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The composition and dynamic adsorption of crude oil components dissolved in synthetic produced water at different pH Mona Eftekhardadkhah, Kaja Neeb Kløcker, Helle Hofstad Trapnes, Bartlomiej Gawel, and Gisle Øye Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.5b04459 • Publication Date (Web): 25 Feb 2016 Downloaded from http://pubs.acs.org on February 29, 2016

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Industrial & Engineering Chemistry Research

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The composition and dynamic adsorption of crude oil components

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dissolved in synthetic produced water at different pH

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Mona Eftekhardadkhah, Kaja Neeb Kløcker, Helle Hofstad Trapnes, Bartłomiej

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Gaweł, and Gisle Øye*

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Ugelstad Laboratory, Department of Chemical Engineering, Norwegian University of

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Science and Technology (NTNU), N-7491 Trondheim, Norway,

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*Corresponding author:

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[email protected] Phone: (+47) 73 59 41 35, Fax: (+47) 73 59 40 80

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Abstract

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The effect of pH on the extent and type of dissolved components in synthetic

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produced water samples prepared from seven crude oils was investigated. More

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nitrogen containing compounds, probably due to improved water solubility of

18

pyridinic nitrogen functionalities, were seen at the low pH. The affinity of the water

19

soluble compounds for air-water interfaces was in most cases higher at higher pH.

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This was due to increased oxygen content in the water soluble species, probably

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associated with carboxylic acid functionalities. Differences in the affinity of water

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soluble crude oil components to gas bubbles are anticipated to influence the oil

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removal efficiency by gas flotation. The dynamic interfacial adsorption was followed

24

by a maximum bubble pressure tensiometer, while the dissolved species were

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characterized by total organic carbon measurements, total nitrogen measurements,

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FT-IR spectroscopy and UV/Vis spectroscopy.

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Keywords:

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Produced water, water solubility, crude oil components, dynamic adsorption,

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pyridinic nitrogen, carboxylic acids

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1. Introduction

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petroleum production. Worldwide, the water to oil ratio has been estimated to be

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approximately 4:11. The volumes of produced water are expected to increase further

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as the oil fields mature and various water-based enhanced oil recovery methods

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become implemented. Complex mixtures of dispersed oil and solids, dissolved

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inorganic salts and oil components and residual production chemicals are typically

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present in the produced water2. The polluting components must be removed or

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minimized to allowed levels. The threshold of oil in the produced water is limited by

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legislation if the water is to be discharged. Current regulations at the Norwegian

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Continental Shelf require that the oil content is less than 30 mg/l prior to discharge to

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sea3. If the produced water is to be re-injected into reservoirs, the threshold of

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dispersed components is largely determined by operational considerations such as

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the permeability of the reservoirs.

Large volumes of water are normally produced along with oil and gas during

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Induced gas flotation is widely used for removal of dispersed oil from wastewater4, 5.

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The efficiency of this method will depend on the collision frequency between bubbles

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and drops, the probability of attachment between the two and the stability of the

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resulting bubble−drop agglomerates6, 7, 8, 9, 10. The collision frequency mainly

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depends on the hydrodynamic conditions. Formation of bubble−drop agglomerates,

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on the other hand, relies on quick drainage and rupture of the thin aqueous film

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formed upon close approach between drops and bubbles and subsequent spreading

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of the oil drops over the gas bubbles. The latter processes are directly related to

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interfacial properties of both oil drops and gas bubbles6, 9, 11, 12. Moreover, the

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presence of interfacially active components can also influence the size distributions

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of oil drops and gas bubbles, and thereby affect the separation efficiency13.

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Several studies have reported on detailed characterization of water soluble crude oil

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components2, 14, 15, 16, 17, 18, 19, 20. These compounds can be classified as polar and

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non-polar. The non-polar compounds include low molecular weight aromatics like

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benzene, toluene, ethylbenzene and xylenes (BTEX) and high molecular weight

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polyaromatic hydrocarbons (PAHs). The polar compounds can typically contain

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phenol, carboxylic acid and ketone functionalities, as well as functionalities with other 2 ACS Paragon Plus Environment

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nitrogen and sulphur heteroatoms. The solubility of these compounds depends on

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the molecular weight and type of heteroatoms in the molecules, but it is normally

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orders of magnitude higher than the solubility of the pure aromatic hydrocarbons15.

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In a series of recent papers we have investigated the adsorption of the water soluble

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crude oil components onto bubble surfaces21, 22, 23. It was demonstrated that the

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adsorption was rapid and that both the acidic and basic components in the crude oils

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had affinity for the bubble surfaces. However, no correlations to the total acid and

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base numbers of the crude oils were found. Statistical models were also developed

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for predicting the solubility and surface affinity of the dissolved hydrocarbons. This

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demonstrated that detailed knowledge about the crude oil fractions and the water

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phase could give good predictions of the interfacial properties of gas bubbles.

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Furthermore, the drainage and rupture of the thin aqueous film formed upon the

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close approach of a single bubble and a single crude oil drop were studied in a drop-

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bubble micromanipulator system24. It was shown that the adsorption of hydrocarbons

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onto gas bubbles increased the drainage time of the film between bubbles and

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drops, and thereby influenced the attachment between bubbles and drops. It was

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also shown in both laboratory and pilot scale flotation studies that the adsorption of

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the water soluble crude oil components onto bubble surfaces reduced the removal

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efficiency of dispersed oil from water by gas flotation25.

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The primary objective in the current paper was to investigate how pH affected the

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type of crude oil components dissolved into aqueous solutions and how the surface

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affinity depended on the dissolved components. The pH range intendent to reflect

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variations in pressure during petroleum production. Dynamic interfacial tensions at

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gas-water interfaces were followed by maximum bubble pressure tensiometry. The

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water soluble crude oil components were characterized by total organic carbon and

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total nitrogen measurements as well as by FT-IR and UV-vis spectroscopy.

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2. Experimental

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2.1. Crude oils

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Seven crude oils (denoted A, B, C, E, F, H and I) were used to prepare synthetic

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produced water. The oils were previously characterized with respect to

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physicochemical properties like density, viscosity, SARA (saturate, aromatic, resin

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and asphaltene) fractions, total acid and base numbers and heteroatom content of

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the various fractions. Detailed descriptions of the characterization procedures and

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results can be found elsewhere26.

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2.2. Preparation of brine solutions

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Brine solution mimicking a simplified composition of formation water was prepared

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by dissolving analytical grade NaCl (99.5%, Merck, Germany), Na2SO4 (99%, Acros,

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USA), NaHCO3 (99.5%, Merck, Germany), MgCl2·6H2O (99%, Merck, Germany) and

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CaCl2·2H2O (99.5%, Fluka, Czech Republic) in deionized water from a Millipore

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Simplicity System. The ionic composition is given in Table S1 in Supporting

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Information. One part of the brine was kept at the resulting natural pH, while two

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other parts were adjusted to pH 2 and pH 8, respectively, by adding HCl and NaOH.

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All the solutions were continuously stirred by a magnetic stirrer during storage in

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order to prevent precipitation. The pH range reflected variations in pressure that will

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occur during petroleum production. Above pH 8 precipitation of hydroxides and

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naphthenate formation were observed.

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2.3. Preparation of synthetic produced water

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Synthetic produced water samples were prepared by partitioning water soluble

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components of the crude oils into an aqueous phase by mixing 50% crude oil and

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50% of the brine solutions with a shaker (HS 501 digital IKA). The mixing speed was

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kept at 250 rpm at room temperature for 24 hours. The oil and water phases were

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separated by centrifugation (typically 15 minutes at 8000 rpm) and the aqueous

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phase was recovered in a separation funnel. The synthetic produced water samples

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were denoted PW-X, where X represent the crude oil used during preparation of the

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aqueous phase. All the samples were prepared and analyzed in three parallels.

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2.4. Dynamic interfacial tension measurements

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Dynamic interfacial tensions were measured with a maximum bubble pressure

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tensiometer (Krüss BP100, Hamburg, Germany). A hydrophobized glass capillary

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connected to a pressure sensor was immersed into 30 mL sample solution, where air

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bubbles with surface ages from 10 ms to 100 s were created. The surface tension of

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deionized water (from a Millipore Simplicity System) was within 71.99 ± 0.11 mN/m

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before any sample measurements were started. All the measurements were carried

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out at room temperature ( 20 ± 1o C ). The surface pressure ( π ) for the samples was

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estimated as the difference between the first (i.e. clean surface) and the last (i.e.

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close to equilibrium) measurement points, i.e. π = γ (10 ms) - γ (100 s).

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2.5. Total organic carbon and total nitrogen measurements

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The concentrations of total organic carbon (TOC) and total nitrogen (TN) in

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components dissolved in selected produced water samples were determined using

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an IL 550 TOC/TN Analyzer (Hach Lange). The measurements were carried out in

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the GIG Laboratory, Katowice, Poland.

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2.6. UV-vis spectroscopy

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UV-vis spectra of the produced water samples were recorded using a UV-2401PC

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spectrometer (Shimadzu). The spectra were collected from 200 to 800 nm. Brine

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corresponding to the one used during preparation of the sample was used in the

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reference cell. All samples were diluted 3 times with the appropriate brine in order to

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avoid excess absorbance. Gaussian profiles were fitted to the spectra (using Fityk

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ver. 0.9.8) in order to calculate the integrated areas of overlapping peaks. The fitting

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procedures resulted in R2 values above 0.99.

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2.7. FT-IR spectroscopy

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In order to extract the organic components from the produced water samples, the

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aqueous samples were first acidified with 2 mL concentrated HCl in 250 mL Schott

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bottles and gently shaken. Subsequently, 8 ml of a cyclohexane/butyl acetate

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mixture (70/30) was added and the liquids were shaken for 1 minute. The organic

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phase was then isolated using a separation funnel and dried with nitrogen. FT-IR

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spectra of the organic solutions were measured on a Tensor 27 spectrometer 5 ACS Paragon Plus Environment


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(Bruker Optics) equipped with an Attenuated Total Reflection (ATR) cell. A few drops

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of the solution was placed directly on the ATR cell and left for the solvent to

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evaporate. The spectra were collected between 4000 and 600 cm-1 with 4 cm-1

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resolution.

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3. Results and discussions

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The dynamic surface tension of representative produced water samples are shown

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in Figure 1. Common for all the samples was that the initial surface tension was

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close to the surface tension of pure brine (75.6 mN/m), indicating that no

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components were adsorbed at the air - PW interfaces as the time approached zero.

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All the samples also had a rapid decrease in surface tension at short time scales,

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typically within the first 50 ms. However, the extent of this decline and the further

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evolution of surface tension varied. The behavior was divided into two categories.

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For PW-B the surface tension decreased uniformly towards similar equilibrium

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values independent of the pH of the samples, Figure 1A. Comparable trends were

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also seen for PW-A and PW-E (Figures S1 and S2 in Supporting Information). For

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PW-I the samples prepared at the natural and elevated pH decreased towards

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similar equilibrium surface tensions, while the sample at low pH flattened more

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quickly out at higher surface tension values, Figure 1B. The behavior was

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comparable for PW-C, PW-F and PW-H (Figures S3-S5 in Supporting Information).

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As a result, the latter samples had lower surface pressures at pH 2 than at the higher

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pH (Table S2 in Supporting Information).

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The TOC values varied between the produced water samples from different crude

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oils, Table 1. The carbon concentration increased with increasing pH for some of the

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samples (PW-B, PW-H and PW-I), while no clear trends were seen for others.

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Furthermore, the total nitrogen content of the dissolved components was in most

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cases highest at pH 2, Table 1. Only PW-B had an opposite trend.

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The dissolved components were further investigated by UV/Vis analysis of the

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samples. Due to the complexity of the samples it was not possible to attribute the

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observed bands to specific chromophores. However, comparison to aromatic and

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heterocyclic hydrocarbons have previously been used as a convenient way of

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interpreting UV spectral data of complex organic structures27 and natural organic

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matter28, and this approach was also used here.

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For the samples prepared at pH 2, four absorption bands with maximum intensities

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around 210, 240, 275 and 320 nm and decreasing absorption with increasing

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wavelength were normally seen, Figure 2. The region between 180 and 230 nm 7 ACS Paragon Plus Environment


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(region I) were assigned to allowed π −−> π∗ electron transitions in the ring of

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substituted benzenes, while the region between 220 and 250 nm (region II) were

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ascribed to π −−> π∗ electron transitions associated with polar substituents like

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carbonyl, carboxyl, hydroxyl and ester groups on the aromatic rings28. It is well

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known that the substituents in benzenoid aromatic hydrocarbons will give rise to red-

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shifts of the absorption bands, where the extent may vary with the type and position

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of the substituent as well as the degree of conjugation with the ring system27, 29, 30.

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This can account for the variations observed in the maximum of these bands. The

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region between 250 nm and 290 nm (region III), corresponding to forbidden

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π −−> π∗ transitions, was also related to the presence of substituents in the aromatic

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rings28. Finally, the low intensity region from 275 nm to 350 nm (region IV) was

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attributed to electron transitions from electron lone pair n orbitals at heteroatoms to

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unoccupied π∗ orbitals in the aromatic rings27.

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Fewer features and broader absorption bands were generally seen in the spectra for

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the samples prepared at natural pH, Figure 3, and elevated pH (Figure S6 in

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Supporting Information). All the samples had bands in region I, but they overlapped

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significantly with other bands, particularly in region II. Also the bands in region III and

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IV had lower intensity and considerably overlap. Curve fitting was used to resolve

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and estimate the areas of the various bands. The ratios for the areas of the bands in

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region IV and region I are shown in Figure 4 for samples prepared at natural and low

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pH. Since region IV was attributed to heteroatoms with lone electron pairs in the

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molecules and region I to aromatic rings, the ratio was used as a measure of

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heteroatoms in the molecules. In most cases this was highest for the samples

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prepared at pH 2.

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The FT-IR investigations provided information about the chemical functionalities in

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the dissolved components of selected produced water samples. FT-IR spectra of

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PW-B and PW-C at low and natural pH are shown in Figure 5 and 6, respectively.

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The complex and multifunctional nature of the dissolved components is likely to

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cause considerable overlap of characteristic absorption bands from different

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functional groups. This made interpretation and analysis of the spectra difficult, but

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the primary feature of the spectra was the presence of hydrocarbons with oxygen 8 ACS Paragon Plus Environment

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containing functional groups. The detailed band assignments were done in

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accordance with literature31 and are summarized in Table S3 in Supporting

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Information. The broad band between 3600 and 3000 cm-1 may be stretching

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vibrations of hydrogen bonded O-H in carboxylic compounds and alcohols

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overlapping with N-H stretching in aromatic and aliphatic amines. The intense bands

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from 3000 to 2800 cm-1 were attributed to symmetric and asymmetric C-H stretching

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vibrations in methyl, methylene and methine groups. The symmetric and asymmetric

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C-H bending vibrations of these groups were assigned to the bands from 1470 to

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1370 cm-1. The bands between 1700 and 1600 cm-1 were ascribed to C=O stretching

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of carboxylic compounds, ketones, aldehydes and esters, while the bands between

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1280 and 1050 cm-1 were ascribed to C-O stretching of similar functionalities. Finally,

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the absorption bands from 1360 to 1280 cm-1 were attributed to C-N stretching in

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aromatic amines, and the bands from 995 to 670 cm-1 to vinyl and aromatic C-H

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bending.

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The different dissolved compounds in the samples prepared at low and natural pH,

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respectively, did not result in disappearance or appearance of bands, but they gave

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rise to different intensities of absorption bands. For PW-B, the natural pH primarily

256

resulted in lower intensities of the bands above 2400 cm-1, Figure 5. Furthermore,

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the main adsorption bands of the C-H stretching were below 3000 cm-1, which

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suggested a considerable fraction of aliphatic species in the samples. This was

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supported by the intense band around 1700 cm-1 compared to the weaker band

260

around 1625 cm-1. Both bands are associated with C=O stretching but the higher

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frequency is characteristic for non-conjugated carbonyl groups. However, the weak

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bands around 1300 cm-1 and below 900 cm-1, assigned to C-N stretch in aromatic

263

amines and aromatic C-H bending, indicated the presence of aromatic moieties as

264

well.

265 266

The PW-C sample at low pH generally had higher band intensities below 1800 cm-1,

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Figure 6. Also for these samples the C-H stretching bands were below 3000 cm-1,

268

but in this case the carbonyl stretching were stronger around 1650 cm-1 (conjugated)

269

than 1700 cm-1 (non-conjugated). This suggested higher fractions of aromatic

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species compared to PW-B. The weak shoulder around 1600 cm-1 and weak bands

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around 1500 cm-1 and below 1000 cm-1 supported the presence of aromatics. C-H 9 ACS Paragon Plus Environment


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bending bands were seen around 1450 cm-1, while several bands between 1300 and

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1050 cm-1 were attributed to C-O stretching. Furthermore, the absorption band

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around 1080 cm-1 was particularly intense. Previously it was reported that this crude

275

oil had extremely high sulphur content in the polar fractions26, and this absorption

276

might be due to overlapping bands arising from sulphate or sulfonate functionalities.

277 278

In order to reveal structural information about the dissolved components in the

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produced water, relationships between the surface pressure at various pH and the

280

analytical properties reported here were searched for. In addition, relationships to

281

physicochemical and compositional properties of the crude oils previously reported

282

were explored (listed in Tables S4 and S5 in the Supporting Information for

283

convenience). For most of the properties there were no strong relationships to the

284

surface pressure, but some trends were identified and these are discussed below.

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Four of the produced waters were categorized as samples with lower surface

287

pressure at pH 2 than at natural and higher pH. Increasing total nitrogen content was

288

related to increased surface pressure for these samples (marked in red), as seen in

289

Figure 7. A similar relationship could not be seen for the other category of samples.

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Neither was there any relationship between the surface pressure and the amount of

291

heteroatoms determined by UV/vis spectroscopy. This might suggest that not all

292

nitrogen functionalities gave rise to absorption in this region or that other

293

heteroatoms contributed to the absorption band as well.

294 295

Independent of pH, the surface pressure tended to increase with the total oxygen

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content in the crude oils (Figure S7 in Supporting Information). Considering the

297

oxygen content in each fraction of saturates, aromatics, resins and asphaltenes, the

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only systematic trend was that the surface pressure increased with increasing

299

amounts of oxygen in the aromatic fraction, Figure 8. This relationship was strongest

300

for the surface pressure at pH 2, with R2 = 0.66. The surface pressure also increased

301

when the amount of nitrogen in the asphaltene fraction increased, Figure 9. Also in

302

this case the relationship was strongest for the surface pressure at pH 2, with R2 =

303

0.61.

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The surface pressure also increased with decreasing C/H ratio in the asphaltene

306

fraction, Figure 10. This relationship was seen at the natural pH (R2 = 0.79) and at

307

the highest pH (R2 = 0.67).This means that the surface pressure increased when the

308

aliphatic character of the asphaltenes became stronger. However, all the C/H values

309

were high and accordingly associated with high extent of aromaticity and ring

310

condensation. It was also found that the decreasing C/H ratio in the asphaltene

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fraction (exempting PW-C) was related to increasing TOC at natural and elevated pH

312

(Figure S8 in Supporting Information). This revealed that the surface pressure

313

increased with TOC at these conditions.

314 315

The above relationships suggested that dissolved components from the aromatics

316

and asphaltene fractions of the crude oils apparently adsorbed onto the water-air

317

interfaces and increased the surface pressure. The influence of dissolved

318

compounds from the aromatics fraction was perhaps not so unexpected, since the

319

molecules presumably were relatively small and the polarity and solubility would be

320

improved by increasing oxygen content. However, the apparent presence of

321

dissolved compounds from the asphaltene fractions was more surprising. In order to

322

throw some light on this observation, reports on analyses of water soluble crude oil

323

components by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

324

were considered. Such studies have shown that dissolved species can have

325

molecular weights up to about 550 g/mole at seawater salinities15. The typical

326

average molecular weights of asphaltenes are considered to be around 750 g/mole,

327

with a factor 2 in the width of the distribution32. Consequently, it is conceivable that

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highly polar asphaltenes from the lower end of the asphaltene size distribution can

329

dissolve in the aqueous phase. Furthermore, it has been reported that pyridinic

330

(basic) nitrogen compounds have much higher water solubility than pyrrolic (acidic)

331

nitrogen compounds15. Among the basic Nx and NOx classes, N2 and NO2 classes

332

have been found to be the dominant water soluble species. Molecules with two

333

pyridinic functionalities would be an example of the N2 class, while an example of

334

NO2 species would be molecules with both carboxylic and pyridinic functional

335

groups. The highly hydrophilic properties of these functional groups promote water

336

solubility even for relatively large species. The origin of the high water solubility has

337

been attributed to the easy access of lone electron pairs at pyridinic nitrogen that can

338

form strong hydrogen bonds with water33. 11 ACS Paragon Plus Environment


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339 340

The increasing surface pressure with increasing oxygen content in the crude oils can

341

also be accounted for by Fourier Transform Ion Cyclotron Resonance Mass

342

Spectrometry studies. These have shown that O1 and O2 species are abundant in

343

the resin and asphaltene fractions of crude oil34, while aqueous solutions tend to be

344

enriched in O2 species often associated with naphtenic acids15, 19. Typical pKa values

345

for naphthenic acids lay around 5, and both water solubility and surface affinity of

346

such compounds will generally increase when they became dissociated. In addition,

347

the surface affinity depend on adsorption constants of the dissolved molecules. Such

348

constants have been reported to vary widely, both with the chain length and with the

349

type of head group for a range of surfactants35. Overall, the adsorption constant

350

increased with increasing chain length of the surfactants35. This seem to be

351

consistent with increased surface pressure as the aliphatic character of the

352

asphaltenes increased, since more aliphatic character promote surface affinity.

353 354

The results presented in this paper are believed to be of importance for the efficiency

355

of gas flotation as a produced water treatment method. pH of oilfield produced water

356

is largely determined by the equilibrium between CO2 and bicarbonate, which is

357

closely associated with the pressure and temperature of the water. In other words,

358

formation water containing CO2 at elevated pressure and temperature has low pH.

359

Release of CO2 and decrease in temperature during transport and processing will

360

increase the pH of the water. At low pH it can be anticipated that the basic functional

361

groups in molecules become completely ionized while the acidic functional groups

362

are not dissociated when contacted with water. The ionization will increase the water

363

solubility of the compounds with basic functional groups. When pH increase, the

364

basic functional groups become neutral and the acidic functionalities (typically

365

organic and naphtenic acids) will gradually dissociate and become increasingly water

366

soluble. This means that the solubility of crude oil components in the water will

367

increase from the reservoir to the water treatment facilities. In this work it was

368

demonstrated that the amount, type and surface affinity of water soluble components

369

in synthetic produced water were influenced by pH (reflecting pressure differences)

370

of the aqueous solutions. Previously it was shown that water soluble crude oil

371

components prolonged the drainage time of the aqueous film between bubbles and

372

drops24, and subsequently this reduced the removal efficiency of dispersed oil from 12 ACS Paragon Plus Environment

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373

produced water during gas flotation25. Consequently, it seems reasonable to

374

anticipate that conditions giving rise to differences in surface pressure can influence

375

the extent of oil removal during gas flotation. However, any relationship between the

376

magnitude of surface pressure and oil removal need to be verified experimentally.

377

4. Conclusions

378

The amount, type and surface affinity of water soluble components in synthetic

379

produced water depended on the crude oil the samples were prepared from and pH

380

of the aqueous phase. In all cases the type and extent of water soluble species were

381

different at pH 2 compared to the higher pH investigated. This was likely due to

382

improved water solubility of compounds containing pyridinic nitrogen functionalities

383

at the low pH. In most cases, the water soluble components at pH 2 had lower

384

affinity for the water-air interface than water soluble components at higher pH. The

385

higher interfacial affinities in the latter cases corresponded to increased abundance

386

of oxygen containing compounds, where the oxygen most likely can be associated

387

with carboxylic acids.

388 389 390 391

Acknowledgments

392

The authors are grateful to the industrial sponsors (ConocoPhillips Skandinavia, ENI

393

Norge, Schlumberger Norge, PWMS, Statoil Petroleum and Total E&P Norge) for

394

ﬁnancial support to the joint industrial program “Produced Water Management:

395

Fundamental Understanding of the Fluids”.

396 397 398

Supporting Information

399

The supporting Information contains additional data on crude oil properties, surface

400

tension measurements, FT-IR analysis, UV/Vis analysis and correlations between

401

properties. This information is available free of charge via the Internet at http:

402

//pubs.acs.org.

403



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404

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References (1) Duhon, H. Produced Water Treatment: Yesterday, Today, and Tomorrow. Oil and Gas Facilities. 2012, 1(1) 29. (2) Neff, J.; Lee. K.; DeBlois, E. M. Produced Water: Overview of Compositions, Fates, and Effects. In Produced Water; Lee, K., Neff, J., Eds.; Springer: New York, 2011; pp 3-52. (3) Discharges, spills and emissions from offshore oil and gas installations; OSPAR Commission: London, 2009. (4) Rubio, J.; Souza, M. L.; Smith, R. W. Overview of Flotation as a Wastewater Treatment Technique. Miner. Eng. 2002, 15, 139. (5) Melo, M. V.; Sant’Anna, G. L.; Massarani, G. Flotation Techniques for Oily Water Treatment. Environ. Technol. 2003, 24, 867. (6) Grattoni, C.; Moosai, R.; Dawe, R. A. Photographic Observations showing Spreading and Nonspreading of Oil on Gas Bubbles of relevance to Gas Flotation for Oily Wastewater Cleanup. Colloids Surf., A. 2003, 214, 151. (7) Moosai, R.; Dawe, R. A. Gas Attachment of Oil Droplets for Gas Flotation for Oily Wastewater Cleanup. Sep. Purif. Technol. 2003, 33, 303. (8) Nguyen, A. V.; Ralston, J.; Schulze, H. J. On Modelling of Bubble-Particle Attachment Probability in Flotation. Int. J. Miner. Process. 1998, 53 (4), 225. (9) Ralston, J.; Fornasiero, D.; Hayes, R. Bubble-Particle Attachment and Detachment in Flotation. Int. J. Miner. Process. 1999, 56, 133. (10) Min, M. A.; Nguyen, A. V. An Exponential Decay Relationship between Micro-Flotation Rate and Back-Calculated Induction Time for Potential Flow and Mobile Bubble Surface. Miner. Eng. 2013, 40, 67. (11) Schokker, E. P.; Bos, M. A.; Kuijpers, A. J.; Wijnen, M. E.; Walstra, P. Spreading of Oil from Protein Stabilised Emulsions at Air/Water Interfaces. Colloids Surf., B. 2002, 26, 315. (12) Oliveira, R. C. G.; Gonzalez, G.; Oliveira, J. F. Interfacial Studies on Dissolved Gas Flotation of Oil Droplets for Water Purification. Colloid Surf., A. 1999, 154, 127. (13) Duerr-Auster, N.; Gunde, R.; Mäder, R.; Windhab, E. J. Binary Coalescence of Gas Bubbles in the presence of a Non-ionic Surfactant. J. Colloid Interface Sci. 2009, 333, 579. (14) Utvik, T. I. R. Chemical Characterisation of Produced Water from four Offshore Oil Production Platforms in the North Sea. Chemosphere. 1999, 39, 2593. (15) Stanford, L. A.; Kim, S.; Klein, G. C.; Smith, D. F.; Rodgers, R. P.; Marshall, A. G. Identification of Water-Soluble Heavy Crude Oil Organic-Acids, Bases, and Neutrals by Electrospray Ionization and Field Desorption Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry. Environ. Sci. Technol. 2007, 41, 2696. (16) Grewer, D. M.; Young, R. F.; Whittal, R. M.; Fedorak, P. M. Naphthenic Acids and other AcidExtractables in Water Samples from Alberta: What is being Measured? Sci. Tot. Environ. 2010, 408, 5997.


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(17) Headley, J. V.; McMartin, D. W. A Review of the Occurrence and Fate of Naphthenic Acids in Aquatic Environments. J. Environ. Sci. Health, Part A. 2004, 39, 1989. (18) Lewis, A. T.; Tekavec, T. N.; Jarvis, J. M.; Juyal, P.; McKenna, A. M.; Yen, A. T.; Rodgers, R. P. Evaluation of the Extraction Method and Characterization of Water-Soluble Organics from Produced Water by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry. Energy Fuels. 2013, 27, 1846. (19) Headley, J. V.; Peru, K. M.; Fahlman, B.; McMartin, D. W.; Mapolelo, M. M.; Rodgers, R. P.; Lobodin, V. V.; Marshall, A. G. Comparison of the Levels of Chloride Ions to the Characterization of Oil Sands Polar Organics in Natural Waters by Use of Fourier Transform Ion Cyclotron Resonance Mass Spectrometry. Energy Fuels. 2012, 26, 2585. (20) Headley, J. V.; Barrow, M. P.; Peru, K. M.; Derrick, P. J. Salting-out Effects on the Characterization of Naphthenic Acids from Athabasca Oil Sands using Electrospray Ionization. J. Environ. Sci. Health, Part A. 2011, 46 (8), 844. (21) Eftekhardadkhah, M.; Reynders, P.; Øye, G. Dynamic Adsorption of Water Soluble Crude Oil Components at Air Bubbles. Chem. Eng. Sci. 2013, 101, 359. (22) Eftekhardadkhah, M.; Øye, G. Dynamic Adsorption of Organic Compounds Dissolved in Synthetic Produced Water at Air Bubbles: The Influence of the Ionic Composition of Aqueous Solutions. Energy Fuels. 2013, 27, 5128. (23) Eftekhardadkhah, M.; Øye, G. Correlations between Crude Oil Composition and Produced Water Quality: A Multivariate Analysis Approach. Ind. Eng. Chem. Res. 2013, 52, 17315. (24) Eftekhardadkhah, M.; Øye, G. Induction and Coverage Times for Crude Oil Droplets Spreading on Air Bubbles. Environ. Sci. Technol. 2013, 47, 14154. (25) Eftekhardadkhah, M.; Aanesen, S. V.; Rabe, K.; Øye, G. Oil Removal from Produced Water during Laboratory- and Pilot-Scale Gas Flotation: The Influence of Interfacial Adsorption and Induction Times. Energy Fuels. 2015, 29, 7734. (26) Gaweł, B.; Eftekhardadkhah, M.; Øye, G. Elemental Composition and Fourier Transform Infrared Spectroscopy Analysis of Crude Oils and their Fractions. Energy Fuels. 2014, 28, 997. (27) Badger, G. M. The Ultraviolet Absorption Spectra of Polycyclic Heterocyclic Aromatic Compounds, in: Chemistry of Heterocyclic Compounds: Six Membered Heterocyclic Nitrogen Compounds with Three Condensed Rings; Allen, C. F. H., Ed.; John Wiley & Sons, Inc.: Hoboken, NJ, USA, 2008; pp 551-566. (28) Korshin, G. V.; Li, C. W.; Benjamin, M. M.; Monitoring the Properties of Natural Organic Matter through UV Spectroscopy: A Consistent Theory. Water Res. 1997, 31, 1787. (29) Badger, G. M.; Pearce, R. S. Substituted Anthracene Derivatives. Part IV. The Ultra-Violet Absorption Spectra of Meso-Substituted 1: 2-Benzanthracenes. J. Chem. Soc. (Resumed). 1950, 3075. (30) Badger, G. M.; Pearce, R. S.; Pettit, R. Substituted Anthracene Derivatives. Part V. The Conjugating Powers of the Substitution Positions in 1: 2-Benzanthracene. J. Chem. Soc. (Resumed). 1952, 1112.



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(31) Coates, J. Interpretation of Infrared Spectra, A Practical Approach in: Encyclopedia of Analytical Chemistry; Meyers, R. A., Ed.; John Wiley & Sons Ltd.: Chichester, 2000; pp 10815-10837. (32) Sjöblom, J.; Simon, S.; Xu, Z. Model Molecules mimicking Asphaltenes. Adv. Colloid Interface Sci. 2015, 218, 1. (33) Fileti, E. E.; Coutinho, K.; Malaspina, T.; Canuto, S. Electronic Changes due to Thermal Disorder of Hydrogen Bonds in Liquids: Pyridine in an Aqueous Environment. Phys. Rev. E. 2003, 67, 061504. (34) Shi, Q.; Hou, D.; Chung, K. H.; Xu, C.; Zhao, S.; Zhang, Y. Characterization of Heteroatom Compounds in a Crude Oil and its Saturates, Aromatics, Resins, and Asphaltenes (SARA) and NonBasic Nitrogen Fractions analyzed by Negative-Ion Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry. Energy Fuels. 2010, 24, 2545. (35) Fainerman, V. B.; Miller, R.; Möhwald, H. General Relationships of the Adsorption Behavior of Surfactants at the Water/Air Interface. J. Phys. Chem. B. 2002, 106, 809.


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Captions of Tables and Figures Figure 1: The dynamic interfacial tension for PW-B (A) and PW-I (B) when the samples were prepared at low pH (black squares), natural pH (red circles) and elevated pH (green triangles)

Figure 2: UV/Vis spectra for the produced water samples prepared at pH 2 Figure 3: UV/Vis spectra for the produced water samples prepared at natural pH Figure 4: The ratio between band areas of region IV and I for the produced water samples prepared at low and natural pH Figure 5: FT-IR spectra for dissolved components in PW-B when prepared at low (black) and natural (red) pH Figure 6: FT-IR spectra for dissolved components in PW-C when prepared at low (black) and natural (red) pH Figure 7: The relationship between surface pressure and total nitrogen in dissolved components for the samples prepared at low pH. Figure 8: The relationship between surface pressure and amount of oxygen in the aromatics fractions for the samples prepared at low pH. Figure 9: The relationship between surface pressure and nitrogen content in the asphaltene fractions for the samples prepared at low pH. Figure 10: The relationship between surface pressure and C/H ratio in the asphaltene fraction for the samples prepared at natural pH.



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Tables

Table 1: Total organic carbon (TOC) and total nitrogen (TN) content in the produced water samples prepared with different pH. All values in ppm. pH 2 TOC PW-A PW-B PW-C PW-E PW-F PW-H PW-I

146 43 35 210 43 69

pHnat TN 1.3 1.9 2.9 11.0 1.2

Composition and Dynamic Adsorption of Crude Oil ... - ACS Publications

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