Flávia C. de Souza

Synthesis of Thiourea Derivatives and its Evaluation as Corrosion Inhibitor For Carbon Steel

GRAPHICAL ABSTRACT Abstract The inhibitory effect of thiourea-based compounds was evaluated using carbon steel body specimens in hydrochloric acid media. Thiourea derivatives, N-(pyrimidin-2-ylcarbamothioyl)benzamide and N-(6-methylpyridin-2-ylcarbamothioyl)benzamide, were synthesized using a simple route with good yields of approximately 70%. The inhibitory efficiencies were obtained by means of weight-loss experiments and electrochemical techniques (e.g., polarization curves and electrochemical impedance spectroscopy). The presence of a methyl functional group showed a better inhibitory efficiency compared with the derivate inhibitor without such modification. Analyzing Langmuir isotherms, ΔG0ads values indicate the chemical adsorption of thiourea-based compounds. The ECorr values obtained for the thiourea derivative with the methyl functionality was cathodically shifted by approximately −0.08 V, with an inhibition efficiency of 81%.

Flow injection analysis with amperometric detection for morpholine determination in corrosion inhibitors

In this study, an electrochemical method is proposed using flow injection analysis and amperometric detection with screen-printed carbon electrodes for morpholine determination to monitor the quality of morpholine-based commercial inhibitors and the residual concentration of inhibitors that control internal corrosion in oil industry pipelines. The amperometric method resulted in a strong linear correlation coefficient (r = 0.9941) with a linear response over a concentration range of 20-120 mg L-1, a limit of detection of 10 mg L-1 and a limit of quantification of 30 mg L-1. In addition, the method has been shown to be precise, linear and homoscedastic. The recovery for the amperometric method was 100 ± 6%, and the recovery for the real condensate sample was 99 ± 2%. Thus, the proposed method is promising for analysing morpholine-based commercial inhibitors in oil industry pipelines with simple and low-cost methodologies compared with ion chromatography techniques.

Simple enzymatic methods for glycerol analysis in commercial beverages

Two enzymatic methods using amperometric and colorimetric detection based on two coupled activities (glyceroquinase and glycerol-3-phosphate oxidase) were compared for the glycerol content determination. The enzymatic conversion of glycerol consumes oxygen, which is measured amperometrically in a Clark-type electrode and correlated with the glycerol concentration. In addition to the enzymatic-colorimetric method, there is a third enzymatic reaction that can be used to form a coloured compound; this method involves the addition of peroxidase, 4-chlorophenol and 4-aminoantipyrine. The enzymatic methods studied showed good linearity in the range of 4 to 60 μmol L−1 glycerol with a detection limit of 1 μmol L−1. Studies of glycerol recovery in fortified sugar cane liquor showed a recovery of 98 ± 2% for the enzymatic-amperometric method and of 96 ± 1% for the enzymatic-colorimetric method. These two methods were applied to the determination of glycerol in beverages and good correlations were found between these methods.

DETERMINAÇÃO DE GLICEROL LIVRE E TOTAL EM AMOSTRAS DE BIODIESEL POR MÉTODO ENZIMÁTICO COM DETECÇÃO COLORIMÉTRICA

A method based on enzymatic activities was developed using three enzymes (glycerokinase, glycerol-3-phosphate oxidase and peroxidase) and colorimetric detection for the determination of glycerol in biodiesel. The enzymatic conversion of glycerol produces H2O2 that is eliminated by the action of peroxidase, an oxygen acceptor and 4- aminoantipirine, producing water and a colored compound, which was analyzed. This method showed good linear correlation coefficient (r = 0.9937) in the concentration range of 4.95 x 10-5 to 3.96 x 10-4% (w/w) and had experimental limits of detection and quantitation of 7.10 x 10-6 and 2.10 x 10-5% (w/w), respectively.

On the applicability of SiO2/Al2O3/Nb2O5 and SiO2/Al2O3/TiO2 as a biocompatible platform for chloroperoxidase

In the present work, two mixed oxides, namely, SiO2/Al2O3/Nb2O5 and SiO2/Al2O3/TiO2 (designated as SiAlNb and SiAlTi, respectively), obtained using the sol–gel method were used to immobilize chloroperoxidase. Hydrogen peroxide was quantified using potassium hexacyanoferrate(II) as a redox-mediator and amperometric measurements at 0.0 V vs. Ag/AgCl/Cl− (3 M). The SiAlTi biosensor presented higher sensitivity than the SiAlNb biosensor, however, the first one did not present a good response regarding time. The developed biosensor using the SiAlNb mixed oxide provided good signal levels, good linearity, good stability (retaining approximately 70% of its original response after 6 weeks of usage), a low detection limit (3 μM), good sensitivity, a suitable working range (from 4 to 19 μM), fast response and good repeatability. The recovery of the amperometric method for the detection of hydrogen peroxide in synthetic samples was approximately 100 ± 2%, and for Listerine® Whitening Pre-Brush Rinse samples fortified with 1, 2 and 3% (v/v) of hydrogen peroxide, it was 100 ± 3%.

A comparison of amperometric and spectrophotometric methods for the iodide concentration measurement: a tracer in produced water from offshore oil reservoirs

with limits of detection and of quantification of 1 and 3 mg L -1 , respectively. Both methods showed to be accurate, linear, homoscedastic and their recoveries were 101 ± 2 and 100 ± 3%, respectively, while the recoveries for produced reservoir water samples (fortified with iodide) were 97 ± 7 and 100 ± 3%, respectively. High amounts of sulfate interfere in the spectrophotometric method. Both methods are promising, simple and inexpensive alternatives to ion chromatography for the detection of iodide tracer in produced water reservoir samples.

Boron Doped Diamond Electrode as a Novel Sensor for Elemental Sulfur

Problems related to the presence of elemental sulfur (S 0 ) in natural gas have occurred frequently in several countries. The presence of these contaminants has caused failures in the natural gas distribution system causing mostly sulfur deposition in pipelines, control valves and turbine thermal power, which leads to clogging of nozzles, control valves and problem in the control systems. These events have been reported more frequently by carriers and natural gas distributors with the increase in the consumption of fuel. To perform the S 0 detection in natural gas, either directly in the gaseous matrix or after cleaning a certain amount of natural gas with organic solvents it was developed an electrochemical sensor boron doped diamond. This sensor was chosen for its wide potential window in both aqueous and organic solutions, low background current, chemical and mechanical stability, and low adsorption S 0 on the electrode surface. The method validated to detect S 0 in organic solvent using the sensor diamond doped with boron had a detection limit of 0.8 mg L -1 .

Inhibitory Effect of Piper Nigrum L. Extract on the Corrosion of Mild Steel in Acidic Media

Corrosion inhibitors have been used to preserve the integrity of metal components of plant facilities under severe corrosive conditions that would lead to failure or reduction of the operating cycle of essential units. These include risers, columns, wells, pipelines, pressure vessels and distillation towers structures. Several compound classes have been studied as corrosion inhibitors for metallic materials. In special, organic compounds have been tested and applied industrially as corrosion inhibitors due to their low toxicity. Taking into account recent recommendations for eliminating the use of toxic inorganic inhibitors there was a significant increase in studies on the use of natural products as corrosion inhibitors. Natural products are considered environmentally suitable corrosion inhibitors for use on a large scale. Recent studies have shown that black pepper extract is rich in a mixture of alkaloids substances that have excellent anti-corrosion properties in acid conditions. The aim of this study was to investigate the carbon steel corrosion inhibition efficiency of black pepper crude extract and purified piperine (major alkaloid present in the extract) in highly corrosive environment by weight loss measurements. For this reason, weight loss tests were carried out to study the inhibition efficiency. The inhibition efficiencies of different concentrations of the black pepper crude extract was higher than the efficiencies of the same concentrations of pure piperine. The efficiencies were about 97 % for the crude extract and 70 % for the pure piperine.

Use of hg-electroplated-pt ultramicroelectrode for determining elemental sulphur in naphtha samples.

This paper describes the applicability of a Hg-electroplated-Pt ultramicroelectrode in the quantification of elemental sulphur in naphtha samples by square-wave voltammetry. A reproducible deposition methodology was studied and is reported in this paper. This methodology is innovative and relies on the quality of the mercury stock solution to obtain reproducible surfaces required for the analytical methodology. All analyses were performed using a Hg-electroplated-Pt ultramicroelectrode (Hg-Pt UME) due to the low sensibility of such devices to ohmic drops in resistive solutions. The responses of the peak areas in voltammetric experiments were linear in all of the range studied. The method developed here is accurate and reproducible, with a detection limit of 0.010 mg L−1 and a good recovery range for both standard solutions of elemental sulphur (85 to 99%) and real naphtha sample (79%). These results attest to the potential for the application of this electroanalytical methodology in determining elemental sulphur in naphtha samples containing mercaptans and disulphides.