Evaporative Fuel Vapor Emission Control Systems

Abstract

The present application relates to an evaporative fuel vapor emission control system. An evaporative emission control canister system includes an initial adsorbent volume having an effective incremental adsorption capacity at 25°C of greater than 35 grams of n-butane / L between vapor concentrations of 5 vol% to 50 vol% n-butane, and at least one subsequent adsorbent volume having an effective incremental adsorption capacity at 25°C of less than 35 grams of n-butane / L between vapor concentrations of 5 vol% to 50 vol% n-butane, an effective butane working capacity (BWC) of less than 3 g / dL, and a g-total BWC of between 2 grams and 6 grams. The evaporative emission control canister system has a two-day diurnal breathing loss (DBL) emission of no more than 20 mg at no more than 210 liters of purge applied after a 40 g / hr butane loading step.

Description

Technical Field

[0001] The present disclosure, in various embodiments, generally relates to evaporative emission control systems. More specifically, the present disclosure relates to evaporative fuel vapor emission control systems. This application is a divisional application of a patent application with application number 201380064567.9, filed on October 10, 2013, and entitled “Evaporative Fuel Vapor Emission Control System” and a patent application with application number 201711042983.5, filed on October 10, 2013, and entitled “Evaporative Fuel Vapor Emission Control System”. Background Art

[0002] The evaporation of gasoline fuel from a motor vehicle fuel system is a major potential source of hydrocarbon air pollution. Such emissions can be controlled by a canister system that uses activated carbon to adsorb fuel vapors exhausted from the fuel system. In certain modes of engine operation, the adsorbed fuel vapors are periodically removed from the activated carbon by purging the canister system with ambient air to desorb the fuel vapors from the activated carbon. The regenerated carbon is then ready to adsorb additional fuel vapors.

[0003] Increased environmental concerns continue to drive stringent regulations on hydrocarbon emissions from motor vehicles, even when the vehicle is not running. When a vehicle is parked in a warm environment during daytime heating (i.e., daytime heating), the temperature in the fuel tank increases, resulting in an increase in vapor pressure in the fuel tank. Typically, in order to prevent fuel vapor from leaking from the vehicle into the atmosphere, the fuel tank is discharged through a conduit to a canister containing a suitable fuel adsorbent material that can temporarily adsorb fuel vapor. Fuel vapor from the fuel tank enters the canister through the fuel vapor inlet of the canister and diffuses into the adsorbent volume, where it is adsorbed in a temporary reservoir before being released to the atmosphere through the discharge port of the canister. Once the engine is started, ambient air is drawn into the canister system through the discharge port of the canister. Purge air flows through the adsorbent volume in the canister and desorbs the fuel vapor adsorbed on the adsorbent volume before entering the internal combustion engine through the fuel vapor purge conduit. The purge air does not desorb all of the fuel vapor adsorbed on the adsorbent volume, resulting in residual hydrocarbons ("heel") that can be discharged to the atmosphere. In addition, this local equilibrium of the exhaust gas with the gas phase also allows fuel vapor to migrate from the fuel tank through the canister system as an emission. Such emissions typically occur when the vehicle is parked and subjected to daytime temperature changes over a period of several days, and are generally referred to as "diurnal breathing losses". The California Low Emission Vehicle regulations make it desirable that these diurnal breathing loss (DBL) emissions from the canister system be below 10 mg for a certain number of vehicles starting with the 2003 model year ("PZEV"), and below 50 mg for a larger number of vehicles starting with the 2004 model year, typically below 20 mg ("LEV-II"). Now, the California Low Emission Vehicle regulations (LEV-III) require that canister DBL emissions not exceed 20 mg by the Exhaust Emissions Test Procedure (BETP), as written in the California Evaporative Emissions Standards and Test Procedures for 2001 and Later Model Motor Vehicles, dated March 22, 2012.

[0004] Several approaches have been reported to reduce diurnal breathing loss (DBL) emissions. One approach is to significantly increase the volume of the purge gas to increase the desorption of the remaining hydrocarbon tail gas from the adsorbent volume. However, this approach has the disadvantage of complex management of the fuel / air mixture to the engine during the purge step and tends to adversely affect tailpipe emissions. See U.S. Patent No. 4,894,072.

[0005] Another approach is to design a tank with a relatively small cross-sectional area on the discharge side of the tank, either by resizing the existing tank or by installing an appropriately sized auxiliary discharge side tank. This approach reduces the residual hydrocarbon tail gas by increasing the strength of the purge air. One drawback of such an approach is that the relatively small cross-sectional area imparts too much flow restriction to the tank. See U.S. Patent No. 5,957,114.

[0006] Another approach for improving the purge efficiency is to heat the purge air, or a portion of the adsorbent volume with adsorbed fuel vapor, or both. However, this approach increases the complexity of control system management and raises some safety issues. See U.S. Patents 6,098,601 and 6,279,548.

[0007] Another approach is to send fuel vapor through an initial adsorbent volume and then through at least one subsequent adsorbent volume before exhausting to the atmosphere, wherein the initial adsorbent volume has a higher adsorption capacity than the subsequent adsorbent volumes. See US Pat. No. RE38,844.

[0008] Regulation of daytime breathing loss (DBL) emissions continues to drive new developments of improved evaporative exhaust control systems, especially when the level of purge air is low. In addition, daytime breathing loss (DBL) emissions may be more severe for hybrid vehicles that include both an internal combustion engine and an electric motor. In such hybrid vehicles, the internal combustion engine is off for almost half of the time during vehicle operation. Since the adsorbed fuel vapor on the adsorbent is only purged when the internal combustion engine is started, the adsorbent in the canister of a hybrid vehicle is purged with fresh air less than half of the time compared to a conventional vehicle. A hybrid vehicle generates almost the same amount of evaporated fuel vapor as a conventional vehicle. The lower purge frequency of a hybrid vehicle may not be sufficient to clear residual hydrocarbon tail gas from the adsorbent in the canister, resulting in high daytime breathing loss (DBL) emissions.

[0009] Therefore, it is desirable to have an evaporative emission control system that has low diurnal breathing loss (DBL) emissions even when low levels of purge air are used, or when the adsorbent in the canister is purged less frequently (such as in the case of a hybrid vehicle), or both. Although passive approaches are highly desirable, existing passive approaches still leave DBL emissions at levels that are many times the 20 mg LEV-III requirement when only a fraction of the purges that were historically available are now available. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 is a cross-sectional view of an evaporative emission control canister system according to one embodiment of the present disclosure, wherein the canister system has a canister;

[0011] Figure 2 is a cross-sectional view of an evaporative emission control canister system according to one embodiment of the present disclosure, wherein the canister system has a canister;

[0012] Figure 3 is a cross-sectional view of an evaporative emission control canister system according to one embodiment of the present disclosure, wherein the canister system has a canister;

[0013] Figure 4 is a cross-sectional view of an evaporative emission control canister system according to one embodiment of the present disclosure, wherein the canister system has a main canister and an auxiliary canister;

[0014] Figure 5 is a cross-sectional view of an evaporative emission control canister system according to one embodiment of the present disclosure, wherein the canister system has a main canister and an auxiliary canister;

[0015] Figure 6 is a cross-sectional view of an evaporative emission control canister system according to one embodiment of the present disclosure, wherein the canister system has a main canister and an auxiliary canister;

[0016] Figure 7 is a cross-sectional view of an evaporative emission control canister system according to one embodiment of the present disclosure, wherein the canister system has a main canister and an auxiliary canister;

[0017] Figure 8 is a simplified schematic diagram of an apparatus for determining butane adsorption capacity; and

[0018] Figure 9-22 is a simplified schematic diagram of an evaporative emission control canister system according to some non-limiting embodiments of the present disclosure. DETAILED DESCRIPTION

[0019] The present disclosure will now be described more fully below, but not all embodiments of the present disclosure are shown. Although the present disclosure has been described with reference to exemplary embodiments, it will be appreciated by those skilled in the art that various variations may be made, and equivalents may be substituted for elements thereof, without departing from the scope of the present disclosure. In addition, many modifications may be made to accommodate specific structures or materials taught by the present disclosure without departing from its basic scope.

[0020] The drawings of the present application are for exemplary purposes only. They are not intended to limit the embodiments of the present application. In addition, the drawings are not drawn to scale. Common elements between the drawings may retain the same numerical designations.

[0021] In a particular embodiment, the evaporative emission control canister system includes one or more canisters. The evaporative emission control canister system includes an initial adsorbent volume having an effective incremental adsorption capacity at 25°C of greater than 35 grams of n-butane / L between vapor concentrations of 5 vol% to 50 vol% n-butane; and at least one subsequent adsorbent volume having an effective incremental adsorption capacity at 25°C of less than 35 grams of n-butane / L between vapor concentrations of 5 vol% to 50 vol% n-butane, an effective butane working capacity (BWC) of less than 3 g / dL, and a g-total BWC between 2 grams and 6 grams. The initial adsorbent volume and at least one subsequent adsorbent volume are located within a single canister, or the initial adsorbent volume and at least one subsequent adsorbent volume are located in separate canisters connected to allow continuous contact by fuel vapor. The evaporative emission control canister system has a two-day diurnal breathing loss (DBL) emission of no more than 20 mg at a purge of no more than about 210 liters applied after a butane loading step of 40 g / hr.

[0022] Fig.13 Non-limiting examples of some embodiments of evaporative emission control canister systems are shown where an initial adsorbent volume and subsequent adsorbent volume(s) are located within a single canister. Figure 4-7 A non-limiting example of an embodiment of an evaporative emission control canister system comprising more than one canister is shown, wherein an initial adsorbent volume and at least one subsequent adsorbent volume are located in separate canisters connected to permit sequential contact by fuel vapor.

[0023] Figure 1 One embodiment of an evaporative emission control canister system is shown with an initial adsorbent volume and a subsequent adsorbent volume within a single canister. The canister system 100 includes a support screen 102, a dividing wall 103, a fuel vapor inlet 104 from a fuel tank, an exhaust port 105 to atmosphere, a purge outlet 106 to the engine, an initial adsorbent volume 201, and a subsequent adsorbent volume 202.

[0024] When the engine is shut down, fuel vapor from the fuel tank enters the canister system 100 through the fuel vapor inlet 104. The fuel vapor diffuses into the initial adsorbent volume 201, and then diffuses into the subsequent adsorbent volume 202 before being released to the atmosphere through the exhaust port 105 of the canister system. Once the engine is started, ambient air is drawn into the canister system 100 through the exhaust port 105. The purge air flows through the subsequent adsorbent volume 202, and then flows through the initial adsorbent volume 201, and desorbs the fuel vapor adsorbed on the adsorbent volumes 202, 201 before entering the internal combustion engine through the purge outlet 106.

[0025] The evaporative emission control canister system may include more than one subsequent adsorbent volume. By way of non-limiting example, the evaporative emission control canister system 100 may include an initial adsorbent volume 201 and three subsequent adsorbent volumes 202, 203, 204 within a single canister, such as Figure 2 as shown in .

[0026] Additionally, the evaporative emission control canister system may include a void volume within the canister. As used herein, the term "void volume" refers to a volume that does not include any adsorbent. Such volume may include any non-adsorbent, including but not limited to voids, foam insulation, screens, or combinations thereof. Figure 3 In the non-limiting example shown in , the evaporative emission control canister system 100 may include an initial adsorbent volume 201 ; three subsequent adsorbent volumes 202 , 203 , 204 within a single canister; and a void volume 205 between the subsequent adsorbent volumes 203 and 204 .

[0027] By way of non-limiting example, Figure 4-7 An embodiment of an evaporative emission control canister system is shown, wherein the canister system includes more than one canister. Figure 4 As shown in , the canister system 100 includes a main canister 101, a supporting screen 102, a dividing wall 103, a fuel vapor inlet 104 from a fuel tank, an exhaust port 105 to the atmosphere, a purge outlet 106 to the engine, an initial adsorbent volume 201 in the main canister 101, subsequent adsorbent volumes 202, 203, 204 in the main canister 101, an auxiliary canister 300 including a subsequent adsorbent volume 301, and a conduit 107 connecting the main canister 101 to the auxiliary canister 300.

[0028] When the engine is shut down, fuel vapor from the fuel tank enters the canister system 100 through the fuel vapor inlet 104 into the main canister 101. The fuel vapor diffuses through the initial adsorbent volume 201, and then diffuses through subsequent adsorbent volumes (202, 203, and 204) in the main canister 101 before entering the auxiliary canister 300 via conduit 107. The fuel vapor diffuses through subsequent adsorbent volumes 301 within the auxiliary canister 300 before being released to the atmosphere through the exhaust port 105 of the canister system. Once the engine is started, ambient air is drawn into the canister system 100 through the exhaust port 105. The purge air flows through the subsequent adsorbent volume 301 in the auxiliary canister 300, the subsequent adsorbent volumes (204, 203, 202) in the main canister 101, and then flows through the initial adsorbent volume 201 in the main canister 101 to desorb fuel vapor adsorbed on the adsorbent volumes (301, 204, 203, 202, 201) before entering the internal combustion engine through the purge outlet 106.

[0029] Similar to the main canister, the auxiliary canister of the evaporative emission control canister system may include more than one subsequent adsorbent volume. By way of non-limiting example, the auxiliary canister 300 of the evaporative emission control canister system 100 may include subsequent adsorbent volumes 301 and 302, such as Figure 5 as shown in .

[0030] Additionally, the auxiliary canister of the evaporative emission control canister system may include empty volumes between subsequent adsorbent volumes. By way of non-limiting example, Figure 6 As shown in FIG. 1 , the auxiliary canister 300 of the evaporative emission control canister system 100 may include subsequent adsorbent volumes ( 301 , 302 , and 303 ), and an empty volume 304 between the subsequent adsorbent volumes 302 and 303 . Figure 7 In the non-limiting example shown in , the auxiliary canister 300 of the evaporative emission control canister system 100 may include subsequent adsorbent volumes (301, 302, 303), an empty volume 304 between the subsequent adsorbent volumes 301 and 302, and an empty volume 305 between the subsequent adsorbent volumes 302 and 303. As previously described, the term "empty volume" refers to a volume that does not include any adsorbent. Such volumes may include any non-adsorbent, including but not limited to voids, foam insulation, screens, conduits, or combinations thereof.

[0031] Additionally, the evaporative emission control canister system may include a void volume between the main canister and the auxiliary canister.

[0032] When desired, the evaporative emission control canister system may include more than one auxiliary canister. The evaporative emission control canister system may also include one or more empty volumes between the main canister and the first auxiliary canister, between the auxiliary canisters, and / or at the end of the last auxiliary canister. By way of non-limiting example, the evaporative emission control canister system may include a main canister, a first auxiliary canister, a second auxiliary canister, a third auxiliary canister, an empty volume between the main canister and the first auxiliary canister, an empty volume between the first auxiliary canister and the second auxiliary canister, and an empty volume at the end of the third auxiliary canister.

[0033] As mentioned above, Figure 1-7 Only exemplary embodiments of the evaporative emission control canister system are disclosed, and additional embodiments may be devised by those skilled in the art without departing from the scope of the present disclosure.

[0034] When desired, the total adsorbent volume (ie, the sum of the initial adsorbent volume and the subsequent adsorbent volume) may be the same as the volume of the evaporative emission control canister system. Alternatively, the total adsorbent volume may be less than the volume of the evaporative emission control canister system.

[0035] In a particular embodiment, a method of reducing fuel vapor emissions in an evaporative emission control system includes contacting fuel vapor with an initial adsorbent volume having an effective incremental adsorption capacity at 25°C of greater than 35 grams of n-butane / L between vapor concentrations of 5 vol% to 50 vol% n-butane, and contacting at least one subsequent adsorbent volume having an effective incremental adsorption capacity at 25°C of less than 35 grams of n-butane / L between vapor concentrations of 5 vol% to 50 vol% n-butane, an effective butane working capacity (BWC) of less than 3 g / dL, and a g-total BWC between 2 grams and 6 grams. The initial adsorbent volume and at least one subsequent adsorbent volume are located within a single canister, or the initial adsorbent volume and at least one subsequent adsorbent volume are located in separate canisters connected to allow for continuous contact by fuel vapor. The method of reducing fuel vapor emissions has a two-day diurnal breathing loss (DBL) emission of no more than 20 mg at no more than about 210 liters of purge applied after a 40 g / hr butane loading step.

[0036] As used herein, the term "adsorbent component" or "adsorbent volume" refers to the adsorbent material or material containing the adsorbent along the vapor flow path, and may consist of a bed of particulate material, monolith, honeycomb, sheet, or other material.

[0037] As used herein, the term "nominal volume" refers to the sum of the volumes of the adsorbent components and does not include the volume of gaps, voids, tubes, ducts, pipes, chamber spaces, or other volumes of adsorbent material along the length of the vapor flow path that do not span a plane perpendicular to the vapor flow path. Figure 1 , the total nominal volume of the canister system is the sum of the volumes of adsorbent volumes 201 and 202. For example, in Figure 2 and 3 , the total nominal volume of the canister system is the sum of the volumes of adsorbent volumes 201, 202, 203, and 204. Figure 4 The total nominal volume of the tank system is the sum of the volumes of adsorbent volumes 201, 202, 203, 204, and 301. Figure 5 In, the total nominal volume of the tank system is the sum of the volumes of adsorbent volumes 201, 202, 203, 204, 301 and 302. Figure 6 and 7 , the total nominal volume of the tank system is the sum of the volumes of adsorbent volumes 201 , 202 , 203 , 204 , 301 , 302 and 303 .

[0038] Determination of nominal volume apparent density

[0039] As used herein, the term "nominal volume apparent density" is the mass of a typical adsorbent in an adsorbent volume divided by the nominal volume of the adsorbent, where the length of the volume is defined as the in situ distance within the canister system between a vertical plane of the vapor flow path that initially contacts the adsorbent component and a vertical plane of the vapor flow path that leaves the adsorbent component.

[0040] Described herein are non-limiting examples of how to calculate the nominal bulk apparent density of various forms of adsorbents.

[0041] (A) Granular, pelletized or spherical adsorbents having uniform adsorption capacity across the length of the adsorbent component flow path. Adjuncts

[0042] Standard method ASTM D 2854 (hereinafter "Standard Method") can be used to determine the nominal volume apparent density of particulate adsorbents (e.g., granular and pelletized adsorbents of a size and shape typically used for evaporative emission control in fuel systems). The Standard Method can be used to determine the apparent density of an adsorbent volume when the Standard Method provides the same apparent density value as the ratio of the mass and nominal volume of an adsorbent bed found in a canister system. The mass of the adsorbent by the Standard Method is the mass of a typical adsorbent used in adsorption analysis, i.e., inert binders, fillers, and structural components are fairly included or excluded from the adsorbent volume depending on what typical materials are analyzed for the adsorbent sample.

[0043] In addition, the nominal bulk apparent density of the adsorbent volume can be determined using an alternative apparent density method as defined below. The alternative method can be applied to nominal adsorbent volumes that have an apparent density that is not comparably or suitably measured by the standard method. In addition, due to the general applicability of the alternative apparent density method, the alternative apparent density method can be applied to particulate adsorbents in place of the standard method. The alternative method can be applied to adsorbent volumes that can include particulate adsorbents, non-particulate adsorbents, and any form of adsorbent that is augmented by spacers, voids, void additives within the volume, or a continuous similar adsorbent volume to achieve a net reduction in increased capacity.

[0044] In an alternative apparent density method, the apparent density of the adsorbent volume is obtained by dividing the mass of the adsorbent by the adsorbent volume, where:

[0045] (1) The dry mass basis of a typical adsorbent in the adsorbent volume is measured. For example, a 0.200 g typical sample of 25.0 g total adsorbent mass in the adsorbent volume is measured by the McBain method for adsorption capacity. While the McBain method produces g butane adsorption values ​​per g adsorbent, the numerator of the applicable mass for the apparent density of the adsorbent volume is 25.0 g, which then allows the McBain analysis values ​​to be converted to volumetric properties of the adsorbent volume; and

[0046] (2) The volume of the adsorbent component in the denominator of the apparent density is defined as the in-situ geometric volume below which the surface vapor flow path occurs within the canister system. The length of the volume is bounded by the plane perpendicular to the surface vapor flow inlet of the adsorbent volume in question (i.e., the point at which the adsorbent exists on the vertical plane) and the plane perpendicular to the surface flow at the vapor flow outlet of the adsorbent volume in question (i.e., the point at which there is no adsorbent across the plane perpendicular to the vapor flow).

[0047] (B) Honeycomb, monolith or foam adsorbents

[0048] (1) Cylindrical honeycomb adsorbent

[0049] The apparent density of a cylindrical honeycomb adsorbent may be determined according to the procedure of Purification Cellutions, LLC (Waynesboro, GA) SOP 500-115. The volume of an adsorbent is the product of the cross-sectional area (A) and the length (h) of the adsorbent. The length (h) of the adsorbent is defined as the distance between the front plane of the adsorbent perpendicular to the vapor or gas flow entering the adsorbent and the rear plane of the adsorbent where the vapor or gas leaves the adsorbent. The volume measurement is a measure of the nominal volume, which is also used to define the bed volume ratio for purge. In the case of a cylindrical honeycomb adsorbent of circular cross section, the adsorbent cross-sectional area is given by πd 2 / 4, where d is the average diameter measured at four points on each end of the honeycomb. The nominal adsorbent volume and nominal bulk density are calculated as follows:

[0050] Nominal adsorbent volume = hxA

[0051] Nominal volume apparent density = partial mass / (hxA)

[0052] where "partial mass" is the mass of adsorbent for a typical adsorbent sample tested for adsorption properties (including typical proportions of inert or adsorbent binder and filler).

[0053] By way of non-limiting example, Fig. 9 Boundary definitions for the nominal volume of a honeycomb adsorbent 109 having a cross-sectional area A are shown. Vapor or gas flows through the honeycomb adsorbent 109 in the direction from D1 to D2. The vapor or gas enters the front plane (F) of the adsorbent 109, flows through the length (h) of the adsorbent 109, and exits the back plane (B) of the adsorbent 109. The nominal volume of the honeycomb adsorbent 109 is equal to the cross-sectional area A x length h. Similarly, Fig.10 Boundary definitions for the nominal volume of the foam sorbent 110 are shown.

[0054] (2) Pleated, corrugated and sheet adsorbents

[0055] For pleated and corrugated adsorbents, the nominal adsorbent volume includes all void space created by the pleats and corrugations. The volume measurements are measures of the nominal volume, which is also used to define the bed volume ratio for purge. The nominal volume and apparent density of the adsorbent are calculated as follows:

[0056] Nominal adsorbent volume = hxA

[0057] Nominal volume apparent density = partial mass / (hxA)

[0058] in

[0059] "Part mass" is the mass of adsorbent for a typical adsorbent sample tested for adsorption properties including typical proportions of inert or adsorbent binder and filler.

[0060] h is the length of the adsorbent, defined as the distance between the front plane of the adsorbent perpendicular to the vapor or gas flow entering the filter and the rear plane of the adsorbent where the vapor or gas leaves the filter, and

[0061] A is the cross-sectional area of ​​the adsorbent.

[0062] By way of non-limiting example, Fig.11 Shown are boundary definitions for the volume of a stacked corrugated sheet adsorbent monolith 111. It is also within the skill of the art to form such a monolith as an extruded honeycomb.

[0063] In the case of a pleated adsorbent, the cross-sectional area of ​​the adsorbent is determined by LxW, where L is the distance along direction X from one edge of the adsorbent to the opposite edge of the adsorbent, and W is the distance along direction Y from one edge of the adsorbent to the opposite edge of the adsorbent.

[0064] By way of non-limiting example, Fig.12 The boundary definition of the volume for a single corrugation or ripple 112 is shown. Fig.13 The boundary definition of the volume for the corrugated or corrugated sheet 113 is shown, where the vapor flow path is provided through the sheet by some form of permeability to air flow. The face of the sheet is perpendicular to the vapor flow. In contrast, Fig.14 Boundary definitions of volumes for pleats or corrugated sheets 114 are shown, with their faces being angled to the airflow. Fig.15 Boundary definitions of the volume of the adsorbent volume 115 for parallel adsorbent sheets are shown. Fig.16 Boundary definitions for the volume of the sorbent sleeve 116 are shown.

[0065] Determination of nominal increased adsorption capacity

[0066] As used herein, the term "nominal increased adsorption capacity" refers to the adsorption capacity according to the following equation:

[0067] Nominal increased adsorption capacity = [butane adsorbed at 50 vol% - butane adsorbed at 5 vol%] x nominal volume apparent density x 1000

[0068] in

[0069] "Adsorbed butane at 50 vol%" is the gram mass of adsorbed n-butane per gram mass of the adsorbent sample at a butane concentration of 50 vol%;

[0070] "Adsorbed butane at 5 vol%" is the gram mass of adsorbed n-butane per gram mass of the adsorbent sample at a butane concentration of 5 vol%; and

[0071] "Nominal volume apparent density" is as defined above.

[0072] Determination of nominal volume butane working capacity (BWC)

[0073] Standard method ASTM D5228 may be used to determine the nominal volumetric butane working capacity (BWC) of an adsorbent volume comprising granular and / or pelletized adsorbents.

[0074] A modified version of the ASTM D5228 method can be used to determine the nominal volumetric butane working capacity (BWC) of honeycomb, monolithic and / or tablet adsorbent volumes. The modified method can also be used for particulate adsorbents, where the particulate adsorbent includes fillers, voids, structural components, or additives. In addition, the modified method can be used in cases where the particulate adsorbent is not compatible with the standard method ASTM D5228, for example, a typical adsorbent sample cannot be easily placed as 16.7 mL of filler in a sample tube for testing.

[0075] A modified version of ASTM D5228 is as follows. The adsorbent sample is dried at 110±5°C for a minimum of eight hours and then placed in a desiccator to cool. The dry mass of the adsorbent sample is recorded. The mass of the empty test assembly is determined before the adsorbent sample is assembled into the test assembly. Next, the test assembly is installed in the flow apparatus and loaded with n-butane gas at a butane flow rate of 500 ml / min at 25°C and 1 atmosphere for a minimum of 25 minutes (±0.2 minutes). The test assembly is then removed from the BWC test apparatus. The mass of the test assembly is measured and recorded to the nearest 0.001 gram. This n-butane loading step is repeated for consecutive 5 minute flow intervals until a constant mass is reached. For example, the total butane loading time for a 35 mm diameter x 150 m long honeycomb (Example 2, Adsorbent 1) is 66 minutes. For cases where the nominal volume can be removed and tested in its entirety, the test assembly can be a support for a honeycomb or monolithic portion. Alternatively, the nominal volume may need to be a section of the canister system, or a suitable reconstruction of the nominal volume of the contents with appropriate orientation to the gas flow otherwise encountered in the canister system.

[0076] The test assembly was then mounted to the test equipment and purged with 2.00 liters / minute of air at 25°C and 1 atm for a set selected purge time (±0.2 minutes) according to the formula: Purge Time (minutes) = (719 x Nominal Volume (cc)) / (2000 (cc / minute)).

[0077] The direction of the air purge flow in the BWC test is the same as the direction of the purge flow applied in the canister system. After the purge step, the test assembly is removed from the BWC test apparatus. The mass of the test assembly is measured and recorded to the nearest 0.001 gram within 15 minutes of the completion of the test.

[0078] The nominal volumetric butane working capacity (BWC) of the adsorbent sample was determined using the following equation:

[0079] Nominal volume BWC (g / dL) = amount of butane purged (g) / nominal adsorbent volume (dL), where

[0080] "Nominal volume apparent density" is as defined above, and

[0081] The amount of butane purged = the mass of the test assembly after loading - the mass of the test assembly after purging

[0082] As used herein, the term "g total BWC" refers to the amount of grams of butane purged.

[0083] Determination of effective volume properties

[0084] The effective volume of the adsorbent takes into account air gaps, voids, and other volumes between the nominal volume of the adsorbent along the vapor flow path lacking the adsorbent. Thus, the effective volume property of the adsorbent refers to the property of the adsorbent that takes into account air gaps, voids, and other volumes between the nominal volume of the adsorbent along the vapor flow path lacking the adsorbent.

[0085] The effective volume (V) of a given length of vapor flow path eff ) is the nominal volume of adsorbent present along the vapor path length (V nom,i ) plus the adsorbent-free volume along the vapor flow path (V gap,j )

[0086] V eff = ∑V nom, i +∑ V gap,j

[0087] Effective volume (B eff ) is considered as the effective volume (Bnom,j ) multiplied by the individual nominal volumes (V nom,i ) and then divided by the total effective volume (V eff ) is the sum of the properties of the independent nominal volume:

[0088] B eff = ∑(B nom,i xV nom, i ) / V eff

[0089] Thus, the term "effective incremental adsorption capacity" is the sum of the individual nominal incremental adsorption capacities multiplied by the individual nominal volumes and then divided by the total effective volume.

[0090] The term "effective butane working capacity (BWC)" is the sum of the individual BWC values ​​multiplied by each individual nominal volume and then divided by the total effective volume.

[0091] The term "effective apparent density" is the sum of the individual apparent densities multiplied by the individual nominal volumes and then divided by the total effective volume.

[0092] The term "gTotal BWC for the Active Volume" is the sum of the gTotal BWC gram values ​​for the nominal volumes within the Active Volume.

[0093] As a non-limiting example of how to determine the effective volume of an adsorbent, Fig.17 The effective volume of three adsorbent honeycomb nominal volumes connected by gaps of equal cross-sectional area in the flow path is shown, with arrows in the direction of D1 to D2 indicating vapor flow into the effective volume toward the canister system outlet. Fig.18 Three nominal volumes of adsorbent cells connected by conduit segments of different cross-sectional areas compared to the cross-sectional area of ​​the cells are shown. Fig.17 and 18 In FIG. 1 , the cell nominal volume and the gap appear to be symmetrical. However, it is understood that the cell nominal volume and the gap may have different sizes.

[0094] In some embodiments, the volumetric adsorption properties of the adsorbent volume may decrease along the vapor flow path. By way of non-limiting example, the volumetric incremental capacity and butane working capacity (BWC) of the adsorbent volume may decrease toward the discharge direction of the canister system. The reduced volumetric adsorption properties may be achieved by modifying the properties of the individual segments of the adsorbent, by changing the size of the gaps between the nominal volumes of the adsorbent ( Fig.19 ), by individually adjusting the size of the nominal volume of the independent adsorbents ( Fig. 20 and 21 ), or through a combination of them ( Fig. 22 ) to obtain. By way of non-limiting example, Fig. 20 and 21As shown in , the canister system (120, 121) may include adsorbent volume segments "F", "M", and "B" along the flow path in the direction from D1 to D2. The effective butane working capacity (BWC) of the adsorbent volume segments may decrease along the flow path in the direction from D1 to D2 (i.e., effective BWC of adsorbent volume segment F>effective BWC of adsorbent volume segment M>effective BWC of adsorbent volume segment B). In some embodiments, the effective BWC of adsorbent volume segment M and / or segment B may be less than 3 g / dL, while the effective BWC of the canister system may be greater than or equal to 3 g / dL.

[0095] In a particular embodiment, an evaporative emission control system includes: a fuel tank for storing fuel; an engine having an air induction system and adapted to consume the fuel; an evaporative emission control canister system including one or more (multiple) canisters; a fuel vapor inlet conduit from the fuel tank to the canister system; a fuel vapor purge conduit from the canister system to the air induction system of the engine; and a vent conduit for venting the canister system when the engine is shut down and allowing purge air to enter the canister system when the engine is started. The evaporative emission control canister system is defined by a fuel vapor flow path from the fuel vapor inlet conduit toward at least one subsequent adsorbent volume and the vent conduit to the initial adsorbent volume, and by an air flow path from the vent conduit toward the initial adsorbent volume and the fuel vapor purge conduit to the at least one subsequent adsorbent volume. The evaporative emission control canister system includes an initial adsorbent volume having an effective incremental adsorption capacity at 25°C of greater than 35 grams of n-butane / L between vapor concentrations of 5 vol% to 50 vol% n-butane; and at least one subsequent adsorbent volume having an effective incremental adsorption capacity at 25°C of less than 35 grams of n-butane / L between vapor concentrations of 5 vol% to 50 vol% n-butane, an effective butane working capacity (BWC) of less than 3 g / dL, and a g-total BWC of between 2 grams and 6 grams. The initial adsorbent volume and at least one subsequent adsorbent volume are located within a single canister, or the initial adsorbent volume and at least one subsequent adsorbent volume are located in separate canisters connected to allow for continuous contact by fuel vapor. The evaporative emission control canister system has a two-day diurnal breathing loss (DBL) emission of no more than 20 mg at no more than about 210 liters of purge applied after a 40 g / hr butane loading step.

[0096] The disclosed evaporative emission control system can provide low daytime breathing loss (DBL) emissions even under low purge conditions. Even under low purge conditions, the evaporative emission performance of the disclosed evaporative emission control system can be within the regulatory limits defined by the California Exhaust Emissions Test Procedure (BETP), which is 20 mg or less.

[0097] As used herein, the term "low purge" refers to a purge level at or below 210 liters applied after the 40 g / hr butane loading step (ie, 100 bed volumes for a 2.1 liter adsorbent component system).

[0098] The evaporative emission control system can provide low diurnal breathing loss (DBL) emissions even when purged at or below 210 liters applied after the 40 g / hr butane loading step. In some embodiments, the evaporative emission control system can be purged at or below 157.5 liters applied after the 40 g / hr butane loading step.

[0099] The evaporative emission control system can provide low diurnal breathing loss (DBL) emissions even when purged at or below 100 BV (based on the bed volume of 2.1 liters nominal volume of the canister system) applied after the 40 g / hr butane loading step. In some embodiments, the evaporative emission control system can be purged at or below 75 BV (based on the bed volume of 2.1 liters nominal volume of the canister system) applied after the 40 g / hr butane loading step.

[0100] In some embodiments, the evaporative emission control system may include a heating unit to further improve the purge efficiency.By way of non-limiting example, the evaporative emission control system may include a heating unit for heating the purge air, at least one subsequent adsorbent volume, or both.

[0101] Adsorbents suitable for use in the adsorbent volume can be derived from many different materials and in various forms. It can be a single component or a mixture of different components. In addition, the adsorbent (as a single component or a mixture of different components) can include a volume diluting substance. Non-limiting examples of volume diluting substances can include, but are not limited to, spacers, inert gaps, foams, fibers, springs, or combinations thereof.

[0102] Any known adsorbent material can be used, including but not limited to activated carbon, charcoal, zeolite, clay, porous polymer, porous alumina, porous silica, molecular sieve, kaolin, titanium dioxide, cerium dioxide or a combination thereof. Activated carbon can be derived from various carbon precursors. By way of non-limiting example, the carbon precursor can be wood, wood chips, wood powder, cotton wool, peat, coal, coconut, lignite, carbohydrates, petroleum asphalt, petroleum coke, coal tar pitch, fruit core, fruit stone, nut shell, nut core, sawdust, palm, plants such as rice husk or straw, synthetic polymers, natural polymers, wood fiber materials, or a combination thereof. In addition, activated carbon can be produced using a variety of processes, including but not limited to chemical activation, thermal activation or a combination thereof.

[0103] Can use multiple adsorbent forms.The non-limiting examples of adsorbent form can comprise particle, pill, ball, honeycomb, monolith, pellet cylinder, granular medium of uniform shape, granular medium of non-uniform shape, structural medium of extruded form, structural medium of winding form, structural medium of folded form, structural medium of folded form, structural medium of wavy form, structural medium of pouring form, structural medium of connecting form, nonwoven, weaving, sheet, paper, foam or their combination.Adsorbent (as single component or the mixture of different components) can comprise volume dilution material.The non-limiting examples of volume dilution material can include but not limited to spacer, inert gap, foam, fiber, spring or their combination.In addition, adsorbent can be extruded into special thin-wall cross-sectional shape, as, hollow cylinder, star, twisted spiral, star-shaped object, the band of structure, or other shapes in the technical ability of this area.In shaping, inorganic and / or organic binder can be used.

[0104] The honeycomb adsorbent may be of any geometric shape, including but not limited to circular, cylindrical, or square. In addition, the cells of the honeycomb adsorbent may have any geometric shape. A honeycomb of uniform cross-sectional area for flow through the passages (e.g., a square honeycomb with square cross-sectional cells or a spirally wound honeycomb in a wavy form) may perform better than a circular honeycomb with square cross-sectional cells in a rectangular matrix that provides adjacent passages with a range of cross-sectional areas, and therefore passages that are not purged equivalently. Without being bound by any theory, it is believed that a more uniform cell cross-sectional area across the honeycomb faces a more uniform flow distribution within the portion during both the adsorption and purge cycles, and therefore, a lower DBL emission from the canister system.

[0105] In some embodiments, the evaporative emission control system may also include one or more heat input units for heating one or more (multiple) adsorbent volumes and / or one or more (multiple) empty volumes. The heat input unit may include, but is not limited to, an internal resistance element, an external resistance element, or a heat input unit associated with the adsorbent. The heat input unit associated with the adsorbent may be an element separated from the adsorbent (i.e., no contact with the adsorbent). Alternatively, the heat input unit associated with the adsorbent may be a substrate or layer to which the adsorbent is attached, connected, non-connected or physically contacted. The heat input unit associated with the adsorbent may be an adsorbent that is directly electrically heated by having a suitable resistance. The resistance properties of the adsorbent may be modified by adding conductive or resistive additives and adhesives in the initial preparation of the adsorbent and / or in forming the adsorbent into a granular or integral form. The conductive component may be a conductive adsorbent, a conductive substrate, a conductive additive and / or a conductive adhesive. The conductive material may be added in the preparation of the adsorbent, added in the intermediate shaping process and / or added in the adsorbent formed into the final form. Any mode of the heat input unit can be used. By way of non-limiting example, the heat input unit may include a heat transfer fluid, a heat exchanger, a heat conducting element, and a positive temperature coefficient material. The heat input unit may or may not be uniform along the length of the heating fluid path (i.e., providing different local intensities). Furthermore, the heat input unit may or may not be distributed for greater intensity and duration of heating at different points along the length of the heating fluid path.

[0106] Examples

[0107] Determine the increase in adsorption capacity

[0108] Figure 8 A simplified schematic diagram of an apparatus for determining butane adsorption capacity is shown. This is known in the art as the McBain method. Apparatus 800 includes a sample disc 801 and spring 802 in a sample tube 803, a roughing pump 804, a diffusion pump 805, a stopcock 806, metal / O-ring vacuum valves 807-809, a butane cylinder 810, a pressure readout unit 811, and at least one conduit 812 connecting the components of apparatus 800.

[0109] A typical adsorbent composition sample ("Adsorbent Sample") is oven dried at 110°C for more than 3 hours before loading onto a sample disc 801 attached to a spring 802 within a sample tube 803. The sample tube 803 is then installed into the apparatus 800. When the apparent density value determines that the mass of inert binders, fillers, and structural components is reasonably included in its mass numerator, the Adsorbent Sample will include typical amounts of any inert binders, fillers, and structural components present in the nominal volume of the adsorbent composition. Conversely, when the apparent density value reasonably excludes the mass of inert binders, fillers, and structural components from its numerator, the Adsorbent Sample will exclude these inert binders, fillers, and structural components. The general concept is to accurately define the adsorption properties of butane on a volume basis within the nominal volume.

[0110] A vacuum of less than 1 torr is applied to the sample tube, and the adsorbent sample is heated at 105°C for 1 hour. The mass of the adsorbent sample is then determined by the extension of the spring using a differential pressure gauge. Thereafter, the sample tube is immersed in a temperature-controlled water bath at 25°C. Air is pumped out of the sample tube until the pressure inside the sample tube is 10 -4 torr. n-Butane is introduced into the sample tube until equilibrium is reached at the selected pressure. The test is performed for two sets of data for four selected equilibrium pressures, which are obtained at about 38torr and at about 380torr, respectively. The concentration of n-butane is based on the equilibrium pressure in the sample tube. After each test at the selected equilibrium pressure, the mass of the adsorbent sample is measured based on the extension of the spring using a height gauge. The increased mass of the adsorbent sample is the amount of n-butane adsorbed by the adsorbent sample. The mass (gram) of n-butane adsorbed per mass (gram) of the adsorbent sample is determined for each test under different n-butane equilibrium pressures and is plotted in a graph varying with n-butane concentration (% volume). A 5vol% n-butane concentration (volume) at one atmosphere is provided by a 38torr equilibrium pressure in the sample tube. A 50vol% n-butane concentration at one atmosphere is provided by a 380torr equilibrium pressure in the sample tube. Since equilibrium cannot be easily achieved at exactly 38 torr and 380 torr, the adsorbed n-butane mass per adsorbent sample mass at 5 vol% n-butane concentration and 50 vol% n-butane concentration were interpolated from the graph using data points collected at approximately the target 38 and 380 torr pressures.

[0111] Alternatively, microscopy (eg, Microscopy ASAP 2020) can be used to determine the increased butane adsorption capacity in place of the McBain method.

[0112] Determining Diurnal Breathing Loss (DBL) Emissions

[0113] The evaporative emission control systems of Examples 1-13 (labeled below) were assembled with selected amounts and types of adsorbents as shown in Tables 1-3.

[0114] Each example was uniformly pre-conditioned (matured) by repeated cycles of gasoline vapor adsorption using a proven TF-1 fuel (9RVP, 10 vol% ethanol) and 300 nominal bed volumes (e.g., 630 L for a 2.1 L main tank and 450 liters for a 1.5 L main tank) at 22.7 LPM based on a dry air purge of the main tank. The gasoline vapor loading rate was 40 g / hr and the hydrocarbon content was 50 vol%, generated by heating two liters of gasoline to approximately 36°C and bubbling air at 200 ml / min. Two liter portions of fuel were automatically replaced by fresh gasoline every two hours until a breakthrough of 5000 ppm was detected by the FID (flame ionization detector). A minimum of 25 maturation cycles were used on an unused tank. The maturation cycle was followed by a single butane adsorption / air purge step. This step will be to load butane at 40 g / hr at 50 vol% air concentration at one atm to 5000 ppm breakthrough, soak for one hour, then purge with dry air for 21 minutes, where the total purge volume is obtained by selecting a constant air purge rate appropriate for the period. The canister is then soaked with the ports sealed at 20°C for 24 hours.

[0115] DBL emissions were then generated by attaching the tank port of the example to a fuel tank filled with 40 vol% (based on its rated volume) of CARB Phase II fuel (7RVP, 0% ethanol). Prior to attachment, the filled fuel tank was stabilized at 18.3°C for 24 hours while draining. The tank and example were then temperature cycled according to CARB's two-day temperature curve, from 18.3°C to 40.6°C in 11 hours per day, and then returned to 18.3°C in 13 hours. Emission samples were collected from the exemplary exhaust port into polyvinylidene fluoride bags at 5.5 hours to 11 hours during the heating phase. The polyvinylidene fluoride bag was filled with nitrogen to a known total volume based on pressure, and then drawn into the FID to determine the hydrocarbon concentration. The FID was calibrated with a 5000ppm butane standard. The mass of emissions (such as butane) was calculated from the polyvinylidene fluoride bag volume, the emission concentration, and assuming an ideal gas. The mass of emissions at 5.5 hours and 11 hours was added every day. Following CARB's protocol, the day with the highest total emissions is reported as "2-Day Emissions." In all cases, the highest emissions were on Day 2. The procedure is generally described in SAE Technical Paper 2001-01-0733, entitled "Impact and Control of Canister Bleed Emissions," by RS Williams and CR Clontz, and in CARB's LEV III BETP procedure (Paragraph D.12 in California Evaporative Emissions Standards and Test Procedures for 2001 and Subsequent Model Motor Vehicles, March 22, 2012).

[0116] For Examples 1-4, 13 and 7-8, a 68 L fuel tank and a 2.1 liter main tank (Table 1, main tank type #1) were used as the main tank, which had a fuel source side volume (i.e., initial adsorbent volume) filled with 1.8 liters of NUCHAR® BAX 1500 activated carbon adsorbent and an exhaust side volume filled with 0.3 liters of NUCHAR® BAX LBE activated carbon adsorbent. The volume was configured so that there was a 1500 ml fuel source side chamber and a 600 ml exhaust side chamber, wherein the fuel source chamber had a cross-sectional area (CSA) that was 2.5 times the exhaust side CSA. The BAX 1500 activated carbon filled fuel source chamber (similar to Figure 2-7 The volume 201 plus 202 in the discharge side chamber, and the 300 ml immediately downstream volume (similar to Figure 2-7 203 in the volume). 300 mL of BAX LBE activated carbon filled the remaining volume of the discharge side chamber (similar to Figure 7204 in volume). NUCHAR®BAX 1500 activated carbon and NUCHAR®BAX LBE activated carbon are wood-based activated carbon products commercially available from MeadWestvaco, Inc., having an incremental adsorption capacity at 25°C of 80 g n-butane / L and 24 g n-butane / L, respectively, between vapor concentrations of 5 vol% and 50 vol% n-butane ("nominal incremental capacity" in Table 1). For the n-butane post-loading air purge step, the systems of each tank in Examples 1-4, 13, and Examples 7-8 were purged with 157.5 liters of purge air at a purge rate of 7.5 lpm. The purge applied was between 66.0 and 75.0 bed volumes (BV) according to the bed volume ratio of the purge volume divided by the total nominal volume of the tank system.

[0117] For Examples 5-6 and 9-12, a 45 L fuel tank and a 1.5 liter main tank (Table 1, main tank type #2) were used as the main tank, which had a fuel source side volume (i.e., initial adsorbent volume) filled with 1.2 liters of NUCHAR® BAX 1100 activated carbon adsorbent and an exhaust side volume filled with 0.3 liters of NUCHAR® BAX LBE activated carbon adsorbent. The volume was configured so that there was a 1000 ml fuel source side chamber and a 500 ml exhaust side chamber, wherein the fuel source chamber had a cross-sectional area (CSA) that was 2.0 times the exhaust side CSA. BAX 1100 activated carbon filled fuel source chamber (similar to Figure 2-7 The volume 201 plus 202 in the discharge side chamber, and the immediately downstream volume of 200 ml (similar to Figure 2-7 203 in the volume). 300 mL of BAX LBE activated carbon filled the remaining volume of the discharge side chamber (similar to Figure 7 Volume 204 in). Activated NUCHAR® BAX 1100 is a wood-based activated carbon product commercially available from MeadWestvaco, Inc., having an increased adsorption capacity of 52 grams of n-butane / L at 25°C between vapor concentrations of 5 vol% and 50 vol% n-butane. During the butane post-loading air purge step, each tank system was purged with 100 or 150 liters of purge air at a purge rate of 4.75 or 7.14 lpm, respectively. The applied purge was between 55.9 and 91.2 BV, as measured by the bed volume ratio of the purge volume divided by the total nominal volume of the tank system.

[0118] Examples 1-13 all include zero, one, or two additional vent-side adsorbent volumes in series. The first auxiliary tank downstream along the vapor flow path from the main tank (if present) is labeled "Adsorbent 1", and the second auxiliary tank in series downstream along the vapor flow path from Adsorbent 1 (if present) is labeled "Adsorbent 2". One type of additional vent-side adsorbent (similar to Figure 4The auxiliary tank 300 in the figure is described as "35x150", which is a cylindrical carbon honeycomb with a diameter of 35 mm and a length of 150 mm and a capacity of 200 cells per square inch (cpsi). The calculation of the effective volume of the "35x150" adsorbent is similar to that of Fig. 9 The boundaries shown in , i.e., the effective volume is bounded by the vapor entry and exit faces of the honeycomb and is equal to its nominal volume. Figure 7 The auxiliary tank 300 in FIG. 1 is described as "3-35x50", which is three 35mm diameter x 50mm long cylindrical carbon honeycombs at 200 cpsi, including two 35mm diameter x 7mm thick foam insulation. Similar to Figure 7 The gaps 304 and 305 in the foam spacer create a 7 mL void gap between each continuous 50 mm long honeycomb length. The calculation of the effective volume is similar to that of Fig.17 The boundaries shown in are the same, that is, the effective volume is bounded by the vapor entry face of the first of the three honeycombs and the exit face of the third of the three honeycombs, and is equal to the nominal volume of the three honeycombs plus the volume of the 7 mm thick separator. The nominal incremental adsorption capacity at 25°C of n-butane / L between vapor concentrations of 5 vol% and 50 vol% n-butane is shown as "Nominal incremental capacity". When based on the effective volume, the incremental adsorption capacity at 25°C of n-butane / L between vapor concentrations of 5 vol% and 50 vol% n-butane is shown as "effective incremental capacity". Two-day DBL emissions are reported as "2-day DBL emissions" in mg. The reported results are usually the average of several replicates of BETP to verify the findings.

[0119] The evaporative emission control canister systems of Examples 1-4, 13, and Examples 7-8 all included an initial adsorbent volume of BAX 1500 activated carbon adsorbent having a nominal incremental adsorption capacity at 25° C. of 80 g n-butane / L (i.e., greater than 35 g / L) between vapor concentrations of 50 vol% to 50 vol% n-butane, and a subsequent adsorbent volume of BAX LBE activated carbon adsorbent having a nominal incremental adsorption capacity at 25° C. of 24 g / L (less than 35 g / L) between vapor concentrations of 5 vol% to 50 vol% n-butane (less than 35 g / L). This is the main canister type #1 in Table 1.

[0120] Example 1 is an evaporative emission control canister system disclosed in U.S. Pat. No. RE38,844. As shown in Table 2, the evaporative emission control canister system of Example 1 provides 2-day DBL emissions of 215 mg under low purge conditions of 75 bed volumes (BV) of purge air after butane loading (i.e., 157.5 liters). These 2-day DBL emissions are an order of magnitude greater than the 20 mg regulatory limit under the California Exhaust Emissions Test Procedure (BETP). Therefore, the 20 mg regulatory limit under the California Exhaust Emissions Test Procedure (BETP) cannot be achieved by the evaporative emission control canister system disclosed in U.S. Pat. No. RE38,844.

[0121] For Example 2, an additional vent-side adsorbent volume (Adsorbent 1) was added to Example 1 in the form of an activated carbon honeycomb ("35x150") having an effective incremental adsorption capacity at 25°C of 16 g / L (less than 35 g / L) between vapor concentrations of 5 vol% and 50 vol% n-butane (less than 35 g / L), an effective BWC of 4.2 g / dL, and a g-total BWC of 6.1 g. As shown in Table 2, the 2-day DBL emissions for Example 2 with a low purge level of 157.5 liters (applied after butane loading) were 74 mg, which is still above the regulatory limit of 20 mg under the California Exhaust Emissions Test Procedure (BETP). Therefore, at the purge level of 157.5 liters applied after butane loading, the evaporative emission control canister system of U.S. Pat. No. RE38,844, even when used in conjunction with the additional vent-side adsorbent volume (Adsorbent 1), still fails to meet the regulatory limit of 20 mg under BETP.

[0122] For Example 3, a second additional vent-side adsorbent volume in the form of an activated carbon honeycomb (Adsorbent 2) of the same type and properties as Adsorbent 1 ("35x150") was added to the canister system of Example 2. Surprisingly, as shown in Table 2, there was only a small reduction in 2-day DBL emissions to 70 mg from the additional vent-side adsorbent volume in Example 3, and still above the regulatory limit of 20 mg under the California Exhaust Emissions Test Procedure (BETP).

[0123] Example 4 is a variation of Example 3, in which the activated carbon honeycomb is divided into three 50 mm long sections with narrow spacers between them. For Example 4, the spacers reduce the effective incremental capacity of Adsorbents 1 and 2 to 14.6 g / L and reduce the effective BWC to 3.9 g / dL, but by definition, keep the g-total BWC the same at 6.1 g. As shown in Table 2, the 2-day DBL emissions for Example 4 are still high at 52 mg and are still above the 20 mg regulatory limit under the California Exhaust Emissions Test Procedure (BETP).

[0124] In Example 13, Adsorbent 2 was a honeycomb divided into two 50 mm long segments with a narrow partition therebetween. The effective incremental capacity was 6.1 g / L, and the effective BWC was 1.6 g / dL. By definition, the g-total BWC was 1.6 g. As shown in Table 2, the 2-day DBL emissions for Example 13 were still high at 35 mg, and still above the 20 mg regulatory limit under the California Exhaust Emissions Test Procedure (BETP).

[0125] For Example 7, Adsorbent 2 had an effective incremental capacity of 9.8 g / L, an effective BWC of 2.6 g / dL, and a g-total BWC of 4.0 g. For Example 8, Adsorbent 2 had an effective incremental capacity of 10.7 g / L, an effective BWC of 2.8 g / dL, and a g-total BWC of 4.0 g. As shown in Table 2, with a purge of 157.5 liters, the canister systems in Examples 7 and 8 provided 2-day DBL emissions of 10.3 g / dl and 13 g / dl, respectively. Thus, the canister systems of Examples 7 and 8 had 2-day DBL emissions well below the BETP requirement of less than 20 mg for the low purge condition of 157.5 liters (66.0 BV).

[0126] The evaporative emission control canister systems of Examples 5, 6, and 9-12 were based on primary canister type #2 in Table 1.

[0127] Example 12 is an evaporative emission control canister system similar to those disclosed in U.S. Pat. No. RE38,844. As shown in Table 3, the evaporative emission control canister system of Example 12 does not include any additional adsorbent volume on the exhaust side. Example 12 provides a 2-day DBL emission of 175 mg under low purge conditions of 100 bed volumes (BV) (i.e., 150 liters) of purge air after butane loading, which is about nine times the 20 mg regulatory limit under the California Exhaust Emissions Test Procedure (BETP). This confirms that evaporative emission control canister systems similar to those disclosed in U.S. Pat. No. RE38,844 are unable to achieve the 2-day DBL emission requirements under BETP (i.e., less than 20 mg) when using low purge.

[0128] In Example 5, a low purge volume after butane loading of 150 liters was applied, or 91.2 BV for a nominal volume of 1.5 L for a canister system including an additional exhaust side adsorbent volume of "35x150" activated carbon honeycomb as Adsorbent 1. As shown in Table 3, the 2-day DBL emissions were high at 57 mg and above the 20 mg regulatory limit under the California Exhaust Emissions Test Procedure (BETP).

[0129] For Example 6, the applied purge was reduced to 100 liters, or 55.9 BV for a main canister type #2 including the same additional vent side adsorbent volume as Example 4. As shown in Table 3, the 2-day DBL emissions were high at 80 mg and above the 20 mg regulatory limit under the California Exhaust Emissions Test Procedure (BETP).

[0130] The canister systems of Examples 9, 10, and 11 all included an initial adsorbent volume of NUCHAR® BAX 1100 activated carbon adsorbent having an incremental adsorption capacity at 25°C of 52 g / n-butane / L (i.e., greater than 35 g / L) between vapor concentrations of 5 vol% and 50 vol% n-butane as part of a main canister type #2, and at least one subsequent adsorbent volume ("Adsorbent 2" in Table 3) having an effective incremental adsorption capacity at 25°C of less than 35 g / L between vapor concentrations of 5 vol% and 50 vol% n-butane, and a g-total BWC between 2 and 6 g.

[0131] Adsorbent 2 in Example 9 had an effective incremental capacity of 11.7 g / L, an effective BWC of 3.1 g / dL (greater than 3 g / dL), and a g-total BWC of 4.8 g. Figure 3 As shown in , the 2-day DBL emissions of Example 9 at low purge of 100 liters (ie, 55.9 BV) was 51 mg, and is well above the BETP requirement of less than 20 mg.

[0132] In contrast, Adsorbent 2 in Example 10 had an effective incremental capacity of 9.8 g / L, an effective BWC of 2.6 g / dL (less than 3 g / dL), and a g-total BWC of 4.0 g. As shown in Table 3, the 2-day DBL emissions at 100 liters low purge, equal to 55.9 BV, were 13.0 mg and within the BETP requirement of less than 20 mg.

[0133] Similarly, Adsorbent 2 in Example 11 had an effective incremental capacity of 5.9 g / L, an effective BWC of 1.6 g / dL (less than 3 g / dL), and a g-total BWC of 2.4 g. As shown in Table 3, the 2-day DBL emissions at 150 liters low purge, equal to 83.9 BV, were 7.3 mg and within the BETP requirement of less than 20 mg.

[0134] Tables 4 and 5 summarize the canister systems of Examples 1-13, and their measured 2-day DBL emissions. The canister systems of Examples 7, 8, 9, 10, and 11 provide 2-day DBL emissions of less than 20 mg as required under the California Exhaust Emissions Test Procedure (BETP). The requirement of not exceeding 20 mg for BETP at low purge is achieved by meeting a window of adsorption properties for the vent-side volume, where the window is an effective BWC of less than 3 g / dL and a g-total BWC between 2 g and 6 g. Thus, the means to achieve the BETP emissions requirement at low purge conditions is not only a reduction in the working capacity or increased capacity across the vapor flow path of the canister system and specifically the vent-side adsorbent volume to a specified level, but also having sufficient gram working capacity in the vent-side volume to suppress emissions.

[0135] Although the present disclosure is susceptible to various modifications and alternative forms, specific embodiments are shown in the drawings by way of example only and are described in detail herein. However, the present disclosure is not intended to be limited to the specific forms disclosed. On the contrary, the present disclosure will cover all modifications, equivalents and alternatives within the scope of the present disclosure defined by the following appended claims and their legal equivalents.

[0136]

[0137]

[0138]

[0139]

[0140]

[0141]

Claims

1. An evaporative emission control canister system comprising One or more tanks comprising: A volume of adsorbent having an effective volumetric adsorption capacity at 25°C of greater than 35 grams of n-butane / L between a vapor concentration of 5 vol% and 50 vol% n-butane as determined by microscopy adsorption analysis; as well as at least one subsequent adsorbent volume having an effective volumetric incremental adsorption capacity at 25°C of less than 35 grams of n-butane / L between a vapor concentration of 5 vol% and 50 vol% n-butane as determined by microscopy adsorption analysis, an effective butane working capacity of less than 3 g / dL, and a g-total butane working capacity of from 2 g to 6 g, the effective butane working capacity being the sum of the individual butane working capacity values ​​multiplied by the individual nominal volumes and then divided by the total effective volume, the g-total butane working capacity being the g amount of butane purged, Wherein the adsorbent volume and the at least one subsequent adsorbent volume are located within a single canister, or are located in separate canisters connected to permit sequential contact by fuel vapor.

2. The canister system of claim 1 , wherein the at least one subsequent adsorbent volume has an effective volumetric incremental adsorption capacity at 25° C. of 24 grams or less of n-butane / L between vapor concentrations of 5 vol % and 50 vol % n-butane.

3. The canister system of claim 1 , wherein the at least one subsequent adsorbent volume has an effective volumetric incremental adsorption capacity at 25° C. of 16 grams or less of n-butane / L between vapor concentrations of 5 vol % and 50 vol % n-butane.

4. The canister system of claim 1 further comprising at least one additional subsequent adsorbent volume having an effective volumetric incremental adsorption capacity at 25°C of less than 35 grams of n-butane / L between vapor concentrations of 5 vol% and 50 vol% n-butane.

5. The canister system of claim 4, wherein the at least one additional subsequent adsorbent volume has a lower effective volumetric incremental adsorption capacity relative to a previous subsequent adsorbent volume in the flow path from the fuel side to the exhaust side.

6. The canister system of claim 4, wherein each additional subsequent adsorbent volume has a lower effective volume-incremental adsorption capacity than any previous subsequent adsorbent volume.

7. The tank system of claim 1, wherein: The adsorbent volume and the at least one subsequent adsorbent volume are located within a single canister, or are located in separate canisters connected to permit continuous contact by fuel vapor, and wherein the canister system has a two-day diurnal breathing loss emission of no greater than 20 mg at no greater than 210 liters of purge applied after a 40 g / hr butane loading step or no greater than 20 mg at no greater than 100 bed volumes of purge applied after a 40 g / hr butane loading step.

8. The canister system of claim 1, wherein the canister system further comprises at least one heat input unit for heating one or more adsorbent volumes. 9 . The tank system of claim 8 , wherein the heat input unit comprises at least one of an internal resistance element or an external resistance element.

10. The tank system of claim 8, wherein the heat input unit comprises at least one of a heat transfer fluid, a heat exchanger, a heat conducting element, or a positive temperature coefficient material.

11. The canister system of claim 1 , wherein the adsorbent within the adsorbent volume and the at least one subsequent adsorbent volume comprises a component selected from the group consisting of activated carbon, charcoal, clay, porous polymers, porous alumina, porous silica, molecular sieves, kaolin, titania, and ceria.

12. The canister system of claim 1, wherein the sorbent within the sorbent volume and the at least one subsequent sorbent volume comprises a component selected from the group consisting of: activated carbon and charcoal.

13. The canister system of claim 12, wherein the activated carbon is derived from a material comprising components selected from the group consisting of wood, wood chips, wood flour, cotton linter, coal, coconut, petroleum pitch, petroleum coke, coal tar pitch, fruit pits, fruit stones, nut shells, nut pits, sawdust, palm, vegetables, synthetic polymers, natural polymers, and wood cellulosic materials.

14. The canister system of claim 1, wherein the form of the adsorbent within the adsorbent volume and the at least one subsequent adsorbent volume comprises a component selected from the group consisting of particles, pellets, spheres, honeycombs, extruded form structured media, rolled form structured media, folded form structured media, pleated form structured media, corrugated form structured media, poured form structured media, bonded form structured media, nonwovens, wovens, sheets, and foams.

15. The tank system of claim 1, wherein: The at least one subsequent sorbent volume includes a volume of diluting material.

16. The tank system of claim 15, wherein: The volume diluting material includes a component selected from the group consisting of inert spacer particles, entrained air spaces, foams, fibers, and screens.

17. The tank system of claim 15, wherein: The volume diluting substance includes an adsorbent material formed into a highly void shape selected from the group consisting of: a hollow tube, a star, a spiral, a cylinder, a structured ribbon, and a honeycomb.

18. The tank system of claim 14, wherein: The extruded form is selected from the group consisting of: a hollow cylinder, a twisted spiral, a star, and a structured ribbon.

19. An evaporative emission control canister system comprising A volume of adsorbent having an effective volume incremental adsorption capacity at 25°C of greater than 35 grams of n-butane / L between vapor concentrations of 5 vol% and 50 vol% n-butane as determined by microscopy adsorption analysis; and at least one subsequent adsorbent volume having an effective volumetric incremental adsorption capacity at 25°C of less than 35 grams of n-butane / L between vapor concentrations of 5 vol% and 50 vol% n-butane as determined by microscopy adsorption analysis, and an effective butane working capacity of less than 3 g / dL, and a g-total butane working capacity of from 2 g to 6 g, the effective butane working capacity being the sum of the individual butane working capacity values ​​multiplied by the individual nominal volumes and then divided by the total effective volume, the g-total butane working capacity being the g amount of butane purged, wherein the adsorbent volume and the at least one subsequent adsorbent volume are located within a single canister, or are located in separate canisters connected to permit sequential contact by fuel vapor, and wherein the canister system has a two-day diurnal breathing loss emissions as determined by the 2012 LEV III California Exhaust Emissions Test Procedure (BETP) of no greater than 20 mg at no greater than 210 liters of purge applied after a 40 g / hr butane loading step or no greater than 20 mg at no greater than 100 bed volumes of purge applied after a 40 g / hr butane loading step.

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