Activated pyrolytic carbon black recovered and pre-purified from used tires and its application in the manufacture of compounds for the rubber industry, such as components for new tires or new technology products

Abstract

Pyrolytic carbon black obtained from used tires was subjected to an environmentally friendly refining process followed by a surface activation process that imparted reinforcing properties that, when used as a reinforcing filler in new rubber compounds, are clearly superior to those imparted by typical commercial pyrolytic carbon blacks and are comparable in mechanical properties to those obtained with conventional "furnace" blacks of the N772, N550, and N330 types.

Description

[Technical Field]

[0001] [Background technology]

[0002] Carbon black is produced by the pyrolysis of used tires, which is also referred to hereinafter as pyrolytic carbon black (hereinafter abbreviated as CBp). In particular, CBp obtained directly from pyrolysis is referred to as crude pyrolytic carbon black (hereinafter abbreviated as CBp-0) and is contaminated with pyrolytic rubber residues. These pyrolysis residues also contain a mixture rich in polycyclic aromatic hydrocarbons (PAHs). Some PAHs are known to be carcinogenic and are found in the bituminous-tar mass of pyrolytic rubber residues [see F. Cataldo, (2020). On the characterization of carbon black from tire pyrolysis. Fullerenes, Nanotubes and Carbon Nanostructures, 28: 368-376; F. Cataldo, (2021). Pyrolytic carbon black from truck tires: some new analytical approaches. Fullerenes, Nanotubes and Carbon Nanostructures, 29: 304-314]. Ultimately, CBp-0 is a product of limited commercial value, and due to both its insufficient reinforcing capacity and the presence of harmful PAHs, it cannot be used as a reinforcement material in new rubber compounds.

[0003] WO 2021 / 079395 describes a process adapted to purify CBp-0 obtained by pyrolysis of used tires. In particular, WO 2021 / 079395 describes both a purification process for CBp-0 by extraction using a non-toxic, low-impact solvent adapted to remove the pyrolysis rubber residue along with PAHs, and a thermal treatment process for CBp-0 adapted to evaporate the pyrolysis rubber residue along with PAHs. In particular, the thermal process has proven more practical, rapid, and economical because it can be applied immediately after the end of the pyrolysis of used tires and does not necessarily require isolation of CBp-0. Indeed, as described in WO 2021 / 079395, simply maintaining CBp-0 at 600°C to 700°C for several tens of minutes under a nitrogen flow is sufficient to completely remove the residual bitumen fraction and associated PAHs contained therein. The pyrolytic carbon black obtained by this purification (called CBp-1 to distinguish it from the starting CBp-0) is free of pyrolytic rubber residues and PAHs, but it presents a series of problems that make it particularly unattractive as a reinforcement material for high-performance tire manufacturers.

[0004] In particular, the main problem with CBp-1 is its high zinc and sulfur content. In fact, zinc sulfide (ZnS) inevitably forms during the pyrolysis of used tires, and ZnS becomes trapped in CBp-1. When CBp-1 is used as a reinforcing filler in new compounds for tires or technical products, the presence of ZnS may slow the vulcanization rate. Furthermore, zinc is notoriously toxic to aquatic microorganisms, certain fish, and other invertebrates [JF Skidmore, (1964). Toxicity of zinc compounds to aquatic animals, with special reference to fish. The Quarterly Review of Biology, 39: 227-248; S.F. Brinkman, et al. (2012). Acute toxicity of zinc to several aquatic species native to the Rocky Mountains. Archives of Environmental Contamination and Toxicology, 62: 272-281]. Leaching by rainwater releases zinc in ionic form from tires into the environment. For this reason, there is an increasing focus on reducing zinc in rubber compounds, especially for tires, with the aim of minimizing its release into the environment. The presence of ZnS is a drawback to the widespread use of CBp-1 as an environmentally friendly material. In particular, its presence slows down the vulcanization rate, rather than fulfilling any technical function. In fact, rubber compounds containing CBp-1 as a filler always require the addition of zinc oxide (ZnO) as a vulcanization activator.

[0005] WO 2021 / 079395 describes a process for acid purification of CBp-1, which is adapted to remove ZnS according to the following general reaction: ZnS+2H + →Zn 2+ +H2S This reaction can be carried out using mineral acids, or alternatively, biodegradable carboxylic acids derived from renewable resources. The purification process removes not only zinc and sulfur, but also a range of transition metals, such as Cr, Co, Cd, and Pb (which are considered harmful to living organisms and the environment), to very low concentrations. Thus, the product obtained as a result of the purification of CBp-1 (referred to as CBp-2 in WO 2021 / 079395 and hereinafter) is a high-value-added product that is environmentally friendly due to its low zinc and sulfur content and very low transition metal content.

[0006] However, CBp-2 may still contain varying amounts of silica, also derived from the pyrolysis of used tires. Silica is not a problem for the purpose of recycling CBp-2 into new rubber compounds. However, certain applications may require CBp that is also completely free of silica. As described in WO 2021 / 079395, it is also possible to remove silica by changing the mixture of refining acidic agents and obtain a completely clean product (referred to as CBp-3 in WO 2021 / 079395 and hereinafter).

[0007] [Table 1]

[0008] Table 1 shows the elemental analysis by X-ray fluorescence of products CBp-1, CBp-2 and CBp-3, as well as their ash content compared to that of commercially available CBp.

[0009] Table 1 shows that commercially available CBp does not differ significantly from CBp-1 in either the content of some transition metals or the content of some metalloids. With regard to the zinc, sulfur, and ash content, the differences between commercially available CBp and CBp-1 are more pronounced, which is related to the nature of the starting tires used for pyrolysis. However, for the purposes of the present invention, the origin and nature of the tires used for pyrolysis are of little importance and should not be considered limiting factors. In fact, the present invention is applicable to CBp of any origin. Furthermore, as shown in Table 1, what is important is the excellent environmental quality of CBp-2 and CBp-3, obtained in particular by the refining process described in WO 2021 / 079395. In fact, the ash content (essentially silica) is reduced to less than 7.5% in CBp-2 and is almost absent in CBp-3. The iron content in CBp-2 and CBp-3 (a prooxidant for recycling into new rubber compounds) was found to be less than 0.02%, and zinc (toxic to aquatic life [see Skidmore (1964) and Brinkman, et al. (2012) supra]) was reduced from an initial value of over 5% in CBp-1 to an insignificant 0.07% in CBp-2 and CBp-3 through refining. As a result, the sulfur content of CBp-1, at least in part bound to zinc as ZnS, was reduced to 0.5%–0.7% in CBp-2 and CBp-3 as a result of the refining process. This reduces the risk of ZnS slowing the vulcanization rate when CBp-2 and CBp-3 are used as reinforcing fillers in new compounds. The benefit of purifying CBp-1 is also seen in the content of certain transition metals, such as Mn, Co, Ni, and Pb. While the concentrations of such metals in the starting CBp-1 are significant and of concern (see the case of Co), they are reduced to minimal levels in CBp-2 and CBp-3 after purification. Examples 1-5 below detail the processes for producing and purifying pyrolytic carbon blacks described in WO 2021 / 079395.

[0010] Example 1 CBp-1 was produced by pyrolysis of end-of-life tires (hereafter abbreviated ELT) in a rotary tube furnace as follows: 3,500 g of end-of-life tires, pre-ground to 325 mesh, were loaded into the furnace. The tire powder load was brought to 600°C and maintained at this temperature until pyrolysis was complete, at which point approximately 1,150 g of residual carbon black remained in the reactor. After pyrolysis was complete, the resulting CBp was brought to 660°C and maintained at this temperature for 75 minutes under a nitrogen flow. Alternatively, the "cleaning" of the CBp can be completed by raising the temperature to 700°C under a nitrogen flow and maintaining that temperature for 45 minutes to remove pyrolytic rubber residues and PAHs, producing CBp-1. The resulting CBp-1 was recovered from the reactor, cooled to room temperature, and transferred in 1,000 g quantities to a 5 L Duran glass-jacketed reactor equipped with a stirrer. A bubble cooler connected by tap to a Dreschel bottle filled with 1 L of 10% NaOH solution, a valve for introducing inert gas (e.g., nitrogen), and a dropping funnel filled with 3,000 mL of 20% hydrochloric acid were installed on top of the reactor. Purification was performed by rapidly dropping the hydrochloric acid onto CBp-1 under stirring to form a fluid slurry. To facilitate purification, the reactor was heated to a temperature between 60 and 90 °C. The hydrochloric acid reacted with the zinc sulfide present in CBp-1 (which contains up to 82 g / kg of zinc sulfide when derived from OTR (off-road) tires; the ZnS content is significantly lower when derived from PSR (passenger car) tires, i.e., tires for passenger cars, or TBR (truck and bus) tires, i.e., tires for large trucks and buses), resulting in the decomposition of ZnS according to the following reaction: ZnS+2HCl→ZnCl2+H2S

[0011] The zinc leached out and went into aqueous solution, while hydrogen sulfide was released in gaseous form and was carried by a stream of nitrogen (or another inert gas, e.g., compressed air) into a Drechsel bottle, where it was bubbled into the NaOH solution and captured as sodium sulfide. H2S+2NaOH→Na2S+2H2O

[0012] The purification reaction was relatively rapid, with zinc removal nearly complete within 30 minutes. The reaction slurry was then filtered through a Buchner filter, and the CBp-2 cake formed on the filter paper was repeatedly washed with water until the wash water was neutral (at least pH = 5.5-6.0). At that point, the CBp-2 wet cake was transferred to a dryer to completely remove residual water. The yield of CBp-2 after purification was 91.5% from the starting CBp-1 (although depending on the ELT mixture from which CBp-1 is derived, the yield may exceed 91.5%). Analysis of CBp-2 by X-ray fluorescence showed the analytical composition reported in Table 1, and the ash content was determined by thermogravimetric analysis under airflow up to 850 °C. The surface area of ​​CBp-2, measured by nitrogen absorption (BET method), was 65 m, as reported in Table 1. 2 / g~70m 2 The values ​​included in / g were shown.

[0013] Example 2 The procedure was carried out exactly as in Example 1, with the only difference being that the purification mixture consisted of 3,000 mL of 6.0 M hydrochloric acid and 3.0 M hydrofluoric acid. In this case, the purification was not limited to the solubilization of zinc and the removal of sulfur by decomposition of ZnS, as in Example 1, but also proved effective in solubilizing and removing the silica present in CBp-1. In fact, HF dissolved the silica according to the reaction, solubilizing it in the form of hexafluorosilicic acid. 6HF+SiO2→H2SiF6+2H2O Silica was present in CBp-1 because it is now widely used as a reinforcing filler and is added to tire compounds as a reinforcing filler, similar to furnace carbon black. Subsequent filtering and drying of the resulting CBp-3 was identical to that described above in Example 1. Analysis of the resulting CBp-3 was performed by X-ray fluorescence, revealing the elemental composition reported in Table 1, and the ash content of CBp-3 was determined by thermogravimetric analysis under air flow up to 850°C. As expected, CBp-3 was shown to be completely ash-free. The surface area of ​​CBp-3, measured by nitrogen absorption (BET method), was 65 m, as reported in Table 1. 2 / g~70m2 The values ​​included in / g are shown.

[0014] In general, commercial CBp-1 exhibits limited reinforcing capacity compared to the predictions derived from surface area measurements. Clearly, despite its large surface area, the surface of CBp-1 is not very active and is hardly suitable for the chemisorption and physisorption processes that underlie the reinforcement mechanism in rubber compounds. The same problem occurs in the cases of CBp-2 and CBp-3 in Examples 1 and 2. Like commercial CBp-1, both CBp-2 and CBp-3 can be reused in rubber compounds by subjecting them to a conventional grinding process, more precisely, micronization. Micronization partially breaks down carbon black agglomerates as well as agglomerates, reducing their diameter to less than 40 μm. Micronization facilitates the dispersion of CBp in the rubber matrix and enhances its reinforcing capacity. However, even with micronization, the reinforcing effect of various types of CBp is often lower than expected. Summary of the Invention

[0015] The solution according to the invention fits this situation: the aim of the invention is to provide a method for recovering carbon black obtained by pyrolysis of used tires, which makes it possible to overcome the limitations of the refining processes according to the prior art.

[0016] These and other results are obtained in accordance with the present invention by providing a method for recovering carbon black obtained by pyrolysis of used tires, which comprises the steps of: A process in which carbon black is heat-treated at a temperature in the range of 550°C to 800°C in an inert atmosphere to obtain purified carbon black (CBp-1). Optionally, further purification is carried out by the following steps: a subsequent step of selectively extracting zinc from the purified carbon black (CBp-1) using an aqueous solution containing a carboxylic acid selected from citric acid and tartaric acid, or an inorganic acid selected from hydrochloric acid and sulfuric acid, preferably an inorganic acid selected from hydrochloric acid and sulfuric acid, to obtain purified carbon black (CBp-2) having a low zinc content and a low sulfur content; The aqueous solution optionally further comprises hydrofluoric acid along with the carboxylic acid or inorganic acid, thereby obtaining a purified carbon black (CBp-3) having a low silica content. The method further comprises the steps of: Activating the surface of the purified carbon black with a reactive gas selected from nitrogen, argon, carbon dioxide, superheated steam and mixtures thereof, preferably carbon dioxide, superheated steam and mixtures thereof.

[0017] According to the present invention, the heat treatment in an inert atmosphere is preferably carried out at a temperature in the range of 600°C to 780°C under a flow of an inert gas selected from N2, Ar, CO2, superheated steam or a combination thereof.

[0018] In particular, also according to the present invention, the surface activation of purified carbon black using a reactive gas is carried out using CO and / or superheated steam at a flow rate ranging from 150 ml / min to 400 ml / min, with a heating ramp ranging from 10°C / min to 40°C / min, a maximum final temperature ranging from 800°C to 950°C, and a residence time ranging from 30 minutes to 60 minutes.

[0019] A further object of the present invention is the recovered carbon black obtained by the above defined method as well as the use of said recovered carbon black in the manufacture of rubber compounds.

[0020] In accordance with the present invention, it has been surprisingly discovered that by subjecting microparticulated CBp-1, CBp-2, and CBp-3 to a reactive gas surface etching (or surface activation) process, it is possible to control and particularly increase the surface area of ​​the carbon blacks, as well as to activate the surface to increase the number of active sites and make it more suitable for both chemisorption and physisorption of rubber, thereby achieving results that rival or even surpass the reinforcing effect of "furnace" black, a traditional petroleum-derived carbon black. In other words, a method has been discovered for reactivating the surface of CBp-1, and particularly CBp-2 and CBp-3, by reactive gas surface etching. This treatment results in CBp-2 and CBp-3 producing a substantial and surprising reinforcing effect when used as a reinforcing filler in new rubber compounds, which is not observed with similar unactivated CBp. Thus, CBp-2 and CBp-3 are not only environmentally friendly carbon blacks in that they are free of zinc, sulfur, toxic transition metals, and silica (in the case of CBp-3), but also, when subjected to the reactive gas etching process detailed in Example 3 below, highly reinforcing carbon blacks. DETAILED DESCRIPTION OF THE INVENTION

[0021] Example 3 to Example 5 A horizontal Carbolite-Gero "TSO Rotary Reactor Tube Furnace" equipped with a semi-rotating fluted quartz reactor vessel was loaded with 300 g of CBp-1, CBp-2, or CBp-3 (as detailed in Table 2). The pyrolytic carbon black described above had previously been micronized and sieved to less than 40 μm. The selected CBp was heated to a temperature of 800°C or another temperature reported in Table 2 under a continuous flow of carbon dioxide (CO). The temperature was then maintained for a specified time (detailed in Table 2), again under a continuous gas flow, and the preselected CBp powder was remixed under a semi-rotating movement of the quartz reactor vessel. After completion of the treatment, it was again cooled to room temperature under strict CO flow. The reactive gas-activated selected CBp was subjected to analysis. The results are shown in Table 2. It was subsequently used for testing in the rubber compounds of the following examples.

[0022] The effect of the reactive gas is evident from Table 2. The reactive gas results in a significant increase in the surface area of ​​CBp, making it possible to control the surface area by simply changing the reaction temperature (shown in Table 2) or reaction time. After such treatment, the surface area of ​​CBp can even double compared to the starting value of crude CBp. In fact, as shown in Table 2, for CBp-1, the surface area of ​​the initial 50 m 2 / g to 98m 2 / g, and in CBp-2 and CBp-3, the initial 65m 2 / g~70m 2 / g to 110m 2 / g. Another effect of the action of CO2 on pyrolytic carbon black is to impart a degree of microporosity to the treated carbon black, which was largely absent in the starting CBp. Surface area was measured by the standard BET method according to ASTM D-6556, and microporosity was determined from the difference between the BET surface area value and the STSA (Statistical Thickness Surface Area) procedure, also standard according to ASTM D-6556. In the absence of microporosity, the BET and STSA surface areas are identical, and the value derived from the difference between [BET] and [STSA] corresponds to the microporosity value [Table below].

[0023] [Table 2]

[0024] To further characterize CBp-1, CBp-2, and CBp-3 from Examples 3 through 5 above, a series of structural parameters were determined by X-ray diffraction using a conventional, so-called "furnace" black, derived from petroleum and bearing ASTM code N772, as the reference carbon black. Fundamental structural parameters commonly used to "anchor" the structural characteristics of amorphous carbon blacks were obtained from the X-ray diffraction data.

[0025] The formulas for calculating such parameters are detailed in, for example, Ismagilov, ZR, et al. (2019). Structural analysis of needle coke. Coke and Chemistry, 62: 135-142. The parameters calculated from the X-ray diffraction patterns are shown at the bottom of Table 3 for both N772 and each CBp. The interplanar distance of the graphene planes (d 002 ), the packing density of the graphene planes (ρ), the longitudinal dimension of the structural planes (La), the thickness of the superposed graphene layers (Lc), and finally the number of graphene layers in each "crystallite" (N). From the structural parameters reported in Table 3, it is possible to infer a striking structural similarity between the "furnace" black N772 chosen as a reference and the carbon blacks CBp-1, CBp-2, and CBp-3 obtained by pyrolysis of used tires (after appropriate acid purification in the case of CBp-2 and CBp-3).

[0026] [Table 3]

[0027] Another distinctive result derived from X-ray diffraction analysis of non-activated CBp-1 is the presence of ZnS in the crystalline modification known as sphalerite, which is easily identified by the presence of reflections at 2θ of 28.450, 47.435, and 56.269. The polymorph formed from sphalerite at high temperatures is the crystalline modification of ZnS known as wurtzite. X-ray diffraction of thermally activated CBp-1 is distinct from non-activated CBp-1 precisely due to the presence of wurtzite, which has characteristic reflections at 2θ of 26.8074, 28.4810, 30.460, 39.453, 47.4579, 51.662, and 56.289. A distinctive aspect under X-ray diffraction analysis of both activated and non-activated CBp-2 and CBp-3 relates to the complete absence of any reflections attributable to the crystalline structure of sphalerite or wurtzite, indicating that all zinc present has been completely removed by the refining process.

[0028] As shown in the following examples, it has been further surprisingly found that pyrolytic carbon blacks obtained from ELT, purified according to Examples 1 and 2, and activated according to Examples 3 to 5, when used as reinforcing materials in rubber compounds, produce a reinforcing effect that is clearly superior to that imparted by commercial CBp or even "furnace" black, i.e., petroleum-derived, such as carbon black N772. It is therefore an object of the present invention to surface activate CBp-1, CBp-2, and CBp-3 according to Examples 3 to 5, and as a result, to impart surprising reinforcing effects to the rubber compounds of Examples 6 to 12.

[0029] Example 6 to Example 12 ELT-derived pyrolytic carbon black CBp-1, prepared according to WO 2021 / 079395, and pyrolytic carbon blacks CBp-2 and CBp-3, prepared as described in Examples 1 and 2, were subjected to activation as described in Examples 3 to 5 and then tested in the following standard natural rubber-based formulations: natural rubber (Hevea cis-1,4-Polyisoprene from Brasiliensis, type CV60: 100 phr ("phr" indicates the number of parts of each compound component added per 100 parts of rubber, a field-specific way of describing rubber compounds), carbon black: 52 phr ("furnace" blacks, i.e., petroleum-derived, are N330, N550 and N772, used as reference materials, and CBp-1, CBp-2 or CBp-3 prepared according to Examples 3 to 5, were used as pyrolytic carbon blacks. Commercially available CBp was also used as a further reference material), plasticizing oil type T-DAE (Treated Distillate Aromatic Extract). Extract (i.e., aromatic): 5 phr, stearic acid: 1 phr, zinc oxide (3 phr), IPPD (isopropylphenyl-p-phenylenediamine) as antiozonant: 1.5 phr, TMQ (polymerized trimethylquinoline) as antioxidant: 1 phr, sulfur: 1.5 phr, and CBS (cyclohexylbenzothiazole sulfenamide) as accelerator: 1.5 phr.

[0030] Each rubber compound in Examples 6 to 12 was prepared using a 1.5-liter laboratory mixer (Banbury mixer) capable of preparing over 1 kg of compound per batch. The components of the compounded compounds in the previous paragraph were carefully weighed out, strictly adhering to the correct ratio. The rubber was added first to the mixer, and mechanically masticated for several minutes. Next, carbon black (the only component that varied between the compounds in Examples 6 to 12; the type added for all examples is shown in Table 4) was added along with the plasticizing oil. The carbon black was thoroughly blended with the rubber and oil, and finally, zinc oxide, stearic acid, antiozonant, and antioxidant were added. Mixing was continued until a homogeneous compound was obtained, which was then removed from the Banbury mixer and repeatedly passed through a special mill known to those skilled in the art to form a thin layer approximately 0.5 cm thick. The compound thus prepared was cooled at room temperature. After cooling, the compound was again loaded into the Banbury mixer, and the vulcanizing agents (sulfur and accelerator) were added, weighed out to strictly adhere to the correct ratio. Mixing was continued until a homogeneous compound was obtained. After removing the compound from the Banbury, it was passed repeatedly through a mill to form a thin layer, followed by cooling at room temperature. For vulcanization, a quantity of compound sufficient to fill a mold for a specimen was extracted for technical tests according to ASTM or UNI standards (see Table 4 for the standards followed for each technical test) and vulcanized in a press by heating at 160°C for 15 minutes for thin specimens and 20 minutes for larger specimens. Technical tests on the vulcanized specimens were carried out according to ASTM or UNI standards. The standards selected and applied for the technical tests are shown in Table 4.

[0031] [Table 4]

[0032] The natural rubber-based compounds for the examples in Table 4 were chosen for illustration as standard compounds used preferentially, but not exclusively, for the rubber components of heavy truck tires or other compounds for the rubber industry in general.

[0033] From the data on mechanical properties shown in Table 4, it can be readily inferred that the pyrolytic carbon blacks CBp-1, CBp-2, and CBp-3 activated according to Examples 3 to 5 exhibit a surprising reinforcing effect compared to, for example, commercially available CBp. To highlight this surprising reinforcing effect, one needs to consider the data on modulus or tensile strength shown in Table 4. It can be observed that the values ​​measured for the compounds prepared using CBp-1, CBp-2, and CBp-3 activated according to Examples 3 to 5 are significantly higher than those for the commercially available CBp. This demonstrates that the reinforcing effect of CBp-1, CBp-2, and CBp-3 activated according to Examples 3 to 5 is greater due to the surface treatment, and that their performance is in all respects comparable to that of conventional carbon blacks (petroleum-derived "furnace" blacks) such as N330, N550, and N772, which were studied as reference materials in Table 4. In particular, a comparison of the modulus and tensile strength of compounds prepared using CBp-1, CBp-2, and CBp-3 activated according to Examples 3-5 shows surprising values ​​far superior to those of furnace blacks N772 and N550. The superior performance of CBp-1, CBp-2, and CBp-3 activated according to Examples 3-5 is also evident in the natural rubber-based compounds of Table 4, again in terms of high tear strength and minimal wear loss, as well as response to permanent set, compared to commercial CBp and to "furnace" blacks N772 and N550. From the perspective of viscoelastic properties, CBp-1, CBp-2, and CBp-3 activated according to Examples 3-5 exhibit low mechanical hysteresis, a highly desirable property for tire compound applications; low hysteresis means reduced dissipation of rotational energy in the form of heat, ultimately resulting in reduced fuel economy compared to other carbon blacks, given comparable compound formulations. For purposes of applying natural rubber based compounds to the hypothetical application of heavy truck tires, a combination of high modulus values ​​and high tensile strength are among the qualities desired for the application.This is because such properties result in a longer product life and higher tear strength (as confirmed in Table 4 for CBp-1, CBp-2 and CBp-3 activated according to Examples 3 to 5 compared to commercial CBp), as well as superior abrasion resistance compared to commercial CBp (mm of material abraded in the abrasion resistance test). 3 This is because the volume of worn material exhibited by CBp-1, CBp-2, and CBp-3 activated according to Examples 3 to 5 is clearly smaller than that measured for the commercially available CBp (see Table 4). Regarding permanent set tests, Table 4 shows that CBp-1, CBp-2, and CBp-3 activated according to Examples 3 to 5 exhibit lower permanent set (a desirable property for application purposes) compared to the commercially available CBp. Finally, both the rebound resilience and viscoelasticity are measures of the dynamic mechanical properties of the compound, particularly the mechanical hysteresis (which, as mentioned above, must be as low as possible in tire applications to minimize fuel consumption). In this case, a higher elastic modulus (E') is also a more pronounced manifestation of the reinforcing effect of the considered filler, even under dynamic conditions. Table 4 indeed confirms that the compounds prepared using CBp-1, CBp-2, and CBp-3 activated according to Examples 3 to 5 produce significantly higher elastic moduli compared to compounds containing commercially available CBp. Thus, carbon blacks CBp-1, CBp-2 and CBp-3 activated according to Examples 3 to 5 detailed in this patent, including acid purification and heat activation, result in products with surprising reinforcing properties that are of clear technological interest, given both the low environmental impact (see Table 1) and the excellent technical performance of natural rubber compounds shown in Table 4.

[0034] Example 13 to Example 19 ELT-derived pyrolytic carbon black CBp-1 prepared according to WO 2021 / 079395, and pyrolytic carbon blacks CBp-2 and CBp-3 prepared as described in Examples 1 and 2 were activated according to Examples 3 to 5 and subsequently tested in the following standard styrene-butadiene copolymer-based formulations: S1502: 100 phr ("phr" indicates the number of parts of each compound component added per 100 parts of rubber, a typical way of expressing rubber compounds used by those skilled in the art), carbon black: 52 phr ("furnace" blacks, i.e., N330, N550, and N772, which are derived from petroleum, were used as reference materials, and CBp-1, CBp-2, or CBp-3 were tested according to Examples 3 to 5. ~ carbon black prepared according to Example 5, a commercial CBp was also used as a further reference), plasticizing oil type T-DAE (treated distilled aromatic extract, i.e., aromatic): 5 phr, stearic acid: 1 phr, zinc oxide (3 phr), IPPD (isopropylphenyl-p-phenylenediamine) as antiozonant: 1.5 phr, TMQ (polymerized trimethylquinoline) as antioxidant: 1 phr, sulfur: 1.5 phr, CBS (cyclohexylbenzothiazole sulfenamide) as accelerator: 1.0 phr, TBzTD (tetrabenzylthiuram disulfide) as accelerator: 0.3 phr, and DPG-80 (80% diphenylguanidine) as accelerator: 0.2 phr.

[0035] Each rubber compound in Examples 13 to 19 was prepared using a 1.5-liter laboratory mixer (Banbury mixer) capable of preparing over 1 kg of compound per batch. The components of the compounded compounds in the previous paragraph were carefully weighed out, strictly adhering to the correct ratio. The rubber was added first to the mixer, and mechanically masticated for several minutes. Next, carbon black (the type added for all examples is shown in Table 5), the only component that varied among the compounds in Examples 13 to 19, was added along with plasticizing oil. The carbon black was thoroughly blended with the rubber and oil, and finally, zinc oxide, stearic acid, antiozonant, and antioxidant were added. Mixing continued until a homogeneous compound was obtained, which was then removed from the Banbury mixer and repeatedly passed through a special mill known to those skilled in the art to form a thin layer approximately 0.5 cm thick. The compound thus prepared was allowed to cool at room temperature. After cooling, the compound was again loaded into the Banbury mixer, and the vulcanizing agents (sulfur and various accelerators) were added, weighed out to strictly adhere to the correct ratio. Mixing was continued until a homogeneous compound was obtained. The compound thus obtained was removed from the Banbury and passed repeatedly through a mill to form a thin layer of approximately 0.5 cm, after which it was cooled at room temperature. For vulcanization, a quantity of compound sufficient to fill a mold for a test specimen was extracted for technical testing according to ASTM or UNI standards (see Table 5 for the standards followed for each technical test) and vulcanized in a press by heating at 160°C for 15 minutes for thin specimens and 20 minutes for larger specimens. Technical tests on the vulcanized specimens were carried out according to ASTM or UNI standards as described above. The standards selected and applied for the technical tests are shown in Table 5.

[0036] The styrene-butadiene copolymer-based compounds (SBR) employed in the examples of Table 5 were chosen for illustrative purposes as standard compounds used preferentially, but not exclusively, for rubber components of automobile tires or other compounds for the rubber industry in general.

[0037] Even in this type of SBR-based polymer matrix, the mechanical property data shown in Table 5 readily suggest that the pyrolytic carbon blacks CBp-1, CBp-2, and CBp-3 prepared according to Examples 3 to 5 exhibit a surprising and unexpected reinforcing effect, compared to the reinforcing properties of, for example, the commercial CBp used as a reference material. Indeed, the modulus or tensile strength data reported in Table 5 show surprisingly high values ​​for the compounds prepared using activated CBp-1, CBp-2, and CBp-3 according to Examples 3 to 5 compared to the commercial CBp. This demonstrates that the reinforcing effect of CBp-1, CBp-2, and CBp-3 is greater due to the surface treatments used in Examples 3 to 5, and that their performance is in all respects comparable to that of conventional carbon blacks (petroleum-derived "furnace" blacks) such as N330, N550, and N772, which were studied as reference materials in Table 5. The surprisingly excellent performance of CBp-1, CBp-2 and CBp-3 activated according to Examples 3 to 5 is also evident in the SBR type polymer matrix in Table 5 in terms of tear strength and abrasion loss, as well as response to permanent set, with performance clearly superior to that of the commercial CBp.

[0038] From the perspective of viscoelastic properties, CBp-1, CBp-2, and CBp-3 activated according to Examples 3 to 5 also exhibit low mechanical hysteresis (tan δ) that is comparable to or better than petroleum-derived carbon blacks N330, N550, and N772, as well as the commercially available pyrolytic carbon black CBp. The results obtained by measuring the tan δ values ​​are further supported by measuring the rebound resilience values. Low mechanical hysteresis is highly desirable for tire applications, as it directly relates to reduced fuel consumption.

[0039] [Table 5]

[0040] Furthermore, in terms of elastic modulus E', the three CBps of this patent outperform both the commercial CBp and carbon black ASTM N772, which also confirms their better reinforcing effect under dynamic conditions.

[0041] Example 20 to Example 26 The ELT-derived pyrolytic carbon black CBp-1 prepared according to WO 2021 / 079395, and the pyrolytic carbon blacks CBp-2 and CBp-3 prepared according to Examples 1 and 2 and activated according to Examples 3 to 5, were subsequently tested in the following standard acrylonitrile-butadiene copolymer-based compounds: NBR3345: 100 phr ("phr" indicates the number of parts of each compound component added per 100 parts of rubber, a field-specific rubber compounding method), carbon black: 52 phr ("furnace" blacks, i.e., petroleum-derived ones are N330, N550 and N772, used as reference materials). The carbon blacks used and prepared according to the invention were designated CBp-1, CBp-2, or CBp-3 (commercially available CBp was also used as a further reference), plasticizer type DINP (diisononyl phthalate): 5 phr, stearic acid: 1 phr, zinc oxide (3 phr), IPPD (isopropylphenyl-p-phenylenediamine) as antiozonant: 1.5 phr, TMQ (polymerized trimethylquinoline) as antioxidant: 1 phr, sulfur: 1.5 phr, CBS (cyclohexylbenzothiazole sulfenamide) as accelerator: 1.0 phr, and TBzTD (tetrabenzyl thiuram disulfide) as accelerator: 0.3 phr.

[0042] Each rubber compound in Examples 20-26 was prepared using a 1.5-liter laboratory mixer (Banbury mixer) capable of preparing over 1 kg of compound per batch. The components of the compounded compounds described in the previous paragraph were carefully weighed out, strictly adhering to the correct ratio. The rubber was added first to the mixer, which was mechanically masticated for several minutes. Next, carbon black (the only component that varied between the compounds in Examples 20-26; the type added for all examples is shown in Table 6) was added along with the plasticizing oil. The carbon black was thoroughly blended with the rubber and oil, and finally, zinc oxide, stearic acid, antiozonant, and antioxidant were added. Mixing was continued until a homogeneous compound was obtained, which was then removed from the Banbury mixer and repeatedly passed through a special mill known to those skilled in the art to form a thin layer approximately 0.5 cm thick. The compound thus prepared was cooled at room temperature. After cooling, the compound was again loaded into the Banbury mixer, and the vulcanizing agents (sulfur and various accelerators) were added, weighed out to ensure the correct ratio. Mixing was continued until a homogeneous compound was obtained. The compound thus obtained was removed from the Banbury and passed repeatedly through a mill to form a thin layer of approximately 0.5 cm, after which it was cooled at room temperature. For vulcanization, a quantity of compound sufficient to fill a mold for a test specimen was extracted for technical testing according to ASTM or UNI standards (see Table 6 for the standards followed for each technical test) and vulcanized in a press by heating at 160°C for 15 minutes for thin specimens and 20 minutes for larger specimens. Technical tests on the vulcanized specimens were carried out according to ASTM or UNI standards. The standards selected and applied for the technical tests are shown in Table 6.

[0043] The acrylonitrile-butadiene copolymer-based compound (NBR) used in the examples of Table 6 was chosen for illustrative purposes as a standard compound for molding technical rubber products for applications other than tires. In other words, the purpose of using this NBR-based compound is to demonstrate that the pyrolytic carbon blacks CBp-1, CBp-2, and CBp-3 activated according to Examples 3 to 5 offer surprising technical advantages even when applied as reinforcement materials in compounds other than tires, and are therefore specialized for technical products in general.

[0044] As shown in Table 6, even in NBR-based polymer matrices, the pyrolytic carbon blacks CBp-1, CBp-2, and CBp-3 confirm the surprisingly superior reinforcing effect previously observed for natural rubber- and SBR-based compounds, as seen previously for NR- and SBR-based matrices, compared to, for example, commercially available CBp. Indeed, from the data on modulus or tensile strength shown in Table 6, it can be observed that the values ​​measured for the compounds prepared with CBp-1, CBp-2, and CBp-3 activated according to Examples 3 to 5 are significantly higher than those for the commercially available CBp. This demonstrates that the reinforcing effect of CBp-1, CBp-2, and CBp-3 is greater due to the surface treatment, and that their performance is in all respects comparable to that of the conventional petroleum-derived "furnace" blacks currently in use [see table below].

[0045] [Table 6]

[0046] The NBR-based compounds of Examples 20 to 26 are essentially technical product compounds designed for static applications. For this reason, neither viscoelastic properties nor abrasion resistance were measured. However, even in this case, CBp-1, CBp-2, and CBp-3 exhibit better mechanical hysteresis than the commercial CBp, as measured by rebound resilience. With regard to permanent set, CBp-1, CBp-2, and CBp-3 activated according to Examples 3 to 5 also outperform the commercial CBp, due to their lower permanent set.

[0047] Thus, it was found that the pyrolytic carbon blacks CBp-1, CBp-2 and CBp-3, obtained from used tires and all activated according to Examples 3 to 5 (the latter two having been previously purified to remove undesirable constituents (zinc, transition metals and sulfur in the case of CBp-2, and also silica in CBp-3)), when tested as reinforcement in compounds based on natural rubber or cis-1,4-polyisoprene (NR or IR) (Examples 6 to 12), in compounds based on styrene-butadiene copolymers (SBR) (Examples 13 to 19), or in compounds based on acrylonitrile-butadiene copolymers (NBR) (Examples 20 to 26), provided (in each case) a surprisingly excellent reinforcing effect, as measured by modulus and tensile strength values, which completely surpassed the performance of commercial CBp and were comparable to or even superior to the performance of certain petroleum-derived "furnace" blacks, such as N772, N550 and N330. This is therefore the object of the present invention. The surprising performance of CBp-1, CBp-2 and CBp-3 activated according to Examples 3 to 5, and the object of this patent, extends to other mechanical properties such as excellent tear strength, minimal abrasion loss, limited permanent set and low mechanical hysteresis as measured in terms of tan δ and rebound modulus, completely surpassing in some respects the performance of commercial CBp and of certain "furnace" blacks, such as N772 and even N550.

Claims

1. heat-treating the carbon black at a temperature in the range of 550°C to 800°C in an inert atmosphere to obtain purified carbon black (CBp-1); activating the surface of the purified carbon black at a temperature in the range of 800°C to 1,000°C with a reactive gas selected from nitrogen, argon, carbon dioxide, superheated steam, and mixtures thereof, preferably carbon dioxide, superheated steam, and mixtures thereof; 1. A method for recovering carbon black obtained by pyrolysis of used tires, comprising:

2. After the heat treating step and before the surface activating step of the purified carbon black, a step of selectively extracting zinc from the purified carbon black (CBp-1) using an aqueous solution containing a carboxylic acid selected from citric acid and tartaric acid, or an inorganic acid selected from hydrochloric acid and sulfuric acid, preferably an inorganic acid selected from hydrochloric acid and sulfuric acid, to obtain purified carbon black (CBp-2) having a low zinc content and a low sulfur content, or to obtain purified carbon black (CBp-2) having a low zinc content; 2. The method for recovering carbon black obtained by pyrolysis of used tires according to claim 1, further comprising:

3. 3. The method for recovering carbon black obtained by pyrolysis of used tires according to claim 2, wherein the aqueous solution further comprises hydrofluoric acid together with the carboxylic acid or inorganic acid according to claim 2, thereby obtaining purified carbon black (CBp-3) having a low silica content.

4. The method for recovering carbon black obtained by pyrolysis of used tires according to any one of claims 1 to 3, wherein the heat treatment in an inert atmosphere is carried out at a temperature in the range of 600°C to 780°C.

5. The heat treatment in an inert atmosphere is carried out using N ２ , Ar, CO ２ 5. The method for recovering carbon black obtained by pyrolysis of used tires according to claim 1, wherein the method is carried out under a flow of an inert gas selected from the group consisting of superheated steam and a combination thereof.

6. The step of activating the surface of the purified carbon black with the reactive gas is carried out by using CO at a flow rate in the range of 150 ml / min to 400 ml / min. ２ and / or superheated steam, with a heating gradient in the range of 10°C / min to 40°C / min up to a final temperature, preferably a maximum final temperature in the range of 800°C to 950°C, with a residence time in the range of 30 to 60 minutes.

7. A recovered carbon black obtained by the method according to any one of claims 1 to 6.

8. 10. Use of the recovered carbon black of claim 7 in the manufacture of rubber compounds.

9. A rubber compound based on natural rubber (NR, cis-1,4-polyisoprene) containing the recovered carbon black of claim 7.

10. A styrene-butadiene copolymer (SBR) based rubber compound comprising the recovered carbon black of claim 7.

11. An acrylonitrile-butadiene copolymer (NBR) based rubber compound comprising the recovered carbon black of claim 7.

12. 10. A rubber compound based on a mixture of natural rubber (NR, cis-1,4-polyisoprene), and / or styrene-butadiene copolymer (SBR), and / or polybutadiene homopolymer (BR), and / or acrylonitrile-butadiene copolymer (NBR), and / or ethylene-propylene-diene copolymer (EPDM), and / or ethylene-propylene copolymer (EPM), and / or chloroprene rubber or neoprene rubber, and / or butyl rubber, and / or chlorobutyl rubber, and / or bromobutyl rubber, and / or ethylene-vinyl acetate rubber, and / or chlorinated polyethylene rubber and / or chlorosulfonated polyethylene rubber, and / or acrylic rubber, and / or epichlorohydrin rubber, and / or fluoroelastomer rubber, and / or silicone rubber, and / or fluorosilicone rubber, and / or polyester rubber and polyether rubber, and / or polyurethane elastomer, and / or thermoplastic elastomer in general, comprising the recovered carbon black according to claim 7.

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