The invention relates to a method for recovery of rubber and wire from waste automobile tires, freed from any undesired components.

Tires are made of a tire tread adjacent to the proper tire. Maintenance of the constant shape of a tire, made of elastic and flexible rubber, requires a strengthening with wraps made of steel wire and resistant fibres. Therefore, tires, apart from rubber, consist of wraps made of wire and fibres attached to steel reinforcements. These components are glued and sealed with rubber, and as a whole create a tire. The vast majority of post-consumer tires not suitable for a retread is crushed in order to recover rubber or for energetic use, mostly in cement mills. In both cases, rubber and most of the steel wire are isolated from the mixture of crushed tires, and the remaining part comprises all the components of a tire, i.e. rubber and steel wires joined with fragmented rough fibres made of viscose, plastics and glass fibres with firmly adhered pieces of rubber.

This mixture, due to the presence of rough fibres made of viscose, plastics and glass fibres, is difficult to incinerate and, at the same time, is not suitable for use in the production of asphalt or as an additive for cements, as it deteriorates their quality and durability. So far, this problem has not been solved, and the unprocessed residue constitutes approximately 10 to 15% of post-consumer tires. Preferably, all fibrous materials should be removed from the mixture, as they inhibit or even block the separation of pieces of rubber and thin wire, which has been confirmed by successful attempts to use this mixture for further processing. Fabrics and wraps used for reinforcements of tires are made of very strong fibres fairly resistant to cracking and breaking, even at elevated temperatures exceeding 100°C. However, during the crushing of post-consumer tires, they are stretched, distended and broken, which causes their additional torsion, rippling and ruffling, and the effects of electrostatic attractions prevent the separation of individual fibres combined with rubber, due to additional entanglement supported by small pieces of twisted wire.

This problem is not important in the case of pyrolysis or incineration of tires. However, in case of an attempt to recover a possibly huge amount of rubber, the unprocessed residue constitutes an important share in the total weight of post- consumer tires.

Polish patent application PL 185449 discloses a method for production of rubber goods from post-consumer tires, which consists in that the tire is cut transversely in at least one place, it is spread flat using a rolling mill, and the front of the tire together with the tread are cut out along both its edges. The obtained patches are subjected to roughening which makes their surface sufficiently rough. Afterwards, they are arranged in layers and connected in a permanent manner using known methods, and the product of a chosen shape is then formed.

Polish patent application P.396583 discloses a method for the recovery of wire from post-consumer tires. The wire contained in the cut tire is separated by means of heat treatment and is subsequently mechanically cleaned and separated using a magnetic separator. The wire recovered in this way is then heated with an inductor. The remaining rubber is not separated from viscose fibres, plastics and glass.

Polish patent application P.392151 discloses a method for the recovery of rubber from post-consumer tires, which consists in that a known device used to generate high pressure is fed with water, which is subsequently compressed to a pressure of approximately 150-300 MPa and directed to at least one rotary head comprising nozzles, and from there, it continually and/or periodically hits the surface of the tires, separating rubber and fabric components from the metal wrap. In this method, the wire is separated from the residue, but the residue still does not constitute pure rubber.

According to the invention, post-consumer tires are crushed and then treated with polyols soluble in water, applied individually or in a mixture, at a temperature of above 160°C for several to several dozen hours. Preferably, glycols and/or glycerol are used. Under such conditions, the fibres dissolve, pass into a solution, and simultaneously the wire separates from the rubber. The mixture undergoes separation into pieces of rubber and wires settling on the bottom and a solution containing small amounts of easily removable impurities. The process of dissolution can be reduced to a time from several to several dozen minutes by the addition of 1% by weight per mass of the raw material of sodium hydroxide or potassium hydroxide or their salts with weak organic acids, such as carbonic, acetic or formic acid. The wire can be separated from the rubber using known, preferably magnetic methods. The rubber is then separated from the solution, and the applied unreacted polyol or a mixture thereof is distilled from the remaining solution. Ground tires, or ground tires after a preliminary partial removal of rubber and wire by means of a known process, are used as a raw material.

The method, according to the invention, allows for a full recovery of pure rubber, freed from undesired components and suitable for re-use. Furthermore, the method allows for easy recovery of all valuable components of the tires, i.e. rubber and wire.

Example 1. The raw material comprises ground tires after a partial removal of rubber and wire, of the approximate composition: steel wire 2% by weight, rubber 38% by weight, tangled fibres 60% by weight. The apparatus in the laboratory was arranged by placing a three-necked, round-bottom flask with a capacity of 2 litres, equipped with a thermometer, and a Vigreux column with a height of 300 mm, closed with a cover equipped with a thermometer, discharging vapour to a Liebig condenser, on an electric heater. The flask was filled with 323 g of the raw material and 560 g of ethylene glycol and pieces of porcelain, the heating was switched on, and first running was distilled in ah amount of 1.4 g until the temperature of the fumes reached more than 160°C. The temperature in the flask exceeded 165°C. 0.20 g of technical sodium carbonate was then placed in the flask, and the heating was continued at a constant temperature of 196-199°C. 20 minutes from the moment of the addition of sodium carbonate, another 0.20 g of sodium carbonate was added, and the flask was further heated. After 25 minutes, the heating was stopped. When the temperature in the flask was reduced to 80°C, the apparatus was disassembled, and the entire contents were filtered to separate the liquid from the precipitate, which after the removal of porcelain pieces was transferred to a beaker, to which 560 g of water were added, and the mixture was subsequently heated to 45°C. The pieces of wire were removed from the beaker using a 5 mm thick steel rod with a magnet attached to its end and then gathered on a tissue paper to remove ethylene glycol. The suspension from the beaker was filtered to separate the precipitate of the rubber, which was rinsed with water and dried. The filtrates were combined, and ethylene glycol was distilled until a temperature of the liquid of 215°C was achieved.

Obtained

Wires (steel scrap) 6.4 g

Rubber precipitate without fibres 121.7 g

Residue after glycol distillation 263.9 g

It has been verified that the precipitate of rubber can be added to the rubber recovered before the chemical treatment and used as a full-value fuel in cement mills or re-used.

It has been verified that the residue after glycol distillation can be combined with used oils applied for energy purposes. The experiment was repeated using the same raw materials and procedure, except that no sodium carbonate was added. Heating until total dissolution of the fibres lasted 16 hours. The obtained results were the same as before.

Example 2. The raw material comprises ground tires having the following composition: rubber 70% by weight, tangled fibres 22% by weight, wires 7% by weight, ground paper and cotton 1 % by weight.

A flask with a capacity of 3 litres, equipped as in Example 1 , was charged with 874 g of the raw material, 1053 g of glycerine and a piece of porcelain. After heating the content of the flask to a temperature of 210°C, a previously prepared solution of 2.5 g potassium hydroxide in 25 g of glycerine was added, the mixture was maintained at 210°C for 30 minutes, and the heating was then switched off. When the temperature in the flask decreased to 80°C, the apparatus was disassembled, the liquid was filtered, and the precipitate was transferred into a flask, to which 1053 g of glycerine was added, and the mixture was subsequently treated as in Example 1 , except that glycerine was evaporated under a vacuum of 30 mmHg to obtain:

Wires (steel scrap) 61.2 g

Rubber precipitate without fibres 616.8 g

Residue after glycol distillation 630 g As in Example 1 , the quality of recovered components allowed for their re-use without additional operations.

Example 3. The raw material comprises ground tires after partial removal of rubber and wires having an approximate composition: rubber 16% by weight, tangled fibres 80% by weight, wires 2% by weight, ground paper and cotton 2% by weight. The apparatus and the method was as in Example 2, wherein the flask was charged with 240 g of the raw material and 1360 g of a mixture of glycols being a waste in the production of ethylene oxide and ethylene glycol, comprising di-, tri-, tetra-, penta- and hexaethylene glycols. This mixture was dehydrated and heated to 220°C, adding 3 g of sodium acetate in 25 g of ethylene glycol after 20 min. and after one hour, and after another hour, the heating was switched off. When the temperature decreased to 80°C, the mixture was filtered, the precipitate was mixed with 250 g of a mixture of glycols, and wires were removed from the precipitate as in Example 1. After distillation of glycols under a vacuum of 0.1 mmHg to a temperature of 240°C, the following components were obtained from the solution:

Wires (steel scrap) 4.8 g

Rubber precipitate without fibres 43.3 g

Residue after glycol distillation 621.9 g

The suitability for use of the recovered components was similar as in Examples 1 and 2.