Fingerprinting of Some Petroleum Fractions Treated with Potassium Aluminium Sulphate

This research investigates alteration in the composition of diesel and engine oil due to their treat ment with 35g of Potassium Alu miniu m Sulphate, (KAl(SO4)2) for seven days at room temperature. Results reveal that after treatment, the Total Petroleu m Hydrocarbon (TPH) o f diesel increased fro m 7688.38mg/ l to 12505.10mg/l whereas that of engine oil increased fro m 4967.48mg/l to 7700.47mg/l. Th is suggests that within these seven days, the salt was able to alter the composition of the samples by breaking down h igher mo lecular weight hydrocarbon fractions within and above the C40 range to smaller mo lecular weight fractions with in the C6 to C40 range. The TPH of the treated diesel oil was similar to that of kerosene after treat ment and that of the treated engine oil was similar to that of the untreated diesel sample. Ratios calculated fro m fingerprints of the samples such as nC20/nC24, nC18/nC24, nC18/nC20, nC7/nC9, and ∑K/∑D for the treated diesel samp le (0.76, 0.57, 0.75, 0.16, and 0.84) respectively were slightly similar to that of kerosene (0.65, 0.79, 1.20, 0.5, and 1.08), but different fro m that of the untreated sample whereas ratios like nC10/nC11, nC11/nC12, nC14/nC16, nC11/nC20 and nC24/nC28 for the treated diesel sample (0.53, 0.35, 1.02, 0.67 and 4.44) were similar to that of the untreated diesel sample (0.52, 0.36, 0.92, 0.46 and 5.47). None of the ratios for the treated engine o il sample were similar to either those of the untreated engine oil samp le or those of diesel. Therefore, though the treatment of the samples with 35g of the salt caused alterations in the chemical co mposition of the samples, it d id not totally transform them to the fraction obtained before them during distillation process.


Introduction
The Concise Oxford dict ionary defines Petroleu m (L. petroleum, fro m Greek: petra (rock) + Latin : oleu m (oil) or crude oil as a naturally occurring, flammable liquid consisting of a co mp lex mixtu re of hydrocarbons of various mo lecular weights and other liquid o rganic co mpounds, that are found in geologic formations beneath the Earth's surface [1]. Petro leu m is recovered mostly through oil drilling. This latter stage comes after the studies of structural geology (at the reservoir scale), sedimentary basin analysis, and reservoir characterization (mainly in terms of porosity and permeable structures) [2], [3].
In its strictest sense, petroleum includes only crude oil, but in common usage it includes all liquid, gaseous, and solid (e.g., paraffin ) hydrocarbons. Under surface p ressure and temp eratu re cond it io ns, light er h yd rocarbo ns meth ane, ethane, propane and butane occur as gases, while pentane and heav ier ones are in t he fo rm o f liqu ids or so lids.
However, in an underground oil reservoir the proportions of gas, liquid, and solid depend on subsurface conditions and on the phase diagram of the petroleu m mixture [4], [5].
An oil well produces predominantly crude oil, with some natural gas dissolved in it. Because the pressure is lower at the surface than underground, some of the gas will co me out of solution and be recovered (or burned) as associated gas or solution gas.
The proportion of light hydrocarbons in the petroleum mixtu re varies greatly among different oil fields, ranging fro m as much as 97% by weight in the lighter o ils to as litt le as 50% in the heavier oils and bitumens. Whenit is refined and separated, most easily by boiling point, a large number of consumer p roducts, fro m petrol, kerosene and diesel to lubricating oil, asphalt and chemical reagents used to make plastics and pharmaceuticals. Kerosene contains hydrocarbons with between 9 to 16 carbon atoms, diesel contains hydrocarbons with between 10 to 20 carbon atoms while engine oil contains hydrocarbons with between 24 to 38 carbon atoms [6].
The hydrocarbons in crude oil are mostly alkanes, cycloalkanes and various aromatic hydrocarbons while the other organic compounds contain nitrogen, oxygen and sulfur, and trace amounts of metals such as iron, nickel, copper and vanadium. The exact mo lecular compositionvaries widely fro m fo rmation to formation but the proportions of chemical elements vary over fairly narrow limits as follows [7].
Four different types of hydrocarbon molecules appear in crude oil. These include: Paraffins, Naphthenes, Aromatics and Asphaltics. The relative percentage of each varies from oil to o il, determining the properties of each oil [5].
Potash alum (Potassium Alu min iu m Su lphate) is an inorganic salt with the mo lecular formu la KA l(SO 4 ) 2 . Potassium A lu min iu m Su lphate forms a solid, wh ite powder at room temperature. It is a hygroscopic material which when exposed to air, hydrates (absorbs water). It is an important part of many products created by the pharmaceutical, cosmetic, and food industries because of its astringency property. It is also used in the manufacture of paper, dyes, glue, and exp losives. Additionally, it helps in the water purification process, is used to speed up the hardening of concrete and plaster, and acts as a catalyst in various chemical reactions [8], [9].
Fingerprinting is a technique which involves the use of a gas chromatograph (GC -FID or GC-M S) for analysing samples for hydrocarbons fractions (TPH, PAH, and BTEX) present in them. This largely depends on the calibration of the equipment. A chro matogram wh ich is obtained on complet ion of the analysis shows the components of the analysed sample and these components can be used in calculating various ratios. These ratios have a wide range of applications [10], [11].
In Akwa Ibo m state, during scarcity of kerosene in the early nineties, diesel t reated with Potassium Alu miniu m Sulphate was used as a substitute for kerosene. This paper therefore looks at the effect of treatment of diesel and engine oil with35g of Potassium Alu miniu m Sulphate, KAl(SO 4 ) 2 ) for seven days and also tries to ascertain if this treatment makes the samples similar to the fractions obtained before them during the distillat ion process. 35g of the salt was chosen because reference [12] reported that it gave the best results in two days.

Sample Collection
About 1000ml of Diesel o il was collected using a 500ml glass bottle fro m Onne port located in Port Harcourt, Rivers state, Nigeria while the inorganic salt, Kerosene and Engine oil were obtained fro m vendors in Uyo, A kwa Ibo m State, Nigeria. On arrival at the laboratory, the diesel, kerosene and engine oil samples were stored in a refrigerator at 4 o C till commencement of analyses while the Potash alum was stored in a cabinet.

Sample Preparation
Potash alum was dried at 80 o C in the oven for about 12 hours. After drying the salt, it was kept in the desiccator for cooling before 35g of the salt was introduced into 50mls of the diesel oil and engine oil in dry and clean 100ml bottles. The resulting mixtures were thoroughly shaken daily and allo wed to react at roo m temperature in the Laboratory for seven days.

Oil Extracti on and Gas Chromatographic Anal yses
1g of each of the samples was weighed into well labeled clean and dry vialsand 10mls of pentane was added to them. The samples weighed stirred using a magnetic stirrer for about 5 minutes before they were allowed to concentrate to 1ml.The extracts were fractionated into aliphatic fractions by adsorption liquid chro matography using a column of alu mina and silica gel, while pentane was used as gradient solvent. The extracts were concentrated to 1ml and these were subjected to analyses [13], [14].
The TPH of the samples were determined using a Hewlett Packard 6890 gas chromatograph made by Agilent (USA) with the follo wing operational conditions; flow rate (H 2 30ml/ min, air 300ml/ min and N 2 30ml/ min), injection temperature (50 o C), detector temperature(320 o C). For signals, the GC was interfaced to a Hewlett Parker (hp) computer.

Results and Discussions
The treatment of the samples with 35g of Potassium Aluminiu m Sulphate altered the total petroleu m hydrocarbon (TPH) of the samples within the seven days of treatment (table i). The results revealed that the TPH of the diesel increased from 7688.38mg/l to 12505.10mg/ l whereas that of engine oil increased fro m 4967.48mg/ l to 7700.47mg/l. This suggests that within these seven days, the salt was able to breakdown higher mo lecular weight hydrocarbon fractions within and above the C40 range to smaller mo lecular weight fractions wh ich fell within the C40 range. This is corroborated by the increment and decrement in the concentrations of some o f the fract ionsandthe presence of C6 to C12 fractions in the fingerprints of the treated engine oil sample which was absent in the untreated engine oil sample. The similarity in the TPH of the treated engine oil and that of the untreated diesel also supports this. For instance, the concentration of the C6 and C18 fraction in the untreated diesel oil was 1711.61mg/l and 1507.06mg/ l whereas after the treatment, it drastically reduced to 21.66mg/l and 891.65mg/lrespectively, the difference between them being statistically significant at 95% confidence limit. On the contrary, the remaining fract ions recorded increased concentrations. This also supports alteration in the composition of the sample. On looking at the total concentration of fractions within the diesel, engine o il and kerosene range in the samples, it revealed that the concentration of fract ions in the kerosene range (table ii) for the treated diesel sample (8247.0 mg/l) was a little similar to that of kerosene (11361.95mg/l) but very different fro m that of the untreated diesel sample(2347.26mg/ l). Also, the concentration of fractions in d iesel range for the treated engine oil sample was similar to that of the untreated sample. Statistical analysis (students' t-test) shows that the difference between the TPH of the treated diesel sample and that of kerosene was not significant at 95% confidence limit .For the treated engine oil samp le, the result shows that the total concentration of fractions within the engine oil range (6861.14mg/l) was still similar to that of the untreated sample (4349.52mg/ l), thus suggesting that though the sample had undergone alterations in its composition, it still retained the characteristics of engine oil.   The fingerprints of the samples (Fig. 1, Fig. 2 and Fig. 3) also confirm alterat ions in the composition of the samples though the alterations did not make it very similar to kerosene which is the fraction obtained before it during the distillat ion process. Of all the ratios calculated using the fingerprints of the samples, only few of them were slightly similar wh ile one (nC 9 /nC 16 = 0.04) was the same for the untreated and treated diesel sample. The n C 20 /nC 24 , nC 18 /nC 24 , nC 18 /nC 20 , nC 7 /nC 9 , and ∑K/∑D rat ios for the treated diesel sample (table 4) of 0.76, 0.57, 0.75, 0.16, and 0.84 respectively were slightly similar to that of kerosene (0.65, 0.79, 1.20, 0.5, and 1.08), but different fro m that of the untreated sample. These show that though the treated sample had not undergone enough alteration in composition to make it have the same properties as kerosene, it had some characteristics of kerosene. Reference [12] also reported that though the treatment of diesel with 35g of Potassium Aluminiu m Sulphate had effects on the physicochemical characteristics of diesel oil, the treated diesel o il cannot be used as kerosene. The similarities in the TPH of the t wo samples confirm th is. On the contrary, rat ios like n C 10 /nC 11 , nC 11 /nC 12 , nC 14 /nC 16 , nC 11 /nC 20 and nC 24 /nC 28 for the treated diesel sample (0.53, 0.35, 1.02, 0.67 and 4.44) were similar to that of the untreated diesel sample (0.52, 0.36, 0.92, 0.46 and 5.47). These suggest that the treated diesel sample still had some characteristics of diesel [15]. On the contrary, for the engine oil, none of the ratios were similar to the ratios for either the untreated engine oil samp le or the untreated diesel sample. Th is therefore suggest that the engine oil had undergone enough alteration to make it different fro m the untreated engine oil but the alterat ion was not enough to make it exhib it some characteristics of diesel oil. The presence of peaks within the C6 to C12 region affirms this.

Conclusions
The results obtained from the analyses of samples of diesel and engine oil treated with 35g of Potassium Aluminiu m Sulphate has shown that the treatment of the samples for seven days altered the TPH of the samples. So me of the fractions recorded increment in their concentrations whereas others had decreased concentrations. The C6 and C18 fractions drastically reduced after treat ment of the d iesel oil while the treated engine oil sample had peaks within the C6 to C12 reg ion, though it was not present in the untreated sample. These suggest that the inorganic salt may have been able to breakdown (crack) the hydrocarbon fractions in the samples to fractions within above the C6 to C40 range, thus confirming the alteration in the co mposition of the samples. Fro m the above, it could be concluded that though the treatment of the samp les with the salt altered their compositions, the alteration was not enough to make the samples similar to the fract ions obtained before them during the distillation process.
Where: ∑K -su m of fract ions within the kerosene range ∑D -sum of fractions within the diesel range ∑E -sum of fractions within the engine oil range