US2379966A - Hydrocarbon conversion system - Google Patents

Description

July 10,-1945. a A JOHNSON 2,379,965

. HYDROCARBON CONVERSION SYSTEM Filed nec. s1, 1940 Gasaz'zze Emana/wma@ sEpR/ITOR PIPE sruzs @fari/.2%.

meines July 1o, 194s nrpnocmos coNvsnsIoN srs'rasr Everett A. Johnson, Park Ridge, Ill., assigner to Standard Oil Company, Chicago, Ill., a corporation of Indianl 'Application December si, 194e, serial No. 372,509

19 clams. (el. 1st-52)` v Y pended in a regeneration gas and is ilnally re- This invention relates` to a hydrocarbon conversion system and it pertains more particularly to a system for converting gas oils or heavier hydrocarbons into high quality motor fuels.

Catalytic cracking processes produce high octane number gasoline and low gravity gas oils. The heaviercomponents of such gas oils may be cracked more satisfactorily by thermal'processes than by catalytic processes. The gasoline produced by the thermal conversion of these heav ier hydrocarbons is characterized :by a lower octane number than the catalytically cracked product. Heretofore it has been necessary to subject the thermally cracked naphtha to a separate conversion step such as reforming or isoforming in order to increase its clear octane number. An object ofv my invention is to obtain this clear oc- Vtane number increase in the thermally cracked naphtha.without the necessity oil-.employing a separate conversion system f A furtherobject of the invention is to provide an improved methodand means for utilizing a cracking catalyst more fully and to greater advantage than it-has been utilized in any previous conversion system. A further object is to provide a new and improved integration 'of thermal and catalytic processes which will greatly reduce cap-l ital investments and operating` costs and, at the same time, increase the quality'and yields of gasoline obtainable from a given charging stock. A further object is to provide a method and means for simultaneously treatingthermally crackednaphtha with catalytic conversion prod-4 ucts in a moving catalyst system so that the cata.

lyst which has already produced some cat,A conversion of the sas oil will in a later stage sis multaneously eilect cracking of gas oil and octane improvement of ,the thermally cracked naphtha. A furtherobiect is to' providean improved means ford'controlling the ilnal stage `oi catalytic sas oil cracking ope tion 'and for preventing undesirable reactions erein.

A further object is to provide an improved sys' temi for correlating solvent extraction with' therturned for effecting further reaction. The reaction products are fractionated to separates1 cycle gas oil from the gasolineand lighter hydrocarbons. 'This cycle gas oil may be solvent extracted' to remove polycyclic aromatics or other components which may be V'undesirable in subsequent conversion steps, v i.

The gas oil or gas oil raiiinate is then passed through a.thermal conversion system and the thermal conversion products are roughly fractionated to remove tar and to separate a naphF tha from one or more gas oil fractions, the latter being charged to either.the\thermal orcatalytic conversion steps either before or after solvent extraction.` The hot'therxnally cracked naphtha either with or without-the addition of-further heat is then introduced into the catalytic con-1` version streamat such a point that it will not interfere with the desired catalytic cracking of the gas oil and will not itself be over-treated by the catalyst but will undergo a reforming change which markedly improves its octane number.

In many cases the hot thermally cracked naph'- .tha may be introduced into the catalytic cracking reaction stream at the point wherein` theyr stream is introduced into the' separation stage 3^( since the contact of the thermally cracked vapors,y in the separator may be suiiicient to markedly improve itsoctane number. In other cases the thermally' cracked naphtha may be introduced v inthe ilnal stage orone ofthe latter stages of the catalytic cracking or in the transfer line leading to'such stage or stages or in the transfer line ieadingirom` the last stage to the separation stage. In any event, the thermally cracked vapers/will contact catalyst which has already performed its function in the catalytic conversion of gas oil and which has become coated witha octane number of the thermally cracked naph. Y

mal and catalyticnracking systems whereby dele-` 45 I l system. The use of a separate reforming system terlous materials may be removed both from the `charging and recycle stocks to the thermal and to the catalytic conversion steps. Other objects et the invention proceeds.

Iri,practicing my invention I` prefer to employ the .so-called iluid catalyst system -wherein a solid .catalyst is `suspended in reaction vapors duringv the conversion step. is then separated i'romconversion. products. lis next' regenerated carbonaceous deposit and has thus become partially spent. IV have found that this spent catalyst is still eilective to eii'ect an increase in the tha and that thisincrease can be eiected directly in the latterpart of the catalytic-conversion is thus eliminated and the reformed" thermall naphthaisseparated from the catalyst and Airactionated in the same system with the cracked My invention not only provides a means for more complete utilization of catalystand for increasing the. clear octane number of thermally cracked naphtha without appreciable additional expense but it provides a means whereby unde sirabie reactions may .be inhibited m .the meer stages of the catalytic conversion of gas oil. 'I'he invention is applicable to moving bed catalyst systems as well as to the powdered or fluid type systems.

The invention will be more fully understood from .the following detailed description and from the accompanying drawing which forms a part of the speciilcation and which is a ilow diagram schematically illustrating a preferred embodiment of my invention.

The charging stock to my system may be a gas oil or heavier hydrocarbon produced from petroleum or from any other source. Synthetic hydrocarbons resulting from the Fischer process of carbon monoxide-hydrogen synthesis or hydrocarbons from the ordinary hydrogenation of carbonaceous material provide excellent sources for such charging stock. I will describe thef invention, however, as applied to the conversion of a 35 A. P. I. gravity Mid-Continent gas oil.

The catalyst employed in this system may be an activated clay such-as the ac id treated .ben-

tonite commercially marketed as Super Filtrol.`

` dried and heated to about 1ooo F. No invention is claimed in any particular catalyst and.

since cracking catalysts are well known in the art a further description of them is unnecessary. The best catalysts are of the metal oxide type, particularly of the silica-metal oxide type.

In the fluid type system I prefer to employ the catalysts in the form of a powder ranging in particle size from about 200 to 400 mesh. Such a powder in compactedform has a density of about .7, i. e., it weighs about to 45 pounds per cubic foot. When aerated ata gas velocity of about .05 to .2 feet per second, the catalyst becomes uent and may have a density of about 20 to 40 pounds per cubic foot. At gas or vapor velocities of about .3 to 3 feet per second, preferably about 1 to 2 feet per second, the catalyst density may be about 10 to 20 pounds per cubic foot and I prefer to employ such catalyst density in my reaction and regeneration zones.

Referring to the drawing, the gas oil charge is introduced through line- I0 by pump II to coils asvaaoo fer line. I prefer to employ catalyst-to-oil weight ratios of about 1,:1 to 5:1. for example about 3:1. The temperature in the reactor may be 800 to 1000 F., for example 925 F.

Reactor I1 may be a cylindrical vessel with a conical inlet and outlet respectively and of such size and cross-sectional area as to retain the necessary amount of catalyst for effecting the desired amount of conversion. The cross-sectional area should be such as to insure a vertical vapor velocity of about .3 to 3 feet per second if the reaction is to be eifected under the desired dense phase conditions. It should be understood, however, that my invention is not limited to any particular reactor size and shape and that it is only necessary to provide a contact of the vapors with a suillcient amount of catalyst to eiect the desired conversion. For a catalyst holding time in the reactor of about 3 minutes the oil contact time may be about 10 seconds in order to obtain about 40% conversion. My invention is not limited to the particular conditions above recited; generally speaking the vapor velocities in the reactor should be sui'cient to maintain a catalyst density therein of `about 1 to 35 pounds per cubic foot, preferabb about 10 to 20 polmds per cubic foot. 'I'he amount of catalyst in the reactor for a given amount of conversion is de' pendent on the activityof the catalyst which is dependent in turn on its residence time in the reactor. I prefer to use a residence time and amount of catalyst as defined by the followingr equation:

T=at-s34 where T is -tons of catalyst in the reactor per 100 barrels of stock charged thereto, pz is a constant ranging from .3 to 3.0, preferably about 1.2, and t is catalyst residence time in minutes in the total reactor space.

Vapors carry catalyst from the top reactor I1 through line I8 to reactor I9 at the same rate as catalyst is introduced into reactor I1. Reactor I9 is preferably of larger cross-sectional area so that about the-same vapor velocities may be obtained therein as were obtained in reactor II in spite of the addition of alarge amount of hot thermally cracked naphtha vapors introduced through line l0. These thermally cracked naphtha vapors may be characterized by octane number of about 65 to 70 while the octane number of catalytically cracked naphtha may be about 80. The catalyst which has already eifected the catalytic cracking of gas oil vapors is in accordance with my invention utilized for obtaining an octane number increase on the thermally cracked vnaphtha ofas much as 5 to 15 -units and this I2- of pipe still I 3 wherein the oil is vaporized and heated to give a transfer line temperature of about 800 to 1100 F., for example, 900 F. anda transfer line pressure of about atmospheric to about 50 pounds 'per square inch, preferably about 10 to 15 pounds per square inch. e

' As the heated vapor passes throughtransfer line I4, it picks up hot powdered catalyst from standpipe or catastat I5. .The catalyst is introduced into the transfer line in amounts regulated. by slide valve or star feeder I6. It should .be

understood, of course, that steam or a mechanical screw or any other suitable means may be used for introducing the catalyst into transfer line I4v and that the catalyst is carried by the vapors in said line to up-iiow reactor |11. 1f desired, the

catalyst may'be injected directly into the ref actor instead of being introduced into thetransincrease in octane number is obtained without any appreciable loss in thermally cracked naphtha yield. v

s The time of vapor contact in reactor I8 may be only about ,Ik to $60 of that required for the catalytic cracklng of gas oil although itshould be understood that gas oil cracking takes place in y reactor I9 simultaneously with the reforming of the thermally cracked naphtha. I prefer to introduce the thermally cracked naphtha through line 20 at a temperature of about 900 F. In reactions wherein quenching is desired the `temperatures of thisl introduced stream maybe as l'owas 800 or 8'15"l F. Usually, however, I-prefer to add heat at` this point in order to effect a further catalytic cracking of the gas. oil in reactor -IS along with the reforming of the thermally. cracked naphtha. Forthispurposethetempera asvaeae ture of the added stream may be about 950 to 1050 or 1100 F.

Instead of introducing the hot thermally cracked naphtha through line 20 I may introduce it through line 2l at an intermediate point of the reactor. In fact, I may use a single reactor in place of reactors I1 and I9 and merely introduce the hot thermally cracked naphtha near the top of said single reactor. This latter expedient is less desirable in dense phase operations than in operations wherein there is uniform movement of the catalyst through the reactor.

The reaction vapor stream together with suspended catalyst leaves the top of reactor l through line 22 and is conveyed therein to cyclone separator 23. The thermally cracked naphtha may be introduced into this line 22 through line 24 or line 25 or it may be introduced directly to the separator through line 26. The exact point or points of introduction will depend partly upon the amount of thermally cracked naphtha vapors to undergo reforming or isoforming, partly upon the nature of the catalyst and the extent to which it has previously been coated with carbonaceous deposit and partly upon reaction conditions. As hereinabove stated, the treatment is only l to lu of that .required for the catalytic conversion itself.

The catalyst separated from vapors in separator 23 falls into hopper or stripper 21" which in turn discharges the catalyst 'into standpipe or catastat 28. 'I'his standpipe is aerated by means of an inert gas such as steam introduced through line 29 and additional gas may be introduced through line 30 for maintaining desired aeration or stripping in hopper 21. Gases from hopper 21 are vented through line 3l to line 32 which is the line conveying reaction vapors from separator 23 to further catalyst separators (not shown) lif required and rthence to fractionating tower 33.

Gasoline and gases are taken overhead from tower 33 through line 34 and cooler 35 to receiver 55. Gas may be vented from this receiver through line 31. A portion of the liquids may be recycled through line 3B as reux for tower 33. The rest of the liquid is introduced through line 30 to stabilizer 40.

Propane and `lighter gases are taken overhead from the stabilizervthrough line 4I and cooler conversion. I prefer to use relatively high temperatures and low pressures in this conversion step although the pressure and soaking factors should be suillcient to obtain the desired crack per pass, usuallyabout 15 to 45%, Preferably about 25 or 30%. In a Apreferred example, a transfer line temperature of about 975 F. and pressure of about 200 to 300 lpounds per square inch may be employed. Thermal cracking temperature may range from about 850 to 1100 F. and pressures may range from aboutatmospheric to 1000 pounds per square inch.

The thermal cracking may be effected in the coils themselves or in a separate soaking drum vmethod of operation the heavy gas oil is` recycled to line 49 for further conversion and the lighter gas on of about 60o to 'zoo end point is returned through line 60 to line I0.

Gas oil fractions from any or all of lines 48, 58 and 59 may be introduced through lines 6|, 52 and 63 respectively to solvent extraction system 5t. Similarly, the original feed stock to the system may be charged to this extraction system through line 65. In the extraction system the gas oil may be countercurrently or in any other conventional manner extracted with a selective solvent such as sulfur dioxide, nitroparains such as nitro methane and nitroethane, nitroparafn- SO2, benzol-acetone, furfural, SO2-bengel or any other solvent known to the art for the removal of polycyclic aromatic hydrocarbons or any other components which may be detrimental in either` rate stocks or the separate stocks may beseparately or simultaneously extracted in a single system. The raffinate or rafiinates from such system or systems maybe introduced through ,line 60 to the thermal conversion system or through line 51 to the catalytic conversion system. Heavy polynuclear extracts are undesirable in the catalytic conversion system but may be introduced into the thermal cracking system through line 68 or Withdrawn through line 69 to storage.

Spent catalyst from catastat 28 is introduced through valve or star feeder 10 by means of an oxygen containing gas such as' air from line 1l into line 12 and conveyed therein to up-flow regenerator 13. Here again it should be understood that the catalyst may be introduced directly into the regenerator. The regenerator may be a cylindrical vessel similar in size and shape to reactor i1 since I prefer to burn the carbonaceous deposit from the catalyst while the catalyst is in the suspended dense phase condition that is obtainable with the use of vertical vapor velocities of about 1 or .2 feet per second.

Regeneration temperatures may be held within close limits, preferably below 1050 F. by recycling cool regenerated catalyst, by introducing steam or co'oling gases (provided that this can be done without exceeding desired vapor velocities)4 or by the use of heat exchange coils in the regenerator. Regenerated catalyst is carried out of the top of the regenerator either through line 14 directly to cyclone separator 15 or through line 16 and heat exchanger 11. The regeneration gases separated from the catalyst in separator 15 are withdrawn through line 18 and both heat and catalyst may be recovered therefrom in any conventional manner.

Catalyst from separator 15 falls to hopper 19 and thence to standpipe or catastat ll5. Aerating gas is introduced through lines and 8| and such gas is preferably withdrawn from the top of hopper 19 through line 82.

The hot thermally cracked naphtha vapors from the top of fractionator 51 may be passed directly through lines 83 and 84 for introduction into the last portion of the catalytic reaction system through lines 20, 2|, 24, 25 or 26. Alternatively, these hot thermally cracked naphtha vapors may be passed through line 85 and heat exchangerV 11 before being introduced into the catalytic system through any of the aforesaid lines. It` should be understood that while heat exchange has been illustrated between the hot naphtha vapors and the hot regeneration gases,

various other modications of the invention will be apparent to those skilled in the art from the above description and I do not limit myself to any of the details hereinabove set forth except as defined by the following claims.

I claim:

1. In a hydrocarbon conversion system wherein gas oil is cracked by a catalyst suspended in gas oil vapors and is subsequently separated from said vapors and wherein a thermally cracked naphtha is produced by thermal cracking of heavier-than-gasoline hydrocarbons Separated from catalytically cracked gasoline, the method of increasing the octane number of said thermally cracked naphtha which comprises contacting said thermally cracked naphtha va- .pors at a temperature of about 800 to 1l00 F.

with a catalyst that has previously become coated with a carbonaceous deposit in said gas oil cracking step.

2. The method of converting a heavier-thangasoline Ahydrocarbon charging stock into large yields of high quality motorfuel which comprises vaporizing and heating said stock t a temperature of about 800Ato 1100 F., suspending a solid catalyst in said heated vapors and contacting said vapors with said catalyst -in an elonthermally cracked gas oil to one of said cracking steps,.and commingling thermally cracked naphtha vapors and partially spent cracking cat alyst in a later stage of the catalytic cracking operation, thereby increasing the octane number of said thermally cracked naphtha.

5. The method of converting a hydrocarbon charging stock heavier than gasoline into large yields of high octane number motor fuel, the steps comprising solvent-extracting the said charging stock, recovering a raffinate and an extract therefrom, catalytically cracking said raiiinate to produce gasoline anda catalytically cracked gas oil, thermally cracking said extract to produce a thermally cracked naphtha and a thermally cracked gas oil, recycling at least a portion of one of said gas oils to one of said cracking steps, and contacting said thermally cracked naphtha vapors with the partially spent catalyst in a later stage of said catalytic cracking operation whereby the octane number of said thermally cracked ,naphtha is increased.

6. In a vcombination thermal and catalytic cracking system the method of increasing the octane number of thermally cracked naphtha produced by 'thermal cracking of heavier-thangasoline hydrocarbons, which method comprises catalytically cracking a charging stock in first and second zones and introducing hot thermally cracked naphtha vapors at a temperature of about `800 to 1100c F. into said second cata- 40 lytic-cracking zone along with partially cracked gated reaction zone, introducing hot thermally crackednaphtha vapors into said reaction zone at a point in said zone wherein substantial conversion of the charging stock has already beeny effected whereby catalyst which has already effected catalytic conversion of charging stock effects reforming of said thermally cracked naphtha vapors, separating the products of cracking and reforming from said catalyst and vseparating gasoline from said products.

piments of products resulting from the catalytic cracking.

4. The method of converting a hydrocarbon fresh feed heavier-than-gasoline into large 8. 'Ihe method of claim 6 wherein the time of contact of thethermally cracked naphtha with the cracking catalyst is within the approximate range of V2 to 1/50 of the time of contact of said charging stock with said catalyst.

9. The method of claim-6 wherein the thermally cracked naphtha vapors are introduced into said second zone at a temperature which is higher than the temperature of cracked gas oil vapors from the rst zone.

10. The method of claim 6 which includes the i steps of effecting catalytic cracking by means of a continuously moving catalyst stream, contacting gas oil vapors with said stream in both of said rst and second zones andcontacting said thermally lcracked naphtha with said moving i stream in only the second of said zones.

EVE'RET'I A. JOHNSON.

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