CA1203191A

CA1203191A - Middistillate production

Info

Publication number: CA1203191A
Application number: CA000415946A
Authority: CA
Inventors: Susan Bradrick
Original assignee: Chevron Research and Technology Co
Current assignee: Chevron USA Inc
Priority date: 1982-02-11
Filing date: 1982-11-19
Publication date: 1986-04-15
Also published as: GB2114594A; BE895873A; FR2521156B1; DE3246678C2; DE3246678A1; GB8303000D0; FR2521156A1; NL8300053A; GB2114594B; JPS58147495A

Abstract

ABSTRACT OF THE DISCLOSURE

"MIDDISTILLATE PRODUCTION"

A process for selectively producing middistillates using steamed/dealuminated faujasites is disclosed.

Description

12~?31~
i-~ 936-153 a MIDDISTILLATE PRODUCTION
TECHNICAL FIELD
One of the most important characteristics -that a modern petroleum refinery must have is flexibility. The ability to use different feedstocks, ranging from shale oils and heavy oils to light oils, to produce differen-t product slates in response to changin~ consumer demands is crucial to profitability. Feedstocks, for example, are now shifting to higher boiling, lower quality mixtures having I0 more metal, nitrogen, and sulfur contaminants than feeds previously used. Forecasts of consumer demand are predicting shifts from gasoline-range hydrocarbons to heavier, higher boiling products such as diesel fuels, fuel oils, and turbine fuels.
Hydrocracking, used either in a one-step process or in multistep processes coupled wi:~hhydrodesulfurization and hydrodenitrogenation steps, has been used extensively to upgrade poor-quality feeds and to produce gasoline-range materials. Over the years, much development work has gone into finding improved hydrocracking conditions and catalysts.
Tests have used catalysts containing only amorphous materials and catalysts containing zeolites composited with amorphous materials.
Among the zeolites disclosèd in the literature are Y (U.S 3,130,007); decationized Y (U.S. 3,130,006);
ultrastable Y (U.S. 3,293,192 and U.S. 3,449,070); and ultrahydrophobic Y (U.K. 2,014,970, published September 5, 1979). Disclosures have appeared which relate -to modifying zeolites. U.S. 3,367,884, Reid, February 6, 1968, discloses ~Z~?331 9~

reduclng the activity of superactive zeolites by calcining, leaching procedure. The catalyst is disclosed as being especially useful for cracking yas oils to gasoline. U.S.
3,506,400, Eberly et al., April 14, 1970 and U.S. 3,591,488, Eberly et al., July 6, 1971, disclose improving the stab-ility of the crystalline lattice of zeolites by a steam-ing and acid extraction process. The product, a stabilized zeolite, may be used in hydrocracking and is disclosed as having improved selectivity as shown by higher gasollne yield and lower coke make.
Other research has resulted in disclosures rela-ting to producing midbarrel products. U.S. 3,853,72, Ward, December 10, 1974, discloses hydrocracking high-boiling feeds to produce midbarrel products using a catalyst con-taining a steamed zeolite. U.S. 4,120,825, Ward, October 17, 1978, also discloses improving the production of mid-barrel products by hydrocracking with a catalyst containlng a steamed zeolite.
I have discovered that middistillate products can be selectively produced by hydroprocessing with an expanded-pore zeolitic catalyst.
TECHNICAL DISCLOSURE
My discoveries are embodied in the process for selectively producing middistillate hydrocarbons, comprising:
(a) contacting under hydroprocessing conditions a hydrocarbonaceous feed boiling above about 600 F (316 C) with a catalyst comprising a hydrogenation component and an expanded pore zeolite which consists of a faujasitic zeolite which has been steamed then dealuminated; and ~)3~9~L
-2a-(b) recovering a hydrocarbonaceous effluent of which more than about 40 percent by volume boils above about 300F (149C) and below about 700F (371C).
I have discovered that faujasitic zeoli-tes which have been dealuminated after high-temerpature steaming have surprising stability and activity for producing middistill-ates from higher-boiling feeds. By faujasitic zeolites is meant crystalline aluminosilicates, synthetic or natural, which have the crystalline structure of the large-pore zeo-lite, faujasite. These zeolites include faujastie, zeolite X, zeolite Y, and zeolites derived from them. For example, there are numerous processes known to the art for treating zeolite Y to produce "decationized Y", "ultrastable Y", "Z14-US", and others. The preferred faujasitic zeolite is zeolite Y, as well as derivative -~2~3~g~

01 _3_ zeolites having the crystal lattice characteristics of zeolite Y. The most pre~erred faujasitic zeolite is an 05 ultrastable Y zeolite having a sodium content of less than about 0 5 wt. % (as Na2O).
As prepared, the large-pore zeolites typically contain significant amounts of alkali metal. Because the alkali metals tend to poison the acid sites of the zeo-lite, standard ion-exchange procedures are used to remove them. The alkali metal content (calculated as oxide) is preferably reduced to below 5 weight percent before any heat treatments, and to less than about ~00 ppm by weight in the final zeolite The faujasitic zeolite being treated is calcined at high temperatures in the presence of water. During this high-temperature steaming, it is desired that at least 2 weight percent of the atmosphere above the zeolite be water, preferably more than 10 weight percent, more preferably greater than 25 weight percent. The most convenient way to calcine the zeolite is to place the zeolite which has undergone aqueous ion exchange into an autoclave and allow steaming to take place under auto genous pressure. The temperature of the steaming step is normally above 1000F t538C~, preferably above 1200F
(649C), and most preferably above 1~00F (760C)~ The time of the steam calcining can range from one-half hour to twenty-four hours or more.
It appears that the steam calcining causes 3~ aluminum to be removed from the crystal lattice and silicon to be volatilized to repair the holes left in the lattice by the aluminum. Thus, the integrity of the lattice is largely maintained and total collapse is avoided. Nevertheless, there is some loss o~ crystal-linity. The steaming also creates gross cracks andfissures in the crystalline particles. I~he aluminum removed from the lattice appears to form amorphous alumina deposits in the lattice pores and channels. These amorphous deposits are removed by the dealumination procedure. Dealumination typically involves leaching the ~03191 01 _4_ steamed zeolite with organic chelating agents such as EDTA
or with organic or inorganic acids. Dilute inoryanic 05 acids, particularly hydrochloric acid and sulfuric acid, are most preferred. Where acids are used, the pH of the leaching solution is preferably below about 2. It can be appreciated that if the pH is too high, dealumination will take inconveniently long, while if the acid concentration 1~ is too high, the zeolite's crystal lattice can be attacked. Typical acid solutions are from about 0.01 N to about 10 N.
The final zeolitic product will have a smaller crystal lattice and a higher silica:alumina mole ratio than is normally obtained. Steamed, dealuminated zeolite will typically have a cubic cell constant less than about 24.40 Angstroms and a silica-alumina mole ratio greater than about 10:1, and most preferably greater than about 20:1. The final dealuminated product will also have a higher surface area than the starting material. The steaming/calcining treatment surprisingly also improves the catalytic characteristics of ultrastable Y zeolites.
Even though the alumina content of the steamed/leached faujasitic zeolites is very low compared to the starting materials, they retain surprising activity and they gain significant selectivity for the valuable middistillates.
The final catalyst composite includes both the faujasitic zeolite and an inorgànic oxide matrix. Inor-ganic oxides are standard supports for zeolites used in hydroprocessing and ~an include alumina, silica, magnesia, titania, and combinations thereof. The preferred support is alumina. A wide variety o~ procedures can be used to combine the zeolite with the refractory oxide. For example, the zeolite can be mulled with a hydrogel of the oxide followed by partial drying if required and extruding or pelletizing to form particles of the desired shape.
Alternatively, the refractory oxide can be precipitated in the presence of the zeolite. This is accomplished by increasing the pH of the solution of a refractory oxide precursor such as sodium aluminate or sodium silicate. As -~L2~3~9~

described above, the combination can then be partially dried as desired, tableted, pelleted, extruded, or formed 05 by other means and then calcined, e.y., at a temperature above 600F (316C), usually above 800F (427C).

Processes which produce larger pore size supports are preferred to those producinq smaller pore size su~orts when cogelling. Additionally, if the steamed zeolite is added to an acidic solution of inorganic oxide precursor, the leaching step can be carried out in situ in the cogellation mixture without a separate leaching step.

The catalyst should contain less than about 50, preferably less than about 30 weight percent of the lS zeolite based on the dry weight of zeolite and refractory oxide. However, æeolite content should exceed 0.5 and ls usually above 2 weight percent.

The final catalyst composite includes at least one hydrogenation component. The hydrogenation component is typically a transition or Group IV-A metal, and is usually a Group VI-B or VIII metal or combination of metals or their oxides or sulfides.

The hydrogenation components preferably are molybdenum, tungsten, nickel and cobalt metals, oxides and sulfides. Preferred compositions contain more than about 5 weight percent, preferably about 5 to about ~0 weight percent molybdenum or tungsten or both, and at least about 0.5, and generally about 1 to about 15 weight percent of nickel or cobalt or both, determined as the corresponding oxides. The catalysts are often presulfided before use as sulfide form of these metals tends to have higher activity, selectivity and activity retention.

The hydrogenation components can be added by any one of numerous procedures. They can be added either to the zeolite or the support or a combination of both. In the alternative, ~he Group VIII components can be added to the zeolite by comulling, impregnation, or ion exchange and the Group VI components, i.e., molybdenum and tungsten, can be combined with the refractory oxide by ~ impregnation, comulling or co-precipitation.

~L2~)3~L9I

Ol -6-The hydrogenation components can be incorporated at any one of a number of stages in the catalyst prepara-05 tion. For example, metal compounds such as the sulfides,oxides or water-soluble salts such as ammonium hepta-molybdate, ammonium tungstate, nickel nitrate and cobalt sulfate can be added by comulling, impregnation or preci-pitation to either the zeolite or the refractory oxide or both before the zeolite is finally calcined and combined with the support or after its final calcination but be~ore combination with the refractory oxide. These components can be added to the finished catalyst particle by impreg-nation with an a~ueous or hydrocarbon solution of soluble compounds or precursors.
The hydrocarbonaceous feeds used in these processes boil primarily above about 600F (316~C).
Preferably, at least about ~0 percent of the feed will boil between about 700F (371~) and about 1200F
(649Cj. Feedstocks having these characteristics include gas oils, vacuum gas oils, coker gas oils, deasphalted residua and catalytic cracking cycle stocks. The feed to the hydrocracking zone generally contains at least about 5 ppm and usually between about 10 ppm and Ool weight percent nitrogen as organonitrogen compounds. It can also contain substantial amounts of mono- or polynuclear aromatic compounds corresponding to at least about 5, and generally about 5 to about 40 volume percent aromatics.
Although the catalysts used in these methods exhibit superior stability, activity and midbarrel selec-tivity, reaction conditions must nevertheless be correlated to provide the desired conversion rates while minimizing conversion to less desired lower-boiling products. The conditions required to meet these objec-tives will depend on catalyst activity and selectivity andfeedstock characteristics such as boiling range, as well as organonitrogen and aromatic content and structure.
They will also depend on the most judicious compromise of overall activity, i.e., conversion per pass and selec-tivity. For example, these systems can be operated at 12~3~ ~

01 ~7~
relatively high conversion rates on the order of 70, ~0 oreven 90 percent conversion per pass. However, higher 05 conversion rates generally result in lower selectivity.
Thus, a compromise must be drawn between conversion and selectivity. The balancing of reaction conditions to achieve the desired objectives is part of the ordinary skill of the art.
1~ Reaction temperatures generally exceed about 500F (260C) and are usually above about 600F (316C), preferably between 600F (316C) and 900F (482C).
Hydrogen addition rates should be at least about ~00, and are usually between about 2,000 and about 15,000 standard cubic feet per barrel. Reaction pressures exceed 200 psig (13.7 bar) and are usually within the range of about 500 to about 3000 ~sig (32.4 to 207 bar). Liquid hourly space velocities are less than about 15, preferably between a~out 0.2 and about 10.
The overall convèrsion rate is primarily controlled by reaction temperature and liquid hourly space velocity. However, selectivity is generally inversely proportional to reaction temperature. It is not as severely affected by reduced space velocities at otherwise constant conversion. Conversely, selectivity is usually improved at higher pressures and hydrogen addition rates.
Thus, the most desirable conditions for the conversion of a specific feed to a predetermined product can be best obtained by converting the feed at several different temperatures, pressure, space velocities and hydrogen addition rates, correlating the effect of each of these variables and selecting the best compromise of overall conversion and selectivity.
The conditions should be chosen so that the overall conversion rate will correspond to the production of at least about 40 percent, and preferably at least about 50 percent of products boiling below about 700F
(371C) per pass. Midbarrel selectivity should be such that at least about 40, preferably at least about 50 percent of the product is in the middistillate range.

~2S)3~9~

Ol -8-The process can maintain conversion levels in excess of about 50 percent per pass at selectivities in excess of 60 05 percent to middistillate products boiling between 400F
(204C) and 700F (371C).
My process can be operated as a single-stage hydroprocessing zone. It can also be the second stage of a two-stage hydrocracking scheme in which the first stage l~ removes nitrogen and sulfur from the feedstock before contact with the middistillate-producing catalyst. My process can also be the first stage of a multistep hydrocracking scheme. In operation as the first stage, the middistillate-producing zone also denitrifies and desulfurizes the feedstock; in addition, it allows the second stage to operate more efficiently so that more middistillates are produced overall than in other process configurations, This method of operating with the middistillate-producing zone first~ followed by at least one further hydroprocessing zone is especially preferred for increasing middistillate production.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. l illustrates the difference in ~ouling rate and activity between a standard amorphous catalyst used to produce middistillates and the catalyst used in my invention.
FIG. 2 illustrates the effect of the amount of acid used in the leaching solution on the silica:alumina mole ratio of the zeolite.
FIG. 3 illustrates the effect of the amount of acid used in the leaching solution on the crystallinity of the product zeolite as compared to the reactant steamed zeolite.
FIGS~ 4, 5, and 6 illustrate the superiority of my invention in producing middis~illate. Catalysts con-taining steamedjleached, steamed, and untreated ultra-stable Y zeolites were contrasted. FIG. 4 illustrates the higher middistillate diesel yields of the steamed/leached catalyst; FIG. 5 illustrates the lower heavy naphtha 4~ yields of the steamed/leached catalyst; and FIG. 6 ~2()3~9~

_9_ illustrates the lower aromatics content of the middis-tillate produced by the steamed/leached catalyst. The 05 yields are plotted against conversion to below 670F
(354C).
FIG. 7 contrasts the pore size distribution of a steamed and steamed/leached Y zeolite.
Example 1 A catalyst containing steamed, leached Y zeolite was compared to a nickel-tungsten, nonzeolitic catalyst ~silica/alumina/titania cogel base) used to prepare mid-distillates to compare activity and fouling rates. The zeolitic catalyst contained 15 weight percent zeolite steamed at 1475F (802C) for 1 hour and washed with 1 N
hydrochloric acid. The zeolite was mulled with alumina and had a final metals content of 3.9 weight percent nickel and 20.5 weight percent tungsten. The feed was a straight-run Arabian Heavy gas oil having the following characteristics:

AP~ 21.8 Aniline Pt. 173F (78C) S, Wt. % 2.62 N, ppm 846 Distillation (D-1160), C:
St/5 332 / 388 ~51 70/90 468 / 4g9 Reaction conditions included an LHSV of 0.75; 1400 psig (96.5 bar); and 5000 SCF H2/bbl feed. The results are shown in FIG. 1. The zeolitic catalyst is significantly more active with a significantly lower fouling rate than the nonzeolitic catalystO

3~L9~

Example 2 A series of experiments was performed to examine OS the effect o~ acid washing on silica:alumina mole ratio and product zeolite crystallinity. The starting material was NH4y having a sodium content of less than 1 percent and a silica:alumina mole ratio of S.l:l. The zeolite was steamed for 1 hour at 800C and then acid washed. The washing solutions ~lere prepared on the basis of volumes of concentrated hydrochloric acid per gram of the zeolite (0.8 ml concentrated HCl i5 the stoichiometric amount of acid required to raise the Sio2/Al2o3 mole ratio from 5:1 to 30:1), the measured acid was then diluted to about 1.1 lS M or 8.5 M and the zeolite was washed ~ith the resulting solution. The silica:alumina mole ratio was determined by neutron activation analysis; percent crystallinity was measured as percent X-ray diffraction intensity relative to Na-Y. As can be seen from FIGS. 2 and 3, Sio2/Al2o3 mole ratio and percent crystallinity appear to vary linearly and unexpectedly with the amount of acid used to prepare the wàshing solution rather than with the strength of the washing solution~ It is preferred to retain at least 50 percent crystallinity measured as percent X-ray

2~ diffraction intensity relative to Na-Y in the product as compared to the starting material.
Example 3 A series of experiments was performed to compare the products obtained with different zeolitic hydrocrack-ing catalysts. ~atalysts A and B were steamed for 1 hourat 800C and Catalyst B was leached with 1 N hydrochloric acid to remove the alumina debris. The zeolites were composited with alumina by comulling and then extruded.
The extrudate was impregnated with the hydrogenation 3S metals using standard procedures. The catalysts had the following characteristics:

1~13~91 Catalyst A B C
Zeolite Steamed Steamed/ Ultra-05 Ultra- Dealuminatedstable Y
stable Y Ultra-stable Y
Wt. ~ Zeolite 15 15 15 Wt. ~ Ni 6.9 4.0 3.4 Wt. % W 17.2 21.0 20.0 Cell Constant, A 24.44 24O36 24.58 SiO2:A12O3 5:1 2901 5:1 The catalysts were tested in a one-step hydrocracking process using a straight-run Arabian Light vacuum gas oil feed having the foilowing characteristics:

API 22.9 Aniline Pt., F (C) 177.5 (81C) Sr weight percent 2.15 N, ppm 877 Distillation (D-1160), C:
St/5 339 / 374 Reaction conditions included an LHSV of 1.2; 1470 psig H2 (101 bar); and 5000 SCF/bbl feed recycle gas.
The highly desirable product characteristics produced by my process are illustrated in FIGS~ 4, 5, and 6. The steamed/leached zeolite produces significantly more middistillate ( FIGo 4) of lower aromatics content (FIG~ 6) than the steamed and untreated Y zeolite.
Additionally, cracking of the feed to naphtha-range materials occurs to a significantly lower extent (FIG~ 5) with the steamed/dealuminated zeolite catalyst.

1~319~

Example 4 A steamed (1375F; 746C) Y zeolite having a 05 silica~alumina mole ratio of 5.1:1 was washed with an approximately 1 M ~Cl solution (0.7~ cc concentrated HCl/g zeolite). The leached product had a silica:alumina mole ratio of 9.6:1. The pore size distributions for both materials (relative pore volume dV/d (log d) as a function of pore diameter) are contrasted in FIG. 7.

2~

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for selectively producing middistillate hydrocarbons, comprising:
(a) contacting under hydrocracking conditions a hydrocarbonaceous feed boiling above about 600°F (316°C) with a catalyst comprising a hydrogenation component and an expanded pore zeolite which consists of a faujasitic zeolite which has been steamed then dealuminated; and (b) recovering a hydrocarbonaceous effluent of which more than about 40 percent by volume boils above about 300°F (149°C) and below about 700°F (371°C).

2. The process of Claim 1 wherein said faujasitic zeolite is a Y zeolite.

3. The process of Claim 2 wherein said faujasitic zeolite is an ultrastable Y zeolite.

4. The process of Claim 3 wherein said faujasitic zeolite has a sodium oxide content of less than about 0.5 wt. %.

5. The process of Claim 2, 3, or 4 wherein said expanded pore zeolite has a cubic cell constant less than about 24.40 Angstroms and a silica to alumina mole ratio greater than about 10:1.

6. The process of Claim 1 wherein said silica to alumina mole ratio is greater than about 20:1.

7. The process of Claim 1 wherein said expanded pore zeolite contains less than about 200 ppm by weight of alkali metal oxide.

8. The process of Claim 1, 2, or 3 wherein said faujasitic zeolite is dealuminated by contacting said faujasitic zeolite with an acid at a pH less than about 2.

9. The process of Claim 1 wherein said faujasitic zeolite is steamed at a temperature above about 1000°F (538°C) for more than about 1 hour.

10. The process of Claim 9 wherein said steaming is stagnant.

11. The process of Claim 1 wherein said hydrogenation component is a nickel, cobalt, molybdenum, or tungsten com-pound, or mixtures thereof, and said catalyst further comprises an inorganic oxide matrix.

12. The process of Claim 11 wherein said matrix is alumina.

13. The process of Claim 1 wherein said feed boils above about 700°F (371°C) and more than about 40 percent by volume of said effluent boils above about 400°F (204°C) and below about 700°F (371°C).

14. The process of Claim 13 wherein said feed is a gas oil.

15. The process of Claim 1 further comprising the step of (c) hydrocracking at least part of said hydrocarbonaceous effluent.