Abstract:
A process for preparing benzene which involves heating a selected hydrocarbon stock containing condensed polynuclear aromatic rings in the presence of hydrogen under critical reaction conditions.

Description:
This application is a continuation-in-part application of our U.S. Patent Application Ser. No. 688,106, filed May 19, 1976, entitled &#34;Process for Producing Benzene,&#34; now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a process for converting a selected hydrocarbon stock containing substantial amounts of condensed polynuclear aromatic rings to a product containing significant amounts of benzene. 
     2. Description of the Prior Art 
     Hydrocarbon stocks have been subjected to treatment at elevated temperatures in the presence of hydrogen to obtain lower-molecular weight hydrocarbons, but the reactions described have not resulted in the production of reaction products containing substantial amounts of benzene. Such processes are described in U.S. Pat. Nos. 2,875,150 to Schuman, 2,885,337 to Keith et al and 3,178,272 to Dent et al. 
     SUMMARY OF THE INVENTION 
     We have found that we can obtain a product containing a substantial amount of benzene from a hydrocarbon stock by heating the same in the presence of hydrogen under critical reaction conditions. The hydrocarbon charge stock used herein is selected from the group consisting of FCC Furnace Oils, FCC Decanted Oils and coal liquids derived from the hydrogenation of coal. By &#34;FCC Furnace Oil&#34; we mean to include the product from a conventional fluid catalytic cracking process having a boiling point range at ambient pressure of about 220° to about 345° C., and by FCC Decanted Oil we mean to include the product from a conventional fluid catalytic cracking process having a boiling point range at ambient pressure of about 345° to about 510° C. 
     The process is simply carried out by heating the hydrocarbon charge defined above in the presence of hydrogen, preferably by passing the mixture through a non-catalytic bed composed, for example, of particulate material, such as bauxite, sand, zircon, quartz, magnesia, alumina, magnesia-alumina, silica-alumina, etc. However, the conditions needed to convert the defined charge to a product containing substantial amounts of benzene are critical. 
     The average temperature in the reaction zone must be within the range of about 650° to about 1100° C., preferably within the range of about 700° to about 930° C. By &#34;average temperature&#34; we mean the volume average temperature of the fraction of the reactor which is above 650° C. In addition, it is necessary that the temperature in the reaction zone reach a minimum level of 700° C., preferably about 760° C. The total pressure in the reaction zone must be between about 800 to about 2500 pounds per square inch gauge (about 56 to about 175 kilograms per square centimeter), preferably in the range of about 900 to about 2000 pounds per square inch gauge (about 63 to about 140 kilograms per square centimeter). The hydrogen partial pressure must be within the range of about 500 to about 2000 pounds per square inch gauge (about 35 to about 140 kilograms per square centimeter), preferably about 800 to about 1600 pounds per square inch gauge (about 56 to about 112 kilograms per square centimeter). By &#34;hydrogen partial pressure&#34; we mean the total pressure in the reactor multiplied by the mol fraction of hydrogen in the gas feed. When the sole gas in the reaction system is hydrogen, then the hydrogen partial pressure and total pressure will be the same. The hydrogen ratio must be at least about 0.5, preferably in the range of about 1.0 to about 3.0. By &#34;hydrogen ratio&#34; we mean the ratio of hydrogen in the gas feed to that theoretically required for substantially complete conversion of all of the carbon in the liquid feed to methane. The residence time must be at least three seconds but no more than about 120 seconds, preferably at least about four seconds but no more than about 45 seconds. Although these conditions, as set forth above, are critical in order to maximize the amount of benzene produced, it is understood that best results are obtained by a close correlation of the above parameters, one with the other, than can easily be determined in practice. 
     By following the above dictates we have found that, per pass, the benzene yield is at least about 14 weight percent based on the hydrocarbon feed, but in general the benzene yield based on the hydrocarbon feed ranges from about 16 to about 50 weight percent. Substantially all of the benzene produced is obtained as a result of the conversion of the condensed polynuclear aromatic compounds in the charge. The benzene and the remaining individual liquid components can be recovered from the reaction product in any suitable manner, for example, by fractionation, after the gaseous products have been previously removed from the reaction product by reducing the pressure thereon and venting. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     A number of runs was carried out in which various feeds, together with hydrogen, were passed downwardly through a reactor to obtain a product containing benzene. The reactor was 135/8 inches (34.6 centimeters) long, 1/2-inch (1.27 centimeters) inner diameter, had a total volume of 2.51 cubic inches (41.2 cubic centimeters) and contained a 1/8-inch (0.318 centimeter) thermowell down the center. The reactor was packed with -10 to +20 mesh quartz packing and had a void volume of 1.10 cubic inches (18.1 cubic centimeters). The charge stocks used were a FCC Decanted Oil, a FCC Furnace Oil and coal liquids obtained from the hydrogenation of a Big Horn coal, the coal liquids (A) and (B) having a boiling range at atmospheric pressure of 316° to 343° C. and 232° to 426° C., respectively. The properties of the feedstocks used are set forth below in Table I. 
     
                                           TABLE I__________________________________________________________________________                             Coal             FCC     FCC     Liquids             Decanted Oil                     Furnace Oil                             A      B__________________________________________________________________________Gravity, ° API.sup.1             8.1     12.1    2.10   0.0Elemental Analysis, WeightPer CentCarbon            89.88   91.27   90.48  90.48Hydrogen          9.04    8.50    7.40   6.94Oxygen            0.14    0.10    1.60   1.60Nitrogen          0.12    0.014   0.43   0.60Sulfur            0.93    0.48    0.15   0.14Hydrocarbon Analysis,Volume PercentAromatics         91.3.sup.2                     98.0.sup.2                             98.7.sup.2                                     66.sup.6Saturates         8.7     2.0     1.3    30Benzene, Weight Per Cent ofAromatic Fraction 2.1     1.1     0.4    --Asphalthenes, Weight Per Cent             0.42    0.13    0.61   1.49Carbon Residue, Weight Per Cent.sup.3             3.34    0.10    0.34   0.70Distillation10 Per Cent        310° C.sup.4                      250° C.sup.5                             Not Taken                                     334° C.sup.450 Per Cent       384° C                     265° C                             Not Taken                                    448° C90 Per Cent        442° C.sup.6                     298° C                             Not Taken                                    524° C__________________________________________________________________________ .sup.1 ASTM D-180 .sup.2 ASTM D-1319 .sup.3 ASTM D-189 .sup.4 ASTM D-1160 .sup.5 ASTM D-86 .sup. 6 Cracked at 80%; distillation to 80% given 
    
     It can be seen that there was very little benzene in the feed stocks. Upon completion of the runs, the reaction product obtained was analyzed and the data obtained are set forth in the tables below. 
     
                                           TABLE II__________________________________________________________________________Hydrogenation of FCC Furnace Oil__________________________________________________________________________Run No.               1    2    3   4   5   6    7__________________________________________________________________________Liquid Feed Rate (Grams Per Hour)                 16.8 34   41.2                               40.1                                   41.3                                       8.6  16.6Total Gas Feed (Liters Per Hour At STP)                 125  250  323 323 323 162  323Hydrogen Concentration In Gas, MolPer Cent.sup.1        100  100  100 100 100 40   40Total Reactor Pressure, PSI (Kg/Cm.sup.2)                 1500 1500 1200                               900 600 1500 1500                 (105)                      (105)                           (84)                               (63)                                   (42)                                       (105)                                            (105)Partial Pressure Of Hydrogen In Feed,PSI (Kg/Cm.sup.2)     1500 1500 1200                               900 600 600  600                 (105)                      (105)                           (84)                               (63)                                   (42)                                       (42) (42)Residence Time, Seconds                 16   7    3   2   1   3    1Hydrogen Ratio        2.9  2.8  3.0 3.1 3.0 2.9  3.0Average Reactor Temperature, ° C                 774  774  774 774 774 774  774Maximum Temperature Reached, ° C                 843  843  843 843 843 843  843Product Yields, Per Cent By WeightBased On Liquid FeedBenzene               18.1 24.2 22.4                               9.9 4.9 14.9 3.5Toluene               0.4  0.6  0.3 0.2 0.3 0.5  0.1Xylenes And/Or Ethylbenzenes                 0.2  0.2  0.1  --  --  --  0.1Naphthalenes          12.3 24.0 13.1                               19.0                                   32.3                                       9.8  9.3Anthracene And/Or Phenanthrene                 0.5  0.5  0.5 6.8 2.9 0.4  3.0Methane               61.2 41.4 46.4                               49.4                                   35.0                                       2    2Ethane And/Or Ethylene                 17.8 15.8 19.8                               23.7                                   21.3                                       40.6 44.5__________________________________________________________________________ .sup.1 Balance is methane .sup.2 Large quantity of methane in feed makes material balance exceedingly difficult 
    
     
                                           TABLE III__________________________________________________________________________Hydrogenation of Coal Liquids__________________________________________________________________________Run No.          Coal Liquids A    Coal Liquids BRun No.          8  9  10 11 12 13 14  15 16 17 18 19 20__________________________________________________________________________Liquid Feed Rate (Grams Per Hour)            34.1               67.0                  68.0                     36.0                        33.5                           16.7                              36.7                                  18.4                                     36.6                                        17.0                                           35.5                                              22.9                                                 8.88Hydrogen Feed Rate (Liters PerHour At STP).sup.1            125               250                  500                     500                        250                           125                              250 125                                     250                                        125                                           250                                              75 30Total Reactor Pressure, PSI(Kg/Cm.sup.2)    1500               1500                  1500                     1500                        1500                           1500                              1500                                  1500                                     1500                                        750                                           1500                                              1500                                                 1500            (105)               (105)                  (105)                     (105)                        (105)                           (105)                              (105)                                  (105)                                     (105)                                        (53)                                           (105)                                              (105)                                                 (105)Residence Time, Seconds            14 7  3  3  7  15 6   15 5  7  7  25 39Hydrogen Ratio   1.4               1.4                  2.8                     1.4                        2.8                           2.8                              2.5 2.5                                     2.5                                        2.7                                           2.6                                              1.2                                                 1.2Average Reactor Temperature, ° C            774               774                  774                     774                        774                           774                              774 774                                     691                                        774                                           774                                              774                                                 774Maximum Temperature Reached, ° C            843               843                  846                     849                        843                           845                              843 843                                     704                                        843                                           843                                              846                                                 843Product Yields, Per Cent By WeightBased on Liquid FeedBenzene          31.2               34.0                  26.5                     25.6                        23.8                           25.0                              35.8                                  28.7                                     7.7                                        4.2                                           30.0                                              50.2                                                 17.6Toluene          6.4               1.3                  1.1                     1.5                        0.8                           0.4                              0.3 0.2                                     -- -- 1.0                                              0.5                                                 0.4Xylenes And/Or Ethylbenzenes            1.2               1.5                  0.1                     0.1                        0.1                           0.1                              --  -- -- -- 0.1                                              0.1                                                 --Naphthalenes     21.2               26.5                  28.7                     29.5                        20.0                           14.3                              10.0                                  2.9                                     23.1                                        22.5                                           22.3                                              6.8                                                 2.2Anthracene And/Or Phenanthrene            4.6               7.1                  7.6                     8.9                        7.0                           3.4                              1.0 0.6                                     29.1                                        20.9                                           11.7                                              0.7                                                 1.1Methane          40.5               24.0                  30.4                     22.3                        34.6                           40.9                              Not 61.4                                     10.8                                        32.7                                           29.6                                              23.2                                                 91.0                              TakenEthane And/Or Ethylene            11.6               10.3                  15.6                     11.4                        15.6                           13.2                              Not 16.5                                     10.9                                        8.9                                           11.8                                              2.0                                                 9.1                              Taken__________________________________________________________________________ .sup.1 Gas feed is all hydrogen 
    
     
                       TABLE IV______________________________________Hydrogenation of FCC Decanted OilRun No.               21       22     23______________________________________Liquid Feed Rate (Grams Per Hour)                 17.2    33.7    67.0Hydrogen Feed Rate (Liters Per Hour At                 125     250     500STP).sup.1Total Reactor Pressure, PSI (Kg/Cm.sup.2)                 1500    1500    1500                 (105)   (105)   (105)Residence Time, Seconds                 12      6       2Hydrogen Ratio        2.9     3.0     3.0Average Reactor Temperature, ° C                 774     774     774Maximum Temperature Reached, ° C                 843     843     846Product Yields, Per Cent By WeightBased On Liquid FeedBenzene               19.5    23.6    9.5Toluene               0.2     0.5     0.6Xylenes And/Or Ethylbenzenes                 --      --      --Naphthalenes          6.7     14.7    15.4Anthracene And/Or Phenanthrene                 1.3     5.8     13.2Methane               57.0    51.8    33.5Ethane And/Or Ethylene                 20.6    18.6    21.1______________________________________ .sup.1 Gas feed is all hydrogen 
    
     The data in Tables II, III and IV above amply demonstrates the criticality of operating within the defined limits herein to obtain a product containing large amounts of benzene. Thus, when the reaction conditions defined herein were strictly maintained in the treatments of the defined charges in each of Runs Nos. 1 to 3, 6, 8 to 15 and 18 to 22 excellent yields of benzene were obtained. When operation in Runs Nos. 4 (residence time too low), 5 (total pressure and residence time too low), 7 (residence time too low), 16 (maximum reactor temperature too low), 17 (total reactor pressure too low) and 23 (residence time too low), was outside of the defined critical limits, the benzene yields were low. 
     Obviously, many modifications and variations of the invention, as hereinabove set forth, can be made without departing from the spirit and scope thereof and, therefore, only such limitations should be imposed as are indicated in the appended claims.