Catalyst – solid sorbent – or support therefor: product or process – Zeolite or clay – including gallium analogs – And additional al or si containing component
Reexamination Certificate
1998-09-16
2001-04-10
Dunn, Tom (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Zeolite or clay, including gallium analogs
And additional al or si containing component
C502S060000, C502S063000
Reexamination Certificate
active
06214758
ABSTRACT:
This invention relates to a method of making hydrophilic small pore sizes molecular sieve bodies by shaping a plasticized mixture of the molecular sieve and a silicone resin binder that is provided as an emulsion. Use of the silicone resin as an emulsion results in production of a stronger body for a small pore size hydrophilic molecular sieve than if the silicone resin were dissolved in a solvent.
BACKGROUND OF THE INVENTION
Molecular sieve monoliths, such as zeolite monoliths find use in catalytic applications such as catalysts, catalyst supports, or adsorbing structures, where they must be strong and of uniform composition throughout the body. Depending on their pore size, they are suitable for adsorbing various molecular size contaminants or for catalyzing various chemical reactions, or for moisture removal. They are made by shaping e.g. extruding plasticized mixtures of the molecular sieve and various binders and vehicle such as water. One effective binder is silicone resin. Ordinarily the silicone resin is dissolved in a solvent as described in U.S. Pat. Nos. 4,631,267 and 5,633,217. For hydrophobic molecular sieves such as e.g. ZSM zeolites, this poses no problem. However, with hydrophilic molecular sieves, repelling of the silicone resin binder solution poses a problem. For example, in forming a plasticized batch of a hydrophilic zeolite small pore such as A4 zeolite with silicone resin dissolved in a solvent, the batch becomes soft and gummy upon addition of the silicone resin solution prior to addition of the water vehicle. Though rods and ribbons can be extruded, the products are so gummy and soft that it is impossible to maintain their shapes for further processing.
When the monoliths are honeycombs especially honeycombs with thin walls, it is even more important that the plasticized mixture be stiff and able to maintain its shape, otherwise the honeycomb walls will collapse.
U.S. Pat. No. 5,492,883 relates to shaping zeolites using a silicone resin emulsion as a binder. However, the zeolites are medium to large pore size.
It would be desirable to have a method of shaping plasticized mixtures of small pore molecular sieves wherein the shaped products would have strength in both the green state and the final heat-treated structure.
SUMMARY OF THE INVENTION
In accordance with one aspect of the invention, there is provided a method of making a small pore molecular sieve monolithic body that involves forming a plasticized mixture of hydrophilic molecular sieve powder having a pore size of no greater than about 5.0 angstroms, temporary binder, silicone resin binder emulsion, and polar vehicle, shaping the mixture into a green monolithic body, and drying and heat-treating the green monolithic body to impart strength to the green body and form the product molecular sieve monolith.
In accordance with another aspect of this invention, there is provided a small pore hydrophilic molecular sieve monolithic body having a pore size of no greater than about 5.0 angstroms, and made up of about 80% to 95% by weight molecular sieve with the balance being silica binder.
DETAILED DESCRIPTION OF THE INVENTION
This invention provides a method to shape small pore hydrophilic molecular sieves into monolithic bodies of sufficient strength to maintain their shape through handling, drying, and heat-treating operations. The bodies are shaped from a plasticized mixture of the molecular sieve, temporary binder, silicone resin binder emulsion, and polar vehicle which is preferably water.
The Molecular Sieve
This invention is useful for hydrophilic molecular sieves of small pore size. By hydrophilic is meant those having a SiO
2
:Al
2
O
3
mole ratio of no greater than about 30:1, and preferably between about 30:1 to 1:1 and more preferably about 10:1 to 1:1. By small pore size according to this invention is meant pore sizes no greater than about 5.0 angstroms. These molecular sieves find use in specialized adsorption applications and/or where water absorbing capability is desired.
Some suitable molecular sieves that fit this description are A3, A4, A5, ferrierite, erionite, and chabazite. Especially suited are A3, A4, and A5, with A4 being especially preferred.
Temporary Binders
Temporary binders are so called because they are removed during the final heat-treatment. The temporary binders are plasticizing organic binder with optional additions of a co-binder.
The plasticizing Organic Binder
The organic binder contributes to the plasticity of the mixture for shaping into a body. The plasticizing organic binder according to the present invention refers to cellulose ether binders. Some typical organic binders according to the present invention are methylcellulose, ethylhydroxy ethylcellulose, hydroxybutyl methylcellulose, hydroxymethylcellulose, hydroxypropyl methylcellulose, hydroxyethyl methylcellulose, hydroxybutylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, sodium carboxy methylcellulose, and mixtures thereof. Methylcellulose and/or methylcellulose derivatives are especially suited as organic binders in the practice of the present invention with methylcellulose, hydroxypropyl methylcellulose, or combinations of these being preferred. Preferred sources of cellulose ethers are Methocel A4M, F4M, F240, and K75M from Dow Chemical Co. Methocel A4M is a methylcellulose, while Methocel F4M, F240, and K75M are hydroxypropyl methylcellulose.
The organic binder content is typically is about 2% to 12% and preferably about 3 to 8 wt. %.
Co-binders
Co-binders can be used to enhance the plasticity of the mixture. Some co-binders that are useful are low molecular weight water-soluble binders such as for example, polyvinyl alcohols such as those available from Air Products, Allentown Pa., under the designation Airvol, e.g. Airvol 205 (molecular weight 31,000-50,000) and Airvol 350 (molecular weight 124,000-186,000). Other useful water soluble binders include polyvinylpyrrolidones such as those available from GAF, Linden, N.J., under the designation PVP K-30 (row 40,000) and PVP K-60 (row 160,000). Airvol 205S is particularly useful. Polyvinyl acetate is also suitable.
The silicone resin binder emulsion
Aqueous silicone resin emulsions such as phenylmethyl silicone resin emulsions available from Dow Corning Corporation, Midland Mich. and sold under the designations 1-0468 and 1-0469 for example are particularly useful for the practice of the invention. These silicone resin emulsions are characterized by about 60 weight percent resin solids that sinter to yield about 52 weight percent silica having a particle size of about 7000 Angstroms, and can contain very small amounts (0.5 to 1 lb/gal of the emulsion) of an organic aromatic solvent.
A homogeneous formable mixture is made of the raw material, permanent binder and/or permanent binder precursors, temporary binder, and vehicle. Although any vehicle can be used that is safe, feasible and does not adversely affect the mixture, the preferred vehicle in extrusion processing is water
The water content is typically about 12% to 50 wt. %, and preferably about 28% to 45 wt. %.
The weight percents of the organic components and vehicle are calculated as superadditions with respect to the non-organic solids by the following formula:
weight
of
organic
component
,
vehicle
,
or
other
additives
fired
weight
units
of
inorganic
powder
(
molecular
sieve
+
silica
)
×
100
Normally, the molecular sieve and silicone resin binder emulsion are provided in amounts sufficient to result in a weight ratio of molecular sieve to silica in the product of about 80:20 to 95:5.
One advantageous mixture composition consists essentially of in percent by weight based on the fired zeolite and silica, about 2% to 12% temporary binder that is methylcellulose and/or methylcellulose derivatives, about 12% to 50% water, sufficient zeolite to result in about 80% to 95% zeolite on a fired basis, and s
Wu Shy-Hsien
Zaun Kenneth E.
Corning Incorporated
Dunn Tom
Gheorghiu Anca C.
Herzfeld L. Rita
Ildebrando Christina
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