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`Attorney Docket No. CHA 2001-79 (reissue)
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`EXPRESS MAIL NO. EU59264045 l US
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`

`US 6,540,815 Bl
`
`This application claims the benefit of U.S. Provisional 5
`Application No. 60/335,897 filed on Nov. 21, 2001.
`
`BACKGROUND OF THE INVENTION
`
`1
`METHOD FOR REDUCING EMISSIONS
`FROM EVAPORATIVE EMISSIONS
`CONTROL SYSTEMS
`
`2
`capacity for 100% butane vapor ("butane activity," g/100
`g-carbon), and purgeability ("butane ratio"), specifically, the
`proportion of adsorbed butane from the sat_uration 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 etfecti ve butane "working capacity"
`("BWC", g/dL), measured by ASTM 05228-92, which has
`been established in the art as a good predictor of the canister
`working capacity for gasoline vapors. Carbons that excel for
`10 this application have high BWC, typically 9 to 15+g/dL
`1. Field of the Invention
`BWC, as a result of high saturation capacities on a
`This invention relates to a method for reducing emissions
`volumetric-basis for butane (the product of density and
`from evaporative control systems including activated carbon
`butane activity), and high butane ratios (>0.85). In terms of
`particulate-filled canisters and adsorptive monolith-
`isothermal equilibrium adsorption capacities across all
`containing canisters, which monoliths include activated
`carbon, and to using said adsorbing canisters to remove 15 vapor concentrations, these carbons characteristically have
`volatile organic compounds, and other chemical agents from
`high incremental capacity as a function of increased vapor
`fluid streams. More particularly, this invention relates to
`concentration (i.e., isotherm curved upward on a semi-log
`using said vapor-adsorbing materials in hydrocarbon fuel
`graph). This isotherm upward curve reflects the high work-
`consuming engines.
`ing capacity performance feature of these carbons, in that
`20 gasoline vapors are adsorbed in high quantity at high con-
`•
`centrations but readily released in high concentration to an
`2· Description of Related Art (Including Information
`Disclosed Under 37 CFR 1.97 and 37 CFR 1.9s)
`air purge stream. In addition, these carbons tend to be
`granular (somewhat irregularly shaped) or cylindrical pellet,
`(a) Standard Working Capacity Adsorbents
`typically of a size just about 1-3 mm in diameter. It has been
`Evaporation of gasoline from motor vehicle fuel systems
`is a major potential source of hydrocarbon air pollution. The 25 found that somewhat larger sizes hinder diffusional transport
`automotive industry is challenged to design engine compo-
`of vapors into and out of the carbon particle during dynamic
`nents and systems to contain, as much as possible, the almost
`adsorb and purge cycles. On the other hand, somewhat
`one billion gallons of gasoline evaporated from fuel systems
`smaller size particles have unacceptably high flow restric-
`each year in the United States alone. Such emissions can be
`tion for displaced air and hydrocarbon vapors during refu-
`controlled by canister systems that employ activated carbon
`eling.
`to adsorb and hold the vapor that evaporates. Under certain
`(b) Diurnal Breathing Loss (DBL) Requirements
`modes of engine operation, the adsorbed hydrocarbon vapor
`Recently, regulations have been promulgated that require
`is periodically removed from the carbon by drawing air
`a change in the approach with respect to the way in which
`through the canister and burning the desorbed vapor in the
`vapors must be controlled. Allowable emission levels from
`engine. The regenerated carbon is then ready to adsorb 35 canisters would be reduced to such low levels that the
`additional vapor. Under EPA mandate, such control sy5tems
`primary source of emitted vapor, the fuel tank, is no longer
`have been employed in the U.S. for ~bout 30 years, and
`the primary concern, as current conventional evaporative
`during that time gove~e~t regulations have gradually
`emission control appears to have achieved a high efficiency
`reduced the allowable enuss1on levels for these systems. In
`of removal. Rather, the concern now is actually the hydro-
`response, improvements i~ the control ~ystems have_ been 40 carbon left on the carbon adsorbent itself as a residual "heel"
`largely focused on improvmg the capacity of the activated
`after the regeneration (purge) step. Such emissions typically
`carbon to hold hydrocarbon vapor. For example, c~rrent
`occur when a vehicle has been parked and subjected to
`canist~r systems •. containing activate? carbon of ~ruform
`diurnal temperature changes over a period of several day~,
`capacity, are read1lr capable ~f captun?g and releasmg ~00
`commonly called "diurnal breathing losses." Now, the Cali-
`grams of vapor dunng adsorptmn and mr purge regeneratton 45 fornia Low Emission Vehicle Regulation makes it desirable
`cycling. These canister systems also must have low flow
`for these diurnal breathing loss (DBL) emissions from the
`restrictions in order to accommodate the bulk flow of
`canister system to be below 10 mg ("PZEV") for a number
`displaced air and hydrocarbon vapor from the fuel tank
`of vehicles beginning with the 2003 model year and below
`. 59 mg, typically below 20. mg, ("LE'\'.'~If') for a larger.
`during i:efueli~g .. Improvements in activa~ed carb~ns for
`automotive elll1ss1on control systems are disclosed m U.S. 50 number of vehicles beginning with the 2004 model year.
`Pat. Nos.: 4,677,086; 5,204,310; 5,206,207'. 5,250,491'.
`("PZEV" and "LEV-II" are criteria of the California Low
`5,276,000; 5,304,527; 5,324,703; 5,416,056, 5,538,932,
`Emission Vehicle Regulation.)
`5,691,270; 5,736,481; 5,736,485; 5,863,858; 5,914,294;
`While standard carbons used in the commercial canisters
`6,136,075; 6,171,373; 6,284,705.
`excel in terms of working capacity, these carbons are unable
`A typical canister employed in a state of the art auto 55 to meet DBL emission targets under normal canister opera-
`emission control system is shown in FIG. 1. Canister 1
`tion. Furthermore, none of the standard measures of working
`includes support screen 2, dividin~ w_all 3, a vent port 4 to
`capacity properties correlate with DB~ erni~si~n perfor-
`the atmosphere (for when the engme 1s off), a vapor source
`mance. Nonetheless, one option for meeting enuss10n targets
`connection 5 (from the fuel tank), a vacuum purge connec-
`is to significantly increase the volume of purge gas during
`tion 6 (for when the engine is running), and adsorbent 60 regeneration in order to reduce the amount of residual
`material fill 7.
`hydrocarbon heel in the carbon bed and thereby reduce
`Other basic auto emission control system canisters are
`subsequent emissions. This strategy, however, has the draw-
`disclosed in U.S. Pat. Nos. 5,456,236; 5,456,237; 5,460,136;
`back of complicating management of the fuel/air mixture to
`and 5,477,836.
`the engine during purge regeneration and tends to adversely
`Typical carbons for evaporative emission canisters are 65 affect tailpipe emissions, i.e., moving or redefining the
`characterized by standard measurements of bed packing
`problem rather than solving it. (See U.S, Pat. No. 4,894,
`density ("apparent density," g/mL), equilibrium saturation
`072.)
`
`30
`
`10
`
`

`

`US 6,540,815 Bl
`
`4
`DESCRIPTION OF THE PREFERRED
`EMBODIMENT(S)
`
`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
`· The disclosed invention relates to the use of multiple beds
`purge air), either by redesign of the existing canister dimen-
`sions or by the installation of a supplemental, auxiliary 5 (or layers, stages, or chambers) of adsorbent materials,
`vent-side canister of appropriate dimensions. This altema-
`which, in combination, significantly reduce DBL emissions
`tive has the effect of locally reducing residual hydrocarbon
`while maintaining the high working capacity and low flow
`heel by increasing the intensity of purge for that vent-side
`restriction properties of the canister system. (See FIG. 2.)
`portion of the bed, thereby improving its ability to retain
`These adsorbents include activated carbon from a variety of
`vapors that would otherwise be emitted from the canister 10 raw materials, including wood, peat, coal, coconut, synthetic
`system under diurnal breathing conditions. The drawback is
`or natural polymer, and a variety of processes, including
`that there is a useful limit to which a portion of the bed can
`chemical and/or thermal activation, as well as inorganic
`be elongated at reduced cross-sectional area without other-
`adsorbents, including molecular sieves, porous alumina,
`wise incurring excessive flow restriction by the canister
`pillared clays, zeolites, and porous silica, and organic
`system. In practice, this limit does not allow employing a 15 adsorbents, including porous polymers. The adsorbents may
`sufficiently narrowed and elongated geometry to meet emis-
`be in granular, spherical, or pelletized cylindrical shapes, or
`sion targets. (See U.S. Pat. No. 5,957,114.)
`may be extruded into special thin-walled cross-sectional
`Another option for increasing the purge efficiency of a
`shapes, such as hollow-cylinder, star, twisted spiral, asterisk,
`fuel vapor/air mixture fraction adsorbed in the pores of the
`confi~u.r:d ribbons, or other _sha~es wit~in the technic'.31
`adsorbent material is suggested by the teachings of U.S. Pat. 20 c~pab1lit1es of the art. In shaping, morgaruc and/or organic
`Nos. 6,098,601 and 6,279,548 by providing a heating capa-
`bmders may be used. The adsorbents may be formed into a
`bility internal of the canister, or a section thereof, either to
`monolith or honeycomb part. The adsorbents may be incor-
`increase pressure in the vapor storage canister to expel hot
`porated into a canister as one or more layers, or separate
`vapor through the vapor/purge conduit back into the fuel
`chambers, or they may be inserted in the fluid stream flow
`tank where it condenses at the lower ambient temperature 25 as auxiliary cani5ler beds.
`therein (' 601) or to increase the purging efficiency of hydro--
`One common feature for all of these approaches is to have
`carbons from the heated adsorbent material and carry the
`a vent-side adsorbent with a relatively flat-shaped isotherm.
`purged fuel vapor to the induction system of an associated
`This_ isotherm shape is important for reasons related to purge
`engine ('548). However, this increases the complexity of
`efficiency across the adsorbent bed depth. For an adsorbent
`control system management, and there appears some inher- 30 with a flat adsorption isotherm, the concentration of hydro-
`ent safety concerns in providing heating internal of a can-
`carbon vapor in equilibrium with adsorbed hydrocarbon, by
`ister for trapping fuel vapors.
`definition, decreases further as the adsorbed hydrocarbon is
`remove_d compared with an adsorbent wi~h ~ more steeply
`Thus, an acceptable remedy, which does not have draw-
`backs as the cited alternative approaches, is greatly desired.
`sloped isotherm. Thus, when such a. maten~ 1s employed as
`It is submitted that the invention disclosed and claimed 35 an adsorbent volume on the vent-side region of a canister,
`herein provides the desired solution.
`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
`SUMMARY OF THE INVENTION
`this concentration reduces the bleed emission level. The
`An invention is disclosed for sharply reducing diurnal
`breathing loss emissions from evaporative emissions canis- 40 degree of removal of adsorbed hydrocarbon during purge is
`ters by the use of multiple layers, or stages, of adsorbents.
`determined by the difference between the concentration of
`On the fuel source-side of the canister, standard high work-
`hydrocarbon picked up in the purge gas and the concentra-
`ing capacity carbons are preferred. On the vent-side, the
`tion in equilibrium with the adsorbent at any point in the bed.
`preferred adsorbent volume exhibits a flat or flattened adsor-
`Thus, adsorbent in the immediate vicinity of the purge inlet
`bent isotherm on a volumetric basis in addition to certain 45 will be most thoroughly regenerated. At points deeper in the
`characteristically desirable adsorptive properties across
`adsorbent bed, less hydrocarbon will be removed because
`broad vapor concentrations, specifically relatively low incre-
`the purge gas will already contain hydrocarbon removed
`mental capacity at high concentration vapors compared with
`from previous points in the bed. An adsorbent with a flatter
`the fuel source-side adsorbent volume. Tuo approaches are
`adsorption isotherm will give up less vapor into the purge
`described for'attaining the preferred properties for the vent- so stream and this purge will theri be'more efficient in reducing
`side adsorbent volume. One approach is to use a filler and/or
`vapor concentrations deeper into the bed. Therefore, for a
`bed voidages as a volumetric diluent for flattening an
`given quantity of purge gas, it will be possible to reduce the
`isotherm. A second approach is to employ an adsorbent with
`vapor concentration in a volume of adsorbent with a flat
`the desired isotherm properties and to process it into an
`adsorption isotherm to a lower level than the concentration
`appropriate shape or form without necessarily requiring any 55 in the same volume of an adsorbent with a steep adsorption
`special provision for dilution. Both such approaches provide
`isotherm. Bleed emission from such a volume will therefore
`a substantially lower emissions canister system without a
`be lower when the adsorbent has a flatter adsorption iso-
`significant loss in working capacity or an increase in flow
`therm.
`restriction compared with prior art adsorbents used for
`A region within a canister containing particulate or in an
`automotive emissions control.
`60 adsorbent-containing monolith with the preferred adsorption
`BRIEF DESCRIPTION OF THE DRAWINGS
`isotherm properties for achieving low bleed emission levels
`will, however, have a relatively low adsorption working
`FIG. 1 shows, in cross-section, a prior art canister system.
`capacity compared to the activated carbons commonly used
`FIG. 2 shows, in cross-section, one embodiment-of the
`in automotive evaporative emission control. For example,
`invention canister comprising multiple adsorbents.
`the BWC of a low capicity adsorbent will be about 6 g/dL
`FIG. 3 shows butane isothenn properties for different
`compared to the 9 g/dL to 15+g/dL range as used in typical
`activated carbon adsorbents.
`automotive carbons. Therefore, in order to maintain the
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`US 6,540,815 Bl
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`these low BWC materials for inclusion into a canister
`required hydrocarbon capacity for normal emission control
`system operation, the low-bleed adsorbent will be used in a
`system as a vent-side layer to produce low emissions was
`vent-side auxiliary region within the canister or outside the
`only realized once the dynamics within the adsorbent bed
`canister in combination with an fuel source-side region
`were realized (i.e., the significance of low residual vapor
`containing a volume of the high capacity carbon normally
`5 concentration within the vent-side bed volume and the
`employed. When two different adsorbents are used, for
`interactive effect that the vent-side bed volume has on the
`ex.ample, system design will involve providing sufficient
`distribution and diffusion of vapor across the entire canister
`volume of the high capacity carbon in the main part, or fuel
`system during the diurnal breathing loss period).
`source-side, of an emisssion control canister to achieve the
`Therefore, it has been found that the preferred vent-side
`desired working capacity, and a sufficient volume of the
`10 adsorbent properties, in addition to a relatively low BWC,
`low-bleed adsorbent to contain vapor emitted from the main
`includes butane ratios between 0.40 and 0.98, which in total
`bed to such an extent that such vapor does not materially
`are substantially different properties compared with adsor(cid:173)
`affect the bleed emissions from the low-bleed adsorbent.
`bents previously conceived as useful for these canister
`systems.
`In the context of the invention, "monolith" is intended to
`include foams, woven and non-woven fibers, mats, blocks 1s
`The proposed alternative approaches described above are
`shown to be effective in canister bleed emission control in
`and bound aggregates of particulates.
`the following examples. One approach for preparing the
`It is notable that the emission of vapor from the main,
`vent-side adsorbent is to volumetrically dilute a high work-
`high-capacity fuel source-side volume of adsorbent into the
`ing capacity adsorbent so that its resulting isotherm is
`auxiliary lower capacity vent-side volume is significantly
`affected by the presence of that vent-side volume. During 20
`flattened on a volumetric basis. A second approach is to
`purge, a vent-side adsorbent volume having a flat adsorption
`isotherm will give up a relatively small hydrocarbon load
`begin with an adsorbent that has the desired adsorption
`capacity and flat isotherm shape and process it into a shape
`into the purge gas. Therefore, the concentration of vapor
`or form, such as a pellet or honeycomb.
`carried by the purge gas will be low as it emerges from the
`low-bleed vent-side volume and enters the high-capacity, 25 A particular preferred embodiment for a canister with
`fuel source-side volume. This allows good regeneration of multiple adsorbents is shown in FIG. 2. FIG. 2 shows a
`canister system comprising a primary canister body 1, a
`the high-capacity adsorbent in the vicinity of the junction of
`support screen 2, a dividing wall 3, a vent port 4 to the
`the two adsorbent volumes, and helps protect the vent-side
`atmosphere, a vapor source connection 5, a vacuum purge
`volume from emissions from the fuel source-side region of
`connection 6, a fuel source-side region 7, vent-side canister
`the canister during diurnal breathing flow. Specifically, the
`greater regeneration efficiency of the fuel source-side vol-
`regions 8-11 of varying low-capacities, supplemental can-
`ister body 12, and connecting hose 13 permitting fluid
`ume reduces diurnal emissions by retarding the rate of bulk
`phase diffusion across the flow length of the canister system.
`stream flow from the primary canister body 1 to the supple-
`mental canister body 12. Additional embodiments, as dis-
`Since bulk phase diffusion is a major mode of vapor trans-
`port during diurnal breathing conditions, by reducing the
`cussed above, are also envisioned to be within the scope of
`vapor concentration difference across the flow length of the 35
`the subject of the invention.
`canister system by enhanced regeneration, the redistribution
`of vapors within the canister system and subsequent emis-
`The desired results for the subject matter of the invention
`sions into the vent-side volume and out of the vent port are
`can be attained with a single vent-side uniform lower
`reduced.
`capacity adsorbent material as the subsequent adsorbent
`Examples of adsorbents with isotherms having the pre- 40 material. The option of multiples of lower capacity adsor-
`ferred shape to provide low bleed performance are compared
`bents with the desirable adsorptive properties across broad
`with standard canister-fill carbons (Westvaco Corporation's
`vapor concentrations is demonstrated merely as one embodi-
`BAX 1100 and BAX 1500) in FIG. 3. It is important to note
`ment.
`that, as shown in this figure, the isotherm properties must be
`The measures for gasoline working capacity (GWC) and
`defined in terms of volumetric capacity. On this basis, the 45 emissions in the Table were derived from the Westvaco DBL
`preferred low-bleed adsorbent portion will have an incre-
`test that uses a 2.1 L canister. The pellet examples were
`tested as a 300 mL vent-side layer within the canister, with
`mental n-butane capacity of less than about 35 g/liter
`between 5 and 50 volume percent n-butane vapor concen-
`the 1800 mL of BAX 1500 pellets as the remaining canister
`tration.
`fill. The honeycomb was tested as an auxiliary bed canister
`While in some instances, known adsorbents may have the 50 that was placed in-line with the 2.1 L main canister of BAX
`preferred properties for the vent-side, these adsorbents
`1500 pellets. For all examples, the canister system was
`would not be expected to be useful in an evaporative
`uniformly first preconditioned by repetitive cycling of gaso-
`line vapor adsorption and air purge (400 bed volumes air).
`canister. In some cases, these materials have low purgeabil-
`This cycling generated the GWC value. Butane emissions
`ity (butane ratio less than 0.85) and low working capacity
`were subsequently measured after a butane adsorption and
`(BWC less than 9 g/dL) as measured by the standard BWC 55 an air purge step, specifically during a diurnal breathing loss
`test for qualifying canister carbons. Common wisdom and
`period when the canister system was attached to a
`temperature-cycled fuel tank. The reported value is the znt1
`experience in the art associate low butane ratio with high
`residual hydrocarbon heel, which is the potential source for
`day DBL emissions during an 11-hour period when the fuel
`high emissions. Furthermore, low BWC adsorbents were not
`tank was wanned and vapor-laden air was vented to the
`considered useful for inclusion into a canister system as 60 canister system and exhausted from the vent-side adsorbent
`working capacity for gasoline vapors would be assumed
`where the emissions were measured. The procedure
`impaired, with no expectation that there would be a utility
`employed for measuring DBL emissions has been described
`forreducingemissions.Infact,onepreferredembodimentof
`in SAE Technical Paper 2001-01-0733, titled "Impact and
`Control of Canister Bleed Emissions," by R. S. Williams and
`this invention, lower capacity adsorbents have BWC values
`preferably below 8 g/dL, whic