CA1207736A

CA1207736A - Paper containing activated carbon

Info

Publication number: CA1207736A
Application number: CA000430638A
Authority: CA
Inventors: James K. Dix; James A. Wheat
Original assignee: Minister of National Defence of Canada
Current assignee: Minister of National Defence of Canada
Priority date: 1983-06-17
Filing date: 1983-06-17
Publication date: 1986-07-15

Abstract

ABSTRACT

The invention disclosed is a paper material for adsorb-ing chemical contaminants in liquid or vaporous form. The paper employs activated carbon in powder form as the adsorbent. Various additives are included to improve the loading of activated carbon in the paper and to maintain or improve various physical properties of the resulting paper material, while at the same time not sub-stantially poisoning or de-activating the activated carbon.

Description

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This invention relates to an adsorbent paper material and in particular to a paper ma-terial containing activated carbon as an adsorbent for chemical contaminants in liquid or vaporous form.
When military or civilian personnel have been sprayed with chemical warfare (CW) agents or have walked -through a pre-viously con~aminated area and -then move to a clean area they can trans-Eer liquid agent on ~heir boots, clothing or equipment. In some instances the person may not know that he has been in contact wlth such agents. Transerred liquid is a hazard since many agents are percutaneously active and vapor emitted from the liquld is a respiratory hazard even in vexy small amounts because of their high toxicity. Clean areas which might become contaminated in this manner include tracked or wheeled vehicles, aircraft, tents, collective protectors or other shelters, first-aid posts and decontamination facilitles. When casualties from a (CW) environ-ment, either chemical or other, are brought into a shelter for treatment they must fir~t be decontaminated in a contamina-tion control facility to remove further hazards to themselves and those treating them. Contaminated clothing is removed but the indivi-dual's protective mask must remain with him. It has been shown that vapor emitted from the mask is a problem in the clean area of the shelter. In the decontamination facility relatively high vapor concentratlons will exist and an airlock system must be used to prevent transfer of vapor to the clean treatment area.
After each use the airlock must be purged of toxic vapor.
In chemical and other industries, for example in plants where pesticides are prepared and packaged, there are simi]ar problems in the control of liquid spills and emission of vapor.

, - 1 -~(1 7~316 Many common pesticides are organophosphorus compounds similar to the nerve a~ent type oE chemical war~are agent. In yeneral, in industrial locations a wide range of protective materials and equipment and accident fightiny facilities such as detectors, exhaust fans and filters can be provided which cannot be supplied to troops on the battlefield. Howe~er at sites where pesticides are being sprayed on crops or forests, the situation is similar -to that on the battleEield and individuals could transfer toxic materials to vehicles, aircraft and even offices or homes.
0 At present numerous procedures are recommended for military situations. Aircrew are to wear disposable covers for boots which will be removed on entering aircraft or shelters. As mentioned, contamina-ted clothing is removed from casualties entering treatment areas and of course from individuals entering oollective protectors for sleeping and eating. Collective protec-tor is the term applied to a shelter (which may be a vehicle) supplied with clean filtered air so that respiratory protection need not be worn. This is true only if there is no source of contamination within the shelter. Respiratory protection in ~0 vehicles can also be achieved by supplying clean air to a mask from a blower system. Fullers earth, an adsorbent type clay, in a special decontaminating mitt is provided to Canadian Forces to decontaminate skin, clothing and personal equipment.
Standard chemical safety procedures recommend that pes-ticide operators have a supply of lime, coarse clay, sand, sawdust or other absorbent to soak up spilled material. One example is a product called Imbiber Beads marketed by ANCO Chemicals Limited, Maple, Ontario. The product consists of beads which swell to many times their original volume when brought into contact with 0 the spilled li~uid.

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Materials such as cloths, sand, sawdust, etc. which merely absorb the liquid do no-t reduce the vapor pressure of the liquid and the absorbed liquid will be as great a vapor hazard as the spilled liquid. The contaminated absorbent can however be collected up and removed from the site for disposal later.
Adsorbents such as activated carbon and adsorbent -t~pe clavs will reduce the vapor hazard. Any method of absorbing or adsorbing a liquid will be effective only if a sufficient quantity of the material being used is brought into direct contact with the liquid.
The fuller's earth decontaminating mitt is an effective item but in some instances the messiness of the used powder lying about could be a disadvantage.
To remove toxic vapor from a room or huilding an exhaust fan ls generally used to draw contaminated air from the room and allow fresh air to enter. If desired the exhaust air may be passed through a charcoal filter or the like to prevent discharge to the atmosphere and the inlet air can also be filtered.
For collective protectors in a contaminated or potentially con-taminated area the shelter is maintained at a positive pressure by blowlng filtered air in-to it~
If toxic liquid is brought into a shelter or a vehicle which would otherwise be clean and safe and personnel are required to weax protective clothing or a mask, the usefulness of the shelter for respite from individual protection has been defeatedO
Adsorbent paper materials containing activated carbon have been described in the literature, for example, in Chemical Abstracts Vol. ~5:48579C, 1976, P~. 110 Fujinami, Nobuaki et a].
wherein wood-pulp mixed with 0.1 to 0~5% poly(ethylenimine) as a retention aid and 10 - 95~ activated carbon formed in-to a sheet by a wet method, is described.

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According to one aspect of the lnventlon a novel paper material for adsorbing a chemical ~ontaminant in liquid or vapor form is contemplated, comprising wood-pulp fibers, activated carbon in powder form, 2-5%/w of activ;ated carbon of a dispersing agent, 0.5 to 5%/w of activated carbon o~ a protective colloid and 5-30~/w of activated carbon of a latex binder, wherein said di~persing agent, protective colloid and binder are substantially : fxee from any substances which subs-tantial.ly de-ac-tlvate the activated carbon.
L0 According to another aspect of the invention, a novel method for making a paper material containing activa-ted carbon dispersed therein is also contemplated, said method comprising a) dispersing activated carhon in powder form and a dispersiny agent in water, b) adding a protective colloid and a la-tex binder to the dispersion, c) mixiny, d) adding the mixture to a water suspension of beaten wood-pulp fibers, and e) forming the paper oaterial, wherein said dispersing agent, protective colloid and latex binder are free from any substances which substantially de-activate the activated carbon.
The proposal is -to use a fine powder of ac-tivated carbon dispersed in a paper sheet. For liquid spills the activated carbon would adsorb the contaminant and its vapor emission would be much less than from a material that merely absorbs the liquid.
Activated carbon is an erfective adsorbent for almost all organic vapors except for low boiliny compounds. For vapors, the activated carbon would adsorb vapor in contact with it and reduce the con-centration in the air. lt would be necessary of course to circu-late the air or to allow natural convec-tion -to bring the vapor -: ~ 4 -into contac-t with the activated carbon. E'or soaking up liqui~s the paper would be usecl as a flat sheet or as several layers o~
flat sheets. For vapor, the paper could be pleate~ to present a larger surface area in a given space. It could also be used where contamination might occur but has not been actually identi-fied by placiny one or more layers on the floor or by hanging pleated material along the walls. Paper that has been used and ; has become contaminated can be disposed of by burning.
In its simplest form the material would consist of wood-pulp fibers and activated carbon formed by a paper-making process into a paper~like sheet. To ensure a good dispersion of the carbon it is flrst dispersed in water using a dispersing agent and then a protective colloid to maintain the dispersion. ~ latex binder is included to improve the dry and wet strength of the paper especially since addin~ the carbon reduces the strength. A reten-tion aid can also be used to improve retention. All additives must be selected so as not to "poison" the carbon. In other words, the dispersing agent, protective colloid and binder are free from any substances which substantially de-activate the activated carbon.
Papers have been prepared using laboratory handshee-t apparatus and also a pilot paper machine.
Examples of water insoluble binders used in the form of a dispersion in water often referred to as a latex include natural and synthetic rubbers, polymers and co-polymers of vinyl esters, vinyl acetals, acrylic esters, methacrylic esters, styrene, buta-diene, acryloni-trile, chloroprene, ethylene and propylene.
Since water is used as the medium of the impregnation suspension it is usually desirable to add a dispersing agent to assist in dispersion of the activate~ carbon and prevent floccu-la-tion of dispersed activated carbon. When the blnder is in the ~orm of an aqueous dispersion of a water insoluble bin~er such as the la-tex form of natural rubber, polyethylacrylate or polyvinyl acetate it is desirable to add a stabilizing agent to the suspen-sion of activated carbon in water before incorporating the binder, so as -to prevent mu-tual flocculation of -the activated carbon and the latex binder. It is believed that in the absence of such a stabili~ing agent, the emulsifying and dispersing agents added ]0 durin~ manufacture of a late~ binder and which are essential for its stability are preferentially adsorbed by the activated carbon and the latex becomes so unstable as to flocculate. Substances have been found which function as dispersing agents as well as stabilizing agents, and examples of these include ammonium caseinate, the sodium salt of a co-polymer oE styrene and maleic anhydride; the sodium salt of the condensation pr~duct of formalde-hyde and naphtha]ene sulphonic acid; -the sodium or ammonium salt o~ sulphonated lignin; the sodium salt of carboxymethyl cellulose;
methylcellulose and polyvinyl pyrrolidone. ~lastomeric binders such as natural rubber, synthe-tic rubbers and polyethylacrylate are preferred when flexibility is required, but when some rigidity is acceptable non~elastomeric binders such as polyvinyl acetate may be used.
More specifically, the method of manufacture of the paper material is as follows. The activa-ted carbon particles having a mass median diameter of up to 25 ~m but preferably 5 to 10 ~m are dispersed in water with one of the dispersing agents in Table I. S~ 1440H at 3~ of the weight oE activated carbon is :, :

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preferred. The mlxture is passed through a colloid mill to further disperse the activated carbon. Then the protective colloid (Table II, CM~) 7HF a-t 0.5 to 1% of activated carbon weight preferred) and latex (Table III) are mixed into the bath.
Latex Ucar~ 874 has been typically used at 20% ~activated carbon weight basis). The protective colloid increased the viscosity of -the mixture and causes the activated carbon to remain in suspension. The mixture is added to a water suspension of beaten wood-pulp fibers and o-ther optional additives and paper is pro-duced in a conventional manner. From 5 -to 100% activated carbon (on a wood-pulp weight basis) can be incorporated in the paper.

TABLE I: Dispersing Agen-ts ITrade Name I Type Range of % Loading ¦ ! on Charcoal ~asis 6MA~ 1440H , Styrene Maleic Anhydride 3-4 ~arasperse~ N Lignosulfonate 3 20 ~omar~ D I Sulfonated Naphthalene 2.5-5 L Con_ensate Useful range: 2-5 TABLE II: Protective Collo.id Trade Name ~ Typ~ Range of % Loading I on Charcoal Basis _ Casein Protein 3-5 Methocell~ Mc15 Methylcellulose 3 IC~I~ 7L Low molecular weight 0.5-1 l Sodium Carboxyrnethylcellulose ,CMC~ 7HF High molecular weight 0.5-1 Sodium Carboxymethylcellulose _ .' ~.
Useful range: 0.5 to 5%

TABLE III: Latex Trade Name Type ~UCar~ 874 Self-crosslinking acrylic latex IUCar~ 891 ,Hycar~ 2671 ,- ................. .. ,-IRhoplex~ 621 l olysar~ 778 Styrene/Butadiene plus monomers for carboxyl groups Useful range: 5-30%

The other additives used are as follows:
a. Parez~ 607. A melamine formaldehyde wet-streng-th resin from Cyanamid. This is a cationic material used to confer we-t s-trength to a variety of papers. It is also recommended as an agent for coagulating la-tex binders on to cellulose fibers.

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We have used it at 0-5% of the pulp and 3% appears to be optimum.
b. Papermakers' alum. Alum is frequently added to paper stocks for a varie-ty of reasons. It too is cationic and tends to coagulate latexes on to fibers. It is also used to precipitate rosin and modified rosin sizes. We have used alum at levels from 0 to 5% of the pulp. The amount does not seem critical.
c. Kymen ~ 557H. An epoxy-type wet-strength resin from Hercules. This is a cationic wet-strength resin which is not as effective as melamine-formaldehyde types but can be used at neutral pH's which is important for some applications. It also functions as a retentlon aid which is important for the charcoal paper. We have used it at up to 3% of the pulp but recommend 1.5~ as optimumD It gives much better retention than Pare ~ alone but not as good as Pare ~ used with Lufax~ 295.
d. Lufax~ 295. A cationic polyectrolyte which func-tlons as a retention aid and as a coupling agent for acrylic emulsions from ~ohm ~ Haas. In one experiment ~with Parez(~ and alum) 0.1% Lufax~ increased charcoal retention from 77% to 97%.
At 0.2% the retention was 98%. With Kymene~ and alum the reten-tion was 95%. We normally use 0.2~ I,ufa $ based on pulp weightadded continuously to the head box of the paper machine as recommended by the supplier.
The promising combinations are therefore Pare ~ 607 with Lufax~ 295, or Kymene~ 557H. Since alum is cheap and does no harm we use it at 2% of -the pulp. The charcoal mix should have a dispersing agent and, for ease of han~ling, ~he protective colloid as described previously. Tt is to be noted that these addltives do not poison the charcoal to any significant extent.

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I'he paper is formed by conventional paper-makiny proces-ses. A web is formed on a travelling screen and then consolidated on the screen b~ vacuum suction. Water draining through the screen is collected and recycled to dilute the incoming s-tock.
Wet web is transferred from the screen to a moving belt and passed one or more times between squeeze rolls to remove as much water as possible. The remaining water is xemoved by evaporation by passiny the paper over heated rolls and then to a wind-up stand.
No chemicals need be applied at a size press and calendering is L0 not recommended.
The activated carbon which is preferably used may be produced by heat treatemen-t of vegetable matter, animal matter, coal, liynite, petroleum residues or synthetic organic polymers either with or without the additlon of chemicals, and characterized by rapid and effective adsorption.
We prefer to use a softwood, sulfate (kraft) pulp because of its strength but sulfite could be used too. Some hardwood pulp could be mixed with softwood but it would reduce the strength.
The pulp is preferably fairly highly beaten (325-375 mL) to increase both strength and charcoal retention.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A paper material for adsorbing a chemical contaminant in liquid or vapor form, comprising wood-pulp fibers, activated carbon in powder form, 2-5%/w of activated carbon of a dispersing agent, 0.5 to 5%/w of activated carbon of a protective colloid and 5-30%/w of activated carbon of a latex binder, wherein said dispersing agent, protective colloid and binder are substantially free from any substances which substantially de-activate the activated carbon.

2. A paper material according to claim 1, wherein the dispersing agent is selected from the group consisting of a styrene maleic anhydride type, a lignosulfonate type and a sulfonated naphthalene condensate type.

3. A paper material according to claim 2, wherein the protective colloid is selected from the group consisting of methylcellulose, a low molecular weight sodium carboxymethyl cellulose, a high molecular weight sodium carboxymethyl cellulose and casein.

4. A paper material according to claim 3, wherein the latex is selected from the group consisting of a self-crosslinking acrylic latex and styrene/butadiene plus monomers for carboxyl groups.

5. A paper material according to claim 4, wherein the activated carbon is of a particle size of 5-10 µm.

6. A paper material according to claim 1, 4 or 5, wherein 5 to 100%/w of wood pulp fiber of activated carbon is incorporated in the paper material.

7. A method for making a paper material containing activa-ted carbon dispersed therein, comprising a) dispersing activated carbon in powder form and a dispersing agent in water, b) adding a protective colloid and a latex binder to the disper-sion.
c) mixing, d) adding the mixture to a water suspension of beaten wood-pulp fibers, and e) forming the paper material, wherein said dispersing agent, protective colloid and latex binder are free from any sub-stances which substantially de-activate the activated carbon.

8. A method according to claim 7, wherein the dispersing agent is selected from the group consisting of a styrene maleic anhydride type, a lignosulfonate type and a sulfonated naphtha-lene condensate type.

9. A method according to claim 8, wherein the protective colloid is selected from the group consisting of methylcellulose, a low molecular weight sodium carboxymethyl cellulose, a high molecular weight sodium carboxymethyl cellulose and casein.

10. A method according to claim 9, wherein the latex is selected from the group consisting of a self-crosslinking acrylic latex and styrene/butadiene plus monomers for carboxyl groups.

11. A method according to claim 10, wherein the activated carbon is of a particle size of 5-10 µm.

12. A method according to claim 7, 10 or 11, wherein 5 to 100%/w of wood-pulp fiber of activated carbon is incorporated in the paper material.