HPLC Analysis of Surfactants (S

0

, S

1

, and S

2

)

Amir Amini, Clarence Miller, and George Hirasaki Rice Consortium Meeting April 26, 2011 1

Column

HPLC Columns

Surfactant C18

Brand and size Packing Average pore size Dionex Acclaim Surfactant, 4.6 × 250mm Dionex Acclaim C18, 4.6 × 250mm 5µm silica coated with linear alkyl chains, tertiary amino and polar amide groups 5µm silica coated with octadecyl dimethyl siloxane 12 nm 12 nm Separation mechanism Mobile phase Operating PH range Reversed phase, ion-exchange, and dipole-dipole interactions ACN/NH 4 OAC or Methanol/DI, 0%-100% organic in mobile phase 2.5

– 7.5

Reversed phase ACN/DI or Methanol/DI, 15%-100% organic in mobile phase 2.0 – 8.0

What Can HPLC Do For Us?

• Measuring surfactant concentration – Total surfactant concentration – Individual concentration of components in a mixture • Separation of Mixtures • Thermal Stability • Quality Control 3

↑ Ionic Strength Mobile Phase pH Organic Modifier ** Temperature***

Method Development*

Retention time for different surfactant

Anionic Cationic Nonionic ↓ ↓ ↑ ↑ ↓ ↓ ↓ ↓ ↓ ↓ *Product manual for Acclaim Surfactant column from Dionex **Acetonitril is preferred over methanol because it generates less back pressure on the column.

***Temperature has little effect on the selectivity of surfactants. Higher temperature makes all the surfactants elute earlier.

Example: Triton X100 Analysis By Surfactant Column

0.4 wt% Triton X100, Injection: 10 µL, Temperature 25 o C, Mobile Phase: 45% ACN / 55% Ammonium Acetate (50mM), Flow rate: 1 ml/min

Evaporative Light Scattering Detector (ELSD)

• Mobile phase should be a solvent with low boiling point.

• If any acids, bases and salts are used to modify mobile phase, they also need to be readily • .

evaporated. The intensity of the scattered light is a function of the mass of the scattering particles and generally follows a power-law relationship

PART I

HPLC Analysis of S

1

(old & new commercial samples

as well as the lab sample), S 0

, and Their Mixtures

S 1 S 1

old sample (commercial): activity = 19.45 wt% new sample (commercial): activity = 19.45 wt%

S 1

lab sample: activity = 84.32 wt%

S 0

lab sample: activity = 85.50wt%

S 1

new /

S 0

lab mixture: (70 wt% S 1 , 30 wt% S 0 ) 7

Motivation

• Oil/brine/surfactant phase behavior using different samples of S 1 shows non-identical results as surfactant Are these surfactants the same? • No middle-phase microemulsion (type III) was observed (direct transition from type I to II with increase of salinity) !

Constituent components of a surfactant may partition differently into the oil phase ?

Can chromatographic separation occur when S 1 , S 0 into the reservoir?

or their mixture is injected Need a way to analyze these surfactants, both qualitatively and quantitatively 8

Experimental Conditions for HPLC Analysis of PART I

• Mobile Phase: Acetonitrile (B) / DI water (A) • Column: C18 column at 25 o C • Flow Rate: 1mm/min • Sample Volume: 50 µL • Detector: Evaporative light scattering (ELSD) at 60 o C and 3.5 bar • Gradient: Linear 0/80/95/110 min with 40/60/80 /80 %B 9

Area Under the ELSD Signal Curve Concentration ?

Peak Area = a .(Concentration) b 10

old sample contains more of the salts (sulfates, …) and other hydrophilic components Q: origin? A: hydrolysis as indicated by the slightly acidic PH of the sample.

11

Lab sample has

more

of the

high PO number

and

less

of the

low PO number

components

Components with lower number of PO groups elute earlier from the column 13

The mixture signal is

NOT

the linear superposition of the individual components signal!

Total areas are within 5% of each other:

16.8

vs

16.0

V.min

14

PART II

HPLC Analysis of S

1

(new commercial sample), S2, and Their Mixture

S 1

new sample (commercial): activity = 19.45 wt%

S 2

(commercial): activity = 22.38wt%

S 1

new /

S 2

mixture: (90 wt% S 1 , 10 wt% S 2 ) 15

Motivation

• Composition of a blend of two surfactants may change as salinity changes (e.g. in phase behavior experiments) or as it interacts with rocks and oil (e.g. in core flooding experiments) Can we separate a blend of two surfactants into their pure components ? • Evaluating the concentration of each component in S 1 /S 2 blend after : possible partitioning into oil phase, dynamic adsorption, core flood How can we measure the concentration of each component?

Need a way to analyze these surfactants, both qualitatively and quantitatively 16

Experimental Conditions for HPLC Analysis of PART II

• Mobile Phase: Acetonitrile (B) / 100mM Ammonium Acetate, PH=5.5 (A) • Column: Surfactant column at 25 o C • Flow Rate: 1mm/min • Sample Volume: 50 µL • Detector: Evaporative light scattering (ELSD) at 60 o C and 3.5 bar • Gradient: Linear 0/60/80 min with 25/80/80 %B 17

Several gradient patterns were tried BUT surfactant column was not able to separate S 1 and S 2 18

19

S 1 and S 2 are separated!

Now we can measure the concentration of S 1 and S 2 individually in their mixture 20

Conclusion

• Composition changes in different batches of the same surfactant can be identified • Chromatographic separation of S 1 /S 0 surfactant flooding and S 1 /S 2 may occur during • Blends of S 1 and S 2 can be separated; this gives a way to measure the concentration of each of those components: – – Analysis of oleic and aqueous phases to determine partitioning Analysis of effluent in surfactant flooding, dynamic adsorption, etc.

21

• Tiorco • Kinder Morgan • Addax

Acknowledgement

22

Back-Up Slides

23

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25

26

27

28

29

Gas waste to exhaust hood N 2 ELSD Liquid waste Chemstation 30