Particulate filter and method of use

Abstract

A particulate filter particularly suited for analytical gravimetric weighing applications is disclosed. The particulate filter includes a polytetrafluoroethylene (PTFE) media supported by a ring and yields stable microgram and submicrogram weighing results. The support ring may be PTFE, metal foil, or another non-hygroscopic polymer such that the mass of the filter does not vary with changes in atmospheric moisture. The filter simplifies the discharge of electrostatic charge buildup such that when a conductive filter media is combined with a conductive ring device, the discharge may be accomplished by placing the filter on a grounded weighing pan or other surface. The particulate filter can simplify filter identification by including identification symbols imprinted on each side of the filter media. Due to the chemically inert qualities of its components, the particulate filter is particularly suited for extraction techniques used during the detection of polycyclic hydrocarbons as is conducted in emissions and ambient air testing.

1 . A particulate filter comprising: 
 a fluoropolymer filter membrane;    an identification symbol printed on first and second sides of the filter membrane; and    a support ring fused to an outer rim of the filter membrane,    wherein the particulate filter is substantially non-hygroscopic and moisture invariable, and substantially inert to dissolution by organic solvents.    
   
   
       2 . The particulate filter of  claim 1 , wherein the filter membrane comprises a polytetrafluoroethylene (PTFE) material, and wherein the support ring is welded to the filter membrane.  
   
   
       3 . The particulate filter of  claim 2 , wherein a porosity of the filter membrane ranges from about 70 percent to about 95 percent.  
   
   
       4 . The particulate filter of  claim 2 , wherein the filter membrane has an average pore size ranging from about 0.05 micrometers to about 3.0 micrometers.  
   
   
       5 . The particulate filter of  claim 4 , wherein the average pore size ranges from about 1.0 micrometers to about 2.5 micrometers.  
   
   
       6 . The particulate filter of  claim 2 , wherein the filter has an airflow of at least about 1.0 cfm/ft 2  at 0.5 inches of water.  
   
   
       7 . The particulate filter of  claim 6 , wherein the airflow is at least 2.0 cfm/ft 2  at 0.5 inches of water.  
   
   
       8 . The particulate filter of  claim 2 , wherein the filter membrane has a thickness in the range of about 0.0005 inches to about 0.0035.  
   
   
       9 . The particulate filter of  claim 8 , wherein the filter membrane has a thickness of about 0.0012 inches.  
   
   
       10 . The particulate filter of  claim 2 , wherein the filter captures at least 99 percent of 0.1 micrometer particles at about 10.5 fpm air velocity.  
   
   
       11 . The particulate filter of  claim 10 , wherein the filter captures at least 99.99 percent of 0.1 micrometer particles at about 10.5 fpm air velocity.  
   
   
       12 . The particulate filter of  claim 2 , wherein the support ring comprises a material selected from the group consisting of PTFE; polymers of tetrafluoroethylene, perfluorovinylether, and perfluoroalkoxy; polymers of tetrafluoroethylene and ethylene; polyvinylidine fluoride; polymers of tetrafluorothylene and hexafluoropropylene; ethylene-chlorotrifluoroethylene copolymer; polymethylpentene; polyester; polypropylene; polyethylene; a metal foil; and a moldable thermoplastic.  
   
   
       13 . The particulate filter of  claim 2 , wherein the support ring is overmolded to the filter membrane, and wherein the support ring comprises a material selected from the group consisting of a thermoplastic polyurethane resin; a thermoplastic elastomer; a liquid crystal polymer; and a polyphenylene sulfide.  
   
   
       14 . The particulate filter of  claim 2 , wherein the filter membrane comprises a PTFE material and a material selected from the group consisting of a carbon filler, a carbon powder, a carbon fiber, and a ceramic material, to vary an electrical conductivity characteristic of the particulate filter.  
   
   
       15 . The particulate filter of  claim 1 , wherein the identification symbol comprises a dot-coded identification symbol.  
   
   
       16 . The particulate filter of  claim 1 , wherein the identification symbol printed on the first side is offset from the identification symbol printed on the second side.  
   
   
       17 . The particulate filter of  claim 16 , wherein the identification symbol comprises a unique start character to differentiate the identification symbol on the first side from the identification symbol on the second side.  
   
   
       18 . The particulate filter of  claim 1 , wherein the identification symbol comprises printed ink.  
   
   
       19 . The particulate filter of  claim 18 , wherein the ink comprises a known chemical profile.  
   
   
       20 . The particulate filter of  claim 18 , wherein the ink is insoluble.  
   
   
       21 . The particulate filter of  claim 1 , wherein the particulate filter is substantially circular and the support ring is welded concentrically to the filter membrane.  
   
   
       22 . The particulate filter of  claim 21 , wherein the particulate filter has a diameter of less than about 100 millimeters and the support ring has a diameter of less than about 10 millimeters.  
   
   
       23 . The particulate filter of  claim 22 , wherein the particulate filter has a diameter of about 47 millimeters and the support ring has a diameter of about 3 millimeters.  
   
   
       24 . The particulate filter of  claim 1 , wherein the particulate filter has a hygroscopic absorption rate that is generally proportional to a mass of the particulate filter.  
   
   
       25 . The particulate filter of  claim 24 , wherein a particulate filter having a mass of about 0.14 grams to about 0.16 grams has a hygroscopic absorption rate of less than about 0.4 micrograms per percent of relative humidity change.  
   
   
       26 . The particulate filter of  claim 1 , wherein the particulate filter is substantially inert to dissolution by organic solvents selected from the group consisting of dichloromethane, acetone, toluene, cyclohexane, hexane, a mixture of ethanol and toluene, benzene, methylenechloride, methanol, and combinations of the foregoing.  
   
   
       27 . The particulate filter of  claim 1 , wherein the particulate filter is less than about 7 millimeters from flat over an entire surface.  
   
   
       28 . The particulate filter of  claim 27 , wherein the particulate filter is about 2 micrometers thick.  
   
   
       29 . A method of analytical gravimetric weighing using a particulate filter comprising the steps of: 
 equilibrating a particulate filter comprising a fluoropolymer filter membrane and a perfluoroalkoxy polymer support ring to an ambient pre-test environment;    identifying the particulate filter by an identification symbol printed on a first and a second side of the particulate filter;    dissipating electrostatic charge buildup on the particulate filter;    pre-weighing the particulate filter;    conducting a testing application using the particulate filter;    equilibrating the particulate filter to an ambient post-test environment;    identifying the particulate filter by the identification symbol printed on a clean side of the particulate filter;    post-weighing the particulate filter; and    determining a net load of particulate collected by the particulate filter in the testing application based upon the pre-weighing and the post-weighing.    
   
   
       30 . The method of  claim 29 , wherein the fluoropolymer comprises a polytetrafluoroethylene material.  
   
   
       31 . The method of  claim 29 , further comprising the steps of: 
 exposing the particulate filter to a volume of air in the testing application; and    calculating a load of particulate within the volume of air from the net load of particulate collected.    
   
   
       32 . The method of  claim 29 , wherein the step of dissipating electrostatic charge buildup on the particulate filter comprises placing the particulate filter on a grounded surface.  
   
   
       33 . The method of  claim 29 , wherein the step of dissipating electrostatic charge buildup on the particulate filter comprises using a Polonium 210 and an alpha emitter radioactive element.  
   
   
       34 . The method of  claim 29 , wherein the steps of identifying the particulate filter by an identification symbol further comprise scanning the identification symbol.  
   
   
       35 . The method of  claim 29 , wherein the step of conducting a testing application using the particulate filter comprises conducting an engine test to detect a polycyclic aromatic hydrocarbon.  
   
   
       36 . A method of detecting polycyclic aromatic hydrocarbons (PAHs) using a particulate filter comprising the steps of: 
 identifying a particulate filter comprising a polytetrafluoroethylene filter membrane and a perfluoroalkoxy polymer support ring by an identification symbol printed on a first and a second side of the filter membrane;    collecting a particulate sample by the filter;    identifying the filter by the identification symbol printed on at least one of the first and second side of the filter membrane;    extracting the particulate sample from the filter; and    analyzing the extracted sample for PAHs.    
   
   
       37 . The method of  claim 36 , further comprising the step of dissipating electrostatic charge buildup on the particulate filter.  
   
   
       38 . The method of  claim 36 , wherein the step of collecting a particulate sample comprises exposing the particulate filter to a combustion engine exhaust stream.  
   
   
       39 . The method of  claim 36 , wherein the steps of identifying the filter by an identification symbol further comprise scanning the identification symbol.  
   
   
       40 . The method of  claim 36 , wherein the step of extracting the particulate sample comprises extracting the particulate sample using an organic solvent.  
   
   
       41 . The method of  claim 36 , wherein the step of extracting the particulate sample comprises one of the extraction methods selected from the group consisting of Soxhlet extraction, ultrasonic extraction, and microwave extraction.  
   
   
       42 . The method of  claim 36 , wherein the step of analyzing the extracted sample comprises analyzing the extracted sample by gas chromatography/mass spectrometry/selective ion monitoring in a positive ion electron impact mode.  
   
   
       43 . The method of  claim 36 , wherein the step of analyzing the extracted sample comprises ignorning a component attributable to a known chemical profile of an identification symbol ink.  
   
   
       44 . A method of manufacturing a particulate filter used for analytical gravimetric weighing comprising the steps of: 
 welding a support ring comprising a polymer of perfluoroalkoxy to a filter membrane comprising a fluoropolymer;    printing an identification symbol on a first side of the filter membrane; and    printing the identification symbol on a second side of the filter membrane offset from the identification symbol on the first side.    
   
   
       45 . The method of  claim 44 , wherein the step of welding comprises heat welding the support ring to the filter membrane.  
   
   
       46 . The method of  claim 44 , further comprising the step of utilizing an ink jet printer for printing the identification symbols on the first side and the second side.  
   
   
       47 . The method of  claim 46 , wherein the step of selecting an ink comprises selecting an ink based at least in part upon a solubility property of the ink.  
   
   
       48 . The method of  claim 46 , wherein the step of selecting an ink comprises selecting an ink having a known chemical profile.  
   
   
       49 . The method of  claim 44 , wherein the fluoropolymer comprises polytetrafluoroethylene.  
   
   
       50 . The method of  claim 44 , further comprising the step of varying a conductive electrical property of the particulate filter by compounding the fluoropolymer with a material selected from the group consisting of carbon filler, carbon power, carbon fiber, and a ceramic material.  
   
   
       51 . A particulate filter comprising: 
 a fluoropolymer membrane; and    a polypropylene support scrim,    wherein the polymeric support scrim comprises a material selected from the group consisting of polyester, polypropylene, polyethylene, and polyamide.    
   
   
       52 . The particulate filter of  claim 51 , wherein the fluoropolymer membrane comprises a polytetrafluoroethylene (PTFE) material.  
   
   
       53 . The particulate filter of  claim 52 , wherein a porosity of the membrane ranges from about 70 percent to about 95 percent.  
   
   
       54 . The particulate filter of  claim 53 , wherein the membrane has an average pore size ranging from about 0.05 micrometers to about 3.0 micrometers.  
   
   
       55 . The particulate filter of  claim 54 , wherein the average pore size ranges from about 1.0 micrometers to about 2.5 micrometers.  
   
   
       56 . The particulate filter of  claim 52 , wherein the filter has an airflow of at least about 1.0 cfm/ft 2  at 0.5 inches of water.  
   
   
       57 . The particulate filter of  claim 56 , wherein the airflow is at least 2.0 cfm/ft 2  at 0.5 inches of water.  
   
   
       58 . The particulate filter of  claim 52 , wherein the membrane and support scrim have a thickness in the range of about 0.005 inches to about 0.020 inches.  
   
   
       59 . The particulate filter of  claim 58 , wherein the membrane and support scrim have a thickness of about 0.010 inches.  
   
   
       60 . The particulate filter of  claim 52 , wherein the filter captures at least 99 percent of 0.1 micrometer particles at about 10.5 fpm air velocity.  
   
   
       61 . The particulate filter of  claim 60 , wherein the filter captures at least 99.99 percent of 0.1 micrometer particles at about 10.5 fpm air velocity.  
   
   
       62 . The particulate filter of  claim 51 , wherein the polymeric support scrim has a thickness of less than about 0.0100 inches.  
   
   
       63 . The particulate filter of  claim 62 , wherein the polymeric support scrim has a thickness of less than about 0.0045 inches.  
   
   
       64 . The particulate filter of  claim 51 , wherein the polymeric support scrim has an air permeability of at least 770 cubic feet per minute per square foot at 0.5 inches of water.  
   
   
       65 . The particulate filter of  claim 51 , wherein the polymeric support scrim has a moisture absorption of less than about 1 percent at 65 degrees Fahrenheit and 65 percent relative humidity.  
   
   
       66 . The particulate filter of  claim 51 , wherein a porosity of the polymeric support scrim ranges from about 20 percent to about 80 percent.  
   
   
       67 . The particulate filter of  claim 66 , wherein a porosity of the polymeric support scrim ranges from about 40 percent to about 70 percent.