Separations

The objective of this portion of the research was to experimentally evaluate surfactant effects on the liquid-liquid separation of hydrophobic oils from a surfactant system. For pump-and-treat subsurface remediation in the absence of surfactant, contaminated ground water would be pumped from the subsurface and through a liquid-liquid extraction column where the contaminant partitions from the aqueous phase into an extraction solvent phase. In the absence of surfactant, the driving force for partitioning is a function of the contaminant hydrophobicity. In the presence of surfactants, the contaminant is subject to competitive partitioning (i.e., into the micelles and into the extracting oil).

By maximizing the contact area between extraction solvent and surfactant-solubilized hydrophobic oil contaminant through the use of state-of-the-art hollow fiber membrane columns, we hypothesize that hydrophobic oil contaminants can be separated from surfactant solutions without macroemulsification. For this research we were interested in the partitioning of the hydrophobic oil from the hydrophobic environment of the micelle via its aqueous concentration into a more preferred extracting solvent.

We began the batch squalane extraction studies by mixing 30 mls of the middle phase from the surfactant system 10% SDBS/17% IPA/12.4% NaCl/dodecane (Figure 6) with 30 mls. of squalane. The solutions were mixed for 10 minutes on a wrist action shaker and allowed to separate. Coalescence was rapid and complete in 5 minutes. The squalane rich phase was separated, and both phases were analyzed for dodecane and SDBS by the methods described previously. These results are summarized in Table V. The batch study was encouraging since 98% of the original solubilized dodecane from Figure 6 (12.4% NaCl ) partitioned into squalane. All the surfactant remained in the aqueous phase, as expected.

Continuous flow column extraction was operated at 1:2 squalane volume to middle phase volume ratio which is lower than the 1:1 ratio for the batch studies. From Table VI it is encouraging that the separation of dodecane from surfactant is very good and not much different from the batch extraction study. This result may be attributed to the long contact time (15.8 min.) and the large contacting surface area These results demonstrate that counter-flow column extraction via state-of-the-art porous hollow fiber membranes effectively separate hydrophobic oils from surfactant solutions, thereby regenerating the surfactant for reuse. These results are thus very encouraging with respect to the overall system economics, (i.e., it is feasible to regenerate and reuse hydrophobic oil-laden surfactant systems)

Table V, Batch Squalane extraction results by mixing 30 m!s of the middle phase from the system

10% SDBS/17% IP A/12.4% NaCl/dodecane (Figure 6) with 30 mis, of squalane.

Table V, Batch Squalane extraction results by mixing 30 m!s of the middle phase from the system

10% SDBS/17% IP A/12.4% NaCl/dodecane (Figure 6) with 30 mis, of squalane.

Phase

Event

Volume

SDBS

Dodecane

(ml)

(gilOO ml.)

(ml/100 ml.)

Before mixing

30

18.1

1032

Middle Phase

(Squalane

After mixing and

deficient

coalescence

27

20.2

0.19

phase)

Before mixing

30

0

0

Squalane rich

phase

After mixing and

Below

coalescence

33

detection limit

9.23

Table VI. The results for the liquid-liquid extraction via continuous counter-flow through porous hollow fiber membranes.

Phase Event Flow Rate SDBS Dodecane

Middle Phase

Before Extraction

6.32 (during

18.1

10.3

(Squalane

extraction)

deficient

phase)

After Extraction Before Extraction

6,32 (during extraction) 3.16 (during

19.9

0.28

extraction)

0

0

Squalane rich phase

After Extraction

3.16 (during

Below

20.1

extraction)

detection Limit

0 0

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