Fuel Processing Technology 91 (2010) 1736–1741

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Fuel Processing Technology

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Oxidative desulphurization study of gasoline and keroseneRole of some organic and inorganic oxidants

M. Shakirullah, Waqas Ahmad ⁎, Imtiaz Ahmad, M. IshaqInstitute of Chemical Sciences, 25120, K.P.K, University of Peshawar, Pakistan

⁎ Corresponding author.E-mail address: waqasaswati@yahoo.com (W. Ahma

0378-3820/$ – see front matter © 2010 Elsevier B.V. Adoi:10.1016/j.fuproc.2010.07.014

a b s t r a c t

a r t i c l e i n f o

Article history:Received 30 March 2010Received in revised form 13 July 2010Accepted 21 July 2010

Keywords:DesulphurizationSodium perchlorateKeroseneGasolineOxidation

Desulphurization of gasoline and kerosene was carried out using organic and inorganic oxidants. Among theorganic oxidants used were hydrogen peroxide in combination with acetic acid, formic acid, benzoic acid andbutyric acid, while inorganic oxidants used included potassium permanganate and sodium perchlorate. Theoxidation of each petroleum oil was carried out in two steps; the first step consisted of oxidation of the feedat moderate temperature and atmospheric pressure while in the second step, the oxidized mixture wasextracted with azeotropic mixture of acetonitrile–water. A maximum desulphurization has occurred withNaClO4 and hydrogen peroxide and acetic acid, which are 68% and 61%, respectively in case of gasoline and66% and 63%, respectively in case of kerosene oil. The FTIR study of the whole and variously desulphurizedgasoline and kerosene was also carried out. The results indicate considerable desulphurization by absence ofbands that corresponds to sulphur moieties in NaClO4 and hydrogen peroxide treated samples.

d).

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1. Introduction

The atmospheric emission of sulfur oxides (SOx) due to combustionof petroleum-derived fuels is a threat for environmental degradationand ambient air quality deterioration. Strict regulations on the sulfurcontent of fuels to control these emissions have been recommendedworldwide [1,2] to avoid the degradation of environment. The majorpartners i.e., refineries and the users have to comply with theseregulations for minimum or zero sulfurous emissions. This is onlypossible if the petroleum-based oils are made sweet at the refiningunits before supply to the consumers. Currently, the most commonlyused industrial method for desulphurization is hydrodesulphurization(HDS) process. The process has economic disadvantages due torequirement of severe process conditions such as high hydrogenpressure and high temperature to catalytically decompose the morerefractory organo-sulfur compounds [3]. Moreover, high active HDScatalysts are being requested by the industry [4]. Therefore, alternateprocesses are required to be investigatedwith the objectives that theseshould be low cost and can be operated at moderate conditions.

Among alternate processes to the conventional hydrodesulphur-ization, desulphurization through adsorption [5], biodesulphurization[6,7], ionic liquid extraction [8], electrochemical oxidation [9] andoxidative desulphurization [10] have been reported in the literature.Oxidative desulphurization is gaining more popularity in recent years

because of its simple processing and high efficiency. The processconsists of two steps, oxidation of the sulphur compounds withsuitable oxidants, whereby these compounds are converted intosulphones and sulphoxides. These are preferentially extracted due torelative high polarity with suitable solvent. Various oxidants havebeen reported to be used for oxidation of sulphur compounds, whichinclude hydrogen peroxide in combination with acetic acid [11],hydrogen peroxide with formic acid [12], and molecular oxygen andaldehyde [13], Ozone [14] and tert-butyl hydroperoxide [15].

In the present work, the efficiency of some organic and inorganicoxidants is investigated and compared. The inorganic oxidants usedinclude NaClO4 and KMnO4 while among the organic oxidants usedare hydrogen peroxide in combination with acetic acid, formic acid,benzoic acid and butyric acid.

2. Experimental

2.1. Sample collections

A sample of crude petroleum of Jhal Magsi oil field was collectedfrom Oil and Gas Development Corporation limited (OGDCL), Islama-bad, Pakistan in a metal can. The crude oil was subsequently distilledusing laboratory distillation apparatus for obtaining gasoline (b.pt. 30–180 °C), kerosene (b.pt. 180–250 °C), diesel (b.pt. 250–320 °C) andheavy residue (b.pt. N320 °C) (Fig. 1). The fractions obtained wereanalyzed for their various physicochemical properties, employing thestandard procedures of ASTM and API, as described below. Results areprovided in Table 1.

Fig. 1. % Desulphurization of gasoline with organic and inorganic oxidants.

1737M. Shakirullah et al. / Fuel Processing Technology 91 (2010) 1736–1741

All the chemicals used in the study were of analytical grade(Aldrich). Oxidative desulphurization was carried out in two steps,the first step involved oxidationwith the oxidants and the second stepinvolved extraction with acetonitrile–water azeotropic mixture.

2.1.1. Distillation of the crude petroleumDistillation study was performed adopting the IP-24/84 standard

method using Stanhope-Seta limited model 11860-0 distillationapparatus. A 100 ml sample of each crude oil was taken in distillationflasks fitted with a thermometer (ranging up to 400 °C temperatures).The sample was evaporated by heating through a built-in heatingsystem of the apparatus. The evaporated part of the crude wascondensed in the cooling tube, and collected in themeasuringgraduatedcylinder. When the first drop of condensed crude was recovered, thetemperature (initial boiling point) was noted.

2.1.2. Specific gravitySpecific gravity was determined with the help of the specific

gravity bottle. The bottle was washed thoroughly, dried and weighedcarefully. The bottle was filled with sample and weighed again. Thedifference in the weights of the empty and filled bottle wasdetermined and then divided by the volume of the bottle to find outthe specific gravity. API gravity was calculated using the givenformula.

API gravity =141:5

Sp:gr:60 = 60F−131:5

2.1.3. Kinematic viscosityA setavis kinematic [Stan Hope Seta limited England model

83541-0, serial D383] viscometer was used for determining viscosity.Before the experiment and between the successive determinationsthe viscometer was cleaned several times by rinsing with anappropriate solvent like hexane, carbon tetrachloride and heptanethat was miscible with the sample followed by a volatile solvent.Temperature of bath was maintained at 100 °F. The capillary tube ofthe viscometer was charged with the sample with the help of a

Table 1Physicochemical characterization of gasoline and kerosene fractions.

Characteristics Method used Gasoline Kerosene

Specific gravity IP-160/87 0.7507 0.7902API gravity – 55.67 45.81Kinematic viscosity(mm2/s) 37.77 oC

ASTM-D 455-04 1.17 2.217

Aniline point (oC) ASTM-D 611-04 58 60Flash point (oC) IP-34/87 42.5 46.3Ash contents (wt.%) ASTM-D 482-03 0.055 0.065Conradson carbon residue (wt.%) IP-13/92 0.14 0.18Total sulphur (wt.%) ASTM D 129-83 0.29 1.18

graduated syringe. The flow time of the sample between the twomarks on the tube of the viscometer was recorded. Kinematicviscosity was calculated from the flow time and the constant of theviscometer by the following formula.

Kinematic viscosity = c × t

c Calibration constantt Time between the two marks.

2.1.4. Aniline pointAniline pointwas determined using an aniline point apparatus. The

apparatus was thoroughly cleaned and dried. 10 ml portion of thesample and 10 ml of the aniline were taken in the test tube with thehelp of a pipette. An agitator and a thermometerwerefitted in the tubewith the help of a cork. The test tubewas fitted in the outer socket tubecontaining paraffin oil and placed in the water bath. At roomtemperature, aniline was not miscible with the sample. The temper-ature of the bath was increased at a rate of 1 °C per minutetemperature rise until the sample became completely miscible withaniline. The temperature was recorded as T1. The apparatus was thenallowed to cool until the layers separated, the temperature wasrecorded as T2. The average of both temperatures was recorded asaniline point.

2.1.5. Pour pointPourpointwasdeterminedusingapour point apparatus.The sample

was placed in the glass jar having a flat bottom up to the mark on thetube. The jar was tightly closed with the help of a cork carrying athermometer with a temperature measuring range of −36 to 120 °F.The jarwas placed in the jacket, whichwas in turn immersed in freezingmixture. The jar was brought out from time to time and checked untilthe oil did not show anymovementwhen the jarwas horizontally tiltedfor 5 s. This temperaturewas recorded, and to this temperature 3 °Cwasadded and was expressed as pour point of the sample.

2.1.6. Flash pointFlashpointwasdeterminedusingaCleave landopencupflash tester.

Before performing the apparatus was thoroughly cleaned withpetroleum spirit and dried. The sample cup was filled with the sampleup to themark. A stirrer and a thermometerwere inserted in the samplecup. The sample cupwas placed in the apparatus and the apparatus wasturned on. Heat was supplied at a rate of 6 °C per minute rise in thetemperature.

The test flame was applied after each 1 °C rise in the temperature,until a distinct flash was observed inside the cup. The temperaturewas recorded as a flash point.

2.1.7. Conradson carbon residueA known amount of sample was taken in a silica crucible. This

crucible was placed in the centre of a Skidmore crucible. Both thecrucibles were covered loosely and placed in the iron crucible whichwas placed on the nichrome wire triangle. The sheet iron hood wasplaced on the crucibles. The sample was heated strongly. When thesmoke appeared above the chimney, the burner was tilted slightly forvapours to catch fire. When all the vapours ceased and smokedisappeared, the burner was removed and allowed to cool. TheSkidmore crucible was cooled in a desiccator and weighed. Carbonresidue was calculated as percentage of that of the original sample.

Carbon residue =wW

× 100

w weight of the carbon residue in gramsW weight of the sample.

Fig. 2. % Desulphurization of kerosene with organic and inorganic oxidants.

1738 M. Shakirullah et al. / Fuel Processing Technology 91 (2010) 1736–1741

2.1.8. Ash contentsAsh content of crude oil samplewasdetermined adopting the IP 4/81

standard method. A porcelain evaporating dish of 120 ml capacity waswashed, cleaned and dried at 800 °C for 10 min. The cruciblewas cooledto room temperature in a desiccator and weighed. China dish washeated and cooled several times until constant weight was attained.Crude oil samplewas taken in thedish andwas reweighed. The dishwasheated and the sample was ignited with a flame. Temperature wasmaintained in such a way that sample burned with a uniform andmoderate rate leaving behind only ash and carbon residues.

The heavy residue was heated in the muffle furnace at 800 °C untilall the carbonaceous material disappeared. The dish was cooled in adesiccator to room temperature and weighed. The dish was reheatedup to 800 °C for 30 min, cooled and weighed. Heating and weighingwere repeated until constant weight was attained. Ash was calculatedas a percentage of the original sample, as follows.

Ash contents% =wW

× 100

w weight of the ash in gramsW weight of the sample.

2.2. Oxidation with acetic acid and hydrogen per oxide

A mixture of 21 g (98%) of acetic acid and 11 g (35%) of hydrogenper oxide was prepared. 2 ml of this mixture was taken and added to40 ml of the sample and stirred for 2 h at 60 °C [16]. The mixture wasthen transferred to a separating funnel and the oil phase wasrecovered. The half portion of it was reserved for the analysis of thesulfones and sulfoxides, and the rest was extracted with distilledwater twice and then with 80% acetonitrile solution. The extractedsample was preserved for total sulphur analysis.

2.3. Oxidation with benzoic acid and hydrogen per oxide

Ethanolic benzoic acid solution (20%) was prepared by dissolving20 g of solid benzoic acid in 80 g of ethanol. 10 ml of this solution wasmixedwith 1.2 g of hydrogen per oxide (35%). Themixture was addedto 40 ml of the sample and was stirred for 2 h at 60 °C. The oil layerwas separated in the separating funnel, half of it was preserved andthe rest was extracted twice with distilled water and once with 80%acetonitrile solution.

2.4. Oxidation with formic acid and hydrogen per oxide

A mixture of 21 g of formic acid (99%) and 11 g of hydrogenperoxide (35%) was prepared. 2 ml of this solution was mixed with40 ml of sample. The mixture was stirred at 60 °C for 2 h. The oil layerwas then separated and extractedwith distilledwater and acetonitrilein the same manner as previously described.

2.5. Oxidation with KMnO4 in acidic medium

Acetic acid (2 ml) was added to 40 ml sample was mixed. Themixture was warmed for a few minutes and then 1 ml of 3% aqueousKMnO4 solutionwas added to themixture. The solutionwas stirred for40 min at 50 °C. The mixture was then shifted to a separating funneland the oil layer was separated, the half portion of it was preserved forthe analysis of oxidized products and the remaining half portion wasextracted twice with water and once with 80% acetonitrile solution.

2.6. Oxidation with NaClO4

NaClO4 solution was prepared by dissolving 2 g of NaClO4 in 30 mlof 1:1 mixture of distilled water and ethanol. 4 ml of this solution was

added to 40 ml of sample and stirred for 2 h at 60 °C. Furthermoreseparation and extraction were carried out as aforementioned.

2.7. Oxidation with butanoic acid and hydrogen per oxide

A portion of 21 g of butanoic acid (96%) was mixed with 11 g ofhydrogen peroxide (35%). 2 ml of this mixture was added to 40 ml ofsample and stirred at 60 °C for 2 h. The oil layer was then separatedand extracted with distilled water and 80% acetonitrile.

2.8. Products analysis

Total sulphur in the hydrocarbons fuels was analyzed by acomputer software controlled Leco SC-144DR carbon sulphur analyz-er and also employing the standard method of ASTM designation D129-83 and IP designation 61/84 (Bombwashingmethod). The natureof the sulphur compounds in the fractions was also characterized byFTIR spectrophotometer model no. FTIR-8201 ICP (Shimadzu, Japan).

3. Results and discussion

3.1. Physicochemical characterizations of the fractions

After distillation of crude oil, two distillate fractions of interest i.e.gasoline and kerosene were obtained (Fig. 2). Various physicochem-ical properties like distillation behavior, specific gravity, kinematicviscosity, relative density, API gravity, carbon content, ash content,flash point, aniline point and pour point were determined. Thephysicochemical properties of the various fractions are summarized inTable 1.

In case of distillate fractions i.e. gasoline and kerosene, the specificgravity increaseswith increase in boiling points, in the case of gasolinevalue of specific gravity is 0.7507 and in the case of kerosene it is0.7902 g/cm2. On the other hand, their API gravity decreases, forgasoline and kerosene its value is 55.67 and 45.81, respectively.Kinematic viscosity is a function of the chemical nature of anyfractions. In case of gasoline and kerosene, the value of kinematicviscosity is found to be 1.17 and 2.27 mm2/s, respectively. The reasonis that with the increase in boiling point, the complexity of thecomponents of that fraction increases. Aniline point and flash pointshowed an increase in the same manner. For both distillates fractions,the value of aniline point increases from 58 °C in gasoline) to 60 °C inkerosene), similarly the value of flash point increases from 0.055 ingasoline to 46.3 in kerosene. These properties depend upon the natureof hydrocarbons prevailing in the respective fractions.

Ash contents and Conradson carbon residue are also related to thenature of the hydrocarbons, their values increase with an increase inboiling point of the fractions. The values of ash contents andConradson carbon residue, in the case of gasoline is given as 0.055and 0.14 wt.% respectively, whereas in the case of kerosene it is 0.065and 0.18 wt.% Sulphur content also increases with the increase of

Table 2% Desulphurization of gasoline through oxidative desulphurization, using variousoxidants.

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boiling range of the fractions. As sulphur compounds exist in differentforms at different boiling ranges. In the case of gasoline the value oftotal sulphur content is 0.29, and in the case of kerosene it is 1.18 wt.%.

Oxidants used Sulphur contents (wt.%)a % Desulphurization

Acetic acid and H2O2 0.115±0.004 61.06Benzoic acid and H2O2 0.173±0.003 41.63Butanoic acid and H2O2 0.166±0.005 44.01Formic acid and H2O2 0.125±0.003 57.66KMnO4 0.158±0.006 46.74NaClO4 0.094±0.004 68.16

a Sulphur contents of original gasoline 0.29 (wt.%).

Fig. 3. FTIR spectra of the original and treated gasoline through oxidation followed byliquid–liquid extraction. (a) original (b) oxidized with acetic acid and (c) oxidized withsodium perchlorate.

3.2. Oxidative desulphurization of gasoline

The desulphurization data in Table 2 show that among the organicoxidants used the highest desulphurization of 61% has beeneffectuated by hydrogen peroxide in combination with acetic acid,followed by hydrogen peroxide with benzoic acid, butanoic acid andwith formic acid which attained desulphurization of 41%, 44% and57%, respectively. In case of inorganic oxidants used, sodium perchlorate was found to be the most efficient oxidant, causing 68%desulphurization. While in case of potassium permanganate in acidicmedium, the poor desulphurization yield is obtained i.e. 46%.

It is clear from Table 2, that in the case of gasoline, the highestdesulphurization yield is attained with acetic acid and formic acid incombination with hydrogen peroxide while using organic oxidants.The previous studies indicate that these oxidants bear high selectivitytowards the oxidation of the sulphur moieties in heteroaromaticshydrocarbons [17–21], besides the sulphur compounds mostlyprevailing in gasoline include lowmolecular weight sulphides thioles,sulphides and simple thiophenes, which are relatively easily oxidizedby these oxidants than complex polynuclear thiophenes, therebyshowing high desulphurization yield. Being a weak acid, acetic acideasily donates a proton which is required by hydrogen peroxideduring the course of reaction. The mechanism of oxidation of sulphurbearing molecules by hydrogen peroxide is reported elsewhere [16].

Mechanism of oxidation with hydrogen per oxide in the presenceof a proton.

The same mechanism is also followed by oxidation reaction offormic acid. Formic acid is a stronger acid, and also readily donates aproton, therefore exhibiting high oxidation potential. For benzoic acidand butanoic acid, the desulphurization yield is considerably poor.This may be because of higher acidity of these oxidants. In case ofbenzoic acid due to the formation of a resonance stabilized benzoateion while donating proton, benzoic acid shows vigorous and nonselective oxidation which oxidizes other functional groups instead ofsulphur moieties i.e. olefins and aliphatic hydrocarbons. On the otherhand, butanoic acid is a weak acid, as the (butanoate ion) anionformed is destabilized by the electron withdrawing effect of alkyl

(butyl) group. Therefore, the anion formed back reacts with proton toform acid, without being utilized for oxidation.

In case of inorganic oxidants used, sodium perchlorate has shownhigh desulphurization efficiency. Sodium periodate has been reportedto be used for the oxidation of thiophene and its derivativesconverting them to sulphones and sulphoxides [22,23], which showits selectivity towards sulphur bearing functional groups. Whilesodium perchlorate is a stronger oxidant than sodium periodate dueto high E.N value of chlorine than iodine, it must be a more selectiveand efficient oxidant for sulphur moieties. In case of potassiumpermanganate, the oxidation yield is very poor. The reason may bedue to its non selectivity towards sulphur bearing molecules, becauseof its vigorous oxidation. As potassium permanganate is extensivelyused for the epoxidation of olefins and the oxidation of alkyl groups torespective alcohols and carbonyl compounds, therefore, it might beconcluded that oxidation with KMnO4 has resulted in the oxidation ofolefins and alkyl groups rather than oxidation of sulphur bearingmolecules to respective sulphones and sulphoxides.

From the above discussion, it is clear that among all of the oxidantsemployed for desulphurization of gasoline, NaClO4 has broughtmaximum sulphur depletion. It suggests highest selectivity andspecificity of NaClO4 towards the oxidation of sulphur functional groupspresent in sulphur bearing molecules prevailing in the gasoline stream.

The FTIR spectrum of the original gasoline in Fig. 3(a) shows strongand broad absorption bands at 2930 cm−1 and 2860 cm−1 whichindicate methyl (CH3) C–H bond and methylene (=CH2) C–H bonds,respectively. A weak and broad absorption band at 2340 cm−1

indicates S–H bond of mercaptans. High intensity band positionedaround 1725 cm−1 indicates carbonyl C=O of ketones. A group ofweak absorption bands in the range of 1600 to 1550 cm−1 pointsaromatic C=C bonds. Strong intense band in the range of 1456 cm−1

characterizes methylene (CH2) C–C bonds. A sharp and highly intenseband at the range of 1376 cm−1 corresponds to the S=O bond ofsulphones [22,23].

Table 3% Desulphurization of kerosene through oxidative desulphurization, using variousoxidants.

Oxidants used Sulphur contents (wt.%)a % Desulphurization

Acetic acid and H2O2 0.400±0.005 66.21Benzoic acid and H2O2 0.930±0.004 21.49Butanoic acid and H2O2 0.858±0.006 27.54Formic acid and H2O2 0.549±0.003 53.63KMnO4 0.734±0.002 38.06NaClO4 0.428±0.004 63.86

a Sulphur contents of original kerosene 1.18 (wt.%).

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In case of the spectra of gasoline oxidized with acetic acid Fig. 3(b)and sodium perchlorate Fig. 3(c) followed by extraction withacetonitrile, the absorption bands showing aliphatic (CH3 and CH2)C–H, aromatic C=C and methylene (CH2) C–C are present. Whereasthe absorption bands indicating mercaptans S–H, carbonyl C=O andsulphones S=O are missing, which is an evidence that theseconfigurations are eliminated during oxidation followed by theextraction process. Detailed peak positions are given in Table 4(a).

3.3. Oxidative desulphurization of the kerosene

The oxidative desulphurization of kerosene follows the samepattern like that of gasoline. The highest desulphurization wasattained with acetic acid/hydrogen peroxide, formic acid/hydrogenperoxide and sodium perchlorate, with the difference only indesulphurization yields. The marginal increase in the case of kerosenemight be due to the different chemical natures of sulphur compoundsin both of these fractions. From thedata in Table 3, it is clear that in caseof kerosene oil, while using organic oxidants, maximum desulphur-ization is achieved with acetic acid and formic acid in combinationwith hydrogen peroxide, resulting in 66% and 53% desulphurization,respectively, followed by benzoic acid and butanoic acid in combina-tion with hydrogen peroxide have resulted in very poor desulphuriza-tion of 21% and 27%, respectively. Amongst inorganic oxidants, highsulphur depletion is effectuated by NaClO4, that is 63%, whereasdesulphurization achieved with potassium permanganate is also notsatisfactory, causing only 38% desulphurization.

As mentioned earlier, the highest desulphurization yield attainedwith acetic acid and formic acid in combination with of hydrogenperoxide is due to their high selectivity towards the oxidation of thesulphur moieties of the heteroaromatics hydrocarbons. Both of theseoxidants readily donate proton required by hydrogen per oxide to adda hydroxyl ion to the sulphur atom in the target molecule. However,acetic acid is more efficient in donating proton, being a weak acid than

Fig. 4. FTIR spectra of the original and treated kerosene through oxidation followed byliquid–liquid extraction. (a) original (b) oxidized with acetic acid and (c) oxidized withsodium perchlorate.

formic acid which is a strong acid and its tendency to donate a protonis less, and, therefore, the desulphurization yield of formic acid islower than acetic acid. The poor desulphurization yield attained withbenzoic acid is because of the formation of a resonance stabilizedbenzoate ion, which causes uncontrolled or vigorous and nonselective oxidation, oxidizing other functional groups instead ofsulphur moieties i.e. olefins and aliphatic hydrocarbons side chains ofthe aromatic sulphur compounds. On other hand butanoic acid is aweak acid, and its tendency to donate a proton is lower because of the(butanoate ion) anion formed which is destabilized by the electronwithdrawing effect of alkyl (butyl) group, rendering the retardedoxidation capability of butanoic acid.

Sodium periodate is reported elsewhere [24,25], to be used for thetransformation of thiophene and its derivatives to respectivesulphones and sulphoxides, which shows its selectivity towards theoxidation of specific sulphur bearing molecules. The highest desul-phurization yield resulted with sodium perchlorate may be explainedon the same ground due to the same structure. Sodium perchloratemay follow the same course of reaction as that of sodium periodate.The proposed mechanism followed by sodium perchlorate during theoxidation of sulphur compounds, is given as follow.

Proposed mechanism for the oxidation of the sulphur functionalgroup by NaClO4.

On the other hand, poor desulphurization yield was obtained withpotassium permanganate. This may be attributed to its non selectivitytowards sulphur bearing molecules. Potassium permanganate is avigorous oxidant, which retards its selectivity. It is extensively usedfor the epoxidation of olefins and the oxidation of alkyl groups torespective alcohols and carbonyl compounds. As the concentration ofolefins is higher in case of kerosene oil, therefore, it might beconcluded that oxidation with KMnO4 has resulted in the oxidation ofolefins and alkyl groups rather than the oxidation of sulphur bearingmolecules to respective sulphones and sulphoxides.

The desulphurization yield attained in case of kerosene is relativelysmaller than in the case of gasoline. The reason may be due to thecomplex structures of sulphur compounds prevailing in kerosene. Inkerosene, the proportion of heteroaromatic sulphur (thiophenes) ismore than sulphides and thioles,wherein the sulphur functional groupis stearically hindered. However, in both of the fractions, it isnoteworthy that the desulphurization yield attained with organicoxidants is smaller than that attained in organic oxidants. Hence, it canbe concluded that, inorganic oxidant (sodium perchlorate) is more

Table 4Position and intensity of bands correspond to sulfur in the FTIR spectra of originalgasoline and that of oxidized gasoline (a) and original kerosene and that of oxidizedkerosene (b) with acetic acid and NaClO4.

Sample Position Intensity Assigned sulphur(cm−1) (%T) configuration

(a)Gasoline (original) 2930 Strong CH3 (aliphatic)

2860 Strong CH2 (aliphatic)2340 Medium S–H (marcaptnes)1725 Strong C=O (ketone)1500–1600 Medium C=C (aromatics)1456 Weak C–C (methylene)1376 Strong S=O (sulphones)

Gasoline oxidized withacetic acid in combinationwith H2O2

2925 Strong CH3 (aliphatic)2855 Strong CH2 (aliphatic)1500–1600 Strong C=C (aromatics)1453 Weak C–C (methylene)

Gasoline oxidized withsodium per chlorate

2918 Strong CH3 (aliphatic)2855 Strong CH2 (aliphatic)1500–1600 Strong C=C (aromatics)1457 Weak C–C (methylene)

(b)Kerosene (original) 3417 Broad NH or OH (sulphonamide)

2922 Strong CH3 (aliphatic)2866 Strong CH2 (aliphatic)2352 Medium S–H (marcaptnes)1730 Strong C=O (ketone)1500–1600 Medium C=C (aromatics)1476 Weak C–C (methylene)

Kerosene oxidized withacetic acid in combinationwith H2O2

2935 Strong CH3 (aliphatic)2860 Strong CH2 (aliphatic)2357 Medium S–H (marcaptnes)1500–1600 Medium C=C (aromatics)1454 Weak C–C (methylene)

Kerosene oxidized withsodium per chlorate

2915 Strong CH3 (aliphatic)2830 Strong CH2 (aliphatic)2352 Medium S–H (marcaptnes)1500–1600 Medium C=C (Aromatics)1453 Weak C–C (methylene)

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efficient in oxidation of stearically hindered sulphur atoms in the caseof heteroaromatic molecules (substituted thiophenes).

The FTIR spectrum of the original kerosene oil Fig. 4(a) shows awide band at 3417 cm−1 evident of the presence of NH or OH whichmay correspond to the bond associated with sulphonamides [22],followed by strong absorption bands in the range of 2922 cm−1 and2866 cm−1 , indicating methyl and methylene C–H bonds. Aprominent band positioned at 2352 cm−1 shows S–H bonds ofmercaptans. A low intensity medium absorption band at 1730 cm−1

indicates carbonyl C=O bond, whereas broad absorption bandranging from 1500 to 1600 cm−1 indicates aromatic C=C [23]. Astrong absorption band positioned at 1476 cm−1 represents methy-lene C–C.

As in the case of gasoline, the behavior of kerosene towardsoxidation is the same. The samples oxidized with acetic acid Fig. 3(b)and sodium perchlorate Fig. 4(c) and then extracted with acetonitrileshow the major absorption bands corresponding to methyl andmethylene C–H, aromatic C=C, and metylene C–H. In comparisonwith original kerosene, the absorption bands showing sulphonamideNH or OH, mercaptans S–H, carbonyl C=O are missing. Hence, it isconcluded from the above discussion that sulphur compounds areoxidized with acetic acid and NaClO4 and then extracted successfullywith acetonitrile. Detailed peak positions are given in Table 4(b).

4. Conclusion

Oxidative desulphurization can be used as a complementaryprocess to HDS. Among the organic oxidants used acetic acid incombination with hydrogen peroxide followed by extraction throughacetonitrile–water blend caused significant desulfurization. Amongthe inorganic oxidants sodium perchlorate proved effective.

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