Preliminary study of metalloporphyrins in some oil shales, red sea… · 2017. 1. 17. · FULL...

Egyptian Journal of Petroleum (2016) xxx, xxx–xxx

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Egyptian Petroleum Research Institute

Egyptian Journal of Petroleum

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FULL LENGTH ARTICLE

Preliminary study of metalloporphyrins in some oilshales, red sea, Egypt

* Corresponding author.

E-mail address: [email protected] (F.M. Harb).

Peer review under responsibility of Egyptian Petroleum Research

Institute.

http://dx.doi.org/10.1016/j.ejpe.2015.11.0041110-0621 � 2015 The Authors. Production and hosting by Elsevier B.V. on behalf of Egyptian Petroleum Research Institute.This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Please cite this article in press as: S.M. El-Sabagh et al., Preliminary study of metalloporphyrins in someoil shales, red sea, Egypt, Egypt. J. Petrol. (2016), hdoi.org/10.1016/j.ejpe.2015.11.004

S.M. El-Sabagh, S. Faramawi, Fatma M. Harb *, M. Farouk

Egyption Petroleum Research Institute, Nassr City, Hei-Al-Zehour, 11727 Cairo, Egypt

Received 31 March 2015; revised 27 October 2015; accepted 10 November 2015

KEYWORDS

Crude oil;

Metalloporphyrins;

Distribution;

Characterization

Abstract Occurence and distribution of metalloporphyrins were studied in asphaltene and maltene

fractions of some Egyptian oil shales from the main producing mines (Abu-Shegeili, El-Beida, El-

Nakheil and Abu-Tundub I, II) in red sea area (Fig. 1).

Metalloporphyrins were extracted using adsorption column chromatography. The presence of

Ni, Fe and Vo-porphyrins was monitored in each fraction by means of UV–Visible spectrometry,

the result indicated that metalloporphyrins could be a mixture of Etio and DPEP types. Each frac-

tion using UV–Visible spectrometry cannot differentiate between Ni and Fe porphyrins, so the

extracted metalloporphyrins were subjected to purification and separation from each other by using

thin layer chromatography (TLC).

HPLC was used for fingerprinting Vo, Ni and Fe-porphyrins, it was found that the different por-

phyrins exhibited wide different chromatograms. HPLC technique could be used as a successful tool

to characterize Fe and Ni-porphyrins.� 2015 The Authors. Production and hosting by Elsevier B.V. on behalf of Egyptian Petroleum Research

Institute. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/

licenses/by-nc-nd/4.0/).

1. Introduction

1.1. Chemistry of metalloporphyrins

Oil shale can be defined as an organic rich sedimentary rockfrom which oil and or gas can be produced by pyrolysis [1].Oil shales consist of organic and inorganic compounds [2].

The organic material is normally classified into two compo-nents, natural bitumen (smallest fraction) and kerogen (majorfraction). The inorganic part consists mainly of quartz, clay,

different types of carbonates (CaCO3, mgCO3) pyrite and

Fe2O3 besides trace elements such as, B, Mo, Ni, V and Fe[3,4]. Trace elements have been used to characterize crude oils,soluble organic matter in sedimentary rocks, insoluble organic

matter (kerogen) of petroleum source rocks and oil shales[5–7].

The most studied metal complexes associated withpetroleum, in source rocks and oil shale are Ni and Vo

porphyrins. Oil shale is generally known to have much lowerconcentrations of Ni and Vo (10 ppm in average) and havedifferent metals in the porphyrins ring such as Fe [8]. The total

metal content of crude oil can provide a distinctive fingerprintwhich has been used to correlate oils with source rocks [9](see Fig. 1).

ttp://dx.

http://creativecommons.org/licenses/by-nc-nd/4.0/http://creativecommons.org/licenses/by-nc-nd/4.0/mailto:[email protected]://dx.doi.org/10.1016/j.ejpe.2015.11.004http://dx.doi.org/10.1016/j.ejpe.2015.11.004http://www.sciencedirect.com/science/journal/11100621http://dx.doi.org/10.1016/j.ejpe.2015.11.004http://creativecommons.org/licenses/by-nc-nd/4.0/http://dx.doi.org/10.1016/j.ejpe.2015.11.004http://dx.doi.org/10.1016/j.ejpe.2015.11.004

Figure 1 Location map of the oil shale samples.

2 S.M. El-Sabagh et al.

1.2. Structure of porphyrins

Porphin nucleus consists of four pyrrole rings joined by fourmethene bridges giving a cyclic tetrapyrrole structure Fig. 2.Treibs [10] was the first one who isolated and identified the

major metalloporphyrins in petroleum and oil shale and heproved that petroleum was derived from plant and animalorganic remains and thus explained the origin of petroleum.

Porphyrins are important biological markers in which theircarbon skeletons are preserved after having undergoneaccumulation and diagenesis that can still be correlated with

the original biological precursors.The literature [11–13]reported the presence of five main

porphyrins: two major types series, etioporphyrins (Etio) and

deoxophylloerthroetioporphyrin (DPEP) and three minorseries, tetrahydrobenzoDPEP (THBD), benzo (rahodo) Etioand benzo (rhodo) DPEP, Fig. 2.

Please cite this article in press as: S.M. El-Sabagh et al., Preliminary study of metallodoi.org/10.1016/j.ejpe.2015.11.004

In the present work the metalloporphyrins in bitumenfraction of five oil shale samples namely Abu-Shegeili,

El-Beida, El-Nakheil and Abu-Tundub I, II were isolatedand characterized by the aid of different techniques in orderto shed light on the distribution of Ni, Vo and Fe-porphyrins,

and finding an appropriate tool to differentiate between Niand Fe-porphyrins.

2. Materials and methods

2.1. Preparation of oil shale samples

Five oil shale samples Table 1 were grinded, then sieved and anaccurate weight of a portion of

Figure 2 (A) Structure of porphin nucleus. (B) Types of

porphyrins.

Preliminary study of metalloporphyrins in some oil shales 3

2.2. Extraction of bitumen

Bitumen was extracted from oil shale using soxhlet extractionwith benzene/methanol (70/30). The extracts of asphaltene andmaltene (from thebitumen), isolation of Ni and Vo porphyrinsare shown in Fig. 3.

Table 1 Concentration of Ni, VO and Fe in bitumen extracted fro

Sample no Bed name (depth, m) Ni-conten

1 Abu-Shigeili (5–10) 265

2 El-Beida (5–15) 455

3 El-Nakheil (5–15) 322

4 El-Tundub-I (10–20) 253

5 Abu-Tundub-II (10–20) 198


3. Results and discussion

The preliminary UV–Visible spectrometric analysis of bitumenof the studied samples showed no characteristic absorption

peaks for Ni or Vo-porphyrins, due to the nature of matrixof the sample that masks the absorption of metallo-porphyrins [14]. In the present work the metal-porphyrins in

maltene and asphaltene fractions have been isolated andcharacterized by the aid of different analytical techniques.

3.1. Isolation of metalloporphyrins

3.1.1. Extraction by column chromatography

The metalloporphyrins were extracted from maltene and

asphaltene fractions using silica gel column chromatographyas shown in Fig. 3. Eight fractions obtained by gradual elutionusing different solvent systems have different polarities

(n-hexane–toluene–methylene chloride–toluene and methylenechloride).

Based on the literature [15], the chromatographic column of

asphaltene fractions exhibits brown, dark red and pink coloredzones, these zones may be indications of resins Vo andFe-porphyrins, respectively. And the chromatographic columnof maltene fractions exhibited three colored zones of brown,

red and yellow due to resins, Vo and Ni-porphyrins,respectively.

From these primarily observation, it can be suggested that

asphaltene fraction contains Fe and Vo porphyrins, whereas,maltene fraction contains Ni and Vo porphyrins.

It was stated that Ni complexes in crude oil are associated

with the oily components and Vo-porphyrins are associatedwith the heavy asphaltic ends [16].

The microwave ashing followed by ICP spectrometry of

bitumen fraction of all samples showed considerable amountsof Fe compared to the corresponding concentration of NiTable 1, the high concentration of Fe may be considered asan evidence of the occurrence of Fe-porphyrins in asphaltene

fractions. Tables 2 and 3 summarize the results of metallopor-phyrins isolated from asphaltene and maltene factions of El-Beida oil shale as an example. From these tables it is clear that

asphaltene fraction showed absorption bands at 545 nm,515 nm, for Ni or Fe. Whereas the spectra of Ni and Fe por-phyrins are almost identical [17] and bands at 565 nm and

525 nm characteristic of Vo-porphyrins.

3.1.2. Purification by TLC

To differentiate between Ni and Fe-porphyrins by column

chromatography, the extracted metallo-porphyrins were

m different studied oil shale samples.

t, ppm V-content, ppm Fe-content, ppm

19 630

6170 1731

1250 262

111 1651

1074 1199

porphyrins in someoil shales, red sea, Egypt, Egypt. J. Petrol. (2016), http://dx.

http://dx.doi.org/10.1016/j.ejpe.2015.11.004http://dx.doi.org/10.1016/j.ejpe.2015.11.004

Figure 3 Separation of nickel and vanadyl porphyrins from bitumen of oil shale samples.

Table 2 Results of metalloporphyrins isolation from asphaltene fraction of El-Beida oil shale sample.

Fraction no. Solvent UV–Visible bands Chelating type

k = 545 k= 515 k= 565 k= 525

1 Hexane –

2 Hexane–toluene (1:1) + + Fe

3 Toluene + + Fe

4 Methylene chloride–toluene (1:4) + + Fe

5 Methylene chloride–toluene (2:3) + + VO



8 Methylene chloride + + VO


Please cite this article in press as: S.M. El-Sabagh et al., Preliminary study of metalloporphyrins in someoil shales, red sea, Egypt, Egypt. J. Petrol. (2016), http://dx.doi.org/10.1016/j.ejpe.2015.11.004


Table 3 Results of metalloporphyrins isolation from maltene fraction of El-Beida oil shale sample.

Fraction no Solvent UV–Visible bands Chelating type

k= 545 k= 515 k = 565 k= 525

1 Hexane –

2 Hexane–toluene (1:1) + + Ni

3 Toluene + + Ni

4 Methylene chloride–toluene (1:4) + + Ni




8 Methylene chloride + + VO

Table 4 Occurrence of metalloporphyrins in different oil shale samples.

Sample no Bed name Fraction Type of chelating

Fe Ni VO

1 Abu-Shigeili Maltene – – –

Asphaltene – – –

2 El-Beida Maltene – + +

Asphaltene + – +

3 El-Nakheil Maltene – + +

Asphaltene + – +

4 Abu-Tundub-I Maltene – + +

Asphaltene + – +

5 Abu-Tundub-II Maltene – + +

Asphaltene + - +

Figure 4 UV–Visible spectra of nickel porphyrins extracted from

maltene of El-Beida oil shale.

Figure 5 UV–Visible spectra of iron porphyrins extracted from

asphaltene of El-Beida oil shale.




Figure 6 UV–Visible spectra of vanadyl porphyrins extracted

from maltene of El-Nakheil oil shale.Figure 7 UV–Visible spectra of vanadyl porphyrins extracted

from asphaltene of El-Nakheil oil shale.


subjected to purification and further separation of chelatingporphyrins from each other by means of TLC.

The asphaltenic–metalloporphyrins showed two bands onsilica gel plate at Rf values of 0.27–0.60 and 0.15–0.27 whichhave pink and red color for Fe and Vo porphyrins, respec-

tively. The maltenic–metalloporphyrins showed two bandsrelated to Ni and Vo-porphyrins.

Table 4 shows that maltene fraction contains Ni and

Vo-porphyrins whereas asphaltene fraction contains Fe andVo-porphyrins except Abu-Shegeili sample. Ni, Fe andVo-porphyrins zones were extracted with methylene chloride

and stored for further investigation.

Table 5 UV–Visible spectrometry of nickel porphyrins obtained fr

Sample no Location of oil shale Fraction of bitumen

2 El-Beida Maltene

3 El-Nakheil Maltene

4 Abu-Tundub-I Maltene

5 Abu-Tundub-II Maltene


3.2. UV–Visible spectrometry of metalloporphyrins

The porphyrins, obtained from TLC, were analyzed by meansof UV–Visible spectroscopy, the spectra of Ni andFe-porphyrins extracted from maltene and asphaltenefractions of El-Beida sample are shown in Figs. 4 and 5,

respectively.The spectra revealed a sort band at 390 nm and two

characteristic absorption peaks assigned as / and b at545 nm and 515 nm, respectively. A representative spectra

om TLC of metalloporphyrins mixture.

UV–Visible bands / =bk= 545 k= 515 k = 390 Ratio

(/)(sort) (b) (sort)+ + + 2.21

+ + + 2.26

+ + + 2.23

+ + + 2.21



Table 6 UV–visible spectrometry of iron porphyrins obtained from TLC of metalloporphyrins mixture.

Sample no Location of oil shale Fraction of bitumen UV–Visible bands / =b/bk= 545 (/) k= 515 b k= 390 (sort) Ratio

2 El-Beida Asphaltene + + + 2.40

3 El-Nakheil Asphaltene + + + 2.28

4 Abu-Tundub-I Asphaltene + + + 2.79

Table 7 UV–Visible spectrometry of vanadyl porphyrins obtained from TLC of metalloporphyrins mixture.

Sample no Location of fraction oil shale of bitumen UV–Visible bands / =bk = 565 / k= 525 (b) k = 405 (sort) Ratio

2 El-Beida maltene + + + 1.33

2 El-Beida asphaltene + + + 1.39

3 El-Nakheil maltene + + + 1.24

3 El-Nakheil asphaltene + + + 1.58

4 Abu-Tundub-I maltene + + + 1.21

4 Abu-Tundub-I asphaltene – – – –

5 Abu-Tundub-II maltene + + + 1.22

5 Abu-Tundub-II Asphaltene + + + 1.56


for Vo-porphyrins extracted from maltene and asphaltenefractions of EL-Beida sample are shown in Figs. 6 and 7,

respectively, the spectra revealed a short band at 405 nm andtwo peaks / and b) at 565 nm and 525 nm , these results arein agreement with those obtained early[17–19]. The / =b ratiosare calculated from the heights of the two characteristicabsorption peaks / and b (h1 and h2), as shown in Figs. 3–6for Ni, Fe and Vo porphyrins, respectively. The results of

/ =b ratios of metalloporphyrins extracted from maltene andasphaltene fractions of the studied oil shale samples are pre-sented in Tables 5 and 6, Table 5 shows that / =b ratio forNi porphyrins from TLC of maltenic–metalloporphyrins frac-

tion has intermediate values ranging between (2.21–2.26).These values are very close to those of Ni DPEP. Table 6shows that / =b ratio for Fe porphyrins has values between(2.40 and 2.79) which are higher than those of Ni DPEP.

The maltenic Vo-porphyrins Table 7 exhibit lower / =bratios (1.21–1.33) than those for asphaltenic fractions

(1.39–1.58), it was mentioned [15] that / =b ratios of DPEPVo and Etio Vo-porphyrins were 2.00–1.3, respectively, so themaltenic Vo-porphyrins are of type DPEP, whereas the asphal-tenic Vo-porphyrins may be a mixture of DPEP and Etio.

From the above discussion it is clear that UV–Visible spec-trometry cannot accurately differentiate between Ni and Feporphyrins, therefore HPLC technique was used for this

purpose.

3.3. High performance liquid chromatography (HPLC)

The HPLC chromatograms of Vo, Ni and Fe-porphyrins,extracted from TLC plats are shown in Fig. 7, for


Vo-porphyrins. Fig. 8(a) reveals peaks at retention time (Rt)ranging between 13 min and 54 min. The chromatogram shows

the max at 54 min for Ni-porphyrins. Fig. 8(b) shows peaks inthe range from 40 to 111 min of (Rt) and a strongest peak at84 min. for Fe-porphyrins. Fig. 8 (c), the peaks are found at

higher (Rt) 79–138 min. and a max. conc. of Fe-porphyrinsappears at (Rt) 133 min. From these results it can be suggestedthat the elution of metalloporphyrins could be related to the

differences in their polarity.It seems that the polarity of metallo-porphyrins increases in

the following order: Vo-porphyrins < Ni-porphyrins < Fe-porphyrins.

From the HPLC results it is clear that this technique couldbe used as a successful tool to characterize Fe-porphyrin fromNi-chelating complexes.

4. Conclusion

(1) It has been noticed that maltene fraction of all samples

contains Ni and Vo-porphyrins whereas asphaltene frac-tion contains Fe and Vo porphyrins, this is with theexception of Abu-Shegeili sample where metallo-porphyrins were not observed in its maltenic or asphal-

tenic fractions.(2) HPLC was used for fingerprinting Vo, Ni and Fe-por-

phyrins because it was found that Vo, Ni and Fe-por-

phyrins exhibited a wide different chromatograms.

So HPLC technique could be used as a successful tool to

characterize Fe porphyrins from Ni chelating complex.



Figure 8 HPLC Spectra of (a) vanadyl (b) nickel and (c) iron porphyrins extracted from El-Nakheil oil shale.





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Preliminary study of metalloporphyrins in some oil shales, red sea, Egypt1 Introduction1.1 Chemistry of metalloporphyrins1.2 Structure of porphyrins

2 Materials and methods2.1 Preparation of oil shale samples2.2 Extraction of bitumen

3 Results and discussion3.1 Isolation of metalloporphyrins3.1.1 Extraction by column chromatography3.1.2 Purification by TLC

3.2 UV–Visible spectrometry of metalloporphyrins3.3 High performance liquid chromatography \(HPLC\)

4 ConclusionReferences

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