BACKGROUND OF THE INVENTION [0002] There is a continuing need in the petroleum refining and chemical industries for catalyst and process technology that result in increase yields of desirable products and lower yields of undesirable components, especially those related to environmental concerns. One such process technology, hydroprocess- ing, has been subjected to increasing demands for improved heteroatom removal, aromatic saturation, and boiling point reduction. More active catalysts and improved reaction vessel designs are needed to meet these demands. Counter- current hydroprocessing, where the liquid feedstream flows counter to upflowing treat gas, has the potential of meeting some of these demands because they offer certain advantages over co-current process where the liquid feedstream and treat gas flow co-currently. Countercurrent hydroprocessing is well known, but it has never reached its commercial potential, primarily because of flooding problems.

[0003] In a countercurrent flow reactor, catalyst bed voidage and particle hydraulic diameter are significant concerns as they are the major factors influencing the hydraulic regime in which the reactor will be operable. For hydraulic reasons one would tend to select large cylindrical catalyst extrudates so that the reactor would be operable at higher gas and liquid fluxes. Large cylindrical catalyst, however, are undesirable from a diffusion resistance standpoint in that their surface area to volume ratio is low. While shaped shaped catalysts such as hollow cylinders, microliths, wagon wheels, etc. , would be expected to provide a balance balance between hydraulics and diffusion resistance, they would suffer from very high cost of fabrication and/or low strength. In conventional cocurrent flow reactors lobed catalyst extrudates have been found to be the optimum balance between pressure drop, diffusion resistance, cost of production, and particle strength. Larger diameter trilobe catalyst extrudates are the current catalyst of choice for use in commercial countercurrent reactors, but a superior catalyst shape would be of value.

[0004] A particulate containing feed, which would not cause noticeable fouling or operating difficulties when processed in a cocurrent flow reactor, is known to cause significant fouling of a countercurrent flow reactor. This fouling will cause the countercurrent flow reactor to be inoperable due to flooding. It is suspected that reactive species (i. e. , dienes, peroxides, etc. ) that could form polymeric material are the cause for fouling in a countercurrent reactor. Thus, it is highly desirable that particulates be removed from feedstreams that are to be processed in such reactors.

[0005] The tendency to flooding in countercurrent reactors also affects the operation of the reactor at optimum feed-catalyst contacting. The relatively high velocity of the upflowing treat gas prevents the downward flow of the liquid feed, which can lead to flooding since the liquid thus cannot pass through the catalyst bed. While flooding is undesirable, catalyst contacting by the reactant liquid improves as the bed approaches a flooded condition. However, operating close to the point of incipient flooding leaves the process vulnerable to fluctua- tions in pressure or temperature or in liquid or gas flow rates. This could result in a disturbance large enough to initiate flooding, and process unit shutdown in order to recover stable operation. Such disruptions are highly undesirable in a continuous commercial operation. Reactor temperature gradients include axial gradients, radial gradients, and localized hot spots. Axial temperature gradients cause refluxing which decreases the kinetic efficiency of the reactor and can make the reactor hydraulically inoperable. All of the temperature gradients contribute to the potential for reactor runaway, decreased reaction selectivity, and less than optimum kinetic/thermodynamic performance. The potential for runaway is particularly important as it restricts the usage of catalysts systems such as those that promote hydrocracking. Conventional temperature control- quench (gas or liquid) and inter bed heat exchange-does not fully solve these problems.

[0006] Conventional countercurrent reactors also exhibit undesirable performance when higher-molecular weight species become part of the upwardly-moving vapor phase. Within a counter current flow reactor the up flowing treat gas becomes saturated with reaction products and lighter components of the feed. Typical reaction products of consequence are H2S, NH3, H2O, and light hydrocarbon products due to cracking, saturation, or heteroatom removal. These species increase the mass flux of the vapor phase thereby reducing the hydraulic capacity of a given diameter reactor; they also depress hydrogen partial pressure thereby reducing favorable reaction kinetics and thermodynamics. The condensable portions of these species present additional problems because as they move up the reactor into cooler or reduced treat gas (due to consumption) regimes they may condense increasing the down flowing liquid rate. This phenomenon can create a reflux loop within the reactor that can exceed the fresh feed rate. The refluxing is detrimental for two reasons: hydraulic capacity of the given reactor diameter is reduced and feed dilution results in less favorable reaction kinetics and thermodynamics. Moreover, the heavier molecules in the vapor phase product of countercurrent hydroprocessing decrease its quality and make further hydroprocessing of the vapor phase product difficult.

[0007] Therefore, there exists a need for improved countercurrent hydro- processing methods.

SUMMARY OF THE INVENTION [0008] In an embodiment, there is provided a process for hydroprocessing a hydrocarbonaceous feedstream, which process comprises: a) treating said feedstream to remove particulates and/or foulant precursors; b) introducing said treated feedstream into a reaction vessel upstream from at least one reaction zone and passing said feedstream through one or more reaction zones operated at hydroprocessing conditions, wherein each reaction zone contains a bed of hydroprocessing catalyst; c) introducing a hydrogen-containing treat gas at the bottom of said reaction vessel and passing it upward through at least one reaction zone countercurrent to the flow of liquid feedstream, thereby reacting with said feedstream in the presence of said hydroprocessing catalysts and resulting in a liquid phase product stream and a vapor phase product stream; d) passing the liquid phase product out of the bottom of said reaction vessels; and e) removing the vapor phase product stream overhead of said reaction zones.

[0009] In a preferred embodiment of the present invention said treating is done in contact with a hydrogen-containing treat gas in a reaction zone contain- ing a catalyst which is effective for converting said foulant precursors to non foulant components. In another preferred embodiment of the present invention the physical aspects of the catalyst are such that the catalyst bed physically filters the largest 10% of the particles present in the feedstream. In yet another preferred embodiment of the present invention the filtration is achieved by a mechanical filtration means to remove the largest 10% of the particles.

[0010] In another embodiment, there is provided a process for hydroprocess- ing a hydrocarbonaceous feedstream, which process comprises: (a) introducing said feedstream into a reaction vessel upstream from at least one reaction zone and passing said feedstream through one or more reaction zones operated at hydroprocessing, wherein each reaction zone contains a bed of hydroprocessing catalyst; (b) introducing a hydrogen-containing treat gas at the bottom of said reaction vessel and passing it upward through each reaction zone countercurrent to the flow of liquid feedstream, thereby reacting with said feedstream in the presence of said hydroprocessing catalysts and resulting in a liquid phase product stream and a vapor phase product stream; (c) passing the liquid phase product out of the bottom of said reaction vessels; (d) removing the vapor phase product stream overhead of said reaction zones; and (e) controlling the temperature of the reaction vessel with one or more heat exchange devices either internal or external of said reaction vessel.

[0011] In another embodiment, there is provided a process for hydroprocess- ing a hydrocarbonaceous feedstream, which process comprises: (a) passing said feedstream through two or more reaction zones operated at hydroprocessing conditions wherein each reaction zone contains a bed of hydroprocessing catalyst; (b) passing a hydrogen-containing treat gas through said two or more reaction zones wherein it passes countercurrent to the flow of liquid feedstream in at least one of said reaction zones, thereby reacting with said feedstream in the presence of said hydroprocessing catalysts and resulting in a liquid phase product stream and a vapor phase product stream; (c) collecting a liquid phase product stream from said reaction zones; (d) collecting the vapor phase product stream from said reaction zones; (e) purging at least a portion of said vapor phase product stream between one or more reaction zones; and (f) replacing at least a portion of said vapor phase product stream with fresh or recycled treat gas.

[0012] In a preferred embodiment of the present invention at least a portion of the vapor phase product stream purged from said reaction vessel is replaced with fresh hydrogen-containing treat gas. In another preferred embodiment of the present invention at least a portion of said vapor phase product stream purged from said reaction vessel is treated to remove higher boiling components, then recycled to one or more of said reaction zones. In yet another preferred embodiment of the present invention said purging is accomplished through use of a bypass device internal to the reaction vessel which allows a portion of the upflowing treat gas to bypass one or more of the reaction zones in the upper portion of the reaction vessel and wherein said fresh hydrogen containing treat gas is supplied by a bypass device internal to the reactor vessel which allows a portion of the gas introduced at the bottom of the reaction vessel to bypass one or more of the reaction zones in the lower portion of the reaction vessel.

[0013] In another embodiment, there is provided a process for hydroprocess- ing a hydrocarbonaceous feedstream, which process comprises: (a) introducing said feedstream into a reaction vessel upstream from at least one reaction zone and passing said feedstream through one or more reaction zones operated at hydroprocessing conditions, wherein each reaction zone contains a bed of hydroprocessing catalyst; (b) introducing a hydrogen-containing treat gas at the bottom of said reaction vessel and passing it upward through at least one reaction zone countercurrent to the flow of liquid feedstream, thereby reacting with said feedstream in the presence of said hydroprocessing catalysts and resulting in a liquid phase product stream and a vapor phase product stream; (c) passing the liquid phase product out of the bottom of said reaction vessels; (d) removing the vapor phase product stream overhead of said reaction zones; (e) condensing a portion of said vapor phase product stream to produce a liquid stream comprised of the higher boiling point fractions and a vapor stream comprised of hydrogen-containing treat gas and the lower boiling point fractions; and passing said liquid phase stream with a hydrogen containing treat gas through a trickle bed reactor operated at hydroprocessing conditions and containing a hydroprocessing catalyst.

[0014] In a preferred embodiment of the present invention the hydrogen- containing treat gas in (f) is fresh hydrogen-containing treat gas. In another preferred embodiment of the present invention the hydrogen-containing treat gas in (f) is the vapor stream of (e).

BRIEF DESCRIPTION OF THE FIGURES [0015] Figure 1 hereof shows a preferred process configuration of the present invention relating to vapor product purge.

[0016] Figure 2 hereof shows a preferred process configuration of the present invention relating to trickle bed processing of the vapor product stream.

DETAILED DESCRIPTION OF THE INVENTION [0017] The invention relates to hydroprocessing processes including the hydroconversion of heavy petroleum feedstocks to lower boiling products; the hydrocracking of distillate boiling range feedstocks; the hydrotreating of various petroleum feedstocks to remove heteroatoms, such as sulfur, nitrogen, and oxygen; the hydrogenation of aromatics; the hydroisomerization and/or catalytic dewaxing of waxes, particularly Fischer-Tropsch waxes; and demetallation of heavy streams. It is preferred that the reaction vessels used in the practice of the present invention be those in which a hydrocarbon feedstock is hydrotreated and hydrogenated, more specifically when heteroatoms are removed and when at least a portion of the aromatic fraction of the feed is hydrogenated.

[0018] The practice of the present invention is applicable to all liquid-vapor countercurrent refinery and chemical processes. Feedstocks suitable for use in the practice of the present invention include those ranging from the naphtha boiling range to heavy feedstocks, such as gas oils and resids. Typically, the boiling range will be from about 40°C to about 1000°C. Non-limiting examples of such heavy feedstocks include vacuum resid, atmospheric resid, vacuum gas oil (VGO), atmospheric gas oil (AGO), heavy atmospheric gas oil (HAGO), steam cracked gas oil (SCGO), deasphalted oil (DAO), and light cat cycle oil (LCCO).

[0019] The feedstocks of the present invention are subjected to countercurrent hydroprocessing in at least one catalyst bed, or reaction zone, wherein feedstock flows countercurrent to the flow of a hydrogen-containing treat gas. Typically, the hydroprocessing unit used in the practice of the present invention will be comprised of one or more reaction zones wherein each reaction zone contains a suitable catalyst for the intended reaction and wherein each reaction zone is immediately preceded and followed by a non-reaction zone where products can be removed and/or feed or treat gas introduced. The non-reaction zone will typically be a void (with respect to catalyst) horizontal cross section of the reaction vessel of suitable height, although it may contain inert packing material.

[0020] If the feedstock contains unacceptably high levels of heteroatoms, such as sulfur, nitrogen, or oxygen moieties, it can first be subjected to hydro- treating. In such cases, it is preferred that the first reaction zone be one in which the liquid feed stream flows co-current with a stream of hydrogen-containing treat gas through a fixed-bed of suitable hydrotreating catalyst. The feedstock hydrotreating can be conducted in a separate reaction vessel. When the feedstock is a Fischer-Tropsch reaction product stream, the most troublesome heteroatom species are the oxygenates.

[0021] In an embodiment, the feedstock can be introduced into a first reaction zone co-current to the flow of hydrogen-containing treat-gas. The vapor phase effluent fraction is separated from the liquid phase effluent fraction between reaction zones; that is, in a non-reaction zone. This separation between reaction zones is also referred to as catalytic distillation. The vapor phase effluent can be passed to additional hydrotreating, or collected, or further fractionated and sent to additional processing. The liquid phase effluent will then be passed to the next downstream reaction zone, which will preferably be a hydroisomerization countercurrent reaction zone. In other embodiments of the present invention, vapor or liquid phase effluent and/or treat gas can be withdrawn or injected between any reaction zones.

[0022] The term"hydrotreating"as used herein refers to processes wherein a hydrogen-containing treat gas is used in the presence of a catalyst that is primarily active for the removal of heteroatoms, such as sulfur, and nitrogen species with some hydrogenation of aromatics. The term"hydroprocessing" includes hydrotreating, as well as other processes that are primarily active toward the hydrogenation, hydrocracking, and hydroisomerization. Ring- opening, particularly of naphthenic rings, for purposes of this invention can also be included in the term"hydroprocessing". Hydrotreating catalysts suitable for use in the present invention are any conventional hydrotreating catalyst and includes those which are comprised of at least one Group VIII metal, preferably Fe, Co and Ni, more preferably Co and/or Ni, and most preferably Co, and at least one Group VI metal, preferably Mo and W, more preferably Mo, on a high surface area support material, preferably alumina. Other suitable hydrotreating catalysts include zeolitic catalysts, as well as noble metal catalysts where the noble metal is selected from Pd and Pt.

[0023] Suitable hydrotreating catalysts for use in the present invention are any conventional hydrotreating catalyst and includes those which are comprised of at least one Group VIII metal, preferably Fe, Co and Ni, more preferably Co and/or Ni, and most preferably Ni; and at least one Group VI metal, preferably Mo and W, more preferably Mo, on a high surface area support material, prefer- ably alumina. Other suitable hydrotreating catalysts include zeolitic catalysts, as well as noble metal catalysts where the noble metal is selected from Pd and Pt.

It is within the scope of the present invention that more than one type of hydro- treating catalyst be used in the same bed. The Group VIII metal is typically present in an amount ranging from about 2 to 20 wt%, preferably from about 4 to 12%. The Group VI metal will typically be present in an amount ranging from about 5 to 50 wt%, preferably from about 10 to 40 wt%, and more preferably from about 20 to 30 wt%. All metals weight percents are on support. By"on support"it is meant that the percents are based on the weight of the support. For example, if the support were to weigh 100 g. then 20 wt% Group VIII metal would mean that 20 g. of Group VIII metal was on the support. Typical hydro- processing temperatures will be from about 100°C to about 450°C at pressures from about 50 psig to about 2,000 psig, or higher. If the feedstock contains relatively low levels of heteroatoms, then the co-current hydrotreating step can be eliminated and the feedstock can be passed directly to the hydroisomerization zone.

[0024] Rifled trilobes catalyst extrudates are the most preferred catalyst shape for use in countercurrent hydroprocessing technology. Rifled extrudates are the optimum balance between pressure drop, diffusion resistance, cost of production, and particle strength. The rifled extrudates may be conventional rifled trilobe or <BR> <BR> may be any other rifled extrudate (i. e. , rifled quadralobes, rifled pentalobes,<BR> etc. ); lobes need not be symmetric. It is more preferred that the lobes be shaped such that the concavity index is greater than one but values less than one may still be superior to non-rifled catalyst.

[0025] It will be understood that the treat-gas need not be pure hydrogen, but can be any suitable hydrogen-containing treat-gas. It is preferred that the countercurrent flowing hydrogen treat-rich gas be cold make-up hydrogen- containing treat gas, preferably hydrogen. The countercurrent contacting of the liquid effluent with cold hydrogen-containing treat gas serves to affect a high hydrogen partial pressure and a cooler operating temperature, both of which are favorable for shifting chemical equilibrium towards saturated compounds. The liquid phase will typically be a mixture of the higher boiling components of the fresh feed. The vapor phase in the catalyst bed of the downstream reaction zone will be swept upward with the upflowing hydrogen-containing treat-gas and collected, fractionated, or passed along for further processing. It is preferred that the vapor phase effluent be removed from the non-reaction zone immediate upstream (relative to the flow of liquid effluent) of the countercurrent reaction zone.

[0026] If the vapor phase effluent contains an undesirable level of hetero- atoms, it can be passed to a vapor phase reaction zone containing additional hydrotreating catalyst and subjected to suitable hydrotreating conditions for further removal of the heteroatoms. It is to be understood that all reaction zones can either be in the same vessel separated by non-reaction zones, or any can be in separate vessels. The non-reaction zones in the later case will typically be the transfer lines leading from one vessel to another. It is also within the scope of the present invention that a feedstock which already contains adequately low levels of heteroatoms fed directly into a countercurrent hydroprocessing reaction zone. If a preprocessing step is performed to reduce the level of heteroatoms, the vapor and liquid are disengaged and the liquid effluent directed to the top of a countercurrent reactor. The vapor from the preprocessing step can be processed separately or combined with the vapor phase product from the countercurrent reactor. The vapor phase product (s) may undergo further vapor phase hydroprocessing if greater reduction in heteroatom and aromatic species is desired or sent directly to a recovery system. The catalyst may be contained in one or more beds in one vessel or multiple vessels. Various hardware, i. e., distributors, baffles, heat transfer devices, may be required inside the vessel (s) to provide proper temperature control and contacting (hydraulic regime) between the liquid, vapors, and catalyst. Also, cascading and liquid or gas quenching may also be used in the practice of the present, all of which are well known to those having ordinary skill in the art.

[0027] The upflowing vapor phase will contain a range of boiling point components, including relatively heavy, or higher boiling components that will escape with the vapor phase unless separated therefrom. It is preferred that these higher boiling components be separated and recycled to the reactor for further processing. There are various ways this can be done in accordance with the present invention. For example, the vapor phase stream can be contacted with a hydrocarbon stream in a stripping zone after the vapor phase stream exits the reaction zone, thereby stripping heavy components from said vapor phase product stream. The contacting can be done in a liquid continuous or a gas continuous mode. Further, the contacting may be facilitated by structures such as gas distributors/redistributors, liquid distributors/redistributors, trays, or structured packing, random packing. If packing is used it may also have catalytic activity. A heat exchange means may also be integrated with the contacting operation. The liquid (containing the stripped heavier components) after contacting may be collected as a discrete product, or it may be re-introduced into the reactor at any suitable location. For example, it may be mixed with incoming feed, or introduced between catalyst beds. If it is re- introduced in a downstream portion of the reactor, it can be used as a quench.

[0028] The higher boiling components can also be separated from the vapor phase product stream by passing at least a portion of said vapor phase product stream to a condensation zone thereby resulting in a vapor phase product stream having a lower average boiling point and a condensate containing the higher boiling components. The condensate may be collected as a discrete product, or it may be re-introduced into the reactor at any suitable location as discussed above.

[0029] Also, the higher boiling components can be separated from the vapor phase stream by injecting a liquid stream having a high average boiling point into the reactor so that is flows downward counter to the flow of the vapor phase stream, thereby stripping (refluxing) the heavier components from the vapor stream. Non-limiting examples of high boiling point streams include raw feed or product from one or more upstream reaction stages, partial condensate of the vapor phase stream, liquid withdrawn from between the beds, or a bottoms product.

[0030] In an embodiment, countercurrent contacting of an effluent stream from an upstream reaction zone with hydrogen-containing treat gas strips dissolved heteroatom impurities from the effluent stream, thereby improving both the hydrogen partial pressure and the catalyst performance. That is, the catalyst may be on-stream for substantially longer periods of time before regeneration is required. Further, higher heteroatom removal levels will be achieved by the process of the present invention.

[0031] Having now briefly described certain aspects of countercurrent hydroprocessing, further improvements will be discussed in more detail. Unless otherwise stated herein, the terms"downstream"and"upstream"are with respect to the flow of liquid that will flow downward. Further, the vessels of the present invention need not be limited to catalytic chemical reactions, but can also be used in gas-liquid contacting towers such as those used for extraction or stripping. In such cases, no reaction is necessarily involved and the upward- moving gas contacts a downward-moving liquid, typically to achieve mass transfer between the two streams.

I. Improvements Resulting from the Removal of Particulates [0032] Counter current flow reactors have been discovered to be more susceptible to fouling induced problems than a comparable cocurrent flow reactor. A particulate containing feed, which would not cause noticeable fouling or operating difficulties when processed in a cocurrent flow reactor will cause significant fouling of a countercurrent flow reactor. This fouling will cause the countercurrent flow reactor to be inoperable due to flooding. It is suspected that <BR> <BR> reactive species (i. e. , dienes, peroxides, etc. ) that could form polymeric material are the cause for fouling in a countercurrent reactor. Thus, it is highly desirable that particulates be removed from feedstreams that are to be processed in such reactors.

[0033] The removal of particulates from feedstreams can accomplish in several ways. For example, a reactive filter can be used for the removal of both particulates and foulant precursors. An example of a reactive filter would be a very high LHSV cocurrent reactor (bulge in the line) with a very low TGR (-100 SCF/B or even just dissolved hydrogen) and relatively small catalyst to remove particulates by mechanical filtration (similar to a sand filter) and foulant precursors by reaction prior to putting feed into the countercurrent reactor. Two may be required in parallel to allow change out during operation. It may be desirable to put the reactive filter between multiple preheat exchangers to do diene hydrogenation on cracked stock before the temperature gets too high and begins to form polymer within the heat exchangers.

[0034] While the reactive filter may be operated in two phase flow, it is preferred that a single phase flow be used because the dynamics of filtration in a single phase flow are very different than the mechanism of filtration in two phase flow. For example, the pressure drop buildup in single phase flow is very slow compared to two phase flow, and also it is much easier to use a single phase filter as a deep bed filter (i. e. , no cake or low cake formation) compared to a two phase filter. Using only soluble hydrogen is one way to keep the filter as single phase.

One could also use a gas bypass pipe in the filter which becomes operative only when the filter pressure drop increases; this way the filter can start as a two phase filter and gradually becomes a single phase filter.

[0035] In another embodiment, means for discrete mechanical filtration, including conventional means, may be coupled with a cocurrent reactor to remove foulant precursors. The two steps may be performed in either order, but mechanical filtration first is preferred.

II. Improvements Resulting from the use of Reactor Temperature Control [0036] Temperature control may be beneficial for a countercurrent flow reactor due to the heat release associated with the exothermic reactions conducted in the reactor. Conventionally, temperature control is achieved by addition of a cooler fluid, either gas or liquid. Previously, it had been thought that the liquid quench would need to be a stream with very low heteroatom content so that heteroatoms were not introduced deep into the reactor where it was desirous to have a low heteroatom environment. The use of this liquid quench is expensive because it requires additional equipment; increases the liquid loading in the reactor resulting in a larger reactor diameter and larger down stream equipment; and it does not remove any heat from the system merely dilutes the heat so that additional heat removal is still required.

[0037] In an embodiment, improved temperature control is achieved by withdrawing the down flowing liquid from the countercurrent flow reactor, cooling it in a conventional heat exchanger, and reintroducing it to the bed below. Similarly, the up flowing vapor phase can be withdrawn, cooled, and reintroduced to the bed above. Cooling of the vapor stream cannot achieve as much heat removal from the reactor due to the lower thermal capacity of the vapor stream. Cooling of the vapor stream does as much heat removal from the reactor due to the lower thermal capacity of the vapor stream. Cooling of the vapor stream does however have an additional benefit of allowing the condensa- tion of vaporized hydrocarbon and its optional removal from the system so as to reduce hydraulic loading in the countercurrent reactor. In some cases it will be desirable to cool both the liquid and vapor streams. The removal and reintroduction can be done using any collectors and distributors known to those skilled in the art of tray design. If only one of the streams-liquid or vapor-are being cooled, equipment may be required to balance pressure drop on the stream not being cooled. The use of this invention is particularly desirable when a large temperature adjustment is required (i. e. , for a large temperature adjustment between a heteroatom removal step and an aromatics saturation step.

[0038] In another embodiment, improved temperature control is achieved by placing one or more heat exchange devices (i. e. , coil) in the reactor and circulat- ing a cooling media through the device. The heat exchange device may be contained within a catalyst bed, in the vapor space between catalyst beds, or submerged in the liquid on redistributor trays. Applying the invention by cooling the liquid on the distributor trays is the more preferred route as this the way that ensures uniform radial temperature. The heat removal media may be selected from the group consisting of: water, preferably steam; feed with the additional benefit of preheating the feed to reaction temperature without investment in additional heat exchange area and heat source; and other media familiar to those skilled in the art. The use of the instant invention is particularly desirable when a large temperature adjustment is required (i. e. , for a large temperature adjustment between a heteroatom removal step and an aromatics saturation step).

[0039] The present invention would be of use for the full range of feeds currently envisioned for countercurrent hydroprocessing technology. The countercurrent reactor may be one of only countercurrent flow, or it can be a split flow reactor (countercurrent flow with a co-current vapor phase reaction zone above the feed point). The present invention can also be coupled with other temperature control mechanisms.

III. Improvements Relating to Vapor Product Purge [0040] In an embodiment, vapor product purge improvements can be described with respect to Figure 1. Miscellaneous reaction vessel internals, such as thermocouples, heat transfer devices etc. , are not shown for simplicity.

Figure 1 shows reaction vessel R which contains liquid inlet LI for receiving a feedstock to be treated, and a liquid outlet LO for removing liquid reaction product. There is also provided treat gas inlet GI and gas, or vapor phase outlet GO. The reaction vessel contains three serially disposed reaction zones, ri, r2, and r3. Each reaction zone is immediately preceded and immediately followed by a non-reaction zone, nrl, nr2, nr3, and nr4. The non-reaction zone is typically void of catalyst; that is, it will be an empty section in the vessel with respect to catalyst. Liquid distribution means LD can be situated above each reaction zone in order to more evenly distribute downflowing liquid to the next downstream reaction zone. Each reaction zone is comprised of a bed of catalyst suitable for the desired reaction. There is also provided a condensation zone C.

[0041] In an embodiment, the process can be practiced by introducing the feedstock to be treated into liquid inlet LI of reaction vessel R. A suitable treat gas, such as a hydrogen-containing gas, is introduced via port GI into the reaction vessel countercurrent to the downward flow of the liquid feedstock. It is to be understood that the treat gas need not be introduced only at the bottom of the reaction vessel at GI, but may also be introduced into any one or more of the non-reaction zones, for example at Gig and/or GIb. Treat gas can also be injected into any one or more of the catalyst beds. An advantage of introducing treat gas at various points in the reaction vessel is to control the temperature within the reaction vessel. For example, cold treat gas can be injected into the reaction vessel at various points to moderate any exothermic heat of reaction. It is also within the scope of this invention that all of the treat gas can be introduced at any one of the aforesaid points as long as at least a portion of it flows countercurrent to the flow of liquid in at least one reaction zone.

[0042] Within a counter current flow reactor the up flowing treat gas becomes saturated with reaction products and lighter components of the feed. Typical reaction products of consequence are H2S, NH3, H2O, and light hydrocarbon products due to cracking, saturation, or heteroatom removal. These species increase the mass flux of the vapor phase thereby reducing the hydraulic capacity of a given diameter reactor; they also depress hydrogen partial pressure thereby reducing favorable reaction kinetics and thermodynamics. The condensable portions of these species present additional problems because as they move up the reactor into cooler or reduced treat gas (due to consumption) regimes they may condense increasing the down flowing liquid rate. This phenomenon can create a reflux loop within the reactor that can exceed the fresh feed rate. The refluxing is detrimental for two reasons: hydraulic capacity of the given reactor diameter is reduced and feed dilution results in less favorable reaction kinetics and thermodynamics.

[0043] For example, as shown in Figure 1, a portion of the vapor phase product stream can be purged from the reaction vessel via line 10. It can either be passed to recovery facilities or it can be passed, as shown in the Figure to condensation zone C, thereby producing a condensate containing the higher boiling components and the remaining vapor phase product stream now contains only the lighter gases, as well as gaseous products resulting from the reaction, such as H2S and NH3. The condensate may be collected via line 16 as a discrete product. The remaining light fraction of the vapor phase product stream can then be recycled to the reaction vessel at any suitable point via lines 12 and or 14.

[0044] Improved countercurrent reactor performance can be achieved by withdrawing all or part of the up flowing vapor phase and replacing it with fresh treat gas (fresh is here meant to also mean cleaned recycle gas). The fresh treat gas can be introduced to the reactor cold thereby also sometimes performing desirable temperature control. The treat gas can also be heated before introduction into the reactor. Withdrawing and addition may be done either through the wall of the reactor or through partial bypassing with internal conduits. This embodiment of the invention has the advantage in that it removes non-condensable species (H2S, Cl, C2, etc. ).

[0045] Improved countercurrent reactor performance can also be achieved by withdrawing all or part of the up flowing vapor phase, cooling to condense all or part of the condensable hydrocarbon, separating the condensate and vapor phase, and reintroducing all or part of the hydrocarbon depleted vapor to the bed above (directly or further above). The hydrocarbon depleted vapor can be reintroduced to the reactor cold or heated as discussed above. The condensate can be collected as a discrete product, blended with another product stream, used as quench, and/or added back to the feed to the reactor. This embodiment of the invention has the advantage in that the total treat gas supply and recovery facilities are relatively small.

[0046] The use of a vapor product purge is particularly desirable when a large temperature gradient, high hydrogen consumption, or substantial boiling point conversion (cracking) is being performed in the reactor.

[0047] In an embodiment, the process invention is operated at suitable temperatures and pressures for the desired reaction. For example, typical hydroprocessing temperatures will range from about 40°C to about 450°C at pressures from about 50 psig to about 3,000 psig, preferably 50 to 2,500 psig.

The liquid feedstock passes downward through the catalyst bed of reaction zone rl, where it reacts with the treat gas on the catalyst surface. Any resulting vapor- phase reaction products are swept upwards by the upward-flowing treat gas.

Such vapor-phase reaction products may include relatively low boiling hydro- carbons and heteroatom components, such as H2S and NH3. Any unreacted feedstocks, as well as liquid reaction product pass downwardly through each successive catalyst bed of each successive reaction zone r2 and r3. Figure 1 shows an optional liquid distribution means LR that can be positioned above each catalyst bed (reaction zone). The type of liquid distribution tray used is not believed to limit the practice of the present invention and the reaction vessel may therefore employ any conventional distribution trays, such as sieve trays, bubble cap trays, etc. The liquid effluent exits the reaction vessel via port LO and vapor phase effluent exits via port GO.

[0048] It is within the scope of the present invention that more than one type of hydrotreating catalyst be used, either in the same catalyst bed or in separate catalyst beds. Suitable catalysts and catalytic hydroprocessing conditions are described above.

[0049] In an embodiment, the"hydrogen-containing treat gas"is a treat gas stream containing at least an effective amount of hydrogen for the intended reaction. Preferably, the treat gas stream used herein contains at least about 50 vol%, more preferably at least about 75 vol. % hydrogen. It is preferred that the hydrogen-containing treat gas be make-up hydrogen-rich gas, preferably substantially pure hydrogen.

[0050] In the case where the first reaction zone is a co-current hydrotreating reaction zone, the liquid effluent from said hydrotreating reaction zone will be passed to at least one downstream reaction zone where the liquid is passed through a bed of catalyst countercurrent to the flow of upflowing hydrogen- containing treat-gas. The most desirable reaction products resulting from hydroprocessing, preferably when gas oils are the feedstocks, are those containing reduced levels of sulfur and nitrogen species. Product streams containing paraffins, especially linear paraffins are often preferred over naphthenes, which are often preferred over aromatics. To achieve this, at least one downstream catalyst will be selected from the group consisting hydrotreat- ing catalysts, hydrocracking catalysts, aromatic saturation catalysts, and ring- opening catalysts. If it is economically feasible to produce a product stream with high levels of paraffins, then the downstream zones will preferably include an aromatic saturation zone and a ring-opening zone.

[0051] If one of the downstream reaction zones is a hydrocracking zone, the catalyst can be any suitable conventional hydrocracking catalyst run at typical hydrocracking conditions. Typical hydrocracking catalysts are described in U. S.

Patent No. 4,921, 595 to UOP, which is incorporated herein by reference. Such catalysts are typically comprised of a Group VIII metal hydrogenating component on a zeolite cracking base. The zeolite cracking bases are sometimes referred to in the art as molecular sieves, and are generally composed of silica, alumina, and one or more exchangeable cations such as sodium, magnesium, calcium, rare earth metals, etc. Crystal pores of relatively uniform diameter between about 4 and 12 Angstroms further characterize them. It is preferred to use zeolites having a relatively high silica/alumina mole ratio greater than about 3, preferably greater than about 6. Suitable zeolites found in nature include mordenite, clinoptiliolite, ferrierite, dachiardite, chabazite, erionite, and faujasite. Suitable synthetic zeolites include the Beta, X, Y, and L crystal types, e. g. , synthetic faujasite, mordenite, ZSM-5, MCM-22 and the larger pore varieties of the ZSM and MCM series. A particularly preferred zeolite is any <BR> <BR> member of the faujasite family, see Tracy et al. Proc. of the Royal Soc. , 1996, Vol. 452, p. 813. It is to be understood that these zeolites may include demetallated zeolites that are understood to include significant pore volume in <BR> <BR> the mesopore range, i. e. , 20 to 500 Angstroms. Non-limiting examples of Group VIII metals that may be used on the hydrocracking catalysts include iron cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium, and platinum.

Preferred are platinum and palladium, with platinum being more preferred. The amount of Group VIII metal will range from about 0.05 wt% to 30 wt%, based on the total weight of the catalyst. If the metal is a Group VIII noble metal, it is preferred to use about 0.05 to about 2 wt%. Hydrocracking conditions include temperatures from about 200°C to 425°C, preferably from about 220°C to 330°C, more preferably from about 245°C to 315°C ; pressure of about 200 psig to about 3,000 psig; and liquid hourly space velocity from about 0.5 to 10 V/V/Hr, preferably from about 1 to 5 V/V/Hr.

[0052] Non-limiting examples of aromatic hydrogenation catalysts include nickel, cobalt-molybdenum, nickel-molybdenum, and nickel tungsten. Non- limiting examples of noble metal catalysts include those based on platinum and/or palladium, which is preferably supported on a suitable support material, typically a refractory oxide material such as alumina, silica, alumina-silica, kieselguhr, diatomaceous earth, magnesia, and zirconia. Zeolitic supports can also be used. Such catalysts are typically susceptible to sulfur and nitrogen poisoning. The aromatic saturation zone is preferably operated at a temperature from about 40°C to about 400°C, more preferably from about 260°C to about 350°C, at a pressure from about 100 psig to about 3,000 psig, preferably from about 200 psig to about 1,200 psig, and at a liquid hourly space velocity (LHSV) of from about 0.3 V/V/Hr. to about 2 VlV/Hr.

[0053] The liquid phase in the reaction vessels used in the present invention will typically be the higher boiling point components of the feed. The vapor phase will typically be a mixture of hydrogen-containing treat gas, heteroatom impurities, and vaporized lower-boiling components in the fresh feed, as well as light products of hydroprocessing reactions, and a relatively heavy tail gas. The vapor phase in the catalyst bed of a countercurrent reaction zone will be swept upward with the upflowing hydrogen-containing treat-gas and collected, fractionated, or passed along for further processing. If the vapor phase effluent still requires further hydroprocessing, it can be passed to a vapor phase reaction zone containing additional hydroprocessing catalyst and subjected to suitable hydroprocessing conditions for further reaction. It is to be understood that all reaction zones can either be in the same vessel separated by non-reaction zones, or any can be in separate vessels. The non-reaction zones in the later case will typically be the transfer lines leading from one vessel to another. It is also within the scope of the present invention that a feedstock that already contains adequately low levels of heteroatoms be fed directly into a countercurrent hydroprocessing reaction zone for aromatic saturation and/or cracking. If a preprocessing step is performed to reduce the level of heteroatoms, the vapor and liquid can be disengaged and the liquid effluent directed to the top of a countercurrent reaction vessel. The vapor from the preprocessing step can be processed separately or combined with the vapor phase product from the reaction vessel of the present invention. The vapor phase product (s) may undergo further vapor phase hydroprocessing if greater reduction in heteroatom and aromatic species is desired or sent directly to a recovery system.

[0054] In an embodiment of the present invention, the feedstock can be introduced into a first reaction zone co-current to the flow of hydrogen- containing treat gas. A vapor phase effluent fraction can then be separated from the liquid phase effluent fraction between reaction zones. That is, in a non- reaction zone. The vapor phase effluent can be condensed and the resulting condensate recycled to one or more reaction zones and the remaining vapor fraction passed to additional hydrotreating, or collected, or further fractionated.

In other embodiments of the present invention, vapor phase effluent and/or treat gas can be withdrawn or injected between any reaction zones.

[0055] The countercurrent contacting of liquid from an upstream reaction zone with upflowing treat gas strips dissolved H2S and NH3 impurities from the effluent stream, thereby improving both the hydrogen partial pressure and the catalyst performance. The resulting final liquid product will contain a substantially lower level of heteroatoms and substantially more hydrogen then the original feedstock. This liquid product stream may be sent to downstream hydroprocessing or conversion processes.

IV. Improvements Relating to Trickle Bed Processing of Vapor Effluent [0056] In an embodiment related to the embodiments set forth in Section III, the process is practiced in accordance with Figure 2 by introducing the feedstock to be treated into liquid inlet LI of reaction vessel R. A suitable treat gas, such as a hydrogen-containing gas, is introduced via port GI into the reaction vessel countercurrent to the downward flow of the liquid feedstock. It is to be under- stood that the treat gas need not be introduced only at the bottom of the reaction vessel at GI, but may also be introduced into any one or more of the non-reaction zones, for example at GIa and/or GIb. Treat gas can also be injected into any one or more of the catalyst beds. An advantage of introducing treat gas at various points in the reaction vessel is to control the temperature within the reaction vessel. For example, cold treat gas can be injected into the reaction vessel at various points to moderate any exothermic heat of reaction. It is also within the scope of this invention that all of the treat gas can be introduced at any one of the aforesaid points as long as at least a portion of it flows countercurrent to the flow of liquid in at least one reaction zone.

[0057] It is often desirable to further process the vapor phase product stream from countercurrent hydroprocessing, especially if it is a virgin stream. As previously mentioned above further processing the vapor phase product stream in a vapor phase reactor has various limitations. For example: (a) it is limited by heat capacity resulting in significant temperature rise; (b) all of the components have equally short residence time; and (c) any catalyst is subjected to poisoning <BR> <BR> from the H2S, NH3, H2S, etc. , produced in reactor. The limited heat capacity is particularly important if one wishes to conduct aromatic saturation or hydrocracking on the overhead stream.

[0058] Partial condensation of the overhead vapor phase product stream and further processing of the total vapor/condensate steam in a conventional down flow trickle bed reactor overcomes the first two limitations. Such a configuration allows moderation of heat rise and increases residence time of the heavier fractions of the overhead product stream since they are now liquid phase rather than gas phase. This configuration is advantageous when processing of the entire overhead stream is desired for additional heteroatom removal and particularly advantageous when hydrocracking or aromatic saturation is desired. Instead of using a heat exchanger to reduce the temperature, a cooler quench liquid could also be used to achieve a liquid phase.

[0059] Returning to Figure 2, at least a portion of the vapor phase product stream is passed to condensation zone Cl via line 10 thereby resulting in a condensate of heavier components and a lighter vapor phase stream which contains gaseous reaction products from the reaction zones, such as H2S and NH3. The condensate is passed via line 12, with hydrogen-containing treat gas via line 14, to trickle bed reactor TB which contains a catalytically effective amount of a catalyst suitable for the intended reaction, e. g. a hydroprocessing catalyst. The light vapor phase product is collected overhead via line 16. The product from the trickle bed reactor is passed via line 18 to a second condensa- tion zone C2 where the resulting condensate is collected via line 20 and the vapor phase fraction, which is the recovered hydrogen-containing treat gas, is sent to a vapor recovery section or recycled to one or more reaction zones.

[0060] The catalyst used in the trickle bed reactor is an independently selected hydroprocessing catalyst. In other words, the catalyst may be the same or different from the catalyst selected for use in the upstream countercurrent reactor (s). If there is a need to overcome limitations with respect to catalyst poisons, for example to use a noble metal containing catalyst, the condensation can be performed and only the liquid phase can be passed to the further hydro- processing with fresh hydrogen supplied as the treat gas. Treat gas from this step could in some cases be cascaded back to the reactor. In an embodiment, the trickle bed reactor is operated under catalytic hydroprocessing conditions. For example, typical hydroprocessing temperatures will range from about 40°C to about 450°C at pressures from about 50 psig to about 3,000 psig, preferably 50 to 2,500 psig.

[0061] The trickle bed process of the present invention does not preclude the combined use with an all vapor phase reactor. In fact, the use of a vapor phase reactor can be used to reduce sulfur and nitrogen prior to gas/liquid separation.

This is desirable to reduce the heteroatom content of the liquid going to the sensitive catalyst.

[0062] The liquid product from the trickle bed reactor may be retained as a discrete product, blended with one or both of the products from the main countercurrent reactor, or re-introduced into the reactor for further processing and/or as a quench. Further processing of this material in the lower portions of the countercurrent reactor is particularly attractive if deep hydrocracking or deep aromatic saturation is desired.

[0063] In an embodiment, the process is operated under process conditions set forth in previous sections, where reaction sequence, catalyst choice, and suitable temperatures and pressures are described in detail. For example, typical hydroprocessing temperatures will range from about 40°C to about 450°C at pressures from about 50 psig to about 3,000 psig, preferably 50 to 2,500 psig.

The liquid feedstock passes downward through the catalyst bed of reaction zone rl, where it reacts with the treat gas on the catalyst surface. Any resulting vapor- phase reaction products are swept upwards by the upward-flowing treat gas.

Such vapor-phase reaction products may include relatively low boiling hydro- carbons and heteroatom components, such as H2S and NH3. Any unreacted feedstocks, as well as liquid reaction product pass downwardly through each successive catalyst bed of each successive reaction zone r2 and r3. Figure 2 shows an optional liquid distribution means LR that can be positioned above each catalyst bed (reaction zone). The type of liquid distribution tray used is not believed to limit the practice of the present invention and the reaction vessel may therefore employ conventional distribution trays, such as sieve trays, bubble cap trays, etc. The liquid effluent exits the reaction vessel via port LO and vapor phase effluent exits via port GO.