Plastic and nonmetallic article shaping or treating: processes – Outside of mold sintering or vitrifying of shaped inorganic... – Producing microporous article
Reexamination Certificate
1999-06-24
2001-07-24
Fiorilla, Christopher A. (Department: 1731)
Plastic and nonmetallic article shaping or treating: processes
Outside of mold sintering or vitrifying of shaped inorganic...
Producing microporous article
C264S669000, C264S679000
Reexamination Certificate
active
06264881
ABSTRACT:
FIELD OF INVENTION
1. Technical Field
The present invention relates to the production of faujasite agglomerates with a low silicon/aluminium ratio and with a low content of inert binder.
2. Background Art
Most zeolites are mainly synthesized by nucleation and crystallization of aluminosilicate gels, which results in a zeolite made of very small crystals. Powders are spoken of, in this respect. However, these powders are difficult to employ industrially and it is preferable to have a granular agglomerated form. These agglomerates, whether in the form of bars, balls of extrudates, are commonly composed of a zeolite powder, which constitutes the active component, and of a binder intended to provide for the cohesion of the crystals in the form of grains. This binder has no adsorbing property, its function being to give the grain sufficient mechanical strength to resist the vibrations and movements to which it is subjected during its various uses. These granules are prepared by forming a paste of the zeolite powder with a clayey paste, in proportions of the order of 80% of powder per 20% of binder, then shaping as balls, bars or extrudates, and heat treatment at high temperature to fire the clay and reactivate the zeolite.
This results in zeolitic bodies, with a particle size of a few millimetres, which, if the choice of the binder and the granulation are made according to the rules of the art, exhibit an array of satisfactory properties, in particular of porosity, of mechanical strength and of resistance to abrasion. The applicative properties are, obviously, reduced in the ratio of the active powder to the powder and its inert agglomeration binder.
Various means have been provided for overcoming this disadvantage of the binder of being inert with respect to the adsorbing performances, including the conversion of the binder, in all or part, into zeolite. This operation is easily carried out when use is made of binders of the kaolinite family calcined beforehand at temperatures of between 500° C. and 700° C. An alternative form consists in moulding kaolin grains and in converting them to zeolites: this principle is explained in “Zeolite Molecular Sieves” by D. W. Breck, John Wiley and Sons, New York. This technology has been applied with success to the production of grains of zeolite A or X composed up to 95% by weight of the zeolite itself and of an unconverted residual binder (see, to this end, Howell, U.S. Pat. No. 3,119,660), the addition of a silica source being recommended when it is desired to obtained a zeolite X (“Zeolite Molecular Sieves”, Breck, p. 320).
Kuznicki and coworkers show, in U.S. Pat. No. 4,603,040, that it possible to convert a kaolin agglomerate into zeolite X with an Si/Al ratio equal to 1; nevertheless, the reaction, in order to be virtually complete, that is to say to result in the formation of a grain composed of approximately 95% zeolite X, requires approximately 10 days at 50° C., which makes the operation unfeasible industrially. If the reaction is carried out in combination with a maturing period of 5 days at 40° C., followed by crystallization at a higher temperature, the resulting solid is composed of 80% faujasite and 15% zeolite A.
JP-05163015 (Tosoh Corp.) teaches that it is possible to form grains of zeolite X with a low Si/Al ratio, of the order of 1, by mixing a zeolite X powder, with an Si/Al ratio equal to 1, with kaolin, potassium hydroxide, sodium hydroxide and carboxymethylcellulose. Shaping is carried out by extrusion. The grains thus obtained are dried, calcined at 600° C. for 2 hours and then immersed in a sodium hydroxide and potassium hydroxide solution at 40° C. for 2 days.
These two documents teach that it is possible to prepare mechanically strong solids mainly composed of zeolite X in which the Si/Al ratio is substantially lower than that of the zeolites X conventionally manufactured by the gel route, the Si/Al ratio of which is between 1.1, approximately, and 1.5. Nevertheless, the associated processes are inelegant and suffer either from an excessive reaction time or from the number of stages involved. It may be feared, moreover, that the heat treatment as claimed in JP 05-163015, after the shaping stage, does not contribute to the amorphization of the grain and that the object of the caustic digestion which follows is to recrystallize it, which would explain the slowness of the process.
DISCLOSURE OF INVENTION
In the present application, the designation LSX (Low Silica X) will be reserved for zeolites X with a low Si/Al ratio, namely zeolites X with an Si/Al ratio equal to 1, reasonable experimental deviations around this unit value being accepted, the lower values very definitely corresponding to inaccuracies in the measurement and the higher values corresponding to the presence of inevitable impurities with a higher silica content and containing sodium ions and possibly potassium ions. It is shown here that it is possible to prepare zeolitic bodies composed of at least 95% of zeolite having an Si/Al ratio equal to 1, by virtue of the use of a much simpler and faster process which consists in:
a) agglomerating a zeolite LSX powder with a binder containing at least 80% of a clay which can be converted to zeolite,
b) shaping the mixture obtained in a),
c) drying it and then calcining it at a temperature of 500-600° C.,
d) bringing the solid product resulting from c) into contact with a caustic aqueous solution,
e) washing, drying and activating at a temperature of 500-600° C.
Conversion of the binder to zeolite takes place during the stage d) by the action of the caustic solution, which must be at least 0.5 molar and which can be a sodium hydroxide and potassium hydroxide solution in which the potassium hydroxide is present at a maximum content of 30 molar % (with respect to the combined sodium hydroxide+potassium hydroxide). It can be advantageous to use a sodium hydroxide solution. The process is carried out at a temperature sufficient to obtain a reasonable rate of conversion to zeolite.
The clay which can be converted to zeolite belongs to the kaolinite, halloysite, nacrite or dickite family. Kaolin is very simply used.
REFERENCES:
patent: 3119660 (1964-01-01), Howell et al.
patent: 3906076 (1975-09-01), Goytisolo et al.
patent: 4603040 (1986-07-01), Kuznicki et al.
patent: 5993773 (1999-11-01), Funakoshi et al.
patent: 6036939 (2000-03-01), Funakoshi et al.
patent: 24 46 974 (1975-04-01), None
patent: 299635 (1992-04-01), None
patent: 196043 (1986-10-01), None
patent: 4-198011 (1992-07-01), None
patent: 5-163015 (1993-06-01), None
patent: 6-183725 (1994-07-01), None
Zeolite Molecular Sieves, D.W. Breck, John Wiley and Sons, Aug. 1979 pp. 1-28.
CECA S.A.
Fiorilla Christopher A.
Smith , Gambrell & Russell, LLP
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