US2356744A - Combination catalytic and thermal cracking - Google Patents

Description

Aug. 29, 1944. J. M. BARRON COMBINATION CATALYTIC AND^'`HERMAL CRCKING Filed July 2, 1943 P-atente'd 1944 COMBINTION CATALYTIC THERMAL CRACKING Joseph Mason Barron, Port Arthur, Tex., asslgnor to The Tasas Company, New York, N. corporatiomof Delaware Application July 2, 194s, sensi 10.493.206

(ci. 19e-49) i claims.

This invention relates to a combination catalytic and thermal method of cracking hydrocarbons for the production of gasoline or motor fuel.

The invention contemplates a process in which hydrocarbons are subjected to thermal cracking in a reaction zone in which liquid and vapors are in countercurrent contact at cracking temperature and in which the separated vapors from the thermal reaction zone are subjected to catalytic cracking. In accordance with the invention relatively light hydrocarbons undergoing cracking are introduced to the lower portion of a thermal reaction zone and a higher boiling hydrocarbon oil is introduced into an upper portion of the re,

action zone to flow countercurrently to the upwardly rising vapors therein and the separated vapors are passed directly to a catalytic cracking l step. The refluxing to which the vapors are sub-A jected while undergoing cracking in the countercurrent cracking zone functions to prevent the delivery to the subsequent catalytic cracking zone of certain heavy potential carbon-forming polymers with the result that the vapors from the countercurrent cracking zone may be subjected directly to catalytic cracking without injurious deposition of carbon o n the catalyst. It is not necessary to subject the vapors from the reaction zone to any intervening dephlegmation in order that the vapors may be in a suitable condition for catalytic cracking. By carrying on a thermal cracking step in which the vapors undergoing cracking are dephlegmated with the higher boiling stock, the carbon residue of the vapor steam may be kept suiiiciently low that the vapors may be contacted .directly with the catalyst and subjected to catalytic cracking.

In accordance with the invention relatively low boiling hydrocarbons, such as naphtha and normally gaseous hydrocarbons, are passed through a heating zone and subjected to thermal conversion, while relatively higher boiling condensate stocks, such as kerosene and gas oil, are passed through a second heating zone and subjected to thermal conversion and the heated eluent from these heating zones is distributed between the countercurrent thermal cracking zone and the catalytic cracking zone. Thus, in accordance with the invention, the heated eilluent from the heating zones may bre-combined and a portion of the combined eiiluent introducedcto the lower portion of the countercurrent cracking zone and the other portion combined with the vapor stream issuing from the countercurrent reaction zone for delivery to the catalytic cracking zone. In an alternative method contemplated by the invention and heat-insulated to the heated eiiiuent from one of the heating zones is introduced to the lower portion of the countercurrent cracking zone, while heated eiiluent from the other heating zone is combined with the vapors issuing from the countercurrent cracking zone for delivery to the catalytic cracking zone. In this way the temperature of the vapor stream passing from the countercurrent thermal reaction zone to the catalytic cracking zone is modied and vapors are delivered to the catalytic cracking zone at the exact temperature desired.

- The invention will be more clearly understood, from the following description and from .the accompanying drawing or flow diagram which il-- lustrates diagrammatically` a preferred embodiment of the apparatus or system adapted for carrying out my improved combination cracking process.

Crude petroleum, or topped crude, is introduced by a pump I0 to a heating coil I"I disposed in a furnace I2 wherein the oil is heated suiciently to flash oil the fractions desired. 'I'he heated oil is passed to a. fractionator or a ash tower I3 wherein vapors separate from residue and wherein the vapors are fractionated to obtain a,l plurality of fractions, such as a higher boiling condensate collected in a tray I4, an intermediate condensate collected in a tray I5, and a lighter vapor frac-l tion which is passed to a condenser coil I6. In case the crude oil contains light gasoline-constituents it is preferable to'rst distill oifthe light gasoline, as by means of heat exchange with hot products of the system, and to charge the skimmed or topped crude to the heating coil II and take oil a heavy naphtha fraction as the overhead fraction.

Gas oil is withdrawn from tray I4 and directed by a pump I1 to a heating coil I8 disposed in furnace I9 wherein the oil is heated to a cracking temperature and subjected to thermal crack g. The heated eiiiuent from the cracking coll;n I 8 passes through a transfer line 20 which extends to the lower portion of a thermal reaction /chamber 2 I. A heavy naphtha fraction is withdrawn from tray I5 and directed by a pump 22 to-a heating coil 23 disposed in a furnace 24 wherein the gasolinev constituents are subjected to cracking temperatures adequate to eiect thermal reforming into constituents of increased anti-knock quality. AThe products .of the reforming -pass through a transfer vline 25 which is connected to the transfer line 20.

The reaction chamber 2l 'is vertically disposed maintain thermal cracking temperatures therein. The transfer line 20 ex- '30 disposed in a .either subjected to mere preheating or 1s subtends within the lower portion of the reaction chamber and terminates in an enlarged pipe or section 26 through which the heated products arel discharged in an upward direction against a baille 21. In practice with a three-inch transfer line the element 26 may be composed of a six-inch pipe The products passing from either or bothI of the cracking coils 23 and I8 will consist largely of vapors and gases and, upon being discharged through the enlarged pipe 26 against the barile 21, an efcient diffusion of the vapors and gases is accomplished.

Residue from the flash tower I3 is directed by a pump 28 through a line 23 to a heating coil furnace 3| wherein the oil is jected to temperatures suicient for cracking or visbreaking. The heated residue passes through a transfer line 32 to the upper portion of the thermal reaction chamber 2|. A by-pass line 33 is provided so that any portion or all of the crude residue may be passed directly to the reaction chamber 2I. The line 32 extends Within the reaction chamber and terminates in a distributor or spray nozzle 34. The spray 34 is arranged to spray the liquid oil in a downward direction through the chamber so as to bring the liquid into intimate contact with the rising vapors. It is desired to have an unobstructed space between the distributor 21 and the spray nozzle 34 free from bailies or other contact elements upon which coke might deposit. Thusthe l,

crude residue, either with or without a preceding visbreaking in the heating coil 30, is subjected to thermal cracking in countercurrent with the rising vapors in the reaction chamber.

The separated vapors from the thermal reaction chamber 2| pass through a vapor line 35 to a catalytic cracking zone 36 and hot products are introduced through a line 31 into the vapor stream flowing to the catalytic reaction zone. The line 31 is provided with a branch line 38 communicating with the transfer line 20 prior to the juncture of the latter with the transfer line 25; the line 31 is also provided with a branch line 39 communicating directly with the transfer line 25 and with a branch line 40 communicating with the transfer line 20 beyond the point of juncture with the line 25. These connections provide for the following methods of operation: the delivery of all from the heating coil I8 through line 31 to the catalytic cracking zone 36, the delivery of al1 or a portion of the effluent from reforming coil 23 through the line 31 to the catalytic cracking zone, and the ,delivery of any desired portion of the mixed eiiluent from these heating coils through the line 31 to the catalytic cracking zone, with the delivery in each case of the remainingfeiiluent to the lower portion of the thermal reaction chamber 2 I. The counterflow method of' cracking in the reaction chamber 2| enables the maintenance of relatively high cracking temperatures therein, such as temperatures in excess of 900 F., without coking and, consequently, facilitates the delivery of'a vapor stream from the thermal reaction chamber to the catalytic cracking zone at temperatures approximating `those suitable for catalytic cracking. By directing heated products from either or both of the heating coils 23 and I8 into the vapor stream flowing to the catalytic cracking zone the vapor stream is raised to the exact temperature desired for the catalytic cracking. In contact with the catalyst, conversion into lower boilor a portion of the effluent` the Super-Filtrols and acid-treated and metalsubstituted natural or artificial zeolites, such as the artificial zeolite known as Doucil may be employed. yVarious metals such as uranium, molybdenum, manganese, lead, zinc, zirconium, nickel and the like, may be substituted in the clays or zeolites.v Likewise, Athe combination of certain acid-treated active clays of the character of Filtrol, together with added proportions of alumina or silica or both may be employed. Alumina alone may be used under certain conditions. -The synthetic alumina catalysts can be improved by the addition of other constituents such as zirconium oxide or molybdenum oxide. The catalyst may be provided as a stationary bed through which the vapors pass, or the vapors may pass over a continuously moving mass of granular catalyst, or the catalyst in a finely divided, comminutedor powdered form may be suspended in the vapors being introduced into the reaction chamber, or suspended in a gaseous medium whereby the catalyst is carried along with the vapors through the reaction zone. In the fixed bed method of catalytic cracking a. plurality of catalyst the catalyst may be regenerated without interrupting the continuity of the complete process, and in the case of the moving catalyst, the catalyst may be removed from the contacting reaction zone to a regenerating zone.

The products of the catalytic cracking are directed through a line The frationator 42 is formed with a separating or evaporating section 43 into which the catalytically cracked products are discharged and a fractionating section 44 with an intervening condensate tray 45. Reflux condensate collecting in the tray 45 is withdrawn by a pump 46 and directed through a heating coil 41 disposed in a furnace 48 wherein the oil is heated to a cracking temperature and subjected to thermal cracking. The eiliuent from charged into the evaporating section 43 for fractionation together with the effluent from the cata.- lytic cracking operation. Residue is withdrawn through a line 49. Uncondensed vapors pass from the fractionating section 44 to a condenser 5|) and the gasoline or naphtha distillate is co1- lected in an accumulator or gas separator 5|.

Residue from the thermal cracking chamber 2| is withdrawn through a line 52 to a coking drum 53. The residue is withdrawn rapidly from the reaction chamber so as to prevent the accumulation of liquid residue therein. By reason of the countercurrent method of operation in the reaction chamber, temperatures in excess of 900 F.`may be maintained therein without coking and by merely flashing the withdrawn residue in the coking drum, a conversion to a coke residue may be accomplished therein solely by means of the contained heat of the withdrawn residue. In practice a plurality of coking drums are employed so as not, to interrupt the continuous operation of the complete process for the purpose of coke removal. The vapors from the coking drum pass to a fractionator 54, being subjected tov a primary dephlegmation in a primary chambers may be used so that 4| to a fractionator 42.

the cracking coil is dis-A `tated silica and alumina. catalytic cracking-are fractionated and the catal 56. Primary dephlegmate or polymer fuel oil` is withdrawn through a line 51. Redux condensate from fractionating zone 56 is withdrawn through a line 58. This condensate is normally conducted by a pump 59 through a line 60 and combined with the straight-run gas oil being charged to the heating coil I8. The overhead vapors from the fractionator 54 pass to a condenser'll, thence to a distillate receiver .or gas separating drum 52. This distillate may be withdrawn from the system or refluxed in the fractionator 44; preferably, however, it is combined with the condensate being directed to the heating coil i8 by the pump 59.

In a modification of the invention the heated products from the cracking coild'l may be directed to the lower portion of the countercurrent reaction chamber 2|, although generally it is preferable to discharge the heated products to the separating zone 43 or to fractionate the heated products separately.

In an example of the invention straight-run naphtha is passed through a heating coil and subjected to thermal reforming at a temperature of 1050-l100 F. Sraight-run gas oil is 'subjected to thermal cracking by passage through a heating coil with a temperature of l020 F. in the coil outlet. Topped crude, at a temperature of 760 F., is introduced to the upper part of the thermal countercurrent reaction chamber.. The entire product from the reforming coil and a' portion of the effluent from the gas oil cracking coil are delivered to the bottom of the countercurrent reaction chamber which is maintained under a pressure -of 400 p. s. i. and with a temperature approximating 930-o F. in the lower part of the chamber. Residue is withdrawn from the bottom of thechamber and flashed to coke by means of its contained heat. Vapors are withdrawn from the top of the countercurrent cracking chamber` at a temperature of 910 F. and the other portion of the eiliuent from the gas oil cracking coil is combined with the withdrawn vapors to raise the temperature of the vapor stream which .is subjected to catalytic cracking at a temperature of 960 F. under a pressure of '75 p. s. i. in contact with a synthetic composite comprising precipi- The products of the lytic gas oil is subjected to recycling thermal cracking in the heating coil at 980 F. under 600 p. s. i.

In a second example the process is conducted as in the preceding example except that gas oil obtained in fractionatin'g the vapors from the coking operation is added to the straight-run gas oil for passage through the gas oil cracking coil.

In a third example straight-run naphtha is subjected to thermal reforming at a temperature in the outlet of the coil of 1000 F. and introduced to the lower part of the thermal reaction chamber while topped crude. at a temperature of 760 F., is introduced to the upper part of the thermal reaction chamber, which is maintained under a pressure of 400 p. s. i. and `with a temperature in the lower part of about 930 F The residue is withdrawn and ashed to coke by means of its contained heat. Straight-run gas oil is passed through a heating coil and rapidly raised to a temperature of 975 F., with the time of subjection to the high cracking temperatures being so limited that thermal cracking is reduced to a minimum. The entire product from the heating coil is combined with the vapors passing from the top of the thermal reaction chamber and the commingled stream is subjected to catalytic cracking in contact with a synthetic silica- -alumina catalyst at a temperature of 880 F. In

this operation the straight-run gas oil, without substantial thermal cracking, is subjected to catalytic cracking while the thermally reformed naphtha is subjected toa catalytic reforming or ni'shing operation serving to further-increase uct and, in such case, it is sometimes advan-v tageous to 'obtain from the rectification a normally gaseous fraction consisting essentially of C3 and C4 hydrocarbons, and to combine this fraction with the straight-run naphtha for naphtha reversion in the coil 23 or to combine the fraction for reversion with the gas oil undergoing cracking in the heating coil I8. In lieu of subjecting the normally gaseous fraction to conversion with naphtha or gas oil it may be subjected to a polymerizing action in a separate conversion coil which may discharge into the transfer line 20 for introduction to the thermal reaction chamber.

Although a preferredembcdiment of the invention has been described herein, it will be understood that various changes and mcdications may be made therein, while securing'to a greater or less extent some or all of the benets of the invention, without departing from the spirit and scope thereof.

I claim:

1. In the combination thermal and catalytic cracking of hydrocarbon oils the process that comprises passing hydrocarbon oil through a heating zone wherein it is heated to a cracking temperature and subjected to thermal cracking. introducing a portion of the resultant heated products into'the lower portion of -a vertically disposed reaction chamber, introducing a higher boiling hydrocarbon oil to the upper portion of the vertically disposed reaction chamber to flow countercurrently to the upwardly rising vapors therein. maintaining a cracking temperature in said reaction chamber and separating vapors from residue therein, passing the separated vapors to a catalytic cracking zone wherein the vapors are contacted with a catalyst and subjected to catalytic cracking; and combining the other portion of the heated products from said heating zone with the vapors passing to the catalytic cracking zone to control the temperature therein.

2. In the combination thermal and catalytic temperature in said reaction chamber to letlect` thermal cracking. passing the separated vapors to a catalytic cracking zone wherein the vapors are contacted with a catalyst and subjected to catalytic cracking, passing a lower boiling hy. drocarbon through a heating zone wherein it is subjected to thermalconversion, passing a higher .boiling stock through a second heating 'zone lizing the effluent from one of said heating zones to constitute the said heated products introduced to the lower portion of the vertically disposed reaction chamber, and combining the eilluent from the other of said heating zones with said vapors passing to the catalytic cracking zone.

'3. In the combination ythermal and catalytic cracking of hydrocarbon oils the process that comprises introducing heated vapors to the lower portion of a vertically disposed reaction chamber wherein separation of vapors from liquid residue takes place, introducing a residual oil to the upper portion of the vertically disposed4 reaction chamber to ow countercurrently to the upwardly rising vapors therein, maintaining a cracking temperature in said reaction chamber to veffect thermal cracking, passing the separated vapors to a catalytic cracking zone wherein the vapors are contacted with a catalyst and subjected to catalytic cracking, passing a lower boiling hydrocarbon through a heating zone wherein it is subjected to thermal conversion, passing a higher boiling stock through a second heating zone wherein it is subjected to thermal cracking, combining the efiluent from said heating zones, utilizing a portion of the mixture to constitute the said heated products introduced to the lower portion of the verticallydisposed reaction chamber and combining the other portion with the va l pors passing to the catalytic cracking zone.

4. In the combination thermal and catalytic cracking of hydrocarbon oils the process that comprises distilling a crude petroleum to obtain residue and vapors and fractionating the vapors to obtain a higher boiling fraction and a lower boiling fraction therefrom, passing said lower boiling fraction through a heating zone wherein it is subjected to thermal conversion, introducing the resultant heated products to the lower portion of a vertically disposed reaction chamber wherein separation of vapors from liquid residue takes place, introducing said residue to the upper portion of the vertically disposed reaction chamber to ow countercurrently to the upwardly rising vapors therein, maintaining a cracking .temperature in said `reaction chamber to eiect thermalcracking, passing theseparated vapors l to a catalytic cracking zone wherein the vapors are contacted with a catalyst and subjected to catalytic cracking, passing the higher boiling fraction obtained in fractionating the crude' oil vapors through a heating zone wherein it is subjected to thermal cracking, and combining the resultant heated products with said vapors`passing tgthe catalytic cracking zone.

' 5.*'In the combination thermal and catalytic cracking of hydrocarbon oils the process that comprises fractionating crude petroleum to separate naphtha, gas oil and residual fractions, passing the naphtha fraction through a heating zone wherein it is subie d ,to reforming, introducing the resultant heate ro'ducts to the lower portion of a vertically dispo g `reaction chamber wherein separation of van from liquid residue takes place, introducing the residual fraction to the 2,856,74 wherein it is subjected to thermal cracking, uti-v upper portion of the vertically disposed reaction chamber to flow countercurrently to the upwardly rising vapors therein, maintaining a cracking temperature in said reaction chamber to effect thermal cracking, passing the separated' vapors to a catalytic cracking zone wherein the vapors are contacted with a catalyst and subjected to catalytic cracking, passing the gas oil fraction through a heating zone wherein it is subjected to thermal cracking, and combining resultant heated products with said vapors passing to the catalytic cracking zone.

6. In the combination thermal and catalytic crackingv of hydrocarbon oils the process that comprises introducingheated vapors to the lower portion of a vertically disposed reaction chamber wherein separation of vapors from liquid residue takes place, introducing a residual oil to the upper portion of the vertically disposed reaction chamber to flow countercurrently to the upwardly rising vapors therein, maintaining a cracking temperature in said reaction chamber to effect thermal cracking, passing the separated vapors to a catalytic cracking zone wherein the vapors are contacted with a catalyst and subjected to catalytic cracking, passing a; lower boiling hydrocarbon through a heating zone kwherein it is subjected to thermal conversion, passing a higher boiling stock through a second heating zone wherein it is subjected to thermal cracking, utilizing the eilluent from one of said heating zones to constitute the said heated products introduced to the lower portion of the vertically disposed reaction chamber, combining Lthe eiiluent from the other of said heating zones with said vapors passing to the catalytic cracking zone, fractionating the resultant products from the catalytic cracking to separate lower boiling products from higher boiling products and subjecting lsaid higher boiling products to cracking conditionsl of temperature and pressure to effect thermal cracking. y

7. In the combination thermal and catalytic cracking of hydrocarbon oils the process that comprises passing naphtha through a heating zone wherein it is heated to a cracking temperature adequate to effect thermal reforming, delivering the resultant heated products to the lower` `portion of a vertically disposed reaction chamber wherein separation of vapors from liquid residue takes place, introducing a residual oil to the upper portion of the vertically disposed reaction chamber to flow countercurrently to the upwardly rising vapors therein| maintaining a crackingJ temperature in said reaction chamber to effect thermal cracking, passing the separated vapors to a catalytic cracking zone wherein the vapors fare contacted with a catalyst and subjected to catalytic cracking, passing a gas oil stock through a heating zone -wherein it is rapidly raised to a cracking temperature, removing the resultant heated products from the heating zone before substantial thermal ,cracking takes place and combining the heated products with the vapors passing to the catalytic cracking zone.

`JOSEPH MASON BARRON.

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