US2022803A - Process for cracking oil - Google Patents

Description

Dec- 3, 1935 G. EGLol-F PROCESS FOR CRAGKING oIL Filed Nov. 4, 1929 Patented Dec. 3, 1935 UNITED STATES PATENT OFFICE 2 claims. (ci. 19e-48)r This invention relates to the production of lower boiling hydrocarbons from those of higher boiling range and, more particularly, relatesv to the cracking or thermal decomposition of heavy hydrocarbon oils into low boiling hydrocarbon oils suitable for motor fuel.

In the cracking of high boiling and heavy hydrocarbon oils to produce motor fuels the former are heated usually under pressure to a conversion temperature where a substantial portion of the higher boiling oils are converted to lower boiling and lower molecular weight hydrocarbons.

In the older processes the oil was directly 'heated in a shell or cylindrical still equipped with dephlegmation, cooling, condensing and collecting means. The modern processes utilize tubular heating elements while bringing the oil to the conversion temperature and, in most cases, the reaction-is allowed to continue in an expansion element or reaction chamber and the low boiling product of the processes is subsequently subjected to dephlegmation, cooling and condensing and is finally collected in a receiver. In a modern process in extensive use the reflux condensate from a dephlegmator is returned to the heating element to be subjected to further heat treatment and conversion.

In the present invention I make use of a dephlegmating meansso arranged as to permit the 30 separation and segregation of a light and heavy reux condensate which may be separately sub- J'ected to heat treatment under conditions more suitable to the conversion of the particular kind of reflux so as to obtain the maximum yield of 35 gasoline of high antiknock quality.

I will now describe my process, making use of the accompanying drawing:

The raw oil charging stock is fed by means of pump I throughline 2 and may be diverted into dephlegmator 3 at various levels, for example, through lines 4 controlled by valves 5. The raw oil passing downwardly through the dephlegmator counter current to the vapors arising therein becomes heated by and in turn removes heat from theyapors, thus effecting an eiflcient heat exchange and assisting insthe fractionation `of the vapors. The reux condensate leaving the lower section 3b of dephlegmator 3 together with y raw oil is picked up by hot oil pump 6, from 5 which it may be pumped directly into heating coil or element 'I located in furnace setting 8 or a. portion or all of the combined feed consisting of heavy reux from dephlegmator 3 and raw oil y be passed through line 9 controlled by valga III into the transfer line I2 controlled by valve I2'. 'I'he heated. oil leaving transfer line I2 enters reaction chamber I3. Any non-vaporized or residual oil in said chamber I3 may be drawn through line I4 controlled by valve I5. The vapors leaving reaction chamber I3 pass 5 through vapor line I6 controlled by valve I'I into dephlegmator 3, Where the aforementioned heat cXchange occurs between the descending raw oil and the ascending vapors.A Dephlegmator 3 is so arranged as to permit the collection of a light 10 reux on element 3' located at the bottom of section 3a in dephlegmator 3. The light reflux collecting on the deck or tray 3 is pumped by means of pump I8v through line I9 into heating element 20 located in furnace setting 2| wherein 15 the clean distillate is heated and brought to a cracking temperature, preferably in the vapor phase or state. The highly heated vapors leaving heating coil or element 2D pass through line 22 controlled by valve 23 into the transfer line 20 I2 and into reaction chamber I3. A

It may be readily understood that the oil passing through heating element 'I can be increased in temperature not only independently but also by the introduction of the highly heated oil leav- 25 ing the heating coil or element 2l). Similarly, the

' oil passing through the transfer line I2 may be cooled by the lraw oil and heavy reflux diverted through line 9. In this manner a balance may be obtained between the temperature and the time of heating.

The vapors leavingy dephlegmator 3 pass through vapor line 22' controlled by valve 23 into cooler and condenser 24 and the pressure distillate is finally collected in receiver 25. The gas produced by the process is released at line 26 controlled by valve 21 and the pr ssure distillate product of the process is removi from the receiver through line 28 controlledby valve 29. A portion of the pressure distillatemay. be returned to the dephlegmator 3 byfieans of pump 30 through line 3I controlled by valve 32. A cooling medium such as straight run gasoline may be used in section 3a of tower 3, line 33 and valve 34 furnishing means for its introduction. The pressure and temperatures which I employ may be varied over a wide range. For example, I may employ temperatures in coil I up to approximately 1000 F.,but preferably Within the range of '150 to 950 F., while in coil 20 I preferably em- 50 ploy temperatures exceeding approximately 950 F., for example, from 950 F. to 1200 F.. mo're or less. -The pressures upon the various elements in the system will vary, depending upon the particular results desired, and I contemplate As an example of the yield of products obtained by my process, starting with a Mid-Continent 26 A. P. I. gravity fuel oil I am able to obtain approximately 75% of distillate containing :80%

of gasoline based on the distillate or 60% based on the oil charged, having an antiknock value in excess of approximately 35% benzol and, in addition, I may make approximately of coke and gas, based on the charging oil when using the i non-residuum method of operation. Or I :may

make, when using the residuum method of operation known as the flashing process, approximately of distillate `containing approximately of gasoline based on the distillate or approximately 45 per cent of motor fuel of high anti-knock properties based on the charging stock, 25 per cent of fuel oil residue containing less than 2 per cent`-B. S. and of a viscosity suitable for general use or'sale, and 10 per cent of coke and gas. 'I'he transfer temperature in heating element 'I in the above example is approximately 900 F. and that in heating element 20 is approximately 1050 F.

The pressures used in the entire system will vary from 50pounds per square inch to 1000 pounds per square inch more or less and I may even use atmospheric pressures in heating element 20 and pressures exceeding 1000 pounds in the coil 1.

The above examples are given by way of illususing pressures which may range from 50 to i500 tration only and, in view of the many modications in operating conditions, are not to be construed as limitations upon the spirit and broad scope of the invention.

Having thus disclosed my invention, what I 5 claim is: y

1. A process which comprises fractionating a vaporous mixture of hydrocarbons to obtain therefrom relatively heavier 'and lighter cuts of higher boiling point than gasoline, heating a por- 10 tion of said heavier cut to cracking temperature while maintained under sufcient pressure to retain a substantial portion thereof in the liquid phase, separately cracking said lighter cut in the vapor phase by heating the same to higher l5 temperature than said heavier cut, diverting another portion of said heavier cut from the liquid phase heating step and introducing the same to said lighter cut. subsequent to the heating of the latter to vapor phase cracking tem- 20 perature, commingling the cracked products of said heavier and lighter cuts and subjecting the commingled vapors to dephlegmation and condensation.

2. A process which comprises dephlegmating 25 thevaporous mixture of an oil cracking process and obtaining therefrom a vaporous gasoline-like fraction and relatively heavier and lighter cuts of higher boiling point than said gasoline-like fractions, lheating a portion of said 30 heavier cut to cracking temperature while maintaining a substantial portion thereof in the liquid phase, separately heating said lighter cut to a higher temperature than the heavier cut and cracking the same in the vapor phase, divertingv another portion of lsaid heavier cut from the liquid phase heating step and introducing the same to said lighter-cut subsequent to the heating of the latter to vapor phase cracking temperature, commingling the heated heavier and 40 lighter cuts in an enlarged vapor separating zone, and removing the cracked vapors for dephlegmation and condensation.

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