CA1189052A - High porosity catalyst - Google Patents
High porosity catalystInfo
- Publication number
- CA1189052A CA1189052A CA000419653A CA419653A CA1189052A CA 1189052 A CA1189052 A CA 1189052A CA 000419653 A CA000419653 A CA 000419653A CA 419653 A CA419653 A CA 419653A CA 1189052 A CA1189052 A CA 1189052A
- Authority
- CA
- Canada
- Prior art keywords
- water
- catalyst
- gel
- acid
- weight
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 239000003054 catalyst Substances 0.000 title claims abstract description 80
- 239000011148 porous material Substances 0.000 claims abstract description 43
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 42
- 238000000034 method Methods 0.000 claims abstract description 23
- 239000002253 acid Substances 0.000 claims abstract description 17
- 229910052751 metal Inorganic materials 0.000 claims abstract description 17
- 239000002184 metal Substances 0.000 claims abstract description 17
- 229910044991 metal oxide Inorganic materials 0.000 claims abstract description 12
- 150000004706 metal oxides Chemical class 0.000 claims abstract description 12
- 238000009835 boiling Methods 0.000 claims abstract description 7
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 claims description 14
- 229910017604 nitric acid Inorganic materials 0.000 claims description 14
- 238000001354 calcination Methods 0.000 claims description 12
- 238000001035 drying Methods 0.000 claims description 10
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 claims description 4
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 claims description 4
- 238000002156 mixing Methods 0.000 claims description 3
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims description 2
- 239000001117 sulphuric acid Substances 0.000 claims description 2
- 235000011149 sulphuric acid Nutrition 0.000 claims description 2
- 238000004517 catalytic hydrocracking Methods 0.000 abstract description 7
- 238000004523 catalytic cracking Methods 0.000 abstract description 3
- 239000000499 gel Substances 0.000 description 17
- 238000006243 chemical reaction Methods 0.000 description 13
- 150000002739 metals Chemical class 0.000 description 11
- 229910001593 boehmite Inorganic materials 0.000 description 5
- 230000003247 decreasing effect Effects 0.000 description 5
- 238000009792 diffusion process Methods 0.000 description 5
- FAHBNUUHRFUEAI-UHFFFAOYSA-M hydroxidooxidoaluminium Chemical compound O[Al]=O FAHBNUUHRFUEAI-UHFFFAOYSA-M 0.000 description 5
- 239000000203 mixture Substances 0.000 description 5
- 239000000376 reactant Substances 0.000 description 5
- 238000005245 sintering Methods 0.000 description 5
- SVPXDRXYRYOSEX-UHFFFAOYSA-N bentoquatam Chemical compound O.O=[Si]=O.O=[Al]O[Al]=O SVPXDRXYRYOSEX-UHFFFAOYSA-N 0.000 description 4
- 230000007423 decrease Effects 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- MWUXSHHQAYIFBG-UHFFFAOYSA-N Nitric oxide Chemical compound O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- 230000003197 catalytic effect Effects 0.000 description 2
- 238000000151 deposition Methods 0.000 description 2
- 238000009826 distribution Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- QSHDDOUJBYECFT-UHFFFAOYSA-N mercury Chemical compound [Hg] QSHDDOUJBYECFT-UHFFFAOYSA-N 0.000 description 2
- 229910052753 mercury Inorganic materials 0.000 description 2
- 238000002459 porosimetry Methods 0.000 description 2
- 239000007787 solid Substances 0.000 description 2
- 229910002651 NO3 Inorganic materials 0.000 description 1
- 229910021536 Zeolite Inorganic materials 0.000 description 1
- 150000007513 acids Chemical class 0.000 description 1
- 239000011959 amorphous silica alumina Substances 0.000 description 1
- 150000001450 anions Chemical class 0.000 description 1
- 239000010426 asphalt Substances 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000000571 coke Substances 0.000 description 1
- HNPSIPDUKPIQMN-UHFFFAOYSA-N dioxosilane;oxo(oxoalumanyloxy)alumane Chemical compound O=[Si]=O.O=[Al]O[Al]=O HNPSIPDUKPIQMN-UHFFFAOYSA-N 0.000 description 1
- 239000012153 distilled water Substances 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
- 230000008020 evaporation Effects 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 239000012530 fluid Substances 0.000 description 1
- 239000000295 fuel oil Substances 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 239000013628 high molecular weight specie Substances 0.000 description 1
- 229910010272 inorganic material Inorganic materials 0.000 description 1
- 239000011147 inorganic material Substances 0.000 description 1
- 150000002605 large molecules Chemical class 0.000 description 1
- 229920002521 macromolecule Polymers 0.000 description 1
- 150000004682 monohydrates Chemical class 0.000 description 1
- -1 nitrate ions Chemical class 0.000 description 1
- 229960003753 nitric oxide Drugs 0.000 description 1
- 235000019391 nitrogen oxide Nutrition 0.000 description 1
- 239000003921 oil Substances 0.000 description 1
- 150000002902 organometallic compounds Chemical class 0.000 description 1
- 239000008188 pellet Substances 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 239000010457 zeolite Substances 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J35/00—Catalysts, in general, characterised by their form or physical properties
- B01J35/60—Catalysts, in general, characterised by their form or physical properties characterised by their surface properties or porosity
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
- B01J37/06—Washing
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J35/00—Catalysts, in general, characterised by their form or physical properties
- B01J35/60—Catalysts, in general, characterised by their form or physical properties characterised by their surface properties or porosity
- B01J35/61—Surface area
- B01J35/615—100-500 m2/g
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J35/00—Catalysts, in general, characterised by their form or physical properties
- B01J35/60—Catalysts, in general, characterised by their form or physical properties characterised by their surface properties or porosity
- B01J35/63—Pore volume
- B01J35/635—0.5-1.0 ml/g
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Organic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Catalysts (AREA)
Abstract
Abstract:
A method is described for producing a catalyst or catalyst support having both high surface area, e.g.
greater than 150 m2/g, and large pore sizes, e.g.
greater than 1.0 ml/g of macropores having diameters between 1 and 50 nm. According to the method, a metal oxide is mixed with water and an acid to form a dilute metal gel, preferably containing at least 70% by weight water and consisting of a loose three dimensional network of oxide containing the water evenly dispersed throughout.
This gel is slowly dried at a temperature below the boil-ing point of water whereby a substantial proportion of the water is removed from the interior of the pore structure, leaving the three dimensional network intact. Thereafter, the dried product is calcined to form a novel catalyst or catalyst support having both high surface area and large pore sizes. The novel catalyst is useful as a component of a catalytic cracking catalyst or a hydrocracking catalyst.
A method is described for producing a catalyst or catalyst support having both high surface area, e.g.
greater than 150 m2/g, and large pore sizes, e.g.
greater than 1.0 ml/g of macropores having diameters between 1 and 50 nm. According to the method, a metal oxide is mixed with water and an acid to form a dilute metal gel, preferably containing at least 70% by weight water and consisting of a loose three dimensional network of oxide containing the water evenly dispersed throughout.
This gel is slowly dried at a temperature below the boil-ing point of water whereby a substantial proportion of the water is removed from the interior of the pore structure, leaving the three dimensional network intact. Thereafter, the dried product is calcined to form a novel catalyst or catalyst support having both high surface area and large pore sizes. The novel catalyst is useful as a component of a catalytic cracking catalyst or a hydrocracking catalyst.
Description
39~2 High porosity catal~st This invention relates to a novel catalyst or catalyst support having both high surface area and large pore s;zes and a method for its production~
Many conventional catalysts consist of chemically active components plus a catalytic support. The support ' may or may not participate in the reactions being catalyzed. It is frequently desirable for catalysts to have a large sur~ace area which is normally provided by the catalyst support. Generally the larger the surface area, the greater the reaction rate since the catalyst functions by having species react on catalytic centers located on the surface. Usually high surface area catalysts are very porous materials. The chemical reactants usually diffuse through the pores of the catalyst and eventually become chemisorbed on its surface.
The reactions are thought to occur on the sites where chemisorption takes place. The total reaction rate will increase as the surface area per unit weight of catalyst increases.
Variations in manufacturing procedures, such as high temperature treatment (sintering) may cause changes in the surface area of the support. As the surface area per unit weight of catalyst increases, there is often a simultaneous decrease in the size of the pores within the catalyst. In other words, as the surface area increases, the pore size decreases. If the pores become sufficiently small, .~
;S2 diffusion limitations can result. In other words, the rate of reaction is limited by the rate at which reactant molecules can diffuse from the bulk fluid surrounding a catalyst support through the catalyst pore structure to a vacant reactive site in its interior. ~;enerally it is desirable to maximize the catalyst surface area in such a manner that the reaction rate is not limited by the rate of diffusion of either reactant or product molecules.
This effect tends to occur during the hydrocracking of high molecular weight species, such as those organic molecules present in oil sands bitumen or heavy oils. The mclecules have large dimensions and, as a result, when standard hydrocracking catalysts having pore diameters of 7 nm are used, it is generally found that diffusion limit-ations become a problem. Another problem during hydro-cracking is catalyst fouling. This results rom organo-metallic compounds depositing their metals, carbonaceous species forming coke and other inorganic materials present in the feedstock which deposit on the catalyst. In particular, it has been noted that the metals tend to accumulate at the exterior surfaces of the catalyst pellets or catalyst extrudate shapes. When such catalysts are physically examined, it is found that there are large concentrations of metals at the outside surface of the catalyst shapes whereas the interior of the catalyst contains metals in only very low concentrations.
The prior art describes studies which were performed in order to manufacture large pore catalysts by sintering the catalysts at high temperatures. This is described, for example, in U.S. Patent 4,124,699, issued November 8, 1978. While this technique increases the pore sizes in the catalyst, it also decreases the catalyst surface area.
It has been found that there is a general relationship such that as one property increases, the other decreases.
Several phenomena have been observed when large pore catalysts prepared by high temperature sintering have been 5%
used for hydrocracking reactions. Thus, it has been shown that as the pore size increases, the reaction rate per unit surface area also increases. This is an indication of declining diffusion limitations. Furthermore, as the pore size increases, the metals profile in the catalyst shape also improves in that there are lower concentrations of metals at the exterior surface of the catalyst shape.
In contrast, the metals concentration within the interior of the catalyst increases. This is a desirable effect in that a greater quantity of metals can be loaded into the catalyst shape before it becomes fully deactivated. In this way, the catalyst life with respect to metals fouling can be extended.
Finally, it has been found that the large pore catalysts of the prior art produced by sintering caused decreased conversions. Although the reaction rate per unit surface area increased, the surface area per unit catalyst weight decreased to a greater extent. The result was that the overall extent of reaction decreased as the catalyst pore size increased. In summary, it was apparent that increasing the catalyst pore size by high temperature sintering was not a beneficial procedure.
Accordingly, there has remained a need to develop a large pore catalyst having greater surface areas.
According to the present invention there has been developed a catalyst or catalyst support having both high surface area and large pore sizes. It is produced by a method comprising mixing a metal oxide, preferably alumina, with water and an acid to form a dilute metal gel consisting of a loose three dimensional network of oxide containing a large amount of water evenly dispersed throughout. This gel is slowly dried at a temperature below the boiling point of water whereby a substantial proportion of the water is removed from the interior of the pore structure, leaving the three dimensional network intact. Thereafter, the dried product is calcined to form 5~
a catalyst or catalyst support having both high surface area and large pore sizes.
The catalyst support obtained according to the method of the present invention permits the reacting species to diffuse further towards the catalyst interior before reacting and fouling the catalyst by depositing its metals. In this way, the catalyst of the invention can be loaded more fully with metals before it becomes completely deactivated. The increase in catalyst pore size also tends to remove diffusion limitations so that the large molecular weight species also have access to the reaction sites in the catalyst interior.
One of the features of the present invention is the use of a low temperature, slow drying technique. During drying, the temperature of the aquagel is maintained below the boiling point of water. It is generally recognized in drying practice that when the temperature of the material exceeds the boiling point of the solvent, i.e. water, evaporation will occur within the aquagel at the point where the water is present. On the other hand, when the temperature of the aquagel is below the boiling point of water, the water will diffuse from its location in the gel to the exterior, where it subsequently evaporates.
This mechanism is believed to eliminate the high surface tension forces at the liquid-vapor-solid contact line, thereby preventing the collapse of the pore structure.
The aquagel is formed from three dimensional networks of a metal oxide which branch and hold water in their interior. The extent of gel formation is a complicated function of acid addition and resulting pH level. The second important feature of the invention is the addition of an appropriate amount of acid to develop a gel consist-ing of a loose, three dimensional network of oxide contain-ing a large amount of water which is evenly dispersed throughout. During the drying, it is desirable to remove the water from the interior of the pore structure and leave the three dimensional network intact.
~9~
In one embodiment, the water content of the gel before drying is normally at least 500 parts by weight per lO0 parts by weight of metal oxide, preferably with a low acid concentration. During the low temperature drying the water content is preferably decreased to below 20~ by weight. Of course, it is desirable to have the water content as low as possible before calcining, e.g. less than 5% by weight.
Among the acids that may be used, there can be mentioned nitric acid, sulphuric acid, and hydrochloric acid. The nitric acid is particularly preferred because it will not contribute undesirable anions to the catalyst after the calcining period. During high temperature calcining, the nitrate ions from nitric acid are evolved as nitrogen-oxide gases. The acid content of the gel is preferably less than 5%.
It is also possible to produce gels having very high acid concentrations of at least 250 parts of concentrated nitric acid per lO0 parts by weight metal oxide and lower water contents of at least lO~ by weight.
The slow drying of the gel is normally conducted at a temperature in the range of about 30 to 100C with a tem-perature of 50 to 99C being particularly preferred. The calcining was conducted at a usual temperature range of about 300 to 1000C with a range of ~00 to 650C being particularly preferred.
The resulting product has a very large surface area of greater than 200 m2/g and also a very large pore volume of greater than 0.2 ml/g of macropores having diameters between l and 50 ~m. Preferably the volume of macropores is greater than 0.7 ml/g with the high acid gels.
The catalyst support of this invention is well suited for forming one component of a catalytic cracking catalyst.
It has particular value for processing heavier feedstocks because the larger molecules can enter the large pores and react. The product molecules from the large pores can react further in the smaller pore diameter components of ,.....
'I 'i `I "
~ .
3905~
conventional catalysts. Typical o~ the conventional catalytic cracking catalysts that can be combined with the catalyst of this invention is amorphous silica-alumina with zeolite.
It can also be used as a component of a hydrocracking catalyst, particularly for processing heavy feedstocks.
The very large molecules can react in the large pores and the products from the large pores can then react further in the oth~r components of a conventional hydrocracking catalyst, such as sulphided CoO-MoO3-A12O3.
Certain preferred features of the present invention are illustrated by the following examples. In the drawings referred to in the examples, Figure 1 is plots showing surface areas and pore volumes with different percentages of water and Figure 2 shows surface areas and pore volumes with different amounts of acid.
Example 1 A series of oxide catalyst supports were prepared using alumina monohydrate (Boehmite) as the metal oxide. This was combined with distilled water and a solution 70 wt %
nitric acid and thoroughly mixed in the proportions set out in Table 1 below:
Porous Catalysts Prepared With Various Amounts of Water ___.__ CatalystBoehmite Water70% HNO3 Gel wt % wt % wt % Condi-tion A 9.4 85.2 5.4 very watery B 15.6 79.1 5.3 watery C 32.4 65.3 2.3 firm D 49.8 49.6 0.7 firm The above mixture was prepared using nitric acid up to a maximum of approximately 5 wt % in order to obtain a ~8~i2 relatively stiff gel. In this series of experiments, the water to Boehmite ratio was changed in the different mix-tures. Each mixture was dried at 60C for approximately 24 hours.
Mercury porosimetry measurements were made on the dried material in order to determine its pore size distribution.
After drying, the material was further calcined at 500C
for six hours and further mercury porosimetry measurements were made to determine the pore si~e distribution in the calcined material. The results are shown in Figure 1. It will be seen from Figure 1 that large surface areas were obtained for all the catalyst supports. The volume of micropores, i.e. those having diameters between 3.5 and 10 nm, increased on calcining. Also, there was no increase in micropore volume with increasing water to Boehmite ratio.
The macropores (pore diameters between 1 and 50 ~m) had volumes similar before and after calcining. However, there was a large increase in macropore volume when the amount of water added was greater than 80 wt ~. It was apparent that large volumes of macropores could be incorp-orated into the catalyst at high water to Boehmite ratios.
Example 2 A second series of catalyst supports were prepared following the same procedures described in Example 1. The proportions of reactants are set out in Table 2 below:
Porous Catalysts Prepared With Various Amounts of 70% HNO3 __ Catalyst Boehmite Water 70% HNO3 Gel wt % wt % wt % Condition E 9.1 90.9 - no gel formed F 8.7 86.7 4.6 firm gel G 8.1 80.5 11.4 watery gel H 6.5 64.9 28.6 clear solution plus firm gel J 6.6 - 93.4 crusty solid ~8~S~
As in Example 1 the resulting mixture was dried and calcined and the final results obtained are shown in Figure 2. A11 of the resulting catalyst supports had large sur~ace areas. As the amount of acid added to the mixture increased, the macropore volume decreased and was eventually eliminated. The macropore volume increased upon acid addition. Maximum macropore vo:lume was obtained by using more than 20 wt % concentrated (70%) nitric acid.
The results in Figure 2 show that catalyst supports having both large surface areas and a large volume of large diameter pores can be prepared. The large pores admit reactant molecules having high molecular weights.
The high surface areas present a large number of reaction sites.
Many conventional catalysts consist of chemically active components plus a catalytic support. The support ' may or may not participate in the reactions being catalyzed. It is frequently desirable for catalysts to have a large sur~ace area which is normally provided by the catalyst support. Generally the larger the surface area, the greater the reaction rate since the catalyst functions by having species react on catalytic centers located on the surface. Usually high surface area catalysts are very porous materials. The chemical reactants usually diffuse through the pores of the catalyst and eventually become chemisorbed on its surface.
The reactions are thought to occur on the sites where chemisorption takes place. The total reaction rate will increase as the surface area per unit weight of catalyst increases.
Variations in manufacturing procedures, such as high temperature treatment (sintering) may cause changes in the surface area of the support. As the surface area per unit weight of catalyst increases, there is often a simultaneous decrease in the size of the pores within the catalyst. In other words, as the surface area increases, the pore size decreases. If the pores become sufficiently small, .~
;S2 diffusion limitations can result. In other words, the rate of reaction is limited by the rate at which reactant molecules can diffuse from the bulk fluid surrounding a catalyst support through the catalyst pore structure to a vacant reactive site in its interior. ~;enerally it is desirable to maximize the catalyst surface area in such a manner that the reaction rate is not limited by the rate of diffusion of either reactant or product molecules.
This effect tends to occur during the hydrocracking of high molecular weight species, such as those organic molecules present in oil sands bitumen or heavy oils. The mclecules have large dimensions and, as a result, when standard hydrocracking catalysts having pore diameters of 7 nm are used, it is generally found that diffusion limit-ations become a problem. Another problem during hydro-cracking is catalyst fouling. This results rom organo-metallic compounds depositing their metals, carbonaceous species forming coke and other inorganic materials present in the feedstock which deposit on the catalyst. In particular, it has been noted that the metals tend to accumulate at the exterior surfaces of the catalyst pellets or catalyst extrudate shapes. When such catalysts are physically examined, it is found that there are large concentrations of metals at the outside surface of the catalyst shapes whereas the interior of the catalyst contains metals in only very low concentrations.
The prior art describes studies which were performed in order to manufacture large pore catalysts by sintering the catalysts at high temperatures. This is described, for example, in U.S. Patent 4,124,699, issued November 8, 1978. While this technique increases the pore sizes in the catalyst, it also decreases the catalyst surface area.
It has been found that there is a general relationship such that as one property increases, the other decreases.
Several phenomena have been observed when large pore catalysts prepared by high temperature sintering have been 5%
used for hydrocracking reactions. Thus, it has been shown that as the pore size increases, the reaction rate per unit surface area also increases. This is an indication of declining diffusion limitations. Furthermore, as the pore size increases, the metals profile in the catalyst shape also improves in that there are lower concentrations of metals at the exterior surface of the catalyst shape.
In contrast, the metals concentration within the interior of the catalyst increases. This is a desirable effect in that a greater quantity of metals can be loaded into the catalyst shape before it becomes fully deactivated. In this way, the catalyst life with respect to metals fouling can be extended.
Finally, it has been found that the large pore catalysts of the prior art produced by sintering caused decreased conversions. Although the reaction rate per unit surface area increased, the surface area per unit catalyst weight decreased to a greater extent. The result was that the overall extent of reaction decreased as the catalyst pore size increased. In summary, it was apparent that increasing the catalyst pore size by high temperature sintering was not a beneficial procedure.
Accordingly, there has remained a need to develop a large pore catalyst having greater surface areas.
According to the present invention there has been developed a catalyst or catalyst support having both high surface area and large pore sizes. It is produced by a method comprising mixing a metal oxide, preferably alumina, with water and an acid to form a dilute metal gel consisting of a loose three dimensional network of oxide containing a large amount of water evenly dispersed throughout. This gel is slowly dried at a temperature below the boiling point of water whereby a substantial proportion of the water is removed from the interior of the pore structure, leaving the three dimensional network intact. Thereafter, the dried product is calcined to form 5~
a catalyst or catalyst support having both high surface area and large pore sizes.
The catalyst support obtained according to the method of the present invention permits the reacting species to diffuse further towards the catalyst interior before reacting and fouling the catalyst by depositing its metals. In this way, the catalyst of the invention can be loaded more fully with metals before it becomes completely deactivated. The increase in catalyst pore size also tends to remove diffusion limitations so that the large molecular weight species also have access to the reaction sites in the catalyst interior.
One of the features of the present invention is the use of a low temperature, slow drying technique. During drying, the temperature of the aquagel is maintained below the boiling point of water. It is generally recognized in drying practice that when the temperature of the material exceeds the boiling point of the solvent, i.e. water, evaporation will occur within the aquagel at the point where the water is present. On the other hand, when the temperature of the aquagel is below the boiling point of water, the water will diffuse from its location in the gel to the exterior, where it subsequently evaporates.
This mechanism is believed to eliminate the high surface tension forces at the liquid-vapor-solid contact line, thereby preventing the collapse of the pore structure.
The aquagel is formed from three dimensional networks of a metal oxide which branch and hold water in their interior. The extent of gel formation is a complicated function of acid addition and resulting pH level. The second important feature of the invention is the addition of an appropriate amount of acid to develop a gel consist-ing of a loose, three dimensional network of oxide contain-ing a large amount of water which is evenly dispersed throughout. During the drying, it is desirable to remove the water from the interior of the pore structure and leave the three dimensional network intact.
~9~
In one embodiment, the water content of the gel before drying is normally at least 500 parts by weight per lO0 parts by weight of metal oxide, preferably with a low acid concentration. During the low temperature drying the water content is preferably decreased to below 20~ by weight. Of course, it is desirable to have the water content as low as possible before calcining, e.g. less than 5% by weight.
Among the acids that may be used, there can be mentioned nitric acid, sulphuric acid, and hydrochloric acid. The nitric acid is particularly preferred because it will not contribute undesirable anions to the catalyst after the calcining period. During high temperature calcining, the nitrate ions from nitric acid are evolved as nitrogen-oxide gases. The acid content of the gel is preferably less than 5%.
It is also possible to produce gels having very high acid concentrations of at least 250 parts of concentrated nitric acid per lO0 parts by weight metal oxide and lower water contents of at least lO~ by weight.
The slow drying of the gel is normally conducted at a temperature in the range of about 30 to 100C with a tem-perature of 50 to 99C being particularly preferred. The calcining was conducted at a usual temperature range of about 300 to 1000C with a range of ~00 to 650C being particularly preferred.
The resulting product has a very large surface area of greater than 200 m2/g and also a very large pore volume of greater than 0.2 ml/g of macropores having diameters between l and 50 ~m. Preferably the volume of macropores is greater than 0.7 ml/g with the high acid gels.
The catalyst support of this invention is well suited for forming one component of a catalytic cracking catalyst.
It has particular value for processing heavier feedstocks because the larger molecules can enter the large pores and react. The product molecules from the large pores can react further in the smaller pore diameter components of ,.....
'I 'i `I "
~ .
3905~
conventional catalysts. Typical o~ the conventional catalytic cracking catalysts that can be combined with the catalyst of this invention is amorphous silica-alumina with zeolite.
It can also be used as a component of a hydrocracking catalyst, particularly for processing heavy feedstocks.
The very large molecules can react in the large pores and the products from the large pores can then react further in the oth~r components of a conventional hydrocracking catalyst, such as sulphided CoO-MoO3-A12O3.
Certain preferred features of the present invention are illustrated by the following examples. In the drawings referred to in the examples, Figure 1 is plots showing surface areas and pore volumes with different percentages of water and Figure 2 shows surface areas and pore volumes with different amounts of acid.
Example 1 A series of oxide catalyst supports were prepared using alumina monohydrate (Boehmite) as the metal oxide. This was combined with distilled water and a solution 70 wt %
nitric acid and thoroughly mixed in the proportions set out in Table 1 below:
Porous Catalysts Prepared With Various Amounts of Water ___.__ CatalystBoehmite Water70% HNO3 Gel wt % wt % wt % Condi-tion A 9.4 85.2 5.4 very watery B 15.6 79.1 5.3 watery C 32.4 65.3 2.3 firm D 49.8 49.6 0.7 firm The above mixture was prepared using nitric acid up to a maximum of approximately 5 wt % in order to obtain a ~8~i2 relatively stiff gel. In this series of experiments, the water to Boehmite ratio was changed in the different mix-tures. Each mixture was dried at 60C for approximately 24 hours.
Mercury porosimetry measurements were made on the dried material in order to determine its pore size distribution.
After drying, the material was further calcined at 500C
for six hours and further mercury porosimetry measurements were made to determine the pore si~e distribution in the calcined material. The results are shown in Figure 1. It will be seen from Figure 1 that large surface areas were obtained for all the catalyst supports. The volume of micropores, i.e. those having diameters between 3.5 and 10 nm, increased on calcining. Also, there was no increase in micropore volume with increasing water to Boehmite ratio.
The macropores (pore diameters between 1 and 50 ~m) had volumes similar before and after calcining. However, there was a large increase in macropore volume when the amount of water added was greater than 80 wt ~. It was apparent that large volumes of macropores could be incorp-orated into the catalyst at high water to Boehmite ratios.
Example 2 A second series of catalyst supports were prepared following the same procedures described in Example 1. The proportions of reactants are set out in Table 2 below:
Porous Catalysts Prepared With Various Amounts of 70% HNO3 __ Catalyst Boehmite Water 70% HNO3 Gel wt % wt % wt % Condition E 9.1 90.9 - no gel formed F 8.7 86.7 4.6 firm gel G 8.1 80.5 11.4 watery gel H 6.5 64.9 28.6 clear solution plus firm gel J 6.6 - 93.4 crusty solid ~8~S~
As in Example 1 the resulting mixture was dried and calcined and the final results obtained are shown in Figure 2. A11 of the resulting catalyst supports had large sur~ace areas. As the amount of acid added to the mixture increased, the macropore volume decreased and was eventually eliminated. The macropore volume increased upon acid addition. Maximum macropore vo:lume was obtained by using more than 20 wt % concentrated (70%) nitric acid.
The results in Figure 2 show that catalyst supports having both large surface areas and a large volume of large diameter pores can be prepared. The large pores admit reactant molecules having high molecular weights.
The high surface areas present a large number of reaction sites.
Claims (14)
- Claims:
l. A method of producing catalysts or catalyst supports having both high surface area and large pore sizes which comprises mixing a metal oxide with water and an acid to form a dilute metal gel consisting of a loose three dimensional network of oxide containing a large amount of water evenly dispersed throughout, said water being present in an amount of at least 500 parts by weight per 100 parts by weight of metal oxide slowly drying the gel at a temperature below the boiling point of water whereby water is removed from the interior of the pore structure to a water content of less than 20% by weight leaving the three dimensional network intact, and thereafter calcining the dried product to form a catalyst or catalyst support having a surface area greater than 200 m2/g and a volume of greater than 0.2 ml/g of macropores having diameters between l and 50 nm. - 2. The method of claim l wherein the metal oxide is alumina.
- 3. The method of claim 2 wherein the dilute metal gel contains a low concentration of up to 5% by weight acid.
- 4. The method of claim 2 wherein the gel is dried to a water content of less than 5% by weight prior to calcining.
- 5. The method of claim 3 wherein the acid is selected from nitric acid, sulphuric acid and hydrochloric acid.
- 6. The method of claim 3 wherein the acid is nitric acid.
- 7. The method of claim 2 wherein the gel is dried at a temperature in the range of 30 to 100°C.
- 8. The method of claim 7 wherein the calcining is con-ducted at a temperature of 300 to 1000°C.
- 9. A method of producing catalysts or catalyst supports having both high surface area and large pore sizes which comprises mixing a metal oxide with water and nitric acid to form a metal gel consisting of a loose three dimensional network, the acid being present in an amount of at least 250 parts of concentrated HNO3 per 100 parts of metal oxide, slowly drying the gel at a temperature below the boiling point of water whereby water is removed from the interior of the pore structure to a water content of less than 20% by weight, leaving the three dimensional network intact, and thereafter calcining the dried product to form a catalyst or catalyst support having a surface area greater than 200 m2/g and a volume of greater than 0.7 ml/g of macropores having diameters between 1 and 50 m.
- 10. The method of claim 9 wherein the metal oxide is alumina.
- 11. The method of claim 10 wherein the metal gel is a dilute gel containing at least 10% by weight of water.
- 12. The method of claim 10 wherein the gel is dried to a water content of less than 5% by weight prior to calcining.
- 13. The method of claim 10 wherein the gel is dried at a temperature in the range of 30 to 100°C.
- 14. The method of claim 13 wherein the calcining is conducted at a temperature of 300 to 1000°C.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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CA000419653A CA1189052A (en) | 1983-01-18 | 1983-01-18 | High porosity catalyst |
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Application Number | Priority Date | Filing Date | Title |
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CA000419653A CA1189052A (en) | 1983-01-18 | 1983-01-18 | High porosity catalyst |
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CA1189052A true CA1189052A (en) | 1985-06-18 |
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Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO1994026406A1 (en) * | 1993-05-18 | 1994-11-24 | Hoechst Aktiengesellschaft | Method for the sub-critical drying of aerogels |
-
1983
- 1983-01-18 CA CA000419653A patent/CA1189052A/en not_active Expired
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO1994026406A1 (en) * | 1993-05-18 | 1994-11-24 | Hoechst Aktiengesellschaft | Method for the sub-critical drying of aerogels |
US5705535A (en) * | 1993-05-18 | 1998-01-06 | Hoechst Aktiengesellschaft | Method for the subcritical drying of aerogels |
US5811031A (en) * | 1993-05-18 | 1998-09-22 | Hoechst Aktiengesellschaft | Method for the subcritical drying of aerogels |
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