US2525814A - Catalytic conversion of hydrocarbons - Google Patents

Description

Oct. 17, 1950 H. D. RADFORD CATALYTIC CONVERSION oF HYDRocARBoNs Filed July 12, 1947 mmv www

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@um O #EQ m@ n@ mm Patented Oct. 17, 1950 CATALY'IIC CONVERSION 0F HYDROCARBONS Herschel D. Radford, Columbia, Mo., assignor to Pan American Refining Corporation,` Texas City, Tex., a corporation of'Delaware Application July 12, 1947, Serial No. 760,577

Claims.

This invention relates to a process of converting hydrocarbon oils such as gas oil, reduced crude oil, and other heavy petroleum stocks into gasoline. More particularly the invention relates to an improved combination of processes wherein a more extensive conversion of the heavy oil into` gasoline is obtained by the co-action of hydroiiuoric acid and argllaceous catalysts acting separately in successive stages.

One object of the invention is to improve the operation of the catalytic cracking process employing refractory solid argillaceous and refractory oxide catalysts by refining the heavy oil charging stock employed therein, thereby increasing catalyst life and extent of conversion and improving` product distribution. Another object of the invention is to eliminate from the i recycle stock in an oxide catalyst cracking system carbon-producing ingredientssuch as aromatics and naphthenes without losing the potential gasoline-producing capacity derivable from these constituents. Yet another object of the invention is to eliminate combined fluorine from I-IF conversion gas oil and simultaneously activate oxide conversion catalyst therewith. Other objects of the invention will be apparent from the following description thereof.

The invention is illustrated by a drawing which shows diagrammatically an apparatus suitable for carrying out the process.

l'n the catalytic cracking of heavy oils such as gas oil and reduced crude oil, the heated oil which may or may not be vaporized is charged to the catalyst and contacted therewith for a short time at temperatures of the order of 85() to 1000o F. Catalysts for this reaction are usually natural clays, preferably acid-treated clays of `the montmorillonite type, or metal oxides, active silica, alumina, boron oxide, zirconium oxide, magnesia, or mixtures thereof. One of the best known synthetic catalysts for the reaction is silica gel promoted with about l0 to 25 per cent of aluminum oxide or magnesium oxide While the most commonly used natural catalyst is Super Filtrol, an acid-treated montmorillonite clay. These catalysts, hereinafter referred to as oxide catalysts, may be employed in the form of porous beds, either fixed or moving beds thru which the hydrocarbon vapors are passed, or they may be employed in the form of powders mixed with the hydrocarbon vapors in the socalled fluid cracking process.

In either case a substantial part of the hydrocarbon material is converted to non-volatile car- Abonaceous deposits commonly termed` coke which forms on the surface of the catalyst. This coke mustbe removed from the catalyst from time to time by burning in order to maintain catalystactivity. The amount of potential fuel lost in this way is a very considerable item in the cost of operating the process, for a number of reasons. First, the actual inventory loss on a weight basis amounts to about 5% or more depending upon the character of the stock employed. When charging reduced crude oil the Aloss is substantially greater, e. g. 7 to l0 per cent.

` In addition to the actual` weight loss, there is the cost of supplying tothe process the large volume of air required for effective combustion of the coke. Another important cost is the increased cost of the apparatus required for dissipating the heat evolved in the combustion and for handling the large volume of gases in the combustion-regeneration. It is characteristic of aromatic-type charging stocks that more coke is produced by their use and thisis also true to a lesser extent of the naphthenicstocks, whereas the paraiiinic-type charging stocks produce a minimum amount of coke and are therefore preferred for the oxide catalyst cracking process. Even where parafnic stocks are available, however, it has been found that the so-called cycle stock produced in the process is of highly aromatic or naphthenic character and is generally unsuitable for recycling to the catalytic cracking operation because of its high coke-forming tendency which increases the cost of the conversion operation disproportionately, resulting in lower net gasoline recovery and lower rate of conversion of this catalytic cycle stock to gasoline.

For the purpose of this invention, I class as aromatic cracking stocks those oils having a Watson characterization factor (K) below about 11.75, andas parafnic stocks those having a K value above about `11.75. The characterization factor,

wherev Tb=molal average boiling point, Rankine, and s=sp. gr. at /60" F., is described in a publication by Watson and Nelson--Ind. & Eng. Chem., vol. 25 (1933), page 880.

According to my invention, I eliminate the recycle fractions boiling higher than gasoline obtained from the solid oxide catalyst cracking step and subject these fractions to conversion with hydrouoric acid catalyst at considerably lower temperatures than those employed with the refractory argillaceous oxide catalysts. The hyi by une se and valve 35.

temperatures and used eciently as a constituent of liquid fuels or for other purposes where such material is adapted as in paving, coating, plasticizing, etc. Thus the combination of refractory solid catalyst in one stage with hydrofluoric acid catalyst in another stage results in maximum production of gasoline and minimumlosses by .way of coke formation. The production of .permarient gases such as methane and ethane is also reduced substantially.

Referring to the drawing, the paraiinic feed stock, for example Pennsylvania or Mid-Continentgas oil, is charged by line Il] to heater il wherein it is heated to the desired cracking temperature or simply preheated, for example to 500-900 F. The charge passes by line i2 thru catalyst eductor i3 and thenceby line is to re actor S5. Powdered solid catalyst from standpipe i5 is introduced into the vapors at i3, usually at the ratio of about 2 to l0 pounds of catalyst per pound of hydrocarbons, altho catalyst: oil ratios as high as to 2*() may be employed. In

I reactor I5 a fluidized dense suspension of catalyst is maintained with a density of .the order of 15 to 35 pounds per cubic foot, the density being v.determined by the character of the catalyst, its

particle size, and by the velocity of the upilowing vapors in the reactor. A suitable velocity is about l to 3 feet per second. The vapors separate from the luidized body of catalyst in the reactor and are withdrawn thru cyclone separator Il and vapor line i8 leading to fractionator i9. The

vcatalyst overthrows into downcomer 2li leading to stripper 2l supplied by a current of steam o-r other stripping gas by line 22 for the removal of adhering volatilizable hydrocarbons. The stripping gas and vapors pass by line 23 into the main products stream in the top of the reactor l5. rlhe catalyst flows from thestripper by line 2d and is conductedby line 25 to a loW point in regenerator Z6. Air or` other carrier gas is .introduced by line 2l and serves to distribute the catalyst evenly in the regenerator, where a dense phase is maintained by controlling the upflow gas velocity atabout l to 3 feet per second. Additional air for combustion ofcoke on .the` catalyst can be supplied by line 23. Spent regeneration gases escape from the regenerato-r by cyclone separator 29 line 39, while the regenerated catalyst returns to the reactor by standpipe l5. Cooling of the regenerator by external cycling of catalyst thru a cooler or by other means is now shown.

In fractionatcr i9, the products are separated into gasoline, light gas oil, heavy gas oil, and slurry oil containing ne catalyst carryover from I5. The gasoline vapors and `uncondensable gases are conducted by line 3l to condenser 32 and thence f to receiver 33, whence uncondensed gases including methane, ethane and propane are discharged Light gas oil is withdrawn by line 36 and may be recycled tc the catalytic cracking step by pump Sl. Heavy gas oil is conducted by lines 33 and 39 to be treated with hydrofluoric acid as hereinafter described. If desired, part or all of the light gas oil may also be transferred by line 35 into line 39 for treatment with HF. The slurry oil is withdrawn by line and returned to the oxide catalyst system in the feed stock cr through the eductor i3 by suitable connections, not shown.

The so-called cycle gas oil from the oxide catalyst system is discharged by line 39 into HF reectorrll which is illustrated equipped with mechanical agitator It for obtaining satisfactory Vcontact between HF and hydrocarbon phases altho other means of obtaining contact may be provided. The temperature in reactor 4l is maintained above about 250 F., by internal heating coils, not sho-wn, or by heating the feed stock above the reaction temperature by conventional heating means. A temperature of the order of 300 to 450 F. is effective forconverting the hydrocarbons therein. It is alsopreferred to maintain a vsubstantial pressure, preferably a pressure somewhat above thevapor pressureof liquid HF .at the temperature employed. Liquid HF is supplied to the reactor from tank 43 by line M At the preferred reaction temperature of about 350 to 425 F. the HF phase is usually lighter than the hydrocarbon phase and passesto the top of reactor :El whence it is withdrawn by line 45 to settler 46 and Vthence byline dito cooler 48 and separator d valtho where a highly aromatic feed stock is charged to the reactor the hydrocarbon phaseinay be lighter and Ybecome the upper layer. In normal operation, any hydrocarbon phase entrained in the HF phase in liriejfii isA returned tc thereactor l by line 5B. On cooling in is aphase separation occurs and the HF phase nov/'collects onthe bottom of separator 49 whence it is withdrawn by line 5l leading to pressure-reducing valve 52 and stripper 53 where the HF is driven off by heating and the hydrocarbon tar fraction, liquid when hot, is withdrawn .by

.valved line 5i. The recovered HFis conducted by line 5,5, condensed in condenser 56, separated from lighthydrocarbon oil in 5l, andreturned by pump 58 and line :'59 to reactor lli. Light liquid hydrocarbon, usually unsaturated olenic stock which separatesin 5,1, is withdrawn via line B0.

Liquid hydrocarbons separated in 49 as an upper layer are conductedby line 5I t0 fractionator 62 where gasoline is separated and Vwithdrawn by line 63 and higher boiling fractions are recycled tothe reactor by line ed. Uncondensed gases from separatore@ are conducted by linei to compressor-.56 where the pressure is restored to that maintained in reactor lll. A portion of the gases including most of the HF vapor Vcontained therein condenses andis separated by separator El, the liquid returning by lineV Sil to reactor-J1!` Uncondensable gases including methane are discharge `from the system by line 59.

. Fromy thebase of .reactor 4l, the Vhydrocarbon phase'is Withdrawn by line 7i) leading to separator l! from whichy any entrained liquid HFv is returned by line l2 to the reactor. The hydrocarbon product is thence conducted .by line. i3. thru cooler 'Hl to separator 'l5 wherein a separation into a hydrocarbon .andan vHF phase occurs at the lower temperature maintained therein, e. g. to 150 F. The separated HF passesby line 'I6 back to reactor 4L The hydrocarbon upper layer in separator I5 is withdrawn by line l? thru valve. 13 to fractionator 'I9 where a gasoline fraction is .distilled off and withdrawn by line Sil. Gasoline from "line 63 may be admixed therewith if desired.

The gases lighter than gasoline, e. g. methane, propane and butane, pass by line 8i to stabilizer 82 wherein any HF and condensable hydrocarbons, particularly butane, are recovered and either returned by line 83 and pump 84 to reactor 4L or recovered as a separate stream. UncondensableA gases primarily propane with some methane and any ethane produced in the operation are removed from the system by line 85.

Paramnic hydrocarbon products boiling above the boiling point of gasoline are collected in the base of fractionator 19 and conducted by line 86 and pump 87 to heater Il after which these hydrocarbons are subjected to further cracking with oxide catalyst as hereinbefore described. Flourine combined in this stock, usually to the extent of 0.01 to 0.1 per cent, is eliminated by reaction with the oxide catalyst to form a metal iluoride having a promoting action on that catalyst.

If desired, I may charge to the HF conversion reactor directly a naphthenic or aromatic feed stock supplied by line 88. For this purpose gas oil or residuum from naphthenic crudes are satisfactory, examples of which are gas oil or residuum from Winkler County, Texas, crude,

C Slaughter crude from West Texas, Rangely crude or California crudes of high aromatic content such as that from Elk Hills. Heavy refractory stocks from thermal cracking processes may also be added directly to the HF conversion reaction.

`The process may be supplied by feed stock from either i9 and 83 simultaneously or from either source alone if desired. Where the process is charged with a reduced crude oll it is preferred to feed it to the HF stage thru line 88 and feed the oxide catalyst stage with the parafnic gas oil produced in the HF conversion operation thru` `transfer' line 86. As a general rule, I can charge vating effect on the oxide catalyst in the solid oxide conversion stage and I prefer to charge such stocks directly to the HF stage by line 88 where the bases are quantitatively removed by absorption in the HF.

The hydrocarbon gases produced in the oxide catalyst stage of the process and eliminated by line 35 may, if desired, be conducted by line 89 to the HF catalyst stage thru the same vapor system employed for handling light hydrocarbons from separator 49. It is important, however, to avoid transferring water vapors with such gases and it may be desirable to subject them to drying by means not shown. If there is a substantial amount of dissolved water in the stocks iiowing thru lines 36 and 38 into reactor 4i by line 39, it may also be necessary to employ a dryer for these stocks to prevent excessive H2O contamination of the HF catalyst in reactor 4I. In general, it is desirable to maintain the HF in reactor 4| near anhydrous condition, a concentration of 95 to 99 per cent being desirable based on the combined Weight of HF and H2O present.

In the operation of the HF conversion stage, i

45 is controlled to maintain a substantial amount of BIF-soluble hydrocarbon in reactor 4|, as it has been found that the rate of reaction is substantially increased by an amount of HF-soluble Heavy HF Conversion Product Suitable for Oxide Catalyst Conversion Original Gas Oil Gravity A. P. I degrees 60% ASTM degrees F Characterization Factor (Watson) Inspection of these data shows that the gas oil charge to the HF conversion unit was substantially improved inits characteristics for oxide catalyst cracking while at the same time a high quality gasoline distillate was obtained from the HF treatment. The amount of the gasoline products in the HF treatment depends partly on the character of the` charging stock and partly on the conditions employed in HF treating. The amount of gasoline may be equal to the weight of product gas oil produced or two to three times the weight of the product gas oil. In general, it is not possible to operate under such conditions that only gas oil is produced in the HF conversion stage to the exclusion of gasoline production.

Another indication of the powerful hydrogen reproportioning action of the HF-hydrocarbon complex employed in the HF conversion stagea residuum having an A. P. I. gravity of 21.7 was charged thereto and the resulting tar eliminated at 54 was obtained with an A. P. I. gravity of less than 10, i. e. a product of such low hydrogen content that it is heavier than Water. In general, it is desirable to Operate the process to produce an HF tar product having an A. P. I. gravity less than that of water, usually within the range of 5 to 10 A. P. I.

In a typical operation, there was charged to the HF conversion stage a naphthenic gas oil of 31 A. P. I. gravity. The HF contacting reactor was maintained at 400 F. and at a pressure of about 900 p. s. i. The ratio of HF to oil charged was 3.1, the rate of charge being 0.83 volume of oil per hour per volume of liquid HF in the reactor corresponding to a contact time in the reactor of 7.2 minutes, assuming the specic gravity of HF at 400 F. to be 0.3. The product recovery was 97.6 per cent based on charge. The following products were obtained:

Per cent by Weight Dry gas 0.4

Excess isobutane 3.2

Gasoline, 10 lb. R. V. P 27.0

Gas oil insoluble in HF 39.6

Gas oil soluble in HF 6.0

Tar boiling above 650 F 23.8

Total conversion 54.4

The gasoline had-an A. S. T. M. motoroctane number of 75.3. The HP1-insoluble gas oil vwas characterizedby an A. P. I. gravity of `3(1.6 and ideally suitedfor conversion into gasoline-by contacting With refractory oxide catalysts as hereinabove described for the preparation of motor fuel of 78-82 octane number (A. S. T. MJ.

Having thus described my invention what I claim is:

1. The process of converting hydrocarbon oils which comprises contacting a heavy parainic hydrocarbon charging stock having a characterization factor above 11.75 with a refractory oxide catalyst at conversion temperature in an oxide catalyst conversion operation, recovering therefrom a gasoline fraction and an aromatic heavierthan-gasoline fraction, contactingI a heavy aromatic charging stock having a characterization factor below 11.75 with liquid hydrofluoric acid atr conversion temperature of about 300 to 450 F. in an HF conversion operation whereby it is substantially converted into gasoline and a paraflnic heavier-than-.gasoline fraction having a characterization factor above 11.75 substantially less aromatic than said aromatic charging stock, charging said heavy paraflinic fraction produced in said HF conversion operation to said oxide catalyst conversion operation and charging said heavier-than-gasoline aromatic fraction from the rst-named'conversion operation directly to -said HF conversion operation.

2. The process of claim 1 wherein all the parafinic stock charged to said oxide conversion operation comprises the Vheavy paraiilnic fraction produced in said HF conversion operation.

3. The process of claim 1 wherein all the aromatic charging stock supplied to said HF conversion operation comprises the heavy aro natio fraction of the nrotlucts recovered from said oxide catalyst conversion operation.

4. The process of converting hydrocarbon oils which comprises converting a heavy aromatictype hydrocarbon oil having a characterization factor below 11.75 by contacting with liquid HF at a temperature of about 390 to 450o F. in a HF conversion operation, separating the products into gasoline, gas, tar and paraninic-type gas oil having a characterization factor' above 11.75, converting heavy parafnic hydrocarbons by contacting with a refractory oxide catalyst at conversion temperature in an oxide catalyst conversion operation and separating the products thereof into gas, gasoline and a heavy aromatic gas oil fraction having a characterization factorv below 11.75, charging said heavy aromatic gasoil fraction to said HF conversion operation, charging said parafnic-type gas oil fraction to said oxide conversion operation and charging hydrocarbon gas from both HF and oxide `conversion operations to said HF conversion operation.

5. The process of claim 4 wherein an HF-soluble hydrocarbon phase is retained in the Hi conversion zone for a period of time sufficient to produce a product tar fraction having an A. P. I. gravity of about 5 to 10 and a melting point, A. S. T. M., above about 200 C.

HERSCHEL D. RADFORD.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,228,510 Dearborn et al. Jan. 14, 1941 2,343,841 Burk Mar. 7, 1944 2,368,704 Carlson Feb. 6, 1945 2,378,762 Frey June 19, 1945 2,495,995 Burk Aug. 2o, 1946 2,415,530 Porter Feb. 11, 1947 2,428,715 Marisic Oct. 7, 1947 2,454,615 Ridgway et al Nov. 23, 1948

Claims (1)

1. THE PROCESS OF CONVERTING HYDROCARBON OILS WHICH COMPRISES CONTACTING A HEAVY PARAFFINIC HYDROCARBON CHARGING STOCK HAVING A CHARACTERIZATION FACTOR ABOVE 11.75 WITH A REFRACTORY OXIDE CATALYST AT CONVERSION TEMPERATURE IN AN OXIDE CATALYST CONVERSION OPERATION, RECOVERING THEREFROM A GASOLINE FRACTION AND AN AROMATIC HEAVIERTHAN-GASOLINE FRACTION, CONTACTING A HEAVY AROMATIC CHARGING STOCK HAVING A CHARACTERIZATION FACTOR BELOW 11.75 WITH LIQUID HYDROFLUORIC ACID AT CONVERSION TEMPERATURE OF ABOUT 300 TO 450* F. IN AN HF CONVERSION OPERATION WHEREBY IT IS SUBSTANTIALLY CONVERTED INTO GASOLINE AND A PARAFFINIC HEAVIER-THAN-GASOLINE FRACTION HAVING A CHARACTERIZATION FACTOR ABOVE 11.75 SUBSTANTIALLY LESS AROMATIC THAN SAID AROMATIC CHARGING STOCK, CHARGING SAID HEAVY PARAFFINIC FRACTION PRODUCED IN SAID HF CONVERSION OPERATION TO SAID OXIDE CATALYST CONVERSION OPERATION AND CHARGING SAID HEAVIER-THAN-GASOLINE AROMATIC FRACTION FROM THE FIRST-NAMED CONVERSION OPERATION DIRECTLY TO SAID HF CONVERSION OPERATION.

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