The art relating to particulate porous alumina particles, shaped catalyst supports derived therefrom, supports impregnated with various catalytically active metals, metal compounds and/or promoters and various uses of such impregnated supports as catalysts, is extensive and relatively well developed.
While the prior art shows a continuous modification and refinement of such particles, supports, and catalysts to improve their catalytic activity, and while in some cases highly desirable activities have actually been achieved, there is a continuing need in the industry for improved catalyst supports and catalysts derived therefrom, which have enhanced activity and life mediated through a desirable balance of morphological properties.
Alumina is useful for a variety of applications including catalyst supports and catalysts for chemical processes, catalyst linings for automotive mufflers, and the like. In many of these uses it will be desirable to add catalytic materials, such as metallic ions, finely-divided metals, cations, and the like, to the alumina. The level and distribution of these metals on the support, as well as the properties of the support itself are key parameters that influence the complex nature of catalytic activity and life.
Alumina useful in catalytic applications has been produced heretofore by a variety of processes, such as the water hydrolysis of aluminum alkoxides, precipitation of alumina from alum, sodium aluminate processes and the like. High costs arise from the latter two methods because the quantity of by-products, such as sodium sulfate, actually exceed the quantity of desired product obtained, i.e., boehmite. Typically, the cost of boehmite will be 4 times as expensive as active alumina.
Generally speaking, while alumina from these sources can be used for catalyst supports, such use is subject to certain limitations. This stems from the fact that for supported catalysts used in chemical reactions, the morphological properties of the support, such as surface area, pore volume, and pore size distribution of the pores that comprise the total pore volume are very important. Such properties are instrumental in influencing the nature and concentration of active catalytic sites, the diffusion of the reactants to the active catalyst site, the diffusion of products from the active sites, and catalyst life.
In addition, the support and its dimensions also influence the mechanical strength, density and reactor packing characteristics, all of which are important in commercial applications.
Hydroprocessing catalysts in petroleum refining represent a large segment of alumina-supported catalysts in commercial use. Hydroprocessing applications span a wide range of feed types and operating conditions, but have one or more of common objectives, namely, removal of heteroatom impurities (sulfur, nitrogen, oxygen, metals), increasing the H/C ratio in the products (thereby reducing aromatics, density and/or carbon residues), and cracking carbon bonds to reduce boiling range and average molecular weight.
More particularly, the use of a series of ebullated bed reactors containing a catalyst having improved effectiveness and activity maintenance in the desulfurization and demetallation of metal-containing heavy hydrocarbon streams are well known.
As refiners increase the proportion of heavier, poorer quality crude oil in the feedstock to be processed, the need grows for processes to treat the fractions containing increasingly higher levels of metals, asphaltenes, and sulfur.
It is widely known that various organometallic compounds and asphaltenes are present in petroleum crude oils and other heavy petroleum hydrocarbon streams, such as petroleum hydrocarbon residua, hydrocarbon streams derived from tar sands, and hydrocarbon streams derived from coals. The most common metals found in such hydrocarbon streams are nickel, vanadium, and iron. Such metals are very harmful to various petroleum refining operations, such as hydrocracking, hydrodesulfurization, and catalytic cracking. The metals and asphaltenes cause interstitial plugging of the catalyst bed and reduced catalyst life. The various metal deposits on a catalyst tend to poison or deactivate the catalyst. Moreover, the asphaltenes tend to reduce the susceptibility of the hydrocarbons to desulfurization. If a catalyst, such as a desulfurization catalyst or a fluidized cracking catalyst, is exposed to a hydrocarbon fraction that contains metals and asphaltenes the catalyst will become deactivated rapidly and will be subject to premature replacement.
Although processes for the hydrotreating of heavy hydrocarbon streams, including but not limited to heavy crudes, reduced crudes, and petroleum hydrocarbon residua, are known, the use of fixed-bed catalytic processes to convert such feedstocks without appreciable asphaltene precipitation and reactor plugging and with effective removal of metals and other contaminants, such as sulfur compounds and nitrogen compounds, are not common because the catalysts employed have not generally been capable of maintaining activity and performance.
Thus, certain hydroconversion processes are most effectively carried out in an ebullated bed system. In an ebullated bed, preheated hydrogen and resid enter the bottom of a reactor wherein the upward flow of resid plus an internal recycle suspend the catalyst particles in the liquid phase. Recent developments involved the use of a powdered catalyst which can be suspended without the need for a liquid recycle. In this system, part of the catalyst is continuously or intermittently removed in a series of cyclones and fresh catalyst is added to maintain activity. Roughly about 1 wt. % of the catalyst inventory is replaced each day in an ebullated bed system. Thus, the overall system activity is the weighted average activity of catalyst varying from fresh to very old i.e., deactivated.
In general, it is desirable to design the catalyst for the highest surface area possible in order to provide the maximum concentration of catalytic sites and activity However, surface area and pore diameter are inversely related within practical limits. Sufficiently large pores are required for diffusion as the catalyst ages and fouls, but large pores have a lower surface area.
More specifically, the formulator is faced with competing considerations which often dictate the balance of morphological properties sought to be imparted to supports or catalysts derived therefrom.
For example, it is recognized (see for example, U.S. Pat. No. 4,497,909) that while pores having a diameter below 60 Angstroms (within the range of what is referred to herein as the micropore region) have the effect of increasing the number of active sites of certain silica/alumina hydrogenation catalysts, these very same sites are the first ones clogged by coke thereby causing a reduction in activity. Similarly, it is further recognized that when such catalysts have more than 10% of the total pore volume occupied by pores having a pore diameter greater than 600 Angstroms (within the region referred to herein generally as the macropore region), the mechanical crush strength is lowered as is the catalyst activity. Finally, it is recognized, for certain silica/alumina catalysts, that maximization of pores having a pore diameter between 150 and 600 Angstroms (approximately within the region referred to herein as the mesopore region) is desirable for acceptable activity and catalyst life.
Thus, while increasing the surface area of the catalyst will increase the number of the active sites, such surface area increase naturally results in an increase in the proportion of pores in the micropore region. As indicated above, micropores are easily clogged by coke. In short, increases in surface area and maximization of mesopores are antagonistic properties.
Moreover, not only must the surface area be high, but it should also remain stable when exposed to conversion conditions such as high temperature and moisture. There has therefore been a continuing search for high pore volume, high surface area, hydrothermally stable alumina suitable for catalyst supports. The present invention was developed in response to this search.
U.S. Pat. No. 4,981,825 is directed to compositions of inorganic metal oxide (e.g., SiO.sub.2) and clay particles wherein the oxide particles are substantially segregated from each other by the clay particles. Suitable clays include Laponite.RTM.. The disclosed ratio of metal oxide:clay is between 1:1 to 20:1 (preferably 4:1 to 10:1). The subject composition is derived from an inorganic oxide sol having a particle size of 40 to 800 Angstroms (0.004 to 0.08 microns). The particle size of the final product is dependent on the size of the particles in the starting sol, although the final particle size is unreported. It is critical that the metal oxide and clay particles have opposite charges so that they will be attracted to each other such that the clay particles inhibit aggregation of the metal oxide particles. Thus, the clay particles are described as being placed between the sol particles. Control of the charges on the two different types of particles is determined by the pH of the sol. The pH of the inorganic oxide is controlled to be below its isoelectric point by acid addition thereby inducing a positive charge on the inorganic oxide particles. While suitable inorganic metal oxides are disclosed to also include Al.sub.2 O.sub.3, no examples of carrying out the invention using Al.sub.2 O.sub.3 are provided. Consequently, translating this concept to Al.sub.2 O.sub.3 is not without difficulty. For example, the isoelectric point of Al.sub.2 O.sub.3 is at a basic pH of about 9. However, Al.sub.2 O.sub.3 sols only form at a low pH of less than about 5. If the pH exceeds about 5, an Al.sub.2 O.sub.3 Sol will precipitate from dispersion or never form in the first place. In contrast, SiO.sub.2 sols do not have to be acidic. Consequently, while any point below the isoelectric point is acceptable for SiO.sub.2 sols, the same is not true of Al.sub.2 O.sub.3 sols. Rather, one must operate at a pH well below the isoelectric point of the Al.sub.2 O.sub.3 in the pH region where alumina sols form. Moreover, this patent discloses nothing about the pore properties of the resulting composite and its thrust is only directed toward obtaining high surface area. As indicated above, surface area and high mesopore pore volume are typically antagonistic properties.
In contrast, the presently claimed invention neither starts with an Al.sub.2 O.sub.3 sol nor forms a sol during rehydration. The pH at which the presently claimed composites are formed is too high for a sol to form during rehydration and the starting alumina particles are too big for a sol to form initially.
Another area of technology relating to combinations of various clay and metal oxides is known as intercalated clays. Intercalated clays are represented by U.S. Pat. Nos. 3,803,026; 3,887,454 (See also U.S. Pat. No. 3,844,978); 3,892,655 (See also U.S. Pat. No. 3,844,979); 4,637,992; 4,761,391 (See also U.S. Pat. No. 4,844,790); and 4,995,964. Intercalated clay patents typically have in common the requirement that large clay:sol ratios be employed. Intercalated clays generally have most of their surface area in micropores unless freeze-dried.
U.S. Pat. No. 3,803,026 discloses a hydrogel or hydrogel slurry comprising water, a fluorine-containing component and an amorphous cogel comprising oxides or hydroxides of silicon and aluminum. The amorphous cogel further comprises an oxide or hydroxide of at least one element selected from magnesium, zinc, boron, tin, titanium, zirconium, hafnium, thorium, lanthanum, cerium, praseodymium, neodymium, and phosphorus, said amorphous cogel being present in the hydrogel or hydrogel slurry at an amount of from 5 to 50 wt. %. The slurry is subjected to a pH of 6 to 10 and conversion conditions create a substantial amount of crystalline aluminosilicate mineral, preferably in intimate admixture with a substantial amount of unreacted amorphous cogel. The silica/alumina molar ratio is at least 3:1 and the resulting material is referred to as a synthetic layered crystalline clay-type aluminosilicate mineral and the unreacted amorphous co-gel exists mostly as SiO.sub.2. At column 5, lines 39 et seq., it is disclosed that the resulting aluminosilicate can be broken into particles, pulverized into a powder, the powder dispersed in a hydrogel, or hydrogel slurry to which is added components selected from precursor compounds of, inter-alia, alumina. The resulting mixture is then dried and activated. Notwithstanding the above disclosure, no specific examples employing a mixture of silica-aluminate with alumina is disclosed. Consequently, neither the starting alumina, the final alumina, nor the amounts employed of each material are disclosed.
U.S. Pat. No. 3,887,454 (and its parent U.S. Pat. No. 3,844,978) discloses a layered type dioctahedral, clay-like mineral (LDCM) composed of silica, alumina, and having magnesia incorporated into its structure in controlled amounts. Preferred clays are montmorillonite and kaolin. At column 6, lines 24 et seq., it is disclosed that the clay material can be combined generally with inorganic oxide components such as, inter-alia, amorphous alumina. In contrast, the presently claimed composite utilizes crystalline boehmite alumina. Similar disclosures are found in U.S. Pat. Nos. 3,892,655; and 3,844,979, except that these latter patents are directed to layer-type, trioctahedral, clay-like mineral containing magnesia as a component thereof (LTCM) and illustrated with a sapounit type clay.
U.S. Pat. No. 4,637,992 is an intercalated clay patent which employs colloidal suspension of inorganic oxides and adds a swellable clay thereto. While specific ranges illustrating the ratio of clay to inorganic oxide are not disclosed, it appears that the final material is still referred to as being a clay based substrate into which is incorporated the inorganic oxide. Consequently, this suggests that the final material contains a major amount of clay rather than a predominate amount of aluminum oxide and very minor amounts of clay as in the present invention. See for example, column 5, lines 46 et seq., of the '992 patent.
U.S. Pat. No. 4,844,790 (division of U.S. Pat. No. 4,761,391) is directed to a delaminated clay prepared by reacting a swellable clay with a pillaring agent which includes alumina. The ratio of clay to pillaring agent is 0.1:1 to 10:1, preferably between 1:1 to 2:1. The primary thrust of the patent, however, is clay containing alumina and not alumina containing less than 10 wt. % clay. It is reasoned that the metal oxides prop apart the platelets of the clay and impart acidity thereto which is responsible for the catalytic activity of the delaminated clay. The preferred clay is a Laponite.RTM..
U.S. Pat. No. 4,995,964, is directed to a product prepared by intercalating expandable clay (hectorite, saponite, , montmorillonite) with oligimers derived from rare earth salts, and in particular, trivalent rare earths, and polyvalent cations of pillaring metals, such as Al.sup.+3. The aluminum oxide material is an aluminum containing oligimer which is used in providing the pillars of the expanded clays. The claimed invention does not use or produce oligimers of aluminum hydroxy materials.
U.S. Pat. No. 4,375,406 discloses compositions containing fibrous clays and precalcined oxides prepared by forming a fluid suspension of the clay with the precalcined oxide, agitating the suspension to form a codispersion, and shaping and drying the codispersion. The ratio of fibrous formed clay to precalcined oxide composition can vary from 20:1 to 1:5. These amounts are well above the amounts of clay employed in the presently claimed invention. Moreover, fibrous clay is not within the scope of the swellable clays described herein.
A number of patents are directed to various types of alumina and methods of making the same, namely, Re 29,605; SIR H189; and U.S. Pat. Nos. 3,322,495; 3,417,028; 3,773,691; 3,850,849; 3,898,322; 3,974,099; 3,987,155; 4,045,331; 4,069,140; 4,073,718; 4,120,943; 4,175,118; 4,708,945; 5,032,379; and 5,266,300.
More specifically, U.S. Pat. No. 3,974,099 is directed to silica/alumina hydrogels from sodium silicate and sodium aluminate cogels. The essence of this invention is directed to the precipitation of Al.sub.2 O.sub.3 onto silica-alumina gel which stabilizes the cracking sites to hydrothermal deactivation. (Column 2, lines 43 et seq.) The resulting material typically has about 38.6% alumina oxide when all the excess sodium aluminate is removed. In contrast, the silica employed in the presently claimed invention is an additive which coats the surface of the alumina/clay composite particles since it is added after the composite formation.
U.S. Pat. No. 4,073,718 discloses a catalyst base of alumina stabilized with silica on which is deposited a cobalt or nickel catalyst.
U.S. Pat. No. 4,708,945 discloses a cracking catalyst of silica supported on boehmite-like surface by compositing particles of porous boehmite and treating them with steam at greater than 500.degree. C. to cause silica to react with the boehmite. 10% silica is usually used to achieve a surface monolayer of silica to improve thermal stability.
U.S. Pat. No. 5,032,379 is directed to alumina having greater than 0.4 cc/g pore volume and a pore diameter in the range of 30 to 200 .ANG.. The alumina is prepared by mixing two different types of rehydration bondable aluminas to produce a product having a bimodal pore distribution.
U.S. Pat. No. 5,266,300 discloses an alumina support prepared by mixing at least two finely divided aluminas, each of which is characterized by at least one pore mode in at least one of the ranges (i) 100,000 to 10,000 .ANG., (ii) 10,000 to 1,000 .ANG., (iii) 1,000 to 30 .ANG..
U.S. Pat. No. 4,791,090 discloses a catalyst support with a bidispersed micropore size distribution. Column 4, lines 65, discloses that two sizes of micropores can be formulated by mixing completely different materials having different pore sizes such as alumina and silica.
U.S. Pat. No. 4,497,909 is directed to silica/alumina carriers having a silica content less than about 40% by weight and at least one noble metal component of Group VII of the Periodic Table and wherein the catalyst contains pores having a diameter smaller than 600 .ANG. occupying at least 90% of the total pore volume, and pores having a diameter of 150 to 600 .ANG. occupying at least about 40% of the total pore volume made up of pores having a diameter smaller than 600 .ANG..
The following patents disclose various types of clays: U.S. Pat. Nos. 3,586,478; 4,049,780; 4,629,712; and PCT Publication Nos. WO 93/11069; and WO 94/16996.
The following patents disclose various types of agglomerates which can be formed from alumina: U.S. Pat. Nos. 3,392,125; 3,630,888; 3,975,510; 4,124,699; 4,276,201 (see also U.S. Pat. No. 4,309,278); 4,392,987; and 5,244,648.
U.S. Pat. No. 4,276,201 discloses a hydroprocessing catalyst which utilizes an agglomerate support of alumina, e.g., beaded alumina, and silica wherein the silica is less than 10 wt. % of the support. The agglomerate support has a surface area of 350-500 m.sup.2 /g. A total pore volume (TPV) of 1.0 to 2.5 cc/g with less than 0.20 cc/g of the TPV residing in pores having a diameter greater than 400 .ANG..
U.S. Pat. No. 5,114,895 discloses a composition of a layered clay homogeneously dispersed in an inorganic oxide matrix such that the clay layers are completely surrounded by the inorganic oxide matrix. The inorganic oxide matrix is selected from alumina, titania, silica, zirconia, P.sub.2 O.sub.5 and mixtures. Suitable clays include bentonite, sepiolite, Laponite.TM., vermiculite, montmorillonite, kaolin, palygorskite (attapulgus), hectorite, chlorite, beidellite, saponite, and nontronite. To get the clay homogeneously dispersed within the inorganic oxide matrix, a precursor of the inorganic oxide is dispersed as a sol or hydrosol and gelled in the presence of the clay. While clay contents of 5 to 70 wt. % are disclosed broadly, the Examples employ at least 30 wt. % clay. In addition, none of the pore properties or the resulting product are disclosed.
U.S. Pat. No. 4,159,969 discloses a process for the manufacture of agglomerates of aluminum oxide by contacting a hydrous aluminum oxide gel with an organic liquid immiscible with water wherein the amount of said liquid is a function of the water in the hydrous aluminum oxide gel. An amount of clay, such as bentonite or kaolin, sufficient to increase the strength of the agglomerates may be added to the aluminum oxide during or after gelation. No specific amount of clay is disclosed and kaolin is not a swellable clay. None of the examples employ clay.
U.S. Pat. No. 3,630,888 discloses a catalyst having a structure in which access channels having diameters between about 100 and 1000 .ANG. units constitute 10 to 40% of the total pore volume and in which access channels having diameters greater than 1000 .ANG. units constitute between about 10 to about 40% of the total pore volume, while the remainder of the pore volume comprises 20 to 80% of micropores with diameters less than 100 .ANG..
The following patents disclose various hydroprocessing operations and use of catalysts therein: U.S. Pat. Nos. 3,887,455; 4,657,665; 4,886,594; PCT Publication No. WO 95/31280.
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