T. N. Castro Dantas

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.

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.

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.

Hydraulic Gel Fracturing

Fracturing gel is a critical component of the hydraulic fracturing treatment. Its main functions are to open the fracture and to transport a propping agent along the length of the fracture. The most common fracturing gels use natural polymers, such as guar, crosslinked by borate to form viscoelastic gels. Due to serious limitations of many polymeric gels, a new generation of fracturing gels based upon viscoelastic surfactants has been developed. This work describes the commonly used fracturing gels.

Microemulsion System as a Steel Corrosion Inhibitor

Abstract The inhibition effect of surfactant systems on the corrosion of carbon steel (AISI 1010) by 0.1 M hydrochloric acid (HCl) was investigated by polarization measurement techniques. Dodecylammonium bromide (DDAB) surfactant was used as a micellar solution in aqueous 0.1 M HCl and as an active component of a microemulsified oil-in-water system, containing n-butanol, n-hexane, and aqueous 0.1 M HCl. The adsorption of DDAB followed the Langmuir isotherm equation for both interfaces studied, and the largest βc was observed, in the cathodic range, when the concentration of the inhibitor was increased. The results obtained from electrochemical measurements were discussed, and it was observed that the microemulsion had a better inhibition effect than the pure surfactant solution.

Oil Recovery Performance of Surfactant Solutions and Adsorption in Sandstone

Abstract In this article, five nonionic surfactants with different ethoxylation degrees (R70, R95, R120, R150, and R200) were evaluated in surfactant adsorption experiments and oil recovery tests. Both sets of tests were carried out in a surfactant flooding apparatus using 30 psi as pressure gradient. The concentration of the solutions injected in adsorption tests were 30% above the critical micelle concentration (c.m.c.) to ensure micelle formation. In oil recovery tests, the solution concentration varied from the c.m.c. until 500% above it. The results obtained showed that adsorption was higher for R120 and the better oil recovery was for R200.

The Influence of Surfactant Solution Injection in Oil Recovery by Spontaneous Imbibition

Imbibition is the spontaneous displacement of fluids through porous media that occurs until capillary equilibrium is reached. Factors such as wettability and high interfacial tensions may negatively affect the process, requiring additional work to enhance oil recovery. This work aims to explain some aspects of the dynamics of oil recovery by spontaneous imbibition using different fluids. Static imbibition and contact angle experiments were performed using sandstones of the Botucatu Formation (Brazil). The plug samples were exposed to immersion in brine and in surfactant solutions, and the progression of oil recovery was monitored with time. The results showed that the capillary imbibition rate and the oil recovery factor were higher when an ionic surfactant was used. The inverse Bond number and the shape of the recovery profile showed different trends of the capillary imbibition dynamics. Higher oil recovery factors for ionic surfactant were also an effect of the contact angles observed.