Physicochemical studies on the desulfurization process of organosulfur compounds occur in crude oil by metallo-complexation method

Article abstract of DOI:10.1016/j.molliq.2017.01.095

All over the world researchers in accelerating to development the new and modern methods of desulfurization process to overcome the presence of residual sulfur compounds in the crude oil, which has harmful effects and undesirable. Out of these important r

Full text of DOI:10.1016/j.molliq.2017.01.095

Accepted Manuscript
Physicochemical studies on the desulfurization process of
organosulfur compounds occur in crude oil by metallo-
complexation method
A. Alhadhrami, Mosad A. Al-Ghamry, Aly H. Atta, Ahmed I. El-
Shenawy, Moamen S. Refat, Mohamed A. Al-Omar, Ahmed M.
Naglah
PII:
S0167-7322(17)30212-X
doi: 10.1016/j.molliq.2017.01.095
MOLLIQ 6897
DOI:
Reference:
To appear in:
Journal of Molecular Liquids
Received date:
Accepted date:
16 January 2017
30 January 2017
Please cite this article as: A. Alhadhrami, Mosad A. Al-Ghamry, Aly H. Atta, Ahmed I. El-
Shenawy, Moamen S. Refat, Mohamed A. Al-Omar, Ahmed M. Naglah , Physicochemical
studies on the desulfurization process of organosulfur compounds occur in crude oil by
metallo-complexation method. The address for the corresponding author was captured
as affiliation for all authors. Please check if appropriate. Molliq(2017), doi: 10.1016/
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ACCEPTED MANUSCRIPT
Physicochemical studies on the desulfurization process of organosulfur compounds occur
in crude oil by metallo-complexation method
1
2,3
3,4
3,5
A. Alhadhrami , Mosad A. Al-Ghamry , Aly H. Atta , Ahmed I. El-Shenawy , Moamen
1
*,6
7
7,8
S. Refat , Mohamed A. Al-Omar and Ahmed M. Naglah
1
Department of Chemistry, Faculty of Science, Taif University, Al-Hawiah, Taif, P.O. Box 888
Zip Code 21974, Saudi Arabia
2
Department of Chemistry, Faculty of Education, Ain Shams University, Roxy, Cairo, Egypt
3
Department of Chemistry, Faculty of Science, Dammam University, Kingdom Saudi Arabia
4
Department of Chemistry, Faculty of Science, Suez University, Suez, Egypt
5
Department of Chemistry, Faculty of Science, Benha University, Egypt
6
Department of Chemistry, Faculty of Science, Port Said University, Port Said, Egypt
7
Department of Pharmaceutical Chemistry, Drug Exploration & Development Chair, College of
Pharmacy, King Saud University, Riyadh 11451, Saudi Arabia
Peptide Chemistry Department, Chemical Industries Research Division, National Research
8
Centre, 12622-Dokki, Cairo, Egypt
msrefat@yahoo.com
Abstract
All over the world researchers in accelerating to development the new and modern
methods of desulfurization process to overcome the presence of residual sulfur compounds in the
crude oil, which has harmful effects and undesirable. Out of these important research aims to use
various copper(II) salts as catalysts to break the bond between the carbon and sulfur in thiourea
compound as one of the initial organic compounds containing the sulfur element, which is
present in many of the organic compounds present in crude oil. In literature survey at room
temperature the chemical reactions between thiourea and different copper(II) salts give
copper(II) complex with octahedral geometry and molecular formula as [Cu(NH CSNH ) ]X
2
2
2 6
-
-
-
-
--
where X= Cl , Br , CH COO , NO , SO . The novelty of our study is precipitated yellow sulfur
3
3
4
o
element and black copper(II) sulfide at elevated temperature ~90 C through the molar ratio 1:6
+
+
(
Cu : thiourea) in aqueous media. The infrared spectra of the resulted precipitated product
clearly indicate the absence of bands due to thiourea. The scanning electron microscopy (SEM)
and X-ray energy dispersive spectrometer (EDX) are scanned to check the morphological
surfaces and the basic elements constituting the reaction products. A chemical mechanisms
discussing the formation of sulfur and copper(II) sulfide are suggested.
Keywords: Desulfurization; infrared spectra; copper(II) ions; thiourea; SEM; EDX.

ACCEPTED MANUSCRIPT
1
- Introduction
The variuos transition/non-transition metal complexes of thiourea as rich donating
chelation exhibit an interesting efficiency for biological activity including anticancer [1],
antimicrobial [1-3], antibacterial [4], antifungal [5], antimalarial [6] and anti-tuberculosis [7].
Many scientific researchers were studied the coordination chemistry of benzoyl-substituted
thioureas and related ligands toward metals where the ligand usually coordinated via sulfur and
oxygen atoms, giving a six membered ring moiety [3-5]. These chelations able to coordinated to
as neutral ligands or as anionic ligands with arrange metal centers [8-10]. The cobalt(II)
complexes of thiourea derivatives form tetrahedral geometry with general formula CoL X
2
2
(where X= nitrate or acetate; L= thiourea derivatives) [11].
The desulfurization processes have been developed in order to removal of the inorganic
sulfur from coal before combustion [12], but on the other hand, these methods have not been
successful to removing organic sulfur such as thiophenols, aryl sulfides, and thiophenes [13-15]
which predicted formed from organic sulfur component of coal. Commonly, there are no official
methods and no basic documents in the chemistry of organic sulfur compounds depending on
chemical reagents and conditions helpful in the oxy-desulfurization processes (oxidation of
sulfur) [12-16]. However, the first oxidizing process for the organic sulfur compounds was
accomplished by enhanced chemical reactivity of functionalities of electrophilic reagents (e.g.,
sulfoxides, sulfones, and sulfonic and sulfinic acids) in the presence of molten alkali (KOH or
NaOH) [17]. Desulfurization processes of different organic sulfur moieties (e.g.,
benzothiophenes derivatives) were one of the most interesting topics in petroleum and chemical
industries because of their application in the reduction of environmental pollution by
desulfurization of coal fuels [18-22]. It is worth mentioning that the desulfurization of
benzothiophenes derivatives converted to biphenyl have been discussed, but these reactions
taken times [23, 24], high temperatures [25–27], and low yields [28]. The desulfurization
processes of both dibenzothiophene sulfoxide and dibenzothiophene sulfone [29–33] using
oxidizers agents [27] have been discussed. Morales, et. al., [34] were described new
desulfurization methodology for the dibenzothiophenes derivatives (dibenzothiophene sulfoxide
and dibenzothiophene sulfone) using lithium and sodium mixture to produced a high yield of
biphenyl as shown in formula 1.
2

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-
M2S
S
Dibenzothiophene
Li/Na
Dioxan
-
M SO
2
Reflux
S
Biphenyl
O
Dibenzothiophene sulfoxide
-
M SO
2 2
S
O
O
Dibenzothiophene sulfone
Formula 1: Desulfurization of dibenzothiophene, dibenzothiophene sulfoxide and
dibenzothiophene sulfone organosulfur compounds using sodium-lithium mixture.
The hydrodesulfurization treatment process was discussed as a one of techniques helpful
in the removal of organic sulfur existed in the petroleum fuels to reach the good quality of sulfur
levels. The chemical mechanism of this method depend on the conversion of organosulfur
compounds to hydrogen sulfide in the presence of some transition metal ions as a powerful
catalyses which produced metal sulfides and liberated of hydrogen gas [35]. The cleavage of the
bond between C–S atoms is an important aim to scientists working in the field of petroleum
industrial, for example the hydrodesulfurization process of thiophene and its derivatives was a
target to removal of sulfur impurities in petroleum ore [36-38] to achievement the satisfied
environmental levels. Some articles [39-41] were focused on the using of transition metal
complexes as probe catalyses in the carbon-sulfur bond. The rhodium dimmer, binuclear iridium,
palladium and nickel(II) organmetallic complexes [42-44] have been successful in C–S cleavage
process for dibenzothiophene and related compounds see formula 2.
3

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Ph
Pri2
Pri
Pri
i
2
2
Pr 2
P
P
o
P
P
H
S
7
0 C
Rh Rh
Rh Rh
H
H
P
Pr
P
Pr
P
Pr
P
Pr
S
i
i
i
i
2
2
2
2
Formula 2: The C–S cleavage process for dibenzothiophene using rhodium hydride dimmer
complex
This research paper aimed to use thiourea as a model for organosulfur compounds which
containing sulfur element that is non-desirable exhibited in petroleum fuels and trying to removal
of sulfur by cleavage of C–S bond using copper(II) salts as an interesting catalysts.
2
- Experimental
2
-1-Synthesis
Reagent and chemicals are in high grade and used without purifications. In a six 250 mL
volumetric flask thiourea (4.62 g, 60 mmol) was dissolved in deionized water (100 mL). To these
was added 10 mmol of dissolved/suspended of CuCl , CuSO , Cu(CH COO) , Cu(NO ) , CuBr
2
4
3
2
3 2
2
or CuCO in 10 mL deionized water. The mixtures were heated at reflux for 15 h. The yellow
3
and/or black precipitations of sulfur or copper sulfide compounds were filtered and washed
o
several times with hot water then dried at 70 C in an oven for 3 h till constant weight. The yields
were in ratio 60-67 %.
2
-2- Instruments
The elemental analyses of carbon, hydrogen, nitrogen and sulphur contents were
performed using a Perkin Elmer CHN 2400 (USA). The content of copper metal was determined
using iodometric titrations [45]. The infrared spectra with KBr discs were recorded on a Bruker
-1
FT-IR Spectrophotometer (4000–400 cm ). Scanning electron microscopy (SEM) images were
taken in Quanta FEG 250 equipment and Energy Dispersive X-ray Detection (EDX) was taken in
Joel JSM-6390 equipment, with an accelerating voltage of 20 KV.
4

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3
- Results and discussion
At room temperature, there are number of thiourea-metal complexes have been
investigated [46] and it was found that the first class of metals studied (Pt, Pd, Zn, and Ni) form
M-S bonds, since the C-N bond stretching frequency increases and the C-S bond stretching
frequency decreases upon coordination without an appreciable change of the (NH) stretching
frequency. Using the same criterion, thiourea complexes of Fe(II), Mn(II), Co(II), Cu(I), Hg(II),
Cd(II), and Pb(II) were also shown to be S-bonded [47, 48]. The only metal that is reported to be
N-bonded in its complexes with thiourea is titanium (IV) [49]. The octahedral copper(II) thiourea
2
+
complex [Cu(TU) ] , (TU= thiourea; formula 3) has been prepared and investigated [47, 48].
6
H N
NH2
2
C
NH2
H N
2
S
H N
C
S
S
S
C
NH2
2
Cu
S
H N
2
C
S
C
NH2
H N
2
NH2
C
H N
2
NH2
2
+
Formula 3: The octahedral copper(II) thiourea complex [Cu(TU) ] at room temperature
6
The chemical reactions in aqueous solutions between thiourea and (CuCl , CuSO ,
2
4
Cu(CH COO) , Cu(NO ) , CuBr or CuCO ) salts with 1: 6 (copper(II) salt: thiourea) molar ratio
3
2
3 2
2
3
o
at ca. ~90 C formed a yellow and black solid precipitations for the (CuCl , CuSO ,
2
4
Cu(CH COO) , or Cu(NO ) ) and (CuBr or CuCO ) salts reacted with thiourea, respectively.
3
2
3 2
2
3
The infrared spectral bands of the solid precipitated materials are represented in Fig. 1A-G.
These IR bands have not been recorded any bands assigned to coordinated thiourea, also, there
are no absorption bands in the infrared spectra of copper(II) thiourea systems at elevated
temperature. This strongly confirms that the reactions were completely finished and the reaction
products are yellow sulfur and black copper(II) sulfide. This paper shows a significant point for
the pathways to get the copper(II) sulfide salt and sulfur element in a pure grade and simple
procedures. It is difficult to generalize the result, which was obtained on all transition metal salts,
5

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but we can say that the metals and their different ions have an important role in the control
outputs of chemical reactions. This fact has been confirmed in this paper where we found that the
chloride, nitrate, acetate, and sulfate ions, all gave pure yellow sulfur while bromide and
carbonate ions gave copper(II) sulfide black. Generally, we can review the role of the copper
metal ions as a catalyst to break the bond between the carbon and sulfur atoms in a thiourea
compound briefly illustrated by the following reaction mechanisms;
1
- Reaction mechanism to form copper(II) sulfide
o
9
0 C
i- 6(NH ) CS + 12H O  6(NH ) S + 6CO2
2
2
2
4 2
o
9
0 C
ii- 6(NH ) S + 6CuX 
4
2
2
1
2NH X + 6CuS (ppt)
4
(Where: X= Br or CO3)
2
- Reaction mechanism to form sulfur
o
0 C
i- 6(NH ) CS+12H O+ nH O  6(NH ) S + 6CO + nH O
9
2
2
2
2
4 2
2
2
o
9
0 C
ii- 6(NH ) S+6CuX + nH O  12NH X+6CuS+ nH O
4
2
2
2
4
2
o
9
0 C
iii- 12NH X+6CuS+ nH O  2[Cu(NH ) ].2X +6H S+4[Cu(H O) ].4X + nH O
4
2
3 6
2
2
2
6
2
2
o
9
0 C
iv- 2[Cu(NH ) ].2X +6H S+4[Cu(H O) ].4X 
3
6
2
2
2
6
2
2
[Cu(NH ) ].2X +6H + S (ppt) +4[Cu(H O) ].4X
3 6 2 2 2 6 2
(
Where: X = Cl , SO , (CH COO) or (NO ) )
2 2 4 3 2 3 2
Subsequently, in the reaction mechanism to form copper(II) sulfide and pure sulfur element,
thiourea was hydrolyzed by water molecules to form ammonium sulfide and carbon dioxide,
which further reacted with copper(II) ions to form copper sulfide compound and ammonium
salts. Furthermore, the third and fourth steps in case of reaction mechanism to form sulfur
element, the formation of two soluble copper(II) complexes as [Cu(NH ) ].2X and
3
6
2
[
Cu(H O) ].4X play an essential role for the hydrodesulfurization treatment to liberate hydrogen
2 6 2
gases and remain sulfur residue. The X-ray powder diffraction patterns of the titled compound
resulted from the chemical reactions between copper(II) bromide or carbonate with thiourea at
6

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o
++
~
90 C in aqueous media with 1:6 molar ratio (Cu : thiourea) was indexed with the copper(II)
sulfide structure (JCPDS: 24-0060). The SEM image of CuS and S element are shown in Fig. 2
and shows copper sulfide particles in the range of 1 m in diameter.
EDX spectra in Fig. 3 confirmed the presence of copper and sulfur in the samples formed
from the reaction of CuCO and CuBr , while EDX recorded only sulfur element in case of the
3
2
reaction between CuCl , CuSO , Cu(CH COO) or Cu(NO ) and thiourea.
2
4
3
2
3 2
4
- Conclusions
This article was introduced simple, effective and cheap method for the desulfurization of
thiourea compound. This study is a paved road for a lot of studies that can be used with sulfur
compounds to break the bond between the carbon and sulfur and get rid of the harmful effects
caused by environmental pollution with sulfur.
7

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1
00
8
6
4
2
0
0
0
0
0
4
000 3500 3000 2500 2000 1500 1000 500
-
1
cm
Fig. 1: Infrared spectra of A: thiourea, and B: CuBr , C: CuCO , D: CuCl , E: Cu(NO ) , F:
2
3
2
3 2
o
Cu(CH COO) and G: CuSO thiourea reaction products at 90 C.
3
2
4
8

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1
0

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Fig. 2: SEM images of A: CuBr , B: CuCO , C: CuCl , D: Cu(NO ) , E: Cu(CH COO) and F:
2
3
2
3 2
3
2
o
CuSO thiourea reaction products at 90 C.
4
1
1

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1
2

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1
3

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Fig. 3: EDX spectra of A: CuBr , B: CuCO , C: CuCl , D: Cu(NO ) , E: Cu(CH COO) and F:
2
3
2
3 2
3
2
o
CuSO thiourea reaction products at 90 C.
4
1
4

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Acknowledgments
The project was financially supported by King Saud University, Vice Deanship of Research
Chairs.
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Highlights


Copper(II) salts used as catalysts
Desulfurization of thiourea compound in aqueous media using simple, effective and
cheap method.


This experimental method study the break bond between the carbon and sulfur.
A chemical mechanisms discussing the formation of sulfur and copper(II) sulfide.
1
8