US3761394A - Catalytic cracking of naphtha - Google Patents

Abstract

LOW OCTANE NAPHTHAS ARE CATALYTICALLY CRACKED WITH A ZEOLITIC CATALYTIC CRACKING CATALYST CONTAINING ZEOLITE X OR ZEOLITE Y YIELDING PRODUCTS BOILING BELOW THE INITIAL BOILING POINT OF THE NAPHTHA AND A NAPHTHA HAVING AN INCREASED OCTANE RATING.

Description

United States Patent O US. Cl. 208-120 3 Claims ABSTRACT OF THE DISCLOSURE Low octane naphthas are catalytically cracked with a zeolitic catalytic cracking catalyst containing zeolite X or zeolite Y yielding products boiling below the initial boiling point of the naphtha and a naphtha having an increased octane rating.

CROSS REFERENCE TO RELATED APPLICATIONS- This is related to application Ser. No. 77,479 which discloses the fluid catalytic cracking, in separate risers, of gas oil and low octane naphtha in combination with several recycle streams and application Ser. No. 77,480 which discloses the fluid catalytic cracking, in separate risers, of low octane naphtha and a recycle stream of full range naphtha or heavy naphtha.

BACKGROUND OF THE INVENTION This invention relates to the catalytic cracking of hydrocarbons. In particular, this invention relates to the fluid catalytic cracking of naphtha having a low octane rating and boiling in the range of 100 to 450 F.

Gasolines are blended from naphtha stocks whose octane ratings are often increased through catalytic reforming. Both virgin and cracked stocks may be upgraded by reforming operations. Catalytic reformers are usually operated to provide the desired octane improvement with the least conversion of gasoline to butanes and lighter materials.

The gasoline blending pool is maintained by a variety of operations--isobutane and butenes are charged to alkylation units and light olefins are polymerized to pro vide high octane blending components while the catalytic cracking of gas oil augments the supply of naphtha as well as providing additional feed for the alkylation and polymerization units. Although hydrocracking provides additional quantities of gasoline blending naphthas, the heavy naphtha from hydrocracking often has a relatively low octane number which may be increased by catalytic reforming.

Recently the introduction of zeolitic cracking catalysts has effected significant improvements in the catalytic cracking process. When employed for gas oil cracking in existing catalytic cracking units these highly active catalysts have produced increased throughput and improved product quality. Although these zeolite catalysts increase the supply of high quality naphtha, yields of the lighter hydrocarbons are substantially lower than from conventional catalytic cracking. In the future, therefore, the supply of isobutane, propylene and butenes for alkylate production and of these and other light hydrocarbons for polymerization and petrochemical manufacture will continually decline. A process which will upgrade naphtha streams for use in gasoline blending and supply additional quantities of C and lighter hydrocarbons is highly desirable.

Naphtha is a more difiicult stock to crack than gas oil and up to the present time limited success has been obtained in cracking naphtha catalytically. Traditional cracking catalyst, such as silica-alumina, exhibited relatively poor selectivity and activity when employed to crack naphtha resulting in the formation of relatively large amounts of gas and coke and producing small amounts of desirable olefins and aromatics. US. 3,284,341 discloses a process for the catalytic cracking of naphtha with a silica-alumina catalyst to produce substantial quantities of olefins and aromatics by maintaining the space velocity above about 4.5, the pressure between 0 and 20 p.s.i.g. and the reaction temperature between 1000 and 1200 F.

The new zeolite cracking catalysts are being employed extensively in gas oil cracking operations but their utility for the conversion of light naphtha has yet to be fully explored. US. 3,247,098 discloses that hydrogen mordenite, a crystalline aluminosilicate, is an extremely active catalyst for the conversion of light naphtha to lighter components together with improving the octane number of the resultant naphtha. The utility of the mordenite aluminosilicate as a cracking catalyst for naphtha was found to be surprising in view of the ineffectiveness of a magnesium faujasite catalyst to satisfactorily crack naphtha. The magnesium faujasite was known to be a highly effective gas oil cracking catalyst. The development of additional catalysts which may be usefully employed for the cracking of naphtha and which would be selective for the production of light olefins and parafiins, as well as naphthas having enhanced octane ratings is highly desirable.

SUMMARY OF THE INVENTION Broadly, our invention is directed to the catalytic cracking of hydrocarbons boiling in the gasoline range to increase the octane rating of the naphtha and to yield substantial quantities of lighter materials to serve as feed for petrochemical, polymer and alkylate manufacture. Zeolitic cracking catalysts containing type X or type Y aluminosilicates have been found to oifer particular utility in the catalytic cracking of such feed streams.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Broadly, we have found that the catalytic cracking of hydrocarbons boiling in the range of about to 450 F. with zeolitic cracking catalysts comprising type X or type Y aluminosilicates results in substantial improvement in the octane rating of the feedstream as well as the production of substantial quantities of materials boiling below the initial boiling point of the feed stream which find particular utility in petro-chemical, polymer and alkylate manufacture.

Our invention contemplates a process for the fluid catalytic cracking of naphtha which comprises:

(a) Contacting a naphtha boiling in the range of about 100 to 450 F. under cracking conditions with a catalytic cracking catalyst comprising a crystalline aluminosilicate selected from the group consisting of zeolite X and zeolite Y, and

(b) Recovering products boiling below the initial boiling point of the naphtha and a naphtha having an increased octane rating.

In accordance with this invention hydrocarbons boiling in the range of 100 to 450 F. comprisethe feedstock for this process. Many refinery streams having low economic value may be upgraded by employing the process of our invention. Useful feedstocks are usually highly paraffinic and include such light hydrocarbon fractions as low octane naphthas, Udex raffinate, low octane naphthas from thermal cracking or hydrocracking operations and straight run naphthas. As used therein, the term low octane naphtha refers to these useful feedstocks.

Because these feed streams are difiicult to crack it was unexpected that subjecting them to catalytic cracking conditions in the presence of type X or type Y zeolitic cracking catalysts would result in improving the qualities of these streams. Products from the process of our invention include naphthas with improved octane ratings. and hydrocarbons boiling below the initial boiling point of the feed which find particular utility as feedstreams for petrochemical, polymer gasoline, and alkylate manufacture.

The catalyst employed in the instant invention is a cracking catalyst of the zeolitic type as exemplified by those catalysts wherein the aluminosilicate is dispersed in a siliceous matrix. The catalysts which may be usefully employed in the process of our invention are those zeolitic cracking catalysts comprising aluminosilicates of type X or type Y, including both the naturally occuring and synthetic varieties. Because of their extremely high activity these zeolitic materials are composited with a material possessing a substantially lower level of catalytic activity, a siliceous matrix which may be of the synthetic, semisynthetic or natural type. These materials may include silica-alumina, silica-gel, silica-beryllia, silica-magnesia, silica-thoria, or silica-zirconia which have been successfully employed heretofore. In general, the composite crystalline zeolitic catalyst comprises about 1 to 50 wt. percent zeolite, about to 50 wt. percent alumina and the remainder silica. The crystalline aluminosilicate portion of the catalyst composition is a natural or synthetic, type X or type Y, alkali metal, crystalline aluminosilicate which has been treated to replace all or at least a substantial portion of the original alkali metal ions with other ions such as hydrogen and/or a metal or combination of metals such as barium, calcium, magnesium, manganese or rare earth metals, for example, cerium, lanthanum, neodymium, praseodymium, sarnarium and yttrium. The crystalline zeolites contemplated above may be represented by the formula where M represents hydrogen or a metal, 11 its valance, x has a value ranging from 2 to and y ranges from 0 to 10, in dehydrated zeolites, y will be substantially 0. In the instant invention the crystalline zeolites are either natural or synthetic zeolite X or zeolite Y. In highly preferred embodiments in is selected from the group consisting of hydrogen, calcium, magnesium and the rare earth metals.

The operating conditions contemplated herein to catalytically crack naphtha include: a reactor temperature of 700 to 1600 F., preferably 8501200 F., a reactor contact time between 0.5 seconds and minutes, preferably 1 second to 10 minutes and a catalyst to oil ratio between 0.5 and 30, preferably between 2 and 15. When employing a fluid catalytic cracking unit to practice the process or our invention and particularly one in which riser cracking is employed the following additional conditions are employed: a contact time in the riser of 0.5 to 30 seconds, preferably 5 to seconds and a contact time in the reactor bed of 0 to 15 minutes, preferably 0 to 10 minutes and regenerator temperature of 1000 to 1500 F., particularly 11001350 F.

Those skilled in the art will readily appreciate that any of the catalytic cracking equipment currently employed in the petroleum industry may be utilized to practice our invention including a fixed bed catalyst reactor, a moving bed unit or a fluid catalytic cracking unit of varying types including those employing riser cracking. If a fixed bed reactor is employed, it will be periodically removed from operation for regeneration of the catalyst. In moving bed or fluid catalyst systems the catalyst is continually regenerated.

The naphtha feed is introduced into the catalyst reactor under the operating conditions described above to effect the desired conversion of the feedstock. After passing from the reactor the efiluent is introduced into conventional recovery equipment which will include distillation equipment for the purpose of separating the vaporous effluent into products including naphtha and hydrocarbons lighter than naphtha whose high content of olefins and isobutane make them particularly useful as alkylate feedstocks and whose general characteristics make them particularly useful as petrochemical and polymer gasoline feeds.

The following exemplifies the practice of our invention and its advantage over conventional and prior art processes. All of the nine test runs were performed in a fluidized fixed bed bench model unit. In this pilot plant unit between 400 and 1000 cc. of naphtha were charged over 400 grams of catalyst using a processing time of 15 minutes. The reactor temperature was varied between 880 and 1025 F. A heavy straight run gasoline served as the charge stock for all test runs. Its properties are set forth in Table I.

TABLE I Feedstock analysis Description: Heavy straight run gasoline Gravity, API 54.5 Sulfur, X-ray, wt. percent 0.011 Bromine No. 1.5 Aniline point, F 122.5 Research octane, clear 50.6 Research octane, plus 3 cc. TEL 74.8 ASTM distillation, F:

IBP/5% 240/248 10/20% 250/254 30/40% 257/260 50/60% 267/273 70/80% 280/288 /95% 300/308 EP 331 FIA-MS, vol. percent:

Aromatics 13.6 Paraffins 48.2 Naphthenes 37.8

Octane rating with addition of 3 cc. tetraethyllead per gallon.

The test runs demonstrating the prior art employed the following catalysts:

(a) a conventional amorphous silica-alumina catalyst-- Davisons high alumina catalytic cracking catalyst;

(b) an aluminosilicate catalyst-Nortons Zeolon H, a synthetic hydrogen mordenite. In runs employing this catalyst, the hydrogen mordenite was mixed with the Davison high alumina catalyst in ratios of 50:50 and 11:89.

The silica-alumina catalyst was employed in Runs 1 and 6 while a mixture of hydrogen mordenite and silica alumina was employed in Runs 4 and 8.

The test runs demonstrating the advantages of our invention employed the following catalysts:

(a) Zeolite No. 1 was Aerocat Triple S-4. This fluid catalytic cracking catalyst contains approximately 3 wt. percent of type Y zeolite composited in a silica-alumina matrix and containing rare earth metal cations;

(b) Zeolite No. 2 was Davison XZ-25-This zeolitic cracking catalyst contains approximately 11 wt. percent of type X zeolite composited in a silica-alumina matrix and contains cations of rare earth metals;

(c) Zeolite No. 3 was a high zeolite content catalyst containing approximately 40 wt. percent of type X zeolite composited in a silica-alumina matrix and containing rare earth metal cations. Zeolite No. 1 was employed in Runs 2 and 7; Zeolite No. 2 in Runs 3 and 9 and Zeolite No. 3 in Run 5.

Runs 1 to 3 were conducted at a temperature of 1025 F. and a space velocity of 3.6. Run 1 demonstrates the prior art and Runs 2 and 3 the process of our invention.

'Runs 4 and 5 were conducted at a temperature of 880 F. and a space velocity of 7.2. Run 4 demonstrates the prior art and Run 5 the process of this invention. Runs 6 and 7 were conducted at approximately 895 F. and a space 'velocity of 3.6. Run 6 exemplifies the prior art; Run 7, the process of this invention. Runs 8 and 9 were conducted at approximately 910 F. and a space velocity of 3.6. Run 8 demonstrates the prior art and Run 9, the process of this invention.

Each of the catalysts was subjected to an activation step by heating at 1480" F. for 17 hours before a test run was made.

The operating conditions and the test results for all runs are summarized in Table II.

said aluminosilicate selected from the group consisting of zeolite X and zeolite Y and comprising cations selected from the group consisting of hydrogen, barium, calcium, magnesium, manganese, rare earth metals and mixtures thereof and (b) recovering products boiling below the initial boiling point of the low octane naphtha and a naphtha having an increased octane rating.

2. A process according to claim 1 wherein the cracking conditions comprise a temperature of 700-1600 F., a catalyst-to-oil ratio between 0.5 and and a content time of 0.5 second to 15 minutes.

3. A process according to claim 1 wherein the cracking conditions comprise a temperature of 850-1200 F., a

TABLE II Run number Mordenite H Mordenite H Silica- Zeolite zeolite plus silica- Zeolite Silica- Zeolite plus silica- Zeolite Cracking catalyst alumina o. 1 No. alumina 4 No. 3 alumina o. 1 alumina 6 No 2 Approximate zeolite content, wt. pe ent None 3 11 50 None 3 11 11 Reactor temperature, F 1, 025 1, 025 1 025 880 880 898 895 908 910 Space velocity, w./hr./w 3.6 3, 6 3. 6 7.2 7.2 3.6 3.6 3. 6 3.6 Yields, wt. percent:

Calm 1.8 0.6 0.9 1.2 1.4 0.9 0.6 0.4 0.4 Propylene 4.7 3.7 4.0 1.1 0.9 1.0 1.6 2.2 1.7 Butylene--- 1.5 2.2 1.6 0.6 0.8 0.9 1.1 1.2 1.0 Isobutane 2.8 4.7 8.6 3.4 8. 2 2.2 5.3 3.1 5.5 C4 and lighter con on, w percent 14. 9 19.1 23.8 8.4 19.8 6.0 12.4 7.0 14.9 Conversion, l vol. percent 39.2 46.3 49.8 30. 7 53.2 23.3 39. 2 29.0 43.2 Selectivity 2 0.188 0.246 0.361 0.404 0.413 0,365 0.426 0.328 0.369 100/430 F. naptha octane, RON 3 79.6 84.4 87. 5 79.3 93.9 8.0 83.3 79.2 85.5 FIA-MS, vol. percent:

100/240 F., naphtha:

0lefins 9.1 7.3 6.8 4.6 1.8 3.5 3.6 4.7 1.7 Aromatics 14.7 18.8 21.9 12.3 22.5 11.8 13.0 11.4 13.2 Paraflins 45.9 39.2 48.8 46.4 56.0 52.6 55.4 49.0 57.2 Naphthenes 30.3 24.7 22.5 36.7 19.7 32.1 28.0 34.9 27.9 210/430 F., naphtha:

Olefin 1.4 1.1 1.2 0.8 0.4 0.5 0.5 0.5 0.9 Aromatics 23.0 31. 7 37.8 17.1 57.4 17. 8 27.4 17.7 31.9 Paralfins.- 44. 5 42. 8 39. 1 43.5 29. 9 45. 6 46. 1 45.5 44.2 Naphthenes 31.1 24-4 21.9 38.6 12.3 36.1 26.0 36.3 22.5

1 Conversion=(100 vol. percent 240l430 F., naphtha yiel 3 Se1ectivity=1sobutane (wt. percentflbutanes and lighter (wt. percent).

Research octane number, 3 cc. tetraethyllead per gallon.

4 Weight ratio of 50:50.

5 Weight ratio of 11:89.

The results of these test runs show the advantages of the process of our invention. In all test runs where a zeolitic catalyst containing type X or type Y aluminosilicate was employed, the yield of C and lighter hydrocarbons was higher as was the overall conversion of materials boiling below 240 F. Further, the research octane number of the naphtha was significantly higher than that obtained from the prior art runs. In addition, those runs demonstrating the process of our invention showed a high selectivity for producing isobutane. Also, the naphthas produced from the test runs employing our invention contained more aromatics and less naphthenes than the product naphthas from the runs using conventional or mordenite catalysts. Also, the data generally indicate lower olefin contents for the runs of our invention. Finally, the benefits of our invention were obtained over a wide temperature range.

We claim:

1. A process for catalytic cracking of naphtha which comprises:

(a) contacting a low octane naphtha boiling in the range of about 100 to 450 F. under'cracking conditions with a catalytic cracking catalyst comprising a crystalline aluminosilicate composited in a siliceous matrix,

catalyst-to-oil ratio between 2 and 15 and a contact time of 1 second to 10 minutes.

References Cited UNITED STATES PATENTS 3,617,496 11/1971 Bryson 208- 3,448,037 6/ 1969 Bunn, Jr. et a1 208-74 X 3,649,521 3/1972 Martin 208-120 3,652,449 3/ 1972 Young et al. 208-111 3,647,682 3/1972 Rabo et a1 208-120 3,649,522 3/ 1972 Martin 208-120 3,644,200 2/1972 Young 208-120 3,663,430 5/1972 Morris 208-120 3,692,667 9/1972 McKinney et a1. 208-120 3,700,585 10/1972 Chen et a1 208-111 3,639,228 2/1972 Carr et al. 208-120 DELBERT E. GANTZ, Primary Examiner J. M. NELSON, Assistant Examiner Us. 01. X.R. 252-455