Abstract:
A process and apparatus for quenching a hydrocracked stream to prepare it for hydroisomerization. A fractionated hydroisomerized stream is recycled to quench a hot hydrocracked stream prior to hydroisomerization. Sufficient quenching can inactivate the hydroisomerization catalyst bed. The hydroisomerization catalyst bed can be heated back to hydroisomerization temperature and can actively hydroisomerize again.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority from Provisional Application No. 62/357,244 filed Jun. 30, 2016, the contents of which cited application are hereby incorporated by reference in its entirety. 
     
    
     FIELD 
       [0002]    The field is the hydroisomerization of hydrocarbon streams, particularly the hydrocracking and hydroisomerization of hydrocarbon streams. 
       BACKGROUND 
       [0003]    Hydroprocessing can include processes which convert hydrocarbons in the presence of hydroprocessing catalyst and hydrogen to more valuable products. Hydrocracking is a hydroprocessing process in which hydrocarbons crack in the presence of hydrogen and hydrocracking catalyst to lower molecular weight hydrocarbons. Depending on the desired output, a hydrocracking unit may contain one or more fixed beds of the same or different catalyst. Hydroisomerization or dewaxing is a hydroprocessing process that increases the alkyl branching on a hydrocarbon backbone in the presence of hydrogen and hydroisomerization catalyst to increase cold flow properties of the hydrocarbon. 
         [0004]    Diesel fuel streams must meet cold flow property specifications particularly for winter fuel use. One cold flow property is “pour point” which is the temperature at which a hydrocarbon stream becomes semi-solid and loses its flow characteristics. A high pour point is generally associated with a higher normal paraffin content or a normal paraffin content comprising higher carbon number. Another cold flow property is “cloud point” which is the temperature below which wax in the hydrocarbon stream begins to form a cloudy appearance. The “cold filter plugging point” of diesel fuel is the temperature at which the presence of solidified waxes clogs fuel filters and injectors in engines. The wax also can accumulate on cold surfaces such as on a pipeline or heat exchanger tube and form an emulsion with water. 
         [0005]    When hydrocracking gas oil, cold flow property specifications for diesel product can limit the obtainable diesel yield by requiring a lower diesel cut point. Unconverted oil (UCO) is the material boiling above the diesel cut point. A portion of UCO can be recycled in a single-stage or two-stage hydrocracking process configuration as recycle oil or simply recovered as UCO in a once-through hydrocracking process configuration. It is desirable to decrease the product diesel cold flow property temperature values without reducing the diesel cut point to preserve more diesel yield. This can be accomplished by adding a hydroisomerization unit to decrease cold flow property temperature values without decreasing the cut point for the UCO. 
         [0006]    There is a continuing need, therefore, for improved methods and apparatuses for hydrocracking and hydroisomerizing hydrocarbon streams. 
       BRIEF SUMMARY 
       [0007]    We have discovered an apparatus and process for hydroisomerizing a hydrocarbon stream after it is hydrocracked. To achieve the desirable hydroisomerization feed temperature, the hydrocracked effluent stream is quenched with a recycle oil stream. If desired, the recycle oil stream can be cooled to such an extent to cool the hydroisomerization catalyst bed to inactivate the hydroisomerization catalyst bed during warmer months. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a schematic drawing of a hydrocracking unit. 
           [0009]      FIG. 2  is a schematic drawing of an alternative two-stage hydrocracking unit. 
           [0010]      FIG. 3  is a plot of cloud point temperature and catalyst temperature over time. 
       
    
    
     DEFINITIONS 
       [0011]    The term “communication” means that material flow is operatively permitted between enumerated components. 
         [0012]    The term “downstream communication” means that at least a portion of material flowing to the subject in downstream communication may operatively flow from the object with which it communicates. 
         [0013]    The term “upstream communication” means that at least a portion of the material flowing from the subject in upstream communication may operatively flow to the object with which it communicates. 
         [0014]    The term “direct communication” means that flow from the upstream component enters the downstream component without undergoing a compositional change due to physical fractionation or chemical conversion. 
         [0015]    The term “column” means a distillation column or columns for separating one or more components of different volatilities. Unless otherwise indicated, each column includes a condenser on an overhead of the column to condense and reflux a portion of an overhead stream back to the top of the column and a reboiler at a bottom of the column to vaporize and send a portion of a bottoms stream back to the bottom of the column. Absorber and scrubbing columns do not include a condenser on an overhead of the column to condense and reflux a portion of an overhead stream back to the top of the column and a reboiler at a bottom of the column to vaporize and send a portion of a bottoms stream back to the bottom of the column. Feeds to the columns may be preheated. The overhead pressure is the pressure of the overhead vapor at the vapor outlet of the column. The bottom temperature is the liquid bottom outlet temperature. Overhead lines and bottoms lines refer to the net lines from the column downstream of any reflux or reboil to the column unless otherwise indicated. Stripping columns omit a reboiler at a bottom of the column and instead utilize feed preheat and provide additional heating requirements and separation impetus from a fluidized inert vaporous media such as steam. 
         [0016]    As used herein, the term “True Boiling Point” (TBP) means a test method for determining the boiling point of a material which corresponds to ASTM D-2892 for the production of a liquefied gas, distillate fractions, and residuum of standardized quality on which analytical data can be obtained, and the determination of yields of the above fractions by both mass and volume from which a graph of temperature versus mass % or liquid volume % distilled is produced using fifteen theoretical plates in a column with a 5:1 reflux ratio. 
         [0017]    As used herein, the term “initial boiling point” (IBP) means the temperature at which the sample begins to boil using ASTM D-86. 
         [0018]    As used herein, the term “T5” or “T95” means the temperature at which 5 volume percent or 95 volume percent, as the case may be, respectively, of the sample boils using ASTM D-86 or ASTM D-1160. 
         [0019]    As used herein, the term “diesel boiling range” means hydrocarbons boiling in the range of between about 132° C. (270° F.) and the diesel cut point between about 343° C. (650° F.) and about 399° C. (750° F.) using the TBP distillation method. 
         [0020]    As used herein, the term “separator” means a vessel which has an inlet and at least an overhead vapor outlet and a bottoms liquid outlet and may also have an aqueous stream outlet from a boot. A flash drum is a type of separator which may be in downstream communication with a separator which latter may be operated at higher pressure. 
       DETAILED DESCRIPTION 
       [0021]    Breaking carbon-carbon bonds is an endothermic reaction. However, hydrotreating reactions that inevitably occur in conjunction with cracking reactions such as the re-hydrogenation of hydrocracking reaction intermediates are exothermic which cause the hydrocracked effluent to be higher in temperature than the feed temperature. The hydrocracked effluent is typically at a temperature higher than the optimal feed temperature for the hydroisomerization reaction. Hence, we propose to quench the hydrocracked effluent with recycle oil before it enters the hydroisomerization reaction zone. This will lower the temperature of the hydrocracked effluent and also subject the unconverted recycle oil to a second stage of hydroisomerization reaction. 
         [0022]    We have also found that by cooling the recycle oil to a sufficiently low temperature and feeding it to the hydroisomerization reaction zone, the hydroisomerization catalyst can be inactivated. Consequently, the hydroisomerization catalyst bed can be located in the same reactor vessel downstream of a hydrocracking catalyst bed. The hydroisomerization catalyst bed can be turned off during the warmer seasons when cold flow properties are not so stringent to preserve more of the valuable diesel product. 
         [0023]    The process and apparatus has been demonstrated in pilot plant studies of being capable of meeting the Arctic Diesel Specifications of a Cloud Point Temperature of −40° C. and Pour Point of −45° C., while providing an increase in distillate yield in the range of 4 to 5 wt % relative to the next best alternative case in which the diesel cut point is reduced to achieve the same cold flow specifications. 
         [0024]    The apparatus and process  10  for hydrocracking and hydroisomerizing a hydrocarbon stream comprise a hydroprocessing unit  12  and a fractionation section  14 . A hydrocarbonaceous stream in hydrocarbon line  18  and a make-up hydrogen stream hydrogen line  24  are fed to the hydroprocessing unit  12 . 
         [0025]    In one aspect, the process and apparatus described herein are particularly useful for hydroprocessing a hydrocarbon feed stream comprising a hydrocarbonaceous feedstock. Illustrative hydrocarbonaceous feed stocks include hydrocarbon streams having initial boiling points (IBP) above about 288° C. (550° F.), such as atmospheric gas oils, vacuum gas oil (VGO) having T5 and T95 between about 315° C. (600° F.) and about 600° C. (1100° F.), deasphalted oil, coker distillates, straight run distillates, pyrolysis-derived oils, high boiling synthetic oils, cycle oils, hydrocracked feeds, catalytic cracker distillates, atmospheric residue having an IBP at or above about 343° C. (650° F.) and vacuum residue having an IBP above about 510° C. (950° F.). 
         [0026]    A hydrogen stream in hydrogen line  22  is partially provided by the make-up hydrogen stream from line  24 . The hydrogen stream may join the hydrocarbonaceous stream in feed line  18  to provide a hydrocarbon feed stream in a hydrocarbon feed line  26 . The hydrocarbon feed stream in the hydrocarbon feed line  26  may be heated by heat exchange with a hydroisomerized effluent stream in line  48  and in a fired heater. The heated hydrocarbon feed stream in line  28  may be fed to a hydrotreating reactor  30 . 
         [0027]    Hydrotreating is a process wherein hydrogen is contacted with hydrocarbon in the presence of hydrotreating catalysts which are primarily active for the removal of heteroatoms, such as sulfur, nitrogen, oxygen and metals from the hydrocarbon feedstock. In hydrotreating, hydrocarbons with double and triple bonds such as olefins may be saturated. Aromatics may also be saturated. Some hydrotreating processes are specifically designed to saturate aromatics. 
         [0028]    The hydrotreating reactor  30  may comprise a guard bed of hydrotreating catalyst followed by one or more beds of higher activity hydrotreating catalyst. The guard bed filters particulates and reacts with contaminants in the hydrocarbon feed stream such as metals like nickel, vanadium, silicon and arsenic which are detrimental to the higher activity hydrotreating catalyst. The guard bed may comprise material similar to the hydrotreating catalyst. 
         [0029]    Suitable hydrotreating catalysts for use in the present invention are any known conventional hydrotreating catalysts and include those which are comprised of at least one Group VIII metal, preferably iron, cobalt and nickel, more preferably cobalt and/or nickel and at least one Group VI metal, preferably molybdenum and tungsten, 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 palladium and platinum. More than one type of hydrotreating catalyst may be used in the same hydrotreating reactor  30 . The Group VIII metal is typically present in an amount ranging from about 2 to about 20 wt %, preferably from about 4 to about 12 wt %. The Group VI metal will typically be present in an amount ranging from about 1 to about 25 wt %, preferably from about 2 to about 25 wt %. 
         [0030]    Preferred reaction conditions in the hydrotreating reactor  30  include a temperature from about 290° C. (550° F.) to about 455° C. (850° F.), suitably 316° C. (600° F.) to about 427° C. (800° F.), a pressure from about 2.1 MPa (gauge) (300 psig), preferably 4.1 MPa (gauge) (600 psig) to about 20.6 MPa (gauge) (3000 psig), suitably 12.4 MPa (gauge) (1800 psig), a liquid hourly space velocity of the fresh hydrocarbonaceous feedstock from about 0.1 hr −1 , suitably 4 hr −1 , to about 8 hr −1 , preferably from about 1.5 to about 3.5 hr −1 , and a hydrogen rate of about 168 Nm 3 /m 3  (1,000 scf/bbl), to about 1,011 Nm 3 /m 3  oil (6,000 scf/bbl), preferably about 168 Nm 3 /m 3  oil (1,000 scf/bbl) to about 674 Nm 3 /m 3  oil (4,000 scf/bbl), with a hydrotreating catalyst or a combination of hydrotreating catalysts. 
         [0031]    The hydrotreating reactor  30  provides a hydrotreated stream that exits the hydrotreating reactor  30  in a hydrotreating effluent line  32 . The hydrogen gas laden with ammonia and hydrogen sulfide may be removed from the hydrotreated hydrocarbon stream in a separator, but the hydrotreated hydrocarbon stream is typically fed directly to the hydrocracking reactor  40  without separation. The hydrotreated hydrocarbon feed stream may be mixed with a hydrocracking hydrogen stream in a hydrocracking hydrogen line  33  from the hydrogen line  22  and optionally a recycle oil stream from a second recycle oil line  184  and is fed through a first inlet  32   i  to the hydrocracking reactor  40  to be hydrocracked. 
         [0032]    Hydrocracking refers to a process in which hydrocarbons crack in the presence of hydrogen to lower molecular weight hydrocarbons. The hydrocracking reactor  40  may be a fixed bed reactor that comprises one or more vessels, single or multiple catalyst beds  42  in each vessel, and various combinations of hydrotreating catalyst, hydroisomerization catalyst and/or hydrocracking catalyst in one or more vessels. It is contemplated that the hydrocracking reactor  40  be operated in a continuous liquid phase in which the volume of the liquid hydrocarbon feed is greater than the volume of the hydrogen gas. The hydrocracking reactor  40  may also be operated in a conventional continuous gas phase, a moving bed or a fluidized bed hydroprocessing reactor. 
         [0033]    The hydrocracking reactor may provide a total conversion of at least about 20 vol % and typically greater than about 60 vol % of the hydrocarbon feed to products boiling below the diesel cut point. A hydrocracking reactor may operate at partial conversion of more than about 30 vol % or full conversion of at least about 90 vol % of the feed based on total conversion. A hydrocracking reactor may be operated at mild hydrocracking conditions which will provide about 20 to about 60 vol %, preferably about 20 to about 50 vol %, total conversion of the hydrocarbon feed stream to product boiling below the diesel-cut point. The diesel cut point can be selected to maximize the production of diesel. 
         [0034]    The hydrocracking reactor  40  comprises a plurality of catalyst beds  42 . If the hydroprocessing unit  12  does not include a hydrotreating reactor  30 , the first bed in the hydrocracking reactor  40  may include hydrotreating catalyst for the purpose of saturating, demetallizing, desulfurizing, deoxygenating or denitrogenating the hydrocarbon feed before it is hydrocracked with hydrocracking catalyst in subsequent vessels or catalyst beds  42  in the hydrocracking reactor  40 . Otherwise, the first or an upstream bed in the hydrocracking reactor  40  may comprise a first hydrocracking catalyst bed  42   a.    
         [0035]    A hydrocracking catalyst may utilize amorphous silica-alumina bases or low-level zeolite bases combined with one or more Group VIII or Group VIB metal hydrogenating components if mild hydrocracking is desired to produce a balance of middle distillate and gasoline. In another aspect, when middle distillate is significantly preferred in the converted product over gasoline production, partial or full hydrocracking may be performed in the first hydrocracking reactor  40  with a catalyst which comprises, in general, any crystalline zeolite cracking base upon which is deposited a Group VIII metal hydrogenating component. Additional hydrogenating components may be selected from Group VIB for incorporation with the zeolite base. 
         [0036]    The zeolite cracking bases are sometimes referred to in the art as molecular sieves and are usually composed of silica, alumina and one or more exchangeable cations such as sodium, magnesium, calcium, rare earth metals, etc. They are further characterized by crystal pores of relatively uniform diameter between about 4 and about 14 Angstroms (10 −10  meters). It is preferred to employ zeolites having a relatively high silica/alumina mole ratio between about 3 and about 12. Suitable zeolites found in nature include, for example, mordenite, stilbite, heulandite, ferrierite, dachiardite, chabazite, erionite and faujasite. Suitable synthetic zeolites include, for example, the B, X, Y and L crystal types, e.g., synthetic faujasite and mordenite. The preferred zeolites are those having crystal pore diameters between about 8 and 12 Angstroms (10 −10  meters), wherein the silica/alumina mole ratio is about 4 to 6. One example of a zeolite falling in the preferred group is synthetic Y molecular sieve. 
         [0037]    The natural occurring zeolites are normally found in a sodium form, an alkaline earth metal form, or mixed forms. The synthetic zeolites are nearly always prepared first in the sodium form. In any case, for use as a cracking base it is preferred that most or all of the original zeolitic monovalent metals be ion-exchanged with a polyvalent metal and/or with an ammonium salt followed by heating to decompose the ammonium ions associated with the zeolite, leaving in their place hydrogen ions and/or exchange sites which have actually been decationized by further removal of water. Hydrogen or “decationized” Y zeolites of this nature are more particularly described in U.S. Pat. No. 3,100,006. 
         [0038]    Mixed polyvalent metal-hydrogen zeolites may be prepared by ion-exchanging first with an ammonium salt, then partially back exchanging with a polyvalent metal salt and then calcining. In some cases, as in the case of synthetic mordenite, the hydrogen forms can be prepared by direct acid treatment of the alkali metal zeolites. In one aspect, the preferred cracking bases are those which are at least about 10 wt %, and preferably at least about 20 wt %, metal-cation-deficient, based on the initial ion-exchange capacity. In another aspect, a desirable and stable class of zeolites is one wherein at least about 20 wt % of the ion exchange capacity is satisfied by hydrogen ions. 
         [0039]    The active metals employed in the preferred hydrocracking catalysts of the present invention as hydrogenation components are those of Group VIII, i.e., iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium and platinum. In addition to these metals, other promoters may also be employed in conjunction therewith, including the metals of Group VIB, e.g., molybdenum and tungsten. The amount of hydrogenating metal in the catalyst can vary within wide ranges. Broadly speaking, any amount between about 0.05 wt % and about 30 wt % may be used. In the case of the noble metals, it is normally preferred to use about 0.05 to about 2 wt % noble metal. 
         [0040]    The method for incorporating the hydrogenation metal is to contact the base material with an aqueous solution of a suitable compound of the desired metal wherein the metal is present in a cationic form. Following addition of the selected hydrogenation metal or metals, the resulting catalyst powder is then filtered, dried, pelleted with added lubricants, binders or the like if desired, and calcined in air at temperatures of, e.g., about 371° C. (700° F.) to about 648° C. (1200° F.) in order to activate the catalyst and decompose ammonium ions. Alternatively, the base component may first be pelleted, followed by the addition of the hydrogenation component and activation by calcining. 
         [0041]    The foregoing catalysts may be employed in undiluted form, or the powdered catalyst may be mixed and co-pelleted with other relatively less active catalysts, diluents or binders such as alumina, silica gel, silica-alumina co-gels, activated clays and the like in proportions ranging between about 5 and about 90 wt %. These diluents may be employed as such or they may contain a minor proportion of an added hydrogenating metal such as a Group VIB and/or Group VIII metal. Additional metal promoted hydrocracking catalysts may also be utilized in the process of the present invention which comprises, for example, aluminophosphate molecular sieves, crystalline chromosilicates and other crystalline silicates. Crystalline chromosilicates are more fully described in U.S. Pat. No. 4,363,718. 
         [0042]    By one approach, the hydrocracking conditions may include a temperature from about 290° C. (550° F.) to about 468° C. (875° F.), preferably 343° C. (650° F.) to about 445° C. (833° F.), a pressure from about 4.8 MPa (gauge) (700 psig) to about 20.7 MPa (gauge) (3000 psig), a liquid hourly space velocity (LHSV) from about 0.4 to less than about 2.5 hr −1  and a hydrogen rate of about 421 Nm 3 /m 3  (2,500 scf/bbl) to about 2,527 Nm 3 /m 3  oil (15,000 scf/bbl). If mild hydrocracking is desired, conditions may include a temperature from about 315° C. (600° F.) to about 441° C. (825° F.), a pressure from about 5.5 MPa (gauge) (800 psig) to about 13.8 MPa (gauge) (2000 psig) or more typically about 6.9 MPa (gauge) (1000 psig) to about 11.0 MPa (gauge) (1600 psig), a liquid hourly space velocity (LHSV) from about 0.5 to about 2 hr −1  and preferably about 0.7 to about 1.5 hr −1  and a hydrogen rate of about 421 Nm 3 /m 3  oil (2,500 scf/bbl) to about 1,685 Nm 3 /m 3  oil (10,000 scf/bbl). 
         [0043]    The hydrotreated hydrocarbon feed stream is hydrocracked over the first hydrocracking catalyst bed  42   a  in the presence of a hydrogen stream to provide a hydrocracked stream. Subsequent catalyst beds  42  in the hydrocracking reactor may comprise hydrocracking catalyst over which additional hydrocracking occurs to the hydrocracked stream. Hydrogen manifold  44  may deliver supplemental hydrogen streams to one, some or each of the catalyst beds  42 . In an aspect, the supplemental hydrogen is added to each of the catalyst beds  42  at an interstage location between adjacent beds, so supplemental hydrogen is mixed with hydroprocessed effluent exiting from the upstream catalyst bed  42  before entering the downstream catalyst bed  42 . 
         [0044]    At least one downstream catalyst bed may comprise a first hydroisomerization catalyst bed  42   b.  The hydrocracked stream is hydroisomerized over a first hydroisomerization catalyst bed in the presence of a supplemental hydrogen stream from a manifold branch line  44   b  to provide a hydroisomerized stream. The first hydrocracking catalyst bed  42   a  and the first hydroisomerization catalyst bed  42   b  may be located in the first hydrocracking reactor  40 . Additional hydrocracking catalyst beds  42  may be located between the first hydrocracking catalyst bed  42   a  and the first hydroisomerization catalyst bed  42   b.    
         [0045]    The hydroisomerization catalyst can comprise an unbound 10-member ring pore, one-dimensional zeolite in combination with a low surface area metal oxide refractory binder, both of which are selected to obtain a high ratio of micropore surface area to total surface area. Alternatively, the zeolite has a low silica to alumina ratio. Suitable catalysts include 10-member ring pore zeolites, such as EU-1, ZSM-35 (or ferrierite), ZSM-11, ZSM-57, NU-87, SAPO-11, and ZSM-22. Preferred materials are EU-2, EU-11, ZBM-30, ZSM-48, or ZSM-23. ZSM-48 is most preferred. Note that a zeolite having the ZSM-23 structure with a silica to alumina ratio of from about 20:1 to about 40:1 can sometimes be referred to as SSZ-32. Other molecular sieves that are isostructural with the above materials include Theta-1, NU-10, EU-13, KZ-1, and NU-23. 
         [0046]    The hydroisomerization catalyst can further include a metal hydrogenation function, such as a Group VI or Group VIII metal, and suitably a Group VIII noble metal. The metal hydrogenation component is typically a Group VI and/or a Group VIII metal. The metal hydrogenation component may be a Group VIII noble metal. Preferably, the metal hydrogenation component is a combination of a non-noble Group VIII metal with a Group VI metal. Suitable combinations can include nickel, cobalt, or iron with molybdenum or tungsten, preferably nickel with molybdenum or tungsten. 
         [0047]    The metal hydrogenation component may be added to the catalyst in any convenient manner. One technique for adding the metal hydrogenation component is by incipient wetness. For example, after combining a zeolite and a binder, the combined zeolite and binder can be extruded into catalyst particles. These catalyst particles can then be exposed to a solution containing a suitable metal precursor. Alternatively, metal can be added to the catalyst by ion exchange, where a metal precursor is added to a mixture of zeolite (or zeolite and binder) prior to extrusion. 
         [0048]    The amount of metal in the catalyst can be at least about 0.1 wt % to about 10 wt % based on catalyst. Preferably, the hydroisomerization catalysts have a low ratio of silica to alumina. In various embodiments, the ratio of silica to alumina can be from 30:1 to 200:1, 60:1 to 110:1, or 70:1 to 100:1. The hydroisomerization catalysts may also include an optional binder having a low surface area such as 100 m 2 /g or less, or 80 m 2 /g or less, or 70 m 2 /g or less. A zeolite can be combined with binder by starting with powders of both the zeolite and binder, combining and mulling the powders with added water to form a mixture, and then extruding the mixture to produce a bound catalyst of a desired size. Extrusion aids can also be used to modify the extrusion flow properties of the zeolite and binder mixture. The amount of framework alumina in the catalyst may range from 0.1 to 3.33 wt %, or 0.1 to 2.7 wt %, or 0.2 to 2 wt %, or 0.3 to 1 wt %. 
         [0049]    The hydroisomerization catalyst maintains catalytic activity even if substantial sulfur is present in the hydrocracked stream such as when hydrogen sulfide gas is not removed from the hydrogen stream following hydrotreating or hydrocracking. The hydrocracked stream may contain up to about 4.0 wt % at least about 0.1 wt % of sulfur and be effectively hydroisomerized. Sulfur content may be measured by standard ASTM methods D2622. 
         [0050]    Process conditions in the hydroisomerization catalyst bed may include a temperature of from 200 to 450° C., preferably 270 to 400° C., a hydrogen partial pressure of from 1.8 mPa (250 psi) to 34.6 mPa (5000 psi), preferably 4.8 mPa (667 psi) to 20.8 mPa (3005 psi), a liquid hourly space velocity of from 0.2 to 10 v/v/hr, preferably 4 to 8 v/v/hr, and a hydrogen circulation rate of from 35.6 Nm 3 /m 3  (200 scf/B), to 1781 Nm 3 /m 3  (10,000 scf/B), preferably 890 Nm 3 /m 3  (5000 scf/B) to 1424 Nm 3 /m 3  (8000 scf/B). The hydroisomerization process is conducted at a lower temperature than the hydrocracking process and at a lower temperature than the temperature of the effluent from the first hydrocracking catalyst bed  42   a  or other downstream hydrocracking catalyst bed(s)  42  comprising the hydrocracked stream. Accordingly, a first fractionated stream is recycled to the first isomerization catalyst bed  42   b  to quench the hydrocracked stream entering the first hydroisomerization catalyst bed  42   b  from the superjacent catalyst bed  42 . The first fractionated stream in line  46  may be cooled in a heat exchanger  45  before entering the first isomerization catalyst bed  42   b.  The first fractionated stream in line  46  may be fed to the first hydrocracking reactor  40  through an intermediate inlet  46   i  which is downstream of the first inlet  32   i  to the first hydrocracking catalyst bed  42   a.  The first fractionated stream may be fed from line  46  to the intermediate inlet  46   i  after receiving a supplement hydrogen stream from the manifold branch  44   b  from the hydrogen manifold  44  to the first isomerization catalyst bed  42   b.  The first fractionated stream reduces the overall temperature of the combined stream comprising the hydrocracked stream, the supplemental hydrogen stream and the first fractionated stream entering the first hydroisomerization catalyst bed to a desired hydroisomerization reaction temperature. 
         [0051]    The addition of the second fractionated stream to the first catalyst bed  42   b  increases the residence time of the hydrocracked product on the hydroisomerization catalyst and increases the space velocity on all the downstream catalyst beds  42  to about 6 to about 10 hr −1 . The catalyst volume can be increased to hold the space velocity to typical value of about 5 to about 8 hr −1  if desired. 
         [0052]    In summer months, when cold flow specifications are not as stringent, the first hydroisomerization catalyst bed  42   b  can be inactivated by cooling the first fractionated stream in line  46  sufficiently, so the temperature of the combined stream entering the first hydrocracking catalyst bed  42   b  has an inactivation temperature between about 274° C. (525° F.) and about 302° C. (575° F.) or about 307° C. (585° F.), preferably less than about 288° C. (550° F.) and certainly less than about 260° C. (500° F.). We have found at these temperatures, the hydroisomerization catalyst is inactive, such that it does not chemically alter the composition of the hydrocracked stream entering the first hydroisomerization catalyst bed. We have also found that the hydroisomerization catalyst can be reactivated by heating the combined stream entering the first hydroisomerization catalyst bed  42   b  to above the inactivation temperature. The reactivated hydroisomerization catalyst bed  42   b  has a hydroisomerization catalyst activity substantially the same as it was before it was inactivated. Partial inactivation of the hydroisomerization catalyst bed can be achieved by reducing the temperature of the combined stream sufficiently to reduce the temperature of the first hydroisomerization catalyst bed  42   b  to 22° C. (40° F.) below hydroisomerization reaction temperature which can fluctuate depending on the activity of the hydrocracking catalyst, space velocity, etc. 
         [0053]    The hydroisomerized stream from the first hydroisomerization catalyst bed  42   b  may enter into a subsequent hydrocracking catalyst bed(s)  42  to be hydrocracked over hydrocracking catalyst over a supplemental hydrogen stream from the hydrogen manifold  44  and/or enter into a subsequent hydroisomerization catalyst bed(s)  42  to be hydroisomerized over hydroisomerization catalyst over a supplemental hydrogen stream from the hydrogen manifold  44  or be taken directly to the fractionation section  14 . Even if this stream from the first hydroisomerization catalyst bed  42   b  is subsequently hydrocracked, it is still considered a hydroisomerized stream. 
         [0054]    The hydroisomerized stream may be separated in the fractionation section  14  in downstream communication with the hydrocracking reactor  40 . The fractionation section  14  comprises one or more separators and fractionation columns in downstream communication with the hydrocracking reactor  40 . 
         [0055]    The hydroisomerized stream in hydroisomerized line  48  may in an aspect be heat exchanged with the hydrocarbon feed stream in line  26  to be cooled before entering a hot separator  50 . The hot separator separates the hydroprocessed effluent stream to provide a hydrocarbonaceous, hot gaseous stream in a hot overhead line  52  and a hydrocarbonaceous, hot liquid stream in a hot bottoms line  54 . The hot separator  50  may be in downstream communication with the hydrocracking reactor  40 . The hot separator  50  operates at about 177° C. (350° F.) to about 371° C. (700° F.) and preferably operates at about 232° C. (450° F.) to about 315° C. (600° F.). The hot separator  50  may be operated at a slightly lower pressure than the hydrocracking reactor  40  accounting for pressure drop through intervening equipment. The hot separator  50  may be operated at pressures between about 3.4 MPa (gauge) (493 psig) and about 20.4 MPa (gauge) (2959 psig). The hydrocarbonaceous, hot gaseous separated stream in the hot overhead line  52  may have a temperature of the operating temperature of the hot separator  50 . 
         [0056]    The hot gaseous stream in the hot overhead line  52  may be cooled before entering a cold separator  56 . As a consequence of the reactions taking place in the hydrocracking reactor  40  wherein nitrogen, chlorine and sulfur are removed from the feed, ammonia and hydrogen sulfide are formed. At a characteristic sublimation temperature, ammonia and hydrogen sulfide will combine to form ammonium bisulfide and ammonia, and chlorine will combine to form ammonium chloride. Each compound has a characteristic sublimation temperature that may allow the compound to coat equipment, particularly heat exchange equipment, impairing its performance. To prevent such deposition of ammonium bisulfide or ammonium chloride salts in the hot overhead line  36  transporting the hot gaseous stream, a suitable amount of wash water may be introduced into the hot overhead line  52  upstream of a cooler at a point in the hot overhead line where the temperature is above the characteristic sublimation temperature of either compound. 
         [0057]    The hot gaseous stream may be separated in the cold separator  56  to provide a cold gaseous stream comprising a hydrogen-rich gas stream in a cold overhead line  58  and a cold liquid stream in a cold bottoms line  60 . The cold separator  56  serves to separate hydrogen rich gas from hydrocarbon liquid in the hydroisomerized stream for recycle to the hydrocracking reactor  40  in the cold overhead line  58 . The cold separator  56 , therefore, is in downstream communication with the hot overhead line  52  of the hot separator  50  and the hydrocracking reactor  40 . The cold separator  56  may be operated at about 100° F. (38° C.) to about 150° F. (66° C.), suitably about 115° F. (46° C.) to about 145° F. (63° C.), and just below the pressure of the hydrocracking reactor  40  and the hot separator  50  accounting for pressure drop through intervening equipment to keep hydrogen and light gases in the overhead and normally liquid hydrocarbons in the bottoms. The cold separator  56  may be operated at pressures between about 3 MPa (gauge) (435 psig) and about 20 MPa (gauge) (2,901 psig). The cold separator  56  may also have a boot for collecting an aqueous phase. The cold liquid stream in the cold bottoms line  60  may have a temperature of the operating temperature of the cold separator  56 . 
         [0058]    The cold gaseous stream in the cold overhead line  58  is rich in hydrogen. Thus, hydrogen can be recovered from the cold gaseous stream. The cold gaseous stream in the cold overhead line  58  may be passed through a trayed or packed recycle scrubbing column  62  where it is scrubbed by means of a scrubbing extraction liquid such as an aqueous solution fed by line  64  to remove acid gases including hydrogen sulfide and carbon dioxide by extracting them into the aqueous solution. Preferred aqueous solutions include lean amines such as alkanolamines DEA, MEA, and MDEA. Other amines can be used in place of or in addition to the preferred amines. The lean amine contacts the cold gaseous stream and absorbs acid gas contaminants such as hydrogen sulfide and carbon dioxide. The resultant “sweetened” cold gaseous stream is taken out from an overhead outlet of the recycle scrubber column  62  in a recycle scrubber overhead line  68 , and a rich amine is taken out from the bottoms at a bottom outlet of the recycle scrubber column in a recycle scrubber bottoms line  66 . The spent scrubbing liquid from the bottoms may be regenerated and recycled back to the recycle scrubbing column  62  in line  64 . The scrubbed hydrogen-rich stream emerges from the scrubber via the recycle scrubber overhead line  68  and may be compressed in a recycle compressor  70  to provide the hydrogen stream in the hydrogen line  22  and a supplemental hydrogen stream in a supplemental hydrogen manifold  44 . The scrubbed hydrogen-rich stream in the scrubber overhead line  68  may be supplemented with make-up hydrogen stream in the make-up line  24  upstream or downstream of the compressor  70 . The recycle hydrogen manifold  44  feeds portions of the recycle hydrogen stream to catalyst beds  42  in the hydrocracking reactor  40  to control the inlet temperature of the downstream catalyst beds. The recycle scrubbing column  62  may be operated with a gas inlet temperature between about 38° C. (100° F.) and about 66° C. (150° F.) and an overhead pressure of about 3 MPa (gauge) (435 psig) to about 20 MPa (gauge) (2900 psig). 
         [0059]    The hydrocarbonaceous hot liquid stream in the hot bottoms line  60  may be fractionated. In an aspect, the hot liquid stream in the hot bottoms line  54  may be let down in pressure and flashed in a hot flash drum  80  to provide a flash hot gaseous stream of light ends in a flash hot overhead line  82  and a flash hot liquid stream in a flash hot bottoms line  84 . The hot flash drum  80  may be in direct, downstream communication with the hot bottoms line  54  and in downstream communication with the hydrocracking reactor  40 . In an aspect, light gases such as hydrogen sulfide may be stripped from the flash hot liquid stream in the flash hot bottoms line  84 . Accordingly, a stripping column  100  may be in downstream communication with the hot flash drum  80  and the hot flash bottoms line  84 . 
         [0060]    The hot flash drum  80  may be operated at the same temperature as the hot separator  50  but at a lower pressure of between about 1.4 MPa (gauge) (200 psig) and about 6.9 MPa (gauge) (1000 psig), suitably no more than about 3.8 MPa (gauge) (550 psig). The flash hot liquid stream in the flash hot bottoms line  84  may be further fractionated in the fractionation section  14 . The flash hot liquid stream in the flash hot bottoms line  84  may have a temperature of the operating temperature of the hot flash drum  80 . 
         [0061]    In an aspect, the cold liquid stream in the cold bottoms line  60  may be directly fractionated. In a further aspect, the cold liquid stream may be let down in pressure and flashed in a cold flash drum  86  to separate the cold liquid stream in the cold bottoms line  60 . The cold flash drum  86  may be in direct downstream communication with the cold bottoms line  60  of the cold separator  56  and in downstream communication with the hydrocracking reactor  40 . 
         [0062]    In a further aspect, the flash hot gaseous stream in the flash hot overhead line  82  may be fractionated in the fractionation section  14 . In a further aspect, the flash hot gaseous stream may be cooled and also separated in the cold flash drum  86 . The cold flash drum  86  may separate the cold liquid stream in line  60  and/or the flash hot gaseous stream in the flash hot overhead line  82  to provide a flash cold gaseous stream in a flash cold overhead line  88  and a flash cold liquid stream in a cold flash bottoms line  90 . In an aspect, light gases such as hydrogen sulfide may be stripped from the flash cold liquid stream in the flash cold bottoms line  90 . Accordingly, a stripping column  100  may be in downstream communication with the cold flash drum  86  and the cold flash bottoms line  90 . 
         [0063]    The cold flash drum  86  may be in downstream communication with the cold bottoms line  60  of the cold separator  56 , the hot flash overhead line  82  of the hot flash drum  80  and the hydrocracking reactor  40 . The flash cold liquid stream in the cold bottoms line  60  and the flash hot gaseous stream in the hot flash overhead line  82  may enter into the cold flash drum  86  either together or separately. In an aspect, the hot flash overhead line  82  joins the cold bottoms line  60  and feeds the flash hot gaseous stream and the cold liquid stream together to the cold flash drum  86  in a cold flash feed line  92 . The cold flash drum  86  may be operated at the same temperature as the cold separator  56  but typically at a lower pressure of between about 1.4 MPa (gauge) (200 psig) and about 6.9 MPa (gauge) (1000 psig) and preferably between about 3.0 MPa (gauge) (435 psig) and about 3.8 MPa (gauge) (550 psig). A flashed aqueous stream may be removed from a boot in the cold flash drum  86 . The flash cold liquid stream in the flash cold bottoms line  90  may have the same temperature as the operating temperature of the cold flash drum  86 . The flash cold gaseous stream in the flash cold overhead line  88  contains substantial hydrogen that may be recovered. 
         [0064]    The fractionation section  14  may further include the stripping column  100 , a atmospheric fractionation column  130  and a vacuum fractionation column  160 . The stripping column  100  may be in downstream communication with a bottoms line in the fractionation section  14  for stripping volatiles from a hydroisomerized stream. For example, the stripping column  100  may be in downstream communication with the hot bottoms line  54 , the flash hot bottoms line  84 , the cold bottoms line  60  and/or the cold flash bottoms line  90 . In an aspect, the stripping column  100  may be a vessel that contains a cold stripping column  102  and a hot stripping column  104  with a wall that isolates each of the stripping columns  102 ,  104  from the other. The cold stripping column  102  may be in downstream communication with the hydrocracking reactor  40 , the cold bottoms line  60  and, in an aspect, the flash cold bottoms line  90  for stripping the cold liquid stream. The hot stripping column  104  may be in downstream communication with the hydrocracking reactor  40  and the hot bottoms line  54  and, in an aspect, the flash hot bottoms line  84  for stripping a hot liquid stream which is hotter than the cold liquid stream. The hot liquid stream may be hotter than the cold liquid stream, by at least 25° C. and preferably at least 50° C. 
         [0065]    The flash cold liquid stream comprising a hydroisomerized stream in the flash cold bottoms line  90  may be heated and fed to the cold stripping column  102  at an inlet which may be in a top half of the column. The flash cold liquid stream which comprises a hydroisomerized stream may be stripped of gases in the cold stripping column  102  with a cold stripping media which is an inert gas such as steam from a cold stripping media line  106  to provide a cold stripper gaseous stream of naphtha, hydrogen, hydrogen sulfide, steam and other gases in a cold stripper overhead line  108  and a cold stripped stream in a cold stripper bottoms line  110 . The cold stripper gaseous stream in the cold stripper overhead line  108  may be condensed and separated in a receiver  112 . A stripper net overhead line  114  from the receiver  112  carries a net stripper gaseous stream for further recovery of LPG and hydrogen in a light material recovery unit. Unstabilized liquid naphtha from the bottoms of the receiver  112  may be split between a reflux portion refluxed to the top of the cold stripping column  102  and a liquid stripper overhead stream which may be transported in a condensed stripper overhead line  116  to further recovery or processing. A sour water stream may be collected from a boot of the overhead receiver  112 . 
         [0066]    The cold stripping column  102  may be operated with a bottoms temperature between about 149° C. (300° F.) and about 288° C. (550° F.), preferably no more than about 260° C. (500° F.), and an overhead pressure of about 0.35 MPa (gauge) (50 psig), preferably no less than about 0.70 MPa (gauge) (100 psig), to no more than about 2.0 MPa (gauge) (290 psig). The temperature in the overhead receiver  112  ranges from about 38° C. (100° F.) to about 66° C. (150° F.) and the pressure is essentially the same as in the overhead of the cold stripping column  102 . 
         [0067]    The cold stripped stream in the cold stripper bottoms line  110  may comprise predominantly naphtha and kerosene boiling materials. A portion or all of the cold stripped stream in line  110  may be recycled in a cold stripper transfer line  111  to the first isomerization catalyst bed  42   b  as a first fractionated stream in the first recycle line  46 . A remaining portion or all of the cold stripped stream in the cold fractionator feed line  113  comprising a hydroisomerized stream from the cold stripper bottoms line  110  may be heated and fed to the atmospheric fractionation column  130 . The atmospheric fractionation column  130  may be in downstream communication with the cold stripper bottoms line  110  of the cold stripping column  102  and the stripping column  100 . In an aspect, the atmospheric fractionation column  130  may comprise more than one fractionation column. The atmospheric fractionation column  130  may be in downstream communication with one, some or all of the hot separator  50 , the cold separator  56 , the hot flash drum  80  and the cold flash drum  86 . 
         [0068]    The flash hot liquid stream comprising a hydroisomerized stream in the hot flash bottoms line  90  may be fed to the hot stripping column  104  near a top thereof. The flash hot liquid stream may be stripped in the hot stripping column  104  of gases with a hot stripping media which is an inert gas such as steam from a line  120  to provide a hot stripper overhead stream of naphtha, hydrogen, hydrogen sulfide, steam and other gases in a hot stripper overhead line  118  and a hot stripped stream in a hot stripper bottoms line  122 . The hot stripper overhead line  118  may be condensed and a portion refluxed to the hot stripping column  104 . However, in the embodiment of  FIG. 1 , the hot stripper overhead stream in the hot stripper overhead line  118  from the overhead of the hot stripping column  104  may be fed into the cold stripping column  102  directly in an aspect without first condensing or refluxing. The inlet for the cold flash bottoms line  90  carrying the flash cold liquid stream may be at a higher elevation than the inlet for the hot stripper overhead line  118 . The hot stripping column  104  may be operated with a bottoms temperature between about 160° C. (320° F.) and about 360° C. (680° F.) and an overhead pressure of about 0.35 MPa (gauge) (50 psig), preferably about 0.70 MPa (gauge) (100 psig), to about 2.0 MPa (gauge) (292 psig). 
         [0069]    At least a portion of the hot stripped stream comprising a hydroisomerized stream in the hot stripped bottoms line  122  may be taken in a hot fractionator feed line  123 , heated and fed to the atmospheric fractionation column  130 . Another portion of the hot stripped stream in the hot stripped bottoms line  122  may be transferred in a hot transfer line  125  to the first recycle line  46  for recycle as a first fractionated stream to the first isomerization catalyst bed  42   b  . The atmospheric fractionation column  130  may be in downstream communication with the hot stripped bottoms line  122  of the hot stripping column  104 . The hot stripped stream in line  122  may be at a hotter temperature than the cold stripped stream in line  110 . 
         [0070]    In an aspect, the hot stripped stream in the hot fractionator feed line  123  may be heated and fed to a prefractionation separator  124  for separation into a vaporized hot stripped stream in a prefractionation overhead line  126  and a liquid hot stripped stream in a prefractionation bottoms line  128  which both comprise hydroisomerized streams. The vaporous hot stripped stream may be fed to the atmospheric fractionation column  130  in the prefractionation overhead line  128  The liquid hot stripped stream may be heated in a fractionation furnace and fed to the atmospheric fractionation column  130  in the prefractionation bottoms line  128  at an elevation below the elevation at which the prefractionation overhead line  126  feeds the vaporized hot stripped stream to the atmospheric fractionation column  130 . In the embodiment illustrated, the liquid hot stripped stream in the prefractionation bottoms line  128  may be heated in a fractionation furnace and fed to an optional vacuum fractionation column  160 . 
         [0071]    The atmospheric fractionation column  130  may be in downstream communication with the cold stripping column  102  and the hot stripping column  104  and may comprise more than one fractionation column for separating stripped hydroisomerized streams into product streams. The atmospheric fractionation column  130  may fractionate hydroisomerized streams, the cold stripped stream, the vaporous hot stripped stream and the liquid hot stripped stream, with an inert stripping media stream such as steam from line  132  to provide several product streams. The product streams from the atmospheric fractionation column  130  may include a net fractionated overhead stream comprising naphtha in a net overhead line  134 , an optional heavy naphtha stream in line  136  from a side cut outlet, a kerosene stream carried in line  138  from a side cut outlet and a diesel stream in line  140  from a side cut outlet. 
         [0072]    An atmospheric unconverted oil stream may be provided in an atmospheric bottoms line  142 . A portion or all of the atmospheric unconverted oil stream in the atmospheric bottoms line  142  may be transferred in atmospheric transfer line  144  to the first recycle line  46  for recycle to the first hydroisomerization catalyst bed  42   b  as the first fractionation stream. Alternatively, the portion, some or all of the atmospheric unconverted oil stream in the atmospheric bottoms line  142  may be transferred in an atmospheric transfer line  152  to the hydrocracking reactor  40  in a second recycle line  184  as the second fractionation stream particularly in an embodiment which omits a vacuum fractionation column  160 . The remaining portion, if there is one, may be fed to an optional vacuum fractionation column  160  in a vacuum fractionation feed line  146 . 
         [0073]    Heat may be removed from the atmospheric fractionation column  130  by cooling at least a portion of the product streams and sending a portion of each cooled stream back to the fractionation column. These product streams may also be stripped to remove light materials to meet product purity requirements. A fractionated overhead stream in an overhead line  148  may be condensed and separated in a receiver  150  with a portion of the condensed liquid being refluxed back to the fractionation column  130 . The net fractionated overhead stream in line  134  may be further processed or recovered as naphtha product. The atmospheric fractionation column  130  may be operated with a bottoms temperature between about 260° C. (500° F.), and about 385° C. (725° F.), preferably at no more than about 350° C. (650° F.), and at an overhead pressure between about 7 kPa (gauge) (1 psig) and about 69 kPa (gauge) (10 psig). A portion of the unconverted oil stream in the atmospheric bottoms line  142  may be reboiled and returned to the atmospheric fractionation column  130  instead of adding an inert stripping media stream such as steam in line  132  to heat to the atmospheric fractionation column  130 . 
         [0074]    The liquid hot stripped stream in the prefractionation bottoms line  128  or the hot fractionator feed line  123  may be heated in a fired heater and fed to a vacuum fractionation column  160 . In the vacuum fractionation column  160 , the liquid hot stripped stream may be fractionated to separate diesel from unconverted oil. The atmospheric unconverted oil stream in the vacuum fractionator feed line  146  may also be fed to the vacuum fractionation column  160  at an inlet above the inlet for the liquid hot stripped stream. In the vacuum fractionation column  160 , the unconverted oil stream in the vacuum fractionator feed line  146  may also be fractionated to separate diesel from unconverted oil. The vacuum fractionation column  160  is therefore in downstream communication with the cold stripping column  60 , but the atmospheric fractionation column  130  may be in downstream communication with the cold stripping column  102  upstream of the vacuum fractionation column  160 . Consequently, the atmospheric fractionation column  130  is in upstream communication with the vacuum fractionation column  160 . 
         [0075]    An inert gas such as steam from vacuum media line  162  may provide heat to the vacuum fractionation column  160  to help fractionate lighter components from heavier components. The vacuum fractionation column  160  produces a diesel product stream in line  164  from a side cut outlet. Heat may be removed from the vacuum fractionation column  160  by cooling the diesel stream in line  164  and sending a portion of the cooled stream back to the column. The diesel stream in line  164  may also be stripped to remove light materials to meet product purity requirements. The vacuum fractionation column operates to produce a diesel stream with a diesel TBP cut point of between about 370° and about 390° C. and a T95 of no more than 380° C. and preferably no more than 360° C. The diesel stream also meets the Arctic Diesel Specifications of a Cloud Point Temperature of −40° C. and a Pour Point of −45° C. A vacuum fractionated stream in a vacuum transfer line  182  may be taken as a side cut from a side outlet  182   o  to be recycled to the first isomerization catalyst bed  42   b  as the first fractionation stream in line  46 . 
         [0076]    A heavy return stream may be provided from an upper half of the vacuum fractionation column from an overhead outlet in overhead line  166  and/or a side line from a side cut outlet (not shown) and fed in a heavy return line  170  to the atmospheric fractionation column  130 . The inlet for the heavy return stream in line  170  in downstream communication with the heavy return line  170  may be at a higher elevation than the inlet for the cold stripped stream in the cold fractionator line  113  or the feed inlet for the vaporous hot stripped stream from the prefractionation overhead line  126  to the atmospheric fractionation column  130 . A vacuum unconverted oil stream in a vacuum bottoms line  168  may be recovered from a bottom of the vacuum fractionation column  160 . The vacuum unconverted oil stream has a boiling point above the diesel cut point and may be recycled to the hydrocracking reactor  40  or to a second hydrocracking reactor as a second fractionation stream in a second recycle line  184 . Additionally, a heavy polynuclear aromatic stream concentrated in heavy polynuclear aromatics may be recovered from the unconverted oil stream in the vacuum bottoms line  168  before the unconverted oil stream is recycled in the second recycle line. 
         [0077]    The vacuum fractionation column  160  is operated at below atmospheric pressure in the overhead. The overhead stream in overhead line  166  may feed a vacuum generating device  172 . The vacuum generating device  172  may include and eductor in communication with an inert gas stream  174  such as steam which pulls a vacuum on the overhead stream in the overhead line  166 . A condensed hydrocarbon stream in line  176  from the vacuum generating device  172  may supply the heavy return stream  170  by itself or with another upper stream from a side line (not shown). A condensed aqueous stream may also be removed from a boot in the vacuum generating device. A hydrocarbonaceous vaporous stream may be removed from the vapor generating device in line  178 . 
         [0078]    The vacuum fractionation column  160  may be operated with a bottoms temperature between about 260° C. (500° F.), and about 370° C. (700° F.), preferably about 300° C. (570° F.), and at an overhead pressure between about 10 kPa (absolute) (1.5 psia), preferably about 20 kPa (absolute) (3 psia), and about 70 kPa (gauge) (10 psig). A portion of the unconverted oil in the vacuum bottoms line  168  may be reboiled and returned to the vacuum fractionation column  160  instead of using steam stripping to add heat to the vacuum fractionation column  160 . 
         [0079]    The first fractionation stream in the first recycle line  46  may be cooled in the heat exchanger  45  and fed to the first hydroisomerization catalyst bed  42   b  in the first hydrocracking reactor  40  to be further hydroisomerized in the presence of a supplemental hydrogen stream from branch line  44   b.  The first fractionation stream and the supplemental hydrogen stream in branch line  44   b  may be co-distributed in a common distributor to the interbed location at the intermediate inlet  46   i.  The intermediate inlet  46   i  may be in downstream communication with the fractionation section  14  and, in an aspect, with the side outlet  182   o  of the vacuum fractionation column  160 . 
         [0080]    The second fractionation stream comprising unconverted oil in the second recycle line  184  may be recycled to the first inlet  32   i  to the hydrocracking reactor  40  to be further hydrocracked over the first hydrocracking catalyst bed  42   a  and perhaps other hydrocracking catalyst beds  42  along with the hydrocarbon feed stream and the hydrogen stream and hydroisomerized over the first hydroisomerization catalyst bed  42   b.    
         [0081]      FIG. 2  shows an embodiment of the apparatus and process  10 ′ that includes a second hydrocracking reactor  200  in the hydroprocessing unit  12 ′. Elements in  FIG. 2  with the same configuration as in  FIG. 1  will have the same reference numeral as in  FIG. 1 . Elements in  FIG. 2  which have a different configuration as the corresponding element in  FIG. 1  will have the same reference numeral but designated with a prime symbol (′). The configuration and operation of the embodiment of  FIG. 2  is essentially the same as in  FIG. 1  with the following exceptions. 
         [0082]    The second hydrocracking reactor receives the second fractionation stream and a second hydrocracking hydrogen stream in a second hydrocracking hydrogen line  202  through a second inlet  184   i  in downstream communication with the fractionation section  14 ′. The second hydrocracking hydrogen stream in the second hydrocracking hydrogen line  202  is taken from the hydrogen stream in the hydrogen line  22 ′. A first hydrocracking hydrogen stream in the first hydrocracking hydrogen line  33 ′is taken from the hydrogen stream in the hydrogen line  22 ′ provides hydrogen to the first hydrocracking reactor  40 . The second fractionation stream comprises an unconverted oil stream from either the atmospheric fractionation column  130  and/or the vacuum fractionation column  160  in the second recycle line  184 ′. Accordingly, the second inlet  184   i  may be in downstream communication with an atmospheric bottoms line  142  of the atmospheric fractionation column  130  and/or the vacuum bottoms line  168  of the vacuum fractionation column  160 . 
         [0083]    The second hydrocracking reactor  200  comprises a plurality of catalyst beds  204 . A second hydroisomerization catalyst bed  204   a  may be located in the second reactor  200 . A second hydrocracking catalyst bed  204   b  may also be located in the second reactor  200 . The second hydrocracking catalyst bed  204   b  may be located downstream of the second hydroisomerization catalyst bed  204   a.  In the second hydrocracking reactor  200 , the second fractionated stream is hydroisomerized in the presence of a second hydrocracking hydrogen stream over the second hydroisomerization catalyst bed  204   a  to provide a second hydroisomerized stream. In the second hydrocracking reactor  200 , the second fractionated stream is hydrocracked in the presence of the second hydrocracking hydrogen stream over the second hydrocracking catalyst bed  204   b  to provide a second hydrocracked stream. In an aspect, the second fractionation stream may also be a second hydroisomerized stream after it is hydroisomerized in the second hydroisomerization catalyst bed  204   a  and before it is hydrocracked in the second hydrocracking reactor  200 . In an aspect, the upstream catalyst beds  204  in the second hydrocracking reactor  200  will suitably be hydroisomerization catalyst beds and the downstream catalyst beds  204  will be hydrocracking catalyst beds. A second hydrogen manifold  208  provides supplemental hydrogen streams to some or all of the catalyst beds  204  at the interbed locations. If a catalyst bed  204  comprises a hydroisomerization catalyst bed downstream of a hydrocracking catalyst bed  204  in the second hydrocracking reactor  200 , a portion or all of the first fractionation stream from the first recycle line  46  may be used to quench the hydrocracked stream entering the hydroisomerization catalyst bed  204 . 
         [0084]    The second hydrocracked stream in line  210  may exit the second hydrocracking reactor  200 . The second hydrocracked stream in line  210  may be joined to the first hydroisomerized stream in line  48  and be separated and fractionated in the fractionation section  14 ′ with the first hydroisomerized stream. 
       EXAMPLE 
       [0085]      FIG. 3  shows the effect of inactivating and reactivating hydroisomerization catalyst on cold flow properties, in this case Cloud Point. Two different VGO feeds were mixed with hydrogen and sequentially fed to a bed of hydrocracking catalyst and then to a bed of hydroisomerization catalyst in a pilot plant. The hydrocracking catalyst temperature is indicated by the triangles in  FIG. 3 . The hydroisomerization catalyst temperature is represented by the circles in  FIG. 3 . Catalyst temperature values are presented on the right vertical axis. Cloud point temperature values are represented by the squares and are presented on the left vertical axis. Hours on stream is presented on the horizontal axis. The vertical line at 2700 hours indicates the switching from one VGO feed to another VGO feed. 
         [0086]    Hydrocracking catalyst temperature stayed generally between 700 and 800° F. during the entire run. Hydroisomerization catalyst temperature was maintained around 750° F. between 2100 and 2400 hours. During that time cloud point temperature stayed above −20° F. meaning that clouds do not form in the product diesel until the diesel temperature descends to or below the cloud point, in this case around −20° F. At 2400 hours, the hydroisomerization catalyst temperature was reduced to 585° F., at which time cloud point temperature rose to −5° F. Hydroisomerization catalyst temperature was allowed to cool to 450° F. resulting in cloud point staying at about −5 or −6° F. until 2550 hours at which time the cloud point spiked and fell to a higher stabilized cloud point temperature of 0° F. A new VGO feed was introduced at 2700 hours, and cloud point temperature rose to about 10° F. which is probably attributed to quality of the new feed because the hydroisomerization catalyst temperature was still at about 450° F. While the hydroisomerization catalyst was below 600° F., and particularly below 500F, it was effectively inactive as shown by the significantly higher cloud point temperature of the produced diesel. 
         [0087]    At after 2900 hours, the hydroisomerization catalyst temperature was increased to 750° F. The cloud point temperature immediately descended to −30° F. When the hydroisomerization catalyst temperature was increased to 775° F., cloud point temperature of the diesel product moved to below −40 F a superb quality. 
         [0088]    We conclude that hydroisomerization catalyst can be operated with hydrocracking catalyst to improve cold flow properties of the hydrocracked diesel product. Moreover, the hydroisomerization catalyst temperature can be reduced to inactivate the hydroisomerization catalyst during warmer months when cold flow properties are less desired. Furthermore, when the warmer months are over, the same hydroisomerization catalyst can be reactivated by heating it up or not cooling it and the catalyst can begin to effectively hydroisomerized where it left off before it was cooled. 
       SPECIFIC EMBODIMENTS 
       [0089]    While the following is described in conjunction with specific embodiments, it will be understood that this description is intended to illustrate and not limit the scope of the preceding description and the appended claims. 
         [0090]    A first embodiment of the invention is a process for hydrocracking and hydroisomerizing a hydrocarbon stream comprising hydrocracking a hydrocarbon feed stream over a first hydrocracking catalyst bed to provide a hydrocracked stream; hydroisomerizing the hydrocracked stream over a first hydroisomerization catalyst bed to provide a hydroisomerized stream; fractionating the hydroisomerized stream in a fractionation section to provide a first fractionated stream; and recycling a first fractionated stream to the first isomerization catalyst bed to quench the hydrocracked stream. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising hydrocracking a second fractionated stream over the first hydrocracking catalyst bed. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising hydrocracking a second fractionated stream over a second hydrocracking catalyst bed to provide a second hydrocracked stream. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the first hydrocracking catalyst bed and the first hydroisomerization catalyst bed are located in a first reactor and the second hydrocracking catalyst bed is located in a second reactor. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising cooling the first fractionated stream to inactivate the first hydroisomerization catalyst bed. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the fractionation comprises stripping gases from the hydroisomerized stream to provide a stripped stream and recycling a portion of the stripped stream to the first isomerization catalyst bed as the first fractionated stream. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the fractionation comprises fractionating the hydroisomerized stream under vacuum and recycling a vacuum fractionated stream to the first isomerization catalyst bed as the first fractionated stream. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the first fractionated stream is taken as a side cut from a vacuum fractionation column. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the second fractionated stream is taken from a bottom of a fractionation column. 
         [0091]    A second embodiment of the invention is a process for hydrocracking and hydroisomerizing a hydrocarbon stream comprising hydrocracking a hydrocarbon feed stream over a first hydrocracking catalyst bed in a first reactor to provide a hydrocracked stream; hydroisomerizing the hydrocracked stream over a first hydroisomerization catalyst bed in the first reactor to provide a hydroisomerized stream; fractionating a first effluent stream from the first reactor to provide a first fractionated stream and a second fractionated stream; recycling the first fractionated stream to the first isomerization catalyst bed in the first reactor to quench the hydrocracked stream; and hydrocracking the second fractionated stream over a second hydrocracking catalyst bed in a second reactor to provide a second hydrocracked stream. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph further comprising cooling the first fractionated stream to inactivate the first hydroisomerization catalyst bed. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph wherein the fractionation comprises stripping gases from the first effluent stream and recycling a portion of the stripped stream to the first isomerization catalyst bed as the first fractionated stream. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph wherein the fractionation comprises fractionating the first effluent stream under vacuum and recycling a vacuum fractionated stream to the first isomerization catalyst bed as the first fractionated stream. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph wherein the first fractionated stream is taken as a side cut from the vacuum fractionation column and the second fractionated stream is taken from a bottom of the vacuum fractionation column. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph wherein the fractionation comprises fractionating the first effluent stream and the first fractionated stream is taken as a side cut and the second fractionated stream is taken from a bottom of a fractionation column. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph further comprising fractionating another portion of the stripped stream to provide the second fractionated stream. 
         [0092]    A third embodiment of the invention is an apparatus for hydrocracking and hydroisomerizing a hydrocarbon stream comprising a first hydrocracking reactor having a first inlet to the first hydrocracking reactor and an intermediate inlet to the first hydrocracking reactor downstream of the first inlet; a fractionation section downstream of the first hydrocracking reactor; and the intermediate inlet to the first hydrocracking reactor in downstream communication with the fractionation section. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the third embodiment in this paragraph further comprising a second hydrocracking reactor having a second inlet to the second hydrocracking reactor in downstream communication with the fractionation section. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the third embodiment in this paragraph wherein the fractionation section comprises a fractionation column and the second inlet is in downstream communication with a bottoms line of the fractionation column. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the third embodiment in this paragraph wherein the intermediate inlet is in downstream communication with a side outlet of the fractionation column. 
         [0093]    Without further elaboration, it is believed that using the preceding description that one skilled in the art can utilize the present invention to its fullest extent and easily ascertain the essential characteristics of this invention, without departing from the spirit and scope thereof, to make various changes and modifications of the invention and to adapt it to various usages and conditions. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limiting the remainder of the disclosure in any way whatsoever, and that it is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims. 
         [0094]    In the foregoing, all temperatures are set forth in degrees Celsius and, all parts and percentages are by weight, unless otherwise indicated.