Methane zeolite

Adsorption isotherms of methane in silicalite have also been predicted in a number of calculation studies (62, 155, 156). Goodbody et al. (62) predicted a heat of adsorption of 18 kJ/mol and simulated the adsorption isotherm up to 650 bar. From the adsorption isotherm, they found that the sinusoidal pore volume contains more methane molecules at all pressures. Snurr et al. (155) performed GC-MC and MD simulations over a wide range of occupancies at several temperatures. The intermolecular zeolite-methane potential parameters were taken from previous MD studies (11, 87) and the methane-methane parameters from MD simulations were adjusted to fit experimental results for liquid methane (157). Electrostatic contributions were neglected on account of the all-silica framework, and methane was represented by a rigid, five-center model. 

E. Cohen de Lara, R. Kahn, and A. M. Goulay, /. Chem. Phys., 90,7482 (1989). Molecular Dynamics by Numerical Simulation in Zeolites Methane in NaA. 

An interesting point is that infrared absorptions that are symmetry-forbidden and hence that do not appear in the spectrum of the gaseous molecule may appear when that molecule is adsorbed. Thus Sheppard and Yates [74] found that normally forbidden bands could be detected in the case of methane and hydrogen adsorbed on glass this meant that there was a decrease in molecular symmetry. In the case of the methane, it appeared from the band shapes that some reduction in rotational degrees of freedom had occurred. Figure XVII-16 shows the IR spectrum for a physisorbed H2 system, and Refs. 69 and 75 give the IR spectra for adsorbed N2 (on Ni) and O2 (in a zeolite), respectively. 

Truong T N 1997 Thermal rates of hydrogen exchange of methane with zeolite a direct ab initio dynamics study on the importance of quantum tunneling effects J. Rhys. Chem. B 101 2750... 

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. 

Synthesis of Porous Materials Zeolites, Clays, and Nanostructures, edited by Mario L. Occelli and Henri Kessler Methane and Its Derivatives, Sunggyu Lee... 

A zeolite catalyst operated at 1 atm and 325-500 K is so active that the reaction approaches equilibrium. Suppose that stack gas having the equilibrium composition calculated in Example 7.17 is cooled to 500 K. Ignore any reactions involving CO and CO2. Assume the power plant burns methane to produce electric power with an overall efficiency of 70%. How much ammonia is required per kilowatt-hour (kWh) in order to reduce NO , emissions by a factor of 10, and how much will the purchased ammonia add to the cost of electricity. Obtain the cost of tank car quantities of anhydrous ammonia from the Chemical Market Reporter or from the web. 

A very recent example of the first case is presented by Vilaseca et al. [71] where an LTA coating on a micromachined sensor made the sensor much more selective to ethanol than methane. Moos et al. [72, 73] report H-ZSM5 NH3 sensor based on impedance spectroscopy using the zeolite as active sensing material. At elevated temperatures (>673 K) NH3 still adsorbs significantly in contrast to CO2, NO,... 

BIOMIMETIC FEATURES OF FeZSM-5 ZEOLITE 3.1. a-Oxygcn methane oxidation... 

Fig 3 shows the results of two temperature-programmed experiments. In the first (blank) experiment CH4 reacts with a "bare" FeZSM-5 zeolite, while in the second one it reacts with the zeolite after a-oxygen loading on its surface. Obviously, the bare surface is quite inert towards methane (Fig 3a) after reactor opening a weak CH4 adsorption occurs at room temperature. A slight heating results in a complete recovery of the CH4 pressure. 

Fig. 5.3.8 Photograph of the detection region of the NMR probe with radiofrequency coil. A methane—air mixture was ignited above the zeolite pellets. The mixture also contained xenon for NMR detection. Hp-129Xe NMR spectra with 30% xenon (from high-density xenon optical pumping) in 70% methane is depicted. (1) The spectrum in the absence of combustion and (2) the spectrum during combustion. Adapted from Ref. [2],...

Methane Conversion. Proceedings of a Symposium on the Production of Fuels and Chemicals from Natural Gas, Auckland, April 27-30, 1987 edited by D.M. Bibby, C.D. Chang, R.F. Howe and S. Yurchak Innovation in Zeolite Materials Science. Proceedings of an International Symposium, Nieuwpoort, September 13-17, 1987... 

Without any doubt, the zeolite framework porous characteristics (micropores sizes and topology) largely govern the zeolite properties and their industrial applications. Nevertheless for some zeolite uses, as for instance, host materials for confined phases, the zeolite inner surface characteristics should be precised to understand their influence on such low dimensionality sorbed systems. In that paper, we present illustrative examples of zeolite inner surface influence on confined methane phases. Our investigation extends from relatively complex zeolite inner surface types (as for MOR structural types) to the model inner surface ones (well illustrated by the AFI zeolite type). Sorption isotherm measurements associated with neutron diffraction experiments are used in the present study. 

Figure 6. Translational molecular mobility Dt of neopentane and methane phases confined in model AlP04-5 zeolite micropores.

Figure 8 Schematic representation of the methane commensurate dimmers" chain confined in the model AlP04-5 zeolite micrpores.

Pt/H-MCM-22 catalysts for methane combustion have been prepared by ion-exchange of a highly crystalline H-MCM-22 zeolite using [Pt(NH3)4](N03)2. The activation procedure of the catalyst precursor has been optimized and all steps monitored by HRTEM, SEM and FTIR of CO adsorbed. The preliminary decomposition/calcination of the ion exchanged sample is very crucial in that influence the final properties of platinum active species. 

Figure 1. Methane sorption isotherms measured at T = 77.35 K on four different AlP04-5 zeolite samples S(l), S(2), S(3) and S(4).

---