Catalyst Activation and Influence of the Oil Matrix on Extractive

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Catalysis and Kinetics

Catalyst activation and influence of the oil matrix on the extractive oxidative desulfurization using aqueous polyoxometalate solutions and molecular oxygen Benjamin Bertleff, Johannes Claußnitzer, Wolfgang Korth, Peter Wasserscheid, Andreas Jess, and Jakob Albert Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b01514 • Publication Date (Web): 05 Jul 2018 Downloaded from http://pubs.acs.org on July 10, 2018

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Catalyst activation and influence of the oil matrix on the extractive oxidative desulfurization using aqueous polyoxometalate solutions and molecular oxygen Benjamin Bertleff1, Johannes Claußnitzer2, Wolfgang Korth2, Peter Wasserscheid1,3, Andreas Jess2 and Jakob Albert1* 1

Lehrstuhl für Chemische Reaktionstechnik, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstr. 3, 91058 Erlangen, Germany; [email protected]

2

Lehrstuhl für Chemische Verfahrenstechnik, Zentrum für Energietechnik (ZET), Universität Bayreuth, Universitätsstr. 30, 95447 Bayreuth, Germany

3

Forschungszentrum Jülich GmbH, Helmholtz-Institut Erlangen-Nürnberg for Renewable Energy (IEK-11), Egerlandstr. 3, 91058 Erlangen, Germany

Abstract Our contribution describes the oxidative desulfurization of dibenzothiophene (DBT) from model oils using an aqueous H8PV5Mo7O40 (HPA-5) catalyst solution and molecular oxygen as oxidant. In contrast to common oxidative desulfurization (ODS) protocols, the organic sulfur compound DBT is oxidized to water-soluble compounds, such as sulfuric acid (50-55 %), sulfoacetic acid (20-25 %) and sulfobenzoic acid (2530 %) which are extracted in-situ into the aqueous catalyst phase. We describe the activating effect of oxalic acid on the ODS performance of the catalyst and propose a mechanism for the catalyst activation. Moreover, we report on the influence of various organic solvents i.e. n-alkanes and aromatics on the oxidative DBT removal. Remarkably, the rate of DBT oxidation and removal enhances with increasing chain length of the alkane matrix whereas aromatic compounds in the oil matrix inhibit the desulfurization rate. Moreover, we demonstrate that the aqueous catalyst phase can be reused at least five times without loss in catalytic performance.

Keywords: oxidative desulfurization, extraction, dibenzothiophene, Keggin polyoxometalates, oxygen, sulfuric acid, catalyst activation mechanism

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Introduction The state-of-the-art technique for desulfurization of fuels is hydrodesulfurization (HDS). In this process, the organic sulfur compounds are removed from the hydrocarbon oil mixture by catalytic hydrogenation to H2S. The HDS process is highly efficient for the removal of non-aromatic sulfur compounds, such as mercaptanes, sulfides, and disulfides. However, the HDS unit has to be operated under much harsher

reaction

conditions

if

aromatic

sulfur-containing

compounds

dibenzothiophene (DBT) and its alkylated analogues have to be removed.

[1]

like

In order

to meet the legal threshold values for sulfur in fuels (10 ppmw S for diesel and gasoline in the EU),[2] high temperatures and high hydrogen pressures are required in the respective HDS process. This leads to an increasing hydrogen consumption and less favorable process economics. Oxidative desulfurization (ODS) is one of the most promising alternative approaches for deep desulfurization of fuels. The process can be conducted under mild operating conditions and does not require hydrogen. Most of the literature dealing with ODS describes the selective partial oxidation of the organic sulfur compounds to their corresponding sulfones. For this purpose, H2O2[3-9] or organic peroxides[10] are typically used as oxidants. Only in very few cases molecular oxygen has been applied as oxidant for ODS,[11-16] despite the fact that O2 is cheap and abundant. With molecular oxygen as oxidant, predominantly vanadium containing polyoxometalates (POMs) have been used as desulfurization catalysts.[11,13,14] Apart from POMs, several transition metal oxides[3,5,17],carbon nanotubes[10], or even supported metal catalysts[18,19] have been applied as catalysts for ODS. The sulfones formed during typical ODS procedures need to be removed from the hydrocarbon matrix by either a subsequent separation step or by in situ extraction during the course of the ODS reaction. For the latter option a suitable in situ extraction solvent has to meet the following requirements: (i) stability under process conditions, (ii) high distribution coefficients for the sulfones to be separated, and (iii) a high miscibility gap with the organic oil matrix. Suitable extraction solvents discussed in

the

literature

include,

e.g.,

ionic

liquids[20-22],

acetonitrile[23]

or

dimethylformamide[24]. Water could be an interesting alternative extraction solvent because it is cheap and abundant. However, water has not been used extensively as


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extracting agent in combination with ODS due to the very low water solubility of sulfones. We have recently presented a new approach for extraction-coupled oxidative desulfurization (ECODS) of model fuels using molecular oxygen as oxidant and an aqueous POM-solution as catalytically active phase. In this study, the model sulfur compound benzothiophene (BT) has been completely removed from the model oil (2,2,4-trimethylpentane) by oxidation to water-soluble compounds, such as sulfuric acid and sulfonic acids. All sulfur-containing products have been successfully extracted in situ into the aqueous H8PV5Mo7O40 (HPA-5) catalyst phase.[25] A fundamental understanding of the catalyst system and the role of the oil matrix in oxidative desulfurization is necessary in order to systematically optimize our desulfurization system. Therefore, in this study, we focussed on the catalyst behaviour and the influence of the nature of the oil matrix on the ODS reaction using aqueous HPA-5 solutions. Especially various catalyst activation/deactivation mechanisms were investigated using

51

V-NMR spectroscopy. As model system for

our catalytic investigations, we chose the oxidative removal of dibenzothiophene (DBT) from various model oils mimicking technical deep-desulfurization processes. Moreover, the reuse of the aqueous catalyst solution in ECODS reaction is described.

Results and Discussion

Influence of reaction temperature and catalyst activation on the DBT removal Our first set of experiments aimed at demonstrating that also the ECODS of DBT (1044 ppm S) from tetradecane using an aqueous HPA-5 catalyst solution

[26-31]

forms water-soluble and extractable sulfur compounds. Figure 1 shows the desulfurization results at different temperatures. We limited the maximum temperature to 130 °C as the oil matrix starts to decompose at temperatures higher than 140 °C. DBT is removed completely from the model diesel after 12 h at 130 °C, 24 h at 120 °C and 36 h at 110 °C, respectively. In contrast to Qiu et al[18] and Long et al[19], increasing temperatures above 105 °C increase extractive oxidative 3 Environment ACS Paragon Plus

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desulfurization using our catalyst system. However, the time for complete desulfurization using our catalyst system (12 h) is longer compared to other ODS approaches where the sulfur compounds are only partially oxidized to sulfones (1-2 h)[18,19]. In comparison, in these studies mainly peroxide species are used as oxidant in excess and a further separation step for the sulfones formed during the desulfurization reaction is necessary. Advantageous in our approach is the use of a cheap precious-metal free catalyst system in combination with molecular oxygen as oxidant and water as the environmentally benign in situ extracting agent for the oxidized decomposition products. No further separation steps are necessary after oil/water phase separation using our approach. Moreover, ICP analysis of the aqueous phase after the reaction confirmed that all sulfur containing oxidation products were extracted in situ into the aqueous catalyst phase. Furthermore, no additional organic extracting agent is necessary for this complete extraction.[7,32,33] Analysis of the aqueous phase indicated that DBT is converted to sulfuric acid (ca. 50-55 %), sulfoacetic acid (ca. 20-25 %) and 2-sulfobenzoic acid (ca. 25-30 %). Sulfoacetic acid and 2-sulfobenzoic acid are intermediates of the oxidative desulfurization reaction (see ESI, Figure S1). 2-sulfobenzoic acid is further converted to sulfoacetic acid or to 2-sulfoxybenzoic acid.[25] The latter acids are finally transformed into sulfuric acid (Scheme 1). As non-sulfur containing decomposition products, formic acid, acetic acid and oxalic acid were detected in the aqueous phase. Moreover, carbon dioxide and carbon monoxide were found in the gas phase. Scheme 1 shows the DBT oxidation pathway derived from our product analysis.


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100

degree of desulfurization [%]

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80 60 40 20

110 °C 120 °C 130 °C

0 0

5

10

15

20

25

30

35

time [h]

Figure 1: Desulfurization of DBT from model diesel for different temperatures. (Reaction conditions: 0.5 mmol HPA-5 dissolved in 100 mL water, DBT in 10 mL n-tetradecane (1044 ppm S), 20 bar O2, 1000 rpm).

OSO3H

S

COOH

SO3H

H2SO4 COOH HOOC

SO3H

Scheme 1: Sulfur containing intermediates and products obtained during the ECODS of dibenzothiophene from model diesel (only sulfur containing reaction products are shown).

Interestingly, an induction period was observed for lower temperatures. For the first 6 h at 110 °C and the first 3 h at 120 °C (see Figure 1) no DBT conversion was detected. At 130 °C, the induction period was not visible indicating a much faster formation of the reactive POM species at higher temperatures. This finding is well inline with results published by Evtuguin et al. These authors attributed the higher catalytic activity of HPA-5 at higher temperatures to the increased POM dissociation leading to faster reaction kinetics.[34] Moreover, these authors claim that a partial initial reduction of V5+ to V4+ within the HPA-5 catalyst structure using a sacrificial reduction agent can decrease the induction period. In order to confirm whether the


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induction period observed in our experiments is due to the required partial reduction of vanadium in the HPA-5 catalyst, we conducted experiments with adding oxalic acid to the reaction mixture as sacrificial reducing agent (see Figure 2). Oxalic acid partially reduces the catalyst (i.e. V5+ to V4+) and is thereby oxidized to carbon dioxide detected by GC in the gas phase. Figure 2 shows that the addition of oxalic acid does indeed lead to a much shorter induction period. The experimental data indicate that partial reduction of the catalyst at the initial stage of the reaction leads to a faster oxidation and desulfurization of DBT.

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n-tetradecane + oxalic acid n-tetradecane

80 60 40 20 0 0

5

10

15

20

25

time [h]

Figure 2: Comparison of DBT removal from n-tetradecane with and without the addition of 0.5 mmol oxalic acid. (Reaction conditions: 0.5 mmol HPA-5 dissolved in 100 mL water, DBT in 10 mL n-tetradecane (1044 ppm S), 120°C, 20 bar O2, 1000 rpm).

Based on these findings, we propose a mechanism for the activation of our HPA-5 catalyst as shown in Scheme 2. First, the fully oxidized V5+ species in the POM framework containing only fully oxidized vanadium is reduced by a substrate (S) to form a respective V4+ POM species. In a second step, the activated V4+ species is reoxidized by oxygen to form an active V5+ peroxo species.[14] The peroxo species oxidizes the organic sulfur compound DBT, faster than the parent HPA-5. With DBT being present in the reaction system as the only substrate for oxidation, the first step is slow. However, the step can be accelerated by the addition of a reducing agent like oxalic acid (see Scheme 2). The reoxidation of the V4+ to the V5+ species by molecular oxygen is much faster than the reduction of HPA-5 containing only V(V) atoms by DBT at high oxygen pressures.[35,36] The here presented mechanism is also 6 Environment ACS Paragon Plus

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supported by the

51

V-NMR measurements of the aqueous catalyst phase during the

progress of the desulfurization (see ESI, Figure S2). There is no change in the

51

V-

NMR spectra within the course of DBT oxidation at the applied temperatures. Consequently, the catalyst remains stable and active. Additionally, no catalyst leaching into the organic phase was detected by our

51

V-NMR spectroscopy

measurements (detection limit of the applied method is 500 ppm; see ESI, Figure S3).

Sox

OH

OH

V5+

V5+

HOOCCOOH or S 2CO2 + 2H2O or Sox

O

S + H2 O O

O V4+

V5+

V5+

V4+ O

O

O2 Scheme 2: Proposed mechanism for the catalyst activation. Since no activity was observed in the oxidative desulfurization reaction using HPA-x with x

n-tetradecane

>

n-hexadecane, the amount of DBT in water is expected to drop as well. However, the observed trend can be explained by assuming that the water solubility in the alkane matrix is the critical factor. As depicted in Figure 3, the solubility of water in n-alkanes increases in the order of n-decane < n-tetradecane < n-hexadecane (5.7x10-2 mol% for n-decane and 6.8x10-2 mol% for n-hexadecane), [40] and thus the amount of aqueous catalyst phase in the organic matrix also goes up. Hence, we suppose that the initial oxidation of DBT mainly takes place in the organic phase carrying small amounts of the aqueous catalyst solution whereas the consecutive oxidation of water-soluble intermediates like sulfoacetic acid, 2-sulfobenzoic acid and 2sulfoxybenzoic acid occurs in the aqueous phase. Furthermore, the observed induction period decreases from 6 h in n-decane and 3 h in n-tetradecane to practically zero in n-hexadecane perfectly confirming our interpretation.

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n-Decan n-Tetradecan n-Hexadecan

80 60 40 20 0 0

5

10

15

20

25

time [h]

Figure 3: Comparison of DBT removal from different n-alkane matrices. (Reaction conditions: 0.5 mmol HPA-5 dissolved in 100 mL water, 0.25 mmol DBT in 10 mL n-alkane, 120°C, 20 bar O2, 1000 rpm).

Figure 4 shows a comparison of the removal of DBT from tert-butylbenzene, n-tetradecane, n-decane and a mixture of tert-butylbenzene/n-tetradecane/n-decane (10/45/45 wt.-%) as organic matrix. For tert-butylbenzene, no DBT was removed even after 24 h and only 22 % of DBT was removed from a mixture of tertbutylbenzene/n-tetradecane/n-decane (10/45/45 wt.-%) after 24 h. This indicates that 8 Environment ACS Paragon Plus

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even with a concentration of only 10 wt.-%, the aromatic compound tert-butylbenzene strongly inhibits the desulfurization. The inhibition effect of aromatic compounds in the oxidative desulfurization with Keggin POMs was also reported by Xiao et al.[38] These authors supposed that the inhibiting effect of aromatic compounds is due to a competitive aromatics oxidation reaction. However, we could not detect any decomposition products of the organic matrix in the ODS reaction. Encouraged by the finding that a reducing agent can promote oxidative desulfurization when using the HPA-5 catalyst, an additional desulfurization experiment for DBT from the oil matrix tert-butylbenzene/n-tetradecane/n-decane (10/45/45 wt.-%) was carried out adding initially oxalic acid as reductive activator. As shown in Figure 4, the removal of DBT from the oil mixture can be enhanced significantly within the first 6 h by adding oxalic acid to the aqueous catalyst solution. Hereby, oxalic acid activates the catalyst according to the mechanism proposed in Scheme 2 and is converted almost completely to CO2 within the first 6 h. After this time, the rate of desulfurization decreases significantly due to the above-described inhibiting effect of the aromatic compound. We assume that by further addition of oxalic acid during the reaction the inhibiting effect of the aromatic matrix can again be overcome and thus the overall degree of desulfurization can be further increased.

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n-decane n-tetradecane tert-butylbenzene oil mixture oil mixture + oxalic acid

80 60 40 20 0 0

5

10

15

20

25

time [h]

Figure 4: Comparison of the oxidative removal of DBT from different organic matrices without and with addition of 0.5 mmol oxalic acid. (Reaction conditions: 0.5 mmol HPA-5 dissolved in 100 mL water, 0.25 mmol DBT in 10 mL organic solvent, 120°C, 20 bar O2, 1000 rpm).


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Catalyst phase recycling A very important aspect of catalytic oxidative desulfurization is the longterm stability of the applied catalyst. To confirm the required robustness of the catalytic system, the aqueous catalyst phase was reused in five consecutive experiments without product isolation from the aqueous phase (Figure 5).

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80 60 40 20 0

run 1

run 2

run 3

run 4

run 5

Figure 5: Desulfurization of DBT in n-tetradecane (130 °C, 20 bar O2, 1000 rpm, reaction time 12 h) – reuse of the aqueous catalyst phase without extraction of oxidation products.

As clearly evidenced by the results of these aqueous phase recycling experiments, the catalyst phase can be reused at least five times without losing performance in the oxidative desulfurization of DBT in n-tetradecane. However, accumulation of the strongly acidic oxidation products will lead over time to a decreasing pH value of the aqueous catalyst phase which is known to affect the catalyst performance negatively.[25] Therefore, efficient separation of the acidic oxidation products will be necessary to maintain the optimum performance of the catalyst system. Attempts to extract the acidic oxidation products from the aqueous catalyst solution are currently made in our laboratories and will be published in due time.

Conclusion In this contribution, we investigate the activation behaviour of a vanadium-containing catalyst for the oxidative desulfurization of dibenzothiophene (DBT) from model fuels 10 Environment ACS Paragon Plus

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using an aqueous HPA-5 solution and molecular oxygen as oxidant. DBT is oxidized mainly to water-soluble compounds, such as sulfuric acid and sulfonic acids, which are in situ extracted into the aqueous catalyst phase. Our work demonstrates that the HPA-5 catalyst is activated in situ by partial reduction of the active vanadium centres. This activation can be accelerated significantly by a sacrificial reducing agent, such as oxalic acid, that can be added prior or during the ODS reaction. Furthermore, experiments regarding the influence of different organic matrices on the DBT removal were performed. Key results of this part of our studies are that the rate of desulfurization increases with increasing chain length of the n-alkane matrix, and that aromatic compounds in the oil matrix show a strongly inhibiting effect on the desulfurization. Finally, we could demonstrate that the aqueous catalyst phase can be reused at least five times without losing performance in the oxidative desulfurization of DBT.

Experimental details All commercial reagents and solvents were used as received unless otherwise stated. The heteropolyacid (HPA-5) catalyst was synthesized based on literature known procedures[36,42] and characterized by ICP-OES giving a P/V/Mo ratio of 1/4.50/6.83. Dibenzothiophene was obtained from Alfa Aesar with a purity higher than 98 %. N-decane, n-tetradecane, n-hexadecane and tert-butylbenzene were purchased from Sigma Aldrich with a purity higher than 99 %. ICP-OES analysis have been performed using a Perkin Elmer Plasma 400, and NMR spectra were carried out on a Jeol ECX-400 MHz at room temperature. Identification of watersoluble compounds was made by Ion chromatography using an ICS-3000 system (DIONEX) equipped with a conductivity detector using a GC11-HC/AS11-HC (2 mm x 250 mm) column set (DIONEX) and an AMMS300 (DIONEX) suppressor. Gaschromatographic analyses of the organic phases were conducted on a Bruker 430-GC with a flame ionisation detector (FID) using a CP7351-Sil PONA CB (50 m x 0.21 mm) column from Agilent. A Varian GC 450 equipped with a 2 m x 0.75 mm ID ShinCarbon ST column was used to identify gaseous compounds.

As a reaction setup for the desulfurization experiments, we used a 600 mL Hastelloy C276 autoclave equipped with a gas entrainment impeller. An extra probing valve 11 Environment ACS Paragon Plus

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was installed allowing to take samples during the course of the reaction. All reactants were charged into the vessel before starting the experimental run. Then, the system was purged three times with oxygen to remove all impurities from the reaction zone. Afterwards, the stirrer was set to 300 rpm and electrical heating was switched on. After the desired reaction temperature was reached, the oxygen pressure was increased to 20 bar and the stirring speed was set to 1000 rpm. After finishing the experiment, the electrical heating was switched off and the stirrer was set again to 300 rpm to stop gas entrainment and to allow for cooling down.

Working with oxygen in presence of organic solvents Carrying out reactions using pressurized oxygen in combination with volatile organic solvents and an oxidation catalyst can cause extreme hazards and form explosive atmospheres. Therefore, we recommend to take extreme care when performing these and similar experiments. In order to avoid potential hazards, all experiments have been conducted in high-pressure equipment capable to manage the pressure formation caused by rapid oxidation. The applied apparatus was equipped with appropriate safety equipment (rupture discs, pressure-relief valves) and was operated in an explosion protected shelter. Neither an explosion nor an uncontrolled exothermic decomposition reaction has been observed in all of the experiments conducted so far.


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Acknowledgements The authors would like to thank the Deutsche Forschungsgemeinschaft (DFG) for financial support through their projects JE 257/20-1 and WA 1615/14-1. Additional support by the Erlangen Cluster of Excellence “Engineering of Advanced Materials” (www.eam.fau.de) is also gratefully acknowledged.

References 1) B. C. Gates, H. Topsøe, Reactivities in deep catalytic hydrodesulfurization: challenges, opportunities and the importance of 4-methyldibenzothiophene and 4,6-dimethyldibenzothiophene. Polyhedron 1997, 16(18), 3213-3217, 2) Amtsblatt der Europäischen Union. L140; Europäische Union, 2009, Vol. 52, L140/88-L140/113. 3) M. C. Capel-Sanchez, J. M. Campos-Martin, J. L. G. Fierro, Removal of refractory organosulfur compounds via oxidation with hydrogen peroxide on amorphous Ti/SiO2 catalysts. Energy Environ. Sci. 2010, 3, 328-333. 4) F. M. Collins, A. R. Lucy, C. Sharp, Oxidative desulphurisation of oils via hydrogen peroxide and heteropolyanion catalysis. Journal of Molecular Catalysis A: Chemical 1997, 117, 397-403. 5) Y. Jia, G. Li, G. Ning, Efficient oxidative desulfurization (ODS) of model fuel with H2O2 catalyzed by MoO3/ᵧ-Al2O3 under mild and solvent free conditions. Fuel Processing Technology 2011, 92, 106-111. 6) L. Lu, S. Cheng, J. Gao, G. Gao, M.-Y. He, Deep oxidative desulfurization of Fuels catalyzed by Ionic Liquids in the Presence of H2O2. Energy Fuels 2007, 21(1), 383-384. 7) S. Otsuki, T. Nonaka, N. Takashima, W. Qian, A. Ishihara, T. Imai, T. Kabe, Oxidative Desulfurization of Light Gas Oil and Vacuum Gas Oil by Oxidation and Solvent Extraction. Energy Fuels 2000, 14(6), 1232-1239. 8) W. Zhu, B. Dai, P. Wu, Y. Chao, J. Xiong, S. Xun, H. Li, H. Li, GrapheneAnalogue Hexagonal BN Supported with Tungsten-based Ionic Liquid for Oxidative Desulfurization of Fuels. ACS Sustainable Chem. Eng. 2015, 3(1), 186194. 9) P. Wu, W. Zhu, A. Wei, B. Dai, Y. Chao, C. Li, H. Li., S. Dai, Controllable Fabrication of Tungsten Oxide Nanoparticles Confined in Graphene Analogous Boron Nitride as an Efficient Desulfurization Catalyst. Chemistry – A European Journal 2015, 21, 15421-15427. 10) D. Wang, E. W. Qian, H. Amano, K. Okata, A. Ishihara, T. Kabe, Oxidative desulfurization of fuel oil: Part I. Oxidation of dibenzothiophenes using tertbutylhydroperoxide. Applied Catalysis A: General 2003, 253, 91-99. 13 Environment ACS Paragon Plus

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11) N. Tang, Z. Jiang, C. Li, Oxidation of refractory sulfur-containing compounds with molecular oxygen catalysed by vanadoperiodate. Green Chem. 2015, 17, 817820. 12) W. Zhang, H. Zhang, J. Xiao, Z. Zhao, M. Yu, Z. Li, Carbon nanotube catalysts for oxidative desulfurization of a model diesel fuel using molecular oxygen. Green Chem. 2014, 16, 211-220. 13) H. Lü, J. Gao, Z. Jiang, Y. Yang, B. Song, C. Li, Oxidative desulfurization of dibenzothiophene with molecular oxygen using emulsion catalysis. Chem. Commun. 2007, 150-152. 14) X. Liao, D. Wu, B. Geng, S. Lu, Y. Yao, Deep oxidative desulfurization catalyzed by (NH4)xH4-xPMo11VO40 (x = 1,2,3,4) using O2 as oxidant. RSC Adv. 2017, 7, 48454-48460. 15) W. Zhu, C. Wang, H. Li, P. Wu, S. Xun, W. Jiang, Z. Chen, Z. Zhao, H. Li, Onepot extraction combined with metal-free photochemical aerobic oxidative desulfurization in deep eutectic solvent. Green Chem. 2015, 17, 2464-2472. 16) P. Wu, W. Zhu, Y. Chao, J. Zhang, P. Zhang, H. Zhu, C. Li, Z. Chen, H. Li, S. Dai, A template-free solvent-mediated synthesis of high surface area boron nitride nanosheets for aerobic oxidative desulfurization. Chem. Commun. 2016, 52, 144-147. 17) C. Yang, K. Zhao, Y. Cheng, G. Zeng, M. Zhang, J. Shao, L. Lu, Catalytic oxidative desulfurization of BT and DBT from n-octane using cyclohexanone peroxide and catalyst of molybdenum supported on 4A molecular sieve. Separation and Purification Technology 2016, 163, 153-161. 18) L. Qiu, Y. Cheng, C. Yang, G. Zeng, Z. Long, S. Wei, K. Zhao, L. Luo, Oxidative desulfurization of dibenzothiophene using a catalyst of molybdenum supported on modified medicinal stone. RSC Adv. 2016, 6, 17036-17045. 19) Z. Long, C. Yang, G. Zeng, L. Peng, C. Dai, H. He, Catalytic oxidative desulfurization of dibenzothiophene using catalyst of tungsten supported on resin D152. Fuel 2014, 130, 19-24. 20) A. Bösmann, L. Datsevich, A. Jess, A. Lauter, C. Schmitz, P. Wasserscheid, Deep oxidative desulfurization of diesel fuel by extraction with ionic liquids. Chem. Commun. 2001, 2494-2495. 21) H. Zhao, G. A. Baker, Oxidative desulfurization of fuels using ionic liquid: A review. Front. Chem. Sci. Eng. 2015, 9, 262-279. 22) W. Jiang, W. Zhu, H. Li, X. Wang, S. Yin, Y. Chang, H. Li, Temperatureresponsive ionic liquid extraction and separation of the aromatic sulfur compounds. Fuel 2015, 140, 590-596. 23) K. Yazu, Y. Yamamoto, T. Furuya, K. Miki, K. Ukegawa, Oxidation of Dibenzothiophenes in an Organic Biphasic System and Its Application to Oxidative Desulfurization of Light Oil. Energy & Fuels 2001, 15, 1535-1536. 14 Environment ACS Paragon Plus

Page 14 of 16

Page 15 of 16 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

24) L. F. Ramirez-Verduzco, E. Torres-Garcia, R. Gomez-Quintana, V. GonzalezPena, F. Murrieta-Guevara, Desulfurization of diesel by oxidation/extraction scheme: influence of the extraction solvent. Catalysis Today 2004, 98, 289-294. 25) B. Bertleff, J. Claußnitzer, W. Korth, P. Wasserscheid, A. Jess, J. Albert, Extraction Coupled Oxidative Desulfurization of Fuels to Sulfate and WaterSoluble Sulfur Compounds Using Polyoxometalate Catalysts and Molecular Oxygen. ACS Sustainable Chem. Eng. 2017, 5 (5), 4110-4118. 26) E. G. Zhizhina, V. F. Odyakov, M. V. Simonova, Catalytic Oxidation of Organic Compounds with Oxygen in the Presence of Mo-V-Phosporic Heteropoly Acid Solutions. Kinetics and Catalysis 2008, 49(6), 773-781. 27) V. F. Odyakov, E. G. Zhizhina, Y. A. Rodikova, L. L. Gogin, Mo-V-Phosphoric Heteropoly Acids and Their Salts: Aqueous Solution Preparation – Challenges and Perspectives. Eur. J.Inorg. Chem. 2015, 3618-3631. 28) M. T. Pope, T. F. Scully, Geometrical isomerism arising from partial substitution of metal atoms in isopoly and heteropoly complexes. Possibilites for the Keggin structure. Inorg. Chem. 1975, 14(4), 953-954. 29) D. V. Evtuguin, C. P. Neto, J. Rocha, J.D. Pedrosa de Jesus, Oxidative delignification in the presence of molybdovanadophosphate heteropolyanions: mechanism and kinetic studies. Applied Catalysis A: General 1998, 167, 123139. 30) A. A. Shatalov, D. V. Evtuguin, C. P. Neto, Cellulose degradation in the reaction system O2/heteropolyanions of series [PMo(12-n)VnO40](3+n)-. Carbohydrate Polymers 2000, 43, 23-32. 31) L. Pettersson, I. Andersson, A. Selling, J. H. Grate, Multicomponent Polyanions. 46. Characterization of Isomeric Keggin Decamolybdodivanadophosphate Ions in Aqueous Solution by 31P and 51V NMR. Inorg. Chem. 1994, 33, 982-993, 32) W.-H. Lo, H.-Y. Yang, G.-T. Wie, One-pot desulfurization of light oils by chemical oxidation and solvent extraction with room temperature ionic liquids. Green Chem. 2003, 5, 639-642. 33) P. S. Tam, J. R. Kittrell, J. W. Eldrige, Desulfurization of Fuel Oil by Oxidation and Enhancement of Extraction Oil Yield. Ind. Eng. Chem. Res. 1990, 29, 321324. 34) D.V. Evtuguin, C. P. Neto, J. Rocha, J.D. Pedrosa de Jesus, Oxidative delignification in the presence of molybdovanadophosphate heteropolyanions: mechanism and kinetic studies. Applied Catalysis A: General 1998, 167, 123129. 35) J. Albert, „Der Erlanger OxFA-Prozess", SVH-Südwestdeutscher Verlag für Hochschulschriften, ISBN 978-3-8381-5331-5, 2016. 36) J. Albert, D. Lüders, A. Bösmann, D. M. Guldi, P. Wasserscheid, Spectroscopic and electrochemical characterization of heteropoly acids for their optimized 15 Environment ACS Paragon Plus

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

application in selective biomass oxidation to formic acid. Green Chem., 2014, 16, 226-237. 37) V. E. Tarabanko, V. N. Sidelnikov, I. V. Kozhevnikov, Mechanism of the LiquidPhase Oxidation of Diethyl Sulfide Catalyzed by Heteropoly Acids. React. Kinet. Catal. Lett. 1982, 21 (1-2), 109-114. 38) J. Xiao, L. Wu, Y. Wu, B. Liu, L. Dai, Z. Li, Q. Xia, H. Xi, Effect of gasoline composition on oxidative desulfurization using a phosphotungstic acid/activated carbon catalyst with hydrogen peroxide. Applied Energy 2014, 113, 78-85. 39) S. Zeppieri, J. Rodriguez, A. L. Lopez de Ramos, Interfacial Tension of Alkane + Water Systems. J. Chem. Eng. Data 2001, 46, 1086-1088. 40) A. H. Demond, A. S. Lindner, Estimation of Interfacial Tension between Organic Liquids and Water. Environ. Sci. Technol. 1993, 27, 2318-2331. 41) C. Y. Wang, R.V. Calabrese, Drop Breakup in Turbulent Stirred-Tank Contactors – Part II: Relative Influence of Viscosity and Interfacial Tension. AIChE Journal 1986, 32(4), 667-676. 42) V. F. Odyakov, E. G. Zhizhina, A Novel Method of the Synthesis of Molybdovanadophosphoric Heteropoly Acid Solutions. React. Kinet. Catal. Lett. 2008, 95, 21-28.


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Catalyst Activation and Influence of the Oil Matrix on Extractive

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