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Extraction of Xylene and Naphthalene From Crude Oil

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‫‪Amel A Nimer,, Abdelshakour A. Mohamed and Ali A. Rabah‬‬ ‫‪NILE BLEND CRUDE OIL: WAX SEPARATION USING‬‬ ‫‪MEK-TOLUENE MIXTURES‬‬ ‫* ‪Amel A Nimer, Abdelshakour A. Mohamed and Ali A. Rabah‬‬ ‫‪Department of Chemical Engineering, University of Khartoum‬‬ ‫‪P.O. Box 321, Khartoum, Sudan‬‬ ‫اﻟﺨﻼﺻـﺔ:‬ ‫ﺗﻘﺪم هﺬﻩ اﻟﻮرﻗﺔ اﻟﻈﺮوف اﻟﺘﺸﻐﻴﻠﻴﺔ ﻹﻧﺘﺎج اﻟﺸﻤﻊ ﻣﻦ ﻣﺰﻳﺞ اﻟﻨﻴﻞ , وﻳﻌﺪ اﻟﺰﻳﺖ اﻟﺴﻮداﻧﻲ زﻳﺘﺎ ﺣﻠﻮا ﺑﻨﺴﺒﺔ ﻋﺎﻟﻴﺔ ﻣﻦ ﻣﺤﺘﻮى اﻟﺸﻤﻊ )% 78.52‬ ‫ً‬ ‫ً‬ ‫ﺑﺎﻟﻮزن(. وﻗﺪ ﺗﻢ ﻋﻤﻞ ﻃﺮﻳﻘﺔ اﺳﺘﺨﺪام اﻟﻤﺬﻳﺐ ﺑﺎﺳﺘﺨﺪام ﺧﻠﻴﻂ اﻟﺘﻮ
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  Amel A Nimer,, Abdelshakour A. Mohamed and Ali A. Rabah    October 2010    The Arabian Journal for Science and Engineering, Volume 35, Number 2B    17 NILE BLEND CRUDE OIL: WAX SEPARATION USINGMEK-TOLUENE MIXTURES Amel A Nimer, Abdelshakour A. Mohamed and Ali A. Rabah *    Department of Chemical Engineering, University of KhartoumP.O. Box 321, Khartoum, Sudan   :  , %)25.87 (. )MEK .(  )28-70C( )5-30( )16:132:1( )50-100%MEK .(  %9275V%MEK  50C20  20:117C 0  . ,,,,, ,  . )C 10 -C 16 ( %6 C45+%10.   _______________  *Corresponding Author:E-mail:rabahss@hotmail.com   ________________________________________________________________________________________________________ Paper Received May 14, 2009; Paper Revised September 10, 2009; Paper Accepted October 12, 2009  Amel A Nimer,, Abdelshakour A. Mohamed and Ali A. Rabah    The Arabian Journal for Science and Engineering, Volume 35, Number 2B October 2010    18 ABSTRACT This paper presents the operational conditions for wax production from Nile Blend; a Sudanese oil, characterizedas sweet oil with a high level of wax content (25.87 wt%). The method of solvent extraction was employed using aMethyl Ethyl Ketone (MEK)- Toluene mixture as a solvent. The study covered a wide range of mixing temperatures(28 to 70 o C) and residence time (5 to 30 minutes), solvent to oil ratio (16:1 to 32:1), and solvent compositions (50-100%MEK). The result showed that 92% of the wax in the crude can be extracted with a mixture of 75v% MEK at amixing temperature of 50 o C, residence time of 20 minutes, and solvent to oil ratio of 20:1 at a filtration temperatureof -17 o C. The wax produced is characterized by a slightly greasy feel and is soluble in Naphtha, Toluene, Xylene,Kerosene, Benzene, Ethyl Alcohol, Acetone, and Carbon Tetra Chloride. The gas chromography analysis showedthat the light products ( C  10 -C  16  ) constitute 6% of the produced wax and C  45+ is 10%.  Key words : Nile blend, dewaxing, MEK-Toluene mixtures  Amel A Nimer,, Abdelshakour A. Mohamed and Ali A. Rabah    October 2010    The Arabian Journal for Science and Engineering, Volume 35, Number 2B    19 NILE BLEND CRUDE OIL: WAX SEPARATION USING MEK-TOLUENE MIXTURES 1. INTRODUCTION On delivery to the refinery, the storage of waxy crude stream is difficult as it produces massive gel and sludge inthe storage tank [1]. This raises pumping expenses and cleaning costs. To overcome this problem, chemicaladditives, known as pour point depressants (PPD), are state-of-the-art practice. Recent studies have indicated thatthese chemicals are the prime cause of corrosion in equipment and piping systems of the refinery [2]. If the waxcould be removed prior to shipment to the internal refinery process, the problems of accumulation in storage and piping system corrosion caused by chemical additives could be minimized. These are the justifications of this work.Due to the fact that the commercial production of Nile Blend started in the late 1990’s, the available literatureregarding its thermodynamic characteristics are extremely limited. On the other hand, the dewaxing process ismostly aimed at the feedstock of lube oil, the bottom product of atmospheric or vacuum distillate. Hence, theavailable literature on dewaxing is mostly concerned with dewaxing of lube oil feedstock.There are mainly two different methods for wax removal: solvent and catalytic. Solvent dewaxing is moreselective for removing both heavier normal and non-normal hydrocarbons. Catalytic dewaxing removes the normal paraffins more evenly over the boiling range, while the light non-normal hydrocarbon are removed more selectively.Oil obtained from solvent dewaxing has higher yield and viscosity index than that of catalytic dewaxing [3]. Theremoval of wax from oil by means of solvent extraction involves mixing crude oil with solvent to form a solutionfollowed by cooling (chilling) the mixture (oil + solvent + wax) to form wax-crystal-lattice and, finally, separatingthe crystal lattice from the solution. The dewaxing is influenced by many parameters such as type of solvents,cooling rate, and temperature and solvent to oil ratio.Several pure solvents or mixtures of solvents have been in use for solvent dewaxing. These includeMethylisobutylketone (MIBK), Dichloromethane, Trichlorethylene, and a mixture of Methyl Ethyl Ketone (MEK)and Toluene and MEK/Benzene. Pure Toluene is an excellent oil solvent, and, has good solvent power for wax aswell. If it is used alone, a tight lattice of wax will form that hinders filtration [4]. In contrast, MEK shows lowsolvent power to paraffinic compound ( i.e., low selectivity) and as such it precipitates the wax very well. Previousstudies on Arabian   light oil indicated that optimum wax separation occurs at MEK-toluene solvent compositionranges from 40–75 v% MEK [4, 5]. Dewaxing of West Siberian   crude with MEK-Toluene mixtures indicated thatwith increasing MEK in the mixture, the filtration time increases ( i.e., the filtration viscosity increases) and the oilyield decreases. With increasing MEK, the viscosity of the oil index increases, but the solid point remains constant[6].In solvent dewaxing, most of the energy consumption goes into pumping and regeneration of solvent. Therefore,the current trend is to use lower solvent dilution ratios and smaller amounts of solvent in washing the precipitate(wax cake) on filters. At the other hand, an increase in solvent to oil ratio will enhance the filtration rate becausesolvent prompts the crystal growth and lowers the viscosity of the mixture (oil + solvent). It also increases thedewaxed oil yield and decreases the oil content in the wax yield. The previous literature indicates that the solvent tooil ratio is between 16:1 to 32:1 on mass basis [7].The rate of cooling (high or low) has a strong influence on crystal formation and particle characteristic. For example, a high cooling rate is found to promote the formation of small crystals but they are of the needle type thatclogs the filter. Previous experiments showed that the optimum cooling rate varies between 0.56–4.4 o C per minutedepending on the type of crude oil. The chilling or filtration temperature is usually in the order of -20 o C [8].Due to the fact that crude oil differs from place to place and as such the operation conditions for wax extractionvaries from crude to crude, the aim of this work is to study the operational conditions for wax production from NileBlend. The influence of solvent composition, mixing temperature, residence time, and solvent to oil ratio on waxextraction will be studied. 2. MATERIALS AND METHODS It has to be mentioned that all the experimental analyses were performed at the Central Petroleum Laboratory(CPL), Ministry of Energy and Mining, Sudan. The level of accuracy of the equipment and apparatus hereinmentioned are supplied by CPL. 2.1. Materials Two liters of Nile Blend, a grade of Sudanese crude oil, was provided by the Ministry of Energy and Mining.Table 1 shows the result of the analysis of this sample. The analysis was performed in CPL using standard methods  Amel A Nimer,, Abdelshakour A. Mohamed and Ali A. Rabah    The Arabian Journal for Science and Engineering, Volume 35, Number 2B October 2010    20 as indicated in the said table. Table 2 shows the properties of MEK and Toluene used in this work. These are themanufacturers’ data. The manufacturer for both chemicals is Fischer Scientific, UK. Table 1. Properties of Nile BlendProperty Test Method Unit Value Salt Content ASTM D 3230 mgNaCl/L 9.12Density at 15 o C ASTM D 5002 kg/m 3 850.4Wax Content UOP 46 wt% 25.87Flash Point IP 170 o C 21.5Pour Point ASTM D97 o C 33.0Kinematic Viscosity at 50 o C ASTM D 445 mm 2 / s 22.64Kinematic Viscosity at 80 o C ASTM D 445 mm 2 / s 8.884Water Content by Distillation ASTM D 4006 v% 0.09Ash content ASTM D 482 wt% 0.043Asphaltene Content IP 143 wt% 0.11Sulfur Content ASTM D4294 wt% 0.051 Table 2. Properties of MEK and Toluene (Manufacturer 's Data)Property MEK Toluene Molecular Formula C 4 H 8 O C 7 H 8  Molecular Weight 72 92.1Boiling Point o C 79.6 111Melting Point o C -86 95Flash Point o C -6 4Vapor Pressure at 20 o C (mmHg) 77.5 22Vapor Density 15 o C 2.42 3.14Lower Explosive Limit % 2 1.2Upper Explosive Limit % 10 77Solubility in Water at 20 o C 27.5% Nearly InsolubleManufacturer Fischer Scientific, UK Fischer Scientific, UK Purity w% 98 98 2.2. Experimental Apparatus Figure 1 shows a schematic presentation of the dewaxing processes. These include mixing and heating, cooling(chilling), filtration, and evaporation. The mixing and heating were carried out using a magnetic stirrer with ahotplate. It was type Heidolph Hei-Tec Magnetic Stirrers manufactured by Brinkmann and Eppendorf. It has a speedup to 1000 rpm. The level of uncertainty of the rotational speed is 1% of the maximum speed. The chiller is athermostat type FP50 (HD) manufactured by Julabo (Germany). The thermostat employes ethylene glycol and iscapable of producing cooling and heating levels in the range of -25 to 50 o C. Its highly accurate PID temperaturecontroller with digital readout has an accuracy of 0.02K. The filtration system consists of a Gooch crucible placed ona flask and the flask is connected to a vacuum pump. On top of the Gooch crucible glass, wool was placed. Thevacuum pump is type N 035 AN and is capable of producing a vacuum pressure of 10 -4 mbar. A rotary evaporator type RE 100 (BIBBY) was used to evaporate the solvent and Naphtha from wax. The heating is provided using water  bath type RE 100B. Mixer and heaterChillerFiltrationCrude oilSolventOil + solvent +traces (wax)EvaporatorNaphtha + traces of solventWax + traces (oil) Naphtha   Figure 1: Schematic of experimental setup
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