Combination operation to maximize fuel oil product of low pour

Abstract

A combination operation is described comprising catalytic cracking and ZSM-5 type crystalline aluminosilicate catalyst upgrading of light fuel oil product under selected conditions designed to particularly increase the yield of light fuel oil product of desired low pour point.

Description

BACKGROUND OF THE INVENTION

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 that of Jewell 2,882,218. Naturally occurring clay type catalysts were initially employed and subsequently replaced with synthetic silica-alumina amorphous type cracking catalysts. These catalysts were more active for accomplishing the desired conversion reactions and thus permitted many processing variations and equipment changes. The development of a crystalline alumino-silicate conversion catalyst has provided additional opportunity to develop more efficient conversion operations as well as substantially improving the equipment in which employed. The present invention is concerned with processing crude oil and distillation products thereof under conditions to improve the recovery of fuel oil boiling range products of desired pour point.

SUMMARY OF THE INVENTION

The present invention is concerned with a processing combination comprising a hydrocarbon conversion operation designed particularly for the increased production of a light fuel oil product. More particularly, the present invention is concerned with the cracking of cude oil and distillation products thereof such as gas oil and higher boiling hydrocarbons with catalysts of selected activity characteristics maintained under conditions particularly promoting the formation of relatively large yields of fuel oil boiling range product which is selectively converted with a small pore crystalline zeolite under conditions to reduce the pour point of the fuel oil product of cracking.

The fluid cracking operation of this invention is a relatively mild conversion operation as compared with an operation primarily directed to the production of gasoline. It is particularly accomplished under conversion conditions restricted to less than 45 vol. percent in the presence of recycle material. More particularly, it is preferred to restrict a first pass conversion of fresh feed passed to the cracking operation to less than 40 vol. percent and more usually to within the range of 25 to 35 vol. percent. Under these restricted conditions, conversion is defined as the volume percent of gas oil converted to material boiling in the gasoline boiling range or lighter. Gasoline as referred to herein is defined as a debutanized hydrocarbon with 90 vol. percent of the material boiling below 400.degree.F. in an ASTM atmospheric distillation still.

In the limited conversion fluid cracking operation of this invention, the product effluent thereof is separated in a product fractionation zone to recover a desired light cycle oil product from lighter and heavier oil product material of the conversion operation. The light cycle oil will normally boil to include materials boiling above gasoline product up to about 700.degree.F. at its 90 percent ASTM distillation point. Higher boiling material recovered from the fractionation zone as heavy cycle oil is recycled to the cracking operation for further conversion to lower boiling desired product. Recycle rates will usually be in the range of 1.5 to about 1.8 or less than 2.2 but greater than about 1.25. The fluid cracking operation herein discussed is preferably carried out in one or more riser conversion zones for fresh and recycle hydrocarbon feed materials maintained at predetermined selected conversion temperature conditions less than about 1000.degree.F., preferably not above about 950.degree.F. and more usually in the range of 800.degree.F. to about 900.degree.F. Operating pressure conditions may be in the range of atmospheric up to about 100 psig.

The catalyst employed in the riser cracking operation herein described may comprise an amorphous silica-alumina cracking catalyst, a faujasite type of crystalline zeolite of the "X" or "Y" type or mixtures thereof provided with an activity level based on the FAI (fluid activity index) test within the range of about 18 to about 45, it being preferred to restrict the catalyst activity to within the range of 20-40 FAI. The fluid cracking catalyst may be an amorphous cracking component alone or a Y type of crystalline faujasite alone or a combination thereof. Furthermore, either one or both of these cracking components may be combined with a relatively small amount up to about 10 weight percent of a ZSM-5 type of crystalline zeolite or a mordenite type of crystalline zeolite. A crystalline zeolite cracking component in the form of a rare earth exchanged Y crystalline zeolite may be in an amount within the range of 1 to about 15 weight percent dispersed in a suitable silica containing matrix material. A ZSM-5 type crystalline zeolite component within the range of 1 to about 10 weight percent may be combined with the faujasite catalyst. The Y type crystalline zeolite cracking component may also be combined with a mordenite type of crystalline zeolite in a suitable support matrix material in which composition the mordenite component may be within the range of 1 to 10 weight percent. On the other hand, a ZSM-5 type of crystalline zeolite may be used alone as herein provided dispersed in a silica-clay matrix using from about 2 to about 15 weight percent of the zeolite.

A catalyst composition suitable for use in the combination operation of this invention comprises a mixture of crystalline zeolites varying in pore size, structure and silica to alumina ratio. For example, the catalyst composition employed in the fluid cracking operation of this invention may comprise a crystalline zeolite of at least 8 A. pore size of the X or Y faujasite type of crystalline zeolite material activated by a rare earth exchange material. The faujasite cracking component is used in a minor or major proportion in combination with equal, a smaller, or a larger amount of a crystalline zeolite of a generally smaller pore size such as a ZSM-5 type of crystalline zeolite or a mordenite type of crystalline zeolite which vary in structure and silica-alumina ratio from the larger pore faujasite type material. The crystalline zeolites whether used alone or together as herein discussed are dispersed in a porous matrix material suitable for encountering the high operating temperatures to which they will be exposed. The smaller pore crystalline zeolite used in the combination operation of this invention either alone or in admixture with a larger pore material of the X or Y faujasite type material is preferably a ZSM-5 type of catalyst composition. A ZSM-5 type catalyst composition is described in U.S. Pats. Nos. 3,702,886 and 3,729,409 and the description thereof is incorporated herein by reference thereto. A more complete description of a large pore crystalline zeolite suitable for use in this invention may be found in U.S. Pat. No. 3,556,988 issued Jan. 17, 1971. The description of such catalyst compositions is incorporated herein by reference.

By porous matrix material it is intended to include inorganic and organic compositions which may be catalytically active or substantially inactive to the hydrocarbon conversion reactions encountered. A preferred porous matrix may be selected from the group comprising clay, acid treated clay, silica, alumina and mixtures thereof. A silica-alumina cracking catalyst of a selected and relatively low activity may be used as the primary or major catalyst component with or without the presence of a faujasite crystalline zeolite, a ZSM-5 type zeolite or a mordenite type zeolite in the fluid cracking operation, as suggested above.

As suggested above, the cracking catalyst may include a mordenite type of crystalline zeolite of the large or small pore variety discussed in the prior art. In this catalyst combination, the mordenite component will usually be only a fraction of the faujasite component and selected from within the range of 1 to 10 weight percent.

The light fuel oil product of catalytic cracking obtained by the fluid cracking operation particularly defined herein, normally will boil in the range of about 320.degree.F. up to 400.degree.F. as its initial boiling point up to about 700.degree.F. at its 90 percent ASTM distillation level, and will have a pour point within the range of -30 to about + 40.degree. F. depending upon the kind or type of hydrocarbon feed used. To selectively improve or reduce the pour point of the light fuel oil product of catalytic cracking obtained as herein defined, the separated light fuel oil product is thereafter passed in contact with a ZSM-5 type of crystalline zeolite conversion catalyst alone maintained under selective hydrodewaxing conditions particularly designed to further reduce the light fuel oil product pour point. The ZSM-5 type zeolite catalyst may be employed in a fixed or fluid bed of catalyst or as an upflowing fluid mass of catalyst such as in a riser conversion zone. In this hydrodewaxing operation, conversion of the separated light fuel oil product of the fluid cracking operation is promoted by contact with a ZSM-5 type of crystalline aluminosilicate catalyst at a temperature maintained within the range of 500.degree. to about 900.degree.F., more preferably within the range of 600 to about 800.degree.F. at a pressure in the range of 200 to 600 psig and a liquid hourly space velocity within the range of 0.5 to 2.0 v/v/hr. It is preferred to conduct the pour point reduction operation in the presence of hydrogen in an amount sufficient to maintain a hydrogen to hydrocarbon mole ratio in the range of 2 to 10/1.

In the combination catalytic operation above described, it is contemplated providing a hydrotreating operation before or after the ZSM-5 catalyst hydrodewaxing operation for the purpose of removing sulfur from the light fuel oil material to about 3 weight percent. However, high levels of sulfur may be tolerated in the ZSM-5 conversion operations and it may not be necessary to reduce the sulfur level. Also the cracking feedstock may be a low sulfur material which does not need to be desulfurized.

As mentioned above, the fluid cracking operation of this invention may be conducted in the presence of a faujasite crystalline zeolite conversion catalyst in combination with a ZSM-5 type of crystalline zeolite material. The ZSM-5 type component for the cracking operation may be provided by cascading this component from the downstream hydrodewaxing operation to the fluid cracking operation periodically as required to maintain a desired level of this ZSM-5 crystalline zeolite component activity in the fluid faujasite cracking catalyst. Thus, in a fluid catalyst hydrodewaxing operation, the ZSM-5 zeolite catalyst component is transferred, particularly when regeneration thereof is required, to the fluid cracking operation at intervals as required. Makeup of this small pore crystalline component to the overall combination is provided through the hydrodewaxing operation alone or in combination with the cracking operation. On the other hand, the hydrodewaxing operation may include its own catalyst regeneration step thereby precluding the necessity for cascading this catalyst component as above discussed.

In the combination operation of this invention, it is to be noted that with a given reactor configuration and catalyst composition, the pour point of the light cycle oil (light fuel oil) is largely a function of its ninety percent cut point and its initial boiling point is set by the gasoline end point desired. The gasoline end point may be in the range of 320.degree.F. up to about 400.degree.F. Using a hydrodewaxing operation as herein provided, allows a much heavier end point to be selected than possible in prior art processes for the light cycle oil product of this invention. This wider boiling range light cycle oil material of heavier end point and suitable as feed in the hydrodewaxing operation also permits the use of a less severe fluid cracking operation to produce a given volume of the wide boiling light fuel oil product separated therefrom. In addition, the yield of light fuel oil using the combination operation of this invention will considerably increase for the same pour point and sverity characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. I is a graph depicting the product selectivity obtained with REY cracking catalysts at low conversion cracking of Durban fresh feed.

FIG. II is a graph depicting the pour point and composition of light fuel oil from low conversion cracking of Durban fresh feed with REY catalysts.

FIG. III is a graph depicting the response in conversion to temperature, contact time and catalyst to oil ratios for different activity zeolite catalysts.

FIG. IV is a graph depicting the product selectivity obtained over HZSM-5 containing catalyst compared to REY catalysts.

FIG. V is a graph depicting the properties of the 650.degree.F. (+) cycle stock obtained by conversion of Durban fresh feed.

FIG. VI is a graph depicting the product selectivity obtained with HZSM-5 containing catalysts compared to REY catalysts.

FIG. VII is a graph depicting the product selectivity obtained with H-mordenite + REY compared with REY catalyst.

FIG. VIII is a graph depicting the pour point and composition of light fuel oil from HZSM-5 containing catalysts compared to REY catalyst.

FIG. IX is a graph depicting the pour point and composition of light fuel oil from H-mordenite containing catalysts compared to REY catalysts.

FIG. X is a graph depicting the pour point and composition of light fuel oil obtained from coke deactivated REY catalysts compared with a fresh clean burned REY catalyst.

FIG. XI is a schematic drawing in elevation of a combination process comprising fluid catalytic cracking, product separation and hydrodewaxing of a light fuel oil product of cracking.

In FIGS. IV, VI, VII, VIII, IX and X briefly defined, the results obtained with REY catalysts is shown by a dotted line for comparison with other results plotted. Further discussion of the graphs will be provided below.

DISCUSSION OF SPECIFIC EMBODIMENTS

A Durban fresh gas oil feed defined below in Table I was subjected to a series of low conversion cracking evaluation in the presence of several different catalyst compositions. The operation parameters studied were: temperature in the range of 850.degree.-950.degree.F.; hydrocarbon residence time in the range of 2.5 to 4.5 seconds; and catalyst/oil ratios in the range of 2-20. FIG. III is a graphical representation of the response of conversion to temperature, contact time and catalyst to oil ratio for various catalysts.

The data and graphs referred to hereinafter identify the effects of catalyst type and operating variables on product yields, product compositions and product properties.

TABLE I ______________________________________ DURBAN FRESH FEED ______________________________________ Gravity, API 23.8 Sulfur, % wt. 2.08 Nitrogen, % wt. 0.10 Conradsen Carbon, % wt. 0.23 Hydrogen, % wt. 12.3 Molecular wt. 357 Distillation, ibp, .degree.F. 520 5% vol. 622 10% vol. 660 20% vol. 705 30% vol. 740 40% vol. 774 50% vol. 804 60% vol. 837 70% vol. 866 80% vol. 897 90% vol. 937 95% vol. 960 Composition, Paraffin % wt. 25.3 Naphthenes 27.3 Aromatics 47.4 % C, (Aromatic Ring Carbon) 19.0 ______________________________________

Selectivity Comparison between Amorphous Silica/Alumina and REY type Catalysts (Rare earth exchanged Y faujasite crystalline zeolite).

The maximum light fuel oil (LFO) yields obtained by cracking with an amorphous silica/alumina catalyst were found to be had at about 35 % conversion (to less than 430.degree.F. products) for a 650.degree.F. end boiling point (EBP) light fuel oil; at 30 % conversion for a 690.degree.F. EBP light fuel oil and 20 percent conversion for a 720.degree.F. EBP light fuel oil.

The maximum light fuel oil yields obtained by cracking with a (REY) rare earth exchange Y faujasite type conversion catalyst, on the other hand, were found to be had at 40 percent conversion for a 650.degree.F. end boiling point (EBP) light fuel oil; 35 percent conversion for a 690.degree.F. EBP light fuel oil and at 25 percent conversion for a 720.degree.F. EBP light fuel oil. Thus, the level of conversion could be much higher with the faujasite conversion catalyst than with the amorphous silica-alumina catalyst. Also, the light fuel oil yields were found to be higher when the cracking temperature is about 850.degree.F. instead of a higher temperature of about 950.degree.F. FIG. I graphically reproduces the product selectivity obtained by low conversion cracking of Durban fresh feed (Table I) using REY catalysts and shows the 850.degree.F. operation producing more fuel oil than the 950.degree.F. operation.

Table II below provides a comparison of the yields obtained for the silica-alumina and REY catalysts at a 30 wt. percent conversion level.

Table II __________________________________________________________________________ Silica/Alumina REY 850.degree.F. 950.degree.F. 850.degree.F. 950.degree.F. __________________________________________________________________________ Coke 2.0 wt.% 1.5 wt.% 1.9 wt.% 1.1 wt.% Dry Gas 1.7 2.8 1.4 2.2 C.sub.4 's 4.1 3.5 3.0 3.0 C.sub.5 + Gasoline 22.2 22.2 23.7 23.7 430/650 LFO 27.5 25.5 28.0 27.3 430/690 LFO 34.9 33.6 35.7 34.4 430/720 LFO 41.2 40.0 43.0 41.6 __________________________________________________________________________

It will be observed from the above data, graphically presented in FIG. V, that the REY type crystalline zeolite catalyst is more selective for the production of gasoline and light fuel oil product than the silica-alumina catalyst. Catalyst activity for the above reported catalysts was identified as 23 to 32 FAI for the amorphous silica-alumina catalyst and 40 to 68 FAI for the REY catalyst.

Properties and Composition of Light Fuel Oil Cuts

The pour point of the 430.degree.-650.degree. F; 430.degree.-690.degree. F. and 430.degree.-720.degree. F. fuel oil cuts separated from a Durban fresh gas oil feed were reduced by cracking at a relatively low conversion level. A relatively severe cracking operation appears to have little effect on the light fuel oil pour point obtained by either a silica-alumina or REY cracking catalyst. FIG. II is a plot of the data obtained with the REY catalysts. The data are essentially self-explanatory. For example, the graph shows that the 650.degree.F. light fuel oil produced at 850.degree.F. with the REY catalyst has a lower point than the 690 or 720 light fuel oil produced at a higher temperature.

A comparison of the light fuel oil products of cracking obtained at a 30 wt. % conversion level to 430.degree.F. minus products is provided in Table III below.

Table III __________________________________________________________________________ Uncracked Silica/Alumina REY Feed 850-950.degree.F. 850-950.degree.F. __________________________________________________________________________ Pour Point 430/650.degree.LFO 20.degree. 5.degree. 2.degree. Pour Point 430/690.degree.LFO 35.degree. 23.degree. 15.degree. Pour Point 430/720.degree.LFO 40.degree. 30.degree. 32.degree. % Aromatics in 650.degree. LFO 37% 56% 54% % Paraffin in 650.degree. LFO 37% 23% 24% % Naphthenes in 650.degree. LFO 26% 21% 22% % n-Paraffins in 650.degree. LFO 16% 8% 10% __________________________________________________________________________

The cloud points of the light fuel oil products obtained at the 30 wt. percent conversion level are presented in Table IV below. It will be noted from these data that there is a surprisingly small difference between the pour point and the cloud point of these different fuel oil fractions.

Table IV ______________________________________ Uncracked Silica/ PEY Feed Alumina ______________________________________ Cloud Point 430/650.degree.LFO 28.degree. 15.degree. 11.degree. Cloud Point 430/650.degree.LFO .about. 40.degree. 26.degree. 15.degree. Cloud Point 430/720.degree.LFO 46.degree. 40.degree. 36.degree. ______________________________________

Properties of Heavy Cycle Oil

The hydrogen content and API gravity were determined for the 650.degree.F. plus heavy cycle oil product of the cracking operations. The data obtained are plotted in FIG. V as a function of the amount of heavy cycle oil remaining from the cracking operation. In the figure, the severity of the cracking operation is shown increasing from right to left. The heavy oil product obtained with the REY catalyst is observed to be more aromatic than that obtained with the silica-alumina catalyst as indicated by the lower hydrogen content and lower API gravity of the product. The 1000.degree.F. temperature cracking runs with the silica-alumina catalyst, on the other hand, produced a heavy cycle oil which is more aromatic than that obtained at the 850.degree.F. and 950.degree.F. cracking conditions.

Effects of HZSM-5, H-Mordenite and Coke on REY type Conversion Catalysts

The catalyst/oil ratio response of various catalyst compositions was determined and a comparison thereof is plotted and shown in FIG. III at two different riser residence times of 2.5 and 4.5 seconds. The figure is self-explanatory. An activity comparison of the various catalysts tested using a fixed catalyst bed FAI test, cracking a light East Texas gas oil at 850.degree.F. and with the Durban charge stock at 850.degree.F. and a fixed catalyst/oil ratio is provided in Table V. The activity of the several catalysts tested is reported in the legend beneath the graphs of FIG. III.

Table V __________________________________________________________________________ Comparison of Low Activity Catalysts by FAI Test* Catalyst FAI Wt.% C Wt.% Yields (Vol.% Conv.) on cat. Conv. C.sub.5 + Gaso. C.sub.4 's Dry Gas Coke __________________________________________________________________________ Si/Al 22.7 0.16 22.2 16.6 3.36 1.85 0.36 10% Al.sub.2 O.sub.3 Si/Al 31.5 0.35 31.0 21.6 5.44 3.13 0.78 20% Al.sub.2 O.sub.3 2% REY/Si-Clay- 40.0 0.104 39.3 31.7 4.57 2.79 0.23 Zi Spent Torr. 20.2 0.06 .DELTA. 19.9 16.7 2.06 1.01 0.14 (0.8% C) 2% REY + 2% 40.9 0.10 40.2 29.4 5.98 4.58 0.23 HZSM-5 on D10 matrix 2% REY + 10% HZSM-5 48.5 0.17 47.1 32.3 8.81 5.61 0.37 2% HZSM-5 17.7 0.06 17.3 12.3 2.79 2.01 0.14 2% REY + 2% H- Mord. 41.4 0.094 40.7 34.4 4.14 1.95 0.21 2% REY + 10% H- Mord. 38.6 0.095 37.8 33.8 2.32 1.47 0.22 __________________________________________________________________________ Comparison of Relative Catalyst Activities: LETGO in Dense Bed vs. Durban Fresh Feed in Riser Catalyst LETGO at 850.degree. Durban at 850.degree. 2 C/O, 5 mm.t.sub.c 8 C/O, 41/2 sec. t.sub.c __________________________________________________________________________ Wt.% Conv. Wt.% Cat. Wt.% Conv. Wt.% Cat. 2% HZSM-5 17.3 .06 22.7 .14 Spent Torrance FCC (.86%C) 19.9 .06 .DELTA. 23.0 .08 .DELTA. Spent Ashland/Durban FCC (.92%C) -- -- 32.4 .17 .DELTA. 2% REY + 10% H-Mordenite 37.8 .10 37.6 .17 2% REY 39.3 .10 38.5 est. .18 est. 2% REY + 2% H-Mordenite 40.7 .10 39.0 .18 2% REY + 2% HZSM-5 40.2 .10 42.5 .20 __________________________________________________________________________ *LETGO, 850.degree.F., 5 mm. on-stream fixed bed.

From these activity comparison tests it has been observed that the addition of 2 weight percent HZSM-5 or 2 and 10 weight percent H-Mordenite to a 2 weight percent REY faujasite crystalline zeolite dispersed in a silica-clay-zirconia matrix has little effect on catalyst activity.

Selectivity Differences

Product yields obtained with two HZSM-5 catalysts are plotted in FIG. IV and compared to a 2 weight percent REY alone catalyst. It is found that the HZSM-5 type zeolite with and without a REY type zeolite catalyst, lowers gasoline and light fuel oil selectivity by increasing the dry gas and C.sub.4 yields. The dash line curves identified at 850.degree.F. and 950.degree.F. for the REY alone catalyst provide comparison with the results obtained with the HZSM-5 containing catalysts at the 850.degree.F. and 950.degree.F. temperature of conversion. Comparison at 30 weight percent conversion to 430.degree.F. minus products is provided below in Table VI.

Table VI __________________________________________________________________________ 2% REY + 2% REY 2% HZSM-5 2% HZSM-5 850.degree. 950.degree. 850.degree. 950.degree. 850.degree. 950.degree. __________________________________________________________________________ Coke 1.9 wt.% 1.1 wt.% 1.2 wt.% 1.0 wt.% 1.7 wt.% 1.2 Dry Gas 1.4 2.2 3.0 3.3 3.5 4.9 C.sub.4 's 3.0 3.0 4.7 4.5 5.9 4.9 C.sub.5 + Gasoline 23.7 23.7 21.1 21.1 19.0 19.0 430/650.degree. LFO 28.0 27.3 26.4 25.7 26.4 25.7 430/690.degree. LFO 35.7 34.4 34.7 33.6 34.7 33.6 430/720.degree. LFO 43.0 41.6 42.0 40.9 42.0 40.9 __________________________________________________________________________

Product yields obtained with two H-Mordenite type crystalline zeolite catalysts combined with 2 weight percent REY are compared with a 2 weight percent REY alone type zeolite cracking catalyst in FIG. VII. It will be observed that the mordenite component has very little effect on the light products and gasoline selectivity. Coke make is slightly lower when H-Mordenite is present along with a slight gasoline yield improvement. The mordenite containing catalysts provided with an FAI of 41.4 and 38.6 (FIG. III) show a definitely higher gasoline selectivity (solid line) over REY alone (dashed line). FIG. VII also shows the presence of higher light fuel oil yields (solid line) for each light fuel oil fraction as an effect of the mordenite component on the catalyst. A comparison is provided in Table VII below.

Table VII __________________________________________________________________________ 2% REY + 2% REY + 2% REY 2% H-Mordenite 10% H-Mordenite 850.degree. 950.degree. 850.degree. 850.degree. 950.degree. __________________________________________________________________________ Coke 1.9 wt.% 1.1 wt.% 1.1 1.1 0.8 Dry Gas 1.4 2.2 1.5 1.5 1.9 C.sub.4 's 3.0 3.0 3.0 3.0 3.0 C.sub.5 + Gasoline 23.7 23.7 24.3 24.3 24.3 430/650 LFO 28.0 27.3 29.5 29.5 28.4 430/690 LFO 35.7 34.4 37.5 37.5 36.0 430/720 LFO 43.0 41.6 -- -- -- __________________________________________________________________________

Properties and Composition of Light Fuel Oil Cuts

FIGS. VIII and IX provide a plot of the data obtained showing the pour point and the composition of the fuel oil cuts made by cracking a Durban fresh feed defined above in Table I over catalysts containing HZSM-5 type zeolites and H-Mordenite type zeolites. The dashed line represents the results obtained with the REY catalyst. The light fuel oil cuts obtained with the HZSM-5 and Mordenite containing catalyst have higher pour point than the REY produced product. In addition, a comparison of the results obtained at a 30 weight percent conversion level to 430.degree.F. minus product is provided in Table VIII below.

Table VIII __________________________________________________________________________ Uncracked 2% REY HZSM-5 H-Mordenite Spent FCC Feed containing containing Catalyst catalyst catalyst __________________________________________________________________________ Pour Point 430/650 LFO 20.degree. 2.degree. 7.degree. 3.degree. 3.degree. Pour Point 430/690 LFO 35.degree. 15.degree. 21.degree. 22.degree. -- Pour Point 430/720 LFO 40.degree. 32.degree. -- -- -- % Aromatics in 650.degree. LFO 37% 54% 57% 54% 54% % Paraffins in 650.degree. LFO 37% 24% 22% 24% 24% % Napthenes in 650.degree. LFO 26% 22% 21% 22% 22% % n-Paraffins in 650.degree. LFO 16% 10% -- -- -- __________________________________________________________________________

A 650.degree.F. light fuel oil product of zeolite cracking restricted to about 30 percent conversion with a REY-Mordenite cracking catalyst and identified by FIG. IX as having a pour of +5 was selected as a charge for pour point reduction by contact with a ZSM-5 crystalline zeolite hydrodewaxing catalyst. An estimated reduction in pour of the above identified light fuel oil product and operating conditions is provided in Table IX below.

Table IX ______________________________________ Calculated Reduction of 650.degree.F. Light Cycle Oil of +5 ______________________________________ Pour ZSM-5 Catalyst Operating Conditions Pressure, psig. 550 LHSV, v/hr/v 1.5 H.sub.2 circulation, scf/b 2000 Temperature, .degree.F. 530-750.degree.F. Age cycle Yields, % Wt. Vol. C.sub.1 0.05 -- C.sub.2 0.1 -- C.sub.3 0.5 -- C.sub.4 0.8 1.3 C.sub.5 0.9 1.3 C.sub.6 --330.degree.F. Naphtha 3.2 4.0 330+.degree.F. Gas Oil 94.6 93.3 Total 100.15 99.9 Charge 330+ Btm. Product +5 Pour -10 ______________________________________

The hydrodewaxing of light straight run petroleum fractions with ZSM-5 type zeolites such as a light straight run material boiling in the range of 350.degree.F. to about 550.degree.F. is disclosed in U.S. Pat. No. 3,700,585 issued Oct. 24, 1972.

A straight run petroleum distillate boiling in the range of about 450.degree.F. to about 700.degree.F. was subjected to pour point reduction by contact with a ZSM-5 crystalline zeolite. Table X below presents the results obtained and operating conditions employed in this operation.

Table X ______________________________________ LHSV 1.5 Pressure 400 H.sub.2 Circ. 2500 Temp., .degree.F. 530-750 Wt. Vol. C.sub.1 0.01 -- C.sub.2 0.04 -- C.sub.3 0.77 -- C.sub.4 's 1.97 2.85 C.sub.5 's 2.08 2.78 C.sub.6 --180.degree.F. 0.98 1.22 180-330+.degree.F. 2.06 2.40 330+.degree.F. Btm. 92.76 91.95 Total 100.70 101.20 Charge Product ______________________________________ 350-700.degree.F. 330+.degree.F.Btm., API 32.7 (34) API +5 Pour Point, .degree.F. -15 +10 Cloud Point, .degree.F. -5 ______________________________________

In the combination operation of the present invention, it is thus contemplated hydrodewaxing straight run petroleum distillates as well as cracked products boiling in the light fuel oil boiling range and combining the hydrodewaxed material to further improve the yield of low pour light fuel oil product of relatively wide boiling range.

Referring now to the drawing of the process combination, FIG. XI, there is shown schematically in elevation one arrangement comprising a fluid cracking operation followed by product separation and hydrodewaxing of light fuel oil product to reduce its pour point to a desired lower level. The drawing shows schematically a regeneration vessel 2 wherein a fluid catalyst used in a cracking operation is regenerated with oxygen containing gas to remove deposited hydrocarbonaceous material by burning thereby heating the catalyst to an elevated temperature up to about 1400.degree.F. and suitable for providing a substantial portion of the endothermic heat required in a subsequent cracking operation. Regeneration flue gases are removed from an upper portion of the regeneration vessel by conduit 4. Regenerated catalyst at an elevated temperature in the range of about 1100.degree. to 1350.degree.F. is removed from the regeneration zone by catalyst transfer conduits 6 and 8 respectively for transfer to the lower portion of riser reactor A and riser reactor B. A single riser reactor system may be employed in place of the dual riser system shown. However, the dual riser system provides greater flexibility in operating conditions and arrangements and thus will be specifically discussed.

In the dual riser cracking operation schematically depicted in the drawing, riser "A" is employed for converting a mixture of fresh gas oil feed and heavy cycle oil (HCO) at mix ratios discussed above and cracking temperature conditions selected to restrict conversion to less than about 45 vol. percent. Cracking of the fresh feed and heavy cycle oil is accomplished by mixing hot regenerated catalyst with the oil feed to form a suspension at a catalyst to oil ratio of about 6 based on fresh feed and a temperature within the range of 800.degree.F. to 950.degree.F. and preferably not over 900.degree.F. The suspension thus formed is passed upwardly through the riser conversion zone under velocity conditions providing a hydrocarbon residence time less than 10 seconds before the suspension is cyclonically separated in vessel 10 adjacent the upper end of the riser. There may be a plurality of interconnected cyclonic separating means provided for this purpose. Riser "B" on the other hand, is employed for cracking of virgin naphtha and/or recracking gasoline product of the cracking operation either alone or in combination with a recycled intermediate light cycle oil material. On the other hand, the dual riser operation may be employed for separately cracking light gas oil and heavy gas oils. In any event, a suspension of hydrocarbons which at least includes the recycled intermediate light cycle oil combined with regenerated catalyst and existing at a temperature selected from within the range of 800.degree.F. to about 1000.degree.F. is passed upwardly through riser B under predetermined limited conversion conditions preferably less than about 30 volume percent. The suspension in riser B is separated in cyclonic separating means provided at the end of riser B in vessel 10 into a hydrocarbon phase and a catalyst phase. Catalyst separated by cyclonic means and recovered in vessel 10 is stripped of entrained hydrocarbon in the lower portion of vessel 10 with stripping gas before the catalyst is transferred to the regeneration vessel by conduit 12. Hydrocarbon materials separated from catalyst in vessel 10 and comprising products of conversion separated from risers A and B and stripped products are conveyed by conduit 14 to a product fractionator 16.

In fractionator 16, the hydrocarbon product of conversion is cooled and separated into a clarified slurry oil (CSO) removed therefrom by conduit 18, a heavy cycle oil (HCO) removed by conduit 20, an intermediate cycle oil (ICO) removed by conduit 22 and a light cycle oil (LCO) removed by conduit 24. Materials boiling lower than light cycle oil and comprising gasoline product of the conversion operation and lower boiling gasoline product of the conversion operation and lower boiling gasiform material is removed from an upper portion of fractionator 16 by conduit 26. The material in conduit 26 is cooled in cooler 28 and then passed by conduit 30 to a drum 32 wherein gasoline boiling material is separated from lower boiling gaseous products. The gaseous products are withdrawn by conduit 34. The separated gasoline is withdrawn by conduit 36 and a portion thereof is recycled as reflux to the fractionator by conduit 38. The remaining portion of the gasoline product is recovered by conduit 40.

The intermediate cycle oil (ICO) in conduit 22 is withdrawn or recycled by conduit 42 to the bottom or lower inlet of riser B. The heavy cycle oil (HCO) in conduit 20 is withdrawn or recycled by conduit 44 to the bottom or lower inlet of riser A. An interconnecting conduit 46 with valve means connecting conduit 44 and 42 permits passing heavy cycle oil and intermediate cycle oil to either riser inlet as desired.

The light cycle (fuel) oil (LCO) or No. 2 fuel oil in conduit 24 is passed by pump 48 and conduit 50 to furnace 52 wherein it is heated in the presence of hydrogen to a temperature within the range of 500.degree. to 900.degree.F. before being transferred by conduit 54 for contact with a hydrodewaxing catalyst bed 56 in vessel or zone 58. The ZSM-5 type zeolite hydrodewaxing catalyst maintained in zone 58 is usually maintained at a pressure within the range of 100 to 800 psig. In the event that the light cycle oil product is undesirably high in sulfur content, it is contemplated subjecting it to a relatively mild hydrotreating operation which will reduce the level of sulfur in the light fuel oil product not to exceed about 3 weight percent. Typical hydrotreating operations known in the art may be used for this purpose. Thereafter the hydrotreated product is passed to zone 58. It is also contemplated and preferred to effect hydrotreating the light fuel oil product of cracking after hydrodewaxing thereof rather than before hydrodewaxing for sulfur reduction. Catalyst bed 56 in zone 58 is preferably a dense fluid bed of ZSM-5 type of crystalline zeolite catalyst hereinbefore described. In catalyst bed 56 the light cycle oil or No. 2 fuel oil is selectively converted or hydrodewaxed in the presence of hydrogen so as to reduce its pour point a desired amount and to within the range of -40.degree. to +15.degree.F. Fresh ZSM-5 makeup catalyst may be added to bed 56 by conduit 60 when desired. The light fuel oil product of reduced pour point and obtained by the selective conversion operation performed in vessel 58 is separated from catalyst in an upper portion thereof and withdrawn from the vessel by conduit 62, cooled in cooler 64 and conveyed by conduit 66 to drum 68. In drum 68, a hydrogen rich recycle gas is separated from higher boiling condensed product. The separated hydrogen rich gas is conveyed or recycled by conduit 70 for admixture with the light cycle oil feed in conduit 50. Hydrogen make-up gas may be added to the hydrogen rich recycle gas by conduit 72. Condensed liquid material is withdrawn from drum 68 by conduit 74 communicating with separation vessel or fractionator 76. In separator 76, a fuel oil product of desired low pour point is separated from lower boiling components. The fuel oil is withdrawn from the bottom of vessel 76 by conduit 78 as product of the combination process. A portion of this fuel oil product is recycled by conduit 80, cooler 82 and conduit 84 to maintain the temperature in the bottom portion of vessel 76 of about 650.degree.F. Components of the selective conversion operation and boiling below the desired fuel oil product, that is, below about 400.degree.F., are withdrawn from the top of the tower by conduit 86. The material in conduit 86 is cooled in cooler 88 and then conveyed by conduit 86 is cooled in cooler 88 and then conveyed by conduit 90 to drum 92. In drum 92 conditions of temperature and pressure are maintained to separate a fuel gas product comprising C.sub.4 and lower boiling hydrocarbons withdrawn by conduit 94 from higher boiling material falling in the gasoline boiling range. Condensed liquid is withdrawn by conduit 96 and a portion thereof is recycled as reflux by conduit 98 to the top portion of separator vessel 76. The remaining portion of the condensed liquid boiling below the fuel oil product and comprising gasoline boiling range components is withdrawn by conduit 100.

In the combination operation above described, the hydrodewaxing operation in zone 58 is usually at a much higher pressure than the cracking operation and within the range of about 200 to about 600 psig, and thus higher than that of fractionator 16 or vessel 10 wherein separated catalyst is collected and stripped before passage to the catalyst regeneration zone. Thus, to provide and maintain a crystalline zeolite cracking activity in the fluid cracking operation depleted as by catalyst attrition, it is contemplated passing the ZSM-5 type catalyst from the higher pressure vessel 58 by conduit 102 containing valve 104 to the bed of fluid cracking catalyst collected in vessel 10. Thus regeneration of the cascaded ZSM-5 catalyst component may be accomplished in zone 2 in addition to maintaining a desired level of ZSM-5 type crystalline component in the cracking catalyst. In this arrangement, zone 58 is provided with fresh ZSM-5 catalyst by conduit 60.

Within the operating concepts of this invention, it has been observed that the catalyst mixture of Y faujasite type crystalline zeolite and mordenite type crystalline zeolites perform better at a temperature of about 850.degree.F. than at 950.degree.F. within a conversion level in the range of 20 to 45 vol. percent. Also, the catalyst mixture was observed to perform better for the purpose intended, that is, produce a desired light fuel oil product than a Y faujasite crystalline zeolite alone. Furthermore, the mordenite containing catalyst gives slightly higher gasoline yields along with making less coke.

It will be understood by those skilled in the art that the hydrocarbon materials charged to the combination operation of this invention may vary considerably in boiling range and will vary with the composition of the fresh feed. For example, a fresh gas oil feed may boil in the range of 500.degree.F. to about 1050.degree.F. and produce in addition to the light fuel oil and gasoline products an intermediate cycle oil boiling in the range of 550.degree.F. to about 800.degree.F. and a higher boiling cycle oil boiling in the range of about 650.degree.F. to about 950.degree.F. Thus, since the fractionation zone downstream of the cracking operation is considered a relatively rough separation operation there will be some considerable overlap in the boiling range of products separated therefrom.

Having thus generally described the combination operation of the present invention and discussed specific embodiments pertaining thereto, it is to be understood that no undue restrictions are to be imposed by reasons thereof except as defined by the following claims. We claim:

Claims

1. A method for improving the yield of low pour light fuel oil product which comprises,

catalytically cracking a mixture comprising fresh gas oil feed and heavy cycle oil product of cracking in a first conversion zone under conditions selected to restrict conversion to less than 45 volume percent,

separating the product of said first conversion zone to recover gasoline and lower boiling components from a light fuel oil fraction, an intermediate cycle oil fraction and a heavy cycle oil fraction, recycling the heavy cycle oil fraction to said first conversion zone,

passing the intermediate cycle oil fraction to a second conversion zone and restricting catalytic conversion thereof to increase the yield of desired light fuel oil,

separating the product of the intermediate cycle oil conversion operation to recover gasoline and lower boiling components from light fuel oil and higher boiling cycle oil and

reducing the pour point of the light fuel oil fraction of the combination catalytic cracking operation by contacting it with a ZSM-5 type crystalline zeolite under hydrodewaxing conditions.

2. The method of claim 1 wherein conversion of the intermediate cycle oil fraction is restricted to less than 30 volume percent.

3. The method of claim 1 wherein conversion of the hydrocarbon feeds is accomplished with a catalyst of restricted activity within the range of 20-40 FAI.

4. The method of claim 1 wherein limited cracking of the intermediate cycle oil is accomplished in the presence of naphtha.

5. The method of claim 1 wherein the recovered light fuel oil product of the cracking operation boils in the range of from about 320.degree.F. up to about 700.degree.F. at its 90 percent ASTM distillation point.

6. The method of claim 1 wherein a faujasite conversion catalyst of restricted activity is employed in each of said conversion zones.

7. The method of claim 6 wherein the faujasite conversion catalyst is combined with from 1 to 10 weight percent of a ZSM-5 type or a mordenite type of crystalline zeolite.

8. The method of claim 1 wherein ZSM-5 type crystalline zeolite is cascaded from the ZSM-5 hydrodewaxing operation to the cracking operation at intervals when regeneration of ZSM-5 catalyst is required.

9. The method of claim 1 wherein freshly regenerated catalyst is passed to each conversion zone and the ratio to catalyst to oil in the first conversion zone is about 6 based on fresh feed.

10. The method of claim 1 wherein the hydrodewaxing operation is accomplished at a temperature within the range of 500.degree. to 900.degree.F. and cracking of the fresh and recycle oils charged to the first conversion zone is accomplished at a temperature below 950.degree.F. in a riser conversion zone providing a relatively short hydrocarbon residence time.

11. A method for converting high boiling hydrocarbons to light fuel oil product which comprises,

converting relatively high boiling hydrocarbon materials and recycle conversion products thereof higher boiling than a desired light fuel oil product with a faujasite containing crystalline zeolite cracking catalyst of 20 to 40 FAI activity under conditions restricting fresh feed conversion to less than 45 volume percent,

separating a light fuel oil product of conversion from a gasoline product with a boiling point of about 700.degree.F. at its 90 percent ASTM distillation point, and

reducing the pour point of said desired light fuel oil product by contact with a ZSM-5 type crystalline zeolite under hydrodewaxing conditions.

12. The method of claim 11 wherein a crystalline zeolite of the class selected from a ZSM-5 type crystalline material or a mordenite type of crystalline material is in admixture with said faujasite crystalline zeolite.

13. The method of claim 11 wherein an intermediate cycle oil boiling between said desired light fuel oil product and a heavier cycle oil product is separately converted to desired light fuel oil product.

14. The method of claim 13 wherein a fresh gas oil feed and a higher boiling recycle product of conversion are converted in a zone separate from the intermediate cycle oil conversion zone.

15. The method of claim 14 wherein the fresh gas oil feed is converted in a zone separate from a conversion zone for the intermediate cycle oil and higher boiling recycle product.

16. The method of claim 11 wherein the desired light fuel oil product has an initial boiling point within the range of 320.degree.F. to about 400.degree.F.