US2303107A - Multistage catalytic conversion of hydrocarbons - Google Patents

Description

Nov. 24, 1942. w. L. BENEDICT MULTISTAGE CATALYTIC GONVERSION OF HYDROCARBONS Filed Jan. so, 1959 fllll.

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Patented Nov. 24, 1942 MULTISTAGE CATALYTIC CONVERSION F H YDROCARBON S Wayne L. Benedict, Chicago, Ill., assigner to Universal Oil Products Company, Chicago, Ill., a vcorporation of Delaware Application January 30, 1939, Serial No.'253,6v20

sclaims. (c1. 19e- 49) This invention relates tothe catalytic conversion of hydrocarbon distillates produced by the distillation of heavy hydrocarbonaceous materials, and more particularly dis'tillates which are vaporizable Without substantial decomposition. Although usually from petroleum sourc'es, in certain instances distillates produced from coal tars,

, shale oils, and the like may be converted by this DIOCESS.

specifically catalytic cracking of high boiling hydrocarbon distillates to produce gasoline and gas is not so well comprehended. Such deductions as have been made are largely of an empirical nature and a discussion of these reactions is, therefore, best confined to facts..

Many catalysts have been proposed to assist the thermal conversion of hydrocarbon distillates into gasoline and gas, among which are certain types which promote as the predominating reaction, the formation of gas rather than gasoline. Such catalysts include the reduced metal catalysts, such as nickel and iron and their ores. These catalysts are, furthermore, subject to poisoning by sulfur compounds and tend to produce coke-like materials which deposit 'as a film around the catalyst particles and render unconverted oil from a lower temperature stage with the raw charge to a succeeding higher temperature stage, and recycling a major portion of the unconverted oil from the iinalA conversion stage to said stage. v

It has been found that certain stocks require somewhat different conditions of cracking for l the .production of maximum yields depending upon the character of the crude oils from which More specifically, the invention is concerned m they are derived. Also that charging stocks of with the conversion of hydrocarbons by meansv varying boiling range from a given crude oil of specially prepared catalysts whichare selecsource require different temperature conditions tive in promoting the formation of high octane and space velocities to produce extensive catanumber gasoline, and gases of a particularly delytic conversion. For example, for a given catasirable composition. lyst, higher temperatures are required for the The art of producing gasoline and gas by therreforming of ,naphthas than are needed for the mal cracking of petroleum oils is extensive and cracking of kerosene distillates, and these in has been developed to the point where the printurn require higher temperatures than do, gas Y ciplesinvolved .are well understood. .The cataoils which have a higher boiling range. Morelytic conversion of hydrocarbons, and more 30 over, considerable benefit may be obtained by l catalytically cracking an oil intwo or more relatively narrow boiling fractions under optimum conditions for each fraction over cracking the total distillate in one step. In the latter case the high boiling material would necessarily be overcracked if the low boiling material were treated at suciently high temperature to obtain suitable conversion. Likewise if the high boiling material is cracked under the best conincreased and the deposition ofv coke and the formation of gas to be reduced.

In addition it has been found that the unconverted portion of the original charging stock` them inactive. Other types of catalysts'promote dehydrogenation reactions, that is, splitting at the carbon-hydrogen bond rather than at the carbon-carbon linkage, and as a consequence thel character of the gases and the antiknock properties of the gasoline produced are considerably different from thosewhich are produced according to the present invention.

In one speciflc'embodiment my invention comprises the separation of crude petroleum into a plurality of fractions, contacting eachlfraction stage at a temperature suitablyadjusted for (i. e., bottoms remaining after conversion and separation of gasolineand gas) is of a somewhat with a cracking catalyst in a separate conversion maximum catalytic conversion of said fraction,

said temperature being generally Aprogressively higher for progressively lower boiling fractions, separating gasoline and gas between each con'- version stage, combining a major portion of the more refractory nature than the virgin stock which cannot be readily attributed to its physical and chemical characteristics. It has been found vthat cracking the unconverted bottoms under the same conditions as the virgin oil ref .ture whereby both virgin distillate and recycle oil are jointly cracked under conditions designed to produce the best yield. A portion of the unconverted bottoms may be withdrawn continuously from any or all of these conversion stages but preferably only from the final stage, and a major portion of the unconverted oil is recirculated to said final stage. This method of operation has the advantage that each portion of the distillate as well as the recycle stock, is treated under the optimum conditions for maximum conversion to motor fuel and a minimum of gas and carbon formation.

As an alternative operation a portion of the' heavier, unconverted oil from each conversion stage may be recycled to said conversion stage for further treatment.

Although the present process may have more or less applicability when using various types of l this type.

recognized cracking catalysts such as those which may be produced by the acid or'other chemical treatment of naturally occurring clays, the preferred catalysts comprise specially prepared synthetic masses, for example, silica-alumina, silicazirconia, silicia-alumina-zirconia, and silicaalumina-thoria having a very high degree of catalytic activity. These masses are prepared by combining the constituents in various ways such as mixing, coprecipitation and the like under conditions whereby alkali metal ions are excluded. In these catalysts the ratio of the components may vary within wide limits and the masses may be considered to comprise intimate or possible molecular admixtures, all of the components indicating more or less low activity individually but in the aggregate displaying high activity. The activity also is not an additive function of the individual component, it being relatively constant for a wide range of proportions whether in molecular, or fractions of molecular proportions. It appears that no one component can be determined as the one component for which the remaining components may be considered as the promoter according to conventional terminology. In the present invention these catalysts are used in the form of sized particles or other formed shapes such as pellets produced by compression or extrusion methods. vThe pressed composites after drying and forming into definite shapes are calcined at temperatures above 800 F.` prior to contacting with the hydrocarbons.

'I'he character of the catalysts described may vary depending upon the exact method of preparation and their composition- All of them have been found to have good catalytic activity although they are not necessarily exactly equivalent in this respect. Some catalysts may-be more u seful for the conversion of naphthas or reform- Ving of gasolines, others more emcient for the cracking of kerosene, and still others for the conversion of higher boiling distillates. The catalysts have been found to accelerate the van undesirable character.

cracking of petroleum and other hydrocarbon distillates to increase the yields of high octane number gasoline, as well as the yields of polymerizable oleflns which are readily converted to high octane number motor fuel. 'Ihese particular catalysts have been found to be selective in bringing about the reactions resulting in the productionof premium quality gasoline, and at the same time are of such a character that they stand up under severe conditions of handling, as

well as the changing conditions ofe successive operation and regeneration. They are further characterized by the ease and accuracy with which they may be reproduced.

The removal from the synthetic catalytic masses of the alkali metal ions and particularly sodium during preparation is of particular importance, which may possibly cause a decrease at elevated temperatures in the internal surface and porosity of the catalysts resulting in reduction of activity to an extent such that the predominant reaction is no longer of a catalytic nature. It may also be possible that the alkali metal compounds tend to catalyzereactions of Whatever the explanation, the removal of alkali metal compounds is important -and the preferred catalysts are of Under certain circumstances it may be desirable to use catalysts of different composition in the different conversion steps of our process, although from a practical standpoint this is seldom the case.

One embodiment of the present invention is illustrated in the attached drawing. However, it should be borne in mind that the exact conditions, flow or apparatus employed therein are not to be construed as limiting the invention in exact correspondence therewith. The drawing is given as an example and illustration of one method of conducting our process. The crude oil is pumped through line I, valve 2, pump 3, and

valve 4 into coil 5in furnace 6 from which itpasses through line 1 and valve 8 into the crude fractionating column 9 where it is divided into l whatever fractionsl are to be treated in the suc- Gas and a light gasoline fraction may be removed through line I2, and valve I3 to suitable stabilizers and coolers and finally to storage. A heavy'gas oil may be withdrawn through line I4 and valve I5, pump I6 and valve I1 into coil I II which is disposed in furnace I9 wherein it is heated to a desired cracking temperature and passed through line 20 and valve 2| to catalytic converter 22 which is operated at a suitable temperature to produce substantial yields of cracked gasoline and of gas high in polymerizable olens. The reaction products pass through line 23 and valve 24 into a fractionator and separator 25 where the gasoline and gas are separated and passed through line 26 and valve 21 to the common gasoline rundown line 28. The gasoline may properly pass through an intermediate stabilizer for separation of gases and production of proper vapor pressure and thence through heat exchangers and condensers not shown to storage. The unconverted oilmay pass through line 29 and valve 30 to join with line 3| in which light gas oil or kerosene removed from the crude fractionator 9 passes to mingle with the unconverted bottoms from fractionator 2l and be pumped by means of pump 33 through .valve 34 into coil 35 in furnace 38. passes through line 31valve 38 t o catalytic converter 39 which is operated at a substantially higher temperature than converter 22 although it may have similar structure. The conversion products pass through line 40 and .valve 4I' to fractionatorand separator 42 in which the gasoline and gas are removed through line 43, valve 44 to the rundown line 28. The unconverted or partially converted oil may then pass through line 45, containing valve 46 into line 41 where it mingles with a primary light fraction which may suitably be of the nature of a heavy naphtha and include some of kerosene boiling range distillate Iwhich passes from the fractionator 9 through line line 58 and valve 51 to fractionator and separator 58. The gasoline and gas pass through line 59 and valve 80 to the run-down line 28. The unconverted and insuiciently converted oil from separator 58 passes through line 6I and valve 62 by means of pump 63 and valve 64 where it joins with the incoming charge from line 41 and is recirculated tocatalytic converter 55 by previously described routes. A minor portion of the oil may be suitably withdrawn through line 65 and valve 66' although it is preferable to withdraw the heavier bottoms through -line 61 and valvesv 68 and 82. Alternative methods of operation are to return a portion of the heavy recycle oil from fractionator through line 69 and valve 10 by means of pump 1I through line 12 yand valve 13 to line I4 where it passes through through line 19 and thence to the crude fractionator 9 by means of line I and previously described routes. In this way the lighter gravity material may be returned to the catalytic conversion system while the heavy oil will combine with the reduced crude oil and be passed to whatever means of disposal has been provided for it, such as to use as fuel oil or as charging stock for thermal cracking. Valves 80, 8I, and

82 are drain lines from the various fractionators. Valves 83 is' acontrol valve in the gasoline-gas collection system. Valve 84 permits the withdrawal from the crude fractionating system of a portion or all of the high boiling naphtha cut, should this be desired. l

The process is highly flexibleand the number of stages used will be entirely Adependent uponl the crude input which, of course, governs the amount of any given distillate which can be produced. The number of fractions and their respective boiling ranges and gravity will be entire- The combined distillate then.

The oil passes through line 53 ly dependent upon the specic needs of the refiner, for example, the out taken for conversion4 in the rst catalytic converter 22 may be a heavy gas oil having gravity, for example, of approximately 20 A. P. I'. and may be cracked at temperatures of G-930 F. The next higher cut which is processed in converter 39 may suitably be of a light gas oil with an initial, for example, in the `kerosene boiling range and an end point approximately that of the' initial of the heavy distillate processed in the rst stage, and may be processed at 930-ll00 F. vThe distillate removed for the third and nal catalytic stage may suitably consistof a heavy naphtha which may include some material in the lowerI limits of the kerosene boiling range and may be cracked at 10501200 F. Normally the material boiling below 250-300 F. has good antiknock properties and is not processed. It may be 'removed and later blended back with the nished gasoline. In certain instances it may be practical to include still another conversion stage v and it is understood that such additional confractionator, and the unconverted bottoms from fractiona'tor 42 are processed alone in the third conversion stage at a suitably high temperature to produce substantial conversion to gasoline. As in the previously described operation a major portion of the recycle oil is returned to the iinal conversion stage and a minor portion is withdrawn and used. as a domestic fuel oil, or if desired returned to the crude fractionator as described above. In this case with the present hook-up it would only be necessary to increase the top temperature of the crude fractionating column to remove end point gasoline and to close valve 48 so that no naphtha side cut is removed.

Since the catalyst employed in these reactions is of atype that decreases in activity because of the accumulation of carbon, it is necessaryyto regenerate at intervals.` This may be carried out in any suitable manner. `For example, the catalytic converter which may` comprise tubes filled with catalyst, or chambers or cases of various types may be arranged in pairs whereby the distillate is treated in 'one reactor while the other reactor is being regenerated. The regeneration is accomplished by treating the catalyst with regulated quantities of oxygencontaining lgases Awhereby the carbon deposited on the'catalytic surface is burned oi. The temperature during this treatment is controlled to prevent excessive shrinkage and decreased activity of the catalyst. 'I'he means of regeneration and the type of reactor employed are not a featureI of 'the present invention; Any suitable method of carrying out the reactivation may be employed. Coolers, stabilizers, heat exchangers and such equipment which are obviously necessary for carrying out the operation are not shown in the attached drawing in the interests of simplifying said drawing.

The following example is given to illustrate my invention and is not intended in any way to limit the invention to the exact conditions given therein. A Pennsylvania crude oil was distilled to produce the following fractions, a cut boiling up to 250 F; and having an octane number of 6'5 was removed for use as a blending stock in .other refinery operations. A heavy naphtha having an end point of 520 F., a light gas oil cut and a heavy gas oil cut were removed as charging stocks for catalytic cracking. The heavy gas oil distillate was cracked in the first conversion stage at 920 F., the light gas oil fraction was cracked at 975 F., in the second conversion stage and the naphtha fraction was cracked in the final conversion stage at a temperature of 1050 F. Small portions of the unconverted oil from the first two conversion stages were recycled to said conversion stages, the major portion of the unconverted oil passing to the succeeding conversion stage where it was processed at the higher temperature. The major portion of the recycle oil from the final conversion stage was returned to'said conversion stage for further cracking and a portion thereof was withdrawn continuously from the system for use as a domestic fuel oil. The gasoline and gas from the various fractionators were separated in a stabilizer and the gases were then passed through a catalytic polymerization plant where the gaseous olefins were converted to motor fuel and blended with the cracked gasoline produced in the catalytic cracking plant. The overall yield of 81 octane number gasoline including the polymer amounted to 86% of the total oil charged to the various catalytic conversion stages.

I claim as my invention:

1. A process which comprises separating hydroca'rbon oil into a plurality of fractions, maintaininga series of separate conversion steps of progressively increasing temperature, contacting eachl of said fractions with a cracking catalyst in a conversion stage maintained at the temperature suitable for optimum conversion of each fraction, combining unconverted oil from a lower temperature stage with the fraction Vcharged'to a succeeding higher temperature stage, separating gasoline and gas between conversion stages a portion of the unconverted oil from the final conversion stage to the zone in which the chargtion, maintaining the conversion stages as suc-V cessively higher temperatures, ranging between 800 F. and 1200 F. combining unconverted oil from a lower temperature stage with the fraction charged-to a succeeding higher temperature stage, separating gasoline and gas between conversion stages, and recycling heavy unconverted oil from the final stage to the first-mentioned separating step', l'

3. A process which comprises separating crude hydrocarbon oil into a plurality of fractions, maintaining a series of separate conversion steps of progressively increasing temperature ranging between G-1200 F., contacting each of said fractions with a cracking catalyst in aconversion stage maintained at the temperature suitable for maximum conversion of cach fraction, returning a minor portion of unconverted oil from each stage to the same stage, combining a major portion of unconverted oil from a lower temperature stage with the fraction charged to asucceeding higher temperature stage, and separating gasoline and gas between stages from the unconverted oil.

4. The process claimed in claim 3, wherein at least a portion of heavy unconverted oil from the final stage .is returned to the zone wherein the crude oil is separated into fractions.

5. A hydrocarbon oil conversion process which comprises fractionating the charging oil and separating therefrom relatively light and heavy fractions, subjecting the heavier fraction to catalytic cracking in a first conversion stage, subjecting the lighter fraction to catalytic cracking at higher temperature in a second conversion stage, supplying a major portion of the unconverted oil from the first stage to the second stage for further cracking treatment, therein at the from the unconverted oil and returning at least v higher temperature in admixture with the lighter fraction, and returning a minor portion of said unconverted oil to the first stage for retreatment therein together with said heavier fraction.

WAYNE L. BENEDICT.

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