Process parameters methane conversion

GP 8] [R 7] Ignition occurs at a rhodium catalyst at catalyst temperatures between 550 and 700 °C, depending on the process parameters [3]. Total oxidation to water and carbon dioxide is favored at low conversion (< 10%) prior to ignition. Once ignited, the methane conversion increases and hence the catalyst temperature increases abruptly. 

The outside tubeskin temperature was taken to be identical to that generated in the previous simulation. The input data were also identical. Radial process temperature profiles are given in Figure 7. The ATg between the bed centerline and the wall amounts to 33°C, which is not excessive and permits the radially averaged temperature to be accurately simulated by means of the one dimensional model with "equivalent" heat transfer parameters, as discussed above. The methane conversion at the wall never differed more them 2% absolute from that in the centerline of the bed. The more detailed description which is possible by the two dimensional model would only be required if thermodynamic s predict possible carbon formation, and therefore catalyst deactivation, at locations different from those simulated by the one dimensional model. 

Methane-coupling reaction conversions and yields less than 25 percent initially were—and still are—below those acceptable for commercial fuel and chemical feedstock production. But worldwide research and development in more recent years continue to suggest that variations in process parameters, reactor design, and catalyst composition and structure may bridge this gap. Lower reaction temperatures—in the 300-400°C range may... 

Clear and convincing dependences of the main parameters of the DMTM process in a quartz flow reactor at P = 91 atm, T = 427 °C, and a residence time of fr = 35 s were presented in [98]. The experiments were performed with natural gas containing up to 4% ethane and 1% C3+ hydrocarbons. Figure 3.36 shows dependences plotted based on the averaged data from this work. As can be seen, over a wide range of oxygen concentrations, from 1.5 to 12.5%, the methane conversion increased linearly with the oxygen concentration (Fig. 3.36). 

For the range of industrially relevant conditions, the developed model could accurately predict both the observed CO conversion and the products distribution up to n = 49, in terms of total hydrocarbons, n-paraffins, and a-olefins. In particular, using thirteen adaptive parameters, the model is able to describe the typical deviations of the product distribution from the ASF model, i.e., the methane high selectivity, the low selectivity to C2 species, and the change of the slope of the ASF plot with growing carbon number. Accordingly, the present model can be applied to identify optimized process conditions that are suitable to grant the desired conversion with the requested products distribution. 

The potential of these reactions for methane production can be compared in terms of theoretical yields and heat recovery efficiencies. Theoretical methane yield is defined by the chemical equations. Theoretical heat recovery efficiency is defined as the percent of the higher heating value of the coal which is recovered in the form of methane product. These idealized parameters provide a measure of the ultimate capability of conversion systems and are useful for evaluating actual conversion processes. 

FIG. 18. Reaction parameters for n-hexane conversion by Ni and Ni-Cu alloys at 330°C Ai = log rw (rate per gram of catalyst) A2 = log rs (rate per square centimeter of total surface) Eact is activation energy of the overall process S is the selectivity for producing Cg products M is a fission parameter whose value inversely reflects the degree of multiple fragmentation to methane (102). 

Since the isotopic transient technique involves the number and type of intermediates on the catalyst surface, independent transient experiments (with or without the use of isotopes) have also been used to determine these parameters. The simplest reaction for analysis by the isotopic transient kinetic technique for the conversion of syngas is the production of methane. Studies of methanation provide a background to the isotopic transient kinetic studies and independent justification for the number and type of adsorbed species involved in FTS. Furthermore, the production of methane is undesirable for FTS and an understanding of the mode of its production will aid in FTS catalyst and process design. 

Because carbon is the limiting factor, the carbon conversion to methanol, also referred to as carbon efficiency, is an important operating parameter for overall ener efficiency. Carbon efficiency is a measure of how much carbon in the feed is converted to methanol product. There are two commonly used carbon efficiencies, one for the overall plant and one for the methanol synthesis loop. For the overall plant all the carbon-containing components in the process feedstock from the battery limits and the methanol product from the refining column are considered. For a typical plant and natural gas feedstock, an overall carbon efficiency is about 75%. The methanol synthesis loop carbon efficiency for the same plant is about 93%. The synthesis loop carbon efficiency is calculated using only the carbon in the reactive components in the makeup gas (CO and C02). Carbon in the form of methane is not considered because it is inert in the methanol synthesis reaction and is ultimately purged from the loop and burned. The carbon in the product for this calculation is that in the form of methanol in the crude leaving the methanol synthesis loop. 

The works [158,185—188] investigated the effect of various parameters on the reaction onset temperature and the yield of the products. At pressures of 1 and 5 atm, the increase of the initial concentration of NO to 1% significantly, by 100 °C, decreased the temperature of the process, although the maximum obtainable conversion of methane was almost the same. However, the increase of the NO concentrations to 1.5% produced practically no effect. At these pressures, the selectivity of formation of oxygenates (methanol, formaldehyde, and nitromethane) reached a maximum at an NO concentration of 0.5%, so this concentration was adopted as optimal. The ethane formation selectivity decreased rapidly with increasing NO concentration, nearly to zero. Diluting the mixture with helium, at least up to 60%, had a moderate effect on the process. Even the CH4/O2 ratio, a key parameter of the... 

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