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`US 20030168383Al
`
`(19) United States
`(12) Patent Application Publication
`Hoekstra et al.
`
`(10) Pub. No.: US 2003/0168383 Al
`Sep. 11, 2003
`(43) Pub. Date:
`
`(54) DISTILLATE DESULFURIZATION PROCESS
`
`Publication Classification
`
`(76)
`
`Inventors: George R. Hoekstra, Wheaton, IL
`(US); Larry W. Kruse, Donnellson, IA
`(US)
`
`Int. CI.7 ..................................................... Cl0G 45/02
`(51)
`(52) U.S. Cl. ............................................ 208/213; 208/210
`
`Correspondence Address:
`CAROL WILSON
`BP AMERICA INC.
`MAIL CODE 5 EAST
`4101 WINFIELD ROAD
`WARRENVILLE, IL 60555 (US)
`
`(21)
`
`Appl. No.:
`
`10/093,567
`
`(22)
`
`Filed:
`
`Mar. 6, 2002
`
`(57)
`
`ABSTRACT
`
`A process is disclosed for the ultradeep desulfurization of a
`sulfur-containing distillate feedstock.
`
`The hydrodesulfurization process conditions employed in
`the process of the invention include a hydrogen circulation
`rate of at least five times the molar consumption rate of
`hydrogen and a feedstock vaporization of at least 30 mole
`percent.
`
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`Patent Application Publication Sep. 11, 2003
`
`US 2003/0168383 Al
`
`FIG.1
`
`Desulfurization response to gas rate at 812psi, 650F, 2 LHSV
`
`---·-
`
`100.0
`
`90.0
`
`80.0 -
`
`\
`
`E 70.0
`C.
`c..
`60.0
`.:
`
`::i -:i 50.0
`th -(.)
`"C e c.. 30.0
`
`::i 40.0
`
`20.0
`
`10.0
`
`0.0
`
`0
`
`1000
`
`2000
`
`3CXX)
`4000
`Gas/oil rate SCFB
`
`5000
`
`~
`
`6000
`
`7000
`
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`US 2003/0168383 Al
`
`Sep. 11,2003
`
`1
`
`DISTILLATE DESULFURIZATION PROCESS
`
`BACKGROUND OF THE INVENTION
`
`[0001] The desire to provide a cleaner environment has
`resulted in substantial regulation of fuels and in particular
`the sulfur contents of fuels. Sulfur in diesel fuel can result
`in the catalytic oxidation of SO2 to SO3 in diesel engine
`exhaust gases where a catalytic emission control device is
`used. This SO3 combines with water to form sulfuric acid
`emitted as a mist particulate. Further, sulfur containing
`exhaust gases can result in exhaust gas emission catalyst
`poisoning with respect to NOx conversion activity.
`
`[0002] The US Environmental Protection Agency is tar(cid:173)
`geting a level of sulfur less than 15 ppm in 2006 for on-road
`diesel. The European Union specification will be less than
`50 ppm in 2005. Further the World Wide Fuels Charter as
`supported by all global automobile manufacturers proposes
`even more stringent sulfur requirements of 5 to 10 ppm for
`the Category IV fuels for "advanced' countries. In order to
`comply with these regulations for ultra-low sulfur content
`fuels, refiners will have to make fuels having even lower
`sulfur levels at the refinery gate. Thus refiners are faced with
`the challenge of reducing the sulfur levels in fuels and in
`particular diesel fuel within the time frames prescribed by the
`regulatory authorities.
`
`[0003] A hydrodesulfurization process is often employed
`to reduce the concentration of organosulfur compounds in
`hydrocarbons. The hydrodesulfurization is carried out by
`contacting a hydrocarbon feedstock with hydrogen at
`elevated temperatures and pressures in the presence of a
`hydrodesulfurization catalyst in order to convert the orga(cid:173)
`nosulfur compounds to hydrogen sulfide.
`
`[0004]
`In conventional hydrodesulfurization processes
`those skilled in the art typically will operate the reaction
`zone with a hydrogen circulation rate of approximately three
`times the chemical hydrogen consumption rate on a molar
`basis. This circulation rate is maintained in order to maintain
`the hydrogen partial pressure and avoid excessive increase
`in the concentration of hydrogen sulfide. Generally, the
`heavier the feedstock the greater the chemical hydrogen
`consumption rate and hence the desired hydrogen circulation
`rate. Thus for distillate feedstock desulfurization, the circu(cid:173)
`lation rate would generally be in the range of about 600 to
`about 2000 standard cubic feet per barrel of feedstock
`("SCFB"). Above this range the hydrogen partial pressure
`and hydrogen sulfide partial pressure tend to level off so
`there is no incentive for increasing the circulation rate
`beyond about three four times the hydrogen consumption
`rate. In fact, there are considerable economic disincentives
`to increasing the hydrogen circulation rate because of the
`increased utility costs and capital costs associated with the
`compression and circulation of the hydrogen and the
`increased pressure drop associated with a higher circulation
`rate.
`
`[0005]
`In order to reach these desirable low levels of
`sulfur, the prior art discloses many hydrodesulfurization
`processes including many multi-step processes. Typical rea(cid:173)
`sons for using multi-step processes are that such processes
`permit the separation of liquid and vapor between stages, the
`use of a sulfur sensitive catalyst in a second stage, the
`improvement of color of diesel fuel with special second
`stage reaction conditions, the use of alternative reactor
`
`designs in the different stages, the hydrogenation of aromat(cid:173)
`ics, the processing of heavier feedstocks, and the preparation
`of various specialty products other than low-sulfur fuel.
`
`[0006]
`In this connection, U.S. Pat. No. 6,171,477 Bl
`(Morel et al.) discloses a multi-step process that includes a
`desulfurization step with a heavy hydrocarbon feedstock
`having an initial boiling point of at least 360° C. and a final
`boiling point of at least 500° C. wherein the hydrogen
`circulation step is about 100 to about 5000 normal cubic
`meters (Nm3
`) per cubic meter (m3
`) of liquid charge (594 to
`29,700 SCFB) with a most preferable charge of about 300 to
`about 500 Nm 3/m3 (1782 to 2970 SCFB). This feedstock is
`a much heavier feedstock than the distillates used for diesel
`production, and consumes much more hydrogen and there(cid:173)
`fore requires much higher hydrogen circulation to supply
`hydrogen for consumption, to maintain hydrogen partial
`pressure, and to control buildup of hydrogen sulfide.
`
`[0007] U.S. Pat. No. 5,403,470 (Kokayeff et al.) discloses
`a two-stage process for improving the color of a diesel
`feedstock wherein the first hydrotreating stage is carried out
`to decrease the organosulfur content to less than 800 ppmw
`with a gas recycle rate of 400 to about 4000 standard cubic
`feet per barrel of feedstock. This process is a two-stage
`process in which the purpose of the second stage is to
`improve product color.
`
`[0008] U.S. Pat. No. 5,316,658 (Ushio et al.) discloses a
`two-stage process for the production of low sulfur diesel gas
`oil having a Saybolt color number of -10 or higher. Spe(cid:173)
`cifically the hydrodesulfurization is carried out in the first
`stage at a hydrogen to oil ratio of 200 to about 5000 scf/bbl
`and more preferably 500 to 2000 scf/bbl. The purpose of the
`second stage is to improve the product color.
`
`[0009] U.S. Pat. No. 5,068,025 (Bhan) discloses a two(cid:173)
`stage process for the concomitant hydrogenation of aromat(cid:173)
`ics and sulfur bearing hydrocarbons in a diesel boiling range
`hydrocarbon feedstock. The subject process discloses that
`the hydrogen feed rate will typically be 100 to about 5000
`scf/bbl.
`
`[0010] U.S. Pat. No. 4,431,526 (Simpson et al.) discloses
`a two-stage process for hydroprocessing heavier feedstocks
`such as "hydrocarbon containing oils" including all liquid
`and liquid/vapor hydrocarbon mixtures such as crude petro(cid:173)
`leum oils and synthetic crudes, e.g. top crudes, vacuum and
`atmospheric residual fractions, heavy vacuum distillates,
`shale oils, oils from bituminous sands, coal compositions
`which contain sulfur and contaminant metal. Due to the
`heavy nature of these feedstocks, the hydrogen circulation
`rate is disclosed to be in the range of about 1000 to about
`15,000 scf/bbl.
`
`[0011] U.S. Pat. No. 5,114,562 (Haun et al.) discloses
`another two-stage process with inter-stage stripping wherein
`a middle distillate petroleum stream is hydrotreated to
`produce a low sulfur and low aromatic product. The second
`stage employs a sulfur sensitive noble metal catalyst to
`saturate the aromatics which saturation consumes hydrogen.
`The circulation rate in the first reaction zone is disclosed as
`ranging from 400 for light naphthas to 20,000 scf/bbl for
`cycle oils and preferably between 1,500 and 5,000 scf/bbl.
`The subject patent indicates that the average molecular
`weight of the feedstream is reduced by the virtue of the
`production of gasoline and LPG.
`
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`US 2003/0168383 Al
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`Sep. 11,2003
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`2
`
`[0012] U.S. Pat. No. 3,147,210 (Hass et al.) discloses yet
`another two-stage hydrogenation process with inter-stage
`stripping, using a sulfur-sensitive noble metal catalyst in the
`second stage with a goal of high aromatics saturation. The
`hydrogen circulation rate is disclosed as ranging from 200 to
`12,000 scf/bbl, preferably 1,000 to 8,000 scf/bbl for the
`hydrofining stage. The example discloses a circulate rate of
`700 s.c.f./b for the hydrofining stage.
`[0013] U.S. Pat. No. 6,251,262 Bl (Hatanaka et al.) dis(cid:173)
`closes a three-stage hydrodesufurization process for diesel
`gas oil wherein the hydrogen to oil ratio is about 1000 to
`about 5000 scf/bbl wherein a product having a sulfur content
`of 0.005 wt. % is recovered.
`[0014] U.S. Pat. No. 5,110,444 (Haun et al.) discloses
`another three-stage process. This process uses three stages
`with counter current gas/liquid flow, inter-stage stripping,
`and noble metal catalysts in 2nd and 3rd stages. The patent
`refers to gas rates as high as 20,000 SCFB, with preferred
`range of 1,500 to 5,000 SCFB. The use of higher gas rates
`in the 2nd and/or 3rd stages, accommodates the H2 con(cid:173)
`sumption engendered by aromatics saturation catalyzed by
`the noble metal catalysts.
`[0015] U.S. Pat. No. 6,251,263 Bl (Hatunaka et al.) dis(cid:173)
`closes a three-reaction zone hydrogenation process that uses
`specific catalysts in specific ratios using hydrogen circula(cid:173)
`tion rates of 1000 to 5000 scfb/bbl. While the Patentees
`maintain they can reach deep desulfurization level of 0.0001
`wt % (1 ppmw), the examples only disclose higher levels
`with Example 3 showing an effluent having 30 ppmw where
`the feedstock was a Middle East straight run gas oil.
`[0016] U.K. Patent 1,385,288 discloses a multi-stage pro(cid:173)
`cess for the simultaneous production of a jet fuel and motor
`fuel which comprises passing a hydrocarbon oil into a
`hydrotreating zone and passing the effluent from
`the
`hydrotreating zone to a multi-stage hydrocracking zone. The
`patent discloses a hydrogen circulation rate of 1,000 to
`50,000 SCFB. This is a hydrocracking process which cracks
`heavy feeds into lighter products and in so doing consumes
`much more hydrogen than a hydrodesulfurization process.
`[0017] There is a need to develop a hydrodesulfurization
`process that achieves the deep desulfurization of distillates
`to levels wherein the product will have sulfur contents no
`greater than 50 ppmw, preferably less than 15 ppmw and
`most preferably less than 10 ppmw. Further inasmuch as
`refiners are up against aggressive regulatory timetables,
`there is a need to achieve this deep desulfurization effica(cid:173)
`ciously and quickly without the use of exotic new catalysts.
`This desired deep desulfurization will require a process that
`can convert the highly difficult- to-desulfurize compounds
`present in the high boiling fraction of a distillate feedstock.
`[0018]
`It has now been discovered that such deep desulfu(cid:173)
`rization of distillate feedstocks can be effected without the
`use of exotic catalysts by increasing the hydrogen circula(cid:173)
`tion rate to a distillate hydrodesulfurization zone well
`beyond the levels disclosed and recommended in the prior
`art while concomitantly increasing the volatilization of the
`feedstock to a relatively high level.
`
`SUMMARY OF THE INVENTION
`
`[0019] The process of the present invention achieves deep
`desulfurization of distillate hydrocarbon feedstock to a level
`
`below 50 ppmw sulfur in a conventional hydrodesulfuriza(cid:173)
`tion process reaction zone in the presence of a conventional
`hydrodesulfurization catalyst wherein the process is carried
`out at hydrogen circulation rate of at least 5 times the molar
`chemical hydrogen consumption rate and wherein the dis(cid:173)
`tillate feedstock is vaporized in the reaction zone to at least
`about 30 mole percent of the total feedstock. In another
`embodiment, the process of the present invention involves
`carrying out the hydrodesulfurization process in a multi(cid:173)
`stage process wherein at least one stage is carried out at
`conventional operating conditions including a conventional
`hydrogen circulation rate and a conventional feedstock
`vaporization wherein the more reactive sulfur compounds
`are removed and wherein at least one additional downstream
`stage is carried out at process conditions that include a
`hydrogen circulation rate of at least 5 times the chemical
`hydrogen consumption rate and wherein the distillate feed(cid:173)
`stock vaporization is at least about 30 mole percent of the
`total feedstock.
`
`BRIEF DESCRIPTION OF THE DRAWING
`[0020] FIG. 1 is a graph showing the relationship between
`desulfurization as achieved by the hydrodesulfurization pro(cid:173)
`cess of the present invention versus the desulfurization
`achieved by a process employing the prior art hydrogen
`circulation rate and vaporization rate.
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENT(S)
`
`[0021] The hydrocarbon feedstock suitable for use with
`the present invention generally comprises a substantial por(cid:173)
`tion of a distillate hydrocarbon feedstock, wherein a "sub(cid:173)
`stantial portion" is defined as, for purposes of the present
`invention, at least 50% of the total feedstock by volume. The
`distillate hydrocarbon feedstock processed in the present
`invention consists essentially of any one, several, or all
`refinery streams boiling in a range from about 150° F. to
`about 700° F., preferably 300° F. to about 700° F., and more
`preferably between about 350° F. and about 700° F. at
`atmospheric pressure. For the purpose of the present inven(cid:173)
`tion, the term "consisting essentially of" is defined as at least
`95% of the feedstock by volume. The lighter hydrocarbon
`components in the distillate product are generally more
`profitably recovered to gasoline and the presence of these
`lower boiling materials in distillate fuels is often constrained
`by distillate fuel flash point specifications. Heavier hydro(cid:173)
`carbon components boiling above 700° F. are generally more
`profitably processed as fluidized catalytic cracking process
`("FCC") feed and converted to gasoline. The presence of
`heavy hydrocarbon components in distillate fuels is further
`constrained by distillate fuel end point specifications.
`[0022] The distillate hydrocarbon feedstock can comprise
`high and low sulfur virgin distillates derived from high- and
`low-sulfur crudes, coker distillates, catalytic cracker light
`and heavy catalytic cycle oils, and distillate boiling range
`products from hydrocracker and resid hydrotreater facilities.
`Generally, coker distillate and the light and heavy catalytic
`cycle oils are the most highly aromatic feedstock compo(cid:173)
`nents, ranging as high as 80% by weight (FIA). The majority
`of coker distillate and cycle oil aromatics are present as
`monoaromatics and di-aromatics with a smaller portion
`present as tri-aromatics. Virgin stocks such as high and low
`sulfur virgin distillates are lower in aromatics content rang-
`
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`3
`
`ing as high as 20% by weight aromatics (FIA). Generally,
`the aromatics content of a combined hydrogenation facility
`feedstock will range from about 5% by weight to about 80%
`by weight, more typically from about 10% by weight to
`about 70% by weight, and most typically from about 20% by
`weight to about 60% by weight. In a distillate hydrodes(cid:173)
`ulfurization facility with limited operating capacity, it is
`generally preferable (most economical) to process feed(cid:173)
`stocks in order of highest aromaticity, since catalytic pro(cid:173)
`cesses often proceed to equilibrium product aromatics con(cid:173)
`centrations. In
`this manner, maximum distillate pool
`dearomatization is generally achieved.
`
`[0023] The distillate hydrocarbon feedstock sulfur con(cid:173)
`centration is generally a function of the high and low sulfur
`crude mix, the hydrodesulfurization capacity of a refinery
`per barrel of crude capacity, and the alternative dispositions
`of distillate hydrodesulfurization feedstock components.
`The higher sulfur distillate feedstock components are gen(cid:173)
`erally virgin distillates derived from high sulfur crude, coker
`distillates, and catalytic cycle oils from fluid catalytic crack(cid:173)
`ing units processing relatively higher sulfur feedstocks.
`These distillate feedstock components can range as high as
`2% by weight elemental sulfur but generally range from
`about 0.1 % by weight to about 0.9% by weight elemental
`sulfur.
`
`[0024] The distillate hydrocarbon feedstock nitrogen con(cid:173)
`tent is also generally a function of the nitrogen content of the
`crude oil, the hydrodesulfurization capacity of a refinery per
`barrel of crude capacity, and the alternative dispositions of
`distillate hydrodesulfurization feedstock components. The
`higher nitrogen distillate feedstocks are generally coker
`distillate and the catalytic cycle oils. These distillate feed(cid:173)
`stock components typically have total nitrogen concentra(cid:173)
`tions ranging as high as 2,000 ppm, but generally range from
`about 1 ppm to about 900 ppm.
`
`[0025] The hydrodesulfurization process of the present
`invention generally begins with a distillate feedstock pre(cid:173)
`heating step. The feedstock is preheated in feed/effluent heat
`exchangers prior to entering a furnace for final preheating to
`a targeted reaction zone inlet temperature that will assist in
`achieving the vaporization rate in accordance with the
`present invention. The feedstock can be contacted with a
`hydrogen stream prior to, during, and/or after preheating.
`
`[0026] The hydrogen stream can be pure hydrogen or can
`be in admixture with diluents such as low-boiling hydrocar(cid:173)
`bons, carbon monoxide, carbon dioxide, nitrogen, water,
`sulfur compounds, and the like. The hydrogen stream purity
`should be at least about 50% by volume hydrogen, prefer(cid:173)
`ably at least about 65% by volume hydrogen, and more
`preferably at least about 75% by volume hydrogen for best
`results. Hydrogen can be supplied from a hydrogen plant, a
`catalytic reforming facility, or other hydrogen-producing or
`hydrogen-recovery processes.
`
`[0027] The reaction zone can consist of one or more fixed
`bed reactors containing the same or different catalysts. A
`fixed bed reactor can also comprise a plurality of catalyst
`beds. The plurality of catalyst beds in a single fixed bed
`reactor can also comprise the same or different catalysts.
`
`[0028]
`In another embodiment, the process of the present
`invention as explained in greater deal below, comprises a
`multi-stage process having more than one reaction zone.
`
`[0029] Since the hydrodesulfurization reaction is gener(cid:173)
`ally exothermic, interstage cooling, consisting of heat trans(cid:173)
`fer devices between catalyst beds in the same reactor shell,
`can be employed. At least a portion of the heat generated
`from the hydrodesulfurization process can often be profit(cid:173)
`ably recovered for use in the hydrodesulfurization process.
`A suitable heat sinks for absorbing such heat provided by the
`hydrodesulfurization reaction exotherm can and generally
`includes the feedstock preheat section of the hydrodesulfu(cid:173)
`rization process upstream of the reactor preheat furnace
`described hereinabove. Where this heat recovery option is
`not available, cooling of the reaction zone effluent may be
`performed through cooling utilities such as cooling water or
`air, or through use of a hydrogen quench stream injected
`directly into the reactors.
`
`[0030] The reaction zone effluent is generally cooled and
`the effluent stream is directed to a separator device to
`remove the hydrogen. Some of the recovered hydrogen can
`be recycled back to the process while some of the hydrogen
`can be purged to external systems such as plant or refinery
`fuel. The hydrogen purge rate is often controlled to maintain
`a minimum hydrogen purity and to remove hydrogen sul(cid:173)
`fide. Recycled hydrogen is generally compressed, supple(cid:173)
`mented with "make-up" hydrogen, and reinjected into the
`process for further hydrodesulfurization. Hydrogen is pref(cid:173)
`erably passed through the reaction zone or zones in a
`multi-stage process, in a co-current fashion.
`
`[0031] The separator device liquid effluent can then be
`processed in a stripper device where light hydrocarbons can
`be removed and directed to more appropriate hydrocarbon
`pools. The stripper liquid effluent product is then generally
`conveyed to blending facilities for production of finished
`distillate products.
`
`[0032]
`It is an essential feature of the present invention
`that the hydrogen circulation rate be at least 5 times the
`chemical molar hydrogen consumption rate. It is preferable
`that the rate be at least 10 times the chemical molar
`hydrogen consumption rate and most preferably at least 20
`times the chemical molar hydrogen consumption rate. For a
`typical distillate feedstock having a hydrogen consumption
`rate of 600 SCFB, these hydrogen circulation values corre(cid:173)
`spond to 3,000 SCFB, 6,000 SCFB, and 12,000 SCFB,
`respectively.
`
`[0033]
`It is another essential feature of the present inven(cid:173)
`tion that the percentage feedstock vaporization be at least 30
`mole %, preferably at least 40 mole % and most preferably
`at least 50 mole %. Generally, the feedstock vaporization is
`a complex function of the feedstock boiling range and
`composition, reactor temperature, reactor pressure, and
`hydrogen circulation rate. Those skilled in the art can readily
`calculate the percentage vaporization or employ one of the
`commercially available software programs such as Hysis or
`PRO-II to compute the percentage vaporization. When the
`temperature, pressure, and circulation rate are predeter(cid:173)
`mined refiners operate the hydrodesulfurization process at
`the percentage vaporization determined by the forgoing set
`conditions. Percentage vaporization in the hydrodesulfuriza(cid:173)
`tion reaction zone is a dependent variable that the refiner
`generally does not monitor. In the process of the present
`invention, the hydrogen circulation rate is used to manipu(cid:173)
`late the percentage vaporization and to set the vaporization
`at a desired level in accordance with the present invention.
`
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`US 2003/0168383 Al
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`Sep. 11,2003
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`4
`
`The percentage vaporization should be set at the high levels
`of the present invention in order to concentrate the sulfur
`reactants in the liquid phase and thereby accelerate their
`reaction.
`
`hr.- 1 to about 4.0 hr.- 1
`, and most preferably from about 1.0
`hr.- 1 to about 2.0 hr.- 1 for best results. Excessively high
`space velocities will result in reduced overall hydrodesulfu(cid:173)
`rization.
`
`[0034] The hydrogen circulation rates required by the
`process of the present invention can be achieved by adding
`more compressors, or by running the compressors at greater
`severity, or by feeding less feedstock to increase the gas(cid:173)
`to-oil ratio.
`
`[0035]
`In conventional distillate desulfurization, at typical
`operating conditions, the mole percent vaporization of feed
`is about 15% at about 1000 SCFB gas/oil circulation rate and
`about 25% at about 2000 SCFB gas/oil circulation rate. In
`accordance with this invention, the feed vaporization is
`increased to at least 30 mole % by increasing gas/oil
`circulation rates to about 5000 SCFB, or higher for a typical
`feedstock. Essentially, full vaporization of the feed typically
`occurs at gas rates of 10,000 to 20,000 SCFB.
`
`[0036]
`In another embodiment of the process of the
`present invention the hydrodesulfurization process is carried
`out in two or more-stages.
`
`[0037] The first stage or stages upstream of a stage oper(cid:173)
`ated at conditions in accordance with this invention can be
`operated at conventional operating conditions wherein the
`more reactive sulfur compounds are removed. At least one
`subsequent, downstream stage (or stages) is operated in
`accordance with conditions that include a hydrogen circu(cid:173)
`lation rate of 5 times the chemical hydrogen consumption
`rate, preferably 10 times the chemical hydrogen consump(cid:173)
`tion rate and most preferably 20 times the chemical hydro(cid:173)
`gen consumption rate. The conditions in the subsequent or
`downstream stage or stages also include a feedstock vapor(cid:173)
`ization value of at least 30 mole %, preferably at least 40
`mole %, and most preferably at least 50 mole %. Because
`not all of the stages are are exposed to the hydrogen
`circulation rates and feedstock vaporization rates of the
`present invention the multi-stage process minimizes overall
`capital cost, utility consumption and pressure drop. In accor(cid:173)
`dance with the multi-stage embodiment of the present inven(cid:173)
`tion a new recycle loop can be added to feed extra gas to one
`or more of the stages.
`
`[0038] Other operating conditions used in the hydrodes(cid:173)
`ulfurization process of the present invention include an
`average reaction zone temperature of from about 400° F. to
`about 750° F., preferably from about 600° F. to about 750°
`F., and most preferably from about 650° F. to about 750° F.
`for best results. Reaction temperatures below these ranges
`can result in less effective hydrodesulfurization. Excessively
`high temperatures can cause the process to reach a thermo(cid:173)
`dynamic aromatic reduction limit, hydrocracking, catalyst
`deactivation, product instability, and increase energy costs.
`
`[0039] The process of the present invention generally
`operates at reaction zone pressures ranging from about 300
`psig to about 2,000 psig, more preferably from about 500
`psig to about 1,500 psig, and most preferably from about 600
`psig to about 1,200 psig for best results. Excessively high
`reaction pressures increase energy and equipment costs and
`provide diminishing marginal benefits.
`
`[0040] The process of the present invention generally
`operates at a liquid hourly space velocity (LHSV) of from
`about 0.2 hr.- 1 to about 10.0 hr.- 1
`, preferably from about 0.5
`
`[0041] While not wishing to be bound by theory, it is
`believed that the deep desulfurization achieved by the pro(cid:173)
`cess of the present invention is possible because the mark(cid:173)
`edly increased hydrogen circulation rate increases the per(cid:173)
`centage volatilization. For deep desulfurization one needs to
`remove the remaining "difficult-to desulfurize" species
`present in the high boiling range fraction of the feedstock.
`Because of the high volatilization achieved by the process of
`the invention the remaining liquid phase has a very high
`concentration of the "difficult-to-desulfurize species." This
`means that the partial pressure of these sulfur species is
`increased inasmuch as the partial pressure is a function of
`the liquid mole fraction and the vapor pressure of the sulfur
`species.
`
`[0042]
`Increasing the gas-to-oil rate is known to be ben(cid:173)
`eficial for increasing hydrogen partial pressure and reducing
`H2S partial pressure. These effects are well known and are
`generally accounted for in a process design. But the effects
`of gas rate on hydrogen and H2S partial pressures are not
`large enough to explain the substantially increased deep
`desulfurization achieved by the process of the present inven(cid:173)
`tion in response to the increased gas and vaporization rates.
`
`[0043]
`It is believed this strong response is due to the
`effect of changes in the partial vaporization of the feed. In
`mixed-phase operation, when the gas-to-oil rate is increased,
`the feed vaporization increases. This increase in feed vapor(cid:173)
`ization increases the liquid mole fractions, the partial pres(cid:173)
`sures, and the reaction rates of the high-boiling sulfur(cid:173)
`containing hydrocarbons that need to be removed to achieve
`the deep desulfurization of the present invention.
`
`[0044]
`It is believed this effect becomes very significant as
`desulfurization severity is increased to produce ultra-low
`sulfur diesel.
`
`[0045] The effect of gas-to-oil ratio and feed vaporization
`on desulfurization of an individual sulfur compound can be
`described by the following equation:
`
`kmixedpho.se = kvaporphase X
`
`P,/ P,
`H
`1-a+P,jP,(a+M)
`
`[0046] where:
`[0047] kmixedphase=l st order rate constant observed in
`mixed-phase operation
`[0048] k,,apmphase=lst order rate constant observed in
`all-vapor phase operation
`
`[0049] P v=vapor pressure of the sulfur compound
`
`[0050] a=mole fraction of oil feed that is vaporized
`
`[0051] P,=total pressure
`
`[0052] H=molar flow rate of gas (excluding vapor(cid:173)
`ized oil)
`
`[0053] M=molar flow rate of oil
`
`6 of 8
`
`REFINED TECHNOLOGIES, INC.
`EXHIBIT 2003
`
`

`

`US 2003/0168383 Al
`
`Sep. 11,2003
`
`5
`
`[0054] This equation assumes that, in mixed phase opera(cid:173)
`tion, the liquid and vapor are in phase equilibrium through(cid:173)
`out the reactor. The equation accounts for the fact that in
`mixed phase operation, changes in partial vaporization
`change the liquid phase mole fractions and the partial
`pressures of the sulfur-containing reactants.
`
`[0055] When the gas-to-oil rate is increased at constant
`temperature and pressure in mixed-phase operation, the feed
`vaporization (a) increases. For a high boiling sulfur com(cid:173)
`pound having a low vapor pressure (with low P v), the third
`term in the denominator is very small. For these compounds,
`the apparent rate constant in mixed-phase operation changes
`in roughly direct proportion to 1/(1-a). So, for example, if
`the gas-to-oil ratio were increased such that partial vapor(cid:173)
`ization a increases from 0.2 to 0.6, then this factor would
`change from 1/0.8 to 1/0.4, and the reaction rate of the
`heaviest sulfur compounds would roughly double.
`
`[0056] A physical interpretation of this is that increased
`gas rate strips light hydrocarbon from the liquid, concen(cid:173)
`trating the highest-boiling sulfur compounds in the liquid.
`The liquid phase mole fractions, the partial pressures, and
`the reaction rates of the high boiling sulfur compounds
`consequently increase. This effect is largest for the highest
`boiling sulfur compounds that are being desulfurized in
`ultra-deep desulfurization. This effect is cumulative to the
`beneficial effects of increased gas rate on hydrogen and
`decreased hydrogen sulfide partial pressures.
`
`[0057] Changes In partial vaporization also affect the
`partial pressures of aromatic and nitrogen-containing inhibi(cid:173)
`tors. This probably also contributes to the observed effects
`when carrying out the process of the present invention.
`
`[0058] The performance of conventional diesel desulfur(cid:173)
`ization catalysts can be greatly enhanced by carrying out the
`hydrodesulfurization process in accordance with this inven(cid:173)
`tion. The effect is especially large with high-activity NiMo
`catalysts at deep desulfurization levels. Under these condi(cid:173)
`tions, doubling the gas-to-oil rate can increase the apparent
`catalyst activity by 80%. In some cases, it is possible to more
`than triple the apparent catalyst activity by increasing the
`gas rate.
`
`[0059] The hydrodesulfurization catalysts used in the pro(cid:173)
`cess of the present invention can be any conventional
`commercially available distillate hydrodesulfurization cata(cid:173)
`lysts which comprise a hydrogenation component and a
`catalyst support.
`
`[0060] While not wishing to limit the scope of the present
`invention, a hydrodesulfurization catalyst support compo(cid:173)
`nent generally comprises a weakly acidic refractory inor(cid:173)
`ganic oxide .. The refractory inorganic oxide can be, but is
`not limited to catalytically active alumina, silica, and mix(cid:173)
`tures of silica and alum