During the petroleum dehydration process, it is necessary to use chemical demulsifiers to break the water-oil emulsions that are formed during oil extraction. The majority of the products used are formulations containing nonionic surfactants based on poly(ethylene oxidepropylene oxide) (PEO-PPO) block copolymers with different ethylene oxide/propylene oxide molar ratios. In this work, PEO-PPO block copolymers of different structures were used. The physical-chemical properties of aqueous PEO-PPO solutions and their mixtures were analyzed, along with their effectiveness as water-oil emulsion destabilizing agents. The results showed that all the PEO-PPO copolymers could reduce the interfacial tension between water and oil. Nevertheless, the most efficient water-oil emulsion demulsification was achieved by the PEO-PPO branched copolymer, whose structure presented hydrophilic segments [poly(ethylene oxide) and OH] side by side at the free end of the molecule. This copolymer also exhibited the highest water solubility. Such behavior could be attributed to its structure, which promoted better interaction with the water droplets dispersed in the water-oil emulsion. The performance of the surfactant mixtures appeared to be related to their capacity to reduce the water-oil interfacial tension. The addition of a surfactant at a concentration of roughly 30% without demulsifying action does not compromise the action of a well-performing surfactant.

Evaluation of the physical-chemical properties of aqueous solutions of nonionic surfactants based on polyoxides can be performed by different methods. Depending on the technique used, there can be a significant variation in the critical micelle concentration (CMC) found. This is related to the sensitivity of the technique regarding the unimers and micelles present in the solution as well as the structure of the surfactant evaluated. In this work, the CMC values of aqueous solutions of linear and branched poly(ethylene oxide-polypropylene oxide) (PEO-PPO) block copolymers were determined by tensiometry, fluorescence, and particle size analysis, using copolymers having adjacent structures (that is, hydrophilic and hydrophobic segments located adjacently in the copolymer) and alternating structures. Tensiometry was used to measure the surface tension as a function of the copolymer concentration in aqueous solution. Fluorescence was used to determine the fluorescence intensity of pyrene to plot the graphs of the I 1 /I 3 and I E /I M relations according to the surfactant concentration. Finally, particle size analysis was used to determine the diffusion coefficient of the particles. The results showed that the fluorescence and particle size techniques provide lower (and mutually concordant) CMC values and can be considered more precise because these methods directly analyze the bulk of the solution.

The aqueous extract of Joazeiro stem bark (EJSB) and its high molecular weight fraction (HMWF) were examined as potential corrosion inhibitors of mild steel in 1 mol L−1 hydrochloric acid media, using weight-loss measurements, potentiodynamic polarization curves and an electrochemical impedance spectroscopy (EIS).Varying the concentration of the inhibitors from 100 to 800 mg L−1, the results show an increase in anticorrosive efficiency from 85.4 to 89.8 and 89.8 to 93.0% for EJSB and its HMWF, respectively, using the data of the gravimetric essay, and from 84.5 to 94.5 and 89.9 to 94.7% for EJSB and its HMWF, respectively, from the impedance data. The composition of the crude extract was chemically characterized by liquid chromatography-high resolution mass spectrometry. Additionally, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were used, respectively, to morphologically and chemically characterize the surface. Considering that the saponin molecules, the main constituent from juá, are responsible for its inhibitory action, quantum chemical calculations showed that the C67, C69 and O144 atoms likely have an important role in the process of electron-donation of saponin to metal, due to the higher values of ƒk+ and %HOMO observed on these atoms.