Methane life-time

Fig. 7 High temperature HZSM5 deactivation during methanol conversion. Amount of deposited coke, and average selectivities of coke and methane in correlation to catalyst life time.

The initial molar propane/propene-ratio (at 10 % of catalyst life time) is a measure of catalyst activity. It grossly correlates with the catalyst Si/Al-ratio. Fig. 7 concerns further proofs of catalyst life time. No correlation is observed between the amount of coke deposited and the total amount of methanol which is converted during the catalyst life time. However, a correlation appears to exist between (1) coke selectivity and catalyst life time and (2) methane selectivity and coke selectivity. 

The cracking of w-hexane and -butane as catalytic test reactions show unexpected results upon laser heating of the samples. Methane/coke deposits were obtained. The assignment of the intermediates which have life times of some seconds requires further work. 

The major sink for atmospheric methane is oxidation by highly reactive hydroxyl radicals ( OH formed by photolytic dissociation of water molecules in the atmosphere Crutzen 1988 Eisele et al. 1997). The life-time of methane in the atmosphere is, consequently, relatively short and unlikely to have exceeded 100 years... 

Figure 2a Intracrystalline near, life times determined from nmr tracer desorption studies on zeolite NaX for methane < , c = 94 ngg-, R = 25 pa) ethane t. 0, 113 mgg 25 urn n-butane (, 165 mgg 25 pm) and n-hexane (A, 165 mgg, ...

Figure 3 Intracrystaliine t a> and long-range selfdiffusion coefficients and intracrystaliine mean life times rinii c 1 and r1 of methane in granulated zeolite KaCaA, and comparison with the break-through capacities for a petroleum raffinate (e) and the specific retention volume for n-pentane if), in dependence on the temperature of hydrothermal pretraatment applied over a time interval of 7 h ( > and 14 h (Oi, respectively (Reproduced with permission iron Ref. t>. Copyright lya Butterworth)...

Figure t gives a comparison of the intracrystalline mean life times of methane in ZSK-5 type monocrystais alter diiferent coxing times, and the values of t 1, calculated from the... 

Figure 6 Intracrystalline mean life times t,<. > and Tini,, "1" (<4 ) for methane at 296 K and a sorbate concentration of 3 molecules per channel intersection in H ZSM-5 coked by n-hexane (full symbols and mesitylene (open symbols in dependence on the time on stream (Reproduced with permission from Ref. 6. Copyright 1 >S7 Butterworth ...

The use of natural gas condensates, cheaper and easier to obtain than naphta, is growing. These raw materials are often contaminated by mercury and arsenic compounds. The presence of arsenic or mercury in crude oil can cause not only environmental pollution and equipment corrosion, but also reduction of metallic catalysts life time [1]. For example, in the case of steam reforming or methanation reactions, the presence of arsenic causes severe poisoning of the nickel catalysts [2]. 

Fig. 8 Values for the intracrystalline mean life time tintra ( M) and the quantity (A,A) for methane in H-ZSM5 which has been coked by n-hexane (filled symbols) and mesitylene (open symbols) as a function of the coking time (methane concentration 12 molecules per unit cell measuring temperature 296 K). From [116] with permission...

Fig. 4-75 Pyrolysis of Distillation Bitumen and its Colloidal Components in 10 bar Methane Half Life Time ty/2 versus Temperature Line 1 Distillation bitumen Line 2 Dispasion medium Line 3 Petroleum resins line 4 Asphaltenes...

When life began, over 3.8 billion years ago, the first cells were anaerobic. The atmosphere at that time was probably a mixture of nitrogen with gases such as carbon monoxide and water vapour, or perhaps methane. Like any other organisms, these primitive bacteria needed some source of energy to drive their biochemical... 

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