Plastic and nonmetallic article shaping or treating: processes – Pore forming in situ – Of inorganic materials
Reexamination Certificate
2001-08-01
2003-09-09
Fiorilla, Christopher A. (Department: 1731)
Plastic and nonmetallic article shaping or treating: processes
Pore forming in situ
Of inorganic materials
C264S628000
Reexamination Certificate
active
06616873
ABSTRACT:
TECHNICAL FIELD
This invention relates to a process for making low density abrasion and high temperature resistant, open/closed cellular spheres with or without a central core cavity inter and cross linked to zigzag pore conduits formed in sphere wall of desired thickness having high crush strength and forming low-to-high temperature loose fill spheres for use as catalyst carriers or for being moulded to form refractory bricks/monoliths for use in a wide range of mobile or stationary and other refractory applications.
DEFINITIONS
The following expressions wherever appearing throughout this specification shall include the meaning set there against as under:
“Indialite Spheres’—means low-to-high temperature loose fill and moulded macro porous spheres made by the process of this invention.
‘PVA Aqua Sol’ means cold water soluble inorganic binder with 2% low ash content of PVA (Poly-Vinyl-Alcohol)
‘Burnable core’ means herein stated organic/inorganic filler/binder mass forming burnable core particles.
PRIOR ART BACKGROUND
It is known that the catalyst carrier materials used for oxidation/reduction reaction possess high stability. High porosity of inert ceramic carrier enables applications as well as anchoring of any other high surface area enhancing materials such as ‘Gamma’ or ‘Theta’ Alumina which in turn increases the degree of dispersion of the catalyst species.
These dispersions retard activity loss from agglomeration or coalescence of catalyst species during sintering and increase the availability of catalyst surface area for catalytic reactions.
The use of a wide variety of inorganic refractory metal oxides and metal oxide mixtures as catalysts supports is well known in chemical engineering and such supports are made in many forms such as loose fill packing of spheres of uniform or different sizes, rings and the like, or entire structures in reticule or honeycomb and the like form.
These supports have been utilised for carrying metal catalysts such as Pt, Pd, Rh and the like and base metal catalysts including alumina, magnesia, titania and the like either alone or any desired admixtures thereof.
Therefore, it is obviously desirable that the catalyst carrier should possess high geometric surface area, and should preferably be able to promote a degree of turbulence in order that reacting fluids or gases passing through the catalytic bed encounter as much reactive catalytic surface as possible during residence time of reaction mixture in catalyst bed.
On the other hand it is also necessary that the catalyst bed should present very little resistance to the flow of reacting fluids or gases while passing through the packed column of catalyst bed. Both the above requirements are contradictory to each other and hence an optimal combination of the two factors is necessary for achieving the best results.
It is known that catalyst carriers, in general, are inactive with decreasing level of porosity for use in conjunction with high surface area coating on which the catalyst carrier can be distributed to produce desired level of gases or fluids that come in contact with them while being circulated through said carriers in catalvst bed. To enable strong adherence of said high surface area coating, the carrier material should also have optimal pore structure and pore size distribution.
Many catalyst carriers are known in prior art, as catalvst support in the form of spheres or otherwise shaped monoliths such as honeycomb monoliths. For example, C. F. Schafer and R. C. Bedford have described an alumina based thermally stable catalyst carrier described in U.S. Pat. No. 4,31,565.
Many such patents on catalyst supports are predominant but they principally deal with active alumina. Most of the earlier references on catalvst carriers referring to ‘Cordierite’ composition deal with honey-comb shapes and rarely on ‘Cordierite’ spheres.
Numerous patents on ‘Cordierite’ honeycomb shapes are known in the prior art for instance:
U.S. Pat. No. 5,549,725 discloses a process for making a ‘Cordierite’ ceramic honeycomb for use as filter material.
U.S. Pat. Nos. 5,773,103 and 4,871,693 disclose methods of making porous ‘Cordierite’ ceramic formed from hollow spherical glass ceramic powders that are obtained through spray thermal decomposition of expensive organic or aqueous-organic solvents, as starting materials.
U.S. Pat. No. 4,37,044 provides a method for preparation of ‘Cordierite’ bead type support structure with a raspberry-like or dimpled surface having high decree of macro porosity in which colloidal silica has been used to create raspberry-like dimpled surface. Though the use of such raspberry-like sphere surface enhances the geometric surface it is prone to attrition in turbulent flow of gases and the sharp edged sphere surface tends to smoothen out, over a period of time, due to high velocity flow stream as, for example, in automotive exhaust applications in two-stroke engine vehicle.
In all the earlier references pertaining to the Cordierite catalvst carrier of any form the cordierite precursor is subjected to firing schedule of over 48 to 72 hours which includes the soaking time at the maximum temperature of 1390 to 1410° C. This invention discloses a process wherein the firing schedule of less than an hour yielding >90% Indialite, a high temperature polymorph of cordierite, as the only principal phase in the fired body.
OBJECTS OF THE INVENTION
The principal object of this invention, therefore, is to offer a rapid process for making hollow or solid cellular macro porous ‘Indialite’ ceramic spheres having hitch crush strength up to 23 lbs.(point load strength) capable of extending crush strength upto 32 lbs. by homogenizing zirconia fibers in the green mass of compositions of Table-1 and burnable core mass for attaining herein stated benefits for use as loose fill catalyst carriers and also which when moulded into refractory bricks and monoliths provide high temperature insulation in refractory applications.
It is further object of this invention to provide a method for production of a highly macroporous Indialite type spherical pelleted or beaded catalyst support that is made of low cost easily available raw materials following a method of pyroprocessing schedule of less than an hour under rotary motion of the spheres in air atmosphere which enables uniform thermal treatment of the pellets and which in turn results in in-situ formation of high temperature polymorph of Cordierite (Indialite) from its precursor materials.
It is yet another object of this invention to provide a method for forming of judiciously proportioned raw materials which yields narrow size distribution of pellets which on sintering in rotary kiln gives rise to Indialite body with less than 5% volume shrinkage, while maintaining high decree of uniformly distributed pores of 1-10 micron size. Other objects are apparent from the herein described process.
The incorporation of zirconia fibers in the homogenised product mix of TABLE-1 is also found to be very effective in bonding together network cage of inter and cross linked macro pores form reinforcement for the said spheres having high crush strength upto 23 lbs psi. In certain cases, the ‘Indialite’ spheres reinforced with zirconia fibers favourably enhance not only their crush strength upto 32 lbs. but also enhance their catalytic activity to otherwise inert catalyst carriers.
STATEMENT OF INVENTION
Novel process according to this invention for making open or closed cellular macro porous ‘Indialite’ ceramic spheres with or without a central core cavity cross/inter linked with zigzag macro porous conduits from naturally occurring herein stated TABLE-1 composites homogenized with burnable organic/inorganic core particles forming filler/binder; sprinkling said mass over a pan-pelletizer separately wetted with <2% cold water soluble PVA (Poly Vinyl Alcohol) aqua sol and rolling to form compact green phase of spheres having <25% moisture dry compacting in pelletizer said spheres before air or oven drying at 90-110 deg. C. till said moisture and core particles are par
Anjan Kumar Chatterjee
Duraiswami Venkateswaran
Minocher Cursetji Rustom
Parvez Vajifdar
Associated Cement Companies Ltd.
Dickstein , Shapiro, Morin & Oshinsky, LLP
Fiorilla Christopher A.
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