Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Reexamination Certificate
2001-09-25
2004-01-06
Dunn, Tom (Department: 1725)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
C502S314000, C502S315000
Reexamination Certificate
active
06673741
ABSTRACT:
FIELD OF THE INVENTION
The present invention is related to a guard catalyst and a process for its preparation, more particularly, it is related to a guard catalyst containing tungsten and/or molybdenum and nickel and/or cobalt and a process for its preparation.
BACKGROUND OF THE PRIOR ART
Hydrogenation stocks usually contain small amounts of impurities such as resins, asphaltene, carbon residue, and iron, etc., which convert to coke deposit and metal sulfides during the hydrogenation and deposit on the surface of the catalyst, and thereby plug the pores and lower the activity of the catalyst rapidly. Therefore, a catalyst bed or a reactor wherein a guard catalyst is loaded usually installed on top of the major catalyst bed to trap the impurities and thereby retard the deactivation of the catalyst by passing the hydrogenation stock though the bed or reactor.
In order to lodge metals and deposited coke, the guard catalyst must have large pores for resins, asphaltene and metals to deposit therein as much as possible. Because of the undulation of the temperature during reaction, if the strength of the guard catalyst is not high enough, the catalyst is prone to break and the pressure drop of the catalyst bed will increase, therefore the guard catalyst must have high strength. Therefore, it is very important to develop a guard catalyst with high strength, large pore size, large pore volume, and low deactivation rate.
U.S. Pat. No. 4,448,896 discloses a guard catalyst for removing sulfur and heavy metals, which comprises (1) at least one metal component selected from the group consisting of metals in groups VIB and VIII as an active component of the catalyst and (2) a porous support of active alumina. This support is prepared by molding the mixture of carbon black powder and active alumina or a precursor of active alumina and calcining the dried mixture in an oxygen-containing atmosphere to burn off the carbon black powder. This catalyst has a specific surface of 100-350 m
2
/g, preferably 200-300 m
2
/g, a pore volume of 0.5-1.5 ml/g, preferably 0.5-1.5 ml/g. It is preferable that at least 90% of the total pore volume is taken up by the pores with diameters of 35.7-1000 Å, and there is a peak at a diameter smaller than 100 Å and a peak in the range of 100-1000 Å respectively. The volume of the pores with diameters of 37.5-100 Å is at least 0.2 ml/g, preferably 0.4-0.7 ml/g, and the volume of the pores with diameters of 100-1000 Å is at least 0.2 ml/g, preferably 0.2-0.5 ml/g. The catalyst uses carbon black powder as a pore expander, and the prepared catalyst has a lager pore volume, but the strength of the catalyst is greatly lowered since the amount of the carbon black powder is up to over 10%. In addition, using a large amount of carbon black powder is unfavorable to the control of the temperature in the calcination of the catalyst support, and a run away of the temperature is easy to take place.
CN 1,179,356A discloses a catalyst support and a process for its preparation. The catalyst support consists of &ggr;-alumina, which has a pore volume of 0.65-0.88 ml/g and a specific surface of 225-290 m
2
/g. The volume of the pores with diameters of 7-13 nm accounts for 80-95% of the total pore volume, that with diameters smaller than 7 nm accounts for 2-15% of the total pore volume, and that with diameters greater than 13 nm accounts for 2-15% of the total pore volume. The process for preparing the catalyst support comprises weighing pseudo-boehmite dry gel, adding an aqueous alkali solution in the amount of 20-60 wt % of the pseudo-boehmite dry gel, adding an aqueous acidic solution in an amount of 40-60 wt % of the pseudo-boehmite dry gel after sufficient kneading, molding by extrusion after sufficient kneading, drying at 80-140° C. for 1-5 h, calcining at 700-900° C. for 2-5 h. The catalyst has a larger pore volume and a larger specific surface, and a concentrated pore distribution. However, this catalyst is prepared by first adding alkali aqueous solution and then adding acid aqueous solution. Although the peptization is decreased and the pore diameter is enlarged by the neutralization reaction, the strength of the support is sacrificed.
CN 1,160,602A discloses a large pore alumina support and a process for its preparation. This alumina support has a pore volume of 0.8-1.2 ml/g, a most probable pore diameter of 15-20 nm, a bulk density of 0.5-0.6 g/ml, a specific surface of 110-200 m
2
/g. The process for preparing the alumina support comprises mixing pseudo-boehmite with water or an aqueous solution, kneading the mixture into a plastic mass, molding by extrusion, drying and calcining. The improvement is the addition of a pore expander of combustible solid particulate and a pore expander containing phosphor, silicon, or boron compounds which can react with pseudo-boehmite or alumina. This alumina support also has a drawback of low strength.
CN 1,103,009A discloses a process for preparing an alumina having a dual pore structure. This alumina is prepared by mixing and molding two sorts of alumna or its precursors with different pore distributions with a carbon black powder, a surfactant, a peptizator and water, and then drying and calcining. More particularly, the process for preparing the alumna comprises mixing two sorts of alumna or its precursors with different pore distributions to uniformity, mixing the mixed alumina with a carbon black powder, a surfactant, a peptizator in the ratio of 1: 0.05-0.1: 0.05-0.1: 0.02-0.05 and water, molding, drying at 100-130° C., and then calcining at 550-650° C. for 1-4 h. In this alumina, the volume of the pores with diameters of 100-200 Å accounts for over 50% of the total pore volume, and the volume of the pores with diameters over 1000 Å accounts for 5-30% of the total pore volume. The alumina support prepared by using this process has higher strength. Compared to the process disclosed in U.S. Pat. No. 4,448,896, this process uses less carbon black powder and suits the industrial application.
It is well known that an alumina support itself possesses some acidity, which is the site for coke deposit. In order to reduce the coke deposit, silica is typically used as a catalyst support. However, silica is difficult to be molded, leading to a poor strength of the catalyst. When alumina is used as a support, the strength of the catalyst is better, but the catalyst is prone to coke deposition. All the above prior arts have not considered the problem of the coke deposition of the catalyst.
The objectives of the present invention are to overcome the drawbacks prone to coke deposition and of low strength and provide a guard catalyst which is not prone to coke deposition and has a higher strength. Another objective of the present invention is to provide a process for preparing the catalyst.
SUMMARY OF THE INVENTION
The guard catalyst provided by the present invention comprises an alumina support and molybdenum and/or tungsten and nickel and/or cobalt supported on the alumina support. The total ammonia integral adsorption heat of said alumina support does not exceed 25 J/g, wherein the percentage of the ammonia integral adsorption heat with the ammonia differential adsorption heat greater than 100 kJ/mol does not exceed 10% of the total ammonia integral adsorption heat.
The process provided by the present invention for preparing the catalyst comprises mixing a hydrated alumina, a carbon black powder, an organic pore expander, a peptizator and water, molding by extrusion, drying, calcining, impregnating metal components, and drying and calcining again, wherein said carbon black powder has been regulated and the wet powder has a pH of at least 8. The amount of each component is such that 1 part by weight of alumina corresponds to 0.03 to less than 0.05 part by weight of carbon black powder, 0.05-0.2 part by weight of organic pore expander, and 0.02-0.05 part by weight of peptizator.
In a preferred catalyst provided by the present invention, said total ammonia integral adsorption heat of said alumina support is 20-
Dong Weizheng
Kang Xiaohong
Wang Kui
Yang Qinghe
Zhu Li
China Petroleum and Chemical Corporation
Cooke Colleen P.
Dunn Tom
Pennie & Edmonds LLP
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