SPECTROSCOPIC DETERMINATION OF CARBON IN AROMATIC RINGS IN PETROLEUM KEROSENES

On the basis of the composition of aromatic carbon in the petroleum kerosenes being exclusively mono and di-ring systems; which absorb UV light in a distinct region; the slope of the plot of the total absorbance in the region 250 to 290 nm Vs known concentration of authentic model kerosene mixture, may be utilized to determine the percentage of carbon in aromatic rings in a sample kerosene.

The area under the aromatic envelope curve ; whether expressed as a function of direct instrumental measurements of the total absorbance at = 250, 260,270,280 and 290 nm, or actually traced and evaluated; of a 1 ml kerosene sample dissolved in 500 ml iso- propyl alcohol, enables the estimation of the percentage of carbon in aromatic rings ( %CA ) using a mathematically derived expression for this purpose. This spectroscopic method was applied to determine % CA in Libyan kerosene samples, sequentially subjected to aromatic carbon depletion by adsorbents.     

CHANGES IN THE COMPOSITION AND PROPERTIES OF THE VACUUM RESIDUES AS A RESULT OF VISBREAKING

ABSTRACT

Two vacuum residues of heavy petroleum blends and residues of the products of their visbreaking, on a commercial unit, were investigated by means of column chromatography, cryoscopic analysis, elemental analysis, NMR spectroscopy, etc. An increase in the contents of asphaltenes and saturated, increase in asphaltenes/polar components ratio, and decrease in the aromatics contents during visbreaking were observed for both kinds of feed. The N/C ratio increased, the S/C ratio did not change significantly. Most of the nickel and vanadium were concentrated in the asphaltenes and aromatics. The length of the paraffinic chains of the saturated decreases during visbreaking from about 50 to 30 carbon atoms. The number of carbon atoms per alkyl chain and the number of naphthenic rings in the average molecule of the aromatics decreased, whereas the number of aromatic rings increased. About 2/3 of the total aromatic carbon in the aromatics are non-bridged. The average asphaltenes molecule contains about 36-38 aromatic rings (mostly condensed), 5-7 naphthenic rings and 12-16 alkyl substituents having relatively short (n = 5-6) chains. Two contrary processes, relating asphaltenes, take place during visbreaking: 1) cracking of asphaltenes, which results in a decrease in their content and molecular weight, decrease in the number of the side chains and their length, and increase in asphaltenes aromaticity; 2) asphaltenes formation from the polar components of the feed. The resulting process may be expressed both in a decrease and in an increase in the asphaltenes content. Reactions of condensation of the asphaltenes precursors (resins, etc.) prevail for the light stocks. For heavier stocks, cracking of the asphaltenes plays a more significant role, and the increase in asphaltenes content takes place mainly due to concentrating them in the visbreaking residue as a result of the distillation of the visbroken product.     

NMR SPECTROSCOPY IN THE CHARACTERIZATION OF EIGHT SELECTED ASPHALTS

ABSTRACT

Nuclear Magnetic Resonance (NMR) spectroscopy has been used to partially characterize eight selected asphalts. This report describes the initial efforts in this endeavor. Proton and carbon spectra have been collected and analyzed for percent aromatic content as well as aromatic substitution. DEFT results, chemical shifts and literature precedent have been used to assign the major resonances in the aliphatic region to chemical entities. Finally, using elemental analysis data, molecular weight data and NMR results, average structures for the eight asphalts have been derived     

QUANTIFICATION OF ASPHALTENE CONTENT IN VISCOUS CRUDE BY K-RATIO DUAL-WAVE LENGTH SPECTROPHOTOMETRY

ABSTRACT

In this paper is a novel method for the quantification of asphaltene content in viscous crude by K-ratio dual-wave length spectrophotometry proposed. The principle of the method is discussed in detail. The detailed operation steps are described and discussed according to merits and shortcomings. By selecting the dual wavelength as 750 nm and 800 nm and calculating of the K-ratio, which is very important for the method, the asphaltene content is obtained. The influence of sample quantity, temperature of preparation, laying time and toluene content on the absorbance of the sample are all discussed. After evaluation of all the factors having effects on the measurement the optimum operating parameters are determined. The experiment results show that the accuracy of the method is up to 0.700% and the linear correlation coefficient is 0.9898.     

Investigation of Asphaltene Precipitation Process for Kuwaiti Reservoir

Abstract

As part of an Enhanced Oil Recovery (EOR) research program, Asphalting precipitation processes were investigated for a Kuwaiti dead oil sample using different hydrocarbons and carbon dioxide as precipitants at the ambient and high pressure of 3000 psig conditions. The hydrocarbons used as precipitants were ethane (C2), propane (C3), butane (C4), normal pentane (n-C5), normal hexane (n-C6), and normal heptane (n-C7). The equipment used for this investigation was a mercury-free, variable volume, fully visual JEFRI-DBR PVT system with laser light scattering. The minimum critical value of precipitants concentration for the oil sample has been identified at the ambient and high-pressure conditions for each precipitant. Our investigation has revealed that for this oil sample the most powerful asphaltene precipitant were CO₂ followed by C2, C3, C4, n-C5, n-C6, and n-C7. Moreover, the effect of pressure and temperature on the asphaltene precipitation has been investigated experimentally for CO₂, n-C5, n-C6, and n-C7. The precipitation and redissolution of asphaltene upon the addition and removal of CO₂ and light alkanes (C2–C4), at 3000 psig and ambient temperatures, have shown evidence of reversibility of asphaltene precipitation. A comprehensive fluid characterization analysis for the oil sample has been performed including, physical properties of crude oil, compositional, molecular weight (Mw), and SARA analyses. Advanced analytical techniques such as 1H and 13C NMR and IR spectrometers have been utilized to investigate the molecular structure of the asphaltene for this sample. It was concluded that the asphaltene molecules for this oil contain 120 total aromatic carbons with 42 aromatic rings, 114 naphthenic rings, and 5–7 sets of condensed aromatic rings.     

SOLVENT EXTRACTION OF PAKISTANI COALS (ii): EXTRACTION AND CHARACTERIZATION OF METHANOL-BENZENE EXTRACTS

ABSTRACT

Structural characterization of the solvent extracts from four different Pakistani lignitic coals has been carried out by their proximate, elemental analysis and FT-Infrared and ¹H n.m.r. spectra. The yield of each extracts was greater with 1:1 benzene-methanol mixture in comparison to the total yield obtained by separate extractions with benzene and methanol. The extracts contained significantly less amount of ash and fixed carbon along with an increase in the percentage of volatile matter. The FTIR and ¹H n.m.r. spectra indicated that basically all the extracts contained less condensed aromatic rings in comparison to the coal. The FTIR spectra showed sharp well resolved peaks which have been assigned to various functional groups.

The ¹H n.m.r. spectra were used to obtain average structural parameters for all the extracts. A detailed analysis of the FTIR and n.m.r. spectra of the coal and their extracts provided an important in-sight into the differences between various extracts and also between various coals and their corresponding extracts.     

NAPHTHALENE AND ITS PRECURSORS IN IOMEX

ABSTRACT

Iomex, an aromatic rich concentrate from kerosene feedstock is a potential source for production of naphthalene which has a variety of industrial applications. Four analytical procedures were standardized for compositional study of iomex according to chemical class wise. Hydrocarbon group type separation ( saturates, mono-and diaromatics ) and quantitation was reported using column chromatography, gas chromatography, high performance liquid chromatography and mass spectrometry. Data generated by these techniques are in good agreement with each other. A diaromatic fraction containing naphthalene and its precursors was studied in detail by gas chromatography mass spectrometry (GC-MS). Capillary GC could resolve each and every component of the diaromatic fraction, whereas quantitation and characterization of 27 components were obtained by mass spectrometry.     

DETERMINATION OF PARAFFINIC,NAPHTHENIC AND AROMATIC CARBON IN PETROLEUM DERIVED MATERIALS BY CARBON-13 NMR SPECTROMETRY

ABSTRACT

A carbon-13 NMR method gives results for paraffinic, naphthenic, and aromatic carbon which compare well with those obtained from ASTM D2140. In order to be fully applicable for analysis by NMR, the sample must be of natural origin - preferably petroleum, shale oil or tar sands - and boil above about 200^°C. Otherwise, the samples may have been processed or separated by any method. The rationale for the present method, the restricted applicability of other NMR methods, and prospects for further detailed information on carbon functional groups are discussed.     

APPLICATION OF MULTICOLUMN VALVE SWITCHING GAS CHROMATOGRAPHY FOR THE ANALYSIS OF NAPHTHA AND KEROSENE FRACTIONS OF SAUDI ARABIAN LIGHT CRUDE OIL

Abstract

The straight run naphtha and kerosene fractions of Saudi Arabian Light crude oil were analyzed for paraffins, olefins, naphthenes and aromatics (PONA) using a gas chromatographic technique. This method is based upon group type separation according to carbon numbers using a programmed multiple valve switching sequence and employing multicolumn approach. The chromatographic operating conditions and carrier gas flow rates were selected to determine PONA contents of naphtha and kerosene fractions. These straight run fractions were produced by an automatic true boiling point (TBP) apparatus. Boiling range distributions of these fractions were determined using a standard ASTM method of simulated distillation. PONA results were compared with the literature. Total paraffins, naphthenes and aromatics agreed with each other.     

STRUCTURAL CHARACTERIZATION OF AROMATIC FRACTIONS OF SOME TYPICAL SOLVENT REFINED COALS USING MASS SPECTROMETRIC TECHNIQUES

ABSTRACT

ABSTRACT

Three aromatic fractions from two typical Chinese solvent-refined coals (one, FS2, derived from bituminous-sapropelitic cannel coal, and the other two, DT2A and DT2B, derived from a bituminous, weakly caking coal) were characterized for their chemical composition and molecular weight distribution using field ionization (FI) and field desorption (FD) mass spectrometric techniques. Some characteristic components derived from the chemical ionization technique were subjected to further fragmentation analyses using tandem mass spectrometry.

The FS2 fraction is composed of 3-5 ring condensed aromatics of cata configuration with abundant naphthenic groups fused with an aromatic cluster. The most abundant component -- cyclopentachrysene -- is resolved at M/Z 268, which may possibly be the product of aroir.atization of hopanes existing in the source material during dia- and catagenesis. Sample DT2A contains polycyclic aromatic hydrocarbons with a higher degree of aromatic condensation and 3-5 ring clusters. The concentration of C-4 substituted phenanthrene was especially high, indicating the probable presence of retene derived from triterpanic acid in the land plantresins during geological conversion of coal. The second aromatic fraction, DT2B, is differentiated from DT2A mainly by the aromatic ring number (6-9 rings for DT2B) and degree of aromatic condensation (mainly cata configuration). The suitability for producing advanced carbon materials of the three samples studied is discussed.     

Structural Aspects of Crude Oil Derived Asphaltenes by NMR and XRD and Spectroscopic Techniques

Abstract

Asphaltene samples obtained from crude processed at two Indian refineries were characterized for chemical composition and structure by nuclear magnetic resonance (NMR), X-ray diffractometry (XRD), fluorescence spectroscopic techniques, and chromatographic (column and GPC) techniques. Estimation of NMR average structural parameters were obtained by combined ¹H, NMR ¹³C, NMR DEPT-45, and QUAT pulse sequence spectral editing techniques. The macrostructure and crystalline parameters of these samples were obtained by XRD. The nature of the functional groups have been obtained by IR technique. A combined NMR and XRD parameters were used to estimate the size of average aromatic structural units. Asphaltenes from one of the crudes (ASP-A) was found to be highly pericondensed, highly substituted, and higher molecular size compared to ASP-B asphaltene molecules. The number of aromatic sheets per unit sheets are 3.7 and 2.5 in the sample ASP-A and ASP-B, respectively. Both the asphaltene molecules in the samples have periodically and systematic arrangement of aromatic sheets in the unit sheet. The number of aromatic rings per unit sheet in ASP-A and ASP-B are 6.0 and 5.0, respectively. The fluorescence spectral studies has also exhibited λ _max (the wavelength of maximum intensity) at 505 and 509 nm confirming to pericondensed higher polycondensed aromatic ring system in both the samples. The analysis of liquid chromatographic fractions of these samples show that each sample is composed of several polycondensed aromatic systems where unit sheet of ring sizes vary from 1.8 to 6.3 with varying molecular sizes. These structural parameters allowed a model structure of the asphaltenes to be constructed.     

DELAYED COKING OF HYDROTREATED REDUCED CRUDE

ABSTRACT

A laboratory coking unit was designed and constructed for an experimental study of the delayed coking process of hydrotreated Kirkuk reduced crude. The yield and analysis of coke, gases and liquid products were obtained for each experiment. The gas < C₄. and gasoline yield decrease by increasing Liquid hourly space velocity (LHSV) while the yields of kerosene and gas oil increase and no effect of LHSV on petroleum coke yield was observed, The specific gravity of gasoline, kerosene and gas oil decreases by increasing LHSV. The increase in LHSV (decrease in residence time) decreases the olefinic hydrocarbons of produced gas oil and fraction 350-450^°C. Sulfur content of produced coke and coking residue increases by increasing residence time while it changes slightly for kerosene and gas oil. By increasing the recycle ratio (RR), the yield of gas decreases while the coke yield increases. Sulfur content of gas oil and coking residue increases with an increase in the recycle ratio while it decreases for coke. Metals content of coke decreases with an increase in the recycle ratio and coke with accepted properties for aluminum anode manufacture could be produced when a recycle ratio of 1.4 was used.     

Characterization of Asphalt Fractions by NMR Spectroscopy

Abstract

Petroleum asphalt was separated into saturates, naphthalene aromatics, polar aromatics, and asphaltenes using the Corbett method. These asphalt fractions were characterized by H-1 and C-13 nuclear magnetic resonance spectroscopy (NMR). The spectra of saturates illustrate only traceable quantities of aromatic hydrogen and aromatic carbon. Naphthalene aromatics, polar aromatics, and asphaltenes all have broad bands in the aromatic regions of both H-1 and C-13 NMR spectra. These broad bands demonstrate the presence of polycondensed aromatic rings present in the structure of naphthalene aromatics, polar aromatics, and asphaltenes. Based on available literature, numerous NMR resonance bands are identified. The quantitative estimations for various kinds of protons and carbons in the asphalt fractions are compared.     

ALIPHATIC C-H BOND RESPONSES IN THE 900-700 cm−1 REGION OF THE FTIR SPECTRA OF COAL TARS

ABSTRACT

Four bituminous coals were comprehensively separated by column chromatography into a number of fractions. Four aromatic hydrocarbon fractions of each tar were analyzed by FTIR spectroscopy, and the 900-700 cm^?1 spectral region was evaluated. This spectral region was found to be composed of at least 14 separate bands, which were resolved by using self-deconvolution and curve-fitting procedures. The bands near 821 cm^?1, 791 cm^?1, and 784 cm^?1 were proposed to originate from rocking vibrations of aliphatic C-H bonds. For the tar samples with a proton aromaticity between 0.21 and 0.37, these bands account for on average 12% of the total integral intensity of the 900-700 cm^?1 region. This percentage cannot likely be neglected in a correct quantitative evaluation of the region and calculation of the aromatic hydrogen concentration. However, a correct resolution of the bands can be very difficult in the FTIR spectra of a complex material, such as coal.     

STUDY OF STRUCTURAL FEATURE OF PEAT,LIGNITE AND HUMIC ACID BY SOLID STATEl3C NMR SPECTROSCOPY

Abstract

Four low rank coals (peat and lignite) and their derived humic acids have been investigated by the^l3C CP/MAS/TOSS NMR technique. The NMR analysis indicates that the peat contains a significant amount of unaltered plant components including cellulose, hemicellulose, lignin, waxes, and resins.

Variable contact time and dipolar dephasing experiments were performed on each sample. The data from above experiments, together with normal CP/MAS integration over selected chemical shift range, were used to derive 12 parameters of carbon skeletal structure including the aromaticity.From the ratio of aromatic bridgehead carbons, f_a ^cp, to the aromatic peripheral carbons, f^cpxBp as measured by NMR, the aromatic cluster size may be estimated for each coal.     

Yield Stress of Wax Gel using Vane Method

Abstract

Wax gel formation occurs in pipelines under quiescent conditions during a scheduled or emergency shutdown of flow. Paraffinic wax precipitates from the bulk oil when oil temperature decreases below the characteristic wax precipitation temperature, while the gelling begins as the temperature decreases below the pour point. Further temperature reductions below the pour point result in the development of a stronger gel. In this study, the gel strength was measured by determining the yield stress using the vane method. The method consisted of identifying the maximum torque exerted on the sample at various temperatures. Model oils were prepared by mixing low vacuum gas oil wax, mineral oil, and kerosene. Linear increase in gel strength with decreasing temperature was observed in the measured temperature range. As the wax content increased, so did the yield strength of the gel below the solution pour point. The slope of the yield-stress versus temperature line was also steeper for the model oil containing higher amount of wax. Recovery of gel strength was also examined by aging at the same temperature and by decreasing temperatures after breaking the gel at certain temperature.     

COMPARISON OF OILS PRODUCED FROM KENTUCKY OIL SHALES BY FLUID BED AND FISCHER ASSAY RETORTING

ABSTRACT

Physical properties and chemical composition of oils produced from a master sample of the Ohio Shale by bench scale fluid bed and Fischer Assay retorting are compared. The fluid bed oil was found to have a higher nitrogen content, lower H/C ratio, more heteroaromatic and heavy hydrocarbons, higher alkene/alkane ratios, a higher naphthalene/(C₁₁ + C₁₂) ratio and a higher aromatic carbon content than the Fischer Assay oil. Since vapor phase cracking is the major source of oil loss during fluid bed retorting with coking being near zero, these results are in agreement with correlations developed for western U.S. shales. Additionally, there is evidence to suggest that under fluid bed conditions, raw shale aromatic carbon is converted to oil.     

Structural Characterization of Different Asphaltenes of Kuwaiti Origin

Abstract

Asphaltenes obtained by precipitation from crude Kuwaiti oils have been analyzed by proton magnetic resonance (¹H-NMR), carbon-13 nuclear magnetic resonance (¹³C-NMR) and Infrared (IR) spectral techniques. The molecular weight and elemental analysis were also determined. These combined analytical data were used for the characterization of these Kuwaiti oils. The asphaltenes molecular weights range from approximately 4200–6500 with an H/C ratio of 0.91–1.1 with an average 45–71% aromatic carbons. The average side chain length was of 4–6 carbons. It can also be concluded that the asphaltenes under investigation contain 5–9 sets of condensed aromatic rings joined together by bridges of alkyl chains or other hetero atoms and the average number of each of these sets of condensed aromatic rings is nearly 7. There are a number of alicyclic rings and condensed alicyclic rings in asphaltene. The IR spectra showed main molecular groups including OH, NH, SH, C=O and aliphatic and aromatic C-H′s.     

SOLVENT EXTRACTION OF PAKISTAN COALS (III) EXTRACTION AND CHARACTERIZATION OF THE EXTRACTS BY SPECTROSCOPIC TECHNIQUES

Abstract

The Makerwal coal of Pakistan gives higher extractibi1ity with Tetrahydrofuran ( THF ) as compared to Sharigh, Sor-Range and Lakhra coals. The structural characterization of Pakistan coal extracts by FT-IR spectroscopy indicates that all the extracts contained less condensed aromatic rings in comparision to their original coal.     

Gas chromatographic analyses of kerosene bioremediation displayed distinctive pattern of n-alkane degradation

Abstract

Kerosene, being one of the most commonly spilled petroleum products, needs to be removed from the polluted areas before it spreads over large habitats. Bioremediation is an environmental friendly approach for the cleanup of contaminated sites and exploits the potential of naturally occurring microbial populations or microorganisms with a known ability to degrade the contaminants. Therefore, it is important to get bacterial isolates with high kerosene degradation abilities for their potential use in kerosene bioremediation. For this reason, twenty previously identified hydrocarbon degraders were further analysed for their potential to degrade kerosene. Primary selection of kerosene degraders was done by using conventional enrichment culture containing 1% kerosene as a sole source of carbon. Gas chromatographic (GC) analyses of 17 pre-selected kerosene degraders displayed distinctive degradation pattern of n-alkanes including C₁₁-C₁₅, C₁₇ and C₁₉ fractions. The bacterial isolates Staphylococcus aureus Ba01, Delftia acidovorans Cd11, Acinetobacter calcoaceticus Fe10, Pseudomonas koreensis Hg11 and Acinetobacter johnsonii Sb01 sharing this distinctive degradation pattern displayed 70–84% degradation abilities in 21-day incubation. Among them, the isolates D. acidovorans Cd11 and A. johnsonii Sb01 with almost 81–84% degradation abilities and 0.08–0.09?mg/mL/day degradation rates showed the highest potential for kerosene bioremediation, respectively.