Methane clinoptilolite

Methane/Nitrogen Gas Separation over the Zeolite Clinoptilolite by the Selective Adsorption of Nitrogen... 

Since methane diffusion is much slower than nitrogen diffusion into clinoptilolite, it is reasonable to suspect that the presence of CH4 on the zeolite surface will effectively slow the uptake of N2. If true, then it would be much more appropriate to measure DN2 in the presence of CH4 rather than in the pure gas... 

We have examined whether a simple non-bonded potential can be developed to be (i) transferable from one zeolite to another and (ii) to simulate without parameter adjustment isosteric heats at different temperatures and sorption uptake isotherms. The sorption of methane into Na- and K- zeolite X, and Na-and K-clinoptilolites was considered. Models for Na-X and K-X were constructed based on the averaged crystallographic results. The non-bonded parameters in a Lennard-Jones potential were iteratively adjusted so as to best reproduce the experimental isosteric heats in Na-X and K-X over a small temperature range. Methane-methane interaction parameters were taken from earlier work [89] and a final iteration was made so as to better fit the experimental sorption isotherms in clinoptilolite. This single and simple non-bonded potential parameter set then reproduces to a reasonable degree... 

Hydrogen and toluene are reacted over a solid mineral catalyst containing clinoptilolite (a crystalline silica-alumina) to yield methane and benzene ... 

Over Pd/clinoptilolite catalyst (III) the CO2 conversion showed self-sustained oscillation over a long period of time along with oscillation in the output temperature. The overshoots in CO2 concentration start sharp and decay much slower indicating an autocatalytic process. The self-sustained oscillation is present not only in m-xylene system, but in methane-m-xylene mixture, too as shown in Fig. 4. 

A zeolite and carbon molecular sieves (CMS) have been examined for N2/CH4 separation. A process using 4A zeolite for this separation was developed by Habgood (1958), but this process was limited to low temperatures (—79 to 0°C) and a high-methane feed content (>90%). Ackley and Yang (1990) have demonstrated the use of carbon molecular sieve (CMS) for separation of N2/CH4 mixtures in pressure swing adsorption (PSA) processes but have also shown that the potential for CMS to achieve the desired pipeline quality (90% methane) is doubtful. The only two promising sorbents are clinoptilolites and titanosilicates, as discussed below. 

Frankiewicz and DonneUy (1983) showed the promise of a calcium-exchanged clinoptilolite for N2/CH4 separation by a PSA process, but the product was below pipeline quality. This work stimulated a good deal of interest in further investigation. Two Japanese patent applications (61-255,994, in 1986, and 62-132,542 in 1987, see Chao, 1990) disclosed the use of natural clinoptilolite and Ca-exchanged forms for nitrogen removal from methane. Chao (1990) suggested the use of Mg-exchanged clinoptilolite for N2/CH4 separation. 

Figure 10.43. High-pressure nitrogen and methane isotherms on purified clinoptilolite at 22 °C (Jayaraman et al., 2002).

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