|Publication number||US3287254 A|
|Publication date||Nov 22, 1966|
|Filing date||Jun 3, 1964|
|Priority date||Jun 3, 1964|
|Publication number||US 3287254 A, US 3287254A, US-A-3287254, US3287254 A, US3287254A|
|Inventors||Paterson Norman J|
|Original Assignee||Chevron Res|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (3), Referenced by (46), Classifications (9)|
|External Links: USPTO, USPTO Assignment, Espacenet|
Nov. 22, 1966 N. J. PATERsoN 3,287,254
RESIDUAL OIL CONVERSION PROCESS Filed June 5, 1964 2 Sheets-Sheet 1 INVENTOR NORMAN J. PA7'ERSON u ATToRNEs Nov. 22, 1966 N. J. PATERSON RESIDUAL OIL CONVERSION YPROCESS 2 Sheets-Sheet 2 Filed June 5, 1964 Unted States Patent O 3,287,254 RESIDUAL OIL CONVERSION PROCESS Norman J. Paterson, San Rafael, Calif., assigner to Chevron Research Company, a corporation of Delaware Filed June 3, 1964, Ser. No. 372,253 6 Claims. (Cl. 208-68) This application is a continuation-in-part of copending application Serial No. 333,666, filed December 26, 1963, now U.S. Patent No. 3,245,900.
This invention relatesto hydrocarbon conversion processes. More particularly, the invention is concerned with a combination of treating processes for converting the heaviest portions of petroleum and similar hydrocarbonaceous materials to light distillates, predominantly gasoline.
f In the prior art, crude petroleum has been separated into fractions of different boiling range and the separate fractions treated individually by thermal, catalytic, hydrogenative, and hydrocatalytic processes. In each of these processes it is characteristically observed that a portion of the feed is converted to desired products while another portion is converted to less desired by-products, i.e., material which is less readily converted than the feed. For example, in catalytic cracking of gas oils a. part of the feed is converted to the desired gasoline product, a part is converted to coke, and another part is converted to light and heavy cycle oils which are considerably more refractory, i.e., more diicult to crack, than the feed. The excess cycle oils produced are generally disposed of in heavy -fuel oil. Similarly, solvent deasphalting processes applied to residuum separate the residuum into a portion which is suitable -for catalytic cracking and another asphaltic portion which is less suitable for catalytic cracking than the whole crude or residuum. Likewise, in catalytic hydrocracking processes it is observed that a portion of the feed is readily hydrocracked to lower boiling distillates, but another portion becomes hydrogenated and more resistant to hydrocracking. The asphaltic residuum from solvent extraction is generally disposed of in heavy fuel oil, and the hydrocrackate resistant to further hydrocracking may also be blended into the heavy fuel oil.
Because the light distillates, particularly gasoline, demand a much higher price per barrel than the fuel oil, it is desired to maximize conversion to gasoline and to minimize production of heavy fuel oil. The incremental cost of upgrading to gasoline the refractory materials blended into fuel oil, however, has been prohibitively high by known methods.
The present invention is directed to the problem of substantially reducing or eliminating the production of undesired heavy fuel oil as a by-product of crude oil upgrading. In the invention there is employed `in a particular combination: a vacuum separation unit; a solvent extraction unit; a catalytic cracking unit; a catalytic hydrogenation unit; and a catalytic hydrocracking unit. It has been found that in the particular combination of treating units, the portion of the products of conversion formed in one unit which is resistant to further conversion therein can be converted more readily to desired products in another of the units, to which it is passed. Thus, the present invention can convert the heaviest portions of crude petroleum predominantly to gasoline, While minimizing the pro- (IeY duction of heavy fuel oil, by of refractory by-products.
In accordance with the invention a heavy residual oil such as a heavy crude oil, topped crude oil, or atmospheric reduced crude oil, is separated under vacuum into a light vacuum gas oil, a heavy vacuum gas oil, and a residuum'. The residuum is treated with a solvent in a solvent extraction zone to obtain a deasphalted residual oil and an asphaltic residue. The heavy vacuum gas oil is catalytically cracked to obtain gasoline and a heavy cracked cycle oil. The light vacuum gas oil, deasphalted residual oil, and heavy cracked cycle oil, are catalytically hydrogenated to obtain gasoline, a low nitrogen-content hydrogenated gas oil, and a high nitrogen content hydrogenated residual oil. The low nitrogen content hydrogenated gas oil is catalytically hydrocracked to obtain gasoline. The high-nitrogen content hydrogenated residueliminating the formation al oil is -catalytically cracked to obtain additional gasoline and heavy cracked cycle oil, which heavy cracked cycle oil is then catalytically hydrogenated as above.
In the attached drawing, FIGURE 1 is a schematic block flow diagram showing essential process units in the process ofthe invention and the manner in which they may be combined; and FIGURE 2 is a schematic block oW diagram showing specific alternatives and preferred embodiments in combining the process units in accordance with the invention. Methods-are known for carrying out individually each of the conversion and treating steps used in the present invention, and persons skilled in the art `relating to each step will recognize the possibility of using various combinations of apparatus and conditions therein to obtain equivalent results within the requirements of the invention set forth herein for that step. Accordingly, the several steps are represented in the gures merely as square boxes.
Referring -to FIGURE 1, .a heavy residual oil such as heavy crude oil or atmospheric residuum is passed through line 11 to vacuum separation zone 12. The vacluum separation zone may comprise one or more vacuum flash towers, vacuum distillation columns, or vacuum stripping operations such as a lresiduum stripper employing steam to reduce the hydrocarbon partial pressure. In `vacuum separation zone 12 the residual oil is separated into 4at least three primary fractions comprising a liirst relatively .light fraction obtained in line 13, a second heavier fraction obtained in line 14, and a residuum obtained in line 15. The residuum is passed via line 15 to solvent deasphalting zone 16 wherein it is separated into a deasphalted residual Oil recovered in line 17 and an asphaltfic residuum Withdrawn through line 18. The deasphalting zone may comprise one or more contacting towers or columns wherein the residuum is contacted with a suitable solvent for separating the constituents of the residuum primarily on the bases of molecular weight and polarity. It is desired that the asphaltic residuum obtained in line 18 be composed primaly of the condensed ning aromatic structures comprising most of the organic metal compounds, and those compounds classified as asphaltenes and resins. Thus, the extracting solvent may Icomprise an aromatic hydrocarbon which dissolves the asphaltenes and like materials, but preferably it is a parain or mixture of light parailns, such as normally gaseous parafns, which selectively dissolve the oily constituents of the residuum. In the case of solvent deasphalting rwith a normally gaseous hydrocarbon solvent such as a mixture of propane and butane, there is obtained a deasphalted residual oil in line 17, from which solvent has been recovered, and an asphaltic residue in line 18, from which solvent has been recovered.
The heavy vacuum gas oil in line 14 is passed to catalytic cracking zone 19, which may comprise any of the well known conventional catalytic cracking processes such as those employing uidized catalyst powder, or gravltating catalyst particles. Generally, a natural or synthetic silica-alumina catalyst is employed and passed continuously in a cycle from a reaction stage to a regeneration stage, wherein coke is burned off the catalyst, and back :to the reaction stage. In the reaction stage a portion of the heavy gas oil feed is converted to gasoline, recovered through line 20, while another portion is converted to refractory cycle oils including heavy cycle oil, recovered through line 21.
The relatively lighter `vacuum gas oil in line 13 is passed to catalytic hydrogenation zone 22. There lare also passed to the catalytic hydrogenation zone the deasphalted residual oil of line 17 and the heavy cracked cycle oil of line 21. Zone 22 may comprise a single stage hydroning unit operating under hydrocracking conditions, but preferably it comprises at least two catalytic stages including a rst stage wherein substantial hydrocracking occurs and a second, hydrolining, stage operated lprimarily to substantially completely remove organic nitrogen contaminants by converting them to ammonia, which may be accompanied by substantial hydrocracking. A portion of the three streams shown as passed to zone 22 may .pass only through the rststage of such a two-stage unit; another portion may pass only through a second stage; and another portion may pass through both stages.` In any event, there is recovered from the catalytic zone 22 la :gasoline product fraction in line 23, a hydrogenated gas oil of relatively low nitrogen content in line 24, and another hydrogenated gas oil of relatively higher nitrogen content in line 25. These gas oils are found to be quite resistant 4to further hydrofming and hydrocracking at the conditions employed in zone 22. The relatively low nitrogen content gas oil in line 24, however, can be readily converted to light distillates including gasoline -at different catalytic hydrocracking conditions employed in catalytic hydrocracking zone 26, to rwhichit is accordingly passed. The lrelatively higher nitrogen content gas oil in line 25 contains residual materials derived from the residuals in the deasphalted oil of line 17. It is found that this hydrogenated residual oil is quite readily converted toV lower boiling distillates including gasoline at the catalytic cracking conditions of zone 19, to which it is accordingly passed. A portion of the hydrogenated residual oil which is not converted to gasoline or to coke in the catalytic cracking unit reappears as heavy cracked cycle oil in line 21 and is returned to the catalytic hydrogenation zone 22.
In catalytic hydrocracking zone 26 there is employed a hydrocracking catalyst having strong acidity, and which is accordingly adversely affected by nitrogen compounds. In contrast thereto, the catalysts employed in the cat-` alytic hydrogenation unit or stages of zone 22 are sulfactive hydrogenation catalysts which are non-acidic or only weakly acidic hydrocracking catalysts. Thus, catalytic hydrocracking unit 26 may operate at lower temperatures whereby a different type of h-ydrocracking reaction is selectively promoted to convert a substantial portion of the .'hydrofined g-as oil feed to lower boiling distillate products, including gasoline recovered in line 27. It is .generally possible to convert `all of 4the low nitrogen content hydroined gas oil to light products in catalytic hydrocracking zone 26 by employing extinction recycle hydrocracking of unconverted materials. However,` in many instances it is advantageous to withdraw lates withdrawn via line 35,` medium to heavy straight` run atmospheric gas oil withdrawn via line 36, and atmospheric reduced crude in line 37. The atmospheric reduced crude in line 37 is passed via line 38 to vacuum distillation column or columns 39 wherein it is separated into light vacuum gas oil withdrawn through line 40heavy vacuum gas oil withdrawn through line 41, and vacuum Ireduced crude residuum withdrawn through line 42.1 The combination of atmospheric and vacuum distillation is to obtain in line 42 a short residuum boiling entirely above about 900 F. Preferably, the vacuum distillation is carried out at low pressures of a few millimeters mercury absolute so as to obtain the maximum vaporization and recovery of oil as vacuum gas oil. The extent of distillation is restricted primarily by the desire to exclude from heavy vacuum gas oil, to be passed to the catalytic crack. ing unit, oil containing above about 2 p.p.m. heavy metals other than iron. Thus, depending on the crude oil properties, the initial boiling point of vacuum residuum in line` 42 may be as high as1200 F. with certain rare crudes, frequently at least 1050 F., but sometimes only 800# 900 F.
The vacuum residuum in line 42 is passed to solvent extraction zone 44 wherein it is separated into an asphaltic residue, in line 46, and a deasphalted residual oil, in`
line 45. IThe feed to the solvent extraction zone may include some atmospheric residuum introduced through;
line 43, but preferably the vacuum residuum is the predominant portion of the feed. The solvent extraction is carried out so as to obtain the highest feasible yield `of deasphalted residual oil. In general, the yield obtained is so high that the deasphalted residual oil contains an amount of organic metal rcompounds such that the deasphalted oil would not be a suitable feed for catalytic cracking. It is desired, however, that the Ramsbottom carbon or Conradson carbon jof the deasphalted oil be not excessively high. In general, the Ramsbottom carbon should not exceed about 6 weightpercent, and preferably is in the range between 2 and 6, which generally results 1n a metal content in the deasphalted oil of between 10 and 100 p.p.m. total of nickel and vanadium. Preferably,
the total metal content is lessthan about 50 p.p.m. and the Ramsbottom carbon less than about 4. Thus, with typical crudes, a propane-butane solvent may be used in;
a ratio to 900 F.| short` residuum feed of between 43 and 10 volumes to obtain a yield of deasphalted oil which is above 40 weight percent based on residuum feed, preferably between 45 and 80 percent yield.
The deasphalted-residual oil in line 45 is passed to catalytic hydrocracking zone 47 wherein it is contacted` with hydrogen and a sulfactive hydrogenation catalyst at elevated temperature of 700-900" F. and pressure of 1500-4000 p.s.i.g. The hydrocracking zone serves to remove substantially all the metal contaminants, to thor-` oughly hydrogenate the residual portion of the deasphalted oil, and to convert between about `30 and 70% of the deasphalted oil to distillate oil boiling below 900 `F. Suitable catalysts for use in zone 47 include the sulfactive hydrogenation catalysts of no more than weak acidity, comprising combinations of Group VI and Group `VIII metals, their oxides and their sulfldes, especially nickel sulfide together with molybdenum sulfide or tungsten sulde, associated with an inorganic refractory oxdecarrier such as alumina, silica-alumina, silica-magnesia, and the like. Strongly acidic hydrocracking catalysts, such as those comprising Group VIII metals, their oxides and suliides, associated with an active silica-alumina cracking catalyst carrier wherein silica is a major component, are not suitable because they rapidly lose their activity and do not exhibit suflicient hydrogenation activity at the conditions employed. The feed to catalytic hydrocracking zone 47 may include a portion of heavy vacuum gas oil, represented by line 48 taken off from line 41, if said vacuum gas oil has a content of organic metal contaminants making it unsuitable or less desirable for catalytic cracking feed. Thus, the vacuum distillation in zone 39 may be carried to such an extent as to provide as feed for catalytic hydrocracking zone 47 a portion of oil which would normally he included in the deasphalted residual oil recovered from solvent extraction zone 44 if the vacuum distillation were carried only to the point to exclude metal contaminants appearing in the vacuum gas oil.
In zone 47 a portion of the feed is converted to light distillates, including `gasoline withdrawn through line 49, a distillate gas oil hydrocrackate withdrawn through line 50, and a residual hydrocrackate withdrawn through line 51. The cut point between the distillate gas oil hydrocrackate and the residual hydrocrackate is between about 650 F. and 1100 F.; i.e., the distillate gas oil hydrocrackate has an end boiling point above 650 F., and the residual hydrocrackate includes all the material boiling above 1100 F. The cut point and relative amounts of distillate and residual hydrocrackate may be controlled in relation to the relative amounts of light and heavy vacuum gas oil obtained in the distillation, and depending on the relative nitrogen contents of the oils, as will be further described hereinafter.
The residual hydrocrackate from zone 47 is passed via line 51 to catalytic cracking zone 52. In -addition there is passed to the catalytic cracking zone 52 at least a portion of the heavy vacuum gas oil of line 41, via lines 53 and 54. In addition, there may be passed to the catalytic cracking zone a portion of the light vacuum gas oil of line 40 via lines 55 and 54. Moreover, a portion of atmospheric gas oil may be passed to the catalytic cracking zone from line 36 via lines 56, 53, and 54. In general, it is desirable that the catalytic cracking process handle as much as possible of the highest boiling straight run distillates in addition to the residual hydrocrackate, as limited by the coke burning and gas handling capacities of the particular catalytic cracking unit. The catalytic cracking zone is preferably of the well known uid bed type or the gas lift or bucket elevator type wherein cracking catalyst such as silic-a-alumina powder or pellet is continuously circulated between a reaction zone and a regeneration zone, using conversion conditions of 8501l00 F. and regeneration conditions of 900-l150 F., at near atmospheric pressure. The manner of controlling the catalytic cracking process, primarily by means of the catalyst circulation rate and feed preheat temperature, to maintain a balance between the heat released by burning coke from the catalyst in regeneration and the heat absorbed by the cracking reactions, is well known. The catalytic cracking process converts a major portion of the heavy vacuum gas oil and residual hydrocrackate Vto light products, including gasoline withdrawn through line 57. It is found that the residual hydrocrackate of line 51 converts in very high yield to gasoline, and in combination with the vacuum gas oil enhances the conversion of said gas oil to gasoline with less production of coke and light gases. There are also produced, however, refractory cycle oils including heavy cracked cycle oil withdrawn through line 58. In addition, light cracked cycle oil and/ or a heavier slurry or decant oil may be withdrawn through line 59. In the combination process of the invention, the recycling of cycle oil in the catalytic cracking unit is generally less than in the conventional catalytic cracking of heavy gas oils and/or deasphalted oil, and in particular, heavy cracked cycle oil may be withdrawn through line 58 at a greater rate than would ordinarily be practiced.
The cat-alytic cracking process operates as a partial denitn'fication zone by Icracking, the organic nitrogencompounds to NH3 and it will be found that the heavy cracked cycle oil of line 58 has a lower nitrogen content than the combined feed of lines 51 and 54. The cycle oil of line 58 may include both light and heavy cycle oils, and may boil from just above the end boiling point of gasoline up to the maximum end point of distillates produced in catalytic cracking. Preferab1y, however, the end point is limited to the range SOO-850 F. to exclude the very high nitrogen content heaviest oils. It is understood that only distillate oils are produced in catalytic cracking because the products are recovered only from a vapor eluent.
The heavy cracked -cycle oil of line 58, the distillate hydrocrackate of line S0, and at least a portion of the light vacuum gas oil of line 40 are passed to catalytic hydrofning zone 60, the latter straight run gas oil vialine 61. In addition there may be passed to zone 60 a portion of straight run atmospheric gas oil of line 36 via line 61. In zone 60, there is employed the same type of sulfactive hydrogenation catalyst as described for use in zone 47, at similar processing conditions. In general, however, a lower temperature in the range 600-850 F. may be used in zone 50 as compared to zone 47 in the illustrated embodiment, as the primary function of zone 60 is to produce low nitrogen content hydioiined gas oil recovered in line 65, from the eluent of zone 60 in line 62 by separating gasoline and other by-products in still 63. Thus, it is advantageous to use in zone 60 a catalyst and operating conditions favoring more hydrogenation and less hydrocracking as compared to zone 47. It is found that whereas' the heavy cracked cycle oil of line 58 is resistant to further conversion in zone 52, and whereas the distillate hydrocrackate of line 50 is resistant to further conversion in zone 47, said oils are more amenable to processing for removing organic nitrogen compounds by hydrogenation to ammonia in zone 60 by virtue-of their previous partial conversion.
The straight run distillate gas oil passed to zone 60 represents portions of oil which would normally be catalytically cracked, but which have been displaced from that operation by virtue `of the catalytic cracking zone now being fed residual hydrocrackate fromzone 47. Thus, the relative amounts and boiling range of straight run distillates passed to zone 60 will`vary depending on the nature of the crude oil charge. For example, with a very heavy oil a larger proportion of the crude will tend to pass as vacuum residuum to solvent extraction zone 44, as residual deasphalted oil through line 45 to zone 47, and -as a residual hydrocrackate through line 51 to zone 52. The amount of light vacuum gas oilin line 40 will be less. In that case, it is preferable to raise the cut point in distillation separation of the efluent of zone 47 so as to pass a higher boiling distillate hydrocrackate through line 50 from zone 47 to z-one 60, whereby more vacuum gas oil may be included in the catalytic -cracker feed and more distillate hydrocrackate be included in the feed to hydrofining zone 60.
In the illustrated embodiment of FIGURE 2, the hydroning zone 60 is operated in association with catalytic hydrocracking zone 66. Conditions in zone 60 are such as to reduce the nitrogen content of the products therefrom to below about p.p.m., preferably to below 10 p.p.m. nitrogen. The eluent of zone 60 is passed via line 60 to recovery zone 63, comprising one or more distillation columns, wherein light distillates produced in hydroning zone 60 are withdrawn, including gasoline in line 64. Low nitrogen content gas oil is withdrawn from zone 63 and passed through line 65 to hydrocracking zone 66. In zone 66 there is employed a strongly acidic hydrocracking catalyst, such as exemplified by the combination of at least one Group VIII metal, oxide or sulde, especially nickel sulfide, associated with an inorganic refractory oxide carrier having cracking activity, such as a silica-alumina cracking catalyst. Preferably, a lower temperature of 50G-800 F. and pressure of 50G-2500 p.s.i.g.y are employed in zone 66 as compared to zones 47 and 60, and when the gas oil feed has a low nitrogen content a high per pass conversion to light distillates is achieved. The eluent of zone 66 is also passed to recovery zone 63 via line 67 to recover the light distillate products, including gasoline withdrawn in line 64, and to obtain for recycle any unconverted gas oil in line 65.
Thus, the heaviest portion of crude oil, including gas oils and residuals, is converted to light distillates, predominantly gasoline, and asphaltic residuum by the abovedescribed process of the invention. Additional light distillate and gasoline values can be recovered by passing all or a portion of the asphaltic residuum in line 46 to thermal cracking zone 71. Preferably, there is also passed to thermal cracking zone 71 a less viscous oil such as a cracked cycle oil from catalytic cracking zone 50, via line 59, to reduce the viscosity of the asphaltic residuum thus permitting higher throughputs and increased seveties in the cracking oils so that higher rates and yields of lighter products are obtained. In addition, the presence of the aromatic cycle oils in the cracking tubes permits a higher cracking severity to be realized with increased yields of lighter products, including gasoline recovered through line 72, and a heavy fuel oil component of improved stability suitable for blending into fuel oil, in line 73. As indicated, the cracked residual oil of line 73 may be blended with a portion of asphaltic residuum of line 46 whichis not cracked but instead withdrawn through line 74 and combined with the material in line 73 to form fuel oil in line 75. Another portion of asphaltic residuum may be Withdrawn from line 74 through line 76 for production of asphalt. Additionally, part of the material in line 76 may be burned directly as fuel oil.
When, in accordance with the invention, the solvent extraction in zone 44 is carried out so as to obtain a high yield, above 50% of deasphalted oil in line 45 from vacuum residua, thermal cracking of the asphaltic residue in line 46 in admixture with catalytically cracked light cycle oi-l of line 59 is found to give unusually good gasoline yields. For example, by thermal cracking 12,400 b.p.d. of residua in admixture with 6500 b.p.d. of cycle oil there is obtained 6600 b.p.d. more gasoline and 7000 b.p.d. less fuel oil than are obtained by thermal cracking the cycle oil alone and blending unconverted cycle oil with theresidue. Best results are obtained when the amount of cycle oil diluent is minimized to obtain a viscosity in the blend of feed to the thermal cracking unit that does not result in a loss of capacity due to pump limitations. Thus, it is particularly advantageous to pass only that amount of cycle oil needed for diluent via line 59 to zone 71, and to use the light cycle oil since less is required to lower the viscosity of the mix, the remainder of the cycle oil including heavy cycle oil being passed via line 58 to zone 60.
To further upgrade the gasoline produced in the several processing units, al1 or a portion of the gasoline boiling range materials,fin line 49 produced by catalytic hydrocracking, in line 57 produced by catalytic cracking, in -line 72 produced by thermal cracking, and in line 64 produced by catalytic hydrofining and catalytic hydrocracking, may be passed to a catalytic reforming zone to produce high octane gasoline.` It will be understood that not all of the gasoline produced need be catalytically reformed nor is it desirably so treated, but only the portions thereof which have undesirably low octane number. Also, it will be appreciated that the portions of gasoline boiling range material produced in catalytic hydrocracking zone 47, catalytic cracking zone 52, and thermal cracking zone 71 may require additional hydrofining to remove nitrogen. Thus, the gasoline fractions in lines 49, 57, and 72 may be passed via line 70 to catalytic hydrofining zone 77. The hydrofined oil 8` then is passed via line 78 to catalytic reforming in zone 68. On the other hand, the gasoline product of line 64 is already of accepta'bly low nitrogen content, and it may be passed directly to zone 68.` In catalytic reforming unit 68 there may be employed, for example,.a well` known reforming catalyst such as platinum on alumina, or halided platinum on alumina, at temperatures above 850 F. and pressures below about 800 p.s.i.g. High octane gasoline is recovered in line 69.
It will be recognized by those skilled in the artthat in the practice of the invention `as described there will be produced and recovered additional distillate products besides gasoline. =In particular, in veach of the catalytic and thermal treating units, there will be produced light gases and also middle distillate fractions whichcan `be recovered as products. Also, in catalytic hydrocracking zone 66 there will be produced light isoparaffins including iso-butane and iso-pentane, and there may also be recovered kerosene (jet fuel) and middle distillate products.
The details of product separation and recovery have been without appreciable adverse effect on the catalyst activity, and it is expected that even greater amounts can beperrnitted to build up. Ultimately, however, a point will be` reached at which the catalyst is physically obscured `or blinded by deposited metals. Some of the metals are absorbed in the pores of the catalyst, whereas other metals such as iron may deposit as line powder external` of the catalyst, causing an increased pressure drop through the reactor. When this has occurred to an undesirable extent, the metals may be removed by chemicaland/or physical means to restore the catalyst lto its fresh activity.
This may be accomplished in situ in some cases, but pref` erably may be accomplished in a catalyst treating plant elsewhere;` In such event, it will be found suitable and desirable to use in catalytic hydrocracking zone 47 Ithe catalyst from catalytic hydroning zone 60. A fresh charge of more active catalyst may then be installed in` the catalytic hydroining zone 60, wherein it is desired that high activity be maintained to insure having the` ability to convert nitrogen compounds to ammonia yso as to recover hydroiined distillate oil in line 62` having the desired low nitrogen content.
Example 1 From atmospheric distillation of 36,000 b.p.d. of crude oil there is obtained 21,300 b.p.d. of atmospheric residuum. The 21,300 b.p.d. of atmospheric residuum isdistilled under vacuum to obtain 10,400 b.p.d. of light vacuum gas oil, 1300 b.p.d. of heavy vacuum gas oil, and
9600 b.p.d. of vacuum residuum boiling entirelyabove.
900 F. Of the vacuum residuum 1600 b.p.d. is withdrawn for asphalt manufacture, and 5100 b.p.d.y is passed along with 41,500 b.p.d. of a heavy crudeA oil to a residuum stripper wherein the top of the column is maintained at about 50 mm. Hg absolute. The feed inlet, is to the rflash zone, which is maintained at about mrn.` Hg, and the unvaporized portionsof the feed pass to a bottoms steam stripping zone. Overhead there is withdrawn from the process 8300 b.p.d. of light gas oil derived primarily from the heavy crude. There` is `also obtained 21,200 b.p.d. of heavy vacuum resid stripper gas It is found that metal deposits Iup to. about 10 weight percent of the catalyst can be tolerated` a mixed, liquid, propane-butane solvent at near the critical temperature and pressure for the solvent. Multiple con- -tacting stages are provided in the tower and a solvent:oil ratio above 4:1 is used so that there is obtained 11,500 b.p.d. of deasphalted residual oil (57% yields) and 8500 b.p.d. of asphaltic residuum. The deasphalted oil contains 20 p.p.m. nickel and vanadium and has a Ramsbot- Y tom carbon content of 3 weight percent. There are thus obtained, with reference to FIGURE 2, the following stocks:
In line 40: 10,400 b.p.d. of 830 F. E.P. vacuum gas oil to be passed to zone 60.
In line 41: 22,500 b.p.d. of l100 F. EP. vacuum gas oil to be passed to zone 52.
In line 45: 11,500 b.p.d. of 900 F. I.B.P. deasphalted oil to be passed to zone 47.
In line 46: 8,500 b.p.d. of 900 F. I.B.P. asphaltic residuum to be passed to zone 71.
The deasphalted oil is mixed with 7000 s.c.f. Hz-rich gas per barrel and passed through reactors in zone 47 containing sulded .Ni-W-silica-magnesia catalyst at 740 F., 3000 p.s.i.g., and 0.5 LHSV. The effluent is cooled, Hz-rich gas separated and by-product NH3 and H2S scrubbed out, and the oil is distilled to remove 1700 b.p.d. of a broad gasoline cut, 2100 b.p.d. of 400-650 F. middle distillate, 800 b.p.d. of 650-725 F. distillate hydrocrackate, and 8000 b.p.d. of 725| F. residual hydrocrackate which is the remainder of the once-through eiluent. The 8000 b.p.d. of residual hydrocrackate and the 22,500 b.p.d. of heavy vacuum gas oils are passed to an FCC unit in zone 52 operated at 50% conversion. The cracked reaction mix is separated into 4800 b.p.d. of a C3/C4 cut, 10,800 b.p.d. gasoline, 7500 b.p.d. of 550- 800 F. heavy cycle oil, and 7500 b.p.d. of mixed light cycle oil and so-called decant oil (boiling above 800 R). The heavy cycle oil, distillate hydrocrackate, and light vacuum gas oil make up 18,700 b.p.d. of feed passed to hydrolining zone 60 with 7000 s.c.f. Hg-richV gas per barrel for contacting a sulfactive hydrogenation catalyst, the same as used in zone 47, at the same pressure and space velocity, at 690 F. The eiuent is cooled,`
I-IZ-rich gas separated, and by-product NH3 and HZS scrubbed out. The remaining liquid oil portion contains less than l p.p.m. nitrogen. The oil is combined for distillation with the liquid oil portion of the eiuent of catalytic hydrocracking zone 66 to recover gasoline and lighter products formed in zones 60 and 66, yielding in line 67 as the gross feed to zone 66 24,000 b.p.d. low nitrogen content oil boiling above 450 F. The light products are worked up into 3000 b.p.d. of C3/C4 cut, 8600 b.p.d. light gasoline, and 10,900 b.p.d. heavy gasoline.
Of the 8500 b.p.d. of asphaltic residuum remaining after extraction with propane-butane, 1800 b.p.d. is burned directly as fuel, 500 b.p.d. is blended into heavy fuel oil with 2700 b.p.d. of the cracked cycle oil, and 6200 b.p.d. is combined with 4800 b.p.d. of the cracked light cycle oil and thermally cracked in a single coil, recycle thermal unit. The broad gasoline cut separated from the efuent of hydrocracking deasphalted residual oil (in zone 47) is combined for distillation with the thermal cracked products, as the gasoline qualities are similar. The products are worked up Ainto 1300 b.p.d. of a C3/C4 cut, 5400 b.p.d. gasoline, and 6000 b.p.d. fuel oils. Thus, over-all, the following net yields are obtained from atmospheric reduced crude and heavy crude, exclusive of portions not processed in at least one of the combined solvent deasphalting, hydr-ocracking-hydrofining, catalytic cracking, and hydrocracking zones:
results obtained when various important steps in the i11- vention are omitted or carried out improperly, making specific reference for clarification to FIGURE 2.
Example 2,-No distillate hydrocrackate from zone 47 to zone 60 When no distillate hydrocrackate (line 50 of FIGURE 2) is separated from the effluent of hydrocracking zone 47, but is instead included in the residual hydrocrackate passed to catalytic cracking zone 52, the amount of heavy vacuum gas oil passed to zone 52 is less, and the amount and boiling range of light vacuum gas oil passed to zone 60 are greater. The distillate hydrocrackate, especially the portion boiling below about 725 F., is not catalytically cracked as readily as the residual hydrocrackate, especially the portion boiling above about 900 F., land does not produce the high gasoline yield characteristic of the residual hydrocrackate. Thus, there are more light and heavy cycle oils produced in catalytic cracking. Hydroiining zone 60 has to be enlarged and/or operate at more severe, less economic, conditions.
If no distillate hydrocrackate is to be separated, then it would seem that zone 47 could be operated more economically at lower temperature and pressure as a hydrodemetalizer so as to provide a residual feed for catalytic cracking free of metal contaminants and of low Conradson or Ramsbottom carbon contents. Less hydrogen would then be required. It is found, however, that such a hydroned or hydrodemetalized deasphalted residual oil does not produce the synergistic eifect on heavy gas oil cracking to gasoline characteristic of the hydrocracked deasphalted residual oil, as disclosed in my pending application Serial No. 333,666, filed December 26, 1963, entitled Hydrocarbon Conversion Process. This is illustrated by the following comparative data obtained by catalytic cracking in a Fluid Catalyst Testing Unit (at conditions giving the same coke yield at 5 minutes cycle time, 950 F., 3.16-3.36 LHSV, and 3.6-3.8 catalyst/oil ratio): (A) a heavy gas oil, (B) a 50/50 blend of the heavy gas .oil with hydroned deasphalted residual oil, and (C) a 50/50 blend of the heavy gas oil with hydrocracked deasphalted residual oil.
When the hydrocracked residual oil alone was cracked'r in the FCTU at conditions as above giving 4.14 weight percent coke make, conversion was 75.4 weight percent, C2 minus gas 2.67 weight percent, and C3-430 F. gasoline 49.75 volume percent. Thus, when blended 50/50 with the heavy gas oil, there would be expected 58.2% conversion but only 41.18 volume percent gasoline yield.
In the above tests, the heavy gas oil, hydroiined de- 11 asphalted residual oil, hydrocracked residual oil, and blends, had the following inspections:
Stock Gas Oil Hydro- Blend Hydro Blend A lined Oil B cracked C Gravity, API 20. 2 19. 5 19. 4 25. 0 25. 2 Auiline Point, F 165. 4 200.3 258. 5 Viscosity, SSU at 210 F 53. 55 177. 0 82. 28 163 81. 83 Ramsbottom Carb n,
wt. percent 0. 72 1.12 0. 79 0. 11 Sulfur, wt. percent 0. 76 0. 20 0. 49 0. 04 0. 4 Nitrogen, wt. percent--. 0. 404 0. 52 0. 084 0. 28 N ickel-I-Vaua dium,
p.p.n1 2. 06 0.50 0. 93 1. l ASTM D-1160, F.:
Start 502 460 502 934 531 636 803 672 968 688 730 932 780 1, 001 816 791 1, 014 882 931 852 967 948 Conditions used in hydroconversion of the deasphalted residual oil to prepare the hydroned oil and hydrocracked oil were as follows:
Hydroning Hydrocracking Demetalation Demetalation Catalyst (l) (2) Temperature, F- 670 770 lressure, p.s.i.g 1, 000 2, 350 Space Velocity, LH SV-. 0. 62 0. 5 Hydrogen Flow, s.c.f.[bb1 1, 500 5, 000 Net Hydrogen Consumed, s.c 500 2, 000
2 Ni-W Silica Magnesia.
It appears that a hydrogen consumption of at least 1000 s.c.f./bbl.fis needed to impart to the .residual oil the property of enhancing catalytic cracking of straight run heavy rgas oil with high gasoline yields.
Example 3.-N0 residual hydrocrackate from zone 47 to zone 52 When no residual hydrocrackate (line 51 of FIGURE 2) is separated from Ythe effluent of hydrocracking zone 47, but is instead included in the material passed to zone 60 via line 50, less light vacuum gas oil can be included in the feed to zone 60 and must instead pass to catalytic cracking zone 52. The gasoline yield from catalytic cracking is lower. More gas, coke, and cycle oils are produced. Hydrolining zone 60 must be enlarged and/or operated at more severe, less economic, conditions. Otherwise, the hydrocracking catalyst in zone I66 deactivates rapidly.
Example 4.No residual hydrocrackatev from zone 47 lo either zone 52 or zone 60 The residual hydrocrackate could be passed directly to hydrocracking zone 66 if it could be made sufn'ciently clean, i.e., having only a low nitrogen content. This may be done by enlarging zone 47, operating at more severe conditions, and recycling to extinction the high boiling portion of the eluent which does not meet the nitrogen specification. Zone 66 must also be enlarged. Over-all, less gasoline is produced and at a higher cost `as compared to operation in accordance with the invention. The situation is improved with respect to ease of purifying the deasphalted oil if 4a lower yield is taken in extraction zone 44 so as to reject more oil in the asphaltie residue of line 46. There is then produced less gasoline and more fuel oil. The combinationofcatalytic cracking and hydroning is a superior route for eliminat-- Example 5.-No heavy cycle oil from zone 52 to zone 60 When heavy catalytically cracked cycle oil is not passed to zone 60 (via line .58 of FIGURE 2), but is instead recycled to a greater extent in the catalytic cracker to obtain greater conversion therein, the increased conversion shows up mainly as coke and gas rather thanas gasoline. In addition, the fresh feed capacity of the catalytic cracker is reduced due to the increased recycling, resulting in more straight run gas oil being fed to zone 60. Due to the higher nitrogen content of the vacuum gas oil relative to the heavy cycle oil, zone 60 must be enlarged and/or operated at more severe, less economic, conditions. This is attributable to another `unusual property of the hydrocracked deasphalted oil in the catalytic cracker feed, namely that it appears to crack readily to the same gasoline yield and total conversion;
up to 75%, but produces less gasoline at conversion above 75%. This is illustrated by the following FCTU data obtained with the hydrocracked oil described in Example 2.
Cycle time, min 5 5 5 Temperature, F 925 950 975 Space Rate, LHSV- 3.14 3. 14 3. 14 Catalyst/oil wt. ratio 3. 82 3. 82 3. 82 Conversion, Wt. percent 73 75. 4 76. 2 Coke, wt. percent 3. 87 4. 14 4. 60. Cz minus gas, Wt. percent 2. 32 2. 67 4.07 C5-430" F. gasoline, vol. percent 49.7 49. 75 47` By comparison, conversion of conventional catalytic cracker heavy gas oil feed drops from 41% to 35% when the temperature is lowered from 950 F. to 925 F., and
gasoline yield drops proportionately. Thus, the heavy cycle oil is derived primarily from the Vacuum gas oil portion of the catalytic cracker feed, and the more it is recycled the less advantage there is gained by having the hydrocracked deasphalted oil in the feed. Hence, .itV is important in the invention both that hydrocracked der: asphalted oil be passed to the catalytic cracker and that. heavy cracked cycle oil be passed to zone 60. The catalytic cracker may thus approach once-through operation.`
If this is done instead, `by passing the heavy cycle oil via line 59 to thermal cracking with asphaltic residua of line 46, less gasoline is obtained over-all and the productsy are of lower quality.
Example"6.-Nu hydrocracking of deasphalted residual oil It has been proposed to catalytically crack propane det asphalted oil alone or in admixture with heavy gas oil. The deasphalted oil of 'line 45 of FIGURE 2, however,
when obtained in accordance with the invention, isnot suitable for use as catalytic cracker feed because it has too high a content of organic metal compounds and too high a Ramsbottom carboncontent. The metals deposit on the cracking catalyst, rapidly building up to high concentrations causing excessive gas and coke producing activity and poor gasoline selectivity. To obtain acceptably clean deasphalted "oil from most vacuum residua it is necessary to restrict the yield of deasphalted oil to about 30% or lower, thereby rejecting more oil into heavy If udl 1 As mentioned, in the invention theyield from de. asphalting -is above 40%, preferably above 50%, as much oil.
higher metal and carbon `contents can be tolerated in hydrocracking zone 47.
Example 7.`"N0 solvent extraction or deasphalting is provided The vacuum distillation in `zone 39 may `bedone at a more perfect vacuum and highertemperature to cut deeper.
into the vacuum residua. This may be carried to the extent Where organic metal compounds appear in the heavy vacuum gas oil of line 41 in concentrations making the gas The metal-conyoil unsuitable for catalytic cracker feed. taminated vgas oil may be passed via line 48 to catalytic ing coke production. The synergistic effect of increasing conversion to gasoline is not observed, however, -as that appears t-o be a property peculiar to the residual, nondistillable, hydrocrackates. Further, the vacuum distillation cannot approach the yield obtainable by solvent extraction, so that the amount of asphaltic residue remaining to be thermal cracked or blended into fuel oil is greater. More cycle oil, obtained at considerable processing expense, must be blended into the residual to make viscosity speciiications.
1. A process for converting heavy residual oil predominantly to gasoline employing in combination at least one vacuum separation unit, at least one solvent extraction unit, at least one catalytic cracking unit, at least two catalytic hydrogenation units, and at least one catalytic hydrocracking unit; comprising:
passing heavy residual oil selected from the group consisting of heavy crude oil, topped crude oil, and atmospheric reduced crude oil to a vacuum separation unit and therein separating the heavy residual oil into a light vacuum gas oil, a heavy vacuum gas oil, and a residuum;
passing residuum so-obtained to a solvent extraction unit and therein separating the residuum by solvent extraction into a deasphalted residual oil and an asphaltic residue;
passing heavy vacuum lgas oil so-obtained to a catalytic cracking unit, therein subjecting the heavy vacuum gas oi-l to catalytic cracking conditions, and recovering cracked products including gasoline and heavy cracked cycle oil;
passing light vacuum gas oil so-obtained, deasphalted residual oil so-obtained, and heavy cracked cycle oil so-obtained to the catalytic hydrogenation units, therein subjecting the respective oils to catalytic hydrogenation conditions, in one of said units subjecting at least said deasphalted residual oil to catalytic hydrogenation conditions causing substantial hydrocracking conversion of from 30 to 70% of said deasphalted oil to distillate oil boiling below 900 F., recovering products including ta distillate gas oil hydrocrackate, and in another of said units subjecting at least said distillate -gas oil hydrocrackate to catalytic hydrogenation conditions causing substantially cornplete conversion of organic nitrogen in the oil passed thereto to NH3, and recovering hydrogenated products including gasoline, a low nitrogen content hydrogenated gas oil, and a high nitrogen content hydrogenated residual oil;
passing high nitrogen content hydrogenated residual oil so-obtained to the catalytic crackin-g unit wherein said heavy vacuum gas oil is treated, for cracking therein and recovery of cracked products including gasoline and said heavy cracked cycle oil;
and passing low nitrogen content hydrogenated gas oil so-obtained'to a catalytic hydrocracking unit, therein subjecting the hydrogenated gas oil to catalytic hydrocracking conditions, fand recovering hydr-ocracked products including gasoline.
2. A process in accordance with claim 1 wherein said catalytic hydrogenation units comprise a first stage unit employing a sulfactive hydrogenation catalyst at conditions causing substantial hydrocracking of oil passed thereto, and a second stage unit employing a sulfactive hydrogenation catalyst at conditions causing substantially complete conversion of organic nitrogen in oil passed thereto to ammonia; wherein said deasphalted residual oil is passed to said first stage unit and the eluent therefrom is separated into products including gasoline, a distillate gas oil hydrocrackate, and a residual hydrocrackate; said residual hydrocrackate is passed to the catalytic cracking unit as the aforesaid high nitrogen content hydrogenated residual oil; and wherein said distillate gas oil hydrocrackate, said light vacuum gas oil, and said heavy cracked cycle oil are passed to said second stage unit and said l-ow nitrogen content hydrogenated gas oil -is recovered from the eluent therefrom.
3. A process in accordance with claim 2 wherein said vacuum separation unit comprises a vacuum distillation stage wherein atmospheric reduced crude oil is separated by distillation into said light vacuum gas oil and vacuum residuum, and a residuum stripping stage wherein vacuum residuum and heavy crude oil are separated by steam stripping under vacuum into said heavy gas oil yand said residuum.
4. A .process in accordance with claim 2 wherein in said solvent extraction unit said residuum is contacted with a liquid propane-butane solvent at conditions controlled to obtain as the extract deasphalted residual oil containing at least l0 p.-p.m. total of nickel and vanadium and having a Ramsbottom carbon content below about 6 weight percent, in a yield of at least 40% by volume based on residuum feed to the solvent extraction.
5. A process in accordance with claim 2 wherein in each of the catalytic hydrogenation units there is employed the same sulfactive hydrogenation catalyst comprising a Group VII metal sulfide and a Group VI metal sulfide associated with a refractory oxide carrier, having no more than weak acidity, and in the catalytic hydrocracking unit there is employed a strongly acidic hydrocracking catalyst comprising a Group VIII metal sulde associated with a refractory oxide carrier having cracking activity.
6. A process for converting heavy residual oil predominantly to gasoline employing in combination at least one vacuum separation unit, at least one solvent extraction unit, at least one catalytic cracking unit, at least two catalytic hydrogenation units, lat least one catalytic hydrocracking unit, and at least one thermal cracking unit; comprising:
passing heavy residual oil selected from the group consisting of heavy crude oil, topped crude oil, and atanospheric reduced crude oil to a vacuum separation unit and therein separating the heavy residual oil into a light Vacuum gas oil, a heavy vacuum gas oil, and a residuum;
passingresiduum yso-obtained to a solvent extraction unit and therein separating the residuum by solvent eX- traction into a deasphalted residual oil and an asphaltic residue;
passing heavy vacuum gas oil so-obtained to a catalytic cracking unit, therein subjecting the heavy vacuum gas oil to catalytic cracking conditions, and recovering cracked products including gasoline, light cracked cycle oil, and heavy cracked cycle oil;
passing light cracked cycle oil so-obtained and asphaltic residue so-obtained by solvent extraction to a thermal cracking -unit and therein subjecting the mixture to thermal cracking conditions, and recovering thermal cracked products including gasoline and heavy fuel oil;
passing ydeasphalted residual oil so-obtained to a first stage catalytic hydrogenati-on unit employing a sulfactive hydrogenation catalyst, therein subjecting the deasphalted oil to catalytic hydrogenation conditions causing substantial hydrocracking of the oil passed thereto, separating the eflluent therefrom into products including gasoline, a distillate gas oil hydrocrackate, and a residual hydrocrackate comprising high nitrogen content hydrogenated residual oil; passing light vacuum gasoil so-obtained, heavy cracked cycle oil so-obtained, and distillate gas oil hydrocrackate so-obtained to a second stage catalytic hydrogenation unit employing a sulfactive hydrogenation catalyst, therein subjecting the respective oils to catalytic hydrogenation conditions causing substantially complete conversion of organic nitrogen in oil passed thereto to ammonia, recovering low nitrogen content hydrogenated gas oil from the eiiluent therefrom; passing high nitrogen content hydrogenated residual oil so-obtained to the catalytic cracking unit wherein said V15 l 16 heavy vacuum gas oil is treated, for cracking therein References Cited by the Examiner and recovery of cracked products including gasoline l UNITED STATES PATENTS 'and Sad heavy facked Cycle 011; 2,925,374 2/1960 Gwin en a1. 208-86 and passlng low nitrogen content hydrogenated gas 011 3,019,180 1/1962 Schreiner et aL 208%80 so-obtained to a catalytic hydrocracking unit, therein 5 3,072,560 1/1963 Paterson et a1 208-110 subjecting the hydrogenated gas oil to catalytic hydrocracking conditions, and recovering hydrocracked DELBERT E- GANTZ Prmay Exammef" products including gasoline. HERBERT LEVINE, Assistant Examiner.V
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