Characterization of shale oil by spectroscopic and ...Shale oil is defined as an oil that be derived...

82

ISSN: 2313-3759 www.ijsrit.com

Characterization of shale oil by spectroscopic and chromatographic

techniques

Yahya H. Khraisha a, 1

, Jamil J. Asfarb, Ahmad A. Radwan

a

a Department of Chemical Engineering Department, University of Jordan, Amman, 11946, Jordan

b Department of Mechanical Engineering Department, University of Jordan, Amman, 11946, Jordan

Abstract

Spectroscopic and chromatographic techniques were used to investigate the composition and

chemical structure of the extracted shale oils. The shale oils were extracted from two Jordanian oil

shale fields using autoclave devise and fluid solvents at sub- and supercritical conditions. The

analyses show that the variation of sub-and supercritical extraction conditions, particle size, solvent

type and shale field has a slight effect on the composition and chemical structure of the produce oil.

Ultraviolet visible (UV-vis) spectra show two clear signals in the ranges of 210-235 nm and 275-

280 nm. The first could be attributed to benzenic compounds and the other one to naphthenic

compounds. The 1HNMR results indicate that the protons of methyl and methylene represent a high

proportion of the hydrogen (75-85%) in most shale oil samples. GC analysis shows that the oil

samples contain n- alkane (n-C25) with a high predominant proportion. FT-IR results also support

these findings.

Keywords: Shale oil; UV-vis spectroscopy; FT-IR; 1HNMR; GC

1. Introduction

Shale oil is defined as an oil that be derived from the organic matter (kerogen) of the oil shale

sedimentary rocks using different techniques from direct and indirect heating to recently solvent

critical extraction [1-4]. This oil is considered an important prospective energy sources in the

world since it represents about one third greater than the proven resources of conventional crude

oil [5].

Jordan is highly influenced by the world energy situation since it is a non-oil producing country.

It has a future plan or prospect that oil shale utilization will be one of Jordan's future energy

sources. Oil shale resources in Jordan are estimated to be more than 50 billion tons, in which the

oil content is about 4 billion tons [6]. Its large deposits are widely distributed all over the

country, particularly in the central region [7].

1 Correspondence to Y. H. Khraisha, Chemical Engineering Dept., University of Jordan, Amman,

Jordan. Email: [email protected]

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International Journal of Scientific Research and Innovative Technology Vol. 7 No. 2; March 2020

Shale oil is similar to petroleum hydrocarbons with extremely complex molecular structure

containing oxygen, nitrogen, sulfur and metal elements. It is often produced by the thermal

destructive distillations at temperatures 500-600 °C . The chemical and physical properties of

the extracted shale oil were found to change for the investigated oil shales depending on the

origin or nature of kerogen, the type of the extracting technique as well as the operating

conditions. The extracted oil could be highly aromatic, aliphatic, naphthenic or somewhere in

between. In general, shale oil has a low API gravity (18 – 22), low hydrogen to carbon ratio and

high concentration of nitrogen, arsenic, sulfur, and metals. Therefore, it cannot be processed

directly without upgrading [8].

Investigators have used chromatographic methods (capillary GC, HPLC, GC-MS), infrared

spectroscopy (FT-IR) and nuclear magnetic resonance (1H NMR,

13C NMR) to obtain qualitative

and quantitative information on the compositional and structural analysis of heavy

hydrocarbons, bitumen, and petroleum fractions. For example, Khraisha et al. [9] have analyzed

Jordanian shale oil samples derived from an oil shale flash pyrolysis unit using spectroscopic

and GC instruments. The 1H NMR results have shown that the protons of methyl and methylene

represent the bulk of the hydrogen in the most shale oil samples. In addition, the GC analysis

indicates that the oils contain n-alkanes with a predominant proportion of n-C25. Chham et al.

have analyzed Moroccan oil shale samples using FTIR spectroscopy [10]. The results of FT-IR

spectra have indicated that the shale oil contains a substantial proportion of aromatic

hydrocarbon compounds and fewer amounts of paraffins. However, the nature and the type of

kerogen affects significantly the quality and composition of the produced shale oil. Hufnagel et

al. [11] have investigated a Jordanian oil shale deposits and shown that the organic material of

the oil shale consists largely of prebitumen bituminous ground-mass. This was formed during

the early diagenetic process by mainly microbial influence, from initial plant and animal

materials with a lipidic composition. The level of temperature as well as the extraction

technique influence the composition of the produced shale oil. For instant, at high temperature ~

500°C, aliphatic C-C and ether C-O bonds are broken and rearranged to yield aromatic

hydrocarbons [12]. Feng et al. have studied the chemical composition of bitumens in pyrolyzed

Green River oil shale by 13

C NMR spectroscopy [13]. The results have revealed that the bitumen

which formed during the intermediate stage of kerogen decomposition becomes more aromatic

(less aliphatic) with increasing maturity.

In short, shale oil is a complex mixture of hydrocarbon compounds in which the analysis using

different instrumental techniques provides important information that impacts on the handling,

transportation, upgrading and refining. In this study, spectroscopic (FT-IR, UV-Vis, 1HNMR)

and chromatographic (temperature programmed-GC) analyses have been done on oil samples

derived from Jordanian oil shale under sub and supercritical critical conditions of fluid

solvents.

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2. Experimental

2.1 Oil samples

The oil samples were derived from two Jordanian deposits; El-Lajjun and Sultani. The fluid

supercritical extraction was conducted in an autoclave devise under a high pressure of inert

atmosphere. The apparatus and procedure of oil extraction have been given in detail

elsewhere [14]. Table 1 shows the conditions, variables and the analytical techniques for the

different shale oil samples.

Table 1. Conditions and analytical methods for different shale oil samples derived from

extraction unit. Sample T, °C P, bar T, min dp. µm Solvent GC UV 1HNMR IR Field

ST1 100 42 60 850-1400 Toluene X El-Lajjun

ST2 150 42 60 850-1400 Toluene X X X X El-Lajjun



SD1 318 42 60 850-1400 Toluene X X Sultani

SD2 318 42 60 500-850 Toluene X X El-Lajjun

SD3 318 42 60 255-355 Toluene X X X X El-Lajjun



St1 318 42 20 850-1400 Toluene X X Sultani

St2 318 42 40 850-1400 Toluene X X X X Sultani

St3 318 42 80 850-1400 Toluene X X Sultani

SP1 318 10 60 850-1400 Toluene X X El-Lajjun

SP2 318 20 60 850-1400 Toluene X X El-Lajjun

SP3 318 30 60 850-1400 Toluene X X X X El-Lajjun

SSo1 273 60 60 850-1400 Trichloroethylene X X Sultani

SSo2 240 80 60 850-1400 Methanol X X Sultani

SSo3 240 50 60 850-1400 Benzene X X Sultani

2.2 Analytical methods

2.2.1 Fourier Transform Infrared Spectroscopy (FTIR) Analysis

The infrared analysis was performed using an FTIR Nicolet, Impact 400 infrared

spectrometer for detecting functional groups and characterizing covalent bonding

information in shale oil samples.

2.2.2 Ultraviolet spectroscopy (UV-Vis)

A Milton Roy, Spectronic instrument 1201 UV was used to measure the electronic

spectra of shale oil samples. The samples were dissolved in n-hexane.

2.2.3 Proton nuclear magnetic resonance spectroscopy (1H NMR)

A Bruker Avance DPX300 MHz Solution State 1H NMR spectroscopy was used to

analyze the oil samples. The samples were dissolved in dichloromethane.

2.2.4 Gas chromatography (GC)

Shale oil samples were analyzed using a Vraian gas chromatograph, Model 3300. The

sample concentration was 0.5g in 5ml hexane. In order to specify the peak's identity,

pure n-paraffins (C12, C14, C16, C18 and C20) were firstly injected, and hence, the

retention time for each paraffin peak was determined. However, to specify the other n-

alkanes carbon atom, gas oil was injected and its peaks were compared with pure n-

paraffins, and the others extrapolated. To certain this calibration procedure, the gas oil

spectrum was compared with other published gas oil spectra, analyzed at the same

operating and packing conditions [15].

International Journal of Scientific Resea

3. Results and Discussion

3.1. Fourier Transform Infrared Spec

The FTIR is a useful tool to underst

and the functional groups present in i

shale oil samples, ST2, ST4, SD3, SP

general, the figure indicates a comple

the tested samples have shown a si

spectra were based on the informatio

intensity band at 3050 cm-1

represent

at 2924 cm-1

and 2853 cm-1

are du

stretching, respectively. The bands fa

C=O group. The samples also show

(1375 cm-1

) and aromatic oxygenate

wavelength bands at 873, 774, 772 cm

3.2.UV-visible spectroscopy analysis

Figure 2 shows a typical examp

ST2, SD3, SP3, St2 and SSo2 at

plots represent the wavelength ve

In general, most of the samples s

to 1.4. The shale oil sample w

absorbance value compared to the

the absorbance value, the lower

Therefore, it can be concluded

(toluene); ST2, ST4, SD3, SP3

sample extracted by polar solvent

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esearch and Innovative Technology Vol. 7 No

Spectroscopy (FTIR) Analysis

nderstand the chemical composition of a liquid heavy

nt in it. Figure 1 shows a typical example of the FTIR

D3, SP3, St2 and SSo3 at different extracting conditio

omplex composition of the oil with a high number of

n a similar spectrum with slight differences. Interpr

rmation acquired from the literature [16,17]. For ex

resents aromatic C-H stretching. The strong absorptio

due to methyl C-H stretching compounds and m

ands falling between 1708 and 1724 cm -1

are attribu

show C-H bending (1454-1459 cm-1

), C-H bending in

genated compounds such as aromatic ether at 1073

772 cm-1

are considered aromatic C-H bending out-of

alysis (UV-vis spectra)

xample of ultraviolet – visible spectra for shale oil

So2 at different extracting conditions as mentioned

gth versus the absorbance over a range of 200 – 600 n

ples show similar spectra with maximum absorbanc

ple which was extracted by methanol (SSo2) sho

to the others extracted by toluene. It has been shown

lower the aromatic content in the heavy oil hydr

luded that the shale oil samples extracted by no

, SP3 and st2 have a higher content of aromatics t

olvent (methanol).

7 No. 2; March 2020

heavy hydrocarbons

e FTIR spectra of the

nditions (table 1). In

ber of peaks. Most of

nterpretations of the

or example, the low

orption bands falling

and methylene C-H

ttributed to carbonyl

ing in methyl groups

1073 cm-1

. The long

of-plan.

le oil samples; ST4,

ioned in table 1. The

00 nm wavelength.

orbance (λmax) of 0.5

) shows the lowest

shown that the lower

l hydrocarbons [18].

nonpolar solvent

atics than that SSo2

ISSN: 2313-3759

Figure 1(A). FT

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FT-IR spectra of shale oil samples; ST4, ST2, SP3

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, SP3


Most of the tested samples show

The first signal range could be

naphthenic compounds [9, 19, 20

Figure 1 (B) FT

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show clear signals in the ranges of 210-235 nm an

uld be attributed to benzenic compounds and the

19, 20].

) FT-IR spectra of shale oil samples; SD3, St2, SSo3

7 No. 2; March 2020

nm and 275-280 nm.

the second one to

ISSN: 2313-3759

Figure 2. UV-Vis spectra of shale oil

3.3. Proton Nuclear Magnetic Resona

Figure 3 illustrates the 1H NMR

samples. Figure 4, for example,

shale oil sample. The absorption

saturated carbons in terms of

aromatic protons can be observe

indicates the detailed assignmen

distribution of the shale oil samp

hydrogen, Har, represents 15-25 %

high proportion of Har (90 %).

SP3) which were extracted by to

about of 40 %, 10-14% of the t

protons represent about 75% of t

by toluene.

88

ale oil samples; ST4, ST2, SD3, SP3, St2, SSo2.

esonance Spectroscopy (1H NMR Spectra)

NMR Spectra for ST4, ST2, ST3, St2, SD3, SP3 and

mple, shows the detailed shape of the 1H NMR spe

rptions in region 0.5 to 2 ppm indicate the presence

s of methyl and methylene groups. Moreover, th

bserved in regions 4 to 5 and 7 to 8 ppm, respect

gnments of the bands of the 1H NMR spectra and

l samples [9]. From the results (table 2), it is clear th

25 % of the total protons except the sample SSo3

%). By contrast, the oil shale samples (ST4, ST2, S

by toluene indicate a hydrogen of types Hβ and Hγ

the total hydrogen, respectively. In short, methyl

% of the hydrogen for most shale oil samples particu

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3 and SSo3 shale oil

R spectrum of SD3

esence of protons on

er, the olefinic and

espectively. Table 2

ra and the hydrogen

lear that the aromatic

SSo3 which shows a

ST2, ST3, St2, SD3,

γ (see table 2) of

ethyl and methylene

particularly extracted

89


Figure 3. 1HNMR spectra of ST4, ST2, ST3, St2, SD3, SP3 and SSo3 shale oil.

Table 2: Assignments of the bands in the 1HNMR spectra (Khraisha et al.,2003) of

the shale oil sample

Hydrogen Type Symbol 104 x chemical

shift

Hydrogen distribution, %

ST2 ST3 ST4 SP3 SD3 St2 SSo3

Aromatic Har 6.0 – 9.0 24.01 22.59 25.19 13.29 24.34 21.46 92.28

Ring-joining

methylene Hα, 2 3.5 – 5.0 1.75 1.71 1.94 3.73 4.47 4.19 0.00

CH3, CH2 and CH-α

to an aromatic ring Hα 2.0 – 3.4 24.32 24.72 25.19 20.24 20.37 27.23 1.17

β-CH3, CH2 and CH-β

or further from an

aromatic + paraffinic CH2 and CH

Hβ 1.0 – 2.0 37.52 39.91 36.50 48.94 38.96 34.95 5.35

CH3-γ or further from

an aromatic ring +

paraffinic CH2

Hγ 0.5 – 1.0 12.40 11.08 11.18 13.80 11.86 12.17 1.20

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Figure 4. 1H N

90

H NMR spectra of SD3 shale oil.

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3.4. Gas Chromatography (GC)

Figure 5 (A, B, C) shows GC peak

oil samples, ST1, ST3, SD1, St1, SP

samples.

Figure 5 (A): Packed column gas chro

paraffins, gas oil and shale oil (ST1).

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Gas oil


C peaks of normal alkanes (C12, C14, C16, C18 and C

t1, SP1, SSo1, and SSo2, compared with gas oil and

as chromatography n- alkanes identified by carbon number

ST1).

Pure Paraffins

7 No. 2; March 2020

nd C20) for the shale

il and pure paraffins

umber for pure

ISSN: 2313-3759

Figure 5 (B). Packed column gas ch

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gas chromatography for ST3, St1 and SD1 shale oil sample

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samples.


Figure 5 (C). Packed column gas c

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n gas chromatography for SP1, SSo1 and SSo2 shale o

SSo1

7 No. 2; March 2020

shale oil.

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The distributions of n-alkanes relative to n-C5 (area to area peak’s ratio) for the different analyzed

shale oil samples are given in table 3. Clearly seen, the normal alkanes obtained are n-C15 to n-C32.

Moreover, the n-C25 represents the greatest quantity of the n-alkanes in most shale oil samples. In

general, most of the tested samples indicate close trends except samples SSo1 and SSo2 who show

only one peak (n-C25). On the other hand, the variation of operating conditions as well as the

shale’s field (see table 1) have no significant effect on the chemical structure of the shale oil

produced.

Table 3. Normal alkanes obtained from shale oils analysis by GC

a relative to the area of n-C25

Peak

No.

n-

alkanes

Relative quantitya

ST1 ST2 ST3 ST4 SD1 SD2 SD3 SD4 St1 St2 St3 SP1 SP2 SP3 SSo1 SSo2

C12 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

C13 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

C14 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

1 C15 0 0 0 0 0.060 0 0 0 0 0.064 0 0 0 0.071 0 0

C16 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

C17 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

2 C18 0 0 0 0 0 0 0 0 0.043 0.040 0 0 0 0.019 0 0

3 C19 0 0 0 0 0.094 0 0 0 0 0.016 0 0 0 0 0 0

4 C20 0 0 0.104 0.074 0.113 0 0 0 0 0.017 0 0.160 0.130 .016 0 0

5 C21 0.106 0 0 0 0 0 0 0 0.032 0 0 0 0 0 0 0

C23 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

6 C24 0 0 0 0 0 0 0 0 0.049 0.027 0 0 0 0 0 0

7 C25 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000

8 C26 0 0 0 0 0.039 0 0 0 0 0 0 0.75 0 0.054 0 0

9 C27 0 0 0 0.032 0.041 0 0 0 0 0.034 0 0 0 0.072 0 0

10 C28 0.059 0.064 0.114 0.103 0.038 0 0 0 0.172 0.025 0 0.276 0 0.161 0 0

11 C29 0.035 0.018 0.047 0.055 0.039 0.068 0.052 0.141 0.030 0.037 0.019 0.032 0.116 0.066 0 0

12 C30 0.100 0.043 0.089 0.099 0.095 0.091 0.059 0.099 0.071 0.101 0 0.077 0.05 0.106 0 0

13 C32 0.041 0.038 0.036 0.032 0.042 0.039 0.20 0.038 0.064 0.029 0.035 0.078 0.048 0.033 0 0

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4. Conclusions

Shale oil obtained at supercritical conditions has been analyzed using different spectroscopic

techniques (UV-Vis, FT-IR, 1HNMR) and Gas Chromatography in order to elucidate its

composition and chemical structure. From the results and analyses, the following conclusions

can be drawn.

1. The spectroscopic and chromatographic investigations inform that the variations in

supercritical conditions has no significant effect on the composition of the produced

shale oil.

2. UV-Vis shows two clear signals in the ranges of 210-235 nm and 275-280 nm. The first

could be attributed to benzenic compounds and the other one to naphthenic compounds.

3. Most of the shale oil samples (extracted by toluene) consist of a high proportion of

aliphatic hydrocarbons with a small amount of aromatic and olefinic compounds. 1HNMR supports this finding since the oil contains about 75% of methyl and methylene

protons. Moreover, FT-IR spectra enhance this finding.

4. GC analysis reveals that the oil samples contain n- alkanes with a predominant

proportion of n-C25.

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