A. A. Dantas Neto

Removal of chromium from aqueous solutions by diatomite treated with microemulsion.

In order to evaluate the sorption of heavy metals, a crude diatomite was impregnated with a microemulsion which showed remarkable increase in chromium sorption capacity as compared to untreated diatomite. Samples with two different granulometries were investigated, both yielding practically complete adsorption. The adsorption process is pH dependent and the best results for the initial Cr (III) concentration of 1.5 g/L were obtained at pH 2.95. The effect of the concentration of the chromium synthetic solution was also investigated. The adsorption isotherms were obtained (30. 40 and 50 degrees C) and the Freundlich and Langmuir models were used to determine the adsorption capacity of the adsorbent. Following the adsorption step, a desorption process was carried out using several eluant solutions. The best results were obtained using hydrochloric acid (100%) as eluant.

Heavy metals extraction by microemulsions.

The objective of this study is the heavy metal extraction by microemulsion, using regional vegetable oils as surfactants. Firstly, the main parameters, which have influence in the microemulsion region, such as: nature of cosurfactant, influence of cosurfactant (C)/surfactant (S) ratio and salinity were studied, with the objective of choosing the best extraction system. The extraction/reextraction process by microemulsion consists of two stages. In the first one, the heavy metal ion present in the aqueous phase is extracted by the microemulsion. In a second step, the reextraction process occurs: the microemulsion phase, rich in metal, is acidified and the metal is recovered in a new aqueous phase, with higher concentration. The used system had the following parameters: surfactant-saponified coconut oil; cosurfactant-n-butanol; oil phase-kerosene; C/S ratio=4; salinity-2% (NaCl); temperature of 27+/-1 degrees C; water phase-aqueous solution that varied according to the heavy metal in study (Cr, Cu, Fe, Mn, Ni and Pb). A methodology of experimental planning was used (Scheffé Net) to study the behavior of the extraction in a chosen domain. The extraction was accomplished in one step and yielded extraction percentage higher than 98% for all metals. In the reextraction HCl-8M was used as reextraction agent and the influence of the pH and time were verified. This work showed the great efficiency of the microemulsion, indicating that it is possible to extract selectively the heavy metals from the aqueous phase.

Novel antioxidants from cashew nut shell liquid applied to gasoline stabilization

This study developed a methodology for converting hydrogenated cardanol, a compound extracted from cashew nut shell liquid into compounds with structural characteristics of antioxidants similar to the ones used in products derived from petroleum. The intended changes were carried out through exhaustive alkylation with tert-butyl chloride. The performance of the products was estimated in terms of oxidative stabilization during storage of cracked naphtha samples collected from the outlet of an industrial unit. The compound 2,4,6-tri-t-butyl-pentadecylphenol (new antioxidant) has presented a better efficiency in the storage assays as compared to the commercial additive used as reference in the refinery at the moment of sampling.

Surface charging and dimensions of chitosan coacervated nanoparticles.

Chitosan nanoparticles have been used in several systems destined to controlled release of active agents. In this manuscript the process of formation of chitosan nanoparticles, obtained employing the coacervation method with sodium sulfate is analyzed using zeta potential and small angle X-ray scattering (SAXS) measurements. Dispersions were obtained at pH=1 and pH=3 and presented a behavior, in terms of surface charging, that was independent of pH. However, SAXS results indicated a dependence of size-related behavior on pH. The difference in terms of behavior was explained through the influence of enthalpic and entropically driven components.

The use of microemulsions to remove chromium from industrial sludge.

In this work microemulsion systems were used to remove chromium from leather tannery sediments. The sludge was treated by a solid-liquid extraction process (acid digestion). The effects of particle size, digestion temperature and digestion time with regards to the efficiency of chromium removal were considered. The raw sludge (3 Mesh) was dried, grounded and sieved. Particles with 3, 14, 65, 100, 200, and 325 Mesh were evaluated. Sludge digestion solutions were prepared using each studied granule size at 25 degrees C, 70 degrees C, and 95 degrees C. Microemulsion extraction experiments to remove chromium III from the acid digestion solution were made according to a Scheffé Net experimental design methodology, using microemulsion systems inside the Winsor II region (System I) and inside the microemulsion region (Winsor IV--System II). A statistical treatment was used to obtain the isoresponse plots. Chromium extraction percentages were up to 73.3% for System I and up to 93.4% for System II.

Gallium extraction by microemulsions.

In this work, the use of microemulsion in the extraction of gallium, with Bayer process, has been studied. The studied microemulsion systems were: systems I and II, with saponified coconut oil (SCO) and 4-ethyl,1-methyl,7-octyl,8-hydroxyquinoleine (Kelex-100) as extractants. The extraction essays by microemulsion were carried out by applying an experimental planning method whose microemulsion points were prepared within an experimental domain favorable to the extraction. Gallium and aluminum extraction percentages, in each point, were evaluated via a statistical treatment of the data, with the use of variance analysis and mathematical models. In system I (SCO), percentages of extraction of 85.5% for gallium and 35.4% for aluminum were achieved; in system II (Kelex-100), the yields were 100% for gallium and 99.9% for aluminum. The reextraction study with sulfuric acid presented the same behavior for both systems, with efficiency depending upon the concentration of the acid, and allowing for a selective reextraction of gallium and aluminum.

Rheological properties of a new surfactant-based fracturing gel

Surfactant-based fracturing gels are considered as clean gels due to the absence of insoluble residues in their composition. This kind of fluid has been developed to minimize or eliminate damages to fractures. Therefore, new studies about gel rheological properties become more and more important, namely viscosity, the most important property of fracturing gels. This research was accomplished with the purpose of evaluating a new anionic surfactant-based gel. Steady and oscillatory shear experiments were carried out in order to evaluate the inner structure of the developed gel with variable composition, within the gel region in a pseudoternary diagram. It could be observed that small variations in gel composition resulted in changes in micellar structure.

Alternative fuels composed by blends of nonionic surfactant with diesel and water: engine performance and emissions

Diesel - based microemulsions and a surfactant/diesel blend, using ethoxylated (5 EO) nonylphenol as surfactant, were prepared and tested in a diesel engine to evaluate its performance and emissions. The following properties were evaluated: density, viscosity, cloud point and corrosiveness. Experimental results showed that density and viscosity were greater than those obtained for neat diesel. Cloud point and corrosiveness were not affected by water and surfactant. Specific fuel consumption of the microemulsion systems was greater than that of diesel, but the small droplets of water improved diesel combustion. Compared with diesel, an increase in carbon monoxide (CO) and nitrogen oxide (NOx) emissions and a decrease in black smoke emissions were obtained. In general, only microemulsions with up to 6% water are in accord with Brazilian diesel/biodiesel fuel regulations and specifications.

Application of Surfactants for Obtaining Hydraulic Fracturing Gel

Abstract Insoluble residues left in fractures by fracturing fluids have been the object of study by many authors, since these residues cause damage in reservoirs. The objective of this research was the development of a novel surfactant-based fracturing gel with the purpose of minimizing or eliminating the damage in the fracture. A comparison between the properties of a surfactant-based gel and a crosslinked hydroxypropylguar (HPG) fluid was made. Through rheological tests, fluid loss and setting rate, one can conclude that the obtained gel presents compatible characteristics when compared with the HPG gel.

Oily Wastewater Treatment through a Separation Process Using Bubbles without Froth Formation

Abstract This study seeks to investigate the use of a surfactant derived from coconut oil in the recovery process of organic compounds from oily effluents. To evaluate its efficiency in oil removal and its optimal concentration for each oil/water ratio, experiments were carried out using water/oil emulsions (50, 100, 200, and 400 ppm of oil) and produced water (50 ppm) in a small-scale column. According to these experiments, it was verified that there is an optimum surfactant concentration for each emulsion, and for produced water the extraction efficiency reaches a maximum value (80%) at a surfactant concentration of 0.1 g/L−1.Abstract This study seeks to investigate the use of a surfactant derived from coconut oil in the recovery process of organic compounds from oily effluents. To evaluate its efficiency in oil removal and its optimal concentration for each oil/water ratio, experiments were carried out using water/oil emulsions (50, 100, 200, and 400 ppm of oil) and produced water (50 ppm) in a small-scale column. According to these experiments, it was verified that there is an optimum surfactant concentration for each emulsion, and for produced water the extraction efficiency reaches a maximum value (80%) at a surfactant concentration of 0.1 g/L−1.