Catalytic reforming, or hydroforming, is a well established industrial process employed by the petroleum industry for improving the octane quality of naphthas or straight run gasolines. In reforming, a multi-functional catalyst is employed which contains a metal hydrogenation-dehydrogenation (hydrogen transfer) component, or components, substantially atomically dispersed upon the surface of a porous, inorganic oxide support, notably alumina. Noble metal catalysts, notably platinum, have been widely used commercially in recent years in the production of reforming catalysts, and platinum or alumina catalysts have been commercially employed in refineries for the last few decades. In the last decade, additional metallic components have been added to platinum as promoters to further improve the activity or selectivity, or both, of the basic platinum catalyst, e.g., iridium, rhenium, tin, and the like. Reforming is defined as the total effect of the molecular changes, or hydrocarbon reactions, produced by dehydrogenation of cyclohexanes and dehydroisomerization of alkylcyclopentanes to yield aromatics; dehydrogenation of paraffins to yield olefins; dehydrocyclization of paraffins and olefins to yield aromatics; isomerization of n-paraffins; isomerization of alkylcycloparaffins to yield cyclohexanes; isomerization of substituted aromatics; and hydrocracking of paraffins which produces gas, and inevitably coke, the latter being deposited on the catalyst.
In reforming, a series of reactors constitute the heart of the reforming unit. Each reactor is generally provided with fixed beds of catalyst which receive upflow or downflow feed, and each is provided with a preheater or interstage heater, because the reactions which take place are endothermic. A naphtha feed, with hydrogen, or recycle gas, is cocurrently passed through a preheat furnace and reactor, and then in sequence through subsequent heaters and reactors of the series. The product from the last reactor is separated into a liquid fraction, i.e., a C.sub.5.sup.+ or C.sub.5 /430.degree. fraction, and a vaporous effluent. Hydrogen or gas rich in hydrogen which usually contains small amounts of normally gaseous hydrocarbons, is separated from the latter, and recycled to the first reactor of the unit to minimize coke production. During operation, process temperature is gradually raised to compensate for the catalyst activity loss caused by the coke deposition. Eventually, however, economics dictates the necessity of reactivating the catalyst. Consequently, in all processes of this type the catalyst must necessarily be periodically regenerated, and this is usually done by burning the coke off the catalyst at controlled conditions; and thereafter, reactivation of the catalyst is completed in a sequence of steps wherein the agglomerated metal hydrogenation-dehydrogenation components are atomically redispersed.
In recent months considerable thought has been given to improving reforming processes, particularly by providing short cycle processes which, inter alia, utilize beds of fluidizable magnetizable catalytic particles which are contacted, and fluidized, with a naphtha feed and hydrogen at reforming conditions to produce a naphtha product of improved octane while simultaneously the fluidized beds are subjected to an axially applied magnetic field. In such processes the activity and selectivity of the catalyst throughout the operation approximates that of fresh, or freshly-reactivated catalyst, and preferably the operation is conducted at high severity conditions, as contrasted with present commercially produced reforming operations. In the improved processes, and as described by Application Ser. Nos. 054,032 and 054,033 filed July 2, 1979, continuous operation of all portions of the reforming unit is conducted, and the catalyst is moved therethrough as a more cohesive phase, or phase of narrow age distribution. Such processes are admirably suitable for conducting operations with a wide variety of feeds, particularly at high temperatures and low pressures, or other high severity conditions.
The application of a magnetic field upon a bed of fluidized, magnetizable catalytic particles in its preferred aspects stabilizes the bed and thereby suppresses, or minimizes bubble formation. The characteristics attributed to the stabilized bed greatly improve gas-solids contacting and lessen the need for long residence times; and yet the state of the bed is such that it can be rapidly recycled between reactor and regenerator. The properties of the bed in a magnetically stabilized state approach those of plug flow, thus providing the higher gas-solids contacting efficiencies offered by fixed bed contacting. Yet the magnetically stabilized bed, since it is fluidized, offers the advantages of fluidized beds for purposes of transport. Shorter contact times become feasible, and desirable because of higher average catalyst activity level. Moreover, the small particles which in a fixed bed would have a prohibitively high pressure drop at reasonable gas velocities provide very large surface areas which enhance catalysis and gas-solids contacting.
The catalyst employed in a magnetically stabilized bed operation is necessarily constituted of composite particles, preferably small particles, suitably particles which range in average diameter below about 800 microns, more preferably those which range from about 100 to 300 microns. The particles contain, besides a carrier or support material, a sufficient amount of a ferromagnetic or ferrimagnetic material to make the particles magnetizable, and a hydrogenation-dehydrogenation component, or components. A reforming catalyst also contains a halide component and, preferably, the catalyst is sulfided. Preferred magnetizable materials include ferromagnetic and ferrimagnetic alloys of metals, and metallic metals such as iron, nickel, cobalt. In general, also, the non-magnetizable material will include a vast number of conventional materials which are inert and/or known to catalyze the desired reaction.
The magnetizable component can be directly incorporated with the non-magnetizable material. For example, the non-magnetizable materials may be impregnated with a soluble precursor of a ferromagnetic or ferrimagnetic substance, e.g., an oxide, which is subsequently reduced to render the particles ferromagnetic or ferrimagnetic. Alternatively, the ferromagnetic or ferrimagnetic material may be incorporated into the non-magnetizable component by encapsulation of finely divided ferromagnetic or ferrimagnetic material. Thereafter, the catalytic component, e.g., the Group VIII noble metal, or metals, (Periodic Table of the Elements; Sargent Welch Scientific Company, Copyright 1968) notably platinum and metals used as promoters, if any, are composited with a previously pilled, pelleted, beaded, or extruded particulate support material by the impregnation method. Pursuant to the impregnation method, porous refractory inorganic oxides in dry or solvated state are contacted, either alone or admixed, or otherwise incorporated with a metal or metals-containing solution, or solutions, and thereby impregnated by either the "incipient wetness" technique, or a technique embodying absorption from a dilute or concentrated solution, or solutions, with subsequent filtration or evaporation to effect total uptake of the metallic components. Unfortunately, however, it is found that during impregnation of the catalytic metals onto the carriers, or supports, significant portions thereof are often lost or rendered catalytically inactive, or ineffective, apparently because the metals plate out on the ferromagnetic alloys or metals.
Only iron and cobalt, or alloys of such metals have sufficiently high Curie temperatures to remain magnetic in high temperature operations, notably at the high process temperatures used in refining operations. Unfortunately too, only a few alloys of these metals are sufficiently passive that they can withstand attack by the liquids and gases of process streams; such attack often causing the metal alloys to become rapidly oxidized, this resulting in the loss of their magnetic character. Of the handfull of metal alloys which are suitable for this purpose, e.g., stainless steel alloys, an unacceptable amount of the catalytic metal, e.g., Group VIII noble metal, notably platinum, is deposited on the alloy particles, the deposited catalytic metal being rendered ineffective in the performance of its catalytic function and thereby wasted. Such waste is obviously burdensome, and often intolerable.
It is accordingly a primary objective of the present invention to provide a novel composition, and process for the preparation of magnetic, catalytic composites to improve catalytic metals utilization.
A particular object is to provide a process of such character wherein magnetic ferrous metal alloy components of said magnetic, catalytic composites are passivated to suppress loss of the catalytic effectiveness of Group VIII noble metals, notably platinum, composited therewith.
A more particular object is to provide a novel process for the passivation of magnetic stainless steel to improve the catalytic effectiveness of catalytic metal components, especially Group VIII noble metals, notably platinum, composited therewith.
These objects and others are achieved in accordance with the practice of the present invention which embodies a composition, and process wherein a particulate magnetic alloy of iron or cobalt is contacted with a phosphate ion containing solution and reacted therewith sufficiently to form a surface film thereupon, removed from said solution, preferably dried, then admixed or otherwise incorporated within an inorganic oxide matrix, notably alumina, as inclusions, the composite particle is then contacted with a solution which contains a compound, or compounds, of a Group VIII noble metal, notably platinum, which is deposited within the composite particle in catalytically effective amounts without significant loss of the catalytic metal due to surface deposition of the catalytic metal upon said particulate magnetic alloy inclusions.
In its preferred aspects, a particulate magnetic iron alloy, notably a magnetic stainless steel alloy, is contacted with a phosphate ion containing solution and reacted therewith sufficiently to form a surface film, or coating thereupon, the particulate magnetic stainless steel alloy is removed from said solution, and dried. The powdered alloy is then admixed or otherwise incorporated within the inorganic oxide, or alumina as inclusions, and the composite particle is then contacted with a solution of said Group VIII noble metal compound, or compounds, particularly platinum, which is deposited in catalytically effective amounts within the composite particle without significant loss of the catalytic metal due to surface deposition of the catalytic metal upon said particulate magnetic stainless steel inclusions.
The magnetic alloys are formed into particles of average diameter ranging from about 5 to about 150 microns, preferably from about 10 to about 44 microns, and the particles then contacted, sprayed, or immersed in a dilute solution containing the phosphate ion for a time sufficient to permit the formation of a protective film, or coating thereupon. The particulate magnetic alloy is preferably immersed in the solution, suitably an aqueous solution, a contact time ranging from about 10 minutes to about 30 minutes, preferably from about 10 minutes to about 20 minutes, being sufficient at ambient conditions to form a continuous film. The nature of the film is not known, but a slight, visible change in coloration at the surface of the particles occurs on immersion of the particles within the solution. After the period of contact, or immersion, the magnetic particles are withdrawn from the solution and dried, e.g., by exposure to air, or by removal of the residual solution with an organic solvent such as alchol, alcohol and ether, acetone or the like; this step generally followed by air evaporation.
The dried, particulate now passivated magnetic alloys can be admixed or otherwise incorporated with an inorganic oxide material, notably alumina, in various ways known to the art. The powdered magnetic alloys are dispersed as inclusions, suitably spaced apart one from another and present in dilute concentration within the inorganic oxide material which serves as a matrix. Such composite generally contains from about 0.5 to about 50 percent, preferably from about 5 to about 40 percent of the alloy particles, based on the volume of the total composite particle.
The composite can be suitably formed by cogellation of the magnetic alloy particles with an inorganic oxide support material, preferably by admixture in a slurry or solution with an inorganic oxide precursor which is precipitated from solution with the magnetic alloy particles, the latter becoming inclusions within an inorganic oxide matrix. The composite can then be dried, calcined and impregnated to incorporate the desired catalytic metal, or metals; or a catalytic metal component, or components, can be incorporated within the composite particles at the time of formation by addition to the slurry or solution of a soluble compound, or compounds, of the catalytic metal, or metals. The support per se, aside from the magnetic alloy inclusions, can be constituted of, or contain, for example, one or more of alumina, bentonite, clay, diatomaceous earth, zeolite, silica, magnesia, zirconia, thoria, and the like. The most preferred support is alumina to which, if desired, can be added a suitable amount of other refractory carrier materials such as silica, zirconia, magnesia, titania, etc., usually in a range of about 1 to 20 percent, based on the weight of the support. Exemplary of a support for the practice of the present invention is one having a surface area of more than 50 m.sup.2 /g, preferably from about 100 to about 300 m.sup.2 /g, and higher, a bulk density of about 0.3 to 1.0 g/ml, and higher, an average pore volume of about 0.2 to 1.1 ml/g, and an average pore diameter ranging about 30 A to about 300 A, and higher.
The composite particle is calcined and then, preferably, impregnated with a catalytic metal, or metals. Suitably, the composite particle is calcined at relatively low temperature, preferably at temperatures ranging from about 300.degree. F. to about 800.degree. F., more preferably from about 300.degree. F. to about 500.degree. F. It has thus been found that low calcination temperatures are preferable inasmuch as composite particles calcined at low temperatures prior to impregnation produce catalysts which possess greater activity, and provide higher C.sub.5.sup.+ liquid yields. Moreover, low temperature calcination of the composite particles provides more effective passivation of the magnetic particles on contact with the phosphate ion.
Short contact times are also advantageous during the impregnation. Thus, it has been found that contact times extending beyond about thirty minutes permits greater deposition of precious metals upon the phosphate ion treated magnetic alloy inclusions of the composite, and hence there is little, if anything, to be gained by extensive periods of impregnation. Suitably, the period of impregnation ranges from about 5 minutes to about 30 minutes, preferably from about 10 minutes to about 20 minutes.
Essentially any catalyst component, or components, can be composited with the support particles, or with said inclusions, dependent upon the type of reaction which is to be carried out. For example, in conducting hydrocarbon conversion reactions, e.g., a hydroforming (reforming, with hydrogen) reaction, a catalyst can be formed which comprises a composite of a refractory or inorganic oxide support material, particularly alumina, and a Group VIII noble metal hydrogenation-dehydrogenation component, e.g., ruthenium, rhodium, palladium, osmium, iridium or platinum, notably platinum, to which a promoter metal, e.g., rhenium, iridium or the like may be added to promote the activity and selectivity of the catalysts. Suitably, the reforming catalyst, or composite also contains an added halogen component to provide acidity, particularly fluorine or chlorine, and preferably the promoter component is introduced into the support, or catalyst, by impregnating same with a solution comprising a soluble salt or compound thereof. The catalyst can also be sulfided, as in the conventional manner.
The catalyst composites of this invention may be in the form of powder, beads, tablets, pills, pellets, or extrudates depending upon the type of process.
The invention will be more fully understood by reference to the following selected demonstrations and examples which present comparative data which illustrates its more salient features. All parts are given in terms of weight except as otherwise specified.
The example immediately following describes the preparation and testing of two reforming catalysts under conditions which simulate the short contact times employed in a magnetically stabilized fluidized bed.