Determination of Absorption and Fluorescence Spectrum of Iraqi Crude Oil
Naseer Mahdi Hadi1, *, Ayad Z. Mohammed2, Fareed F. Rasheed2, Shahad Imad Younis2
1Ministry of Science and Technology, Materials Research Directorate, Laser & Electro-Optics Research Center, Baghdad, Iraq
2Laser & Optoelectronics Engineering Department, University of Technology, Baghdad, Iraq
To cite this article:
Naseer Mahdi Hadi, Ayad Z. Mohammed, Fareed F. Rasheed, Shahad Imad Younis. Determination of Absorption and Fluorescence Spectrum of Iraqi Crude Oil. American Journal of Physics and Applications. Vol. 4, No. 3, 2016, pp. 78-83. doi: 10.11648/j.ajpa.20160403.12
Received: February 13, 2016; Accepted: May 17, 2016; Published: June 7, 2016
Abstract: The fluorescence spectroscopy (FS) is increasingly used in petroleum technology due the availability of better optical detection techniques, because FS offers high sensitivity, good diagnostic potential, and relatively simple instrumentation. Absorption and fluorescence spectrum of crude oil was studied at room temperature using optical path cuvette 1 cm. In this work, the absorption spectra were scanned (190-1100) nm while the emission spectra were obtained at different excitation wavelengths (266, 337, 420, and 488) nm. Crude oil was diluted by absolute ethanol to prepare different concentrations of crude oil. Ethanol as a solvent was used to dilute crude oil to obtain a solution transparent and the light could be transmitted. This work considers as an additional spectroscopic tool to develop into a fast responsive system for charchtrize the crude oil.
Keywords: Fluorescence Spectroscopy, Crude Oil, UV-Vis Spectroscopy
Crude oil is a simply unprocessed oil found deep beneath the earth’s surface. It can range in color from clear to black and can be found as a liquid or solid. Overall properties of crude oil are dependent upon their chemical composition and structure. Generally, all crude oil is made up of hydrocarbon compounds. The main hydrocarbons in crude oil are aliphatic, aromatic, and asphaltenic compounds .
Methods of optical absorption spectroscopy are increasingly being used for the analysis of crude oil because they offer high speed, low cost, non-contact, non-destructive testing options, desirable for environmental protection, and process control, or oil exploration purposes. The absorption behavior of crude oil strongly depends on the wavelength range employed. In particular, UV-Vis absorption of crude oils is due to the presence of a wide range of cyclic aromatic compounds, including asphaltenes, with the intensity and the spectral properties of this absorption being directly related to chemical composition .
Fluorescence has been extensively used in the petroleum industry for analysis and classification of different crude oil samples. This field attempt to connect typical fluorescence parameters (intensity, emission wavelength, and lifetime) to physical characteristics of the crude oil such as chemical composition and density (API gravity) . Stelmaszewski [4, 5] study the identification of oil by fluorescence method. Also, he studied the application of fluorescence in detection of petroleum pollutants, determination of oil in water concentration, determination of particular polycyclic aromatic compounds, and identification of oil contaminants. Ryder used steady state and time resolved fluorescence method to study emission spectrum of petroleum . Steffens studied the fluorescence characteristics of solutions containing fixed amount of Nujol pure oil and different concentrations of Brazilian crude oil . Evdokimov and Losev, analyze a possibility of UVVA characterization for fingerprinting of various types of crude oils and describe some effects of crude oil dilution on optical absorbance . Goncalves emploied absorption and fluorescence techniques to study aggregation process in asphaltenes solutions .
Ethanol C2H5OH, (also called ethyl alcohol), is a volatile, colorless liquid. Nearly all the ethanol used industrially is a mixture of 95% ethanol and 5% water, which is known simply as 95% alcohol. Although pure ethyl alcohol (known as absolute alcohol) is available, it is much more expensive and is used only when definitely required . When crude oil and ethanol mixed under vigorous shacking, ethanol extract hydrocarbons from crud oil while the heavy components remain at the bottom.
For the mixture, absorption in the visible range are well known and less intense than crude oil. Moreover using excitation in the visible range it is possible to access only crude oil absorption and consequently only crude oil emission. The possibility of using fluorescence to detect crude oil was reported in the early 1970s .
In this work, absorption and fluorescence spectra at different excitation wavelengths of different concentrations of Al- Nassiiya crude oil were mesared and identified.
2. Materials and Methods
The crude oil samples were obtained from Al- Nassiriya Oil Field to perform fluorescence and absorption measurements. It was necessary to extract crude oil to obtain a transparent solution to the incident light and for this reason ethanol was chosen as a solvent. Five crude oil samples were diluted with ethanol for the measurements, the different dilution are shown inTable 1. The chemical analysis of Al-Nassiriya oil was carried out by Oil Research and Development Center/Ministry of Oil in Iraq; the most salient data is shown in Table 2.
|Sample||Ethanol (ml)||Crude Oil (ml)||Total Volume (ml)||Concentration v%|
|S. No||Properties||Results||ASTM test method|
|1||Kin. Viscosity, cSt, 100° F (37.8°C), min||4.369||D445|
|2||Kin. Viscosity, cSt, 100° F (37.8°C), min||D445|
|3||Kin. Viscosity, cSt, 210° F (98.9°C), min||3.855||D445|
|4||Specific Gravity, 60° F (15.6°C), max||0.888||D1298|
|5||Flash point, (°C), min||22||D93|
|6||Distillation Temp. 90% Point, (°C), max||370||D86|
|7||Pour point, (°C), max||-12||D97|
|8||Cold Filter Plugging Point||-18||D6371|
|9||Ash, ppmw, max Wt%||2.2 Wi %||D482|
|10||Trace Metal Contaminants, ppmw, max||Total= 17.93||See Note below|
|11||Sodium plus Potassium||Na= 0.51 ppm|
|Ca = 4.2 ppm|
|K= 4 ppm|
|13||Vanadium (untreated)||0.57 ppm|
|14||Vanadium (treated 3/1 Wt. ratio Mg/V)||0.91|
|16||Other Trace Metals above 5 ppmw||Fe=7.2ppm|
|Se =17.9 ppm|
|Ni =0.02 ppm|
|Cr =0.002 ppm|
|Al =0.03 ppm|
|Zn =1.2 ppm|
|Na =0.51 ppm|
|K =4 ppm|
|Cd =0.15 ppm|
|Co =0.003 ppm|
|Mn =0.05 ppm|
|17||Filterable Dirt, mg/ 100ml, max||6.8||D2276|
|18||Water & Sediment, Vol. %, max||0.0||D2709/D1796|
|19||Water Content, Vol. %, max||0.0||D95|
|20||Thermal Stability, Tube No., max||D1661|
|21||Fuel Compatibility, Table No., max. (50/50 mix with second fuel)||D1661|
|22||Wax content, Wt%||2.2||D524/D189|
|Wax Melting Point, °F|
|Carbon Residue Wt % (10% Bottoms) max|
|Direct Pressure Atomization|
|Carbon residue, Wt. % (100% sample) max Air Atomization, Low presssure||D 524/D 189|
|Carbon Residue, Wt % (100% sample), Air Atomization, High Pressure||70.46%|
|23||Gross Heat of combustion, Btu/lb||D 4809/D 240|
|24||Distillation range (Not no Residuals)||10%||D 86|
|25||Sulfur, Wt. % max||2.1%||D 129 / D 4294|
|26||Nitrogen, Wt. %, max||0.49||D 5291|
|27||Total ash ppm w, max.||29.53||D 482|
|28||Filterable dirt mg/100 ml||6.8||D 5452 / D 2276|
|29||Reid vapor pressure (RVP) At 37.8°C||2.5 psi||Relevant standard D323|
|30||Asphaltene W %||2.6||Relevant standard|
UV-Vis double beam PC scanning spectrophotometer was used for all absorbance measurements. All measurements were made at room temperature. Samples were analyzed in reduced volume by using 1 cm (1.5 mL total) quartz cuvette with ethanol blank in the reference position.
Varian Cary Eclipse fluorescence spectrophotometer was used for emission measurements. Fluorescence is measured using an excitation source placed at 90o to the detector. Excitation radiation is provided by a Xenon flash lamp. The Xenon flash lamp flashes up to 80 times per second and has a pulse width of approximately 2 to 3 microseconds. This light is then focused through a lens onto the excitation entry slit, then passes through an excitation monochrometer and into the sample. The resulting fluorescence passes through an emission monochrometer and is detected by a photomultiplier.
4.1. Absorption Measurements
In Fig. 1, the absorption of ethanol was taken in order to study the spectrum of the solvent. Ethanol has an absorption band at 337 nm. The absorption spectrum of 16.6% crude oil in ethanol is shown in Fig. 2. The spectrum exhibits a maximum absorbance around 400 nm and a broad band with more than 100 nm. This represents the numerous of hydrocarbon compounds in the crude oil. The absorbance at ~ 400 nm related to n-ᴫ* transition indicated the double bound components in the crude oil. Figure 2 also shows the comparison between the spectra of ethanol and 16.6% crude oil. By looking to the intensity of absorbance, it is shown that the spectrum of ethanol is negligible compare to crude oil. Figure 3 shows absorption spectra of different diluted-samples of crude oil. More dilution led to obtain higher absorbance since more light can be transmitted. However, the absorbance spectrum does not change at high concentration of crude oil (> 28.5%). For that, diluted samples less than 16.6% are preferred to study and characterize the crude oil.
4.2. Fluorescence Measurements
Figure 4 shows the fluorescence spectra of diluted crude oil excited at 266 nm. In this case, the emission bands around 515 nm were appeared, the emission band decrease with the increase of oil concentration.
In contrast to absorbance study, the increase in oil concentration show a decrease in the emission intensity due to decreasing in the light penetration.
Fig. 5 shows the fluorescence spectra of diluted oil excited at 337 nm. In this case the emission band around 515 nm can be observed. A blue shift of 10 nm was occurred at concentration < 37.5% comparing to figure 1. This could be related to the effect of polar solvent (ethanol).
Figures 6 and 7 show fluorescence spectra of diluted oil excited at 420 and 488 nm respectively, flourecence spectra appear around 480 and 525 nm respectively, which decrease with the increase in oil concentration. In figure 6, a blue shift of 25 nm was occurred compare to figure 4 and 5. This is in contrast of other researcher [10, 11]. On other hand, figure 7 shows a red shift of 10 nm was appeared when the oil excited at 488 nm compared to 337 and 226 nm.
Energy transfer process is responsible for long wavelength shift and broadening in spectral band emission. Simultaneously a quenching process reduces emission intensity, the same effect was observed by other authors using solvents as benzene, cyclohexane and n-heptane .
Figure 8 shows the fluorescence spectra at 226, 377, 420 and 488 nm for different oil concentrations. The samples A to E has the same behavior when excited at 266, 337, 420 and 488 nm.
Absorption and fluorescence characteristics of crude oil were studied, ethanol was used to extract and dilut the crude oil for light penetration. Absorption spectra of crude oil are occurred between 320 to 465 nm at different concentration of oil.
Crude oil excited using ultraviolet wavelengths emitted in the visible wavelength, while exited the samples in the visible wavelength resulting fluorescence in the visible range with longer wavelength.
In general, due to low absorption of crude oil in the ultraviolet range, the fluorescence intensity is very low. While the high absorption in the visible range causing an increase in the fluorescence intensity. When the oil concentration increases a reduction in the fluorescence occur due to the effect of quenching particles.
We acknowledge Dr. Faleh Abed Hassan and Mr. Amer for their help in preparing the extracted oil, and our thank also goes to Dr. Azhar A. Kamel for her very careful review of our paper (all of them at Ministry of Science and Technology, Materials Research Directorate, Baghdad, Iraq).