Catalyst – solid sorbent – or support therefor: product or process – Solid sorbent – Free carbon containing
Reexamination Certificate
1997-08-27
2001-02-06
Hendrickson, Stuart (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Solid sorbent
Free carbon containing
C502S009000, C502S010000, C502S432000, C502S433000, C502S434000, C423S44500R
Reexamination Certificate
active
06184177
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method of providing activated carbon particles from spent contaminated synthetic resin ion-exchangers which mostly occur in granular form.
BACKGROUND OF THE INVENTION
Synthetic resin ion-exchangers are porous polymers having numerous chemical groups with exchangeable ions. In general, they consist of a copolymer framework of styrene and divinylbenzene or styrene and acrylic acid, said framework carrying acid groups, in particular sulfonic acid groups, for cation-exchangers and basic groups (amines) for anion-exchangers. Organic ion-exchangers of the kind having a polymer resin matrix selected from the group consisting mainly of polystyrene resins, polyacrylic resins, polyalkyl amine resins or phenol-formaldehyde resins, which may be present as cation- or anion-exchange resins, depending on their functional groups, and adsorbent resins are described in Ullmann's Encyclopedia of Industrial Chemistry, Fifth Edition, Volume A 14, VCH-Verlagsgesellschaft mbH, Weinheim, Germany 1989 in the chapter “Ion Exchangers”, in particular on pages 394-398, and are commercially available under the trade names Lewatit, Dowex, Kastel, Diaion, Relite, Purolite, Amberlite, Duolite, Imac, Ionac, Wofatit. Numerous applications of the ion-exchange resins are also described on pages 399-448 of the cited chapter.
The main purpose of using ion-exchangers is the exchange of undesirable ions present in water for less noxious ions, and the complete removal of ions. If the ions that produce hardness—basically, Ca
2+
and Mg
2+
—are exchanged for Na
+
ions, “hard” water becomes “soft” water. If cations and anions are removed, one obtains demineralized water. Soft water is necessary, for example in the textile industry, and demineralized water in the steam generation, in particular in high-pressure boilers.
In general, ion-exchangers become ineffective by obstruction, i.e. their pores become blocked by suspended particles or inorganic residues, such as iron to compounds. The latter are regularly flushed out, but with time, more pores become progressively blocked and finally the bed has to be replaced. At this point, the problem of disposal of the ion-exchanger arises. As long as no ions that polute the environment are present, the spent ion-exchangers can be disposed of in waste dumps.
Inactive granular organic ion-exchange resins are contaminated with large amounts of inorganic or organic foreign matter, such as suspended particles of all kinds, sludge, microorganisms, algae and various cations, e.g. sodium, potassium, iron, and calcium ions. The amount of these impurities is usually up to 20% by weight, based on the dry substance. The granular ion-exchange resins to be disposed of have in most cases a water content which may amount to up to 50% by weight.
SUMMARY AND DETAILED DESCRIPTION OF THE INVENTION
Subject matter of the invention is a method for the disposal of spent granular organic ion-exchangers of the afore-mentioned kind comprising carbonizing the spent ion-exchanger in a predominantly inert atmosphere at temperatures of from 300° C. to 900° C. and subsequently activating the carbonized material in an oxidizing atmosphere, thus converting the spent ion-exchangers into activated carbon spheres.
It is known in the art to convert specifically defined, polysulfonated macroporous cross-linked vinyl aromatic polymers into carbonaceous adsorber particles by heating to temperatures of up to 1200° C. (U.S. Pat. No. 4,957,897). The sulfonic acid groups are released during pyrolysis, radical sites are generated which lead to strongly cross-linked structures that are not meltable and contain little volatile carbon.
However, it was surprising that high quality abrasionproof activated carbon spheres can be produced also from heavily contaminated spent synthetic resin ion-exchangers by pyrolysis and that the various foreign substances contained therein do not impair the quality and stability of the activated carbon. Surprisingly enough, the macro- and mesopore structure of the feedstock is maintained during the disintegration of the impurities and the carbonization. The accumulated organic and biological products are destroyed or escape without forming any pronounced carbon residues, in particular if the carbonization is conducted in a weakly oxidizing atmosphere.
In spent cation-exchange resins, the cations are usually bonded to sulfonic acid groups and are substantially converted into sulfates at temperatures of up to 400° C. At higher temperatures, they are reduced by carbon, resulting in considerable amounts of sulfides. It is, therefore, advantageous to first convert cation-exchange resins into the H
+
form prior to carbonization. This is preferably done by washing the still moist material with an acid, i.e. prior to drying.
In order to remove the water content, which as already mentioned may amount to up to 50% of the granular organic ion-exchange resin, it is recommended to dry the spent granular resin to be disposed of, preferably in a rotary drier or in a fluidized bed. Prior to attaining the softening point and usually after the drying, the synthetic resin ion-exchangers are preferably mixed (“powdered”) with an inert inorganic powder, preferably carbon powder, to prevent agglomeration and to maintain the granular structure during the entire treatment.
Up to a temperature of 400° C., preferably up to about 300° C. to 350° C., the inert atmosphere of the carbonization step can contain 0.2 to 4 volume % oxygen. The oxygen content is preferably controlled by the addition of air. This preoxidation is recommended not only because of the presence of organic impurities, but also, in connection with the addition of carbon powder and/or a slow rise in temperature which also occurs during the carbonization of gel-type ion-exchangers. In particular, the preoxidation is very important when the resins do not contain sulfonic acid groups, e.g. with anion-exchange resins or adsorbent resins this preoxidation converts the carbon spheres into a non-volatile form. It is recommended to process these resin types together with cation-exchange resins containing sulfonic acid groups.
Minor amounts of cations, such as alkali metal and alkaline earth metal ions, e.g. sodium, potassium etc. or calcium, which were already converted into sulfates at the beginning of the pyrolysis, do not disturb the carbonization and activation, surprisingly enough, they even promote the activation step.
The spent ion-exchange resins of the present invention have an ash content that is generally in the range of from 1-30% and, preferably from 5-10% but always larger than about 1%. Since the ash contains alkaline salts as already mentioned, the activated carbon product in accordance with the present invention is particularly suitable for adsorption of acidic gases.
The activation of the carbonized material follows upon the carbonization at about 700° C. Analogous to the carbonization, it can be conducted in a rotary drier or even better in a fluidized bed. To activate the material, steam and/or carbon dioxide is added in an amount of 3 to 50, preferably 3 to 15 volume %, to the substantially inert atmosphere. The activation temperature can be up to 900° C. To save energy, the activation can be conducted in the same apparatus after the carbonization. However, it might be advantageous for specific technical and procedural reasons to conduct the activation in an independent separate step, all the more since the carbonization up to temperatures of about 500° C. already entails a considerable shrinkage and a weight loss of the feedstock of from 60 to 90%. The carbon content of the activated carbon spheres after activation is more than 90% by weight.
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patent: 4040990 (1977-08-01), Neely
patent: 4242226 (1980-12-01), Siren
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patent: 4851285 (1989-07-01), Brotz
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De Ruiter Ernest
Von Blucher Hasso
Evenson, McKeown, Edwards & Lenahan P.L.L.C.
Hendrickson Stuart
MHB Filtration GmbH and Co. KG
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