US2389176A - Production of aviation gasoline - Google Patents

Description

NOV' 20, 1945- J. A. ANDERSON, JR

PRODUCTION QF AVIATION GASOLINE Filed July 2l, 1944 glow nl 4 hllrtzow (7W Im/NTOR.

Patented Nov. 20, 1945 UNITED STATES PATENT OFFICE PRODUCTION OF AVIATION GASOLINE James A. Anderson, Jr., Goose Creek, Tex., as-

sig'nor to Standard Oil Development Company. a corporation of Delaware Application July 21, 1944, Serial No. 545,976

4 Claims. (Cl. 196-52) The present invention relates to a process for producing aviation fuel from catalytically cracked naphtha. More particularly it is concerned with a process for recovering iso-parafiins from catalytically cracked naphtha substantially free from aromatcs and olens. In its more specific aspects the present invention contemplates the solvent extraction of a selected catalytically cracked naphtha fraction and the recovery of a fraction from the solvent raiinate comprising substantially the iso-parafns.

During the last few years catalytic cracking has reached the stage of development where it has become an important tool of the petroleum reiiner in producing aviation gasoline. While the catalytically cracked naphtha is suitable for the production of aviation gasoline, its use is open to some objection in that drastic chemical treatment is necessary before the fuel is suitable for use in the aviation motor. For example, it is often necessary to treat the catalytically cracked naphtha with a large amount of sulfuric acid to destroy the olefins or to hydrogenate the whole I fraction to make it suitable for aviation fuel. When acid treatment is contemplated, it is often necessary to supplement the acid treatment with inhibition to provide stability for the fraction.

In accordance with the present invention it is unnecessary to resort to the aforementioned processes in producing aviation fuel components from catalytlcally cracked naphtha. In my invention, I extract a fraction boiling up to about 250 F. with a solvent which will separate paraiinic constituents from the alicyclic, olenic and aromatic constituents to obtain a fraction comprising essentially the iso-parafns. In the solvent extraction the alicyclic, oleflnic'and aromatic hydrocarbons are largely concentrated in the extract and may then be recovered therefrom by a treating operation which may involve a second extraction with a solvent, distillation and hydrogenation, as may be desired. My invention allows the obtaining, from a catalytically cracked fraction, of desirable aviation fuel components without treatment of the total fraction.

little aromatics,`it is possible to recover the isoparalns by a very inexpensive process as compared to the more expensive processes asl practiced in the art.

The present invention will be better understood by reference to the accompanying single gure which is a iiow plan illustrating a preferred embodiment.

Referring now to the drawing, numeral I I designates a feed line through which a gas oil boiling in the range of about 450 to 800 F. is introduced into catalytic cracking zone I2. Catalytic cracking zone I2 may be any type of catalytic cracking operation but for purposes of illustration, it will be assumed that it embodies a cracking operation of the so-called fluid catalyst type. In catalytic cracking zone I2, the gas oil is subjected to cracking conditions employing temperatures between 800 and 1100" F. and pressires up to about 50 pounds per square inch. Preferably, pressures of the order gf 15 pounds per square inch are employed. A silica-alumina catalyst either of natural or synthetic origin may be employed satisfactorily.

'I'he catalytic cracking zone I2 may be operated on either a naphthenic type of gas oil or a paralnic type of gas oil. It has been observed that when employing either naphthenic or parafnic gas oils at low conversion and high throughputs formation of iso-paralns is favored; irrespective, however, of the operation of the catalytic cracking zone I2, it is possible to practice my invention and obtain a satisfactorily pure iso- In the catalytic cracking of a gas oil for ex' is possible to solvent extract such a fraction and obtain a railinate fraction comprising essentially the iso-paralilns. By virtue of my discovery that this fraction contains substantially no n-paralns paraiin fraction. The conditions obtaining in catalytic cracking zone I2 are known in the art and do not form part of this invention but are given in some detail to allow proper understandtion zone I4. It is, of course, well understood that the distillation zone I4 may comprise a number of distillation towers each provided with heating means I5, but for ease of description in the present invention, reference will be made to a single tower. Distillation zone I4 is provided with a line I6 for discharge of heavier constituents, line I'I for removal of components boiling above 250 F., line I8 for recovery of a fraction bollingbetween about 105 and 250 F., and line I9 for dis-` charge of products boiling below about 105 F. which may be further processed for recovery of valuable vaporous constituents. The desired and by virtue of the fact that it contains very cracking fraction. boiling at temperatures in the 2E range between about 105 and 250 F. is discharged from fractionatlng zone I4 by line I8 and is introduced into an extraction zone 22. Extraction zone 22 may be either an extractive distillation zone, employing countercurrent contact between a vaporous hydrocarbon feed and a liquid selective solvent, or a conventional liquid phase solvent extraction zone, employing countercurrent contact between a liquid hydrocarbon feed and a liquid selective solvent. It will be understood, of course. by those skilled in the solvent extraction art that. when extractlve distillation is employed'in zone 22, it may be desirable to process a fraction having a narrower boiling range than is described above. For purposes of illustration, however, it will be assumed that extraction zone 22 is of the conventional liquid-liquid phase type, the extraction is carried out on a fraction having the boiling range speciiled above, and the solvent is introduced into zone 22 through lines 20 and 2|.

The type of solvent employed in extraction zone 22 is selected from the class of compounds illustrated by phenol, furfural, diethylene glycol, triethylene glycol and the polyethylene glycols and mixtures thereof. For purposes of illustration only it may be assumed that a mixture of polyethylene glycols and ethylene glycol is employed in extraction zone 22 as the selective solvent. For best results in the process to obtain a rafiinate comprising essentially iso-paraillns a solvent to hydrocarbon ratio in the range between :1 and 15:1 is desirable. The temperature obtaining in solvent extraction zone 22 may be varied considerably, but a temperature of the order of about 150 F. at atmospheric pressure is usually desirable. To obtain the iso-paraftln substantially free from the alicyclic, olefinic and aromatic hydrocarbons, solvent extraction zone 22 should include 30 to 50 stages in which the conditions are adJusted to obtain ramnate and extract phases which are withdrawn therefrom by lines 23 and 24, respectively. 'I'he raiilnate phase, containing a small amount of solvent is discharged by way of line 23 into the solvent stripper 25 which is provided with a heating means 26. The solvent is taken oi! from solvent stripper 25 by line 2| and the iso-paraiiins are discharged from stripper 25 by line `21 and are then suitable for use as an aviation fuel constituent or may be employed as a feed stock for an alkylation process as desired. It is to be understood by the skilled worker that, depending on the boiling point of the solvent employed, in some instances instead of the iso-parain being taken overhead and the solvent withdrawn as bottoms from tower 25 in the manner illustrated, the solvent may be distilled overhead and the iso-paraffins withdrawn as bottoms by way of line 2|.

The extract phase is introduced by line 24 into a second solvent stripper 28 which is similar to stripper 25, and is equipped with a heating means 29. Solvent is recovered from stripper 28 by line 20 and returned to extraction zone 22 while the hydrocarbon constituents of the extract are discharged through line 30 and are introduced thereby into a second extraction zone 3|. In some instances it may bev desirable to discharge the extract hydrocarbons from the system without processing them through extraction zone 3|. In this particular instance, valve 32 in branch line. 33 would be opened and valve 34 in line 30 would be closed oil.

For purposes of illustration, however, it is assumed that it is desired to process the extracted hydrocarbons through the extraction zone 3|. A solvent similar to that employed in extraction zone 22 is introduced through line 35 and conditions are adjusted to obtain railinate and extract phases. In extraction zone 3|, it will be desirable to employ a solvent to hydrocarbon ratio in the range between about 4:1 and 12:1, temperatures of the order of about 150 F., with atmospheric pressures, and utilizing between about 15 to 25 stages. The solvent may be selected from the type of solvents employed in extraction zone 22 with the understanding that adjustments may be made for the composition of the hydrocarbons in the extract discharged to zone 3|.

The rallinate phase is withdrawn from extraction mne 3| through line 36 and introduced thereby into a third solvent stripper 31 in which temperature and pressure conditions are adjusted by heating means 38. Solvent is withdrawn'from stripper 31 by line 39 for reuse in the process while a hydrocarbon component comprising essentially oleiinic and alicyclic constituents is discharged from stripper 31 by line 40. These hydrocarbons may be discharged from the system by opening valve 4| but preferably are routed to hydrogenation zone 42 through line 43 controlled by valve 44. It is understood, of course, that valve 4| is closed oi when the alicyclic and oleflnic constituents are routed to zone 42.

The conditions prevailing in hydrogenation zone 42 have been well established in the patent art and are adjusted to obtain a substantially saturated material which may be discharged from zone 42 through line 45, hydrogen for the saturation of the hydrocarbons in zone 42 being introduced through line 46. The effluent discharged from zone 42 by line 45 may be employed as an aviation fuel as is, or it may be blended with the isoparains recovered by line 21 or blended with other well known blending agents such as isopentane and tetraethyl lead.

The extract phase discharged from extraction zone 3| by line 41 is introduced thereby into a fourth solvent stripper 48 equipped with heating means 49 and provided with lines 50 and 5|. Solvent is withdrawn from stripper 48 through line 50 while aromatics are recovered by way of line 5I. It will be understood, of course, that the amount of aromatics recovered will necessarily be small by virtue of the boiling range of the fraction recovered by line |8. The only aromatics that will be included with the stream from line 5| will be benzene or toluene which are also valuable constituents of aviation fuel and may be used as such, as solvents, or as may be desired.

The blending of the streams or portions of thc streams from lines 21, 45 and 5| to produce an aviation fuel may be accomplished by line 52, branch line 53 containing valve 54, branch line 55 containing valve 56, and branch line 51 containing valve 58. When it is desired to blend isoparailins from line 21, saturated hydrocarbons from line 45 and aromatics from line 5|, valves 58, 56 and 54 may be opened to allow the isoparaiiins, saturated hydrocarbons and aromatics to flow into line 52, where they admix to produce a finished aviation grade fuel.

In a typical operation in accordance with the present invention, 'a fraction having a boiling range between and 210 F. may be obtained from the fractionatng zone |4 of a fluid catalyst cracking operation. llhis fraction comprises hydrocarbons in accordance with the following composition:

Table! Per cent Saturates 50.0 Olefins 47.0 Aromatics 3.0

Table 1r A fraction of the above composition is blended with 4 cc. of tetraethyl lead per gallon and tested for octane number and it is found that the octane'l number of the leaded fraction is 94.7 Since the equivalent octane number of the aromatics is known to be about 95 and since thatiof the corresponding olefins is known to be'considerably lower, the high octane number of the rainate fraction demonstrates that it is largei., isoparafiinic in nature. By milding treating the ramnate having the composition shown. in Table II with sulfuric acid; it is possible to obtain-a fraction comprising essentially the isoparains. "f

The extract resulting from the above described operation is freed of solvent and consists largely of oleiinic components and alicyclic hydrocarbons. These materials on hydrogenation produce excellent aviation fuel components.

From the above typical operations in accordance with my invention, it will be obvious to the skilled worker that a substantial contribution to the art of producing aviation fuels has been made. Not only has it been shown that it is unnecessary to treat the catalytically cracked naphtha of a suitable boiling range drastically and thereby destroy valuable constituents but it has also been shown that it is possible to recover substantially all components of the catalytically cracked naphtha and to make them available for use in aviation fuel. I

The invention is susceptible to considerable variation in the operation of the several steps making up my process. For example the c'onditions obtaining in extraction zones 22 and 3i may be varied widely depending on the type of solvent being employed therein and the boiling range of the fractions being extracted.

In a similar manner the treatment of the isoparaflin concentrate recovered by line 21 may also be varied. When Ithe isoparaffln concentrate forms a feed to an alkylation system it will be unnecessary to remove the residual olens contained therein. On the other hand, when the isoparailin is employed as a blending agent, it may be desirable to treat out the residual olens by subjecting the fraction to the action of a treating agent such as sulfuric acid or any other olefin reacting materials.

Percent Saturates 91.7 Oleiins 6.9 Aromatics 1.4

The present invention is not applicable to all types of craking operations. For example, the conventional thermal cracking operation produces products which are unsuitable as charge stocks for my process. It is reiterated that it is only the catalytic cracking operation which produces a suitable feed to be processed as described. And it is only the selected fractions of the catalytically cracked products that can be treated in accordance with my invention to recover the isoparaillns. Speciiically, my invention is based on the discovery that the fractions contained in catalytically cracked naphtha boiling below about 250 F. comprises essentially isoparins, oleiins, alicyclics with very little normal paramns and aromatics. This discoverey is of considerable importance since it is possible to recover substantially all the isoparamns from the hydrocarbons with which they are usually associated.-

If a fraction having a corresponding boiling range from a vthermal cracking operation is treated in accordance with the steps of the process, a much inferior product containing normal parafdns as well as isoparalns is obtained.

One greatadvantage of operating in accordance with the present invention is the chemical stability of the product obtained therefrom. For example, in the conventional treating processes to produce aviation fuel from catalytically cracked naphtha, the products frequently deteriorate in storage unless the treatment -given the products is suillciently severe to destroy valuable constituents contained therein and unless the treatment is supplemented by use of oxidation inhibiting agents. In my process all of these disadvantages are overcome. The isoparailin concentrate, comprising predominately the saturated hydrocarbons is quite stable in storage. The small amount of oleiin components may be removed by a mild chemical treatment. 0n the other hand the hydrocarbons concentrated in the extract phase may be subjected to hydrogenation treatment which forms a stable product. In the prior processes in which hydrogenation was employed to form a stable product by hydrogenation of the total fraction some 50% of the fraction was'submitted unnecessarily to the hydrogenation treatment.

The nature and objects of the present invention having been described and illustrated, what I wish to claim as new and useful and secure by Letters Patent is:

1. A method for producing an olefin-free aviation grade fuel comprising the steps of subjecting a catalytically cracked naphtha to distillation to separate a fraction boiling between 105 and 250 F., solvent extracting said fraction to form a first railinate fraction and a first extract fraction, separating said first rainate fraction from said first extract fraction, subjecting said rst extract fraction to a second extraction step to separate a second raffinate fraction and a second extract fraction, subjecting said second ramnate fraction to a step of catalytic hydrogenation capable of converting oleflns therein to saturated hydrocarbons, "removing product froml the hydrogenation step and blending it with at least portions of the rst railinate fraction and the second extract fraction to produce an aviation grade fuel.

2. A method for obtaining an aviation grade motor fuel comprising the steps of subjecting a A petroleum fraction boiling in the range of 450 to 800 F. to catalytic cracking in a cracking zone containing a catalyst and maintained at a temperature between 800 and 1100 F., removing cracked product from the catalytic cracking zone, distilling said cracked product to separate a fraction boiling in the range of 105 to 250 F., subjecting said fraction to a first solvent extraction step to form a rst ramnate comprising a major portion of isoparailins and a rst extract, separately removing the first ramnate and first extract from the first extraction zone, passing the first extract to a second extraction zone and separating it into a second rainate comprising a major portion of unsaturated hydrocarbons and a second extract comprising a major portion ot aromatic hydrocarbons, separately removing the second extract and second raillnate from the second extraction zone, subjecting the hydrocarbons in the second rafnate to hydrogenation conditions capable of saturating substantially all of the unsaturated hydrocarbon therein, and blending at least a portion of the hydrocarbon components from the first raflinate, the second hydrogenated raiiinate and the second extract to produce a blended aviation grade fuel.

3. A method for producing an olefin-free aviation grade fuel comprising the steps of fractionally distilling a catalytically cracked naphtha to separate a fraction boiling between 105 and 250 F., solvent extracting said fraction to form a first raiilnate fraction and a first extract fraction, separating said rst rainate fraction from said iirst extract fraction, subjecting the ilrst extract fraction to a second extraction step to separate a second rainate fraction and a second extract fraction, subjecting said second railinate iraction to a step of catalytic hydrogenation capable of converting oleilns therein to saturated hydrocarbons, .removing product from the hydrogenation step and blending it with at least a portion of the ilrst raillnate fraction to produce an aviation grade fuel.

4. A method for obtaining an aviation grade motor fuel comprising the steps of subjecting a petroleum fraction boiling in the range oi 450 to 800 F. to catalytic cracking in a cracking zone containing a-catalyst and maintained at a temperature in the range of 800 to 1100 F., removj ing cracked product from the catalytic cracking zone, iractionally distilling the cracked product to separate a fraction boiling in the range of to 250 F" subjecting said fraction to a rst solvent extraction step in a rst extraction zone to form a rst raillnate comprising a maior portion of isoparafiins and a rst extract, separately removing the rst raffinate and iirst extract trom the rst extraction zone, passing the first extract to a second extraction zone and there separating it into a second railinate comprising a maior portion of unsaturated hydrocarbonsy and a second extract comprising a .major portion oi aromatic hydrocarbons, removing the second raillnate from the second extraction zone, subjecting the second raffinate to hydrogenation conditions capable of saturating substantially all of the unsaturated hydrocarbons therein and blending at least a portion of the hydrocarbon components from the rst rafiinate and the second hydrogenated ramnate to produce an aviation grade fuel.

JAMES A. ANDERSON, JR.

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