US2016651A - Process of cracking large molecular hydrocarbons - Google Patents

Description

Oct. 8, 1935. H. c. PENNRICH PROCESS OF CRACKING LARGE MOLECULAR HYDROCARBONS Filed Sept. 17. 1952 nzummzunnkn 1N VEN TOR. BY

A TTORNEY Patented Oct. 8, 1935 UNITED STATES PATENT OFFICE PROCESS OF CRACKING LARGE MOLECU- LAB HYDROCARBONS Henry C. Pennrich, New York, N; Y. Application September 17, 1932, Serial No. 633,551

4 Claims. (Cl. 196-48) More particularly stated, my invention comstill lower temperature. This then demands prises the process of bringing a moderately preagain a proportionately further increase of the heated gas oil to the cracking or conversion temduration of the reaction in order to complete perature by the rapid admixture of an overheated the conversion. Thus a condensate boiling above 5 mixture of more heat resistant hydrocarbons 680 F. can be efliciently cracked at 150 F. if 5 whereby the temperature of the mixture is the reaction time is 1 hour. brought to or slightly above the cracking tem- I have further discovered that the time of the perature of the ingredient to be converted. When reaction is most easily controlled by the length the reaction is complete, in order to terminate it of the tubes of the cracking or conversion unit quickly, there is admixed to the hot mixture and hence the largest yield of desirable reaction 10 emerging from the cracking unit, a sufficient products is obtained by adjusting the length of quantity of cool vapors or oil. This method of the cracking tubes in inverse proportion to the admixing superheated products to cause the' rereaction temperature or in direct proportion with action and cool products to terminate the reacthe boiling point of the hydrocarbon fraction to be tion is found essential for obtaining considerably cracked. 15 higher yield than usual of the desired product and In this connection, I also found that the time in order to avoid the formation of undesirable byof the reaction, or the velocity with which the products such as polymers, carbon or coke, etc. products travel through the tubes, can be regu- I have further discovered that the actual temlated with-the proportion of the overheated prodperature at which this cracking or converting ucts. For instance, if the proportion of the over- 20 reaction takes place with the highest efficiency heated products is increased, then lessheat is and economy depends roughly on the boiling point necessary from. the outside, but ordinarily a greatand specific gravity of the condensate to be er loss of heat by radiation may take place. For cracked, and that on this temperature in turn dethat reason it may be advisable to increase the pends the time factor of the reaction for the velocity with which the products travel in the 25 highest yield or the greatest output of a desired tubes and thereby the separating out of heavier or preferred product. products can be decreased or prevented.

As an example, I might have a condensate from The following approximate values, which are the distillation of a mixture of hydrocarbons experimentally determined, may serve to illuswhich hasaspeciiic gravity of .800 and an average trate this relation and indicate the proportion- 30 boiling point of about 480 F. Such a condensate ality between the boiling point of the condensate, is usually designated as a low boiling product. its best cracking temperature, the time of the This condensate can be heated by the admixture reaction and the best. length of the cracking t b of hot vapors as above described to a temperaing. These values are approximate and apply ture of 1075 F. without danger of obtaining highto one particular crude oil on]y Consequently, 35 er po y s Ot ab e Y-products. they may vary in the case of other types or kinds Then, of course, the reaction time will be relaof r d 11, tively short, such'as about 1 minute if the diameter of the tubular conversion unit is appropriate, C In F R ti um 40 i. e., over 3 inches. After that time the reaction Fraction boiling at m 6 '40 is usually complete and it is terminated through temperature length (minutes) the admixture of cold vapors as described.

If, however, a heavier, higher boiling con- Dem Fam'mm .131%},

densate is to be cracked, then it is usually found 1..-- 400-550 (kerosene). 1,050-1, 100 200 borless. that it can be heated, even by the method of adg i mafifffgm ZRI$ ggggg 45 mixture of super-hot vapors, to not quite as high a temperature without obtaining the association or polymerization of some molecules and conse- The diameter of the tubing is from 6 to 12 quently of a lower useful yield. But then I inchesfound that by prolonging the reaction time pro- The following process is described in detail in 50 portionately, a completion of the reaction can order to illustrate the prac ical pp at 1' then again'be effected, the fundamental principle of my invention. The

With a still higher boiling hydrocarbon. condrawing illustrates schematically the assemblage densate, the cracking process may have to be of apparatus required for the conversion of a 5 carried out, for obtaining. the highest yield, at a crude hydrocarbon oil, such as tar oil, mineral exchanges (3 and 4). Thus preheated, through pipe (5) it enters the stream of hydrocarbons emerging from the tubular cracking unit (51) at tube (5).

This mixture enters at reduced pressure the vaporizing zone (1) which is well insulated for heat and maintained at a definite temperature, for instance, by refluxing a hot gas oil through pipe (9) and reflux pump (I0).

Tar which may have accumulated at the bottom of this tower is passed on to a flash zone (l2) There the tar is separated into the residue and overhead stream. In this part of the process, low pressure or even reduced pressure may be employed and steam may be used for the passing along of the products. The overhead stream passes through pipe(|3) through the heat exchanger (l4) into a receiver (l5). From there it passes to the tubular conversion unit (20) through pipe (l9) and pump (Mia). The residue from flash tower (I2) is withdrawn on the bottom and sent to the storage tank (3), passing through pipe (l6) and cooler (H).

The vapor compounds leaving the vaporizing zone (1) pass through pipe (8) into the fractionating tower (24) The temperature of. this tower is also controlled by gasoline reflux pump (26) and through pipe (25) Distillates at various temperatures can be taken from this tower, as for instance a low boiling gasoline, ,a high boiling gasoline, a kerosene and a gas oil. In the case here described, only three products are taken off for the purpose of illustration, but any number of condensates may be separated and treated individually as is hereinafter described.

The overhead stream from the distillation tower (24) passes through the heat exchanger (3) the cooler (21), entering the receiving drum (28). A gas containing methane, ethane and other hydrocarbons is taken from the top of the receiver, and, by means of pipe (29) it is sent to the absorption tower (30) in which the low boiling gasoline products are retained. The final products are introduced into the gas holder (3|) To further dispose of condensates, the gasoline fraction taken from the bottom of the receiving drum (28) is sent to a stabilizer unit (31) through pipes (35 and 36). In this unit, hydrocarbons boiling in the range of propane and butane are removed by distillation and sent through pipe (38) to the gas holder (40). Gasoline products free from volatile substances enter through pipe (39) the storage tank (4|).

Another condensate is taken from fractionation tower (24) in the form of a stream of hydrocarbons boiling in the range of kerosene. Through pipe (42), it passes the heat exchanger (4) and enters the receiving drum (43). A part of this stream may be used in the wash tower for removing the gasoline from the waste gas. This part passes the cooler (44), the pipe (32) and enters the absorption tower (30). Another part may pass to the kerosene storage tank 45. The kerosene leaving the bottom of the absorption tower (30) re-enters the fractionating tower (24) by means of pipe (33) and pump (34) The other parts of the kerosene stream collected in the receiver (43) pass through pipe (46) through pump (41) and enter the tubular conversion stage (48). According to its temperature, it may have to be diverted in order to be preheated through the heat exchanger I4) The gas oil fraction from the distillation tower (24) passes through pipe (52) through pump (53) into a tubular preheating zone (54) wherein it,

is raised to a temperature below the cracking temperature. Gaseous hydrocarbons may be taken from the gas holders (40 and 3|) through pipes (58 arid 59) It is usually operated so that part of the gas collected in gas holder (3|) is drawn off to be used outside, while the gas collected in gas holder (40) is used for recirculation. This mixture, picked up by pump (60), enters the tubular heating zone (6|). This part of. the system ordinarily has the highest temperature, as these are the substances which usually tolerate the highest degree of heating, and therefore they represent those substances which can be superheated. Such gases and others which may be heated to this high temperature without undergoing undesirable changes are steam, nitrogen, hydrogen, carbon monoxide and air, in addition to those described in the preceding. By means of pipes (62 and 23) they may be introduced into the conversion zone (20) and by means of pipes (62, 56 and 55) they may be introduced into the conversion unit (51). The pipe (63) is used as a bypass.

The kerosene fraction taken from the distillation tower (24) is converted in the tubular cracking zone (48). The end products of this conversion may be used for heat-carrying purposes in the conversion units (51 and 20). They enter these through pipes (49, 22 and 5|). Pipe (50) is a bypass.

The gas oil fraction taken from the lower part of the distillation tower (24) is preheated in the tubular unit (54) through which it passes on to the gas oil cracking unit (51). Before entering, it is expedient to admix the heat-carrying products from units (6| and 48) whereby the temperature of the gas oil is rapidly brought to the cracking point; Still further heat-carrying products may be admixed to the hydrocarbons in the process of conversion by means of pipe (55). The overhead fraction from the flash tower (I2) is converted in flash distillate cracking unit (20). A part of. the tubes of this unit is used for preheating the oil. The preheated oil is then mixed with part of the final products coming from units (6| and 48), thus rapidly increasing the temperature of the mixture to the cracking condition. The end products from this stage are passed directly through pipe (2|) to the vaporizing tower (1).

Various combinations can be made as required by the individual type of crude oil to be cracked. So, for instance it is possible to pass allthe final products of unit (6|) into the cracking unit (51), or into the unit (20). Similarly it is possible to pass all the final products of unit (48) into the unit (51) or the unit (20). It is also possible to send the final products of units (6|) and (48) directly into the vaporizing tower (1) In this process the pressure may vary between very wide limits and may be as low as one pound per square inch or as high as 6000 pounds per square inch. Usually, the pressure in the conversion units is about 1000 pounds per square inch. The pressure in the vaporizing tower and the main fractionating tower is about 50 pounds per square inch. The'vacuum distillation tower will operate at 50 mm. Hg. pressure. For the use of high pressures, it is ordinarily required to select pipes made of metals which are capable of withstanding the 75 which operate at temperatures above 900 or 1000 CPI degrees F., it is necessary to employ tubings of steel containing cobalt, chromium, molybdenum, tungsten or nickel.

At any point of the process it is possible to employ catalytic agents for the purpose of reducing the reaction time. For instance a mixture of iron oxide and aluminum oxide may be packed into the tubes for the gas heating stage. The sul-' phides of cobalt, iron or copper to which alkali compounds such as magnesium oxide, potassium carbonate, etc. may be added, can be placed in the tubes of the fuel oil conversion unit. Of course,

other well known catalysts can be employed.

.The above described process is for the purpose of illustration only and does not illustrate the broad scope of my invention.

I claim:

1. The method of cracking hydrocarbon 011 comprising the steps of mixing fresh charge oil with cracked products, passing the mixture to a vaporizing zone and separating vapors and gases from unvaporized liquid, fractionating the overhead products to produce a primary condensate, a lighter secondary condensate and incondensible gases, passing the primary condensate in a restricted stream through a cracking zone, passing incondensible gases in a restricted stream through a heating zone and heating said gases to a temperature sufliciently high to adequately crack said primarycondensate, admixing said heated gases with primary condensate entering said cracking zone to raise said primary condensate to cracking temperature, heating said lighter secondary condensate in a restricted stream in a second cracking zone to crackingtemperature, admixing all the cracked products leaving the cracking zones with said fresh charge oil before entering into said vaporizing zone.

2. The method of cracking hydrocarbon oil comprising the steps of mixing fresh charge oil with cracked products, passing the mixture to a vaporizing zone and separating vapors and gases as overhead products from unvaporized liquid, separating said unvaporized liquid with steam into a flash distillate and tar, fractionating the overhead products to produce a primary condensate, a secondary gasoline condensate and incondensible gases, passing the primary condensate in a restricted stream through a cracking zone, passing incondensible gases in a restricted stream through aheating zone and heating said gases to a temperature sufliciently high to adequately crack said primary condensate, admixing said heated gases with primary co densate entering said cracking zone to raise said primary condensate to cracking temperature, heating said flash distillate in a restricted stream in a cracking zone to cracking temperature, admixing all the cracked products leaving the cracking zones with said fresh charge oil before entering into said vaporizing zone.

3. The method of cracking hydrocarbon oil comprising the steps of mixing fresh charge oil with cracked products, passing the mixture to a vaporizing zone and separating vapors and gases as overhead productsv from unvaporized liquid, separating said unvaporized liquid with steam into a flash distillate and tar, fractionating the overhead products to produce a primary condensate, a secondary gasoline condensate and incondensible gases, passing the primary condensate and the flash distillate each in a restricted stream through separate cracking zones, passing incondensible gases in a restricted stream through a heating zone and heating said gases to a temperature sufliciently high to adequately crack said primary condensate and said flash condensate, admixingsaid heated gases with primary condensate and flash condensate entering each its cracking zone to raise said primary condensate and said flash condensate to cracking temperature, admixing all the cracked products leaving the cracking zones with said fresh charge oil before entering into said vaporizing zone.

4. The method. of cracking hydrocarbon oil comprising the steps of mixing fresh charge oil with cracked products, passing the mixture to a vaporizing zone and separating vapors and gases as overhead products from unvaporized liquid, separating said unvaporized liquid into a flash distillate and tar, fractionating the overhead products to produce a primary condensate, a secondary gasoline condensate and incondensible 40 gases, passing the primary condensate and the flash distillate each in a restricted stream through a, separate cracking zone, passing incondensible gases in restricted streams through a multiple of heating zones and heating therein said gases to temperatures suiliciently high respectively to adequ'ately crack said primary condensate and said flash condensate, admixing said heated gases with primary condensate and flash condensate entering each its cracking zone to raise said primary condensate and said flash condensate to cracking temperature, admixing all the cracked products leaving the cracking zones with said fresh charge oil before entering into said vaporizing zone.

HENRY C. PENNRICH. 5

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