US2501023A - Hydrocarbon conversion with hydrogen fluoride in homogeneous phase - Google Patents

Description

March 2l, 1950 P. L. BRANDT ETAL 2,501,023 HYDROCARBQN CONVERSION WITH HYDROGEN FLUORIDE IN HOMOGENEOUS PHASE Filed Dec. 27, 1946 n SAK Patented Mar. 2l, 1950 HYDROCARBON CONVERSION WITH HY- DROGEN FLUORIDE 1N HOMOGENEOUS PHASE Preston L. Brandt, Galveston,

Marque, and John A. Ridgway, Jr., Tex., assignors to Pan American Robert J. Lee, La Texas City, Refining Corporation, a corporation o! Delaware Application December 27, 1946, Serial No. 718,67! 4 Claims. (Cl. ISG-50) This invention relates to the catalytic conversion of hydrocarbons with a hydrogen iiuoride catalyst under homogeneous phase conversion conditions and it pertains more particularly to the cracking of heavier-than-gasoline charging stocks for producing maximum yields of motor fuel in a continuous commercial cracking system.

It is known that when heavy hydrocarbons such as gas oils are contacted with large amounts of liquid hydrogen fluoride at temperatures of the order of 300 to 400 F. under pressure suiicient to maintain two separate liquid phases in the conversion zone and the two phases are intimately contacted for periods of time ranging from about minutes to several hours, the charging stock is catalytically cracked to produce lsobutane, gasoline boiling range hydrocarbons and tar. An object of this invention is to provide an improved hydrogen fluoride conversion process which will be more eflicient and effective than processes heretofore known to the art. A further object is to provide a method and means for effecting conversion in a single homogeneous phase thus eliminating the necessity'of stirring or agitation and innitely improving the contact between catalyst and charging stock. A further object is to provide a more flexible hydrogen fluoride conversion system than has heretofore been possible, one which can be operated with highly varying proportions of hydrogen uoride to oil. A further object is to simplify the construction and operation and decrease the cost of construction and operation of a hydrogen uoride conversion system. Another object is the recovery of a maximum yield of primary cracked products before they are subjected to undesirable secondary reactions. Other objects will be apparent as the detailed description of the invention proceeds.

Briefly, the invention contemplates a system wherein the effectiveness of the hydrogen fluoride catalyst is enormously enhanced by maintaining it as a homogeneous phase with the liquid hydrocarbon undergoing conversion. The invention is particularly applicable to unsaturated charging stocks which are to be converted into lower boiling products. In some cases such charging stock is soluble in hydrogen uoride under ordinary temperature conditions but in most cases the charging stock is not soluble orcompletely miscible with the hydrogen uoride until high temperatures with correspondingly high pressures are employed. Thus while the invention is applicable to the catalytic conversion, e. g. cracking, of a hydrogen nuoride extract from the solvent extraction of a gas oil, lube oil or heavier hydrocarbon wherein the extraction is carried out at temperatures ranging from to about 250 F., it is not limited to the use of such "extract charging stocks but is also applicable to many charging stocks of the gas oil or heavier boiling range which are insoluble in hydrogen iiuoride at extraction temperatures but which are rendered soluble by employing suiliciently high temperatures and pressures in the conversion or cracking step itself.

When an ordinary 37 degree API gravity gas oil is contacted with 5 volumes of hydrogen fluoride at 350 F. and 900 p. s. i. at a rate of about 1 pound per hour of charging stock per pound oi hydrogen uoride in the reaction zone and for a contact time of about 12 minutes it was found that only about 121/2 weight percent of 400 end point gasoline was produced, about 40% of the product was unconverted or cycle gas oil, about 12% was heavy tar and about 30% was a hydrogen uoride soluble heavy oil oi' approximately the same boiling range as the charging stock. At least a part of the charging stock has thus apparently undergone a partial conversion, including dehydrogenation, which has transformed it into hydrogen fluoridesoluble form. The invention is applicable to such hydrogen fluoride soluble oil and in fact to any hydrocarbon charging stock which is completely miscible with hydrogen liuoride at the conversion temperature (although refractory aromatics per se are not as desirable as stock richer in hydrogen).

In practicing the invention the charging stock is simply admixed with the requisite amount of hydrogen uoride at a temperature sufficient to effect substantially complete solution. The solution is maintained at conversion temperature for the requisite time for effecting the conversion. The solution is then cooled for effecting separation of hydrogen fluoride from lower boiling products (which are chieiiy saturated and therefore insoluble in the hydrogen uoride phase. particularly at low temperatures) and the hydrogen il-uoride is removed from tar and other fractions in a. simple and expeditious manner. Although conversion products may separate from the homogeneous charging stock-hydrogen iluoride phase in the conversion zone, this is not a drawback and in fact is a positive advantage becauseit tends to prevent overcracking.

After the first conversion step the substantially saturated products are separated from the hydrogen uoride-tar layer in a settler at relatively 3 high temperature and this separated layer may then be passed. with or without further heating. through a further conversion zone to eiiect still further degradation of the tar and formation of additional lower boiling products. Any number of stages may thus be employed and such a multistage process is simpler and more eiiective than recycling operations heretofore proposed. In a multi-stage there may. of eourse,be separate product recovery and fractionation after each' stage or after each small number of stages. The stepwise product separation prevents overcracking and undesirable reactions that might otherwise occur in the primary products. The process of this invention may constitute the second step of a combined process wherein conversion is effected by contacting separate hydrogen fluoride-oil phases in the rst step. Various other modifications and applications oi the invention will be apparent as the more detailed description of the invention proceeds.

The accompanying drawing which forms a part of this speciiication is a schematic now diagram of a commercial hydrogen iluoride cracking system for producing gasoline from higher boiling hydrocarbons.

The invention will be described as applied to the catalytic cracking of a gas oil which at a temperature of about 400 P. ls substantially completely soluble in hydrogen iiuoride. It should be understood that the invention is also applicable to other types of conversion processes and that it is applicable to other types of charging stock. It may be utilized for example in the cracking of refractory cycle stocks from thermal non-catalytic cracking processes or for other high boiling hydrocarbon fractions produced as a by-f product in rening and which are: not amenable to treatment by other reiining processes such as catalytic cracking with silica-alumina catalysts. Tars or reduced crudes may be subjected to a treatment with a light hydrocarbon such as propane, butane, pentane, or hexane to eliminate the asphaltlnes from HF soluble material. When hydrogen fluoride extraction processes are employed, the extract phases therefrom may be used per .se as the charging stock thus avoiding the necessity of solvent recovery from the extract. Highly parafllnic stocks may require pretreatment with hydrogen iluorlde or other materials in order to render them more soluble in hydrogen fluoride.

The gas oil from source il, which is preferably a naphthenic gas oil, is introduced by pump Il and line I2 to preheater Il wherein the charge is heated to a temperature upwards of 400 F., i. e.

to a temperature suiilcient to maintain the de- Y sired conversion temperature in the reactor. Recycled oil from line Il may be admixed with the charge, and hydrogen iiuoride may be added to the charge from line il. A knot-hole mixer or other conventional mixing means (not shown) may be used to obtain intimate contact and facilitate solution. The ratio of hydrogen iluoride oil may vary within wide limits depending upon the desired extent o! conversion, the particular conversion conditions to be employed and the nature of the charging stock. The hydrogen fluoride oil ratio is usually within the range of about .1 to about and is preferably in the range of about .6 to about 6, e. g. about 3. Advantageous results may be accomplished in many cases, however, with ratios even less than .1 and for obtaining maximum conversion in short contact times the ratios may exceed 10.

Ihe homogeneous mixture or solution of hydrogen uorlde and charging stock at a temperature of about 400 F. and a pressure of about 1000 pounds per square inch is then passed through a reactor which in this instance is a series of coils Il which may either be heavily insulated or immersed in a heating iiuid such as a hot bath o! liquid oil lor other heat exchange material. The coil type reactor tends to prevent short circuiting, i. e. to insure that each portion of the solution remains at reaction temperature for the full contact time which in this case may be in the range of about live minutes to ilfty minutes or more, e. g. about i0 to 15 minutes.

Other types of reactors may of course be em-` ployed as for example a single drum or tower or a plurality of drums or towers connected in series. Where drums or towers are employed they are preferably provided with bailles for preventing undue short circuiting and/or the various enlarged zones are separated by zones of small cross-sectional area in order to minimize short circuiting and insure that each portion of the solution is contacted for the required amount of time. The reactors and other parts of the equipment should of course be fabricated from material which will withstand the corrosive action of hydrogen iluoride, Monel metal having been found suitable for this purpose. While the reaction in this case is effected at a temperature of 400 F. and a pressure of about 1000 p. s. i. it should be understood that desired cracking may be effected within the `general range of about 250-500 F., preferably 350 to 450 F. and at the pressure required for maintaining the homogeneous mixture in liquid phase. The hydrogen iluoride oil ratios can easily be controlled by charge pumps and since there is no recycling in the rcaction per se there is no uncertainty as to time of contact or amount of catalyst employed for effecting the reaction.

The total eilluent from th'e reactor passes to hot settler Il which may operate at substantially reaction temperature. At this high temperature i the hydrogen iiuoride-tar phase is usually lighter than the oil phase so that the latter is withdrawn through line Hand cooler Il to cold settlerl 20. Cold settler 2l is held at substantially condenser water temperature or in fact at any temperature within the ra ge of about 50 to 200 F. In this settler the substantially saturated hydrogen uoride insoluble products separate out as an upper layer and are withdrawn through line 2l and pressure reducing valve Zia to debutanizer tower 22 which is provided with reboiler 23 at its base. The overhead from the debutanizer passes through condenser 24 to receiver 25 which also acts as a settler. Substantially all of the hydrogen fluoride passes overhead and therefore an additional hydrogen iluoride layer may accumulate in settler 2l and be withdrawn continuously or from time to time through line Il to hydrogen fluoride storage tank 11.

Any uncondensed gases from the top of settler Il may pass by line 20 to knockback drum 2l which is provided with a cooler or scrubbing means Ill at its top for preventing the escape of any hydrogen fluoride with gases which are vented through line ll. The knockback liquidv from line 32 joins liquid withdrawn from the settler through line 33 and a portion of this liquid may be passed by pump M and line II to the top of debutanizer l2 to serve as redux. The remainder of this liquid passes to hydrogen fluoride rel maval-system Il which may be a system oi bauxite towers or a hydrogen uoride absorption system for removing all but minute traces of hydrogen uoride from hydrocarbon liquids. The hydrogen fluoride removal means per se forms no part of the present invention and it may be of the type which is for example commercially employed in alkylation systems. Recovered hydrogen fluoride may be returned through line 31 to storage tank 21.

'he hydrogen fluoride-free light hydrocarbon liquid then passes through line 38 to depropanlzer tower 39 which is provided with conventional reboiler means 40, the C4 (and Cs) hydrocarbons being withdrawn from the base of this tower through line 4I. The overhead from tower 39 passes through cooler 42 to receiver 43, a part of the condensate being returned by pump 44 and line 45 to serve as reiux while the net production of propane and lighter hydrocarbons is withdrawn through line 46.

The bottoms from debutanizer 22 are withdrawn through line 41 to fractionator 48 which is provided with conventional reboiler means 49. The overhead from the fractionator passes through condenser 50 to receiver 5I and a portion of the condensate is recycled by pump 52 in line 53 to serve as fractionator reiiux while the net gasoline production is removed through line 54.

Gas oil is withdrawn from the base of the fractionator through line 55 and it may be withdrawn from the system through line 56. However, when the gas oil is of such type that under conversion conditions it is miscible with hydrogen uoride it may be recycled by pump 51 and line 58 back to line i2.

The hydrogen uoride solution which separates as an upper layer in hot settler l1 is withdrawn through line 59 to second reactor 60 which may operate at substantially the same temperature and pressure as rst reactor I6. W'hen the second reactor is to operate at a higher temperature a heater (not shown) may be included in line 59. Reactor 60 may be of the same type as reactor I6, i. e. it may consist of a series of coils or one or more tanks or towers provided with bailies and/or designed to prevent short circuiting and to allow for the required time of contact. The hydrogen iiuoride-to-oil ratio in this case will usually be higher than in the rst reactor, e. g., may be in a range of about 2 to about 12, preferably about 4 to about 9 and in this example may be about 6. The time of contact in the second reactor may be from about 5 to 50 minutes or more and the temperature, as before, in the range of 250 to 500 F. e. g. about 400 F. It is preferred to operate the second reactor at a lower pressure than the first reactor so that no pump will be required in line 59. However substantially liquid phase conditions are maintained in the second reactor.

Reactor 60 discharges into hot settler 6| which may be held at substantially reaction temperature and pressure and here again the hydrogen fluoride phase will usually separate out as an upper layer and the hydrogen iiuoride insoluble oil phase as a lower layer. The oil phase may be withdrawn through line 62 and combined with oil layer withdrawn from the rst settler through line I8 the combined streams passing through cooler I8 to the cold settler and then being further fractionated as hereinabove described. It should be understood, however, that the oil withdrawn through line 62 may be sent to a separate cold settler and the oil product therefrom may be separately fractionated. In this way naphthas a ductility of more than or high boiling compounds may be obtained with special properties. useful for example as weed` killers or as other specialty products.

The hydrogen iiuoride layer containing hydromay be directed to still a above indicated, any number oi reactors or settlers may be employed in series to accomplish any degree of tar degradation and enhancement of gasoline yield. The gasoline yield may be further increased by introducing extraneous hydrogen into one or more of the reactors. The ultimate hydrogen uoride fraction which in this case is that withdrawn through line 63 is introduced through pressure reducing valve 63a into tar stripper 64 which is provided with a conventional reboiler means 65 at its base. 'Ihe overhead from this stripper passes through condenser` 66 to settler 61 in which the hydrogen iiuoride separates out as a lower layer and is withdrawn through line 68 to storage tank 21 or through lines 68a and 63h to reactor 60. The upper hydrocarbon layer from this settler is withdrawn through line 69 and circulated by pump 10 to the lower part of tar stripper 64 to assist in stripping hydrogen iiuoride out of the tar. Any accumulation of upper hydrocarbon phase in settler 61 may be passed by line 1I to line 35 and thence to debutanlzer 22. Similarly any deciency in hydrocarbon for the stripping of the tar may be supplied by hydrocarbons from line 35 to settler 61 via line 1i or may -be supplied from lines 4| or 46.

The stripped tar is removed from the base of the stripper by line 12 and it may be characterizedv by gravity lower than 10 API. a density well above 1, a ring and ball softening point of about 145 F., a penetration of zero at 32 F. 60 seconds and 200 grams, a penetration of about 150 or less at 115 F. with 5 second and 50 grams, 150 at 77 F. with 5 cms/minute, an open cup ilash point of about 340 F., a solubility in carbon tetra chloride of 100 weight percent, solubility in heptane of less than 70 Weight percent, an iodine number of about 140, a fluorine content of 0.5 weight percent or less. a. carbon content of at least about 92 weight percent and a molecular weight upwards of about 425. Of course the properties of the tar will be dependent upon the extent to which tar has been degraded, l. e. will depend on the severity of the cracking which it has undergone in the reaction zone or zones. For example, when a tar of less than F. softening point and having a molecular weight of about 353 and an iodine number of was further degraded with hydrogen uoride at a temperature of about 435 F. and a pressure of about 1675 p. s. i., a degraded tar was obtained which Was characterized by the softening point of about 400 F.. molecular weight of about 462 and an iodine number of about 84. Prior to removal of hydrogen uoride the degraded tar was apparently dissolved or in a colloidal solution or suspension since it was easily removed from the reactor as a liquid stream. Where the reaction leads to the ultimate production of coke the hydrogen iluoride stream may be flashed in the upper part of a tower such as stripper 64 whereby the vaporization of the hydrogen iiuoride leaves solid particles which may be allowed to settle to the base of the tower and which may be further stripped with an inert gas stream in much the same way that a liquid would be stripped. By introducing a fluidizing gas vin small amounts at the base of the tower such solids may 7 be kept in aerated condition so that they will 'behave as a liquid and so that they may be withdrawn through valved conduits to receivers.

Solids obtained in this way may contain carbon bound fiuorine and/or free hydrogen nuoride the amounts being determined by the conditions of separation or hydrogen fluoride and carbonaceous material. After the organically combined fiuorine and/or hydrogen fluoride have been varied orv removed to the desired extent, the solid coke may be used as a fiuidized solid fuel or admixed with a liquid fuel by being suspended in the same or it may be briquetted or used as a binder for finely divided solid fuels of still higher softening point such as other petroleum coke.

The total gasoline produced by this process is rich in isoparaffins such as isobutane and isopentane and with a naphthenic charging stock it may predominate in naphthenes, chieny naphthenes of 6 to 10 carbon atoms. It also may contain about 8 to 10% of aromatics. The gasoline is :remarkably responsive to lead tetra.- ethyl (due in part perhaps to the complete removal of sulfur) and only a small amount of this additive is required to bring its octane rating up to about 80.

From the above description it will be seen that the recovery of hydrogen fluoride from various eilluent streams is achieved in a simple and inexpensive manner so that hydrogen fluoride losses are almost negligible. Make-up hydrogen nuoride may be added from time to time from source 1l vialine 19 to storage tank 21. From this storage tank the hydrogen fluoride is introduced by pump III and line I5 to the oil stream entering the flrst reactor as hereinabove described. The nnal hydrogen fluoride removal from light hydrocarbons may be effected after depropanizer 2! instead of after debutanizer 22. The order of fractionating steps may be varied without in any way departing from the invention but it will be noted that for the most part hydrogen fluoride is eectively separated from hydrocarbon streams in simple settlers I1, 20, 25, 6I and i1. The hydrogen fluoride withdrawn from the base of cold settler may be passed via line 12, pressure reducing valve 14 and lines 15 and 2S to storage tank 21, or may be passed by pump 1l and lines 11 and I5 back to line I2 for direct recycling.

It is not always essential that a single homogeneous phase be maintained in the first reactor since considerable cracking may be obtained when two liquid phases are present, namely, a hydrogen nuoride-insoluble oil phase and a hydrogen iluoride-tar phase, provided of course that the mixing is suiilciently intimate and effective When a two-phase system is employed in the ilrst reactor, however, and'particularly when the hydrogen fluoride to oil ratio is well in excess of 2, a considerable amount of hydrogen fluoridesoluble oil will be separated with hydrogen fluoride in the first settler il and this solution from' the first settler may then be further cracked under single phase conditions in one or more subsequent reactors. By this method of operation and by employing relatively short contact times, i.- e. of the order of about 1 to 20 minutes and preferably less than 10 minutes in the first contacting zone, excessive cracking and gas production may be avoided and remarkably high ultimate gasoline yields may be obtained. An outstan'ding feature of the process is its production from ordinary gas oils of about '7o volume percent of hydrocarbons boiling in the gasoline boiling range with only a small amount of light hydrocarbons lower boiling than isobutane and with only about 35% of heavy tar, the amount, of tar depending of course upon the nature oi th charging stock employed and also depending upon whether or not hydrogen is employed in the various reactors.

While a speciilc example of the invention has been described in considerable detail it should be understood that this example is by way of illustration and is not limitative since many other modifications and alternative procedures and operating conditions will be apparent from the above description to those skilled in the art.

Thus while hydrogen duoride has been described as a catalyst it should be understood that the hydrogen fluoride may be promoted by boron fluoride or other promoters known to the art and/or the conversion may be eected in the presence of a small amount of water.

We claim:

l. The method of eifecting hydrocarbon conversion with a hydrogen fluoride catalyst which method comprises contacting an unsaturated, hydrogen fluoride soluble, hydrocarbon charging stock with hydrogen fluoride under such conditions of temperature and pressure that such charging stock is completely miscible with said hydrogen uoride catalyst, said conditions including a conversion temperature in the range of about 300 to 500 F., a pressure sumcient to maintain both the charging stock and hydrogen fluoride in homzeneous liquid phase and with a time of contact sufficient to give substantial cracking.

2. The method oi cracking an unsaturated hydrocarbon charging stock higher boiling than gasoline and completely miscible with hydrogen fluoride at a cracking temperature within the range of about 300 to 500. F. under a pressure suillcient to maintain liquid phase conditions which method comprises introducing said charging stock and a substantial amount of hydrogen fluoride into a conversion zone, maintaining said conversion zone at said cracking temperature and at a suillcient pressure to maintain a single homogeneous liquid phase within said conversion zone, holding said homogeneous phase within said conversion zone for a period of time suillcient to effect substantial cracking, cooling the eilluent stream from said reaction zone to a temperature sufilciently low to eect phase separation and separating a hydrogen fluoride-insoluble 'product fraction from a hydrogen fluoride soluble tar t fraction.

3. A refining process which comprises contacting an unsaturated hydrocarbon oil higher boiling than gasoline and soluble in hydrogen fluoride at conversion temperature with a substantial amount of hydrogen iluoride in a conversion zone at conversion temperature and under sufficient pressure for maintaining a single substantially homogeneous liquid hydrogen fluoride-hydrocarbon phase, holding said homogeneous liquid Phase in said conversion zone for a time sumcient to effect substantial conversion of said hydrocarbon oil into hydrocarbons of lower boiling range, separating a liquid phase of said hydrocarbons of lower boiling range from hydrogen duoride at a high temperature, cooling said separated hydrocarbons to a lower temperature and eflecting further separation of hydrocarbons from hydrogen fluoride at said lower temperature and iractionatlng hydrocarbons removed from said lower temperature separating zone.

4. The method of claim 3 which includes the REFERENCES CITD The following references are of record in the 15 le of this Patent:

Number 10 UNITED STATES PATENTS Name Date Burk Mar. 7, 1944 Gibson Apr. 25, 1944 Bloch Sept. 5, 1944 Frey June 19, 1945 Frey July 9, 1946 Lee et al Feb. 18, 1947 Frey May 6, 1947 Johnstone Aug. 26, 1947 Lien et a1 Sept. 9, 1947

Claims (1)

1. THE METHOD OF EFFECTING HYDROCARBON CONVERSION WITH A HYDROGEN FLUORIDE CATALYST WHICH METHOD COMPRISES CONTRACTING AN UNSATURATED, HYDROGEN FLUORIDE SOLUBLE, HYDROCARBON CHARGING STOCK WITH HYDROGEN FLUORIDE UNDER SUCH CONDITIONS OF TEMPERATURE AND PRESSURE THAT SUCH CHARGING STOCK IS COMPLETELY MISCIBLE WITH SAID HYDROGEN FLUORIDE CATALYST, SAID CONDITIONS INCLUDING A CONVERSION TEMPERATURE IN THE RANGE OF ABOUT 300 TO 500*F., A PRESSURE SUFFICIENT TO MAINTAIN BOTH THE CHARGING STOCK AND HYDROGEN FLUORIDE IN HOMOGENEOUS LIQUID PHASE AND WITH A TIME OF CONTACT SUFFICIENT TO GIVE SUBSTANTIAL CRACKING.

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