US2115144A - Method for cracking oils in vapor phase - Google Patents

Description

April 26, 1938. P. c. KEn'H, JR 2,115,144

I I METHOD FOR CRACKING OILS IN VAPOR PHASE Original Filed Deo. l, 1928 SISheets-Sheet 1 ATTORNEY 26, p. Q KEW-Hl JR METHOD FOR CRACKING OILS IN YAPR PHASE original Filed Dec. 1, 192eV 209 8 I 225 .sou/ENT EXTRAcTia 2/0 226/ 2l! 10 FRAcn'oNAv-mu .2,2 6 1l #had 9 225 2 725:5 2,4( EZL 1 222 2/6-- :sai INVENTOR 2/7 220 224 PERcv c.KE|TH JR. i :,114 r wwf/AM FRACTIONATION ATTORNEY s sheets-smeet 2 April-26, 1938. P. c. KEITH, JR

METHOD FOR CRACKING OILS IN yVAPOR PHASE 5 Sheets-Sheet 3 R. M mm n Tn E #m v. T mC A m M R D n m rVN f com (fmm Patented Apr. 26, 1938 UNlTEo STATES PATE-NT OFFICE Percy C. Keith, Jr., Peapack, N. J., assignor to Gasoline Products Company,

Incorporated,

Newark, N. J., a corporation of Delaware Original application December 1, 1928, Serial No.

Divided and this application November 9, 1933, Serial No. 697,282

6 Claims.

This invention relates to the pyrogenesis of petroleum oils and is a division of application Serial No. 323,005 led December 1, 1928. The invention will be fully explained in the following description and accompanying drawings, in

which:

Fig. 1 is a diagrammatic representation of a preferred embodiment of apparatus in which my process may be carried out;

Fig. 2 is a diagrammatic representation of an alternative form; p

Fig. 3 is a Vertical section through a form of apparatus which may be employed in conjunction with my process;

Fig. 4 -is a cross section taken on the line 4-4 of Fig. 5;

Fig. 5 is a side elevation with parts in section of a form of apparatus employed in conjunction with my process and with the apparatus shown in Figs. 3 and 4;

Fig. 6 is a diagrammatic representation of apparatus for applying a selective solvent treat. ment to my process; and

Fig. l is a diagrammatic representation of an alternative arrangement of apparatus for applying the solvent treatment.

The pyrogenesis of petroleum oils for production of oils of lower boiling point is carried out by heating crude petroleum, or suchof its distillates as may economically be utilized in this manner, to cracking temperatures with or without pressure. The fraction intermediate between kerosene and lubricating oils known as gas oil is frequently utilized for this purpose because of its lesser market value, although kerosene, lubricating oil fractions and fuel Oils are also employed at times. The fractions so employed are composed of an extended range of compounds as indicated by the range of molecular weights and boiling points. The conglomerate of compounds is subjected to cracking conditions until a certain quantity of material falling within a desired boiling range is produced. Simultaneously with the formation of this product, or products, materials are produced which do not fall within the desired range, for example, when cracking to produce a substantial proportion of gasoline which is a product composed of a large variety of different hydrocarbon compounds, there is simultaneously produced a quantity of tarry and coky materials. Some elements of a conglomerate stock, for reasons which will be given more fully later, require cracking to a degree less than others, and because of the fact that the stock as a whole is subjected to the same conditions the cracking reaction Will be carried too far in the case of some of the constituents of the stock in order to secure the desired quantity of material of a predetermined boiling point range and with the resultant formation of compounds which do not fall within the said range or which are deleterious to the operation, for reasons which will be more fully pointed out. The different cracking rates of some of the constituents of the stock tend to accentuate the condition referred to above. I have discovered that a fundamental increase in the efciency of kthe cracking process may be obtained by separating the cracking stock into a number of distinct fractions of different boiling point ranges and thereafter cracking the individual fractions so generated. I prefer to obtain as nearly as possible, having regard to the conditions imposed by practice, a number of charging Stocks all the constituents of each of which will respond in the Same degree to the conditions to which each of the stocks is subjected. I preferably apply to each such fraction the degree of time, temperature, and/or pressure necessary to its optimum conversion into desired products. These conditions may in any case be determined by preliminary tests. Thus, when conditions have been established by such tests as to yield the Same quantity of desired end products from a series of segregated fractions as is obtainable from cracking conglomerate stock the concomitant loss in gas and/or tarry or coky materials is diminished, or for an equivalent loss the yieldy of the desired end products is relatively increased.

My process is applicable generally in the pyrogenesis of petroleum oils to produce lower boiling point oils, as, for example, cracking to produce either gas, gasoline, kerosene, gas oil or lubricating oil from stocks of respectively higher boiling point.

In the ideal embodiment of my` process the stock is segregated into `a plurality of charging stocks of such character that under the condi-4 tions .of heat, time, and pressure imposed cracking of the various individual compounds composing the fraction will take place at substantially the same rate. However, the limitations imposed by practice require segregation into a Smaller number of stocks than in the ideal method and I therefore segregate into an appropriate number of charging stocks and subject each of such stocks to optimum conditions for the particular segregate.

I have discovered that in high molecular weight hydrocarbons of straight chain structure the inltial scission on cracking frequently occurs adjacent the center of the molecular chain. In one application in my process I aim to obtain by cracking the products of first scission of the molecule, and I therefore prepare charging stocks f which upon their initial scission yield products which fall within the range of physical characteristics of the material desired to be obtained. Thus in the case of gasoline I may proceed by dividing my charging stock into a number of fractions each of which has a molecular weight substantially twice that of a constituent of gasoline, then by cracking the stocks to the extent of one scission I obtain a number of products whose molecular weights fall within the range of molecular weights of the constituents of gasoline. In cases in which the original charging stock contains constituents so heavy that the products of their initial scission will not fall within the range of physical characteristics of the desired products, these constituents may be separated from the remainder of the original charging stock, as by distillation, and treated in one of two ways; i. e. (1) by segregating them from one another as by distillation into individual fractions and then subjecting ea'ch segregated fraction to such conditions as will produce from each segregated fraction a product which will yield, upon refractionation, products which may be decomposed as above into gasoline constituents. This procedure enables me to separate unsaturated constituents to a degree and to then subject such fractions to appropriate treatment. (2) In view of the limitations of practice I may subject the entire heavier 'conglomerate cut to cracking conditions best suitedto obtain the maximum yield of products which can be segregated into charging stocks of the nature described and cracked in the manner above set forth so as to yield gasoline constituents.

Alternatively, I may prepare a number of fractions of charging stock, including some which cannot be converted by a single scission adjacent the center of the molecule into products falling within the desired range, and subject each such fraction to the degree of time, temperature and pressure necessary lto its conversion into products of the desired boiling point range. I

may, however, in such cases crack each such fraction to yield a cracked material having a position with respect to the average molecular weight of the series of cracked materials obtained which corresponds to the position held by the parent fraction-with respect to the other members of the parent series.

In addition to the foregoing I may make a vfurther separation based on chemical characteristics. Thus, I may separate the original cracking stock into two fractions, one containing a preponderance of saturates and theother containing a preponderance of aromatics and unsaturates, as, Afor example, by the application of selective treatment with liquid sulphur dioxide. These individual products may thereafter be separated each into products of different boiling point ranges to be separately cracked as hereinabove described. Alternatively, the fractions of separate boiling point ranges may be first prepared and each thereafter separated-into fractions of different chemical characteristics, as, for example, by treatment with liquid sulphur dioxide. l

In any event, where several fractions of the original charging stock are prepared, as by distillation, the decomposition products rom the several fractions will preferably have average molecular weights whose ratio to each other is approximately the same as the ratio of molecular weights of the parent fractions. For example. in cracking gas oil to produce gasoline the gas oil may be segregated by fractionation into a series of several cuts, each of which has of constituents boiling within a different 50 F. range. T'he average molecular weights of these fractions are in some ratio to their boiling points, the fraction of relatively high boiling point having the highest molecular weight. In cracking these individual fractions conditions are adjusted to produce a series of cracked products havingthe same general relationship. Thus, the fractions of lower average molecular weight will have been cracked to produce a cracked material of lower average molecular weight than will havebeen produced from the parent fractions of relatively higher molecular weight. In this way the lighter constituents of the end product gasoline will have been predominantly produced from those fractions of the cracking stock of lower molecular weight, whereas those fractions of the gasoline of relatively higher molecular weight will have been predominantly produced from the fractions of cracking stock of relatively higher molecular weight.

I achieve a number of distinct advantages by this process, for example, the cracking is carried out on each of the individual cuts under conditions which may be predetermined in view of the rate of dissociation of the particular stock to produce the optimum conversion, while the total number of dissociations or the degree of pyrogenesis to produce any given yield of end product is relatively less than would be necessary with the indiscriminate cracking of a -conglomerate stock, and thus the concomitant losses in gas and/or tar or coke are greatly diminished. A further distinct advantage is that polymerization to form products of a greater molecular weight than the parent stock does not occur to the'same degree as when cracking a conglomerate stock. It is unnecessary to carry the cracking reaction on some of the constituents of the original stock to the-point of forming polymers of a character deleterious to the operation of the process. Thus, in operating upon a conglomerate stock in the manner used at the present time it may be unavoidable to carry the cracking reaction to the point of third, fourth, fifth or higher scission in the case of some of the constituents of the initial charge and to the scission'of polymerized products formed therefrom in order to obtain the desired yield of the end product, whereas inmy process I prefer to confine the reaction to the formation of the products of scission of a lower order. 'I'he scissions of higher order result in an increase in the products of decomposition, or polymerization, which contributes to the formation of the products known as tar and coke. Y

One of the preferred methods of operating my process is to crack each individual cut of the cracking stock to produce a cracked material having an average molecular weight substantiallyv half of 'that of the parent cut, for example, ranging from '75 to 25% ofthe average molecular weight ofthe parent cut. In this way, to an extent at least, with a single decomposition of the various' molecules composing the gas oil fraction. I am enabled to convert them into fractions of the gasoline series, and by working upon a series of individual fractions I am enabled to produce an entire series of products boiling within the l gasoline range with la minimum of individual molecular dissociations, or polymerization. The conditions outlined may, of course, be varied in view of the particular stock or in view of the particular characteristics of the product desired, as, for example, 'to produce a gasoline having a certain definite proportion of material boiling within a certain predetermined range.

The particular method of cracking the individual stocks may be any one of the methods at present employed or hereafter developed. I may, for example, crack these individual cuts in either liquid or vapor phase or in a combination of the two and under any degree of pressure. In a preferred embodiment of my invention, however, I subject the individual cuts to a vapor phase cracking of relatively short duration ranging, for example, from the order of one second up to times of the order of five minutes, at temperatures which may range between 750 and 1500 F. and at pressures which may range from a few atmospheres to partial vacuum. In this way I am enabled to eifect a carefully controlled dissociation of the individual stocks and accurately control the amount of dissociation applied to each of these stocks so that a large proportion of the individual cuts is subjected to a single dissociation, thereby automatically throwing it into the boiling pointv range of the desired end product with a minimum production of undesired products. A further advantage of this procedure that I have discovered is that owing to the relatively short times involved, the temperature range in which cracking is effected and the low specic volume of the gases in the cracking zone, the tendency to polymerization, or reformation of heavier products, is inhibited, the eiiciency oi the operation is increased and I am4 enabled to diminish the formation of tar and/or coke.

In ,determining the conditions under which individual cuts of the initial conglomerate charg-` ing stock are to be cracked consideration must be given to the formation of fixed gas. I believe that the theory at present held that fixed gas produced by a cracking operation is substantially produced by the cracking of tar to coke is mistaken and that in fact such fixed gas is substantially produced by the cracking of constituents falling within the gasoline range. I therefore so select the conditions of operation in the preferred form of my process as to prevent the cracking of such gasoline constituents, as, for example, by removing them from the zone of reaction as quickly as possible. In this respect my process is radically diierent from those at present practiced in which the products falling within the gasoline range, or some of them, are held in the zone of reaction for considerable periods of time. In the processes in use at the present time these products which are extant in the zone of reaction are either retained there by reason of the nature of the apparatus which does not permit of their evacuation immediately upon formation, or are retained there by reason of their solution in liquid since they are in contact with large bodies vof heavier liquid content in the system. This effect is considerably aggravated in many processes by the use of pressure. It will be noted that in my improved process because of the nature of the apparatus and the charging stock used there is substantially no liquid present in the-system at any time and the apparatus issuch that products falling within the gasoline range are removed substantially as quickly as formed.

The selection of the temperature bears a deflf boiler sections at intermediate points.

nite relation to the time element involved in the operation of the apparatus, the more rapid thev evacuation of the products from the zone of vreaction the higher the temperature which may be used, sufficient time being provided to permit the reaction to take place. The effect of removing the products from the zone of reaction is to arrest the reaction, and it may be desirable to cool immediately the products removed to prevent further reaction by reason of the contained heat.

My process will now be described with specific reference to the apparatus diagrammatically indicated in the drawings. Referring specifically to Fig. l a cracking stock such as gas oil is passed through the tubularl heater l, surrounded by the refractory setting 2, and heated by means of a burner such as 3 communicating with the setting throughthe port 4. Any alternative means of heating this stock to a temperature of complete or partial vaporization may be employed, such as a heat exchanger or a still. The partly vaporized cracking stock is delivered through the pipe 5 into the fractionating column 6. This column may be suitably insulated and provided with a number of rectifying devices such as the customary transverse partitions carrying down ow pipes and vapor contacting devices, not

shown. The design of this column is not a feature of the invention and any column or corresponding device which is appropriately designed to separate petroleum oil into a number of fractions by rectication may be alternatively employed. Provision is made for taking off an overhead cut in vapor phase from the column by means of the vapor outlet I and a number of side cuts (ordinarily in liquid phase, but which may be in the vapor phase) from the side outlets 8, 9, I0, Il, l2, i3, I4 and I5. The side cuts may be rectified or stripped in a secondary rectifying column, if desired,.to eliminate light ends, or, alternatively,A any other means for obtaining an enhanced degree of separation may be employed. Any bottoms or heavy ends formed in the column will be removed, preferably in a continuous fashion, by means of the bottom draw-oil I5A. The column may be supplied with cooling coil adjacent to the top or intermediate points and with a heating coil adjacent to the bottom or with re- All such modifications will be incorporated to the degree Anecessary to obtain the desired separation of the individual fractions. The cuts taken 01T through outlets .l to l5, inclusive, are, in view of the necessities of practice, relatively close cut fractions having, for example, 90% of constituents boiling within a 50 F. range, and while these `ranges to some extent overlap, the cuts represent a complete series of charging stocks, each of which approaches, within the limits of commercial practicability, an ideal charging stock as above defined. This series of cuts has a range of boiling points and corresponding molecular weights which increases throughout the series. These various cuts are passed to individual crackers through control apparatuses I6 to 23 inclusive which will be hereinafter more fully described, and from the control apparatuses thecuts pass respectively to the individual cracking apparatuses which have been diagrammatically indicated by the numerals 24 to 3|, inclusive. I may employ any form of cracking apparatus, such' as stills which may be adapted to operate under pressure or tubular kcrackers with or without reaction chambers or tubular stills operated in the vapor phase. In

any event, the cracking is carried out under conditions which may be ascertained in advance by tests to be suited to the individual cut. Preferably, when operating to make gasoline the individual cuts are cracked to such an extent that the average molecular weightoi the cracked ma-I molecular disruptions and recombinations than would be incidental to handling a cracking stock as a conglomerate. For convenience all .of the cracked materials discharged from the crackers 24 to 3|, inclusive, through outlets 32 to 39, in

` clusive, may be conducted by means of the mani.-

fold 48 into the rectifying column 4| which is of suitable construction to permit the separation thereof into the desired end product, as, for example, gasoline which may be taken off in vapor 25 phase, `1f desired, through the outlet 42, and a number of side cuts taken off through the side l outlets 43 to 50, inclusive. These side cuts taken olf through the outlets 43 to 50, inclusive, are prefe rab1y fractionated so that 90% of the constitil 0 uents of each cut boil within a range of 50 F.

and will be hereinafter more fully considered. The column 6 may be operated under any pressure at which appropriate fractionation may be secured, and for purposes of heat economy, is

preferably operated under a vpressure in excessy of atmospheric, say, for example, a pressure not exceeding 100 pounds per square inch. I achieve in this way the additional advantage that the cuts taken oi from the outlets 8 to I5, inclusive, may, in

this manner, be supplied by virtue of their initial pressure tothe respective cracking apparatuses 24 to 3|, inclusive. The column 4I may be operated under pressure preferably less than that obtaining in column 6 so that the progress of ma- 43 terial through the entire system is effected by virtue ofthe initial pressure obtaining in column 5. The side cuts from column 6 fall within the gas oil range and are such as may, to a large extent,'be converted into constituents boiling within the gasoline range, particularly where the cracking is so controlled as to produce molecular disruptions occurring at ornear the mid-point of the molecule.

The plant illustratedis only an approach to the ideal and some polymerization may occur to products whose molecular weight is higher than those taken off through the side outlets 8 to I5. inclusive, of column 6. Such polymerized products are preferably separately processed as outam linedin the preferred manner of processing the cut withdrawn through I5a, but for commercial reasons may be removed from column 4| through the side outlets 5I and diverted through pipe |5a to pipe I5b to be combined with and processed 5 with the products withdrawn from column 6 through outlet I5a.

`The materials delivered through the pipe I5b represent materials which cannot be converted into constituents of the gasoline series by a single Tov disruption adjacent the center of the molecule and, while I may segregate these bottoms by fractionation in the manner described and thereafter crack selectively the individual components and then refractionate and then recrack the individual components falling within the gas oil range to gasoline range, I find it sufiicient to subject these components to a mild cracking by forcing' the same cracking effected in the heater 52 is not intended to convert the stock treated therein predominately to gasoline, but rather to convert a substantial proportion of the stock into stocks having molecular Weights approximating those removed from column 6 through the side outlets 8 to I5, lnclusive. There is of course, the incidental production of a small quantity of gasoline where the operation is not accurately controlled. The stock cracked in this manner is delivered through the outlet 56 into the rectifying column 51, which may be of any suitable construction, in which it is fractionated to form an overhead distillate, for example, taken off through the outlet 58 which may consist of gasoline and. a series of intermediate cuts taken off through the side outlets 59 to 66, inclusive, which are preferably out to have constituents boiling within a. range of 50 F. These constituents boiling within the kerosene and gas oil ranges are such as may to a large extent be converted into constituents of gasoline by a single disruption occurring at or adjacent the mid-point of the individual molecule, Any heavy ends may be taken off through the side outlet 68, and, while they are preferably handled by separation and cracking of the individual segregates, as above outlined, I ilnd it suflicient in commercial practice to carry these compounds by means of the pipe 69 back into the inlet side of the tubular heater 50 for a second cracking operation. Any tarry products collecting in the base of the towers 4|, 5l and 9| are vwithdrawn by means of bottom outlets 50a, 'l0 and |00a, and diverted fromv the system. 'Ihe products obtained from the side outlets 59 and 86 inclusive, represent products which have been cracked and separated into products having a molecular weight approximating those removed from the side outlets on column six. As segregatesi they are passed through the control apparatuses diagrammatically indicated by the numerals 1| to 18, inclusive, discharging into cracking apparatuses 8| to 88, inclusive, which may be of any suitable construction, although they are preferably of the type hereinafter described. The cuts obtained from tower 4| from the side outlets 43 to 50, inclusive, are cuts which have been subjected to cracking and subsequent fractionation. These preferably will be cracked in the same manner as cuts 8 to I5, inclusive, derived from tower 6, but for commercial reasons they may be blended with cuts 59 to 66, inclusive, and passed through the crackers 8| to 88, inclusive. In the ideal embodiment of my process all polymerized cuts, even of the same molecular Weight as the cuts 8 to I5, inclusive, will be treated separately. This is desirable for two reasons, the first being that the dissociation speed of these polymers may be different than those of 8 to |5, inclusive, and further, because I have discovered that the presence of polymerized cuts in contact with undecomposed cuts will enhance the formation of tar.

The cracking accomplished in these cracking apparatuses is conducted under conditions ascertained by test or experience to be best for the particular cuts and may be so adjusted as to produce cracked material having an average molecular weight ranging from 25 to '75% of the average molecular weight of the cut from which the cracked material is derived. In this Way a series of cracked materials of serially larger average molecular weight is produced which have been cracked under conditions conducive to the maximum eiiiciency, under conditions so controlled that the lighter parts of the end product, for example, gasoline, are predominately derived from the lighter cuts of cracked stock, whereas Athe heavier portions of the end product are predominately derived from the heavier portions of the cracked stock, and under conditions producing the minimum of fixed gas and polymerized material. The cuts which have been cracked through apparatuses 8| to 88, inclusive, may be diverted through the common ow line 90 into the rectifying column 9| which may be of any suitable design. From this rectifying column gasoline may be removed through outlet 92. From the side of column 9| a series of cuts, shown as 93 to 99a, inclusive, may be Withdrawn and because of their small quantity may be diverted through crackers 8| to 88, inclusive. It will be understood that if the pressure in, or the location of, the tower 9| is not such as to cause liquid to flow through the lines 93 to 99a, inclusive, into the lines leading to the-crackers 8| to 88, inclusive, suitable pumps and check valves or other Wellknown apparatus may be employed for effecting this purpose.

The cut |00 may be diverted back to the. tubular heater as in the case of cut as is the case likewise with cut 68 from column 51. The cut 68 differs from cuts |00 and 5| in that it represents to a large extent products which have not been converted into those of the desired molecular weight, whereas cuts 5| and |00 are substantially products which have been formed by polymerization since the plant shown is only an approa'ch to the ideal. For the same reason as before outlined, tarry matter may be removed through line |00a.

Referring specifically to Fig. 2 which isthe diagrammatic elevation of apparatus adapted to processing crude oil or other petroleum oils containing constituents of higher boiling point than gasoline. The charging stock is passed through the tubular heater I surrounded by the suitable refractory setting 2, heated by means of the burner diagrammatically indicated at 3, communicating with the setting through the port '4. The crude oil may be heated in heater to a, temperature of substantially complete or partial vaporization and is thereafter discharged through pipe 5 into the rectifying column 6. In the event that it is desired to produce a quantity of gas oil or cracking material in addition to that normally occurring from the crude, conditions in the tubular `heater I may be adjusted to produce a cracking eifect, preferably of a moderate character, to convert heavier materials to a considerable extent into products such as kerosene and gas oil, which products are in turn susceptible to being converted into gasoline by a minimum number of molecular disruptions. This operation is not, of course; conducted under the ideal crackv ing conditions which I have hereinabove de- I scribed, but is utilized only as a matter of expediency. The rectifying column 6 maybe of any suitable type. Provision may, for example, be made to take an overhead cut of gasoline by means of the vapor outlet 1 and a series of side cuts from the outlets 8 to l5, inclusive and I|5 to I8, inclusive. It will, of course, be understood that any alternative number of side cuts may be employed, the design in any case being de termined by the character of the stock to be treated and the number of side cuts which it is desired to make. Assuming that cuts such as kerosene and gas oil are taken off from the side outlets 8 to |5, inclusive, these are preferably fairly closely fractionated vs0 that 90% of the total constituents of each cut will boil Within a range of say 50 F. Products evolved from the tower 6 which are heavier than gas oil, or so heavy that they cannot be converted into gasoline to a large extent by a single disruption adjacent the midportion of the molecule, may be taken olf from the column 6 by means of the side outlets ||5 to |8, inclusive, combined in the manifold l|5a and thereafter treated in the'same manner as the products obtained from the outlet |5a of Fig. 1. Any heavy residue resulting during the operation may be diverted from the system by means of the outlet |20.

The several side cuts taken from column 6 through the side outlets 8 to I5, inclusive, may be handled in the identical manner as the side cuts taken from column 6 of Fig. 1 through the side outlets 8 to I5, inclusive, and inasmuch as the product taken from column 6 'through the side outlets 5 to I8, inclusive, is handled in the identical manner as the products taken from the column 6 in Fig. 1 through the pipe |5a, the subsequent progress of `these materials may be ascertained by referencel to the previous description relating to Fig. 1 and need not be more fully illustrated or described.

Referring specifically to Figs. 3 and 4, the form of cracking apparatus which I prefer to employ for cracking the individual .closely fractionated cuts which have been described from time to time is detailed, which apparatus has been designated for example by numerals 24 to 3|, inclusive, and 8| to 88, inclusive. This apparatus consists of a refractory setting |50 and may be heated through the port |5| by means of the burner diagrammatically indicated as |52. A baille wall such as |53 may be provided and a down draft section |54 communicating with a stack |55. The tubular heaters |56 and |51 in the down draft section may comprise a number of tubes through which oil may circulate by means of inlets and outletsl58, |59, |60, |6|, respectively, and sections of thlscharacter may be utilized for heating or cracking the cuts of relatively wide boiling point corresponding to the operations which have been previously described as conducted in tubular heaters 52. The walls of the setting |50 are preferably lined with a number of relatively short tubular heaters |62 to 11, inclusive, each of which is adapted to the circulation of hydrocarbon materials by means of inlets and outlets such as |660, and |6612, etc. These sections are relatively short being composed of only a few lengths of tubing adapted to be heated to a large extent by the radiant products of combustion evolved. In operation I prefer to maintain these heaters |62 to |11, inclusive, at temperatures intermediate between 750 and 1500 F. and to con-- duct cracking operations therein at relatively low pressures ranging from a few atmospheres to subatmospheric. The total time of heating of the hydrocarbon gases at these temperatures is preferably limited to a period ranging from one second up to the order of ve minutes, which conditions I lnd to favor a symmetrical dissociationv which is amenable to control with a simultaneous formation of a'relatively small quantity of the products of re-association or polymerization. In vapor phase cracking apparatus, such as that shown, I may admix with the petroleum oil un- 1 ited by admixing with the petroleum oil a substance which does not iedeleteriously affect the cracking reaction. In vapor phase reactions I prefer to use a material which is gaseous at the temperature of operation, such as a fixed gas,.

steam, carbon dioxide, hydrogen, etc. All such substances which are not petroleum oils undergoing cracking and which do not deleteriously aect the cracking reaction, will be hereinafter referred to as diluent gases. The cracked and heated hydrocarbons delivered through the respectlve outlets 'of coils |62 to |11, inclusive, are preferably quenched by cooling them immediately either by contact with a liquid or a vapor at temperature below cracking, for example, by contact with steam or by conducting them against relatively cool metal surfaces, for example, through a relatively cool large exchanger. I am thus enabled to c'ontrol the extent to which the reaction is permitted to proceed and thus determine the constitution of the product. The combination, rectification and subsequent disposition of these products has been hereinabove described.

Referring specifically to Fig. 5, this is a diagrammatic 'representation of control apparatus which has been indicated by the numerals I6 to 23, inclusive,| I'to 18, inclusive. This apparatus comprises the side outlet, such as 8, carrying a fraction from any one of the rectifying columns hereinabove described, discharging into cracking apparatus such as diagrammatically indicated by the numeral 24. A cooling coil such as 200 is connected into the outlet 8, preferably adjacent the under side thereof. This coil, controlled by the valve 20|, discharges into the pipe 8 at a point below its origin. The coil 200 may be surrounded by a receptacle, such as A202, through which a cooling fluid is circulated by means of inlets and outlets, such as 203 and 204, respectively, so that any petroleum oil, either in liquid or vapor form, passing through the coil 200 is automatically cooled and discharged in cooled condition back into pipe 8. By manipulation of the valve 20| the amount of cooled material which is reintroduced into the pipe 8 may be carefully controlled, and in this way the temperature of the products passing into the cracking apparatus 24 may be controlled, and hence the temperature of the products discharged from the cracking apparatus 24 may be correspondingly controlled. The form of apparatus which I have just described is particularly adapted to the close control of vapor phase cracking, which -I prefer to conduct in apparatus such as 24 and fractionationl in tower 228, While the constituents` comprising a preponderance of aromatics and unsaturates are removed through pipe 229 for fractionation 'in tower 205. From tower 228 the fractionated vapors are removed through 20G-and a plurality of reflux condensate fractions of different boiling point ranges are withdrawn through pipes 201, 208 and 209 for further cracking similarly, for example, to the fractions removed as side streams from fractionator 6 in Fig. 1. Reference numeral 2| 0' indicates a pipe through which vapors are withdrawn from fractionator 205, while 2| i, 2|2 and 2|3 indicate conduits for the withdrawal of reflux condensates of different boiling point ranges for further cracking, for examplev in a manner similar to those withdrawn from fractionator 6 shown in Fig. 1. In Fig. '7 the reverse operation is shown, the fractionation taking place in tower 2|4 and the solvent extraction yin 2|5 and 2| 6. The oil to be treated is introduced through pipe 2|1 and fractionated in 2|4, from which light vapors are removed through 2| 8 and a plurality of side streams of reflux condensate through 2| 9 and 220, these being subjected to solvent extraction in 2|5 and 2|8 to form fractions 22| and 222 which include preponderantly saturates and fractions 223 and 224 comprising mainly aromatics and unsaturates.

I claim:

1. 'I'he process of treating hydrocarbon oil which comprises separating said oil, by treatment with sulphur dioxide, into two fractions. one containing a preponderance of saturates and the other containing a preponderance of aromatics and unsaturates, dividing Aeach of said fractions into smaller fractions the greater part of the constituents of eachwhich boil within a range of 50 F., independently cracking said smaller fractions Aand forming a desired blended gasoline distillate from the resulting cracked products.

2. A process in accordance with claim 1 wherein said smaller fractions are cracked in the vapor phase for a short period of time under a pressure ranging between a partial vacuum and a few atmospheres. Y 7

3. The process of treating hydrocarbon oil which comprises' separating said oil,by treat- 1 cracked products to form the final desired product.

4. 'Ihe process of treating hydrocarbon oil which comprises separating fresh relatively heavy charging stock into a plurality of componentsby selective solvent action, one'of said components containing a preponderance of saturates and the other containing a preponderance of aromatics and unsaturates, fractionating said components in separate fractionating zones to form a plurality of fractions. of different molecular weights, separately cracking resulting fractions under such conditions that the fractions of lower amolecular weight form mainly the lower molecu- Vlar weight fractions. of gasoline and the fractions of higher molecular weight form mainly the higher molecular weight fractions of gasoline, separating the resulting cracked `products into vapors and liquid residue and forming a desired gasoline distillate from vapors so obtained.

5. Thel process ofy treating hydrocarbon oil which comprises separating said oil, by treatment with sulfur dioxide, in two components, one con'- taining a preponderance of saturates and the other containing a preponderance of aromatics and unsaturates, dividing each of said components into smaller fractions of relatively narrow boiling point ranges, independently cracking said smaller fractions and forming a desired blended gasoline distillate from the resulting cracked products.

6. The process of treating hydrocarbon oil which comprises heating gas oil to a distilling temperature to cause vaporization, fractionally condensing resulting vapors to separate a plurality `of fractional condensates of different boiling point ranges, each of said fractional condensateshaving the greater part of the con.

stituents thereof boiling within a 50- F. range, separating the fractional condensates into a plurality of components, by selective solvent action, in separate zo'nes, one of said components containing a preponderance of saturates and the other containing a preponderance of aromatics and unsaturates, independently cracking said components and forming a nal desired blended .gasoline distillate from the resulting cracked products.

PERCY C. KEITH, Jn.

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