US3481864A - Plural-stage hydrorefining of a naphtha - containing full - boiling range feedstock - Google Patents

Description

Dec. 2. 1969 HALLMAN ET AL 3,481,864

PLURAL-STAGE HYDROREFINING OF A NAPHTHA-CONTAINING FULL-BOILING RANGE FEEDSTOGK Filed Jan. 25, 1967 a S a 3 E Q: Q g a N Q a w --b N b Q g: g s 1 S 5 5 I 1% a a S 51 l q m 5 b g 1+ m 1 T 1 K '2 A t Q INVE/VT'O/FS New M Hal/man Q Robin J. Parker 2 W Z. ATTORNEYS United States Patent PLURAL-STAGE HYDROREFINING OF A NAPH- THA CONTAINING FULL BOILING RANGE FEEDSTOCK Newt M. Hallman, Mount Prospect, and Robin J. Parker,

Western Springs, 11]., assignors to Universal Oil Products Company, Des Plaines, 11]., a corporation of Delaware Filed Jan. 25, 1967, Ser. No. 611,593 Int. Cl. C10g 37/02, 23/02 U.S. Cl. 208-210 9 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION This invention relates to a conversion method. It particularly relates to a method for hydrogen-ating constituents present in petroleum feed stocks in order to saturate olefinic hydrocarbons, to remove sulfur compounds, and/ or to remove nitrogen-containing constituents. It specifically relates to an improved method for conducting hydrogenating reactions wherein naphtha-containing fullboiling range feedstocks are processed through a plurality of hydrogenating stages in the presence of hydrogen-contalning gas.

It is well known in the prior art to remove contaminants such as sulfur and nitrogen compounds from hydrocarbon feedstocks using catalytic means, for converting, for example, the sulfur compounds to hydrogen sulfide, and the nitrogen compounds to ammonia. Typically, the feedstock to be refined is passed over a suitable hydrogenation catalyst at an elevated temperature and pressure to cause such conversion reactions to take place. The hydrogen sulfide and ammonia are removed from the efiluent products, for example, by water washing, and/or liquid absorption, with the desired refined products being recovered from the effluent by fractionation means.

However, in the usual commercial desulfurization of hydrocarbon feedstocks it is necessary that the operating conditions employed for desulfurizing motor fuel boiling range material be appreciably different from the operating conditions employed for the desulfurization of heavier constituents such as those in the gas oil boiling range. Consequently, the prior art schemes normally separate hydrocarbon materials into separate fractions comprising, for example, naphtha, kerosene, gas oil, etc., and thereafter subjecting each of these fractions, as desired, to hydro-refining conditions in order to convert such fractions into desirable end products. Consequently, the prior art schemes require an extreme duplicity of equipment and excessive amounts of catalyst in order to accomplish the desired results. Accordingly, it would be desirable to avoid the problems of the prior art schemes by operating the conversion method in such a way as to minimize capital investment and operating expenses.

Therefore, it is an object of this invention to provide a hydrocarbon conversion method.

3,481,864 Patented Dec. 2, 1969 ice It is another object of this invention to provide a method for hydrogenating a naphtha-containing fullboiling range feedstock.

It is a particular object of this invention to provide a method for hydrogenating a naptha-containing full-boiling range petroleum feedstock in a more facile and economical manner.

SUMMARY OF THE INVENTION The present invention is based upon the discovery that contaminants such as sulfur and nitrogen compounds tend to migrate from relatively heavy hydrocarbon to relatively light hydrocarbon during the hydrogenation reaction. It is believed that this migration is caused at least in part by concomitant cracking of hydrocarbons to lower boiling hydrocarbons during the hydrogenation reaction.

Therefore, according to the present invention, there is provided a method for refining a naphtha-containing full-boiling range hydrocarbon feedstock for removal of sulfur compounds therefrom which comprise contacting said feedstock in a first catalytic reaction zone with hydrogen under relatively severe hydrogenating conditions; introducing the total effiuent from said first zone into separation means under conditions suflicient to produce a gaseous stream comprising hydrogen and relatively light hydrocarbons, and a liquid stream comprising relatively heavy refined hydrocarbons; passing said gaseous stream into a second catalytic reaction zone under relatively mild hydrogenating conditions in the absence of added hydrogen; withdrawing from said second zone an efiluent stream comprising hydrogen and relatively light refined hydrocarbons; separating hydrogen from refined hydrocarbons; and recovering refined hydrocarbons having reduced sulfur content.

Another embodiment of the invention includes the method wherein the efiluent from said second zone is admixed with said liquid stream to form a total product stream containing refined hydrocarbons having reduced sulfur content.

A particular embodiment of the invention includes the method wherein said gaseous stream on a liquid basis comprises from 2% to 50% by volume of said total efliuent.

Therefore, it can be seen from the above recitation of embodiments that the present invention provides a method for hydrogenating a naphtha-containing fullboiling range feedstock by using a plural-stage (preferably, a two-stage) reaction zone having a flash zone between the stages. Contrary to the usual teachings of the prior art, the present invention provides that the lighter material and residual hydrogen from the flash zone comprises the sole feed to the next or second reaction zone. It was found that by operating in the manner described that efficient desulfurization of full-boiling range materials could be easily achieved with a minimum of capital investment and operating expense. As is obvious from the teachings, the preferred embodiment, more fully discussed hereinbelow, encompasses admixing the various efiluent streams prior to hydrogen separation, followed by fractionation of the admixed effiuent into suitable typical fractions for further handling in accordance with means well-known to those skilled in the art. For example, the naphtha fraction of the feedstock can be separated from the combined effluent and, then, passed directly without intervening treatment to a catalytic reforming zone maintained under conditions suflicient to produce upgraded gasoline boiling range products therefrom.

It is to be noted that the prior art schemes which have attempted to hydrogenate other than narrow boiling fractions have resulted in producing extremely poor quality light fractions. In other words, by prior art schemes, if a full-boiling range material, containing a naphtha fraction, were subjected to hydrogenation, the migration of the sulfur compounds from the relatively heavy boiling range materials to the relatively light boiling range materials would render the subsequently separated naphtha fraction, generally, still of unsatisfactory quality, from a sulfur standpoint, for feed to catalytic reforming unit. Consequently, the prior art scheme required additional hydrogenation facilities solely for the naphtha fraction so that satisfactory reforming grade naphtha could be available. Alternatively, the prior art schemes were faced with the prospect of prefractionating the feedstock into separate and distinct fractions so that each distinct fraction could be subjected to catalytic hydrogenation under different operating conditions to produce satisfactory desired sulfur reduction in the hydrocarbon component. As more fully discussed hereinbelow with reference to the preferred embodiment it is clear that the present invention provides a method for hydrogenating a fullboiling range feedstock in a more facile and economical manner than heretofore practiced by the prior art.

In the present description and appended claims the terms feedstock, full-boiling range materials, charge stock, naphtha-containing full-boiling range hydrocarbon feedstock, are used herein interchangeably to connote various straight-run and/ or cracked hydrocarbons and mixtures of such hydrocarbons resulting from various refinery processes which produce feedstocks suitable for charging to the method of the present invention. Such refinery processes include crude oil fractionation, catalytic and/or thermal cracking of petroleum, the destructive distillation of wood or coal, shale oil retorting, delayed and fluid coking operations, and various other pyrolytic reactions. In each case, however, the full-boiling range feedstock for the present invention must contain a significant quantity of what is commonly called naphtha. Typically, the naphtha fraction will have a boiling range from about 160 F. to 400 F.; although, minor deviations from these limits may still provide a naphtha fraction within the intended scope of the present feedstock. In addition to the required naphtha fraction, the full-boiling range feedstock for the present invention must also contain at least one other common fraction, heavier boiling, usually connoted as kerosene, diesel oil, gas oil, etc. and may also contain C and C hydrocarbons. Thus, in its broadest sense, satisfactory feedstocks to the present invention include those hydrocarbon mixtures containing sulfur which boil within the range from 100 F. to 1100 F.

As previously noted, the recited satisfactory feedstocks are subjected to relatively severe hydrogenating conditions in a first catalytic reaction zone. These relatively severe conditions include a temperature from 500 F. to 800 F., a pressure from 500 p.s.i.g. to 1500 p.s.i.g., liquid hourly space velocity (LHSV) of 0.3 to 6 volumes of oil per hour per volume of catalyst present therein, and a hydrogen-to-hydrocarbon ratio of from 500 to 5,000 standard cubic feet per barrel. As those skilled in the art know, operating a hydrogenation reaction at temperatures above 500 F. could cause polymerization of any diolefins present in the feedstock. Therefore, in the practice of the present invention, if it is likely that the lighter feedstocks such as those boiling within the range from 100 F. to 550 F. will contain significant diolefins such that undesirable polymerization may take place; then, .such diolefin-containing feedstocks shall be pretreated such as by mild hydrogenation prior to charging to the method of the present invention.

The total effluent from the first catalytic reaction zone of the invention is charged into separation means, such as a single stage flash zone, in order to remove hydrogen and relatively light hydrocarbons from the relatively heavy refined hydrocarbons. In the practice of the present invention the amount of gaseous materials removed from the flash zone, on a liquid basis, should comprise at least v 4 2% by volume of the total eflluent charged to the flash zone but should not comprise more than 50% by volume of such efiluent. If the gaseous stream is less than 2% it has been found that the second reaction zone, more fully discussed hereinbelow, usually cannot be economically justified. Similarly, if an amount greater than 50% by volume is flashed; then, significant heavy material may be charged to the second reaction stage thereby negating, to some extent at least, the benefits to be derived from the practice of the present invention. Usually, this carryover heavy material is not satisfactorily desulfurized under the relatively mild conditions maintained in the second reaction zone. The amount of material vaporized is on a liquid basis, i.e., the percentages by volume exclude normally gaseous materials such as hydrogen and hydrogen sulfide. In addition, the amount of material flashed should be selected so that the 90% point (ASTM distillation) of the hydrocarbon fraction in the vapor phase is no more than 500 F., and preferably is about 400 F. In any event, since the flash zone operates under equilibrium flash conditions, suitable adjustments in temperature of the flash zone may be necessary to flash into the vapor phase substantially only the naphtha portion of the original feedstock.

As previously noted, the reaction conditions for the second reaction zone are relatively mild. These relatively mild conditions include a temperature within the range V of 500 F. to 750 F., a pressure from 500 p.s.i.g. to

1500 p.s.i.g., and an LHSV of from 2 to 40, preferably 5 to 10 LHSV. The amount of hydrogen present in the second reaction zone, of course, is wholly dependent upon the hydrogen separated in the previous intervening flash zone as discussed hereinabove. Thus, it is to be noted that there is no externally added hydrogen present in the second reaction zone. In other words, the sole feed to the second reaction zone consists entirely of the gaseous material separated in the separation means between the two reaction stages.

The method of the present invention is a catalytic method and the catalyst employed may be of the same chemical and physical compositions in both of the reaction zones. At this point it should be noted that the present invention broadly includes a plurality of reaction zones even though the description thereof is more or less limited to only two reaction zones. As those skilled in the art can foresee, there may be situations where two or more, perhaps as many as three or four reaction zones may be desirable, with each set of reaction zones having a flash zone in between. Suitable hydrorefining catalytic composites comprise at least one metallic component selected from the group consisting of metals of Groups VI-B and VIII of the Periodic Table and compounds thereof. Thus, the catalystwill comprise at least one metallic component selected from the group consisting of chromium, molybdenum, tungsten, iron, cobalt, nickel, rhodium, ruthenium, palladium, osmium, iridium, platinum, and mixtures of two or more, etc. The preferred catalytic composite for utilization in the practice of the present invention comprises molybdenum and at least one metallic component selected from the iron group of the Periodic Table. The molybdenum component will generally be in the greater concentration from about 4% to about 30% by weight, while the iron group metallic component will be present in the amount in the range from about 1% to about 6% by weight calculated on the basis of the elemental metal. An essential feature of the catalytic composite is that the catalytically active metallic component hereinabove set forth be composited with a nonacidic carrier material. Generally, catalytically active metallic components are composited with any suitable refractory inorganic oxide material including alumina, silica, zirconia, thoria, boria, titania, hafnia, mixtures of two or more, etc. Similarly, other components are often combined with the metallic components and carrier material, such as members of the halogen family, such as fluorine and/or chlorine. Those skilled n the art know well from the teachings presented herein how to composite a catalyst satisfactory for use in the present invention.

PREFERRED EMBODIMENT The preferred embodiment of the invention provides a method for hydrogenating a naphtha-containing fullboiling range hydrocarbon feedstock for removal of sulfur compounds therefrom which comprises: (a) contacting said feedstock with hydrogen in a first reaction zone containing a catalytic composite of a nonacidic refractory inorganic oxide, molybdenum, and at least one metallic component of the metals of the iron group of the Periodic Table, under relatively severe hydrogenating conditions including a temperature from 500 F. to 800 F. and a space velocity from 0.3 to 5.0 selected to partially convert sulfur compounds to hydrogen sulfide without substantial cracking of said feedstock to lower boiling hydrocarbons; (b) introducing the total efiluent from said first zone into separation means under conditions sufi'lcient to produce a gaseous stream comprising hydrogen, hydrogen sulfide, and relatively light hydrocarbons containing sulfur compounds, and a liquid stream comprising hydrocarbons having reduced sulfur content; (c) passing said gaseous stream into a second reaction zone containing a catalytic composite of a nonacidic refractory inorganic oxide molybdenum and at least one metallic component from the metals of the iron group of the Periodic Table in the absence of added hydrogen, under relatively mild hydrogenating conditions including a temperature from 500 F. to 800 F. and a space velocity from 2.0 to 10.0 selected to convert sulfur compounds to hydrogen sulfide; (d) admixing the effluent from said second zone with said liquid stream; (e) separating hydrogen from the admixture of step (d); and (f) recovering hydrocarbons having reduced sulfur content.

The distinctly preferred method includes the use of a feedstock having a boiling range from C to 900 F., wherein said first zone conditions include a temperature from 725 F. to 775 F., and a space velocity from 0.5 to 1.5; and wherein said second zone conditions include a temperature from 630 F. to 700 F., and a space velocity from 6 to 9.

ILLUSTRATIVE DRAWING The invention may be more fully understood from the description presented herein with particular reference to the appended drawing which is a schematic representation of the preferred embodiment of the invention.

The feedstock to the invention comprises a full-boiling range coker distillate boiling between C and 889 F. having a sulfur content of 0.52 wt. percent, a bromine number of about 28, and a nitrogen content of about 880 parts per million (p.p.m.). Referring now to the drawing, this feedstock enters the method via line 10 where it is admixed with hydrogen from line 11 in an amount sufficient to provide 3000 standard cubic feet per barrel of hydrogen in line 12. The admixture of feed hydrocarbons and hydrogen is passed through heater 13 wherein it is elevated in temperature to about 750 F. in line 14. The heated mixture is passed from line 14 into reactor 15 which contains a catalyst consisting essentially of about 2.2% by weight of cobalt and about 5.7% by weight of molybdenum calculated as the elements thereof deposited on alumina particles of suitable size and shape.

Relatively severe operating conditions are maintained in reactor 15 and include a reactor outlet temperature of 750 F., a pressure of 1100 p.s.i.g., and a space velocity (LHSV) of 1.5. The total efiiuent from reactor 15 s withdrawn via line 16 and passed into separator 17, which is a single stage flash zone, maintained under substantially the same pressure as is maintained in reactor 15. Preferably, no independent cooling takes place in line 16 and suflicient equilibrium flashing is accomplished so that approximately 10% by volume of the material (excluding hydrogen and hydrogen sulfide) in line 16 is flashed and withdrawn via line 19. The hydrocarbon material in line 19 has a point of about 330 F.

The material in line 19, containing relatively light hydrocarbons boiling in the range, typically, from C to 330 F. and containing sulfur compounds, is passed in admixture with the flashed hydrogen and hydrogen sulfide into reactor 20 which is maintained under relatively mild operating conditions. For example, the operating conditions in reactor 20 are maintained at a temperature of about 650 F. with the pressure being that obtained through the system allowing for normal pressure drop between reactor 15 and reactor 20. The space velocity in reactor 20 is approximately 8.0 LHSV based on the flashed material. As previously mentioned there is no added hydrogen to reactor 20 since sufiicient hydrogen is present in the flashed stream from separator 17 to accomplish hydrogenation of the relatively light hydrocarbons present in line 19 for sulfur removal. It should also be noted that there may be need for heating means (not shown) in line 19 in order to maintain proper operating conditions in reactor 20 to convert sulfur compounds to hydrogen sulfide.

The eflluent from reactor 20 is withdrawn via line 21 and preferably is admixed with the relatively heavy refined hydrocarbons previously removed in separator 17 via line 18. The admixed material in line 22 is cooled by means not shown and passed into separator 23 which is maintained under conditions sufficient to separate hydrogen from the refined hydrocarbons. The separated hydrogen is removed via line 11 and, preferably, recycled for admixture with the feed as previously mentioned. Since a small amount of hydrogen (about 1% by weight) is consumed in the hydrogenation reaction, makeup hydrogen is added to the system via line 25. The refined hydrocarbons are removed from separator 23 via line 24 and passed into product separation means, not shown, such as a fractionation system for recovery of the individual commonly known hydrocarbon fractions originally present in the feedstock.

A distinct advantage of the present invention is embodied in the fact that the feedstock which contains a significant amount of naphtha (from, for example, 10% to 50% by weight of the fresh feed) produces a refined naphtha fraction containing about 1 p.p.m. sulfur which may nOW be passed directly to a catalytic reforming unit without intervening treatment. It is to be noted that, generally, the prior art schemes as discussed hereinabove require an additional hydrogenation treatment of the naphtha fraction before it was of suitable quality to be charged to a catalytic reforming reaction zone. Therefore, it is clear that the present invention has provided an improved hydrogenation method wherein the naphtha portion of the full-boiling range feedstock is converted into satisfactory quality for reforming purposes.

As those skilled in the art know well, catalytic reforming operations utilize a platinum containing catalyst to upgrade relatively low grade naphtha fractions into relatively high grade gasoline quality fractions. The important chemical reactions taking place in catalytic reforming are isomerization of alkylcyclopentane to cyclohexanes; dehydrogenation of hexane to aromatic hydrocarbons; dehydrocyclozation of paraflins to aromatic hydrocarbons; hydrocracking of paraffins and naphthenes; etc. These various reactions take place more or less simultaneously to convert naphtha fractions into gasoline quality fractions. The platinum catalyst may be poisoned by the presence of sulfur and other contaminants and there fore, care must be taken to clean up the feedstock prior to contact with the platinum-containing catalyst. Normally, this is done by hydrogenation techniques which convert the sulfur compounds to hydrogen sulfide which is then removed prior to charging the hydrocarbons to the catalytic reforming reactor. Thus, as previously mentioned, the present invention provides an improved hydrogenation process which produces refining grade naphtha in a more facile and economical manner while simultaneously desulfurizing relatively heavy hydrocarbons boiling up to an end point of about 1100 F.

Typically, operating conditions for the catalytic reforming operations include a temperature within the range of from 800 F. to 900 F., a pressure from about 200 p.s.i.g. to 700 p.s.i.g., and a space velocity from about 1 t0 6. Suflicient hydrogen also must be maintained within the catalytic reforming reaction zone in order to improve catalyst life by minimizing coke deposition. Those skilled in the art are familiar with the catalytic reforming operation and its proper conditions; therefore, a detailed presentation of this process need not be presented herein.

The invention claimed is:

1. Method for refining a hydrocarbon feedstock comprising a naphtha fraction and at least one other higher boiling hydrocarbon fraction for removal of sulfur compounds therefrom Which comprises contacting said feedstock in a first catalytic reaction zone with hydrogen and a catalyst comprising a hydrogenating metal selected from Groups VI-B and VIII of the Periodic Table under relatively severe hydrogenating conditions wherein the reaction temperature is from about 725 F. to about 775 F. and the space velocity is from about 0.5 to about 1.5; introducing the total efiiuent from said first zone into separation means under conditions sufficient to produce a gaseous stream comprising hydrogen and relatively light hydrocarbons, and a liquid stream comprising relatively heavy refined hydrocarbons; passing said gaseous stream into a second catalytic reaction zone under milder hydrogenating conditions than the conditions maintained in said first zone and in the absence of added hydrogen and in contact with a catalyst comprising a hydrogenating metal selected from Groups VI-B and VIII of the Periodic Table, wherein the reaction temperature of said last named milder conditions is from about 630 F. to about 700 F. and the space velocity is from about 6 to about 9; withdrawing from said second zone an eflluent stream comprising hydrogen and relatively light refined hydrocarbons; separating hydrogen from said refined hydrocarbons; and recovering said refined hydrocarbons having reduced sulfur content from each of said zones.

2. Method according to claim 1 wherein at least part of said separated hydrogen is recycled to said first reaction zone.

3. Method according to claim 1 wherein the efiluent from said second zone is admixed with said liquid stream to form a product stream containing refined hydrocarbons having reduced sulfur content.

4. Method according to claim 1 wherein said gaseous stream on a liquid basis comprises from 2% to 50% by volume of said total effiuent and has a 90% point (ASTM distillation) within the range from about 330 F. to about 500 F.

5. Method according to claim 4 wherein the naphtha portion of said recovered refined hydrocarbons is passed directly without intervening treatment to a catalytic reforming zone maintained under conditions suflicient to produce upgraded gasoline-boiling range products therefrom.

6. Method for hydrogenating a hydrocarbon feedstock comprising a naphtha fraction and at least one other higher boiling hydrocarbon fraction for removal of sulfur compounds therefrom which comprises:

(a) contacting said feedstock with hydrogen in a first reaction zone containing a catalytic composite comprising molybdenum and at least one metallic component from the metals of the iron group of the Periodic Table, under relative severe hydrogenating conditions wherein the reaction temperature is from about 725 F. to about 775 F. and the space velocity is from about 0.5 to about 1.5 selected to partially convert sulfur compounds to hydrogen sulfide without substantial cracking of said feedstock to lower boiling hydrocarbons;

(b) introducing the total effluent from said first zone into separation means under conditions sufficient to produce a gaseous stream comprising hydrogen, hydrogen sulfide, and relatively light hydrocarbons containing sulfur compounds, and a liquid stream comprising hydrocarbons having reduced sulfur content;

(c) passing said gaseous stream into a second reaction zone containing a catalytic composite comprising molybdenum and at least one metallic component from the metals of the irongroup of the Periodic Table in the absence of added hydrogen, under milder hydrogenating conditions than the conditions maintained in said first zone wherein the reaction temperature is from about 630 F. to about 700 F. and the space velocity is from about 6 to about 9 selected to convert sulfur compounds to hydrogen sulfide;

(d) admixing the efiluent from said second zone with said liquid stream;

(e) separating hydrogen from the admixture of step (f) recovering hydrocarbons having reduced sulfur content from the separation step of step (e).

7. Method according to claim 6 wherein said gaseous stream of step (b) on a liquid basis comprises from 2% to by volume of said total eflluent and has a point (ASTM distillation) within the range from about 330 F. to about 500 F.

8. Method according to claim 7 wherein the naphtha boiling range portion of said recovered hydrocarbons is passed directly, without intervening treatment, to a catalytic reforming zone maintained under conditions sufiicient to produce gasoline-quality products therefrom.

9. Method according to claim 7 wherein said feedstock has a boiling range from C to 900 F.

References Cited UNITED STATES PATENTS FOREIGN PATENTS 612,265 1/1961 Canada.

DELBERT E. GANTZ, Primary Examiner 0 G. J. CRASANAKIS, Assistant Examiner U.S. Cl. X.R. 20857, 216, 217

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