MXPA98003186A - Process of defluxization of h - Google Patents

Abstract

A process for the devulcanization and functionalization of a rubber vulcanizate by desulphurisation, which involves suspending a piece of rubber vulcanizate in a solvent, which preferably swells the rubber vulcanizate before or during the devulcanization reaction and adds an alkali metal, such like sodium, to the suspension. The alkali metal unfolds the mono-, di- and poly-sulfidic entanglements in the rubber vulcanizate, to release the rubber polymer, which has a molecular weight substantially equal to that of the rubber polymer, before vulcanization. Functional groups derived from the bonds of solvent molecules to the polymeric skeleton of the devulcanized rubber. In addition to the de-vulcanized rubber polymer, the carbon black can also be recovered by re-use according to the process of the present invention. The functionalized devulcanized rubber can be subjected to a revulcanization reaction without separation of the rubber polymer from the solvent, by the addition of an appropriate curing mixture

Description

PROCESS OF DISLOCATION OF THE RUB FIELD OF THE INVENTION The present invention relates to the field of rubber recycling and, in particular, to a devulcanization process for recycling vulcanized rubber, such as tire rubber.

BACKGROUND OF THE INVENTION Since the discovery of the vulcanization process in the mid-1800s, there has been much interest in recycling vulcanized rubber, such as discarded tires and tire factory waste. One method for recycling tire rubber involves shredding and reforming shredded tires into low specification materials, such as rubber mats, rubber blocks, and mud flaps from vehicles. The crumb rubber tire has been suggested as an additive for road asphalt. Another method of recycling tire rubber involves subjecting the tires to a pyrolysis reaction to produce an aromatic, low sulfur oil with high API gravity, which is useful as a fuel. However, these recycling processes are generally non-economic and produce a low quality rubber product. Therefore, discarded tires are currently stacked and / or used as landfills. This is not an adequate solution, as evidenced by the recent large tire fire in Hagersville, Ontario, Canada. Clearly, discarded tires represent a considerable environmental responsibility. In the vulcanization process, the rubber polymer is entangled with the sulfur, usually with the application of heat. Unfortunately, the interlaced rubber polymer can not be recovered into a useful product, merely by heating and reprocessing. Sulfidic entanglement represents a significant problem in the recycling of the rubber vulcanizate and in the recovery of the rubber polymer from the starting material from the vulcanized rubber. A review of methods of devulcanizing vulcanized rubber is presented in "Methods of Devulcanization" (Warner, Walter C. Rubber Chem. Technology 67: 3: 559-566, 1964). The methods reviewed include catalysis with a quaternary ammonium chloride catalyst, which has a large hydrocarbon radical attached to nitrogen; grafting ethyl acrylate on the ground polybutadiene-vulcanized waste; dissolving the rubber in o-dichlorobenzene with the 2, 2A * -dibenza idodiphenyl disulfide; apply microwave energy at a specific frequency and energy level; subject the rubber to ultrasonic waves and biodegradation with thermophilic bacteria. Chemical probes to react with sulfide entanglements are also discussed and include triphenylphosphine and sodium di-n-butyl phosphite, propan-thiol / piperidine, dithiothreitol, lithium-aluminum hydride, sodium aniline solution, phenyl- lithium in benzene and methyl iodide. Many of these processes of the prior art require the use of a digester apparatus and / or require agitation for many hours. Another disadvantage includes costly reagents, inefficient reactions and non-economic processes. Other reactions may involve pyrolysis, which will remove the sulfur, but the polymer decomposes as a result. Therefore, it is convenient to supply a process which can efficiently de-vulcanize a vulcanized rubber matrix to recover the original polymeric constituents, as well as other rubber constituents, such as carbon black. It is an object of the present invention to selectively remove the sulfur entanglements found in the rubber vulcanizate, to recover a reusable rubber polymer.

SUMMARY OF THE INVENTION According to one aspect of the present invention, a process for devulcanizing a rubber vulcanizate by desulfurization is provided, which comprises the steps of: contacting the rubber vulcanized piece with a solvent and an alkali metal , to form a reaction mixture; and heating the reaction mixture in the absence of oxygen and with mixing at a temperature sufficient to cause the alkali metal to react with the sulfur in the rubber vulcanizate, thus devulting this rubber. According to another aspect of the present invention, a process for de-vulcanizing a rubber vulcanizate containing carbon black is provided, which comprises the steps of: contacting the rubber vulcanized piece with a solvent to form a dispersion of the rubber. vulcanized rubber; heating this vulcanized rubber dispersion, in the absence of oxygen, thus forming a carbon black dispersion in a rubber solution; separating at least a portion of the carbon black from the rubber solution; adding an alkali metal to the rubber solution to form a reaction mixture; and further heating the mixture in the absence of oxygen and with mixing at a temperature sufficient to cause the alkali metal to react with the sulfur in the mixture, thereby devulcanizing the rubber.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, which illustrate embodiments of the present invention; Figure 1 is a temperature-time reaction profile of a desulfurization / devulcanization process, according to the present invention; and Figure 2 is an infrared spectrum of a rubber polymer recovered by the process of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES According to a process of the present invention, rubber vulcanizate, such as discarded tires and tire factory debris, is desulfurized and, therefore, devulcanized by the reaction with an alkali metal. The rubber polymer recovered from the process of the present invention has a molecular weight substantially equal to that of the rubber polymer before vulcanization. Devulcanization is defined here as the splitting of the mono-, di- and poly-sulfidic entanglements, formed during the initial vulcanization process of the untreated rubber. Therefore, according to the present invention, devulcanization occurs by desulfurization.

A particularly suitable application of the rubber devulcanization process of the present invention is for the recovery of a rubber polymer that can be used, from discarded tires and scrap tire factory. The tire pieces of the rubber vulcanizate are first crumbled, crushed or cut, in a manner known to those skilled in the art, to a piece of vulcanizate. Discarded tires and waste material from tire mills are first advantageously treated in a manner known to those skilled in the art, to separate any steel and / or fiber from the rim, before or after preparing the piece of rubber vulcanizate . The piece of vulcanized rubber is then dispersed in a solvent, which preferably swells the rubber vulcanizate, before or during the devulcanization reaction. Suitable solvents include one or more of toluene, naphtha, terpenes, benzene, cyclohexane, diethyl carbonate, ethyl acetate, ethylbenzene, isophorone, isopropyl acetate, methyl ethyl ketone, derivatives thereof, and the like. Preferably, the solvent has a relatively low boiling point to help remove this solvent by evaporation, as will be discussed below. Another advantageous property of the solvent is a good solubility of the rubber polymer released. It is believed that the devulcanization reaction can be intensified by solubilizing the rubber polymer released in the solvent during the reaction. Preferably, the solvent does not react and thus consumes the alkali metal. Examples of solvents that consume the alkali metal are mercaptans, chlorinated solvents and amines. Suitably, the solvent is used in an excess to provide a good dispersion of the piece of rubber vulcanized in the solvent. Preferably, the solvent is used in an excess of at least about 2: 1 by weight. The ratio of the solvent to the vulcanized rubber is somewhat dependent on the particle size of the piece and can vary from 2: 1 to 4: 1, to achieve a good mix. A greater ratio of solvent to rubber vulcanizate can be used, however, it will be appreciated by those skilled in the art that it is convenient to use as little solvent as possible for economy and efficient handling. An alkali metal is added to the dispersion of the tire piece. Suitable alkali metals are sodium, potassium, lithium and cesium. The preferred alkaline material is sodium. This alkali metal is used in a molar excess in the range of from 2: 1 to approximately 9: 1, based on the sulfur content in the rubber piece. Typically, the sulfur content in the tire rubber vulcanizate is about 2% by weight. The theoretical molar ratio of the alkali metal to the sulfur is 2: 1 for the desulfurization process of the present invention. However, other components, such as organic acids and zinc oxide, they can be present in the vulcanized rubber, which will consume the alkali metal. Therefore, the molar ratio of the alkali metal to the sulfur is advantageously about 4: 1. Next, references to sodium try to include any alkali metal. A high molar ratio may not be necessary or economical for certain applications of the recovered rubber polymer, in which a small amount of sulfur can be tolerated. Conveniently, the devulcanization process is conducted in the absence of oxygen. Thus, the reaction vessel containing the mixture is purged with nitrogen to replace the oxygen; or, in one embodiment of the present invention, molecular hydrogen is added at a pressure of this hydrogen of about 345 to 3450 kPa. Preferably, the hydrogen pressure is around 1380 kPa. In the process of the present invention, hydrogen capping radicals are formed when the sulfur entanglements are removed by the sodium. When the process is conducted in a nitrogen atmosphere, these formed radicals are capped by internal hydrogen separation reactions, which increase the degree of unsaturation in the resulting polymer. Likewise, carbon-to-carbon entanglement can occur, resulting in an improved rubber. The mixture is stirred, while heated, in the reaction vessel. The cutting rate of the agitation must be sufficient to form sodium with a small particle size and high surface area, when the melting point of sodium is achieved. The heating must be sufficient to cause the sodium metal to react with the sulfur in the vulcanized material; however, the temperature should not exceed that which causes the thermal decomposition of the rubber polymer. Typically, the mixture is heated from room temperature to about 250 ° C and, as can be seen in Figure 1, a rapid exothermic reaction starts at about 1252 ° C in the present system, whose heat release must be considered during the heating step. It is preferred to control the temperature below about 300 ° C or where the thermal decomposition of the rubber begins. Of course, the heating continues for a sufficient time to completely de-vulcanize the rubber and, as shown in Figure 1, it is fast, requiring only several minutes. The pressure at which the process is performed is not critical. Thus, heating and stirring can also be conducted at atmospheric pressure. If a closed reaction vessel is used, higher pressures will be produced, for example pressures up to 200 kPa. In another embodiment of the present invention, the rubber vulcanizate, once dispersed in a solvent, is heated in the absence of oxygen, first for a time and at a temperature sufficient to thermally decompose at least a portion of the rubber and release the black from the rubber. carbon. Preferably, the dispersion is heated to a temperature of less than about 300 ° C, more preferably less than about 250 ° C, but above ambient temperature, to minimize unwanted thermal decomposition of the rubber polymer. The carbon black from the rubber vulcanizate is then separated from the solvent / polymer phase, for example by filtration, centrifugation or hydrocyclone. Other contaminants, for example zinc oxide, which consumes the alkali metal, are greatly removed with the carbon black, thus reducing the amount of the alkali metal required for the subsequent vulcanization reaction. A rubber vulcanizate can contain up to 2% of the zinc oxide, so that the removal of a significant amount of zinc oxide with the carbon black results in a significant reduction in the subsequent consumption of the alkali metal. After removal of the carbon black, the alkali metal is then added to the solvent / rubber polymer dispersion and the reaction vessel is purged of oxygen using nitrogen and / or hydrogen. The mixture is then heated and stirred, as previously described, and the rubber is devulcanized in an exothermic reaction. The desulfurization / devulcanization reaction is rapid and, once the reaction is complete, the reactor begins to cool. Although thermodynamic measurements have not been made for the devulcanization reaction of the present invention, the heat released in the reaction is anticipated to be similar to that of the desulfurization of the methylphenyl sulfide, for example, as shown below: CH3-S-C6H5 + 2Na + 2H? Na2S + CQ Q + CH4 for which? HS at 2982C is -446.8 kJ / mol of methyl-phenyl sulfide. The desulfurization / devulcanization reaction of the present invention can be described generally as follows: [(R) n-S? - (R ') m] y + 2xyNa + yH2? [(R) nH] y + [(R ') mH] y + xyNa2S dondß [(R)? - S? - (R') ?? |] and represents a vulcanized rubber, (R) ny (R ') ) m represents identical or different rubber polymers, having n and m units of monomers, respectively, x is the number of sulfur atoms intertwined in the ono-and poly-sulfide bonds and y is the total length of the rubber vulcanized chain. The devulcanized rubber then undergoes an extinction stage to remove any unreacted sodium metal. Preferably, this extinguishing step is conducted as follows: the mixture is preferably cooled below 2002C; water is injected and the mixture is stirred to convert unreacted sodium to sodium hydroxide. This sodium hydroxide, the sodium salts soluble in water and other inorganic materials used in the formulation of the rim and released during the devulcanization process, are dispersed in the aqueous phase. It is not necessary to cool the reaction mixture prior to water injection, but a cooling step is preferred to minimize the resulting increase in pressure. The carbon black becomes moistened with the water and is easily removed in the aqueous phase from the organic phase of the solvent / rubber polymer by centrifugation, filtration or hydrocycloneation. This carbon black can be used again. The remaining water-soluble salts can be discarded or recovered using techniques known to those skilled in the art. The solvent is evaporated from the resulting solvent / rubber polymer phase to provide a rubber polymer blend having a range in molecular weight that is substantially equal to that of the rubber polymers prior to vulcanization. The resulting polymer mixture can then be revulcanized with sulfur and other components, such as carbon black, to produce a rubber vulcanizate of the desired properties, for example, for new tires. The rubber polymer can also be used as a polymeric gum to bind tire pieces into useful products, such as those previously mentioned herein. Alternatively, the extinguishing step can be conducted by the addition of hydrogen sulfide gas. In this embodiment of the extinguishing step, the solution of the de-vulcanized rubber polymer is preferably cooled to a temperature of less than about 100 ° C to minimize the evaporation of the solvent, when the reaction vessel is vented to the atmosphere. The hydrogen sulfide gas is added at its vapor pressure of approximately 2550 kPa. The extinguishing stage can be conducted without cooling, but it may then be necessary to pump this hydrogen sulfide gas under pressure. The mixture is then heated to a temperature of at least about 100 ° C while stirring at a high cut rate, to react any unreacted sodium with the hydrogen sulphide and form the sodium hydrosulfide. The reactor is cooled, discharged to the atmosphere and purged with nitrogen to remove any unreacted hydrogen sulphide gas. The solids, which include the carbon black, are removed from the organic phase by centrifugation and / or filtration. The solvent is evaporated from the resulting solvent / rubber polymer phase to provide a rubber polymer substantially of the same molestock as the rubber polymers before vulcanization. Sodium sulfide produced during devulcanization is converted to sodium hydrosulfide during the hydrogen sulphide extinction stage. A disadvantage of this extinguishing step, when compared to the preferred extinguishing step described here above, is that some of the carbon black material remains associated with the recovered devulcanized rubber polymer. Nevertheless, if the rubber polymer is to be reused for a product which contains some carbon black, for example for new tires, the presence of some carbon black in the recovered rubber polymer may not represent a significant process problem. . Advantages of the water extinguishing stage over the hydrogen sulfide extinction stage include that the safety, cost of reagents and carbon black separation are facilitated. In another embodiment, the aqueous and organic phases, formed in the aqueous extinction stage described above, do not separate. Instead, a cure mixture that includes rubber cure additives, accelerators and / or antioxidants, in combinations and proportions well known in the art, for example, is added to the aqueous solvent / water / rubber polymer paste. devulcanized, to revulcanizar this polymer. If the carbon black is removed from the rubber polymer during the process, the curing mixture may also include carbon black or other filler. The solvent and water evaporate from the resulting rubberized product. This reaction can also be conducted immediately after the extinction by the addition of hydrogen sulphide. The following examples illustrate the present invention. The rubber vulcanizate used in the examples was a passenger vehicle tire part having a sulfur content of about 1.7% by weight, as determined using the Leco ™ sulfur analyzer.

EXAMPLE 1 100 g of a 30-mesh passenger rim portion, having a sulfur content of 1.7% by weight, was added to a stainless steel autoclave liner. Then 350 g of toluene was added to the tire piece, 4.9 g of sodium metal was added to the dispersion of the tire piece to give a molar ratio of sodium: sulfur of 4.0. The autoclave coating was placed inside an autoclave. This autoclave was purged first with nitrogen to remove any oxygen and then with hydrogen at a hydrogen pressure of 1380 kPa. The heaters were activated and the mixture in the autoclave was initially stirred at a rate of about 600 to 800 rpm as a MagneDrive®II stirrer. At 1002C (sodium melts at about 98ec), the stirring speed was increased to about 1800 rpm to ensure good mixing of the tire piece with the molten sodium. Referring now to the temperature / time reaction profile of Figure 1, a rapid exothermic reaction began at about 1252C and the temperature was raised to a peak temperature of about 275sec. It is during this exothermic reaction that the sulfur was removed from the rubber to produce sodium sulfide.

The heaters were turned off when the temperature reached 2502C, to ensure that this temperature in the autoclave did not exceed 300se, as a result of the exothermic reaction. During the course of the desulfurization / devulcanization reaction, the pressure in the autoclave increased to a maximum of about 2930 kPa. After the reaction was complete, the autoclave was cooled to about 2252C, while stirring was maintained at about 1800 rpm, the reaction mixture was quenched by the addition of 75 ml of water at a rate of 25 ml / min. The water reacted with any unreacted sodium to produce sodium hydroxide. This reaction mixture was then allowed to cool to room temperature. The gas chromatographic analysis for the gas that remained in the autoclave was followed by the extinction stage and after cooling to room temperature showed that very little gas was produced during the reaction, advantageously demonstrating that little, if any, thermal decomposition occurred during the reaction of the present invention. The autoclave was opened and the black paste was observed. The aqueous paste was emptied into a container and placed inside a smoke hood and then in a low temperature oven, to remove toluene and water by evaporation. After removing the solvent, there was a material mat type, elastic, strong.

EXAMPLE 2 The process described in Example 1 was repeated with a piece of 10 mesh rim. However, after cooling, the resulting black aqueous paste was emptied into centrifuge tubes. The reaction products were centrifuged at 13,000 rpm for 2 hours, to separate the organic solvent / polymer phase from the aqueous / solid phase. The phase separation was very good. An organic phase of solvent / polymer of rubber, of a dark brown color, was carefully decanted from the aqueous / solid phase. Carbon black recovered as a solid. The solvent was removed from the solvent / rubber polymer mixture by rotary evaporation. The performance of the rubber polymer was about 60% by weight, based on the weight of the starting material of the tire piece. The rubber polymer was a very sticky material, having an infrared spectrum consistent with the known high molecular weight rubber polymers. The molecular weight of the rubber polymer was determined by gel permeation chromatography, using trichlorobenzene as the solvent, and a refractive index detector. The rubber polymer has a biroodal molecular weight distribution. The highest peak molecular weight had a molecular weight distribution in the range of about 12,000 to 74,000, with an average molecular weight of about 32,000, based on the polystyrene equivalents. The sulfur content was 0.37% by weight.

EXAMPLE 3 The process described in Example 2 was repeated. However, before heating, the autoclave was purged with nitrogen and no hydrogen was added. The sulfur content of the devulcanized rubber polymer was found to be 0.46% by weight. The molecular weight of the resulting rubber polymer had a bimodal distribution with a high molecular weight peak having a molecular weight distribution of about 13,000 to 84,000 and an average molecular weight of about 36,000. A comparison of the high molecular weight peaks of Examples 2 and 3 suggests that some carbon-to-carbon entanglement occurs during the devulcanization reaction, when the reaction is conducted with a nitrogen purge alone and in the absence of molecular hydrogen .

EXAMPLE 4 The reaction of Example 1 was repeated until the extinction stage with water. The autoclave was allowed to cool to about 1002c and the pressure was reduced to less than 345 kPa. Hydrogen sulfide gas was added at its vapor pressure and at room temperature (about 1550 kPa) while stirring the mixture rapidly at about 1800 rpm. The autoclave was then heated to more than about 100 ° C to ensure good contact between any remaining molten sodium metal and the hydrogen sulfide gas. The autoclave was cooled to room temperature and purged with nitrogen before opening. The contents were removed from the autoclave and the toluene was removed by evaporation, supplying a mat-type elastic material. DISCUSSION OF EXAMPLES 1-4 The rubber polymer, recovered in Examples 2 and 3, had a sulfur content of about 0.3 to 0.4% by weight. This is significantly reduced compared to a typical sulfur content of a tire rubber of approximately 2% by weight. Very low sulfur levels (<0.1% by weight) have been achieved with higher Na: S ratios (see Table I). However, it is believed that additional reductions in sulfur content are only possible at a molar ratio of sodium to sulfur of about 6: 1. This high molar ratio may not be necessary or economical for certain reprocessing applications of the recovered rubber polymer. However, it appears that the process of the present invention effectively doubles the mono-, di- and poly-sulfidic entanglements of the rubber polymers. It is believed that at least a portion of the residual sulfur content in the rubber polymer produced in Examples 2 and 3 is due to incomplete mixing in the non-ideal autoclave reactor and / or the entrainment of the microcrystalline sodium sulfide in the polymer. . Analysis of the additional recovered polymer, compared to the starting material of the rubber vulcanizate, are presented in Table I.

TABLE I Sample A represents the starting material in pieces. Sample B represents the heat treatment of the tire pieces in the solvent, without the addition of the alkali metal. Samples C and D are samples treated by the process of the present invention. The results presented in Table I show an increase in the hydrogen content in the desulphurized rubber polymer (Samples C and D), as a result of the hydrogen-binding radicals, formed during the devulcanization reaction. The carbon-carbon double bonds are not hydrogenated under the conditions of temperature and pressure of the reaction. Sample B shows a significantly lower hydrogen content, because the sulfur was not substantially removed in the heat treatment of the tire pieces. Zinc, which is also present in large quantities in the piece of rim (1.9% by weight), was greatly removed by the heat treatment and was completely removed with the addition of sodium. The difference in zinc content between Samples A and B is indicative of the benefits of the embodiment of the process of the present invention, in that dispersion of pieces of rim was heated before the addition of the alkali metal. It is evident from this difference that the alkali metal added to the dispersion can be significantly reduced because it was not consumed much by the zinc oxide. The tire pieces used in the Examples had a particle size in the approximate range of 10 to 30 mesh. It will be appreciated by those skilled in the art that less or more vulcanized may be effectively treated by the process of the present invention with other types of reactors An infrared spectrum of a polymer recovered by the process of the present invention is shown in Figure 2. Although the tire pieces were produced from a variety of tire brands obtained from a variety of polymers, the infrared spectrum of Figure 2 shows a devulcanized rubber polymer, which is representative of the cis-polyisoprene or polybutadiene polymers or the styrene-butadiene copolymers. While not wishing to be bound by any theory, devulcanization, according to the methods of the present invention, is believed to result in the initial formation of a radical on the backbone of the rubber polymer at positions previously occupied by the interlacing sulfur. When the devulcanization reaction is carried out in the presence of a suitable solvent, this radical is capable of extracting hydrogen from the solvent molecule and consequently forming new radicals derived from the solvent molecule. Suitable solvents include toluene, naphtha, terpenes, benzene, cyclohexane, diethyl carbonate, ethyl acetate, ethylbenzene, isophorone, isopropyl acetate, methyl ethyl ketone and their derivatives. Under appropriate conditions, the solvent radicals can react with the devulcanized rubber polymer to form new carbon to carbon bonds, between the solvent radical and the polymer backbone, at sites previously occupied by the sulfur entanglements. When bonded in this way, the solvent molecules are present along the polymer backbone in the same periodicity as the original sulfur entanglement, that is, approximately one molecule of solvent binds to every 100 carbon atoms in the backbone. The rubber devulcanized, functionalized according to this procedure, has different properties of the de-vulcanized that do not contain functionalization. For example, the average molecular weight increases without some change in the length of the average skeleton and improvements in strength, elasticity, solubility and other convenient properties can be obtained.

The foregoing can be illustrated in relation to the devulcanization of cis-1,4-polyisoprene and is as follows: (-CH2-C (CH3) = C-CH2) n | Sy I (-CH2-C (CH3) = C-CH2) r [I (I) Where (I) is devulcanized with an alkali metal, such as sodium, and free radicals (II) are produced, as shown: (-CH2-C (CH3) = C-CH2) n + (-CH2-C (CH3) = C-CH2) m + NaS2 (II) These radicals (II) are then able to extract hydrogen from the molecules (III) of the solvent, forming radicals (IV) of hydrogen and radicals of solvents (V), derived from the solvent molecule as follows: HA (III) supplies H «+» A, which can be added to the polymer as follows: (-CH2-C (CH3) = C-CH2) n I

Claims (33)

1. CLAIMS 1. A process for devulcanizing a rubber vulcanizate by desulphurisation, this process comprises the steps of: contacting pieces of the rubber vulcanizate with a solvent and an alkali metal, to form a reaction mixture; heating this reaction mixture, in the absence of oxygen and with mixing at a temperature sufficient to cause the alkali metal to react with the sulfur in the rubber vulcanizate; and maintaining the temperature below that at which the thermal decomposition of the rubber occurs, thus devulting the rubber vulcanizate.
2. 2. The method of claim 1, wherein the temperature is maintained below 300se.
3. 3. The method of claim 2, wherein the solvent is one capable of inflating the rubber vulcanizate.
4. 4. The method of claim 3, wherein the solvent is one capable of stabilizing the devulcanized rubber.
5. The method of claim 4, wherein the solvent is selected from the group consisting of one or more of toluene, naphtha, terpenes, benzene, cyclohexane, diethyl carbonate, ethyl acetate, ethylbenzene, isophorone, isopropyl acetate, methyl ethyl ketone and its derivatives.
6. 6. The process of claim 5, wherein the solvent is used in an excess of about 2: 1 to 4: 1 by weight, relative to the piece of rubber vulcanizate.
7. The process of claim 6, wherein the alkali metal is used in a molar excess of about 2: 1 to 9: 1, based on the sulfur content in the rubber vulcanizate.
8. The method of claim 7, wherein the alkali metal is sodium.
9. 9. The process of claim 8, wherein the mixture is heated in the presence of nitrogen.
10. The process of claim 9, wherein the hydrogen is added before heating, at a pressure of about 345 to 3450 kPa.
11. The method of claim 1, further comprising the step of quenching the unreacted alkali metal.
12. The method of claim 11, wherein the extinguishing step comprises adding water to the reaction mixture.
13. The method of claim 11, wherein the extinguishing step comprises adding hydrogen sulfide gas to the reaction mixture and heating and stirring the resulting mixture.
14. 14. A process for devulcanizing a rubber vulcanizate, containing the carbon black, this process comprises the steps of: contacting pieces of the rubber vulcanizate with a solvent, to form a dispersion; heating the dispersion of the rubber vulcanizate, in the absence of oxygen, at a temperature sufficient to decompose at least a portion of the rubber, to form a carbon black dispersion in a rubber solution; separating at least a portion of the carbon black from the rubber solution; adding an alkali metal to the separated rubber solution, to form a reaction mixture; and heating the reaction mixture, in the absence of oxygen, and with mixing, at a temperature sufficient to cause the alkali metal to react with the sulfur in the rubber, and maintain the temperature below that in which the thermal decomposition of the metal occurs. rubber, thus devolving the rubber.
15. 15. The method of claim 14, wherein the temperature is maintained below 3002C.
16. 16. The method of claim 15, wherein the solvent is one capable of inflating the rubber vulcanizate.
17. 17. The process of claim 16, wherein the solvent is capable of solubilizing the devulcanized rubber.
18. The method of claim 17, wherein the solvent is selected from the group consisting of one or more of toluene, naphtha, terpenes, benzene, cyclohexane, diethyl carbonate, ethyl acetate, ethylbenzene, isophorone, isopropyl acetate, methyl ethyl ketone, and its derivatives.
19. The method of claim 18, wherein the solvent is used in excess of about 2: 1 to 4: 1 by weight, in relation to the piece of vulcanized rubber.
20. The method of claim 19, wherein the alkali metal is used in a molar excess of t 2: 1 to 9: 1, based on the sulfur content in the rubber vulcanizate.
21. 21. The method of claim 20, wherein the metal is sodium.
22. 22. The method of claim 20, wherein the mixture is heated in the presence of nitrogen.
23. 23. The process of claim 20, wherein hydrogen is added before heating the reaction mixture, in the presence of a pressure of 345 to 3450 kPa.
24. 24. The process of claim 14, further comprising the step of quenching the unreacted alkali metal.
25. 25. The method of claim 24, wherein the extinguishing step comprises adding water to the reaction mixture.
26. 26. The method of claim 24, wherein the extinguishing step comprises adding hydrogen sulfide gas to the reaction mixture and heating and stirring the resulting mixture.
27. 27. A process for preparing a functionalized de-vulcanized rubber, this method comprises: reacting a mixture of rubber vulcanized pieces and an alkali metal, in the absence of oxygen and in the presence of a solvent, at a temperature below the temperature of thermal decomposition of the rubber, in order to form a functionalized devulcanized rubber.
28. 28. The method of claim 27, wherein the devulcanized rubber contains groups that bind to this devulcanized rubber and are derived from the solvent molecules.
29. The method of claim 28, wherein the solvent is selected from the group consisting of one or more of toluene, naphtha, terpenes, benzene, cyclohexane, diethyl carbonate, ethyl acetate, ethylbenzene, isophorone, isopropyl acetate, methyl ethyl ketone and its derivatives.
30. 30. The process of claim 29, wherein the alkali metal is sodium.
31. 31. The method of claim 30, further comprising: (a) adding water to the reaction mixture, thereby forming an aqueous phase containing water and sodium and a non-aqueous phase, containing the functionalized de-vulcanized rubber and a solvent; and (b) separating the functionalized devulcanized rubber from the non-aqueous phase and recovering a functionalized rubber polymer.
32. 32. The product recovered from step (b) of claim 31.
33. 33. The method of claim 31, further comprising the step of vulcanizing the functionalized rubber polymer, in order to form a reinforced vulcanized rubber.