Carbon pores

Mcntasty el al. [35] and others [13, 36] have measured methane uptakes on zeolites. These materials, such as the 4A, 5A and 13X zeolites, have methane uptakes which are lower than would be predicted using the above relationship. This suggests that either the zeolite cavity is more attractive to 77 K nitrogen than a carbon pore, or methane at 298 K, 3.4 MPa, is attracted more to a carbon pore than a zeolite. The latter proposition is supported by the modeling of Cracknel et al. [37, 38], who show that methane densities in silica cavities will be lower than for the equivalent size parallel slit shaped pore of their model carbon. Results reported by Ventura [39] for silica xerogels lead to a similar conclusion. Thus, porous silica adsorbents with equivalent nitrogen derived micropore volumes to carbons adsorb and deliver less methane. For delivery of 150 V./V a silica based adsorbent would requne a micropore volume in excess of 0.70 ml per ml of packed vessel volume. 

Wei S-H, Mahuli S K, Agnihotri R, Fan L-S (1997) High surface area calcium carbonate pore structural properties and sulfation characteristic. Ind Eng Chem Res 36(6) 2141-2148... 

The slope of the lines presented in Figure 5 is defined as k(q/v). The q/v term defines the turnover of the tank contents or what is commonly referred to as the retention time. When q is increased, the liquid contacts the carbon more often and the removal of pesticides should increase, however, the efficiency term, k, can be a function of q. As the waste flow rate is increased, the fluid velocity around each carbon particle increases, thereby increasing system turbulence and compressing the liquid boundary layer. The residence time within the carbon bed is also decreased at higher liquid flow rates, which will reduce the time available for the pesticides to diffuse from the bulk liquid into the liquid boundary layer and into the carbon pores. From inspection of Table II, the pesticide concentration also effects the efficiency factor, k can only be determined experimentally and is valid only for the equipment and conditions tested. 

The properties of porous carbons are important in a wide variety of industrial applications, including both liquid and gas phases [1,2], Access of liquids and gases to the carbon pores and the development of porosity during activation are critical in the selection and production of these materials. 

Kowalczyk P, Tanaka H, Kaneko K, Terzyk AP, and Do DD. Grand canonical Monte Carlo simulation study of methane adsorption at an open graphite surface and in slit like carbon pores at 273 K. Langmuir, 2005 21(12) 5639-5646. 

Comparable results were obtained when an IL (ethyl-methylimmidazolium-bis(trifluoro-methane-sulfonyl)imide EMI-TFSI) was tested using a series of nanoporous carbons with average pore width in the range of 0.65-1.1 nm [18], The ion sizes, calculated as 0.79 and 0.76 nm in the longest dimension for TFSI and EMI ions, respectively, are within the range of carbons pore size. Figure 8.8 points out that, when the average pore size decreases from 1.1 to 0.7 nm, the normalized capacitance increases below 0.7 nm, the normalized capacitance decreases. Since the maximum at 0.7 nm is... 

Increase of the electronic state density in the carbon pore walls with the voltage. Hahn et al. [52] have measured double-layer capacitance and electronic conductance of an activated carbon electrode in an aprotic electrolyte solution, 1 mol/dm3 (C2H5)4NBF4 in acetonitrile. Both quantities show a similar dependency on the electrode potential with distinct minima near the potential of zero charge. This correlation suggests that the capacitance, like the conductance, is governed substantially by the electronic properties of the solid, rather than by the ionic properties of the solution in the interface of the double layer. 

Basically the available capacitance is maximum at low frequency. This may be explained with the longer time available for the ions in the electrolyte to reach the surfaces which are located deep in the carbon pores. At higher frequency, only the superficial carbon surface is accessible for the ions. The capacitance is consequently much smaller. 

Molecular-sieve carbon, pore size distribution, 89... 

Fig. 6. Details of the CO2 density distribution within a 1.15 nm slit carbon pore at (a) 308 and (b) 333K, revealing an ordering transition at 308 K.

Particularly for adsorption studies, it is expected that the well-defined mesoporous structures would be useful as a reference pore system for the development of characterization methods and theoretical modeling for the adsorption in carbon pores. In this regard, we briefly review on the synthesis strategy, structure characterization, and their perspectives. 

The presence of the distinct XRD patterns provides us new opportunities for precisely monitoring various physico-chemical phenomena that take place inside the well-defined carbon pores or at the pore walls such as adsorption, impregnation, framework changes, formation of metal clusters and grafted frmctional groups. The materials constructed with such well defined and controllable pore diameters are suitable as standards or references for the characterization of porosity of the carbons, similar to the already well-known case of the MCM-41 silica. 

The cyclic steps of one of the PSA processes using the molecular sieve carbon as the adsorbent consist of (a) flowing compressed air through a packed bed of the carbon so that O2 can diffuse and adsorb into the carbon pores faster than N2 and At and produce a N2 rich product gas at feed air pressure (Pa), (b) pressure equalizing the adsorber with a companion adsorber, (c) counter-currently depressuring the adsorber to near ambient pressure to produce the O2 enriched gas, (d) pressure equalizing with another adsorber, and finally (e) repressurizing the adsorber to Pa with feed air [4]. 

The SSF membranes, which are produced by carbonization of PVDC, contain nanopores that allow all of the molecules of a feed gas mixture to enter the pore structure. However, the larger and more polar molecules are selectively adsorbed on the carbon pore walls at the high pressure side, and then th dif se selectively to the low pressure side. The smaller molecules are enriched at the high pressure side. These membranes can be used to enrich H2 from mixtures with C1-C4 hydrocarbons or from mixtures with CO2 and CH4. They can also be used to separate CH4-H2S and H2S-H2 mixtures. Table 5 compares performances of SSF carbon and polymeric PTMSP membranes for H2 enrichment from FCC off gas [15]. Clearly, the SSF membrane is much superior for this application. 

Adsorption of methyl mercaptan in moist conditions was performed on numerous samples of activated cartons of various origins. Methyl mercaptan adsorption was tested by a dynamic method. The amount of products of surface reaction was evaluated using thermal analysis. The results revealed that the main product of oxidation, dimethyl disulfide, is adsorbed in pores smaller than SO A. There is apparent competition for adsorption sites between water (moist conditions) and dimethyl disulfi. The comp ition is won by the latter molecule due to its strong adsorption in the carbon pore system. Althou dimethyl disulfide has to compete with water for the adsorption sites it can not be formed in a significant quantity without water. Water facilitates dissociation of methyl mercaptan and thus ensures the efficient removal process. 

Williams PT, Reed AR (2006) Development of activated carbon pore structure via physical and chemical activation of biomass fibre waste. Biomass Bioenergy 30(2) 144-152... 

U. Heinbuch and J. Fischer, Liquid Argon in a Cylindrical Carbon Pore Molecular Dynamics and Born-Green-Yvon Results, Chem. Phys. Lett. 135 (1987) 587-590 Model Studies of Adsorption on Plane Interfaces and in Pores, in Fundamentals of Adsorption, Proc. 2" Engineering Foimdation Conference, ed. A. I. Liapis, Engineering Foundation Press, New York, (1987) 245-254. 

Thus, regarding the effect of thermal treatment of hydrolytic lignin on the size of lignin carbon pores, the optimum regimes of thermal treatment produce sorbents with a pore size of 0.7-1.0 run. A pilot batch of such tnicroporous carbon was produced, its texture... 

Bioactivity in adsorbers has been reported alternately as both advantageous and disadvantageous to the primary adsorption process. As a potential disadvantage, the depth and composition of the biofilm may adversely influence adsorption dynamics by blocking carbon pore openings or by retarding boundary layer... 

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