US2470680A - Process for cracking hydrocarbon oils - Google Patents

Description

Patented May 17, 1949 UNITED STATES PATENT OFFICE PROCESS FOR CRACKING HYDRO- CARBON OILS Application October 19, 1945, Serial No. 623,281

11 Claims.

This invention relates to process for cracking hydrocarbon oils and more particularly to a process of cracking hydrocarbon oils to gasoline in which the normally gaseous hydrocarbon prodnets are returned to the system to increase the production of gasoline.

The ultimate purpose of cracking hydrocarbon oils is to produce gasoline in as large quantities as is possible while maintaining quality, particularly with respect to anti-knock value expressed in terms of octane number. Cracking operations represent a compromise between yield and quality of gasoline. More drastic cracking of relatively heavy stocks tends to result in higher yields of gasoline, while more drastic cracking of relatively light stock, such as naphtha, tends to reduce the yield of gasoline. The more drastic cracking in either case tends to increase the yield of normally gaseous hydrocarbons. One of the more important limiting factors regulating the depth of cracking is the formation of carbon deposit in the conversion zone. Thus, the ultimate aim of an ideal cracking process is to crack as drastically as possible to obtain high yields of gasoline of high octane number but avoid high yields of gaseous hydrocarbons and large amounts of carbon deposit in the conversion zone.

One desirable method of increasing gasoline yield which is known to the prior art utilizes the normally gaseous hydrocarbon fractions, such as the C3 or C4 gases, or mixtures thereof. By this method, C3 and C4 gases are absorbed in the charging stock and delivered to the cracking zone where they are subjected to conversion conditions to increase the gasoline yield. The present invention is concerned with an improvement in this process.

It is an object of the present invention to increase the gasoline yield in a process for cracking hydrocarbon oils.

It is a further object of this invention to increase the gasoline yield in a process for cracking hydrocarbon oils together with normally gaseous hydrocarbons.

It is a further object of this invention to increase the gasoline yield in a process for cracking hydrocarbon oils wherein selected normally gaseous hydrocarbons are introduced at predetermined points in a conversion unit.

These and other objects of this invention are attained by the present process herein disclosed in which relatively light hydrocarbon oils, such as naphtha or light gas oil and normally gaseous hydrocarbons largely parafiinic in character, are subjected to conversion to gasoline under relatively drastic conditions and normally gaseous hydrocarbons of more highly olefinic character are added to the stream thus formed and the combined streams then subjected to further conversion under less drastic conditions.

More specifically, the process is applicable to the cracking of light hydrocarbon oils in which normally gaseous hydrocarbons, particularly C3 or C4 gases which are largely parafiinic in character, are absorbed by the light oil and a stream of this material passed through a cracking coll under relatively drastic conditions, such as temperatures in the range 900 to 1300 F. and preferably 1065 to 1125 F. for a relatively long period or" time. In another section of the cracking coil, normally gaseous hydrocarbons of more highly olefinic character are added to this stream, and the resultant combined stream is subjected to a temperature in the range 800 to 1200 F. and preferably in the range 1000 to 1060 F. for a relatively short period of time. It will be understood that operation within the broader temperature range given will depend upon the stock being used but that in any case the first section of the cracking tube is subjected to more drastic conditions (i. e., higher temperatures and, usually, longer times of contact) than the second section.

It will be understood that the time of residence in the heating coil will be varied depending upon the stock being charged and the particular furnace being used. The time factor is particularly dependent upon pressure, temperature and the heating curve for the furnace and the latter in turn is dependent upon the design and operation of the furnace. The treatment in section I of the coil has been described as relatively drastic, but the term relative is used with reference to section II rather than with usual operating procedures. The following ranges are representative of the time of residence in each section of the heating coil:

Section I: 0.010 to 0.060 cu. ft. coil volume per barrel of charge per day Section II: 0.001 to 0.020 cu. ft. coil volume per barrel of charge per day By the term "normally gaseous hydrocarbons largely parafiinic in character is meant normally gaseous hydrocarbons and particularly C3 or C4 gases containing less than about 25 per cent oleflns. By the term normally gaseous hydrocarbons of more highly olefinic character is meant normally gaseous hydrocarbons and particularly C3 or C4 gases containing more than about 25 per cent olefins, but in any case contalning a substantially greater amount of olefins than the largely paraffinic gases. The amount of highly olefinic gas, which may be from an outside source, shall preferably be in the range of 0.1 to 2.0 volumes of gas on a liquefied basis per volume of light hydrocarbon oil. While the operational pressures will vary, they will usually 'be in the range of 500 to 2000 pounds per square inch.

By the use of the present process, it is possible to obtain a gasoline of predetermined octane number and even with the higher octane gasolinea substantially increased yield is obtainable, as, for' lower-gas recirculationrates' are used in-obtaining.

thesame yield as inthe-conventional' process, or for a greatly increasedyield of the conventional process of the presentinvention allows for the samegas recirculationra'tes. It may be possible to obtain'both'low'er gas=recirculation rates and higher yield but any substantial lower gas recircula'tion rate tends to-'gi-vea-"corresponding reduction inyieldand conversely-,any appreciable increase in yield'is accompanied b'y' a higher gas recirculation rate; 'The following table gives data comparin a, conventionaloperation wherein gas absorbed in naphtha"isputthrough the furnace in the normalmanner'o'f theprior art and-the improved process usingole'fin' gas injection at the point 'in' the coil'described herein. The naphtha in the following table' is an" Eastern Venezuela naphtha containing about 16-volumeper cent of aromatics.

TABLE I Gasinjection on naphthawithoutside propanepropylene'gas"chaTgefcontainin -GO propylene Normal Oper- Gas Injecation tion Run Number 1 2 3 4 Gas to Furnace, F .i 600 700 FurnaceOutlet'lempcraturefF: Q

Section 1 i 1,:090 1,105 1, 070 1, 070 Section 2 1, 050 l, 055 FurnacaPressure, lbs.-/sq nle 1, 500 1, 500' 1, 500 1, 500 Furn'. Vol.-above'750'F., cu. .-/bbl-.-

thruput/day: Section 1 1 -0. 016- 0.016 0. 016 0. 016 Sectio'n2 0.003 0. 003 Gas Recycle, VQL'percent of Naphtha Charge 408 374 391 317 Gas Charge, Vol. Percent of Naphtha Charge 62 60 59 69 Yields, h Vol Percent of N aphtha s Motor Gasoline 108.1- 100. 2 113. 5 110. 9 Excess Butane-Butene. 0. 9. 0. 0- 3. 2 -0. 9 Propane-Propene 7. 7 4. 2 2. 1 7. 3 Gas (C2 and Lighter), F 0. E... 18. 2 22. 6 9. 7 10. 4 Tar l 1 8. 1 l0. 9 16.- 8 l9. 8

Total 1430: 137. 9 139.0 146. 4 Octane N umberof -M0tor- Gasoliner... 77. 6 78. 4 78. 0 78. 9

r. 0; =E.=rue1 oil 'equivalent Fromyield octane"curves-based upon figures in thistable "itis" demonstrated-that for a 78.5 octane numbergasolinathefprocess"of the present invention termed gasinjectiomabove givesan average yield of 13.2 volume per cent more gasoline than is obtained in the normal yield. It will also be noted from the table that an increase in octane number of 1.3 was obtained while also obtaining an increase in gasoline yield of 2.8 per cent. Thus, it is demonstrated that both gasoline yield and octane number may be increased simultaneously by'the present invention as well as a very substantial increase in either octane rating or gasoline yield if the other is held constant.

The data Table II below is similar to that given in Table I except that the naphtha used in this case was a Pennsylvania Mid-Continent naphtha containing only 6 volume per cent of aromatics.

' TABLE II Gas injection of Pennsylvania Mid-Continent naphtha with outside gas Normal Gas Normal Gas Opera- Injee- Opera- Injection tion' tion tion Propane Propyl- Butane-Butane ene 60 Vol. Per 52 Vol. Per Cent Cent Propylene Butenes Gas to Furnace, F 600 600 Furnace Outlet Temporature, F.:

Section I l, 090 1, 075 l, 000 1, 080 Section II 1, l, 040 Furnace Pressure, Lbs/s 1n. (Inlet) 1, 500 1, 500 1, 500 1, 500 Furnace Vol. Above750 F.,

Cu. ft./bbl. thruput/day:

Section I 0.016 0. 016 0. 016 0.016 Section -II 0. 003 0. 003 Gas Recycle, Vol. Per cent of Naphtha Charge 290 268 276 229 Gas Charge, Vol. Per cent of Naphtha Charge 39 42 39 41 Yields, Vol. Percent of Naphtha Charge:

Motor Gasoline 88. 1 97:6 86. 2 101. 6 Excess-Butane-Butene 0.0 0. 2 0.0 1. 6 Propane-Propene 7. 8 2. 8 7. 2 4. 4 Gas, C1 and Lighter,

F. O. E 20.1 18.4 21.2 16.1 Tar 9. 6' 8.6 13. 1 i 8. 0 Total 125.6 127. 2 127. 7 131. 7 Octane Number of Motor Gasoline 76.0 76. 8 75. 7 76. 5

F. O. E.=fuel oil equivalent.

From yield octane curves based'on the data above it was foundthat for a 76.8 octane number gasoline obtained by the use of propane-propylene the process of the'present invention gave an average of 10.6 volume'per cent more gasoline than the conventional operation; From the same curve 'it was found that'fora 76;5 octane number asoline obtained by the use of butane-butene the process of the preserrtinvention'gave an average of 20.0 volume per cent more gasoline than the conventional operation. This shows that the operation of the present invention'is more favorable by the use of the C4 hydrocarbon out than from the C3 hydrocarbon cut and also that the advantage over the prior art is more marked when using the lower aromatic containing stock.

While I am not prepared to explain the reactions precisely, it is believed that both'polymeriization and alkylation'reactions are-entered into by the olefinic gases. Theoretically, the highest possible yield of gasoline'would lee-produced by quantitative alkylation, but this optimum is not actually met, due 'to-theinfiuence' of competing polymerization reactions which consume some olefins. The present process, however, presents a very favorable balance between alkylation and polymerization reactions and a very high yield of gasoline is realized.

A preferred form inwhichmyinvention may be practiced and embodied, by way of example and illustration, is shown in the drawing in which The single figure represents diagrammatically the present invention as applied to a single-coil cracking process.

It will be understood that this drawing is intended to serve primarily as a flow sheet and aD- paratus details, such as heat exchangers, valves, pumps, etc., are omitted, since they will readily suggest themselves to one skilled in the art.

With reference thereto, there is shown a flow sheet of the present invention as applied to a socalled single-coil cracking process. Actually, the coil illustrated is divided into two sections which, for convenience, will be referred to as separate coils in and I! in furnaces l2 and Hi. The feed, which comprises naphtha in which is absorbed largely saturated C3 and C4 gases, enters the coil Iii by conduit I5 and is subjected in furnace l2 to relatively drastic conditions, as, for example, a temperature in the range 1065 to 1125 F. At the beginning of coil H, outside gases, of more highly olefinic character, are introduced by conduit Hi and the conversion conditions in furnace [3 are substantially milder than in furnace i2. For example, the temperature may be in the range 1000 to 1060 F. and the time somewhat shorter than in the coil ID. A quench from conduit 2| is applied to the products from the furnace, as indicated in the drawing, and the products are sent by conduit l8 to tar stripper l9 wherein the tar is removed by conduit 2i! and the overhead passes to conduit 22 to a stabilizer 23 wherein the gasoline is taken out by conduit 25 and the overhead gases pass by conduit 26 to absorber 2'! where they flow up through a quantity of naphtha supplied from an outside source by conduit 29. Unabsorbed gases leave by conduit 30 and the naphtha containing absorbed C3 and C4 gases is returned by conduit l5 to crackins coil Hi.

The hydrocarbon gases of more highly olefinic character are taken from an outside source and they, for example, may contain a propane-propylene mixture containing 60 per cent propylene.

Further, the process illustrated is one in which the largely saturated gases are recycle gases from the process, but they could be outside gases, although no particular advantage would be gained thereby. When the highly olefinic gases are introduced at conduit l6, they lower the temperature of the stream at that point, thus avoiding the necessity of a quench or other cooling means. A pressure release valve may be installed between coils Iii and H to cause a pressure differential between these sections if this is desirable. Likewise, the coil may be enlarged or contracted at this point, if desirable, or as illustrated coil lfi may be longer than coil M. It will be understood that the point of division between coils Ii] and H need not be a fixed point and may be changed as conditions demand. Also alternately, the introduction or the highly olefinic gas may be at several points, as shown by the dotted line in the drawing, instead of at one point.

While naphtha is the preferred charging stock of this process, other cracking stocks may be used, such as, for example, kerosene or light cracked gas oil or recycle stock from the reduction of pressure still tar.

The process of the present invention may be applied to the use of heavy oil as the original charging stock, but some method should be used to convert the oil to a lighter material for gas injection.

While I have described the process as using either gas fraction from any source, it is preferred practice to obtain the highly olefinic gases from other cracking units not utilizing gas absorption and the gases largely saturated will be produced in the process because the recycling cuts down the olefin content. Alternatively a part of the highly olefinic gases may be obtained from the present process itself by dividing the recycle gases into two fractions, one predominantly olefinic and the other predominantly paraffinic.

The present process is particularly adaptable to a continuous operation and it is particularly economical in this respect, since it allows for a greater conversion per pass than is usually attained. This is obtained because the formation of coke is relatively small and the formation of a good quality tar somewhat larger than conventional methods, as well as because of the very low gas yield and hence low gas recirculation rate. While the illustrations have been concerned with cracking processes in which no reaction chamber has been used, the invention is not so limited.

Thus I have described a new and useful process for producing larger yields of gasoline with relatively small yields of coke and gas, which comprises subjecting a stream of light hydrocarbon oil containing largely paraffinic gases to relatively drastic cracking conditions, adding to the stream more highly olefinic gases and subjecting the combined stream to relatively less drastic cracking conditions.

What I claim is:

1. A process for cracking hydrocarbon oils to obtain asoline wherein a stream of light hydro carbon oil containing normally gaseous hydrocarbons largely paraflinic in character is subjected to relatively drastic cracking conditions and normally gaseous hydrocarbons of more highly olefinic character are added to the stream and the combined stream subjected to further crackin under relatively less drastic conditions.

2. A process for cracking hydrocarbon oils to obtain gasoline wherein a stream of light hydrocarbon oil containing normally gaseous hydrocarbons largely paraffinic in character is subjected to relatively drastic cracking conditions and normally gaseous hydrocarbons of more highly olefinic character are added to the stream and the combined stream subjected to further cracking under relatively less drastic conditions, said relatively drastic conditions comprising a temperature in the range 990 to i390 F. for a relatively lon time and said relatively less drastic conditions comprisin a temperature in the range 806 to 1200 F. for a relatively short period of time.

3. A process for cracking hydrocarbon oils to obtain gasoline wherein a stream of light hydrocarbon oil containing normally gaseous hydrocarbons largely paraflinic in character is subjected to relatively drastic cracking conditions and normally gaseous hydrocarbons of more highly olefinic character are added to the stream and the combined stream subjected to further cracking under relatively less drastic conditions, said relatively drastic conditions comprising a temperature in the range 1065 to 1125 F. for a relatively long time and said relatively less drastic conditions comprising a temperature in the range 1000 to 1060 F. for a relatively short time.

4. A process for cracking hydrocarbon oils to obtain gasoline wherein a, stream of light hydrocarbon oil containing normally gaseous hydrocarbons largely paraftinic in character is subjected to relatively drastic cracking conditions 7 and normally gaseous hydrocarbons of .more highly olefinic character are added to the stream and the combined stream subjected to further cracking under relatively less drastic conditions,

said gases largely paraffinic in character containing less than per cent olefins and 'said highly olefinic gases containing more than 25 per cent olefins.

5. A process for cracking hydrocarbon oils to obtain gasoline wherein a stream of light hydrocarbon oil containing normally gaseous hydrocarbons largely paraflinic in character is subjected to relatively drastic cracking conditions and normally gaseous hydrocarbons of more highly olefinic character are addedto'the stream and the combined stream subjected to further cracking under relatively less drastic conditions, said highly olefinic gases'containing'morethan 25 per cent olefins and being present 'in an amount between 0.1 and 2.0 volumes on a liquid basis per volume of light hydrocarbon oil.

6. A-process for cracking hydrocarbon oils to obtain gasoline wherein a stream of .naphtha containing normally gaseous hydrocarbons largely parafiinic in character is subjected to.-

containing about 60 per cent olefinsand beingpresent in an amount between 0.1.and 2 .0 volumes on a liquid basis per volume of naphtha.

8. A process for cracking hydrocarbon oils to obtain gasoline wherein a-stream of light hydrocarbon oil containing normally gaseous hydrocarbons largely paraflinic in character is subjected to relatively drastic cracking conditions and normally gaseous hydrocarbons of more highly olefinic character are added .to the stream at a plurality of points beyond the zone of relatively drastic cracking and the combined stream subjected to further cracking under relatively less drastic conditions, said gases largely .paraffinic in character containing less than 25 per cent olefins and said highly olefinic gases containing more than 25 per cent olefins.

9. A process for cracking hydrocarbon oils to obtain gasoline'comprising allowing a stream of -8 naphtha to absorb normally gaseous hydrocar- :bOIlS largely paraifinic in character produced as hereinafter described, passing said stream of naphtha containing absorbed gas to a cracking coil wherein the stream is subjected to relatively drastic cracking conditions, adding normally gaseous hydrocarbons of more highly olefinic character from an outside source to said stream, subjecting the combined stream to further cracking under relatively less drastic conditions, quenching the stream, removing any tar, removing the gasoline product, and passing the gaseous products largely parafiinic in character to said naphtha absorption.

10. -A process for cracking hydrocarbon oils to obtain-gasoline wherein a stream of light hydrocarbon-oil containing normally gaseous hydrocarbons largely parafiinic in character is subjected to relatively drastic cracking conditions and normally gaseous C4 hydrocarbons of more .highly olefinic character are added to the stream .and the combined streamsubjected to further cracking under relatively less drastic conditions, said relatively drastic conditions comprising a temperature in the range 1065 to 1125 F. for a relativelylong time and said relatively less drastic conditions comprising a, temperature in the range 1000 to 1060".F. for a relatively short time.

11. ,A process for cracking a naphtha low in aromatics to obtain gasoline comprising allowing a stream of naphtha to absorb normally gaseous .hydrocarbons largely paraffinic in character produced as hereinafter described, passing .said stream-of naphtha containing absorbed gas to a cracking-coil wherein the stream is subjected to relatively drastic cracking conditions, adding normally gaseous hydrocarbons of more highly olefinic character from an outside source to said stream, subjecting the combined stream to further cracking under relatively less drastic conditions, quenching the stream, removing any tar, removing the gasoline product, and passing the gaseous products largely parafiinic in character to said naphtha absorption.

HAROLD BEUTHER.

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

UNITED STATES PATENTS Number Name Date 2,017,874 Sullivan Oct. 22, 1935 2,022,221 Sullivan Nov. 25, 1935 2,135,014 Ostergaard Nov. 1, 1938 2,137,825 Sullivan Nov. 22, 1938 2,240,434 Atwell Dec. 29, 1938

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