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Article

Evaluation of Temperature on the Methane Hydrates Formation Process Using Sodium Surfactin and Rhamnolipids

by
Antonio Pavón-García
1,
Abel Zúñiga-Moreno
2,
Ricardo García-Morales
1,
Francisco Javier Verónico-Sánchez
3 and
Octavio Elizalde-Solis
1,*
1
Departamento de Ingeniería Química Petrolera and Sección de Estudios de Posgrado e Investigación, Escuela Superior de Ingeniería Química e Industrias Extractivas, Instituto Politécnico Nacional, Unidad Profesional Adolfo López Mateos, Ed. 8, Lindavista, Ciudad de México 07738, Mexico
2
Laboratorio de Investigación en Fisicoquímica y Materiales, Departamento de Ingeniería Química Industrial, Escuela Superior de Ingeniería Química e Industrias Extractivas, Instituto Politécnico Nacional, Edif. Z-5, 2° piso, Unidad Profesional Adolfo López Mateos, Lindavista, Ciudad de México 07738, Mexico
3
Escuela de Ingeniería y Ciencias, Tecnológico de Monterrey, Carretera Lago de Guadalupe Km.3.5 Atizapán de Zaragoza Col. Margarita Maza de Juárez, Atizapán de Zaragoza 52926, Mexico
*
Author to whom correspondence should be addressed.
Energies 2024, 17(1), 67; https://doi.org/10.3390/en17010067
Submission received: 29 November 2023 / Revised: 15 December 2023 / Accepted: 16 December 2023 / Published: 21 December 2023
(This article belongs to the Special Issue Natural Gas Hydrates: Exploration and Development)
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Abstract

:
The performance of chemical and biological additives in the methane hydrates formation and dissociation processes is of relevance for the development of gas-transport and gas-storage systems. The effect of sodium surfactin, rhamnolipids, and sodium dodecyl sulfate (SDS) on the methane hydrate formation process was assessed in this work at different temperatures and a fixed pressure of 50 bar. The studied parameters were induction time, methane uptake, period to reach 90 percent of the consumed gas, water-to-hydrate conversion, and formation rate. Concentrations for sodium surfactin were 3, 150, 750, 1500, 2000, and 2500 ppm, while rhamnolipids and SDS solutions were analyzed at 1500, 2000, and 2500 ppm. Performance testing of these additives was carried out by means of the isochoric–isothermal method. The experimental setup consisted of an isochoric three-cell array with 300 mL of capacity and magnetic stirring. According to the results, the sodium surfactin promoted the methane hydrate formation since the kinetics were higher and the water-to-hydrate conversion averaged 24.3%; meanwhile, the gas uptake increased as concentration was rising, and the induction time was reduced even at a temperature of 276.15 K.

Graphical Abstract

1. Introduction

In the last decades, technological advances have allowed the economic growth of countries, along with comforts in daily life. All human activity has been intrinsically related to energy consumption, and the world will continue demanding energy to sustain all these actions. For instance, global energy production accounted for 15,124 million tons of oil equivalent (Mtoe) in 2022. The statistics included the primary resources for producing energy: coal, oil, natural gas, electricity, biomass, and heat. Among these, natural gas represented 23%, despite the growth of sustainable energies [1].
Natural gas is a reliable material resource that could solve energy demand for the substitution of oil while the world is looking for green fuels. Natural gas has the advantages of abundance and producing fewer pollutant emissions in contrast to oil. The improvement of natural gas transport and storage, focused on reducing costs, is still an open challenge and gas hydrates look to be a viable option [2]. In addition, the research on the phenomena that intrinsically occur in this media takes more relevance due to the vast distribution of natural gas hydrates around the world [3,4].
Gas hydrates are compounds structured by an ice-like crystalline solid, made of water molecules. Gas is encapsulated within cavities structured by the molecules, which are strongly associated due to hydrogen-bond interactions. Nowadays, the formation of gas hydrates is the focus of some research fields because of their applications in water purification, desalination, energy transport and storage, and gas sequestration [4,5,6,7,8,9].
Methane, as the main constituent of natural gas, has been taking relevance as a key component in preventing or promoting gas hydrate formation. The use of additives to attain those further applications is of particular interest in terms of kinetic, agglomerating, and thermodynamic activities. As a benefit of promoting activity of the additives, classified as kinetic or thermodynamic ones, the appraised parameters under study have been the induction time, temperature onset, gas uptake, kinetic formation, self preservation, temperature, and pressure on the dissociation conditions, as well as thermal, electromagnetic, and mechanical properties [9,10,11,12,13,14].
Considering sustainability criteria on this topic and the friendly environmental impact, fixed bed or dispersed agents (extracted from natural resources or modified by physicochemical treatments) have been analyzed as promoters for testing gas separation, storage, and transport of methane and natural gas. Examples of these agents, known as bioclathrates, are sand, cellulose, coal, and wastes of vegetables [14,15,16,17,18,19,20,21,22,23,24,25]. Alternately, for the promotion of gas hydrates, biological or renewable additives (classified as biosurfactants) have also been tested, like those based on vegetable oils [26] or vegetable materials branched with sodium dodecyl sulfate [27], amino acids [28,29,30], organic amines [31,32], urea [31,33], and oligosaccharides such as dextrin [34,35]. The efficiency of the kinetic activity has been commonly contrasted against sodium dodecyl sulfate on the gas consumption, growth rate, or induction time [36,37].
Biosurfactants synthetized from fungal origin have been evaluated in different conditions on gas hydrates; the most common are surfactin and rhamnolipids. The chemical structures for the mono-, dirhamnolipid, and surfactin are depicted in Figure 1a, 1b, and 1c, respectively. These can be produced by cell cultivars from Bacillus subtilis for rhamnolipids and from Pseudomona aeruginosa for surfactin. Rhamnolipids are glycolipids of low molecular weight consisting of rhamnose molecules linked to fatty acids. Surfactin is a lipopeptide molecule structured of amino acids and fatty acids.
The antiagglomeration activity of rhamnolipids was reported by Lamim et al. [38] in a methane hydrate formation at concentrations of 1000 ppm. The results demonstrated the inhibition effect of this biosurfactant in experiments developed in a PVT apparatus at 277.15 K, with an agitation of 150 rpm, and pressure was modified from 1 to 355 bar with a rate of 1 bar/min. According to Hou et al. [39], rhamnolipids also demonstrated the prevention of methane hydrate agglomeration in octane + water cuts. Chen et al. [40] conducted a study on the same kind of systems (gas + liquid hydrocarbon + water cut) where the rhamnolipids induced an improvement in the dissociation kinetics rate on methane hydrates under diesel + water systems. Concentrations for rhamnolipids were 0, 0.5, 1, and 3 wt%, while the water cut ranged from 0 to 20%.
Arora et al. [41,42] indicated that rhamnolipids are methane hydrate promoters based on experiments under aqueous rhamnolipids solution dossed at 100 and 1000 ppm in a C-type silica gel bed. The parameters evaluated were formation kinetics, induction time, hydrate formation temperature, and mole consumption. The promoting effect of the biosurfactants, rhamnolipids, and surfactin in porous media on methane hydrate was also demonstrated by Carvajal-Ortiz and Pratt [43] for smectite clay constituted mainly of montmorillonite and nontronite. Rogers et al. [44] proved different sand clays and Heydari and Peyvandi [45] tested silica gel.
Jadav et al. [46] appraised rhamnolipids and surfactin (separately) in methane hydrates in pure water solutions from 200 to 1000 ppm; both biosurfactants were produced from the abovementioned microorganism. The gas-formation kinetics and gas-to-hydrate conversion were enhanced while the induction time was reduced. These findings demonstrated better performance for the biosurfactants in contrast with sodium dodecyl sulfate under the lowest concentration of 200 ppm at 273.15 K and 70 bar. Bhattacharjee et al. [47] analyzed the effect of surfactin (contained in a cell-free supernatant) on the methane hydrate formation at 50 bar and 274.15 K. The results proved an enhancement in the kinetics, assuming a promotion activity whose values were comparable against the appliance of sodium dodecyl sulfate. Finally, Zhang et al. [48] analyzed the possible separation of methane and nitrogen via hydrates using rhamnolipids in the intervals of 274.15–276.15 K and 50–70 bar. A favorable separation factor was attained in the range of 200 to 800 ppm as a function of the methane–nitrogen separation effect.
Moreover, research groups have demonstrated that the chemical addition of functional groups or hyperbranched molecules might improve the effect of novel molecules, even for biosurfactants in gas hydrates. This is the case of sodium surfactin, which contains lipopeptides linked to sodium molecules according to Figure 1d. Investigations with sodium surfactin have been accomplished in reference to its rheological properties [49] and interfacial tension [50] in different systems, aiming at further oil and gas applications.
In summary, biodegradable materials could attenuate the environmental damage caused by synthetic additives. Sodium surfactin is a biodegradable surfactant whose constituents (amino acids and fatty acids) have separately demonstrated hydrate-promoting activity; however, this biosurfactant has not been applied in methane hydrates. Therefore, it is necessary to analyze the methane hydrate formation process at temperatures above 273.15 K where the driving forces are reduced. The purpose of the present contribution was to assess the sodium surfactin concentration and temperature effects on the methane hydrates by means of an autoclave array at the intervals of 0–2500 ppm and 273.65–276.65 K. Rhamnolipids and sodium dodecyl sulfate at concentrations from 1500 to 2500 ppm were contrasted against our key biosurfactant on the nucleation and growth processes. The examined variables were induction time, temperature onset, gas uptake, and formation kinetics. Particularly, sodium surfactin was evaluated at diluted concentrations, based on the low critical micelle concentration of 3 ppm.

2. Materials and Methods

Methane with a purity of 99.99% was procured from Infra (Mexico City, Mexico). Sodium surfactin (CAS: 302933-83-1) was kindly provided by Kaneka Co. (Osaka, Japan). The commercial rhamnolipids (R90) produced by AGAE Technologies (Corvallis, OR, USA) were purchased from Sigma-Aldrich (St. Louis, MO, USA); the manufacturer claimed a 90% pure monorhamnolipid and dirhamnolipid mixture; the remaining impurities were rhamnolipid congeners. Sodium dodecyl sulfate (CAS: 68585-47-7) was acquired from Caledon Co. (Caledon, ON, Canada). All these additives were not further purified. Deionized water (resistivity 16.0 MΩ·cm at 293.15 K) was used for the preparation of aqueous solutions.
The experimental apparatus consisted of a three-cell array as schematically shown in Figure 2. The main section consisted of three cells (1A, 1B, and 1C) made of stainless steel with 300 cm3 of capacity and an internal shaft with double blade, each cell had its own measuring instruments: a calibrated pressure manometer (3), a calibrated temperature probe (4), a stirring motor (5), and a needle valve. The peripherical devices were a homemade thermostatic bath (2), three stirring controllers (6), a liquid bath controller (7), a manual syringe pump (8), a digital temperature indicator (9), a gas-supply cylinder (10) and a personal computer (11).
The solutions (concentrations in parts per million) were prepared by weighing the surfactant and measuring the added volume of water into a class A volumetric flask. The aqueous solutions of additives were prepared at 1500, 2000, and 2500 ppm for rhamnolipids and SDS, while the concentrations for sodium surfactin solutions were 3, 150, 750, 1500, 2000, and 2500 ppm.
The entire circuit was initially washed with proper solvents to remove any residues and dried by flushing with nitrogen gas. The isochoric–isothermal method was used in the gas hydrate measurements. It briefly consisted of loading 120 cm3 of fresh sample at the same concentration of the surfactant solution to each cell, followed by hermetical sealing, which allowed for attaining 3 repeatable experiments at least; the results corresponded to the average of more than one set of experimental runs. The cells were immersed in the thermostatic bath and connected to the peripherical devices. The temperature was fixed at 293 K by means of the circulating liquid bath. Afterward, the air was evacuated from the cells and the circuit by degassing with a vacuum pump. Next, the thermostatic bath was cooled down to reach a minimum onset temperature on the cell. Meanwhile, the stirring controller was powered on at a speed of 700 rpm. After stabilization of the temperature, the gas from the cylinder or the syringe pump was fed to the cells to reach the target pressure required in the manometer (50 bar). The beginning of the gas feeding was set as the zero time to start with the measurements. The stirring was turned off after the temperature and pressure were observed to be stable on the data acquisition developed in free software (Phyton, version 2.7.15+). Then, the system was recorded on the computer to monitor the formation process as a function of time. The hydrate formation was verified by the sudden decrease in pressure and temperature increase; then, the elapsed period from zero time up to the occurrence of a temperature increase associated with the beginning of gas hydrate formation (temperature onset) was considered as the induction time. Thereafter, the pressure was still decreasing and reached a minimum value. The experimental run was concluded when a stabilization in temperature and pressure was noticed. Both variables, as well as the time during this interval, were considered to evaluate the gas uptake, conversion, and hydrate formation kinetics rate. Finally, a new experiment was carried out with fresh solution samples following the abovementioned procedure.

3. Results and Discussion

The effect of sodium surfactin and rhamnolipids on the nucleation and formation process for methane hydrates was contrasted with the results obtained using SDS. To the best of our knowledge, methane hydrates in the absence of any additive were not formed for all the explored temperatures after 7 days, and the minimum pressure depletion was ascribed to the gas solubility in water. The same behavior was recognized for temperatures above the explored ones using additives in this work; methane hydrate formation did not occur.
A typical behavior of pressure and temperature along the isothermal experiments is depicted in Figure 3 after the system reached the target temperature. Two main sections can be identified depending on the period, the hydrate nucleation process related to the induction time and the hydrate growth process that occurred during t90 and beyond. The period to attain 90 percent of the complete hydrate formation is known as t90.
In the first section, methane was injected into the cell to reach about 50 bar, causing the temperature to increase; the feed immediately induced alteration in the behavior of variables such as pressure, which diminished slowly due to the gas dissolution on the liquid phase; then, the temperature tended to be stabilized again. Meanwhile, supersaturation was taking part up to the appearance of the first hydrate crystals, noticed by an intense peak of temperature. The second section initialized on the temperature increase that indicated the commencement of the methane hydrate agglomeration and finished on the minimum pressure being reached at a constant temperature. In this section, the determined parameters were the methane uptake, t90, water-to-hydrate conversion, and growth rate. The calculated parameters are summarized in Table 1. The dissociation conditions were estimated by the correlation proposed elsewhere [51].

3.1. Induction Time

The elapsed period in nucleation, where supersaturation conditions are attained to nucleate the first crystals, is known as induction time (tind). Its tendencies are illustrated in Figure 4, which were evaluated between the beginning of pressure set at 50 bar and the sharp increase in temperature, associated with the exothermic crystallization that commonly agreed with a pressure drop.
On each bioadditive, the induction time was very low and did not outline a systematic behavior as a function of concentration, considering the standard deviation depicted in the error bars, at a constant temperature. This random tendency is clearly ascribed to the stochastic phenomena on the nucleation process [52]. Great differences on the tind were observed between the values of rhamnolipids or sodium surfactin and sodium dodecyl sulfate; the induction time for the biosurfactants was shortened in contrast with the SDS at any aqueous solution concentration. Comparing tind between rhamnolipids (Rh) and sodium surfactin (Ss), both data sets were similar, considering the standard deviation. The lowest concentrations of both biosurfactants were enough to overcome the slow nucleation performance using sodium dodecyl sulfate. For instance, the induction time was drastically reduced from 2809.9 min for 2500 ppm SDS to 8 min for 150 ppm sodium surfactin at 274.65 K. In terms of the different temperature onset, the induction time seemed to be prolonged as temperature increased. The driving force associated with the temperature increase was narrowed, requiring more time to attain nucleation [53]. Therefore, these bioadditives improved the nucleation and were able to deal with the problem identified with SDS. For the ranges of 150–750 ppm of sodium surfactin and 1500–2500 ppm of SDS, the induction time was shortened as the quantity of the additives became greater. These trends could be approached by the possible mechanism to attain the nuclei critical size, confirmed by Sun et al. [12] and Moraveji et al. [54]. The formation of hydrate nuclei came from the cluster growth of methane and water molecules, which played the role of precursors. Herein, the addition of surfactants reduced the induction time, it was supposed to be ascribed to the absorption of surfactant that lowered the hydrate’s critical size. Moreover, another synergistic effect that reduced the induction time was the solvating power of water, increased by the surfactant. Then, a great number of methane molecules were available in the liquid phase to form more hydrate structures [14]. Additionally, Jadav et al. [46] revealed efficient performance in the induction time for rhamnolipids and surfactin against SDS. Those results contrasted with our findings; the possible reason relied on the different temperature onset for the experiments.

3.2. Gas Uptake

After nucleation, the gas uptake (∆nmethane) is the difference in the methane mole number between the beginning of the pressure drop (detected by a temperature rising) considered as zero time (t = 0) and the minimum pressure reaching equilibrium conditions on a defined time (t), as indicated in Equation (1). Nevertheless, the evolution of methane consumption could be computed throughout the progressive pressure decrease monitored in real time [55].
∆nmethane = nmethane,t=0 − nmethane,t = (V/R)·(Pt=0/Zt=0Tt=0 − Pt/ZtTt)
The variable V represented the volume of the gas phase in the cell, R corresponded to the ideal gas universal constant, P was the pressure of the gas, T indicated the gas-phase temperature, and the compressibility factor Z for methane was calculated with the Peng–Robinson equation of state detailed in Equation (2):
Z3 − (1 − B)Z2 + (A − 3B2 − 2B)Z − (AB − B2 − B3) = 0
A = 0.45724αPr/Tr2
B = 0.0778Pr/Tr
α = [1 + (0.37464 + 1.54226ω − 0.26992ω2)(1 − Tr0.5)]2
where Pr referred to the reduced pressure, Tr specified the reduced temperature, and the α parameter was a function of the reduced temperature along with the acentric factor ω.
Methane hydrate formation was not obtained in the experimental trials at the critical micelle concentration of sodium surfactin (3 ppm, claimed by the manufacturer). Then, ultimate gas uptake was about 34.06 mmol at 150 ppm, and this parameter raised as the concentration increased, reaching a maximum value of 265.11 mmol at 2500 ppm. A comparison of gas uptake is depicted in Figure 5, from 1500 to 2500 ppm of additives.
The increase in the additive concentration promoted a great number of hydrate cages. This behavior could be supported mainly by the capillary theory, but mass transfer, micellar, adsorption, and water structure also played a crucial role during gas hydrate formation. Herein, the hydrate growth was stimulated by the additives in the gas–liquid interface via a probable coexistence of porous hydrates instead of rigid hydrates; thus, a high surface area was available for capturing methane molecules as the concentration raised [56,57,58]. In addition, the driving forces associated with the temperature downwards benefited the gas consumption; the maximum final gas uptake occurred at the lowest temperature (273.65 K). Conversely, methane consumption did not present a significant rise between 1500 and 2500 ppm, considering standard deviations at fixed temperatures. Then, the concentration of sodium surfactin around 1500 ppm could be sufficient for a proper gas consumption. Sodium surfactin stood out on the gas uptake since ∆nmethane was still taking place at higher temperatures (276.15 K), while the ∆nmethane for SDS and rhamnolipids were not beyond 274.65 and 275.15 K, respectively. On the temperature interval of 273.65–275.15 K, the gas consumption obtained for sodium surfactin was quite similar to those obtained for rhamnolipids and sodium dodecyl sulfate for concentrations at 1500, 2000, and 2500 ppm, herein the additives played the role of methane hydrate promoters. The additives were confirmed to reduce the interfacial surface tension; accordingly, the methane solubility in the liquid phase was improving, and a high amount of dissolved methane in the liquid phase was able to subsequently occupy cage structures formed by water [52,59].

3.3. Methane Conversion and Growth Rate

The water-to-hydrate conversion (X(W/H)) was evaluated with the basis of Equation (3):
X(W/H)/% = 100 × (∆nmethane·Hydration number/nW)
where ∆nmethane corresponded to the methane uptake, nW was ascribed to the mole number of water, and the hydration number was considered to be 6.1, as established in preceding calculations [60].
The longest t90 (about 8836.2 min) agreed with a low water-to-hydrate conversion of 3.1%, which was obtained at 150 ppm of sodium surfactin. The maximum X(W/H) averaged 24.3% at 2500 ppm, while the shortest t90 was 89.5 min at 1500 ppm and 273.65 K. These last values for both parameters confirmed the stimulation of hydrate formation since the low temperature favored the driving forces. The opposite was demonstrated at 750 ppm of sodium surfactin; as the temperature rose, t90 went from 100.2 to 7550.5 min and X(W/H) performed 16.3–20.2%. The concentration of the biosurfactant seemed to alter minimally the conversion and t90 above 750 ppm. Values for t90 did not lower to 90 min but did not exceed 200 min, even though they were similar, considering the standard deviation. The better X(W/H) of about 24.3% was determined at the highest concentration at 273.65 K and the conversion was quite similar at 275.15 K.
Rhamnolipids had the same effect on t90 and X(W/H); for instance, t90 was in the same interval as those reported for sodium surfactin, except for the values reported at 2500 ppm of rhamnolipids, which were slightly superior on the order of 152.9 and 158.3 min. As a hypothesis, a great number of sites on the surface were ready to be nucleated, using any surfactant. Finally, rhamnolipids were not capable of promoting methane hydrates at temperatures above 274.15 K. In this case, the concentration was not the dominant effect; instead, the progressive increase in the initial temperature caused the absence of its corresponding driving force, which was necessary for hydrate formation. Sodium dodecyl sulfate induced a promotion effect, as demonstrated for X(W/H) and t90. Aside from the values for both parameters being within the same range of the above biosurfactants at 274.15 and 274.65 K, t90 was slightly reduced at 273.65 K for SDS concentrations of 1500 and 2000 ppm. The water-to-hydrate conversion for SDS was quite similar while the concentration varied at a fixed temperature. This agreed with the experiments reported elsewhere [46,61,62], which confirmed that maximum conversion was achieved in the range of 500–645 ppm of SDS. On the contrary, water-to-hydrate conversion seemed to reach a limit or tended to slightly diminish as the additive concentration was superior; these conditions were above the critical micelle concentration (CMC) of the additive (CMCSDS = 2350 ppm [63], CMCRh = 200 ppm [64], and CMCSs = 3 ppm) at an ambient condition. The abovementioned behavior could be associated with the proceeding of surfactants in an aqueous solution with respect to the CMC. Below the CMC, the hydrophobic end was oriented toward the gas phase, while the hydrophilic end was targeted to the liquid phase; this arrangement reduced the gas–liquid surface tension. Once the solution reached the CMC, agglomerates were formed and acted as nucleation sites. However, the conversion was hindered as the surfactant concentration increased to values quite above the CMC; the solution was becoming saturated with agglomerates, which tended to precipitate. Nevertheless, a deep analysis of gas hydrate conditions on the critical micelle concentration is worth it. The high pressure and low temperature induced a reduction in the CMC; this effect was proven with ethane and SDS. The hydrate conditions led to a reduction in the CMC to values of 242 ppm for SDS [62].
Calculations for the hydrate formation rate were accomplished by means of Equation (4) [65], which depended on time (t) and the mole number of methane (nmethane); the subscripts i − 1 and i + 1 corresponded to the punctual status on the preceding and subsequent parameters.
r = (1/(ti+1 − ti−1)) · ((nmethane,i−1 − nmethane,i+1)/nW)
The maximum methane hydrate formation rate was delimited to ti+1 = t90 to consider a proper average for r, as listed in Table 1. In addition, two representative hydrate rates are shown in Figure 6.
The rise in the concentration of sodium surfactin increased r from the lowest 0.003 to the highest 0.258 mmolCH4/(min·molH2O). Nevertheless, the formation rate for methane did not benefit and seemed to be independent with this bioadditive concentration. In addition, the rates were reduced as the temperature onset was increased, as demonstrated by Zhang et al. [66], above 270 K using 1,3-dioxolane; the variations were intrinsically ascribed to the long time required for t90. The same progression was observed for the other surfactants, being noticeable SDS as the additive with the highest rate of 0.426 mmolCH4/(min·molH2O).
The evolution of the two distinctive peaks observed at the threshold hydrate formation in Figure 6 has been recently reported by Yu et al. [67] for methane hydrates in cyclopentane. Thus, a two-step formation process could be hypothesized, preserving a unique hydrate structure for methane. Both peaks corresponded to the exothermic nature. The earlier was supposed to belong to the formation of the pure additive hydrates in a major proportion, while few vacancy cages were filled by methane. The second step was considered the main segment, where the remaining empty cages were occupied by methane; hence, this step was slower than the first. Consequently, the above assumptions must be scrutinized and validated via direct measurements to understand the formation phenomena, since several changes were immersed, such as the viscosity of the slurry, the available surface area, and the torque for stirring [68].
The impact of sodium surfactin on methane hydrates infers the possibility of implementing applications such as natural gas storage or transportation and the separation of gases, where the main challenges are the long time taken for hydrate formation and low conversion [69]. Methane hydrates were obtained in this work by means of the bioadditive Ss with kinetic activity. The biodegradability and no toxicity or low toxicity for Ss over synthetic surfactants (as SDS) are distinguished from thermodynamic additives or mechanical methods. Sodium surfactin could be dossed in low quantities and the gas-storage capacity would not be obstructed, in contrast with thermodynamic additives [27]; in addition, the energy consumption would be reduced compared with mechanical methods [70].

4. Conclusions

The effect of methane hydrate formation using aqueous concentrations of sodium surfactin was studied for the first time in this research. The isochoric–isothermal method was applied to explore onset temperatures within the range of 273.65–276.15 K under hybrid stirring conditions. Our findings highlight that:
✓
Methane hydrates were not formed using pure water (zero additive concentration); the same behavior was found for the solution at the critical micelle concentration (3 ppm) of sodium surfactin;
✓
Sodium surfactin had a better impact since methane hydrates were still nucleating and growing even at 276.15 K, while SDS and rhamnolipids were not capable;
✓
The period for nucleation was almost negligible for the three surfactants at the lowest temperature (273.65 K);
✓
The advantage of sodium surfactin and rhamnolipids was notorious at high temperatures in the induction time; tind was still very low and did not overcome 10.6 min, in contrast with the long period observed for SDS, which reached 3808.2 min;
✓
The experiments in the growth section demonstrated the good performance of sodium surfactin above 750 ppm, whose ranges for methane uptake (177.2–265.11 mmol), t90 (89.4–200.7 min), and X(W/H) (19.4–24.3%) are on the order of those obtained for SDS and rhamnolipids.
The reduced nucleation period for sodium surfactin is related to energy-saving costs. The promotion capabilities for sodium surfactin in methane hydrate formation, demonstrated in this work, open the opportunity to explore its inherent phenomena under different conditions to deal with further methane-storage applications.

Author Contributions

Conceptualization, O.E.-S. and A.P.-G.; methodology, O.E.-S. and A.P.-G.; software, R.G.-M.; validation, A.Z.-M.; formal analysis, F.J.V.-S.; investigation, O.E.-S. and A.P.-G.; resources, O.E.-S. and A.Z.-M.; data curation, A.P.-G. and R.G.-M.; writing—original draft preparation, O.E.-S. and A.P.-G.; writing—review and editing, A.Z.-M. and F.J.V.-S.; visualization, O.E.-S. and A.P.-G.; supervision, A.Z.-M.; project administration, A.Z.-M.; funding acquisition, O.E.-S. and A.Z.-M. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Mexican institutions, INSTITUTO POLITÉCNICO NACIONAL, project number 20230336 and CONSEJO NACIONAL DE HUMANIDADES, CIENCIAS Y TECNOLOGÍAS, project number A1-S-27000.

Data Availability Statement

The data presented in this study are available in this article.

Acknowledgments

The authors thank the Instituto Politécnico Nacional for the infrastructure and resources that made possible the publication of this work.

Conflicts of Interest

The authors declare no conflict of interest.

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Energies 17 00067 g001
Figure 1. Chemical structure for: (a) monorhamnolipid; (b) dirhamnolipid; (c) surfactin; (d) sodium surfactin.
Figure 1. Chemical structure for: (a) monorhamnolipid; (b) dirhamnolipid; (c) surfactin; (d) sodium surfactin.
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Figure 2. Schematic representation of the three-cell array.
Figure 2. Schematic representation of the three-cell array.
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Figure 3. A typical pressure and temperature evolution for 750 ppm of sodium surfactin at initial conditions of 276.15 K and 50 bar under the isochoric–isothermal method.
Figure 3. A typical pressure and temperature evolution for 750 ppm of sodium surfactin at initial conditions of 276.15 K and 50 bar under the isochoric–isothermal method.
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Figure 4. Induction time for the studied conditions for sodium dodecyl sulfate (SDS), rhamnolipids (Rh) and sodium surfactin (Ss).
Figure 4. Induction time for the studied conditions for sodium dodecyl sulfate (SDS), rhamnolipids (Rh) and sodium surfactin (Ss).
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Figure 5. Gas uptake for additives at 1500 ppm and different temperatures. Ss: sodium surfactin; Rh: rhamnolipids; SDS: sodium dodecyl sulfate.
Figure 5. Gas uptake for additives at 1500 ppm and different temperatures. Ss: sodium surfactin; Rh: rhamnolipids; SDS: sodium dodecyl sulfate.
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Figure 6. Methane hydrate formation rate for 750 ppm of sodium surfactin at different temperatures.
Figure 6. Methane hydrate formation rate for 750 ppm of sodium surfactin at different temperatures.
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Table 1. Methane gas hydrate at an initial pressure of 50 bar (dissociation conditions Pdis = 50 bar Tdis = 279.91 K [51]).
Table 1. Methane gas hydrate at an initial pressure of 50 bar (dissociation conditions Pdis = 50 bar Tdis = 279.91 K [51]).
AdditiveConcentration (ppm)Tonset
(K)		tind
(min)		Gas Uptake (mol)t90
(min)		Water-to-Hydrate Conversion (%)r mmol CH4 (min·mol H2O)
0>273.65 1--------------------
Sodium surfactin3>273.65 1--------------------
150273.651.947.195736.84.30.003
274.157.334.068180.23.10.003
274.65837.858836.23.50.003
275.15 1--------------------
750273.650.5219.78100.220.20.240
274.151221.15108.920.30.236
274.651.2216.84122.719.90.211
275.152.8194.51134.717.80.205
275.652.8196.38200.718.00.112
276.153.2177.927550.516.30.005
276.65 1--------------------
1500273.651238.5189.521.90.256
274.151.5237.6392.721.80.258
274.653.3230.91119.821.20.242
275.154.3220.2122.920.20.236
275.65 1--------------------
2000273.650.9256.193.423.50.253
274.154.7247.90105.922.70.241
274.655.7239.85125.322.00.230
275.156.4211.68173.519.40.183
275.65 1--------------------
2500273.651.9265.1191.824.30.261
274.155.5258.70113.223.70.251
274.658.5235.54138.021.60.215
275.1510.6211.83150.119.40.179
275.65 1--------------------
Rhamnolipids1500273.653272.3196.425.00.322
274.153.8252.5298.323.20.322
274.65 1--------------------
275.15 1--------------------
2000273.654270.77103.324.80.310
274.155.9247.67101.622.70.316
274.65 1--------------------
275.15 1--------------------
2500273.653.1260.26152.923.90.209
274.154.3245.63158.322.50.202
274.65 1--------------------
275.15 1--------------------
SDS1500273.650252.1165.023.10.427
274.153199.2236.4393.021.70.241
274.653808.2224.34123.820.60.235
275.15 1--------------------
2000273.650248.5574.222.80.426
274.152303.3235.8583.521.90.393
274.652973.2223.96118.120.60.246
275.15 1--------------------
2500273.650243.6098.523.10.253
274.152071.5229.91135.121.10.217
274.652809.9219.24155.020.10.183
275.15 1--------------------
1 No hydrate formation was experienced for the 7-day trial.
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Pavón-García, A.; Zúñiga-Moreno, A.; García-Morales, R.; Verónico-Sánchez, F.J.; Elizalde-Solis, O. Evaluation of Temperature on the Methane Hydrates Formation Process Using Sodium Surfactin and Rhamnolipids. Energies 2024, 17, 67. https://doi.org/10.3390/en17010067

AMA Style

Pavón-García A, Zúñiga-Moreno A, García-Morales R, Verónico-Sánchez FJ, Elizalde-Solis O. Evaluation of Temperature on the Methane Hydrates Formation Process Using Sodium Surfactin and Rhamnolipids. Energies. 2024; 17(1):67. https://doi.org/10.3390/en17010067

Chicago/Turabian Style

Pavón-García, Antonio, Abel Zúñiga-Moreno, Ricardo García-Morales, Francisco Javier Verónico-Sánchez, and Octavio Elizalde-Solis. 2024. "Evaluation of Temperature on the Methane Hydrates Formation Process Using Sodium Surfactin and Rhamnolipids" Energies 17, no. 1: 67. https://doi.org/10.3390/en17010067

APA Style

Pavón-García, A., Zúñiga-Moreno, A., García-Morales, R., Verónico-Sánchez, F. J., & Elizalde-Solis, O. (2024). Evaluation of Temperature on the Methane Hydrates Formation Process Using Sodium Surfactin and Rhamnolipids. Energies, 17(1), 67. https://doi.org/10.3390/en17010067

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