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Detailed Characterization of Petroleum Sulfonates by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry Fernando A. Rojas-Ruiz, Andrea Gomez-Escudero, Zarith Pachon, Alvaro Villar-García, and Jorge Armando Orrego-Ruiz Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.5b02923 • Publication Date (Web): 07 Mar 2016 Downloaded from http://pubs.acs.org on March 7, 2016

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Detailed Characterization of Petroleum Sulfonates by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry Fernando

A.

Rojas-Ruiz††,

Andrea

Gómez-Escudero†,

Zarith

Pachón-Contreras†,

Álvaro Villar-García† and Jorge A. Orrego-Ruiz†. †

ECOPETROL, Instituto Colombiano del Petróleo, Piedecuesta, Santander 681018, Colombia.

††

Grupo de Investigación Recobro Mejorado, Universidad Industrial de Santander, Bucaramanga,

Santander, Colombia.

ABSTRACT

Petroleum sulfonates obtained from heavy vacuum gas oil (HVGO) were characterized by negative Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (-) ESI FT-ICR MS to better understand the chemical nature of their surface-active components. ESI analysis showed that sulfonates contain mainly O3S, O3S2, O4S and NO3S classes which means that the sulfonation reaction does not occur selectively for aromatic HC class compounds as it also reacts with N, S, and O heteroatom classes. Since sulfonates were separated by solubility into lipophilic and hydrophilic categories, it was confirmed that the same classes compose hydrophilic and lipophilic sulfonates. Moreover, this procedure revealed that

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lipophilic sulfonate extracts contain organic acids (O2 class) that are related to the total acid number of the starting HVGO. However, selective isolation of the surface-active species using “Wet-Silica” procedure allowed detecting that these compounds have non surface-active character as they do not interact with the water phase. The new structural information disclosed about petroleum sulfonates and their raw materials might encourage further studies on the rational design and synthesis of novel petroleum surfactants with the desired properties for industrial applications such as Chemical Enhanced Oil Recovery (CEOR).

INTRODUCTION The petroleum industry has to deal with the fact that only a reduced portion (20 to 40 %) of the petroleum originally present in a reservoir can be extracted by conventional mechanisms.1 However, it is possible to obtain higher recovery factors by applying advanced strategies such as Chemical Enhanced Oil Recovery (CEOR), including polymer flooding, surfactant flooding, alkali flooding and its combinations.2-4 Although, the chemical formulations containing surfactants stand out as the most promising approach.5-8 Surfactants enhance oil recovery by reducing capillary forces that traps the oil in porous media; this means that maximizing oil recovery implies a decrease in interfacial tension to ultra-low values. These conditions are obtained using microemulsions.9,10 Microemulsion systems require a delicate hydrophiliclipophilic balance, which means that the repulsion interactions between the surfactant molecules and crude oil molecules must be minimized. These interactions may be considerably reduced when the chemical structure of the surfactants employed within the formulation is similar to the hydrocarbons present in the crude oil.11 In this order of ideas, the more structural information


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that is known of the surface-active species and/or their raw materials, the easier and more accurately surfactants may be designed with the desired properties for CEOR. Petroleum sulfonates stand out among other surfactants for the application in CEOR processes for economical and practical reasons.12-14 Thus, different studies on petroleum sulfonates synthetized from crude oil and from vacuum distillation fractions have been reported.12,15,16 Due to its sulfonation susceptibility, vacuum gas oils are considered a very good source of raw materials for the petroleum sulfonates synthesis16-18 and different gas oil sulfonation conditions have been studied.19 Nevertheless, as a result of the compositional complexity of the materials employed on their synthesis, petroleum sulfonates are obtained as complex mixtures in which the alkyl chain and the aromatic ring content varies in a considerable range. Considering this idea, the analysis of these samples is not trivial, and no research has been carried out in this area recently.17 Anionic surfactants, including petroleum sulfonates, are usually detected, quantified and characterized using chromatographic methodologies20,21 and spectroscopic analyses (UV-Vis and FT-IR);22 but without a thoughtful structural characterization of their active matter molecules. Traditionally, petroleum sulfonates analysis consist on a combination of ASTM D855-56, ASTM D3712-05 and cationic titration methods to develop a rapid and precise process for the analysis with respect to molecular weight and sulfonate content.23,24 Briefly, the sample is dissolved in ethyl ether and converted to sulfonic acid using dilute hydrochloric acid. The sulfonic acid is converted to sodium sulfonate after extraction. The isolated sodium sulfonate and mineral oil are dissolved in chloroform and an aliquot of the chloroform solution is placed on a silica gel column. The oil is eluted with chloroform and the sulfonate is eluted with ethyl alcohol, and both are determined gravimetrically. Average molecular weight is calculated from the average equivalent weight of the sodium sulfonate, which is determined by ashing a portion of


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the isolated sodium sulfonate. These analytical approaches consider the petroleum sulfonates as R-SO3Na active ingredients where R is a naphthenic aromatic nucleus bearing different alkyl side chains; this definition is inaccurate considering the wide diversity of molecules contained in petroleum distillation fractions. It is possible to obtain additional structural information on the side chain by combined chromatography mass spectrometry measurements.25 The molecular weight distribution of petroleum sulfonates as well as their alkyl-aromatic lipophilic nuclei distribution can be characterized by means of High-Temperature Gas Chromatography with mass detection protocols (HT GC-MS),11 but a tedious desulfonation process is still necessary prior to the analysis.26 Therefore it is necessary to develop a fast and precise method in order to achieve a detailed composition of petroleum sulfonates, as well as to support the identification of the best starting materials for their synthesis.

Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS) has emerged as a prominent analytical technique that allows analysis of complex mixtures, including crude oil and petroleum derivative samples at a molecular level, and to perform a detailed analysis of the structure (molecular weight, aromaticity, etc).27 These advantages have allowed introduction of this technique into the study of industrial surfactants of high molecular weight which are mostly obtained from complex mixtures as raw materials. The average molecular weight of Titron surfactants (tert-Octylphenol Ethoxylate Surfactant Polymers) have been studied by means of Laser Desorption FT-ICR MS.28

In this work, a detailed characterization of petroleum sulfonates was achieved by means of (-) ESI FT-ICR MS analysis. Compositional differences were observed between the water-soluble and the oil-soluble petroleum sulfonates extracts. Under the assessment conditions, the O3S was


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the main class within the synthesized surfactants. Additionally, the detection of classes O3S+S (O3S2), O3S+O (O4S) and O3S+N (NO3S) showed that other than HC aromatic nuclei were also sulfonated under the established reaction conditions, producing sulfonates with thiophenic, phenolic and carbazolic moieties on their structures. This information could support further studies on the design and synthesis of novel petroleum surfactants for industrial applications such as CEOR. EXPERIMENTAL SECTION Materials Table 1 shows the physical and chemical properties of the starting raw HVGO. Sulfur and nitrogen content were determined using an ANTEK 7000S analyzer (Antek, Inc., U.S.) according to the ASTM D5453 and ASTM D5762 methods, respectively. Saturates, aromatics, resins and asphaltenes (SARA) compositions of oil samples were determined according to the ASTM D1500 method. Density, API Gravity and Total Acid Number (mg KOH/g) were determined according to ASTM D4052, ASTM D287 and ASTM D664 methods, respectively. Analytical grade toluene and methanol were used as solvents for sample preparation, which were distilled twice and kept in glass bottles with ground glass stoppers before usage. Table 1. Characteristics of petroleum gas oil employed on petroleum sulfonates preparation Parameter

High Vacuum Gasoil (HVGO)

Density at 15°C (g/mL)a API Gravity (°API)b Saturates (%) Aromatics (%) Resins (%) Asphalthenes (%) Aniline point (°C)d Sulfur (w% )e Acid Number (mg KOH/g)f

0.9096 24.0 62.54 35.26 2.20 0.00 79.0 0.830 2.259


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a

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ASTM D4052, b ASTM D287, c ASTM D1500, d ASTM D611, e ASTM D4294, f ASTM D664.

Preparation of Petroleum Sulfonates Sulfonation reactions were conducted according to literature procedures,15,16 and based on modifications performed on our last work.11 From 10 g of oleum (SO3 65 in wt %) approximately 6.0 g of SO3 were bubbled through 50.0 g of heavy vacuum gas oil contained on a round button reactor placed over a 30 °C water bath for 30 min. The reaction mixture was gently stirred in order to obtain a good homogenization. After SO3 addition, the reaction mass was allowed to cool to room temperature and poured into a separation funnel with 50 mL of ice cold water (4°C). After decantation, two phases that contained the hydrophilic and lipophilic sulfonates extracts were obtained (Figure 1).

Figure 1. Sulfonates extraction procedure scheme. The lower phase containing the hydrophilic sulfonic acids were collected on a separated beaker and neutralized with 6 N NaOH to pH 7-8. The hydrophilic petroleum sulfonates extract were then concentrated by evaporation and filtered under vacuum to obtain a viscous-dark oil with 1.75 % Active Matter percentage (AM). The upper phase, comprised of postreaction material and


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the lipophilic sulfonic acids, was kept in the separation funnel. These oil soluble sulfonic acids were then neutralized with a 50 % NaOH solution until a pH value of 7 - 8, and extracted with a 40 % isopropanol solution (2 x 20 mL). The alcoholic fraction was concentrated by removing the alcohol/water mixture using a rotary evaporator. Partially water-soluble yellowish oil was obtained as lipophilic petroleum sulfonates extract with 3.6 %AM. Following the procedures previously described two sulfonate extracts (hydrophilic and lipophilic) were obtained with a 21 % yield of total sulfonation achieved under the employed experimental conditions (Table 2).

Table 2. Petroleum sulfonates preparation results. Surfactant Extract Hydrophilic Lipophilic

Mass (g)

AM (%)*

Yield (%)

Global yield (%)

4.0 0.98

1.75 3.60

14 7.0

21

Isolation of Petroleum Sulfonates by “Wet-Silica” Procedure 100 mg of the surfactant product were dissolved in 5 mL of water, and subsequently 5 mL of n-heptane and 500 mg NaCl were added in order to saturate the aqueous phase. The resulting mixture was vigorously agitated to favor surfactant solubilization in the organic phase. The organic phase was decanted and drained over Na2SO4. Finally, 100 uL of extract were diluted in 10 mL of anhydrous toluene. For the separation procedure, 1.0 g of freshly prepared SiO2-H2O 40% was added to the previous mixture and transferred to a 60 cm x 8.0 mm glass column. The toluene soluble fraction was eluted and collected in a clean and previously weighted flask (EluTol). Thereafter, 4 mL of (2:5 v/v) methanol:toluene solution was added to elute the polar fraction retained in the SiO2-H2O 40% which are mainly surface-active species (EluMetol). Both EluTol and EluMetol fractions were quantified and analyzed by (-) ESI FT-ICR MS. Figure 2 schematizes the procedure described above.


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Figure 2. “Wet-Silica” separation of petroleum sulfonates extracts. FT-ICR MS Analysis FT-ICR MS analysis was performed using a Bruker-Solarix FT-ICR mass spectrometer equipped with an actively shielded 15 T superconducting magnet. Prior to sulfonation process, 10 mg/mL of HVGO solution were diluted with a toluene/methanol mixture (50:50) to 0.1 mg/mL for (-) ESI spectra acquisitions. To enhance the ESI ionization efficiency, ammonium hydroxide (20 µL to 1 mL of sample solution) was added. The procedure mentioned above was applied for the FTICR MS analysis of the postreaction material fraction obtained after the extraction of the lipophilic sulfonates. For sulfonation products characterization, a sample of 50 mg of hydrophilic sulfonates extract (viscous-dark oil) were re-dissolved in toluene:methanol (50:50) and then diluted with the same solvents to 0.025 mg/mL for (-) ESI spectra acquisitions. Likewise, 50 mg of lipophilic sulfonates (yellowish oil) were dispersed in 5.0 mL of water and extracted with 5.0 mL of n-


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heptane (10 mg/mL). Afterwards an aliquot was diluted to 0.1 mg/mL using a toluene:methanol mixture (50:50) for (-) ESI spectra acquisitions. The test samples were infused at a flow rate of 450 µL/h using a syringe pump via an Apollo II electrospray source. Source optics were operated with -220 V for capillary column end and -60 V for skimmer1 voltages. Ions accumulated for 0.050 s in a collision cell with 5 MHz frequency and 350 Vpp of radiofrequency (rf) amplitude. The optimized mass for Q1 was 200 Da. Collision cell was operated at 2 MHz and 1400Vpp rf amplitude. The time-of-flight (TOF) was set to 0.7 ms to transfer the ions to an ICR cell by electrostatic focusing of transfer 4 MHz and 350 Vpp rf amplitude. 30 V collision energy were applied for In Source Fragmentation to promote the fragmentation of ions in the source. The ICR was operated at 13 db attenuation, 2701100 Da mass range, and 4 M acquired data size. The time domain data sets were co-added from 100 data acquisitions. Mass Calibration and Data Analysis The ESI FT-ICR mass spectra for the raw HVGO, the HVGO after reaction and the EluTol fractions were calibrated internally by Data Analysis 4.0 (Bruker Daltonics) using a N1 and O2 species homologous series, while for the EluMetol fractions (sulfonated extract) an O3S homologous series Double Bond Equivalent (DBE) 10 was used. Peaks with relative abundance greater than 5 times of the signal to-noise ratio were exported to a spreadsheet. Elemental composition assignment for each peak was performed by Composer (Sierra Analytics), this software performs a normalization by dividing the relative abundance of each signal of a homologues series by the total relative abundance of whole the assigned signals. In the Supporting Information the distribution error graphs are shown for the classes detected by (-) ESI FT-ICR MS.


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RESULTS AND DISCUSSION (-) ESI FT-ICR MS Analysis In a first approach for understanding the petroleum sulfonates chemical composition, we discuss the main classes detected by (-) ESI for the samples. Figure 3 contains the classes with relative abundances higher than 1.0 % within the raw HVGO (before reaction), its hydro- and lipophilic extracts, and the HVGO after reaction.

% relative abundance

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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50 45 40 35 30 25 20 15 10 5 0

Raw HVGO

Hydrophilic extract

Lipophilic extract

HVGO after reaction

Figure 3. Classes detected by (-) ESI before and after sulfonation. This figure shows that only three classes (N1, O1 and O2) were detected for the raw HVGO. Even though these compounds remain after reaction; the N1 underwent the greatest change by being reduced three times in its relative abundance after reaction. This could be explained considering a light oxidation towards NO and NO2 and its sulfonation towards O3S+N compounds. It has been demonstrated that dehydrogenation and oxidation accompany sulfonation reactions, giving complex mixtures containing hydroxyl and carbonyl


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compounds, as well as carboxylic acids.29 In both hydro- and lipophilic extracts, O3S and O3S+X classes (where X = S, N or O) were detected which prove that sulfonation reaction occurred, because these classes were not present in the raw HVGO. Although Figure 3 shows that the hydrophilic and lipophilic extracts are mainly composed by the same classes, the non-surface-active N1 and O1 compounds were detected in the hydrophilic and O2 in lipophilic extracts. It could be explained by considering the polarity of pyrrolic (N1) and phenolic compounds (O1) and the lipophilicity of long alkyl chained naphthenic acids (O2) that are extracted with 40% iso-propanol during the isolation process. The presence of remaining sulfonates (O3S, O3S+S and O3S+O) in the material after reaction is an evidence of a nonefficient extraction process. In an attempt to achieve a deeper characterization, hydro- and lipophilic extracts were analyzed in more detail from their (-) ESI spectra. By comparing DBE and Carbon Number (CN) distributions from classes O3S, O3S+S (O3S2), O3S+O (O4S), O3S+N (NO3S), it was possible to observe that hydrophilic sulfonates extract have higher DBE values and lower CN compared to lipophilic extract. This can be associated to a higher aromatic character rather than a naphthenic, as alicyclic moieties trend to increase the lipophilicity of a petroleum sulfonate (Figure 4).


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%relative abundance

a

7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0

Hydrophilic Lipophilic

O3S

1

3

5

7

9

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5.0 4.0

O3S

3.0 2.0 1.0 0.0

11 13 15 17 19

16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 Carbon number

5.0

% relativa abundance

b

%relative abundance

DBE

O3S+S

4.0 3.0 2.0 1.0 0.0 1

3

5

7

9

2.5

O3S+S

2.0 1.5 1.0 0.5 0.0

11 13 15 17 19

16 18 20 22 24 26 28 30 32 34 36 38 40 42 44

DBE

2.0

Carbon number

O3S+O


%relative abundance

c

1.5 1.0 0.5 0.0 1

3

5

7

9

0.8

O3S+O 0.6 0.4 0.2 0.0

11 13 15 17 19

16 18 20 22 24 26 28 30 32 34 36 38 40 42 44

DBE

Carbon Number

2.0


d %relative abundance

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


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O3S+N 1.5 1.0 0.5 0.0 1

3

5

7

9

11 13 15 17 19

0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0

O3S+N

16 18 20 22 24 26 28 30 32 34 36 38 40 42 44

DBE

Carbon Number

Figure 4. DBE and CN distributions for classes (a) O3S, (b) O3S+S, (c) O3S+O and (d) O3S+N obtained by (-) ESI for hydrophilic (red) and lipophilic (blue) compounds.


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The most abundant compounds among the O3S class in the hydrophilic products were those with DBE 10 and 11 and CN 26 to 30. Meanwhile the most abundant species for the same O3S class in the lipophilic surfactants bear DBE 9 and 10 and CN 28 to 32 (See figure 4a). Because O3S are the most abundant compounds, this outcome confirms that hydrophilic petroleum sulfonates are mainly constituted by more aromatic cores and short alkyl chains, while lipophilic sulfonates by single ring aromatic cores and longer alkyl chains.11 On the other hand, the detection of O3S+O, O3S+S and O3S+N revealed -for the first time- that beyond hydrocarbon aromatic nuclei, a significant amount of aromatic compounds with O, S and N were also sulfonated under the experimental conditions. DBE and CN distributions for O3S+S (See figure 4b) suggests that the hydrophilic aromatic sulfonates were formed from sulfur containing aromatic compounds with DBE from 7 up to 13 and CN between 25 and 30, whereas their lipophilic analogues were obtained from sulfur containing aromatic molecules with DBE 6 to 9 and CN from 29 to 34. According to the O3S+O distributions detected, the hydrophilic sulfonates are formed mostly by the sulfonation of a small amount of oxygen containing aromatic compounds with DBE 11 to 14 and CN from 25 to 30. On the contrary, the O3S+O lipophilic sulfonates mainly display DBE from 5 to 9 and CN from 29 to 34 (See figure 4c). According to the literature, the presence of oxygen atoms on aromatic nuclei (phenols) increase the reactivity of these species for sulfonation reactions (aromatic electrophilic substitution).30 However, it should be noted that the oxygen containing sulfonates (O3S+O) presented a maximum DBE of 8 (possibly di-aromatic) and 13 (possibly tetra-aromatic) for lipophilic and hydrophilic sulfonates respectively but there is an issue of availability. It means that though phenols are highly reactive, hydrocarbons and sulfur compounds are more abundant and more available for sulfonation reaction, which explains the differences in relative abundances (Figure 3). Furthermore, the O3S+N class was detected in a


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relatively low amount within hydrophilic and lipophilic sulfonates (See figure 4d). According to these results, the hydrophilic extract also contain surfactant species that are formed by the sulfonation of nitrogen containing aromatic compounds with DBE 11 to 13 and CN from 24 to 31. Lipophilic sulfonates, on the other hand, mainly display DBE from 9 to 12 and CN from 27 to 33. Figure 5 shows a reactivity order toward sulfonation using sulfur trioxide for some heterocyclic and polyaromatic compounds.31 Considering the more abundant DBE values for the O3S+S class detected in both lipophilic and hydrophilic extracts (see figure 3b), the sulfur containing aromatic compounds that are sulfonated during reaction should correspond to benzothiophene or dibenzothiophene derivatives with different substitutions on their alkyl chains (DBE 7-12). Although according to Katritzky et. al.31 these aromatic nuclei are less susceptible to electrophilic aromatic substitution reactions compared with other hetero-aromatic compounds, the presence of cyclic/acyclic alkyl substituents might increase the benzothiophene derivatives reactivity (Figure 5).

Figure 5. Reactivity order toward sulfonation using SO3 for some heterocyclic and polyaromatic compounds.


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It can be also observed from figure 5 that even though the indolic and carbazolic compounds highly react toward sulfonation reactions compared to polyaromatic compounds,31 the low concentration of O3S+N sulfonates can be explained as function of the precursor’s aromaticity or low concentration as we mentioned for phenols. As carbazolic compounds increase their aromaticity (DBE > 9) their sulfonation susceptibility decrease since the para- and orthopositions to the pyrrolic N atom are unavailable for electrophilic substitution reaction to occur. This could explain why a considerable amount of N1 compounds remains unaffected in the nonsulfonated HVGO (See figure 3). As a second approach to the structural level analysis of the petroleum sulfonates, based on the “Wet-Silica” extraction procedure reported in the literature,32-34 we performed a selective isolation of the surface-active species present in both, lipophilic and hydrophilic, sulfonate extracts obtained from the sulfonation process. Two different fractions were obtained according to the procedure described in the experimental part and schematized in figure 2. EluTol corresponds to the fraction of compounds that elute from “Wet-Silica” with toluene and EluMetol corresponds to the fraction of compounds that elute with methanol:toluene (2:5) which contains the surface-active components. Each extract fraction (EluTol, EluMetol) was analyzed by (-) ESI FT-ICR MS. According to these results, both sulfonate extracts revealed the presence of surface-active classes O3S and O3S+X (X = S, N or O) without structural differences between hydro- and lipophilic with respect to those mentioned in figure 3. Table 3 shows the classes detected by (-) ESI in the whole sulfonate extract and their “Wet-Silica” fractions.


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Table 3. Relative abundances percentage for the main classes detected. Hydrophilic Extract

Class/Rel. Abundance %

Whole

Lipophilic Extract

EluTol 26.46

EluMeTol

Whole

EluTol

EluMetol

-

-

-

-

N

5.46

NO

-

2.33

-

-

-

-

-

2.84

-

-

-

-

-

6.96

-

-

95.47

41.42 25.19

-

-

52.37 22.1

-

53.91 24.71

8.11

-

5.03

NO2 O

1.81

28.93

O2

-

36.99

O3S

44.98 25.07

-

O3S+S O3S+O

3.88

-

5.79

O3S+N

6.89

-

4.60

2.36

-

1.95

O3S+OS

1.00

-

3.07

1.07

-

2.09

It was observed that in the EluTol hydrophilic fraction nitrogen-containing and oxygencontaining compounds were detected whereas EluMetol showed O3S and O3S+X sulfonates. In the case of the lipophilic extract, EluTol fraction presented the O2 compounds and EluMetol contained sulfonates. O2 class detected in the lipophilic Elutol fraction corresponds to carboxylic acids considering that the starting HVGO has a TAN of 2.30 g KOH/g (See table 1). This data demonstrates that the solid phase extraction using SiO2-H2O-40% allowed us to selectively extract the sulfonate classes O3S+X and distinct them from other non-surface-active classes (N1 and O2) that are also extracted during the treatment of the reaction products.

Finally, table 4 contains the average molecular weight (AMW), CN, DBE and H/C ratio for the most abundant classes detected for the hydrophilic and lipophilic extracts. As it was expected, the lipophilic sulfonates displayed higher H/C ratios, which indicate their higher aliphatic character. The same features are reflected on their lower DBE and higher CN values. On the contrary, the hydrophilic surfactants are formed by highly aromatic structures with short alkyl


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chains. Representative hypothetical structures for hydrophilic and lipophilic extracts are also included based on the average structural values.

Table 4. AMW, CN, DBE and H/C ratio for hydrophilic and lipophilic sulfonates O3S. Hydrophilic Sulfonates Extract Most Average Abundant H/C DBE

Class

AMW

Most Abundant CN

O3S

465.61

29

11

1.33

O3S+S

491.68

28

10

1.41

O3S+O

485.54

29

11

1.34

O3S+N

495.34

27

13

1.30

Class

AMW

Most Abundant CN

O3S

510.07

32

10

1.47

O3S+S

536.24

31

9

1.55

O3S+O

535.99

32

8

1.54

O3S+N

540.26

30

10

1.45

Lipophilic Sulfonates Extract Most Average Abundant H/C DBE

Hypothetical Structure

Hypothetical Structure


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These results support further studies on the individual chemical and interfacial properties of these compounds in order to determine the positive and/or negative effects over the final surfactant properties. Consequently, the information disclosed in this paper encourages studies on a rational design and synthesis of new oil surfactants with the desired properties for industrial applications such as CEOR based on raw material selection and product characterization by FTICR MS. CONCLUSIONS In this work, a molecular level characterization of petroleum sulfonates was achieved by means of (-) ESI FT-ICR MS analysis. The O3S was detected as the main class within the synthesized surfactants, and essential structural differences were observed between the water-soluble and the oil-soluble petroleum sulfonates. As expected, the hydrophilic petroleum sulfonates are mainly constituted by aromatic nuclei with DBE 10 to 11 and short alkyl chains C14 to C40; whereas, the lipophilic sulfonates are mainly composed by comparatively less aromatic centers with DBE 9 to 10 and longer alkyl chains C18 to C47. The classes O3S+S, O3S+O and O3S+N, showed that other than HC aromatic nuclei, a significant amount of sulfur, oxygen and nitrogen containing aromatic compounds are also sulfonated under the established reaction conditions, producing sulfonates with thiophenic, phenolic and carbazolic moieties on their structures. The “wet silica” method allowed us to selectively extract the sulfonate classes O3S+X and to confirm its structural features as well as its surface-active character as they are retained over an aqueous media by ionization at the water surface. Moreover, this procedure allowed showing that lipophilic sulfonate extracts could contain organic acids (O2 class) that depends on the starting material’s TAN. However, these organic acids do not show considerable surface-activity based on the “wet silica” results.


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The new structural information reported here about these surface-active species and/or their raw materials could support further studies on the rational design and synthesis of novel petroleum surfactants with the desired properties for industrial applications such as CEOR. Supporting Information The sulfonates characterization by IR and the distribution error graphs are shown for the classes detected by (-) ESI FT-ICR MS. ACKNOWLEDGEMENTS The authors would like to thank Dr. Steven M. Rowland and Amy C. Clingenpeel (Florida State University) for the valuable discussions on this research, and to the research project Injection of Chemicals in Yariguí-Cantagallo Field (Ecopetrol-ICP).

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Detailed Characterization of Petroleum Sulfonates ... - ACS Publications

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