# Patent

## Title
Method and apparatus for purging unwanted substances from air

## Abstract

An air filter for purging unwanted substances from air, the air filter comprising:

    
    
        an acid-purging stage, wherein the acid-purging stage comprises an air-permeable skeleton which has an acid-neutralizing substance mounted thereto, wherein the air-permeable skeleton comprises fiberglass fibers and the acid-neutralizing substance comprises sodium bicarbonate, and further wherein the sodium bicarbonate is secured to the fiberglass fibers using an adhesive; and
        a solvent-purging stage, wherein the solvent-purging stage comprises solvent-purging granules captured between two air-permeable screens, and further wherein the solvent-purging granules comprise activated carbon granules.

## Background
REFERENCE TO PENDING PRIOR PATENT APPLICATION
This patent application claims benefit of prior U.S. Provisional Patent Application Ser. No. 61/098,440, filed Sep. 19, 2008 by Francois Hauville for METHOD AND APPARATUS FOR PURGING UNWANTED SUBSTANCES FROM AIR AND/OR NEUTRALIZING UNWANTED SUBSTANCES IN AIR, which patent application is hereby incorporated herein by reference.


FIELD OF THE INVENTION
This invention relates to air filters in general, and more particularly to air filters of the sort which purge unwanted substances from air, i.e. to air filters which remove unwanted substances from air and/or neutralize unwanted substances in air.
BACKGROUND OF THE INVENTION
Air filters are used to purge unwanted substances from air. By way of example but not limitation, air filters are commonly used in laboratories to purge unwanted substances from the air in fumehoods before the air is vented from the fumehood, e.g., to the atmosphere or to the ambient air of the laboratory.
In the laboratory application noted above, the air filter typically uses activated carbon granules to purge unwanted substances from the air. Activated carbon is generally preferred for use in air filters because the activated carbon is very effective in purging solvents from air. Furthermore, the use of activated carbon granules is generally highly advantageous, since the activated carbon granules are easily handled, and since they naturally pack into an enclosure with spaces therebetween so as to combine high surface area contact with excellent air flow. Typically, the activated carbon granules are disposed in a simple filter frame, captured between two opposing screens (e.g., meshes, grills, etc.) which pass air therethrough but retain the activated carbon granules therebetween.
While activated carbon granules are extremely effective in purging solvents from the air, they are largely ineffective in purging acids from the air. As a result, where acids may be used within a fumehood, special additives (e.g., rare earth metals, organic metal catalysts, etc.) must be added to the activated carbon granules in order to purge acids from the air. However, these additives tend to reduce the effective surface area of the activated carbon granules, thereby reducing filter capacity. Furthermore, these acid-purging additives are generally only modestly effective in purging acids from the air, and in many cases can comprise relatively toxic materials which may be released in the air by the air flow through the filter.
Thus, incorporating acid-purging additives within the activated carbon granules results in an air filter with reduced efficiency for purging solvents and which has only modest effectiveness for purging acids.
On account of the foregoing, there is a need for a new and improved air filter which is highly effective with respect to both solvents and acids and which works with high efficiency and without using toxic additives.
SUMMARY OF THE INVENTION
These and other objects of the present invention are addressed by the provision and use of a novel air filter which comprises at least two stages, an acid-purging stage and a solvent-purging stage. The acid-purging stage generally comprises an air-permeable skeleton having an acid-neutralizing substance mounted thereto. The solvent-purging stage generally comprises solvent-purging granules packed between two opposing screens (e.g., meshes, grills, etc.).
In one preferred form of the invention, there is provided an air filter for purging unwanted substances from air, the air filter comprising:
an acid-purging stage; and
a solvent-purging stage.
In another form of the invention, there is provided an air filter for purging unwanted substances from air, the air filter comprising:
an acid-purging stage, wherein the acid-purging stage comprises an air-permeable skeleton which has an acid-neutralizing substance mounted thereto, wherein the air-permeable skeleton comprises fiberglass fibers and the acid-neutralizing substance comprises sodium bicarbonate, and further wherein the sodium bicarbonate is secured to the fiberglass fibers using an adhesive; and
a solvent-purging stage, wherein the solvent-purging stage comprises solvent-purging granules captured between two air-permeable screens, and further wherein the solvent-purging granules comprise activated carbon granules.
In another form of the invention, there is provided a method for purging unwanted substances from air, the method comprising:
providing an air filter for purging unwanted substances from air, the air filter comprising:

    
    
        an acid-purging stage; and
        a solvent-purging stage; and
    
    


passing the air which is to be filtered through the air filter so as to purge unwanted substances from the air.
And in another form of the invention, there is provided a method for purging unwanted substances from air, the method comprising:
providing an air filter for purging unwanted substances from air, the air filter comprising:

    
    
        an acid-purging stage, wherein the acid-purging stage comprises an air-permeable skeleton which has an acid-neutralizing substance mounted thereto, wherein the air-permeable skeleton comprises fiberglass fibers and the acid-neutralizing substance comprises sodium bicarbonate, and further wherein the sodium bicarbonate is secured to the fiberglass fibers using an adhesive; and
        a solvent-purging stage, wherein the solvent-purging stage comprises solvent-purging granules captured between two air-permeable screens, and further wherein the solvent-purging granules comprise activated carbon granules; and
    
    


passing the air which is to be filtered through the air filter so as to purge unwanted substances from the air.



BRIEF DESCRIPTION OF THE DRAWINGS
These and other objects and features of the present invention will be more fully disclosed or rendered obvious by the following detailed description of the preferred embodiments of the invention, which is to be considered together with the accompanying drawings wherein like numbers refer to like parts and further wherein:
FIG. 1 is a schematic view showing a novel air filter formed in accordance with the present invention;
FIGS. 2-4 are schematic views showing how the acid-purging stage of the novel air filter can be fabricated; and
FIG. 5 is a schematic view showing further details of the solvent-purging stage of the novel air filter.



DETAILED DESCRIPTION OF THE INVENTION
In General
The present invention provides a new and improved air filter which is effective for purging both solvents and acids from the air with high efficiency. To this end, and looking now at FIG. 1, there is shown a novel air filter 5 formed in accordance with the present invention. Air filter 5 generally comprises two stages, an acid-purging stage 10 followed by a solvent-purging stage 15.
Acid-purging stage 10 generally comprises an air-permeable skeleton 20 having an acid-neutralizing substance 25 mounted thereto. In one preferred form of the invention, acid-purging stage 10 comprises fiberglass fibers which have sodium bicarbonate adhered thereto.
Solvent-purging stage 15 generally comprises solvent-purging granules 30 packed between two opposing, air-permeable screens (e.g., meshes, grills, etc.) 35. In one preferred form of the invention, the solvent-purging granules comprise activated carbon granules.
As a result of this construction, when air is passed through air filter 5, the air first passes through acid-purging stage 10, where acid-neutralizing substance 25 (e.g., sodium bicarbonate) effectively neutralizes any acids which may be present in the air. Thereafter, the air passes through solvent-purging stage 15, where solvent-purging granules 30 (e.g., activated carbon granules) purge any solvents which may be present in the air.
Acid-Purging Stage 10
Looking next at FIGS. 2-4, acid-purging stage 10 generally comprises an air-permeable skeleton 20 having an acid-neutralizing substance 25 mounted thereto.
In one preferred form of the invention, acid-purging stage 10 comprises fiberglass fibers which have sodium bicarbonate adhered thereto. Sodium bicarbonate is extremely effective in neutralizing acids, and is relatively inexpensive, but its powder-like consistency makes it difficult to use in an air filter, where high surface area contact is required. The present invention solves this difficulty, and makes it practical to use sodium bicarbonate in an air filter, by providing a new and improved method for supporting the sodium bicarbonate in an acid-purging stage.
More particularly, and looking now at FIG. 2, acid-purging stage 10 preferably comprises an air-permeable mass of fiberglass fibers which together create the air-permeable skeleton 20. These fiberglass fibers are highly resistant to acids and bases, and easily pass air therethrough with nominal pressure loss. Looking next at FIG. 3, the fiberglass fibers are coated with an adhesive 40. Then, and looking now at FIG. 4, sodium bicarbonate powder is deposited on the fiberglass fibers, with adhesive 40 binding the sodium bicarbonate powder to the fiberglass fibers.
Thus it will be seen that the sodium bicarbonate is interspersed throughout, and adheres to, air-permeable skeleton 20, so that air passing therethrough makes excellent surface area contact with the sodium bicarbonate, whereupon the sodium bicarbonate can neutralize acids in the air.
If desired, acid-purging stage 10 can comprise an air-permeable skeleton 20 made of a material other than, or in addition to, fiberglass fibers (e.g., polyurethane fibers, etc.), and/or acid-purging stage 20 can comprise an acid-neutralizing substance 25 other than, or in addition to, sodium bicarbonate (e.g., sodium hydroxide, potassium hydroxide, sodium carbonate, calcium carbonate, calcium bicarbonate, calcium hydroxide, etc.). However, fiberglass fibers and sodium bicarbonate are the preferred materials for forming acid-purging stage 10.
Solvent-Purging Stage 15
Looking now at FIG. 5, solvent-purging stage 15 generally comprises solvent-purging granules 30 packed between two opposing screens (e.g., meshes, grills, etc.) 35. In one preferred form of the invention, the solvent-purging granules comprise activated carbon granules captured between two opposing screens (e.g., meshes, grills, etc.) which pass air therethrough but retain the activated carbon granules therebetween.
Two-Stage Construction
Returning now to FIG. 1, it will be seen that novel air filter 5 comprises a filter frame 45 having mounted therein two filter stages, the acid-purging stage 10 followed by the solvent-purging stage 15. Acid-purging stage 10 comprises the air-permeable skeleton 20 (preferably fiberglass fibers) which has the acid-neutralizing substance 25 (preferably sodium bicarbonate) mounted thereto. Solvent-purging stage 15 comprises the solvent-purging granules 30 (preferably activated carbon granules). As a result of this construction, when air is passed through air filter 5, the air first passes through acid-purging stage 10, where acid-neutralizing substance 25 (e.g., sodium bicarbonate) neutralizes acids which may be present in the air. Thereafter, the air passes through solvent-purging stage 15, where solvent-purging granules 30 (e.g., activated carbon granules) purge solvents which may be present in the air. Thus, the novel air filter of the present invention is capable of purging both acids and solvents from the air passing through the filter.
Significantly, the foregoing construction provides substantial advantages over the prior art, since it separates the acid-purging operation from the solvent-purging operation, embodying each operation in a separate stage of a singular filter frame, thereby allowing each operation to be optimized for its own particular purpose without detracting from the other operation.
More particularly, the acid-purging stage of the present invention is optimized by, preferably, using highly effective and relatively inexpensive sodium bicarbonate, supported on a fiberglass air-permeable skeleton structure, to neutralize acid. In this respect it should be appreciated that sodium bicarbonate is significantly more effective in neutralizing acids from air than the rare earth metals and organic metal catalysts traditionally used in air filters to purge acids from the air. Significantly, the use of sodium bicarbonate in the air filter also eliminates the toxicity concerns which can be present when using the rare earth metals and organic metal catalysts of the prior art.
Furthermore, the solvent-purging stage of the present invention is optimized by, preferably, using highly effective activated carbon granules to purge solvents from air, but without the addition of the aforementioned acid-purging rare earth metals and organic metal catalysts which can reduce the solvent-purging capacity thereof.
Reversing the Order of the Stages
In the preceding discussion, acid-purging stage 10 precedes solvent-purging stage 15 in the air flow, i.e., air moving through the air filter moves through acid-purging stage 10 before it moves through solvent-purging stage 15. However, it will be appreciated that, if desired, the acid-neutralizing stage can follow the solvent-purging stage, i.e., air moving through the air filter can move through the solvent-purging stage before it moves through the acid-purging stage.
Further Aspects of the Invention
Thus it will be seen that the present invention is unique in a number of ways, including (i) the two-stage composite construction of the air filter, which combines an acid-purging stage with a solvent-purging stage, (ii) the use of sodium bicarbonate in an air filter, and (iii) the manner in which the sodium bicarbonate is supported within the air filter.
Furthermore, the present invention purges acids from the air without requiring the use of toxic additives.
And the present invention purges unwanted acids from the air without diminishing the capacity of the air filter to purge solvents from the air.
Also, the present invention utilizes an inexpensive acid-neutralizing substance to purge acids from the air.
Additionally, the present invention provides for the binding of powders to fibers which can be industrialized in an inexpensive manner.
And the present invention provides a novel air filter which is particularly advantageous for filtering the air in fume hoods.
Still other advantages of the present invention will be apparent to those skilled in the art in view of the present invention.
Modifications
It is to be understood that the present invention is by no means limited to the particular constructions herein disclosed and/or shown in the drawings, but also comprises any modifications or equivalents within the scope of the invention.

## Claims

1. An air filter for purging unwanted substances from air, the air filter comprising:
an acid-purging stage; and
a solvent-purging stage;
wherein the acid-purging stage comprises an air-permeable skeleton which has an acid-neutralizing substance mounted thereto;
wherein the air-permeable skeleton comprises polyurethane fibers; and
wherein the air-permeable skeleton comprises both fiberglass fibers and polyurethane fibers.

2. An air filter according to claim 1 wherein the acid-neutralizing substance comprises sodium bicarbonate.

3. An air filter according to claim 2 wherein the sodium bicarbonate is secured to the air-permeable skeleton using an adhesive.

4. An air filter according to claim 1 wherein the acid-neutralizing substance comprises at least one from the group consisting of sodium bicarbonate, sodium hydroxide, potassium hydroxide, sodium carbonate, calcium carbonate, calcium bicarbonate and calcium hydroxide.

5. An air filter for purging unwanted substances from air, the air filter comprising:
an acid-purging stage; and
a solvent-purging stage;
wherein the acid-purging stage comprises an air-permeable skeleton which has an acid-neutralizing substance mounted thereto; and
wherein the air-permeable skeleton comprises fiberglass fibers, the acid-neutralizing substance comprises sodium bicarbonate, and further wherein the sodium bicarbonate is secured to the air-permeable skeleton using an adhesive.

6. An air filter according to claim 1 wherein the solvent-purging stage comprises solvent-purging granules captured between two air-permeable screens.

7. An air filter according to claim 6 wherein the solvent-purging granules comprise activated carbon granules.

8. An air filter according to claim 1 wherein the acid-purging stage precedes the solvent-purging stage.

9. An air filter according to claim 1 wherein the solvent-purging stage precedes the acid-purging stage.

10. An air filter for purging unwanted substances from air, the air filter comprising:
an acid-purging stage, wherein the acid-purging stage comprises an air-permeable skeleton which has an acid-neutralizing substance mounted thereto, wherein the air-permeable skeleton comprises fiberglass fibers and the acid-neutralizing substance comprises sodium bicarbonate, and further wherein the sodium bicarbonate is secured to the fiberglass fibers using an adhesive; and
a solvent-purging stage, wherein the solvent-purging stage comprises solvent-purging granules captured between two air-permeable screens, and further wherein the solvent-purging granules comprise activated carbon granules.

11. An air filter according to claim 10 wherein the acid-purging stage precedes the solvent-purging stage.

12. An air filter according to claim 10 wherein the solvent-purging stage precedes the acid-purging stage.

13. A method for purging unwanted substances from air, the method comprising:
providing an air filter for purging unwanted substances from air, the air filter comprising:
an acid-purging stage; and
a solvent-purging stage;
wherein the acid-purging stage comprises an air-permeable skeleton which has an acid-neutralizing substance mounted thereto;
wherein the air-permeable skeleton comprises polyurethane fibers; and
wherein the air-permeable skeleton comprises both fiberglass fibers and polyurethane fibers; and

passing the air which is to be filtered through the air filter so as to purge unwanted substances from the air.

14. A method for purging unwanted substances from air, the method comprising:
providing an air filter for purging unwanted substances from air, the air filter comprising:
an acid-purging stage, wherein the acid-purging stage comprises an air-permeable skeleton which has an acid-neutralizing substance mounted thereto, wherein the air-permeable skeleton comprises fiberglass fibers and the acid-neutralizing substance comprises sodium bicarbonate, and further wherein the sodium bicarbonate is secured to the fiberglass fibers using an adhesive; and
a solvent-purging stage, wherein the solvent-purging stage comprises solvent-purging granules captured between two air-permeable screens, and further wherein the solvent-purging granules comprise activated carbon granules; and

passing the air which is to be filtered through the air filter so as to purge unwanted substances from the air.