US3117075A - Hydrocaracking process employing as a feed, a nitrogen containing distillate oil - Google Patents

Description

because United States Patent 3 117 075 HYDRGCRACKING PifGC ESS EMPLOYING AS A FEED, A NITROGEN CGNTAINENG DHSTILLATE This invention relates to a hydrocarbon conversion process and, more particularly, to a process for the catalytic conversion of petroleum distillates to products boiling below the initial boiling point of the feed distillates.

Still more particularly, this invention is directed to the processing of hydrocarbon distillates, including heavier distillates boiling up to about 1050 F., having a high total nitrogen content, to products boiling below the initial boiling point of the feed distillates while concurrently denitrifying said feed distillates and maintaining unusually long catalyst on-stream periods.

The process of the present invention is a type of hydrocracking process conducted in the presence of hydrogen and a catalyst composition comprising a hydrogenatingdehydrogenating component disposed on a solid, active, acidic support. The process is characterized by long onstream periods, for example, several months in duration, without the necessity for catalyst regeneration, conversion of the feed to the desired products with a substantial consumption of hydrogen, feed denitrification, and low pressure operation.

The foregoing characteristics of the present process are highly unusual and heretofore were considered to be unobtainable together. As pointed out in Scott U.S. Patent 2,944,006, issued July 5, 1960, heretofore it has been felt that acceptable conversion levels and adequate on-stream catalyst life could only be achieved if the nitrogen content of the charge stock was maintained at a level below about parts per million total nitrogen. Heretofore in such processes, the effect of a total nitrogen content in excess of 10 parts per million was such a reduction in catalyst activity that the deleterious effect on operational efficiency of the process and upon product distribution was intolerable as were the higher reaction ternperatures necessary to maintain adequate per-pass conversion levels as the nitrogen content increased above the specified maximum. Such higher reaction temperatures cause a disproportionate increase in the amount of product converted to light gases and in the amount of carbonaceous residues deposited on the catalyst surface and thus further decrease catalyst activity. Such further decrease in catalyst activity must be com ensated for by resort to still higher operating temperatures if acceptable conversion is to be maintained. As pointed out in the Scott patent, the on-stream life of the catalyst was unduly shortened at temperatures above about 700 F., partly because of excessive coke laydown, and the nitrogen in the feed was a severe problem at temperatures below 700 F. In other words, heretofore in operating a hydrocracking process, the problem of high feed nitrogen contents could not be solved by raising the operating temperature to diminish the deleterious effect of the nitrogen the higher temperatures would unduly shorten catalyst life, and the high feed nitrogen contents could not be tolerated at the lower operating temperatures. Accordingly, heretofore in operating a hydrocracking process, as pointed out in the Scott patent, it has been necessary to control the nitrogen content of the charge stock to a nitrogen level, expressed as total nitrogen, below about 10 parts per million and preferably below about 2 parts per million. This control has been accomplished by such expedients as hydrofining stages preceding the hydrocracking stage.

As the Scott patent indicates, the effect of nitrogen in the feed in conventional hydrocracking operations conducted above about 800 F., even when present in substantial amounts, is quite small and becomes scarcely noticeable at temperatures above 850 F. While these statements are generally true, they are directed to amounts of nitrogen in the order of 10 to parts per million and do not apply to substantially higher amounts of nitrogen. With the process of the present invention up to 1000 ppm, nitrogen can be successfully dealt with while concurrently avoiding the unacceptable decrease in catalyst activity experienced by the prior art at temperatures above about 700 F.

In accordance with the present invention, there is provided a process for converting a hydrocarbon distillate feed having a total nitrogen content between 10 and 1000 parts per million and boiling in the range from about 320 to 1050 F. to produce fractions boiling below the initial boiling point of said feed in a yield of at least 20% per pass, which comprises passing said feed along with at least 1500 standard cubic feet of hydrogen per barrel thereof at temperatures between 320 F. and 900 F., pressures of at least 500 p.s.i.g., preferably 1500 to 3000 p.s.i.g., and liquid hourly space velocities from 0.2 to 15 v./v./hr., preferably 0.3 to 4.0 v./v./hr., into contact in a hydrocracking zone with a hydrocracking catalyst comprising a hydrogenating-dehydrogenating component disposed on a solid, active, acid, cracking support, said process being characterized by operation during a substantial portion of the on-stream period not less than 100 hours, at temperatures below about 775 F., by a hydrogen consumption of at least 500 standard cubic feet per barrel of feed so converted, by substantial feed denitrification, by total on-stream periods of at least 750 hours without the necessity for catalyst regeneration, all despite the low temperature and low pressure operation and high nitrogen content of the feed.

The 10-1000 p.p.m. total nitrogen content in the feed to the process of the present invention may be either the nitrogen content of an untreated feed to the process, or the nitrogen content resulting from subjecting a stock having a hi her nitrogen content to partial denitrification and/ or dilution with low nitrogen content stocks.

The advantageous results obtainable with the process of the present invention are totally unexpected when viewed in the light of the belief of the prior art that hydrocarbon distillate feeds having the high nitrogen content of those with which the present invention is concerned could not be successfully hydrocracked to convert a large portion of the feed to products boiling below the initial boiling point of the feed unless exceedingly high pressures were used or the feed was first denitrified to very low nitrogen levels. The prior art feeding was correct in that an attempt to obtain the desired results at pressures Within the 500 to 3000 p.s.i.g. pressure range of the present process invariably resulted in such rapid catalyst fouling that the increase in temperature necessary to offset the rapid decline in catalyst activity was not only intolerable, but itself contributed to further decline in catalyst activity, rendering the attempt a failure. In accordance with the present invention, it has been found that such a hydrocracking process can be operated at pressures above 500 p.s.i.g., preferably from 500 to 3000 p.s.i.g., with feeds containing from 10 parts per million to 1000 parts per million nitrogen with a heretofore unobtainable catalyst fouling rate so low that reasonable temperatures may be maintained throughout the catalyst on-stream period and the catalyst on-stream period can be extended for an unexpectedly long time; with the process of the present invention catalyst on-stream periods of more than 750 hours are easily obtainable.

It is of particular importance in the process of the present invention that during the first portion of the on-stream period the organic nitrogen compounds present in the high nitrogen content feed are substantially prevented from being deposited on the catalyst. Surprisingly, it has been found that instead of the necessity for accepting a high rate of catalyst fouling by organic nitrogen compounds during the first portion of the on-stream period, this type of catalyst fouling can be substantially prevented by equilibrating of titrating the catalyst with ammonia. It has been found that the organic nitrogen compounds in the feed are one adequate source of ammonia with which to accomplish the ammonia titration of the catalyst. Alternatively, the catalyst may be pretreated with ammonia before being placed on-stream. If the nitrogen compounds in the feed are relied upon as a source of ammonia, these compounds must be rapidly converted to ammonia during the first portion of the onstream period because when the ammonia is titrated onto the catalyst it thereby selectively excludes or blocks the organic nitrogen compound therefrom. While this ammonia titration is being accomplished, the temperature necessary to maintain a substantially constant conversion will rise rather rapidly; however, the ammonia titration of the catalyst will proceed only to the point where the ammonia chemisorbed on the catalyst is in equilibrium with the ammonia being produced in the reaction zone from the organic nitrogen compounds in the feed. Thereafter, the temperature necessary to maintain substantially constant conversion will increase at a much slower rate, depending upon the small but essential remaining acidity of the catalyst. This slower rate of temperature increase Will continue throughout substantially all of the remainder of the run. This slower rate of temperature increase is not only slower than the rate during the first portion of the on-stream period while the catalyst was becoming equilibrated with ammonia, but also is a slower rate than that which would have been necessary had rapid ammonia titration of the catalyst not been accomplished. This substantially constant rate of temperature increase during the remainder of the run will generally be in the range from 650 to 900 F., preferably from 650' to 850 F.

The operating pressures in the present process will be at least 500 p.s.i.g., preferably 1500 to 3000 p.s.i.g. and still more preferably 1500 to 2500 p.s.i.g. Lower pressures tend to decrease run lengths and higher pressures tend to increase hydrogen consumption.

The space velocities used in the process of the present invention are 0.2 to v./v./hr.; however, exceptionally excellent results are obtained if the space velocities are in the range from about 0.3 to 4.0 v./v./hr.

Hydrocracking catalysts adequate for carrying out the process of the present invention will contain a hydrogenating-dehydrogenating component disposed on, i.e., intimately associated with a solid, active, acidic, cracking support. In the light of the present disclosure, those skilled in the art will be able to select specific catalysts suitable in the particular circumstances with which they are concerned. For purposes of the present invention, it will be sufficient if any of the well-known solid, active, acid, cracking supports used for hydrocracking are se lected, including silica-alumina, activated alumina, alumina-BF combinations, and various fluorided catalyst supports. The hydrogenating-dehydrogenating component may be any component adequate to accomplish the desired hydrogenation and denitrification under the process operating conditions. Nickel sulfide and/or cobalt sulfide are especially suitable. The entire preferred catalyst composite of Scott U.S. Patent 2,944,006 will be especially suitable in the process of the present invention.

The process of the present invention may be operated as a once-through process or in a recycle manner. A

very desirable method of operation is with separation from the hydrocracking zone effluent, of an ammoniafree hydrogen-rich gas stream which is recycled to the hydrocraclcing zone. Various hydrocracking fractions not converted below the initial boiling point of the feed may be recycled to advantage, particularly aromatics-rich fractions. The product fractions from the hydrocracking zone that boil below the initial boiling point of the feed constitute excellent gasoline blending stocks for certain purposes; however, it will be found generally more desirable to send at least the heavier portions of them to a catalytic reformer where they will serve as a most excellent preferred feed for catalytic reforming operations.

The following examples will serve to further illustrate the method of carrying out the process of tie present invention, and the advantages thereof:

Example 1 A light cycle oil comprising a blend of 19.9% raw cycle oil, 41.9% hydrofined cycle oil, and 46.6% of recycle bottoms having a nitrogen content of 60 parts per million based on the total light cycle oil blend was hydrocracked and concurrently denitrified in accordance with the process of the present invention over a catalyst comprising a nickel sulfide hydrogenating-dehydrogenating component on a solid silica-alumina active, acid, cracking support. The hydrocracking and denitrification were accomplished in once-through operation. The light cycle oil feed was accompanied by 6500 standard cubic feet of hydrogen per barrel of feed. In accordance with the process of the present invention, the catalyst immediately after being placed on stream was rapidly titrated with ammonia derived from the nitrogen content of the cycle oil feed at temperatures between 400 F. and 750 F a pressure of 1800 p.s.i.g. and at a liquid hourly space velocity of 0.5. Following such rapid equilibration of the catalyst with ammonia in accordance with the present invention, the operating temperature necessary to maintain a 50% conversion of the feed to products boiling below the initial boiling point of the feed immediately and abruptly leveled off at about 730 F. Thereafter, it was found that the hydrocracking-denitrification operation could be effectively continued for approximately 800 hours without the necessity for raising the operating temperature more than about .033 F. per hour in order to maintain said 50% conversion. Thereafter, it was decided to raise the temperature more rapidly in order to obtain a 60% conversion of said cycle oil to products boiling below the initial boiling point of the feed; accordingly, While of course it was necessary to continually raise the operating temperature at a greater rate in order to maintain such increased conversion, it was found that operation could be continued for almost an additional 1000 hours without the necessity for raising the temperature more rapidly than 0.073 F. per hour. During the first period of operation at 50% conversion, the average temperature was 730 F. During the subsequent period of operation at 60% conversion, the average temperature was only 790 F. The total run length from the time the catalyst was placed on stream until the increasing temperature finally began to cause a prohibitive catalyst fouling rate was approximately 2000 hours, an unheard-of result in the light of prior art experiences with feeds containing so much nitrogen.

Example 2 A raw (unhydrodenitrified) heavy straight-run Arabian gas oil, having an API gravity of 280, boiling over the range 530 F. initial to 862 F. endpoint (ASTM D-1160 distillation), and a total nitrogen content of 570 parts per million, was hydrocracked and concurrently denitrified in accordance with the present invention over the catalyst of Example 1, above. The oil feed was accompanied by 6500 standard cubic feet of hydrogen per barrel of oil. Beginning immediately after the catalyst-containing reactor was placed on stream, the catalyst was equilibrated with ammonia derived from the nitrogen content of the oil feed at temperatures ranging from about 700 F. to 770 F., a total pressure of 2000 p.s.i.g., and a liquid hourly space velocity of 0.5, over an interval of about 200 hours. Following equilibration of the catalyst with ammonia, the operating temperature necessary to maintain a 60% by volume conversion of the feed to products boiling below the initial boiling point of the feed, and to recycle reactor eflluent fractions boiling above the initial of the feedback through the reactor to extinction, gradually leveled olf at substantially 775 F. and remained constant up to a total run length of 800 hours at 0.5 liquid hourly space velocity. Since an object of the run was to determine catalyst life with high nitrogen content feed, and the fouling rate of the catalyst, expressed as the required temperature increase in degrees Fahrenheit per hour to maintain the initial conversion, of 60% in this instance, was less than 002 F. per hour during the first 800 hours of operation, the liquid hourly space rate of oil feed was abruptly raised to 1.0 at the end of 800 hours. Over the ensuing period of about 450 hours, it was necessary to raise the temperature required for 60% conversion at a greater rate than before, and finally when the temperature had reached 880 F., at a total run length of 1250 hours, to terminate the run because of prohibitive catalyst fouling rate. Based on comparable runs with the same catalysts on other stocks, it is possible to estimate that, allowing for the rapidly accelerated fouling rate in this run brought about by the abrupt increase in space rate at 800 hours and the resulting cumulative temperature rise to maintain constant conversion, the run length at the original space rate of 0.5 would have greatly exceeded 2000 hours.

From the foregoing, it may be seen that the process of the present invention solves a number of heretofore unsolved problems that have been faced by the art, particularly in that it enables a hydrocraeking process to be operated both with high nitrogen content feeds and with long catalyst life at reasonable operating temperatures.

Although only specific modes of operation of the process of the present invention have been described, numerous variations could be made in those modes without departing from the spirit of the invention, and all such variations that fall within the scope of the appended claims are intended to be embraced thereby.

We claim:

1. In a hydrocracking process employing a catalyst which comprises a hydrogenating component selected from group consisting of cobalt sulfide and nickel sulfide intimately associated with an active acid cracking support and is susceptible to fouling and consequent deactivation by coke laydown when used to hydrocrack a hydrocarbon distillate feed boiling from 320 to 1050 F. and containing organic nitrogen compounds in a concentration of from to 1000 parts per million total nitrogen, the improvement of retarding catalyst deactivation in said process which improvement consists essentially in initially preferentially titrating said catalyst with ammonia to the substantial exclusion of fouling by organic nitrogen compounds and using the resulting titrated catalyst to hydrocrack said feed in a continuous run of at least 750 hours duration without catalyst regeneration, in the presence of at least 1500 s.c.f. H per barrel of feed, at a temperature in the range between 320 and to 900 F., at a pressure in the range between 5 00 and 3000 p.s.i.g., while con tinuously raising the temperature within the aforesaid range as necessary to maintain substantially constant conversion corresponding to the production of at least 20% per pass of product fractions boiling below the initial boiling point of the feed and to maintain ammonia adsorbed on said titrated catalyst in equilibrium with ammonia being produced from the nitrogen compounds in the feed.

2. The method according to claim 1 wherein said feed is hydrocracked at a liquid hourly space velocity of between 0.3 and 4.0 and wherein at least 500 s.c.f. of said H per barrel of said product fractions are consumed by said product fractions.

3. In =a process for hydrocracking and concurrently denitrifying a distillate feed containing organic nitrogen compounds in a concentration of from 10 to 1000 parts per million total nitrogen and boiling in the range of from 320 to 1050 F., in the presence of a catalyst comprising a hydrogenating component selected from the group consisting of cobalt sulfide and nickel sulfide intimately associated with an active acid cracking support at a temperature of from 320 to 900 F., at a pressure of from 1500 to 3000 p.s.i.g., at a liquid hourly space velocity of from 0.2 to 15 and in the presence of at least 1500 s.c.f. of H per barrel of feed, in a continuous run of at least 750 hours without catalyst regeneration, at substantially constant conversion corresponding to the production of a sustained yield of at least 20% per pass of product fractions boiling below the initial boiling point of the feed, the improvement of retarding catalyst deactivation in said process which consists essential in: (a) selecting a temperature, pressure and space velocity combination within the aforesaid ranges at the beginning of said run to accomplish the desired substantially constant hydrocarbon conversion and concurrently to rapidly convert substantially all of the organic nitrogen compounds in said feed to ammonia to thereby rapidly accomplish ammonia titration of said acid catalyst with minimum fouling thereof by the organic nitrogen compounds; (b) continuously raising the temperature at a relatively high rate and adjusting the pressure and space velocity as necessary within the aforesaid ranges to maintain the desired conversion and said rapid ammonia titration as determined by an abrupt leveling off of the temperature necessary to maintain the desired conversion; and (c) thereafter continuously raising the temperature until the end of said run at a relatively low rate as necessary to maintain the desired con version of feed and equilibration of ammonia on the catalyst with the ammonia being produced in the process from the nitrogen compounds of the feed.

References Cited in the file of this patent UNITED STATES PATENTS 2,851,400 Meyers et al Sept. 9, 1958 2,911,356 Hanson Nov. 3, 1959 2,966,455 Stuart Dec. 27, 1960 3,023,159 Ciapetta et al Feb. 27, 1962

Claims (1)

1. IN A HYDROCRACKING PROCESS EMPLOYING A CATALYST WHICH COMPRISES A HYDROGENATING COMPONENTS SELECTED FROM GROUP CONSISTING OF COBALT SULFIDE AND NICKEL SULFIDE INTIMATELY ASSOCIATED WITH AN ACTIVE ACID CRACKING SUPPORT AND IS SUSCEPTIBLE TO FOULING AND CONSEQUENT DEACTIVATION BY COKE LAYDOWN WHEN USED TO HYDROCRACK A HYDROCARBON DISTILLATE FEED BOILING FROM 320* TO 1050*F. AND CONTAINING ORGANIC NITROGEN COMPOUNDS IN A CONCENTRATION OF FROM 10 TO 1000 PARTS PER MILLION TOTAL NITROGEN, THE IMPROVEMENT OF RETARDING CATALYST DEACTIVATION IN SAID PROCESS WHICH IMPROVEMENT CONSISTS ESSENTIALLY IN INITIALLY PREFERENTIALLY TITRATING SAID CATALYST WITH AMMONIA TO THE SUBSTANTIAL EXCLUSION OF FOULING BY ORGANIC NITROGEN COMPOUNDS AND USING THE RESULTING TITRATED CATALYST TO HYDROCRACK SAID FEED IN A CONTINUOUS RUN OF AT LEAST 750 HOURS DURATION WITHOUT CATALYST REGENERATION IN THE PRESENCE OF AT LEAST 1500 S.C.F. H2 PER BARREL OF FEED, AT A TEMPERATURE IN THE RANGE BETWEEN 320* AND 900*F., AT A PRESSURE IN THE RANGE BETWEEN 500 AND 300 P.S.I.G., WHILE CONTINUOUSLY RAISING THE TEMPERATURE WITHIN THE AFORESAID RANGE AS NECESSARY TO MAINTAIN SUBSTANTIALLY CONSTANT CONVERSION CORRESPONDING TO THE PRODUCTION OF AT LEAST 20% PER PASS OF PRODUCT FRACTIONS BOILING BELOW THE INITIAL BOILING POINT OF THE FEED AND TO MAINTAIN AMMONIA ADSORBED ON SAID TITRATED CATALYST IN EQUILIBRIUM WITH AMMONIA BEING PRODUCED FROM THE NITROGEN COMPOUNDS IN THE FEED