United States Patent (19)
`McCue et al.
`
`Patent Number:
`11
`(45) Date of Patent:
`
`4,677,086
`Jun. 30, 1987
`
`(54) SHAPED WOOD-BASED ACTIVE CARBON
`75) Inventors: John C. McCue, Covington, Va.;
`Albert J. Repik, Charleston; Charles
`E. Miller, Jr., Mt. Pleasant, both of
`S.C.
`73) Assignee: Westvaco Corporation, New York,
`N.Y.
`21 Appl. No.: 611,595
`(22) Filed:
`May 18, 1984
`51) Int. Cl. ......................... B01J 20/12; B01J 20/20
`52 U.S. C. ........................................ 502/62; 502/80;
`502/413; 123/519; 55/387
`58) Field of Search ........................... 502/62, 80,413;
`123/519; 55/387
`
`56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`Re. 25,400 6/1963 Doying ................................. 502/62
`617,079 1/1899 Catlett ...
`... SO2/62
`1,524,843 2/1925 Ruprecht .............................. 502/62
`1,589,081 6/1926 Adler ................................ 502/80 X
`1,985,840 12/1934 Sadtler .............................. 502/80 X
`2,108,860 2/1938 Kauffman ............................. 502/62
`2,391,312 12/1945 Ewing et al. ......................... 502/80
`2,455,509 12/1948 Luaces .................................... 18/55
`2,951,087 8/1960 Hauser .................................. 502/62
`3,454,502 7/1969 Hiltgen et al.
`... 252/428
`3,592,779 7/1971 Kiikka .........
`... 252/421
`3,864,277 2/1975 Kovach ............................... 252/423
`
`
`
`3,960,761 6/1976 Burger et al. ....................... 252/421
`3,960,771 6/1976 Tanaka et al. ......
`... 502/413
`4,029,600 6/1977 Schmitt, Jr. et al. ............... 252/.444
`4,051,098 9/1977 Takemura et al. .................... 260/38
`4,124,529 11/1978 Juntgen et al. .....
`252/421
`4,338,106 7/1982 Mizuno et al. ........................ 55/387
`4,518,704 5/1985 Okabayashi et al. ............... 502/413
`FOREIGN PATENT DOCUMENTS
`69146 4/1984 Japan ................................... 502/413
`341233 1/1931 United Kingdom ................ 502/413
`Primary Examiner-Carl F. Dees
`Attorney, Agent, or Firm-Terry B. McDaniel; Richard
`L. Schmalz
`ABSTRACT
`57
`A shaped activated wood-based carbon with essentially
`no pore volume in pores greater than one micron in
`diameter and a higher apparent density is prepared from
`an active granular wood-based carbon with a significant
`pore volume in pores greater than one micron in diame
`ter and a lower apparent density by the invention pro
`cess of grinding the active granular wood-based carbon
`to a fine powder, mixing the ground carbon with a
`liquid selected from water or other polar molecule and
`a bentonite clay binder, shaping the mixture, drying the .
`shaped active carbon to remove the liquid, and heat
`treating the dried product to calcine, or fix, the clay
`binder.
`
`16 Claims, 1 Drawing Figure
`
`BASF-1023
`U.S. Patent No. RE38,844
`
`

`

`U.S. Patent
`U.S. Patent
`
`Jun. 30, 1987
`Jun. 30, 1987
`
`4,677,086
`4,677,086
`
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`1
`
`SHAPED WOOD-BASED ACTIVE CARBON
`
`10
`
`15
`
`45
`
`BACKGROUND OF THE INVENTION
`(1) Field of the Invention
`This invention relates to an active carbon formed into
`a granular or other suitable shape by using bentonite
`clay as a binder. More particularly, the invention deals
`with a method for producing a shaped wood-based
`activated carbon with essentially no pore volume in
`pores greater than one micron in diameter. Thus, the
`invention product is particularly well adapted for use as
`contact mass in adsorption and catalytic processes.
`(2) Description of the Prior Art
`Granular carbons and carbon pellets are typically
`used in columns or beds for gas and vapor systems and
`also for processing a number of liquids. To qualify for
`this application, a carbon must posses sufficient me
`chanical strength to withstand the abrasion incident to
`20
`continued use. Gas-adsorbing carbons should be as
`dense as is consistent with high adsorptive power so as
`not to require a large space for the adsorber. The devel
`opment of high adsorptive power during thermal acti
`vation, however, is accompanied by a loss of mechani
`25
`cal strength and density; therefore, some compromise is
`required in selecting the degree to which the activation
`is conducted.
`Activated carbon currently produced from wood
`waste has an exceptionally high internal surface area
`30
`and activity level. However, the granular portion is
`relatively soft and its shape is irregular. Therefore, ap
`plication of granular wood-based carbon in general gas
`phase and liquid phase adsorption is limited by a number
`of constraints, to wit: (1) its low apparent density results
`in low volumetric adsorption capacity; (2) its low hard
`35
`ness results in a high fines generation rate (dusting); and
`(3) its limited maximum particle size and its irregular
`granular shape both result in a high pressure drop in gas
`phase applications. It has been found that changes in
`hardness and shape can be effected by agglomerating or
`shaping an active wood-based carbon with bentonite
`clay in the particular manner of the invention which
`achieves properties which provide shipping advantages
`by reducing dusting tendancies, as well as properties
`suited to gas and liquid phase applications. Particularly,
`invention process provides shaped active carbon the
`maximum particle size of which is limited only by the
`equipment used in the shaping process.
`Shaping of carbons, generally, is taught in the prior
`art. U.S. Pat. No. 2,455,509, for example, teaches a
`method of extruding irregularly shaped carbon rods but
`does not teach any particular binder material. The or
`ganic binders most commonly used are substances
`which when heat-treated in an inert or non-oxidizing
`atmosphere yield a high proportion of fixed or residual
`carbon.
`Thus, U.S. Pat. No. 3,454,502 teaches activated car
`bon tablets formed from powdered activated carbon
`with water soluble aliphatic petroleum hydrocarbon
`sulfonate detergent as binder, and U.S. Pat. No.
`3,592,779 teaches the use of acid sludge formed by the
`reaction of a mineral acid with a relatively high molecu
`lar weight hydrocarbon as a binder for particulate car
`bon and the subsequent activation thereof. U.S. Pat. No.
`3,864,277 teaches a hard granular activated carbon and
`preparation by extrusion of a mixture of a carbonaceous
`material, a binder, and an inorganic activating agent
`(phosphoric acid). The binders taught are lignosulfon
`
`4,677,086
`2
`ates and polyvinyl alcohols which are soluble or emulsi
`fiable in water or phosphoric acid solutions.
`U.S. Pat. No. 3,960,761 discloses a method of produc
`tion of strong active carbon moldings by extruding or
`briquetting low ash mineral coals with phenols and
`aldehydes used as binders. In teaching carbon particu
`lates comprising carbon black spheres and a carbon
`binder with desirable pore size distribution, U.S. Pat.
`No. 4,029,600 discloses certain polymers and coal tar
`pitch as the carbon binder. Also, U.S. Pat. No. 4,051,098
`discloses a one step phenol-formaldehyde resin, a modi
`fied phenol-formaldehyde resin or a mixture thereof as
`a binder in a process for manufacturing a shaped active
`carbon. The patentees note that the resins do not dam
`age the adsorption property of the active carbon due to
`their markedly high carbonization rates in the high
`temperature treatment employed in the manufacturing
`process.
`Finally, U.S. Pat. No. 4,124,529 teaches carbona
`ceous adsorbents produced by shaping the carbon with
`elastomeric plastics and thermoplastic materials such as
`polyvinyl alcohol, polypropylene, and polyethylene.
`It has now been discovered that bentonite clay, a
`non-carbon containing material, when mixed with a
`pulverized, activated wood-based carbon in a liquid and
`agglomerated or shaped, dried, and heat-treated, per
`forms as an effective carbon binder to produce a shaped
`active carbon material with higher apparent density and
`hardness, reduced pressure drop in gas phase applica
`tions, and increased volumetric adsorption capacity.
`Particularly surprising is the increased volumetric ad
`sorption capacity of the shaped product in view of the
`fact that the weight bases adsorption capacity has been
`decreased by the presence of the inert clay binder. Ad
`vantageously, the extruded carbon product of this in
`vention produces particles of uniform activity through
`out. Prior art thermally activated granular carbon parti
`cles exhibit high activity on the outer surface with de
`creasing activity toward the center.
`SUMMARY OF THE INVENTION
`A shaped activated wood-based carbon with essen
`tially no pore volume in pores greater than one micron
`in diameter and a higher apparent density is prepared
`from an active granular wood-based carbon with a
`significant pore volume in pores greater than one mi
`cron and a lower apparent density by the invention
`process of grinding the active granular wood-based
`carbon to a fine powder, mixing the ground carbon with
`a liquid selected from water or other polar molecules
`and a bentonite clay binder, shaping the mixture, drying
`the shaped active carbon to remove the liquid, and
`heat-treating the dried product to calcine, or fix, the
`clay binder.
`DESCRIPTION OF THE PREFERRED
`EMBODIMENT(S)
`The invention process involves the steps of (1) grind
`ing activated wood-base carbon to a fine powder, (2)
`mixing the ground carbon with a liquid and a binding
`amount of bentonite clay, (3) agglomerating or shaping
`the mixture, (4) drying to remove the liquid to produce
`shaped carbon which may be easily dispersed to its fine
`powder form upon contact with water, and subse
`quently, (5) heat-treating the shaped carbon at tempera
`tures from above 700 F. to about 1800' F., to fix the
`
`50
`
`55
`
`60
`
`65
`
`

`

`4,677,086
`4.
`3.
`are acceptable, such as a ram extruder, pellet mill, disc
`clay binder (i.e., destroying the water swelling charac
`agglomerator, or briquette press.
`ter thereof).
`Wood-based active carbon typically has a significant
`The extruded shaped carbon is heated at drying tem
`pore volume in pores greater than one micron (10,000
`peratures up to 700 F. to remove the liquid therefrom.
`angstroms) in diameter (0.6 cc/gm). Pores this size do 5
`Attemperatures above about 500 F., heating should be
`not contribute to the carbon's adsorption capacity. In
`conducted in an inert atmosphere to prevent ignition of
`deed, the major result of this pore volume is lower
`the carbon.
`product apparent density. Processing the wood-based
`Following the drying step, the dried shaped carbon
`active carbon, however, results in a shaped active car
`may be heat treated at temperatures from about 700 F.
`bon product with essentially no pore volume in pores
`to 1800" F. to calcine, or fix, the clay binder. Typically,
`greater than one micron in diameter and yields a prod
`the heat treatment may be conducted in a nitrogen envi
`uct with increased apparent density. Therefore, al
`ronment; however, for that portion of the temperature
`though the weight basis adsorption capacity is de
`range up to 1,300 F., steam may be economically em
`creased by the presence of the inert clay binder, the
`ployed to displace oxygen. While a rotary kiln is pre
`volumetric capacity of the carbon is increased, as 15
`ferred for the heat treatment step, other types of equip
`shown in the following table.
`ment are acceptable. The heat treatment temperature is
`dependent upon the pellet dispersal properties desired.
`TABLE I
`Two types of bentonite clay are distinguished-a
`sodium bentonite (also called Wyoming or western) and
`a calcium bentonite (also called southern). Western
`bentonite clay has the property of swelling many times
`it original volume when added to water. High tempera
`ture treatment of the bentonite prevents swelling in
`water. For the shaped product, it is possible to control
`the pellets' physical changes on water contact by con
`trolling the heat treatment temperature. Specific con
`trolled responses for extruded pellets made by the in
`vention process with 14% western bentonite binder are
`reported in Table II as follows:
`TABLE II
`
`Granular
`Nuchar
`WV-B(
`Property
`7.9
`Apparent Density, lb/ft
`05.
`CC4 capacity, gm/100gm.
`30.2
`CC14 capacity, gm/100 cm
`40.7
`Butane capacity, gm/100gm
`11.
`Butane capacity, gm/100 cm
`(Westvaco commercial wood-based active carbon.
`
`10
`
`Granular WV-B,
`Pulverized and
`Extruded with
`14% Clay Binder
`21.2
`96.1
`32.7
`37.8
`12.9
`
`2O
`
`25
`
`30
`
`The removal of pores greater than one micron in
`diameter and the resultant increase in apparent density
`was observed to occur even when using a relatively
`coarse grind in the pulverizing step, such as 60% of the
`sample passing a 325 mesh (44 micron) screen.
`The mutual weight proportions of the carbon and
`clay binder are suitably between 25:75 and 95:5, espe
`cially between 80:20 and 90:10, respectively. The mix
`35
`ture of carbon and clay is formed in the presence of a
`liquid selected from water or other polar molecule,
`which can be removed after the forming, or shaping
`step. The mixture is shaped wet; the proportion of liquid
`in the mixture is chosen to give the consistency required
`for the shaping method to be used, taking into account
`that liquid tends to be withdrawn from the mixture by
`adsorption by the carbon and clay, thus stiffening the
`mixture.
`The proper operation of the mixing step has been
`45
`found to be critical in determining the operability of the
`extrusion step and setting product properties. Because
`the bentonite swells in water and the swelled platelets
`provide the required lubrication to develop plasticity,
`the amount of available water controls the level of plas
`50
`ticity. As noted, the amount of available water is prede
`termined by the total water content of the mix and the
`amount adsorbed into the carbon internal pore struc
`ture. The higher the moisture level, the less viscous the
`plastic mass and, therefore, the lower the extrusion
`pressure. Simply blending together the components in
`the proper proportions is not all that is required. For
`proper operation of the extruder, the batch must be
`mixed in a high shear mixer until the viscosity proper
`ties of the mix do not change with time. If the viscosity
`is still changing, unacceptable extruder operation re
`sults. The preferred mixer is a low speed, high shear
`type muller mixer, although any high shear type is prob
`ably acceptable.
`The preferred method of agglomerating or shaping
`the wet carbon-clay mixture is by extrusion for pellet
`formation with a standard auger extruder with a non
`compressive screw. However, other shaping methods
`
`Heat Treatment
`Temperature (F) Product Properties
`700 F.
`At 12% solids content or greater in water, the
`pellet immediately disintegrates, but the solids
`do not settle out.
`At any solids content, the pellets disintegrate
`and the solids settle from the water into a
`cake.
`The pellets become very soft in water, but
`remain intact. (See FIG. 1.)
`The pellet hardness on water contact. Shows
`negligible change. (See FIG. 1.)
`
`1,000 F.
`
`1,200 F.
`or greater
`
`850 F.
`
`Thus, for pellets heated at 700 F. or less, the wetting
`and dispersal rate, with little or no agitation, is much
`faster than for pulverized wood-based carbon. By tak
`ing advantage of these properties, products with tai
`lored dispersal rates can be manufactured. Such prod
`ucts would provide handling with less dust than pow
`dered carbon products, yet would readily disperse to
`the powder form on contact with water.
`A specific embodiment of the invention relates to the
`application of the shaped wood-based carbon prepared
`by the invention process in an evaporative emission
`control device for adsorbing the gasoline vapors which
`emit from the carburetor of an automobile and also to
`adsorb the gasoline vapors which emit from the fuel
`tank. Accordingly, the shaped carbon is disposed in a
`suitable canister and arranged to receive the vapors
`from the carburetor and/or fuel tank. Preferably, the
`shaped carbon is disposed in such a manner that the
`evaporated fuel from the carburetor and/or fuel tank
`must pass through the shaped carbon where it can be
`adsorbed to prevent it from exhausting into the atmo
`sphere.
`The following examples are provided to illustrate
`further the novelty and utility of the present invention.
`
`55
`
`65
`
`

`

`5
`
`4,677,086
`6
`The treated pellets were separately soaked in water
`and gasoline for 10 days and tested for hardness by a
`standard crushing strength test procedure. The effect of
`calcination temperature on pellet hardness was deter
`mined by graphing the hardness rating of each sample,
`as well as ratings of dry, unsoaked pellets similarly
`treated, representing the original sample hardness. The
`graph appears as FIG. 1.
`The heat treatment temperature at which the gasoline
`soaked pellets approach their original hardness is 1,000
`F. For water soaked pellets, a heat treatment of at least
`1,100 F. is necessary to compare favorably with the
`original sample in hardness after 10 days. No real ad
`vantage is observed for treatment above 1,300 F.
`Therefore, the preferred heat temperature range for
`wood-based active carbons shaped according to the
`invention process for use in emission control of gasoline
`vapors is from 1,000 F. to 1,300 F.
`While the invention has been described and illus
`trated herein by references to various specific materials,
`procedures and examples, it is understood that the in
`vention is not restricted to the particular materials,
`combinations of materials, and procedures selected for
`that purpose. Numerous variations of such details can
`be employed, as will be appreciated by those skilled in
`the art.
`What is claimed is:
`
`5
`EXAMPLE 1
`To show both the operability of the invention process
`and the application of the invention product in evapora
`tive emission control for adsorbing gasoline vapors, a
`commercial wood-based granular active carbon pro
`duced by Westvaco Corporation, designated as WV-B,
`was ground to a fine powder and mixed with water and
`14% (based on the weight of the carbon) sodium ben
`tonite clay in a high shear intensive mixer to form a
`10
`hand packable mass. The mixture was shaped into cylin
`drical pellets having a diameter of 3.2 millimeters by
`extrusion through a standard auger extruder with a
`non-compressive screw and multihole die plate fol
`lowed by cutting with a knife cutter into lengths of
`15
`approximately 3-6 millimeters. The formed pellets were
`then oven dried in air at about 200 F. The drying step
`was followed by a heat treatment in an inert atmosphere
`at 1,000 F. for 10 minutes.
`The shaped carbon thus formed was disposed in a
`20
`canister, and the canister was tested as an evaporative
`emission control device for adsorbing gasoline vapors.
`The test results were compared with the automotive
`manufacturer's specifications, as well as the results of
`similar testing of devices using BPL-3 coal-based active
`25
`carbon and WV-B granular wood-based active carbon.
`The comparison is presented in Table III.
`TABLE III
`EXTRUDED WOOD-BASED CARBON WV-BX
`COMPARISON TO BPL-3, WV-B AND AUTOMOTIVE SPECIFICATIONS
`WV-B
`(Granular Wood
`Base Active)
`14.4
`.23
`42
`4 x 14
`
`Automotive Specification
`Apparent Density (lb)
`Apparent Density (g/cm)
`Abrasion Test
`Particle Size
`
`BPL-3
`(Coal-base)
`18.7-25
`22.8
`.3-4
`365
`55 minimum
`64
`4 x 18
`6 x 16
`
`WV-BX
`21.2
`340
`89
`3.2 mm
`diameter
`0.75
`
`18.9
`
`12.7
`10.5
`32.7
`25.4
`4.66
`
`Pressure Drop (inches
`water column/canister)
`Ash Wt. 26
`Volume Capacities
`(Units = gm/100 cm)
`Butane Capacity
`Butane Working Capacity
`CCI4 Capacity
`CC14 Working Capacity
`Automotive Cycle Test
`Gasoline Working
`Capacity
`"Granular coal-based active commercial carbon currently used in automotive emission control canisters.
`'WW-B carbon extruded with 14% bentonite.
`
`2.5
`
`-
`
`}
`
`2.4
`
`9.9
`
`12.4
`10.4
`33.2
`24.5
`4.34
`
`1.5
`
`3.4
`
`9.4
`8.6
`25.9
`22.9
`3.61
`
`The data presented in Table III show that the shaped
`wood-based carbon prepared according to the inven
`tion process meets the automotive specifications and
`favorably compares to the standard commercial carbon
`in this application.
`
`55
`
`EXAMPLE 2
`To determine the heat treatment temperature re
`quired to obtain hardness stability upon prolonged
`contact with water or gasoline, carbon pellets formed
`according to the procedure of Example 1 (through the
`drying step) were calcined at temperatures of B 1,000
`F., 1,070 F., 1,140°F., 1,200 F., 1,300 F. and 1,800' F.
`for a treatment time of 10 minutes. A seven and one-half
`inch rotary furnace was used; and the atmosphere for
`calcination was steam at all tested temperatures except
`1,800 F., where nitrogen was employed.
`
`1. A composition comprising active wood-based car
`bon particles and, as a binder therefor, a bentonite clay
`in an amount of from 5% to 75% by weight, based on
`the carbon, selected from the group consisting of so
`dium bentonite and calcium bentonite wherein the clay
`is characterized by having been subjected to a calcina
`tion treatment conducted at from about 700 F. to about
`1,800 F. in an oxygen-free atmosphere subsequent to its
`combination with the carbon wherein said composition
`is characterized by a higher apparent density over that
`of the carbon alone.
`2. The composition of claim 1 wherein the calcination
`treatment is conducted at from about 1,000 F. to about
`1,300 F.
`3. The composition of claim 1 wherein the bentonite
`clay is sodium bentonite.
`
`

`

`4,677,086
`8
`7
`8. The process of claim 4 wherein the sodium benton
`4. A process for preparing a shaped carbon composi
`ite is present in an amount of from 10% to 20%, based
`tion from a granular wood-based active carbon material
`on the weight of the carbon.
`comprising:
`9. The process of claim 4 wherein the forming step is
`(a) grinding the granular wood-based active carbon
`accomplished by extrusion, agglomeration, or pressing.
`to a fine powder;
`10. The process of claim 6 wherein the forming step
`(b) mixing with the ground wood-based active carbon
`is accomplished by extrusion.
`from 5% to 75%, by weight, of bentonite clay,
`11. The process of claim 4 wherein the dried carbon
`is heat treated at from about 1,000 F. to about 1,300 F.
`based on the carbon, selected from the group con
`in an atmosphere of steam.
`sisting of sodium bentonite and calcium bentonite,
`10
`12. The process of claim 4 wherein the dried carbon
`in the presence of a liquid, selected from the group
`is heat treated at about 1,800' F. in a nitrogen atmo
`consisting of water and other polar molecules;
`sphere.
`(c) forming the shaped carbon composition from the
`13. The process of claim 4 wherein the heat treatment
`mixtures of the ground carbon and clay;
`is conducted in a rotary furnace.
`(d) subjecting the shaped carbon to sufficient heat to
`14. An evaporative emission control device for ad
`sorbing the gasoline vapors comprising a shaped carbon
`remove the liquid therefrom to provide dried
`composition prepared by mixing fine particles of active
`shaped carbon, which is characterized by being
`wood-based carbon with from 5% to 75%, by weight,
`easily dispersed in its fine powder form upon
`of bentonite clay, based on the carbon, selected from
`20
`contact with water; and
`the group consisting of sodium bentonite and calcium
`(e) heat treating the dried, shaped carbon at from
`bentonite, in the presence of sufficient water to form a
`about 700' F. to about 1,800' F. in an inert atmo
`hand packable mass, shaping the carbon-clay mixture
`sphere.
`by extrusion, removing the free water from the shaped
`5. The process of claim 4 wherein the shaped carbon
`product, and subjecting the shaped product to calcina
`25
`is subject to drying temperatures up to about 700' F.
`tion temperatures of from about 1,000 F. to about
`1,300 F. in an inert atmosphere.
`6. The process of claim 5 wherein the drying step is
`15. The process of claim 10 wherein the clay is added
`conducted in an inert atmosphere at temperatures from
`in the amount of from 10% to 20%, based on the weight
`about 500 F. to about 700 F.
`of the carbon and the inert atmosphere of calcination is
`30
`7. The process of claim 4 wherein the ground carbon
`Stean.
`and clay are mixed in the presence of water by a high
`16. The process of claim 11 wherein the clay is so
`shear intensive mixer and the clay is sodium bentonite in
`dium bentonite in the amount of 14%, based on the
`an amount of from 5% to 75%, based on the weight of
`weight of the carbon.
`the carbon.
`35
`
`15
`
`six
`
`45
`
`50
`
`55
`
`65
`
`