US2281257A - Treatment of cracking stocks - Google Patents

Description

April 1 w. L. BENEDICT arm. 2,281,257

TREATMENT OF CRACKING STOCKS Filed March 27, 1939 SOLVENT EXTRACTION SOLVENT RECOVERY EXTRACT REFINING CATALYTIC CRACKING IN VENTORS WAYNE L. BENEDICT JACOB ELS ON AHLBERG ATTORNEY v Patented Apr. 28, 1942 TREATMENT OF CRACKING STOCKS Wayne L. Benedict and Jacob Elston Ahlberg, Chicago, 111., assignors to Universal Oil Products Company, Chica Delaware go, 11]., a corporation of Application lifarch 27, 1939, Serial No. 264,480

6 Claims.

The present invention concerns an improved method for the catalytic conversion of hydrocarbon distillates, and more particularly-with the method of treating such distillates prior to their conversion by catalytic methods. More specifically, the invention deals with the step of solvent extraction of such distillates with immiscible solvents which have a, selective action in removing undesirable components of ,the charging stock and further treatment of the extracted oil prior to catalytic cracking. While the oils processed are generally from petroleum sources, the scope of this invention is by no means limited to such oils but may include hydrocarbons obtained by the distillation of coal tar, shale oil, etc.

The reactions undergone by hydrocarbons when cracking by non-catalytic methods have been studied and are well understood. When using catalysts to assist the. thermal conversion of distillates, the reactions are not so well-known and as a consequence a discussion involving such reactions is best kept on a factual basis.

The use of treating materials prior to or following non-catalytic cracking has been discussed in the literature, and the primary purpose of such treatment is, (a) the production of an improved product, such as, for example, a gasoline having a reduced sulfur content or improved color; (b) forthe elimination or reduction of corrosion in cracking equipment such as may be caused by the reaction at high temperatures of hydrogen sulfide with the metallieparts of the cracking plant, or corrosion of condensing equipment and ing operating conditions which are unusually severe so thatthe benefits of catalytic cracking are markedly reduced. Such distillates can be improved as charging stocks for the catalytic cracking process by extraction of undesirable substances therefrom by means'of well-known solvents. Among the solvents which may be used for this purpose are sulfur dioxide, furfural,

, nitrobenzene, phenol, cresol, m6 dichlorethylether,

lines by hydrogen chloride formed because of the presence in the crude oil charging stock, of hydrolyzable salts. The pre-treatment of oils does not, however, have the effect of increasing the yields of gasoline obtainable from non-catalytic cracking processes.

In one specific embodiment our invention comprises treating hydrocarbon oils with a selective :solvent to remove therefrom undesirable constituents, recovering the extracted oil, treating said extracted oil with an acidic substance, blending the treated extract with the railinate from the aforementioned extraction step, contacting the blended oil in vaporous form with a. cracking catalyst in one or more conversion stages at catalytic cracking conditions, and recovering the, gasoline and gaseous products formed.

Certain stocks are susceptible to catalytic cracking under moderate conditions, while distillates' from other sources are found to be more refractory so that they cannot be cracked to produce adequate yields of gasoline without employvarious glycol ethers and many others which have selective solvent effects and which are capable of being recovered by one of several well known methods. Such methods include precipitation of the solvent by the addition of another material such as water, which renders the solvent and the oil mutually immiscible and by distillation: where the oil and the solvent boil in different ranges. It should be understood that the solvents mentioned are not exactly equivalent and that in certain instances one solvent is more suitable, while in other instances another solvent gives greater benefit.

Of the many solvents which may be employed in our process, sulfur dioxide is one of those preferred. When preparing oils for catalytic cracking according to our process, it is not, as a rule,- the object to produce a large amount of extracted material but rather to remove relativel small percentages (preferably less than 10%) of impurities'which are particularly deleterious to the oil. This can be controlled to a certain extent by the amount of solvent used or by controlling the temperature'of extraction. In general, increases in temperature of extraction decreases the selectivity of a solvent. The exact conditions and quantities of solvents employed must necessarily be determined for each stock.

Normally, however, nomore than equal volumes these methods since it produces the benefits of of solvent and oil are employed, and, as a rule, the amount of solvent used is less than one volume per volume of oil.

Necessarily, because of the limitations in selectivity of the solvents employed,'certain portions of the hydrocarbon oil which are suitable for catalytic cracking are removedalong with the impurities. It has been found possible, by treating the entire stock by chemical methods, to remove these impurities. It has also been found possible to improve the original charging stock by extracting minor amounts of it with selective solvents.

The present invention is an improvement of both processes and permits recovery of the major tion in chemical consumption. The improvement lies'in the treatment of the extracted oil with a minor quantity of an acidic substance such as a mineral acid, acid salt, or a heavy metal halide selected from the group consisting of halides of aluminum, iron, copper, tin or zinc or their equivalents. When using the metal halides or acid sulfates elevated temperatures may be used. These temperatures should be maintained below the point at which cracking occurs.

By this method we are enabled to improve the charging stocks and at the same time reduce the treating cost materially. This particular mode of operation does not apply where hydrocarbon solvents for precipitation of asphaltenes are employed.

An advantage of the process is that we are enabled to improve the yields of gasoline and polymerizable gaseous olefins which can be obtained by catalytic cracking. Furthermore, the amounts of carbon deposition on the cracking catalyst are decreased so that the time of proc essing as related to regeneration is materially increased. Since the per pass conversion is also increased, the effect is to increase plant capacity for a given size of equipment. The improved properties of the motor fuel resultingfrom our process is 'another advantage of the invention.

The motor fuel products of catalytic cracking are, in general, of a marketable quality and require only sweetening and the addition of gum inhibitors to prevent the formation of objectionable gums, color, or other reaction products during the storage period of the gasoline. The products of thermal cracking, on the other hand, often require extensive treatment prior to marketing. In the case of the catalytic cracking process, the pretreating step is primarily concerned with the production of a suitable charging stock which may be catalytically converted in an economical manner. The reasons for the improvements observed are not known. It may be that there are present in the untreated distillate compounds that tend to inhibit the carbon-carbon cleavage which characterizes catalytic as opposed to non-catalytic cracking. Whatever the explanation, the beneficial effect has been observed in a great many instances, and we do not limit ourselves to any explanation given herein.

Any cracking catalyst which has been found suitable for the conversion of high-boiling hydrocarbons into the gasoline distillate range may be satisfactorily used. This includes catalysts comprising activated alumina in conjunction with various metal oxides such as chromia, as well as the various clays and other natural earths which have been treated with acids or other chemical methods; and synthetic catalysts prepared from silica and various refractory oxides.

Although the present process may have more or less applicability when using cracking catalysts which may be produced by the chemical treatment of naturally occurring clays, the preferred catalyst comprises specially prepared synthetic masses, for example, silica-alumina, silicazirconia, silica-alumina-zirconia, and silicaalumina-thoria havinga very high degree of activity. These masses are prepared by combining the constituents in various ways, such as mixing, coprecipitation, and the like, under conditions whereby alkali metal ions are excluded. In these catalysts the ratio of the components may vary within wide limits and the masses may be considered to comprise intimate or possible molecular admixtures, all of the components indicating more or less low activity individually. but in the aggregate displaying high activity.

The activity also is not an additive function of the individual component, it being relatively constant for a wide range of proportions whether in molecular or fractions of molecular proportions. It appears that no one component can be determined as the one component for which the remaining components may be considered as the promoter according to conventional terminology. In the present invention, these catalysts are used in the form of sized particles or other formed shapes such as pellets produced by compression or extrusion methods. The pressed composites, after drying and forming into dennite shapes, are calcined at temperatures above 800 F. prior to contacting with the hydrocarbons.

The term acidic refining agent as used herein is zunderstood to include mineral acids; acid salts such as acid sulfates; or heavy metal halides such as those of aluminum, iron, tin, and zinc.

The temperatures used in the catalytic cracking step are included in the range of approximately 800-1200 F. The pressures are only such as are sufiicient to cause the oil vapors to pass through the various steps of the process.

The following example is given to illustrate the usefulness of our process and is not intended to limit it'to the exact conditions given therein.

A California gas oil of 323 A. P. I. gravity was extracted with 25% by volume of liquid sulfur dioxide producing thereby approximately"5% by volume of extracted oil. The solvent was removed from both the raflinate and the extract By distillation.. The extract was treated with 5 pounds of 66 B. sulfuric acid per barrel of extract. The treated oil was recovered and blended with the rafllnate from the solvent extraction step. The yield of 400 F. end point 81 octane number gasoline, including that obtainable by the polymerization of Ca and C4 oleflns from the process gases, was 31.1% per pass based on the original crude oil. In addition to this, the amount of carbon deposition on the catalyst was reduced by approximately 50% so that the plant capacity was increased proportionally. The yield of gasoline from the untreated oil was 15.1%.

The accompanying drawing illustrates the process diagrammatically but should not be construed to limit the invention unduly.

Referring to-the drawing, the oil to be treated is introduced through line I and the solvent used for extraction is introduced through line 2. The extraction is carried out in solvent extraction step 3 by any suitable means. The ramnate is passed through line 4 to catalytic cracking step II. The extract phase is removed through line 5 to solvent recovery step 6 from which recovered solvent may be returned through line I to line 2 and thus recycled to the solvent extraction step. The extracted oil passes from solvent recovery step 6 through line I to the extract refining step 8, wherein it may be treated as previously described. The acidic refining agent is introduced through line 9. Spent refining agent, containing the imsequent refining steps through line H. A portion of the oil boiling above the gasoline range may may be recycled to the catalytic cracking step through line It. y

We claim as our invention:

1. A hydrocarbon oil conversion process which comprises extracting the charging oil with a selectivesolvent to remove objectionable components of the oil, separating the resultant extract and raffinate, treating the extract with an acidic refining agent, combining the thus treated extract with said railinate, and subjecting the resultant mixture to catalytic cracking.

2. A hydrocarbon oil conversion process which comprises extracting the charging oil with a selective solvent to remove objectionable components of the oil, separating the resultant extract and raffinate, treating the extract witha mineral acid, combining the thus treated extract with said raflinate, and subjecting the resultant mixture to catalytic cracking.

3. A hydrocarbon oil conversion process which comprises extracting the charging oil with a selective solvent to remove objectionable components of the oil, separating the resultant extract and raflinate, treating the extract with sulfuric acid, combining the thus treated extract with said raflinate, and subjecting the resultant mixture to catalytic cracking.

4. A hydrocarbon oil conversion process which comprises extracting the charging oil with a selective solvent to remove objectionable components of the oil, separating the resultant extract and raflinate, treating the extract with phosphoric acid, combining the thus treated extract with said rafiinate, and subjecting the resultant mixture to catalytic cracking.

5. A hydrocarbon oil conversion process which comprises extracting the charging oil with a selective solvent to remove objectionable components of the oil, separating the resultant extract and raftinate, treating the extract with an acidic refining agent comprising a metallic halide, combining the thus treated extract with said raflinate, and subjecting the resultant mixture to catalytic cracking.

6. A hydrocarbon oil conversion process which comprises extracting the charging oil with a selective solvent to remove objectionable components WAYNE L. BENEDICT. JACOB ELSTON AHL'BERG.

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