US1703528A - Art of cracking hydrocarbons - Google Patents

Description

Feb. 26, 1929.

" E. C. HERTHEL ET AL ART oF CRACKING HYDRocARBoNs Filed Jan. 17, 1925 EQ La Patented Feb. 26, 1929.

UNITED STATESk PATENT OFFICE.

EUGENE C.' HERTHEL AND HARRY L. PELZER, OF CHICAGO, ILLINOIS, ASSIGNORS T0 SINCLAIR REFINING COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ART OF `CRACKI-NG HYDROCARBONS..

Application filed January This invention relates to improvements in the cracking of heavier hydrocarbon oils in pressure stills forthe `production of gasoline or motor spirit or pressure distillate therefrom. The invention comprises an improved process which assists in protecting the heating surfaces 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 for cleaning purposes. This application is in part a continuation of our copending application Serial No. 7 04,926, filed April 8, 1924, which has issued as Patent No. 1,634,666.

In the cracking of heavier petroleum oils in pressure stills for the production of-gasoline or pressure distillate therefrom there are formed during the cracking operation certainy constituents of an asphaltic or pitch-like character. With the continuation of the cracking operation, the amount of such constituents increases and there is a tendency for deposits 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 ordanger of failure of the heating surfaces can be effectively prevented, and the time of operationv of a single run can be somewhat prolonged, with correspondingly greater continuity 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 17, 1925. serial No. 3,007.

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 pitch-like constituents is progressively formed. Such constituents appearto be of varying properties and characteristics. For the most part they remain in solution in the charge during the early portion of the run, and they may i 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.l 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 different character and to have an increased tendency to deposit on the heating surfaces of the still. Furthermore, as the chargebecomes 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 ifthe 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 sulfur-containing compounds. In charging stock which contains sulfur, certain of the sulfur compounds appear to undergo cracking to form sulfur-containing constituents, probably of an asphalt-like character, which are particularly objectionable. Analyses of the carbon deposit on the heated tubes of a cracking still indicate that certain of these sulfur-containing constituents have a preferential aflinity l still charge, and by causing the still charge to circulate repeatedly through said body of metallic oxides during the progress of the cracking operation, We have also found that the maintenance of a body of metallic oxides Within the still charge is of advantage in protecting the heating surfaces of the still from corrosion, overheating and burning out, and in reducing carbon deposition upon the heating Surfaces, Whether or not the operation is carried out over a prolonged'period. The body of metallic oxides which is maintained in the still in contact with the charge, and through which the charge is continuously circulated has a selective action upon certain of these objectionable constituents, including the sulfur-containing compounds, 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 a desulphurizing action or it may be in part a filtering action or absorbent action removing colloidal carbon orprecipitated asphalt-like constituents. Whatever the explanation of the action of the body of metallic oxides may be, it has an important protective effect in preventing objectionable carbon deposit on the heating surfaces of the pressure still.

The metallic oxides Which may be employed in carrying out the present invention include iron 'oxide and copper oxide. The oxides may be employed alone, or they may be employed in con] unction With a supporting material,for example, a bed of metallic oxides may be supported on a bed of suitable filtering material in the still charge so that the charge is circulated through both the bed of metallic oxides and the bed of filtering material. The use of a supporting material in this manner is particularly advantageous with finely divided metallic'oxides or With oxides which otherwise tend to be carried with the circulating oil. The metallic oxides may also be precipitated upon the filtering or supporting material and the still charge circulated through [a body of this composite material. Suitable filtering materials Which may be so employed include asbestos, disintegrated silo-cel brick or fire brick, sand, kieselguhr, diatomaceous earth, pumice, glass Wool or mineral wool, and ground coke or charcoal. Fullers earth or similar absorbent clays, acid treated clays, and silica els may also be used. Circulation of' the still charge through such filtering or supporting material also assists in the removal of objectionable constituents from the charge by a filtering action or selective absorbent action therein in addition to they action of the metallic oxides associated therewith.

The provision of a body of metallic oxides inl direct contact with the pressure still charge arranged for vcirculation ofthe pressure still charge therethrough may assist in prolonging the cracking operation in several Ways. The body of' metallic oxides apparently nhas a filtering action in removing susp-ended pitchor asphaltic constituents and other objectionable constituents. It also apparently reacts With sulfur-containing constituents of the charge to form insoluble sulphides which are retained in the body of metallic oxides, or Where a supporting body of filtering or similar material is employed also on the filtering material. The sulphides may be absorbed or filtered out as formed or they may be removed from the circulating charge as it circulates through the body of metallic oxides and any associated material. A part of the metallic oxides may dissolve in the circulating oil and may react While dissolved with the sulfur-containing constituents of the still charge to form insoluble sulphides Which are filtered out as the oil is recirculated through the body of metallic oxides. Where a part of the metallic oxides are so dissolved, the' desulphurizing reaction'may thus be effected in the zone in which the .oil is subjected to the highest temperatures 1n an advantageous Wa A In some cases, the saturation concentration of pitch andasphaltic constituents in the still charge'may also be increased apparently by theselective ac-' tion of the body of metallic oxideslo'n the most objectionable constituents or on constituents tending to cause deposition on the heating surfaces.

In the improved process of the present 1nvention part of the pitch-like constituents produced during the cracking operation are thus removed by the action of the body of metallic oxides and in some cases the saturation concentration of pitch-like constituents in the charge may also be increased. The metallic oxides may also act upon certain constituents of the charge which tend to cause rapid precipitation of pitch-like constituents so that pitch-like constituents not removed and remaining in the charge are less injurious. Both the nature and the amount of asphaltic and` pitch-like constituents in the oil charge circulated over the heating surfaces of the pressure still are thus regulated by tbe action of the body of metallic oxides, and any asociated material, and the rate of formation of such constituents may also be restricted. The body of metallic` oxides may remove the more objectionable constituents and may act to permit a higher concentration of less objectionable constituents in the charge. Such pitch-like constituents as remain inthe circulating charge after passage through the body of metallic oxides are apparently in solution in the circulating charge. ln carrying out this invention, the entire body of oil charged into the pressure still, for example gas oil, serves to hold in solution, up to the point of saturation, the pitch-like drawal of pitch laden tar.

the process of the invention in this way, both 4culation of the charge through the tubes and constituents that are formed. In the process of the present invention, however, only the pitch-like constituents which are not removed by the body of metallic oxides remain to be held in solution in the charge, and the action of the body, of metallic oxides 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. 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 is also progressively saturated. -In either batch or semi-continuous operation, the cracking operation is terminated when, or before the amount of pitchlikej constituents remaining in the charge,

above the amount removed by the body of metallicloxides and any amount withdrawn as tar, increases to a point where objectionable deposition will take place upon the heating surfaces.

The process of the present invention may also be carried out in a continuous manner by withdrawing pitch-laden tar from the pressure stilland introducing .fresh oil at a regulated rate to maintain the pitch content of I the charge below saturation in the way described in United States Letters Patent No. 1,598,136, granted August 31,v 1926, to the Sinclair Refining Company on an application of Eugene C. Herthel, one of the applicants herein. The concentration of pitchlike and asphaltic 'constituents in the still charge may thus be regulated both by the action of the body of metallic oxidesand by the introduction of fresh oil and the with- In carrying out the nature and the amount of asphaltic or pitch-like constituents contained in 'the charge circulated over the heated surfaces are regulated, the action of the body of metallic oxides removing the more objectionable constituents, and the introduction of fresh feed andwithdrawal of pitch laden tar regulating the concentration of the less objectionablev pitch-like constituents in the charge.

In its broader aspects and embodiments, the improved process of the invention can be carried out in stills of different constructions, including shell stills as well as tube stills. Whatever the type of still, the metallic oxides are supported in the form of a bed through which the entire charge can be circulated, and the still is provided with circulating means for` circulating the charge through the bed of metallic oxides. The bed of metallic oxides is also supported out of contact with the heating surfaces of the still,

oxides within the pressure still itself has the advantage that a large surface area of the metallic oxides is exposed to the charge, and a large area of 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 perforated support extending across theA interior of the still for supporting the bed of metallic oxides in contact with the still charge.

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 metallic oxides maintained in the form of a bed extending across a drum or bulk supply tank containing the main charge of oil,'and with circulation of the oil from such drum through heating tubes and back 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 circulation'. The tube still may thus be one in which there` is stream circulation through a series of tubes in the Iform of a continuous stream; or the circulation maybe 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 thecharge through the heating tubes, or it maybe one in which the circulation through the tubes is effected by mechanical forcing means, such as 'a circulating pump. In suchtube stills the cirthrough the bed of metallic oxides ini the bulk supply tank or drum results in causing' all portions of the circulating charge to pass through the bed of metallic oxides in the bulk supply tank before they recirculate through the tubes, while the entire charge in the-bulk I supply tank is in contact with the bed o f mev tallic oxides through which the charge 1s c1rl 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 arrangenient of 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 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 screen support. f

rlhe pressure still illustrated in the drawings is of the general type 4described and illustrated in United States Letters Patent No. 1,285,200 granted November 19, 1918, to theSinclair Rening Company on' the application of Edward W. Isom. The present invention is of special value and application in connection with pressure stills of this general character.

The pressure still illustrated comprises the drum or bulk supply tank 1 having an outlet vpipe 2 leading to the pump?) 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 tov be heatedby gas or oil, the main furnace chamber 8, andv three passes 9, 1() and 11 separated by baffles for causing the furnace gases to pass over the vertical tubes in aback and forth manner before they escape through the connecting flue 12 to the stack 13. From the drum 1 of the pressure still a vapor line 14 leads to the reflux tower 15 which is shown as a baffle tower having a series of baflies 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 top of the reflux tower 15 to the condenser 19 from which the condensate and uncondensed gas are collected in the receiver 20. Draw-off pipes 21v and 22 are proand the co densate respectively from the revided for ,rawing off the uncondensed gas f the receiver 20. A tar draw-off line 26 is provided; aswell as a-safety valve 28. A feed line 27 is shown for introducing fresh charging stock into the upperlfpnrtion of the reflux tower.

. Vithin 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 metallic oxides indicated at 31. A cross-section of one suitable form ofv screen support is illustrated in Fig. 3. This is. made up of five layers, a top layer 32 of e. g. 5% thick plate with l perforations, a 4 mesh screen 33, a 40 mesh screen 34, another` 4 mesh screen 33a vand another 1% thick steel plate 32a with 1/2 perforations therein.\ A modified and simpler form of support is illustrated in Fig. 4, madeup of the upper and lowv'perforated plates32? having the screen 84b between them. yThe nature of this support can be varied so long as it performs the function of supporting the metallic oxides without leakage. Where finely divided metallic oxides are employed, abed of filtering material: or supporting material may be arranged on the perforated support 29 and the bed of metallic oxides supported thereon.

It will be noted that the perforated support and screen-form afloor over the bottom of the still. With such a screen, thoroughly sealed by welding or riveting at the joints and secured to the walls of the still, the metallic oxides placed upon the support are maintained in the` upper portion of the drum v above the screen.:

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

Where the veloeityof the oil ldisharged from the pipe 6 is such as to cause erosion of the bed of metallic oxides, this bed can be prov the oil is circulated by the circulating pump 3` from the bulk supply tank 1 through lthe connecting pipes 2 and 4 to the heating tubes 5 and then back through the pipes 6 and 6a 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 intothe reflux tower where the heavier ends are condensed by feed introduced into the top of the reflux tower through the feed line27, 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 the pressure control valve to the usual condenser and receiver. Additional feed can bev introduced through the bearings of-the pumphby means l of a feed line B5.

The charge is withdrawn from theJ -drum below the perforated support and is circulated through t-he heating 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 metallic,A oxides, andthe bed of metallic oxides thus has an opportunity of exerting its action pppn the objectionable asphaltic or pitche constituents of the charge. In the ap? paratus illustrated it will be noted that `the bed of metallic oxides 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 compared with the rate of circulation through the heating tubes. Ample opportunity is thus provided for the metallic oxides to act on the charge as it is slowly circulating or filtering downwardly therethrough.

In the apparatus illustrated it will be noted that the fresh feed introduced through the reflux tower and also the reiuxed 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 v35 and the pump bearings. The circulating charge, therefore, is made up of the fresh feed and reflux together with such portioiiof the still charge itself as percolates downwardly through the bed of metallic oxides. The reflux and admixed fresh feed from the reflux tower may also be discharged the pitch-laden oil formed `by 'the cracking operation as the pitch content of the charge lncreases.

The actiolnof the metallic oxides is such that an increased percentage of the charge, includingany fresh oil introduced during the operation, 4can be taken off as pressure distillate,and the pitch-content of the circulating charge can be carried to an increased amount during the run without objectionable carbon depositen the heating tubes or surfaces. l As considerably above saturation, the metallic oxides -will remove from the circulating charge objectionable constituents which would otherwise tend to separate out on the heating tubes.

. In carrying out a run according to the present invention, the still can be chargedl 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 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 pitchllike'constituents formed are in part removed by the metallic oxides and in part held in solution in the remaining constituents of the charge. As the reaction proceeds, the pitch constituents formed which are not removed by the metallic oxides continue to dissolve in the oil and may progressively approach, or pass,

the saturation point. Fresh oil may be in-l ther assists in holding the unabsorbed pitch constituents in solution. i The action of the metallic oxides 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 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. Before the pitch content reaches the saturation point, the withdrawal of tar through the line 26 may be begun and the ratepf introduction of fresh oil into the still maybe proportionately increased to maintain approximately a uniform level in lthe yperiod just preceding the time at which the still, and the rate of tar withdrawal and oxides in the still, and the action of the metallic oxide bed thus supplemented by the maintenance of a regulated pitch concentration.

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 another way of carrying out the invention, the metallic oxides may be precipitated on a supporting material and a body of this `composite material employed in the pressure still. For example, fullers earth may be with a suitable salt solution, for exampleiaxaqueous solution of iron chloride or iron sulphate, and the corresponding metallic hydrate precipitated on the earth by suitable treatment with an alkaline solution, for example an aqueous solution of soduim carbo` nat-e or of ammon1a,"-and the earth and precipitate dried and `dehydrated by roasting or the like.

The metallic oxide employed may be revivified after use in the process of the invention by burning or roasting. The metallic content of the original oxide material may thus be reconverted to oxide and the reviviied or regenerated metallic oxide reused in the process of the invention. Sulfur present in combination. with the oxide material may be converted vto sulfur dioxide and separated as a gas which can also be recovered if desired. v

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-in theneighborhood of to 100 lbs. or up to 125 lbs. or more can be used. With a lighter kerosene charging stock, a

`higher pressure, for example.' from 125 lbs.

up tot300 lbs. or more is used with advantage. The pressure can be regulated by a pressure reducing valve arranged between the still and condenser, or the condenser can be maintained under still pressure and the pressure regulated by a pressure regulating valve arranged in the outlet of the receiver. The character of the charging stock used inthe process can also be varied. In particular, a charging stock which contains constituents which otherwise would tend to cause an in- .creased 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 in this respect overcome or greatly reduced by the action of the bed of metallic oxides,

We claim:

1. In the cracking of hydrocarbon oils by distillation under pressure 'in pressure still systems in which the charge of oil is circulated from a bulk supply tank through an externally heated tubular heater and back to the bulk supply tank, the improvement comprising maintaining'a bed of material containing uncombined metallic oxides in the bulk supply tank submerged in, directly exposed to and extending entirely across the charge of oil therein and supported upon a support adapted to retain said material but to permit free vpassage of the still charge, supplying oil to the heating tubes from below said bed of material, and discharging the oil from the heating tubes directly into the charge of oil in the bulk supply tank above the support and material thereon.

2. In' the cracking of hydrocarbon oils by distillation under pressure in pressure still systems in which the charge of oil is circulated from a bulk supply tank through an externally heated tubular heater and back to the bulk supply tank, the improvement comprising maintaining a bed of material containing uncombined metallic oxides in the bulk supply tank submerged in, directly exposed to and extending entirely across the charge of oil therein' and supported upon a support adapted to retain said material but to permit free passage of the .still charge, supplying oil to the heating tubes from below said bed of material, discharging the oil from the heating tubes directly into the charge of oil in the bulk supply tank above the support and material thereon and preventing saturation of the still chargewith pitch by feeding fresh oil to the pressure still and drawing off pitch-laden oil therefrom.

' 3.- In the cracking of hydrocarbon oils by distillation under pressure in pressure stil systems in which the charge of oilv is circulated from a bulk supply tank through an externally heated tubular heater and back to the bulk supply tank, the improvement comprising maintaining a bed of material containing uncombined metallic oxides in the bulk supply tank submerged in, directly exposed to and extending entirely across the charge of oil therein and supported free from externally heated surfaces upon a support adapted to retain said material but tof permit -free passage 0f the still charge, supplying oil to the heating tubes from below said bed of material, and discharging the oil from the heating tubes directly into the charge of oil in the bulk supply tank above the support and material thereon.

4. In the cracking of hydrocarbon oils by distillation under pressure in pressure still systems in which the charge of oil is circullated from a bulk supply tank through a heater located away from the bulk supply tank and back to the bulk supply tank, the improvement comprising maintaining a bed of material containing uncombined metallic oxides in the bulk supply tank, submerged in, directly exposed to and extending entirely across the charge of oil therein and supported upon a silpport adapted t0 retain said material but to permit free passage of oil, supplying oil to the heater from below said bed of material, heating the oil to a cracking temperature in the heater by circu-` lating heating and discharging rectly into the charge of oil in the bulk supply tank above the support and material thereon.

, 5. In the cracking of hydrocarbon oils by distillation under pressure in pressure still systems in which the charge of oil is circulated rom a bulk supply tank through an externally heated tubular heater and back to the bulk supply tank, the improvement comprising maintaining a bed of material containing uncombined metallic oxides in the bulk supply tank submerged in, directly exposed to and extending entirely across; the charge of oil therein and supported upon a support adapted to gases externally there-over 'retain said. material but to permit free passage of the still charge, withdrawing oil from below the bed of material and rapidly circulating it through heating tubes and discharging the oil from the oil from the heater di-` the heating tubes directly into the charge of oil in the bulk supply tank above the support and material thereon, and circulatin t e oil relatively slowly through the bed 0 uncombined metallic oxide.

6. In the cracking of hydrocarbon oilssby distillation under pressure in pressure still systems in which the charge of oil is circulated from a bulk supply tank through an externally heated tubular heater and back. to the bulk supply tank, prising maintaining a'bed ofmaterial containing Aunconubined metallic oxides in the bulk supply ,tank submerged in, directly exposed to and extending entirely across the charge of oil therein and supported upon a' support adapted to retain said materialbut to permit free passage of the still charge, withdrawing oil from below the bed of material and rapidly 'circulating it through heating tubes and discharging the' heating oil in the bulk supply .tank above the support and material thereon, circulating the oil relatively slowly through the bed of uncombined metallic oxide, and preventing saturation of the still charge with pitch by feeding fresh oil to the pressure still anddrawing ol'fpitch-laden oil therefrom. u

In testimony whereof we ailix our signatures.

EUGENE c. HERTHEL, HARRY nrELzER.1

the improvement comf the oil from tubes directly into the charge of`

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