US2338020A - Conversion of hydrocarbon oils - Google Patents

Description

De 28,' 1943, J.'M. BARRON CONVERSION oF HYDRoCARBoNbILs File Feb. 25, 1941 :DND @I NOU IosEPu MAou BAazou [N VENTOR A TOR EKS Patented Dec. 1943 CONVERSION OF HYDROCARBON OILS Joseph Mason Barron, Port Arthur, Tex., assignorl by mesne assignments, to The Texas Company, New York, N. Y., a corporation of Dela- Ware Application February 25, 1941, Serial No. 380,443

1 Claim.

This invention relates to a combination thermal cracking and coking and catalytic cracking process for the production of a maximum yield of high antiknock gasoline or motor fuel.

The invention contemplates a method of processing in a unitary operation relatively light charging stocks adapted for catalytic cracking and heavier charging stocks adapted for coking. In accordance with the invention a stock suitable for catalytic cracking, such as gas oil, is subjected to catalytic cracking while a heavier stock such as a crude petroleum residual stock is subjected to coking to produce a coke residue and volatilized constituents which are subjected to thermal cracking. The invention, furthermore, contemplates the cokingof residual components of the catalytically cracked products and the thermal cracking of constituents volatilized in the coking thereof.

In accordance with the invention a charging stock such as crude petroleum or topped crude is subjected to distillation in a common zone into which the products of the catalytic cracking are introduced for distillation. The evolved vapors are fractionated to separate out fractions, comprising constituents of the crude oil and of the catalytically cracked products, which are suitable for catalytic -cracking and these fractions are directed to the catalytic cracking zone. The mixture of residual components of the crude petroleum and catalytically cracked products is subjected to coking to form a coke residue and vapors. The vapors from the coking operation are fractionated to separate the heavier components including tarry constituents from lighter components such as constituents of the gas oil and kerosene boiling ranges which latter constituents are subjected to thermal cracking.

For the purpose of more fully disclosing the invention reference is now had to the accompanying drawing which is a flow diagram illustrating apparatus adapted for the practice of the invention.

Referring to the drawing charging stock such as crude petroleum or topped crude is charged by a pump I0 to a heating coil II wherein the oil is heated to a desired distilling temperature. A portion or al1 of the heating may be supplied by hot products of the system and a pbrtion or all of the heating may be obtained by furnace heat. The charging stock heated to a desired distilling temperature is directed to a stripping and fractionatingtower I2 andis preferably discharged above a tray I3 provided with a run-back line I4 for directing the unvaporized residue to a lower section of the tower which receives hot products introduced through aline I5 from a source which will be presently explained. The tower I2 is provided with conventional fractionating elements and with cooling and reuxing means to effect the desired fractionation of the vapors which separate from the residue collecting in the bottorn of the tower. The overhead vapors from the tower pass to a condenser coil I6 and the distillate is collected in a distillate receiver I1. The tower is preferably equipped with a plurality of trays I8 for collecting a plurality of condensate fractions. Lines I9 extend from the several trays to a header 20 leading to a distillate tank 2l so that a selection may be made with respectto the fractions collected in the distillate tank.

A pump 22 draws distillate from the tank 2| and directs it through a line 23 to a heating coil 24 positioned-in a furnace 25 which discharges the heated oil to a catalytic cracking chamber 26.

l Usually a plurality of catalyst chambers are employed so that the catalyst may be periodically revivified or regenerated without interrupting the continuity of the process.

The catalyst disposed in sists advantageously of a synthetic silica-alumina type of catalyst. Various acid-treated and metal-substituted clays such as the Super-Filtrols and acid-treated and metal-substituted natural or articial zeolites, such as the artificial zeolite known as Doucil may be employed. Various metals such as uranium, molybdenum, nese, lead, zinc, zirconium, nickel and the like, may be substituted in the clays or zeolites. Likewise, the combination of certain acid-treated active clays of the character of Filtrol, together the chamber 26 con- -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.

Line I5 communicates with the catalyst case 26 and serves to direct the products of the catalytic cracking to the distilling tower I2. The

residual components of the catalytically crackedl products collect as liquid residue in the lower portion of the tower I 2, the stripped crude residuum from tray I3 being combined therewith, while the separated vapors pass upwardly through the tower being combined with the crude oil vapors and subjected to fractionation therein.

The residue consisting of a mixture of residual components of the catalytically cracked products and of the crude, petroleum is withdrawn manga-4 the dephlegmator 32.

from the tower I2 by a pump 21 and directed through a line 2l to a heating coil 29 disposed in a furnace 30 wherein the residual constituents are heated to a cracking temperature and to a temperature sufliclent to support coking upon being discharged into a coking chamber 3|. In practice, a plurality of coking drums are used so that one or more drums may be removed from the line and the coke removed while maintaining one or more drums continuously in the line and the continuity of the complete combination process maintained.

The evolved vapors from the coke drum 3l pass to a dephlegmator 32 in which the vapors are given a primary dephlegmation to separate out the heavier constituents including particularly the tarry component of the vapors evolved in the coking operation. Suitable refluxing means not shown may be provided for the tower 32. The uncondensed vapors which include gas oil constituents as well as gasoline constituents pass to a condenser 33 and the distillate is collected in a receiving drum or gas separator 34.

Distillate from receiving drum 34 is directed by a pump 35 through a line 36 to the fractionator 31 of the thermal cracking unit of the process. The thermal cracking unit includes a heating coil 38 disposed in a furnace 39 and reaction chambers 40 and 4I which are preterably insulated against heat loss. A transfer line 42 conducts the heated efliuent from the coil 38 to the reaction chamber 40 and the transfer line 43 conducts the eiiluent from chamber 40 to chamber 4l wherein separation of vapors from liquid residue, takes place, the separated vapors passing through line 44 to the fractionating tower I1 and the residue passing through a line 45 t0 Normally the pressure is reduced in chamber 32 as compared to the pressure obtaining in reaction chamber 4| so that the chamber 32 serves not only as a primary dephlegmator for the coke still vapors but also as a flashing zone for the residue from the thermal cracking zone. The fuel oil product comprising the ashed thermally cracked residue and the tarry component of the coke still vapors is withdrawn as a liquidfuel oil product through the line 46.

The tower 31 is provided with conventional fractionating elements and with suitable cooling and refiuxing means not shown. The cracked vapors from the reaction chambers are subjected to fractionation and the coke still distillate introduced into the tower is subjected to redistillation and refractionation so that a composite y reux condensate consisting of constituents from both the coking and thermal cracking operations is collected in the tower 31 and this reflux condensate is directed by a pump 41 through a line 48 to the heating coil 36-wherein the oil is raised to a cracking temperature and passed to the reaction chambers 40 and 4I wherein cracking temperatures under superatmospheric pressures are maintained.y The overhead vapors from the tower 31 pass to a condenser 49 and the distillate comprising gasoline constituents produced asa result of the thermal cracking and coking operations is collected in a receiving drum or gas separator 50.

In a modification of the invention a portion vof the reux condensate flowingy to the heating coil 38 of the thermal cracking unit may be diverted through a. by-pass line i to the line 23 and passed thence to the heating coil 24 and catalyst case 26.

In another modification or the invention'a portion of the heated eiiiuent from the heating coil 33 may be diverted through a by-pass line 62 so as to combine hot products from the heating coil 38 with the stream of products from the heating coil 24 passing to the catalyst case 26.

In practicing the invention crude oil or a topped crude is preheated by heat exchange with hot products of the system or otherwise heated to temperatures ofthe order of 500 F. to 700 F. and discharged into the distilling tower. Normally, the crude oil constituents will receive additional heat to further raise the temperature in the tower due to the influx of hot products from the catalytic cracking zone. The resultant mixture of bottoms of the catalytic cracking and crude petroleum residual constituents is passed to the heating coil of the coking unit wherein it is heated to temperatures upwards of 850 F. and generally around 900 F. which temperatures will support coking in the coking drum. Low pressures of approximately 15 lbs. to 40 lbs. per square inch are preferred in the coking drum and it is likewise preferred to have no material drop in pressure between the heating coil outlet and the coking drum. Cracking is carried on in the thermal cracking zone under any suitable temperature-pressure conditions for thermal cracking, although usually pressures of 200 lbs. or higher are employed in the reaction chambers. The pressure in the combination flash tower and coke still dephlegmator is very materially lower than that in the thermal reaction zone. Normally, pressures of about 15 to 25 lbs. are employed. The catalytic cracking operation is ad vantageously conducted at pressures not materially over lbs. and in fact, with the catalysts disclosed herein, is best conducted at lower pressures down to approximately atmosphericl the process. The mixture of reduced crude and residual constituents from the catalytic cracking` is heated to a temperature of 910 F. and discharged into the coke drum wherein a. pressure of 20 lbs. is maintained. The coke still gas oil is subjected to thermal cracking with recycling at a temperature of about 910 F. in the reaction chambers under 400 lbs. pressure. The thermally cracked residue is expanded into the coke still dephlegmator wherein a pressure of l5 lbs. is maintained. -A mixture of straight-run and catalytically cracked gas oil is heated to a temperature of 950 F. and is charged into the catalyst case wherein a pressure of 10 lbs. -is maintained.

It is advantageous to direct a portion of the cycle condensate from the thermal cracking operation to the catalytic cracking operation, since the thermally cracked product constitutes a suitable' charging stock for the catalytic cracking unit. In accordance with the invention this cycle stock from the thermal cracking unit may be combined with the mixture of straight-run and catalytically cracked gas oil passing to the heater of the" catalytic cracking unit. In some cases the vapors from the thermal cracking operation may be fractionated to obtain, in addition to the gasoline distillate, a heavier reiiux condensate and a lighter or intermediate reflux condensate, the heavier reflux condensate being cycled to the thermal cracking lzone and the lighter or inter'- mediate condensate being directed to the catalytic cracking zone. Another advantageous operation is to divert a portion of the stream Vfrom the heater of the thermal cracking unit to the catalytic cracking chamber.

While I have described a particular embodiment of my invention for purposes of illustration, it should be understood that various modifications and adaptations thereof which will be obvious to one skilled in the art, may be made within the spirit of the invention as set forth in the appended claim.' S

I claim:

The combination thermal and catalyticcracking process that comprises introducing the cata lytically cracked products and crude petroleum charging stock into a vaporizing and separating zone wherein vaporization of a portion of the charging stock takes place, subjecting resultant separated vapors to fractionation to separate gasoline distillate from higher boiling reflux condensate, directing said higher boiling reflux con-` densate in admixture with additional reux condensate formed as hereinafter specified to a cata- --lytic cracking zone wherein the-oil is subjected to catalytic cracking, passing the resultant products of the catalytic cracking to said vaporizing and separating zone .as aforesaid, directing the resultant residue from said vaporizing and separating zone to a thermal cokng zone wherein the residue is subjected to cokng to produce a coke residue, separately subjecting the evolved vapors from the cokng zone to fractionation to separate higher boiling fractions from a lower boiling condensate, introducing said lower boiling condensate into another fractionating zone for reiractionation in contact with vapors therein and wherein y fractionation to separate gasoline constituents from higher boiling reflux condensate takes place, directing a portion of the reux condensate from the latter fractionating zone to a. thermal cracking zone wherein the oil is subjected to cracking conditions of temperature and pressure to effect thermal cracking, separating the resultant products of the thermal cracking into vapors and residue, passing the separated vapors to the latter fractionating zone and utilizing another portion of the reflux condensate from the latter fractionating zone as the additional reilux condensate being passed to the catalytic cracking zone. n

JOSEPH MASON BARRON.

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