US2421614A - Treating hydrocarbon fluids - Google Patents

Description

Jupe 3, 194.7. H.' J. HALLu TREATING HYDROCARBON FLUDS Filed Dec. 15, 1943 uents containing side chains are too high Patented June 3, 1947 UNITED ASTATES PATENT. OFFICE TREATIN G HYDROCARBON FLUIDS Homer J. Hall, Cranford, N. J., nsslgnor to Standard Oil Development Company, a corporation of Delaware Application December 15, 1943, Serial No. 514.334A

2 Craims. 1

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

Catalytic cracking of petroleum fractions produces gasoline having a relatively high propor-` tion of aromatic constituents, especially when using relatively high temperatures. At the same time, olens, paraillns and na'phthenes are formed. The higher boiling aromatic constitboiling for aviation gasoline.

According to my invention, a catalytically,

cracked naphtha fraction having a, higher initial boiling point than the final boiling point of aviation gasoline is cracked under severe conditions to reduce the boiling points of the aromaticconstituents. If. no steam is added as diluent during the cracking under these severe conditions, a relatively small amount of paraillns is destroyed but an appreciab-le amount of the higher boiling aromatics arefcracked` down into aromatics within the aviation gasoline boiling range.

If steam is added in relatively large amounts as a. diluent, more parafiins are destroyedand the aromatics are broken down in a lesser degree. In the preferred form of my invention, no steam is added to the cracking zone but in some cases `I may add steam as a diluent to reduce tar and coke formation. i

The final boiling point of aviation gasoline may vary between rather wide limits. These limits are dictated partly by the maximum aromatic content desirable, the high octane value of these aromatics, and the manufacture of maximum yields of aviationfuel from a given amount of feed stock. These factors are balanced against the increasing difliculty of maintaining good fuel distribution in a carburetted multicylinder engine as the fuel volatility decreases. Under various circumstances aviation fuels having end points varying from 250 to 350 F. have been used, with the range from 295 to 335 F. being more common.

For purposes of illustration, the present invention will be described in terms of a fuel having a final boiling point of 320 F., it being understood that the `rhoice of this particular temperature is not to be construed as a ma'jor vpart of the invention or a limitation thereon.

An important purpose of lmy invention is to permit the use of existing thermal equipment for upgrading catalytic heavy naphtha boiling above the aviation end `point, to give an additional yield of high quality aviation fuel with- 2 out requiring additional catalytic cracking plant capacity. l

Another purpose of my invention is to crack an aromatic heavy naphtha under severe conditlons so as to break down non-aromatic materials completely into more desirable lightgases, while leaving the aromatics with only a slight decrease in boiling range, sufficient to bring them into the aviation fuel boiling range.

More specically, myinvention comprises se-vl lecting a catalytically cracked naphtha having a boiling range of about 320 to 450 F. and thermally cracking it at a temperature of about l200 F. to 1450" F. for a few seconds or less and then separating a fraction of about 220 F. to 320 F. boiling range. The resulting fraction contains a high concentration of aromatics which are desirable constituents in aviation gasoline or aviation gasoline blending stocks.

In the drawing, I 'have shown one form of apparatus which may b e used in carrying out my process.

Referring now to the drawing, the reference character I0 designates a, line for conducting hydrocarbon oil or vapors to be cracked. The oil may comprise any relatively heavy hydrocarbon, such as gas oil, and the hydrocarbon may be in vapor. or liquid form. When used as a liquid, the fraction is partly preheated and mixed with va sufiicient amount of catalyst or catalyst plus inert solids to raise the hydrocarbon oil to cracking temperature and to supply the heat of cracklng.

Powdered catalyst is introduced into line l0 from line I2. `Line I 2 is supplied with catalyst from a hopper H. Instead of using powdered catalyst, stationary beds' of pill catalyst or moving beds of granular catalyst may be used. Where powdered catalyst is used, the particles have a size between about 200 to 400 standard mesh' or finer. Any suitable cracking catalyst may be used, such as acid-treated bentonites, synthetic silica alumina gels, synthetic silica magnesia gels, etc. I prefer to use the synthetic silica alumina gels as they produce more aromatics at the temperatures used.-

The mixture of hydrocarbon oil and powdered catalyst at a temperature of about 900 to 1000 F., preferably 975 F., is passed through line I6 linto the bottom portion of a reaction zone i8.

l Catalyst and cil feedrates and contact times are adjusted so as to give a ratio of about one ton of oil per hour per ton of catalyst in the reactor, with' a catalyst/oil Weight ratio of the order of 20 to 1. The products of conversion in vapor form, together with entrained catalyst, pass over head from the reaction zone I8 through line 22 and are passed to a separating means 24 for 'into the bottom of the separating means 24 and are withdrawn through line 28. The catalyst particles are regenerated in any suitable manner and returned to the hopper I4 for reuse in the process.

The reaction vapors leave the separating means 24 through line 28 and are cooled by cooler 38 and then introduced into a fractionating tower 32. Uncondensed vapors and gases pass overhead through line 34 and condenser 36 and the cooled and'condensed vapors are passed toa separator 38 for separating C; hydrocarbon gases and lighter from liquid. The C4 and lighter gases pass overhead through line 42 and may be treated in suitable equipment to separate and recover desirable constituents for alkylation, isomerization, dehydrogenation, etc.

The condensed liquid is withdrawn from the bottom oi the separator 38 through line 44 and at least a portion thereof is returned to line 48 by pump 48 to the upper portion of the fractionating tower 32 as reflux. At least a portion of the liquid is withdrawn from the system through line 52. This light fraction has a boiling range of about 60 F. to 200 F., referred to as a C5-200 F, cut, and may be added to aviation fuel. Also,

this C5-200" F. cut may be hydrogenated (converting Cs oleiins into valuable isopentane) or acid-treated vor catalytically after-treated.

A heavier cut, 20G-320 F. is withdrawn from the tower 32 as a. side stream through line 53. This cut may be used in aviation gasoline as is or it may be acid-treated, or in some cases may be catalytically after treated.

A relatively heavy naphtha is'withdrawn from the fractionating tower 32 through line 54 and is further treated as will be presently described. A heavierfraction may be withdrawn through line 56 and used as heating oil, cycle stock, or in any other way desired. Condensate oil containing cycle stock and some entrained catalyst which was carried over with the vapors is withdrawn through line 58. Ii desired, the condensate oil may be recycled to the reaction zone I8 or it may be ltered or settled to recover the catalyst therefrom.

Returning now to the heavy naphtha fraction Vwithdrawn through line 54, this lfraction has a boiling range of about 320 F. to 450 F. and contains aromatic Vconstituents together with nonaromatic constituents. The initial boiling point of this fraction is dictated by the end point of the lower boiling aviation. fuel, which may vary from 250 to 350F., as discussed above, or more generally, from 295 to 335 F. The end point of the heavy naphtha fraction may vary from 410 to 500 F. or as high as 600 F., with, the higher boiling range giving increased total yields accompanied by an increased formation of tar and coke in the subsequent cracking step. A typical composition of this fraction is as follows:

Per cent by volume Aromatics 85 to 95 Parafns Oto 5 Naphthenes Oto 5 Oleflns Oto 5 The heavy naphtha fraction is passed through line 54 bypump 62 and may be mixed with a diluent such as steam introduced through line 64. In the preferred form of my invention where it is desired to break downside chains or higher boiling aromatics, I prefer to omit steam as a diluent. In some cases it may be desirable to use 80 mol per cent of steam to reduce tar formation. The heavy fraction is passed through heating coil 66 in a furnace or heater 68 wherein it is heated to about 10.50 F. to 1450 F. for about 100 seconds to 0.1 second, the shorter times being used for the higher temperatures. The products of conversion are passed through transfer line groups are a principal product.

12 into a quenching zone 14, together with quench oil introduced into transfer line 12 through quench line 1li.Y In this transfer line and quenching zone the temperature ofthe reaction products is quickly reduced to avoid undesirable reactions. Uncondensed vaporous products pass overhead through line 18, and any-heavy tar which separates out is withdrawn through line 88.

The overhead from the quenching zone and separator 14 passes through line 18 to fractionating tower 82. From this tower the light gases and uncondensed vapors pass overhead through line 84. These gasesmay be passed through an absorption tower'or other suitable equipment, to recover olefins and other desirable hydrocarbons. An additional side stream representing butanes, pentanes and other light liquid products may be withdrawn through line 86. A desired aromatic product fraction boiling between about 220 F. and 320 F. is withdrawn as a side stream through line 88. A heavier tar-free cycle stock is Withdrawn from the bottom of tower 82 through line 90. A portion of this cycle stock goes as quench oil,through line 16. Another portion may, if desired, be recycled to the cracking step. through line 94 opening into line 54. The'remainder of the cycle stock is withdrawn at 86.

The fraction withdrawn through line 88 is within the aviationy gasoline boiling range and contalns'a large percentage of `aromatic constituents. The fraction has the following composition:

` Per cent by volume Aromatics 95 to 100 Naphthenes .Oto 2 Olens Oto 5 f During the severe cracking in coil 88 the higher boiling aromatics are broken down to form aromatics which boil in the aviation gasoline boiling range. It will be seen that the fraction going to the thermal cracking zone 86 has a. boiling range above that of aviation gasoline. After the severe cracking a fraction boiling in the aviation gasoline is recovered.

During the cracking reaction, parafilnic compounds or long paraftlnic side chains on aromatic compounds are broken downl vinto smaller molecules. The aromatic nucleus is relatively much more stable under the conditions used, and aromatic fragments containing one or two methyl Practically no non-aromatic material remains in this boiling range, since the non-aromatic fragments are largely gaseous. As a result, the toluene-Xylene fraction from 22o-320 F. contains practically pure aromatics. Higher boiling cuts from the recracking stage will be equally aromatic when the aviation gasoline Withdrawn from line 53 has a higher end point, since the aromatics present in any boiling range will crack down somewhat, while non-aromatics go all the way to light fragments. In various cases it may or may not be desirable to include a benzene cut from 165-220 F. in the nal product, depending upon the amount of non-aromatic material remaining in this portion oi' the product. The final yield of aromatic blending stock, depending on the severity of the recrackiug stage and the aromatic content of the feed stock, is about to 30% by volume of the heavy naphthafra'ction passing through line 54.

The following examples include data obtained by severe thermal cracking of a 335 to 410 F. heavy naphtha fraction obtained by catalytic cracking of gas oil having a boiling range` of about 515 F. to 700 F., an API gravity of 32.4, the catalytic cracking being carried out at a temperature of 975 F. with a catalyst comprising synthetic silica alumina gel. The ratio of catalyst to oil by volume in the catalytic cracking step was about 5.4 to one. Total motor gasoline yield in this one pass operation was about 42.3 volume on feed stock. which is broken down into 22.9 volume aviation naphtha stock, 12.1 volume rentane and lighter, and 7.3 volume of 335-410J heavy naphtha.

In one example. a heavy naphtha fraction comprising a 335-410 F. cut was treated in a heated coil at 1295" F., for a contact time of 3.3 seconds. in the absence of steam. The products recovered included 12.3 weight of dry gas. 3.6 volume of a light fraction from butane through 220 F., 50.9 volume of cycle stock in the range of the feed. and 29.3 volume of aromatic 220335 product. analyzed 97-100% aromatics and had a specific gravity of 0.871.

As a further example, I would state that superior results are obtained by carrying out the thermal recracking step at a temperature of about 1100 F. for a heating time not more than about 4 seconds. Also, if the rec'racking step be carried out at a somewhat higher temperature, to wit. at 1200 F., a shorter treating time of about l second is suflicient for satisfactory results.

A similar run on the same feed stock at 1250* F. coil temperature, for 3.5,seconds contact time in the presence of 78 mol steam, gave 16.8 weight dry gas, 6.0 volume butanes through 220, 59.6 volume recovered as cycle stock having the initial boiling point of the feed, and 17.9% of aromatic aviation blending stock. The product in this case analyzed 96% aromatics.

While I lhave shown one form of apparatus in the drawing and have included examples of thermally cracking catalytically cracked heavy naphtha, it is to be understood that these are by way of example only and by illustration only, and various changes and mcdiiications may be made without departing from the spirit of my invention.

I claim:

1. A method of producing aviation gasoline The aromatic blending stock produced blending stock which comprises catalytically cracking a relatively high boiling hydrocarbon fraction at a temperature of about 900 F. to about 1000 F. to produce lower boiling constituents containing aromatic constituents and parafiins, separating from' .the cracked products an aviation gasoline fraction and a heavy naphtha fraction higher boiling than the endpoint of the aviation gasoline fraction and containing aromatic constituents too high boiling for inclusion in aviation gasoline, said heavy fraction boiling between about 320 F. and 450 F., thermally cracking the said heavy fraction at a temperature of at least 1200 F. for a period of time not in excess of a few seconds to crack high boiling aromatic constituents to lower boiling aromatic constituents and separating from the products of the last cracking step a fraction within the aviation gasoline boiling range and containing substantially only aromatic constituents.

2. In a method of producing aviation gasoline blending stock wherein ahydrocarbon fraction is catalytically cracked at about 925 F. to about 1000 F. in the presence of synthetic silica alumina gel catalyst to produce lower boiling constituents in the gasoline boiling range and containing aromatics, the steps which include separating from the cracked products a fraction having a boiling range of about 320 F. to about 450 LF., heating the said separated traction under non-catalytic conditions for about 1 second to a higher temperature than used in the catalytic cracking step and of the order o! 1200" F. to reduce the boiling point of higher boiling aromatics and separating from the last mentioned heating step a fraction containing aromatics and boiling below about 320 F.

. HOMERI J. HALL.

REFERENCES CITED The following references are of recordin the ille of this patent:

UNITED STATES PATENTS.

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