CN108136311A - Treated Activated Carbon for the removal of airborne organic and inorganic pollutants - Google Patents

Abstract

A filter assembly that effectively reacts with airborne or gaseous organic impurities, such as formaldehyde. The filter assembly is formed from a filter substrate, such as a fiber web or extruded carbon block, treated with tris(hydroxymethyl)aminomethane. This combination unexpectedly results in a longer-lasting filter that adsorbs organic airborne impurities for a longer period of time than untreated filter media of the same type. Formaldehyde removal is a prime example.

Description

Treated Activated Carbon for the removal of airborne organic and inorganic pollutants

technical field

The present invention generally relates to a filter combination that effectively reacts with airborne or gaseous organic and inorganic pollutants, and removes those components of air such as sulfur dioxide, nitrogen dioxide and hydrogen sulfide that may be found in diesel engine exhaust. More specifically, the present invention relates to a filter assembly capable of removing formaldehyde from air. Furthermore, the present invention provides a method for irreversibly removing or reducing organic and inorganic pollutants from ambient air.

Background technique

Airborne impurities such as formaldehyde, sulfur dioxide, nitrogen dioxide, hydrogen sulfide, etc. represent a pervasive and dangerous concern in the environment. As a descriptive example, formaldehyde is a colorless, strong-smelling gas commonly found in aqueous (water-based) solutions. When condensed, the gas is converted to various other forms of formaldehyde (different chemical formulations), which have greater practical value. Commonly used as a preservative in medical laboratories and mortuaries, formaldehyde can also be found in many products such as chemicals, particle board, household items, glues, non-ironing fabrics, paper coatings, fiberboard, and plywood. It is also widely used as an industrial fungicide, bactericide and disinfectant.

Formaldehyde is a stable molecule formed by adding two hydrogen atoms to a carbonyl group. It has the chemical element symbol HCHO (H2C=O). It is the carbonyl group, or function, that makes formaldehyde react so well with other molecules. This function allows formaldehyde to bind tightly to other molecules, making it ideal for linking substances together to form unique, versatile properties.

Formaldehyde, an organic compound and the simplest aldehyde, can be oxidized by reaction with known reagents such as potassium permanganate and potassium hydroxide/potassium iodide, both of which were found to be ineffective. It is the most common aldehyde in the environment. The natural background concentration is <1 μg/m3, with an average of about 0.5 μg/m3 (1 ppm=1.25 mg/m3; 1 mg/m3=0.8 ppm (at 20°C and 1013 kPa)). In urban environments, outdoor air concentrations are more variable and depend on local conditions; annual averages typically range from 1 to 20 µg/m3. Short peaks, such as during heavy traffic or severe temperature inversions, can range up to 100 µg/m3.

The highest levels of airborne formaldehyde have been detected in indoor air, where it is released from various consumer products such as building materials and household items. At least one survey reported indoor formaldehyde levels ranging from 0.10 to 3.68 parts per million (ppm). Higher levels were found in newly manufactured or mobile homes than in older traditional homes.

Acute toxic reactions caused by inhalational stimulation of formaldehyde exposure mainly include effects on the eyes, nose, throat, and nasal cavity. Other visible effects in humans exposed to high levels of formaldehyde are coughing, wheezing, chest pain and bronchitis.

Ingestion of formaldehyde in humans can lead to corrosion of the gastrointestinal tract, inflammation and ulceration of the mouth, esophagus and stomach.

Formaldehyde can be inhaled as a gas or vapour, or absorbed through the skin as a liquid. Human contact may occur during the handling of textiles and during the production of resins. In addition to healthcare professionals and medical laboratory technicians, potentially at-risk groups include funeral workers and teachers and students who handle biological specimens preserved in formaldehyde or formalin.

Formaldehyde is toxic when ingested and can be a strong skin irritant. Formaldehyde is easily absorbed by the skin and is the tenth most common cause of dermatitis. Exposure to high airborne concentrations of formaldehyde can cause severe respiratory irritation and lead to permanent respiratory damage. Exposure to air concentrations exceeding 100 parts per million (ppm air) can cause convulsions, coma, or death.

Formaldehyde reacts almost instantaneously with primary and secondary amines, thiols, hydroxyl groups and amides to form methyl derivatives. As an electrophile, formaldehyde can react with macromolecules such as DNA, RNA and proteins to form reversible adducts or irreversible cross-links. Absorbed formaldehyde can be oxidized to formate in three different ways, and can be exhaled as carbon dioxide or incorporated into biomacromolecules through the tetrahydrofolate-dependent one-carbon biosynthetic pathway.

OSHA has established permissible exposure limits (PEL's) for formaldehyde. Two PEL's have been established for formaldehyde: 8 hour time weighted average (PEL-TWA = 0.75 ppm) and short term exposure limit (STEL = 2.0 ppm).

While many products have the potential to release formaldehyde into indoor air, few are responsible for the significant levels of pollution. Pressed wood products and UFFI (urea-formaldehyde foam insulation) can emit formaldehyde at a greater rate than other products.

Therefore, in the prior art, methods for removing or reducing the formaldehyde content in the air have been sought. Attempts have been made to reduce formaldehyde levels both during the manufacture of potentially formaldehyde-emitting articles and in the environment in which these articles are installed. For example, U.S. Patent No. 4,397,756 issued to Lehmann on August 9, 1983, entitled "Methods and Combinations for Reducing Formaldehyde Emissions from Wood Composite Panels Provides a method and combination for reducing formaldehyde emissions from wood panels," A combination comprising urea, a carbohydrate-based material and an acidic catalyst is taught. U.S. Patent No. 4,517,111, issued May 14, 1985, to Dorman et al., entitled "Absorbents for Formaldehyde in Air," provides a composition of matter that is adsorbed by potassium permanganate salt or chemisorbed to on a solid base support. This combination can be released or contained in a container or cartridge, allowing it to be exposed to formaldehyde-contaminated air.

U.S. Patent No. 7,052,683, issued to Farkas on May 30, 2006, entitled "Combined gaseous detoxification of formaldehyde, in aqueous solution, and protection of human cells against formaldehyde," teaches a compound comprising a detoxifying combination of substances that rapidly Neutralizes and immobilizes toxic formaldehyde vapors to form formaldehyde adducts, where the enzyme plays an important role in the defense against formaldehyde in the oral buccal mucosa and oral epithelial cell lines.

Although more measures have been taken to reduce formaldehyde exposure, there is still a need for improved methods for controlling gaseous formaldehyde to smaller concentrations in the environment. Therefore, it is advisable to develop a filter type device whereby formaldehyde will be irreversibly retained.

Contents of the invention

Considering the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide an activated carbon filter for removing inorganic impurities such as sulfur dioxide, nitrogen dioxide, hydrogen sulfide and organic impurities such as formaldehyde in the air, to name a few example.

Another object of the present invention is to treat fibrous web substrates with activated carbon impregnated with Tris(hydroxymethyl)aminomethane or TRIS as a means for removing organic and inorganic airborne impurities.

The achievement of the above and other objects will be apparent to those skilled in the art in the present invention, which relates to a filter medium for removing organic pollutants in the air, comprising activated carbon medium, which has a first charge and is Chemical impregnation is used to remove formaldehyde and/or other aldehydes from the air, while activated carbon media is used to remove organic compounds.

The chemical reagents may include chemically treating the activated carbon media with a monolayer of tris(hydroxymethyl)aminomethane.

The activated carbon media preferably includes a pH altering material that alters the pH of the influent water such that microbial contaminants present in the influent water maintain a second charge opposite the first charge of the activated carbon media.

Activated carbon media may comprise solid composite filter media, fibrous paper media, or nanofiber filter media.

The activated carbon media preferably has a first charge and is impregnated with chemicals for removal of sulfur dioxide, nitrogen dioxide and/or hydrogen sulfide.

In another aspect, the invention relates to a process for forming a filter medium for removing formaldehyde and/or other aldehydes from air, the process comprising: impregnating activated carbon with tris(hydroxymethyl)aminomethane; providing a substrate web (fibrillating nanofibers); depositing activated impregnated carbon with thermoplastic binder particles on the substrate web; and fusing the activated impregnated carbon fibers and thermoplastic binder particles to the substrate web.

The process may include adding a second substrate layer bonded to the substrate web by a thermoplastic adhesive.

Description of drawings

The features of the invention which are believed to be novel and which are characteristic of the elements of the invention are set forth in the appended claims. These diagrams are for descriptive purposes only and are not intended to draw specifications. The invention itself, however, both as to organization and method of operation, is best understood from the detailed description taken in conjunction with the accompanying drawings:

Figure 1 depicts a graph of formaldehyde concentration over time for non-TRIS-based impregnated carbons;

Figure 2 depicts a graph of formaldehyde concentration over time for TRIS-based impregnated carbons.

Detailed ways

In describing the preferred embodiment of the invention, reference will be made to Figures 1-2 of the drawings, wherein like numerals represent like features of the invention.

Chemisorption is a type of adsorption involving a chemical reaction between a surface and an adsorbate. A new chemical bond is created on the adsorbent surface. Chemisorption occurs when volatile pollutant molecules chemically react with the sorbent surface to form non-volatile products. This mechanism often allows the capture of lower boiling compounds such as formaldehyde. As a result, the filtration capabilities of sorbent filter media such as carbon composites can be significantly enhanced by impregnating them with appropriate chemical agents. The price paid for efficiency is reagent selectivity. As used herein, "adsorbent filter media" or "adsorbent pre-filter media" refers to filter media made with an adsorbent, such as activated carbon. Examples of sorbent filter media are Commercially available from KX Technologies, LLC, West Haven, Connecticut.

The present invention incorporates composite filter media, such as activated carbon filter media, such as It generally includes a charged medium and a pH altering material that changes the pH of the feed water such that microbial contaminants present in the feed water maintain a first charge opposite to the charged medium having a second charge. The charged composite filter media can be any charged media known to those skilled in the art, such as solid composite filter media, fibrous paper media, and nanofiber filter media, to name a few.

use Composite filter media serves as an illustrative example, but does not limit the invention to only such activated carbon composites. Activated carbon is a high-surface-area porous material widely used in purification, material separation, catalysis, and medicine. Activated carbons have high adsorption capacity, surface activity, and range of pore sizes; factors that are useful properties in many applications. Activated carbon can be made from a variety of sources: natural products such as coal, coconut shells, wood, peat or bone, and synthetic materials such as polymers.

The filter media typically has a moisture content of less than 10% and contains a 50:50 mix of 20×50 mesh activated carbon. An unexpected result was that when this composite filter medium was chemically treated with tris(hydroxymethyl)aminomethane, an organic compound represented by the formula (HOCH2)3CNH2.

TRIS was added to create a filter media for removing formaldehyde and other aldehydes from the air, while utilizing activated carbon to remove organic compounds. TRIS reacts with aldehydes such as formaldehyde to form oxazolidine compounds, and two aldehyde molecules react with TRIS to form oxazolidines, providing high-performance air-purifying adsorbents.

The reaction of formaldehyde with TRIS reagent is an example of a carbonyl compound containing an ammonia derivative. The reaction scale results in the bonding of the carbonyl carbon to the amine nitrogen and can be used for the collection and characterization of aldehydes and ketones.

This newly treated activated carbon also reacts with components of diesel exhaust such as sulfur dioxide, nitrogen dioxide and hydrogen sulfide.

The flat panel test data demonstrate the superior performance of TRIS-based composites compared to conventional (KI-impregnated) activated carbon. Figure 1 is a graph of formaldehyde concentration over time for non-TRIS based impregnated carbons. Figure 2 is a graph of formaldehyde concentration versus time for TRIS-based impregnated carbons. In both cases, the initial air formaldehyde concentration was established at 30 ppm, 50% relative humidity, and delivered at a velocity of 0.25 m/s.

In Figure 1, the untreated (non-TRIS-based) impregnated carbon would saturate and no longer provide formaldehyde filtration capacity within about 50 to 60 minutes. During this time period, the initial concentration of formaldehyde in the air will approach a similar level downstream of the activated carbon filter (30ppm).

In Figure 2, treated (TRIS-based) impregnated carbon was used as filter media. The breakthrough point for saturation, or formaldehyde, does not occur until 150 to 240 minutes, which means that treated carbon filters are three to four times more effective at removing formaldehyde from the air than untreated carbon filters. This unexpectedly led to the combination of composite filter media treated with monolayer chemistry of tris(hydroxymethyl)aminomethane.

A process for treating an activated carbon filter, preferably in paper form, comprising providing a first substrate web, for example comprising fibrillated nanofibres. Next, activated (impregnated) carbon is deposited along with particles of thermoplastic binder, which are fused into the first substrate web and impregnated carbon. The impregnated carbon is impregnated with tris(hydroxymethyl)aminomethane.

Such a web may also include a second substrate layer bonded to the first substrate by a thermoplastic adhesive.

Webs formed from fiber paper with activated carbon impregnated with TRIS have the advantage that formaldehyde removal efficiencies equal to or greater than other commercially available products using heavier activated carbons can be achieved using lower composite weights.

As mentioned earlier, treated activated carbon filters also react with components of diesel exhaust such as sulfur dioxide, nitrogen dioxide and hydrogen sulfide. Furthermore, the combination of activated carbon and TRIS on these air impurities also unsurprisingly produces enhanced filtration.

Although the invention has been described in conjunction with specific preferred embodiments, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art from the foregoing description. It is therefore contemplated that the appended claims will embrace any such alternatives, modifications and changes without departing from the true scope and spirit of the invention.

Claims (9)

1. a kind of for removing the filter media of organic in air and inorganic pollution, it includes activated carbon medias to have first Charge and the chemical reagent dipping for being used to remove formaldehyde in air and/or other aldehyde, while utilize the activated carbon media Remove organic compound.

2. the filter media of claim 1, wherein the chemical reagent includes the unimolecule stratification with water-soluble tertiary amine It learns and handles the activated carbon media.

3. the filter media of claim 1, wherein the pH that the activated carbon media includes changing water inlet pH value changes material Material so that microorgranic contaminant present in water inlet maintains the second charge with the first opposite charge of the activated carbon media.

4. the filter media of claim 1, wherein the activated carbon media includes solid composite filter device medium, fiber Paper delivery medium or nanofiber filter medium.

5. the filter media of claim 2, wherein the water-soluble tertiary amine includes three (methylol) aminomethanes.

6. the filter media of claim 2, wherein the activated carbon media includes the first charge and by chemical reagent It impregnates to remove sulfur dioxide, nitrogen dioxide and/or hydrogen sulfide.

7. a kind of for removing the formation process of the filter media of formaldehyde in air and/or other aldehyde, the technique includes：

With three (methylol) aminomethane impregnated activated carbons；

Substrate web (fibrillated nanofiber) is provided；

The active impregnated carbon is deposited on thermoplastic adhesives particle on the substrate web；And

It will be on the active impregnated carbon and the thermoplastic adhesives particle fusion to the substrate web.

8. including adding second substrate layer, it is fine to be bonded to the substrate by thermoplastic adhesives for the technique of claim 7 Dimension is online.

9. the technique of claim 8, wherein the second substrate layer includes polypropylene, polyester and/or nylon substrate.