Process for producing purified carbon blacks with reduced content of oxidized polycyclic aromatic hydrocarbons

Abstract

A process for producing a purified carbon black with a reduced content of oxidized polycyclic aromatic hydrocarbons, such as oxy-polycyclic aromatic hydrocarbons (oxy-PAHs) and / or nitro-polycyclic aromatic hydrocarbons (nitro-PAHs) is provided. The process comprises providing a carbon black comprising an initial content of oxidized polycyclic aromatic hydrocarbons, and subjecting the provided carbon black to a thermal treatment comprising heat treating the carbon black at a temperature of less than 280°C in a vacuum or inert gas atmosphere. Also disclosed are purified carbon blacks obtainable by such process, and applications and uses of these purified carbon blacks.

Description

[0001] PROCESS FOR PRODUCING PURIFIED CARBON BLACKS WITH REDUCED CONTENT OF OXIDIZED POLYCYCLIC AROMATIC HYDROCARBONS

[0002] TECHNICAL FIELD

[0003]

[0001] The present invention relates to a process for purifying carbon blacks, and more specifically makes use of a thermal treatment under moderate conditions, for producing carbon blacks that have a reduced content of polycyclic aromatic hydrocarbon impurities, specifically oxidized polycyclic aromatic hydrocarbon impurities. The invention also relates to purified carbon blacks obtainable by this process, and applications and uses of such purified carbon blacks.

[0004] TECHNICAL BACKGROUND

[0005]

[0002] Carbon blacks are widely employed in industry as an additive for various different applications, for example as a coloring agent or pigment, reinforcing filler or conductive agent in the manufacture of paints, coatings, inks, electrodes or plastic or rubber articles. Depending on the respective application, carbon blacks with different properties are required, which can be controlled by the carbon black production process and possible aftertreatment. Carbon blacks are produced by controlled thermal or thermal-oxidative decomposition of hydrocarbon precursors such as oils, natural gas or acetylene. Established carbon black production processes include the furnace black process, the gas black process, originally developed by Degussa, the channel black process, the lamp black process, the acetylene black process or the thermal black process. In the gas black process feedstock oil is heated in a vaporizer and the resultant vapors are carried by a hydrogen-rich gas into a gas tube that is fitted with a multiplicity of burners. The individual flames impinge on the surface of a water- cooled drum, where formed carbon black is deposited. As a result of contact with oxygen at high temperatures during the production process, significant amounts of oxygen-containing functional groups are formed on the surface of the gas black particles, and likewise for channel blacks. Gas blacks and channel blacks accordingly generally have a notable oxygen content and volatiles content. Carbon blacks from other production processes such as furnace blacks, which account for more than 90% of the total amount of carbon blacks produced nowadays, have as-produced typically only low oxygen content. Oxidative aftertreatment using for example nitrogen dioxide, ozone or other oxidants allows to further increase the content of oxygen-containing surface groups significantly, which may be used for example for increasing the hydrophilicity of the carbon black, improving wettability and dispersibility in binders or rheological properties for pigment applications.

[0006]

[0003] Depending on the carbon black production process, used hydrocarbon precursor materials, process conditions and if applicable aftertreatment, different impurities such as metals, sulfur and organic compounds can contaminate the obtained carbon blacks. Such impurities, particularly when present in relatively high amounts, may adversely affect the carbon black performance and therefore be undesirable in certain applications.

[0007]

[0004] Carbon blacks can in particular contain as impurities organic compounds that have a skeleton with a polycyclic aromatic structure, which are commonly referred to as polycyclic aromatic hydrocarbons (PAHs). PAHs are believed to be harmful to the health and environment as for example discussed in Sudip K. Samanta, Om V. Singh and Rakesh K. Jain: “Polycyclic aromatic hydrocarbons: environmental pollution and bioremediation”, TRENDS in Biotechnology, Vol. 20, No. 6, Jun. 2002, pages 243-248. Therefore, the PAH content of carbon blacks is subject to increasingly demanding customer needs and official regulations for applications such as use in food or beverage contact situations, pharmaceuticals, cosmetics, or the manufacture of toys and articles for children. For instance, the American Food and Drug Administration (FDA) has limited the total PAH content of high purity furnace blacks in goods with food contact to 0.5 ppm (cf. U.S. Code of Federal Regulations (CFR) 21 Sec.178.3297), whereby the PAH content is defined as the sum of 22 PAH compounds (PAH22 content).

[0008]

[0005] Moreover, it is known that carbon blacks formed or aftertreated under oxidative conditions may among the polycyclic aromatic hydrocarbons (PAHs) contaminating carbon blacks include relatively high amounts of oxidized polycyclic aromatic hydrocarbons such as oxy-polycyclic aromatic hydrocarbons (oxy-PAHs) and / or nitro- polycyclic aromatic hydrocarbons (nitro-PAHs). Such oxidized polycyclic aromatic hydrocarbons are believed to be hazardous to health especially due to their ascribed carcinogenicity and mutagenicity (cf. e.g. Peter P. Fu and Diogenes Herreno-Saenz: "Nitro-polycyclic aromatic hydrocarbons: A class of genotoxic environmental pollutants", Journal of Environmental Science and Health, Part C: Environmental Carcinogenesis and Ecotoxicology Reviews, Vol. 17, No. 6, 1999, pages 1 -43; A. Clerge, J. Le Goff, C. Lopez, J. Ledauphin, R. Delepee (2019): "Oxy-PAHs: occurrence in the environment and potential genotoxic / mutagenic risk assessment for human health", Critical Reviews in Toxicology). Some oxidized polycyclic aromatic hydrocarbons such as 1 ,6-dinitropyrene are believed to be particularly hazardous. For instance, 1 ,6- dinitropyrene has been reported to be about 80,000 times as mutagenic as benzo(a)pyrene, commonly used as a reference, and exhibiting a potency equivalency factor (PEF) expressing carcinogenicity relative to benzo(a)pyrene of 10 (cf. e.g. J. F. Collins, J. P. Brown, G. V. Alexeeff, A. G. Salmon, “Potency Equivalence Factors for some Polycyclic Aromatic Hydrocarbons and Polycyclic Aromatic Hydrocarbon Derivatives”, Regulatory Toxicology and Pharmacology, vol. 28, 1998, pages 45-54). Therefore, there is a specific desire for reducing the amount of oxidized PAHs in carbon blacks.

[0009]

[0006] The PAH content of carbon blacks can to some extent be controlled by the conditions in the carbon black production process. For instance, high temperatures and / or late quenching in a furnace reactor typically reduce the PAH content in the obtained carbon blacks. However, adjustment of the process conditions in the carbon black production process also affects other properties of the produced carbon blacks, such as their structure, particle size distribution and surface area, which makes such approach rather inflexible and limits the range of obtainable carbon blacks.

[0010]

[0007] Other approaches for reducing the PAH content of carbon blacks rely on an aftertreatment of carbon blacks and are thus generally independent of the respective production process. For instance, WO 2008 / 058114 A2 discloses a treatment of carbon blacks by Soxhlet extraction using organic solvents such as toluene or by a thermal treatment in an inert gas or vacuum atmosphere for producing carbon blacks having a low PAH content. The heat treatment is conducted at temperatures from 300°C to 950°C (typically about 400°C to 500°C), considered necessary to desorb the PAHs from the carbon black. Further, US patent no. 4,138,471 describes purifying carbon blacks from PAH contaminants by heat treating the carbon black in a fluidized bed with air at temperatures between 1 ,150°F (621 °C) and 1 ,850°F (1 ,010°C). It has however been found that such conventional thermal treatments at the above- mentioned high temperature levels can substantially alter physicochemical properties of the carbon black and adversely affect their performance in applications. Moreover, these conventional approaches are thus relatively energy intensive and accordingly costly. A use of organic solvents is moreover unfavorable due to environmental and safety considerations.

[0011]

[0008] The conventional approaches for providing carbon blacks with a reduced content of PAHs known from the art relate moreover mostly to non-oxidized PAHs. There is accordingly a lack of dedicated processes for providing carbon blacks specifically with a reduced content of oxidized PAHs.

[0012]

[0009] WO 2022 / 128674 A1 discloses a process for producing a purified carbon black, which has been shown to enable also a purification of carbon blacks from nitro-PAH compounds. The process is based on a supercritical fluid extraction using an extraction agent comprising carbon dioxide in a supercritical state to extract the contaminants from the carbon black. This process is certainly suitable for a purification of carbon blacks from PAH contaminants, including nitro-PAHs, however it requires generating and handling supercritical media, demanding for costly high-pressure equipment compatible with the conditions used in the supercritical fluid extraction, typically 100 bar or more.

[0013]

[0010] Hence, there is a need for means of effectively purifying carbon blacks and obtaining carbon blacks with a reduced content of oxidized PAHs, if possible without adversely affecting other properties of the carbon black and without a need for energy intensive and / or expensive technology or means associated with any environmental, health or safety concerns.

[0014]

[0011] Accordingly, it is an objective of the present invention to provide a process for effectively removing oxidized PAHs, and optionally also non-oxidized PAHs, from carbon blacks and to provide carbon blacks having a significantly reduced content of such impurities, which overcomes or alleviates at least some of the above-mentioned deficiencies and limitations of the prior art. The process should for example enable efficient purification ideally without substantially altering physicochemical properties of the carbon black and adversely affecting its performance in applications. The purification process should further, if possible, be applicable to all kinds of carbon blacks obtained by different production processes and be economic, safe and environmental-friendly.

[0015] SUMMARY OF INVENTION

[0012] The present invention accordingly provides a process for producing a purified carbon black with a reduced content of oxidized polycyclic aromatic hydrocarbons, such as oxy-polycyclic aromatic hydrocarbons (oxy-PAHs) and / or nitro-polycyclic aromatic hydrocarbons (nitro-PAHs). The process comprises:

[0016] (a) providing a carbon black comprising an initial content of oxidized polycyclic aromatic hydrocarbons, and

[0017] (b) subjecting the provided carbon black to a thermal treatment comprising heat treating the carbon black at a temperature of less than 280°C, such as at a temperature in a range from 100°C to less than 280°C, in a vacuum or inert gas atmosphere to remove at least a portion of the oxidized polycyclic aromatic hydrocarbons from the carbon black to thereby obtain a purified carbon black with a lower content of oxidized polycyclic aromatic hydrocarbons than the initial content of oxidized polycyclic aromatic hydrocarbons.

[0018]

[0013] The present invention also relates to a purified carbon black obtainable by the process described above and, in more detail, herein below. Compositions comprising such purified carbon black and articles of manufacture made from such purified carbon black or a composition comprising the same are also within the scope of the invention.

[0019]

[0014] The process of the present invention may provide several advantages. Surprisingly, it has been found by the inventors to the present application that oxidized polycyclic aromatic hydrocarbons can be removed from carbon blacks with very high efficiency by a thermal treatment under mild conditions, at temperature levels well below those conventionally used in the art for thermally removing non-oxidized PAH contaminants from carbon blacks. Herein, also species, which are considered to be particularly harmful, such as 1 ,6- dinitropyrene can be removed practically completely. In fact, it has unexpectedly been found that despite of the mild conditions it is at least in some cases possible to remove in addition to the oxidized PAHs also at least a substantial proportion of non-oxidized PAHs from the carbon black by the process according to the present invention. The mild conditions under which the process of the invention can be carried out enable further to avoid or restrict to an acceptable extent thermally induced changes to the physicochemical properties of the carbon black. The purified carbon blacks obtainable by the process of the present invention can provide equivalent or sometimes even better application performance compared to the respective corresponding non-purified carbon blacks. The process of the invention enables thus effectively purifying carbon blacks and obtaining carbon blacks with a significantly reduced content of oxidized PAHs, optionally also a reduced content of non-oxidized PAHs, without substantially altering physicochemical properties of the carbon black or adversely affecting its performance in applications. The provided process is moreover flexible and applicable to various kinds of carbon blacks, independent of their production process and can be implemented and carried out in an economic, safe and environmental-friendly manner.

[0020]

[0015] The purified carbon black provided by the process according to the present invention can be used in various applications, such as all kind of applications where carbon blacks are conventionally used, but in particular in those kinds of application, which demand for a high purity of the carbon black with regard to PAH-type contaminants such as in food or beverage, pharmaceutical or cosmetical applications, manufacture of toys and articles for children, or any other health sensitive or human contact-applications. The present invention relates thus also to a use of the purified carbon black as for example pigment, reinforcing filler or conductive agent, particularly in such applications.

[0021]

[0016] These and other optional features and advantages of the present invention will be described in more detail in the following description.

[0022] DETAILED DESCRIPTION

[0023]

[0017] As used herein, the term "comprising" is understood to be open-ended and to not exclude the presence of additional undescribed or unrecited elements, materials, ingredients or method steps etc. The terms "including", "containing" and like terms are understood to be synonymous with "comprising". As used herein, the term "consisting of' is understood to exclude the presence of any unspecified element, ingredient or method step etc.

[0024]

[0018] As used herein, the singular form of “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise.

[0025]

[0019] Unless indicated to the contrary, the numerical parameters and ranges set forth in the following specification and appended claims are approximations. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical values, however, contain errors necessarily resulting from the standard deviation in their respective measurement.

[0026]

[0020] Also, it should be understood that any numerical range recited herein is intended to include all subranges subsumed therein. For example, a range of “1 to 10” is intended to include any and all sub-ranges between and including the recited minimum value of 1 and the recited maximum value of 10, that is, all subranges beginning with a minimum value equal to or greater than 1 and ending with a maximum value equal to or less than 10, and all subranges in between, e.g. 1 to 6.3, or 5.5 to 10, or 2.7 to 6.1.

[0027]

[0021] All parts, amounts, concentrations etc. referred to herein are by weight, unless specified otherwise.

[0028]

[0022] As mentioned above, the present invention relates to a process for producing a purified carbon black with a reduced content of oxidized polycyclic aromatic hydrocarbons. The process comprises (a) providing a carbon black comprising an initial content of oxidized polycyclic aromatic hydrocarbons, and (b) subjecting the provided carbon black to a thermal treatment comprising heat treating the carbon black at a temperature of less than 280°C in a vacuum or inert gas atmosphere to remove at least a portion of the oxidized polycyclic aromatic hydrocarbons from the carbon black to thereby obtain a purified carbon black with a lower content of oxidized polycyclic aromatic hydrocarbons than the initial content of oxidized polycyclic aromatic hydrocarbons.

[0029]

[0023] The term “polycyclic aromatic hydrocarbons (PAHs)” as used herein refers to organic compounds having a skeleton with two or more, such as two to seven, fused aromatic rings, i.e. a polycyclic aromatic structure. Hydrocarbon groups such as alkyl groups can optionally be bound to the skeleton of fused aromatic rings. As used herein, “polycyclic aromatic hydrocarbons (PAHs)” may encompass non-oxidized polycyclic aromatic hydrocarbons (non-oxidized PAHs) as well as oxidized polycyclic aromatic hydrocarbons (oxidized PAHs). As used herein, “non-oxidized PAHs” refers to compounds that have a polycyclic aromatic structure and consist of carbon and hydrogen atoms only. On the contrary, “oxidized PAHs”, as used herein, refers to oxidized derivatives of PAHs that consist not only of carbon and hydrogen, but contain in addition oxygen and optionally one or more other heteroatoms such as nitrogen and / or sulfur. A particular class of oxidized PAH compounds includes for example PAH compounds that have one or more than one nitro functional group(s) (-NO2), which are referred herein as “nitro-PAHs”. “Oxy-polycyclic aromatic hydrocarbons”, also referred to shortly as “oxy-PAHs”, as used herein refer to another class of oxidized PAH compounds that consist not only of carbon and hydrogen, but contain in addition oxygen. In other words, oxy-PAHs represent organic compounds, which have a skeleton with two or more, such as two to seven, fused aromatic rings and which consist of carbon, hydrogen and oxygen atoms. For instance, nitro-PAHs and oxy- PAHs can be derived from corresponding non-oxidized PAHs by substituting one or more hydrogen atom(s) by a nitro group or an oxygen-containing functional group, such as a carboxyl, aldo, hydroxyl or keto group, respectively. Oxy-PAHs include for example polycyclic aromatic ketones, polycyclic aromatic quinones, hydroxylated PAHs, polycyclic aromatic carboxaldehydes, polycyclic aromatic carboxylic acids and anhydrides, and polycyclic aromatic lactones.

[0030]

[0024] In a broad sense, a content of oxidized polycyclic aromatic hydrocarbons may refer to the total content of oxidized aromatic hydrocarbons of a given material such as a certain carbon black. The content of oxidized polycyclic aromatic hydrocarbons may more specifically mean the content of nitro-PAHs and / or oxy-PAHs of the respective material. For the purpose of the present invention, the content of oxy-PAH or nitro-PAH of a carbon black can more specifically refer to the content of a specific group of oxy- PAH or nitro-PAH compounds, such as the oxy-PAH6 or nitro-PAH10 group, as defined infra. Accordingly, a content of oxy-PAH or nitro-PAH of a carbon black indicated herein can in particular mean a content of the compounds of the oxy-PAH6 (also referred to as oxy-PAH6 content) or of the nitro-PAH 10 group (also referred to as nitro-PAH10 content), respectively. Accordingly, a content of oxidized polycyclic aromatic hydrocarbons of a carbon black indicated herein can in particular mean a content of the compounds of the nitro-PAH10 group or of the oxy-PAH6 group or the sum of the nitro-PAH 10 content and the oxy-PAH6 content.

[0031]

[0025] “Nitro-PAH10” as used herein refers to the group of the following ten nitrofunctional PAH compounds: 1 -nitronaphthalene (CAS no. 86-57-7), 2-nitronaphthalene (CAS no. 581 -89-5), 9-nitrophenanthrene (CAS no. 954-46-1 ), 3-nitrofluoranthene (CAS no. 892-21 -7), 1 -nitropyrene (CAS no. 5522-43-0), 2-nitropyrene (CAS no. 798- 07-1 ), 1 ,3-dinitropyrene (CAS no. 75321 -20-9), 1 ,6-dinitropyrene (CAS no. 42397-64- 8), 1 ,8-dinitropyrene (CAS no. 42397-65-9) and 4-nitrobiphenyl (CAS no. 92-93-3). Accordingly, the nitro-PAH10 content is determined as the sum of the amounts of these ten compounds based on the total weight of a carbon black sample. The nitro-PAH10 content of a carbon black sample can be determined by analyzing a toluene extract obtained by Soxhlet extraction of the carbon black sample by GC-MS utilizing deuterated forms of some nitro-PAH10 compound(s) for calibration as set forth in the examples.

[0032]

[0026] “Oxy-PAH6” as used herein refers to the group of the following six oxy-PAH compounds: 9,10-phenanthrendione (CAS no. 84-11 -7), 6H-benzo[cd]pyren-6-one (CAS no. 3074-00-8), benzanthrone (CAS no. 82-05-3), benzo[b]fluoren-11 -one (CAS no. 3074-03-01 ), 9-fluorenone (CAS no. 486-25-9) and 4H- cyclopenta[def]phenanthren-4-one (CAS no. 5737-13-3). Accordingly, the oxy-PAH6 content is determined as the sum of the amounts of these six compounds based on the total weight of a carbon black sample. The oxy-PAH6 content of a carbon black sample can be determined analogously to the determination of the nitro-PAH10 content by analyzing a toluene extract obtained by Soxhlet extraction of the carbon black sample by GC-MS utilizing deuterated forms of some oxy-PAH6 compound(s) for calibration as set forth in the examples.

[0033]

[0027] Similarly, in a broad sense, a content of non-oxidized polycyclic aromatic hydrocarbons may refer to the total content of non-oxidized polycyclic aromatic hydrocarbons of a given material such as a certain carbon black. For the purpose of the present invention, the content of non-oxidized polycyclic aromatic hydrocarbons can more specifically refer to the content of one or more than one specific group(s) of non-oxidized PAH compounds, in particular the PAH22 group, as defined infra. Accordingly, a content of non-oxidized polycyclic aromatic hydrocarbons of a carbon black indicated herein can in particular mean a content of the compounds of the PAH22 group (also referred to as PAH22 content).

[0034]

[0028] “PAH22” as used herein refers to the group of 22 PAH compounds as specified by the American Food and Drug Administration (FDA) in the U.S. Code of Federal Regulations (CFR) 21 Sec.178.3297 and the method entitled “Determination of PAH content of Carbon Black”, dated July 8, 1994, as developed by Cabot Corp., mentioned therein: naphthalene (CAS no. 91 -20-3), acenaphthylene (CAS no. 208-96-8), acenaphthene (CAS no. 83-32-9), fluorene (CAS no. 86-73-7), phenanthrene (CAS no. 85-01 -8), anthracene (CAS no. 120-12-7), fluoranthene (CAS no. 206-44-0), pyrene (CAS no. 129-00-0), benzo(g,h,i)fluoranthene (CAS no. 203-12-3), benz(a)anthracene (CAS no. 56-55-3), cyclopenta(c,d)pyrene (CAS no. 27208-37-3), chrysene (CAS no. 218-01 -9), benzo(b)fluoranthene (CAS no. 205-99-2), benzo(k)fluoranthene (CAS no. 207-08-9), benzo(e)pyrene (CAS no. 192-97-2), benzo(a)pyrene (CAS no. 50-32-8), perylene (CAS no. 198-55-0), dibenzo(a,h)anthracene (CAS no. 53-70-3), benzo(g,h,i)perylene (CAS no. 191 -24-2), indeno(1 ,2,3-cd)pyrene (CAS no. 193-39- 5), anthanthrene (CAS no. 191 -26-4), and coronene (CAS no. 191 -07-1 ). The PAH22 content is thus determined as the total amount of these 22 compounds based on the total weight of a carbon black sample. The PAH22 content can be determined by analyzing a toluene extract obtained by Soxhlet extraction of the carbon black sample using GC-MS utilizing deuterated forms of some PAH22 compound(s) for calibration following the above-mentioned method entitled “Determination of PAH content of Carbon Black”, dated July 8, 1994 as described in the examples.

[0035]

[0029] As mentioned above, a carbon black comprising an initial content of oxidized polycyclic aromatic hydrocarbons is provided as material to be purified in the process according to the present invention. For the sake of clarity, as will be apparent to the skilled reader, “carbon black” is different from “soot” or “black carbon”. Soot or black carbon are used to designate generally unwanted carbonaceous by-products resulting from an incomplete combustion of carbon-containing materials, such as oil, fuel, diesel or gasoline, coal, paper or waste material. Soot and black carbon contain large quantities of organic and inorganic impurities typically containing less than 60% of elemental carbon, based on the total mass, and are composed of rather coarse particles having hardly a well-defined structure or order. On the contrary, carbon black is deliberately produced by incomplete combustion or thermal decomposition of gaseous or liquid hydrocarbons under controlled conditions, and typically has a higher carbon content such as 80 wt.% or more, based on the total mass, and is composed of particles, which have a well-defined structure and high degree of order, and high surface area-to-volume ratio.

[0030] Providing the carbon black comprising an initial content of oxidized polycyclic aromatic hydrocarbons can comprise manufacturing carbon black by a carbon black production process. Manufacturing the carbon black can make use of any process for the production of carbon black. Different industrial processes for the production of carbon blacks are available and include e.g. the furnace process, gas black process, channel black process, acetylene black process, thermal black process or lamp black process, as for example described in J.-B. Donnet et al., "Carbon Black: Science and Technology", 2ndedition. The carbon black comprising an initial content of polycyclic aromatic hydrocarbons used in the practice of the present invention can for example comprise or be a furnace black, a thermal black, a lamp black, a channel black, a gas black, an acetylene black, a recycled or recovered carbon black or a combination of any of the foregoing. Recycled carbon blacks are carbon blacks obtained from end-of- use carbon black-containing products, such as waste tires, and obtainable by recycling processes, typically involving a pyrolysis step for the decomposition of organic components such as rubbers or plastics. A wide variety of carbon blacks with different properties that can be used in the present invention are commercially available from carbon black manufacturers such as for example Cabot Corporation, Mitsubishi Chemical Company, Tokai Carbon, Denka, Birla Carbon or Orion Engineered Carbons GmbH. Non-limiting examples thereof include carbon blacks marketed under the ECORAX®, PUREX®, CORAX®, PRINTEX®, AROSPERSE®, HIBLACK®, COLOUR BLACK, SPECIAL BLACK, or NEROX® brands by ORION Engineered Carbons GmbH.

[0036]

[0031] Depending on the production process used, specifically in case of the gas black process or channel black process, the provided carbon black can have a notable amount of oxygen-containing functional groups in particular at the surface of the carbon black particles. Providing the carbon black comprising an initial content of oxidized polycyclic aromatic hydrocarbons as material to be purified in the process according to the present invention can moreover optionally comprise subjecting the as- produced carbon black, e.g. carbon black produced by any one of the above- mentioned carbon black production processes, such as a furnace black, thermal black or gas black, to an oxidative aftertreatment. Hence, the carbon black comprising an initial content of oxidized polycyclic aromatic hydrocarbons used in the practice of the present invention can comprise a carbon black which either has been subjected to an oxidative treatment or has not been subjected to an oxidative treatment. The optional oxidative aftertreatment can be accomplished in any manner known for the oxidation of carbon blacks, as for example described in J.-B. Donnet et al., "Carbon Black: Science and Technology", 2ndedition. The oxidative aftertreatment generally comprises oxidizing the as-produced carbon black with an oxidizing agent. The oxidative aftertreatment can for example be accomplished by treatment with an oxidizing agent such as oxygen gas, ozone, NOx, peroxides such as hydrogen peroxide, persulfates such as sodium and potassium persulfates, hypohalites such as sodium hypochlorite, nitric acid, and transition metal-containing oxidants such as permanganate salts, osmium tetroxide, chromium oxides, ceric ammonium nitrates, and mixtures or combinations thereof. According to the present disclosure, the oxidative aftertreatment may in particular utilize a gaseous oxidizing agent such as ozone, oxygen, air, NOx or a mixture or combination thereof.

[0037]

[0032] The process according to the present invention may be particularly useful with respect to oxidized carbon blacks since for these carbon blacks oxidized PAHs may particularly be significant as contaminants. The carbon black comprising an initial content of oxidized polycyclic aromatic hydrocarbons can accordingly in particular comprise an oxidized carbon black. The oxidized carbon black can for example be a (optionally oxidatively aftertreated) gas or furnace black. As used herein, an "oxidized carbon black" means a carbon black, which comprises a notable content of oxygen, typically including oxygen-containing functional groups in particular at the surface of the carbon black particles. The oxygen-containing functional groups can be exemplified, but are not limited to, alcohol, quinone, carboxyl, phenol, lactol, lactone, anhydride, chinone, peroxidic, ether, and ketone groups. For example, oxidized carbon blacks that can be used according to the present invention can have an oxygen content of 0.5 wt.% or more, such as 1 wt.% or more, or 2 wt.% or more, or 5 wt.% or more, or 10 wt.% or more, based on the total weight of the oxidized carbon black. Typically, the oxygen content does not exceed 20 wt.%, based on the total weight of the oxidized carbon black material. For example, the oxidized carbon black can contain from 0.5 wt.% to 20 wt.%, or from 1 wt.% to 15 wt.%, or from 2 wt.% to 10 wt.%, or from 5 wt.% to 15 wt.% of oxygen, based on the total weight of the oxidized carbon black material. An oxidized carbon black provided as carbon black comprising an initial content of oxidized polycyclic aromatic hydrocarbons in the process according to the present invention may have an oxygen content in a range between any of the above-mentioned values.

[0038]

[0033] The carbon black provided for purification according to the process of the present invention has an initial content of oxidized polycyclic aromatic hydrocarbons. The initial content of oxidized polycyclic aromatic hydrocarbons content can vary significantly, depending on the type of carbon black employed and its production method and optional aftertreatment. For example, the initial content of oxidized polycyclic aromatic hydrocarbons can vary from as low as a few ppm or even less to 1 ,000 ppm or even more. For instance, the carbon black to be purified in the process of the present invention may have an initial content of oxidized polycyclic aromatic hydrocarbons of 1 ppm or more, or 5 ppm or more, or 10 ppm or more, such as 20 ppm or more, 50 ppm or more, 100 ppm or more, 200 ppm or more, or 300 ppm or more. The carbon black can have an initial content of oxidized polycyclic aromatic hydrocarbons of 1 ,000 ppm or less, such as 500 ppm or less, or 300 ppm or less, or 200 ppm or less, or in some cases 100 ppm or less, such as 50 ppm or less. The carbon black to be purified in the process of the present invention may have an initial content of oxidized polycyclic aromatic hydrocarbons in a range between any of the recited values, such as in a range from 1 ppm to 1 ,000 ppm, or a range from 5 ppm to 500 ppm, or a range from 10 ppm to 300 ppm.

[0039]

[0034] When the carbon black is provided for instance under oxidizing conditions in the presence of a nitrogen-containing compound, such as NOx as oxidizing agent, there may be a tendency to form favorably nitro-PAHs, whereas other production or aftertreatment conditions may favor the formation of oxy-PAHs.

[0040]

[0035] The carbon black provided for purification according to the process of the present invention can for example have an initial oxy-PAH6 content of 1 ppm or more, such as 2 ppm or more, or 3 ppm or more, or 4 ppm or more, or 5 ppm or more, or 10 ppm or more, or 20 ppm or more, or 30 ppm or more, or 40 ppm or more, or 50 ppm or more, or 60 ppm or more, or 80 ppm or more, or 100 ppm or more. The carbon black can for example have an initial oxy-PAH6 content of 300 ppm or less, such as 200 ppm or less, or 100 ppm or less, in some case of 50 ppm or less, such as 20 ppm or less, or 10 ppm or less. The carbon black to be purified in the process of the present invention may have an initial oxy-PAH6 content in a range between any of the recited values, such as in a range from 1 ppm to 300 ppm, or a range from 2 ppm to 100 ppm, or a range from 2 ppm to 50 ppm.

[0041]

[0036] Alternatively or in addition, the carbon black provided for purification according to the process of the present invention can have a certain initial nitro-PAH10 content. For example, the carbon black may have an initial nitro-PAH10 content of 1 ppm or more, such as 2 ppm or more, or 3 ppm or more, or 4 ppm or more, or 5 ppm or more, or 10 ppm or more, or 20 ppm or more, or 30 ppm or more, or 50 ppm or more, or 80 ppm or more, or 100 ppm or more, or 200 ppm or more, or 300 ppm or more. The carbon black can for example have an initial nitro-PAH10 content of 1 ,000 ppm or less, or 500 ppm or less, such as 200 ppm or less, or 100 ppm or less, in some case of 50 ppm or less, such as 20 ppm or less, or 10 ppm or less. The carbon black to be purified in the process of the present invention may have an initial nitro-PAH10 content in a range between any of the recited values, such as in a range from 1 ppm to 500 ppm, or a range from 2 ppm to 200 ppm, or a range from 10 ppm to 100 ppm. Among the nitro-PAH compounds initially contained by the carbon black may specifically be 1 ,6- dinitropyrene, which is considered as potentially particularly harmful contaminant. The carbon black provided for purification according to the process of the present invention can for example have an initial content of 1 ,6- dinitropyrene of 0.2 ppm or more, such as 0.5 ppm or more, or 1 ppm or more, or 5 ppm or more, or 10 ppm or more. The carbon black can for example have an initial content of 1 ,6- dinitropyrene of 200 ppm or less, such as 150 ppm or less, or 100 ppm or less, or 50 ppm or less, or 20 ppm or less, or 10 ppm or less, such as 5 ppm or less, or 2 ppm or less. The carbon black to be purified in the process of the present invention may have an initial content of 1 ,6- dinitropyrene in a range between any of the recited values, such as in a range from 0.2 ppm to 150 ppm, such as from 0.5 ppm to 10 ppm, or from 0.5 ppm to 2 ppm.

[0042]

[0037] The carbon black having an initial content of oxidized polycyclic aromatic hydrocarbons provided for purification according to the process of the present invention may optionally further comprise an initial content of non-oxidized polycyclic aromatic hydrocarbons, such as compounds of the PAH22 group. In such case, subjecting the carbon black to the thermal treatment in step (b) of the process may also remove at least a portion of the non-oxidized polycyclic aromatic hydrocarbons from the carbon black such that the obtained purified carbon black can also have a lower content of non-oxidized polycyclic aromatic hydrocarbons than the initial content of non-oxidized polycyclic aromatic hydrocarbons. It has unexpectedly been found that despite of the mild conditions applied in the process of the present invention it is at least in some cases possible to remove in addition to the oxidized PAHs also at least a portion of non-oxidized PAHs from the carbon black by the process according to the present invention.

[0043]

[0038] The initial content of non-oxidized polycyclic aromatic hydrocarbons content can again vary significantly, depending on the type of carbon black employed and its production method and optional aftertreatment. For example, oxidative conditions in the carbon black production or aftertreatment tend to reduce the content of nonoxidized polycyclic aromatic hydrocarbons and favor in turn the formation of oxidized polycyclic aromatic hydrocarbons. Oxidized carbon blacks may therefore have a relatively low initial content of non-oxidized polycyclic aromatic hydrocarbons, whereas other carbon blacks may include substantial amounts of non-oxidized carbon blacks, which can significantly exceed the content of oxidized carbon blacks.

[0044]

[0039] The carbon black to be purified in the process of the present invention may for example have an initial content of non-oxidized polycyclic aromatic hydrocarbons, such as initial PAH22 content, from as low as a few ppm to 5,000 ppm or even more. For instance, the carbon black to be purified in the process of the present invention may have an initial content of non-oxidized polycyclic aromatic hydrocarbons, such as an initial PAH22 content, of 1 ppm or more, or 5 ppm or more, or 10 ppm or more, such as 20 ppm or more, 30 ppm or more, 50 ppm or more, 80 ppm or more, or 100 ppm or more, or 200 ppm or more, or 500 ppm or more, or 1 ,000 ppm or more. The carbon black can for example have an initial content of non-oxidized polycyclic aromatic hydrocarbons, such as an initial PAH22 content, of 5,000 ppm or less, such as 3,000 ppm or less, or 2,000 ppm or less, or 1 ,000 ppm or less, or 800 ppm or less, or 500 ppm or less, or 400 ppm or less, or 300 ppm or less, or 200 ppm or less, or 100 ppm or less, or 80 ppm or less, or 60 ppm or less, or 50 ppm or less, or 40 ppm or less, or 30 ppm or less, or 20 ppm or less. The carbon black may have an initial content of nonoxidized polycyclic aromatic hydrocarbons, such as an initial PAH22 content, in a range between any of the recited values, such as in a range from 1 ppm to 5,000 ppm, or a range from 5 ppm to 500 ppm, or a range from 10 ppm to 100 ppm.

[0040] The carbon black provided for purification according to the process of the present invention can have any combination of the initial oxy-PAH6 content, initial nitro- PAH10 and / or initial PAH22contents specified above.

[0045]

[0041] For example, the provided carbon black comprising an initial content of oxidized polycyclic aromatic hydrocarbons can comprise a relatively high PAH22 content, such as 500 ppm or more, or 1 ,000 ppm or more and concomitantly a relatively low nitro- PAH1 0 and / or oxy-PAH6 content such as 50 ppm or less, or 20 ppm or less, or 10 ppm or less, or 5 ppm or less. Such carbon black can for instance be exemplified by a carbon black not oxidatively aftertreated.

[0046]

[0042] In another example, the provided carbon black comprising an initial content of oxidized polycyclic aromatic hydrocarbons may have a relatively low PAH22 content such as 100 ppm or less, or 50 ppm or less, or 20 ppm or less, or 10 ppm or less and concomitantly a relatively high nitro-PAH10 and / or oxy-PAH6 content such as 50 ppm or more, or 100 ppm or more, or 200 ppm or more, or 300 ppm or more. Such carbon black can for instance be an oxidized carbon black.

[0047]

[0043] The carbon black comprising an initial content of oxidized polycyclic aromatic hydrocarbons provided in step (a) of the process can optionally further be characterized by having one or more than one or all of the following properties.

[0048]

[0044] Thus, the carbon black comprising an initial content of oxidized polycyclic aromatic hydrocarbons provided in step (a) of the process may be characterized by its ash content. The carbon black can for example have an ash content of 5 wt.% or less, such as 3 wt.% or less, or 2 wt.% or less, or 1 wt.% or less, or 0.5 wt.% or less, or 0.2 wt.% or less, or 0.1 wt.% or less, based on the total weight of the carbon black. The carbon black can for example have an ash content of 0.001 wt.% or more, such as 0.005 wt.% or more, or 0.01 wt.% or more, or 0.05 wt.% or more, or 0.1 wt.% or more, or 0.2 wt.% or more, or 0.5 wt.% or more, based on the total weight of the carbon black. The carbon black to be purified in the process of the present invention may have an ash content in a range between any of the recited values, such as in a range from 0.001 wt.% to 5 wt.%, or from 0.005 wt.% to 3 wt.%, or from 0.01 to 0.3 wt.%. The ash content of the carbon black can be determined according to ASTM D1506-15.

[0045] Further, the carbon black comprising an initial content of oxidized polycyclic aromatic hydrocarbons can be characterized by a content of volatiles. The content of volatiles can be determined by heating to 950°C according to DIN 53552:1977. The carbon black can for example have a volatile content of 25 wt.% or less, such as 20 wt.% or less, or 15 wt.% or less, or 10 wt.% or less, or 5 wt.% or less, or 3 wt.% or less, or 1 wt.% or less, based on the total weight of the carbon black. The carbon black can for example have a volatile content of 0.5 wt.% or more, such as 0.8 wt.% or more, or 1 wt.% or more, or 1 .5 wt.% or more, or 2 wt.% or more, or 3 wt.% or more, based on the total weight of the carbon black. The carbon black to be purified in the process of the present invention may have a volatile content in a range between any of the recited values, such as in a range from 0.5 wt.% to 25 wt.%, or from 0.8 wt.% to 15 wt.%, or from 2 to 15 wt.%.

[0049]

[0046] Moreover, the carbon black comprising an initial content of oxidized polycyclic aromatic hydrocarbons can be characterized by its moisture content. For example, the carbon black can have a moisture content of 15 wt.% or less, such as 10 wt.% or less, or 5 wt.% or less, or 3 wt.% or less, or 1 wt.% or less, based on the total weight of the carbon black. The carbon black can for example have a moisture content of 0.1 wt.% or more, such as 0.2 wt.% or more, or 0.3 wt.% or more, or 0.5 wt.% or more, or 1 wt.% or more, based on the total weight of the carbon black. The carbon black to be purified in the process of the present invention may have a moisture content in a range between any of the recited values, such as in a range from 0.1 wt.% to 5 wt.%, or from 0.2 wt.% to 3 wt.%. The moisture content of the carbon black can be determined according to ASTM D1509-18.

[0050]

[0047] The carbon black comprising an initial content of oxidized polycyclic aromatic hydrocarbons can be characterized by its pH. The pH can be determined according to ASTM D1512-21 (Test Method B - Sonic Slurry). The carbon black can for example have a pH of 10 or less, such as 8 or less, or 7 or less, or 6 or less, or 5 or less. The carbon black can for example have a pH of 2 or more, such as 3 or more, or 4 or more. The pH of the carbon black comprising an initial content of oxidized polycyclic aromatic hydrocarbons provided in the process of the present invention can have a pH in a range between any of the recited values, such as in a range from 2 to 10, or from 2 to 5.

[0048] The carbon black comprising an initial content of oxidized polycyclic aromatic hydrocarbons can further be characterized by its carbon content. For example, the carbon black can have a carbon content of 80 wt.% or more, such as 85 wt.% or more, or 90 wt.% or more, or 95 wt.% or more, or 97 wt.% or more, or 98 wt.% or more, based on the total weight of the carbon black. The carbon black can for example have a carbon content of up to 99.9 wt.%, such as 99.5 wt.% or less, or 99 wt.% or less, or 98 wt.% or less, or 97 wt.% or less, or 95 wt.% or less. The carbon black to be purified in the process of the present invention may have a carbon content in a range between any of the recited values, such as in a range from 80 wt.% to 99.9 wt.%, or from 80 wt.% to 97 wt.%, or from 85 to 95 wt.%. The carbon content can be determined by elemental analysis.

[0051]

[0049] The carbon black comprising an initial content of oxidized polycyclic aromatic hydrocarbons can further be characterized by its oxygen content. For example, oxidized carbon blacks that can be used according to the present invention can have an oxygen content of 0.1 wt.% or more, such as 0.5 wt.% or more, or 1 wt.% or more, or 2 wt.% or more, or 5 wt.% or more, or 10 wt.% or more, based on the total weight of the oxidized carbon black. Typically, the oxygen content does not exceed 20 wt.%, based on the total weight of the carbon black. The carbon black can for example have an oxygen content of 20 wt.% or less, or 15 wt.% or less, or 10 wt.% or less, or 7 wt.% or less, or 5 wt.% or less. The carbon black to be purified in the process of the present invention may have an oxygen content in a range between any of the recited values, such as in a range from 0.1 wt.% to 20 wt.%, or from 1 wt.% to 15 wt.%, or from 2 wt.% to 10 wt.%, or from 5 wt.% to 15 wt.%, based on the total weight of the carbon black material.

[0052]

[0050] The carbon black comprising an initial content of oxidized polycyclic aromatic hydrocarbons can further be characterized by a specific surface area. For example, the carbon black can have a BET surface area of 30 m2 / g or more, such as 50 m2 / g or more, or 80 m2 / g or more, or 100 m2 / g or more, or 150 m2 / g or more, or 200 m2 / g or more. The carbon black can for example have a BET surface area of 1 ,000 m2 / g or less, such as 800 m2 / g or less, or 700 m2 / g or less, or 600 m2 / g or less, or 500 m2 / g or less, or 400 m2 / g or less, or 300 m2 / g or less. The carbon black to be purified in the process of the present invention may have a BET surface area in a range between any of the recited values, such as in a range from 30 to 1 ,000 m2 / g, or from 50 to 700 m2 / g, or from 100 to 300 m2 / g. The BET surface area can be measured by nitrogen adsorption according to ASTM D6556-21 .

[0053]

[0051] The carbon black comprising an initial content of oxidized polycyclic aromatic hydrocarbons that is provided in step (a) can in addition or alternatively be characterized by a statistical thickness surface area (STSA). The statistical thickness surface area (STSA) can be determined according to ASTM D6556-21. The carbon black can for example have a STSA of 20 m2 / g or more, such as 30 m2 / g or more, or 50 m2 / g or more, or 60 m2 / g or more, or 80 m2 / g or more, or 90 m2 / g or more, or 100 m2 / g or more, or 120 m2 / g or more, or 150 m2 / g or more. The carbon black can for example have a STSA of 500 m2 / g or less, such as 400 m2 / g or less, or 300 m2 / g or 250 m2 / g or less, or 200 m2 / g or less. The carbon black can for example have a STSA in a range between any of the above-mentioned values. For example, the carbon black can have a STSA in a range from 20 to 500 m2 / g, such as from 50 to 400 m2 / g, or from 90 to 250 m2 / g.

[0054]

[0052] In the process according to the present invention a single carbon black or a mixture of two or more different carbon blacks, which may each be as described above, can be provided as carbon black material to be purified.

[0055]

[0053] As set forth above, in the process according to the present invention, the provided carbon black with the initial content of oxidized polycyclic aromatic hydrocarbons, which has been described above, is then subjected to a thermal treatment to remove at least a portion of the oxidized polycyclic aromatic hydrocarbons from the carbon black and obtain a purified carbon black with a lower content of oxidized polycyclic aromatic hydrocarbons than the initial content of oxidized polycyclic aromatic hydrocarbons. The thermal treatment comprises heat treating the carbon black at a temperature of less than 280°C in a vacuum or inert gas atmosphere. An inert gas atmosphere as used herein is to be understood as referring to a gas atmosphere which does not noticeably react chemically with the carbon black under the applied conditions of the thermal treatment. The inert gas atmosphere may accordingly be substantially free of gases that are reactive towards the carbon black under the applied conditions of the thermal treatment. Examples of reactive gases may include for example NOx, SOx, ozone or halogens. Substantially free of reactive gases means that the respective atmosphere does not contain reactive gases or only as incidental impurities. The concentration of reactive gases, if present as incidental impurities, can for example be less than 1 ,000 ppm, or less than 500 ppm, or less than 100 ppm, such as less than 10 ppm, or less than 1 ppm, or less than 0.1 ppm, or less than 0.01 ppm. For the sake of clarity, the atmosphere, in which the heat treatment of the carbon black is carried out according to the process of the present invention is a gas atmosphere, which may optionally be under vacuum. A gas atmosphere refers to a fluid medium that is in the gaseous state, i.e. in the gaseous region of the respective phase diagram. A gas atmosphere is accordingly distinguished and does not encompass supercritical fluids. A supercritical fluid is obtained at a temperature and pressure above the critical temperature and pressure (critical point), i.e. in the supercritical region of the respective phase diagram. The process according to the present invention typically does not involve treating the carbon black with a medium that is in a supercritical state. It is therefore distinguished from supercritical fluid extraction processes known from the art and can avoid drawbacks associated therewith. For instance, the process of the present invention can be carried out without the need for a high-pressure resistant reactor.

[0056]

[0054] The gas atmosphere in which the carbon black is heat treated can in particular comprise or be made of an inert gas. Inert gas means any gas or gas mixture that is not reactive towards the carbon black under the applied conditions of the thermal treatment. Non-limiting examples of inert gases that can be used include helium, nitrogen, neon, argon, steam, carbon dioxide or mixtures or combinations thereof. For cost reasons, nitrogen, argon or mixtures or combinations thereof are preferably used.

[0057]

[0055] The gas atmosphere in which the carbon black is heat treated, such as an inert gas atmosphere as described above, can also be a vacuum atmosphere. Vacuum atmosphere means a gas atmosphere, which is under a vacuum, that is which has a subatmospheric pressure. The atmospheric pressure under standard conditions is 1 ,013.25 hPa. The applied vacuum is not particularly limited and can comprise low vacuum, moderate vacuum, high vacuum or ultra high vacuum. Due to cost reasons low to high vacuum, in particular low or moderate vacuum, may preferably be used. The atmosphere in which the heat treatment is carried out can for example have a pressure of 100 hPa or less, such as 10 hPa or less, or 1 hPa or less, or 0.1 hPa or less, or 0.01 hPa or less. The atmosphere in which the heat treatment is carried out can for example have a pressure of 10’9hPa or more, or 10’6hPa or more, or 10’5hPa or more, or 10’4hPa or more, or 0.001 hPa or more. Application of a vacuum may be favorable as it can promote removal of PAH contaminants from the carbon black at moderate temperatures. The process of the present invention however does not require application of a vacuum and can also be carried out at pressures about the atmospheric pressure or moderate overpressure. The heat treatment of the carbon black can accordingly also be carried out in a gas atmosphere which has a pressure corresponding to about atmospheric pressure, for example within ±20% of the atmospheric pressure, or moderate overpressure. The gas atmosphere, such as an inert gas atmosphere as described above, can for example have a pressure of 500 hPa or more, 800 hPa or more, 900 hPa or more, or 1 ,000 hPa or more. It can have for example a pressure of 2,000 hPa or less, such as 1 ,500 hPa or less, or 1 ,200 hPa or less. The atmosphere in which the carbon black is heat treated can have a pressure in a range between any of the above-mentioned values such as in a range from 10’9hPa to 100 hPa, or from 10’5hPa to 10 hPa, or from 0.001 hPa to 10 hPa, or from 1 to 100 hPa, or from 1 hPa to 1 ,500 hPa, or from 800 hPa to 1 ,500 hPa.

[0058]

[0056] As set forth above, the thermal treatment comprises heat treating the carbon black at a temperature of less than 280°C in the vacuum or inert gas atmosphere. The thermal treatment may for example comprise heat treating the carbon black in the vacuum or inert gas atmosphere at a temperature of 50 °C or more, or 80°C or more, or preferably 100°C or more, or 120°C or more, or more preferably 150°C or more, or 180°C or more, or 200°C or more. The carbon black may for example be heat treated in the vacuum or inert gas atmosphere at a temperature of 270°C or less, or 260°C or less, or 250°C or less, or 240°C or less, or 230°C or less, or 220°C or less. The carbon black can be heat treated according to the present invention at a temperature in a range between any of the above-mentioned values such as in a range from 100°C to less than 280°C, or at a temperature in a range from 150°C to 270°C, preferably in a range from 180°C to 260°C, or in a range from 200°C to 250°C. It has surprisingly been found, as also demonstrated in the Examples below, that despite of such relatively low temperatures, an efficient removal of oxidized PAHs can be achieved by the process of the present invention.

[0059]

[0057] The thermal treatment of the carbon black in the process according to the present invention can optionally comprise subjecting the treated carbon black to a gas flow, such as a continuous gas flow. Heat treating of the carbon black at a temperature of less than 280°C in the vacuum or inert gas atmosphere can accordingly comprise exposing the carbon black to a gas flow, such as a continuous gas flow, in particular of an inert gas as described above. The average gas flow rate can vary widely, e.g. depending on the size of the apparatus used and / or the amount of carbon black that is heat treated therein. The average flow rate of the gas can for example be 1 NL / h or more, such as 5 NL / h or more, or 10 NL / h or more, or 20 NL / h or more, or 50 NL / h or more, or 80 NL / h or more, or 100 NL / h or more, or 150 NL / h or more, or 200 NL / h or more. For example, the average flow rate of the gas can be 10,000 NL / h or less, such as 5,000 NL / h or less, or 2,000 NL / h or less, or 1 ,000 NL / h or less, or 500 NL / h or less, or 300 NL / h or less. The average flow rate can be in a range between any of the recited values, such as in a range from 5 NL / h to 10,000 NL / h, or from 10 NL / h to 1 ,000 NL / h, or from 50 NL / h to 300 NL / h. Typically in a heat treatment device with a comparatively small volume treatment chamber as employed in the examples described infra, the average flow rate is in a range from 50 NL / h to 300 NL / h. The average flow rate of the gas is calculated based on the total volume which the supplied amount of the gas would have under standard conditions (101.325 kPa, 0°C) and the overall treatment time. The volume of gas can be measured for example by a mass flow meter, which measures the amount of gas per unit time at a certain temperature and pressure, e.g. at room temperature and atmospheric pressure. Integration over time yields then the total volume of gas. The measured total volume of gas can then be converted to a total volume of gas under standard conditions by using the ideal gas law. The total volume of gas under standard conditions expressed in norm liters [NL] is divided by the total treatment time to calculate the average flow rate under standard conditions.

[0060]

[0058] The average flow rate of the gas (in NL / h) per unit volume of the treatment chamber of the device used for the heat treatment (in L) can for example be 1 NL h’1L’1or more, or 5 NL h’1L’1or more, such as 10 NL h’1L’1or more, or 20 NL h’1L’1or more, or 50 NL h’1L’1or more, or 100 NL h’1L’1or more. For example, the average flow rate of the gas per unit volume of the treatment chamber of the heat treatment device (in L) can be 5,000 NL h’1L’1or less, such as 3,000 NLTr1L’1or less, or 2,000 NL h’1L’1or less, or 1 ,000 NL h’1L’1or less, or 500 NL h’1L’1or less or 300 NL h’1L’1or less. The average flow rate of the gas per unit volume of the treatment chamber of the heat treatment device can be in a range between any of the recited values, such as in a range from 1 NL h’1L’1to 5,000 NL h’1L’1, or from 5 NL h’1L’1to 1 ,000 NL h’1L’1, or from 10 NL h’1L’1to 500 NL h’1L’1.

[0061]

[0059] The average flow rate of the gas (in NL / h) per mass unit of the amount of treated carbon black (in kg) can for example be 5 NL h’1kg’1or more, such as 10 NL h’1kg’1or more, or 20 NL h’1kg’1or more, or 50 NL h’1kg’1or more, or 100 NL h’1kg’1or more, or 200 NL h’1kg’1or more. For example, the average flow rate of the gas per mass unit of the amount of treated carbon black (in kg) can be 3,000 NL h’1kg’1or less, such as 2,000 NL h’1kg’1or less, or 1 ,000 NL h’1kg’1or less, or 500 NL h’1kg’1or less. The average flow rate of the gas per mass unit of the amount of treated carbon black (in kg) can be in a range between any of the recited values, such as in a range from 5 NL h’1kg-1to 5,000 NL h’1kg’1, or from 10 NL h’1kg’1to 1 ,000 NL h’1kg’1, or from 20 NL h’1kg’1to 500 NL h’1kg’1.

[0062]

[0060] The carbon black can be heat treated at a temperature of less than 280°C, such as any temperature described above, in the vacuum or inert gas atmosphere in the process according to the present invention for any desirable time. The treatment time will generally be determined by conditions applied for the thermal treatment, the desired degree of purification as well as economic considerations. For example, the carbon black can be heat treated at a temperature of less than 280°C in the vacuum or inert gas atmosphere for a time of 10 minutes or more, such as 20 minutes or more, or 30 minutes or more, or 40 minutes or more, or 1 hour or more, or 2 hours or more, or 4 hours or more. The carbon black can for example be heat treated at a temperature of less than 280°C in the vacuum or inert gas atmosphere for a time of up to 24 hours, such as 12 hours or less, or 10 hours or less, or 8 hours or less, or 6 hours or less. The heat treatment of the carbon black can be carried out for a for a time in a range between any of the recited values, for example from 10 minutes to 24 hours, or from 30 minutes to 12 hours, or from 1 hour to 8 hours.

[0063]

[0061] Adjusting the temperature to the above-mentioned temperature used for heat treating the carbon black in the vacuum or inert gas atmosphere for a suitable duration as specified above can be achieved by heating-up or cooling-down according to the respective needs. The temperature can be adjusted herein in any suitable manner, e.g. linearly or non-linearly and / or with any suitable rate, which may depend on the available equipment and its limitations. The average rate of the change in temperature can for example be in a range from 1 K / min to 100 K / min, such as from 5 K / min to 50 K / min.

[0064]

[0062] The thermal treatment of the carbon black according to the process of the present invention removes at least a portion of the oxidized polycyclic aromatic hydrocarbons, and optionally also of non-oxidized polycyclic aromatic hydrocarbons, from the carbon black. For instance, heat treating the carbon black at a temperature of less than 280°C in a vacuum or inert gas atmosphere as set forth herein can comprise removing at least 50 wt.%, such as 70 wt.% or more, or 80 wt.% or more, or 90 wt.% or more, or 95 wt.% or more, or 97 wt.% or more, or 98 wt.% or more, or 99 wt.% or more, or 99.5 wt.% or more, or 99.7 wt.% or more, or 99.8 wt.% or more, or 99.9 wt.% or more of the initial content of oxidized polycyclic aromatic hydrocarbons from the carbon black. More specifically, heat treating the carbon black at a temperature of less than 280°C in a vacuum or inert gas atmosphere as set forth herein can comprise removing at least 50 wt.%, such as 70 wt.% or more, or 80 wt.% or more, or 90 wt.% or more, or 95 wt.% or more, or 97 wt.% or more, or 98 wt.% or more, or 99 wt.% or more, or 99.5 wt.% or more, or 99.7 wt.% or more, or 99.8 wt.% or more, or 99.9 wt.% or more of the initial oxy-PAH6 content and / or of the initial nitro-PAH10 content and / or specifically of the initial content of 1 ,6-dinitropyrene from the carbon black. Optionally, heat treating the carbon black in the process at set forth herein can further comprise removing at least 30 wt.%, such as 50 wt.% or more, or 70 wt.% or more, or 80 wt.% or more, or 85 wt.% or more, or 90 wt.% or more, or 95 wt.% or more, of the initial content of non-oxidized PAHs, such as specifically of the initial PAH22 content, from the carbon black.

[0065]

[0063] The thermal treatment according to the process of the present invention can be carried out with any equipment or device available for heat treating solid materials under conditions as set out herein. For example, the thermal treatment of the carbon black can be conducted, without being limited thereto, in a convective oven, electric oven, infrared oven, gas fired oven, vacuum oven, conveyor oven, batch oven, fixed bed reactor, fluidized bed reactor, rotary kiln, Auger reactor or a combination thereof. Preferably, the thermal treatment of the carbon black is conducted in a fluidized bed reactor. The heat treatment device is generally constructed to withstand the temperatures and conditions used in the thermal treatment according to the process of the present invention. The heat treatment device generally comprises heating means for controlling the temperature in the heat treatment step. The heating means can be any conventional heating means. The heat treatment device generally comprises a treatment chamber, in which the carbon black is provided for the heat treatment. The treatment chamber can for example have a volume of 0.1 L or more, or 0.5 L or more, or 1 L or more, or 5 L or more, or 10 L or more, or 50 L or more, or 100 L or more, or 200 L or more, or 500 L or more. The treatment chamber can for example have a volume of 5,000 L or less, or 2,000 L or less, or 1 ,000 L or less. The volume of the treatment chamber can be in a range between any of the recited values such as in a range from 0.1 L to 5,000 L, or from 1 L to 1 ,000 L, or from 10 L to 500 L. A heat treatment device can comprise a single treatment chamber or two or more treatment chambers. Providing a carbon black comprising an initial content of oxidized polycyclic aromatic hydrocarbons can comprise introducing an amount of said carbon black into the treatment chamber(s) of the heat treatment device. Typically, the treatment chamber(s) is fed with gas, in particular inert gas, through an inlet connected to a feeding line from one or more sources of the gas. Optionally, a vacuum can be generated in the treatment chamber(s), e.g. by a connected pump. Polycyclic aromatic hydrocarbons removed from the carbon black can be withdrawn, e.g. with a gas flow, from the treatment chamber(s) through an outlet and connected effluent line, optionally promoted by vacuum generating means such as a connected pump, if used. The heat treatment device may further comprise conventional means for flow and / or process control such as sensors, pressure or flow regulation means, valves, and controllers. Preferably, the one or more than one treatment chamber(s) is designed such that a flow of gas may be forced through the carbon black to be treated, such as to form a fluidized bed, rather than flowing gas for example over the carbon black to be treated.

[0066]

[0064] The process can further comprise retrieving and / or collecting the purified carbon black after the thermal treatment step. This can involve cooling of the heat treated carbon black, for example to a temperature of 60°C or less, such as to ambient or slightly elevated temperature, and transferring the cooled purified carbon black from the heat treatment device to a receptacle. Generally, the process according to the present invention can be conducted as a continuous process, as a semi-batch or as a batch process. In case of a continuous process, carbon black comprising an initial content of oxidized polycyclic aromatic hydrocarbons can for example be continuously fed to a heat treatment device where it is heat treated according to the process described herein, and the purified carbon black obtained thereby be continuously withdrawn from the heat treatment device. Preferably, such continuous process can be carried out in a manner with no substantial mixing of the carbon black particles fed at different times into the heat treatment device such that the residence time in the heat treatment device and thus the time of the heat treatment is approximately the same. Moreover, a flow of gas from the inlet to the outlet may be in an opposite direction, the same direction, a perpendicular direction or any other angular configuration to the conveying direction of the carbon black particles. In case of a batch or semi-batch process, a batch of carbon black comprising an initial content of oxidized polycyclic aromatic hydrocarbons can to be loaded to a heat treatment device and heat treated according to the process described herein for a desired time under controlled conditions to produce a purified carbon black having a reduced content of oxidized PAHs. After the desired time, the heat treatment can be stopped and the purified carbon black be retrieved from the heat treatment device.

[0067]

[0065] The process of the present invention can generally be carried out independently of carbon black production or aftertreatment processes. It can accordingly be applied to a wide variety of different carbon black grades. The process can nevertheless advantageously be implemented in a carbon black production plant and be carried out e.g. after a carbon black production process or aftertreatment process. For example, the process disclosed herein can be implemented downstream of a carbon black production, such as for example downstream of a carbon black production reactor and / or downstream of a carbon black aftertreatment unit such as for example an oxidative aftertreatment unit.

[0068]

[0066] The purified carbon black obtainable by the process according to the present invention has a lower content of oxidized polycyclic aromatic hydrocarbons than the initial content of oxidized polycyclic aromatic hydrocarbons of the carbon black provided for purification. The purified carbon black can for example have a content of oxidized PAHs, which corresponds to 50 wt.% or less, such as 30 wt.% or less, or 20 wt.% or less, or 10 wt.% or less, or 5 wt.% or less, or 3 wt.% or less, or 2 wt.% or less, or 1 wt.% or less, or 0.5 wt.% or less, or 0.3 wt.% or less, or 0.2 wt.% or less, or 0.1 wt.% or less, or 0.05 wt.% or less of the initial content of oxidized polycyclic aromatic hydrocarbons. For instance, the purified carbon black can have an oxy-PAH6 content, which corresponds to 50 wt.% or less, such as 30 wt.% or less, or 20 wt.% or less, or 10 wt.% or less, or 5 wt.% or less, or 3 wt.% or less, or 2 wt.% or less, or 1 wt.% or less, or 0.5 wt.% or less, or 0.3 wt.% or less, or 0.2 wt.% or less, or 0.1 wt.% or less, or 0.05 wt.% or less of the initial oxy-PAH6 content. Alternatively or in addition, the purified carbon black can have a nitro-PAH10 content, which corresponds to 50 wt.% or less, such as 30 wt.% or less, or 20 wt.% or less, or 10 wt.% or less, or 5 wt.% or less, or 3 wt.% or less, or 2 wt.% or less, or 1 wt.% or less, or 0.5 wt.% or less, or 0.3 wt.% or less, or 0.2 wt.% or less, or 0.1 wt.% or less, or 0.05 wt.% or less of the initial nitro-PAH10 content. In particular, the purified carbon black can have a content of 1 ,6- dinitropyrene, which corresponds to 20 wt.% or less, such as 10 wt.% or less, or 5 wt.% or less, or 3 wt.% or less, or 2 wt.%, or 1 wt.% or less, or 0.5 wt.% or less, or 0.3 wt.% or less, or 0.2 wt.% or less, or 0.1 wt.% or less, or 0.05 wt.% or less of the initial content of 1 ,6-dinitropyrene. Moreover, the purified carbon black obtainable by the process according to the present invention may optionally further have a lower content of nonoxidized PAHs than the initial content of non-oxidized PAHs of the carbon black provided for purification. For instance, the purified carbon black can have a content of non-oxidized PAHs, such as PAH22 content, which corresponds to 70 wt.% or less, such as 50 wt.% or less, or 30 wt.% or less, or 20 wt.% or less, or 15 wt.% or less, or 10 wt.% or less, or 5 wt.% or less of the initial content of non-oxidized PAHs, such as of the initial PAH22 content.

[0069]

[0067] The purified carbon black obtained by the process according to the present invention can for example have a content of oxidized polycyclic aromatic hydrocarbons of 200 ppm or less, or 100 ppm or less, such as 50 ppm or less, or 30 ppm or less, or 20 ppm or less, or 10 ppm or less, or 5 ppm or less, or 3 ppm or less, or 1 ppm or less, or 0.5 ppm or less. The purified carbon black can for example have an oxy-PAH6 content of 50 ppm or less, such as 30 ppm or less, or 20 ppm or less, or 10 ppm or less, or 7 ppm or less, or 5 ppm or less, or 3 ppm or less, or 1 ppm or less, or 0.5 ppm or less, or 0.2 ppm or less, or 0.1 ppm or less. Alternatively or in addition, the purified carbon black can for example have a nitro-PAH10 content of 20 ppm or less, such as 10 ppm or less, or 5 ppm or less, or 3 ppm or less, or 1 ppm or less, or 0.5 ppm or less, or 0.3 ppm or less, or 0.2 ppm or less, or 0.1 ppm or less, or 0.05 ppm or less. The purified carbon black can specifically have a content of 1 ,6- dinitropyrene of 0.1 ppm or less, such as 0.05 ppm or less, or 0.01 ppm or less, or 0.005 ppm or less. The purified carbon black obtainable by the process according to the present invention may further have a content of non-oxidized PAHs, such as PAH22 content, of 500 ppm or less, such as 200 ppm or less, or 100 ppm or less, or 50 ppm or less, or 30 ppm or less, or 20 ppm or less, or 10 ppm or less, or 5 ppm or less, or 3 ppm or less, or 2 ppm or less, or 1 ppm or less, or 0.5 ppm or less. The purified carbon black can have any combination of the contents of oxidized PAHs, such as oxy-PAH6 and / or nitro-PAH10 and / or 1 ,6- dinitropyrene contents, and optionally non-oxidized PAHs content, such as PAH22 content, specified above. The purified carbon blacks obtainable according to the process according to the present invention can have a content of oxidized PAHs, such as oxy-PAH6 and / or nitro-PAH10, and optionally content of non-oxidized PAHs, such as PAH22 content, that ensures compliance with official regulations for applications of the purified carbon blacks in areas such as use in food or beverage contact situations, pharmaceuticals, cosmetics, or the manufacture of toys and articles for children, e.g. compliance with FDA regulations.

[0070]

[0068] The purified carbon black obtainable by the process according to the present invention can further have any of the other characteristics and properties described above for the carbon black with the initial content of oxidized PAHs provided for purification, such as carbon content, oxygen content, volatile content, ash content, moisture content, pH, BET surface area and / or STSA surface area. These properties may remain substantially unaffected by the thermal treatment of the carbon black within the process disclosed herein. Thus, the purified carbon black may apart from the content of oxidized PAHs and optionally non-oxidized PAHs substantially correspond to the carbon black provided as material to be purified. For instance, the carbon content, oxygen content, volatile content, ash content, moisture content, pH, STSA surface area and / or BET surface area of the purified carbon black can correspond to the respective value of the carbon black provided as starting material, as described above, ±30%, or ±20%, or ±10%, or ±5%. Specifically, the BET surface area and / or statistical thickness surface area (STSA) can differ by no more than 30%, such as no more than 25%, or no more than 20%, from the respective value determined for the carbon black with the initial content of oxidized PAHs provided in step (a) of the disclosed process.

[0071]

[0069] The purified carbon blacks obtained according to the present invention can be used in any application, where carbon blacks are conventionally employed or useful. The purified carbon blacks according to the present invention can for example be used as pigment, reinforcing filler or conductive agent, such as for the manufacture of plastic or rubber articles, paints, inks, coatings, electrodes or energy storage devices. The purified carbon blacks of the present invention can accordingly be formulated with further ingredients to form compositions such as a plastic or rubber composition, a paint, ink or coating composition or electrode composition. From the purified carbon black or a composition comprising the same various articles of manufacture can be produced, such as plastic or rubber articles, coatings, electrodes etc. Formulation of such compositions and manufacture of such articles can be achieved using common ingredients and existing technology and is therefore not further described herein. The purified carbon blacks according to the present invention are particularly useful in applications, where there is an increased awareness or concern regarding PAHs or where PAH-related official regulations exist, such as in food or beverage contact situations, pharmaceuticals, cosmetics, or the manufacture of toys and articles for children.

[0072]

[0070] Having generally described the present invention above, a further understanding can be obtained by reference to the following specific examples. These examples are provided herein for purposes of illustration only, and are not intended to limit the present invention, which is rather to be given the full scope of the appended claims including any equivalents thereof.

[0073] EXAMPLES

[0074]

[0071] All parts and percentages indicated throughout the Examples refer to weight, unless specified otherwise.

[0075] Thermal treatment of carbon black

[0076]

[0072] An exemplary carbon black (post oxidized regular color gas black, commercially available from Orion Engineered Carbons GmbH), which is conventionally used as pigment for coloring and tinting applications, was subjected to a thermal aftertreatment at different temperatures (200°C, 250°C, 400°C or 500°C, respectively) for investigating the potential of thermally removing contaminants, particularly PAH-type contaminants, and prepare a corresponding purified carbon black.

[0073] The thermal treatment of the carbon black was each carried out in a high- temperature fluidized bed reactor. The setup comprises a vertically arranged tube made of Inconel having a length of 1 ,500 mm and inner diameter of 108 mm defining the reactor chamber. The Inconel tube is enclosed on its outer surface along the long axis by insulation and heating modules made from in total eight Fibrothal semishells (each having a power of 2,500 W), forming four heating zones. A gas flow is introduced at the bottom end of the tube from a connected gas supply system. The first heating zone from the bottom end of the tube is used for heating up the gas flow to the desired temperature, the remaining heating zones are for heat treating material filled into the reactor chamber at the desired temperature. Controlling of the heating shells is done via thermal elements, being positioned between the reactor’s external wall and the corresponding heating shell. The temperature in each heating zone is further measured inside the reaction chamber by temperature sensors. Filling of the discontinuous operating fluidized bed is done via the reactor’s head. Evaporating gases at the reactor’s head are introduced to an exhaust system and a combustion system. After cooling the thermally treated carbon black can be filled into a bucket or a bag supported by a pusher.

[0077]

[0074] For the thermal aftertreatment, the reaction chamber of the reactor was filled to about half its volume with the carbon black to be treated, corresponding to an amount of about 500-800 g. The heating modules were then powered (100% power) and the carbon black heated to the respective target temperature (200°C, 250°C, 400°C or 500°C, respectively) under a continuous flow of nitrogen gas (flow rate: 100-120 Nl / h). When the respective target temperature was approached the power supplied to the heating modules was regulated to hold the respective target temperature. The sample was then maintained at the respective target temperature for a dwell time of 6 hours under the continuous flow of nitrogen gas. Subsequently, the heating modules were switched off and the sample was cooled down under the continuous flow of nitrogen gas to ambient temperature and then exposed to air and removed from the reactor for characterization and testing of the obtained thermally treated carbon black.

[0078] Characterization of carbon blacks

[0075] The pristine (i.e. non-thermally treated) carbon black, as a reference, and the carbon blacks obtained by the above-described thermal treatment at the different temperatures were analyzed for their physicochemical properties as follows.

[0079]

[0076] The BET surface area was determined by nitrogen adsorption according to ASTM D6556-21.

[0080]

[0077] The statistical thickness surface area (STSA) of the carbon blacks was determined according to ASTM D6556-21 .

[0081]

[0078] The content of volatiles of the carbon blacks was determined by heating to 950°C according to DIN 53552:2023-07.

[0082]

[0079] The thus determined physicochemical properties are summarized in Table 1.

[0083] Table 1

[0084] *: Comparative Example

[0085]

[0080] As can be seen from Table 1 heat treating the carbon black leads to an increase of the BET and STSA surface area, while the volatiles content decreases compared to the pristine, non-heat treated carbon black. At the lower treatment temperatures, the changes are however moderate (about 20 % or less for treatment temperatures of up to 250°C) such that the physicochemical properties of the carbon black remain similar to the corresponding non-heat treated carbon black. At the higher treatment temperatures, the heat treated carbon blacks differ significantly more in their physicochemical properties from the corresponding non-heat treated carbon black.

[0081] The pristine (i.e. non-thermally treated) carbon black, as a reference, and the carbon blacks obtained by the above-described thermal treatment at the different temperatures were moreover analyzed for their content of different PAH contaminants.

[0086]

[0082] Thus, the investigated carbon blacks were analyzed for their content of nonoxidized PAHs, determined as PAH22 content, after the thermal treatment and compared to the initial PAH22 content determined for the pristine (non-heat treated) carbon black as a reference. The PAH22 content was each determined following the method entitled “Determination of PAH content of Carbon Black”, dated July 8, 1994, as developed by Cabot Corp., and incorporated by the American Food and Drug Administration (FDA) in the U.S. Code of Federal Regulations (CFR) 21 Sec.178.3297, as follows:

[0087]

[0083] The carbon black material was crushed in a mortar with a pestle until a homogenous powder was obtained. A suitable amount (up to 10 g) of the powder was precisely weighed in a cellulose extraction thimble (MN 645, Macherey-Nagel, Duren, Germany). A glass wool plug and cellulose pieces from an extraction thimble were put on top of the carbon black and the filled thimble then loaded in the extraction chamber of a 100 mL Soxhlet apparatus with a 250 mL round bottom flask. Toluene was added to the flask and the condenser of the apparatus was gently flushed with nitrogen. The sample was then subjected to Soxhlet extraction with toluene in the Soxhlet apparatus for 48 h under light protection at a rate of approx. 10 cycles per hour. The obtained raw extract was then concentrated to slightly over 5 mL by means of a rotary evaporator operated at 40°C and a pressure reduction of 5 kPa as a minimum (Buchi Rotavapor R-200, Buchi Labortechnik AG, 9230 Flawil, Switzerland). The extract was then transferred to a 10 mL volumetric flask and brought to the mark by adding fresh toluene. To an aliquot of the extract were added 17 deuterated PAH standards (Ds- Naphthalene, Ds-Acenaphthylene, Dw-Acenaphthene, Dw-Fluorene, Dw- Phenanthrene, Dw-Anthracene, Dw-Fluoranthene, Dw-Pyrene, D12- Benzo[a]anthracene, Di2-Chrysene, Di2-Benzo[b]fluoranthene, D12- Benzo[k]fluoranthene, Di2-Benzo[a]pyrene, Di4-Dibenz[a,h]anthracene, D12- Benzo[g,h,i]perylene, Di2-lndeno[1 ,2,3-c,d]pyrene and Di2-Coronene, each in an amount of 200 ng). Then, the extract aliquot was cleaned-up by treatment with a silica gel column (1 g silica gel / 13% H2O, 8 to 10 mm inner diameter and 5 cm3capacity). Subsequently, a further deuterated compound, Di2-Perylene, was added to the cleaned-up extract as recovery standard in an amount of 200 ng. The thus obtained solution was then used for HRGC / LRMS analysis (Capillary gas chromatography coupled with low resolution mass spectrometry) for PAH identification and quantification using the following instrumentation and conditions: Gas chromatograph: Thermo Scientific GC-Ultra with PTV injector, GC-column: 60 m DB5-MS, 0.25 mm ID, 0.25 pm film thickness; temperature program GC oven: preheating oven to 80°C, sample injection, holding for 2 min at 80°C, heating with a rate of 25°C / min to 180°C, heating with a rate of 8°C / min to 220°C, heating with a rate of 2°C / min to 250°C, heating with a rate of 3°C / min to 280°C, heating with a rate of 5°C / min to 320°C, hold at 320°C for 21 min and 18 seconds; Mass spectrometer: Thermo Scientific Trace DSQ LRMS, operated in the electron impact mode (El) and Selected Ion Monitoring (SIM Mode); mass resolution: 1 amu; monitoring of molecular and fragment ions for the individual PAH compounds. Calibration check of the instrument was performed for each analysis sequence by injection of mixtures containing all native PAHs of interest and the above-mentioned deuterated standards. Identification of the PAH species was achieved by analysis of the relative retention time, the molecular and fragment ions, and the fragmentation ratio. Quantification was performed using the instrumentation software via the deuterated internal PAHs using the isotope dilution and internal standard method. The PAH22 content was calculated by summing up the individual determined concentrations of the 22 PAH compounds, whereby for compounds, whose concentration were below the limit of quantification (LOQ), the LOQ was adopted as the respective concentration. The co-eluting isomer dibenz(a,h)anthracene and dibenz(a,c)anthracene could not be separated by the GC column and where thus taken as one substance, reported herein as “dibenz(a,h)anthracene”.

[0088]

[0084] Furthermore, the investigated carbon blacks were analyzed for their content of oxidized PAHs in terms of both, nitro-PAHs as well as oxy-PAHs, determined as nitro- PAH10 and oxy-PAH6 content, after the thermal treatment and compared to the initial nitro-PAH10 and oxy-PAH6 content determined for the pristine (non-heat treated) carbon black as a reference. The determination of the nitro- and oxy-PAH content was carried out in analogy to the determination of the PAH22 content as described above, based on the same analytical methods. In particular, the extraction of the carbon black, the volume reduction of the raw extract and the adjustment of a defined volume were performed exactly in the same manner as described above. The further steps were carried out as described above with the following nitro- and oxy-PAH specific adaptations: To an aliquot of the extract (48h Soxhlet extraction with toluene under nitrogen flush of the condenser) were added as internal standards two deuterated nitro- PAHs and a deuterated oxy-PAH (D7-1 -Nitronaphthalene, D9-1 -Nitropyrene and D8- 9-Fluorenone in an amount of 100 ng each) instead of the above-mentioned 17 deuterated PAH standards. The nitro- and oxy-PAH extract aliquot containing the deuterated internal standards was directly subjected to High Resolution Mass Spectrometry (HRGC / HRMS) without further treatment. The following instrumentation and conditions were applied: Thermo Scientific GC-Ultra 2000 with PTV injector, GC- column: 30 m DB5-MS, 0.25 mm ID, 0.1 pm film thickness, temperature program GC oven: preheating oven to 80°C, sample injection, holding for 4 min and 24 seconds at 80°C, heating with a rate of 35°C / min to 180°C, heating with a rate of 6°C / min to 209°C, heating with a rate of 20°C / min to 250°C, heating with a rate of 6°C / min to 290°C, hold at 290°C for 5 min; mass spectrometer: Thermo Scientific DFS HRMS, operated in the electron impact mode (El) and Selected Ion Monitoring (SIM Mode); mass resolution: <8.000 amu, monitoring of molecular and fragment ions for the individual nitro- and oxy-PAH compounds. Calibration check of the HRMS instrument was performed for each analysis sequence by injection of mixtures containing the 10 nitro- and 6 oxy- PAHs and the above-mentioned 3 deuterated standards. Identification of the nitro- and oxy-PAH species was achieved by analysis of the relative retention time, the molecular and fragment ions, and the fragmentation ratio. Quantification was performed using the instrumentation software via the deuterated internal nitro- and oxy PAHs using the isotope dilution and internal standard method.

[0089]

[0085] The results of the conducted analysis for nitro-PAH10 content and oxy-PAH6 content are summarized in Table 2 below, those for PAH22 content in Table 3 below, each for the carbon blacks obtained by the above-described thermal treatment at temperatures or 200°C or 250°C, respectively, in comparison to the pristine (i.e. non- thermally treated) carbon black as a reference. The reported relative purification degrees have been calculated according to the formula 1-(x(heat treated sample) / x(reference)), wherein x(heat treated sample) and x(reference) represent the detected amount of the indicated compound or detected total amount of the indicated group of compounds for the given heat treated carbon black and the pristine reference carbon black, respectively. Table 2

[0090] *: Comparative Example

[0091]

[0086] The results summarized in Table 2 show that surprisingly oxidized PAHs can be effectively removed from carbon black by a thermal treatment at relatively low temperature, such 250°C or 200°C. Particularly for nitro-PAHs, the purification degree was consistently high (99.7 % or more) even at the lower investigated treatment temperature of 200°C. Herein, specifically also the dinitropyrene species, which are considered to be particularly hazardous, are removed practically completely. Regarding oxy-PAHs the purification efficiency was less than for the nitro-PAHs, however still clearly more than 90% over the full oxy-PAH6 class even at the lower investigated treatment temperature of 200°C, and above 99 % for the carbon black treated at 250°C.

[0092] Table 3

[0093] *: Comparative Example

[0094]

[0087] The data in Table 3 show that non-oxidized PAHs are removed from the carbon black with a lower efficiency than the oxidized PAHs. Nevertheless, a thermal treatment under mild conditions, such as at 250°C or 200°C, surprisingly enables to remove in addition to oxidized PAHs also at least a substantial portion of non-oxidized PAHs.

[0095] Preparation and testing of coating compositions with carbon blacks

[0096]

[0088] The pristine non-heat treated carbon black, as a reference, and the purified carbon blacks obtained therefrom by the above-described thermal treatment at different temperatures, having the properties as set forth in Tables 1 to 3 above, were each used and tested in a standard water-borne PU-based coating formulation. The ingredients and their respective amounts used in the millbase preparation for the water-borne coating composition are shown in Table 4.

[0097] Table 4 1: Wetting and dispersing agent, commercially available from Evonik Operations GmbH, Germany, active matter content about 35%

[0098] 2: Defoamer, commercially available from Evonik Operations GmbH, Germany

[0099]

[0089] To prepare the millbases, the components were added to a beaker in the amounts listed in Table 4 and pre-dispersed using a Pendraulik LR 34 dissolver for 5 minutes at 4000 RPM. After the pre-dispersion, the pH of the thus obtained millbase composition was measured using a pH Meter and, if necessary, adjusted to be in a range from 8.7 to 9.2 by adding additional drops of DMEA. Then, 540 g of steelbeads (size dia. 3mm) were added and the samples were dispersed using a Lau Shaker DAS 200 for 60 min. After having separated the beads from the paste, the pH-value of the thus obtained millbase was measured again and, if necessary, adjusted to be in a range from 8.2 to 8.7 by adding additional drops of DMEA.

[0100]

[0090] Final water-borne coating formulations were prepared by mixing the respective millbase with a letdown in a speedmixer for 2 minutes at 2000 RPM. The letdown was prepared by mixing 454.8 parts by weight of Alberdingk® U 9800 (aliphatic polyester polyurethane dispersion, 35% solids content), 78 parts by weight butyl glycol, 60 parts by weight of deionized water, 6 part by weight of additives (wetting agent, defoamer) and 1.2 parts by weight of DMEA. The millbase and letdown were used in relative amounts yielding a concentration of 1 .5 wt.% of the respective carbon black, based on the coating formulation.

[0101]

[0091] The obtained water-borne coating formulations were applied on glass panels by a bar applicator (slot height: 200 pm) and dried at room temperature for 15 min. Afterwards, the panels were dried in an oven for 15 minutes at 60°C and then used for coloristic measurements.

[0102]

[0092] Coloristic characteristics of the thus obtained films prepared from the aqueous coating compositions were measured using a Pausch Q - Color 35 spectrophotometer (4570° spectrophotometer) and the BCSWIN software. The measurement is made through the glass after calibration with a white calibration tile and a black hollow body. The spectrometer averages over five individual measurements for each sample.

[0103] The hue-independent black value MY and hue-dependent black value Me are calculated as follows from the tristimulus (XYZ) data derived from the measurement:

[0104] The hue-independent black value MY is calculated according to equation 2 from the tristimulus component Y of the measurement (illuminant D65 / 100):

[0105] MY= 100 ■ log

[0106] Subsequently, the hue-dependent black value is calculated according to equation 3:

[0107] ( / Xn\ / Zn\ / Yn\\ (3)

[0108] Mc= 100 ■ log ( log (— ) — log(— ) + log (— )

[0109] \ \ A / \ / \ I / / wherein Xn / Zn / Yn(DIN6147) are tristimulus values of the coordinate origin, based on the illuminant and the observer (DIN5033 / part 7 / illuminant D65 / 100) with Xn= 94.81 Zn= 107.34 Yn= 100.0. The absolute hue contribution dM (“undertone”) is calculated according to equation 4 from the black values Mc and MY: dM = Mc- MY(4).

[0110]

[0093] Furthermore, gloss and haze of the black colored films were measured using a haze-gloss instrument from BYK-Gardner at an angle of 20 degrees. Measurements were performed at five different locations of each sample and reported as an average value.

[0111]

[0094] The thus obtained coloristic characteristics determined for the films obtained from the water-borne coating compositions prepared using the different investigated carbon blacks as set forth above, are summarized in Table 5 below. Table 5

[0112] *: Comparative Example

[0113]

[0095] As can be seen from Table 5 the coating compositions containing the carbon blacks thermally treated according to the present invention yielded equivalent jetness and gloss as well as a comparable undertone (slightly negative dM) and a comparable or even slightly lower haze compared to the corresponding coating composition containing the reference pristine carbon black. On the other hand, the comparative carbon blacks heat treated at higher temperatures yielded a different undertone (dM zero or positive) and significantly higher haze compared to the corresponding coating composition containing the reference pristine carbon black, thus exhibiting notably different appearance characteristics. The higher haze indicates also an inferior compatibility of these comparative carbon blacks with the polymeric matrix of the water-based coating formulation.

[0096] The above results demonstrate the potential of the process of the present invention to effectively provide in an economical manner based on a thermal treatment under mild conditions purified carbon blacks having a significantly reduced content of PAH contaminants, specifically oxidized PAHs, while keeping changes to the physicochemical properties of the carbon black low and provide equivalent or even improved performance as a pigment in applications such as in coating formulations.

[0114] The purified carbon blacks obtainable according to the present invention can thus provide ready-to-use substitutes to the corresponding pristine carbon blacks from which they can be derived in various applications, particularly those demanding for a reduced content of PAH contaminants.

Claims

CLAIMS1 . A process for producing a purified carbon black with a reduced content of oxidized polycyclic aromatic hydrocarbons, such as oxy-polycyclic aromatic hydrocarbons (oxy-PAHs) and / or nitro-polycyclic aromatic hydrocarbons (nitro- PAHs), the process comprising:(a) providing a carbon black comprising an initial content of oxidized polycyclic aromatic hydrocarbons, and(b) subjecting the provided carbon black to a thermal treatment comprising heat treating the carbon black at a temperature of less than 280°C in a vacuum or inert gas atmosphere to remove at least a portion of the oxidized polycyclic aromatic hydrocarbons from the carbon black to thereby obtain a purified carbon black with a lower content of oxidized polycyclic aromatic hydrocarbons than the initial content of oxidized polycyclic aromatic hydrocarbons.

2. The process according to claim 1 , wherein providing the carbon black comprising an initial content of oxidized polycyclic aromatic hydrocarbons comprises manufacturing carbon black by a carbon black production process and optionally subjecting the produced carbon black to an oxidative aftertreatment, wherein the oxidative aftertreatment preferably utilizes a gaseous oxidizing agent such as NOx, air, oxygen, ozone, or a mixture or combination thereof.

3. The process according to any one of claims 1 or 2, wherein the carbon black comprising an initial content of oxidized polycyclic aromatic hydrocarbons comprises an oxidized carbon black, wherein the carbon black is preferably a gas black or furnace black.

4. The process according to any one of the preceding claims, wherein the content of oxidized polycyclic aromatic hydrocarbons is determined as the oxy-PAH6 content and / or the nitro-PAH10 content, wherein the carbon black comprising an initial content of oxidized polycyclic aromatic hydrocarbons may for example have- an initial oxy-PAH6 content of 1 ppm or more, such as 2 ppm or more, or 5 ppm or more, or 10 ppm or more, or 20 ppm or more, or 40 ppm ormore, or 60 ppm or more, or 80 ppm or more, or 100 ppm or more; and / or- an initial nitro-PAH10 content of 1 ppm or more, such as 2 ppm or more, or 5 ppm or more, or 10 ppm or more, or 20 ppm or more, or 50 ppm or more, or 80 ppm or more, or 100 ppm or more, or 200 ppm or more, or 300 ppm or more.

5. The process according to any one of the preceding claims, wherein the carbon black comprising the initial content of oxidized polycyclic aromatic hydrocarbons provided in step (a) further has one or more than one or all of the following: a. a pH as determined according to ASTM D1512-21 (Test Method B - Sonic Slurry) of 10 or less, such as 5 or less, for example in a range from 2 to 5; b. a volatile content (in wt.%), determined by heating to 950 °C according to DIN 53552:2023-07 of greater than 0.8 wt.%, such as in a range from 0.8 to 25 wt.%, for example from 2 to 15 wt.%; c. an ash content determined according to ASTM D1506-15 of 3 wt.% or less, such as 0.5 wt.% or less, or 0.2 wt.% or less or 0.1 wt.% or less; d. a moisture content determined according to ASTM D1509-18 of 10 wt.% or less, such as in a range from 0.1 to 5 wt.%; e. a carbon content as determined by elemental analysis of 80 wt.% or more, 85 wt.% or more, 90 wt.% or more, or 95 wt.% or more, or 97 wt.% or more, or 98 wt.% or more; f. an oxygen content as determined by elemental analysis of 20 wt.% or less, such as 15 wt.% or less, or 10 wt.% or less, or 7 wt.% or less, or 5 wt.% or less; g. a BET surface area, determined according to ASTM D6556-21 , in a range from 30 to 1 ,000 m2 / g, such as in a range from 50 to 700 m2 / g, or from 100 to 300 m2 / g, h. a statistical thickness surface area (STSA), determined according to ASTM D6556-21 , in a range from 20 to 500 m2 / g, such as in a range from 50 to 400 m2 / g, or from 90 to 250 m2 / g.

6. The process according to any one of the preceding claims, wherein the carbon black is heat treated in the vacuum or inert gas atmosphere at a temperature in a range from 100°C to less than 280°C, such as at a temperature in a range from 150°C to 270°C, preferably in a range from 180°C to 260°C, or in a range from 200°C to 250°C.

7. The process according to any one of the preceding claims, wherein the vacuum or inert gas atmosphere comprises an inert gas such as nitrogen, helium, argon, carbon dioxide, steam or mixtures or combinations thereof and / or has a pressure of 1 ,500 hPa or less, such as in a range from 1 hPa to 1 ,500 hPa, for example from 1 to 100 hPa, and / or wherein the thermal treatment of the carbon black in step (b) comprises subjecting the treated carbon black to a continuous gas flow, wherein the average flow rate of the gas is for example in a range from 1 NL / h to 10,000 NL / h, such as from 50 to 300 NL / h, and / or the average flow rate of the gas (in NL / h) per unit volume of the treatment chamber of the device used for the heat treatment (in L) is for example in a range from 5 NLTr1L’1to 5,000 NL h’1L’1.

8. The process according to any one of the preceding claims, wherein the carbon black is heat treated at a temperature of less than 280°C in the vacuum or inert gas atmosphere in step (b) for a time of 30 minutes or more, such as 1 hour or more, or 2 hours or more, or 4 hours or more, and / or of up to 24 hours, such as 12 hours or less, or 8 hours or less, or 6 hours or less.

9. The process according to any one of the preceding claims, wherein the thermal treatment of the carbon black in step (b) is conducted in a convective oven, electric oven, infrared oven, gas fired oven, vacuum oven, conveyor oven, batch oven, fixed bed reactor, fluidized bed reactor, rotary kiln, Auger reactor or a combination of any of the foregoing, preferably in a fluidized bed reactor, and / or wherein the process is conducted as a continuous process, as a semi-batch or as a batch process.

10. The process according to any one of the preceding claims, wherein the process does not involve treating the carbon black with a medium that is in a supercritical state.11 . The process according to any one of the preceding claims, wherein heat treating the carbon black at a temperature of less than 280°C in the inert or vacuum atmosphere in step (b) comprises removing at least 50 wt.%, such as 70 wt.% or more, or 80 wt.% or more, or 90 wt.% or more, or 95 wt.% or more, or 97 wt.% or more, or 98 wt.% or more, or 99 wt.% or more, of the initial content of oxidized polycyclic aromatic hydrocarbons, such as of the initial oxy-PAH6 content and / or of the initial nitro-PAH10 content and / or specifically of the initial content of 1 ,6-dinitropyrene, from the carbon black, and / or wherein the obtained purified carbon black has:- a content of oxidized polycyclic aromatic hydrocarbons, such as oxy-PAH6 content and / or nitro-PAH10 content, which corresponds to 50 % or less, such as 30 % or less, or 20 % or less, or 10 % or less, or 5 %, or 3 % or less, or 2 % or less, or 1 % or less of the initial content of oxidized polycyclic aromatic hydrocarbons, such as of the initial oxy-PAH6 content and / or of the initial nitro-PAH10 content; and / or- a content of 1 ,6-dinitropyrene, which corresponds to 20 % or less, such as 10 % or less, or 5 % or less, or 3 % or less, or 2 %, or 1 % or less, or 0.5 % or less, or 0.3 % or less of the initial content of 1 ,6-dinitropyrene; and / or- a BET surface area and / or statistical thickness surface area (STSA), which differs by no more than 20% from the respective value determined for the carbon black provided in step (a).

12. A purified carbon black obtainable by the process according to any one of preceding claims 1 to 1 1 , the purified carbon black preferably having a nitro- PAH10 content of less than 1 ppm and / or a content of 1 ,6-dinitropyrene of less than 0.1 ppm and / or an oxy-PAH6 content of less than 10 ppm.

13. A composition comprising a purified carbon black according to claim 12, wherein the composition comprises for example a plastic or rubber composition, a paint, ink or coating composition or electrode composition.

14. An article of manufacture made from a purified carbon black according to claim 12 or from a composition according to claim 13.

15. Use of a purified carbon black according to claim 12 as pigment, reinforcing filler or conductive agent, for example for the manufacture of plastic or rubber articles, paints, inks, coatings, electrodes or energy storage devices.

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