Process for Making High-Strength Alumina Substrates and Catalysts and Products Made Therefrom

This invention relates to processes and compositions for making high strength alumina substrates and catalysts with predetermined pore structures and products made thereby and/or therefrom; and processes, compounds and products having a sulfonated polymeric product incorporated therein.

Alumina is a widely used material in various fields mainly due to the ability of preparing it with a wide variety of morphological properties. Specifically, it can be prepared with surface areas of up to several hundred square meters per gram and pore size distributions with diameters ranging from a few nanometers to several hundred nanometers. One application of particular importance is the use of alumina as a base material in making heterogenous catalysts, particularly for petroleum refining. In this application, alumina powders are shaped into various forms such as spheres, pellets or extrudates. The properties that are considered to be important for this application are the surface area (SA), the mechanical strength (MS) and the pore size distribution (PSD) of the formed alumina. In general, the three properties are interrelated in that alumina with large pores normally has low surface area and poor mechanical strength.

During recent years, it has become increasingly important to design and manufacture alumina catalyst support materials and catalysts having wide pores while maintaining reasonably high mechanical strength. The alumina materials are particularly important for processing petroleum heavy residues, coal liquids, or other feedstocks. Such feedstocks contain large asphaltenic molecules that are chemically resistant to cracking and hydrotreatment, and high percentages of foulant metals mostly associated with the asphaltenic molecules that deposit on the surface of the catalyst support. Thus if the catalyst has small pores, the tendency of the foulant metals is to deposit on the outer surface of the pellet due to the small size of the pore mouth. The continuous deposition of the foulant metals on the pellet surface eventually blocks the entry to the inner pores and leads to the deactivation of the catalyst. Hence, intensive efforts have been made during the past two decades to make alumina extrudates with larger pore diameters to overcome this problem.

Accordingly, there is a need for a sufficiently flexible process that can be used to make extrudates having a narrow distribution of pore sizes, with the desired average pore diameter, and at the same time maintaining sufficient strength to withstand the vigors of petroleum processing. It is also desirable to provide a process for making catalysts supports with a narrow distribution of large diameter pores and relatively high strengths for hydrotreating heavy petroleum residues.

In the past, there have been numerous approaches for producing alumina catalysts and supports with controlled pore sizes. For example, D. L. Trimm and A. Stanislaus in "The Control of Pore Size in Alumina Catalyst Supports: A Review," Applied Catalysis, 21 (1986) 215-238 discusses the state of the art at that time. As pointed out therein, it is often necessary to control both large and small pores and there are a number of approaches for doing so. For example, large pores generally originate from inter-particle spaces and their size may be controlled by mixing alumina powder with graphite, pelleting and then removing the graphite. Small pores originate from spaces within the particle caused for example by removal of water between the crystal planes.

The Trimm and Stanislaus article also points out that the control of pore size in alumina, i.e., the larger pore sizes can be accomplished by control of particle agglomeration, size and shape of the agglomerates and that polymer additives may increase macroporosity as a result of space filling.

Several methods have been utilized in the literature to vary the pore structure of extrudates. Such methods include varying the microcrystal structure and agglomerate size of the alumina, the type of alumina salt used, the precipitating agent, the operating condition during precipitation such as temperature, pH and aging of the solution and the method and conditions of drying. Other factors affecting pore structure include pelleting or extruding conditions, such as pressure and temperature, particularly with respect to macropores, i.e., pores with diameters greater than 50 nm (500 Angestrom Units) and the effect of pore forming additives such as polymers and carbon powders used to generate macropores. Such additives have been added to an alumina during kneading and then when the extrudates or pellets are calcined, the organic material decomposes or burns forming water and then volatile oxides, thus leaving voids in place of the decomposed substances.

It has now been found that substrates and catalysts may be produced by the processes described herein with pore structure tailored to a specific application, and that such substrates can be produced with narrow monomodal pore-size distribution having different average pore diameters ranging from small diameters of around 50 angstrom to as much as 1000 angstrom units. Substrates with narrow bimodal pore size distribution with one set of small pores having relatively small average diameters and large pores having large average diameters can also be produced.

It has also been found that substrates having wide pores produced by the presently disclosed process have relatively high strength as compared to the wide pore substrates reported in the prior art literature.

In essence, the present invention contemplates methods and compositions for making alumina substrates and catalysts and products made thereby and therefrom.

The method for making an alumina substrate having predetermined pore structures and relatively high strength comprises the steps of providing a mixture of alumina powder, water and a peptizing agent and forming a paste like mass from the mixture. This paste like mass is then kneaded to obtain a wet free flowing paste, and a sulfonated resin solution is added to the wet free flowing paste with continued kneading. And after the foregoing step, the free flowing paste is formed into a shaped body, dried, calcined, and thermally treated with a reagent in an autoclave.

The method for forming a catalyst according to the present invention includes each of the above steps and in addition impregnating the shaped body or extrudates with suitable metallic salts.

The invention also contemplates the novel catalysts and supports therefore made from the foregoing processes and the novel compositions which are disclosed herein.

FIG. 1 illustrates the pore size distribution of alumina extrudate samples of examples 1 and 2.

FIG. 2 illustrates the pore size distribution of alumina samples prepared in accordance with examples 3, 4, 5 and 6.

FIG. 3 illustrates the pore size distribution of alumina samples of examples 7, 8 and 9.

FIG. 4 shows a comparison of Hydrodesulfurization activities of catalyst samples prepared in accordance with examples 10 and 11.

The process for preparing alumina extrudates, tablets, or pellets and catalysts using a novel alumina paste composition disclosed herein contemplates the use of special additives to obtain high plasticity and high workability. As a result, the extrudates can have a wide range of pore structure and pore size distribution and can be used in a wide variety of applications, particularly, as catalysts for various refining processes. More specifically, the extrudates can be prepared with a narrow monomodal or bimodal pore structure with large average pore diameter while maintaining high mechanical strength.

In preparing such extrudates, an alumina paste is formed by kneading commercially available alumina powders in either hydrated or calcined forms with a solution of an inorganic or organic acid such as nitric acid or acetic acid. Nitric acid is preferred. The concentration of the acid solution ranges between 0.5 to 10%, and preferably 1-3% by weight, and the amount of acid solution added to 1000 parts of alumina range between 100-1000 parts. The kneading is continued and additional water in the range of 0-900 parts are added to 1000 parts of alumina to obtain a wet but free flowing paste. To this paste, a solution of sulfonated resins in water such as sulfonated melamine formaldehyde, sulfonated urea melamine formaldehyde, sulfonated naphthalene formaldehyde, or lignosulfonate resins is added in the range of 10-150 parts of resin for 1000 parts of alumina powder. The concentration of resin solution is in the range of 2-30% by weight. This addition of the resin solution is carried out with continuous kneading over a period of 15- 30 minutes. Along with the resin solution other additives such as carbon black, binders, etc., can be added and the kneading continued for an additional 10-20 minutes.

The paste prepared according to the above is extruded through nozzles having desired diameters, dried at 110.degree. C. for 10-48 hours, preferably 20-30 hours. The dried extrudates are then calcined under programmed temperature conditions up to a maximum temperature of 500.degree.-600.degree. C. for a total duration of 3-10 hours, preferably 4-6 hours.

The alumina extrudates prepared in accordance with the above were thermally treated in an autoclave at temperatures ranging between 100.degree.-400.degree. C., with various reagents including water, bases, preferably ammonium hydroxides, or acids, preferably a low molecular weight organic acid such as acetic acid. The duration of the treatment varies between 30 minutes and 24 hours and preferably from 1-8 hours.

Hydroprocessing catalysts are prepared using alumina extrudates with wide average pore diameter made in accordance with the above procedure by impregnating the extrudates with suitable metallic salts. Thus, to 100 parts of alumina extrudates, 5-20 parts, preferably 8-15 parts, of molybdenum or tungsten and 1-5 parts, preferably 2-4 parts, of nickel or cobalt are added in the form of water soluble salts. The resulting product is dried at 80.degree.-150.degree. C., preferably at 110.degree.-130.degree. C. for 20-30 hours. The extrudates are then calcined at 450.degree.-600.degree. C. for 4-8 hours.

The methods and compositions or raw batch mixes for making alumina substrates having a predetermined pore structure and relatively high strength, and hydroprocessing catalysts and products made thereby and therefrom will be further described below by the following examples which are intended for illustration and are not to be construed as limiting the invention.

Alumina extrudates were prepared from boehmite (alpha-alumina monohydrate) gel powder. The boehmite powder was mixed with the peptizing solution and kneaded to prepare a heavy paste suitable for extrusion. In a typical experiment, 250 g of boehmite powder was mixed with 200 ml of 1.5% nitric acid, which was added at a constant flow rate over 20 minutes with continuous kneading.

A Linden Model D-5277 (West Germany) kneading machine was used for mixing the paste. Kneading was continued for 10 minutes after completely adding the peptizing agent. Total kneading time was 30 minutes. The paste was then extruded through 1.5 mm nozzles using a NETZCH (West Germany) screw-type extrusion machine. The extrudates were dried at 110.degree. C. in an oven for 24 hours. The dried extrudates were then calcined under programmed temperature conditions (at 370.degree. C. for 2 hours, 450.degree. C. for 1 hour and 550.degree. C. for 2 hours). Characteristics of the extrudates are presented in Table 1 and the pore size distributions are shown in FIG. 1.

Alumina extrudates were prepared in accordance with the procedure described in Example 1, except that 5 parts of a commercial sulfonated melamine formaldehyde resin were added to the paste exactly after 20 minutes from the start of the mixing, when the acid addition was completed. Kneading was continued for another 10 minutes after adding the resin and the paste was extruded. The characteristics of the extrudates prepared by the procedure are summarized in Table 1 and pore size distribution in FIG. 1.

Alumina extrudates, prepared in accordance with Example 2, were heated at 150.degree. C. in an autoclave in presence of water for 1 hour such that the weight ratio of alumina to water is 1:1. Following the heating, the extrudates were calcined at 550.degree. C. Surface area and mechanical strength of the resulting product are shown in Table 2. The pore size distribution of the resulting extrudates is shown in FIG. 2.

Alumina extrudates prepared in accordance with Example 2, were treated as in Example 3 except that the thermal treatment was increased to 8 hours. The properties of the resulting extrudates are listed in Table 2 and the pore size distribution is shown in FIG. 2.

Alumina extrudates, prepared in accordance with Example 2, were treated at 300.degree. C. in an autoclave in presence of water such that the ratio of alumina to water is 1:1 for 1 hour. The extrudates were then calcined at 550.degree. C. The properties of the extrudates are listed in Table 2 and the pore size distribution is shown in FIG. 2.

Alumina extrudates prepared in accordance with Example 2, were treated as in Example 5 except that the thermal treatment was extended to 8 hours. The properties of resulting extrudates are listed in Table 2 and the pore size distribution is shown in FIG. 2.

Alumina extrudates, prepared in accordance with Example 2, were treated with aqueous ammonia such that the weight ratio of aqueous ammonia to alumina is 1:1 for 1 hour at 300.degree. C. The extrudates were then calcined at 550.degree. C. The properties of the resulting product are listed in Table 2 and the pore size distribution is shown in FIG. 3.

Alumina extrudates, prepared in accordance with Example 2, were treated with aqueous ammonia as in Example 7 except that the temperature was 200.degree. C. and the duration is 4 hours. The properties of the extrudates are listed in Table 2 and the pore size distribution is shown in FIG. 3.

Alumina extrudates, prepared in accordance with Example 2, treated with acetic acid such that the weight ratio of acetic acid to alumina is 1:1 for 1 hour at 300.degree. C. The extrudates were then calcined at 550.degree. C. The properties of the resulting product are listed in Table 2 and the pore size distribution is shown in FIG. 3.

To 41 g of alumina extrudates prepared in accordance with Example 2, 26 ml of ammonium heptamolybdate solution (pH 5.3) was added. The concentration of the ammonium heptamolybdate solution was adjusted such that the desired level of molybdenum loading on the catalyst is achieved by a single complete pore-filling impregnation. The sample was dried in an oven at 110.degree. C. and calcined at 500.degree. C. The calcined molybdena containing extrudates were subsequently impregnated with 26 ml of nickel nitrate solution (pH 4.3). The catalyst was then dried in the oven at 110.degree. C. for 3 hours. The final catalyst contained 4.5% NiO and 13.5% MoO.sub.3.

A catalyst is prepared as in Example 10 except alumina extrudates of Example 8 were used instead of alumina of Example 2.

Catalysts prepared in accordance with Examples 10 and 11 were used as hydrotreating catalysts for vacuum residues. Properties of the feedstock are summarized in Table 3. The desulfurization activities of both catalysts are presented in FIG. 4, showing clearly the advantages of the present invention in maintaining high activity for large average pore diameter alumina extrudates.

Alumina extrudates were prepared in accordance with the procedure described in Example 1, except that 5 parts of a lignosulfonate resin were added to the paste exactly after 20 minutes from the start of the mixing, when the acid addition was completed. Kneading was continued for another 10 minutes after adding the lignosulfonate resin and the paste were extruded. The characteristics of the extrudates prepared by the procedure are summarized in Table 4.

Alumina extrudates were prepared in accordance with the procedure described in Example 1, except that 5 parts of a sulfonated melamine formaldehyde resin prepared in accordance with U.S. Pat. No. 4,677,159 was added to the paste exactly after 20 minutes from the start of the mixing, when the acid addition was completed. Kneading was continued for another 10 minutes after adding the sulfonated melamine formaldehyde resin. The characteristics of the extrudates prepared by the procedure are summarized in Table 4.

Alumina extrudates were prepared in accordance with the procedure in Example 1, except that 5 parts of a sulfonated aminoformaldehyde resin prepared in accordance with U.S. Pat. No. 4,663,387 was added to the paste exactly after 20 minutes from the start of the mixing, when the acid addition was completed. Kneading was continued for another 10 minutes after adding the sulfonated aminoformaldehyde resin and the paste was extruded. The characteristics of the extrudates prepared by the procedure are summarized in Table 4.

Alumina extrudates were prepared in accordance with the procedure described in Example 1, except that 5 parts of a sulfonated naphthalene formaldehyde resin was added to the paste exactly after 20 minutes from the start of the mixing, when the acid addition was completed. Kneading was continued for another 10 minutes after adding the sulfonated naphthalene formaldehyde resin and the paste was extruded. The characteristics of the extrudates prepared by the procedure are summarized in Table 4.

Alumina extrudates were prepared in accordance with the procedure described in Example 1, except that 12.5 parts of a sulfonated melamine formaldehyde resin prepared in accordance with U.S. Pat. No. 4,677,159 was added to the paste exactly after 20 minutes from the start of the mixing, when the acid addition was completed. Kneading was continued for another 10 minutes after adding the sulfonated melamine formaldehyde resin and the paste was extruded. The characteristics of the extrudates prepared by the procedure are summarized in Table 4.

Alumina extrudates were prepared in accordance with the procedure described in Example 1, except that 12.5 parts of a sulfonated aminoformaldehyde resin prepared in accordance with U.S. Pat. No. 4,663,387 was added to the paste exactly after 20 minutes from the start of the mixing, when the acid addition was completed. Kneading was continued for another 10 minutes after adding the sulfonated aminoformaldehyde resin and the paste was extruded. The characteristics of the extrudates prepared by the procedure are summarized in Table 4.

Alumina extrudates were prepared in accordance with the procedure described in Example 1, except that 12.5 parts of a lignosulfonate resin were added to the paste exactly after 20 minutes from the start of the mixing, when the acid addition was completed. Kneading was continued for another 10 minutes after adding the lignosulfonate resin and the paste was extruded. The characteristics of the extrudates prepared by the procedure are summarized in Table 4.

Alumina extrudates were prepared in accordance with the procedure described in Example 1, except the 12.5 parts of a sulfonated naphthalene formaldehyde resin were added to the paste exactly after 20 minutes from the start of the mixing, when the acid addition was completed. Kneading was continued for another 10 minutes after adding the sulfonated naphthalene formaldehyde resin and the paste was extruded. The characteristics of the extrudates prepared by the procedure are summarized in Table 4.

Alumina extrudates were prepared in accordance with the procedure described in Example 1, except that 25 parts of a sulfonated melamine formaldehyde resin prepared in accordance with U.S. Pat. No. 4,677,159 were added to the paste exactly after 20 minutes from the start of the mixing, when the acid addition was completed. Kneading was continued for another 10 minutes after adding the sulfonated melamine formaldehyde resin and the paste was extruded. The characteristics of the extrudates prepared by the procedure are summarized in Table 4.

Alumina extrudates were prepared in accordance with the procedure described in Example 1, except that 25 parts of a sulfonated aminoformaldehyde resin prepared in accordance with U.S. Pat. No. 4,663,387 were added to the paste exactly after 20 minutes from the start of the mixing, when the acid addition was completed. Kneading was continued for another 10 minutes after adding the sulfonated aminoformaldehyde resin and the paste was extruded. The characteristics of the extrudates prepared by the procedure are summarized in Table 4.

Alumina extrudates were prepared in accordance with the procedure described in Example 1, except that 25 parts of a lignosulfonate resin were added to the paste exactly after 20 minutes from the start of the mixing, when the acid addition was completed. Kneading was continued for another 10 minutes after adding the lignosulfonate resin and the paste was extruded. The characteristics of the extrudates prepared by the procedure are summarized in Table 4.

The role of the sulfonated polymer used in the aforementioned compositions and processes is not for pore generation. It is believed that the sulfonated polymers provide a lubricating action between the alumina particles so that those particles become more closely compacted and thus provide substrates with higher mechanical strength. It is also believed that the generation of the pores in the presently disclosed processes is attributed to the thermal treatment of the substrates after the powder is shaped into a tablet or extrudate.