Abstract:
A hydrocracking process for treating a first and a second heavy hydrocarbon feedstream, in which the first heavy hydrocarbon feedstream contains undesired nitrogen-containing compounds, sulfur-containing compounds and poly-nuclear aromatic compounds. The process includes contacting the first heavy hydrocarbon feedstream with adsorbent material to produce a hydrocarbon stream having a reduced content of nitrogen-containing, sulfur-containing compounds and poly-nuclear aromatic compounds. The second heavy hydrocarbon feedstream is combined with the adsorbent-treated heavy hydrocarbon stream. The combined stream is charged to a hydrocracking reaction unit. The hydrocracked effluent is fractioned to recover hydrocracked products and a bottoms stream containing heavy poly-nuclear aromatic compounds, and bottoms are contacted with adsorbent material to produce an adsorbent-treated fractionator bottoms stream having a reduced content of heavy poly-nuclear aromatic compounds, and are recycled to the hydrocracking reaction unit.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to hydrocracking processes, and in particular to hydrocracking processes adapted to receive multiple feedstreams. 
     2. Description of Related Art 
     Hydrocracking processes are used commercially in a large number of petroleum refineries. They are used to process a variety of feeds boiling in the range of 370° C. to 520° C. in conventional hydrocracking units and boiling at 520° C. and above in the residue hydrocracking units. In general, hydrocracking processes split the molecules of the feed into smaller, i.e., lighter, molecules having higher average volatility and economic value. Additionally, hydrocracking processes typically improve the quality of the hydrocarbon feedstock by increasing the hydrogen to carbon ratio and by removing organosulfur and organonitrogen compounds. The significant economic benefit derived from hydrocracking processes has resulted in substantial development of process improvements and more active catalysts. 
     In addition to sulfur-containing and nitrogen-containing compounds, a typical hydrocracking feedstream, such as vacuum gas oil (VGO), contains small amount of poly nuclear aromatic (PNA) compounds, i.e., those containing less than seven fused benzene rings. As the feedstream is subjected to hydroprocessing at elevated temperature and pressure, heavy poly nuclear aromatic (HPNA) compounds, i.e., those containing seven or more fused benzene rings, tend to form and are present in high concentration in the unconverted hydrocracker bottoms. 
     Heavy feedstreams such as de-metalized oil (DMO) or de-asphalted oil (DAO) have much higher concentration of nitrogen, sulfur and PNA compounds than VGO feedstreams. These impurities can lower the overall efficiency of hydrocracking unit by requiring higher operating temperature, higher hydrogen partial pressure or additional reactor/catalyst volume. In addition, high concentrations of impurities can accelerate catalyst deactivation. 
     Three major hydrocracking process schemes include single-stage once through hydrocracking, series-flow hydrocracking with or without recycle, and two-stage recycle hydrocracking. Single-stage once through hydrocracking is the simplest of the hydrocracker configuration and typically occurs at operating conditions that are more severe than hydrotreating processes, and less severe than conventional full pressure hydrocracking processes. It uses one or more reactors for both treating steps and cracking reaction, so the catalyst must be capable of both hydrotreating and hydrocracking. This configuration is cost effective, but typically results in relatively low product yields (e.g., a maximum conversion rate of about 60%). Single stage hydrocracking is often designed to maximize mid-distillate yield over a single or dual catalyst systems. Dual catalyst systems are used in a stacked-bed configuration or in two different reactors. The effluents are passed to a fractionator column to separate the H 2 S, NH 3 , light gases (C 1 -C 4 ), naphtha and diesel products boiling in the temperature range of 36-370° C. The hydrocarbons boiling above 370° C. are unconverted bottoms that, in single stage systems, are passed to other refinery operations. 
     Series-flow hydrocracking with or without recycle is one of the most commonly used configuration. It uses one reactor (containing both treating and cracking catalysts) or two or more reactors for both treating and cracking reaction steps. Unconverted bottoms from the fractionator column are recycled back into the first reactor for further cracking. This configuration converts heavy crude oil fractions, i.e., vacuum gas oil, into light products and has the potential to maximize the yield of naphtha, jet fuel, or diesel, depending on the recycle cut point used in the distillation section. 
     Two-stage recycle hydrocracking uses two reactors and unconverted bottoms from the fractionation column are recycled back into the second reactor for further cracking. Since the first reactor accomplishes both hydrotreating and hydrocracking, the feed to second reactor is virtually free of ammonia and hydrogen sulfide. This permits the use of high performance zeolite catalysts which are susceptible to poisoning by sulfur or nitrogen compounds. 
     A typical hydrocracking feedstock is vacuum gas oils boiling in the nominal range of 370° C. to 520° C. DMO or DAO can be blended with vacuum gas oil or used as is and processed in a hydrocracking unit. For instance, a typical hydrocracking unit processes vacuum gas oils that contain from 10V % to 25V % of DMO or DAO for optimum operation. 100% DMO or DAO can also be processed for difficult operations. However, the DMO or DAO stream contains significantly more nitrogen compounds (2,000 ppmw vs. 1,000 ppmw) and a higher micro carbon residue (MCR) content than the VGO stream (10W % vs. &lt;1W %). 
     The DMO or DAO in the blended feedstock to the hydrocracking unit can have the effect of lowering the overall efficiency of the unit, i.e., by causing higher operating temperature or reactor/catalyst volume requirements for existing units or higher hydrogen partial pressure requirements or additional reactor/catalyst volume for the grass-roots units. These impurities can also reduce the quality of the desired intermediate hydrocarbon products in the hydrocracking effluent. When DMO or DAO are processed in a hydrocracker, further processing of hydrocracking reactor effluents may be required to meet the refinery fuel specifications, depending upon the refinery configuration. When the hydrocracking unit is operating in its desired mode, that is to say, producing products in good quality, its effluent can be utilized in blending and to produce gasoline, kerosene and diesel fuel to meet established fuel specifications. 
     In addition, formation of HPNA compounds is an undesirable side reaction that occurs in recycle hydrocrackers. The HPNA molecules form by dehydrogenation of larger hydro-aromatic molecules or cyclization of side chains onto existing HPNAs followed by dehydrogenation, which is favored as the reaction temperature increases. HPNA formation depends on many known factors including the type of feedstock, catalyst selection, process configuration, and operating conditions. Since HPNAs accumulate in the recycle system and then cause equipment fouling, HPNA formation must be controlled in the hydrocracking process. 
     Lamb, et al. U.S. Pat. No. 4,447,315 discloses a single-stage recycle hydrocracking process in which unconverted bottoms are contacted with an adsorbent to remove PNA compounds. Unconverted bottoms having a reduced concentration of PNA compounds are recycled to the hydrocracking reactor. 
     Gruia U.S. Pat. No. 4,954,242 describes a single-stage recycle hydrocracking process in which an HPNA containing heavy fraction from a vapor-liquid separator downstream of a hydrocracking reactor is contacted with an adsorbent in an adsorption zone. The reduced HPNA heavy fraction is then either recycled to the hydrotreating zone or introduced directly into the fractionation zone. 
     Commonly-owned U.S. Pat. No. 7,763,163 discloses adsorption of a DMO or DA0 feedstream to a hydrocracker unit to remove nitrogen-containing compounds, sulfur-containing compounds and PNA compounds. This process is effective for removal of impurities including nitrogen-containing compounds, sulfur-containing compounds and PNA compounds from the DMO or DAO feedstock to the hydrocracker unit. A separate VGO feedstock is also shown as a feed to the hydrocracker reactor along with the cleaned DMO or DAO feed. However, a relatively high concentration of HPNA compounds remains in unconverted hydrocracker bottoms. 
     While the above-mentioned references are suitable for their intended purposes, a need remains for improved process and apparatus for efficient and efficacious hydrocracking of heavy oil fraction feedstocks. 
     SUMMARY OF THE INVENTION 
     In accordance with one or more embodiments, a hydrocracking process is provided for treating a first heavy hydrocarbon feedstream and a second heavy hydrocarbon feedstream, in which the first heavy hydrocarbon feedstream contains undesired nitrogen-containing compounds, sulfur-containing compounds and PNA compounds. The process includes the following steps: 
     a. contacting the first heavy hydrocarbon feedstream with an effective amount of adsorbent material to produce an adsorbent-treated heavy hydrocarbon stream having a reduced content of nitrogen-containing, sulfur-containing compounds and PNA compounds; 
     b. combining the second heavy hydrocarbon feedstream with the adsorbent-treated heavy hydrocarbon stream; 
     c. introducing the combined stream and an effective amount of hydrogen into a hydrocracking reaction unit that contains an effective amount of hydrocracking catalyst to produce a hydrocracked effluent stream; 
     d. fractionating the hydrocracked effluent stream to recover hydrocracked products and a bottoms stream containing HPNA compounds; 
     e. contacting the fractionator bottoms stream with an effective amount of adsorbent material to produce an adsorbent-treated fractionator bottoms stream having a reduced content of heavy poly-nuclear aromatic compounds; 
     f. integrating the adsorbent-treated fractionator bottoms stream with the combined stream of steps (b); and g. introducing the combined stream into the hydrocracking unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing summary as well as the following detailed description of preferred embodiments of the invention will be best understood when read in conjunction with the attached drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and apparatus shown, in the drawings, in which: 
         FIG. 1  is a process flow diagram of an integrated hydrocracking process with feed/bottoms pretreatment; 
         FIG. 2  is a process flow diagram of an embodiment of a desorption apparatus; and 
         FIG. 3  is a process flow diagram of an integrated hydrocracking process with separate feed and bottoms treatments. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Integrated processes and apparatus are provided for hydrocracking hydrocarbon feeds, such as a combined feed of VGO and DMO and/or DAO, in an efficient manner and resulting in improved product quality. The presence of nitrogen-containing compounds, sulfur-containing compounds and PNA compounds in DMO or DAO feedstreams, and the presence of HPNA compounds in hydrocracker bottoms, have detrimental effects on the performance of hydrocracking unit. The integrated processes and apparatus provided herein remove or reduce the concentration of nitrogen-containing compounds, sulfur-containing compounds, PNA compounds and HPNA compounds to thereby improve process efficiency and the effluent product quality. 
     In general, the processes for improved cracking includes contacting a first heavy hydrocarbon feedstream and a hydrocracking reaction bottoms stream, with an effective quantity of adsorbent material in which nitrogen-containing compounds, sulfur-containing compounds, PNA compounds and HPNA compounds are removed. The adsorbent effluent, which generally contains about 85 V % to about 95 V % of the first heavy hydrocarbon feedstream and about 10 V % to about 60 V %, in certain embodiments about 20 V % to about 50 V %, and in further embodiments about 30 V % to about 40 V % of the hydrocracking reaction bottoms stream (i.e., the recycle stream), is combined with a second hydrocarbon feedstream and cracked in the presence of hydrogen in a hydrocracking reaction zone. Excess hydrogen is separated from hydrocracking effluent and recycled back to the hydrocracking reaction zone. The remainder of the hydrocracking effluent is fractionated, and the hydrocracking reaction bottoms stream is contacted with adsorbent material as noted above. 
     In particular, and referring to  FIG. 1 , a process flow diagram of an integrated hydrocracking apparatus  100  including feed/bottoms treatment is provided. Apparatus  100  includes an adsorption zone  110 , a hydrocracking reaction zone  130  containing hydrocracking catalysts, an optional high-pressure separation zone  150 , and a fractionating zone  160 . 
     Adsorption zone  110  includes an inlet  114  in fluid communication with a source of a first heavy hydrocarbon feedstream via a conduit  102 , and hydrocracking reaction product fractionator bottoms via a conduit  164 , which is in fluid communication with an unconverted/partially converted fractionator bottoms outlet  162  of fractionating zone  160 . Optionally, inlet  114  of adsorption zone  110  is also in fluid communication with a source of elution solvent via conduit  104 , for instance, straight run naphtha which can be derived from the product collected from the fractionating zone  160  or from another source of solvent. In addition, adsorption zone  110  includes a cleaned feedstream outlet  116  in fluid communication with an inlet  136  of hydrocracking reaction zone  130  via a conduit  120 . In embodiments in which a solvent elution stream is employed, the solvent can be distilled off, for instance, at an optional fractionator  118  between the cleaned feedstream outlet  116  and the inlet  136  of hydrocracking reaction zone  130 . 
     Feed inlet  136  of hydrocracking zone  130  is also in fluid communication a source of second heavy hydrocarbon feedstream via a conduit  132 . In addition, inlet  136  is in fluid communication with a source of hydrogen via a conduit  134  and optionally a hydrogen recycle stream from outlet  154  of high-pressure separation zone  150  via a conduit  156 , e.g., if there is an excess of hydrogen to be recovered. An outlet  138  of hydrocracking reaction zone  130  is in fluid communication with an inlet  140  of high-pressure separation zone  150 . In embodiments in which there is not an excess of hydrogen to be recovered, i.e., stoichiometric or near-stoichiometric hydrogen feed is provided, high pressure separation zone  150  can be bypasses or eliminated, and outlet  138  of hydrocracking reaction zone  130  is in fluid communication with inlet  158  of the fractionating zone  160 . 
     High-pressure separation zone  150  includes an outlet  152  in fluid communication with an inlet  158  of the fractionating zone  160  for conveying cracked, partially cracked and unconverted hydrocarbons, and an outlet  154  in fluid communication with inlet  136  of the hydrocracking reaction zone  130  for conveying recycle hydrogen. Fractionating zone  160  further includes outlet  162  in fluid communication with inlet  114  of adsorption zone  110  and a bleed outlet  163 , and an outlet  166  to discharge cracked product. 
     In operation of the system  100 , a combined stream including a first heavy hydrocarbon feedstream via conduit  102  and a hydrocracking reaction bottoms stream via conduit  164 , and optionally solvent via conduit  104  from fractionating zone  160  or from another source, are introduced into the adsorption zone  110  via inlet  114 . Solvent can be optionally used to facilitate elution of the feedstock mixture over the adsorbent. The concentrations of nitrogen-containing compounds, sulfur-containing compounds and PNA compounds present in the in the first heavy hydrocarbon feedstream, and HPNA compounds from the hydrocracking reaction bottoms stream, are reduced in the adsorption zone  110  by contact with adsorbent  112 . 
     An adsorbent-treated hydrocracking feedstream is discharged from adsorption zone  110  via outlet  116  and conveyed to inlet  136  of hydrocracking reaction zone  130  via and conduit  120 , along with the second hydrocarbon feedstream which is introduced into inlet  136  of hydrocracking reaction zone  130  via conduit  132 . In embodiments in which elution solvent is utilized, it is distilled and recovered in fractionator  118 . 
     An effective quantity of hydrogen for hydrocracking reactions is provided via conduits  134  and optionally recycle hydrogen conduit  156 . Hydrocracking reaction effluents are discharged from outlet  138  of hydrocracking reaction zone  130 . When an excess of hydrogen is used, the hydrocracking reaction effluents are conveyed to inlet  140  of high-pressure separation zone  150 . A gas stream, which mainly contains hydrogen, is separated from the converted, partially converted and unconverted hydrocarbons in the high-pressure separation zone  150 , and is discharged via outlet  154  and recycled to hydrocracking reaction zone  130  via conduit  156 . Converted, partially converted and unconverted hydrocarbons, which includes HPNA compounds formed in the hydrocracking reaction zone  130 , are discharged via outlet  152  to inlet  158  of fractionating zone  160 . A cracked product stream is discharged via outlet  166  and can be further processed and/or blended in downstream refinery operations to produce gasoline, kerosene and/or diesel fuel. At least a portion of the fractionator bottoms from the hydrocracking reaction effluent, including HPNA compounds formed in the hydrocracking reaction zone  130 , are discharged from outlet  162  and are recycled to adsorption zone  110  via conduit  164 . A portion of the fractionator bottoms from the hydrocracking reaction effluent is removed from bleed outlet  163  to remove a portion of the HPNA compounds, which could causes equipment fouling. The concentration of HPNA compounds in the hydrocracking effluent fractionator bottoms is reduced in adsorption zone  110 . In particular, in system  100 , both the hydrocracking reaction fractionator bottoms and the first heavy hydrocarbon feedstream are combined and contacted with adsorbent material  112  in adsorption zone  110 . The adsorbent-treated hydrocracking feed is combined with the second heavy hydrocarbon feedstream for cracking in the hydrocracking reaction zone  130 . 
     In certain embodiments, the adsorption zone includes columns that are operated in swing mode so that production of the cleaned feedstock is continuous. When the adsorbent material  112  in column  110   a  or  110   b  becomes saturated with adsorbed nitrogen-containing compounds, sulfur-containing compounds, PNA compounds and/or HPNA compounds, the flow of the combined feedstream is directed to the other column. The adsorbed compounds are desorbed by heat or solvent treatment. 
     In case of heat desorption, heat is applied, for instance, with an inert nitrogen gas flow to adsorption zone  110 . The desorbed compounds are removed from the adsorption columns  110   a ,  110   b  via a suitable outlet (not shown) and can be conveyed to downstream refinery processes, such as residue upgrading facilities, or is used directly in fuel oil blending. 
     Referring to  FIG. 2 , a flow diagram of a solvent desorption apparatus  100   a  is provided. A solvent inlet  174  of adsorption zone  110  is in fluid communication with a source of fresh solvent via a conduit  172  and recycled solvent via a conduit  186 . 
     Adsorption zone  110  further includes an outlet  176  in fluid communication with an inlet  182  of a desorption fractionating zone  180  via a conduit  178 . A solvent outlet  184  of desorption fractionating zone  180  is in fluid communication with the adsorption zone inlet  174  via a conduit  186 , and a bottoms outlet  188  is provided to discharge the desorbed nitrogen-containing compounds, sulfur-containing compounds, PNA compounds and/or HPNA compounds. 
     In one embodiment, fresh solvent is introduced to the adsorption zone  110  via conduit  172  and inlet  174 . The solvent stream containing removed nitrogen-containing compounds, sulfur-containing compounds, PNA compounds and/or HPNA compounds is discharged from adsorption zone  110  via outlet  176  and conveyed via conduit  178  to inlet  182  of fractionation unit  180 . The recovered solvent stream is recycled back to adsorption zone  110  via outlet  184  and conduit  186 . The bottoms stream from the fractionation unit  180  containing the previously adsorbed nitrogen-containing compounds, sulfur-containing compounds, PNA compounds and/or HPNA compounds is discharged via outlet  188  and can be conveyed to downstream refinery processes, such as residue upgrading facilities, or is used directly in fuel oil blending. 
     Referring to  FIG. 3 , a process flow diagram of an integrated hydrocracking apparatus  200  including feed pretreatment and bottoms treatment is provided. Apparatus  200  includes a first adsorption zone  210 , a hydrocracking reaction zone  230  containing hydrocracking catalysts, a high-pressure separation zone  250 , a fractionating zone  260 , and a second adsorption zone  290 . 
     First adsorption zone  210  includes an inlet  214  in fluid communication with a source of first heavy hydrocarbon feedstream via a conduit  202  (and optionally a source of solvent as described with respect to  FIG. 1 , not shown in  FIG. 3 ), and a cleaned feedstream outlet  216  in fluid communication with an inlet  236  of hydrocracking reaction zone  230  via a conduit  217 . 
     Feed inlet  236  of hydrocracking reaction zone  230  is also in fluid communication with a source of second hydrocarbon feedstream via a conduit  232 . In addition, inlet  236  is in fluid communication with a source of hydrogen via a conduit  234  and hydrogen recycle stream from outlet  254  of high-pressure separation zone  250  via a conduit  256 . As noted with respect to the discussion of apparatus  100  in  FIG. 1 , the high pressure separation zone can be bypasses or eliminated, for instance, if there is little or no excess hydrogen. Hydrocracking reaction zone  230  includes an outlet  238  in fluid communication with an inlet  240  of high-pressure separation zone  250 . 
     High-pressure separation zone  250  also includes an outlet  252  in fluid communication with an inlet  258  of fractionating zone  260  for conveying cracked, partially cracked and unconverted hydrocarbons, and an outlet  254  in fluid communication with the hydrocracking reaction zone  230  for conveying recycle hydrogen. Fractionating zone  260  further includes outlet  262  in fluid communication with inlet  292  of second adsorption zone  290 , and an outlet  264  to discharge cracked product. 
     Second adsorption zone  290  includes inlet  292  in fluid communication with fractionating zone outlet  262  (and optionally a source of solvent as described with respect to  FIG. 1 , not shown in  FIG. 3 ), and an outlet  294  in fluid communication with inlet  236  of hydrocracking reaction zone  230  via a conduit  296 . 
     In operation of the system  200 , a first heavy hydrocarbon feedstream is conveyed via conduit  202  to inlet  214  of first adsorption zone  210 . The concentrations of nitrogen-containing compounds, sulfur-containing compounds and PNA compounds in the first heavy hydrocarbon feedstream are reduced in first adsorption zone  210 . 
     An adsorbent-treated first heavy hydrocarbon feedstream is discharged from outlet  216  of adsorption zone  210  and conveyed to inlet  236  of hydrocracking reaction zone  230  via conduit  217 . A second hydrocarbon feedstream is also introduced into the hydrocracking reaction zone  230  via conduit  232 . An effective quantity of hydrogen for hydrocracking reactions is provided via conduits  234 ,  256 . Hydrocracked effluents are discharged via outlet  238  to inlet  240  of high-pressure separation zone  250 . A gas stream, which primarily contains hydrogen, is separated from the converted, partially converted and unconverted hydrocarbons in the high-pressure separation zone  250 , and is discharged via outlet  254  and recycled to hydrocracking reaction zone  230  via conduit  256 . Converted, partially converted and unconverted hydrocarbons, including HPNA compounds formed in the hydrocracking reaction zone  230 , are discharged via outlet  252  to inlet  258  of fractionating zone  260 . A cracked product stream is discharged via outlet  264  and can be further processed and/or blended in downstream refinery operations to produce gasoline, kerosene and/or diesel fuel. Unconverted and partially cracked fractionator bottoms, including HPNA compounds formed in the hydrocracking reaction zone  230 , are discharged from outlet  262  and at least a portion thereof is conveyed to inlet  292  of second adsorption zone  290 , with the remainder removed via a bleed outlet  263 . The concentration of HPNA compounds in the unconverted fractionator bottoms is reduced in the second adsorption zone  290 , therefore improving the quality of the recycle stream. Adsorbent-treated unconverted fractionator bottoms are sent to the hydrocracking reaction zone  230  via outlet  294  in fluid communication with inlet  236  for further cracking. 
     By employing distinct adsorption zones  210 ,  290 , the content of the individual feeds to these adsorption zones can be specifically targeted. That is, nitrogen-containing compounds, sulfur-containing compounds and PNA compounds from the initial feed can be removed in the first adsorption zone  210  under a first set of operating conditions and using a first adsorbent material, and HPNA compounds formed during the hydrocracking process can be removed in the second adsorption zone  290  under a second set of operating conditions and using a second adsorbent material. 
     The feedstreams for use in above-described system and process can be a partially refined oil product obtained from various sources. In general, the first heavy feedstream is one or more of DMO from a solvent demetalizing operations or DAO from a solvent deasphalting operations, coker gas oils from coker operations, heavy cycle oils from fluid catalytic cracking operations, and visbroken oils from visbreaking operations. The first heavy feedstream generally has a boiling point of from about 450° C. to about 800° C., and in certain embodiments of from about 500° C. to about 700° C. 
     The second heavy hydrocarbon feedstream is generally VGO from a vacuum distillation operation, and contains hydrocarbons having a boiling point of from about 350° C. to about 600° C., and in certain embodiments from about 350° C. to about 570° C. 
     Suitable reaction apparatus for the hydrocracking reaction zone include fixed bed reactors, moving bed reactor, ebullated bed reactors, baffle-equipped slurry bath reactors, stirring bath reactors, rotary tube reactors, slurry bed reactors, or other suitable reaction apparatus as appreciated by one of ordinary skill in the art. In certain embodiments, and in particular for VGO and similar feedstreams, fixed bed reactors are utilized. In additional embodiments, and in particular for heavier feedstreams and other difficult to crack feedstreams, ebullated bed reactors are utilized. 
     In general, the operating conditions for the reactor of a hydrocracking zone include: reaction temperature of about 300° C. to about 500° C., in certain embodiments about 330° C. to about 475° C., and in further embodiments about 330° C. to about 450° C.; hydrogen partial pressure of about 60 Kg/cm 2  to about 300 Kg/cm 2 , in certain embodiments about 100 Kg/cm 2  to about 200 Kg/cm 2 , and in further embodiments about 130 Kg/cm 2  to about 180 Kg/cm 2 ; liquid hourly space velocity of about 0.1 h −1  to about 10 h −1 , in certain embodiments about 0.25 h −1  to about 5 h −1 , and in further embodiments about 0.5 h −1  to about 2 h −1 ; hydrogen/oil ratio of about 500 normalized m 3  per m 3  (Nm 3 /m 3 ) to about 2500 Nm 3 /m 3 , in certain embodiments about 800 Nm 3 /m 3  to about 2000 Nm 3 /m 3 , and in further embodiments about 1000 Nm 3 /m 3  to about 1500 Nm 3 /m 3 . 
     In certain embodiments, the hydrocracking catalyst includes any one of or combination including amorphous alumina catalysts, amorphous silica alumina catalysts, natural or synthetic zeolite based catalyst, or a combination thereof. The hydrocracking catalyst can possess an active phase material including, in certain embodiments, any one of or combination including Ni, W, Mo, or Co. In certain embodiments in which an objective is hydrodenitrogenation, acidic alumina or silica alumina based catalysts loaded with Ni—Mo or Ni—W active metals, or combinations thereof, are used. In embodiments in which the objective is to remove all nitrogen and to increase the conversion of hydrocarbons, silica alumina, zeolite or combination thereof are used as catalysts, with active metals including Ni—Mo, Ni—W or combinations thereof. 
     The adsorption zone(s) used in the process and apparatus described herein is, in certain embodiments, at least two packed bed columns which are gravity fed or pressure force-fed sequentially in order to permit continuous operation when one bed is being regenerated, i.e., swing mode operation. The columns contain an effective quantity of absorbent material, such as attapulgus clay, alumina, silica gel silica-alumina, fresh or spent catalysts, or activated carbon. The packing can be in the form of pellets, spheres, extrudates or natural shapes, having a size of about 4 mesh to about 60 mesh, and in certain embodiments about 4 mesh to about 20 mesh, based on United States Standard Sieve Series. 
     The packed columns are generally operated at a pressure in the range of from about 1 kg/cm 2  to about 30 kg/cm 2 , in certain embodiments about 1 kg/cm 2  to about 20 kg/cm 2 , and in further embodiments about 1 kg/cm 2  to about 10 kg/cm 2 , a temperature in the range of from about 20° C. to about 250° C., in certain embodiments about 20° C. to about 150° C., and in further embodiments about 20° C. to about 100° C.; and a liquid hourly space velocity of about 0.1 h −1  to about 10 h −1 , in certain embodiments about 0.25 h −1  to about 5 h −1 , and in further embodiments about 0.5 h −1  to about 2 h −1 . The adsorbent can be desorbed by applying heat via inert nitrogen gas flow introduced at a pressure of from about 1 kg/cm 2  to about 30 kg/cm 2 , in certain embodiments about 1 kg/cm 2  to about 20 kg/cm 2 , and in further embodiments about 1 kg/cm 2  to about 10 kg/cm 2 . 
     In embodiments in which the adsorbent is desorbed by solvent desorption, solvents can be selected based on their Hildebrand solubility factors or by their two-dimensional solubility factors. Solvents can be introduced at a solvent to oil volume ratio of about 1:1 to about 10:1. 
     The overall Hildebrand solubility parameter is a well-known measure of polarity and has been calculated for numerous compounds. See  The Journal of Paint Technology , Vol. 39, No. 505 (February 1967). The solvents can also be described by their two-dimensional solubility parameter. See, for example, I. A. Wiehe,  Ind . &amp;  Eng. Res.,  34(1995), 661. The complexing solubility parameter component, which describes the hydrogen bonding and electron donor acceptor interactions, measures the interaction energy that requires a specific orientation between an atom of one molecule and a second atom of a different molecule. The field force solubility parameter, which describes the van der Waals and dipole interactions, measures the interaction energy of the liquid that is not destroyed by changes in the orientation of the molecules. 
     In accordance with the desportion operations using a non-polar solvent or solvents (if more than one is employed) preferably have an overall Hildebrand solubility parameter of less than about 8.0 or the complexing solubility parameter of less than 0.5 and a field force parameter of less than 7.5. Suitable non-polar solvents include, e.g., saturated aliphatic hydrocarbons such as pentanes, hexanes, heptanes, paraffinic naphtha, C 5 -C 11 , kerosene C 12 -C 15  diesel C 16 -C 20 , normal and branched paraffins, mixtures or any of these solvents. The preferred solvents are C 5 -C 7  paraffins and C 5 -C 11  paraffinic naphtha. 
     In accordance with the desportion operations using polar solvent(s), solvents are selected having an overall solubility parameter greater than about 8.5, or a complexing solubility parameter of greater than 1 and field force parameter of greater than 8. Examples of polar solvents meeting the desired minimum solubility parameter are toluene (8.91), benzene (9.15), xylenes (8.85), and tetrahydrofuran (9.52). 
     Advantageously, the present invention reduces the concentrations of nitrogen-containing compounds, sulfur-containing compounds and PNA compounds in a heavy feedstream to a hydrocracking unit such as a DMO or DAO feedstream. In addition, in recycle hydrocracking operations, the concentration of HPNA compounds that are formed in the unconverted fractionator bottoms is reduced. Accordingly, the overall efficiency of operation of the hydrocracking unit is improved along with the effluent product quality. 
     EXAMPLE 
     Attapulgus clay having the properties set forth in Table 1 was used as an adsorbent to treat a blend of de-metalized oil stream and unconverted hydrocracker bottoms (1:2 ratio). The virgin DMO contained 2.9 W % sulfur and 2150 ppmw nitrogen, 7.32 W % MCR, 6.7 W % tetra plus aromatics as measured by a UV method. The unconverted hydrocracker bottoms was almost free of sulfur (&lt;10 ppmw), nitrogen (&lt;2 ppmw) and contained &gt;3000 ppmw coronene and its derivatives and about 50 ppmw of ovalene. The mid-boiling point of the DMO stream was 614° C. as measured by the ASTM D-2887 method. The unconverted hydrocracker bottoms had much lower mid boiling point (442° C.). The de-metalized oil and HPNA blend was mixed with a straight run naphtha stream boiling in the range of 36° C. to 180° C. containing 97 W % paraffins, the remainder being aromatics and naphthenes at 1:10 V:V % ratio and passed to the adsorption column containing attapulgus clay at 20° C. The contact time for the mixture was 30 minutes. 
     The naphtha fraction was distilled off and 94.7 W % of adsorbent treated DMO/unconverted hydrocracker bottoms mixture was collected. The molecules adsorbed on the adsorbent material, was desorbed in two steps. A first desorption step was conducted with toluene, and after distilling the first desorption solvent, the yield was 3.6 W % based on the total weight of the blend feed. A second desorption step was conducted with tetrahydrofuran, and after distilling the second desorption solvent, the yield was 2.3 W % based on the initial feed. After the treatment process, 75 W % of nitrogen-containing compounds, 44 W % of MCR and 2 W % of sulfur-containing compounds were removed from the blend sample. 95 W % of the HPNA was also removed from the blend. 
     The treated de-metalized oil and unconverted hydrocracker bottoms were hydrocracked using a stacked-bed reactor. Using the treated de-metalized oil and unconverted hydrocracker bottoms according to the process herein, the hydrocracking reactions occurred with a decrease in 10° C. in reactivity temperature as compared to untreated oil as shown in Table 2, thereby indicating the effectiveness of the feedstream treatment process of the invention. Table 3 shows product yields for both configurations 
     The reactivity, which can be translated into longer cycle length for the catalyst, can result in at least one year of additional cycle length for the hydrocracking operations, processing of a larger quantity of feedstream, or processing of heavier feedstreams by increasing the de-metalized oil content of the total hydrocracker feedstream. In addition, the treatment of unconverted hydrocracker bottoms stream resulted in clean recycle stream and eliminated the indirect recycle to the vacuum tower or other separation units such as solvent de-asphalting. 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Property 
                 Unit 
                 Attapulgus Clay 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Surface Area 
                 m 2 /g 
                 108 
               
               
                   
                 Pore Size 
                 °A 
                 146 
               
               
                   
                 Pore Size Distribution 
                 °A-cc/g 
                 97.1 
               
               
                   
                 Pore Volume 
                 cc/g 
                 0.392 
               
               
                   
                 Carbon 
                 W % 
                 0.24 
               
               
                   
                 Sulfur 
                 W % 
                 0.1 
               
               
                   
                 Arsenic 
                 ppmw 
                 55 
               
               
                   
                 Iron 
                 ppmw 
                 10 
               
               
                   
                 Nickel 
                 W % 
                 0.1 
               
               
                   
                 Sodium 
                 ppmw 
                 1000 
               
               
                   
                 Loss of Ignition @500° C. 
                 W % 
                 4.59 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                 VGO/DMO 
               
               
                   
                 VGO/DMO 
                 Blend With 
               
               
                   
                 Blend No 
                 treated DMO 
               
               
                 Feedstream 
                 Treatment 
                 Treatment 
               
               
                   
               
             
             
               
                 VGO/DMO Ratio 
                 85:15 
                 85:15 
               
               
                 Temperature 
                 398° C. 
                 388° C. 
               
               
                 Pressure 
                 115 Kg/cm2 
                 115 Kg/cm2 
               
               
                 Hydrogen to Oil Ratio 
                 1,500 
                 1,500 
               
               
                 LSHV 
                 0.70 h−1 
                 0.70 h−1 
               
               
                 Catalyst 1 
                 Ni—W on 
                 Ni—W on 
               
               
                   
                 Silica Alumina 
                 Silica Alumina 
               
               
                 Catalyst 2 
                 Ni—W on Zeolite 
                 Ni—W on Zeolite 
               
               
                 Catalyst 1/Catalyst 2 V:V % 
                 3:1 
                 3:1 
               
               
                 Overall Conversion of 370° C.+ 
                   95 
                   95 
               
               
                 Hydrocarbons, W % 
               
               
                 Recycle of 370° C.+, W % 
                   15 
                   15 
               
               
                 Bleed of 370° C.+ Hydrocarbons, 
                    0 
                    0 
               
               
                 W % 
               
               
                   
               
             
          
         
       
     
     
       
         
               
               
               
             
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                   
                 VGO/DMO 
                   
               
               
                   
                 Blend No 
                 VGO/DMO Blend With 
               
               
                 Feedstream 
                 Treatment 
                 treated DMO Treatment 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Light Naphtha 
                 20.01 
                 22.02 
               
               
                 Heavy Naphtha 85-185° C. 
                 39.64 
                 37.34 
               
               
                 Kerosene 185-240° C. 
                 8.68 
                 8.58 
               
               
                 Light Diesel Oil 240-315° C. 
                 6.41 
                 6.42 
               
               
                 Heavy Diesel Oil 315-375° C. 
                 4.42 
                 4.56 
               
               
                 Bottoms 375-FBP ° C. 
                 20.84 
                 21.07 
               
               
                   
               
             
          
         
       
     
     The method and system of the present invention have been described above and in the attached drawings; however, modifications will be apparent to those of ordinary skill in the art and the scope of protection for the invention is to be defined by the claims that follow.