Result 3Tandem mass spectra of deprotonated surface-active materials

Figure 3. MS2 CAD spectra of selected ions obtained from sample P and W. using (-)ESI. Figures A and B were obtained for crude oil P. Figures C and D were obtained for crude oil W.

Figures A and B show MS2 CAD spectra for ions with m/z values of 293 and 283, respectively; Figures C and D show MS2 spectra for ions with m/z values of 307 and 389, respectively. The mass spectra were obtained for ions isolated using an isolation window of 1 and collision energy of 30.

Figure A shows an MS2 spectrum of parent ion with m/z 293, wherein the fragment ion of m/z 97 corresponds to a sulfate group2. Figure 3B shows an MS2 spectrum of parent ion with m/z 283, wherein the losses of neutral molecules with MW of 18 Da and 44 Da reveal the presence of a carboxylate group. Figures 3C and 3D show MS2 spectra of parent ions with m/z 307 and 389, respectively, that fragment similarly to the ion shown in Figure B, thus suggesting that they are carboxylatesHydrophilic-lipophilic balance (HLB) of surface-active materials

By using a formula proposed by Davies1

m: number of hydrophilic groups. 1 is used for m value here; Hi: Value for hydrophilic groups; the value for a carboxylate group is 19.1 and sulfate group 38.7; n: number of lipophilic groups; this number is obtained from average of MW of hydrophilic groups of surface-active compounds divided by 14. The approximate HLB value of surface-active materials in sample W is ~14 and in sample P 21~40 The HLB value ~14 corresponds to a detergent and oil-in-water emulsifier. An HLB value above 20 corresponds to a solubilizing agent. This explains the stable emulsion formed for crude oil sample W.

Comparison of surface-active materials in two crude oils by using solid phase extraction and LQIT-Orbitrap Mass spectrometry

Xueming Dong, Chunfen Jin, Ravikiran Yerabolu, Hilkka KenttamaaPurdue University West Lafayette, IN

Overview

Goal: • Identification of surface-active compounds in crude oils and the

compounds’ relationship with crude oil’s emulsion propensityMethods:• Anion exchange solid phase extraction• Tandem mass spectrometryResults:• Two crude oils were studied, W that forms strong emulsions and P that does

not, according to manufacturer • Surface-active compounds in these samples were found to contain

carboxylate and sulfate groups• Extracted emulsifying compounds were found to act as de-emulsifying

compounds when placed in another crude oil (destructive interaction)

IntroductionCrude oil emulsions have been studied for several years by using various techniques. During crude oil refining processes, different types of emulsions (e.g. water-in-oil or oil-in-water) are preferred, and during transportation processes, low viscosity emulsions are desired. A better understanding on the interactions between emulsifying reagents and crude oils is needed to be able to manipulate emulsions. In this study, two crude oil samples, P and W, were analyzed and compared.

Methods

Result 4

Surface-active material added into crude oils

Figure 4. Emulsions generated after adding extracted surface-active material to crude oilsFigures A and B show emulsions formed when surface-active material from crude oils P and W was added into crude oil W, respectively. Figures C and D show emulsions formed when surface-active material from crude oils W and P was added into crude oil P, respectively.

Emulsifying ability of the crude oils was not affected when “native” surface-active materials were added. However, “foreign” surface-active material acted as a de-emulsifying reagent in both crude oil samples. This demonstrates a destructive interaction between surface-active materials and the crude oils. An example of constructive interaction between surface-active materials would be adding a combination of sodium dodecyl sulfate and naphthenic acids into a crude oil (data not shown) generates a stronger emulsion than when the two compounds are added separated.

Conclusions

Surface-active materials from two crude oils were isolated using anion exchange solid phase extraction technique and characterized by tandem mass spectrometry. Crude oils without these surface-active materials lost their ability to form stable emulsions. The surface-active materials are mainly composed of a carboxylate with a MW of ~ 400 Da for crude oil W and a carboxylate and a sulfate with a MW of ~ 200 Da for crude oil P. The approximate HLB value for surface-active materials in crude oil W was ~ 14 and in crude oil P 20~40. This explains why more stable emulsions were observed for crude oil W than crude oil P. This study also provided a MS based approach to predict crude oils’ emulsifying ability.Furthermore, a destructive interaction between emulsifying reagents was observed. The crude oils formed much weaker emulsions when “foreign” surface-active materials were added.

Reference

1. Davies, J. In A quantitative kinetic theory of emulsion type, I. Physical chemistry of the emulsifying agent, Gas/Liquid and Liquid/Liquid surface. Proceedings of the International Congress of Surface Activity, 1957; pp 426-438.2. Lyon PA, Stebbings WL, Crow FW, Tomer KB, Lippstreu DL, Gross ML. Analysis of anionic surfactants by mass spectrometry/mass spectrometry with fast atom bombardment. Analytical Chemistry. 1984;56(1):8-13.

Acknowledgements

• This work was supported by ConocoPhillips and Pioneer Oil Company • Thanks for Dr. James Riedeman for his valuable advice.

A B C D

Result 1

Emulsions generated by vigorous shaking and sonication of crude oils before and after anion exchange extraction

Figure 1.. Figures A and B correspond to attempted emulsion formation for sample P before and after anion exchange extraction; Figures C and D correspond to attempted emulsion formation for sample W before and after extraction. All samples were allowed to settle for 12 hours.

Before extraction, crude oil sample P formed a slightly weaker emulsion than crude oil sample W, as expected. Stable emulsions did not form for either sample after extraction, indicating that anionic surface-active compounds are needed to stabilize the emulsions.

Result 2

ESI(-) mass spectra of surface-active materials extracted from crude oils show deprotonated molecules.

Figure 2. ESI(-) mass spectra of surface-active materials extracted from crude oil samples.Figure A corresponds to sample P; Figure B corresponds to sample W.

Mass spectra presented in Figure 2, suggest that crude oil samples W and P have surface-active materials with very different average molecular weights. As demonstrated next, the majority of these ions contain a carboxylate group. Based on their HLB values (discussed next), these crude oil samples have interface-active materials that correspond to different categories of surfactant which may account for their different emulsion properties.

Average MW ~ 200 Da Average MW ~ 400 Da

A B C D

A B