Catalysed oxidation of quinoline in model fuel and the selective extraction of quinoline n oxide with imidazoline based ionic liquids

Catalysed oxidation of quinoline in model fuel and the selective extraction of quinoline N oxide with imidazoline based ionic liquids Egyptian Journal of Petroleum xxx (2017) xxx–xxx Contents lists av[.]

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Full Length Article

Catalysed oxidation of quinoline in model fuel and the selective

extraction of quinoline-N-oxide with imidazoline-based ionic liquids

Adeniyi S Ogunlajaa,⇑, Olalekan S Aladeb

a Department of Chemistry, Nelson Mandela Metropolitan University, P.O Box 77000, Port-Elizabeth 6031, South Africa

b

Petroleum and Petrochemical Engineering Laboratory, Department of Chemical Engineering, Obafemi Awolowo University, Ile-Ife, Osun State, Nigeria

a r t i c l e i n f o

Article history:

Received 4 December 2016

Revised 9 February 2017

Accepted 15 February 2017

Available online xxxx

Keywords:

Vanadium(IV) catalyst

Hydrogen peroxide (H 2 O 2 )

Quinoline

Oxidation

Ionic liquids

a b s t r a c t

Synthesised vanadium-coordinated N,N-bis(o-hydroxybenzaldehyde)phenylene diamine catalyst, [VO (sal-HBPD)] and supported catalyst, p[VO(sal-HBPD)] were employed for the oxidation of quinoline The use of [VO(sal-HBPD)] and p[VO(sal-HBPD)] for the oxidation of quinoline, (Quinoline-to-H2O2ratio 1:7) showed oxidation selectivity as quinoline-N-oxide (100%) was recorded as the oxidation product Quinoline-N-oxide was confirmed as the oxidation product through GC–MS Density functional theory (DFT) revealed hydroxylperoxido-species [VOO(sal-HBPD)] (II) as the reactive oxidized oxidovanadium specie responsible for the oxidation Ionic liquids, 3-methylimidazolium chloride and 1-butyl-3-methylimidazolium nitrate extracted 96% and 87% quinoline-N-oxide respectively

Ó 2017 Egyptian Petroleum Research Institute Published by Elsevier B.V This is an open access article

under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)

1 Introduction

Environmental concerns have resulted in stringent

specifica-tions for petroleum products including fuel oils; and had

necessi-tated the development of processes to upgrade heavy oil to

environmental friendly products[1] The current crude oil

reser-voirs are known to be of heavier and sourer composition, i.e the

produced oils (as well as their products) come with

organo-sulfur,-oxygen and -nitrogen compounds also known as

heteroa-toms[2–4] The Organo-nitrogen and –sulfur compounds in fuels,

are reported to (i) poison refining catalysts, (ii) emit NOx and

SOx to the environment when combusted, hence reacting with

water to form acid rain, (iii) reduce air quality, and (iv) possibly

lead to global warming[5]

The elimination of organosulfur compounds from fuel has been

largely reported, through the use of hydrodesulfurization (HDS)

process while literature reports on denitrogenation processes are

limited Organo-nitrogen compound removal is required to

main-tain NOx emissions below regulatory levels of <1 ppm, as

hydro-denitrogenation (HDN) process that is currently being employed

for the removal of nitrogenated compounds suffer limitations in

achieving the nitrogen content requirement Catalyst deactivation

as well as the reactivity of N-compounds of some nitrogen-containing compounds (quinoline, indoles, carbazoles, benzcar-bazoles, pyridines, pyrrole, azapyridines, aniline, phenantridines and porphyrins) have been identified as important factor affecting HDN processes Oxidative denitrogenation (ODN), a complemen-tary technique to the HDN, involves the oxidation of nitrogen-containing compounds to N-oxides compounds followed by the selective adsorption of the N-oxides[6] Several adsorbents such

as activated carbon, zeolites, silica, nanofibers, ion-exchange resins have been applied for the removal of nitrogen compounds in fuel oil [6–14] However, a great challenge is the development of an effective adsorbent with high surface area and can selectively adsorb nitrogen compounds in fuel An alternative approach is the use of ionic liquids (ILs) which offered better nitrogen com-pound extraction properties[15–17] In the recent years, ILs have attracted rising attention in the petroleum and petrochemical industries due to their versatility and prospective applications in various areas including flow assurance of viscous and bituminous hydrocarbons for improved production and transportation, upgrading and catalytic removal of heteroatoms and coke from the heavy oil, and surface activeness and potential use in the enhanced oil recovery of heavy oil[18–20]

In the present paper, we present the oxidation of a basic nitrogen compounds found in hydro-treated fuel, quinoline, using vanadium-coordinated N,N-bis(o-hydroxybenzaldehyde) phenylene diamine catalyst, [VO(sal-HBPD)] [21] as a catalyst and H2O2 as an oxidant The oxidation progress was monitored http://dx.doi.org/10.1016/j.ejpe.2017.02.004

1110-0621/Ó 2017 Egyptian Petroleum Research Institute Published by Elsevier B.V.

This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ).

Peer review under responsibility of Egyptian Petroleum Research Institute.

⇑ Corresponding author.

E-mail address: adeniyi.ogunlaja@nmmu.ac.za (A.S Ogunlaja).

Contents lists available atScienceDirect Egyptian Journal of Petroleum

j o u r n a l h o m e p a g e : w w w s c i e n c e d i r e c t c o m

Please cite this article in press as: A.S Ogunlaja, O.S Alade, Catalysed oxidation of quinoline in model fuel and the selective extraction of quinoline-N-oxide

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2 Experimental

2.1 Materials

Quinoline (98%, Sigma-Aldrich), hydrogen peroxide (30%, H2O2)

and absolute methanol (Merck Chemical) were used as received

2.2 General procedure for synthesis of catalysts

Vanadium-coordinated N,N-bis(o-hydroxybenzaldehyde)

phenylene diamine ligand, [VO(sal-HBPD)] synthesized and fully

characterized by Ogunlaja et al.[21]was also employed for the

oxi-dation of quinoline Both unsupported [VO(sal-HBPD)] and

sup-ported p[VO(sal-HBPD)] catalysts were employed for the studies

2.3 Metal content determination and leaching studies

Vanadium content on p[VO(sal-HBPD)] was determined by

weighing out 0.0025 g into a vial, and 5 mL of TraceSelect HNO3

(69%) was added This mixture was heated at 50°C for 48 h to leach

out the vanadium The acid-leached solution was then diluted with

deionized-distilled water to 100 mL, filtered with 0.45mM filters

and analysed by Atomic Adsorption Spectrometer (AAS)

2.4 Catalytic oxidation procedure

The catalytic oxidation of a known quantity of quinoline

(2.58 mL, 0.02 mol) was carried out using [VO(sal-HBPD)]/p[VO

(sal-HBPD)] (0.000167 mol of vanadium) and H2O2(0.14 mol) as

an oxidant In a 25 mL round bottom flask containing quinoline,

10 mL of methanol was added and the solution was heated at

drawing aliquots from the reactor at fixed time intervals and analyzing using a gas chromatograph GC conditions were Opti-mized to efficiently separate the products from the reactants in the Zebron Phenomenex ZB-5MSi capillary column (30 m 0.25 mm 0.25lm) on the GC-FID/GC–MS Helium was used as carrier gas at a flow rate of 1.63 mL min1with an average velocity

of 30.16 cm.sec1and a pressure of 63.73 kPa The analysis run was started with an oven temperature of 50°C ramping to 250 °C @

15°C min1 The oxidation products were confirmed using an Agilent 7890A gas chromatograph-mass chromatography (GC–MS) fitted with a 30 m 0.25 mm 0.25 mm DB-5 capillary column 2.6 Computational studies

Density functional theory (DFT) using Becke’s three-parameter hybrid exchange functional in combination with the gradient-corrected correlation functional provided by Perdew/Wang 91 (B3PW91) method[22]with LanL2DZ level was employed in deter-mining the electronic properties of [VO(sal-HBPD)] using the Gaus-sian[23]program (calculated at 298 K)

2.7 Ionic liquid synthesis Ionic liquids, butyl-3-methylimidazolium chloride and 1-Butyl-3-methylimidazolium nitrate were synthesized according

to the procedure reported by Ogunlaja et al.[24] For the purpose

of this report, the synthesis of 1-butyl-3-methylimidazolium chloride was achieved by refluxing a mixture of 1-methylimidazole (25 mL, 0.31 mol) and 1-chlorobutane (36 mL, 0.35 mol) in 50 mL of toluene at 110°C under vigorous stirring for 24 h The resulting brown viscous oil was allowed to cool down for approximately

24 h (Scheme 1), decanted, and then washed with acetonitrile

fol-Scheme 1 Synthesis of 1-butyl-3-methylimidazolium chloride and 1-butyl-3-methylimidazolium nitrate.

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lowed by ethyl acetate.1

H NMR (d, ppm in DMSO): 9.67 (1H, s), 7.99 (2H, d), 4.22 (2H, t), 3.98 (3H, s), 1.69 (2H, m), 1.09 (2H, m),

0.72 (3H, t) 1-Butyl-3-methylimidazolium nitrate:

1-butyl-3-methylimidazolium chloride (0.29 mol) in dichloromethane was

added to a solution of AgNO3(0.32 mol), and the resulting mixture

was stirred for 24 h (Scheme 1) The white suspended precipitate

of AgCl was filtered over Celite The complete replacement of Cl

with NO3 was established by further addition of a concentrated

AgNO3 solution to the ionic liquid until no precipitation of AgCl

Fig 1 (I) An ORTEP view of [VO(sal-HBPD)] with ellipsoids drawn at 50% probability level and (II) molecularly modelled [VO(sal-HBPD)].

Table 1

Some experimental and optimized calculated bond lengths [Å] parameters of [VO(sal-HBPD)] calculated by DFT (B3PW91) methods with LanL2ZD basis set.

Table 2

Some experimental and optimized calculated bond angles [°] parameters of [VO(sal-HBPD)] calculated by DFT (B3PW91) methods with LanL2ZD basis set.

Table 3

UV electronic properties of [VO(sal-HBPD)].

[VO(sal-HBPD)]

k = wavelength; f = oscillator strength.

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closely compare with the experimental data.

3.1.2 Electronic properties (UV adsorption analysis) The electronic properties of [VO(sal-HBPD)] were calculated using the TD-DFT approach on the previously optimized ground-state geometry of the complexes The calculations were performed

in gas phase as carried-out in the experimental studies

TD-DFT calculations predict three transitions in the visible region of the vanadium species with varying intensities and ener-gies The electronic transitions of [VO(sal-HBPD)] in gas phase are presented inTable 3 The maximum absorption wavelength corre-sponds to the electronic transition from the HOMO to LUMO The calculated excitation energies (E), oscillator strength (f) and wave-length (k) and spectral assignments are given inTable 3

Wavelength (nm)

0

1

V

O after 5 h

Fig 2 Spectrophotometric titration of [VO(sal-HBPD)] with H 2 O 2 (2 10 2 M) in

MeOH.

E(LUMO) = -6.75659

E(HOMO) = -9.80835 ΔE= 3.05176

E(LUMO) = -6.80067

E(HOMO) = -9.37977 ΔE= 2.57910

E(LUMO) = -6.78326

E(HOMO) = -9.46059 ΔE= 2.67733

Fig 3 The HOMO and LUMO molecular orbital position of the various oxidovanadium species, [VO(sal-HBPD)] (I) and the two proposed hydroxylperoxido species (II and III) [VOO(sal-HBPD)].

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3.2 Oxidation reaction

3.2.1 Electronic properties of oxidized VO(sal-HBPD)

The oxidation reaction progressed steadily on addition of the

oxidant, H2O2, to quinoline in the presence of catalyst

[VO(sal-HBPD)][21]at 70°C (Quinoline-to- H2O2ratio 1:7) UV/Vis studies

showed that intermediate species were formed during the catalytic

oxidation process through the gradual disappearance of the d–d

bands around 401 nm (Fig 2)[21], hence confirming the oxidation

of oxidovanadium(IV) to dioxidovanadium(V) and oxidoperoxido

species The oxidoperoxido species protonates to form the

hydroxyl-peroxidovanadium(V) species responsible for the

oxida-tion reacoxida-tion

3.2.2 HOMO-LUMO band gap analysis Several authors have revealed the protonation of peroxido moiety leading to a significant drop in the activation barrier for oxi-dation[25,26] However, the position of the protonation of

peroxo-VV-complexes may vary within the moiety[26] Herein, we explore the electronic properties of two proposed peroxido species (II and III), which may occur The molecular orbital plays an important role

in the electric and optical properties of [VO(sal-HBPD)] (I) and the two proposed hydroxylperoxido species (II and III) The HOMO rep-resents the ability to donate an electron, LUMO as an electron accep-tor[25] The plots of the HOMO and LUMO orbitals for the various oxidovanadium species, [VO(sal-HBPD)] (I) and the two proposed hydroxylperoxido species (II and III) were modelled in MeOH, and shown inFig 3 From the computation, it is found that the HOMO positions of complexes I, II and III are localized mostly around

Atoms

-0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8

1.0

species II species III

Mulliken's plot

Fig 4 The Mulliken atomic charge plot of the proposed hydroxylperoxido species (II and III).

Table 4

Mulliken atomic charges of [VOO(sal-HBPD)] species (II) and (III) using LanL2DZ basis

set.

Atoms Species (II) Species (III) Atoms Species (II) Species (III)

Table 5 Occupancy of natural orbitals (NBOs) and hybrids of [VO(sal-HBPD)] (I) calculated by the DFT level with LanL2DZ.

s(0.00%) p(100.00%)

s(33.19%) p(66.81%)

s(39.74%) p(60.26%)

s(35.21%) p(64.79%)

s(34.28%) p(65.72%)

s(46.95%) p(53.05%)

s(24.67%) p(75.33%)

s(25.09%) p(74.91%)

r*

s(35.48%) p(64.52%)

s(31.76%) p(68.24%)

r*

s(24.96%) p(75.04%)

* Underlined atoms represent the hybridized position.

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3.2.3 Mulliken atomic charge

The charge distribution on [VOO(sal-HBPD)] species (II and III)

was modelled to determine the possible species responsible for

the oxidation reaction and also to ascertain its influence on

vibra-tion spectra Mulliken net charges calculated at the DFT level with

LanL2DZ atomic basis set in methanol using Gaussian 09[23] The

vanadium atom V(1) attract the positive charge from the oxygen atom O(40) Atoms O(41) and O(42) of specie [VOO(sal-HBPD)] (II) are more negatively charged as compared to specie [VOO(sal-HBPD)] (III) confirming that its ability to donate more electron, hence more reactive

3.2.4 NBO analysis After establishing the reactivity of [VOO(sal-HBPD)] (II) via energy gap studies, NBO analysis was further performed on [VO (sal-HBPD)] (I) and [VOO(sal-HBPD)] (II) at the DFT level with LanL2DZ in order to elucidate the intra molecular re-hybridization and delocalization of electron density within the complexes[24,27] Three classes of NBOs were observed and these include, (i) Lewis-type (randpbonding or lone pair) orbital’s, (ii) valence non-Lewis (acceptors formally unfilled) orbital’s and (iii) Rydberg NBOs, which originate from orbitals outside the atomic valence shell The calculated occupancies of natural orbitals, calcu-lated natural hybrids on atoms are also given inTables 5 and 6 3-Dimensional plot of the atomic orbital occupancies against the various energies of the vanadium atom in [VO(sal-HBPD)] (I) and [VOO(sal-HBPD)] (II) are providedFig 5 Ther(V1-O40) bond is formed from sp4.11hybrid on O40 (which is the mixture of 19.55%

s and 80.45% p atomic orbital’s), thep(V1-O40) observed bond is formed from sp hybrid on O40, which is predominantly p atomic orbital’s But therandr⁄of [VO(sal-HBPD)] (I) and [VOO (sal-HBPD)] (II) are generally hybrid p-character (Tables 5 and 6)

Table 7 presents the perturbation energies of donor-acceptor interactions of some atoms in [VO(sal-HBPD)] (I) and [VOO(sal-HBPD)] (II)

Table 6

Occupancy of natural orbitals (NBOs) and hybrids of [VOO(sal-HBPD)] (II) calculated

by at the DFT level with LanL2DZ.

s(17.44%) p(82.56%)

s(41.96%) p(58.04%)

s(28.35%) p(71.65%)

s(35.33%) p(64.67%)

s(22.03%) p(77.97%)

s(22.70%) p(77.30%)

s(31.19%) p(68.81%)

r*

s(32.59%) p(67.41%)

s(27.25%) p(72.75%)

r*

*

Underlined atoms represent the hybridized position.

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

5 10 15 20

-2.5 -2.0 -1.5 -1.0 -0.5 0.0

0.5

upancy

NA O

Energ y

I

-1 0 1 2 3 4

5 10 15 20

-2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5

upancy

NA O

Energ y

II

NAO 1

20

Fig 5 A 3D plot of natural atomic orbital occupancies against the various energies for [VO(sal-HBPD)] (I) and [VOO(sal-HBPD)] (II).

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[VO(sal-HBPD)] (I) perturbation energies of the various

donor-acceptor interactions; [N(4) – C(26)] to [V(1) – O(40)] and

[N(3) – C(36)] to [V(1) – O(40)] are 0.68 kJ/mol and 1.31 kJ/mol

respectively The [N(3) – C(36)] to [V(1) – O(40)] interaction gave

high energies, hence providing a stronger stabilization to the

[VO(sal-HBPD)] (I)

[VOO(sal-HBPD)] (II) perturbation energies of the various

donor-acceptor interactions are provided inTable 7 [V(1) – O(2)]

to [V(1) – N(3)], [V(1) – O(2)] to [V(1) – O(40)] and [V(1) – N(3)]

to [V(1) – O(40)] are 14.81 kJ/mol, 15.27 kJ/mol and 20.53 kJ/mol

respectively The [V(1) – N(3)] to [V(1) – O(40)] interaction gave

high energies, hence providing a stronger stabilization to the

[VOO(sal-HBPD)] (II) [VOO(sal-HBPD)] (II) offered relatively higher

energies as compared with [VO(sal-HBPD)] (III), hence making

[VOO(sal-HBPD)] (II) a more reactive intermediate

3.2.5 Quinoline oxidation From the computationally modelled electronic study, the hydroxyl-peroxidovanadium(V) specie [VOO(sal-HBPD)] (II) is responsible for the electron pairing between the nitrogen atom of quinoline and an oxygen atom of the hydroxyl-peroxidovanadium (V) species, hence leading to bond formation and oxidation (Scheme 2)

Further oxidation mechanism was also followed with EPR anal-ysis (Fig 6), hyperfine interaction lines predominately ascribed to

V4+, [VO(sal-HBPD)] disappeared upon the addition of H2O2

(Fig 6B), indicating the oxidation of the V4+ to V5+ Addition of quinoline to this solution resulted in reduction of the metal center

to V4+ species, (Fig 6C) This occurrence indicates that electron

Table 7

Second order perturbation theory analysis of the Fock matrix in NBO basis.

[VO(sal-HBPD)] (I)

[a.u.]

[VOO(sal-HBPD)] (II)

[a.u.]

a

E(2) means energy of hyper conjugative interaction (stabilization energy).

b

Energy difference between donor and acceptor i and j NBO orbitals.

c

F(i; j) is the Fock matrix element between i and j NBO orbitals.

Scheme 2 Simplified catalytic mechanism for the oxidation of quinoline H + from

H 2 O may protonate peroxido to form the hydroxyl-peroxidovanadium(V) species

(1) Here L may refer to donor atom.

A

B

C

D

Field (Guass)

2800 3000 3200 3400 3600 3800 4000

Fig 6 First derivative EPR spectra of [VO(sal-HBPD)] (0.000167 mol) (A) in MeOH; (B) addition of 7 equiv of H 2 O 2 to the solution of (A); (C) addition of quinoline (0.02 mol) to the solution of (B); and (D) solution of (C) after 24 h.

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transfer processes to occur between quinoline and the V5+specie

(hydroxyl-peroxidovanadium(V) species) After a 48 h period, the

catalyst recovers (Fig 6D) with an indication of a slight change in

the vanadium co-ordination geometry

The oxidation of quinoline gave rise to quinoline-N-oxide

(100%), with a turnover frequency (TOF) of 997 h1, while the

supported catalyst p[VO(sal-HBPD)] also gave rise to 100%

quinoline-N-oxide The product (quinoline-N-oxide) was isolated

and analyzed by GC-FID (Fig 7) and GC–MS (Fig 8)

3.3 Adsorption studies

3.3.1 Adsorption of quinoline-N-oxide in model fuel using ionic liquids

5 mL of ionic liquid was contacted with 5 mL of

quinoline-N-oxide (200 ppm) in a mixture of toluene and dichloromethane was

stirred for 3 h at 50 rpm, and thereafter it was allowed to stand for

1 h for a better phase separation A total of 96% and 87%

quinoline-N-oxide were removed when1-butyl-3-methylimidazolium

chlo-ride and 1-butyl-3-methylimidazolium nitrate were employed

respectively (Fig 9)

excited states[28] From the 1-butyl-3-methylimidazolium chloride/quinoline-N-oxide adduct (Fig 10), HOMO originated from the chlorine anion

of 1-butyl-3-methylimidazolium chloride ionic liquid as well as the quinoline-N-oxide molecule while the LUMO position arises from the quinoline-N-oxide (Fig 10) This clearly confirmed that

Time (min)

oxidant

Fig 7 GC-FID chromatograms of quinoline oxidation: Quinoline (2.58 mL,

0.02 mol) and [VO(sal-HBPD)] (0.000167 mol of vanadium).

0 1000 2000 3000 4000 5000 6000 7000 8000 9000

m/z >

145.0

117.0

90.0

63.0 39.0 51.0

75.0

Fig 8 GC–MS chromatogram of quinoline-N-oxide.

Ionic liquid phase

Quinoline-N-oxide in

DCM/Toluene phase

Fig 9 1-Butyl-3-methylimidazolium chloride (IL-Cl) and 1-butyl-3-methylimida-zolium nitrate (IL-NO 3 ) and quinoline-N-oxide.

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interaction between 1-butyl-3-methylimidazolium chloride and

quinoline-N-oxide through electron transfer took place With

1-butyl-3-methylimidazolium nitrate/quinoline-N-oxide adduct,

both the HOMO and LUMO center emanates from the

quinoline-N-oxide of the ionic liquid (Fig 11)

4 Conclusions

The use of [VO(sal-HBPD)] and p[VO(sal-HBPD)] for the

oxida-tion of quinoline, presented oxidaoxida-tion selectivity as

quinoline-N-oxide (100%) was recorded as the oxidation product UV studies

of [VO(sal-HBPD)] confirmed the formation of

species, DFT electronic studies also confirmed

hydroxylperoxido-species (II) as the reactive oxidized oxidovanadium specie

responsible for the oxidation Ionic liquids,

1-butyl-3-methylimidazolium chloride and 1-butyl-3-1-butyl-3-methylimidazolium

nitrate extracted 96% and 87% quinoline-N-oxide respectively

Acknowledgements

We are thankful for financial support provided by THRIP (SA)

and Sasol (Pty) Ltd as the industrial partner The authors thank

the Center for High Performance Computing (CHPC), Cape Town,

South Africa for providing the platform in carrying out the

molec-ular modelling studies on the Gaussian09 software We would also

like to acknowledge Prof Zenixole R Tshentu (Department of

Chemistry, Nelson Mandela Metropolitan University) for the

research advice as well as providing chemicals employed for the

research study

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Fig 11 (A) HOMO and (B) LUMO positions of 1-butyl-3-methylimidazolium nitrate/quinoline-N-oxide adduct.

Fig 10 (A) HOMO and (B) LUMO positions of 1-butyl-3-methylimidazolium chloride/quinoline-N-oxide adduct.

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