(12) United States Patent
`Hiltzik et al.
`
`USOO6540815B1
`US 6,540,815 B1
`Apr. 1, 2003
`
`(10) Patent No.:
`(45) Date of Patent:
`
`(54)
`
`(75)
`
`(73)
`
`(21)
`(22)
`
`(60)
`
`(51)
`(52)
`(58)
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`(56)
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`METHOD FOR REDUCING EMISSIONS
`FROM EVAPORATIVE EMISSIONS
`CONTROL SYSTEMS
`
`Inventors: Laurence H. Hiltzik, Charleston, SC
`(US); Jacek Z. Jagiello, Charleston, SC
`(US); Edward D. Tolles, Charleston,
`SC (US); Roger S. Williams,
`Lexington, VA (US)
`Assignee: MeadWestvaco Corporation,
`Stamford, CT (US)
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`Notice:
`
`Appl. No.: 10/100,362
`Filed:
`Mar 18, 2002
`Related U.S. Application Data
`Provisional application No. 60/335,897, filed on Nov. 21,
`2001.
`Int. Cl.......................... F02M 33/02; B01D 53/04
`U.S. Cl. ............................ 95/146; 95/900; 123/519
`Field of Search ............................ 95/90, 146, 148,
`95/900–903; 96/132, 133, 147; 123/518,
`519; 502/416
`
`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 Tolles et al. ...
`... 123/519
`5,206.207 A * 4/1993 Tolles ...........
`... 5O2/423
`5,207,808 A * 5/1993 Haruta et al. ..
`... 123/519
`5,238,470 A * 8/1993 Tolles 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 .............
`... 5O2/416
`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
`
`7/2001
`11 1316.3
`EP
`2002012826 A * 2/2002
`KR
`WO 92/O1585
`9/1992
`WO
`WO 01/62367
`8/2001
`WO
`Primary Examiner David A. Simmons
`ASSistant Examiner-Frank M. Lawrence
`(74) Attorney, Agent, or Firm Terry B. McDaniel; Daniel
`B. 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
`
`BASF-1005
`U.S. Patent No. RE38,844
`
`

`

`US 6,540,815 B1
`Page 2
`
`U.S. PATENT DOCUMENTS
`
`5,456.237 A * 10/1995 Yamazaki et al. .......... 123/519
`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................. 502/18O
`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 Bragget al. ...
`... 55/519
`6,171,373 B1 * 1/2001 Park et al. .....
`... 95/138
`6.279,548 B1 * 8/2001 Reddy ........
`123/519
`6.284,705 B1 * 9/2001 Park et al. .................. 502/18O
`6,488,748 B2 12/2002 Yamafuji et al.
`* cited by examiner
`
`
`
`

`

`u////u////
`
`

`

`US. Patent
`
`Apr. 1, 2003
`
`Sheet 2 0f 3
`
`US 6,540,815 B1
`
`FIGURE 2
`
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`

`

`U.S. Patent
`
`Apr. 1, 2003
`
`Sheet 3 of 3
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`US 6,540,815 B1
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`FIGURE 3
`
`n-Butane Adsorption isotherm at 25°C
`
`: BAX 1500
`
`Example 3
`
`Example 1
`
`
`
`-
`
`--
`
`N Example 2
`
`18O
`
`160
`
`140
`
`8 O
`
`6 O
`
`4 O
`
`2 O
`
`O.1
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`1
`10
`n-Butane Vapor Concentration, volume percent
`
`100
`
`

`

`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.
`
`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 EPA 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
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`capacity for 100% butane vapor (“butane activity,” g/100
`g-carbon), and purgeability (“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 diffusional 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.)
`
`

`

`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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`4
`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
`55
`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 2"
`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
`
`

`

`7
`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 A3000), bentonite clay (7.2
`wt %), and phosphoric acid (0.3 wt %). The pellets were
`tumbled for four minutes, dried overnight at 105 C., and
`Subsequently heat-treated insteam 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).
`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
`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
`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) extruding an extrudable mixture through an extrusion
`die 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
`temperature and for a time period Sufficient to react the
`ceramic forming material together and form a ceramic
`
`15
`
`25
`
`US 6,540,815 B1
`
`8
`matrix. The extrudable mixture is capable of maintaining the
`shape of the monolith after extrusion and during drying of
`the monolith.
`In this example, the extrusion formulation ingredients
`partially dilute the carbon adsorbent, and in addition, the
`adsorbent is further diluted by the open cell structure of the
`extruded part. These cells create more bed Voidages within
`the part, compared with a similar bed volume of pellets (65
`vol % voidages for the honeycomb versus 35 vol % for
`pellets or granules). The cell structure and high bed voidages
`have the added advantage of imposing minimal additional
`flow restriction compared with a bed of pellets, thereby
`allowing the honeycomb to be installed to the main canister
`as an add-on auxiliary device of greatly reduced croSS
`Sectional area (see Supplemental canister body 12 in FIG. 2).
`Example 3: Special Precursor Pellets: These 2 mm pellets
`were prepared by Selecting the adsorbent to be extruded
`according to its intrinsic flat isotherm adsorption properties.
`In this example, there was no special provision for filler in
`the formulation or bed voidage dilution from the extruded
`shape. The ingredients for the extrusion blend producing the
`tested activated carbon pellets consisted of SX 1 grade
`activated carbon produced by NORIT (93.2 wt %) and
`sodium carboxymethyl cellulose binder system (6.8 wt %).
`The pellets were tumbled for four minutes, dried overnight
`at 105 C., and Subsequently heat-treated in air at 150° C. for
`three hours.
`AS noted above, the comparisons of these activated car
`bon containing materials, prepared as Set forth in the
`examples, is shown in the following Table.
`
`TABLE
`
`Performance, Properties, and Formulations for Alternative Vent-Side Adsorbents
`Ceramic-
`Special
`Bound
`Precursor
`Honeycomb
`Pellet
`
`Filled
`Pellet
`
`Prior Art: High
`Working Capacity Carbons
`
`Fuel source-side BAX 1500
`Volume:
`Vent-Side Adsorbent Type:
`Vent-Side Mode:
`Vent-Side Adsorbent Volume:
`
`Canister System Performance:
`Westvaco DBL Test
`
`Gasoline Working Capacity, g:
`2" Day DBL Emissions, mg-C
`Note:
`Vent-Side Properties (6)
`Incremental Adsorption. At 25 C.
`
`1800 mL 2100 mL.
`
`1800 mL 1800 mL.
`
`1800 mL.
`
`“Ex. 2
`“Ex. 1
`Auxiliary Bed
`Layer
`300 mL 200 mL.
`41 mm diameter x
`150 mm long,
`200 cpsi
`
`BAX 1100 BAX 1500
`“Ex. 3
`Layer
`Layer
`Layer
`300 mL 300 mL.
`300 mL.
`
`138
`29
`(1)
`
`144
`1O
`(2)
`
`132
`13
`(3)
`
`143
`88
`(4)
`
`139
`221
`(5)
`
`5-50 vol% butane vapor, g/L:
`Apparent Density, g/mL:
`Butane Activity, g/100g:
`BWC, g/dL:
`Butane Ratio:
`
`24
`O.869
`7.0
`5.7
`O.929
`
`16
`0.355
`13.1
`4.0
`O.852
`
`18
`O453
`18.5
`5.0
`O.593
`
`52
`O.358
`39.0
`11.9
`O.852
`
`8O
`O.284
`64.7
`16.0
`O868
`
`(1) Two DBL Test; Averaged data for GWC (400 bed volume purge) and DBL emissions (150 bed volume
`purge); 2.1L canister, 1500 mL fuel source-side chamber, 600 mL vent-side cham