Characterization Of Nigerian Crude Oil Using

International Journal of Scientific Research and Engineering Studies (IJSRES) Volume 2 Issue 5, May 2015 ISSN: 2349-8862

Characterization Of Nigerian Crude Oil Using ASTM86 Test Method For Design Of Mini Refinery

Victor Adekunle Adetoro Sunday Christopher Aduloju Eton Udeme Priscilla N. Duru Adeyemi Adeniji National Engineering Design Development Institute, Nnewi, Nigeria

Abstract: Some physical and chemical properties of samples of light Nigerian crude have been measured and reported in this paper. The crude oil have also been characterized by fractional distillation; D86 method. The importance of the physicochemical properties and the significance of fractional distillation method to industrial process operations have been discussed.

I.

INTRODUCTION

Crude oil is a naturally occurring mixture, consisting predominantly of hydrocarbons with other elements such as sulphur, nitrogen, oxygen, etc. appearing in the form of organic compounds which in some cases form complexes with metals [1]. Elemental analysis of crude oil shows that it contains mainly carbon and hydrogen in the approximate ratio of six to one by weight [2]. The mixture of hydrocarbons is highly complex and the complexity increases with boiling range. The instrumental techniques of chromatography, ultraviolent and infrared spectroscopy together with mass spectrometry facilitate knowledge of the detailed hydrocarbon type composition of crude oil [3]. Over the years the chemical utilization of crude oil and its refined products has been on the increase globally. As a result concerted efforts are being made to understand its composition, structure and properties. This understanding will result in improved process conditions for improved yield and quality of products. The net effect is further enhancement of the utilization of crude oil and its products. Thus studies on crude oil and its products have utilized several analytical techniques after fractionation to aromatics and nonaromatics [4]. Mair and Rossini [5] carried out the isolation of hydrocarbons in crude oil by fractionation, crystallization, and solvent extraction as well as the analysis of the fractions. Karr www.ijsres.com

and co-workers [6] used the technique of elution chromatography for the fractionation of virgin crude oils while Crowley et al. [7] reported hydrocarbon class separation scheme for crude oil using liquid chromatography glass capillary chromatography. Some literature reports [8-13] have utilized different chromatographic techniques for separation of crude oil, crude oil fractions, or petroleum products into acid, base, neutral, saturates and aromatic fractions. In other reports, further fractionation of the aromatics into monoaromatics, diaromatics and polyaromatics were carried out [9]. The fractions were characterized using ultraviolent and infrared spectrophotometry [4], X-ray fluorescence spectrometry [3] as well as proton and carbon-13 nuclear magnetic resonance spectrometry [14-15]. The metal contents of crude oils and its products have also been determined using methods such as UV-visible spectrophotometry [16] and atomic absorption spectroscopy (ASS) method [17]. The nonmetal constituents of crude oil and crude oil products, and especially sulphur, nitrogen and their derivatives have also been studied [18-21]. These non-metals as well as the metals constitute the impurities crude oil. In this paper, the result of physical and chemical characterization of Nigerian light crude oil is presented. The crude oil sample analyzed is the Bonny light obtained from Warri Refinery and Petrochemical Company.

II. METHODOLOGY A. TEST METHODS a.

ASTM D86: This is the Standard Test Method for Distillation of Petroleum Products atAtmospheric Pressure. This test method covers the atmospheric Page 62


b.

c.

d.

distillation of petroleum products using a laboratory batch distillation unit to determine quantitatively the boiling range characteristics of such products as natural gasolines, light and middle distillates, automotive spark-ignition engine fuels, aviation gasolines, aviation turbine fuels, I-D and 2-D regular and low sulfur diesel fuels, special petroleum spirits, naphthas, white spirits, kerosines, and Grades 1 and 2 burner fuels. The test method is designed for the analysis of distillate fuels; it is not applicable to products containing appreciable quantities of residual material. This test method covers both manual and automated instruments. ASTM D 445: This is the Standard Test Method for Kinematic Viscosity of Transparent and Opaque Liquids. It covers the determination of the kinematic viscosity of liquid petroleum productsboth transparent and opaque, with the exception of Bitumens by measuring the time of flow of afixed volume of liquid at a given temperature through calibrated glass capillary instruments, using "gravityflow." ASTM D 1298: This is the Standard Practice for Density, Relative Density (Specific Gravity) or API Gravity of Crude Petroleum and Liquid Petroleum.This test method covers the laboratory determination using a glass hydrometer, of the density, relative density (specific gravity), or API gravity of crude petroleum, petroleum products, or mixtures of petroleum and nonpetroleum products normally handled as liquids, and having a Reid vapor pressure of 101.325 kPa (14.696 psi) or less. Values are measured on a hydrometer at either the reference temperature or at another convenient temperature, and readings corrected to the reference temperature by means of the Petroleum Measurement Tables; values obtained at other than the reference temperature being hydrometer readings and not density measurements. Values determined as density, relative density, or API gravity can be converted to equivalent values in the other units at alternate reference temperatures by means of the Petroleum Measurement Tables. ASTM D 2892: This is the Standard Test Method for Distillation of Crude. This test method covers the procedure for the distillation of stabilized crude petroleum to a final cut temperature of 400oCAtmospheric Equivalent Temperature (AET). It employs a fractionating column having an efficiency of 14 to 18 theoretical plates operated at a reflux ratio of 5:1. Performance criteria for the necessary equipment are specified. This Test Method offers a comprise between efficiency and time in order to facilitate the comparison of distillation data between laboratories. It can also be applied to any petroleum mixture except liquefied petroleum gases, very light naphthas, and fractions above 400oC.

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B. TEST PROCEDURE Sample collection and analysis of oil sample was carried out in line with recommended procedures of the American Society of Testing and Materials-ASTM. During sampling all glassware were rinsed properly with water and properly airdried. The wares were later rinsed with the crude oil to be sampled before the sample for analysis was collected. Samples were obtained in triplicates. Also, all the chemical reagents used in this study were of analytical reagent grade. The following physical and chemical properties of samples of crude oils were determined following well established procedures: API gravity, density, viscosity, temperature, molecular weight and Watson factor. The fractionation distillation of each sample was carried out in a distillation apparatus which consists of the distillation flask, graduated cylinder, cooling bath and heat source. After carefully introducing the crude oil into the distillation flask and making all necessary connections, heat was supplied to distill the oil. The volume of distillate fraction collected at each 25oCincrease in temperature was recorded until 370oC was reached. Then the heating of the flask was stopped to allow the condenser to drain into the receiver and the volume of distillate collected was recorded.

III. RESULTS AND DISCUSSION A. PHYSICOCHEMICAL PROPERTIES The physicochemical properties of the crude oil and its fractions are summarized in Tables1-3 and the data in Table1 show that the API gravity of the light crude is above 30owhich agreed with published data [13]. Parameter

Test Method ASTM D1298

Result API

Density Molecular (g/cm3) Weight (g) Crude oil 32 0.8364 190 Gasoline 88 0.6210 90 Naphtha 81 0.6425 106 Kerosene 48 0.7604 130 Gasoil 35 0.8186 172 Fuel oil 20 0.9016 218 Table 1: Physicochemical properties of crude oil and fractions Parameter Test Method Result ASTM D1298 Watson Factor (Crude Oil) 11.6078 Sulphur Content (WT %) 0.37 Water (Vol %) Nitrogen (ppm) 1000 Pour Point (oC) 43.0 Salt Content (PTB) 4.0 Table 2: Physicochemical properties of crude oil

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International Journal of Scientific Research and Engineering Studies (IJSRES) Volume 2 Issue 5, May 2015 ISSN: 2349-8862 Cumulative fraction

Test Method ASTM D445

Viscosity @40oC, cSt

Viscosity @100oC, cSt

Gasoline 0.9604 0.8047 Gasoline+Naphtha 0.9787 0.8974 Gasoline+Naphtha 1.1018 0.9521 +Kerosene Gasoline+Naphtha 1.3109 1.3033 +Kerosene+Gasoil Gasoline+Naphtha 1.7246 1.7040 +Kerosene+Gasoil + Fuel oil Table 3: Viscosity of fractions API gravity determines the grade or quality of crude oils. Generally, crude oil samples with API gravity greater than 31 are classified as light crude oils, those with API gravity of between 22 and 31 are classified as medium crude while those with API gravity of 20 and less are referred to as heavy crude oil. A comparison of the value of API gravity obtained for the crude oil in this study with that of API Standard [22] shows that, the crude oil obtained from Warri Refinery and Petrochemical Company is light crude oil. % sulphur content determines whether a particular crude is sweet or sour. Crude oil samples are classified as sweet if it sulphur content is less than 0.5%. Anything greater than 0.5% is termed sour. With respect to its sulphur content, the crude oil used in this study was found to be of low sulphur. This crude oil sample can thus be classified as sweet crude. Sweet crude samples are generally preferred to sour because it has less corrosion/pollution potential which leads to increase cost of production and is therefore more suited for the production of the most valuable refined products. Viscosity is a measure of internal friction of a liquid which is the reluctance of a liquid to flow. It therefore indicates the flowing ability of Crude oil from one point to another. The result of this study shows that the crude oil sample is relatively of low viscosity. Viscosity of petroleum is of importance in studying the energy loses during production. Any engineering activities including piping and pipeline construction require the knowledge of the viscosity of the crude oil to enhance transportation. Viscosity also plays an important role in reservoir simulations as well as in determining the structure of liquids. Therefore, the low viscosityobtained for the crude oil blends indicates that the sample can easily flow when transported trough pipes thus making for easy transportation. The values for water and % nitrogen contents were also appreciably low in the sample. A knowledge of water and % nitrogen contents content of any crude oil is important in the refining, purchase and sales of crude oil because corrosion problems associated with these parameters. The low water and % nitrogen contents of the crude oil sample also show that it is of high value. Pour point of a petroleum specimen is an index of the lowest temperature of its utility for certain applications. The pour point value of the sample is low and indicates that the oils can easily be utilized under low temperature conditions. www.ijsres.com

Salt content and acid number are important index for refining operations. High values of any of these parameters indicate high corrosion tendency of crude oil. The values of these parameters obtained for the crude oil sample show that it possesses very low corrosion potentials. Heavy metals are often found to be part of crude oil samples. Possible sources of trace metals in crude oil are: through incorporation and diagenesis of metal complexes of the original biological materials; through incorporation into the organic matrix during diagenesis of the biological materials in the source rocks either from clay minerals or interstitial aqueous solution; through an aqueous phase during primary and secondary migration and from formation waters or reservoirs’ rock minerals. The levels of most of the trace elements obtained in this study were generally low. This agrees with reports that light crude oil samples usually contain relatively low trace metal contents compared to the heavy crudes. The final properties of the finished products depend on the properties of the source crude as well as the process conditions and final treatments. B. FRACTIONAL DISTILLATION The experimental data from fractional distillation of the crude oil sample are also presented in Tables 4-10. The data clearly shows that the crude oil sample yielded a greater proportion of light fractions (naphtha). In a petroleum refinery the physical and chemical operations are integrated, and both atmospheric and vacuum distillation processes are involved. Thus the products are expected to be more in number and to show a wider range than obtained in this study. However, the present result show that the product distribution of atmospheric fractional distillation of crude oil is a function of the nature of the crude oil. The boiling point of the distillate fractions increases as the volume percent of the fraction increases. Moreover, as expected, Gasoil has a higher boiling point than kerosene which in turn has a higher boiling point than gasoline for all the fractions collected. Parameter Test Method Result Crude Assay ASTM D2892 Fractions Temp. Range Yield (oC) (%) Gases 370 13.0 Losses 0.8 Table 4: Fractional Distillation of crude oil Crude Test Method Result Recovery ASTM D86 Crude oil Temperature Yield (oC) (%) Page 64


Fractions Recovery Gasoline

Fractions Recovery

Naphtha

Fractions Recovery Kerosene

Fractions Recovery Gasoil

144 10 170 20 216 30 258 40 290 50 340 60 385 65 Table 5: Crude oil recovery Test Method Result ASTM D86 Temperature Yield (oC) (%) 88 20 100 40 108 50 118 60 132 70 162 80 262 90 Table 6: Gasoline recovery Test Result Method ASTM D86 Temperature Yield (%) (oC) 158 20 180 40 192 50 208 60 224 70 244 80 280 90 300 94 Table 7: Naphtha recovery Test Result Method ASTM D86 Temperature Yield (oC) (%) 158 20 180 40 192 50 208 60 224 70 244 80 280 90 300 94 Table 8: Kerosene recovery Test Method Result ASTM D86 Temperature Yield (oC) (%) 242 20 258 40 264 50 272 60 www.ijsres.com

Fractions Recovery Fuel oil

284 300 336 340 Table 9: Gasoil recovery Test Method Result ASTM D86 Temperature (oC) 302 322 338 352 372 Table 10: Fuel oil recovery

70 80 90 92

Yield (%) 20 40 50 60 64

Figure 1: Variation of yield of fractions against temperature

IV. CONCLUSION The result of this study has shown that the crude oil sample obtained from Warri Refinery and Petrochemical Company contains low level of sulphur. The sample is also of light crude oil category grade. Therefore, it can be classified as light-sweet crude oil. The low values of viscosity obtained for the sample indicate that, this oil sample can flow easily. This makes it easy for transportation through pipelines without the necessary addition of diluents at regular intervals often associated with heavy crude oil samples. On the whole, the low levels % of water, salt contents and pour point observed for the oil sample coupled with other physiochemical parameters show that, the crude oil has characteristics which enhance its preferences inthe oil market and refinery operations.

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