ANIMAL LITTER

Abstract: A moisture and odour absorbing composition suitable for use as animal litter, has a core comprising activated carbon surrounded by a porous, coherent and mechanically resistant outer layer having a lower carbon content than the core. The composition may be made by preparing granules of a composition comprising inorganic and carbonaceous components and heating the granules until carbon or carbonaceous material in an outer layer of the granules is combusted or otherwise wholly or partly removed and any carbonisable material in the interior of the granules is carbonised and recovering the product having an activated carbon core.

Description: ANIMAL LITTER The present invention relates to animal hygiene. It provides a granular absorbent material and a method of producing such material. The invention also relates to the use of such material as litter for animals, more especially domestic pets. Granular absorbent compositions, which may be used as absorbents for various liquids or as animal litter, are already known. Such compositions may consist of inorganic materials such as clay, cellulosic or other organic materials, or a mixture of inorganic and.organic materials. W086/00496 describes the manufacture of an absorbent composition, for use as a pet litter, by mixing clay with cellulosic material, pelletising the mixture, drying the resultant pellets and heating the pellets to a temperature of from 550-1100"C. Diiring heating, the cellulosic material is fully combusted, and the result is a composition in the form of porous ceramic or sintered clay pellets. It has now been discovered that substantial advantages are obtained by the provision of an absorbent material in the form of a pelleted or other granular product, the granules of which have a core coir-prising activated carbon, surrounded by a porous, coherent, and mechanically resistant outer layer having a lower carbon content than the core. At least the surface layer of the granules is preferably substantially free from carbon or carbonised residues. The core may have a substantially black appearance while the outer layer may be lighter in colour and is preferably substantially white. The composition is preferably made by preparing pellets or other granules corrprising an inorganic component capable of providing a hardened structure on heating and a carbonaceous component, which may be carbon or carbonisable material, and heating the granules under conditions such that the carbonaceous component in an outer layer of the granules is combusted, volatilised or otherwise wholly or partly removed, thereby producing a porous structure, while the carbonaceous material in the interior is substantially retained as activated carbon or an activated carbonised residue. The inorganic component is preferably hardenable by sintering or calcination so that, while the carbonaceous component in the outer layer of the granules is combusted or otherwise removed, the inorganic component -is hardened to reinforce the granule and in particular the porous outer layer. It has been discovered that the product of this invention is not only highly absorbent for liquids, but can absorb urine and the like with substantial reduction in odour, owing to the activated carbon centres of the granules. Unli-ke conventional active charcoal absorbents, the product of the present invention is clean to handle, substantially free from dust and has less propensity for scattering. By the choice and quantity of inorganic components, the density can be adjusted to provide a product which is not too heavy for convenience of carrying, while not so light as to promote scattering. The bulk density of the product is preferably from 400 to 500 grams per litre, but may extend over the range from 300-700 g/1. The product can be made at a neutral pH value without the use of buffering agents. The product preferably has a porosity of 50 to 300%, more preferably 200 to 250%, and a water absorbtion capacity of 50 to 200% more preferably 100 to 150%, by weight. Thepreferred carbonaceous starting materials are finely divided combustible materials of low ash residue, for example amorphous carbon, lamp black, soot, bone char, or charcoal. Other materials having a substantial carbonaceous content, perhaps in combination with inorganic components, for example lignite, can also be used. The heat-hardenable inorganic component is preferably a clay, for example kaolinite, and can be used to increase the strength and density of the product or to produce a product with a differently coloured exterior. In a product manufactured from a mixture of organic and inorganic starting materials, the particle size of the organic material will determine the subsequent size of the pores in the outer layer of the final product. In the preferred process for manufacture of the absorbent material according to this invention, carbonaceous material is milled, where necessary, to the desired particle size. An inorganic material, such as clay, may then be admixed, preferably in a weight ratio to the carbon o carbonisable content of the carbonaceous material of between 2:1 and 4:1, and sufficient water added to produce a granulating consistency. The mixture is dried at a temperature below the carbonising point, for example in the range 100-200°C, either before or after division into granules. The dried granules are then heated under carbon activating conditions at a temperature and for such a time as to activate the carbon, if necessary during or after carbonisation of carbonisable material, and subsequently or simultaneously heated to remove at least a part of the carbonaceous material in the outer layer of the granules while ret-aining a core containing activated carbon. This removal of carbonaceous material produces pores in the outer layer of the granules. The moistened mix may optionally be spread or extruded, and after drying may be broken up into its final granular form. Fines produced at this stage can be removed by screening and recycled to the mixing stage. The temperature for both the activation/carbonisation step and the removal step may be in the range of 500°C to 1200°C. The activation/carbonisation step may be carried out under an atirosphere containing steam or carbon dioxide or a reducing atmosphere for a period which depends on temperature, type of carbon or carbonaceous material used and size of granule, but may be of the order of 10 minutes at a temperature of 800 to 900°C although considerably longer times may be necessary in some circumstances. Following the activation/carbonisation step the atmosphere may be changed, if necessary, to an atmosphere, for example, an oxidising atirosphere in which during further heating carbonaceous material is removed, for example, by combustion or volatilisation. Both steps are preferably carried out in the same heating apparatus. It is preferred that the granules should be agitated during heating, in order to ensure that all granules are evenly fired and acquire the desired porous, mechanically resistant outer layer and c--arbon-containing inner zone. The colour of the outer layer becomes lighter as oxidative firing proceeds, while the strength of the outer layer increases. Other things being equal, the lighter the colour the stronger the surface layer on the granule. If it is desired to produce a highly porous product from a starting material with a relatively low carbon content, which may be desirable in enviromental ground, the inorganic coπponent may be a foamed or foamable material or a material which is inherently porous. The following are examples of the production of absorbent materials according to this invention:- Example I White kaolinite was mixed with charcoal or other carbonaceous material in a ratio of preferably 4 parts clay and 1 part carbon. Water was added and mixed with the powders in a Hobart (Trade Mark) blender to bind and granulate the mixture. The granules were dried and fired in a mu fle furnace for about 8 hours at a temperature between 800 and 900°C. Granules with a whitish speckled external appearance and dar core were obtained. Example II White kaolinite was mixed with charcoal or other carbonaceous material in a ratio of preferably 4 parts clay and 1 part carbon. Water was added and mixed-with " the powders in a Hobart (Trade Mark) blender to bind and granulate the mixture. The granules were dried and fired in a muffle furnace for about 8 hours at a temperature between 800 and 900°C. For the first 10 minutes of heating the furnace conditions were adjusted to produce a reducing atmosphere to activate the carbon and the granules. Following this initial heating step the furnace conditions were changed to produce an oxidising atmosphere to remove carbon from the outer layer to produce an outer layer of enhanced porosity and light colour attractive appearance. Granules with a whitish speckled external appearance and dark core were obtained. The product: should be cooled under a reducing atmosphere.

Claims: CLAIMS 1. An odour and moisture absorbing composition in granular form, the granules having a core comprising activated carbon, and the core being si-irrounded by a porous, coherent and mechanically resistant ' outer layer having a lower carbon content than the core. 2. A composition according to claim 1 which comprises an inorganic material which provides a hardened structure -n at least the outer layer of the granules. 3. A composition according to claim 2 in which the core of the granules is substantially black and the surface is substantially white. 4. A composition according to claim 1, 2 or 3 in which the carbon is in the form of a carbonised carbonaceous material. 5. A composition according to any preceding claim in which the inorganic material is a clay. 6. A composition according to any preceding claim having a density in the range 400-500 grams per litre. 7. A method of making an odour and moisture absorbing composition, which comprises preparing granules of a composition comprising inorganic and carbonaceous components, heating the granules until carbon or carbonisable material in an outer layer of the granules is combusted or otherwise wholly or partly removed and any carbonisable material in the interior of the granules is carbonised, and recovering a granular product containing activated carbon in the interior -and having a porous outer layer with a lower carbon content than the core. 8. A method of making an absorbent composition, which comprises preparing granules of a composition comprising inorganic and carocr-aceous components, treating the granules to carbonise any carbonisable material and to activate the carbon and/or carbonised material and heating the granules until carbon or carbonised material in an outer layer of the granules is combusted or otherwise wholly or partly removed, and recovering a granular product retaining activated .carbon in the interior and having a porous outer layer with a lower carbon content than the core. 9. method according to claim 7 or claim 8, wherein the carbon is - activated by heating in an atmosphere of steam or carbon dioxide or a reducing atmosphere. 10. A method according to any one of claims 7 to 9, in which the granules are heated at a temperature in the range of 500-1200°C for a time insufficient to combust or otherwise remove carbon or carbonised material in the interior of the granules. 11. A method according to any of claims 7 to 10, in which the composition for the granules is prepared in a moist condition and dried at a temperature in the range of 100-200°C, and the formed granules are subsequently heated at a higher temperature. 12. A method according to claim 11, in which the dried composition is broκen up into individual granules from which fines are separated and recycled to the -mixing stage. 13. A method according to claim 11 or claim 12, in which the mixture contains clay in a weight ratio to the carbon and/or carbonisable content of the carbonaceous material of between 2:1 and 4:1. 14. Odour and moisture absorbing animal litter comprising a granular composition according to any of claims 1 to 6 or produced by a method according to any of claims 7 to 13.

Inventors: WALTERS JOHN, WALTERS, JOHN
Applicants: MARS G B LTD, MARS G. B. LIMITED
Application year: 1990
Main classification: B01J20
IPC codes: A01K1, B01J20