US2378067A - Process of cracking petroleum - Google Patents

Description

Junelz, 1945. W, C, DORSETT ETAL 2,378,067

PROCESS OF .CRACKING PETROLEUM Filed Sepidz. 28, 1942 HTTNEY Patented June l2, 1945 PROCESS F CRACKING PETROLEUM William C. Dorsett, Curren C. Sperling, and Orange C. Walker, Elizabeth, N. J., assignors to Petroleum Conversion Corporation, Elizabeth, N. J., a corporation of Delaware Application September 28, 1942, Serial No. 460,034

13 Claims.

This invention relates to petroleum conversion systems, more particularly to systems of the true vapor phase type which are characterized by the use of a .gaseous heat carrier which is commingled with a stream of vapors heated to high temperature. As is well understood bythoseskilled in the art, systems of the true vapor phase type the invention, substantially no free carbon is produced which in terms of practical operation means that systems built in accord with the inventionmay be operated for long periods of time without need of shutting down to clean carbon from tubes or vessels.

In carrying out the invention in one form thereof, any desired charging stock may be utilized although debutanized natural gasoline, a light or heavy naphtha, or an aromatic distillate are preferred charging stocks. A stream of vapors heated to high temperature is commingled with a gaseous hydrocarbon heat carrier which is concurrently heated to a high temperature. By limiting the reaction time to not more than twenty-five one-hundredths (0.25) of a second, preferably from three (0.03) to ve onehundredths (0.05) of a second for a mix` temperature of from 1300 F. to 1500 F., under a pressure preferably below 'one hundred pounds per square inch, and' by proper control of the composition of the heat carrier and of the charge, end-products are obtained which consist primarily of the aromatic compounds, ethylene and butadiene.

With regard to the vaporizable charge, a recycle ratio is preferably maintained; thatgis an aromatic recycle stock may be withdrawn and a portion of it returned to the system preferably in ratio of from 1:1 to 2:1 with respect to the charge` The aromatic distillate must be substantially entirely removed from the reaction products prior to reboiling operations and prior to the additon of heat for fractionation. With respect to the gaseous heat carrier, it should consist of hydrocarbons to a. large extent lighter than 04's and the presence of hydrogen and methane should be minimized. The cycle gas or heat carrier should include a substantially large percentage of unsaturated hydrocarbons` having from two to three carbon atoms per molecule. An unusual feature of the Ipresent invention is the fact that no gasoline is produced. On the contrary, the principal end-products are benzene, toluene, 'the xylenes, styrene, butadiene, the butenes, and ethylene.

Each of these end-products is valuable and in accordance with the present invention they may be produced directly from petroleum by means of a relatively inexpensive process and in a form in which they may be readily puriied to any desired degree.

For a more complete understanding oi the invention, reference should be had to the more dem tailed description which follows, and tp the drawing in which:l

Fig, 1 diagrammlatically illustrates a, system embodying the invention with the connecting pipe lines for the most part shown by single lines; and

Fig. 2 illustrates a curve showing the selective production oi certain of the end-products.

As indicated above, the conditions of temperature, reaction time, and the character of the hydrocarbons within the reaction zone are of material importance. For convenience, the system will be described starting with the heater I0, diagrammatically shown as a double end-flred heater, and there will be later ldeveloped a, detailed description of the character of the charging stock and of the heat carrier gas.

A gas-enriched charge enters the convection section Il of the heater I0 by way of line l2, is vaporized, and during passage through iloor tubes I3 and roof tubes I4 is heated in vapor phase to a temperature within the range of l100 F. to

drocarbons enter the oor tubes l5`by Way of line i6 and during their passage through the iioor tubes and the roof tubes il are heated to a temperature between 1400`F. and 1600 F., or higher. It is to be understood that separate heaters may be used for each stream and in many cases separate heaters will be preferred, to lprovide adequatacapaci-ty and. wholly independent control of the heating of the two streams. While serial flow of the stream-.s through the respective tube banks is indicated, it is to be understood that the heater tubes will normally be connected in Q parallel or series-parallel and that they will be of adequate size to minimize pressure drop therethrough, Furthermore the heating rate must be u suiiiciently high for the elevation in temperature of the respective streams to their nal outlet temperatures during time intervals taround one-tenth of a second above 1200 F.) insumcient for material cracking of either stream to'occur prior to their mixture one with the other. Such heating .requirements have been attained yand heaters are available which will satisfactorily meet these requirements.

The gas-enriched charge includes gases absorbed from an absorption operation and the charge includes arecycle stock which to large extent consists of an aromatic distillate. The normally gaseous stream of hydrocarbons is utilized not only as a heat carrier but the hydrocarbons enter into the reaction and by their -presence they also control the direction and the extent of completion of the complex chemical reactions which occur and which result in the production of end-products to`large extent comprising the aromatics, the unsaturates, and butadiene.

A After the heating'of both streams in the manner aforesaid, the heat carrier is commingled with the highly heated vapors. As shown; the two streams are mixed togetherin a transfer line i8 preferably ofvery short length and which leads directly to a reactor or reaction zone or chamber I9. The reaction chamber which may be the transfer line itself is preferably heat-insulated asl indicated at |3a and is of a size with reference to the volume of the commingled streams as to A provide a time interval of from about three to twenty-live hundredths of a second for the cornplexreactions to take place. For time intervals within this range, the mix temperature, or the temperature of the mixture should be within the approximate range of 1300 F. to 1500 F.

In accord with the present invention the afore- The reaction-arresting or quenching medium may be a low gravity residuum circulated from the bottom of a combined scrubber-fractionating 'column 22 by way of line 23, a. cooler 24, and accumulator 25 and by pump 26 forced through the line 2| in the vdesired quantity. If desired, some of this material may be withdrawn from the accumulator 25, or `make-up may be introduced into the accumulator@ Preferably the transfer line 20 includes mechanical means indicated at 29 for the removal of possible carbon or tarry deposits -in the transfer line. These ordinarily are negligible and such a provision is precautionary and guards against the formation of such deposits during the starting and shutting down of the unit or system embodying the invention. A 4 I 'he commingled reaction products and the quenching medium are discharged from the transfer line 20 into the lower part of the scrubber section of the column'or vessel 22 where there is a separation of the liquid and the vaporous products. The vapors rise upwardly through the column in counter-current relation to descending reux. The vessel 22 is preferably provided with After the aforesaid time interval, the reaction products exit fronrthe reaction zone or chamber i3 through a transfer line 2li in which is introduced a relatively large quantity of a relatively cool (150 F. to 250 F.) liquid hydrocarbon, which liquid may enter through the line 2|. By introducing the cool liquid hydrocarbon into the transfer line rapid and thorough mixing is accomplished and the cracking reactions are abruptly terminated.

We prefer to maintain in the reaction chamber' a pressure of about twenty-five pounds and less than one hundred pounds per square inch, gage. It the pressure is less than twenty-five pounds per square inch, the compressor cost becomes excessively high and if the pressure is greater than one hundred pounds per square inch the cost of the heater tubes becomes excessive. even if available for operations at higher tempera tures and pressures.

By the concurrence of the aforesaid conditions of temperature and time, and byscontrolling the character of the hydrocarbons subjected to the crackingl reactions, there is produced a yield of lbutadiene unexpectedly high and higher than heretofore achieved or believed possible in syis-` tems or the true vapor phase type. Moreovercooler 39 and into an accumulator lill. The cooler numerous bubble-trays (not shown) which provide for the more emcient fractionation of the rising vapors and inL manner well understood by those skilled in the. art. The overhead stream from the fractionating column 22 passes by way of line 28 to a condenser 30 where it is mate h rially cooled to between 90 F. and 150 F. It is then introduced into an accumulator 3| where the resulting condensate and gasses separate. Reux for the fractionating column 22 is derived from the accumulator 3| and is returned to the I column 22 by the pump 32 by way of the transfer line 33. The condenser 30 is preferably supplied .with cooling water 34 under the control of valve 30a.

For convenience, where cooling wateris indi- 39 is provided withl a control valve 33a. for the regulation of the supply of cooling `water 34.

The vaporlzable condensate in the accumulator 3| consists largely of an aromatic distillate; that is. -a distillate having av gravity of around l35 A. P.'I. and which includes aromatics inproportrast with systems o1' other types where particu- HV`-larchirging stocks are required for the production 0|."butadiene,V which charging stocks such as the butanes are greatly in demand for other pur-V POSS Y tion of'about 1Z0-25% benzene, :iB-22% toluene, 443% unsaturates, andthe remainder heavier aromaticssuch as Styrene,the xylenes. etc.

way of line 4I under the control of valve 4|a.

Preferably the recycle stock consists of aromatic distillate in amount which with the gaseous fractions bears la Weight relation of from 1:1 to 2: 1 with that of the charging stock.

As a result of the cooling of the vapors and gases compressed by the compressor 36, there is a. further separation of condensate within an accumulator 40. The uncondensed vapors and gases from the accumulator pass by way of' line 42 into the lower portion of an absorber 43 where they are counter-currently contacted with the charge introduced into the absorber by way of pump 44, cooler 45, and line 46. The absorber is provided with bubble trays (not shown) or other means for insuring intimate contact between the gases and vapors and the charging stock and for the maximum absorption of desirable constituents. One or more intercoolers may also be Drovided, one of which, the inter-cooler 41 being shown.

The free hydrogen and unabsorbed gaseous hydrocarbons, largely gases having one or two carbon atoms per molecule are withdrawn from the absorber 43 by way of line 50 and under the control of valve 53 may be discharged from the system as the make gas. The make gas is conventionally understood as the excess gas produced by the system, or the gas which in this case it is desired substantially to exclude from the reaction zone. It is important substantially to eliminate from the cycle gas and from the reaction zone recycled hydrogen and methane and these gases are removed from the absorber together with some of the C2 s.' vThe latter may comprise as much as 53% by weight of make gas and of the Css, 85% by weight will be ethylene. The latter is a valuable end-product and may be recovered in manner well understood by the art. Hence,

even from' the make gas there may be recovered a valuable end-product.

'Ihe charging stock, though it may vary widely in character, is preferably a naphtha or depentanized natural gasoline which after enrichment by the absorption of gaseous and vaporous constituents within the absorber 43 is withdrawn therefrom by way of line 54 and in line 56 commingles with the condensate -from the accumulator 40. The latter condensate consists largely vof hydrocarbons having more than three carbon atoms per molecule. The mixture then passes by way of line 56 and with the assistance of a pump not shown through a heat exchanger 51 in which it is heated by indirect heat exchange with a heating medium circulated through the exchanger by way of lines 58. After its elevation in temperature the mixture is discharged into the midportion of a, iractionating ytower or column 6I!v operating at from 200 to 400 pounds per square inch gage pressure which has for its function the removal of propane and lighter gases. Heat is supplied to the liquid material in the base of the tower 60 as by a reboiler 6I through which a heating medium circulates by way of lines 58.

It may be again observed that introduction of any aromatic distillate into the tower 60 has been avoided. Inasmuch as such aromatic distillate contains styrene, the addition of heat by the reboiler 6| and the relatively long time interval within the base of the tower 60 would result in the formation of polymers which would soon clog and choke the trays and lines associated with the tower 60.

'I'he reboiler 6| operates in manner well understood by the art. the material coming from the bottom ofthe tower 60 being heated in the reboiler, the lighter fractions being returned to the tower through the line 62 and the propane-free material passing by way of line 68 through a cooler 69 and into the ilnal fractionating tower 10 which operates at from 30 to 80 pounds per square inch gage pressure. The tower 10 has for its function the removal of butadiene, or the fraction which includes butadiene and sometimes called the C4 fraction.

The overhead products from the tower 60, large- 1y propane and lighter gases are cooled in a cooler 64 and discharged into an accumulator 65. Condensate is withdrawn by pump 63 and returned as reflux for the tower 60. Gases are withdrawn from the accumulator 65 by 'way of line 66 and they pass under the control of valve 66a into the line I6 leading to the heater I0. All, or at least the major part, of the cycle' gas or heat-carrier is derived 1from the accumulator 65. In the event there is a deiiciency of the heat carrier, make-up gas may be withdrawn from the line 50 under the control of the valve 63a and discharged into the cycle gas line I6. y l

The cycle gas itself preferably consists of a substantial proportion of unsaturated Czs and Cas for example, the C2 fraction may consist of about %l of the unsaturatevethylene, and the remainder of ethane, a saturate. The C3 fraction may consist of about of the unsaturate propylene, and the remainder of propane, a saturate.

A reboiler 1I supplies heat to the material withdrawn from the bottom of the tower 10. The lighter products are returned to the tower by way of line lla. The overhead products from the tower 10 pass by way of line 12 to a condenser 13 and thence into an accumulatpr 14. Normally all of the overhead products will be condensed although a valve 15 may be provided for venting the accumulator 14. Some of the condensate is returned by way of pump 16 as reux for the tower 10 and the remainder of the condensate is withdrawn through the line 11 as an end-product of the system which includes the butadiene fraction.

While the invention has been illustrated in a simple form thereof, it is to be understood vthat many ,additional refinementsv may be made such for example as by the use of additional fractionating equipment in which an additional absorbing menstruum, consisting of bottoms from a debutanizing tower, may be introduced into the absorber below the point of entry of the raw charge.

An unusual feature of the invention is the 'fact that substantiallyk no free carbon is produced; only traces of carbon may be found in the residuum which is recirculated by the pump 26 as the quenching medium. This material, with a gravity of around 6 A. P. I. may be withdrawn as a free owing liquid even though of such low gravity about 80% -will vaporize at 600 F. and at atmospheric pressure. In accord with the invention, the production of free carbon is inhibited by the presence in the reaction zone of a substantial proportion of the unsaturated Czs and Css and-the aromatic distillate. If the aromatic distillate, 'or the aromatlcs, are not returned tov the reaction zone a considerable amount of free carbon will be formed. I1' in addition the unsat urated Ca's and Czs are not returned to the reaction zone, free carbon will be formed at a substantial rate. However, when both are present,

the formation of free carbon is practically elimwww have been produced in terms of weight percentage of the raw charge, benzene, toluene and the xylenes in amounts varying between 4 and 8%, styrene around 1.2%: butadiene from 6 to 10%; and butenes from 12 to 18%. As earlier stated, a

feature of the present invention is the production of the relatively large quantities of aromatics and butadiene.

In Fig. 2, a fractional part of a true `boiling point distillation'c'urve is shown for the aromatic distillate. with volume per cent distilled as asbscissae and temperature as ordinates. The aromatic distillate represents about oi' the raw charge. As shown in Fig. 2, as the temperature rises from 160 F. to about 176 F., less than 3% ci' the distillate has been removed. At around 176 .F. benzene is distilled of! and as shown the benzene plateau represents about 20% of the distillate. The temperaturel then rises to about 230 F. at which temperature there is a toluene plateau. The flat toluene portion of the curve represents about 20% of the distillate.

Similarly, likeplateaus or dats (not shown) are present at the higher temperatures. Quantitative analyses confirm the foregoing and show that there are present, styrene above six percent, the xylene around 20%. the heavier aromatics around and unsaturates about 9%. By way of further illustration of the invention a charging stock of straight run naphthagrav `ity 52 A. P. I.; initial bOiling DOlnt 0f 200 F.:

and an end point of 400 F., was utilized as the absorbing menstruum for the absorber The enriched naphtha after passage through the fractionating equipment including towers Il 4and l0 was to a large extent denuded of its Cis and lighter fractions. From tower 1I, and in mixture with fractions heavier than the Cts the naphtha was by pump |20. charged to the heater coil ii. The fractions heavier than the lCts and lilihter than the aromatic distillate include unsaturated Css and C's, pentenes and hexenes. These comethylene 19.35%, and the ethane 6.55% were to large extent removed from the system as the make gas. The Cas, propylene and propane, comprised about 2.26%. The C4 fraction included butadiene 6%, the butenes, 12%, the butanes, 1%. and the Ct's, l%. -Tiie aromatic distillate was 20%, with a residue of 20%, and 0.42% distillation loss.

' With a charging stock of West Virginia depentanized natural gasoline, gravity 75.2 A. P. I., initial 130 F. and an end point of 260 F., the foregoing products were for the sainev operating conditions produced in substantially the same percentages.

Gas oil has also been successfully-used as charging stock.

The present invention differs from previous true vapor phase systems by the control of the complex chemical reactions for the production of the aforesaid characteristic products. Other than benzene and toluene, it will be observed y a very small percentage of products suitable for inclusion in motor fuel is produced whereas in the past such were the major products. The principal differences include the fixing of the timetemperature relations as above set forth and the recyclingof a part of the aromatic distillate.

By the use of the heat-carrying cycle gas of the character aforesaid, there is an increase in the yield o! hydrocarbons having four andy more atoms of carbon per molecule; and an increased lyield materially above that reported for systems prise a part of the recycle stock. the aromatic distillate comprising the otherpart. Y

The cycle or heat carrier gas was derived from the depropanizer, as at the accumulator 6l. It

porized and heated to 13751". and c ommingledl utilizing steam. The heat-carrying cycle gas may be mixed with the superheated vapors as above described for convenient control of the reaction time. That is, the desired reaction time, below twenty-five one hundredths of a second may be fixed and maintained' during continuous operation of the system. This results from the use of more refractory cycle gas which may be heated `to its high temperature and then used substantially instantaneously to elevate the vapors to their final cracking temperature.

The vaporous vreaction products; mayV then be quickly and abruptly cooled to terminate the cracking reactions after the cracking time, which produces the high yields of desirable products, as

above described.

While we prefer to recycle' the aromatic distil late it is to be understood a once-through operation may be utilized; and the aromatic distillate may be charged to the process from an external source of supply. 4

While we have described a preferred embodiment of our invention, it is to -be understood other modifications may be made and we therefore intend by the appended claims to cover any auch modifications as fall within the spirit and scope of our invention.

What we claim is:

- l. Aprocess of cracking petroleum which comprises supplying a stream of normally liquid hydrocarbon materials as charging stock, which stock is substantially free of aromatica and unsaturates, mixing with said stream vaporizable hydrocarbons predominantly aromatic and in quantity at' least one-'half that of said charting with cycle gas heated to 1550 The cyclegas was maintained in quantity of about 1000 cubic feet per barrel of the charge to the heater coil.

.With a reaction time 'of four hundredths of a second and rapid cooling with a '200 F. quenchoil, the following reaction-products in terms o! per cent by weight of fresh naphtha charge were obtained. The hydrogen 0.42%, methane 14%,.

stock, heating saidy mixture to a high temperature within approximate range'oi' from 1200 F. to 1400 F., heating to a high temperature within ltlie approximate range of from'1400" F. to 1600 F.

' ly -unsatura a stream ofinormally gaseous hydrocarbons, mostand largely those having from two to three carbon atoms per molecule, the relative desreeofheatingofsaidtwostreamsbeingsuch as to produce a temperature of the commingled streams within the range of from 1300 F. to 1500 F., Vcommingling said two streams, and within fromv three hundredths to twenty-ve hundredths of a second after said commingling abruptly cooling said commingled streams to terminate the cracking reactions, whichv reactions are characterized by the production of a. maximized quantity of butadiene and a substantial quantity of aromatlcs.

2. The process as set forth in claim 1, and in which the reaction products are fractionated and a stream of said aromatics derived therefrom, and in which the stream of cycle gas consisting largely of unsaturated Czs and Cas is derived from the process.

3. A cracking process in which the end products consist primarily of aromatic compounds, butadiene, butenes, and ethylene which comprises, heating a stream of vaporizable normally liquid hydrocarbons heavier than propane to a temperature within the approximate range of 1200 F. to 1400 F.- during a time interval in- .suii'icient for material cracking to occur, said stream comprising a charging stock substantially free of aromatics and unsaturates and including a recycle stock predominantly aromatic, concurrently heating within the approximate range of from 1400* F. to 1600 F. and within a time in terval insucient for material cracking to occur a cycle gas consisting of hydrocarbons toa large extent lighter than C4s and heavier than methane and which includes a relatively small proportion of saturates, in a reaction zone commingling said heated hydrocarbons, in a time interval thereafter of from three hundredths to'twenty-ve hundredths of a ysecond terminating the cracking reactions by rapid cooling of the reaction products, and fractionating said products to separate therefrom said aromatic compounds as said recycle stock and a C4 fraction containing butadiene, and mixing a substantial proportion of said aromatic compounds with said stream of vaporizable normally liquid hydrocarbons ilowing to said reaction zone.

4. The process set forth in claim 3, in which the aromatic compounds bear a quantity ratio of from 1:1 to 2:1 with reference to said vaporizable stream of normally liquid hydrocar-A bons.

5. The combination as set forth in claim 3, in which saturates having from one to two carbon atoms per molecule are substantially excluded from said cycle gas, and in which said cycle gas is derived from the process. Y

6. The method of producing butadiene which comprises heating a stream of vaporizable normally liquid hydrocarbons heavier than propane to a temperature within the approximate range of 1200 F. to 1400 F. within a time interval of heating not materially in excess of 1% of a second above 1200 F., said stream including added vaporizable aromatic hydrocarbons, concurrently heating to within the approximate rangeof 1400 F. to 1600 F. and Within a time interval of heating not in -excess of 116 of a second above 1200 F. a heat carrier gas consisting of normally gascous hydrocarbons to large extent lighter than C4s and heavier than methane, in a reaction zone commingling said heated hydrocarbons, after a reaction time of from about three onehundredths to twenty-ve one-hundredths of a second terminating the cracking reactions by rapid quenching of the reaction products, separating from said reaction products said vaporizablc aromatic hydrocarbons and separating from said products a stream of C4 hydrocarbons having butadiene in quantity of from fteen percent .to forty percent thereof.

7. The method of producing butadiene whic comprises concurrently heating a vaporizable stream of normally liquid hydrocarbons and a normally gaseous stream of hydrocarbons to temperatures which will produce in a reaction zone a temperature of the commingled streams within the range of approximately 1300o F. to 1500 F., said rst-namedstream including added vaporizable aromatic hydrocarbons, in said reaction zone commingling said streams, terminating the cracking reactions within from three one-hundredths to twenty-ve one-hundredths of a second by abruptly cooling said commingled streams, and separating from the reaction products a petroleum fraction including the butadiene and a stream including said vaporizable aromatic hydrocarbons.

8. The method as set forth in claim 7, in which all normallyr gaseous hydrocarbons from the reaction zone are subjected to an absorbing menstruum for the extraction therefrom of hydrocarbons of the approximate boiling range of butadiene and in which the absorbed hydrocarbons are subsequently fractionated for the production of a hydrocarbon fraction which contains butadiene in relatively high proportion and in excess of 15% of said fraction.

9. The method as Set forth in claim 7, in which the vaporizable normally liquid hydrocarbons are elevated to their temperature during a time interval insuilicient for material cracking to occur, and in which said normally gaseous hydrocarbons are elevated to their temperature during a. time interval insufcient for material cracking thereof.

l0. The method as set forth in claim '7 in which said vaporizable normally liquid hydrocarbons are elevated to a temperature in excess of 1100" F. during a time interval insufficient lfor material cracking to occur, and in which a suiicent quantity of said normallyl gaseous hydrocarbons is velevated during a time interval insufficient for material cracking to a temperature adeqaute to raise the temperature of said heated vaporizable hydrocarbons to said temperature within said range of 1300" F. to 1500 F.

1l. A method of producing butadiene by the conversion in the substantial absence of all gaseous products lighter than propane of normally liquid hydrocarbons in vapor phase and characterized 'by-the use of a heat-carrying cycle gas, which comprises cooling and fractionating the reaction products toproduce an aromatic distillate, withdrawing a. part of said distillate as an end-product, another part of said distillate forming a source of supply of recycle stock, in an absorbing zone utilizing vaporizable uncracked liquid hydrocarbons for absorption of substantially all of the hydrocarbons having three and more carbons atoms per molecule, withdrawing from the absorbing zone the lighter unabsorbed gases, heating and then fractionating said liquid hydrocarbons and their absorbed gases for the separation therefrom of normally gaseous hydrocarbons having less than four carbon atoms per molecule, the so-separated gases forming the principal supply of the heatcarrying cycle gas. in a subsequent fractionating zone separating hydrocarbons having four carbon I atoms per molecule, a substantial percentage of which consists of butadiene, commingling said aromatic distillate andthe remaining hydrocarbons having more than four carbon atomsper molecule, applying heat to the aforesaid mixture to vaporize the same and to elevate the temperature thereof to at least 1100 F. during a time interval insumcient for material conversion to occur, concurrently heating said cycle gas to raise its temperature materially above 1300.

F., commingling said cycle gas with said mixture to produce simultaneous conversion of all of said commingled hydrocarbons, and in less than twenty-tive one-hundredths of a second terminating the cracking reactions by abrupt cooling thereof.

12. In a vapor phase cracking system in which a heat-carrying cycle gas consisting of gaseous hydrocarbons is commingled with a stream of heated hydrocarbon vapors to produce controlled 'cracking thereof, .the method which comprises counter-currently contacting with a debutanized un'cracked charging stock normally gaseous hydrocarbons made during said cracking for ab sorption of a substantial quantity of said gases and for substantially eliminating gases lighter than Cas, that is, hydrocarbons having three carbon atoms per molecule, commingling said enriched charging stock with a condensate containing reaction products, in 'successive fractionating `zones separating from said mixture the Cas and the Crs, the Cas and lighter gases formin the principal source of supply Voi? said cycle g and the C4s containing a substantial percentage of butadiene, commingling aromatic distillate with the remaining hydrocarbons heavierhan the C4s, heating the mixture to a high temperature in a short time, concurrently heating said cycle gas to a temperature within the range of 1400 F. to 600 F. and in quantity adequate for the elevation of said highly heated mixture to within the range of 1300' F. to 1500 F.,

commingled with the hydrocarbons heavier than the Cis, that is, those having four carbon atoms per molecule.

13. The method of producing butadiene which comprises heating a stream of vaporizable normally liquid hydrocarbons heavier than propane to a temperature of approximately 1375 F. within a relatively short time interval of heating above 1200 F., said stream comprising a charging stock substantially free of aromatica and unsaturates, and including a recycle stock predominantly aromatic, concurrently heating to approximately 1500 iF. within a relatively short stock predominantly time interval of heating above 1200 F. a heat carrier consisting of normally gaseous hydrocarbons to large extent lighter than -C4s and heavier than methane, in a reaction zone commingling said heated hydrocarbons, after-a reaction time of approximately four one-hundredths of a secondterminating the cracking reactions by rapid quenching of the reaction products, separating from said products a stream of C4 hydrocarbons which includes butadiene in quantity .of approximately thirty percent thereof, and

separating from said reaction products a recycle aromatic for mixture with said stream..

WILLIAM C. DORSETT. CURREN C. SPERLING.,

QRANGE C. WALKER.

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