US2358149A - Cracking hydrocarbon oils - Google Patents

Description

Sept. 12, 1944. H. B. coKE 2,358,149

cRAcKING HYDRocARBoN 0111s Filed Dec. 23, 1938 4 sheets-sheet 1\ Sept. l2, 1944.

H. B. COOKE CRACKING HYDROCARBON OILS wfv@ Sept. l2, 1,944. H. B. cooKE CRACKING HYDROCARBON OILS Filed Dec. 23, 1958 4 sheets-sheet s Horace .5. O00}%y Sept. l2, l

H. B. coQKE 2,358,149 CRACKING HYDROCARBON `OILS Flednec. 2s, 1958Y 4 sheets-sheet 4 Horace@ Cooke, Y'

Patented Sept. 12, 1,944

2,358,149 oRAcKING nYDRocAR'BoN oILs Horace B. Cooke, Alexandria, Va., assignor to Gulf Oil Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Application December 2.3, 1938, Serial No. 247,504

rc1. 19e-9) '7v Claims.

My invention relates to p1 ocesses for cracking hydrocarbon oils to obtain gasoline hydrocarbons useful as motor fuel and having high anti-knock value when so used. It relates more particularly to improved methods of obtaining gasoline hydrocarbons from crude petroleum stocks, wherein such stocks are rst distilled in order to recover a plurality of fractions of different boiling-point ranges, these fractions are segregated and subjected to catalytic cracking and thermal cracking respectively, and normally gaseous hydrocarbons thereby produced are recovered and delivered to the thermal cracking operation in order to promote the degree of cracking obtained therein and to effect a conversion of said gaseous hydrocarbons to gasoline-like hydrocarbons of high anti-knock value; all as more fully-set forth and described hereinbelow in further detail.

Within the past few years great strides have been made in the art of cracking petroleum oils. These advances, for the most part, derive from the ever-increasing incentive to produce a maximum yield of motor fuel of maximum anti-knock value. Those processes which are believed to have made substantial progress in this direction may in general be divided into two categories; first, processes involving conversion or polymerization of the normally gaseous hydrocarbons produced in oil-cracking operations, and` second, catalytic oil-cracking processes. But while much thought and time has been expended in the development of these individual types of processes,

comparatively little thought has been given to methods of combining them in a unitary conversion operation.

A considerable number of separate gas-polymerization processes have been proposed and some have been operated cna large scale. The opinion is growing, however, that such processes are likelyto nd their greatest utility either for the recovery of gasoline-like hydrocarbons from natural gases or, as in the case of certain catalytic-type polymer-ization processes, for the relatively small scale manufacture of special fuels, such as iso-octane, the market for which is still comparatively limited. In so far as gases derived from refinery cracking operations are concerned, it is believed that the greatest advance in the art has been made inthe development of oilcracking processes of the so-called gas-reversion type, in which normally gaseous hydrocarbons l producd in cracking the hydrocarbon oil are recirculated to the conversion zone. A process of this character is disclosed in prior U. S. Patents conditions remaining the same.

.highly advantageous results.

Nos. 2,135,014, 42,135,108 and 2,135,109 to Povl Ostergaard. Others prior to Ostergaard had proposed to recirculate-Ca and C4 hydrocarbons to the cracking zone of an ordinary oil-cracking operation, but at least in such cases as involved the return of these gases for reaction purposes and without the presence of non-reactive or diluent gases, had confined themselves to operations conducted under the ordinary oil-cracking conditions which would have obtained for. the `same oil. Ostergaard increased the degree of conversion per pass and the operating temperature in an operation of this kind, above those which would normally obtain and in fact above those which could be maintained under otherwise similar conditions and without carbon deposition, if the same oil were cracked in the same apparatus without recirculation of the reactive normally gaseous hydrocarbons.

The gas-reversion process has been successfully applied to' a wide variety of cracking stocks, with Strikingly enough, however, it has been found that the optimum advantages of the gas-reversion type of system generally are obtained when the process is applied to the cracking or re-forming of naphthas and similar light stocks containing substantial amounts of hydrocarbons within the gasoline boilingpoint range, no doubt partly because of the high temperatures possible when operating on light stocks of this character. On the other hand,

this type of process is also especially useful and advantageous in conjunction with the cracking of very heavy or residual stocks, such for example as reduced crudes. The conversion temperatures employed in such operations are, of course, considerably lower than those employed in re-forming or cracking lighter and more refractory stocks, but are 4nevertheless considerably higher than would be used if the same heavy stock were cracked in the absence of the recirculated normally gaseous hydrocarbons, other I For this reason, the gas-reversion process as applied to such heavy stocks is highly advantageous, primarily from the standpoint of the far greater conversion per pass possible with respect to the heavy oil, as distinguished from the conversion per pass of the normally gaseous. hydrocarbons. Gas conversion is of course eiected, but the conversion per pass of the normally gaseous hydrocarbons is naturally lower when cracking a heavy residual stock than when cracking naphtha or other light stock. This in turn makes it possible to produce a far greater amount of gas-oil charging stock suitable for subsequent cracking to gasoline. It is not intended to imply that a gas-reversion process is not applicable to the cracking of gas-oil. As a matter of fact the process has been successfully applied to the cracking of gas-oil, and as so applied results in an increase in both the yield and anti-knock quality of the nal gasoline produced as compared with thermal cracking processes in which gas recirculation is not employed. However, the advantages of the process are believed to show up more strongly and its'economies are believed to be most evident, in connection with the re-forming of naphthas and light stock, on the one hand, and the cracking'or so-called viscosity-breaking of very heavy stocks, on the other hand.

VA large number of catalytic cracking processes have been proposed,v all characterized by the presence of a catalyst of one type or another in the conversion zone and usually-by the employment of relatively low pressures. The Houdry process, employing as a typical catalyst an activated hydrosilicate of alumina or the like, is a process of this type. On account of the necessary periodic interruption of this type of process, in order to eiect periodic regeneration of the catalyst employed, and for certain other reasons, the pressures employed in these catalytic processes are for the most part extremely low, rarely if ever exceeding 50 pounds per square inch in the catalyst contact zone. For this reason it is somewhat dicult to combine gas recirculation with such catalytic cracking operations in an eiilcient and eiective manner.

Moreover, these types of processes in general tend to produce rather high yields of normally gaseous hydrocarbons, as is true of low-pressure operations generally, and they are for the most part lacking in ultimate economyI and advantages witli respect to the cracking or re-forming of naphthas and similar light stocks. AThat is especially true in instances where the lead susceptibility of the cracked gasoline product is low, as is usually the case. Moreover, there is considerable difliculty in applying a catalytic process of this character to the conversion of heavy residual stocks, which on account of their carbon-forming tendencies 'tend to interfere with the effectiveness of the catalyst employed.

In accordance with my invention, however, it is possible to secure the maximum advantages andeconomies of both types of processes described hereinabove, together with advantages and economies which could not be obtained with respect to either type of operation considered alone.

Myinvention contemplates the separation, by distillation, of a crude petroleum into a plurality of fractions of ldifferent boiling-point ranges, including a naphtha fraction suitable for reforming to high anti-knock gasoline motor fuel, and at least one heavier fraction. The naphtha thus recovered is re-formedin a gas-reversion type operation @preferably of the Ostergaard type) in which the naphtha is 'subjected to thermal conversion in the presence of recirculated normally gaseous hydrocarbons containing 3 to 4 carbon atoms per molecule, a considerable portion of which are produced in the re-.forming operation itself. A heavier fraction recovered from the distillation of the original crude is subjected to separate catalytic cracking, ordinarily at low pressures, and normally gaseous hydrocarbons containing 3 tov 4 carbon atoms permolecule produced in this operation are deversion units.

livered to the naphtha re-forming operation referred to hereinabove.

As will be shown hereinbelow, the heavy fraction thus subjected to catalytic cracking may comprise a reduced or topped crude, or it may comprise a virgin gas-oil fraction. In the latter event, the residual reduced crude is, in accordance with some embodiments of my invention, subjected to cracking in the presence o recirculated C3 and C4 hydrocarbons in the manner generally similar to that employed with respect to the naphtha re-forming operation reierred to hereinabove. In one embodiment of my invention described hereinbelow,'such a reduced crude fraction is subjected' toA a viscosity-breaking or mild cracking operation conducted in the presence of Ca and C4 hydrocarbons and the vaporous products of conversion in this operation are returned to the crude distilling operation in such a, manner that the gas-oil produced j in this conversion-stage is commingled with the gas-oil derived directly from the crude, and subsequently delivered to the catalytic cracking zone.

The segregation of the C3 and C4 hydrocarbons produced in the several cracking operations may be variously accomplished but in the main is effected by subjecting the fractionated gasoline-free products of conversion to scrubbing with the naphtha fraction about to be deliveredinto the thermal conversion zone. In some instances gas-oil condensate may also be withdrawn at one or more points in the system, cooled, and employed as an absorbent for the recovery of C3 and C4 hydrocarbons from one or more of the cracking operations. When this is done, it is usually desirable to employ the thereby enriched gas-oil as a quenching and cooling medium in one or more of the thermal con- In order to lighten the load on the nal absorber and in order to provide additional iiexibility, a pressure condensation step may be provided ahead of the absorber in order` to recover a liquefied propane-butane fraction, which is then returned to one or more of the conversion zones in admixture with the oil traversing the same. These and yother modifications will be described more fully hereinbelow.

i My invention also contemplates such additlonal operating details and modifications, and such additional operative advantages and economies, as will hereinafter be found to obtain.

In order that my invention may be fully set forth and understood, I now describe, with reference to the drawings accompanying and formmg a part of this specification, a number of forms and manners in which my invention may be practiced and embodied. In these drawings Figuresl 1, 2, 3 and 4 are more or less diagramtemperatures in various portions of the unit and the like, the application of which will be obvious to those skilled in the art.

Similar reference numerals designate similar parts in the several views of the drawings,

In the embodiment illustrated in Fig. 1, a crude petroleum charging stock is introduced into the i system through pipe I by means of a pump 2 and is preheated in a suitable manner, as for example by means of a heated pipe coil 3 located within a furnace 4, to a suitable distilling temperature, usually a temperature at which no substantial cracking is effected. Such preheating temperatures will be of the order of 700 to 150 F. It will be understood that the preheating may be accomplished in various manners, as for example by heat exchange in other portions of the system to be described hereinbelow, and that the same considerations will apply to many instances in which heating and cooling operations are involved.

The preheated crude then passes through a line 5 having a valve 6 into a distilling column or flash tower 1 of more or less conventional design. This column is provided with suitable cooling or reuxlng means such as a coil 8, with suitable gasand-liquid-contact devices such as bell trays 9 and with one or more naphtha trap-out trays I0. By reason of the heat imparted to the crude oil and the low or atmospheric pressure maintained in the column 1, distillation takes place and a considerable portion of the crude oil is distilled. The light products, including any fixed gases which may be present and light virgin gasoline, are withdrawn from .the head of the column throughv a line l2 to a condenser I3 and a separator I4 from which the xed gases and the light virgin gasoline are removed through lines l5 and i6, respectively. Heavy virgin naphtha suitable for re-forming is withdrawn as a side stream from the trap-out trayy i0 and passes through a line l1 to a cooler l8. As will be understood by those skilled in the art, the cooler1 I8 and all other coolers and condensers subsequently shown are water-cooled devices of more or less conventional type, effective to reduce the temperature of the vapors or oil passing therethrough to approximately atmospheric temperature or a little above. However, it will be understood that more drastic cooling may be applied wherever necessary or desirable.

If desired, various cuts may be withdrawn as side streams from the tower 1 in addition to the naphtha cut withdrawn from the trap-out tray I0. Thus kerosene, gasoline and gas-oil cuts may be so withdrawn. In the instance shown, however, all ,of the crude oil constituents not vaporized and removed through the line l2 or removed as a side stream from the trap-out tray l0 are retained in the reduced or topped crude, which is eventually withdrawn from the bottom of the tower 1 through a line 20.,

The reduced crude fraction so withdrawn is then delivered by means of a pump 2l to suitable heating means, such as a still or pipe coil 22 located within a furnace 23, and in passing through the coil 22 is heated to a temperature suiiicient to promote conversion in the presence of the catalyst with which the oil or a portion thereof is subsequently to be brought into contact. In the instances shown, in which the cracking of this stock is effected in accordance with the sc-called Houdry process, the reduced crude ordinarily emerges from the pipe '22 at a temperature somewhere around 880 F. or at any rate at such temperature as will be sucient to effect vaporization of all but the very heaviest constituents thereof, and at this temperature passes through a valved line 24v into a vaporizer 25. Tar is withdrawn from the vaporizer 25 through a valved line 26 while the vapors pass through a valved manifold vapor line 21 into one of a plurality of catalyst cases 28. These catalyst cases are provided with inlet and outlet manifold connections as shown in such a manner that they may be alternated as desired, so that regeneration of the catalyst in one or more of the cases may be effected while the catalyst in another case is on stream.

While I do not wish to limit myself to any particular catalyst or any specic conditions of temperature and pressure, it may be stated that a suitable catalyst used in the Houdry'process comprises an activated hydrosilicate of alumina and that typical conditions of temperature and pressure at this point are from 800 to 900' F. and from atmospheric to 20 pounds per square inch gauge pressure. Various modifications of the Houdry process are, however, disclosed in an article entitled Catalytic processing by the Houdry process, found at l'page R-5'10 of the National Petroleum News for November 30, 1938, and in the patents listed in that article, while various other catalytic cracking processes are described in prior patents and in the literature,

Under the influence of the catalyst and the heat applied to the oil, conversion takes place resulting in the formation of gasoline and other useful hydrocarbons. The converted vapors leave the on-stream catalyst case 28 through a manifold line 29 and enter a fractionating column 30 which, as shown, may be of more or less conven. tional design and which is operated to condense and recover constituents having boiling points higher than those desired in the nal gasoline fraction. The gas-oil condensate thus obtained is removed from the bottom of the column 30 through a line 3l, while the gasoline and lighter vapors pass through a line 33 to a condenser 34,

and thence through a line 35 into a separator 35. Condensed gasolinev is withdrawn from the separator 36 through a valved line 31, while the gases and vapors remaining uncondensed pass through a line 38 into an absorber 39. A pump or compressor 40 may be provided in the line 38 for the purpose of maintaining elevated pressures, for example pressures of or 200 pounds per square inch gauge, in the absorber 39 wherever this proves desirable for the purpose of promoting efciency of absorption.

In the instance shown, I provide for the recovery of C3 and C4 hydrocarbons from the gases entering the absorber 39 through the introduction to the absorber of a portion of the naphtha recovered in the crude flash tower 1. The naphtha so recovered, after leaving the cooler I8, passes through a line 42 having a pump 43 and communicating with a valved branch line 134 leading into the top of the absorber 39. The gases from the catalytic operation, entering the absorber 39, flow countercurrent to a stream of cool naphtha thus introduced, and the conditions within the absorber are so regulated. in accordance with the amount and character -of the gases introduced as to effect an absorption of the C3 and C4 hydrocarbons, or any desired portion thereof, from the gases. The residual gases, comprising for the most part C3 and lighter hydrocarbons, leave the top of the absorber through a valved outlet line 45.

The enriched naphtha leaving the absorber 39 and containing C3 and C4 hydrocarbons removed by absorption in the absorber 39, then passes through a line 46 to a pump 41 which in turn delivers it through a line 48 into an elongated pipe coil 49 of restricted cross-sectional area condenser and rectifier '60.

the naphtha is subjected to thermal conversion at an elevated temperature in the presence' of the C3 and C4 hydrocarbons. Substantial conversion is obtained at various temperatures and pressures, ranging for example from about 950 to 1400c F. and from about 100 to 2000 pounds per square inch gauge pressure, but the best results are obtained when the operation is conducted in the manner set forth and claimed in U. S. Patent No. 2,135,014 to Povl Ostergaard. That is to say, the admixture of oil and normally gaseous hydrocarbons is subjected to a high cracking temperature substantially in excess of the maximum temperature to which the oil alone could be subjected in identical apparatus and under otherwise identical conditions of y conversion without such excessive deposition of carbon as to prevent continuous operation of the unit for extended periods of time, and ordinarily ranging from about 25 to 300 higher than the aforesaid maximum temperature.

During the passage of the oil and normally gaseous hydrocarbons through the coil 49 conversion takes place and the heated products are then discharged through a vapor-transfer line 52 having a pressure-reducing valve 53 into a tar separator 54. Under the influence of the pressure reduction and cooling, supplied as will hereinafter be shown, vapor separation takes place, tar being withdrawn from the bottom of the separator 54 through a valved line 55. The separated vapors are then passed through a line 56 into a fractionating column 51 which, as shown, may be of more or less conventional design.

In the fractionating column51, sulicient cooling is effected to cause the condensation of constituents heavier than are desired to be retained in the final gasoline condensate. These condensed constituents, which may be referred to as gas oil, are withdrawn from the bottom of the fractionating column 51 through a line 58. All or a portion of the gas oil thus withdrawn is then delivered by means of a pump 59 to a cooler 60 and thence in part through a valved quenching line 62 to the vapor-transfer line 52, and in part through a valved reflux line 63 into the tar separator 54.

The uncondensed vapors leaving the top of the column 51 pass through a line 65 into a gasoline paratus may be used at this point flor condensing and stabilizing the gasoline produced in the system, such, for example, as that shown and claimed in U. S. Patent No. 2,134,816 to Povl.

Ostergaard. In the instance shown, however, I have for simplicitys sake shown a conventional rectifying column provided with suitable plates or trays 61, cooling means 68 located in the head of the column and heating means 69 located in the foot of the column. The heat supplied to the heating coil 69 may be obtained from hot oil produced elsewhere in the system, as for example by causing all or a portion of the gas-oil condensate to traverse this coil. In any event, however, rectification takes place in the column 66 with the result that stabilized gasoline condensate is withdrawn from the bottom thereof through a valved line 1| while the remaining gases pass overhead through a line 12 leading to a condenser 13 and a separator or accumulator 14.

By virtue of the pressures maintained in this portion of the system, and which will ordinarily run from 100 to 300 pounds per square inch, a portion of the C3 and C4 constituents present in Various types of aIJ-` 'located within a heating furnace 50, and wherein the gases are caused to be condensed in the condenser 13 and collect in the accumulator 14 in.

liquefied form. Operation of the cooler 13 at temperatures somewhat below atmospheric may be resorted to in order to condense any desired portion of the Ca and C4 hydrocarbons at this point.

The condensate thereby obtained, comprising liquid butane and propane together with their unsaturated analogues, isremoved from the accumulator 14 through a line 15. 'I'he line 15 is in communication with the inlet to coil 49 through a branch line 16 having a pump 11 and a valve 18, and with the inlet to the pipe coil 22 of the catalytic cracking unit through a branch line 18 having a valve 80. This apparatus makes it possible to deliver any desired portion or all of the liquid condensate from the accumulator 14 either to the coil 49 or to the coil 22, or to distribute the liquid condensate to the two coils mentioned in any desired proportion.

The gas and vapors remaining uncondensed in the condenser 13 leave the accumulator 14 through a line 82 and enter the bottom of an absorber 83. That portion of the virgin naphtha removed in the tower 1 and not used in the absorber 39 is delivered to the upper portion o1' the absorber 83 through a valved line 84 and in passing downwardly through the absorber 83 effects a removal, by absorption, of C3 and C4 hydrocarbons'present in the'gas traversing the absorber. The gases remaining uncondensed, and comprising for the most part C3 and lighter hydrocarbons, are removed from the top of the absorber 83 through a valved exit line 85, while the enriched naphtha reaching the bottoml of the tower 83 is withdrawn through a line 86 having a pump 81 and communicating with the line 48. This enriched naphtha is delivered to the pipe coil 49 located within the furnace 50 and is there subjected to thermal conversion along with the enriched naphtha from the absorber 38.

The system illustrated in Fig. 2 is generally similar to that illustrated in Fig. 1 and described hereinabove with the exception that provision is made for effecting absorption of C3 and C4 hydrocarbons in the absorbers 39 and 83 in a different manner or manners. In some instances, it may be desirable to use all of the virgin naphtha removed from the ash tower 1 as the scrubbing medium in the absorber 83, or in the absorber 39, and in such instance it is, of course, necessary to provide a suitable `absorbent for use in whichever one of the two absorbers 39 and 83 is not Supplied with this naphtha. As shown in Fig. 2, gas oil condensate removed from the bottom of the fractionating column 51 is delivered after the cooling either to the absorber 39 or to the absorber 83.' After absorption, the enriched gas-oil is then returned to the thermal cracking unit at a point subsequent to the conversion zone. *Referring to Fig. 2 in greater detail, gas oil condensed in the fractionating column 51 is withdrawn therefrom through a line |00 and is delivered by means of a pump |0| and aline |02 to a cooler |03 and thence through a. line |04 which is in communication with branch lines |05 and |06, having valves |01 and |08 and leadj ing to the tops 'of the absorbers 83 and 39, respectively. Enriched oil from the bottom of the absorber 83 is removed therefrom by a line ||0 having a pump and may be delivered either through a valved branch line I2 into the line 48 and thence into the pipe coil 49, or through a valved branch line ||3 and a line ||4 into the valved conduits 62 and 63 and thence into the transfer line 52 and the tar separator 54 in any desired proportions. Similarly, enriched oil withdrawn from the absorber 39 is withdrawn therefrom through a line H having a pump H6 and this oil may be delivered either through a valved branch line H1 into the line 48 andthe pipe coil 49, or through a valved branch line ||8 and the lines H4, 62 and 63 into the transfer line 52 and the tar separator 54. y

In the preferred instance, all of the naphtha withdrawn from the trap-out tray |0 of the tower 1 passes through the lines 42 and 84 into the absorber 83 and after passing through the absorber 83 the thereby enriched oil is delivered through the lines H0, H2 and 48 to the pipe coil 49. Gas oil withdrawn from the fractionating column 51, or any desired portionthereof, is delivered through the lines |00, |02, |04 and |06 into the absorber 39 and the enriched oil after absorption of C3 and C4 hydrocarbons in the .absorber 39 is then returned through lines H5, H8, H4, 62 and 63 into the transferline 52 of the tar separator 54. The C3 and C4 hydrocarbons thus absorbed in the absorber 39 are not in this instance delivered directly to the pipe coil 49, but are eventually picked 'up in the absorber 83 in the naphtha used therein and then pass to the pipe coil 49. This system has the advantage that it increases the concentration of C: and Crhydrocarbons in the fractionating system of the thermal cracking unit and hence the eilciency of condensation and absorption of these constituents in that unit.

Alternatively, all of the naphtha removed from the crude ash tower 1 may be passed through the absorber 39, the enriched naphtha then passing through lines H5, ||1 and 48 to the pipe coil 49. In this instance, gas-oil withdrawn from the base ofthe fractionating column 51 is delivered through lines |00, |02, |04 and |05 into the ab sorber 83 and the enriched gas-oil is then returned through lines H0, H3, H4. 62 and 63 into the transfer line 53 (as a quenching medium) and the tar separator 54 (as a reuxing medium).

In the system illustrated in Fig. 3, provision is made for subjecting a light cut, such as virgin naphtha, and a heavy cut, such as reduced crude, to separate thermal conversion with gas recirculation, and for subjecting an intermediate or gas-oil fraction also recovered in the distillation of the crude to catalytic cracking. The gases in the catalytic cracking unit are combined with the gases' from the thermal cracking units for recirculation into the latter. made for delivering gas-oil condensate from the thermal cracking unit into the catalytic cracking unit for conversion.

Referring to Fig. 3 in greater detail, one or more trap-out trays |30 are provided lin the crude ash tower 1 at apoint located below the naphtha trap-out tray |0,.and more specifically at such a point as will enable the withdrawal therefrom of avirgin gas-oil-fraction. The gasoil fraction thus withdrawn is delivered through a pipe |3| andv a pump |32 to the pipe coil 22 of the catalytic conversion unit, and thnce directly through the valved manifold line 21 to one of the catalyst cases 28. A vaporizer, similar to the vaporizer shown in Fig. 2 may be provided, but will ordinarily be unnecessary .when cracking such a non-residual stock. Heavy reduced crude unvaporized in the flash tower 1 is withdrawn ltherethrough through a line |33 having a. pump |34 and is delivered to a pipe coil |35 located Provision is also y within a heating furnace |36. Before being passed through the coil |35, however, this reduced crude is joined by propane-lbutane condensaterecovered in the separator 14, vand which in this instance. is withdrawn from the separator 14 through a valved line |40 and delivered by means of a pump |4| and a line |42 into the line The temperatures and pressures employed in the coil |35 will, of course, be lower than those employed in the coil 49, which in this instance receives enriched naphtha from the absorber 83. Typical operating temperatures and pressures will run from 850 to 1000 F. and from 100 to 2000 pounds per square inch. In any event, how-v ever, the best results are secured, as in the coil 49, by operating in the manner disclosed and claimed in U. S. Patent No.A 2,135,014 to Povl Ostergaard and as referred to hereinabove, keeping in mind the character of each individualv charging stock.

The hot products of conversion leaving the coil |35 are discharged through a, transfer line |31 into the transfer line 52, where they mingle with the products of conversion of thecoil 49 and then pass into the tar separator 54 and subsequent' Gases remaining uncon-A fractionating units. densed in the accumulator 14 are delivered to the absorber 83 Where they are scrubbed with virgin naphtha recovered in the crude flash tower 1. The enriched naphtha, containing C3 and C4 constituents recovered from the gases in the absorber .83, is'then delivered through the line 86, the pump 81 and the line 48 into the pipe coil 49. In the instance shown, the gases remaining uncondensed in the separator 36 of the catalytic cracking unitare passed through a line |43 to a pump or compressor |44 where/they are raised to a pressure equal to that obtaining in absorber 83 and then pass through a line |45 into the bottom of the absorber 83. Gas-cil condensate recovered in the fractionating column 51 is withdrawn therefrom through a line and passes through a pump |5| to a cooler |52. One portion of this cooled gas oil may be delivered through a valved Vline |53 into the tar separator 54, another portion through a valved quenching line |54 into the transfer line 52, and a third portion through a valved quenching line |55 into the transfer line |31, while any remaining gas-oil from this source may be delivered through a valved line |56 into the line |3| where it joins virgin gas-oil withdrawn from the tower 1 and enters the pipe coil 22 of the catalytic conversion unit.

In the apparatus just described in connection with Fig. 3, the fractionated products leaving the heavy oil conversion coil |35 are combined with and fractionated with the products leaving the re-forming coil 49. In the system illustrated in Fig. 4, however, the cracking or viscosity breaking of the heavy oil is accomplished in conjunction With the crude flash tower, and the products from the heavy-#oil conversion or viscositybreaking coil are fractionated in the crude ash tower along with the crude undergoing fractionation.

Referring to Fig. 4 in greater detail, a reduced crude fraction is withdrawn from the tower 1, which in this instance serves as a fractionating tower for the combined products of crude distillation and viscosity-breaking, by means ota trap-out tray 200 located at a point below the point of entry of the preheated crude. This reduced crude fractionis deliveredlby. I neans of j a line20| and a pump 202 to a pipe coil 203 loy cated within a furnace 204. Butane-containing condensate recovered in the accumulator 14 of the thermal re-forming unit is in this instance withdrawn by a line 205 and delivered by means of.a pump 206 and a line 201 to the line thereby causing this liqueed gas fraction to be commingled with the reduced crude withdrawn from the trap-out tray 200 before the latter passes to the conversion coil 203. The conversion operation conducted in the coil 203 isessentially similar to that described hereinabove in connection with the operation of the coil of the system shown in Fig.` 3. In this instance, however, the products leaving the coil 203 pass through a transfer line 2I0 having a pressurereducing valve 2| I into the lower part of the flash tower 1.. Residue or tar separating in the bottom of the ash tower 1 is withdrawn by a line 2I2, while the flashed vapors pass upward through the tower 1 and are fractionated therein.

It will be obvious that in this system the fraction withdrawn from the'trap-out tray |30 of the tower 1 comprises both virgin gas-oil constituents and gas-oil constituents produced by the mild cracking effect in the coil 203. This fraction passes through the line |3I into the pipe coil 22 of the catalytic conversion unit, as in the system illustrated in Fig. 3.

As in that system, virgin naphtha recovered from the flash tower 1 is delivered by means of the line I1, the pump 43 and the line 42 into the absorber 83 of the thermal cracking unit, and the enriched naphtha leaving the bottom of the absorber 83 is delivered through the lines 86 and into the re-forming coil 49.

In this system, inasmuch as normally gaseous hydrocarbons are delivered to the viscositybreaking or mild cracking operation conducted in the coil 203, considerable quantities of Cs and C4 hydrocarbons are present in the overhead products from the tower 1. I have illustrated in Fig. 4 means whereby these may be recovered. As shown, gases leaving the separator I4 through the line I5 arepicked up by a pump or compressor 2|9, where they are raised to a pressure equal to that obtaining in absorber 83, and the compressed gases are then delivered into the bottom of the absorber 83 through a line 220 provided for that purpose.

I have also illustrated in Fig. 4 a procedure absorber 83 sometimes contain substantial quantities of C3 and higher boiling constituents which it may be desired torecover for use and ultimate conversion in the system. To that end, the gases leaving the top of the absorber 83 are delivered through a line 22| to a second absorber 222. Gas oil recovered in the fractionating column 51, or any desired portion thereof, is withdrawn therefrom through a valved line 223, wherein are located'a pump 224 and a cooler 225, and passes to the upper part of the absorber 222. In passing down through the absorber 222, the gas oil thus introduced absorbs Ca and C4 hydrocarbons as well as any heavier constituents which may be contained in the gases entering the absorber. The enriched gas oil leaving the bottom of the absorber 222 is delivered through a line 230 having a pump 23| into the lines 62 and 63 leading -t0 the transfer line 52 and the tar separator 54, respectively. In this case, as in al1 other instances in which oil is delivered to one of the transfer lines leading from one of the conversion zones, the purpose in thus introducing oil is to arrest and control the reactions initiated in the respective conversion zone.

Gases remaining uncondensed in the absorber 222 are removed through a valved exit line 232 s and pass out of the system,

With reference to all of the systems shown in Figs. 1 to 4 hereinabove, any gas-oil constituents recovered in the fractionating column 30 of the catalytic conversion unit may be recycled to the catalytic conversion unit or cracked in a separate coil, with or without a catalyst, and the products of cracking may be fractionated along with other products of conversion, in a marmer which will be evident to any one skilled in the art from the foregoing. However, for purposes of simplicity, I have omitted the details of such operation from the drawings.

Moreover, the various gasolines recovered in the systems illustrated and described hereinabove, for example at I6, 31 and 1|, may be combined and blended in any desired proportions to produce the final motor-fuel product, or they may be used separately. Moreover, these gasolines may be blended with additional agents for use, as forv example, with the usua1 anti-knock agents, such as tetraethyl lead and the like.

In this case it may be noted that in general the lead susceptibility of catalytically cracked gasolines does not usually compare with the lead susceptibility of thermally cracked gasolines such as those produced in the thermal cracking zones of the systems illustrated. hereinabove. This fact constitutes one of the reasons why, as I have stated, the re-forming of straight run gasoline is best carried out in a thermal conversion zone of the. type indicated hereinabove rather than in a catalytic cracking zone.. 4For this reason, the overall anti-knock value and lead susceptibility of the products obtained in accordance with my invention represent a distinct improvement over prior art processes.

In referring to catalytic cracking processes I 'have in mind in general those processes, usually carried out at pressures of less than pounds per square inch at elevated temperatures ranging from 700 to 1100o F., wherein a catalyst of some sort or another is employed to promote conversion reactions tending to form gasoline-like hydrocarbons. I have referred principally here.. inabove to the Houdry process, but it will be understood that other types of catalytic processes and other catalysts may be employed in those instances where catalytic cracking-is indicated. Such catalytic cracking processesA are numerous and well known in the art and need not be catalogued here in full. However, by way of exemplication, it may be stated that among the catalysts which have been proposed for use in processes of this character and Which to the extent that they are individually useful and advantageous may be employed in the catalytic cracking zones of the processes described hereinabove, are the following: nickel and compounds thereof, such as nickeloxide; chromium and compounds thereof, such as chromlc oxide; compounds of nickel and chromium, such as nickel chromate; phosphorus compounds, especially metaphosphates, including those of chromium and uranium; aluminas; adsorbent clays; floridin; bauxite; molybdenum sulde; and a wide variety of other compounds, particularlycompounds of metals and alkaline earth metals.

others alkylation'reactions, but for the purposesof the present invention, all of these may be j considered to come under the general category of catalytic cracking catalysts. Most of these catalysts are preferably employed at low pressures, with regeneration at periodic intervals, but my invention, in so far as it deals withl catalytic cracking, is not so limited.

In referring to normally gaseous hydrocarbons .having 3 to 4 carbon atoms permolecule, I mean propane, propylene, butanes and butylenes, all of which are normally gaseous in a'pure state under atmospheric pressure and temperature conditions. It will be understood, however, that these constituents may or may not exist in gaseous form at different points in the systems illustrated. and consequently the expression referred to is not intended to imply that these constituents are actually present as gases, for at many points they will exist in the liquid form, by virtue of the pressures employed or because of the presence of liquid oils in which they are absorbed, or both.

While I have described and illustrated my invention hereinabove with respect to numerous operating examples and specific operating details, it is not my intention to limit my invention in its broadest aspect to such details or exemplications. My invention may 4be variously practiced and embodied Within the scope of the claims hereinafter made.

What I claim is: y

l. The process of producing gasoline motor fuel of high anti-knock value from a crude petroleum, which comprises: fractionally distilling a, crude petroleum to recover a naphtha fraction and a higher-boiling fraction; subjecting said higher-boiling fraction to conversion at a relatively low pressure in the presence of a catalyst effective to promote pyrolysis reactions,. and fractionating the resultant products of conversion to recover gasoline and heavier constituents, including a gas-oil fraction, therefrom; subjecting said naphtha fraction to thermal conversion at a high cracking temperature and under a relatively high super-atmospheric pressure. effective to cause the formation of gasoline-like products having an increased anti-knock value, and separately fractionating the `resultant products of conversion to recover gasoline and heavier constituents, including a gas-oil fraction, therefrom; recovering normally gaseous hydrocarbons having 3 to 4 carbon atoms per molecule from the thereby fraction- `ated products of conversion of one of the conversion operations referred toabove by absorption in said naphtha fraction, prior to conversion thereof as aforesaid; delivering the thereby enriched naphtha fraction containing gaseous hydrocarbons to the thermal conversion operation for conversion as aforesaid; recovering normally gaseous hydrocarbons having 3 to 4 carbon atoms per molecule from the products of conversion of the other operation referred to above, by absorption in a gas-oil fraction recovered as aforesaid; and delivering the thereby enriched gas-oil constituents to the hot products of conversion in the thermal conversion operation, as a cooling medium.

2. The process of producing gasoline motor.

troleum, which comprises: fractionally distilling a crude petroleum to recover a naphtha fraction and a higher-boiling fraction; subjecting said higher-boiling fraction to conversion at -a relatively low pressure in the presence of a catalyst effective to promote pyrolysis reactions, and fractionating the resultant products of conversion to recover gasoline and heav1er constituents therefrom; subjecting said naphtha fraction to'thermal conversion at a high cracking temperature and under a relatively high superatmospheric pressure, effective to cause th'e formation of gasoline-like products having an increased anti-knock value, and separatelyfractonating tite resultant products of conversion to 'recover gasoline and heavier constituents, including a gas-oil fraction, therefrom; recovering normally gaseous hydrocarbons having 3 to 4 carbon atoms per molecule from the thereby fractionated products of conversion of the thermal conversion operation referred to above by absorption in said naphtha fraction before conversion thereof as aforesaid; 'delivering the thereby enriched naphtha containing said normally gaseous hydrocarbons to the thermal conversion operation for conversion as aforesaid; recovering normally gaseous hydrocarbons from the fractionated products of conversion in the catalytic cracking operation by absorption in said, gas-oil fraction; and delivering the thereby enriched gas-oil fraction to the hot products of conversion in the thermal cracking operation, as a cooling medium.

3. The process of producing gasoline motor fuel of high anti-knock value from a crude petroleum, which comprises: fractionally distilling a. crude petroleum to recover a naphtha fraction and a higher-boiling fraction; subjecting said higher-boiling fraction to conversion at a relalively low pressure in the presence of a catalyst effective to promote pyrolysis reactions, and fractionating the resultant products of conversion to recover gasoline and heavier constituents, including a gas-oil fraction, therefrom; subjecting ,said `naphtha fraction to thermal conversion at a high cracking temperature and under a relatively high super-at-j mospheric pressure, effective to cause the formation of gasoline-like products having an increased anti-knock value` anzl separately fractionating the resultant products of conversion to recover gasoline and heaver constituents, including a gas-oil fraction, therefrom; recovering normally gaseous hydrocarbons having 3 to 4 carbon atoms per molecule from the thereby fractionated products of conversion of the catalytic conversion operation by absorption in said naphtha fraction prior to conversion thereof; deliverngthe thereby enriched naphtha fraction containing said normally gaseous hydrocarbons to the thermal conversion operation for conversion as aforesaid; recovering normally gaseous hydrocarbons having 3 to 4 carbon atoms per molecule from the fractionated products of conversion in the thermal cracking operation l"by absorption in a gas-oil fraction produced as aforesaid; and recycling the thereby enriched gas-oil fraction' into the thermal conversion operation.

4. The process of producing gasoline motor fuel of highganti-knock value from a crude petroleum which comprises fractionally distilling a crude petroleum to recover a naphtha fraction, a gas-oil fraction and a residual fraction; subjecting said residual fraction to thermal constituents therefrom;

version at a mild cracking temperature and under superatmospheric pressure; separating tarry constituents from the products of conversion therebyobtained and commingling the separated hot products of conversion thereby obtained with the crude petroleum undergoing fractionation; subjecting said gas-oil fraction to conversion at a relatively low pressure in the presence of a catalyst capable of promoting pyrolysis reactions, and separately fractionating the resultant products of conversion to obtain gasoline and heavier constituents therefrom; subjecting said naphtha fraction to thermal conversion at a high cracking temperature and under a relatively high superatmospheric pressure, effective to cause the formation of gasoline-like products having an increased antiknock value, and fractionating the resultant products of conversion to. recover gasoline andheavier constituents therefrom; recovering normally gaseous hydrocarbons having 3 to 4 carbon atoms per molecule from the gaseous products leaving the crude fractionating operation, the catalytic conversion operation and the naphtha re-forming operationreferred to above; and subjecting said normally gaseous hydrocarbons to conversion in admixture: with the residual fraction and the naphtha fraction subjected to conversion as aforesaid, respectively.

5. 'I'he process of producing gasoline motor fuel of high anti-knock value from a crude petroleum which comprises fractionally dis'tillinga crude petroleum to recover a naphtha fraction, a gasoil fraction and a residual fraction; subjecting said residual fraction to thermalconversion at a mild cracking temperature and under superatmospheric pressure; separating tarry constituents from the products of conversion thereby obtained and commingling the separated hot products of conversion thereby obtained with the crude petroleum undergoing fractionation; subjecting said gas-oil fraction to conversion at a relatively lcw pressure in the presence of a catalyst capable of promoting pyrolysis reactions, and separately fractionating the resultant products of conversion to obtain gasoline and heavier consubjectjng said naphtha fraction to thermal conversion` at a high cracking temperature and under a relatively high superatmospheric pressure, effective to cause the formation -of gasoline-like products having an increased anti-knock value, andl fractionating the resultant products of conversion to recover gasoline and heavier constituents therefrom; recovering normally gaseous hydrocarbons having 3 to 4 carbon atoms per molecule from the fractionated gasoline-free products of the naphtha re-forming operation referred to above; subjecting said normally gaseous hydrocarbons to con- Version in admixture with said residual fraction subjected to conversion as aforesaid; combining the remaining gaseous products from the naphtha re-forming operation with the fractionated gaseous products 'from the catalytic cracking operation; scrubbing the thus combined products' gas-oil is'4 recovered by fractionation of the products of conversion of the naphtha re-forming operation, the combined gaseous products after being scrubbed with said naphtha fraction as set forth in claim 18 are scrubbed with said gas-oil fraction, and the thereby enriched gas-oil fraction is introduced into the hot .products of conversion leaving the naphtha conversion zone, as a cooling medium.

'7. The process ,of producingl gasoline motor fuel cf high anti-knock value from a crude re,- troleum which comprises fractionally distilling a crude petroleum to recover a virgin naphtha fraction, Virgin gas-oil constituents and a residual fraction; subjecting said residual fractie.A to thermal conversion at a mild cracking temperature and under superatmospheric pressure; separating tar constituents from the products of conversion thereby obtained and fractionating the products of conversion to recover cracked gas-oil constituents; subjecting virgin and cracked gas-oil constituents recovered as aforesaid to conversion at a relatively low pressure in the presence of a catalyst capable of promoting pyrolysis reactions, and separately fractionating the resultant products of conversion to recover gasoline andheavier constituents therefrom; subjecting said naphtha fraction to thermal conversion at a high cracking temperature and under a relatively high superatmospheric pressure, effective to cause the formation of gasoline-like products having an increased anti-knock value, and fractionating the resultant products of conversion to recover gasoline and heavier constituents therefrom; recovering normally gaseous hydr'ocarbons having 3 to 4 carbon atoms per molecule from the gaseous products leaving the several cracking operationsreferred to above; and subjecting portions of said normally gaseous hydrocarbons to conversion in admixture with the residual fraction and the naphtha fraction subjected to conversion as aforesaid, respectively.

HORACE B. COOKE.

OERTEEICATE OE CORRECTION. Patent No. 2,558,1LL9. september 12, 19ML.

HORACE B. COOKE,

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 8, sec- 0nd Column, line 20, claim 6, for the Claim reference numeral "18" read -5; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the Oase in the Patent Office. C I

Signed. and sealed this llth day of November, A. D. 19ML.

Leslie Fraz-er (Seal) Acting; Commissioner of Patents.

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