RU2151696C1 - Method for cleaning of metal cord and fitting of polymeric materials - Google Patents

Abstract

FIELD: removal of the mass of polymeric material from metal fitting in the process of salvage of worn-out tyres, mechanical rubber goods, products of cable industry, polymeric facing of containers and other reinforced products. SUBSTANCE: method is based on digestion of polymeric materials in fused NaOH-KOH with addition of metal oxides of variable valency used as catalyst, through which air is bubbled. The method is accomplished in a single stage, and no coke residue is formed at digestion. Low temperature of the process prevents formation of nitrogen oxides. Catalytic oxidation of polymeric material is not accompanied by separation of gaseous organic substances, soot, which reduces harmful effect on the environment. EFFECT: facilitated procedure. 3 cl, 1 tbl

Description

 The invention relates to the field of processing of polymeric materials when removing their arrays from metal fittings during the disposal of worn tires, rubber products, cable industry products, polymer cladding, containers and other reinforced products.

 In order to extract metal cord from worn tires and metal fittings from polymeric materials, mechanical methods are used.

 There is a method according to which in the process of processing used car tires are pressed during heating (RU 2042511, CL B 29 B 17/00, 1995 - (1)). After forcing the rubber through the dies, there remains a metal cord (wire fragments) containing 5 to 15% by weight of rubber. It is impossible to use a similar cord by remelting due to the high sulfur content in the rubber (5 - 10% by weight of rubber).

 A known method of separating rubber from metal in the process of processing worn metal cord tires by exposure to high-pressure jets of liquid (RU 2024400, CL B 29 B 17/00, 1994). The disadvantages of this method include the need to create a high pressure fluid, as well as the formation and the specific location of the jets of fluid around the perimeter of the tire, which is accompanied by a large flow of fluid.

 According to other methods, metal reinforcement and cord are extracted from the polymer massif mechanically, and in order to reduce mechanical stresses when leveling the metal cord, the latter is heated with superheated steam (SU 1813044, class B 29 B 17/02, 1993) or as a result of processing with high-frequency radiation ( SU 1581583, class B 29 B 17/00, 1990; SU 1497021, class B 29 B 17/02, 1989; SU 1770137, class B 29 B 17/00, 1992) until the adjacent polymer layers are melted. In addition to the high energy costs, the disadvantages of such methods include the need for additional cleaning of the cord and reinforcement, and intense gas evolution as a result of the pyrolysis of polymeric materials requires the creation of plants for neutralizing or utilizing the resulting gases. These methods cannot be used to clean the metal fittings contained in reinforced hoses in which the metal wire is woven into an openwork system.

 In order to reduce the likelihood of pyrolysis of the polymer material, a method is used in which the products are placed in a dielectric liquid (kerosene) and heated until the adjacent polymer layers are melted, after which the metal reinforcement is separated from it (SU 1787113, class B 29 B 17/02, 1993 )

 The disadvantage of this method is the length of the heating time, the use of combustible liquids and the need for their regeneration.

 Methods are also known where polymers (for example, polyurethanes) are dissolved in solvents, after which the cord and the solution are separated (DE 4202586, CL B 29 B 17/02, DE 4204176, CL B 29 B 17/02, publ. ISM N 1, 1995). These methods require large expenditures of solvents, the regeneration of which in large volumes is a difficult economic and environmental task. In addition, the methods are not universal: for each type of polymer, different solvents are required, and in the case of complex compositional materials, it is necessary to use a mixture of solvents or stepwise dissolution in different solvents. The process of dissolution of polymers, as a rule, proceeds when heated for a long time.

Closest to the proposed solution is a method in which a metal cord with rubber residues formed during the processing of worn tires (for example, by pressing method (I)) is subjected to oxidation at 500 - 700 ^o C in an atmosphere of air, and then upon reaching a residual rubber content of 10 - 20% is heated without air supply (SU 1685721, CL B 29 B 17/00, 1991). The process is slow, part of the rubber is pyrolyzed to gaseous and liquid hydrocarbons, and the base is a coke residue, which is crushed by passing metal cord through rollers.

 The disadvantages of the prototype method include multi-stage, the need to capture the product of the oxidation and pyrolysis of polymers, as well as grinding formed on steel cord or reinforcement coke.

 The objective of the invention is to reduce the negative environmental impact of burning polymer materials without the formation of coke residues, lowering the temperature of combustion, accelerating the processing process.

To solve this problem, the metal cord and reinforcement are cleaned of polymer materials by burning them in a molten catalyst, through which air is bubbled. As a catalyst, a NaOH-KOH melt with additives of 5-10 wt.% Of metal oxides of variable valence is used. The burning of polymeric materials is carried out at a temperature of 350 - 600 ^o C.

 The carbon dioxide formed during the oxidation of polymers is partially absorbed by the melt, as well as sulfur dioxide and trioxide released during the oxidation of rubber. This forms a mixture of salts. At the process temperature in the presence of air oxygen and water vapor, alkali metal carbonates partially decompose with the release of carbon dioxide, so the spent catalyst is a mixture of carbonates, sulfites and sulfates, as well as metal salts of variable valency, as a result of which the pressure melting temperature of this mixture rises.

Variable valence metal oxides contained in the melt are a catalyst for the oxidation of organic substances and promote the afterburning of coke in the melt, and also catalyze the oxidation of sulfur in SO ₂ and SO ₃ and the decomposition of carbonates. Oxides and salts of metals of variable valency increase the solubility in the oxygen melt (Kinetics and Catalysis. Moscow, 1985, N 2, pp. 356 - 362), which intensifies the process of catalytic oxidation of polymers and protects the melt from recovery in case of overdose of the cord with the remains of polymer materials.

 At a concentration of metal oxides of variable valency below 5 wt.%, Their effect on the catalytic oxidation of polymers is not noticeable (see Table 1). Increasing the concentration of metal oxides of variable valency above 10 wt.% Is impractical due to their high cost, and also because it increases the melting temperature of the catalyst and the viscosity of the melt, which reduces the likelihood of absorption of oxygen and sulfur oxides by the catalyst.

Hydroxides of sodium and potassium have low melting points, so the process is carried out at 350 - 600 ^o C. As the transition of hydroxides to carbonates of alkali metals, the melt melting temperature increases.

 Carrying out the process in the indicated temperature range prevents the formation of nitrogen oxides, and sulfur does not go into the composition of the alloy from which the metal cord is made.

 The deep oxidation of organic substances in the molten salt through which air is barbored is known (SU 911091, class F 23 G 7/00, 1982; Journal of the Russian Chemical Society named after D.I. Mendeleev, vol. 37, No. 3, p. 22 - 25).

In this case, the melt plays the role of a medium for carrying out the process, and also due to the high heat and thermal diffusivity it is used as a heat transfer medium with the aim of removing heat from the reactor. The melt can simultaneously serve as a catalyst for the oxidation of organic substances. However, at high concentrations of V ₂ O ₅ (up to 83 wt.%), The melt melting temperature rises (the process is carried out at 400 - 900 ^o C, and due to the low content of K ₂ O, the melt cannot effectively absorb S ₂ O and SO ₃ .

The use of a mixture of NaOH-KOH, which melts at 250 ^o C, allows the process of burning polymers contained on the cord, at a sufficient speed at a temperature of 350 ^o C. The literature does not describe the use of the melt NaOH-KOH, including with the addition of metal oxides variable valency, for catalytic oxidation of organic substances.

 For the practical implementation of the proposed method as the objects of study used samples of reinforced hoses, the polymer of which includes a mixture of rubbers, high-pressure polyethylene, plasticizers (dibutyl phthalate, paraffin, rosin, etc.), as well as scraps of cord extracted from used car tires pressing method (1), which contained a different amount of rubber.

 The catalytic oxidation of the polymer on the samples of reinforced hoses was slower than the oxidation of rubber on a metal cord extracted from car tires. This is explained by the more complex composition of the polymer on the hose and the method of weaving a metal wire on it, which makes it difficult for the polymer to contact the catalyst.

 Example 1

290 g of potassium hydroxide and 290 g of sodium hydroxide were charged into a reactor made of X18H10T steel, whose internal diameter is 48.7 mm. The reactor was placed in an electric furnace, the temperature of which was maintained by a high-precision temperature controller. After the catalyst was melted, air (1 L / h) was bubbled through the melt for two hours at a temperature of 400 ^° C. The bubbler height of the catalyst was 155 mm. The temperature in the reactor was reduced to 370 ^o C and placed in the molten catalyst sample, which is a piece of reinforced steel wire hose. At certain intervals, a sample was removed from the reactor and the completeness of combustion of the polymer was noted. 15 minutes after the sample was in the reactor on the inside, its polymer had not yet burned.

 Examples 2 to 5.

 The results of experiments carried out analogously to example 1, but at different temperatures, are presented in the table.

 Examples 6 and 7.

The experiments were carried out analogously to example 1, with the difference that the temperature was maintained respectively 450 and 510 ^o C and as a catalyst used a mixture of 250 g NaOH, 250 g KOH, which was added 80 g V ₂ O ₅ , which is 16% by weight oxides of potassium and sodium. The results are presented in the table. It can be seen from them that due to the high viscosity of the molten catalyst of this composition, the polymer oxidation process proceeds slowly.

 Examples 8 to 17.

The experiments were carried out analogously to example 1, with the difference that 10 wt.% V ₂ O _{5 was} added to the NaOH-KOH melt, and the temperature from experiment to experiment was varied in the range 400 - 630 ^o C. The experimental results presented in the table show that at 400 ^o C complete polymer oxidation is achieved within 25 minutes (experiment 9), and at 620 ^o C the polymer on the sample oxidizes within 4 minutes (experiment 17).

 Examples 18-24.

The experiments were carried out analogously to examples 8-17, with the difference that 7 wt.% CuO was added to the melt. As can be seen from the results of the experiments (see table), the addition of NaOH-KOH to the melt containing 10 wt.% V ₂ O ₃ , 7 wt.% CuO does not change the activity of the catalyst.

 Examples 25 to 28

The experiments were carried out similarly to examples 18-24, with the difference that cord with rubber residues was used as the sample, which was obtained by pressing used automobile tires by the method (1). The experiments were carried out at 480, 343, 445 and 545 ^o C, respectively. The experimental results are shown in the table, from which it is seen that the catalytic combustion of rubber on the cord proceeds faster and at a lower temperature than the catalytic oxidation of a polymer on a reinforced hose.

 Examples 29 to 31

The experiments were carried out analogously to example 1, with the difference that 3 wt.% Was added to the NaOH-KOH melt. % CuO, and cord with rubber residues was used as a sample. The experiments were carried out at a temperature of 350, 440 and 540 ^o C, respectively. As can be seen from the examples in the table, even at 350 ^o C there is a complete catalytic oxidation of the rubber in 20 minutes, and at 445 ^o C the rubber burns out in 5.5 minutes.

 Examples 32 to 35.

The experiments were carried out analogously to examples 29 - 31, with the difference that 5 wt.% CuO was added to the NaOH-KOH melt. The experiments were carried out at 460, 355, 545 and 650 ^o C. As can be seen from the results of the experiments (see table 1), this composition of the catalyst shows a higher activity than the catalyst containing 3 wt. % CuO. For example, at 355 ^o C the rubber on the image burns out in 13 minutes (experiment 33), and at 545 ^o C - in 3 minutes (experiment 34).

 Examples 36 to 38.

The experiments were carried out analogously to examples 32 - 35, with the difference that 7 wt. % V ₂ O ₅ . The experiments were carried out at 355, 445 and 550 ^o C, respectively. The results of the experiments are shown in the table. It is seen that the additive 7 wt. % V ₂ O ₅ to the NaOH-KOH melt containing 5 wt.% CuO does not change the catalytic activity of the melt.

 Using the proposed method provides compared with the known following advantages.

 1. The cleaning of the metal cord and reinforcement from the remnants of polymeric materials occurs in one step.

 2. Burning occurs without the formation of coke residue.

 3. The relatively low process temperature eliminates the possibility of the formation of nitrogen oxides, and the catalytic oxidation of the cutters is not accompanied by the release of gaseous organic substances, soot, which reduces the harmful effects on the environment.

Claims (3)

 1. A method of cleaning metal cord and reinforcement from polymeric materials by burning them, characterized in that the combustion is carried out in a NaOH-KOH melt with additives of metal oxides of variable valency as a catalyst through which air is bubbled.  2. The method according to claim 1, characterized in that the additives of oxides of metals of variable valency are 5 to 10 wt.%. 3. The method according to PP.1 and 2, characterized in that the burning of polymeric materials is carried out at 350 - 600 ^o C.

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