US2143917A - Method for cracking oils in vapor phase - Google Patents

Description

Jan. 17, 1939. C, KEN-Hy JR 2,143,917

METHOD FOR CRACKING OILS IN VAPOR PHASE ATTORNEY Jan, 17, 1939. P. c. KEITH, JR 2,143,917

METHOD FOR CRACKING OILS IN VAPOR PHASE Original Filed Deo. l, 1928 Sheet's-Sheet 2 lNvENToR PERCY C. KEITH JR.

ATTORNEY Jan. 17, 1939.. p. c, KEITH, JR 2,143,917

METHOD FOR CRACKING OILS IN VAPOR PHASE Original Filed Dec. l, 1928 3 Sheets-Sheet 3 g N N OOOGOOOO T122 "rs ATTORNEY Patented Jan. 17, 1939 UNITED STATES PATENT GFFIQE METHOD FOR CRACKING OILS IN VAPOR PHASE Percy C. Keith, Jr., Peapack, N. J., assigner', by

mesne assignments, to Gasoline Products Company, Inc., Newark, Delaware N. J., a corporation of 3 Claims.

This invention relates to the pyrogenesis of petroleum oils and is a division of application Serial No. 323,005 led December l, 1928 which has noW matured as Patent 1,972,149. The infiV Vention will be fully explained in the following description and accompanying drawings in which:

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

Fig. 2 is a diagrammatic representation oi an alternative form;

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. 3; and i 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.

The pyrogenesis of petroleum oils for production of oils of lower boiling point is carried out by heating crude petroleum, or such of its distillates r as may economically be utilized in this manner,

to cracking temperatures with or without pressure. The fraction intermediate 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 diierent 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 oi the constituents of the stock tend to accentuate the condition referred to above. I have discovered that a fundamental increase in the eiiiciency of the 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 i 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 yield of the desired end products is relatively increased.

My process is applicable generally in the pyrogenesis of petroleum oils to produce lower boiling i 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 conditions 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 .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 initial 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 rst scission of the molecule, and I therefore prepare charging stocks 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 o-f 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. (l) by segregating them from one another as by distillation into individual fractions and then subjecting each segregated fraction to such conditions as will produce from eachl 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 suited to 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 to 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 further separation based on chemical characteristics. rIhus, I may separate the original cracking stock into twof fractions, one containing a preponderance of saturates and the other containing a preponderance of aromatics and unsaturates, as, for 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 rst prepared and each thereafter separated into fractions of different chemical characteristics, as, for example, by treatment with liquid sulphur dioxide.

In any event, where several fractions of the original charging stock are prepared, as by distillation, the decomposition products from 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. The 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 having the 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 have been 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 thusthe 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 in my process I prefer to conne the reaction to the formation of the products of scission of a lower order. The 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.

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 substantially half of that of the parent cut, for example, ranging from 75 to 25% of the average molecular weight of the 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 gasoline range with a 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 75 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 oi relatively short duration ranging, for example, from the order of one second up to times of the order of ve 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 effect 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 point range of the desired end product with a minimum production of undesired products. A further advantage of this procedure that Ihave 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 efficiency of the operation is increased and I am enabled to diminish the formation of tar and/or coke.

In determining the conditions under which in dividual cuts of the initial conglomerate charging 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 xed 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 different 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 evacua tion immediately upon formation, or are retained there by reason of their solution in liquid since they are in contact with large bodies of 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 is such that products falling within the gasoline range are removed substantially as quickly as formed.

The selection of the temperature bears a denite relation to the time element involved in the operation of the apparatus, the more rapid the evacuation of the products from the Zone of reaction 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 tubular heater I, surrounded by the refractory setting 2, and heated by means of a burner such as 3 communicating with the setting through the 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 into the fractonating column 6. This column may be suitably insulated and provided with a number of rectifying devices such as the customary transverse partitions carrying down flow 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 over-head 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, I2, I3, I4 and I5. The side cuts may be rected or stripped in a secondary rectifying column, if desired, to eliminate light ends, or, alternatively, 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-01T I5A. The column may be supplied with cooling coils adjacent to the top or intermediate points and with a heating coil adjacent to the bottom or with re-boiler sections at intermediate points. All such modifications will be incorporated to the degree necessary to obtain the desired separation of the individual fractions. The cuts taken off through outlets 1 to I5, inclusive, are, in View of the necessities of practice, relatively close cut fractions having, for example, 90% of constituents boiling within a 5 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 It to 23 inclusive which Will be here inafter more fully described, and from the control apparatuses the cuts pass respectively to the individual cracking apparatuses which have been diagrammatically indicated by the numerals 24 to 3 I inclusive. I may employ any form of cracking apparatus, such as stills whichmay be adapted to operate under pressure or tubular crackers 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 weight of the cracked material produced from an individual cut ranges from 25 to 75% of that of the `parent fraction. I obtain in this Way a series of cracked products with serially larger molecular weights corresponding in order to the molecular Weights of the original fractions of cracking stock. The desired end product is therefore obtained by the selective cracking of preferred stocks and with less actual 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, inclusive, may be conducted by means of the manifold 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 oif in vapor phase, if desired, through the outlet 42, and a number of side cuts taken off through the side outlets 43 to 5|), inclusive. |Ihese side cuts taken off through the outlets 43 to 59, inclusive, are preferably fractionated so that 90% of the constituents of each cut boil Within a range of 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 pressure in excess 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 olf from the outlets 8 to l5, inclusive, may, in this manner, be supplied by virtue of their initial pressure to the respective cracking apparatuses 24 to 3|, inclusive. The column 4| may be operated under pressure preferably less than that obtaining in column G so that the progress of material through the entire system is effected by virtue of the initial pressure obtaining in column 6. The side cuts from column E 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 or near the mid-point of the molecule.

The plant illustrated is only an approach to the ideal and some polymerization may occur to products Whose molecular Weight is higher than those taken oif through the side outlets 8 to l5, inclusive, of column 6. Such polymerized products are preferably separately processed as outlined in the preferred manner of processing the cut withdrawn through |5a, but for commercial reasons may be removed from column 4| through the side outlets 5| and diverted through pipe |5a to pipe |517 to be combined with and processed with the products withdrawn from column 6 through outlet la.

The materials delivered through the pipe |51) represent materials which cannot be converted into constituents of the gasoline series by a single 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 nd it suflcient to subject these components to a mild cracking by forcing the same through the tubular heater 52 surrounded, for example, by the refractory setting 53 heated through the port 54 by means of the burner 55. 'Ihe cracking effected in the heater 52 is not intended to convert the stock treated therein predominantly 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 l5, inclusive. 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 5l, 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 86, inclusive, which are preferably cut to have 90% 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 olf through the side outlet S8, and, While they are preferably handled by separation and cracking of the individual segregates, as above outlined, I und it suiicient in commercial practice to carry these compounds by means of the pipe t9 back into the inlet side of the tubular heater 5G for a second cracking operation. Any tarry products collecting in the base of the towers 4|, 5l and Si are Withdrawn by means of bottom outlets 5Go, 'lil and lima, and diverted from the system. The products obtained from the side outlets 59 and 66 inclusive, represent products which have been cracked and separated into products having a molecular weight approximating those removed from the side outlets on column 6. As segregates they are passed through the control apparatuses diagrammatically indicated by the numerals to I8, inclusive, discharging into cracking apparatuses 8| to 88,111- clusive, which may be of any suitable construction, although they are preferably of the type hereinafter described. The cuts obtained from tower 4l from the side outlets lil to 56, 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 l5, inclusive, derived from tower il, but for commercial reasons they may be blended with cuts 5e to 65, inclusive, and passed through the crackers 8| to 38, inclusive. In the ideal embodiment of my process all polymerized cuts, even of the saine molecular Weight as the cuts ll to i5, inclusive, will be treated separately. This is desirable for two reasons, the rst being that the dissociation speed of these polymers may be different than those of B to l5, 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 tc the maximum efficiency, under conditions so controlled that the lighter parts of the end product,

for example, gasoline, are predominantly derived from the lighter cuts of cracked stock, whereas the heavier portions of the end product are predominantly 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 iiow 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 83 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 89a, inclusive, into the lines leading to the cackers 8| to 88, inclusive, suitable pumps and check valves or other well-known apparatus may be employed for effecting this purpose.

The cut may be diverted back to the tubular heater as in the case of cut as is the case likewise With cut 88 from column 51. The cut 88 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 cutsl5| and |00 are substantially products which have been formed by polymerization since the plant shown is only an approach to the ideal. For the same reason as before outlined, tarry matter may be removed Y through line |00a.

Referring specifically to Fig. 2 which is the 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 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.

.y The crude oil may be heated in heater I to a temperature of substantially complete or partial vaporization and is thereafter discharged through pipe 5 into the rectifying column 8. 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 may be adjusted to produce a cracking effect, 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 cracking conditions which I have hereinabove described, but is utilized only as a matter of eX- pediency. The rectifying column 8 may be 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 ||5 to ||8, inclusive. It will, of course, be understood that any alternative number of side cuts may be employed, the design in any case being determined 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 l5, inclusive, these are preferably fairly closely fractionated so that 90% of the total constituents of each cut will boil within a range of say 50 F. Products evolved from the tower 8 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 mid-portion of the molecule, may be taken off from the column 8 by means of the side outlets l5 to |8, inclusive, combined in the manifold ||5a and thereafter treated in the same manner as the products obtainedfrom 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, inclusvamay be handled in the identical manner as the side cuts taken from column 8 of Fig. 1 through the side outlets 8 to i5, inclusive, and inasmuch as the product taken from the column 8 through the side outlets ||5 to H8, inclusive, is handled in the identical manner as the products taken from the column 8 in Fig. l through the pipe |5a, the subsequent progress of these materials may be ascertained by reference 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 baiile wall such as |53 may be provided and a down draft section |54 communicating with a stack |55. The tubular heaters |58 and |51 in the down draft section may comprise a number of tubes through which oil may circulate by means of inlets and outlets |58, |58, |88, |8I, respectively, and sections of this character 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 |82 to |11, inclusive, each of which is adapted to the circulation of hydrocarbon materials by means of inlets and outlets such as |8811 and |681), 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 |82 to |11, inclusive, at temperatures intermediate between 750 and 1500 F. and to conduct cracking operations therein at relatively low pressures ranging from a few atmospheres to sub-atmospheric. 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 find to favor a symmetrical dissociation which is amenable to control with a simultaneous forma tion of a relatively small quantity of the prode ucts of re-association or polymerization. In vapor phase cracking apparatus, such as that Shown, I may admix with the petroleum oil undergoing cracking in the vapor phase a material to limit the formation of polymers. I have discovered the formation cf polymers is inuenced, among other things, by the concentration of the spondingly controlled.

unsaturates produced by decomposition per unit of space and that this concentration and consequent polymerization may be inhibited or limited by admixing with the petroleum oil a substance which does not deleteriously 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 Xed gas, steam, carbon dioxide, hydrogen, etc. All such substances which are not petroleum oils undergoing cracking and which do not deleteriously aiect the cracking reaction, will be hereinafter referred to as diluent gases. The cracked and heated hydrocarbons delivered through the respective outlets of coils S2 to il?, inclusive, are preferably quenched by cooling them immediately either by Contact with a liquid or a vapor at temperature beloyvi 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 control the extent to Which the reaction is permitted to proceed and thus determine the constitution of the product. The combination, rectiiication and subsequent disposition of these products has been hereinabove described.

Referring speciiically to Fig. 5, this is a diagrammatic representation of control apparatus which has been indicated by the numerals i6 to 23, inclusive, and i to '18, inclusive. rIhis apparatus comprises the side outlet, such as carrying a fraction from any one of the rectifying columns hereinabove described, discharging into cracking apparatus such as diagrammatically indicated by the numeral 2li. A cooling coil such as 2t@ is connected into the outlet 8, preferably adjacent the under side thereof. This coil, controlled by the valve 2M, discharges into the pipe 8 at a point belowits origin. The coil 2% may be surrounded by a receptacle, such as 202, through which a cooling fluid is circulated by means of inlets and outlets, such as 293 and 2M, respectively, so that any petroleum oil, either in liquid or vapor form., passing through the coil G is automatically cooled and discharged in cooled condition back into pipe 8. By manipulation of the valve 23E 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 2 may be controlled, and hence the temperature of the products discharged from the cracking apparatus Eil may be corre- 'Ihe 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 to which I prefer to subject the various fractions into which I separate my original cracking stock.

I claim:

1. The process of treating hydrocarbon oil Which comprises dividing said oil by distillation into a plurality of hot fractions heavier than gasoline and having different boiling ranges, passing said fractions While hot through individual confined paths in a common heating zone, supplying sufcient heat to said heating zone to raise said fractions to the desired cracking temperature, counteracting any variations from said desired cracking temperature by cprrectively adjusting the temperature of the several hot fractions, prior to their introduction into said confined paths, combining the resulting cracked products and separating therefrom gasoline of the desired characteristics.

2. The process of treating hydrocarbon oil for the production of gasoline, which comprises producing a plurality of separate hot bodies of hydrocarbon oil, passing separate streams of oil from said bodies in individual confined paths through a common heating Zone, supplying sufcient heat t0 said common heating zone to raise said streams of oil to the desired cracking temperature, removing the resulting cracked products and forming a desired blended gasoline distillate therefrom, and selectively cooling said streams of oil prior to their introduction to said common heating zone, to such a ratio that during their subsequent passage through said heating zone said streams of oil undergo cracking to substantially the desired extent.

3. The process of forming a plurality of highly heated bodies of oil, which comprises establishing a plurality of individual quantities of oil at elevated temperatures less than those desired for said bodies of oil, cooling certain of said quantities of cil with respect to other of said quantities of oil, then passing said quantities of oil at their respective resulting temperatures in a plurality of individual streams through a common heating zone wherein each stream is subjected to heat from the same source as each of the other streams and is thereby raised to a desired high temperature, and correcting any undesired variation in said high temperature by controlling the cooling step mentioned so that the bodies of oil emerging from said individual streams have the desired individual temperatures.

PERCY C. KEITH, JR.

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