US2412868A - Catalytic cracking of hydrocarbon oils - Google Patents

Description

"Patented Dec. 17,

ca'ranrric CBACKgIWEISOF maocannon Cecil Brown, Baton Rouge, La., assignor to Standard Oil Development Company, a corporation oi Delaware no Drawing. Application April 25, 1945,

Serial No. 590,315

4 Claims. .(Cl. 196-52) This invention relates to the cracking of hydrocarbon oils in the presence of a catalyst and is directed more particularly to a method of maintaining the activity of the catalyst.

It is known that the activity of catalysts com- .monly employed for the cracking of hydrocarbon oils is impaired by continuous contact with steam under temperature and pressure conditions normally prevailing in a catalytic cracking process.

- stripping of the volatilizable hydrocarbons from the catalyst is important not only because it prevents excessive losses of the charge stock, but it also reduces the amount of heat which would otherwise be liberated durin'gregeneration.

The conventional method of removing en- :trained or adsorbed volatilizable material from the catalyst following the cracking treatment is to subject the catalyst to a stripping or purging treatment in which the spent catalyst from the cracking operation is subjected to contact with steam which tends to desorb or replace the volatilizable material from the catalyst.

It is also a common practice to inject relatively large volumes of steam into the oil charging stock to facilitate or assist in the vaporization of the oil. Also, even with highly effective stripping, a substantial amount of hydrogen from the cracking operation finds its way into the regenerating 'zone and is burned in the regenerator with the resultant formation of water vapors.

As previously mentioned, however, it has been found that the presence of water vapor or steam in substantial amounts, and particularly in the regenerating zone, materially impairs the activity I of the catalyst and materially increases its rate of deactivation. In view of this, it has been proposed to replace the steam wherever possible with other inert gas, such as spent combustion gas. However, the use of other inert gases requires additional equipment, such as an'inert gas burner or additional compressors and purifying equipment.

It has been found that the adverse effect of steam on the activity of the catalyst can be re- 2 duced by the injection of ammonia gas in any of the high temperature portions of the cracking equipment in which substantial amounts of water vapor may be present, such as in the stripping zone or in the cracking or regenerating zone.

The inhibiting effect of the ammonia on the steam in reducing the catalyst deactivation will be illustrated by the results obtained in the followmg experiment: a

A synthetic silica-alumina gel of a composition normally used for catalytic cracking and containing about 12% alumina formed by impregnating a purified silica hydrogel with an aluminum sulfate solution followed by decomposition of the sulfate with ammonium hydroxide, when tested under standard test conditions normally results in a conversion of about of the charging stock into gasoline. The standard test conditions in- 'volve passing anEast Texas gas'oil of about 32.8 A. P. I. gravity through a fixed-bed of catalyst maintained at 850 F. for an operating period-of two hours, at a space velocity of 0.6 volume of liquid oil per volume of catalyst per hour. A cat- "alyst prepared as above described was given a preliminary treatment in which the catalyst was heat-treated at 1050 F. and under a pressure of 72 lbs. per square inch in an atmosphere'iormed by vaporizing a concentrated ammonium hydroxide solution containing about 29 mol per cent of ammonia (NHs). Following this treatment, the catalyst when treated under the standard test conditions above described gave a gasoline conversion of about 32.5%.

The same catalyst when pretreated in a steam atmosphere at 1050 F. and under similar steam partial pressure for the same period resulted in a conversion of about 28%.

From these data it will be seen that the presence of the ammonia in the steam atmosphere resulted in a material improvement in the activity of the catalyst.

The amount of ammonia vapor introduced into i the cracking equipment containing the water va- Having described the preferred embodiments of the invention, it will be understood that it embraces such other variations and modifications as come within the spirit and scope thereof.

'Iclaim:

i. In a. process for catalytic cracking of hydrocarbon oils in the presence of a steam-sensitive catalyst wherein the catalyst is alternately subjected to cracking and regeneration and wherein the catalyst is exposed to'the action of steam during the operation, the method of maintaining the activity of said catalyst which comprises introducing ammonia into the zone in which the catalyst is initially exposed to th steam. I

2. In a process for catalytic cracking of hydrocarbon oils wherein a steam-sensitive catalyst is alternately subjected to cracking and regeneration and wherein the spent catalyst following the cracking treatment is purged with steam to remove volatilizable hydrocarbons contained thereon prior to regenerating said catalyst, the improvement which comprises introducing ammonia into the purging zone to inhibit-the adverse effect of the steam on said catalyst.

3. In a process for catalytic cracking of hydrocarbon oils in the presence of a steam-sensitive catalyst which is alternately subjected to cracking and regeneration and wherein the catalyst following the cracking treatment is exposed to the action of steam in a steaming zone to remove volatilizable constituents therefrom, the improvement which comprises introducing ammonia into said steaming zone in an amount at least 5 mol per cent of the water vapor present therein.

4. In the process defined by claim 3 wherein the amount of ammonia is between 5 and 50 mol per cent of the steam present, v

CECIL L'. BROWN.