Regina C. L. Guimarães

Chloride determination by ion chromatography in petroleum coke after digestion by microwave-induced combustion

Microwave-induced combustion was applied to petroleum coke digestion in closed vessels for further chloride determination by ion chromatography. Samples were pressed as pellets and placed on a quartz holder. Combustion was performed using oxygen pressure of 2 MPa and 50 microl of 6 moll(-1) NH(4)NO(3) as aid for ignition. Recoveries from 97 to 102% were obtained for all studied absorbing solutions (water, H(2)O(2), Na(2)CO(3) or (NH(4))(2)CO(3)). Accuracy was evaluated using certified reference materials with agreement better than 98% using water as absorbing solution with reflux step. The limit of quantification was 3.8 microg g(-1).

Total sulfur determination in residues of crude oil distillation using FT-IR/ATR and variable selection methods.

Total sulfur concentration was determined in atmospheric residue (AR) and vacuum residue (VR) samples obtained from petroleum distillation process by Fourier transform infrared spectroscopy with attenuated total reflectance (FT-IR/ATR) in association with chemometric methods. Calibration and prediction set consisted of 40 and 20 samples, respectively. Calibration models were developed using two variable selection models: interval partial least squares (iPLS) and synergy interval partial least squares (siPLS). Different treatments and pre-processing steps were also evaluated for the development of models. The pre-treatment based on multiplicative scatter correction (MSC) and the mean centered data were selected for models construction. The use of siPLS as variable selection method provided a model with root mean square error of prediction (RMSEP) values significantly better than those obtained by PLS model using all variables. The best model was obtained using siPLS algorithm with spectra divided in 20 intervals and combinations of 3 intervals (911-824, 823-736 and 737-650 cm(-1)). This model produced a RMSECV of 400 mg kg(-1) S and RMSEP of 420 mg kg(-1) S, showing a correlation coefficient of 0.990.

Characterization of naphthenic acids using mass spectroscopy and chromatographic techniques: study of technical mixtures

By the classical definition naphthenic acids (NAs) are a complex mixture of monocarboxylic acids containing one or more alkyl-substituted alicyclic rings or only aliphatic carbon chains. Based on the great interest of the oil industry in the elucidation and characterization of naphthenic acids in petrochemical samples, and the lack of efficient methodologies for the total characterization of these compounds, the goal of this study is to compare three techniques (GC/qMS, ESI-MS/MS and GC × GC/TOF-MS) for the analysis of two technical mixtures of NAs. The results presented here demonstrate the applicability of these techniques and the main advantages of each one. GC/qMS is widely used in the naphthenic acid analysis and still presents a good performance; however the ESI-MS-MS allowed a very quick analysis that provided a general profile of each sample, very useful in preliminary classification of petrochemical mixtures, while GC × GC/TOF-MS delivered a thorough evaluation of the different components of each sample. Technical mixtures analyzed showed different profiles confirmed through the three techniques applied. The mixture SA (Sigma Aldrich) presented a predominance of aliphatic acids (Z = 0) while the mixture MN (Miracema-Nuodex) was composed mainly of naphthenic monocyclic acids.

Feasibility of low frequency ultrasound for water removal from crude oil emulsions.

The feasibility of indirect application of low frequency ultrasound for demulsification of crude oil was investigated without using chemical demulsifiers. Experiments were performed in an ultrasonic bath with frequency of 35 kHz. Synthetic emulsions with water content of 12%, 35% and 50% and median of droplet size distribution (DSD), median D(0.5), of 5, 10 and 25 μm were prepared from crude oil with API density of 19 (heavy crude oil) and submitted to the proposed ultrasound-assisted demulsification procedure. Experimental conditions as temperature, time of exposition to ultrasound and ultrasonic power were evaluated. Separation of water from crude oil emulsion was observed for all emulsions investigated. Demulsification efficiency up to 65% was obtained for emulsion with 50% of water content and DSD of 10 μm. Higher efficiency of demulsification was achieved using US temperature of 45 °C and ultrasound power of 160 W by 15 min. Results obtained in this study showed that ultrasound could be considered a promising technology for industrial crude oil treatment and respective water removal.

Microwave-induced combustion of crude oil for further rare earth elements determination by USN–ICP-MS

A procedure for light and heavy crude oils digestion by microwave-induced combustion (MIC) is proposed for the first time for further rare earth elements (REE) determination by inductively coupled plasma mass spectrometry (ICP-MS) equipped with an ultrasonic nebulizer (USN). Samples of crude oil (API density of 10.8-23.5, up to 250 mg) were inserted in polycarbonate capsules and combusted using 20 bar of oxygen and 50 μL of 6 mol L(-1) ammonium nitrate as igniter. Nitric acid solutions (1-14.4 mol L(-1)) were evaluated for analyte absorption and a reflux step was applied after combustion (5 min of microwave irradiation at 1400 W) in order to achieve better analyte recoveries. Accuracy was evaluated using a spiked sample and also by comparison of results obtained by microwave-assisted digestion combined to ultraviolet radiation (MW-UV) and by neutron activation analysis (NAA). Using 3 mol L(-1) HNO3, quantitative recoveries (better than 97%) were obtained for all analytes. Blank values were always negligible. Agreement was higher than 96% for La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y by comparison of results with those obtained by MW-UV and by NAA (only for La, Ce, Nd, Sm, and Yb). Residual carbon content in digests using MIC was always below 1%. As an advantage over conventional procedures for crude oil digestion, using MIC, it was possible to use diluted acid as absorbing solution, obtaining better limits of detection and avoiding interferences in REE determination by USN-ICP-MS.

Effect of ultrasonic frequency on separation of water from heavy crude oil emulsion using ultrasonic baths

In this work, a comprehensive study was performed for the evaluation of ultrasound (US) frequency for demulsification of crude oil emulsions. Experiments were performed using ultrasonic baths operating at the following frequencies: 25, 35, 45, 130, 582, 862 and 1146kHz. Synthetic water-in-oil emulsions with 12%, 35% and 50% of water and medians of droplet size distribution (DSD, D(0.5)) of 5, 10 and 25μm were prepared using a heavy crude oil (API density of 19). Crude oil demulsification was achieved at frequencies in the range of 25-45kHz for all tested emulsions. When frequencies higher than 45kHz were applied, no changes in the characteristics of the crude oil emulsions were observed. Demulsification efficiencies of about 65% were achieved at a frequency of 45kHz after 15min of US application (emulsions with original water content of 50% and D(0.5)=10μm). An important aspect is that no addition of chemical demulsifiers was performed, and the demulsification efficiency was considered high, taking into account that the results were obtained using a non-conventional crude oil. Contrary to the normal application of low-frequency US that has been used for emulsification, the proposed approach seems to be a promising technology for water removal from crude oil emulsions.

Separation of Heavy Crude Oil Emulsions Using Microwave Radiation for Further Crude Oil Analysis

Microwave radiation in closed vessels was used for the separation of heavy crude oil emulsions for further oil characterization. Operational conditions were studied and the following parameters were evaluated: water content, density, viscosity, N, S, V, Ni, and Cl. Using the proposed procedure it was possible to reduce the water and Cl content in crude oil to values lower than 1% and 300 µg g−1, respectively. It was possible to determine important crude oil properties without interferences caused by excessive water and salt concentrations. The proposed procedure is relatively fast and it was possible to obtain a suitable condition for water and salt removal from heavy crude oil emulsions without using demulsifiers or toxic reagents.

Determination of Basic Nitrogen in Residues of Crude Oil Distillation Using ATR-FTIR and Chemometric Methods

A method for basic nitrogen determination in residues of crude oil distillation using infrared spectroscopy and chemometrics algorithms was developed. Interval partial least squares, synergy interval partial least squares, and backward interval partial least squares were evaluated for calibration model construction. The samples were divided into a calibration and prediction set containing 40 and 15 samples, respectively. The first derivative with a Savitzky-Golay filter and the mean centered data showed the best results and were used in all calibration models. The backward interval partial least squares algorithm with spectra divided in 60 intervals and combinations of 4 intervals (1407 to 1372; 1117 to 1082; 971 to 936; 914 to 879 cm−1) showed the best root mean square error of prediction of 0.016 wt%. This calibration model displayed a suitable correlation coefficient between reference and predicted values.

DETERMINAÇÃO SIMULTÂNEA DE METAIS E ENXOFRE POR ICP-OES EM RESÍDUOS DE DESTILAÇÃO DE PETRÓLEO

A method for digestion of crude oil distillation residues (atmospheric residue, AR and vacuum residue, VR) using microwave-induced combustion (MIC) was developed for simultaneous determination of metals (Ba, Co, Fe, Mg, Mn, Ni and V) and sulfur by inductively coupled plasma optical emission spectrometry (ICP-OES). Samples were wrapped in polyethylene films and combusted using 20 bar of oxygen. Nitric acid solutions were evaluated using 5 min of reflux after combustion. Accuracy was evaluated using certified reference material and comparison with the results obtained by microwave-assisted wet digestion (MAWD). No statistical difference was observed between the certified values and those obtained using MIC as well as between the values obtained using MAWD or MIC. In spite of both methods have been apparently suitable for crude oil digestion, MIC was preferable in view of the possibility of using 3 mol L-1 HNO3 as absorbing solution. Furthermore, it is important to notice that using MIC, C content in digests was lower than 10 mg L-1, preventing interferences in ICP-OES. In addition, the simultaneous digestion of eight samples was possible in less than 30 min and without using concentrated acids and/or longer heating times, making the proposed method well-suited for routine analysis.

Monitorando a degradação da poliamida 11 (PA-11) via espectroscopia na região do infravermelho médio com transformada de fourier (FTIR)

O potencial da tecnica de espectroscopia de infravermelho com transformada de Fourier e acessorio de reflexao total atenuada (FTIR-ATR) foi avaliado para o monitoramento da degradacao da poliamida 11 (PA-11) usada em dutos flexiveis. As amostras foram submetidas a envelhecimento em reatores com pressao controlada e atmosfera inerte. Os corpos de prova foram imersos em agua deionizada (pH 7), nas temperaturas de 110, 120 e 140 ÂoC por um periodo de ate 50 dias. A tecnica recomendada para monitoramento da degradacao da PA-11 e a viscosimetria, atraves de medidas da viscosidade inerente corrigida (VIC) e a analise termogravimetrica (TGA). O comportamento observado para a VIC e TGA durante o envelhecimento possibilitou a construcao de modelos que correlacionam com a tecnica de FTIR-ATR. A partir dos resultados de FTIR-ATR, a variacao na intensidade da banda atribuida a fase amorfa, 1161 cm-1, possibilitou o monitoramento do envelhecimento quando associamos a tecnica a modelos quimiometricos como o de regressao dos minimos quadrados parciais, PLS. Portanto, a tecnica FTIR-ATR pode ser uma nova alternativa no monitoramento da degradacao hidrolitica da PA-11, eliminando assim o uso de solventes orgânicos toxicos e reduzindo, consequentemente, o tempo de analise.