US3114701A

US3114701A - Catalytic hydrodenitrification process

Info

Publication number: US3114701A
Application number: US12319A
Authority: US
Inventors: Robert L Jacobson; Robert H Kozlowski
Original assignee: California Research LLC
Current assignee: California Research LLC
Priority date: 1960-03-02
Filing date: 1960-03-02
Publication date: 1963-12-17
Anticipated expiration: 1980-12-17
Also published as: DE1470524A1; DE1470520A1; NL123195C; GB963941A; NL261905A

Description

17, 1963 R. JACOBSON ETAL 3, 4,7

CATALYTIC HYDRODENITRIFICATION PROCESS Filed March 2, 1960 ,woeoelflv OIL 4 COMPRESSOK 79 M 3-D sr /PP/A/e COLUM IV oEPAzA T/ON DRUM FUR/FIE D 0/ L INVENTORS ROBERT 1.. JACOBSON ROBERT H. KOZLOWSK/ United States Patent 3,114,701 CATALYTIC HYDRQDENTTRTFICATHON PRQIHIESS Robert L. Jacobson, Pinole, and Robert H. Kozlowslti,

Berkeley, Calif assignors to California Research Corporation, San Francisco, (Jaliil, a corporation of Delaware Filed Mar. 2, 1960, Ser. No. 12,319 9 lClaims. (Cl. 208-254) This invention relates to processes for the selective hydrogenative removal or" nitrogen compounds from hydrocarbon streams. In a particular embod ment, the invention is concerned with a catalytic process for the substantially complete removal of nitrogenous contaminants from distillable hydrocarbon oils to be used as feed stocks in subsequent catalytic conversion processes.

It has long been known that nitrogen compounds could be removed to some extent from petroleum hydrocarbons by conventional hydrofining processes. However, even in the case of relatively low boiling feed stocks, substantially complete nitrogen removal cannot be accomplished by conventional hydrofining Without the use of rather se- Vere conditions of temperature and pressure and a relatively low space velocity. In the hydroiining process the hydrocarbon oil is treated with hydrogen at elevated temperature and pressure in contact with various catalysts generally comprising chromium and/or molybdenum oxide together with iron, cobalt, and/or nickel oxides on a porous oxide support, such as alumina or silica-alumina. Previous investigations into the eifect of the metals content of the hydrofining catalysts on their activity have indicated that there is little to be gained by the use of metal contents above about 14%. For example, it is indicated in Patent Number 2,758,957 to K. Nozaki that increasing the total metals concentration above 15% by Weight is of little benefit, and that decreasing the nickel content of a Ni-Mo catalyst to an atomic'ratio of 1:3 increased the activity for hydrogenation.

The present invention is based upon the discovery that for the purpose of substantially completely removing contaminating nitrogen compounds from distillable hydrocarbon oils to low residual nitrogen levels, catalysts containing large concentrations of both nickel and molybdenum are outstanding in their properties and are not the equivalent of the large group of catalytic materials disclosed in the prior art. Specifically, the catalysts used in the hydrodenitrification process or" this invention comprise sulfided nickel and molybdenum on predominantly alumina carriers, containing 410% nickel together with 15 .530% molybdenum by Weight, expressed as the metals. The preferred catalysts contain 68% nickel and 2123% molybdenum. The process comprises contacting the hydrocarbon oil with a sulfided high metals content nickel-molybdenum-alumina catalyst in the presence of hydrogen at critical conditions of temperature, pressure, and space velocity.

There are several aspects to this invention. In one aspect the invention provides a process whereby more than 99.9% of the initial nitrogen content of non-refractory hydrocarbon oils boiling up to about 600 F. may be readily removed using relatively mild conditions of temperature and pressure and/or high space velocities. In many cases 99.99% or more or" the nitrogen is removed. In another aspect the invention provides a process whereby more than 99.9% of the initial nitrogen content of highly refractory hydrocarbon oils boiling up to about 750 F. may be removed using convenient conditions of temperature and pressure and moderate space velocities, which degree of nitrogen removal was heretofore unattainable in a commercially practical process. In another aspect the invention provides a process whereby Zillifldl Patented Dec. 17, 1963 more than 99% of the initial nitrogen content of refractory or high boiling hydrocarbon oils boiling up to about 860 F. may be removed using moderate conditions of temperature, pressure, and space velocity, which degree of nitrogen removal was heretofore unattainable at economically feasible operating conditions. In still another aspect the invention provides a process whereby more than of the initial nitrogen content of heavy hydrocarbon distillates boiling up to about 1050 F. may be removed using relatively mild conditions of temperature, pressure, and/ or space velocity, which degree of purification was heretofore unattainable without the use of conditions resulting in substantial cracking and coke formation.

The feed stocks which may be treated by the process of this invention are distillable hydrocarbon oils. By this is meant those non-residual hydrocarbon streams normally processed in petroleum refineries, and including naphthas, kerosenes, straight run and cracked distillates, distillates derived from shale oil or gilsonite deposits, light and heavy cycle oils, and gas oils. In short, the process is applied to predominantly liquid hydrocarbon streams having an initial boiling point above about 180 F. and an end point below about l050 F.

Hydrocarbon oils contain varying amounts of nitrogen compounds, ranging from several parts per million up to 1-3 depending on the boiling range of the oil and the nature of the crude petroleum or other hydrocarbons.- ceous deposit from which it Was derived. It is not uncommon to report both total nitrogen and basic nitrogen in analyzing hydrocarbon oils. As used herein, the term nitrogen content refers to total nitrogen, determined by Kjeldahl analysis, expressed in parts per million of nitrogen.

The removal of contaminating nitrogen compounds from hydrocarbon distillates to very low residual levels is of particular value where the distillate is to be converted in a low temperature hydrocracking process. In the low temperature hydrocracking process a hydrocarbon distillate of low nitrogen content is contacted with certain dual function catalysts, such as cobalt or nickel sulfide on a silica-alumina cracking catalyst support, under controlled conditions of temperature, pressure, hydrogen throughput, and space velocity, to eflect a substantial conversion of the feed to liquid products boiling below the initial boiling point of the feed and containing a high ratio of isoto normal paraflins, with negligible coke production and only a very small production of light gaseous hydrocarbons. Such a process has been denominated by the proprietary name lso cracking. Pretreatment of the feed to a low temperature hydrocracking process to reduce the nitrogen content to less than 10 ppm. permits the use of lower operating temperatures (e.g., below 700 F), extends the on stream time, and results in a more favorable product distribution. More favorable results are obtained when the feed has a nitrogen content of only 1-2 ppm. Nitrogen contents below 1 ppm. are considerably more advantageous.

A typical light cycle oil derived from a fluid catalytic cracking process had a gravity of 25.4 API, an initial boiling point of 415 R, an end point of 550 F., and an initial nitrogen content of 900 ppm. This material can be virtually quantitatively converted to gasoline boiling range hydrocarbons by low temperature hydrocracking provided the nitrogen content is first reduced to less than 10 ppm. The inability of conventional hydroflucatalysts to eiiect such a degree of nitrogen removal at ordinary processing conditions is shown by the data given in Table l. The light cycle oil was contacted with each of the catalysts described in Table I at 615-620 F., 800 p.s.i.g., in the presence of 4000 s.c.f. H /bbl., at a 3 liquid hourly space velocity (Ll-ISM) of 1.0 v./v./hr. based on the light cycle oil feed.

TABLE I Hydrofining of Light Cycle Oil Catalyst A is a commercially available hydrofining catalyst prepared by the method described in Patent Number 2,878,193 to l. W. Scott. The method comprises solution impregnation of a cobalt salt (followed by calcining to the oxide) on a coprecipitated molybdenum oxidealumina support. Catalyst B and catalyst C are other commercial hydrofining catalysts wherein the metals molybdenum, nickel, and/ or cobalt are supported on alumina. Catalyst D is a nickel-molybdenum-alumina catalyst prepared by impregnating an alumina carrier with an aqueous solution of nickel nitrate, drying and calcining, and then impregnating with aqueous ammonium molybdate, drying and calcining. Catalyst E was prepared in the same manner as catalyst D, but using more concentrated impregnating solutions to provide a total metals content greater than has been found exemplified in the hydrofining or denitritlcation art. It is apparent that this increase in metal content was of no benefit, as predicted by the prior art. All of the catalysts were sulfided to convert the metal oxides predominantly to metal sulfides prior to contacting with the light cycle oil.

Catalyst A, being intermediate in activity to catalysts B and C, has been assigned a relative activity for hydrodenitrification of 1.00 expressed on a space velocity basis. We have found that the hydrodenitrification reaction close- 1y approximates a pseudo first-order rate reaction with respect to the fractional removal of the initial nitrogen content over the range of operating conditions utilized, i.e., log (1-x)=kt, where x is the percent nitrogen removal expressed as a decimal, t is the contact time (inversely proportional to LHSV), and k is the reaction rate constant (proportional to relative activity). From this it can be shown that to reduce the nitrogen content of the light cycle oil from the initial 900 p.p.m. to less than p.p.m. would require the use of a catalyst having a relative activity of about 3.5 under the conditions of the above test. For the substantially complete hydrodenitrification of distillates having a greater initial nitrogen content or of a more refractory nature (with respect to ease of denitrification) than the light cycle oil, a catalyst having a relative activity of about 4 or better is required.

We have found that to obtain the high activities required for the substantially complete removal of nitrogen compounds, in accordance with this invention, the catalyst must contain at least 15.5% molybdenum and must also contain at least 4% nickel. Specifically, the highly active catalysts utilized in the process of this invention have nickel contents in the range 410% by weight and molybdenum contents in the range l5.530% by weight. The catalysts are conveniently prepared by impregnating an alumina support with nickel and molybdenum compounds convertible to the oxides by calcination to give the finished catalyst the desired metals content, calcining, and then sulfiding to convert the nickel and molybdenum oxides predominantly to the sulfides.

When the li ht cycle oil described previously, having a nitrogen content of 900 p.p.m., was contacted with the nickel-molybdchum-alumina catalysts of this invention under the same operating conditions as were used in the previous test, the nitrogen was substantially completely removed, as shown in Table ll.

TABLE II Hydrodenitrification of Light Cycle Oil Catalyst 3 K L M N P Wt. percent Molybdenunh. 18. 9 2 3 22.0 21. 8 a 21. 8 21. 7 Wt. percent Nick 4. 7 4.1 5. 9 7. 6 10. 0 4. 9

Wt. percent Metals, TotaL- 23. 6 28. 4 27. 9 29. 4 31. 8 26.6 Product:

p.p.m. Nitrogen -7 4 1 4. 5 3 1. 5 1 4 6 Percent Nitrogen Removal 99. 55 99. 5 99. 8 99. 8 99. 55 99. 3 Catalyst Relative Activity 3. 8 3. 7 4. O 4. 6 3. S 3. 5

1 Corrected value based on data at 570575 F.

As shown by the data of Table II, nickel-molybdenumalumina catalysts containing 4 to 10% Ni together with from about 19 to 25% Mo are remarkably active with respect to hydrodenitrification, a fact which could not be predicted from a consideration of the catalysts containing lesser quantities of the metals. The molybdenum content may be as low as 15.5% or as high as 30%, but the use of more than 25% M0 is generally unwarranted.

It will be observed that to determine the percent nitrogen removal required the accurate measurement of residual nitrogen concentrations of less than 10 p.p.m. The analyses Were made in a nitrogen-free laboratory, set aside for the purpose, by a modified Kieldahl procedure involving the extraction of a fairly large sample gm.) with 92% sulfuric acid. Highly purified water and caustic must be used, and all glassware should be cleaned with hot caustic. At the 1 p.p.m. level the analyses are considered accurate to $0.1 p.p.m.

Catalysts J, K, L, M, N and P were prepared by su stantially the same procedure in order to insure that the results would be indicative solely of the effect of the metals content. Catalysts D and E of Table I Were prepared in this same manner, namely, alternate impregnation of alumina with aqueous solutions of nickel and molybdenum compounds convertible to the oxides by calcination. The exact procedure is exemplified by the preparation of catalyst M, described in the following example.

EXAMPLE 1 A high grade alumina, obtained commercially in the form of extrusions, having a pore volume of 0.65 cc./gm. and a surface area by nitrogen adsorption of 270 m. gm. (B.E.T. method), was immersed for 2 hours at room temperature in an aqueous solution of nickel. nitrate, prepared by adding 2 parts by weight to 1.5 parts H O. The pH was about 5.2. The im-- pregnated particles were dried for 10 hours at 400 F, and then calcined for 4- hours at 900 F. The calcined particles were then immersed for 2 hours in an aqueous solution of ammonium molybdate, prepared by mixing 3.9 parts of 20% NH OH, 3.2 parts of H 0, and 2.9 parts of M00 by weight. The pH was maintained at about 8.8 by the addition of more ammonium hydroxide solution. The impregnated particles were dried for 10 hours at 400 F, and then calcined for 4 hours at 900 F. The catalyst was then given a second molybdenum impregnation in the same manner, dried, and calcined as before. The nickel oxide-molybdenum oxide-alumina catalyst so produced contained 7.6% Ni and 21.8% Mo, calculated as the metals, and had a surface area of 119 m. gm. The oxide catalyst was then placed in a test reactor, and hydrogen was passed therethrough for about 1 hour, while raising the temperature to 650 F., at a pressure of 800 p.s.i.g. A vaporized solution of dimethyldisulfide in heptane was added to the H and fed to the reactor for a ten-hour period, at which time approxi-- mately 2.8 times the amount of sulfur required to convert the NiO and M to Ni S and M had been introduced. The ratio of dimethyldisulfide to hydrogen was about 1 to 12, by volume, at the reactor inlet. The final catalyst had a relative activity of 4.6.

The above order of impregnation, namely, first nickel and then molybdenum, is preferred. When the reverse order was used, there was a tendency for molybdenum to be leached out of the catalyst during the second (nickel) impregnation. In addition, somewhat higher activities are obtained by following the preferred order of impregnation. Catalyst P was prepared by the reverse order of impregnation, as described in the following example.

EXAMPLE 2 Two hundred and fifty cc. of alumina, obtained commercially in the form of 8-14 mesh pieces, having a pore volume of 0.49 cc./ gm. and a surface area by nitrogen adsorption of 180 m. /gm., was immersed for 24 hours at room temperature in a solution of ammonium paramolybdate, prepared by adding to 94.6 gms. of (NHQ5MO7O24'4H2O sufiicient water to make up 200 ml. of solution. The impregnated alumina was then drained free of excess solution, dried for 24 hours at 250 F, and calcined for 6 hours at 900 F. This material was then vacuum impregnated with molybdenum using an ammonium paramolybdate solution of the same molybdenum content as in the first impregnation, to which 0.2 cc. of concentrated ammonium hydroxide had been added per gram of ammonium molybdate. The once-impregnated alumina was placed in a flask, the flask evacuated, and 200 ml. of the ammonium molybdate solution was introduced. The vacuum was released, and the mixture was allowed to stand for minutes at atmospheric temperature and pressure. After drying and calcining as before, this material was given a third molybdenum impregnation in the same manner as the second impregnation. After drying and calcining as before, the alumina-molybdenum oxide catalyst was vacuum impregnated with nickel, in the same manner, using a solution prepared by adding to 319 grams of sufficient water to make up 200 ml. of solution. The four-times impregnated catalyst was then dried at 250 F. for 24 hours and calcined at 900 F. for 6 hours. The nickel oxide-molybdenum oxide-alumina catalyst so produced contained 4.9% Ni and 21.7% Mo, calculated as the metals, and had a surface area of 93 m. /gm. The oxide catalyst was then sulfided with dimetliyldisulfide in the same manner as in Example 1. The final catalyst had a relative activity of 3.5.

To obtain high activity for the hydrodenitrification process the high metals content nickel oxide-molybdenum oxide-alumina catalysts must be sulfided prior to contacting with the hydrocarbon oils to be treated. Sulfiding is preferably accomplished in the manner described in Example 1, by passing over the oxide catalyst a sulfiding agent such as H 8, CS mercaptans, disulfides, and the like. When H 8 is used, the sulfiding may be effected with or without a carrier gas such as hydrogen or nitrogen. High activity catalysts, comparable to those de scribed in Table II, have been prepared by sulfiding directly with pure H S. Where sulfur compounds other than H 8 are employed, hydrogen should also be present, preferably under pressure, and the temperature should be sutllciently elevated for ready conversion of the sulfur compound to H 8, say about 400 F. in the case of mercaptans and disulfides. Extensive reduction of the oxides to the metals is preferably avoided, since usually more active catalysts result if the oxides are sulfided directly. Further, to minimize reduction of the oxides, the temperature during sulfiding preferably should not exceed 750 F., and more preferably is at or below 650 F.

In a preferred method of sulfiding, mercaptan or organic disulfide addition is continued over a period of about 2-10 hours until at least 1.5 times the theoretical amount of sulfur required to convert the nickel and molybdenum ovides to Nlgsz and M05 respectively, has been added. The exact form of the metals in the final catalyst is not known, and it is not meant to represent that the nickel and molybdenum are quantitatively converted to Ni S and M08 However, it is important that an excess of the sulfiding agent be used in order to insure conversion of the metal oxides predominantly to the sulfides. When the oxide catalysts of this invention are contacted directly with the hydrocarbon oil and hydrogen at or slightly below the normal operating temperatures, relying on the inherent sulfur content of the hydrocarbon oil to effect sulfiding, the hydrodenitrification activity is only slightly better than that of the catalysts described in Table I.

The preferred catalyst support is substantially a micro- 'porous alumina, such as is commercially available or may be prepared by Well known methods. The inclusion in the support of a small amount of silica, say up to 5%, would not be expected to affect the catalyst activity materially, and may be advantageous in stabilizing the catalyst in some cases. Highly active catalysts have also been prepared by impregnating a coprecipitated molybdenum oxide-alumina carrier with nickel and additional molybdenum to provide metal concentrations in the required range, i.e., about 15.5% molybdenum and about 5% nickel. Alumina base hydrofining catalysts of conventional molybdenum and cobalt content may also be utilized as the support if the area and pore volume are adequate. Cobalt cannot be substitu ed for nickel, as cobalt-molybdenum catalysts containing 4-l0% cobalt and 155-3 0% molybdenum are only about half as active for denitrification as the corresponding nickel-molybdenum catalysts. However, the inclusion of a small amount of cobalt in the catalyst in addition to the 410% nickel does not materially affect the basic and novel characteristics of the catalyst for denitrification, nor does the inclusion of minor amounts of zinc, copper, or similar metals. The inclusion of such metals appears to be somewhat deleterious, and they are preferably excluded. The support should be predominantly alumina.

To permit the required incorporation in the alumina carrier of more than 19% by weight of the metals, nickel and molybdenum, without substantially filling the pores, the alumina should have an initial pore volume in excess of about 0.2 cc./ gm. It is preferred that the alumina have a pore volume of greater than about 0.4 cc./gm. Since the impregnation with large quantities of nickel and molybdenum results in a reduction of the surface area, it is most desirable to start with a carrier having a surface area in excess of about 150 m. /gm., as determined by nitrogen adsorption; although the surface area may be as loW as mP/gm. if, for example, the catalyst is to contain only 4-5% Ni and 15.5l9% M0. The alumina may be calcined if desired prior to impregnation with the metals, but precalcining does not appear to be essential.

Where the catalyst is to be employed in a fixed bed process, the alumina is preformed, as in the shape or" small spheres, pellets, rods, or irregular pieces. In the preferred method of preparation, a preformed alumina ca rrier is first immersed in an aqueous solution of a nickel compound readily convertible to the oxide by calcination, such as nickel nitrate, nickel acetate, and the like. Nickel sulfate is a less desirable impregnating compound, and nickel chloride is even less desirable, because of the high temperatures required for decomposition or conversion to the oxide. The preferred medium is an aqueous solution of nickel nitrate containing 212% Ni, depending on the final nickel concentration desired in the catalyst. The impregnated carrier is then dried and cal- '2 cined or otherwise treated to convert the nickel compound to an insoluble form, preferably nickel oxide.

The nickel oxide-alumina catalyst is then impregnated with an aqueous solution of a molybdenum compound convertible to the oxide by calciniation, such as ammonium molybdate, or a solution of molybdic acid in oxalic acid solution containing nitric acid, etc. When ammonium molybdate is used, the pl-l should be controlled at above about 7.7 to prevent precipitation of molybdenum oxide. Preferably, the pH is maintained at about 8.7 or above to avoid the formation of a molybdenum oxide crust on the outer surface of the catalyst. The twice-impregnated catalyst is then dried and calcined. This catalyst can then be given an additional molybdenum impregnation, again followed by drying and calcining, when it is desired to prepare a catalyst containing above 16% molybdenum. However, molybdenum contents up to about 19% by weight in the finished catalyst l ave been obtained by a single impregnation with ammonium mo lybdate.

The final calcination is efifected at temperatures in the range 600-110tl F. When a high nickel and molybdenum content catalyst was calcined at or slightly above 1200" F., the relative activity for hydrodenitrilication was approximately halved. Thus, when the nickel is incorporated after the molybdenum, the nickel compound used should be one convertible to the oxide at a temperature below 126i? F. The optimum calcining temperature appears to be between 800 F. and 1000" F. The calcinations are usually carried out in the presence of hot air, but an inert gas atmosphere may instead be used since oxygen is already available in the preferred impregnating compounds.

Although the hydrodenitrification process may be car ried out in a number of ways, such as by maintaining the catalyst in a fluidized bed or as a downilowing column of granular solids, the process is most suitably carried out using a fixed bed of catalyst in the manner depicted in the attached drawing. Since the nickel-molybdenum catalysts of this invention maintain their high activity over protracted periods of use, a continuous non-regenerative type of operation is obtainable and is normally preferred. The catalysts may be regenerated periodically by the oxidative removal of carbon deposits formed during extended use.

Referring to the drawing, the hydrocarbon oil to be treated enters the process via line 1. Hydrogen-rich gas is admixed with the hydrocarbon oil feed via line 2, and the admixture, after heating to the desired operating temperature, passes to reactor 4 via line 3-. Alternately, the hydrocarbon and hydrogen streams may be separately heated before mixing. Reactor l is packed with sulfided high metals content nickel-molybdenum-alumina catalyst in the form of small particles such as spheres, pellets, or extmdates. The hydrocarbon oil feed may be completely vaporized in the case of low boiling feed stocks, but mixed phase iiow is preferred in the case of higher boiling stocks. in passing through reactor the nitrogen compounds in the hydrocarbon oil are substantially converted to ammonia with concomitant consumption of hydrogen. The reactor eiiluent leaves via line 5, and is cooled to condense the normally-liquid hydrocarbon portion and then passed via line '7 to separation drum ti. To assist in the removal of ammonia from the ellluent, water or acidulated water may be added through line s. A water phase contain ng dissolved Nll which then separates in drum 8 may be withdrawn via line Al and discarded. A major portion of the ammonia formed may be removed in this fashion.

Hydrogen-rich recycle gas is separated in drum 8 and withdrawn through line 9 to compressor lb, for return to the reaction zone in combination with additional feed via lines 11 and 12;. Make-up hydrogen is introduced through line "13 to compensate for that consumed in the process. It may be desirable to withdraw a small bleed 3 stream of recycle gas via line 12 to sit the build-up in the recycle stream of light gaseous hydrocarbons, such as may be introduced with the make-up hydrogen.

Liquid hydrocarbon effluent, containing residual ammonia and other hydrogenated impurities, is withdrawn from drum and passed to distillation Zone 16 via line 15. Zone 316 is operated at a materially lower pressure than drum 3, and may comprise another simple separation drum, or it may be a strippin. column, as shown. Steam, hydrogen, or other inert stripping gas is introduced via line 1"! to assist in the complete removal of ammonia and other light gaseous by-products overhead via line 19. Purified hydrocarbon oil substantially free of nitrogen compounds is recovered in line l8. Alternately, or in addition to water washing and/ or distillation, equivalent means for removing the Nl-l may be provided, for example, by adsorption on a microporous metal-alurninosilicate (molecular sieve), activated earth, etc.

Conditions of temperature, pressure, hydrogen throughput, and space velocity in the reactor are correlated to provide the desired degree of nitrog n removal. Higher temperatures, pressures, and/or hydrogen throughputs are required when treating the higher boiling feed stocks and those containing the more refractory nitrogen compounds. A particular advantage of the process is that it permits the hydrodenitrification of reiractory stocks at comparatively mild conditions or" temperature and pressure and/or the use of high space velocities. The term refractory is used herein the reference to the relative difficulty with which nitrogen is removed from the respective feed stocks. .ln general, the complex nitrogen compounds found in high boiling hydrocarbon fractions and cracked cycle oils are more resistant to hydrogenation than the lower boiling compounds.

Temperature has a large influence on the rate of conversion of the nitrogen compounds and is adjusted upwards to maintain the hydrodenitrification rate as the catalyst ages or is deactivated through protracted use. The temperature should be in the range Still-850 -F., preferably soc-750 The rate of hydrodenitrification is fairly low at temperatures below 550 i At temperatures much above 860 F. substantial cracking of the hydrocarbon oil and coke formation normally occurs, and tie production of light gases increases markedly. With less active catalysts than those of the present invention the temperature at the start of the run must be much higher, and the on stream time between catalyst regenerations is correspondingly reduced. The active hydrodenitr-ification catalysts of the present invention make possible the use of temperatures at be lower end of the operating range for long periods of time. Hence, a special feature of this invention is the relatively low temperature of operation and the resultant long catalyst life.

Elevated pressures advantageously influence the rate of hydrodenitrification as well as extending the catalyst activity and life. Fressures as low as 280 p.s.i.g. may be employed when treating light naphthas, whereas pressures up to 4600 p.s.i.g. may be advisable for the substantially complete hydrodenitrification or" highly refractory and high boiling stocks. Using the highly active catalysts of this invention the pressure will generally be in the range zoo-2on0 p.s.i.ig.

Hydrogen throughput rate is maintained above about 500 s.c.f./bbl. of hydrocarbon oil, and is preferably in the range l009-l060 s.c.f./bbl. More generally, at least sul'iicient hydrogen is provided to supply that consumed in the conversion of the nitrogen compounds and to compensate fo' incidental hydrogenation of unsaturates and oxygen, sulfur, and halogen compounds, while maintaining a significant hydrogen partial pressure. The use of more than 10,080 s.c.f. of H /bbl. does not generally produce suflicient improvement in conversion rate to justify the increased cost.

Table presents physical inspection data on several TABLE III Boiling Range Grav- Initial, Hydrocarbon Oil ity, ppm

API N(to- IBP 50% 95% EP tal) Cracked Napl1tha- 274 291 331 402 419 44. 8 220 FCC Light Cycle Oil 415 451 480 523 550 257 4 900 Colrcr Distillate 380 447 507 582 605 24. 8 2, .500 Arabian Gas Oil 585 620 671 714 723 29. 1 462 Heavy Cycle Oil 505 631 704 700 840 22. 6 566 Heavy Gas Oil 513 602 718 818 862 19. 5 2, 500

14 18% Cat. Cracker Feed 385 625 925 1, 045 20. 6 4, 000

The cracked naphtha and the light cycle oil of Table III are examples of relatively non-refraotory hydrocarbon oils. The removal of more than 99.9% of the initial nitrogen content from such dist-illates is readily accomplished by the hydrodenitrification process. For example, Table IV below presents typical and preferred operating conditions which can be used to reduce the nitrogen content of these and similar stocks to less than 1 ppm. using the preferred nickel and molybdenum content catalysts, having relative activities or about 4 or better. Using the highly active catalysts disclosed herein, containing 440% Ni and 15 .5-25% Mo, feed stocks for low temperature hydrocracking containing less than about l ppm. nitrogen can be prepared from non-refractory hydrocarbon distillates similar to the cracked naphtha and light cycle oil, boiling up to about 60 F. and having initial nitrogen contents up to about 10,000 p.p.rn., by hydrodcnitrification under the indicated preferred operating conditions.

TABLE IV Hydrodenizrificarion of Non-Refractory Oils Operating Conditions Typical Preferred Range Feed Cracked Naphtha. 45G F., EP.

Naphtlias.

Initial, p.p.n1. N 220 10,000.

Final, p.p m. N

Percent Nitrogen Rcmoval.- 99.999.99+.

Temperature, F 500-700.

Pressure, p.s.i 2001,000.

Hz Throughput, s.o.i./bbl 500-5,000.

Space Velocity, LHSV 2 Feed 6C=0 F., E.P.

Middle Distillatcs.

Initial, ppm. N 10,000.

Final, p.1).n1. N 1 1- Percent N itrogcn Rcmoval. 99.9 -99.99.

Temperature F 550-750.

Pressure, p.s.i.g 5001,5G0.

H Throughput, s.c.f./bbl l,000-10,000.

Space Velocity, LHSV 0.5-5.

When the cracked naphtha is contacted with the hydrofining catalyst (catalyst A, as described above) at 800 psig, 4000 s.c.f. H /bbl, and 2 LHSV, the temperature rn-u st be raised to above 650 F. to obtain the same degree of nitrogen removal. At 65 0 F. a space velocity of about 8 or better can be used with the active catalysts of this invention. 'ihus, a particular advantage of the invention is that it permits the use or high space velocities in treating light hydrocarbons. Similarly, using catalyst A to treat the light cycle oil at 800 p.s.i.g., 4000 s.c.f. H /bbL, and l LHSV, the temperature must be raised to above 750 F. to obtain the indicated degree of nitrogen removal.

The coker distillate and the Arabian gas oil of Table iii are highly refractory stocks, and they require more severe conditions to effect the removal of more than 99.9% of the nitrogen compounds. Table V presents TABLE V Hydrodem'trification of Refractory Oils Operating Conditions Typical Preferred Range Feed Colrer Dis- Arabian 750 F., E. P. tillnte. Gas Oil. Gas Oil Distillattes. l0,000. 10. 99-99159.

659-800. soc-2,000.

LOGO-10,000.

Initial, p.p.1n. N

Final, p.p.n1. N 1

Per-sent Nitrogen Removal.

Temperature, F.

Pressure, p.s.i.g a-

Space Velocity, LHSV When the colrer distillate or the Arabian gas oil are contacted with the hydrofining catalyst (catalyst A) at 12.00 p.s.i.g., 6000-6500 sci. li /ibbl, and 0.5 LHSV, the temperature must he raised to above 850 'F. to obtain the indicated typical nitrogen removal. At such high temperatures excessive cracking of the feed stocks occurs, and the catalyst is rapidly deactivated by coke formation.

Hydrocarbon distillates such as the cracked naphtha, light cycle oil, coir-er distillate, and gas oil, after substantiaily complete removal of the contaminating nitro gen compounds, are particularly good feed stocks for the low temperature hydroorackiug process. in that process the purified oil is contacted at 350-750 1 500-3000 p.s.i.a. H partial pressure, 0.3-5 LHSV, and in the presence of 2000-15000 sci. H /b-bl. with a low temperarture hydrocracking catalyst. The advantages gained by pretreatment of such hydrocarbon oils in accordance With this invention are illustrated by the following example:

EXAMPLE 3 The FCC light cycle oil of Table 1H was contacted at 620 F., 800 p.s.i.g., in the presence of 4000 s.c.f. H /bbi, and at a space velocity of 1 LHSV with catalyst M, prepared as described in Example 1, comprising 7.6% Ni and 21.8% Mo (calculated as the metals) supported on alumina and presullided With dimethyldisulfide. After water Washing and distilling to remove NH the product oil analyzed 1.5 ppm. nitrogen (total). When the temperature Was raised to 650 F. the product analyzed only 0.1 ppm. nitrogen. Under the latter higher temperature conditions the pnoduct contained 100 p.p.rn. nitrogen when the conventional hydrofining catalyst (catalyst A) Was used. When the light cycle oil containing 1.5 ppm. nitrogen is contacted with a low temperature hydrocracking catalyst, comprising 6% nickel sulfide supported on a silica-alumina cracking catalyst, the hydrocracking process may be initiated at 570 F, 1500 p.s.i.g., 8000 s.c.f. H /bbl., and 1.0 LHSV, and 60% conversion per pass may he maintained for over 25 00 hours by gradually raising the hydrocraching reactor temperature to 715 F. When the feed contains only 0.1 ppm. nitrogen, the same conversion may be maintained for over 4000 hours before a temperature of 715 F. is reached. But, if 100 ppm. nitrogen Were present in the feed, the temperature would have to be raised to above 700 F. very early in the run, and the hydrocracking run length (terminated at 715 F.) would be reduced to less than 100 hours.

In the treatment of high boiling stocks such as the heavy H2 Throughput,

cycle oil, heavy gas oil, and cat cracker feed described in Table III, a broad range of conditions may be used depending on the degree of nitrogen removal desired and the use to which the stock is to be put. Table VI presents typical and preferred operating conditions which can be employed to remove more than 99% of the nitrogen from the heavy cycle oil and heavy gas oil using the preferred catalysts of this invention. As shown in Table VI, the nitrogen content of such high boiling oils, boiling up to about 860 F., can be sufliciently reduced by this hydrodenitrification process such that these and similar stocks may also be subjected to low temperature hydrocracking.

TABLE VI Hydrodenitrification of High Boiling Oils Operating Conditions Percent Nitrogen Re- 9999.9.

moval.

Temperature, F.

Pressure, p.s.i."

set/obi. Space Velocity,

LI'ISV.

As shown in Table VI the substantially complete hydrodenitrification of refractory and high boiling oils, such as the heavy gas oil, requires rather severe conditions even when using the high metal content catalysts. On the other hand, such a degree of nitrogen removal is incapable of being accomplished at economically feasible operating conditions using the hydrofining catalysts. For example, to obtain the indicated 99.6% nitrogen removal from the heavy gas oil with catalyst A as 1600' p.s.i.g., 4 000 s.c.f. H /bbL, and 0.5 LI-ISV, requires the use of a temperature in excess of 900 F. Similarly, to obtain the indicated degree of nitrogen removal from the heavy cycle oil at 1200 p.s.i.g., 4000 s.c.f. H bbl. and 0.5 LHSV with catalyst A, requires the use of a temperature above 800 F.

Although the hyduodenitrification process is of particular value for use in the preparation of a feed stock for low temperature hydrocracking, improved operation and prodnot distribution are also obtained in isomerizat-ion, hydrogenation, reforming, catalytic cracking, and like processes when the feed is first pretreated to remove nitrogen. In particular, we have found that isomerization catalysts, especially the solid acid or the dual function type, are rapidly poisoned by basic nitrogen compounds. The ability to remove the nitrogen compounds normally present in hydrocarbon oils makes possible a wide variety of processes for the upgrading of inferior stocks. Thus, high quality jet fuel of low ireezing point may be prepared by a process wherein a kerosene boiling range distillate of appreciable nparafiin content, normally unsuited for jet fuel usage, is first treated for the removal of nitrogen compounds in accordance with the process of this invention. The purified oil is then contacted with an isomerization catalyst, such as halided platinum-on-alumina or nickel-molybdenmn i011 silica alumina, at 300700 F, 100-2000 p.s.i.g., at a liquid hourly space velocity of from about 0.1 to 5, and in the presence of added hydrogen. Similarly, lubricating oils of low pour point and high viscosity index may be produced by hydrodenitrification of crude Wax or wax-bearing distillates and lubricating oils in the manner set forth herein, followed by isomerization at elevated pressure and temperature, in the range 400800 F., and at a liquid hourly space velocity of from about 0.01 to 4, in contact with a catalyst such '12 as the aforementioned platinum-alumina type or, for example, comprising alumina on which is deposited vanadium or tungsten together with molybdenum, cobalt, or nickel.

For many purposes a lesser degree of nitrogen removal is of considerable value provided that relatively moderate processing conditions can be used. For example, it has been found that when a heavy gas oil, similar to the heavy gas oil of Table III, with its nitrogen content reduced to ppm. is fed to a catalytic cracking pilot unit operating at 900 F., a space rate of 1.5, and a catalyst to oil ratio of 1:5, a total conversion of 5 l volume percent and a 37 volume percent gasoline yield are obtained. At a nitrogen content of 2500 ppm. the stock is only 33 volume percent converted with a 25 volume percent gasoline yield, at the same operating conditions. Table VII presents typical and preferred operating conditions which can be employed to remove the greater portion of the nitrogen contaminants from stocks such as the heavy gas oil and the full boiling range cat cracker feed of Table III using the high activity catalysts of this invention.

TABLE VII Hydrodenitrification of Heavy Oils Operating Conditions Under the indicated operating conditions of Table VII only about 50% of the nitrogen is removed when the hydrofining catalyst (catalyst A) is used for treating either the heavy gas oil or the cat cracker feed.

In the foregoing comparisons, namely, Tables IV, V, VI and VII, it would appear that substantially complete hydrodenitrification could be accomplished using conventional hydrofining catalysts by resorting to operation at extremely low space velocities, for example, less than 0.2 LHSV. The use of such low space velocities is particularly undesirable not only because of the greatly increased equipment and catalyst costs involved but also because of the necessarily increased time of contact with the catalyst at elevated temperature. Protracted exposure of hydrocarbon oils to high temperatures and catalytic agents in many cases intensifies degenerative side re actions, notably thermal cracking and degradation of color and stability. In contrast thereto, for any desired degree of nitrogen removal the highly active, high nickel and molybdenum content catalysts permit the use of more moderate temperature conditions and higher space velocities. Under such comparatively mild conditions it has been found that many stocks may be substantially decolorized by the hydrodenitriiication process. For example, the treatment of the light cycle oil under the conditions of Example 3 yielded a product which was essentially colorless (+15 Saybolt). Thus, it is contemplated that the utilization of the active nickelmolybdenum catalysts in the manner disclosed herein may provide a method whereby many stocks such as stove oils, lube oil fractions, transformer oils, waxes, and special products may be purified to an extent not heretofore considered possible.

We claim:

1. A process for the substantially complete removal of contaminating nitrogen compounds from a distillable hydrocarbon oil without substantial cracking and coke formation, which comprises contacting said oil at a temperature in the range of from 500 to 800 F. and at a pressure in the range of from 500 to 4000 p.s.i.g., and at a liquid hourly space velocity based on said oil of 0.2 to 10, together with 500 to 10,000 s.c.f. of H per barrel of said oil, with a sulfided nickel-molybdenumalumina catalyst containing 4 to weight percent nickel and about 19 to weight percent molybdenum, calculated as the metals, removing the resulting ammonia, and recovering denitrified oil.

2. The process of claim 1 wherein the catalyst contains 6 to 8 percent nickel and 21 to 23 percent molybdenum.

3. A process for the substantially complete removal of contaminating nitrogen compounds from a hydrocarbon oil boiling below about 860 F. and having an initial nitrogen content below about 10,000 ppm, which comprises passing said hydrocarbon oil at a temperature in the range 500-850 F. together with 50010,000 s.c.f. H /bbl. of said hydrocarbon oil, at a pressure in the range 200-4000 p.s.i.g., and at a liquid hourly space velocity based on the hydrocarbon oil in the range 0.2-10, through a fixed bed of particulate catalyst prepared by impregnating a preformed predominantly alumina carrier with nickel and molybdenum compounds convertible to the oxides by calcination, to provide a nickel content in the range 4-10% by Weight, expressed as the metal, and to provide a molybdenum content in the range about 19-30% by weight, expressed as the metal, and calcining to convert the metal compounds to metal oxides, said catalyst having been sulfided prior to contacting with said hydrocarbon oil, cooling the effluent vapors to condense the normally liquid hydrocarbons therein, separating from said liquid hydrocarbons at substantially the reactor pressure a recycle gas comprising hydrogen, removing ammonia from the said hydrocarbons, and recovering as the product a feed stock for a low temperature hydrocracking process containing less than 10 ppm. nitrogen.

4. A process for the removal of contaminating nitrogen compounds from a distillable hydrocarbon oil, which comprises contacting said hydrocarbon oil at a temperature in the range 500-850 F. together with 50010,000 s.c.f. H /bbl. of said hydrocarbon oil, at a pressure in the range 200-4000 p.s.i.g., and at a liquid hourly space velocity based on the hydrocarbon oil in the range (12-10, with a catalyst prepared by impregnating an alumina support having a pore volume in excess of 0.4 cc./ gm. and a surface area in excess of 150 m. /gm., as determined by nitrogen adsorption, with an aqueous solution of nickel nitrate to provide a nickel content in the finished catalyst in the range 6-8% by weight expressed as the metal, calcining, then impregnating with an aqueous solution of ammonium molybdate to provide a molybdenum content in the finished catalyst in the range 21-23% by weight expressed as the metal, calcining, and contacting the impregnated and calcined alumina with a sulfiding gas to convert the nickel and molybdenum oxides predominantly to the sulfides.

5. A process for the removal of more than 99.9% of the contaminating nitrogen compounds from a non-refractory hydrocarbon middle distillate boiling up to about 600 F. and having an initial nitrogen content below about 10,000 ppm, without substantial cracking or coke formation, which comprises contacting said distillate at 550-750 R, together with 500-10000 s.c.f. H /bbl., at a pressure of 200-1500 p.s.i.g. and at a liquid hourly space velocity based on the distillate in the range 0.5-10, with a sulfided nickel-molybdenum-alumina catalyst, separating ammonia from the contacted middle distillate, and

recovering a feedstock for low temperature hydrocracking containing less than 1 ppm. nitrogen, said catalyst having been prepared by impregnating a predominantly alumina carrier with nickel and molybdenum compounds convertible to the oxides by calcination in an amount sufiicient to provide a total content of nickel and molybdenum expressed as the metals in the ranges 410% by weight nickel and about 19-25% by weight molybdenum, calcining, and sulfiding the impregnated and calcined catalyst to convert the metal oxides predominantly to metal sulfides.

6. A process for the removal of more than 99.9% of the contaminating nitrogen compounds from a refractory hydrocarbon gas oil distillate boiling up to about 750 F. and initially containing from about 400 to about 10,000 ppm. nitrogen, without substantial cracking or coke formation, which comprises contacting said distillate at 650-800 F. together with 1000-10000 s.c.f. H /bbl. of said distillate at a pressure of 500-2000 p.s.i.g., and at a liquid space velocity based on the distillate in the range 0.2-5, with a sulfided nickel-molybdenum-alumina catalyst, separating ammonia from the contacted gas oil, and recovering a feedstock for low temperature hydrocracking containing less than 1 ppm. nitrogen, said catalyst having been prepared by impregnating a predominantly alumina carrier with nickel and molybdenum compounds convertible to the oxides by calcination, in an amount suflicient to provide a total content of nickel and molybdenum expressed as the metals in the range 4-10% nickel and about 19-25% molybdenum, by Weight, calcining, and sulfiding the impregnated and calcined catalyst to convert the metal oxides predominantly to metal sulfides.

7. A process for the removal of more than 99% of the contaminating nitrogen compounds from a refractory hydrocarbon gas oil boiling up to about 860 F, without substantial cracking or coke formation, which comprises contacting said oil at 650-800" F. together with 1,000- 10,000 s.c.f. H2/bb1. of said oil at a pressure of 500- 2,000 p.s.i.g., and at a liquid hourly space velocity based on the oil in the range 0.2-5, with a catalyst prepared by impregnating a predominantly alumina support with nickel and molybdenum compounds convertible to the oxides by calcination, in amounts sufiicient to provide a total content of nickel and molybdenum expressed as the metals in the range 4-10% nickel and about 19-25% molybdenum, by weight, calcining, and sulfiding the impregnated and calcined catalyst to convert the metal oxides predominantly to metal sulfides, separating arnmonia from the contacted gas oil, and recovering contacted gas oil containing less than 10 ppm. nitrogen.

S. A process for the removal of contaminating nitrogen compounds from a heavy gas oil catalytic cracker feed stock boiling up to about 1,050 E, which comprises contacting said gas oil at 600-S00 F. together with 1,000-10,000 s.c.f. Hg/bbl. of gas oil, at a pressure of 500-4,000 p.s.i.g., and at a liquid hourly space velocity based on the gas oil in the range 02-10, with a catalyst prepared by impregnating a predominantly alumina support with nickel and molybdenum compounds convertible to the oxides by calcination, in amounts suflicient to provide a total content of nickel and molybdenum expressed as the metals in the range 4-10% nickel and about 19-25% molybdenum, calcining to convert the niche and molybdenum compounds to the metal oxides, and sulfiding the impregnated and calcined catalyst to convert said metal oxides predominantly to metal sulfides.

9. A catalyst composition having high activity for the hydrodenitrilication or" distillable hydrocarbon oils, which comprises sulfided nickel and molybdenum on an alumina support, the quantity of nickel expressed as the metal being in the range 4-10% by weight and the quantity of molybdenum expressed as the metal being in the range 19-25% by weight, prepared by impregnating a preformed alumina support, having a pore volume in excess 15 of 0.4 cc./gn1. and a surface area in excess of 150 mP/gm. as determined by N adsorption, with an aqueous solution of a nickel compound convertible to the oxide by calcination, calcining at 6004160 F, then impregnating with an aqueous soiution of a molybdenum com pound convertible to the oxide by calcination, calcining at 600-1100 F., again impregnating with an aqueous solution of a molybdenum compound convertible to the oxide by calcination, calcining at 6G01100 E, and

sulfiding to convert the nickel and molybdenum oxides predominantly to metal sulfides.

References Cited in the file of this patent UNITED STATES EATENTS 2,905,636 Watkins et al Sept. 22, 1959 2,944,006 Scott July 5, 1960 2,983,676 Howland May 9, 1961 2,988,501 Inwood June 13, 1961

Claims

1. A PROCESS FOR THE SUBSTANTIALLY COMPLETE REMOVAL OF CONTAMINATING NITROGEN COMPOUNDS FROM A DISTILLABLE HYDROCARBON OIL WITHOUT SUBSTANTIAL CRACKING AND COKE FORMATION, WHICH COMPRISES CONTACTING SAID OIL AT A TEMPERATURE IN THE RANGE OF FROM 500* TO 800*F. AND AT A PRESSURE IN THE RANGE OF FROM 500 TO 4000 P.S.I.G., AND AT A LIQUID HOURLY SPACE VELOCITY BASED ON SAID OIL OF 0.2 TO 10, TOGETHER WITH 500 TO 10,000 S.C.F. OF H2 PER BARREL OF SAID OIL, WITH A SULFIDED NICKEL-MOLYBDENUM-