US3852186A - Combination hydrodesulfurization and fcc process - Google Patents

Abstract

A process is described for fixed bed hydrodesulfurizing a nonasphaltic oil feed or feed blend for a zeolitic FCC riser cracking system in which cracking occurs at a space velocity sufficiently high to prevent formation of a catalyst bed. It is found that sulfur dioxide emissions from the zeolite catalyst regenerator associated with the riser are reduced to a lower extent than total sulfur removal from the feed oil. This indicates uneven sulfur removal in the hydrodesulfurization step whereby a smaller portion of sulfur is removed from the heavy portion of the feed from which the coke is derived than from the lighter portion of the feed. The present invention demonstrates a synergistic effect upon sulfur removal from the heavy portion of the feed by widening the boiling range of the feed and this synergistic effect is converted to practical advantage by reducing the amount of hydrodesulfurization catalyst in proportion to said synergistic effect, thereby keeping hydrocracking to a specified low level. The hydrodesulfurization effluent is charged to the FCC process wherein the ratio of gasoline to total conversion is enhanced by reducing the amount of hydrodesulfurization catalyst and hydrocracking as permitted by said synergistic effect.

Description

United States Patent 19.1

Christman et a1.

Dec. 3, 1974 Appl. No.: 346,121

[52] US. Cl 208/89, 208/61, 208/216 [51] Int. Cl C10g 23/04 [58] Field of Search 208/89, 216, 58, 61

[56] References Cited UNlTED STATES PATENTS 2,600,931 6/1952 Slater 208/61 2,897,143 7/1959 Lester et a1 i i 208/216 2,938,857 5/1960 Johnson eta1 i i 208/89 2,958,654 11/1960 Honeycutt 208/89 3,011,971 12/1961 Slyngstad et a1. 208/216 3,193,495 7/1965 Ellor et a]. 2(18/216 3,287,254 11/1966 Paterson 208/89 3,475,327 10/1969 Eng et a1 208/216 3,617,512 ll/197l Bryson et a1 i 208/80 3,700,586 10/1972 Schulman 208/89 Primary ExaminerDelbert E. Gantz Assistant Examiner.lames W. Hellwege [57] ABSTRACT A process is described for fixed bed hydrodesulfurizing a non-asphaltic oil feed or feed blend for a zeolitic FCC riser cracking system in which cracking occurs at a space velocity sufficiently high to prevent formation of a catalyst bed. It is found that sulfur di oxide emissions from the zeolite catalyst regenerator associated with the riser are reduced to a lower extent than total sulfur removal from the feed oil. This indicates uneven sulfur removal in the hydrodesulfurization step whereby a smaller portion of sulfur is removed from the heavy portion of the feed from which the coke is derived than from the lighter portion of the feed. The present invention demonstrates a synergistic effect upon sulfur removal fromthe heavy portion of the feed by widening the boiling range of the feed and this synergistic effect is converted to practical advantage by reducing the amount of hydrodesulfurization catalyst in proportion to said synergistic effect, thereby keeping hydrocracking to a specified low level. The hydrodesulfurization effluent is charged to the FCC process wherein the ratio of gasoline to total conversion is enhanced by reducing the amount of hydrodesulfurization catalyst and hydrocracking as permitted by said synergistic effect.

9 Claims, 7 Drawing Figures PAIENIL'DBEB 3mm 852, 1 6

SHEET 10F 6 FIGJ HYDRODESULFURIZATION OF KUWAIT GAS OIL AND VARIOUS KUWAIT LUBE OIL EXTRACT BLENDS: SULFUR REMOVED VERSUS TEMPERATURE Coiolysf: lll6'inch NiCoMo on Alumina Operating Condihons: OOO PSIG, 2.0LHSV, ZOOOSCF/BbI. Of 70% H (Recycle Gas scrubbed) 85% H Makeup Light Lube Extroncf g, (5.06% s;-,|o-s0% a R. =695-B !OF)// E 4: l4 u E In I U) j Br ghI Stock U l2 A/ Extra" 2 4.9m. s, O-9Q%B.R o I was 32m s /"D a: I IO J-Y 70%Goa 01 and 30% 5) Exfr lct lend J (APlusEorA us C/ A B l I I Full Range Gas 0 I s sqqu n Average Reactor Temperature F PATENTLU [353 31974 SHEET 2 OF 6 F/GZ DESULFURIZATION OF KUWAIT C 68OF DISTILLATE CHARGE Blend of 43.5% Deb. Nophtho and 56.5% Furnace Oil 5 Content of Nophtho S Content of Furnuce Oil CONDITIONS! 4.0-5.0 LHSV, 700psig press, 200 SCF of H -rich (90%)gus/bbl, gas scrubbed with amine, 400psi H pp ut outlet.

5.0 ILHSV 4 CL? 5V 0 5 O 5 o 5 3 2 2 I.

2: f /-E(n;o NAPHTHA 1 PRESENT) s 4 M w m w m c0200; :0 30:5 *0 CO Z QQQ TEMPERATUREZF PATENTEDBEE awn 3,852, l saw 3 or 6 DESULFUR IZATION OF HEAVY OIL PLUS LIGHT OIL Sulfur in Heuvy Portion Only of the Product Sulfur Weight Percent r in Total id Product 0 I00 Peint 0t lnyection of Light Oil: Percent of Bed Depth (Heavy Oil Injected at 0 Percent Bed Depth In all Cases) Temperature of 90 Temperature of IO Difference Between 80ond 90 Percent PointszF Percent Pomr. F

Percent Points: F

I PATENTED 31974 $852,186

SHEET t 0F 6 (30 Percent DistillntW Point) 920 r} 1 (IO Pbrcenm'isrumion Point) 640 630 330 320 La I 3 I o e A YE) 290 4 (e0 1 (NF 0 I 2 2.74 2222250., WW Sulfur Removed: weight Percent of Feed 551%??? (Reactor Length) Feed) ASTM DISTILLATION TEMPERATURE F 8BR! 5 OF 6 HYDRODESULFURIZATION OF DISTILLATE I CONTAINING 0.3! WEIGHT PERCENT SULFUR I050 WEIGHT PERCENT OESULFURIZATION COMBINATION HYDRODESULFURIZATION AND F CC PROCESS The present invention is directed to the hydrodesulfurization of non-asphaltic distillate or extract oils. The present invention is particularly directed to the hydrodesulfurization of distillate or extract oils prior to riser cracking of the oils with a zeolite catalyst at a low riser residence time'without catalyst bed formation in the riser reaction flow path.

This application is related to five other applications filed on even date herewith under the same inventive entity entitled I-Iydrodensulfurization Process Involving Regulation of Amount of Catalyst in Relation to Feed Boiling Range to Limit Hydrocracking, Hydrodesulfurization Process Involving Blending Low Boiling and High Boiling Streams, I-Iydrodesulfurization Process with a Portion of the Feed Added Downstream in the Reactor, Hydrodesulfurization and FCC of Blended Stream Containing Coker Gas Oil and Hydrodesulfurization Process for Producing Fuel Oil and FCC Feed.

In accordance with this invention, in riser cracking processes charging sulfur-containing feeds, the sulfur content of the feed is reduced by hydrodesulfurization in order to reduce sulfur emissions to the atmosphere. One means of reducing each sulfur emissions to the atmosphere is to hydrodesulfurize substantially an entire gas oil feed stream prior to cracking by passing the gas oil feed stream containing sulfur in the presence of hydrogen downflow over a fixed compacted bed of catalyst particles comprising at least one Group VI and at least one Group VIII metal catalyst on a suitable noncraking support such as alumina which may or may not contain a stabilizing but non-cracking quantity of silica, i.e., less than about I or 0.5 weight percent silica. Examples of suitable hydrodesulfurization catalysts include nickel-cobalt-molybdenum, cobalt-molybdenum, nickel-tungsten -tungsten, and nickel-molybdenum. Suitable hydrodesulfurization conditions include a temperature range of 650 to 800F., generally, and 670 to 800F., preferably, a pressure range of 500 to 1800 psig, generally, 800 to 1500 psig, preferably, and 800 to 1200 psig, most preferably, a space velocity range of 0.5 to 5 LI-ISV, based upon the heavy portion of the total feed only (e.g. 650 to 1050F. feed) generally, and 0.7 to 2 Ll-ISV, preferably, and a circulation rate of 1000 to 8000 SCF/B, generally, and 2000 to 3000 SCF/B, preferably, based on the heavy feed portion of the total feed (i.e., the 650 to 1050F. feed portion) of hydrogen or a gas containing generally about 75 to 80 percent hydrogen. Hydrogen consumption varies depending on process conditions, feed sulfur content, etc. and can range from 100 to 500 SCF/B, based on said heavy portion of the feedstock, generally. For example, in a feed containing about 3.0 weight percent sulfur, about 400 SCF/B of hydrogen consumption occurs at about 1000 psig and about 500 SCF/B of hydrogen is consumed at about 1800 psig. The above ranges are based upon the heavy oil portion only of a total feed, which can also contain a light portion (such as 400F. to 600 or 650F. furnace oil), because the primary objective of the hydrodesulfurization is the removal of the sulfur from the heavy oil portion and it is the heavy oil portion in which most of the sulfur is concentrated.

When a desulfurized feed is charged to a zeolite FCC riser operated without hydrogen addition thereto and having a catalyst regenerator associated therewith for continuous catalyst regeneration, removal of sulfur from the feed stream results in a reduction in sulfur emitted in the product gases from the riser and also results in a reduction in sulfur emitted from the flue gases of the regenerator. However, we have found that the reduction of sulfur emitted from the riser is greater than the reduction of sulfur emitted from the regenerator. This is a disadvantageous feature because the sulfur emitted from the FCC riser is emitted in the form of hydrogen sulfide which is formed by the scission of a molecule at an internal sulfur atom by means of splitting off hydrogen sulfide from the molecule, thereby producing olefinic fragments of the parent molecule. The formation of hydrogen sulfide is not particularly serious because the hydrogen sulfide can be scrubbed from gases from the FCC riser with an amine solution, such as monoethanolamine, which is known to be capable of removing hydrogen sulfide. Therefore, the hycombustion in the regenerator in'the presence of oxygen, the sulfur in the coke-is converted to sulfur dioxide or sulfur trioxide, while the carbon is converted to carbon monoxide or carbon dioxide. The sulfur oxides formed in the regenerator form a more serious atmospheric pollution problem than the hydrogen sulfide formed in the FCC riser because the sulfur oxides cannot be easily removed by scrubbing of the regenerator flue gas prior to reaching the atmosphere. Therefore, sulfur oxides formed by combustion in the regenerator are emitted to the atmosphere in the regenerator flue gas as noxious atmospheric pollutant. For a diagrammatic scheme of a riser-regenerator system of the type contemplated in this invention, see FIG. 3 of US. Pat. No. 3,617,512, which is hereby incorporated herein, wherein sulfur dioxide is removed from the regenerator through line 74 while hydrogen sulfide is removed from the riser through line 56, from which it can be aminescrubbed.

We have found that, disadvantageously, for any degree of sulfur removal in the total hydrocarbon feed stream to the FCC riser the percent reduction in the noxious sulfur dioxide formed in the regenerator is less than the overall percent of sulfur removed from the total feed stream. The reason is that the sulfur dioxide formed in the regenerator is derived from sulfur present in the higher boiling molecules of the feed which are the molecules in the feed which are the most difficult to hydrodesulfurize. These high boiling molecules do not vaporize when the feed stream contacts hot regenerated catalyst at the equilibrium flash vaporization temperature at the bottom of the riser and therefore are converted to the coke which is formed on the catalyst in the bottom of the riser. In one test it was found that the desulfurization of a West Texas gas oil blend reduced the sulfur content from a feed sulfur content of 1.75 weight percent to 0.21 weight percent (88.0

' 1.75 weight percent sulfur was cracked without hydrodesulfurization the weight fraction of feed sulfur which ended up in the regenerator flue gas was 0.051 whereas when the feed was hydrodesulfurized as described the weight fraction of sulfur in the hydrodesulfurization feed which appeared in the flue gas increased to 0.087. Multiplying 1.75 pounds of sulfur per 100 pounds of non-hydrodesulfurized feed times the 0.051 weight fraction equals 0.089 pounds of sulfur emitted; whereas multiplying 0.21 pounds of sulfur per 100 pounds of hydrodesulfurized feed times the 0.087 weight fraction equals 0.018 pounds of sulfur. This represents a reduction of only 79.8 percent in .theweight of sulfur emitted from the regenerator flue gas as compared to a total reduction of 88.0 percent reduction in sulfurin the feed.- Therefore an 88 percent reduction of sulfur content in the feed stream results in only a 79.8 percent reduction in sulfur emitted from the FCC regenerator stack gases.

The following table shows how hydrodesulfurizationof the aforementioned gas oil feed stream changed the distribution of sulfur in the various streams associated with an FCC riser. The non-desulfurized feed contained 1.75 weight percent sulfur. The desulfurized feed contained 0.21 weight percent sulfur.

SULFUR DISTRIBUTION IN PERCENT NON-DESULFURIZED FEED in Regenerator The above data show that, although the total amount of sulfur in the flue gas is reduced, the proportion of total remaining sulfur that ends upin the regenerator flue gas almost doubles as a result of desulfurization of the feed. Hydrodesulfurization of the feed oil clearly results in uneven removal of sulfur from the feed oil. The above data indicate that any hydrodesulfurization process for the removal of sulfur from the feed stream to an FCC zeolite cracking riser (fluid catalytic cracker) should be encouraged to be more favorable to removal of sulfur from the highest boiling molecules as compared to the lowest boiling molecules inthe feed. This is because the data show a disproportionate increase in sulfur in the regenerator flue gas and in the cycle oil, both of which streams are derived from the sulfur in the highest boiling portions of the feed. This presents a difficult problem because the desulfurization reaction rate constant for the lower boiling molecules in the cracking feed stream is exponentially higher than the desulfurization reaction rate constant of the higher boiling molecules. For example, the dew]- furization reaction rate constant of a feed having a volume average boiling point of 493F. is 185 whereas the desulfurization reaction rate constant of a feed having a volume average boiling point of 1043F. is only 2.75. The exponential relationship between desulfurization reaction rate constant and volume average boiling point of a hydrocarbon feed is shown in Table 1.

TABLE 1 Volume Average Desulfurization The above data illustrate the great difficulty associated with removing sulfur from the high boiling portions of 'a feed stream as compared with the low boiling portions of the same feed when the feed source has a significantly wide boiling range.

In accordance with the present invention we have discovered a means of improving desulfurization of the higher boiling components in a hydrocarbon feed stream. Our discovery is based upon data showing the existence of a synergistic effect in desulfurization reaction rate between the lowest and the highest boiling sulfur-containing molecules in the hydrodesulfurization process wherein desulfurization of the highest boiling sulfur-containing molecules is enhanced at the expense of desulfurization of the lower boiling sulfurcontaining molecules but because the higher boiling portions of the feed are richer in sulfur there is a net positive effect in terms of total sulfur removal due to the synergism. We have found that when the hydrodesulfurization reaction is controlled in such a manner that there is a high degree of selectivity toward desulfurization as contrasted to hydrocracking the synergistic effect may be used to maximum advantage. The low boiling molecules assist the high boiling molecules in the desulfurization process, perhaps by alternating use of the same reaction sites wherein the rapidly reacting lighter molecules utilize a given site between utilization of the site by consecutive slower reacting heavy molecules. Because the lighter molecules react so rapidly, the active sites are available to the heavy molecules a greater portion of the time than when the heavy molecules are processed along at the same space velocity. We have observed that as the boiling range of a hydrocarbon feed I barrel of feed diminishes as compared to the hydrodesulfurization of the high and low boiling portions of the same stream in separate reactors at the same condi tions, indicating the occurrence of a synergistic sulfur removal effect between molecules of different boiling points. For example,Table 2 shows that for a particular crude source as the difference in temperature between the end point and the initial boiling point of a feed stream having a volume average boiling point of 850F. increases there is a proportional reduction in catalyst requirement, compared to that required for treating the light and heavy halves of the feed separately, to accomplish a given amount of sulfur removal. Table 3 shows that for the same crude source, as the difference in 5 temperature between the end point and the initial boilthat required for treating the light and heavy halves separately, without changing other conditions. The reduction in catalyst requirement to accomplish a given amount of sulfur removal without changing other reaction conditions is different when the feed has a volume average boiling point of 750F. as compared to a feed having a volume average boiling point of 850F. In both cases, the reduction in catalyst requirement increases as the breadth of boiling range increases. The basis for comparison in determining the reduction in catalyst requirement in Tables 2 and 3 is the amount of catalyst that would be required if the same amount of feed oil containing a given amount of sulfur is treated, except that the temperature differential between the E. P. and I. B. P. is changed as indicated. For example, the 0 data point in Tables 2 and 3 represent a given quantity of oil, all of which boils at 850 and 750F., respectively. The second data point represents the same quantity of oil having a boiling range extending over 100F. The third data point represents the same quantity of oil having a boiling range extending over 200F. The data show that significant reductionsin catalyst requirements become possible when the boiling range of the feed oil is at least 400 or 500F. wide when the volume average boiling point of the feed is at least 750F. Even greater savings in catalyst becomes possible if the range between the feed IBP and EP is at least 600F.

TABLE 2 Reduction in Catalyst Requirement for Feed Having a Volume E.P. I.B.P.

Average B.P. of of 850F. Percent Feed F.

0 O 0.2 100 3 200 7 300 l l 400 I6 500 TABLE 3 Reduction in Catalyst Requirement for Feed Having a Volume E.P. I.B.P.

Average B.P. of of 750F. Percent Feed F It is important to the present invention that the catalyst economy permitted by broadening the feed boiling range be correlated with the synergistic effect to remove a substantial amount of the most refractory sulfur in the feed with diminished hydrocracking. Therefore, in accordance with the present invention the synergistic effect should not be permitted to reduce the catalyst quantity to the extent that the 90 percent point of the feed is not reduced at least 10F. or F indicating a substantial removal of the most refractory sulfur in the feed in spite of the reduced quantity of catalyst. At the same time, the catalyst reduction should be sufficient so that the 10 percent distillation point of the feed is not lowered more than 20 "F. more than the 90 percent distillation point, and in any event the 10 percent distillation point is not lowered more than 50F. In this manner, the amount of catalyst is limited to advantageously permit both enhanced desulfurization (cleavage of carhon-sulfur bonds) while significantly inhibiting hydrocracking (cleavage of carbon-carbon bonds). Therefore, in accordance with this invention, under the same reaction conditions proportionately more catalyst is required to remove the same amount of sulfur from the higher-boiling half of the total feed when it is treated by itself than if the higher-boiling half of the total feed is hydrodesulfurized in blend with a lower boiling half of a total feed stream. With certain feeds, the reduced catalyst requirement when treating the blend permits the blend-treatment process to be terminated before decreasing the boiling characteristics of the feed beyond that described above.

Data were taken (Table 4 and FIG. I) to illustrate that the synergistic effect of the present invention is highly surprising and is a synergistic effect based upon the sulfur removal reaction. For example, data were taken employing as a hydrodesulfurization feed a full range gas oil containing 2.93 percent sulfur. The l0 and 90 percent distillation points of the full range gas oil were 680 and 101 1F. respectively. Thereupon, blends of the gas oil and lubricating oil extracts were prepared, each lubricating oil extract stock having about the same sulfur content but a different boiling range and a different viscosity. In one case the lubricating oil extract was a light lubricating oil extract containing 5.06 weight percent sulfur having 10 and 90 percent distillation points of 695 and 820F., respectively. The light lubricating oil had a boiling range within the boiling range of the full range gas oil and was of about the same viscosity. In the second case the lubricating oil extract was a bright stock extract whose boiling range extented considerably outside the boiling range of the full gas oil on the high side, having a 10 percent distillation point of l0l0 and an estimated 90 percent distillation-point of ll32F., respectively, and was considerably more viscous than the gas oil. The bright stock extract had a sulfur content of 4.97 weight percent. In each case where a gas oil-lubricating oil extract blend was desulfurized, the blend comprised percent of a portion of the same gas oil together wtih 30 percent of the particular lubricating oil extract, i.e., either the light lubricating oil extract or the bright stock extract.

' It would be expected that the blend containing the bright stock extract would have been more difficult to desulfurize because it had a higher average boiling point and was more viscous than the blend containing the light lubricating oil extract which had a boiling point within the range of the gas oil with which it was blended and about the same viscosity. This expectation is especially true since data show that the bright stock extract, by itself, was considerably more difficult to hydrodesulfurize than the light lubricating oil extract, by itself. However, it was unexpectedly found that there was a considerable synergistic effect in regard to sulfur removal in the case of the blend of the bright stock extract and the gas oil, even though the bright stock boiled considerably above the upper boiling point of the gas oil and had a considerably higher viscosity,

which would be expected to slow the reaction rate. It

was further found that there was no synergistic effect in regard to sulfur removal in the case of the blend of the gas oil and the light lubricating oil extract whose boiling range was within the boiling range of the gas oil.

is more easily desulfurized than the unblended and more viscous bright stock extract under similar conditions. Tables 4 and 4A show that a synergistic effect becomes controlling due to a widening of feed boiling These results are shown in Table 4 and are illustrated range by blending a material having an overlapping, in FIG. 1. continuous or broader boiling range. As explained be- TABLE 4 HYDRODESULFURIZATION OF KUWAIT GAS OIL AND BLENDS OF KUWAIT GAS OIL AND KUWAIT LUBE 01L EXTRACTS Charge and Product lnsgctions Full Range 70% (3.0. 30% 70% 6.0. 30%

gas Oil Light Lube Extract Bright Stock Extract I Charge Charge Charge l-lydrodesulfurization (Not hydro- (Not hydro- (Not hydro Temperature: F. desulfurized) desulfurized) 680 710 desulfurized) 680 710 Inspections Gravity: "APl 22.4 18.1 23.6 24.4 19.2 23.9 24.5

Sulfur: 96 by weight 2.93 3.63 0.91 0.60 3.66 0.94 0.61 Viscosity: SUS

100F. 301.4 550 1320 130F. 119.3 220 82.3 74.9 310 171.2 146 210F. 48.7 42.2 41.0 55.1 52.1

Distillation, Vacuum: D1160 10% at F. 689 700 671 643 710 710 687 754 738 728 719' 792 803 777 8 l 8 780 773 765 894 903 864 70% 897 845 837 827 999 1004 964 90% 1011 948 944 936 1079 1110 1061 End Point: F; 1015 I The surprising results in regard to Table 4 are shown in the following summation entitled Table 4A which contains data directly extracted from Table 4.

TABLE 4A low, the synergistic effect upon reaction rate upon blending is also illustrated in FIG. 1, by comparing curves B and C and observing that in blend they both 70% G.O. 30% Light Lube Extract Hydrodesulfurization Temperature: F.

Sulfur in Feed Weight Percent Sulfur in Product Weight Percent lncrease in difference between the 10 and 90 percent distillation points due to hydrodesulfurization Temperature of 90 percent point: F.

B right Stock Extract Table 4A shows that the mixture containing the gas oil and light lube extract had about the same sulfur con- 5 0 tent as the mixture containing the gas oil and bright stock extract. Table 4A further shows that at desulfurization temperatures of 680 and 710F., respectively, about the same degree of sulfur removal occurred with each charge stock. These data tend to obscure and hide the discovery of the present invention since they tend to show that any feedstock having a fixed feed sulfur content is desulfurized to the same extent at the same desulfurization conditions. However, the results shown in Table 4A become surprising when it is realized that the bright stock extract mixture is much more viscous than the mixture containing the light lube oil extract and therefore would have been expected to result in a lower degree of sulfur removal due to diffusion difficulties arising from its higher viscosity. This expectation is especially true in view of FIG. 1 which shows that the unblended and less viscous lightlubricating oil extract produce curve D. I I a Table 4A also shows that the gas oil-light lubricating oil extract blendwas not capable of hydrodesulfurization without an increase in the temperature difference between 10 and percent distillation points of more than 20F., indicating the onset of significant hydrocracking, whereas the 710F. test with the gas oilbright stock extract blend resulted in only a 5F. increase in this temperature differential, indicating very little hydrocracking accompanying the desulfurization reaction, while the 90 percent point dropped from 1079 to 1061F. (18F), indicating a significant removal of sulfur from the highest boiling, most viscous portion of the feed. In the test in which there was only a 5F. temperature differential increase, this low temperature differential increase was accomplished because there was no increase in quantity of catalyst upon widening the boiling range of the feed. lf the quantity of catalyst were increased, as by lengthening the catalyst bed, extensive hydrocracking would have been encountered when low sulfur levels were reached because the presence of sulfur serves to inhibit onset of extensive hydrocarcking. Therefore, the sulfur-removal synergistic effect of the present invention requires that the quantity of catalyst be controlled or limited as the boiling range of the feed oil is widened if extensive hydrocracking is being experienced with that boiling range. Thereby, the savings in catalyst required increases as 'the boiling range of the feed widens.

FIG. 1 illustrates diagrammatically the synergistic effect based upon the data in Table 4 and Table 4A. Referring to FIG. 1, line A shows the desulfurization characteristics versus reaction temperatures of the full range gas oil by itself. Line B shows the desulfurization characteristics of the light lubricating oil extract by itself versus reaction temperatures. Line C shows the desulfurization characteristics of the much heavier bright stock extract by itself versus reaction temperatures. FIG. 1 shows that even though the bright stock extract had about the same amount of sulfur in the feed as the light lubricating oil extract, because of its higher viscosity, and lower reaction rate due to its higher boiling range, as expected, less sulfur was removed when it was treated by itself. This shows that when the bright stock extract is treated by itself and when the light lubricating oil extract is treated by itself viscosity and reaction rate due to boiling range (see Table 1) is a controlling feature in the hydrodesulfurization reaction.

Line D in FIG. 1 represents the sulfur removal characteristics versus reaction temperatures of (1) the blend of the gas oil of curve A and the light lubricating oil extract curve B, and also 2) the separate blend of the gas oil of curve A and the bright stock extract of curve C. Line D unexpectedly shows the same desulfurization results are achieved when a 70 percent 30 percent blend of gas oil is made up with either the light lubricating oil extract or the much heavier and more viscous bright stock extract. Line D therefore shows there is a synergistic effect in reaction rate between the bright stock extract, which boils above the boiling range of the gas oil, which overcomes the diffusion limitation due to viscosity whereas there is no synergistic effect in the case of the blend of the gas oil and the light lubricating oil extract wherein the light lubricating oil boils within the boiling range of the gas oil. In general, the wider the boiling range to which a feedstock can be extended, the greater will be the synergistic effect between the lightestand heaviest-boiling components in regard to hydrodesulfurization synergism.

' provide the same hydrodesulfurization characteristics as the blend of the lower boiling light lubricating oil extract and gas oil. Since the bright stock extract has a boiling range higher than the gas oil, it is not only more viscous than the gas oil and therefore should provide a high diffusion resistance in the hydrodesulfurization reaction but also, as shown in Table 1, it has a lower reaction rate constant because of its high average boiling point, as compared to the lower boiling light lubricating oil extract. However, both (1) the high viscosity diffusion effect which provides resistance against the hydrodesulfurization reaction in the absence of blending and (2) the lower reaction rate constant of the bright stock extract due to its higher average boiling point were overcome to the extent that the bright stock extract blend with the gas oil exhibited the same hydrodesulfurization characteristics as the blend of the light lubricating oil extract with the gas oil, the latter blend not having overlapping boiling ranges. Therefore, there is a considerable synergistic effect in reaction rate by combining stocks having overlapping boiling ranges causing the boiling range of the blend to be wider than the boiling range of either component alone. The same effect could be obtained by preparing directly via distillation a hydrodesulfurization feedstock having a very wide boiling range. The advantageous result of the present invention can be achieved by combining feedstocks in a single reactor which ordinarily are hydrodesulfurized in several reactors such as furnace oil, light gas oil, heavy gas oil, light and medium lubricating oil, light and medium lubricating oil extracts, coker gas oil, FCC cycle oil, and so forth, in a manner that the improved synergism in regard to the sulfur removal reaction rate is greater than the detriment due to the inhibited diffusion effect and low reaction rate contributed by the higher-boiling component. Example 7 shows a special effect occurs when a virgin gas oil is blended with coker gas oil. One or all of the mixed streams can be separated from the hydrodesulfurized blend effluent, if desired. For example, heavy gas oil and furnace oil can be blended priorto hydrodesulfurization and then separated following desulfurization, with the furnace oil being employed as a'fuel and the heavy gas oil being employed as an FCC feedstock.

Tables 48 and 4C present a tabulation of the feed and product data from which curves B and C of FIG. 1 were obtained. In Table 4C, certain boiling points of the feed were estimated because of the difficulty of distillation of very high boiling material.

TABLE 4B I-IYDRODESULFURIZATION OF KUWAIT LIGHT LUBE EXTRACT at 1000 psig, 2 vol/hr/vol and 2000 "SCF/B Hydrodesulfurization TABLE 4c i HYDRODESULFURIZATION OF KUWAIT BRIGHT STOCK EXTRACTS at 1000F., 2 vollhr/vol and 2000 SCFIB Hydrodesulfurization Charge Temperature F. (Not hydro- 680 710 740 desulfurized) Inspections Gravity: APl 12.3 17.4 18.7 19.5 Sulfur: by weight 4.97 2.41 1.63 0.98 Desulfurization: 51.5 67.2 80.4 Distillation, Vacuum: D1160 at F. 1010 956 883 832 I034 I005 988 930 1057 1046 1040 1022 1086 1093 90% 1132 End Point Further tests were performed to illustrate the syner- 20 on the low-temperature side of the range. Tests were gistic effect in hydrodesulfurization reaction rate utilizing a nickel-cobalt-molybdenum on alumina catalyst (all hydrodesulfurization tests reported herein utilized this type of, catalyst composition unless otherwise noted) when the added. stream has a boiling range which overlaps, is'contiguous with or extends beyond that of the primary stream, but where the extension is made in which a blend containing 35 weight percent of furnace oil having a boiling range of 475 to 638F. was added to full range gas oil having a boiling range of 615 to 1O05 F. containing light lubricating oil extract having a boiling range of 706 to 840F. The results of these tests are shown in Table 5 and in Table 6.

TABLE 5 HYDRODESULFURIZATION OF BLENDED CHARGE STOCKS Conditions: 680F., 940 psig, 0.8 LHSV, 2000 SCF/B H Charge Sulfur Content Kuwait Product Sultur Content l 1 ppm 1.43 weight Furance Oil Product Yield 97.91 wt of fresh feed (475638F. Unit Hydrogen Consumption 387 SCFIB BR.) Aromatics decreased from 36 to 2| vol Charge Sulfur Content Kuwait Full Product Sulfur Content 0.18 wt 2.74 weight Range Gas Product Yield 96.65 wt of fresh feed i1 Unit Hydrogen Consumption 499 SCF/B (615-1005F. Aromatics decreased from 51 to 41 vol B.R-)

Charge Sulfur Content Kuwait Lube Product Sulfur Content 0.88 wt 6.03 weight Oil Extract* Product Yield 94.52 wt of fresh feed (706840F. Unit Hydrogen Consumptionn 1024 SCFIB B.R.) Aromatics decreased from 88 to 81 vol Hydrodesulfurizing a Blend of 35 wt Kuwait Furnace Oil 53 wt Kuwait Full Range Gas Oil 12 wt Kuwait Lube Oil Extract Charge Sulfur Content Calc. Results Product Sulfur Content 0.20 wt 2.68 weight for the Product Yield 96.84 wt of Fresh Feed Blended Hydrogen Consumption 514 SCFIB Material Aromatics 38.2 vol Charge Sulfur Content Observed Results Product Sulfur Content 0.14 wt 2.68 wt for the Blended Product Yield 96.26 wt of fresh feed Material Unit Hydrogen Consumption 463 SCFIB Aromatics 40.0 vol This run was made at 3000 SCFIB reactor gas rate to compensate for high hydrogen consumption. Results calculated by algebraic combination of component results shown above.

TABLE 6 HYDRODESULFURIZATION OF BLENDED CHARGE STOCKS Conditi0ns: 680F., 940 psig, 1.6 LHSV, 2000 SCFIB (80% H Charge Sulfur Content 1.43 weight 4 n... Kuwait Furnace Oil (475-638F.

F TABLE 6 Continued HYDRODESULFURIZATION OF BLENDED CHARGE STOCKS Conditions: 680F., 940 psig, 1.6 LHSV, 2000 SCF/B (80% H Charge Sulfur Content Kuwait Full Product Sulfur Content 0.37 wt 2.74 weight Range Gas Product'Yield 97.00 wt of fresh feed Oil Unit Hydrogen Consumption 356 SCF/B (6151005F. B.R.)

Charge Sulfur Content Kuwait Lube Product Sulfur Content 1.71 wt 6.03 weight Oil Extract* Product Yield 96.40 wt of fresh feed (706-840F. Unit Hydrogen Consumption 884 SCF/B I-Iydrodesulfurizing a Blend of 35 wt Kuwait Furnace Oil 53 wt Kuwait Full Range Gas Oil 12 wt Kuwait Lube Oil Extract Charge Sulfur Content Calc. Results Product Sulfur Content 0.40 wt 2.68 weight for the Blended Product Yield 97.29 wt of fresh feed Material Hydrogen Consumption 383 SCF/B Aromatics 40.5 vol Charge Sulfur Content Observed Results Product Sulfur Content 0.28 wt 2.68 weight for the Blended Product Yield 97.39 wt of fresh feed Material Unit Hydrogen Consumption 370 SCF/B Aromatics 40.9 v

' This run made at 3000 SCF/B reactor gas rate to compensate for high hydrogen consumption.

"Results calculated by algebraic combination of component results shown above.

Table 5 shows that when the full range gas oil, the light lubricating oil extract andthe furnace oil is each hydrodesulfurized by itself, the calculated results would indicate -a product having 0.20 weight percent sulfur but that when the streams were blended and desulfurized together the product had a sulfur content of 0.14 weight percent sulfur, indicating the existence of a synergistic effect upon the reaction rates by blending a stream (the furnace oil) which extends beyond the boiling range of the primary stream on the lower boiling side. Table 6 shows a proportionally similar synergistic effect occurs (sulfur removal is increased from an expected value of 85 percent to a value of 90 percent) with the same system when the space velocity is doubled from 0.8 to 1.6 LHSV. Tables 5 and 6 also show that unit hydrogen consumption (chemical hydrogen consumption by free hydrogen balance around the unit) is lower when the blend is treated than would have been expected, even though more sulfur is removed than expected. This demonstrates the synergistic effect, whereby sulfur removal is high while the extent of undesirable hydrogen-consuming reactions (hydrogenation and hydrocracking) are limited, Of course, limiting hydrogen consumption is economically advantageous, and controlling both hydrogenation and hydrocracking leads to the production of a superior gasoline in the subsequent riser crasking step.

Table 7 shows the characteristics of the furnace oil feedstock of Tables 5 and 6 and the furnace oil effluent from the hydrodesulfurization reactor at a space velocity of both 0.8 and 1.6 when the furnace oil is hydrodesulfurized by itself.

TABLE 7 TABLE 7 Continued HYDRODESULFURIZING OF KUWAIT FURNACE ()ll.

Table 8 shows the characteristics of the light lubricating oil feedstock extract of Tables 5 and 6 and the effluent from the hydrodesulfurizing reactor when the light lubricating oil extract feedstock is hydrodesulfurized by itself at space velocities of 0.8 and 1.6.

TABLE 8 I-IYDRODESULFURIZING OF KUWAIT LUBE OIL EXTRACT HYDRODESULFURIZING OF KUWAIT FURNACE OIL Average Reactor Temperature: F. 680 680 Reactor Pressure:

psig 939 939 LHSV: vol/hr/vol 1.60 0.80 Gas Rate: SCF/B 1942 1963 H Content of Reactor Gas: vol 81.0 80.7

Average Reactor TABLE 8-Continued m EesL Total Liquid Product Yield: wt of fresh feed 94.52 96.40

Gravity: AP1 9.3 18.6 18.1 Sut'lur: wt 6.03 0.88 1.71 Distillation, ASTM D86: F. Vacuum: 10 M Table 9 shows the characteristics of the gas oil feedstock of Tables 5 and 6 and the gas oil hydrodesulfurized effluent when the gas oil feedstock is hydro- HYDRODESULFURIZING OF KUWAIT GAS OIL Average Reactor Temperature: F. 680 681 Reactor Pressure:

' psig 939 939 Ll-ISV: vol/hr/vol 0.82 1.60 Gas Rate: SCF/Bbl 1940 1947 H, Content of Reactor Gas: vol 79.9 79.3

Hydrogen Consumption: SCF/Bbl (Unit) 499- 356 Total Liquid Product Yield: wt of fresh feed 96.65 97.00 Liquid Product Inspections Eegd Gravity: API 25.0 29.6 28.8 Sulfur: wt 2.74 0.18 0.37 Distillation, ASTM D86: F. Vacuum: 10 MM teristics of the effluent from the hydrodesulfurization reactor when this feedstock blend is hydrodesulfurized at a space velocity of about 0.8 and 1.6.

TABLE 10 HYDRODESULFURIZING OF A BLENDED CHARGE STOCK Charge:

Average Reactor Temperature: T. 680 680 Reactor Pressure:

psig 937 939 LHSV: vol/hr/vol 1.64 078 Gas Rate: SCF/Bbl 1907 2000 H Content of Reactor Gas: vol 79.4 80.3

Hydrogen Consumption: SCF/Bbl (Unit) 370 463 Total Liquid Product Yield: wt of fresh feed 97.39 96.26

Total Product Inspections Feed Gravity: "AP! 26.3 30.3 31.9 Sulfur: wt 2.68 0.28 0.14 Distillation, ASTM D86: F. Vacuum: 10 MM EP 987 961 958 5% 509 497 489 10% 543 528 521 v 20% 589 574 574 30% 629 610 603 40% 662 643 634 50% 698 673 667 60% 737 710 702 781 757 750 832 81 1 81 1 900 876 876 942 921 921 The present hydrodesulfurization process can be advantageously applied to a situation where a relatively low-boiling, low sulfur-containing hydrocarbon stream from a first crude source, such as furnace oil boiling between 400 and 600 or 650F., which does not meet commercial sulfur requirements (which is 0.2 weight percent sulfur, or lower) and therefore would require desulfurization in a first reactor while in the same refinery a relatively high-boiling, high sulfur-containing gas oil from a second crude source having a volume average boiling point above 750F. is hydrodesulfurized in a second reactor. In accordance with the present invention, a relatively high boiling portion of the furnace oil, after separation from the furnace oil, is blended with the gas oil to produce a total hydrodesulfurization feed oil blend having a volumetric average boiling point of at least 700 or 750F., but lower than the original volume average boiling point of the gas oil. Sufficient high boiling high sulfur-containing material is separated from the furnace oil for blending with the gas -oil that the remaining light furnace oil is sufficiently low in sulfur to meet commercial domestic sulfur specifications (below 0.2 weight percent) without requiring passage through a hydrodesulfurization zone. In this manner, the boiling range of the heavy gas oil is advantageously broadened to impart a synergistic sulfurremoval effect to it, while no desulfurizer is required for the light furnace oil, thereby avoiding construction of a furnace oil desulfurizer.

Similarly, the present invention can be applied to combining an entire light oil stream (such as furnace oil) with an entire gas oil stream (boiling between 600 or 650 and 1050F.) to produce a wide-boiling blended total stream having a high synergistic effect which is processed in a single reactor, instead of charging the separate streams to separate reactors because the lighter oil is destined for use as a furnace oil whereas the heavier gas oil is destined for use as an FCC feed. IF desired, the hydrodesulfurized blend can be charged in its entirety to the FCC riser or it can be fractionated and the furnace oil can be used as a fuel oil and the gas oil only can be charged to the FCC riser. The blend of the two streams should have an average boiling point of at least 700 or 750F.

Additional tests were conducted to illustrate the hydrodesulfurization of blends of oils to show the effect upon sulfur removal in the lower boiling point of the blend. In these tests a blend of a naphtha range feed with a furnace oil feed was hydrodesulfurized with a catalyst comprising nickel-cobalt-molybdenum on alumina. The results of the tests are shown in FIG. 2.

FIG. 2 not only shows that the sulfur content in the lighter portion of the feed, that is the naphtha, is much lower (0.04 weight percent or 400 ppm) as compared to the sulfur content in the furnace oil (1.02 weight percent) but also that the sulfur in the naphtha oil portion of the blend at any given hydrodesulfurization temperature is removed relatively more easily than the sulfur of the heavier furnace oil fraction. FIG. 2 compares the sulfur content of the naphtha portion of the effluent and the furnace oil portion of the effluent when operating at space velocities of 4.0 and 5.0, respectively. Line E of FIG. 2 shows the level of sulfur removal that would occur in the furnace oil at 5 LHSV if the naphtha was not present in the blend. Line E shows that the naphtha exerts a synergistic effect upon sulfur removal of the heavier furnace oil portion of the feed.

Data were also taken by hydrodesulfurizing a heavier naphtha alone, without the presence of furnace oil, and these data tend to show that the presence of the heavier furnace oil inhibits removal of sulfur from the lighter naphtha portion of the blend. Therefore, the mechanism of the synergistic effect upon reaction rate is apparently'that the lighter portion of the blend advantageou'sly tends to increase sulfur removal from the heavier portion of the blend while the heavier portion of the blend tends to inhibit sulfur removal from the lighterportion of the blend and the net effect is an overall enhancement of sulfur removal due to blending. The important feature of the present invention is that the presence of lighter material assists removalof sulfur from the heavier material. This fact is important because, as noted above, it is the sulfur in the heavier material which is not easily vaporized and which is therefore present in the coke in any subsequent FCC reaction and it is the coke sulfur which ultimately ends up as sulfur dioxide, which is an atmospheric pollutant because it cannot be removed from FCC regenerator flue gases by amine scrubbing. On the other hand the sulfur present in the lighter portion of the feed which is easily vaporized and cracked in the FCC riser is largely re moved in the FCC riser as hydrogen sulfide which can be scrubbed from riser off-gases with an amine, such as diethanolamine, and is thereby prevented from polluting the atmosphere. Furthermore, it was shown above that in any hydrodesulfurization process sulfur removal from the light feed material occurs more easily and to a greater extent than sulfur removal from a heavier material present in the hydrodesulfurizing feed whereby a smaller percentage reduction in sulfur dioxide is observed than the percent reduction in total sulfur in the feed to an FCC- unit.

Table 1 1 shows the characteristics of the naphtha in the feed of the blend of FIG. 2 and also shows the characteristics of the naphtha portion in the product from the hydrodesulfurization process in FIG. 2.

TABLE 1 l INSPECTION DATA FOR C 380F. NAPHTHA PRODUCTS FROM DESULFURIZATION AT A FEED RATE OF 5.0 LHSV C 680F Charge Distillate Operating Conditions LHSV: vol/hr/vol 5.0 Reactor Pressure:

psig 700 Average Reactor Temperature: F. 640 Gas Rate: SCF/B 1200 H Content: 90

Naphtha C 380F. Fraction Distillate from in Feed Desulfurizer Inspections Gravity: D287:

API 64.7 62.9 Distillation,

D86: F. Over Point 103 1 17 End Point 366 376 5% 137 I51 10% I53 166 20% 177 189 30% 199 209 40% 221 229 50% 240 249 60% 258 267 273 287 295 306 315 326 328 341 Sulfur, ppm

by weight 400 1 content in the naphtha portion of the hydrodesulfurization product is about 1 ppm. It is noted that the data points in FIG. 2 for the naphtha product show that less severe conditions did not produce a 1 ppm sulfur naphtha product when the naphtha was present in a blend with furnace oil.

Table 12 shows the results of a test treating a higher boiling naphtha in an unblended condition with a similar catalyst to hydrodesulfurize the naphtha at conditions of 300 psig, 600F., 5.6 LHSV and 300 SCF/B of hydrogen. Each one of these test conditions is much less severe than the comparable condition employed in the hydrodesulfurization reaction illustrated in Table 11. The characteristics of the unblended naphtha feed and the unblended naphtha hydrodesulfurization product of these tests are illustrated in Table 12.

TABLE 12 HYDRODESULFURIZATION OF A LOW SULFUR CONTENT VIRGIN NAPHTHA AT LOW HYDROGEN PARTIAL PRESSURE Operating Conditions Temperature: F. 600

TABLE 12-Continued HYDRODESULFURIZATION OF A LOW SULFUR CONTENT VIRGIN NAPHTHA AT LOW HYDROGEN PARTIAL PRESSURE Table 12 shows that under much less severe hydrodesulfurizing conditions, when employing an unblended naphtha feed the sulfur content of 1 the product was reduced to about the same level, i.e., about 1 ppm, as when the naphtha was treated in the presence of furnace oil but under much more severe conditions, indicating that the presence of a heavier material with the naphtha feed tended to inhibit sulfur removal in the naphtha portion of the blend. As noted above and as shown in FIG. 2, in a blended condition the naphtha required the full reaction severity indicated to achieve thel ppm sulfur level. These data indicate that although according to the synergistic sulfur removal reaction effect of the present invention the presence of a lighter material enhances the rate of sulfur removal of the heavier portion of the blend, at the same time the sulfur removal from the lighter portion of the blend tends to be inhibited.

A variation of the present invention is presented in the process illustratedin FIG. 3 wherein the synergistic effect of this invention can be partially foregone with advantage. FIG; 3 illustrates the degree of sulfur removal when a blend of two different feed portions having adjacent or overlapping boiling ranges including a light portion (such as a furnace oil having a boiling range between 400 and 650F.) and a heavy portion (such as gas oil having a volumne average boiling point above 750F.) are added to a hydrodesulfurization reactor employing the same type of nickel-cobaltmolybdenum on alumina catalyst employed in the prior tests, together with hydrogen, in downflow reactor operation over a stationary bed of compacted catalyst particles. In the system of FIG. 3, a virgin oil which has a relatively high boiling range, and a relatively high sulfur content, is the heavy portion of theblend and the effluent sulfur content of this fraction only of the total product is indicated by line G in FIG. 3.

Line F of FIG. 3 illustrates the sulfur content in the total product when a virgin oil having a lower boiling range (volume average boiling point below 750F.) and having a lower sulfur content is combined with the heavy oil (volume average boiling point above 750F.). In the abscissa of the curve of FIG. 3 it is shown that when the total blend employing the light oil together with the heavy oil is charged to the inlet of the reactor percent of bed depth), the sulfur in the total product cated by point K, indicates the sulfur content of the heavy gas oil effluent when the heavy oil is charged through the entire catalyst bed without any of the light oil. Point K shows that the total absence of light oil permitted maximum desulfurization of the heavy oil because the heavy oil did not have to compete with the iight oil for catalyst sites. Therefore, although the light oil provides the synergistic effect of this invention, it also inherently produces a negative dilution effect and the following discussion of FIG. 3 illustrates a system wherein the synergistic effect of the light oil can be partially obtained while holding to a minimum its negative effect of dilution of the heavy oil.

Referring to FIG.'3, the unusual feature is observed that very close to a minimum level of sulfur content in the total product, as indicated by point H, is achieved if the heavy oil portion of the total blend only is added to the top of the catalyst bed and permitted to pass through about 80 percent of the catalyst bed undiluted by light oil while the light oil portion of the total blend only is added to the reactor at a point about 80 percent downwardly into the bed depth. The total blend has a volume average boiling point of at least 750F. FIG. 3 shows that when the heavy oilportion of the blend is added with hydrogen at the top of the catalyst bed and the light oil is added at a point about 90 percent downwardly into the bed depth, the sulfur content in the heavy oil fraction of the product and in the total product is about equal, since this is the point at which curves F and G cross. FIG. 3 further shows, that if the light oil portion (having a volume average boiling point below 750F.) of the blend is not added to the hydrodesulfurization reactor but the heavy oil alone (having a volume average boiling point above 750F.) passes through the entire catalyst bed having access to catalystsites which is uninhibited by the presence of the light greatest extent (point K). FIG. 3 also shows that if the 7 light oil in a nondesulfurized condition is blended with the hydrodesulfurized heavy gas oil effluent, the sulfur content of the total product is a maximum, and is at an unacceptably high value (point J), which indicates a highly inefficient mode of operation, and may not even constitute percent sulfur removal from the total feed including both high and low boiling portions. Therefore, according to FIG. 3, the most advantageous mode of operation for sulfur removal from the heavy oil is to add the heavy oil at the top of the reactor bed and not to add light oil to the reactor at all. But if the light'oil is ultimately to be blended with the heavy oil, or if the light oil must be desulfurized, FIG. 3 indicates the most economical mode of operation is to add the light oil fraction to a point at about 80 percent downwardly in the bed depth so that the sulfur content in the total effluent is nearly a minimum, as indicated by point H, while the sulfur content in the heavy oil portion only of the total product nearly approaches its minimum value at point K (see point I). Although this mode of opeation gives up the synergistic effect contributed by the light portion along the top 80 percent of the catalyst bed, it does have the advantage of not diluting the refractory sulfur-containing molecules in the heavy fraction along the top 80 percent of the bed depth and thereby permitting greater sulfur removal from the heavy fraction only while employing a smaller reactor and a smaller quantity of catalyst and thereby achieving a large economic advantage while giving up only a small advantage in terms of the sulfur content in the total product. I

If the synergistic effect of this invention is the only consideration, it would be advantageous to charge the light oil portion to the top of the catalyst bed together with the heavy oil portion so that the light oil portion can exert a maximum sulfur removal synergistic effect upon the heavy portion of the total product, However, by adding the light portion late to the reactor an additional advantage is achieved in that it is easier for the process to achieve 80 percent total desulfurization with a limited amount of catalyst and without increasing the temperature differential between the and 90 percent distillation points of the total feed more than 20F., although the temperature drop of the 90 percent point is more easily lowered at least 10 or F., indicating'enhanced sulfur removal from the high-boiling portion and rendering the high-boiling high-sulfur compounds more easily vaporizable in a subsequent FCC riser, to reduce sulfur dioxide formation. Whatever mode of operation is employed the entire effluent can be charged to the FCC step or the effluent can be distilled to recover light oil for use as furnace oil, and heavy oil, for charging the FCC riser. Points H and I of FIG. 3 indicate that operation of the hydrodesulfurization reactor by injecting the light portion at about 80 percent of the bed depth represents an ideal compromise between the synergistic and dilution effects of the light oil in that the sulfur level in the total product is almost a minimum (Point H) while the sulfur level in the heavy portion only of the product is also close to a minimum (Point I). Injection of the light oil at greater than 80 percent of the bed depth improves sulfur removal from the heavy portion of the product only slightly while greatly increasing the sulfur level in the total product. FIG. 3 illustrates results with a particular feed blend but with other feed blends the optimum point of injection of the light oil (point H) might be elsewhere in the bed, e.g. at 50, 60, 70 or even at a deeper percentage of the bed depth.

An especially important feature of the present invention is illustrated in FIG. 4. FIG. 4 represents the variation of the 10 percent distillation point and the 90 percent distillation point in a feed oil during a hydrodesulfurization process of the present invention. Suitable feed oils for this invention include the overhead of atmospheric or vacuum distillations and include oils in the furnace oil and gas oil boiling ranges. The 90 percent distillation point represented by line M in FIG. 4 is particularly important because the 90 percent distillation point material represents the heavy material in the system in which the sulfur content is richest, from which itis most difficult to remove sulfur, and which contains the sulfur which is present in the coke of a subsequent FCC riser which ends up as sulfur dioxide in an FCC regeneration operation. A significant drop in the 90 percent distillation point, i.e. at least 10, 15, F, or more, is tangible evidence of significant removal of sulfur from the heaviest material in the feed stream. Therefore, it is important to a hydrodesulfurization process of the present invention that a significant drop occur in the 90 percent distillation curve of a feed moving through a hydrodesulfurization reactor. In the process of FIG. 4, the feed and hydrogen flow downwardly over a fixed, stationary bed of nickelcobalt-molybdenum on alumina catalyst particles.

The line L in FIG. 4 represents the drop in temperature of the 10 percent distillation point. The 10 percent distillation point drops more readily than the 90 percent distillation point because it represents the accu mulation of all light components produced due to either sulfur removal or hydrocracking of higher boiling materials. The removal of sulfur fromthe 10 percent distillation point material of the feed occurs most readily because, as shown in Table 1, above, the desulfurization reaction rate constant is low in high boiling materials but increases exponentially as the boiling point of the sulfur-containing component decreases. However, it is noted that the 10 percent point should not drop more than 40 or 50F. At point P, which repan inhibitor against appreciable hydrocracking in the hydrodesulfurization system. Hydrocracking is indicated by a very rapid drop in the 10 percent distillation point. Hydrocracking, which is the severance of carbon-carbon bonds, as contrasted to sulfur removal by severance of carbon-sulfur bonds, is highly undesirable in the present invention because it represents a needless consumption of hydrogen in the preparation in the feed for an FCC process wherein hydrogen is not added and cracking occurs without consuming hydrogen. Therefore, the consumption of hydrogen to accomplsih cracking is an economicwaste in the preparation of a feed for an FCC process. Furthermore, gasoline range components produced by hydrocracking have a lower octane number due to the saturation of olefins caused by the presence of hydrogen. Olefins are known gasoline octane-improvers. On the other hand, gasoline produced in a zeolitic FCC riser in the absence of added hydrogen is rich in olefins and these olefins contribute to a high octane number gasoline product. One means of inhibiting hydrocracking is to use recycle hydrogen as a coolant or quench to be injected at various posi tions in the hydrodesulfurization reactor to accomplish cooling. It is advantageous to employ a single hydrodesulfurization reactor chamber, with one or a plurality of separated beds, with the total feed hydrocarbon blend introduced at the reactor inlet and with the total hydrogen either added at the reactor inlet or divided and added both to the reactor inlet and also at several positions along the length thereof, preferably between catalyst beds, to provide a quenching effect.

A further reason for avoiding extensive hydrocracking in the hydrodesulfurization process is that the hydrodesulfurization operation of the present process is designed to accomplsih a synergistic effect in sulfur removal between the light (represented by the 10 percent distillation point of FIG. 4) components and the heavy (represented by the percent distillation point of FIG. 4) components in the feed blend moving through the hydrodesulfurization reactor. As explained above, this synergistic effect in the sulfur removal reaction between high reaction rate components and low reaction rate components can be translated into a savings in catalyst required per, barrel of feed and also a savings in hydrogen consumed per barrel of feed due to the smaller catalyst bed. If the feed traveling through the reactor is permitted to remain in the reactor sufficiently long to permit extensive hydrocracking at the reactor outlet region, this is evidence that the catalyst bed is excessively great in length in relation to its sulfur-removing function and therefore the catalyst savings that could be achieved due to the synergistic effect of this invention if the reaction were limited essentially to sulfur removal isrendered innocuous, to say nothing of resulting wasteful hydrogen consumption.

Since it is an objective of the present invention to remove as much sulfur as possible from the 90 percent distillation point components of the feed, as evidenced by a drop in the 90 percent distillation point of the material traveling through the reactor, sufficient catalyst should be present to permit as great a drop as possible in the 90 percent distillation point. However, in order not to exceed the range of the synergistic effect advantage of the present invention, the amount of catalyst present, and therefore the depth of the reactor bed, should be limited to a range such that the sulfur-level does not become sufficiently low that the inhibitory power of sulfur against extensive hydrocracking is avoided. This objective is realized by a limitation in the drop of the IQ percent distillation point of the material traveling through the reactor. We have found that the present invention is best performed to accomplish reduction in the 90 percent distillation point (representing the most desirable sulfur removal) without encountering an excessive reduction in the 10 percent distillation point (representing excessive hydrocracking) by employing a catalyst bed of sufficient depth so that at least 80 percent of the sulfur is removed from the hydrocarbon feed while permitting the temperature difference between the 90 percent and the 10 percent distillation points to increase but not to increase by an amount exceeding 10, 15 or 20F. It is important that at least 80 percent of the sulfur be removed, because line M of FIG. 4 shows that in the removal of only 50 or 60 percent of the total sulfur in the feed, very little effect upon the 90 percent distillation point is apparent, while line L shows most of the initial sulfur removal was from the lighter material.

Referring again to FIG. 4, line N illustrates the increase in temperature differential between the 10 percent distillation point and the 90 percent distillation point of the feed as it travels through the reactonAt position on line N, 80 percent of the total sulfur in the feed has been removed, satisfying the requirements of this invention. At the same time, the 90 percent distillation point has dropped at least F indicating a significant amount of the sulfur removal was from the most refractory sulfur, which would be likely to be present in the coke formation of a subsequent cracking unit. At position 0, the temperature differential between the 10 percent point and the 90 percent has not yet increased by 20F, also satisfying the requirements of this invention. It is not until position P on line N has been reached that the increase in temperature differential between the 10 percent and 90 percent distillation points just reaches 20F. It is noted that line N begins to move abruptly upwardly in an exponential manner once the 20F. increase is achieved. It is at this point that the sulfur level becomes so low that the amount of sulfur in the feed is inadequate to effectively inhibit hydrocracking so that hydrocracking begins to occur at an excessive and undesirable rate. As already stated, hydrocracking at an excessive and undesirable rate is to be avoided because it results in an economic waste of hydrogen and because it produces gasoline having a lower octane number than the gasoline that can be produced in a subsequent FCC riser operation in the substantial absence of added hydrogen. The reaction of the present invention is terminated at least at the catalyst depth (reactor length) represented by point P. More particularly, the catalyst depth should be in the region represented between the points 0 and P, i.e., the bed depth is great enough to accomplish at least 80 percent sulfur removal, with a drop in the 90 percent distillation point of at least 10F with an increase in temperature differential between the 10 percent and 90 percent distillation points but without the temperature differential increase exceeding 20F. and without the 10 percent point dropping more than or F. When the bed depth is between the points indicated by O and P of FIG. 4, the catalyst savings due to the synergistic sulfur removal effect of the present invention is realized. A savings in reaction time and in prevention of excessive hydrocracking is also realized. If the catalyst bed depth exceeds that represented by point P, the total sulfur removal is greater but the catalyst economy feature of this invention becomes valueless because insufficient sulfur remains in the stream for effective synergism in sulfur removal, as evidenced by the fact that the additional catalyst contributes relatively more heavily to hydrocracking reactions rather than to hydrodesulvention is a transient advantage which becomes useless when the increase temperature differential between the 10 and 90 percent distillation points exceeds 20F. Preferably, the increase in the temperature differential can be below 15F. It is noted that further widening of the boiling range of the feed of FIG. 4 by addition of a furnace oil would permit a higher degree of desulfurization of the gas oil than that indicated by point P without excessive hydrocracking.

It has already been noted that the presence of sulfur in the feed material must be sufficiently great to inhibit hydrocracking. While FIG. 4 indicates that the feed sulfur content is 2.74 weight percent, FIG. 5 illustrates the hydrodesulfurization of a feed containing only 0.3] weight percent sulfur. FIG. 5 shows the variation in the 10, 30, 50, and 90 percent distillation points (the average of which represents the volume average boiling point of a hydrocarbon stream). with increasing levels of desulfurization with a feed containing this low level of sulfur content. Referring to FIG. 5, it is seen that at percent desulfurization of the feed the temperature differential between the 10 percent and the percent distillation points has increased 25F., as compared to the feed, which is beyond the permissible 20 temperature differential at 80 percent desulfurization in accordance with this invention. FIG. 5 shows that the temperature differential had already reached 20F. when only 75 percent of the feed sulfur was removed. Therefore, the'feed illustrated in FIG. 5 has too low a level of sulfur to be included within the present invention.

Y The sulfur level of such a feed is so low that it cannot adequately inhibit hydrocracking with its attendant expense in hydrogen consumption .while it accomplishes desulfurization. As noted earlier, it is desired to reserve cracking for the subsequent FCC unit. Furthermore, the level of sulfur in the feed of FIG. is so low that the requirement for the synergistic sulfur removal effect of the present invention is not as important as withthe feed illustrated in FIG. 4. Moreover, the low feed sulfur level shown in FIG. 5 indicates that the feed will not be a major source of sulfur dioxide contamination in a subsequent regeneration unit of a downstream FCC riser cracker.

FIG. 6 presents data to illustrate the importance to the hydrodesulfurization process of the present invention of avoiding a catalyst containing silica. The data shown in FIG. 6 were taken by passing a Kuwait gas oil having 2.93 weight percent sulfur, an ASTM 10 percent point of 689F. and an ASTM 90 percent point of l01lF., downflow over a bed of 1/16 inch nickelcobalt-molybdenum on alumina catalyst particles at a pressure of 1000 psig, 2000 SCF/B of 70 to 75 percent hydrogen, a LI-ISV of 2.0, while scrubbing the recycle gas with NaCaOH. In the upper curve of FIG. 6, the alumina support is essentially silica-free while in the lower cum/e of FIG. 6 the catalyst is promoted with 0.5 weight percent silica. It is seen from FIG. 6 that at all temperatures, the promotion of the catalyst with silica results in a lower weight percent desulfurization of the feed oil. The data of FIG. 6 show the importance of employing a hydrodesulfurization catalyst having less than 0.5 weight percent silica and preferably of employing catalyst containing less than 0.25 weight percent silica or even 0.1 weight percent silica, or less.

The present invention is to be distinguished from prior art processes in which a cracking feed is hydrogenated or hydrodesulfurized in advance of a cracking operation in order to accomplish a hydrogen donation effect in the cracking operation. Hydrogen donation, is a direct transfer of hydrogen from certain partially or completely saturated ring compounds, such as aromatics or naphthenes, to other refractory compounds during cracking without the addition of free hydrogen in order to render the refractory compounds less refractory. It occurs during a cracking operation which permits sufficient residence time for such hydrogen donation to occur. Hydrogen donation has the overall effect of rendering the feed less refractory even though no free hydrogen is added to the cracking system. In such hydrogen transfer processes, hydrogen is added to easily hydrogenated aromatic or naphthenic compounds in a prehydrogenation stage and then during cracking the hydrogen is transferred directly to a more refractory, hydrogen deficient compound to render the more refractory compound more susceptible to cracking. However, as stated, such hydrogen donation requires sufficient residence time for its occurrence. The cracking operation of the present invention occurs with a highly active zeolite cracking catalyst at a residence time of less than five seconds, preferably less than 2 or 3 seconds, and occurs with hydrocarbon feed and regenerated or fresh catalyst flowing concurrently upwardly through the reactor at about the same velocity, without permitting catalyst bed formation (whereby backmixing of hydrocarbon occurs) anywhere in the reaction flow path. Such a riser cracking process is described in US. Pat. No. 3,617,512, which is hereby incorporated by reference. In FIG. 3 of US. Pat. No. 3,617,512, chamber 2 could comprise a hydrodesulfurization reactor of this invention. The residence time in the cracking riser is preferably three seconds or less and can be one or two seconds or less. The top of the riser is capped and provided with lateral exit slots to insure immediate disengagement of reactants and catalyst at the riser exit, thereby preventing overcracking of gasoline after vapors and catalyst leave the riser. To illustrate the absence of hydrogen donation in a cracking riser of the present invention, a cracking riser test is illustrated in Table 13. As shown in Table 13, two tests were conducted, one of which employed percent cyclohexane (the saturated aromatic) as feed and the other employing a 2:1 mole ratio of cyclohexane to pentene-2, pentene-Z constituting the hydrogen-deficient compound. The cyclohexane-pentene-2 blend had an impurity of 0.16 weight percent isopentane.

TABLE 13 2:1 Mole Ratio of Cyclohexanc/ Pentene-Z with 0.16 wt 1C,

Feed Impurity Operating Conditions Riser I emperature:

Less iC; yield than was present as a feed impurity Comparing the two tests shown in Table 13, at the very low residence time of the riser cracking reaction it is seen that hydrogen transfer from the cyclohexane to the pentene-2 was so low that there was a net loss of hydrogen from the pentene-2 rather than a net gain in that the yield of the second test contained only 0.14 weight percent total pentanes, which is lower than the 0.16 weight percent isopentane impurity present in the feed. Therefore, no hydrogen donation occurred from the cyclohexane to the pentene-2. It is noted that the cyclohexane and the pentene-2 are both materials boiling within the gasoline boiling range. Materials boiling within the gasoline boiling range are much more refractory than materials boiling above the gasoline range. Due to this refractoriness, both tests illustrated in Table 13 showed that essentially no cracking occurred during the tests. This absence of cracking allows the data to illustrate quite pointedly that under the standard cracking conditions of this invention which are adapted for cracking material boiling above the gasoline range down to the gasoline range with minimal overcracking of gasoline range material itself, no hydrogen transfer occurs.

Claims (9)

1. A PROCESS FOR IMPROVING THE RATIO OF GASOLINE TO TOTAL CONVERSION IN A ZEOLITE RISER CRACKING OPERATION COMPRISING PASSING A NON-ASPHALTIC SULFUR-CONTAINING PETROLEUM HYDROCARBON FEED OIL HAVING A VOLUME AVERAGE BOILING POINT OF AT LEAST 700*F. TOGETHER WITH HYDROGEN DOWNFLOW OVER A FIXED BED OF HYDRODESULFURIZATION CATALYST COMPRISING GROUP VI AND GROUP VIII METALS ON A NON-CRACKING ALUMINA SUPPORT TO REMOVE AT LEAST 80 WEIGHT PERCENT OF THE SULTUR FROM THE FEED OIL, REGULATING THE AMOUNT OF HYDRODESULFURIZATION CATALYST IN THE BED TO AVOID EXCESSIVELY DECREASING THE BOILING CHARACTERISTICS OF THE FEED OIL WHEREBY AN INCREASE IN THE TEMPERATURE DIFFERNTIAL BETWEEN THE 10 AND 90 PERCENT BOILING POINTS OF THE FEED STREAM OCCURS BUT DOES NOT EXCEED 20*F. WHILE THE 90 PERCENT BOILING POINT OF THE FEED IS DECREASED AT LEAST 10*F., PASSING EFFLUENT FROM THE DHYDRODESULFURIZATION ZONE BOILING ABOVE THE GASOLINE RANGE TO A ZEOLITE RISER CRACKING PROCESS WHICH AVOIDS FORMATION OF A CATALYST BED IN THE REACTION FLOW PATH, AND RECOVERING A CRACKED HYDROCARBON PRODUCT HAVING AN INCREASED RATIO OF GASOLINE TO TOTAL CONVERSION AS COMPARED TO THE RATIO OBTAINABLE WITH SAID FEED OIL UNDER THE SAME CRACKING CONDITIONS IN THE ABSENCE OF SAID HYDRODESULFURIZATION.

2. The process of claim 1 wherein the riser temperature is 900* to 1000*F.

3. The process of claim 1 wherein the residence time in the riser is at least 0.5 but less than five seconds.

4. The process of claim 1 wherein the temperature in the riser is 950* to 1050*F.

5. The process of claim 1 wherein the residence time in the riser is 0.5 to 2.5 seconds.

6. The process of claim 1 wherein said feed oil has a volume average boiling point of at least 750*F.

7. The process of claim 1 wherein the hydrodesulfurization pressure is 800 to 1200 psi.

8. The process of claim 1 wherein the hydrodesulfurization hydrogen consumption is 100 to 500 standard cubic feet per barrel of feed oil boiling above 650*F.

9. The process of claim 1 wherein the feed oil comprises gas oil.

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