US2394716A - Production of aviation gasoline - Google Patents

Description

Feb. 12, 1946. l D. READ; JR 2,394,716

PRODUCTION oF AVIATION GAsoLIuE l Filed Nov. 9, 1942 ZejfZ-'Izz'f 6`Q50zz'7ze @kfw-@MT Patented Feb. i2, 194e Davis Read, Jr., Riverside, Ill.,

vernal Oil Products Company, Chicago, corporation of Delaware assignor to Uni- Ill., a

Application November 9, 1942, Serial No. 464,986 2 Claims. (Cl. 26o-683.4)

This invention relates to a method for prepar-z ing aviation gasoline blending stock from an oleilnic gasoline. More specifically, it is concerned with an operation for the conversion of an oleiinic gasoline having a low lead response to a less oleiinic gasoline having a high lead response and being suitable as an aviation fuel blending stock by reprocessing and alkylation.

Although olennic gasolines produced by cracking or reforming operations, particularly catalytic cracking or reforming, have high initial octane numbers, they are generally unsuitable as aviation fuel blending stocks because of their high olen content and low lead susceptibility. It has been necessary, .therefore to develop process for retreatlng" or "reprocessing" these olelinic gasolines to reduce their oletln content in order to make them suitable for use in aviation fuel. Usually, this retreating or reprocessing oper ation is conducted by contacting the olenic gasoline charging stock with a cracking catalyst of the silica-alumina type at temperatures usually ranging from 500 to 950 F., the catalyst being maintained at high activity by frequent regeneration, to effect the conversion of some of the oleilnic molecules .to parains and of other olefinic molecules to aromatics without. however,

producing substantial amounts of free hydrogen.-

I have found that often the greater part of the C5 oleilns contained in the gasoline are destroyed by cracking, etc., in the retreating operation and do not undergo saturation to as great an extent as do the higher oleiins. With this in mind, it is an object of my invention to substantially depentanize the olenic gasoline before it is sub- 35 iected to contact with the retreating catalyst in order that the Cu olens maybe conserved and converted to more valuable products.

It is a further object of my invention to subject the C fraction obtained fromI the depentani'zing 40 step to alkylation with isobutane to substantially completely saturate the olens contained in this fraction by alkylation and to form a liquid product which is made up predominantly of residual Cs paramns (mostly isopentane), lower boiling paranlns, and products of the alkylation reaction. When this liquid product is blended in the proper proportions with the gasoline fraction obtained by retreating the depentaniaed oleflnlc gasoline charge, a suitable aviation gasoline stock may be In one embodiment, the process of this inven= tion comprises subjecting an oleilnic gasoline containing C ole'nns to a fractionation treatment t0 Beprte therefrom a liquid product substantlally Ct free and thereafter contacting said lid-- uid product with a cracking catalyst to reduce the oleiln content of said product.

In a more specific embodiment, the present invention comprises a process for preparing a gasoline fraction low in oleiins from a gasoline fraction high in olens and containing Ct oleflns which comprises fractlonating the gasoline boiling range charging stock to separate a liquid product substantially free of Cs and lower boiling hydrocarbons and a fraction consisting predominantly of Cs and lower boiling hydrocarbons, contacting said liquid product with a cracking catalyst at conditions adequate to eiiect a substantial reduction in the olefin content thereof, subjecting the Ct fraction to alkylation with isobutane to substantially completely react the olellns contained therein and blending at least a portion of the liquid fraction obtained from the alkylation treatment with gasoline boiling range hy-V drocarbons obtained from the olen reduction treatment of said liquid product to prepare a gasoline having a low olein content and a high lead response.

The accompanying flow drawing illustrates diagrammatically one particular form of the combination .of steps which may be used in accomplishingthe objects of this invention.

Referring now to the drawing, an oleilnic gasoline such as that obtained from a catalytic cracking operation, and containing Cu olens, is supplied through line I to separation zone 2 wherein r it is separated into various fractions. In the event that the gasoline is unstabilized, a Cz and lighter fraction may be withdrawn throughline 3. Furthermore, if the gasoline contains quantities of higher boiling hydrocarbons which would be unsatisfactory for further treatment, the higher boiling hydrocarbons may be withdrawn through line 4. A substantially depentanized gasoline fraction is also separated in zone 2 and withdrawn through line 5. A pentane-pentene fraction is separated and withdrawn through line 6. If Ca and C4 hydrocarbons are present in the charge,

they may also be separated in zone 42, withdrawn from that zone through line I and if desired re,- covered as a product of the process through line 8. In order to effect the separation of the various hydrocarbon fractions, separation zone 2 may include the necessary fractionators, reboi1ers,'con densers, and other auxiliary equipment conventionally used to obtain relatively narrow boiling hydrocarbon fractions.

' The substantially depentanized gasoline withdrawn from zone 2 is supplied through line 5 with acatalyst at conditions such that a substantial reduction in the oleiln content ofthe gasoline is effected. Associations of silica with alumina. magnesia or zirconia are usually employed as the catalyst, although other catalysts such as phosphoric acid may also be used at lower temperatures. The temperature Vin this zone may vary over a range of from 400 to 1000 F., preferably from 500 to 950 F., and the pressures from substantially atmospheric to 1000 pounds per square inch or `more,\the higher pressures usually` being employed with the lower temperatures. Space velocities of from-0.2 to 8 unit weights of hydrocarbon charged per hour perunit weight of catalyst in the reaction zone are usually employed. The retreating zone may include the necessary heaters. reactors, regeneration equipment and other necessary equipment ordinarily used in this catalytic operation. In this zone the hydrocarbons to be treated may be passed upwardly through a turbulent bed of powdered catalyst in accordance with the fluidized" technique recently developed, or they may be passed 'through a xed bed of granular catalyst. In any event, the function of the retreating zone 9 is to substantially reduce the bromine number of the gasoline fraction charged thereto, and preferably to form a product, the normally liquid components of which have an olen content as measured by the bromine number or iodine number of less than half that of the gasoline charged to this zone. The products from retreating zone 9 are sup.. plied through line I to separation zone H wherein, if the end-point of the liquid product is too high, a bottoms fraction may be removed through line I2. Light hydrocarbons, in some cases including Cs hydrocarbons may be removed through line I3, while the greater portion of the products, namely the fractions boiling" within the gasoline range, are removed through line I4. Separation vzone II may include the necessary fractionators,

stabilizers, etc., and other conventional equipment needed to eiect the desired separation The Cs hydrocarbons removed from zone 2 through line E are suppliedptogether with, if desired, all or a portion of the -Cs and C4 hydrocarbons removed from zone 2 through line 1, to the alkylation zone I5 wherein the oleflns contained in the hydrocarbon fraction arev alkylated with isobutane supplied through line I6. In some cases, a certain amount of the isoparaiiins present in the C4 and Cs fractions will also be consumed in alkylating the oleflns present in the same fractions. U'sually, however, the greater part of the isopentane present in the Cs fraction is not removed with the products of alkylation. Preferably the alkylation is conducted in the presence of a catalyst such hydrouoric acid or sulfuric acid, although in some cases thermal alkylation may be used. 'I'he alkylation zone may include the necessary contactors, heat exchangers, fractionators, etc.. to provide for the control o'f the reaction temperature'and to maintain by means of internal recycling a high ratio of isobutanezolefin in order thatV the reaction will be selective. The products of the reaction together Awith the I unconverted paraiiins present in the charging mafrom the remainder'of the product and removed I 'through line 20. Separation zone I8 may include the necessary rractionators and stabilizers, etc., to accomplish this operation. The stabilized liquid product so obtained is removed from zone I8 throughlineZI.

I n many instances, the proportion of Cs hydrocarbons in the alkylate are such that on blending of the alkylate with the retreated fraction, avia- Vtion gasoline having the required 100 octane num` ber with 4 cc. of tetraethyl lead per gallon may be obtained. In other operations, however, a portion of the alkylate and pentane fraction removed trom zone I8 or a portion of the gasoline fraction removed from zone I I may be withdrawn sep- 'arately and the remaining alkylate and pentane acted in the alkylation zone and is therefore refraction and gasoline fraction combined through lines 22 and 23..l It is Usually possible, however, to balance the operation so that the predominating portions of the liquid gasoline fractions removed from zones II and I8 may be combined to furnish a suitable aviation fuel.

The following example illustrates the advan-l tage of employing the process of this invention when a catalytically cracked gasoline is to be retreated to form an aviation fuel stock.

Taking as a basis 1000 barrels of debutanized catalytically cracked gasoline, the relative proportions of the C5 and higher boiling hydrocarbons in this fraction are as follows:

Barrels Pentenes 143 Pentanes 204 Hexanes and higher boiling hydrocarbons--- 653 If the 653 barrels of hexane and higher boiling hydrocarbons are contacted with a silica-alumina catalyst at 1.27 space velocity and 900 F. in a retreating operation to reduce the bromine number or, in other words, to reduce the olen content of the fraction, a product distribution such as that shown below may be obtained:

Distributionlof products from retreating l Barrels Ca, C: and C4 hydrocarbons 55 Pentenes l5 Pentanes 27 Hexanes and higher boiling hydrocarbons-" 570 Owerhead from depentaneing operation Barrels Pentenes 143 Pentanes 204 lowing distribution of product per 1000 barrels of debutanized charge is obtainable:

- I Barrels Cz, Ca and C4 hydrocarbons 118 Pentenes 74 Pentanes 222 Hexanes and higher boiling hydrocarbons 601 of which are apparently cracked to lower boiling assura hydrocarbons and, therefore, at least partially lost. On the other hand, if the charging material is rst debutanized and then subjected to retreating, a net gain of C hydrocarbons is obtainable and these Cs hydrocarbons may be subjected to alkylation to further increase the yields of aviation quality gasoline that are obtainable by the process of this invention.

I claim as my invention:

1. A process for reducing the olen content of an olefinic gasoline containing Cs hydrocarbons which comprisesseparating said olenic gasoline into a lower boiling fraction containing the Cs hydrocarbons and a higher boiling fraction containing the Cn and heavier hydrocarbons, subjecting said lower boiling fraction in admixture with an oleiln content and blending the product ofysaid alkylating step with the gasoline Iproduct from the last mentioned conversion step to form a full boiling range gasoline of low olefin content.

2. The process of claim 1 further characterized in that isobutane is supplied to the alkylating step. DAVIS READ, Ja.

Images