(527d) Saponin-Based Surfactant: Chemistry, Properties, and Applications on Enhanced OIL Recovery – Towards Sustainability

Surfactants are one of the most versatile compounds due to their wide field of industrial applications. The utilization of synthetic surfactants is growing globally, being more than 15 million tonnes/year. However, around 60% ends in aquatic streams and marine environments, generating adverse environmental effects and causing contamination. Hence, it is imperative to seek more environmentally-friendly [1]. Hence, it is essential to seek novel natural sources as an alternative to synthetic ones but with similar surfactant properties [2]. Saponins are secondary compounds, heterosides, and phytochemicals formed by various aglycones or triterpenoid steroids and one or more carbohydrate moieties. Also called sapogenin and glucosaponins. Typically, they have high molecular weight and complex structures, giving them a variety of physical, chemical, and biological properties. Widely distributed in the plant kingdom, they are rich in functional compounds such as surfactants with potential and numerous applications such as moisturizing, foaming, detergent, emulsifying, solubilizing, and hemolytic properties, and others; among which the ability to form foam stands out. Historically, various compounds have been developed, based on saponins properties, having commercial potential in different industries such as food, chemical, cosmetic, pharmaceutical, textile, paints, lubricants, and cleaning products. However, various studies have established a more precise saponin definition based on its molecular structure and biosynthetic origin [3].

Similarly, research around the world has developed novel processes of extraction techniques, purification strategies, and technological applications [4]. The main objective of this study is to determine the interfacial behavior of a natural surfactant extracted from quinoa (Chenopodium quinoa) residues and determine its ability to produce foaming fluids within an oil reservoir to sweep large portions and recover larger quantities of crude oil from the reservoirs. Hence, this work aims to evaluate the efficiency of a natural saponin-based surfactant to minimize environmental impact and maximize cost efficiency as an ecologically sustainable replacement for synthetic surfactants.

The wet saponification was performed using the quinoa saponin extraction method, and spectrophotometric analysis was used for quantification. The quinoa residue samples were initially weighed, sieved, and mixed with distilled water using a magnetic stirrer, followed by vacuum filtration, centrifugation, and storage (Figure 1a). Subsequently, the methodology proposed by Monje, Yarko, and Raffaillac [5] was followed to quantify the percentage of quinoa saponins by applying the spectrophotometric method based on the construction of the calibration curve from the saponin sample Sigma-Aldrich 47036- 50G-F (standard) as a reference profile. Liebermann-Buchard (LB) color reagent was prepared and obtained by mixing acetic anhydride and concentrated sulfuric acid (1:5). Dilutions of the commercial sample were prepared at 0.1; 0.20; 0.3; 0.4; 0.5; 0.6 and 0.7 mg/mL; 0.600 mL of each were taken, to which 1 mL of LB the reagent was added, stirred for 20 s in a vortex, and left to stand for 37 min. Then, the calibration curve was built, measuring the absorbance for the different concentrations, at a wavelength of 528 nm, with a reading speed of 1 nm/s. An aliquot of the quinoa saponin samples was taken to be analyzed. Finally, the parameter R5* (hfoam t=5min-hfoam t=0min) was determined to estimate the stability of the foam.

Two analyses confirmed the chemical and physical characteristics of the saponin extract as a surfactant. FITR analyses were performed using Agilent Technologies Cay 630 equipment, following the KBr pillbox method, employing approximately 0.050 g of surfactant sample. The measurement parameters were: wavelength interval from 4000 to 600 cm^-1, resolution of 2 cm^-1, and eight scans. For the second analysis, the PerkinElmer STA 8000 equipment took 10 mg of the saponin sample. The test is heating started from 25 °C until reaching 800 °C at a rate of 5 °C/min, using 10 mL/min nitrogen flow as carrier gas. Subsequently, the flow of formulated foams was simulated and modeled for crude oil recovery by injecting it through a simple one-dimensional system in a heterogeneous porous medium. Several concentrations were initially prepared, varying salinity (NaCl), electrolyte charge (CaCl₂), pH (0.5 M citric acid or 0.5 M NaOH), and quinoa saponin concentration (0.01; 0.1; 1 and 5%). Then, foams produced by commercial surfactants (Tween 80 and Tween 20) were also performed as a comparison.

The presence of saponins in the quinoa wash water was confirmed by physical observation by stirring, filtering, and rotary evaporating when foaming. In addition, the mixture of the quinoa washing water was tested with LB color reagent, presenting a pinkish-reddish color, characteristic of triterpenes (Figures 1b). The linear equation obtained by the calibration curve using the commercial saponin was: Y = 6.2766 X – 0.1355 and R² = 0.9946. This equation quantified the concentration of saponins in the analyzed samples, obtaining a range between 49% and 66.9%. However, the range reported in the literature varies from 47.3% to 56.2% [6]. Additionally, the relationship R5* parameter determined that the 0.5% saponin solution was 86% (metastable), representing excellent stability of the generated foam over time (Figures 1b).

The FTIR spectra of the saponins (Figures 1c) were similar to those of other already reported saponins [7]. Different signals or asymmetric stretching vibrations and the functional groups for this type of saponin were identified, with the alcoholic group at 3281 cm^-1 and the active methyl group at 2942 cm^-1. However, between 2500 cm^-1 and 1900 cm^-1, there is no absorption; that is, there is no accumulation of double and triple bonds, so the width of the band corresponds to the presence of hydrogen bonds, this peak confirms the presence of the C-O bond, and finally, the spectrum shows about 1377 cm^-1 the presence of the C=C double bond, and at 1020 cm^-1 a stretching signal C-O-C.

The TGA test showed the thermal stability of the saponins (Figures 1d). The pronounced mass loss occurred in three regions. The first stage ranged between 100 °C and 200 °C, attributable to the evaporation of moisture and surface water present in the natural surfactant, a range in which it presents a weight loss of 8.075%. In the second stage, the weight loss was 53.807%, which ranged between 100 °C and 500 °C, attributed to loss of chemically bound water, at which point carbohydrates are broken down. Finally, in the third and last stage, between 500 °C and 800 °C, the weight loss is accelerated by breaking the carbon bonds at high temperatures, with a weight loss of 9.566%. In summary, from the TGA test, it follows that the most significant weight loss occurs between 200 and 400 °C, so this implies that natural surfactant can be used in the oil field, where the reported reservoir temperature is between 60 and 150 °C since in this range the natural surfactant has adequate thermal stability.

The next step in this research will be to evaluate the influence of foam injection (formulated using saponin as a natural surfactant) in a porous medium as an improved hydrocarbon recovery technique “EOR” (Figures 1e), as an ecological, low-cost surfactant, and raw material alternative for sustainability production.

In conclusion, when mechanically shaken, the analyzed samples formed foam, evidencing the presence of triterpene type saponin (LB color reagent test). Saponin was quantified between 49 and 66.9%. It was found that the parameter R5* is over 50%, which indicates that the foams are stable over time. Different asymmetric stretching signals and functional groups for this type of saponin were identified through the FTIR test. The TGA test showed that the most significant weight loss occurs between 200 and 400°C, implying that natural surfactants can be used in oil fields, where the reservoir temperature ranges between 60 and 150°C, as an improved hydrocarbon recovery technique and as an alternative for sustainability production, ecological and low-cost technique.

References

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[4] A. A. Muir, A.D., Paton,D.,Ballantyne, K., and Aubin, “Process for recovery and purification of saponins and sapogenins from quinoa,” Chenopodium quinoa, 2002.

[5] R. J. P. Monje C. Y., “Determination of total saponin in quinoa (Chenopodium Quinoa Will) Spectrophotometric method,” Mem. IV Natl. Congr. Boliv. Plant Prot. Assoc. Oru. April 5 to 7, vol. . C.E.A.C., 2006.

[6] M. Lozano, E. Ticona, C. Carrasco, Y. Flores, and G. R. Almanza, “CUANTIFICACIÓN DE SAPONINAS EN RESIDUOS DE QUINUA REAL,” no. 2, pp. 131–138, 2012.

[7] M. S. Almutairi and M. Ali, “Natural Product Research : Formerly Natural Product Letters Direct detection of saponins in crude extracts of soapnuts by FTIR,” no. March 2015, pp. 37–41, 2014, doi: 10.1080/14786419.2014.992345.