US2758958A - Hydrocarbon conversion process - Google Patents

Description

United States Patent fiice I HYDROCARBON CONVERSION PRGCESS Victor J. Auhorn, Oakmont, Meredith M. Stewart, Penn Township, Allegheny County, and Wallace E. Morrow, Allison Park, Pa., assignors to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware No Drawing. Application February 25, 1952, Serial No. 273,335

'2 Claims. (Cl. 19650) This invention relates to catalytic processes for the conversion of normally liquid hydrocarbons, especially hydrocarbons boiling in the gasoline or naphtha boiling range, in the presence of hydrogen.

The more important processes that have been practiced or proposed for the catalytic conversion of hydrocarbons in the presence of hydrogen involve operating under such conditions, including pressures of about 100 to 1500 pounds per square inch and temperatures of at least 700 F., that a carbonaceous material or coke is deposited on the catalyst, which deposit is burned oil the catalyst in an oxidative regeneration period of the process. Such processes are advantageous as compared with extremely high pressure processes in which no deposit is formed in the catalyst in that equipment and operating costs (e. g. cost of compressing gases and the like) are lower and the products are improved products. Processes of this type include operations wherein a rela tively heavy liquid hydrocarbon or mixture of hydrocarbons such as a gas oil, Whole crude, reduced crude, coke still distillate, and the like, is contacted with a catalyst in the presence of hydrogen under these elevated temperature conditions, preferably temperatures of about 800 to 1100" F. In this type of process the hydrocarbons are subjected to hydrocracking which involves scission of carbon to carbon bonds, dehydrogenation, hydrogenation and related changes in structure of the hydrocarbons. Also, some desulfurization occurs in every case and excellent desulfurization takes place with the use of selected catalysts.

Another type of conversion process carried out in the presence of hydrogen is employed for the treatment of hydrocarbons boiling in the gasoline or naphtha boiling range and may be referred to as catalytic reforming in the presence of hydrogen or hydroreforming. In this process the objective is primarily to accomplish isomerization and aromatization of the hydrocarbons making up the charge and consequent increase in the octane number of the product. In this type of operation there is ordinarily very little difference between the average molecular weight of the charge and that of the product although some cracking may occur, particularly under high conversion conditions. The temperature employed in catalytic reforming in the presence of hydrogen is in excess of 700 F., a temperature of about 800 to 1100" F. generally being preferred, and the pressure should be about 100 to 1000 pounds per square inch. A version of this process is generally referred to as hydroisomerization. The charge to a hydroisomerization process is largely parafiinic and may consist of a single normal parafiin such as normal pentane or normal hexane. The principal result here is to convert the normal paraffins to isoparaflins.

As stated previously, processes of these types are carried out at pressures which may vary from about to about 1500 pounds per square inch. The hydrogen pressure maintained in the reaction Zone has an effect upon the type of conversion taking place, other conditions being maintained constant. The maintenance of high hydrogen pressures Within this range is generally effective to permit conversion with longer on-stream periods. When lower hydrogen pressures within this range are used, the conversion involves a more rapid formation of a carbonaceous deposit on the catalyst. Such processes, therefore, comprise a cyclic operation in which frequent regeneration is necessary.

The catalysts that have been employed for the conversion of hydrocarbons in the presence of hydrogen comprise a recognized class. These catalysts are referred to as hydrogenation catalysts and include one or more of the metals of Groups V, VI, and VIII of the Periodic Table and the oxides of these metals. The more important of these metals are chromium, molybdenum, tungsten, cobalt and nickel. While these metals or metal oxides may be used alone, for example in the form of gels, it is the usual practice to employ catalysts which comprise one or more of these metals or metal oxides deposited on a suitable support such as activated alumina, kieselguhr, silica-alumina composites containing a major proportion of silica, activated clays, and the like. A particularly valuable support is an activated alumina containing a relatively small amount of silica, for example about 5 per cent by Weight, which serves to improve the surface characteristics of the support.

We have discovered in accordance with the invention that improved results can be obtained by carrying out a process for the conversion of hydrocarbons as above described in the presence of a catalyst of the above class in which at least a part of the metal is in the form of the nitride. The nitrides of these metals can be prepared by separately contacting the catalyst with a nitn'ding agent, preferably ammonia, at an elevated temperature. While it is not necessary to convert all of the metal to the nitride in order to achieve the advantages of the invention, the nitriding operation should be carried out in such manner as to convert at least 25 per cent, and preferably at least 50 per cent, by Weight of the metal in the catalyst to the nitride form. The metal nitrides are relatively stable and will continue to be effective during a normal on-stream period. It is preferred in most cases to nitride the catalyst after oxidative regeneration to insure that an important part of the metal in the catalyst is in the nitride form at the beginning of the reaction period.

The efiect of the nitriding treatment is in general'to increase the activity of the catalyst, although the specific result of this increase in activity will vary depending upon the type of conversion operation in which the catalyst is used, the particular catalyst employed and otherfactors. For example, the hydrocracking activity of-a Patented Aug. 14, 1956..

catalyst is improved by nitriding where the charge stock is a heavy hydrocarbon mixture. In hydroreforming; a higher octane product is obtained with the use of a nitrided catalyst than is obtained with the use of the untreated catalyst at the same conditions. The efiect of the nitriding treatment is especially noticeable when conditions adapted to result in high conversion of the charge are maintained.

In accordance with a preferred embodiment of the invention, a naphtha fraction of petroleum is subjected .1

to hydroreforming in the ,presence of a nitrided hydrogenation catalyst. While any of the hydrogenation catalysts are more or less satisfactory for this process, a preferred catalyst is one consisting. of molybdena deposited on an activated alumina. support. and preferably sucha support containing about 5 per cent: by weight of silica. Ordinarily, the molybdena, consider to beMoOs, constitutes about 8 to 12 per cent by weight of the. finished catalyst. Depending upon the specific results that are desired to be obtained, such as the length of the process period,-the pressure employed may be'from about 100 to about 1000 pounds per square inch; Within this pressure range the length of the on-stream period can be varied :by varying the pressure and the hydrogen recycle rates. When using the catalyst referred to above to obtain a high octane product, the conversion ispreferabl'y carried out at a temperature .within the range of about 850 to about 950 F. These conditions result in anet' production of hydrogen in the reaction zone. The hydrogen introduced into the reaction zone and'fbrmed' in that zone is separated from the product and at least a part is recycled to the reaction zone. The charge. to the reaction zone should comprise about 1,000ito 10,000 standard cubic feet (s. 'c.. f.) of hydrogen per barrel of naphtha charged and preferably about 1,000 to about 5,000 s. c. f.

The operating cycle for this process preferably comprises (l) reducing the catalyst with hydrogen, (2') nitridingv the catalyst, (3) the reaction period, (4) purging the catalyst, and (5) regenerating the catalyst by burnilng d the carbonaceous deposit formed in the reaction period. The step of: reducing the catalyst with hydrogen canbe. omitted; however, in such case more nitriding agent is required to convert the same amount. of the catalytic metal to the nitride. When reduction is pract ti'ced the catalyst is reduced with hydrogen at an elevated temperature, for example. at a temperature of the order of 700" to 1100" F. and. preferably about 900. to 1000 FL, a-t reaction pressure or ata lower pressure.

It, is preferred to reduce at atmospheric pressure- This reducing, operation is continued for a time sufficie'nt' to. convert, at least a substantial proportion of the MoO to M002,v which is usually about 1 to hoursin. the preferred temperature range. The reduced catalyst is then u'itridied,v preferably by contacting, it with ammonia at an elevated temperature... The nitriding, temperature. should be within the range of about 700" to 1 1010 F. andprefera'bl'y about 900; to, about 1000 F1 The nitrid-ingoporation is. continued until at least per cent, and prefcrabby at. least 50 per cent by. weight off the molybdenum is, present in the form of. the. nitride, which ordinarily requires about 1 to. 5 hours under the preferred conditions. Lower temperatures. can. be employed. in nitriding treatment but are-not. preferred because a. longer treating time is. required. Following the nitridi'ng, treat.- ment, the. naphtha charge and. hydrogen are contacted with the catalyst. under. the reaction conditions outlined above until the qualityof the product falls below a. selected level. The catalyst is then purged to remove-oceluded. hydrocarbons andhydrogen and: is subjectedrto oxidative regeneration. The regeneration is preferably. accomplished by contacting the catalyst. with air or an.- other 'oxygemoontaininggas; The. regenerated. catalyst is; themin condition forthe reducing, treatment-described above.

The hydroreforming process as described can be carried out with thecatalyst deposited in a stationary-fixed bed, in which case the catalyst is usually employed in the form of granules or pellets. When using the catalyst in a fixed bed, the above cycle of operations is carried out on the catalyst in the reaction zone. Inasmuch as the reaction is endothermic, provisions are made for supplying heat to the catalyst bed during the reaction period.

This process may also be carried out utilizing the catalyst in fluidized state. In this operation a finely divided catalyst is employed. While the above cycle of operations may in this case also be carried out on the catalyst while the catalyst is in the reaction zone, it is generally preferred to provide a separate regenerator to which catalyst from the reactor may be conveyed either periodically or continuously. The regeneration may be accomplished at about the pressure in the reactor or-at about atmospheric pressure. When the regeneration is carried out in a vessel separate from the reactor, the-steps ducing the catalyst withhydrogen and contacting; the catalyst with a nitriding agent should preferably baconducted in a vessel into which the catalyst fromthe'regenerator is introduced.

In order. that the invention may be understoodmore fully, the following specific example" will be described. This example is concerned with the hydroreforming of a West Texas straight run naphtha having the following characteristics Inspection data: 481-6 The. catalyst employed consisted of about 11 weight per cent molybdenum oxides calculated as M003 and a finely divided activated alumina base which contained about 5. per cent silica. The cycle of operations involved in hydroreforming was carried out on this catalystdisposed in a fixed fluidized bed. under the conditions set out thefollowing Table I. The catalyst, initially in oxidized form, was: first reduced by contacting it with hydrogen atmospheric pressure and a temperature-of about-950" F. Inthisv operation a hydrogen gas space velocity (volumes of hydrogen. at standard temperature and pressure/volume of catalyst/hour) of 620 was maintained for-five hours.- The catalyst was then nitrided by contacting it' ammonia gas at a space velocity of approximately 500 (volumes. of ammonia gas at standard temperature and pressure/volume of catalyst/hour), at a temperature of about950 F. and a pressure of 5" pounds per-squareihcl'r gauge for a: period of three hours. Another batch oi? the; same molybdena-alumina catalyst waslalso: empteyer in. the hydroreforming of this naphtha. This eatenwas treated as described above except thatthe nit-riding treat meet: was; omitted. In carrying out hydroreforniing of the naphtha using these catalysts, the: tenrperawre in the first part. of each". run was maintained" at: about 875 F5, the product. obtained in: operation at: this: temperature for. the; throughput interval indicated in Table-I was solslected andthereafter the. temperature was raised? toe 900" and the product, from; the. indicated. throughput intervalat. this higher temperature was separately 601* lected. The results; obtained are: apparent: from: the. data given in the following Table I.

Table I Unnitrided catalyst N itrided catalyst run run A B O D Reaction conditions:

Temperature, F 875 920 875 897 Pressure, p s i g 500 500 500 500 Hz concen f./B 4, 805 5, 000 4, 910 5, 050 Charge rate, wt./ 1.0 0. 9 0. 99 0. 96 Throughput interval, wt.

charge/wt. catalyst 12.0-24.0 40. 646.0 19. 4-29. 3 34. 3-45. 8

Recovery, volume percent of charge:

04's 8. 4 10. 3 12. 4 11. 6 400 F. E. P. gasoline 78. 3 74. 8 74. 4 68. l Residue 3.0 6. 8 2. 6 2. 7

Total 89. 7 91. 9 89. 4 4

400 F. E. P. gasoline AV'P-Ca free) 88. 8 81. 5 81. 1 .0 Excess C4 2. 1 3. 6 5. 7 4. 7

Total 86. 7 85. 1 86. 8 79. 7

Inspection data:

Total product (as produced):

Gravity, API 52. 2 52. 9 51. 1 50. 7 Distillation, F.:

I. B. P 100 92 88 95 10%.. 164 173 144 157 50%- 288 285 274 266 90% 361 361 363 363 E. P 422 396 431 426 Total aromatics 35. 7 33. 4 43. 4 48.0 Aniline point, F 91. 8 90.0 71. 2 60.6 Bromine number 2. 0 1. 2 2. 5 2. 4 Sulfur wt. percent- 0. 010 0. 009 0. 015 0. 010 Research octane numbers:

Clear (unc0rr.) 75. 7 74. 4 85. 6 89. 0 +3 cc. TEL (uncorr.) 90.0 89. 1 96. 5 98.0 Clear (1011). AVE- 0 ee) 77. 3 76. 2 86.2 89.4 +3 cc. TEL (10 AVP Cs free) 91. 5 90. 8 96. 2 98. 5

The results given in this table show that the nitriding of the catalyst substantially increased its activity in the hydroreforming process. Thus, considering the 10 lb. vapor pressure-C3 free gasoline containing 3 ccs. of tetraethyl lead per gallon produced in Period A, it will be seen that the octane number of the gasoline was 91.5 whereas the octane number of the gasoline produced in comparable Period C, using the nitrided catalyst, was 96.2. Similarly, in the operations carried out at about 900 F. and somewhat above, the octane number of the gasoline in the case of the untreated catalyst was 90.8, whereas the octane number of the gasoline obtained when using the nitrided catalyst was 98.5, despite the fact that the temperature was higher in the period using the untreated catalyst.

In another set of runs, a West Texas naphtha was subjected to hydroreforming in the presence of a molybdenaalumina catalyst of the type employed in the runs described in Table I. This catalyst had been regenerated and was in the fully oxidized state. One batch of it was nitrided without a prior reducing treatment; i. e., the nitriding was carried out on a catalyst in which the molybdenum was present at least largely in the form of M003. The nitriding treatment consisted of passing NHs in contact with the catalyst for three hours at a temperature of about 1050 F. and a pressure of about 50 pounds per square inch gauge. Another batch of the same regenerated catalyst was reduced by contacting it with hydrogen for three hours at a temperature of about 1050 F. and a pressure of about 50 pounds per square inch gauge. The naphtha charge was contacted in separate runs with these two catalysts under conditions similar to those described previously except that the temperature was about 900 F., the pressure about 800 pounds per square inch guage, and the charge rate (weight of charge per weight of catalyst per hour) was 2.0. It is noted that the charge Table II Unnitrided catalyst Nitrided catalyst run run E F G H Reaction conditions:

Temperature, F. 896 901 902 902 Pressure, p. s. i. g. 800 800 800 800 H: concentration,

f. B 5,200 5,050 6,230 5, 176 Charge rate, wt./wt./hr 2.0 2.0 2. 0 2. 0 Throughput interval, wt.

charge/Wt. catalyst 9. 9-19. 8 49. 7-54. 9 10. 0-20. 0 49.9-59.9

Recovery, volume percent of charge:

Ois 3. 3 4. 2 5. 7 6. 2 400 F. E. P. gasoline Total 99.1 95. 4 90. 6 96. 9

0 F. E. P. gasoline (10 AVP- ee) 106. 8 103. 9 96.3 104.0

Inspection data:

Total product (as pro- 't API ravl y, 52. 5 52. 6 54. 5 54. 5 Distillation, F.:

I. B. P 117 116 106 99 232 205 182 186 301 298 291 295 342 340 337 338 382 381 380 379 cent 22. 5 29. 0 25. 8 23. 7 Aniline point, F 112. 2 103. 7 106. 0 111. 5 Bromine number- 1. 9 1. 3 1. 6 1. 0 Sulfur, wt. percent.-. 0. 013 0. 023 0. 008 0.010 Research octane numbegs]:

ear uncorr. 58.2 64.7 67.2 .4 +3 cc.)TEL (un- 63 corr. 79. 0 81. 7 85. 2 2. 01 ar (1o)1b. AVP 8 4 3 es 62.0 68. 2 70. 2 6. +3 cc. TEL (10 6 7 lb. AVP Catree) 82. 3 84. 9 87. 5 85. 3

It will be noted by comparing the results of Period E carried out on the reduced and unnitrided catalyst with the results of Period G in which the nitrided catalyst was employed, that the octane numbers of the product obtained in Period E are substantially lower than those obtained in Period G. It will also be noted that with longer operation the results obtained on the two catalysts tend to become the same. This indicates that the activity of the nitrided catalyst is especially good at low throughputs. Accordingly, if these data are considered in connection with a continuous hydroreforming operation where the oil to catalyst ratios might vary from say 5:1 to 1:1 whereas the oil/ catalyst ratio for a throughput of 10 is 10: 1, the data indicate that the efiect of the nitriding treatment should be even more pronounced in such an operation than is indicated by the data given in the table.

It will be understood that the foregoing examples are merely illustrative of the invention and that comparable results can be obtained by using nitrided hydrogenation catalysts in other processes for the conversion of hydrocarbons in the presence of hydrogen. As will be seen from the result obtained in the above examples, it is not necessary to subject the catalyst to a hydrogen reducing treatment prior to nitriding as it appears only necessary in order to obtain the advantages of the invention to convert a substantial proportion of the metal of the catalyst to the nitrided form. Because ammonia is readily available and easy to use, it is the preferred nitriding agent. However, a wide variety of non-oxidizing nitrogencontaining compounds which are in vapor thenitriding agent is itself not a: reducing agent, suchas iszammoniagt it is: necessary to accomplish some reduction of the catalyst prior to n'itn'ding. The nitriding treatment goes smoothly with the use of ammonia, and a promoter is not necessary, but promoters can be employed if desired. Thus, for example, the catalyst may bevlightly impregnated with a lithium compound befiore' beginning: the nitriding treatmem. In view ofthe fact that; the catalytic-metal is converted 'to the metal nitride in the present process whether the-metal of the catalyst is in the metalform orthe oxide form prior to the nitriding treatment (thus either molybdenummetat or mo1ybdenum oxide is believed: to be converted to Mio'zN), where a catalyst: comprising, a metal is referred, to inthe claims it. will. be understood. that the oxides as Well as the free metals are included;

With respect to the hydrogen concentration that, should be: employed in the. present. process, it will be understood that. the optimum comzen'trationv in each case will vary depending-upon the particular operation being carried out, but there must be suii cient hydrogen to make the operation what might be termed a hydroconversion procass. Thus, the hydrogen concentration should be about 1,000 to; 30,000 standard cubic feet of hydrogen per' barrel (:42 U. shgallonsyof chargehydrocarbonsr Obviously many." modifications and variations of the invention, as hereinabove set forth may. be' made without. departing from, the spiritand .scope thereof and therefore: only such limitations;- should be imposed as are indicated inthe appended claims;

We claim:

1. A process for hydroreforming naphtha which comprises contacting said naphtha under hydroreforming conditions including temperature of about 850 to 950 F., pressure betweenv about 100% and 1000 pounds per square inch! and; hydrogen concentration of about 1000 to 10,000 standard cubic feet of hydrogen per banteltof.

said hydrocarbons with a molybdenum catalyst: supportedonactivated alumina in which atleast 25 percent by weight of'the molybdenum is in the form of the nitride,

said catalysthaving been prenitrided by separately contac'ting it with at vaporized nitriding, agent at a temperature above 700 F. until at least, 25 percent by Weight of the molybdenum is in; the form of the nitride.

2. A process for hydroreforming naphtha which comprises contacting said naphtha under hydroreforming conditions including temperature of about 800 to 110'0" Ft, pressure of about 100 to 1000 pounds per square inch and hydrogen conc'entration' of about 1000 to 10,000 standard cubic feetgof hydrogen per barrel ofrsaid hydrocarbons with a prenitrided molybdenum catalyst supported on activated: alumina, said catalyst having been prenitrided by separately contacting it with ammonia at temperature of about 900 to about- 1000 F. for: about one to five hours.

References; Cited: in the file of this patent UNITED STATES PATENTS 1 ,890,434 Kt'a uch et al. Dec. 6, 1932 2 ,623,860 Haensel Dec. 30; 1952 2,642,385 Berger eta'l 111116 16, 1953 FOREIGN PATENTS 424,531 Great Britain Feb; 22, 1935

Claims (1)

1. 2. A PROCESS FOR HYDROREFORMING NAPHTHA WHICH COMPRISES CONTACTING SAID NAPHATHA UNDER HYDROREFORMING CONDITIONS INCLUDING TEMPERATURE OF ABOUT 800* TO 1100* F., PRESSURE OF ABOUT 100 TO 1000 POUNDS PER SQUARE INCH AND HYDROGEN CONCENTRATION OF ABOUT 1000 TO 10,000 STANDARD CUBIC FEET OF HYDROGEN PER BARREL OF SAID HYDROCARBONS WITH A PRENITRIDED MOLYBDENUM CATALYST SUPPORTED ON ACTIVATED ALUMINA, SAID CATALYST HAVING BEEN PRENITRIDED BY SEPARATELY CONTACTING IT WITH AMMONIA AT TEMPERATURE OF ABOUT 900* TO ABOUT 1000* F. FOR ABOUT ONE TO FIVE HOURS.