CA1048434A - Process for producing light fuel oil - Google Patents

Abstract

A PROCESS FOR PRODUCING LIGHT FUEL OIL

ABSTRACT

The production of light fuel oil by catalytic cracking is accomplished in a single riser conversion zone by cracking a recycle oil product of cracking initially in the riser with freshly regenerated catalyst under restricted severity conditions and a fresh gas oil feed is cracked with coke deactivated zeolite cracking catalyst in an upper portion of the riser under restricted severity conditions.

Description

:1048434 BACKGROUND OF THE INVENTION

Fluid cracking operations to produce a variety of useful products have been practiced since early 1940. A prior art patent of particular interest directed to restricted conversion operations is +hat of Jewell 2,882,218.
Fluid cracking of distillation products of crude oil has been practiced sirce early 1940. Naturally occurring clay - type catalysts were initially employed and subsequently re-placed ~dth synthetic silica-alumina amorphous type crackin~
catalysts. These catalysts were more active for accomplishing the desired reactions and thus permitted many processing variations and equipment changes. The development of crystalline alurninosilicate conversion catalyst has provided additional opportunity to develop more efficient conversion operations as well as substantially improving the equipment irl which employed. m e present invention is particularly concerned with processing crude oil distillation products under conditions to improve the recovery of fuel oil boiling range products of desired pour point using improved crystalline zeolite conversiGn catalyst of recent development.

SUMMARY OF THE INVENTION

The present invention relates to the production of lsght fuel oil and lower boiling products by catalytic cracking.
More particularly, t,he present invention relates to improvin~
~5 the yield of light fuel oil product of a fluid catalyst crackingoperation by conta~ting a fresh gas oil boiling ange feed with a coked catalyst of reduced activity characteristics in the ~048434 upper portion of a riser cracking zone at a temperature within the range of 800 to 900F. and subsequent to contacting freshly regenerated catalyst passed to a lower inlet of the same riser cracking zone with a heavy cycle oil product of the cracking operation at a temperature within the range of 900 to 1000F.
It has been observed from acquired data that the maximum yield of light fuel oil product obtained by cracking a gas oil feed in a single pass riser conversion operation occurs under relatively low severity cracking conditions in which the fresh gas oil feed is exposed for a contact time within the range of 2 to 4 seconds to a low activity catalyst within the range of 20 to 40 FAI at a temperature in the range of 800F. to about 900F. In`this operational environment it has also been observed that a coked zeolite cracking catalyst containing up to lO weight percent REY and comprising from about 0.5 to about 1.2 weight percent carbon has an activity within the above identified desired activity level in combi-nation with good selectivity to particularly promote a maximi-zation of light fuel oil product. Furthermore, it has been observed that within the operational parameters herein defined, that from about 40 to about 60 weight percent of a heavy distillate material is also produced. This heavy distillate material so obtained can then be reprocessed or recracked at much more severe cracking conditions than required by the fresh gas oil feed to yield additional light fuel oil product. In fact, the maximum light ~uel oil prcduct yield obtainable from cracking the heavy distillate results from using a much more active catalyst at a higher temperature and higher catalyst/oil ratio than was found to be ~ptimum for r~aximizing the l ght f~lel oil from crack~ng the fresh gas oil feed.
Thus, in the concept of this invention, a fresh gas oil feed preheated to an elevated temperature in the range of about 700F. to about 800F. is charged to an upper portion of a riser conversion zone wherein it is brought in contact with a hydrocarbon-catalyst suspension partially deactivated by hydrocarbonaceous deposits of recycle oil cracking to form a second oil-catalyst suspension comprising from about 0.5 to Io about 1.2 weight percent of carbonaceous deposits identified as carbon. A mix temperature of the fresh gas oil feed with the recycle oil product-catalyst suspension above identified of about ~OO~F. to about 900F. is desirable. In this environment conversion of the fresh gas oil feed is considerably restricted not to exceed about 35 vol.% and preferably is less than about 30 vol.~. The more dilute suspension thus formed with the fresh gas oil feed traverses the remaining portion of the riser conversion zone for a li~ited contact time within the range of 1 to 4 seconds before it is discharged into suitable separating means such as cyclonic separating means for separating a hydrocarbon p~ase from a catalyst phase.
m e catalyst phase is stripped with s~ripping gasiform material such as steam to remove entrained hydrocarbon before it is passed to a catalyst regeneration zone.
In the catalyst regeneration zone, the deposited carbonaceous material is substantially completely removed from the catalyst by burning with an oxygen containing gas thereby heating the catalyst to ar. elevated temperature within ~048434 the range of 1~00F. up to about 1400F. The carbonaceous deposits substantially completely removed from the c~talyst during regeneration and remaining as residual coke, is reduced to at least about 0.2 weight percent.
The hydrocarbon phase separated as above provided or by any other suitæble separating arrangement, is passed to the product fractionator wherein a separation is made for the separate recovery of a naphtha stream and lower boiling gasiform materials, a light fuel oil stream and a heavy cycle oil ~trea~. A clarified slurry stream may also be recovered from the lower portion of the fractionator. m e heavy cycle oil comprising an initial boiling point within the range of 650 to 720F. is passed as charge to the bottom portion of a riser reactor or conversion zone for admixture with hot 15- freshly regenerated catalyst to form a suspension. The heavy cycle oil at a relatively low temperature n the range of about 350F. up to about 500F. is combined with the hot freshly regenerated catalyst to form a suspension at a mix temperature less than about 1000F. and more usually above about 850F. but not above about g5ooF~ The conversion conditions maintained in the lower portion of the riser conversion zone are selected to provide a conversion of the heavy cycle oil to lower boiling products including gasoline and particularly a light fuel oil product. During conversion of the heavy cycle oil in the .ower portion of the riser conversion zone, carbonaceous deposits are formed on the catalyst in an a~ount of at least 0.5 ~-eight percent. Also, conversion of the heavy cycle oil to gasoline and lower - 1048~34 boiling products is restricted usually not to exceed about 65 vol.%. For example, conversion of the heavy cycle oil may be restricted to produce about 10 weight percent (wt.~) gas, 35 wt.% gasoline, 20 wt.% light fuel oil, 5 wt.% coke and 30 wt.% of unconverted 650F. plus material.
The combination operation of tne present invention is unique in several respects and particularly unique in that fresh gas oil feed contacts a process generated catalyst of reduced activity at a lower catalyst to oil ratio than that used for converting heavy cycle oil product of the combina~ion operation. Furthermore, the overall conversion of the hydro-carbon feeds can be maintained at a selected high level with a low steady state concentration of heavy cycle oil and the light fuel oil product thereof will be maximized because of the particularly selected low severity conditions that it encounters as a result of its first pass contact with the catalyst of reduced activity particularly employed in the operation.
The catalyst employed in the combination operation of this invention may be substantially any cracking catalyst known in the art provided its activity is selectively reduced with hydrocarbonaceous material to within the range of 20-40 FAI during conversion of a heavy cycle oil and prior to contact with a fresh gas oil feed. Thus, the catalyst may be an amorphous silica-alumina cracking catalyst, a crystalline zeolite cracking catalyst, or a combination thereof. A
preferred catalyst is a rare earth exchanged "Y" type crystalline faujasitF- in an amount up to about 15 weight percent and more usually within the range of 2 to 10 weight percent dispersed in a suitable matrix material. For example, a more preferred catalyst comprises as much as about 10 weight percent of a rare earth exch~ged "Y" faujasite crystalline zeolite dispersed in a silica clay matrix and provided with a small amount of zirconia. Such preferred catalysts are more completely defined in U.S. Pætent 3~556,988 issued January 17, 1971.

DISCUSSION OF SPECIFIC EMBODI~ENTS

The yield data obtained by passing a Durban fresh gas oil feed over cracking catalyst compositions deac'ivated by carbon deposits is presented in Table I.

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The data obtained by con~erting a hea~y cycle oil product of the Durban gas oil cracking in the presence of a more active regenerated catalyst composition, clean burned and containing a small amount of residual carbon thereon is presented in Table II.

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Table III combines two comparisons cf products obtained when processing a fresh gas oil feed over a coke containing catalyst and the heavy fuel oil trecycle) product thereof over regenerated catalyst at two different conversion levels. From the data presented in Table III, it will be observed that the combination of I, II and III produced higher yields of light fuel oil than the combinatlon of I, IV ~nd V.
The data presented in Tables I, II and III above have been developed to form Figures I through VI discussed below.

BRIEF DESCRIPTION OF THE FIGURES
Figure I graphically presents the response of conversion to catalyst/oil ratio in cracking a 650F. heavy cycle oil and a Durban fresh feed with a 55~57 FAI catalyst - 15 comprising a rare earth exchanged "Y" crystalline faujasite cracking catalyst.
- Figure II graphically presents the product se~ectively from cracking 650F.~ heavy cycle oil and Durbæn fresh feed over a 55 FAI REY type crystalline zeolite cracking catalyst.
Figure III graphically presents the effect of 650F.
heavy recycle on the overall yield of products on a fresh feed baæis.
Figure IV graphically presents a comparison of the Cs+ gasoline products octane number.
Figure V graphically presents the pour point and API gravity of the 430-650F. light fuel oil (IFO) fraction ~ade from cracking Durban fresh feed and from 650F.+ hea-~y cycle oil.

104843~ -Figure VI graphically presents a yield and pour point comparison of the 690F. end point light fuel oil (LFG) obtained from Durban fresh feed and from a 550F.+ heavy cycle oil (HCO) by cracking with coked and clean REY type zeolite cracking catalysts.
Figure VII is a diagrammatic sketch in elevation of one arrangement of ~pparatus comprising a riser crackir.g zone and a catalyst regeneration zone interconnected by suitable catalyst transfer conduit means and a product recovery zone for separation, recovery and recycle of desired hydrocarbon product material to the cracking operation.

DISCUSSIO~J OF SPECIFIC E~ODII~ENTS

Figures I through VI herein presented are essentially self-explanatory and clearly represent the processing advantages of the concept of the present invention with respect to product yield and quality.
In Figure I, for example, it is shown that the fresh feed hydrocarbon charge is more conversion responsive than the 650F. plus heavy cycle oil feed to catalyst to oil ratio and temperature variations for a given activity crystalline zeolite cracking catalyst.
In Figure II it is graphically shown that the fresh feed converted at 1000F. produced greater yields than the 650F.+ heavy cycle oil processed at 850F. and ~50F. Also the gasoline yield was generally higher from the fresh feed cracking operation. Ve~y little difference, if any, is noted in the yields of dry gas and C4 hydrGcarbons. Variations in ~14-the coke yields for different conversion levels is readily observed.
In Figure III the data of Table III is graphically presented. In this figure it is shown that the 850F, single pass operation combined with the 850F, recycle operation produced similar levels of light fuel oil product at conversion levels in the range of 45 to 55 and was much better than the single pass operations graphically depicted. Also at conversion levels less than 50 weight percent the yields of C4 hydro-carbons, dry gas and coke are not materially different.
In Figure IV the first pass gasoline octane number (O,N,) processing fresh feed at 950F, with a coked catalyst was much higher than that obtained at 850F. and at either - temperature with the heavy cycle oil feed, On the other hand, the blended gasoline octane number obtained at the 850F, single pass fresh feed operation combined with the gasoline product of the 950F, recycle operation provided an octane number (R+O) in excess of 85.
- In Figure V it is graphically shown that the pour point of the light fuel oil (430-650F) and obtained fro~
the fresh feed and the heavy cycle oil is satisfactory and relatively stable at conversion levels up to about 55 weight percent. ~ne gravity of the oil steadily drops off, however, Figure VI graphically shows the influence of tempera-ture and conversion on cracking the fresh feed and recracking a heavy cycle oil product thereof on the yield of a light fuel oil product therefrom, The curves plotted and attached identifications clearly support the improved cracking combination 10~843~
- of the presen~ invention.
In the drawing Figure VII, a fresh gas oil feed is introduced by conduit 2 to furnace 4 wherein preheating of the feed to a desired elevated temperature is accomplished.
Preheating of the gas oil feed should be sufficient to form a suspension mix temperature in the upper portion of the riser within the range of 800 to 900F. The preheated feed is then passed by conduit 6 to an upper portion of riser conversion zone 8 identified at "B". At this point of fresh feed introduction, a suspension is formed with previously used catalyst of reduced activity and comprising from about 0.5 to about l.2 weight percent carbon deposit.
m e suspension thus formed will comprise a catalyst to fresh feed weight ratio within the range of 3 to 9 to give a fresh feed conversion to gasoline and lower boiling products within the range of lO to 40 weight percent. The suspension thus formed and diluted with the products of heavy cycle oil recracking obtained as discussed below pass upwardly through the remaining portion of the riser into a catalyst separation zone lO. The fresh feed-catalyst-suspension is provided a hydrocarbon contact time within the range of l to 4 seconds under the conditions specified above.
In separation zone lO provided with cyclonic separating means 12, separation of the suspension into a catalyst phase and a hydrocarbon phase is accomplished. The hydrocarbon phase is recovered and withdrawn by conduit 14 co~municating with fractionation zone 16. The separated catalyst pnase is collected and passed down, usually through an annular stripping zone l~ countercurrent to stripping gas 1~)48434 introduced to a lower portion thereof by conduit 25.
Catalyst stripped of entrained hydrocarbon vapors but deactivated with carbonaceous products of cracking is then passed by conduit 22 to regeneration zone 24. Tn regeneration ~one 24, the catalyst activity is restored by burning carbonaceous deposits with, for example, air introduced to the lower portion of the regeneration zone by conduit 26. Gaseous products of combustion comprising flue gas are withdrawn from the regeneration zone by conduit 28.
The catalyst of restored activity by the re-generation procedure and heated to an elevated temperature up to about 1400F. is withdrawn by conduit 30 and passed to the lower portion of riser 8. In the lower portion of riser 8, the freshly regenerated catalyst comprising a small amount of residual carbon is admixed with a heævy cycle oil product of the cracking operation in conduit 32, boiling above about 650F. to form a catalyst/oil suspension at a mix temperature within the range of 900 to about 1000F.
Preheating of the cycle oil product of cracking before forming - the suspension is contemplated. Also, the catalyst to oil ratio is preferably selected from within the range of 10 to 20. Under the conditions above defined the cycle oil catalyst suspension is provided a contact time within the range of 4 to 8 seconds before the suspension is diluted with the fresh gas oil feed as defined above In ~he ccmbination operation above described, it is important that the operat'ng parameters be selected to 1~48434 deposit an amount of carbonaceous material on the catalyst to reduce its activity within the range of 20 to 40 (~AI) fluid activity index before contact is made with the fresh gas oil feed under selected conversion conditions particularly for the production of light ~uel oil product.
The products of converting heavy cycle oil and fresh gas oi~ feedstocks under the above recited conversion conditions are conveyed by conduit 14 to fractionator 16.
In fractionator 16, the hydrocarbon products of catalytic cracking are separated into a gaseous phase removed by conduit 34, a naphtha phase removed by conduit -3~., a light fuel oil phase removed by conduit 38, a heavy cycle oil phase removed by conduit 32 and a bottom or clarified slurry oil phase removed by conduit 40.
Having thus generally described the combination operation of the present invention and discussed specific embodiments going to the very essence thereof, it is to be - understood that no undue restrictions are to be imposed by reason thereof except as defined by the following claims.

Claims (10)

I CLAIM:

1. A method for producing light fuel oil and lower boiling hydrocarbons which comprises:
combining a heavy cycle oil product of catalytic cracking with freshly regenerated catalyst particles to form a suspension at a temperature in the range of 900°F. to 1000°F., passing the suspension upwardly through a riser conversion zone under limited conversion conditions designed to produce light fuel oil product and deposit from about 0.5 to about 1.2 weight percent carbon on the suspended catalyst particles, combining a fresh gas oil feed with said suspension of carbon containing catalyst and cycle oil conversion products in an amount to form a second suspension of reduced temperature within the range of about 800°F. to about 900°F., passing the second suspension through a riser conversion zone under conversion conditions selected to particularly produce light fuel oil product, separating the hydrocarbon product of said cycle oil and said gas oil conversion from catalyst particles and then into hydrocarbon fractions comprising gasoline and lower boiling components, a light fuel oil product fraction, a heavy cycle oil product fraction and a high boiling residual material, and recracking the separated heavy cycle oil fraction with freshly regenerated catalyst as above defined.

2. A method for cracking gas oils and higher boiling material which comprises:
initially catalytically cracking a heavy cycle oil product of cracking in a riser conversion zone at a temperature above 900°F. under conversion conditions restricted to limit conversion of the cycle oil charge and deposit from about 0.8 to about 1.2 weight percent carbon on the catalyst, combining a fresh gas oil feed with the cycle oil conversion product containing catalyst with said deposited carbon to form a suspension at a temperature below 900°F.
maintained at a contact time within the range of 2 to 4 seconds to restrict conversion of the fresh gas oil feed, separating the suspension into a hydrocarbon phase and a catalyst phase, regenerating the catalyst phase, separating the hydrocarbon phase into desired product fractions comprising a heavy cycle oil and recycling said heavy cycle oil product of cracking as charge for contact with freshly regenerated catalyst in the initial portion of the riser conversion zone.

3. A method for converting hydrocarbons to gasoline and fuel oil products which comprises:
passing a cracking catalyst suspended in a hydrocarbon phase upwardly through a riser conversion zone under decreasing temperature and catalyst activity conditions, the hydrocarbon phase in the lower portion of the riser conversion zone initially limited to a heavy cycle oil product of the conversion operation, the hydrocarbon phase in an upper portion of the riser conversion zone comprising fresh gas oil feed material, restricting conversion of the gas oil feed in the upper portion of the riser conversion zone by limiting the conversion condition to a temperature within the range of 800 to 900°F., separating the product of said riser conversion operation to recover light fuel oil and lower boiling products from higher boiling material comprising heavy cycle oil, and recycling the heavy cycle oil to the lower portion of said riser conversion zone.

4. The method of claim 3 wherein the heavy cycle oil is mixed with freshly regenerated catalyst to form a suspension at a temperature in the range of 900°F. to about 1000°F.

5. The method of claim 4 wherein conversion of the heavy cycle oil deposits carbon on the catalyst thereby-reducing the activity of the catalyst to within the range of 20 to 40 FAI.

6. The method of claim 5 wherein the fresh gas oil feed is brought in contact with the carbon deactivated catalyst after the catalyst has attained a 20 to 40 fluid activity index level to form a mixture at a conversion temperature within the range of 800°F. to about 900°F.

7. The method of claim 5 wherein each of said cycle oil feed and said fresh gas oil feed are preheated before contact with catalyst in said conversion zone.

8. The method of claim 7 wherein the residence time of the fresh gas oil feed in the riser is restricted to within the range of 2 to 4 seconds and the heavy cycle oil feed conversion is restricted to provide increased yields of light fuel oil.

9. The method of claim 8 wherein the catalyst comprises a crystalline zeolite cracking component.

10. The method of claim 9 wherein the crystalline zeolite is a rare earth exchanged "Y" faujasite crystalline zeolite.