Introduction

Produced water is pumped to the surface with oil and gas as either a result of a natural water layer (formulation water) in the reservoir, or water that returns to the surface after steam is pumped into the reservoir to assist oil recovery in a process called steam-assisted gravity drainage (SAGD). An estimated 210 million barrels of produced water are recovered each day costing petroleum companies ~40 billion USD

1annually for treatment and disposal. Characterization of the water-soluble organics at the molecular level is essential to assist in the treatment and disposal of produced water. Liquid-liquid extraction (LLE), the established method for extraction of water-soluble organics from produced water, is time consuming, inefficient, costly, and environmentally unfriendly due to the large volume of dichloromethane

2(DCM) required for each extraction (1.2 L of DCM per 100 mL of water). Here, we demonstrate a method for the extraction of organics from produced water by solid-phase extraction (SPE). SPE cartridges are cheap, disposable, and only 6 mL of solvent are required for elution. Water-soluble organics extracted by LLE and SPE from a water sample prepared in the laboratory are characterized by Fourier transform ion cyclotron mass spectrometry (FT-ICR MS) to determine compositional similarities and differences of the extracts. Finally, two SAGD water samples obtained from a petroleum company demonstrate the capability of SPE for real-world applications.

Methods

Produced water was generated in the lab by stirring 25 g of Arabian heavy crude oil in 350 mL of HPLC grade water for eight days. 100 mL of the recovered water were extracted by LLE as described by Stanford et

2al. Acids (1) and bases with neutrals (2) were collected separately and the final yields of dried product were recorded. A SPE method first

3described by Dittmar et al. was modified for extraction of organics from the water. First, 100 mL of water was basified to pH 12 with 1M NaOH. Bond-Elute Plexa cartridges (Agilent Tech., Santa Clara, CA) were conditioned with 12 mL MeOH. The water was then passed through the

-1cartridges at a flow rate of ~10 mL min . The effluent was collected in a beaker for later use. The cartridges were dried under a stream of dry N 2

before sequential elution with 6 mL of MeOH, acetone, THF, and DCM. The collected water effluent was acidified to pH 2. The method described above was repeated on the acidified water. Each sample was

-1diluted to yield a final concentration of 250 μg mL for APPI FT-ICR MS analysis.

Figure 1. Schematic of the SPE (left) and LLE (right) of water-soluble organics from a water sample. Significantly less volume of organic solvent is required for SPE relative to LLE.

Figure 4. (+) APPI DBE vs carbon number images for O class extracted 1

by LLE (left) and SPE with acetone (right). Elution with solvents with different polarity increases solid-phase extraction efficiency of classes not eluted with MeOH.

Figure 3. APPI images of double bond equivalents (DBE = number of rings plus double bonds to carbon) versus number of carbons for the acid (top) and base (bottom) classes of highest relative abundance extracted by LLE (left) and SPE (right).

Figure 2. Heteroatom class distribution of acidic (top) and basic (bottom) water-soluble extracts from Arabian heavy crude oil by LLE (black) and SPE eluted with MeOH (red), THF (blue), and acetone (green). A zoom inset shows the basic classes without O S .1 1

Figure 5. Heteroatom class distribution of acid (top) and base (bottom) water-soluble solid-phase extracts from SAGD produced water #1 (black) and SAGD produced water #2 (red).

Figure 6. (+) APPI DBE vs carbon number images for SPE acid (top) and base (bottom) classes from SAGD produced water #1 (left) and SAGD produced water #2 (right).

Conclusions

SPE is a cheap, efficient, and environmentally friendly alternative to LLE for extraction of water-soluble organics from produced water. Comparison of water-soluble organic extracts by SPE and LLE from synthetic produced water show similar class and compositional coverage. Classes not extracted by MeOH may be eluted by changing solvent polarity. Compositional differences and similarities of two SAGD produced water samples extracted by SPE were determined. The results demonstrate the applicability of the SPE technique to real-world samples.

Acknowledgments

Work supported by NSF Division of Materials Research (DMR-06-54118), BP/The Gulf of Mexico Research Initiative, the FSU Future Fuels Institute, and the State of Florida.

References

(1) Khatib, Z. and Verbeek, P., J. Petrol. Technol. 2003, 55 (1), 26-28.(2) Stanford, L. A.; Kim, S.; Klein, G. C.; Smith, D. F.; Rodgers, R. P.; Marshall, A. G. Environ. Sci. Technol. 2007, 41,2696-2702.(3) Dittmar, T.: Koch, B; Hertkorn, N.; Kattner, G., Limnol. Oceanogr-Methods 2008, 6, 230- 235.

A Simple, Efficient Method for Extraction of Water-Soluble Organics from Petroleum Characterized by Atmospheric Pressure Photoionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

1 2 3 2,3 2,3Juan O. Sanchez , David C. Podgorski , Jacqueline M. Jarvis , Ryan P. Rodgers , Alan G. Marshall1 Department of Chemistry, Dartmouth College, 6128 Burke Laboratory, Hanover, NH 03755 USA2 National High Magnetic Field Laboratory, Florida State University, 1800 East Paul Dirac Drive, Tallahassee, FL 32310 USA

3Department of Chemistry and Biochemistry, Florida State University, 95 Chieftan Way, Tallahassee, FL 32306 USA