US1703529A - Cracking of heavier hydrocarbon oils - Google Patents

Description

'Feb. 2 1929. 1,703,529

E. C. HERTHEL ET AL CRACKING OF HEAVIER HYDROCARBON OILS Filed May 28, 1925 7 PIES OIL (lb CONDENSED MPO 4N0 64555 Z0 INVENTORS Eugene C. f/erzheZ vflurry l. PeZzer EwQ IQWZM+M ATTORNEYS Patented Feb. 26, 1929.

UNITED STATES EUGENE C. HERTHEL AND HARRY L. IELZER, OI CHICAGO, ILLINOIS, ASSIGNOBS 'IO PATENT OFFICE.

SINCLAIR REFINING COMIANY, OF CHICAGO, ILLINOIS, A. CORPORATION OF MAINE.

CRACKING 0F HEAVIEB HYDROGARBON': OILS.

Application filed May 28, 1925.

- cation is in part a continuation of our copending application Serial No. 704,926, fi1ed April 5, 1924, which has issued a Patent 1,634,666. The invention comprises an improved process which assists in protectin, the heating tubes of the cracking still and which also enables the cracking operation to be continued for a prolonged period of time before the deposition of carbon begins or before it is necessary to shut down the cracking still for cleaning pur oses.

In the cra king o heavier petroleum oils in pressure stills for the production of gasoline or pressure distillate therefrom there are formed during the cracking operation certain constituents of an asphaltic or pitch-like character. With continuation'of the crack ing operation, the amount ofsuch constituents 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 thestill and the prelimi nary heating of the still to bring the fresh charge u to cracking conditions, all require time, an 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 in the heating tubes of the pressure still is retarded or reduced so that overheating or danger of failme of the heating tubes can be effectively prevented, and the time of operation of a single run can be somewhat prolonged, with corre spondingly less loss of time and greater production per still per day. I

When a. pressure still is charged with gas oil or other charging stock tosubjected to Serial No. 38,390.,

cracki'n and when the charge is heated to the crac ring temp.erature,.th e crackingtakes place n a gradual and progressive manner. The l1ghter 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 asphaltic or'pitchlike constituents is progressively formed. Such constituents appear to be of varying pro erties and characteristics. For the most par the 'remain in solution in the charge during t e early portion ofthe run, 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 ofsuch asphalti'c 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 ofa different character and to heating surfaces of the still. Furthermore, as the charge becomes supersaturated with the less objectionable pitch-like constituents. there is an increased danger of de sit of pitch or carbon on the heating sur aces of have an increased tendency to deposit on the the still, with corresponding danger of overl heating and failure of the heatedsurfaces w -i 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 seem to be. particularly objectionable are certain of the sulfur-containing compounds. With chargingv Q5 stock which contains. sulfur, certain of'the sulfur compounds appear to undergo ctacking toform sulfur-containing constituents, probably of an asphalt-like character, which are particularly objectionable. Analyses of the carbon deposit on the heating tubes of a cracking still indicate that certain of these sulfur-containing constituents have a preferential afiinity for the heated surfaces, or tend to separate out on such surfaces, to give a deposit containing both iron and sulfur in proortions approximating those of iron sulde. It may be also that asphalt-like constituents of a colloidal character, or even colloidal carbon, formed as a result of the cracking operation, tend to separate out in the heating tubes of the still ina preferential manner.

' The present invention relates more particularly to an improved method of cracking heavier oils in tubular pressure stills in a batch or semi-continuous operation, and in volves the maintenance within the pressure still of a body of fullers earth in directcontact with the still charge through which the still charge is circulated during the cracking operation.

We have found that the length of timeduring which the operation of a tubular pressure still can be continued can be somewhat prolonged b maintaining within the pressure still a ody of fullers earth, in direct contact with the still charge, and by causing the still charge to circulate repeatedly through said body of fullers earth during the progress of the cracking operation. We have also found that the maintenance of a body of fullers earth within the still charge is of advantage in protecting the heating tubes of the still from corrosion, overheating and burning out, and in reducing carbon dep: osition upon the heating surfaces, whether or not the operation is carried out over a prolonged period.

The bed of fullers earth which is maintained in the still in contact. with the charge, and through which the charge is continuous- 1y circulated, does not remove from the charge all of the pitch-like constituents; but

- it hasa selective 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 heating tubes ofthe 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 sulfur containing constituents, etc. Whatever the explanation of the action of the fullers earth may be, it has an important protective eflect in preventing objectionable carbon deposit. The fact that Without the fullers earth the carbon dc osit contains an important and relatively arge percentage of sulfur, whereas in the process of the present invention such objectionable sulfur containing deposit is avoided, or reduced, indicates that the fullers earth has a selective desulphurizing action upon the pressure still charge, selectively removing therefrom certain of the objectionable sulphur containing constituents of the charge. It is also probable that constituents of an asphalt-like character produced by the cracking operation and which tend to separate out from the charge as suspended ever, only the pitch-like constituents whichv are not removed by the fullers earth bed remain to be held in solution in the charge, and the fullers earth, in'addition to its selective action upon the charge, apparently increases the amount of pitch-like constituents which the charge will hold in solution. Where no tar is withdrawn during the operation, or where a relatively small amount of tar is withdrawn, the pitch content gradually increases and approaches the saturation point, and during the latter portion of the operation, the pitch concentration may reach and even greatly exceed the saturation point in the remaining oil of the still charge. Where 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 crackedand as additional portions of the charge already in the still are also cracked, the increasedvsolvent efiect of the fresh charging stock is overcome and the unvaporized portion of the fresh charging stock also becomes progressively saturated. the improved process of the present invention, part of the pitch-like constituents produced during the cracking operation are removed by the action of the body of fullers earth, and, in some cases, the saturation concentration or pitch-like constituents in the still charge may also be increased. his latter possibility is apparently due to t e character of the components of the charge removed by the body of fullers earth, and to a selective action of the earth uponcertain of'the constituents of the charge which .tend to cause rapid precipitation of pitch-like constituents and also to the fact that those pitch-like constituents not removed and remaining in the charge are less injurious. In either batch or semi-continuous operation, the cracking operation is terminated when, or before, the amount of pitch-like constituents remaining in the charge, above the amount removed by the fullers earth bed and any amount withdrawn as tar, increases to a point where objectionable deposition will take place in the heating tubes of the still.

In the process of the present invention, accordingly, both the nature of asphaltic or pitch-like constituents contained in the charge circulated through the heating tubes is controlled and the amount of such constituents or the rate of formation of such constituents is somewhat restricted, the selective action of the fullers earth removing what we consider to be the more objectionable constituents and permitting a higher concentration of less objectionable pitch-like constit ents in the charge. Such pitch-like constituents as remain in the circulating charge, after its passage through the fullers earth bed, and up to the point where objectionable deposition begins, we consider to be held in solution in the circulating charge.

In one particularly advantageous way' of carrying out the improved process of the present invention, fullers earth is maintained in the form of a bediextending across the drum or bulk supply tank containing the main charge-of oil, and the oil is circulated from such drum through heating tubes and back to the drum. The fullers earth is supported in the form of a bed through which theentire charge can be circulated, and the still is rovided with circulating means for circulating the charge through the fullefis earth bed. The fullers earth is also sup ported out of contact with the heating surfaces of the still, and provision is made for circulation of the oil through the heating tubes as well as through the fullers earth bed. The circulating charge thus circulated through the heating tubes thus contains only the constituents which are not removed by the circulation through the fullers earth bed. 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 rovided for circulation of the charge theret rough. The pressure still con: structionneed not be changed by the provision of additional external equipment; but tubular circulatory pressure still s stems of present day construction can rea ily be I provided with a perforated support extend ing across the interior of the still for supporting the bed of 'earth in contact with the still charge. The heating tubesmay be either horizontal or vertical, and maybe in either bank or continuous arrangement with mass or stream circulation. The tube still may thus be one in which there is stream circulation through a series of tubes in the form of a continuous stream; or the circulation may be in parallel 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 efiected by mechanical means, such as a circulating pump. In such tubular stills the'circulation of the charge through the heating 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 heating 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 accompany ing drawing which shows in a somewhat conventional and diagrammatic manner, one form of tubular pressure still embodying the invention and adapted for the practice of the process of the invention; but it is intended and will be understood that the invention is not limited to the specific construction and operation so described.

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 a tubular pressure still embodying the invention and adapted for carrying out the process of the invention;

Fig. 2 is a sectional view of the drum or bulk supply tank of Fi 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 screen 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 and three passes 9, 10 and 11 separated by baflles for causing the furnace gases to pass over the vertical tubes in a back and forth manner before.v they escape through the connecting flue 12 to the stack 13. From'the drum 1 of the ressure still a vapor line 14 leads to the re ux tower 15 which is shown as a ballie tower having a-series of battles v 16 therein. 'This tower hasa return pipe 17 leading from the bottom and discharging into the outlet pipe-2.= The vapor line 18 leads from the tops-of the reflux tower 15 to the condenser 19 from which the condensate and uncondensed gas are c ollectedin the receiver 20. Draw-off pipes 21 and 22 are provided for drawing ofi the uncondensed gas and t] 1e condensate respectively from the receiver 20.

A pressure regulating valve 23 is provided provided; as well as a safety valve 28. A

feed line 27 is shown for introducing fresh charging stock into the upper portion of the reflux tower.

forated plates Within the still is provided a perforated support 29 suitably secured to the shell of the drum, e. g., by welding, and upon this perforated screen or support is maintained a relatively deep body of .fullers earth or like absorbent material indicated at 31. A cross-section of one suitable form of screen support is illustrated in Fig. 3. This is made up of live layers, a top layer 32 of e. g. thick plate with perforations, a 4 mesh screen 33, a 40 mesh screen 34, another 4.- mesh screen 33 and another thick steel plate 32 with A perforations therein. A modified and simpler form of support is illustrated in Fig.4, made up of the upper and lower per- 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. lVhere finely divided earth is used, the sup port should be sufliciently fine to prevent escape of the earth therethrough. We have found it advantageous, however, to use relatively coarse fullers earth, 0. g. earth of 15 to mesh, in conjunction with a coarser supporting means. It will be noted that the perforated support and screen form a floor over the bottom of the still. \Vith such a screen,

thoroughly sealed by welding or riveting at 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 approximate 1y 2 ft. above the bottom of the drum, and a bed of fullers earth of for example 10 to 1.8 inches in depth and containing aboutt 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 6 discharging to the remote end of the drum from that at which the outlet 2 is arranged. Where 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.

Inthe operation of the pressure still, and in the carrying out of the cracking process of the present invention therein, the still is charged and heated to the cracking temperature and pressure. The still may be charged for example through the charging line 36 which may also serve as a tar draw-off at the end of the run. During the cracking operation, the oil is circulated by the circulating pump 3 from the bulk supply tank 1 through the connecting pipes 2 and 4 to the heating tubes 5 and then back through the pipes 6 and 6 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 fresh oil 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-back line to the pump circulation. The uncondensed vapors pass through the vapor line from the reflux tower through thepressure control valve to the usual condenser and receiver. Additional feed can be introduced through the bearings of the pump by means of a feed line 35. The charge is with drawn from the drum below the perforated support and is circulated through theheating tubes and back to the drum or bulk supply tank above the perforated support. The unvaporized 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 below the normal liquid level and is completely submerged or immersed in the body of the charge and that it provides a large surface area in contact with the charge and a large sectional area through which the charge can flow downwardly at a relatively reduced rate as comparedwith the rate of circulation through the heating tubes. Ample opportunity is thus provided for the earth to exert its selective absorbent action as the charge is slowly circulating or filtering downwardly therethrough.

The bed of absorbent material is not, however, relied upon alone to take care of the pitch-like constituents formed by the cracking operation up to the saturation point, or somewhat beyond the saturation point, in the remaining solvent constituents of the original charge. In the apparatus illustrated it will be noted that the fresh feed introduced through the reflux tower and also the refiuxed vapors from the still are returned to the outlet pipe 2 from the bulk supply tank and that additional feedv may be introduced through the pipe 35 and the pump bearings. 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 ent material part of the pitch-laden oil content of the charge increases.

The absorbent action of fullers earth or like material is such that an increased percentage of the charge, includin any fresh oil introduced during the operations, can be taken off as pressure distillate, and the pitch- I content of the circulating charge can be carried to an increased amount during the run without objectionable carbon deposit on the heating tubes. As the pitch content of the charge approaches saturation, the removal from the clrculating charge of the constituents which are removed by the fullers earth prolongs the period of operation preceding saturation and 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 carried to a point considerably above saturation, the fullers earth will remove from the circulating charge objectionable constituents which would otherwise tend to separate out in the heating tubes.

The fullers earth of commerce is obtained in varying degrees of fineness. The finest grades of earth such as are commonly used 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 supportin screen and enter the circulating stream of oil We have found Olmstead earth of 1530 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. Other absorbent 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 otherwise holds particles of colloidal carbon or asphaltic constituents, etc., thus removing them from the cir culating charge, other filtering materials 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 removin in a selective manner the objectionable sul ur-containing constituents of the circulating charge, for example, silica Our use of fullers earth indicates it to el %e a particularly advantageous material foruse in the process of the invention, inasmuch as it appears to combine in itself valuable filtering, selective absorbent, desulfurizing and other properties which favorably affect and benefit the pressure still operation.

In carrying out arun according to the present invention, the still can be charged with fresh chargin stock in the usual way. The charging stoc may, for example, be gas oil or other suitable charging stock which is to be cracked for the production of gaso line 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 forming the 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 by the fullers earth and in part held in solution in the remaining constituents of the charge. As the reaction proceeds the unabsorbed pitch constituents continue to dissolve in the oil and progressively approach, or pass, the saturation point. Fresh oil may be introduced as the operation progresses, and the solvent capacity of fresh oil so introduced further assists in holding the unabsorbed pitch constituents in solution. The action of the absorbent material may also be supplemented by Withdrawing part of the pitch laden oil formed by the cracking reaction as the operation progresses. For example, a part of the pitch laden oil may be withdrawn during the period just preceding the time at which the pitch concentration reaches the saturation point, and the withdrawal of tar may be continued for all or part of the remaining period of operation until the operation is terminated. A

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 up to to lbs. per square inch or even up to 125 lbs. or more can be used. With a lighter kerosene charging stock, a higher pressure, e. g. from'up to 125 lbs. to around 300 lbs. or more can be 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 III I pressure, and the 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 practice 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 mesh and the still was charged with 7 tons of the raw earth forming a bed approximately 18 inches deep on a perforated support of the character illustrated which was arranged approximately 2 feet above the bottom of the drum, the drum being about 9'feet in diameter and about'31.6 feet long. I. The still was charged with 8000 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 125 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 through the reflux tower Was begun, the amount correspondin approximately to about 115% of the overhead distillate taken ofl. The rate of distillate taken off was about 820 gallons an hour, and the rate of feed through the tower was about 940 to 950 gallons an hour. During the run, tar was withdrawn at a rate corresponding approximately to about 15% of the overhead distillate. The rate of circulation through the heating tubes was about 2000 gallons a minute. About 31,000 gallons of pressure distillate of 47.5 Baum ravity was obtained from a throughput or about 43,700 gallons representing a yieldof about 71% of the. charge as pressure distillate.

Where the Withdrawal of tar, even though in relatively small amount, is omitted the period during which the operation can be carried out without objectionable carbon deposit is somewhat reduced. The operation is preferably conducted to a. point such that the charge remaining in the still can be withdrawn in a fluid condition. Where the operation has been carried to a point such that the unabsorbed pitch in the oil materially exceeds the saturation point, part of the pitch-like constituents present in the remaining charge will be in solution and part in suspension.

In carrying out the process of the invention, an increased percentage of the charging can be taken off as distillate, the fullers earth inhibiting the formation of objectionable carbon deposit. When the still is operated to obtain a higher percentage of the charge off as distillate, a somewhat more unsaturated product may be obtained and the' amount of tar to be drawn off and to be redistilled or otherwise treated or disposed of will be less. In some cases, further treatment of the tar may be avoided. With higher prcentages ofthe charge off as distillate,

less heat is required in heating up the additional stock and more heat is available for cracking. With higher, percentages of the charge off as distillate, a material saving in fuel may be effected, due to the greater percentage of distillate and also due to the decrease in time required to bring the still to cracking conditions of temperature and pressure for a given amount of char e. Where the tar i redistilled, a farther savmg in fuel is effected, due to the decreased amount of tar withdrawn.

per day, while at the same time ro onging the run and reducing the proportlon 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 of the 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 be regenerated, or may be otherwise utilized or disposed of.

The gasoline production can in this way be greatly increased er still When a run is 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.

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,

until e saturation point is'reached, such 'of the pitch-like or asphaltic constituents,

still charge for such pitch-like constituents- -will progressively decrease until saturation is reached. The operation is preferably terminated when the concentration of pitchlike constituents present in the charge exceeds .ture in a circulatory pressure still in which the oil is heated to a cracking temperature in a tubular heater, which comprises maintaining in said still charge a body of fullers earth on a support adapted to permit free passage of oil and extending entirel across the charge of oil in the pressure sti l, withdrawing oil from beneath said supportand discharging the oil directly int-o the charge of oil above said support and the material supported thereon, and continuing the operation until the pitch content of the still charge builds up at least to saturation.

2. The improvement in the cracking of hydrocarbon oils by distilling a charge of the oil under pressure at a cracking temperature in a circulatory pressure still in which the oil is heated to a cracking temperature in a tubular heater, which comprises maintaining in said still charge a body of absorbent material 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 discharging the oil directly into the charge of oil above said support and the material supported thereon, and continuing the operation until the pitch content of the still charge builds up at least to saturation.

3. The improvement in the cracking of hydrocarbon oils by distillin a charge of the oil under pressure at a crac ing temperature in a circulatory pressure still .in which the oil is heated to a cracking temperature in a tubular heater, which comprises maintaining in said still charge a body of filtering material 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 dischar ing the oil directly into the charge of oil a ove said support and the material supported thereon, and continuing the operation until the'pitch content of the still charge builds up at least to saturation.

4. The improvement in the cracking of hydrocarbon oils by distillin a charge of the oil under pressure at a crac ing temperature in a circulatory pressure still in which the oil is heated to a cracking temperature in a tubular heater, which comprises maintaining in said still charge a body of desulfurizing material on a support adapted to permit free passage of oil and extending entirel across the charge of oil in the pressure stil withdrawing oil from beneath said support and discharging the oil. directly into the charge of oil above said support and the material supported thereon, and continuing the operation until the pitch content of the still charge builds up at least to saturation.

5. The improvement in the cracking of hydrocarbon oils by distilling a charge of the oil under pressure at a cracking temperature in a circulatory pressure still in which the oil is heated to a cracking temperature in a tubular heater, which comprises maintaining in said still charge a body of fullers earth 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 dischar ing the oil directly into the charge of oil a ove said support and the material supported thereon, feeding fresh oil to the pressure still,

and continuing the operation until the pitch content of the still charge builds up at least to saturation.

6. The improvement in the cracking of hydrocarbon oils by distilling a charge 0 the oil under pressure at a crackmg temperature in a circulatory pressure still in which the oil is heated to a cracking temperature in a tubular heater, which comprises maintaining in said still charge a body of fullers earth 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 discharging the oil directly into t e charge of oil above said support and the material supported thereon, withdrawing pitch-laden oil from the pressure still and continuing the operation while controlling the withdrawal of pitch-laden oil to cause the pitch content of the still charge to build up at least to saturation. i

7. The improvement in the cracking of by drocarbon oils by distilling a charge of the oil under pressure at a cracking temperature in a circulatory pressure still in which the oil is heated to a cracking temperature in a tubular heater, which comprises maintaining in said still charge a body of fullers earth 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 discharging the oil directly into the charge of oil above said support and the material supported thereon, feeding fresh oil-to and wit drawing pitch-laden oil from the pressure still, and continuing the operation while controlling the feed of fresh oil and withdrawal 8. The improvement in the cracking of hydrocarbon oils by distilling a charge of the oil under pressure at a cracking tem erature in acirculatory pressure still in w ich the oil is heated to a cracking temperature in a tubular heater, which comprises maintaining in said still charge a body of fullers earth on a support adapted to permit free passage of oil and extending entirely across the charge of oil in the pressure still, withdraw.

ing oilfrom beneath said support and dis charging the oil directly into the charge of oil above said support and the material supported thereon, and continuing the operation until the pitch content of the still charge exceeds saturation.

' the oil directly into the charge of oil above said support and the material supported thereon, continuing the distillation until the pitch content of the still charge builds up at still while in a fluid condition.

supply tank a body least to saturation and thereafter withdrawing the remaining charge from the 101 The improvement in the cracking of hydrocarbon 'oils under pressure in circulatory pressure stills'in which the oil is heated to acracking temperature in a tubular heater,

which comprises circulating the still charge of oil froma drum or bulk supply tank, through heating tubes and back to the drum or bulk supply tank, distilling the circulating oil under pressure and at a cracking temperature, maintaining in the drum or bulk of fullers earth, supported in the still charge upon a support adapted topermit free passage of oil and extending entirely across the charge of oil in the drum or bulk supply tank and dividing the same into upperand lower compartments, withdrawing the oil from the lower compartment below said support and discharg.

ing the oil from the heating tubes directly into the upper compartment above said support and the material supported thereon, and

pressure I continuing the distillation until the pitchcontent of the still charge builds up at least to saturation.

In testimony whereof we aflix our signatures.

EUGENE C. HERTHEL. HARRY L. PELZER.

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