Abdelrahman H. Hegazi

Application of gas chromatography with atomic emission detection to the geochemical investigation of polycyclic aromatic sulfur heterocycles in Egyptian crude oils

Twelve crude oils from a number of producing wells in the Gulf of Suez and Western Desert, Egypt were characterized by a variety of saturate biomarker compositions. The biomarker distribution clearly grouped the Gulf of Suez oils into two source-related types but revealed significant differences among the Western Desert oils. The oils were fractionated into saturates, mono- and polyaromatics; and the distribution of polycyclic aromatic sulfur heterocycles (PASH) in the polyaromatics fraction was investigated by gas chromatography (GC) with atomic emission detector (AED) in the carbon- and sulfur-selective modes. This makes possible the evaluation of the distribution patterns of PASHs even in cases where their relative abundance is low. The thiophenic distribution fingerprints were utilized for oil/oil correlations. Significant differences in the relative abundance of benzothiophenes and dibenzothiophenes were obvious between the Gulf of Suez and Western Desert oils. Moreover, the PASH pattern distinguished between oils derived from carbonate and siliciclastic source rocks. Maturity parameters based upon methyldibenzothiophene isomers were found consistent with other maturity-dependent saturate biomarkers.

High-molecular weight sulfur-containing aromatics refractory to weathering as determined by Fourier transform ion cyclotron resonance mass spectrometry

Biomarkers and low-molecular weight polyaromatic compounds have been extensively studied for their fate in the environment. They are used for oil spill source identification and monitoring of weathering and degradation processes. However, in some cases, the absence or presence of very low concentration of such components restricts the access of information to spill source. Here we followed the resistance of high-molecular weight sulfur-containing aromatics to the simulated weathering condition of North Sea crude oil by ultra high-resolution Fourier transform ion cyclotron resonance mass spectrometry. The sulfur aromatics in North Sea crude having double bond equivalents (DBE) from 6 to 14 with a mass range 188-674Da were less influenced even after 6 months artificial weathering. Moreover, the ratio of dibenzothiophenes (DBE 9)/naphthenodibenzothiophenes (DBE 10) was 1.30 and 1.36 in crude oil and 6 months weathered sample, respectively reflecting its weathering stability. It also showed some differences within other oils. Hence, this ratio can be used as a marker of the studied crude and accordingly may be applied for spilled oil source identification in such instances where the light components have already been lost due to environmental influences.

Characterization of polycyclic aromatic sulfur heterocycles for source identification

There are chemical compound classes, which are used as markers for different properties, reflecting the complexity of crude oil. Among these are the polycyclic aromatic sulfur heterocycles (PASHs), which play a major role among the constituents of petroleum and its refined products. This chapter provides recommendations that are directed particularly toward the characterization of PASHs for forensic purposes of any petroleum-derived pollutant that is likely to be encountered mainly in the marine environment and that arrived there through accident or oversight. Photo oxidation affects the aromatic compounds in crude oil and converts them to polar species of higher aqueous solubility. To identify the PASHs in environmental samples, the extract (or oil recovery) must not only be isolated from its particular matrix, but requires separation into specific fractions. Sulfur-selective detectors have not found much prominence in forensic studies where the mass selective detector is preferentially used, probably because the PASHs can be determined together with many other classes of compounds in one chromatographic run. Despite the fact that they are present in easily measured concentrations using routinely available techniques, some analytical quality considerations must not be overlooked.

Weathering trend characterization of medium-molecular weight polycyclic aromatic disulfur heterocycles by Fourier transform ion cyclotron resonance mass spectrometry.

Different weathering factors act to change petroleum composition once it is spilled into the environment. n-Alkanes, biomarkers, low-molecular weight polyaromatic hydrocarbons and sulfur heterocycles compositional changing in the environment have been extensively studied by different researchers and many parameters have been used for oil source identification and monitoring of weathering and biological degradation processes. In this work, we studied the fate of medium-molecular weight polycyclic aromatic disulfur heterocycles (PAS2Hs), up to ca. 900Da, of artificially weathered Flotta North Sea crude oil by ultra high-resolution Fourier transform ion cyclotron resonance mass spectrometry. It was found that PAS2Hs in studied crude oil having double bond equivalents (DBE) from 5 to 8 with a mass range from ca 316 to 582Da were less influenced even after six months artificial weathering experiment. However, compounds having DBEs 12, 11 and 10 were depleted after two, four and six months weathering, respectively. In addition, DBE 9 series was more susceptible to weathering than those of DBE 7 and 8.

Utilization of GC/AED for Investigating the Effect of Maturity on the Distribution of Thiophenic Compounds in Egyptian Crude Oils

The polyaromatic compositions of 12 Egyptian crude oil samples from the Western Desert and Gulf of Suez regions were analyzed using gas chromatography in conjunction with sulfur-selective atomic emission detection. The results show the variation in distributions of benzothiophenes and dibenzothiophenes in oils with different maturity levels. The ratio of benzothiophenes to dibenzothiophenes has been applied successfully as tool to evaluate maturity changes where it correlates well with other maturity parameters. A cross-plot of benzothiophenes/dibenzothiophenes versus isoprenoid/n-alkane ratios consistently classified oils according to their maturity rank.

Polycyclic aromatic sulfur heterocycles as source diagnostics of petroleum pollutants in the marine environment

Source identification of petroleum pollutants in the marine environment is a very difficult but important task for both environmentalists and governments and many markers are used to reach this goal. Among these are the polycyclic aromatic sulfur heterocycles (PASHs) that are presented here. This chapter discusses sulfur compounds in crude oil and petroleum products, the changes in PASH patterns upon treatment of petroleum in refineries, the stability of these compounds in the marine environment, and the analytical methods and techniques used for petroleum PASH analysis. The chapter focuses on how PASHs can be used both as source and weathering markers in spilled petroleum pollutant source identification.

Environmentally weathered residues source diagnostic by high-molecular-weight polycyclic aromatic sulphur heterocycles

ABSTRACT High-molecular-weight polycyclic aromatic sulphur heterocycles (HMPASH) were applied in a forensic chemical analysis to identify the source(s) of environmentally weathered residues polluting the beaches of the Mediterranean city of Alexandria, Egypt, and to assess their weathering trends. The HMPASH were investigated by Fourier transform ion cyclotron resonance mass spectrometry in residues and an Egyptian crude as a possible source oil. The dibenzothiophenes/naphthenodibenzothiophenes (DBE 9/DBE 10) parameter indicated that two studied residues were likely to have originated from Egyptian crude oils, whereas the third residue could have had a foreign source. The residues displayed different stages of weathering. HMPASH having double bond equivalent (DBE) 1–5 were more influenced by weathering processes than those having DBE 6–17, probably because they are aliphatic sulphides and not aromatic compounds.

Role of non-hydrocarbon constituents in crude oils correlation and heavy fractions processing studies

Eleven crude oils from the Gulf of Suez and Western Desert of Egypt have been used for the geochemical study. They have been analyzed for their metals, nitrogen and sulfur contents. Application of geochemical markers based upon these constituents has shown that crude oils could be correlated or differentiated according to their geologic age. The V/Ni, Ni/S, V/N, Ni/N, and S/N markers were almost uniform in Miocene oils, revealing the same origin, yet showing marked differences in Cretaceous crude oils reflecting varying degrees of their maturity, source materials, depositional environment and migrational history. The significance of analyzing the non-hydrocarbon constituents of the heavy petroleum fractions were extended to protecting the catalyst used in cracking processes. The results showed that trace metals and nitrogen contents are within the permissible limits in gas and diesel oils yet they are much beyond those limits in the heavier fractions.

The Improvement of the Quality of Raffinate Obtained from Solvent Extraction of Lubricating Oils

Abstract Vacuum distillates of an Egyptian crude oil were subjected to solvent extraction process applying N-methyl-2-pyrrolidone (NMP) and furfural as dearomatization solvents. The study shows that the extraction solvent together with the temperature and solvent-to-oil ratio have a significant effect on the yield and quality of produced lubricating oils. The optimum temperature for extracting light waxy distillates with NMP is 55°C at the solvent-to-feed ratio 2:1. These conditions are appropriate to remove the major portion of aromatics from the raffinate. The apparent activation energy (Ea), enthalpy (ΔH*), entropy (ΔS*), and free energy of activation (ΔG*) were calculated for the solvent dearomatization process.