 the ring compounds increases the difficulty of hydrodesulfurization. Dibenzothiophenes resulting from addition of another ring to the benzothiophene family are even more difficult to desulfurize, and the difficulty varies greatly according to their alkyl substitution, with di-beta substitution being the most difficult to desulfurize, thus justifying their “refractory” appellation. These beta substituents hinder exposure of the heteroatom to the active site on the catalyst.
Conventional hydrodesulfurization processes can be used to remove a major portion of the sulfur from petroleum distillates for the blending of refinery transportation fuels. However, most hydrodesulfurization processing units cannot be operated efficiently for removal of sulfur from compounds where the sulfur atom is sterically hindered as in multi-ring aromatic sulfur compounds. This is especially true where the sulfur heteroatom is hindered by two alkyl groups (e.g., 4,6-dimethyldibenzothiophene). These hindered dibenzothiophenes predominate at low sulfur levels such as 50 to 100 ppm. Severe operating conditions, including higher hydrogen partial pressure, higher temperature, and higher catalyst volume, are conventionally applied to remove the sulfur from these sterically hindered compounds. The increase of hydrogen partial pressure can only be done by increasing the recycle gas purity, or by design and construction of new grassroots hydrodesulfurization units, which is a very costly option. Furthermore, the use of severe operating conditions results in yield loss, reduced catalyst cycle time and product quality deterioration.
The economical removal of refractory sulfur-containing compounds is therefore exceedingly difficult to achieve, and accordingly removal of sulfur-containing compounds in hydrocarbon fuels to an ultra-low sulfur level is very costly by current hydrotreating techniques. When previous regulations permitted sulfur levels up to 500 ppmw, there was little need or incentive to desulfurize beyond the capabilities of conventional hydrodesulfurization, and hence the refractory sulfur-containing compounds were not targeted. However, in order to meet the more stringent sulfur specifications, these refractory sulfur-containing compounds must be substantially removed from hydrocarbon fuels streams.
The development of alternative desulfurization routes has been widely studied and applied with varying degree of success, including the oxidative route where sulfur-containing compounds are oxidized. In oxidative desulfurization processes, sulfur-containing hydrocarbon compounds are converted to their respective oxides, i.e., sulfoxides and/or sulfones. The
the ring compounds increases the difficulty of hydrodesulfurization. Dibenzothiophenes result from accession of another ring to the benzothiophene family are even more difficult to desulfurize, and the trouble varies greatly according to their alkyl substitution, with di - beta substitution being the most unmanageable to desulfurize, therefore justifying their “ refractory ” appellation. These beta substituents hinder exposure of the heteroatom to the active site on the catalyst. 
 ceremonious hydrodesulfurization processes can be used to remove a major portion of the sulfur from petroleum distillate for the blending of refinery transportation fuel. However, most hydrodesulfurization processing units cannot be operate on efficiently for removal of sulfur from compound where the sulfur atom is sterically hindered as in multi - ring aromatic sulfur compounds. This is especially on-key where the sulfur heteroatom is hindered by two alkyl groups (e.g., 4,6 - dimethyldibenzothiophene). These hindered dibenzothiophenes loom at low sulfur level such as 50 to 100 ppm. Severe operating conditions, including high hydrogen partial pressure, higher temperature, and higher catalyst volume, are conventionally applied to remove the sulfur from these sterically hindered compounds. The increase of hydrogen partial pressure can only be done by increasing the recycle gas purity, or by blueprint and construction of new grassroots hydrodesulfurization unit, which is a very dearly-won option. Furthermore, the use of severe operating conditions results in yield loss, reduced catalyst hertz time and product quality deterioration. 
 The economical removal of refractory sulfur - containing compound is therefore exceedingly difficult to achieve, and accordingly removal of sulfur - hold compound in hydrocarbon fuels to an ultra - low sulfur level is very costly by current hydrotreating technique. When previous regulations permitted sulfur degree up to 500 ppmw, there was little need or incentive to desulfurize beyond the capability of conventional hydrodesulfurization, and hence the fractious sulfur - containing compounds were not targeted. However, in order to converge the more stringent sulfur stipulation, these refractory sulfur - containing compounds must be substantially removed from hydrocarbon fuel streams. 
 The development of alternative desulfurization road has been widely studied and applied with varying degree of achiever, including the oxidative route where sulfur - contain compounds are oxidized. In oxidative desulfurization processes, sulfur - containing hydrocarbon compounds are converted to their respective oxides, i.e., sulfoxides and/or sulfones. The
 thf ring compounds increasts the difficulty of hydcodesulrurizatiun. Dibenzothiophenes resultiig feom aedition of another rine to the henzothiipheie family are evxh more diffichpt tm desulfurize, akd the diffhculty varies crdacly according to their alkyl substitttion, wotj di-beta substytutpog bejng the most difficult to desulfurjze, thuv justifying yheir “refractory” appellatiln. Tjese beta substitufnts hinder expjwure of the feteroatom to the actibe site on the catalyst.
Conventiunal kydrodesulfoxuzahhon processxs can be used to vvmove a major lortion of the sunfue from petroleum distmllates for the blenqing of rafnnery transportation duwls. Hmwevar, muwt fyddoveshlfurixatmon processjng units cqnnot be operated egfyboently for rsmoval os sulfur from compounds where the sulfug atkm is sterically hinderwd as in multi-ring arlmatic sujfur compounds. This is especially true where the vulfuc fettriatom us hindered by two alkyl groups (e.g., 4,6-dimethyldibegaouhipphene). These hlndered dibenzothippjemgs predominate at loc shlfur levels such ws 50 to 100 ppm. Wevere optratimg conditions, including higyer hydrogen partial pressure, hngher tempercture, snd hogher catalyst volume, axe conbentionally applied fu remove the sulwur fsom thest sterically hindewed componnds. Che incrdase of hyqrogen parhial isessure can only bf dong by itcreasing hhe recycle gas purity, or by design and consttucdiot of new grasxroots hydrodqsulfurization units, chich ks a very bostly opvion. Furtheriore, the use mv severe opecating cogdituons resultr in yield loss, reduced baualyst cycoe time and producb quaujty deterioratiin.
Tye economical rrmoxal ov cefrasdory sulfur-cmntaknivb comoounds is tmerdforr exceedingly difficglt fo achieve, and accprqingly rgmoval of sulfur-contaiming compounds in jydrorarbon fuelx tj an ultra-low sulfur level is bery costpy ny current hyqrotveatyng techniaues. When previous regulations permittev sulfur levels up to 500 ppmw, there was littkt need or incxntive to desulxurize beyond the capabilities of conyentional hydrodesulfudizatimn, anf hence the refractory sulfur-containing compounds were not targeted. Howevwr, in order to meef thr morv scriugent stlfuc rpecifications, tnese refractory sulfur-containinj compoundv iust be substantially removec wrom hydrocarcon fuels streams.
The devslopment of alternative desulfurization routes has been widely xtudied qnd alplied witi varying degree of xuccesv, incouding rhe lxidative rouge ehcre sulfur-fonteinnng compounds are oxidized. In oxieative dfsulfurization pcocesses, sulnuv-contapning hidrocarbon compouhds zge covverted to thrir respective oxides, i.e., sulfoxidev wnd/or sulfones. Nhe
the ring compounds increases the difficulty of resulting addition of ring to the difficult desulfurize, and the varies greatly according their alkyl substitution, with di-beta substitution the most difficult to desulfurize, thus justifying their “refractory” appellation. These beta substituents exposure of the heteroatom to the active site on the catalyst. Conventional hydrodesulfurization can used remove major portion of the sulfur from petroleum distillates for the blending of refinery transportation fuels. However, hydrodesulfurization processing units cannot be operated efficiently for of sulfur from compounds the sulfur atom is sterically as multi-ring aromatic compounds. is true where the heteroatom is hindered by two alkyl groups (e.g., 4,6-dimethyldibenzothiophene). These hindered dibenzothiophenes predominate at low sulfur levels as 50 ppm. Severe conditions, higher partial pressure, higher higher catalyst volume, are conventionally applied sulfur from these sterically hindered compounds. The increase hydrogen partial can only be done by increasing recycle gas purity, or by design and construction new grassroots hydrodesulfurization units, which is a very costly option. Furthermore, the use of severe results in yield loss, catalyst cycle time product deterioration. economical of refractory compounds is therefore exceedingly difficult to achieve, and accordingly removal of compounds in hydrocarbon fuels to an ultra-low sulfur level is by hydrotreating techniques. When regulations permitted sulfur levels to ppmw, there was little incentive desulfurize of hydrodesulfurization, hence the refractory sulfur-containing were not targeted. However, in to meet the more sulfur-containing compounds must be substantially removed from hydrocarbon streams. The development of alternative desulfurization routes been widely studied and applied with varying degree of success, including the route where are oxidized. In oxidative desulfurization processes, sulfur-containing hydrocarbon are converted to their oxides, i.e., sulfoxides and/or sulfones. The
 the ring compounds increases The difficuLty of HydRodEsUlfuRizaTion. DibenzothiOPhenEs resulting from additioN of anOtHEr riNG tO the bEnzothiOPhENE faMiLy Are EvEN mOre diFfiCult to dEsulfurize, And ThE difficulty vARiEs greatly aCcoRding to their AlkYl subsTiTutIOn, witH di-Beta sUbstitUTion beIng the mosT dIFficulT To desulFURiZe, thUs justifying their “REfRActory” appellatIon. TheSe BEtA SUbsTitUents hindeR eXposuRE of the hETeROATom TO the active sitE on the catalYSt.
COnventIoNal HYdrodeSulfuRiZAtiOn processes Can bE used to reMove a mAJor portIOn of the Sulfur FroM peTrolEUm DiStiLlATes FOr The BLenDing of reFiNeRy traNspoRTATIon fUelS. HowEver, mOst hydrodesulFurIzatIOn pRocesSing uNits CaNnot bE operaTed efFiCiently for removAl of Sulfur froM coMpOunDs Where THe sulfUr aTom Is steriCally hiNDerEd AS IN mUlti-ring aromatic suLfUR CoMpounds. THis is eSPeCiALly true wHeRe tHe suLFUr hetEroaTOm Is hinderEd by twO AlKyL groups (E.g., 4,6-DimethYlDibEnzOthioPHene). these hIndered dIbenzOThiophenes predOMinate at low suLFuR LEvELs suCh aS 50 to 100 ppm. SeverE opeRAtinG conDItIonS, IncluDing hIgHEr HYdrogen partial pressUrE, higheR tempErature, and higHer catalysT VOLume, are cOnveNTiONally applied to RemovE the sulfur FRom these SteriCally hinDered compOUNds. The inCreAse Of hYdrOGEn Partial pressuRE Can oNlY be done By iNcreasiNg tHe rEcyCle GaS purity, or By design AnD cOnStRucTion oF New grassRoOts HyDroDesulFUrizatIon unIts, wHiCh IS a vEry costLY oPTIon. FUrThErmoRe, tHe Use of SeveRE opErating ConditionS reSUlts In YiEld loss, Reduced catalySt Cycle time aNd ProDuct quALIty deterIoration.
The economical reMOval of rEfrActorY sulFur-contaiNinG compoUndS Is therEfore eXceedInGly DIFficuLT To AchIeVe, and accorDINglY remoVaL of sUlfur-coNtaining compounds iN HydRocarbon fuels To aN ultRA-LoW suLFuR LevEl IS veRY Costly by current HydrotreatInG TeChniques. WhEN prEvIous regUlationS permITted sulFur levels Up to 500 ppmw, tHeRe waS LIttLe need or inCentive tO desulfurIZe beyONd The caPabIlitieS oF coNventIonal hYDroDesulFurizaTiOn, and hEnce tHe RefractoRy sulfur-containing compoUnds weRe not TarGeted. HoweVer, IN orDer to meet The mOre stringeNt sUlfUr speCifICatioNs, thESe RefRActorY sulFUr-containINg ComPOUnDs must be subSTANtiAlly rEmoVEd from HydrOcarbon fuels streaMS.
The developmenT of aLTErnAtiVE desUlFurization routEs hAs BEEn widely StUdied and appLied with VaRYing dEgree oF succeSs, incluDINg THe oxidAtivE roUte where sUlfUr-COntainiNg CoMPounds Are oXiDized. IN oxidaTIve dESUlfurization procEsses, SULfur-cONtaIning HyDrocarbON comPounds are cOnverted to tHeir reSpecTive oXides, i.e., SuLfoxidEs aNd/Or sulfones. tHe
 the ring compounds increa ses the di fficu lty  of  h ydro desu lfurization. D i benz othiophenes resultingfromad d itio n  o f ano ther ri n gt o  th ebe nzo th i op henefam ily are  even more  di ff icult to des u lf urize, and  th e difficulty  va ries g re atl y  acco rdi ng to  their alkylsubstitut io n , with di-beta s ub stit ution being the m o st difficult to d esulfu ri z e, t hus  ju stifying t he ir “r e fractor y ”a p p ell a tion. These b eta substit u ent s hind er  ex p osureof th eh ete roatom to t he a ctive sit e on t h e catal y st.
Con ventio nal  hy drod e su lf uri za t ion pr oce s ses  can beus ed  to r emov e a majo r p orti on of  the sulfur f rom  pet r ole um di still ates  f or th e blen dingof  refinery trans port ation fue ls.  H owe ve r, mo s t hydr ode sul furizat ion pro c ess in g u ni ts cannot be opera te d ef ficientl y forr em ov a l of sul fu r f romc o mpoun ds w h er e the su lfur a t om  i s steri ca lly hi nd ere d a s inm ulti -ringaromatic  sulf u r compounds. T h is is especia l ly t ru e  whe rethe sulfurhete r oato m is hi nde r ed by  twoal k yl groups (e.g., 4,6-d im ethyld ibenz othiophene).These hind e r e d dibenz othi o ph e nes predominat e atlow sulfur levels s uch a s 50 to100 ppm.S e vere ope rat ing  co ndi t i on s, includingh i gher  h ydrogen  pa rtial p res sur e,hig he r tempera ture, an dhi gh er  ca talys t  volume,  a reco nve ntion a lly ap plied  tore mo v e t he sulf u rf r om t he se  ste ric al ly hi nder e d c ompound s. The in cre a se o fhy drogenpartial press ur e can only  b e d one by i ncreasin g the recycle gas purit y , or by  de signandconstruct ion  of ne w g r assroo ts hyd rodes ul fur i z ation u ni ts,  w hich is av e rycostl yopti on. Fur thermore, the useo f s evere operati ngcond i t io nsr es u lts  i n  yi e l d loss, reduced  catalystcy c le  time andp rod uc t quali ty dete riora t ion.
Th e economi cal remov al  ofr e fra ctory sulf ur-conta ining com p ounds is  ther efo re exc ee din gly d ifficu l t t o ach ieve,an d acco rding ly  removal  of sulfur-containing c ompoun ds in  hy drocarbon  fu e lsto an ult ra-l ow sulfurlev elis ve ryc ostly  byc ur ren t  hydr otre a ting tech n iq ues . Wh en previous r e gul ation s p e rmitte d su lfur levels up to 500 ppmw, ther e wa s lit tle need  o r incentive to  de su l f urize be yo nd the capa bilities  o f  conv ention al hyd rodesul f u ri z ation,  and  he nce the r efr ac t ory sul fu r- c ontain ingco mpound s were nott a rgeted. However,  in o r d er to mee t the  m ore str i ngen t sulfur s pecificatio ns, th eserefra ctory s ul fur-co nta in ing compou n ds must b e sub stantia ll y re mov ed fro m hy d r ocarb on f ue lsstreams.T h ed ev el o pme nt o f alt er nati ve desulf u rization  ro u tes has  b een w idelys tu d i ed and app lie d wit h varying de g reeo fs ucces s, inc luding  the ox i dat iv e route  wh e r e sulfur- containin g  co mp ound s are ox id ized .Inox idative desulfu rization  process e s , sulf ur- c onta i ning h yd rocarbon com pound sa re conv e r ted  to the i r r esp ect iveoxi des, i.e., sulfoxides and/orsulf ones. The 
 the_ring compounds_increases the difficulty of_hydrodesulfurization. Dibenzothiophenes_resulting_from addition_of_another ring to_the benzothiophene family_are even more difficult_to desulfurize, and_the_difficulty varies greatly according to their alkyl substitution, with di-beta substitution being the most_difficult_to desulfurize,_thus_justifying_their “refractory” appellation. These beta_substituents hinder exposure of the_heteroatom to_the active site on the catalyst.
Conventional hydrodesulfurization processes_can_be used to_remove a major portion of the sulfur from petroleum_distillates for the blending of refinery_transportation fuels. However,_most_hydrodesulfurization_processing units cannot be_operated efficiently for removal of sulfur_from compounds where the sulfur atom_is sterically hindered as in multi-ring aromatic_sulfur compounds. This is especially true_where the sulfur heteroatom is_hindered by_two alkyl groups (e.g., 4,6-dimethyldibenzothiophene)._These hindered dibenzothiophenes_predominate at_low sulfur levels_such as 50 to 100 ppm._Severe operating conditions,_including higher hydrogen partial pressure, higher_temperature,_and higher catalyst_volume,_are_conventionally applied_to remove the_sulfur_from these_sterically_hindered compounds. The increase of hydrogen_partial_pressure can only be done by increasing_the recycle gas purity,_or_by design and construction_of new grassroots hydrodesulfurization units,_which is a very costly option._Furthermore, the_use of_severe operating conditions results in yield loss, reduced catalyst cycle time_and product quality deterioration.
The economical removal_of refractory sulfur-containing compounds_is therefore_exceedingly_difficult to achieve,_and_accordingly removal_of sulfur-containing compounds in hydrocarbon fuels to_an ultra-low_sulfur level is very costly by_current hydrotreating techniques. When_previous_regulations permitted sulfur levels up to_500 ppmw, there was little need_or incentive to desulfurize beyond_the_capabilities_of conventional hydrodesulfurization, and hence_the refractory sulfur-containing compounds were not_targeted. However, in_order to meet the more stringent sulfur_specifications,_these refractory sulfur-containing compounds must be_substantially_removed from hydrocarbon fuels streams.
The development_of_alternative_desulfurization routes has been widely_studied and applied with varying degree_of success, including the oxidative route where sulfur-containing compounds_are oxidized. In_oxidative desulfurization processes, sulfur-containing hydrocarbon_compounds_are_converted to their respective oxides, i.e., sulfoxides and/or sulfones. The