US1972149A - Method for cracking oils in vapor phase - Google Patents

Description

sep1.'4, 1934. P. C. KEITH; JR 1,972,149

METHOD FOR CRACKING OILS IN VAPOR PHASE Filed Dec. 1, 1928 s sheets-Sheet 1 Sept. 4, 1934. P. c. KEITH, JR 1,972,149

METHOD FOR CRACKING OILS IN VAPOR PHASE Filed nec. 1. 1928 s sheets-sheet 2 Sept. 4, 1934. P, c, Kl-:m-l, JR

METHOD Fon cRAcxING oILs 1N VAPOR PHASEl Filed Dec. 1, 1928 3 Sheets-Sheet 5 w ws fj/m

- Patented Sept. 4, 1934 l UNITED STATES PATENT; OFFICE METHOD For. cRAcKmG oILs IN varon PHASE Percy C. Keith, Jr., Bernardsvi'lle, N. J., assigner, by mesne assignments, to Gasoline Products Company, Inc., a corporation of Delaware vApplication December 1, 1928, SerialNo. 323,005

Claims. (Cl. 196-49) This invention relates to the pyrogenesis of cracking rates of some of the constituents'of petroleum oils and will be'understood from the. the stock tend to accentuateA the condition refollowing description read in conjunction with ferred to above. I have discovered that a fundathe drawings, in which; mental increase in the eiiiciency of the cracking b Fig. 1 is a diagrammatic representation of a process maybe obtained by,Vr separating the crackpreferred embodiment of apparatus in which my ing stock into a number of distinct fractions of processmay be carried out; diiIerent boiling point ranges and thereafter Fig. 2 is a diagrammatic representation of an cracking the individual fractions so generated. alternative for-m; I prefer to obtain as nearly as possible, having 66 Fig. 3 is a vertical section through a form of regard to the conditions imposed by practice, a apparatus which may be employed in conjuncnumber of charging stocks all the constituents tion with my process; of each of which will respond in the same degree Fig. 4 is a cross section taken ai the line 4-4 tothe conditions to which each of the stocks is of Fig. 3; and subjected. I preferably apply to each such frac- Fig. 5 is a side elevation with parts in section tion the degree of time, temperature, and/or m of a form ofapparatus employed in conjunction pressure necessary to its optimum conversion into with my process and with the apparatus shown desired products. 'I-hese conditions may in any in Figs. 3 and 4. casel be determined by preliminary tests. Thus,

The pyrogenesis of petroleum oils forproducwhen conditions have been established by such tion of oils of lower boiling point is carried out` tests as to yield the same quantity of desired end by heating crude petroleum, or such of its disproducts from a series of segregated fractions as tillatesv as may economically be utilized in this iS Obtainable from cracking Conglmrate Stock manner, to cracking' temperatures with or withthe concomitant loss in gas and/or tax-ry or coky out pressure. The fraction intermediate between materialsis diminished, or forv an equivalent loss kerosene `and lubricating oils known as* gas oil the yield of the desired end products is relatively is frequently utilized for this purpose because of increased. its lesser market value, although kerosene, lubri'- My process is applicable generally in the pyroeating oil fractions and fuel oils are also emgenesis vof petroleum oils toproduce lower boiling ployed at times. The fractions so employed are point oils, as, for example, cracking'to produce composed of an extended range of compounds as either gas, gasoline, kerosene, gas" oil or lubriindicated by the range of molecular weights and eating oil from stocks of respectively higher boilboiling points. The conglomerate of compounds ing point. is subjected to cracking conditions until a certain In the ideal embodiment of my process the quantity of material falling within a desired stock is segregated into a plurality of charging boiling range is produced. Simultaneously with stocks of such character that under the condithe formation of this product, or products, mations of heat, time, and pressure imposed, crackterials are produced which do not fall Within ing of the various individual compounds composthe desired range, for example, when cracking ing the fraction -willtake place at substantially to produce a substantial proportion of gasoline the same rate. However, the limitations imwhich is a product composed of a large variety posed by practice require segregation into a of different hydrocarbon compounds, there yis smaller number of stocks than in the ideal methsimultaneously produced a quantity of tarry and od and I therefore segregate into an appropriate coky materials. Some elements of aconglomerate number of charging stocks and subject each or stock, for reasons which will ,be given more such stocks to optimum conditions for the parfully later, require cracking to a degree less than ticular segregate. 100

others, and because of the fact that the stock I have discovered that in\ high molecular as' a whole is subjected tothe same conditions weight hydrocarbons of straight chain structure the cracking reaction will be carried too far in the initial-scission on cracking frequently occurs the case :of some of the constituents of the stock adjacent the center of the molecular chain. In

in order to securev the desired quantity of maone application in my process I aim to obtain 105 terlal of a predetermined boiling point range and by cracking the products of rst scission of the with the resultant formation of compounds which molecule, and I therefore prepare charging do not fall within'the said range or which are stocks which upon their initial scission yield deleterious to the operation, for reasonsv which products which fall within the range of physical will be morefully pointed out. The diierent characteristics of the'material desired tobe ob- 110 ceed 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 constituentsv 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 each segregated fraction to such conditions as will produce from each segregated fraction a product which will yield, upon refractionation, products whichxnay be decomposed as above into gasoline constituents. 'Ihis 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 yi'eld a cracked material having a position with respect to the average molecular weightof 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. I

In addition to the foregoing I may make a further separation based on chemical characteristics. Thus, I may separate the original cracking stock into two fractions, one containing a preponderance of saturates and the other containing a preponderance of aromatics and unf saturates,as, for example, by the application of 55 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 rangesmay be fr t prepared and each thereafter separated into fractions of dierent chemical characteristics, as for example, by treatment with liquid sulphur di-l oxide.

' constituents boiling within a different 50 F.

range. 'I'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 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 'welghti 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 thefcase 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 confine the reaction to the formation of the products of scission of a lower order. The scissions off higher order result in an increase in the products of recomposition, 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 to 25% of the average molecularweight 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 lenabled to convert them into fractions of the of the particular stock or in view of the particular characteristics of the product desired, as, for example, to produce av 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 ve minutes, at temperatures which may range between 750 and 1500F. and' at pressures which may range from a few atmospheres to partial vacuum. In this way I am enabled to effect a carefully controlled dissocia- Vtion 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 vautomatically throwing it into the boilingpoint 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 specific volume of the gases in the cracking zon'e, the tendency to polymerization, or reformation of heavier products, is inhibited, the eiciency of the operation is increased and I am enabled to diminish the formation oftar and/or coke.

In determining the conditions under which individual 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 fixed gas is substantially produced by the cracking of constituproducts 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 of heavier liquid content inthe system. 'I'his 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 s'uch that products falling within the gasoline range are removed substantially as quickly as formed. The selection of the temperature bears a definite 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, suicient time being provided to permit'the reaction to take place. The effect of removing theE 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 specic reference to the apparatus diagrammatically indicated in the drawings. Referring specifically to Fig. 1 a cracking stock such as gas oil is passed Y throughthe tubular heater 1, 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 heatiexchanger 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 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 overhead cut in vapor phase from the column by means of the vapor outlet 'l and a number of side cuts (ordinarily in liquid phase, but which may be inthe vapor phase) from the side outlets 8, 9, 10, 1l, 12, 13, 14 and 15. The side cuts may be rectified 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 ion, by means of the bottom draw-off 15A. The

(column maybe 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 oi through outlets '7 Vto 15, inclusive, are in view of the necessities of practice, relatively close cut fractions having, for example, 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 ycuts 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 16 to 23 inclusive which will be hereinafter 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 31, inclusive. I

may employany form of cracking apparatus, such as stills which may be adapted to operate under pressure or tubular crackers with or with' out reaction chambers or tubular stills operated in the vapor phase. In any event, the cracking i is carried out under conditions which may be ascertained in advance by tests tojbe suited to the individual cut. Preferably, when operating to make gasoline the individual cuts are cracked to 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 andwith less actual molecular disruptions and recombinations than would be incidental to handling a cracking stock as a conglomerate.

For convenience al1 of the cracked materials dis` charged from the crackers 24 to 31, inclusive, through outlets 32 to 39, inclusive, may be conducted by means of the manifold 40 into the rectfying column 41 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 phase, if desired, through the outlet 42, and a number of side cuts taken olf through the side outlets 43 to 50, inclusive. These side cuts taken off' through the outlets 43 to 50, inclusive, are preferably fractionated so that of the constituents of each cut boil Within a range of 50 F. and will behereinafter more fully considered. The column 6 may be ,operated under any pressure at which appropriate fractionation may be se-- cured, and for purposes of heat economy, is preferably operated under a pressure in excessv of atmospheric, say, for example, a pressurenot exceeding 100 pounds per square inch. I achieve in this Way the additional advantage that the cuts taken off from the outlets 8 to 15, inclusive. may, in this manner, be supplied by virtue of A their initial pressure to\the respective cracking apparatuses 24 to 31, inclusive. The column 41 may be operated under pressure preferably less than that obtaining in column 6 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 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 or near the mid-point of the molecule.

The plant illustrated is only an approachto the ideal and some polymerization may occur to products whose molecular Weight is higher than those taken off through the side'outlets 8 to 15, inclusive, of column 6. Such polymerized prod.- ucts are preferably separately processed as utlined in the preferred manner of processing the cut withdrawn through 15a, but for commercial reasons may be removed from column 41 through the side outlet 51 and diverted through pipe 15ato pipe 15b to be combined with and processed with the products withdrawn from column- 6 through outlet 15a.

The materials delivered through the pipe 15b represent materials which cannot be converted int-o constituents pf 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 withinhthe gas oil range to gasoline range, I find it sumcient 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 A heated through the port 54 by means of the'burner 55. The cracking/effected in the heater 52 is not intended to convert the stock treated thereinpredominately 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 15, inclusive. Ihere is of course, the incidental production of a small quantity of gasoline where the operation is not accurately controlled. 'Ihe stock cracked in this manner is delivered through the outlet 56 into the rectifying column 57, which may be of any suitable construction, inwhich it is fractionated to form an overhead distillate, for example, taken off through the outlet 58 whichmay consist of gasoline and a series of intermediate cuts taken olf throughthe side outlets 59 to 66, inclusive, which are preferably cut to have 90% constituents boiling within a range of 50 F. These constituents boilingwithin 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 oir through the side outlet 68, and, while they are preferably handled by separation and cracking of the individual segregates, as above outlined,

I 11nd it sufficient in commercialpractice to carry these compounds by means of the pipe 69 back into the inlet side of the tubular heater 52 for a second cracking operation. Any tarry products-collecting in the base of the towers 41, 57 and 91 are withdrawn by means of bottom outlets 50a, 70 and 100a, 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 co1- umn six. As'segregates they are passed through the control apparatuses diagrammatically indicated by the numerals 'Il to '18, inclusive, discharging into cracking apparatuses 81 .to 88, inclusive, which may be of any suitable construction, although they are preferably of the type hereinafter described. The cuts obtained from tower 41 from the side outlets 43 to 50, inclusive, are cuts which have been subjected to cracking and subsequent fractionation. These preferably willbecrackedinthesamemannerascutsto 15, inclusive, derived from tower 6, but for commercial reasons they may be blended with cuts 59 to 66, inclusive, and passed through the crackers 81 to 88, inclusive. In the'ideal embodiment of my process all polymerized cuts, even of the same molecular weight as the cuts 8 to 15, 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 15, inclusive, and further, becauseI have discovered that the presence of polymerized cuts in contact with undecomposed cuts will enhance the formationof tar.

The cracking accomplished in these cracking apparatuses is conducted underconditions ascertained by testor experience to be best for the particular cuts and may be sd adjusted as to produce cracked material having an average molecular'w'eight ranging from 25 to '75% of the average molecular vweight of the cut from which the cracked material is derived. In this way a seriesof cracked materials of serially larger average molecular weight is produced which have been cracked under conditionsconducive to the maximum emciency, under conditions so controlled. that the lighter parts of the end product, for example, gasoline, are predominately derived Lorano from the lighter cuts of cracked stock, whereas the 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 81 to 88, inclusive, may be ,diverted through the common flow line into the rectifying column 91 which may be of any suitable design. From this rectifying column gasoline may be removed. through outlet 92. From the side of column 91 a series of cuts, shown as 93 to 99a, inclusive, may be withdrawn and because of .their small quantity may be diverted through crackers 81 to 88, inclusive. Itv will be understood that if the pressure in, or the location of, the tower 91 is not such as to cause liquid to now through the lines 93 to 99a, inclusive, into the lines leading to the crackers 81 to 88, inclusive, suitable pumps and check valves or other well-known apparatus may be. employed for effecting this purpose.

The cut 100 may be diverted back to the tubular heater as in the case of ut 51 as is the case likewise with cut 68 from column 57. The cut 68v differs from cuts 100 and 51 in that it represents to a large extent products which have not been converted into those of the desired molecular weight, whereas cuts 51 and 100 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 through line 100a.

Referring specifically to Fig. 2 which is the diagrammatic elevation of apparatus adapted to processing crude koil or other petroleum oils containing constituents of higher boiling point than gasoline. The charging stock is passed through the tubular heater 1 surrounded by .the suitable refractory' setting 2, heated by means of the burnerv diagrammatically indicated at 3, communicating with the setting through the port 4. The crude oil may be heated in heater 1 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 1 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 vare in turn susceptible' to being converted into gasoline by a minimum number of molecular disruptions. This operatio'n is not, of course, conducted under the ideal cracking conditions which I have hereinabove described, but is utilized only as a matter of expediency. The rectifying column 6 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 7 and a series of side cuts from the outlets 8 to 15, inclusive,and 115 to 118, inclusive. It will, of course, be understood that any alternative number of sidecuts may be employed, the design in any case being determined by the character of the stockto be treated and the number of side cuts which it is desired to make. Assuming that cuts such as kerosene an'd gas oil are taken off from the side outlets 8 to 15, 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 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 mid-portion of the molecule, may be taken off from the column 6 by means of the side outlets 115 to 118, inclusive, combined in the manifold 115a and thereafter treated in the same manner as the products obtained from the outlet 15a of Fig. l. Any heavy residue resulting during the operation may be diverted from the system by means of the outlet 120.

The several side cuts taken from columns 6 through the side outlets 8 to 15, 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 15, inclusive, and inasmuch as nthe product taken from column 6 through the side outlets-115 to 118, inclusive, is handled in the identical manner as the products taken from the column 6 in Fig. 1 through the pipe 15a, 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 31, inclusive, and 81 to 88, inclusive. This ap' paratus consists of a refractory setting 150 and -may be heated through the port 151 by means vof the burner diagrammatically indicated as 152. A baille wall such as 153 may be provided and a down draft section 154 communicating with a stack 155. 'I'he tubular heaters 156 and 157 in the down draft section may comprise a number of tubes through which oil may circulate by means of inlets and outlets 158, 159, 160, 161, respectively, and sections of this character may be utilized for heating or cracking the cuts of relatively wide boiling point correspond- Ving to the operations which have been previously described as conducted in tubular heaters 1, 52. The walls of the setting 150 are preferably lined with. a number of relatively short tubular heaters 162 to 177, inclusive, each of which is adapted to the circulation of hydrocarbon materials by means of inlets and outlets such as 166a and 16612, 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 cornbustion evolved. In operation 1 prefer to maintain these heaters 162 to 177, 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 toa period ranging from one second up to the order of five minutes, which conditions Il find to favor a symmetrical dissociationvwhich is amenable to control with a simultaneous formation of a relatively small quantity of the products of reassociation 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 of polymers is influenced, among other things, by the concentration of the-unsaturates 1,510

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 fixed gas, steam, carbon dioxide, hydrogen, etc. All. such substances which are not petroleum oils undergoing crack-V ing and which do not deleteriously affect the` cracking reaction, will be hereinafter referred to as diluent gases. The cracked and heated hydrocarbons delivered through the respective outlets of coils 162 to 177, inclusive, are preferably quenched by cooling them immediately either by contact with a liquid or a vapor at temperatures below cracking, for example, by

contact with steam or by conducting them I paratus 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 201, discharges into the pipe 8 at a point below its origin. 'I'her coil 200 may be surrounded by a receptacle, such as 202, 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 201 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 theproducts 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 to which I prefer to subject the various fractions. into which I separate my original cracking stock.

It will, of course, be understood that the method and apparatus hereinabove specifically described is intended as an illustration of the specific embodiment of., my inventionand not as a limitation of its scope. It is my intention that' the invention be limited only by the appended claims in which I have endeavored to claim broadly all inherent novelty.

1. A continuous. unitary' process of cracking petroleum oils which comprises subjecting a cracking stock from a single source to cracking temperature to effect a primary cracking, subjecting the aresultant cracked 'material to fractionation to form a nal light distillate, a plurality of intermediate condensate fractions and a residue, directly subjecting the several intermediate fractions, while still hot, to separate cracking operations in which each fraction is subjected to a cracking temperature adapted for the conversion of such fraction to effect a secondary cracking thereof, combining the resultant hot cracked material from the several secondary cracking operations, subjecting the combined malterial `to fractionation in another fractionating zone to form an additional'quantity of final light distillate, a plurality of intermediate condensate fractions adapted' for further cracking and a liquid residue, and preventing the return to, any of said cracking operations of intermediate condensate from a subsequent fractionating operation.

2. A continuous unitary process of cracking petroleum oils which comprises subjecting a cracking stock from a single source to cracking temperature to effect a primary cracking, subjecting the resultant cracked material to fractionation to form a final light distillate, a plurality of intermediate condensate fractions and a heavier fraction, directly subjecting the several intermediate fractions, while still hot, to separate cracking operations in which each fraction is subjected to a cracking temperature adapted for the conversion of such fraction to effect a secondary cracking thereof, combining the resultant hot cracked material from the several secondary cracking operations and subjecting the combined material to fractionation in a separate fractionating zone to form an additional quantity of final light distillate, a plurality of intermediate condensate fractions and a heavier "fraction, passing said heavier fractions obtained in the fractionation of the products of the primary and secondary cracking operations immediately through a separate cracking zone and subjecting them therein to cracking temperature to effect a comparatively light cracking of said heavier fractions, and fractionating the resultant cracked material to separate out an additional quantity of nal light distillate.

3. A continuous unitary process of cracking petroleum oils which comprises subjecting a cracking stock from a single source to cracking temperature to effect a primary cracking, subjecting the resultant cracked material to fractionation to form a final light distillate, a plurality of intermediate condensate fractions and a heavier fraction, subjecting the several intermediate fractions, while still hot, to separate cracking operations in which each fraction is subjected to a cracking temperature adapted for the conversion of such fraction to effect a secondaryl cracking thereof, combining the resultant hot cracked material from the several secondary cracking operations and subjecting it toy fractionation in another fractionating zone to form an additional quantity of final light distillate, a plurality of intermediate condensate fractions and a heavier fraction, passing said heavier fractions obtained in the fractionation of the products of the primary and secondary ucracking operations, while still hot through a separate cracking zone and subjecting them therein to cracking temperature to effect a comparatively light cracking of said heavier fractions, subjecting the resultant products of conversionv of said heavier fractions to fractionation ina sep#` intermediate condensate fractions and a residue, combining while hot fractions of approximately the same boiling point range as obtained in the fractionation of the cracked material formed in said secondary cracking `operation and in the fractionation of the products of cracking said heavier fractions and subjecting the several composite fractions to cracking temperature to effect a further cracking of said constituents, and fracof the system, combining the hot products formed in the said several cracking zones constituting said one of the successive cracking zones and subjecting the composite material to fractionation in a fractionating zone to separate out a final lightdistillate and a plurality of fractions, passmg' said' fractions, while `still not; directly to separate and individual cracking zones constituting a second successive cracking zone and subjecting the fractions to cracking temperatures adapted for the conversion of such fractions to effect a further cracking thereof, combining the hot products formed in the said separate and individual cracking zones and subjecting the composite material to fractionation in another fractionating zone to separate out -a nal light distillate and a plurality of fractions adapted for further cracking.V

5. The continuous unitary process of treating hydrocarbon oils which comprises separately cracking a plurality of different oil charging stocks which have had substantially the same previous heat treatment, combining the resulting hot cracked products, separating the combined cracked products in a fractionating zone into a f' plurality of different intermediate fractions and a nal desired distillate, cracking said fractions individually while preventing mixtures thereof with said charging stocks, and combining the resulting cracked products in a second fractionating zone, and removing from said second zonea iinal desired distillate. f

PERCY C KEITH. JR.

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