Simple Solid-Phase Extraction Method for High Efficiency and Low

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Simple Solid-Phase Extraction Method for High Efficiency and LowCost Crude Oil Demulsification Karen M. Higa,†,§ Augusto Guilhen,§ Luis C. S. Vieira,† Rogério M. Carvalho,‡ Ronei J. Poppi,§ Mariana Baptistaõ ,∥ Angelo L. Gobbi,† Renato S. Lima,† and Leandro W. Hantao*,†,§ †

Laboratório de Microfabricaçaõ , Laboratório Nacional de Nanotecnologia, Centro Nacional de Pesquisa em Energia e Materiais, Campinas, São Paulo 13083-100, Brazil ‡ Centro de Pesquisas e Desenvolvimento Américo Miguez de Mello, Petrobras, Rio de Janeiro, Rio de Janeiro, Brazil § Instituto de Química, Universidade Estadual de Campinas, Campinas, São Paulo 13083-970, Brazil ∥ Agilent Technologies Brasil, Barueri, São Paulo 06455-000, Brazil S Supporting Information *

ABSTRACT: A novel and simple method for petroleum emulsion breaking and desalting is described and applied to crude oil. Such complex samples consist of stable water−oil emulsions. The oil phase is comprised of petroleum whereas the aqueous phase is composed of brine, including seawater, with varying salt content. Herein, crude oil dewatering was performed by applying a small aliquot of sample to a supported-liquid extraction cartridge. Multiphasic equilibration allowed the aqueous phase to adsorb onto the surface of porous diatomaceous earth (e.g., Celite). Organic solvents such as n-heptane, methylene chloride, and toluene easily desorbed the remaining oil phase. Potentiometric Karl Fisher titration and conductivity analysis confirmed near exhaustive (>98%) water and salt removal alongside particulate matter. This phenomenon was strikingly observed in both mild and harsh salt content conditions with concentrations ranging from zero to 200 000 ppm; the latter is found in Brazilian presalt crude oil samples. Quantitative petroleum recoveries (>98% of maltenes and >82% of asphaltenes) were also observed. Original composition of maltenes, including three important biomarker classes such as C10 demethylated terpanes, tri, tetra-, and pentacyclic terpanes, and ααα-steranes were preserved. Minor asphaltene adsorption (30 ms). A 4.0 mL min−1 flow of auxiliary gas (helium) enabled sample modulation every 2.50 s, and 40.0 ms injection pulses. Column set comprised of 30 m × 320 μm DB-5MS (0.25 μm film thickness) (Agilent Technologies) primary column and a 2 m × 200 μm MEGAWAXHT (0.15 μm film thickness) secondary column. A 40 cm × 250 μm fused silica capillary was used as flow restrictor. Gas chromatography/mass spectrometry (GC/MS) analyses of biomarkers were performed on Shimadzu TQ8030 gas chromatograph coupled to triple quadrupole mass spectrometer (Kyoto, Japan). Such an analyzer was used in Q3 scan mode. MS transfer line and ion source operated at 300 and 220 °C, respectively. Mass channels from m/z 50 to 500 were collected at 10 spectras·s−1, yielding an average of 40 scans·peak−1. Separations were executed on 30 m × 250 μm Restek Rtx-5MS (0.25 μm film thickness) GC column (Bellefonte, PA, USA). Hydrogen was used as carrier gas at a constant flow rate of 1.5 mL· min−1. One microliter sample injection was made in splitless mode (1 min sampling time). All samples were analyzed in triplicate. Maltene separation in both systems was attained using the following temperature programming: 60−330 °C at 6 °C min−1, except for MEGAWAX-HT (maximum allowable operating temperature of 300 °C). 2.8. Asphaltene Characterization. Analysis of asphaltenes was accomplished using 1 H NMR spectroscopy and electrospray ionization-mass spectrometry (ESI-MS). Steps for preparing asphaltene samples were solvent removal and dilution in deuterated chloroform. Final solution had a concentration of 10.0 mg·mL−1. Such experiments used cryoprobe-equipped 600 MHz Agilent Inova NMR spectrometer (Agilent Technologies). ESI-MS analyses of polar asphaltenes were performed on LTQ XL linear ion trap mass spectrometer (Thermo Scientific). Dry asphaltene samples were dissolved in toluene to 1.00 mg·mL−1, followed by dilution with 1:1 (v/v) toluene/methanol. Final solution exhibited a concentration of 250 μg·mL−1. Prior to sample dilution, methanol was acidified with 1% (v/v) formic acid. Sample was infused at 5.00 μL·

3. RESULTS AND DISCUSSION Proof-of-concept experiments were designed to be simple and to use commonly available laboratory facilities. With this in mind, SLE used conventional 3 mL glass syringes dry packed with diatomaceous earth (Figure S1A, Supporting Information).37 This aspect is essential as it reduces the method cost and allows use of disposable devices. Petroleum-based emulsion must be loaded into an SLE cartridge and allowed to flow into a sorbent bed. Such a process is driven by gravity and, as a consequence, is slow. However, sample equilibration is necessary to yield quantitative retention of the aqueous phase from crude oil. W−O emulsion was fractionated into two large classes, maltenes (nonpolar fraction) and asphaltenes (polar fraction). As seen from the elution profile (Figure 1), petroleum elution with 8.0 mL of n-heptane achieved quantitative desorption of maltenes. Besides, 4.0 mL of toluene allowed recovery of asphaltenes. Such samples exhibited different colorations as noticed by naked eye inspection. Maximum molecular absorbances were λmaltene = 259 nm and λasphaltene = 284 nm. 3.1. Water Removal. Initial experiments evaluated the sorbent material’s ability to retain water. A critical stage of the proposed protocol is sample loading. During sample application, water uptake by diatomaceous earth is likely to be regulated by mass transfer of analyte from sample’s bulk to adsorbent’s surface.38,39 Hence, extraction kinetics is dictated by (i) water diffusion through the boundary layer and (ii) adsorption onto surface of porous sorbent material.40 Water diffusion is driven by the concentration gradient in heterogeneous systems. Herein, molecular diffusion is attenuated due to high medium viscosity. The latter is in agreement with Fick’s second law41 and the Stokes−Einstein equation derived from hydrodynamic motion.42 Thus, sample (multiphasic) equilibrium and sorbent material in excess are required to enable exhaustive water retention. Karl Fischer titration protocol was adopted for residual water quantitation in W−O emulsion.43 W−O emulsions with 50% (w/w) initial water content were demulsified and analyzed. In all samples average water concentration (n = 6) lower than quantitation limits (0.05% (v/w)) was found, showing the diatomaceous earth effectively eliminated aqueous phase from C

DOI: 10.1021/acs.energyfuels.6b00553 Energy Fuels XXXX, XXX, XXX−XXX

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Figure 1. Supported-liquid extraction method optimization. Elution profiles of the nonpolar (maltenes) and polar fraction (asphaltenes) as a function of desorption solvent: n-heptane (A) and toluene (B). Experiments were performed in triplicate. Quantitative desorption of maltenes (λmaltene = 259 nm) and asphaltenes (λasphaltene = 284 nm) were attained with 8.0 mL of n-heptane and 4.0 mL of toluene. Insets: maltene (A) and asphaltene (B) extracts. Relative standard deviations (RSD) were below 5%.

Figure 2. Comparative analysis of maltenes by GC × GC-FID. GC × GC-FID chromatograms of volatile and semivolatile fraction of maltene samples obtained by reference protocol (A) and the proposed supported-liquid extraction route (B). Scores graph of a twodimensional multiway principal component analysis (MPCA) model (C). Data projection attained by MPCA enables prompt access to useful information. Such accomplishment is otherwise hindered by univariate data analysis of chromatographic peak areas. This plot highlights the absence of statistical differences between evaluated protocols for sample preparation. High resolution chromatograms are in Supporting Information. For interpretation of the color information, the reader is referred to the web version of this article.

petroleum. Similar observations have been reported regarding the ability of diatomaceous earth to immobilize aqueous phases, but for very different purpose.27−29 In addition, sorbent material acted also as a filtering media by removing particulate when seawater from Santos (SP, Brazil) was used as the aqueous phase. In this case, we observed the absence of particulate matter in both maltene and asphaltene fractions. Such observation is corroborated by previous reports, wherein diatomaceous earth was used in filtration processes (e.g., Celite).44−46 3.2. Desalting Efficiency. Our initial data showed quantitative retention of water by adsorption onto porous hydrophilic structure of diatomaceous earth. Accordingly, it is expected that such immobilized phase retains hydrophilic interfering compounds on the extraction device like salts. Noteworthy, this fact is valid for substances with greater solubility in water than in the used organic solvents. Conductivity measurements investigated the desalting efficiency (n = 4). Seawater-based brine (712 μS cm−1) was used to prepare stable W−O emulsions. Blank conductivity measurements were obtained with processed petroleum. An average value of only 30 μS cm−1 was determined in agreement

with previous findings.6 After sample fractionation, the aqueous phase was eluted with deionized water (720 ± 10 μS cm−1). Comparative analysis of conductivities of both aqueous solutions was performed. Salt recovery (or retention) of 100% was attained using brine of seawater. This result indicates both aqueous phase and hydrophilic salts remain immobilized on SLE cartridge during sample cleanup and petroleum elution/fractionation. The former indirectly validates Karl Fischer findings and confirms the ability of the proposed method for emulsion breaking. Such observation is critical for desalting methods, where the presence of salts dampens chemical analysis, such as ion suppression in ESI-MS.47,48 The second concentrated brine sample (200 000 ppm of NaCl with approximately 2.00 mS cm−1) was used to simulate an extreme condition that may be found in Brazilian O&G, D


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such as presalt petroleum. After measurements of conductivity (n = 4, 1.97 mS cm−1), a salt recovery of 98% further confirmed the excellent ability for desalting. Furthermore, conductivities of two additional aqueous phases (after liquid−liquid extraction with maltenes and asphaltenes) were identical to blank measurements. Thereby, we can state negligible amounts of salt were back-extracted by the water-immiscible organic phases during sample elution (n-heptane and toluene). These results are in agreement with previous conductivity data and ensure the potential of the proposed SLE method for small-scale crude oil demulsification and desalting. 3.3. Petroleum Characterization: Maltenes. Maltene recoveries of 98 ± 3% (n = 8) were attained using the proposed protocol, indicating quantitative elution of petroleum from SLE cartridges. In order to ascertain the integrity of oil phase, the chemical composition of maltenes was assessed using both methods (reference vs SLE). Comparative inspection of maltene chemical fingerprint was evaluated using high resolution GC × GC-FID and spectrometry-based analysis. GC-FID chromatograms, as seen in Figure S2 (Supporting Information), showed highly congested regions (also referred as unresolved complex

Figure 3. Assessment of biomarker equivalence by GC/MS. GC/MS chromatograms of maltene samples obtained by reference protocol (black) and proposed supported-liquid extraction (red). Extracted ion chromatogram of m/z 177 (C10 demethylated terpanes) (A), m/z 191 (tri, tetra-, and pentacyclic terpanes) (B), and m/z 217 (ααα-steranes) (C). This comparison ascertains maltene integrity between evaluated protocols for sample preparation. Baseline of reference analysis was offset to facilitate chromatogram visualization.

Figure 4. Asphaltene fingerprinting by NMR and MS-based techniques for comparative analysis. Positive ESI-MS spectra of asphaltene samples: reference protocol (A) and supported-liquid extraction (B). Comparison of sample’s profiles by 1H NMR using reference protocol (C) and supported-liquid extraction (D). Evidence of major sample alteration/degradation is discarded. Minor alterations were detected in low-intensity signals (E, F), which ascertain a small degree of asphaltene adsorption on silica. E


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(Supporting Information). Such chemometric model was validated through inspection of loadings graph. Peaks corresponding to linear alkanes and branched hydrocarbons contributed most to the first principal component (Figure S6), while the second PC exhibited additional contributions from aliphatic and monoaromatic hydrocarbons. Scores graph is presented in Figure 2C; exploratory analysis underlined maltene samples obtained by both methods exhibit similar composition, independent of sample preparation method. To ascertain such finding, additional GC/MS analyses were performed. Numerous biological markers (biomarkers) are found in nonpolar fraction (maltenes). Such complex compounds are derived from biochemical fossils such as lipids. These biomarkers are frequently adopted as geochemical parameters to rank the relative maturity of petroleum throughout O&G exploration. Traditional protocols use GC/MS to generate sensitive measurements to correlate light oils and condensates, where biomarkers are found in low concentrations.6 In particular, nonaromatic hydrocarbons, including terpanes and steranes, are of particular interest in O&G.32,33 Extracted ion chromatograms (EIC) of samples obtained using SLE and reference method are displayed in Figure 3. Such data illustrates three of the most important biomarker classes monitored in geochemistry. The chromatographic profiles of C10 demethylated terpanes (EIC of m/z 177) (Figure 3A) and ααα-steranes (m/z 217) (Figure 3C) obtained by both methods are in excellent agreement. However, tri, tetra-, and pentacyclic terpanes (m/z 191) (Figure 3B) exhibited minor composition variation. Source inspection of this phenomena indicated that tri, tetra-, and pentacyclic terpanes of this particular oil showed increased intraclass variation. Accordingly, maltene integrity was likely conserved. 3.4. Petroleum Characterization: Asphaltenes. Asphaltene recoveries of 82 ± 6% (n = 10) were attained using the proposed protocol, indicating near quantitative elution of petroleum from SLE cartridge. Total recovery of asphaltenes from silica-based surfaces is dampened by strong adsorption.52 Inclusion of tetrahydrofuran, pyridine, dimethyl sulfoxide, and N-methyl-2-pyrrolidone to alternative eluotropic series may alleviate such limitation, but not preclude asphaltene adsorption.52 Asphaltene characterization was performed by combining ESI-MS and NMR data. ESI-MS was used to probe the composition of highly polar compounds found in asphaltenes by taking up the low ESI ionization efficiency of nonpolar compounds. Remaining constituents were assessed by NMR experiments. From positive ESI-MS spectra (Figure 4A,B), we readily noticed the presence of common ions in both mass spectra (m/z < 700). Hence, chemical compositions between both samples using the forenamed sample preparation protocols are essentially identical. Minor variations in signal intensity were expected as a result from infusion MS analysis. A matter of interest is the presence of three mass clusters above m/z 700 with nominal masses of 715, 729, and 741. This fact is likely attributed to attenuated ion suppression in SLE samples, resulting from adsorption of interfering asphaltenes subclasses.52 1 H NMR spectra were measured to probe additional information on nonpolar asphaltenes, as seen in Figure 4C,D. Oil composition seemed unaffected by sample preparation through inspection of the most intense signals, including monoaromatic CH (δ = 7.295 ppm), aliphatic CH2 (δ = 1.289 ppm), and γ-CH3 (δ = 0.916 ppm). However, significant

Figure 5. SARA oil analysis of a Brazilian presalt petroleum sample. Proposed method allows crude oil demulsification and fractionation into saturate, aromatic, and resin fraction. FT-IR/ATR spectra of saturated hydrocarbons (A), aromatic hydrocarbons (B), and resins (C) ascertains correct sample fractionation.

mixture),49,50 where coelution dampens any attempt of peak integration. Therefore, GC × GC-FID was used to probe volatile and semivolatile composition of maltenes. The excellent agreement between both sample preparation methods makes regions of chromatogram nearly indistinguishable (e.g., aliphatic and aromatic hydrocarbons). In addition, a common starting point would be a univariate approach (plot of individual samples or variables). Nevertheless, this path can be dangerously misleading as any covariation is neglected and important information is ignored, due to increased information density in GC × GC data (Figure 2).51 Thus, MPCA was used for pattern recognition because this method significantly reduces size and complexity of data.51 A two-component MPCA model was built to explain 99.35% of variance in original data (Figure S3, Supporting Information). No outliers were detected as shown in Figure S4 F


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Table 1. Comparison of Methods for Emulsion Breaking/Phase Separation Procedures Highlighting Operating Principles, Advantages, and Limitations method

selectivity

advantage

centrifugationa

particle size and density

conserves sample integrity

distillationa

vapor pressure

SLE-based

relative solubility

conserves nonvolatile sample fraction profile bypasses specialized instruments

chemical demulsification (addition of additives)14 ultrasonic radiation treatment15,16 microwave heating17

Gibbs free energy of dispersion

biotechnology18

differential acoustic impedance conversion of electromagnetic radiation to thermal energy (microwave absorption by polar molecules) metabolite of microorganism displaces emulsifiers at oil/water interface

electrostatic-based19,20

electrocoalescence

micro- and nanotechnology56−58

effect of micro- and nanomaterials on emulsion stability

application to crude oil

restriction

conserves sample integrity

polar asphaltenes stabilize emulsion at interface;54chemical additives may aid emulsion breaking,55 but may compromise chemical fingerprinting loss of volatile fraction of petroleum

yes

minor asphaltene adsorption

yes

influences sample matrix effect/auxiliary techniques are required to accelerate process

yes

limited efficiency

no

yes

yes

demulsification occurs under mild operation conditions

bypasses specialized instruments

such metabolites may compromise chemical fingerprinting

yes

auxiliary instrument/device is used to separate and collect oil/water droplets; additive may aid in emulsion breaking sample adsorption onto substrate is unknown

yesb yes

a Petrobras internal protocol was adopted as standard method.54 bApplication of microfluidic technologies for crude oil emulsion breaking has not been reported so far.

processing was facilitated by using a sorbent-based “separation” protocol. 3.6. Comparative Study. The described SLE method for crude oil emulsion breaking and simultaneous desalting does not require use of sophisticated instruments and “expert” operators, in comparison to alternative approaches as ultrasonic radiation treatment, electrostatic-based, and microwave assisted methods (Table 1). Hence, such output may be operated in resource-limited environments due to inherent simplicity. In addition, use of a simple solid-phase experiment allowed a 10fold reduction in sample preparation time (5 min versus 50 min), compared with the reference approach (centrifugation). Furthermore, sample dewatering, desalting, and fractionation were combined into a single recipient. This feature is important to eliminate undesired analyte loss during sample manipulation. Altogether, the principle explored for petroleum demulsification is compatible with method automation and miniaturization. Miniaturization enables processing of trace amounts of crude oil, while automation ensures precise sample fractionation, including reproducible asphaltene precipitation. Moreover, such an approach increases sample throughput, reduces solvent consumption, and minimizes production of hazardous waste. Lastly, our approach minimizes sample degradation and eliminates introduction of foreign additives to sample matrix compared with chemical demulsification, biotechnology-based methods, and distillation (Table 1). Such care is vital for chemical characterization of petroleum samples commonly used to evaluate oil quality.6

alterations to sample composition of trace components were observed in less intense bands, as diaromatic CH (δ = 7.428 ppm), olefinic CH/CH2 (δ = 5.05 ppm), and CH2 α-to-2 aromatics (δ = 3.68 ppm). These discrepancies arise from partial asphaltene adsorption on silica, as supported by Combariza and co-workers’ detailed findings.53 Accordingly, such results warrant conservation of sample integrity of majoritary components during emulsion breaking. Minor alterations to trace asphaltenes were detected (Figure 4E,F). Therefore, additional investigations are required when developing asphaltene class-specific preparation methods using SLE. 3.5. SARA Oil Analysis. Our SLE method for crude oil demulsification was combined with SARA (saturate, aromatic, resin, and asphaltene) oil analysis. Such a standard fractionation method is extensively used in O&G. The modification described herein enables crude oil demulsification and desalting, followed by petroleum fractionation (Figure S7, Supporting Information). Maximum absorbance of saturate, aromatic, and resin fractions was determined by molecular absorbance spectroscopy as being 265, 270, and 260 nm, respectively. Additional FT-IR/ATR characterization (Figure 5B−D) confirms identities of SARA fractions. Saturated hydrocarbons (Figure 5A) exhibits reflectance bands corresponding to aliphatic hydrocarbons, including sp3 C−H stretching (2920 cm−1) and [−(CH2)−] angular deformation (1450 cm−1). In addition, aromatic hydrocarbons (Figure 5B) and resins (Figure 5C) display more intense bands compatible with aromatic moieties, such as sp2 C−H stretching (3070 cm−1), aromatic C−C stretching (1400−1500 cm−1 and 1585− 1600 cm −1), weak overtones (1585−2000 cm−1), and [−(CH)−] out-of-plane bending (675−900 cm−1). Resins, in addition to aforementioned reflectance bands, exhibit characteristic CO (1650 cm−1) and O−H stretching bands (3300 cm−1) related to the presence of organic acids, such as naphthenic acids.54 In this context, laboratory-scale crude oil

4. CONCLUSIONS Proposed SLE extraction protocol proved to be a powerful output for combined small-scale crude oil demulsification and desalting. Such a practice is particularly challenging, as petroleum is both chemically and physically complex. Deployed sample preparation is remarkable by taking into account crucial advantages; namely, sample integrity was conserved with minor G


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alterations to asphaltenes, oil recovery was quantitative (>98% of maltenes and >82% of asphaltenes), and removal of water and salt was outstanding (near absolute). Accordingly, results reported herein demonstrate the potential of SLE for combined crude oil dewatering, desalting, and fractionation. Considering the inherent simplicity of extraction method, emulsion breaking/desalting devices may be deployed in resource-limited environments (like offshore oil platforms) once the dependence on sophisticated and nonportable instruments was eliminated. A direct consequence of such innate abilities (simplicity, compatibility with lab automation and miniaturization) is the reduction of the experimental gap between point-of-use technologies and petrochemistry. In addition, such an approach is of great interest for class-specific petroleum applications, as adequate eluotropic series may be explored. Concurrent application is processing of trace crude oil samples using miniaturized SLE-based devices to probe the chemical properties of petroleum.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.energyfuels.6b00553. Figure S1. Crude oil demulsification and fractionation. Figure S2. Comparative analysis of maltenes by gas chromatography-flame ionization detection. Figure S3. Multi-way principal component analysis (MPCA) modelling. Figure S4. MPCA outlier inspection. Figure S5. Comparative analysis of maltenes by comprehensive two-dimensional gas chromatography; Figure S5. Comparative analysis of maltenes by comprehensive twodimensional gas chromatography. Figure S6. MPCA loadings graph indicating which peaks contributed to the first and second principal component. Figure S7. SARA oil analysis of a Brazilian pre-salt petroleum sample (PDF)

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AUTHOR INFORMATION

Corresponding Author

*Address: Centro Nacional de Pesquisa em Energia e Materiais Rua Giuseppe Máximo Scolfaro, 10 000 13083-100 Campinas, SP, Brazil. Tel.: +55 19 3512-3566. Fax: +55 19 3518-3104. Email: [email protected]. Notes

Views, opinions, and/or findings contained in this report are those of the authors and should not be constructed as the official method unless so designed by official documentation. The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Fundaçaõ de Amparo à Pesquisa do Estado de São Paulo (FAPESP, Grant 2015/05059-9) and Petrobras (2014/002284) are gratefully acknowledged for financial support. We are indebted to Prof. Fabio Augusto for providing GC/MS system; Dr. Camila Caldana and Juliana Aricetti for their skillful ESI-MS analysis (Proposal MET-19461); Dr. Ana Zeri for access to NMR facility (Proposal RMN-19391). Stefano Galli (MEGA snc) is thanked for proving GC columns. H


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