US2363532A

US2363532A - Vapor phase cracking process

Info

Publication number: US2363532A
Authority: US
Publication date: 1944-11-28
Anticipated expiration: 1961-11-28

Description

Nov. 28, 1944. w. o. KEELING VAPOR PHASE CRACKING PROCESS Filed March@J 1932 Patented Nov. 28 `1944 UNITED STATES* PATENT OFFICE i VAPOR PHASE CRACKINGPRocEss William "0. Keeling, Independence, Mo.

" Application March 9, 1932, serial No. 597,692

2v claims. o (cl. 19e-61) My invention relates to` a vapor `phase cracking process and more particularly to a process in which the majorv portion `of the heat for vaporization andcracking is supplied by indirect heat exchange and a certain portion of the conversion is carried on by' direct heat exchange with the highlyheated gases.

This invention is a continuation inpart of my co-pending application, Serial No. 585,939, filed January 11, 1932. l i V In my application of Serial No. 585,939, I show a process for `converting hydrocarbons in; the

vapor phase in which a Vhighly heated gas is used to supply all of` the heat for the conver sion. It is generally conceded that a pipe still is the mosteconomical means to heat hydrocarbon oils. The latent heat of vaporization of hydrocarbon oil is about 100 B. t. u. To` raise the oil to a given temperature, an average sensible heat of about .65 of a B. t; u. per degree per pound is required. The heat of conversion is about 50G-1000 B. t. u. `per pound, depending upon the nature of the oil being converted. In

order to raise the oil`- from its,temperature of vaporization toA atemperature required for conversion and to supply the` heat` of conversion, a large volume of heated gas is necessary.V When `cracking process for cracking hydrocarbons in the vapor `phase which `will avoid the disadvantages of cracking in a tube still and cracking solely by hot gases `of combustion and will combine the advantages of each type of process.

Another object of my invention is to provide a process for crackinghydrocarbons in the vapor phase by highly heated gases in which thesize of the equipment is considerably reduced.

Another object of my invention is to provide` a process which will produce a motor fue] having an extremely high antiknock quality. l

Other objects of my invention will appear from the following description. In the accompanying drawing,` which 'forms part of the instant specification and is to be read in conjunction therewith, the ligure shows a large quantity of heated gas is employed, the

size of the reaction chambers and of subsequent equipment is greatelyincreased. `It is of some disadvantage to have a large quantity of gas go-` ing through the fractionating tower. Then, too, the size of the gas absorption plant is materially increased.` Furthermore, the addition of large quantities of inert gases serves to `reduce the` caloric value of the nal fixed gasextracted C from the absorbing system'. l v

Itis generally conceded thatl the` initial .por-

`tion of the cracking operation is accompanied in a pipe still, such as in thevapor phase cracking processes of DeFlorez, (irre'esnstzeet,y and Hall, and in the Gyro process, Without the formation of excessive carbon and Withoutmaterial parasitic cracking. When `oil is converted inthe vapor phase in a pipe still, the high skintemperature of the tubes causes considerable parasitic cracking when` the vaporsare retained in the tubes` for a` sufficient -length of time to accomplish the cracking of the more diiiiculty convertedl hydrocarbons. `The parasitic; cracking causes a heavy carbon deposition, aswell as the formation of fixedgaseslwhich represents a direct loss in anoperation inwhichthe object is toobtain hydrocarbons suitable for use in Vmotor fuels.

One object of my invention is to `provide a a schematic view oi a process embodying one mode of carrying out my invention.

In generaLmy invention contemplates passing a charging stock in direct contact with theproducts of reaction to obtain heat exchange and to scrub the products of reaction. `The charging stock so heated is passed through a vaporizing coil of a pipe still and heated. The heated prod#- ucts are liashed into vapors in ailash evaporator.

r Vapors are led from the iiash evaporator and passed through a vapor phase cracking' coil in the manner of the Vwell known vapor phase cracking processes of DeF'loreZ, Greenstreet, I-Iall and in the Gyro process, with the important dilerence, however, that the cracking coil is considerably shorter and designed to permit a sufliciently rapid passage of the products therethrough to prevent morethan thel initial cracking from occurring.` That is, the more easily cracked hydro-` carbons are cracked in the pipe still and the greater portion of the heat is thus supplied. It will `be obvious that the major portion of the Sensible heatthe latent heat. of vaporization and a portion of theheat of conversionwill vbe supplied in the pipe still in the most eiiicient manner. Independently of my pipe still, I generate hot gases of combustion, though itis to be understood that the heated carrier gas might be employed if desired. 'Ifhehighly heated gases are then mixed with the products from the cracking coil of my pipe still in one or a` plurality of stages. The mixing of the hot products of` combustion in the manner contemplated by my process precludes any parasitic cracking due to the fact that the gases are thoroughly com'mingled.

I provide a sufficient` time of reaction and then pass the products of reaction through a scrubber l in which any carbon present is'removed and in which operation the incoming charging stock is preheated. The products of reaction are then i character, is charged through line I, through valve 2, and is pumped by pump 3 optionally through spray pipe 4 orline 5. The chargemay be split so that a portion of it will pass through vicinity of 1500 F. The hot gases issuing from line 43 are commingled with theproducts leaving the cracking coil in mixing chamber 45, from which the admixture passes into a refractory lined reaction chamber` 46 in which a sufncient time interval-for reactionis allowed. If desired, in order to reduce the size of the equipment, I

may crack by hot gases of combustion in a` plurality of successive steps; that is, the products ofreaction from. chamber 46 may be admixed in mixing chamber 41 with further hot gases passing through line 48 which is controlled by valve 49-,and passed through valve controlled line 50 spray 4 and also through line 5.v This. may be controlled by valves 6 and 1 respectively. The portion of the charge passing throughn line 5v y duel tol the 'actthat there is a complete admixpasses through heat exchanger 8 into line 9rwhere i it flows into scrubber I0 in heat exchange relationship with the reaction'products entering i through-'pipe II. The por-tion' of the charge passing into the fractionating tower I2 ,through spray pipe 4- courses downwardly through the fractionating tower in scrubbing and heat exchange relationshipwith the products of reaction entering the fractionating tower Athrough pipe I3 andisrpumped by pump I4 through pipe I5 where it joins the portion of the charge entering through pipe 9. and passes into the scrubberv I0.

tom .of the scrubber through valve controlled line I8. The bottoms from the scrubber pass through line I9 to storage. An intermediate cut from one of the traysof the scrubber, lwhich may be. of any suitable'` fractionating tower construction, is pumped through' line 20 by pump 2I through valve 22 through the vaporizing coil. 23 of mypipei still 24. The pipe still 24 may be of any suitablel construction. The oil passing through the vaporizing coil is heated to a vaporizing temperature and leaves the pipe still. 24 through line 25 controlled by valve 26 and passes into the ash evaporator 21. The` unvaporized portions of the heated stock are withdrawn fromV the flash evaporator through linev 28,` controlled by valve 29 and. may be reiiuxed, if desired,

through valve controlled linel.` Steam is introduced within the flash evaporator 21 to induce an addedevap'oration. The vapors leave the flash evaporator throughy mist extractor or Tracy purifier 32. and 'pass through line 33' controlled by valve 34 into the vapor phase cracking coil 35 in which the initial portion of the cracking in the vapor phase occurs. Valve 36 controls line 31 through which the products leave the cracking coil 35. Simultaneously with the above described ioperation, hot combustion gases are, being generated in burner 38 into which air is introduced'through line 39, and iuelthrough line 40.

lIt is to be understood that, while I have shown a particulartype of burner, that any suitable I neansl may be" used forfgenerating hot gases of combustion or, if desired, heating a carrier gas. The highly heated gases` leave the'burner t8 through lineV 4I which is lined with refractory material 42. The highly heated gases rpass through refractory lined line 43` which is controlled by gate valve 44 which may be lined with v refractory material or may be cooled by water circulation in order to resist the high heat of the hot gases of combustion which may be inthe A reiux line I=6. is provided` so that areflux may bepumped by pump I1 from the bot-- through valve controued une 3| situatedl into a second reaction chamber 5I in which a further timer-interval of reaction is permitted to insurel the cracking of the more diihcultly cracked hydrocarbons. 'It will be readily understood that,

ture of the hot` gases of combustion with the vapors to be cracked, that local overheating from which` parasitic .cracking results is avoided. I may choose the desired temperaturev tofobtain any desired product; that's, at a temperature of reaction of about 1050 F.I am enabled to obtain a motor fuel havingan exceedinglyhigh antiknock quality. By raising the. temperature of my highly heated gases, I am. enabled vto kobtain y a reaction temperature, which is considerably higher, and obtain benzol; Similarly, I- may in.- crease the reaction temperaturel still further and obtain toluol or, by a corresponding increase in temperature,-obtainvxylol. There is practically no limitation as to the temperature at which I may carry on my cracking operation except the limitingA temperature atwhichI-may generate hot -gases of combustion. vDue to the fact that a certain portion of the heat of the hot gases of combustion will be required to raise the vapors to be cracked to the conversion temperature and a still further quantity of heat will'berequired to effect` the conversion, the temperature of the highly heated gases entering the mixing chamber is` considerably in excess of the temperature of the vapors to be converted; For example, i1".A it bedesired to obtain a high antiknock motor vfuel, the products leaving the cracking coil 35 and passing through line' 31 willbe superheated and will be at a temperature'of about 900 F. Atthis temperature, the 'highly heated gases passing through pipe 43` need" only be about 1350o F. to

1 give al resultant mixture'having` a temperature of about 1050 F., at which temperature I` havel found that a motor fuelof high antiknock value is produced.

The productsof chamber 5I through valvev controlledqline II andpass into the scrubber I0 wherethe-prod ucts of reaction pass in heat exchange relationship with the incoming charging stock entering the scrubber through line I5, 'pass 4upwardly through the scrubber, leaving it' through valve controlled line 52, through-'heatexchanger 8,' line I3, into fractionating tower I2, coursing up# wardly therethrough. The vapors containing thev products of reaction consist chieflyv of hydro'- carbon's having low boiling points and a cerv tain amount of xed gasesvare withdrawn Vfrom the fractionating tower throughline 53, and pass through condenser' 54,k valve controlled line 55, into accumulator 56. The gasoline-like.v hydrocarbons' arewithdrawn through valve .controlled line 51 and pass' to storage. The uncondensed gasesare withdrawnA throughv valveV controlled line 58 and compressed by compressor.` 59'," passed through -cooler 6U,- through f valve .controlled line reaction leave the reaction l valve controlled line i of radiation.

6|, into the gasoline absorption tower 62 in which n the gases are scrubbed by lean oil passing into t the tower throughvalve controlled line 63. The valuable hydrocarbons, is absorption column through fat oil, containing withdrawn from the 65 and passed to a still in which the absorption oil is heated to drive therefrom the light hydrocarbons absorbed thereby.`

These products are recovered in the usual manner. The fixed gases leave the top of the stripping column through line that a smaller quantity of tion is used in my process, sorption tower will be rich suitable as fuel. These gas main 'lll and used to 4I for use in my burner.` A portion of the fixed gases is withdrawn through line 66 controlled by valve B1 and pumped by compressor 68 into line 68 for use as a tempering gas. By tempering gas, I mean that the gaspassing into the burner through line 66 is used to bring the hot products of combustion to the desired temperature. It is to be understood that, inasmuch as the hot gases are generated at about 3500 F. that, to bring them down to the desired temperature, as pointed out above, it will be necessary to cool them or temper them to the desired temperature. I do this by admixing with the hot gases a sufficient quantity of a cooler gas, coming in through line 66 to bring the hot gases to the desired temperature so that the gasesleaving the burner` and passing through

lines

43 and 48 into the mixing chambers will be at the proper temperature for admixture with the vapors `to give the desired temperature of conversion to obtain the desired product as pointed out above.

It will be understood -that all lines and equipment in which high temperatures exist are suitably lagged with lagging to prevent heat losses in hydrocarbon gases may be collected in a It is believed that the operation of my process will be fully understood from the above description. My process `has `many advantages. By combining certain feat es of a pipe still process for converting in the vapor phase with a hot gas process of conversion, I am enabled to eliminate the disadvantages of each type process and retain all the advantages thereof. I am enabled to obtain a light product having a high antiknock value of any desired nature due to the fact that I am enabled to convertultimately at temperatures far in excess of those capable of use in a pure pipe still process. By converting the initial portion of the hydrocarbons in the `pipe still,

I am enabled to reduce the size of the equipment necessary to convert by 4use of hot gases and to eliminate the necessity of `passing a large quantity of hot gases through my fractionating and absorption system,` thus enabling the size of this equipment to be greatly reduced. It will be appreciated that my system is extremely flexible and that the quantity and nature of the hydrocarbons ultimately recovered can be governed to any desired extent by the temperatures of the hot gases entering the freactiorr chamber or chambers. I am enabled to avoid the parasitic cracking which would result from a high supply fuel gas to line 64. Due to the fact `hot gases of combusthe gas from the abtemperature by resorting to admixingthe hot gases directly with the hydrocarbons to be cracked. The products recovered will have a high antiknock value due to their composition and I am enabled to obtain these products without the formation of an excessive quantity of iixed gas.

It will be understood that certain features and sub-combinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and is within the scope of my claims. It is further obviousthat various changes may be made in details within the scope of my claims without` departing from the spirit of my invention. It is, therefore, to be understood that my invention is not to be limited vto the specific details shown and described.

Having thus described my invention, what I claim is: l

1. A process for converting hydrocarbon oils into hydrocarbons having a lower molecular weight, including `the steps of vaporizing the hydrocarbons, passing said vapors in an elongated coniined stream through a zoneheated to the conversion temperature and allowing a sufficient time interval to permit the cracking of a portion of said vapors, thereafter intimately commingling an inert gas highly heated to suchA temperature that the resultant mixture will have a predetermined temperature, at which temperature the hydrocarbons will be converted into the hydrocarbons having the desiredmolecular weight, allowing a sufficient time interval to permit the reaction to take place and recovering the hydrocarbons of lower molecular weight thus formed, wherein the highly heated inert gas is admixed with the vapors being converted in a plurality of successive stages, and a plurality of successive time intervals of reaction are permitted.

2. A process for converting hydrocarbon oil into hydrocarbons of lower molecular weight including the steps of `heating the hydrocarbon oil in an elongated, confined stream, to Vaporizing temperatures, flashing the oil into vapors and unvaporized oil, separately removing the vapors from the evaporation zone and passingv them in an elongated, confined stream at a rate slow enough to permit a conversion in the: vapor phase to take place, simultaneously generating hot gases of combustion, physically commingling the hot gases of combustion with the cracked vapors in suicient quantity and at sulcient `temperature so that the resulting mixture` will have a temperature in excess of 1000 mitting a time interval of conversion whereby further low boiling hydrocarbons are formed, passing the resulting mixture into a third conversion zone and there physically commingling F., perfurther hot gases of combustion at suflicienttemperature to raise the resulting `mixture to a F., permitting i