Cyclic Naphthenic Acids Research Articles

The cooperative effect between cyclic naphthenic acids and surfactant enhances the separation efficiency

• Naphthenic Acids (NAs) are self-organized at oil–water interfaces, and the distribution coefficient was determined; • The presence of rings in the NA structures helps to stabilize the interaction with hydrocarbons, especially with toluene; • CPC micelle carry the NAs both by absorption and adsorption on the micelle surface; • The CPC micelle grows up and does not lose stability when carrying the NAs; • A cooperative effect between cyclic NAs and surfactants allows the micelle to carry a larger amount of aliphatic NA. Naphthenic Acids (NAs) are responsible for corrosion, produced water pollution, and are toxic to marine life. Therefore, more efficient NAs extraction techniques, such Micellar-Enhanced Ultrafiltration (MEUF), have been developed. In this work, Molecular Dynamics simulations were employed to deepen the comprehension of the behavior and properties of NA in interfacial systems and micellar systems. The calculated distribution coefficient (log D) in different water/oil interfaces demonstrated the greater affinity between NA and cyclic structures, showing a more negative free energy in the systems with toluene. Furthermore, simulations with different NAs and surfactant showed that micelle is effective in NAs carriage by two different interaction conformations, both by intercalation and adsorption of NAs on micelle surfaces, guiding to a micelle increase of about 5%. Radial distribution, hydrogen-bond, and non-bonded analysis indicated that NAs affect interactions between surfactant molecules' by diminishing the Lennard-Jones contribution. Moreover, the incorporated alicyclic molecules are responsible for facilitating the absorption of more NAs by the micelle. So, to enhance NAs separation from oil or produced water, cyclic molecular systems may be employed.

Co-biodegradation of naphthenic acids in anoxic denitrifying biofilm reactors

ABSTRACT Anoxic co-biodegradation of linear and cyclic naphthenic acids (NAs) namely octanoic acid, trans-4-methyl-1-cyclohexane carboxylic acid (trans-4MCHCA), cis- and trans-4-methyl-1-cyclohexane-acetic acids (cis-4MCHAA and trans-4MCHAA) was investigated in denitrifying biofilm reactors. In all evaluated compositions, co-biodegradation of NAs was coupled to denitrification, with octanoic acid showing the fastest biodegradation rate (1180.4 mg L−1 h−1 at loading rate of 1180.4 mg L−1 h−1), followed by trans-4MCHCA (398.1 mg L−1 h−1 at loading rate of 435.8 mg L−1 h−1), trans-4MCHAA (25.7 mg L−1 h−1 at loading rate of 221.7 mg L−1 h−1), and cis-4MCHAA (5.3 mg L−1 h−1 at loading rate of 16.9 mg L−1 h−1). Biodegradation of octanoic acid and trans-4MCHCA were not influenced by the presence of recalcitrant NAs (cis- and trans-4MCHAA). Co-biodegradation of cis- and trans-4MCHAA with octanoic acid, trans-4MCHCA, or their combination enhanced the biodegradability of these recalcitrant NAs, with the positive impact being more pronounced for trans-4MCHCA. Finally anoxic co-biodegradation of NAs under denitrifying conditions proceeded at rates that were faster than the aerobic rates obtained in similar mixtures. Anoxic biodegradation, therefore, is an effective alternative for in situ treatment of oil sands process water in anoxic stabilization ponds amended with nitrate, or as an ex situ treatment approach in denitrifying bioreactors whereby the cost and technical challenges of aeration are eliminated.

Biodegradation of surrogate naphthenic acids and electricity generation in microbial fuel cells: bioelectrochemical and microbial characterizations.

Waters contaminated with naphthenic acids (NAs) and associated tailings are one of the major environmental challenges associated with the processing of oil sands and production of heavy oil. In the current work biodegradation of linear and cyclic naphthenic acids, namely octanoic acid and 4-methyl-1-cyclohexane carboxylic acid (trans-4MCHCA), individually and in mixture were evaluated in microbial fuel cells (MFCs). In batch MFCs with single rod electrodes and freely suspended bacteria, biodegradation rate increased as NA initial concentration increased from 100 to 250mg L-1 with no further improvement when a concentration of 500mg L-1 was evaluated. During the co-biodegradation, diauxic microbial growth and preferential use of octanoic acid were observed. Moreover, the presence of octanoic acid enhanced the biodegradation of trans-4MCHCA. In the continuous flow MFCs with granular graphite electrodes and biofilm, increases in NA concentration and loading rate led to higher biodegradation rates and improvement of electrochemical output. Furthermore, MFC operated with octanoic acid outperformed its counterpart that was fed with trans-4MCHCA, with the maximum biodegradation rate, current and power densities for octanoic acid and trans-4MCHCA being 49.9 and 36.5mg L-1 h-1, 6000.0 and 4296.3mA m-3, and 963.0 and 481.5mW m-3, respectively. Co-biodegradation of NAs in continuous flow MFCs with biofilm acclimated to octanoic acid or trans-4MCHCA revealed development of distinctly different microbial communities, simultaneous biodegradation of NAs albeit at faster rates for octanoic acid, and superior performance of MFC with the biofilm developed with trans-4MCHCA.

Solar photocatalytic degradation of naphthenic acids in oil sands process-affected water.

Bitumen mining in the Canadian oil sands creates large volumes of oil sands process-affected water (OSPW), the toxicity of which is due in part to naphthenic acids (NAs) and other acid extractable organics (AEO). The objective of this work was to evaluate the potential of solar photocatalysis over TiO2 to remove AEO from OSPW. One day of photocatalytic treatment under natural sunlight (25 MJ/m(2) over ∼14 h daylight) eradicated AEO from raw OSPW, and acute toxicity of the OSPW toward Vibrio fischeri was eliminated. Nearly complete mineralization of organic carbon was achieved within 1-7 day equivalents of sunlight exposure, and degradation was shown to proceed through a superoxide-mediated oxidation pathway. High resolution mass spectrometry (HRMS) analysis of oxidized intermediate compounds indicated preferential degradation of the heavier and more cyclic NAs (higher number of double bond equivalents), which are the most environmentally persistent fractions. The photocatalyst was shown to be recyclable for multiple uses, and thus solar photocatalysis may be a promising "green" advanced oxidation process (AOP) for OSPW treatment.

Genotoxic potential of several naphthenic acids and a synthetic oil sands process-affected water in rainbow trout (Oncorhynchus mykiss)

The exploitation of oil sands has raised major environmental concerns, particularly regarding the presence of high concentration in contaminants such as polycyclic aromatic hydrocarbons (PAHs) and naphthenic acids (NAs) in oil sands process-affected water (OSPW). The purpose of this study was, first to evaluate the genotoxic impact of OSPW-related compounds such as NAs and PAHs in a salmonid species and secondly to assess if OSPW exposure leads to genotoxicity. For this purpose, rainbow trout hepatocytes were exposed in vitro to environmentally relevant concentrations of synthetic NAs, naphtalene, benzo(a)pyrene, and extracts of synthetic OSPW (generated by a laboratory bitumen extraction) and of oil sands leaching water (OSLW, mimicking leaching of oil sands in river water). Primary DNA damage was assessed by the formamidopyrimidine-DNA glycolyase (Fpg)-modified comet assay. Genotoxicity was observed in hepatocytes exposed to several NAs, mixture of them, OSPW and OSLW extracts. The chemical structure of NAs influences the genotoxicity potential: among the NAs tested, the most cyclic NA was the most genotoxic. It also appears that genotoxicity was more marked for OSPW than for OSLW. Because exposure to OSPW led to oxidative DNA damage, while after exposure to several NAs, these types of DNA damage were limited, the NAs tested in this study could not be qualified as the only major contaminants responsible for OSPW genotoxicity. Notwithstanding, it should be noteworthy that exposure to NAs resulted in genotoxic impact at concentrations lower than those documented by literature for fresh OSPW. Further research is needed to explore the relationships between the chemical structure of NAs and their genotoxicity in the light of the distribution of NAs in fresh OSPW samples as well as in surface waters.

Continuous Co‐biodegradation of linear and cyclic naphthenic acids in circulating packed‐bed bioreactors

Continuous co‐biodegradation of a linear and three cyclic surrogate naphthenic acids namely octanoic acid, trans‐4‐methyl‐1‐cyclohexane carboxylic acid (trans‐4MCHCA), and cis‐ and trans‐4‐methyl‐1‐cyclohexane‐acetic acids (cis‐4MCHAA and trans‐4MCHAA) at concentrations of 100, 50, and 50 mg/L, respectively, was investigated in two circulating packed‐bed bioreactors. Using different combinations of naphthenic acids in the bioreactor influent effects of loading rate on biodegradation of each compound was evaluated. In all tested mixtures biodegradation of octanoic acid proceeded with the fastest rate, followed by trans‐4MCHCA, trans‐4MCHAA, and cis‐4MCHAA. Biodegradation of the linear compound (octanoic acid) was not influenced by the presence of any cyclic compound, even the most recalcitrant naphthenic acid with the highest removal rate of 372.8 mg/L‐h observed at a loading rate of 666.7 mg/L‐h. Presence of octanoic acid negatively impacted the biodegradation of trans‐4MCHCA, with the removal rates of trans‐4MCHCA in the presence and absence of octanoic acid being 74.6 and 208.8 mg/L‐h, respectively. With cis‐ and tran‐4MCHAA, presence of octanoic acid improved the biodegradation of these compounds. In a mixture containing all three cyclic compounds, the maximum removal rates for cis‐ and trans‐4MCHAA were 0.5 and 1.3 mg/L‐h, respectively, which improved to 1.7 and 2.4 mg/L‐h when octanoic acid was included in the mixture. © 2013 American Institute of Chemical Engineers Environ Prog, 33: 835–843, 2014

Effect of Molecular Structure on the Relative Reactivity of Naphthenic Acids in the UV/H2O2 Advanced Oxidation Process

The large volume of oil sands process-affected water (OSPW) produced by the oil sands industry in Northern Alberta, Canada, is an environmental concern. The toxicity of OSPW has been attributed to a complex mixture of naturally occurring acids, including naphthenic acids (NAs). Highly cyclic or branched NAs are highly biopersistent in tailings ponds, thus understanding structure-reactivity relationship for NAs is very important for OSPW reclamation. In this study, we hypothesized that large, branched and cyclic NAs may be better oxidized in the UV/H(2)O(2) process than small, linear and acyclic NAs. Relative rate measurements using binary mixtures of model NA compounds confirmed that reactivity favored compounds with more carbons, and also favored NAs with one saturated ring, relative to the corresponding linear NA. However, for model compound with three rings, no increased reactivity was observed relative to monocyclic NA. UV/H(2)O(2) treatment of OSPW confirmed our findings with model compounds, indicating that the compounds with more carbons are favored for degradation. However, increasing the number of rings (or double bond equivalents) in OSPW NAs did not show any clear structure-reactivity. Microbial degradation studies of the UV/H(2)O(2) treated OSPW should be conducted to examine the overall benefit of this treatment for the real applications.

Use of a (Quantitative) Structure–Activity Relationship [(Q)Sar] Model to Predict the Toxicity of Naphthenic Acids

Naphthenic acids (NA) are a complex mixture of carboxylic acids that are natural constituents of oil sand found in north-eastern Alberta, Canada. NA are released and concentrated in the alkaline water used in the extraction of bitumen from oil sand sediment. NA have been identified as the principal toxic components of oil sands process-affected water (OSPW), and microbial degradation of lower molecular weight (MW) NA decreases the toxicity of NA mixtures in OSPW. Analysis by proton nuclear magnetic resonance spectroscopy indicated that larger, more cyclic NA contain greater carboxylic acid content, thereby decreasing their hydrophobicity and acute toxicity in comparison to lower MW NA. The relationship between the acute toxicity of NA and hydrophobicity suggests that narcosis is the probable mode of acute toxic action. The applicability of a (quantitative) structure–activity relationship [(Q)SAR] model to accurately predict the toxicity of NA-like surrogates was investigated. The U.S. Environmental Protection Agency (EPA) ECOSAR model predicted the toxicity of NA-like surrogates with acceptable accuracy in comparison to observed toxicity values from Vibrio fischeri and Daphnia magna assays, indicating that the model has potential to serve as a prioritization tool for identifying NA structures likely to produce an increased toxicity. Investigating NA of equal MW, the ECOSAR model predicted increased toxic potency for NA containing fewer carbon rings. Furthermore, NA structures with a linear grouping of carbon rings had a greater predicted toxic potency than structures containing carbon rings in a clustered grouping.