US2520149A

US2520149A - Process for producing olefins

Info

Publication number: US2520149A
Application number: US540248A
Authority: US
Inventors: William O Keeling
Original assignee: Koppers Co Inc
Current assignee: Beazer East Inc
Priority date: 1944-06-14
Filing date: 1944-06-14
Publication date: 1950-08-29
Anticipated expiration: 1967-08-29

Description

Aug. 29, 1950 w. o. KEELING PROCESS FOR PRODUCING OLEFINS 3 Sheets-Sheet 1 Filed June 14, 1944 wwmwwwmw oumuohmq owjnia .Ew mo Pzmu mm&

30 4o 50 so 20 so PER CENT LENGTH OF DEACTION CHAMBER INVENTOR. Maw 0 M4 Aug. 29, 1950 w. o. KEELING PROCESS FOR PRODUCING OLEFINS 3 Sheets-Sheet 2 Filed June 14, 1944 M m I II W EN) 535 25% M mm dub Q 6 wznuaouxo ww 200.5 23 55 0 80 mm mwm an?) 55 3a 3 JHO umfiuom \m. Illll J L 4 w Mn RN 1 n Ma h 3 (m rdop moa m 340E200 XL m Ju m4 N953 9 H I f 1 /300 wzu mo w Rs TE J 3 5: Q323 zoiuqmm m wu t uu zu=u 3 3m Aug. 29, 1950 w. o. KEELING PROCESS FOR PRODUCING OLEFINS 3 Sheets-Sheet 3 Filed June 14, 1944 aumnauum A W DH u IUZUDG a mw uzunnbd Um IWwNL muzudukiuk INVENTOR w I L M K a m m L L M uohau m WITNESSES:

' ATTORNEY mama A 29, 1950 r PROCESS FOR PRODUCING OLEFINS William 0. Keeling, Mount Lebanon Township, Allegheny County, Pa., assignor to Koppers Company, Inc., Pittsburgh, Pa., a corporation of Delaware Application June 14, 1944, Serial No. 540,248

Claims. (Cl. 280-683) This invention relates to a process for producing light olefines, di-olefines, such as butadiene, acetylenes, and aromatics such as benzene, toluene, xylenes, and alkenyl aromatics as styrene, vinyl naphthalenes, etc, More specifically, it relates to a pyrolytic conversion process by means of which a wide variety of hydrocarbon charging stocks can be converted into one or more of these products in a new and novel manner.

This application is a continuation-inpart of my co-pending application Serial No. 597,692 filed March 9, 1932, Patent No. 2,363,532 issued November 28, 1944 and covers improvements on the invention disclosed in the parent application which was, broadly, a process for converting hydrocarbons into motor fuels, unsaturates, aromatics, or fixed gases. whichever is desired, in which the charging stock is vaporized, the vapors further heated in a pipestill coil by indirect heat exchange and partially cracked therein, and the conversion then completed by directly admixing the partially cracked vapors with a suitable heat-carrier gas. The total heat necessary for the conversion, therefore, is suppliedin two stages by separate, independent supplies and oil-flowing of heating mediums to permit separate and independent control of the heating done in each of the two stages and with the wasting of the spent heating medium used in the firststage. Thereby the quantity of heat-carrier gas required and used in the second, or direct, heating stage isreduced to a small fraction of that. which would be required if only superheating of the vapors in the first stage were practiced, or if the total heat input of the process were supplied by the heat-carrier gas in the direct heating stage; as well as making possible the use'of separate heating agents having different properties in each of the two heating stages.

One object of the present invention is the improvement of the process disclosed in my co-pendingapplication Serial No. 597,692, whereby it becomes more suitable for the production of selected primary reaction products by the pyrolysis of I quantities of methane and other light saturated hydrocarbons and heavy tar and/or carbon.

Another object of the invention is to provide a-novel method and means whereby the selected quantity of pyrolytic heat delivered and its effective period of application to hydrocarbon charging stocks is made easily controllable within very narrow limits, so that there is recoverable high yields of selected primary pyrolytic products such as acetylenes, ethylene, butadiene, butylenes, propylene and light aromatics, and alkenyl aromatics, etc., with a minimum further conversion of desired products into unwanted products by secondary pyrolytic reactions.

The invention has for further objects such other improvements and such other operative advantages or results as may be found to obtain in the processes or apparatus hereinafter described or claimed.

In prior processes for producing motor fuels,

the type of cracking employed may be termed digestive cracking because the charging stock, being converted, is retained in the reaction zone for a period of time suflicient to permit the formation of not only primary reaction products but also further or secondary reactions of, or between, the primary products. These secondary reactions consist of further scissions of carbonto-carbon and/or carbon-tohydrogen linkages in the primary products, alkylation, polymerization, and aromatization. These secondary reactions are highly desirable when producing motor fuels because they decrease the degree of unsaturation of the resulting motor fuel and very materially increase its octane value. They are a disadvantage in that they very materially increase the amount of the charging stock converted into hydrogen and saturated fixed gases, largely methane, and heavy ful oil or tar. Because of their nature, the fixed gases and tars are of little value for anything but fuel for heating purposes, The total amount of charging stock converted into motor fuel, fixed gases, and tars and the ratio between the yields of each of these products depends largely upon the nature of the charging stock and the cracking conditions. W. L. Nelson, on pages 315 to 319 of his book, "Petroleum Refinery Engineering," published by McGraw-Hill, first edition, gives a set of empirical equations for calculating the yields of these three products obtainable from any given charging stock by digestive cracking. It will be found from these equations, and confirmed by other operating data in the literature, that the combined fixed gas and tar yields from any given charging stock varies from about 20% of very light charging stocks to about of very heavy charging stocks. It is 3 thus readily apparent that the digestive type of cracking is wasteful of the charging stock, at least insofar as its conversion into useful and more valuable products, other than motor fuel, is concerned.

I have discovered that by adding certain steps, modirying others, and by operating within certain limits with respect to temperatures and time intervals, all of which will be described herein, the invention disclosed in the parent application, Serial No. 597,692, can be adapted to selectively produce, from a wide range of charging stocks, maximum yields of ethylene, propylene, butylenes,

'amyienes and other oleiines, di-olen'nes such as butadiene, actylenes, benzol, toluol, xylenes, alkenyl aromatics, etc., all of which are badly needed for the production of various war materials such as synthetic rubber, IOU-octane aviation fuel, alcohol, explosives, etc. The net effect of these modifications is to change the process disclosed in Serial No. 597,692 from a primarily digestive-type conversion process-to one. which for want of a more description term, will be called an explosive-type of conversion process, from which the products obtained are markedly different in character, being very largely primary conversion products, as compared to the secondary conversion products largely obtained by the digestive-type conversion.

The explosive-type cracking is characterized by the substantially instantaneous application of a measured amount of heat energy suflicient only to accomplish the pyrolytic conversion desired at a predetermined temperature level. This heat is applied to the molecules of the charging stock which has already been heated just to, or above temperatures at which the atomic carbon-tocarbon and/or carbon-to-hydrogen linkages begin to rupture. The sudden application of the additional quantity of heat causes substantially instantaneous rupture of the linkages of the molecules of the charging stock at their points of greatest weakness. The rupture is then followed by substantially instantaneous cooling of reaction products to temperature levels at which no further primary conversion can occur. I have found that by using this procedure, the products obtained are predominantly primary reaction products consisting principally of light unsaturates, suitable as starting materials in the synthesis of various organic compounds and a relatively small amount of light, liquid products containing a large percentage of benzene, toluene, xylenes, and some naphthalenes and anthracenes, but little, if any, heavy tar. Furthermore, I have found that I can vary the yield of any given unsaturate or aromatic by varying the temperature levels employed for the conversions and by careful control of the temperature differential between the superheated vapors of the material to be converted and material carrying the heat energy required for the conversion.

Although I use the preferred explosive-type of cracking for the production of primary products, I have found that when cracking to butadiene, a small amount of acetylenes are also formed. These acetylenes are very troublesome in the subsequent butadiene purification steps and, unless removed, seriously affect the properties of the syn thetic rubber made therefrom. It is of advantage, therefore, to either prevent acetylene formation or to hold the quantities made below certain limits. Owin to the nature of pyrolysis, it is impossible to prevent acetylene formation at the temperatures required for butadiene production.

4 But I have found that if a limited digestive period follows the formation of the primary products, the quantities of acetylenes formed can be reduced by as much as a half. This digestive period will normally vary from about a third to twice the time interval required for the completion of the desired primary reactions, depending on the digestion temperatures employed. Experiments indicate that if this digestion period does not exceed approximately 0.2 second, the loss of primary products, other than acetylenes, and the increase in tar formation will be negligible. Then immediately following the digestion step, the reaction products are quenched to temperatures at which no further thermal reactions can occur.

The following table shows the effect oi this limited digestive period, following the cracking period, upon the acetylenes content of the products made when cracking cyclohexane at various temperatures.

a n Wt? Reaction m a Time Acety enos Temp Second: in Reaction Products 1, son o. 00 a. o 1, son 0. 178 1. 1 1, 875 o. 00 a o l, 875 0. 123 1. 2 1, 876 0. 184 1. 0 1, W) 0. 060 3. 0 1, 900 0. car a 1 1, 9&0 0. 0o 2. 8 1, 950 0. 117 1. 7 1, 950 0. 131 1. 6 7, (I!) 0. 043 5. 5 2, 000 o. 000 2. 1

But where the production of acetylenes is desired, no digestive period is to be used. Instead, high reaction temperatures and short reaction times are preferred.

According to the present invention, the total heat requirements for the desired conversion is applied in two stages. In the first stage, part or all of the charging stock, depending on its composition, is vaporized and the resulting vapors are then further heated very rapidly to temperatures at which the hydrocarbon molecules become unstable or even begin to decompose, but with this diflerence over the prior art. Such decomposition, or cracking, as may occur is confined to primary pyrolytic reactions and preferably to scission of cabon-to-carbon linkages. In the case of pure hydrocarbons, such as cyclohexane, or light mixtures such as natural gasoline or light naphthas, the maximum yields of certain desired products such as butadiene will be obtained by bringing the charging stock only to the point of molecular instability in this stage and confining the explosive, or substantially instantaneous, disruption of the molecules to the second stage under conditions to be described later.

In the case of heavy hydrocarbon mixtures such as gas oils or residual oil charging stocks, the reactions in the first stage are confined to primary pyrolytic reactions by means of which the boiling point range is narrowed and the thermal stabilities of the hydrocarbons in the stock are made more uniform by primary cracking of the heavier and more easily cracked hydrocarbons. The charging stock now rendered more uniform as to boiling point and thermal stability will yield more nearly the same products when subjected to the much more severe explosive-type disruption in the second stage. I have found that this preliminary treatment oi-the charging stock can be confined to the production of a suitable. predigested charge for the second conversion stage by carying out the treatment in the first stage in such a manner that any normally gaseous conversion products formed thereby will contain not more than 10% and preferably not more than by weight of methane. The heating is done very rapidly by indirect heat exchange in pipestill coils, out of direct contact with the heating medium and confining such primary cracking as occurs to the production of primary cracked products equivalent to not more than approximately 40% of the total cracking occurring in both the first and second conversion stages. Such a procedure keeps to a minimum the yields of unwanted hydrogen, methane and tars from the charging stocks. I I have found that for the maximum production of any particular product from a given charging stock, careful control of reaction temperatures and times used in the conversion reaction mustbc practiced, as well as the maintenance of definite relationships between the temperatures of the vapors leaving the first conversion stage, the average conversion temperature, and the tempertaure of the heat-carrier medium prior to the latter's admixture with the vapors from the first conversion stage.

For the production of heavy unsaturates such as butylenes, amylenes, etc., reaction times of approximately 0.2 second, or less, are used with an average reaction temperature ranging from 1300 to 1500 R, depending on the stock being cracked. For the production of butadiene a temperature range of 1400 to 1550" F. should be employed over a time interval of 0.2 second, or less. For the production of ethylene, conversion temperatures of 1500 to 1700 F. over a period of 0.2 second, or less, should be used. For the production of aromatics, a temperature range about the same as that used for ethylene production is best, but somewhat longer periods of time should be used. For the production of styrene from ethylbenzene or vinyl-naphthalene from ethyl-naphthalene, a temperature range of 1350 to 1650 F. is required over atime interval not exceeding 0.2 second. There appears to be no definite optimum temperature range for the production of .acetylenes as they begin to appear at about 1300 1". and progressively increase in quantities up to a temperature of about 2200 F. But the time interval should be less than approximately 0.2 second and preferably less than 0.1 second.

For the maximum yields of desirable products from a given, charging stock, it is necessary to hold to a minimum the amount of the stock converted to the undesirable hydrogen, methane, and tar, or even carbon. I do this by close control, or the maintenance of definite relationships between the temperature of the vapors leaving the first conversion stage, the mean temperature utilized in the second or direct heating conversion stage. and the temperature of the heat-carrier medium just prior to its admixture with the vapors from-the primary conversion stage. As the vapors leave this latter stage, they are at, or above, the temperature at which rupture of the carbon-to-carbon and/or carbon-to-hydrogen linkages begins. Consequently, the hydrocarbon molecules are very sensitive to thermal shocks. And if the shock is too violent, as when using too high temperatures in the heat-carrier medium, a considerable number of the molecules break down completely to hydrogen, methane,

Q and carbon. I have found that best results are obtained when the ratio of the diflerence in temperature between the heat-carrier medium and the mean temperature used in the direct conversion stage and the difference between this mean conversion temperature and the temperature of the vapors leaving the primary conversion stage is not less than approximately 1 to 1 and not more than approximately 2 to 1.

By carrying out the conversion reactions of the second stage in a heavily insulated chamber, the conversion takes place therein without loss of heat from the reaction chamber. Since most, or all, of the primary conversion reactions are endothermic, this means that as heat is consumed by the reactions, the temperature of the reaction mixture will drop, due to the decrease in sensible heat remaining in the mixture. I have found that this fact can be utilized when the reaction products are susceptible to further decomposition at the highest reaction temperatures, by supplying substantially instantaneously only sufiicient heat to carry out the desired reactions to a predetermined degree of completion. When that point has been reached, the temperature of the mixture has dropped sufilciently to protect the reaction products. The quantity oi. heat supplied is regulated by the temperature and volume of the heat-carrier gas used. A good illustration of the procedure can be gotten from the following table and Figure 1, containing data obtained when cracking cyclohexane to butadiene with superheated steam when admixing the steam substantially instantaneously with cyclohexane at a single point of admixture.

Temp. steam, F 2, 019 2, 013 1, 900 Temp. cyclohexane vapors, F 1,082 1,085 l, 115 Temp. mixture entering reactor, "F l, 416 l, 497 l, 360 Temp. mixture leaving reactor, F 985 1, 000 913 Theoretical maximum mixture temperature,

l, 800 1, 565 Mo] ratio steam to cyclohexane 11.8: l 23. 7:1 13.6:1 Contact time, Seconds 0. 060 0. 04 3 0. 000 Percent conversion per pass 3i. 2 61. 8 20. 0 Ultimate Molar Yields in Per cent of Theoretical:

Butadiene 56. 5 47. 1 60. 7 Ethylene. 89. 6 99. 0 Hydrogen 123. 4 87. 5

The theoretical primary products of the thermal decomposition of 1 mol of cyclohexane are 1 mol of butadiene, 1 mol of ethylene, and 1 mol of hydrogen. But butadiene is susceptible to further conversion at high temperatures and long reaction times, hence it should be protected from further conversion, after it is formed, by a re-- duction of the reaction temperature to levels at which it is relatively stable. From Figure 1, it

will be seen that about 76% of the available heat supplied for conversion is absorbed in the first 50% of the length of the reaction chamber. This means that substantially 76% of the total conversion occurs in the first half of the allotted reaction time and that during the remainder of the time only 24% of the primary conversion of the cyclohexane occurred plus such secondary conversion of the butadiene produced as the resulting temperature permits. Inspection of the table shows that if the temperature and quantity the calculated temperatures of the mixtures of heat carrier gas and charging stock vapors after admixture is completed but before any cracking occurs. It is calculated from the weights of vapors and heat carrier gases entering the mixture, their temperatures before admixture and their specific heats. Because a small but definite time interval is required for complete admixture and because some cracking of vapors occurs befor admixture is completed, any measured mixture temperature will always be lower than the theoretical mixture temperature by an amount corresponding to the sensible heat of the mixture absorbed by the endothermic heat involved in the cracking reaction which has already occurred up to the point in the reaction zone where the temperature measurement is taken.

The more nearly instantaneous is the mixture of the vapor and heat carrier gases, the more nearly the measured mixture temperature will approach the theoretical maximum mixture temperature.

Thus the table shows the actual yield obtained by cracking as compared with the theoretical calculated yield. In other words the table shows the amount of heat available for cracking which was supplied at predetermined temperature levels and the yield of products obtained by cracking.

In another embodiment of the invention, the heat-carrier gas is rapidly admixed with the superheated vapors to be converted at more than one point, allowing a substantial degree of the desired conversion to occur between each successive point of injection. The temperature of the heat-carrier gas admitted at each point may be the same. Or the temperature of the heat-carrier gas at any one point of admixture may differ from that at any other point of admixture.

By way of illustration only, sufiicient heat-carrier gas is admitted at the first point of admixture to supply suflicient available heat to raise the temperature of the reaction mixture to the desired reaction temperature level plus an additional amount sufiicient to cause, say half of the desired primary conversion and then at the second point of injection, sufilclent additional heatcarrier gas is injected to provide the quantity of available heat necessary to complete the remainder of the desired primary conversion. It is to be understood, however, that I do not wish to limit myself to two successive points of injection of heat-carrier gas nor to the accomplishment of any fixed amount of primary conversion after each point of admixture, for the number of points of injection and the amount of conversion accomplished after each point of iniection will vary with the type of charging stock processed and conversion products desired. By means of this embodiment of the invention, it is possible to maintain more nearly uniform the optimum temperature level for the production of any desired conversion product than could be accured by use of a single injection point. It makes possible the supply of a greater quantity of available heat for any desired conversion without raising the temperature of the vapors to be converted to a temperature so high that undesirable primary conversion occurs, such as excessive disruption of the molecules of the charging stock to hydrogen, methane. and carbon, or other undesirable products. It makes possible the maintenance of the optimum diiferentials between the temperature oi the vapors to be converted and the heat-carrier gas, prior to admixture, without at the same time unduly limiting the quantity of available heat which can be supplied for desired conversion reactions. In other words, it makes possible greater yields of desired products per pass where recycle operations must "be used, as well as the greatest possible yields of desired products where single pass operation is to be employed.

When using the invention for the production of actylenes or other highly unsaturated products, yields may be enhanced by the introduction of any-suitable oxidizing agent into the heatcarrier gas, prior to admixture with the vapors to be converted, or into the stream of partially converted hydrocarbons at a point subsequent to the first admixture of said vapors and heatcarrier gas. Such an oxidizing agent should not exceed, in amount, the equivalent of 0.5 mol of free oxygen per mol of hydrocarbons to be converted. By oxidizing agent is meant any substance capable of removing hydrogen atoms from the molecules of the conversion products.

Precise control of reaction times is obtained by carefully proportioning the free space of the reaction chamber to the volume of vapors and gases to be passed therethrough, so that the vapors and gases can remain in the chamber for only the desired time interval.

For substantially instantaneously quenching, or arresting the progress of conversion in the materials leaving the second conversion stage, I prefer'to inject a spray of a liquid which can be easily separated from the final conversion products and which will introduce no extraneous impurities into these products. Two examples of such desirable quenching agents are water and light previously formed distillates made by the process. When operating on low boiling charging stock to produce low boiling products, I ordinarily prefer to use water as the quenching agent and then immediately further cool the reaction products by passing them through a washbox such as is used in the manufactured gas industry in the manner shown diagrammatically in Figure 2. When operating on high boiling charging stocks where part of the products are also high boiling, it sometimes is of advantage to quench, with either water or a previously formed distillate, to temperatures of 400 to 700 F., scrubbing out the highest boiling conversion products with a suitable heavy oil and then further cooling to condense and absorb the remaining high boiling conversion products to separate them from the fixed gases. or lightest conversion products, in the manner shown diagrammatically in Figure 3.

Where maximum yields of any particular product is desired, those portions of the conversion products of lesser value and suitable for further treatment, after separation from the desired products, may be recycled for further conversion.

The method of separation of desired products from the rest of the conversion products will depend upon the particular properties of the desired products. In general, the methods used will be fractional distillation, liquefaction followed by fractional distillation, treatment with selective solvents, or any other well known means.

Appended to these specifications and forming a part thereof are drawings of which:

Figure 1 presents a graph showing the rate of heat absorption above a selected temperature level by primary thermal reactions, when cracking cyclohexane to butadiene, as the reacting I for insuring substantially mixture progresses through a reaction chamber in which it resided for a total of 0.08 second;

Figure 2 presents a schematic flow-diagram of one modification of the invention in which superheated steam is used as the heat-carrier gas and in which single-point injection of the heat-carrier gas is practiced;

Figure 3 presents a, schematic flow-diagram of another modification of the invention in which combustion gases are used as the heat-carrier gas and in which two-point injection of the heatcarrier gas is practiced.

Referring now to Figure 1, there is disclosed a graph depicting the percent of the required conversion heat absorbed, above a given temperature level, plotted against the percent of the total length of the reaction chamber at which the absorption occurred. In the particular cracking run, during which the measurements were made, the total reaction time was 0.08 second. The curve shows that the rate of heat absorption in approximately the first 30% of the reaction chamber is very rapid and that as the conversion mixture nears the end of the reaction chamber,

.the rate of heat absorption, which is a measure of the amount of conversion occurring, rapidly decreases until in the last of the length of the chamber, a negligible amount of conversion occurred. This illustrates very forcefully the self-quenching feature of the invention as described above. It also illustrates very forcefully the absolute necessity of providing suitable means instantaneous and thorough admixture of the oil vapors and heatcarrier gas. 1 were obtained from thermo-couple readings of temperatures at a. series of points distributed along the length of the axis of the reaction chamber. Samples of the mixture of oil vapors and heat carrier gas were taken from the reaction chamber axis atpoints adjacent the points where the thermo-couples were located.

Referring now particularly to Figure 2, there is disclosed a modification of the invention in which single-point injection of the heat-carrier gas is practiced. Steam is shown as the heatcarrier gas although any other inert gas could be used. The charging stock is pumped through .vaporizer coil 6, located in pipestill l, and heated to its boiling point, or above. If the stock contains heavy fractions, undesirable as cracking stock, the heated stock passes through valve 1, valve 32 being closed, into evaporator 2 where the lighter, desirable charging stock is vaporized and the vapors separated from the undesirable .heavy fractions remaining in the liquid phase, and the separated vapors pass through valve 34 into the cracking coil 9. The liquid residue is withdrawn from the evaporator through valve II. If the-charging stock is of narrow boiling point range and it all constitutes a desirable cracking stock, the entire stock may be vaporized in coil 6 and the vapors pass through valve 32 and into line 33 into cracking coil 9, valves I and it being closed.

While passing through cracking coil 9, the vapors are heated to, or above, the temperature at which the hydrocarbons become unstable, but

The points on the curve of Figure flu any cracking occurring therein is confined to the bility, not more than approximately 5% by weight of the stock should be converted into products boiling below the initial boiling point of the original charge and no substantial amount of materials should be formed boiling at a temperature higher than the end point of the original charge. If heavy charging stocks are to be partially cracked in coil 9, the same procedure is followed except that the fixed gases formed should preferably not contain more than 10% by weight of methane and no substantial amounts of products having a higher boiling point than the end point of the portions of the original charging stock passed, as vapors, through the coil.

The oil in coil 6 and vapors in coil 9 are heated by indirect heat exchange with hot products of combustion formed in the combustion chamber of the still and by radiation from the burning fuel, but no part of the combustion gases formed in the still ever come in contact with the oil or its vapors.

The heated oil vapors leave cracking coil 9 and enter the mixing chamber, or zone III, which, in this case, is shown as the throat of a Venturi tube. At this point, the heated vapors are thoroughly and substantially instantaneously admixed with the heat-carrier gas from pipe 20. For proper mixing, the heat-carrier gas and oil vapors should mix by means of turbulent flow in the mixing zone and the velocity of approach of the vapors and ga es to the mixing zone should be such that neither nters the mixing zone as a jet strong enough to interfere seriously with or destroy turbulent fiow in the mixing zone. It is to be understood, however, that any other suitable means for insuring substantially instantaneous and thorough admixture and turbulent flow may be used.

The mixture of heat-carrier gas and oil vapors is discharged from the mixing zone l0 into the reaction zone 4, through which they continue to move by turbulent fiow. In this modification, the reaction zone consists of the diverging cone of the Venturi tube. and is of such length as to provide the precise time interval required for the completion of the primary thermal reactions desired above the temperature level at which the conversion products leave the reaction chamber. Both the mixing and reaction zones are housed in a heavily insulated structure so that all ther-: mal reactions occurring therein without loss of heat by conduction or radiation from the reaction chamber.

The conversion products are" discharged from .box 5, such as is used in conventional water-gas machines. The quench water can be partly fresh water supplied to pump 29 through line 30 and partly used water drawn into pum 29 from the wash-box. The water is forced through line 3| and through the sprays 26, for quenching the reaction products. As a safety measure against failure of the float 35 and valve 28, an adjustable, vented syphon water level controller 21 can be provided to prevent the water level from ever exceeding a predetermined maximum level. The temperatures maintained in the wash-box are such that the desired conversion products remain in the vapor phase and pass out of the wash-box through pipe 24 to conventional final coolers and separating equipment not shown. The heavier products condensing in the wash-box accumulate on the surface of the water and are withdrawn asaaisa through a superheater where it is heated to the desired temperature. If desired, coil llcan be eliminated from the pipestill and the steam passed directly into the-superheater. The superheaters used for illustration are shown as blast furnace type stoves s and I, but any other means capable of heating the steam to the desired temperatures may be used. In order to operate continuously, two or more blast furnace type stoves are provided, so that while steam is passing through one stove, the other, or others. are being ilred to store up the necessary heat in their checkerwork. As shown, steam leaving coil ll passu through valve ll, valves I1 and "being closed, into stove l and thence through valve l8 and

lines

25 and 20 into the mixing zone ll. When the temperature of the steam leaving stove 8 falls below the required level, valves I! and II are closed and valves l1 and II are opened and the steam from coil ll now passes through valve ll into stove I and out through valve II and lines fl and ii into the mixing zone It. To maintain the temperature of the steam, entering the mixing zone ll, constant, a portion of the steam leaving coil it is by-passed around the stoves through valve l4 and line ll into line II. The amount by-passed is that necessary to keep the temperature of the highly heated steam, ml; the stoves, at the temperature level de- Ifanoxidizing gasistobeusedforsecuring a greater degree of unsaturaticn in the conversion products, a suitable oxidizing gas is admitted through valve l2 into the steam passing to the superheater coil II and blast furnace stoves l and I. It is to be understood, however, that if superheating of the oxi l s gas is unnecessary or undesirable, said gas can be introduced into the steam at the mixing zone ll or any point in the steam supply system prior thereto.

Although steam, heated in blast furnace stoves, has been shown as the heat-carrier gas, it is to be understood that I do not intend to limit myself to this particular combination. For any inert gas, heated in any manner to a suitable temperature, could be used. If combustion ases are preferred, they may be generated and tempered in the manner shown in Figure 3.

Referring now to Figure 3, there is discloud a modification of the invention in which combustion gases are used as the heat-carrier gas and in which two-point injection of the heat-carrier gas is practiced, but it is to be understood that any suitable heat-carrier gas may be used with suitable changes in equipment for producing or heating such gases. The charging stock is picked up by pump 31 and forced through vaporizer coil 38, I

located in pipestill a, and into evaporator ll where the vaporized fractions are separated from any liquid residue remaining. The residue is withdrawn from the evaporator through valve 41 and can be withdrawn to storage or can be sent to the scrubber ll through pipe 42, by means not shown, for use as a scrubbing menstruum.

The vapors released in evaporator ll leave that 13 1 vesselthroushpipeuand assthroughmc i l coil ll, located in pipcetill It. in which the vapor! are rapidly heated to temperatures at which primary conversion begins but for a length of time which prevents more than approximately 40% of the total amount of conversion from occurring in the coil ll.

The partially converted vapors from coil ll are injected into a rapidly moving stream of part of the heat-carrier gas at point ll, just prior to an abrupt change of direction of flow of the resulting mixture, to obtain thorough admixture, and thenpasses throughtheilrstpartcf the reaction chamber 48. where the selected. portion of the primary conversion is accomplished, and thence through the throat of the Venturi type mixer 44, where the partially converted hydrocarbons are admixed with the remainder of the heat-carrier gas. The resulting mixture then passes into the diverging cone ll of the Venturi mixer which serves as the second part of the reaction chamber ll and in which the remainder of the desired primary conversions occur.

The reaction mixture is then discharged into stand-pipe It in which it is quenched or shockchilled to approximately 500 F. by a spray of quench liquid introducedthrough pipe II.

The cooled vapors, and any condensate formed by the cooling, are discharged from the standpipe directly into the lower-part ofscrubber ll, in which the vapors are counter-currently scrubbed with a heavy oil for removal of high.

boiling conversion products, tars, etc. The nature and amounts of the higher boiling conversion products passing from the scrubber with the gas and lighter conversion products can be regulated in the well known manner by the temperature and amount of scrubbing oil introduced into the scrubber through pipe I! and the amount and temperature of that recycled from the base of the scrubber through pump it, cooler l4, and pipe ll, back over the top trays of the scrubber. Surplus scrubber oil and heavy condensate are withdrawn from the scrubber through valve II and sent to fuel oil storage or disposed of otherwise. The cooling medium used in cooler N can be any suitable material. One example would be part, or all, of the fresh scrubbing oil to be introduced through pipe I! in bringing it to the proper temperature for introduction onto the top trays.

The gases and vapors leaving the scrubber can either be passed through cooler I by opening valves II and II and closing valve It or can be passed through the by-pass around the cooler by opening valve It and closing valves '0 and I, depending upon the stock being cracked and the products made. The products passing through or around the cooler 51 flow through a line a to the base of the direct cooler ll. If heavy aromatics or strongly emulsifying products are being made or where the smallest possible volume of cooling agent is to be circulated through direct cooler ll, then cooler II can be used. Or if it is desired to do all the cooling of the products in the direct cooler, cooler IT can be by-passed. The gases and conversion products are discharged into the base of the direct cooler II where they are counter-currently cooled and washed with a suitable menstruum, introduced through pipe 02, condensing or absorbing the hydrocarbon products, boiling above a predetermined temperature, by regulating the temperature and volume of the washing menstruum used, in the well known manner.

The wash menstruum, together with any condensate, water and dissolved hydrocarbons gravitate to the bottom of the direct cooler collecting in a pool in the base. An indirect heating coil may be submerged in the pool of liquid to heat the collected oil to a temperature sufficiently high to expel the highest boiling hydrocarbon it is desired to carry out of the cooler in the fixed gases. The liquids, forming a seal in the base of the direct cooler, are withdrawn from the cooler through the overflow syphons 63, having a vent 84 for breaking the vacuum, or by any other suitable device, to an oil-water separator where any water is separated from the oil and discarded and the oil is then separately processed to recover any desired conversion products it might contain by any suitable means, not shown. I

The fixed gases, containing the lighter conversion products, pass from the direct cooler through valve 65 and pipe 68 to suitable equipment, not shown, for separating therefrom any, or all, of the lightest conversion products it might be desired to recover.

In this modification of the invention, combustion gases are shown as the heat-carrier gas used, although it is to be understood that with suitable apparatus modification any other suitable gas might be used, such as steam as in the modification disclosed in Figure 2.

Air for combustion is compressed and stored in air tank 81. The pressure maintained in this container is greater than the pressure maintained in the conversion system by an amount necessary to force the air from the container through the inspirator, to draw in the fuel gas and discharge the air-fuel mixture into the combustion zone against conversion system pressure. This pressure differential is maintained by a suitable loading of the diaphragm-type throttle valve 88. placed in pipe 89 between the air tank 81 and inspirator 10.

Fuel gas is compressed and stored in gas tank H. The pressure maintained in this container is substantially the same as the pressure maintained in the conversion system.

Air .is drawn through valve I2 by compressor 18 and discharged into air tank 61. As long as the pressure in this container remains at aconstant differential above that maintained in the conversion system, this inlet valve I2 remains open. As soon as the pressure in air tank 81 begins to exceed the proper differential, the diaphragm begins to close valve 12 so that the air supply to the compressor is reduced or even cut off. As soon as the air pressure in the tank drops to the proper differential, the valve begins to open up. In this fashion, the air supply in the container is maintained constant at constant pressure.

Fuel gas is drawn through a diaphragm-type valve 14 by compressor I5 and discharged into gas tank I I. Pressure in this tank is maintained constant at substantially conversion system pressure by means of a diaphragm-type throttle valve I8 placed in gas line 11 between the gas tank and inspirator I0. If the pressure in the gas tank 14 side of the diaphragm is maintained at the pressure of the air tank II by means of line 98.

By thus maintaining the air and gas supplies at constant pressures and by use of a properly sized orifice in the gas line at the inspirator, the air-fuel-gas mixture supplied to the burner is constantly proportioned, regardless of any pressure changes in t e conversion system. Hence the .combustion gases formed will have a uniform composition regardless of any pressure changes in the conversion system. Conversion system pressures are communicated to the control valves through pipe 18 and its branches I9, and II.

The air-fuel mixture is discharged through pipe 82 into the burner, preferably a surfacecombustion type placed in the insulated duct 88 where combustion is rapid and complete. The combustion gases formed are too hot to directly admix with the hydrocarbons to be converted, for reasons stated above. They are, therefore, first cooled by admixture with a cooler gas; such as steam, admitted through valve 84 in pipe 88. In order to maintain a uniform heat-carrier gas temperature, the quantity of the cooler gas admitted is regulated by thermostatic control of valve 84. A thermostat 86, placed in the path of the tempered combustion gas, actuates the mechanism of valve 84 so that the latter will admit only sufllcient cooler gas to maintain constant the temperature at which the thermostat is set.

The tempered heat-carrier gas leaves duct 88 through two orifices 81 and 88 and enters the reaction chamber 43 for admixture with the hydrocarbons to be converted. These orifices are so sized that the proper amount of heat-carrier gas is admitted through orifice 81 to accomplish the portion of the conversion desired in the first part of the reaction chamber, and'through 88 to complete the conversion in the second part of the reaction chamber.

If an oxidizing agent is to be used to obtain a greater degree of unsaturation in the conversion products, it ean'be introduced as excess air' used for combustion, or with the tempering gas introduced through valve 84 and pipe 85. But I find thatbetter results are obtained if the oxidizing agent is introduced after the formation of at least part of the unsaturated primary conversion products. For this reason, I prefer to introduce the oxidizing agent through valve 89 into that portion of the heat-carrier gas passed through orifice 88 and used to complete the conversion.

If heat-carrier gas at different temperatures is to be used at the various points of admixture, such gas may be separately generated and tempered for each point of admixture, in a manner similar to that shown, or in the manner shown by passing a portion of the tempering gas in pipe through valve 98 into the stream of heatcarrier gas passing through orifice 81, at the point 91 situated between the orifice 81 and the point 80 at which the hydrocarbon vapors are introduced. a

For illustrating the results obtainable when practicing the invention, the following data, de-' termined by laboratory and pilot plant operations, are cited as specific examples.

.The first set of data illustrates the influence of the differential between the temperature of the heat-carrier gas and the superheated hydrocarbon vapors when cracking substantially pure cyclohexane to butadiene and ethylene as well as the desirability of superheating the vapors to incipient cracking beiore admixture with the heatcarrier gas. I

It is to be understood that the temperature at which the weakest carbon-to-carbon linkage of cyclohexane starts to rupture is in the vicinity of 1100' 1". Example 3 shows clearly the advantage of superheating the cyclohexane vapor to 1100' before finishing the cracking with the heat-car- Thus the above table shows the actual yield obtained by cracking as compared to the theoretical calculated yield. In other words the table shows the amount of heat available for cracking which was supplied at predetermined temperature levels and the yields of products obtained by cracking.

The next set 01 data illustrates theini'iuence of the differential between the temperature of the heat-carrier gas and the superheated hydrocarbon vapors and the influence of conversion temperature upon the yields of various conversion products from petroleum hydrocarbons with single pass operation. It also shows that the selection of charging stocks is not without intluence on the yields of certain conversion prodnote. In the following tables the diflerent mean conversion temperatures are due to the diflerent volumes of carrier gas which were mixed with the hydrocarbon vapors for cracking. In column I is shown the excessive volume of methane formed and the high carbon loss due to excessive temperatures which cause secondary reactions.

10 version products having greater molecular weights than that of propylene, but after the removal of benzene, toluene. xylene, and tar.

Ultimate yields of ethylene obtained by Tet-1 1W The foregoing descriptions are merely illustrative of two modifications or my invention, but it is to be understood that various changes and alternative arrangements may be made within the scope of the appended claims.

I claim as my invention:

1. A process (or converting low boiling carbons into primary conversion products such as ethylene and propylene olenns comprising: fiaporinng the hydrocarbon to be converted, rapidly superheating the vapors by indirect heat exchange to a cracking temperature or 10.50 to 1100' l". for a period where the carbon to carbon linkage oi the hydrocarbon vapor starts to nipture thoroughly admixing the superheated vapors with a heat carrier gas maintained at a temperature above 1000' 1"., passing the resulting mixture into a reaction chamber of such volume as to permit the time interval necessary for completing the desired primary conversion and controlling the 'volume and temperatures of the superheated vapors and heat carrier gas to maintain a mean conversion temperature in the reaction chamber such that the ratio of the tem- Pounds 0 products per 100 mm of charging stock mm Nlpllthl Heavy manna wf imam am a a o a a r n r KflU-fll'lk gal temp., F I. 100 1 1m 1. 1m 21! 3,4! 1, 1m 1. 100 I, 100 2, 1m Vapil p.. 9 1, 1M 1, 1m 1, 1M 1, 1m 1. mo 1, 113 1, 113 1,110 1, 112 Hun conversion terms, '1' 1,400 1, 4) 1, 4G) 1, m 1, too 1, 501 1, 472 1, I11 1, 502 Approximate contact time, Seconds.. l3 0. l3 0. 13 0. 13* 0. 18 0. 18 0. 18 0. 11 0. is tconverslonperpam 42.0 77.4 46.2 N. 78.0 72.1 0.0 0.4 84.0 Yields, Lblllw Lbs. Charging Stock:

0.42 1.43 0.50 0.7 0.53 1." 0.87 1. 1.78 3. 64 6. 37 0. 40 7. 07 15. 58 11. 01 12. 15 13. 11 10. 58 K 0.74 25.48 14. use 12.78 a. an 170 37.50 0.84 3.14 1.12 2.50 1.71 1.04 0.00 0.84 8.47 8. oo 1 15. 11 0. 41 13. u I. 04 11. U 15. 04 13. U 11. 57 3.01 6.84 3.15 5. 52 3.40 I. 5.05 2.70 0.8 4.01 0.87 5.38 0.81 4.70 2. 13.10 11 4.36 8. 27 11. 3. 47 0. 74 0. 55 4. a 1k 03 10. N 3. 83 58. 02 2. 57 53. l) 30. 45 31 01 I7. 10. 13 10. 01 15. 90 3.24 1.00 1.73 0. 11.84 3.1!) 1.50 1.50 1.50

100. 00 me (I) 100. M 11!). (IL 10). M 100. M 1m. on 10a no no. (I!

1 A11 mawili boiling above pentene.

! 'lotal distillate irom crude oil distilled to 572 F. undc 15 mm. absolute pro-ore and represents %by volume at the crude oil.

The next set of data shows the influence of conversion temperatures and stocks upon the ultimate yields of ethylene and the aromatics, (benaene, toluene, and xylenes) obtained by recycling operations, when using a heat-carrier gas temperature of 2100 1". and reaction time of 0.13 second. The recycle stock consisted of all conperature diflerential between the temperature of 70 the heat carrier gas and the mean conversion temperature and between the mean conversion temperature and the temperature oi. the superheated vapors beiore admixture is between 1:1 and 2:1 to eilect conversion by heat only. shock chilling the conversion products before a substantial amount of secondary reaction takes place to a temperature at which no further conversion 'can occur and separating and collecting the reaction products.

2. The process defined in claim 1 for the production of oleflnes in which the hydrocarbons being cracked have C4 or less carbon atoms to the molecule and are superheated to a temperature where the carbon-to-carbon linkages of the hydrocarbon molecule have started to rupture.

3. The process defined in claim 1 for the production of oleflnes in which the hydrocarbons being cracked have C5 and higher carbon atoms to the molecule and are superheated to a temperature where substantial cracking to form primary products only occurs before mixing the hydrocarbons with heat-carrier gas, and holding the vapors in contact with the heat carrier gas for less than 0.15 second.

4. The process defined in claim 1 in which the heat-carrier gas is superheated steam.

5. The process defined in claim 1 forthe production of butadiene and ethylene from cyclohexane wherein the vapors are superheated to a temperature above 1100 F. and the superheated vapors are cracked with superheated steam maintained at a temperature of approximately 18001".

WILLIAM O. KEELING.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,428,311 Adams Sept. 5, 1922 1,811,195 Watson June 23, 1931 1,842,321 Sachs Jan. 19, 1932 1,847,238 Frey et a1. Mar. 1, 1932 1,847,239 Frey et a1. Mar. 1, 1932 1,892,534 Rembert Dec. 27, 1932 1,900,739 Schmidt et a1. Mar. 7, 1933 1,928,494 Irwin Sept. 26, 1933 1,981,144 Held Nov. 20, 1934 2,113,536 Grebe Apr. 5, 1938 2,129,269 Furlong Sept. 6, 1938 2,174,288 Klein et a1. Sept. 26, 1939 2,176,453 Clark Oct. 17, 1939 2,207,552 Putt July 9, 1940 2,371,147 Burk Mar. 13, 1945 2,377,847 Allen June 12, 1945

Claims

1. A PROCESS FOR CONVERTING LOW BOILING HYDROCARBONS INTO PRIMARY CONVERSION PRODUCTS SUCH AS ETHYLENE AND PROPYLENE OLEFINS COMPRISING: VAPORIZING THE HYDROCARBON TO BE CONVERTED, RAPIDLY SUPERHEATING THE VAPORS BY INDIRECT HEAT EXCHANGE TO A CRACKING TEMPERATURE OF 1050* TO 1100*F, FOR A PERIOD WHERE THE CARBON TO CARBON LINKAGE OF THE HYDROCARBON VAPOR STARTS TO RUPTURE THOROUGHLY ADMIXING THE SUPERHEATED VAPORS WITH A HEAT CARRIER GAS MAINTAINED AT A TEMPERATURE ABOVE 1800*F., PASSING THE RESULTING MIXTURE INTO A REACTION CHAMBER OF SUCH VOLUME AS TO PERMIT THE TIME INTERVAL NECESSARY FOR COMPLETING THE DESIRED PRIMARY CONVERSION AND CONTROLLING THE VOLUME AND TEMPERATURES OF THE SUPERHEATED VAPORS AND HEAT CARRIER GAS TO MAINTAIN A MEAN CONVERSION TEMPERATURE IN THE REACTION CHAMBER SUCH THAT THE RATIO OF THE TEMPERATURE DIFFERENTIAL BETWEEN THE TEMPERATURE OF THE HEAT CARRIER GAS AND THE MEAN CONVERSION TEMPERATURE AND BETWEEN THE MEAN CONVERSION TEMPERATURE AND THE TEMPERATURE OF THE SUPERHEATED VAPORS BEFORE ADMIXTURE IS BETWEEN 1:1 AND 2:1 TO EFFECT CONVERSION BY HEAT ONLY, SHOCK CHILLING THE CONVERSION PRODUCTS BEFORE A SUBSTANTIAL AMOUNT OF SECONDARY REACTION TAKES PLACE TO A TEMPERATURE AT WHICH NO FURTHER CONVERSION CAN OCCUR AND SEPARATING AND COLLECTING THE REACTION PRODUCTS.