• Energy Research

Abstract The continuously increasing demand for natural gas as an available and clean energy source indicates an inevitable transition to develop more promising technologies such as solidified natural gas (SNG) storage. Herein, we present a comprehensive experimental and computational study of the utilization of sunflower oil as a renewable biomass source to design highly efficient promoters based on the properties of sodium dodecyl sulfate (SDS) for methane hydrate formation. The effect of sunflower oil-based promoters (SFOPs) on methane hydrate kinetics was investigated theoretically via molecular dynamics (MD) simulation and experimentally under both dynamic (stirred reactor) and static (in the presence of porous media) conditions. SFOP1 considerably reduced induction time and overall time of the hydrate formation process compared to SDS under both conditions. In addition, SFOP1 significantly enhanced the kinetic constant of hydrate formation by 13.5 times, 3.7 times, and 2.5 times compared to pure water, SFOP2, and SDS systems, respectively, (in dynamic conditions). Moreover, both SFOPs improved the number of moles of gas consumed up to 450 mM in dynamic and 200 mM in static conditions compared to the pure water test. In contrast to the SDS solution, no foam formation was observed in the solution containing SFOPs. The MD results revealed that the SFOPs increased the transfer of methane molecules to the growing hydrate surface, which lead to enhance the kinetics of methane hydrate formation. Besides, more hydrate was formed by the addition of SFOP1 because of the improvement in the hydrogen bonds between water-water molecules in comparison with SFOP2. These findings clearly confirm that sunflower oil can be used for the development of green and more efficient promoters than SDS for methane hydrate formation without foam generation during the process.

The feasibility study of utilizing sunflower oil as renewable biomass source to develop highly effective inhibitors for mild steel corrosion (MS) in the 15% HCl medium was done by weight loss, potentiodynamic polarization (PDP), dynamic electrochemical impedance spectroscopy (DEIS), and electrochemical impedance spectroscopy (EIS), supported with energy-dispersive X-ray (EDX), atomic force microscopy (AFM), and field-emission scanning electron microscope (FESEM) techniques. Moreover, a complementary theoretical investigation was carried out to clarify the inhibition mechanism of inhibitors by density functional theory (DFT), density functional based tight-binding (DFTB), and molecular dynamics (MD) simulation approaches. The obtained results confirm that sunflower-oil-based corrosion inhibitor (SFOCI) has a significant anticorrosion property toward the dissolution of MS in 15% HCl solution in the temperature range 20-80 °C. In addition, the results show that SFOCI could provide an inhibition efficiency of 98 and 93% at 60 and 80 °C, respectively. The inhibition mechanism of SFOCIs was mixed-type and their adsorption on the surface of MS was mainly chemisorption. The FESEM and EDX studies proved the presence of SFOCI molecules on the surface of MS. In addition, the adsorption energy of SFOCI indicated an intense interaction between the inhibitor and surface of Fe. The results of this study could open a new window for the design and development of scalable and effective eco-friendly vegetable-oil-based corrosion inhibitors for highly corrosive solutions at high temperatures.

AbstractHeavy oil and vacuum residue were used to obtain road bitumen BND 50/70 using two different methods of steam distillation at 323–362 °C and by oxidation, a method using packed column at temperature of 211–220 °C. The obtained residues using two methods steam distillation and oxidation are known as non-oxidized bitumen and oxidized bitumen, respectively. The products were evaluated using different standards including GOST 33133-2014, GOST 22245-90, and ASTM D5. The results showed that the yield of oxidized bitumen reached a maximal rate of 89.59% wt., while that of non-oxidized bitumen is 55% wt. The softening point of oxidized bitumen is 49–57 °C compared to non-oxidized bitumen (46–49 °C). Remarkably, the previous softening point and penetrability of 47–71 points of oxidized bitumen are consistent with norms to BND 50/70 bitumen, according standard. The non-oxidized bitumen has a relatively low softening point and a higher penetration value of 71–275, which refers to BND 200/300 bitumen. Comparatively, the use of a packed column is beneficial than the steam distillation, due to high capability of the nozzles to strengthens contact between feedstock and compressed air in the reaction zone and decreases the reaction time to 4.15 h.

Compatibility problems are observed during the co-injection of corrosion and gas hydrate inhibitors inside oil and gas pipelines, which reduces their performance. In this study, the newly synthesized dual-purpose inhibitors (DPIs) were developed to overcome the compatibility challenge between the inhibitors. A detailed experimental and computational study was performed to investigate the inhibition activity of DPIs. The results of constant cooling experiments showed that the inhibitors significantly prevented natural gas hydrate formation. DPI2 with a propyl pendant group was the best sample by providing a subcooling temperature of 18.1 °C at 5000 ppm. DPI1 and DPI3 decreased gas consumption by 2.6 and 2.4 times, respectively, compared to pure water. In addition, molecular dynamics simulation revealed that the transportation of gas molecules to the growing hydrate cages was disrupted due to DPI2 adsorption on the surface of the hydrate, which partially covered it and acted as a mass transfer barrier. Furthermore, the interaction of the anion part of the inhibitor with the nearest neighbor water molecules lowered the water activity to form the hydrogen-bonding networks for the hydrate formation. According to corrosion measurements, DPIs suppressed the corrosion rate of mild steel in H2S–CO2 saturated oilfield-produced water, and a maximum inhibition efficiency of 96.3% was obtained by adding 1000 ppm of DPI2. Moreover, the estimated adsorption energy of DPI2 were relatively high and matched with experimental data, implying that the inhibitor has a high degree of adsorption on the metal for forming a protective layer on the mild steel surface. These findings signified that DPIs provide a potential hybrid inhibition of corrosion and gas hydrate formation for flow assurance applications and reduce the operation costs.

Surfactants have been reported as the most efficient gas hydrate promoters (GHPs) for gas storage and transportation; however, slow kinetics of nucleation and growth of hydrate crystals and foam formation during hydrate dissociation severely impact their applications. Here, a new class of chemical additives based on ethylenediaminetetraacetic acid bisamides was developed to control methane hydrate formation for gas storage and flow assurance applications. Synthesized molecules contain both polar fragments (carboxyl and amide groups) and hydrophobic alkyl groups with different sizes and branching. The obtained results revealed that bisamides with short alkyl chains ( n -propyl and isopropyl) promoted the formation of methane hydrate and significantly reduced foam stability during hydrate decomposition compared to sodium dodecyl sulfate (SDS). Moreover, by increasing the length of the alkyl substituent up to propyl, the nucleation time increased. However, the conversion of gas to hydrate escalated remarkably. A transition from promotion to inhibition properties is observed with a further increase in the alkyl chain from propyl to butyl. Nevertheless, bisamides with hexyl groups showed surfactant properties, which is responsible for their poor promotion efficiency. In addition, the studied compounds practically do not form foam and are less toxic compared to SDS as a well-known GHP. The results of this study can be useful for the design and development of effective additives for gas storage and flow assurance applications.

Although anionic surfactants are considered the most efficient kinetic gas hydrate promoters for gas storage applications, gas recovery and reuse of surfactants are difficult due to high foam formation during hydrate melting. Additionally, most anionic surfactants are toxic, which has an intense environmental effect. In this study, novel amino acid derivatives (ACDs) were developed as the first class of superior promoters compared to surfactants without foaming during the formation and recovery of gas hydrates. The results of high-pressure autoclave experiments indicated that all ACDs significantly enhanced the kinetics of methane hydrate formation at 500 ppm. ACD5 derived from leucine showed the best promotion effect in distilled water by providing a total mole consumption of 436.1 mmol. ACD5 increased the degree of water-to-hydrate conversion from 39.6% in pure water to 94.3%, which was higher than in sodium dodecyl sulfate (SDS) solution (87.8%). Moreover, differential scanning calorimetry experiments demonstrated that ACDs could form methane hydrates at relatively lower temperatures than pure water. They increased the onset temperature of methane hydrate formation from −15 °C in pure water to −12 °C at 500 ppm. A higher promotion activity than SDS was also observed for ACDs in salt water, suggesting that seawater can be used to produce methane hydrate instead of pure water to reduce gas storage costs. Besides, visual observations revealed that no foam was formed during melting hydrates and releasing methane in the presence of ACDs. These findings show that a slight modification of amino acids makes them efficient candidates for improving gas hydrate formation for seawater desalination and gas storage applications.