Method for reducing emissions from evaporative emissions control systems

Abstract

Disclosed is a method for sharply reducing diurnal breathing loss emissions from automotive evaporative emissions control systems by providing multiple layers, or stages, of adsorbents. On the fuel source-side of an emissions control system canister, high working capacity carbons are preferred in a first canister (adsorb) region. In subsequent canister region(s) on the vent-side, the preferred adsorbent should exhibit a flat or flattened adsorption isotherm on a volumetric basis and relatively lower capacity for high concentration vapors as compared with the fuel source-side adsorbent. Multiple approaches are described for attaining the preferred properties for the vent-side canister region. One approach is to use a filler and/or voidages as a volumetric diluent for flattening an adsorption isotherm. Another approach is to employ an adsorbent with the desired adsorption isotherm properties and to process it into an appropriate shape or form without necessarily requiring any special provision for dilution. The improved combination of high working capacity carbons on the fuel source-side and preferred lower working capacity adsorbent on the vent-side provides substantially lower diurnal breathing emissions without a significant loss in working capacity or increase in flow restriction compared with known adsorbents used in canister configurations for automotive emissions control systems.

1. A method for reducing fuel vapor emissions in automotive evaporative emissions control systems comprising the steps of contacting the fuel vapor with an initial adsorbent volume having incremental adsorption capacity at 25° C. of greater than 35 g n-butane/L between vapor concentrations of 5 vol % and 50 vol % n-butane and at least one subsequent adsorbent volume having an incremental adsorption capacity of less than 35 g n-butane/L between vapor concentrations of 5 vol % and 50 vol % n-butane. 
     
     
       2. The method of  claim 1  comprising a single subsequent adsorbent volume. 
     
     
       3. The method of  claim 1  comprising multiple subsequent adsorbent volumes. 
     
     
       4. The method of  claim 2  wherein the initial adsorbent volume and the subsequent adsorbent volume are located within a single automotive evaporative emission control canister. 
     
     
       5. The method of  claim 3  wherein the-initial adsorbent volume and the subsequent adsorbent volumes are located within a single automotive evaporative emission control canister. 
     
     
       6. The method of  claim 2  wherein the initial adsorbent volume and the subsequent adsorbent volume are located in separate canisters that are connected to permit sequential contact by the fuel vapor. 
     
     
       7. The method of  claim 3  wherein the initial adsorbent volume and at least one subsequent adsorbent volume are located in separate canisters that are connected to permit sequential contact by the fuel vapor. 
     
     
       8. The method of  claim 1  wherein the initial adsorbent volume and the subsequent adsorbent volume are activated carbon derived from materials selected from the group consisting of wood, peat, coal, coconut, lignite, petroleum pitch, petroleum coke, coal tar pitch, fruit pits, nut shells, sawdust, wood flour, synthetic polymer, and natural polymer having been activated by a process selected from the group consisting of chemical, thermal, and combined chemical/thermal activation methods. 
     
     
       9. The method of  claim 1  wherein the initial adsorbent volume and the subsequent adsorbent volume are inorganic materials selected from the group consisting of zeolites, porous silica, porous alumina, pillared clays, and molecular sieves. 
     
     
       10. The method of  claim 1  wherein the initial adsorbent volume and the subsequent adsorbent volume are porous polymers. 
     
     
       11. The method of  claim 1  wherein the subsequent adsorbent volume exhibits adsorption capacities achieved by volumetric dilution. 
     
     
       12. The method of  claim 11  wherein the volumetric dilution is accomplished by the addition of a non-adsorbing filler as a co-ingredient by an addition process selected from the group consisting of addition with the activated carbon raw material prior to activation, addition with the adsorbent before forming into a shaped particle or monolith, and a combination thereof. 
     
     
       13. The method of  claim 11  wherein the volumetric dilution is accomplished by forming the adsorbent into high voidage shapes selected from the group consisting of stars, hollow cylinders, asterisks, spirals, cylinders, and configured ribbons. 
     
     
       14. The method of  claim 11  wherein the volumetric dilution is accomplished by forming the adsorbent into a honeycomb or monolith shape. 
     
     
       15. The method of  claim 11  wherein the volumetric dilution is accomplished by the use of inert spacer particles, trapped air spaces, foams, fibers, and screens external to the adsorbent. 
     
     
       16. The method of  claim 12  wherein the non-adsorbing filler is a solid after processing. 
     
     
       17. The method of  claim 12  wherein the non-adsorbing filler is volatized or combusted to form voidages larger than 50 Å width within the shaped particle or monolith. 
     
     
       18. In a method of reducing fuel vapor emissions in an automotive evaporative emissions control system comprising removing at least one volatile organic compound from a volatile organic compound-containing fuel vapor by routing the fuel vapor through a vapor adsorbent, the improvement comprising sequentially routing the fuel vapor through an initial adsorbent material-containing volume wherein the initial adsorbent material is characterized by an incremental adsorption capacity at 25° C. of greater than 35 g n-butane/L between vapor concentrations of 5 vol % and 50 vol % n-butane before routing the fluid stream through at least one subsequent adsorbent-containing volume prior to venting to the atmosphere wherein the subsequent adsorbent-containing volume is characterized by an incremental adsorption capacity at 25° C. of less than 35 g n-butane/L between vapor concentrations of 5 vol % and 50 vol % n-butane. 
     
     
       19. The method of  claim 18  wherein the initial adsorbent volume and the subsequent adsorbent volume are located in a single automotive evaporative emissions canister. 
     
     
       20. The method of  claim 18  wherein the initial adsorbent volume and the subsequent adsorbent volume are located in separate canisters that are connected to permit sequential contact by the fuel vapor. 
     
     
       21. The method of  claim 18  wherein the initial adsorbent volume and the subsequent adsorbent volume are activated carbon derived from materials selected from the group consisting of wood, peat, coal, coconut, lignite, petroleum pitch, petroleum coke, coal tar pitch, fruit pits, nut shells, sawdust, wood flour, synthetic polymer, and natural polymer and activated by chemical and/or thermal activation methods. 
     
     
       22. The method of  claim 18  wherein the initial adsorbent volume and the subsequent adsorbent volume are inorganic materials selected from the group consisting of zeolites, porous silica, and molecular sieves. 
     
     
       23. The method of  claim 18  wherein the initial adsorbent volume and the subsequent adsorbent volume are porous polymers. 
     
     
       24. The method of  claim 18  wherein the subsequent adsorbent volume exhibits adsorption capacities achieved by volumetric dilution. 
     
     
       25. The method of  claim 24  wherein the volumetric dilution is accomplished by the addition of a non-adsorbing filler as a co-ingredient by an addition process selected from the group consisting of addition with the activated carbon raw material prior to activation, addition with the adsorbent before forming into a shaped particle or monolith, and a combination thereof. 
     
     
       26. The method of  claim 24  wherein the volumetric dilution is accomplished by forming the adsorbent into high voidage shapes selected from the group consisting of stars, hollow cylinders, asterisks, spirals, cylinders, and configured ribbons. 
     
     
       27. The method of  claim 24  wherein the volumetric dilution is accomplished by forming the adsorbent into a honeycomb or monolith shape. 
     
     
       28. The method of  claim 24  wherein the volumetric dilution is accomplished by the use of inert spacer particles, trapped air spaces, foams, fibers, and screens external to the adsorbent. 
     
     
       29. The method of  claim 25  wherein the non-adsorbing filler is a solid after processing. 
     
     
       30. The method of  claim 25  wherein the non-adsorbing filler is volatized or combusted to form voidages larger than 50 Å width within the shaped particle or monolith. 
     
     
       31. In an evaporative emissions control system for a vehicle comprising, in combination, a fuel tank for storing a volatile fuel, an engine having an air induction system and adapted to consume the fuel, a canister containing an initial volume of fuel vapor adsorbent material for temporarily adsorbing and storing fuel vapor from the tank, a conduit for conducting fuel vapor from the tank to a canister vapor inlet, a fuel vapor purge conduit from a canister purge outlet to the induction system of the engine, and a vent/air opening for venting the canister and for admission of air to the canister during operation of the engine induction system, wherein the canister is defined by a fuel vapor flow path via the canister vapor inlet through the initial volume of vapor adsorbent within a first region of the canister toward the vent/air opening, and an air flow path through a subsequent volume of adsorbent within a second region of the canister at the vent/air opening and the first region at the purge outlet, such that fuel vapor formed in the tank flows through the vapor inlet into the initial volume of adsorbent where it is adsorbed and, during operation of the engine induction system, ambient air flows in a path to and through the vent/air opening and along the air flow path in the canister through the initial volume and the purge outlet to the induction system of the engine, the flow of air removing a portion of the adsorbed fuel vapor but leaving a residue of fuel in the initial volume,
   the improvement wherein at least one subsequent volume of vapor adsorbent material comprises a volume of  1   %  to  100   %  of the first volume and is located either inside of the canister within the second region thereof or outside of the canister, and wherein the initial volume of vapor adsorbent material is characterized by an incremental adsorption capacity at  25 ° C. of greater than  35  g n - butane/L - bed between vapor concentrations of  5  vol  %  and  50  vol  %  n - butane before routing the air flow through at least one subsequent volume of vapor adsorbent material wherein the subsequent volume of vapor adsorbent material is characterized by an incremental adsorption capacity at  25 ° C. of less than  35  g n - butane between vapor concentrations of  5  vol  %  and  50  vol  %  n - butane.     
     
     
       32. The system of  claim 31  wherein the second volume of vapor adsorbent material is located outside the canister in a separate subsequent canister. 
     
     
       33. The system of  claim 31  wherein the initial volume of vapor adsorbent material and the subsequent volume of vapor adsorbent material are activated carbon derived from materials selected from the group consisting of wood, peat, coal, coconut, lignite, petroleum pitch, petroleum coke, coal tar pitch, fruit pits, nut shells, sawdust, wood flour, synthetic polymer, and natural polymer having been activated by a process selected from the group consisting of chemical, thermal, and combined chemical/thermal activation methods. 
     
     
       34. The system of  claim 31  wherein the initial volume of vapor adsorbent material and the subsequent volume of vapor adsorbent material are inorganic materials selected from the group consisting of zeolites, porous silica, porous alumina, pillared clays, and molecular sieves. 
     
     
       35. The system of  claim 31  wherein the initial volume of vapor adsorbent material and the subsequent volume of vapor adsorbent material are porous polymers. 
     
     
       36. The system of  claim 31  wherein the subsequent volume of vapor adsorbent material exhibits adsorption capacities achieved by volumetric dilution. 
     
     
       37. The system of  claim 36  wherein the volumetric dilution is accomplished by the addition of a non- adsorbing filler as a co - ingredient by an addition process selected from the group consisting of addition with the activated carbon raw material prior to activation, addition with the adsorbent before forming into a shaped particle or monolith, and a combination thereof.   
     
     
       38. The system of  claim 36  wherein the volumetric dilution is accomplished by forming the adsorbent material into high voidage shapes selected from the group consisting of stars, hollow cylinders, asterisks, spirals, cylinders, and configured ribbons. 
     
     
       39. The system of  claim 36  wherein the volumetric dilution is accomplished by forming the adsorbent into a honeycomb or monolith shape. 
     
     
       40. The system of  claim 36  wherein the volumetric dilution is accomplished by the use of inert spacer particles, trapped air spaces, foams, and screens external to the adsorbent. 
     
     
       41. The system of  claim 37  wherein the non- adsorbing filler is a solid after processing.   
     
     
       42. The system of  claim 37  wherein the non- adsorbing filler is volatized or combusted to form voidages larger than  50  Å width within the shaped particle or monolith.   
     
     
       43. A canister operative for use in automotive systems for emission control defined by a canister vapor inlet to permit a fuel vapor flow path through an initial volume of vapor adsorbent within a first region of the canister toward a canister vent/air opening to permit a continued air flow path through a subsequent volume of adsorbent within a second region of the canister at the vent/air opening and the first region at a canister purge outlet, such that fuel vapor formed in a tank for storing volatile fuel flows through the canister vapor inlet into the initial volume of adsorbent where it is adsorbed and, during operation of an engine induction system, ambient air is caused to flow in a path to and through the vent/air opening and along the air flow path in the canister through the initial volume and the purge outlet to the induction system of the engine, wherein the flow of air removing a portion of the adsorbed fuel vapor but leaving a residue of fuel in the initial volume, and wherein at least one subsequent volume of vapor adsorbent material comprises a volume of  1 %  to  100   %  of the initial volume and is located either inside of the canister within the second region thereof or outside of the canister, and wherein the initial volume of vapor adsorbent material is characterized by an incremental adsorption capacity at  25 ° C. of greater than  35  g n - butane/L - bed between vapor concentrations of  5  vol  %  and  50  vol  %  n - butane before routing the air flow through at least one subsequent volume of vapor adsorbent material wherein the subsequent volume of vapor adsorbent material is characterized by an incremental adsorption capacity at  25 ° C. of less than  35  g n - butane between vapor concentrations of  5  vol  %  and  50  vol  %  n - butane.   
     
     
       44. The canister of  claim 43  wherein the second volume of vapor adsorbent material is located outside the canister in a separate subsequent canister. 
     
     
       45. The canister of  claim 43  wherein the initial volume of vapor adsorbent material and the subsequent volume of vapor adsorbent material are activated carbon derived from materials selected from the group consisting of wood, peat, coal, coconut, lignite, petroleum pitch, petroleum coke, coal tar pitch, fruit pits, nut shells, sawdust, wood flour, synthetic polymer, and natural polymer having been activated by a process selected from the group consisting of chemical, thermal, and combined chemical/thermal activation methods. 
     
     
       46. The canister of  claim 43  wherein the initial volume of vapor adsorbent material and the subsequent volume of vapor adsorbent material are inorganic materials selected from the group consisting of zeolites, porous silica, porous alumina, pillared clays, and molecular sieves. 
     
     
       47. The canister of  claim 43  wherein the initial volume of vapor adsorbent material and the subsequent volume of vapor adsorbent material are porous polymers. 
     
     
       48. The canister of  claim 43  wherein the subsequent volume of vapor adsorbent material exhibits adsorption capacities achieved by volumetric dilution. 
     
     
       49. The canister of  claim 48  wherein the volumetric dilution is accomplished by the addition of a non- adsorbing filler as a co - ingredient by an addition process selected from the group consisting of addition with the activated carbon raw material prior to activation, addition with the adsorbent before forming into a shaped particle or monolith, and a combination thereof.   
     
     
       50. The canister of  claim 48  wherein the volumetric dilution is accomplished by forming the adsorbent material into high voidage shapes selected from the group consisting of stars, hollow cylinders, asterisks, spirals, cylinders, and configured ribbons. 
     
     
       51. The canister of  claim 49  wherein the volumetric dilution is accomplished by an adsorbent formed into a honeycomb or monolith shape. 
     
     
       52. The canister of  claim 48  wherein the volumetric dilution is accomplished by the inclusion of inert spacer particles, trapped air spaces, foams, and screens external to the adsorbent. 
     
     
       53. The canister of  claim 49  wherein the non- adsorbing filler is a solid after processing.   
     
     
       54. The canister of  claim 49  wherein the non- adsorbing filler is volatized or combusted to form voidages larger than  50  Å width within the shaped particle or monolith.