US2385325A - Catalytic cracking of petroleum oils - Google Patents

Description

Sept 25, 1945. w. ABAILEY, JR

CATALYTIC CRAKING 0F PETROLEUM OILS Filed June 19, 1944 NJIIIIIIIIIII im.. .cm

LOtPcOwNE UE 006W EHII' Invenl'or: William A.Bnleg Jn Bg his Aorneg; g%

:E200 @Enamel tions taken from the middle Patented Sept. 25, 1945 OFFICE CATALYTIC CRACKING OF PETROLEUM OILS William A. Bailey, Jr., Wilmington,

Calif., assignor to Shell Development Company, San Francisco, Calif., a corporation of Delaware Application June 19, 1944, Serial No. 541,051 '1 claims. (ci. iss-5o) This invention relates to an improved process for the production of valuable products from petroleum involving catalytic cracking. More particularly the invention relates to a combina` tion of process steps whereby excellent yields of high quality gasoline may be obtained along with improved yields of other valuable products from that portion of petroleum oils boiling above gasoline, v l

When petroleum oil is received at the renery the gases and so-called straight run gasoline are removed leaving a partly reduced crude. The reiiner is then faced with the problem of producing the maximum quantity of quality products from this partly reduced crude. One of the most valuable products desired is gasoline, and considerable effort and attention has therefore been given to various ways and means for producing the maximum quantity of gasoline of the best obtainable quality. One of the most important of the available tools at the reilners disposal is catalytic cracking. Due to the large demand for gasoline, catalytic cracking is becoming almost universally used. Even with the best means available, however, it is not practical to convert all of this partly reduced crude to gasoline and there is left therefore a considerable volume of by-product materials of lesser value. In the past the emphasis has been largely on the production of the maximum quantities of gasoline of the best quality and the by-products formed or left have largely determined the quantity and quality of secondary products such as fuel oil, kerosene, stove oil, asphalt, coke, etc.

The various fractions of the partly reduced crude are considerably different in composition and some are much more amenable to catalytic cracking than others. In general the preferred feed for catalytic cracking units are those fracof the partly reduced crude. These fractions are of the nature of light gas oil or stove oil. The lower boiling components of the nature of heavy gasoline, naphtha and kerosene, are more refractory and are generally used in secondary products or treated by thermal methods, although in a few cases they are catalytically cracked along with the light gas oil. Also, the bottom fraction, or reduced crude, is not suited for vapor phase catalytic cracking. In practice the gas oil is removed as completely as possible under ordinary fractionation conditions to leave a reduced crude which is suitable for use as fuel oil. In a few cases this reduced crude has been vaporized in a so-called contact vaporizer and the vapors cracked along with the gas oil. 'Inis is not usually economical however. since no fuel oil is produced, and a large amount of coke must be burned in the contact vaporizers. In ,all of these methods poor quality Diesel oil is produced as a by-product. When handling the petroleum by these methods excellent yields of quality gasoline are generally produced, but only at the expense ofthe quantity and quality of various other petroleum products. It is the purpose of this invention to provide a method whereby the petroleum may be utilized to better advantage by producing quality gasoline from the more refractory fractions'of the partly reduced crude without sacricing yield or quality of secondary products.

It has been found that certain refractory frac- -tions of petroleum, such in particular as the lighter naphtha fractions and the very heavy fractions, may be advantageously cracked catalytically if these fractions are cracked together under suitable conditions, and that by so doing excellent yields of quality gasoline may be produced without sacrifice of quality Diesel fuel or fueloil,

.The process of the invention in ltsbroader aspect comprises separating the partly reduced crude by distillation into a light naphtha fraction, a heavy reflux condensate, and a reduced crude, subjecting the reduced crude to a flash distillation under reduced pressure to produce a heavy flashed distillate and a'heavy residue, catalytically cracking the heavy flashed distillate together with the light naphtha under selected conditions, separating from the product a light fraction containing gasoline components and a heavy condensate,` and blending the heavy condensate with the heavy residue to replace the `heavy flashed distillate and produce a saleable fuel oil.

The above general outline of the process of the invention will be amplified and the more important features and modifications will be rie--v scribed in more detail in the following description in connection with the accompanying drawing in which a specific embodiment of the invention is set forth for purposes of illustration. In the accompanying drawing, which is in the form of a simplified flow diagram,`there is shown by means of diagrammatic gures, not drawn to scale, one suitable assembly of apparatus arranged for operation according to the present process.

The charging stock, when operating according to the present invention is a crude petroleum or/ one from which the gasoline has been substantiaiiy removed. If a crude petroleum containing gasoline is used, the gasoline is preferably rst removed to leave a partly reduced crude having an initial boiling point of at least 300 F. The partly reduced crude is then separated by distillation into a naphtha fraction, a heavy reflux condensate and a reduced crude.r The cut point between the naphtha and the reiiux condensate may vary considerably, but is preferably between about 400 F. and 500 F. This separation may be effected in conventional equipment in a numbcr of ways. In the modification illustrated in the attached drawing the crude petroleum enters via line I and is charged by pump 2 to a stripping column 3 wherein gasoline and naphtha. are separated. The gasoline and naphtha are removed overhead via. line 4. Part of the condensate is returned as reflux and the remainder is passed to a fractionation column 5 wherein gasoline is separated from the naphtha.. The gasoline passes overhead via line 6. The napbtha fraction having a boiling range of for instance, 320 to 400 F. is removed via line 1. The bottom product from column 3 is passed through e. suitable heater and then via line 8 to a fractionating column 9. In column 9 substantially all of the hydrocarbon components which can be removed at atmospheric pressure without substantial cracking are removed. The various products may be removed in a single stream or may be segregated into various fractions as desired. Thus, for example, in the arrangement shown, a heavy naphtha or kerosene fraction is removed via line I0; a light gas oil fraction suitable for use as Diesel fuel is taken offkvia line Ii; and a heavy gas oil fraction suitable for use as Diesel fuel or for stove oil is taken oif via line I2. The bottom product is a reduced crude suitable for use as fuel oil.

The reduced crude is passed throughffheating coils in a suitable heater and then via line I3 to a vacuum fia-sh column I4 wherein it is vacuum dashed under conditions chosen to remove overhead from between about 40% and about r15% of a heavy flashed distillate. One set of typical conditions isLfor example, a temperature of about 750 F. and 100 mm. absolute pressure. Steam may be injected via line I6 to aid-in decreasing the residence time and prevent cracking. The ashing operation does not involve any appreciable amount of cracking. This is indicated by the average molecular weight of the flashed distillate. Thus, the average molecular weight of the asheddistillate when taking 45% overhead is about 280, and the average molecular weight when taking '70% overhead is about 345. Ingeneral a distillate having an average molecular weight in this range is indicated. This flashed distillate, it is seen, represents the heaviest portion of the petroleum that can be vaporizet with available equipment without substantial cracking. It is dilcult to vaporize, and invariably contains appreciable amounts of nitrogen compounds and other impurities.

The material removed from the bottom of the flash column I4 is a heavy viscous residue. This material is totally unsuited for fuel oil, but pro duces a readily saleable fuel oil when blended with aromatic reux condensate as hereinafter described. n

In a preferred modification of the process of the invention the iiashing operation is carried out under somewhat more severe conditions to effect a minor amount of cracking. The amount of cracking is adjusted to give between about 50% peinture.

and '75% of a flashed distillate having an average molecular weight between about 280 and 360. This may be and is preferably effected With the formation of not more than 1% gas and not more than 1% of gasoline. The conditions of tempressure and residence time to give this result cannot be stated with any degree of definiieness due to the interrelaton of these factors and. the diiierences due to the particular petroleum source and apparatus effects. However, these conditions are adjusted in the known manner and may be readily arrived at in any particular case. The distillate obtained under such conditions is hereinafter referred to as flash cracked distillate.

The iiashed distillate or flash cracked distillate produced as described is combined with the refractory light naphtha fraction from Vcolumn 5 and the mixture is subjected to suitable catalytic cracking treatment. The catalytic cracking treatment may be effected in any one of the various known systems and with any of the proprietary cracking catalysts. For reasons which will be pointed out below, however, the catalytic cracking systems employing iinely divided catalysts which`are continuously regenerated are particularly suitable for this operation. Very suitable catalysts are, for example, the activated clays such as Filtrol, and the synthetic catalysts such as the composites of silica-alumina, boric oxide-alumina, boric oxide-alumina-silica, silicaalumina-zirconia, silica-magnesia, etc.

As in all cracking processes, the conditions in the cracking zone may vary individually over a considerable'range. The approximate ranges of the individual conditions for optimum results are as follows:

Temperature 950--1050 F. Pressure 0-50 p. s. i. g. Weight hourly space velocity 0.5-4 lb/hn/lb. Catalyst oil ratio (fiuid system) 10: 1-30zl, Steam 045% oi oil In the system illustrated in the attached flow diagram the ashed distillate coming from the vacuum flash column via line l5 is blended with the naphtha fraction from column 5 and the mix ture is passed via line 1 through the coils of a suitable heater l1. Steam may be added ii desired via line I8. The pre-heated mixture picks up regenerated flnely divided catalyst entering via standpipe I9 and the mixture of oil tapers and finely divided catalyst is passed *o a cracking reactor 20. 'The ilows oil vapor and catalyst are adjusted in the known manner to maintain a bed of the catalyst in reactor 20 in a so-called iiuidized state. Catalyst is continuously withdrawn from cracking reactor 20 -via standpipe 2i. This material is picked up by a stream of air or other regeneration gas and c'arriedvia line 22 to a fluid c'nzafvst regenerator 23. The spent regeneration leaves the regenerator via line 24. Regenerated catalyst is removed from the vregenerator via standpipe I9. The oil vapors leave the reactor via line 25 and pass to a fractionator 2d, wherein the gasoline and gas are separated from the heavier cracked and uncracked material. The gasoline and gas are removed overhead via line 2t. The gas which is separated and removed via line 28 may be sent to a suitable adsorption plant. Part of the gasoline is returned to the column 2E for reflux and the remainder is withdrawn via line 29.

A heavy highly aromatic condensate is removed via line 30 and 9, heavy residue is removed via line 3i. This heavy residue contains a small amount of catalyst and may be advantageously recycled back to the crackingr reactor via lines 3| and 1. The condensate consists largely of highly refractory aromatic hydrocarbons produced in the cracking zone. This material is passed to a mixing tank 32 wherein it is blended with the hot vacuum ilashed residue, coming from the vacuum flash column i4 via. line 33. A portion of this material may be recycled via line 311 to fractionator 26 to serve as reflux. In View of the highly aromatic nature of the condensate it blends well with the very heavy vacuum flashed residue to produce a stable and superior fuel oil. Also due to its extreme refractivity and low ratio of Yhydrogen to carbon it is a very poor cracking stock and also a very poor Diesel fuel. On the other hand, this relatively small volume of material is capable of converting a relatively large `volume of heavy vacuum flashed residue into a superior fuel oil. Thus, in general it requires only about 50 parts of the aromatic condensate to convert 100 parts of the heavy flashed residue into a superior 100 second fuel oil. When blended 1:1 the heavy ashed residue is converted to a stable second fuel cil meeting the Navy Special grade specifications.

The relative amounts of the light naphtha and liashed distillate available from a given petroleum depends upon the particular petroleum, the boiling range of the naphtha fraction, and the depth of flashing, and may vary considerably. .I n some cases the available refractory naphtha of say 32o-450 F. boiling range may be more than enough to forni a satisfactory blend with the flashed distillate. In this case the boiling range of the light naphtha may be reduced to say 320- 405" F., or part of the naphtha may be used for other purposes. Also, certain other heavy residues may be added to the reduced crude to increase the amount of flashed distillate. In'general ratios of :dashed distillate to naphtha of from about 1:1 to about 10:1 are preferred.

It is to be noted that according to .the prevalent belief in the art, the described blend of ilashed distillate and light naphtha would not be considered a desirable feed for catalytic cracking. The light naphtha, it will be noted, contains appreciable quantities, and may even consist essentially, of hydrocarbons which can properly be considered as gasoline components. In fact, the light naphtha could in many'cases also be called a heavy straight run gasoline. When cracking gas oill stove oil, and similar intermediate clistillates, it is known that the presence of gasoline constituents in the feed is quite hanmful. The prevalent belief in the art is that such gasoline components should be absent from all catalytic cracking stocks. In the present process this harmful effect of gasoline components is not no-` ticed, and as pointed out above, the light naphtha in the present process is distinctly beneficial in certain respects.

Example A crude petroleum was fractionated as described above to produce various products suchV Table I Flash dis Naphtha miste Gravity ".fl. P. I 41.9 26.7 Aniline point, FM .5 155 Sulfur, percent by We 19 Pour point, "F Molecular weight.

. B. P. Less than 100 F., perccnl by volume The conditions used and the yields of products are shown in Table II.

Table II Run number Flaslicd distillate/naphtha ratio. 1:1 3:1 3:1 3:.1

Reactor conditions Pressure. 11.5. i. g l2 12 l2 12 Temperature, uF 1,002 1,000 1. 000 1.002 Space velocity, lh/hr/ lh 0. 99 0. 97 1.00 0. 63 Catalyst/oil. weight ratio 25 25 21 23 Catalyst bed density, Ib/lt. .5 34. 0 35. 8 36.0 Catalyst holding time. minute .4 2. 5 2. 8 4. l Steam, percent of feed .3 19 19.1 16.7

Regenerate.' conditions Pressure p.s.i.g l2 l2 l2 '12 Temperature, F.. 1,122 1,124 1.127 1,121 Catalyst bed density, lb/i' t 34. 3 29. 7 33. 2 32.8 Catalyst holding time, minutes 6. 4 6. 4 7. 2 6.8 Carbon on spent catalyst, percentm.. 0529 0.37 0. 39 0. 56 Carbon oli regenerated catalyst.. percent 0. 03 0. 05 0. 06 0. 10

Yields, percent B. W.

2-217 i 4.0 4.6 6.o :1. omi-201 3.3 2.9 2.1 2. cuasi-288 F 4.1 3.a 4.2 4. 28B-320 F 2.8 3.9 2.6 2. s20-340 r s i 4.4 5. 4 4. ai0-400 r 15.0 11.7 10.1 7. 400I 21.9 26.9 27.8 24. coke 0.4 8.2 7.0 12.

The 400 E+ material remaining after removing the gases and gasoline is highly refractory and highly aromatic. Thirty-four parts of the 400 F.+ fractions blended with sixty-six parts of the heavy flashed residue gave a Navy No. 2 grade fuel oil which was superior to the usual fuel oils of this viscosity prepared with cracked residues. Fifty-one parts of the aromatic 400 F.+ material blended with forty-nine parts of the flashed residue produced a superior Navy Special grade fuel oil.

oils.

The operations described in the above to illustrate the invention may be modified in many par ticulars such as the arrangement and order of the fractionation. steps, types of equipment used, etc., while still employing the essential features of separating by fractional distillation (l) a naphtha fraction, (2) an intermediate fraction of the nature of gas oil and, (3) a reduced crude, subjecting the reduced crude to the described treatment to produce a flashed distillate or a flash cracked distillate, subjecting the flashed distillate or flash cracked distillate together with the naphtha fraction to a catalytic cracking treatment, separating gasoline and heavy aromatic condensate from the product and blending the flashed residue or the flash cracked residue with the heavy aromatic condensate. However, the cracking operation is preferably one in which a continuously regenerated finely divided catalyst is used. As pointed out above, the naphtha fraction cracked according to the present process is quite refractory and requires fairly high crackingl temperatures. When this material is cracked alone it is difficult to maintain the optimum high cracking temperatures. On the other hand the flash distillates and flash cracked distillates invariably contain considerable amounts of impurities such as nitrogen compounds. If these materials are cracked alone, large amounts of carbon are formed and the conversions are low, ap-I parently due to the poisoning effect of the nitrogen bases. When, however, the naphtha fraction and the flashed distillate or flash'cracked distil late are blended and cracked together these dis advantages tend to cancel each other to a certain extent. Thus, the naphtha tends to reduce the concentration of nitrogen bases and the flash distillate tends to increase the carbon production over that of the naphtha alone, thus providing more heat in the regeneration zone. This heat is largely conveyed to the reaction zone by the hot regenerated catalyst. Furthermore, the flashed distillates and flash cracked distillates are quite heavy and difficult to vaporiae and maintain entirely in the vapor phase without the use of a large amount of steam. The relatively light naphtha acts as a diluent and is very beneficial in this respect also.

The present process, it will be seen, allows the production of considerable yields of excellent Diesel fuel from the virgin naphtha without impairing the quantity or quality of gasoline produced. The gasoline is produced largely from the flashed distillate or flash cracked distillate while taking advantage of some gasoline production from the refractory naphtha and at the' same time producing therefrom a refractory aromatic condensate which Iis compatible with ashed residue and flash cracked residue and may be used to convert these residues to superior fuel Thus, the process of the present invention allows the petroleum to be utilized to better advantage without sacrificing yield or quality of secondary products.

I claim as my invention:

1. In the production of useful products includ.- ing gasoline and fuel oil from petroleum, the process comprising separating petroleum by distillation into a gasoline fraction, a light naphtha fraction boiling between about 320 F. and 400 F., a heavy reflux condensate, and a reduced crude, subjecting the reduced crude to a flash distillation under vacuum and under mild cracking conditions to produce a heavy residue and between and 75% of a heavy ash cracked assesses distillate having a molecular weight between about 280 and 300 with the formation of less than 1% gas and less than 1% gasoline, subjecting said heavy ash cracked distillate together with said light naphtha to catalytic cracking, separating the cracked product into a gasoline fraction and a second heavy reflux condensate and combining said second heavy reflux condensate with said heavy residue to produce fuel oil.

2. In the lproduction of useful products including gasoline and fuel oil from petroleum, the process comprising separating petroleum by distillation into a gasoline fraction, a light naphtha fraction, a heavy reflux condensate, and a reduced crude, subjecting the reduced crude to a flash distillation under vacuum and under mild cracking conditions to produce a heavy'residue and between 50% and 75% of a heavy flash cracked distillate having a molecular weight between about 280 and 300 with the formation of less than 1% gas and less than 1% gasoline, subjecting said heavy flash cracked distillate together with said light naphtha to catalytic cracking, separating the cracked product into a gaso line fraction and a second heavy reflux condensate and combining said second heavy reflui: condensate with said heavy residue to produce fuel oil.

3. In the production of useful products including gasoline and fuel oil from petroleum, the process comprising separating petroleum by distillation'lnto a gasoline fraction, a light naphtha fraction boiling between about 320 F. and 400 F., a heavy reflux condensate, and a reduced crude, subjecting the reduced crude to a flash distillation under vacuum to produce a heavy residue and between'about 40% and '75% of a heavy flashed distillate having a molecular weight between about 270 and 350, subjecting said heavy flashed distillate together with said light naphtha to catalytic cracking, separatingthe cracked product into a gasoline fraction and a second heavy reflux condensate and combining said second heavy reflux condensate with said heavy residue to produce fuel oil.

4. In the production of useful products including gasoline and fuel oil from petroleum, the process comprising separating petroleum by dis* tillation into a gasoline fraction, a light naphtha fraction, a heavy reflux condensate, and a reduced crude, subjecting the reduced crude to a flash distillation under vacuum to produce a heavy residue and between about 40% and 75% of a heavy flashed distillate having a molecular weight between about 270 and 350, subjecting said heavy flashed distillate together with said light naphtha to catalytic cracking, separating the cracked product into a gasoline fraction and a second heavy reflux condensate and combining said second heavy reflux condensate with said heavy residue to produce fuel oil.

5. In the production of useful products including gasoline and fuel oil from petroleum, the process comprising separating petroleum by distillation into a gasoline fraction, a light naphtha fraction boiling between about 320 F. and 400 F., a heavy reflux condensate, and a reduced crude, subjecting the reduced crude to a flash distillation under vacuum to produce a heavy flashed distillate and a heavy residue, subjecting said heavy flashed distillate together with said light naphtha to catalytic cracking, separating the cracked product into a gasoline fraction and a second heavy reflux condensate and combining gether with ysaid light naphtha. to catalytic cracking, separating the cracked product into a gasoline fraction and a heavier aromatic condensate and combining said heavier aromatic condensate with said heavy flashed residue to produce fuel oil.

7. Process according to claim 6 in. which the catalytic cracking is carried out with a finely divided catalyst which is continuously regenerated.

WILLIAM A. BAILEY, JR.

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