US2340814A - Process for converting hydrocarbon oils - Google Patents

Description

Feb-1,1944 R; E. LIDOV Q 4- .PROCESS FOR CONVERTING HYDROCARBON QILS Filed April 2, 1940 t RIM 37K RECEIVER I C'ON VERTER FUR/W7 C E FURNHCE INVENTOR- F'y E, A fa/ay ATTORNEYS Patented Feb. 1, 1944 PQWESS FUR WTHTG DRO- CN @Ha Ben E. Lilies, Portland, @i'eg. Application April 2, 19%, Serial No. earn-7c This invention process for the relates to an improved catalytic conversion of hydrocarbon oils to gases containing large proportions of oleflnes and liquids in the motor fuel boiling range having a high octane number and a high octane blending value. 1

An object of the invention is to provide a novel process for the gasiflcation of hydrocarbon oils, yielding as by-products, liquids in the gasoline boiling range which possess high octane numbers and high octane blending numbers, and are valuable as motor fuel or as blending fluids for the improvement of motor fuel.

Another object is to provide a catalytic process for the production in high yields of ethylene and other short chain carbon compounds in the ethylene series, from hydrocarbon oils, together with high B. t. 11. gas suitable for use for heating, cooking, or fuel, together with liquid byproducts of the type heretofore mentioned.

Another object is to provide a commercially practical process for converting relatively low grade oils into more valuable products.

Another object is to provide a catalytic conversion process of the type above indicated having novel and improved combinations of steps and conditions of operation.

Another object is to provide a catalytic process of the above type which is capable of utilizing various charging stocks for the production of fuel gases, gaseous oleflnes and aromatics or.

liquids of the type above mentioned.

Another object is to utilize-a suitable catalyst for use in the above process, which is not deleteriously affected either itself or in its ability to act catalytically for the process by the presence of varying amounts of steam.

Various other objects and advantages will be apparent as the nature of the invention is more fully disclosed.

The present process, with suitable changes in operating conditions, is adapted to convert hydrocarbon charging stocks of-various characteristics such as, for example, a gasoline fraction or a gas oil fraction from crude petroleum or recycle stock, or topped crude, into products containing hydrocarbon gases, gaseous oleflnes and a liquid fraction in the motor fuel boiling range,'rich in the aromatics ben'zol, toluol and xylol, from which these aromatics may be separately obtained, or which in its entirety may be used as a motor fuel or as a motor fuel blending agent, or containing a liquid fraction in the motor fuel boiling range chiefly distinguished by e (cries-521 useful as a motor fue agent.

In accordance with the present invention, the charging stock is first heated to a temperature to completely vaporize the same under conditions such that substantially no cracking takes place. If the nature of the charging stock is such that it cannot. be completely vaporized under these conditions, the material may be passed to a flash chamber and separator for removing the nonvaporizable portion. The vapors only are then or a motor fuel blending passed into the conversion zone wherein they are its high octane and octane blending numbers and contacted with a suitable catalyst under conditions of temperature, pressure and space velocity which favor the formation of the, desired products.

The conversion zone, in one embodiment, comprises a plurality of tubes containing a catalyst, which are externally heated by suitable means to supply the necessary heat for raising the vapors to the desired outlet temperature.

The portion of the charge converted to gases is generally dependent upon temperature, a greater gas yield being obtained at higher temperatures mass velocity and the pressure in the converter unit, decreasing as the space mass velocity increases, and to a lesser extent, decreasing as the pressure increases. The gas composition in gen- .eral is butlittle affected by temperature or space mass velocity, but the liquid composition is affected, the liquid becoming less aromatic with increasing space mass velocity and decreasing temperature.

system is constant the pressure affects both the space mass velocity and the related factor, the contact time of hydrocarbon vapors with the catalyst in the conversion zone. I have found that aside from the changes exerted by pressure because of its eflect on the contact time, it exerts an independent effect on the nature of the products as a result of the changes it induces in the equilibria of the reactions in the conversion zone. In general, the yield of oleflnes and particularly the yield of ethylene, decreases as the pressure increases and to a very much lesser extent the liquids tend to become more aromatic. It is obvious, of course, that the effect of changes in pressure on the contact time and the resultant effect on the products can be eliminated by a proper selection of flow rate or by other methods which will be made clear hereinafter. Consequently. by suitable control of these factors,

The gas yield is also related to the space which is derived from a later stage of the process.

The quench oil. is preferably of such a nature that it does not crack or coke under the conditions to which it is subjected, .leaves no residue and introduces no undesirable constituents which require additional steps or apparatus for their subsequent removal.

The vapor stream, after quenching, contains the desired products and the hydrocarbon used for quenching and may be treated in a suitable manner for the removal of the higher boiling residues and the subsequent separation of the gaseous olefines, the fuel gases and the motor fuel fraction. The oleflnes may be further separated into their components such, for example, as ethylene, propylene and butylene if desired. The liquid boiling in the motor fuel range may consist essentially of benzol, toluol and xylol and in its entirety will possess a high octane number and high octane blending number which renders it suitable with but little subsequent treatment for use directly as a motor fuel or as a blending agent for increasing the octane number of other motor fuel. It may also be used as a source'for the production of the aromatics benzol, toluol and xylol in pure form. The liquid fraction, depending on the operating conditions above mentioned, may have a smaller proportion of the aforesaid aromatics but will, in any event, be characterized by high octane and high octane blending values which render it, after but little subsequent treatment, suitable for use as a motor fuel or as a blending agent for increasing the octane number of other motor fuel.

Although the novel features which are believed to be characteristic of this invention are more particularly pointed out in the claims appended hereto, the invention itself may be better understood by referring to the following description,

taken in connection with the accompanying drawing, in which a specific embodiment thereof has been set forth for purposes of illustration.

In the drawing. the figure represents diagrammatically a converter plant embodying the pres.- ent invention.

Referring to thedrawlng more in detail, the charging stock is supplied by a pump 9 through a charge line H) and heat exchanger II to a vaporizer coil l2. In the embodiment shown, this vaporizer coil comprises a bank of tubes ll in a suitable heater I! of any standard type, such as a furnace, a flue through which hot combustion gases pass, the convection zone of the converter furnace to be described, aheat exchanger, or the like.

The charging stock is heated in the heater II to a temperature such that complete vaporization takes place. It is to be understood, however, that if the nature of the charge is such that complete vaporization without cracking cannot be obtained in the vaporizer coil, the unvaporized portion of the charge may be removed by suitable separating apparatus not shown. The heat exchanger ll serves to pre-heat the charge prior to passage to the vaporizer coil. It may, however, be omitted if desired.

The vapors from the heater l5 are passed through a line I6 to the conversion zone, shown as a furnace I! having therein a plurality of converter tubes l8 which are indicated diagrammatically as vertical tubes arranged in four banks, each having an inlet header l9and an outlet header 20. It is to be understood that the tubes may extend either vertically or horizontally and that they may be arranged in vertical or horizontal banks. Suitable heating means, such as burners, not shown, may be provided for externally heating the tubes to the desired temperature. Vapors are supplied through the line [6 and a set of inlet valves 2| to the various inlet headers I9. The vapors, after conversion in the tubes I 8, are taken from the outlet headers 20 through valves 22 to a line 25 by which they are supplied to suitable separating apparatus, shown as a fractionating column 26.

The cracked vapors emerging from the tubes l8 are immediately cooled to below conversion temperature by introduction of a suitable quench oil into the vapor stream. In the embodiment stream and to cool the same substantially instantaneously to a temperature below that at which further reaction takes place.

The excess of the side out taken from the stripper 21, over that required for quenching purposes may pass through a line 36,-control1ed by valve 31, to storage or for use as fuel oil, or may be recycled as charging stock for theprocess by means of a pump 38 and a line 39 controlled by a valve 39a. This excess may be removed and 'recycled either before or after it passes through the heat exchanger I l.

The fractionating column 28 is operated at temperatures and pressures to separate the residue, which may be of the nature of a heavy fuel oil. This residue may be withdrawn from the bottom of the column 28 through a line 43 and a cooler II to storage. The overhead vapors,

containing the desired products such as the fuelgas, oleflne gas and the motor fuel fraction, are passed through a line 45 and a cooler 48 to a separator 41 which is operated at a temperature and pressure adapted to make a primary separation of the gases from the liquid motor fuel fraction, the former being taken from overhead by a line 48 to a suitable gas separating unit and the latter being taken from the bottom of the separator 41 through a line 49 to a treating unit which is adapted to condition the liquid for use as amotor fuel or as a blending agent or it may be taken if desired when it is largely aromatic, to subsidiary equipment designed for the separation therefrom of the aromatics toluol, benzol and xylol. A portion of the liquid may be returned by a pump 50 and a line 5| to the top of the fractionating column 28 as reflux for-temperature control purposes.

Steam and air for reactivating the catalyst may be supplied from a steam line 55 and an air line 33 respectively, controlled by valves 51 and 58, through a line 59 to a coil 00, which may constitute a preheater or superheater coil, in the have travelled through th first 40% of the conheater is, thence through a line 6| and branch lines 62, controlled by individual valves 53 to the supply headers I9. The outlet headers 20 may be connected to a blow down line M through lines 65 and valves 65.

When a bank of tubes is to be reactivated, the corresponding valves 28, 22 and 35 are closed to remove the bank from the vapor stream and to interrupt the supply of quench oil to the outlet header 20. By opening the valves to and 6G associated with the bank to be reactivated, and by suitable control of the valves 51 and 58, air and steam may be supplied to the tubes from lines 55 and 56 in regulated quantities as required for reactivation purposes and the reactivation products may be removed through the blow down line 54.

In carrying out the present process for the conversion of a charging stock within the gasoline boiling range (100 F. to 380 F.) or a charging stock, such as gas oil (380 F. to 750 F.)

which contains no non-volatile reject, the charge may be heated in the vaporizer coil to' a temperature of 650 F. to 850 F. at a pressure varying from a partial vacuum to about 150 lbs., the particular temperature and presure conditions being selected so that no substantial cracking will take place prior to the conversion step. In the event that the charging stock is a topped crude, or a recycle stock containing a fraction which cannot be vaporized without cracking'at the above temperatures, the latter is removed by passing the vapors through a suitable flash chamber or otherseparation means.

The vapors from the vaporizer coil or from the flash chamber are passed directly into the conversion unit where they are contacted with the catalyst in the tubes l8 under conditions of term perature, pressure and space mass velocity adapted to favor the formation of the desired product. It has been found that with 2%" tubes 15' long, with an outlet temperature of between 1150 F. and 1500" F. and at pressures between sub-atmospheric and about 50 lbs. per sq. in., the fiow rate or space mass velocity may vary from 1 to 10 units, a unit being defined as the velocity required to pass 62.4 lbs. of oil per hour per cu. ft. of catalyst space. This velocity may, for example, result in a time of contact with the catalyst of from 0.2-3.0 seconds, depending upon the porosity of the catalyst and the percentage of free space in the tubes.

It will be readily apparent that some finite time will be required to bring the oil vapors in the conversion zone from the temperature of approximately 850 F. at which they enter, to a final temperature within the limits of 1l50-1500 F. The vapors may be made to attain a temperature in excess of the desired final temperature in their passage through the first 10-15% of the conversion zone but a point is then reached at which an extremely rapid drop in the vapor temperature takes place, to a temperature well below the desired final outlet temperature, despite the fact that heat in large quantities is constantly supplied to the conversion zone. Following this rapid drop, the vapor temperature then rises to the desired final temperature and the vapors can then be made to complete their passage through the conversion zone at temperatures within 50 F. plus or minus of the desirable final outlet temperatures. The period of rapid temperature drop is normally completed by the time the vapors version zone. It is likely that the zone in which the fall in vapor temperature occurs represents that zone in which gasification takes place most rapidly with consequent rapid absorption of the endothermic reaction heat by the vapors. It is possible, by controlling the rate of heat input at various parts of the conversion zone, to fix the peak temperature attained by the vapors before the point of rapid temperature drop is reached, and also to hr the shape of the temperature curve in the last 50% of the conversion zone.

In its preferred embodiment the present process should be provided with a heat input into the conversion zone of such a type that a temperature well in excess of the desired final temperature is attained before the point of rapid temperature drop is reached, and such that, following the temperature drop, the vapors again rise to the desired outlet temperature as rapidly as possible and remain at that temperature for the balance of the time they are in the conversion zone. However, the present invention is not intended to be limited to use with such heat input.

but for ease of practical design the temperature gradient may be varied as desired to produce the optimum average temperature.

An important feature of the present invention resides in the elimination of the necessity for careful control of temperatures along the conversion zone, it being required only that the vapors be passed through the zone under conditions of contact time and pressure herein disclosed,

and made to attain by the end of the passage a temperature in the range l-1500 F., in accordance with the products desired.

It should be further understood that any limiting control tending to maintain the vapor temperature below the final temperature in the first half of the conversion zone is not ordinarily desirable.

The percentage of olefines and the relativev proportion of the difi'erent olefines is influenced by the selection-of the catalyst as well as by the other factors above mentioned. The catalysts selected will accordingly depend upon the product desired. It is to be understood that the term "catalyst is used in a broad sense and is not in tended as a definition of the action of the material. The material may act asa true chemical catalyst to promote the reaction or may act mechanically by surface contact or in various other ways. It has been found that .the presence of certain substances favors the formation of certain products and these substances are herein,

for convenience, called catalysts.

I have found that silicon carbide is particularly suited to act as a catalyst for the above process. This material aids the conversion of the hydrocarbon 01! to gases containing a high proportion of olefines and enhances, though to a lesser-extent, the formation of aromatics when the process is carried out in the higher temperature ranges. In its preferred form, the silicon carbide may be present in the form of irregularly shaped porous particles which have been obtained by binding fine mesh silicon carbide powder with about 20% to 25%- of ceramic cement which is, itself, catalytically inert. Binding, of course, may be accomplished by light temperature treatment of the mixed powders. A suitable removable filler may be added to the composition before the silicon bond is formed in order to insure a hig'hdegree of porosity in the finished product. The bonding may also be accomplished by molding or extruding the powder by suitable methods, or ceramically by other procedures than the one above outlined.

The silicon carbide may also be used in the form of non-porous grains of the proper size or as non-porous grains formed by appropriate bonding of silicon carbide powder. The material may also be used, where desired, as pellets formed in any of the above mentioned fashions.

Silicon carbide is particularly desirable as a catalyst for this process because of its strength, and because of its inertness towards steam and oxygen at the high temperatures employed and at the even higher temperatures encountered during the regeneration procedure.

Various other catalysts may also be used in, the present process, such as; difflcultly reducible metal oxides in active form, preferably supported on a suitable carrier such as silicon carbide; metals in such form as tobe catalytically inert for the decomposition of hydrocarbons to carbon and hydrogen, etc. The catalyst selected will depend upon the operating conditions and the other requirements of the operations involved as well as upon the product to be obtained.

The tubes are filled with the selected material and suitable provision is made to retain the catalyst in place. Preferably, the catalyst is used in grains of various mesh sizes which are themselves either porous or non-porous and which are so disposed within the tube as to create a maximum of turbulence and surface contact. The selection of the size of grain to be used will dependupon a number of factors, among which may be mentioned'the length and diameter of the catalyst bed, the rate of flow to be employed and the permissible pressure drop through the catalyst bed, the latter having an effect upon the total pressure in the system and consequently, as elsewhere explained, on the nature of the products obtained. The tubes themselves should be made of a material which does not interfere with the catalytic cracking of the vapors therein and which does not, itself, catalytically direct the cracking into undesirable directions. Tubes comprising an al- 45 loy 18% chromium, 8% nickel, and the remainder for the most part iron, have been found to be satisfactory, but it is not intended that the invention is limited to use with such tubes.

The quench oil is introduced into the outlet headers to cool the vapors below the reaction temperature as soon as .the desired reaction has taken place. With an oil of the above type, the vapors should 'be cooled to a temperature of from 650 F. to-750 F. In the embodiment shown in the drawing this is accomplished by injecting an oil spray into the outlet headers 20. It is to be understood, however, that this is merely for purposes of illustration and that the oil may be introduced at other points and in other ways or the vapors may be bubbled through an oil bath. In any event, the arrangement is such that the vapors are cooled rapidly before undesirable reactions take place.

In the embodiment shown, the quench oil comprises a side out taken from the fractionating column 26. This side out may constitute a fraction within the gas oil boiling range which, having already been subjected to conversion conditions. will not, under the conditions prevailing in the quenching zone, readily further crack or coke, which vaporizes at the temperature of the vapor stream without leaving a residue and which introduces no undesirable constituents which require special steps or apparatus for their subsequent removal. It is to be understood, of course, that other quench oils may be employed if desired in any particular instance. The quench oil is shown as cooled by heat interchange with the charging stock for purposes of heat conservation.

The vapors entering the fractionating column contain the gaseous olefines, fuel gas, a minor amount of other permanent gases, the motor fuel fraction and heavier residues. The frac tionating column may be operated under suitable conditons of temperature and pressure to separate the residue, which is withdrawn from the bottom as a heavy fuel oil, and, where desired, to separate as a side out material in the gasoline and gas oil boiling ranges suitable for use as a quenching stock or as recycle stock, or as light furnace oil. The overhead vapors containing the permanent gases and the motor fuel fraction may be treated at a suitable temperature and pressure in the separator 41, to effect a primary separation of the permanent gases and liquid fractions The gases will contain the desired olefines such as ethylene, propylene and butylene, and the fuel gases such as hydrogen, methane, and ethane,

. together with minor amounts of liquid hydrocarbons having high vapor pressures, such as amylene, benzol, hexylene, etc., which may be present as unseparated vapors. These various constituents may be separated by any suitable means not shown. The liquid fraction may be treated to condition it for use as a motor fuel or as a blending agent for improving the octane number of other motor fuels or when it is produced under conditions which make it highly aromatic, it may be treated to separate therefrom the aromatics such as benzol, toluol and xylol, and other materials or mixtures of materials suitable for various purposes.

In carrying out thisprocess, it has been found that periodic regeneration of the catalyst is required, probably because of carbon deposition thereon. The converter tubes are accordingly arranged so that one of the banks may be removed from the stream and regenerated while the process is continued with the remaining banks. In regenerating the catalyst, after the converter tubes have been removed from the stream they are preferably first blown with dry steam to remove any residual vapors and to prevent the formation of explosive mixtures therein. Thereafter, a suitable mixture of dry steam and air may be supplied to burn out the carbon, the

quantity of air being controlled so as to avoid an excessive rate of combustion. The tubes may or may not be removed from heat transfer relationship with the furnace during this part of the process. After the carbon has been completely burned out, the tubes may again be blown with dry steam to remove residual air before being returned to stream.

The air or the air and steam mixture may be preheated or the steam mixtures may be superheated in the coil 60 so as to prevent cooling the tubes to below reaction temperatures during reactivation and also to prevent introduction of moisture into the system or into contact with the hot catalyst, which might result in tube ruptures.

By the use of four banks of catalyst tubes, it will be noted that three banks are always on stream, that is, three-fourths of the converter capacity is always in productive use. Obviously, if the number of banks is increased the relative proportion of banks in productive use will be increased. Four banks have been shown merely for purposes of illustration. This system of cat conversion process in which the flow of products is not interrupted or greatly disturbed during reactivation periods.

In a specific embodiment of the invention, utilizing Michigan gas oil of about 39 gravity and operating to favor the production of ethylene, the charging stock may-be supplied to the vaporizer coil l2 at a temperature of about 80 F. and a pressure of 100 lbs. per sq. inch. In the vaporizer coil the temperature may be raised to about 800 F. and the vapors supplied to the inlet headers 20 at about 60 lbs. pressure for distribution to the converter tubes l8 wherein they are contacted witha silicon carbide catalyst. The vapors mayleave the converter tubes 18 at an outlet tem-' perature of about 1400 F. and are immediately quenched in the outlet headers 20 to a temperature of about 650 F., at which temperature they are supplied to the fractionating column 26. The fractionating column may be operated at a temperature gradient from top bottom of from 310 to 600 F. and at a pressure of about 24 lbs. The separator 41 to which the overhead vapors from the fractionating column are supplied may be operated at about 90 F. and 20 lbs. pressure. I

In another embodiment of the invention, operating-the converter at an outlet pressure substantially atmospheric and using the type of charge above specified, the charge may be raised to a temperature of about 400 in the heat exchanger H and to a temperature or" about 800 F. in the vaporizer coils it. The charge may be supplied to the vaporizer coil at 100 lbs. pressure and to the converter. tubes containing silicon carbide, as above mentioned, at a pressure or about 30 lbs. I'he converter tubes may have an outlet temperature of about 140075. and an out-- rated at a later stage by suitable separator means.

As above described, the pressure on the system exerts'changes in the nature of the products obtained for two reasons-one, the result of the pressure as such, and the other, a result of the effect of pressure on the contact time. It is obvious that this second effect can be overcome by the introduction into the vapor stream of steam or some other inert gaseous diluent which will increase the rate at which the gases pass through the conversion zone, and it may be found desirable in order to maintain the contact time independent of the pressure at which the system is operated, to introduce water with the hydrocarbon oil or to introduce steam, or other inert gaseous diluents into the hydrocarbon vapor for this purpose. The water vapor or the other diluents employed will, of course, beseparated at a later stage by suitable separator means.

The other inert gaseous diluents may take the form of nitrogen, methane, or carbon dioxide, etc., inert as it is here used, being intended to mean only that the material employed shall L unafiected, and in general takes no part in the reactions at the temperatures employed.

It has been found, in general, that a lower operating pressure changes the gas yield and also increases the difi'iculty of gas separation because of the large amount of the liquid fraction which is carried along in the gas stream as vapor. It is therefore to be understood that suitable separation apparatus may be required in addition to that set forth in'detail in the drawing. Such boiling between 380 Rand 750 F. with a concolumn is intended to representdiagrammatically a suitable separation apparatus and, if desired, a portion of the fixed gases may be separated prior to the application of the vapor stre to the fractionating column. For the low pressure operation above specified, the iractionating Gas -75 Motor fuel 20-10 Recycle stock. 24-12 -Non-volatile reject-.. 6- 3 used and the characteristics of the product which it is desired to obtain.

It may be found desirable to operate the converter unit at a sub-atmospheric pressure so as toiavor the production of oleflne gases. This may conveniently be accomplished by passing steam or some other inert gaseous diluent'jwith the vapors through the converter tubes so as to reduce the partial pressure of the vapors and verter tube outlet temperature of between 1375 F. and 1450 F., the oil @processed, depending on the rate of how, pressure and catalyst, may yield on a once-through basis about the foll wing products:

- Per cent by weight The gas may contain, by volume, not less than Per cent Ethylene 26 Propylene 12 Butylene 8 in the range of 1200 to 1375" F., the oil processed may have the following composition:

Per cent by weight Gas 20-40 Motor fuel- 32-20 Recycle stock. 38-32 Non-volatile reject 10- 8 the gas will contain not less than:

.' Per cent Ethylene 2a Propy 14 Butylene 6 and may contain not more than 49% of methane,

I ethane and hydrogen. gasoline range will, in this case, be substantially less aromatic than that produced under the The liquid boiling in the higher temperature conditions of the first example but will be characterized by its high octane values and will be suitable for use either directly as a motor fuel or as a blending agent for improving the octane number of motor fuels. It

will have an octane number in excess of 75, and a blending value in excess of 90.

The above are given as examples only and it is to be understood that other variations in operating conditions will produce products having other compositions.

While the novel cooperative relationship between the various steps of the process combine to eiiect an improved, eflicient and commercially practical conversion unit, many of the novel features are adaptable to use in other combinations and in other types of cracking processes and for the treatment of other materials. Various other features and advantages of the invention, both in the individual steps and in the various combinations thereof will be readily apparent to those familiar with the oil treating art. It is accordingly to be understood that the invention is not to be restricted to the specific embodiments herein set forth, but is only to be restricted in accordance with the scope of the following claims.

What is claimed is:

l. The process for converting hydrocarbon oil charging stock into products containing a large proportion of gaseous oleilnes, the balance being fuel gas and a liquid fraction in the motor fuel boiling range having a high octane number and a high octane blending. value, which comprises supplying hydrocarbon vapors to a conversion zone comprising a plurality of parallel connected,

externally heated paths containing a silicon car-' bide catalyst and terminating individually in a common transverse outlet path forming a header,

heating th vapors in said conversion zone to a conversion temperature suited to the formation of the above mentioned products, injecting into the vapors in said outlet'header a quench oil suited to cool the vapors to a temperature sufficiently low to stop the conversion reaction, and separating the oleflnic and motor fuel fractions from the remaining'reaction products.

2. The process for converting hydrocarbon oil charging stock into products containing a large proportion of gaseous oleilnes, the balance being fuel gas and a liquid fraction in the motor fuel boiling range having a high octane number and a high octane blending value, which comprises supplying hydrocarbon vapors to a conversion zone comprising a plurality of parallel connected, externally heated paths containing a silicon carbide catalyst and terminating individually in a common transverse outlet path formg ing a header, heating the vapors in said con- .version zone to a temperature between 1150 F.

and 1500 F. and at an outlet pressure of not more than 50 pounds per square inch while passing the vapors through said zone at a velocity to maintain a contact time therein of between about 0.2 to 3.0 seconds to form the above mentioned products, injecting into the vapors in said outlet header a quench oil suited to cool the vapors to a temperature between about 650 F. and 750' F. to stop the conversion reaction, and separating the olefinic and motor fuel fractions from the remaining reaction products. Y

3. The process for converting hydrocarbon oil charging stock into products containing a large proportion of gaseous oleflnes, the balance being fuel gas and a liquid fraction in the motor fuel boiling range having a high octane number and a high octane blending value, which comprises heating said stock in a vaporizing zone to a vaporizing temperature, supplying vapors from said vaporizing zone to a conversion zone comprising a plurality of parallel connected, externally heated paths containing a silicon carbide catalyst and terminating individually in a common transverse outlet path forming a header, heating the vapors in said conversion zone to a conversion temperature suited to the formation of the above mentioned products, injecting into the vapors in said outlet header a quench oil suited to cool the vapors to a temperature sufficiently low to stop the conversion reaction, supplying the conversion products to a fractionating zone, withdrawing the oleflnic and motor fuel fractions as a vapor from the top of said fractionating zone, separating the oleflnes from said motor fuel fraction, withdrawing a side out from said fractionating zone and supplying the same for use as the quenching oil above mentioned.

' 4. A system for converting hydrocarbon oils for the production of products containing large proportions of gaseous olefines, the balance being fuel gas and a liquid fraction in the motor fuel boiling range having a high octane number and a high octane blending value, which comprises a I converter furnace having at least one bank comprising a plurality of parallel connected, externally heated converter tubes containing a silicon carbide catalyst and terminating in a common outlet header, means for supp ying hydrocarbon vapors to said converter tubes, means for heating the vapors therein-to a conversion temperaturesuited to the formation of the above mentioned

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