Cell within a cell monolith structure for an evaporative emissions hydrocarbon scrubber

A monolith for use in an evaporative emissions hydrocarbon scrubber is disclosed. The monolith, which is concentrically disposed with a shell, has at least one cell group disposed around at least two individual cells, such that the cell group comprises at least three thick walls. The individual cells comprise at least on thin wall, with the thick walls being thicker than the thin wall. A method for using the evaporative emissions hydrocarbon scrubber is also disclosed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS When evaporative emissions are released from the fuel tank due to diurnal pressure and/or temperature changes, the emissions can be captured in an evaporative canister. The monolith can be employed in the main evaporative canister, an auxiliary canister, or a combination thereof. While different designs of monoliths exist, including circular or rectangular designs, reference to a particular monolith design is intended to also represent similar components in other monolith designs, where applicable. Additionally, this monolith design can be employed as a single and only canister, or in conjunction with additional canisters. FIG. 1 illustrates a cross-sectional view of the cell within a cell monolith structure 20 for an evaporative emissions hydrocarbon scrubber. The monolith 20 comprises a combination of thin walls 24 and thick walls 22 . These walls, which preferably run the length of the monolith 20 , can be disposed perpendicular to the axis of the monolith. Typically, the walls 22 , 24 are disposed horizontal and vertical, at an angle perpendicular to the axis. The thicker walls 22 define cell groups 26 comprising several cells 28 defined by the thin walls 24 . Depending upon the specific size and geometry of the monolith, the number of connected main cell groups 26 can vary. The quantity of thin and thick walls is a balance between the desired structural integrity and the surface area desired to adsorb a sufficient amount of hydrocarbons in the fuel vapors. Generally, there are more thinner walls 24 disposed within the monolith 20 than thicker walls 22 . The geometry of the cells, both those defined by thick walls 22 and those defined by thin walls 24 , is also based upon the desired structural integrity, surface area, and optionally upon ease of manufacture. Possible designs range from rounded to multi-sided figures, e.g., square, rectangle, oblong, circular, triangular, hexagonal, octagonal, and the like, as well as combinations comprising at least one of the foregoing geometries defining either the individual cells 28 and/or the main cell groups 26 . For example, the interlaced thick and thin walls 22 , 24 can perpendicularly intersect creating a square design as illustrated by individual cell 28 , with the exception of when the interlaced thick and thin walls 22 , 24 intersect with the outer wall 30 . Additionally, the thin walls 24 can form different shaped cells than the cell groups 26 . For example, the cell group 26 may comprise a rectangular geometry while the cells 28 within the cell group 26 may comprise a square geometry. The location and orientation of the thick and thin walls 22 , 24 can be dependent upon the overall shape of the monolith 20 , such as, e.g., circular, oval, rectangular, trapezoidal, non-circular, and other similar geometric configurations, and the like. The cell shape and size is based upon the overall cell density. The number of cells within the monolith can be about 200 to about 600 individual cells, with about 200 to about 400 individual cells preferred. The number of individual cells within each cell group can vary, with at least four individual cells per cell group preferred, and at least nine individual cells per cell group especially preferred. The thickness of the thick and thin walls 22 , 24 is typically dependent upon the desired overall structural integrity of the monolith 20 . The thickness is preferably sufficient to impart the desired overall structural integrity, without inhibiting the passage of evaporative emissions. Preferably, the thickness of the thicker walls 22 can be about 0.008 inches (in.) or greater, with about 0.008 in. to about 0.020 in. preferred, and about 0.010 in. to about 0.012 in. especially preferred. The thickness of the thinner walls 24 can be less than about 0.008 in., with about 0.001 in. to about 0.008 in. preferred, and about 0.003 in. to about 0.004 in. especially preferred. The monolith 20 can be comprised of a sorbent that removes hydrocarbons from an air/vapor flow, including, but not limited to, activated carbon, and the like. This sorbent can be mixed with a binder to allow for the formation into the desired shape. The various amounts of sorbent and binder can readily be determined by an artisan based upon the desired structural integrity of the monolith and the monolith production method. One example of a monolith production process is disclosed in U.S. Pat. No. 5,914,294 to Park et al., which is hereby incorporated by reference. Once formed into the cell within a cell structure, the monolith is concentrically disposed within a shell or housing (i.e., a canister), and disposed in fluid communication with the fuel tank and the atmosphere external to the motor vehicle. During operation, fuel vapor and air flow into a first end of the canister, and through the monolith, where the sorbent strips the hydrocarbons from the gas stream, releasing the treated air to the atmosphere. The canister is fluidly connected by a valved purge conduit to the combustion air intake of the motor vehicle engine. When the engine is running, the combustion air intake is at sub-atmospheric pressure, and the valve is opened to thereby connect the purge port to the combustion air intake. Fresh air is drawn by the sub-atmospheric pressure through the vent port and into the second end of the evaporative canister. The fresh air flows through the monolith, stripping the sorbent of stored hydrocarbons. The thinner walls 24 increases the desorption capability of the monolith 20 , allowing for a more thorough cleaning of the monolith of hydrocarbons. The performance of the monolith 20 improves as the desorption capability is increased, since the ability to capture the fuel vapor and/or hydrocarbons is more rapidly restored. The use of the thicker walls 22 , defining the main cell groups 26 , increases the structural integrity of the monolith 20 without compromising the open area for air flow. The plurality of the main cell groups 26 does not add any significant pressure differential across the monolith 20 , when compared to a monolith with uniform thicknesses, as illustrated in the prior art FIG. 1 . While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the apparatus and method have been described by way of illustration only, and such illustrations and embodiments as have been disclosed herein are not to be construed as limiting to the claims.