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4НЕКОТОРЫЕ АСПЕКТЫ ТРАНСПОРТА МОЛЕКУЛЯРНОГО ВОДОРОДА В НАНОСТРУКТУРИРОВАННЫХ УГЛЕРОДНЫХ МЕМБРАНАХ
1 2 3
О.К. Алексеева, Ю.С. Нечаев , Б.Л. Шапир, А. Окснер'
Институт энергии и технологии плазмы, РРК «Курчатовский институт», Россия 123182, Москва, пл. Курчатова, д.1 'Институт металловедения и физики им. Курдюмова, Институт черной металлургии им. Бардина, Россия 105005, Москва, Вторая Бауманская ул., 9/23 тел.+495-7779301, e-mail: yuri@inbox.ru 2Факультет прикладной механики, Технический университет Малайзии 81310, UTM Скудай, Йогор, Малайзия
^Университетский центр массо- и теплопереноса, Инженерный факультет, Университет Ньюкасла Каллахан, Новый Южный Уэльс 2308, Австралия
Композитные мембраны с наноструктурированным углеродным селективным слоем перспективны для выделения и очистки водорода. Наш подход к их созданию основан на карбонизации полимерных слоев, нанесенных на неорганические пористые высокотемпературные подложки. При определенных условиях карбонизация полимеров позволяет синтезировать углеродные наноструктуры, включая нанотрубки. Однако выводы относительно молекулярного транспорта в углеродных нанотрубках, сделанные в некоторых исследованиях, являются противоречивыми. В статье с использованием новых (нестандартных) концептуально-методологических подходов сделан анализ возможных механизмов молекулярного транспорта в композите, содержащем углеродные (графитовые) наноструктуры. В частности, наш анализ показал необходимость рассмотрения важных вопросов о природе и механизмах адсорбции и кинетики (диффузии). Следует обратить особое внимание на возможные процессы хемосорбции водорода. Развитие такого подхода необходимо для оптимизации синтеза, направленного на создание мембран, соответствующих современным технологическим требованиям.
SOME ASPECTS OF MOLECULAR HYDROGEN TRANSPORT IN NANOSTRUCTURED CARBON MEMBRANES
O.K. Alexeeva, Yu.S. Nechaev1, B.L. Shapir, A.Ochsner2'3
Hydrogen Energy and Plasma Technology Institute, RRC "Kurchatov Institute" Pl.Kurchatova 1, Moscow 123182, Russia 1Kurdjumov Institute of Metals Science and Physics, Bardin Institute for Ferrous Metallurgy, Vtoraya Baumanskaya St., 9/23, Moscow 105005, Russia Phone +495-7779301, e-mail: yuri@inbox.ru 2Dept. Applied Mechanics, Technical University of Malaysia 81310 UTM Skudai, Johor, Malaysia;
3University Centre for Mass and Thermal Transport, School of Engineering The University of Newcastle Callaghan, New South Wales 2308, Australia
Composite membranes with nano structured carbon selective layer are promising candidates for hydrogen gas separation and purification. Our approach to their production is based on the carbonization of polymeric layers on the porous inorganic high temperature supports with definite structure. This process under special conditions allows synthesize carbon nanostructures including nanotubes. However, conclusions concerning molecular transport in carbon nanotubes and other nanostructures made in several investigations are conflicting. Using new methodological approaches possible molecular transport mechanisms have been analyzed in the present paper for the composite containing carbon (graphite) nanostructures. In particular our analysis shows that significant issues concerning nature, kinetics (diffusion) and limiting sorption of hydrogen by carbon nanostructures should be taken into consideration. Attention should be focused on several possible processes of hydrogen chemisorption. The development of this approach is necessary for the optimization of synthesis aimed at creation of membranes corresponding to the modern technology requirements.
Introduction
Further development of hydrogen energy and subsequent transition to hydrogen economy is impossible without progress in the separation and purification processes. Currently three major technologies exist - pressure swing adsorption, fractional/cryogenic distillation and membrane separation. Using membranes is the most
promising and efficient method for the separation and purification of hydrogen produced by various conversion methods from raw hydrocarbons. However, existing polymeric and inorganic membranes have limitations: e.g. polymeric membranes cannot be used at high temperatures, high permeability of these membranes corresponds to low selectivity and vice versa; selectivity of porous ceramic membranes is insufficient etc. Thus,
creation of novel membrane materials is necessary. Membranes based on these materials should provide better selectivity in combination with high permeability, thermal and chemical stability. Carbon membranes appeared to be promising for gas separation. They can be a real alternative both to inorganic and polymeric membranes and enlarge possibilities of membrane methods of gas separation. In some processes selectivity of such membranes is close to that of polymeric ones, or even better in a number of cases, and permeability, thermal and chemical stability are comparable with corresponding characteristics of inorganic membranes.
Carbonization of organic polymeric compounds (precursors) is now a well known method for carbon materials synthesis. Koresch and Soffer [1] were the first to use pyrolytic carbonization of polymeric hollow fibers for the preparation of carbon molecular sieve (CMS) membranes. Since then many attempts have been made to obtain nanoporous carbon membranes. Depending on the type of precursors (polymers), the coating method and the carbonization conditions selective high-temperature membranes characterized by different gas separation mechanisms can be produced: molecular sieve membranes - e.g. from phenolic resins [2], polyetherimides [3, 4]; membranes with surface selective flow - from polyvinylidene chloride [5]; combined ones (membranes with shape-selected transport) - from poly(furfurol alcohol) [6, 7]. However until now, there are no reliable production methods of membranes with specified mechanical strength and high functional performance. Attention is not focused on carbon structural peculiarities though they may be of significant importance as discussed below. Our investigations [8-12] and some data of other authors showed that complex properties can be provided by carbonization of thin continuous polymeric layers on the porous inorganic high temperature supports. Various carbon nanostructures (active carbon, carbon molecular sieves, carbon nanotubes (CNT), carbon and graphite fibers etc.) can be formed during the process thus improving membrane properties of these supports. It should be noted that lately special attention was given to the investigation of fluids inside carbon nanotubes (CNT) and other nanostructures [13]. This important issue will be discussed in more detail below.
Carbon nanostructures from polymeric precursors
Experimental data show that synthesis of carbon nanostructures (including CNT and nanofibers) from polymeric precursors can be promoted either by use of catalysts or by the application of membrane supports with certain structure. For example, carbonization of a mixture containing poly(ethylene glycol) as the carbon source and NiCl2 as the catalyst precursor leaded to the synthesis of platelet graphite nanofibers [14]. Carbon nanotubes were obtained from polyethylene precursors in the presence of Ni-catalysts [15]; catalytic graphitization of polyvinyl alcohol produced multiwalled graphite nanotubes [16]. Authors of [17] also focused on formation of CNT by
thermal conversion of polymeric precursors containing metal catalysts (e.g. Fe). Recently, multiwalled carbon nanotubes were synthesized from novolac type phenolformaldehyde resin mixed with ferrocene (Fe precursor) [18]. It is especially interesting as carbonization of these polymers without iron gives only amorphous carbon. Some other examples of nanocaibon materials production from polymers are listed in [8].
Carbonization of thin continuous polymeric layers on the mesoporous inorganic high temperature supports with definite structure opens new possibilities for carbon nanostructure production [8]. However, few works study substrate effects. Authors of [19] have shown that unique carbon nanostructures can be formed at temperatures below 1000° C without any catalyst, for example, by carbonization of phenolic resin on ceramic substrates. It is important that the carbon which is synthesized from the same precursor under the same conditions but not coated on ceramic does not show such a structure. Our previous results showed that ordered carbon structures can be formed at carbonization of polymer coatings on alumina ceramics in contrast with the same polymers carbonization without substrate [20]. Carbons formed on different phases of alumina from different precursors revealed a strong effect of the ceramic substrate on the porous carbon structure [21].
In general the influence of the support on the membrane which is formed as a result of carbonization is complicated and should be investigated in each specific case.
Design of nanostructured carbon gas separation membranes
As was mentioned above, carbon nanotubes and other carbon nanostructures appeared to be very promising as membrane materials. However, first experimental samples based on carbon structures were very small - up to 50 micron (e.g. [13]). Therefore, despite of excellent transport properties they cannot be used for practical industrial applications. The possibility to scale up such membranes is very important. Composite membranes with alumina support and nanostructured carbon selective layer are optimal. Several approaches to the production of such membranes with necessary operation characteristics can be used. Recently, vertically aligned multi-walled CNT membranes were obtained on flat porous alumina support by CVD, filling of inter-CNT gaps with polysterene and final removing of the polys-terene over-layer and CNT tips by polishing and acid treatment [22]. However, the diameter of the support is only 2 cm (the authors hope to apply this method to the production of larger membranes).
Our approach is based on the carbonization of polymeric layers deposited on ceramic supports. As was said above, various carbon nanostructures can be synthesized from polymers under appropriate conditions. Such composite carbon membranes are suitable for operation at high temperatures in the presence of organic vapors, in acid or alkaline (nonoxidizing) medium. Composite membranes
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with carbon selective layer are more durable than brittle and fragile carbon membranes. Thermal and chemically stable tubular ceramics is used as supports in our work as tubular membrane configuration is preferable for various industrial applications. Ceramic tubes are coated with polymers from solutions in organic solvents via multiple dipping (with and without pressure differential) with intermediate drying at room temperature. Pyrolysis (carbonization) is conducted in a wide temperatures range in the presence of flowing nitrogen. The possibility to control the carbon structure (controllable carbonization) results from the use of certain supports, necessary surface modification of these supports, choice of polymeric precursors and carbonization conditions.
The technology allows promoting formation of necessary nanostructures by introduction of catalysts in the precursor or by production of additional catalytic sites on the support surface (gas phase fluorination, deposition of additional layers by magnetron sputtering etc.).
Our previous results concerning the influence of supports, type and concentration of precursor solutions, pre-treatment and carbonization conditions on the characteristics of the selective layer are presented in [8-12, 20, 23]. Based on these data, commercially available a-Al2O3 - based ceramic tubes (mean pore size of 0.2 ^m) with an outer diameter of 8 mm and a length of 30-60 mm and ceramic macroporous (mean pore size of 5 ^m) alumina tubes with an outer diameter of 16 mm have been selected as supports (Fig. 1). Commercially produced in RF solutions of phenol-formaldehyde resins (PFR) (concentration 24-76 mass% PFR) have been used as the main precursor for membrane production. Modified ceramic supports (mean pore size of 0.2 ^m) with additional surface layers (Mo, Ti, Cr, Cr - carbides, Si) deposited by physical or chemical methods have been also used. In some cases catalysts (Ni fine powder) were introduced in the precursor.
Рис. 1. Некоторые образцы исходных и синтезированных мембран
Fig. 1. Some samples of initial and synthesized membranes
The characteristics of the polymeric layer carbonization process and the carbon selective layer formation have been investigated by thermogravimetric analysis, XRD method and electron microscopy. The possibility of the formation of two different membrane types based on the chemical and thermal stable alpha-alumina ceramic supports was shown: type A with surface carbon
selective layer, and type B - with modified pores of the near-surface layer (for macroporous ceramics where significant PFR penetration into supports takes place). Structural transformation has been shown to depend on the type (structure, composition, porosity) of the supports. Novel structuring showing graphite fragments (crystallites) formation can be developed to a variable degree at the thermal treatment under the same conditions. It is interesting to note that the best results (for the samples without catalyst introduction) were obtained for carbonization of PFR on ceramic support with an additional surface layer containing Cr. XRD data of several samples, especially those synthesized with nano-nickel powder, supported the possibility of nanostructures formation (Fig. 2). These membranes showed higher gas permeances.
Int. (a.u.)
Рис. 2. Данные XRD некоторых образцов, синтезированных с Co (серая кривая) и добавлением нано-никелевого порошка (черная кривая). Данные, полученные для графитовых образцов, показаны в сравнении Fig. 2. XRD data of several samples synthesized with Co (gray curve) and nano-nickel powder (black curve) addition.
Data obtained for graphite sample are shown for comparison
However, it is insufficient to carry out only experimental research. Another important condition of successful forecasting of membrane efficiency and purposeful synthesis of carbon nanostructured membranes with necessary selectivity/permeability is to study the gas transport mechanisms.
Mechanisms of gas transport in carbon nanostructures
Even though many research projects are devoted to carbon nanoporous membranes, only few of them consider the mechanisms of gas (fluid) transport. This process combines adsorption and diffusive transport effects and both are important. Sorption of gas molecules can occur physically or chemically depending on the nature of the force between the gas molecules and the surface. Chemisorption occurs when the interactions are strong, for example, in the dissociative adsorption of hydrogen molecules on catalytic sites. Sorption describes the interactions between gas molecules and the membrane surface, and diffusion determines the rate of gas flow through the membrane. The contribution of each process
to the permeance differs according to such variables as the temperature, pressure, or pore configuration. In general for porous membranes the following major kinds of flow take place (according to permselectivity increase): viscous (Poiseuille) flow, Knudsen flow, surface diffusion/selective adsorption, capillary condensation, molecular sieving. (e.g. [24]). Viscous flow dominates when large pores are present. Gas molecules collide with each other and not with the pore walls. When the mean free path of the molecules is close or even more than pore diameters, diffusion is called Knudsen diffusion or Knudsen flow. Gas molecules collide with pore walls more often than with each other. Gas transport by Knud-sen diffusion occurs without involvement of adsorption. The Knudsen permeation rate of each component is then inversely proportional to the square root of its molecular weight and temperature. Selective surface flow is characterized by the selective adsorption of certain gas mixture component in the pores and surface flow of these molecules along the pore walls. Under appropriate temperature and pressure certain gas molecules in the mixture can condense in the pores (usually micropores) by capillary condensations and flow as a condensed phase eliminating the diffusion of non-condensed molecules. Molecular sieving takes place when the pore size is close to the dimensions of smaller gas molecules and only these molecules can enter and diffuse through the pores.
These mechanisms can also work together. Usually molecular sieving is considered as the dominant in carbon microporous membranes. Several authors conclude that the separation is based on the kinetics of diffusion rather than on the thermodynamics of adsorption [7]. As considered in [25] the adsorption kinetics do not depend only on the kinetic diameters of molecules but are a complex function of size, shape and electronic structure of gas molecules relative to the adsorbent pore type and size and surface functional groups. The authors have prepared carbon molecular sieve membranes by compression of the activated carbon fibers (ACF) with phenolic resin followed by heat treatment. ACF have uniform outer opened micropores which leads to high adsorption rates. For the interpretation of the data the empirical phenomenological model for mass transfer in gas adsorption (so called linear driving force (LDF) mass transfer kinetic model) has been used. Membranes effective for hydrogen-hydrocarbon mixtures separation by the surface diffusion mechanism have been produced by Rao and Sircar (e.g. [5]). A layer of nanoporous carbon on a mesoporous inert support such as graphite or alumina has been obtained by polymeric precursor carbonization. As the transport mechanism differs from the molecular sieving mechanism, these membranes were named as selective surface flow (SSFTM) membranes.
As mentioned above lately special attention was focused on the investigation of behavior of gases and liquids inside carbon nanotubes (CNT) and other nanostructures. Even though available data are insufficient and sometimes contradictory, it is clear that CNT - based membranes (composite, hybrid etc.) would differ mark-
edly from polymeric, zeolite and other inorganic membranes. First Skoulidas (2002) has shown theoretically (by molecular dynamics simulations) that the transport of gases inside single-walled CNT (SWNT) is orders of magnitude faster than in any known nanoporous materials [26]. Flow enhancement was attributed mainly to the extraordinary smoothness of the potential-energy surface. Then first membranes have been fabricated from aligned multiwalled CNT (MWNT) embedded in impermeable polymer film [27] and aligned double walled CNT and MWNT in silicon nitride matrix [13]. Authors [27] indicated that nitrogen permeance was consistent with Knudsen diffusion, but according to [13] the gas (air) flow exceeded the Knudsen model values by more than an order of magnitude. However, single-component selectivity for hydrogen, nitrogen, oxygen and other gases corresponded to the Knudsen model with the exception of hydrocarbons whose selectivities were higher. Authors attributed it to surface diffusion or possibly solubility/diffusion mechanism. Recently, Skoulidas et al. have used atomic simulations to study the adsorption and diffusion of CO2 and N2 in SWNT and concluded that the observed diffusion is not of Knudsen type [28]. Using molecular dynamics and grand canonical Monte Carlo simulations Arora and Sandler [29] demonstrated the possibility of fabrication molecular sieving membranes using SWNT.
Although selectivity is also a very important membrane parameter, to date only single-component transport has been investigated experimentally. A detailed model for the permeation of CH4/H2 mixtures through membranes constructed from close packed bundles of SWNT is presented in [30]. The calculations predict that such membranes would be strongly selective for CH4 over H2 and would exhibit very large fluxes. It is supposed that the first property is mainly the result of the significant adsorption selectivity for CH4 over H2 and the second one is a consequence of the extremely fast diffusion of molecules adsorbed inside SWNTs both as single species and in adsorbed mixtures.
As is obvious from the foregoing, conclusions concerning molecular transport are conflicting; supposition about Knudsen diffusion made by several authors (taking into account "mirror" walls) is disproved in other works. Using new methodological approaches possible molecular transport mechanisms have been analyzed for the composite containing carbon (graphite) nanostructures by the example of hydrogen. In particular our analysis shows that significant issues concerning nature, kinetics (diffusion) and limiting sorption of hydrogen by carbon nanostructures [31-33] are not taken into consideration. Attention should be focused on several possible processes of hydrogen chemisorption. Analysis shows that uncommon properties discovered by several groups of investigators for membrane based on CNT and other carbon nanostructures (e.g. diffusion more rapid than Knudsen one, selectivity equaling 10-20 for methane-hydrogen which does not correspond to Knudsen flow) probably can be explained using diffusion models and
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characteristics taking into account four possible processes of hydrogen chemisorption in graphite and relative carbon nanomaterials with sp2 hybridization [31, 32, 34, 35]. Processes I and II (Table, Fig. 3) are dissociative-associative hydrogen chemisorption from initial molecular gas state on the surface of carbon nanostructures (in-
cluding central nanotube canal) and in intergranul or defective regions of these carbon nanostructures, respectively. Processes III and IV (Table, Fig. 3) are dissociative hydrogen chemisorption between graphene sheets (nanostructures graphite, graphite nanofibers etc.) and in defective regions of graphite lattice, respectively.
Characteristics of hydrogen chemisorption and diffusion in isotropic graphite and related carbon nanostructures (herein, Refs., Figs. & Eqns. correspond to those of [31]) Характеристики водородной хемосорбции и диффузии в изотропическом графите и подобных углеродных наноструктурах (в том числе им соответствуют тот же список литературы и те же рисунки [31])
Hydrogen chemisorption in sp2 carbon materials Chemisorption and diffusion models and the energies of formation of chemical bonds linking the hydrogen atoms to the material Characteristics of the processes Type of sorption isotherm
Process III in isotropic graphite [51, 53] (Figs. 5 and 7, a, TPD peak III), in GNFs [12] (Fig. 6, peak y (III)), and in nanostructured graphite (14,52-56] (Figs 7, b and c, III) Dissociative chemisorption of hydrogen between graphene layers [reactions (1)-(4)]. Bulk diffusion of hydrogen atoms with a reversible diffusant capture at chemisorption centers in graphene layers (Fig. 8, model F*); AH(3)II = -243 ± 3kJmol-1(H) A^(4)III « VZkHdis + ^(3)III « « -19 ± 1 kJmol-1(H); AS(4)III/R « —14.7(-15.4) atXm « 0.5(1.0); Eqns (5X7). Aii = Doiiiexp(-Qiii/RT); D0III « 310-3 cm2s-1; QIII « Q1 - ляда « « 250 ± 3 kJmol-1(H); Q1 « 7 ± 4 kJmol-1(H); Eqns (8), (9) Sieverts-Langmuir Equations (5), (5, a)
Process II in isotropic graphite (51, 53] (Figs 5 and 7, a, II), in GNFs [12] [Fig. 6, peak B (II)], in nanostruc-tured graphite [53,54] (Figs 7, b and c peak II), and in defective single-wall [61] and multiwall [62] nano-tubes Dissociative-associative chemisorption of H2 in intergranular or defective (surface) regions [reactions (10)-(13)]. Diffusion of H2 in these regions with reversible diffusant dissociation and capture at sorption centers (Fig. 8, model H); AH(12)ii = -560 ± 10 kJmol-1(2H) ЛЯ(13)11 « ЛЯdis + ЛЯ(12)11 « « -110 kJmol-1(H2); ^(i3)II/R « -30 atXIIm « 0.5(0.25); Eqns (14)-(16). Du = D0iiexp(-Qn/RT); D0II « 1.8103 cm2s-1; Qii « Qdef - ЛЯ(13)П « « 120 ± 2 kJmol-1(H2); Qdef « 10 ± 5 kJmol-1(H2); Eqns (17), (18) Henry-Langmuir Equations (14), (14, a)
Process I in isotropic graphite [51, 53] (Fig. 5, TPD peak I), in single-wall nanotubes [26, 63, 64], and in multiwall nanotubes [62] (Section 5.1) Dissociative-associative chemisorption of H2 in surface layers of the material [reactions (10)-(13) and (12a)]. Diffusion of H2 in these layers with reversible diffusant dissociation and capture at chemisorptioncenters (Fig. 8, models G and F); AH(12,12a)I = -460 ± 10 kJmol-1(2H) ЛЯ(13)1 « ЛЯdis + ЛЯ(12, 12a)I « « -10 ± 7 kJmol-1(H2); M(13)I/R « -20 atXIm « 0.5(0.25); Eqns of the (14)-(16). Di = DMexp(-Qi/RT); D0I « 310-3 cm2s-1; Qi « Q3 - ЛЯ0з)1 « « 20 ± 2 kJmol-1(H2); Q3 « 10 ± 8 kJmol-1(H2); Eqns (17), (18) Henry-Langmuir Equations (14), (14, a)
Process IV in isotropic (51, 53] (Fig. 5, peak IV) and in pyrolytic [60] and nanostructured [52, 53] (Fig. 7, a, peak IV) graphite Dissociative chemisorption of H2 in defective regions of the graphite lattice [reactions (1)-4)] Bulk diffusion of hydrogen atoms in defective regions with reversible diffusant capture by chemisorption-centers (Fig. 8, models C and D); AH(3)IVI = -364 ± 5 kJmol-1(H) ЛЯ(4)1У « 1/2ляdis + ЛЯ(3)1У « « -140 ± 5 kJmol-1(H); Eqns (5)-(7). Div = DMyexp(-Qiv/RT); D0IV « 6102 cm2s-1; QIV « - ЛЯ(3)IV « « 365 ± 50 kJmol-1(H); Eqns(8),(9) Sieverts - Langmuir Equations (5), (5, a)
Note. D0III, D0II, D0I, and D0IV are the pre-exponential (entropic) factors of hydrogen diffusivities (Dm, DII, DI, and DIV) for carbon materials corresponding to the respective processes.
G Н
Рис. 3. Теоретические модели хемосорбции атомов водорода на графите; это рис. 8 в [31] Fig. 3. Theoretical models of hydrogen atom chemisorption on graphite; it's Fig. 8 in [31]
The mean free path of hydrogen molecules under real conditions (temperature, pressure of industrial processes) is in the range of 2.7-10 nm, thus Knudsen diffusion can be significant. Surface diffusion along pore walls and combination of transport mechanisms are also possible [23]. In all these cases, processes I-IV (Table 1, Fig. 3) should be taken into account. "Anomalous" Knudsen flow can be caused by monolayer hydrogen chemisorption (including its chemisorption from hydrogen-methane mixture) on carbon sites of chemisorption corresponding to the processes I and II (and to a less degree - to the processes III and IV) [31, 32, 34, 35]. Here, enhancement of hydrogen molecules elastic repulsion (and of methane molecules to an even more degree) from carbon "walls" "decorated" by chemisorbed hydrogen atoms and/or molecules (Figs. 4, 5) occurs. If the selective layer of A-type carbon membranes described above contains carbon nanotubes or graphite nanofibers (produced, e.g., by means of catalysts nanoparticles dispersing on the surface) processes I and II would have a significant effect. At support large pore modification (B-type carbon membranes) processes III and IV theoretically are also possible though less likely (in the case of graphene sheets formation on the internal pore surface).
Рис. 4. Центры водородной хемосорбции в ОСНТ (презентация модели, см. текст в [32]) Fig. 4. Hydrogen chemisorption centres in SWNT (a model representation, see text in [32])
Рис. 5. Модель (5,5) ОСНТ с 50% покрытием (при сравнении с предельным «углерод-водородным» наполнением) с водородом (стабильная структура, см. текст в [32]) Fig. 5. A model of a (5,5) SWNT with 50% coverage (as compared to the ultimate "carbohydride" filling) with hydrogen (a stable structure, see text in [32])
Conclusion
Carbon nanostructures are promising candidates for gas separation membranes production. The developed production technology of composite membranes with a carbon selective layer is directed to the formation of certain structures (nanostructures) which should improve not only membrane mass exchange properties (permeability, selectivity) but also performance properties. This technology can be also used for production of polymeric membranes with introduced nanotubes. However, it is extremely important to clarify transport mechanisms which would allow purposeful synthesis of gas separation and filtration membranes. For more accurate determination of the special carbon layer structure influence on selectivity future research is necessary, in particular estimation of the chemisorption efficiency for various gases at specific pressures and temperatures and also
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assessment of possible surface diffusion. The development of this approach is necessary for the optimization of synthesis aimed at creation of membranes corresponding to the modern technology requirements.
The work was supported by RFBR (grant number 06-08-00614a).
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EP SHANGHAI 2009 - 7-Я МЕЖДУНАРОДНАЯ ЭНЕРГЕТИЧЕСКАЯ ВЫСТАВКА ОБОРУДОВАНИЯ И ТЕХНОЛОГИЙ
Время проведения: 08.07.2009 - 10.07.2009 Место проведения: Китай, Шанхай Темы: Энергетика, Электроника и электроэнергетика
EP Shanghai 2009 будет проходить в Международном выставочном центре г. Шанхай совместно с 6-й Международной выставкой по электрооборудованию Electrical Shanghai.
Выставка проводится попеременно в Пекине и Шанхае. Среди спонсоров и организаторов выставки крупнейшие энергетические компании КНР и государственные организации.
Общая площадь EP Shanghai 2007 достигла 14000 кв. м. 300 компаний из 21 страны мира представили свое оборудование и услуги многочисленным посетителям, которых было зарегистрировано 26800 человек. С национальными павильонами на выставке в этом году решили принять участие Германия, Корея, США и Великобритания. Одновременно с EP Shanghai 2007 проводились конференция и ряд технических семинаров. 91% участников EP Shanghai 2007 оценили отдачу работы на выставке не только на отлично, но и даже поторопились забронировать площадь на выставке 2008 г.
Профили выставки:
• Оборудование для выработки электроэнергии на ТЭС, ГЭС и АЭС.
• Оборудование и технологии передачи и распределения электроэнергии.
• Системы электроснабжения (SCADA/DMS/EMS).
• Контрольно-испытательное оборудование и приборы.
• Инженерно-строительные услуги «под ключ».
• Нетрадиционные источники электроэнергии - ветровая, геотермальная, солнечная, приливная и т.д.
• Информационные технологии для энергетики.
• Телекоммуникационное оборудование для энергетики.
• Технологии энергосбережения и охраны окружающей среды.
• Промышленное оборудование для выработки электроэнергии (турбины, дизели и т.д.).
• Оборудование и материалы для производства электроэнергии.
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