METHOD FOR PRODUCING A CELLULAR BODY

Abstract: Method of producing a cellular body for adsorption of preferably organic substances in purification plants, to which end a cellular structure is impregnated with a hydrophobic zeolite. Impregnation takes place using a sludge of the hydrophobic zeolite and an inorganic binder, the impregnated cellular structure being heated to a temperature at which the constituents thereof begin to sinter together.

Description: Method for Producing a Cellular Body. The discharge of organic substances front industrial processto the surroundings has become a serious enviroππisntal threat and methods for reducing such discharges have become more and more important. For a long time, it has been known that with the aid of certain sαrbtiσn agents a considerable part of the cσπt^aminants in question can be strapped and subsequently rendered harmless or recovered. Lately, interest has been focused on a group of inorganic substances, so-called zeolites as sorbtion agents, primarily since it has been possible to give them selectivity in sorbtion capacity with respect to the gaseous constituents in the contaminating agent, a selectivity which to a great degree excludes sorbtion of water vapour in spite of the fact that the injurious contaminants are separated with high efficiency. An example of how such a so-called hydrophobic zeolite can be built up is given in the Swedish Patent No. 8604873-3. ϋαe hyάrophobic zeolites eliminate a large problem with previously used sorbtion agents in the often recurring operational cases where the cxxrtaminating agent contains water vapour. The sorbtion capacity of the sorbtion agent has in such cases been appropriated to a large degree by the water vapour, reducing to a corresponding degree the sorbtion capacity for the injurious part of tfte containinant. m turn, this has lead to lowered capacity of the sorbtion plant and furthermore to heavily increased operational costs for regenerating the sorbtion agent. Ihe less teridency for water vapour sorbtion by the hydrophobic zeolites which could be provided, the more effective and operationally cheap the purification process has become. An effective utilization of the sorbtion capacity of the hydrophobic zeolites repjuires, inter alia, that they are exposed in a fixed geometric structure in the ∞ntamirjating agent, this structure per¬ mitting an intimate contact between zeolite and the flowing medium while at the same time permitting a large medium flow without a too high pressure drop. Such structures in the form of cellular bodies having alternatingly flat and pleated thin layers, which are caused •IV to support each other at mutually separated places so that through- ducts or gaps are formed have long been successfully used, e.g. for drying air. A particularly advantageous embodiment is one where the starting material is a paper built up of sparcely layered mineral fibres, preferably glass fibres, which after building up the cellular structure are supplied with powder and binder filling out the gaps between the fibres and thereby sealing the layer simultaneously as the powder and binder combine to stiffen up the layer so that it is given high mechanical strength. This cellular body is described in the Swedish Patent No. 8003175-0. Among the powders used has been the type of zeolite intended for absorbing moisture from air, and as a binder the precipitate ccx-urring when waterglass is exposed to such as carbon dioxide or calcium chloride. It has been apparently obvious to apply the same technique for achie- ving a cellular body for the hydrophobic zeolites, but in practice it has not been found possible to achieve acceptable results in this way. The binding agents which have been suggested have namely had hygroscopic properties, which is not a disadvantage when it is a question of bodies intended for the removal of moisture. In such a case, the hygroscopic capacity has even been desirable. However, when it is a question of fixing the hydrophobic zeolites in the cell structure, there is the requirement that the finished cellular body does not contain any hygroscopic components which would reduce the effect of the hydrophobic properties of the zeolites. It is the object of this invention to form a cellular body of the kind described, where the hydrophobic zeolites are bonded in the layers with rion-hygroscopic binders while the layers are given a great degree of mechanical stiffness. It is also one of the objects of the invention to provide this without the binder substantially blocking access to the pores of the zeolites for the ∞ntaminants which are to be absorbed, or affect the pore structure of the zeolite so that the hydrophobic properties are deteriorated. In addition, it is an object to achieve a cellular body of exclusively inorganic, non-inflammable constituents so that the body can be regenerated at a high air temperature. These objects are achieved by the cell structure in accord * an _ceΉwith the invention being iπpregnated with a sludge of the hydrophobic zeolite and an inorganic binder, after which the irnpregnated cellular r< -•» structure is heated to a temperature at which sintering between the constituents begins to occur and the cellular body is given sufficient strength. The starting material for the cellular structure is preferably layers of iriorganic artificial fibres, impregnation taking , place by the produced structure being doused or dipped in the sludge of zeolite and binder. For getting the desired amount of the sludge into the cellular structure, impregnation optionally takes place in several steps and the cellular body is heated between the steps for drying out water vapour. Zeolites which have a high hydrophobic capacity, e.g. de-aluminized zeolite, are used as an active substance or adsorbent. The inorganic binder includes clay. Particularly favourable results have been obtained with a sludge of kaolin-type clay of an alkaline nature or with alkaline additives to the sludge. In such a case, the pH value should be as high as possible without the hydrophobic pro¬ perties of the zeolite being negatively affected. As mentioned, the cellular body is impregnated with a sludge of zeolites and binder, and the mixing ratio between binder and zeolite is preferably between 0.05 and 1.00 based on dry weights, the range 0.10 = 0.35 having been found to be particularly suitable. The mixing ratio shall be as low as possible, inter alia so that the binder will not block access to the pores of the zeolite, but primarily for maximizing the amount of zeolite in the cellular body. __ ≠- r After impregnation by the sludge, optionally in several steps with intermediate drying, the cellular body is fired at a temperature causing sintering together of the constituents in the impregnated cellular structure and preferably at a temperature at whicli any ability of the binder to absorb water is successively redu»d, e.g. at least 500-600 β C. During the heat treatment, the organic substances or binder which can have been in the cell structure from the beginning are also fired away. _______ Paper made from inorganic artificial fibres is used for the production of a cellular body which is formed to a cellular structure in accor¬ dance with the method described in the introduction. An aqueous sludge of zeolites and clay in a mixing ratio 12% zeolite, 4% clay and 84% water, giving a dry substance of 16% was used. Treat¬ ment of the cellular body was carried out by dipping twice with irrtermediate drying, a final firing being carried out at 600 β C. This treatment gave a cellular body with a zeolite content of 60% by weight, good strength and excellent hdrophobiσity. With the aid of the described production of a cellular body by im¬ pregnation with a sludge of a hydrophobic zeolite and an inorganic binder together with heating to a temperature at which sintering takes place, there is provided a cellular body which is extremely well-suited to adsorbtion of organic substances, such as solvents from the air in industrial discharges. The inventicn is naturally not limited to the described example but can be varied within the scope of the following Claims. Accordingly, the cellular body, although it has been described for purifying gas such as air, can also be used for purifying other media such as liquids, e.g. water from ∞ntaminants of an organic nature. The binder used can also be more or less hydrophobic before heat treatment, but where possible water vapour sorbtion capacity of the binder is present, this shall be reduced by the heat treatment.

Claims: CΓALMS 1. Method of producing a cellular body for absorption of preferably organic substances in purification plants in which a cellular structure is iinpregnated with a hydrophobic zeolite, ch a r a c t e r i z e d in that the iπpregnation takes place using a sludge of the hydrophobic zeolite and an inorganic binder, and in that the iinpregnated cellular structure is subsequently heated to a temperature at which the constituents thereof are sintered together. 2. Method as claimed in Claim 1, c h ar a ct e r i z ed in that the iinpregnated cellular body is heated to a temperature at which the possible water sorbtion capacity of the binder is reduced. 3. Method as claimed in Claim 1 or 2, ch a ra cte r i z e d in that clay is used as inorganic binder. 4. Method as claimed in any one of Claims l to 3, ch ar a c -t e r i z e d in that the mixing ratio between binder and zeolite lies between 0.05 and 0.50 based on dry weight, preferably 0.10-0.25. 5. Method as claimed in any one of Claims l to 4, ch a r a c -t e r i z e d in that impregnation takes place in a plurality of steps. 6. Method as claimed in Claim 5, cha r a ct e r i z ed in that the cellular body is heated between the iinpregnation steps for drying so that water vapour departs. 7. Method as claimed in any one of Claims l to 6, char a c -t e r i z e d in that the starting material in the cellular body is layers of inorganic artificial fibres. 8. Method as claimed in any one of Claims 2 to 7, cha r a c -t e r i z e d in that a sludge is used which is alkaline, by using alkaline clay and/cr by using additives of alkaline substances for the sludge. 9. Method as claimed in any one of Claims ltoδ, charac-te r i z e d in that the binder used is more or less hydrophobic before the heat treatment.

Inventors: FAELTH LARS, HAAKANSSON ULF, FAELTH, LARS, HAAKANSSON, ULF
Applicants: MUNTERS ZEOL AB
Application year: 1990
Main classification: B01J20
IPC codes: B01J20, C01B39