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Demetalation methods were applied on Heavy Fuel Oil (HFO), Vacuum Residue (VR), Heavy Crude Oil (HCO) and Asphaltene samples. HFO, VR, and HCO were taken from National Refinery Limited, Pakistan. Asphaltenes were precipitated from HFO, VR and HCO by a method as described in detail in this chapter.
HEAVY FUEL OIL (HFO) OR PETROLEUM DISTILLATION RESIDUE (PDR)
Black, viscous, residual material remaining as the result of refinery distillation of crude oil either alone or in blend with light components, having 20 to 70 carbon atom chains and which is used for thermal power plant, marine diesel engine operation, and various industrial process. In USA classification of Fuel oil it is named No.6 fuel oil and class H in United Kingdom. It is also called Residual Fuel Oil, Furnace Oils, Petroleum Distillation Residue or only Fuel Oil . Characteristics of Heavy Fuel oil are specified in British Standard BS2869: 2006. Specification of Heavy Fuel Oil are summarized in Table 7.1.
VACUUM RESIDUE (VR)
After extracting Lubricating Oil and wax from Distillation Residue or Heavy Fuel Oil by Distillation under vacuum, high boiling point residue called Vacuum Residue is left behind. It has more Asphaltene and metal content then HFO and hard to flow.
HEAVY PAKISTANI CRUDE OIL (HPCO)
Crude oil is extracted from the ground, on land or under the oceans. It contains a mixture of hydrocarbon compounds and relatively small quantities of other materials such as oxygen, nitrogen, and sulphur compounds, and salt and water .
Low API gravity (Less then 20) or high specific gravity (more then 0.933) crude oils are classified as Heavy Crude Oil (HCO). This mostly results from crude oil getting degraded by being exposed to bacteria, water or air resulting in the loss of its lighter fractions while leaving behind its heavier fractions . Chak Naurang and Toot field of Punjab province of Pakistan having heavy crude oil. Propertes of HPCO are summarized in Table 7.2.
CONDENSATE PAKISTANI CRUDE OIL (CPCO)
Condensate Crude Oil is a low viscosity, High API gravity and Low density crude oil. It is obtained by the condensation of hydrocarbon vapors from gas fields . Balochistan Province of Pakistan is rich with gas and Condensate Pakistani Crude Oil. Detailed properties are given in Table 7.3.
Asphaltenes are molecular substances that are found in crude oil, along with resins, aromatic hydrocarbons, and alkanes. Asphaltenes consist primarily of carbon, hydrogen, nitrogen, oxygen, and sulfur, as well as trace amounts of vanadium and nickel. The C:H ratio is approximately 1:1.2, depending on the asphaltene source. Asphaltenes are defined operationally as the n-heptane (C7H16)-insoluble, toluene (C6H5CH3)-soluble component of a carbonaceous material such as crude oil, bitumen or coal. Asphaltenes have been shown to have a distribution of molecular masses in the range of 400 u to 1500 u with a maximum around 750 u .
REACTIONS, PROCEDURES AND METHODOLOGY
Research and industrial practice literature concerning the removal of nickel and vanadium from petroleum and its fractions were reviewed and arranged into groups as follows:
1. Processes employing hydrocarbon (non-polar) solvents, used to modify the oily matrix solubility parameter in such a way that asphaltenes is separated. Because a fraction of total metals present are associated to asphaltenes, deasphaltation implies partial demetalation.
2. Processes using polar solvents, scarcely miscible with petroleum and able to selectively extract from its organo-metallic complexes of heteroatomic legends (e.g. metalloporphyrins).
3. Processes not based on molecular phase equilibria like i) and ii) but on the formation, by contact with aqueous solutions, of a separate, colloidally stabilized phase. Either surface-active agents were added or the surface activity of substances naturally occurring in petroleum is promoted.
4. Processes based on extraction with chemical reaction (oxidation, chelation) ion exchange between organometallic species in petroleum and legends in solution of non-miscible media.
5. Physical methods like distillation and centrifuge.
Some chemical demetalation methods were tested on petroleum distillation residue and asphaltene; most metal containing compounds are concentrated in the asphaltene and study of demetalation of asphaltene can apply on crude oils, residues and other petroleum products.
Demetalation by centrifuge method is largely used for the removal of sodium contents in diesel engine operation in power plants and ships; therefore this method is included in the study.
Effect of light on demetalation was tested by keeping the mixture of toluene, HFO and hydrochloric acid in a ratio of 10:85:5 in an open area for 7 days in the month of June. Environment was clear for most of the days and temperature was between 32 °C to 38 °C. Same mixture was also kept in dark and analyzed vanadium and nickel contents in both solution.
Alfa Laval solids retaining centrifugal separators with purifier chemical were used for separating water and particulate contamination in fuel oil. Separation took place in a solids-retaining bowl, the fuel oil was fed into the separator through the center and it was separated by centrifugal force into two phases. The heaviest phase (sludge and water) was forced outwards to the perimeter of the centrifuge bowl. The sodium, vanadium and nickel contents in residue (original, and after centrifugal separation) were determined by ICP and percent removal was calculated.
The viscosity of feed (HFO) was maintained 20cSt through temperature. RPM of centrifuges were fixed at 7500.
Analytical grade Ethyleacetate, Hexane, Heptane, mixture of polar and non-polar solvent (Ethyleacetate and Hexane), highly polar solvents Acidified Ethyleacetate with H3PO4, and H2SO4 were used for solvent extraction.
Weighed sample in a conical flask and added solvent in a desired ratio and boiled the mixture under reflux for 1 hour. Removed the flask and contents from reflux, cooled, closed with a ground-glass stopper, and stored in dark for time.
Placed the folded filter paper in the filter funnel using forceps and without agitation, decanted the liquid into the filter paper. Transferred the residue in the filter paper as completely as possible, using successive quantity of hot n-heptane , with the aid of the stirring rod as necessary.
Removed the filter paper and contents from the funnel and placed in solvent extractor (Figure 7.1) reflux with solvent until solvent in the extractor become clear.
Stop the extraction, stay to cool the apparatus and then remove the filter paper from the extractor with the help of forceps. Dry the filter paper with asphaltenes at 50 °C in oven filled in a tinted bottle and keep in dry and dark place. Analyzed both maltenes and asphaltenes by ICP.
In another experiment effect of time on Demetallization of HFO was studied with 1% H2SO4 in Ethyleacetate. Bulk mixture of HFO and solvent in a ratio of 1:20 (total 2 liters) was kept for 40 days. Continuous samples were taken in different intervals. Samples were filtered and analyzed maltenes for vanadium and nickel by ICP.
Heavy Pakistani Crude Oil (HPCO) was demetalated and deasphalted by solvent extraction with Condensate Pakistani Crude oil (CPCO). HPCO and CPCO were mixed at a ratio of 1:10 and apply different conditions (temperature and reagent). Mixture was filtered and washed with successive amount of CPCO. Maltenes were analysed by ICP.
The reaction mixtures were prepared by adding a weight amount of the selected reagent in a known volume of chosen solvent to 100 g of residue. The system was heated in a thermostatic bath under stirring; when the mixture reached the selected reaction temperature, the heating was continued for a period of 15 minutes. The vanadium and nickel contents in the residue (original, and after reactions) were determined by Atomic absorption and ICP and percent removal was calculated.
For acid treatment, 200 g of oil sample (HFO/ VR/or Asp) was stirred and heated under nitrogen blanket to about 150o C. Five weight percent of acid was added and temperature was gradually raised to 250o C and maintained for about 30 minutes at this temperature. The sample was allowed to cool to room temperature and the solids were removed. The oil sample was dried to remove water. Metal analyses were done by ICP.
PREPARATION OF ASPHALTENES
A quantity of HPCO, HFP or VR is dissolved in n-pentane (1:10 ratio) and the insoluble material, consisting of asphaltenes is separated by filter paper Wattman No.42, under hot reflux with n-pentane and dries. Scrap the asphaltenes and is kept in tight glass bottle in dark.
Condenser, Reflux Extractor, Conical Flasks, Evaporating Dish, Filter Funnel, Filter Papers, Balance (0.1 mg or better), Forceps (stainless steel), Watch or Stopwatch, Oven, Graduated Cylinders (50ml, 100ml).
Weigh HFO, VR or HPCO in a conical flask, in the range of 10 to 25 gram and add n-heptane in the ratio of 8 ml to each gram of sample, and boil the mixture under reflux for 1 hour. Remove the flask and contents from reflux, cool, close with a ground-glass stopper, and store in a dark for 3 hours approximately.
Place the folded filter paper in the filter funnel using forceps and without agitation, decant the liquid into the filter paper. Transfer the residue in the filter paper as completely as possible, using successive quantity of hot n-heptane , with the aid of the stirring rod as necessary.
Remove the filter paper and contents from the funnel and place in an extractor (Figure 7.1) reflux with n-heptane for many hours, until n-heptane in the extractor become clear.
Stop the extraction, stay to cool the apparatus and then remove the filter paper from the extractor with the help of forceps. Dry the filter paper with asphaltenes at 50 °C in oven filled in a tinted bottle and keep in dry and dark place.
SAMPLE PREPARATION FOR ANALYSIS
7.5 MICROWAVE ASSISTED ACID DIGESTION PROCEDURE FOR METAL ANALYSIS
All the components in direct contact with sample were soaked in 10% nitric acid for over night finally washed, rinsed with distilled water and oven-dried. Approximately 0.1 g asphaltene sample was weighed and transferred to VHP vessel. The inner liner (VHP vessel) was inserted into outer vessel and reagents were dispensed in order, 0.5 ml HCl, 4ml fuming HNO3, 1ml H2O2, 1ml HF. Rupture dick was set underside the OVP valve to sit flat. OVP plug was pressed against the disk underside the OVP valve. OVP valve was threaded into the TFM vessel top and tighten up using OPV wrench. TFM top was inserted into outer vessel cap (ULTEM Cap). The outer vessel cap was placed on the VHP vessel contained in outer vessel and twisted to screw up. The sensor vessel was prepared in the same way by adding distilled water upto 2/3 the volume of vessel, TFM top fitted with rupture disk and set in the outer vessel. The TFM top was pressed onto sensor vessel and outer vessel was screw-tighten over the vessel. The sensor vessel was placed in outer circle of the circular rack on the third tire of vessel carousel.
The standard vessels containing samples were placed in rest of the position. Placed the lid of the rack and fixed by locking pins and inserted the end of vent tubes into vent pot. Rack was adjusted into the oven. The cable of temperature sensor was connected to BNC connector and screwed to grasp the umbilical cord of sensor to BNC plug.
Closed the oven door/ shield and turned on. Sample was run on the selected program. which was made through the editing of desired method. After completion of run sample was allowed to cool down to room temperature and finally sample was transferred in graduated cylinder and volume made up to the mark.
Arrora MW 500 microwave temperature programming as follow high pressure (725psi) is given in Table-7.4.
Analysis was carried out on inductively coupled plasma spectroscopy iCAP 6500. The calibration was achieved by multi-element Plasma standard solution by Alfa Acer. Wavelengths used for the analysis of metals are given in Table-7.5.
7.6 LIQUID CHROMATOGRAPHY
Oil was toped at 100 C on water bath for 1 hour and deasphalted as described in 7.7.1. Then the toped and deasphalted oil was fractionated by colum chromatography in to saturates, aromatic and polar fractions.
For this purpose 10 mm dia and 760 mm hight glas colum was selected (Figure-7.1). Introduced a small plug of glass wool into the column, pressing it firmly into the lower end to prevent the flow of silica gel from the column. Clamped the column in a vertical position and poured 1 ml n-hexane to wet the column. Small increaments of wet silica gel with n-hexane was added, while the column was being vibrated along its length, until the tightly packed silical gel extended to the lower mark (at 60 mm) on the chromatographic clumn.continued to vibrate the column and added bauxite until the bauxite layer extended to the upper mark (at 760 mm) on the chromatographic column. Column was being vibrated till the setteling of silica gel and bauxite was stoped.
Warmed the sample and weigh 1 gram sample in a beaker and added samll quantity of n-hexane (2-5 ml). Shake the mixture over warm water. Removed the cap of column tip to remove additional n-hexane of colum. When the liquid level reached the top of the bauxide bed, the sample was transferd to the top of the column. Rinced the beaker with three succesive small (2-3 ml) washes of n-hexane and each wash was added to the top of column. Then rinced the walls of the column bulb with 2-3 ml portion of n-hexane. Finally add 35 ml of n-hexane to the colum bulb.
Placed a 50-mL beaker under the column to collect the eluate. The elution rate was approximately 1-1.5 mL/min. Gas pressure was also applied to the top of the column when necessary to maintain the elution rate.
When the n-pentane level reached the top of the bauxite bed, added 80 mL of benzene (necessary safety precautions were taken). Connected the pressuring gas to the top of the column and adjusted the pressure to maintain an elution rate of 1 to 2 mL/min.
Collected 50 ml of n-hexane eluted in the beaker. Tip of the column was rinsed with 1-2 ml of n-hexane and added to the 50 ml. Placed the beaker on water bath to evaporated the solvent and weighted.
When the benzene level reached the top of the bauxite bed, released the gas pressure and added aproximate100 mL of mixture of methanol and dichloromethane (1:1) to the top of the column. Reconnected the gas pressuring system and continued the elution till the brown ring of aromatic compounds was completely eluted from the colum. When eluate had been collected in the beaker, rinsed the column tip with 1 mL of benzene and added the rinse to the 100-mL beaker. Labeled the beaker as benzene-eluted fraction. Treated the benzene elute same as n-hexane elute and weigh it.
Placed new beaker for the elute of methanol and dichloromethane. The mobile phase was being added to the top of column till dark brown ring of polar compounds was completely eluted from the column. Tip of the column was rinsed with 1 to 2 ml mixture. Elute was treated same as, n-hexane and benzene elutes were treated and weighted.
7.7 GC-MS ANALYSIS
Varin gas chromatograph CP-3800 connected with Varian mass spectrometer 4000MS was used for this study. VF-1ms, 30 meter long, 0.25mm dia, and 0.25 µm film thickness column was chosen. One micro liter 10 % sample in dichloromethane was injected through Combipal auto sampler in the type 1079 injector. Initial temperature of GC program was 45 °C with a hold time of 5 minute. Temperature increased at a ramp of 10 °C per minutes up to 270 °C and hold for 13 minutes. Injector temperature was 250 °C in split mode of 50:1 ratio. Carrier gas was helium with constant flow of 1 ml per minute. Total analysis time was 40 minutes. Ionization source in MS was external and damping gas was helium at 8 ml per minutes. Temperature of ion source was 260 °C, Ion trap temperature was 180 °C, and transfer line temperature was 300 °C. Instrument was kept on for 48 hours before analysis and tune the MS with standard perfluorotributylamine (PFTBA).
Deasphalted crude oil, saturate fraction and aromatic fraction were analyzed on Varian Quadropole Ion Trap GC-MS/MS 4000. Compounds were identified by retention time of standards and specific mas of their fragments (m/z). Identified compunds were also confermed by reference chromatograms and fragmentograms in previous publications and literature [2-4], and comaring compunds spectra in NIST (National Institute of Science and Technology) library.
Benzene was indentifed by m/z 78, toluene was identified by m/z 92, m-xylene, p-xylene, o-xylene and ethylbenzene were identified by m/z 92 and 106. Isoprenoid C9, ethylcyclohexane, pristane, phytane and normal alkanes up to carbon no. 36 were identified by m/z 57, 71 and 85 (Figure-1 and Figure-2).
Hopane and sterane biomarkers were identified by m/z 191 and 217 respectively. These biomarkers gave very valuable information about the oil, which is discussed in chapter-9.
Aromatic biomarker families Methylnapthalene compounds, dimethylnapthalene compounds, methylbiphenyl compounds, dibenzofuran, trimethylnapthalene compounds, phenanthrene, dimethylbiphenyl compounds, dibenzothiophene, methylphenanthrene compounds, dimethycarbazole compounds, dimethyldibenzofuran compounds, methyldibenzothiophene compounds, ethylphenantherene and dimethylphenanthrene compounds were also identified by their respective ions. Compounds and their respective m/z ratios are given in Table 7.6
Properties of PDR or Heavy Fuel Oil
Flash Point PMCC
Heat of Combustion (Net)
Physical and Chemical Properties of Heavy Pakistani Crude Oil
Read Vapor Pressure
Initial Boiling Point (IBP)
Max. Temp. Observed
Physical and Chemical Properties of Condensate Pakistani Crude Oil
Read Vapor Pressure
Arrora MW 500 microwave temperature programming
Wavelengths used for the analysis of metals
Thermo iCAP 6500 ICP Emission Spectrometer
Specific m/z ratios of Compounds
Normal and Iso Alkanes
57, 71 and 85
92 and 106
Hopanes, tricyclic terpanes, tetracyclic terpanes, moritanes, olenane
217 and 218
Ethyl naphthalenes and dimethylnaphthalenes
Methylbiphenyls, and Dibenzofuran
Dimethylphenenantherenes and ethylphenenantheren
Liquid Chromatography Column