US1974683A - Process of cracking hydrocarbon oil - Google Patents

Description

Sept. 25, 1934 N. MAYER 1,974,683

' PROCESS OF GRACKING HYDROCARBON OIL i Filed Sept. 29. 1930 dem ,Wr/1,

Patented Sept. 25, 1934 1,9%,983` yrRooEss or CRACKING HYnRooARBoN oIL Nikolaus Mayer, Vienna, Austria, assignor Vof fifty-four ton, D. C.

per cent to Alfred Oberle, Washing- Application september 29, 1939, serial No. 485,189 In Austria. October 8, 1929 3 Claims.

This invention relates to a method of cracking hydrocarbons and more especially to a method in which the hydrocarbons are continuously highly heated under high pressure to a cracking temperature in a coil or other device, and then allowed to expand in an enlarged reaction-chamber by suddenly reducing this high pressure to a lower one, whereby vaporization of a part of the highly heated oil occurs and the residue (coke and asphaltic matters) is separated out, and whereby both vapo-rs and liquid products are removed from this chamber for further treatments, such as separation and condensation.

In the rst zone of those processes where the "l5 hydrocarbon oil is heated under high pressure to a cracking temperature it is well kno-wn topreve'nt the deposition or separating out of coke, with more or less success, by using a bath of molten metal confined in a still or reto-rt, or by using a `r`` high speed of the streaming oil if a coil is used,

30` liquid products and coke are separated out.

or by admixing steam or gas tothe oil, or by using an excessively high pressure, or by coating the tubes with metals other than iron, such as chromium or aluminium, or by using 'any other methods which have beenv proposed. i

At the moment of the above mentioned pressure reduction, a sudden vaporization of a part of the heated oil occurs, consuming a large part of the heat contained in the oil, and the unvaporized In consequence of this loss of heat and drop in temperature it has been found that the residue contains not only coke and asphaltic matters, but also a considerable amount of heavy oils such as gas oil fractions and solid hydrocarbons of Athe paraflin and naphthene series, which it would be more useful to crack again or to separate from the residue for further treatment, such as making lubricating oils.

To avoid the disadvantageous consequences caused by the drop in temperature at the moment of the pressure reduction and the resulting expansion, it would be necessary to add heat at this moment in order to replace or compensate immediately the heat which is being lost during this expansion. Of course the addition of heat during expansion is known, and it has also been found that a greater yield of gasoline-like fractions is obtained in this way, but this addition of heat increases the formation of coke to such an extent that this method is not practicable. To avoid or to decrease the formation of coke at the moment of expansion it has been proposed to cool the expanding vapors and liquid products at the moment of the pressure reduction by adding a cooling medium, but this method is not very economical.

and in intimate contact With it.

In this manner the pressure reduction and consequent expansion and vaporization take place within the mass of the molten metal so that the coke separates out in a iinely divided condition Within the mixture formed by the expanding vapors, liquid products and the molten metal. A well known air-lifting device may be used to bring the molten metal into a circulating condition and to mix it rapidly with the oil and vapors.

In this manner it is not only possible to avoid the above mentioned drawbacks, inherent to the drop of temperature, but it has also been found that the yield of gasoline-like fractions has greatly inceased to such an extent that the amount of it is nearly double that which is genorally obtained by the cracking process.

`It may be that this greatly increased yield of gasoline is due to an additional cracking which has taken place in consequence of the change of equilibrium caused by the drop of pressure.

But if it is considered that this extraordinary effect is also produced, When the pressure in this zone of lower pressure is relatively low in respect to the atmospheric pressure, this explanation can not be entirely satisfactory, in consideration of the following arguments: The increase of the yield of the gasoline-like fractions is typical for the iniiuence which the high pressure is exerting on the thermal disassociation of hydrocarbons, whichhas been confirmed by practice, it is further evident that by vaporization the hydrocarbons escape the action of heat, while for Vaporphase cracking higher temperatures are required.

'I'he reaction may be this: The molecules disassociate while the oil is heated under high pressure to a cracking temperature and this high pressure having substantial and decisive iniiuence on the manner in which this disassociation occurs and this primary disassociation being reversible (Gurwitsch), presents therefore an unstable equilibrium. The molecules so formed, being highly unsaturated are unstable.

It is further evident that the unsaturated compounds are more refractory than the saturated ones, because if a saturated compound is subjected to sufficient heat it decomposes into an unsaturated one. As a secondary reaction these highly unsaturated compounds are converted into compounds of a more saturated, more stable and more refractory character by a change in their affinity or by the formation of more complex compounds due to addition, condensation and polymerization-whereby the high pressure is favorable to the formation of heavier or larger molecules, while pressure reduction is unfavorable to this formation of heavier molecules, provided the temperature of disassociation is maintained.

It actually has been found that the heavier fractions resulting from the cracking operation are more refractory than those resultingr from the normal distillation of crude oil, so that the former can not be identical with the latter. By reducing the pressure and maintaining the temperature of disassociation these heavier fractions decrease, while the gasoline-like fractions increase.

Instead of a coil, any other apparatus may be used, such as an autoclave containing a molten metal or a pipestill, which means that the apparatus in which the oil is heated under high pressure to a cracking temperature or is cracked may be of any well known kind, and that the molten metal bath mentioned in this invention is disposed after this apparatus and in such a manner that the pressure maintained in, or above, the molten metal is substantially lower than the pressure in the coil, so that there is maintained a difference or" pressure on the oil in the coil and the molten metal. Said diierence of pressure is. of course, substantially greater than the weight of the column of the molten metal. In order to maintain this high pressure in the coil and the difference of pressure between the coil and the molten metal it has been found that an automatic pressure release valve (loaded valve) gives the best results.

The following example and the accompanying drawing may illustrate how this process may be performed and carried out in practice. Any given oil is heated to a cracking temperature under high pressure while advancing it through a coil (A.) disposed in a furnace (B). The pressure may be for example 100() pounds per square inch, but it will of course be understood that this is illustrative only and that the pressure may be higher or lower. The temperature depends on the character of the oil to be treated, and generally varies from 750-950 F. The end of the coil (A) is submerged in a molten metal bath (C) which may be arranged in an enlarged expansion lchamber` (D).. A pressure reduction valve (F) or a similar device is provided in the tube before it enters the expansion chamber (D) in order to maintain the high pressure in the coil (A) and the above mentioned difference of pressure. The oil advancing through the coil passes the reduction valve (F) where the high pressure is suddenly stepped down and the oil enters rapidly into the molten metal (C) where the reduction of pressure and the consequent expansion takes place. The resulting vapors and liquid products may be continuously removed from the reaction or expansion chamber (D) in any known manner. The pressure in this expansion chamber may be atmospheric, higher or lower than the atmospheric, but always substantially lower than the pressure in the rst heating zone. The molten metal may be circulated and brought into intimate contact with the oil and vapors by means of any well known device, such as an air-lifting device (E) or a stirrer. The process may be carried out in the presence of steam or gases. Untreated oil may also be introduced by means of the tube (G) and conducted onto the surface of the molten metal in order to hold the carbon impurities in suspension.

I-Iaving now particularly described the nature of my invention and in what manner the same is to be performed, I claim:

1. A process of cracking hydrocarbons consisting in raising the oil to a cracking temperature under high pressure while advancing in a stream through a heating zone, then suddenly stepping down this high pressure to a substantial lower pressure and in immediately introducing the oil into a molten metal-bath in such a manner that this release of pressure and the consequent expansion and vaporization takes place within the mass of the molten metal and in intimate contact with it.-

2. A process oi? cracking hydrocarbons consisting in raising the oil to cracking temperature under high pressure while advancing through a heating zone, in suddenly stepping down this high pressure to a substantial lower pressure and simultaneously introducing the oil into a molten metal-bath in such a manner that this release of pressurel and the consequent expansion takes place within the mass of the molten metal andin intimate contact with it, and in utilizing the energy made available by the release of pressure of the oil undergoing conversion to produce a circulating condition in the molten metal.

3. A process of cracking hydrocarbons according to claim 1, further characterized in that a stream of substantially cool oil is introduced onto the surface of the molten metal, contacting with the cracked products passing through said molten metal bath.

NIKOLAUS MAYER.

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