Enhanced aqueous solubility of polycyclic aromatic hydrocarbons by green diester-linked cationic gemini surfactants and their binary solutions

The Total Solubility of the Co-Solubilized PAHs with Similar Structures Indicated by NMR Chemical Shift

The synergism/inhibition level, solubilization sites and the total solubility (S_t) of co-solubilization systems of phenanthrene, anthracene and pyrene in Tween 80 and sodium dodecyl sulfate (SDS) are studied by ¹H-NMR, 2D nuclear overhauser effect spectroscopy (NOESY) and rotating frame overhauser effect spectroscopy (ROESY). In Tween 80, inhibition for phenanthrene, anthracene and pyrene is observed in most binary and ternary systems. However, in SDS, synergism is predominant. After analysis, we find that the different synergism or inhibition situation between Tween 80 and SDS is related to the different types of surfactants used and the resulting different co-solubilization mechanisms. In addition, we also find that three polycyclic aromatic hydrocarbons (PAHs) have similar solubilization sites in both Tween 80 and SDS, which are almost unchanged in co-solubilization systems. Due to the similar solubilization sites, the chemical shift changes of surfactant and PAH protons follow the same pattern in all solubilization systems, and the order of chemical shift changes is consistent with the order of changes in the St of PAHs. In this case, it is feasible to evaluate S_t of PAHs by chemical shift. In both Tween 80 and SDS solutions, the ternary solubilization system has relatively high S_t rankings. Therefore, in practical applications, a good overall solubilization effect can be expected.

Synthesis of Novel Ethoxylated Quaternary Ammonium Gemini Surfactants for Enhanced Oil Recovery Application

Two aspects are always considered in the design and development of new surfactants for oilfield application. One of them is that surfactant must be sufficiently stable at reservoir temperature and the other is the solubility of the surfactant in the injection water (usually seawater) and the formation brine. Most industrially applied surfactants undergo hydrolysis at elevated temperature and the presence of reservoir ions causes surfactant precipitation. In relevance to this, a novel series of quaternary ammonium gemini surfactants with different length of spacer group (C8, C10, and C12) was synthesized and characterized using FT-IR, 13C NMR, 1H NMR, and MALDI-TOF MS. The gemini surfactants were prepared by solvent-free amidation of glycolic acid ethoxylate lauryl ether with 3-(dimethylamino)-1-propylamine followed by reaction with dibromoalkane to obtain quaternary ammonium gemini surfactants. The gemini surfactants were examined by means of surface properties and thermal stabilities. The synthesized gemini surfactants showed excellent solubility in the formation brine, seawater, and deionized water without any precipitation for up to three months at 90 °C. Thermal gravimetric data revealed that all the gemini surfactants were decomposed above 227 °C, which is higher than the oilfield temperature (≥90 °C). The decrease in critical micelle concentration (CMC) and surface tension at CMC (γcmc) was detected by enhancing spacer length in the order C8 ˃ C10 ˃ C12 which suggested that the larger the spacer, the better the surface properties. Moreover, a further decrease in CMC and γcmc was noticed by enhancing temperature (30 °C ˃ 60 °C) and salinity (deionized water ˃ seawater). The current study provides a comprehensive investigation of quaternary ammonium gemini surfactants that can be further extended potentially to use as a suitable material for oilfield application.

Solubility Enhancement of Polycyclic Aromatic Hydrocarbons by an Eco-Friendly Ester-Linked Gemini Surfactant and its Mixtures with Conventional Surfactants

The present study deals with the solubility enhancement of the two polycyclic aromatic hydrocarbons (PAHs) anthracene and pyrene in the aqueous micellar system of the cationic ester-containing cleavable gemini surfactant ethane-1,2-diyl-bis(N,N-dimethyl-N-tetradecylammoniumacetoxy) dichloride (14-E2-14 = C14H29(CH3)2N+(CH2COOCH2)2N+(CH3)2C14H29 · 2Cl−)), and its equimolar binary mixtures with some typical conventional cationic, anionic and non-ionic surfactants. The surface tension and conductivity measurements were used to evaluate the physicochemical parameters such as the critical micelle concentration (CMC), the interaction parameter (βm) and Gibbs excess free energy of micellization (ΔGexm) of the systems. The extent of solubilization of the micellar systems towards PAHs has been quantified in terms of molar solublization ratio (MSR), micellar/water partition coefficient (ln Km) and the standard Gibbs free energy of solubilization (ΔGs0). Above the CMC, all studied single as well as binary gemini-conventional surfactant systems show an increase in solubilization of the PAHs. For pure systems, the MSR value of Brij 58 was found to be significantly higher than that of the other amphiphiles. Amongst the mixed surfactant systems, the solubility enhancement of anthracene is found to be maximum in the 14-E2-14 + SDS/SDBS system whereas the system14-E2-14 + Brij 58 shows a higher solubility for pyrene.

Surfactant-enhanced remediation of polycyclic aromatic hydrocarbons: A review

Polycyclic aromatic hydrocarbons (PAHs) are toxic, mutagenic and carcinogenic organic compounds that are widely present in the environment. The bioremediation of PAHs is an economical and environmentally friendly remediation technique, but it is limited because PAHs have low water solubility and fewer bioavailable properties. The solubility and bioavailability of PAHs can be increased by using surfactants to reduce surface tension and interfacial tension; this method is called surfactant-enhanced remediation (SER). The SER of PAHs is influenced by many factors such as the type and concentration of surfactants, PAH hydrophobicity, temperature, pH, salinity, dissolved organic matter and microbial community. Furthermore, as mixed micelles have a synergistic effect on PAH solubilisation, selecting the optimum ratio of mixed surfactants leads to effective PAH remediation. Although the use of surfactants inhibits microbial activities in some cases, this could be avoided by choosing an optimum combination of surfactants and a proper microbial community for the targeted PAH(s), resulting in up to 99.99% PAH removal. This article reviews the literature on SER of PAHs, including surfactant types, the synergistic effect of mixed micelles on PAH removal, the impact of surfactants on the PAH biodegradation process, factors affecting the SER process, and the mechanisms of surfactant-enhanced solubilisation of PAHs.

Metabolical shifts towards alternative BTEX biodegradation intermediates induced by perfluorinated compounds in firefighting foams

The type and concentration of perfluorinated compounds (PFCs) can induce different types of enzymes and promote alternate patterns of BTEX transformation. However, it is not known how the presence of active fluorocarbon-degrading microbial populations affects the transformation of BTEX. In addition to chemical analysis at the molecular level, our research approached the aqueous film forming fire-fighting foams (AFFF) and BTEX co-contamination at a large-scale with respirometers to quantify the total microbial metabolism of soil via CO₂ output levels. The intended outcome of this research was to obtain and characterize shifts in BTEX degradation at a set realistic environmental condition while measuring byproducts and CO₂ production. Both methodologies complimentarily provided an in-depth knowledge of the environmental behavior of fire-fighting foams. The biodegradation was monitored using headspace sampling and two types of gas chromatography: thermal conductivity detector and flame ionization detector. Headspace samples were periodically withdrawn for BTEX biodegradation and CO₂ production analysis. Our research suggests the discovery of an altered metabolic pathway in aromatic hydrocarbons biodegradation that is directly affected by fluorinated substances. The fluorinated compounds affected the BTEX biodegradation kinetics, as PFCs may contribute to a shift in styrene and catechol concentrations in co-contamination scenarios. A faster production of styrene and catechol was detected. Catechol is also rapidly consumed, thus undergoing further metabolic stages earlier under the presence of PFCs. The release of AFFF compounds not only changes byproducts output but also drastically disturbs the soil microbiota according to the highly variable CO₂ yields. Therefore, we observed a high sensitivity of microbial consortia due to PFCs in the AFFF formulation, therefore shifting their BTEX degradation routes in terms of intermediate products concentration.