WO1997022401A1

WO1997022401A1 - Method and apparatus for filtering volatile organic compounds

Info

Publication number: WO1997022401A1
Application number: PCT/US1995/016326
Authority: WO
Inventors: Richard Scott Moore
Original assignee: Airguard Industries Inc.
Priority date: 1995-12-15
Filing date: 1995-12-15
Publication date: 1997-06-26

Abstract

Volatile organic compounds are removed from an airstream by a granular room temperature adsorbent contained within the cells of a honeycomb matrix and normally maintained at ambient temperature. Periodically, the matrix is heated to drive off the components and rejuvenate the adsorbent. The adsorbent may be either activated carbon or a catalyst and, when the adsorbent is a catalyst, heating of the matrix propagates catalytic oxidation of the volatile organic components into carbon dioxide and water vapor.

Description

METHOD AND APPARATUS FOR FILTERING VOLATILE ORGANIC COMPOUNDS

BACKGROUND OF THE INVENTION This invention relates generally to method and apparatus for filtering contaminants from air. More particularly, the invention relates to the filtration of airstreamε through the use of a granular room temperature adsorbent capable of adsorbing certain odoriferous components in the air.

While the filter of the invention has many applications, it is particularly well-suited for filtering volatile organic compounds (e.g., toluene and benzene) from ambient temperature airstreams such as found in paintspray or other coating operations and in corrosion control operations. Due to high cost, many operations do not have apparatus for effectively removing volatile organic compounds from airstreams and thus are forced to discharge contaminated air to atmosphere rather than recirculating the air. When air is discharged to atmosphere, energy must be expended in heating or cooling make-up air.

Volatile organic compounds also are present in air circulated in buildings which experience so-called building related illness and sick building syndrome and also in air which is brought into or recirculated in vehicle passenger compartments. Previously, there has been no provision in these applications for economical removal of the volatile organic compounds and the odor resulting therefrom.

BRIEF SUMMARY OF THE INVENTION

The general aim of the present invention is to provide a relatively low cost and comparatively long life filter for removing volatile organic compounds from airstreams.

A more detailed object of the invention is to achieve the foregoing by advantageously using a metal honeycomb- type matrix in conjunction with a room temperature granular adsorbent and by periodically heating the matrix in order to purge the adsorbent of volatile organic compounds captured at ambient temperature, thereby to rejuvenate the adsorbent for further use.

Still another object of the invention is to provide the honeycomb-type matrix with an adsorbent which, when heated, propagates catalytic oxidation of the volatile organic components into harmless water vapor and carbon dioxide so that the filtered air may be recirculated in order to reduce the cost of heating and cooling a building.

These and other objects and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings .

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a top plan view of a new and improved filter incorporating the unique features of the present invention with successive layers of the filter being broken away to show underlying layers .

FIGURE 2 is a fragmentary cross-section taken substantially along the line 2-2 of FIGURE 1.

While the invention is susceptible of various modifications and alternative constructions, certain illustrated embodiment hereof has been shown in the drawings and will be described below in detail. It should be understood, however, that there is no intention to limit the invention to the specific form disclosed, but on the contrary, the intention is to cover all modifications, alternative constructions and equivalents falling within the spirit and scope of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The air filter 10 of the present invention utilizes a matrix 11 made of temperature-resistant material and defining a plurality of cells 12. A particularly advantageous matrix structure is a so-called honeycomb in which a substantial majority of the cells are six-sided, three sides of each cell being defined by one strip of material while the remaining three sides are defined by a second strip abutting the first strip at spaced locations. The ends of the strips are welded to frame members 14. Preferred materials for the strips and the frame members are stainless steel, copper, nichrome or alloys thereof.

In accordance with the invention, the cells 12 of the honeycomb matrix 11 are at least partially filled with a granular adsorbent 15 which is capable of adsorbing volatile organic compounds in an ambient temperature airstream and which, when heated, purges itself of the captured compounds. When the air being filtered is recirculated or when conditions dictate that air discharged to atmosphere be free of volatile organic compounds, the adsorbent that is used is a catalyst which is capable when heated of propagating catalytic oxidation of the captured compounds and releasing the contaminants as harmless carbon dioxide and water vapor. When the adsorbent 15 is a catalyst, various precious metal catalysts such as palladium, platinum or the like may be employed. From an economical standpoint, however, the preferred catalyst is a base metal catalyst and more specifically is a mixture of manganese dioxide and copper oxide. One particularly well-suited catalyst of this type is that sold under the trade designator Hopcalite by the Callery Chemical Division of Mine Safety Appliance, Inc. Hopcalite is granular in nature, and that which is used is 4 x 8 or 8 x 14 U.S. sieve size or mixtures thereof. After the honeycomb matrix 11 has been fabricated, a gas pervious and high temperature-resistant sheet or screen 17 of sufficient mesh to retain the catalyst 15 or other adsorbent is welded to the underside of the frame members 14 of the honeycomb. The cells 12 then are filled with the adsorbent, after which a second screen 18 is welded to the top sides of the frame members to retain the catalyst in the cells. When the filter 10 is used, for example, as a filter in a paintspray operation, a paint-laden airstream is directed through the screens 17 and 18 and the intervening catalyst 15. When the filter is at room temperature, the catalyst adsorbs volatile organic components such as toulene, benzene, alcohol and isooctane in the airstream. Periodically, the catalyst is heated to a temperature ranging between 250 and 600 degrees F to cause the catalyst to propagate catalytic oxidation of the captured volatile organic components and to cause the components to be driven from the catalyst as carbon dioxide and water vapor. The preferred way of heating the catalyst in a paintspray operation is to apply a voltage directly to the metal honeycomb 11 to cause the grids of the honeycomb to act as electrical resistance heating elements around the catalyst.

The filter 10 is maintained at the purge temperature

(preferably about 500 degrees F) for approximately five minutes and then is allowed to cool to ambient temperature.

Upon cooling, the rejuvenated catalyst again becomes effective to adsorb volatile organic components. The frequency with which the catalyst is heated depends upon the flow rate of the airstream and the degree of contamination therein and may be controlled by appropriate sensors acting in conjunction with a microprocessor. By virtue of the catalyst 15 converting the volatile organic compounds into their basic constituents, the air which is cleaned by the filter 10 may be recirculated in the building and need not be exhausted to atmosphere. Accordingly, heating and cooling costs are reduced while avoiding atmospheric pollution. Also, the filter reduces the lower explosive limit (LEL) in paintspray and corrosion control operations and thus promotes a safer working environment .

The filter 10 of the invention may be used in commercial building HVAC systems in OEM units and also is useful for filtering the air (either fresh or recirculated) of the passenger compartment of a vehicle. When the filter is used in a vehicle, it resides at ambient temperature and in an adsorption stage during the majority of time. When the filter requires rejuvenation, a damper is closed to shut off the flow of air through the filter and then the filter is heated, either electrically by the electrical system of the vehicle or by means of the exhaust or other heat generated by the engine. After the filter is allowed to cool, the damper is re-opened to resume the flow of air to the passenger compartment via the filter. The filter thus is very effective to remove odor from the air introduced into or recirculated in the passenger compartment .

In certain instances, the adsorbent 15 need not be a catalyst but may, for example, be a granular room temperature adsorbent such as activated carbon. The latter material will adsorb volatile organic components at ambient temperature and, when heated to a temperature of at least 250 degrees F, will drive off the contaminants in order to rejuvenate itself. In the case of activated carbon, however, the volatile organic components are not oxidized but instead are merely driven from the adsorbent in their original volatile form when the adsorbent is heated. Accordingly, activated carbon is effective as an adsorbent only in those cases where the air may be exhausted to atmosphere or to another filtration system during the purging cycle.

Claims

WHAT IS CLAIMED IS:

1. A filter for filtering contaminants present in a gas comprising a matrix made of high temperature-resistant material and defining a plurality of cells, an adsorbent at least partially filling said cells, screens made of high temperature-resistant material on opposite sides of said matrix and retaining said adsorbent in said cells while permitting said gas to flow through said matrix whereby said contaminants are captured by said adsorbent when the latter is at ambient temperature, and a means for periodically heating in situ said adsorbent to a predetermined temperature ranging between 250 degrees F and 600 degrees F.

2. A method of filtering contaminants from a contaminated gas, said method comprising the steps of: (A) flowing said gas through a filter comprising (i) a matrix made of high temperature-resistant material defining a plurality of cells, (ii) a catalyst at least partially filling said cells, said catalyst being capable of oxidizing said contaminants to carbon dioxide and water vapor, and (iii) gas pervious sheets of high temperature- resistant material on opposite sides of said matrix, and retaining said catalyst in said matrix; (B) closing off the flow of said gas through said filter while said catalyst is at ambient temperature whereby said contaminants are adsorbed by said catalyst; (C) heating said catalyst to a temperature of at least 250 degrees F to cause said catalyst to release the adsorbed contaminants; and (D) reopening the flow of said gas through said filter.

3. The filter according to claim 1, wherein a substantial majority of said cells are six-sided and said heating means is integral with said filter.

4. The filter according to claim 3, wherein three sides of each of said six-sided cells are made of one strip of high temperature-resistant material.

5. The filter according to claim 4, wherein said high temperature-resistant material is selected from the group consisting of stainless steel, copper, and nichrome.

6. The filter according to claim 3, wherein said adsorbent is capable of catalytically oxidizing said contaminants to carbon dioxide and water vapor.

7. The filter according to claim 6, wherein said adsorbent is selected from the group consisting of a base metal catalyst and a precious metal catalyst .

8. The filter according to claim 7, wherein said base metal catalyst consists of a mixture of manganese dioxide and copper oxide.

9. The filter according to claim 8, wherein said catalyst is Hopcalite.

10. The filter according to claim 9, wherein said adsorbent is activated carbon.

11. The filter according to claim 7, wherein said precious metal catalyst is selected from the group consisting of palladium and platinum catalysts.

12. The filter according to claim 1, wherein said means for periodically heating said adsorbent comprising applying a voltage to said matrix whereby said matrix acts as resistive heating element .

13. The method according to claim 2, wherein said catalyst is a mixture of manganese dioxide and copper oxide .

14. The method according to claim 13, wherein said contaminant is a volatile organic compound.

15. The method according to claim 14, wherein said volatile organic compound is selected from the group consisting of benzene, toluene, alcohol, and isooctane.

16. The method according to claim 2, wherein said catalyst is periodically heated by applying a voltage to said matrix whereby said matrix acts as a resistive heating element.

17. A method of filtering contaminants from a contaminated gas, said method comprising the steps of:

(A) providing a filter comprising (i) a matrix made of high temperature-resistant material and defining a plurality of cells, wherein a substantial majority of said cells are six-sided and three of the six sides are made of one strip of high-temperature resistant material, (ii) a granular activated carbon adsorbent at least partially filling said cells, and (iii) pervious sheets of high- temperature resistant material on opposite sides of said matrix;

(B) flowing said gas through said filter while said adsorbent is at ambient temperature whereby said contaminants are adsorbed by said adsorbent; and

(C) periodically heating said adsorbent to a temperature of at least 250 degrees F to cause said adsorbent to release the adsorbed contaminants, wherein said periodical heating is carried out by applying a voltage directly to said high-temperature resistant material .

18. The method according to claim 17, wherein said contaminant is a volatile organic compound.

19. The method according to claim 18, wherein said volatile organic compound is selected from the group consisting of benzene, toluene, alcohol, and isooctane.