US2158811A - Conversion of hydrocarbon oils - Google Patents

Description

May 16, 1939. J. G. ALTHER CONVERSION OF HYDROCARBON OILS Filed Nov. 30, 1936 liw/wzfort' Ja /1 Gilt/Mr ,y lee Patented May 16, 1939 UNITED STATES PATENT OFFICE CONVERSION OF HYDROCARBON OILS Application November 30, 1936, Serial No. 113,429

7 Claims.

This is a continuation in part of my co-pending application Serial No. 355,704, filed April 17, 1929, now Patent No. 2,091,261.

This invention relates to improvements in a process for hydrocarbon oil conversion and refers more particularly to improvements designed for the efiicient cracking of hydrocarbon oils to convert and produce therefrom products having higher commercial value.

The utility of the invention as well as many objects and advantages thereof will be brought out in the following description.

The principal object of the invention is to subject hydrocarbon oil to such conditions of temperature and pressure as to produce maximum yields of low-boiling products suitable for use as motor fuel with a relatively small production of coke and gas.

Another object is to provide, in a cracking process and apparatus, steps and means whereby it is possible to approach dry distillation.

Another object is to carry out the operation in such manner as to cause the non-vaporous residue or coke to accumulate in a low pressure zone.

Another object is to provide for lowering the reflux ratio by making it possible to convert a greater proportion of the charging stock per pass through the system. This is of particular importance in effecting the capacity and thermal efficiency of the process.

In one type of operation practised commercially on a large scale, the conditions of operation are so controlled as to mainly produce a gasoline-like product suitable for use as motor fuel, which is the desired product of conversion, and a substantially solid coke-like residue. Such operation is commonly called the non-residuum type of operation, the expression residuum in such instance meaning liquid residue. The operation is carried out in a tube and chamber type of apparatus wherein the oil is heated to cracking temperature at superatmospheric pressure in the tube bank or cracking coil and discharged into a chamber, also operated at substantial superatmospheric pressure, wherein conversion continues and separation takes place between the light and heavier reaction products, the latter being'reduced to coke in the chamber.

In a conventional non-residuum type of operation it is possible to approach dry distillation in the chamber leaving only a coke-like residue of low volatility due, in part, to the large amount of time given to the heavy material in the chamber under the high temperature and high pressure conditions maintained therein, whereby cracking, polymerization and distillation proceed simultaneously and reduction of the residue to substantially dry coke is accomplished. This could, obviously, not be done if it were not for the fact that a large amount of heat is constantly supplied to the drum by the incoming oil to carry on the reactions.

As is now well known, due to the polymerizing and cracking reactions which occur under the conditions maintained in the coking zone, the conventional non-residuum type of operation produces a high yield of coke, decreasing the actual onstream time and the yield of lighter, more desirable products. To obviate this disadvantage and still obtain fairly high yields of motor fuel, the liquid conversion products from the high pressure reaction chamber of a cracking system are now often flash distilled in a separate unheated zone, operated at substantially reduced pressure and commonly termed a flash chamber, wherefrom the heavy liquid residue which remains unvaporized by the flash distillation is recovered. A flashing operation of this type has advantages as well as disadvantages, one of the advantages being a long time onstream before shutting down due to the relatively small amount of coke formation and the production of liquid residue, which is continuously removed from the system. Some of the disadvantages are a somewhat decreased gasoline yield, as compared with a non-residuum operation, and a relatively high yield of liquid residue or fuel oil, which is, of course, not as valuable as gasoline and may not find a ready market.

In the non-residuum type of operation, there stantially all of the desirable volatile matter is removed from the chamber through the vapor line and what remains in the chamber is substantially a solid. The flashing operation is different-a relatively lower percentage of the oil leaving the pressure chamber leaves that zone through the vapor line in the form of vapors and an additional quantity of desirable low-boiling products is withdrawn with the heavier oil from the bottom of the pressure chamber and discharged into the reduced pressure flash chamber where,due to the pressure reduction, latent heat is liberated from the oil and utilized to carry on vaporization of the desirable low-boiling frac tions with a minimum of cracking and polymerization in the reduced pressure zone.

From the foregoing it will be apparent that there is a distillation (involving cracking and polymerization) in the pressure chamber and a is practically a complete distillation, that is, subsecond distillation (Without substantial cracking and polymerization) in the reduced pressure flash chamber". Obviously the liquid residue recovered from the flash distilling operation will contain vapcrizable components which, in the non-residuum type of operation are subjected to further cracking for the production of additional yields of gasoline and, whereas the nonresiduum operation involves excessive cracking and polymerization in the high pressure chamber, resulting in the excessive production of coke, the flashing operation produces higher yields of residual products at the expense of the more valuable light distillate product.

The purpose of the present invention is to embody, in an eflicient process, the desirable features of the non-residuum and flashing types of operation, the conditions being so controlled in the flash chamber as to produce a lower yield of substantially dry coke as compared with the non-residuum type of operation and a higher yield of low-boiling material, such as gasoline, the yield of the latter being even higher, in most cases than that produced in the non-residuum operation.

Another purpose of the invention resides in the employment of means to increase the decomposition of both the vapors and liquid from the pressure chamber under independently controlled conditions designed to accomplish the best results. This feature not only has the effect of increasing the yields of lighter hydrocarbons obtained from the operation but also improves their quality, especially for use as gasoline, in that they are of higher anti-knock value.

The pressures on the high pressure reaction chamber may be substantially that of the coil outlet or lower, but in the preferable operation this pressure should be as high as possible, without substantial coke formation in this zone, in order to increase the capacity of the unit and raise the thermal efliciency of the process.

Briefly, the process of the present invention is as follows:

The charging stock plus reflux will be pumped through a furnace having a heating coil from which the heated oil may be transferred to a high pressure reaction chamber. This chamber may be unheated but lagged against excessive radiation losses. vaporization and cracking takes place in the chamber, from which vapors may be withdrawn separately from the liquid products and passed to a fractionator or,preferab1y through a vapor heating coil wherein they are further cracked and then into a zone of lower pressure into which residual oil from the reaction chamber will be directed. In certain operations, either when the vapors are not subjected to further cracking or are not supplied to the low pressure chamber, and/ or when additional cracking of the liquid residue is desired, additional heat may be supplied to the latter before it enters the low pressure chamber. In any case the liquid residue from the reaction chamber is supplied with additional heat within or prior to its introduction into the low pressure chamber for the purpose of effecting its reduction to coke in this zone.

From this point on the usual operation takes place, i. e., all the vapors from the flashing still are directed to a fractionator wherein their sufficiently converted fractions are separated from their insufiiciently converted fractions or heavy ends, which latter are condensed as reflux condensate by contact in the fractionator with incoming cold raw oil or other cooling medium,

said reflux being returned to the cracking coil for retreatment.

From the foregoing it will be appreciated that one of the fundamentals of the invention requires that coke or carbon formed in producing a maximum yield of gasoline is formed outside of the pressure zone.

In order to more clearly understand the invention, I have shown the accompanying drawing, which is a diagrammatic View, but not to scale, of an apparatus suitable for carrying out the invention.

Referring to the drawing and to the operation of the process, oil to be treated is directed through line I and valve 3 into heating coil l located in a furnace 5.

In heating coil 4 the oil is heated to a temperature within the cracking range under a suitable pressure. The amount of oil passed through the coil per unit time and the size of the apparatus are so correlated that, under the temperature and pressure used, the degree of cracking obtained in the heating coil is preferably short of that at which substantial formation of coke and sludge-like matter occurs.

The heated oil is directed from coil 4 through line 8 and valve 9 into chamber ll].

Chamber Ii] may take any desired form and size in relation to the capacity of the apparatus. It may be unheated and insulated against loss of heat by radiation or it may be heated, by well known means not illustrated, for the purpose of maintaining the material in chamber II] at the proper temperature, preferably not substantially higher than the temperature at which the oil is discharged from heating coil 4.

While, for the treatment of most oils, it may be desirable not to raise the temperature of the materials entering chamber It] to a temperature substantially higher than that prevailing at the discharge of the heating coil 4, this is not to be taken as a limitation, since charging stocks, particularly the lighter ones, may be heated in chamber H] to a temperature above that prevailing at the discharge of coil 4. On the other hand, particularly for the heavier charging stocks and depending upon the limitations imposed upon the amount of coke and sludge to be formed or contained in the products, it may be desirable to maintain the materials in chamber In at a lower temperature and/or pressure than that reached at the discharge of heating coil 4 to decrease the rate at which the reaction proceeds in chamber Ii). To this end chamber I8 may be unheated or the oil may be cooled in a manner hereinafter described.

The vapors pass out of chamber it) through line I!) having valve 20 to fractionator 2|. As a feature of the invention I may subject all or part of the vapors removed from chamber to additional heating at elevated temperature to effect a controlled degree of so-called vapor-phase cracking whereby I am enabled to produce lighter valuable distillates having the characteristics of motor fuels or gasoline, possessing high antiknock properties due to the presence of controlled proportions of aromatic and unsaturated hydrocarbons formed by said vapor cracking.

For this purpose a vapor coil 22 may be positioned in furnace 5 and located therein in such a manner that the combustion gases pass over coil 22 before passing over coil 4. In this manner and because the combustion gases passing over coil 22 are at a higher temperature than when they pass over coil 4, a greater degree of radiant heat may be utilized in coil 22 than in cont: Coil 22 may be connected to vapor line l9 throughbr'anches 23 and 24, controlled respectively by valves 25 and 26. By proper regulationof va'lves'ZO, 25 and'26, any desiredamount or vapors separated in chamber In may be passed through the'vapor' heating coil 22.

Referring now to the fractionator 2|, the vapors remaining uncondensed therein leave the upper part thereof through line 21, having valve 28, through condenser 29 and thence to receiver 30. Receiver 30 is provided with the usual gas release line 3|, having valve 32, and distillate release line 33, having valve 34. A' portion of the distillate collected in receiver 30 may be returned, by well known means not illustrated, to the upper portion'offractionator 2|, to serve as a cooling and refluxing medium in this zone.

Provision is made for diverting regulated quantitles of the vapors from line I9 through line It!) and valve IOI and introducing the same into chamber 54, by m ans of valves 51, eitherabove or below the' liquid level maintained therein. If full advantage of the partial pressure effect of these vapors and their heat content is to be obtained they should enter chamber 54 at a relatively low point therein and pass upwardly through the material undergoing coking in this zone to increase vaporization and assist the coking operation.

The reflux condensate formed in fr-actionator 2| may be withdrawn from the bottom thereof through line 39, in which may be interposed a hot oil pump 40 and valve 42, and through which said reflux condensate may be directed to the main feed line whereby it may be returned for retreatment to the heating tubes 4 with a supply of fresh charging stock.

Raw oil to be treated in the process may be drawn from suitable storage tanks (not shown) through line 43 and pump'44. From line 43 and by suitable control of the valves shown, all or a portion of the raw oil to be trfeated in the process may be diverted through line 45, having valve 46, then to line4'l which connects with the main feed line I, whereby all or a portion of the charging stock may be fed directly to the heating tubes 4, mixing before entering therein with reflux condensate, directed through line 39. Or, all or a portion of the raw oil may be diverted from line 43 through branch 48, having valve 49, and then through line 50 from which it may be directed to the dephlegmator 2| to help fractionate the vapors therein. Raw oil fed to dephlegmator 2| is thereby preheated and mixed with reflux condensate and the mixture may be directed to the heating coil 4, through lines 39 and I as heretofore described. If desired, the line 511 may terminate in a closed coil (not shown) connected at its dischargeend tothe' feed lines 39 or 4'! instead of mixing directly with the vapors. I have discovered thatw hen the degree of conversion obtained in the cracking zone, such as heating coil 4 and chamber I 0, is so controlled that the heavier liquidproducts separated thereindo not contain more than, ordinarily, 5 percent and preferably less than 2 percent, of sludge or coke-like materials, as may be determined by so-called benzol centrifuge method, said heavier liquid products comprise a substantial proportionoffraotions, which, when separated from such solids or sludge like materials under proper conditions, may be subjected advantageously to additional conversion forthe formation of substantial additional yields of motor fuel. This may be effected by regulating the conditions in coil 4an'd'ch-amberl0, or by subjecting the heavier liquidproducts withdrawn from chamber ID to such additional treatment, as will hereinafter be described, that a so-called dry distillation thereof is effected, leaving in the zone of distillation a substantially solid residue, the remaining fractions having been vaporized to produce a material which may be advantageously subjected to additional cracking.

The heavier liquid products are withdrawn preferably from the bottom of chamber I0 through line 5| and may be directed through valves 52 and 53 in this line into chamber 54.

I By means of the pressure reduction obtained by proper control of valves shown, a large portion of said unvaporized liquid products may be vaporized in Chamber 54. Depending upon the conditions under which the operation is carried out and upon the charging stock used, such reduction in pressure may be sufficient to distill or vaporize said heavier liquid products substantiallyto dryness by means of the self-contained heat. However, I have found that generally this self-contained heat is not sufficient and in a majority of cases it is necessary to supply additional heat to the heavy liquid products withdrawn from the reaction zone, before and/or during their flash distillation, in order to obtain vaporization thereof to substantial dryness.

Accordingly one of the features of the invention of this application, as distinguished from my companion applications, Serial Nos. 113,427, 113,428 and 113,430, filed on even date herewith provides for directing any desired portion or all of the" heavier liquid products withdrawn from the reaction having valves a heating coil zone It! through branch lines 55, 56 interposed therein, and through 58 located in furnace 5.

It is desirable to regulate theheating of the heavier liquid products of reaction in such a manner that, while they receive the necessary additional heat to cause substantially dry distillation by simultaneous or subsequent reduction of pressure, at the same time the additional heat treatment to which such products are subjected does not cause sufficient additional cracking thereof to effect the formation of an excessive amount of sludge or coke-like constituents in the heating coil.

Therefore, the heating coil 58, in which the heavier products of reaction receive additional heat, may be located in furnace 5, at such a point that rapid heat transfer takes place, so that the amount of heat required may be transmitted'to the heavier liquid products of reaction in the shortest possible time. In this manner I materially decrease the additional cracking and polymerization to which such products are subjected in the heating coil as compared with that obtained with lower rates of heating and more prolonged time in this zone. For this purpose I have shown, in the drawing, the heating coil 58 positioned near the hottest part of furnace 5, whereby, With the help of intense radiant heat and high temperature combustion gases and nonvaporized products withdrawn from chamber ll! may be raised rapidly to the required temperature.

The sizes of heating coil 58 must be carefully "proportioned relative to the amount of materials to be fed therethrough and the degree of heat transfer employed therein. To assist in theregulatiQn oi the heat transfer in heating coil 4, vapor coil 22 and coil 58 respectively,

which may be more or less independent of each other, I may provide furnace 5 with such means as are well known to regulate the temperature and the amount of combustion gases therein. Such means are, for instance, flue gas recirculation, superheated steam injection and additional burners properly located in furnace 5. Such additional means have not been shown on the attached drawing, as I believe they are well known and would simply complicate the drawing.

By the proper control of the degree of reaction obtained in the zones 4 and I0 and by proper control of valves 52 and 56, as well as by the control of the heat transfer to coil 58 more or less independently of the heat transfer to the other coils shown, as heretofore explained, any desired additional amount of heat may be given to the heavier liquid products withdrawn from chamber In in the shortest possible time. In this manner, and coupled with proper control of the degree of reduction of pressure to which said heavier liquid products may be subjected by means of either valves 52, 56 or 53, substantially dry distillation of said heavier liquid products is effected in chamber 54 without excessively increasing the comparative amount of coke formed in the process. Coke formed in the operation of the process and deposited in chamber 54 may be removed therefrom through top or bottom manholes in the usual manner (not illustrated) One of the principal features of this invention resides in depositing the bulk of the carbon or coke outside the zone of high pressure. This permits the use of much cheaper equipment and minimizes the danger of explosion.

It is to be understood that the preferred method of operation is of the low level type, wherein a minimum quantity of residual oil is maintained in chamber 10. That is, residual oil is withdrawn from chamber 10 before it has had sufficient time to form more than 5 percent or thereabouts of sludge or coke-like constituents.

Vapors separated in chamber 54 may be removed therefrom through line 66 having valve 61 wherefrom they may be passed, by well known means not illustrated, directly to condensing and collecting means of well known form, not shown, and may thence be removed from the process or returned, in part, to the heating zone for retreatment. However, as shown in the drawing, the Vapors from chamber 54 are preferably supplied to fractionator 69, wherein they are subjected to controlled partial condensation by introducing a suitable cooling medium into this zone through line 10 having valve 1|; or raw oil to be charged to the process may be diverted from line 43 through line 12, having valve 13, and introduced into column 69 to assist cooling and fractionation therein.

Vapors uncondensed in column 69 may be removed therefrom through upper draw-off line 14, having valve 15, and passed through condenser 16 to receiver 11 which has the usual gas release valve 18 and distillate release valve 19.

The fractions of the vapors condensed in column 69, comprising reflux condensate, may be discharged from the bottom thereof through line 89, in which may be interposed pump 8|. Thence, they may be diverted through branch 82 having valve 83, which connects with line 58, whereby said fractions may be returned via fractionator 2| to further cracking in coil 4. Or, the fractions condensed in tower 59 may be passed through branch 84, having valve 85, connected with feed line 41, whereby said fractions may be returned directly to heating coil 4.

It will be apparent from the drawing that by suitable control of valves 13, 49, 46, 85 and 83, any desired proportion of fresh raw oil or of materials withdrawn from the bottom of tower 69, independently of each other, or together, may be directed to dephlegmator 21 or to the heating coil 4.

It may be desirable to control the degrees of reaction taking place in heating coil 4, chamber l8 and vapor coil 22, respectively, by controlling the temperature, characteristics and quantity of the material passing through these respective zones. For instance it may be desirable to introduce into the stream of heated products passing from heating coil 4 to chamber 10 a regulated portion or all of the hydrocarbon oil charging stock for the process or liquid products such as condensates from other parts of the system. It may be desirable to introduce one or more various oils such as charging stock and/or reflux condensate from iractionator 2| or fractionator 69 into the stream of vaporous products passing from chamber IE) to heating coil 22. To accomplish this, oil, comprising either reflux condensate from fractionator 69 or charging stock from line 43 or a mix ture of the two, may be diverted from line 41 through line 98 and valve 98' into line l9, while oil from line 39, comprising either reflux condensate from fractionator 2! or a mixture of the same with charging stock supplied to this zone, may be diverted through line 88 and valve 89 into line 80 and introduced into line I6. In a similar manner oil from line 39 may be directed through valve 86 and line 81 into line 3 or oil from line 4"! may be directed through line 86' and valve 81' into line 86 and thence into line 8.

While I have diagrammatically indicated in the drawing specific types of construction for the various parts of the apparatus, it is to be understood that other forms of apparatus and other types of construction may be used for such parts. For instance, a vapor-phase cracking chamber, suitably heated, may be substituted for the vapor heating coil 22. A so-called soaking coil or digestion chamber may be substituted for chamber 50, preferably with a separating chamber following the soaking coil or digestion chamber. As another modification it may be desirable to interpose a separator in the discharge line from vapor heating coil 22 or its equivalent, whereby heavy liquid products of polymerization and cracking formed in coil 22 may be separated from the vapors before introducing the latter into fractionator 2 I.

While I have illustrated a specific arrangement of the various heating coils of the process and a specific construction for furnace 5 it is entirely within the scope of the invention to use other arrangements of these parts providing that such alternative arrangements permit operation of the process for the purpose and with the desired results heretofore mentioned. For example, each of the heating coils 4, 22 and 58 may be disposed in separate furnaces or independently heated zones of the same furnace, in which case the furnace or heating zone in which coil 22 and coil 58 are located are preferably of such type as will permit the use of rapid heat transfer rates such as caused by the use of intense radiant heat. On the other hand heating zones 4, 22 and 58 or their equivalents may be positioned in separate heating chambers wherein, in addition to or independently aiisaii of heat which may be produced by burners, the products of combustion which leave the heating zonesmaintained at relatively high temperatures may be utilized as a part or all of the heating medium for the zones maintained at lower temperatures.

As an illustration of the temperature and pressure conditions which may be employed in an apparatus such as illustrated to accomplish the desired results, the oil supplied to heating coil 4 may be subjected to a temperature, measured at the outlet from this zone, of from 850 to 960 F; or thereabouts, preferably at a superatmospheric pressureof from 100 to 500 pounds, or more, per square inch. Substantially the same or somewhat lower temperatures and/or pressure conditions may be maintained in chamber l and the materials supplied to heating coil 22 may be heated, for example, to a temperature of from 950 to 1100 F., or thereabouts, at substantially the same or lower pressure than that maintained in chamber Ill. The heavy liquid products removed from chamber ID may be passed through coil 58 and quickly heated to a temperature ranging, for example, from 925 to 1050 F. and thence introduced into chamber 3, without allowing the oil suflicient time in the heating coil and communieating lines to permit any substantial formation and deposition of coke therein. The pressure maintained at the outlet from heating coil 58 may range from substantially the same as that employed in chamber l0 down to substantially atmospheric or a low superatmospheric pressure of, for example, 25 pounds, or thereabouts, per square inch. The pressure maintained in chamber 5 may be substantially the same or somewhat lower than that employed at the outlet from heating coil 58 and preferably is substantially lower than the pressure maintained in chamber Ill. The fractionating, condensing and collecting portions of the system may employ pressures substantially the same or somewhat lower than the pressure employed in the preceding equipment.

As a specific example of an operation of the process as it may be conducted in an apparatus such as illustrated and above described, the charging stock, which is a Mid-continent topped crude of approximately 25 A. P. I. gravity, is supplied, together with reflux condensate from fractionator 69, to heating coil l from which the heated products are discharged into chamber II! at a temperature of approximately 940 F. and at a superatmospheric pressure of approximately 500 pounds per square inch. Chamber l0 and heating coil 22 are maintained at approximately this same pressure. Vaporous and liquid conversion products are separately Withdrawn from chamber ill, the vapors passing through heating coil 22 wherein they are maintained at a substantially'uniform temperature of approximately 975 F. While the liquid products are quickly heated in coil 58 to a temperature of approximately 950 F. at a superatmospheric pressure of about 75 pounds per square inch, the heated products from coil 58 being introduced into the upper portion of chamber 54 and the heated products from coil 22 being introduced into the lower portion of this zone. Chamber 56 is maintained at a superatmospheric pressure of approximately 50 pounds per square inch and the residual product produced in this zone is substantially dry coke. Vaporous products from chamber 54 are subjected to fractionation in iractionator 69 wherefrom reflux condensate is returned to heating coil 4 while the overhead vaporous products from fractionator 69,

5 comprising distillate of good antiknock value within the, boiling range of gasoline and gaseous products of theprocess, ,are passed through condenser 16 into receiver 17 wherefrom the distillate and uncondensed gases are separately recovered.

The above described operation will yield, per lprarrel of charging stock, approximately 65 percent of,400 F. end-point gasoline having an octane number, by the motor method, of approximately 72 and approximately '70 pounds of low volatile coke, suitable for sale as domestic fuel, the remainder being chargeable principally to uncondensable gas. v

I claim as my invention:

1 A process for the pyrolytic conversion of hydrocarbon oils which comprises cracking an oil at elevated temperature and substantial superatriiospheric pressure in a heating coil and comniiihicating enlarged reaction chamber, separately r'e'rrio'ving resultant vaporous and liquid conversion products from the reaction chamber, quick- 1y reheating said liquid conversion products separately'iwithdrawn from the reaction chamber to a sufll ci'ently high temperature, in a separate heatmg coil, to inducetheir subsequentreduction to coke, introducing the reheatedmaterialsiinto a coking zone operated at substantially reduced pressure relative to that employed in thereaction chamber wherein their reduction to coke is eff'e'cted, independentlyheating vaporous products removed from the reaction chamber to vapor phase cracking temperature and then introducing thes'ame to the coking zone to assist the coking operation, removing vaporous products from the coking zone and subjecting the same to said fracticnation subjecting fractionated vapors of the desired boiling point to condensation, recovering and separating the resulting distillate and gas iiidreturhihg reflux condensate formed by said fractionation, to .the for, further cracking. 25A process for the pyrolytic conversion of hydrocarbon oils which comprises subjecting an oil to cracking conditions of elevated temperature the products, separately subjecting said vaporous and liquid products each to additional independently controlled cracking conditionsv of temperature and pressure, commingling heated products from both of the last mentioned heating operations and reducing their non-vaporous residual components o coke, subjecting the vaporous components of the commingled products to fractionation for the formation of reflux condensate, subjecting fractionated vapors of the desired endboiling point, comprising materials of good antiknock value within the boiling range of gasoline, to condensation and recovering the resulting distillate.

3. A process for the pyrolytic conversion of hydrocarbon coils which comprises subjecting an oil to cracking conditions of elevated temperature and superatmosp-heric pressure, separating the resultant vaporous and liquid conversion products, separately subjecting said vaporous and liquid products each to additional independently controlled cracking conditions of temperature and pressure, commingling heated products of both of the last mentioned heating operations and reducing their non-vaporous residual components to coke, subjecting the vaporous components of the commin-gled products to fractionation for the formation of reflux condensate, returning reflux condensate formed by said fractionation to the first-mentioned heating coil first mentioned cracking step, subjecting fractionated vapors of the desired end-boiling point, comprising materials of good antiknock value within the boiling range of gasoline, to condensation and recovering the resulting distillate.

4. A process for the pyrolytic conversion of hydrocarbon oils which comprises subjecting hydrocarbon oil charging stock to conversion conditions of cracking temperature and substantial superatmospheric pressure in a heating coil and communicating enlarged reaction chamber, separately removing resultantvaporous and liquid conversion products from the reaction chamber, subjecting liquid products thus withdrawn from the reaction chamber to additional heating in a separate heating coil, introducing the heated oil from said separate heating coil into a coking zone, subjecting vaporous products Withdrawn from said reaction chamber to additional cracking in another separate heating coil, introducing heated products discharged from the last mentioned heating coil into the coking zone wherein they commingle with the residual materials supplied thereto and assist their reduction to coke, removing vaporous products from the coking zone and subjecting the same to fractionation for the formation of reflux condensate, subjecting fractionated vapors of the desired end-boiling point to condensation and recovering the resulting distillate comprising materials of good antiknock value within the boiling range of gasoline.

5. A conversion process which comprises subjecting hydrocarbon oil to cracking conditions of temperature and pressure in a heating coil and separating resultant products into vapors and unvaporized oil in an enlarged chamber, removing unvaporized oil from the chamber and heating the same to cracking temperature under pressure in a second heating coil and then distilling the same to coke in a second chamber, separately removing vapors from the first-named chamber and heating the same to vapor phase cracking temperature independently of the first-mentioned oil and said unvaporized oil, discharging heated products of the last-mentioned heating step into the second chamber to assist the coking operation therein, removing vapors from the second chamber and fractionating and condensing the same.

6. In the conversion of hydrocarbon oil wherein the oil is cracked under pressure in a cracking zone and hydrocarbon vapors and residual liquid separately withdrawn from said zone, the method which comprises passing the residual liquid through a heating coil and heating the same therein to cracking temperature under pressure, discharging the heated products from said coil into a reduced pressue coking zone and reducing the same to coke therein, passing hydrocarbons removed as vapor from the cracking zone through a separate heating coil and therein heating the same to higher temperature than the oil in the cracking zone and the first-named coil, discharging heated products from said separate coil into the coking zone to assist the coking operation therein, removing vapors from the coking zone and iractionating and condensing the same.

7. A conversion process Which comprises heating hydrocarbon oil in a heating coil sufliciently to vaporize a substantial portion thereof and separating the same into vapors and unvaporized oil in an enlarged chamber, removing unvaporized oil from the chamber and heating the same to cracking temperature under pressure in a second heating coil and then distilling the same to coke in a second chamber, separately removing vapors from the first-named chamber and heating the same to vapor phase cracking temperature independently of the first-mentioned oil and said unvaporized oil, discharging heated products of the last-mentioned heating step into the second chamber to assist the coking operation therein, removing vapors from the second chamber and fractionating and condensing the same.

JOSEPH G. ALTHER.

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