Initial methanation temperature

The effect of type and purity of activated carbon on methanation. Initial methanation temperature is related to element composition of six activated carbon made by different carbon materials, such as coconut shell (ACl), wood sawdust (AC2), peach shell (ACS), apricot shells (AC4), coal(AC5) and graphite (C6) as shown in Table 6.53.223-224... 

The effect of crystal structure of activated carbon on methanation. As mentioned above, the initial methanation temperature of activated carbon derived from coal is more than 500°C and above 600°C for graphite. Although low purity of activated carbon derived from coal, they have strong resist-methanation ability, which indicates the effect of micro-crystal structure on methanation is very significant. The main reason of methanation of activated carbon is the unsaturated dangling bonds of edge carbon atoms, which is confirmed from the crystal structure of carbon materials (Fig. 6.70). ... 

Due to the extremely high bond saturated degree of graphite surface, there cannot occur obviously methanation reaction below 600° C. The methanation degree of activated carbon derived from coal is low and the initial methanation temperature... 

Sample Micropore volume/ — 1 cm" g Mesopore volume/ cm Total volume/ —1 cm" g Micropore Mesopore areas/ aresis/ m -g m -g Total areas/ m Initial methanation temperature/ C... 

R is found that the outlet methane concentrations are very low (beyond the instrument detection limit) for the above catalysts that can be detected when the micro-CH4 at above 500°C. The initial temperature of methanation is higher over 8.9% Ru/AC than that over 1.9% Ru/AC. But initial methanation temperature of the latter has exceeded the operation temperature in industry, which shows that the above catalyst has high stability for methanation. Therefore, methanation is mainly determined on the nature of support, for example the degree of graphitization. The ruthenium content has nearly no influenced on methanation. 

It decreases the initial methanation temperature from 493°C to 475°C. It can be seen from Fig. 6.73 that the initial methanation temperature is increased with the increasing content of Ba. The role gradually weakens after the Ba content reaches 4%. Therefore, the optimum content of Ba is about 4%. It can be seen from Fig. 6.74... 

Rare earth oxide. The inhibition effect of lanthanide oxides on methanation should be obviously due to their high melting points and the low mobihty. It can be seen from Table 6.56 that lanthanum (La), cerimn (Ce) and samarium (Sm) have good ability to inhibit methanation, thereinto Sm is the best, whose initial methanation temperature reaches 534° C. The optimum mole ratio of La/Ru is about 0.5-1.0 (Fig. 6.76) and Sm/Ru= 1 (Fig. 6.77), and the role of increasing content is very small. 

Table 6.59 Effect of H2 content on initial methanation temperature...

The activation energy is 33 kJ mol for forward and 105kJ mol for reverse reaction of the dissociation of H2 on the Fe (110) surface. The activation energy of H2 dissociation is very low, which is a fast step of these processes. It can be seen from Table 6.59 that the effect of hydrogen content on the initial methanation temperature is insignificant, which indicates that the effect of diffusion rate of H2 on surface of activated carbon for methanation is very small. The results where little methane escapes at temperatures above 550°C based on the H2-TPD MS indicates that there has existence of CHx in adsorption process of H2. 

Thus, the elementary cellular structure could be regarded as an intrinsic characteristic of fhe detonation in a mixture at given initial composition, temperature, and pressure. The dimension of X is of fhe order of magnitude of millimeters or less for gaseous mixfures with oxygen, but several centimeters for less sensitive mixtures (even larger, for methane/air af afmospheric pressure). It decreases when the initial pressure increases. Its variation with the initial temperature is more complicated and depends on the value of fhe reduced activation energy of fhe chemical reactions. The value of... 

For the catalytic functionalization of methane 0.21 mmol of compoimd 18 and 100 equivalents K2S2O8 are suspended in a mixture of 60 mL trifluoroacetic acid and 10 mL trifluoroacetic acid anhydride and are transferred into an autoclave. With an initial methane pressure of 20 atmospheres and a temperature of 80 °C the only product is trifluoroacetic acid methylester (510% yield relative to palladium). 

Of particular interest are the curves in Fig. 5. This form corresponds to the most common case when the temperature T0 is so low that, even when very little heat transfer is present, self-ignition is completely out of the question. For all ordinary explosive mixtures of hydrogen, carbon monoxide, methane and other industrial combustible gases with air, at initial room temperature, self-ignition is completely impossible. However, for sufficient fuel concentration and sufficient calorific value of the mixture, the temperature which develops in combustion may be large enough to ensure a very rapid chemical reaction or to ensure the possibility of steady combustion (branch AB of the curve). 

At relatively low temperatures (< 800 °C), over most catalysts investigated, the catalytic partial oxidation of methane to synthesis gas is thought to follow the so-called indirect scheme, according to which initially methane is combusted until all... 

Another reason that isothermal heating methods are used in the initial screen is to identify materials that have time dependent thermal stability. These materials have a thermal decomposition that does not follow a simple Arrhenius relationship in which the reaction rate increases exponentially with an increase in temperature. Instead an extended induction period is required before the decomposition becomes detectable. An example of this behavior is shown in Figure 2. The DTA isothermal test recorder traces of methane sulfonic acid, 3,7-dimethyloctyl ester at different test temperatures are shown. The induction time varies from less than 1 hr. at 180 C to 46 hr. at 130 C. As with this compound, it is not unusual that once decomposition is detected it proceeds very rapidly, releasing all of the heat in a short period of time. Dynamic heating methods do not indicate if this type of thermal instability is present if it is, the initial detection temperature from dynamic tests will be grossly misleading as to the thermal stability of the material. 

The maximum temperature increase in a PBR is independent of the gas flow rate and it is dependent on the heat of reaction, the heat capacity of the gas and especially the solid material weight fraction. In particular, the active weight content in the OC (yoc,act) an important role in the maximum temperature increase. In the case of reduction, the maximum temperature change depends on the fuel (methane or H2/CO species as shown in Figures 5.16 and 5.17) and the OCs used, and it can be both exothermic and endothermic. The reduction reactions between the fuel species and the OCs are mainly affected by the initial solid temperature that strongly influences the kinetics. 

The purity of crude activated carbon derived from coconut shell is 90.86% and initial methanation temperatm-e is 478°C. Its purity is increased to 91.44% after treatment by H2 at 600°C-700°C for 6 h, and the initial temperature of methanation is increased to 493° C, which indicated that increasing purity is favorable to inhibit methanation of activated carbon. 

Lanthanum oxide has often been used as a major constituent of patented OCM formulations. Lacombe et al. [94] proposed that on La203 catalysts CO2 is formed on its surface, involving a slow step of methyl radical oxidation, while CO issues from C2-1- hydrocarbons. Two types of active sites have been identified on theLa203 surface. Low coordination metal sites localized on step edges are related to the total oxidation pathway, while basic sites associated with oxygen vacancies enable the oxygen activation that leads to the initial methane activation. Proper modification of the lanthana surface by specific additives inhibits CO2 formation. Thus, Sarkany et al. [95] reported the lowest temperature for methane coupling, which in turn... 

Aldehydes are important products at all pressures, but at low pressures, acids are not. Carbon monoxide is an important low pressure product and declines with increasing pressure as acids increase. This is evidence for competition between reaction sequence 18—20 and reaction 21. Increasing pressure favors retention of the parent carbon skeleton, in concordance with the reversibiUty of reaction 2. Propylene becomes an insignificant product as the pressure is increased and the temperature is lowered. Both acetone and isopropyl alcohol initially increase as pressure is raised, but acetone passes through a maximum. This increase in the alcohoLcarbonyl ratio is similar to the response of the methanoLformaldehyde ratio when pressure is increased in methane oxidation. 

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