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Founded Year

1997

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Unattributed VC | Alive

Total Raised

$14.84M

Last Raised

$10.3M | 1 yr ago

About Micropore

Micropore manufactures reactive plastics which incorporate various powders into a molded matrix. The company's first product uses a CO2 adsorbent powder which is formed into a cartridge to create a CO2 adsorbent system used in rebreathing and life support applications. The CO2 adsorbent cartridges are marketed under the ExtendAir brand name and are used for life support in the fire-fighting, medical, dive, submarine and military markets.

Micropore Headquarter Location

1000 Konica Drive

Elkton, Maryland, 21921,

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302-731-4100

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Improving the Micropore Capacity of Activated Carbon by Preparation under a High Magnetic Field of...

May 16, 2019

Improving the Micropore Capacity of Activated Carbon by Preparation under a High Magnetic Field of 10 T Subjects Abstract The influence of an applied magnetic field on the formation of carbon materials from coal tar pitch is investigated. Under an applied magnetic field, crystallites in a mesophase resembling liquid crystals are magnetically oriented during the carbonization process. Compared with that under a nonmagnetic field, carbonized coal tar pitch under a strong magnetic field of 10 T, generated by a superconducting magnet, has a highly oriented structure of carbon crystallites. The orientation of samples prepared under 2 T, which can easily be supplied by an electromagnet, was insufficient. Activation by potassium hydroxide is effective for affording a precursor for activated carbon. The activated carbon obtained under a strong magnetic field has a unique adsorption ability, which arises from its increase in relative surface area and total pore volume compared with those of an activated carbon sample prepared from a precursor produced under zero magnetic field. The precursor carbonized under a magnetic field of 10 T contains a larger number of crystallites than that carbonized under a 0-T magnetic field, which leads to high-performance activated carbon. Introduction Carbon materials, such as activated carbon and graphite, are very useful functional materials. For example, carbon materials are important in applications such as gas separation using pressure swing adsorption, water purification, air cleaning, electrodes in metal refining, pencils, and lubricants. Recently, nanocarbon, for example, carbon nanotubes and graphene, has attracted attention, but conventional carbon materials have still been applied and used in advanced technology, such as activated carbon in electric double-layer capacitors and carbon fibre-reinforced plastic for the wings of airplanes. Carbon materials are becoming increasingly important in our lives; therefore, the amount of carbon materials that is produced will need to increase to meet the demand. The carbon source, preparation conditions such as temperature and atmosphere, and preparation methods have an important influence on the properties of carbon materials because the structure of carbon materials controls their properties 1 , 2 . The discovery of new controlling methods will lead to the refinement of carbon materials as advanced functional materials. Coal tar pitch, which is a mineral and contains not only carbon but also other elements such as nitrogen, oxygen, and sulfur, has been used as a raw material for carbon products, including both activated carbon and graphite. A general preparation method for activated carbon and graphite from coal tar pitch is shown in Fig. 1 3 . Graphite is prepared by thermal treatment processes, which can be separated into the crystallite growth process in an unreactive atmosphere at less than 1200 K (carbonization) and subsequent crystallite connection to make large graphene sheets at up to 4000 K (graphitization). A carbon hexagonal layer grows well during the carbonization process and is called the graphite precursor (graphitizable carbon). If a raw material is stabilized in an oxidative atmosphere around its softening point, because oxygen acts as a cross-linker between carbon crystallites, the growth of hexagonal carbon is inhibited during thermal treatment above the stabilization temperature. As a result, the base of each pore is constructed of crystallites. This carbon material is called the activated carbon precursor (non-graphitizable carbon). Figure 1 (3) Here, μ0 is the magnetic permeability in vacuum, and θ is the angle between the direction of a magnetic field and the easy axis of magnetization. The magnetic anisotropy Δχ 22 is the difference between perpendicular (χ⊥) and parallel (χ//) magnetic susceptibilities, as illustrated in Eq. ( 2 ), while the molar magnetic susceptibility χM is determined using Eq. ( 3 ). The plane of the benzene ring is assigned as χ//, which aligns with the easy axis of magnetization, and the direction perpendicular to the ring is χ⊥, which aligns with the hard axis of magnetization. Since a B2 effect is expected, it is reasonable that the magnetic flux density increases sharply at 3 T or above. However, the magnetic field effect was saturated above 6 T. The crystallite size estimated from the XRD results was 2.9 × 2.9 × 2.7 nm3. If we assumed that only a layered graphene structure was obtained, the anisotropic magnetic susceptibility was calculated as Δχ = −8.6 × 10−7 m3 mol−1 17 . Since the thermal energy was approximately 6.6 kJ mol−1 at 793 K, it was calculated that the magnetic orientation could be sufficiently complete at more than 6 T by overcoming Brownian motion, with only approximately 4000 crystallites moving cooperatively. In fact, the crystallite contained other atoms, such as oxygen and sulfur; therefore, the actual value of anisotropic susceptibility was slightly smaller than the ideal value, and it seemed that more crystallites moved cooperatively. Nevertheless, considering the size of the mesophase microspheres (diameter on the micrometre scale), this result was quite reasonable. We called this material a highly oriented carbonized pitch (HOCP) as opposed to general carbonized pitch (GCP). There have been many precedents for preparing composite materials while orienting carbon materials, such as graphene and nanotubes, in a magnetic field. However, applying a strong magnetic field to the preparation process of a functional carbon material to drastically change the structure has never been reported. In the days when only electromagnets could be used, the strength of the magnetic field was lower than that provided by modern equipment. Additionally, to prepare the material, the distance between the poles of an electromagnet would be insufficient. Preparation by using a superconducting magnet may be expected to be beneficial not only for the application of a high magnetic field but also for the large preparation space compared with that of an electromagnet. We attempted to prepare a high-performance carbon material in this study by preparing activated carbon from HOCP. Results and Discussion Optimization of magnetic field effects on carbonized process To clarify the optimal temperature for the magnetic field effect, we carried out only the carbonization treatment of coal tar pitch with the temperature varied from 553 K to 973 K (see Fig. S1(a) , process A), which was based on the general method for preparing a graphite precursor. The intensity of the XRD peak at 26°, assigned to the (002) plane of carbon hexagonal layers prepared in the absence and presence of a 10-T magnetic field, at each temperature is plotted in Fig. 2(a) . Carbonization did not progress below 650 K, so naturally, no magnetic field effect was observed in this temperature region. Carbonization occurred gradually from 650 K until approximately 1000 K under zero magnetic field. In contrast, the (002) peak intensity of the samples prepared under a 10-T magnetic field increased rapidly with increasing heat-treatment temperature until 800 K and then became saturated above this temperature. The difference between the (002) XRD peak intensities of carbon materials prepared in the absence and presence of the 10-T magnetic field, denoted by I(10T)/I(0T), is also shown in Fig. 2(a) . The maximum magnetic field effect was observed at approximately 800 K. We considered this finding as evidence for a magnetic field effect caused by magnetic orientation because this is the temperature at which the mesophase of coal tar pitch, which is a liquid crystal-like structure containing carbon crystallites, appears. Figure 2 (a) Heat-treatment-temperature dependence of the (002) XRD peak intensity of carbon materials prepared in the absence (solid line, closed squares) and presence (dashed line, open squares) of a 10-T magnetic field. Relative value of the intensities of the (002) XRD peaks at 10 and 0 T, I(10T)/I(0T) (dashed-dotted line, circles). (b) Stabilization time dependence of the (002) XRD peak intensity of activated carbon precursors prepared in the absence (solid line, closed squares) and presence (dashed line, open squares) of a 10-T magnetic field. The micropore volume was almost completely dependent on the tendency of the surface area, as shown in Fig. 8(b) , owing to the Type 1 adsorption isotherm. However, as shown on the right axis of Fig. 8(b) , the optimum KOH ratio differed between the cases in which fine micropores and relatively large micropores were formed. The rate of increase in the number of fine micropores was the largest at a KOH:precursor ratio of 3. However, the relationship between fine micropores and relatively large micropores was reversed at a KOH:precursor ratio of 5. If relatively large micropores are required, a combination of P-HOCP and a KOH:precursor ratio of 5 was recommended. It seems that the selectivity for pore size can be improved by combining P-HOCP with an appropriate amount of KOH. Conclusion We demonstrated the effect of an applied magnetic field on the preparation of carbon materials. The adsorption ability of an activated carbon sample prepared under a magnetic field was larger than that of sample prepared without a magnetic field by approximately 35%. The most appropriate temperature for carbonization under an applied magnetic field was approximately 800 K; this temperature is where the mesophase of carbon materials appeared. The magnetic field effect on carbonized materials under an unreactive atmosphere was explained by the magnetic orientation in the mesophase, which resembled a liquid crystal. This magnetic field effect disappeared with stabilization treatment. The magnetic field effect on the precursor resulted in the construction of a large number of crystallites, which led to the formation of a large number of micropores. Although the activation of precursors prepared under a magnetic field is difficult, pore formation was effectively performed by the same activation method as that of HOPG. A KOH:precursor ratio of 3 was most suitable for the formation of micropores, and the pore size distribution in samples prepared from P-HOCP was sharper than that in samples prepared from P-GCP. The micropore capacity of activated carbon was improved by preparation under a magnetic field, and we can expect a molecular sieve effect arising from the sharper pore size distribution. Hence, the magnetic field effect can be obtained at a relatively low temperature in the carbonization region, so there is no need to carry out activation at high temperature under a magnetic field, which is very important from an application point of view. These results may also lead to the property control of other carbon materials, such as graphite, because the activated carbon precursor used in this study is optimal for graphite fabrication. Furthermore, many materials other than carbon are categorized as having a negative magnetic susceptibility, which are termed non-magnetic materials; thus, magnetic orientation achieved using this effective procedure can be used to control the properties of such materials. Materials and Methods Preparation Coal tar pitch (2.0 g) with a softening point at 553 K, provided by Ad’all Co., Ltd. (Uji, Japan), was heat-treated roughly by two kinds of processes, process A and process B (see Fig. S1(a) ). Process A was based on the general method for preparing a graphite precursor. In process A, only the carbonization treatment was carried out with the temperature varied from 553 K to 973 K. Process B was based on the general method for preparing an activated carbon precursor. In process B, stabilization was carried out before carbonization with the time varied from 0 to 120 minutes. The temperature was raised at a rate of 4 K/min. The stabilization process and carbonization process were conducted in atmospheres of air and nitrogen (N2), respectively, with a flow rate of 500 sccm. A magnetic field was applied the whole time during heating for process A. Although no magnetic field effects on the stabilization process were observed in our previous study 17 , we applied a magnetic field from time tb in process B in the present study to examine the effect of the magnetic field on the carbonization process. Chemical activation was carried out as shown in Fig. S1(b) using carbonized coal pitch washed by pyridine. The maximum temperature of chemical activation was 1073 K and was maintained for 60 minutes. The ground precursor was immersed in potassium hydroxide (KOH) aqueous solution (the volume ratio of KOH to precursor was 1, 3, 5, 8, or 10) for 3 h before being placed in a furnace. N2 gas was flowed at a rate of 500 sccm. The activated sample was washed by enough water. Furnace system An electric furnace system was constructed in the bore (diameter ϕ = 100 mm) of a superconducting magnet (HF-10-100 VHT-4, Sumitomo Heavy Industries, Ltd.), as shown in Fig. S2(a) . A ceramic bobbin with a length of 600 mm, wound with Kanthal (Fe-Cr-Al) wire, was housed in a stainless-steel vessel covered with a non-magnetic water cooling jacket and tightly fixed to a 10-T superconducting magnet. A quartz or ceramic tube with an inner diameter of 23 mm and length of 1000 mm was inserted into the furnace bore with an inner diameter of 30 mm. Applying a maximum direct current (DC) voltage of 100 V to the furnace provided an output power of 1520 W and a temperature of 1523 K. The temperature distribution in the quartz tube inserted into the furnace at 798 K in the centre is shown in Fig. S2(b) . A uniform temperature of 798 K was maintained with an error of ±5 K. The magnetic field distribution at 10 T in the centre is also presented in Fig. S2(b) , which demonstrates the relationship between the furnace and magnet. The temperature at the sample position, which coincided with the centre of the magnetic field, was controlled by a proportional-integral-differential (PID) thermocontroller (E5CN-R2HBT, Omron Co.) with a K-type thermocouple. Strictures and properties The microscopic structures of the prepared carbon materials were characterized by powder X-ray diffraction (XRD) measurements on a Multiflex diffractometer (Rigaku; CuKα radiation). The X-ray source was operated at 40 kV and 20 mA. Samples were scanned at a rate of 4°/min at 0.02° intervals over the range of 2° ≤ 2θ ≤ 80°. The macroscopic structure of the carbonized coal tar pitch was confirmed by an epi-type polarizing microscope (BX51P, Olympus Co.), Photographs of the wide view and magnification view were observed with objective lenses of 5× and 20×, respectively. The morphology of the prepared activated carbon was observed by a JEOL JSM-7600F scanning electron microscope (SEM). The adsorption behaviour of the prepared activated carbon samples was determined from N2 adsorption isotherms measured by using an in-house gravimetric apparatus at 77 K. Prepared samples were ground and preheated at 393 K and 1 mPa for 3 h before observation of the adsorption isotherms. Total pore volumes were estimated from the adsorption isotherms. The obtained isotherms were also analysed to provide information about the relative surface area, pore diameter, and micropore volume through BET plots, t-plots, and Dubinin-Radushkevich (DR) plots, respectively. Pore distributions were analysed by the Horvath–Kawazoe method. Additional information Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. References 2. 3. Yokono, T., Obara, T., Sanada, Y., Shimomura, S. & Imamura, T. Characterization of carbonization reaction of petroleum residues by means of high-temperature ESR and transferable hydrogen. Carbon 24, 29–32 (1986). 4. Otsuka, I., Abe, H. & Ozeki, S. Magnetic field control of structure and function of poly (N-isopropylacrylamide) gels. Sci. Technol. Adv. Mater. 7, 327–31 (2006). 5. Tanimoto, Y., Yamaguchi, R., Kanazawa, Y. & Fujiwara, M. Magnetic orientation of lysozyme crystals. Bull Chem. Soc. Japan 75, 1133–4 (2002). 6. Kimura, T. Study on the effect of magnetic fields on polymeric materials and its application. Polymer 35, 823–43 (2003). 8. Boamfa, M. I. et al. Mesogene-polymer backbone coupling in side-chain polymer liquid crystals, studied by high magnetic-field-induced alignment. Phys Rev Lett. 90, 025501/1–4 (2003). 9. Christianen, P. C. M., Shklyarevskiy, I. O., Boamfa, M. I. & Maan, J. C. Alignment of molecular materials in high magnetic fields. Physica B 346–347, 255–61 (2004). 10. Ozeki, S., Kurashima, H. & Abe, H. High-magnetic-field effects on liposomes and black membranes of dipalmitoylphosphatidylcholine: magnetoresponses in membrane potential and magnetofusion. J. Phys. Chem. B 104, 5657–60 (2000). 11. Ozeki, S., Kurashima, H., Miyanaga, M. & Nozawa, C. Magnetoresponse in electrical properties of black lipid membranes. Langmuir 16, 1478–80 (2000). Kurashima, H., Abe, H. & Ozeki, S. Magnetic-field-induced deformation of lipid membranes. Mol. Phys. 100, 1445–50 (2002). 13. Saravanan, G. & Ozeki, S. Magnetic field control of electron tunneling pathways in the monolayer of (ferrocenylmethyl)dodecyldimethy-lammonium bromide on a gold electrode. J. Phys. Chem. B 112, 3–6 (2008). 15. Brooks, J. D. & Taylor, G. H. The formation of graphitizing carbons from the liquid phase. Carbon 3, 185–93 (1965). 16. Shiraishi, M. & Kobayashi, K. X-ray study of coal tar pitch. Bull. Chem. Soc. Japan 46, 2527–8 (1973). 17. Sakaguchi, A. et al. Magnetic orientation of hexagonal carbon layers at high temperatures. Chem. Lett. 41, 1576–8 (2012). 18. Hishiyama, Y., Kaburagi, Y., Inagaki, M., Imamura, T. & Honda, H. Graphitization of oriented coke made from coal tar pitch in magnetic field. Carbon 13, 540–2 (1975). 19. Imamura, T., Yamada, Y., Oi, S. & Honda, H. Orientation behavior of carbonaceous mesophase spherules having a new molecular arrangement in a magnetic field. Carbon 16, 481–6 (1978). 20. Kovac, C. A. & Lewis, I. C. Magnetic orientation studies of synthetic mesophase pitches. Carbon 16, 433–7 (1978). 21. Delhaes, P., Rouillon, J. C., Fug, G. & Singer, L. S. Physical properties of a magnetically-oriented carbonaceous mesophase. Carbon 17, 435–40 (1979). 22. Tanimoto, Y. Magneto-Science: Magnetic field effects on materials: Fundamentals and applications (Springer Series in Materials Science), (eds Yamaguchi, M. & Tanimoto, Y.) 1st ed. 17–22 (Kodansha-Springer, 2006). 23. Fujiwara, M., Fukui, M. & Tanimoto, Y. Magnetic orientation of benzophenone crystals in fields up to 80.0 KOe. J. Phys. Chem. B 103, 2627–30 (1999). 24. Sing, K. S. W. et al. Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity. Pure Appl. Chem. 57, 603–19 (1985). 25. Thommes, M. et al. Physisorption of gases, with special reference to the evaluation of surface area and pore size distribution. Pure Appl. Chem. 57, 1051–69 (2015). 26. Horvath, G. & Kawazoe, K. Method for the calculation of effective pore size distribution in molecular sieve carbon. J. Chem. Eng. Jpn. 16, 470–5 (1983). 27. Dombrowski, R. J., Lastoskie, C. M. & Hyduke, D. R. The Horvath-Kawazoe method revisited. Colloids Surf. A 187–188, 23–29 (2001). 30. Jagtoyen, M. & Derbyshire, F. Activated carbons from yellow poplar and white oak by H3PO3 activation. Carbon 36, 1085–97 (1998). Rights and permissions Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/ .

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Micropore Patents

Micropore has filed 9 patents.

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