|1.||In a method of cracking a hydrocarbon feed under FCC conditions, wherein a catalyst feed mixture of regenerated used catalyst and fresh catalyst is contacted with the hydrocarbon feed and said fresh catalyst comprises a particulate mixture of zeolite and matrix, the improvement comprising: said fresh catalyst containing at least 1 wt% of an additive comprising zeolite crystallized as a layer on the surface of a porous aluminacontaining matrix, said zeolitelayered matrix arranged in a configuration to provide macropores in which the zeolite layer is provided on the walls of the macropores.|
|2.||The method of claim 1, wherein the matrix of said additive is derived from a kaolin calcined through the exotherm.|
|3.||The method of claim 2, wherein said matrix of said additive is a kaolin calcined through the exotherm without any substantial formation of mullite.|
|4.||The method of claim 2, wherein said matrix of said additive is formed from a kaolin calcined through the exotherm beyond 1, 050° C.|
|5.||The method of claim 1, wherein said crystallized zeolite of said additive is zeolite Y.|
|6.||The method of claim 1, wherein said additive has a mercury porosity of greater than 0.27 cc/gm for pores of 40 20, 000 A diameter.|
|7.||The method of claim 1, wherein said additive has a mercury porosity of at least 0.30 cc/gm for pores of 40 20, OOOA diameter.|
|8.||The method of claim 1 wherein said zeolite of said additive is crystallized insitu on the surface of said matrix.|
|9.||The method of claim 1, wherein said porous matrix of said additive is configured as a planar structure having opposing surfaces, said zeolite being provided as a layer on each of said opposing surfaces.|
|10.||The method of claim 1, wherein said addtive is substantially free of an added binder.|
|11.||The method of claim 4 wherein said matrix of said additive has 2080% of the integrated Xray diffraction peak areas of fully crystalline mullite.|
|12.||The method of claim 1, wherein said additive has a mercury porosity of at least 0.07 cc/gm for pores of 600 20,000 A diameter.|
|13.||The method of claim 11, wherein said additive has a mercury porosity of at least 0.07 cc/gm for pores of 600 20,000 A diameter.|
|14.||The method of claim 1, wherein said additive has a mercury porosity of at least 0.10 cc/gm for pores of 600 20,000 A diameter.|
|15.||The method of claim 1, wherein said additive has a BET surface area of less than 500 m2/g.|
|16.||The method of claim 1, wherein said additive has a BET surface area of less than 475 m2/g.|
|17.||The method of claim 1, wherein said additive has a BET surface area of between about 300450 m2/g.|
|18.||The method of claim 12, wherein said additive has a BET surface area of less than 500 m2/g.|
|19.||The method of claim 13, wherein said additive has a BET surface area of less than 500 m2/g.|
|20.||The method of claim 1, wherein said hydrocarbon feed and said catalyst feed mixture are contacted for a time of no more than 7 seconds.|
|21.||The method of claim 1, wherein said catalyst feed mixture and said hydrocarbon feed are contacted for a time of no more than 3 seconds.|
|22.||The method of claim 1, wherein said fresh catalyst comprises 1 to 50 wt% of said additive.|
|23.||The method of claim 1, wherein said fresh catalyst comprises 10 to 30 wt% of said additive.|
|24.||In a method of cracking a hydrocarbon feed under FCC conditions, wherein a catalyst feed mixture of regenerated used catalyst and fresh catalyst is contacted with the hydrocarbon feed and said fresh catalyst comprises a particulate mixture of zeolite and matrix, the improvement comprising: said fresh catalyst containing at least 1 wt% of an additive comprising microspheres containing insitu crystallized Yfaujasite, and a nonzeolitic matrix, said having a microspheres mercury porosity of greater than about 0.27 cc/g for pores having diameters in the range of 40 20,000 A.|
|25.||The method of claim 24, wherein said microspheres comprise a nonzeolitic, aluminamatrix derived from a kaolin calcined through the characteristic exotherm, said calcined kaolin being derived from a pulverized ultrafine kaolin wherein 90 wt. % of said ultrafine kaolin is in particles having a diameter of less than 2 microns.|
|26.||The method of claim 24, wherein said additive has a mercury porosity of at least about 0.30 cc/g for pores having diameters in the range of 4020,000 A.|
|27.||The method of claim 25, wherein said kaolin has been calcined through its characteristic exotherm with or without formation of mullite.|
|28.||The method of claim 25, wherein said kaolin calcined through its characteristic exotherm has 2080% of the integrated Xray diffraction peak areas of fully crystallized mullite.|
|29.||The method of claim 24, wherein said additive contains 0.512% by weight rare earth oxides.|
|30.||The method of claim 24, wherein said additive has a mercury porosity of at lest 0.07 cc/gm for pores of 600 20,000 A diameter.|
|31.||The method of claim 28, wherein said additive has a mercury porosity of at lest 0.07 cc/gm for pores of 600 20,000 A diameter.|
|32.||The method of claim 24, wherein said additive has a mercury porosity of at lest 0.10 cc/gm for pores of 600 20,000 A diameter.|
|33.||The method of claim 24, wherein said additive has a BET surface area of less than 500 m2/g.|
|34.||The method of claim 24, wherein said additive has a BET surface area less than 475 m2/g.|
|35.||The method of claim 24, wherein said additive has a BET surface area in the range of about 300450 m2/g.|
|36.||The method of claim 30, wherein said additive has a BET surface area of less than 500 m2/g.|
|37.||The method of claim 1, wherein said additive contains rare earth oxides in an amount of from about 0.5 to 12 wt. %.|
|38.||The method of claim 1, wherein said additive contains 3 to 6 wt. % rare earth oxide.|
|39.||The method of claim 24, wherein said additive contains 3 to 6 wt. % rare earth oxide.|
|40.||The method of claim 24, wherein said hydrocarbon feed and said catalyst feed mixture are contacted for a time of no more than 7 seconds.|
|41.||The method of claim 24, wherein said catalyst feed mixture and said hydrocarbon feed are contacted for a time of no more than 3 seconds.|
|42.||The method of claim 24, wherein said fresh catalyst comprises 1 to 50 wt% of said additive.|
|43.||The method of claim 24, wherein said fresh catalyst comprises 10 to 30 wt% of said additive.|
|44.||In a method of cracking a hydrocarbon feed under FCC conditions, wherein a catalyst feed mixture of regenerated used catalyst and fresh catalyst is contacted with the hydrocarbon feed and said fresh catalyst comprises a particulate mixture of zeolite and matrix, the improvement comprising: said fresh catalyst containing at least 1 wt% of an additive comprising microspheres containing insitu crystallized Yfaujasite, and having a mercury porosity of greater than about 0.27 cc/g for pores having diameters in the range of 4020,000 A, said active microspheres comprising: a nonzeolitic, alumina matrix derived from a calcined alumina, said calcined alumina having an incipient slurry point of less than 57% solids.|
|45.||The method of claim 44, wherein said calcined alumina has an incipient slurry point of no more than 52% solids.|
|46.||The method of claim 44, wherein said calcined alumina is derived from a pulverized gray kaolin containing at least about 0.6 wt. % iron oxide.|
|47.||The method of claim 44, wherein said calcined alumina is delaminated kaolin which has been pulverized and calcined.|
|48.||The method of claim 44, wherein said additive has a mercury porosity of greater than 0.30 cc/g for pores having diameters in the range of 4020, 000 A.|
|49.||The method of claim 44, wherein said calcined aluminua is kaolin that has been calcined through its characteristic exotherm with or without the formation of mullite.|
|50.||The method of claim 49, wherein said kaolin calcined through its exotherm has 20 to 80% of the integrated Xray diffraction peak areas of fully crystallized mullite.|
|51.||The method of claim 44, wherein said additive contains 0.512 wt. % rare earth oxides.|
|52.||The method of claim 51, wherein said additive contains 36 wt. % rare earth oxide.|
|53.||The method of claim 44, wherein said additive has a mercury porosity of at lest 0.07 cc/gm for pores of 600 20,000 A diameter.|
|54.||The method of claim 44, wherein said additive has a mercury porosity of at lest 0.10 cc/gm for pores of 600 20,000 A diameter.|
|55.||The method of claim 44, wherein said additive has a BET surface area of less than 500 m2/g.|
|56.||The method of claim 44, wherein said additive has a BET surface area less than 475 m2/g.|
|57.||The method of claim 44, wherein said additive has a BET surface area in the range of about 300450 m2/g.|
|58.||The method of claim 44, wherein said alumina matrix is further derived from a coarse alumina source having an incipient slurry point of greater than 57%.|
|59.||The method of claim 44, wherein said hydrocarbon feed and said catalyst feed mixture are contacted for a time of no more than 7 seconds.|
|60.||The method of claim 44, wherein said catalyst feed mixture and said hydrocarbon feed are contacted for a time of no more than 3 seconds.|
|61.||The method of claim 44, wherein said fresh catalyst comprises 1 to 50 wt% of said additive.|
|62.||The method of claim 44, wherein said fresh catalyst comprises 10 to 30 wt% of said additive.|
Since the 1960's, most commercial fluid catalytic cracking catalysts have contained zeolites as an active component. Such catalysts have taken the form of small particles, called microspheres, containing both an active zeolite component and a non-zeolite component. Frequently, the non-zeolitic component is referred to as the matrix for the zeolitic component of the catalyst. The non-zeolitic component is known to perform a number of important functions, relating to both the catalytic and physical properties of the catalyst. Oblad described those functions as follows: "The matrix is said to act as a sink for sodium in the sieve thus adding stability to the zeolite particles in the matrix catalyst. The matrix serves the additional function of: diluting the zeolite; stabilizing it towards heat and steam and mechanical attrition; providing high porosity so that the zeolite can be used to its maximum capacity and regeneration can be made easy; and finally it provides the bulk properties that are important for heat transfer during regeneration and cracking and heat storage in large-scale catalytic cracking. "A. G. Oblad Molecular Sieve Cracking
Catalysts, The Oil And Gas Journal, 70,84 (March 27, 1972).
In prior art fluid catalytic cracking catalysts, the active zeolitic component is incorporated into the microspheres of the catalyst by one of two general techniques. In one technique, the zeolitic component is crystallized and then incorporated into microspheres in a separate step. In the second technique, the in-situ technique, microspheres are first formed and the zeolitic component is then crystallized in the microspheres themselves to provide microspheres containing both zeolitic and non-zeolitic components.
It has long been recognized that for a fluid catalytic cracking catalyst to be commercially successful, it must have commercially acceptable activity, selectivity, and stability characteristics. It must be sufficiently active to give economically attractive yields, it must have good selectivity towards producing products that are desired and not producing products that are not desired, and it must be sufficiently hydrothermally stable and attrition resistant to have a commercially useful life.
Two products that are particularly undesirable in commercial catalytic cracking processes are coke and hydrogen. Even small increases in the yields of these products relative to the yield of gasoline can cause significant practical problems. For example, increases in the amount of coke produced can cause undesirable increases in the heat that is generated by burning off the coke during the highly exothermic regeneration of the catalyst.
Conversely, insufficient coke production can also distort the heat balance of the cracking process. In addition, in commercial refineries, expensive compressors are used to
handle high volume gases, such as hydrogen. Increases in the volume of hydrogen produced, therefore, can add substantially to the capital expense of the refinery.
U. S. Patent No. 4,493, 902, the teachings of which are incorporated herein by cross-reference, discloses novel fluid cracking catalysts comprising attrition-resistant, high zeolitic content, catalytically active microspheres containing more than about 40%, preferably 50-70% by weight Y faujasite and methods for making such catalysts by crystallizing more than about 40% sodium Y zeolite in porous microspheres composed of a mixture of two different forms of chemically reactive calcined clay, namely, metakaolin (kaolin calcined to undergo a strong endothermic reaction associated with dehydroxylation) and kaolin clay calcined under conditions more severe than those used to convert kaolin to metakaolin, i. e. , kaolin clay calcined to undergo the characteristic kaolin exothermic reaction, sometimes referred to as the spinel form of calcined kaolin. In a preferred embodiment, the microspheres containing the two forms of calcined kaolin clay are immersed in an alkaline sodium silicate solution, which is heated, preferably until the maximum obtainable amount of Y faujasite is crystallized in the microspheres.
In practice of the 902 technology, the porous microspheres in which the zeolite is crystallized are preferably prepared by forming an aqueous slurry of powdered raw (hydrated) kaolin clay (Al203 : 2Si02 : 2H20) and powdered calcined kaolin clay that has undergone the exotherm together with a minor amount of sodium silicate which acts as fluidizing agent for the slurry that is charged to a spray dryer to form microspheres and then functions to provide physical integrity to the components of the spray
dried microspheres. The spray dried microspheres containing a mixture of hydrated kaolin clay and kaolin calcined to undergo the exotherm are then calcined under controlled conditions, less severe than those required to cause kaolin to undergo the exotherm, in order to dehydrate the hydrated kaolin clay portion of the microspheres and to effect its conversion into metakaolin, this resulting in microspheres containing the desired mixture of metakaolin, kaolin calcined to undergo the exotherm and sodium silicate binder.
In carrying out the invention described in the 902 patent, the microspheres composed of kaolin calcined to undergo the exotherm and metakaolin are reacted with a caustic enriched sodium silicate solution in the presence of a crystallization initiator (seeds) to convert silica and alumina in the microspheres into synthetic sodium faujasite (zeolite Y). The microspheres are separated from the sodium silicate mother liquor, ion-exchanged with rare earth, ammonium ions or both to form rare earth or various known stabilized forms of catalysts. The technology of the 902 patent provides means for achieving a desirable and unique combination of high zeolite content associated with high activity, good selectivity and thermal stability, as well as attrition-resistance.
The aforementioned technology has met widespread commercial success. Because of the availability of high zeolite content microspheres which are also attrition- resistant, custom designed catalysts are now available to oil refineries with specific performance goals, such as improved activity and/or selectivity without incurring costly mechanical redesigns. A significant portion of the FCC catalysts presently supplied to domestic and foreign oil refiners is based on this technology. Refineries whose FCC
units are limited by the maximum tolerable regenerator temperature or by air blower capacity seek selectivity improvements resulting in reductions in coke make while the gas compressor limitations make catalysts that reduce gas make highly desirable. Seemingly a small reduction in coke can represent a significant economic benefit to the operation of an FCC unit with air blower or regenerator temperature limitations.
Improvements in cracking activity and gasoline selectivity of cracking catalysts do not necessarily go hand in hand. Thus, a cracking catalyst can have outstandingly high cracking activity, but if the activity results in a high level of conversion to coke and/or gas at the expense of gasoline the catalyst will have limited utility.
Catalytic cracking activity in present day FCC catalysts is attributable to both the zeolite and non-zeolite (e. g., matrix) components. Zeolite cracking tends to be gasoline selective. Matrix cracking tends to be less gasoline selective. After appropriate ion-exchange treatments with rare earth cations, high zeolite content microspheres produced by the in situ procedure described in the 902 patent are both highly active and highly gasoline selective.
As zeolite content of these unblended microspheres is increased, both activity and selectivity tend to increase.
This may be explained by the decrease in matrix content with increase in zeolite content and the decreasingly prominent role of nonselective matrix cracking. Thus, increases in the zeolite content of the high zeolite content microspheres have been reported to be highly desirable.
The activity and selectivity characteristics of the catalysts formed by the process of the 902 patent are achieved even though, in general, the catalysts have
relatively low total porosity as composed to fluid catalytic cracking catalysts prepared by incorporating the zeolite content into a matrix. In particular, the microspheres of such catalysts, in some cases, have a total porosity of less than about 0.15 cc/g. or even less than about 0.10 cc/g. In general, the microspheres of the 902 patent have a total porosity of less than 0.30 cc/g. As used herein,"total porosity"means the volume of pores having diameters in the range of 35-20, OOOA, as determined by the mercury porosimetry technique. The 902 patent noted that it was surprising that microspheres having a total porosity of less than about 0.15 cc/g. exhibit the activity and selectivity characteristics found. For example, such a result is contrary to the prior art disclosures that low pore volumes "can lead to selectivity losses due to diffusional restrictions." It is believed that the relatively low porosity of the catalyst microspheres formed as in the 902 patent does not adversely effect activity and selectivity characteristics, since the microspheres of the 902 patent are not diffusion limited relative to the typical FCC processing conditions which were used at the time of the patent. In particular, catalyst contact time with the feed to be cracked was typically 5 seconds or more. Thus, while typical FCC catalysts formed by mechanically incorporating the zeolite within a matrix may have been more porous, the reaction time in prior art FCC risers did not yield any advantage in activity or selectivity. This result inspired the conclusion that transport processes were not at all limiting in FCC catalysts, at least outside the zeolite structure.
Assertions made to the contrary were inconsistent with the facts and easily dismissed as self-serving. Importantly,
the attrition resistance of the microspheres prepared in accordance with the 902 patent was superior to the conventional FCC catalysts in which the crystallized zeolite catalytic component was physically incorporated into the non-zeolitic matrix.
Recently, however, FCC apparatus have been developed which drastically reduce the contact time between the catalyst and the feed which is to be cracked.
Conventionally, the reactor is a riser in which the catalyst and hydrocarbon feed enter at the bottom of the riser and are transported through the riser. The hot catalyst effects cracking of the hydrocarbon during the passage through the riser and upon discharge from the riser, the cracked products are separated from the catalyst. The catalyst is then delivered to a regenerator where the coke is removed, thereby cleaning the catalyst and at the same time providing the necessary heat for the catalyst in the riser reactor.
The newer riser reactors operate at lower residence time and higher operating temperatures to minimize coke selectivity and delta coke. Several of the designs do not even employ a riser, further reducing contact time to below one second.
Gasoline and dry gas selectivity can improve as a result of the hardware changes. These FCC unit modifications are marketed as valuable independent of the type of catalyst purchased, implying an absence of systematic problems in state of the art catalyst technology.
The processing of increasingly heavier feeds in FCC type processes and the tendency of such feeds to elevate coke production and yield undesirable products have also led to new methods of contacting the feeds with catalyst. The methods of contacting FCC catalyst for very short contact periods have been of particular interest. Thus, short
contact times of less than 3 seconds in the riser, and ultra short contact times of 1 second or less have shown improvements in selectivity to gasoline while decreasing coke and dry gas production. However, higher contact times are more prevalent in older FCC units where the times can be up to 7 seconds but are more typically 5 seconds.
To compensate for the continuing decline in catalyst to oil contact time in FCC processing, the"equilibrium" catalysts in use have tended to become more active. Thus, increases in the total surface area of the catalyst need to be achieved and as well, the level of rare earth oxide promoters added to the catalysts are increasing. Moreover, cracking temperatures are rising to compensate for the reduction in conversion. Unfortunately, it has been found that the API gravity of the bottoms formed during short contact time (SCT) often increases after a unit revamp, leading some to suggest that the heaviest portion of the hydrocarbon feed takes longer to crack. Further, while a high total surface area of the catalyst is valued, the FCC process still values attrition resistance. Accordingly, while not obvious to those participating in the art, it has become increasingly likely that an optimization of FCC catalysts for the new short contact time and ultra short contact time processing which is presently being used is needed.
It is now theorized, that under the short contact time processing of hydrocarbons, that further improvements can be gained by eliminating diffusion limitations that may still exist in current catalysts. This is being concluded even as these materials excel at the application. It is theorized that improvements in these catalysts may be produced by optimization of catalyst porosity and the elimination of
active site occlusion and diffusional restrictions of the binder phases present in catalysts prepared by the so-called incorporation method.
While the present assignee has produced zeolite microspheres with increased zeolite content and increased activity by increasing the macroporosity of the spray dried microsphere zeolite precursors, the porosity of the formed zeolite microsphere catalysts has not before been considered a problem since there has been found no diffusion limitation under the previous FCC processing techniques. For example, commonly assigned, U. S. Patent No. 4,965, 233, to Speronello discloses increasing the zeolite content of an in-situ catalyst by forming highly porous precursor microspheres, which allow increased amounts of zeolite to grow within the porous matrix. The highly porous precursor microspheres are formed by spray drying a slurry of hydrous kaolin clay, which is characterized by the presence of a major amount of large (greater than 2 microns) kaolin stacks along with spinel calcined clay. When spray dried, the coarse hydrous kaolin results in microspheres having a desired high content of macropores in which the zeolite Y can grow. Likewise, commonly assigned, U. S. Patent No. 5,023, 220, to Dight, et. al. also increases the macroporosity of the precursor microspheres by spray drying a mixture of hydrous clay, metakaolin and spinel. These catalyst microspheres have a substantial level of zeolite and are very active and selective. Further, the high alumina, silica-alumina matrix portion of the catalysts is often totally surrounded by the zeolite formed in-situ such that the matrix is only now understood to provide a reduced level of bottoms cracking under the short contact time FCC conditions.
SUMMARY OF THE INVENTION In accordance with this invention, novel zeolite microspheres are formed which are macroporous, have sufficient levels of zeolite to be very active and are of a unique morphology to achieve effective conversion of hydrocarbons to cracked gasoline products with improved bottoms cracking even under SCT FCC processing. The novel zeolite microspheres of the invention are particularly useful as additives to any other FCC catalyst so as to enhance and control the activity of the equilibrium catalyst for cracking gas oil to resid feedstocks. The catalysts of this invention hereinafter referred to as"activity enhancing additives", "catalytic additives"or"additives" are particularly useful in view of the high activity and reduced coke making properties thereof. Thus, the use of the activity enhancing additives in amounts of less than 100% of fresh catalyst feed to the cracking apparatus can be used to control, and, in particular, enhance the activity of other zeolite/matrix, FCC catalysts without unduly affecting the heat balance and/or coke make of the reactor as do other activity enhancing methods, such as by increasing zeolite surface area or increasing the rare earth metals content of the catalyst.
The activity enhancing additives of this invention are produced by novel processing, which is a modification of technology described in U. S. Patent No. 4,493, 902. It has been found that if the non-zeolite, alumina-rich matrix of the additive is derived from an ultrafine hydrous kaolin source having a particulate size such that 90 wt. % of the hydrous kaolin particles are less than 2 microns, and which is pulverized and calcined through the exotherm, a
macroporous zeolite microsphere can be produced. More generally, the additive matrix useful in this invention to achieve the desired macroporosity is derived from alumina sources, such as kaolin calcined through the exotherm, that have a specified water pore volume, which distinguishes over prior art calcined kaolin typically used to form the matrix of a FCC catalyst. The water pore volume is derived from an Incipient Slurry Point (ISP) test, which is described below.
The morphology of the microsphere additives which are formed is unique relative to the in-situ microsphere catalysts formed previously. Use of a pulverized, ultrafine hydrous kaolin calcined through the exotherm yields in-situ zeolite microspheres having a macroporous structure in which the macropores of the structure are apparently coated or lined with zeolite subsequent to crystallization.
Macroporosity as defined herein means the additive has a macropore volume in the pore range of 600-20,000 A of at least 0.07 cc/gm mercury intrusion. The activity enhancing additives of this invention should also have a BET surface area less than 500 m2/g. The additive of this invention is optimal for FCC processing, including the short contact time processing in which the hydrocarbon feed is contacted with a catalyst for times of about 3 seconds or less and which is able to enhance the activity of any zeolite/matrix FCC catalyst when used as only a portion of fresh catalyst feed.
In the broadest sense, the invention is not restricted to macroporous additives having a non-zeolite matrix derived solely from kaolin. Thus, any alumina source which has the proper combinations of porosity and reactivity during zeolite synthesis and can generate the desired macroporosity and morphology can be used. The desired morphology comprises
a matrix which is well dispersed throughout the additive, and the macropore walls of matrix are lined with zeolite and are substantially free of binder coatings. Accordingly, not only is the large pore surface area of the additive vastly improved over previous catalysts, and the active matrix dispersed throughout the microsphere, the zeolite crystals are readily accessible to the hydrocarbon feed. While not wishing to be bound by any theory of operation, it appears that previous catalysts in which the zeolite is incorporated into a matrix by physical mixing and glued with binder have sufficient macroporosity, however the binder coats the active zeolite catalyst thereby blocking accessibility thereto. The present microsphere additives have a morphology which allows fast diffusion into the catalytic additive due to the macroporosity and enhanced dispersion of the matrix, and further provides the highest accessibility to the zeolite inasmuch as the zeolite is freely coated onto the walls of the pores. The term"freely"means that the zeolite phase is present on the surface of the matrix and is unobstructed by any binder phases.
BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is an SEM photograph of the zeolitic microsphere of this invention as prepared in Example 6.
Figure 2 is a graph showing the nitrogen hysteresis loops of the inventive catalytic additive and a comparative catalyst.
DETAILED DESCRIPTION OF THE INVENTION The additive microspheres of this invention are produced by the general process as disclosed in commonly
assigned U. S. Patent No. 4,493, 902. Importantly, the non- zeolitic, alumina-rich matrix of the additives of the present invention is preferably derived from a hydrous kaolin source that is in the form of an ultrafine powder in which at least 90 wt. % of the particles are less than 2.0 microns, preferably at least 90 wt. % less than 1 micron.
The ultrafine hydrous kaolin is pulverized and calcined through the exotherm. Typical zeolite microspheres have been formed with an alumina-rich matrix derived from kaolin having a larger size than used in this invention and which is calcined at least substantially through its characteristic exotherm. Satintone@ No. 1, (a commercially available kaolin that has been calcined through its characteristic exotherm without any substantial formation of mullite) is a material used initially on a commercial basis to form the alumina-rich matrix. Satintone No. 1 is derived from a hydrous kaolin in which 70% of the particles are less than 2 microns. Other sources used to form the alumina-rich matrix include finely divided hydrous kaolin (e. g., ASPs 600, a commercially available hydrous kaolin described in Engelhard Technical Bulletin No. TI-1004, entitled"Aluminum Silicate Pigments" (EC-1167) ) calcined at least substantially through its characteristic exotherm.
Booklet clay has found the most widespread commercial use and has met tremendous success worldwide. Before the present invention, these larger clay particles represented the state of the art in forming the alumina-rich matrix of FCC catalyst microspheres and had no perceived deficits.
While the procedure for forming an in-situ zeolite microspheroidal catalyst as described in U. S. Patent No.
4,493, 902, is essentially followed, the alumina-rich matrix,
however, is derived from an ultrafine hydrous kaolin. What is meant by"ultrafine"powder is that at least 90 wt. % of the hydrous kaolin particles must be less than 2 microns in diameter, preferably less than 1 micron determined by SedigraphTM (or sedimentation). It has been found that, in particular, use of hydrous kaolin pigments with this particle size distribution upon pulverization and calcination through the characteristic exotherm results in a greater quantity of macroporosity even in the catalyst additive microsphere subsequent to zeolite crystallization.
The loose packing of the calcined ultrafine kaolin, which has been found, can be likened to a"house of cards"in which the individual particulates are aligned randomly with respect to adjacent particles in a non-parallel manner.
Moreover, the calcined ultrafine kaolin exists as porous aggregates of the"house of cards"morphology, providing not only a porous aggregate but additional porous areas between aggregates. Pulverization of the ultrafine hydrous kaolin is required to provide the random stacking of the individual kaolin platelets.
Kaolin clays or pigments are naturally-occurring hydrated aluminum silicates of the approximate formula Al203. 2Si02. XH20, wherein X is usually 2. Kaolinite, nacrite, dickite and halloysite are species of minerals in the kaolin group. It is well-known that when kaolin is heated in air, that a first transition occurs at about 550° C. associated with an endothermic dehydroxylation reaction.
The resulting material is generally referred to as metakaolin. Metakaolin persists until the material is heated to about 975° C. and begins to undergo an exothermic reaction. This material is frequently described as kaolin,
which has undergone the characteristic exothermic reaction.
Some authorities refer to this material as a defect aluminum-silicon spinel or as a gamma alumina phase. See Donald W. Breck, Zeolite Molecular Sieves, published by John Wiley and Sons, 1974, pp. 314-315. On further heating to about 1, 050° C. , high temperature phases including mullite begin to form. The extent of conversion to mullite is dependent on a time-temperature relationship and the presence of mineralizers, as is well-known in the art.
In the preferred embodiments of this invention, the pulverized ultrafine hydrous kaolin used to derive the alumina-rich matrix is calcined through its characteristic exotherm with or without the formation of mullite. An especially preferred matrix source which is used in this invention to form the macroporous zeolite microspheres is Ansilexs 93. Ansilexs 93 is made from the fine size fraction of a hard kaolin crude, by spray drying, pulverizing and calcining to prepare low abrasion pigments as described in U. S. Patent No. 3,586, 523, to Fanselow, et. al. , the entire contents of which are herein incorporated by reference. The ultrafine hydrous matrix source is spray dried, pulverized and then calcined through the exotherm, optionally to mullite. The aforementioned U. S. Patent No.
4,493, 902 discloses calcining the kaolin clay to mullite until the X-ray diffraction intensities are comparable to a fully crystalline reference standard. While it is within the scope of the present invention to calcine the kaolin beyond the exotherm such that the X-ray diffraction intensities are comparable to a fully crystalline referenced standard as disclosed in the 902 patent, it is preferred to calcine the kaolin beyond the characteristic exotherm so as to convert the kaolin to small crystallite size mullite.
The small crystallite size mullite has the appropriate diffractional lines and leached chemical composition of a fully crystalline mullite standard, but the diffractional lines are weaker inasmuch as the crystallites are smaller.
The relationship between diffraction intensity/line width and crystallite size is well-known. It is preferred to calcine the kaolin beyond the exotherm to a small crystallite mullite matrix inasmuch as fully calcining the kaolin to mullite takes excessive time and temperature in practice. Furthermore, calcining kaolin beyond the exotherm to fully crystalline mullite can result in the macroporosity being lost due to sintering. Moreover, the ISP and bulk density after calcining kaolin to fully crystalline mullite can be substantially increased. Thus, it is preferred that the ultrafine kaolin calcined through the exotherm has 20- 80% of the integrated X-ray diffraction peak areas of a kaolin reference sample containing well crystallized mullite. More preferably, the ultrafine kaolin is calcined through the exotherm such that it has 50-70% of the integrated X-ray diffraction peak areas of fully crystallized mullite.
What is unusual about the use of the Ansilex material is that it is derived from hard kaolin clay. Hard kaolin clays typically have a gray tinge or coloration and are, thus, also referred to as"gray clays". These hard kaolins are further characterized by breaking into irregularly shaped fragments having rough surfaces. Hard kaolin clays also contain a significant iron content, typically about 0.6 to 1 wt. % of Fe203. Hard kaolin clays are described in Grim's"Applied Clay Mineralology", 1962, MaGraw Hill Book Company, pp. 394-398 thereof, the disclosure of which is incorporated by reference herein. The use of these
materials to form the alumina-rich matrix for in situ FCC microsphere catalysts has not been known previous to this invention, although their use in the incorporated routes is well established. Hard kaolin clays have also occasionally been used as sources of metakaolin for in situ microspheres, but not with advantage. Without wishing to be bound by any theory, it would appear that previous use of the calcined gray clays in the in situ matrix art would be precluded by (a) the high iron content thereof and the possibility that this could lead to coke and gas production, and (b) the dilatant nature of slurries formed therefrom, leading to apparently senseless waste of process time and increased cost in making down high viscosity slurries which spray dry at low solids. We now believe these dilatancy problems and porosity benefits are intrinsically and fundamentally linked. As for the former point, reduced coke and gas was an especially sought-after object for in situ catalysts, since the original formulations of Haden made coke and gas commensurate with their extraordinarily high level of amorphous matrix activity. This led to lower and lower levels of iron and spinel in subsequent inventions. We have made the surprising finding that there appears to be no relationship between the iron and coke and gas selectivities after all.
The alumina-rich matrix can be derived from alumina- containing materials more generally characterized by the porosity thereof provided during the packing of the calcined material. A test has been developed to determine the pore volume of the calcined alumina-containing material which ultimately forms the matrix of the inventive additive. The test characterizes the water pore volume of the calcined alumina-containing material by determining the minimum
amount of water needed to make a slurry from a sample of the solids. In the test, a powder sample is mixed with water containing a dispersant such as, for example, Colloid 211, Viking Industries, Atlanta, GA, in a cup using a stirring rod or spatula. Just enough water is added to the dry sample to convert the dry powder to a single mass of dilatant mud which only just begins to flow under its own weight. The incipient slurry point (ISP) is calculated from the weights of the sample and water used. The incipient slurry point can be calculated as follows: ISP = [ (grams of dry sample)/ (grams of dry sample plus grams of water added)] x 100. The units are dimensionless and are reported as percent solids.
This amount of water is larger than the (internal) water pore volume of the sample, but is clearly related to the water pore volume. Lower incipient slurry point percent solids values indicate higher water absorption capacities or higher pore volume in the sample. The calcined alumina- containing materials from which the high-alumina matrix is derived in accordance with this invention will have incipient slurry points less than 57% solids, preferably 48 to 52% solids. This compares with Satintoneæ No. 1 which yields over 58% solids in the incipient slurry point test.
Accordingly, not only is the ultrafine hydrous kaolin useful as an alumina-containing material from which to derive the matrix of the catalytic additive microspheres, but the matrix may also be derived from delaminated kaolin, platelet alumina and precipitated alumina. Means for delaminating booklets or stacks of kaolin are well-known in the art. Preferred are those methods, which use a particulate grinding medium such as sand, or glass microballoons as is well-known. Subsequent to delamination,
the platelets are pulverized to derive the random packing or "house of cards"morphology.
The pulverize-calcine-pulverize processing of hydrous kaolin is preferred to make the matrix precursor of the invention because it appears that, when the foregoing is used with hydrous kaolin as the metakaolin source to form the reactive precursor microspheres, superior attrition resistance results at high pore volume. While less preferred, matrix precursors may also be wet milled to further de-agglomerate the precursor. The milling appears to reduce microsphere pore volume, all other things held constant. A method to reduce microsphere pore volume is useful when pre-calcined metakaolin powder is used to form the reactive precursor microspheres. Dight has disclosed that employing metakaolin powder increases precursor microsphere pore volume, but excessive levels of zeolite and surface area can be required to make these microspheres acceptably attrition resistant. While helping to moderate the required zeolite content and also perhaps improving the dispersion of said milled matrix in the microsphere, the de- agglomeration appears to have the effect of breaking strong bonds which could have otherwise strengthened the final catalytic additive, and so is not preferred.
It is also within the scope of this invention to derive the matrix from chemically synthesized spinel and/or mullite. Thus, Okata, et al. ,"Characterization of spinel phase from SiOz-Alz03 xerogels and the formation process of mullite", Journal of the American Ceramic Society, 69  652-656 (1986), the entire contents of which are incorporated herein by reference disclose that two kinds of xerogels can be prepared by slow and rapid hydrolysis of tetraethyoxy silane and aluminum nitrate nonahydrdate
dissolved in ethanol. The slow hydrolysis method involves gelling the above mixture in an oven at 60° C. for one to two weeks whereas the rapid hydrolysis method involves adding ammonium hydroxide solution to the mixture and drying in air. Xerogels prepared by the slow hydrolysis method crystallized mullite directly from the amorphous state on firing whereas the xerogels formed by rapid hydrolysis crystallized a spinel phase before mullite formation. As long as such calcined synthetic materials have a water pore volume within the scope of this invention, such materials can be used to derive the high-alumina matrix of the activity enhancing additive of this invention.
Preferably, the pore volume of the crystallized zeolite microsphere of this invention, which is formed using the high water pore volume alumina-containing materials as determined by the ISP test to form the additive matrix, is greater than 0.27 cc/gm, preferably greater than 0.30 cc/gm of Hg in the range of 40-20, OOOA diameter. More particularly, the additive of this invention has a macropore volume within pores having a size range of 600 to 20, OOOA of at least 0.07 cc/gm of Hg, and preferably at least 0.10 cc/gm of Hg. While conventional zeolite-incorporated catalysts have macroporosities comparable to the catalytic additives of this invention, the incorporated catalysts do not have the novel zeolite-on-matrix morphology nor performance of the additives of this invention. The catalytic additives of this invention will have a BET surface area less than 500 m2/g, preferably less than 475 m2/g and most preferably within a range of about 300-450 m2/g. The moderate surface area of the additives of this invention in combination with the macroporosity achieves the
desired activity and selectivities to gasoline while reducing gas and coke yields.
One skilled in the art will readily appreciate that it is the steam-aged surface area and activity that is truly significant and which must be balanced against the available pore volume. The cited preferred surface areas for finished product (fresh) catalyst additive are chosen such that the surface area after a 1500° F, four hour steaming at 1 atm steam pressure are generally below 300 m2/gm.
It has further been found that the macroporosity of the activity enhancing additive of this invention can be maintained even if a portion of the matrix is derived from coarse alumina-containing materials which otherwise do not meet the water pore volume desired by this invention as determined by the ISP test. Thus, it was found that blends of booklet kaolin clay and ultrafine kaolin clays that are calcined through the exotherm produce catalyst additives with high pore volume, wide macropores but with a lower zeolite content. Such additives can be valuable for exceptionally severe cracking environments.
The general procedure for manufacturing the FCC microspheres of this invention is well-known in the art and can be followed from the procedure disclosed in U. S. Patent No. 4,493, 902. As disclosed therein, an aqueous slurry of reactive finely divided hydrous kaolin and/or metakaolin and alumina-containing material which forms the matrix such as the ultrafine kaolin that has been calcined through its characteristic exotherm is prepared. The aqueous slurry is then spray dried to obtain microspheres comprising a mixture of hydrous kaolin and/or metakaolin and kaolin that has been calcined at least substantially through its characteristic
exotherm to form the high-alumina matrix. Preferably, a moderate amount of sodium silicate is added to the aqueous slurry before it is spray dried. During and after spray drying the sodium silicate functions as a binder between the kaolin particles.
The reactive kaolin of the slurry to form the microspheres can be formed of hydrated kaolin or calcined hydrous kaolin (metakaolin) or mixtures thereof. The hydrous kaolin of the feed slurry can suitably be either one or a mixture of ASP 600 or ASP 400 kaolin, derived from coarse white kaolin crudes. Finer particle size hydrous kaolins can also be used, including those derived from gray clay deposits, such as LHT pigment. Purified water- processed kaolin clays from Middle Georgia have been used with success. Calcined products of these hydrous kaolins can be used as the metakaolin component of the feed slurry.
The higher pore volume obtained using metakaolin can be offset by wet milling the matrix precursor. Silicate for the binder is preferably provided by sodium silicates with Si02 to Na20 ratios of from 1.5 to 3.5 and especially preferred ratios of from 2.88 to 3.22.
A quantity (e. g. , 3 to 30% by weight of the kaolin) of zeolite initiator may also be added to the aqueous slurry before it is spray dried. As used herein, the term"zeolite initiator"shall include any material containing silica and alumina that either allows a zeolite crystallization process that would not occur in the absence of the initiator or shortens significantly the zeolite crystallization process that would occur in the absence of the initiator. Such materials are also known as"zeolite seeds". The zeolite initiator may or may not exhibit detectable crystallinity by x-ray diffraction.
Adding zeolite initiator to the aqueous slurry of kaolin before it is spray dried into microspheres is referred to herein as"internal seeding". Alternatively, zeolite initiator may be mixed with the kaolin microspheres after they are formed and before the commencement of the crystallization process, a technique which is referred to herein as"external seeding".
The zeolite initiator used in the present invention may be provided from a number of sources. For example, the zeolite initiator may comprise recycled fines produced during the crystallization process itself. Other zeolite initiators that may be used include fines produced during the crystallization process of another zeolite product or an amorphous zeolite initiator in a sodium silicate solution.
As used herein, "amorphous zeolite initiator"shall mean a zeolite initiator that exhibits no detectable crystallinity by x-ray diffraction.
The seeds may be prepared as disclosed by in 4,493, 902.
Especially preferred seeds are disclosed in 4,631, 262.
After spray drying, the microspheres may be calcined directly, or alternatively acid-neutralized to further enhance ion exchange of the catalytic additive after crystallization. The acid-neutralization process comprises co-feeding uncalcined, spray dried microspheres and mineral acid to a stirred slurry at controlled pH. The rates of addition of solids and acid are adjusted to maintain a pH of about 2 to 7, most preferably from about 2.5 to 4.5 with a target of about 3 pH. The sodium silicate binder is gelled to silica and a soluble sodium salt, which is subseqently filtered and washed free from the microspheres. The silica gel-bound microspheres are then calcined. In either case, calcination is done at a temperature and for a time (e. g.,
for two hours in a muffle furnace at a chamber temperature of about 1, 350° F. ) sufficient to convert any hydrated kaolin component of the microspheres to metakaolin, leaving the previously calcined kaolin components of the microspheres essentially unchanged. The resulting calcined porous microspheres comprise a mixture of metakaolin and kaolin clay calcined through its characteristic exotherm in which the two types of calcined kaolin are present in the same microspheres. Alternatively any appropriate calcined alumina can replace the kaolin calcined through the exotherm as previously described. In general, the weight ratio of metakaolin to calcined alumina should be about 1: 0.66 to 1: 4, preferably 1: 1.5 to 1: 3. Thus, calcined the microspheres should generally comprise about 25-60% by weight metakaolin and about 40-75% by weight kaolin that has been calcined through its characteristic exotherm.
Preferably 30-40% by weight metakaolin and 60-70% by weight kaolin calcined through the exotherm are provided.
Also present is Na2O and Si02 derived from sodium silicate binder.
Y-faujasite is allowed to crystallize by mixing the calcined kaolin microspheres with the appropriate amounts of other constituents (including at least sodium silicate and water), as discussed in detail below, and then heating the resulting slurry to a temperature and for a time (e. g. , to 200°-215° F. for 10-24 hours) sufficient to crystallize Y- faujasite in the microspheres. The prescriptions of 4,493, 902 may be followed as written. Equivalent, reformatted recipes are provided as follows, however.
The crystallization recipes we employ are based on a set of assumptions and certain raw materials. The seeds are described by 4,631, 262 and are preferably used externally.
The Si02, A1203, and Na20 components of metakaolin, seeds, sodium silicate solution calcined sodium silicate binder, and silica gel are assumed to be 100% reactive. The alumina and silica in kaolin calcined through the exotherm to the spinel form are assumed to be 1% and 90% reactive respectively. Although these two values are in use, they are not believed to be accurate. The alumina and silica in kaolin calcined through the exotherm to the mullite form are assumed to be 0% and 67% reactive, respectively. These two values are believed to be accurate, representing the inertness of 3: 2 mullite in crystallization and the full solubility of the free silica phase. Since metakaolin alumina is the limiting reagent in the synthesis and the volume of zeolite is much larger than the corresponding volume of metakaolin, it is important to limit the zeolite yield appropriately for a given microsphere pore volume.
Otherwise, there will result little or no residual pore volume after crystallization. Such is the case for the prior art. On the other hand, if insufficient limiting reagent is available in the microsphere to grow sufficient zeolite to appropriately harden the catalytic additive, additional nutrient alumina may be added in the form of metakaolin microspheres, as is well known in this art.
Thus, tight process control is enabled for pore volume and attrition.
Using these assumptions, the following weight ratios for reactive components are used in the overall crystallization recipes. Inert components do not enter into the ratios, except in the case of the seeds dose, which is defined as the ratio of the grams of seeds A1203 to total grams of microspheres. Weight Ratios Si02/Na2O SiOz/AlzO3 H20/Na2O Seeds A1203/MS Broadly 2.50-3. 1 4.5-15 5-15. 01-0. 0001 Preferred 2. 55-2.95 5. 5-8 5. 5-8 0. 006-0.001 Typical 7. 0 7. 0 0. 004 (mullite) 2.575 (spinel) 2.75 (Acid-neutr) 2.9
The sodium silicate and sodium hydroxide reactants may be added to the crystallization reactor from a variety of sources. For example, the reactants may be provided as an aqueous mixture of NO Brand sodium silicate and sodium hydroxide. As another example, at least part of the sodium silicate may be provided by the mother liquor produced during the crystallization of another zeolite-containing product.
After the crystallization process is terminated, the microspheres containing Y-faujasite are separated from at least a substantial portion of their mother liquor, e. g. , by filtration. It may be desirable to wash the microspheres by contacting them with water either during or after the filtration step. The purpose of the washing step is to remove mother liquor that would otherwise be left entrained within the microspheres.
"Silica Retention"may be practiced. The teachings of U. S. Patent No. 4,493, 902 at column 12, lines 3-31, regarding silica retention are incorporated herein by cross- reference.
The microspheres that are filtered contain Y-faujasite zeolite in the sodium form. Typically, the microspheres contain more than about 8% by weight Na20. To prepare the
microspheres of the present invention, a substantial portion of the sodium ions in the microspheres are replaced by ammonium or rare earth ions or both.
Ion exchange may be conducted by a number of different ion exchange methods. Preferably, the microspheres are first exchanged one or more times with an ammonium nitrate solution at a pH of about 3-4. The ion exchange (s) with ammonium ions are preferably followed by one or more ion exchanges with rare earth ions at a pH of about 3-4. The rare earth may be provided as a single rare earth material or as a mixture of rare earth materials. Preferably, the rare earth is provided in the form of nitrates or chlorides.
The microspheres of the invention are ion exchanged to contain between 0% and 12% by weight REO, preferably 0.5% to 8% by weight REO, most preferably between 3 to 6% by weight REO and less than about 0.5%, more preferably less than about 0.4%, and most preferably about 0.2% by weight Na2O.
As is well known, an intermediate calcination will be required to reach these soda levels.
After ion exchange is completed, the microspheres are filtered and dried. The procedure described above for ion exchanging the FCC microsphere catalytic additive of this invention is well-known and, as such, such process, per se, does not form the basis of this invention.
The microspheres of the invention are used as additives to enhance the activity of other FCC zeolite/matrix catalysts. Typically, the present additives are used in amounts of 1 to less than 100% by weight relative to the fresh catalyst feed to the reactor. Preferably the additives are used in amounts of 1 to 50% and, most preferably, the activity enhancing additive is provided in amounts of 10 to 30% by weight of fresh catalyst feed. What is meant by
"fresh catalyst feed"is that catalyst added to the catalyst circulating in the FCC system. Typically, the fresh catalyst feed is called"make-up"catalyst and is added to the catalyst circulating in the FCC system ("equilibrium catalyst") to maintain the FCC catalyst inventory. The use of the additive of this invention is not to be equated with catalyst change-over wherein a new catalyst is added to the reactor to replace the FCC catalyst previously run through the reactor. In catalyst change over situations, 100% of the fresh or make-up catalyst is the new catalyst. As described above, the additive of this invention is used to control activity by being incorporated into the reactor as a percentage less than 100% relative to fresh catalyst feed.
The additive is not for the purpose of replacing the equilibrium catalyst, but only as an additive, which can incrementally increase activity. It is known to one skilled in the art that activity can be measured by several factors such as increased conversion to gasoline, more desirable cycle oil yields, and other such positive product selectivity benefits. Further, increased activity can be used in other operational applications to increase flexibility and improve refinery profits.
The catalytic additive of this invention is preferably added directly to the catalyst inventory in the FCC reactor from a supply source different from the supply of fresh or make-up catalyst. The catalytic additive can be alternatively mixed with the make-up catalyst from a separate source prior to entering the catalytic reactor. In either way, the amount of additive incorporated into the catalyst inventory of the reactor can be widely varied so as to provide the desired amount of activity enhancement. While it is possible to premix the additive with the make-up
catalyst and provide the premixed fresh catalyst from a single source, such a method reduces the variability of the process and reduces the ability to incrementally enhance the activity of the equilibrium catalyst.
While the invention is particularly directed to a catalytic additive having the physical and/or chemical properties delineated herein, in its broadest aspect, the invention is directed to an FCC catalyst additive to a fresh zeolitic/matrix catalyst, which additive contains zeolite and non-zeolitic matrix components and which has enhanced activity preferably without excessive dry gas and coke make.
It is believed there is an advantage of adding an activity enhancing additive which itself comprises a zeolite and non- zeolitic matrix particulate over other means of enhancing activity such as by increasing the rare earth content of the equilibrium or make-up catalysts or increasing surface area of the zeolite either on the equilibrium or make-up catalysts or by adding separate zeolite particles. A zeolite/matrix particulate additive has the ability to uniformly mix with the FCC catalyst inventory. A benefit of using a catalytic additive which contains a zeolite and non- zeolitic matrix to enhance the activity of the equilibrium catalyst is that the FCC system heat balance can be maintained in a cost effective and flexible manner.
Further, by using the additive, additional operational flexibility can be achieved through using the increased activity to affect other product yields and selectivity.
The preferred catalytic additive of the invention comprises microspheres containing at least 40% and preferably from 50% to 65% by weight Y-faujasite, expressed on the basis of the as-crystallized sodium faujasite form of zeolite. As used herein, the term Y-faujasite shall include
synthetic faujasite zeolites exhibiting, in the sodium form, an X-ray diffraction pattern of the type described in Breck, Zeolite Molecular Sieves, p. 369, Table 4.90 (1974), and having a crystalline unit cell size, in the sodium form (after washing any crystallization mother liquor from the zeolite), of less than about 24.75 A as determined by the technique described in the ASTM standard method of testing titled"Determination of the Unit Cell Size Dimension of a Faujasite Type Zeolite" (Designation D3942-80) or by an equivalent technique. The term Y-faujasite shall encompass the zeolite in its sodium form as well as in the known modified forms, including, e. g. , rare earth and ammonium exchanged forms and stabilized forms. The percentage of Y- faujasite zeolite in the microspheres is determined when the zeolite is in the sodium form (after it has been washed to remove any crystallization mother liquor contained within the microspheres) by the technique described in ASTM standard method of testing titled"Relative Zeolite Diffraction Intensities" (Designation D3906-80) or by an equivalent technique. It is important to equilibrate the microspheres carefully before X-ray evaluations are made since equilibration can have a significant effect on the results.
Figure 1 illustrates the unique morphology of the catalytic additive of this invention achievable from a unique alumina-containing material used to derive the additive matrix. The additive microspheres of this invention have a substantially different morphology than the previous FCC catalyst microspheres, especially with respect to the increased pore volume, zeolite-on-matrix morphology, and moderate surface area. Attrition resistance of these
additives is good and effective for the SCT FCC processing conditions.
As can be seen from Figure 1, the activity enhancing additives of this invention include a macroporous matrix in which the macropores of the matrix are formed from a random configuration of porous matrix planar structures which are lined on the opposing surfaces of the planes with the zeolite crystals. Thus, the macropores of the additive are lined with the active zeolite crystals. In Figure 1, the mesoporous matrix planes are formed from mullite particles.
The macroporosity of the additive allows the hydrocarbons to enter freely and the increased macropore surface area thereof allows such hydrocarbons to contact the catalytic surfaces. Importantly, the hydrocarbons can contact the zeolite unobstructed, rendering the catalytic additive very active and selective to gasoline. While conventional incorporated zeolite catalysts, in which the zeolite crystals are incorporated within a binder and/or matrix, have a highly porous matrix, at least a portion of the binder coats or otherwise obstructs the zeolite crystals.
In the present microspheroidal addtives, there is no need for a separate physical binder which glues the zeolite to the matrix surface other than any minute amounts of silicate which may remain subsequent to zeolite crystallization. It is believed that the microsphere additives formed in accordance with the process of the present invention yield the highest accessibility to the zeolite of any zeolite/matrix catalyst.
It has been found that the microspheroidal additives of the present invention provide high conversions via low coke selectivity and higher selectivities to gasoline relative to previous FCC catalysts presently on the market. It is
surprising that this catalytic additive can consistently outperform conventional incorporated catalysts of similar or even higher porosity and lower surface area. This shows that having added porosity alone is not sufficient. It is now believed that the novel structured catalytic additive, being both macroporous and with the macropore walls lined with zeolite and with the mesoporous or microporous matrix substantially behind the zeolite layer are the reasons the additive excels at gasoline, LCO and coke selectivity. The present additive is sufficient to crack the heavier hydrocarbons and improve the API gravity of the bottom fraction, especially during the short contact time processing.
The examples which follow illustrate the manufacture of the additive of the present invention. These examples are provided in copending, commonly assigned U. S. Serial No.
09/956,259 filed September 20,2001.
Example 1 A microsphere was prepared containing 30 parts of metakaolin (MK), 20 parts of wet media-milled Ansilex 93TM, 20 parts of media-milled HiOpaqueTM pigment calcined beyond 1, 050° C. , and 30 parts of NuSurfTM pigment which had been directly calcined beyond 1, 050° C. , pulverized and fluid- energy milled. To this mixture of calcined kaolins was added 15 parts of Si02 added from N-brandy sodium silicate.
This microsphere was not acid-neutralized. The metakaolin source was MetamaxTM, a pulverized powder, made down at 55% solids in tap water with 3 ml Colloid 211 surfactant (Viking Industries, Atlanta, GA) per kg of calcined kaolin. An air- driven Cowles mixer was used in a batch process where the
dry kaolin was added to the water that already contained the surfactant. The kaolin was added more slowly to the water as the mixture thickened. A very dilatant slurry was formed but continued mixing reduced the viscosity. Gradual addition of the kaolin and continued mixing during 45 minutes or more led to a slurry for which the dilatancy was no longer apparent by casual inspection.
The media-milled Ansilex 93 TM pigment was derived from a mixture of commercially produced slurries of 50% and 60% solids content. About 7 gallons of these slurries was placed in a stirred feed tank of a 4 L agitated media mill (Premier Mill Corp. , Reading PA). Three passes through the mill at about 4 minutes residence time each gave 90% less than 1.66 um by laser scattering (Horiba) at 51% solids.
HiOpaque TM is a calcined pigment derived from delaminated kaolin. Commercially produced pigment was further calcined using cordierite trays and a pre-heated high temperature electric furnace at 2350° F. during four hours, in order to obtain the maximum yield of well- crystallized mullite. The furnace product was then crushed to form a powder, made down and wet media milled as above in four passes. The final product was 90% < 3.24 um by laser scattering and at 37% solids by specific gravity. Both wet- milled slurries were very low in viscosity.
NuSurfTM is a coarse fraction of delaminated hydrous kaolin. This product was calcined at 2350° F. for four hours in cordierite trays to obtain maximal yield of well- crystallized mullite, crushed, then fluid energy milled with air (Micron Master Jet Pulverizer, Jet Pulverizer Co., Palmyra, NY) to 90% < 8.51 um particle size. This material was easily made down at 50% solids using tap water and 3 ml
Colloid 211 per kg of dry kaolin in a Cowles mixer to form a non-dilatant slurry. The ease of the make-down suggested that the hydrous pigment was not optimally pulverized before calcination or the fluid energy milling had compressed the aggregates.
Each of the four component slurries was maintained in suspension by rolling in sealed jugs until required for blending.
The slurry for spray drying was formed by mixing the four component slurries in the 30: 20: 20: 30 ratio on a 4 kg overall dry basis, as noted above, in a Cowles mixer.
Directly to this slurry 2.14 kg of N-brand@ Sodium Silicate was added to form a mixture at 45.7% solids which was sufficiently fluid to pump and spray dry. The material was spray dried using a 0.6 mm single fluid nozzle at 700 psi.
The as-sprayed material had a 0.71 gm/ml ABD (apparent bulk density) and analyzed with 3.9% Na20, or 13.1% binder as Si02. This product was calcined directly at 1500° F. in a pre-heated furnace using open cordierite trays during two hours. The product had 0.356 cc/gm pore volume in the 40- 20,000 A diameter range by mercury porosimetry, a 76 um APS and 14.2 wt. % acid-solubles (U. S. Patent No. 5,023, 220; column 18, line 59) and a 0.71 gm/cc ABD.
Example 2 A microsphere was prepared containing 30 parts of MK, 20 parts of wet media-milled Ansilex 93 tu 20 parts of ball- milled NuSurfTM pigment calcined beyond 1, 050° C. , and 30 parts of NuSurfTM mullite aggregates prepared by pulverizing the hydrous pigment before calcining beyond 1, 050° C. , plus
15 parts of Si02 added from N-brand@ sodium silicate. This microsphere was acid-neutralized.
The MK source was a second batch of MetamaxTM made down at 55% solids with C211 dispersant. The media-milled Ansilex 93 TM was the same slurry as prepared in Example 1.
The ball-milled NuSurfTM mullite was prepared by calcining the hydrous delaminated pigment at 2350° F. for four hours in cordierite trays in a pre-heated furnace.
This material was crushed, pulverized, and then wet ball milled at 46% solids. The final product was a low viscosity slurry with 90% <2 um by laser scattering.
The NuSurfTM mullite in this example was prepared to assure the formation of high pore volume aggregates with a house of cards structure. NuSurf delaminated hydrous pigment was slurried with water and dispersant, spray dried into densely packed microspheres, and subsequently pulverized to obtain a low density powder. This hydrous powder was calcined at 2350° F. in cordierite trays for four hours to form well-crystallized mullite. The product was crushed and pulverized to a powder, then made down at 50% solids using 4 ml C211 per kg of calcined kaolin using a Cowles mixer. This slurry was initially very dilatant and difficult to make down. Mixing was continued until the dilatancy was no longer apparent. The particle size by laser scattering was 90% < 14.75 um.
Each of the four component slurries was maintained in suspension by rolling in sealed jugs until required for blending.
The slurry for spray drying was formed by mixing the four component slurries in the 30: 20: 20: 30 ratio on a 3.93 kg overall dry basis as noted above in a Cowles mixer.
Directly to this slurry 2.11 kg of N-brand @ Sodium Silicate was added to form a mixture at 48% solids, which was sufficiently fluid to pump and spray dry. The material was spray dried using a 0.6 mm single fluid nozzle at 700 psi.
The as-sprayed material had a 0.72 gm/ml ABD and analyzed with 4. 01% Na20, or 13. 5% Si02 binder. This product was acid-neutralized by feeding the as spray dried microspheres to a bucket of cool stirred tap water, while co-feeding sufficient 40 Wt. % H2SO4 to keep the pH of the slurry between about 2.5 and 4. After all of the solids were added, the pH was monitored and controlled for 10 minutes before filtering and washing with about 2 gallons of tap water per Kg of microspheres, and then dried overnight at about 350° F.
The acid-neutralized microspheres were calcined directly at 1500° F. in a pre-heated furnace using open cordierite trays during three hours. The product had 0.402 cc/gm pore volume in the 40-20,000 range by mercury porosimetry, a 77 um APS and 14.4 wt. % acid-solubles and a 0.66 gm/cc ABD.
Example 3 A microsphere of exceptionally high pore volume and with unusually wide macropores was prepared with 30 parts of MK and 70 parts of NuSurfTM mullite aggregates; the latter prepared by pulverizing before calcining beyond 1, 050° C.
The calcined kaolin mixture was spray dried with 15 parts of Si02 added from N-brandy sodium silicate. This microsphere was acid-neutralized.
The MK source was the same batch of MetamaxTM made down in Example 2. The NuSurfTM mullite (aggregates) was also the same batch made down for Example 2. The two slurries were kept in suspension by rolling in sealed jugs until needed for blending.
The slurry for spray drying was formed by mixing the two component slurries in the 30: 70 ratio on a 4.00 kg overall dry basis as noted above in a Cowles mixer. To this slurry 2.14 kg of N-brandy Sodium Silicate was added to form a mixture at 48% solids, which was sufficiently fluid to pump and spray dry. The material was spray dried using a 0.6 mm single fluid nozzle at 700 psi.
The as-sprayed material had a 0.56 gm/ml ABD and analyzed with 3.92% Na20, or 13.1% Si02 binder. This product was acid-neutralized and dried as per the procedure of Example 2. The acid-neutralized microspheres were calcined directly at 1500° F. in pre-heated furnace using open cordierite trays during three hours. The product had 0.407 cc/gm pore volume in the 40-20,000 A diameter range and an additional 0.156 cc/gm in the 20,000 to 40,000 A diameter range by mercury porosimetry, a 86 um APS and 10.6 wt. % acid-solubles with a 0.53 gm/cc ABD.
The microspheres of Examples 1-3 were crystallized during 23 hours to form zeolite Y by conventional procedures (4,493, 902, and 5,395, 809) with the following results. The seeds are described by 4,631, 262.
Table 1 Crystallization Example 4 Example 5 Example 6 Microsphere of Example 1 Example 2 Example 3 Crystallization Recipe Grams MS 245. 0 225. 0 230. 0 Seeds, grams 171. 9 157. 9 161. 4 N-BRAND, grams 403. 0 414. 4 415. 0 50% NaOH, grams 66. 8 90. 6 87. 6 H20, grams 462. 0 435. 9 429. 6 Sodium-form properties UCS, A 24. 62 24.62 24.63 BET, m2/gm 446 447 420 MSA, m2/gm 66 69 54 ZSA, m2/gm 380 379 366 Hg TPV, 40-20K, 0.283 0.328 0.508 cc/gm Roller, wt. %/hr 26 36 128
The mercury pore volume of these materials is considerably higher than provided for by the prior art of in situ crystallization. The sodium-form catalysts were then ion-exchanged to finished products as follows. Sodium-form catalyst was added to 27 wt. % ammonium nitrate solution at 180° F and pH of 2.8-3. 2 while stirring and adding 50% HN03 drop-wise to control pH. After all of the catalyst was added, the slurry was stirred for 15 minutes, filtered, and the cake washed with twice the dry catalyst weight of de- ionized water. Two such exchanges were done where the weight ratio of catalyst to 27 wt. % ammonium nitrate was 1: 2. The samples were then rare earth exchanged at 180° F. and pH of 4 to yield about 3% REO on the catalyst. The Na20 content at this point was 1.8 to 1.9 Wt. , considerably lower than prior art formulations.
The partially-exchanged materials were dried and then calcined at 1150° F. in pre-heated furnaces for two hours in covered silica trays while initially containing 25 Wt. % moisture. After calcination, the ammonium exchange
procedure was repeated either five (Example 4) or three (Examples 5,6) times, then calcined again at 25% moisture and 1150° F. to form the finished product. The results are as follows: Table 2 Example 4 Example 5 Example 6 UCS, A 24. 52 24.51 24.48 Roller, Wt%/hr 20 47 ABD VF, gm/cc 0. 600 0. 569 0. 463 Hg Pore Volume by Diameters (A) 40 - 200 Å 0.076 0.090 0.069 200 - 2000 Å 0.186 0.166 0.125 2000-20,000 A 0. 068 0. 098 0. 317 40-20,000 A 0. 329 0. 353 0. 511 BET, m2/gm 383 361 299 MSA, m2/gm 71 76 57 ZSA, m2/gm 312 285 242 Al203, Wt. % 41. 8 43. 8 43. 5 Si02, Wt. % 52. 8 50. 8 51. 2 Na20, Wt. % 0. 1 0. 1 0. 21 Fe203, Wot. % 0. 54 0. 47 0. 4 TiO2, Wt. % 0. 85 0. 83 0. 79 P205, ppm 400 300 300 REO, Wt. % 2. 92 2. 41 2. 58
It can be seen that the use of increasing amounts of properly pre-pulverized hydrous delaminated kaolin leads to more pore volume and wider macropores. An SEM image of the product of Example 6 is shown in Figure 1. The dark areas are the macropores which are clearly formed by the random or "house of cards"configuration of the sheets of matrix derived from delaminated pigment. The smaller granules sandwiched between the larger crystals of zeolite have been positively identified as mullite crystals. The larger crystals coated or otherwise lining the mullite matrix have been positively identified as zeolite Y.
Inclusion of both mullite and spinel leads to a tri- modal pore size distribution. The porosity intrinsic to the spinel and mullite phases are visible in the mercury pore size data, indicating that these mesoporous matrices are not occluded by the zeolite which grows upon them. This is confirmed by the reduced volume within the nitrogen hysteresis loops (Figure 2) obtained for finished products that were steamed at 1500° F. in 100% steam for four hours.
Two comparative Examples are shown from U. S. Patent No.
Example 7 This example describes the use of blends of coarse and fine matrix kaolins useful for lower surface area formulations which retain wide macropores and excellent catalytic performance.
A series of short test runs to convert kaolins to mullite and silica were conducted on a production-scale rotary calciner that was direct-fired with natural gas. In one case booklet-type clays (NOKARBTM) calcined to form the matrix for the FCC catalysts described by U. S. Patent Nos.
4,493, 902 and 5,395, 809 were being produced, and at the end of the campaign the calciner severity was raised to maximize the yield of mullite. A product was collected for pilot spray drying work. Later, Ansilex 93 TM (A93) pigment was to be made. A93 is made from gray clay having 90% finer than 1 um by sedimentation. The fractionated hydrous kaolin has been spray dried and then pulverized to a low density powder. Just before the A93 production run the calciner severity was increased to raise the mullite content of the initial product to the maximum extent possible, and a sample was taken of this product ("M93"). Much later it was
determined that this material was in fact derived from a mixture of booklet clays and the ultrafine hydrous kaolins.
The exact proportions of the mixture could not be determined, but Fe203, SEM and water pore volume results confirmed that intermixing had indeed occurred. The M93 was about 58% converted to fully crystallized mullite by X-ray diffraction.
A microsphere was made from the M93 mixed calcined kaolin product by diluting 33.3 parts (dry basis) of LHT hydrous pigment slurry with water in a Cowles mixer and then adding 66.7 parts of dry M93 in a batch process, along with sufficient dispersant to make a fluid mixture. The mixture contained 50% solids but exhibited some residual dilatancy.
The slurry was fed to a spray dryer with a wheel atomizer having a single row of circular openings. 4.1 parts (as Si02) of sodium silicate binder solution having a 2.88 SiO2/Na2O were injected into the slurry at the entrance of an in line static mixer placed just upstream of the atomizer.
The microspheres were calcined to convert the hydrous kaolin to metakaolin but without reaching the characteristic exotherm. The NazO content was 1.40 wt. %, the acid solubles were 14.72 wt. %, the APS was 91 um, the ABD 0.6 gm/cc, and the Hg pore volume between 40 and 20,000 A diameter was 0.520 gm/cc.
Example 8 The microspheres of Example 7 were crystallized during 22 hours to form zeolite Y by conventional procedures (U. S.
Patent Nos. 4,493, 902; 5,395, 809) with the results as shown in Table 3.
Table 3 Crystallization Example 8 Microsphere Example 7 Crystallization recipe Grams MS 170. 0 Seeds, grams 109. 7 N-BRAND grams 398. 3 50% NaOH, grams 76.5 H20 grams 418. 3 Reaction product properties UCS, A 24. 62 BET, m2/gm 464 MSA, m2/gm 82 ZSA, m2/gm 382 Roller, Wt. %/hr 12
The sodium-form catalyst was ion exchanged to 1.75 wt.
% Na20 and 3.14 wt. % REO as above, calcined as above and then ammonium exchanged as above to 0.23 wt. % Na20, then calcined as prescribed above to obtain the finished product.
The finished product was steamed at 1500° F. in 1 atm of steam in an open quartz tube for four hours. The properties were as found in Table 4.
Example 9 This is a comparative example. A commercially-prepared catalyst made substantially by the methods of U. S. Patent No. 5,395, 809 were obtained, analyzed and tested.
Example 10 This is a comparative example. A sample of FCC catalyst by the name of"GDO"was analyzed and tested. The method of manufacture is not specifically known, however it
is presumed that this is representative of the state of the art for incorporated catalysts made with an aluminum chlorohydrol binder and formulated with additional granular alumina for bottoms cracking.
Table 4 Example 8 Example 9 Example 10 UCS, A 24.47 24.53 24.57 Roller, Wt%/hr 14 5 ABD VF, gm/cc 0. 59 0. 75 0. 70 40-100 A Hg PV 0. 061 0. 074 0. 061 100-600 A, Hg PV 0. 139 0. 024 0. 073 600-20,000 A, Hg 0.168 0.030 0.067 PV 40-20, 000 A, Hg 0.368 0.129 0.201 PV BET, m2/gm 377 402 222 MSA, m2/gm 90 108 85 ZSA, m2/gm 287 294 137 Al203, Wt. % 40. 30 31. 9 50. 7 Si02, Wot. % 53. 70 61. 5 44. 7 Na20, Wt. % 0. 23 0. 28 0. 14 Fe203, Wt. % 0. 69 0. 27 0. 62 Ti02, Wt. % 1. 46 1. 25 0. 87 P205 0. 03. 080. 1 REO, Wt. % 2. 85 3. 00 1. 96 Properties after Steaming 1500 F, four hours in 100% steam BET, m2/gm 249 241 133 MSA, m2/gm 73. 4 76 50 ZSA, m2/gm 175.6 165 83 UCS, A 24. 34 24. 33 24. 29
Example 11 A fractionated (90% < 1 um by sedimentation) hydrous kaolin slurry derived from a gray clay deposit was spray dried and pulverized as disclosed in U. S. Patent No.
3,586, 523. The material was then calcined at higher severity so as to convert it 50% to 80% of the way to well- crystallized mullite, as measured by X-ray diffraction line intensities relative to a kaolin which had been fully converted as in the 902 patent, Example 4. Typical properties of this material, also designated M93, are listed in Table 5, along with comparative materials.
The preferred calcined kaolins used as FCC catalyst matrix precursors have ISP percent solids below about 57%, more preferably, below 55% solids, and most preferably in the range of 48-52% solids. This is to say, having higher water pore volumes than precursors used in the prior art.
The laser particle size we prefer is 90% less than about 10 um, so that suitable microspheres can be formed. The simplest test for acceptability is the tamped bulk density, and this should be less than about 0.45 gm/cc, more preferably less than 0.40 gm/cc. Tamped bulk density, loose bulk density, mercury volume and ISP solids all correlate with each other.
The kaolin-based materials may have any value of mullite index so long as they meet the previous requirements, but they must have passed substantially through the exotherm in order to yield residual mesoporous or microporous matrix. The resulting matrix surface area and modal pore diameter varies smoothly as the relative mullite crystallite size is varied.
Table 5 Typical properties of calcined products Property ISP Laser Hg pore Tamped scattering volume, 40-bulk Particle 20,000 A Density size Diameter Units % solids 90% <, um cc/gm Gm/cc M93,48-52% 9 to 10 um 1.4 to 1.5 0.38 Example 11 M93,55% 7.89 um 1.13 0.45 Example 7 A93 spinel 48-52% 5 to 7 um 1. 45 0. 3 Satintone 1 58% 0. 48 Spinel from 66% 19 um 0.73 0.69 NOKARB@, Example 8 Mullite 58. 76% 10.66 um 0. 93 0. 55 from Satintone 2, 902 Example 4 process Mullite 51. 38% 9. 66 1. 159 0. 53 from A93, 902 process: 2200° F. for 7 hours CE Minerals 77% 117 Nonporous 1. 66 Mullite
The M93 of the present example along with C211 dispersant was added on a continuous basis to a dispersed slurry of LHT pigment in water using a staged Cowles system.
The addition rates were controlled such that the blended slurry contained 33 parts of LHT hydrous pigment to 67 parts of M93 calcined matrix precursor at 48 to 50% solids. The mixture was then spray dried to form microspheres.
Additional water was added as needed to control dilatancy and improve atomization. The slurry was fed to a spray dryer
with a wheel atomizer. 4 parts (as Si02) of sodium silicate binder solution having a 2.88 Si02/Na20 were injected into the slurry at the entrance of an in line static mixer placed just upstream of the atomizer. The resulting microspheres were calcined in a direct-fired rotary calciner to convert the hydrous kaolin in the mixture to metakaolin but without reaching the characteristic exotherm.
The Na20 content was 1.73 wt. %, the acid solubles were 16.23 wt. %, the APS was 82 um, the ABD 0.47 gm/cc, and the Hg pore volume between 40 and 20,000 A diameter was 0.679 gm/cc.
The microspheres were crystallized in plant-scale reactors using about 950 gallons of seeds, 8,612 gals 30 wt.
% recycled and concentrated sodium di-silicate, 600 gallons of 19% NaOH, 938 gals of water, 23, 897 lbs of the above microspheres, and an additional 3,259 lbs of metakaolin microspheres, these latter microspheres prepared substantially as described by U. S. 3,647, 718. The amount of the metakaolin microsphere was chosen to control the porosity and roller attrition of the finished product tightly to specification. The residuals of this second microsphere are believed to have been largely removed by centrifugal separation devices.
The product of the crystallizations were filtered, washed to remove excess mother liquor, ion exchanged to about 2.5% Na20 and 3% REO, calcined in rotary calciners to migrate the sodium but not substantially reduce unit cell size, ammonium exchanged again to about 0.2% Na2O, then calcined again to reduce the zeolite unit cell size. These catalyst work-up processes are previously known and merely adopted without modification for the present work.
Example 12 The catalyst of Example 11 was provided to an FCC unit following the use of a conventional FCC catalyst. The unit was equipped with modern feed nozzles and riser termination devices and had a riser contact time of 2.0 to 2.5 seconds.
After introduction of the catalyst of Example 11, the conversion of the unit was observed to increase by 3 LV%, at constant coke. Gasoline yield was increased concurrently with increased light olefins, and most significantly, bottoms API gravity was reduced to levels not previously observed. The improvement in bottoms cracking was remarkable since it came without a penalty in dry gas yield or delta coke.
Once given the above disclosure, many other features, modifications, and improvements will become apparent to the skilled artisan. Such other features, modifications, and improvements are, therefore, considered to be a part of this invention, the scope of which is to be determined by the following claims.