Photometric determination of mercaptans in light petroleum products

A procedure for the photometric determination of mercaptan sulfur in light petroleum products was developed. This procedure is based on the formation of colored analytical species in an aqueous extract to an alkaline solution of sodium nitroprusside. The determination level was 3 mg/L at a sample volume of 1 mL.     

Solid solutions of normal paraffins

The results of the X-ray diffraction and thermal X-ray diffraction studies of the paraffins C_nH_2n+2 are revised based on new principles asserting the existence of several types of rotator states of paraffins. Along with the known isomorphism factors, such as the parity (symmetry) of the starting components and the difference between the chain lengths of their molecules (Δn), there is a factor that is specific to paraffins: differences in the energy state of molecules entering solid solutions. St. Petersburg State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 5, pp. 929–938. September–October, 1996. Translated by L. Smolina     

Simplified determination of the normal paraffin content of petroleum fractions

Summary A greatly simplified method for the determination of the total normal paraffin content in petroleum fractions is described where the use of open-tubular columns and up-to-date data handling contribute to the criterion of separation before quantitation.     

The determination of chlorinated long-chain paraffins in water,sediment and biological samples

Methods are described for the routine determination of traces of industrial chloro-n-paraffins having 13–30 carbon atoms and chlorine contents of 42–45% (frw/w), in environmental samples of water, sediments and biota. The procedures are based on thin-layer chromatography detection and measurement. All samples are cleaned up by liquid—solid adsorption chromatography and thin-layer chromatography but those rich in lipids require preliminary solvent extraction. The methods distinguish between chloro-n-paraffins based on long carbon chains (C₂₀–C₃₀) and those based on shorter chains (C₁₃–C₁₇). The methods cover the ranges 500 ng l^?1 to 8 μg l^?1 for water (i.e. from about the solubility limit upwards) and 50 μg kg^?1 to 16 mg kg^?1 for sediments and biota. The precision of the methods ranges from ± 50% relative at the lowest concentrations to ± 12% relative at the highest. Recoveries are about 90% for water, 80% for sediments and between 80 and 90% for biota according to sample type.     

Sample preparation in the determination of metals in oil and petroleum products by ICP MS

Comparative elemental analysis of the Tengiz oil and diesel fuel is performed by inductively coupled plasma mass-spectrometry with autoclave digestion, digestion, dilution with organic solvents, and also rotating coiled columns (RCCs). The advantages and drawbacks of each of the listed sample preparation techniques for the separation of microelements are discussed. In contrast to the other versions, the use of RCCs is shown to provide a unique opportunity to preconcentrating microelements from oil and petroleum products into tiny volumes of aqueous solutions (10 mL of 0.5 M HNO₃). The eluate prepared can be used in the subsequent analysis by ICP MS with no extra sample preparation steps. The RCC preconcentration of elements from oil and petroleum products makes it possible to determine metals in concentrations from μg/kg to ng/kg.     

Isotope dilution ICP-MS with laser-assisted sample introduction for direct determination of sulfur in petroleum products

Inductively coupled plasma isotope dilution mass spectrometry (ICP-IDMS) with direct laser-assisted introduction of isotope-diluted samples into the plasma, using a laser ablation system with high ablation rates, was developed for accurate sulfur determinations in different petroleum products such as sulfur-free premium gasoline, diesel fuel, and heating oil. Two certified gas oil reference materials were analyzed for method validation. Two different ³⁴S-enriched spike compounds, namely, elementary sulfur dissolved in xylene and dibenzothiophene in hexane, were synthesized and tested for their usefulness in this isotope dilution technique. The isotope-diluted sample was adsorbed on a filter-paper-like material, which was fixed in a special holder for irradiation by the laser beam. Under these conditions no time-dependent spike/analyte fractionation was only observed for the dibenzothiophene spike during the laser ablation process, which means that the measured ³⁴S/³²S isotope ratio of the isotope-diluted sample remained constant—a necessary precondition for accurate results with the isotope dilution technique. A comparison of LA-ICP-IDMS results with the certified values of the gas oil reference materials and with results obtained from ICP-IDMS analyses with wet sample digestion demonstrated the accuracy of the new LA-ICP-IDMS method in the concentration range of 9.2 g g^–1 (sulfur-free premium gasoline) to 10.4 mg g^–1 (gas oil reference material BCR 107). The detection limit for sulfur by LA-ICP-IDMS is 0.04 g g^–1 and the analysis time is only about 10 min, which therefore also qualifies this method for accurate determinations of low sulfur contents in petroleum products on a routine level.This article is dedicated to Wilhelm Fresenius who has continuously supported the academic career of Klaus G. Heumann and the analytical work of his group.     

Determination of vanadium in petroleum and petroleum products using atomic spectrometric techniques

Vanadium is recognized worldwide as the most abundant metallic constituent in petroleum. It is causing undesired side effects in the refining process, and corrosion in oil-fired power plants. Consequently, it is the most widely determined metal in petroleum and its derivatives. This paper offers a critical review of analytical methods based on atomic spectrometric techniques, particularly flame atomic absorption spectrometry (FAAS), electrothermal atomic absorption spectrometry (ET AAS), inductively coupled plasma optical emission spectrometry (ICP OES), inductively coupled plasma mass spectrometry (ICP-MS). In addition an overview is provided of the sample pretreatment and preparation procedures for vanadium determination in petroleum and petroleum products. Also included are the most recent studies about speciation and fractionation analysis using atomic spectrometric techniques.     

Carbazoles,phenazines and dibenzofuran in petroleum products; methods of isolation,separation and determination

Alkylindoles, -carbazoles and -phenazines were isolated from a petroleum distillate by adsorption on activated aluminum oxide and desorption with methanol. After removal of methanol and dilution with benzene, the concentrate was extracted with 72% perchloric acid to obtain the alkylindoles and alkylcarbazoles as soluble perchlorates. These compound types were then isolated from the acidic layer by addition of water and extraction with benzene. A concentrate of the benzene extract was separated by gas chromatography into alkylindoles and 6 different carbazoles, the latter being characterized by ultraviolet and mass spectrometric techniques. The carbazoles were determined photometrically with 2-bromo-2-nitroindandione-1,3 reagent and by gas chromatography. Phenazine and several alkylphenazines were isolated from the nitrogen compound concentrate as solid perchlorates, liberated by alkali treatment of their perchlorates, and separated by gas chromatography ; ultraviolet and mass spectra were used for their identification. Dibenzofuran was identified in the residual concetrate after the acid extraction.     

Behaviour of chemical modifiers in the determination of arsenic by electrothermal atomic absorption spectrometry in petroleum products

Most comparative studies on the efficiency of chemical modifiers have been conducted in aqueous media. In the present work, we proposed a detailed study of the use of different chemical modifiers for direct determination of arsenic in complex organic matrices by electrothermal atomic absorption spectrometry (ETAAS). Palladium, rhodium, tungsten, silver, lanthanum and a mixture of palladium and magnesium were tested. The figures of merit used for evaluation and comparison were acquired in the optimal conditions for each modifier, established by multivariate optimization of the main variables based on Doehlert designs. Singular features were observed for the chemical behaviour of some modifiers in organic matrices compared to aqueous media, such as the worse performance of Pd + Mg modifier and no notice of severe tube corrosion from La application. Lanthanum was chosen as the best chemical modifier for the present application, according to predefined criteria. Lanthanum showed the minimum limit of detection, characteristic concentration and blank signal among all tested species and no effect of the concomitants usually present in petrochemical feedstocks. Using a 200 mg L⁻¹ lanthanum solution as a chemical modifier, the average relative standard deviations of 7 and 16% (at 3-15 μg L⁻¹ level) and characteristic concentrations of 0.47 and 0.77 μg L⁻¹ for naphtha and petroleum condensates, respectively, were observed.     

Development of a species-specific isotope dilution GC-ICP-MS method for the determination of thiophene derivates in petroleum products

A species-specific isotope dilution technique for accurate determination of sulfur species in low- and high-boiling petroleum products was developed by coupling capillary gas chromatography with quadrupole ICP-MS (GC-ICP-IDMS). For the isotope dilution step ³⁴S-labeled thiophene, dibenzothiophene, and mixed dibenzothiophene/4-methyldibenzothiophene spike compounds were synthesized on the milligram scale from elemental ³⁴S-enriched sulfur. Thiophene was determined in gasoline, ‘sulfur-free’ gasoline, and naphtha. By analyzing reference material NIST SRM 2296, the accuracy of species-specific GC-ICP-IDMS was demonstrated by an excellent agreement with the certified value. The detection limit is always limited by the background noise of the isotope chromatograms and was determined for thiophene to be 7 pg absolute, which corresponds to 7 ng sulfur/g sample under the experimental conditions used. Dibenzothiophene and 4-methyldibenzothiophene were determined in different high-boiling petroleum products like gas oil, diesel fuel, and heating oil. In this case a large concentration range from about < 0.04 to more than 2,000 μg g⁻¹ was covered for both sulfur species. By parallel GC-ICP-MS and GC-EI-MS experiments (EI-MS electron impact ionization mass spectrometry) the substantial influence of co-eluting hydrocarbons on the ICP-MS sulfur signal was demonstrated, which can significantly affect results obtained by external calibration but not those by the isotope dilution technique.     

The accurate determination of total sulphur and disulphide and polysulphide compounds in petroleum products by metal reduction and flame emission spectrometry

Conditions for the determination of total sulphur and disulphide/polysulphide in petroleum products are described. The sulphur is reduced by heating with sodium or Devarda's alloy under reflux with subsequent liberation of H₂S and measurement of the chemiluminescent S₂ emission intensity in a hydrogen—argon diffusion flame. The precision and accuracy are good. Applications to light distillates and waxy residues are discussed.     

Feasibility of high-resolution continuum source molecular absorption spectrometry in flame and furnace for sulphur determination in petroleum products

For the first time, high-resolution molecular absorption spectrometry with a high-intensity xenon lamp as radiation source has been applied for the determination of sulphur in crude oil and petroleum products. The samples were analysed as xylene solutions using vaporisation in acetylene-air flame or in an electrothermally heated graphite furnace. The sensitive rotational lines of the CS molecule, belonging to the ?ν = 0 vibrational sequence within the electronic transition X¹∑⁺ → A¹П, were applied. For graphite furnace molecular absorption spectrometry, the Pd + Mg organic modifier was selected. Strong interactions with Pd atoms enable easier decomposition of sulphur-containing compounds, likely through the temporal formation of Pd_xS_y molecules. At the 258.056 nm line, with the wavelength range covering central pixel ± 5 pixels and with application of interactive background correction, the detection limit was 14 ng in graphite furnace molecular absorption spectrometry and 18 mg kg⁻¹ in flame molecular absorption spectrometry. Meanwhile, application of 2-points background correction found a characteristic mass of 12 ng in graphite furnace molecular absorption spectrometry and a characteristic concentration of 104 mg kg⁻¹ in flame molecular absorption spectrometry.The range of application of the proposed methods turned out to be significantly limited by the properties of the sulphur compounds of interest. In the case of volatile sulphur compounds, which can be present in light petroleum products, severe difficulties were encountered. On the contrary, heavy oils and residues from distillation as well as crude oil could be analysed using both flame and graphite furnace vaporisation. The good accuracy of the proposed methods for these samples was confirmed by their mutual consistency and the results from analysis of reference samples (certified reference materials and home reference materials with sulphur content determined by X-ray fluorescence spectrometry).     

Multidimensional gas chromatographic determination of paraffins, olefins and aromatics in naphthas

In order to cope with the increasing demand for gasoline and the need to reduce environmental impact for sustainable development, refineries have installed refining technology by introducing cracking, reforming, isomerization and alkylation. The standard EN 228: 2004 outlines the specification that gasoline, deriving from the blend of several fractions, must have for use in modem piston engines. Naphtha is one of the products from distilling crude oil that can be used as starting material in the reforming process whose derivatives, which are a fraction of gasoline, depend on the composition of the naphtha. Knowledge of the naphtha composition thus enables to provide the final composition of the products of reforming, the efficiency of the plant and also provides information about the crude oil used. In this paper some naphtha samples were analysed by multidimensional gas chromatography. This technique allows in a single analysis a good separation of the hydrocarbon types and within each hydrocarbon type a good carbon number separation.     

A new procedure for the determination of distillation temperature distribution of high-boiling petroleum products and fractions

The distribution of distillation temperatures of liquid and semi-fluid products, including petroleum fractions and products, is an important process and practical parameter. It provides information on properties of crude oil and content of particular fractions, classified on the basis of their boiling points, as well as the optimum conditions of atmospheric or vacuum distillation. At present, the distribution of distillation temperatures is often investigated by simulated distillation (SIMDIS) using capillary gas chromatography (CGC) with a short capillary column with polydimethylsiloxane as the stationary phase. This paper presents the results of investigations on the possibility of replacing currently used CGC columns for SIMDIS with a deactivated fused silica capillary tube without any stationary phase. The SIMDIS technique making use of such an empty fused silica column allows a considerable lowering of elution temperature of the analytes, which results in a decrease of the final oven temperature while ensuring a complete separation of the mixture. This eliminates the possibility of decomposition of less thermally stable mixture components and bleeding of the stationary phase which would result in an increase of the detector signal. It also improves the stability of the baseline, which is especially important in the determination of the end point of elution, which is the basis for finding the final temperature of distillation. This is the key parameter for the safety process of hydrocracking, where an excessively high final temperature of distillation of a batch can result in serious damage to an expensive catalyst bed. This paper compares the distribution of distillation temperatures of the fraction from vacuum distillation of petroleum obtained using SIMDIS with that obtained by the proposed procedure. A good agreement between the two procedures was observed. In addition, typical values of elution temperatures of n-paraffin standards obtained by the two procedures were compared. Finally, the agreement between boiling points of polar compounds determined from their retention times and actual boiling points was investigated.     

On the possibility of chain folding in solutions of normal paraffins and polyethylene

A simple statistical thermodynamic argument is presented in which the probability of intramolecular chain folding of normal paraffins and polyethylene in solution is examined. This possibility is based on the existence of low-energy intramolecular conformations which are stable enough to overcome the tendency of a chain molecule to assume a random arrangement in solution. Some rough estimates of the magnitudes of energetic interaction in straight-chain hydrocarbons are made to demonstrate the plausibility of this hypothesis. The experimental support for this model arises from NMR spectra of normal paraffins in aromatic hydrocarbon solvents.