US3658693A

US3658693A - Catalytic cracking method

Info

Publication number: US3658693A
Application number: US884174A
Authority: US
Inventors: George R Hettick; Shelby D Lawson
Original assignee: Phillips Petroleum Co
Current assignee: Phillips Petroleum Co
Priority date: 1969-12-11
Filing date: 1969-12-11
Publication date: 1972-04-25
Anticipated expiration: 1989-04-25

Abstract

A process for increased production of naphtha from crude stocks. The crude is fractionated to recover straight run naphtha, and bottom product is cracked to produce largely naphtha and lighter, with only minor by-products production of carbon black oil and coke.

Description

United States Patent [1 1 3,658,693

Hettick et al. [451 Apr. 25, 1972 [54] CATALYTIC CRACKING METHOD 3,053,752 9/1962 Swanson ..208/l64 3,115,455 12/1963 Ashwill ..208/93 [72] Inventors: George R. Hettick; Shelby D. Lawson,

both of Bamesvme, Okla 3,303,123 2/1967 Payton et a]. ..208/164 [73] Assignee: Phillips Petroleum Company Primary Examiner-flerbefl Levine At: Y and 22 Filed: Dec. 11, 1969 21 Appl. No.: 884,174 ABSTRACT A process for increased production of naphtha from crude 52 U.S.Cl ..20s/93,20s 92 stocks- The crude is fractionated to recover Straight run 5 1m, I Clog 11 13 naphtha, and bottom product is cracked to produce largely [58] Field of Search ..208/92, 93 naphtha and g h y minor y-pr c s prod c ion of carbon black oil and coke. f t d [56] Re e 7 Claims, 2 Drawing Figures UNITED STATES PATENTS 2,958,645 11/1960 Kimberlin et a1. ..208/93 FUEL 22 23 a H2 UNIT, 5 I2 .1 1 +1 a. 20 T CE I o (I FUEL ,9 FUEL I GAS \H 2| 1 Q g 1: g o m g a: o: w ,9 -9 -|7 L 2 2 W 1 1 1 LEE, MIXED c ac 13 CARBON 5 BLACK on. 0 l5 AIR 8 HEAVY CYCLE OI L DEBUTANIZER ENAPHTHA CATALYTIC CRACKING METHOD This invention pertains to a method of converting crude oil to stocks useful for petrochemical production. In another aspect, it has relation to a method of converting a crude stock into naphtha and lighter with a minimum of by-product and coke formation.

BACKGROUND OF THE INVENTION Conventional refinery operation charges the incoming crude to a crude still. The primary function of the crude still is to cut the crude, according to boiling range, into about four distinct cuts for further processing. The first cut is a straight run naphtha from the initial boiling point of the crude up to about 400 F. This fraction is usually further divided to yield a product of from 200 to 400 F. for feed to a catalytic reformer, and the balance from the initial boiling point up to about 200 F. is stabilized and sent directly to motor fuel blending. The next heaviest fraction from the crude, of about 400 to 650 F., is termed the straight run distillate and is usually further processed to yield kerosene, No. l distillate, No. 2 distillate, and the straight run diesel fuels. The third fraction, of from about 650 to about 800 F., is a gas oil fraction with little commercial value of itself, usually serving as part of the feedstock to a cracking unit. The bottoms from the crude still operation is the cut from 800 F. to end point and is processed in various manners, such as in a vacuum still where a gas oil is produced as a distillate to supplement the feedstock to a cracking unit. Material boiling above l,l F. is processed to asphalt, fuel oil, coker feed, and similar.

However, the methods as outlined above are no longer fully satisfactory. There is an increasing demand for petrochemicals and the myriad of products made from petrochemicals, such as polymers and fibers, Thus there is a continuing search for methods to get more and more naphtha and equivalent range products as well as lighter components from crude stocks, and at the same time waste less and less of the crude in formation of other and less desirable components including coke.

A need exists for an effective process to maximize the yield of most needed and valuable materials, and minimize the production of less desired and of waste products.

BRIEF SUMMARY OF THE INVENTION We have discovered and developed an effective direct process that converts crude oil into a yield of substantially naphtha and lighter components, and with only two other endproducts, these latter in quite minor amounts. More particularly, our process converts crude oil into a high yield of naphtha and lighter, less than about 5 percent of a still valuable oil for carbon black production, and less than about I percent actual waste as coke.

Our process is unique from several aspects. Fluid catalytic cracker naphtha as a chemical feedstock itself is unique. The

usual effluent from fluid catalytic cracking is insufficient in aromatic stocks for petrochemical processing, contains olefins in proportions making it difficult to handle for petrochemical requirements, frequently contains catalyst particles, and normally requires catalytic reforming as a succeeding step in order to provide an aromatic content for petrochemical purposes. In our process we are utilizing a fluid catalytic cracking effluent ultimately as a petrochemical feedstock. Further, the feedstock to our fluid catalytic cracking unit is the full range crude bottom, i.e., all material not boiling up to about 350 to 375 F. Additionally, no straight run distillates are produced.

The fluid catalytic cracking unit produces a small proportion of carbon black feedstock which itself is a valuable material, a very minor amount of coke on the catalyst,'and otherwise produces all valuable products. The only light products from the catalytic cracking operation are materials boiling below about 375 F. including naphtha and lighter ends for further processing. Heavier materials, other than the small amounts of high quality carbon black feedstock, are recycled to the catalytic cracker.

BRIEF DESCRIPTION OF DRAWINGS The process of our invention can be visualized most readily by referring to the attached drawings.

FIG. 1 represents the heart of the process of out invention.

FIGS. 2, 3, and 4 show additional versatility in the handling of lighter ends produced by the process'of our invention.

Briefly, FIG. l-shows that the crude oil is first fractionated to produce primarily naphtha or gasoline and with all heavier material yielded as a bottoms product. The heavier material is sent to a reactor, a fluid catalytic cracking unit, which effectively cracks the feedstock to a large proportion of naphtha. The cracked stream is fractionated to recover this additional naphtha together with lighter ends, plus a stream of carbon black feedstock, and some recycle oil which latter is returned to the reactor for further cracking. The only other product is a minor amount of coke which accumulates on the catalyst and burns off as flue gas during catalyst regeneration.

FIGS. 2, 3, and 4 show a variety of ways of handling the mixed C and C components, the lighter components separated from the naphtha produced .as a result of the catalytic cracking process. The C and C components can be utilized in alkylation, or appropriate specific components separated for liquified petroleum gas, and the like.

DETAILED DESCRIPTION OF THE INVENTION mulator 4. The lighter more volatile components 5 from accumulator 4are withdrawn for various plant fueling requirements, leaving the remainder 6 from accumulator 4 as a straight run naphtha, or, as we term the cut hereafter, a first light fraction.

V The bottoms of the crude feed 1 to fractionator 2, i.e., all of the material not boiling below about 350 to 375 F., is joined by recycle oil 14, hereinafter described, to form combined feed 8 to a fluid catalytic cracker 9. The incoming feedstock 8 can be at a temperature in the range of from about to 750 F., more usually 400 to 600 F. In the fluid catalytic cracker 9, the feed 8 is catalytically cracked, typically at a temperature of from about 850 F. to 1,000 F using from about 25 to 75 pounds of water or steam per barrel of feed, and a WHSV of 1.2 to 1.5 weight hourly space velocity based on total feed, so that a substantial proportion of the feed 8 is converted to components of reduced molecular size.

In the fluid catalytic cracking operation, a finely divided particulate catalyst is used, such as activated clay, synthetic gels such as silica-alumina, silica-zirconia, alumina-boria, silica-magnesia, and particularly the natural and synthetic zeolites, more particularly the synthetic materials known as molecular sieves. The finely divided particulate catalyst is heated to a high temperature in a regeneration zone, and brought into admixture with the hydrocarbon feedstock. The admixture is taken to a reaction zone where the cracking takes place and products are separated to a fractionator and spent catalyst returns to the regeneration zone.

In the fluid catalytic cracker 9, the particulate catalyst accumulates coke in the reaction zone tending to reduce the activity of the catalyst. The catalyst is regenerated periodically by exposure to a high temperature typically in the range of from about l,050 to l,200 F, in the presence of an oxygen-contaming gas.

Conduits

15 and 16 conduct the coke-bearing catalyst to regenerator 17. The air supply line 18 joins spent catalyst transfer line 15. The air supply acts both as the fluidizing gas in the regenerator 17 as well as the source of oxygen for coke burnoff. The major portion of the coke is burned off, and exhausted as a flue gas l8 at about 7 psi. After burnoff of the coke in reactor 17, the now regeneratedcatalyst is taken by line 19 to join the fluid catalytic cracker feed 8. While for clarity FIG. 1 shows a separate reactor 9 and regenerator 17, these units are more usually combined in a single unit, such as a reactor section above a regenerator section.

The effluent stream 10 at about 10 psi from the reactor 9 is then taken to a second fractionator'll for separation by thermal distillation. The second fractionator 11 produces an overhead stream 12 at about 400 F. and psi which is the naphtha fraction together with such lighter components as have been produced by the cracking; a recycle oil 14 which becomes part of feed 8 as hereinbefore described to reactor 9; and a bottoms 13 boiling at over about 700 F. consisting of carbon black oil.

The overhead 12 from fractionator 11 is cooled by means of indirect heat exchange (not shown) to form a second light naphtha fraction 21 in accumulator 20 under about 1 psi and 1 F. The effluent 21 from accumulator 20 can be combined with the first light naphtha fraction 6 to form a combined --naphtha stream for use in a varietyof ways as hereinbefore discussed.

More preferably, the second light fraction 21 is first separately treated to remove lighter components, C, to C saturates and unsaturates. Volatile overhead 22 from accumulator 20 preferably is compressed in compressor 23 and returned by conduit 24 to be combined with accumulator effluent stream 21. The light overhead 22, however, optionally can be used for general plant fuel usages.

Hence, the second light fraction 21, optionally combined with light overhead 24, is taken at about 100 F. from accumulator 20 to a deethanizing absorber 25 for removal of very light materials. Absorber 25 receives a portion of recirculated purified naphtha 33 as absorbent at about 90 F. Lighter materials H C,, C,, and C are removed at about 95 F. and 150 psi from absorber 25 as an overhead 26 and can be utilized as fuel 27 for various plant heating or fuel requirements, or optionally can be utilized in a hydrogen production unit 28 as shown by ghost lines in FIG. 1.

From absorber 25 the bottom fraction 29 at about 200 F. is taken to debutanizer 30 where mixed C, and C, components are removed at about 120 F and 150 psi as overhead 31 to various end-uses as shown by FIGS. 2, 3, and 4. The bottoms stream 32 from debutanizer 30 is the purified second light naphtha fraction. A portion of this is fed as stream 33 back to the deethanizing absorber 25 hereinbefore described, and the balance 34 of the stream 32 then is combined with the first light naphtha stream 6 as a total naphtha production stream. Optionally, if desired, a portion of the first light naphtha fraction 6 can be utilized as all or a part of the necessary naphtha absorbent 33 to absorber 25.

The high proportion of total naphtha production, the combined streams 6 and 34, become further apparent on study of the material balances in our examples presented hereinafter.

FIGS. 2, 3, and 4 show various methods of utilization of the mixed C and C stream 31, hereinbefore described. A number of alternatives are described, with typical operating conditions, which are illustrative and should not be limitative.

FIG. 2 shows utilization of the mixed C and C, stream 31 as feed to C C, fractionator 40 which splits stream 31 into an overhead 41 at about 120 F. and 285 psi of mixed C components, and a bottoms fraction 42 of mixed C, components. The overhead mixed C stream 41 is taken to a fractionator 43 whose bottom product 44 is primarily saturated C components which can be utilized for liquified petroleum gas, and whose overhead 45 at about psi can be utilized as a petrochemical feedstock such as for polymerization, being primarily unsaturated C components.

The bottoms 42 of mixed C, components from (,C, frac tionator 40 is used as feed to an alkylation unit 46. The hydrogen fluoride alkylation unit 46 produces essentially nbutane stream 47 and a valuable alkylate product 48. A useful HF alkylation process is described in 'U.S. Pat. No. 3,21 l,802 to Dixon et al.

In FIG. 3, the mixed C and C stream 31 is utilized as feed to an HF alkylation unit 50 directly. The feed of materials to the HF alkylation unit 50 requires augmentation with additional C components. In the method of FIG. 3 the mixed C and C stream 31 has not first been fractionated to remove C components, as was done in the process of FIG. 2. Therefore,

'a separate additional feed of n-C, is supplied by conduit 51,

usually combined as stream 52 with recycle n-C, by conduit 56 from HF alkylation unit 50, and subjected to skeletal isomerization in isomerization unit 53. The isomerized feed54 is used as a part of the feed to alkylation unit 50, along with the mixed C and C,.stream 31. The HF alkylation unit 50 produces a C stream 55 useful for production of liquified petroleum gas, a n-C, recycle stream 56, and valuable alkylate 57.

FIG. 4 represents still another method of handling the mixed C and C stream 31. Here stream 31 is taken to a fractionator 40, which separates the mixed C and C, stream 31 into a mixed C stream 41 as overhead, and a mixed C, stream 42 as bottoms. The overhead 41 of mixed C components are fractionated in fractionator 43 to produce a bottoms 47 of saturates useful for liquified petroleum gas, and an overhead 44 of unsaturated C useful for liquified various petrochemical production requirements.

EXAMPLES To illustrate the effectiveness of our process, and to show most graphically the high naphtha productivity of our process, operational runs were made utilizing crudes from two different sources, a Libyan crude and a Nigerian crude.

Each of these crudes was treated as we have described relative to our drawings. Data shown is based on an input of 78,000 B/D (barrels per day) of crude for each example.

EXAMPLE I.-LIBYAN CRUDE Stream 3 5 5 7 12 13 25 29 31 34 41 IIES, n1.c.r./d 95 Hz,m.c.t./d 12,000 12,900 C1,m.e.f./c}a. 6,880 880 Total 29,873 2,028 27,845

Stream 42 44 45 47 4s 51 52 54 55 50 57 05', old. 5,100 Ca,b./d. 2,955 c4". b./d 3,995 1C4. b./d. 5, 730

cl.b./d 1,445 Alkylate, b./d

Total 11, 170

EXAMPLE I1.NIGERIAN CRUDE Stream a v 8 5 6 ./d .I.. Carbon black feed, b./d Fract. btms., b./d

Total 18, 487

Example I, the Libyan crude, shows a production by our process of over 72 volume per cent of combined naphtha, combination of streams 6 and 34; over 24 volume percent mixed C and C stream 31; and only about 3 volume percent carbon black oil.

Example I], the Nigerian crude, shows a production by our process of almost 68 volume percent combined naphtha, over volume percent mixed C and C and less than 4 volume percent carbon black oil.

The versatility of the process of our invention is shown by comparing the yields of streams 6 and 34 which reflect basic differences in crude character, yet the overall yield of naphtha is high in each case, as is the combined naphtha plus C and The preceding examples show the efiectiveness of the process of our invention as demonstrated by runs on two separate and distinct crude stocks. The operating data shown in these examples demonstrate that crude oils can be processed according to our invention into highly desirable streams for petrochemical production requirements with but minor amounts of other products.

Reasonable variations and modifications of our invention are possible within the scope of our disclosure, without departing from the spirit and scope thereof as we have disclosed in the specification hereinabove and the claims hereinafter.

We claim:

1. An improved process for substantially increased production of naphtha from crude oil which comprises: 7

a. thermally distilling said crude oil and thereby separating said crude oil into streams comprising a first overhead fraction and a heavies stream as residue fraction, said first overhead fraction having an end point from about 350 to 375 F., and said heavies stream comprising the remainder of said crude oil,

. separating lighter materials from said first overhead fraction from said step (a) into a second overhead, and leaving the remainder as a first or straight run naphtha stream,

. catalytically cracking said heavies stream from said step (a) combined together with a recycle oil from step (e) hereinafter recited under fluid catalytic conditions including a particulate catalyst and thereby producing a major amount of a catalytically cracked mixture and a minor amount of coke, said coke being deposited on said particulate catalyst,

d. thermally distilling said catalytically cracked mixture from said step (c) and thereby separating said catalytically cracked mixture into a third overhead stream comprising those components of said catalytically cracked mixture distillable from initial boiling point up to a maximum of about 400 F., a carbon black oil comprising 0 recycling a portion of said those components of said catalytically cracked mixture boiling at over about 700 F. and comprising less than about 5 volume percent of said crude oil, and said recycle oil comprising those components boiling from about 400 to 700 F.,

e. recycling said recycle oil from said step (d) to said step recovering said carbon black oil as a product,

separating lighter components from said third overhead stream from said step (d) leaving a second or cracked naphtha stream,

h. combining said first naphtha stream with said second naphtha stream as a naphtha product, and thereby substantially increasing naphtha production from a crude oil.

2. A process according to claim 1 wherein said step (g) comprises:

contacting said third overhead stream from said step (d) in an absorber under absorption conditions, thereby substantially moving hydrogen and C through C hydrocarbons from said third overhead stream and leaving a deethanized light fraction,

separating said deethanized light fraction into an overhead comprising a mixed C and C stream, and a thus purified bottoms stream comprising said second naphtha stream.

3. A process according to claim 2 further including purified naphtha stream as absorbent in said absorber.

4. A process according to claim 3 wherein said cracking step (c) is conducted at a temperature of from about 850 to about l,000 F., and said combined naphtha product constitutes at least about volume percent of said crude oil.

5. A process according to claim 4 wherein further said mixed C and C stream from said step (g) is treated by steps which comprise:

fractionating said mixed C and C stream into an overhead consisting essentially of a mixed C stream, and a bottoms consisting essentially of a mixed C stream, and

further fractionating said mixed C stream into an essentially unsaturated C stream as overhead and an essentially saturated C stream as bottoms.

6. A process according to claim 5 wherein further said mixed C stream is treated by steps which comprise:

combining under HF alkylation conditions at least a portion of the components of said mixed C stream and thereby forming an alkylate, separating said alkylate from unreacted components and recovering said alkylate as a product.

7. A process according to claim 4 wherein further said mixed C and C stream from said step (g) is treated by steps which comprise:

feeding said mixed C and C stream to an HF alkylation of the components of said feed to form alkylate,

zone as at least a portion of the feed thereto, separating said alkylate from unreacted components and feeding make-up n-C to said HF alkylation zone as a recovering said alkylate as a product.

further portion of said feed thereto, combining under HF alkylation conditions at least a portion 5 k i: r

Claims

2. A process according to claim 1 wherein said step (g) comprises: contacting said third overhead stream from said step (d) in an absorber under absorption conditions, thereby substantially moving hydrogen and C1 through C2 hydrocarbons from said third overhead stream and leaving a deethanized light fraction, separating said deethanized light fraction into an overhead comprising a mixed C3 and C4 stream, and a thus purified bottoms stream comprising said second naphtha stream.
3. A process according to claim 2 further including recycling a portion of said purified naphtha stream as absorbent in said absorber.
4. A process according to claim 3 wherein said cracking step (c) is conducted at a temperature of from about 850* to about 1,000* F., and said combined naphtha product constitutes at least about 65 volume percent of said crude oil.
5. A process according to claim 4 wherein further said mixed C3 and C4 stream from said step (g) is treated by steps which comprise: fractionating said mixed C3 and C4 stream into an overhead consisting essentially of a mixed C3 stream, and a bottoms consisting essentially of a mixed C4 stream, and further fractionating said mixed C3 stream into an essentially unsaturated C3 stream as overhead and an essentially saturated C3 stream as bottoms.
6. A process according to claim 5 wherein further said mixed C4 stream is treated by steps which comprise: combining under HF alkylation conditions at least a portion of the components of said mixed C4 stream and thereby forming an alkylate, separating said alkylate from unreacted components and recovering said alkylate as a product.
7. A process according to claim 4 wherein further said mixed C3 and C4 stream from said step (g) is treated by steps which comprise: feeding said mixed C3 and C4 stream to an HF alkylation zone as at least a portion of the feed thereto, feeding make-up n-C4 to said HF alkylation zone as a further portion of said feed thereto, combining under HF alkylation conditions at least a portion of the components of said feed to form alkylate, separating said alkylate from unreacted components and recovering said alkylate as a product.