Experimental and computational approaches of sustainable quaternary bisammonium fluorosurfactants for corrosion inhibition as protective films at mild steel/H₂SO₄ interface

Highlights

• Three novel quaternary bisammonium fluorosurfactants were designed and synthesized.

• PDP plots confirmed that the prepared fluorosurfactants are mixed-type inhibitors.

• Surface topology investigations indicated that the synthesized fluorocarbon surfactants impeded mild steel corrosion.

• DFT calculations and MD simulations were performed to confirm the experimental results.

Abstract

Three novel quaternary bisammonium fluorosurfactants (FGS-4, FGS-6, and FGS-8) were designed and synthesized using furan-2,5-diylbis(methylene) bis(2-bromoacetate) with N-(3-(dimethylamino)propyl)-1,1,2,2,3,3,4,4,4-nonafluoroalkan-1-sulfonamide through a heterocyclic spacer of 3,3′-((furan-2,5-diylbis(methylene))bis(oxy))bis(3-oxopropan-1-ylium) to connect two fluorocarbon tails. Their corrosion protection characteristics of mild steel/1.0 M H₂SO₄ solution interface at different temperatures were inspected by electrochemical (PDP and EIS) and weight loss measurements. The PDP plots established that the three-quaternary bisammonium fluorosurfactants are mixed-type inhibitors; EIS experiments exhibited that the as-prepared surfactants possess the superior protection capacities of 93.5 % (FGS-4), 95.5 % (FGS-6), and 96.6 % (FGS-8) at the optimum dose of 2.00 mmol L⁻¹. The Adsorption considerations showed that the three additives demonstrated both the physisorption and chemisorption mechanisms and followed the Langmuir model. Surface morphology investigations indicated that the synthesized fluorocarbon surfactants impeded mild steel corrosion. The relationships between the protection performance of the fluorocarbon surfactants, their molecular configurations, and the adsorption mode were checked by DFT calculations and MD simulations, which confirmed that FGS-8 has a higher protection power than FGS-4 and FGS-6. The current investigation exhibited that quaternary bisammonium fluorosurfactants could be used as eco-friendly, economic, and efficient inhibitors for mild steel corrosion with the probable for extensive applications.

Introduction

In petroleum manufacturing, steel alloys are usually employed in pipelines, casings, tubes, and in the stockpiling structure and other facilities. Nevertheless, the apparatus surface in oil manufacture frequently faces scaling and corrosion issues owing to variations in the temperature, pressure, and installation [1,2]. Particularly, for the energizing procedure, acidic solutions such as HCl and H₂SO₄ are generally inserted into the line pipe to dissolve the rock formation at high temperatures to increase the eliminate scale and movement pathway [3,4]. When immersed in aggressive acids, tubing and other metallic constructions are extremely deteriorate concerning constituent integrity, leakage, and line pipe rupture, which significantly influence the efficacy of oil manufacture and bring other hazards for the manufacturing. Furthermore, failure or corrosion might need maintenance or replacement of the apparatus and so could result in economic, loss closure, and shutdown time. A cost-effective and applied method to prevent or inhibit the corrosion in acidic solutions is the use of corrosion additives (inhibitors) due to their low-price, easy operation, and high-efficiency [[5], [6], [7], [8], [9], [10]].

Surfactants science has been attracted the attention of researchers from all over the world because of the large extent of their application fields such as petroleum oil recovery, corrosion inhibitor, drug, detergent, demulsifier, etc. Additionally, the more significant auxiliary role for surfactants in catalysis and nanotechnology sciences [[11], [12], [13], [14]]. Polyfluorinated compounds (PFCs) are exceptional anthropogenic compounds that possessed incorporated into a range of important products throughout the past six decades. The fluorocarbon chains have both oleophobic and hydrophobic, which endows fluorosurfactants with huge potentials in different fields compared to commonly used surfactants [15]. Fluorinated surfactants possessed much interest since very low values of critical micellar concentration have been assessed and have a high effect than hydrogenated surfactants since their lower surface tensions are noted [16,17]. Moreover, Fluorinated surfactants containing perfluorohexylsulfonyl (C₆F₁₃SO₂-) and perfluorooctylsulfonyl (C₈F₁₇SO₂-) groups showed a poor insecticidal activity (low toxicity) against Culex pipiens compared to piperine as a natural product [18]. They possessed more than 200 applications [[16], [17], [18], [19]] including plane hydraulic fluids, coatings, soil and stain-repellents, paints, firefighting foams for clothing fabrics, carpets, paper coatings, leather, photographic emulsifiers, electroplating, polishes, waxes, insecticides, pharmaceuticals, etc. Additionally, the physico-chemical indices of per- and poly-fluoroalkyl materials have completed them considered chemicals in various high-tech and industrial implementations, and in miscellaneous yields such as cookware, oil-resistant garments, water, food packaging, and aqueous layer-forming foams (AFFFs) [20]. Polyfluoroalkyl surface active agents are major constituents of AFFF formulations due to their greater heat resistance and unparalleled surface characteristics, promoting the development of a tinny surface layer at the fuel-foam interface that is impenetrable to fickle fuel vapors and divests the oxygen fire, thus prohibiting re-ignition and so they usually used at manufacturing plants, oil refineries, airports, firefighting departments, and military amenities to resist the hydrocarbon-fueled fires [21].

In some previously reported studies, metal surface adsorptive functionalities have been used as polar head groups of fluorinated surfactants, enabling the making of protective films on the electrode interface, thus providing the role of anti-corrosion to the metal surface. Because of these advantages, until now, fluorinated surfactants were widely examined. For instance, Guo et al. [22] prepared hybrid sulfated ester surfactants via a methine linker to bond hydrocarbon and fluorocarbon tails, which accomplished a strong ability to lower the surface tension and a good affinity with both hydrocarbon and water liquids [23]. A series of nonionic, anionic, and cationic surfactants that bonded the hydrocarbon fluorocarbon tails with rigid benzyl or phenyl as suitable linkers, exhibiting their more interface-active indices and hydrolytic stabilities have been reported by Yoshino et al. [24]. Miyazawa et al. utilized ethylidene to bond hydrocarbon and fluorocarbon chains, then after sulfonation, the fluorinated surfactants showed some greats indices, such as thermal responsiveness and the micelle formation [25]. Moreover, the triazole ring was utilized as a linker for preparing a fluorinated surfactant library, which may be a benefit in drug delivery and self-assembly [26]. Interestingly, Maimaiti et al. described a series of fluorinated cationic surfactants using perfluorobutylsulfonyl and perfluorohexylsulfonyl chains that were employed as promising metal corrosion inhibitors [27].

Thus, in this study, three newly cationic Gemini surfactants (FGS-4, FGS-6, and FGS-8) were designed and smoothly synthesized. The elucidation of the as-prepared surfactant structures was carried out via various spectroscopic tools. The corrosion mitigation features of the 3 FGS for mild steel (MS) in molar H₂SO₄ solution were investigated by electrochemical tools (PDP and EIS), contact-angle method, and weight-loss measurements. The elemental configurations and topological features of the adsorption layer at the interface of MS/H₂SO₄ solution were inspected by EDX and FE-SEM, respectively. DFT calculations and MD simulations were completed to examine their comparative corrosion mitigation routine from a theoretical viewpoint. Our pains will be favorable to enhanced understand of the alkyl chain effect and deliver novel possible considerations for the preparation of applied cationic Gemini surfactants- type inhibitors for MS in pickling solutions.