Characterization of petroleum sulfonate synthesized via gas-phase SO3 sulfonation in rotating packed bed and its application in enhanced oil recovery

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Highlights

  • PS with good EOR performance was prepared via gas-phase SO3 sulfonation in the RPB.

  • The definite chemical composition of PS was characterized at the molecular level.

  • The CMC method was adopted for the optimization of the PS surfactant concentration.

Abstract

In this work, petroleum sulfonate (PS), which can be used for enhanced oil recovery (EOR), was synthesized by sulfonation of distillate oil using gaseous SO3 in a rotating packed bed. The prepared PS was characterized by FT-IR, NMR, negative electrospray ionization fourier transform ion cyclotron resonance mass spectrometry [(−) ESI FT-ICR MS] and thermal gravimetric analysis (TGA). Results showed that the PS contains N1, O1, O2, O3, N1O2, O3S, O4S, and N1O3S classes, among which O3S, O4S, and N1O3S are the three main classes. And the chemical composition of the PS was obtained by the combined analysis of the double-bond equivalent (DBE) and carbon number (CN). TGA results showed that PS is thermally stable at the conventional reservoir temperature (less than 200 °C). In addition, the EOR performance of PS was studied by measuring surface tension, interfacial tension (IFT), wettability alteration and core-flooding experiments. Critical micelle concentration (CMC) of the prepared PS with a value of 0.2% was also determined by surface tension method. An ultra-low oil-water IFT value 1.327 × 10−3 mN/m was obtained at the CMC of PS solution. It was also found that adding PS into brine can decrease the contact angle below 90°, indicating that it can alter the rock wettability from oil-wet to water-wet surface which contributes to enhancing oil recovery. Finally, core-flooding experiments were carried out with different PS concentrations. The results showed that an additional recovery of about 30% after conventional water flooding can be obtained at a PS concentration of 0.3%. This study indicated that the PS synthesized by gas-phase SO3 sulfonation in RPB has good EOR performance, and the work is helpful for the learning of the relationship between PS composition and EOR performance and give the guidance for PS’s synthesis.

Introduction

Nowadays, oil resources around the world are increasingly scarce, and oil companies have made great efforts to improve oil recovery to keep pace with the increased oil demand (Muggeridge et al., 2014). There are nearly 60–70% of the crude oil remaining under the ground after primary and secondary recovery processes (water and gas flooding). Thus, the enhanced oil recovery (EOR) techniques have been developed (Egbogah, 1994, Babadagli, 2007) for the recovery of the residual oil trapped in the reservoir. Among these, chemical flooding has been widely used for the EOR process, while surfactant flooding is one of the most efficient EOR methods (Hosseinzade Khanamiri et al., 2016, Yuan et al., 2015, Santanna et al., 2009, Pal et al., 2018). It can greatly reduce the oil–water interfacial tension (IFT) to ultralow value, and changes the rock’s wettability from oil-wet surface to water-wet surface in the reservoir. Therefore, types of surfactants were developed for surfactant flooding, including petroleum sulfonates (PS), alkyl benzene sulfonates, petroleum carboxylates, gemini surfactants, lignin sulfonates, etc (Negin et al., 2017). PS with similar chemical structure to crude oil’s (Pachón-Contreras et al., 2014), strong interfacial activity, thermal stability, and relatively low production cost becomes the preferred and greatly used surfactant for EOR.

PS is a complex mixture in which the alkyl chain lengths and aromatic ring contents vary in a considerable range depending on the distillate oil composition and sulfonation process. It is mainly composed of effective active matter, unsulfonated oil, inorganic salts and volatiles (Basu and Shravan, 2008). Previous studies have shown that the composition of PS has significant effect on its performance for EOR process (Sandvik et al., 1977). Therefore, the deep understanding of the PS chemical composition from a molecular point of view is crucial for the guidance of its synthesis and application. However, the study on molecular composition analysis of PS is relatively few. In general, PS is usually characterized and quantified using high performance liquid chromatography (Bear, 1988), mass spectrometry (Philip et al., 1984), ultraviolet-visible (UV-vis), and Fourier transform infrared spectroscopy (FT-IR)] (Hummel and Fröhlich, 1996) but without a detailed chemical composition study on their active matter (AM) molecules. The above analytical methods regard the R-SO3Na as the active components of PS, where R is aromatic ring with different alkyl chains. This ambiguous definition is due to the molecular diversity of the distillate oil composition. Shi et al. (2010) have studied crude oil composition by negative electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry [(−) ESI FT-ICR MS] to identify the heteroatom compounds in crude oil. Afterwards, Rojas-Ruiz et al., 2016a, Rojas-Ruiz et al., 2016b) and Li et al (2016) have characterized the composition of PS by means of [(−) ESI FT-ICR MS] to detect the heteroatom classes of PS. Also, the possible chemical composition of the PS was conjectured according to their characterized results. At present, limited literature elaborate on the relationship between PS composition and its application performance such as IFT reduction, wettability alteration, and recovery efficiency, and so on. Therefore, the composition of PS and the distillate oil should be characterized in detail at a molecular level for the better understanding of PS composition and its EOR performance, which are helpful for the optimization of the PS’ EOR performance via synthesis process.

Generally, PS is mainly synthesized via sulfonation of distillate with concentrated or fuming sulfuric acid, liquid sulfur trioxide, or gaseous sulfur trioxide (SO3), followed by the neutralization with sodium hydroxide or ammonia. The sulfonation process using sulfuric acid as a sulfonating agent requires high reaction temperature and high equipment costs (Katritzky et al., 2009). While using liquid-phase SO3 as sulfonating agent is easy to over-sulfonate and form carbonization and coking for its high reactivity. In addition, solvent recovery is required in the liquid-phase SO3 process. While gas-phase SO3 sulfonation process with a lower cost and high-quality products (Norman, 1997) has drawn the researchers’ focus. The characteristics of sulfonation process has fast reaction rate and great viscosity changes in the system, easily resulting in excessive sulfonation and easy coking which is caused by the mismatch between its fast sulfonation rate and low micro-mixing efficiency. In our previous research, it has been proved that rotating packed bed (RPB) with the advantages of short residence time, high micro-mixing and mass transfer efficiency can be used for the gas-phase SO3 sulfonation process to achieve the match between micromixing and reaction (Ma et al., 2019).

In this work, PS was synthesized in the RPB via gas-phase sulfonation process. The prepared PS was characterized by FT-IR, NMR, [(−) ESI FT-ICR MS] and TGA analysis. The possible composition of the distillate oil and PS can be inferred based on the analysis of double-bond equivalent (DBE) and the carbon number (CN). Critical micelle concentration (CMC) of the prepared PS, which was determined by surface tension, was developed to explore a method to evaluate the usage of PS in EOR. In addition, the performance of PS in EOR application has been studied by measuring interfacial tension (IFT), contact angle and core-flooding experiments.

Section snippets

Materials

Chemical reagents such as pentane, isopropanol (IPA), sodium hydroxide (NaOH), sodium carbonate (Na2CO3) and sodium chloride (NaCl) were purchased from Aladdin Industrial (Shanghai). Table 1 shows the physical and chemical properties of the distillate oil. Saturates, aromatics, resins, and asphaltenes (SARA) compositions of the distillate oil were determined according to the reference ‘‘NB/SH/T 0509-2010 for Petroleum Asphalt Four-Component Determination Method’’.

Synthesis of PS

The PS was synthesized by

FT-IR analysis

Fig. 3 shows the FT-IR spectrum of the distillate oil and PS. The chemical functional groups in the distillate oil and PS were identified by the absorption peaks. The stretching vibrations peak of –OH are observed at 3443.44 cm−1. Absorption bands at 2924.22 cm−1 and 2853.54 cm−1 correspond to asymmetrical stretching vibration and symmetrical stretching vibration of CH2 respectively. The absorption bands of 1618.14 cm−1 and 1459.44 cm−1 can be assigned to the frame vibration of benzene ring,

Conclusion

In this work, the PS was synthesized via gasous SO3 sulfonation in the RPB, and the chemical composition of the distillate oil and the prepared PS was characterized by means of (−) ESI FT-ICR MS analysis at the molecular level. It was found that the prepared PS with the main O3S1 sulfonated class had a high active matter of 40.61%, indicating there is no oversulfonate in the proposed synthesis process. The critical micelle concentration (CMC) value of the synthesized PS, 0.2%, were determined

CRediT authorship contribution statement

Xiaoke Ma: Conceptualization, Methodology, Writing - original draft. Bing Liu: Investigation. Tianxiang Ma: Supervision. Hai-Kui Zou: Supervision. Guang-Wen Chu: Funding acquisition. Bao-Chang Sun: Supervision, Resources, Funding acquisition. Liangliang Zhang: Supervision. Yong Luo: Supervision. Jian-Feng Chen: Funding acquisition.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

This work was financially supported by National Key R&D Program of China (No. 2016YFB0301500).

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