United States Patent (19)
`Miller
`
`IIIMINIII
`
`US00569.1270A
`11) Patent Number:
`45 Date of Patent:
`
`5,691,270
`Nov. 25, 1997
`
`54 SHAPED LIGNOCELLULOSIC-BASED
`ACTIVATED CARBON
`
`(75) Inventor: James R. Miller, Mt. Pleasant, S.C.
`73) Assignee: Westvaco Corporation, New York,
`N.Y.
`
`(21) Appl. No.: 613,270
`22 Filed:
`Mar 8, 1996
`(51) Int. Cl. ... B01.J. 20/02
`52 U.S. Cl. ............................ 502/416: 502/80; 502/423;
`502/428; 502/429; 502/174; 502/180; 502/182
`(58) Field of Search ..................................... 502/416, 423,
`502/428,429, 80, 174, 180, 182
`References Cited
`U.S. PATENT DOCUMENTS
`6/1987 McCue et al. ............................ 502/80
`4,677,086
`Primary Examiner-Glenn Caldarola
`
`(56)
`
`Assistant Examiner. In Suk Bullock
`Attorney, Agent, or Firm-Terry B. McDaniel; Daniel B.
`Reece, IV; Richard L. Schmalz
`57
`ABSTRACT
`Extruded pellets comprising a majority of activated carbon
`particles and a minority of a binder material are disclosed to
`provide improved performance when processed through
`tumbling equipment while the pellets are in their "green"
`state (i.e., pellets which are freshoff the extruder and contain
`activated carbon), binder material, and water and have not
`been subjected to any thermal processing (drying or
`calcining). The tumbling action both Smooths and densifies
`(i.e., reduces void volume within) the pellet, thereby closing
`any cracks and greatly improving appearance. Improved
`performance results from an ability to increase the weight of
`carbon pellets which can be packed into a fixed volume and
`thereby increase the volumetric working capacity of the bed
`for adsorbing/desorbing vapors. Another benefit is to greatly
`reduce the levels of dust associated with the carbon, both the
`initial dust and the dust attrition.
`8 Claims, 2 Drawing Sheets
`
`
`
`Activated Carbon POWoder
`Binder -
`Water
`
`Calcine
`
`Product
`
`BASF-1025
`U.S. Patent No. RE38,844
`
`

`

`U.S. Patent
`US. Patent
`
`Nov. 25, 1997
`Nov. 25, 1997
`
`Sheet 1 of 2
`Sheet 1 of 2
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`5,691,270
`5,691,270
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`EH
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`

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`U.S. Patent
`
`Nov. 25, 1997
`
`Sheet 2 of 2
`
`5,691,270
`
`?OnpOud
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`

`

`1.
`SHAPED LGNOCELLULOSC-BASED
`ACTIVATED CARBON
`
`5,691,270
`
`10
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`15
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`2
`Carbons of suitable mechanical strength and density for
`use in an evaporative emission control device (automotive
`canister) for adsorbing gasoline vapors preferably also
`exhibit a butane working capacity of about 10 to about 17
`g/100 cc and an apparent density from about 0.25 to about
`0.40 g/cc.
`In addition to gas column (or, packed bed) requirements
`for high mechanical strength and high density, it is also
`desirable to reduce the bed void volume in order to maxi
`mize the carbon content of the bed, and subsequently
`maximize the adsorptive capacity. This is primarily deter
`mined by the shape of the granular or pelleted carbon. In
`fact, because of the irregular shape of granular carbon, more
`regularly shaped carbon pellets are preferred for their better
`"packing.” However, as a result of uneven cutting of the
`extrudate to form the pellets, the pellets are, in fact, irregu
`larly shaped, and fissures and cavities often appear along the
`pellet surface. This creates two problems. The resulting
`irregularities in shape prevent optimization of bed (or
`column) packing and detract from maximizing the carbon
`content for a given pellet volume. In addition, the surface
`irregularities are often removed from the pellet due to
`abrasion. These material losses, in addition to debris caused
`by cutting the pellets to size, present another problem: dust.
`Typically, dusting due to abrasion, or dust attrition, may be
`retarded or precluded by spraying a coating on the surface of
`the pellet. Invariably, this remedy is at the expense of butane
`working capacity; thereby providing another trade-off for
`the working life of the active carbon material.
`Besides having a product which may appear to
`disintegrate, attrited dustin a packed bed, such as a column
`or an automotive canister, can fill the bed voids to create
`high pressure drops and impede the flow-through of vapors
`to be treated. A particular problem in the automotive appli
`cation is concern that the dust will act to interfere with
`various sensing devices connected to the canister to monitor
`performance, resulting either in false readings or in failure
`of the sensing devices altogether.
`Therefore, an object of this invention is to provide an
`improved lignocellulosic-based activated carbon pellet of a
`smoother surface and more uniform shape which provides
`optimal bed packing, exhibits increased density, and is less
`susceptible to dust attrition. An additional object of this
`invention is to provide an improved method of manufacture
`of such activated carbon pellet.
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 shows a block flow diagram of the invention
`process wherein tumbling is carried out on the green
`extrudate, followed by drying and calcination.
`FIG. 2 shows a block flow diagram of the invention
`process whereby tumbling is carried out on the green
`extrudate as it is being dried, followed by calcination.
`SUMMARY OF THE INVENTION
`The object of the invention is achieved in the discovery
`that extruded pellets comprising a major portion of activated
`carbon particles and a minor portion of inorganic or organic
`binder provides improved performance when processed
`through tumbling equipment while the pellets are in their
`"green" state. Green pellets are those which are fresh off the
`extruder and contain activated carbon, binder, and moisture
`(from 50-70% water, by weight) and have not been sub
`jected to any thermal processing (i.e., drying or calcining).
`The tumbling action both smooths and densifies (i.e.,
`reduces interparticle voids within) the pellet, thereby
`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`This invention relates to an active carbon pellet prepared
`by extruding activated lignocellulosic-based carbon with a
`binder material. More particularly, the invention relates to an
`improved active carbon pellet characterized by low pellet
`void volume and low dust attrition.
`2. Description of the Prior Art
`Granular carbons and carbon pellets are typically used in
`columns or beds for gas and vapor systems as well for
`processing a number of liquids. Such carbons have been
`used in canisters in automobiles through which gasoline tank
`and carburetor vapors are directed prior to release to the
`environment. To qualify for this application, a carbon must
`possess sufficient mechanical strength to withstand the abra
`sion incident to continued use.
`There generally is a direct correlation between the
`mechanical strength of the granular activated carbon product
`and the mechanical strength of its precursor raw material.
`Thus, coal-based active carbon generally exhibits a high
`mechanical strength and density; whereas, lignocellulosic
`based active carbons, derived from a much "softer” precur
`sor relative to coal, generally exhibit low mechanical
`strengths and densities.
`Also, gas-adsorbing carbons should be as dense as is
`consistent with high adsorption capacity so as not to require
`a large space for the adsorber. The development of high
`adsorption capacity during thermal activation, however, is
`accompanied by a loss of mechanical strength and density;
`therefore, some compromise is required in selecting the
`degree to which the activation is conducted. So, with igno
`cellulosic precursors (or, for lignocellulosic-based active
`carbons), the problem is compounded.
`Several approaches have been taken to address the prob
`lem of low mechanical strength and density of
`lignocellulosic-based active carbons. In U.S. Pat. No. 3,864,
`277, Kovach emphasizes the binder additive in teaching the
`phosphoric acid activation of wood, straw, or low-rank
`brown coals in the presence of a carbonaceous binder
`material such as lignosulfonates and polyvinyl alcohol,
`followed by forming solid granular shaped particles from the
`mixture, and heat-treating at less than 650° C. to give a
`granular product having a ball-pan hardness of greater than
`85%. Given the teaching of Kovach and employing the
`knowledge of the relationship of precursor mechanical
`strength and density with those characteristics of the active
`carbon product, MacDowall (in U.S. Pat. No. 5,162.286)
`teaches increasing lignocellulosic-based active carbon den
`sity by the use of young carbonaceous vegetable products
`high (>30%) in natural binding agent, such as nut shell, fruit
`stone, almond shell, and coconut shell, as precursors for
`treatment with phosphoric acid followed by carbonization.
`A third approach, which relates to the present invention,
`is taught by McCue et al. in U.S. Pat. No. 4,677,086. To
`achieve, in a wood-based active carbon, the mechanical
`strength and product density approaching that achieved with
`coal-based products, McCue et al. teach extruding an active
`wood-based carbon with bentonite clay, followed by calcin
`ing the extruded active carbon/clay pellets. This technology
`has been the basis for the commercial products NUCHARO)
`65
`BAX-950 and NUCHARGE BAX-1100 marketed by West
`vaco Corporation.
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`5,691,270
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`3
`sealing, or otherwise closing, any cracks and greatly improv
`ing appearance. (Interestingly, debris caused by cutting the
`pellets to size is assimilated by the tumbling pellets.)
`Improved performance results from an ability to increase the
`weight of carbon pellets which can be packed into a fixed
`volume and thereby increase the volumetric working capac
`ity of the bed for adsorbing/desorbing vapors. Another
`benefit is to greatly reduce the levels of dust associated with
`the carbon, both the initial dust and the dust attrition.
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENT(S)
`The process steps for the alternative embodiments of the
`invention process are set forth in the drawings. FIG. 1 shows
`that activated carbon powder (produced from grinding
`granular lignocellulosic-based activated carbon), binder
`material, and water are sequentially mulled, extruded,
`tumbled, dried, and calcined to produce the invention active
`carbon pellet. FIG. 2 shows the activated carbon powder,
`binder material, and water to be sequentially mulled,
`extruded, dried while tumbling, and calcined to produce the
`invention active carbon pellet, The process steps are
`described in greater detail in the Examples which follow.
`Also, with the exception of the invention improvement, the
`process generally follows the teaching of U.S. Pat. No.
`4,677,086, which disclosure is incorporated herein by ref
`eece
`Basically, the blend of activated lignocellulosic-based
`carbon, binder material, and water are mixed and then fed
`through an extrusion device. The generally continuous
`extrudate is cut at consistent intervals to produce a cylin
`drical pellet, relatively uniform in length and diameter. The
`invention process improvement involves taking these
`"green" pellets soon after they are generated and subjecting
`them to a tumbling process for a period of time sufficient to
`produce a pellet that, upon subsequent drying and/or
`calcination, exhibits a pellet void fraction of less than 0.19
`(determined as the actual pellet density divided by the base
`pellet density and subtracted from 1) and a dust attrition rate
`of less than 1.2 mg/100 cc/minute. In a preferred embodi
`ment of the invention composition, the pellet void fraction
`is less than 0.17 and the dust attrition rate is 1.0 mg/100
`cc/minute. In the most preferred embodiment, the pellet void
`fraction is less than 0.15 and the dust attrition rate is less
`than 0.8 mg/100 cc/minute. In particular, it has been found
`that the rambling step is effective to provide the improved
`composition of the invention if it is performed in lieu of
`immediately drying the green pellets in additional equip
`ment.
`It is envisioned that the moisture level of the green pellets
`is important in the effectiveness of the tumbling step, and
`that a critical moisture level may exist below which densi
`fication and reduction of dust levels may not occur. As a
`result, in an additional embodiment of the invention, the
`tumbling equipment can also be used to dry the green
`pellets, if the dryingrate is kept to a level low enough to give
`a sufficient residence time before the critical moisture level
`is reached. The critical moisture level is in the range of
`50-70% water, by weight. A preferred moisture level is
`55-65% water, by weight. The most preferred moisture level
`for the tumbling operation of the green pellets is 58-62%
`water, by weight.
`Any commercial tumbling equipment, based on the nature
`and volume of material to be treated and whether the process
`is to be batch or continuous, is considered suitable for use in
`the invention process. Equipment which would be expected
`
`4
`to produce the beneficial product properties in the invention
`composition are considered to be equivalent to the equip
`ment employed in the examples below. The tumbling opera
`tion may be employed for up to 30 minutes. The process is
`considered to offer little or no benefit once the moisture level
`in the pellets is significantly reduced (<50%).
`The lignocellulosic material precursor to the
`lignocellulosic-based active carbon used in the invention
`process to form the invention composition is selected from
`the group consisting of wood chips, wood flour, sawdust,
`coconut shell, nut shells, fruit pits, kernal, olive stone, and
`almond shell.
`The binder materials include bentonite clays or chemi
`cally modified bentonite clays. Preferred binders are sodium
`bentonite and calcium bentonite.
`In the Examples to follow, the various analyses were
`performed in measurements determining the benefits of the
`invention product and process:
`Apparent Density (AD)-ISO No. 960-050: weight of dry
`carbon per unit volume of the carbon bed;
`Butane Working Capacity (BWC)-ISO No. 960-080:
`weight of butane purged from a sample of dried carbon after
`it had been saturated with butane per unit volume of the
`carbon bed;
`Dusting Attrition (DA)-ISO No. 960–380: weight of dust
`attrited from a 100 ml sample of carbon per unit time;
`Initial Dust (ID)- same as dusting attrition: Weight of dust
`initially present on a 100 ml sample of carbon prior to
`attrition test;
`Actual Pellet Density (APD); weight of dry carbon per
`unit volume of entire carbon pellet, determined using mer
`cury porosimetry;
`Base Pellet Density (BPD); weight of dry carbon per unit
`volume of carbon pellet including only pore space less than
`0.5 microns equivalent diameter, determined using mercury
`porosimetry;
`Bed Void Fraction (BVF): volume of space between
`carbon pellets per unit volume of carbon bed, determined by
`the equation 1-(AD/APD); and
`Pellet Void Fraction (PVF) (pellet interparticle void
`fraction): volume of space within a carbon pellet including
`only pore space greater than 0.5 microns equivalent diameter
`per unit volume of entire carbon pellet, determined by the
`equation 1-(APD/BPD).
`The invention process and composition are further
`described in the following specific examples:
`EXAMPLE 1.
`Ground wood-based activated carbon was mixed with
`bentonite clay and water in a muller mixer. The dry basis
`clay concentration was 14 wt %. The mixture was mulled
`until it reached a consistency which could be extruded. It
`was extruded in a twin screw auger extruder through a die
`plate containing 2 mm holes and cut as it exited the die plate
`into "green” pellets ranging in length from 2-6 mm. The
`green pellets had amoisture content of approximately 55-60
`wt % (wet basis). Following extrusion, a portion of the green
`pellets was loaded into a rotating disc pan pelletizer in order
`to tumble the pellets. The pan was angled above the hori
`zontal to retain the pellets and rotated at 15 rpm for 5
`minutes. After 5 minutes, pellets were collected from the pan
`and dried in a batch, convection oven. The portion of green
`pellets which was not tumbled was also dried in the same
`oven for the same amount of time. The two batches of dried
`pellets were calcined separately to 1200° F in a batch
`
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`5
`indirect-fired rotary furnace for 15 minutes. Following
`calcination, they were discharged and cooled separately
`under a nitrogen purge prior to analysis.
`The pertinent properties of each product are shown in
`Table I. From the data, it can be seen that BWC increased
`7.5%, apparent density increased 9.2%, initial dust was
`reduced by 70%, and dust attrition was reduced by 45%
`(from 2.16 to 1.19).
`
`TABLE I
`
`BWC
`(g/100 cc)
`
`AD
`(gfcc)
`
`D
`(mg)
`
`DA
`(mg/min)
`
`10.7
`
`11.5
`
`0.336
`
`58.8
`
`0.367
`
`17.8
`
`2.16
`
`1.19
`
`10
`
`15
`
`Batch I.D.
`
`C-95-0342
`-Not Tumbled
`C-95.0343
`-Tumbled
`
`20
`
`25
`
`EXAMPLE 2
`Ground lignocellulosic-based activated carbon was mixed
`with bentonite clay and water in a Muller mixer. The dry
`basis clay concentration was 9 wt %. The mixture was
`mulled until it reached a consistency which could be
`extruded. It was extruded in a single screw auger extruder
`through a die plate containing 2 mmholes and cut as it exited
`the die plate into "green” pellets ranging in length from 2-6
`mm. The green pellets had a moisture content of approxi
`mately 55-60 wt % (wet basis). Following extrusion, a
`portion of the green pellets was taken and loaded into a 24
`inch diameterx19 inch deep rotating drumin order to tumble
`the pellets. The drum was angled above the horizontal to
`retain the pellets and rotated at 15 rpm for 5 minutes. After
`5 minutes, pellets were collected from the drum and dried in
`a batch, convection oven. The portion of green pellets which
`was not tumbled was also dried in the same oven for the
`same amount of time. The two batches of dried pellets were
`calcined separately to 1200° F in a batch indirect-fired
`rotary furnace for 15 minutes. Following calcination, they
`were discharged and cooled separately under a nitrogen
`purge prior to analysis.
`The pertinent properties of each product are shown in
`Table II. From the data, it can be seen that the performance
`of the carbon pellets improved as in Example 1. Specifically,
`BWC increased 9.0%, apparent density increased 8.0%,
`45
`initial dust decreased 74%, and dust attrition decreased 84%
`(from 2.72 to 0.426).
`
`30
`
`35
`
`5,691,270
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`6
`
`TABLE I
`
`Batch ID.
`
`C-95-0752
`-Not Tumbled
`C-95-0751
`-Tumbled
`
`BWC
`(g/100 cc)
`
`AD
`(gfcc)
`
`D
`(mg)
`
`DA
`(mg/min)
`
`12.2
`
`13.3
`
`0.338
`
`36.6
`
`2.72
`
`0.365
`
`9.44
`
`0.426
`
`EXAMPLE 3
`
`Ground lignocellulosic-based activated carbon was mixed
`with bentonite clay and water in a Muller mixer. The dry
`basis clay concentration was 14 wt %. The mixture was
`mulled until it reached a consistency which could be
`extruded. It was extruded in a twin screw auger extruder
`through a die plate containing 2 mm holes and cut as it exited
`the die plate into "green” pellets ranging in length from 2-6
`mm. The green pellets had a moisture content of approxi
`mately 55-60 wt % (wet basis). Following extrusion, the
`pellets were tumbled through a continuous rotating cylinder.
`Different tumbling conditions were established by varying
`feed rate, bed depth, rotational speed, and design of internal
`flights. The different internals tested included (1) none
`(smooth wall), (2) longitudinal lifters, and (3) zig-zag lifters.
`Residence time was measured as the parameters were varied.
`At each condition, the tumbled pellets were collected from
`the discharge and dried in a batch, convection oven. The
`portion of green pellets which was not tumbled was also
`dried in the same oven for the same amount of time. The two
`batches of dried pellets were calcined separately to 1200°F.
`in a batch indirect-fired rotary furnace for 15 minutes.
`Following calcination, they were discharged and cooled
`separately under a nitrogen purge prior to analysis.
`The pertinent properties of each product are shown in
`Table III. From the data, it can be seen that there is no
`advantage of using internal flights and that bed depth is not
`a factor as dam height is varied from 3 to 5 inches.
`Additionally, over the conditions tested, residence time did
`not have a significant impact on BWC, initial dust, or dust
`attrition improvement. On average, the continuous unit
`showed that BWC increased 4%, apparent density increased
`5%, initial dust was reduced by 69%, and dust attrition was
`reduced by 73% (to as low as 0.19).
`
`TABLE
`
`ROTATIONAL
`SPEED
`(pin)
`
`FLIGHT
`DAM
`()
`
`RESIDENCE
`TIME
`(sec)
`
`DA
`)
`BWC AD
`(g/100 cc) (gfcc) (mg) (mg/min)
`
`FEED RAE
`(1b/min)
`BATCHID
`Baseline #1 (no tumble)
`0.325 56.2
`110
`N/A
`N/A
`NAA
`C-95-1042
`N/A
`Constant feed rate and rotational speed; vary flight design with no dam - compare with baseline #1
`C-95-1048
`20
`16
`zig-zag flights
`90
`11.6
`0.333 17.3
`C-95-1049
`20
`16
`straight flights
`70
`11.4
`O.328 28.5
`Baseline #2 (no tumble)
`O.323 53.4
`11.1
`N/A
`N/A
`N/A
`C-95-1054
`N/A
`Constant rotational speed and bed depth; vary feed rate with no internal flights - compare with baseline #2
`C-95-1050
`20
`16
`3.5" dam
`127
`11.6
`O.342. 27.4
`C-95-105
`11
`16
`3.5"
`248
`11.4
`0.343 28.4
`dam
`3.5"
`dam
`
`C-95-1052
`
`7
`
`16
`
`280
`
`1.7
`
`0.343 22.8
`
`1.3
`
`0.6
`0.7
`
`19
`
`0.2
`0.3
`
`0.6
`
`Baseline #3 (no tumble)
`1290-R-95
`N/A
`
`N/A
`
`N/A
`
`N/A
`
`11.0
`
`0.330 150
`
`1.28
`
`

`

`7
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`5,691,270
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`8
`
`TABLE III-continued
`
`RESIDENCE
`FLIGHT
`ROTATIONAL
`DA
`D
`BWC AD
`TME
`DAM
`SPEED
`FEED RATE
`(g/100 cc) (gfcc) (mg) (mg/min)
`(sec)
`()
`(rpm)
`(1b/min)
`BATCHD
`Constant feed rate and rotational speed; vary bed depth with no internal flights - compare with baseline #3
`1235-R-95
`21
`16
`3" dam
`108
`115
`0.350 1.7
`1287-R-95
`2O
`16
`4" dam
`160
`11.4
`0.340 0.3
`1286-R-95
`20
`16
`5" dam
`223
`115
`0.350 0.6
`
`O.3
`0.25
`0.19
`
`als
`
`is
`
`9.
`
`2O -
`
`TABLE TV-continued
`BWC
`AD APD BPD
`(g/100 cc) (gcc) (gfcc) (gfcc)
`114
`O.362 0.573 0.664
`
`14
`18
`18
`
`0.358 0.584 0.673
`0.381 0.576 0.659
`0.384 0.571 0.643
`
`PWF BWF
`O.14
`0.37
`
`0.13
`0.13
`O.11
`
`0.39
`0.34
`O.33
`
`11.5
`
`0.366 0.51 0.662
`
`0.14
`
`0.36
`
`EXAMPLE 4
`Ground ignocellulosic-based activated carbon was mixed
`with bentonite clay and water in a Muller mixer. The dry
`Batch D
`basis clay concentration was 14 wt.%. The mixture was
`C-95.0353
`mulled until it reached a consistency which could be
`-Tumbled
`extruded. It was extruded in a twin screw auger extruder
`through a die plate containing 2 mmholes and cut as it exited SE
`the die plate into "green pellets ranging in length from 2–6 29 E.
`mm. The green pellets had a moisture content of approxi-
`-Tumbled
`mately 55-60 wt % (wet basis). Following extrusion, a
`C-95.0346
`portion of the green pellets was taken and loaded into a
`Tumbled
`rotating disc panpelletizer in order to tumble the pellets. The 25 Tumbled
`pan was angled above the horizontal to retain the pellets and
`Average
`rotated at 15 rpm. After 5 minutes, pellets were collected
`from the pan and dried in a batch, convection oven. A
`portion of green pellets which was not tumbled was also
`dried in the same oven for the same amount of time. The
`batches of dried pellets were calcined separately to 1200°F.
`in a batch indirect-fired rotary furnace for 15 minutes.
`Following calcination, they were discharged and cooled
`separately under a nitrogen purge prior to analysis.
`The pertinent properties of each product are shown in
`Table IV. From the data, it can be seen that, on average,
`BWC increased 6.5%, apparent density increased 11.3%,
`actual pellet density increased 7.1%, base pellet density
`stayed virtually constant, pellet void fraction decreased
`30%, and bed void fraction decreased 5.3%.
`The rambling step resulted in a reduction in individual
`pellet void fractions for an average reduction from 0.21 to
`0.14. Also, the average (of the samples) bed void fraction
`was reduced from 0.38 to 0.36.
`
`35
`
`TABLE IV
`
`AD APD BPD
`BWC
`(g/100 cc) (gfoc)
`(gfcc) (gfcc)
`
`PVF BWF
`
`45
`
`Batch. ID.
`
`C-95.0347
`-Not Tumbled
`C-95-0349
`Not Tumbled
`C-95-0342
`-Not Tumbled
`C-95.0079
`
`-Not Tumbled
`Not Tumbled
`Average
`C-95.0350
`-Tumbled
`C-95-0343
`-Tumbled
`C-95-0344
`-Tumbled
`C-95-0351
`Tumbled
`C-95-O352
`-Tumbled
`
`10.3
`
`10.4
`
`10.
`
`O.
`
`10.5
`
`11.0
`
`11.5
`
`11.6
`
`11.6
`
`11.5
`
`O.323 O.518 0.647
`
`0.2O
`
`0.38
`
`50
`
`O.320 0.517 O.653
`
`O.2
`
`0.38
`
`0.336 0.543 0.667
`
`0.19
`
`O.38
`
`O.333 0.517 O.T.O.
`
`0.26
`
`0.36
`
`55
`
`0.328 0.524 O.66
`
`O.22
`
`O.38
`
`0.342 O,558 0.660
`
`0.15
`
`0.39
`
`O.36
`
`0.566 O.673
`
`0.6 0.35
`
`0.37O 0.561 O,657
`
`0.15
`
`0.34
`
`0.367 0.578 O.667
`
`O.13
`
`0.36
`
`0.364 O.572 0.659
`
`0.13
`
`0.36
`
`65
`
`It is noted from the tabular data in the various examples
`that, in addition to the invention improvements of reduced
`pellet void volume and reduced dust attrition, the invention
`carbon pellets exhibit a butane working capacity of from
`about 10 to about 17 g/100 cc and an apparent density from
`about 0.25 to about 0.40 g/cc.
`As will be appreciated by those skilled in the art, the
`present invention may be embodied in other specific forms
`without departing from the spirit or essential attributes
`thereof; and, accordingly, reference should be made to the
`appended claims, rather than to the foregoing specification,
`as indicating the scope of the invention.
`What is claimed is:
`1. A composition of an active carbon pellet prepared by
`sequentially extruding activated lignocellulosic-based car
`bon particles with an inorganic binder material in the pres
`ence of water and subjecting the extruded pellet to a
`mechanical tumbling treatment prior to calcination
`temperatures, said carbon pellet exhibiting abutane working
`capacity of from about 10 to about 17 g/100 cc, an apparent
`density from about 0.25 to about 0.40 g/cc, a pellet void
`fraction of less than 0.19, and a dust attrition value of less
`than 1.2 mg/100 cc/minute, in the absence of an applied
`coating on the pellet.
`2. The composition of claim 1 wherein the inorganic
`binder is selected from bentonite clays.
`3.The composition of claim 2 wherein the binder material
`is selected from the group of bentonite clays consisting of
`sodium bentonite and calcium bentonite.
`4. The composition of claim 1 comprising from about 5%
`to about 30%, by weight, binder material.
`5. The composition of claim 1 further characterized by a
`butane working capacity from about 10 to about 17 g/100 cc
`and an apparent density from about 0.25 to about 0.40 g/cc.
`6. The composition of claim 1 wherein the pellet void
`fraction is less than 0.17 and the dust attrition rate is less
`than 1.0 mg/100 cc/minute.
`7. The composition of claim 6 wherein the pellet void
`fraction is less than 0.15 and the dust attrition rate is less
`than 0.8 mg/100 ccfminute.
`
`

`

`5,691,270
`
`9
`8. An improved active carbon pellet composition com
`prising active wood-based carbon 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 sodium bentonite and calcium bentonite,
`wherein the clay is characterized by having been subjected
`to a calcination treatment conducted at from about 700°F. to
`about 1,800°F in an oxygen-free atmosphere subsequent to
`its pellet formation with the carbon in the presence of water
`wherein said composition is characterized by a higher appar
`
`10
`ent density over that of the carbon alone, and wherein the
`improvement comprises subjecting the pellets, prior to said
`calcination treatment, to a mechanical tumbling treatment
`for a time sufficient such that the calcined pellet composition
`exhibits a butane working capacity from about 10 to about
`17 g/100 cc, an apparent density from about 0.25 to about
`0.40 g/cc, a pellet void fraction of less than 0.19, and a dust
`attrition rate of less than 1.2 mg/100.
`
`