US2398846A - Making gasoline - Google Patents

Description

- J. c. MUNDAY MAKING GASOLINE Filed July 6, 1944 April 23, 1946.

v2 Odo duomium Juan ,0! 3

w uobaimw John C. mundaz Unverzbcr e n r o b b Patented Apr. 23. 1946 John C. Munday,

Cranford, N. J., assignor to Standard Oil Development Company, a corporation of Delaware Application July 6, 1944, Serial No. 543,626

Claims.

The present invention relates to an improved process for the production of gasoline and other light hydrocarbons from heavier hydrocarbon oils by catalytic cracking.

The catalytic cracking of hydrocarbon oils,

, such as gas oil, to form cracked gasoline has now become common practice in the petroleum refining industry, While the raw racked gasoline has, of course, many advantages over the gasoline produced by the older thermal cracking methods, nevertheless it has to undergo considerable after-treatment and/or refining in order to produce finally a satisfactory commercial product. In general, there are two main considerations presented to the refinery in after-treating or handling the material recovered from a cracking reactor or zone. In the first place, the raw product is not 100. per cent gasoline and contains sustantial quantities of unconverted ga oil or heavier ends which, during cracking, have undergone some change which makes them less desirable for recracking than the original feed stock. Thus the unconverted gas oil commonly called cycle oil," since it is returned or recycled in whole or in part to the cracking zone, acquires as a result of the operation high molecular-weight aromatics containing two or more benzene rings in a condensed nucleus. The presence of these aromatics is detrimental to the operation of cracking, since they decompose during the cracking orrecracking to .form unduly large quantities of so-called coke, a carbonaceous deposit which forms on. the catalyst. Consequently,

'it is desirable to treat this cycle oil to improveits qualities before cracking.

Withrespect to the gasoline itself, particularly where the object of the process is to produce aviation gasoline, the same invariably contains substantial quantities of normally liquid olefinic hydrocarbons which .are undesirable particularly when the gasoline is eventually to be blended it is againsubjected to .with lead tetraethyl, since such an olefin-containing gasoline is less responsive to octane number improvement by the addition of lead tetraethyl than a, saturated material would be. In other words, such a gasoline fraction is said to have a lower lead susceptibility (a technical term in this particular art) having the significance indicated.

The main object of the present invention is to gasoline so as to renderit more suitable for re-- treatment in a cracking zone.

A secondary object of my invention is to improve gasoline fractions and the cycle oil in the absence of a fraction boiling between the gasoline and the initial feed stock in order to im: prove the economics of the overall process, in particular to effect the saving in hydrogen which is one of the materials I employ in my process.

A third object of the present invention is to improve the quality of both the gasoline and the cycle oil recovered from a catalytic cracking operation in a more expeditious and economical manner than has been possible heretofore.

Other and further objects of the present invention will appear from the following more detailed description and claims.

In the accompanying drawing, I have shown diagrammatically merely the essential apparatus of a unit in which a preferred modification of my invention may be carried into practical effect,

f with only so much of the accessory apparatus as improve the normally liquid cracked portions of a cracked gasoline and, at the same time, to improve the so-called cycle oil or that portion of the original feed stock which is not converted to is necessary to aiiord a clear understanding of the invention.

Referring in detail tolthe drawing, a gas oil,

which may be a West Texas crude oil boiling in the range of from 500 F. to 800 F. and having an A. P. I. gravity of about 30, is introduced into the system through line I, thence heated in a fired coil 3, or other suitable means, to a temperature of, say, 900 F., whereupon it is Withdrawn through line 5 and discharged into a cracking vessel l0 containing a catalyst C. The pressure employed in the cracking operation may be atmospheric or thereabouts, for example in the range 0 to lbs. per square inch gauge. The catalyst may be a natural or acid-treated bentonitic clay, or a synthetic gel of silica and alumina. In the modification of my invention which I have shown to illustrate my invention, the cracking is carried out in a stationary bed type of catalyst contained in a cylindrical or other suitable case l0. Since cokeis formed on the catalyst during cracking, it is generally desirable to provide more than one catalyst case so that by proper alternation the oil flow can be made continuous even while coke is being removed by periodic burning with air. It should be appreciated that I may carry out my process of cracking in any of the known methods; such as the so-called fluid catalyst type of operation where the catalyst in powdered condition is passed through a so-called delayed settler type of reaction and regeneration zones, in the form of a fluidized mass of catalyst admixed with reaction and regeneration vapors,

7 detail the cracking process.

or I may use other known types of operation where the catalyst in the form of grains, granules lumps. and the like, moves by gravity or forced circulation through a reaction zone and a regeneration zone. However, since the gist of my invention resides in thesubsequent treatment of the crackedproduct rather than in a specific type of cracking, it will not be necessary to describe in Cracked products from the illustration I have shown are withdrawn from the reactor through a line l2 and immediately discharged into a fractional distillation zone M where the crude cracked products are fractionated into the following fractions: First, there is taken overhead through line It that portion of the total product which includes the lighter fractions up to the C5 hydr0carbons.- This material is passed through cooler l6 into separator ll; light gases are removed overhead from the separator through line It and liquid hydrocarbons, including C4 and some C3, are removed through line I9 and may be utilized in alkylation and polymerization processes. A second fraction comprising the CIR-325 F. hydrocarbons is withdrawn through line 22, and acycle oil fraction boiling above about 500 F. or 550 F. is withdrawn through line 24, These two fractions are combined and it is with respect to the refining of these particular said fractions that my invention is principally concerned. In treating these fractions, I first pass them by means of a pump (not shown) through line 22 and through a heating means, such as fired coil 30, and thence through line 32 and then into a hydrogenation reactor 40. Simultaneously, hy-

drogen from some source is passed from line 50 through a suitable heating means 55, which may be afired coil, and thence discharged via line 56 into line 32 where it admixes with the heated hydrocarbons and is discharged with the latter into the'hydrogenation reactor 40. The hydrogen employed is preferably that produced in the cracking step, separated from cracked products in separator i1 and passed through line l8 into line 50.

In the hydrogenation reactor, the desired result is to saturate the olefins in the (Is-325 F. fraction of the gasoline withdrawn from fractionating column I4, and at the same time to hydrogenate the aromatics, particularly the high molecular weight aromatics having two or more benzene rings in a condensed nucleus, which are contained in the heavy bottoms withdrawn from fractionating column 14 through line 24. To accomplish this end, I maintain the following conditions in hydrogenator 40:

Temperature 600 F. to 800 F. Pressure 200 lbs. to 3000 lbs.

. per sq. in. auge Oil feed rate 1 to 5 v./v./hr. Hydrogen, cu. ft.

per barrel feed 1000 to 6000 Under the conditions I have set forth in the are group VI and VIII metals and metallic oxides,

such as nickel or molybdenum oxide or chromium oxide. The catalyst is also preferably supported asoaaec does not deactivate the catalyst. The oxidized catalyst maybe treated with hydrogen before placing it back on stream, if desired.

The treated materials are withdrawn from hydrogenator 40 through line 80, thence discharged into a hydrogen separator 62 from which the hydrogen may be withdrawn through line 55 and recycled to line 50 for further use in the process. It may be and often is desirable to pass the hydrogen-containing gas in line 50 through a scrubber where it contacts in countercurrent flow an absorption oil, such as, say, a light naphtha which scrubs out and/or dissolves light hydrocarbons thereby enriching the raflinate in hydrogen content. The bottoms withdrawn from separator 62 through line 10 carrying a pressure reducing valve 13 are then discharged into a fractionator 15 from which the now saturated Cs-325,F. gasoline fraction is withdrawn through line and delivered to storage drum 8!.

. The bottoms from fractionator I5 are withdrawn through line 83, and this material which is the cycle oil previously mentioned, improved as'to its cracking properties, is discharged into feed inlet line I for further treatment in the cracker i0. The normally gaseous hydrocarbons and possibly some hydrogen which are contained in the crude product withdrawn from 40 are withdrawn overhead from fractionator 15 through line and these may be disposed of in any convenient manner.

Of course, it will be understood that the raw gasoline collected in storage 8| may be corrected as to volatility by the additionof suitable blending agents thereto, or bythe removal of light ends and of course may be blended with up to 4 cc. of

to standard practice.

The cycle oil fraction which is subjected to mild hydrogenation has an initial boiling point above about 500 F. or 550 F., and in a preferred operation has a boiling range similarto that of the fresh feedstock. If the aviation gasoline fraction, which is hydrogenated along with the cycle oil, boils up to 325 F. as mentioned above, it will contain the Ca aromatics, the xylenes and ethyl benzene. In some cases, for example when the capacity of the hydrogenation unit or the amount of hydrogen available is limited, it may be desirable to bypass the C8 aromatic fraction boiling between 265 F. and 325". F. around the hydrogenation step, by passing it from fractionator I4 through line 82 to line 80 and thence to storage drum 8|. If the toluene concentration is high, it may be desirable to bypass the 221 F.-325 F. fraction through line 82.

An intermediate fraction boiling between the cycle oil and the aviation gasoline, in example between 325 F. and 550 F., is withdrawn from fractionator l4 and is rejected from the system, whereas by mild hydrogenation the aviation gasoline is improved in quality and the cycle oil is made more amenable toward cracking to high quality gasoline. Hydrogenation of the intermediate fraction is imdesirable since its quality as a motor fuel is degraded by hydrogenation, and its value as a cracking stock even after hydrogenation is far less than that of cycle oil or fresh feed. Rejection of the intermediate fraction therefore has the eiiect of increasing the overall quality of the aviation gasoline produced and of plant capacity, and also of keeping hydrogen consumption in line with hydrogen production in the cracking step.

Hydrogen consumption may also be decreased by bypassing the Ca fraction of the cracked products around the hydrogenation zone, by passing it from fractionator ll through lines 84 and 80 into storage drum 8 I For example, a Southwest Louisiana wide-cut gas oil having an A. P. I. gravity of 32, an aniline point of 1'75, and a boiling range correspondingto per cent at 484, 50 per cent at 622, and an end point of 700 F. is cracked at 975 F. employing a powdered silica-alumina catalyst in 13:1 catalyst to oil weight ratio and a weight-space velocity of 4. On a volume per cent fresh feed basis, there are obtained 28 per cent aviation gasoline of 7 lbs. vapor pressure which has an acid heat of a 141 E, a bromine number of 74, and a boiling range of 110 F. to 332 F., and 26 per cent cycle oil boiling above 500 F. The intermediate fraction which has a low octane number (65-70 C. F. R. Motor method) is rejected from the process.

The aviation gasoline is fractionated into a light fraction and a heavier fraction boiling above 221 F. which contains xylenes and a small amount of toluene. The heavier fraction is bypassed around the hydrogenation step. The light aviation fraction-and the cycle oil fraction are combined and are hydrogenated at 730 F., 3000 lbs. per square inch pressure, 6000 cubic feet of hydrogen per barrel, and 1.0 v/v./hr. space velocity, employing tungsten sulfide catalyst.

The hydrogenation product is fractionated, the light fraction is combined with the bypassed aromatic fraction, and the heavier hydrogenated fraction is recycled to the cracking step. The

- oil feed, while increasing coke formation from 4.2

to only 5.0 weight per cent based on feed. Numerous modifications of my invention failing within'the scope thereof may be made by 'those familiar with this art.

What I claim is: 4

1. In the refining of the total products of a I catalytically cracked gas oil. the improvement which comprises withdrawing the product from a catalytic cracking zone, fractionally distilling the same into a fraction consisting of- C5 hydrocarbons to those boiling up to about 325 F. and a second fraction comprising the hydrocarbons 1 boiling above about 500 R, combining the segrecombined fractions comprise an aviation gasoline having an aviation octane number of 96.5 by the AFB-1C method as compared to 92 for the original cracked aviation gasoline, each being tested at '7 lbs. vapor pressure with 4 cc. lead tetraethyl per gallon.

Recycle of the heavy hydrogenated cycle oil to the cracking stepincreases the yield of aviation gasoline from 28 to 37.3 per cent based on gas gated fractions, subjecting the combined fractions to a mild catalytic hydrogenation in the presence of added hydrogen wherein the oleiins are saturated andthe aromatics in the fraction boiling above about 500 F. are substantially converted to naphthenes, in a hydrogenation zone,

withdrawing the hydrogenated products from the hydrogenation zone, fractionally distilling the hydrogenated products to recover a saturated aviation gasoline boiling up to 325 F., separately r'ecoveringa fraction boiling above 500 F., and recycling'the last-named fraction to the cracking zone. 2. The method of claim 1 in which the hydrogenation is carried out in the presence of a regenerable catalyst.

3. In the production of high quality aviation gasoline,the steps of catalytically cracking a gas oil, in a cracking zone, withdrawing the cracked products and fractionally distilling the same into non-aromatic and aromatic fractions boiling in the aviation gasoline range, and a heavy cycle oil fraction, combining the non-aromatic aviation gasoline fraction with the said heavy cycle oil fraction, subjecting the mixture to a mild catalytic hydrogenation, separating the hydrogenated products into an aviation gasoline fraction and a- 5. The method of claim 3 in which the heavy,

recycle oil boils above about 500 F.

Joan c. MUNDAY.

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