Plastic and nonmetallic article shaping or treating: processes – Outside of mold sintering or vitrifying of shaped inorganic... – Producing microporous article
Reexamination Certificate
1999-06-23
2002-04-02
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
C264S640000, C264S641000, C419S002000
Reexamination Certificate
active
06365092
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a shaped sintered porous body exhibiting a large surface area to volume ratio, a three-dimensional complex shape and an open three-dimensional porosity with a large surface area to volume ratio. The invention further relates to bodies produced by the method and the use thereof, such bodies for use as reactor elements, e.g. reactors for the chemical and process industry.
By way of example, commercial distillation is normally practiced as a multistage, counter current gas and liquid operation in a tower containing devices such as packing to facilitate the gas-liquid contacting that is necessary for both mass and heat transfer. The sintered porous body of the present invention is, in one application, for use as such a packing device. The term mass transfer relates to the contact efficiency of one medium to another and specifically refers to material moving from one phase to another. In a distillation process for example no reaction may be ocurring, however, improved contacting of one fluid, e.g., a liquid with another fluid, a gas or liquid, or a gas with a gas or a liquid with liquid is desired in the distillation process.
Since multiple equilibrium stages exist in a distillation tower, the compositions of the vapor and the liquid change throughout the tower length. The desired products can be removed as either liquid or vapor at an optimum location in the tower. The more efficient he mass transfer, the shorter the tower or more energy efficient the tower to achieve the same number of equilibrium stages. Mass transfer devices of the prior art typically are separated trays which allow vapor to pass upwards through a small height of liquid or continuous packings which contain surfaces for gas-liquid contacting. The advantage of structured packings in distillation processses are high efficiency coupled with low vapor pressure drop. Low pressure drops are desired because of the increased cost to force gases upwardly in the tower to overcome high pressure differentials, if present, and also because high pressure differentials tend to result in column “flooding,” where the liquid can no longer pass down the column.
Efficiency in a catalytic converter depends upon efficient contact of one fluid with another (gases or liquids in various combinations) or with a catalyst (a solid) and so on. Also, improved contact, i.e., mass transfer, is desired between fluids and/or fluids and solids since reaction rate depends upon th efficiency of th mass transfer with a solid catalyust. Thus improved contacting or mixing is desired to provide enhanced mass transfer or reaction rate in accordance with a given implementation. Sorption is thus desired in these processes whether adsorption or absorption.
Examples of catalytic distribution structures are disclosed in U.S. Pat. No. 4,731,229 to Sperandio, U.S. Pat. No. 5,523,062 to Hearn, U.S. Pat. No. 5,189,001 to Johnson, and U.S. Pat. No. 5,431,890 to Crossland et al.
Improved prior art packing structures have been developed comprising composite substrate structures, sometimes referred to as micromesh, which are porous products comprising a fibrous network of material. US Pat. Nos. 5,304,330; 5,080,962; 5,102,745 and 5,096,663, incorporated by reference herein, disclose the production of porous composite substrates comprising fibrous networks of material. A substrate mixture is comprised of typically metallic fibers for forming the porous composite and a structure forming agent which functions as a binder, which are dispersed in an appropriate liquid. After preforming, the liquid is removed and the composite heated to effect sintering of the fibers at junction points to produce a porous substrate composite comprised of a three-dimensional network of fibers. The structure forming agent is removed during or after sintering.
However, the porous material substrate in a packing structure of the type described above does not normally provide for fluid communication through the pores for the gases and liquids in the distillation process to provide for the needed desired contact while maintaining the desired low pressure drop. This is attributed to possibly capillary action due to the substrate material relatively small pore size. Such material may be for example 100 micron thick sheets (generally about 0.5-0.075 mm thick in one or more layers according to the desired strength) having the stiffness of conventional cardboard material, and sometimes referred to as a “paper,” although comprising metal fibers and stronger than paper of cellulose fibers. Such material has a high surface to void volume, comprising approximately 90-98% voids.
One common design criteria for reactor elements is that they preferably offer a high surface area to volume ratio which in most cases is combined with a low pressure drop in the reactor. This is to optimize mass transfer. To increase this ratio, reactor elements are in the form of assemblies made from sheet material which have been press-formed into corrugations and so on and joined to form a system of larger internal passage-ways or channels. The sheets may be solid, with or without openings, i.e., perforations, or have an open mesh-like structure. Mesh-like metallic sheets with a woven cloth-like structure are used to provide catalytic surfaces. Reactor elements with a catalytic function typically comprise a catalytic material, which may be included as wire in the mesh but are typically applied as a coating or deposition on the mesh.
Before assembling the reactor elements in a reactor, the sheet material is often shaped by pressing to simple shapes like corrugated sheet and the like or punched to provide holes or openings. This shaping is a costly additional step and requires extreme care in handling delicate porous paper-like porous sheet material. The shaped sheets are subsequently assembled either in a framework or by joining using suitable methods such as soldering and/or spot-welding.
In accordance with the production of fibrous mesh in the latter above-noted US patents, a mixture is provided comprised of fibers for forming the porous composite body and a structure forming agent, in particular cellulose fiber, which function as a binder, which are dispersed in an appropriate liquid. After performing into a desired form, liquid is removed and the composite body is heated to a temperature to effect sintering of the fibers at junction points to produce a porous composite body comprised of a three-dimensional network of fibers. The structure forming agent is removed before or during the sintering process or may be removed after the sintering process.
Japanese Patent Publication JP-A-95/97 602 discloses sheets of the non-woven type comprising metallic fibers and formed with methods similar to conventional paper-making methods and subsequently subjected to heat for removal of paper fiber and formation of thermal bonds between the metallic fibers. The sheets are subsequently shaped or assembled to bodies suitable for use as reactor elements. These sheets are preferably coated with catalytic material.
Also this type of sheet material is shaped before assembly to reactors, using the same shaping, assembling and joining methods discussed above. These shaping processes typically are mechanical, employing dies and the like which are cumbersome and may be complex and costly to implement. The shaping of fibrous non-woven sheets is difficult as there is a need to avoid damaging the sheet material during formation. Such shaping at a minimum thus requires the sheet material to be formed and then later processed to produce the three-dimensional shape, such as corrugations and the like needed for the reactor processes.
However, with known bodies and methods for producing such bodies there are still restrictions in the freedom in design of bodies and in particular for use in reactor environments, and there is still a long felt need for an increase in surface area to volume ratio for many applications. There is also a need for new manufacturing methods for suc
Backa Stefan
Fdhila Rebei Bel
Rissanen Markku
ABB Lummus Global Inc.
Carella Byrne Bain Gilfillan
Fiorilla Christopher A.
Olstein Elliott M.
Squire William
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