain length on the purified surfactants and with a decrease in solute chain length. Concentration-time data are fit with a linear driving force model to yield effective mass transfer coefficients. Correlations of mass transfer coefficients are developed that suggest that surfactant structure, solute size, and micelle capacities are key factors in predicting solubilization rates. The flow rate-concentration data from the flow reactor were modeled using a two-dimensional simulator, assuming a linear driving force mass transfer term at the interface. Fitted mass transfer coefficients (using a volume concentration driving force) are found to be independent of solute chain length and surfactant ethoxylate chain length (except for Witconol 2722). The mass transfer coefficients from the flow reactor are smaller than those from the batch reactor. The experimental results are used to identify potential rate-limiting mechanisms in each experimental system. The mechanisms of diffusion, micellar dissociation, monomer sorption, desorption of the organic-laden micelle (budding), and collision transfer are considered. Experimental observations suggest that collision transfer and budding are the dominant rate-limiting mechanisms in the batch and flow reactor systems, respectively. It was also shown that flow reactor trends with alkane chain length are similar to rate-limited mass transfer trends exhibited during flow interruption in soil columns, while batch reactor trends with alkane chain length are similar to trends observed during flow variation in soil columns. It is anticipated that these processes will influence the efficiency of SEAR at the field scale.Ph.D.Applied SciencesChemical engineeringEngineering, Sanitary and MunicipalEnvironmental engineeringEnvironmental scienceHealth and Environmental SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/131267/2/9840593.pd

Densities, Viscosities, and Speeds of Sound of <i>n</i>‑Tetradecane and <i>n</i>‑Alkylcyclohexane Binary Mixtures within the Temperature Range (288.15–333.15) K

This work reports on the densities, viscosities, and speeds of sound of 2-component mixtures of n-tetradecane and n-alkylcyclohexanes (methyl-, ethyl-, propyl-, butyl-, pentyl, hexyl-, heptyl-, octyl-, decyl-, and dodecylcyclohexane) at select temperatures between 288.15 and 333.15 K and pressure of 0.1 MPa. Decreases in mixture densities, viscosities, and speeds of sound were found with increases in temperature and in the component with the lower property value, except for the speeds of sound of n-butylcyclohexane mixtures in which the equimolar mixture had a speed of sound lower than the individual component values. Lengthening the alkyl chain on the n-alkylcyclohexanes (1) decreased the mixture excess molar volumes (VmE), (2) decreased the excess speeds of sound (cE’s) and viscosity deviations (Δη) until minimums were reached after which the cE’s and Δη’s increased, and (3) increased the excess isentropic compressibilities (KsE’s) until a maximum was reached after which it decreased. For all alkylcyclohexanes tested, except methylcyclohexane, VmE’s and KsE’s had the same sign, suggesting that the changes in the volume occupied by the molecules influence the mixture compressibility. In contrast, methylcyclohexane had the largest positive VmE but a negative KsE, which indicates that the expanded volume was not more compressible. Most of VmE’s, cE’s, and Δη’s of n-tetradecane mixtures fell between those reported for n-tridecane and n-hexadecane. n-Tetradecane could be used in fuel surrogates where larger density, viscosity, and speeds of sound are needed to emulate the real fuel

Densities and Viscosities at 293.15–373.15 K, Speeds of Sound and Bulk Moduli at 293.15–333.15 K, Surface Tensions, and Flash Points of Binary Mixtures of <i>n</i>‑Hexadecane and Alkylbenzenes at 0.1 MPa

The viscosities and densities (293.15–373.15 K), speeds of sound (293.15–333.15 K), surface tensions (room temperature), and flash points were measured for binary mixtures of <i>n</i>-hexadecane and alkylbenzenes (hexylbenzene, octylbenzene, dodecylbenzene), which are components of diesel fuel. Increasing the temperature decreased densities, and excess molar volumes of mixtures were higher for hexylbenzene mixtures than for octylbenzene mixtures and insignificantly different from zero for dodecylbenzene mixtures. The decrease in excess molar volume with increasing alkyl chain length is consistent with other binary mixtures of <i>n</i>-hexadecane and alkylbenzenes. Increasing the temperature decreased viscosities, and the McAllister three-body model successfully modeled viscosity with the compound in the mixture with the highest individual viscosity having the largest fitted interaction parameter. Mixture flashpoints, speed of sounds, bulk moduli, and surface tensions fell between the pure component values. For <i>n</i>-hexadecane/<i>n</i>-hexylbenzene mixtures, as the mole fraction of hexylbenzene increased, the speed of sound remained constant until a mole fraction of 0.5; then the speed of sound increased. On the basis of these data, binary mixtures of these compounds could be formulated to have property values that match those found in diesel fuel, except for surface tension, and thereby be potential fuel surrogates