A PROCESS FOR PREPARING LOW POUR MIDDLE DISTILLATES AND LUBE OIL USING A CATALYST CONTAINING A SILICOALUMINOPHOSPHATE MOLECULAR SIEVE
BACKGROUND OF THE INVENTION
The present invention relates to a process for preparing low pour point middle distillate hydrocarbons and lube oil. More specifically, the invention relates to a hydrocracking and isomerization process for selectively preparing low pour point middle distillate hydrocarbons and lube oil from a hydrocarbonaceous feedstock boiling above about 600βF by contacting the feedstock with a catalyst comprising an intermediate pore size silicoaluminophosphate molecular sieve and a hydrogenation component.
DESCRIPTION OF THE PRIOR ART
Hydrocracking, used either in a one-step process or in a multi-step process coupled with hydrodenitrogenation and/or hydrodesulfurization steps, has been used extensively to upgrade poor-quality feeds and produce middle distillate materials. Over the years, much work has been done to develop improved cracking conditions and catalysts. Tests have been carried out using catalysts containing only amorphous materials and catalysts containing zeolites composited with amorphous materials.
Large pore size zeolites such as zeolites X and Y are presently considered the most active hydrocracking catalysts. However, high activity is not the only essential characteristic of midbarrel cracking in catalysts. Midbarrel selectivity, namely, the percentage of total conversion accounted for by products boiling within the
SUBSTITUTE SHEET
midbarrel range of from about 300°F to about 725°F is also important. As noted in U.S. Patent No. 3,853,742, many commercial midbarrel hydrocracking processes do not use zeolitic catalysts due to their relatively low midbarrel selectivity.
Also, middle distillates conventionally serve as fuels such as diesel oils, jet fuels, furnace oils, and the like. For convenience in the handling and use of these middle distillates, it is desirable for the pour point to be as low as practical consistent with the temperatures to which they may be exposed. Specifications for these products often include a requirement that the pour point or freeze point not exceed a certain maximum value. In some instances, it is necessary to subject these distillate fuels to additional processing, the principle purpose of which is to reduce the pour point of the feed stream. Pour point can also be lowered by lowering the distillate end point, however this reduces yield.
As noted in U.S. Patent No. 4,486,296, although zeolite catalysts have been employed in hydrocracking processes and may be effective in providing distillate yields having one or more properties consistent with the intended use of the distillate, these catalysts suffer the disadvantage of providing product yields that do not have good low temperature fluidity characteristics, particularly reduced pour point and viscosity.
The prior art has utilized a separate dewaxing process to reduce the pour point of middle distillates wherein selective intermediate pore size zeolites such as ZSM-5 (U.S. Patent No. RE. 28,398), and ZSM-23 (European Patent Application No. 0092376) are employed.
Other methods in the art for producing middle distillates possessing acceptable viscosity and pour point properties include processes wherein the hydrocarbon feeds are concurrently or sequentially subjected to hydrocracking and dewaxing in a continuous process using a large pore size zeolite hydrocarbon cracking catalyst such as zeolite X or zeolite Y and an intermediate pore size zeolite dewaxing catalyst such as ZSM-5 (U.S. Patent No. 3,758,402).
These processes have two drawbacks. The first is that while the pour point is reduced, the viscosity is increased, possibly above acceptable limits. The second drawback is that the process operates by cracking wax primarily to light products (e.g., ,-C4) thereby significantly reducing distillate yield. PCT International Application WO86/03694 discloses a hydrocracking process to produce high octane gasoline using a catalyst comprising silicoaluminophosphates, either alone or in combination with traditional hydrocracking catalysts such as zeolite aluminosilicates.
As set forth in co-pending application Serial No. 07/002,087, applicant has discovered that middle distillate products can be selectively produced in a simplified process over a single catalyst in high yields which exhibit reduced pour points and viscosities as compared to prior art processes. Applicant has found that heavy hydrocarbon oils may be simultaneously hydrocracked and hydrowaxed to produce a midbarrel liquid product of improved yield and satisfactory pour point and viscosity by using a catalyst containing an intermediate pore size silicoaluminophosphate molecular sieve component and a hydrogenation component to promote isomerization.
High-quality lubricating oils are critical for the machinery of modern society. Unfortunately, the supply of natural crude oils having good lubricating properties, e.g., Pennsylvania and Arabian Light feedstocks, is not enough to meet present demands. Additionally, because of uncertainties in world crude oil supplies, it is necessary to be able to produce lubricating oils efficiently from ordinary crude feedstocks.
Numerous processes have been proposed to produce lubricating oils by upgrading the ordinary and low-quality stocks which ordinarily would be converted into other products.
The desirability of upgrading a crude fraction normally considered unsuitable for lubricant manufacture into one from which good yields of lube oils can be obtained has long been recognized. Hydrocracking processes have been proposed to accomplish such upgrading. U.S. Patent Nos. 3,506,565, 3,637,483 and 3,790,472 teach hydrocracking processes for producing lubricating oils.
Hydrocracked lubricating oils generally have an unacceptably high pour point and require dewaxing. The bottoms from distilling the hydrocracked product are generally recycled back to the hydrocracker for further conversion to lower boiling products. It would be of utility if the hydrocracking process produced a distillation bottoms fraction of low pour point and high viscosity index which could therefore be used as a lube oil.
Solvent dewaxing is a well-known and effective process but is expensive. More recently, catalytic methods for dewaxing have been proposed. U.S. Patent No. Re. 28,398 discloses dewaxing petroleum charge stocks using ZSM-5 type zeolites.
U.S. Patent No. 3,755,145 discloses a process for preparing low pour point lube oils by hydrocracking a lube oil stock using a catalyst mixture comprising a conventional cracking catalyst and ZSM-5.
It has also been suggested that in order to improve the oxidation resistance of lubricants it is often necessary to hydrogenate or hydrofinish the oil after hydrocracking, with and without catalytic dewaxing as illustrated in U.S. Patent Nos. 4,325,805; 4,347,121; 4,162,962; 3,530,061; and 3,852,207. U.S. Patents Nos. 4,283,272 and 4,414,097 teach continuous processes for producing dewaxed lubricating oil base stocks including hydrocracking a hydrocarbon feedstock, catalytically dewaxing the hydrocrackate and hydrofinishing the dewaxed hydrocrackate. These patents teach the use of catalysts comprising zeolite ZSM-5 and ZSM-23, respectively, for the dewaxing phase.
European Patent Application No. 225,053 discloses a process for producing lubricant oils of low pour point and high viscosity index by partially dewaxing a lubricant base stock by isomerization using a large pore, high silica zeolite dewaxing catalyst followed by a selective dewaxing step.
The prior art does not provide a process whereby both low pour mid-distillate hydrocarbons and lube oil can be prepared in the same reactor.
Generally, the high boiling bottoms from distilling the hydrocracked product are high in pour point and therefore are of limited value without further processing. These bottoms therefore are generally recycled back to the hydrocracker for further conversion to lower boiling products. It would be of utility if the hydrocracking
process were to produce a distillation bottoms fraction of low pour point and high viscosity index which could therefore be used as a lube oil.
SUMMARY OF THE INVENTION
The present invention overcomes the disadvantages of the prior art by providing a process for simultaneously preparing low pour and freeze point mid-distillate hydrocarbons and low pour point lube oil base stock in the same reactor.
It is an object of the invention to provide a process for preparing both low pour mid-distillates and lube oil base stock wherein the amount of bottoms recycled is reduced or eliminated thereby providing increased throughput.
It is a further object of the invention to provide a process for producing low pour middle distillate hydrocarbons and low pour, high viscosity index lube oil in the same reactor.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by means of the instrumentalities and combinations, particularly pointed out in the appended claims.
To achieve the objects and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a process for selectively preparing low pour middle distillate hydrocarbons and low pour, high viscosity index, low viscosity lube oil comprising
SUBSTITUTE SHEET
(a) contacting under hydrocracking conditions a hydrocarbonaceous feed wherein at least about 90% of said feed has a boiling point greater than about 600°F, with a catalyst comprising an intermediate pore size silicoaluminophosphate molecular sieve and at least one hydrogenation component; (b) recovering a hydrocarbonaceous effluent wherein greater than about 40% by volume of said effluent boils above 300°F and below from about 675°F to about 725°F and has a pour point below about 0βF; and (c) distilling the hydrocarbonaceous effluent to produce a first fraction containing middle distillate products having a boiling point below from about 675°F to about 725°F, and a second fraction containing a lube oil having a boiling point above about 700°F.
In the process of the invention, the hydrocarbon feedstock is contacted with the intermediate pore size silicoaluminophosphate molecular sieve catalyst under conversion conditions appropriate for hydrocracking. During conversion, the aromatics and naphthenes present in the feedstock undergo hydrocracking reactions such as dealkylation, ring opening, and cracking, followed by hydrogenation. The long-chain paraffins present in the feedstock undergo mild cracking reactions to yield non-waxy products of higher molecular weight than products obtained using prior art dewaxing zeolitic catalysts such as ZSM-5. At the same time, a measure of isomerization occurs so that not only is the pour point reduced by the cracking reactions described above, but in addition, the n-paraffins become isomerized to isoparaffins to form liquid-range materials which contribute to low viscosity, low pour point products. In the bottoms portion of the effluent, a measure of hydrocracking and isomerization takes place which contributes not only to the low pour point and viscosity of
the lube oil base stock but also to its high viscosity index, since isoparaffins are known to have high viscosity indices.
The process of the invention enables heavy feedstock, such as gas oils, boiling above about 600°F to be more selectively converted to middle distillate range products having improved pour points than prior art processes using large pore catalysts, such as zeolite Y. Further, in the process of the invention, the consumption of hydrogen will be reduced even though the product will conform to the desired specifications for pour point and viscosity. Further, the process of the invention provides bottoms having a low pour point, low viscosity and high viscosity index which are suitable for use as lube oil.
In comparison with prior art dewaxing processes using shape selective catalysts such as zeolite ZSM-5, the yields of the process of the invention will be improved and the viscosity kept acceptably low. The latter is ensured because the bulk conversion involves not only the cracking of low viscosity paraffins but high viscosity components (e.g., multi-ring naphtheneε) as well. In addition, unlike the prior art ZSM-5 catalyst, the process of the invention provides low pour point middle distillates and high viscosity index lube oil base stock due to a measure of isomerization which produces isoparaffins which contribute not only to the low pour point and viscosity, but also to the high viscosity index in the bottoms. Thus, the present process is capable of effecting boil conversion together with simultaneous dewaxing. It is also possible to operate at partial conversion, thus effecting economies in hydrogen consumption while still meeting pour point and viscosity requirements.
Overall, the present process reduces or eliminates the amount of bottoms recycled, thereby increasing throughput.
The accompanying drawings, which are incorporated in and constitute a part of this specification illustrate several exemplary embodiments of this invention and together with the description, serve to explain the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a ternary diagram showing the compositional parameters of the silicoaluminophosphates of U.S. Patent No. 4,440,871 in terms of mole fractions of silicon, aluminum and phosphorous.
FIG. 2 is a ternary diagram showing the preferred compositional parameters of the silicoaluminophosphates in terms of mole fraction so silicon, aluminum, and phosphorous.
FIG. 3 is a graph showing a comparison for a crystalline silicoaluminophosphate catalyst used in the process of this invention and a sulfided cogelled nickel-tungsten-silica-alumina catalyst with respect to yields.
FIG. 4 is a graph showing a comparison for a crystalline silicoaluminophosphate catalyst used in the process of this invention and a ZSM-5 catalyst with respect to yields.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Reference will now be made in detail to the preferred embodiments of applicant's invention.
FEEDSTOCKS
The feedstock for the process of the invention comprises a heavy hydrocarbon oil such as a gas oil, coker tower bottoms fraction, reduced crude, vacuum tower bottoms, deasphalted vacuum residε, FCC tower bottoms, or cycle oils. Oils of this kind generally boil above about 600°F (316°C) although the process is also useful with oils which have initial boiling points as low as 436°F (260°C). Preferably, at least 90% of the feed will boil above 600°F (316°C). Most preferably, at least about 90% of the feed will boil between 700°F (371°C) and about 1200°F (649°C). These heavy oils comprise high molecular weight long-chain paraffins and high molecular weight ring compounds with a large proportion of fused ring compounds. During processing, both the fused ring aromatics and naphthenes and paraffinic compounds are cracked by an intermediate pore size silicoaluminophosphate molecular sieve catalyst to middle distillate range products. A substantial fraction of the paraffinic components of the initial feedstock also undergo conversion to isoparaffins.
The process is a particular utility with highly paraffinic feeds because with such feeds, the greatest improvement in pour point may be obtained. The degree of paraffinicity will depend to some degree on the viscosity index desired in the product. For example, when the paraffinic content is greater than about 50% by weight, a viscosity index of at least about 130 can be obtained. The higher the paraffinic
content, the higher the viscosity index. Preferably, the paraffinic content of the feed employed is greater than about 20% by weight, more preferably greater than about 40% by weight. The* most preferable paraffinic content of the feed will be determined by the viscosity index requirements of the product.
The feedstocks employed in the process of the present invention may be subjected to a hydrofining and/or hydrogenation treatment, which may be accompanied by some hydrocracking, prior to use in the present process.
SILICOALUMINOPHOSPHATE MOLECULAR SIEVE CATALYSTS
As set forth above, the process of the invention combines elements of hydrocracking and isomerization. The catalyst employed in the process has an acidic component and a hydrogenation component. The acidic component comprises an intermediate pore size silicoaluminophosphate molecular sieve which is described in U.S. Patent No. 4,440,871, the pertinent disclosure of which is incorporated herein by reference.
Among other factors, the present invention is based on my discovery that the use of a catalyst containing an intermediate pore size molecular sieve and a Group VIII metal in a hydrocracking and isomerization reaction of hydrocarbonaceous feeds boiling above about 600°F results in unexpectedly high yields of middle distillates and lube oil base stock having excellent pour point characteristics.
The most preferred intermediate pore size silicoaluminophosphate molecular sieve for use in the process of the invention is SAPO-11. When combined with a
hydrogenation component, the SAPO-11 produces a midbarrel liquid product and a lube oil base stock of improved yields and satisfactory pour point and viscosity.
SAPO-11 comprises a silicoaluminophosphate material having a three-dimensional micropours crystal framework structure of [PO-], [AlO-] and [Si02l tetrahedral units whose unit empirical formula on an anhydrous basis is:
mR:(SiχAlyPz)02 (I)
wherein "R" represents at least one organic templating agent present in the intracrystalline pore system; "m" represents the moles of "R" present per mole of (Si Al P O. and has a value of from zero to about 0.3, "x", "y" and "z" represent respectively, the mole fractions of silicon, aluminum and phosphorus, said mole fractions being within the compositional area bounded by points A, B, C, D and E on the ternary diagram of FIG. 1 or preferably within the area bounded by points a, b, c, d and e on the ternary diagram of FIG. 2. The silicoaluminophosphate molecular sieve has a characteristic X-ray powder diffraction pattern which contains at least the d-spacings (as-synthesized and calcined) set forth below in Table I. When SAPO-11 is in the as-synthesized form, "m" preferably has a value of from 0.02 to 0.3.
TABLE I
All of the as-synthesized SAPO-11 compositions for which X-ray powder diffraction data have been obtained to date have patterns which are within the generalized pattern of Table II below.
SUBSTITUTESHEET
TABLE II
Another intermediate pore size silicoaluminophosphate molecular sieve preferably employed in the process of this invention is SAPO-31. SAPO-31 comprises a silicoaluminophosphate material having a three-dimensional microporous crystal framework of _PO~_, [AlO~] and [SiO.]
1 tetrahedral units whose unit empirical formula on an 2 anhydrous basis is: 3 4 mR:(SiχAlyPz)02 5 6 wherein R represents at least one organic templating agent 7 present in the intracrystalline pore system; "m" represents 8 the moles of "R" present per mole of (SixAlyPz)0_<fa, and has a 9 value of from zero to 0.3, "x", "y" and "z" represent 0 respectively, the mole fractions of silicon, aluminum and 1 phosphorus, said mole fractions being within the 2 compositional area bounded by points A, B, C, D and E on the 3 ternary diagram of FIG. 1, or preferably within the area 4 bounded by points a, b, c, d and e on the ternary diagram of
15 FIG. 2. The silicoaluminophosphate has a characteristic
16 X-ray powder diffraction pattern (as-synthesized and
17 calcined) which contains at least the d-spacings set forth
18 below in Table III. When SAPO-31 is in the as-synthesized
19 form, "m" preferably has a value of from 0.02 to 0.3. 20
21 TABLE III
22
23 Relative
24 2Θ intensity 2 255 8.5-8.6 10.40-10.28 m-s 26 20.2-20.3 4.40-4.37 m
21.9-22.1 4.06-4.02 w-m
27 22.6-22.7 3.93-3.92 vs
28 31.7-31.8 2.823-2.814 w-m
29
30 All of the as-synthesized SAPO-31 compositions for which
__. X-ray powder diffraction data have presently been obtained __ have patterns which are within the generalized pattern of __ Table IV below.
34
1 TABLE IV
02
03 2Θ d 100 x I/I
04
05 0_!
06 60-72
07 7-14 1-4 0 088 1-2 09 1-8
2-4 1 100 2-3
44-55 11 6-28 1 122 32-38 13 100 2-20 1144 3-4 15 2-3 1-4 1166 8-10 17 0-2 4-5 1188 15-18 19 0-3
5-8 2 200 1-2 21 1-2
2-4 2 222 2-3 23 1
1 2 244 1-2 25 1
2
26 1
* Possibly contains peak from a minor impurity. 29 30
SAPO-41, an intermediate pore size silicoaluminophosphate 31 molecular sieve, also preferred for use in the process of 32 the invention, comprises a silicoaluminophosphate material 33 34 having a three-dimensional micropours crystal framework
structure of [PO-], [AlO-l and [SiO-l tetrahedral units whose unit empirical formula on an anhydrous basis is:
mR: ( SiχAlyPz )02
wherein "R" represents at least one organic templating agent present in the intracrystalline pore system; "m" represents the moles of "R" present per mole of (SixAly,Pz)0 Λ_,t and has a value of from zero to 0.3; "x" , "y" , and "z" represent respectively, the mole fractions of silicon, aluminum and phosphorus, said mole fractions being within the compositional area bounded by points A, B, C, D and E on the ternary diagram of FIG. 1, or preferably within the area bounded by points a, b, c, d and e on the ternary diagram of FIG. 2, said silicoaluminophosphate having a characteristic X-ray powder diffraction pattern (as-synthesized and calcined) which contains at least the d-spacings set forth below in Table V. When SAPO-41 is in the as-synthesized form, " " preferably has a value of from 0.02 to 0.3.
TABLE V
Relative
2Θ d Intensity L 13.6-13.8 6.51-6.42 w-m 20.5-20.6 4.33-4.31 w-m 21.1-21.3 4.21-4.17 vs 22.1-22.3 4.02-3.99 m-s 22.8-23.0 3.90-3.86 m 23.1-23.4 3.82-3.80 w-m 25.5-25.9 3.493-3.44 w-m
All of the aε-εyntheεized SAPO-41 compositions for which X-ray powder diffraction data have presently been obtained have patterns which are within the generalized pattern of Table VI below.
TABLE VI
2Θ
The above silicoaluminophosphates are generally syntheεized by hydrothermal crystallization from a reaction mixture comprising reactive sources of silicon, aluminum and phosphorus, and one or more organic templating agents. Optionally, alkali metal(s) may be present in the reaction mixture. The reaction mixture is placed in a sealed pressure vessel, preferably lined with an inert plastic material, such as polytetrafluoroethylene, and heated, preferably under autogenous presεure at a temperature of at leaεt about 100°C, and preferably between 100°C and 250βC, until crystalε of the silicoaluminophosphate product are obtained, usually for a period of from two hours to two weeks. While not eεsential to the synthesis of SAPO compositions, it has been found that in general, stirring or other moderate agitation of the reaction mixture and/or seeding of the reaction mixture with seed crystals of either
the SAPO to be produced or a topological similar composition, facilitates the crystallization procedure. The product is recovered by any convenient method such as centrifugation or filtration.
After crystallization the SAPO may be isolated and washed with water and dried in air. As a result of the hydrothermal crystallization, the as-synthesized SAPO contains within its intracrystalline pore system at least one form of the template employed in its formation. Generally, the template is a molecular species, but it is possible, steric considerations permitting, that at least some of the template is present as a charge-balancing cation. Generally, the template is too large to move freely through the intracrystalline pore syεtem of the formed SAPO and may be removed by a poεt-treatment process, such as by calcining the SAPO at temperatureε of between about 200°C and about 700°C εo as to thermally degrade the template, or by employing some other post-treatment process for removal of at least part of the template from the SAPO. In some instanceε the poreε of the SAPO are εufficiently large to permit transport of the template, and accordingly, complete or partial removal thereof can be accompliεhed by conventional deεorption procedureε such as are carried out in the case of zeoliteε.
The SAPOε are preferably formed from a reaction mixture having a mole fraction of alkali metal cation that is sufficiently low to not interfere with the formation of the SAPO composition. Although the SAPO compositions will form if alkali metal cations are present, reaction mixtures, having the following bulk composition are preferred:
aR20 : ( SiχAl Pz ) 02 : bH20
SUBSTITUTE SHEET
wherein "R" is a template; "a" has a value great enough to conεtitute an effective concentration of "R" and iε within the range of from greater than zero to about 3; "b" haε a value of from zero to 500; "x", "y" and "z" repreεent the mole fractions, respectively, of silicon, aluminum and phosphorus wherein x, y and z each have a value of at least 0.01. The reaction mixture is preferably formed by combining at least a portion of the reactive aluminum and phosphoruε εourceε in the εubεtantial abεence of the εilicon source and thereafter combining the resulting reaction mixture comprising the aluminum and phosphoruε εourceε with the εilicon εource. When the SAPOε are εynthesized by this method the value of "m" iε generally above about 0.02.
Though the presence of alkali metal cations are not preferred, when they are present in the reaction mixture, it is preferred to first admix at least a portion of each of the aluminum and phosphoruε εources in the subεtantial absence of the εilicon εource. Thiε procedure avoidε adding the phoεphoruε εource to a highly basic reaction mixture containing the silicon and aluminum source.
The reaction mixture from which these SAPOs are formed contain one or more organic templating agents (templates) which can be most any of those heretofore proposed for use in the synthesiε of aluminosilicates. The template preferably containε at leaεt one element of Group VA of the Periodic Table, more preferably nitrogen or phoεphoruε and most preferably nitrogen. The template contains at least one alkyl, aryl, araalkyl, or alkylaryl group. The template preferably contains from 1 to 8 carbon atoms, although more than eight carbon atoms may be present in the template. Nitrogen-containing templateε are preferred, including amineε and quaternary ammonium compoundε, the latter being
represented generally by the formula R1N+ wherein each R' is an alkyl, aryl, alkylaryl, or araalkyl group; wherein R' preferably contains from 1 to 8 carbon atoms or higher when R' is alkyl and greater than 6 carbon atoms when R' is otherwise. Polymeric quaternary ammonium salts such as I (ci4H32N2^OH^2'x wnerein "x" haε a value of at least 2 may also be employed. The mono-, di- and tri-amines, including mixed amines, may also be employed as templates either alone or in combination with a quaternary ammonium compound or another template.
Representative templates, phosphoruε, aluminum and εilicon εources as well aε detailed process conditions are more fully described in U.S. Patent No. 4,440,871, which is incorporated herein by reference.
The procesε of the invention may also be carried out by using a catalyst comprising an intermediate pore size nonzeolitic molecular sieve containing AlO. and PO-, tetrahedral oxide units, and at least one Group VIII metal. Exemplary suitable intermediate pore size nonzeolitic molecular sieveε are set forth in European Patent Application No. 158,977 which is incorporated herein by reference.
The intermediate pore size molecular sieve is used in admixture with at least one Group VIII metal. Preferably, the Group VIII metal is selected from the group conεiεting of at leaεt one of platinum and palladium, and optionally, other catalytically active metals such as molybdenum, nickel, vanadium, cobalt, tungsten, zinc, and mixtures thereof. More preferably, the Group VIII metal iε εelected from the group conεiεting of at leaεt one of platinum and palladium. The amount of metal rangeε from about 0.01% to
about 10% by weight of the molecular sieve, preferably from about 0.2% to about 5% by weight of the molecular sieve. The techniques of introducing catalytically active metals into a molecular sieve are disclosed in the literature, and preexisting metal incorporation techniques and treatment of the molecular sieve to form an active catalyst such as ion exchange, impregnation or occulεion during εieve preparation are suitable for uεe in the preεent proceεε. Such techniqueε are diεclosed in U.S. Patent Nos. 3,236,761; 3,226,339; 3,236,762; 3,620,960; 3,373,109; 4,202,996; 4,440,781 and 4,710,485 which are incorporated herein by reference.
The term "metal" or "active metal" as uεed herein meanε one or more metalε in the elemental εtate or in εome form such as sulfide, oxide and mixtureε thereof. Regardless of the state in which the metallic component actually exists, the concentrations are computed as if they existed in the elemental εtate.
The physical form of the catalyst depends on the type of catalytic reactor being employed and may be in the form of a granule or powder, and is desirably compacted into a more readily usable form (e.g., larger agglomerates), usually with a silica or alumina binder for fluidized bed reaction, o pills, prills, spheres, extrudates, or other εhapeε of controlled size to accord adequate catalyst-reactant contact. The catalyst may be employed either as a fluidized catalyst, or in a fixed or moving bed, and in one or more reaction εtageε.
The intermediate pore εize molecular sieve can be manufactured into a wide variety of physical forms. The molecular sieves can be in the form of a powder, a granule,
(—* . tr-* -*t.-**-|- "
or a molded product, such as an extrudate having a particle size sufficient to pass through a 2-mesh (Tyler) screen and be retained on a 40-mesh (Tyler) screen. In cases wherein the catalyst is* molded, such as by extrusion with a binder, the silicoaluminophosphate can be extruded before drying, or dried or partially dried and then extruded.
In a preferred embodiment, the final catalyst will be a composite and includes an intermediate pore size silicoaluminophoεphate molecular εieve, a platinum or palladium hydrogenation metal component and an inorganic oxide matrix. The moεt preferred silicoaluminophosphate iε SAPO-11, the moεt preferred metal component iε palladium and the moεt preferred support iε alumina. A wide variety of procedures can be used to combine the molecular sieve and refractory oxide. For example, the molecular εieve can be mulled with a hydrogel of the oxide followed by partial drying if required and extruding or pelletizing to form particleε of a deεired shape. Alternatively, the refractory oxide can be precipitated in the presence of the molecular sieve. This is accomplished by increasing the pH of the solution of a refractory oxide precursor such aε sodium aluminate or sodium silicate. The combination can then be partially dried as desired, tableted, pelleted, extruded, or formed by other meanε and then calcined, e.g., at a temperature above 600°F (316°C), uεually above 800°F (427°C). Proceεεeε which produce larger pore εize supports are preferred to those producing smaller pore size supports when cogelling.
The molecular sieves may be composited with other materials resistant to temperatures and other conditions employed in the process. Such matrix materials include active and inactive materials and synthetic or naturally occurring
zeoliteε aε well as inorganic materials such as clays, silica and metal oxides. The latter may be either naturally occurring or in the form of gelatinous precipitates, solε or gelε including mixtureε of silica and metal oxides. Inactive materials εuitably εerve aε diluentε to control the amount of conversion in the hydrocracking process so that products can be obtained economically without employing other means for controlling the rate of reaction. The εilicoaluminophoεphate molecular sieve may be incorporated into naturally occurring clays, e.g., bentonite and kaolin. These materials, i.e., clays, oxides, etc., function, in part, aε binderε for the catalyst. It is desirable to provide a catalyst having good crush strength, because in petroleum refining, the catalyst is often subjected to rough handling. This tends to break the catalyst down into powder-like materials which cause problems in procesεing.
Naturally occurring clayε which can be compoεited with the catalyst include the montmorillonite and kaolin families, which familieε include the εub-bentonites, and the kaolins commonly know as Dixie, McNamee, Georgia and Florida clays or others in which the main mineral constituent is halloysite, kaolinite, dickite, nacrite or anauxite. Fibrouε clayε εuch aε halloysite, sepiolite and attapulgite can alεo be uεed as supportε. Such clayε can be uεed in the raw εtate aε originally mined or initially subjected to calcination, acid treatment or chemical modification.
In addition to the foregoing materialε, the molecular εieve can be compoεited with porouε inorganic oxide matrix materialε and mixtureε of matrix materialε εuch aε εilica, alumina, titania, magneεia, εilica-alu ina, εilica-magneεia, εilica-zirconia, εilica-thoria, εilica-beryllia, εilica-titania, titania-zirconia, aε well aε ternary
SUBSTITUTESHEET
compositionε εuch aε εilica-alumina-thoria, silica-alumina-titania, silica-alumina-magneεia and silica-magnesia-zirconia. The matrix can be in the form of a cogel.
The hydrocracking step of the invention may be conducted by contacting the feed with a fixed stationary bed of catalyst, with a fixed fluidized bed, or with a transport bed. A εimple and therefore preferred configuration iε a trickle-bed operation in which the feed is allowed to trickle through a stationary fixed bed, preferably in the presence of hydrogen.
The hydrocracking conditions employed depend on the feed used and the desired pour point. Generally, the temperature is from about 260°C to about 482°C, preferably from about 316°C to about 482°C. The pressure is typically from about 200 pεig to about 3000 psig, preferably from about 500 psig to about 3000 psig. The liquid hourly space velocity (LHSV) is preferably from about 0.05 to about 20, more preferably from about 0.2 to about 10, most preferably from about 0.2 to about 5.
Hydrogen iε preferably present in the reaction zone during the hydrocracking process. The hydrogen to feed ratio is typically from about 500 to about 30,000 SCF/bbl (standard cubic feet per barrel), preferably from about 1,000 to about 20,000 SCF/bbl. Generally hydrogen will be separated from the product and recycled to the reaction zone.
The crystalline catalyst used in the hydrocracking step provides εelective converεion of the waxy components to non-waxy components as well as conversion of 700°F + boiling feed components to middle distillate hydrocarbons. During
SUBSTITUTESHEET
proceεεing, isomerization of the oil occurs to reduce the pour point of the unconverted 700°F+ components below that of the feed and form a lube oil which has a low pour point and excellent viscoεity index.
Becauεe of the εelectivity of the intermediate pore εize molecular εieve uεed in this invention, the yield of product boiling below middle distillate made by cracking is reduced, thereby preserving the economic value of the feedstock.
PROCESS CONDITIONS
Although the catalyst uεed in this method exhibits excellent stability, activity and midbarrel selectivity, reaction conditions must neverthelesε be correlated to provide the deεired converεion rateε while minimizing converεion to leεs desired lower-boiling products. The conditions required to meet these objectives will depend on catalyst activity and selectivity and feedstock characteristics such as boiling range, aε well as organonitrogen and aromatic content and structure. The conditions will also depend on the most judicious compromise of overall activity, i.e., conversion and selectivity. For example, these syεtemε can be operated at relatively high converεion rateε on the order of 70, 80 or even 90% converεion. However, higher converεion rateε generally reεult in lower εelectivity. Thuε, a compromiεe muεt 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.
The overall conversion 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 for pour point reduction of lube oil iε usually improved at lower pressures. 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, pressureε, space velocities and hydrogen addition rates, correlating the effect of each of theεe variables and εelecting the beεt compromiεe of overall converεion and selectivity.
The conditions should be chosen so that the overall conversion rate will correspond to the production of at least about 40%, preferably at least about 50%, of the products boiling below from about 675βF (343°C) to about 725°F (385°C) in the middle distillate range. Midbarrel εelectivity εhould be εuch that at least about 40%, preferably at leaεt about 50% of the product iε in the middle diεtillate range, preferably below from about 675°F to about 725°F and above about 300°F. The proceεε can maintain conversion levels in excess of about 50% at selectivitieε in exceεs of 60% to middle distillate products boiling between 300°F (149°C) and about 675°F (343°C) to about 725°F (385°C). Preferably, the hydrocarbonaceous effluent contains greater than about 40% by volume boiling above about 300°F and below from about 675°F to about 725°F and has a pour point below about 0°F, more preferably below about -20°F. The lube oil produced by the procesε of the invention haε a low pour point, for example, below about 30°F, and a high viscosity index, for example, from about 95 to about 150.
The procesε can be operated as a εingle-εtage hydroprocessing zone. It can alεo be the εecond εtage of a
ITUTE SHEET
two-εtage hydrocracking εcheme in which the firεt εtage removes nitrogen and sulfur from the feedstock before contact with the middle distillate-producing catalyst.
NITROGEN CONTENT OF FEEDSTOCKS
While the process herein can be practiced with utility when the feed contains organic nitrogen (nitrogen-containing impurities), for example as much as several thousand parts per million by weight of organic nitrogen, it is preferred that the organic nitrogen content of the feed be leεε than 50 ppmw, more preferably less than 10 ppmw. Particularly good resultε, in terms of activity and length of catalyst cycle (period between successive regenerations or start-up and first regeneration), are obtained when the feed contains less than 10 ppmw of organic nitrogen. This is surpriεing in view of the art (εee, for example, U.S. Patent No. 3,894,938).
SULFUR CONTENT FEEDSTOCKS
The preεence of organic εulfur (εulfur-containing impuritieε) in the feedεtock does not appear to deleteriously affect the desired hydrocracking of the feed, for example, in terms of activity and catalyst life. In fact, hydrodesulfurization of the feed of organic εulfur iε in large part a εignificant concurrent reaction. However, the reεulting product will uεually contain at leaεt εome thiolε and/or thioetherε aε a reεult of inter-reaction of hydrogen εulfide and olefinic hydrocarbons in the effluent product stream. Thus, it may be deεirable in εome inεtanceε that the feed prior to uεe in the proceεε herein by hydrofined or hydrotreated for at leaεt substantial removal of both organic εulfur- and nitrogen-containing compoundε.
Upstream hydrodenitrogenation can be performed in the reactor with the molecular sieve-containing catalyst or preferably in a separate reactor, when a separate hydrodenitrogenation reactor is used, it may be desirable to remove, e.g., flash, light gaseous products such as NH, upstream of the reactor containing the molecular sieve-containing catalyst. If the hydrotreating is performed in the same reactor, the molecular sieve-containing catalyst is disposed in one or more layers downstream of an active hydrodenitrogenation catalyst. The single reactor should preferably be operated under hydrotreating conditions sufficient to reduce the organic nitrogen of the feed to 10 ppmw or lesε before the feed encounterε the molecular εieve-containing layer. The volume of hydrodenitrogenation catalyεt relative to molecular sieve-containing catalyst can vary over a wide range, such as from about 0.1 to 1 to 20 to 1, preferably at least 0.2 to 1 and more preferably at leaεt 0.5 to 1. The ratio dependε upon εuch parameters as: (a) the organic nitrogen content of the feedstock; (b) the hydrodenitrogenation and hydrocracking activities of the upstream hydrotreating catalyst; and (c) the degree of overall hydrocracking desired.
The upstream hydrotreating catalysts can be any of the conventional catalysts having hydrodenitrogenation and hydrocracking activity. See, for example, U.S. Patent No. 3,401,125 incorporated herein by reference. In general, such hydrotreating catalysts are porous compositeε or inorganic matrix oxideε εuch aε alumina, εilica, and magnesia, which contain one or more hydrogenation componentε εuch as transition elements, particularly elements of Group VIB or Group VIII of the Periodic Table of the Elements. Handbook of Chemistry and Phyεicε, 45th Ed.,
Chemical Rubber Company. The Group VIB and/or Group VIII or other transition elements can be present as metals, oxides, or sulfides. The hydrotreating catalyst can also contain promoters such as phosphorus, titanium and other materials known in the art, present as metals, oxides or sulfides. The upstream hydrotreating catalyst need not contain a silicoaluminophoεphate component. Typical upεtream hydrogenation catalyεtε suitable for uεe herein contain 10 to 30 wt.% amorphous silica, 20 to 40 wt.% amorphous alumina, 15 to 30 wt.% Group VIB metal oxide, such as WO,, 5 to 15 wt.% Group VIII metal oxide, such as NiO and 2 to 15 wt.% of a promoter oxide, such as Ti02. The hydrotreating catalyst should have an average pore εize in the range of about 30 to 200 Angstroms and a surface area of at least about 150 square meters per gram.
Following the hydrocracking step over the silicoaluminophosphate catalyst, the middle diεtillate and lighter boiling products are separated from the lube oil base stock by distillation. It is often desirable to then treat this base stock by mild hydrogenation referred to as hydrofinishing to improve color and produce a more εtable oil. Hydrofiniεhing is typically conducted at temperatures ranging from about 190°C to about 340°C, at pressures from about 400 psig to about 3000 psig, at space velocities (LHSV) from about 0.1 to about 20, and hydrogen recycle rates of from about 400 to about 15,000 SCF/bbl. The hydrogenation catalyst employed must be active enough not only to hydrogenate the olefinε, diolefinε and color bodies within the lube oil fractions, but also to reduce the aromatic content. The hydrofinishing step is beneficial in preparing an acceptably stable lubricating oil.
Suitable hydrogenation catalysts include conventional metallic hydrogenation catalysts, particularly the Group VIII metalε εuch aε cobalt, nickel, palladium and platinum. The metalε are typically associated with carriers such as bauxite, alumina, silica gel, silica-alumina compositeε, and cryεtalline aluminoεilicate zeoliteε. Palladium iε a particularly preferred hydrogenation metal. If desired, non-noble Group VIII metalε can be used with molybdates. Metal oxideε or εulfides can be used. Suitable catalystε are disclosed in U.S. Patent Nos. 3,852,207; 4,157,294; 3,904,513 and 4,673,487, which are incorporated herein by reference.
The high viscoεity index lube oil produced by the process of the present invention can be used as a blending component to raise the viscosity index of lube oils to a higher value. The lube oil is particularly suitable for use aε a blending component when the lube oil has a high viscoεity index, for example, greater than 130. Since yield decreaεeε with increaεing viεcoεity index in either hydrocracking or εolvent refining, the uεe of an ultra-high viεcosity oil to increase the viεcosity index improves yield.
The invention will be further clarified by the following examples, which are intended to be purely exemplary of the invention.
Example 1
SAPO-11 was prepared as described below and identified as such by x-ray diffraction analysis. More specifically, 115.6 g of 85% H,P04 were added to 59 g of H20 and cooled in an ice bath. To this were slowly added 204.2 g of aluminum isopropoxide ( [ (CH, CHO Al) and mixed until homogeneous.
SUBSTITUTESHEET
120 g of H20 were added to 30 g of Cab-O-Sil M-5 silica and the mixture added to the above with mixing until homogeneouε. 45.6 g of di-n-propylamine were then εlowly added with mixing, again until homogeneouε. Syntheεiε waε carried out in a Teflon bottle in an autoclave at 200°C for 5 dayε.
The anyhdrouε molar composition of the calcined sieve was
0.4 Si02:Al203:P205
The εieve was bound with 35% Catapal alumina and made into 1/10-inch extrudate. The extrudate was dried in air for 4 hours at 250°F, then calcined 2 hours at 450°F and 2 hours at 1000°F. The extrudate was then impregnated by the pore-fill method with 0.5 wt.% Pd uεing an aqueouε εolution of Pd(NH,).(NO,)2. The catalyεt waε dried for 2 hourε at 250°F, then calcined in air for two hourε at 450°F and two hourε at 900°F. It waε then crushed to 24-42 mesh.
Example 2
The catalyst of Example 1 was used to hydrocrack a hydrodenitrified vacuum gas oil (Table VII) at 700°F, 2200 psig, 1.3 LHSV, and 8M SCF/bbl once-through H2 at a converεion below 725°F of 60 wt.%, where percent conversion is defined as
wt.% 725°F+(feed)-wt.% 725°F- (product) X 100 wt.% 725°F+(feed)
Inspectionε of the 725°F- productε are given in Table VIII.
Inεpectionε of the 725°F+ productε are given in Table IX, εhowing this oil to have both very high VI and very low pour point.
TABLE VI I
odenitrified Vacuum Gas Oil
38.2 246.4
10 Diεtillation, ASTM D1160, eF
11
,_ ST/5 688/732
12 10/30 751/782
13 50 815
_. _ 70/90 856/928
14 95/EP 966/1024 15
16 TABLE VIII
17 ι o x Inspections of 725°F- Product from Hydrocracking 19 Hydrodenitrified Vacuum Gas Oil over Pd/SAPO-11 at 700°F, 2200 pεig, 1.3 LHSV, and 8M SCF/bbl H2
21 Conversion <725°F, Wt.% 60
22
Product Selectivity, Wt.%
23
'4-. 10.6
24 Cς-230°F 14.0
230-284°F 6.2
25 284-482°F 22.4
26 482-725βF 46.8
27 482-725°F 28
Pour Point, °F -55
29
30 Distillation, D86, LV%, °F
_. ST/10 467/522
31 30/50 572/618
32 70/90 646/673
33 W 7"
34
TABLE IX
Inspectionε of 725°F+ Product from Hydrocracking Hydrodenitrified Vacuum Gaε
Oil over Pd/SAPO-11 at 700°F, 2200 pεig, 1.3 LHSV, 8M SCF/bbl H2 and 60% Converεion <725°F
Pour Point, °F -30
Cloud Point, βF 0 Viεcoεity, St, 40°C 25.76
100°C 5.172 VI 135 Simulated Distillation, LV%, °F ST/5 718/733 10/30 745/784 50 822 70/90 872/963
95/99 1007/1085
Example 3
A. Comparative Example
The hydrodenitrified vacuum gas oil of Table VII was hydrocracked over a sulfided cogelled nickel-tungsten-εilica-alumina catalyεt containing 7.7 wt.% Ni and 19.4 wt.% W. The conditions were a catalyεt temperature of 670°F, a reactor preεεure of 2200 pεig, a liquid hourly εpace velocity (LHSV) of 1.3, and a once-through hydrogen rate of 8 MSCF/bbl. The converεion below 700°F was 56 wt.%, where percent conversion is defined as
Wt.% 7000F- (feed)- Wt.% 700°F-ι-(product) x 100 Wt.% 700°F+(feed)
The liquid product was distilled into fractions boiling in the following ranges: C5~230°F, 230-284°F,
284-482°F, 482-698°F, and 698°F+, where the middle distillate fractions are those with the ranges 284-482°F and 482-698°F. The yields of the 698°F- fractions are shown in FI*G. 3, which showε a dieεel (482-698°F) yield of 36 wt.%. The inεpectionε of the diesel cut are given in Table X below, showing a pour point of +5°F.
SAPO-11 was prepared as described below and identified as such by X-ray diffraction analysis. More specifically, 115.6 g of 85% H,PO. were added to 59 g of H2°" To this were slowly added 204.2 g of aluminum isoproxide ( [CH,)~CHO],A1) and mixed until homogeneous. 8 g of H20 were added to 60.2 g of Ludox AS-30 (30% silica aqueous sol) and the mixture slowly added to the above with mixing until homogeneouε. 45.6 g of di-n-propylamine were then slowly added with mixing, again until homogeneouε. Synthesis was carried out in a Teflon bottle in an autoclave at 150°C for 5 days.
The anhydrous molar composition of the calcined εieve was
0.2SiO2:Al2O3:P2O5
The εieve waε bound with 35% catapal alumina and made into 1/10-inch extrudate. The extrudate waε dried in air for 4 hours at 250°F, then calcined 2 hours at 450°F and 2 hours at 1000°F. The extrudate was then impregnated by the pore-fill method with 0.5 wt.% Pd using an aqueous solution of Pd(NH,) .(NO-. ) ~• The catalyst waε dried for 2 hours at 250°F, then calcined in air for two hours at 450°F and two hours at 900°F. It was then crushed to 24-42 mesh and used to hydrocrack the feed of the above example at 750°F, 2200 psig.
1.0 LHSV, and 8M SCF/bbl once-through H2 to give 44 wt.% conversion below 700°F. Product yields are compared to those for the Comparative Example catalyst in FIG. 3 showing the 482-698°F diesel yield to be 7 wt.% higher. The inεpectionε of the diesel cut are given in Table X below showing a pour point of -40°F.
The catalyst of Example B waε alεo run at 750°F, 1.3 LHSV, 2200 pεig, and 8M SCF/bbl once-through H2 to give 47 wt.% converεion below 725°F. The dieεel end point waε extended from 698°F to 725°F, thereby increaεing dieεel yield another 11 wt.%. Deεpite the higher end point, the pour point waε εtill exceedingly low (-50°F). The inεpections of the diesel cut are given in Table X below.
01 TABLE X
02
03 Dieεel Cut from Hydrocracking
04 Hydrodenitrified Vacuum Gaε Oil
05
06 Catalyεt Ni-W/SiO2-Al203 Pd/SAPO-11 Pd/SAPO-11
07 Conversion, Wt.% 56<700°F 44<700°F 47<725°F
08 c Selectivity, Wt.% 35.8 42.5 53.4
03 09 c I
H 10 Selectivity to Total H Middle Diεtillate, Wt.% 64.7 75.4 77.3 I C 11 H 12 -40 -50
-20 -14
78.7 78.3
16 480/510 481/526
540/572 578/623
17 604/640 647/666
19
20
23
24
Example 4
SAPO-5 was grown according to U.S. Patent No. 4,440,871 and identified aε such by X-ray diffraction analysiε. The. anhydrouε molar compoεition of the calcined εieve waε
0.lSiO2:Al2O,:P2O5
The sieve was extruded with 35% Catapal alumina, impregnated with 0.5 wt.% Pd, and calcined in the same manner as the catalyεt of Example 3B. Thiε catalyεt waε then uεed to hydrocrack the εame vacuum gaε oil at 1.3 LHSV, 2200 pεig, and 8M SCF/bbl once-through H2> At 775°F, the converεion below 725°F waε 51 wt.%. The product yieldε are given in Table XI. The pour point of the 482-725°F dieεel cut waε +48°F.
TABLE XI
To further show the uniquenesε of SAPO-11 in hydrocracking for low pour middle diεtillateε, the following two catalyεtε
were teεted for dewaxing a +100°F pour point lube oil (Table XII) to +30°F pour point at 1 LHSV, 2200 psig, and 8M SCF/bbl H2.
a. 0.8 wt.% Pt impregnated on HZSM-5 bound with 35% Catapal alumina.
b. 1.0 wt.% Pt impregnated on SAPO-11 bound with 35% Catapal alumina.
FIG. 4 shows that while ZSM-5 catalyst dewaxed the feed, it produced eεεentially no 350-800°F liquid, making moεtly C3-350°F. The SAPO-11 catalyεt, on the other hand, produced mainly liquid boiling in the 350-800°F range.
TABLE XII +100°F Pour Point Lube Oil
Gravity, °API 34.0
Aniline Point, °F 244.0 Sulfur, ppm 0.4 Nitrogen, ppm 0.1 Pour Point, °F +100 Viscosity, cS, 100°C 6.195
Flash Point, °F 420 P/N/A/S, LV% 25.0/62.1/12.8/0 Simulated Distillation, LV%, °F
ST/5 313/770
10/30 794/841 50 873 70/90 908/968 95/EP 998/1061