US2279550A - Treatment of cracking stocks - Google Patents

Description

Pa tented Apr. 14, 1942 TREATMENT 2,219,550 or caacxmc s'rocxs Wayne L. Benedict and Jacob Elston Ahlberg, I

Chicago, Ill.,

assignors to Universal Oil Products Company, Chicago, 111., a corporation of Delaware Application March 31, 1939, Serial No. 265,216 8 Claims. (c1. 196-43) 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 solvent extraction .of such distillates by means of immiscible solvents which have a selective action of removing undesirable components of the charging stock and further treatment of the extracted material prior to conversion of such stocks to motor fuel by means of 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 in- .clude 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 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 practiced before, 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) for the elimination or reduction of corrosion in cracking equipment such as may be caused by the reaction at high temperatures of hydrogen sulfide with the metallic parts of the cracking plant; or corrosion of condensing equipment and lines by hydrogen chloride formed because of the presence in the crude oil charging stock of hydrolyzable salts; and (c) to reduce coke deposition. The pretreatment of oils does not, however, have the efiect of materially increasing the yields of gasoline obtainable from non-catalytic cracking processes.

In one specific embodiment the invention con'iprises treating hydrocarbon oils with selective solvents to remove therefrom undesirable components, recovering the extracted oil, hydrogenating said extract in contact with a hydrogenation catalyst at hydrogenating conditions, contacting said hydrogenated oil and the rafflnate from the extraction step, in vaporous form and in the same or separate stages, with a cracking catalyst at catalytic cracking conditions, separating the gas and gasoline, and returning the unconverted or insufliciently converted oil to the solvent extraction step.

as charging stocks for 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 employing operating conditions which are excessively severe and the benefits of catalytic cracking are materially reduced. Such oils can be improved the catalytic cracking process by extraction therefrom by well known solvents of the materials which bring about the undesirable effects observed. Among the solvents which may be used for this purpose are liquid sulfur dioxide, furfural, nitrobenzene, phenol, cresol, ppdichlorethylether, various glycol ethers and many others which have selective solvent effects and which are capable of being recovered from the oil by one of several well known methods. Such methods include precipitation of the solvent by the addition of another material which renders it immiscible with the oil, and by distillation where the oil and the solvent boil in different ranges.

Of the many solvents useful in our process, liquid sulfur dioxide is preferred. The method of carrying out the extraction step is well known and need not be described in detail. The selectivity of the solvent can be varied by the amount of solvent and temperature of the extraction.

It has been found that hydrogenation of the oil prior to catalytic cracking results in considerable improvement in its properties as a charging stock. It is known that the unconverted bottoms from catalytic cracking are not as readily susceptible to conversion as the original crude fraction. These bottoms can be improved so as to reduce the amount of oil recycled during the catalytic cracking step because of increased conversion per pass of the hydrogenated bottoms over the yields obtainable under the same conditions with unhydrogenated bottoms. There is,

however, in the uncoverted oil a considerable amount of material which is readily converted to gasoline without further treatment.

The present invention deals with a method of separating by a solvent that portion of the unconverted oil remaining after contact with a cracking catalyst, which does not respond readily to catalytic cracking and treating this extract with hydrogen in the presence of a, hydrogenation catalyst and at hydrogenating' conditions, thereby converting it to a suitable stock for catalytic cracking. The hydrogen is preferably obtained from the gases produced in the cracking step. The catalysts may include any hydrogenation catalyst, but the preferred catalysts are those which are not readily poisoned by sulfur compounids, such as molybdenum oxide and sulfide. In the absence of catalyst poisons the reduced metal catalysts such as nickel, copper, iron, cobalt, etc., may be used.

In many cases the hydrogenated oil is comhas been found advantageous in many cases to catalytically crack the rafiinate in'one conversion stage at conditions most suitable for its conversion and to crack the hydrogenated extract in a separate conversion stage. The raifinate will, of course, contain a portion of the oil which has passed through the catalytic cracking step at least once, since both the incoming oil and the unconverted oil are extracted in the same step. The two stocks are somewhat different in character, of course, and may require suitable adjustments of cracking conditions in order to obtain the optimum results.

By extracting the combined feed and hydrogenating the extracted oil only, it is possible to reduce the amount of oil to be hydrogenated so that smaller size hydrogenation equipment may the course action. Whereas, in certain instances when cracking untreated oils the catalytic efiect is apparently suppressed, treating the same distillate permits the catalytic benefit to be realized.

The motor fuel products of catalytic cracking are, in general, of a marketable quality, requiring only sweetening and the of thermal cracking, on the other hand, often require drastic treatment prior to marketing.

In the the p etreating step terizes catalytic as opposed to non-catalytic cracking. Whatever the explanation, the beneexplanation given herein.

Any cracking catalyst which has been found suitable for the conversion of high-boiling hydrocarbons into the gasoline distillate range may be case of the catalytic cracking process,'

junction satisfactorily used in our process. This includes catalysts comprising activated alumina in conwith various metal oxides, such as refractory'oxide 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, silica-zirconia, silica-alumina-zirconia, and silica-alumina-thoria having a 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 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.

passage of the oil vapors through the process.

The accompanying drawing illustrates the process diagrammatically. In the drawing, charging oil from line I and solvent from line 2 are introduced to solvent extraction zone 3 from returned to line 2 insufficiently con-,

may be recycled through line 22 to, the solvent extraction zone 3. Y

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 equal parts by volume of liquid sulfur dioxide. The sulfur dioxide was removed from the extract and rafiinate by distillation and recovered for further use. The extract was passed to a hydrogenation step, wherein it was hydrogenatedin the presence of a molybdenum sulfide catalyst and the hydrogenated oil was passed together with the rafiinate into contact with a silica-alu 'na cracking catalyst at a temperature of 932 F. and a liquid space velocity of four. The gasoline and gas were separated, the unconverted bottoms were returned to the solvent extraction step wherein, together with the incoming crude fraction, they were extracted as previously described and the extract passed into the hydrogenation step and mixture catalytically cracked. In this manner a total yield of 86% of 81 octane number gasoline was obtained as compared with 78% of gasoline when the combined solvent extraction the hydrogenated and hydrogenation steps were omitted. These yields included the gasoline obtained by polymerizing the gaseous The hydrogen for the hydrogenation step was obtained from the gases produced in the catalytic cracking step. The low-boiling gaseous hydrocarbons, methane, ethane, and ethylene were also present since no attempt was made to separate the hydrogen in pure form. There was a reduction in carbon deposition on the cracking catalyst amounting to approximately 50%, so that the ratio of the time for regeneration compared with the time of processing was reduced considerably. This, together with the fact that the per pass conversion was improved, resulted in a material increase in the capacity of the plant.

We claim as our invention:

1. A process which comprises extracting hydrocarbon oil in the presence of a selective solvent, recovering the extracted oil, subjecting said extracted oil to the action of hydrogen in the presence of a hydrogenation catalyst under conditions adequate to effectsubstantial hydrogenation, contacting the vapor or the hydrogenated extract and the rafiinate from the extraction step with a cracking catalyst under conditions adequate to effect substantial catalytic cracking thereof, separating the gas and gasoline, and

returning the unconverted oil to the solvent ex-' traction step.

olefins produced in the process.'

' witha cracking catalyst 2. The process of claim 1 wherein the solvent comprises essentially liquid sulfur dioxide.

3. A process which comprises extracting hy-.

drocarbon oil with a selective solvent, recoverin the extracted oil, subjecting said extracted oil to the action of hydrogen in the presence of'a hydrogenation catalyst under conditions adequate to eflect substantial hydrogenation, contacting the hydrogenated extract and the rafllnate from the extraction step in vaporous form with a composite consisting essentially of a major part of line, and returning an especially prepared silica and a minor part bon oil with a selective solvent, recovering the extracted oil, subjecting said extract to the action of hydrogen in the presence of a hydrogenation catalyst under conditions adequate to effect substantial hydrogenation, contacting the raflinate from the extraction step in vaporous form with a cracking catalyst under conditions adequate to effect catalytic cracking, separately contacting the hydrogenated extract in vaporous form with a separate body of cracking catalyst under conditions adequate to effect substantial catalytic cracking thereof, recovering the gas and gasoline, and returning the unconverted oil from both of said cracking steps to the solvent extraction step.

6. A process comprising extracting hydrocarbon oil with a selective solvent, recovering the extracted oil, subjecting said extract to the action of hydrogen in the presence of a hydrogenation catalyst under conditions adequate to effect substantial hydrogenation, contacting the ramnate from the extraction step in vaporous form comprising essentially a composite consisting of a major part of specially prepared silica and a minor part of a component selected from the group consisting of alumina and zirconia and substantially free of alkali metal compounds, under conditions adequate to efiect substantial catalytic cracking, separately contacting the hydrogenated extract in vaporous form with a separate body of cracking catalyst under'conditions adequate to effect substantial catalytic cracking, recovering the gas and gasothe unconverted oil from both of said cracking steps to the solvent. extraction step.

extracting said products with a selective solvent.

hydrogenating the resultant extract, and returning the hydrogenated extract to the catalytic cracking operation.

8. A hydrocarbon oil conversionsprocess which comprises extracting the charging oil with a selective solvent, separating the resultant extract and raflinate, hydrogenating the extract, catalytically cracking the hydrogenated extract and said ramnate, separating the cracked gasoline and gas from insufliciently converted products. and recycling at least a portion of said products to the solvent extraction step.

WAYNE L. "BENEDICT. JACOB ELSTON AHLBERG.

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