US2431515A - Production of an aromatic gasoline - Google Patents

Description

Nov. 25, 1947. R. M. sHEPARDsoN 2,431,515

PRODUCTION OF N AROMATIC-GASOLINE Filed Deo. 24

Patented Nov. 25, 1947 PRODUCTION 0F AN AROMATIC GASOLINE Robert M. Shepardson, Madison, N. J., assignor to Standard Oil Development Company, a corporation of Delaware Application December 24, 1943, Serial No. 515,495

(Cl. 1mi-49) I 9 Claims.

This invention relates to treating hydrocarbon fluids to produce motor fuels, and more particularly, relates to the production of aviation gasoline blending stocks.

Standards for aviation gasoline are being continuously raised in order to produce aviation fuels permitting high power outputs under rich mixture conditions. The Army and Navy specifications on aviation gasoline are being raised so that the aviation gasoline will have a higher supercharged rich mixture performance on the B-C engine as measured by the indicated mean effective pressure or IMEP than at present. This method is known as Aviation Fuels Division -S-C- Rich Mixture Octane Number Method (AFD-3C- Rich Mixture). The IMEP is registered in a standard supercharged aviation gasoline test engine in pounds per square inch at the specified intensity of knocking where the comparison against a reference fuel is made. The IMEP is then the maximum pressure capable of being developed in the test engine by the fuel being tested without detonation and is accordingly a measure of the power output attainable with the given fuel. The higher the IMEP the higher the power output of a given fuel or material and the more desirable the fuel or material is. Modern aviation engines require fuels of high rich mixture performance in order to permit take-off from the ground when the airplane is heavily loaded or in other situations where large power outputs are needed.

Catalytic reforming, preferably in the presence of hydrogen, or hydroforming, of a virgin naphtha fraction boiling from about 290 to 350 F. results in the production of motor fuel containing aromatic constituents. About 50% of the starting material is converted into a fraction boiling from about 215 to 350 F. which has an aromatic concentration of about 95%. Although the aromatic concentration of this product is very high, its quality for aviation gasoline is quite poor as this material has an IMEP blending value under rich mixture conditions on the S-C supercharged engine of only 200. Since this IMEP blending value is slightly poorer than the present requirement for 100 octane gasoline, it is apparent that the hydroformed material cannot be used to elevate poorer quality fractions into aviation gasoline. This poorer quality is undoubtedly due to the presence of Ca, C9 and C10 aromatics some of which are of extremely poor quality for inclusion in aviation gasoline.

According to my invention, naphtha, preferably virgin naphtha, having a boiling range of about to 400 F., preferably 275 F. to 350 F., is catalytically reformed, preferably in the presence of hydrogen, to produce aromatics and then a fraction boiling between about 250 to 450 F. is separated from the reaction products and thermally cracked at a temperature of about 1200 to 1600 F. for a relatively short time to modify the structure of non-aromatic hydrocarbons so that they no longer boil within the range of the feed stock. At the same time, during the thermal cracking operation, there is a reduction of higher boiling aromatics to form additional amounts of benzene and toluene. During the thermal cracking, olefins and diolefins are formed in a small quantity and a smaller quantity of aromatics with olen side chains of the styrene type are formed. The dioleiins and the aromatics of the styrene type are not satisfactory for inclusion in the aviation gasoline and can be removed by acid treatment or any other well known method of removing hydrocarbons of this type.

My process can also be used to produce nitrationgrade benzene or toluene by acid-treating the thermally cracked products and then re-v running or fractionating the acid-treated products to separate benzene and/or toluene.

As the amount of benezene is limited in the aviation gasoline specifications, any excess of benzene may be alkylated with propylene to produce cumene which is of extremely high quality for inclusion in aviation gasoline.

In the drawing, the figure represents one form of apparatus which may be used to carry out my invention.

Referring now to the drawing, the reference character l0 designates a line through which naphtha feed is pumped by pump l2 and passed through the heating coil i4 in a furnace i6. The feed passing through line it is preferably a naphtha boiling from about 300 to 400 F. Either cracked or virgin fractions are suitable, although the best results will be obtained by choosing a fraction containing a large quantity of naphthenes and/or cyclo-oleflns, preferably more than 40% of these two types of hydrocarbons combined, Virgin naphthas are preferable. During passage through the heating coil i4 the naphtha is heated to about 850 to 1100 F., preferably 950 to 1100 F. The naphtha is under a pressure of about 30 to 400 lbs/sq. in. The heated naphtha is passed through line I8 to a reaction Zone 22 containing a suitable reforming catalyst.

Hydrogen or hydrogen containing gas may be passed through line 24 and heating coil 26 in a heater 28 and the temperature of the hydrogen is raised to about 850 to 1100 F. or about the same temperature as the naphtha feed. The heated hydrogen is then passed through line 32 and mixed with the heated naphtha feed leaving heater I6 through line I8. The mixture is then passed through the reaction Zone 22. The hydroforming is so carried out that there is no net consumption of hydrogen and/or there is net production of hydrogen.

The hydrogen is used in an amount of about 1000 to 4000 cu. ft./bbl. of naphtha feed, preferably 1500 to 3500 cu. ft./bbl. The catalyst is preferably molybdenum oxide on activated or peptized alumina with about 3 to 10% of Ymolybdenum oxide and the balance alumina. Other reforming catalysts may be used, such as alumina. and chromium oxide. Catalysts, such ,as oxides-or .suldes of metals of the 6th group of the periodic system, may be used alone or in combination with other materials Which may serve as supports or carriers and may also have some catalytic activity.

About .3 to volumes of a liquid naphtha per hour are passed over one volume of catalyst. The reaction products are passed overhead through line 34 provided with a reducing valve 30 and a cooler 38 to a fractionating tower 42. The reaction products are fractionated to separate an aromatic product boiling from approximately 250 to 400 F. or 450 F. withdrawn as a side stream through line 43 and a light fraction boiling lbelow approximately 250 F. taken overhead through line 44. Higher boiling constituents are withdrawn from the bottom of fractionating tower 42 through line 45.

The lighter fraction passes overhead through line 44 as vapors and the vapors are condensed in a condenser 48 and then passed to a separator 49 for separating gases from liquid. The gases passing overhead through line 50 will contain a large quantity of hydrogen, say 25 to '75%, and a portion of this gas may serve as the source of hydrogen used in the reforming step, being returned to linel 24 and heater 26 by means of li-ne 50, compressor 5I and line 52. Any excess gas will be withdrawn through line 53. The liquid is withdrawn from the bottom of the separator through line 56 and at lleast a portion thereof is passed through line -58 by pump 62 and returned to the top ofthe fractionating tower 42 as reilux. This light naphtha is of high quality and would normally be employed directly in aviation gasoline.

The intermediate fraction boiling from 250 to 850 or 450 F. is passed through line 43 and pump 64, after which it is admixed with a gaseous diluent, such as steam, introduced into line 65 through line 66. The amount of steam is about 50 to 90 mol per cent of the mixture, preferably about 80 mol per cent. Other diluents, such as hydrocarbon gases or the like, may be used. In some instances the di-luent gas may be omitted.

The intermediate aromatic fraction passing through line 43 Acontains more than 75% aromatics by volumeand, in a typical example, has about Vthe following composition:

Per cent Non-aromatics-.largely parains 15 Ca aromatics 20 C9 aromatics 10i Higher aromatics above C9 551' Many of the higher aromatics above C9 and orthoxylene, as well as the non-aromatics, are poor ingredients in aviation gasoline and the next step in my process eliminates most Yof the non-aromatics or converts many of the higher aromatics,

particularly those above C9, to lower boiling aromatics which are of higher anti-knock quality as well as more volatile, both of which qualities are extremely important for aviation gasoline blending agents. Methyl groups attached to benzene are hard to remove but ethyl groups and higher are much easier to remove. For example, ethyl benzene in my process is converted to benzene.

The intermediate fraction passing through line 55 with or without an added diluent gas is passed through heating coil 68 in heater I2 where the temperature is rapidly raised to about 1200 to 1600 F. The time of reaction is maintained from about a few seconds, i. e. about 10 seconds, to a fraction of a second depending on the temperatures used, shorter times being used at the higher temperatures. sion or reaction is sufficiently high to remove practically all of the non-aromatics from the boiling range of the feed stock and at the same time cause a reduction in the molecular weight of the higher aromatics. At the same time olens and diolens are produced.

The products of reaction are passed through line 14 to a quenching tower 16 wherein the products of reaction are immediately quenched to a temperature of about 600 to 1000 F. by the introduction of water through line ll. The quenching water is introduced into the top of the quenching tower H6 and the products of reaction are cooled to below the boiling point of water so that normally liquid hydrocarbons are condensed together with the water and the hydrocarbons and Water are collected in the bottom of the quenching tower 16.

Uncondensed gases .pass overhead from the kquenching tower through line 82. These gases contain a small percentage of higher boiling hydrocarbons and these hydrocarbons may be recovered by passing the gases through a scrubbing zone or other means. Or these gases may be combined with light hydrocarbons hereinafter referred to.

The condensed Water collects as a bottom layer B4 in the quenching tower and is withdrawn from the .bottom through line 88. The water may be further cooled and recycled to line 18 and to the top of the quenching tower 'I6 or it may be withdrawn from the system. The condensed hydrocarbons form an upper layer and are withdrawn through line .92 by means of pump 94. The condensed hydrocarbons are then passed through a heating coil 96 in heater 98 to vaporize the hydrocarbons and the vapors are passed through line l02 to a second fractionating tower |04 for separating the desired aromatic fraction from other constituents. The lighter hydrocarbons combined with the gases from line 82 containing C1 to C5 hydrocarbons are passed overhead through line |06. This lighter fraction contains olens, such as ethylene, propylene, butylene, and also contains butadiene, isoprene, piperylene, etc. This lighter fraction is preferably treated yto recover desired constituents therefrom.

Tar or fuel oil is withdrawn from the bottom 0f the fractionating tower |04 through line |08. A heavy naphtha fraction is withdrawn from the lower portion of the tower |04 through line l l2. This heavy naphtha fraction contains more than aromatics and may be used as a solvent or is of excellent quality for use in ordinary motor fuels. Also, this heavy naphtha, when cut to an end point of 430 E'. or higher, will-contain reasonably large .quantities of naphthalene, possibly- Thenaphthalene can be recovered in a The temperature during convermuch purer state by chilling the heavy naphtha, or preferably a narrow boiling fraction in the naphthalene boiling range (40G-435 F.) followed by ltration, the solid naphthalene then being suitable for the manufacture of many chemicals, such as phthalic anhydride, dyes, explosives, etc.

The desired light aromatic fraction boiling between about 160 to 325 F., or 350 F., is withdrawn as a side stream through line H4 and, in a typical example, a fraction having a boiling range of about 170 F. to 335 F., contains more than 95% of aromatics. This aromatic fraction contains benzene, toluene, and xylenes for the most part, and also includes a smallvquantity of olefins, diolens and aromatics with olefin side chains, such as styrene, which are not desired in the nal aviation gasoline or aviation blending stock. These undesirable constituents may be separated by passing the aromatic fraction through an acid-treating unit IIS wherein the aromatic fraction is treated with about 5-25 lbs. of sulfuric acid per barrel of aromatic fraction. The concentration of the sulfuric acid is preferably from about 90 to 98%. After acid treatment, the fraction is rerun to remove polymers formed in this step. Also, these undesirable constituents may be removed by treatment with fullers earth at 30D-500 F. or other suitable polymeriation catalysts followed by rerunning to separate the polymers.

This acid treatment removes the undesirable constituents and leaves the desired aromatics. The refined aromatic fraction is withdrawn through line IIE. This fraction forms about 40 to 80% of the feed passing through pump E@ to the severe cracking step in coil S8. rIhe recovered aromatic fraction has an IMEP blending value of about 280 or higher, and it will be seen that this fraction can be employed to elevate much poorer quality of materials to aviation gasoline of the desired performance.

Generally, the aromatic fraction passing through line I I3 will be combined with the light fraction withdrawn through line 51, this blend then being employed to elevate other poorer quality aviation fractions to the desired anti-knock level.

If desired, the aromatic fraction passing through line I I8 may be fractionated to separate nitration grade benzene and toluene of over 99% purity.

In the severe cracking step the temperature in degrees Fahrenheit must be equal to or greater than 1332-107.6 log S-l-lOS-1-45 where S is the actual time of Contact in seconds at the temperature in question. This formula and its application is more fully described in my copending case Serial No. 485,797, filed May 6, 1943.

Under the present specifications for aviation gasoline, the benzene concentration is limited to a maximum of 5 volume per cent due to the possibility of freezing troubles which might be experienced with higher concentrations of this particular aromatic constituent. Any excess benzene may be alkylated with propylene which is also produced in the severe cracking step to produce cumene which has an extremely high quality for inclusion 4in aviation gasoline. In this alkylation step a suitable catalyst, such as phosphoric acid, may be used. About 1 volume of benzene to 0.9 volume of liquid propylene are used. During the reaction the pressure is maintained at about 20G-600 lbs/sq. in. and the temperature is about 40G-500 F. This alkylation step produces about 145 gallons of product or cumene from each 6 gallons of benzene, thus greatly increasing the quantity of aviation gasoline blending agent obtained.

While I have shown one form of apparatus for carrying out my invention and have given certain specic conditions and compositions of certain of the fractions, it is to be understood that these are by way of illustration only and changes and modications may be made without departing from the spirit of my invention.

I claim:

1. A method of producing aviation gasoline blending stock which comprises catalytically hydroforming naphtha under such conditions that there is no net consumption of hydrogen, separating from the reaction products a fraction boiling between about 250 and 400 F. and containing aromatic and non-aromatic constituents, heating the separated fraction to a temperature atleast asY high as 1200 F. for a relatively short time to convert non-aromatic constituents largely to olens and diolens and to convert high boiling aromatics to benzene and toluene, quenching the products of reaction from the high temperature cracking step and recovering a fraction boiling in the aviation gasoline range which fraction consists essentially of aromatic constituents.

2. A method of producing aviation gasoline blending stock which comprises catalytically reforming naphtha in the presence of hydrogen, separating from the reaction products a fraction boiling between about 250 F. and 400 F. and containing aromatic and non-aromatic constituents, heating the separated fraction to about 1200 F. to 1600" F. for less than 10 seconds to convert nonaromatic constituents in the selected fraction largely to oleiins, diolens and aromatic constituents and to convert high boiling aromatic constituents to lower boiling constituents, quenching the products of reaction from the high temperature cracking step and recovering from thequenched products a fraction boiling in the aviation gasoline boiling range.

3. In a method for producing aviation gasoline blending stock wherein naphtha is catalytically hydroformed to produce constituents in the gasoline boiling range, the steps which include separating a fraction containing a preponderance 0f aromatics in the Cs to C12 range from the reaction products, said fraction containing a small quantity of paraflins and having a boiling range of about 250 to 450 F., heating the separated fraction to about 1200 to 1600 F. to convert the parafns mostly to olens and diolens and to convert the high boiling aromatics to lower boiling aromatics and separating oleiinic hydrocarbons from the reaction products to produce an aromatic fraction in the aviation gasoline boiling range.

4. A method of producing aviation gasoline blending stock which comprises catalytically hydroforming virgin naphtha to produce aromatic constituents in the gasoline boiling range, separating a fraction boiling between about 250 and 400 F. from the reaction products, said fraction containing a preponderance of aromatic and a lesser quantity of non-aromatic constituents, heating the separated fraction to about 1200 to 1600" F. from about 10 seconds to a fraction of a second, shorter times being used for the higher temperatures to convert non-aromatic constituents in the selected fraction largely to olens and dioleiins and to convert the high boiling aromatics into lower boiling aromatics, quenching the products of reaction from the high temperature 7 cracking step, removing non-aromatic constituents and reco-vering a fraction boiling in the aviation gasoline range which fraction consists essentially of aromatic constituents.

5. A method according to claim 4 wherein the 250 F. to 400 F. fraction contains by volume more than 75% aromatics, before the high temperature cracking step.

6. A method according to claim 4 wherein the 250 F. to 400 F. fraction contains by volume about 7E-85% aromatics before the high temperature cracking step and the separated aromatic fraction after the high temperature cracking step contains more than 95% of aromatics and has a boiling range of about 170 F. to 335 F.

7. A method of producing aviation gasoline blending stock which comprises catalytically hydroforming virgin naphtha to produce aromatic constituents in the gasoline boiling range, separating a fraction boiling between about 250 and 400 F. from the reaction products, said fraction containing a preponderance of aromatic and a lesser quantity of non-aromatic constituents, heating the separated fraction to about 1200 to 1600o F. from about 10 seconds to a fraction of a second, shorter times being used for the higher temperatures to convert non-aromatic constituents in the selected fraction largely to olens and cliolens andto convert the high boiling aromatics into lower boiling aromatics, quenching the products of reaction from the high temperature cracking step, fractionating the reaction products to recover a fraction boiling in the aviation gasoline boiling range and containing aromatic and 8 non-aromatic constituents and treating the recovered last-mentioned fraction to remove substantially all of the non-aromatic constituents therefrom.

8. A process according to claim '7 wherein the last-mentioned fraction is acid-treated to remove olefins.

9. A process according to claim 7 wherein the aromatic fraction after separation of non-aromatic constituents has a boiling range of about F. to 350 F.

ROBERT M. SI-IEPARDSON.

.REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS

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