OBTAINED

Description

The present invention relates to a method for processing mixed rubber waste streams, such as waste steams originating from production processes of tyre manufacturing processes and mixed waste rubber from the technical rubber goods sector, comprising materials chosen from the group of unvulcanised rubber slabs, unvulcanised tyres, strips and extrusions, for producing a carbon black powder. The present method furthermore relates to a carbon black powder having specific characteristics.

An estimated 30 million tons of new tyres are manufactured every year and an estimated 17 million tons of discarded tires every year. The re-use of waste tires is done in several ways. The most energy- efficient way of re-using tires is retreading, which means vulcanization of a new running surface on a used tire carcass. The casing of a tire hardly deteriorates during its first life. Retreading is common amongst truck tires, but not so much for car tires. This is partially caused by the relatively low costs of new car tyres and the fact that consumers put less trust into retreaded tyres. Approximately 9% of waste truck tires was retreaded in 2012. Tires of which the carcass is worn as well, can be recycled. 39% of waste tires were recycled in 2012. Products like mats, athletic tracks and asphalt are made using shredded tires. A considerably higher share of material recycling can be achieved if tire material can be used in a real recycling loop: tires back into tires. It is currently investigated how to create a process of converting waste car tire rubber into rubber compounds for new car tires. Another way of using waste tires is by energy recovery, by using shredded tires as fuel, to produce heat. A percentage of 37% of all waste tires have been used for energy recovery in 2012. The cement industry is one of the greatest waste tire consumers with tires being added to cement kilns as fuel.

Methods and apparatuses for recovering carbon black/minerals from scrap tires as well as a carbon black/mineral filler are known in the art.

For example EP2465904A1 relates to a method for manufacturing of carbon black/mineral filler from scrap tires involving pyrolysis of shredded scrap tires, the method comprising the steps of: obtaining a carbon product by pyrolyzing the shredded scrap tires with the presence of a catalyst in a pyrolysis reactor, the reactor heated to a temperature 350-440°C by a heating jacket, inside of which flows a mix of hot exhaust gases of the reactor heating furnace and cooled exhaust gases of the heating jacket, separating, in a magnetic separator, steel cord from the carbon product to obtain a refined carbon product, in a grinding apparatus, grinding in an impact mill the refined carbon product, and separating, using a cyclone separator, particles having a size from 1pm to 50pm from the ground carbon product to obtain a carbon black/mineral filler. The apparatus comprises a pyrolysis reactor comprising a heating jacket for heating the pyrolysis reactor to a temperature of 350-440°C by a mix of hot exhaust gas from the reactor heating furnace and exhaust gas of the heating jacket, wherein the apparatus further comprises a magnetic separator for separating steel cord from the carbon product to obtain a refined carbon product, a grinding apparatus comprising an impact mill for grinding the refined carbon product, and a cyclone separator having a bag filter for separating the ground carbon product particles in order to obtain a carbon black/mineral filler having a size from 1pm to 50 pm.

US2008286192 discloses a pyrolysis process, comprising the steps of: providing a quantity of whole tires; and shredding the whole tires to form the quantity of waste to be deposited in the porous container, the porous container adapted to allow at least one convective stream of substantially anaerobic gas to flow therethrough; inserting the porous container into a pyrolysis thermal processor; sealing the thermal processor; circulating the at least one convective stream of gas in the pyrolysis thermal processor; heating the waste with the convective stream of gas according to a predetermined time- temperature profile to pyrolyze the waste and form a carbonaceous char; cooling the carbonaceous char by circulating the at least one convective stream of gas through a cooler; and collecting at least one of a carbon black product, an oil product, a gaseous hydrocarbon product, and a recyclable metal product.

US2002119089A1 discloses a process for pyrolyzing tire shreds, comprising: feeding tire shreds to a pyrolysis reactor; pyrolyzing the tire shreds in a pyrolysis reactor to produce a gas stream comprising hydrocarbon and a solid comprising carbon; removing the solid comprising carbon from the pyrolysis reactor; directing the gas stream comprising hydrocarbon into a separator; contacting the gas stream comprising hydrocarbon with an oil spray in the separator thereby washing particulate from the gas stream and condensing a portion of the gas stream to oil; removing and cooling the oil from the separator; directing non-condensed gas from the gas stream comprising hydrocarbon away from the separator; and directing a portion of the cooled oil removed from the separator to an inlet of the separator for use as the oil spray in the separator.

W00053385A1 discloses a pyrolysis process for reclamation and recovery of desirable constituent materials from vehicle tires shredded into tire pieces, the process comprising the steps of: transferring the product pieces from a supply into a pyrolysis chamber; heating the product pieces at a first temperature in a first heating zone of the pyrolysis chamber; transferring the product pieces from the first heating zone to a second heating zone in the pyrolysis chamber; heating the product pieces at a second temperature in the second heating zone, the second temperature being independent from the first temperature; transferring the product pieces from the second heating zone to a third heating zone in the pyrolysis chamber; heating the product pieces at a third temperature in the third heating zone, the third temperature being independent from the second temperature; and removing the product pieces from the pyrolysis chamber and separating the desirable materials.

W02011035812A1 discloses a process for multistage thermal treatment of rubber waste, in particular scrap tires, comprising the steps of: transferring a product granulate of the rubber waste from a supply into a reactor, heating the product granulate at a first temperature between 100° to 200°C, preferably 150° to 180°C, in a first heating zone of the reactor so long until light oils are no longer emitted, transferring the product granulate from the first heating zone to a second heating zone in the reactor, heating the product granulate at a second temperature between 200° to 350°C in the second heating zone of the reactor so long until medium heavy oils are no longer emitted, transferring the product granulate from the second heating zone to a third heating zone in the reactor, heating the product granulate at a third temperature between 300° to 600°C in the third heating zone so long until heavy oils are no longer emitted, removing the product granulate from the reactor and separating the desirable solid materials, wherein the process is carried out within a low pressure environment.

EP2319899A1 discloses a continuous pyrolysis system which is used for the treatment of waste tires, comprising: a reactor having a charge port, a discharge port and a first gas outlet and a first axial transporting structure installed therein; a heat source generator for supplying heat necessary for carrying out a pyrolysis reaction in the reactor; a solid product reformer for performing a reforming process for a solid product of the pyrolysis reaction, having a first solid product inlet, a first solid product outlet and a second gas outlet, and a second axial transporting structure installed therein, wherein the first solid product inlet communicates with the discharge port of the reactor; and a gas barrier component for preventing a gas product of the pyrolysis reaction from entering the solid product reformer and transporting the solid product of the pyrolysis reaction into the solid product reformer, the gas barrier component being installed in a channel communicating the first solid product inlet and the discharge port of the reactor.

US6525105B1 discloses a method for separating a vulcanized rubber composition containing a vulcanized rubber and at least carbon black wherein the vulcanized rubber composition is immersed in an organic solvent containing 0.01 to 50% of a peroxide with or without agitation to liquidify the vulcanized rubber composition for separation of a rubber component as a liquid phase and a carbon black component as a solid phase in the vulcanized rubber composition, wherein said immersion is conducted such that the ratio of the vulcanized rubber composition (mg)/the organic solvent (ml) is lower than 50.

WO2013095145A1 discloses a method for recycling a scrap rubber, in particular tyres, which method comprises the following steps: pyrolyzing a scrap rubber to obtain a char material; milling the char material to obtain a carbon black powder, wherein the pyrolysis comprises at least a two-stage pyrolysis process, wherein the two-stage pyrolysis process comprises: a first pyrolysis stage to obtain an intermediate char material and a second pyrolysis stage to obtain a char material, wherein at least one of the stages is carried out in a rotary kiln.

US5264640 discloses a process for recovering a monomer from a vulcanized addition polymer feedstock formed from the monomer, wherein the addition polymer feedstock is rubber polymer recovered from used tires, comprising the steps of: (a) exposing the addition polymer feedstock to gaseous ozone under conditions sufficient to rupture chemical bonds formed during the vulcanization process of the addition polymer feedstock and thereby form one or more intermediate products; (b) mixing the intermediate products of step (a) with silica to form a mixture; (c) heating the mixture formed in step (b) to a temperature and for a time sufficient to depolymerize the addition polymer and form the monomer; and (d) removing the monomer following its formation from the mixture.

US5087436A discloses a carbon black produced by vacuum pyrolysis of used rubber tires at a temperature in the range of about 490 °C to about 510 °C under an absolute pressure of less than about 5 kPa, and having an iodine adsorption number of about 130 to about 150 mg/g, a DBP adsorption of 80 to 100 ml/100 g and a tint strength number of 55 to 63.

US5853687A discloses a method of manufacturing carbon black by pyrolysis of ground, scrap-depleted rubber waste comprising conducting the pyrolysis in the presence of carbon dioxide, in a rotary kiln indirectly heated by combustion of gases generated during said pyrolysis, said kiln having an inlet and an outlet in which the pyrolysis area is operated at between approximately 600 °C and 1100 °C the product being collected at a temperature of between approximately 150 °C and 350 °C, wherein the ground rubber waste has a particle size between approximately 2 and 5 mm, further comprising treating the carbon black produced with acid, whereby mineral fillers are removed.

W02005033213 discloses a method of refining carbon black char comprising the steps of pyrolysation of scrap tyres to produce an impure carbon black char feed, classification of the carbon black char feed, pyrolysation of the carbon black char feed, acid washing of the carbon black char feed, alkali washing of the carbon black char feed, demineralized water washing of the carbon black char feed, and processing of the carbon black char feed to produce a carbon black product comprising the steps of milling and dispersion of the carbon black char feed. The pyrolysation step occurs at a temperature of 800 °C.

US3823221 discloses a process of producing a rubber reinforcing agent which comprises pyrolyzing at 1000 to 2500 F (537 to 1371 °C) in the substantial absence of oxygen, vulcanized scrap rubber containing metal compounds and producing oil- contaminated char, removing substantially all of the oil from the char by steam-treatment at 1000 to 2500 F (537 to 1371 °C), treating the char with aqueous mineral acid to reduce the ash content substantially to below 10% and after the acid treatment grinding so that the resulting char is of such particle size that at least 50 percent will pass through a 325- mesh screen.

Disposal of industrial wastes has nowadays become a serious social problem, and in the case of tires, the amount discarded is enormous and not only use as a fuel by incineration but also recovery and reuse of the raw materials included in the tire, namely, the rubber and the rubber subsidiary materials has become an urgent agenda.

Recovered carbon blacks (rCBs) produced from end-of-life tyres contain small amounts of crystalline silica. In the US any raw materials that contain more than 0.1% crystalline silica must carry a warning label as potential carcinogen on the packaging bags and on the corresponding safety data sheets (SDS). The same rules apply in Europe but with a threshold limit of 1%. There is growing widespread concern within the industries that use carbon black as a raw material that prevent many of them from using recovered carbon black as a circular and sustainable raw material.

The crystalline silica in rCBs originates from stones, grit and sand that are embedded in the tyre feedstocks. It is further known that the crystalline silica content in rCBs does not originate from the conversion of synthetic amorphous precipitated silica (commonly used in tyre manufacturing) due to its exposure to pyrolysis conditions of temperature, residence time and pressure. Even the extremes of temperature used in tyre pyrolysis are far too low to induce a phase transition from amorphous silica to crystalline forms.

Processes such as tyre shredding, size reduction and granulation remove a large number of embedded stones/grit/sand, therefore rCBs produced from granulated feedstocks will have lower concentrations of crystalline silica than pyrolysis processes that use whole tyres or large tyre shreds.

Other processes, such as jet-milling and size classification of a tyre-char to produce a finely milled powder - when produced from granulated tyre feedstock - will further remove particles of stones/grit/sand because of their higher specific gravity (around 2.6 to 2.8) relative to the specific gravity of the recovered carbon black (1.8 - 1.9)

The present inventors found that notwithstanding the reduction of stones/grit/sand mentioned above, the crystalline silica content of rCBs produced from granulated tyre feedstock after jet milling and size classification can typically exceed 0.1 wt.%.

The present inventors found that within the tyre manufacturing sector and the technical rubber goods sector there is need to find a solution for recycling the mixed rubber waste streams resulting from their production processes. Due to the vastly different visco-elastic properties of unvulcanised rubber compounds compared with vulcanized rubber compounds, these waste streams cannot be recycled in the same way as end-of- life tyres - so for example they cannot be shredded or granulated at a tyre recycler specialized in conventional end-of-life shredding and granulation processes.

An object of the present invention is to find a method for recycling/upcycling of mixed rubber waste streams from tyre manufacturers.

Another object of the present invention is to provide a method for manufacturing a recovered carbon black grade having a low crystalline silica content. The present invention thus relates to a method for processing mixed rubber waste streams, such as waste steams originating from production processes of tyre manufacturing processes and mixed waste rubber from the technical rubber goods sector, comprising materials chosen from the group of unvulcanised rubber slabs, unvulcanised tyres, strips and extrusions, for producing a carbon black powder, which method comprises the following steps: i) pyrolyzing said mixed rubber waste streams to obtain a char material; ii) further processing the char material obtained in step i) to obtain a carbon black powder; wherein the pyrolysis in step i) comprises at least a two-stage pyrolysis process, wherein said two-stage pyrolysis process comprises: a) a first pyrolysis stage of said mixed rubber waste streams in a pyrolysis batch reactor to obtain an intermediate char material, and b) a second pyrolysis stage of said intermediate char material obtained in step a) in a rotary kiln to obtain a char material.

The present inventors found that by using the above method for processing mixed rubber waste streams one or more of the present objects are achieved. In an embodiment of the present method the first step of pyrolyzing mixed rubber waste streams is preceded by a step of pre-sorting the rubber waste streams according to their chemical compositions and according to the desired chemical composition of the resulting rCBs.

In an embodiment of the present method the first pyrolysis stage a) is carried out by heating said mixed rubber waste streams to a temperature between 350 and 500 °C, preferably between 350 and 400°C under a nitrogen atmosphere with a residence time between longer than 8 hours and less than 50 hours, preferably longer than 15 hours and less than 40 hours, to obtain an intermediate char material.

In an embodiment of the present method the second pyrolysis stage b) is carried out by heating said intermediate char material to a temperature between 550 and 850 °C, preferably between 650 and 800 °C, more preferably between 700 and 750 °C, under an inert atmosphere with a residence time longer than 10 minutes and less than 50 minutes, preferably between 15 and 40 minutes, preferably between 20 and 25 minutes, to obtain a char material. In an embodiment of the present method the internal rotary kiln pressure in the second pyrolysis stage b) is less than 2000 Pa, preferably less than 1000 Pa, more preferably less than 500 Pa.

In an embodiment of the present method the inert atmosphere in the second pyrolysis stage b) is a nitrogen atmosphere.

In an embodiment of the present method the step of further processing of the char material obtained in step i) comprises one or more steps chosen from the group of char cooling, pre-crushing by impact milling, jet milling, pelletizing and drying, to obtain a carbon black powder.

In an embodiment of the present method the step of pre-crushing by impact milling is carried in such a way to obtain a D99 particle size of between 0.1 to 2 mm.

In an embodiment of the present method the step of jet milling is carried in such a way to obtain a D99 particle size of between 2 and 20 microns, preferably < 10 microns, more preferably < 3 microns.

The present invention also relates to a carbon black powder having a BET Surface Area (m ² /g) in a range of higher than 50 and less than 120, preferably 70 - 110, measured according to ASTM D-6556.

The present invention also relates to a carbon black powder, wherein the STSA surface area (m ² /g) is in range of 40-100, preferably 60 - 90, measured according to ASTM D-6556.

In an embodiment of the present invention the carbon black has a value for OAN (ml/100 g) in range of 55-120, preferably 65 - 95, measured according to ASTM D-2414.

In an embodiment of the present invention the carbon black powder has a hydrocarbon volatile content (%) is in a range of 1 - 5, measured according to TGA.

In an embodiment of the present invention the carbon black powder has a PAH content (mg/kg, ppm) less than 50, preferably less than 20, measured according to FDA Method 63.

In an embodiment of the present invention the carbon black powder has a pH value in a range of 7.5 - 8.5, measured according to ASTM D-1512,

In an embodiment of the present invention the carbon black powder has a crystalline silica content (%) of less than 0,1, preferably less than 0,05, measured according to XRD. The present invention also relates to the use of a scrap rubber derived carbon black powder discussed above, or obtained according to the method discussed above, as a filler or a reinforcing agent in a rubber composition, an ink, a paint, a bitumen, a thermoplastic composition or a thermoplastic elastomer.

According to the present invention the stage 1 pyrolysis is performed in a pyrolysis batch reactor by heating under nitrogen. This stage 1 pyrolysis will yield approximately 30 - 38 wt.% char, 62 - 70 wt.% volatiles (oil + gas). The char thus obtained in the stage

1 pyrolysis is subsequently pyrolyzed a second time in a rotary kiln to reduce the total PAH content (when tested according to FDA Method 63 (Soxhlet / 48 h boiling in toluene / N2 flush) to less than 50 ppm, preferably to less than 20 ppm. Pyrolysis conditions in stage

2 pyrolysis are heating the intermediate char material to a temperature between 550 and 850 °C, preferably between 650 and 800 °C, more preferably between 700 and 750 °C, under an inert atmosphere with a residence time between 10 and 50 minutes, preferably between 15 and 40 minutes, preferably between 20 and 25 minutes, to obtain a char material. In an embodiment subsequent processes are char cooling, pre-crushing by impact milling to a D99 particle size of between 0.1 to 2 mm, jet milling to a D99 particle size of between 2 and 20 microns, pelletizing/drying to produce a pellet having a D50 particle size distribution between 0.5 and 1 mm and a D99 size of 2 to 3 mm. Residual steel content in the char will be removed by the jet milling process.

The materials i.e. mixed rubber waste streams, that can be processed according to the present method are one or more streams chosen from the group of rubber compound slabs, unvulcanised, rubber compound slabs, partially vulcanised (scorched), rRubber strips, wig-wag extruded, curing bladders, unvulcanised and vulcanised, fabrics impregnated with rubber (fractioned fabrics), rubber compounds in various forms, unvulcanised, different tyre positions, end-of-life curing bladders, off-spec vulcanised whole tyres (all types), off-spec unvulcanised whole tyres (all types), tyre flash, vulcanised, buffing dust, vulcanised, and whole tyres, off-spec, unvulcanised. Examples of mixed rubber waste streams are waste steams originating from production processes of tyre manufacturing processes and mixed waste rubber from the technical rubber goods sector.

The present invention thus relates to a recovered carbon black having the following characteristics. Property Unit j Typical Value/Range j Test Method

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