Process for Producing Carbon Blacks with Reduced Content of Oxy-Polycyclic Aromatic Hydrocarbons (Oxy-PAHS) Utilizing Supercritical Fluid Extraction

Abstract

It is provided a process for producing a purified carbon black with a reduced content of oxy-polycyclic aromatic hydrocarbons, the process including: (a) providing a carbon black including an initial content of oxy-polycyclic aromatic hydrocarbons of 1 ppm or more, (b) treating the carbon black including an initial content of oxy-polycyclic aromatic hydrocarbons with an extraction agent including carbon dioxide in a supercritical state to extract at least a portion of the oxy-polycyclic aromatic hydrocarbons from the carbon black, and (c) removing the extraction agent including the extracted oxy-polycyclic aromatic hydrocarbons from the carbon black to obtain a purified carbon black with a lower content of oxy-polycyclic aromatic hydrocarbons than the initial content of oxy-polycyclic aromatic hydrocarbons. It is furthermore provided a carbon black obtained through said production process and articles made therefrom.

Claims

1. A process for producing a purified carbon black with a reduced content of oxy-polycyclic aromatic hydrocarbons (oxy-PAHs), the process comprising: (a) providing a carbon black comprising an initial content of oxy-polycyclic aromatic hydrocarbons of 1 ppm or more, (b) treating the carbon black comprising an initial content of oxy-polycyclic aromatic hydrocarbons with an extraction agent comprising carbon dioxide in a supercritical state to extract at least a portion of the oxy-polycyclic aromatic hydrocarbons from the carbon black, and removing the extraction agent comprising the extracted oxy-polycyclic aromatic hydrocarbons from the carbon black to obtain a purified carbon black with a lower content of oxy-polycyclic aromatic hydrocarbons than the initial content of oxy-polycyclic aromatic hydrocarbons.

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

3. The process according to claim 1, wherein the content of oxy-polycyclic aromatic hydrocarbons is determined as the oxy-PAH6 content or is determined as the content of 9,10-phenantrenedione, wherein the carbon black comprising an initial content of oxy-polycyclic aromatic hydrocarbons may for example have an initial oxy-PAH6 content of 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 an initial content of 9,10-phenantrenedione of 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 process according to claim 1, wherein the carbon black provided in (a) further comprises an initial content of polycyclic aromatic hydrocarbons (PAHs), treating the carbon black in (b) with an extraction agent comprising carbon dioxide in a supercritical state extracts at least a portion of the polycyclic aromatic hydrocarbons from the carbon black, and step (c) further comprises removing the extraction agent comprising the extracted polycyclic aromatic hydrocarbons from the carbon black to obtain a purified carbon black with a lower content of polycyclic aromatic hydrocarbons than the initial content of polycyclic aromatic hydrocarbons.

5. The process according to claim 4, wherein the content of polycyclic aromatic hydrocarbons (PAHs) is determined as the 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. The process according to claim 1, wherein the extraction agent 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 extraction agent.

7. The process according to claim 1, wherein the extraction agent further comprises one or more auxiliary agents or wherein the extraction agent consists of supercritical carbon dioxide.

8. The process according to claim 1, wherein treating the carbon black with the extraction agent in step (b) is conducted at a temperature of 75 C. or more, such as at a temperature in a range from 75 C. to 400 C., preferably from 100 C. to 350 C., such as from 100 C. to 300 C., and/or at a pressure of 75 bar or more, such as a pressure in a range from 75 bar to 700 bar, preferably from 100 bar to 500 bar, such as from 150 bar to 400 bar and/or wherein treating the carbon black with the extraction agent in step (b) is conducted for a time of at least 1 minute, such as a time of at least 1 hour and/or of up to 48 hours.

9. The process according to claim 1, wherein treating the carbon black with the extraction agent in step (b) comprises exposing the carbon black to a flow of the extraction agent, wherein the average flow rate of the extraction agent per mass unit of the amount of treated carbon black (in kg) corresponds preferably to 1,000 NL.Math.h.sup.1.Math.kg.sup.1 or more, such as 5,000 NL h.sup.1.Math.kg.sup.1 or more, for example from 5,000 NL h.sup.1.Math.kg.sup.1 to 100,000 NL.Math.h.sup.1.Math.kg.sup.1.

10. The process according to claim 1, wherein treating the carbon black with the extraction agent 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 oxy-PAH content, such as of the initial oxy-PAH6 content or of the initial content of 9,10-phenantrenedione, from the carbon black.

11. The process according to claim 4, or claims dependent thereon, wherein treating the carbon black with the extraction agent in step (b) comprises extracting 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 of the initial PAH22 content, from the carbon black.

12. The process according to claim 1, wherein the purified carbon black obtained in step (c) has: a content of oxy-polycyclic aromatic hydrocarbons, such as oxy-PAH6 content or content of 9,10-phenantrenedione, which corresponds to 50 wt. % or less, such as 30 wt. % or less, such as 20 wt. % or less, such as 10 wt. % or less, such as 5 wt. % or less of the initial oxy-PAH content, such as of the initial oxy-PAH6 content or of the initial content of 9,10-phenantrenedione; and/or a content of polycyclic aromatic hydrocarbons (PAHs), such as PAH22 content, which corresponds to: 60 wt. % or less, such as 30 wt. % or less, such as 20 wt. % or less, such as 10 wt. % or less, such as 5 wt. % or less of the initial PAH, content, such as of the initial PAH22 content.

13. The process according to claim 1, further comprising one or more or all of the following: drying the carbon black comprising an initial content of oxy-polycyclic aromatic hydrocarbons prior to treating it with the extraction agent; separating at least a portion of the oxy-polycyclic aromatic hydrocarbons and optionally polycyclic aromatic hydrocarbons from the extraction agent comprising the extracted polycyclic aromatic hydrocarbons removed from the carbon black in step (c), such as by reducing the pressure, and optionally recycling the thus obtained extraction agent for use in step (b); detecting the amount of oxy-polycyclic aromatic hydrocarbons and/or polycyclic aromatic hydrocarbons extracted by the extraction agent, such as by an online measurement, wherein preferably the treatment of the carbon black with the extraction agent in step (b) is controlled based on the detected amount of extracted oxy-polycyclic aromatic hydrocarbons and/or polycyclic aromatic hydrocarbons.

14. The process according to claim 1, wherein the process is conducted as a continuous process, as a semi-batch or as a batch process and/or wherein the process is carried out in a pressure-resistant reactor with heating means.

15. A purified carbon black obtainable by the process according to claim 1.

16. The carbon black according to claim 15 having a content of 9,10-phenantrenedione 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 a purified carbon black according to claim 15 as pigment, reinforcing filler or conductive agent, for example for the manufacture of plastic or rubber articles, paints, inks, coatings, electrodes or energy storage devices.

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

Description

EXAMPLES

[0072] All parts and percentages indicated throughout the Examples refer to weight, unless specified otherwise.

Employed Materials:

[0073] Carbon blacks: [0074] Carbon Black A: Printex U, a commercially available gas black from Orion Engineered Carbon GmbH, as an example of a carbon black having a negligible initial oxy-PAH content (Comparative Example). [0075] Carbon Black B: Ozone-oxidized Carbon Black A, as an example of a carbon black having a considerable initial oxy-PAH content. [0076] Extraction agent: Carbon dioxide with a purity of 99.995 volume-%, supplied in pressurized liquid form in a 50 L dip tube bottle, commercially available from Westfalen AG.

Supercritical Fluid Extraction Setup:

[0077] Supercritical fluid extraction of samples of the above-identified investigated carbon blacks was carried out in a custom-made high-temperature, high-pressure supercritical fluid extraction setup using supercritical carbon dioxide as extraction agent. The setup comprises a tube-shaped 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 its opposite end. The extraction chamber was mounted in an aluminum block equipped with four heating cartridges (Horst Heizpatronen 230 V, diameter 12.5 mm, length 160 mm, nominal power 500 W) for heating the extraction chamber. Two thermocouples (type K) were mounted within the aluminum block and used in combination with heating controllers (Eurotherm Universalregler 818 and 808) for measurement and regulation of the temperature of the aluminum block. The dip tube bottle containing carbon dioxide was connected via conventional tubes to the inlet of a pump (Knauer 80 P with an 100 mL pump head equipped with a cooling unit utilizing a Huber Ministat 125w cc1 cryostat) and from the outlet of the pump via a pressure line (Swagelok IPT series, outer diameter ) to the inlet of the extraction chamber for feeding the extraction agent to the extraction chamber. An exhaust pressure line (Swagelok IPT series, outer diameter ) connected to the outlet of the extraction chamber leads via a back-pressure regulator (customized Equilibar blockage resistant BPR equipped with a polyimide membrane and Kalrez membranes) for reducing the pressure below the critical value into an absorption chamber located downstream of the extraction chamber to pass the (then gaseous) extraction agent laden with oxy-PAHs and PAHs through a volume of acetonitrile provided as absorbing medium in the absorption chamber and releasing the purified extraction medium into the atmosphere by passing it through a mass flow meter (Bronkhorst F-201 CV) and a valve. Two filters (Swagelok IPT high pressure filters with each a 2 um pore and a 0.5 m pore filter element) were placed in the pressure lines upstream of and downstream of the extraction chamber, respectively, to avoid contamination of the pressure lines. The feed and exhaust pressure lines were moreover mantled with heating tapes (Horst Heizleitungen HS 450 C. controlled by Eurotherm Universalregler) for heating of the extraction agent upstream and downstream of the extraction chamber to avoid precipitation and plugging of the lines. Flow rate and pressure of the continuous flow of extraction agent through the extraction chamber were controllable independently on the one hand by the pump connected to the feeding pressure line and on the other hand by the back-pressure regulator located downstream of the extraction chamber. The reference pressure applied to the dome of the BPR was delivered by a bypass line branching off from the feeding pressure line between the pump and the inlet of the extraction chamber.

Supercritical Fluid Extraction:

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

[0079] The thus obtained extracted carbon black samples were analyzed for their PAH22 and oxy-PAH content as described below.

Determination of PAH22 and oxy-PAH Content:

[0080] The investigated carbon blacks were analyzed for their PAH22 content after supercritical fluid extraction and compared to the initial PAH22 content determined for a reference sample of the respective pristine carbon black that has not been subjected to supercritical fluid extraction. The PAH22 content was each determined following the method entitled Determination of PAH content of Carbon Black, dated Jul. 8, 1994, as developed by Cabot Corp., and incorporated by the American Food and Drug Administration (FDA) in the U.S. Code of Federal Regulations (CFR) 21 Sec.178.3297, as follows:

[0081] The carbon black material was crushed in a mortar with a pestle until a homogenous powder was obtained. A suitable amount (up to 10 g) of the powder was precisely weighed in a cellulose extraction thimble (MN 645, Macherey-Nagel, Dren, Germany). A glass wool plug and cellulose pieces from an extraction thimble were put on top of the carbon black and the filled thimble then loaded in the extraction chamber of a 100 mL Soxhlet apparatus with a 250 mL round bottom flask. Toluene was added to the flask and the condenser of the apparatus was gently flushed with nitrogen. The sample was then subjected to Soxhlet extraction with toluene in the Soxhlet apparatus for 48 h under light protection at a rate of approx. 10 cycles per hour. The obtained raw extract was then concentrated to slightly over 5 mL by means of a rotary evaporator operated at 40 C. and a pressure reduction of 5 kPa as a minimum (Bchi Rotavapor R-200, Bchi Labortechnik AG, 9230 Flawil, Switzerland). The extract was then transferred to a 10 mL volumetric flask and brought to the mark by adding fresh toluene. To an aliquot of the extract were added 17 deuterated PAH standards (D.sub.8-Naphthalene, D.sub.8-Acenaphthylene, D.sub.10-Acenaphthene, D.sub.10-Fluorene, D.sub.10-Phenanthrene, D.sub.10-Anthracene, D.sub.10-Fluoranthene, D.sub.10-Pyrene, D.sub.12-Benzo[a]anthracene, D.sub.12-Chrysene, D.sub.12-Benzo[b]fluoranthene, D.sub.12-Benzo[k]fluoranthene, D.sub.12-Benzo[a]pyrene, D.sub.14-Dibenz[a,h]anthracene, D.sub.12-Benzo[g,h,i]perylene, D.sub.12-Indeno[1,2,3-c,d]pyrene and D.sub.12-Coronene, each in an amount of 200 ng). Then, the extract aliquot was cleaned-up by treatment with a silica gel column (1 g silica gel/13% H.sub.2O, 8 to 10 mm inner diameter and 5 cm.sup.3 capacity). Subsequently, a further deuterated compound, D.sub.12-Perylene, was added to the cleaned-up extract as recovery standard in an amount of 200 ng. The thus obtained solution was then used for HRGC/LRMS analysis (Capillary gas chromatography coupled with low resolution mass spectrometry) for PAH identification and quantification using the following instrumentation and conditions: Gas chromatograph: Thermo Scientific GC-Ultra with PTV injector, GC-column: 60 m DB5-MS, 0.25 mm ID, 0.25 um film thickness; temperature program GC oven: preheating oven to 80 C., sample injection, holding for 2 min at 80 C., heating with a rate of 25 C./min to 180 C., heating with a rate of 8 C./min to 220 C., heating with a rate of 2 C./min to 250 C., heating with a rate of 3 C./min to 280 C., heating with a rate of 5 C./min to 320 C., hold at 320 C. for 21 min and 18 seconds; Mass spectrometer: Thermo Scientific Trace DSQ LRMS, operated in the electron impact mode (El) and Selected Ion Monitoring (SIM Mode); mass resolution: 1 amu; monitoring of molecular and fragment ions for the individual PAH compounds. Calibration check of the instrument was performed for each analysis sequence by injection of mixtures containing all native PAHs of interest and the above-mentioned deuterated standards. Identification of the PAH species was achieved by analysis of the relative retention time, the molecular and fragment ions, and the fragmentation ratio. Quantification was performed using the instrumentation software via the deuterated internal PAHs using the isotope dilution and internal standard method. The PAH22 content was calculated by summing up the individual determined concentrations of the 22 PAH compounds, whereby for compounds, whose concentration were below the limit of quantification (LOQ), the LOQ was adopted as the respective concentration. The co-eluting isomer dibenz(a,h)anthracene and dibenz(a,c)anthracene could not be separated by the GC column and where thus taken as one substance, reported herein as dibenz(a,h)anthracene.

[0082] The investigated carbon black samples were also analyzed for their content of 9,10-phenantrenedione, which served as an indicator of the oxy-PAH content, after supercritical fluid extraction and compared to the initial content of 9,10-phenantrenedione determined for a reference sample of the pristine carbon black that has not been subjected to supercritical fluid extraction. The determination of the oxy-PAH content was carried out in analogy to the determination of the PAH22 content as described above, based on the same analytical methods. In particular, the extraction of the carbon black, the volume reduction of the raw extract and the adjustment of a defined volume were performed exactly in the same manner as described above. The further steps were carried out as described above with the following oxy-PAH specific adaptations: To an aliquot of the extract was added as internal standard a deuterated nitro-PAH (D.sub.9-3-Nitrofluoranthene in an amount of 250 ng) instead of the above-mentioned 17 deuterated PAH standards. The oxy-PAH extract aliquot containing the deuterated internal standard was directly subjected to High Resolution Mass Spectrometry (HRGC/HRMS) without further treatment. The following instrumentation and conditions were applied: Thermo Scientific GC-Ultra 2000 with PTV injector, GC-column: 30 m DB5-MS, 0.25 mm ID, 0.1 um film thickness, temperature program GC oven: preheating oven to 80 C., sample injection, holding for 3 min and 42 seconds at 80 C., heating with a rate of 35 C./min to 180 C., heating with a rate of 6 C./min to 290 C., hold at 290 C. for 37 seconds; mass spectrometer: Thermo Scientific MAT 95 HRMS, operated in the electron impact mode (EI) and Selected Ion Monitoring (SIM Mode); mass resolution: <8.000 amu, monitoring of molecular and fragment ions for the oxy-PAH compound. Calibration check of the HRMS instrument was performed for each analysis sequence by injection of mixtures containing 9,10-phenantrenedione, 9-Nitrofluoranthene and the above-mentioned deuterated standard. Identification of the oxy-PAH species was achieved by analysis of the relative retention time, the molecular and fragment ions, and the fragmentation ratio. Quantification was performed using the instrumentation software via the deuterated internal nitro-PAH using the standard method.

[0083] The PAH22 content and content of 9,10-phenantrenedione of the extracted Carbon Black A and Carbon Black B samples was each determined as described above. The results are summarized in Table 1 below in comparison to the initial PAH22 content and content of 9,10-phenantrenedione determined for the pristine carbon blacks A and B that have not been subjected to SFE as a reference. The reported relative extracted amount has been calculated according to the formula 1(x(example)/x(reference)), wherein x(example) and x(reference) represent the detected amount of the indicated compound or detected total amount of the indicated group of compounds for the given extracted carbon black and the respective pristine reference carbon black, respectively.

TABLE-US-00001 TABLE 1 Reference 1 Example 1 (Comparative Example) Reference 2 Example 2 Carbon Black type: A A B B SFE treatment: none 250 C., 300 bar, 150 NL/h, 4 h none 250 C., 300 bar, 60 NL/h, 5 h CAS No. Compound name ppm (mg/kg) ppm (mg/kg) rel. extracted amount ppm (mg/kg) ppm (mg/kg) rel. extracted amount Oxy-PAH 84-11-7 9,10-Phenantrenedione <0.25 <0.25 9.77 0.84 0.914 PAH 91-20-3 Naphthalene 215 2.98 0.986 20.5 1.37 0.933 208-96-8 Acenaphthylene 325 0.70 0.998 0.31 0.02 0.935 83-32-9 Acenaphthene <1 <0.1 <0.02 <0.02 86-73-7 Fluorene 6.47 <0.1 >0.985 0.39 <0.02 >0.948 85-01-8 Phenanthrene 841 26.2 0.969 18.4 3.90 0.788 120-12-7 Anthracene 137 8.43 0.938 1.83 0.19 0.896 206-44-0 Fluoranthene 212 17.9 0.916 4.06 1.24 0.695 129-00-0 Pyrene 146 16.8 0.885 0.82 0.10 0.878 203-12-3 Benzo(g,h,i)fluoranthene 35.5 17.5 0.507 0.27 0.17 0.370 56-55-3 Benz(a)anthracene 13.7 2.01 0.853 0.27 0.17 0.370 27208-37-3 Cyclopenta(c,d)pyrene 25.1 <0.1 >0.996 0.15 0.09 0.4 218-01-9 Chrysene 13.7 2.65 0.807 0.39 0.31 0.205 205-99-2 Benzo(b)fluoranthene 27.4 15.6 0.431 0.38 0.38 207-08-9 Benzo(k)fluoranthene 21.4 8.46 0.605 0.17 0.22 192-97-2 Benzo(e)pyrene 11.8 9.56 0.190 0.05 0.04 0.2 50-32-8 Benzo(a)pyrene 18.5 8.23 0.555 0.04 0.03 0.25 198-55-0 Perylene 7.69 4.38 0.430 <0.02 <0.02 53-70-3 Dibenz(a,h)anthracene 3.78 2.28 0.397 <0.02 <0.02 191-24-2 Benzo(g,h,i)perylene 18.9 17.5 0.074 <0.02 <0.02 193-39-5 Indeno(1,2,3-cd)pyrene 30.5 21.0 0.311 0.04 0.05 191-26-4 Anthanthrene 6.95 4.04 0.419 <0.02 <0.02 191-07-1 Coronene 6.12 5.08 0.170 <0.02 <0.02 PAH22 class: 2125 191.3 0.910 48.1 8.28 0.828

[0084] As illustrated by Example 1 in Table 1, conventional carbon blacks not oxidatively aftertreated typically have a negligible content of oxy-PAHs, but may contain significant amounts of PAHs (Reference 1). Purified carbon blacks with a significantly reduced content of polycyclic aromatic hydrocarbons compared to the starting material (Reference 1) can be obtained through the supercritical fluid extraction with carbon dioxide as extraction agent (Example 1). On the other hand, as illustrated by Example 2, oxidation with an oxidation agent as ozone, can yield carbon blacks, which have a significantly reduced PAH content, but a considerable amount of oxy-PAHs (Reference 2). As demonstrated by Example 2, supercritical fluid extraction with carbon dioxide as extraction agent allows however to effectively remove also the oxy-PAHs from the carbon black. Thus, purified carbon blacks with a significantly reduced content of oxy-PAHs (as well as PAHs) compared to the starting material (Reference 2) can be obtained through the supercritical fluid extraction with carbon dioxide as extraction agent (Example 2).