US2421615A - Treating hydrocarbon fluids - Google Patents

Description

51m@ 3, 1947. R. M. sHEPARDsoN TREATING HYDROCARBON FLUIDS Filed Deo. 2s, 1945 Patented June 3, 1947l TREA'EING HYDROCARBON FLUIBS` Robert M. Shepardson, Madison, N. J., assigner to Standard Oil Development Company, a corporation of Delaware Application December 28, 1943, Serial No. 515,898

1 Claim. (C1. 19d-4 9) This invention relates to the conversion of hy` drocarbons to produce aviation gasoline blending stocks.

Catalytic cracking of petroleum fractions produces gasoline having a relatively high proportion of aromatic constituents, particularly when using relatively high temperatures. The quantity of benzene formed is relatively small but toluene and higher boiling aromatics are frequently found in as high as 90% concentration in narrow fractions ofthe aviation gasoline boiling range'.

By choosing a boiling range fraction of about 225 F. to 350o F., a fraction containing about 50 to 80 of aromatics of reasonably good quality for inclusion in aviation gasoline can be produced from a catalytic cracking process. However, this fraction suffers in quality due to the presence of non-aromatic constituents, such as parafns, which are of extremely poor quality for inclusion in aviation gasoline, the quality of the entire fraction selected, therefore, being considerably poorer than that possible if the non-aromatic constituents are removed.

But the non-aromatic constituents boil at about the same temperature as the aromatic constituents in the aviation gasoline boiling range and so cannot be removed by simple distillation. Also, the preponderance of aromatics present in the selected fractions are composed of Ca, C9 and Cio hydrocarbons and some of these aromatics are of much poorer quality than others. For example, ortho-xylene is a poor aromatic constituent for inclusion in aviation gasoline whereas para-xylene, benzene and toluene are of high quality.

The Army and Navy specifications on aviation gasoline are being raised so that the aviation gasoline will have a supercharged rich mixture performance on the 3C engine as measured by the indicated mean effective pressure or IMEP of 218. This method is known as Aviation Fuels Division-SC-Rich Mixture Octane Number method (AFD-BC-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. lThe 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.

According to my invention, the fraction boiling fromA about 200 to 500, F., and preferably from 200 to` 350 F. or 400 F., from the catalytic cracking operation is severely cracked at a temperature of about 1200 to 1600 F. for a few seconds or a part of a second at the higher temperatures to produce aromatics of a very high degree of purity. By merely acid-treating the resulting product it is possible to produce an aromatic fraction of high purity and of very much better quality for aviation gasoline blending than is fthefraction before `the severe cracking treatment.

The improvement in quality is the result of converting non-aromatic constituents in the selected fraction to-lower molecular Weight olens, largely ethylene, propylene and butylene, the formation of some additional aromatics in the aviation gasoline boiling range and the scission of alkyl side chains of aromatic rings of higher boiling aromatics. Duringr the severe cracking treatmentabove referred to, the relatively low boiling aromatics, such as benzene and toluene, remain unchanged and are not cracked by the severe cracking treatment.

The catalytically cracked fraction, before the severe thermal treatment, has an IMEP blending value of about 150 to 225 and it is apparent that this fraction is very poor for elevating poor fractions to a quality of 2,18` IMEP. By thermal processing under severe conditions of the catalytically cracked fraction, it is possible to obtain about 4'0 to 30% of an aromatic fraction having anllViEP blending value of 275 to 350 from which it is readily apparent that this fraction can be employed to elevate much poorer quality of materials to aviation gasoline of thedesired performance.

In the drawing, the figure represents one form of apparatus which may be used in carrying out my process.

Referring now to the drawing, the reference character I0 designates a line through which material to be cracked is passed by pump i2. For catalytic cracking the stock may be any relatively high boiling stock, such as gas oil, reduced crude, or the like. Where the feed stock contains unvaporizable constituents, the feed stock may be heated to a high temperature, say, G-900 F., following which unvaporized constituents are separated. However, when using powdered catalyst at a relatively high temperature, liquids containing unvaporizable constituents may be directly mixed` with the powdered catalyst which will cause substantially complete vaporization by cracking, the necessary heat for vaporization and cracking being supplied by the catalyst or catalyst .plus inert powdered material.

The hydrocarbon fraction is passed through heating coil I4 in a heater i6 to vaporize the oil and raise it to cracking temperature. The vapors are passed through line I8 to a catalytic reactor 22` which contains any suitable cracking catalyst, such as acid-treated bentonites, synthetic silica alumina gels, silica magnesia gels, or other cracking catalyst. For aviation gasoline production synthetic silica alumina gels are preferred.

The oil to be cracked is heated to a temperature of about 800 to 1050 F., preferably about 925 to 975 F., and where a stationary bed of catalyst is used, about 1.0 volume of liquid oil per volume of catalyst per hour is passed through the reactor 22. During conversion, carbonaceous material or coke is deposited on the catalyst and the cracking stage is short, perhaps 10-60 minutes. After the cracking stage, the4 catalyst is purged and regenerated before being used in other cracking stages. Where stationary catalysts are used, a plurality of reactors will be used so that the cracking may be maintained continuously while some of the catalyst is being regenerated in certain of the reactors. While the invention is being specically described in connection with a stationary bed of catalyst, it is to be understood that powdered catalyst may be used which is mixed with the vapors or liquidoil and passed through a conversion zone after which the catalyst particles are separated and regenerated before reuse in another conversion operation. Also, granular moving bed processes may be used.

'Ihe products of conversion leave the reactor 22 through line 24 and are passed to a fractionating tower 26 for separating light hydrocarbon fractions from higher boiling hydrocarbons. Preferably the reaction products passing through line-24 are cooled before being introduced into the fractionating tower 26. Londensate oil or final oil boiling above about S50-500 F. is withdrawn from the bottom of the tower 26 through line 28 and may be withdrawn from the system or recycled to inlet line l0 for further cracking treatment.

The lower boiling constituents boiling up to about ZOO-.225 F. pass overhead through line 32 and through a condenser 34 before being passed to separator 36 wherein separation of gases and liquid is effected. The gases pass overhead through line 38 and the liquid is withdrawn from the bottom of the separator through line 42. 'I'he liquid comprises alight naphtha fraction in the gasoline boiling range. A portion of the liquid is passed through line 44 by pump 46 and returned to the top of the fractionating tower 26 as reflux liquid. A heavier fraction is withdrawn through line 48 as a side stream.

The light gasoline fraction withdrawn from the separator 36 through line 42 comprises a good motor fuel but is generally not suitable as aviation gasoline or aviation gasoline blending stock. The quality of this light naphtha may be further improved to a suitable level for inclusion in aviation gasoline by treatment with sulfuric or phosphoric acid or by treatment at 'YGO-900 F. with the same type of catalyst as that employed in the cracking step followed by rerunning t0 remove polymers produced in treating and light fractions boiling below pentane if a cracking catalyst is 4 employed. This improved quality is largely the result of removal of olens either by cracking or polymerization, these oleiins generally being of poorer quality than the remainder of the gasoline. ,During the catalytic cracking some aromatic constituents are formed, the higher cracking temperatures favoring the .production of aromatics. The quantity of benzene produced is relatively small but toluene and higher boiling aromatics are frequently found in as high as 90% concentration in narrow fractions of the gasoline boiling range. By choosing a boiling range of about 225 to 350 F. a fraction containing about 50 to 80% of arcmatics of reasonably good quality for inclusion in aviation gasoline can be obtained. Or a fraction may be selected with a boiling range of about 200 to 4007 F. However, such fractions contain non-aromatic fractions which are of extremely poor quality for inclusion in aviation gasoline. The quality of the fraction can be improved if the non-aromatic fractions are removed. However, the non-aromatic constituents, such as paraflins, boil in about the same range as the aromatics and it is not possible to separate the aromatic from non-aromatic constituents by distillation. Also, the fraction contains higher boiling aromaticsV which are of poorer quality than the lower boiling aromatics. According to my invention, a selected fraction from the catalytic cracking operation having a boiling range of about 200 to 500 Fgbut preferably 200 to 350 F. is further treated toV remove the non-aromatic constituents. Such a fraction contains about 65% aromatics by volume. The fractionation in the tower 26 is so carried out that the hydrocarbon fraction withdrawn as a side stream through line 4'8 has a boiling range of about 200 to 350 F. The selected fraction is passed through line 48 bypump 49 and is mixed with a diluent gas, such as steam, hydrocarbon gases, Vor the like, introduced through line 52. Preferably steam is used and the amount of steam may be about mol per cent 0f the mixture. More or less steam may be used. In some instances the diluent gas may be omitted. Y

The volatile fraction with or without an added diluent gas is passed through heating coil 54 in heater 56 where the temperature is rapidly raised to about l200 F, to about 1600 F, The time of reaction is maintained from about a few seconds, i. e, about 10 seconds, to a fraction ofV a second depending on the temperatures used, shorter times being used at the higher temperatures. The temperature during conversion or reaction is-sufficiently high to destroy substantially all of the non-aromatic constituents, such as the parain compounds, and at the same time olens, diolei'lns, and desired aromatic compounds are produced. During the reaction, ethylene, propylene and butylene, and in addition, butadiene, isoprene,` piperylene, etc., are produced. Also, during the conversion long alkyl side chains of aromatic rings are broken off.

The products of reaction are passed through line 58 to a quenching -tower 62 wherein the cracked products are immediately quenchedrto a temperature of about 600 to 1000o F. by the introduction of water through line 64. The quenching water is introduced into the top of the quenching tower 62 and the cracked products are cooled to below the boiling point of water so that normally liquid hydrocarbons are condensed together with` water and the hydrocarbons and water are collected in the bottom of the quench-` 'ingaid cooling tower '62."Uncondensed gases pass overhead through line 66. These gases contain a `small percentage of higher boiling hydrocarbons and the gases may be passed through a scrubbing zone for recovering valuable higher boiling hydrocarbons. Other means of recovery may be used, Y

The condensed water collects as a bottom layer 68 and is withdrawn from the bottom of the cooling and quenching tower 62 through line 14. The water may be further -cooled and recycled through line 64 to the tower 6.2 or may be withdrawn from the system. The condensed hydrocarbons from upper layer 12 are withdrawn through line 16 by means of pump 18. The condensed hydrocarbons .are passed-through a heating coil 82 in heater 84 and the vapors are passed through line `86 `to a second fractionating tower 92 for separating the desired aromatic fraction from other constituents. The lighter hydrocarbons consisting of substantially C4 to C6 hydrocarbons pass overhead through line 94. This lighter fraction combined with the gases from line 66 contains olens, such as ethylene, propylene, butylene, and also contains butadiene, isoprene, piperylene, etc., and this volatile fraction is preferably treated to recover any or all of the desired constituents.

Tar or fuel oil is withdrawn from the bottom of the. fractionating tower 92 through line 96. A heavy naphtha fraction is withdrawn from the lower portion of the tower 92 through line 98. The heavy fraction contains aromatics and may be added to ordinary motor fuels or recycled to the thermal cracking zone in furnace 56. This heavy naphtha fraction will contain 90% or more aromatics and may be used as a solvent, or is of high quality for use in motor fuel. Also, the heavy naphtha may be used as a source of naphthalene. If the charge stock to the thermal cracking step, namely, furnace 56, is cut to include the naphthalene from catalytic. cracking, i. e., with an end point of 430 F. or higher, the heavy naphtha withdrawn through line 98, also with an end point of 430 F. or higher, will contain l-40% of naphthalene. The naphthalene can be recovered in a much purer state by chilling the heavy naphtha, or preferably a narrow boiling fraction in the naphthalene boiling range (40G-430 F.), followed by filtration, the solid naphthalene then being suitable for the manufacture of many chemicals, such as phthalic anhydride, dyes, explosives, etc.

The desired relatively light aromatic fraction boiling in the aviation gasoline boiling range is withdrawn as a side stream through line |02. This aromatic fraction contains benzene, toluene, Xylenes, for the most part, and also includes a very small quantity of olefinic hydrocarbons which are not desired in the final aviation gasoline or aviation blending stock. The oleflnic constituents may be separated by passing the aromatic fraction through an acid-treating unit |04 wherein the aromatic fraction is treated with about 5-25 lbs. of sulfuric acid per barrel of aromatic fraction, after which the acid-treated material is rerun to remove polymerized olens. The concentration of the sulfuric acid is preferably from 90 to 98%. The oleiins may also be removed by treatment with fullers earth at about 30D-500 F. followed by rerunning to remove the polymerized fractions.

The refined aromatic fraction which contains more than about 90% of aromatics by volume is withdrawn through line |06. This fraction forms 48 to the `severe cracking .stepin coil 54,` The recovered fraction containing aromatics has an ill/IEP blending Value of about'275 to 3150 `and it `will be seen that this fraction can be employed to elevate much poorer quality of `materials to aviation gasoline of the desired perfomance.

If desired, the aromatic fraction .passing through line |06 may be fractionated to separate benzene and toluene, `and the benzene and tolu- -ene so separated form `nitration grade material of over 99% purity.

In the severe cracking step, the temperature `in degrees Fahrenheit must be equal to or greater than 1332-1016 log .S'+.10S1-15 where S is the actual time of contact in seconds at the tem- `perature in question. This formula and. its application is more fully described in my copending case Serial No. 485,797, filed May` 6, 1943.

The following example includes data obtained ina run using my process. The feed `stock `to the catalytic cracking unit was Southwest Louisiana wide cut gas oil having an API gravity of 32.2, a boiling range `of 40G-880 F., an aniline` point of 176 and viscosity at 100 F. of 45.3 seconds Saybolt. The temperature of cracking was 975 F. and the amount of conversion to gasoline and lighter constituents plus coke was 65% with 35% cycle oil remaining.

From the cracked products a 20D-400 F. fraction was separated and steam-cracked under the following conditions:

Coil outlet temp F 1400 Coil outlet pressure 1bs./sq.in. 15 Mol per cent steam Equivalent contact time at coil outlet temp.

sec. (approximately 1 The following yields on fresh feed were obtained:

Per cent by volume -350 F. cut 45.2 Benzene, on 145-350u F. cut 7.7 Tuolene, on F15-350 F. cut 29.2

(Represents yield of 13.2% of toluene as feed stock contained about 8.6% of toluene.)

Total aromatics, on 145-350 F. cut 91.9

The 145-350 F. cut was then clay-treated to produce a finished aviation gasoline blending stock. The clay-treating was carried out at about 400 F., 100 lbs/sq. in. and at a rate of 1 volume of the 145-350 F. fraction to 1 volume of clay per hour.

Yield, on 20D-400 F. feed per cent by voL- 40.6 Gravity, API 31.8 AFD-3C rating of blend--S-i-cc. tetraethyl lead per gallon (Blend consists of 20% by vol. of :aro-

matic blending stock produced by my process plus 72.6% by volume of reference fuel containing 1/2 of alkylate and 1/2 virgin naphtha, plus 7.4% isopentane with 4 cc. tetraethyl lead per gallon.) Reference IMEP of blend AFD-3C rating of baseS-|-cc. tetraethyl lead per gallon (Base consists of about 91% by volume of reference fuel containing 1/2 of alkylate and 1/2 of virgin naphtha, plus about 9% by volume of isopentane plus 4 cc. of tetraethyl lead per gallon.) Reference IMEP of base Blending reference IMEP (aromatics only) 287 While I `have shown one form of apparatus for carrying out my invention and have given 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:

A method of treating hydrocarbons which comprises charging a relatively high boiling hydrocarbon fraction in the gas oil boiling range to a catalytic cracking zone and maintaining it therein at a temperature in the range of 800 F. to 1050 F. to cause substantial cracking thereof, removing the resulting products from said catalytic cracking zone, separating from the removed products a gasoline fraction boiling between about 225 F. and 350 F., passing said last mentioned fraction to a thermal cracking zone maintained at a temperature of about 1400" F. and maintaining the fraction in said thermal cracking zone for a time of about 1 second to cause cracking of the fraction, removing the resulting products from said thermal cracking zone and fractionating the last mentioned removed products to separate a gasoline fraction boiling in the aviation gasoline boiling range.

The following references are of record in the ROBERT M. SI'IEPARDSON.

REFERENCES CITED file of this patent: 1

UNITED STATES PATENTS 10 Number Number

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