[Elearnica.ir]-Desulfurization and Denitrogenation Process for Light Oils Based on Chemica

8/10/2019 [Elearnica.ir]-Desulfurization and Denitrogenation Process for Light Oils Based on Chemica

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Desulfurization and Denitrogenation Process for Light Oils Based

on Chemical Oxidation followed by Liquid-Liquid Extraction

Yasuhiro Shiraishi, Kenya Tachibana, Takayuki Hirai,* and Isao Komasawa

Department of Chemical Science and Engineering, Graduate School of Engineering Science, and

Research Center for Solar Energy Chemistry, Osaka University, Toyonaka 560-8531, Japan

A desulfurizat ion a nd denitrogenat ion process for light oils ha s been investiga ted ba sed on thechemical oxidation of sulfur- and nitrogen-containing compounds using hydrogen peroxide anda cetic a cid a s oxidizing a gent. Sulfur a nd nit rogen compounds, when dissolved in n-tetradecanea nd xylene, w ere oxidized un der moderat e conditions a nd w ere removed successfully. B y use ofthis basic process, although nitrogen content of actual light oils was reduced to


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compounds (B T, DB T, an d their methyl-substitutedderivatives)5,20 and nitrogen compounds (aniline, indole,a n d ca rba zo le)4,6 w e re t h e s a m e a s t h os e u s ed f orprevious st udies. Three light oils, stra ight-run light ga soil (LGO), commercial light oil (CLO), and light cycleoil (LC O), w ere used a s feedstocks. The sulfur contentof the CLO lies just below th e previous regulatory va luet h a t a p p lied p rev iou s ly in J a p a n (0.2 wt %). Th e

re le va n t p rop ert ie s o f t h e s e o ils a re s u mma rized inTable 1.

2. Apparatus and Procedure. The desulfuriza tionand denitrogenation experiments were carried out asfollows: light oil (50 mL) wa s mixed with a queous H2O2s o lu t io n a n d h e a t e d t o t h e de s ig n a t e d t e mp e ra t u re .AcOH was added carefully to the heterogeneous mix-ture. The result ing mixture was then cooled to roomtemperature, and any viscous products were recoveredb y f il t r a t ion . Th e oi l w a s t h en s ep a r a t e d f r om t h eaqueous phase by decantat ion, and the oil was washeds ev er a l t i m es w i t h a n e q ua l v ol um e o f w a t e r . Th eextraction of the sulfones, from the resulting light oils,was conducted by mixing the oil with an acetonitrile/

w a t e r m i xt u r e f or 10 m i n a t 298 K . To c la r i fy t h erelative reactivities of various compounds, n-tetradec-an e, containing a n individua l sulfur compound (54 mM)corresponding t o a sulfur content 0.2 wt %, a nd xylene,cont a ining a nit rogen compound (20 mM) correspondingto a n itrogen content 240 ppm, w ere also used a s modellight oils.

3. Analysis. Concentra t ions of th e model sulfur a ndnitrogen compounds and of the aroma tics in tetra decan ea n d x y le n e we re a n a ly zed by G C-F I D (Sh ima dzu G C-14B). Total sulfur and nitrogen concentrations of lightoils w ere an alyzed using an inductively coupled argonplasma at omic emission spectrophotometer (NipponJ a rre l l-As h I CAP -575 M a rk I I ) a n d t o t a l n i t rog enanalyzer (Mitsubishi Chemical Corp., TN-100), respec-tively. The concentrations of the individual sulfur andnitrogen compounds in light oils w ere ana lyzed by ga schroma tography using an at omic emission detector (GC-AE D , H e w l et t -P a ck a r d 6 890 , e q u ip pe d w i t h AE DG2350A), in accordan ce w ith a previously describedprocedure.4-6,20 H 2O2 concentra t ions in a queous pha sewere determined by t itrimetric analysis using sodiumt h ios u lf a t e a n d K I a s in dica t o r . I R s p ect ra we re me a -sured using a n FT/IR-610 infr a red spectrophotometer(J a sco Corp.) on KB r disks. G a s chroma togra phy/ma ssspectrometr y (GC /MS) an a lyses w ere carried out on aJ EOL J MS-DX303HF ma ss spectrometer.20 The netelectron density on the sulfur atom and dipole momentfor the relevant sulfur compounds were calculated using

the WinMOPAC ver. 3.0 software (Fujitsu Ltd.), accord-ing to procedure previously described.5

Results and Discussion

1. Desulfurization Reactivity of Sulfur-Contain-ing Compounds from Tetradecane. 1.1. Desulfu-rization Reactivity of DBT and BT. The S-oxidationbet we e n D B T diss olve d in h y droca rbo n s olve n t a n doxidizing agents (H 2O2 and AcOH) has been studied indetail by Heimlich and Wallace.18 I t is re p o rt e d t h a tDBT is S-oxidized to give rise to the correspondingsulfoxide, wh ich is furt her oxidized to sulfone. Also thera t e of D B T o xida t ion is a c ce le ra t e d wit h in cre a s in gtempera ture an d exhibits a f irst-order dependency onDB T concentra t ion. The B T in t etradecane w as foundvia high-performa nce liquid chroma tography (HP LC)analysis to be oxidized by react ion with the oxidizinga gent int o the corresponding sulfone, which is removedfrom t etradecane, as also the case for D B T. During t hereaction, the BT sulfoxide wa s scarcely detected neitherin tetra decane nor th e aqueous phase, thus suggesting

that the formed sulfoxide is oxidized very quickly tosulfone. The desulfurization of BT from tetra deca ne wa saccelerated with an increase in react ion temperatureand init ial concentrat ion of BT in tetradecane, as alsothe case for DBT (Supporting Information available).The desulfurizat ion rates for both DBT and BT couldbe expressed by first-order reaction rate dependency onthe init ial DB T an d B T concentra t ions,18 respectively.Thus

wh e re k i s t h e f irs t - o rde r ra t e c o n s t a n t a n d t i s t h e

reaction t ime. The ra te constants, k, w ith 100- a nd 50-fold molar excesses of H 2O2 a n d A c O H , ba s e d o n t h einit ial concentrat ion of sulfur compounds, were est i-ma t e d a s 0 . 103 h-1 f o r D B T a n d 0. 081 h-1 for B T,respectively, thus revealing that DBT is desulfurizedmore e ff ect iv ely t h a n B T. Arrh e n iu s p lot s f or t h edesulfurizat ion of both DB T an d B T gave stra ight lineplots (Supporting Information available), such that theactivat ion energies for desulfurizat ion could be est i-ma ted a s 65.3 kJ /mol for DB T and 61.9 kJ /mol for B T,respectively.

The reactivity of the S-oxidation between DBTs andthe oxidizing agent d epends on the net electron densityof the S atom for DBT.13 To clar ify th e reactivit y for B Ts,

Table 1. Properties and Composition of the Feed Light Oils

commercial lightoil (CL O)

stra ight-run lightgas oil (LGO)

light cycleoil (LC O)

den sit y @ 288 K (g/m L ) 0.8313 0.8548 0.8830h ydr ogen (w t %) 85.5 85.6 87.9ca r bon (w t %) 13.5 13.0 11.5sulfur (w t %) 0.179 1.380 0.132n it r ogen (ppm ) 80.4 160.0 243.1ba sic n it r ogen 54.7n eut r a l n it r ogen 80.4 160.0 188.4

saturated fract iona

(vol %) 77.9 75.4 33.7aromatics a,b (vol %)on e-r in g 17.5 14.9 36.4t w o-r in g 4.6 9.7 29.9

a By the J PI-5S-49-97 norma l-phase H P LC m ethod. b Three-and greater-than-three-ring aromatic compounds are present only in traceq u a n t i t ie s (


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the relat ionship between the desulfurizat ion ra te con-s t a n t , kB T, for several alkyl-substituted BTs in tetra-decane and the net electron density on the S atom, asest imated by MO calculat ion, wa s studied. The resultsare summarized in Figure 1, in which linear relat ion-ships are obtained between the electron density a nd thera t e con s t a n t , k, for both th e B Ts a nd the D BTs. Thisin dica t e s t h a t bot h B Ts a n d D B Ts , o f h ig h e le ct ro ndensity, a re desulfurized more effect ively. The ra teconstant dependencies on electron density for the DBTsa n d t h e B T s a re h o we v e r di f f e re n t a s s h o wn by t h ediffering slopes of the straight line plots. The rate ofnucleophilic oxidat ion between S atom and oxidizinga g e n t i s a f f ect e d b y t h e p r es en ce of a n e le ct r on -wit h dra w in g g rou p on t h e s u lf u r comp ou n ds .21 As

shown in Figure 2b, the B T has nucleophilic unsatur-a t e d bo n d o n t h e C2-C3 posit ion, which thus affectsthe desulfurization reactivity for BTs. This is probablythe cau se of the different dependencies of the reactivityof DBTs a nd B Ts on th eir electron density on S at om.

Actual light oils conta in a large number of differingD B Ts a n d B Ts , w it h s ev era l t y p es a lk y l s u bs t i t u en t sof carbon number C 0-C 6, on several posit ions of theDB T an d B T, as shown in Figure 2a,b.5,22 The desulfu-rizat ion react ivity of alkyl-substituted DBTs and BTswa s s t u die d in de t a i l ba s e d o n M O c a lc u la t io n . T h eelectron densities of a ll the DB Ts a nd B Ts, ha ving a lkylsubstituents of carbon number C 0-C 6 (including bothstraight- and branched-chain) were calculated, on allp os it i on s of t h e D B T a n d B T. Th e a v er a g e v a l ue so bt a in e d a re s u mma rize d in F ig u re 3 a n d a re s h o wnwith respect to the carbon number of alkyl substituents,n f or D B T a n d m for BT. The electron density valuesfor both DB Ts an d B Ts increase with increasing carbonnumber of the alkyl substituents. From these results,it is t herefore expected tha t w hen t he process is a ppliedto the desulfurization of actual light oils, DBTs and BTs,ha ving alkyl substituent s of higher carbon number, willbe desulfurized more easily.

1.2. Effect of Aromatic Hydrocarbons on Desul-furization. Act u a l l ig h t oi ls , a s s h own in Ta ble 1,conta in large q uan tit ies of a romatic hydrocarbons. I t isnecessary to identify reaction products of these aromat -ics formed during the present process. Tetralin and

naphth alene w ere used as model components t o repre-sent the one-and two-ring aromatics in light oils 5,6 a n dwere treated with H 2O2an d AcOH for 3 h a t 323 K. Theresulting mat erials were extracted wit h dichlorometha ne,wa s h ed wit h wa t e r , a n d con ce n t ra t e d by e va p ora t io n .GC /MS an alysis of the products for n aphtha lene dem-onstrated a single peak having a molecular ion at m/z156, which was identified as naphthalene-1,4-dione, 1,a s indicat ed in Figur e 2c. The sa me product is reportedto be produced by react ion of naphthalene with H 2O2and formic acid.23 G C/MS an a lysis for the products oftetra lin demonstra ted four new peaks, ha ving molecularions a t m/z148, 146, 162, and 170, respectively. Thesepeak compounds were identified as 1,2,3,4-tetrahydro-

1-naphthol, 2, 1,2,3,4-tetrahydronaphthalene-1-one, 3,1,2,3,4-tetrahydronaphthalene-1-one-4-ol,4, and 1,2,3,4-tetrahydronaphthalene-1,4-dione, 5, respectively. Fol-lowing further 10 h of react ion of the t etralin, only thepeak for compound 5 remained, whereas the other peaksdisappeared. These results suggest, as shown in Figure2d, t h a t t e t ra l in is f i rs t o x idize d t o i t s h y dro x y la t e dcompound 2, which is then oxidized to form the finaldicarbonyl compound 5.

The effect of ar omat ics on t he desulfuriza tion of DB Ta n d B T f rom t e t ra de ca n e wa s s t u die d wit h re s pe ct t odesulfurization yield, aromatics conversion, and selec-t i v i t y . T e t r a l i n a n d n a p h t h a l e n e w e r e a d d e d t o t h et e t ra de ca n e t o ge t h er wit h t h e D B T or B T f or e xp eri-

Figure 1. Correlat ion between the desulfurizat ion ra te constant ,k, for both DBTs and BTs from tetradecane and the net electrondensity on the sulfur a tom, as est ima ted by MO calculat ion. Thenet electron density is the sum of all the occupied orbitals on thesulfur a tom. Key: 1, DB T;2, 4-methyl-DBT;3, 4,6-dimet hyl -DB T;4, 2,8-dimethyl-DBT(solid symbols); 5, B T;6, 3-met hyl-BT;7, 2,3-dimethy l-B T (open sy mbols).

Figure 2. Structure of (a) DBTs and (b) BTs in actual light oils,and the react ion pathways for (c) naphthalene, (d) tetralin withH 2O2 a n d Ac OH , a n d (e ) s u lf u r oxid a t ion in t h e p r es e n ce ofcarbonyl compound and H 2O2.

4364 Ind. E ng. C hem. Res. , Vol. 41, No. 17, 2002


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mental study. The results a re summa rized in Table 2,where selectivity,5 R, is defined as

The desulfurization yield for BT, as shown in Table 2(runs 6-10), decreases with an increase in amount ofboth tetralin and naphthalene added. This is becausethe S-oxidation of BToccurs competitively with aromaticoxidat ion. Na phtha lene decreases t he desulfurization ofBT more significantly t han tetra lin. As shown in Table2 (runs 1-5), however, the desulfurization yield for DBTincreases with increasing concentrations of both naph-tha lene an d tetra lin. Sha ripov et a l.24 ha ve reported tha t

t h e ox ida t io n of s u lf ide , u s in g H 2O2 a n d AcO H , isaccelerated by the presence of carbonyl compounds.Reaction proceeds via oxidation of sulfide by R-oxyhy-droperoxide, which is formed via the r eaction of ca rbonylcompounds with H 2O2. The a ccelera tion in the desulfu-rizat ion of DB T, w hen in the presence of ar omatics, iscaused by R-oxyhydroperoxide,6, formed via the rea c-t ion of the oxidat ion products of tetra lin and na phtha-

lene (1, 3-

5) w i t h H 2O2. This is shown schemat icallyin Figure 2e by the case of 1,2,3,4-tetrahydronaphthal-ene-1-one, 3, for instance. The oxidat ion react ivity ofsulfur compounds t o R-oxyhydroperoxide is reported todepend on the net electron density on the S a tom.21 Th elack of any accelera tion in th e desulfurizat ion of B T, inthe presence of carbonyl compound (Table 2, runs 6-10),is therefore due to the low electron density on the Satom for BT (Figure 1). The selectivity values, R, a r efound to decrease in the presence of aromatics (Table2). Select ivity however is st ill high (0.80-0.91) andcomp a ra ble t o t h e v a lu es obt a in e d a ccordin g t o t h ephotochemical process25 a n d t o t h e a l ky la t i on a n dprecipitat ion process.5

Act u a l l ig h t oi ls con t a in la rg e a mou n t s of a lk y l-

substituted DBTs and BTs, such that the effect of theaddition of naphthalene on the desulfurization of alkyl-s u bs t i t u t e d D B T s a n d B T s wa s in v e s t ig a t e d u s in g amodel light oil . The results a re summa rized in F igure4, where a react ivity rat io, , the rat io of the desulfu-riza t ion y ield o f D B Ts a n d B Ts in t h e p res en ce o fn a p h t h a le n e t o t h a t obt a in e d in t h e a bs e n ce o f n a p h -thalene,5 is defined as

The reactivity ratio, , for the alkyl-substituted DBTs,as shown in Figure 4a, is larger than that for nonsub-st ituted DBT. This suggests that the oxidat ion of themethyl-substituted DBTs is accelerated by the R-oxy-hydroperoxide of the n aphtha lene, in th e sam e ma nnera s s h own in F ig u re 2e. Th e re a c t ivi t y ra t io f o r t h ecompounds lies in the order 4,6-dimethyl-DB T > 4-methyl-DBT> D B T, wh ich is t h e s a me a s t h a t f or t h enet electron densit y on the S at om (Figure 1). As shownin Figure 4b for BTs, alth ough the reactivity for BT a nd3-methy l-B T is decreased by the presence of napht ha l-ene, the rea ctivity of 2,3-dimethyl-B T is increased, w itha resultant order 2,3-dimethyl-BT > B T > 3-methyl-B T . T h i s i s a l s o t h e s a m e o r d e r a s t h a t f o r t h e n e t

Table 2. Effect of the Addition of Aromatic Hydrocarbons on the Desulfurization of the Model Sulfur-ContainingCompounds from Tetradecane Solution and the Selectivity, ra

r unsulfur compounds

(mM)n a p h t h a le n e

(mM)tetralin

(mM)desulfurization yield ofsulfu r compoun ds (%)

conversion ofna phth alene (%)

conversion oftet ra lin (%)

selectivity,R

1 D B T, 27 79.0 12 D B T, 27 270 87.1 20.4 0.8103 D B T, 27 270 89.0 9.6 0.9034 D B T, 27 540 96.5 14.8 0.8675 D B T, 27 540 89.7 13.1 0.8736 B T, 27 87.4 1

7 B T, 27 270 66.1 6.7 0.9088 B T, 27 270 83.9 8.9 0.9049 B T, 27 540 67.4 16.7 0.80110 B T, 27 540 77.0 8.9 0.896

a Desulfurization conditions: temperature, 323 K; reaction time, 8 h; tetradecane volume, 50 mL; [sulfur compounds] initial ) 1.35 mmol;[H 2O2] ) 135 mmol; [AcOH] ) 67.5 mmol.

Figure3. Var iat ion in the net electron density on the sulfur atomfor (a) DBTs by the substitution of alkyl groups of carbon numberC 0-C 6 on t h e C1-C 4 a n d C 6-C9 posit ions of the DB T moleculeand (b) BTs by the substitution of alkyl groups of carbon numberC 0-C 6 on t h e C2-C7 positions of the BT molecule.

R ) [desulfuriza tion y ield of sulfur compound]/

([desulfuriza tion y ield of sulfur compound] +

[rea ction yield of ar omat ic compound]) (2)

) [desulfurization (denitgenation) yield in the

presence of hy drocar bon or sulfur compoud]/

[desulfurization (denitrogenation) yield in the

a bsence of hyd rocarbon or sulfur compoud] (3)

Ind. Eng . C hem. R es. , Vol. 41, No. 17, 2002 4365


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electron density on the S at om for B Ts (Figure 1). Thissuggests that the desulfurization of sulfur compounds,of high electron density, is accelerated by the presenceof aromat ics owing t o the oxidat ion by R-oxyhydroper-oxide, whereas the desulfurization of compounds, of lowe le ct ro n de ns i t y , is de ce le ra t e d by t h e p res en ce ofar omatics owing to competitive oxidation of the a romat -ics to that of the sulfur compounds by the oxidizingagent. From these results, when the present process isapplied to the desulfurizat ion of actual l ight oils, thehighly a lkyl-substituted D BTs a nd B Ts in high-ar omatic-

con t e n t l ig h t oi ls , o f h ig h e le ct ro n de n si t y , m a y beexpected to be desulfurized more easily. In the currentHDS process, the desulfurizat ion of DBTs from high-aromatic-content oils is quite difficult. 1,2 The desulfu-rizat ion react ivity of DBTs, in the present process, iscompletely different from that of the HDS process.

2. Desulfurization of L ight Oils. 2.1. Desulfuri-zation Reactivity of Different Light Oils. Thedesulfurizat ion react ivity of actual l ight oils, such asLGO, CLO, and LCO, of differing sulfur and aromaticconcentrations, was studied. Time-course variations inthe rema ining percenta ge of sulfur in t he light oils a reshown in Figure 5a,b. The remaining percentage forL G O a n d CL O , wh e n t h e re a c t io n is c a rr ie d o u t wit h100- a nd 50-fold molar excesses of H

2O

2 and AcOH,

bas ed on the initia l sulfur concentra tion of the feed oils(Figure 5a) is seen to decrease a t f irst , but for t he ra teto become slower with increasing reaction time. Underthe condit ion, the remaining percentage for LCO re-ma ins consta nt a nd is not decreased a t a ll. The addit ionof 1000-a nd 500-fold mola r excesses of H 2O2and AcOHshowed no drast ic accelerat ion in the desulfurizat ion(Figure 5b). The desulfurizat ion yields obta ined a resignificantly smaller than those as expected from themodel experiments using t etra decan e. The desulfuriza-t ion efficiency for light oils l ies in the order LGO >C L O > L CO . Th is is t h e s a me a s t h a t of t h e a roma t icconcentration in light oils (Table 1), and demonstratestha t h igh-a roma tic-content light oil is difficult t o desul-

f u rize . Th e mo de l e xp erimen t s in t h e p res e n ce ofa r o ma t i cs (Ta b l e 2 a n d F i gu r e 4), r ev ea l t h a t t h epresence of aromatics accelerates desulfurization. Thedesulfurizat ion efficiency for actual l ight oils is thusin con s ist e n t wit h t h o se a s e xp ect e d f rom t h e mode lexperiment.

Sin ce , in t h e p re s en t re a ct ion , a la rg e a mou n t ofaromatics in light oils is oxidized, the above low desul-furizat ion efficiency w as assumed to be at tributa ble tothe low concentra tion of the oxidizing a gent. The a bovebat ch react ion procedure wa s t herefore repeated threetimes over. The light oil, following desulfuriza tion, wa srecovered by decanta t ion, wa shed with w at er, and thent r ea t e d a g a i n w i t h f r es h a q u eou s H

2O

2 solution and

AcOH. The va riat ions in the remaining percenta ge ofsulfur in each of the light oils a nd a lso the H 2O2 in t h ea q u e o u s p h a s e a r e s u m m a r i z e d i n p a r t s a a n d b o fFigure 6, respectively. The remaining percentage valuesof sulfur in all the light oils were decreased slightly, witheach fresh addition of oxidizing agent. The decrease inthe rema ining percentages of sulfur, however, w as nota s l a r g e a s t h a t ob t a i n ed i n t h e s i n gl e-s t a g e b a t c hexperiments (Figure 5). As shown in Figure 6a, almosta l l t h e H 2O2 a dded, du rin g t h e re pe a t e d t h re e-s t a g eprocess, remains without significan t decomposit ion.These results suggest that the low desulfurization yieldsfor light oils are not overcome by the addit ion of thefresh oxidizing agents and that the init ial conjecture

Figure4. The varia tion in reactivity rat io,, for a lkyl-substituted( a ) D B T s a n d ( b ) B T s , in t e t r a d e c a n e a n d in t h e p r e s e n c e ofnapht ha lene. The va lue foris defined as t he ra tio of the obta ineddesulfurization yield for the compounds, both in the presence andin t h e a b s en c e of n a p h t h a le n e, a s d e fin ed in e q 3 . R e a ct ion

condit ions: react ion t ime, 4 h; temperature, 323 K; tetra decanevolume, 50 mL; [sulfur compounds]initial ) 2.7 mmol; [H2O2] ) 270mmol; [AcOH] ) 135 mmol; [naphthalene]initial ) 200 mM.

Figure 5. Time-course variat ion in the remaining percentageof ( a a n d b ) s u l f u r a n d ( c a n d d ) n i t r og e n in l ig h t oi ls , d u r in greact ion in the presence of differing concentra t ions of H 2O2 a n dAc OH . R e a ct ion c on d it ion s : t e m p er a t u r e , 3 43 K ; (a a n d c )[H 2O2] ) 100- an d [AcOH] ) 50-fold and (b and d) [H 2O2] ) 1000-and [AcOH] ) 500-fold molar excess based on t he init ia l sulfurconcentration of feed light oils.



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concerning t he course of low d esulfuriza tion efficiencywa s incorrect .

I t is necessary t o clarify furth er the cause of the lowdesulfuriza tion efficiency for light oils. The a ddition ofoxidizing agents to the light oils leads to the formationof dark red viscous precipitates. The IR spectrum forthe precipitat e obta ined from all the light oils, as shownin F ig u re 7b, de mo n s t ra t e d t wo a bs o rp t io n ba n ds a t1130 and 1280 cm-1, which are at tributable to sulfonegroups, and also a band at 2800-3000 cm-1, which isattributable to alkyl groups on aromatic and thiophenicring. This suggests that the precipitates formed thusconsist of alkyl-substit uted D B T an d B T sulfones. Thelight oils obta ined following desulfurizat ion demon-stra ted a dar k red-yellow color, w hereas t he feed lightoils are pale yellow in color. The sulfur-specific GC-AEDch roma t o g ra ms f or t h e f e ed a n d f or t h e t re a t e d l ig h toil, following desulfurization, a re shown in Figure 8. Oncompar ison of the tw o chromat ograms, th e peaks for th etreat ed light oil are seen to appear a t higher retentiont ime s t h a n t h o s e f o r t h e f e e d o i l . A ida e t a l .11,12 a n dO t su k i e t a l .13 h a v e r e por t ed t h a t t h e s a m e f la m ephotometric detector gas chromatography (GC-F P D )

chromatograms are obtained by the reaction of light oilw i t h H 2O2 in the presence of AcOH or formic acid and

Figure 6. Time-course variat ion in the remaining percentage

of (a) H 2O2 in t he a queous phase a nd (b) sulfur a nd (c) nitrogeni n l ig h t o il s, w h e n t h e r e a c t io n i s ca r r i ed ou t t h r ee t i m essequentially using fresh H 2O2and AcOH at each stage. React ioncondit ions: temperature, 343 K; [H 2O2] ) 3000- and [AcOH] )1500-fold molar excess based on initia l sulfur concentr at ion of thefeed light oils.

Figure 7. IR spectra for (a) DBT sulfone, synthesized accordingto the standard procedure, 19 (b) the precipitate, obta ined by ther e a c t ion of L CO w it h H 2O2 and AcOH, (c) indole, and (d) thep r od u c t of t h e in d ole ob t a in e d b y t h e r e a c t ion w it h H 2O2 a n dAcOH: closed circle sym bols, N-H group; open circle symbols, CdO group; open square symbols, OH group; closed square symbols,sulfonyl gr oup; open tria ngle symbols, a liphat ic hydrogen.

Figure 8. Sulfur-specific (181 nm) GC-AED chromatograms for(a) feed LGO and (b) LGO, following react ion (30 h) a t 323 K, inthe pr esence of 1000- an d 500-fold molar excess of H2O2and AcOH,based on the init ia l sulfur concentrat ion of the feed LGO.



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tha t t he peaks a re at tributa ble to the sulfones of DB Tsand BTs. These suggest that the sulfones formed are

not only removed into the aqueous phase but also forman insoluble precipitat e and rema in in th e light oil. Thelow desulfuriza tion efficiency for light oils, as shown inFigures 5 and 6, is therefore caused by the accumulationof sulfones in the resulting oil.

2.2. Sulfones and Sulfides Remaining in LightOils following Desulfurization. The sulfides (unoxi-dized sulfur compounds) a nd sulfones, remaining in th elight oil following desulfurization, were then examinedfor quantitative determination. The light oils, obtainedfollow ing rea ction for 3 h w ith 1000- a nd 500-fold molarexcess of H 2O2and AcOH, were used for this investiga-tion. The sulfur concentrations for each light oil were0.9997 w t % (desulfuriza tion yield 27.6%) for LG O,0.1487 wt %(18.4%) for C LO, a nd 0.1184 wt %(10.3%)

for LCO. To separate the sulfides from sulfones, thel ig h t o i l wa s f ra c t io n a t e d a n d c o n c e n t ra t e d p rio r t oanalysis, according to the procedure described previ-ously,4 b u t w i t h s li gh t m od if ica t i on s , w h ich a r e a sfollows: The light oils (50 mL) were a dsorbed onto 20 gof activated aluminum oxide, packed in a glass column(20 mm i.d.; 450 mm length). The oil was eluted firstby a dichrolometha ne/n-hexa ne m ixt ur e (20/80, 100 mL )f or s a t u r a t e s, a r o ma t i cs , a n d s u lf id es , a n d t h en b ydichloromethane (100 mL) for nitrogen compounds, andfinally by a dichlorometha ne/a cetone mixture (50/50,100 mL) for sulfones.

The first sulfide fraction was concentrated by evapo-rat ion a nd a na lyzed by G C-AED , following solution indichlorometha ne. The percenta ge of sulfide in th e lightoils followin g desulfuriza tion [{sul fid es/(sulfid es + sul-fones)} 100] wa s 17.4%for LG O, 21.6%for CLO, a nd35%for LCO, thus suggesting tha t t he ma jority of thes u lf ur r em a i n in g i n t h e l ig h t oi l i s a t t r i b ut a b l e t osulfones. The rea ction yield for th e sulfides [{1-(sulfidesin light oil follow ing r eaction/tota l sulfur in feed lightoil)} 100] wa s estim a ted a s 87.4%for L G O, 82.4%forC L O , a n d 68. 6% f or L C O , t h u s r ev ea l i ng t h a t t h esulfides in high-a roma tic-content light oil rema in moredifficult to desulfurize compared to those in low-aromatic-con t e n t oi l. Th e re a c t io n y ie ld f or D B Ts a n d B Ts[{1-(DB Ts or B Ts in light oil follow ing rea ction/DB Tsor BTs in feed light oil)} 100] wa s est imat ed a s 88%and 85%for LGO, 89%and 65%for CLO, and 91%and

34%for LCO. This suggests that the reaction yield forDBTs is increased with an increasing aromatic concen-

tration of the light oil in the order LCO>

C LO>

L G O ,wh ile t h a t f o r B T s is de c re a s e d in t h e o rde r L G O >C L O > LCO. The low desulfurizat ion yield for high-ar omat ic-content light oil (Figures 5 a nd 6) thus resultsowing t o the desulfuriza tion of the B Ts being suppressedby t h e p re s e n c e o f la rg e q u a n t i t y o f a ro ma t ic s . T h econcentrations of the individual sulfides, remaining inthe light oil, ar e summa rized in Table 3.ii and the da taa re plott ed in Figur e 9 (open symbols), as a function ofthe carbon number of a lkyl substituents. The rema iningpercentages for BTs and DBTs tend to decrease withincreasing carbon number of substituents. This indi-cates that the present process desulfurizes the highlys u bst i t u t e d B Ts a n d D B Ts more e ff ec t iv ely . Th e setendencies agree well with those obtained by the MO

calculation (Figure 3).The sulfones, rema ining in the light oils, following

desulfurizat ion, w ere then determ ined. The a bove thirdsulfone fract ion was concentrated by evaporat ion andthen a nalyzed. As shown in Figure 10, the car bon- an dsulfur-specific chromat ogram s resemble each other, t husdemonstra t ing tha t the th ird fract ion conta ins only thes u lf on es of t h e D B Ts a n d B Ts . Al l t h e p ea k s t h a tappeared were t herefore identified from their m olecularweight da ta , as obtained by G C/MS, an d the concentr a-t ion of each sulfone wa s determined by GC -AED . Theresults obta ined are summa rized in Table 4. i, a nd t hedata are plotted in Figure 9 (closed circle symbols), asa function of the carbon number of a lkyl substituents,n for DBT-O

2 a nd m for B T-O

2. The remaining per-

centa ges for both B T-O2 and DBT-O2 in light oils tendto increase with an increase in the carbon number ofthe substituents, in the ra nge of C 0-C 3B T-O2and DB T-O2, but decrease in the range of both C 4-C 6B T-O2a n dDB T-O2. The sulfones are reported to have rather higherpolarity tha n the corresponding sulfides.13 The dipolemoment (dynes) for DB T-O2a nd B T-O2, when calculatedby the MO method, were 5.451 and 5.580 dyn, respec-tively, which are actually rather higher than those forunoxidized DBT (1.363 dyn) and BT (1.090 dyn). Thes olu bili t y of s u lf on e s in n on p ola r l ig h t oi ls s h ou ldtherefore be quit e low. The subst itut ion of hydrophobicalkyl substituents, however, decreases the solubility inthe a queous phase,26 such tha t t he remaining percent-

Table 3. The Quantities of Alkyl-Substituted BTs and DBTs in (i) Feed and (ii) Treated Light Oils following theReaction with H2O2 and AcOHa

s tr a ig ht -r un l ig ht g a s oi l (L G O) com m er ci a l l ig ht oil (C L O) li gh t cy cl e oil (L C O)

species (i) (w t %) (ii) (w t %) (i) (w t %) (ii) (w t %) (i) (w t %) (ii) (w t %)

C 6B T 0.17938 0.02442 0.01319 0.00347 0.00696 0.00352

B Ts (t ot a l) 0.56355 0.08192 0.04896 0.01699 0.05374 0.03521D B T 0.03258 0.00550 0.00301 0.00034 0.00501 0.00067C 1D B T 0.09325 0.01543 0.01475 0.00142 0.01706 0.00179C 2D B T 0.14333 0.02273 0.01840 0.00231 0.01521 0.00140C 3D B T 0.14400 0.02084 0.01777 0.00213 0.00550 0.00056C 4D B T 0.09050 0.00896 0.01223 0.00126 0.00189 0.00021C 5D B T 0.02664 0.00250 0.00361 0.00040 0.00051 0.00004C 6D B T 0.28614 0.01702 0.06058 0.00648 0.03308 0.00241D B Ts (t ot a l) 0.81644 0.09298 0.13035 0.01434 0.07826 0.00704t ot a l sulfur 1.37999 0.17490 0.17900 0.03133 0.13200 0.04225

a Desulfurizat ion condit ions: t ime, 3 h; temperatur e, 343 K; [H 2O2] ) 1000- and [AcOH] ) 500-fold molar excesses based on initialsulfur concentration of the feed light oils. b


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age of sulfones for C 0-C 3DBTs and BTs increases withincreasing carbon number of the substituents. The causeof the low remaining percenta ge for C 4-C 6 sulfones int h e c a s e of D B Ts a n d B Ts is p ro ba bly bec a u s e t h e s ecompounds precipita te, owing t o their low solubility bothin light oil an d in aq ueous solution.

2.3. Extraction of Sulfones Remaining in LightOils. It is necessary to remove the sulfones, remainingin light oils followin g rea ction w ith H 2O2an d AcOH . As

re p o rt e d in t h e l i t e ra t u re s c o n c e rn in g t h e O D S p ro -cess,10-13 the liquid-liquid extraction technique usingwater-soluble polar solvents (DMSO, DMF, and aceto-nitrile) is usually employed. The former tw o solventshave a high extra ctability for sulfones but have a highboiling point a t 573 K, wh ich is close to the boiling pointof t h e s u lfon e s, a n d t h u s t h e y ma y n ot be re u s ed f orfurther extraction based on recovery by distillation. Inthe present process, acetonitrile wa s used a s the extra c-

Figure 9. Rema ining percenta ge of a lkyl-substitut ed (i) DB Ts a nd (ii) BTs (open sym bols) an d (i) DBTs-O 2a nd (ii) BT-O2(closed sym bols)in (a) LGO, (b) CLO, and (c) LCO, w ith r espect t o the carbon number of the alkyl subst ituents , n for DBTs, m for BTs, nfor D B T-O2, a n dm for B T-O2. Open and closed circle symbols represent the sulfur compounds in light oils following reaction with AcOH and H 2O2. Theclosed squar e symbols represent th e sulfones, followin g extra ction wit h a cetonitr ile/wa ter a zeotropic mixtur e (84/16 v/v). The initia l am ountof each a lkyl-substit uted DB T an d BT in the feed light oils, as sh own in Table 3.i is set as 100%. Reaction condit ions: [H2O2] ) 1000-foldand [AcOH] ) 500-fold m olar excess ba sed on t he init ia l concentrat ion of the feed light oils ; t ime, 3 h; t emperat ure, 343 K. E xtract ionconditions: light oil/azeotrope volume rat io ) 1/1; tempera tur e 298 K, t ime 10 min .

Table 4. The Quantities of Sulfones of Alkyl-Substituted BTs and DBTs, Remaining in L ight Oils, (i) following Reactionwith H2O2 and AcOHa and (ii) Subsequent Extraction by Acetonitrile/Water Mixture (84/16 v/v)b

s tr a ig ht -r un l ig ht g a s oi l (L G O) com mer ci al l ig ht oi l (C L O) l ig ht cy cle oil (L C O)

species (i) (w t %) (ii) (w t %) (i) (w t %) (ii) (w t %) (i) (w t %) (ii) (w t %)

C 6B T-O2 0.06715 0.00393 0.00616 0.00012 0.00201 0.00021B Ts-O2(t ot a l) 0.30819 0.01104 0.04388 0.00319 0.03003 0.00850D B T-O2 0.01411 0.00211 0.00201 0.00045 0.00221 0.00178C 1DB T-O2 0.06129 0.00289 0.01075 0.00098 0.00981 0.00547C 2DB T-O2 0.10882 0.00359 0.01540 0.00115 0.01022 0.00614C 3DB T-O2 0.10221 0.00317 0.01277 0.00118 0.00526 0.00123C 4DB T-O2 0.08349 0.00321 0.01223 0.00081 0.00107 0.00029C 5DB T-O2 0.01423 0.00229 0.00404 0.00018 0.00027 0.00004C 6DB T-O2 0.13246 0.00381 0.01262 0.00090 0.01728 0.00097DBTs-O2(t ot a l) 0.51661 0.02107 0.07082 0.00565 0.04612 0.01592

t ot a l sulfur 0.82480 0.03211 0.11470 0.00884 0.07615 0.02442

a Desulfurizat ion condit ions: t ime, 3 h; temperatur e, 343 K; [H 2O2] ) 1000- and [AcOH] ) 500-fold molar excesses based on initialsulfur concentrat ion of the feed light oils . b Extr act ion condit ions: t ime, 10 min; temperature, 298 K; oil/azeotropic mixture volumer a t io ) 1/1. c


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tion solvent, since it has a relatively low boiling point(355 K) and is separated easily from the sulfones by

distillation. When acetonitrile is contacted with light oil,a l a r g e q u a n t i t y of a r o ma t i cs i s e x t r a ct e d s i m u lt a -neously w ith the sulfones. The a ddit ion of w at er how-ever suppresses the extra ction of aroma tics, thus ma in-ta ining the high fa vora ble extra ctability of the sulfones.4

The light oils, obtained following 3 h of reaction, with1000- and 500-fold molar excess of H 2O2 and AcOH,were used for experiments. The oils w ere mixed w ithdifferent concentrations of aqueous acetonitrile solutionfor 10 min a t 298 K. The var iat ions in the recovery a ndd es u lf ur i za t i on y ie ld a r e s h ow n i n p a r t s a a n d b ofF i gu r e 11. I n a l l ca s e s, t h e d es u lf ur i za t i on y ie ld sin cre a s e wit h a n in cre a s in g a c et o n it r i le p e rce n t a g econcentra t ion in the wa ter. The yield lies in the orderLG O > C LO > L CO , wh ich is t h e s a me a s t h a t f o r t h ear omat ic concentra tion in th e light oils. The pola rity ofthe light oil increases with increasing aromatic concen-trat ion, such that the solubility of the sulfones in theoil also increases with increasing aromatic concentra-tion. As a result, the extractability of the sulfones fromhigh-ar omatic-content oil is relat ively low. Recoveryvalues for th e oils (Figure 11a ) decrea se wit h increasinga c et o n it r i le con ce n t ra t ion in wa t e r . F or a c et o nit r i leconcentrations in the region of 80-90%, h owever, th esulfur cont ents st ill decrea se effectively, suppressing t hedecrease in the oil recoveries. Acetonitrile forms anaz eotropic mixtur e wit h w a ter (acetonitrile/w at er, 84/16 v/v (bp 349 K)). As show n in Figu re 12, t he d esulfu-rization yields, when the extraction is conducted using

the azeotrope composit ion solution, increase with in-creasing a zeotrope/oil rat io, such t ha t the su lfur con-tent s of CLO a nd LC O, at a zeotr ope/oil ra tio ) 5, weredecreased successfully to less tha n 0.05 wt %, w ithma int a ining a recovery y ield of 92%. The yield is h ighert h a n t h a t ob t a i n ed u s in g D M F . 10 Although, with thepresent condit ions, the sulfur content of LGO wa s notdecreased to the target level, further oxidat ion of theLG O did reduce the sulfur content to


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decrease with increasing carbon number of the substit-uents. The results show t ha t, in th is extraction process,the highly substituted sulfones of DBTs and BTs areremoved m ore easily compa red t o those sulfones ha vingalkyl substituents of low carbon number. The extra ct-ability of sulfones depends on the dipole moment valuesfor th e compounds. 26 To clar ify th e extra ction beha viorof sulfones, according to the present process, dipole

moment va lues w ere est imat ed by MO calculat ion an dcompared to the results obtained by experiment. Thedipole moment for all DBT-O 2and BT-O2, having alkylsubstituents of carbon number C 0-C 6 (including bothstra ight a nd bra nched cha ins) on all the positions of themolecu le, we re ca lc ula t e d. Th e a v e ra g e v a lu es a resummarized in Figure 13 and are shown with respectto the carbon number of alkyl substituents. The dipolemoment va lues for DB T-O2 decrease by substitution ofalkyl groups of carbon number C 2 bu t in c re a s e wit hincreasing carbon number of the substituents. For BT-O2 a ls o , t h e dip o le mo me n t v a lu e s in c re a s e wit h in -cre a s ing ca rbo n n u mber of t h e s u bst i t u en t s . Th e seresults suggest that highly alkyl-substituted DBT-O 2and BT-O2, of h ig h dipole mome n t v a lu es , s h ou ldtherefore be extra cted easily from light oil into a ceto-nitrile solution. As shown by th e closed squa re symbolsin Figure 11a. i and ii , the remaining port ion for bothD B T-O2 and BT-O2 in light oils, following extract ionwit h a cetonitrile/w at er mixture, tends to decrea se within cre a s in g ca rbo n n u mber of t h e s u bst i t u en t s . Th eresults thus a gree reasonably w ell with those obta inedby MO calculation.

As described previously,27 t h e s u lf o n e s , wh e n dis -solved in a queous H 2O2 solution, m ay be a dsorbed onto alum inum oxide adsorbent w ithout decomposition ofH 2O2 taking place, and pure H 2O2 solution may there-fore be regenerated. On this basis, a f low scheme foroverall desulfurization process, involving the recovery

of acetonitrile and w at er, has been formulat ed and t hisis s h own in F ig u re 14. Th e p roce ss s e q ue n ce is a sf ol lows : (1) F ee d l ig h t oi l a n d ox idizin g a g e n t a reintroduced to the reactor. (2) The recovered oxidizing

agent from the reactor is sent to an adsorption column,in which the sulfones, dissolved in the aqueous H 2O2solution, a re a dsorbed onto the a dsorbent. The purifiedoxidizing a gent is t hen reused for further desulfuriza-t ion . Th e re cov ere d l ig h t oi l f rom t h e re a ct o r (1),following desulfurizat ion, is then m ixed w ith an azeo-tropic acetonitrile/wa ter mixture for the extract ionremoval of sulfones (3). The recovered light oil is thenwashed with water to recover the dissolved acetonitrile(4). The recovered wa ter, conta ining a sma ll am ount ofacetonitrile, is then mixed with the azeotropic mixtureconta ining t he sulfones. The a zeotropic extra ction m ix-ture is th en regenera ted by distilla tion (5), and the purewa ter regenera ted by sequentia l distillat ion, leaving th esulfones a t t he bottom of th e distilla tion column (6). Therecovered a zeotropic mixture is then used for furtherextra ction of sulfones. The recovered wa ter m a y a lso beu s ed t o wa s h t h e ra f f in a t e l ig h t oi l. Th e p rop os edprocess is thus made up of very simple stages and isoperated at moderate atmospheric pressure conditions.As shown in Figure 2c,d, the aromatics in light oils areoxidized, in t his process, to their corresponding ca rbonylcompounds, w hich must be removed to improve t hecombustion property of the light oils. H owever, thesecarbonyl compounds are reported to be removed moree a s i ly by t h e H D S p ro c e s s t h a n a re t h e s u lf u r c o m-pounds. I f therefore, the HDS process is employed tofollow the present process in sequence, carbonyl com-pounds may also be removed quite easily under more

Figure 12. Variat ions in t he desulfurizat ion yield for light oils ,following extra ct ion with acetonitrile/wa ter azeotropic mixture(84/16 v/v), as a funct ion of t he a zeotr ope/ligh t oil volum e ra tio.The extract ion condit ions a nd t he light oils used a re identical tothose shown in Figure 11.

Figure 13. Variat ion in the dipole moment va lues for (a) DB T-O2by the subst itut ion of the a lkyl groups of carbon number C 0-C 6 on t h e C1-C 4 a n d C 6-C9 positions of the DBT-O 2 moleculean d (b) B T-O2by the substit ution of alkyl groups of car bon numberC 0-C 6 on t h e C2-C7 positions of the BT-O 2 molecule.



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relat ively mild conditions. The proposed oxidat ion a ndsubsequent extra ct ion process t hus shows potential as

an energy-efficient desulfurization process for light oils.3. Denitrogenation of Nitrogen Compounds.3.1.Denitrogenation Reactivity of Nitrogen Com-pounds from Xylene. The individual nitrogen com-pounds in light oils were identified by GC -AED an d G C/MS analyses in a previous paper.4 I t w a s s h o w n t h a tCLO a nd LG O conta in only alkyl-substituted carba zoles,w hile L CO cont a ins a nilines (23%), indoles (36%), an dcarbazoles (41%). To exam ine the feasibility of thepresent process to denitrogenation of l ight oils, th reemodel nitr ogen compounds (an iline, indole, carba zole),each dissolved in xylene, were treated with H 2O2 a ndAcOH. The product of an iline w a s ident ified by G C/MSto be azoxybenzene. Sonawane et al .28 a n d Se lv a m e ta l. 29 h a v e re port e d t h a t a n i l ine is ox idize d, by t h e

re a c t io n wit h H 2O2 a n d t i t a n iu m s i l ic a t e c a t a ly s t , t of orm t h e s a me p rodu ct . F o r ca rba zo le, t h e G C /M Sanalysis detected a single peak, having a molecular iona t m/z 197 a n d v a riou s f ra g me n t ion s (Su p port in gInformation available). The product was identified ascarbazole-1,4-dione, thus suggesting that the reactionof carbazole with oxidizing agent does not occur on theN a tom but occurs on the H at om on its a romatic ring.The oxidat ion products, a zoxybenzene an d carbazole-1,4-dione, remain in the resulting xylene. These com-pounds, however, are insoluble in nonpolar solventssuch a s light oil , owing to the high polarity.

F o r in do le , t h e G C- A E D a n a ly s is o f t h e re s u lt in gxylene solution demonstrated no peak other than thesta rting indole, thus suggesting t ha t indole is convertedinto compounds th a t a re difficult to vaporize therma lly.To identify the products, indole is treated with oxidizinga g e n t wit h o ut x y le n e, a n d t h e p rodu ct wa s e x t ra c t edwith dichlorometha ne, concentra ted by evapora tion, andthen a na lyzed. The IR spectrum for t he product (Figure7d) demonstra tes a bsorption ba nds a t 1700-1800 an d1200-1500 cm-1, at tributable to CdO an d OH groups,respectively. A broad band, attributable to N-H group,also appeared at 3000-3800 cm-1. 1H NMR spectrumfor the product exhibits resonan ces due t o N-H , O-H ,and a romatic protons, and the 13C NMR spectrum showsa l a r g e n u m b e r o f p e a k s d u e t o CdO, C-O H , a n daromatic carbons (Supporting Information available).These findings suggest tha t t he product of indole is not

the sole product but conta ins different types of N-H ,CdO, and OH groups on its polymeric structure. Konge t a l .30 h a v e re port e d t h a t t h e H a t o ms o n t h e C2-C 3positions of indole are deprotonated electrochemicallyto produce a polymerized material. The electron densityfor the unsa tura ted bond on the C2-C3 positions of t heindole is significa ntly la rge.6 In t he present process, theH atoms on the C2-C3 positions of indole a re likely tobe deprotonated by oxidizing agents, which causes achain polymerization of indole. The products of indoleremain in the result ing xylene but were insoluble ton on p ola r s olve n t s , a s a ls o t h e ca s e f or a n i l in e a n dcarbazole.

The time-course variat ion in the concentrat ion ofn i t rog en comp ou n ds in t h e x y le n e s olu t ion , du rin goxidation, is shown in Figure 15. The denitrogenationof a niline a nd indole proceeds very effect ively witha lmo st 100% de n it ro ge n a t ion y ields bein g a t t a in e dfollowing 30 min and 4 h of reaction, respectively. Thereactivity of the nitrogen compounds lies in t he orderaniline > indole > carbazole. The denitrogenation ratefor carbazole is significantly lower than those for theother nitrogen compounds and desulfurization rate forBT and DBT. The denitrogenation of carbazole from

Figure 14. A basic flow scheme for the proposed desulfurization process. The individual sections are (1) desulfurization, (2) sulfoneadsorption, (3) sulfone extra ct ion, (4) wat er w ashing of the light oil and recovery of th e acetonitrile in the light oil , (5) dist illa t ion w ithacetonitrile/wa ter a zeotropic mixture regenerat ion, and (6) dist illa t ion w ith wa ter r egenerat ion and condensat ion of sulfur.

Figure 15. Time-

course var iat ion in the concentrat ion of nitro-gen (open symbols) and sulfur (closed symbols) compounds froma xylene solut ion (50 mL). React ion condit ions: temperature,323 K; [nitrogen and sulfur compounds]initial ) 20 mM (1 mmol);[H 2O2] ) 100 mmol (ca. 9 mL); [AcOH] ) 50 mmol (ca. 3 mL).



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x y le n e wa s a c c e le ra t e d wit h a n in c re a s e in re a c t io ntempera ture a nd init ia l concentra t ion of the carba zole,as also the case for B T an d D B T. The denitrogena tionrat e for carbazole may therefore be expressed by f irst-order r eaction ra te dependencies on the init ial car bazolec o n c e n t ra t io n , a s e q 1. T h e ra t e c o n s t a n t , k, i n t h epresence of 100- a nd 50-fold molar excesses of H 2O2a n dAcOH based on the init ial carbazole concentrat ion at3 4 3 K , w a s e s t i m a t e d a s 0 . 0 7 8 h-1, w h o s e v a l u e i ssignifican tly sma ller tha n tha t for BT (0.447) and DB T

(16.85). The activation energy for denitrogenation ofcarba zole wa s est ima ted to be 70.59 kJ /mol, wh ich ishigher than that for DBT (36.8) and BT (35.4).

E f f ect of a ro ma t ics a n d s u lf u r c omp ou n ds on t h edenitrogenation of model nitrogen compounds fromxylene w as then st udied. In th is case, 200 mM of eachhydrocarbon and sulfur compound was added to xylenetogether w ith 20 mM of each nit rogen compound for t heinvestigat ions. The results are summarized in Figure16, wh e re t h e re a ct iv it y ra t io , , f or e a ch n i t rog e ncompound is defined in eq 3. The va lues of the rea ctivityrat io for aniline were ha rdly decreased by the presenceof both aromatic and sulfur compounds. The react ionrate for indole decreased by the presence of all fourmodel compounds. A greater decrease in the reactivityrat io was found in the presence of sulfur compoundstha n in the presence of aroma tics. This is because theoxidation of aromatics or sulfur compounds proceedscomp et i t ive ly wit h t h e in dole o xida t ion a n d t h e S-oxidat ion occurs more easily tha n t he a romatic oxida-tion. The reactivity ratio for carbazole decreases by thepresence of sulfur compounds, w here th e decrea se in thedenitrogenation yield is more significant ly tha n t hat ofindole. The presence of a romatics, on the contra ry,in cre a s ed t h e re a ct iv it y ra t io of ca rba zo le. Th is isbecause R-oxyhydroperoxide, formed via the oxidationof the products for aromatics, accelerates the oxidationo f c a rba zo le , a s in t h e s a me me c h a n is ms f o r t h e a c -ce le ra t ion in t h e ox ida t io n of s u lf u r comp ou n ds , a s

s h o wn in F ig u re 2e . T h e s e re s u lt s s u g g e s t t h a t t h ep res en t p roce ss is e xp ect e d t o be e ff ec t iv e f or t h edenitrogenation of carba zole from high-ar omatic- an dlow-sulfur-content light oil.

3.2. Denitrogenation of Light Oils.As shown inFigure 7b, the IR spectru m for the precipita tes, formedb y t h e r ea c t ion of l ig h t oi l w i t h ox id iz in g a g e nt s ,demonstrated a broad absorption band at 3000-3700cm-1 a n d a b a n d a t 1 7 0 0-1800 cm-1, a t t r ibu t a ble t o

N-

H a n d Cd

O groups, respectively. These a re consis-tent with those obtained from the products of modelnitrogen compounds, as sh own in F igure 7d, suggestingt h a t t h e p recipi t a t e s f or l ig h t oi l con t a in ox idizednitrogen compounds or polymerized materials for in-doles as w ell as sulfones. The var iat ions in the residua lpercentage of nitrogen in the light oils, following deni-trogena tion, are shown in F igure 5c,d. The rema iningpercentage of nitrogen for all the light oils, when thereaction is car ried out with 100- and 50-fold m olarexcesses of H 2O2 and AcOH based on the init ia l sulfurconcentra tion of th e feed light oils (Figur e 5c), decreasesg ra du a l ly wit h in c re a s in g re a c t io n t ime , bu t t h e de -crease in t he percentages is compara ble for each lightoil. The decrease in the remaining percentage became

much larger, when the react ion was carried out in thepresence of 1000- and 500-fold molar excesses of H 2O2and AcOH (Figure 5d), with the efficiency lying in theorder LCO > C L O > LG O. This order differs completelyfrom that obtained in the desulfurizat ion of l ight oils(LGO > C L O > LCO). Compar ing t he denitrogena tionand desulfurizat ion yields, the denitrogenat ion ra te isfaster than the desulfurizat ion rate. The low desulfu-rizat ion yield results because the sulfones formed a reremoved insufficiently into the aqueous phase or as aninsoluble precipita te but remain in t he result ing lightoi l. F ig ure 6c s h o ws t h e v a ria t io ns in t h e re ma in in gpercenta ge of nitrogen, w hen t he a bove bat ch react ionp ro c e du re is re p e a t e d t h re e t ime s o v e r . A s a ls o f o r

desulfurizat ion, the remaining percenta ge of nit rogenfor a ll the light oils wa s ha rdly decreased so large, witheach fresh addit ion of oxidizing agent . This suggeststhat the repeated three-stage process is ineffective forboth desulfurizat ion a nd denitrogenation of l ight oils.In t his process, the nitrogen content of all the light oils,following 30 h of r eact ion with 3000- a nd 1500-foldmolar excesses of H 2O2 and AcOH ba sed on th e init ialsulfur concentration of the feed light oils, was decreasedsuccessfully to less than 22%of the feed concentrations.Un der the sa me conditions, the sulfur concentra tion wa sdecreased t o 40-45%of th e corresponding feed values.

The denitrogena tion reactivity of individua l nitrogencompounds in light oils was then studied. The light oils,obtained following reaction for 30 h with 1000-and 500-fold molar excesses of H 2O2a nd AcOH, w ere used. Thenitrogen concentrations of each light oil are 90.1 ppm(denit rogena tion yield 43.7%) for L G O, 33.6 ppm (58.2%)for C LO, a nd 92.1 ppm (62.1%) for LC O. To separ a tethe nitrogen compounds from the other constituents, thelight oil wa s fra ctiona ted into unoxidized basic nitrogencompounds (anilines, fraction 1), saturates, aromatics,and sulfur compounds (fraction 2), unoxidized neutralnitr ogen compounds (indoles and carba zoles, fra ction 3),and polar compounds (fraction 4), prior to the analysisby e xt ra c t ion f ol lowe d by s ep a ra t io n u s in g colu mnchroma togra phy, a s described previously.4 The oxid izednitrogen compounds were expected to be contained infra ctions 2 or 4, but t he presence of nitr ogen compounds

Figure 16. V a r ia t i on in r e a ct iv i t y r a t io, , f or t h e n i t r og e n -c on t a in in g m ode l c om p ou n d s in a x y len e s olu t ion a n d in t h epresence of aroma tic and sulfur-conta ining compounds. The valuefor is defined as t he ra t io of the obtained denitrogenation yieldsfor nitrogen compounds, both in th e presence and in t he a bsenceof t h e h y d r oc a r b on a n d s u l f u r c om p ou n d s , a s d e f in e d in e q 2 .R e a ct ion c on d it ion s : x y len e v olu m e, 5 0 m L ; [n i t r og e n c om -

pounds]initial ) 1 mm ol; [H2O2] ) 100 mmol; [AcOH] ) 50 mmol;[aroma tics a nd sulfur compounds]initial ) 10 mmol; reaction time,1 h; temperature, 323 K for experiments for aniline and indole;react ion t ime 6 h and temperature 343 K for carbazole.



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wa s h a rdly de t e ct e d e i t h er in f ra c t ion 2 o r in 4, t h u ssuggesting tha t a ll the oxidized nitrogen compounds a reremoved successfully from the light oils during thereaction, whereas the sulfones formed remain in the oils.Th e v a ria t ion in t h e comp os it ion of t h e in div idu a l

nitrogen compounds in light oils, following denitroge-n a t i on , i s s u mm a r i z ed i n Ta b l e 5 f or a n i li ne s a n dindoles a nd in Ta ble 6 for carba zoles, respectively. Thedenitrogenation yield of anilines and indoles from LCOwa s 88.3%a nd 67.4%, and the va lues were higher t ha ntha t of carba zoles (43.1%), with the order an ilines >indoles > c a rba zo le s . T h is a g re e s we ll wi t h t h a t o b-tained for the model compounds in xylene (Figure 15)and is a lso the same as t ha t obtained for the HDN 3 a ndthe proposed processes using photoreaction4 a n d a lk y -lat ion6 technologies. The higher denitrogenation yieldfor LC O, as sh own in F igure 5c,d, is due to the presenceof highly reactive nitrogen compounds such as anilinesa n d in doles . Th e ca rba zo les a re t h e mos t di ff icu l tcompounds t o denitrogenize by the present process. Asshown in Tables 5 and 6, the remaining percentages ofin div idu a l a n i l ine s , in doles , a n d ca rba zo les f or a l lfeedstocks increase w ith increasing carbon number ofthe a lkyl substituents, and especially carba zoles havinga large carbon number of alkyl substituents a re the mostdifficult compounds t o denitr ogenize. This tendency ist h e s a m e a s w a s a l s o f o u n d i n t h e p r o c e s s e s u s i n gphotoreaction4 a n d a lk y la t io n6 techniques.

As described for desulfurization, the extraction pro-cess w a s employed using a n a cetonitrile/w at er a zeotro-pic mixture for the removal of sulfones, remaining inlight oils following reaction with oxidizing agents. Thevariat ions in the remaining percentage of nitrogen inlight oils during the extra ction a re shown in Figure 11c.

T h e re ma in in g p e rc e n t a g e f o r a l l t h e l ig h t o i ls wa sdecreased successfully w ith increasing a cetonitrile per-centa ge concentra t ion in wa ter, as a lso the case for thedesulfurization (Figure 11b). These results suggest thatthe extraction procedure for the removal of sulfones iscarried out successfully without the dissolution of ac-etonitrile into the resulting light oils. The decrease int h e r em a i n in g p er ce nt a g e l ie s i n t h e or d er C L O >L G O > LCO. The low denitrogenation yield for LCOresults since the LCO ha s higher polarity owing to thehigh aromatic concentration. As shown in Figure 14, aba sic flow scheme for the overa ll desulfuriza tion process,involving the recovery of acetonitrile and water, hasbeen fully developed. The above results suggest that theproposed process, if a pplied t o the refining of light oil,is a ble t o re du c e bo t h t h e s u lf u r a n d n i t ro g e n c o m-p o u n ds , in wh ic h t h e a c e t o n it r i le a n d wa t e r c a n bereused for further refining.

Conclusion

A desulfurizat ion a nd simultaneous denitrogenat ionprocess for light oils, based on chemical oxidat ion ofsulfur and nitrogen compounds using H 2O2 and AcOHfollowed by extraction of the resulting compounds, has

been investigated, and the following results were ob-t a in e d.

(1) DB Ts a nd B Ts, wh en dissolved in tetra decan e, areS-oxidized by the addit ion of oxidizing a gents to formthe corresponding sulfones, which are removed success-fully from tetra decan e. The desulfurizat ion react ivityf o r t h e D B T s a n d B T s de p e n ds o n t h e n e t e le c t ro ndensity on the sulfur atom. Aromatics, present in lightoils, ar e also oxidized to form the hy droxyl and carbonylcompounds.

(2) The simple desulfurizat ion of l ight oils, by there a c t io n o f H 2O2 a n d A c O H , is u n s u c c e s s f u l a s t h esulfone compounds, produced during the reaction, areaccumulated in the resulting light oil. These compoundsmay, however, be removed successfully by subsequentextra ction, using a n a cetonitrile/w a ter a zeotr opic mix-ture, to improve the oil recovery obtained.

(3) The extra cta bility of sulfone compounds, u sing t heacetonitrile/wa ter azeotrope extracta nt from the lightoil , is increased with increasing car bon number of thealkyl substituent on the DBT and BT molecule. Thistendency agrees reasonably well with the increase indipole mome n t , a s e st ima t e d by s e mie mpirica l M Ocalculation.

(4) The denitrogenation of l ight oils proceeds ef-f ect i ve ly , a n d t h e p re se nt p roce ss i s s h ow n t o b eapplicable as desulfurizat ion and simultaneous deni-trogena tion process. The denitrogenation yields ar ehigher than the desulfurizat ion yields for all the light

Table 5. Quantities of Anilines and Indoles in (a) FeedLC O and in (b) the Oil Obtained following the Reactionwith H2O2 and AcOHa

s peci es (a ) (ppm ) (b) (ppm ) r em a in in g (%)b

a n ilin e 0.9 0 0C 1-a n ilin e 8.1 0 0C 2-a n ilin e 19.6 2.0 10.2C 3-a n ilin e 7.5 1.0 13.3C 4-a n ilin e 18.6 3.4 18.3t ot a l a n ilin es 54.7 6.4

in dole 3.2 0 0C 1-in dole 14.8 4.1 27.7C 2-in dole 28.1 12.7 45.2C 3-in dole 27.5 12.1 44.0t ot a l in doles 88.6 28.9

a Denitrogenation condit ions: t ime, 30 h; temperature, 343 K;[H 2O2] ) 1000- and [AcOH] ) 500-fold molar excesses based onin i t ia l s u l fu r c on c en t r a t ion of t h e f ee d l igh t oils . b The init ia lamounts of each alkyl-substituted anilines and indoles in the feedLCO (a) a re set as 100%.

Table 6. Quantities of Carbazoles in (a) Feed Light Oils and in (b) the Oils Obtained following the Reaction with H2O2and AcOHa

C L O L G O L C O

species(a )

(ppm)(b)

(ppm)remaining b

(%)(a )

(ppm)(b)

(ppm)remaining b

(%)(a )

(ppm)(b)

(ppm)remaining b

(%)

ca r ba zole 7.1 1.8 25.4C 1-ca r ba zole 1.2 0 0 5.2 1.6 30.7 40.2 19.0 47.3C 2-ca r ba zole 7.2 2.4 33.3 19.3 6.9 35.8 40.9 25.2 61.6C 3-ca r ba zole 29.6 10.0 33.8 58.1 32.2 55.4 11.6 10.8 93.1C 4-ca r ba zole 42.4 21.2 50.0 77.4 49.4 63.8t ot a l ca r ba zoles 80.4 33.6 160.0 90.1 99.8 56.8

a Desulfurizat ion condit ions: t ime, 30 h; temperature, 343 K; [H 2O2] ) 1000- and [AcOH] ) 500-fold molar excesses based on initialsulfur concentration of the feed light oils. b The init ia l amount of each alkyl-subst ituted a nilines and indoles in the feed light oils (a) isset as 100%.



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oils. The carba zoles, especially those ha ving a largeca rbo n n u mbe r o f a lk y l s u bs t i t u en t s , a re t h e mo s tdifficult compounds t o denitr ogenize.

Acknowledgment

The a uthors a re gra teful for t he f inancial support ofGrants-in-Aid for Scientific Research (No. 12555215)from the Ministry of Education, Culture, S ports, S ciencean d Technology, J apa n, a nd t o the Division of ChemicalEngineering for the Lend-Lease La bora tory S ystem.

Supporting Information Available: Effects oftempera tur e and concentra tion of sulfur compounds onthe desulfurization from tetradecane (data 1), Arrheniusplot for desulfurization of DBTand BTfrom tetradecane(data 2), variation in net electron density on S atom forDBTs (data 3) and BTs (data 4), variat ions in dipolemoment for DBT sulfones (da ta 5)a nd BT sulfones (dat a6), G C/MS spectru m for product of carba zole (da ta 7),a n d 1H a n d 13C NMR spectra for product of indole (data8). Th is ma t e ria l is a v a i la ble f re e o f c h a rg e v ia t h eIn ter net a t h tt p://pubs.a cs.org.

Nomenclature

k ) des ulfuriza t ion (denit rogena t ion) ra t e cons t a n t forsulfur (nitrogen) compounds, h-1

n) carbon number of alkyl substituent on DBT moleculem ) carbon number of alkyl substituent on BT moleculen ) ca r b on n u m b er of a l k y l s u bs t i t u en t on D B T-O2

moleculem) carbon num ber of alkyl substit uent on B T-O2moleculeR ) selectivity of desulfurization yield of sulfur-containing

compounds defined in eq 2 ) reactivity ra tio of sulfur (nitrogen) compounds defined

in eq 3

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Resubmitted for review December 30, 2001Revised man uscript received May 24, 2002

Accepted J une 2, 2002

IE010618X


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