1. Introduction
The most important property of diesel fuel is cetane number [1] , the refineries in the world and researchers in this area are working to improve the cetane number by using environment friendly materials [2] . Cetane number improvers raise the cetane number of the fuel. Within a certain range, a higher number can reduce combustion noise and smoke and enhance ease of starting the engine in cold climates [3] . The magnitude of the benefit varies among engine designs and operating modes, ranging from no effect to readily perceptible improvement [3] .
2-Ethylhexyl nitrate (EHN) is the most widely used cetane number improver. It is also called octyl nitrate. EHN is thermally unstable and decomposes rapidly at high temperatures in the combustion chamber [4] .
The increase in cetane number from a given concentration of EHN varies from one fuel to another. It is greater for a fuel which natural cetane number is already relatively high. The incremental increase gets smaller as more EHN is added, so there is little benefit in exceeding a certain concentration. EHN typically is used in the concentration range from 0.05 to 0.4 percent mass and may yield a three to eight cetane number benefit [5] [6] [7] . In the study, the furfural was used to improve the Sudanese petrodiesel fuel because the furfural is an available material.
2. Materials and Methods
2.1. Materials
All chemicals used were of analytical reagent grade (AR): Nitric acid, Furfural. Deionized water and Petrodiesel sample.
2.2. Instrumentation
2.2.1. Gas Chromatography Mass Spectrometry
(Thermo Scientific Co. Thermo GC-TRACE ultra ver.: 5.0, Thermo MS DSQ II). Experimental conditions of GC-MS system were as follows: TR 5-MS capillary standard non-polar column, dimension: 30 Mts, ID: 0.25 mm, Film thickness: 0.25 μm. Flow rate of mobile phase (carrier gas: He) was set at 1.0 ml/min. In the gas chromatography part, temperature program (oven temperature) was 75˚C raised to 250˚C at a rise of 5˚C/min, and held for 30 min.
2.2.2. Inductively Coupled Plasma
The analytical determination of metals was carried out by ICP (Inductively Coupled Plasma): ELAN 9000 (Perkin Elmer Sciex Instrument, Concord, Ontario, Canada).
2.3. Procedures
The experimental work was conducted at chemistry lab―Omdurman Islamic University, Central lab―University of Khartoum and central lab―Khartoum Refinery, Khartoum and Central Petroleum Laboratories―SUDAN.
2.3.1. Treatment of Petrodiesel Fuel by Furfural
Petrodiesel fuel sample (1000 mL) was treated by furfural (500 mL) in separating funnel then upper layer was separated and washed with deionized water (1000 mL).
2.3.2. Physicochemical Properties of Petrodiesel Fuel [8] [9] [10] [11]
The Physicochemical Properties were characterized before and after treatment by furfural according to standard method described by ASTM. Tests includ: Density (D4052), flash point (D93), cloud point (D5773), distillation (D86), kinematic viscosity (D7042), color (D1500), sulfur Content (D5453), water content (D95), copper strip corrosion (D130), carbon Residue (D4530), ash content (D482) and cetane number (D613).
2.3.3. Gas Chromatography Mass Spectrometry (GC/MS) Analysis of Petrodiesel Fuel
The GC/MS analysis of petrodiesel fuel before and after treatment by furfural was performed on a GC-MS equipment. The injection volume was 1 μl and sample was injected in splitless mode. Finally the sample was run fully at a range of 50 - 650 m/z and the results were compared by using Wiley Spectral library search program [12] [13] .
2.3.4. Characterization of Elements Composition of Petrodiesel Sample by ICP Technique
The elements composition of petrodiesel fuel was characterized before and after treatment by furfural.
a) Calibration
The ICP calibration was carried out by external calibration with the blank solution and three working standard solutions (10, 20 and 30 μg/L) for all elements.
b) Preparation of Sample
About 30 ml of solvent methyl isobutyl-ketone was taken, 5 ml of buffer solution added and then 0.1 g of iodine weighted and transferred to the solution; 5 ml of petrodiesel fuel was also added to the solution and the solution finally com- pleted to mark in a 100 ml volumetric flask with methyl isobutyl ketone [14] .
3. Results and Discussion
3.1. GC/MS of Petrodiesel before and after Treatment by Furfural
The organic compounds in petrodiesel sample before and after treatment are shown in Table 1 and Table 2, respectively.
The data obtained from GC/MS revealed that the furfural has shown high ability to extract aromatic, branched and cyclo organic compounds (Table 3).
The extracted aromatic, branched and cyclo compounds from petrodiesel sample has confirmed the improvement of its quality, although furfural has extracted Nonadecane yet this has shown high positive effect on CN.
3.2. The Physicochemical Characteristics of Petrodiesel before and after Treatment by Furfural
All physicochemical characteristics of petrodiesel sample before and after treatment by furfural were found to be within permissible limits assigned by ASTM Table 4.
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Table 2. Organic compounds of petrodiesel sample after treatment by furfural.
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Table 3. Extracted organic compounds by furfural.
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Table 4. Physicochemical properties of used petrodiesel sample before and after treatment.
No limits had been assigned for the density by ASTM, because they depend to a greater extent on the temperature prevailing in the country [15] [16] [17] The density has been decreased. Results were found to be within the Khartoum Refinery limit to operate diesel engines [18] .
The viscosity of Sudanese petrodiesel sample was decreased after treatment; this result confirmed the quality improvement of petrodiesel fuel.
The decrease of flash point temperature was indicative of overall delay of flammability and hazard [15] . Cloud point was increased to 5.0˚C.
The colour of Sudanese petrodiesel is within ASTM specification [16] although has become intense, this result can be attributed to the brown colour of furfural.
Increase of ash content in diesel may lead to decrease of quality because it may precipitate in engine tank. The ash content of Sudanese petrodiesel sample has been decreased from 0.02% to 0.01% w/w.
Other physicochemical such as distillation, micro carbon residue and water content properties were improved by furfural and their results have been found within ASTM specification.
3.3. Elements Composition of Petrodiesel before and after Treatment by Furfural
The data depicted in Table 5 has revealed that the petrodiesel metal concentrations of As, Ca and Fe were the highest. It has shown slight decrease after improvement. A result which might have been the cause to decrease the ash content [19] . While some metal concentrations remained unchanged.
Furfural is an important renewable, non-petroleum based feedstock. It has acted as a selective solvent in refining petrodiesel fuel. Aromatics, cyclic and branched hydrocarbons were extracted and removed from petrodiesel by means of furfural extraction. Cetane number has increased without the decomposition of furfural, hence furfural can act as a biobased alternative to the thermally unstable 2-ethylhexyl nitrate.
4. Conclusions
Based on the previous discussion, conclusion can be summarized:
・ The organic compounds of Sudanese petrodiesel sample have been evaluated by using Gas Chromatography Mass Spectrometry GC/MS technique, before and after treatment by furfural.
・ A total of 81 organic compounds have been extracted from Sudanese petrodiesel sample. Most of the extracted compounds are aromatic, cyclic, and branched organic compounds.
・ The physicochemical Characteristics of Sudanese Petrodiesel sample have been investigated before and after treatment by furfural according to American Society for Testing and Materials, characteristic include: density, viscosity, flash point, colour, cloud point, water content, ash content, micro carbon residue, copper strip corrosion, sulfur content and cetane number.
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Table 5. Elements composition of sudanese petrodiesel before and after treatment by furfural.
・ The furfural has shown a slight intensity on colour of Sudanese Petrodiesel but all other results were within permissible limits assigned by ASTM.
・ The elements composition of Sudanese petrodiesel sample has been performed by Inductively Coupled Plasma Technique.
・ The concentrations of Na, Mg, Ca, Fe, Al and As have been slightly decreased after treatment by furfural, these results led to decrease of ash content.
・ Furfural has proved to be an efficient non-expensive, sulfur compound adsorbent and thermal stable cetane number improver for the quality improvement of Sudanese petrodiesel fuel.