Method for producing carbon black with reduced content of oxy-polycyclic aromatic hydrocarbons (oxy-PAH) using supercritical fluid extraction

Abstract

Provided is a method for producing purified carbon black with a reduced content of oxy-polycyclic aromatic hydrocarbons, which includes: (a) providing carbon black containing an initial content of oxy-polycyclic aromatic hydrocarbons of 1 ppm or more; (b) treating the carbon black containing the initial content of oxy-polycyclic aromatic hydrocarbons with an extractant containing carbon dioxide in a supercritical state to extract at least a part of the oxy-polycyclic aromatic hydrocarbons from the carbon black; and (c) removing the extractant containing the extracted oxy-polycyclic aromatic hydrocarbons from the carbon black to obtain purified carbon black containing an oxy-polycyclic aromatic hydrocarbon content lower than the initial content of oxy-polycyclic aromatic hydrocarbons. Further provided are carbon black obtained by the above production method and an article manufactured therefrom.

Description

Technical Field

[0001] The present invention relates to a method for purifying carbon black, and more specifically, to a method for producing carbon black with a reduced content of oxy-polycyclic aromatic hydrocarbons and optionally other polycyclic aromatic hydrocarbon impurities using supercritical fluid extraction (SFE), in particular an extractant containing supercritical carbon dioxide. The present invention further relates to the purified carbon black obtained by this method, as well as the applications and uses of such purified carbon black.

Background Art

[0002] Carbon black is widely used in the industry as an additive for various different applications, for example, as a colorant or pigment, a reinforcing filler or a conductive agent in the production of paints, coatings, inks, electrodes or plastic or rubber articles. Depending on each application, carbon black having different properties is required, which can be controlled by the carbon black production method and possible post-treatment. Carbon black is produced by the controlled thermal decomposition or thermo-oxidative decomposition of hydrocarbon precursors such as oil, natural gas or acetylene. Established carbon black production methods include the furnace black process, the gas black process originally developed by Degussa, the channel black process, the lamp black process, the acetylene process, or the thermal black process.

[0003] Depending on the carbon black production method, the hydrocarbon precursor material used and the process conditions, impurities such as metals, sulfur and organic compounds may contaminate the resulting carbon black. Such impurities can particularly have an adverse effect on the performance of carbon black when present in relatively large amounts, and are therefore undesirable for certain applications.

[0004] Carbon black may contain, especially as impurities, organic compounds having a polycyclic aromatic structure generally called polycyclic aromatic hydrocarbons (PAHs). PAHs are considered harmful to health and the environment and are described, 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, June 2002, pages 243 - 248. Therefore, the PAH content of carbon black is subject to increasing customer needs and official regulations for applications such as use in food or beverage contact situations, pharmaceuticals, cosmetics, or the manufacture of toys and articles for children. For example, the US Food and Drug Administration (FDA) limits the total PAH content of high - purity furnace black in articles that contact 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, oxygenated derivatives of PAH compounds can contaminate carbon black. Polycyclic aromatic hydrocarbon derivatives that consist not only of carbon and hydrogen but also contain oxygen are generally referred to as oxygenated PAHs or oxy-PAHs. Examples of oxy-PAHs include polycyclic aromatic ketones, polycyclic aromatic quinones, hydroxylated PAHs, polycyclic aromatic carboxaldehydes, polycyclic aromatic carboxylic acids and anhydrides, and polycyclic aromatic lactones. Oxy-PAHs are frequently found, for example, in carbon black oxidized with certain oxidizing agents such as ozone and may be formed during such oxidation treatment of carbon black. Oxy-PAH compounds are likewise considered to be harmful to health, particularly due to their mutagenicity (e.g., A. Kra - Je, J. Le Goff, C. Lopez, J. Le Duffan, R. Doury - Pipy (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 amount of oxy-PAHs in carbon black.

[0006] Accordingly, an object of the present invention is to provide a method for effectively removing oxy-PAHs from carbon black and, if possible, also removing PAHs, and ideally, without adversely affecting other properties of the carbon black and / or without using harmful or expensive substances in an economical and environmentally friendly manner, to provide carbon black with a reduced content of such impurities. SUMMARY OF THE INVENTION

[0007] This object and additional advantages described herein are unexpectedly achieved by providing the method defined in independent claim 1 below.

[0008] Accordingly, the present invention relates to a method for producing purified carbon black with a reduced content of oxy-polycyclic aromatic hydrocarbons (oxy-PAHs). The method comprises (a) Providing carbon black containing an initial content of oxy-polycyclic aromatic hydrocarbons of 1 ppm or more. (b) Treating the carbon black containing the initial content of oxy-polycyclic aromatic hydrocarbons with an extractant containing carbon dioxide in a supercritical state to extract at least a part of the oxy-polycyclic aromatic hydrocarbons from the carbon black. (c) Removing the extractant containing the extracted oxy-polycyclic aromatic hydrocarbons from the carbon black to obtain a purified carbon black containing an oxy-polycyclic aromatic hydrocarbon content lower than the initial content of the oxy-polycyclic aromatic hydrocarbons. This includes the above steps.

[0009] The present invention also relates to a purified carbon black obtained by the method according to the present invention disclosed above and described in more detail below.

[0010] The present invention further relates to the use of such a purified carbon black as a pigment, a reinforcing filler or a conductive agent, for example, for the production of plastic articles or rubber articles, paints, inks, coatings, electrodes or energy storage devices.

[0011] Furthermore, the present invention relates to the use of supercritical carbon dioxide for removing oxy-polycyclic aromatic hydrocarbons from carbon black.

[0012] The method of the present invention, which involves treating carbon black with an extractant containing supercritical carbon dioxide, offers several advantages. Thus, the present invention is flexibly applicable to various types of carbon black, regardless of its manufacturing method. The method of the present invention can effectively purify carbon black without substantially adversely affecting other properties of the carbon black, or without using a purifying agent that is expensive, harmful, or difficult to remove from the carbon black product, enabling the obtainment of carbon black having a low oxy-PAH content and optionally a low PAH content. The use of the extractant in the supercritical state beneficially combines a density similar to that of a liquid with a solute diffusivity and viscosity close to those of a gas, thereby enabling a high mass transfer rate and a rapid and efficient extraction of oxy-PAH and PAH from the carbon black. Furthermore, the solvent strength can be varied herein by a simple change in the applied pressure and / or temperature, or by the addition of a suitable modifier. Additionally, carbon dioxide has the advantages of being non-toxic, non-flammable, and inexpensive. The critical temperature is as low as 304.2 K (31 °C) in conjunction with a critical pressure of 72.8 atm (7,380 kPa). Thus, extraction with an extractant containing carbon dioxide can be carried out under relatively mild conditions, thereby reducing the tendency for undesirable changes to the carbon black during the purification process. Moreover, supercritical carbon dioxide can be easily separated from the carbon black, for example, by pressure release that results in the evaporation of carbon dioxide. Thus, a dedicated step for drying or solvent removal after extraction is not necessary.

[0013] These and any other features and advantages of the present invention will be described in more detail in the following description.

Mode for Carrying Out the Invention

[0014] Detailed Description As used herein, the term "comprising" is to be understood in an open-ended sense, and is not to be taken to exclude the presence of additional elements, materials, components, or method steps that are not described or recited. The terms "including", "containing", and like terms are to be understood as being synonymous with "comprising". As used herein, the term "consisting of" is to be understood as excluding the presence of any unspecified element, component, or method step, etc.

[0015] As used herein, the singular forms "a", "an", and "the" include plural referents unless the context clearly dictates otherwise.

[0016] Unless otherwise indicated, the numerical parameters and ranges set forth in the following specification and the appended claims are approximations. Numerical ranges and parameters setting forth broad limits of the invention are approximations, but the numerical values set forth in the specific examples are reported as accurately as possible. However, any numerical value inherently contains errors resulting from the standard deviation found in their respective measurements.

[0017] It should also be understood that any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, the range "1 to 10" is intended to include all sub-ranges between and including the recited minimum value 1 and the recited maximum value 10, i.e., all sub-ranges beginning with a minimum value of 1 or more and ending with a maximum value of 10 or less, such as, for example, all sub-ranges between 1 and 6.3, or between 5.5 and 10, or between 2.7 and 6.1.

[0018] All parts, amounts, concentrations, etc. referred to herein are on a weight basis unless otherwise specified.

[0019] As described above, the present invention relates to a method for producing purified carbon black with a reduced content of oxy-polycyclic aromatic hydrocarbons. The method includes: (a) providing carbon black containing an initial content of 1 ppm or more of oxy-polycyclic aromatic hydrocarbons; (b) treating the carbon black containing the initial content of oxy-polycyclic aromatic hydrocarbons with an extractant containing carbon dioxide in a supercritical state to extract at least a part of the oxy-polycyclic aromatic hydrocarbons from the carbon black; and (c) removing the extractant containing the extracted oxy-polycyclic aromatic hydrocarbons from the carbon black to obtain purified carbon black containing an oxy-polycyclic aromatic hydrocarbon content lower than the initial content of oxy-polycyclic aromatic hydrocarbons.

[0020] The term "polycyclic aromatic hydrocarbon (PAH)" as used herein refers to an organic compound having a skeleton with two or more, for example, 2 to 7 condensed aromatic rings, that is, a polycyclic aromatic structure. A hydrocarbon group such as an alkyl group may be bonded to the skeleton of the condensed aromatic ring. As used herein, "polycyclic aromatic hydrocarbon (PAH)" is an unsubstituted compound having such a polycyclic aromatic structure, that is, each compound consisting only of carbon atoms and hydrogen atoms. In contrast, "oxy-polycyclic aromatic hydrocarbon" as used herein, also abbreviated as "oxy-PAH" herein, refers to an oxygenated derivative of PAH that contains not only carbon and hydrogen but also oxygen. In other words, oxy-PAH represents an organic compound having a skeleton with two or more, for example, 2 to 7 condensed aromatic rings and consisting of carbon atoms, hydrogen atoms, and oxygen atoms. For example, oxy-PAH can be derived from unsubstituted PAH by substituting one or more hydrogen atoms with an oxygen-containing functional group such as a carboxyl group, an aldehyde group, a hydroxyl group, or a ketone group. Examples of oxy-PAH include polycyclic aromatic ketones, polycyclic aromatic quinones, hydroxylated PAH, polycyclic aromatic carboxyaldehydes, polycyclic aromatic carboxylic acids and anhydrides, and polycyclic aromatic lactones. According to the present invention, oxy-PAH can particularly contain one or more ketone groups, that is, oxy-PAH can be a polycyclic aromatic ketone.

[0021] For the purposes of the present invention, the content of carbon black oxy-polycyclic aromatic hydrocarbons (oxy-PAHs) or polycyclic aromatic hydrocarbons (PAHs) can more specifically refer to the content of one or more specific (group of) oxy-PAH compounds or PAH compounds, such as 9,10-phenanthrenedione, oxy-PAH6 or PAH22 groups. Thus, the content of carbon black oxy-polycyclic aromatic hydrocarbons shown herein can in particular mean the content of compounds of the oxy-PAH6 group (also called the oxy-PAH6 content) or the content of 9,10-phenanthrenedione. Similarly, the content of carbon black polycyclic aromatic hydrocarbons (PAHs) shown herein can in particular mean the content of compounds of the PAH22 group (also called the PAH22 content).

[0022] "PAH22", as used herein, refers to the group of the following 22 PAH compounds identified by and referred to in the U.S. Food and Drug Administration (FDA) in 21 C.F.R. § 178.3297 and developed by Cabot Corporation in the method entitled "Measurement of PAH Content of Carbon Black" dated July 8, 1994: 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), chrysene (CAS No. 218-01-9), benzo(b)fluoranthene (CAS No. 205-99-2), benzo(k)fluoranthene (CAS No. 207-08-9), benzo(e)pyrene (CAS No. 192-97-2), benzo(a)pyrene (CAS No. 50-32-8), perylene (CAS No. 198-55-0), dibenzo(a,h)anthracene (CAS No. 53-70-3), benzo(g,h,i)perylene (CAS No. 191-24-2), indeno(1,2,3-cd)pyrene (CAS No. 193-39-5), anthanthrene (CAS No. 191-26-4), and coronene (CAS No. 191-07-1). Thus, the PAH22 content is measured as the total amount of these 22 compounds based on the total weight of the carbon black sample. The PAH22 content can be measured by analyzing the toluene extract obtained by Soxhlet extraction of the carbon black sample using GC-MS utilizing the deuterated form of PAH22 for calibration, in accordance with the above method entitled "Measurement of PAH Content of Carbon Black" dated July 8, 1994, as described in the Examples.

[0023] As used herein, "oxy-PAH6" refers to a group of the following six oxy-PAH compounds: 9,10-phenanthrenedione (CAS No. 84-11-7), 6H-benzo[cd]pyren-6-one (CAS No. 3074-00-8), benzanthrone (CAS No. 82-05-3), benzo[b]fluorene-11-one (CAS No. 3074-03-01), 9-fluorenone (CAS No. 486-25-9), and 4H-cyclopenta[def]phenanthren-4-one (CAS No. 5737-13-3). Thus, the oxy-PAH6 content is measured as the sum of the amounts of these six compounds based on the total weight of the carbon black sample. The oxy-PAH6 content of a carbon black sample can be measured in the same manner as the measurement of the PAH22 content by analyzing the toluene extract obtained by Soxhlet extraction of the carbon black sample by GC-MS using the deuterated form of the oxy-PAH6 compound for calibration. Alternatively, the content of oxy-polycyclic aromatic hydrocarbons in carbon black can be measured as the content of 9,10-phenanthrenedione in carbon black. The content of 9,10-phenanthrenedione can be measured as described in the examples.

[0024] According to the present invention, carbon black containing an initial content of 1 ppm or more of oxy-polycyclic aromatic hydrocarbons is provided as a starting material to be purified. For the sake of clarity, as will be apparent to those skilled in the art, "carbon black" is different from "soot" or "black carbon". Soot or black carbon is used to denote generally undesirable carbonaceous by-products resulting from the incomplete combustion of carbon-containing materials such as oil, fuel, diesel or gasoline, coal, paper or waste. Soot or black carbon contains a large amount of organic and inorganic impurities typically containing less than 60% elemental carbon by total mass and is composed of fairly coarse particles having little clear structure or order. In contrast, carbon black is intentionally produced by the incomplete combustion or pyrolysis of gaseous or liquid hydrocarbons under controlled conditions and typically has a higher carbon content of, for example, 80 wt% or more based on total mass, and is composed of particles having a high degree of order including a clear structure and a graphene-like arrangement of carbon atoms and having a high surface area to volume ratio.

[0025] This initial carbon black provided as a starting material to be purified in the process of the present invention can, in principle, be based on any method for the production of carbon black. Different industrial processes for the production of carbon black are available, for example, the furnace process, the gas black process, the acetylene black process, the thermal black process or the lamp black process, as described in J.-B. Donnet et al., "Carbon Black: Science and Technology", 2nd Edition. Thus, the carbon black containing the initial content of oxy-polycyclic aromatic hydrocarbons used in the practice of the present invention can, for example, include or be furnace black, thermal black, lamp black, channel black, gas black, acetylene black, recycled black, or any combination of the above. Recycled black is obtained from used carbon black-containing products such as waste tires and can be obtained by a recycling method that typically includes two steps: a pyrolysis step for decomposing organic components such as rubber or plastic and a desalting step for dissolving inorganic additives or impurities. A wide variety of carbon blacks with different properties that can be used in the present invention are commercially available from carbon black manufacturers such as Cabot Corporation, Mitsubishi Chemical Corporation, Tokai Carbon Co., Ltd., Denka Co., Ltd., Birla Carbon or Orion Engineered Carbons. Non-limiting examples thereof include carbon blacks sold under the brand names of ECORAX®, PUREX®, CORAX®, PRINTEX®, AROSPERSE®, HIBLACK®, Color Black, Special Black, or NEROX® by Orion Engineered Carbons.

[0026] The carbon black used as a starting material in the method of the present invention may or may not be subjected to any post-treatment. Typically, the carbon black containing the initial content of oxy-polycyclic aromatic hydrocarbons used in the practice of the present invention includes carbon black that has been subjected to an oxidation treatment. Carbon black that has been subjected to an oxidation treatment, also called "oxidized carbon black", contains oxygen-containing functional groups, particularly on the surface of the carbon black particles. Examples of oxygen-containing functional groups include, but are not limited to, alcohol groups, quinone groups, carboxyl groups, phenol groups, lactol groups, lactone groups, anhydride groups, quinone groups, peroxide groups, ether groups, ketone groups, etc. The oxidation treatment can be achieved, for example, by treating with oxidizing agents such as oxygen gas, ozone, peroxides such as hydrogen peroxide, persulfates such as sodium persulfate and potassium persulfate, and hypohalites such as sodium hypochlorite, and also transition metal-containing oxidizing agents such as permanganate, osmium tetroxide, chromium oxide and cerium ammonium nitrate, and further mixtures thereof. In particular, the carbon black containing the initial content of oxy-polycyclic aromatic hydrocarbons used in the practice of the present invention can be ozone-oxidized carbon black. Oxidized carbon black typically has a significant oxygen content. For example, the oxidized carbon black that can be used in accordance with the present invention can have an oxygen content of 0.5 wt% or more, for example 1 wt% or more, 2 wt% or more, 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%, 1 wt% to 15 wt%, 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 a starting material according to the present invention may have an oxygen content in the range between any of the above values.

[0027] The carbon black purified by the method of the present invention has an initial content of oxy-PAH of 1 ppm or more. For example, the carbon black purified by the method of the present invention may have an initial content of oxy-PAH6 of 1 ppm or more. The carbon black may have, for example, an initial content of oxy-polycyclic aromatic hydrocarbons of 2 ppm or more, 3 ppm or more, 4 ppm or more, 5 ppm or more, or 10 ppm or more, such as 20 ppm or more, 30 ppm or more, 40 ppm or more, 50 ppm or more, 80 ppm or more, 100 ppm or more, 150 ppm or more, 200 ppm or more, 250 ppm or more, or 300 ppm or more, for example, an initial content of oxy-PAH6. The carbon black may have, for example, an initial content of oxy-PAH of 5,000 ppm or less, such as 2,000 ppm or less, 1,000 ppm or less, 800 ppm or less, 600 ppm or less, or 500 ppm or less, for example, an initial content of oxy-PAH6. The carbon black purified by the method of the present invention may have an initial content of oxy-PAH in the range between any of the recited values, such as in the range of 1 ppm to 1,000 ppm, or 5 ppm to 500 ppm, or 10 ppm to 100 ppm, for example, an initial content of oxy-PAH6. The carbon black purified by the method of the present invention may have an initial content of 9,10-phenanthrenedione of 1 ppm or more, such as 2 ppm or more, 3 ppm or more, 4 ppm or more, 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. The carbon black may have, for example, an initial content of 9,10-phenanthrenedione of 500 ppm or less, such as 300 ppm or less, 100 ppm or less, 80 ppm or less, 60 ppm or less, or 50 ppm or less. The carbon black purified by the method of the present invention may have an initial content of 9,10-phenanthrenedione in the range between any of the recited values, such as in the range of 1 ppm to 500 ppm, or 2 ppm to 300 ppm, or 5 ppm to 80 ppm.

[0028] The carbon black provided for purification by the method of the present invention can further have an initial content of polycyclic aromatic hydrocarbons (PAHs). The initial content of polycyclic aromatic hydrocarbons can vary significantly depending on the type of carbon black used and its manufacturing method. For example, the initial content of polycyclic aromatic hydrocarbons can vary from as low as a few ppm to up to 10,000 ppm or more. For example, the carbon black purified by the method of the present invention may have an initial content of polycyclic aromatic hydrocarbons of 10 ppm or more, 20 ppm or more, 50 ppm or more, for example 100 ppm or more, 250 ppm or more, 500 ppm or more, 800 ppm or more, or 1,000 ppm or more. The carbon black can have an initial content of polycyclic aromatic hydrocarbons of 10,000 ppm or less, for example 5,000 ppm or less, 3,000 ppm or less, 2,000 ppm or less, 1,000 ppm or less, 800 ppm or less, 500 ppm or less, 400 ppm or less, 300 ppm or less, 200 ppm or less, or 100 ppm or less. The carbon black purified by the method of the present invention may have an initial content of polycyclic aromatic hydrocarbons in a range between any of the recited values, such as in the range of 10 ppm to 10,000 ppm, in the range of 50 ppm to 5,000 ppm, or in the range of 200 ppm to 800 ppm.

[0029] For example, the carbon black purified by the method of the present invention may have an initial content of PAH22 of 10 ppm or more, for example, 20 ppm or more, 30 ppm or more, 50 ppm or more, 80 ppm or more, 100 ppm or more, 250 ppm or more, 500 ppm or more, 800 ppm or more, or 1,000 ppm or more. The carbon black can have an initial content of PAH22 of 10,000 ppm or less, for example, 5,000 ppm or less, 3,000 ppm or less, 2,000 ppm or less, 1,000 ppm or less, 800 ppm or less, 500 ppm or less, 400 ppm or less, 300 ppm or less, 200 ppm or less, 100 ppm or less, or 50 ppm or less. The carbon black purified by the method of the present invention may have an initial content of PAH22 in the range between any of the listed values, such as in the range of 10 ppm to 10,000 ppm, 500 ppm to 3,000 ppm, or 10 ppm to 200 ppm.

[0030] The carbon black can have any combination of initial PAH content such as the PAH22 content specified above and initial oxy-PAH content such as oxy-PAH6 content or 9,10-phenanthrenedione content.

[0031] The carbon black provided in step (a) of the method, including the initial content of oxy-polycyclic aromatic hydrocarbons and any PAHs, can be further characterized by one or more or all of the following properties.

[0032] Thus, the carbon black provided in step (a) of the present method, including the initial content of oxy-polycyclic aromatic hydrocarbons and any PAHs, is characterized by its ash content. The carbon black can have, for example, an ash content of 20% by weight or less, such as 15% by weight or less, 10% by weight or less, 5% by weight or less, 3% by weight or less, 1% by weight or less, 0.5% by weight or less, or 0.1% by weight or less, based on the total weight of the carbon black. The carbon black can have, for example, an ash content of 0.001% by weight or more, such as 0.005% by weight or more, 0.01% by weight or more, 0.05% by weight or more, 0.1% by weight or more, 0.2% by weight or more, 0.3% by weight or more, 0.5% by weight or more, 1% by weight or more, 2% by weight or more, or 3% by weight or more, based on the total weight of the carbon black. The carbon black purified in the method of the present invention can have an ash content in the range between any of the recited values, such as in the range of 0.001% by weight to 20% by weight, 0.005% by weight to 5% by weight, or 0.1 to 1% by weight. The ash content of the carbon black can be measured according to ASTM D1506-15.

[0033] Furthermore, the carbon black including the initial content of oxy-polycyclic aromatic hydrocarbons and any PAHs can be characterized by the content of volatile matter. The content of volatile matter can be measured by heating to 950 °C according to DIN53552:1977. The carbon black can have, for example, a volatile matter content of 20% by weight or less, such as 15% by weight or less, 10% by weight or less, 5% by weight or less, 3% by weight or less, or 1% by weight or less, based on the total weight of the carbon black. The carbon black can have, for example, a volatile matter content of 0.1% by weight or more, such as 0.2% by weight or more, 0.3% by weight or more, 0.5% by weight or more, 1% by weight or more, 2% by weight or more, or 3% by weight or more, based on the total weight of the carbon black. The carbon black purified in the method of the present invention can have a volatile matter content in the range between any of the recited values, such as in the range of 0.1% by weight to 20% by weight, 0.2% by weight to 15% by weight, or 1 to 10% by weight.

[0034] Furthermore, carbon black containing an initial content of oxy-polycyclic aromatic hydrocarbons and any PAHs can be characterized by its moisture content. For example, the carbon black can have a moisture content of 15 wt% or less, such as 10 wt% or less, 5 wt% or less, 3 wt% or less, or 1 wt% or less, based on the total weight of the carbon black. The carbon black can have a moisture content of 0.1 wt% or more, such as 0.2 wt% or more, 0.3 wt% or more, 0.5 wt% or more, or 1 wt% or more, based on the total weight of the carbon black. The carbon black purified in the method of the present invention can have a moisture content in the range between any of the recited values, such as in the range of 0.1 wt% to 15 wt%, 0.2 wt% to 10 wt%, or 0.3 to 3 wt%. The moisture content of the carbon black can be measured according to ASTM D1509-18.

[0035] Carbon black containing an initial content of oxy-polycyclic aromatic hydrocarbons and any PAHs can be further characterized by its carbon content. For example, the carbon black can have a carbon content of 80 wt% or more, such as 85 wt% or more, 90 wt% or more, 95 wt% or more, 97 wt% or more, or 98 wt% or more, based on the total weight of the carbon black. The carbon black can have a carbon content of 99.9 wt% or less, such as 99.5 wt% or less, 99 wt% or less, 98 wt% or less, 97 wt% or less, or 95 wt% or less. The carbon black purified in the method of the present invention can have a carbon content in the range between any of the recited values, such as in the range of 80 wt% to 99.9 wt%, 80 wt% to 97 wt%, or 85 to 95 wt%. The carbon content can be measured by elemental analysis.

[0036] Carbon black containing an initial content of oxy-polycyclic aromatic hydrocarbons and any PAHs can be further characterized by its specific surface area. For example, the carbon black is 10 m 2 / g or more, such as 20 m 2 / g or more, 30 m 2 / g or more, 50 m 2 / g or more, 80 m 2 / g or more, 100 m 2 / g or more, 150 m 2 / g or more, 200 m 2 / g or more, 300 m 2 / g or more, 500 m 2 / g or more, or 1,000 m 2 It can have a BET surface area of / g or more. Carbon black is, for example, 2,000 m 2 / g or less, for example 1,500 m 2 / g or less, 1,000 m 2 / g or less, 800 m 2 / g or less, 500 m 2 / g or less, 300 m 2 / g or less, or 200 m 2 It can have a BET surface area of / g or less. The carbon black purified by the method of the present invention is 10 to 2,000 m 2 / g, 30 to 500 m 2 / g, or 50 to 300 m 2 / g, etc., and can have a BET surface area in the range between any of the described values. The BET surface area can be measured by nitrogen adsorption according to ASTM D6556-19a.

[0037] In the method according to the present invention, a single carbon black, or a mixture of two or more different carbon blacks as described above respectively, can be used as the carbon black material to be purified.

[0038] As described above, in the method according to the invention, provided carbon black having an initial content of oxy-polycyclic aromatic hydrocarbons and optional PAHs is treated with an extractant to extract at least some of the oxy-polycyclic aromatic hydrocarbons and optionally at least some of the polycyclic aromatic hydrocarbons from the carbon black. Here, the extractant comprises carbon dioxide in a supercritical state. "Supercritical state" means that the extractant is in the state of a supercritical fluid. A supercritical fluid is obtained at a temperature and pressure above the critical temperature and critical pressure (critical point), i.e., in the supercritical region of the respective phase diagram. The critical point represents the highest temperature and highest pressure at which each substance can exist in equilibrium as a gas and a liquid. A supercritical fluid exhibits intermediate properties between a gas and a liquid. The use of the extractant in the supercritical state can, for example, advantageously combine a liquid-like density with a gas-like diffusivity and viscosity, which promotes a high mass transfer rate and a rapid and efficient extraction of oxy-PAHs and PAHs from carbon black. Specifically, carbon dioxide has a relatively low critical temperature of 304.2 K (31 °C) and a relatively low critical pressure of about 74 bar (7,380 kPa). Therefore, extraction with an extractant containing carbon dioxide can be carried out under relatively mild conditions, thereby reducing the tendency for undesirable changes to the carbon black during the purification process. Furthermore, supercritical carbon dioxide can be easily separated from the carbon black, for example, by pressure release which results in the evaporation of carbon dioxide. Therefore, a dedicated step for drying or solvent removal after extraction is not necessary. Additionally, carbon dioxide has the advantages of being non-toxic, non-flammable, and inexpensive.

[0039] The extractant used in accordance with the present invention can contain, for example, at least 50% by weight, such as at least 70% by weight, at least 80% by weight, at least 90% by weight, at least 95% by weight, at least 99% by weight, or at least 99.5% by weight of carbon dioxide, based on the total weight of the extractant. In a preferred variant, the extractant can consist of supercritical carbon dioxide, i.e., it does not substantially contain any other components other than carbon dioxide. "Does not substantially contain" means that if substances other than carbon dioxide are present, they are generally contained in the extractant only as small amounts of impurities of 0.2% by weight or less, such as 0.1% by weight or less, or 0.005% by weight or less, based on the total weight of the extractant. Alternatively, the extractant can contain, in addition to carbon dioxide, one or more auxiliary agents. Such auxiliary agents can be used, for example, to control or modify 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, air, oxygen, nitrogen, methane, water, and organic solvents such as methanol, toluene, and dichloromethane, or any combination thereof, but are not limited thereto. The auxiliary agents can be used in any amount in the extractant as required. For example, one or more auxiliary agents can be used in a total amount of 50% by weight or less, such as 30% by weight or less, 20% by weight or less, 10% by weight or less, 5% by weight or less, 1% by weight or less, or 0.5% by weight or less, based on the total weight of the extractant. The amount of the auxiliary agent in the extractant can also be changed over time during the treatment of the carbon black in step (b). However, preferably, the extractant used in the practice of the present invention does not contain any auxiliary agents.

[0040] According to the method disclosed in this specification, carbon black containing an initial content of oxy-polycyclic aromatic hydrocarbons and any PAHs is treated with an extractant containing supercritical carbon dioxide to extract at least some of the oxy-polycyclic aromatic hydrocarbons and any at least some of the polycyclic aromatic hydrocarbons from the carbon black. Thus, 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 under a temperature exceeding the critical temperature of the extractant and a pressure exceeding the critical pressure. The critical temperature and the critical pressure can be derived from the phase diagram of each extractant and correspond to the temperature and pressure at the critical point. The treatment of carbon black with carbon dioxide as the extractant can be carried out, for example, at any temperature above the critical temperature of carbon dioxide (31 °C) and a pressure above the critical pressure of carbon dioxide (73.8 bar). According to the present invention, the treatment of carbon black with the extractant can be carried out, for example, at a temperature of 31 °C or higher, 50 °C or higher, 75 °C or higher, 100 °C or higher, 150 °C or higher, 200 °C or higher, or 250 °C or higher. This treatment can be carried out, for example, at a temperature of 500 °C or lower, for example 400 °C or lower, 350 °C or lower, or 300 °C or lower. The treatment of carbon black with the extractant can be carried out at a temperature in the range between any of the listed values, such as in the range of 75 °C to 400 °C, preferably 100 °C to 350 °C, for example 100 °C to 300 °C. Furthermore, the treatment of carbon black with the extractant can be carried out, for example, at a pressure of 73.8 bar or higher, for example 75 bar or higher, 100 bar or higher, 120 bar or higher, 150 bar or higher, or 200 bar or higher. This treatment can be carried out, for example, at a pressure of 700 bar or lower, for example 500 bar or lower, 400 bar or lower, 300 bar or lower, or 250 bar or lower. The treatment of carbon black with the extractant can be carried out at a pressure in the range between any of the listed values, such as in the range of 75 bar to 700 bar, preferably 100 bar to 500 bar, for example 150 bar to 400 bar.For example, in the method according to the present invention, the treatment of carbon black with an extractant can be carried out at a temperature in the range of 75 to 350 ° C, preferably 120 to 300 ° C, more preferably 150 to 280 ° C, and a pressure in the range of 150 to 400 bar, preferably 180 to 350 bar, more preferably 200 to 320 bar.

[0041] In the method of the present invention, the treatment of carbon black with the extractant can include exposing the carbon black to the flow of the extractant. The average flow rate can vary widely, for example, depending on the size of the reactor used and / or the amount of carbon black treated with the extractant therein. The average flow rate of the extractant can be, for example, 5 NL / h or more, such as 10 NL / h or more, 20 NL / h or more, 50 NL / h or more, 100 NL / h or more, 150 NL / h or more, 200 NL / h or more, 250 NL / h or more, 500 NL / h or more, 1,000 NL / h or more, 5,000 NL / h or more, 10,000 NL / h or more, 50,000 NL / h or more, 100,000 NL / h or more, 500,000 NL / h or more, 1,000,000 NL / h or more, or 5,000,000 NL / h or more. 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, 5,000,000 NL / h or less, 1,000,000 NL / h or less, 500,000 NL / h or less, 100,000 NL / h or less, 50,000 NL / h or less, 10,000 NL / h or less, 5,000 NL / h or less, 1,000 NL / h or less, 500 NL / h or less, 400 NL / h or less, 300 NL / h or less, 250 NL / h or less, 200 NL / h or less, 150 NL / h or less, or 100 NL / h or less. The average flow rate can be in the range between any of the recited values, such as in the range of 5 NL / h to 10,000,000 NL / h, 50 NL / h to 500,000 NL / h, 100 NL / h to 10,000 NL / h, 150 NL / h to 300 NL / h, or 200 NL / h to 250 NL / h. Typically, in a reactor having a relatively small extraction chamber as used in the examples described below, the average flow rate is in the range of 50 NL / h to 250 NL / h. The average flow rate of the extractant is calculated based on the total volume that the supply amount of the extractant would have under standard conditions (101.325 kPa, 0 °C) and the total extraction time. The volume of the extractant can be measured, for example, by a mass flow meter disposed downstream of the extraction chamber, and this mass flow meter measures the amount of the extractant in the gaseous state per unit time at a specific temperature and pressure, for example, room temperature and atmospheric pressure. By time integration, the total volume of the extractant is obtained.Next, the total volume of the extractant measured can be converted to the total volume of the extractant under standard conditions by using the ideal gas law. The total volume of the 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.

[0042] The average flow rate of the extractant per unit volume (L) of the extraction chamber of the reactor is, for example, 50 NL / h -1 ·L -1 or more, for example, 100 NL / h -1 ·L -1 or more, 200 NL / h -1 ·L -1 or more, 500 NL / h -1 ·L -1 or more, 1,000 NL / h -1 ·L -1 or more, 2,000 NL / h -1 ·L -1 or more, 2,500 NL / h -1 ·L -1 or more, or 3,000 NL / h -1 ·L -1 or more. For example, the average flow rate of the extractant per unit volume (L) of the extraction chamber of the reactor is 6,000 NL / h -1 ·L -1 or less, for example, 5,000 NL / h -1 ·L -1 or less, 4,000 NL / h -1 ·L -1 or less, 3,000 NL / h -1 ·L -1 or less, 2,500 NL / h -1 ·L -1 or less, 2,000 NL / h -1 ·L -1 or less, or 1,000 NL / h -1 ·L -1 or less. The average flow rate of the extractant per unit volume of the extraction chamber is 50 NL / h -1 ·L -1 ~6,000 NL / h -1 ·L -1 , 500 NL / h -1 ·L -1~5,000 NL·h -1 ·L -1 、1,000 NL·h -1 ·L -1 ~4,000 NL·h -1 ·L -1 、または2,000 NL·h -1 ·L -1 ~3,000 NL·h -1 ·L -1 It can be in the range between any of the listed values such as 500 NL·h -1 ·L -1 ~3,000 NL·h -1 ·L -1 .

[0043] The average flow rate of the extractant per unit mass (kg) of the treated carbon black is, for example, 100 NL·h -1 ·kg -1 or more, for example 500 NL·h -1 ·kg -1 or more, 1,000 NL·h -1 ·kg -1 or more, 5,000 NL·h -1 ·kg -1 or more, 10,000 NL·h -1 ·kg -1 or more, 20,000 NL·h -1 ·kg -1 or more, or 50,000 NL·h -1 ·kg -1 or more. For example, the average flow rate of the extractant per unit mass (kg) of the treated carbon black is 100,000 NL·h -1 ·kg -1 or less, for example 80,000 NL·h -1 ·kg -1 or less, 50,000 NL·h -1 ·kg -1 or less, 20,000 NL·h -1 ·kg -1 or less, 10,000 NL·h -1 ·kg -1 or less, 5,000 NL·h -1·kg -1 Hereinafter, 2,000 NL·h -1 ·kg -1 or less, or 1,000 NL·h -1 ·kg -1 or less can be. The average flow rate of the extractant per unit mass (kg) of the amount of carbon black processed is 100 NL·h -1 ·kg -1 ~100,000 NL·h -1 ·kg -1 、1,000 NL·h -1 ·kg -1 ~50,000 NL·h -1 ·kg -1 、or 5,000 NL·h -1 ·kg -1 ~20,000 NL·h -1 ·kg -1 It can be in the range between any of the listed values, such as in the range of 5,000 NL·h -1 ·kg -1 ~100,000 NL·h -1 ·kg -1 、for example 5,000 NL·h -1 ·kg -1 ~20,000 NL·h -1 ·kg -1 is.

[0044] Carbon black can be treated with an extractant for any desired time in the process according to the present invention. The treatment time is generally determined by the applied extraction conditions and on the one hand the desired degree of purification and on the other hand economic considerations. For example, carbon black can be treated with an extractant for at least 1 second, such as at least 10 seconds, at least 30 seconds, at least 1 minute, at least 2 minutes, at least 5 minutes, at least 10 minutes, at least 20 minutes, at least 30 minutes, at least 40 minutes, at least 50 minutes, at least 1 hour, at least 2 hours, at least 4 hours, at least 6 hours, at least 10 hours, or at least 15 hours in the process according to the present invention. The treatment of carbon black with an extractant in the process according to the present invention can be carried out, for example, for up to 48 hours, such as 24 hours or less, 20 hours or less, 16 hours or less, 10 hours or less, 6 hours or less, 4 hours or less, 2 hours or less, 1 hour or less, 50 minutes or less, 40 minutes or less, 30 minutes or less, 20 minutes or less, 10 minutes or less, 5 minutes or less, 2 minutes or less, 1 minute or less, 30 seconds or less, or 10 seconds or less. This time can be, for example, in the range of 10 minutes to 45 minutes. Carbon black can be treated with an extractant for a period between any of the recited values, such as 1 minute to 48 hours, 5 minutes to 24 hours, 10 minutes to 4 hours, or 20 minutes to 1 hour.

[0045] In the method according to the present invention, conditions such as the pressure, temperature, and flow rate of the treatment of carbon black with the extractant can be kept substantially constant during the treatment or can be varied in a time-controlled manner. This can be advantageous since, on the one hand, solvent properties such as the solute diffusion rate, viscosity, and mass transfer rate of the supercritical extractant and, on the other hand, the solubility and vapor pressure of oxy-polycyclic aromatic hydrocarbons and PAHs depend on pressure and / or temperature, respectively. Thus, changing the temperature, pressure, and / or flow rate of the extractant during the treatment step can contribute to optimizing the extraction efficiency. The temperature and / or pressure during the treatment step can be changed, for example, stepwise, i.e., the carbon black can be treated with the extractant at a first temperature and a first pressure for a predetermined first time, followed by 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 during the treatment step in any possible way, 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 zones of the extraction chamber and / or between different extraction chambers.

[0046] In the method according to the present invention, the conditions of the treatment step are such that the treatment of carbon black with the extractant extracts at least 50 wt%, at least 70 wt%, at least 80 wt%, at least 90 wt%, at least 95 wt%, at least 99 wt% of oxy-polycyclic aromatic hydrocarbons from the carbon black, based on the initial content of oxy-polycyclic aromatic hydrocarbons. More specifically, the treatment of carbon black with the extractant can include extracting at least 50 wt%, at least 70 wt%, at least 80 wt%, at least 90 wt%, at least 95 wt%, or at least 99 wt% of the initial content of oxy-PAH6 or the initial content of 9,10-phenanthrenedione from the carbon black. Further, the treatment of carbon black with the extractant can include extracting at least 30 wt%, for example at least 40 wt%, at least 50 wt%, at least 70 wt%, at least 80 wt%, at least 90 wt%, at least 95 wt%, at least 99 wt%, at least 99.5 wt%, at least 99.8 wt%, at least 99.9 wt%, or at least 99.95 wt% of the initial content of PAH, for example the initial content of PAH22, from the carbon black.

[0047] It should be noted that PAH and oxy-PAH may be present on the surface and / or inside of the carbon black particles, and their distribution depends on the conditions of the manufacturing method and the conditions of possible post-treatment steps. (Oxy-)PAH molecules present on the surface of the particles can typically be more easily removed during supercritical fluid extraction than the molecules incorporated into the carbon black particles. Thus, for example, (oxy-)PAH mainly present on the surface of the particles can be removed more completely compared to (oxy-)PAH that is more uniformly distributed between the particle surface and the particle volume.

[0048] The method of the present invention further comprises removing from the carbon black an extractant containing the extracted oxy-polycyclic aromatic hydrocarbons and optionally the extracted PAHs to obtain a purified carbon black containing oxy-polycyclic aromatic hydrocarbons in an amount lower than the initial content of the oxy-polycyclic aromatic hydrocarbons and optionally polycyclic aromatic hydrocarbons in an amount lower than the initial content of the polycyclic aromatic hydrocarbons. For example, the carbon black can be treated as described above with a stream of the extractant such that the extractant containing the extracted oxy-polycyclic aromatic hydrocarbons and optionally the extracted PAHs is continuously removed from the treated carbon black, and accordingly, it is gradually purified as the treatment time progresses. The deposition of the extracted oxy-polycyclic aromatic hydrocarbons and optionally the extracted PAHs in the extraction chamber or in the periphery such as a pressure line connected thereto should generally be avoided as this can lead to recontamination of the carbon black and / or clogging of the pressure line. The deposition of the extracted oxy-polycyclic aromatic hydrocarbons and optionally the extracted PAHs in the extraction chamber and the pressure line connected thereto can be prevented, for example, by heating them to a sufficiently high temperature to retain the oxy-polycyclic aromatic hydrocarbons and optionally the extracted PAHs dissolved in the extractant.

[0049] The method disclosed herein may optionally further include separating at least a portion of the oxy-polycyclic aromatic hydrocarbons and any PAHs from the extractant containing the oxy-polycyclic aromatic hydrocarbons and any PAHs removed and extracted from the carbon black. This can be achieved, for example, by phase separation or reduction of solubility of the oxy-polycyclic aromatic hydrocarbons and PAHs in the extractant. For example, the temperature and / or pressure of the extractant containing the extracted oxy-polycyclic aromatic hydrocarbons and any PAHs can be adjusted such that the extractant changes to a gaseous state and the extracted oxy-polycyclic aromatic hydrocarbons and any 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 oxy-polycyclic aromatic hydrocarbons and any PAHs can be adjusted such that the extracted oxy-polycyclic aromatic hydrocarbons and any PAHs condense and / or precipitate, but the extractant remains in a supercritical state. The oxy-polycyclic aromatic hydrocarbons and any PAHs can also be separated from the extractant by passing the extractant containing the extracted oxy-polycyclic aromatic hydrocarbons and any PAHs through a suitable filter such as an adsorption medium or an absorption medium for oxy-PAH / PAH. For example, the extractant containing the extracted oxy-polycyclic aromatic hydrocarbons and any PAHs can be passed through a liquid absorbent medium that may include, for example, one or more organic solvents to absorb at least a portion of the oxy-polycyclic aromatic hydrocarbons and any PAHs and obtain an extractant depleted of oxy-PAH and any PAHs. A suitable absorbent medium is, for example, acetonitrile. The extractant containing the extracted oxy-polycyclic aromatic hydrocarbons and any PAHs can be contacted with the absorbent medium after being converted to a supercritical state or a non-supercritical state, for example, a gaseous state. In the latter case, the temperature and pressure conditions can be selected such that only a portion of the oxy-polycyclic aromatic hydrocarbons and any PAHs condense or precipitate before passing through the absorption medium, or essentially no condensation or precipitation occurs.The separation of at least a portion of the oxy-polycyclic aromatic hydrocarbons and any PAHs from the extractant can also include converting the extractant to a gaseous state, separating at least a portion of the extracted oxy-polycyclic aromatic hydrocarbons and any PAHs from the gaseous extractant as a liquid phase and / or a solid phase by condensation and / or precipitation, and further separating at least a portion of the remaining oxy-polycyclic aromatic hydrocarbons and any PAHs from the extractant by passing through an absorbent medium.

[0050] The method of the present invention can further include recycling the extractant thus obtained for use in the above-described step of treating carbon black containing the initial content of oxy-polycyclic aromatic hydrocarbons and any PAHs, after separating at least a portion of the extracted oxy-polycyclic aromatic hydrocarbons and any PAHs from the extractant. Preferably, the recycled extractant is substantially free or completely free of oxy-polycyclic aromatic hydrocarbons and PAHs. "Substantially free" means, in this regard, that the recycled extractant contains less than 0.5% by weight, for example less than 0.1% by weight, of oxy-polycyclic aromatic hydrocarbons and PAHs. "Completely free" means that the recycled extractant contains no oxy-polycyclic aromatic hydrocarbons and PAHs, except for trace amounts that may be present as randomly distributed impurities.

[0051] Optionally, the methods disclosed herein can further include detecting the amount of oxy-polycyclic aromatic hydrocarbons and / or PAHs extracted by treating carbon black with an extractant. For this purpose, for example, an extractant containing oxy-aromatic hydrocarbons and any PAHs removed and extracted from the carbon black described above, such as a continuous effluent stream from an extraction chamber, can be analyzed for the content of the extracted oxy-polycyclic aromatic hydrocarbons and / or PAHs. The analysis can be performed continuously or discontinuously, for example, as an on-line measurement, i.e., while the extraction process is in progress, and can utilize any analytical technique that provides measurements enabling quantitative or qualitative inferences regarding the current or accumulated amounts of oxy-PAHs and / or PAHs extracted from the carbon black. For example, if the extracted oxy-polycyclic aromatic hydrocarbons and any PAHs are at least partially separated from the extractant by passing through a liquid absorbent medium as described above, the absorbance or change in absorbance of the absorbent medium at one or more characteristic wavelengths within the electromagnetic spectrum, e.g., within the UV or visible range of the electromagnetic spectrum, can be measured over time. From such measurements, an estimate of the current extraction amount and / or the total amount of the extracted oxy-polycyclic aromatic hydrocarbons and / or PAHs can be obtained. Such information regarding the detection of the amount of oxy-polycyclic aromatic hydrocarbons and / or PAHs extracted by treating carbon black with an extractant can further be used to control the treatment of carbon black with the extractant. Thus, for example, if analysis indicates that a certain amount of oxy-polycyclic aromatic hydrocarbons and / or PAHs are being extracted over time, it can be used to control the extraction time, such as by terminating the treatment of carbon black with the extractant. Additionally, the detected information can be used in a feedback mechanism for controlling extraction conditions such as pressure and / or temperature in the treatment of carbon black with the extractant. For example, carbon black containing an initial content of oxy-polycyclic aromatic hydrocarbons and any PAHs can first be exposed to the extractant at a first temperature and a first pressure.Subsequently, for example, when the current extraction amount or extraction rate of oxy-PAH and / or PAH is below a threshold as indicated by the detected information, the pressure and / or temperature can be adjusted to treat the carbon black with the extraction agent at a second temperature and a second pressure. In this way, the extraction parameters can be adjusted to optimize the extraction of different oxy-PAH species and PAH species from the carbon black to be gradually purified. Thereby, for example, different conditions for extracting oxy-PAH and any PAH from the carbon black in the initial extraction stage or the carbon black in the later extraction stage purified to a certain extent can be defined, and / or oxy-PAH and / or PAH located on or near the surface of the carbon black particles, or oxy-PAH and / or PAH located within the carbon black particles (which may have different extraction characteristics) can be extracted. This can increase the extraction efficiency while simultaneously minimizing the influence on other properties of the carbon black, such as surface oxygen-containing groups.

[0052] Optionally, the method according to the invention may further comprise drying the carbon black comprising the initial content of oxy-polycyclic aromatic hydrocarbons and any PAHs before treatment with the extractant. The drying step, if any, is carried out such that the residual moisture is removed from the supplied carbon black sample to a predetermined level that is considered acceptable, for example not exceeding 0.5 wt% or 0.1 wt%, if possible, without substantially changing the surface chemistry of the carbon black particles. Drying is typically carried out by heating the carbon black sample at a high temperature of, for example, 50 °C or higher, 100 °C or higher, or 150 °C or higher, for a time of 1 minute or more, for example 10 minutes or more, 30 minutes or more, 60 minutes or more, or 90 minutes or more, in the range of temperatures of, for example, 100 °C to 200 °C, or 120 °C to 180 °C. Heating can be achieved by any conventional means. Drying can be carried out in a gas atmosphere, for example in a stream of a gaseous medium that can be preheated to a high temperature. The gaseous medium can be, for example, air or nitrogen. However, the gaseous medium can in particular contain one or more components used in the extractant that will later be used during supercritical fluid extraction, but in gaseous state. Thus, the gaseous medium can, for example, contain carbon dioxide or consist of carbon dioxide. In one embodiment, the drying step is carried out at a temperature of about 150 °C, in gaseous carbon dioxide, at a pressure of about 10 bar for about 1.5 hours. For example, the carbon black provided can have an initial moisture content as described above, which can be reduced by drying the carbon black, thereby removing, for example, 80% or more, for example 90% or more, or 95% or more of the initial moisture content from the carbon black. During the drying step, the carbon black can, for example, be present in a reactor, such as the extraction chamber of such a reactor, that will subsequently be used for supercritical fluid extraction as described below, or drying can be carried out outside such a reactor or in a separate unit.

[0053] The method according to the invention can be carried out in a pressure-resistant reactor. Reactors for supercritical fluid extraction are commercially available, for example, from Uhde High Pressure Technologies, Herne, Germany and Thar Process, PA, USA. The reactor is generally configured to withstand the temperature and pressure required for supercritical fluid extraction. The reactor can be made of a suitable metallic structural material such as stainless steel, for example. The reactor generally includes heating means for temperature control in the treatment step using the extractant. The heating means can be any conventional heating means. The reactor can include an extraction volume such as an extraction chamber, into which carbon black is provided for treatment with the extractant. The extraction chamber can have a volume of, for example, 0.01 L or more, such as 0.05 L or more, 0.1 L or more, 0.5 L or more, 1 L or more, 5 L or more, 10 L or more, 50 L or more, 100 L or more, 200 L or more, 500 L or more, or 1,000 L or more. The extraction chamber can have a volume of, for example, 10,000 L or less, such as 5,000 L or less, 2,000 L or less, 1,000 L or less, 500 L or less, 200 L or less, 100 L or less, 50 L or less, 20 L or less, 10 L or less, 5 L or less, 2 L or less, 1 L or less, 0.5 L or less, 0.2 L or less, or 0.1 L or less. The volume of the extraction chamber can be in the range between any of the listed values, such as in the range of 0.01 L to 5,000 L, 0.05 L to 0.5 L, 1 L to 2,000 L, or 10 L to 1,000 L. The reactor can include a single extraction chamber or two or more extraction chambers. For example, a reactor having two or more extraction chambers can be used, enabling batch mode or semi-continuous operation, in which case one or more extraction chambers are filled with the initial carbon black to be treated or the treated carbon black is discharged therefrom while carbon black is extracted in one or more other extraction chambers of the reactor. Thus, the provision of carbon black containing the initial content of oxy-polycyclic aromatic hydrocarbons and any PAHs can include introducing a certain amount of the above carbon black into the extraction chamber of the reactor. Typically, the extractant is supplied to the extraction chamber through an inlet connected to a supply line from one or more sources of the extractant.Extractants containing oxy-polycyclic aromatic hydrocarbons and any PAHs can be removed from the extraction chamber via the outlet and the connected effluent line. The reactor typically further comprises conventional means for flow and process control, such as sensors, pressure or flow regulating means, valves, pumps and controllers. Typically one or more extraction chambers are designed such that the flow of the extractant is forced to pass through rather than over, for example, a carbon black material. In this way, the contact time of the extractant with the carbon particles can be increased and thus the extraction efficiency can be enhanced.

[0054] For example, carbon dioxide can be supplied as an extractant in a pressurized vessel. Carbon dioxide can be withdrawn from the vessel, for example, to establish a continuous flow at a predetermined flow rate adjusted by one or more pumps and / or flow control means connected to the supply line. The pressure and temperature of the extractant can be adjusted by pressure regulating means and heating means, and the extractant is provided in a supercritical state. Pressure adjustment can be achieved, for example, by control of pumps, valves, and backpressure regulators within the system, while heating can be achieved, for example, by heating the supply line, such as by providing an electric heating jacket, heating tape, etc. to the supply line, and / or by one or more heating elements that heat the extraction chamber, which can be of, for example, a resistive electric heater type. The resulting flow of supercritical carbon dioxide extractant contacts the carbon black within the extraction chamber and extracts therefrom oxy-PAHs and any PAHs. Optionally, an adjuvant as described above can be supplied to the flow of carbon dioxide at a predetermined constant or variable ratio at any stage of the reactor, such as upstream of the extraction chamber.

[0055] The method can further include recovering and / or collecting the purified carbon black. This can include stopping the supply of the extractant, removing the extractant or the purified carbon black from the extraction chamber, or separating the purified carbon black from the extractant. Generally, the method according to the invention can be carried out as a continuous process, as a semi-batch process, or as a batch process. In the case of a continuous process, carbon black containing an initial content of oxy-polycyclic aromatic hydrocarbons and any PAHs can be continuously fed, for example, into an extraction chamber treated with an extractant, and the purified carbon black can be continuously removed from the extraction chamber, for example, using a continuous flow of the extractant. Preferably, such a continuous process can be carried out such that carbon black particles fed into the extraction chamber at different times are not substantially mixed so that the residence time in the extraction chamber, and thus the extraction time, is substantially the same. Further, the flow of the extractant from the inlet to the outlet can be in a direction opposite to, the same as, perpendicular to, or any other angular configuration with respect to the transport direction of the carbon black particles.

[0056] In the case of a batch or semi-batch process, a batch of carbon black containing the initial content of oxy-polycyclic aromatic hydrocarbons and any PAHs is loaded into an extraction chamber and treated with an extractant for a desired time under controlled conditions to extract the oxy-PAHs and any PAHs, and a purified carbon black having a reduced oxy-PAH content and any reduced PAH content can be produced. After the desired time, the treatment is stopped and the purified carbon black can be recovered, for example, by releasing the pressure and removing the purified carbon black from the extraction chamber. Before removing the purified carbon black from the extraction chamber, the extractant can optionally be removed from the extraction chamber, for example, by exchanging it 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 oxy-polycyclic aromatic hydrocarbons and any PAHs contained in the extractant can be avoided. Separation of any residual extractant from the purified carbon black can be achieved by reducing the pressure and / or temperature to below the respective critical values for the extractant, thereby converting the extractant to the gaseous state. Since carbon dioxide is a gas under ambient conditions, separation from the purified carbon black can be achieved in a simple manner according to the present invention, and no further drying or purification steps that may be required when an organic solvent or steam is used for extraction are needed either.

[0057] The method of the present invention can generally be carried out independently of the method of manufacturing or treating carbon black. Thus, the present invention can be applied to a wide variety of different carbon black grades. Nevertheless, the method can advantageously be carried out in a carbon black production plant, for example, after a method of manufacturing or treating carbon black. For example, the method disclosed herein can be carried out downstream of carbon black production, such as downstream of a furnace reactor, and upstream or downstream of other carbon black post-treatment methods, such as oxidation treatment.

[0058] The purified carbon black obtained by the method according to the present invention has an oxy-polycyclic aromatic hydrocarbon content that is lower than the initial content of oxy-polycyclic aromatic hydrocarbons in the carbon black provided for purification. The purified carbon black can have, for example, an oxy-polycyclic aromatic hydrocarbon content corresponding to 50 wt% or less, 30 wt% or less, 20 wt% or less, 10 wt% or less, 5 wt% or less, 1 wt% or less, 0.5 wt% or less, 0.2 wt% or less, 0.1 wt% or less, or 0.05 wt% or less of the initial content of oxy-polycyclic aromatic hydrocarbons. For example, the purified carbon black can have an oxy-PAH6 content or a 9,10-phenanthrenedione content corresponding to 50 wt% or less, 30 wt% or less, 20 wt% or less, 10 wt% or less, 5 wt% or less, 1 wt% or less, 0.5 wt% or less, 0.2 wt% or less, 0.1 wt% or less, or 0.05 wt% or less of the initial content of oxy-PAH6 or the initial content of 9,10-phenanthrenedione. Furthermore, the purified carbon black obtainable by the method according to the present invention can optionally further have a PAH content that is lower than the initial PAH content of the carbon black provided for purification. For example, the purified carbon black can have a PAH content, such as a PAH22 content, corresponding to 60 wt% or less, 50 wt% or less, 30 wt% or less, 20 wt% or less, 10 wt% or less, 5 wt% or less, 1 wt% or less, 0.5 wt% or less, 0.2 wt% or less, 0.1 wt% or less, or 0.05 wt% or less of the initial PAH content, such as the initial PAH22 content.

[0059] The purified carbon black obtained by the method according to the present invention can have, for example, a PAH22 content of less than 1,500 ppm, less than 1,000 ppm, less than 700 ppm, less than 500 ppm, less than 200 ppm, less than 150 ppm, less than 100 ppm, less than 50 ppm, less than 20 ppm, less than 10 ppm, less than 5 ppm, less than 3 ppm, less than 2 ppm, less than 1 ppm, or less than 0.5 ppm.

[0060] The purified carbon black obtained by the method according to the present invention can further have an oxy-PAH6 content of less than, for example, 200 ppm, for example, less than 100 ppm, less than 50 ppm, less than 25 ppm, less than 10 ppm, less than 5 ppm, less than 3 ppm, or less than 1 ppm. The purified carbon black obtained by the method according to the present invention can in particular have a content of 9,10-phenanthrenedione of less than 1 ppm.

[0061] The purified carbon black can have any combination of the PAH22 and oxy-PAH6 and / or 9,10-phenanthrenedione contents specified above. The purified carbon black obtained by the method according to the present invention has a PAH content, such as an oxy-PAH content and / or a PAH22 content, that can ensure compliance with official regulations, such as FDA regulations, for the application of purified carbon black in fields such as use in food or beverage contact situations, pharmaceuticals, cosmetics, or the manufacture of children's toys and articles.

[0062] The purified carbon black can further have any one of the 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 surface area. These properties can remain substantially unaffected by the purification method disclosed herein. Thus, apart from the content of oxy-PAH and any 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 surface area of the purified carbon black can correspond to the respective values of the carbon black provided as the starting material as described above, ±30%, or ±20%, or ±10%, or ±5%.

[0063] The purified carbon black obtained according to the present invention can be used in any application where carbon black has been conventionally used or is useful. The purified carbon black according to the present invention can be used, for example, as a pigment, a reinforcing filler, or a conductive agent for the production of plastic articles or rubber articles, paints, inks, coatings, electrodes, or energy storage devices. The purified carbon black according to the present invention is particularly useful in applications where the awareness or concern regarding oxy-PAH and / or PAH is increasing, or in applications where there are public regulations related to PAH, such as in contact situations with food or beverages, pharmaceuticals, cosmetics, or the production of toys and articles for children.

[0064] The present invention has been generally described above. However, a further understanding can be obtained 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. Rather, the present invention should be given the full scope of the appended claims, including any equivalents thereof.

Examples

[0065] All parts and percentages shown throughout the examples refer to weight, unless otherwise specified.

[0066] Materials Used: Carbon black:

[0067] Carbon black A: As an example of a carbon black having a negligible initial content of oxy-PAH, Printex U, a gas black commercially available from Orion Engineered Carbons (comparative example).

[0068] Carbon black B: As an example of a carbon black having a significant initial content of oxy-PAH, ozone-oxidized carbon black A.

[0069] Extraction agent: Carbon dioxide with a purity of 99.995% by volume, supplied in a pressurized liquid form to a 50 L dip tube bottle commercially available from Westfalen.

[0070] Supercritical Fluid Extraction Device: Using a custom-built high-temperature and high-pressure supercritical fluid extraction apparatus that uses supercritical carbon dioxide as the extraction agent, supercritical fluid extraction of the carbon black sample identified above was performed. The apparatus includes a stainless-steel tubular extraction chamber (inner diameter 1.43 cm, length 50 cm, volume 0.080 L) (Swagelok, IPT series 316 / 316L), having an inlet at one end and an outlet at the opposite end. The extraction chamber was attached to an aluminum block equipped with four heating cartridges (Horst Heizpatronen, 230 V, diameter 12.5 mm, length 160 mm, nominal output 500 W) for heating the extraction chamber. Two thermocouples (type K) were installed inside the aluminum block, and heating controllers (Eurotherm, Universalregler 818 and 808) were used in combination for measuring and controlling the temperature of the aluminum block. A dip-tube bottle containing carbon dioxide was connected via a conventional 1 / 4” tube to the inlet of a pump (Knauer 80P having a 100 mL pump head with a cooling unit using a Huber Ministat 125w cc1 cryostat), and from the outlet of the pump, via a pressure line (Swagelok, IPT series, outer diameter 1 / 4”), to the inlet of the extraction chamber for supplying the extraction agent to the extraction chamber. The exhaust pressure line (Swagelok, IPT series, outer diameter 1 / 4”) connected to the outlet of the extraction chamber was led, via a back-pressure regulator (customized Equilibar closed-back pressure resistor BPR equipped with a polyimide membrane and a Kalrez (registered trademark) membrane), into an absorption chamber located downstream of the extraction chamber to reduce the pressure below the critical value. The extraction agent containing oxy-PAH and PAH (here, in gaseous form) passed through the volume of acetonitrile provided as the absorption medium in the absorption chamber and, by passing through a mass flow meter (Bronkhorst, F-201CV) and a valve, the purified extraction medium was released into the atmosphere. To avoid contamination of the pressure line, two filters (Swagelok IPT high-pressure filters each having a filter element with 2 μm pores and 0.5 μm pores) were placed in the pressure lines upstream and downstream of the extraction chamber, respectively.Furthermore, the supply pressure line and the exhaust pressure line were covered with heating tapes (Holst High Temperature Patrone HS450℃ controlled by Eurotherm, Universalregler), and the extractant was heated upstream and downstream of the extraction chamber to avoid line deposition and clogging. The flow rate and pressure of the continuous flow of the extractant through the extraction chamber could be independently controlled, on the one hand, by a pump connected to the supply pressure line, and on the other hand, by a backpressure regulator arranged downstream of the extraction chamber. The reference pressure applied to the dome of the BPR was delivered by a bypass line branching from the supply pressure line between the pump and the inlet of the extraction chamber.

[0071] Supercritical Fluid Extraction: For supercritical fluid extraction, the extraction chamber was filled with approximately 5 g of carbon black to be extracted. The carbon black was fixed between two glass wool plugs. Then, the extraction chamber was heated to an extraction temperature of 250°C, a continuous flow of the extractant through the extraction chamber was provided, and the flow rate and pressure of the extractant were controlled by the pump and the backpressure regulator. Then, the samples were subjected to continuous supercritical fluid extraction for 4 - 5 hours each, using supercritical carbon dioxide as the extractant, at a pressure of 300 bar, a temperature of 250°C, and an estimated average flow rate of the extractant through the extraction chamber of 150 or 60 NL / h (average flow rate per unit volume of the extraction chamber: 1,866 or 746 NL·h -1 ·L -1 ). After that, the flow of the extractant was stopped, the pressure was released from the system, and the samples were cooled to ambient temperature. The extracted carbon black samples thus obtained were analyzed for their PAH22 content and oxy-PAH content as described below.

[0072] Measurement of PAH22 Content and Oxy-PAH Content: The carbon black investigated was analyzed for its PAH22 content after supercritical fluid extraction and compared with the initial PAH22 content measured for each reference sample of the carbon black in its initial state that had not been subjected to supercritical fluid extraction. The PAH22 content was measured as follows, according to the method entitled "Measurement of PAH Content in Carbon Black" dated July 8, 1994, developed by Cabot Corporation and incorporated by the US Food and Drug Administration (FDA) into Title 21 of the Code of Federal Regulations (CFR) 21 Sec. 178.3297.

[0073] The carbon black material was ground with a pestle until a homogeneous powder was obtained. An appropriate amount (up to 10 g) of the powder was accurately weighed into a cellulose extraction thimble (MN645, Macherey-Nagel, Duren, Germany). A glass wool plug and cellulose pieces from the thimble were placed on top of the carbon black, and the filled thimble was loaded into the extraction chamber of a 100 mL Soxhlet apparatus with a 250 mL round-bottom flask. Toluene was added to the flask, and the condenser of the apparatus was gently flushed with nitrogen. The sample was then subjected to Soxhlet extraction with toluene in the Soxhlet apparatus at a rate of approximately 10 cycles / hour for 48 hours under light protection. The resulting crude extract was then concentrated to just over 5 mL using a rotary evaporator (Buchi evaporator R-200, Buchi Labortechnik AG, Flawil 9230, Switzerland) operating at 40 °C under a reduced pressure of at least 5 kPa. The extract was then transferred to a 10 mL volumetric flask and made up to the mark by adding fresh toluene. To aliquots of the extract, 17 deuterated PAH standards (D8-naphthalene, D8- acenaphthylene, D 10 -acenaphthene, D 10 -fluorene, D 10 -phenanthrene, D 10 -anthracene, D 10 -fluoranthene, D 10 -pyrene, D 12 -benzo[a]anthracene, D 12 -chrysene, D 12 -benzo[b]fluoranthene, D 12 -benzo[k]fluoranthene, D12 - Benzo[a]pyrene, D 14 - Dibenz[a,h]anthracene, D 12 - Benzo[g,h,i]perylene, D 12 - Indeno[1,2,3-c,d]pyrene and D 12 - Coronene (200 ng each) were added. Subsequently, the extract aliquots were cleaned up by treatment with a silica gel column (1 g of silica gel / 13% H2O, 8 - 10 mm inner diameter and 5 cm 3 capacity). Thereafter, further deuterated compounds, 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 combined with low-resolution mass spectrometry) for the identification and quantification of PAHs using the following equipment and conditions. Gas chromatograph: Thermo Scientific, GC-Ultra with PVT injector, GC-column: 60 m DB5-MS, 0.25 mm ID, 0.25 μm film thickness; Temperature program GC oven: The oven was preheated to 80 °C, the sample was injected and held at 80 °C for 2 minutes, heated to 180 °C at a rate of 25 °C / min, heated to 220 °C at a rate of 8 °C / min, heated to 250 °C at a rate of 2 °C / min, heated to 280 °C at a rate of 3 °C / min, heated to 320 °C at a rate of 5 °C / min, and held at 320 °C for 21 minutes and 18 seconds; Mass spectrometer: Thermo Scientific Trace DSQ LRMS, operated in electron impact mode (EI) and selected ion monitoring (SIM mode) was chosen; Mass resolution: 1 amu; Molecular ions and fragment ions were monitored for individual PAH compounds. The calibration check of the equipment was performed for each analysis sequence by injection of a mixture containing all natural PAHs of interest and the deuterated standards described above. Identification of PAH species was achieved by analysis of relative retention times, molecular ions and fragment ions, and fragmentation ratios. Quantification was performed using the instrument software via deuterated internal PAHs using isotope dilution and internal standard methods. The PAH22 content was calculated by summing the individually measured concentrations of 22 PAH compounds, and for compounds with concentrations below the limit of quantification (LOQ), the LOQ was adopted as the respective concentration. The co-eluting isomers dibenzo(a,h)anthracene and dibenzo(a,c)anthracene cannot be separated by the GC column and can thus be considered as one substance reported herein as "dibenzo(a,h)anthracene".

[0074] The investigated carbon black samples were analyzed for the content of 9,10-phenanthrenedione, which serves as an indicator of the oxy-PAH content, after supercritical fluid extraction and compared with the initial content of 9,10-phenanthrenedione measured for the reference samples of carbon black in the initial state that had not undergone supercritical fluid extraction. The measurement of the oxy-PAH content was carried out in the same manner as the measurement of the above-mentioned PAH22 content, based on the same analytical method. In particular, the extraction of carbon black, the volume reduction of the raw material extract, and the adjustment of the specified volume were carried out in exactly the same manner as above. The next steps were carried out as described above with the following modifications specific to oxy-PAH: To the aliquots of the extract, deuterated nitro-PAH (D9-3-nitrofluoranthene, 250 ng) was added as an internal standard instead of the above-mentioned 17 deuterated PAH standards. The oxy-PAH extraction aliquots containing the deuterated internal standard were directly subjected to high-resolution mass spectrometry (HRGC / HRMS) without further treatment. The following equipment and conditions were applied. Thermo Scientific, GC-Ultra2000 with PVT injector, GC column: 30 m DB5-MS, 0.25 mm ID, 0.1 μm film thickness, temperature program GC oven: The oven was preheated to 80 °C, the sample was injected, and held at 80 °C for 3 minutes and 42 seconds, heated to 180 °C at a rate of 35 °C / min, heated to 290 °C at a rate of 6 °C / min, and held at 290 °C for 37 seconds; Mass spectrometer: Thermo Scientific MAT95HRMS, operated in electron impact mode (EI) and selected ion monitoring (SIM mode) was chosen; Mass resolution: <8,000 amu, the molecular ions and fragment ions of the oxy-PAH compounds were monitored. The calibration check of the HRMS instrument was carried out for each analysis sequence by injecting a mixture containing 9,10-phenanthrenedione, 9-nitrofluoranthene, and the above-mentioned deuterated standards. The identification of the oxy-PAH species was achieved by analysis of the relative retention time, molecular ions and fragment ions, and fragmentation ratios. Quantification was carried out using standard methods via the deuterated internal nitro-PAH using the instrument software.

[0075] The PAH22 content and the content of 9,10-phenanthrenedione of the extracted carbon black A sample and carbon black B sample were measured as described above. The results were summarized in Table 1 below, compared with the initial content of PAH22 and the initial content of 9,10-phenanthrenedione measured for the initial state of carbon black A and B not subjected to SFE as a reference. The reported relative extraction amount was calculated according to the formula: 1 - (x(example) / x(reference)), where x(example) and x(reference) represent the detected amount of the aforementioned compound or the total detected amount of the aforementioned compound group for a given extracted carbon black and an individual reference carbon black in the initial state, respectively.

[0076]

Table 1

[0077] As exemplified by Example 1 in Table 1, conventional carbon black that is not post-treated oxidatively typically has a negligible content of oxy-PAH but can contain a significant amount of PAH (Reference 1). Purified carbon black with a significantly reduced content of polycyclic aromatic hydrocarbons compared to the starting material (Reference 1) can be obtained by supercritical fluid extraction using carbon dioxide as an extractant (Example 1). On the other hand, as shown in Example 2, oxidation with an ozone oxidant can result in carbon black having a significantly reduced PAH content but a significant amount of oxy-PAH (Reference 2). However, as demonstrated by Example 2, supercritical fluid extraction using carbon dioxide as an extractant enables the effective removal of oxy-PAH from carbon black as well. Therefore, purified carbon black with a significantly reduced content of oxy-PAH (as well as PAH) compared to the starting material (Reference 2) can be obtained by supercritical fluid extraction using carbon dioxide as an extractant (Example 2).

Claims

1. A method for producing purified carbon black with reduced oxy-polycyclic aromatic hydrocarbon (oxy-PAH) content, (a) To provide carbon black containing an initial content of 1 ppm or more of oxy-polycyclic aromatic hydrocarbons, (b) Extracting at least a portion of the oxy-polycyclic aromatic hydrocarbons from carbon black by treating carbon black containing an extractant with supercritical carbon dioxide, and (c) Removing the extractant containing the extracted oxy-polycyclic aromatic hydrocarbons from the carbon black to obtain purified carbon black containing oxy-polycyclic aromatic hydrocarbons at a lower content than the initial content of oxy-polycyclic aromatic hydrocarbons, A method for producing refined carbon black.

2. Carbon black containing an initial content of oxy-polycyclic aromatic hydrocarbons, containing oxidized carbon black, and / or The method according to claim 1, wherein the carbon black containing an initial content of oxy-polycyclic aromatic hydrocarbons exhibits one or more or all of the following: - Ash content of 20% by weight or less, as measured according to ASTM D1506-15. - Volatile content of 20% by weight or less, determined by heating to 950°C in accordance with DIN 53552:1977. - Moisture content of 15% by weight or less, as measured according to ASTM D1509-18, and / or - Carbon content of 80% by weight or more, as measured by elemental analysis.

3. The content of oxy-polycyclic aromatic hydrocarbons is measured as oxy-PAH6 content or as 9,10-phenantradione content. Carbon black containing an initial content of oxy-polycyclic aromatic hydrocarbons, - Initial content of oxy-PAH6 of 1 ppm or more, and / or - Having an initial content of 9,10-phenantrendione of 1 ppm or more, The method according to claim 1 or 2.

4. The carbon black provided in step (a) further contains an initial content of polycyclic aromatic hydrocarbons (PAHs), The treatment of carbon black with an extractant containing supercritical carbon dioxide in step (b) extracts at least a portion of the polycyclic aromatic hydrocarbons from the carbon black, The method according to claim 1 or 2, further comprising step (c) removing the extractant containing the extracted polycyclic aromatic hydrocarbons from the carbon black to obtain the purified carbon black containing polycyclic aromatic hydrocarbons at a lower content than the initial content of the polycyclic aromatic hydrocarbons.

5. The content of polycyclic aromatic hydrocarbons (PAHs) was measured as PAH22 content. The method according to claim 4, wherein the carbon black provided in step (a) has an initial PAH22 content of 10 ppm or more.

6. The method according to claim 1 or 2, wherein the extractant contains at least 50% by weight of carbon dioxide based on the total weight of the extractant.

7. The method according to claim 1 or 2, wherein the extractant further comprises one or more auxiliary agents, or the extractant comprises supercritical carbon dioxide.

8. The carbon black treatment with the extractant in step (b) is carried out at a temperature of 75°C or higher and / or at a pressure of 75 bar or higher, and / or The method according to claim 1 or 2, wherein the treatment of carbon black with an extractant in step (b) is carried out for a period of at least one minute.

9. The treatment of carbon black with an extractant in step (b) includes exposing the carbon black to a flow of extractant, The average flow rate of the extractant per unit mass of the amount (kg) of processed carbon black is 1,000 NL·h. －１ ・kg －１ The method according to claim 1 or 2, which corresponds to the above.

10. The treatment of carbon black using the extractant in step (b) - This includes extracting at least 50% by weight of the initial oxy-PAH content from carbon black. The method according to claim 1 or 2.

11. The treatment of carbon black using the extractant in step (b) - This includes extracting at least 40% by weight of the initial PAH content from carbon black. The method according to claim 1 or 2.

12. The refined carbon black obtained in process (c) - A content of oxy-polycyclic aromatic hydrocarbons equivalent to 50% by weight or less of the initial content of oxy-polycyclic aromatic hydrocarbons, and / or - Having a PAH content equivalent to 60% by weight or less of the initial content of polycyclic aromatic hydrocarbons (PAHs), The method according to claim 1 or 2.

13. The method according to claim 1 or 2, further comprising one or more or all of the following: - Before treatment with the extractant, dry the carbon black containing the initial content of oxy-polycyclic aromatic hydrocarbons. - Separating at least a portion of oxy-polycyclic aromatic hydrocarbons and any polycyclic aromatic hydrocarbons from the extractant containing extracted polycyclic aromatic hydrocarbons removed from carbon black in step (c), and optionally recycling the extractant thus obtained for use in step (b). - To detect the amount of oxy-polycyclic aromatic hydrocarbons and / or polycyclic aromatic hydrocarbons extracted by the extractant.

14. The method described above may be carried out as a continuous method, a semi-batch method, or a batch method, and / or The method according to claim 1 or 2, wherein the method is carried out in a pressure-resistant reactor having a heating means.

15. A purified carbon black obtained by the method described in claim 1.

16. The carbon black according to claim 15, having a 9,10-phenantradione content of less than 1 ppm and / or a PAH22 content of less than 1,500 ppm.

17. Use of the purified carbon black according to claim 15 or 16 as a pigment, reinforcing filler, or conductive agent.

18. The use of supercritical carbon dioxide to remove oxy-polycyclic aromatic hydrocarbons from carbon black.