JPH0152328B2 - - Google Patents

Description

[Detailed description of the invention] The present invention has crystal structures of boehmite and pseudoboehmite.
A novel crystalline alumina hydrate that is intermediate between
and amorphous alumina. The common forms of catalysts are solid supports and supports.
This solid support consists of a supported catalytic material;
Usually particles of porous material, e.g. alumina.
Ru. These particles typically range from 1 mm in diameter to
The size is equivalent to a spherical particle up to 15 mm. porous
For example, alumina has a particle form,
For example, it is necessary to create a sphere, spherule, pill, or cylinder.
These materials are important in the present invention.
The material before printing is called the "carrier material", and the material used for printing
The latter is called a "shaped carrier". of the present invention
Novel alumina hydrate and its amorphous aluminum
The mixture with Na is a carrier material in this sense.
the fine spherical particles are made of the carrier material of the present invention or the like;
In this sense, it can be made from any of a variety of materials.
These microscopic carriers are
The spheres are catalytic when added with a catalytic agent. Activity, efficiency, stability and
Durability depends on the catalyst precursor, i.e. the support material and
chemical, physical, and
Structural properties and catalysts on shaped supports
Depends on quality nature and distribution. to these properties
Small changes in can make substantial differences in catalyst performance.
It can occur. Preferably a support that increases catalytic activity
The properties of the material depend on the properties of the shaped carrier particles.
Retained. In general, shaped carriers and carrier-based
Catalysts made of small amounts of catalytic material are essentially the same
physical and structural properties that affect the thermal activity of the catalyst.
There is only a slight difference in these properties due to the effect.
Ru. Internal porous structure of catalyst particles and their precursors
is the surface area available for contact between the catalyst material and the reaction components.
Determine extent and accessibility. Increased pore size
Then, the reaction components and products entering and exiting the catalyst particles
the rate of diffusion of is large, and this is often
Resulting in improved catalytic activity. However, the hole
The extent to which the magnitude of can be advantageously increased is limited.
As the pore size increases, the reaction occurs
Area increases. An excellent catalyst has a high specific surface area,
Balanced combination of cumulative pore volume and multi-macroporosity
It should have a certain character. High polymacroporosity is due to the diameter
Pore size with a relatively high proportion of pores larger than 1000 Å
distribution. Furthermore, the density is low and eventually the thermal inertia
Small alumina and formed alumina are
It will produce a catalyst that quickly reaches the reaction temperature.
cormorant. Catalyst supports are often porous refractory inorganic oxidants
materials, such as silica, alumina, magnesia,
Zirconia, titania, and combinations thereof
It is set. Alumina is inherently highly porous;
in the temperature range normally encountered in many catalytic reactions.
Because it maintains a relatively high surface area across the
is a desirable carrier material. However, high temperatures
If used for a long time under the conditions, the overheating of alumina will cause sintering.
This changes the crystal phase of alumina and alumina.
For example, to cause a loss of surface area available for catalysis,
catalytic activity. Alumina is fine powder or
or macro-sized particles formed from powder.
It is used as a catalyst support in the form of Physical and chemical properties of alumina in its manufacture
Because it is highly dependent on the means used to
The manufacturing method is for its use as catalyst support material.
It has been developed in an attempt to optimize its properties. Aluminum
Na is an aluminum salt, such as aluminum sulfate.
aluminum, aluminum nitrate, or aluminum chloride
A water-soluble acidic aluminum compound that can be
and alkali metal aluminates, e.g.
Combined with sodium mate or potassium aluminate
Often precipitated by letting. but
While the properties of the composition obtained after washing and drying
has high surface area, multi-macroporosity, phase stability, and
Generally disadvantageous in one or more of low densities
It had a Aluminum with some of the properties desired in a carrier material
A typical manufacturing method for Mina is described in U.S. Patent No. 2988520,
Described in Nos. 3520654, 3032541 and 3124418
It is. U.S. Patent No. 3,864,461 is based on its X-ray band.
Confirmed to be identical to pseudo-boehmite, low
bulk density, if any mixed with small amounts of bayerite
Discloses a method for producing crystalline alumina.
And I'm particularly interested. The surface area, porosity, and density of the starting alumina material
In addition to retaining its properties, fine alumina
The method of forming particles has low shrinkage, high abrasion resistance
and should form alumina with high fracture strength.
It is. Ordinary low-density carriers generally have structural uniformity.
Lacks physicality. Alumina unless stabilized
Particles lose their geometric volume when exposed to high temperatures during use
considerably shrinks. Excessive shrinkage can lead to filling in the catalyst bed.
Forms a channel that does not leak
passes through the channel without contacting the medium. High wear resistance improves structural integrity under conditions of mechanical stress
Provides integrity and retention of activity. into the reaction zone
During transport, filling, and long-term use, catalyst particles
The child is subjected to multiple collisions, resulting in material being ejected.
Lost from the lateral layers. present in the outer volume of the particle.
Wear of the catalytically active layer affects catalyst performance.
and also reduce the volume of material in the reaction zone
let Highly packed and densely packed in a fixed catalyst bed
Due to shrinkage and/or abrasion of retained particles
The loss of volume makes the particles loose and during vibration
It tends to increase movement and collisions. filled with
Once a floor becomes loose, wear tends to increase.
There is a direction. During storage, catalysts often sit on the back waiting to be charged.
is filled into tall containers. Moreover, the weight of the particles
In order to withstand the forces generated, the catalyst has a high fracture resistance.
You have to show strength. Particle size, size distribution, and shape are
affects both the structural integrity and the activity of the catalyst.
vinegar. These properties make catalysts that can be packed in fixed beds
volume, pressure drop across the bed, and reactant components and
Determine the external surface area available for contact. fine aluminum
Mina can be pelletized, tableted, molded, or
Extrude to create macrosize of desired size and shape.
can be made into particles of Typically, Mac
Ro-sized particles have a diameter of 1/32 to 1/4 inch (approximately
0.79~6.35mm), length to diameter ratio of approximately 1:1~
It is a cylinder with a ratio of 3:1. Examples of other shapes are prolate spheres
Shape: multilobed, figure-8, cloverleaf, bell-shaped
What is it? The spherical shape can be used as a catalyst support without any protrusions or irregularities.
Particles with an ivy-shaped surface, and
For example, they offer a number of advantages over extruded cylinders.
Ru. “Spheroids” here generally means
A particle that is spherical but not exactly a sphere, and
For example, this means that it may be a rotating ellipsoid.
The spherical particles fill the catalyst bed evenly.
reduces fluctuations in pressure drop through the floor
and therefore create a bypass for a portion of the floor.
Reduce channel formation. of particles of this shape
Another advantage in use is that the spherical shape is suitable for handling, transporting or
shall not exhibit sharp edges that may wear out during use.
That is true. The most described method of producing spherical alumina particles
One of the methods is the oil-drop method, in which
A drop of aqueous acidic alumina material flows through a water-immiscible liquid.
While falling, it gels into a sphere and under basic PH conditions.
to solidify. The activity and durability of alumina supported catalyst
Attempts to provide enhanced structural and mechanical properties
A number of oil-drop technologies have been developed. spherical raw
The density, surface area, porosity and uniformity of the composition are
The nature of the lumina feed, as well as its breaking strength and abrasion.
It changes greatly with the wear resistance, and the production of feed,
hardening and gelling steps and subsequent drying and
It depends on the conditions used for the baking process. internal game
added to the feed prior to droplet formation and
Release ammonia into heated immiscible liquid
to a weak base such as hexamethylenetetramine.
Gelation of alumina is carried out by the most common oil-drop method.
It is. U.S. Patent No. 3,558,508 (Keith et al.)
ammonia in a column containing a water-immiscible liquid
the droplet is solidified by contact with its outer surface.
An oil-drop method using an external gelation technique is described.
There is. This method can be applied to fine aluminum to a considerable extent.
Certain aluminum produced by acid hydrolysis of aluminum
based on the use of natural supplies. In addition, spherical alumina particles
The children were Olechowska et al.
“Preparation of Spherically Shaped Alumina
Oxide”,International Chemical Engineering,
Vol 14, No. 1, pages 90-93, January 1974 issue
Formed by the hydrocarbon/ammoniac character described
can. In this method, nitric acid and dehydrated water are
Drops of slurry with aluminum oxide pass through the air.
Column containing hydrocarbon phase and ammonia phase
fall inside. A drop passes through a water-immiscible liquid
It takes on a spherical shape and then solidifies in a coagulation medium.
It becomes spherical beads or pellets. Pseudo-sol child
A similar method using feed and hydrochloric acid is as follows:
It is stated in the dedication: 1 Katsobashvili et al., “Formation of
Spherical Alumina and Aluminum Oxide
Catalysts by the Hydrocarbon−Ammonia
Process−1. The Role of Electrolytes in
“The Formation Process”Kolloidnyi
Zhurnal, Vol.28, No.1, pages 46-50,
January-February, 1966; 2 Katsobashvili et al, “Preparation of
Mechanically Strong Alumina and
Aluminum Oxide Catalysts in the Form of
Spherical Granules by the Hydrocarbon−
Ammonia Forming Method” Zhurnal
Prikladnoi Khimii, Vol.39, No.11, 2424−
Page 2429, November, 1966; and 3 Katsobashvili et al., “Formation of
Spherical Alumina and Aluminum Oxide
Catalysts by the Hydrocarbon−Ammonia
Process−Coagulational Structure
“Formation During the Forming Process”
Kolloidnyi Zhurnal, Vol.29, No.4, 503−508
Page, July-August, 1967. Catalysts are used to convert pollutants in automobile exhaust to less objectionable substances.
Noble metals can be used as the main catalyst component or can be present in small amounts to promote the activity of the base metal system. US Pat. No. 3,189,568 (Hauel) and US Pat. No. 3,932,309 (Graham et al.) disclose the use of precious metal catalysts for the control of automobile exhaust emissions. US Pat. No. 3,455,843 (Briggs et al.) is typical of noble metal promoted base metal catalysts. Unpromoted base metal catalysts are described in US Pat. No. 3,322,491 (Barrett et al.). The activity and durability of automotive exhaust catalysts has historically depended on the location and distribution of precious metals on the support. Since the use of precious metals is largely limited by cost, small amounts of precious metals should be positioned on the support in such a way as to achieve the best overall performance over the life of the catalyst. Several opposing phenomena are involved in surface treatment. Impregnation of the maximum amount of carrier particles provides the maximum amount of impregnated surface area. However, due to the high gas velocities and short contact times in automobile exhaust systems, the oxidation rates of carbon monoxide and hydrocarbons and the reduction of nitrogen oxides are controlled by diffusion. Therefore, the depth of impregnation should not exceed the distance that allows effective diffusion of the reactive components into the pore structure of the particles. A combined balance between impregnated surfaces and proper dispersion and accessibility should be achieved to produce practical catalysts. The accessibility and dispersion of the catalytic metal will provide high initial catalytic activity once the catalyst reaches operating temperature. However, because significantly higher amounts of hydrocarbons, carbon monoxide, and other partially combusted substances form in the exhaust gas during early engine startup, the catalyst operates efficiently when the reaction zone is at a relatively low temperature. should have low thermal inertia in order to Common disadvantages of exhaust catalysts are high temperatures, mechanical vibrations and poisons present in the exhaust, such as lead, phosphorus,
When exposed to compounds such as sulfur over long periods of use, up to 50,000 miles, activity decreases. An effective catalyst can inhibit the growth of precious metal crystals, poisons,
Retains its activity due to crystalline phase changes and resistance to physical degradation. Optimal high temperature alumina catalyst supports have low density and high macroporosity while retaining substantial surface area and fracture strength and abrasion resistance. Furthermore, it is stable in the crystalline phase and in the filled geometric volume. Achieving the right balance of these interrelated and sometimes opposing properties and combining alumina carrier technology and metal impregnation technology to reduce vehicle exhaust emissions to levels required by current and future government standards. Difficulties are encountered in providing catalytic converters that can We have now discovered a new, crystalline, alumina monohydrate that can be converted into shaped supports with a unique and valuable combination of desired properties. According to the present invention, a structure intermediate between that of boehmite and that of pseudoboehmite, and from about 6.2 to about 6.5
A crystalline α-alumina monohydrate is provided characterized by a [020]d spacing of Å. This boehmite is used to make shaped carriers.
Pseudo-boehmite intermediate is mixed with a small amount of alumina gel, approximately 70-85% of the total alumina in the mixture
should be in crystalline form. Such mixtures are part of this invention. We have also discovered a method for producing this new alumina, especially in the form of a mixture already with alumina gel. According to the present invention, the novel alumina of the present invention, which has properties uniquely suited to form spherical particles having the combination of properties specified below, is characterized by It is produced by precipitation at a temperature of 100 ml for an hour and a pH of 100 ml, and ripening at a higher PH, followed by filtration. The rate of addition of the reactants can be adjusted to obtain the desired balance of crystalline and amorphous alumina in the mixture. The method of the present invention consists of the following steps: 1 The Al ₂ O ₃ concentration is 5 to 9% by weight and the temperature is
An aqueous solution of an aluminum salt of a strong mineral acid, preferably aluminum sulfate, at a temperature of about 140 to about 170 °C (about 60 to about 71 °C)
77 °C); the amount of aluminum salt added is sufficient to adjust the pH in the mixture to 2-5; 2 _{the Al2O3} concentration is 18-22% by weight and the temperature is
Simultaneously add to the mixture an aqueous solution of sodium aluminate (or other alkali metal aluminate) and an additional amount of aqueous aluminum sulfate (or other aluminum salt) solution that is between 130 and 160 °C (about 54 and about 71 °C) - this precipitates alumina to form an alumina slurry. The addition of alkali metal aluminate increases the PH of the mixture to values in the range of PH7 to PH8, and the PH of the slurry and temperature during precipitation are 7 to 8 and 140 to 180, respectively (about 60 to about
82° C.) and maintain a certain addition rate of the solution to form a boehmite-pseudoboehmite intermediate alumina; 3. Then adjust the pH of the slurry to 9.5-10.5.
The slurry is then optionally aged, followed by straining the slurry and washing the filter cake to form substantially pure alumina. The process is reproducible and produces hydrated alumina from which process impurities can be easily removed by water washing and filtration. temperature, time, speed,
Adjusting the concentration and PH produces a substantially pure microcrystalline pseudoboehmite-boehmite intermediate alumina with Al ₂ O ₃ present in crystalline form from about 70 to about 85% by weight of the total amount. Substantially uniform spherical alumina particles with an unexpected combination of low density, high surface area, multi-macroporosity, phase stability, and mechanical strength are produced in the present application from wet or dry boehmite-pseudoboehmite intermediates. can be prepared by the improved external gelation method disclosed in the divisional application of . A slurry of alumina is prepared in an acidic aqueous medium and the drops of this slurry are passed through a column containing an upper body of water-immiscible liquid and ammonia and a lower body of an aqueous alkaline coagulant. The resulting spherical particles are aged in an aqueous medium to achieve the desired hardness. The aged particles are dried and calcined. In addition, the catalyst consisting of a catalytically active metal or metal compound impregnated on spherical alumina particles prepared by the external gelation method described above has excellent activity and durability in many catalyst systems. I understood. Due to the fast light-off and long-term activity of this catalyst under the high temperatures and mechanical vibrations present in the exhaust system, this catalyst is particularly suitable for eliminating pollutants in motor vehicle exhaust streams. The catalyst support made by the "external gelation" method, preferably made from the novel boehmite-pseudoboehmite intermediate of the present invention, is in the form of spherical particles and is characterized by: (i) About 0.1 to about 1000 to 10000 Å diameter pores.
(ii) a surface area of about 80 to about 135 m ² /g; (iii) abrasion loss of about 5% or less; and (iv) about 20 to about 36 pounds per cubic foot ⁽ about 0.32 ~
(v) a total pore volume of about 0.8 to about 1.7 ^{cm 3 /} g; (vi) in pores of diameter 100 to 1000 Å; Approximately 0.5 to approximately 1.0
and ( ^vii ) 0 to about 0.06 in pores smaller than 100 Å in diameter.
pore volume of cm ³ /g; and further characterized by: (viii) a volumetric shrinkage of not more than about 6% upon exposure for 24 hours at a temperature of 1800〓 (982°C); and (ix) a volumetric shrinkage of at least Breaking strength of 5 pounds (2.3Kg). The alumina manufacturing method of the present invention consists of five main steps. The stage is acidic PH in a very dilute aqueous system
involves the formation of boehmite crystal seeds in the nucleation stage. The stage is the main stage and includes precipitation and crystallization of alumina at a pH of about 7 to about 8. During this step, crystals of boehmite or pseudoboehmite grow from the hydrated precipitated alumina onto the crystal seeds. The stages are called precipitation and crystal growth stages. The step involves changing the PH of the system by adding an alkaline solution to reduce the electrical surface charge on the alumina precipitate. During this stage, the positive charge on the alumina particles gradually decreases until it becomes essentially zero at pH 9.4-9.6. In this state, the alumina precipitate is said to exist at its isoelectric point. that the surface exhibits no charge
This is a point in PH. The stage is therefore called the surface charge reduction stage. Optional steps include aging the system for a predetermined period of time, and steps include filtering and washing the resulting slurry to remove unwanted electrolytes or impurities. An optional final step of the method is drying of the washed cake to a powder material. This can be done with or without the inclusion of special additives to reduce the absorption of impurities. The reaction components used to carry out the process of the invention are water-soluble aluminum salts, such as aluminum sulfate, aluminum nitrate, aluminum chloride, etc.; alkali metal aluminates, such as sodium aluminate, potassium aluminate, etc. In certain embodiments, preferred reaction components are
Aluminum sulfate and sodium aluminate because of their cost, availability, and desirable properties in the practice of this invention. The reaction components are used in the form of aqueous solutions. Aluminum sulfate can be used in a wide range of concentrations, from about 5% by weight and above, but for practical reasons it is preferred to use concentrations as high as about 6 to about 8% by weight equivalent Al ₂ O ₃ . The sodium aluminate solution should be a relatively freshly prepared solution that exhibits no precipitated or undissolved alumina. Sodium aluminate can be characterized by its purity and equivalent alumina concentration, which is about 16% by weight or more,
Preferably about 18-22% by weight _{equivalent Al2O3} . Additionally, it is alkali, e.g. at least equivalent
It should contain Na ₂ O to ensure dissolution of the alumina. This condition is about 1.2 or more, preferably about
Of course, for economic and practical reasons, the upper limit of the molar ratio should not be too large, which is approximately satisfied by a molar ratio of Na ₂ O to Al ₂ O ₃ of 1.35 or more. For that reason, in practical industrial processes the molar ratio does not exceed about 1.5. Impurities, insufficient concentration of soda, and high dilution make sodium aluminate unstable. Before starting this method, the reaction solution should be heated to about 130 to about
Temperature of 160〓 (about 54 to about 71℃), preferably about 140℃
〓Heat to (60℃). The reaction begins with a nucleation step in which an initial charge or "heel" of deionized water is introduced into a suitable reaction vessel. Stir this water and add approximately 140 to 170 〓 (approximately 60
Heat to a temperature of ~77°C). Generally, the temperature of this heel is about 5 to about 10 degrees lower than the target temperature at which the reaction occurs. An initial charge of aluminum sulfate is added to the water in a very small amount sufficient to adjust the PH of the mixture to a value of about 2 to about 5, preferably about 3 to about 4. At this point, the equivalent alumina concentration in the mixture is approximately 0.1
It should not exceed % by weight, preferably about 0.05% by weight. The combination of very low temperature, low PH, and high temperature partially hydrolyzes the aluminum sulfate, concomitantly forming very small crystals of boehmite. This nucleation occurs rapidly and the onset of the stage begins immediately after the first addition of aluminum sulfate. However, it is preferred to wait up to about 10 minutes, preferably up to about 5 minutes, to ensure that the nucleation step is proceeding and the system is properly seeded. The second step of the process is carried out by simultaneously adding sodium aluminate and aluminum sulfate to the mixture consisting of a heel of water containing crystal seeds. These solutions are added simultaneously from separate streams to the reactor at set essentially constant rates to precipitate the alumina and form an alumina slurry. However, since the reaction is conducted at a PH of about 7 to about 8, the rate of addition of one of the reaction components can be adjusted somewhat during the run to ensure that the PH of the slurry quickly reaches the desired range. During this stage, the PH will rise rapidly from about 2 to about 5 to about 7 to about 8. As the reactants are added to the initial heel, the alumina concentration in the resulting slurry will gradually increase. Under certain conditions, the alumina precipitate will tend to crystallize into the crystalline alumina intermediates boehmite and pseudoboehmite. If the precipitation rate exceeds the crystallization rate, excess hydrated alumina will remain in the precipitation as an alumina gel (amorphous alumina). The alumina produced in the present invention contains a crystalline boehmite pseudoboehmite intermediate and a gel. This requires that the rate of precipitation exceeds the rate of crystallization of hydrous alumina to the boehmite-pseudoboehmite intermediate, depending on the rate of addition of the reactants; the excess portion of the rate of addition of the reactants is approximately 70-85% Controlled to leave crystalline alumina and amorphous gel. The pH and temperature of the slurry and the rate of addition of reaction components are maintained such that a crystalline boehmite-pseudoboehmite intermediate and an amorphous gel are formed during precipitation. Since the rate of crystallization is primarily set by the temperature of the system, the rate of addition of the reactants will vary depending on the particular temperature at which the reaction is carried out. At the lower end of the operating temperature range,
The rate of crystallization will be relatively low and eventually the addition of the reactants will proceed at a low rate. Generally, the temperature is approximately
Maintain the temperature between 140 and 180〓 (about 60 and 82℃). For example, for temperatures in the range of about 140 to about 150 °C (about 60 to about 66 °C), the addition rate is such that the flow of reactants remains substantially constant during the entire precipitation stage,
It will last for at least 70 minutes, preferably for at least 70 minutes. On the other hand, on the high temperature side of the operating temperature range, for example about 170
At temperatures between about 180° C. and about 77° C. to about 82° C., the addition rate can be increased significantly so that the step is carried out for a shorter period of time, such as about 15 to about 30 minutes. In preferred precipitation reactions, the temperature is about 150 to about 170〓 (about 66 to about
77°C), and the precipitation rate slows the reaction from about 30°C to about
It should be arranged to run over a period of 70 minutes, preferably about 40 minutes to about 60 minutes. In a very specific embodiment, the reaction is between 155 and 165
〓 (68-74℃), and the addition of reaction components is approximately 48℃.
By maintaining the flow of the reaction components essentially constant during the entire precipitation step over a period of ~52 minutes, and adjusting the relative flows as necessary, the following procedure was carried out: Obtain a programmed PH: [Table] In general, the exothermic nature of the reaction will provide sufficient heat to maintain the temperature at the desired level, as long as the water heel and reaction components are preheated as described above. Probably. If there is difficulty maintaining the desired temperature, external cooling or heating can be applied to ensure proper temperature control. Carrying out the precipitation reaction under the aforementioned conditions will ensure the formation of precipitated alumina exhibiting the desired balance between crystalline α-alumina monohydrate (boehmite-pseudoboehmite intermediate) and gel. . At the end of the stage, the equivalent weight in the slurry
The concentration of Al ₂ O ₃ should range from about 5 to about 9% by weight, preferably from about 6 to about 8% by weight. Balance the reactant materials added at this point with Na ₂ O
Sodium expressed as moles of H ₂ SO ₄
The ratio of sulfate, expressed as moles, is at least 0.80, preferably at least 0.88, but can be at most 0.97. At the end of the stage, when the desired amount of alumina has precipitated, the flow of alumina sulfate is stopped. Steps are then carried out to reduce the charge on the surface of the precipitated alumina from a strongly positive level to zero or possibly a low negative value. This is accomplished by adjusting the PH to a value near or somewhat above the isoelectric point of the alumina, which is anywhere from about 7 to about 8 to 9.4 to 9.6 at the end of the stage. Generally, the PH of the slurry is adjusted to about 9.5 to 10.5, preferably about 9.6 to about 10.0. Changes in PH can be made by using any alkaline solution, such as sodium hydroxide. However, from a practical point of view it is desirable to continue to use the initial sodium aluminate reaction component solution as the alkaline solution. By doing so, additional amounts of alumina could be added to the slurry while the PH change occurs to increase yield and lower cost. Finally, in a preferred embodiment of the invention, the step is carried out by adding sodium aluminate continuously at a slow rate. This ensures that the target value of PH is not exceeded, or that local excess concentrations of sodium aluminate result in a high PH that favors the formation of undesirable crystalline phases, e.g. bayerite (β-alumina trihydrate). It is ensured that no precipitation of alumina occurs under the conditions. During stages, maintain the temperature of the slurry as in stages and continue stirring. Sodium aluminate until the PH rises to about 9.5 to about 10.0.
First slowly and continuously, then discontinuously if necessary, in addition to reaching the final target PH value.
During this stage, the sulfate ions immobilized on the surface of the alumina particles cease to exist as the positive charge on the alumina surface decreases to zero or becomes somewhat negative. 9.5 to 10.5, preferably about 9.6 to about 10.0
When a pH of
It can be for a period as long as 20 minutes, and preferably the step should be carried out for a period of about 6 to about 12 minutes. After adding all the reaction components, the slurry can be aged for up to several hours.
This time depends on practical considerations such as preparation of equipment for use in the subsequent steps of filtration and washing. Generally, a maturation of about 30 minutes is used. In either case, large batches of alumina slurry produced in stages may not be processed in a single batch, but can be carried out continuously over a period of time so that a portion of the material is It will be matured. The alumina slurry can then be filtered and the filter cake washed to remove unwanted impurities.
Preferably, deionized water is used as a washing liquid to remove water-soluble impurities. The use of water containing impurities such as calcium and magnesium chlorides, carbonates or bicarbonates is undesirable. However, depending on the ultimate use of the alumina, some of these impurities, such as volatile impurities, may be tolerated. However, metal impurities, such as calcium, magnesium, iron, silicon, nickel, etc., are unacceptable except in very low concentrations. As used in the detailed description of the invention and in the claims, the term "substantially pure alumina" is used to refer to alumina whose impurity concentration does not exceed the following limits on a dry basis: as _Na2O . Calcium, expressed as CaO, 0.15% by weight; Magnesium, expressed as MgO, 0.15% by weight; Silicon, expressed as _SiO2 , 0.80% by weight; _Iron , expressed as _F2O3 , 0.07% by weight %; Nickel expressed as NiO, 0.07% by weight. A pure alumina product is obtained using deionized water. Deionized water is usually heated to facilitate electrolyte removal and heated to a temperature of 120 to about 180〓 (49 to about 82
℃). Removal of electrolyte during washing is facilitated by the crystalline nature of the precipitate.
Crystalline materials have a lower tendency to occlude impurities and are easier to clean due to improved turbidity properties. The amount of deionized water required to achieve good product quality can vary depending on the particular filtration equipment used. However, the amount is usually about 1 kg of Al ₂ O ₃ (dry basis) in the overcake.
It ranges from 20 to 100Kg. In certain embodiments, the washed percake can be used to prepare a satisfactory feed in the production of alumina spheroids, as detailed below. This can be carried out by removing as much water as possible during the process and using special additives for the preparation of the feed together with the dehydrated percake. In a preferred embodiment, the percake is dried to produce an alumina powder that can be conveniently stored without deterioration for extended periods of time until further processing.
Drying of the percake can be accomplished in several ways, such as tray drying, belt drying, and the like. However, a preferred method consists of adding water to the percake to form a pumpable slurry and rapidly removing the water by methods such as spray drying or flash drying. In these cases, the pumpable slurry contains from about 15 to about 20 weight percent solids. The slurry is ejected from a nozzle as fine droplets into a drying chamber. The drops come into contact with hot drying gas. for example,
In a spray dryer, the inlet temperature of the drying gas is approximately
800 to about 700〓 (about 427 to about 371℃). Adjust the slurry addition rate to maintain the outlet temperature at approximately 250〓
(121℃) or higher, but below about 400〓 (204℃), preferably about 300 to about 350〓 (about 149 to about 177℃).
℃). Use of these conditions allows partial removal of water without destroying the crystalline nature of the alumina. If the drying gases are products of combustion of the fuel used, these gases contain substantial concentrations of carbon dioxide. Carbon dioxide will be absorbed upon contact with the alkaline slurry and will likely react chemically on the surface. In such cases, the final product will contain small amounts of carbon dioxide as an impurity. This carbon dioxide is not a major problem in most of the subsequent steps. However, if necessary, carbon dioxide uptake can be reduced by pre-acidifying the pumpable slurry with a trace amount of acid to a pH of about 7 or less. Preferred acids in this step are thermally decomposable organic acids,
Examples are acetic acid and formic acid. Mineral acids may fix impurities that affect the process in later steps or, in the case of nitric acid, may be an undesirable source of pollution. During spray drying, a portion of the gel fraction of the precipitate crystallizes into boehmite-
It will be a pseudo-boehmite intermediate. Spray-dried products are not completely dry and contain a certain proportion of water. Generally, the spray dried product contains at least 18% water by weight and can contain up to about 33% water. Preferably, the moisture range is about 20 to
It would be about 28% by weight. As used herein, alumina refers to an alumina material containing Al ₂ O ₃ , water of hydration, water of association, and the like. The degree of dryness of alumina can be expressed in terms of the weight percent of Al ₂ O ₃ in it. Drying at 1200° C. for 3 hours is considered to produce 100% Al ₂ O ₃ . Partially dried hydrated alumina produced by the controlled reaction of sodium aluminate and aluminum sulfate is an intermediate between boehmite and pseudoboehmite. This form of alumina is alpha-alumina monohydrate with extra water molecules occluded within the crystal structure and has the formula Al ₂ O ₃ xH ₂ O,
Here, x is a value greater than 1 and less than 2. The boehmite-pseudoboehmite nature of the product, including its crystal structure, degree of crystallinity and average size of individual crystals, can be determined by X-ray diffraction techniques. Pseudoboehmite is Papee, Tertian and
Biais, “Recherches sur la Constitution des
Gels et des Hydrates Cristallises
d'Alumine”, Bulletin de la Societe Chimique
Discussed in de France 1958, pages 1301-1310. Boehmite is a long-known and well-defined mineral whose crystalline properties and X-ray diffraction pattern are included in Card No. 5-0190 of the American Society's X-ray Diffraction Index for Testing Materials. Are listed. Other properties that characterize the product of the invention are: its behavior during ripening under alkaline conditions; its ability to chemisorb anions such as sulfate ions at various PH; after severe heat treatment. its crystalline properties and stability; high temperature stability of its surface area, pore volume and pore size distribution; All of the above properties derive from the unique balance of crystalline and amorphous gel components in the product and its exceptional overall chemistry. The X-ray diffraction technique used for the determination of crystallinity is as follows: the X-ray diffraction pattern of the research product is analyzed using several commercially available X-ray diffraction units, such as a Norelco X-ray diffractometer. Measure using one of the following methods. A pattern is obtained that gives the positions and intensities of the diffraction peaks. Compare this pattern with the data given in ASTM Card No. 5-0190 given to boehmite. All matches of the diffraction peaks indicate that the product is boehmite.
However, if the [020] peak moves to 6.6-6.7 Å while the other peaks remain essentially unchanged,
This indicates the presence of pseudo-boehmite. The properties of the product can be further determined by measuring the exact position of the [020]d interval. Intermediate values between 6.2 and 6.5 Å indicate the presence of materials of intermediate nature.
The [020] peak can further be used to determine the crystallinity of a substance. The area under this diffraction peak is measured with a planimeter and compared to the area under the corresponding peak of a reference sample experiment under the same conditions in an X-ray diffractometer. The reference sample is chosen from products known to contain a high proportion of boehmite and defined as "100% boehmite". The ratio of these areas gives a relative measure of the crystallinity of the study sample. Finally, the properties of the crystal can be investigated in more detail by measuring the width of the [020] diffraction peak. Mathematical correlations are derived from others,
It is described in the literature and can be used to calculate the average crystal size (Å) as a function of the peak width measured at the center of the largest peak. For a particular diffraction peak, the average crystal size is inversely proportional to the width of the peak at half its maximum intensity.
Relative measurements can be made by simply measuring the width at half the maximum intensity of the [020] diffraction peak. Larger values of width correspond to smaller crystal sizes, while smaller values of width correspond to larger crystal sizes. For example, obtained by dehydration of large, well-defined crystals of α-alumina trihydrate,
100% crystalline α-alumina monohydrate gives a very tall, narrow peak. In this substance,
The [020] reflection occurs at 6.1 Å, indicating that the product is boehmite rather than pseudoboehmite, and the width at half maximum intensity is only about 0.2 Å, indicating the presence of large crystals. shows. In contrast, microcrystalline pseudoboehmite is 6.6
[020] peaks at values ranging from ~6.7 Å are shown. These materials exhibit very broad peaks with values at half maximum intensity of about 2 Å or more. In other words, these materials exhibit crystalline sizes that are approximately an order of magnitude smaller than 100% crystalline alpha-alumina monohydrate. The size of boehmite crystals is about 200 Å, while the size of pseudo-boehmite crystals is about 20 Å. The products of the invention exhibit a structure intermediate between that of boehmite and that of pseudoboehmite, ranging from about 6.2 to about
Characterized by a [020] d spacing of 6.5 Å, preferably about 6.3 to about 6.4 Å. [020] The width of the half maximum intensity of the peak is about 1.65 to about 1.85 Å, preferably about 1.75 to about 1.80 Å. This indicates a small crystal size, ie closer to the micro size of pseudo-boehmite than the macro size of boehmite. Expressed in terms of relative crystallinity, the product of the process of the invention has a total amount of Al ₂ O ₃ present in crystalline form of about 70 to about 85
% by weight, with the remainder of the alumina in amorphous form. The boehmite-pseudoboehmite product of the present invention has high crystal purity, small crystal size - i.e., microcrystallinity and relatively high relative crystallinity. Characterized by. In these respects, the product is unique due to the fact that it is produced under conditions that give a high ratio of crystalline material to amorphous gel. This contrasts with prior art materials in that the fraction of amorphous gel in the product is very high or essentially absent as in boehmite. The crystallinity and intermediate crystal size properties of the materials of the invention make them unique in their application as starting powders for the production of catalyst supports of very good and unexpected properties. . The nature of the balance between crystalline and amorphous materials in the products of the invention is further characterized by the following tests: Surface chemisorption of anions at different PH. Amorphous hydrated alumina has a tendency to crystallize.
The particular crystalline phase obtained depends on the nature of the environment around the alumina during crystallization. Materials consisting of boehmite or pseudoboehmite and containing a high proportion of gel components crystallize into beta trihydrate (bayerite) upon prolonged exposure to high temperatures in an alkaline aqueous environment. In contrast, materials containing little or no gel components will not develop bayerite crystalline phases under similar conditions of alkaline ripening. For example, alumina produced at low temperatures and consisting primarily of pseudoboehmite containing a high proportion of internally dispersed gel can be produced in an aqueous sodium hydroxide solution with a high pH, e.g.
(49°C) for at least about 18 hours, bayerite develops while others remain essentially unchanged and maintain their crystalline nature. This indicates that the formation of bayerite is not due to the sacrifice of pseudoboehmite or its disappearance, but that bayerite is formed from amorphous alumina gel. In contrast, a product of the invention treated under the same conditions will not show any presence of bayerite. This indicates that the amount of gel in the material of the invention is very small or otherwise the gel is so stable. The anion chemical absorption test involves preparing a slurry of the alumina powder to be studied with deionized water and potentiometrically titrating this slurry with dilute sulfuric acid of known molar concentration over the PH range in which the alumina is insoluble. Consisting of This titration was carried out slowly,
Ensure that there is sufficient time for the acid to diffuse into the structure of the alumina product. About 9 to 4 questions
Over the PH range, alumina is insoluble, so titration with sulfuric acid is considered a measure of sulfate fixed or chemisorbed onto the alumina surface at a constant PH. For different aluminas, the amount of acid required to reach a particular PH from a common starting point is an indirect measure of the extent of the alumina interface exposed to the aqueous medium. Materials that exhibit very high crystallinity and very large crystal size have small interfacial areas, and thus require less acid to produce a given change in pH. In contrast, materials with very high gel content exhibit a large interfacial area and, ultimately, require a large amount of acid to effect the same PH change. intermediate crystal/
Products with gel properties require intermediate amounts of acid to effect the same PH change. For example, 100% crystalline α-alumina monohydrate, consisting of large, well-defined crystals, has a PH
It takes only about 53 milliequivalents of sulfuric acid per mole of alumina to change from an initial value of about 8.3 to a final value of about 4.0. In contrast, alumina produced at low temperatures and exhibiting pseudo-boehmite properties, percentage crystallinity and crystal size exhibiting a low degree of crystallinity and high gel content requires only 1 mole of alumina to undergo the same PH change. Approximately 219 milliequivalents of sulfuric acid are required per sample. The compositions of the invention are characterized by an intermediate requirement for sulfuric acid to effect the PH change. about 130 to about 180 milliequivalents per mole of alumina,
Preferably about 140 to about 160 meq. of sulfuric acid will change the PH of the slurry of the compositions of the present invention from about 8.3 to about 4.0. The application of the alumina powder product of the present invention in the production of suitable supports for automotive exhaust catalysts requires that the material exhibit excellent stability of its structural properties at high temperatures. For example, after severe heat treatment that simulates what the catalyst encounters in service, its measured pore volume and surface area should remain high and stable. These high temperature properties are highly dependent on the purity of the initial material and its structural characteristics as well as the crystalline nature of the product after heat treatment. When heated, the materials of the invention gradually lose their hydration water and other associated or bound water. This dehydration transforms the crystal structure into γ-alumina. When heated to even higher temperatures, γ-alumina becomes δ-
It will be converted to alumina and finally to θ-alumina. All of these aluminas are high surface area and pore volume transition aluminas. Further heating to higher temperatures produces alpha-alumina or corundum, which is not transitional alumina and exhibits very low surface area and pore volume. The final transformation to α-alumina is so strong that its formation is accompanied by a significant reduction in pore volume and surface area. Excellent alumina powder, which can be turned into a support for excellent automobile exhaust catalysts, is thermally stable and can be used at moderate high temperatures, such as 1800-1900〓 (982-1038℃).
shows no transition to α-alumina. Generally, alumina with a high gel content tends to sinter to alpha-alumina at relatively moderate temperatures, such as 1800-1900°C (982-1038°C). Materials produced at low temperatures and having a high gel content as determined by some of the tests described herein exhibit an undesirable α-alumina appearance when heated, for example, to 1010°C for 1 hour. Will. In contrast, a product of the invention containing only a small amount of amorphous gel will remain stable and exhibit no α-alumina upon the same heat treatment.
After heating the composition of the present invention to about 1850°C (1010°C) for about 1 hour,
-Has an X-ray diffraction pattern of alumina. Furthermore, the products of the invention retain very substantial surface area and pore volume at those temperatures and they will remain stable even for long periods of time during severe heat treatments. The products of the invention exhibit a BET nitrogen surface area of from about 100 to about 150 m ² /g, and usually from about 110 to about 140 m ² /g, after heat treatment at about 1850°C (1010°C) for about 1 hour. Will. Also, it is about 0.60 ~
about 0.75 cm ³ /g, most commonly about 0.64 to about 0.72
It will exhibit a nitrogen pore volume of cm ³ /g. Furthermore, the pore structure of this heat treated material will not exhibit a high percentage of microporosity as measured by nitrogen pore size distribution methods. Typically, the products of the present invention are about 80 Å in size or less, often 100 Å in size or less.
It will exhibit less nitrogen pore volume. Throughout the detailed description and claims, "nitrogen pore volume" is referred to as S. Brunauer, P.
Emmett, and E. Teller, J. Am. Chem. Soc.
60, page 309 (1938). This method relies on the condensation of nitrogen into the pores, and the pore diameter
Effective for measuring pores in the 600 Å range. Throughout the detailed description and claims,
Surface area is defined by Brunauer, Emmett and
Nitrogen BET surface area measured by the method also described in the Teller literature. The volume of nitrogen absorbed is related to the surface area per unit weight of the support. Formation of Shaped Supports from Alumina Dry alumina powder or washed alumina percake with suitable crystalline properties, such as those produced according to the present invention, are preferably used in the preparation of the feed for the oil drop formation process. However, other suitable starting alumina compositions, such as those described below, may be used to form the spherical alumina particles. Alumina and an acidic aqueous medium, such as an aqueous solution of an acid or an acidic salt, are combined to form a slurry. Preferably, an aqueous solution of a monobasic mineral acid is mixed with water and alumina to form a slurry. When using a monobasic acid,
A homogeneous plastic slurry of the desired viscosity forms. Hydrochloric acid and other strong monobasic acids can be used to wash the support to remove these electrolytes. Aluminum nitrate can be used. Nitric acid is preferred in this method because it can later be decomposed and removed from the bulb by heating, so that cleaning of the bulb is unnecessary. In order to minimize the nitrogen oxides produced as toxic emissions in later stages, the nitric acid is replaced with a degradable monobasic organic acid, such as acetic acid (hereinafter designated by the symbol CH ₃ COOH), formic acid, or a mixture thereof. It is preferred to substitute the main moiety, for example about 0.5 to 5
A mixture of organic acid and nitric acid in a molar ratio of can be used. The bulk density and compressive strength of the spherical product depend on the composition of the feed. Increasing the alumina and/or acid content of the feed increases these physical properties. If the concentration of alumina and/or acid is too high, the spheres will crack when drying, and if the concentration is too low, weak, powdery spheres will result. Due to the gel content of the alumina used to make the feed, a small amount of acid is sufficient to form a plastic slurry. The slurry can contain from about 1 to about 12% by weight monobasic acid or mixtures thereof, and the slurry generally contains from about 10 to about 40, preferably from about 24 to about 32% by weight alumina, and from about 0.05 to about 0.50% by weight alumina. with an acid to alumina molar ratio of . The amount of water is sufficient to produce a slurry with these acid and alumina contents. Standardizing this system with respect to 1 mole of alumina, the molar ratio of inorganic acid varies between 0.5 and 0.03, preferably 0.06, and the molar ratio of organic acid varies from about 5 to about 50, preferably from about 10 to It can be about 20. A particularly preferred slurry has a molar composition of (Al ₂ O ₃ ) _1.00 (CH ₃ COOH) _0.12 (HNO ₃ ) _0.06
(H ₂ O) _14.0±1.5 . Slurries can be prepared from a single alumina composition or a blend of alumina compositions. Blends are used to take advantage of some specific properties of the individual components of the blend. For example, an alumina filter cake can be acidified with acetic acid to about PH 6.0 to reduce carbon dioxide absorption before spray drying. High carbonate content in the powder can result in balls that crack when drying. Therefore, 20 parts of this low carbonate alumina can be combined with 80 parts of untreated dry powder to form a formulation with an acceptable carbonate level. Preferably, the alumina powder and an acidic aqueous medium are mixed by stepwise addition of the powder to the medium to acidify the alumina, which may be present in the spray-dried alumina powder.
Decrease the level of _CO2 . For example, 80% of the alumina required for a given batch of product can be mixed into water containing the desired amount of acid. After a period of mixing, the remaining 20% of the powder is added to the batch. In addition, recycled calcined product fines can be added in an amount up to about 15% of the total alumina. This reduces the tendency of the product to shrink to about 2 to about 3% by volume. It also has the advantage of being able to recycle scrap products, such as fines.
What makes this method so economical? Agitation and aging of the slurry provides a homogeneous material with a viscosity that allows for proper formation of droplets that can produce low shrinkage spheres. Agitation of the slurry can be accomplished by a variety of means ranging from simple hand agitation to high shear mixing. Aging of the slurry can be from a few minutes to a few days. Aging time is inversely proportional to energy input during mixing. Therefore, the alumina powder can be stirred into the acid and water mixture by hand for 10 minutes and aged overnight to the appropriate consistency for droplet formation. For example, in a particularly preferred method using approximately 10 pounds (4.5 Kg) of powder, 60% of the powder is mixed with all of the acid and water and a 3 inch (7.6 cm) blade is approximately
0.5hp Cowles rotating at 3500rpm
About 2 to about 30 minutes in a dissolver, preferably about 15 to about 20 minutes
Mix vigorously for a minute. Then the remaining 40% of the powder
and stir for about 5 to about 60 minutes, preferably about 30 to 40 minutes. After stirring, the slurry is stirred for about 1 to about 5 hours to the proper consistency. During mixing, the PH increases, with the final PH generally being about 4.0 to about 4.8, preferably about 4.3 to about 4.4.
Immediately after the preferred compounding technique, the viscosity of the slurry is approximately
It can vary between 60 and about 300 centipoise (cps). For optimal drop formation, approximately 200 to approx.
A slurry viscosity of 1600 cps, preferably from about 800 to about 1200 cps is desired. Although viscosities as high as 2000 cps can be used, the slurry is difficult to pump. Under actual operating conditions in the plant, the slurry may have to wait a long time before further processing. Under these conditions, the viscosity of the system may exceed the transportable range. Such thickened slurry does not need to be discarded. It can still be used according to either of the following two operations: The viscous slurry can be diluted with a controlled amount of water and stirred vigorously for a short time. This will cause a sharp decrease in viscosity and the system will be in the pumping range. The viscous slurry can be mixed with a freshly prepared slurry exhibiting a low viscosity of about 60 to about 300 cps. The resulting mixture has a viscosity in the pumpable range. These measures can be implemented without adversely affecting the properties of the finished product and subsequent processing steps. The viscosity of the slurry described in the Detailed Description of the Invention, Examples, and Claims is the viscosity measured with a Bruckfield viscometer. Spheroidal particles are formed by gelation in the organic and aqueous phases. Drops of the aged slurry form in the air above a column containing an upper body of water-immiscible liquid and ammonia and a lower body of aqueous alkaline coagulant. The droplets become spherical while passing through the upper phase and then solidify into hard spherical particles in the lower phase. The ammonia in the upper phase gels the outer layer of the droplet sufficiently so that the spherical shape can be retained as the droplet crosses the liquid interface and enters the lower phase. Excessive interfacial tension between the phases can cause the droplets to be held in the organic phase and deform the droplets. In such cases, a small amount, for example about 0.05 of the upper body
The presence of ~0.5% by volume surfactant at the interface, preferably 0.1% to about 0.2% by volume, allows the spheres to easily penetrate the interface. Liquinox,
Detergents sold by Alconox, Inc., New York, NY and other such surfactants can be used. The water-immiscible liquid has a specific gravity lower than water, preferably lower than about 0.95, and can be, for example, any of mineral oils or mixtures thereof.
The organic liquid should not drop so quickly as to interfere with proper sphere formation. Furthermore, it should not exhibit high interfacial tensions that could hold and deform the particles. Examples of suitable mineral oils are kerosene, toluene, heavy naphtha, light gas oil, paraffin oil, and other lubricating oils, coal tar oil, and the like. Kerosene is preferred because it is inexpensive, commercially available, non-toxic, and has a relatively high flash point. The organic liquid should be able to dissolve small amounts of anhydrous ammonia gas or form a suspension containing trace amounts of water containing dissolved ammonia. An essential requirement of this process is that the organic phase contains a sufficient but small amount of base, preferably ammonia, to be able to partially neutralize and gel the outer layer of the falling drop.
The rate of introduction of ammonia into the organic liquid should be sufficient to reach a working concentration at which hard particles form during a short period of fall. however,
The concentration of ammonia should not be so high as to cause essentially instantaneous gelation of the slurry droplets as they enter the organic liquid. Under these conditions, the droplet will not have enough time to build up surface tension to spheroidize it, and will gel into brittle particles. Furthermore, if the concentration of ammonia in the upper region of the organic liquid is high, ammonia gas will evaporate into the air pocket where the nozzle is located. Excessive ammonia concentration in this region can cause the droplets to prematurely gel before they are separated from the nozzle. Ammonia is a preferred coagulant because it forms excellent spheres, exhibits convenient solubility, and can be conveniently introduced to the bottom of the organic liquid. In a preferred embodiment, the organic liquid is contacted with anhydrous ammonia gas in a separate device called an ammonia adder and circulated through the column. In such a case, the organic liquid from the ammonia adder is introduced below the organic phase in the column, and this organic liquid flows upward through the column, forming countercurrent with the falling drops. The organic liquid is withdrawn at the top of the column and returned to the ammonia adder where it is replenished with ammonia. Under steady state conditions, a gradient in ammonia concentration develops within the organic phase of the column. This gradient is created by the reaction of falling drops of acidic alumina slurry with rising ammonia carried by the organic phase. Since the ammonia concentration in the top of the column is low, the droplets have enough time to form a spherical shape as they descend, and then gradually gel. Ammonia concentration in organic liquids can be determined by titration with hydrochloric acid to the bromothymol blue endpoint, approximately
It can be maintained between 0.01 and about 1.0% by weight, preferably between about 0.04 and about 0.07%. Lower concentrations generally result in flat spheres, and higher concentrations result in deformations such as tail formation. Column lengths can vary widely and will typically be about 3 to 20 feet (0.91 to 6.10 m) high. The organic phase is generally about 1/3 to about 2/3 of the length of the column.
and the solidification phase can be the remainder. The aqueous medium can contain any substance that induces gelation and has a suitable specific gravity, ie, a specific gravity lower than that of the slurry droplets. This allows the sphere to pass through the aqueous medium. Aqueous solutions of alkalis, such as sodium hydroxide, sodium carbonate or ammonia, can be used as coagulation media. A preferred medium is an aqueous solution of ammonia. This is because ammonia and its neutralization products can be easily separated from the spheres in subsequent processing steps. There is no need to remove ammonium residues since washing will remove sodium residues. The ammonia concentration in the aqueous phase is about 0.5 to 28.4% by weight, preferably about 1.0 to about 4.0
% by weight. During long-term use,
Ammonium nitrate and ammonium acetate are produced,
May accumulate to steady state levels in the aqueous phase. There are products of the neutralization reactions that occur during gelation of the spheres. The steady state concentration of the product will depend on the acid concentration in the alumina slurry feed. In developing the method, ammonium acetate and ammonium nitrate were added to the aqueous ammonia phase to simulate the effects of the ultimate steady state values of these salts. For the preferred slurry composition, the concentrations used were typically about 1.3% and about 0.8% by weight, respectively. In continuous operation, ammonia must also be constantly added to the aqueous phase to replace that used for gelling the spheres. In a preferred embodiment, the aqueous phase is circulated between the column and the ammonia addition tank. This tank also serves as a reservoir with a batch collection system that takes in the aqueous ammonia solution displaced from the column as the balls fill the collection vessel. The aqueous phase is withdrawn from the column to maintain a constant interfacial level. In a continuous ball withdrawal system, the ammonia additive sump feature of the aqueous phase is unnecessary. Any type of collection system can be used. The cross-sectional area of the column depends on the number of nozzles used. For one nozzle, a 1 inch (2.54 cm) diameter column provides a cross-sectional area of approximately 5 ^cm2 ;
This is sufficient to prevent uncoagulated droplets from impinging on the column walls and from sticking and contaminating the column walls.
A 4 inch (10.2 cm) diameter column provides sufficient cross-sectional area for up to about 16 to 20 nozzles, allowing droplets to pass through the column independently without contacting each other or the walls. In one embodiment of a suitable column, the aged slurry is pumped into a pressurized multi-orifice feed distribution arrangement. This distributor is located at the top of the oil column and is approximately 0.5 inch above the organic liquid.
Contains numerous nozzles located at 1.3 inches).
The feed distributor pressure depends on the viscosity of the slurry. Pressures of about 0.1 to about 15 psi (about 0.007 to 1.054 Kg/cm ² ) gauge are typically used. The pressure in the feed distributor regulates the rate of droplet formation. The droplet formation rate is about 10~
It varies between about 250 drops/min, preferably about 140 to about 180 drops/min. Approximately 1.5~2.5psi (0.105~
A distributor pressure of 0.176 Kg/cm ² ) provides the desired drop velocity when the slurry viscosity is between about 800 and about 1200 cps. Particles of desired size can be formed by changing the diameter of the nozzle used. For example, inner diameter 0.11
An inch (0.28 cm) nozzle will produce a sphere approximately 1/8 inch (0.32 cm) in diameter. Preferably, an air flow can be generated around the nozzle to prevent ammonia vapor from prematurely gelling the droplets. Droplets of slurry are formed in air at the tip of the nozzle and fall through the air into the body of water-immiscible liquid. When a drop of slurry initially contacts a water-immiscible liquid, the drop is typically lens-shaped. As the droplets fall through the ammoniated organic liquid, they gradually form into spherical particles, which are fixed in this shape by the coagulating ammonia and further solidified by the aqueous ammonia phase below. The particles are then aged in aqueous ammonia at about 0.5-28.4% by weight, preferably the same concentration as the column. The particles also develop hardness so that they do not deform during subsequent transport and processing steps. Generally, the particles are aged for about 30 minutes to about 48 hours, preferably about 1 to 3 hours. The particles are then drained and dried. Approximately 210~
Forced air drying to about 400° C. (about 98.9° to about 204° C.) for about 2 to 4 hours is advantageous, although other drying methods can be used. In a preferred drying method,
Drying is done at a temperature of about 300°C (149°C) gradually and uniformly.
This can be done for 3 hours by programming the temperature to rise to The amount of air used is 1 pound of Al ₂ O ₃ (0.454
Approximately 400~600 standard cubic feet (11.3~
can usually vary between ^17.0m3 ). In some circumstances, a portion of the air may be recirculated to control the humidity of the drying medium. The spheres are usually spread out on a perforated holding surface or screen to a thickness of 1 to 6 inches (2.5 to 15.2 cm), preferably 2 to 4 inches (5.1 to 10.2 cm). Shrinkage usually occurs during drying, but the spheres retain their shape and integrity. Deviating from the prescribed conditions for the preparation of the starting materials often results in significant changes in the resulting product. Excessive powder particle size, crystallinity, and impurity levels can cause cracking and fracture during drying.
On the other hand, excessive levels of gel in the powder or pseudoboehmite will cause excessive shrinkage and densification during drying, which also leads to cracking. Alumina compositions suitable for forming spheres other than the products of the invention generally have a boehmite or pseudoboehmite crystal structure, preferably a microcrystalline structure, a nitrogen pore volume of 0.4 to 0.6 cm ³ /g, and a surface area of 50 m ² /g or more. It will contain a sticky, amorphous gel. The dried spherical product is then treated at elevated temperatures to convert the crystalline alumina hydrate and amorphous gel components to transitional alumina. This can be carried out by a batch or continuous calcination process by contacting the product with a hot gas, which can be a directly heated gas or a conventional fuel-air combustion gas. Regardless of the particular method used, the product is calcined at a particular temperature range depending on the particular transitional alumina desired. For example, to obtain gamma type alumina,
The product can be conveniently calcined at a temperature of about 1000° to about 1500° C. (about 538° C. to about 816° C.). For applications that retain high temperature stability while maintaining high surface area and high porosity, the target material can be θ-alumina. Primarily theta-alumina products are approximately
1750 to about 1950〓 (about 954 to 1066℃), preferably about
At 1800 to about 1900〓 (about 982 to about 1038℃),
It can be obtained by calcining for about 30 minutes to about 3 hours, preferably about 1 to about 2 hours. For automotive exhaust catalysts, the high temperature treatment step is often referred to as stabilization. The catalyst support, consisting of spherical alumina particles and obtained after stabilization, has properties in the following ranges: Properties Approximate General Range Surface Area (m ² /g) 80-135 Packed Bulk Density (lbs/ft3)
20−36 Total pore volume (cm ³ /g) 0.8−1.7 Pore size distribution (cm ³ /g) Less than 100Å 0−0.06 100−1000Å 0.5−1.0 1000−10000Å 0.1−0.4 Greater than 10000Å 0−0.4 Destruction Strength (lb-force) 5-15 Volume shrinkage (%) 0-6 Abrasion loss (%) 0-5 Mesh size -4+10 However, when using preferred starting materials under preferred manufacturing conditions, the range of properties Properties Typical Range Surface Area (m ² /g) 90-120 Packed Bulk Density (lbs/ft3) 26-32 Total Pore Volume (cm ³ /g) 0.9-1.2 Pore Size Distribution ( cm ³ /g) Less than 100Å 0-0.04 100-1000Å 0.6-0.9 1000-10000Å 0.2-0.3 Greater than 10000Å 0-0.3 Breaking strength (lb-force) 7-12 Volume shrinkage (%) 2-4 Abrasion Loss (%) 0-2 Mesh size -5+7 Surface area is nitrogen BET surface area and other properties specified above were determined by the following method.
These methods can also be applied to finished catalysts. Packed Bulk Density A constant weight of activated spheres is placed in a graduated cylinder and contained within a graduated volume. As used here, the term "activated" refers to
This means processing in a forced draft oven at 320°C (160°C) for 16 hours. This activation ensures that all materials are tested under the same conditions. The graduated cylinder is then shaken until all settling has stopped and a constant volume is obtained.
Next, calculate the weight of the sample occupying a unit volume. Total Specific Pore Volume A fixed weight of activated spheres is placed in a small container (eg, a vial). Using a water-filled micropipette, the sample is titrated with water until all pores are filled, and the end point of the titration occurs at the initial wetting of the surface. These measurements agree with the total porosity calculated from the following equation: p=f/D-1/ρ p=total specific porosity (cm ³ /g) f=volume filling fraction (for spheres) typically 0.64
±0.04) D = Filled bulk density (g/cm ³ ) ρ = Crystal density of framework alumina (g/cm ³ ) (typically 3.0-3.3 g/cm ³ for transitional alumina) Mercury pore size distribution The pore size distribution within the activated spherical particles was determined by mercury porosimetry. Mercury penetration technology is based on the principle that the smaller a given pore, the greater the mercury pressure required to force mercury into the pore. That is, by exposing the activated sample to mercury, applying pressure in increments, and reading the volume of mercury at each increment, the pore size distribution can be determined. The relationship between pressure and the smallest pore through which mercury can pass at that pressure is given by: γ = -2σCOSθ/P where γ = surface tension θ = contact angle P = pressure 60000 psi (4218 Kg/cm ² ) using a pressure up to the gauge and a contact angle of 140°, the range of pore diameters covered is
It is 35-10000 Å. Average breaking strength Breaking strength is measured using a Pfizer hardness tester (Pfizer hardness tester).
Hardness Tester) TM141−33 (Charles Pfizer
and Co., Inc. 630 Flushing Avenue, Brooklyn,
It is measured by placing a spherical particle between two parallel plates in a testing machine such as the New York (New York). Gently move the board closer together with your hands. The amount of force required to break the particles is written on the dial corrected to pounds of force. Destroy a sufficient number of particles (eg, 50) to obtain a satisfactory estimate of significance for the total number. Calculate the average value from the individual results. Shrinkage A certain amount of particles is placed in a graduated cylinder and shaken until settling no longer occurs, as in the measurement of packed bulk density. Next, this sample is placed in a Matsufuru furnace at 1800°C (982°C) for 24 hours. At the end of this exposure, after shaking until sedimentation no longer occurs, the volume is measured again. Volume loss after heating is calculated based on the original volume and reported as percentage shrinkage. Abrasion Losses A settling volume (60 c.c.) of the material to be treated is placed in a specially constructed inverted Ernmeyer flask connected to a metal orifice inlet. 14 Place a large (1 inch) outlet covered with mesh mesh on the flat side of the flask. High velocity dry nitrogen gas is passed through the inlet orifice to cause the particles to (1) circulate and abrade each other, and (2) collide with each other in the top region of the flask to break up as a function of strength.
Process the material for 5 minutes and weigh the remaining particles.
The weight loss expressed as the initial feed after the test is
Expressed as wear loss. Nitrogen flow is approximately 3.5-4.0, depending on the density of the material
It will range from about 99 to 113 cubic feet per minute. The flow rate must be sufficient to impact the particles in the top region of the flask. Fines produced by abrasion are carried away from the flask by the nitrogen stream, causing a weight loss of the original feed material. The alumina of the present invention and the above sphere forming conditions are:
Spherical alumina particles are provided that have a highly unexpected and unique combination of desirable properties. The spheres have a total pore volume ranging from about 0.8 to about 1.7 cm ³ /g.
Although this is a high total pore volume, it is not exceptional in itself. What makes this pore volume exceptional is the distribution of the pores that make up this volume and its high temperature stability. The large volume part is composed of micropores (>1000 Å). Most of the remainder of the pores are in the 100-1000 Å range.
A very small number of micropores (<100 Å) are present.
This type of distribution is important for catalyst activity and stability. In a heterogeneous process, the activity of a catalyst depends on the rate of diffusion of reaction components into and rate of reaction products leaving the catalytic sites. Therefore, reactions in catalysts containing large amounts of macropores are less dependent on diffusion. However, the macropores occupy only a small portion of the surface area of the sample. The medium sized pores provide the surface area necessary for catalyst activity.
This surface area has two components: a component required by the catalytically active clusters themselves and a component required to keep the clusters separate. When the clusters fuse together,
The catalytic surface area of the cluster will eventually decrease and the catalytic activity will increase. Microporosity, of course, gives a very large surface area, but this does not necessarily give good catalytic activity. reaction components and/or
Or product diffusion may be the rate controlling factor. The pores may be closed by sintering that occurs during use of the catalyst, or by the deposition of catalyst poisons, such as lead compounds in automobile exhaust systems. In either case, the activity of the catalyst in the closed pores will be lost. The surface area of the product spheres is high, but not unusually high. The surface area ranges from about 350 m ² /g to about 500 m ² /g for spheres heated to 1000〓 (538°C) and for spheres thermally stabilized at 1800-1900〓 (982-1038°C). Approximately 80m ² /g ~ approximately 135m ² /
g. Importantly, however, most of the surface area is associated with medium-sized pores and not with micropores. This favorable porosity distribution and its pore volume stability are a direct result of the unique combination of properties in the alumina powder used to make the spheres.
In particular, its purity and high ratio of crystalline material to alumina gel aid in minimizing microporosity. These properties also help explain the high temperature stability of the spheres. The spheres exhibit low volumetric shrinkage, preferably about 4% or less. The spheres retain a transitional alumina structure. α-Alumina is not detected even at temperatures of 1950°C (1066°C). It is well known that impurities act as sintering aids. Therefore, high impurity levels can promote shrinkage and alpha-alumina formation. High gel content also leads to the formation of α-alumina at high temperatures. High microporosity can result in high volumetric shrinkage as the pores are closed during sintering. The spheres also have an unusual combination of low bulk density and relatively high breaking strength. Low bulk density is important for fast light off, ie high initial activity. The crystallinity of the alumina composition is a contributing factor to both the low bulk density and high fracture strength. The low wear losses exhibited by the sphere are a direct result of the sphere's shape and strong construction. A smooth surface will not wear as easily as an irregular surface exhibiting corners and/or edges. Also, gelling methods produce cohesive, uniform particles rather than the layered particles that result from some mechanical boring methods. Mechanically formed particles can flake off during wear. Another feature of the sphere formation method is the close control of sphere size. In a given batch, more than 95% of the balls will fall within one mesh size, ie, within the range of -5+6 or -5+7. That is, 95% of the spheres pass through the 4 mm aperture sieve, but are retained on the 3.55 mm aperture sieve.
Small variations in the major or minor axis of the sphere
It is 0.015 inch (0.38 mm). That is, a controlled distribution of sphere sizes can be obtained by using an appropriate nozzle size distribution. This can facilitate regulating the pressure differential across the packed catalyst bed, which is an important factor in automotive exhaust catalytic systems. The nature of the spherical product defines a unique sphere that, taken as a whole, makes an excellent catalyst support. Such supports are characterized by low density, high macroporosity, high fracture strength, high temperature shrinkage resistance, good abrasion resistance and controlled size and shape. Process for Preparation of Supported Catalysts Catalysts consisting of spherical alumina supports impregnated with a catalytically effective amount of at least one catalytically active metal or metal compound are highly effective in many catalyst systems, especially those operating at high temperatures. It is effective for Alumina itself is catalytically active and is usually impregnated with a suitable catalytic material and activated to promote its activity. The choice of catalyst material, its amount, impregnation method and activation method will depend on the nature of the reaction for which the catalyst is to be used. Preferably, the catalytically active metal is a platinum group metal consisting of platinum, palladium, ruthenium, iridium, rhodium, osmium, and combinations thereof. The catalysts described above have the high initial and sustained activity necessary to meet the increasingly stringent exhaust gas controls required by state and federal laws of the United States and the laws of other countries. The catalyst agent therein is distributed at specific locations within the catalyst particles. Catalytic agents typically used in automotive exhaust catalysts are platinum group metals. Due to the high price of these metals, it is uneconomical to use large quantities. Therefore, it is important to position these metals in the most efficient and skillful manner. Examples of suitable platinum group metals are platinum, palladium, rhodium, ruthenium, iridium, and osmium and combinations thereof. The use of platinum group metals in automotive exhaust catalysts has been constrained by the natural occurrence of these metals. Most of the world's supply comes from South Africa, where the main metals are platinum, palladium and rhodium, which occur naturally in the approximate proportions of 68 parts platinum, 27 parts palladium and 5 parts rhodium. Typically, the total precious metal content of an automotive exhaust catalyst is from about 0.005 to about
1.00% by weight, preferably about 0.03-0.30% by weight, this range being both economical and technically possible. Of course, the optimal combination of metals will give the catalyst specific performance benefits, such as high levels of palladium for the more rapid oxidation and excellent thermal stability of generalized carbon, or greater catalyst poison resistance and hydrocarbons. combinations that provide high amounts of platinum for excellent resistance to oxidation, or high concentrations of rhodium for improved conversion of nitrogen oxides to nitrogen. Catalysts using spherical alumina as a carrier can contain only one type of platinum group metal, but usually contain several types.
The ratio of metals can vary over a wide range, but preferably the catalyst contains about 50% each of platinum and palladium.
or platinum, palladium and rhodium in a weight ratio of about 68 parts, 27 parts and 5 parts, respectively. Various noble metal compounds are well known and described in the literature. The type of compound used depends largely on the nature of the surface of the carrier and the interaction that occurs with it. For example, the anion or cation of platinum can be converted into H ₂ PtCL ₆ or Pt
(NH ₃ ) ₄ (NO ₃ ) ₂ can be used. The introduction of the noble metal compound used into the support ensures that once the noble metal compound is decomposed into the active form (metal or metal oxide), it is highly dispersed and positioned in specific positions in the catalyst particles. It should be ensured that the According to our research, for a high degree of initial activity there is a favorable positioning for the metals as well as a favorable distribution of one metal with respect to the other, which is particularly important for sustained durability. I found out something. The ability to control positioning and dispersion depends on the noble metal compound used. US patent to Graham et al.
The complex described in No. 3932309 has been found to be particularly useful. In this method, the catalyst is prepared by impregnating a support with a sulfite-treated platinum and palladium salt solution. These sulfite complexes give a high degree of dispersion when applied to a carrier. The cationic form of the complex, e.g.
By varying the _NH4 ⁺ or H ⁺ form, the depth of metal impregnation within the particles can be varied. Our research has shown that for high initial activity and, more importantly, high sustained activity, the precious metal should be located such that approximately 50% of the total precious metal surface area is deeper than approximately 50 microns. I understand. Regarding the specific positioning of the precious metal, it has been found that the preferred positioning of the precious metal should be such that about 50% of the active metal is located deeper than about 75 microns. Measurement of the noble metal surface area is carried out by hydrogen titration of oxygen. Detailed methods for performing this quantification can be found in DEMears and RCHansford, J.
of Catalysis, Vol. 9, 125-134 (1967). Elemental analysis is performed using conventional analytical methods. A method called the chloroform abrasion method is used to measure the surface area and precious metal concentration at specific depths within catalyst particles. This method is
It consists of stirring a certain weight of catalyst in a liquid (chloroform) for a certain length of time depending on the amount of surface to be abraded. Separate the worn material from the unworn remainder, dry and weigh.
By knowing the initial dimensions of the catalyst particles and the shape and weight of the particles, the depth removed can be determined. The wear material is analyzed for its precious metal surface area and precious metal content. From these data,
The noble metal surface area and noble metal content can be calculated as a function of depth into the catalyst particles. The activity and durability of the catalyst was finally tested in several ways. Bench scale testing is conducted in a manner that simulates the cold start experienced by the catalyst on a vehicle. Once the catalyst is heated, after a certain time it reaches an essentially steady state, at which time the efficiency is at a level that depends on the inherent activity of the catalyst. In a bench-scale test, a 13 ^cm3 sample was contacted with the gas at a sufficient total gas flow rate.
Achieve a gas hourly space velocity of 38000/hour. The simulated exhaust gas contains 1700ppm carbon as propane,
Contains 4.5% carbon monoxide by volume, with the balance made up of nitrogen. The preheat gas, if containing oxidizing species, will heat the catalyst bed to 700°C (371°C). However, due to the presence of carbon monoxide and hydrocarbons, the temperature increase in the catalyst bed is accelerated due to the exothermic oxidation reaction. In this test, the important parameters are the rate of light-off, measured by the time to reach 50% conversion of carbon monoxide and hydrocarbons, and the monoxide that occurs when the catalyst reaches essentially steady state. Carbon and hydrocarbon conversion efficiency. Catalysts with spherical alumina supports reach 50% conversion in a very short time and have very high conversions of hydrocarbons and carbon monoxide. With the phenomenon of fluctuating temperature conditions, lead, sulfur,
The catalyst is aged in a pulse flame combustor system to evaluate its durability when exposed to fuel additives containing phosphorus and phosphorus. In this system, a fuel doped with all of the toxic precursors found in normal fuel is burned.
Poisons to the catalyst, such as lead, sulfur and phosphorous compound deposits, formed. The fuel, which is hexane doped with tetramethyl lead antiseptics, trimethyl phosphite and thiophene, contains 0.23 g/gal (0.06 g/) lead, 0.02
Contains equivalents of g/gal (0.005 g/) phosphorus and 0.03% sulfur by weight. Fuel flow is 15ml/
It's time. 2000 and 500 for nitrogen and oxygen respectively
Mix at standard cm ³ /min. An additional 50 standard cm ³ of oxygen is added after the combustion point to ensure an oxidizing atmosphere. A detailed description of pulse flame combustor operation can be found in K.
Otto, RADalla Betta and H.C.Yao, J. Air
Pollution Control Association , Vol.No.6,
Pages 596-600, June 1974.
A ^13cm3 sample was heated to 1300㎓ (704℃) for 1 hour and
Exposure to repeated temperature cycles consisting of 2 hours at 1000°C (538°C). Temperatures are average catalyst bed temperatures. During extended aging periods of up to 500 hours, samples are periodically tested for activity by removing the sample from the pulsator unit and testing it on a bench scale activity unit. Small scale activity and aging tests are valuable in screening many catalysts; however, the ultimate test is a full scale vehicle or engine dynamometer evaluation. For a detailed explanation of the engine power test, please DM
Herod, MV Nelson and WMWang,
Society of Automotive Engineers , Paper
No.730557, reported in May1973. This test is similar to previously reported bench-scale activation tests. An ambient temperature catalyst contained within a full-scale converter is contacted with hot exhaust gas from the engine in a tightly controlled manner. The conversion of carbon monoxide, hydrocarbons and nitrogen oxides is monitored as a function of time. Detailed in the July 1970 Federal Register, and 1971
Federal Test Act as amended by notice in the Federal Register of July 2, 2015
A correlation has been developed that can predict the extent of a catalyst's performance when tested in a CVS test performed by a method (Procedure). Durability testing of full-scale converter charges of catalysts by JCPassassa and DGBeyerlin,
Society of Automotive Engineers , Paper
No. 730558, May 1973. Once the catalyst passes the laboratory engine dynamometer activity and durability tests, it is then subjected to fleet testing on standard production type vehicles.
Vehicles are tested in accordance with the Federal Testing Laws set forth above and incorporated herein by reference. This method is designed to quantify hydrocarbons, carbon monoxide and nitrogen oxides in gas emissions from motor vehicles while simulating an average trip in an urban area of 7.5 miles from a cold start. The test consisted of starting the engine and driving the car on the Chassis dynamometer according to a specified driving schedule consisting of a total of 1371 seconds.
A proportionate portion of the diluted gas emissions is continuously collected for subsequent analysis using a fixed volume sampler. The dynamometer test consists of two tests, one of which is a cold start after a minimum waiting period of 12 hours;
The other is a hot start test with a 10 minute wait between the two tests. Starting the engine, running it through the operating schedule, and shutting down the engine constitute a complete cold start test. Starting the engine and running for the first 505 seconds of the run chart completes the hot start test. The engine emissions are diluted with air to a constant volume and a portion is taken in each test. The composite sample is collected in a bag and analyzed for hydrocarbons, carbon monoxide, carbon dioxide and nitrogen oxides. Parallel samples of diluted air are similarly analyzed for hydrocarbons, carbon monoxide and nitrogen oxides. Vehicle aging of the catalyst is performed in accordance with the operating schedule set forth in the Appendix "D" table of the aforementioned US Federal Test Methods. This table consists of 11 3.7 mile laps of stop and go driving with lap speeds varying from 30 to 70 m/hr, repeated for 50,000 miles. The average speed is 29 m/hour. Periodically, the vehicle is tested on a Chassis dynamometer to evaluate the durability of the emissions control system. Catalysts designed for three-way control of carbon monoxide, hydrocarbons, and nitrogen oxides are carriers with excellent physical integrity due to variations in the reducing or oxidizing nature of the exhaust environment. Requires. Additionally, catalysts require supports with low densities and high macroporosity due to the inherent difficulty in achieving the excellent carbon monoxide removal and fast light-off required for excellent overall performance. shall be. Rhodium is typically a catalytic agent added for improved three-way regulation, and because its production is low, it must be used efficiently and strategically located. As with oxidation catalysts, three-way catalysts have high initial activity as well as excellent long-term performance when the active metal is properly positioned. We believe that for the combined high initial activity and long-term catalytic durability,
We have discovered that the precious metals should be located such that about 50% of the total precious metals are present at depths greater than about 75 microns. Laboratory measurements of the activity of three-way catalysts are made by contacting 13 cm ³ of catalyst with a gas flow sufficient to reach a gas hourly space velocity of 40,000/hour. Gas composition: 1% carbon monoxide, 250ppm
hydrocarbon consisting of a 3/1 mixture of propylene and propane, 0.34% hydrogen, 1000 ppm NO,
It consists of 12% carbon dioxide, 13% water and varying amounts of oxygen to change its properties from reducing to oxidizing.
Nitrogen is added as a balance. A measure of the reducing or oxidizing nature of the exhaust gas environment (φ) is given by: φ = actual concentration of oxygen in the feed composition/stoichiometrically required concentration of oxygen The catalysts are evaluated at various values of φ and various steady state temperatures. Bench scale durability testing is performed in essentially the same manner as for oxidation catalysts. Periodic tests are carried out for the period of the aging table. Full-scale engine or chassis dynamometer evaluation in technically and economically possible systems is
This is done by closely adjusting the air/fuel ratio. Aging is carried out in a system in which the exhaust gas environment exposing the catalyst is similarly controlled. Periodic tests of three-way performance are performed over the aging table period. The new catalyst with a spherical alumina support was tested by a number of methods developed by automobile manufacturers to measure catalyst performance. In one particular test, 1000〓(538℃) and
The conversion efficiency is measured at a gas hourly space velocity of 75000/h. This test is particularly specific in determining the relative ability of catalysts to oxidize hydrocarbons. Typical ranges of the performance of our new highly favorable catalyst compared to the performance achieved by commonly produced typical catalysts are as follows: Other useful tests used to distinguish new catalysts from commonly produced catalysts are:
The test measures the temperature at which 50% of the carbon monoxide in the test gas mixture is oxidized at a gas hourly space velocity of 1400/hour. Lower temperatures produce higher average activity. The following is a typical range of performance for our new highly preferred catalyst compared to the performance of commonly produced typical catalysts:
Due to the low density and multi-macroporous nature of the alumina spheres described above, catalytic agents, such as platinum group metals, can be utilized very efficiently when applied at appropriate locations and distributions within the catalyst. Because of this efficient use, the catalyst does not need to have precious metals at levels beyond its economic limits. Therefore, the range of amounts of total precious metals used is as follows: Wide Range Typically Weight % Total Precious Metals Used 0.005-1.0 0.03-0.30 The particular choice of catalyst used will depend on the performance characteristics desired for the system. Depends on. Predominantly, the precious metals used in automotive exhaust emission control are platinum, palladium, rhodium and mixtures thereof. The approximate range of these main components is as follows: [Table] %)
Rhodium (% of total) 0-20% 5-15%
The high degree of multi-macroporosity created in the support allows the precious metal to be located deeper than in normally prepared typical catalysts, making it highly dispersed and susceptible to crystal growth. It is resistant. The catalyst is therefore characterized as having a high and stable metal surface area. The following ranges distinguish our new advanced catalyst from commonly produced typical catalysts. [Table] Range
Our novel catalysts are further characterized by the specific depth to which the catalytic agent is deposited. Significant differences exist between these catalysts and the typical catalysts commonly produced, as can be seen below: Due to the unique performance characteristics given to
Their distribution and location are the distinguishing characteristics of the new catalyst. Although the total proportions of the catalyst can be fixed as a whole, these components are specifically located within these catalysts. The following shows the preferred ranges of depth and distribution that characterize these catalysts: Approximate maximum depth of penetration Platinum Wide Typical 125-400 microns Preferred 125-250 Microns Palladium Wide Typical 125-400 Microns Preferred 125-250 Micron Rhodium Wide Typical 125-250 microns Preferred 125-200 microns Our catalyst is characterized by the following performance characteristics that distinguish it from commonly produced typical catalysts. [Table] Media
t ₅₀ CO = Time required for conversion rate of 50% carbon monoxide (seconds).
[Table] Parameter Typical Typical

Claims (1)

[Claims] 1 (a) An aqueous solution of an aluminum salt having an Al ₂ O ₃ concentration of 5 to 9% by weight and a temperature of 130 to 160°C (about 54 to about 71°C) is heated to a temperature of 140°C. ~170〓 (approx.
60-77°C), the solution is
(b) add an additional amount of aluminum salt solution to the mixture, simultaneously but separately providing that _{the Al2O3} concentration is 18-22% by weight and the temperature is 130~160〓(approx. 54~approx. 71
℃) to precipitate the alumina to form an alumina slurry, thereby reducing the pH of the mixture to PH7.
(c) Raise the pH of the slurry to a value in the range of ~ 8 to 8, and (c) raise the PH of the slurry to 7-8 and the temperature of the slurry.
140 to 180 °C (about 60 to about 82 °C) and the addition rates of the aluminum salt solution and alkali metal aluminate solution to precipitate the boehmite-pseudoboehmite intermediate and amorphous alumina, (d ) adjusting the pH of the slurry to between 9.5 and 10.5 by addition of an alkaline solution; and (e) filtering the slurry and washing the filter cake. Manufacturing method. 2. The method according to claim 1, wherein the aluminum salt is aluminum sulfate. 3 Aluminum sulfate solution has SO ₄ ^-- /
3. Process according to claim 2, characterized in that it has a molar ratio of Al ₂ O ₃ . 4. Claim 1, characterized in that the amount of the aluminum salt solution added in step (a) is sufficient to adjust the pH of the mixture to 3-4.
The method described in item 2 or 3. 5. The method according to claim 1, 2, 3 or 4, wherein the alkali metal aluminate is sodium aluminate. 6. The method according to claim 5, characterized in that the pH is adjusted in step (d) by adding a sodium aluminate solution. 7. Claim characterized in that the solution of sodium aluminate added in step (d) is sufficient to adjust the pH of the mixture to between 9.6 and 10.0, and the mixture is aged at this pH for 6 to 12 minutes. The method described in item 6. 8 Step (b) is carried out for 48 to 52 minutes, and the temperature of the slurry is 155 to 165〓 (about 68 to about 74
8. The method according to any one of claims 1 to 7, characterized in that the temperature is maintained at 9 Furthermore, (f) re-slurry the filter cake,
9. A method according to claim 1, further comprising the additional step of drying the resulting slurry. 10. The method according to claim 9, characterized in that the slurry is spray-dried and acidified to a pH of 7 or less before spray-drying. 11. Claim 9 or 1, characterized in that the product is dried to a moisture content of 18 to 33% by weight.
The method described in item 0. 12. Process according to claim 11, characterized in that the product is dried to a moisture content of 20 to 28% by weight. 13 The amount of sulfate solution added in step (a) is sufficient to adjust the PH of the mixture to between 3.0 and 4.0, step (b) is carried out for 48 to 52 minutes, and the temperature of the slurry is equal to or lower than that in step (c). ), and the pH of the slurry was maintained at 155 to 165〓 (about 68 to about 74℃) in step (d).
13. A method according to any one of claims 1 to 12, characterized in that the temperature is maintained between 9.6 and 10.5. 14. The method according to any one of claims 1 to 13, characterized in that the system is aged for 30 minutes or more after the pH adjustment in step (d) and before step (e).