GB2622610A

GB2622610A - A method for obtaining carbon black, the carbon black obtained therefrom and the use thereof

Info

Publication number: GB2622610A
Application number: GB2213853.1A
Authority: GB
Inventors: John Naden Benjamin
Original assignee: Ppp Portglenone Ltd
Current assignee: Ppp Portglenone Ltd
Priority date: 2022-09-22
Filing date: 2022-09-22
Publication date: 2024-03-27
Also published as: GB202213853D0

Abstract

Method for obtaining a carbon black composition may comprise providing an aqueous mixture comprising a carbonaceous solid, an alkali hydroxide, and an acid. The aqueous mixture of carbonaceous solid may be mixed with either the alkali or the acid, followed by filtering and washing the solids with water. The filtered solids may then be mixed with the other of the acid or alkali hydroxide, followed by filtering and washing the solids with water. The obtained solids may then be used in place of the original aqueous mixture comprising carbonaceous solid and the method repeated at least once. A carbon black composition derived from pyrolytic char may comprise less than 1% w/w of ash and greater than 99% w/w of carbon black, based on the total weight of carbon black composition. Alternating acid and alkali hydroxide mixing steps is intended to provide more efficient demineralisation and higher purity carbon black.

Description

A Method for Obtaining Carbon Black, the Carbon Black Obtained Therefrom and the Use Thereof

Technical Field of the Invention

The present invention relates to a method for obtaining carbon black. In particular, the method relates to a method for obtaining carbon black from pyrolytic char produced by the pyrolysis of rubber, in particular the pyrolysis of automobile tyres. The present invention also relates to carbon black obtained by the method according to the invention. Moreover, the method relates to the use of the obtained carbon black and to compositions comprising the carbon black.

Background to the Invention

Carbon black is typically used as a reinforcing filler in tyres and other rubber products. In plastics, paints and inks, carbon black is used as a colour pigment. The production of carbon black (i.e. virgin carbon black) requires considerable amounts of raw materials and energy. Moreover, conventional processes to produce carbon black generate significant amounts of carbon dioxide.

Largely due to the environmental impact of producing virgin carbon black, there has recently been considerable attention given to methods of obtaining (recovered) carbon black from sources of carbonaceous materials. To this end, carbon black can be produced by pyrolysis of carbonaceous materials, for example automobile tyres. In the United Kingdom, around 500,000 tonnes of scrap lyres are produced each year. In comparison, the European Union and USA produce around 3 million tonnes and 4.5 million tonnes of scrap tyres each year, respectively. Due to the costly and technically challenging processes required to recycle scrap tyres, significant amounts of scrap tyres are sent to landfill each year.

Known processes to obtain carbon black from sources of carbonaceous materials, such as scrap tyres, typically include the pyrolysis of the waste materials to form pyrolytic char comprising steel, volatile gases and carbonaceous char. The carbonaceous char can be processed and purified to obtain (recovered) carbon black.

Several drawbacks exist with known methods of obtaining carbon black and the 30 carbon black obtained by such methods.

Pyrolytic char has a high ash (approximately 16% w/w) because of minerals added during the tyre manufacturing process, and polycyclic aromatic hydrocarbon content, formed during the pyrolysis of the tyre rubber. The ash primarily comprises silica, zinc oxide, sulphur, calcium carbonate, aluminium oxide and iron oxide.

Removal, or at least removal of significant amounts, of these minerals is required to provide a carbon black product that is suitable for use in tyre manufacturing or as a pigment additive for paints, coatings, inks and plastics. The high ash content restricts possible applications of the recovered carbon black. For example, if the recovered carbon black is used in tyre manufacture, the tyres produced using the carbon black often exhibit reduced strength of the rubber. Moreover, if the recovered carbon black is used as a colour pigment for paints, inks and plastics, the pigment often exhibits a reduced colour or 'black value', therefore, limiting the use of such products.

Current methods to recover carbon black from scrap tyres do not sufficiently address the problem of removal of ash from pyrolytic char. As such, the resulting carbon black product is not an adequate alternative to virgin carbon black produced by non-recycling means.

It is believed that an ash content of less than 1% w/w is required in the recovered carbon black in order to produce a carbon black product suitable for a wide range of industrial and commercial applications. The conventional methods currently used to obtain recovered carbon black do not reduce the ash content to less than 1% w/w.

Further, current methods employed to recover carbon black from scrap tyres often rely on using peroxides and organic solvents and high temperatures and pressures, or use microwave radiation. The use of peroxides and organic solvents is environmentally disadvantageous due to the waste materials produced and require careful handling, and processes using microwave radiation are expensive and do not produce consistent reliable results.

Further, current methods to recover carbon black do not address the problem of high polycyclic aromatic hydrocarbon content in the pyrolytic char.

Embodiments of the present invention seek to ameliorate these or other 30 disadvantages and/or to provide an improved method for obtaining carbon black from pyrolytic char, which provides recovered carbon black which is of the same or at least comparable, purity as virgin carbon black.

It is an aim of embodiments of the invention to overcome or mitigate at least one problem of the prior art, whether expressly disclosed herein or not.

Summary of the Invention

According to a first aspect of the invention, there is provided a method for obtaining a carbon black composition from a carbonaceous solid, the method comprising the steps of: a. Providing an aqueous mixture comprising a carbonaceous solid; b. Providing an alkali hydroxide; c. Providing an acid; d. Mixing the aqueous mixture of step (a) with the alkali hydroxide of step (b) or the acid of step (c); e. Filtering and washing with water the composition obtained in step (d); f. Mixing the composition obtained in step (e) with the alkali hydroxide of step (b) or the acid of step (c) which was not used in step (d); and g. Filtering and washing with water the composition obtained in step (1), wherein the composition obtained in step (g) is used in place of the mixture of step (a) to repeat steps (a) to (g) at least once.

Surprisingly, it has been found that the method of the invention provides a carbon black composition with less than 1% w/w ash. Moreover, it has been found that the method of the invention provides a carbon black composition with greater than 99% w/w carbon black. Advantageously, the method of the invention provides a recovered carbon black composition that is of the same, or at least comparable, purity to virgin carbon black.

It is believed that the alternating sequence of alkali hydroxide and acid mixing steps optimises leaching efficiency and ash removal. Moreover, alternating between alkali hydroxide and acid mixing steps provides more efficient demineralisation (i.e. ash removal) than multiple alkali washes followed by multiple acid washes. It is believed that this is because each alkali hydroxide mixing step exposes soluble species that were previously unavailable for efficient acid leaching, and vice versa.

Advantageously, the method of the invention is more environmentally friendly compared to methods of the prior art. This is because the method of the invention does not use peroxides and organic solvents, or other reagents deemed considerably harmful to the environment. Moreover, the method of the invention provides significant cost benefits compared to methods of the prior art which rely on expensive laboratory techniques such as microwave radiation.

Advantageously, the method of the invention reduces the polycyclic aromatic hydrocarbon (PAH), for example naphthalene, content of the pyrolytic char such that the method of the invention provides a carbon black composition with 30% less, 40% less, 50% less, 60% less, 70% less, 80% less, 90% less, 95% less, 96% less, 97% less, 98% less or 99% less, PAH content than that of the respective pyrolytic char from which the carbon black composition is derived.

The acid of step (c) may be selected from the group comprising hydrochloric acid, nitric acid, sulphuric acid, hydrofluoric acid, hydrobromic acid, hydroiodic acid, perchloric acid and chloric acid.

Advantageously, each of the acids selected from the group comprising hydrochloric acid, nitric acid, sulphuric acid, hydrofluoric acid, hydrobromic acid, hydroiodic acid, perchloric acid and chloric acid. are relatively cheap, easy to handle and are readily available.

Preferably, step (d) comprises mixing the aqueous mixture of step (a) with the alkali hydroxide of step (b), and step (f) comprises mixing the composition obtained in step (e) with the acid of step (c).

Steps (a) to (2) may be repeated once, twice or three times.

Preferably, steps (a) to (g) are repeated three limes. That is to say that the method of the invention may overall comprise four steps of mixing with alkali 30 hydroxide and four steps of mixing with an acid, for example an acid selected from the group comprising hydrochloric acid, nitric acid, sulphuric acid, hydrofluoric acid, hydrobromic acid, hydroiodic acid, perchloric acid and chloric acid. It is believed that repeating steps (d) to (g) three times provides the greatest degree of ash removal while providing a method which is cost-effective and more commercially viable compared to

methods of the prior art.

Step (a) may further comprise micronizing the aqueous mixture comprising the carbonaceous solid to obtain a carbonaceous solid mean particle size of between about 1 and about 15pm, between about 2 and about 13 pm. between about 3 and about 11gm, between about 4 and about 9gm, between about 5 and about 7pm, or about 6pm. The carbonaceous solid mean particle site obtained from micronizing the aqueous mixture comprising the carbonaceous solid may be less than 100gm, less than 90pm, less than 80pm, less than 70pm, less than 60pm, less than 50pm, less than 40pm, less than 30gm, less than 20pm, less than 18pm, less than 16pm, less than 14pm, less than 12pm, less than 10pm, less than 9pm, less than 8gm, less than 7pm or less than 6p.m. Micronizing may be carried out using a high shear mixer, media mill, ultrasonication or dual asymmetric centrifuge. The high shear mixer may be a high-speed saw-tooth blade or rotor-stator mixer.

Advantageously, it was found that micronizing the aqueous mixture comprising the carbonaceous solid to obtain a carbonaceous solid particle size of between about 1 20 and about 15pm provided significant improvement in ash removal efficiency and ash content of the recovered carbon black composition.

The aqueous mixture of step (a) may comprise between about 1 and about 80% w/w of carbonaceous solid, between about 3 and about 70% w/w of carbonaceous solid, between about 5 and about 60% w/w of carbonaceous solid, between about 10 and about /5 50% w/w of carbonaceous solid, between about 10 and about 45% w/w of carbonaceous solid, between about 10 and about 40% w/w of carbonaceous solid, between about 12 and about 38% w/w, between about 14 and about 36% w/w, between about 16 and about 34% w/w, between about 18 and about 32% w/w, between about 20 and about 30% w/w, between about 22 and about 28% w/w, between about 24 and about 26% w/w, or about 25% w/w of carbonaceous solid, based on the total weight of the aqueous mixture.

Advantageously, an aqueous mixture of step (a) comprising between about 10 and about 40% w/w of carbonaceous solid optimises the rate of micronisation. It was found that a higher concentration of carbonaceous solids provided a mixture that was difficult to mix clue to high viscosity, and a lower concentration of carbonaceous solids reduced the efficiency of particle size reduction because of lower particle attrition interactions and, therefore, a lower shear rate available.

The alkali hydroxide of step (b) may be at a concentration of between 1M and 10M, between 2M and 9M, between 2M and 8M, between 3M and 7M, between 4M and 6M, or at a concentration of 5M. The alkali hydroxide of step (b) may be added as solid pellets of 100% alkali hydroxide, or as an aqueous solution of up to about 0.5%, about 1%, about 2%, about 4%, about 6%, about 8%, about 10%, about 15%, about 20%, about 25%, about 30%, about 35%, about 40%, about 45%, about 50%, about 55%, about 60%, about 65%, about 70%, about 75%, about 80%, about 85%, about 90%, about 95%, or up to about 100% concentration alkali hydroxide. The alkali hydroxide of step (b) may be added as an aqueous solution of between about 0.5% and about 80%, between about 1% and about 75%, between about 2% and about 70%, between about 4% and about 65%, between about 6% and about 60%, between about. 8% and about 55%, between about 10% and about 50%, between about 12% and about 45%, between about 14% and about 40%, between about 15% and about 35%, between about 16% and about 30%, between about 17% and about 25%, between about 18% and about 24%, between about 19% and about 22%, or about 20% concentration alkali hydroxide.

The acid of step (c) may be at a concentration of between 1M and 12M, between 2M and 10M, between 2M and 8M, between 3M and 7M, between 4M and 6M, or at a concentration of 5M.

The acid of step (c) may be added as a liquid of 100% concentrated acid, or as an aqueous solution of up to about 0.5%, about 1%, about 2%, about 4%, about 6%, about 8%, about 10%, about 15%, about 20%, about 25%, about 30%, about 35%, about 40%, about 45%, about 50%, about 55%, about 60%, about 65%, about 70%, about 75%, about 80%, about 85%, about 90%, about 95%, or up to about 98% concentration acid. The acid of step (c) may be added as an aqueous solution of between about 0.5% and about 98%, between about 1% and about 95%, between about 2% and about 90%, between about 4% and about 85%, between about 6% and about 80%, between about 8% and about 75%, between about 10% and about 70%, between about 12% and about 60%, between about 14% and about 50%, between about 15% and about 40%, between about 16% and about 30%, between about 17% and about 25%, between about 18% and about 24%, between about 19% and about 22%, or about 20% concentration acid.

In step (d), mixing the aqueous mixture of step (a) with the alkali hydroxide of step (b) or the acid of step (c), may be carried out at a weight ratio of aqueous mixture of step (a) to alkali hydroxide of step (b) or acid of step (c) of between about 1:0.1-10, between about 1:0.5-8, between about 1:1-8, between about 1:2-8, between about 1:37. between about 1:4-6 or about 1:5.

In step (d), mixing the aqueous mixture of step (a) with the alkali hydroxide of step (b) or the acid of step (c), may be carried out at a weight ratio of aqueous mixture of step (a) to alkali hydroxide of step (b) or acid of step (c) of less than about 1:10, less than about 1:9, less than about 1:8, less than about 1:7, less than about 1:6, less than about 1:5.5, less than about 1:5, less than about 1:4, less than about 1:3, less than about 1:2, less than about 1:1, less than 1:0.8, less than 1:0.6, less than 1:0.4, or less than 1:0.2.

In step (I), mixing the composition obtained in step (e) with the alkali hydroxide of step (b) or the acid of step (c), may be carried out at a weight ratio of composition obtained in step (e) to alkali hydroxide of step (b) or acid of step (c) of between about 1:1-10, between about 1:2-8, between about 1:3-7, between about 1:4-6 or about 1:5.

In step (1), mixing the composition obtained in step (e) with the alkali hydroxide of step (b) or the acid of step (c), may be carried out at a weight ratio of composition obtained in step (e) to alkali hydroxide of step (b) or acid of step (c) of less than about. 1:10, less than about 1:9, less than about 1:8, less than about 1:7, less than about 1:6, less than about 1:5.5 or less than about 1:5.

Preferably, in step (e), filtering and washing with water the composition obtained in step (d) comprises filtering and washing with water the composition obtained in step (d) to approximately neutral pH, for example to between pH 5 and pH 9, to between pH 6 and pH 8, or to pH 7.

Preferably, in step (g), filtering and washing with water the composition obtained in step (f) comprises filtering and washing with water the composition obtained in step (I) to approximately neutral pH, for example to between pH 5 and pH 9, to between pH 6 and pH 8, or to pH 7.

The alkali hydroxide of step (b) may be selected from the group comprising sodium hydroxide, potassium hydroxide, calcium hydroxide, lithium hydroxide, rubidium hydroxide and caesium hydroxide. Advantageously, each of the alkali hydroxides selected from the group comprising sodium hydroxide, potassium hydroxide are relatively cheap, easy to handle and are readily available.

Step (d) may comprise mixing the aqueous mixture of step (a) with the alkali hydroxide of step (b) or the acid of step (c) at between about 100 and about 1000 rpm, between about 200 and about 900 rpm, between about 300 and about 800 rpm, between about 400 and about 700 rpm, between about 450 and about 600 rpm, between about 475 and about 550 rpm, or about 500 rpm.

Step (d) may comprise mixing the aqueous mixture of step (a) with the alkali hydroxide of step (b) or the acid of step (c) at at least about 100 rpm, about 200 rpm, about 300 rpm, about 400 rpm, about 500 rpm, about 600 rpm, about 700 rom, about 800 rpm, about 900 rpm, or at least about 1000 rpm.

Advantageously, applying high shear during mixing of step (d) maintains micronized char particles and increases the rate of reaction between the alkali hydroxide or acid and carbonaceous solids.

Step (d) may comprise mixing the aqueous mixture of step (a) with the alkali hydroxide of step (b) or the acid of step (c) for between about 10 and about 180 minutes, between about 20 and about 160 minutes, between about 30 and about 140 minutes, between about 35 and about 120 minutes, between about 40 and about 100 minutes, between about 45 and about 80 minutes, between about 50 and about 75 minutes, between about 55 and about 70 minutes, between about 55 and about 65 minutes, or about 60 minutes.

Step (d) may comprise mixing the aqueous mixture of step (a) with the alkali hydroxide of step (b) or the acid of step (c) for at least 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, or at least 60 minutes.

Step (f) may comprise mixing the composition obtained in step (e) with the alkali hydroxide of step (b) or the acid of step (c) at between about 100 and about 1000 rpm, between about 200 and about 900 rpm, between about 300 and about 800 rpm, between about 400 and about 700 rpm, between about 450 and about 600 rpm, between about 475 and about 550 rpm, or about 500 rpm.

Step (t) may comprise mixing the composition obtained in step (e) with the alkali hydroxide of step (b) or the acid of step (c) at at least about 100 rpm, about 200 rpm, about 300 rpm, about 400 rpm, about 500 rpm, about 600 rpm, about 700 rom, about 800 rpm, about 900 rpm, or at least about 1000 rpm.

Advantageously, applying high shear during mixing of step (f) maintains micronized char particles and increases the rate of reaction between the alkali hydroxide or acid and carbonaceous solids.

Step (f) may comprise mixing the composition obtained in step (e) with the alkali hydroxide of step (b) or the acid of step (c) for between about 10 and about 180 minutes, between about 20 and about 160 minutes, between about 30 and about 140 minutes, between about 35 and about 120 minutes, between about 40 and about 100 minutes, between about 45 and about 80 minutes, between about 50 and about 75 minutes between about 55 and about 70 minutes, between about 55 and about 65 minutes, or about 60 minutes.

Step (f) may comprise mixing the composition obtained in step (e) with the alkali hydroxide of step (b) or the acid of step (c) for at least 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, or at least 60 minutes.

Step (d) and/or step (f) may be carried out at between about 25 and about 150°C, between about 35 and about 140°C, between about 45 and about 130°C, between about 55 and about 120°C, between about 65 and about 110°C, between about 70 and about 105°C, between about 80 and about 100°C, between about 85 and about 95°C, or about 90°C. Advantageously, increasing the temperature above room temperature increased the rate of reaction between the alkali hydroxide or acid and carbonaceous solids.

Step (e) may further comprise diluting the filtered and washed composition solids obtained in step (d) with water to form a slurry comprising between about 1 and about 80% w/w of the filtered and washed composition solids, between about 3 and about 70% w/w, between about 5 and about 60% w/w, between about 10 and about 50% w/w, between about 10 and about 45% w/w, between 10 and 40% w/w, between about 12 and about 38% w/w, between about 14 and about 36% w/w, between about 16 and about 34% w/w, between about 18 and about 32% w/w, between about 20 and about 30% w/w, between about 22 and about 28% w/w, between about 24 and about 26% w/w, or about 25% w/w of the filtered and washed composition.

Advantageously, a slurry comprising between about 10 and about 40% w/w of the filtered and washed composition solids optimises the rate of micronisation. It was found that a higher concentration of filtered and washed composition solids provided a mixture that was difficult to mix due to high viscosity, and a lower concentration of filtered and washed composition solids reduced the efficiency of particle size reduction because of lower particle attrition interactions and, therefore, a lower shear rate available.

The slurry comprising between about. 10 and about 40% w/w of the filtered and washed composition solids may be mixed using a high shear mixer, before step (f).

The mixing of step (d) and/or step (f) may be high shear mixing. The high shear mixing may be carried out using a high shear mixer, media mill, ultrasonication or dual asymmetric centrifuge. The high shear mixer may be a high-speed saw-tooth blade or rotor-stator mixer.

The composition obtained in step (g) may be dried at a temperature between about 25 and about 150°C, between about 35 and about 140°C, between about 45 and about 130°C, between about 55 and about 125°C, between about 65 and about 120°C, between about 75 and about 115°C, between about 85 and about 110°C, between about 90 and about 105°C, between about 95 and about 105°C, or about 100°C. The composition obtained in step (g) may be dried at a temperature above 100°C, for example at least 100°C. at least 105°C, at least 110°C, at least 115°C. at least 120°C, at least 125°C, at least 130°C, or at least 135°C. The composition obtained in step (g) may be dried at a temperature sufficient to remove any water present, that is until there is no further reduction in mass. The composition obtained in step (g) may be dried under reduced pressure to reduce drying time and/or temperature. By reduced pressure, we mean a pressure lower than atmospheric pressure.

The carbonaceous solid may be pyrolytic char. The pyrolytic char may be obtained by the pyrolysis of automobile tyres. The automobile tyres may be end-of-life automobile tyres.

The composition obtained in step (g) (i.e. the recovered carbon black) may comprise less than 1% w/w of ash, less than 0.95% w/w, less than 0.90% w/w, less than 0.85% w/w, less than 0.80% w/w, less than 0.75% w/w, less than 0.70% w/w, less than 0.65% w/w, less than 0.60% w/w, less than 0.55% w/w, or less than 0.50% w/w of ash based on the total weight of the composition obtained in step (g).

Advantageously, the method of the invention provides a recovered carbon black composition that is of the same, or at least comparable, purity to virgin carbon black. A recovered carbon black comprising less than 1% w/w ash beneficially provides a recovered carbon black that has significant industrial and commercial viability compared to recovered carbon black compositions of the prior art. Moreover, the recovered carbon black obtained by the method of the invention does not require any further processing in order to further reduce the ash content.

The composition obtained in step (g) may comprise greater than 99% w/w of carbon black, greater than 99.05% w/w, greater than 99.10% w/w, greater than 99.15% w/w, greater than 99.20% w/w, greater than 99.25% w/w, greater than 99.30% w/w, greater than 99.35% w/w, greater than 99.40% w/w, greater than 99.45% w/w, or greater than 99.50% w/w of carbon black, based on the total weight of the composition obtained in step (g).

Advantageously, the method of the invention provides a recovered carbon black composition that is of the same, or at least comparable, purity to virgin carbon black. 30 A recovered carbon black comprising greater than 99% w/w carbon black beneficially provides a recovered carbon black that has significant industrial and commercial viability compared to recovered carbon black compositions of the prior art. Moreover, the recovered carbon black obtained by the method of the invention does not require any further processing in order to further increase the carbon black content.

According to a second aspect of the invention, there is provided a carbon black composition derived from pyrolytic char, wherein the composition comprises: a. less than 1% w/w of ash; and b. greater than 99% w/w of carbon black, based on the total weight of the carbon black composition.

The carbon black composition may be obtained according to the method of the first aspect of the invention, including any optional features of the invention according to first aspect.

The invention according to the second aspect may optionally include any of the features of the invention according to the first aspect.

According to a third aspect of the invention, (here is provided a use of a carbon Mack composition according to the second aspect of the invention or obtained according to the method of the first aspect of the invention as a filler or reinforcing agent in a rubber composition, an ink, a paint a coating, a plastic a thermoplastic composition or a thermoplastic elastomer.

The invention according to the third aspect may optionally include any of the features of the invention according to the first aspect or second aspect.

According to a fourth aspect of the invention, there is provided a rubber composition comprising a carbon black composition according to the second aspect of the invention or obtained according to the method of the firs( aspect of the invention.

The invention according to the fourth aspect may optionally include any of the features of the invention according to the first aspect or further aspects.

According to a fifth aspect of the invention, there is provided a pigment comprising a carbon black composition according to the second aspect of the invention or obtained according to the method of the first aspect of the invention.

The invention according to the fifth aspect may optionally include any of the features of the invention according to the first aspect or further aspects.

Detailed Description of the Invention

In order that the invention may be more clearly understood one or more embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, of which: Figure 1 is a schematic block diagram of a method according to an embodiment of the present invention, and Table 1 is a table showing the % weight composition of pyrolytic char described herein.

Referring to Figure 1, a carbonaceous solid 1 is initially selected. In this embodiment, the carbonaceous solid 1 is a pyrolytic char obtained by the pyrolysis of automobile tyres. As shown in Table 1, the pyrolytic char comprises 17% w/w ash.

At step 101, the carbonaceous solid 1 is diluted with deionised water to 20 form an aqueous mixture comprising 25% w/w of carbonaceous solid 1.

At step 102, the aqueous mixture is micronized by high shear mixing using a high shear mixer. The carbonaceous solid 1 is micronized until the carbonaceous solid 1 is in the form of a suspended solid having a mean particle size of approximately 6tun.

At step 103, an alkali hydroxide 2 is provided. In this embodiment, the alkali hydroxide 2 is sodium hydroxide at a concentration of 5M.

At step 104, the aqueous mixture obtained from step 102 is mixed with the alkali hydroxide 2 from step 103 in a 1:6 (aqueous mixture: 5M alkali hydroxide) ratio. At step 104, mixing is effected by stirring the aqueous mixture from step 102 and the alkali hydroxide 2 from step 103 at 500 rpm for 1 hour at a temperature 90°C.

At step 105, the mixture obtained from step 104 is filtered and the solid particles retained. The solid particles are washed with deionised water to remove residual alkali hydroxide 2.

At step 106, the filtered and washed solid particles obtained from step are diluted with deionised water to form an aqueous mixture comprising 25% w/w of filtered and washed solid particles. The aqueous mixture is micronized by high shear mixing using a high shear mixer. The filtered and washed solid particles are micronized until the filtered and washed solid particles are in the form of a suspended solid having a mean particle size of approximately 6htm.

At step 107, an acid 3 selected from the group comprising hydrochloric acid, nitric acid, sulphuric acid and hydrofluoric acid, etc is provided. In this embodiment, the acid 3 is hydrochloric acid at a concentration of 5M.

At step 108, the filtered and washed solid particles obtained from step 106 are mixed with the acid 3 from step 107 in a 1:5 (filtered and washed solid particles: 5M acid) ratio. At step 108, mixing is effected by stirring the filtered and washed solid particles obtained from step 106 and the acid 3 from step 107 at 500 rpm for 1 hour at a temperature 90°C.

At step 109, the mixture obtained from step 108 is filtered and the solid particles retained. The solid particles are washed with deionised water to remove residual acid 3.

At step 110, steps 101 to 109 are repeated in order three times. By way of example, this means that the first repetition proceeds as follows; the solid particles obtained from step 109 are diluted with deionised water to form an aqueous mixture comprising 25% w/w of the filtered solid particles (step 101) and this aqueous mixture is micronized by high shear mixing using a high shear mixer until the filtered solid particles are in the form of a suspended solid having a mean particle size of approximately 611m (step 102); an alkali hydroxide 2 in the form of sodium hydroxide at a concentration of 5M is provided (step 103); the aqueous mixture comprising the filtered solid particles is mixed with the alkali hydroxide 2 in a 1:5 (aqueous mixture: 5M alkali hydroxide) ratio by stirring at 500 rpm for 1 hour at a temperature 90°C (step 104); the mixture obtained is filtered and the solid particles retained and washed with deionised water to remove residual alkali hydroxide 2 (step 105); the filtered and washed solid particles are diluted with deionised water to form an aqueous mixture comprising 25% w/w of the filtered solid particles and this aqueous mixture is micronized by high shear mixing using a high shear mixer until the filtered solid particles are in the form of a suspended solid having a mean particle size of approximately 6htm (step 106); an acid 3 in the form of hydrochloric acid at a concentration of 5M is provided (step 107); the aqueous mixture comprising the filtered solid particles is mixed with the acid 3 in a 1:5 (aqueous mixture: 5M acid) ratio by stirring at 500 rpm for 1 hour at a temperature 90°C (step 108); and the mixture obtained is filtered and the solid particles retained and washed with &ionised water to remove residual acid 3 (step 109).

In this embodiment., the sequence of acid or alkali mixes is as follows: alkali-acid-alkali-acid-alkali-acid-alkali-acid. However, in an alternative embodiment, the sequence of acid and alkali mixes could be acid-alkali-acid-alkali-acid-alkali-acid-After the third repetition, at step 110, the filtered and washed solid particles are dried at 130°C for 1 hour to form a recovered carbon black composition 4.

In this embodiment, the recovered carbon black composition 4 has an ash content of less than 1% w/w and a carbon black content of greater than 99% w/w, based on the total weight of the recovered carbon black composition 4.

The recovered carbon black composition 4 has applicability in a number of industrial uses, for example as a filler or reinforcing agent in a rubber composition, a pigment in an ink, a paint, a coating, a plastic, a thermoplastic composition or a thermoplastic elastomer.

The one or more embodiments are described above by way of example only. Many variations are possible without departing from the scope of protection afforded 30 by the appended claims.

Claims

CLAIMS1. A method for obtaining a carbon black composition from a carbonaceous solid, the method comprising the steps of: a. Providing an aqueous mixture comprising a carbonaceous solid; b. Providing an alkali hydroxide; c. Providing an acid; d. Mixing the aqueous mixture of step (a) with the alkali hydroxide of step (b) or the acid of step (c); e. Filtering and washing with water the composition solids obtained in step (d); f. Mixing the composition solids obtained in step (c) with the alkali hydroxide of step (b) or the acid of step (c) which was not used in step (d); and g. Filtering and washing with water the composition obtained in step (f).wherein the composition obtained in step (g) is used in place of the mixture of step (a) to repeat steps (a) to (g) at least once.
2. A method for obtaining a carbon black composition from a carbonaceous solid according to claim 1, wherein steps (a) to (g) are repeated once, twice or three times.
3. A method for obtaining a carbon black composition from a carbonaceous solid according to any preceding claim, wherein step (a) further comprises micronizing the aqueous mixture comprising the carbonaceous solid to obtain a carbonaceous solid mean particle size of between about 1 and about 15[1m.
4. A method for obtaining a carbon black composition from a carbonaceous solid according to claim 3, wherein micronizing is carried out using a high shear mixer, media mill, ultrasonication or dual asymmetric centrifuge.
5. A method for obtaining a carbon black composition from a carbonaceous solid according to any preceding claim, wherein the aqueous mixture of step (a) comprises between 1 and 80% w/w of carbonaceous solid.
6. A method for obtaining a carbon black composition from a carbonaceous solid according to any preceding claim, wherein the alkali hydroxide of step (b) is an aqueous solution of between about 0.5% and about 80% alkali hydroxide.
7. A method for obtaining a carbon black composition from a carbonaceous solid according to any preceding claim, wherein the alkali hydroxide of step (h) is selected from the group comprising sodium hydroxide, potassium hydroxide, calcium hydroxide, lithium hydroxide, rubidium hydroxide and caesium hydroxide.
8. A method for obtaining a carbon black composition from a carbonaceous solid according to any preceding claim, wherein step (d) comprises mixing the aqueous mixture of step (a) with the alkali hydroxide of step (b) or the acid of step (c) at between 100 and 1000 rpm for between 10 and 180 minutes.
9. A method for obtaining a carbon black composition from a carbonaceous solid according to any preceding claim, wherein step (d) and/or step (f) is carried out at between 25 and 150°C.
10. A method for obtaining a carbon black composition from a carbonaceous solid according to any preceding claim, wherein step (e) further comprises diluting the filtered and washed composition solids obtained in step (d) with water to form a slurry comprising between 1 and 80% w/w of the filtered and washed composition solids.
11. A method for obtaining a carbon black composition from a carbonaceous solid according to claim 10, wherein the slurry is mixed using a high shear mixer, before step (f).
12. A method for obtaining a carbon black composition from a carbonaceous solid according to any preceding claim, wherein the acid of step (c) is an aqueous solution of between about 0.5% and about 98% acid.
13. A method for obtaining a carbon black composition from a carbonaceous solid according to any preceding claim, wherein step (f) comprises mixing the aqueous mixture of step (e) with the alkali hydroxide of step (b) or the acid of step (c) at between 100 and 1000 rpm for between 10 and 180 minutes.
14. A method for obtaining a carbon black composition from a carbonaceous solid according to any preceding claim, wherein the mixing of step (d) and/or step (1) is high shear mixing at between 100 and 1000 rpm for between 10 and 180 minutes.
15. A method for obtaining a carbon black composition from a carbonaceous solid according to any preceding claim, wherein the acid of step (c) is selected from the group comprising hydrochloric acid, nitric acid, sulphuric acid, hydrofluoric acid, hydrobromic acid, hydroiodic acid, perchloric acid and chloric acid.
16. A method for obtaining a carbon black composition from a carbonaceous solid according to any preceding claim, wherein the carbonaceous solid is pyrolytic char.
17. A method for obtaining a carbon black composition from a carbonaceous solid according to claim 16, wherein the pyrolytic char is obtained by the pyrolysis of automobile tyres.
18. A method for obtaining a carbon black composition from a carbonaceous solid according to any preceding claim, wherein, in step (d), mixing the aqueous mixture of step (a) with the alkali hydroxide of step (b) or the acid of step (c), is carried out at a weight ratio of aqueous mixture of step (a) to alkali hydroxide of step (b) or acid of step (c) of less than about 1:8.
19. A method for obtaining a carbon black composition from a carbonaceous solid according to any preceding claim, wherein, in step (t), mixing the composition obtained in step (e) with the alkali hydroxide of step (b) or the acid of step (c), is carried out at a weight ratio of composition obtained in step (e) to alkali hydroxide of step (Yr) or acid of step (c) of less than about 1:8.
20. A method for obtaining a carbon black composition from a carbonaceous solid according to any preceding claim, wherein the composition obtained in step (2) comprises less than 1% w/w of ash.
21. A method for obtaining a carbon black composition from a carbonaceous solid according to any preceding claim, wherein the composition obtained in step (2) comprises greater than 99% w/w of carbon black.
22. A carbon black composition derived from pyrolytic char wherein the composition comprises: a. less than 1% w/w of ash; and b. greater than 99% w/w of carbon black, based on the total weight of the carbon black composition.
23. A carbon black composition according to claim 22, wherein the carbon black composition is obtained according to the method of any of claims 1 to 21.
24. The use of a carbon black composition according to claims 22 to 23 or obtained according to the method of any of claims 1 to 21 as a filler or reinforcing agent in a rubber composition, an ink, a paint, a coating, a plastic, a thermoplastic composition or a thermoplastic clastomer.
25. A pigment comprising a carbon black composition according to claims 22 or 23 or obtained according to the method of any of claims 1 to 21.