US2123960A - Method of cracking hydrocarbon oils - Google Patents

Description

@Fuy H9, i938. Q H. c. PENNRICH 2,323,960

METHOD OF CRACKING HYDBOCRBON OILS l Filed Aug. 29, 1935 Separor Ceo/@r .y Dlsl/laion Tower y Tar Flash Tawer 4:

` Fresh'eed Frasi? Fed 2 kIl QQIa 2l .n

Cracking l Zone @as s @Il Healng l2 Haarmg 2mm I7 Z one INVENToR.

Henry C. Pennrlch.

Patented July 1.9, 1938 2,123,960 METHOD F CRACKIG HYDROCARBON Henry C. Pennrlch,-Brussels, Belgium Application August 29, 1935, Serial No. 38,362

Claims.

This invention relates to the cracking of hydrocarbon oils and it refers more particularly to the production of motor fuels having high antiknock values.

In my former applications, Serial No. 610,346, originally led May 10, 1932 and Serial No. 633,551, led September 17, 1932, a method of cracking hydrocarbon oils is disclosed, in which normally incondensable hydrocarbon gases, obtained as a byproduct of the cracking and following distillation of hydrocarbon oils, are subjected to high pressure and temperature and are admixed to the fresh charge oil to be cracked under conditions wherein the reaction time and temperature of the oil cracking process are carefully controlled. An improved gasoline is thus produced at a distinctly higher yield and with considerably lower gas formation.

Under the above conditions, many of the compounds present in the cracked gases undergo conversion and form normally liquid hydrocarbons. This conversion is generally the result of the polymerization of unsaturated hydrocarbons present or formed from saturated constituents by the cracking reaction. These normally incondensable gases, obtained coincident with the cracking operation, contain the compounds butane, propane, ethane and the corresponding unsaturated hydrocarbons as well as the so-called xed gases methane, hydrogen, carbon monoxide and carbon dioxide. It is generally found that the fixed gasesare highly stable and generally that they do not readily undergo conversion under the above conditions and thus it is found that through the presence of the xed gases the conversion of the higher boiling compounds becomes incomplete.

Based on these observations I found it highly advantageous to remove the fixed gases from the cracked gases before they are compressed and heated for admixture and to subject only the remaining higher boiling incondensable hydrocarbons to higher pressure and temperature wherethrough they-are very readily and completely converted and thus they then form the valuable products as Yrequired for the Aabove indicated purpose. 4

Thus when the highly stable or the xed gases methane, hydrogen etc. are absent, then the products in the remaining mixture are present at higher concentrations and `for that reason the conversion will naturally proceed further giving a greater yield of liquid products. These conversion products may be formed either from the gas constituents alone or they may be reaction products from these and the fresh hydrocarbon oil products with which they are mixed. In general, the results of this process are a greater gasoline yield, less gas formation and a smoother reaction and performance of the cracking proc- 5 ess; this may in part also be attributed to the' greater amount of heat available due to the exothermic character of the reaction of polymerization and the more highly concentrated gas mixture.

'I'he method of 'separating the low molecular or fixed gas constituents from the cracked gases' can be carried out in a variety of ways but in practice the following process was found to be most convenient and economical. A mixture of vgasoline and cracked gases obtained by distillation is brought toa pressure of about 150 pounds per square inch and a temperature at which the gasoline is completely liquefied. Under these conditions, the higher boiling gas constituents are dissolved while a gas 4rich in methane and hydrogen remains unabsorbed and `is removed. The solution is then heated whereby the dissolved gas constituents are again set free. They are compressed, heated and passed on into the principal cracking unit.

One example of a practical unit embodying` the features of my invention is illustrated in the accompanying drawing and it is to be operated as follows: 30 The fresh feed, such as a crude oil or products obtained from crude oils and similar products, enters through pipe I and is mixed with the cracked products at point 2 and from there the mixture is sent into the flash tower 3. Heavy tar and overhead vapors are separated from the mixture by condensation in the tower and it is continuously withdrawn from the bottom by means of pipe 4. The overhead vapors are passed by means of pipe 5 'into the distilling tower 6. A condensate consisting mainly of gas oil is collected .in the cooler 8 and is sent to the separator 9. The separator contains gasoline as a solvent for the higher molecular compounds and is operated at a pressure of ,150 pounds per square inch 'and a gas is. separated from the liquid. This gas comprises the xed'gases .and consists of methane, hydrogen, CO and CO2 and is withdrawn by means of pipe I3. The liquid is -sent into the second separator. I0 by means of pipe I4, in which the liquid is heated to around '300 F. under substantially the samek pressure. The heating is obtained by the use of steam circulating through the steam coil 22. A stabilized gasoline is' withdrawn into the storage tank by 55 means of pipe 23 and a gas is taken from the top of the stabilizer or separator. This gas contains the hydrocarbons ethane, propane, butane and the corresponding unsaturates. The gas is recycled through pipe I5 and its pressure is increased to around 1000 pounds per square inch before the gas enters the heating zone I6.

In the heating zone consisting of tubes placed in a furnace the temperature of the recycle gas is raised to around 1050 F. The heated gas is sent into the oil cracking zone I9 by means of. the

pipe I8. The pipe I1 is a bypass and contains.

the control valve 20.

The condensate of the distillation tower 6 leaving by way of pipe 'I is compressed to around 1000 pounds per square inch. Additional distillates can be added to this stream by way of pipe II. The stream enters the oil heating zone I2 which consists of tubes placed in a furnace. In this zone, the temperature of the oil is raised to around 800 F.

The heated oil of zone I2 is mixed with the heated gas of zone I 6 in proportion to obtain a temperature of between 840 and 880 F. The mixture is passed through the oil cracking zone I9 consisting of tubes placed in a furnace. The

. furnace is only moderately heated in order to replace the heat lost during the course of the cracking process. Additional amounts of gas may also be added into the cracking zone at various intermediate points along zone I9 which are not shown. The cracking zone is made sumciently long to assure a cracking time of around 10 minutes. The temperature of the oil gas mixture at the beginning and at the end of this zone are about the same. 'I'he products leaving the crackingzone are decreased in pressure by means of pressure valve 2i and from then on the pressure will be around 200 pounds per square inch. The products are mixed with fresh charge oil entering through pipe I whereby the temperature is brought to about '700 F. and then the mixture is sent to the flash tower 3.

The conditions of pressure and temperature may vary from those given above according to the type and kind of oil to be converted and the products desired. In general, in the heating and the cracking zones, the pressure may be between 300 and 3000 pounds per square inch while the pressures in all other parts of the operation such as in the distillation vand separation tower should be below 300 pounds per square inch. The temperature of the oil cracking zone is to range between 840 and 960 F. for most of the stocks, while in the gas heating zone it is to be still lower than these temperatures.

Having thus described one typical example of my process, I do not bind myself to the exact details given in the above description, but rather consider this as one example illustrating the general broad idea ofmy invention.

I claim:-

1. The method of cracking hydrocarbon oils comprising the steps of separating normally incondensible hydrocarbon gases into a nrs-t 'fraction rich'in methane and into a second fraction substantially free from methane. heating said second fraction under a-pressure of between 500 and 3000 pounds per square inch to a temperature sufficient to start exothermic polymerization and not exceeding 1200 F., and keeping said teml perature substantially constant whereby a fully controlled polymerization product is obtained.`

drocarbon oil to be cracked, said hydrocarbon oil being heated to a temperature below its cracking temperature and said mixture being in proportions suflicient to cause cracking of apart of said oil, passing said mixture through a cracking zone, and maintaining said pressure on said mixture in the cracking zone, removing the mixture from the cracking zone andadding cold fresh feed to the cracking mixture.

2. The method of cracking hydrocarbon oils to obtain a high-grade anti-knock motor fuel comprising the steps of separating from normally incondensible hydrocarbon gases the fixed gases methane, carbon monoxide and dioxide. ethane, nitrogen, hydrogen etc., subjecting the remaining normally incondensible hydrocarbon gases to a pressure between 500 and 3000 pounds per square inch and to a temperature to start polymerization but not exceeding 1200 F., and,

maintaining said temperature to control said polymerization, mixing said heated gases with a hydrocarbon oil to be cracked, said hydrocarbon oil being heated to a temperature below its cracking temperature and said mixture being in such proportion as to result in cracking of a part of said oil passing said mixture through a cracking zone, and maintaining said pressure on said mixture in the cracking zone, removing the cracking mixture from said cracking zone while reducing said pressure and adding fresh feed to the mixture.

' 3. The method of cracking hydrocarbon oil to produce a high-grade anti-knock motor fuel comprising the steps of freeing normally incondensible hydrocarbon gases of gases rich in methane, ethane, hydrogen, carbon monoxide and dioxide, which are diiilcult to condense and thereby separating from incondensible gases a condensible portion, compressing said condensible portion to between 500 and 3000 pounds per square inch and heating it to a high temperature until polymerization starts but not over 1200 F. and preventing said temperature from rising in order to control the polymerization products, mixing said polymerization products with normally liquid hydrocarbon oil heated in a heating unit to a temperature below its cracking temperature and at the same pressure as imposed on said condensible portion and in proportions that the temperature of the mixture causes cracking, passing said mixture through a cracking zone, and maintaining said pressure on said mixture in the cracking zone, removing the mixture from said cracking zone, decreasing said pressure and temperature, adding fresh feed and separating desired compounds from the mixture.

4. ''he method of cracking hydrocarbon oil as claimed in claim 1, the step of separating the fraction rich in methane from normally incondensible hydrocarbon gases being carried out by compressing the gases at low temperature and in contact with gasoline as a solvent. removing the non-condensed gases and reevaporating the dissolved gases.

5. The method of cracking hydrocarbon oil as claimed in claim 3; the step of separating the portion rich in methane, ethane, hydrogen, nitrogen, carbon monoxide and dioxide, from normally incondensible hydrocarbon gases being carried out by compressing the gases at low temperature and'in contact with saturated hydrocarbon oils as a solvent, removing the non-condensed gases and reevaporating the dissolved gases.

HENRY C. PENNRICH.

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