United States Patent [19J
`Park et al.
`
`[54] ADSORPTIVE MONOLITH INCLUDING
`ACTIVATED CARBON AND METHOD FOR
`MAKING SAID MONLITH
`
`[75]
`
`Inventors: Minwoo Park, Lilburn; Frank R.
`Rhodes; Jack H. L'Amoreaux, both of
`Lawrenceville, all of Ga.; Frederick S.
`Baker, Wanda, S.C.; Robert K.
`Beckler, Lexington; John C. McCue,
`Covington, both of Va.
`
`[73] Assignees: Applied Ceramics, Inc., Doraville, Ga.;
`Westvaco Corporation, New York,
`N.Y.
`
`[21] Appl. No.: 08/636,700
`
`[22] Filed:
`
`Apr. 23, 1996
`
`[51]
`
`Int. Cl.6
`
`............................. BOU 20/02; B0lJ 21/18;
`C04B 33/24
`[52] U.S. Cl. .......................... 502/417; 502/427; 502/436;
`502/180; 501/100; 501/143
`[58] Field of Search ..................................... 502/417, 427,
`502/436, 180; 501/100, 143
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`Re. 25,400
`617,079
`1,524,843
`1,589,081
`1,985,840
`2,108,860
`2,391,312
`2,439,358
`2,439,538
`2,455,509
`2,951,087
`3,089,195
`3,454,502
`3,592,779
`3,632,385
`3,690,634
`3,825,460
`3,859,421
`3,864,277
`3,891,574
`3,927,186
`3,960,761
`3,960,771
`4,029,600
`4,051,098
`
`6/1963 Doying .................................... 252/428
`1/1899 Catlett .
`2/1925 Ruprecht .
`6/1926 Adler ........................................ 502/80
`12/1934 Sad tier .. ... ... ... .... ... ... ... ... ... .... ... . 131/31
`2/1938 Kauffman . ... ... .... ... ... ... ... ... .... ... . 131/31
`12/1945 Ewing et al.
`........................... 252/235
`4/1948 Divoll ... ... ... ... .... ... ... ... ... ... .... ... ... .. 7 4/5
`4/1948 Burgess ................................... 252/265
`12/1948 Luaces ........................................ 18/55
`8/1960 Hauser .................................... 260/448
`5/1963 Woodburn, Jr ........................... 18/47.5
`7/1969 Hiltgen et al. .......................... 252/428
`7/1971 Kiikka ..................................... 252/421
`1/1972 Schmitt ..................................... 117/46
`9/1972 Enya ..................................... 266/33 R
`7/1974 Yoshikiawa et al. ................... 156/296
`1/1975 Hucke ..................................... 423/445
`2/1975 Kovach ................................... 252/423
`6/1975 Kobayashi et al. ..................... 252/421
`12/1975 Vinton et al. ........................... 423/447
`6/1976 Burger et al. ........................... 252/421
`6/1976 Tanaka et al. .......................... 252/446
`6/1977 Schmitt, Jr. et al. ................... 252/444
`9/1977 Takemura et al. ........................ 260/38
`
`I 1111111111111111 11111 lllll lllll lllll lllll 111111111111111 111111111111111111
`US005914294A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,914,294
`Jun.22,1999
`
`4,058,483
`4,124,529
`4,220,553
`4,225,569
`4,259,299
`4,338,106
`4,399,052
`4,518,704
`4,677,086
`4,808,559
`4,923,843
`4,954,469
`4,968,651
`4,999,330
`5,043,310
`5,215,690
`5,306,675
`5,356,852
`5,376,609
`5,389,325
`5,403,809
`
`11/1977 Henbest .................................. 252/446
`11/1978 Jiintgen et al.
`......................... 252/421
`9/1980 Krause .................................... 252/428
`9/1980 Matsui et al. ........................... 423/445
`3/1981 Hagiwara et al.
`...................... 423/210
`7/1982 Mizuno et al.
`........................... 55/316
`8/1983 Sugino .................................... 252/421
`5/1985 Okabayashi et al. ..................... 502/80
`6/1987 McCue et al. ............................ 502/62
`2/1989 Sommer et al. .......................... 502/63
`5/1990 Saforo et al. ........................... 502/415
`9/1990 Robinson .................................. 502/80
`11/1990 Crabtree ... .... ... ... ... ... .... ... ... ... ... . 502/63
`3/1991 Bose et al. .............................. 502/402
`8/1991 Takeuchi et al. ....................... 502/404
`6/1993 Golino et al. .......................... 264/29.4
`4/1994 Wu et al. .................................... 502/5
`10/1994 DeLiso et al. .......................... 502/402
`12/1994 Guile ......................................... 502/62
`2/1995 Bookbinder et al. .............. 264/177.12
`4/1995 Miller et al. ............................ 502/416
`
`FOREIGN PATENT DOCUMENTS
`
`1567491
`59-69146
`2409
`3078
`341233
`
`4/1969 Germany .
`4/1984
`Japan .
`9/1865 United Kingdom .
`9/1865 United Kingdom .
`1/1931 United Kingdom .
`
`Primary Examiner-Glenn Caldarola
`Assistant Examiner-fo Suk Bullock
`Attorney, Agent, or Firm-Jones & Askew, LLP
`
`[57]
`
`ABSTRACT
`
`An adsorptive monolith made by extruding a mixture of
`activated carbon, a ceramic forming material, a flux
`material, and water, drying the extruded monolith, and firing
`the dried monolith at a temperature and for a time period
`sufficient to react the ceramic material together and form a
`ceramic matrix. The extrudable mixture may also comprise
`a wet binder. The monolith has a shape with at least one
`passage therethrough and desirably has a plurality of pas(cid:173)
`sages therethrough to form a honeycomb. The monolith may
`be dried by vacuum drying, freeze drying, or control humid(cid:173)
`ity drying. The monolith is useful for removing volatile
`organic compounds and other chemical agents such as ozone
`from fluid streams. Particularly useful applications include
`adsorptive filters for removing ozone from xerographic
`devices and other appropriate office machines and volatile
`organic compounds from automobile engine air intake sys(cid:173)
`tems.
`
`63 Claims, 3 Drawing Sheets
`
`BASF-1010
`U.S. Patent No. RE38,844
`
`

`

`U.S. Patent
`U.S. Patent
`
`Jun. 22, 1999
`Jun.22,1999
`
`Sheet 1 of 3
`Sheet 1 of 3
`
`5,914,294
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`

`

`U.S. Patent
`
`Jun.22,1999
`
`Sheet 2 of 3
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`5,914,294
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`APPARENT DENSITY VERSUS TEMPERATURE
`0.4 . . . - - - - - - - - - - - - - - - - - - - ,
`
`0.35
`
`0.3
`
`• 30% CARBON WITH FLUX
`v 50% CARBON WITH FLUX
`-A- 30% W/0 FLUX
`-B 50% W/0 FLUX
`
`0.25 ~ ~
`0.2 ~-=-=--___ ___,1.._ ___ ____,Ji..___ _ _ _ ~
`1600
`1800
`2000
`1400
`TEMPERATURE
`(deg. F)
`
`APPARENT
`DENSITY
`(g/ml)
`
`FIG. 4
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`

`

`5,914,294
`
`1
`ADSORPTIVE MONOLITH INCLUDING
`ACTIVATED CARBON AND METHOD FOR
`MAKING SAID MONLITH
`
`TECHNICAL FIELD
`
`5
`
`2
`economical conditions such as a lower temperature and a
`shorter time, has sufficient strength to withstand handling
`and use as an adsorptive filter, and has a shape which
`accommodates sufficient fluid flow throughput.
`
`SUMMARY OF THE INVENTION
`
`This invention relates to adsorptive monoliths including
`activated carbon and more particularly to adsorptive mono(cid:173)
`liths including ceramic material and activated carbon and
`using said monolith to remove volatile organic compounds,
`ozone, and other chemical agents from fluid streams.
`
`BACKGROUND OF THE INVENTION
`
`Activated carbon is useful in the removal of chemical
`agents such as volatile organic compounds from fluid 15
`streams and is also useful as a catalyst substrate for special
`applications. To remove chemical agents from a fluid stream
`with activated carbon, the fluid stream is directed adjacent
`the activated carbon. The activated carbon can be in the form
`of particles in a packed column, a coating on a substrate, a 20
`monolith with passages for fluid flow therethrough, and the
`like.
`It is desirable in some activated carbon applications to
`have a high rate of fluid flow adjacent to the activated carbon
`and a low level of back pressure. Thus, packed columns of
`activated carbon are sometimes unsuitable because of the
`high level of back pressure created. Formed bodies contain(cid:173)
`ing activated carbon and having open passages there through,
`such as a honeycomb-shaped activated carbon monolith, are
`desirable for applications wherein a reasonably high rate of
`fluid flow and a low level of back pressure are required, but
`formation of such shapes with a level of strength sufficient
`to withstand handling and use as an adsorbent filter is
`problematic. Activated carbon monoliths formed without a
`binder do not have sufficient strength for some applications. 35
`U.S. Pat. No. 4,518,704 to Okabayashi et al. discloses a
`formed body comprising activated carbon and a ceramic
`material. This structure has improved strength properties but
`Okabayashi teaches firing at a temperature of 1100° C. for
`a period from 1 to 4 hours to achieve desired bonding and
`strength. Firing at such a high temperature and for such a
`long period of time is economically undesirable.
`Another problem with making adsorptive monoliths com(cid:173)
`prising activated carbon and a ceramic material is that it is 45
`difficult to extrude a mixture of activated carbon and ceramic
`forming material without a high level of water in the mixture
`due to the high porosity of the activated carbon. To success(cid:173)
`fully extrude a mixture of activated carbon and ceramic
`forming material into a shape such as a honeycomb, a water 50
`content of 30 to 65 percent by weight is required. This
`moisture must be substantially removed from the extruded
`monolith before firing to protect the integrity of the formed
`monolith. A ceramic article subjected to increased tempera(cid:173)
`ture during firing, without first having been relieved of most 55
`of its moisture content, will usually suffer significant dam(cid:173)
`age in the forms of cracks, pop-outs or explosions due to
`rapid conversions of its remaining moisture to steam.
`Drying of a wet, extruded monolith of ceramic forming
`material and activated carbon is a sensitive process. An 60
`unfired ceramic product generally shrinks as it loses
`moisture, and a monolith can crack if the rate of moisture
`loss from the monolith during drying is not uniform through(cid:173)
`out the monolith.
`Accordingly, there is a need for a formed body comprising
`activated carbon that can be formed by extrusion, can be
`dried and fired without cracking, can be fired at more
`
`10
`
`This invention solves the above-described problems by
`providing a method of forming an adsorptive monolith
`comprising extruding an extrudable mixture including an
`activated carbon, a ceramic forming material, water, and a
`flux material. The flux material enhances the fusing of the
`ceramic forming material upon firing by lowering the tem(cid:173)
`perature at which the ceramic forming material fuses and
`forms ceramic bonds. This allows the monolith to be fired at
`a lower temperature and for a shorter time. In addition, the
`invention encompasses methods of drying the wet extruded
`monolith including vacuum drying, freeze drying, and
`humidity control drying. Such drying methods allow the wet
`extruded monolith to be dried without cracking of the
`monolith.
`More particularly, this invention encompasses a method
`of forming an adsorptive monolith comprising the steps of
`(a) extruding an extrudable mixture through an extrusion die
`25 such that a monolith is formed having a shape wherein the
`monolith has at least one passage therethrough and the
`extrudable mixture comprises activated carbon, a ceramic
`forming material, a flux material, and water, (b) drying the
`extruded monolith, and (c) firing the dried monolith at a
`30 temperature and for a time period sufficient to react the
`ceramic forming material together and form a ceramic
`matrix. The extrudable mixture is capable of maintaining the
`shape of the monolith after extrusion and during drying of
`the monolith.
`A suitable ceramic forming material is ball clay. In
`addition, the ceramic forming material desirably includes a
`filler for reducing shrinkage of the monolith during the steps
`of drying and firing. A suitable filler is calcined kaolin clay.
`A suitable flux material is a feldspathic material,
`40 particularly, nepheline syenite.
`Desirably, the extrudable mixture includes a wet binder
`for enhancing strength and maintaining the shape of the wet
`extruded monolith. A particularly suitable wet binder is
`methylcellulose. Acrylic binders are also suitable and can be
`used in combination with methylcellulose.
`The extrudable mixture can also include sodium silicate
`which, as a binder, enhances the strength of the monolith
`during drying and, as a flux material, enhances the strength
`of the monolith after firing.
`Desirably, the adsorptive monolith has a plurality of
`passages therethrough and is in the shape of a honeycomb.
`The extruded monolith may be dried by vacuum drying
`which includes placing the extruded monolith in a vacuum
`chamber initially having room ambient temperature and
`atmospheric pressure within the vacuum chamber, reducing
`the pressure within the vacuum chamber at a rate and to a
`level sufficient to freeze the water in the monolith, and
`maintaining the reduced pressure within the vacuum cham(cid:173)
`ber for a time sufficient for the frozen water to sublime until
`the monolith is dried. More particularly, the pressure within
`the vacuum chamber may be reduced, within about 1
`minute, from atmospheric pressure to a pressure less than
`about 1 torr, and desirably within the range from 30 microns
`65 to 1 torr.
`The method of freeze drying the wet extruded monolith
`comprises the steps of (1) freezing the water in the extruded
`
`

`

`5,914,294
`
`3
`monolith, (2) placing the frozen extruded monolith in a
`vacuum chamber initially having a pressure within the
`vacuum chamber of atmospheric pressure, (3) reducing the
`pressure and/or temperature within the vacuum chamber at
`a rate and to a level sufficient to keep the water in the 5
`monolith frozen, and (4) maintaining the reduced pressure
`and/or temperature within the vacuum chamber for a time
`sufficient for the frozen water in the monolith to sublime
`until the monolith is dry. Desirably, during the freezing step,
`the water in the monolith is frozen within about 10 seconds 10
`to 10 minutes after the extrusion step and the monolith is
`subjected to a temperature of less than about -25° F. More
`desirably, during the freezing step, the monolith is subjected
`to a temperature of less than about -80° F.
`The method of humidity control drying the wet extruded
`monolith comprises the steps of (1) placing the extruded
`monolith in a chamber initially having a relative humidity
`within the chamber of at least 95 percent and (2) gradually
`reducing the relative humidity within the chamber until the
`monolith is dry.
`This invention encompasses an adsorptive monolith made
`according to the foregoing process and a method of remov(cid:173)
`ing chemical agents such as volatile organic compounds and
`ozone from a fluid air stream comprising the step of routing
`through the adsorptive monolith a fluid stream initially
`including such a chemical agent.
`The adsorptive monolith of this invention comprises
`ceramic material and activated carbon dispersed throughout
`the matrix. The ceramic material is reacted together such
`that a ceramic matrix is formed and the activated carbon is
`supported by the matrix. The monolith desirably has a
`plurality of passages therethrough to receive a flow of fluid
`and is in the shape of a honeycomb. In addition, the monolith
`desirably has an open frontal area greater than 70% and up 35
`to 85% and an axial crushing strength from about 500 to
`about 1600 psi.
`Thus, an object of the present invention is to provide an
`improved adsorptive monolith comprising activated carbon
`and an improved method of making such a monolith.
`Another object of the present invention is to provide an
`adsorptive monolith for removing chemical agents such as
`volatile organic compounds and ozone from fluid streams.
`Yet another object of the present invention is to provide an
`adsorptive monolith with desirable strength characteristics. 45
`Still another object of the present invention is to provide
`improved methods of drying a wet extruded monolith com(cid:173)
`prising activated carbon, ceramic forming material, and
`water.
`Other objects, features, and advantages of the invention
`will become more readily apparent from the following
`description of embodiments of the invention.
`
`30
`
`BRIEF DESCRIPTION OF DRAWINGS
`FIG. 1 is a perspective view of an adsorptive monolith
`made in accordance with an embodiment of this invention.
`FIG. 2 is a partial side elevation view of the monolith of
`FIG. 1 with a portion of the skin removed to illustrate the
`flow of fluid through the honeycomb passages of the mono(cid:173)
`lith.
`FIG. 3 is a graph comparing the axial crushing strength of
`monoliths made in accordance with embodiments of this
`invention with that of monoliths made without flux material.
`FIG. 4 is a graph comparing the apparent density of 65
`monoliths made in accordance with embodiments of this
`invention with that of monoliths made without flux material.
`
`20
`
`25
`
`4
`DETAILED DESCRIPTION OF DRAWINGS
`As summarized above, this invention encompasses an
`adsorptive monolith comprising activated carbon, a method
`for making such a monolith including methods for drying
`the monolith, and methods for adsorbing chemical agents
`such as volatile organic compounds. As used herein, mono(cid:173)
`lith means a block of solid-phase material. FIG. 1 illustrates
`a monolith 10 made according to an embodiment of the
`present invention. The monolith 10 shown in FIG. 1 is an
`extruded monolith comprising activated carbon and ceramic
`material and having a honeycomb shape. The monolith has
`a plurality of passages 12 extending through the monolith
`from a frontal end 14 to a rearward end 16. The passages 12
`are substantially square in cross section, linear along their
`15 length, and formed by surrounding walls 18 of the extruded
`material; however, the passages can have other cross(cid:173)
`sectional shapes such as rectangular, round, triangular,
`hexagonal, oval, eliptical, and the like. The passages 12 are
`encased by an outer skin 20 of the extruded material.
`The monolith 10 is useful as an adsorptive filter to adsorb
`a variety of chemicals from gaseous or liquid phases and as
`a catalyst substrate. For example, when the monolith 10 is
`disposed in the air intake system of a fuel injected internal
`combustion engine, the activated carbon of the monolith
`adsorbs fuel vapors that escape from injector ports as fuel
`leakage when the engine is turned off. When the engine is
`restarted, incoming air sweeps back through the honeycomb
`structure and desorbs the fuel. The fuel is then combusted in
`the engine. FIG. 2 illustrates the flow of fluid through the
`passages 12 in the monolith 10. The material to be adsorbed
`is adsorbed by the activated carbon held in the walls of the
`monolith structure.
`In another example, the monolith 10 is positioned in the
`exhaust air stream of a xerographic device and the activated
`carbon of the honeycomb structure adsorbs ozone. The
`ozone is captured by the carbon, and is either converted to
`oxygen ( catalytically) or carbon dioxide (by chemical inter(cid:173)
`action with the carbon) or held captive long term by adsorp-
`40 tion. More probably, combinations of the foregoing actually
`occur. En any case, the adsorptive monolith or filter removes
`ozone from the air stream, eliminating the discomfort and
`possible health hazard which ozone presents to the eyes and
`respiratory tissues of office workers in the area.
`Generally described, the monolith 10 is made by mixing
`together activated carbon, ceramic forming material, flux
`material, binder, and water to make an extrudable mixture.
`The extrudable mixture is extruded through an extrusion die
`to form the monolith having the honeycomb structure. After
`50 extrusion, the extruded honeycomb monolith retains its
`shape while it is dried and then fired at a temperature and for
`a time period sufficient to react the ceramic forming mate(cid:173)
`rials to form a monolith having activated carbon dispersed
`throughout the structure and sufficient strength for its
`55 intended end use.
`Desirably, the method for making the monolith 10
`includes first mixing the dry ingredients of the extrudable
`mixture and then adding the liquid ingredients to the dry
`mixture; however, the order in which the ingredients are
`60 added to the extrudable mixture can be varied by alternating
`mixing of dry and liquid ingredients as long as the proper
`amount of moisture is added to make an extrudable mixture
`which holds its shape during and after extrusion.
`The activated carbon is desirably present in the extrudable
`mixture in an amount from about 20 to about 70 parts, by
`weight, and more desirably, in an amount from about 30 to
`about 50 parts, by weight. The activated carbon adsorbs
`
`

`

`5,914,294
`
`10
`
`5
`volatile organic compounds and other chemical agents such
`as ozone. A variety of activated carbons can be used in this
`invention. The most suitable activated carbon will depend on
`the intended application, particularly the nature of the mate(cid:173)
`rial to be adsorbed. Thus, the physical properties of the 5
`activated carbon, such as the surface area and the pore
`structure, may vary depending on the application. Desirably,
`the activated carbon has a nitrogen B.E.T. surface from
`about 600 to about 2000 m2/g. More desirably, the activated
`carbon has a nitrogen B.E.T. surface from about 800 to about
`1800 m2/g, and even more desirably has a nitrogen B.E.T.
`surface from about 1000 to about 1600 m2/g. Suitable
`activated carbon can also be characterized by having a
`particle size such that more than 40% by weight of the
`activated carbon passes through a 325 mesh screen, and 15
`more desirably, by having a particle size such that more than
`65% by weight of the activated carbon passes through a 325
`mesh screen.
`Activated carbon suitable for use in the present invention
`may be made from a variety of precursors including bitu- 20
`minous coal, lignite, peat, synthetic polymers, petroleum
`pitch, petroleum coke, coal tar pitch, and lignocellulosic
`materials. Suitable lignocellulosic materials include wood,
`wood dust, wood flour, sawdust, coconut shell, fruit pits, nut
`shell, and fruit stones. A particularly desirable commercially 25
`available activated carbon is NUCHAR® activated carbon
`available from Westvaco Corporation of New York, N.Y.
`The ceramic forming material is present in the extrudable
`mixture in an amount from about 20 to about 60 parts, by
`weight, and more desirably, in an amount from about 30 to
`about 50 parts, by weight. The term ceramic forming mate(cid:173)
`rial means alumina/silicate-based material which, upon
`firing, is capable of reacting together to form a high strength,
`crystal/glass mixed-phase ceramic matrix. In this
`application, the reacted ceramic material provides a matrix
`for supporting the activated carbon and has sufficient
`strength to withstand handling and use of the monolith in the
`intended application and maintain its intended shape without
`cracking or otherwise disintegrating. The ceramic forming
`material desirably includes a substantial portion of moldable
`material which is plastic in nature and thus, when mixed
`with liquid, can be molded or extruded into a shape and will
`maintain that shape through drying and firing. Such a
`suitable plastic or moldable material is ball clay. A particu(cid:173)
`larly suitable commercially available ball clay is OLD
`MINE # 4 ball clay available from Kentucky-Tennessee
`Clay Company of Mayfield, Ky. Other suitable plastic-like
`ceramic forming materials include plastic kaolins, smectite
`clay minerals, bentonite, and combinations thereof. Bento(cid:173)
`nite and smectites are desirably used in combination with 50
`ball clay or kaolin.
`The ceramic forming material also desirably includes a
`filler material which is non-plastic and reduces shrinkage of
`the monolith during the steps of drying and firing. Such a
`suitable ceramic filler is calcined kaolin clay. A particularly 55
`suitable commercially available calcined kaolin clay is Glo(cid:173)
`max LL available from Georgia Kaolin Company, Inc. of
`Union, N.J. The filler desirably is present in the extrudable
`mixture in an amount up to about 15 parts, by weight, more
`desirably, from about 1 to about 15 parts, by weight, and 60
`even more desirably, from about 3 to about 10 parts, by
`weight. Other suitable filler materials include calcined
`kyanite, mullite, cordierite, clay grog, silica, alumina, and
`other calcined or non-plastic refractory ceramic materials
`and combinations thereof.
`The flux material is present in the extrudable mixture in
`an amount from about 4 to about 20 parts, by weight, and
`
`6
`aids in forming the ceramic bond between the ceramic
`forming materials by causing the ceramic forming material
`particles to react together and form a ceramic matrix at a
`lower firing temperature than if the flux material was not
`present. More desirably, the flux material is present in the
`extrudable mixture in an amount from about 4 to about 10
`parts, by weight. Suitable flux materials include feldspathic
`materials, particularly nepheline syenite and feldspar,
`spodumene, soda, potash, sodium silicate, glass frits, other
`ceramic fluxes, and combinations thereof. A particularly
`desirable commercially available flux material is MINEX®
`Nepheline Syenite available from Unimin Specialty
`Materials, Inc. of Elco, Ill.
`The wet binder is present in the extruded mixture in an
`amount from about 0.5 to about 5 percent, by weight, based
`on the solids content of the binder, and enhances the strength
`of the monolith after extrusion so that the extruded monolith
`maintains its shape after extrusion and through drying and
`firing. The wet binder is desirably present in the extruded
`mixture in an amount from about 1 to about 3 percent, by
`weight, based on the solids content of the binder. A particu(cid:173)
`larly suitable wet binder is methylcellulose and a suitable
`commercially available methylcellulose is METHOCEL
`A4M methylcellulose available from Dow Chemical Com(cid:173)
`pany of Midland, Mich. Desirably, methylcellulose is
`present in the extrudable mixture in an amount from about
`0.5 to about 5 parts, by weight, of the extrudable mixture,
`and more desirably, from about 1 to about 3 parts, by weight
`Another suitable binder, used in combination with
`methylcellulose, is an acrylic binder. Examples of such
`30 polymers are JONREZ D-2106 and JONREZ D-2104 avail(cid:173)
`able from Westvaco Corporation of New York, N.Y. and
`Duramax acrylic binder which is available from Rlohm &
`Haas of Montgomeryville, Pa. The acrylic polymer, having
`a medium to high glass transition temperature, is desirably
`35 present in an amount up to about 4 parts, by weight, of the
`extrudable mixture, based on the solids content of the acrylic
`binder and more desirably is present in an amount from
`about 1 to about 4 parts, by weight, of the extrudable
`mixture, based on the solids content of the acrylic binder.
`40 Other suitable binders include hydroxypropyl methylcellu(cid:173)
`lose polymers, CMC, polyvinyl alcohol, and other tempo(cid:173)
`rary binder/plasticizer additives.
`Another desirable component of the extrudable mixture is
`sodium silicate which increases the strength of both the dry,
`45 but unfired monolith and the fired monolith, and is a flux
`material. The sodium silicate is thus both a binder when the
`monolith is in the dry state and a flux material, and is added
`to the extrudable mixture as a solution. The sodium silicate
`is desirably present in the extrudable mixture in an amount
`up to about 7 parts, by weight, based on the solids content
`of the sodium silicate, and more desirably in an amount from
`about 2 to about 7 parts, by weight, based on the solids
`content of the sodium silicate. A suitable commercially
`available sodium silicate solution is a 40% solids, Type N
`solution, available from PQ Corporation, Industrial Chemi(cid:173)
`cals }Division, Valley Forge, Pa. Other suitable binders for
`the dried monolith include silica sol and alumina sol.
`The extrudable mixture includes water in an amount
`sufficient to make an extrudable mixture and desirably
`includes from about 60 to about 130 parts water, by weight.
`Preferably, the water is chilled before it is added to the
`mixture and more preferably is added to the system at or
`near 0° C. This low temperature helps keep the ingredients
`cool during mixing, and helps to overcome any exotherm
`65 which may occur as a result of mixing the ingredients, or as
`a result of heating of the mixture, which occurs as a result
`of the mechanical action of mixing.
`
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`7
`The extrudable mixture is formed into a shape which will
`be the shape of the final monolith by passing the extrudable
`mixture through an extrusion die. The monolith has a block
`shape and includes at least one passageway along its length
`and desirably includes a plurality of passageways extending
`along the length of the monolith. The monolith is designed
`to be placed in the stream of a fluid containing a material to
`be adsorbed such that the fluid is forced through the passages
`in the monolith. Edealy, the amount of internal surface area
`of the monolith exposed to the fluid is maximized to
`maximize the efficiency of the adsorption. A honeycomb(cid:173)
`shaped structure is preferred for the monolith. Honeycomb
`extruders are known in the art of ceramics and have been
`used to produce ceramic monoliths.
`Desirably, the honeycomb structure of the monolith 10
`has an open frontal area greater than 70 percent and up to
`about 85 percent, and desirably about 73.8 percent, after
`drying and firing. The open frontal area of the monolith is
`the percentage of open area of the monolith taken across a
`plane substantially perpendicular to the length of the mono(cid:173)
`lith. Furthermore, the monolith 10 desirably has a honey(cid:173)
`comb pattern with square cells and about 540 cells per
`square inch. The honeycomb structure desirably has a cell(cid:173)
`to-cell pitch of about 0.043 inches, a cell wall thickness of
`about 6 mils, and an open frontal area of about 0.0014 square 25
`inches per cell. More broadly, for a variety of applications,
`the cell density may vary from 1 to 800 cells per square inch
`or higher, with the cell wall thickness ranging from about
`150 mils to about 5 mils and the cell-to-cell pitch varying
`from about 1 to about 0.035 inches.
`The extruded honeycomb monolith 10 is dried in a
`manner so as to prevent cracking of the structure. To
`alleviate cracking, the monolith is dried so that water is
`removed at substantially the same rate throughout the mono(cid:173)
`lith. Preferred drying methods include vacuum drying,
`freeze drying and humidity control drying. More conven(cid:173)
`tional drying methods can be used to dry the monolith of the
`present invention but are less practical commercially. Such
`conventional methods include dielectric drying and warm air
`drying with the monolith wrapped in plastic.
`Vacuum drying of the extruded honeycomb monolith
`includes placing the extruded monolith in a vacuum cham(cid:173)
`ber initially having ambient room temperature and atmo(cid:173)
`spheric pressure within the vacuum chamber, reducing the
`pressure within the vacuum chamber at a rate and to a level 45
`sufficient to quickly freeze the water in the monolith, and
`maintaining a reduced pressure within the vacuum chamber
`for a time sufficient for the frozen water in the monolith to
`sublime until the monolith is dried. This drying cycle may be
`interrupted temporarily to remove the monolith to another so
`chamber after the monolith has been frozen. Freezing of the
`water in the monolith immobilizes the water and stabilizes
`the size and shape of the monolith. The initial vacuum
`desirably is a deep vacuum to quickly and uniformly freeze
`the monolith. The vacuum freezes the monolith more uni- ss
`formly than if the monolith were frozen in a cold chamber
`at a