Analysis of corrosion scales formed on steel at high temperatures in hydrocarbons containing model naphthenic acids and sulfur compounds

Corrosive naphthenic acids and sulfur compounds in crude oils present a major challenge for refineries from a corrosion perspective. Although it is accepted that some sulfur compounds may form protective FeS scales on the metal surface and deter corrosion, attempting to correlate the characteristics of FeS scale with its protective properties has not been successful. Given the complex chemical compositions of real crudes, model sulfur compound and model naphthenic acids were used to mimic the corrosion by crude fractions in the present study. The iron sulfide scale formed by the model sulfur/acid compounds was challenged by naphthenic acids under high‐velocity conditions to examine its protectiveness against corrosion. Moreover, the scale was analyzed with transmission electron microscope/energy dispersive X‐ray spectroscopy technique, and a layer of iron oxide formed on the 5Cr steel was found when naphthenic acids were present in the solution. The iron oxide layer appeared to be important for maintaining protection against naphthenic acid corrosion, and further analysis revealed that it was composed of magnetite. Copyright © 2015 John Wiley & Sons, Ltd.     

Cationic amphiphiles based on diethanolamine esters with amino acids in the polar block

A series of new cationic amphiphiles based on diethanolamine esters with Gly, βAla, GABA, Lys, Orn amino acid residues in the hydrophilic block were prepared. The sample containing the Lys residue showed the best activity against gram-positive and gram-negative bacteria. For model membranes comprising combinations of DOPC, DOPG and DOPE phospholipids, the sample can electrostatically bind to the surface of a bacterial cell and destroy it by formation of through defects.     

Effect of ATP and amino acids on the properties of cationic amphiphiles in solution and on the surface

Russian Chemical Bulletin - The interaction between a number of cationic surfactants bearing the head group with different structures (triallyl, morpholinium, including hydroxyethyl-substituted)...     

Langmuir films of naphthenic acids at different pH and electrolyte concentrations

Langmuir films of naphthenic acids at different pH and electrolyte concentrations are reported. The polydisperse naphthenic acids were commercially available, while two single-component naphthenic acids [5#(H)-cholanoic acid and 1-naphthalenepentanoic acid, decahydro- (9CI)] were synthesized. 1-naphthalenepentanoic acid, decahydro- is too water-soluble to form stable monolayers. 5#(H)-Cholanoic acid and Fluka naphthenic acid form stable films when cations are present in the aqueous subphase. At lower pH the cations are less influential since the naphthenic acids are not protolysed and metal naphthenates cannot be formed. pK_a^s for 5#(H)-cholanoic acid is determined to 5.65. The micellisation of the naphthenates at high pH is described.     

Studies on the non-uniformity of fine dispersive mixtures by instrumental activation method

The uniformity of ferrit charge component distribution affects significantly the magnetic properties of the final products. A characteristics feature of mixing efficiency is the concentration distribution of the components present in low concentration. It was the aim of the present research to investigate the variants of the instrumental activation technique to measure cobalt, sodium, and copper in ferrite charge. All data obtained were treated by the technique of the simple dispersion analysis. The effect of some systematic errors on the statistical parameters under consideration have been studied. Means of quantitative estimation of non-uniformity have also been discussed.     

Amino acids: Building blocks for the synthesis of greener amphiphiles

Amino acid-based amphiphiles have attracted much attention as environmentally friendly surfactants because of their biodegradability, low toxicity and the use of renewable sources of raw materials for their syntheses. With respect to molecular design, the amino acid-based architecture allows the possibilities of multiple structures of amphiphiles with varying head groups and chain lengths. This review focuses on the synthetic strategies for the development of various types of surfactants derived from amino acids. Their properties in terms of surface, biological and catalytic activities are illustrated.     

Analysis of naphthenic acids in produced water samples by capillary electrophoresis-mass spectrometry

A capillary electrophoresis-mass spectrometry method was used to analyze naphthenic acids in produced water samples. It was possible to detect cyclopentanecarboxylic, benzoic, cyclohexanebutyric, 1-naphthoic, decanoic, 3,5-dimethyladamantane-1-carboxylic, 9-anthracenecarboxylic, and pentadecanoic acids within ca. 13 min using a buffer composed of 40 mmol/L ammonium hydroxide, 32 mmol/L acetic acid and 20% v/v isopropyl alcohol, pH 8.6. The proposed method showed good repeatability, with relative standard deviation (RSD) values of 6.6% for the sum of the peak areas and less than 2% for the analysis time. In the interday analysis, the RSD values for the sum of the peak areas and migration time were 10.3% and 10%, respectively. The developed method demonstrated linear behavior in the concentration range between 5 and 50 mg/L for benzoic, decanoic, 3,5-dimethyladamantane-1-carboxylic and 9-anthracenecarboxylic acids, and between 10 and 50 mg/L for cyclopentanecarboxylic, cyclohexanebutyric, 1- naphthoic, and pentadecanoic acids. The detection limits values ranged from 0.31 to 1.64 mg/L. Six produced water samples were analyzed and it was possible to identify and quantify cyclopentanecarboxylic, benzoic, cyclohexanebutyric, and decanoic acids. The concentrations varied between 4.8 and 98.9 mg/L, proving effective in the application of complex samples.     

Electrostatic effects on nanofiber formation of self-assembling peptide amphiphiles

Self-assembling peptide amphiphile molecules have been of interest to various tissue engineering studies. These molecules self-assemble into nanofibers which organize into three-dimensional networks to form hydrocolloid systems mimicking the extracellular matrix. The formation of nanofibers is affected by the electrostatic interactions among the peptides. In this work, we studied the effect of charged groups on the peptides on nanofiber formation. The self-assembly process was studied by pH and zeta potential measurements, FT-IR, circular dichroism, rheology, atomic force microscopy, scanning electron microscopy and transmission electron microscopy. The aggregation of the peptides was triggered upon neutralization of the charged residues by pH change or addition of electrolyte or biomacromolecules. Understanding the controlled formation of the hydrocolloid gels composed of peptide amphiphile nanofibers can lead us to develop in situ gel forming bioactive collagen mimetic nanofibers for various tissue engineering studies including bioactive surface coatings.     

水-乙醇混合溶剂中弱酸电离的溶剂效应

本文用LKB2277Bioactivity monitor微量流动热量计测定卤代乙酸. 脂肪酸在水-乙醇混合溶剂中的标准电离焓,计算了热力学函数.结合文献数据,计算各酸根离子从水迁移到混合溶剂的迁移自由能,并讨论溶剂效应对弱酸电离的影响1.     

Solution behavior of aqueous mixtures of low and high molecular weight hydrophobic amphiphiles

Mixtures of a hydrophobic triblock copolymer (L121, PEO₅PPO₆₈PEO₅) and a hydrophobic anionic surfactant (AOT, Sodium bis(2-ethylhexyl)sulfosuccinate), each alone forming turbid vesicular solutions in water, aggregate to produce a thermodynamically stable, transparent, and isotropic solution. Mixed AOT/L121 aggregates could be confirmed by fluorescence, surface tension, differential scanning calorimetry (DSC), and isothermal titration calorimetry. In an isotropic region, where mixed aggregates are formed, there is a synergistic interaction between monomers of AOT and L121 in the mixture. In addition, small-angle neutron scattering experiments provided evidence that mixed aggregates have the shape of either spheres (with a certain polydispersity) or very short ellipsoids (axial ratio below 2), confirming a transition from giant multilamellar vesicles to small aggregates upon mixing the two hydrophobic amphiphiles. Upon dilution, the morphology changes to disk-like. From an examination of the results of all the methods the peculiar behavior of the mixed AOT/L121 system is explained.     

有机酸取代基和溶剂效应的静电模型

本文根据气相实验结果和以往的静电理论, 建立了一个描述有机酸电离取代基和溶剂效应的静电模型。该模型不仅满足气相边界条件, 而且其参数B具有较明确的物理意义, 即与酸官能团的溶剂化半径以及取代基与溶剂分子之间特殊相互作用有关, 因而是描述溶质-溶剂相互作用的重要参数。     

Cosolvent effects on the stability of catanionic vesicles formed from ion-pair amphiphiles

Four ion-pair amphiphiles (IPAs), derived from the pairing of alkyltrimethylammonium chlorides and sodium alkyl sulfates, were used to form catanionic vesicles in water upon the mechanical dispersion method. For the first time in the literature, short-chained alcohols (methanol, ethanol, 1-propanol, and 1-butanol) were added as cosolvents at a variety of concentrations and systematically studied for their effects on the stability of the ensuing vesicles. Dynamic light scattering measurements indicated that vesicles formed from one of the IPAs (i.e., dodecyltrimethylammonium dodecyl sulfate) could be efficiently and successfully stabilized by the addition of appropriate amounts of 1-propanol and 1-butanol. Maximum lifetimes of more than 1 year and 132 days for stable vesicles in 5% 1-butanol and 15% 1-propanol solutions, respectively, were observed, and this demonstrates that a novel method for the stabilization of catanionic vesicles formed from IPAs becomes available by means of cosolvent addition. Furthermore, the stability of catanionic vesicles was found to be strongly dependent on cosolvent concentration. In general, the vesicle stability increased with increasing the cosolvent concentration, reached a maximum at a specific concentration, and thereafter decreased with further increasing the concentration. The vesicles finally disintegrated into constituent molecules in solutions of high cosolvent concentrations. An explanation of cosolvent effects based on the medium dielectric constant was proposed.     

石油沥青质的NMR测定及其模型分子推测

从6种不同原油中分离提取了正己烷不溶的沥青质，测定了沥青质的1H NMR(Nuclear Magnetic Resonance)和13C NMR谱，从不同类型氢和碳原子的质量分数计算得到了一系列平均结构参数，结合相对分子质量测定和元素分析，给出了沥青质基本结构单元的平均分子式，推测了模型分子的结构。结果表明，沥青质的基本结构单元可以用稠环芳烃连接环烷烃和烷基侧链并含氧、氮和硫等杂原子的单元表示，结构单元之间形成缔合体，缔合数为4～6。     

Solvent effects on the dissociation of aliphatic carboxylic acids in water—N,N-dimethylformamide mixtures

The autoprotolysis constants of several water-_N,N-dimethylformamide mixtures were determined. The acid dissociation constants of formic, acetic, propionic, n-butyric, isobutyric, n-valeric, isovaleric, 2-methylbutyric and trimethylacetic acids were evaluated in the same media by potentiometric titration. Empirical equations for the calculation of autoprotolysis constants and acid dissociation constants at 25° C in the mixed solvents are proposed. Approximate solvation numbers were obtained by multiple linear regression analyses of pK_a values.     

Substitution effects on the liquid crystalline properties of D,L-xylitol amphiphiles

In this article we describe the self-assembling properties of alkyl substituted xylitols in relation to both thermotropic and lyotropic liquid crystalline mesophases. Three series of substituted xylitols were prepared where aliphatic chains of varying length were attached to a xylitol moiety via ether, thioether and ester linking groups. The thermotropic properties were investigated by thermal polarized light microscopy and differential scanning calorimetry, and evaluated as a function of chain length and linking group. The lyotropic phase behaviour was investigated via the addition of water to each material at room temperature. The efficiency for forming thermotropic phases was found to be reversed for the lyotropic phases in respect of the three series, i.e. as a function of the linking unit.     

Stable vesicles composed of monocarboxylic or dicarboxylic fatty acids and trimethylammonium amphiphiles

The self-assembly of cationic and anionic amphiphile mixtures into vesicles in aqueous media was studied using two different systems: (i) decanoic acid and trimethyldecylammonium bromide and (ii) hexadecanedioic acid (a simple bola-amphiphile) and trimethyldecylammonium bromide. The resulting vesicles with varying amphiphile ratios were characterized using parameters such as the critical vesicle concentration, pH sensitivity, and encapsulation efficiency. We also produced and observed giant vesicles from these mixtures using the electroformation method and confocal microscopy. The mixed catanionic vesicles were shown to be more stable than those formed by pure fatty acids. Those containing bola-amphiphile even showed the encapsulation of a small hydrophilic solute (8-hydroxypyrene-1,3,6-trisulfonic-acid), suggesting a denser packing of the amphiphiles. Compression and kinetics analysis of monolayers composed of these amphiphiles mixtures at the air/water interface suggests that the stabilization of the structures can be attributed to two main interactions between headgroups, predominantly the formation of hydrogen bonds between protonated and deprotonated acids and the additional electrostatic interactions between ammonium and acid headgroups.     

An algebraic approach to the study of the titration curves of weak acids and their mixtures

It is shown that the titration curves of weak acids and their mixtures which have rational mole-fractions of the components can be transformed into polynomials. These protonation polynomials are called normal or abnormal according to whether their coefficients do or do not satisfy certain inequalities derived from statistical considerations. The normality of a second-degree polynomial is shown to be a characteristic equivalent to the reality of its zeros. Protonation polynomials with real zeros are shown to be normal, but the converse of this statement is not necessarily true. The titration curve of a polyfunctional acid is identical with that of an equimolar mixture of monofunctional acids if and only if the protonation polynomial has real zeros. A method for determining the functionality of an acid from its titration curve by using protonation polynomials is outlined.     

Determination of dissolved naphthenic acids in natural waters by using negative-ion electrospray mass spectrometry

Naphthenic acids (NAs) have been implicated as some of the most toxic substances in oil sands leachates and identified as priority substances impacting on aquatic environments. As a group of compounds, NAs are not well characterized and comprise a large group of saturated aliphatic and alicyclic carboxylic acids found in hydrocarbon deposits (petroleum, oil sands bitumen, and crude oils). Described is an analytical method using negative-ion electrospray ionization mass spectrometry (ES/MS) of extracts. Preconcentration was achieved by using a solid-phase extraction procedure utilizing a crosslinked polystyrene-based polymer with acetonitrile elution. Recovery of the Fluka Chemicals NA mixture was highly pH-dependent, with 100% recovery at pH 3.0, but only 66 and 51% recoveries at pHs 7 and 9, respectively. The dissolved phase of the NA was very dependent on sample pH. It is thus critical to measure the pH and determine the appropriate mass profiles to identify NAs in natural waters. The ES/MS analytical procedure proved to be a fast and sensitive method for the recovery and detection of NAs in natural waters, with a detection limit of 0.01 mg/L.     

Fourier transform ion cyclotron resonance mass spectrometry of principal components in oilsands naphthenic acids

Naphthenic acids present formidable challenges for the petroleum industry and are a growing concern in the aquatic environment. For example, these acids are responsible for corrosion of refinery equipment, leading to the incurrence of additional costs to the consumer, and are toxic to aquatic wildlife, making disposal and remediation of contaminated waters and sediments a significant problem. The detection and characterization of naphthenic acids is therefore of considerable importance. Fourier transform ion cyclotron resonance mass spectrometry is presented as a technique with inherently ultra-high mass accuracy and resolution, affording unequivocal assignments. The suitability of the technique for environmental applications is demonstrated to characterize two different commercial mixtures of naphthenic acids and one oilsands tailings pond sample.