US1634666A - Cracking of hydrocarbons - Google Patents

Description

Jul 1927.

y 5 E. c. HERTHEL ET AL CRACKING OF HYDROCARBONS Filed April 8. 1924 INVENTORS ATTORNEYS Patented July 5, 1927.

UNITED STATES PATENT OFFICE.

EUGENE C. HERTHEL AND HARRY L. PELZER, OF CHICAGO, ILLINOIS, ASSIGNORS TO SINCLAIR REFINING COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF MAINE.

CRACKING OF HYDROCARBONS.

Application filed April 8, 1924. Serial No. 704,926.

This invention relates to improvements in the cracking of heavier oils in pressure stills for the production of gasoline or motor spirit or pressure distillate therefrom. The invention comprises an improved process which can be continued for a radically prolonged period of time before it is necessary f certain constituents of an asphaltic or pitch:

like character. With continuation of the cracking operation, the amount of such c onstituents increases and there is a tendency for deposit of carbon or coke to form on the heated surfaces of the still, thus necessitating the shutting down of the still for cleaning purposes between successive runs. The shutting down of a pressure still, the Withdrawal 'of the charge therefrom, the cleaning of the still, the recharging of the still and the preliminary heating of the still to bring the fresh charge up to cracking conditions, all require time, and the total amount of time so required in ordinary commercial operations means a corresponding reduction in the proportion of the time when the still is operating for carrying out the desired cracking operation.

According to the present invention, the deposition of pitch or carbon on the heating surfaces of the pressure still is prevented or greatly-reduced so that overheating or danger of failure of the heating surfaces can be-efl'ectively prevented, and the time of operation of a single run can be greatly prolonged, with correspondingly greater conti unity of' operation, less loss of time, and greater production per still per day.

When a pressure still is charged with gas oil or other charging stock to be subjected to cracking, and when the charge is heated to the cracking temperature, the cracking takes place in a gradual and progressive manner. The lighter constituents produced by the'cracking operation, which go to make up the pressure distillate, are removed from the still progressively during the cracking operation. Other constituents, such as heavier hydrocarbons formed by the cracking operation, may remain and mix with the charge of the still. A small amount of asiron sulfide.

phaltic or pitch-like constituents is progressively formed. Such constituents appear to be of varying properties and characteristics. For the most part they remain in solution .in the charge during the early portion of the rim, and they may remain completely in solution during the early portion of the run. With gradual and progressive cracking of the charge however the amount of such asphaltic or pitch-like constituents gradually and progressively increases until sooner or later the amount of such constituents increases beyond the saturation point. Furthermore, certain of these constituents, which appear to be relatively small in amount as compared with the total amount of the pitch-like constituents formed, appear to be of a diflerent character and to have an increased tendency to deposit on the heating surfaces of the still. Furthermore, as the charge. becomes supersaturated with the less objectionable pitch-like constituents, there is an increased danger'of deposit of pitch or carbon'on the heating surfaces of the still, with corresponding danger of overheating and failure of the heated surfaces if the still is not shut down at more or less frequent intervals to remove this deposit.

Among the constituents produced by the cracking operation which seems to be particularly objectionable are certain 'of the sulfur-containing compounds. In charging stock which contains sulfur, certain of the sulfur compounds app ear to undergo cracking to form sulfur-containing constituents, probably of an asphalt-like character, which are particularly objectionable. Analyses of the carbon depositon the heated tubes of a cracking still indicate that certain of these sulfur-containing constituents have a preferential aflinity for the heated surfaces, or tend to separate out on such surfaces, to give a deposit containing both iron and sulfur: in proportions approximating those of It may be also that asphaltlike constituents of a colloidal character, or even colloidal carbon, formed as a result of the cracking operation, tend to separate out on the heated surfaces of the still in a preferential manner.

In'the prior application of one of us Serial No. 574,380 filed July 12, .1922, patented Aug. 31, 1926, No, 1,598,136 there is described an improved process of cracking oil according to which the length of time during which the cracking operationcan be continued is prolonged by withdrawmg pitchladen tar from the pressure still and introducing fresh feed at a regulated rate to maintain the pitch content of the charge below the saturation point.

The present invention involves a further improvement upon the process of said prior application, and similarly involves the carrying out of the cracking operation with the introduction of fresh feed and the withdrawal of pitch laden-tar to maintain the ;still charge below saturation.

We have found that the length of time during which the operation of the pressure 4 still can be continued can be greatly propitch laden tar, we have found that the length of the pressure still run can be pro longed far beyond anything which has heretofore been considered feasible, so far as we are aware, in the operation of pressure stills for the production of pressure distillate therefrom.

The bed of fullers earth which is maintained in the still in contact with the charge, and through which the "charge is continuously circulated, does not remove from the charge all of the pitch-like -constituents; but it has aselective action upon certain of these constituents, and apparently removes those constituents which are particularly objectionable from the standpoint of forming a carbon deposit on the heated surfaces of the still. This selective action may be in part a filtering action, or a selective absorbent action for colloidal carbon or precipitated asphalt-like constituents, or sulfurcontaining constituents, etc. Whatever the explanation of the'action of the fullers earth may be, it has an important protective effect in preventing objectionable carbon deposit. The fact that without the fullers earth the carbon deposit contains an important and relatively large percentage of sulfur, whereas in the process of the present nvention such objectionable sulfur-containmg deposit is avoided, indicates that the fullers earth has a selective desulfurizing action upon the pressure still charge, selectively removing therefrom certain of the objectionable sulfur-containing constituents of the charge. It is probable also that constituents of an asphalt-like character roducedlby the cracking operation and w 'ch tend to separate out from the charge as suspended particles are removed from the circulating charge by the filtering or selective absorbent action of the fullers earth bed.

In addition to the selective action of the fullers earth upon the charge, the pitch content of the charge is regulated by the introduction of fresh feed and the withdrawal of pitch laden tar, so that the pitch content of the charge as a whole is maintained below the point which would cause objectionable carbon deposit on the heated surfaces of the still.

Accordingly, in the process of the present invention, both the nature and the amount of the asphaltic or pitch-like .con stituents in the charge are regulated, certain of these constituents being selectivelyremoved by the circulation of the charge through the bed of fullers earth, and the content of remaining constituents in the charge being regulated and controlled by the withdrawal of pitch laden tar and the introduction of fresh feed during the cracking operation.

The entire body of oil charged into the pressure still, for example, gas oil, serves to ,hold in solution the pitch-like constituents that are formed. In the processof the present invention, however, only the pitchlike constituents which are not removed by the fullers earth bed remainto be held in solution in the charge. In a batch run, that is, a run in which no tar is withdrawn, the pitch content gradually increases until finally the saturation point is reached, and during the latter portion of the run, the pitch concentration may be greatly in excess of saturation in the remaining oil of the still charge. When fresh charging stock is introduced during the cracking operation,

this also assists in holding the pitch-like constituents in solution but as part of the fresh charging stock is cracked and as additional portions of the charge already in the still are also cracked, the increased solvent effect of the fresh charging stock will not take care of the increased amount of pitch like constituents formed and sooner or later the amount of such constituents will increase to a point where objectionable deposition will .take place on the heating surfaces. Inthe improved process of the present invention this is prevented in part by selectively removing a part of the objectionable constituents and holding them in the still and preventing their contact with the heatifnlgl surfaces by the action of the bed of ersearth, and in part by the regulation of the pitch content of the charge by intro duction of fresh feed and regulated withdrawal of pitch laden tar.

In the process of the present invention, accordingly, both the nature and the amount of. asphaltic or pitch-like constituents conllO tained in the charge circulated over the heated surfaces are regulated, the selective action of the fullers earth removing what we consider to be the more objectionable constituents, and the introduction of fresh feed and withdrawal of pitch laden tar regulating the concentration of the less-objectionable pitchlike constituents in the charge. Such pitch-like constituents as remain in the circulating charge, after its passage through the fullers earth bed, we consider to be held completely in solution in the circulating charge, where the amount of tar withdrawn and of fresh feed introducedis regulated to maintain the pitch content be low the saturation point.

In its broader aspects and embodiments, the improved process of the invention can be carried out in stills of different constructions. Whatever the type of still, the fullers earth is supported in the form of a bed through which the entire charge can becirculated, and the still is provided with circulating means for circulating the charge through the fullers eartlr bed. The fullers earth is also supported out of contact with the heating surfaces of the still, and circulation of the oil over such heating surfaces as well as through the fullers earth bed is provided for. The circulating charge thus circulated in contact with the heating surfaces thus contains only the constituents which are not removed by the circulation through the fullers earth bed, and only such a content of .such constituents as is permitted by the regulated introduction of feed and withdrawal of pitch laden tar.

The provision of a large bed of fullers earth Within the pressure still itself has the advantage that a large surface area of the earth is exposed to the charge, and a large area of earth bed is provided'for circulation of the charge therethrough. The pressure still construction need not be changed by the provision of additional external equipment; but pressure stills of present day construction can readily be provided with a suitable support extending across the interior of the still for supporting the bed'of earth in contact with the still charge and permitting free passage of the charge thereth ngh.

The improved process of the present invention is particularly advantageous in the cracking of oils in tubular cracking stills or so-called tube stills, with the fullers earth maintained in the form of a bed'extending across the drum or bulk supply tank containing the main charge of oil, and with circulation of the oil from such drum through heating tubes and backv to the drum.

The'tube stills may have either horizontal or vertical tubes, and may be of the bank or continuous type, with mass or stream circulationr The tube still may thus be one in whichvthere is stream circulation through a through a large number of heating tubes.

The still may be one in which thermal action is relied upon to cause the circulation of the charge through the heating tubes, or it may be one in which the circulation through the tubes is effectedby mechanical means, such as a circulating pump.

In such tube stills the circulation of the charge through the tubes and through the bed of fullers earth in the bulk supply tank or drum results in causing all portions of the circulating charge to pass through the bed of earth in the bulk supply tank before they recirculate through the tubes, while the charge in the bulk supply tank is in contact with a large area of the fullers earth through which the charge is circulated.

The invention will be further described and illustrated in connection with the accompanying drawing which shows in a somewhat conventional and diagrammatic manner, one form of tubular pressure still adapted for the practice of the process of the invention; but it is intended and will be understood that the invention is not limit-- ed to the specific construction and operation so describe In the accompanying drawing, Fig. 1 shows, in a somewhat conventional and diagrammatic manner, and with part in section and part in elevation, one arrangement of a tubular pressure still adapted for carrying out the process of the invention;

Fig. 2 is a sectional View of the drum or bulk supply tank of Fig. 1;

Fig. 3 is an enlarged detailed sectional View of one form of screen support by which the fullers earth or like material is supported in the still; and

Fig. 4 is a similar view of a modified construction of screw support.

The pressure still illustrated comprises the shell or bulk supply tank 1 having an outlet pipe 2 leading to the pump 3 by which the oil is pumped through the lower connecting pipe 4 to the distributing pipes and headers of the vertical tubes 5. From these tubes the oil is returned through the upper headers and connecting pipes and the return lines 6 to the bulk supply tank 1.

. The vertical tubes 5 are shown as enclosed within a furnace having one or more burners 7 adapted to be heated by gas or oil, the main furnace chamber 8, and three passes 9. 10 and 11 separated by bafiies for causing the furnace gases to pass over the vertical tubes in a back and forth manner before they escape through the connecting flue 12 to the stack 13. i

From the drum 1 of the pressure still a vapor line 14 leads to the reflux tower 15 which is shown as a bafiie tower having a series of baflies 16 therein. This tower has a return pipe 17 leading from the bottom and discharging into the outlet pipe 2. The vapor line 18 leads from the top of the refiux tower to the condenser 19 from which the condensate and uncondensed gas are col lected in the receiver 20. Draw-off pipes 21 and 22 are provided for drawing off the uncondensed gas and the condensate respectively from the receiver 20.

A pressure regulating valve 23 is provided between the still and condenser, or the presa relatively deep body of fullers earth or earth of 15 to 30 mesh. 1

like absorbent material indicated at 31. A

' cross-section of one suitable form of screen 4 mesh screen 33, a 40"mesh screen 34, an-

other 4 mesh screen 33 and another 3/8 thick steel plate 32 with perforations therein. A modified and simpler form of support is illustrated in Fig. 4, made up of the upper and lower perforated plates 32 having the screen 34 between them. The nature of this support can be varied so long as it performs the function of supporting the earth without leakage. L

Where finely divided earth is used, the support should be sufiiciently fine to prevent escape of the earth therethrough.

We have found it advantageous, however, to use relatively coarse fullers earth, e. g.

It will be noted that the perforated support and screen form a floor over the bottom of the still. With such a screen, thoroughly sealed by welding or rivetin at the joints and secured to the walls, or the still, the earth placed upon the support cannot leak past it and collect in the circulating system, but is all maintained in the upper portion of the drum above the screen. With a" tubular cracking still of the character illustrated, and with the bulk supply drum about 9 ft. in diameter, the perforated floor may advantageously be located approximately 2 ft. above the bottom of the drum, and a bed of fullers earth of for example 10 to 18 inches in depth and containing about 4 to 7 tons of earth may advantageously be used, although the depth and amount of the earth can be varied.

From Fig. 1 it will be noted that the return pipes 6 extend a considerable distance into the drum 1 and terminate in extensions 0 6 discharging to the remote end of the drum from that at Which the outlet.2 is arranged.

.l/Vhere the velocity of the oil discharged from the pipe 6 is such as to cause erosion of the bed of fullers earth, this bed can be protected by a plate at the point of greatest velocity so as to prevent objectionable erosion. 7

In the operation of the pressure still, and

in the carrying out of the cracking process eration, the oil is circulated by the circulating pu1np'3 from the bulk supply tank 1 through the connectip pipes 2 and 4: to the heating tubes 5 and t ren back through the pipes 6 and (S to the drum 1, discharging into this drum at the far end. Vapors from the oil are released in the bulk supply tank and pass up through the vapor line 14 into the reflux tower where the heavier ends are condensed by feed introduced into the top of the reflux tower through the feed line 27, and pass with such feed through the reflux tower and the run-hack line to the pump circulation. The uncondensed vapors pass through the vapor line from the reflux tower through the pressure control valve to the usual condenser and receiver.- feed can be introduced through the bearings of thepump by means of a feed line 35.

The charge is Withdrawn from the drum below the perforated support and is circulated through the heating tubes and back to the drum or bulksupply tank'above the perforated support. The unvapoi'ized portion of the charge,'before it can again be withdrawn and passed through the heating tubes, must pass downwardly through the bed of earth, and the bed of'earth thus has an opportunity of exerting its selective absorbent action upon the objectionable asphaltic or pitch-like :constituents of the charge. In the apparatus illustrated it will be noted that the bed of earth is completely submerged or immersed in the body of the charge and that it providesa large surfacearea in contact with the charge and a large sectional area through which the charge can flow downwardly at a relatively reduced rate as compared with the rate of circulation through the heating tubes. 'Ainple opportunity is thus provided for the earth to exert its selective absorbent action as the charge' is slowly circulating or filtering downwardly therethrough. f if The bed of absorbent :material is not, however, relied upon alone to take care of the pitch-like constituents formed by the cracking operation. In the apparatus illustrated Additional it will be noted that the fresh feed introduced through the reflux tower and also the refluxed vapors from the. still are returned to the outlet pipe 2 from the bulk supply tank and that additional feed may be introduced through the pipe 35 and the pump bearing. The circulating charge, therefore, is made up of the fresh feed and reflux together with such portion of the still charge itself as percolates downwardly through the bed of absorbent material. The oil after circulation through the heating tubes is discharged into the upper compartment of the bulk supply tank above the bed of absorbent material.

As thepitch content of the charge increases, and before the pitch content reaches the point of saturation, tar is drawn oil through the line 26 from the body of oil above the bed of absorbent material and in this way a part of the pitch-laden charge of the still is withdrawn from the still. This withdrawal of tar combined with the introduction of fresh feed serves to hold down the concentration of pitch in the charge and to maintain'the pitch content considerabl lower than it would otherwise be if the pitch were permitted to'accumulate in the charge. The main burden of removing the pitch is thus taken away from the body of absorbent material which is however relied upon to remove certain of the pitch-like constituents.

At no time during the run, therefore, does thepitch content of the charge circulated through the heating tubes increase to such a point nor does the circulating charge contain constituents of such a. character as to cause objectionable deposition of pitch or carbon on the heating surfaces. This deposition is prevented in part by the withdrawal of tar with the pitch in solution and the introduction of fresh charging stock to the still, and in part by the absorbent action of the body of fullers earth or like material upon the portion of the charge which is recirculated through the heating tubes.

The absorbent action of the fullers earth or like material is such that an increased percentage of the charge can be taken off as pressure distillate, and an increased pitch content can be maintained in the circulating charge during the run, without objectionable carbon deposit' on the heating tubes. Even where the pitch content of the charge approaches saturation, the removal from the circulating charge of the constituents which are removed by the fullers earth enables the operation to be continued for a much longer period of time without objectionable carbon deposit on the heating tubes. Even where the pitch content is maintained considerably above saturation, the fullers earth will remove from the circulating charge objectionable constituents which would otherwise tend to separate out. on the heating tubes.

' The fullers earth of commerce is obtained in varying degrees of fineness. The finest for oil refining, are not so well adapted for use in the process of the present invention as the coarser grades, e. g., from 15 to 30 mesh, which permit ready flow of the circulating oil therethrough, and which do not tend to leak through the supporting screen and enter the circulating stream of oil. We have found Olmstead earth of 15-30 mesh well adapted for use in the process of the invention. Fullers earth is of a clay-like character, and may be considered as an absorbent clay. Otherabsorbent clays having similar properties can similarly be used in the process of the invention. In so far as the action of the fullers earth is a filtering action in which the earth absorbs or adsorbs or otherwise holds particles of colloidal carbon or asphaltic constituents, etc., thus removin them from the circulating charge, other filteringmaterials can be used to obtain similar results. Other absorbent materials, having a similar selective absorbent action upon the objectionable asphaltic or pitch-like constituents of the circulating charge can also be used. So also, from the standpoint of the desulfurizing action of the fullers earth, other porous or finely divided materials'having a similar desulfurizing action can be used to remove or assist in removing in a selective manner the objectionable sulfur-containing constituents of the circulating charge, for example, silica gel. Our use of fullers earth indicates it to be a particularly advantageous material for use in the process of the invention, inasmuch as it appears to combine in itself valuable filtering, selective absorbent, desulfurizing and other properties which favorably afi'ect and benefit the pressure still operation.

In carrying out a run according to the present invent-ion, the still can be charged with fresh charging stock in the usual way. The charging stock may be, for example, gas oil or other suitable charging stock which is to be cracked for the production of gasoline or pressure distillate therefrom. The still charge is brought to the required cracking temperature and pressure in the usual manner. After the cracking temperature is reached, cracking begins and takes place in a gradual and progressive manner, the lighter vapors formlngthe pressure distillate passing off and being removed from the still, while the heavier vapors are refluxed back to the still. The asphaltic or pitch-like constituents formed are in part absorbed b the fullers earth and in part held in so ution in the remaining constitgrades of earth such as are commonlyused Ian uents of the charge. As the reaction proceeds, the unabsorbed pitch constituents continue to dissolve in the oil and would ultimately approach the saturation point therein. During this period of formation of pitch however the charge is subjected to the absorbent action of the fullerfs earth or like.

- the rate of tar withdrawal and of increased introduction of fresh feed is so regulated that the pitch content is held below the saturation point in the still. The circulating charge is thus kept of a regulated pitch content, while the\ circulating charge is also subjected to the absorbent action of the body of absorbent material therein, and. the maintenance of a regulated pitch content in the charge is thus supplemented by the selective absorbent action of the absorbent material.

Fullers earth has been found to be a particularly advantageous material to use in the process of the present invention. It can advantageously be charged into the still in an uncalcined condition. and the earth will be dehydrated during the bringing up of the still to cracking conditions, and the water present in the earth will be driven off along with the drips before the still reaches cracking conditions. Calcined earth can however be used. A bed of fullers earth approximately 10 to 18 inches deep has been found satisfactory.

It will be evident that the pressure maintained during the cracking operation can vary, depending upon the character of the charging stock and other considerations. For example, with a gas oil charging stock, a pressure of around to lbs. or even up to 125 lbs. can be used. kerosene charging stock, a higher pressure, e. g. from 125 lbs. up to around 300 lbs. is used with advantage. The pressure can be regulated by a pressure reducing valve maintained between the still and condenser, or the condenser can likewise be maintained under still pressure, and the pressure regulated by a pressure regulating valve at the outlet of the receiver.

The character of the charging stock used in the process can also be varied. In particular, a charging stock which contains constituents which otherwise would tend to cause an increased deposit of carbon or coke on the heating surfaces can be used in the process and the apparatus of the present invention and their objectionable tendency overcome or greatly reduced, owing to the selective or preferential. absorption of such impurities by the fullers earth bed.

The following is an example of the prac- VVith a lighter tice of the present invention as'carried out in a still of the character illustrated in the drawing:

The fullers earth used was Olmstead fullers earth of 16 to 30 mesh and the still was charged with seven tons of the raw earth forming a bed approximately eighteen inches deep on a perforated support of the character illustrated which was arranged approximately two feet above the bottom of the drum, the drum being about nine feet in diameter. The still was charged with ten thousand gallons of gas oil charging stock. The still charge was heated, drips were taken off and the charge was brought to a working pressure of about one hundred and twentyfive pounds. The still was then opened to the condenser and the distillate began to pass over. At about the same time or shortly thereafter, the introduction of fresh charging stock into the still was begun, the amount corresponding approximately to the amount of overhead distillate taken off, e. g., about one thousand gallons per hour, this representing a rate of distillate off of about ten percent of the charge. During the early portion of the run the pitch content of the charge increased, there being no withdrawal from the still except of distillate during this period. Before the pitch content reached saturation, however, the withdrawal of tar was begun and the rate of charge of fresh feed was correspondingly increased so that it was approximately equal to the distillate off plus the tar withdrawn. The drawing. off of tar or heavy oil was continued throughout the remaining portion of the run. While the rate of tar withdrawal can be somewhat Varied, an advantageous rate has been found to be such that approximately sixty percent of the hourly charge is withdrawn as tar and approximately forty percent as overhead distillate. For example, the still may be continually charged during the run, after the withdrawal of tar is begun, with approximately twenty-five hundred gallons an hour of fresh charging stock, and about a thousand gallons an hour or forty percent of the hourly charge withdrawn as overhead distillate and the remaining sixty percent or approximately fifteen hundred gallons an hour withdrawn as tar. During this continuation of the run. the still charge which is circulated through the heating tubes will be subjected to the absorbent action of the body or bodies of fullers earth or like material in the manner above referred to.

In another run the still was charged with eight thousand gallons of gas oil, and about seven tons of raw Olmstead fullers earth of 16 to 30 mesh was charged into the still, forming a bed about 18 inches deep. The

earth was supported on a support such as illustrated in Fig. 4, made up of a 28 mesh lift) screen between two inch plates having inch perforations. The size of the still drum was about 9 feet in diameter and about 31.6 feet long. Thebringing up period was about 12 hours, and the still was maintained on stream for 178 hours at. about 95 lbs. pressure: During the first three hours the feed was equal to the distillate off. Thereafter the drawing oifsof tar was begun and the.

feed increased. I The rate of distillate was about 600 gallons an hour, the rate of tar draw-off about 900 gallbns an hour, the rate of feed through the reflux tower about 900 gallons an hour, and the rateof feed through the pump about 600 gallons an hour. The

rate of c rculation through the heating tubes was about 2000 gallons :1 minute. A total charge of about 250,000 gallons was treated, giving about or about 100,000 gallons of gravity-distillate. The coke removed from the tubes on cleaning, after the run was terminated, was about 167 lbs. of soft coke, probably for the most part or entirely left from adhering tar when the still wastion, a higher percentage can be taken off as distillate, the fullers earth inhibiting the formation of objectionable carbon deposit. For example, "in continuous operation, instead of taking off thirty to forty per cent as distillate, from forty to fifty per cent of distillate, or more, can be taken off. When the still is operated to obtain a higher percentage of distillate off, a somewhat more unsaturated product may be obtained, and

the amount of tar to be drawn ofl", and to be redistilled or otherwise treated or disposed of will be less. With higher percentages off as distillate, less Heat- 'is required in heating up the additional stock and more heat is available for cracking.

\Vith higher percentages 013? as distillate,'a material saving in fuel is effected, due to the greater percentage of distillate and also due to the proportionate decrease in time re quired to bring the still to crackingconditions of temperature and pressure for a given amount of total charge. Where the tar is redistilled, a further saving in fuel is effected, due to the decreased. amount of tar withdrawn. The gasoline production can in this way be greatly increased per still per day, while at the same time prolonging the run and reducing the proportion of time now lost for shutting down and cleaning, and decreasing the fuel consumption.

We have used the same bed of earth in successive runs, with removal of only a few inches ofthe top layer and replacement of it With a fresh layer of earth. After continued use, however, the fullers earth becomes spent or exhausted, and must be replaced by fresh earth.. The spent earth can e regenerated, or-may be otherwise utilized or disposed of. When a runis terminated, and the charge has been withdrawn and the still steamed out, we have found the top of the earth covered with a thin layer or crust composed of earth and pitch or coke, with the earth bed underneath dry and granular. The plates and screen supporting :the earth were free from coke, as was also the bottom circulatory line from the bulk supply tank to the heating tubes, owing to the protective action of the earth in removing constituents which would otherwise tend to deposit on such surfaces.

In the process of the present invention, the entire body of the charging stock and of the still charge is relied upon to hold in solution such of the pitch-like or asphaltic constituents, formed by the cracking operation, as are not removed by the fullers earth bed. Such constituents of the charge as are converted into the pressure distillate constituents or into pitch or asphaltic constituents will no longer be present to exert their solvent action upon the remainder of the charge; but with the progressive cracking of the charge and the gradual and progressive formation of pitch-like constituents, the relative amount of such pitch-like constituents with reference to the remainder of the charge will progrcssivelyjncrease and the solvent capacity of the still charge for such pitch-like constituents will progressively decrease. These relative proportions however will be regulated by the withdrawal of tar and the introduction of fresh charging stock to maintain the pitch content below saturation; while this regulation of the pitch content will be supplemented by the action of the absorbent material upon certain of the pitch constituents. I n

As compared with cracking operatlons 1n which a body or bodiesof absorbent material are not used and in which the maintenance of the pitch concentration below saturation does not occur, the process of the present invention not only enables a greatly prolonged run to be effected; but it enables a heavier charging stock to be more satisfactorily cracked. A heavy gas oil charging stock, for example, can be used in the process of the present invention,'and the fresh charging stock introduced during the progress of the cracking operation can also be heavier in cha acter, since the fullers earth or like materia serves to absorb and remove selectively certain of the pitch-like constituents which would otherwise cause trouble, and since the regulation of the pitch content of the charge, in combination with such selective removal of pitch-like constituents, serves to protect the heating surfaces from objectionable carbon deposit.

The rocess of the present invention can also a vantageously be carried out upon lighter charging stock, for example, charghydrocarbon oils under pressure which comprises heating a charge of the oil in a pressure still to the cracking temperature under pressure, maintaining in said still charge a body of fullers earth or similar absorbent material supported on a support adapted to permit free passage of oil and extending entirely across the charge of oil in the pressure still, Withdrawing oil from beneath said support and circulating it through heating tubes and discharging the oil from said tubes directly into the body of oil above such absorbent material.

2. The improvement in the cracking of hydrocarbon oils under pressure which comprises heating a charge of the oil in a pressure still to the cranking temperature under pressure, maintaining in said still charge a body of filtering material supported on a support adapted to permit free passage of oil and extending entirely across the charge of oil in the pressure still, withdrawing oil from beneath said support and circulating it through heating tubes and discharging the oil from said tubes directly into the bodyof oil above such filtering material.

3. The improvement in the cracking of hydrocarbon oils under pressure which comprises heating a charge of the oil in a pressure still to the cracking temperature under pressure, maintaining in said still charge a body of desulphurizing material supported on a support adapted to permit free passage of oil and extending entirely across the charge of oil in the pressure still, withdrawing oil from beneath said support and circulating it through heating tubes and discharging the oil from said tubes directly into the body of oil above such desulphurizing material.

4. The improvement in the cracking of hydrocarbon oils under pressure which comprises heating a charge of the oil in a pressure stilltothe cracking temperature, maintaining in said still charge a body of fullers earth or similar absorbent material supported on a support adapted to permit free passage of oil and extending entirely across the prises heating a charge of the oil in a pres-.

sure still to the cracking temperature, maintaining in said still charge a body of filt'ering material supported on a support adapted to permit free passage of oil and extending entirely across the charge of oil in the pressure still, withdrawing oil from beneath said support and circulating it'through heating tubes and discharging the'oil from said tubes directly into the body of oil above such filtering material, and preventing the saturation of the still charge with pitch by feeding fresh charging stock and withdrawing pitchladen oil from the still.

6. The improvement in the cracking of hydrocarbon oils under pressure which comprises heating a charge of the oil in a pressure st1ll to the cracking temperature, maintaining in said still charge a body of d'esul-v phurizing material supported on a support adapted to permit free passage of oil and extending entirely across the charge of oil in the pressure still withdrawing oil from beneath said support and circulating it through heating tubes and discharging the oil from said tubes directly into the body of oil above such desulphurizing material, and

preventing the saturation of the stillcharge" with pitch by feeding fresh charging. stock and withdrawing pitch laden oil from the still.

7'. The improvement in the cracking of hydrocarbon oils under pressure which comprises heating a charge of the oil in a pres-- sure still to the cracking temperature under pressure, maintaining in said still' charge a body of fullers earth or similar absorbent material supported on a support adapted to permit free passage of oil'and extending entirely across the charge of oil in the pressure still, withdrawing oil from beneath said support and rapidly circulating it through heating tubes and discharging the oil from said tubes directly into the body of oil above such absorbent material, and circulating the oil relatively slowly through the absorbent material.

8. The improvement in the cracking of hydrocarbon oils under pressure which comprises heating a charge of the oil in a pressure still to the cracking temperature under pressure, maintaining in said still charge a body of filtering material supported on a support adapted to permit free passage of oil and extending entirely across the charge of oil in the pressure still, withdrawing oil from beneath said support and rapidly circulating it through heating tubes and discharging the oil from said tubes directly into the body of oil above such filtering material, and circulating the oil relatively slowly through the filtering material.

9. The improvement in the cracking of hydrocarbon oils under pressure which comprises heating a charge of the oil in a pressure still to the cracking temperature under pressure, maintaining in said still charge a body of desulphurizing material supported on a support adapted to permit free passage of oil and extending entirely across the charge of oil in the pressure still, withdrawing oil from beneath said support and rapidly circulating it through heating tubes and discharging the oil from said tubes directly into the body of oil above such desulphurizing material, and circulating the .oil relatively slowly through the desulphurizing material.

10. The improvement in the cracking of hydrocarbon oils under pressure which comprises heating a charge of the oil in a pressure still to the cracking temperature, maintaining in said still charge a body of fullers earth or similar absorbent material supported on a support adapted to permit free passage of oil and extending entirely across the charge of oil in the pressure still, withdrawing oil from beneath said support and rapidly circulating it through heating tubes and discharging the oil from said tubes directly into the body of oil above such absorbent material, circulating the oil relatively slowly through the absorbent material, and preventing the saturation of the still charge with pitch by feeding fresh stock and withdrawing pitch laden oil.

11. The improvement in the cracking of hydrocarbon oils under pressure which comprises heating a charge of the oil in a pressure still to the cracking temperature, maintaining in said still charge a body of filtering material supported on a support adapted to permit free passage of oil and extending entirely across the charge of oil in the pressure still, withdrawing oil from beneath said support and rapidly circulating it through heating tubes and discharging the oil from said tubes directly into the body of oil above such filtering material, circulating the oil relatively slowly through the filtering material, and preventing the saturation of the still charge with pitch by feeding fresh stock and withdrawing pitch laden oil.

12. The improvement in the cracking of hydrocarbon oils under pressure which comprises heating a charge of the oil in a pressure still to the cracking temperature, maintaining in said still charge a body of desulphurizing material supported ona support adapted to'permit free passage of oil and extending entirely across the charge of oil in the pressure still, withdrawing oil from beneath said support and rapidly circulating it through heating tubes and discharging the oil from said tubes directly into the body of oil ab v such desulphurizing material, circulating the oil relatively slowly through the desulphurizing material, and preventing the saturation of the still charge with pitch by feeding fresh stock and withdrawing pitch laden oil.

13. The improvement in the cracking of hydrocarbon oils under pressure which comprises heating a charge of the oil in a pressure still to'the cracking temperature under pressure, maintaining in said still charge a body of fullers earth or similar absorbent material supported on a support adapted to permit free passage of oil, and extending entirely across the charge of oil in the pressure still, withdrawing oil' from beneath said support and circulating it through heating tubes and discharging the oil from said tubes directly into the body of oil above such absorbent material, and feeding fresh oil to the pressure still and drawing oflf pitch-laden oil therefrom, this pitchladen oil being withdrawn from the body of oil above such absorbent material.

14. The improvement in the cracking of hydrocarbon oils under pressure which comprises heating a charge of the oil in a pressure still to the cracking temperature under pressure, maintaining in said still charge a body of filtering material supported on a support adapted to permit free passage of oil, and extending entirely across the charge of oil in the pressure still, withdrawing oil from beneath said support and circulating it through heating tubes and discharging the oil from said tubes directly into the body of oil above such filtering material, and feedin sure still and drawing ofi' pitch-laden oil therefrom, this pitch-laden oil being withdrawn from the body of oil above such filtering material.

15. The improvement in the cracking of hydrocarbon oils under pressure which comprises heating a charge of the oil in a pressure still to the cracking tem erature under pressure, maintainin in said still charge a body of desulphurizing material supported on a support adapted to permit free passa e of oil, and extending entirely across t e fresh oil to the pres-.

charge of oil in the pressure still, Withdrawing oil from beneath said support and circulating'it through heating tubes and discharging the oil from said tubes directly 5 into the body of oil above such desulphurizing material, and feeding fresh oil to the pressure still and drawing 0H pitch-laden oil therefrom, this pitch-laden oil being Withdrawn from the body of oil above such clesulphurizing material. m

In testimony whereof We aflix'our signatures.

EUGENE C. HERTHEL. HARRY L; PELZER.

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