`10100362
`
`10100362
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`Application
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`papers.
`
`031802
`
`INITIALS V /.
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`CONTENTS
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`U.S. Patent No. RE38,844
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`INDEX OF CLAIMS
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`SERIAL NO.
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`APPUCANT(S)
`
`FILING DATE
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`1st AMENDMENT |
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`100
`TOTAL
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`16
`17
`18
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`20
`21
`22
`23
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`25
`26
`27
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`37
`38
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`
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`CLAIMS 3 ο 1
`
`* MAY BE USED FOR ADDITIONAL CLAIMS OR ADMENDMENTS
`
`■
`
`FORM PTO-2022 (1-98)
`
`U.S.QEPARTMENT OF COMMERCE
`Patent and Trademark Office
`‘U.S. Oovemmenl Printing Ο111οβ: 1998 - 433-214/70303
`
`4
`
`
`
`(ΐ2) United States Patent
`Hiltzik et al.
`
`US006540815B1
`
`US006540815B1
`US 6,540,815 Β1
`Apr. 1,2003
`
`(ΐο) Patent No.:
`(45) Date of Patent:
`
`(54) METHOD FOR REDUCING EMISSIONS
`FROM EVAPORATIVE EMISSIONS
`CONTROL SYSTEMS
`
`(75) Inventors: Laurence Η. Hiltzik, Charleston, SC
`(US); Jacek Ζ. Jagiello, Charleston, SC
`(US); Edward D. Tolies, Charleston,
`SC (US); Roger S. Williams,
`Lexington, VA (US)
`
`(73) Assignee: MeadWestvaco Corporation,
`Stamford, CT (US)
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(21) Appl. No.: 10/100,362
`Mar. 18, 2002
`(22) Filed:
`
`Related U.S. Application Data
`(60) Provisional application No. 60/335,897, filed on Nov. 21,
`2001.
`Int. Cl.7.......................... F02M 33/02; B01D 53/04
`(51)
`(52) U.S. Cl................................ 95/146; 95/900; 123/519
`(58) Field of Search ............................. 95/90, 146, 148,
`95/900-903; 96/132, 133, 147; 123/518,
`519; 502/416
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`4,677,086 A * 6/1987 McCue et al.................... 123/519
`4,894,072 A * 1/1990 Turner et al..................... 123/519
`5,204,310 A * 4/1993 Tolies et al...................... 123/519
`5,206,207 A * 4/1993 Tolies .............................. 502/423
`5,207,808 A * 5/1993 Haruta et al..................... 123/519
`5,238,470 A * 8/1993 Tolies et al......................... 95/143
`5,250,491 A * 10/1993 Yan .................................. 264/117
`5,276,000 A * 1/1994 Matthews et al................ 502/424
`5,304,527 A * 4/1994 Dimitri ............................ 502/416
`5,324,703 A * 6/1994 McCue et al.................... 502/424
`5,337,721 A * 8/1994 Kasuya et al.................... 123/519
`
`5,408,976 A * 4/1995 Reddy ....................... 123/198 D
`5,416,056 A * 5/1995 Baker ............................. 502/425
`5,456,236 A * 10/1995 Wakashiro et al.............. 123/519
`(List continued on next page.)
`FOREIGN PATENT DOCUMENTS
`11 13163
`7/2001
`ΕΡ
`2002012826 A *
`2/2002
`KR
`WO 92/01585
`9/1992
`WO
`WO 01/62367
`8/2001
`WO
`Primary Examiner—David A. Simmons
`Assistant Examiner—Frank Μ. Lawrence
`(74) Attorney, Agent, or Firm—Terry Β. McDaniel; Daniel
`Β. Reece, IV; Thomas A. Boshinski
`(57)
`ABSTRACT
`
`Disclosed is a method for sharply reducing diurnal breathing
`loss emissions from automotive evaporative emissions con
`trol systems by providing multiple layers, or stages, of
`adsorbents. On the fuel source-side of an emissions control
`system canister, high working capacity carbons are preferred
`in a first canister (adsorb) region. In subsequent canister
`region(s) on the vent-side, the preferred adsorbent should
`exhibit a flat or flattened adsorption isotherm on a volumet
`ric basis and relatively lower capacity for high concentration
`vapors as compared with the fuel source-side adsorbent.
`Multiple approaches are described for attaining the preferred
`properties for the vent-side canister region. One approach is
`to use a filler and/or voidages as a volumetric diluent for
`flattening an adsorption isotherm. Another approach is to
`employ an adsorbent with the desired adsorption isotherm
`properties and to process it into an appropriate shape or form
`without necessarily requiring any special provision for dilu
`tion. The improved combination of high working capacity
`carbons on the fuel source-side and preferred lower working
`capacity adsorbent on the vent-side provides substantially
`lower diurnal breathing emissions without a significant loss
`in working capacity or increase in flow restriction compared
`with known adsorbents used in canister configurations for
`automotive emissions control systems.
`
`30 Claims, 3 Drawing Sheets
`
`5
`
`
`
`US 6,540,815 Β1
`Page 2
`
`U.S. PATENT DOCUMENTS
`* 10/1995 Yamazaki et al................ 123/519
`5,456,237 A
`5,460,136 A
`* 10/1995 Yamazaki et al................ 123/519
`5,477,836 A
`* 12/1995 Hyodo et al...................... 123/519
`5,538,932 A
`* 7/1996 Yan et al........................... 502/424
`5,564,398 A
`* 10/1996 Maeda et al...................... 123/519
`5,691,270 A * 11/1997 Miller ............................. 502/174
`5,736,481 A * 4/1998 Miller ............................. 502/174
`5,736,485 A * 4/1998 Miller ............................. 502/174
`
`5,863,858 A * 1/1999 Miller et al...................... 502/180
`5,914,294 A * 6/1999 Park et al......................... 501/100
`5,914,457 A * 6/1999 Itakura et al..................... 123/519
`6,136,075 A * 10/2000 Bragg et al......................... 55/519
`6,171,373 Β1 * 1/2001 Park et al............................ 95/138
`6,279,548 Β1 * 8/2001 Reddy ............................. 123/519
`6,284,705 Β1 * 9/2001 Park et al......................... 502/180
`6,488,748 Β2 12/2002 Yamafuji et al.
`* cited by examiner
`
` 6
`
`
`
`U.S. Patent
`
`Apr. 1, 2003
`
`Sheet 1 of 3
`
`US 6,540,815 Β1
`
`FIGURE 1
`PRIOR ART
`
` 7
`
`
`
`U.S. Patent Apr. 1, 2003
`
`Sheet 2 of 3
`
`US 6,540,815 Β1
`
`FIGURE 2
`
`2
`
` 8
`
`
`
`U.S. Patent
`
`Apr. 1, 2003
`
`Sheet 3 of 3
`
`US 6,540,815 Β1
`
`FIGURE 3
`
`n-Butane Adsorption Isotherm at 25°C
`
`n-Butane Vapor Concentration, volume percent
`
`Mass adsorbed, g/L
`
`9
`
`
`
`1
`METHOD FOR REDUCING EMISSIONS
`FROM EVAPORATIVE EMISSIONS
`CONTROL SYSTEMS
`
`This application claims the benefit of U.S. Provisional
`Application No. 60/335,897 filed on Nov. 21, 2001.
`
`5
`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`This invention relates to a method for reducing emissions
`from evaporative control systems including activated carbon
`particulate-filled canisters and adsorptive monolith-
`containing canisters, which monoliths include activated
`carbon, and to using said adsorbing canisters to remove
`volatile organic compounds, and other chemical agents from
`fluid streams. More particularly, this invention relates to
`using said vapor-adsorbing materials in hydrocarbon fuel
`consuming engines.
`2. Description of Related Art (Including Information
`Disclosed Under 37 CFR 1.97 and 37 CFR 1.98)
`(a) Standard Working Capacity Adsorbents
`Evaporation of gasoline from motor vehicle fuel systems
`is a major potential source of hydrocarbon air pollution. The
`automotive industry is challenged to design engine compo
`nents and systems to contain, as much as possible, the almost
`one billion gallons of gasoline evaporated from fuel systems
`each year in the United States alone. Such emissions can be
`controlled by canister systems that employ activated carbon
`to adsorb and hold the vapor that evaporates. Under certain
`modes of engine operation, the adsorbed hydrocarbon vapor
`is periodically removed from the carbon by drawing air
`through the canister and burning the desorbed vapor in the
`engine. The regenerated carbon is then ready to adsorb
`additional vapor. Under ERA mandate, such control systems
`have been employed in the U.S. for about 30 years, and
`during that time government regulations have gradually
`reduced the allowable emission levels for these systems. In
`response, improvements in the control systems have been
`largely focused on improving the capacity of the activated
`carbon to hold hydrocarbon vapor. For example, current
`canister systems, containing activated carbon of uniform
`capacity, are readily capable of capturing and releasing 100
`grams of vapor during adsorption and air purge regeneration
`cycling. These canister systems also must have low flow
`restrictions in order to accommodate the bulk flow of
`displaced air and hydrocarbon vapor from the fuel tank
`during refueling. Improvements in activated carbons for
`automotive emission control systems are disclosed in U.S.
`Pat. Nos.: 4,677,086; 5,204,310; 5,206,207; 5,250,491;
`5,276,000; 5,304,527; 5,324,703; 5,416,056; 5,538,932;
`5,691,270; 5,736,481; 5,736,485; 5,863,858; 5,914,294;
`6,136,075; 6,171,373; 6,284,705.
`A typical canister employed in a state of the art auto
`emission control system is shown in FIG. 1. Canister 1
`includes support screen 2, dividing wall 3, a vent port 4 to
`the atmosphere (for when the engine is off), a vapor source
`connection 5 (from the fuel tank), a vacuum purge connec
`tion 6 (for when the engine is running), and adsorbent
`material fill 7.
`Other basic auto emission control system canisters are
`disclosed in U.S. Pat. Nos. 5,456,236; 5,456,237; 5,460,136;
`and 5,477,836.
`Typical carbons for evaporative emission canisters are
`characterized by standard measurements of bed packing
`density (“apparent density,” g/mL), equilibrium saturation
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`US 6,540,815 Β1
`
`2
`capacity for 100% butane vapor (“butane activity,” g/100
`g-carbon), and purge ability (“butane ratio”), specifically, the
`proportion of adsorbed butane from the saturation step
`which can be recovered from the carbon by an air purge step.
`The multiplicative product of these three properties yields a
`measure of the carbon’s effective butane “working capacity”
`(“BWC”, g/dL), measured by ASTM D5228-92, which has
`been established in the art as a good predictor of the canister
`working capacity for gasoline vapors. Carbons that excel for
`this application have high BWC, typically 9 to 15+g/dL
`BWC, as a result of high saturation capacities on a
`volumetric-basis for butane (the product of density and
`butane activity), and high butane ratios (>0.85). In terms of
`isothermal equilibrium adsorption capacities across all
`vapor concentrations, these carbons characteristically have
`high incremental capacity as a function of increased vapor
`concentration (i.e., isotherm curved upward on a semi-log
`graph). This isotherm upward curve reflects the high work
`ing capacity performance feature of these carbons, in that
`gasoline vapors are adsorbed in high quantity at high con
`centrations but readily released in high concentration to an
`air purge stream. In addition, these carbons tend to be
`granular (somewhat irregularly shaped) or cylindrical pellet,
`typically of a size just about 1-3 mm in diameter. It has been
`found that somewhat larger sizes hinder diflusional transport
`of vapors into and out of the carbon particle during dynamic
`adsorb and purge cycles. On the other hand, somewhat
`smaller size particles have unacceptably high flow restric
`tion for displaced air and hydrocarbon vapors during refu
`eling.
`(b) Diurnal Breathing Loss (DBL) Requirements
`Recently, regulations have been promulgated that require
`a change in the approach with respect to the way in which
`vapors must be controlled. Allowable emission levels from
`canisters would be reduced to such low levels that the
`primary source of emitted vapor, the fuel tank, is no longer
`the primary concern, as current conventional evaporative
`emission control appears to have achieved a high efficiency
`of removal. Rather, the concern now is actually the hydro
`carbon left on the carbon adsorbent itself as a residual “heel”
`after the regeneration (purge) step. Such emissions typically
`occur when a vehicle has been parked and subjected to
`diurnal temperature changes over a period of several days,
`commonly called “diurnal breathing losses.” Now, the Cali
`fornia Low Emission Vehicle Regulation makes it desirable
`for these diurnal breathing loss (DBL) emissions from the
`canister system to be below 10 mg (“PZEV”) for a number
`of vehicles beginning with the 2003 model year and below
`50 mg, typically below 20 mg, (“LEV-II”) for a larger
`number of vehicles beginning with the 2004 model year.
`(“PZEV” and “LEV-II” are criteria of the California Low
`Emission Vehicle Regulation.)
`While standard carbons used in the commercial canisters
`excel in terms of working capacity, these carbons are unable
`to meet DBL emission targets under normal canister opera
`tion. Furthermore, none of the standard measures of working
`capacity properties correlate with DBL emission perfor
`mance. Nonetheless, one option for meeting emission targets
`is to significantly increase the volume of purge gas during
`regeneration in order to reduce the amount of residual
`hydrocarbon heel in the carbon bed and thereby reduce
`subsequent emissions. This strategy, however, has the draw
`back of complicating management of the fuel/air mixture to
`the engine during purge regeneration and tends to adversely
`affect tailpipe emissions, i.e., moving or redefining the
`problem rather than solving it. (See U.S. Pat. No. 4,894,
`072.)
`
`
`10
`
`
`
`US 6,540,815 Β1
`
`3
`Another option is to design the carbon bed so that there is
`a relatively low cross-sectional area on the vent-side of the
`canister system (the first portion of the bed to encounter
`purge air), either by redesign of the existing canister dimen
`sions or by the installation of a supplemental, auxiliary
`vent-side canister of appropriate dimensions. This alterna
`tive has the effect of locally reducing residual hydrocarbon
`heel by increasing the intensity of purge for that vent-side
`portion of the bed, thereby improving its ability to retain
`vapors that would otherwise be emitted from the canister
`system under diurnal breathing conditions. The drawback is
`that there is a useful limit to which a portion of the bed can
`be elongated at reduced cross-sectional area without other
`wise incurring excessive flow restriction by the canister
`system. In practice, this limit does not allow employing a
`sufficiently narrowed and elongated geometry to meet emis
`sion targets. (See U.S. Pat. No. 5,957,114.)
`Another option for increasing the purge efficiency of a
`fuel vapor/air mixture fraction adsorbed in the pores of the
`adsorbent material is suggested by the teachings of U.S. Pat.
`Nos. 6,098,601 and 6,279,548 by providing a heating capa
`bility internal of the canister, or a section thereof, either to
`increase pressure in the vapor storage canister to expel hot
`vapor through the vapor/purge conduit back into the fuel
`tank where it condenses at the lower ambient temperature
`therein (’601) or to increase the purging efficiency of hydro
`carbons from the heated adsorbent material and carry the
`purged fuel vapor to the induction system of an associated
`engine (’548). However, this increases the complexity of
`control system management, and there appears some inher
`ent safety concerns in providing heating internal of a can
`ister for trapping fuel vapors.
`Thus, an acceptable remedy, which does not have draw
`backs as the cited alternative approaches, is greatly desired.
`It is submitted that the invention disclosed and claimed
`herein provides the desired solution.
`SUMMARY OF THE INVENTION
`An invention is disclosed for sharply reducing diurnal
`breathing loss emissions from evaporative emissions canis
`ters by the use of multiple layers, or stages, of adsorbents.
`On the fuel source-side of the canister, standard high work
`ing capacity carbons are preferred. On the vent-side, the
`preferred adsorbent volume exhibits a flat or flattened adsor
`bent isotherm on a volumetric basis in addition to certain
`characteristically desirable adsorptive properties across
`broad vapor concentrations, specifically relatively low incre
`mental capacity at high concentration vapors compared with
`the fuel source-side adsorbent volume. Two approaches are
`described for attaining the preferred properties for the vent-
`side adsorbent volume. One approach is to use a filler and/or
`bed voidages as a volumetric diluent for flattening an
`isotherm. A second approach is to employ an adsorbent with
`the desired isotherm properties and to process it into an
`appropriate shape or form without necessarily requiring any
`special provision for dilution. Both such approaches provide
`a substantially lower emissions canister system without a
`significant loss in working capacity or an increase in flow
`restriction compared with prior art adsorbents used for
`automotive emissions control.
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 shows, in cross-section, a prior art canister system.
`FIG. 2 shows, in cross-section, one embodiment-of the
`invention canister comprising multiple adsorbents.
`FIG. 3 shows butane isotherm properties for different
`activated carbon adsorbents.
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`DESCRIPTION OF THE PREFERRED
`EMBODIMENT(S)
`The disclosed invention relates to the use of multiple beds
`(or layers, stages, or chambers) of adsorbent materials,
`which, in combination, significantly reduce DBL emissions
`while maintaining the high working capacity and low flow
`restriction properties of the canister system. (See FIG. 2.)
`These adsorbents include activated carbon from a variety of
`raw materials, including wood, peat, coal, coconut, synthetic
`or natural polymer, and a variety of processes, including
`chemical and/or thermal activation, as well as inorganic
`adsorbents, including molecular sieves, porous alumina,
`pillared clays, zeolites, and porous silica, and organic
`adsorbents, including porous polymers. The adsorbents may
`be in granular, spherical, or pelletized cylindrical shapes, or
`may be extruded into special thin-walled cross-sectional
`shapes, such as hollow-cylinder, star, twisted spiral, asterisk,
`configured ribbons, or other shapes within the technical
`capabilities of the art. In shaping, inorganic and/or organic
`binders may be used. The adsorbents may be formed into a
`monolith or honeycomb part. The adsorbents may be incor
`porated into a canister as one or more layers, or separate
`chambers, or they may be inserted in the fluid stream flow
`as auxiliary canister beds.
`One common feature for all of these approaches is to have
`a vent-side adsorbent with a relatively flat-shaped isotherm.
`This isotherm shape is important for reasons related to purge
`efficiency across the adsorbent bed depth. For an adsorbent
`with a flat adsorption isotherm, the concentration of hydro
`carbon vapor in equilibrium with adsorbed hydrocarbon, by
`definition, decreases further as the adsorbed hydrocarbon is
`removed compared with an adsorbent with a more steeply
`sloped isotherm. Thus, when such a material is employed as
`an adsorbent volume on the vent-side region of a canister,
`purge is able to reduce the vapor concentration in the area of
`the purge inlet to a very low level. Since it is the vapor near
`the purge inlet that eventually emerges as bleed, decreasing
`this concentration reduces the bleed emission level. The
`degree of removal of adsorbed hydrocarbon during purge is
`determined by the difference between the concentration of
`hydrocarbon picked up in the purge gas and the concentra
`tion in equilibrium with the adsorbent at any point in the bed.
`Thus, adsorbent in the immediate vicinity of the purge inlet
`will be most thoroughly regenerated. At points deeper in the
`adsorbent bed, less hydrocarbon will be removed because
`the purge gas will already contain hydrocarbon removed
`from previous points in the bed. An adsorbent with a flatter
`adsorption isotherm will give up less vapor into the purge
`stream and this purge will then be more efficient in reducing
`vapor concentrations deeper into the bed. Therefore, for a
`given quantity of purge gas, it will be possible to reduce the
`vapor concentration in a volume of adsorbent with a flat
`adsorption isotherm to a lower level than the concentration
`in the same volume of an adsorbent with a steep adsorption
`isotherm. Bleed emission from such a volume will therefore
`be lower when the adsorbent has a flatter adsorption iso
`therm.
`A region within a canister containing particulate or in an
`adsorbent-containing monolith with the preferred adsorption
`isotherm properties for achieving low bleed emission levels
`will, however, have a relatively low adsorption working
`capacity compared to the activated carbons commonly used
`in automotive evaporative emission control. For example,
`the BWC of a low capicity adsorbent will be about 6 g/dL
`compared to the 9 g/dL to 15+g/dL range as used in typical
`automotive carbons. Therefore, in order to maintain the
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`required hydrocarbon capacity for normal emission control
`system operation, the low-bleed adsorbent will be used in a
`vent-side auxiliary region within the canister or outside the
`canister in combination with an fuel source-side region
`containing a volume of the high capacity carbon normally
`employed. When two different adsorbents are used, for
`example, system design will involve providing sufficient
`volume of the high capacity carbon in the main part, or fuel
`source-side, of an emisssion control canister to achieve the
`desired working capacity, and a sufficient volume of the
`low-bleed adsorbent to contain vapor emitted from the main
`bed to such an extent that such vapor does not materially
`affect the bleed emissions from the low-bleed adsorbent.
`In the context of the invention, “monolith” is intended to
`include foams, woven and non-woven fibers, mats, blocks
`and bound aggregates of particulates.
`It is notable that the emission of vapor from the main,
`high-capacity fuel source-side volume of adsorbent into the
`auxiliary lower capacity vent-side volume is significantly
`affected by the presence of that vent-side volume. During
`purge, a vent-side adsorbent volume having a flat adsorption
`isotherm will give up a relatively small hydrocarbon load
`into the purge gas. Therefore, the concentration of vapor
`carried by the purge gas will be low as it emerges from the
`low-bleed vent-side volume and enters the high-capacity,
`fuel source-side volume. This allows good regeneration of
`the high-capacity adsorbent in the vicinity of the junction of
`the two adsorbent volumes, and helps protect the vent-side
`volume from emissions from the fuel source-side region of
`the canister during diurnal breathing flow. Specifically, the
`greater regeneration efficiency of the fuel source-side vol
`ume reduces diurnal emissions by retarding the rate of bulk
`phase diffusion across the flow length of the canister system.
`Since bulk phase diffusion is a major mode of vapor trans
`port during diurnal breathing conditions, by reducing the
`vapor concentration difference across the flow length of the
`canister system by enhanced regeneration, the redistribution
`of vapors within the canister system and subsequent emis
`sions into the vent-side volume and out of the vent port are
`reduced.
`Examples of adsorbents with isotherms having the pre
`ferred shape to provide low bleed performance are compared
`with standard canister-fill carbons (Westvaco Corporation’s
`BAX 1100 and BAX 1500) in FIG. 3. It is important to note
`that, as shown in this figure, the isotherm properties must be
`defined in terms of volumetric capacity. On this basis, the
`preferred low-bleed adsorbent portion will have an incre
`mental n-butane capacity of less than about 35 g/liter
`between 5 and 50 volume percent n-butane vapor concen
`tration.
`While in some instances, known adsorbents may have the
`preferred properties for the vent-side, these adsorbents
`would not be expected to be useful in an evaporative
`canister. In some cases, these materials have low purgeabil-
`ity (butane ratio less than 0.85) and low working capacity
`(BWC less than 9 g/dL) as measured by the standard BWC
`test for qualifying canister carbons. Common wisdom and
`experience in the art associate low butane ratio with high
`residual hydrocarbon heel, which is the potential source for
`high emissions. Furthermore, low BWC adsorbents were not
`considered useful for inclusion into a canister system as
`working capacity for gasoline vapors would be assumed
`impaired, with no expectation that there would be a utility
`for reducing emissions. In fact, one preferred embodiment of
`this invention, lower capacity adsorbents have BWC values
`preferably below 8 g/dL, which is well below the 9-15+g/dL
`BWC level normally deemed suitable for use in evaporative
`emission control canister systems. The preferred selection of
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`these low BWC materials for inclusion into a canister
`system as a vent-side layer to produce low emissions was
`only realized once the dynamics within the adsorbent bed
`were realized (i.e., the significance of low residual vapor
`concentration within the vent-side bed volume and the
`interactive effect that the vent-side bed volume has on the
`distribution and diffusion of vapor across the entire canister
`system during the diurnal breathing loss period).
`Therefore, it has been found that the preferred vent-side
`adsorbent properties, in addition to a relatively low BWC,
`includes butane ratios between 0.40 and 0.98, which in total
`are substantially different properties compared with adsor
`bents previously conceived as useful for these canister
`systems.
`The proposed alternative approaches described above are
`shown to be effective in canister bleed emission control in
`the following examples. One approach for preparing the
`vent-side adsorbent is to volumetrically dilute a high work
`ing capacity adsorbent so that its resulting isotherm is
`flattened on a volumetric basis. A second approach is to
`begin with an adsorbent that has the desired adsorption
`capacity and flat isotherm shape and process it into a shape
`or form, such as a pellet or honeycomb.
`A particular preferred embodiment for a canister with
`multiple adsorbents is shown in FIG. 2. FIG. 2 shows a
`canister system comprising a primary canister body 1, a
`support screen 2, a dividing wall 3, a vent port 4 to the
`atmosphere, a vapor source connection 5, a vacuum purge
`connection 6, a fuel source-side region 7, vent-side canister
`regions 8-11 of varying low-capacities, supplemental can
`ister body 12, and connecting hose 13 permitting fluid
`stream flow from the primary canister body 1 to the supple
`mental canister body 12. Additional embodiments, as dis
`cussed above, are also envisioned to be within the scope of
`the subject of the invention.
`The desired results for the subject matter of the invention
`can be attained with a single vent-side uniform lower
`capacity adsorbent material as the subsequent adsorbent
`material. The option of multiples of lower capacity adsor
`bents with the desirable adsorptive properties across broad
`vapor concentrations is demonstrated merely as one embodi
`ment.
`The measures for gasoline working capacity (GWC) and
`emissions in the Table were derived from the Westvaco DBL
`test that uses a 2.1 L canister. The pellet examples were
`tested as a 300 mL vent-side layer within the canister, with
`the 1800 mL of BAX 1500 pellets as the remaining canister
`fill. The honeycomb was tested as an auxiliary bed canister
`that was placed in-line with the 2.1 L main canister of BAX
`1500 pellets. For all examples, the canister system was
`uniformly first preconditioned by repetitive cycling of gaso
`line vapor adsorption and air purge (400 bed volumes air).
`This cycling generated the GWC value. Butane emissions
`were subsequently measured after a butane adsorption and
`an air purge step, specifically during a diurnal breathing loss
`period when the canister system was attached to a
`temperature-cycled fuel tank. The reported value is the 2nd
`day DBL emissions during an 11-hour period when the fuel
`tank was warmed and vapor-laden air was vented to the
`canister system and exhausted from the vent-side adsorbent
`where the emissions were measured. The procedure
`employed for measuring DBL emissions has been described
`in SAE Technical Paper 2001-01-0733, titled “Impact and
`Control of Canister Bleed Emissions,” by R. S. Williams and
`C. R. Clontz.
`Example 1: Microsphere Filler Pellets. These 2 mm
`pellets are an example of the volumetric dilution method by
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`adding a solid filler to the extrusion formulation. The pellets
`were prepared from an extrusion blend consisting of West-
`vaco SA-1500 powder (12.8 wt %), solid glass microsphere
`filler (79.7 wt % PQ Corporation Α3000), bentonite clay (7.2
`wt %), and phosphoric acid (0.3 wt %). The pellets were 5
`tumbled for four minutes, dried overnight at 105° C., and
`subsequently heat-treated in steam at 650° C. for 15 minutes.
`An appropriate non-adsorbing filler reduces adsorption
`capacities across all vapor concentrations, resulting in a
`flattened adsorption isotherm (“Example 1” in FIG. 3). 10
`Alternative methods for diluting the vent-side region are to
`co-mix adsorbent granules or pellets with inert filler par
`ticles of similar size, to form the extrusion paste into high
`voidage shapes such as hollow cylinders, asterisks, stars, or
`twisted, bent, or spiral ribbon pieces, or to place multiple 15
`thin layers of non-adsorbing particles or porous mats (e.g.,
`foam), or simply trapped air space between layers of adsor
`bent.
`Example 2: Ceramic-Bound Honeycomb. The 200 cpsi
`(cells per square inch) carbon-containing honeycomb is 20
`another example of the volumetric dilution method. The
`honeycomb in the Table was prepared according to the
`method described in U.S. Pat. No. 5,914,294, which dis
`closes forming an adsorptive monolith comprising the steps
`of (a) extmding an extrudable mixture through an extrusion 25
`die such that a monolith is formed having a shape wherein
`the monolith has at least one passage therethrough and the
`extmdable mixture comprises activated carbon, a ceramic
`forming material,