Abstract:
In an ebullated bed process, a nominal 1000° F.+ boiling point vacuum residuum is hydrotreated at a first temperature of 750° F. to 875° F. and total pressure of 1900 psig to 3000 psig. Hydrogen partial pressure is controlled by changing total reactor pressure in the range of 1700 psig to 2300 psig to achieve a selected yield of 650° F.- boiling material.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to an improved ebullated bed process. In the improved process hydrogen partial pressure is adjusted by adjusting total reactor pressure to achieve a selected 650° F. minus yield. Individual component yields boiling below 650° F. are also affected to different degrees. 
     2. Description of Other Relevant Methods in the Field 
     The ebullated bed process comprises the passing of concurrently flowing streams of liquids or slurries of liquids and solids and gas through a vertically cylindrical vessel containing catalyst. The catalyst is placed in random motion in the liquid and has a gross volume dispersed through the liquid medium greater than the volume of the mass when stationary. The ebullated bed process has found commercial application in the upgrading of heavy liquid hydrocarbons such as vacuum residuum or atmospheric residuum or converting coal to synthetic oils. 
     The ebullated bed process is generally described in U.S. Pat. Re. No. 25,770 issued Apr. 27, 1965 to E. S. Johanson. In Example 1, a residual hydrocarbon oil having a gravity of 8.3° API is treated at a temperature of 830° F., pressure of 3000  psig and hydrogen supplied at 1000 SCF H 2  per barrel of charge stock, to yield a cracked product reduced in sulfur. 
     U.S. Pat. No. 3,412,010 to S. B. Alpert et al. discloses an ebullated bed process for the production of fuels such as diesel oil. A crude feedstock is passed to an ebullated bed at a temperature of 750° F. to 900° F., pressure of 1000 to 5000 psig with at least 2500 scf/bbl of hydrogen. It was found that with recycle, the yield of naphtha and furnace oil could be adjusted. 
     U.S. Pat. No. 3,681,231 to S. B. Alpert et al. describes an ebullated bed process wherein a petroleum residuum feed material is treated at a temperature of 600° F. to 900° F., a total pressure of 500 psig to 5000 psig and a hydrogen partial pressure in the range of from about 65% to 95% of the total pressure to yield fuel oils such as diesel oil. 
     U.S. Pat. No. 3,773,653 to G. Nongbri et al. discloses an ebullated bed process for the production of coker feedstocks. In the process a residuum feed is passed through an ebullated bed of particulate hydrotreating catalyst at a hydrogen partial pressure between 1500 and 3000 psi, temperature between 700° F. and 900° F. and space velocity between 0.3 and 1.5 volume of feed per hour per volume of reactor. 
     SUMMARY OF THE INVENTION 
     The invention is an improvement in an ebullated bed process which hydrocracks a nominal 1000° F.+ boiling point vacuum residuum in the presence of a particulate catalyst. The process comprises passing the residual oil along with a hydrogen-containing gas upwardly through a zone of ebullated hydrogenation catalyst at a temperature of 750° F. to 875° F. The total pressure is about 1900 psig to 3000 psig and the space velocity is 0.1 to 1.5 volume of oil per hour per volume of reactor. Hydrogen partial pressure is controlled by changing total reactor pressure in the range of 1700 to 2300 psig to achieve a selected yield of 650° F. minus boiling range material. Each hydrocarbon yield boiling below 650° F. minus is affected in the process simultaneously. The novelty exists in the method of changing the hydrogen partial pressure, since all known ways to change hydrogen partial pressure do not yield the same advantage as when hydrogen partial pressure is varied by changing reactor pressure. 
     There are four ways to control hydrogen partial pressure: by changing reactor pressure as is disclosed in this application, by changing hydrogen gas rate at constant reactor pressure (see Example 3), by changing hydrogen feed gas purity (see Example 4), or by addition of gas phase material with the feed (addition of light liquid hydrocarbons). Each of these four methods will be discussed in further length in the Examples to follow. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     During an evaluation of the effects of reactor outlet hydrogen partial pressure when processing a nominal 1000° F.+ boiling point vacuum residuum, it was discovered that raising the reactor pressure increased the yields of all materials boiling below 650° F. and decreased the yield of 650° F. to 1000° F. boiling material without affecting the conversion of 1000° F. plus boiling range material. This invention is better shown by way of Example. 
     EXAMPLE 
     In all the following Examples, an ebullated bed system using two reactors in series was employed. The pilot unit used is a nominal 5 barrel per day unit utilizing a pseudo-equilibrated (age distributed) catalyst. Catalyst is replaced at a given rate each day to affect the age distribution. A two-stage system was utilized to give improved hydrogenation activity over a single stage unit, but it not believed to be necessary to affect the observed change in product yields. No interstage separation of gas and liquid was utilized during this study. The feed stock used during this study was obtained from a mixture of vacuum residuum obtained from both domestic and foreign sources. Properties of the feed are shown in Table I. It should be noted that the feed is a nominal 1000° F.+ boiling point vacuum residuum. 
     Examples 1 and 2 show the affects of varied reactor outlet hydrogen partial pressure accomplished by changing total reactor pressure at two different levels of 1000° F.+ conversion to 1000° F.- material. The reactor pressure was changed by changing the amount of back pressure held on the hydrocracking zone. Note the increase in all light hydrocarbon yields as the outlet hydrogen partial pressure increased. This is unexpected and novel in light of Examples 3 and 4. 
     A nominal 1000° F.+ boiling point vacuum residuum was chosen for this experiment to obtain a feed typical of commercial operations. It is suspected that lighter feeds such as atmospheric residuum or atmospheric gas oils would not give the same unexpected results seen in Examples 1 and 2. The quantity of 650° F. minus boiling point material in these other feeds could be sufficient to inhibit the observed change in 650° F. minus yield. 
     
                       TABLE I______________________________________FEED DETAILED DATA SECTION               TOTAL  1000° F.+______________________________________Gravity, API (ASTM D-287)                 5.1      4.8X-Ray Sulfur, wt % (ASTM D-4294)                 4.60     4.64Carbon Residue, wt % (ASTM D-189)                 22.85    23.56Total Nitrogen, wppm  3767     3857(Chemiluminescence)CHN Analysis, wt %(LECO Combustion Analysis)Carbon                85.3Hydrogen              10.2Nitrogen              .9Metals, wppmV                     92.8     96.8NI                    33.4     34.9FE                    8.6      19.4CR                    .5       .5NA                    11.4     11.9Ash, wt % (ASTM D-482)                 .02Pentane Insolubles, wt %                 22.10(by solvent extraction)Heptane Insolubles, wt %                 8.17(by solvent extration)Toluene Insolubles, wt %                 .09(by solvent extraction)Asphaltenes, wt % (by substraction)                 8.08Kinematic Viscosity, CST (ASTM D-445)@ 212 Deg F.          1948.0@ 250 Deg F.          500.0@ 30  Deg F.          135.0______________________________________ Explanation of Abbreviations API = American Petroleum Institute wt % = weight percent wppm = weight parts per million CST = centistokes Deg F. = degrees Fahrenheit 
    
     
         ______________________________________EXAMPLE 1COMPARISON OF YIELDS AT LOW CONVERSION______________________________________Run Number       1228D       1228SNumber of Stages 2           2Operating ConditionsAvg RX Temp., Deg F.            781         780LHSV, V/Hr/V     .30         .30H.sub.2 Partial PressureInlet, psia      2526        1971Outlet, psia     2276        1795Gas Rates, SCFB  TOTAL    H.sub.2                            TOTAL  H.sub.2Make-up Gas      6903     6903   6649   6649Reactor Conditions            RX1      RX2    RX1    RX2Avg Rx Temp., Deg F.             782      779    780    7801000+°F. Conv., Vol %            41.9        43.5Material Balance WT %        WT %NH.sub.3, Ammonia            .14         .06H.sub.2 S, Hydrogen Sulfide            3.86        3.24H.sub.2, Hydrogen            -1.26       -1.10C.sub.1, Methane .97         .80C.sub.2, Ethane  .76         .64C.sub.3, Propane .95         .72iC.sub.4, Isobutane            .07         .03nC.sub.4, Normal Butane            .79         .47iC.sub.5, Isopentane            .23         .11nC.sub.5, Normal Pentane            .48         .24IBP-180° F.            .59         .48180-360° F.            4.54        3.81360-650°F.            12.33       10.36650° F. Minus            21.71       17.66650-1000° F.            29.24       30.62Reactor 2 Outlet Pressure, psig            2489        1935______________________________________ Explanation of Abbreviations Deg F. = degrees Fahrenheit SCFB = standard cubic feet per barrel of fresh feed V/Hr/V = volume of oil/hour/volume of reactor psia = pounds per square inch absolute psig = pounds per square inch gauge Vol % = volume percent Rx1 = reactor one Rx2  = reactor two WT % = weight percent 
    
     
         ______________________________________EXAMPLE 2COMPARISON OF YIELDS AT HIGHER CONVERSION______________________________________Run Number       1229A       1229LNumber of Stages 2           2Operating ConditionsAvg Rx Temp., Deg F.            788         791LHSV, V/Hr/V     .301        .303H.sub.2 Partial PressureInlet, psia      2525        2176Outlet, psia     2251        1929Gas Rates, SCFB  TOTAL    H.sub.2                            TOTAL  H.sub.2Make-up Gas      6659     6659   6569   6569Reactor Conditions            RX1      RX2    RX1    RX2Avg Rx Temp., Deg F.             787      790    792    7891000+° F. Conv., Vol %            53.6        53.3Material Balance WT %        WT %NH.sub.3, Ammonia            .13         .10H.sub.2 S, Hydrogen Sulfide            3.78        3.45H.sub.2, Hydrogen            -1.03       -1.51C.sub.1, Methane 1.16        1.01C.sub.2, Ethane  .88         .81C.sub.3, Propane 1.07        .95iC.sub.4, Isobutane            .09         .08nC.sub.4, Normal Butane            .84         .83iC.sub.5, Isopentane            .20         .18nC.sub.5, Normal Pentane            .36         .36IBP-180° F.            1.18        .80180-360° F.            5.68        5.16360-650° F.            15.65       13.62650° F. Minus            27.11       23.80650-1000° F.            29.78       33.09Reactor 2 Outlet Pressure, psig            2489        2140______________________________________ Explanation of Abbreviations Deg F. = degrees Fahrenheit SCFB = standard cubic feet per barrel of fresh feed V/Hr/V = volume of oil/hour/volume of reactor psia = pounds per square inch absolute psig = pounds per square inch gauge Vol % = volume percent Rx1 = reactor one Rx2 = reactor two WT % = weight percent 
    
     Example 3 shows the affects of changing hydrogen partial pressure by changing gas rates. If hydrogen partial pressure is decreased by decreasing gas rate, the same effect on yields is not observed. Lowering the gas rate in the ebullated bed reactor can decrease the hold-up of gas in the reactor and increase the liquid residence time, thus allowing liquid phase material to further crack to 650° F. minus material. Hence, in the ebullated bed process, the mode by which hydrogen partial pressure is changed unexpectedly affects the resulting product yields. 
     
         ______________________________________EXAMPLE 3COMPARISON AT VARIED GAS RATE______________________________________Run Number       1229Y       1229ZNumber of Stages 2           2Operating ConditionsAvg Rx Temp., Deg F.            800         800LHSV, V/Hr/V     .309        .307H.sub.2 Partial PressureInlet, psia      2394        2519Outlet, psia     2011        1935Gas Rates, SCFB  TOTAL    H.sub.2                            TOTAL  H.sub.2Make-up Gas      5539     5539   4417   4417Reactor Conditions            RX1      RX2    RX1    RX2Avg Rx Temp., Deg F.             800      800    800    8001000+° .F Conv., Vol %            62.4        63.1Material Balance WT %        WT %NH.sub.3, Ammonia            .12         .11H.sub.2 S, Hydrogen Sulfide            3.46        3.55H.sub.2, Hydrogen            -1.49       -1.94C.sub.1, Methane 1.13        1.12C.sub.2, Ethane  98          1.05C.sub.3, Propane 1.17        1.29iC.sub.4, Isobutane            .16         .26nC.sub.4, Normal Butane            .90         .97iC.sub.5, Isopentane            .26         .30nC.sub.5, Normal Pentane            .52         .55IBP-180° F.            1.04        1.04180-360° F.            6.78        7.02360- 650° F.            16.35       15.85650° F. Minus            29.29       29.45650-1000° F.            35.28       35.97Reactor 2 Outlet Pressure, psig            2339        2460______________________________________ Explanation of Abbreviations Deg F. = degrees Fahrenheit SCFB = standard cubic feet per barrel of fresh feed V/Hr/V = volume of oil/hour/volume of reactor psia = pounds per square inch absolute psig = pounds per square inch gauge Vol % = volume percent WT % = weight percent 
    
     Example 4 shows the affects of changing hydrogen partial pressure by changing hydrogen gas purity. If hydrogen gas purity is reduced, total gas rate must increase to maintain a constant hydrogen partial pressure. Gas hold-up can increase and gas yields decrease. If hydrogen sulfide is introduced as in Example 4, additional hydrogenation results due to hydrogen donor activity of the hydrogen sulfide. This results in additional 650° F. minus material at the expense of unconverted vacuum residuum instead of at the expense of 650°-1000° F. boiling range material as seen in Examples 1 and 2. 
     
         ______________________________________EXAMPLE 4COMPARISON AT VARIED HYDROGEN PURITY______________________________________Run Number       1231H       863116Number of Stages 2           2Operating ConditionsAvg Rx Temp., Deg F.            800         800LHSV, V/Hr/V     .274        .275H.sub.2 Partial PressureInlet, psia      2438        2574Outlet, psia     2176        2181Gas Rates, SCFB  TOTAL    H.sub.2                            TOTAL  H.sub.2Make-up Gas      6801     6801   2457   2457Rx Feed Gas      3568     3568   4326   3987Recycle Gas                      3962   3458Reactor Conditions            RX1      RX2    RX1    RX2Avg Rx Temp., Deg F.             801      799    798    8011000+° F. Conv., Vol %            54.2        58.0Material Balance WT %        WT %NH.sub.3, Ammonia            .28         .32H.sub.2 S, Hydrogen Sulfide            3.16        3.20H.sub.2, Hydrogen            -1.27       -2.01C.sub.1, Methane 1.28        1.02C.sub.2, Ethane  .89         .84C.sub.3, propane 1.05        1.12iC.sub.4, Isobutane            .08         .21nC.sub.4, Normal Butane            .85         .89iC.sub.5, Isopentane            .19         .29nC.sub.5, Normal Pentane            .36         .54IBP-180° F.            .31         .44180-360° F.            4.63        7.13360-650° F.            20.80       21.35650° F. Minus            30.44       33.83650-1000° F.            27.59       27.11Reactor 2 Outlet Pressure, psig            2400        2763______________________________________ Explanation of Abbreviations Deg F = degrees Fahrenheit SCFB = standard cubic feet per barrel of fresh feed V/Hr/V = volume of oil/hour/volume of reactor psia = pounds per square inch absolute psig = pounds per square inch gauge Vol % = volume percent Rx1 = reactor one Rx2 = reactor two WT % = weight percent 
    
     The fourth way to affect hydrogen partial pressure is to add light liquid material to the feed which vaporizes or cracks into the gas phase at reactor conditions. This method was not pursued, since light hydrocarbon added to the residuum feed can cause precipitation of asphaltenic type materials and hence unacceptable products. Lighter aromatic diluants are sometimes added to the feed to prevent precipitation of asphaltic materials, however these diluents do not form a high percentage of vapor phase material at typical operating conditions thus they do not change the hydrogen partial pressure to a great degree.