US3524807A - Hydrocracking in the presence of controlled amounts of nitrogen - Google Patents

Description

18, 1970 c. T. LEWIS, JR 3,5

HYDROCRACKING IN THE PRESENCE CF CONTROLLED AMOUNTS OF NITROGEN Filed Dec. 28, 1967 Tlc'l.

142M M'frayen 0'2 fed 2351 00 2 Nap/1M0 505/; 591/; Feed l l l 1 1 1 90 700 710 720 750 740 "/50 760 770 750 790 8 United States Patent G US. Cl. 208-111 5 Claims ABSTRACT OF THE DISCLOSURE Good yields of heavy naphtha are obtained by carrying out the hydrocracking of gas oils and the like in the presence of 25-75 p.p.m. nitrogen based on the weight of hydrocarbon oil charge.

This invention is concerned with a process for the conversion of heavy hydrocarbon oils under controlled conditions to produce lighter products.

The hydrocracking of hydrocarbon oils is well known in the art of petroleum refining. Ordinarily, in the hydrocracking process heavy oils, usually boiling in the gas oil range, are contacted with a hydrocracking catalyst under hydrocracking conditions and are converted to lighter products. A particularly desirable product is heavy naphtha which boils in the range of about 235-400 F. This material is admirably suited for use in gasoline or may be subjected to additional treatment in a catalytic reformer to be converted into a superior grade of motor fuel.

Hydrocracking catalysts, as is well known in the art, are ordinarily subjected to deactivation due to the presence of nitrogen compounds in the feed. US. Pat. No. 2,911,356 indicates that hydrocracking is greatly inhibited by the nitrogen content of the feed stock but that this effect may be lessened by raising the reaction temperature. It is suggested therein that as the nitrogen content of the hydrocarbon feed increases from 0-2.5 the hydrocracking temperature should be increased from 750-975 F. The problem of nitrogen-containing charge stocks is also recognized in US. Pat. No. 3,023,159 where it is sug gested that hydrocracking processes can be operated at substantially constant temperature with the amount of conversion being controlled by regulating the nitrogen content of the feed stock within the range of about 0.01- 1.0% by Weight.

However, operation at high temperatures to overcome the effect of the presence of nitrogen in the feed is unsatisfactory. Not only are high temperatures conducive to the production of undesirably large volumes of product gas and deposition of coke on the catalyst by overcracking but in addition the product liquid does not have good product distribution. It has therefore become conventional in the industry to subject a hydrocracking charge stock to a hydrofining pretreatment to reduce the nitrogen content to an extremely low level as, for example, the less than ppm. recommended in UJS. Pat. No. 2,944,006.

It has now been found that superior yields of heavy naphtha and reduced yields of lower molecular weight hydrocarbons may be obtained when the nitrogen content of the charge is carefully controlled. According to the present invention, there is provided a process for the conversion of a hydrocarbon charge stock having an initial boiling point of at least about 400 F. into a heavy 3,524,807 Patented Aug. 18, 1970 naphtha and lighter hydrocarbon fractions which comprises introducing said charge stock with hydrogen into a catalytic hydrocracking zone maintained at hydrocracking conditions, the amount of nitrogen introduced into said reaction zone being maintained between 25 and ppm. by weight based on the weight of hydrocarbon oil introduced into the hydrocracking zone.

The hydrocarbon feed charged to the process of the present invention is a fraction having an initial boiling point of at least about 400 F. Ordinarily, gas oils having an initial boiling point of 400 F. and an end point ranging from about 650950 F. or even higher may be satisfactorily treated by the process of this invention. The gas oils may be obtained from the various sources such as crude petroleum, cycle oils, shale oil, tar sand oil, and the like.

The charge as introduced into the hydrocracking zone should also have a nitrogen content of between 25 and 75 ppm. If the charge stock has a nitrogen content in excess of the desired range, it may be subjected to a hydrofining treatment in a manner well known in the art to reduce the nitrogen content to within the desired level. The nitrogen content may also be controlled by mixing a high nitrogen content charge with a low nitrogen content material to produce a charge mixture having a nitrogen content within the desired range. In a preferred embodiment, this latter may be effected by recycling to the hydrocracking reactor an unconverted product fraction of low nitrogen content in such an amount that the charge to the reactor contains the desired level of nitrogen.

The amount of nitrogen introduced into the reaction zone includes the amount of nitrogen in the hydrogen and accordingly if the hydrogen is recycled, the nitrogen content of the hydrogen should be included when determining the amount of nitrogen charged to the reactor. In this connection the term nitrogen is intended to mean total nitrogen. Although it is believed that only basic nitrogen affects the activity of the hydrocracking catalyst, apparently most of the total nitrogen which is not basic is converted during its course through the hydrocracking reactor to basic nitrogen, eventually becoming ammonia which is separated from the product liquid with unreacted hydrogen. When the hydrogen is recycled to the hydrocracking reactor, advantageously it is scrubbed for the removal of the ammonia, or a portion of the recycle stream may be bled from the system and replaced With make-up hydrogen of low nitrogen content.

Unconverted liquid hydrocarbon feed is suitable for use as a low nitrogen component and may be recycled and mixed with a high nitrogen charge to produce a feed mixture of the desired nitrogen content.

Temperatures in the hydrocracking zone may range from 550-850 F., a preferred range being 680780 F. Pressures of 500-5000 p.s.i.g. and higher may be used although pressures of 1500-3000 p.s.i.g. are preferred. A space velocity of 0.1-10 volumes of oil per volume of catalyst per hour may be used although satisfactory results have been obtained using a space velocity of 0.5-2 v./v./hr.

The hydrogen used in the process of the present invention may be obtained from any suitable source such as catalytic reformer by-product hydrogen, electrolytic hydrogen or hydrogen obtained by the partial combustion of a carbonaceous material followed by shift conversion and purification. The hydrogen should have a purity of at least 50% and preferably at least about 75%. The

hydrogen may be introduced into the reaction zone at a rate between 500 and 20,000 standard cubic feet per barrel or charge, a range of 800-6000 s.c.f.b. being preferred. As pointed out above the amount of nitrogen in the hydrogen must be taken into consideration when calculating the total amount of nitrogen introduced into the reaction zone.

The catalysts used in the process comprise a hydrogenating component on a cracking support. Hydrogenating components suitably comprise a Group VIII metal or compound thereof optionally used in conjunction with a Group VI metal or compound thereof. Group VIII metals include platinum, palladium, rhodium and iridium although the preferred hydrogenating components are nickel, iron, cobalt, chromium, molybdenum and tungsten and mixtures thereof. Ordinarily the hydrogenating component will be present in the catalyst in an amount between about 0.5 and 40% by weight of the catalyst composite. Particularly suitable catalysts are those containing between 2 and 10% nickel, iron or cobalt and between 5 and 30% molybdenum or tungsten. The cracking component may include coprecipitated mixtures of dilficultly reducible organic oxides such as silica-alumina, silica-magnesia, silica-titania, silica-zirconia and the like. These cracking components may be prompted by treatment with acidic materials such as halides of hydrogen, boron and silicon.

In a preferred embodiment of the invention the cracking component also contains a decationized crystalline zeolite having uniform pore openings of 6-15A used in conjunction with the amorphous coprecipitated mixture of difiicultly reducible oxides. The zeolite should have an alkali metal content of less than 5% by wt., preferably less than 1.0%. Advantageously, the zeolite is prepared by a method which involves treatment of zeolite Y with an ammonium compound to convert the alkali metal form of the zeolite to the ammonium form, drying and calcining the ion exchanged zeolite to convert the ammonium form to the hydrogen form. The calcined zeolite is then subjected to a further ion exchange treatment with an ammonium compound and the product is then again dried and calcined. The resulting twice decationized, twice calcined, zeolite having an alkali metal content of less than 0.5% is then mixed with the amorphous mixture of diflicultly reducible oxides and the hydrogenating component impregnated thereon by means well known in the art.

The following examples are given for illustrative purposes only and are not to be construed as limiting the invention in any manner.

EXAMPLE I In this example the catalyst is sulfided nickel tungsten supported on a mixture of silica-alumina and twice decationized, twice calcined zeolite Y and has the following composition: nickel 5.5%, tungsten 19.4% and sulfur 8.9% based on the total catalyst weight. The support is 14 wt. percent zeolite and 86 wt. percent amorphous inorganic oxides (73% silica and 27% alumina). Charge stock characteristics are tabulated below:

By operating at a 25% conversion to 400 F. and lighter material with recycle of the unconverted liquid, a liquid charge having a nitrogen content of 25 p.p.m. is prepared and the nitrogen content of the feed is varied by varying the amount of nitrogen in the recycle hydrogen. The reaction conditions and other data are tabulated below and the volume percent of 235-400 F. naphtha is plotted in accompanying FIG. 1.

Run

A B C D Operating conditions:

Temperature, F 744 740 742 741 Pressure, p.s.i.g 1, 500 1, 500 1, 500 1, 500 Space velocity, v./v./l1r 2.0 2. 0 2.0 2. 0 Hydrogen rate, s.c.f.b 5, 500 5, 500 5, 500 5, 500 Total nitrogen 25 57 76 125 Yields:

C1-C3 wt. percent 9. 49 6.64 4.61 4. 52 04 vol. percent 25. 73 15. 43 16. 83 15. 07 05 vol. percent 16.85 8. 99 15. 42 14. 10 115-235 F. vol. percent. 30. 47 30. 54 32. 45 31. 40 235-400 F. vol. percent... 47. 03 65. 97 58. 9 61. 22

EXAMPLE II This example encompasses a total of 46 runs patterned after runs A, B and C in Example I, 10 runs at temperatures ranging from about 730770 F. with a feed containing 57 p.p.m. nitrogen, 13 runs at temperatures ranging from 690-780 F. with a feed containing 76 p.p.m. nitrogen and 23 runs at a temperature ranging from 710800 F. with a feed containing 25 p.p.m. nitrogen. The data showing the volume of heavy naphtha are plotted in accompanying FIG. 2.

The data from Example I show, as is taught by the art, that as the nitrogen content of the feed is lowered, the cracking activity of the catalyst increases with an increased production of lighter materials boiling below 235 F. However, in the range of 25-75 p.p.m. nitrogen in the feed there is an unexpectedly sharp increase in the yield of heavy naphtha which permits the production of this valuable material at greatly extended catalyst life.

The data from Example 11 show that this phenomenon exists over a relatively broad temperature range and that the results are consistent.

By operating in the prescribed manner, it is now possible to obtain good yields of valuable heavy naphtha at nitrogen levels which the hydrocracking catalyst can withstand for prolonged periods of time without sutfering appreciable loss in activity.

I claim:

1. In a process for the production of hydrocarbon liquids boiling below about 400 F. by contacting a hydrocarbon liquid boiling above about 400 F. with a hydrocracking catalyst at elevated temperatures and pressures in the presence of hydrogen, the improved method of obtaining increased yields of 235400 F. naphtha which comprises contacting said liquid boiling above about 400 F. with a catalyst comprising a hydrogenating component selected from the group consisting of iron group metals, Group VI metals, their oxides and sulfides supported on a base comprising a crystalline zeolite having uniform pore openings of 615A and having an alkali metal content of less than 5% by weight at a temperature between 730 and 770 F. and introducing nitrogen into the reaction zone in an amount between 25 and p.p.m. by weight based on said hydrocarbon liquid charge.

2. The process of claim 1 in which the nitrogen content is maintained between 30 and 70 p.p.m.

3. The process of claim 1 in which the base comprises a mixture of said zeolite and an amorphous inorganic oxide.

4. The process of claim 1 in which the hydrogenating component comprises sulfided nickel and tungsten.

5. The process of claim 4 in which the zeolite has an alkali metal content less than 0.5% and has been prepared by a series of at least two ion-exchanges and calcinations in alternating sequence.

6 References Cited UNITED STATES PATENTS DELBERT E. GANTZ, Primary Examiner A. RIMENS, Assistant Examiner

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