Patent GB-757365-A (GB)
Title: Improvements in and relating to cracking of heavy hydrocarbon oils
Inventor: KASSEL LOUIS STEVENSON
IPC: C10G63/04
Filed: 1954-02-22
Abstract: Heavy hydrocarbon oils are cracked in the presence of liquid hydrogen fluoride as catalyst, the effluent from the cracking zone is allowed to settle into two liquid phases, viz. a hydrocarbon phase and a hydrogen fluoride phase, gasoline is separated from the hydrocarbon phase, at least a portion of the gasoline is subjected to catalytic reforming under conditions conducive to the formation of free hydrogen, and the hydrogen fluoride phase is treated with this free hydrogen, preferably in the presence of boron trifluoride, in order to hydrogenate the hydrocarbon and other contaminants dissolved therein so that purified hydrogen fluoride may be readily recovered. Gasoline rich in isoparaffins and aromatic hydrocarbons is the primary product of the process. The reforming step, which involves dehydrogenation of naphthenes, is ordinarily carried out in the presence of hydrogen.  Alumina composited with an oxide of molybdenum, chromium or vanadium may be used as reforming catalyst; but a preferred catalyst comprises alumina, platinum, and combined fluorine and/or combined chlorine. A catalyst comprising platinum or palladium, silica and at least one other metal oxide, e.g. alumina, boron oxide, zirconia, magnesia, and thoria, may also be used.  In an example, the feed to the reforming zone is a naphthenic fraction boiling between 93 DEG  and 204 DEG  C. which has been separated by fractional distillation from the hydrocarbon effluent from the cracking step.  This naphthene fraction is passed, together with 0.5 to 15 mols. of hydrogen per mol. of hydrocarbon, to the reforming zone which contains one or more beds of platinum/alumina/combined halogen composite catalyst maintained at a temperature of 400 DEG  to 540 DEG  C. The pressure in the reforming zone is maintained between 18 and 80 atmospheres; and the weight hourly space velocity is adjusted to lie between 0.2 and 40.  The highly aromatic product from the reforming zone is stabilized together with an isoparaffic fraction, boiling below 93 DEG  C., separated from the products from the cracking step.ALSO:<PICT:0757365/III/1> Heavy hydrocarbon oils are cracked in the presence of liquid hydrogen fluoride as catalyst, the effluent from the cracking zone is allowed to settle into two liquid phases, viz. a hydrocarbon phase and a hydrogen fluoride phase, gasoline is separated from the hydrocarbon phase, at least a portion of the gasoline is subjected to catalytic reforming under conditions conducive to the formation of free hydrogen, the hydrogen fluoride phase is treated with this free hydrogen, preferably in the presence of boron trifluoride, in order to hydrogenate the hydrocarbon and other contaminants dissolved therein, as a result of which the impure hydrogen fluoride phase readily separates into a hydrocarbon phase and a purified hydrogen fluoride phase.  The latter may be further treated to remove BF3 and is re-used as catalyst. Gasoline rich in isoparaffins and aromatic hydrocarbons is the primary product of the process.  The reforming step, which involves dehydrogenation of naphthenes, is ordinarily carried out in the presence of hydrogen.  Alumina composited with an oxide of molybdenum, chromium or vanadium may be used as reforming catalyst; but a preferred catalyst comprises alumina, platinum, and combined fluorine and/or combined chlorine.  A catalyst comprising platinum or palladium, silica and at least one other metal oxide, e.g. alumina, boron oxide, zirconia, magnesia, and thoria may also be used.  Gas oils, wax distillates, and topped crude oil may be treated by the process.  The feed is introduced through line 1 and mixed with heavy recycle oil supplied through line 2.  The mixed oil is passed through heater 3, and then mixed in line 4 with recycle hydrogen fluoride passing through line 5, the catalyst to oil weight ratio being from 0.7:1 to 3:1.  The mixture is introduced in cracking reactor 7 which is maintained at a temperature of 93 DEG  to 260 DEG C. and is provided with means for ensuring intimate contact between the two liquid phases. It may at times be desirable to charge hydrogen and/or boron fluoride to the cracking reactor.  The reaction mixture is passed through line 8 to settler 10 where it separates into a upper hydrocarbon layer containing dissolved hydrogen fluoride and a lower contaminated catalyst phase.  The hydrocarbon layer is passed through line 11 to stripper 13 wherein the dissolved HF is stripped therefrom and removed overhead.  The stripped hydrocarbons are passed from the stripper through line 14, and the major portion is introduced into column 17.  Normally gaseous hydrocarbons are withdrawn from the head of column 17 and discharged from the system via line 21.  Liquid hydrocarbons boiling up to 93 DEG C. and comprising highly isoparaffic material are withdrawn from the column through line 23, and are passed to stabilizer 25.  Fuel oil (saturated and aromatic-free) is withdrawn through line 29.  The bottoms from column 17 are recycled o line 1 through line 2.  A 93 DEG -204 DEG C. fraction is withdrawn from column 17 through line 26, and is passed, together with 0.5 to 15 mols of hydrogen per mol of hydrocarbon, to reformer 28 which contains one or more heated beds of reforming catalyst.  If the catalyst comprises a platinum-alumina-combined halogen composite, the reforming is conducted at a temperature between 400 DEG  and 540 DEG C., an absolute pressure of 18 to 80 atmospheres, and at a weight hourly space velocity of 0.2 to 40. Under these conditions and with a charging stock containing an appreciable proportion of naphthenes, there is a relatively large net production of hydrogen.  Some of this hydrogen is withdrawn through line 54 for use in the purification of the contaminated catalyst. The highly aromatic reformate is discharged through line 32 into stabilizer 25.  Gaseous hydrocarbons are discharged from the head of the stabilizer; and stabilized gasoline is withdrawn through line 36. The bulk of this gasoline is passed via line 37 to storage, but a portion is passed through line 39 into the top of catalyst hydrogenation reactor 41, which is a device for contacting a downflowing stream of liquid with a rising stream of gas.  The contaminated catalyst layer from settler 10 is introduced at an intermediate level of reactor 41, and hydrogen containing BF3 is introduced into a lower section of the reactor through line 44.  The temperature in the lower part of reactor 41 is maintained between 95 DEG C. and 315 DEG C., and the pressure is such that the bulk of the catalyst is in the liquid phase.  In the upper part of the reactor, which is maintained at a lower temperature, the rising H2-BF3 gases contact aromatic hydrocarbons introduced through lines 39 and 45; and a (BF3-HF-aromatic hydrocarbon) complex is formed.  This complex is soluble in liquid hydrogen fluoride, and is withdrawn in solution from the base of the reactor.  The liquid from the base of the reactor 41 is passed to settler 48 where it separates into an upper hydrocarbon phase and a lower hydrogen fluoride phase.  The hydrocarbon phase is passed via line 49 to stripper 13.  The hydrogen fluoride phase is passed via line 51 into the top of stripper 53 wherein BF3 is liberated from the dissolved complex by the hydrogen from the reforming unit, which is passed into the lower part of the stripper through line 54.  The overhead gases from stripper 53 are passed through line 44 into the lower part of reactor 41.  The liquid from the base of stripper 53 is introduced through line 57 into settler 59, where an upper aromatic hydrocarbon phase separates from a lower hydrogen fluoride phase.  The aromatic hydrocarbons are supplied to reactor 41 via line 45.  A portion of the hydrogen fluoride phase is also passed to line 45; but the bulk is recycled to the cracking reactor 7 via lines 65 and 5.  A portion of the hydrogen fluoride phase is, however, also passed via line 68 to flash distillation column 70.  Pure hydrogen fluoride is removed from the top of column 70 and is passed to the cracking reactor via line 5. Sludge, comprising hydrocarbons, water, metallic impurities, and sulphur compounds, is discharged from the base of column 70.  The gas leaving the top of reactor 41 is introduced into the lower part of absorber 20 wherein it is freed from hydrogen fluoride by contact with hydrocarbons from stripper 13. The hydrocarbons withdrawn from the base of absorber 20 are returned to stripper 13.  The vapours withdrawn from the top of stripper 13 are passed to condenser 79, which is connected to receiver 80.  Non-condensed gases, containing some hydrogen fluoride, are passed via line 81 to absorber 20. Substantially HF-free gases issuing from the top of absorber 20 are discharged from the system via lines 83 and 21.  The liquid from receiver 80 is discharged into settler 87 where it separates into hydrocarbon and hydrogen fluoride layers.  The hydrocarbon layer is passed via line 88 to stripper 13.  The hydrogen fluoride layer is passed to reactor 41 via line 90.