CN108136311B

CN108136311B - Treated activated carbon for removal of organic and inorganic contaminants from air

Info

Publication number: CN108136311B
Application number: CN201680062078.3A
Authority: CN
Inventors: 罗伯特·W·瑞祖克; 卡提克·菩提库奇
Original assignee: Graver Technologies LLC
Current assignee: Graver Technologies LLC
Priority date: 2015-10-22
Filing date: 2016-10-21
Publication date: 2021-07-27
Anticipated expiration: 2036-10-21
Also published as: CN108136311A; CN114073935A

Abstract

A filter assembly that reacts efficiently with organic impurities in the air or in gaseous form, such as formaldehyde. The filter assembly is formed from a filter substrate, such as a fibrous web or extruded carbon block, treated with tris (hydroxymethyl) aminomethane. An unexpected result of this combination is a more durable filter that is capable of adsorbing organic air impurities over a longer period of time than an untreated filter media of the same type. The removal of formaldehyde is a well-described example.

Description

Treated activated carbon for removal of organic and inorganic contaminants from air

Technical Field

The present invention relates generally to a filter assembly that reacts efficiently with airborne or gaseous organic and inorganic pollutants, and to the removal of those components of air, such as sulfur dioxide, nitrogen dioxide and hydrogen sulfide, that are found in, for example, diesel exhaust. More particularly, 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 contaminants from ambient air.

Background

Impurities in the air, such as formaldehyde, sulfur dioxide, nitrogen dioxide, hydrogen sulfide, etc., represent a ubiquitous hazard concern in the environment. As an illustrative example, formaldehyde is a colorless, strongly odoriferous gas that is typically present in aqueous (water-based) solutions. When condensed, the gas is converted to various other forms of formaldehyde (different chemical formulations) which have greater utility. Formaldehyde is also found in many products, such as chemicals, particle board, household goods, glues, permanent press fabrics, paper coatings, fiber board, and plywood. It is also widely used as an industrial fungicide, bactericide and disinfectant.

Formaldehyde is a stable molecule formed by the addition of two hydrogen atoms to a carbonyl group. It has the chemical element symbol HCHO (H2C ═ O). It is the carbonyl group or function that reacts formaldehyde so well with other molecules. This function allows formaldehyde to bind tightly to other molecules, making it an ideal material for linking materials together into unique, versatile, characteristic attributes.

Formaldehyde, an organic compound and, most simply, an aldehyde, can be oxidized by reaction with known reagents such as potassium permanganate and potassium hydroxide/iodide, both of which have been found to be ineffective. It is the most common aldehyde in the environment. Natural background concentrations <1 microgram/cubic meter, averaging about 0.5 microgram/cubic meter (1ppm ═ 1.25 mg/cubic meter; 1 mg/cubic meter ═ 0.8ppm (at 20 ℃ and 1013 kpa)). In urban environments, outdoor air concentrations are more variable and depend on local conditions; the annual average is typically between 1 and 20 micrograms per cubic meter. Short peaks, for example in heavy traffic or severe adverse temperatures, can range up to 100 micrograms/cubic meter.

The highest levels of formaldehyde in air have been detected in indoor air, which is released from various consumer products such as building materials and household goods. At least one survey reports indoor formaldehyde levels in the range of 0.10 to 3.68 parts per million (ppm). Higher levels are found in newly manufactured or mobile homes than in older conventional homes.

The acute toxic reactions caused by formaldehyde exposure through inhalation stimulation are mainly ocular, nasal, laryngeal, and have an effect on the nasal cavity. Other visible effects of human exposure to high levels of formaldehyde are cough, wheezing, chest pain and bronchitis.

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

Formaldehyde can be inhaled as a gas or vapor and also absorbed through the skin as a liquid. There is a possibility that the human body may be contacted during the treatment of the textile and the production of the resin. In addition to healthcare professionals and technicians in medical laboratories, potentially high risk groups include funeral workers and teachers and students who handle biological specimens preserved with formaldehyde or formalin.

Formaldehyde is toxic after ingestion and can be a strong skin irritant. Formaldehyde is easily absorbed by the skin and is the tenth most common cause of dermatitis. High formaldehyde concentrations in air exposure can lead to severe respiratory irritation and permanent respiratory damage. Exposure to air at concentrations in excess of 100 parts per million (ppm air) can lead to convulsions, coma, or death.

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

OSHA has established allowable exposure limits (PEL's) for formaldehyde. Two PEL's have been established for formaldehyde: an 8 hour time weighted average (PEL-TWA ═ 0.75ppm) and a short term exposure limit (stem ═ 2.0 ppm).

Although many products have the potential to release formaldehyde into the room air, it is rarely responsible for the severe levels of pollution that result. Pressed wood products and UFFI (urea-formaldehyde foam insulation) can release formaldehyde at a greater rate than other products.

Thus, in the prior art, methods have been sought to remove or reduce the formaldehyde content of air. Attempts have been made to reduce the formaldehyde content both at the manufacturing stage of potential formaldehyde-releasing articles and in the environment in which these articles are installed. For example, U.S. patent No. 4397756 issued to Lehmann on 9.8.1983 entitled "methods and combinations for reducing formaldehyde emissions in wood composite panels provides methods and combinations for reducing formaldehyde emissions in wood panels" teaches a combination comprising urea, a carbohydrate-based material, and an acidic catalyst. U.S. patent No. 4517111 entitled "absorbent for formaldehyde in air", issued to Dorman et al on 5/14/1985, provides a combination of substances that are adsorbed by potassium permanganate or chemisorbed onto a solid base support. This combination may be released or contained in a container or cartridge so that it may contact air contaminated with formaldehyde.

U.S. patent No. 7052683 entitled "combining gaseous detoxified formaldehyde, in aqueous solution, and protecting human cells against formaldehyde," issued to Farkas at 30.5.2006, teaches a compound comprising a detoxified combination of substances that rapidly neutralizes and fixes toxic formaldehyde vapor, forming formaldehyde adducts in which enzymes play an important role in the defense against formaldehyde in the buccal mucosa and oral epithelial cell lines.

While 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 desirable to develop a filter type device whereby formaldehyde will be irreversibly retained.

Disclosure of Invention

In view of 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 from air, to name a few.

It is another object of the present invention to treat a web substrate with activated carbon impregnated with TRIS (hydroxymethyl) aminomethane or TRIS as a means for removing impurities from organic and inorganic air.

The above and other objects, which will be apparent to those skilled in the art, are achieved in the present invention, which is directed to a filter medium for removing organic contaminants from air, comprising an activated carbon medium having a first charge and impregnated with a chemical agent for removing formaldehyde and/or other aldehydes from air, while removing organic compounds using the activated carbon medium.

The chemical agent may comprise 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.

The 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 a chemical agent for removing 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 (fibrillated nanofibers); depositing activated impregnated carbon with thermoplastic binder particles on a substrate web; and fusing the activated impregnated carbon fibers and thermoplastic binder particles to the substrate web.

The process can include the addition of a second substrate layer bonded to the substrate web by a thermoplastic adhesive.

Drawings

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

FIG. 1 depicts a graph of formaldehyde concentration over time for a non-TRIS based impregnated carbon;

fig. 2 depicts a plot of formaldehyde concentration over time for a TRIS-based impregnated carbon.

Detailed Description

In describing the preferred embodiment of the present invention, reference will be made to FIGS. 1-2 of the drawings in which like numerals represent like features of the invention.

Chemisorption is a type of adsorption that involves a chemical reaction between a surface and an adsorbate. A new chemical bond is created at the surface of the adsorbent. Chemisorption occurs when volatile contaminant molecules chemically react with the adsorbent surface to form non-volatile products. This mechanism generally allows capture of lower boiling compounds, such as formaldehyde. As a result, the filtration capacity of adsorbent filter media, such as carbon composites, can be significantly enhanced by impregnating them with appropriate chemical reagents. The price paid for the increased efficiency is the selectivity of the reagents. As used herein, "adsorbent filter media" or "adsorbent prefilter media" refers to filter media made with an adsorbent, such as activated carbon. An example of an adsorbent filter media is

Commercially available from KX technology, Inc. of West Haven, Connecticut.

The invention incorporates composite filter media, e.g. activated carbon filter media, e.g.

Which generally includes a charged medium and a pH altering material that alters the pH of the influent water such that microbial contaminants present in the influent water maintain a first charge opposite 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 of

Composite filter media are used as illustrative examples, but do not limit the invention to only such activated carbon composites. Activated carbonIs a porous material with high surface area, and is widely applied to the fields of purification, material separation, catalysis, medicine and the like. The activated carbon has high adsorption capacity, surface activity and pore size range; factors that have useful properties in many applications. Activated carbon can be made from a variety of source materials: 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 x 50 mesh activated carbon. The unexpected result is that when this composite filter media is chemically treated with tris (hydroxymethyl) aminomethane, it is an organic compound represented by the formula (HOCH2)3CNH 2.

TRIS was added to create a filter medium for removing formaldehyde and other aldehydes from air, while removing organic compounds using basic activated carbon. 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 purification adsorbents.

The reaction of formaldehyde with TRIS reagent is an example of a carbonyl compound containing an amino derivative. The grade of reaction results in binding of the carbonyl carbon to the amine nitrogen and is useful for aldehyde and ketone collection and characterization.

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

The plate test data demonstrates 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 a non-TRIS based impregnated carbon. Fig. 2 is a graph of formaldehyde concentration over time for a TRIS-based impregnated carbon. In both cases, the initial air formaldehyde concentration was established at 30ppm, 50% relative humidity, and delivered at a speed of 0.25 m/s.

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

In fig. 2, treated (TRIS-based) impregnated carbon is used as the filter medium. The point of saturation or formaldehyde breakthrough does not occur until 150 to 240 minutes, which means that the treated carbon filter is three to four times more effective at removing formaldehyde from air than the untreated carbon filter. This has surprisingly led to the combination of composite filter media chemically treated with a monolayer of tris (hydroxymethyl) aminomethane.

A process for treating an activated carbon filter, preferably in the form of paper, includes providing a first substrate web, e.g., comprising fibrillated nanofibers. Next, activated (impregnated) carbon is deposited with the particles of thermoplastic binder, which is fused into a 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 fibrous paper with activated carbon impregnated with TRIS have the advantage that formaldehyde removal efficiencies equal to or greater than other products available on the market using heavier activated carbon can be achieved using lower composite weights.

As previously mentioned, the treated activated carbon filter also reacts with components of the diesel exhaust gas, such as sulfur dioxide, nitrogen dioxide, and hydrogen sulfide. Furthermore, the combination of activated carbon and TRIS on these air impurities also produced no unexpected enhanced filtration.

While the present invention has been described in conjunction with certain preferred embodiments, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. It is therefore contemplated that the appended claims will embrace any such alternatives, modifications and variations as falling within the true scope and spirit of the present invention.

Claims

1. A filter media for removing organic and inorganic contaminants from air, comprising:

a substrate web of fibrillated nanofibers;

activated carbon having a first charge and treated with a chemical agent for removing formaldehyde and/or other aldehydes from air, the activated carbon being chemically treated with a monolayer of tris (hydroxymethyl) aminomethane; and

thermoplastic binder particles;

the filter media removes organic compounds with the activated carbon such that the substrate web surface is loaded with the activated carbon impregnated with the chemical agent and the thermoplastic binder particles, and wherein the filter media comprises a fibrous paper media; and is

Wherein the activated carbon includes a pH altering material that alters the pH of the influent water independently of the chemical agent such that microbial contaminants present in the influent water maintain a second charge opposite the first charge of the activated carbon.

2. The filter media of claim 1, wherein the substrate web comprises

A filter media.

3. The filter media of claim 1, wherein the activated carbon having the first charge and impregnated with the chemical agent removes sulfur dioxide, nitrogen dioxide, and/or hydrogen sulfide.

4. A filter media for removing organic and inorganic contaminants from air, comprising:

a substrate web of fibrillated nanofibers and the substrate web is a surface-loaded media;

the activated carbon has a first charge and is treated with a chemical agent for removing formaldehyde and/or other aldehydes from air, the chemical agent being a monolayer of tris (hydroxymethyl) aminomethane, and thermoplastic binder particles;

in removing organic compounds with the activated carbon, the activated carbon with the chemical agent and thermoplastic binder particles are deposited on a surface of the substrate web such that the substrate web surface is loaded with the activated carbon impregnated with the chemical agent, and wherein the filter media comprises a fibrous paper media.