US2895897A - Production of gasoline from petroleum residues - Google Patents

Description

PRODUCTION OF GASOLINE FROM PETROLEUM RESIDUES Filed Aug. 28. 1956 July 1959 w. 1.. SNIDER ETAL 2 Sheets-Sheet 1 wDQwmm Ink-n- INVENTORS Ill m 3552: mm

WARREN L. SNIDER DANTE H. SARNO GEORGE E. LIEDHOLM BY 407% Mob W THEI 23 6mm. H 535 ATTORNEY y 21, 1959 w. L. SNIDER ETAL 2,895,897

PRODUCTION OF GASOLINE FROM PETROLEUM RESIDUES Fil ed Aug. 28, 1956 2 Sheets-Sheet 2 GEORGE E. LIEDHOLM BY mva/ WM THEIR ATTORNEY FlG.Ib

United States Patent PRODUCTEQN 0F GASOLINE FROM PETROLEUM RESIDUES Warren L. Snider, Walnut Creek, Dante H. Sarno, Berkeley, and George E. Liedholm, El Cerrito, Calif., assignors to Shell Development Company, New York, N.Y., a corporation of Delaware Application August 28, 1956, Serial No. 606,618

4 Claims. (Cl. Mitt-57) This invention relates to a new and improved process for the production of catalytically cracked gasoline and light oils of good quality from petroleum residues.

An object of the invention is to provide a process whereby hydrogen available in limited quantities from the reforming of the gasoline boiling range part of the crude petroleum is more efficiently used to upgrade the catalytic cracking feed stock as well as the intermediate light oils used as diesel fuel, light burning oils, and the like.

A further object of the invention is to provide a means whereby catalytically cracked gasoline of better quality is produced through removal of naphtha from the catalytic cracking feed in a practical manner.

' A further object of the invention is to provide a process wherein an important quantity of heat is saved.

A still further object of the invention is to provide simple and practical means for segregating and treating different portions of the catalytic cracking feed stock.

A still further object of the invention isto provide a process wherein poisoning of the hydrogenation catalyst is largely prevented.

These and other objects which will be apparent to those skilled in this art are obtained according to the method of the invention which comprises recovering from petroleum residue two separate distillate fractions of the nature of gas oil both of which boil essentially above gasoline and one of which is lower boiling and of lower molecular weight than the other, passing the heavier of the two said distillates with gas consisting essentially of hydrogen under hydrogenation conditions of temperature and pressure through a bed of hydrogenation catalyst in a hydrogena tion zone at a reciprocal space velocity sufficient to incorporate in said fraction at least about 300 cubic feet of hydrogen per barrel of the distillate, injecting the lighter distillate into the bed of catalyst at one or more points along the length thereof adjusted such that the average space velocity with respect to the lighter distillate is such that the sole hydrogen consumption with respect to the lighter distillate is essentially in the desulfurizatior thereof with residual hydrogen from the hydrogenation of the heavier distillate and is less than about 150 cubic feet per barrel of the lighter distillate. Liquid product comprising the strongly hydrogenated heavy distillate and lightly hydrogenated lighter distillate is recovered from the hydrogenation zone and catalytically cracked and catalytically cracked gasoline and a light gas oil are separated from the products of the cracking.

In a preferred embodiment of the invention vaporized material is recovered separate from unvaporized liquid in the product from the hydrogenation zone. The vaporized product is cooled without release of the pressure to condense a cool light distillate; the pressure on the liquid product from the hydrogenation zone is released 'without cooling to release lighter constituents. The lighter constituents released from the liquid products are combined with the cooled light condensate and the mixture is fractionated to remove hydrocarbons boiling in the gasoline ;range. The remainder is then catalytically cracked along with the uncooled liquid product.

In apreferred embodiment of the invention residual petroleum is heated to incipient cracking temperatures under pressure to partially vaporize it whereupon the hot vapors are separated from the unvaporized liquid and condensed to form a light liquid condensate whereas the unvaporized portion is passed to a low pressure zone to vaporize a further amount of the residue. These latter vapors are then separately condensed to produce a heavy liquid condensate. The heavy liquid condensate is heavily hydrogenated as described above Whereas the lighter liquid condensate from the pressure flashing step is hydrogenated only very mildly With residual hydrogen from the hydrogenation of the heavier condensate.

In a further preferred modification of the process of the inventiona sizeable portion of the heavy liquid condensate separated in the above-mentioned vacuum flash operation is recycled to the heating zone wherein the residual petroleum is heated as described above, the amount of such recycle being adjusted such that contamination of the hydrogenation catalyst by trace metals from the petroleum residue is substantially avoided.

In the usual refinery practice crude petroleum is first fractionated to remove straight-run gasoline and if desired some light oils leaving a black oil residue. The straight run gasoline so separated is for the most part catalytically reformed whereby a certain amount of gas consisting largely of hydrogen is obtained as a by-product.

The residue is normally treated to recover further amounts of relatively clean oil of the nature of gas oil which is then catalytically cracked to produce gasoline as well as catalytically cracked gas oil. The light catalytically cracked gas oil is normally of rather poor quality as regards suitability for use as diesel fuel and burning oil because of its relatively high concentration of aromatic hydrocarbons and sulfur compounds. It has been suggested to improve this material by hydrogenating it with the hydrogen available from the mentioned catalytic reforming. The hydrogen available from this source is usually sulficient for this purpose. However, by this processing scheme the amount of oil suitable as a catalytic cracking feed stock which can be separated from the residue is limited and the catalytically cracked gasoline generally requires further treatment to desulfurize it.

Various methods are used to separate oil suitable as catalytic cracking feed stock from the petroleum residue chief of which are vacuum flashing, solvent deasphaltizing, viscosity breaking, and coking. One of the shortcomings of these methods is that the catalytic cracking feed stock contains small but important amounts of trace metals which are very detrimental.

It is known that catalytic cracking feed stocks may generally be improved as catalytic cracking feed stocks by hydrogenating them. The hydrogen available from catalytically reforming the straight run material is, however, sufficient to effect only a very light hydrogenation of the catalytic cracking feed stock and the manufacture of further amounts of hydrogen for this hydrogenation cannot be economically justified. It is therefore important that the available by-product hydrogen be utilized in the most efficient manner. g

It has been indicated (see for example US. Patent No. 2,717,864) by separating catalytic cracking feed oils in to fractions of difierent hydrocarbon types and separate cracking of the fractions individually and in various blends that the hydrocarbons in the oil which are mainly responsible for the coke made in catalytic cracking are the polycyclic aromatic hydrocarbons, particularly those having three or more fused rings. This hydrocarbon type is found in all portions of the oil separated from petroileum residue as catalytic cracking feed stock. Thus, for

example, the concentration of polycyclic aromatics in fractions of a typical flashed distillate catalytic cracking feed stocks are shown in the following Table I, the quantities being expressed in millimols per hundred grams.

The amount of hydrogen in standard cubic feet per barrel which would be required to hydrogenate the polycyclic aromatics in these oil fractions to monocyclic aromatics is quite small. It would, therefore, be expected that the most eflicient utilization of the limited available hydrogen would be to hydrogenate the full range catalytic cracking feed stock to this extent and as far as reducing the coke make in catalytic cracking this is the case.

However, as shown in copending application Serial No. 398,031, filed December 14, 1953 (now U.S. 2,792,336), it has been unexpectedly found that in terms of the value of the products obtained in catalytic cracking, which is the more important consideration, this represents a very ineflicient utilization of the hydrogen. It is found that considerably better results are obtained if all of the hydrogen available is utilized to deeply hydrogenate a portion of the catalytic cracking feed stock. Any part of the catalytic cracking feed stock may be chosen for this deep hydrogenation. Improved product values are obtained if the hydrogen is reacted with the lighter part of the oil. This is due largely to the improved quality of the light catalytically cracked gas oil. Somewhat lower coke makes are obtained if the hydrogen is reacted with the heavier portion of the oil. Very good results are obtained when the available hydrogen is reacted with the lightest and heaviest portions of the catalytic cracking feed leaving the bulk middle portion unhydrogenated.

In the process of the invention which will be described in more detail below, one feature is that the heavier portion of the catalytic cracking feed is hydrogenated rather deeply and the light portion of the feed is subjected to only a very mild hydrogenation treatment with residual hydrogen from the hydrogenation of the heavier oil. Under these conditions the hydrogen uptake for the light oil is small and the hydrogen that is consumed is consumed almost exclusively in hydrogenating sulfur compounds. Also, by etfecting the process in the manner to be described additional important advantages are obtained. By the particular method of handling the hydrogenation with the oil partly in the vapor phase and partly in the liquid phase removal of gasoline from the product is facilitated and this results in a considerable enhancement of the quality of the catalytically cracked gasoline. Also, a large part of the catalytic cracking feed may be fed directly to the catalytic cracking unit without cooling and reheating. By the particular method of separating the oil from the petroleum residue the required two fractions of oil are produced without separate fractionation facilities and by recycling part of the vacuum flashed oil contamination of the hydrogenation catalyst is greatly reduced thereby improving the life of the hydrogenation catalyst.

The process of the invention will now be described with reference to the accompanying split drawing where in the main equipment and flows are indicated diagrammatically. Crude petroleum fractionation and catalytic reforming of the straightrun gasoline are indicated in the flow diagram inorder to show the relationship of the process of the invention to the refinery practice; they are, however, not part of the process itself. Referring to the drawing Figure 1a, crude petroleum entering by line 1 and pump 2 is preheated in heater 3 and passed to a crude fractionation system indicated diagrammatically by column 4. Straight-run material is passed overhead by line 5 and after further fractionation in fractionator 6 and 7 is passed to a catalytic reforming unit 8. In the catalytic reforming operating a certain amount of by product gas consisting mainly of hydrogen is produced. This gas is withdrawn from the catalytic reforming system and passed by line 9 to the operation of the invention.

Referring again to the crude fractionation facilities the black oil residue is withdrawn by line 10 and passed through heater 11 to a pressure flasher 12. In heater 11 the oil is heated to incipient cracking temperature under a positive pressure which allows a partial vaporization of the oil. The mixture of liquid and vaporized oil entering the pressure flasher 12 is separated into a liquid residue and vapors which are withdrawn overhead and then condensed to produce the light pressure flashed distillate. A portion of this light pressure flashed dis tillate is returned to the pressure flasher by line 13 to act as a knock-back. In the arrangement illustrated this material containing a small amount of de-entrained pitch is recycled by line 14 back to the heater. The pressure in pressure flasher 12 is adjusted such that the desired amount of the lighter pressure flashed distillate is produced and is normally between about 5 p.s.i.g. and p.s.i.g.

The bottom product from the pressure flasher 12 is passed by line 15 to vacuum flasher 16 wherein further amounts of heavier oil referred to as vacuum flashed distillate are vaporized and removed from the pitch residue which is withdrawn by line 17 The vacuum flashed distillate after condensing in condenser 18 is passed by line 19 to the hydrogenation unit. A part of this heavier oil is returned to the vacuum flasher to knock-back entrained pitch. This knock-back oil containing entrained pitch is cycled by line 20 to the heater 11. In the preferred embodiment of the invention a substantial part, e.g. 5 to 20% of the material condensed in condenser 18 is thus recycled. It is found that when such amounts of the material are thus recycled through the heater the heavy oil passed by line 19 to the hydrogenation unit is substantially free of volatile metal compounds which otherwise contaminate the hydrogenation catalyst. This recycle is therefore important.

In the arrangement illustrated the knock-back from the pressure flasher is likewise recycled to the heater 11. In this arrangement this recycle is essential since if the knock-back is allowed to pass with the bottom product by 'line 15 it is found that sutficient heat is not carried with the oil to effect the necessary vaporization in the vacuum flasher 16. It is, however, possible to insert an additional heater in line 15 between the pressure flasher 12 and the vacuum flasher 16 in which case the knock-back may be passed by line 15 along with the bottoms fraction and line 14 may be dispensed with.

By the preferred arrangement described, the desired light and heavy catalytic cracking feed fractions are produced free of contaminants and in the desired proportions without separate fractionation facilities.

The heavier portion of the catalytic cracking feed which may be from 25 to 75% of the total is heated to the desired hydrogenation temperature in heater 21 (Figure 1b) and then passed to the hydrogenation unit 22. Hydrogen for the hydrogenation introduced from line 9 is passed to the reactor by line 23 and heater 21.

The hydrogenation reactor, illustrated here as a single reactor 22, contains an elongated bed of hydrogenation catalyst. Any suitable hydrogenation catalyst which is active in the presence of moderate amounts of sulfur may be used. The temperature may be any suitable hydrogenation temperature between about 500 and 850 F. The pressure in the hydrogenation reactor must be such that the major part of the heavy oil remains in the liquid phase. The size of the hydrogenation reactor and/ or the amount of heavy oil introduced by line 19 should be adjusted such that the hydrogen consumption per barrel of oil is at least about 300 cubic feet and preferably between 400 and 600 cubic feet. The consumption of hydrogen is dependent upon the space velocity which is to say the amount of oil passed in contact with a given amount of catalyst in a given period of time. Liquid hourly space velocities between about 0.5 and 3, depending somewhat upon the activity of the catalyst, will generally be employed, with space velocities between 1 and 2 generally preferred.

The lighter portion of the catalytic cracking feed withdrawn from the pressure flasher 12 by line is passed to the hydrogenation reactor 22 but is introduced near the end of the path of travel of the heavier oil through the catalyst. The point of introduction is adjusted such that the liquid hourly space velocity with respect to this lighter oil is quite high in the range of 4 to 14 whereby the hydrogen consumption with respect to this oil is less than about 150 cubic feet per barrel and preferably in the range of about 25 to 100 SCF per barrel. When effecting the hydrogenation in this way the hydrogen consumed in hydrogenating the lighter of the catalytic cracking feed is residual hydrogen which has not reacted with the heavier oil and is consumed almost entirely in hydrogenating sulfur compounds. This hydrogenation has virtually no eifect on the cracking properties of this oil in the subsequent catalytic cracking operations but is highly beneficial in improving the quality of the gasoline and light catalytic gas oil produced.

The mixture of liquid oil and vapors withdrawn from the hydrogenation reactor by line 25 is separated without reducing the pressure or the temperature into a liquid fraction and a vapor fraction. In the arrangement illustrated this separation is effected in the separator 26. The vapor fraction withdrawn by line 27 is cooled in cooler 28 without reducing the pressure to condense a light oil fraction and passed to separator 29. .The condensate is removed by line 30 and the liquid passed by line 31 and expansion valve 32 into a low pressure flasher 33. The higher boiling liquid withdrawn from separator 26 by line 34 and expansion valve 35 is passed to a low pressure separator 36 without cooling. Upon releasing the pressure a certain amount of lighter boiling material is disengaged. This may be passed by line 37 and combined with the lighter boiling oil in vessel 33. The unvaporized liquid from separator 36 is still essentially at the hydrogenation reaction temperature. This hot oil is then passed by line 38 to the catalytic cracking unit 39.

In separating the catalytic cracking feed stock from the petroleum residue by the heater 11 pressure flasher 12, and vacuum flasher 16, a small amount of thermal cracking takes place with the production of some material boiling in the gasoline boiling range. In fact, the heating of the oil in heater 11 may be purposely raised to such a point that an amount of the order of 5% thermal gasoline is produced. This gasoline is of poor quality as compared to catalytically cracked gasoline and if present in more than very small amounts in the catalytic cracking feed severely degrades the quality of catalytically cracked gasoline. By ordinary methods it is, however, too costly to remove the gasoline boiling range material from the catalytic cracking feed stock. This thermal gasoline requires reforming but is unsuited for catalytic reforming due to its relatively high sulfur content. In the present process this gasoline is desulfurized and is also removed as will be explained.

Also in the hydrogenation of the catalytic cracking feet stock a small amount of gasoline boiling range material is normally produced although the hydrogenation is a plain hydrogenation rather than a destructure hydrogenation process. In the process of the invention this gasoline produced in the hydrogenation reaction as well as that produced in separating the feed stock from the black oil residue is desulfurized in the hydrogenation reactor and since the hydrogenation reactor is operated with only part of the oil in the liquid phase and a substantial part in the vapor phase the desulfurized gasoline is largely concentrated in the vapor fraction. It is thus concentrated in the condensate in separator 29 and is easily removed from the light gas oil passing to vessel 33 by a relatively simple rectification. The desulfurized naphtha which in any case is in quite small amount, e.g., not more than about 5% v. of the cat cracked feed stock, is removed by line 40 to the catalytic reforming unit 8. The light gas oil catalytic cracking feed, now substantially free of material boiling in the gasoline boiling range, e.g. not more than 1% v. is passed by line 41 to the catalytic cracking unit wherein it is cracked along with the heavier oil passed by line 38.

The catalytic cracking unit may be of any type and may be operated under any of the conventional catalytic cracking conditions. The product of the catalytic cracking is passed by line 42'to a fractionator 43 wherein catalytically cracked gasoline and gasesare separated and removed as an overhead product by line 44. Light catalytically cracked gas oil which is of good quality and suitable for use as diesel fuel or light burning oil is also separated. The quality of this light catalytic gas oil is considerably improved by the hydrogenation according to the method of the invention. Due also to the eflicient and simple separation of the small quantities of the naphtha the octane number of the catalytically cracked gasoline is also improved.

We claim as our invention:

1. In the production of gasoline from petroleum residues the improvement which comprises recovering from petroleum residue two separate distillate fractions of the nature of gas oil both of which boil essentially above gasoline and one of which is lower boiling and of lower molecular weight than the other, passing the heavier of the two said distillates with gas consisting essentially of hydrogen under hydrogenation conditions of temperature and pressure through a bed of hydrogenation catalyst in a hydrogenation zone at a reciprocal space velocity sufficient to incorporate in said fraction at least about 300 cubic feet of hydrogen per barrel of said distillate, injecting said lighter distillate into said bed of catalyst at one or more downstream points along the length thereof adjusted such that the average space velocity with respect to said lighter distillate is such that the sole hydrogen consumption with respect to said lighter distillate is essentially in the desulfurization thereof with residual hydrogen from the hydrogenation of said heavier distillate and is less than about cubic feet per barrel of said lighter distillate, recovering liquid product comprising strongly hydrogenated heavy distillate and lightly hydrogenated lighter distillate from said hydrogenation zone, catalytically cracking the mixed distillates so withdrawn and separately recovering from the products of said catalytic cracking a catalytically cracked gasoline and a light gas oil.

2. In the production of gasoline from petroleum residues the improvement which comprises recovering from petroleum residue two separate distillate fractions of the nature of gas oil both of which boil essentially above gasoline and one of which is lower boiling and of lower molecular weight than the other, passing the heavier of the two said distillates with gas consisting essentially of hydrogen under hydrogenation conditions of temperature and pressure through a bed of hydrogenation catalyst in a hydrogenation zone at a reciprocal space velocity sufficient to incorporate in said fraction at least about 300 cubic feet of hydrogen per barrel of said distillate, injecting said lighter distillate into said bed of catalyst at one or more downstream points along the length thereof adjusted such that the average space velocity with respect to said lighter distillate is such that the sole hydrogen consumption with respect to said lighter distillate is essentially in the desulfurization thereof with residual hydrogen from the hydrogenation of said heavier distillate and is less than about 150 cubic feet per barrel of said lighter distillate, separately recovering from the efiiuent of said hydrogenation zone under said hydrogenation conditions of temperature and pressure a liquid product and a vapor product, cooling the said vapor product without release of the pressure to condense a cooled, light condensate, decreasing the pressure on said liquid product from the hydrogenation zone without cooling to release lighter constituents, combining the released lighter constituents with said cooled light condensate and fractionating the resulting mixture to remove hydrocarbons boiling in the gasoline range, and catalytically cracking the remainder along with said liquid product to produce catalytically cracked gasoline.

3. In the production of gasoline from petroleum residues the improvement which comprises heating residual petroleum to incipient cracking temperatures under pressure to partially vaporize the same, passing the resulting mixture of hot vapors and liquid to a separation zone and separating the vapors from the liquid therein, condensing the vapors to form a light liquid condensate, passing the separated liquid to a separation zone under vacuum to vaporize a further amount of said petroleum residue, separating and condensing the resulting vapors from the said vacuum separation zone to. produce heavy liquid condensate, passing the heavier of the two said condensates with gas consisting essentially of hydrogen under hydrogenation conditions of temperature and pressure through a bed of hydrogenation catalyst in a hydrogenation zone at a reciprocal space velocity suflicient to incorporate in said fraction at least about 300 cubic feet of hydrogen per barrel of said condensate, injecting said lighter condensate into said bed of catalyst at one or more downstream points along the length thereof adjusted such that the average space velocity with respect to said lighter condensate is such that the sole hydrogen consumption with respect to said lighter condensate is essentially in the desulfurization thereof with residual hydrogen from the hydrogenation of said heavier condensate and is less than about 150 cubic feet per barrel of said lighter condensate, recovering liquid product comprising strongly hydrogenated heavy condensate and lightly hydrogenated lighter condensate from said hydrogenation zone, catalytically cracking the mixed condensates so withdrawn and separately recovering from the products of said catalytic cracking a catalytically cracked gasoline and a light gas oil.

4. In the production of gasoline from petroleum resimixture of hot vapors and liquid to a separation zone and separating the vapors from the liquid therein, condensing the vapors to form a light liquid condensate, passing the separated liquid to a separation zone under vacuum to vaporize a further amount of said petroleum residue, separating and condensing the resulting vapors from the said vacuum separation zone to produce heavy liquid condensate, passing the heavier of the two said condensates with gas consisting essentially of hydrogen under hydrogenation conditions of temperature and pressure through a bed of hydrogenation catalyst in a hydrogenation zone at a reciprocal space velocity sufiicient to incorporate in said fraction at least about 300 cubic feet of hydrogen per barrel of said condensate, injecting said lighter condensate into said bed of catalyst at one or more downstream points along the length thereof adjusted such that the average space velocity with respect to said lighter condensate is such that the sole hydrogen consumption with respect to said lighter condensate is essentially in the desulfurization thereof with residual hydrogen from the hydrogenation of said heavier condensate and is less than about cubic feet per barrel of said lighter condensate, separately recovering from the efiiuent of said hydrogenation zone under said hydrogenation conditions of temperature and pressure a liquid product and a vapor product, cooling the said vapor product without release of the pressure to condense a cooled, light condensate, decreasing the pressure on said liquid product from the hydrogenation zone without cooling to release lighter constituents, combining the released lighter constituents with said cooled light condensate and fractionating the resulting mixture to remove hydrocarbons boiling in the gasoline range, and catalytically cracking the remainder along with said liquid product to produce catalytically cracked gasoline.

References Cited in the file of this patent UNITED STATES PATENTS 2,321,841 Mekler et a1. June 15, 1943 2,671,754 De Rosset et al. Mar. 9, 1954 2,758,059 Berg Aug. 7, 1956 2,769,753 Hutchings et al Nov. 6, 1956 2,775,544 Corneil et al. Dec. 25, 1956 2,792,336 Kubicek et al. u May 14, 1957

Claims (1)

1. IN THE PRODUCTION OF GASOLINE FROM PETROLEUM RESIDUES THE IMPROVEMENT WHICH COMPRISES RECOVERING FROM PETROLEUM RESIDUE TWO SEPARATE DISTILLATE FRACTIONS OF THE NATURE OF GAS OIL BOTH OF WHICH BOIL ESSENTIALLY ABOVE GASOLINE AND ONE OF WHICH IS LOWER BOILING AND OF LOWER MOLECULAR WEIGHT THAN THE OTHER, PASSING THE HEAVIER OF THE TWO SAID DISTILLATES WITH GAS CONSISTING ESSENTIALLY OF HYDROGEN UNDER HYDROGENATION CONDITIONS OF TEMPERATURE AND PRESSURE THROUGH A BED OF HYDROGENATION CATALYST IN A HYDROGENATION ZONE AT A RECIPROCAL SPACE VELOCITY SUFFICIENT TO INCORPORATE IN SAID FRACTION AT LEAST ABOUT 300 CUBIC FEET OF HYDROGEN PER BARREL OF SAID DISTILLATE, INJECTING SAID LIGHTER DISTILLATE INTO SAID BED OF CATALYST AT ONE OR MORE DOWNSTREAM POINTS ALONG THE LENGTH THEREOF ADJUSTED SUCH THAT THE AVERAGE SPACE VELOCITY WITH RESPECT TO SAID LIGHTER DISTILLATE IS SUCH THAT THE SOLE HYDROGEN

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