INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 3, No 1, Copyright by the authors - Licensee IPA- Under Creative Commons license 3.

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1 INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 3, No 1, 2012 Copyright by the authors - Licensee IPA- Under Creative Commons license 3.0 Research article ISSN Characterization of Polycyclic Aromatic Hydrocarbons (PAHs) in oily sludge from Cameroon petroleum ZE BILO'O Philemon 1,2, NGASSOUM Martin Benoît Laboratory of Chemistry, Faculty of Science, University of Bamenda P.O. Box: 39 Bambili (Cameroon). 2- Laboratory of Active Substances and Pollution (LASP), National School of Agro- Industrial Sciences (ENSAI), University of Ngaoundere P.O. Box 455 Ngaoundere (Cameroon). zebiloop@yahoo.fr doi: /ijes ABSTRACT The National Petroleum Refinery of Cameroon is a crude oil refining company that generates large quantity of oily sludge. The identification and quantification of standard hydrocarbons that can be recovered from oily sludge, the assessment of the distribution of the Polycyclic Aromatic Hydrocarbons (PAHs) of the sludge was realized using a simple gas chromatographic method. The results showed that the samples have an average constitution of 66 % water, 2 % fine particles and 32 % hydrocarbons. It was also found that the 22 identified aliphatic hydrocarbons had a total concentration of 4, ppm of which the major hydrocarbon was n-c 11 (608 ± 47 ppm). The total identified PAHs concentration was 511 ppm and the major compound phenanthrene (98 ± 5 ppm). The chromatograms also showed that the compounds that are not standard heavy PAHs, resins and asphaltenes are present in the samples. Keywords: Oily sludge, hydrocarbons, centrifugation, flocculation, PAHs. 1. Introduction Crude oil is an important source of energy and a common source of environmental pollution (Shuchi et al., 2006). One of the consequences of crude oil exploitation and processing activities is the generation of vast amounts of oily sludge (Lingsheng et al., 2009). The oily sludge, which is part of the most important garbage in oil refineries, is generated by the coalescence of hydrocarbons on solid particles. The processing activities of one kilogram of crude oil can generate grams of oily sludge (Athanasios and Voudrias, 2007). In the oil refineries, the oily sludge is collected at several points such as oil/water separator, dissolved air flotation units, heat exchanger cleanings, tank bottom cleaning, desalter and API decanters (Dibble and Bartha, 1979; Jean et al., 1999; Athanasios and Voudrias, 2007; Boachen et al., 2009; Jianguo et al., 2009). The oily sludge is made up of considerable quantities of solid particles, water and hydrocarbons (Lucena et al., 2003; Lingsheng et al., 2009; Boachen et al., 2009) and of poisonous, carcinogenic or mutagenic compounds (Chun-Teh et al., 1995; Al-Futaisi et al., 2007; Ayotamuno et al., 2007; Lingsheng et al., 2009). The toxic compounds in oily sludge are heavy metals and Polycyclic Aromatic Hydrocarbons (PAHs). PAHs represent a serious environmental hazard due to the fact that they have high persistence in the environment, low Received on June 2012 Published on July

2 biodegradability, high lipophility and some of them are carcinogenic and mutagenic (Moreda et al., 1998). The composition of oily sludge varies from one to another, and also from one oily sludge to another depending on the type of refined crude oil. Our survey is orientated toward the oily sludge of the National Petroleum Refinery of Cameroon that hasn't yet been object of a scientific study. The objective of this work is to carry out preliminary analysis in order to identify and quantify standard aliphatic and polycyclic aromatic hydrocarbons that represent a serious threat for the environment. 2. Material and methods 2.1 Material The sample used was provided by the National Petroleum Refinery of Cameroon. Ten (10) withdrawals of 100 ml each were made at different points of the storage tank located at the wastewater treatment plant. The withdrawals were mixed prior to analysis in order to ensure a representative sample of the oily sludge. 2.2 Methods Solids content The solid content of the oily sludge was determined by incineration in a Normalab analis oven according to the method described in the international norm ASTM D for "Standard Test Method for Ash from Petroleum Products". The analysis was realized in triplicate and the mean of the results was expressed in mass percentage of humid oily sludge Water content The water content was determined by distillation using a trainer fluid (Lucena et al., 2003) which in this case is a mixture of toluene/xylene in the proportions of 80/20 (v:v). The analysis was realized in triplicate and the mean of the results was expressed as mass percentage of humid oily sludge Hydrocarbons content The hydrocarbons content was deducted from the results of previous analysis Sample extraction, cleanup and analysis for hydrocarbons identification The extraction of hydrocarbons was made following the method described by Buyukkamaci and Kucukselek (2007). Two grams of oily sludge sample was refluxed with 100 ml of a mixture of MeOH and hexane in the proportion of 50:50 for 4 h. After the addition of 30 ml MeOH into the reflux distilled mixture, the hexane phase was transferred to glass tubes and concentrated to 1 ml under the rotary evaporator Turbo-vap (Varian) at a temperature around 60 C. Cleanup of the sample took place in a 20 cm chromatographic column with an internal diameter of 0.9 cm. The column was packed with 4 g of silica gel and 4 g of alumina. The filled column was then eluted by 10 ml of hexane and 1 ml concentrated sample was placed on the top of the column. The aliphatic hydrocarbons were obtained in the first separation with 10 ml of n-hexane. Then, 10 ml of the hexane/ethyl acetate mixture (83:17; v:v) were 510

3 passed through the chromatographic column and the second fraction was obtained. Finally, 20 ml of the mixture hexane/ethyl acetate mixture (65:35; v:v) were poured into the chromatographic column in order to obtain the third fraction which is aromatic. Only analysis of the aliphatic hydrocarbons fraction and the aromatic fraction were performed by gas chromatography (GC) with a SHIMADZU GC-14B equipped with an FID detector and a Hewlett Packard integrator. The separation was carried out on a 12-m column of polydiphenyldimethylsiloxane, with a film thickness of 0.2 mm and with an internal diameter of 0.33 µm (US PATENT). The column was held at 40 C, and then heated to 320 C at a rate of 6 Cmin -1. The carrier gas was nitrogen at a pressure of 1.5 bars. The injector and detector were maintained at 300 and 330 C, respectively. A micro-syringe was used to inject 1-µL samples into the chromatograph. Aliphatic hydrocarbons and PAHs resolved peaks of the chromatographic sample were quantified by reference to the response factor of the standards (SUPELCO). Compounds were identified by the Kovats Index or retention index which is determined by the formula: KI = RT * n + i * RT ( x) RT ( C ) n ( ) ( ) C RT C 100 (1) n+ 1 n where: RT(x) is the retention time of the unknown compound. RT(C n ) the retention time of the hydrocarbon with n carbons immediately before the unknown compound. RT(C n+1 ) the retention time of the hydrocarbons with n+1 carbons immediately after the unknown compound, and i the number of spaces unoccupied by lacking compounds on the chromatograms of standards. Compound quantification results are expressed in parts per million (ppm) in the oily sludge sample. 3. Results and discussion 3.1 Sludge constitution The results of solid, water and hydrocarbons content of the oily sludge varied slightly from one test to another but the standard deviation showed that the values were close to the mean. The result of water content (67.33 ± 2.60 %) agreed with that observed by other authors (Lucena et al., 2003; Buyukkamaci and Kucukselek, 2007; Al-Futaisi et al., 2007; Boachen et al., 2009) who reported that the water content of oily sludge ranges between 30% and 90%. The same authors had said that hydrocarbons and solid contents are evaluated in the ranges of 15 50% and 1 10%, respectively. The values measured for our sample are ± 3.27 % for hydrocarbons content and 2.28 ± 0.67 % for solid content. Those compositional values indicate that the oily sludge under study is not out of the interval that obtained for other oily sludges. Due to the fact that the water content is higher than the hydrocarbons content and looking on the aspect of the sample, it can be said that this oily sludge is a water in oil (W/O) emulsion. This W/O emulsion is mixed with solid particles which enhance the stability of the emulsion. 511

4 Due to the stability (low aggregation of water droplet phenomena), this emulsion looks the same (visual aspect) even after a long storage period. 3.2 Aliphatic hydrocarbons The Figure 1 below represents one of the spectra obtained from the first fraction containing aliphatic hydrocarbons using the GC-FID. All spectra were slightly similar except for a quantitative difference in concentration levels quantified obtained by standard deviation (S.D.) as presented in Table 1. As shown in Figure 1, twenty two n-alkanes were identified in the sample with n-c 9 as the lightest and n-c 30 the heaviest, hydrocarbon. The alkane n-c 11 was found to be the major constituent, with a concentration range of ± ppm which represents 13% of identified aliphatic hydrocarbons. It was observed that concentrations decrease as the molar mass goes higher. There was also unresolved complex mixture (UCM) which is typical of spills with petroliferous derivatives (Moreda et al., 1998). This UCM which represents 46.5% of Total Aliphatic Hydrocarbons with a concentration of 4, ppm can be constituted of naphthenic and ramified hydrocarbons compounds with the same number of carbons. These observations are justified by the fact that the sample studied is a petroleum refining residue. They were also pristane and phytane compounds which are isoprenoid hydrocarbons respectively homologous of n-c 17 and n-c 18. Referring to Table 1, it can be noted that levels and evolution of pristane and phytane are very similar to their homologous n-c 17 and n-c 18 in agreement with Moreda et al. (1998). C 10 C 11 C 12 C 13 C 14 C 15 C 16 C 17 Pristane Phytane C 18 C 19 C 9 C 20 U.C.M. C 21 C 22 C 23 C 24 C 25 C 26 C 27 C 28 C 29 C 30 Time Figure 1: Spectrum of aliphatic hydrocarbons in oily sludge 512

5 Table 1: The concentration of aliphatic hydrocarbons found in the oily sludge 3.3 Polycyclic Aromatic Hydrocarbons Identified n-alkanes Mean (ppm) S.D. (ppm) n-c n-c n-c n-c n-c n-c n-c n-c n-c Pristane n-c Phytane n-c n-c n-c n-c n-c n-c n-c n-c n-c n-c n-c n-c The third fraction of the cleanup was analyzed using GC-FID. The obtained spectra present a certain similarity even when compound concentrations are different from one spectrum to another. Figure 2 represents one of the obtained spectra from the third fraction of hydrocarbons containing PAHs. Identification of PAHs from our sample revealed that of the sixteenth standard PAHs acknowledge by US-EPA, only naphthalene was absent. The concentration of identified PAHs compounds ranged from 1.22 to ppm. Phenanthrene is the most abundant PAHs (98.11 ± 4.93 ppm), followed by anthracene (90.33 ± 4.91 ppm). Phenanthrene and anthracene represent respectively 19.17% and 17.65% of total identified PAHs. Concentration means of identified PAHs are recorded in Table 2 below and the quantification limit is 0.80 ppm. A very high abundance of unresolved complex mixture (UCM) was noted with a concentration of 1, ppm which equals 70.36% of total PAHs. This may be due to the fact that our sludge is a petroleum refining byproduct which is characterized by a high abundance of homologous, alkylated (Mostafa et al., 2009), sulfurated (Abbad-Andaloussi et al., 2003), hydroxylated (Wilhem et al., 2008) or nitrogenated PAHs (Heitkamp and Cerniglia, 1988). 513

6 Time (min) Figure 2: Spectrum of polycyclic aromatic hydrocarbons in oily sludge The appearance of regular pecks as shown on the Figure 2 was observed. Those regular pecks indicate the presence of alkanes in the PAHs fraction and allow suggesting that the fractionation was not efficient. This may be due to the quality of the packed bed and the solvent used (ethyl acetate) compare to dichloromethane used by Moreda et al. (1998), Bihari et al. (2006), Athanasios and Voudrias (2007), He et al. (2008) and Mostafa et al. (2009). The high amount of PAHs in the sample may be due to the fact that the sludge has been stored for a long period of about eight years, and leading to the accumulation of PAHs that are known to be persistent. PAHs that are considered as carcinogenic by US EPA (Chrysene, Benzo[a]Anthracene, Benzo[b] Fluoranthene, Benzo[k]Fluoranthene, Benzo[a]Pyrene, Indeno[1,2,3-c,d]Pyrene and Dibenzo[a,h]Anthracene) (Réseau Coopératif de Recherche sur les Déchets, 2007) were all present in considerable concentrations. These carcinogenic PAHs according to US EPA represent 23.85% ( ppm) of total identified PAHs in the sample. Following this result, it's clearly shown that the oily sludge is very harmful for the environment and organisms because of the abundance of compounds that are known to be mutagenic and carcinogenic (Randerath et al., 1999; Bihari et al., 2006). Looking at the end of the chromatogram, it was noted that there are hydrocarbon compounds that are heavier than identified PAHs. The high values of PAHs may be due to the fact that many of PAHs and their homologues coelute in GC column. By then, FID seams to do not be enough sensitive to allow identification and characterization of PAHs compounds based only on the retention time. 514

7 4. Conclusion Table 2: The concentration of PAHs found in the oily sludge N Identified PAHs Mean S.D. (ppm) (ppm) 1 Acenaphthylene Acenaphthene Fluorene Phenanthrene Anthracene Fluoranthene Pyrene Benzo[a]Anthracene Chrysene Benzo[b]Fluoranthene Benzo[k]Fluoranthene Benzo[a]Pyrene Indeno[1,2,3-c,d]Pyrene Dibenzo[a,h]Anthracene Benzo[g,h,i]Perylene Investigations of the constitution of the oily sludge sample revealed ± 2.60 % of water content, ± 3.27 % of hydrocarbons content and 2.28 ± 0.67 % of solids content. The results mainly show that aliphatic hydrocarbons are more abundant than the PAHs. The higher concentration of aliphatic hydrocarbon was found for the n-c11 ( ± ppm). The higher concentration of PAHs was found for the Phenanthrene (98.11 ± 4.93 ppm). It was noted that ethyl acetate used for fractionation is not as efficient as dichloromethane. It was also noted that the UCM for the two studied group of hydrocarbons have a very high level of concentration. The presence of carcinogenic PAHs (Chrysene, Benzo[a]Anthracene, Benzo[b] Fluoranthene, Benzo[k]Fluoranthene, Benzo[a]Pyrene, Indeno[1,2,3-c,d]Pyrene and Dibenzo[a,h]Anthracene) in high concentrations makes the oily sludge to be very harmful for the environment and organisms. Acknowledgement The authors are grateful to the National Petroleum Refinery of Cameroon for providing samples and help in some analytical measurement. 5. References 1. Abbad-Andaloussi S., Warzywoda M., Monot F., (2003), Microbial Desulfurization of Diesel Oils by Selected Bacterial Strains, Oil & Gas Science and Technology Rev. IFP, 58(4), pp Al-Futaisi Ahmed, Jamrah A., Yaghi B., Taha R., (2007), Assessment of Alternative Management Techniques of Tank Bottom Petroleum Sludge in Oman", Journal of Hazardous Materials, 141, pp

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