IN THE UNITED STATES PATENT AND TRADEMARK OFFICE Acting as International Receiving Office (RO/US)

International Patent Application for

METHOD FOR REDUCING EMISSIONS FROM EVAPORATIVE EMISSIONS CONTROL SYSTEMS

This non-provisional application relies on the filing date of provisional U.S. Application Serial No. 60/985,752 filed on November 6, 2007 having been filed within twelve (12) months thereof, and priority thereto is claimed under 35 USC § 1.19(e).

BACKGROUND OF THE DISCLOSURE

1. Field of the Invention

[0001] This invention relates to a hydrocarbon emissions scrubber, and to using the scrubber to remove volatile organic compounds, and other chemical agents from fluid streams. More particularly, this invention relates to using the 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

[0002] 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 components 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. Patent 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.

[0003] A typical canister employed in a state of the art auto emission control system is shown in Figure 1. Canister 1 includes support screen 2, dividing wall 3, a vent port 4 to the atmosphere (the location of the purge inlet for the canister), a vapor source connection 5 (from the fuel tank), a vacuum purge connection 6 (the location of the purge outlet for when the engine is running), and adsorbent material fill 7 in the purge inlet volume 8 and in the purge outlet volume 9. Other basic auto emission control system canisters are disclosed in U. S. Patent Nos.: 5,456,236; 5,456,237; 5,460,136; and 5,477,836. It is common to design the purge inlet volume 8 such that its cross-sectional area is substantially less than that of volume 9 in order to enhance the local removal of adsorbed vapors during purge at the purge inlet by increasing the local purge flow per unit length of flow path, and thereby reduce the adsorbent's local equilibrium vapor pressure for fuel after purge and retard the breakthrough of the mass transfer zone. As a result, the canister has greater working capacity and emits fewer vapors out its vent from diffusional and convective processes during and between uses of the vehicle.

(b) Diurnal Breathing Loss (DBL) Requirements

[0004] 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 hydrocarbon 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 California 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.)

[0005] 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 operation. U.S. RE38,844 teaches the means for sharply reducing diurnal breathing loss emissions from evaporative emissions canisters by the use of multiple layers, or stages, of adsorbents in-series with the vapor flow path. On the fuel source-side of the canister, standard high working capacity carbons are preferred. On the vent-side, the preferred adsorbent volume has a flat or flattened adsorbent isotherm on a volumetric basis, specifically relatively low incremental capacity at high concentration vapors compared with the fuel source-side adsorbent volume. For example, the adsorbent fills in volumes 8 and 9 in Figure 1 might further comprise of materials with different adsorptive properties, particularly placing adsorbent with flattened vapor adsorption isotherm slope in the vent-side volume 8. Figure 2 shows an emission control system 21 with a bleed emission adsorbent scrubber 22 in auxiliary canister 23. In order to avoid excessive flow restriction for vapor flow, such as during a refueling operation for an on-board refueling vapor recovery control system when vapor loading is high volume and rapid, the adsorbent scrubber 22 might be an activated carbon monolith, such as a honeycomb, with a flattened adsorption isotherm slope and a large open area of channels relative to wall material with low resistance to bulk fluid flow between vent port 4 and the main canister volume 8. Substantially lower emissions are attained from the canister systems without a significant loss in working capacity or an increase in flow restriction, as taught in U.S. RE38,844, compared with prior art adsorbents used for automotive emissions control.

[0006] Although the adsorbents-in-series as taught in U.S. RE38,844 are effective for substantial reductions in bleed emissions for typical vehicle designs and engine operation,

recent designs of vehicle engines for improved fuel efficiency, including combination hybrid electric/combustion engine drive trains and engines where multiple cylinders idle during operation, do not achieve comparable reductions in emissions in some instances even with adsorbents-in-series in the evaporative emission control system. These engine designs do not provide enough volume of purge during carbon regeneration in order to sufficiently reduce the amount or alter the distribution of residual hydrocarbon heel in the carbon bed for the needed low levels of emissions during subsequent diurnal breathing conditions. A conventional vehicle engine design might provide over 400 liters of total purge volume per liter of evaporative emission canister carbon volume compared with less than 100 liters of purge per liter carbon volume available with newer engine designs and newer engine operation.

[0007] One option for increasing the purge of adsorbed fuel vapors from evaporative emission control carbon is suggested by the teachings of U. S. Patent Nos. 5,981,930, 6,230,693, 6,279,548, 6,769,415, and 6,896,852 by providing a heating capability internal of the canister, or a section thereof, to increase the purging efficiency of hydrocarbons from the heated adsorbent material and carry the purged fuel vapor to the induction system of an associated engine. However, these prior inventions are lacking in a number of aspects.

[0008] The heated aggregate carbon in U.S. 5,981,930 is subject to uneven heating due to random surface contact points. In addition, aggregate carbon in the vent-side chamber or an auxiliary chamber are particularly subject to nonuniform packing of particulate from wall effects, especially from the use of larger than normal particulate for mitigating flow restriction in a typical vent-side or auxiliary chamber with a constricted cross-sectional area. Such a situation has the effect of exaggerating uneven heating from fewer contact points between particles and especially near the walls of the chamber. Therefore, electrically heated aggregate material is wholly unsuitable for use in bleed control in the vent-side or auxiliary chamber of typical design to factors because of non-uniformity of heating and vapor flow across the chamber cross-section.

[0009] The ceramic heaters, resistive wires, and heat sinks in U.S. 6,230,693, 6,279,548, 6,769,415 and 6,896,852 are added components to the emissions control device and provide an added complexity to the design, fabrication, and operation of the system, as

well as consume space and heat input intended for the adsorbent. In some cases the adsorbent is bound to the heater or heat sink component in an attempt to apply the heat as directly to the adsorbent as possible. As taught in U.S. 6,896,852, the bleed control device is an electrically conductive or semi-conductive substrate material that is coated or associated with the carbon that is presumably nonconductive. However, for strength and thermal shock resistance, the commonly used ceramic and cordierite-based binders and substrate used in making adsorbent honeycombs are typically electrically insulating, as described in U.S. 5,914,294 and 6,097,011. Furthermore, the concept of coating a substrate with adsorbent or an adsorbent precursor is undesirable due to the added complexity of the forming process and added unit operations, such as in the case of first making a substrate, then applying a coating, and possibly activating the coating at elevated temperatures if the coating contains an adsorbent precursor, such as a resin that must be converted into activated carbon.

[0010] A heatable carbon honeycomb monolith with conductive carbon described in U.S. 6,097,011 alludes to the use in a wide variety of applications for which activated carbons have been used in the past for adsorbing a component or components from a fluid stream, including the speculated application for automotive gas tank emissions. However, the proposed use of carbon honeycombs for gas tank emissions since the filing of U.S. 6,097,011, particularly for attaining exceedingly low emissions for vehicles with low amounts of purge available, is in combination with a conventional evaporative emissions canister system and not as a generic standalone device, as the inventors described for a cabin air filter. The patent disclosure provides examples of activated carbon coatings, applied on electrically insulating ceramic substrates and heated by current flow, but does not demonstrate or speculate beyond the known capability of heating activated carbon for enhanced desorption, such as now proposed in the invention disclosed and claimed herein for the use of conductive carbon honeycombs in combination with existing evaporative emission control canisters with new vehicle engine designs for meeting PZEV emissions regulations.

[0011] Thus, an acceptable solution, which does not have the drawbacks of the cited alternative approaches, is greatly desired. It is submitted that the invention disclosed and claimed herein provides such solution.

SUMMARY OF THE DISCLOSURE

[0012] An invention is disclosed for sharply reducing diurnal breathing loss emissions from evaporative emissions canisters by the use of resistively heated, adsorbent honeycomb and monolith scrubbers on the atmosphere vent of the canister. The resistivity of the scrubber is controlled by the resistivity of the adsorbent and the presence of electrically conductive, nonbinding additives. The resistivity of the scrubber is in a resistivity range where typically available electrical wattage in a vehicle for heating the scrubber is sufficient to cleanse the scrubber without overheating and thereby affects a substantial reduction in diurnal breathing loss emissions from the evaporative emissions control system.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 is a sectional view of a conventional evaporative emission control canister.

[0014] Figure 2 is a sectional view of a conventional evaporative emission control system with an auxiliary chamber containing a bleed emission scrubber for low bleed emissions under diurnal cycling conditions.

[0015] Figure 3 is a sectional view of an evaporative emission control system according to the present disclosure with provisions for heating of an auxiliary monolith containing conductive carbon and conductivity additives for low bleed emissions under diurnal cycling conditions for vehicles providing limited purge volumes for vapor recovery.

[0016] Figure 4 is a sectional view of an evaporative emission control system according to the present disclosure with provisions for heating specific volumes of an auxiliary monolith containing conductive carbon and conductivity additives by having formed grooves or notches into the external surface of the monolith.

DESCRIPTION OF THE DISCLOSURE

[0017] The disclosed disclosure relates to the use of multiple stages or chambers of electrically heatable adsorbent monoliths or honeycombs, which, in combination with conventional evaporative emission control canisters, significantly reduces DBL emissions under low purge flow conditions while maintaining the high working capacity and low flow restriction properties of the canister system. (See Figure 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. In shaping, inorganic and/or organic binders may be used. The adsorbents are preferably formed into a monolith or honeycomb shape to provide a "part" for the canister. The shaped adsorbents may be incorporated into a canister as one or more separate chambers, or they may be inserted in the fluid stream flow as auxiliary canister beds. Nonbinding electrical conductivity additives, including metals, polymers, carbon black, and graphite materials, may be added for a dual role of adjusting the adsorption properties to flatten the equilibrium isotherm slope, plus obtaining resistivity within the desired range. The adsorbent material in the monolith may itself have the desired electrical conductivity for attaining the desired resistivity for making the monolith or honeycomb heatable under typically available electrical wattages in vehicles. In the context of the disclosure, "monolith" is intended to include foams, woven and non-woven fibers, papers, mats, blocks and bound aggregates of particulates. Flow channels in the monolith may be designed as parallel with the vapor flow path, may be randomly interconnected passages for a randomly oriented tortuous path, and may be designed with a symmetrical tortuosity.

[0018] A preferred embodiment for a canister with multiple adsorbents is shown in Figure 3. The vapor flow path has an emission control system canister 31 in-line with an auxiliary canister 33 containing a bleed emission adsorbent scrubber 32 with desirable resistivity properties. In order to avoid excessive flow restriction for vapor flow, such as during a refueling operation for an on-board refueling vapor recovery control system when vapor loading is high volume and rapid, the adsorbent scrubber 32 might be an activated carbon honeycomb with moderate electrical resistivity and a large open area with low resistance to bulk fluid flow. Electrical leads 34 are attached to conductive contacts, such as metal bands on the scrubber external surface 35, for applying electrical current for heating the scrubber before and/or during purge for enhanced vapor removal from the scrubber and from the adsorbent downstream in the purge flow vapor path. The monolith may be of any cross sectional shape, including square, rectangular, oval, and circular. The location and attachment of the electrical leads 34 may be at opposite axial ends of the monolith for current to pass across its length, as shown in Figure 3, or the contacts points may be at alternative positions along the monolith length for current flow at less than the full length, parallel to fluid flow. Alternatively, the monolith may have the electrical contacts positioned for the

electrical current to pass perpendicular to fluid flow. Notches and slits in the monolith made parallel or perpendicular to fluid flow may be employed to preferentially direct the electrical current for more intense heating and for more uniform heating at certain portions of the monolith, such as at the section of the monolith first receiving clean purge air from vent port 4. Figure 4 shows the evaporative emission control canister system with a circumferential notch 36 made perpendicular to the fluid flow. Additional embodiments, as discussed above, are also envisioned to be within the scope of the subject of the disclosure.

[0019] The benefits of the disclosed disclosure were initially recognized by testing conventional bleed control carbon honeycombs and demonstrating the heating of alternative carbon honeycombs by applying DC voltages across their length and cross-section. The measures for gasoline working capacity (GWC) and emissions were derived from the Westvaco DBL test that uses a 2. IL canister. The honeycombs were tested as an auxiliary bed canister that was placed in-line with the 2. IL main canister of BAX 1500 pellets. For all examples, the canister system was uniformly preconditioned by repetitive cycling of gasoline vapor adsorption and air purge (400 bed volumes air) desorption. This cycling generated the GWC value. Butane emissions were subsequently measured after a butane adsorption step that was followed by 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 bleed emissions value is the 2 ^nd 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. This 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.

[0020] The effect of heating the honeycomb was determined by applying an electrical current through the carbon honeycomb during every purge step. The effect of the volume of purge was measured by only adjusting the air flow rate during the final purge step prior to the diurnal breathing loss period.

Effect of Conductive Carbon Honeycomb.

[0021 ] This example shows that dramatic reductions in bleed emissions are obtained by heating an electrically conductive carbon honeycomb in combination with a conventional

evaporative emission canister containing pelletized carbon, to levels not otherwise attainable even by substantial increases in the amount of purge volume. Cylindrically shaped honeycombs with 200 cells per square inch (cpsi) cell density were prepared according to the method described in U.S. Patent No. 5,914,294, which discloses 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 matrix. The extrudable mixture is capable of maintaining the shape of the monolith after extrusion and during drying of the monolith.

[0022] 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, as described in U.S. Patent No. RE38,844. 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 23 in Figure 2). Electrical current was applied by adhering wire contacts to bands of copper tape wrapped around opposing ends of the honeycomb (see honeycomb 32 in supplemental canister body 33 with wires 34 in Figure 3). The copper tape was bonded to the honeycomb surface with adhesive of high electrical conductivity.

TABLE I

[0023] Table I shows the working capacity and bleed emission data for 1" diameter x 4" long honeycombs made with conventional nonconductive activated carbon (>1000 ohm resistance, >2000 ohm-cm resistivity, Comparative Example Cl) as compared with a conductive activated carbon example of this disclosure (3.4 ohm resistance, 6.8 ohm-cm resistivity, Example 1). Data are also shown for the evaporative emission canister operated through cycling and bleed emissions testing without a carbon honeycomb attached to its vent- side chamber. In both honeycomb examples at 150 v/v purge before the diurnal step, the addition of the honeycomb greatly reduced the bleed emissions of the pelletized carbon canister/carbon honeycomb evaporative emission system compared with the pelletized carbon

canister alone. The similar reduction in emissions is expected for the similar incremental butane adsorption capacity properties of the honeycombs, as taught in the prior art patent U.S. RE34,844. Working capacity was slightly increased in both cases of adding the honeycomb.

[0024] A conventional means for lowering the amount of bleed emissions is by vastly increasing the amount of purge, as shown in Table I for 400 v/v purge, rather than 150 v/v purge, before diurnal testing. Bleed emissions were reduced by almost one-half, to 7-8 mg, by increasing the purge from 150 v/v to 400 v/v for the evaporative emission control system equipped with Example 1 honeycomb and Comparative Example Cl honeycomb. However, such an increase in purge is not practical for many engine designs and air/fuel management systems. Yet, with the use of a bleed emission control honeycomb containing electrically conductive carbon, an even lower level of emissions was demonstrated at the normal level of purge from the application of an electrical current to through the honeycomb during purge. In Table I, a power input of 42 watts enabled the conductive Example 1 honeycomb to attain 3 mg of bleed emissions at the normal 150 v/v purge, which is greater than a 75% reduction in emissions compared with operating the emission control system without current flowing through the electrically conductive carbon honeycomb. Such an improvement in emissions was not possible with the nonconductive Comparative Example Cl honeycomb due to its excessively high resistivity (>2000 ohm/cm) that did not allow a useful current to flow through the honeycomb. A method of qualifying the heating capability of the conductive carbon honeycomb is to have a moderate current pass through the device with the application of a 12 volt electrical potential to an adsorbate-free honeycomb and to measure the temperature of exhaust air when an inlet flow of 22.7 liters/min air at 77°F (25°C) is passed through the device, equivalent to the purge rate for a 400 v/v purge in a standard GWC test. A nonconductive honeycomb, Example Cl, has an exhaust temperature about equal to the inlet temperature for <0.1 watts of power resulting from an applied 12 VDC potential across its leads. By comparison, a conductive honeycomb has an exhaust flow heated to well above the inlet air flow temperature: exhaust flow temperature of 230 ⁰ F for Example 1 for 42 watts from the equivalent applied 12 VDC electrical potential.

TABLE II

[0025] Example 2: Table II shows the working capacity and bleed emissions data for 29 mm diameter x 100 mm long honeycombs made with conductive activated carbon example of this disclosure (3.4 ohm resistance, 6.8 ohm-cm resistivity, 190 ⁰ F exhaust temperature for 12 volts and 1.4-1.6 amperes current at 22.7 liters/min air flow, Example 2 honeycomb). Data are also shown for the evaporative emission canister operated through cycling and bleed emissions testing without a carbon honeycomb attached to its vent-side chamber. Without electrical current passing through the honeycomb during the final purge

cycle, the bleed emissions under the standard conditions are 16 mg, and the emissions were sharply increased to 95 mg under reduced purge volume of 100 v/v. At 75 v/v final purge, the bleed emissions with the conventional honeycomb are 411 mg, which far exceed the 212 mg level obtained at 150 v/v without a carbon honeycomb attached. However, by application of a modest electrical current through the honeycomb during the 100 v/v purge the bleed emissions were reduced to 20 mg, which is within the range otherwise obtained at the higher, 150 v/v purge with the conventional honeycomb without electrical current. Some reductions in emissions are obtained at 75 v/v purge by the same electrical current to below the 212 mg emissions level otherwise obtained for a conventional canister at 150 v/v purge without a carbon honeycomb.

[0026] Example 3: Extremely low emissions of 4 mg are obtained at 75 v/v purge by an increased heating wattage to the honeycomb and by having formed a circumferential notch 8 mm deep into the skin of the honeycomb, 8 mm from the vent-side end (3.2 ohm resistance, 4.8 ohm-cm resistivity, 250 ⁰ F exhaust temperature for 12 volts and 4.8 amperes current at 22.7 liters/min air flow Example 3). The construction of the honeycomb is of the type shown in Figure 4. In the embodiment of Figure 4, the electrical contacts 35 are positioned as bands around the circumferential surface of the honeycomb on opposite sides of the notch 36 in order to focus the current across a select volume of the conductive carbon honeycomb. An added advantage of a discontinuity in the electrical current flow at the surface of the carbon honeycomb, as embodied by the circumferential notch, is to limit the temperature rise at the exterior surface and prevent an excessively hot outer skin in contact with the auxiliary canister casing 33 in Figure 4.

[0027] The foregoing description relates to embodiments of the present disclosure, and changes and modifications may be made therein without departing from the scope of the disclosure as defined in the following claims.