US1598136A - Process of cracking hydrocarbons - Google Patents

Description

Aug 31, 192a. 598,136

E. c. HERTHEL PROCESS OF CRACKING HYDROCARBONS Filed July 12 1922 Patented Aug. 3T, W2.

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EUGENE O. H'ERTHEL, OF CHICAGO, ILLINOIS, ASSIGNOR TO SINCLAIR REFIENING COMPANY, OF CHLOAGO, ILLINOIS, A CORPORATION OF MAINE.

PROCESS OF CRACKING HYDROCARBONS.

Application filed .i'uly 12,

More specifically stated, my process relates to the destructive distillation or cracking of" gas-oil and the like for the purpose of producing motor spirit. My improvea ment has for its object the increase in the amount of distillate which may be obtained in a single run. In the earlier practice of cracking oils the batch process was followed in which a charge of fuel or gas oil or other to material to be cracked is run into the still and subjected to cracking temperature under the rquired pressure until the practicable amount of distillate has been driven off, there being no addition of material during.

the run. This operation has been improved by increasing the length of the run by feed ing in fresh stock during a certain period of the operation to replace the distillate driven off. The process, however, cannot' be continued indefinitely but is ultimately terminated by the accumulation of coke on the heating surface of the still which ultimately forms such a. thick layer as to more or less insulate the heating wall from the cooling effect of the oil reducing the effective heat transfer and endangering the still. Thus after a relatively short running period it is necessary to terminate the run and clean out the accumulation of coke. It has been pro- 3O rating by gravity and continuously drawing off the solid matters in a very small amount of oil. As the limitation of the run is not dependent on the solid matters held in suspension in the oil but rather on the carbon which deposits on the'heating surface, the removal of these solid matters, especially in connection with such a small amount of oil, would not materially increase the length of the run.

T have reason to believe that in the crack ing process as practiced in pressure stills the first change which takes place is the gradual and progressive dissociation of the charging stock mainly into naphtha and a heavy pitch, there being little or no coke or carbon formed in the first instance. As long as the pitch does not exceed a certain proportion in relation to the oil in the still, which proportion depends so'inewhat upon the character of the charging stock, or in other words, so long as the pitch is held in so ution and the oil does not become saturated therewith, there is no substantial formation of coke. lit is only when pitch becomes present to an posed to further lengthen the run by sepak 1922. Serial No. 574,380.

extent such that it exceeds the saturation polnt that there is any serious formation of coke. Apparently when, and only When this condition exists the pitch is deposited as such on the heating surfaces of the still and is then coked and forms a hard lining thereon. I have found as a matter of practies that ordinarily the oil only becomes saturated with pitch after about has been taken off as distillate, and consequently it is only after-this point in the operation of the process that a serious accumulation of coke forms on the heating surfaces.

Consequently, it have found that if the saturation of the oil with pitch be prevented, the runs of the still may be greatly prolonged and the production of the still correspondingly increased. Therefore accord: ing to my improved method of operation I so conduct the run that the oil does not become saturated with pitch until just prior to the time when it is desired to terminate the run.

The earlier part of the run may be conducted as usual, fresh stock being fed in from about the beginning of the distillation period to replace the oil driven off and maintain appproximately the level of the oil in the still. During this portion of the run pitch is formed but there is substantially no deposition thereof because of the presence in the body of oil of a sufficient quantity of sol: vents to maintain it in solution. The pitch, however, accumulates as cracking proceeds and were no provision made to the contrary it would sooner or later begin to .deposit. Before this can occur, however, I materially increase the feedof fresh stock so that suf ficient additional solvent is present to avoid the pitch being thrown down. All of the hydrocarbons comprising the stock constitute solvents for the pitch. As the constituents of the charge are gradually and progressively cracked, the pitch formed is held in solution in the remaining portion of the charge. All of the hydrocarbons of the charge may be cracked in a gradual and progressive manner, although the rate at which different constituents will be progressively cracked may vary. The heavier hydrocarbons tend to crack more readily, and, to the extent that these or other hydrocarbons are cracked and volatilized'or form pitch,

they lose their function as a solvent for the of the hydrocarbons of the fresh stock, however, to-wit, the lighter of them, such as those of the kerosene range and those-next in order of gravity, are but little affected at the no step taken to prevent; In order to avoid this increase in the quantity of oil in the still I continuously withdraw a stream of oil or tar from the still. Preferably for this purpose I arrange a draw-off in such a location .in the still as t-o receive, so far as possible, the

heaviest oil therein, that is to say the oil containing the largest proportion of pitch. Preferably the drain is located in the bottom of the still and in such a position as not to receive any of the freshly fed stock and reflux. It'is desirable to-maintain approximately a constant level in the still and therefore I set or manipulate the valve-controlling the draw-off so that the removal of oil therethrough, coupled with the distillation, as nearly" as possible equals the addition of fresh stock at all times.

While I haveobtained very satisfactory results in practice by not permitting the amount of distillate at any time to exceed about 50% of the total charge, in some cases this amount may be somewhat exceeded without losing the advantage of my improved process and in other cases it is ad-.

visable that the amount of distillate be kept below this proportion of the total charge,

depending upon the character of the stock.

treated, the-nature of the distillate desired and the length of run desired. Thus, if the runs are lengthened or'the material treated is more susceptible to pitch formation than normal or if a lower specific gravity distillate is desired, the proportion of distillate to total charge at any time should be correspondinglylower. I have been able to handle in a single run more than ten times as muchoil -as could be handled by'a batch run without feed and five times as much as could be handled in the previously described process of the prior art in which the fresh stock is fed in only for the replacement of the oil distilled, before being forced to terminate the operation by reason of the deposit of coke on the tubes.

From the above it is evident that my invention in its broader aspect is not limited in respect to the apparatus employed except in that it must provide for so-called li uid phase cracking and have means for fee 'ng in-fresh stock during .the run and means for withdrawing the necessary amount of heavy I pitch-laden oil.' In the accompanying drawing I have illustrated diagrammatically an apparatus suitable for .the practice of my improved process following essentially the design of the apparatus shown in'Patent No.

1,285,200 granted November 19, 1918, to Sinclair Refining Company upon the application of Edward W. Isom, to which patent reference may be made for amore detailed disclosure of the apparatus. 7

In the drawing of this application the apparatus is shown diagrammatically in side elevation and partly in section.

Referring to the figure: A shell or drum A contains the bulk of the body of oil being treated which is heated to and maintained at the cracking temperature by means of a battery of heating tubes B heated in any suitable manner. The drum is connected to the lower ends of the tubes by a downcomer pipe C, a pump D and a pair of pipes E connected to the lower h'eader F of said battery of tubes. The upper header G of the batteryiof tubes is connected to the drum by pipes H. The pump D, shown as of the double piston rotary variety, is so driven as to force the liquid from the drum to the bottom header of the battery "of tubes and the oil rising through said tubes is heated and returns to the still drum maintaining the temperature of the latter. The action of the pump is as sisted by the thermal effect in the tubes. A reflux tower L is mounted on the still and connected thereto by a vapor line M, as usual. The tower is .provided with baffles O and from the upper end thereof a vapor line P tower into the downcomer pipe C of the heating circulation system. R is a spray head connected to pipe S for the introduction of fresh stock during the run. A- tar drain-off is shown at k.

While the still above described is suitable for the practice of my improved process, it is not essential thereto as my invention is applicable to other forms of liquid phase cracking stills, such as the ordinary shell still. i

In carrying my process into operation, the still is first charged with a suitable amount of gas-oil or the like which is brought to the required cracking temperature and pressure in the usual manner. After'the cracking temperature is reached, cracking beg ns and takes place in a gradual and progressive manner, theheavier components of the gas-- 'oil tending to decompose more readlly, as

A re-.

usual, the lighter cracked products with a small proportion of the lighter uncracked 7 tillate. As the reaction proceeds, the pitch formed continues to dissolve in. the oil and ultimately approaches the saturation point therein. Before, this occurs, however, I begin'to feed in through the line S a continuous stream of fresh stock which may include, in addition to the more readily cracked heavy oils a certain proportion of lighter oil roughly corresponding to the kerosene fraction. During the earlier portion of the run the supply of fresh stock. need not be in excess of that necessary to replace the oil distilled off. Asthe pitch continues to accumulate, however, in order to prevent its deposition in serious quantities, before the saturation point is reached I start feeding in additional quantities of fresh stock to maintain the pitch in solution and in order that the volume of oil in the still may not increase I start and continue drawing off tar or heavier oil in sufiicient quantity to ofi-set the additional supply of fresh stock. In the drawing I have shown the draw-off K as arranged in the bottom of the still drum A where the heavier material is inclined to accumulate.

The following is an example of the practice of my invention on a forty-eight hour schedule: An original charge of 8,000 gallons was filled into a still of suitable capacity. and heat was applied thereto for a pe riod of about eight hours during which time the drips were taken off and the required cracking temperature and pressure, had been attained. The still was'then opened to the condenser and the distillate began to pass over. At about the same time or shortly thereafter I began the introduction of fresh stock into-the still at the rate of about 1,000 gallons per hour, which was substantially equivalent to a. rate of distillate off of about 40% of the charge, distillate being taken off at a rate of about 1,000 gallons per hour, and maintained this rate of feed of fresh stock for about six hours. As at the end of that time the accumulation of pitch was considerable I increased the volume of feed to an extent to hold the percentage of distillate of? to less than 40 to 45% of the entire charge. At about the same time with the increase in feed. I began and continued drawing off tar or heavy oil in sutlicient volume to prevent any marked increase in the amount of oil in the still and continued these running conditions for about sixteen hours. I then discontinued the withdrawal of tar closing the draw-off and permitted the pitch toaccumuwithdrawn,

late in the still for a further period of ap- I proximately seven hours, at which time the run was terminated.

In the process of the above example, after the still charge is heated to the cracking temperature and cracking begins, the constituents of the charge are gradually and progressively cracked, the light distillate is and the pitch constituents formed dissolve in the remaining portion of the charge. With the introduction of fresh stock into the still and continuation of the cracking operation, the amount of pitch constituents tends to increase progressively while the total amount of the charge remains approximately the same. All of the hydrocarbons of the charge, as above pointed out, constitute solvents for the pitch, but with the progressive increase of pitch during the cracking operation, the concentration of the pitch will increase until it will approximate saturation. Before saturation is reached, I

increase the rate of feed and begin drawing off tar or heavy oil in sufficient volume to prevent saturation of the pitch in the charge and to hold the pitch below the saturation point. With the rate of distillate ofi' above referred to in the specific example, namely, 1,000 gallons per hour representing 40 per cent of the entire charge, the rate of tar draw-off .to hold the pitch content approximately constant in the still would be about 1,500 gallons per hour, representing 60 per cent of the charge, and the volume of fresh feed would be about 2,500 gallons per hour. l tthalil Where the process is practiced in a still such as the Isom still above described, in which the oil is rapidly circulated, the fresh stock as it enters the body of oil in the still is immediately intermixed therewith and the circulation further assists in preventing the deposition of the pitch. I therefore prefer to practice the process in a-still provid ing for circulation of the oil therein. But in its broader aspect my invention is independent of circulation.

I claim: 1 1. A process of cracking higher boilingpoint hydrocarbon oils to form lower boiling point. hydrocarbon oils which consists in subjecting a body of the oil to be cracked to in the pitch-containing oil as withdrawn below the saturation point.

2. A process of cracking higher boiling point hydrocarbon oils to form lower boiling point hydrocarbon oils which consists in subjecting a body of the oil to be cracked to distillation under superatmospheric pressure and at a cracking temperature, maintaining said cracking temperature during the main portion of the run and effecting the vapori zation under substantially undimished pressure, feeding in fresh stock during a portion of the run in quantitysufiicient to prevent the pitch formed by the cracking process exceeding the saturation point in the body of oil undergoing distillation, and continuing to feed fresh stock and drawing off pitchladen oil from the said body of oil during a further portion of the run in amounts conjointly regulated to prevent the proportion of pitch in the body of oil undergoing distillation rising above the saturation point in the said body of oil and in the pitch-laden oil as withdrawn.

3. In a process of cracking higher boiling point hydrocarbon oils to form lower boiling point hydrocarbon oils, distilling a body of the oil to be cracked under superatmospheric pressure and at a cracking temperature, driving off the vapors therefrom under substantially undiminished pressure and condensing the same, and preventing the saturation, with pitch formed by the cracking process of the entire body of oil undergoing distillation, including pitch-laden oil as withdrawn therefrom, by feeding fresh oil to the body of oil undergoing distillation and withdrawing pitch-laden oil therefrom during the operation.

4. A process for cracking heavy hydrocarbons. to produce lighter hydrocarbons which consists in heating a body of such hydrocarbons and maintaining it at a cracking temperature, feeding fresh stock and drawing Y off a proportion of pitch laden stock so that at no time more than 50% of the total stock, including feed oil, has been'taken off as distillate. v

5. The process of cracking hydrocarbons to produce lower boiling point hydrocarbons, which consists in maintaining a body of the former under a pressure and at a temperature suflicient to crack the oil-in the liquid phase, distilling off lower boiling point hydrocarbons as they are formed, continuous- 1y adding fresh stock during the earlier portion of the distilling operation to replace hydrocarbons driven off, increasing the addition of fresh stock during a subsequent portion of the run to supply suflicient solvent to prevent the deposition of the pitch and simultaneously with the latter step drawing off sufficient heavier oil to prevent an undue increase of the body of the oil in the still.

6. The improvement in cracking higher lated to maintain the pitch in the body of oil undergoing distillation and in the pitchladen oil as withdrawn below the saturation point.

'7. The improvement in cracking gas oil to form lower boiling point hydrocarbon oils therefrom by pressure distillation, which comprises charging a still with a large quantity of gas oil and heating the charge to a cracking temperature under superatmospheric pressure,taking ofi' vapors from the still charge under substantially undiminished pressure, introducing fresh oil into the still charge during the run and withdrawing pitch-ladenoil from the still charge before the still charge becomes saturated with pitch formed by the cracking process, and conjointly regulating the withdrawal ofvpitchladen oil and of introduction of fresh oil to prevent saturation of the entire still charge and of the pitch-laden oil as withdrawn with pitch.

8. The improvement in the cracking of higher boiling point oils in pressure stills, which comprises introducing fresh charging stock into the still and withdrawing tar from the still during the pressure distillation, the rate of feed and of tar Withdrawal being regulated to maintain the rate of distillation below 50% of the rate of introduction of fresh charging stock. v

9. The improvement in the cracking of higher boiling point oils by pressure distillation, which comprises charging the still and heating the charge to the cracking tempera ture, introducing fresh charging stock to replace the distillate taken off and continuing the pressure distillation until thepitch increases in the still charge to a point short of saturation, then increasing the feed offresh charging stock and withdrawing tar from the still at a rate to maintain the pitch content of the still charge below saturation.

10. The improvement in the cracking of higher boiling point oils by pressure distillation, which comprises charging the still and heating the charge to the cracking temperature, introducing fresh charging stock to replace the distillate taken off and continuing the pressure distillation until the pitch increases in the still charge to a point short of saturation, then increasing'the feed of fresh charging stock and withdrawing tar from the still at a rate to maintain the pitch higher boiling point oils by pressure distilla-.

tion, which comprises introducing fresh feed during the early portion .of the run without withdrawing 'any of the charge other than distillate, withdrawing a portion of the still charge continuously during a later portion of the pressure distillation, and introducing additional charging stock to replace the distillate and the portion of the charge withdrawn, the rate of introduction and of withdrawal being regulated to maintain the pitch content of the still charge below saturation.

12. The improvement in the cracking of higher boiling point oils by pressure distillation, which comprises introducing fresh feed during the early portion of the run without withdrawing any of the charge other than distillate, withdrawing a .portion. of the still charge continuously during a later portion of the pressure distillation, and introducing additional charging stockto replace the distillate and the portion of the charge withdrawn, the rate of introduction and of withdrawal being regulated to maintain the rate of distillation less than one-half the rate of introduction of fresh stock. I

13. Theim'provement in cracking gas oil to form lower boiling point hydrocarbon oils therefrom by pressure distillation, which comprises heating a'still charge of the gas oil to a cracking temperature under superatmospheric pressure, taking off vapors therefrom under substantially undiminished pressure, and preventing saturation of the entire still charge withpitch formed by the I cracking process by feeding fresh charging stock to the still charge and withdrawing pitch-laden oil therefrom, the rate of feed of fresh oil andv the rate of withdrawal of pitch-laden oil being conjointly regulated to maintain the entire still charge and the pitchladen oil as withdrawn below the saturation point. 1

14. The improvement in cracking higher boiling point hydrocarbon oils in pressure stillsby pressure distillation, which comprises charging the pressure still and heating the charge to a cracking temperature under superatmospheric pressure, taking off vapors therefrom under substantially undiminished pressure, circulating the charge, in-

troducing fresh oil into the circulating charge, withdrawing pitch-laden oil from the still charge before the charge becomes saturated with pitch formed by the cracking process, and conjointly regulating such withdrawal and theintroduction of fresh oil to maintain the entire circulating charge and the pitch-laden oil as withdrawn below the saturation point with pitch formed by the cracking process.

15. The improvement in cracking higher boiling point hydrocarbon oils by pressure distillation in tubularpressure stills in whicha charge of the oilis circulated from a drum through heating tubes and back to the drum, which comprises distilling the charge of oil at a cracking temperature under superatmospheri: pressure, the vapors being taken off from the drum under substantially undiminished pressure, introducing fresh oil into the circulating charge duringthe early portion of the run, withdrawing a portion of the still charge continuously during alater portion of the pressure dis tillation and during that portion of the op eration introducing additional fresh oil to replace the distillate and the portion of the charge withdrawn, and eonjointly regulating the rate of introduction of fresh oil and of withdrawal of pitch-laden oil from the charge to maintain the entire circulating body of the still charge and of the pitchla'den oil as withdrawn below the saturation point with pitch formed by the cracking process.

1 16. A process for cracking heavy hydrocarbons to produce lighter hydrocarbons which consists in heating a body of such hydrocarbons and maintaining it at a cracking temperature, feeding fresh stock and'draw-. ing off a proportion of pitch-laden stock so that at no time more than 45% of the total stock including feed oil has been taken off as distillate.

' O. HERTHEL.

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