Method for extracting and producing carbon black with reduced content of oxygen-containing polycyclic aromatic hydrocarbon (oxygen-containing PAH) by using supercritical fluid

Abstract

The present invention provides a method for producing a purified carbon black having a reduced oxygen-containing polycyclic aromatic hydrocarbon content, the method comprising: (a) providing a carbon black comprising an initial content of oxygen-containing polycyclic aromatic hydrocarbons of 1 ppm or more, (b) treating the carbon black comprising the initial content of oxygen-containing polycyclic aromatic hydrocarbons with an extractant comprising carbon dioxide in a supercritical state, and (c) removing the extractant comprising the extracted oxygen-containing polycyclic aromatic hydrocarbons from the carbon black to obtain a purified carbon black having an oxygen-containing polycyclic aromatic hydrocarbon content lower than the initial oxygen-containing polycyclic aromatic hydrocarbon content, and (c) removing the extractant comprising the extracted oxygen-containing polycyclic aromatic hydrocarbons from the carbon black to obtain a purified carbon black having an oxygen-containing polycyclic aromatic hydrocarbon content lower than the initial oxygen-containing polycyclic aromatic hydrocarbon content. The invention also provides carbon black obtained by the production method and articles made therefrom.

Description

Technical Field

[0001] The present invention relates to a method for purifying carbon black, more specifically to the production of carbon black having a reduced content of oxygenated polycyclic aromatic hydrocarbons and optionally other polycyclic aromatic hydrocarbon impurities by supercritical fluid extraction (SFE), in particular using an extractant comprising carbon dioxide in a supercritical state. The invention also relates to purified carbon black obtainable by the method, as well as to the application and use of such purified carbon black. Background Art

[0002] Carbon black is widely used in industry as an additive for a variety of different applications, for example as a colorant or pigment, reinforcing filler or conductive agent in the manufacture of paints, coatings, inks, electrodes or plastic or rubber products. Depending on the respective application, carbon blacks with different properties are required, which can be controlled by the carbon black production process and possible post-treatment. Carbon black is produced by controlling the thermal or thermo-oxidative decomposition of hydrocarbon precursors such as petroleum, natural gas or acetylene. Established carbon black production processes include furnace black process, gas black process (originally developed by Degussa), channel black process, lamp black process, acetylene process or thermal black process.

[0003] Depending on the carbon black production process, the hydrocarbon precursor substances used and the process conditions, impurities such as metals, sulfur and organic compounds may contaminate the resulting carbon black. These impurities, especially when present in relatively high amounts, may adversely affect the properties of the carbon black and are therefore undesirable in certain applications.

[0004] Carbon black may contain impurities of organic compounds with polycyclic aromatic structures, which are generally referred to as polycyclic aromatic hydrocarbons (PAHs). PAHs are considered to be harmful to health and the environment, as discussed, for example, 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 in carbon black is subject to increasingly stringent customer demands and official regulations in the manufacture of products such as food or beverage contact situations, pharmaceuticals, cosmetics or children's toys and products. For example, the American Food and Drug Administration (FDA) has limited the total PAH content of high-purity furnace black in products in contact with food to 0.5 ppm (see US Code of Federal Regulations (CFR) 21 Sec. 178.3297), where the PAH content is defined as the sum of 22 PAH compounds.

[0005] Similarly, oxidized derivatives of PAH compounds may contaminate carbon black. Polycyclic aromatic hydrocarbon derivatives, which are composed not only of carbon and hydrogen but also contain oxygen in addition, are generally referred to as oxidized PAHs or oxygenated PAHs. Oxygenated PAHs include, for example, polycyclic aromatic ketones, polycyclic aromatic quinones, hydroxylated PAHs, polycyclic aromatic aldehydes, polycyclic aromatic carboxylic acids and anhydrides, and polycyclic aromatic lactones. For example, oxygenated PAHs are often present in carbon black oxidized with certain oxidants such as ozone, because they may be formed during the oxidation treatment of carbon black. Oxygenated PAH compounds are also considered to be harmful to health, especially due to their mutagenicity (see, for example, A. Clergé, J. LeGoff, C. Lopez, J. Ledauphin, R. Delépée (2019): "Oxy-PAHs: Occurrence in the environment and potential genotoxic / mutagenic risk assessment for human health", Critical Reviews in Toxicology, DOI: 10.1080 / 10408444.2019.1605333). Therefore, it is desirable to reduce the content of oxygenated PAHs in carbon black.

[0006] It is therefore an object of the present invention to provide a process for the efficient removal of oxygenated PAHs (and if possible PAHs) from carbon black and to provide carbon black having a reduced content of such impurities, ideally in an economical and environmentally friendly manner, without adversely affecting other properties of the carbon black and / or without using hazardous or expensive substances. Summary of the invention

[0007] This object and other advantages described herein are surprisingly achieved by providing a method as defined in the attached independent claim 1 .

[0008] Therefore, the present invention relates to a method for producing purified carbon black having a reduced content of oxygenated polycyclic aromatic hydrocarbons (oxygenated PAHs). The method comprises:

[0009] (a) providing carbon black containing an initial content of oxygen-containing polycyclic aromatic hydrocarbons of 1 ppm or more,

[0010] (b) treating carbon black containing an initial content of oxygen-containing polycyclic aromatic hydrocarbons with an extractant comprising carbon dioxide in a supercritical state to extract at least a portion of the oxygen-containing polycyclic aromatic hydrocarbons from the carbon black, and

[0011] (c) removing the extractant containing the extracted oxygen-containing polycyclic aromatic hydrocarbons from the carbon black to obtain a purified carbon black having an oxygen-containing polycyclic aromatic hydrocarbon content lower than that of the initial oxygen-containing polycyclic aromatic hydrocarbons.

[0012] The present invention also relates to a purified carbon black obtained by the process of the present invention as described above and in more detail below.

[0013] The invention also relates to the use of such purified carbon black as a pigment, reinforcing filler or conductive agent, for example, for the manufacture of plastic or rubber products, paints, inks, coatings, electrodes or energy storage devices.

[0014] In addition, the present invention relates to the use of supercritical carbon dioxide for removing oxygen-containing polycyclic aromatic hydrocarbons in carbon black.

[0015] The method of the present invention involves treating carbon black with an extractant comprising supercritical carbon dioxide, which has multiple advantages. Therefore, it is flexible and can be applied to various carbon blacks regardless of their production methods. The method of the present invention can effectively purify carbon black and obtain carbon black with low oxygenated PAH content and optional PAH content, and does not substantially adversely affect other properties of carbon black or use expensive, harmful or difficult to remove purification agents from carbon black products. The use of a supercritical extractant advantageously combines a density similar to that of a liquid and a solute diffusivity and viscosity closer to that of a gas, thereby achieving a high mass transfer rate and rapid and efficient extraction of oxygenated PAH and PAH from carbon black. In addition, the solvent strength can be changed herein by simply changing the applied pressure and / or temperature or adding a suitable modifier. In addition, carbon dioxide has the advantages of being non-toxic, non-flammable and inexpensive. The critical temperature of carbon dioxide is as low as 304.2K (31°C) and the critical pressure is 72.8atm (7,380kPa). Thus, extraction with an extractant comprising carbon dioxide can be carried out under relatively mild conditions, thereby reducing the tendency of the carbon black to undergo undesirable changes due to purification treatments. Furthermore, the supercritical carbon dioxide can be easily separated from the carbon black, for example by pressure release, resulting in evaporation of the carbon dioxide. Thus, no dedicated drying or solvent removal steps are required after extraction.

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

[0017] As used herein, the term "comprising" should be understood as open-ended and does not exclude the presence of additional undescribed or unrecorded elements, materials, ingredients, or method steps, etc. The terms "including," "containing," and similar terms should be understood as synonymous with "comprising." As used herein, the term "consisting of" should be understood to exclude the presence of any unspecified elements, ingredients, or method steps, etc.

[0018] As used herein, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

[0019] Unless otherwise indicated, the numerical parameters and ranges listed in the following specification and appended claims are approximate values. Although the numerical ranges and parameters setting forth the broad scope of the invention are approximate values, the numerical values ​​listed in the specific examples are reported as accurately as possible. However, any numerical value necessarily contains errors caused by the standard deviation in its corresponding measurement.

[0020] In addition, it should be understood that any numerical range described herein is intended to include all subranges contained therein. For example, a range of "1 to 10" is intended to include any and all subranges between the stated minimum value of 1 and the stated maximum value of 10, i.e., all subranges starting 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, such as 1 to 6.3, or 5.5 to 10, or 2.7 to 6.1.

[0021] Unless otherwise specified, all parts, amounts, concentrations, etc. mentioned herein are by weight.

[0022] As described above, the present invention relates to a method for producing purified carbon black having a reduced content of oxygen-containing polycyclic aromatic hydrocarbons. The method comprises: (a) providing carbon black containing an initial content of oxygen-containing polycyclic aromatic hydrocarbons of 1 ppm or more, (b) treating the carbon black containing the initial content of oxygen-containing polycyclic aromatic hydrocarbons with an extractant containing carbon dioxide in a supercritical state to extract at least a portion of the oxygen-containing polycyclic aromatic hydrocarbons from the carbon black, and (c) removing the extractant containing the extracted oxygen-containing polycyclic aromatic hydrocarbons from the carbon black to obtain a purified carbon black having an oxygen-containing polycyclic aromatic hydrocarbon content lower than the initial oxygen-containing polycyclic aromatic hydrocarbon content.

[0023] The term "polycyclic aromatic hydrocarbons (PAH)" as used herein refers to an organic compound having a skeleton of two or more (e.g., two to seven) fused aromatic rings, i.e., a polycyclic aromatic structure. Hydrocarbon groups (e.g., alkyl groups) may optionally be bonded to the skeleton of the fused aromatic rings. The "polycyclic aromatic hydrocarbons (PAH)" used herein are unsubstituted compounds having such a polycyclic aromatic structure, i.e., corresponding compounds consisting only of carbon and hydrogen atoms. In contrast, the "oxy-polycyclic aromatic hydrocarbons (oxy-polycyclic aromatic hydrocarbons)" used herein, also referred to as "oxy-PAHs", refer to oxygen-containing derivatives of PAHs, which are not only composed of carbon and hydrogen, but also contain oxygen. In other words, oxygen-containing PAHs represent organic compounds whose skeletons consist of two or more (e.g., two to seven) fused aromatic rings, and are composed of carbon, hydrogen, and oxygen atoms. For example, oxygen-containing PAHs can be derived from unsubstituted polycyclic aromatic hydrocarbons by replacing one or more hydrogen atoms with oxygen-containing functional groups (e.g., carboxyl, aldehyde (aldo), hydroxyl, or keto). Oxygenated 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. According to the present invention, the oxygenated PAH may contain one or more keto groups, i.e., the oxygenated PAH may be a polycyclic aromatic ketone.

[0024] For the purposes of the present invention, the content of oxygenated polycyclic aromatic hydrocarbons (oxygenated PAHs) or polycyclic aromatic hydrocarbons (PAHs) in carbon black may more specifically refer to the content of one or more specific oxygenated-PAH compounds or PAH compound (groups), such as 9,10-phenanthrenequinone, oxygenated-PAH6 or PAH22 group (group), as defined below. Thus, the oxygenated polycyclic aromatic hydrocarbon content of carbon black described herein may specifically refer to the content of compounds of the oxygenated PAH6 group (also referred to as oxygenated PAH6 content) or the content of 9,10-phenanthrenequinone. Likewise, the polycyclic aromatic hydrocarbon (PAH) content of carbon black described herein may specifically refer to the content of compounds of the PAH22 group (also referred to as PAH22 content).

[0025] The term "PAH 22" as used herein refers to a method developed by the U.S. Food and Drug Administration (FDA) in accordance with U.S. Code of Federal Regulations (CFR) 21 Sec. 178.3297 and Cabot Corp. on July 8, 1994 entitled "Determination of PAH content of Carbon Black". Black), among which are mentioned: 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), benzo(a)anthracene (CAS No. 56-55-3), cyclopenta(c,d)pyrene (CAS No. 27208-37-3), (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), anthracene (CAS No. 191-26-4) and coronene (CAS No. 191-07-1). Therefore, the PAH22 content is the total amount of these 22 compounds determined based on the total weight of the carbon black sample. The PAH 22 content can be determined by using GC-MS analysis, calibrated with the deuterated form of the PAH 22 compound, on a toluene extract obtained from a Soxhlet extraction of a carbon black sample, following the method of the aforementioned publication entitled "Determination of the PAH Content in Carbon Black" dated July 8, 1994, as described in the Examples.

[0026] As used herein, "oxygenated PAH6" refers to the group of the following six oxygenated PAH compounds: 9,10-phenanthrenequinone (CAS No. 84-11-7), 6H-benzo[cd]pyrene-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-cyclopenten[def]phenanthrene-4-one (CAS No. 5737-13-3). Therefore, the oxygenated PAH6 content is determined by the sum of the amounts of these six compounds based on the total weight of the carbon black sample. The content of oxygenated PAH6 in the carbon black sample can be determined similarly to the determination of the PAH22 content, i.e., by analyzing the toluene extract obtained after Soxhlet extraction of the carbon black sample using GC-MS, calibrated with the deuterated form of the oxygenated PAH6 compounds. Alternatively, the content of oxygen-containing polycyclic aromatic hydrocarbons in carbon black can be determined based on the content of 9,10-phenanthrenequinone in carbon black. The content of 9,10-phenanthrenequinone can be determined as described in the examples.

[0027] According to the present invention, a carbon black containing an initial content of more than 1 ppm of oxygen-containing polycyclic aromatic hydrocarbons is provided as a starting material to be purified. For the sake of clarity, as known to those skilled in the art, "carbon black" is different from "soot" or "black carbon". Soot or black carbon is used to represent the generally unwanted carbonaceous byproducts produced by the incomplete combustion of carbonaceous materials (such as oil, fuel, diesel or gasoline, coal, paper or waste). Soot and black carbon contain a large amount of organic and inorganic impurities, usually containing less than 60% elemental carbon based on the total mass, and are composed of relatively coarse particles with almost no clear structure or order. In contrast, carbon black is deliberately produced by incomplete combustion or thermal decomposition of gaseous or liquid hydrocarbons under controlled conditions, and usually has a higher carbon content, such as more than 80% by weight based on the total mass, and is composed of particles with a clear structure and high order (including a graphene-like arrangement of carbon atoms) and a high surface area-to-volume ratio.

[0028] In the method of the present invention, the initial carbon black provided as the starting material to be purified can in principle be based on any method for producing carbon black. There are different industrial processes for the production of carbon black, and include, for example, furnace processes, gas black processes, acetylene black processes, thermal black processes or lamp black processes, such as described in J.-B.Donnet et al., "Carbon Black: Science and Technology" 2nd edition. Therefore, the carbon black containing the initial content of oxygen-containing polycyclic aromatic hydrocarbons used in the practice of the present invention can, for example, contain or be furnace black, thermal black, lamp black, channel black, gas black, acetylene black, recycled black or any combination of the foregoing. Recycled black is a carbon black obtained from waste carbon black-containing products (such as waste tires) and can be obtained by a recycling process, which generally involves two steps: a pyrolysis step for decomposing organic components such as rubber or plastics and a demineralization step for dissolving inorganic additives or impurities. Various carbon blacks with different properties that can be used in the present invention are commercially available from carbon black manufacturers such as Cabot Corporation, Mitsubishi Chemical Company, Tokai Carbon, Denka, Birla Carbon, or Orion Engineered Carbons GmbH. Non-limiting examples include carbon blacks produced by ORION Engineered Carbons GmbH and COLOUR BLACK, SPECIAL BLACK or Carbon black sold under the brand name.

[0029] The carbon black used as a starting material in the method of the present invention may or may not be subjected to an optional post-treatment. Generally, the carbon black containing an initial content of oxygen-containing polycyclic aromatic hydrocarbons used in the practice of the present invention includes carbon black that has been subjected to an oxidation treatment. The oxidized carbon black, also known as "oxidized carbon black", contains oxygen-containing functional groups, in particular, on the surface of the carbon black particles. Oxygen-containing functional groups can be exemplified, but are not limited to alcohol, quinone, carboxyl, phenol, lactol, lactone, anhydride, chinone, peroxide, ether and ketone groups. The oxidation treatment can be achieved, for example, by treatment with an oxidant, the oxidant including oxygen, ozone, peroxides such as hydrogen peroxide, persulfates such as sodium persulfate and potassium persulfate, hypohalites such as sodium hypochlorite, and transition metal-containing oxidants such as permanganate, osmium tetroxide, chromium oxide, ammonium cerium nitrate; and mixtures thereof. Specifically, the carbon black containing an initial content of oxygen-containing polycyclic aromatic hydrocarbons used in the practice of the present invention can be ozone-oxidized carbon black. Oxidized carbon black generally has a significant oxygen content. For example, the oxygen content of the oxidized carbon black that can be used according to the present invention can be 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 0.5 wt % to 20 wt %, or 1 wt % to 15 wt %, or 2 wt % to 10 wt %, or 5 wt % to 15 wt % oxygen based on the total weight of the oxidized carbon black material. The oxidized carbon black used as the starting material according to the present invention can have an oxygen content within the range between any of the above values.

[0030] The carbon black to be purified in the method of the present invention has an initial oxygenated PAH content of 1 ppm or more. For example, the carbon black to be purified in the method of the present invention may have an initial oxygenated PAH6 content of 1 ppm or more. The carbon black may, for example, have an initial oxygenated polycyclic aromatic hydrocarbon content (such as initial oxygenated PAH6 content) of 2 ppm or more, or 3 ppm or more, or 4 ppm or more, or 5 ppm or more, or 10 ppm or more, such as 20 ppm or more, or 30 ppm or more, or 40 ppm or more, or 50 ppm or more, or 80 ppm or more, or 100 ppm or more, or 150 ppm or more, or 200 ppm or more, or 250 ppm or more, or 300 ppm or more. For example, the carbon black may, for example, have an initial oxygenated PAH content, such as an initial oxygenated PAH6 content of 5,000 ppm or less, such as 2,000 ppm or less, or 1,000 ppm or less, or 800 ppm or less, or 600 ppm or less, or 500 ppm or less. In the method of the present invention, the carbon black to be purified may have an initial oxygenated PAH content, such as an initial oxygenated PAH6 content, ranging between any of the values, such as in the range of 1 ppm to 1,000 ppm, or in the range of 5 ppm to 500 ppm, or in the range of 10 ppm to 100 ppm. The carbon black to be purified in the method of the present invention may have an initial 9,10-phenanthrenequinone 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. The carbon black may, for example, have an initial 9,10-phenanthrenequinone content of 500 ppm or less, such as 300 ppm or less, or 100 ppm or less, or 80 ppm or less, or 60 ppm or less, or 50 ppm or less. The initial 9,10-phenanthrenequinone content of the carbon black to be purified in the method of the present invention can be within a range between any of the stated values, for example, within a range of 1 ppm to 500 ppm, or within a range of 2 ppm to 300 ppm, or within a range of 5 ppm to 80 ppm.

[0031] The carbon black provided for purification according to the method of the present invention may also have an initial content of polycyclic aromatic hydrocarbons (PAH). The initial content of PAHs may vary greatly, depending on the type of carbon black used and its production method. For example, the initial content of PAHs may vary from as low as a few ppm to 10,000 ppm or even more. For example, the initial content of PAHs of the carbon black to be purified in the method of the present invention may be above 10 ppm, or above 20 ppm, or above 50 ppm, such as above 100 ppm, above 250 ppm, above 500 ppm, above 800 ppm, or above 1,000 ppm. The initial content of PAHs of the carbon black may be below 10,000 ppm, such as below 5,000 ppm, or below 3,000 ppm, or below 2,000 ppm, or below 1,000 ppm, or below 800 ppm, or below 500 ppm, or below 400 ppm, or below 300 ppm, or below 200 ppm, or below 100 ppm. The initial content of carbon black polycyclic aromatic hydrocarbons to be purified in the method of the present invention can be within the range between any of the stated values, for example, within the range of 10 ppm to 10,000 ppm, or within the range of 50 ppm to 5,000 ppm, or within the range of 200 ppm to 800 ppm.

[0032] For example, the initial PAH22 content of the carbon black to be purified in the method of the present invention may be 10 ppm or more, such as 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 250 ppm or more, or 500 ppm or more, or 800 ppm or more, or 1,000 ppm or more. The initial PAH22 content of the carbon black may be 10,000 ppm or less, such as 5,000 ppm or less, or 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 50 ppm or less. The initial PAH22 content of the carbon black to be purified in the method of the present invention can be within a range between any of the stated values, for example within a range of 10 ppm to 10,000 ppm, or within a range of 500 ppm to 3,000 ppm, or within a range of 10 ppm to 200 ppm.

[0033] The carbon black may have any combination of an initial PAH content (eg, a PAH 22 content) and an initial oxygenated PAH content (eg, an oxygenated PAH 6 or 9,10-phenanthrenequinone content as described above).

[0034] The carbon black comprising an initial content of oxygenated polycyclic aromatic hydrocarbons and optionally PAH provided in step (a) of the process may also be characterized by one or more or all of the following properties.

[0035] Thus, the carbon black provided in step (a) of the method comprising an initial content of oxygenated polycyclic aromatic hydrocarbons and optionally PAHs can be characterized by its ash content. For example, the ash content of the carbon black can be less than 20% by weight, such as less than 15% by weight, or less than 10% by weight, or less than 5% by weight, or less than 3% by weight, or less than 1% by weight, or less than 0.5% by weight, or less than 0.1% by weight, based on the total weight of the carbon black. The ash content of the carbon black can, for example, be greater than 0.001% by weight, such as greater than 0.005% by weight, or greater than 0.01% by weight, or greater than 0.05% by weight, or greater than 0.1% by weight, or greater than 0.2% by weight, or greater than 0.3% by weight, or greater than 0.5% by weight, or greater than 1% by weight, or greater than 2% by weight, or greater than 3% by weight, based on the total weight of the carbon black. In the method of the present invention, the ash content of the carbon black to be purified can be within the range between any of the above values, for example, within the range of 0.001 wt % to 20 wt %, or within the range of 0.005 wt % to 5 wt %, or within the range of 0.1 to 1 wt %. The ash content of the carbon black can be determined according to ASTM D1506-15.

[0036] In addition, the carbon black containing the initial content of oxygen-containing polycyclic aromatic hydrocarbons and optional PAH can be characterized by the volatile content. The volatile content can be determined by heating to 950° C. according to DIN 53552:1977. For example, the volatile content of the carbon black can be less than 20% by weight, such as less than 15% by weight, or less than 10% by weight, or less than 5% by weight, or less than 3% by weight, or less than 1% by weight, based on the total weight of the carbon black. For example, the volatile content of the carbon black can be more than 0.1% by weight, such as more than 0.2% by weight, or more than 0.3% by weight, or more than 0.5% by weight, or more than 1% by weight, or more than 2% by weight, or more than 3% by weight, based on the total weight of the carbon black. The volatile content of the carbon black to be purified in the method of the present invention can be in the range between any of the values, such as in the range of 0.1% by weight to 20% by weight, or in the range of 0.2% by weight to 15% by weight, or in the range of 1 to 10% by weight.

[0037] In addition, the carbon black containing the initial content of oxygenated polycyclic aromatic hydrocarbons and optional PAHs can be characterized by its moisture content. For example, the moisture content of the carbon black can be less than 15% by weight, such as less than 10% by weight, or less than 5% by weight, or less than 3% by weight, or less than 1% by weight, based on the total weight of the carbon black. For example, the moisture content of the carbon black can be more than 0.1% by weight, such as more than 0.2% by weight, or more than 0.3% by weight, or more than 0.5% by weight, or more than 1% by weight, based on the total weight of the carbon black. The moisture content of the carbon black to be purified in the method of the present invention can be in the range between any of the values, such as in the range of 0.1% by weight to 15% by weight, or 0.2% by weight to 10% by weight, or 0.3 to 3% by weight. The moisture content of the carbon black can be determined according to ASTM D1509-18.

[0038] The carbon black containing the initial content of oxygen-containing polycyclic aromatic hydrocarbons and optional PAHs can be further characterized by its carbon content. For example, the carbon content of the carbon black can be more than 80% by weight, such as more than 85% by weight, or more than 90% by weight, or more than 95% by weight, or more than 97% by weight, or more than 98% by weight, based on the total weight of the carbon black. The carbon content of the carbon black can be, for example, up to 99.9% by weight, such as less than 99.5% by weight, or less than 99% by weight, or less than 98% by weight, or less than 97% by weight, or less than 95% by weight. In the method of the present invention, the carbon content of the carbon black to be purified can be in the range between any of the stated values, such as in the range of 80% to 99.9% by weight, or in the range of 80% to 97% by weight, or in the range of 85 to 95% by weight. The carbon content can be determined by elemental analysis.

[0039] The carbon black containing the initial content of oxygenated polycyclic aromatic hydrocarbons and optionally PAH can be further characterized by the specific surface area. For example, the BET specific surface area of ​​the carbon black can be 10 m 2 / g or more, for example 20m 2 / g or above, or 30m 2 / g or above, or 50m 2 / g or above, or 80m 2 / g or above, or 100m 2 / g or above, or 150m 2 / g or above, or 200m 2 / g or above, or 300m 2 / g or above, or 500m 2 / g or more, or 1,000m 2 The BET specific surface area of ​​carbon black can be, for example, 2,000 m 2 / g or less, for example, 1,500m 2 / g or less, or 1,000m2 / g or less, or 800m 2 / g or less, or 500m 2 / g or less, or 300m 2 / g or less, or 200m 2 In the method of the present invention, the BET specific surface area of ​​the carbon black to be purified may be within the range between any of the above values, for example, within the range of 10 to 2,000 m 2 / g, or in the range of 30 to 500m 2 / g, or in the range of 50 to 300 m 2 The BET specific surface area can be measured by nitrogen adsorption according to ASTM D6556-19a.

[0040] In the method of the present invention, a single carbon black or a mixture of two or more different carbon blacks (which may be separately as described above) may be used as the carbon black substance to be purified.

[0041] As described above, in the method according to the present invention, the provided carbon black having an initial content of oxygenated polycyclic aromatic hydrocarbons and optionally PAHs is treated with an extractant to extract at least a portion of the oxygenated polycyclic aromatic hydrocarbons and optionally at least a portion of the polycyclic aromatic hydrocarbons from the carbon black. Herein, the extractant includes carbon dioxide in a supercritical state. "Supercritical state" means that the extractant is in a state of a supercritical fluid. Supercritical fluids are obtained at a temperature and pressure above the critical temperature and pressure (critical point), i.e., within the supercritical region of the corresponding phase diagram. The critical point represents the highest temperature and pressure at which the corresponding substance exists in equilibrium in the gaseous and liquid states. Supercritical fluids exhibit intermediate properties between gases and liquids. For example, the use of an extractant in a supercritical state can advantageously combine a liquid-like density with a gas-like diffusivity and viscosity, thereby promoting high mass transfer rates and rapid and efficient extraction of oxygenated PAHs and PAHs from carbon black. Specifically, carbon dioxide has a relatively low critical temperature of 304.2K (31°C) and a relatively low critical pressure of about 74 bar (7,380 kPa). Thus, extraction with an extractant comprising carbon dioxide can be carried out under relatively mild conditions, thereby reducing the tendency of the carbon black to undergo undesirable changes due to purification treatments. In addition, supercritical carbon dioxide can be easily separated from the carbon black, for example by pressure release, resulting in evaporation of the carbon dioxide. Therefore, no dedicated drying or solvent removal steps are required after extraction. In addition, carbon dioxide has the advantages of being non-toxic, non-flammable and inexpensive.

[0042] The extractant used in the present invention can comprise at least 50% by weight of carbon dioxide, such as at least 70% by weight of carbon dioxide, such as at least 80% by weight of carbon dioxide, or at least 90% by weight of carbon dioxide, or at least 95% by weight of carbon dioxide, or at least 99% by weight of carbon dioxide, or at least 99.5% by weight of carbon dioxide, for example, based on the gross weight of the extractant. In a preferred variant, the extractant can be composed of supercritical carbon dioxide, that is, substantially free of any other ingredients except carbon dioxide. "Substantially free of" means that the extractant contains substances other than carbon dioxide, if present, only as a small amount of impurities, based on the gross weight of the extractant, usually not more than 0.2% by weight, such as below 0.1% by weight or below 0.005% by weight. Alternatively, the extractant may also comprise one or more auxiliary agents in addition to carbon dioxide. For example, such auxiliary agents may be used to control or change the chemical and / or physical properties of the extractant, such as the viscosity, polarity or solvent strength of the extractant. Useful auxiliary agents include, for example, but not limited to, air, oxygen, nitrogen, methane, water and organic solvents such as methanol, toluene and methylene chloride or any combination thereof. The amount of the auxiliary agent in the extraction agent can be determined according to the corresponding needs. For example, the total amount of the one or more auxiliary agents used can be less than 50 % by weight based on the total weight of the extraction agent, for example, less than 30 % by weight, less than 20 % by weight, or less than 10 % by weight, or less than 5 % by weight, or less than 1 % by weight, or less than 0.5 % by weight. In the process of processing carbon black in step (b), the amount of the auxiliary agent in the extraction agent can also change over time. However, preferably, the extraction agent used in the practice of the present invention does not include any auxiliary agent.

[0043] According to the method disclosed herein, carbon black containing an initial content of oxygenated polycyclic aromatic hydrocarbons and optionally PAHs is treated with an extractant containing carbon dioxide in a supercritical state to extract at least a portion of the oxygenated polycyclic aromatic hydrocarbons and optionally at least a portion of the polycyclic aromatic hydrocarbons from the carbon black. Therefore, the treatment with the extractant is carried out under the condition that the extractant is in a supercritical state. Therefore, the carbon black is treated with the extractant at a temperature and pressure higher than the critical temperature of the extractant and higher than the critical pressure of the extractant, respectively. The critical temperature and critical pressure can be derived from the phase diagram of the corresponding extractant, corresponding to the temperature and pressure of the critical point. The treatment of carbon black using carbon dioxide as an extractant can be carried out, for example, at any temperature equal to or higher than the critical temperature of carbon dioxide (31°C) and at a pressure equal to or higher than the critical pressure of carbon dioxide (73.8 bar). According to the present invention, the treatment of carbon black with an extractant can be carried out, for example, at a temperature above 31°C, or above 50°C, or above 75°C, for example, above 100°C, or above 150°C, or above 200°C, or above 250°C. The treatment can be carried out, for example, at a temperature below 500°C, for example, below 400°C, or below 350°C, or below 300°C. The treatment of carbon black with an extractant can be carried out at a temperature range between any of the values, for example, at 75°C to 400°C, preferably at a temperature in the range of 100°C to 350°C, for example, at a temperature in the range of 100°C to 300°C. In addition, the treatment of carbon black with an extractant can be carried out at a pressure of, for example, above 73.8 bar, for example, above 75 bar, or above 100 bar, or above 120 bar, or above 150 bar, or above 200 bar. The treatment can be carried out, for example, at a pressure of below 700 bar, for example, below 500 bar, or below 400 bar, or below 300 bar, or below 250 bar. The treatment of carbon black with an extractant can be carried out in a pressure range between any of the values, for example, at a pressure range of 75 bar to 700 bar, preferably at a pressure range of 100 bar to 500 bar, for example, at a pressure range of 150 bar to 400 bar. For example, the treatment of carbon black with an extractant in the method of the present invention can be carried out in a temperature range of 75 to 350° C., preferably 120 to 300° C., more preferably 150 to 280° C., and in a pressure range of 150 to 400 bar, preferably 180 to 350 bar, more preferably 200 to 320 bar.

[0044] In the method of the present invention, treating carbon black with an extractant may include exposing the carbon black to an extractant stream. The average flow rate may vary greatly, for example depending on the size of the reactor used and / or the amount of the carbon black treated with the extractant. The average flow rate of the extractant may be, for example, more than 5NL / h, for example more than 10NL / h, or more than 20NL / h, or more than 50NL / h, or more than 100NL / h, or more than 150NL / h, or more than 200NL / h, or more than 250NL / h, or more than 500NL / h, or more than 1,000NL / h, or more than 5,000NL / h, or more than 10,000NL / h, or more than 50,000NL / h, or more than 100,000NL / h, or more than 500,000NL / h, or more than 1,000,000NL / h, or more than 5,000,000NL / h. For example, the average flow rate of the extractant can be 20,000,000 NL / h or less, such as 10,000,000 NL / h or less, or 5,000,000 NL / h or less, or 1,000,000 NL / h or less, or 500,000 NL / h or less, or 100,000 NL / h or less, 50,000 NL / h or less, or 10,000 NL / h or less, or 5,000 NL / h or less, or 1,000 NL / h or less, or 500 NL / h or less, such as 400 NL / h or less, or 300 NL / h or less, or 250 NL / h or less, or 200 NL / h or less, or 150 NL / h or less, or 100 NL / h or less. The average flow rate can be in the range between any of the values, for example, 5NL / h to 10,000,000NL / h, or 50NL / h to 500,000NL / h, or 100NL / h to 10,000NL / h, or 150NL / h to 300NL / h, or 200NL / h to 250NL / h. Typically, in the relatively small reactor of the extraction chamber (extraction chamber) volume adopted in the embodiment described below, the average flow rate is in the range of 50NL / h to 250NL / h. The average flow rate of the extractant is calculated based on the total volume and total extraction time of the extractant supplied under standard conditions (101.325kPa, 0°C). The volume of the extractant can be measured, for example, by a mass flow meter such as that located downstream of the extraction chamber, which measures the amount of the gaseous extractant per unit time at a certain temperature and pressure (such as at room temperature and atmospheric pressure). The total volume of the extractant can be obtained by integrating the time. The measured total volume of extractant can then be converted to the total volume of extractant under standard conditions using the ideal gas law. The total volume of extractant under standard conditions, expressed in standard liters [NL], is divided by the total extraction time to calculate the average flow rate under standard conditions.

[0045] The average flow rate (in NL / h) of the extractant per unit volume (in L) of the extraction chamber of the reactor may be, for example, 50 NL·h -1 ·L -1 Above, for example 100NL·h -1 ·L -1 Above, or 200NL·h -1 ·L -1 Above, or 500NL·h -1 ·L -1 Above, or 1,000NL·h -1 ·L -1 Above, or 2,000NL·h -1 ·L -1 Above, or 2,500NL·h -1 ·L -1 Above, or 3,000NL·h -1 ·L -1 For example, the average flow rate of the extractant per unit volume (in L) of the reactor extraction chamber may be 6,000 NL·h -1 ·L -1 Below, for example 5,000NL·h -1 ·L -1 Below, or 4,000NL·h -1 ·L -1 Below, or 3,000NL·h -1 ·L -1 Below, or 2,500NL·h -1 ·L -1 Below, or 2,000NL·h -1 ·L -1 Below, or 1,000NL·h -1 ·L -1 The average flow rate of the extractant per unit volume of the extraction chamber may be within the range between any of the above values, for example, within the range of 50 NL·h -1 ·L -1 Up to 6,000NL·h -1 ·L -1 , or at 500NL·h -1 ·L -1 Up to 5,000NL·h -1 ·L -1 , or at 1,000NL·h -1 ·L -1 Up to 4,000NL·h -1 ·L -1 , or at 2,000NL·h -1 ·L -1 Up to 3,000NL·h-1 ·L -1 Typically, the average flow rate per unit volume (in L) of the reactor extraction chamber is 500 NL·h -1 ·L -1 Up to 3,000NL·h -1 ·L -1 within the range.

[0046] The average flow rate (in NL / h) of the extractant per mass unit amount of carbon black treated (in kg) may be, for example, 100 NL·h -1 kg -1 Above, for example 500NL·h -1 kg -1 Above, or 1,000NL·h -1 kg -1 Above, or 5,000NL·h -1 kg -1 Above, or 10,000NL·h -1 kg -1 Above, or 20,000NL·h -1 kg -1 Above, or 50,000NL·h -1 kg -1 For example, the average flow rate of the extractant per mass unit amount of the treated carbon black (in kg) may be 100,000 NL·h -1 kg -1 Below, for example 80,000NL·h -1 kg -1 Below, 50,000NL·h -1 kg -1 Below, or 20,000NL·h -1 kg -1 Below, or 10,000NL·h -1 kg -1 Below, or 5,000NL·h -1 kg -1 Below, or 2,000NL·h -1 kg -1 Below, or 1,000NL·h -1 kg -1 The average flow rate of the extractant per mass unit amount of the treated carbon black (in kg) may be within the range between any of the above values, for example, within the range of 100 NL·h -1 kg -1 Up to 100,000NL·h -1 kg-1 , or at 1,000NL·h -1 kg -1 Up to 50,000NL·h -1 kg -1 , or at 5,000NL·h -1 kg -1 Up to 20,000NL·h -1 kg -1 Typically, the average flow rate of the extractant based on the amount of carbon black treated (in kg) per mass unit is within the range of 5,000 NL·h -1 kg -1 Up to 100,000NL·h -1 kg -1 , for example, at 5,000NL·h -1 kg -1 Up to 20,000NL·h -1 kg -1 within the range.

[0047] In the method according to the invention, the carbon black can be processed with the extraction agent for any desired time. The processing time usually depends on the applied extraction conditions and the required degree of purification on the one hand, and on the other hand depends on economic considerations. For example, in the method according to the invention, the carbon black can be processed with the extraction agent for at least one second, for example at least 10 seconds, or at least 30 seconds, or at least 1 minute, or at least 2 minutes, or at least 5 minutes, or at least 10 minutes, or at least 20 minutes, or at least 30 minutes, or at least 40 minutes, or at least 50 minutes, or at least 1 hour, or at least 2 hours, or at least 4 hours, or at least 6 hours, or at least 10 hours, or at least 15 hours. In the method according to the invention, the treatment of carbon black with an extraction agent can be, for example, carried out for up to 48 hours, for example, less than 24 hours, or less than 20 hours, or less than 16 hours, or less than 10 hours, or less than 6 hours, or less than 4 hours, or less than 2 hours, or less than 1 hour, or less than 50 minutes, or less than 40 minutes, or less than 30 minutes, or less than 20 minutes, or less than 10 minutes, or less than 5 minutes, or less than 2 minutes, or less than 1 minute, or less than 30 seconds, or less than 10 seconds. This time period can be, for example, in the range of 10 minutes to 45 minutes. The time that the carbon black can be treated with an extraction agent can be in the range between any of the values, for example, 1 minute to 48 hours, or 5 minutes to 24 hours, or 10 minutes to 4 hours, or 20 minutes to 1 hour.

[0048] Conditions such as pressure, temperature and flow rate for treating carbon black with an extractant in the method according to the invention can be kept substantially constant during the treatment process or can be varied over time in a controlled manner. This is advantageous because the solvent properties of the supercritical extractant, such as solute diffusivity, viscosity and mass transfer rate, on the one hand, and the solubility and vapor pressure of oxygenated polycyclic aromatic hydrocarbons and PAHs on the other hand depend on pressure and / or temperature, respectively. Therefore, changing the temperature, pressure and / or flow rate of the extractant in the treatment step over time can help optimize the extraction efficiency. The temperature and / or pressure during the treatment step can be changed, for example, in a stepwise manner, that is, the carbon black can be treated with an extractant at a first temperature and a first pressure for a predetermined first time, then at a second temperature and a second pressure for a predetermined second time, and so on. However, this is only an example, and the extraction conditions can be changed in any possible way during the treatment step, for example, according to a customized predetermined program. The change of conditions during the treatment step can be achieved, for example, by changing the conditions in the extraction chamber and / or by transferring the carbon black between different regions of the extraction chamber and / or between different extraction chambers.

[0049] The conditions of the treatment step in the method according to the present invention can be selected so that treating the carbon black with the extractant comprises extracting at least 50 wt%, or at least 70 wt%, or at least 80 wt%, or at least 90 wt%, or at least 95 wt%, or at least 99 wt% of the oxygenated polycyclic aromatic hydrocarbons from the carbon black based on the initial content of oxygenated polycyclic aromatic hydrocarbons. More specifically, treating the carbon black with the extractant can comprise extracting at least 50 wt%, or at least 70 wt%, or at least 80 wt%, or at least 90 wt%, or at least 95 wt%, or at least 99 wt% of the initial oxygenated PAH6 content or the initial 9,10-phenanthrenequinone content from the carbon black. Furthermore, treating the carbon black with an extractant may include extracting at least 30 wt %, such as at least 40 wt %, or at least 50 wt %, or at least 70 wt %, or at least 80 wt %, or at least 90 wt %, or at least 95 wt %, or at least 99 wt %, or at least 99.5 wt %, or at least 99.8 wt %, or at least 99.9 wt %, or at least 99.95 wt %, of the initial PAH content, such as the initial PAH22 content, from the carbon black.

[0050] It is worth noting that PAHs and oxygenated PAHs may be present on the surface and / or in the interior of carbon black particles, with their distribution depending on the production process conditions and possible post-treatment steps. During supercritical fluid extraction, oxygenated PAH molecules located on the particle surface are generally more easily removed than molecules inside the carbon black particles. Thus, for example, oxygenated PAHs that are mainly present on the particle surface can be removed more completely than oxygenated PAHs that are more evenly distributed between the particle surface and the particle volume.

[0051] The method of the present invention also includes removing the extractant containing the extracted oxygenated polycyclic aromatic hydrocarbons and the optional extracted PAHs from the carbon black to obtain a purified carbon black having an oxygenated polycyclic aromatic hydrocarbon content lower than the initial content of the oxygenated polycyclic aromatic hydrocarbons and an optional polycyclic aromatic hydrocarbon content lower than the initial content of the polycyclic aromatic hydrocarbons. For example, the carbon black can be treated with an extractant stream as described above, so that the extractant containing the extracted oxygenated polycyclic aromatic hydrocarbons and the optional extracted PAHs is continuously removed from the treated carbon black, so that the purity of the carbon black continues to increase with the treatment time. Precipitation of the extracted oxygenated polycyclic aromatic hydrocarbons and the optional extracted PAHs in the extraction chamber or in peripheral equipment (e.g., a pressure line connected thereto) should generally be avoided, as this may lead to re-contamination of the carbon black and / or blockage of the pressure line. For example, precipitation of the extracted oxygenated PAHs and optionally extracted PAHs in the extraction chamber and the pressure line connected thereto can be prevented by heating the extraction chamber and the pressure line connected thereto to a temperature high enough to keep the oxygenated PAHs and optionally extracted PAHs dissolved in the extractant.

[0052] The methods disclosed herein may also optionally include the step of separating at least a portion of the oxygenated polycyclic aromatic hydrocarbons and optional PAHs from the extractant containing the extracted oxygenated polycyclic aromatic hydrocarbons and optional PAHs removed from the carbon black. For example, this can be achieved by phase separation or reducing the solubility of the oxygenated polycyclic aromatic hydrocarbons and polycyclic aromatic hydrocarbons in the extractant. For example, the temperature and / or pressure of the extractant containing the extracted oxygenated polycyclic aromatic hydrocarbons and optional PAHs can be adjusted so that the extractant is converted to a gaseous state, and the extracted oxygenated polycyclic aromatic hydrocarbons and optional PAHs can be separated from the gaseous extractant, for example, as a liquid phase and / or a solid phase. Alternatively, the temperature and / or pressure of the extractant containing the extracted oxygenated polycyclic aromatic hydrocarbons and optional PAHs can be adjusted so that the extracted oxygenated polycyclic aromatic hydrocarbons and optional PAHs condense and / or precipitate, but the extractant remains in a supercritical state. The oxygenated polycyclic aromatic hydrocarbons and optional PAHs can also be separated from the extractant by passing the extractant containing the extracted oxygenated polycyclic aromatic hydrocarbons and optional PAHs through a suitable filter (e.g., an oxygenated PAH / PAH adsorption or absorption medium). For example, the extractant containing the extracted oxygenated polycyclic aromatic hydrocarbons and optional PAHs can be passed through a liquid absorption medium, which can, for example, contain one or more organic solvents to absorb at least a portion of the oxygenated polycyclic aromatic hydrocarbons and optional PAHs through the liquid phase and produce an extractant that does not contain oxygenated PAHs and optional PAHs. A suitable absorption medium is, for example, acetonitrile. The extractant containing the extracted oxygenated polycyclic aromatic hydrocarbons and optional PAHs can be contacted with the absorption medium, wherein the extractant is in a supercritical state or after being converted to a non-supercritical state (e.g., a gaseous state). In the latter case, the temperature and pressure conditions can be selected so that only a portion or substantially no oxygenated polycyclic aromatic hydrocarbons and optional PAHs condense or precipitate before passing through the absorption medium. Separating at least a portion of the oxygenated polycyclic aromatic hydrocarbons and optionally the PAHs from the extractant may also include converting the extractant into a gaseous state, and separating a portion of the extracted oxygenated polycyclic aromatic hydrocarbons and optionally the PAHs from the gaseous extractant in liquid and / or solid form by condensation and / or precipitation, and further separating at least a portion of the remaining oxygenated polycyclic aromatic hydrocarbons and optionally the PAHs from the extractant by passing through an absorption medium.

[0053] The process of the present invention may further comprise the step of recycling the extractant thus obtained for treating the carbon black containing an initial content of oxygenated polycyclic aromatic hydrocarbons and optionally PAHs as described above, after separating at least a portion of the extracted oxygenated polycyclic aromatic hydrocarbons and optionally PAHs from the extractant. Preferably, the recovered extractant is substantially free of or completely free of oxygenated polycyclic aromatic hydrocarbons and PAHs. "Substantially free" in this context means that the recovered extractant contains less than 0.5% by weight, such as less than 0.1% by weight, of oxygenated polycyclic aromatic hydrocarbons and PAHs. "Completely free" means that the recovered extractant is free of oxygenated polycyclic aromatic hydrocarbons and PAHs, except for trace amounts that may be present as ubiquitous impurities.

[0054] Optionally, the methods disclosed herein may further include detecting the amount of oxygenated polycyclic aromatic hydrocarbons and / or PAHs extracted by treating the carbon black with an extractant. To this end, for example, the content of oxygenated polycyclic aromatic hydrocarbons and / or PAHs extracted by the extractant (including the extracted oxygenated polycyclic aromatic hydrocarbons and optional PAHs, which has been removed from the carbon black as described above, such as a continuous effluent stream from the extraction chamber) can be analyzed. The analysis can be performed continuously or discontinuously, for example as an online measurement, i.e., while the extraction treatment is ongoing, using any analytical technique capable of providing measurement results, quantitatively or qualitatively inferring the current or cumulative amount of oxygenated PAHs and / or PAHs extracted from the carbon black. For example, if the extracted oxygenated polycyclic aromatic hydrocarbons and optional PAHs are at least partially separated from the extractant by a liquid absorption medium as described above, the absorbance or absorbance change of the absorption medium at one or more characteristic wavelengths within the electromagnetic spectrum (e.g., in the UV or visible range of the electromagnetic spectrum) can be measured over time. By this measurement, the amount and / or total amount of oxygenated polycyclic aromatic hydrocarbons and / or PAH currently extracted can be inferred. This information related to the amount of oxygenated polycyclic aromatic hydrocarbons and / or PAH extracted by using an extractant to treat carbon black can also be used to control the treatment of carbon black using an extractant. Therefore, it can be used, for example, to control the extraction time, for example, when the analysis shows that a certain amount of oxygenated polycyclic aromatic hydrocarbons and / or PAH is extracted over time, the carbon black is treated with an extractant. In addition, the detected information can be used in a feedback mechanism to control the extraction conditions, such as pressure and / or temperature, when the carbon black is treated with an extractant. For example, a carbon black containing an initial content of oxygenated polycyclic aromatic hydrocarbons and optional PAH can be first exposed to an extractant at a first temperature and a first pressure. Subsequently, for example, when the amount or extraction rate of oxygenated PAH and / or PAH currently extracted as indicated by the detected information drops below a threshold, the pressure and / or temperature can be adjusted to treat the carbon black with an extractant at a second temperature and a second pressure. In this way, the extraction parameters can be tailored to optimize the extraction of different oxygenated PAH and / or PAH species from increasingly purified carbon black. For example, this can allow different conditions to be defined for extracting oxygenated PAH and optional PAH from carbon black in an initial extraction stage, or for extracting oxygenated PAH and optional PAH from carbon black that has been purified to a certain extent from oxygenated PAH and optional PAH in a subsequent extraction stage, and / or for extracting oxygenated PAH and / or PAH located at or near the surface of the carbon black particles, or for extracting oxygenated PAH and / or PAH located within the carbon black particles, as they may have different extraction characteristics. This can improve the extraction efficiency while concomitantly minimizing the impact on other properties of the carbon black (e.g., surface oxygen-containing groups).

[0055] Optionally, the method according to the present invention may also include drying the carbon black containing the initial content of oxygenated polycyclic aromatic hydrocarbons and optional PAHs before treatment with the extractant. The drying step can be performed so that the water is removed from the provided carbon black sample so that the residual water (if any) does not exceed a predetermined level that is considered to be tolerable, such as 0.5% by weight or 0.1% by weight, if possible, without significantly changing the surface chemical properties of the carbon black particles. Drying is generally carried out at an elevated temperature, such as at a temperature above 50°C, or above 100°C, or above 150°C, for example, heating the carbon black sample to a temperature in the range of 100°C to 200°C, such as 120°C to 180°C, for more than 1 minute, such as more than 10 minutes, or more than 30 minutes, or more than 60 minutes, or more than 90 minutes. Heating can be achieved by any conventional method. Drying can be carried out in a gas atmosphere (e.g., a gas medium flow that can be preheated to a high temperature). The gas medium can be, for example, air or nitrogen. However, the gaseous medium may in particular comprise one or more components used in the extractant subsequently used in the supercritical fluid extraction process, but the extractant is gaseous. Thus, the gaseous medium may, for example, comprise or consist of carbon dioxide. In one embodiment, the drying step is carried out for about 1.5 hours at a temperature of about 150° C. in gaseous carbon dioxide at a pressure of about 10 bar. For example, the carbon black provided may have an initial moisture content as described above, which may be reduced by drying the carbon black, for example, thereby removing more than 80%, for example more than 90%, or more than 95% of the initial moisture content from the carbon black. During the drying step, the carbon black may remain in a reactor subsequently used for the supercritical fluid extraction described below, for example in an extraction chamber of such a reactor, or the drying may be carried out outside the reactor or in a separate unit.

[0056] The method according to the present invention can be carried out in a pressure-resistant reactor. Supercritical fluid extraction reactors are commercially provided, for example, by Uhde High Pressure Technologies GmbH in Hagen, Germany and THAR Process Inc. in Pennsylvania, USA. The reactor is generally configured to withstand the temperature and pressure required for supercritical fluid extraction. The reactor can be made of suitable metal building materials (such as stainless steel). The reactor generally includes a heating device for controlling the temperature in the extraction agent treatment step. The heating device can be any conventional heating device. The reactor may include an extraction volume, such as an extraction chamber, in which carbon black is provided to be processed with an extraction agent. The extraction chamber may, for example, have a volume of more than 0.01L, such as more than 0.05L, or more than 0.1L, or more than 0.5L, or more than 1L, or more than 5L, or more than 10L, or more than 50L, or more than 100L, or more than 200L, or more than 500L, or more than 1,000L. The extraction chamber may, for example, have a volume of 10,000 L or less, such as 5,000 L or less, or 2,000 L or less, or 1,000 L or less, or 500 L or less, or 200 L or less, or 100 L or less, or 50 L or less, or 20 L or less, or 10 L or less, or 5 L or less, or 2 L or less, or 1 L or less, or 0.5 L or less, or 0.2 L or less, or 0.1 L or less. The volume of the extraction chamber may be in the range between any of the values, for example, in the range of 0.01 L to 5,000 L, or in the range of 0.05 L to 0.5 L, or in the range of 1 L to 2,000 L, or in the range of 10 L to 1,000 L. The reactor may include a single extraction chamber or two or more extraction chambers. For example, a reactor with two or more extraction chambers can be used, which can allow quasi-continuous operation in batch mode, wherein one or more extraction chambers are charged with the initial carbon black to be treated, or the treated carbon black discharged therefrom, while the carbon black is extracted in one or more other extraction chambers of the reactor. Therefore, providing a carbon black containing an initial content of oxygenated polycyclic aromatic hydrocarbons and optional PAHs can include introducing a certain amount of the carbon black into the extraction chamber of the reactor. Typically, an extractant is supplied to the extraction chamber through an inlet connected to a feed line from one or more extractant sources. The extractant containing oxygenated polycyclic aromatic hydrocarbons and optional PAHs can be taken out of the extraction chamber through an outlet and a connected effluent line. The reactor typically also includes conventional devices for flow and process control, such as sensors, pressure or flow regulating devices, valves, pumps and controllers. Typically, one or more extraction chambers are designed so that the extractant flow can be forced to pass through the carbon black material rather than, for example, flowing above the carbon black material.In this way, the contact time between the extractant and the carbon particles can be increased, thereby improving the extraction efficiency.

[0057] For example, carbon dioxide can be provided as an extractant in a pressure vessel. Carbon dioxide can be extracted from the container, for example, to establish a continuous flow with a predetermined flow rate, for example, by adjusting one or more pumps and / or flow control devices connected to the feed line. The pressure and temperature of the extractant can be adjusted by pressure regulation and heating devices, so that the extractant is in a supercritical state. Pressure regulation can be achieved, for example, by a pump, a valve and a back-pressure regulator (back-pressure regulator) in a control system, and heating can be achieved, for example, by heating the feed line, for example, by providing an electric heating jacket, a heating tape (heating tape) or the like to the feed line, and / or by one or more heating elements of the extraction chamber, which can be, for example, a resistance electric heater type. The supercritical carbon dioxide extractant stream obtained contacts the carbon black in the extraction chamber to extract oxygenated PAH and optional PAH therefrom. Optionally, those auxiliary agents as described above can be supplied to the carbon dioxide stream at a predetermined constant or variable ratio at any stage of the reactor (for example, the upstream of the extraction chamber).

[0058] The method may also include recovering and / or collecting the purified carbon black. This may include stopping the feed of the extractant, removing the extractant or purified carbon black from the extraction chamber, or otherwise separating the purified carbon black and the extractant. Typically, the method according to the present invention may be performed as a continuous method, a semi-batch method, or a batch method. In the case of a continuous method, carbon black including an initial content of oxygenated polycyclic aromatic hydrocarbons and optional PAHs, for example, using a continuous flow of an extractant, may be, for example, continuously fed to an extraction chamber, where it is treated with an extractant, and purified carbon black may be continuously taken out of the extraction chamber. Preferably, this continuous method may be performed in the following manner: the carbon black particles fed to the extraction chamber at different times are substantially not mixed, so that the residence time in the extraction chamber is approximately the same, thereby the extraction time is approximately the same. In addition, the flow direction of the extractant from the inlet to the outlet may be opposite, the same, vertical, or arranged at any other angle to the conveying direction of the carbon black particles.

[0059] In case of a batch or semi-batch process, a batch of carbon black containing an initial content of oxygenated polycyclic aromatic hydrocarbons and optionally PAHs can be charged into an extraction chamber and treated with an extractant under controlled conditions for a desired time to extract the oxygenated PAHs and optionally PAHs and produce a purified carbon black with a reduced content of oxygenated PAHs and optionally a reduced content of PAHs. After the desired time, the treatment can be stopped and the purified carbon black can be recovered, for example by releasing the pressure, and removed from the extraction chamber. Before removing the purified carbon black from the extraction chamber, the extractant can optionally be removed from the extraction chamber and replaced with a gaseous medium, such as nitrogen or air, and then the temperature or pressure can be reduced, for example to ambient conditions. In this way, condensation or precipitation of the extracted oxygenated polycyclic aromatic hydrocarbons and optionally PAHs included in the extractant can be avoided. Any residual extractant can be separated from the purified carbon black by reducing the pressure and / or temperature below the respective critical value of the extractant, thereby converting the extractant into a gaseous state. Since carbon dioxide is a gas under ambient conditions, it can be separated from the purified carbon black in a simple manner according to the invention without any further drying or purification steps being necessary, as might be necessary, for example, when extracting using organic solvents or steam.

[0060] The method of the present invention can generally be carried out independently of the carbon black production or treatment process. It can therefore be applied to various grades of carbon black. Nevertheless, the method can still be advantageously implemented in a carbon black production plant, and for example, after the carbon black production or treatment process. For example, the method disclosed herein can be implemented downstream of carbon black production, such as downstream of a furnace reactor, and upstream or downstream of other carbon black post-treatment processes (e.g., oxidation treatment).

[0061] The purified carbon black obtained according to the method of the present invention has a lower oxygen-containing polycyclic aromatic hydrocarbon content than the initial oxygen-containing polycyclic aromatic hydrocarbon content of the carbon black used for purification. The purified carbon black may, for example, have an oxygen-containing polycyclic aromatic hydrocarbon content corresponding to 50% by weight or less, or 30% by weight or less, or 20% by weight or less, or 10% by weight or less, or 5% by weight or less, or 1% by weight or less, or 0.5% by weight or less, or 0.2% by weight or less, or 0.1% by weight or less, or 0.05% by weight or less of the initial oxygen-containing polycyclic aromatic hydrocarbon content. For example, the purified carbon black may have an oxygen-containing PAH6 content or a 9,10-phenanthrenequinone content corresponding to 50% by weight or less, or 30% by weight or less, or 20% by weight or less, or 10% by weight or less, or 5% by weight or less, or 1% by weight or less, or 0.5% by weight or less, or 0.2% by weight or less, or 0.1% by weight or less, or 0.05% by weight or less of the initial oxygen-containing PAH6 content or 9,10-phenanthrenequinone content, respectively. In addition, the purified carbon black obtained according to the method of the present invention may optionally further have a PAH content lower than the initial PAH content of the carbon black used for purification. For example, the purified carbon black has a PAH content (e.g., PAH22 content) corresponding to 60% by weight or less, or 50% by weight or less, or 30% by weight or less, or 20% by weight or less, or 10% by weight or less, or 5% by weight or less, or 1% by weight or less, or 0.5% by weight or less, or 0.2% by weight or less, or 0.1% by weight or less, or 0.05% by weight or less of the initial PAH content (e.g., initial PAH22 content).

[0062] The purified carbon black obtained according to the process of the present invention may, for example, have a PAH22 content of less than 1,500 ppm, for example less than 1,000 ppm, or less than 700 ppm, or less than 500 ppm, or less than 200 ppm, or less than 150 ppm, or less than 100 ppm, or less than 50 ppm, or less than 20 ppm, or less than 10 ppm, or less than 5 ppm, or less than 3 ppm, or less than 2 ppm, or less than 1 ppm, or less than 0.5 ppm.

[0063] In addition, the purified carbon black obtained according to the method of the present invention may have, for example, an oxygen-containing PAH6 content of less than 200 ppm, such as less than 100 ppm, or less than 50 ppm, or less than 25 ppm, or less than 10 ppm, or less than 5 ppm, or less than 3 ppm, or less than 1 ppm. The purified carbon black obtained according to the method of the present invention may especially have a 9,10-phenanthrenequinone content of less than 1 ppm.

[0064] The purified carbon black may have any combination of the PAH22 and oxy-PAH6 and / or 9,10-phenanthrenequinone contents specified above. The purified carbon black obtained according to the process of the invention may have an oxygenated PAH content and / or a PAH content (e.g. PAH22 content) such that compliance with official regulations for the use of the purified carbon black in areas such as food or beverage contact situations, pharmaceuticals, cosmetics or the manufacture of children's toys and articles is ensured, for example, compliance with FDA regulations.

[0065] The purified carbon black may further have any other characteristics and properties described above for the carbon black provided as the starting material to be purified, such as carbon content, oxygen content, volatile content, ash content, moisture content and BET specific surface area. These properties may not be substantially affected by the purification process disclosed herein. Therefore, except for the content of oxygenated PAHs and optional PAHs, the purified carbon black can substantially correspond to the carbon black provided as the starting material to be purified. For example, the carbon content, oxygen content, volatile content, ash content, moisture content and / or BET specific surface area of ​​the purified carbon black can correspond to the corresponding values ​​of the carbon black provided as the starting material, as described above, ±30%, or ±20%, or ±10%, or ±5%.

[0066] The purified carbon black obtained according to the invention can be used in any application where carbon black is conventionally used or utilized. The purified carbon black according to the invention can be used, for example, as a pigment, reinforcing filler or conductive agent, for example in the manufacture of plastic or rubber products, paints, inks, coatings, electrodes or energy storage devices. The purified carbon black according to the invention is particularly suitable for applications where there is an increasing awareness or concern about oxygenated PAHs and / or PAHs or where there are official regulations regarding PAHs, for example in food or beverage contact situations, in the manufacture of pharmaceuticals, cosmetics or children's toys and articles.

[0067] The present invention has been generally described above, and the present invention can be further understood by referring to the following specific examples. These examples are provided herein for illustrative purposes only and are not intended to limit the present invention, but to give the full scope of the appended claims of the present invention, including any equivalent schemes thereof.

[0068] Example

[0069] Unless otherwise stated, all parts and percentages mentioned in the examples are by weight.

[0070] Materials used:

[0071] Carbon Black:

[0072] Carbon Black A: Printex U, a gas black commercially available from Orion Engineered Carbon GmbH, was used as an example of a carbon black having a negligible initial oxygenated PAH content (comparative example).

[0073] Carbon Black B: Ozone-oxidized Carbon Black A as an example of a carbon black having a substantial initial oxygenated PAH content.

[0074] Extraction agent: Carbon dioxide with a purity of 99.995% by volume, supplied as a pressurized liquid in a 50 L diptube bottle, commercially available from Westfalen AG.

[0075] Supercritical fluid extraction device (setup):

[0076] The carbon black samples studied above were subjected to supercritical fluid extraction using supercritical carbon dioxide as the extractant using a custom-made high-temperature and high-pressure supercritical fluid extraction apparatus. The apparatus includes a tubular extraction chamber (inner diameter: 1.43 cm, length: 50 cm, volume: 0.080 L) made of stainless steel (Swagelok IPT series 316 / 316L) with an inlet at one end and an outlet at the other end. The extraction chamber is mounted in an aluminum block equipped with four heating cartridges (Horst Heizpatronen 230V, diameter 12.5 mm, length 160 mm, nominal power 500 W) for heating the extraction chamber. Two thermocouples (type K) are mounted in the aluminum block and used in conjunction with a heating controller (EurothermUniversalregler 818 and 808) to measure and regulate the temperature of the aluminum block. The dip tube bottle containing CO2 was connected to the inlet of a pump (Knauer 80P with a 100mL pump head, equipped with a cooling device, using a HuberMinistat 125w cc1 cryostat) via a regular 1 / 4" tubing, and from the outlet of the pump to the inlet of the extraction chamber via a pressure line (Swagelok IPT series, 1 / 4" OD) to deliver the extractant into the extraction chamber. The exhaust pressure line (Swagelok IPT series, 1 / 4" OD) connected to the outlet of the extraction chamber was connected to the extraction chamber through a back pressure regulator (custom Equilibar anti-clogging BPR equipped with polyimide membrane and The extractant is then passed through the acetonitrile provided as an absorption medium in the absorption chamber and the purified extraction medium is released to the atmosphere through a mass flow meter (Bronkhorst F-201CV) and a valve. Two filters (Swagelok IPT high pressure filters, the filters have filter elements with pore sizes of 2 μm and 0.5 μm, respectively) are placed in the pressure lines upstream and downstream of the extraction chamber to avoid contamination of the pressure lines. In addition, the feed pressure line and the exhaust pressure line are also equipped with heating belts (Horst Heizleitungen HS 450°C, controlled by Eurotherm Universalregler) for heating the extractant upstream and downstream of the extraction chamber to avoid precipitation and line blockage. The flow rate and pressure of the extractant continuously flowing through the extraction chamber can be independently controlled on the one hand by a pump connected to the feed pressure line and on the other hand by a back pressure regulator located downstream of the extraction chamber. The reference pressure applied to the BPR dome is delivered by a bypass line branching from the feed pressure line between the pump and the extraction chamber inlet.

[0077] Supercritical Fluid Extraction:

[0078] For supercritical fluid extraction, the extraction chamber was filled with about 5 g of carbon black to be extracted. The carbon black was fixed between two glass fiber plugs. The extraction chamber was then heated to an extraction temperature of 250°C and the extractant was allowed to flow continuously through the provided extraction chamber, with the flow rate and pressure of the extractant being controlled by a pump and a back pressure regulator. The sample was then subjected to continuous supercritical fluid extraction at a pressure of 300 bar and a temperature of 250°C using supercritical carbon dioxide as the extractant, with the estimated average flow rate of the extractant through the extraction chamber corresponding to 150 or 60 NL / h, respectively (average flow rate per unit volume of the extraction chamber: 1,866 or 746 NL·h -1 ·L -1 ), the extraction time is 4-5 hours. The flow of the extractant is then stopped, the system pressure is released, and the sample is allowed to cool to ambient temperature.

[0079] The extracted carbon black samples thus obtained were analyzed for PAH22 and oxygenated PAH contents as described below.

[0080] Determination of PAH22 and oxygenated PAH content:

[0081] The PAH22 content of the studied carbon blacks after supercritical fluid extraction was analyzed and compared with the initial PAH22 content determined for the corresponding original carbon black reference samples that were not extracted with supercritical fluid. The PAH22 content was determined according to the method developed by Cabot Corp. on July 8, 1994, entitled "Determination of PAH Content in Carbon Black" and incorporated into the U.S. Code of Federal Regulations (CFR) 21 Sec. 178.3297 by the U.S. Food and Drug Administration (FDA), as follows:

[0082] The carbon black material is put into a mortar and ground with a pestle until a uniform powder is obtained. In a cellulose extraction sleeve (MN645, Macherey-Nagel, Duren, Germany), an appropriate amount (up to 10g) of powder is accurately weighed. The glass wool plug (glass wool plug) and cellulose pieces (cellulose pieces) of the extraction sleeve are placed on the top (top) of the carbon black, and then the filled sleeve is loaded into the extraction chamber of the 100mL Soxhlet extraction device with a 250mL round-bottomed flask. Toluene is added to the flask and the condenser of the device is gently flushed with nitrogen. Then in the Soxhlet extraction device, the sample is subjected to Soxhlet extraction for 48 hours with toluene at a rate of about 10 cycles per hour under light protection. Then, the crude extract obtained is concentrated to slightly more than 5mL using a rotary evaporator (Büchi Rotavapor R-200, Büchi Labortechnik AG, 9230Flawil, Switzerland) operated at 40°C and the pressure is at least reduced by 5kPa. The extract was then transferred to a 10 mL volumetric flask and fresh toluene was added to the mark. 17 deuterated PAH standards (D8-naphthalene, D8-acenaphthylene, D 10 -Acenaphthene, D 10 -fluorene, D 10 -Philippines, D 10 -Anthracene, D 10 -Fluoranthene, D 10 -pyrene, D 12 -Benzo[a]anthracene, D 12 - D 12 -Benzo[b]fluoranthene, D 12 -Benzo[k]fluoranthene, D 12 -Benzo[a]pyrene, D 14 -Dibenzo[a,h]anthracene, D 12 -Benzo[g,h,i]perylene, D 12 -Indeno[1,2,3-c,d]pyrene and D 12-coronene, each in an amount of 200 ng). Then, a silica gel column (1 g silica gel / 13% H2O, inner diameter 8 to 10 mm, capacity 5 cm 3 ) to purify an aliquot of the extract. Subsequently, another deuterated compound, D-12 perylene, was added to the purified extract in an amount of 200 ng as a recovery standard. The solution thus obtained was then used for HRGC / LRMS analysis (capillary gas chromatography coupled to low resolution mass spectrometry) for identification and quantification of PAH using the following instruments and conditions: Gas chromatograph: Thermo Scientific GC-Ultra with PTV injector, GC column: 60 m DB5-MS, 0.25 mm ID, 0.25 μm film thickness; Temperature program GC oven: preheat oven to 80°C, sample injection, hold at 80°C for 2 minutes, heat to 180°C at a rate of 25°C / min, heat to 220°C at a rate of 8°C / min, heat to 250°C at a rate of 2°C / min, heat to 280°C at a rate of 3°C / min, heat to 320°C at a rate of 5°C / min, hold at 320°C for 21 minutes and 18 seconds; Mass spectrometer: Thermo Scientific Trace DSQ LRMS, operated in electron impact mode (El) with selected ion monitoring (SIM mode); mass resolution: 1 amu; monitoring of molecular and fragment ions of individual PAH compounds. The calibration of the instrument was checked for each analytical sequence by injecting a mixture containing all the natural PAHs of interest and the deuterated standards described above. The PAH species were identified by analyzing relative retention times, molecular and fragment ions, and fragmentation ratios. Quantification was performed by deuterated internal PAHs using the isotope dilution and internal standard method using the instrument software. The PAH22 content was calculated by adding the concentrations determined for each of the 22 PAH compounds, where the LOQ was used as the corresponding concentration for compounds with concentrations below the limit of quantification (LOQ). The coeluting isomers dibenz(a,h)anthracene and dibenz(a,c)anthracene could not be separated by the GC column and were therefore considered as one substance, reported herein as “dibenz(a,h)anthracene”.

[0083] The carbon black samples studied were also analyzed for their 9,10-phenanthrenequinone content after supercritical fluid extraction, which served as an indicator for the oxygenated PAH content and was compared with the initial 9,10-phenanthrenequinone content determined for a reference sample of original carbon black without supercritical fluid extraction. The oxygenated PAH content was determined similarly to the PAH22 content determination described above and based on the same analytical approach. Specifically, the extraction of carbon black, the volume reduction of the original extract and the adjustment of the defined volume were performed in exactly the same way as described above. Further steps were performed as described above with the following specific adjustments for oxygenated PAHs: deuterated nitro PAH (D9-3-nitrofluoranthene, in an amount of 250 ng) was added to an aliquot of the extract as an internal standard, replacing the 17 deuterated PAH standards described above. The oxygenated PAH extract aliquot containing the deuterated internal standard was directly subjected to high-resolution mass spectrometry (HRGC / HRMS) analysis without further treatment. The following instruments and conditions were used: Thermo Scientific GC-Ultra2000 equipped with PTV injector, GC column: 30m DB5-MS, 0.25mm ID, 0.1μm film thickness, temperature program GC oven: preheat oven to 80°C, sample injection, hold at 80°C for 3 minutes and 42 seconds, heat to 180°C at a rate of 35°C / min, heat to 290°C at a rate of 6°C / min, hold at 290°C for 37 seconds; Mass spectrometer: Thermo Scientific MAT 95HRMS, operated in electron impact mode (El) and selected ion monitoring (SIM mode); Mass resolution: <8.000amu, monitoring molecular and fragment ions of oxygenated PAH compounds. The calibration of the HRMS instrument was checked for each analytical sequence by injecting a mixture containing 9,10-phenanthrenequinone, 9-nitrofluoranthene and the above-mentioned deuterated standards. The oxygenated PAH species were identified by analyzing relative retention times, molecular and fragment ions, and fragmentation rates. Quantification was performed using standard methods with deuterated internal nitro-PAH using the instrument software.

[0084] The PAH22 content and 9,10-phenanthrenequinone content of the extracted carbon black A and carbon black B samples were determined according to the above method. The results are summarized in Table 1 below and compared with the initial PAH22 content and 9,10-phenanthrenequinone content determined for the original carbon blacks A and B without SFE treatment as a reference. The reported relative extraction amount is calculated according to the formula 1-(x(Example) / x(Reference)), where x(Example) and x(Reference) represent the detected amount of the indicated compound or the total detected amount of the indicated group of compounds for a given extracted carbon black and the corresponding original reference carbon black, respectively.

[0085] Table 1:

[0086]

[0087] As shown in Example 1 in Table 1, conventional carbon black without oxidative post-treatment generally contains a negligible content of oxygenated PAHs, but may contain a large amount of PAHs (Reference 1). By supercritical fluid extraction with carbon dioxide as an extractant, a purified carbon black having a significantly reduced content of polycyclic aromatic hydrocarbons compared to the starting material (Reference 1) can be obtained (Example 1). On the other hand, as shown in Example 2, oxidation using ozone as an oxidant can produce carbon black whose PAH content is significantly reduced, but the amount of oxygenated PAHs is considerable (Reference 2). However, as shown in Example 2, supercritical fluid extraction using carbon dioxide as an extractant allows the effective removal of oxygenated PAHs from carbon black. Therefore, by supercritical fluid extraction with carbon dioxide as an extractant, a purified carbon black having a significantly reduced content of oxygenated PAHs (as well as PAHs) compared to the starting material (Reference 2) can be obtained (Example 2).

Claims

1. A method for producing purified carbon black having a reduced content of oxygenated polycyclic aromatic hydrocarbons (oxygenated PAHs), the method comprising: (a) providing carbon black containing an initial content of oxygen-containing polycyclic aromatic hydrocarbons of 1 ppm or more, (b) treating carbon black containing an initial content of oxygen-containing polycyclic aromatic hydrocarbons with an extractant comprising carbon dioxide in a supercritical state to extract at least a portion of the oxygen-containing polycyclic aromatic hydrocarbons from the carbon black, and (c) removing the extractant containing the extracted oxygen-containing polycyclic aromatic hydrocarbons from the carbon black to obtain a purified carbon black having an oxygen-containing polycyclic aromatic hydrocarbon content lower than that of the initial oxygen-containing polycyclic aromatic hydrocarbons.

2. The method according to claim 1, wherein the carbon black containing an initial content of oxygen-containing polycyclic aromatic hydrocarbons comprises oxidized carbon black, such as ozone-oxidized carbon black, and / or wherein the carbon black containing an initial content of oxygen-containing polycyclic aromatic hydrocarbons exhibits one or more or all of the following: - an ash content of 20 wt % or less, such as 15 wt % or less, 10 wt % or less, 5 wt % or less, 3 wt % or less, 1 wt % or less, or 0.5 wt % or less, or 0.1 wt % or less, as determined according to ASTM D1506-15, - a volatile matter content of less than 20% by weight, such as less than 15% by weight, such as less than 10% by weight, determined by heating to 950° C. according to DIN 53552:1977, a moisture content of 15 wt % or less, such as 10 wt % or less, 5 wt % or less, 3 wt % or less, or 1 wt % or less, as determined according to ASTM D1509-18, and / or - The carbon content determined by elemental analysis is 80 wt% or more, for example 85 wt% or more, for example 90 wt% or more, for example 95 wt% or more, for example 97 wt% or more, for example 98 wt% or more.

3. The method according to any one of the preceding claims, wherein the content of oxygen-containing polycyclic aromatic hydrocarbons is determined as the content of oxygen-containing PAH6 or as the content of 9,10-phenanthrenequinone, wherein the carbon black containing the initial content of oxygen-containing polycyclic aromatic hydrocarbons can have, for example, - the initial oxygenated PAH6 content is 1 ppm or more, such as 5 ppm or more, 10 ppm or more, 20 ppm or more, 30 ppm or more, 40 ppm or more, or 50 ppm or more; and / or - The initial 9,10-phenanthrenequinone content is 1 ppm or more, such as 2 ppm or more, 3 ppm or more, 5 ppm or more, or 8 ppm or more.

4. The method according to any one of the preceding claims, wherein the carbon black provided in (a) further comprises an initial content of polycyclic aromatic hydrocarbons (PAH), the carbon black is treated in (b) with an extractant comprising carbon dioxide in a supercritical state to extract at least a portion of the PAH from the carbon black, and step (c) further comprises removing the extractant comprising the extracted PAH from the carbon black to obtain a purified carbon black having a PAH content lower than the initial PAH content.

5. The method according to claim 4, wherein the content of polycyclic aromatic hydrocarbons (PAH) is determined as PAH22 content, wherein the carbon black provided in (a) may, for example, have an initial PAH22 content of 10 ppm or more, such as 50 ppm or more, or 100 ppm or more, or 200 ppm or more, or 500 ppm or more, or 800 ppm or more, or 1,000 ppm or more.

6. A method according to any of the preceding claims, wherein the extractant comprises at least 50 wt% carbon dioxide, such as at least 70 wt% carbon dioxide, such as at least 80 wt% carbon dioxide, or at least 90 wt% carbon dioxide, or at least 95 wt% carbon dioxide, or at least 99 wt% carbon dioxide, based on the total weight of the extractant.

7. The method according to any one of claims 1 to 6, wherein the extractant further comprises one or more auxiliary agents or wherein the extractant consists of supercritical carbon dioxide.

8. The method according to any one of claims 1 to 7, wherein the treatment of the carbon black with the extractant in step (b) is carried out at a temperature of above 75°C, for example at a temperature in the range of 75°C to 400°C, preferably in the range of 100°C to 350°C, for example in the range of 100°C to 300°C, and / or at a pressure of above 75 bar, for example in the range of 75 bar to 700 bar, preferably in the range of 100 bar to 500 bar, for example in the range of 150 bar to 400 bar, and / or wherein the treatment of the carbon black with the extractant in step (b) is carried out for a period of at least 1 minute, for example at least 1 hour and / or for a period of up to 48 hours.

9. The method according to any one of claims 1 to 8, wherein treating the carbon black with the extractant in step (b) comprises exposing the carbon black to a flow of extractant, wherein the average flow rate of the extractant per mass unit amount of treated carbon black (in kg) preferably corresponds to 1,000 NL·h -1 kg -1 Above, for example, 5,000NL·h -1 kg -1 Above, for example, from 5,000NL·h -1 kg -1 Up to 100,000NL·h -1 kg -1 .

10. The method according to any one of the preceding claims, wherein treating the carbon black with the extractant in step (b) comprises extracting at least 50 wt. %, such as at least 70 wt. %, such as at least 80 wt. %, or at least 90 wt. %, or at least 95 wt. % of the initial oxygenated PAH content, such as the initial oxygenated PAH6 content or the initial 9,10-phenanthrenequinone content, from the carbon black.

11. The method according to any one of the preceding claims 4 or 5 or claims dependent thereon, wherein treating the carbon black with the extractant in step (b) comprises At least 40 wt %, such as at least 70 wt %, such as at least 80 wt %, or at least 90 wt %, or at least 95 wt % of the initial PAH content, such as the initial PAH22 content, is extracted from the carbon black.

12. The process according to any one of the preceding claims, wherein the purified carbon black obtained in step (c) has: - an oxygenated polycyclic aromatic hydrocarbon content, such as oxygenated PAH6 content or 9,10-phenanthrenequinone content, corresponding to 50 wt %, such as 30 wt %, such as 20 wt %, such as 10 wt %, such as 5 wt % or less of the initial oxygenated PAH content, such as the initial oxygenated PAH6 content or the initial 9,10-phenanthrenequinone content; and / or - a polycyclic aromatic hydrocarbon (PAH) content, such as a PAH22 content, corresponding to less than 60 wt %, such as less than 30 wt %, such as less than 20 wt %, such as less than 10 wt %, such as less than 5 wt % of the initial PAH content, such as the initial PAH22 content.

13. The method according to any one of the preceding claims, further comprising one or more or all of the following: - drying the carbon black containing an initial content of oxygen-containing polycyclic aromatic hydrocarbons before treatment with the extractant; - separating at least a portion of the oxygenated polycyclic aromatic hydrocarbons and optionally polycyclic aromatic hydrocarbons from the extractant comprising the extracted polycyclic aromatic hydrocarbons removed from the carbon black in step (c), for example by reducing the pressure, and optionally recovering the extractant thus obtained for use in step (b); - detecting the amount of oxygen-containing polycyclic aromatic hydrocarbons and / or polycyclic aromatic hydrocarbons extracted by the extractant, for example by online measurement, wherein the treatment of the carbon black with the extractant in step (b) is preferably controlled based on the detected amount of oxygen-containing polycyclic aromatic hydrocarbons and / or polycyclic aromatic hydrocarbons extracted.

14. The process according to any one of the preceding claims, wherein the process is carried out as a continuous process, a semi-batch process or a batch process and / or wherein the process is carried out in a pressure-resistant reactor having a heating device.

15. A purified carbon black obtainable by the method of any one of the preceding claims 1 to 14.

16. The purified carbon black according to claim 15, having a 9,10-phenanthrenequinone content of less than 1 ppm and / or a PAH22 content of less than 1,500 ppm, such as less than 1,000 ppm, or less than 700 ppm, or less than 500 ppm, or less than 200 ppm, less than 150 ppm, or less than 100 ppm, or less than 50 ppm, or less than 20 ppm, or less than 10 ppm.

17. Use of the purified carbon black according to claim 15 or 16 as a pigment, reinforcing filler or conductive agent, for example in the manufacture of plastic or rubber products, paints, inks, coatings, electrodes or energy storage devices.

18. Use of supercritical carbon dioxide for removing oxygen-containing polycyclic aromatic hydrocarbons from carbon black.

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