US3071542A

US3071542A - Two-stage pretreatment of reformer charge naphtha

Info

Publication number: US3071542A
Application number: US748901A
Authority: US
Inventors: Jr Francis Earle Davis; Ramella Amilcare
Original assignee: Socony Mobil Oil Co Inc
Current assignee: ExxonMobil Oil Corp
Priority date: 1958-07-16
Filing date: 1958-07-16
Publication date: 1963-01-01
Anticipated expiration: 1980-01-01

Description

Jan. l, 1963 F. E. DAVIS, JR., ET AL 3,071,542

STAGE PRETREATMENT oF REFORMER CHARGE NAPHTHA TWO- 5 Sheets-Sheet 1 Filed July 16, 1958 .omz odms.

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Jan. l, 1963 F. E. DAVIS, JR., ET AL 3,071,542

TWO-STAGE PRETREATMENT OF REFORMER CHARGE NAPHTHA 5 Sheets-Sheet 2 Filed July 16, 1958 1 u d INI F. Em@ 5Go/1mm BAm danke mella! GENT Jan. 1, 1963 F. E. DAVIS, JR., ET AL 3,071,542

TWO-STAGE PRETREATMENT OF' REFORMER CHARGE NAPHTHA Filed July 16, 1958 5 Sheets-Sheet 3 d1 A w Il y f a i Aq u] N a@ 2 d Q g E59 N 3x51 En.

Z LowNlTRoGE NAPHTHA SEPARATOP.

GENT

Jan. l, 1963 F. E. DAVIS, JR., ETAL TWO-STAGE PRETREATMENT OF REFORMER CHARGE NAPHTHA 5 Sheets-Sheet 4 Filed July 16, 1958 dmmdommfx non xNvENToRg 'REQ/'ile 9 1 Jan l, 1963 F. E. DAvls, JR., ETAL 3,071,542

TWOSTAGE PRETREATMENT OF REFORMER CHARGE NAPHTHA Filed July 16, 1958 5 Sheets-Sheet 5 mdk.

INVE TOR mi NPP-...mm

mnu? NMPP-Jam mm E# United States Patent Oiilce 3,07L542 Patented dan. 1, 1963 3,071,542 TWG-STAGE PRETREATMENT F REFORMER CHARGE NAPHTHA Francis Earle Davis, Jr., Westville, and Amilcare Ramella,

Woodbury, NJ., assignors to Socony Mobil Oil Company, inc., a corporation of New York Filed July 16, 1958, Ser. No. 748,901 7 Claims. (Cl. 203-254) The present invention relates to the pretreatment of naphtha to be reformed over a nitrogen-sensitive catalyst and, more particularly, to the pretreatment of naphtha containing nitrogen compounds under relatively mild conditions prior to reforming the pretreated naphtha over a nitrogen-sensitive catalyst of the platinum type.

For several yea-rs it has been common practice to hydrodesulfurize naphtha prier to reforming the naphtha. In some instances the hydrodesulfurization of the naphtha was to eliminate poisoning of the reforming catalyst but in most instances the hydrodesulfurization of the naphtha was to reduce corrosion of the reforming unit or to reduce the size of the facilities required to remove the sulfur compounds from gases vented to the air.

rior to the increased demand for high octane gasoline it Was unnecessary to reform many stocks containing high concentrations of organic nitrogen compounds which poison nitrogen-sensitive catalysts such as the platinumtype reforming catalysts. With the increased demand for high octane gasoline it has become necessary to reform many of those stocks Which until recently were not reformed.

Hydrodesulfurization of practically lall common naphthas can be carried out under relatively mild conditions of temperature, pressure and hydrogen-to-naphtha ratio and at a relatively high space velocity. Thus, for example, a straight run naphtha from a Kuwait crude containing about 800 parts per million (ppm.) of sulfur and 0.2 ppm. of nitrogen can be hydrodesulfurized and hydrodenitrogenized over a catalyst comprising a mixture of oxides of cobalt and molybdenum on alumina at about 675 F. under about 425 psig. at a hydrogen-to-naphtha ratio of about 500 standard cubic feet (scf.) of hydrogen per barrel of naphtha charged and at a space Velocity (volume of naphtha/hour/volume of catalyst, v./hr./Y.) of about to provide a reformer charge stock containing less than 20 ppm. sulfur and substantially devoid of nitrogen compounds. On the other hand, when a mixture comprising about percent by volume of thermal gasoline containing 66 ppm. of nitrogen `and about 85 percent by volume of straight run naphtha containing about 0.2 ppm. of nitrogen is hydrodecontaminated over the same catalyst under the same operating conditions the nitrogen content of the hydrodecontaminated mixture is reduced from l0 ppm. to 1.4 ppm.

It has been found that to maintain 4a platinum-type reforming catalyst on stream for a practical period of time the nitrogen content of the charge to the reforming reactor must be less than about l p.p.m. of nitrogen.

It has also been `determined that to reduce the nitrogen content of a naphtha containing about 12` ppm. of nitrogen to less than 1 ppm. of nitrogen requires much more severe conditions than the aforedescribed mild conditions. Thus, a naphtha containing l2 ppm. of nitrogen can be hydrodecontaminated to a nitrogen content of less than 1 ppm. over a catalyst comprising a mixture of oxides of cobalt and molybdenum on alumina at a temperature of 775 F., pressure of 425 p.s.i.g., hydrogen-tonaphtha ratio of about 2000 s.c.f./ barrel of naphtha charged and a space velocity of 2.

It has now `been determined that when a naphtha having a high nitrogen content, i.e., in excess of 25 ppm. of nitrogen is first hydrodecontaminated under relatively mild conditions such as set forth hereinbefore and more particularly as `described hereinafter, the treated na-phtha stripped of volatile nitrogen compounds, and the stripped treated naphtha mixed with low nitrogen containing naphtha to provide a blend having not more than about 7 ppm. and the mixture hydrodecontarninatedunder relatively miid conditions as set -forth hereinbefore and more particularly `as described hereinafter, the hydrodecontaminated mixture will contain less than 1 ppm. of nitrogen.

illustrative of the treatment of a high nitrogen naphtha containing in excess of 25 ppm. of nitrogen is the ilowsheet of FIGURE 1. The flowsheet of FIGURE l illustrates the treatment of a naphtha having a high concentration of nitrogen, to wit: Thermal naphtha containing 66 ppm. of nitrogen, over a catalyst combining capabilities of hydrogenate, hydrodesulfurize and hydrodenitrogenize, e.g., a mixture of oxides of cobalt and molybdenum. The partially hydrodecontaminated na-phtha is stripped of volatile hydrogen `derivatives of the contaminants, and the stripped, partially hydrodecontaminated naphtha `containing about 24 ppm. of nitrogen is then mixed with a naphtha having a low nitrogen content, eg., about 0.2 ppm. to provide a mixture containing about 3 ppm. of nitrogen. The mixture is hydrodecontarninated and stripped of volatile hydrogen derivatives of the contaminants to provide a reformer feed containing about 0.3 ppm. of nitrogen and less than 20 ppm. of sulfur. The naphtha feed thus produced is then reformed over a nitrogen-sensitive catalyst, e.g., a platinum-type catalyst comprising about 0.1 to 'about l percent platinum on alumina.

In FGURE l a naphtha containing in excess of 25 ppm. of nitrogen, e.g., thermal naphtha containing about 66 ppm. nitrogen, is drawn from a source not shown through pipe 'l by pump 2. Pump 2 discharges: the thermal naphtha containing about y66 ppm. of nitrogen into conduit 3 at -a pressure in excess of the pressure in secondary decontaminator 10. It is preferred to mix .about 50 to about cubic feet (c f.) of hydrogen per barrel of thermal naphtha with the naphtha prior to heating the naphtha to hydrodecontaminating temperature. Accordingly, hydrogen-rich recycle gas flowing from conduit 9` under control of valve 84- flows through conduit S5 to `conduit; 3i. The mixture of thermal naphtha and the small amount of hydrogen ltlows through conduit 3 to heat exchanger 4 where the thermal naphtha is in indirect heat exchange relation with the effluent of the secondary decontaminator l0 flowing through conduit 11.

From heat exchanger 4 the thermal naphtha and the small amount of hydrogen flow through conduit 5 to coil 6 in heater 7. In coil 6 the thermal naphtha is heated to a hydrodecontaminating temperature Within the range of about 600 to about 85 0 F. The heated thermal naphtha and hydrogen flow from coil 6 through conduit 8 to conduit 9. In conduit 9 the thermal naphtha is mixed with additional hydrogen to provide a total of about 50() to about 2500 scf. of hydrogen per barrel of thermal naphtha. For this purpose hydrogen-rich gas drawn from liquid-gas separator 17 and stripper 24 by compressor 29 as hereinafter `described and `discharged into conduit 9 is used. The heated thermal naphtha and hydrogen-containing gas flow through conduit 9 to secondary decontaminator 10.

In secondary decontaminator 10 the treating conditions for a cobalt `molybdenum ycatalyst are Within the limits set `forth in Table I.

. v Table I Catalyst: 2 to 3A percent cobalt oxide, 9 to 16 percent molybdenum oxide on alumina. Feed: Thermal naphtha containing 66 ppm. nitrogen.

1 Sci. is standard cubic feet.

The thermal naphtha and hydrogen-containing recycle gas pumped from separator 17 and stripper 24 by compressor 29 at a pressure higher than that in the secondary decontaminator flow downwardly through the secondary decontaminator to conduit 11. The partially decontaminated thermal naphtha and recycle gas, hereinafter designated second-ary etiluent, ilow through conduit 11 to heat exchanger 4 where the secondary effluent is in indirect heat exchange relation with the thermal naphtha feed as described hereinbefore.

The secondary eluent Hows from heat exchanger 4 through conduit 12 to heat exchanger 13 where the secondary eluent is in indirect heat exchange relation with the secondary condensate pumped from liquid-gas separator 17 by pump 21 through pipe 22. The cooled secondary eflluent flows from heat exchanger 13 through conduit 14 to cooler 15 Where the temperature of the second-ary eiuent is lowered to that at which C4 and heavier hydrocarbons are liquid at the pressure existing in liquid-gas separator 17.

From cooler 15 the secondary effluent ows through conduit 16 to liquid-gas separator 17. In liquid-gas separator 17 the uncondensed portion of the secondary eflluent separates from the condensed portion of the secondary eluent. The uncondensed portion of the secondary eluent flows from separator 17 through conduit 18 to conduit 19.

The condensed portion of the secondary eiluent ows through pipe 20 to pump 21. Pump 21 discharges the condensed portion of the secondary effluent, hereinafter designated secondary condensate, into pipe 22 through which the secondary condensate ows to heat exchanger 13 where it is in indirect heat exchange relation with the secondary eluent. From heat exchanger 13 the secondary condensate ows through pipe 23 to stripper 24.

The secondary condensate is stripped of volatile hydrogen derivatives of the contaminants sulfur, nitrogen, arsenic, etc., originally present in the thermal naphtha in stripper 24. Preferably a stripping gas eg., hydrogencontaining gas from the primary liquid-gas separator S3 and/or the primary stripper 60 and/or recycle gas from a reformer unit flowing'through conduit 74 as more fully discussed hereinafter is used to assist instripping the volatile hydrogen derivatives of the contaminants present in the thermal naphtha feed from the secondary condensate. The volatile hydrogen derivatives of the aforesaid contaminants, together with light hydrocarbons and stripping gas are taken as overhead through conduit 19. The overhead from stripper 24 flows through conduit 19 and together with the uncondensed portion of the secondary eiuent flowing from separator 17 through conduit 18 (as described hereinbefore) Hows to any suitable means 25 for removing the hydrogen derivatives of nitrogen compounds originally present in the thermal naphtha, to wit, ammonia. For example, the gaseous mixture can be contacted with aqueous acid, for example, sulfuric acid, to remove the ammonia. From the means 25 to remove ammonia the gaseous mixture ilows through conduit 26 to means 27, such as an amine scrubber, for removing hydrogen sulde (the hydrogen derivative of sulfur compounds originally present in the thermal naphtha). Hydrogen sulfide removal means 27 can be by-passed by closing valve 86 and opening valve 88 in conduit 89.

From means 2,7 the purified gaseous mixture designated secondary recycle gas and containing about 50 to aboutv percent hydrogen ilows through conduit 28 to the suction side of compressor 29. Any gas in excess of that required in the secondary decontaminator is vented from conduit 28 through conduit 30 under control of valve 31 for use in other processing or to the renery fuel system. Compressor 29 discharges the secondary recycle gas into conduit 9 as described hereinbefore.

Returning now to stripper 24; the stripped secondary condensate forms a bottoms in stripper 24. A minor portion of the bottoms of stripper 24 iiows from stripper 24 through pipe 32 to heat exchanger 33 and from heat exchanger 33 through pipe 34 back to stripper 24. In heat exchanger 33 the bottoms is heated to a temperature at which under conditions in the stripper Z4 the hydrogen derivatives of the contaminants originally present in the thermal gasoline are volatilized. Any other Vmeans for maintaining the necessary stripping temperature can be used instead of the reboiler shown.

The major portion of the stripper bottoms ilows from stripper 24 through pipe 35 to the suction side of pump 36. Pump 3'6 discharges the bottoms of stripper 24 into pipe 37.

The bottoms of stripper 24 usually contains not more than about p.p.m. of nitrogen. In the illustrative case in which the thermal naphtha feed contained 66 p.p.m. of nitrogen and 1,700 p.p.m. of sulfur the stripper bottoms contained about 24 ppm. of nitrogen and about 82 p.p.m. of sulfur.

Prior to treatment in the primary decontaminator the stripper bottoms is mixed with a low nitrogen naphtha such as a straight run naphtha containing about 0.1 to about l ppm. of nitrogen. In the illustrative case a straight run naphtha containing about 0.2 ppm. of nitrogen was mixed with the bottoms of stripper 24 in proportions to provide a primary decontaminator feed containing not more than about 7 ppm. of nitrogen. In the illustrative case the stripper bottoms and straight run naphtha were mixed in the proportions indicated in Table II.

Accordingly, straight run naphtha drawn from `a source not shown through pipe 38 by pump 39 is pumped through pipe 40 to heat exchanger 41. In heat exchanger 41 the straight run naphtha is in indirect heat exchange relation with primary effluent flowing from primary decontaminator 46 through conduit 47. From heat exchanger 41 the straight run naphtha ilows through pipe 42 to pipe 37 where it is mixed with the stripper bottoms to provide a mixture containing about 50 to about 95 percent by Volume straight run naphtha, said m-ixture containing not more than about 7 ppm. of nitrogen. The mixture of stripper bottoms and straight run naphthia, hereinafter designated primary decont-aminator feed flows through pipe 37 `to coil 43 in heater 44. It is preferred to mix a small amount, say about 50 to about 100 s.c.f. of hydrogen-containing gas such as primary recycle gas pumped yby compressor 67 through conduits 68 and 69 under control `of valve 70 with the primary decontaminator feed prior .to heating the primary decontaminator feed to reaction temperature. The prim-ary decontaminator feed and primary recycle gas are heated in heater 44 to a temperature within the range of about 600 to about 850 F. From coil 43 the primary decontaminator feed .and hydrogen flow through conduit 45 to primary decontaminator 46. In conduit 45 additional hydrogen-containing gas, such as primary recycle gas, pumped by compressor 67 through conduit 68 is mixed with the primary decontaminator feed in amount sufficient to provide a total of about 250 to about 1000 s.c.f. of hydrogen per barrel of primary decontaminator feed. The mixture of primary decontaminator feed and primary recycle gas ilows downwardly through primary decontaminator t6 to conduit (i7.

The operating conditions in primary decontaminator 46 are substantially the same as in second-ary decontaminator lo and are mild operating conditions. For a catalyst having hydrogenating as Well as decontaminating capabilities such as a catalyst comprising about 3 percent cobalt oxide and about 12 percent molybdenum oxide on alumina the operating conditions in primary decontaminator 46 are as set forth in Table HI.

Table III Catalyst: 2 to 3% cobalt oxide, 9 to 16% molybdenum oxide. Feed: not more than 7 ppm. of nitrogen.

From primary deeontaminator 45 the eilluent, designated primary effluent hereinafter, flows through conduit 47 to heat exchanger 4i Where the primary eiiiuent is in indirect heat exchange relation with the straight run naphtha as previously described. From heat exchanger il the primary effluent flows through conduit 48 to heat exchanger 49 where the primary effluent is in indirect heat exchange relation With the condensed portion of the primary eiuent designated primary condensate owing from liquid-gas separator 53. From heat exchanger 49, the primary eiuent ows through conduit 50 to cooler 5l. ln cooler Si the primary e'luent is cooled to a temperature at which C4 and heavier hydrocarbons condense at the pressure existing in liquid-gas separator 53. The cooled primary effluent hows from heat exchanger 51 through conduit 52 to liquid-gas separator S3. In liquidgas separator 53 the uncondensed por-tion `of the primary effluent separates from the condensed portion of the primary effluent (hereinafter designated primary condensate) and flows from separator 53 through conduit 54 to conduit 55.

The primary condensate ilows from separator 53 through pipe `5t to the suction side of pump 57. Pump 57 discharges the primary condensate into pipe 58 through Which the primary condensate flows to `heat exchanger 49. In heat exchanger 49 the primary condensate is in indirect heat exchange relation with the primary eiuent as hereinbefore described. From heat exchanger 49 the primary condensate flows through pipe 59 to stripper 60.

In stripper 60 the primary condensate is stripped of hydrogen derivatives of contaminants present in the primary feed, light hydrocarbons and residual hydrogen, preferably with aid of a stripping gas such as hydrogen* containing gas, for example, reformer recycle gas, pumped from a reformer unit not shown through conduit 651. An overhead comprising the hydrogen derivatives of contaminants present in the primary feed such as ammonia and hydrogen sulfide, hydrogen and light hydrocarbons, hereinafter designated primary recycle gas, is taken from stripper 60 through conduit 62 to conduit 55. The overhead flows through conduit 55 to means 63 `of any suitable type, as for example contact With aqueous acid solut-ion, for removing ammonia. Hydrogen sulde removal means 6'5 can be bypassed by closing valves 90 and 91 and opening valve 92 in conduit 93. From the means 63 for removing ammonia, the overhead ows through conduit di to means for removing hydrogen sulfide 65, for example, an amine scrubber. From the means for removing hydrogen sulfide 65 the primary recycle gas iioWs to the suction side of compressor 67. Compressor 67 discharges the hydrogen-containing primary recycle gas into conduit 63. A small portion, say about 50 to about scri., of primary recycle gas is diverted through conduit 69 under control of valve "tl to conduit 37 for the purpose of mixing the primary recycle gas with the primary decontaminator feed as described hereinbefore. The balance of the primary recycle gas iiows through conduit 6@ to conduit i5 Where it is mixed with the primary decontaminator feed in amounts to provide a total `of about 250 to about 2500 stof. of hydrogen per barrel of primary decontaminator feed as described hereinbefore.

As stated hereinbefore, the stripping gas for stripping the secondary `decontaminator condensate is either a portion of the overhead from stripper 6o or reformer recycle gas or -a mixture of both. Thus, when overhead from stripper 60 is to be used to strip the secondary decontaminator condensate in stripper 24 about 300 to about 500 s.c.f. of overhead from stripper 6G per barrel of high nitrogen feed naphtha flows from conduit 55 through conduit '71 under control of valve 77; to compressor 73. Compressor ydischarges the overhead from stripper 60 yhereinafter designated secondary stripping gas into conduit 74. The secondary stripping gas ows through conduit 7i to stripper 24. When it is necessary or desirable to use reformer recycle gas as stripping gas the required amount of reformer recycle gas is diverted from conduit 6l through conduit 75 under control of valve 76 to conduit 7d through which the reformer recycle gas ilows to stripper Zi. lt follows that a mixture of secondary stripping gas from conduit 55 and reformer recycle gas can be used to strip Ithe secondary decontaminator condensate in stripper 2d by opening both valves 76 'and 72 the required amounts to proportion secondary stripping gas yand reformer recycle gas las is necessary or desirable. In the event that either secondary stripper 24 or primary stripper d@ operates or both operate at pressures higher than that `at which reformer recycle gas is available the pressure of the reformer recycle gas can be raised to that of stripper 2tl- Without raising the pressure of the reformer recycle gas flowing to stripper 60 by opening valve 77. The portion of the reformer recycle gas required in stripper 2d is `diverted under control of valve 77 through conduit 78 to the suction side of compressor 79'. Compressor '79 discharges `into conduit Si?. With valves S3 and 76 closed, the portion of the reformer recycle gas diverted to compressor 7 9 ows from conduit 80 to conduits 7S and 74 to stripper 24. When both stripper 60 and [stripper 2d are operating `at pressures higher than that iat which the reformer recycle gas is available valve 8l is closed, valve 77 is opened and the total flow of reformer recycle gas is passed through conduit 78 to compressor 79. With valve 83 open and valve 76 closed the discharge o-f `compressor 79 flows through conduits 61, 30 and SZ lto stripper e0 and through

conduits

80, 75 and "74 to `stripper 24.

The flowsheet, FIGURE 2, illustrates another embodirnent `of the present invention wherein the secondary condensate is freed from a major portion, if not all, of the ammonia produced in hydrodecontaminating a naphtha having a high nitrogen content, i.e., in excess of 25 ppm. of nitrogen.

Thu-s, a hydrocarbon mixture such as a thermal naphth-a, eig., a coker naphtha containing in excess of 25 ppm. of nitrogen is drawn yfrom a source not shown by pump lill lthrough pipe to2. Pump 101 discharges the hydrocarbon mixture containing in excess of 25` ppm. of nitrogen, hereinafter designated nitrogenous hydrocarbon mixture, into pipe HB3. The nitrogenous hydrocarbon mixture flows through pipe w3 to heat exchanger 104 Where it is in indirect heat exchange relation With the effluent from the secondary decontaminator, hereinafter designated secondary effluent, flowing from secondary decontaminator 110 through conduit 111. From heat exchanger 104 the niitrogenous hydrocarbon mixture flows through pipe 105 to coil 106 in furnace 107 where it is heated to reaction temperature as described hereinbefore. When desirable, a small amount, say about 50-100 scf. per barrel, of hydrogen-containing gas, eg., primary recycle gas tiowing in conduit 109 can be mixed with the nitrogenous hydrocarbon mixture prior to introduction of the nitrogenous hydrocarbon mixture into coil 106.

From heater 107 the heated nitrogenous hydrocarbon mixture flows through pipe 108 to secondary decontaminator 110. At some point in pipe 108 intermediate to heater 1117 and to decontaminator 110 hydrogen-containing gas containing not more than about 0.02 percent ammonia, eg., primary recycle -gas owing `from separator 147 through conduits 14d and 149 to means for removing ammonia 159 and `thence through conduit 109 to pipe S is mixed with the nitrogenous hydrocarbon mixture in an amount to provide about 500 to about 2500 s.c.f. of hydrogen per barrel of nitrogenous hydrocarbon mixture.

The mixture of hydrogen-containing `gas and nitrogenous hydrocarbon mix-ture ows downwardly through second-ary decontaminator 110. The secondary etuent flows from secondary decontaminator 110 through conduit 111 to heat exchanger 104 where the secondary effluent is in indirect heat exchange relation with the nitrogeno-us hydrocarbon mixture as described hereinbefore. From heat exchanger 104 lthe secondary efliuent flows Athrough conduit 112 to heat exchanger 113 where the secondary eiiluent is in indirect heat exchange relation with the condensate drawn from gas-liquid separator 117 through pipe 120 hy pump 121 and discharged into pipe 122. From heat exchanger 113 Kthe secondary effluent p ows :through pipe 114 to cooler (condenser) 115 Where the `secondary effluent is cooled to a temperature at which at the existing pressure the C4 and heavier hydrocarbons are condensed. The cooled secondary efl'luent liows from cooler 115 through conduit 116 to gas-liquid separator 117.

In separator 117 the uncondensed portion of the secondary eiuen-t comprising ammonia, hydrogen sulfide, C3 land lighter hydrocarbons, and hydrogen separates from the condensed portion of the secondary effluent and ows through conduit 11S to conduit 119 and thence to means :for removing ammonia 168 Iand thence through conduit 169 to means for removing hydrogen sullide (not shown) and thence to an absorber (not shown) Where the uncondensed secondary effluent is contacted with hydrocarbon mixture to be hydrodecontaminated. The condensed portion of the secondary efuent, hereinafter designated secondary condensate, flows from separator 117 through pipe 12o to the suction side of pump 121. Pump 121 discharges the secondary condensate into pipe 122. rl`he secondary condensate ows through pipe 122 to heat exchanger 113 as `described hereinbefore. From heat exchanger 113 the secondary condensate, heated to a temperature at which C4 and lighter hydrocarbons are volatile, ilows tluough pipe 123 to stripper 124. In stripper 124 the secondary condensate is contacted with stripping gas, eg., hydrogen-containing gas from separator 147 owing through

conduits

148 and 167 or a mixture of gas from separator 147 and hydrogen-containing reformer ygas owing to stripper `124 through

conduits

137, 154 and 167.

'Ihe overhead from stripper 124 comprising a major portion of C4 hydrocarbons and lighter hydrocarbons together with hydrogen and substantially all of the hydrogen derivatives of contaminants present in the nitro genous hydrocarbon mixture, e.g., ammonia and hydrogen sulfide, ows through conduit 125 to conduit 119 and to means 168 for removal of ammonia and then through conduit 169 to means for removing hydrogen sulde (not shown) and to an absorber Where the overhead is contacted with hydrocarbons to be decontaminated.

A portion of the bottoms of stripper 124 flows through pipe 128 to heat exchanger 129 where the bottoms is heated to a temperature at which a major portion of the C4 hydrocarbons is volatile. Any other means of maintaining the aforesaid temperature in stripper 124 can be used. From heat exchanger 129 the bottoms flows through pipe 130 back to stripper 124.

The balance, and major portion, of the bottoms of stripper 124 containing not more than about 140 ppm. of nitrogen Hows therefrom through pipe `131 to the suction side of pump 132. Pump 132 discharges the stripper bottoms into pipe 133. At some point in pipe 133 intermediate to pump 132 and to coil 134 in heater 13S a hydrocarbon mixture having a nitrogen concentration such that, when mixed with the aforesaid stripper bottoms in the proportion of 50 to 95 parts -by volume to S0 to 5 parts by volume of stripper bottoms, the mixture has a nitrogen concentration of not more than about 7 ppm., is mixed With the stripper bottoms. A suitable low nitrogen hydrocarbon mixture is straight run naphtha containing about 0.2 ppm. of nitrogen. Accordingly, straight run naphtha, for example, is drawn from a source not shown through pipe 160 by pump 161 and pumped through pipe 162 to heat exchanger 141. In heat exchanger 141 the straight run naphtha is in indirect heat exchange relation with the efuent from primary decontaminator 139. The efluent from primary decontaminator 139, hereinafter designated primary effluent, flows from decontaminator 139 to heat exchanger 141 through conduit 140. The straight run naphtha ows from heat exchanger 141 through pipe 172 to pipe 133 where the straight run naphtha is mixed with the stripper bottoms in a proportion to provide a mixture having a nitrogen content not greater than about 7 ppm.

The mixture, of stripper bottoms and straight run naphtha, containing not more than about 7 ppm. of nitrogen, hereinafter designated primary mixture, ows through pipe 133 to coil 134 in heater 135. The primary mixture is heated in coil 134 to a reaction temperature as set forth hereinbefore of about 600 to about 850 F. (Table III). From coil 134 the heated primary mixture ows through conduit 136 to primary decontaminator 139. At some point in conduit 136 intermediate to heater 135 and to primary decontaminator 139 hydrogen-containing gas, for example, reformer gas is mixed with the primary mixture to provide about 250 to about 25010 s.c.f. of hydrogen per barrel of primary mixture. The primary mixture and hydrogen-containing gas flow downwardly through primary decontaminator 139 in contact with a catalyst having capabilities to hydrogenate and dehydrosulfurize and dehydrodenitrogenize the primary mixture. Illustrative of such catalysts is that described hereinbefore. The efuent from primary decontaminator 139, hereinafter designated primary eiiiuent, flows through conduit 140 to heat exchanger 141 Where it is in indirect heat exchange relation with the straight run naphtha as previously described herein. From heat exchanger 141 the primary etiluent flows through conduit 142 to heat exchanger 143 where the primary effluent is in indirect heat exchange relation with the condensate from separator 147 flowing to heat exchanger 143 through pipe 150.

From heat exchanger 143 the primary etliuent ilows through conduit 144 to cooler 145 where the primary eiuent is cooled to a temperature at which C4 a-nd heavier hydrocarbons are condensed under the existing pressure. The condensed and uncondensed portions of the primary effluent flow from cooler 14S through conduit 146 to gasliquid separator 147. In separator 147 the uncondensed portion of the primary effluent comprising hydrogen, ammonia, and light hydrocarbons separates from C4 and heavier hydrocarbons and flows through conduit 148 to conduit 149, ammonia removal means 159, and

conduits

109 and 108 to secondary 110 decontaminator as previously described hereinbefore. The C4 and heavier hydrocarbons, hereinafter designated primary condensate, ow from separator 147 through pipe 15o to heat exchanger 143 `as previously described. From heat exchanger 143 the primary condensate flows through pipe 151 to stripper 152.

In stripper 152. a major portion of the C4 and lighter hydrocarbons together with residual amounts of hydrogen, hydrogen sulfide, and ammonia is taken overhead through pipe 153 to means 170 for removal of ammonia and then through conduit 171 to -an absorber where the overhead is contacted with an absorbent for C4 hydrocarbons.

A minor portion of the bottoms flows through a reboiler comprising pipe 164, heat exchanger 16S and pipe 166. The balance, and majo-r portion, of the bottoms ows through pipe 163 to a` reforming or other catalytic reaction unit employing a catalyst sensitive to more than l p.p.m. of nitrogen. In other words, the bottoms of stripper 152 contain not more than `l p.p.m. of nitrogen.

The ow sheet presented as FIGURE 3 is illustrative of the hydrodecontamination of a hydrocarbon mixture containing more than 25 ppm. of nitrogen wherein the condensate from the gas-liquid separator is fractionated in a splitter to give an overhead containing C5 and lighter hydrocarbons and dehexanized bottoms or a bottoms containing C6 hydrocarbons as controlled by local conditions. Thus, a hydrocarbon mixture containing at -least p.p.m. of nitrogen, for example, a thermally cracked naphtha, hereinafter designated nitrogenous feed, is drawn from a source not shown through pipe 29@ by pump 2431. Pump 261 discharges the nitrogenous feed into pipe 292 at a pressure sufficient to force the nitrogenous feed through the downstream equipment. The nitrogenous feed ows through pipe 202 to heat exchanger 2113 Where the nitrogenous feed is in indirect heat exchange relation with the eiiiuent from the secondary decontaminator flowing therefrom through conduit 210. From heat exchanger 2&13 the nitrogenous feed llows through pipe 294 to coil 20S in furnace or heater 206.

In heater 266 the nitrogenous feed is heated to a reaction temperature such as set forth hereinbefore. The heated nitrogenous feed hows from heater 26o through pipe 2537 to secondary dccontaminator 2%. At some point in pipe 297 intermediate to heater 2% and to decontaminator 2% hydrogen-containing gas containing as little ammonia as practical is mixed with the heated nitrogenous feed in amount to provide about 5G() to about 2500 s.c.f. of hydrogen per barrel of nitrogenous feed. A suitable hydrogen-containing gas for this purpose is the overhead from gas-liquid separator 257 flowing therefrom through

conduits

258 and 252, means for removing ammonia 269 and

conduits

261 and 209.

The mixture of nitrogenous feed and hydrogen-containing gas containing little or no ammonia, i.e., not more than about 0.02 percent by volume cr 20G ppm. based upon the nitrogenous feed, iiows downwardly through the catalyst bed in secondary decontaminator 2%. The catalyst in secondary decontaminator 208 is one having hydrogenating capabilities combined with the capabilties of hydrodecontaminating, i.e., hydrodesulfurizing and hydrodenitrogenizing hydrocarbon mixtures. Illustrative of such catalyst is that described hereinbefore.

The effluent of secondary decontaminator 251-3, hereinafter designated secondary eiiiuent, ows therefrom through conduit 210 to heat exchanger 2113 where the secondary elliuent is in indirect heat exchange relation with the nitrogenous feed as described hereinbefore. From heat exchanger 203 the secondary efliucnt ows through conduit 211 to heat exchanger 212 where the secondary effluent is in indirect heat exchange relation with the condensed hydrocarbons liowing from gas-liquid separator 216 through pipe 218 to pump 219 and thence through pipe 220 to heat exchanger 212. From heat exchanger 212 the secondary eiiiuent ows through con- 10 duit 213 to cooler 214. In cooler 214 the secondary effluent is cooled to a temperature at which at the existing pressure, C4 and heavier hydrocarbons are condensed. The cooled secondary effluent flows from cooler 214 through conduit 215 to gas-liquid separator 216.

In gas-liquid separator 216 the uncondensed portion of the secondary effluent comprising hydrogen and C1 to C3 hydrocarbons and a portion of the hydrogen derivatives of contaminants in the secondary feed such as ammonia, separates from the condensed portion of the secondary eiuent. Ihe uncondensed portion of the secondary eflluent ows from separator 216 through conduit 217 to means 231 for removal of ammonia and then through conduit 282 to an absorber (not shown) Where the uncondensed secondary eiuent is contacted with a mixture of hydrocarbons to be decontaminated. In the absorber light hydrocarbons are extracted from the uncondensed secondary eiiiuent while oxygen and deposit precursors are extracted from the hydrocarbon mixture to be decontaminated. Prom the absorber the uncondensed secondary efliuent flows to the refinery fuel system.

The condensed portion of the secondary eiiiuent separated in gas-liquid separator 216 from the uncondensed secondary effluent flows from separator 216 through pipe 213 to the suction side of pump 219. The condensed secondary effluent, Le., secondary condensate, is discharged by pump 219 into pipe 220x The secondary condensate flows through pipe 22d to heat exchanger 212 as described hereinbefore. From heat exchanger 212 the secondary condensate ows through pipe 221 to splitter 222. In splitter 222 an overhead comprising hydrogen and C1 to C5 hydrocarbons together with all or a portion of C6 hydrocarbons depending upon local operating demands together with the residual ammonia and hydrogen sulfide is taken overhead through conduit 223 to cooler 224. In cooler 224 the overhead is cooled to a temperature at which C4 and heavier hydrocarbons are liquid. From cooler 224 the splitter overhead tiows through conduit 22S to accumulator 226. From accumulator 226 the uncondensed splitter overhead flows through conduit 262 to the refinery fuel gas main. The condensed splitter overhead ows .from accumulator 226 through pipe 227 to the suction side of pump 228. Pump 228 discharges the condensed splitter overhead into pipe 229 through which the condensed splitter overhead ows to splitter 222 for use as reflux. That portion of the condensed splitter overhead in excess of requirements for reux in splitter 222 is diverted through pipe 23) under control of valve 231 to pipe 232 and light naphtha storage, further processing, distribution, etc.

A minor portion of the bottoms of splitter 222 flows to a reboiler system comprising pipe 2.33, heat exchanger 234 and pipe 235 or any other means can be employed for maintaining a temperature in sp-litter 222 at which hydrocarbons having iive to six carbon atoms, as desired, are volatile. The balance, and major portion, of the splitter bottoms substantially devoid of ammonia flows from splitter 222 through pipe 236 to the suction side of pump 237. Pump 237 discharges into pipe 238 through which the splitter bottoms flows to coil 239 in heater 240. While the splitter bottoms are substantially devoid of ammonia and hydrogen sulfide the nitrogen content thereof is nevertheless considerably greater than 1 ppm. Accordingly, the splitter bottoms having a nitrogen content up to about ppm. is mixed with about 50 to about 95 parts by volume of a mixture of hydrocarbons having a low nitrogen content such that when mixed with the splitter bottoms in the proportions set forth hereinbefore the nitrogen content of the mixture is not greater than about 7 ppm. A suitable low nitrogen mixture of hydrocarbons, designated nitrogen-free hydrocarbon mixture, is straight run naphtha containing not more than about 0.5 ppm. of nitrogen.

The nitrogen-free mixture of hydrocarbons, i.e., containing not more than about 0.5 p.p.m. is drawn from a source not shown through pipe 241 by pump 242 and discharged into pipe 243 at a pressure higher than the pressure in pipe 238. The nitrogen-free hydrocarbon mixture flows through pipe 243 to heat exchanger 244 where the nitrogen-free hydrocarbon mixture is in indirect heat exchange relation with effluent from primary decontaminator 249 flowing through conduit 250. From heat exchanger 244 the nitrogen-free mixture of hydrocarbons flows through pipe 245 to a point in pipe intermediate to pump 237 and to heater 240, The mixture of splitter bottoms and nitrogen-free hydrocarbon mixture, hereinafter designated primary feed, tion/s through pipe 238 to coil 239 in heater 240'. In heater 240 the mixture is heated to a reaction temperature within the range of about 600 to about 850 F. From coil 239 the heated primary feed iiows through conduit 21136 to primary hydrodecontaminator 249. At a point in conduit 246 intermediate to heater 240 and to decontaminator 249 hydrogen-containing gas, eg., hydrogen-rich reformer gas is mixed with the primary feed in an amount to provide about 250 to about 2500 s.c.\f. of hydrogen per barrel of primary feed to provide a primary feed mixture.

The primary feed mixture ows downwardly through primary decontaminator 249 which is charged with particle-form solid hydrogenating and hydrodesulfurizing and hydrodenitrogenizing catalyst such as a mixture of oxides of cobalt and molybdenum. The reaction products, designated primary efliuent, flow from primary decontaminator 249 through conduit 250 to heat exchanger 244 where the primary effluent is in indirect heat exchange relation with the nitrogen-free hydrocarbon mixture as described hereinbefore. From heat exchanger 244 the primary efliuent flows through

conduits

251 and 252 to heat exchanger 253 where the primary effluent is in indirect heat exchange relation with the primary condensate iiowing from pump 264 through pipe 265. Fromv heat exchanger 253 the primary etlluent iiows through conduit 254 to cooler 255 where the primary efliuent is cooled t a temperature at which under the em'sting pressure C4 and heavier hydrocarbons are condensed. The cooled primary efiiuent flows from cooler 255 through conduit 256- to gas-liquid separator 257. In gas-liquid separator 257 the uncondensed portion of the primary eiuent separates from the condensed portion of the primary efiiuent. The uncondensed portion of the primary effluent, designated recycle gas, Hows from separator 257 through

conduits

258 and 259 to means 260 for removing ammonia. The recycle gas substantially devoid of, i.e., containing not more than about 0.02 percent by volume of ammonia iiows from means 260 for removing ammonia through

conduits

261 and 209 to conduit 207 for admixture with the nitrogenous hydrocarbon mixture as described hereinbefore.

The condensed primary effluent, designated primary condensate, ows from separator 257 through pipe 263 to the suction side of pump 264. Pump 24 discharges the primary condensate into pipe 265 through which the primary condensate iiows to heat exchanger 253 where the primary condensate is in indirect heat exchange relation with the primary efiiuent as hereinbefore described. From heat exchanger 253 the primary condensate flows through pipe 2655: to splitter 266.

In splitter 266 the temperature is maintained to take overheadthrough conduit 267 a splitter overhead comprising hydrogen, C1-C4 hydrocarbons and C5 and C6 hydrocarbons dependent upon otherfacilities, eg., for isomerizing the C5 and C6 hydrocarbons. The splitter overhead flows through conduit 267 to cooler 263` where the splitter overhead is cooled to a temperature at which C4 and heavier hydrocarbons 'are liquid. Fromv cooler 26S the cooled splitter overhead flows through conduit 269 to accumulator 270. In accumulator 270 the uncondensedsplitter overhead separates from the liquid splitter overhead and flows through conduit 271 to the refinery fuel main. The condensed splitter overhead flows through pipe 272 to the suction side of pump 273. Pump 273 discharges the splitter overhead condensate into pipe 274 through which the splitter overhead condensate flows to splitter 266 for use as reflux. Splitter condensate in excess of that required for reflux in splitter 266 is diverted through pipe 275 under control of valve 276 to further processing, e.g., separation of C5 and C6 and isomerization thereof, storage, distribution, etc.

The major portion of the splitter bottoms containing not more than l ppm. of nitrogen iiows from splitter 266 through pipe 250 to a reformer unit (not shown) as feed thereto. A minor portion of the splitter bottoms flows through a reboiler comprising pipe 277, heat exchanger 273 and pipe 279 or other means for heating the minor portion of the splitter bottoms to a temperature such that the components of the aforesaid splitter overhead are volatilized.

A further embodiment of the present invention is illustrated by the flowsheet FIGURE 4. A nitrogenous hydrocarbon mixture (as defined hereinbefore) is drawn from a source not shown through pipe 301 by pump 302 and discharged into pipe 303 at a pressure sufficient to drive the nitrogenous hydrocarbon mixture through the equipment intermediate to pump 302 and to secondary decontaminator 309. From pump 302 the nitrogenous hydrocarbon mixture ows through pipe 303 to heat exchanger 304 where the nitrogenous hydrocarbon mixture is in indirect heat exchange relation with the secondary eiuent iiowing from secondary decontaminator 309 through conduit 320. From heat exchanger 301i the nitrogenous hydrocarbon mixture lows through pipe 305 to coil 306 in heater 307. In heater 307 the nitrogenous hydrocarbon mixture is heated to a reaction temperature within the range of about 600 to about 850 F. From heater 307 the heated nitrogenous hydrocarbon mixture iiows through pipe 30S to conduit 332 and thence to secondary decontaminator 309.

In conduit 332 the heated nitrogenous hydrocarbon mixture is mixed with hydrogen-containing gas in amount to provide about 500 to about 2500 s.c.f. of hydrogen per barrel of nitrogenous hydrocarbon mixture. A hydrogen-containing gas for this purpose can be hydrogen-rich reformer gas flowing through conduit 331 from a source not shown at the pressure greater than the pressure in secondary decontaminator 309. Hydrogen-containing gas from stripper 32l flowing therefrom through conduits 325 and 326 to means 327 for the removal of ammonia and thence through conduit 328 under control of valve 329 to compressor 374- and conduit 375 to

conduits

331 and 332 is likewise suitable. A mixture of both of the aforesaid hydrogen-containing gases can be used. The mixture of nitrogenous hydrocarbon mixture and hydrogen-containing gas iiows through conduit 332 to secondary decontaminator 309. The aforesaid mixture iiows downwardly through secondary decontaminator 309 which contains a bed of catalyst having hydrogenating, hydrodesulfurizing, and hydrodenitrogenizing capabilities. From secondary decontaminator 309 the reaction products, designated secondary eluent, flow through conduit 310 to heat exchanger 304 where the secondary effluent is in indirect heat exchange relation with the nitrogenous hyrocarbon mixture as described hereinbefore. From heat exchanger 304 the secondary effluent ows through conduit 3M to heat exchanger 312 where the secondary effluent is in indirect heat exchange relation with secondary condensate flowing from gas-liquid separator 316 through pipe 317 to pump 31S and thence through pipe 319 to heat exchanger 312'. From Yheat exchanger 312 the secondary eiiluent flows through conduit 313 to cooler 3M where the secondary efliuent is cooled to a temperature at which7 under the existing pressure C4 and heavier hydrocarbons are condensed. From cooler 314 the cooled 13 secondary efiiuent flows through conduit 315 to gasliquid separator 316.

ln gas-liquid separator 316 the uncondensed secondary eiuent separates from the condensed secondary effluent. The uncondensed secondary effluent, designated primary stripping gas, leaves separator and ows by Way of

conduits

333, 334 and 372 to stripper 335 and primary ydecontarninator 346.

The condensed secondary effluent, designated secondary condensate, ilows from separator 316 through pipe 317 to the suction -side of pump 338. Pump 31S discharges into pipe 319 through which the secondary condensate ows to heat exchanger 312. `In heat exchanger 312 the `secondary condensate is in indirect heat exchange relation with the secondary effluent as described hereinbefore. From heat exchanger 312 the secondary condensate flows through pipe 320 to stripper 321.

ln stripper 321 the secondary condensate is contacted with stripping gas such as hydrogen-containing gas, eg., reformer gas iiowing from conduit 331 through conduit 347 under control of valve 348. A stripper overhead comprising hydrogen, ammonia, hydrogen sulde and a major portion of Ci, and lighter hydrocarbons flows through conduits 325 and 326 to a means 327 for removal of ammonia and thence through conduit 370 to an absorber not shown where the stripper overhead is contacted `with a hydrocarbon mixture to extract C4 and heavier hydrocarbons from `the stripper overhead and to extract water and deposit precursors from the hydrocarbon miX- ture. The stripper o-verhead iiows from the absorber to the renery fuel gas main.

A portion or all of the stripper overhead can be diverted from conduit 376 through conduit 323 under conltrol of valve 329 to compressor 374. `Compressor `374 discharges the stripper overhead through

conduits

375, 331 and 332 for admixture with lthe nitrogenous hydrocarbon mixture as described hereinbefore.

A minor portion of the stripper bottoms hows through a reboiler comprising pipe 322, heat exchanger 323 and pipe 324 or `any other means whereby a temperature is maintained in stripper 321 at which the aforedescribed overhead is produced.

The balance, and major portion, of the stripper bottoms flows from stripper 321 through pipe 336 to the suction side of pump 337. Pump 337 discharges into pipe 338i. The stripper lbottoms owing through pipe 338 contain not more than 140 p.p.m. of nitrogen. At some point in pipe 338 the stripper bottoms is mixed with a hydrocarbon mixture having a low nitrogen content, i.e., not more than about 5 p.p.m. of nitrogen in the proportion of about 50 to about 95 parts of low nitrogen hydrocarbon mixture, designated nitrogen-free hydrocarbon mixture, to about 50 to about 5 parts of ystripper bottoms to provide a primary decontaminator feed naphtha containing not more than 7 p.p.m. of nitrogen. A suitable nitrogen-free hydrocarbon mixture is a straight run naphtha containing `.about 2 p.p.m. of nitrogen.

Such a nitrogen-free hydrocarbon mixture is drawn from a source not shown through pipe 341 by pump 342 and discharged into pipe 330. The nitrogen-free hydrocarbon mixture flows through pipe 330 to heat exchanger 343 where the nitrogen-free hydrocarbon mixture is in indirect heat exchange relation with primary efliuent flowing from primary decontaminator 346 .through conduit 347. From heat exchanger 341-3 the nitrogen-free hydrocarbon mixture flows through pipe 3441 to pipe 338 where it is mixed With the stripper bottoms in the proportions described hereinbefore to provide a primary feed con-taining not more than about 7 ppm. of nitrogen.

The primary feed ows through pipe 338 to coil 339 in heater 340 where the primary feed is heated to a reaction temperature within the range of about 600 to about 850 F. The primary feed flows from heater 340 through conduit 345 to primary decontaminator 346, At some point in conduit 345 intermediate to heater 340 and to 14 primary decontaminator 346 hydrogen-containing gas is mixed with the primary feed to provide about 250 to about 2500 s.c.f. of hydrogen per barrel of primary feed.

A `suitable hydrogen-containing gas is stripper overhead owing from stripper 335 and/ or separator overhead tlowing from separator '316 through conduits 358-, 334 and 361 respectively to means 363 'for removal of ammomia and thence through conduit 363 to compressor 364 and conduit 365 to conduit 345.

The mixture of primary feed and hydrogen-containing gas, i.e., primary feed mixture hows through conduit 345 to primary decontaminator 346. Primary decontaminator 346 is charged with a particle-form solid hydrogenating and hydrosulfurizing and hydrodenitrogenizing catalyst, eg., a mixture of oxides of cobalt and molybdenum. The primary feed mixture flows downwardly through primary decontaminator 346. The eiuent of primary decontaminator 346, i.e., primary effluent, flows through conduit 347 to heat exchanger 343 where the primary effluent is in indirect heat exchange relation with the nitrogen-free hydrocarbon mixture as described hereinbefore. tFrom heat exchanger 343 the primary efiiuent flows through conduit 348 to heat exchanger 349 where the primary effluent in indirect heat exchange relation with the condensate (primary condensate) flowing from separator 353 through pipe 35S. From heat exchanger 349 the primary eiiiuent flows through conduit 350 to cooler 351. In cooler 351 the primary efliuent is cooled to a temperature at which under the existing pressure C4, and heavier hydrocarbons are condensed. fFrom cooler 351 the cooled primary effluent flows through conduit 352 to gas-liquid separator 353. In separator 353 the uncondensed primary eiiiuent comprising hydrogen and C1 to C3 hydrocarbons flows through conduit 354 to means 377 for removal of ammonia and thence through conduit 37 3 to an absorber not shown for recovery of light hydrocarbons in hydrocarbon mixture to be treated and removal of water and deposit precursors `from the hydrocarbon mixture to be treated. From the absorber the uncondensed primary eiiluent flows :to the refinery fuel main.

The condensed primary eiliuent, i.e., primary condensate, flows through pipe 355 to heat exchanger 349 where the primary condensate is in indirect heat exchange relation with the primary effluent as described hereinbefore. From heat exchanger 349 the primary condensate ilows through pipe 356 to stripper 335'. In stripper 335 the primary condensate is contacted with a stripping gas, eg., hydrogen-containing gas, for example, gas from separator 316 and is heated to -a temperature at which hydrogen, ammonia, hydrogen sullide, Clto C3 `and a major portion of the C4 hydrocarbons are volatile. In other words, an overhead comprising hydrogen, ammonia, hydrogen `sulfide and a major portion of the C4 and lighter hydrocarbons is taken overhead. The stripper overhead flows from stripper 335 through conduit 337 to conduit 35d; to a means 377 for removal of ammonia. and thence through conduit '378 to an absorber not shown. A portion yor all of the stripper overhead is diverted from conduit '357 through conduit 358 under control of valve 359 to conduit 361 and thence to means 360 for removal of ammonia.

A m-inor portion of the bottoms of stripper 335 flows through a reboiler comprising pipe 366, heat exchanger 367 and pipe 363 or any other means for maintaining the temperature in stripper 335 required to produce the aforedescribed overhead. The major portion (the balance) of the stripper bottoms containing not more than 1 ppm. of nitrogen flows through pipe 369 to a reformer.

A further embodiment of the present invention is illustrated in FIGURE 5. In FIGURE 5 the owsheet illustrates the use of the hydrogen-containing gas recovered from the effluent of the secondary decontaminator in the primary deeontaminator after removal of ammonia from the uncondensed portion of the secondary efliuent. Thus, a nitrogenous mixture `of hydrocarbons, as defined hereinbefore, is drawn yfrom a source not shown through pipe 401 by pump 402. Pump 402 discharges the nitrogenous hydrocarbon mixture into pipe 403 at a pressure sucient to push the nitrogenous hydrocarbon mixture through the equipment downstream of the pump. The nitrogenous hydrocarbon mixture flows through pipe 403 to heat exchanger 404- where the nitrogenous hydrocarbon mixture is in indirect heat exchange relation with the secondary efuent fiowing from secondary decontaminator 409 through conduit 411. The nitrogenous hydrocarbon mixture containing more than 25 p.p.m. of nitrogen ows from heat exchanger 404 through pipe 405 to coil 406 in heater 407. In heater 407 the nitrogenous hydracarbon mixture is heated .to a reaction temperature within the range of about 600 to about 850 F. From heater 497 the heated nitrogenous hydrocarbon mixture ows through conduit 408 :to secondary decontaminatm 409. At a point in conduit 408 intermediate to heater 407 and to secondary decontaminator 409 hydrogen-containing gas, such `as reformer gas, flowing from a source not shown through conduit 410 is mixed with the heated nitrogenous hydrocarbon mixture in the proportion of about 500 to about 2500 s.c.f. per barrel of nitrogenous hydrocarbon mixture to form a secondary charge mixture.

The secondary charge mixture flows downwardly through secondary decontaminator 409 in contact with a hydrogenating, hydrodesulfurizing and hydrodenitrogenizing catalyst such `as a mixture of oxides of cobalt and molybdenum. As described hereinbefore, conditions in secondary decontaminator 409 are as follows:

Table V Catalyst: 2 3 percent cobalt oxide, 9-16 percent molybdenum oxide. Feed: Nitrogenous hydrocarbon mixture-66 p.p.m. nitrogen.

The effluent from secondary decontaminator 409, designated secondary eiuent, ilows through conduit 411 to heat exchanger 404 where the secondary eiuent is in indirect heat exchange relation with the nitrogenous hydrocarbon mixture as `described previously herein. From heat exchanger 404 the secondary eiiiuent flows through conduit 412 to heat exchanger 413 where the secondary eliuent is in indirect heat exchange relation with secondary condensate drawn from gasliquid separator 417 owing through pipe 422 to pump 423 and discharged into pipe 424 by pump 423. From heat exchanger 413 the secondary effluent flows through conduit 414 to cooler 415 where the secondary effluent is cooled to a temperature at which C4 and heavier hydrocarbons are condensed. The cooled secondary effluent Hows from cooler 415 through conduit 416 to gas-liquid separator 417. In gasliquid separator 417 the uncondensed secondary eiuent separates from the condensed secondary effluent. The uncondensed secondary effluent ows through conduit 418 to means 419 for removal of ammonia. The secondary eiiiuent containing not more than about 0.02 percent by volume ammonia, now designated primary hydrogenating gas, ows from means 419 for removal of ammonia through conduit 420 to conduit 421 where it is mixed with the mixture of the bottoms of splitter 426 and the nitrogen-free hydrocarbon mixture to form a primary charge mixture as described hereinafter.

The condensed secondary effluent iiows from gas-liquid separator 417 through pipe 422 to the suction side of pump 423. The condensed secondary effluent, designated secondary condensate, is discharged by pump 423 into pipe 424 through which the secondary condensate Hows to heat exchanger 413. In heat exchanger 413 the secondary condensate is in indirect heat exchange relation with the secondary efiiuent as previously described herein. From heat exchanger 413 the secondary condensate ows through pipe 425 to splitter 426. In splitter 426 a temperature is maintained at which residual hydrogen, hydrogen derivatives of nitrogen and sulfur, C1 to C5 hydrocarbons with or without C6 hydrocarbons dependent upon the local auxiliary facilities (e.g., isomerizing facilities) are taken yoverhead and C6 and heavier hydrocarbons form a bottoms. The aforesaid overhead is taken from splitter 426 through conduit 427 to cooler 428 Where the splitter overhead is cooled to a temperature at which C4, and heavier hydrocarbons are liquid. From cooler 428 the splitter overhead flows through -conduit 429 to accumulator 430. In -accumulator 430 the uncondensed `splitter overhead separates from the condensed splitter overhead and is vented through conduit 431 to the renery fuel gas main. The splitter overhead condensate, Le., condensed splitter overhead, is drown from accumulator 430 through pipe 432 by pump 433. Pump 433 discharges the splitter condensate into pipe 434. A portion of the splitter condensate iiows through pipe 436 under control of valve 437 to splitter 42o for use as reflux. The bal-ance of the splitter condensate, in excess of that required for reflux in splitter 426, ows through pipe 435 to further processing or storage and/or distribution as light naphtha.

A minor portion of the bottoms of splitter 426 flows through a reboiler comprising pipe 438, heat exchanger 439 and pipe 440 or any other suitable means for heating a portion of the splitter bottoms to a temperature required to maintain a temperature in splitter 426 at which the aforedescribed splitter overhead is produced.

The balance, and major portion, Aof the splitter bottoms containing not more than about 140 ppm. nitrogen is drawn from splitter 426 through pipe 441 by pump 442 and discharged into pipe 443. In order to produce lan effluent from primary decontamin'ator 446 containing not more than 1 p.p.m. of nitrogen under the conditions set forth hereinbefore it is necessary that the hydrocarbon charge to primary decontaminator 446 contain not more than about 7 ppm. of nitrogen. Accordingly, the splitter bottoms containing not more than about 140 p.p.m. of nitrogen is mixed with about 50 to about 95 parts by volume 'of a mixture of hydrocarbons boiling preferably in the gasoline range containing an amount of nitrogen such that when mixed with the splitter bottoms in the proportions set forth hereinbefore the mixture contains not more than about 7 ppm. of nitrogen. Suitable proportions of splitter bottoms having various nitrogen con` centrations and nitrogen-free hydrocarbon mixtures to be mixed therewith to provide a primary feed containing not more than about 7 ppm. 0f nitrogen are listed in Table VI.

A suitable nitrogen-free hydrocarbon mixture or diluent is' straight-run naphtha containing not more than 5.0 ppm. of nitrogen. Accordingly a nitrogen-free hydrocarbon mixture containing nitrogen not in excess of that Which when mixed with the splitter bottoms in a proportion within the range of to 50 volumes per 5 to 50 volumes of splitter bottoms to form a primary feed con- 17 taining not more than about 7` p.p.m. of nitrogen is drawn from a source not shown through pipe 447 by pump 448. Pump 448 discharges the nitrogen-free hydrocarbon mixture or diluent into pipe 477 at a pressure at least equal to that in pipe 443. The nitrogen-freerhydrocarbon mixture or diluent flows through pipe 477 to heat exchanger 449 Where the nitrogen-free hydrocarbon diluent is in indirect heat exchange relation With primary eflluent owing from primary decontaminator 446 through conduit 451. From heat exchanger 449' the nitrogen-free hydrocarbon diluent ilows through pipe `450 `to pipe 443i. In pipe 443 the nitrogen-free hydrocarbon diluent is mixed with the splitter bottoms to form a primary feed containing not more than about 7 p.p.m. of nitrogen. The primary feed flows through pipe 443 to coil 444 in heater 445. In heater 445 the primary feed is heated to -a reaction temperature within the range of about 600 to about 850 F. The heated primary feed ows from heater 445 through conduit 421 to primary decontaminator 446. At some point in the conduit 421 hydrogen-containing gas containing not more than about 0.02 percent ammonia, e.g., hydrogen-containing gas from gas-liquid separator 417 is mixed with the primary feed in .a proportion Within the range of about 250 to about 2500 s.c.f. per barrel of primary feed to form a primary charge mixture. The primary charge Vmixture flows downwardly through primary decontaminator 446 in which the conditions are within the ranges set forth in Table VII.

Table VII Catalyst: 2 to 3 percent cobalt oxide, 9 to 16 percent molybdenum oxide. Feed: Not more than about 7 p.p.m. of nitrogen.

Broad Preferred Temperature, F 600- 850 675-775 Pressure, p.s.i.g 20G-l, 000 40G-50C Hydrogen, Set/b, of Primary Feed 250-2, 500 40G-G00 Space Velocity, v./hr./v ll 2. 5-5 0 conduit 454 to cooler 455 where the primary effluent is.

cooled to a temperature such that Cr and heavier hydrocarbons are condensed. From cooler 455 the cooled, primary ecluent flows through conduit 456 to gas-liquid separator 457. In gas-liquid separator 4'57 the uncondensed primary eluent is separated from the` condensed primary effluent.

In separator 457 the uncondensed pri-mary eiiluent. is vented through conduit 458 to means 478l for removal of ammonia and thence through conduit 479 to an absorber (not shown) where it is contacted with -a hydrocarbon mixture which absorbs Cr and heavier hydrocarbons. At lthe same time the uncondensed primary effluent removes Water and deposit precursorsfrom the hydrocarbon mixture. The uncondensed primary eiuent ilows from the aforesaid absorber to the renery fuel gas mam.

The condensed portion ofthe primary effluent designated primary condensate flows from gas-liquid4 separator 457 through pipe 459 to heat exchanger 453` Where the primary condensate is in indirect heat exchange relation with the primary eiliuent yas described hereinbefore. From heat exchanger 453i the primary condensate is drawn through pipe 460 by pump 461 which discharges the primary condensate into pipe 462. The primary condensate ilows through pipe 462 to splitter 463.

In splitter 463` an overhead comprising hydrogen, ammonia, hydrogen sulfide, C1 to C4 hydrocarbons, and C5 and C6 hydrocarbons dependent upon auxiliary facilities locally available is taken through conduit- 464. For example, in some reneries it can be preferred to take all ofthe C5 and C6 hydrocarbons overhead for isomerization. Therefore, the splitter overhead can becharacterized as comprising hydrogen, ammonia, hydrogen sulfide, and hydrocarbons the major portion of whichy are C5 and lighter hydrocarbons. The overhead from splitter 463 flows through conduit 464 to cooler 465 where the C4 and heavier hydrocarbons are condensed. From cooler 465 the splitter overhead flows .through conduit 466 to accumulator 467. In accumulator 467 the uncondensed splitter :overhead is vented to the -renery fuel gas main through conduit 468. The condensed splitter overhead is drawn from accumulator 467 through pipe 469 by pump 470, Pump 470 discharges the condensed splitter overhead into pipe 471. A portion of thecondensed splitter overhead required for reflux flows through pipe 471 under control of valve 472 to splitter 463i. The balance flows through pipe 473 to storage, further processing, or distribution as light naphtha.

A minor portion of the splitter bottoms is circulated through a re-boiler comprising pipe 474, heat exchanger 475 and pipe `476 or any other suitable means for heating the minor portion of the bottoms to a temperature suchu that the temperature required to produce the aforedescribed splitter overhead is maintained in splitter 463.

The balance, and major portion, of the splitter bottoms flows from splitter 463 through pipe 480 to a reformer unit (not shown) employing a nitrogen-sensitive reforming catalyst. It will be noted that the splitter bottoms owing through pipe 477 contains not more than l` p.p.m. of nitrogen.

In view of the foregoing discussion of the illustrative examples of the present invention it is manifest that the present invention provides for hydrodecontaminating a reformer charge stock containing moreV than 2.5 p.p.m. of nitrogen in the presence of a catalyst having hydrogenating and decontaminating capabilities such as a. mixture of oxides of cobalt and molybdenum under conditions of temperature, pressure, space velocity and hydrogen to charge stock ratio to produce la secondary condensate. The secondary condensate is stripped of volatile hydrogen derivatives of the contaminants originally present in the charge stock to provide a partially decontaminated secondary decontaminator bottoms containing not more than about p.p.m. of nitrogen. The secondary decontaminator bottoms containing not more than about 140 p.p.m. of nitrogen is mixed lwith reformer charge'stock to provide a primary decontaminator feed containing not more than about 7 p.p.m. of nitrogen. The primary decontaminatorV feed isV then hydrodecontaminated in the presence of a catalyst having hydrogenatingand decontam,

inating capabilities and in the presence of hydrogen containing gas containing not more than aboht 0.02 percent ammonia under conditions of temperature, pressure, space velocity and ratioof hydrogen to primary decontaminator feed to produce, after fractionating the primary decontaminatorV condensate, a reformer feed containing less than about lp.p.m. of nitrogen.

The hydrodecontaminating'conditions used in both thesecondary and primary decontaminators are within the limits set forth in Table IV.

19 ,We claim:

1. In the method of preparing a hydrocarbon mixture boiling in the boiling range of naphtha and Vcontaining in excess of 25 p.p.m. of nitrogen for reforming in the presence of nitrogen-sensitive particle-form solid reforming catalyst wherein a first static bed of nitrogenand sulfur-insensitive particle-form solid hydrogenating catalytic material is established in a secondary hydrodecontaminator, wherein a second static bed of nitrogenand sulfur-insensitive particle-form solid hydrogenating catalytic material is established in a primary hydrodecontaminator, wherein a first naphtha containing in excess of 25 ppm. of nitrogen is introduced into said secondary hydrodecontaminator and intimately contacted therein with the aforesaid first static bed of hydrogenating catalytic material at a liquid hourly space velocity in the range of about 1 to about l0, wherein hydrogen is introduced into said secondary hydrodecontaminator and flows therethrough at a rate in the range of about 500 to about 2500 s.c.f. per barrel of the aforesaid first naphtha, wherein hydrodecontaminating conditions of temperature in the range of -about 600 to about 850 F. and a total pressure of about 200 to about 1000 p.s.i.\g. are maintained in the aforesaid secondary hydrodecontaminator, wherein a secondary hydrodecontaminator efHuent comprising ammonia, hydrogen sulfide, hydrogen, and C1 and heavier hydrocarbons is withdrawn from said secondary hydrodecontaminator, wherein the whole of said secondary hydrodecontaminator effluent is mixed with a second naphtha having a relatively low concentration of `organic nitrogen compounds and containing also impurities in the form of organic sulfur compounds to form a primary hydrodecontaminator feed, said second naphtha being a major portion of the normally liquid hydrocarbons of said primary hydrodecontaminator feed, wherein said primary hydrodecontaminator feed is introduced into the aforesaid primary hydrodecontaminator and intimately contacted therein with the aforesaid second static bed of hydrogenating catalytic material at a liquid hourly space velocity in the range of about l to about in the presence of hydrogen in a ratio in the range of about 250 to about 2500 s.c.f. per barrel of naphtha, wherein hydrodecontaminating conditions of a temperature in the range of about 600 `to about 850 F., and of a total pressure in the range of about 200 to about 1000 p.s.i.g. are maintained in said primary hydrodecontaminator, wherein a primary hydrodecontaminator effluent comprising ammonia, hydrogen sulfide, hydrogen, and C1 and heavier hydrocarbons is withdrawn from said primary hydrodecontaminator, wherein said primary hydrodecontaminator eiuent is separated into a plurality of fractions, wherein one of the aforesaid fractions is a C54- hydrocarbon fraction of substantially reduced nitrogen content, and wherein said C54- hydrocarbon fraction is reformed in contact with nitrogen-sensitive particle-form solid reforming catalyst to produce reformer eluent comprising C1 and heavier hydrocarbons and hydrogen, wherein said reformer effluent is separated into reformer recycle gas and reformer make-gas each comprising C1 to C3 hydrocarbons and hydrogen, and reformate comprising C4 and heavier hydrocarbons, and wherein at least a portion of said reformer make-gas is introduced into said secondary hydrodecontaminator, the improvement which comprises with the aforesaid second naphtha to provide a liquid primary hydrodecontaminator fed containing not more than 7 p.p.m. of nitrogen.

2. The 4method set forth in claim 1 wherein the gaseous fraction separated from the secondary hydrodecontaminator efliuent is treated to remove ammonia, and wherein at least a portion of the so-treated gaseous fraction is introduced into the secondary hydrodecontaminator.

3. The method set forth in claim l wherein a gaseous fraction comprising ammonia, hydrogen sulfide, hydrogen, and C1 to C3 hydrocarbons is separated from the primary hydrodecontaminator effluent, wherein ammonia is removed frorn the aforesaid gaseous fraction, and wherein the aforesaid gaseous fraction after said removal of `ammonia is introduced into said primary hydrodecontaminator.

4. The method set forth in claim 1 wherein the gaseous fraction separated from the secondary hydrodecontaminator effluent is treated to remove ammonia, wherein at least a portion ofthe so-treated gaseous fraction is introduced into the secondary hydrodecontaminator, whereing a gaseous fraction comprising ar'monia, hydrogen sulfide, hydrogen, and C1 to C3 hydrocarbons is separated from the primary hydrodecontaminator efliuent, whereseparating the aforesaid secondary hydrodecontaminator in said gaseous fraction is treated to remove ammonia, and wherein the so-treated gaseous fraction is introduced into said primary hydrodecontaminator.

5. The method set forth in claim 1 wherein a gaseous` fraction comprising ammonia, hydrogen sulfide, hydrogen, and C1 to C3 hydrocarbons is separated from the primary hydrodecontaminator effluent', wherein said gaseous fraction is treated to remove ammonia, and wherein said treated gaseous fraction and reformer make-gas are introduced into said primary hydrodecontaminator.

6. The method set forth in claim 1 wherein a gaseous fraction comprising ammonia, hydrogen sulfide, hydrogen, and C1 to C3 hydrocarbons is separated from the primary hydrodecontamin-ator efuent, wherein at least a portion of the reformer make-gas is mixed with the aforesaid separated gaseous fraction to provide diluted primary hydrodecontaminator gaseous fraction, wherein a gaseous fraction comprising ammonia, hydrogen sulfide, hydrogen, and C1 to C3 hydrocarbons is separated from the secondary hydrodecontaminator efliuent, wherein said separated gaseous fraction of secondary hydrodecontaminator efliuent is mixed with a portion of said diluted primary hydrodecontaminator gaseous fraction to provide diluted secondary hydrodecontaminator gaseous fraction wherein the balance of the aforesaid diluted primary hydrodecontaminator gaseous fraction is treated to remove ammonia, wherein said treated diluted primary hydrodecontaminator gaseous fraction is introduced into said primary hydrodecontaminator, wherein said diluted secondary hydrodecontaminator gaseous fraction is treated to remove ammonia, and wherein at least a portion of said treated diluted secondary hydrodecontaminator gaseous fraction is introduced into said secondary hydrodecontaminator.

7. Ihe method set forth in claim 6 wherein at least one of the group consisting of the diluted primary hydrodecontaminator gaseous fraction and the diluted secondary hydrodecontaminator gaseous fraction is treated to remove hydrogen sulfide.

References Cited in the file of this patent UNITED STATES PATENTS 2,728,710 Hendricks Dec. 27, 1955 2,767,121 Watkins Oct. 16, 1956 2,937,134 Bowles Mayv 17, 1960

Claims

1. IN THE METHOD OF PREPARING A HYDROCARBON MIXTURE BOILING IN THE BOILING RANGE OF NAPHTHA AND CONTAINING IN EXCESS OF 25 P.P.M. OF NITROGEN FOR REFORMING IN THE PRESENCE OF NITROGEN-SENSITIVE PARTICLE-FORM SOLID REFORMING CATALYST WHEREIN A FIRST STATIC BED OF NITROGENAND SULFUR-INSENSITIVE PARTICLE-FORM SOLID HYDROGENATING CATALYTIC MATERIAL IS ESTABLISHED IN A SECONDARY HYDRODECONTAMINATOR, WHEREIN A SECOND STATIC BED OF NITROGENAND SULFUR-INSENSITIVE PARTICLE-FORM SOLID HYDROGENATING CATALYTIC MATERIAL IS ESTABLISHED IN A PRIMARY HYDRODECONTAMINATOR, WHEREIN A FIRST NAPHTHA CONTAINING IN EXCESS OF 25 P.P.M. OF NITROGEN IS INTRODUCED INTO SAID SECONDARY HYDRODECONTAMINATOR AND INTIMATELY CONTACTED THEREIN WITH THE AFORESAID FIRST STATIC BED OF HYDROGENATING CATALYTIC MATERIAL AT A LIQUID HOURLY SPACED VELOCITY IN THE RANGE OF ABOUT 1 TO ABOUT 10, WHEREIN HYDROGEN IS INTRODUCED INTO SAID SECONDARY HYDRODECONTAMINATOR AND FLOWS THERETHROUGH AT A RATE IN THE RANGE OF ABOUT 500 TO ABOUT 2500 S.C.F. PER BARREL OF THE AFORESAID FIRST NAPHTHA, WHEREIN HYDRODECONTAMINATING CONDITIONS OF TEMPERATURE IN THE RANGE OF ABOUT 600* TO ABOUT 850*F. AND A TOTAL PRESSURE OF ABOUT 200 TO ABOUT 1000 P.S.I.G. ARE MAINTAINED IN THE AFORESAID SECONDARY HYDRODECONTAMINATOR, WHEREIN IN SECONDARY HYDRODECONTAMINATOR EFFLUENT COMPRISING AMMONIA, HYDROGEN SULFIDE, HYDROGEN, AND C1 AND HEAVIER HYDROCARBONS IS WITHDRAWN FROM SAID SECONDARY HYDRODECONTAMINATOR, WHEREIN THE WHOLE OF SAID SECONDARY HYDRODECONTAMINATOR EFFLUENT IS MIXED WITH A SECOND NAPHTHA