Hydrodenitrification process

Abstract: In a process for the hydrogenation of nitrogen-containing hydrocarbons in a hydrocarbon feedstock, the feedstock is contacted at a temperature between 302 °C and 413 °C and a pressure between 40 bar and 168 bar in the presence of added hydrogen with a first catalyst bed containing a hydrotreating catalyst containing nickel, tungsten and optionally phosphorous supported on an alumina support, and, after contact with the first catalyst bed, the hydrogen and feedstock without modification, is passed from the first catalyst bed to a second catalyst bed where it is contacted at a temperature between 302 °C and 413 °C and a pressure between 40 bar and 168 bar with a hydrotreating catalyst containing nickel, molybdenum and optionally phosphorous supported on an alumina support.

Description: This invention relates to a hydrotreating process for the removal of nitrogen-containing compounds from petroleum fractions. Nitrogen-containing compounds in petroleum fractions can adversely affect end products. For example, nitrogen compounds can adversely affect the storage stability and octane value of naphthas and may poison downstream catalysts. Nitrogen removal improves air quality to some extent, since it lowers the potential for NO x formation during subsequent fuel combustion. Crude and other heavy petroleum fractions are typically subjected to hydrodenitrification prior to being subjected to further processing. A "stacked" or multiple bed hydrotreating system has now been developed for removal of nitrogen-containing feedstocks comprising a Ni-W-optionally P/alumina catalyst "stacked" on top of a Ni-Mo-optionally P/alumina catalyst which offers activity advantages over the individual catalysts for hydrodenitrification. A more active catalyst can be operated at a lower temperature to obtain the same degree of nitrogen conversion as a less active catalyst. A lower operating temperature will prolong catalyst life and decrease operating expenses. The prior art discloses several examples of stacked catalyst beds used to hydroprocess petroleum fractions, such as US patent specifications 3,392,112; 3,766,058; 3,876,530; 4,016,067; 4,016,069; 4,016,070; 4,012,330; 4,048,060; 4,166,026; 4,392,945; 4,406,779; 4,421,633; 4,431,526; 4,447,314; 4,534,852 and 4,776,945. Further, in European application EP-A-0 464 931, there is described the use of a stacked bed of Ni-W-optionally P/alumina catalyst on top of a Co and/or Ni-Mo-optionally P/alumina catalyst for use in a hydrotreating process to saturate aromatics in diesel boiling-range hydrocarbon feedstocks. The present invention comprises a process for the hydrogenation of nitrogen-containing hydrocarbons in a hydrocarbon feedstock having a nitrogen content greater than 150 ppm which process comprises: (a) contacting at a temperature between 302 °C and 413 °C and a pressure between 40 bar and 168 bar in the presence of added hydrogen the feedstock with a first catalyst bed containing a hydrotreating catalyst comprising nickel and tungsten supported on an alumina support, and (b) passing the hydrogen and feedstock without modification, from the first catalyst bed to a second catalyst bed where it is contacted at a temperature between 302 °C and 413 °C and a pressure between 40 bar and 168 bar with a hydrotreating catalyst comprising nickel and molybdenum supported on an alumina support. The present process can be operated at lower temperatures than processes using individual hydrodenitrification catalysts. The present invention relates to a process for reducing the nitrogen content of a hydrocarbon feedstock by contacting the feedstock in the presence of added hydrogen with a two bed catalyst system at hydrotreating and mild hydrocracking conditions, i.e., at conditions of temperature and pressure and amounts of added hydrogen such that significant quantities of nitrogen-containing hydrocarbons are reacted with hydrogen to produce gaseous nitrogen compounds which are removed from the feedstock. The feedstock to be utilized is any crude or petroleum fraction containing in excess of 150 parts per million by weight (ppm) of nitrogen in the form of nitrogen-containing hydrocarbons, suitably more than 300 ppm, preferably more than 500 ppm, most preferably more than 750 ppm. Examples of suitable petroleum fractions include catalytically cracked light and heavy gas oils, straight run heavy gas oils, light flash distillates, light cycle oils, vacuum gas oils, coker gas oil, synthetic gas oil and mixtures thereof. Typically, the feedstocks that are most advantageously processed by the instant invention are feedstocks for first stage hydrocracking units. These feedstocks will usually also contain from 0.01 to 2, preferably from 0.05 to 1.5 percent by weight of sulfur present as organosulfur compounds. Feedstocks with very high sulfur contents are generally not suitable for processing in the instant process. Feedstocks with very high sulfur contents can be subjected to a separate hydrodesulfurization process in order to reduce their sulfur contents to 0.01-2, preferably 0.05-1.5 percent by weight prior to being processed by the present process. The present process utilizes two catalyst beds in series. The first catalyst bed is made up of a hydrotreating catalyst comprising nickel, tungsten and optionally phosphorous supported on an alumina support and the second catalyst bed is made up of a hydrotreating catalyst comprising nickel, molybdenum and optionally phosphorous supported on an alumina support. The term "first" as used herein refers to the first bed with which the feedstock is contacted and "second" refers to the bed with which the feedstock, after passing through the first bed, is next contacted. The two catalyst beds may be distributed through two or more reactors, or, in the preferred embodiment, they are contained in one reactor. In general the reactor(s) used in the instant process is used in the trickle phase mode of operation, that is, feedstock and hydrogen are fed to the top of the reactor and the feedstock trickles down through the catalyst bed primarily under the influence of gravity. Whether one or more reactors are utilized, the feedstock with added hydrogen is fed to the first catalyst bed and the feedstock as it exits from the first catalyst bed is passed directly to the second catalyst bed without modification. "Without modification" means that no (substantial) sidestreams of hydrocarbon materials are removed from or added to the stream passing between the two catalyst beds. Hydrogen may be added at more than one position in the reactor(s) in order to maintain control of the temperature. When both beds are contained in one reactor, the first bed is also referred to as the "top" bed. The volume ratio of the first catalyst bed to the second catalyst bed is primarily determined by a cost effectiveness analysis and the nitrogen and sulfur contents of the feed to be processed. The cost of the first bed catalyst which contains more expensive tungsten is approximately two to three times the cost of the second bed catalyst which contains less expensive molybdenum. The optimum volume ratio will depend on the particular feedstock nitrogen and sulfur contents and will be optimized to provide minimum overall catalyst cost and maximum nitrogen removal. In general terms the volume ratio of the first catalyst bed to the second catalyst bed will range from 1:5 to 5:1, more preferably from 1:4 to 4:1, and most preferably from 1:3 to 3:1. In a particularly preferred embodiment the volume of the first catalyst will be equal to or less than the volume of the second catalyst, that is the volume of the first catalyst will comprise from 10 percent to 50 percent of the total bed volume. The catalyst utilized in the first bed comprises nickel, tungsten and 0-5% wt phosphorous (measured as the element) supported on a porous alumina support preferably comprising gamma alumina. It contains from 1 to 5, preferably from 2 to 4 percent by weight of nickel (measured as the metal); from 15 to 35, preferably from 20 to 30 percent by weight of tungsten (measured as the metal) and, when present, preferably from 1 to 5, more preferably from 2 to 4 percent by weight of phosphorous (measured as the element), all per total weight of the catalyst. It will have a surface area, as measured by the B.E.T. method (Brunauer et al, J. Am. Chem. Soc., 60 , 309-16 (1938)) of greater than 100 m²/g and a water pore volume between 0.2 to 0.6, preferably between 0.3 to 0.5. The catalyst utilized in the second bed comprises nickel, molybdenum and 0-5% wt phosphorous (measured as the element) supported on a porous alumina support preferably comprising gamma alumina. It contains from 1 to 5, preferably from 2 to 4 percent by weight of nickel (measured as the metal); from 8 to 20, preferably from 12 to 16 percent by weight of molybdenum (measured as the metal) and, when present, preferably from 1 to 5, more preferably from 2 to 4 percent by weight of phosphorous (measured as the element), all per total weight of the catalyst. It will have a surface area, as measured by the B.E.T. method, of greater than 120 m²/g and a water pore volume between 0.2 to 0.6, preferably between 0.3 to 0.5. The catalyst utilized in both beds of the present process are catalysts that are known in the hydrocarbon hydroprocessing art. These catalysts are made in a conventional fashion as described in the prior art. For example porous alumina pellets can be impregnated with solution(s) containing nickel, tungsten or molybdenum and phosphorous compounds, the pellets subsequently dried and calcined at elevated temperatures. Alternately, one or more of the components can be incorporated into an alumina powder by mulling, the mulled powder formed into pellets and calcined at elevated temperature. Combinations of impregnation and mulling can be utilized. Other suitable methods can be found in the prior art. Non-limiting examples of catalyst preparative techniques can be found in U.S. patent specifications 4,530,911, and 4,520,128. The catalysts are typically formed into various sizes and shapes. They may be suitably shaped into particles, chunks, pieces, pellets, rings, spheres, wagon wheels, and polylobes, such as bilobes, trilobes and tetralobes. The two above-described catalysts are normally presulfided prior to use. Typically, the catalysts are presulfided by heating in H₂S/H₂ atmosphere at elevated temperatures. For example, a suitable presulfiding regimen comprises heating the catalysts in a hydrogen sulfide/hydrogen atmosphere (5%v H₂S/95%v H₂) for about two hours at about 371 °C. Other methods are also suitable for presulfiding and generally comprise heating the catalysts to elevated temperatures (e.g., 204-399 °C) in the presence of hydrogen and a sulfur-containing material. The hydrogenation process of the present invention is effected at a temperature between 302 °C and 413 °C, preferably between 316 °C and 413 °C under pressures above 39 bar. The total pressure will typically range from 40 bar to 168 bar. The hydrogen partial pressure will typically range from 35 bar to 149 bar. The hydrogen feed rate will typically range from 178 to 1069 vol/vol. The feedstock rate will typically have a liquid hourly space velocity ("LHSV") ranging from 0.1 to 5, preferably from 0.2 to 3. The invention will be further described by the following examples which are provided for illustrative purposes and are not to be construed as limiting the invention. The catalysts used to illustrate the present invention are given in Table 1 below. HYDROGENATION CATALYSTS CATALYST A CATALYST B Metals, Wt.% Ni 2.99 2.58 W 25.81 -0- Mo -0- 14.12 P 2.60 2.93 Support gamma alumina gamma alumina Surface Area, m²/g 133 164 Water Pore Vol., ml/g 0.39 0.44 Properties of the feedstocks utilized to illustrate the present invention are detailed in Table 2 below. PROPERTIES OF FEEDSTOCK Physical Properties FEED A FEED B Density (16 °C) 0.9460 0.9264 Viscosity (21 °C) 2.48 2.09 Elemental Content Hydrogen 10.485wt.% 10.741wt.% Carbon 88.684wt.% 87.818wt.% Oxygen 0.227wt.% 0.253wt.% Nitrogen 0.203wt.% 0.158wt.% Sulfur 0.480wt.% 0.969wt.% Basic Nitrogen 344 ppm 383 ppm Aromatic Content (wt.%) (Measured by UV absorption) Mono 7.78 7.06 Di 20.21 17.46 Tri 8.41 8.01 Tetra 0.56 0.75 Total 36.96 33.28 Boiling Point Distribution °C °C IBP 133 113 10wt.% 209 228 30wt.% 239 269 50wt.% 270 299 70wt.% 300 333 90wt.% 336 358 95wt.% 351 370 97wt.% 362 378 99wt.% 382 391 99.5wt.% 395 402 Four types of catalyst configurations were tested utilizing the catalysts noted in Table 1: A/B, B/A, A and B. The catalysts were diluted with 0.17-0.25 mm (60/80 mesh) silicon carbide particles in a 1:1 volume ratio of catalyst:carbide and 100 cm³ of the mixture was used in the catalyst bed. The catalysts were presulfided in the reactor by heating them to about 371 °C and holding at such temperature for about two hours in a 95 vol.% hydrogen-5 vol.% hydrogen sulfide atmosphere flowing at a rate of about 120 liters/hour. To test the catalysts, the feeds from table 2 were passed down through the catalyst bed at a liquid hourly space velocity of 1 hour⁻¹, a system pressure of 119 bar and a hydrogen flow rate of about 100 liters/hr. The reactor temperature was adjusted to provide a liquid product containing 5 ppm of nitrogen as measured by chemiluminescence. The catalysts were run for about 600 hours. From the temperature required to obtain 5 ppm nitrogen in the product versus time, it was noted that the catalysts had stabilized at about 200 hours. A best fit line was drawn through the stabilized portions of the curves and the temperatures required for 5 ppm of nitrogen were obtained after a run time of 300 hours and are given in Table 3 below. Comparative Hydrodenitrification Results Bed Loading A vol./B vol. Temp. Required for 5 ppm Nitrogen, °C FEED A FEED B 20/80 349 340 30/70 349 336 100/0 354 - 0/100 352 344 80/20 353 - 60/40 356 - As can be seen from the above data, the present invention provides for enhanced catalyst activity (lower temperature to achieve 5 ppm N) when compared to the individual catalysts and when compared to a stacked bed of catalyst B over catalyst A.

Claims: A process for the hydrogenation of nitrogen-containing hydrocarbons in a hydrocarbon feedstock having a nitrogen content greater than 150 parts per million by weight which process comprises: (a) contacting at a temperature between 302 °C and 413 °C and a pressure between 4MPa (40 bar) and 16.8 MPa (168 bar) in the presence of added hydrogen the feedstock with a first catalyst bed containing a hydrotreating catalyst comprising nickel and tungsten supported on an alumina support, and (b) passing the hydrogen and feedstock without modification, from the first catalyst bed to a second catalyst bed where it is contacted at a temperature between 302 °C and 413 °C and a pressure between 4 MPa (40 bar) and 16.8 MPa (168 bar) with a hydrotreating catalyst comprising nickel and molybdenum supported on an alumina support. The process of claim 1 wherein the support for the catalyst in the first catalyst bed has a surface area greater than 100 m²/g and a water pore volume ranging from 0.2 to 0.6 cm³/g and the support for the catalyst in the second catalyst bed has a surface area greater than 120 m²/g and a water pore volume ranging from 0.2 to 0.6 cm³/g. The process of claim 1 or 2 wherein the supports for both catalysts have water pore volumes ranging between from 0.3 to 0.5 cm³/g. The process of any one of claims 1-3 wherein in the catalyst in the first bed the nickel content ranges from 1 to 5 percent by weight of the total catalyst, measured as the metal and the tungsten content ranges from 15 to 35 percent by weight of the total catalyst, measured as the metal and wherein in the catalyst in the second bed the nickel content ranges from 1 to 5 percent by weight of the total catalyst, measured as the metal and the molybdenum content ranges from 8 to 20 percent by weight of the total catalyst, measured as the metal. The process of any one of claims 1-4 wherein in the catalyst in the first bed the nickel content ranges from 2 to 4 percent by weight of the total catalyst, measured as the metal and the tungsten content ranges from 20 to 30 percent by weight of the total catalyst, measured as the metal and wherein in the catalyst in the second bed the nickel content ranges from 2 to 4 percent by weight of the total catalyst, measured as the metal and the molybdenum content ranges from 12 to 16 percent by weight of the total catalyst, measured as the metal. The process of any one of claims 1-5 wherein the catalyst in the first catalyst bed and/or the catalyst in the second catalyst bed additionally comprise phosphorus. The process of any one of claims 1-6 wherein in the catalyst in the first bed the phosphorous content ranges from 2 to 4 percent by weight of the total catalyst, measured as the element and wherein in the catalyst in the second bed the phosphorous content ranges from 2 to 4 percent by weight of the total catalyst, measured as the element. The process of any one of claims 1-7 wherein the temperature in steps (a) and (b) ranges from 316 °C to 413 °C.

Inventors: SMEGAL JOHN ANTHONY, SMEGAL, JOHN ANTHONY
Applicants: SHELL INT RESEARCH, SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1991
Main classification: C10G65
IPC codes: B01J35, C10G65, C10G45, B01J23, B01J27