CA1162904A - Removal of gaseous formaldehyde with solid organic nitrogen compounds - Google Patents
Removal of gaseous formaldehyde with solid organic nitrogen compoundsInfo
- Publication number
- CA1162904A CA1162904A CA000394522A CA394522A CA1162904A CA 1162904 A CA1162904 A CA 1162904A CA 000394522 A CA000394522 A CA 000394522A CA 394522 A CA394522 A CA 394522A CA 1162904 A CA1162904 A CA 1162904A
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- Prior art keywords
- formaldehyde
- protein
- amine
- amide
- solid
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/46—Removing components of defined structure
- B01D53/72—Organic compounds not provided for in groups B01D53/48 - B01D53/70, e.g. hydrocarbons
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- B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
- B01J20/20—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising free carbon; comprising carbon obtained by carbonising processes
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- B01J20/28023—Fibres or filaments
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- B01J20/32—Impregnating or coating ; Solid sorbent compositions obtained from processes involving impregnating or coating
- B01J20/3202—Impregnating or coating ; Solid sorbent compositions obtained from processes involving impregnating or coating characterised by the carrier, support or substrate used for impregnation or coating
- B01J20/3204—Inorganic carriers, supports or substrates
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- B01J20/3206—Organic carriers, supports or substrates
- B01J20/3208—Polymeric carriers, supports or substrates
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- B01J20/3242—Layers with a functional group, e.g. an affinity material, a ligand, a reactant or a complexing group
- B01J20/3244—Non-macromolecular compounds
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- B01J20/3248—Non-macromolecular compounds having a well defined chemical structure the functional group or the linking, spacer or anchoring group as a whole comprising at least one type of heteroatom selected from a nitrogen, oxygen or sulfur, these atoms not being part of the carrier as such
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- B01J20/30—Processes for preparing, regenerating, or reactivating
- B01J20/32—Impregnating or coating ; Solid sorbent compositions obtained from processes involving impregnating or coating
- B01J20/3231—Impregnating or coating ; Solid sorbent compositions obtained from processes involving impregnating or coating characterised by the coating or impregnating layer
- B01J20/3242—Layers with a functional group, e.g. an affinity material, a ligand, a reactant or a complexing group
- B01J20/3244—Non-macromolecular compounds
- B01J20/3246—Non-macromolecular compounds having a well defined chemical structure
- B01J20/3248—Non-macromolecular compounds having a well defined chemical structure the functional group or the linking, spacer or anchoring group as a whole comprising at least one type of heteroatom selected from a nitrogen, oxygen or sulfur, these atoms not being part of the carrier as such
- B01J20/3251—Non-macromolecular compounds having a well defined chemical structure the functional group or the linking, spacer or anchoring group as a whole comprising at least one type of heteroatom selected from a nitrogen, oxygen or sulfur, these atoms not being part of the carrier as such comprising at least two different types of heteroatoms selected from nitrogen, oxygen or sulphur
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- B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
- B01J20/30—Processes for preparing, regenerating, or reactivating
- B01J20/32—Impregnating or coating ; Solid sorbent compositions obtained from processes involving impregnating or coating
- B01J20/3231—Impregnating or coating ; Solid sorbent compositions obtained from processes involving impregnating or coating characterised by the coating or impregnating layer
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- B01J20/3244—Non-macromolecular compounds
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- B01J20/3248—Non-macromolecular compounds having a well defined chemical structure the functional group or the linking, spacer or anchoring group as a whole comprising at least one type of heteroatom selected from a nitrogen, oxygen or sulfur, these atoms not being part of the carrier as such
- B01J20/3255—Non-macromolecular compounds having a well defined chemical structure the functional group or the linking, spacer or anchoring group as a whole comprising at least one type of heteroatom selected from a nitrogen, oxygen or sulfur, these atoms not being part of the carrier as such comprising a cyclic structure containing at least one of the heteroatoms nitrogen, oxygen or sulfur, e.g. heterocyclic or heteroaromatic structures
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- B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
- B01J20/30—Processes for preparing, regenerating, or reactivating
- B01J20/32—Impregnating or coating ; Solid sorbent compositions obtained from processes involving impregnating or coating
- B01J20/3231—Impregnating or coating ; Solid sorbent compositions obtained from processes involving impregnating or coating characterised by the coating or impregnating layer
- B01J20/3242—Layers with a functional group, e.g. an affinity material, a ligand, a reactant or a complexing group
- B01J20/3268—Macromolecular compounds
- B01J20/3272—Polymers obtained by reactions otherwise than involving only carbon to carbon unsaturated bonds
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- B01J2220/00—Aspects relating to sorbent materials
- B01J2220/40—Aspects relating to the composition of sorbent or filter aid materials
- B01J2220/48—Sorbents characterised by the starting material used for their preparation
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- B01J2220/40—Aspects relating to the composition of sorbent or filter aid materials
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- B01J2220/4812—Sorbents characterised by the starting material used for their preparation the starting material being of organic character
- B01J2220/4825—Polysaccharides or cellulose materials, e.g. starch, chitin, sawdust, wood, straw, cotton
Abstract
REMOVAL OF GASEOUS FORMALDEHYDE
WITH SOLID ABSORBENTS
Abstract Formaldehyde is used on large scale in chemical industry and it is incorporated in many resin products which are extensively used by the building industry and public. Since formaldehyde has recently been identified as a carcinogenic agent, proper protection against its inhalation is required for occupational personnel and some members of public. Some systems were developed for the remo-val of gaseous formaldehyde in industrial use, however no suitable system has been available for removing formaldehyde from breathing air at very low concentrations.
In this invention the process of chemisorption is employed to transfer gaseous formaldehyde to solid, nonvolatile compounds and retain it within the absorber. The absorbers, which can be produced in different forms of a filter, are suitable for occupa-tional respiratory protection, atmosphere purification in working and living areas and for formaldehyde absorption from process gases. The absorbents can also preventively be incorporated into resins containing materials to reduce formaldehyde emissions.
WITH SOLID ABSORBENTS
Abstract Formaldehyde is used on large scale in chemical industry and it is incorporated in many resin products which are extensively used by the building industry and public. Since formaldehyde has recently been identified as a carcinogenic agent, proper protection against its inhalation is required for occupational personnel and some members of public. Some systems were developed for the remo-val of gaseous formaldehyde in industrial use, however no suitable system has been available for removing formaldehyde from breathing air at very low concentrations.
In this invention the process of chemisorption is employed to transfer gaseous formaldehyde to solid, nonvolatile compounds and retain it within the absorber. The absorbers, which can be produced in different forms of a filter, are suitable for occupa-tional respiratory protection, atmosphere purification in working and living areas and for formaldehyde absorption from process gases. The absorbents can also preventively be incorporated into resins containing materials to reduce formaldehyde emissions.
Description
2 9 ~) ~
This invention relates to the removal of FormAldehyde tJas from air and other carrier gases.
Formaldehyde is used on a large scale in the chemical indus-try and it is incorporated in many resin products which are extensively used by the building industry and the public. Formerly it had been considered harmless, however recently it was classified as a toxic substance and a potencial carcinogen. A need has arisen for improved protection of occupational personnel and members of the public, exposed to airborne formaldehyde.
Commonly used methods for gaseous formaldehyde collection or removal are based on its scrubbing with water or solutions. However this process introduces moisture into the purified gas and hazardous or undesirable secondary products, such as formic acid, may be formed and released into the purified gas. ~his process also produces liquid chemical waste, safe disposal of which is difficult and expensive.
Scrubbing systems are generally expensive and bulky, their maintenance and operational cost are relatively high.
The physical adsorption process is not sufficiently effective for form-aldehyde removal because several variable factors, such as temperature, relative humidity, gas impurities and gas velocity, have significant ef~ect on ~ormaldehyde adsorption equilibrium. Most adsorbents have low capacj~y for formaldehyde adsorption under normal conditions and its retention is not adequate because adsorption is a reversible process.
Positive change in the above parameters would result in significant desorption of previously collected formaldehyde from the adsorbent.
A method has been patented (Canadian Patent No. 821.316) in which a mixture of salts of sulphurous acid, a hydrophylic subs~ance and a hume-ctant, formed with a large surface area, is used to remove formaldehyde odor from air. No inFormation has been found in the specification on the involved chemical reactions, on the efficiency and capacity of this absorber for gaseous formaldehyde removal and on the volatility and toxicity of reaction products. It can be expected that the absorbent performance depends on the temperature and moisture of the air being ``~ purified and that under conditions of high humidity the hygroscopic action of the collecting agents cause it to become water logged.
The method of recovering commercially usable formaldehyde from water-methanol-formaldehyde vapours in Canadian Patent No. 6~3 062, is based on scrubbing gaseous formaldehyde with an alkaline urea solution, circulating through an absorbing tower at temperature of 25 to 100 C.
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S~gO~1 Activated charcoal and silica gel were also used to collect reversibly formaldehyde from air samples, to increase its concentration for analy-tical purposes.
The disadvantages of the above methods may be eliminated by absorbing formaldehyde gas with solid nonvolatile rnaterials, which form stable~ nonvolatile reaction products. With properly selected absorbent composition the adverse effect of the variability of operational parame-ters can be minimized and the formation of harmfull products can be eliminated.
The absorbers can be made as either active or passive systems:
In the active system gaseous formaldehyde is removed from the purified gas, which is forced through the absorbent by a pressure difference accross the bed. The absorption efficiency is proportional to the rate of formaldehyde reaction with the absorbent components and to the resi dence time of formaldehyde molecules in the absorber bed. With little space requirements and low operational cost, the absorbers can purify large volumes of gas from formaldehyde. Used absorbers can safely and inexpensively be disposed, i. e. buried in ground or incinerated.
In the passive systems the formaldehyde absorbent is dispersed or contained in a film which is applied on walls and other surfaces. No gas mover is present in the passive system, the transport mechanism is based on the diffusion of formaldehyde molecules and movement of the carrier gas, e. g. air currents or turbulence in a room. This system can be used effectively for gaseous formaldehyde removal from residen-tial and working areas where large surfaces can be coated with the absorbent film.
The following major aspects have to be considered in air and gas purification applications:
- high absorption efficiency and capacity of the absorber for gaseous formaldehyde under expected operational conditions (temperature, pressure, gas velocity, etc.) - low chemical affinity of absorbent components to the carrier gas components and moisture, - minimal volatility and toxicity of the absorbent components, - minimal volatility and toxicity of the products of formaldehyde , reaction with the absorbent components, - low production, operational and maintenance costs.
Generally, high absorption efficiency is obtained by using absorbents which, in solid form, have high chemical affinity to gaseous formalde-hyde under normal conditions. Significant improvement in removalef~iciency and retention can be achieved by a process which combines ;; physical adsorption and chem;sorption. The physical adsorption extends s , .
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the residence time and enables the chemical reactions to achieve equili-brium. Catalysis can efficiently improve both the reaction rate and the formaldehyde absorption ca~acity. Finaly, formaldehyde polymerization, which also can be accelerated with physical adsorption and catalysis, may further contribute to the process of formaldehyde fixation~
Many organic nitrogen compou~ds, contained in the following groups, are known to react, mostly as aqueous solutions, with formalde-hyde when reaction conditions are optimal:
Aliphatic and Aromatic ~nines, Amides, Diamides of Organic Acids, Imides, Carbamates, Thioamides, Aminonitriles, Aminoacids and Prote;n;.
The suitability of the above compounds for gaseous formaldehyce removal was preliminarily evaluated from published data. A brief summary follows:
~ormaidehyde readily reacts with primary amines and, at lower rates, with secondary amines. Generally aromatic amines are less volatile than aliphatic amines.
Formaldehyde reacts with solutions of some amides, e.g. urea, at room temperature. Most of the reaction products are nonvolatile and more stable than those produced from amines.
Cyanamide (melamine) has high capacity for formaldehyde absorption.
The reaction product is nonvolatile and stable, however the reaction is slow under normal conditions.
The reactions of formaldehyde with diamides of organic acids and imides are also relatively slow under normal conditions.
Carbamates and thiourea react with formaldehyde at room temperature, however the products are not suffic;ently stable at sliyhtly elevated temperatures.
Proteins have good chemical affinity for formaldehyde which readily reacts with the ~ree amino groups~ forming methy1ene amine linkages, and it may also involve the production of diformals. Chemically stable. non-volatile products, resulting from these reactions, have increased molecu-lar weight and improved resistance to alkalies and water at room tempera-ture. The rate of formaldehyde reaction with most proteins increases with increasing temperature and w;th the pH of the protein solutions.
Reactivity with formaldehyde varies for different proteins. The proteins most commonly used in the production of formaldehyde modified products, are suitable for gaseous formaldehyde removal, e. 9. gelatine, casein, soyabean protein, vegetable proteins, keratin and glue.
Gelatine has good chemical affinity and good capacity for formaldehyde absorption. Gaseous formaldehyde reacts with gelatine in dry formS with a gel and most rapidly with solutions. However the reaction products release formaldehyde ;n hot water and decompose in hydrochloric acid.
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The reactions of the above compounds with formaldehyde are ionic. Some of them are sufficiently rapid in aqueous solutions however the reacti-ons of solid compounds with folrmaldehyde ga's are typically much slower.
Because of their ionic character, the reactions can be catalysed with both the hydroxyl and hydronium ions. However, for this application the optimal pH ;s within the range of 7 - 14, because some reaction products are not sufficiently stable in acidic conditions. Where alkaline pH is undesirable, other known catalysts such as salts of sulphurous and halo-gen acids can be used to accelerate the reactions of formaldehyde with solid organic nitr~gen compounds. Alkali metal salts of ~he above acids can also be applied as catalysts, additional to hydroxyl ions in the m;xture of reactive components.
The reactions of formaldehyde gas with several organic nitrogen compounds were e~perimentally investigated. The results confirmed that the following compounds, in solid form, can react with formaldehyde gas at room temperature:
amines (e.g. aniline, benzidine, aminopyrimidine, toluenediamine, triethylenediamjne, diphenylamine, diaminodiphenylamine, etc~) ~ proteins (e.g. gelatine, soyabean protein, casein~ etc.) - and also, at lower reaction rates, amides (e.g. ben~amide, melamine urea, acetamide, etc.) Their efficiencies for gaseous formaldehyde chemisorption were improved with the assistance of one or more of physical adsorption, hydroxyl ions and/or other catalysts. It was also found that the addition of small quant;ty of triethylenediamine accelera~ed the reaction of formaldehyde gas with several tested amines, amides and proteins more efficiently than similarly alkaline pH from inorganic hydroxides. Tertiary amines, which generally haYe alkaline character, apparently engage b~th the hydroxyl ions and the tertiary amino group in their catalytic action, therefore they qualify as convenient catalysts for this purpose.
For specific use requirements the above absorbent components can be arranged in several combinations and physical configurations:
In active absorbe~ systems a large surface to volume ratio is required to provide for the maximal contact of the absorbent with the purified gas, sufficiently long reaction time and low pressure drop across the absorber bed. The three principles, on which the active absorber systems in this invention are based, are as follows:
- The absorbent, which is composed of one or more of amine(s3, amide(s), protein(s), alkali(es) and/or other catalyst(s~, is incorporated into an adsorbent which has the function of supportinq material and the adsorption process also provides for longer residence time to enable more efficient reaction of formaldehyde with the absorbent.
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i ~ ~29(~l - The absorbent consists of protein(s) or its mixture with one or more of amine(s), amide(s), alkali(s) and/or other catalyst. The protein(s) perform as formaldehyde absorbent and bind the reac~ive and catalysing components to screens, fibres, sponge or other structure with large surFace and low flow resistance.
- Protein(s), or their mixture with one or more of amine(s), amide(s), alkali(s) and/or other catalyst, are selfstructured as fibres, screens, open cell foam or sponge. This arrangement eliminates the need for supporting materials.
- Wool, eventually impregnated with one or more of amine(s), amide(s), additional protein(s), alkali~s) and/or other catalyst, is a typical example of natural protein fibres which can be -Formed as a suitable active system for formaldehyde removal. Artificial protein fibres, produced by spinning protein solutions (casein, soyabean protein or other protein materials) and partially hardened, can form an efficient system for formaldehyde absorption. A mixture of natural and synthe-tic protein fibres can also be used in some applications. Loose fibres can be formed into a required filter shape or can be woven to form a screen or fabric. The protein(s) can also be solidified as a sponge or open cell foam for this purpose.
The active absorber systems are suitable for occupational respiratory protection, atmosphere purification in worl(ing and living areas, formal-dehyde absorption from process gases and for formaldehyde recovery.
In passive absorption systems the absorbent material is disper-sed on surfaces. In the majority of practical applicatiorls it is applied as a film to internal surfaces and walls of areas and systems from which gaseous formaldehyde is to be removed.
The ~ollowing principles are applicable:
- Any of the active absorbent materials, dispersed on surfaces, can perform as a passive system, - The absorbent film can be formed of solid or gelatized protein(s) which can contain one or more of amine(s), amide(s), alkali(s) and/or other catalyst and fungicide.
- The film is formed of a binder, such as latex paint, the constituents of which do not form any volatile or toxic reaction products with formaldehyde and are inert to all reacti~e, pH conditioning and catalysing components o~ the absorbent. Further, the binder is inert to all carrier gas components.
The passive absorption systems are particularly suitable for formaldehyde remoYal from operational and residential areas where the source is releasing formaldehyde at relatively constant rate. Then the equilibrium ~;~
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airborne concentrations of formaldehyde are proportional to the rate of its release and inversely proportional to the chemical affinity o~ the absorbent to formaldehyde, the area coated with the absorbent film, air temperature and the degree of air turbulence in the area.
Practical examples of two active absorbents and one passive absorbent for gaseous formaldehyde follow:
Example 1 - Impregnated Adsorbent An adsorbent, e.g. activated alumina, molecular sieve, charcoal, etc~
is impregnated with a solution containing one or more of amine(s),amide(s) protein(s), alkali~s) and/or other catalyst. The loading of the impreg-nating components is optimized for formaldehyde absorption capacity while sufficient remaining surface activity of the adsorbent is provided.
An absorbent, identified as having a high performance, was made of acti-Yated charcoal, impregnated with 5 % urea. This absorbent, filled in a 40 mm deep bed, removed , 90 % of gaseous formaldehyde from air within the concentration range of 0.1 - 10 ppm, air flow of 300 m3-hr l-m 2 ~face velocity of 5 m-min 1) and ~ 90 % relative humidity. The flow resistance of this absorber was < 25 mm w.g. The efficiency of the absorbent significantly increased under low relative humidity conditions.
Further improvement in its formaldehyde sorption efficiency was achieved by adding a trace of triethylenediamine catalyst to the reactive components mixture.
Both the formaldehyde removal efficiency and the flow capacity of the absorption system can be improved by increasing the absorber depth, when slightly higher flow resistance is acceptable.
All components of this absorbent, as well as the products of their reac-tion with formaldehyde, are nonvolatile and nontoxic therefore the absor-bent can safely be used for the purification of respiratory air.
This absorbent also can remove some other air contaminants, such as acidic gases (S02, N0x, etc), however they somewhat reduce its efficiency for~formaldehyde absorption.
Example 2 ~ Supported Absorbent A suitable supporting fibre, screen or spongy material, e.g. cellulose, cotton, plastic, metal, etc, is coated (by soaking, spraying, etc) w;th a solution of protein(s) or its mixture with amine~s) and/or amide(s).
alkali(s) and/or other catalyst can be added to the viscous solution to maximize the rate of dried components reaction with gaseous formaldehyde and fungicide added to improve the long term stability of the absorbent.
An absorber of this type was made by soaking a cotton screen in hot solution of gelatine and 2,4 Toluendiamine, containing a trace of Tri-ethylenediamine as a catalyst. Its formaldehyde removal efficiency I
was higher than 90 % at room temperature, gelatine loading of 0.1 9 per 1 cm2 of the absorbent and an air flow 150 m3-hr~l-m-2.
The absorbent performance was not significantly influenced by humidity conditions. The absorbent is reasonably stable when used, or stored under normal conditions. No growth of bacteria or fungus occured in nonstabilized absorbent which was exposed to air for six months at 25C
and 60 % relative humidity. For the use under high humidity conditions its stability should be increased by adding a fungicide. The constitu-ents as well as the products of their reaction with formaldehyde are essentially nonvolatile, therefore this absorbent can be used in air cleaning applications. The supported absorbent can be manufactured with large surface to volume ratio which presents negligible pressure drop, therefore a common low pressure air blower can provide sufficiently high purification flow through a deep absorber of this type.
Example 3 - Absorber Film An emulsion of a suitable coating material is homogenized with one or more of amine(s), amide(s), protein(s), alkaline component and/or other catalyst. In the emulsion the film forming components should permit diffusion of formaldehyde to the absorbing constituents, in order to provide for proper absorption capacity. Some paints already contain amines as a stabiliser, however they were never intended for formalde-hyde removal. Therefore they generally do not comply with the require-ments, previously specified for air and gas purification.j passive absorbent of this type was prepared by homogen;zing a common commercial latex paint with 5 % of 2,aminopyrimidine and a trace of tri-ethylenediamine. No visible change in the latex emulsion, no coagula-tion, separation or o~her change occured during several months of storage.
The modified paint was also compatible with all tested pigments. The appearance of the modified paint, after drying, remained the same as the original paint and its abrasion resistance was not reduced. In a dynamic efficiency test a foil of this absorbent removed more than 50 % of airborne formaldehyde from passing air at 5 s. residence time. In an exicator test the equilibrium concentration of airborne formaldehyde from 0.05 % solution, was reduced by the factor of ~. The film of the modified paint was exposed to 0.5 ppm of airborne formaldehyde for six months period, after which no significant change in its efficiency was found.
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A number of absorbents, similar to the above examples, were prepared using several other amines, amides and proteins, catalysed with alkali, tertiary amine and other above mentioned catalysts. Such combinations were found with most of the tested compounds, which formed a solid absorbent suitable for formaldehyde removal. The results of their experimental evaluation substantiated the claims, that the inven-tion is applicable for the use of one or more of amine(s), amide(s), protein(s), or their mixture with akali(s) and/or other catalyst(s), in the described physical configurations, as absorbents for gaseous formaldehyde. The selection of optimal components and physical confi-gurations will depend on specific performance requirements and operati-onal conditions in individual practical applications.
The details in the above examples have been given only for i11ustration. It is not intended to limit this invention by the examples, description, or other details in the above disclosure.
This invention relates to the removal of FormAldehyde tJas from air and other carrier gases.
Formaldehyde is used on a large scale in the chemical indus-try and it is incorporated in many resin products which are extensively used by the building industry and the public. Formerly it had been considered harmless, however recently it was classified as a toxic substance and a potencial carcinogen. A need has arisen for improved protection of occupational personnel and members of the public, exposed to airborne formaldehyde.
Commonly used methods for gaseous formaldehyde collection or removal are based on its scrubbing with water or solutions. However this process introduces moisture into the purified gas and hazardous or undesirable secondary products, such as formic acid, may be formed and released into the purified gas. ~his process also produces liquid chemical waste, safe disposal of which is difficult and expensive.
Scrubbing systems are generally expensive and bulky, their maintenance and operational cost are relatively high.
The physical adsorption process is not sufficiently effective for form-aldehyde removal because several variable factors, such as temperature, relative humidity, gas impurities and gas velocity, have significant ef~ect on ~ormaldehyde adsorption equilibrium. Most adsorbents have low capacj~y for formaldehyde adsorption under normal conditions and its retention is not adequate because adsorption is a reversible process.
Positive change in the above parameters would result in significant desorption of previously collected formaldehyde from the adsorbent.
A method has been patented (Canadian Patent No. 821.316) in which a mixture of salts of sulphurous acid, a hydrophylic subs~ance and a hume-ctant, formed with a large surface area, is used to remove formaldehyde odor from air. No inFormation has been found in the specification on the involved chemical reactions, on the efficiency and capacity of this absorber for gaseous formaldehyde removal and on the volatility and toxicity of reaction products. It can be expected that the absorbent performance depends on the temperature and moisture of the air being ``~ purified and that under conditions of high humidity the hygroscopic action of the collecting agents cause it to become water logged.
The method of recovering commercially usable formaldehyde from water-methanol-formaldehyde vapours in Canadian Patent No. 6~3 062, is based on scrubbing gaseous formaldehyde with an alkaline urea solution, circulating through an absorbing tower at temperature of 25 to 100 C.
.
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S~gO~1 Activated charcoal and silica gel were also used to collect reversibly formaldehyde from air samples, to increase its concentration for analy-tical purposes.
The disadvantages of the above methods may be eliminated by absorbing formaldehyde gas with solid nonvolatile rnaterials, which form stable~ nonvolatile reaction products. With properly selected absorbent composition the adverse effect of the variability of operational parame-ters can be minimized and the formation of harmfull products can be eliminated.
The absorbers can be made as either active or passive systems:
In the active system gaseous formaldehyde is removed from the purified gas, which is forced through the absorbent by a pressure difference accross the bed. The absorption efficiency is proportional to the rate of formaldehyde reaction with the absorbent components and to the resi dence time of formaldehyde molecules in the absorber bed. With little space requirements and low operational cost, the absorbers can purify large volumes of gas from formaldehyde. Used absorbers can safely and inexpensively be disposed, i. e. buried in ground or incinerated.
In the passive systems the formaldehyde absorbent is dispersed or contained in a film which is applied on walls and other surfaces. No gas mover is present in the passive system, the transport mechanism is based on the diffusion of formaldehyde molecules and movement of the carrier gas, e. g. air currents or turbulence in a room. This system can be used effectively for gaseous formaldehyde removal from residen-tial and working areas where large surfaces can be coated with the absorbent film.
The following major aspects have to be considered in air and gas purification applications:
- high absorption efficiency and capacity of the absorber for gaseous formaldehyde under expected operational conditions (temperature, pressure, gas velocity, etc.) - low chemical affinity of absorbent components to the carrier gas components and moisture, - minimal volatility and toxicity of the absorbent components, - minimal volatility and toxicity of the products of formaldehyde , reaction with the absorbent components, - low production, operational and maintenance costs.
Generally, high absorption efficiency is obtained by using absorbents which, in solid form, have high chemical affinity to gaseous formalde-hyde under normal conditions. Significant improvement in removalef~iciency and retention can be achieved by a process which combines ;; physical adsorption and chem;sorption. The physical adsorption extends s , .
.~
o ~
the residence time and enables the chemical reactions to achieve equili-brium. Catalysis can efficiently improve both the reaction rate and the formaldehyde absorption ca~acity. Finaly, formaldehyde polymerization, which also can be accelerated with physical adsorption and catalysis, may further contribute to the process of formaldehyde fixation~
Many organic nitrogen compou~ds, contained in the following groups, are known to react, mostly as aqueous solutions, with formalde-hyde when reaction conditions are optimal:
Aliphatic and Aromatic ~nines, Amides, Diamides of Organic Acids, Imides, Carbamates, Thioamides, Aminonitriles, Aminoacids and Prote;n;.
The suitability of the above compounds for gaseous formaldehyce removal was preliminarily evaluated from published data. A brief summary follows:
~ormaidehyde readily reacts with primary amines and, at lower rates, with secondary amines. Generally aromatic amines are less volatile than aliphatic amines.
Formaldehyde reacts with solutions of some amides, e.g. urea, at room temperature. Most of the reaction products are nonvolatile and more stable than those produced from amines.
Cyanamide (melamine) has high capacity for formaldehyde absorption.
The reaction product is nonvolatile and stable, however the reaction is slow under normal conditions.
The reactions of formaldehyde with diamides of organic acids and imides are also relatively slow under normal conditions.
Carbamates and thiourea react with formaldehyde at room temperature, however the products are not suffic;ently stable at sliyhtly elevated temperatures.
Proteins have good chemical affinity for formaldehyde which readily reacts with the ~ree amino groups~ forming methy1ene amine linkages, and it may also involve the production of diformals. Chemically stable. non-volatile products, resulting from these reactions, have increased molecu-lar weight and improved resistance to alkalies and water at room tempera-ture. The rate of formaldehyde reaction with most proteins increases with increasing temperature and w;th the pH of the protein solutions.
Reactivity with formaldehyde varies for different proteins. The proteins most commonly used in the production of formaldehyde modified products, are suitable for gaseous formaldehyde removal, e. 9. gelatine, casein, soyabean protein, vegetable proteins, keratin and glue.
Gelatine has good chemical affinity and good capacity for formaldehyde absorption. Gaseous formaldehyde reacts with gelatine in dry formS with a gel and most rapidly with solutions. However the reaction products release formaldehyde ;n hot water and decompose in hydrochloric acid.
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2 9 ~ ~
The reactions of the above compounds with formaldehyde are ionic. Some of them are sufficiently rapid in aqueous solutions however the reacti-ons of solid compounds with folrmaldehyde ga's are typically much slower.
Because of their ionic character, the reactions can be catalysed with both the hydroxyl and hydronium ions. However, for this application the optimal pH ;s within the range of 7 - 14, because some reaction products are not sufficiently stable in acidic conditions. Where alkaline pH is undesirable, other known catalysts such as salts of sulphurous and halo-gen acids can be used to accelerate the reactions of formaldehyde with solid organic nitr~gen compounds. Alkali metal salts of ~he above acids can also be applied as catalysts, additional to hydroxyl ions in the m;xture of reactive components.
The reactions of formaldehyde gas with several organic nitrogen compounds were e~perimentally investigated. The results confirmed that the following compounds, in solid form, can react with formaldehyde gas at room temperature:
amines (e.g. aniline, benzidine, aminopyrimidine, toluenediamine, triethylenediamjne, diphenylamine, diaminodiphenylamine, etc~) ~ proteins (e.g. gelatine, soyabean protein, casein~ etc.) - and also, at lower reaction rates, amides (e.g. ben~amide, melamine urea, acetamide, etc.) Their efficiencies for gaseous formaldehyde chemisorption were improved with the assistance of one or more of physical adsorption, hydroxyl ions and/or other catalysts. It was also found that the addition of small quant;ty of triethylenediamine accelera~ed the reaction of formaldehyde gas with several tested amines, amides and proteins more efficiently than similarly alkaline pH from inorganic hydroxides. Tertiary amines, which generally haYe alkaline character, apparently engage b~th the hydroxyl ions and the tertiary amino group in their catalytic action, therefore they qualify as convenient catalysts for this purpose.
For specific use requirements the above absorbent components can be arranged in several combinations and physical configurations:
In active absorbe~ systems a large surface to volume ratio is required to provide for the maximal contact of the absorbent with the purified gas, sufficiently long reaction time and low pressure drop across the absorber bed. The three principles, on which the active absorber systems in this invention are based, are as follows:
- The absorbent, which is composed of one or more of amine(s3, amide(s), protein(s), alkali(es) and/or other catalyst(s~, is incorporated into an adsorbent which has the function of supportinq material and the adsorption process also provides for longer residence time to enable more efficient reaction of formaldehyde with the absorbent.
.. .
i ~ ~29(~l - The absorbent consists of protein(s) or its mixture with one or more of amine(s), amide(s), alkali(s) and/or other catalyst. The protein(s) perform as formaldehyde absorbent and bind the reac~ive and catalysing components to screens, fibres, sponge or other structure with large surFace and low flow resistance.
- Protein(s), or their mixture with one or more of amine(s), amide(s), alkali(s) and/or other catalyst, are selfstructured as fibres, screens, open cell foam or sponge. This arrangement eliminates the need for supporting materials.
- Wool, eventually impregnated with one or more of amine(s), amide(s), additional protein(s), alkali~s) and/or other catalyst, is a typical example of natural protein fibres which can be -Formed as a suitable active system for formaldehyde removal. Artificial protein fibres, produced by spinning protein solutions (casein, soyabean protein or other protein materials) and partially hardened, can form an efficient system for formaldehyde absorption. A mixture of natural and synthe-tic protein fibres can also be used in some applications. Loose fibres can be formed into a required filter shape or can be woven to form a screen or fabric. The protein(s) can also be solidified as a sponge or open cell foam for this purpose.
The active absorber systems are suitable for occupational respiratory protection, atmosphere purification in worl(ing and living areas, formal-dehyde absorption from process gases and for formaldehyde recovery.
In passive absorption systems the absorbent material is disper-sed on surfaces. In the majority of practical applicatiorls it is applied as a film to internal surfaces and walls of areas and systems from which gaseous formaldehyde is to be removed.
The ~ollowing principles are applicable:
- Any of the active absorbent materials, dispersed on surfaces, can perform as a passive system, - The absorbent film can be formed of solid or gelatized protein(s) which can contain one or more of amine(s), amide(s), alkali(s) and/or other catalyst and fungicide.
- The film is formed of a binder, such as latex paint, the constituents of which do not form any volatile or toxic reaction products with formaldehyde and are inert to all reacti~e, pH conditioning and catalysing components o~ the absorbent. Further, the binder is inert to all carrier gas components.
The passive absorption systems are particularly suitable for formaldehyde remoYal from operational and residential areas where the source is releasing formaldehyde at relatively constant rate. Then the equilibrium ~;~
~ ~ ~290~
airborne concentrations of formaldehyde are proportional to the rate of its release and inversely proportional to the chemical affinity o~ the absorbent to formaldehyde, the area coated with the absorbent film, air temperature and the degree of air turbulence in the area.
Practical examples of two active absorbents and one passive absorbent for gaseous formaldehyde follow:
Example 1 - Impregnated Adsorbent An adsorbent, e.g. activated alumina, molecular sieve, charcoal, etc~
is impregnated with a solution containing one or more of amine(s),amide(s) protein(s), alkali~s) and/or other catalyst. The loading of the impreg-nating components is optimized for formaldehyde absorption capacity while sufficient remaining surface activity of the adsorbent is provided.
An absorbent, identified as having a high performance, was made of acti-Yated charcoal, impregnated with 5 % urea. This absorbent, filled in a 40 mm deep bed, removed , 90 % of gaseous formaldehyde from air within the concentration range of 0.1 - 10 ppm, air flow of 300 m3-hr l-m 2 ~face velocity of 5 m-min 1) and ~ 90 % relative humidity. The flow resistance of this absorber was < 25 mm w.g. The efficiency of the absorbent significantly increased under low relative humidity conditions.
Further improvement in its formaldehyde sorption efficiency was achieved by adding a trace of triethylenediamine catalyst to the reactive components mixture.
Both the formaldehyde removal efficiency and the flow capacity of the absorption system can be improved by increasing the absorber depth, when slightly higher flow resistance is acceptable.
All components of this absorbent, as well as the products of their reac-tion with formaldehyde, are nonvolatile and nontoxic therefore the absor-bent can safely be used for the purification of respiratory air.
This absorbent also can remove some other air contaminants, such as acidic gases (S02, N0x, etc), however they somewhat reduce its efficiency for~formaldehyde absorption.
Example 2 ~ Supported Absorbent A suitable supporting fibre, screen or spongy material, e.g. cellulose, cotton, plastic, metal, etc, is coated (by soaking, spraying, etc) w;th a solution of protein(s) or its mixture with amine~s) and/or amide(s).
alkali(s) and/or other catalyst can be added to the viscous solution to maximize the rate of dried components reaction with gaseous formaldehyde and fungicide added to improve the long term stability of the absorbent.
An absorber of this type was made by soaking a cotton screen in hot solution of gelatine and 2,4 Toluendiamine, containing a trace of Tri-ethylenediamine as a catalyst. Its formaldehyde removal efficiency I
was higher than 90 % at room temperature, gelatine loading of 0.1 9 per 1 cm2 of the absorbent and an air flow 150 m3-hr~l-m-2.
The absorbent performance was not significantly influenced by humidity conditions. The absorbent is reasonably stable when used, or stored under normal conditions. No growth of bacteria or fungus occured in nonstabilized absorbent which was exposed to air for six months at 25C
and 60 % relative humidity. For the use under high humidity conditions its stability should be increased by adding a fungicide. The constitu-ents as well as the products of their reaction with formaldehyde are essentially nonvolatile, therefore this absorbent can be used in air cleaning applications. The supported absorbent can be manufactured with large surface to volume ratio which presents negligible pressure drop, therefore a common low pressure air blower can provide sufficiently high purification flow through a deep absorber of this type.
Example 3 - Absorber Film An emulsion of a suitable coating material is homogenized with one or more of amine(s), amide(s), protein(s), alkaline component and/or other catalyst. In the emulsion the film forming components should permit diffusion of formaldehyde to the absorbing constituents, in order to provide for proper absorption capacity. Some paints already contain amines as a stabiliser, however they were never intended for formalde-hyde removal. Therefore they generally do not comply with the require-ments, previously specified for air and gas purification.j passive absorbent of this type was prepared by homogen;zing a common commercial latex paint with 5 % of 2,aminopyrimidine and a trace of tri-ethylenediamine. No visible change in the latex emulsion, no coagula-tion, separation or o~her change occured during several months of storage.
The modified paint was also compatible with all tested pigments. The appearance of the modified paint, after drying, remained the same as the original paint and its abrasion resistance was not reduced. In a dynamic efficiency test a foil of this absorbent removed more than 50 % of airborne formaldehyde from passing air at 5 s. residence time. In an exicator test the equilibrium concentration of airborne formaldehyde from 0.05 % solution, was reduced by the factor of ~. The film of the modified paint was exposed to 0.5 ppm of airborne formaldehyde for six months period, after which no significant change in its efficiency was found.
j._~,, ~ .~ 8 2 ~
A number of absorbents, similar to the above examples, were prepared using several other amines, amides and proteins, catalysed with alkali, tertiary amine and other above mentioned catalysts. Such combinations were found with most of the tested compounds, which formed a solid absorbent suitable for formaldehyde removal. The results of their experimental evaluation substantiated the claims, that the inven-tion is applicable for the use of one or more of amine(s), amide(s), protein(s), or their mixture with akali(s) and/or other catalyst(s), in the described physical configurations, as absorbents for gaseous formaldehyde. The selection of optimal components and physical confi-gurations will depend on specific performance requirements and operati-onal conditions in individual practical applications.
The details in the above examples have been given only for i11ustration. It is not intended to limit this invention by the examples, description, or other details in the above disclosure.
Claims (9)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for removing formaldehyde from air and other gases which comprises converting gaseous formaldehyde to solid, nonvolatile compounds by its chemical reaction with one or more of solid aminocompound(s), amidocompound(s) and/or protein(s).
2. A process, as defined in Claim 1, in which the chemical reaction of formaldehyde with amine(s), amide(s) and/or protein(s) is cata-lysed with one or more of solid inorganic alkali(s), alkaline organic nitrogen compound(s), salt(s) of sulphurous or halogen acids and/or other catalytically functional component(s).
3. A process, as defined in Claims 1 or 2, in which active absorber is made of granulated adsorbent(s), impregnated with one or more of amine(s), amide(s) and/or protein(s).
4. A process, as defined in Claims 1 or 2, in which an active absor-ber, comprised of fibrous, spongy or other large surface substrate, superficially impregnated with one or more of protein(s), amine(s) and/or amide(s), is employed.
5. A process, as defined in Claims 1 or 2, in which active selfsuppor-ting absorber, structured as fibres or in other solid forms with large surface area, made of protein(s) or its mixture with amine(s) and/or amide(s), is employed.
6. A process, as defined in Claims 1 or 2, in which passive absorbents comprise a substrate, carrying a film containing a formaldehyde absorbing amount of amine(s), amide(s), protein(s) or mixtures thereof.
7. Material for the chemisorption of formaldehyde from air or other carrier gas, comprising a particulate material carrying a formal-dehyde absorbing amount of a solid absorbent selected from the group consisting of amines, amides, proteins and mixtures thereof.
8. Material for the chemisorption of formaldehyde from air or other carrier gas, comprising an absorbing amount of protein, amine, amide or mixtures thereof, structured as selfsupported fibres, sponge or in other solid forms with large surface area.
9. An emulsified coating material which, when applied to a substrate and dried, provides a film which is suitable for the chemisorption of formaldehyde from air or other carrier gas, said coating material being characterized by the presence of one or more of amine(s), amide(s) and/or protein(s).
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000394522A CA1162904A (en) | 1982-01-20 | 1982-01-20 | Removal of gaseous formaldehyde with solid organic nitrogen compounds |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000394522A CA1162904A (en) | 1982-01-20 | 1982-01-20 | Removal of gaseous formaldehyde with solid organic nitrogen compounds |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1162904A true CA1162904A (en) | 1984-02-28 |
Family
ID=4121863
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000394522A Expired CA1162904A (en) | 1982-01-20 | 1982-01-20 | Removal of gaseous formaldehyde with solid organic nitrogen compounds |
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| CA (1) | CA1162904A (en) |
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| EP0486015A1 (en) * | 1990-11-16 | 1992-05-20 | Nippondenso Co., Ltd. | Active carbon for deodorization and process for preparation thereof |
| US5328687A (en) * | 1993-03-31 | 1994-07-12 | Tri-Point Medical L.P. | Biocompatible monomer and polymer compositions |
| US5624669A (en) * | 1993-03-31 | 1997-04-29 | Tri-Point Medical Corporation | Method of hemostatic sealing of blood vessels and internal organs |
| WO1999044724A1 (en) * | 1998-03-06 | 1999-09-10 | Fritz Doppelmayer | Method for cleaning interior spaces or objects contaminated by harmful substances such as formaldehyde in particular |
| US6143352A (en) * | 1994-06-28 | 2000-11-07 | Closure Medical Corporation | pH-modified biocompatible monomer and polymer compositions |
| WO2007095926A2 (en) * | 2006-02-23 | 2007-08-30 | Lothar Ernst Wilhelm Weber | Means and process for cleaning pollutants, odorous substances and other unwanted components from ambient air |
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| DE102006062239A1 (en) * | 2006-12-22 | 2008-06-26 | Lothar Ernst Wilhelm Weber | Means for absorbing pollutants or odors u. a. |
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