Micro steady state approximation

The same considerations made before are valid for this case and it is very important to have an available validated reaction mechanism. It can be obtained from three main sources (Blelski et al., 1985 Buxton et al., 1988 Stefan and Bolton, 1998) and it is shown in Table 5. With the available information about the constant k2, k, k, fcg, and k-j, it could be possible to solve a system of four differential equations and extract from the experimental data, the missing constants 4> and k (that in real terms is k /Co2)-This method would provide good information about the kinetic constants, but it is not the best result for studying temperature effects if the same information is not available for the pre-exponential factors and the activation energies. Then, it is better to look for an analytical expression even if it is necessary to make some approximations. This is particularly true in this case, where the direct application of the micro steady-state approximation (MSSA) is more difficult due to the existence of a recombination step that includes the two free radicals formed in the reaction. From the available information, it is possible to know that to calculate the pseudo-steady-state... 

The adsorbed organic substance concentration, / , ds. and the concentration of the association, Ti lOH, can be obtained assuming equilibrium for reactions 3 and 4. If [Ti OH] represents the superficial concentration of bound OH or water that reacts with the holes, we will accept that due to the high water concentration = fcg [Ti" (OH)]. Applying the micro steady state approximation (MSSA) to the [OH ] radicals and calling... 

Once more, the micro steady state approximation may be used to obtain the hole concentration ... 

For initial screening, we have operated our micro-catalytic reactor in a pulsed mode. As is shown below (Results Discussion, Figure 2), the catalyst appears to rather quickly achieve steady-state response, after the first few samples of wood (e.g., <100 mg wood per gram of catalyst). This is confirmed by the approximate mass closures (>80 % typically) from summation of all gaseous species evolving from each wood-vapor pulse, plus measured char yields for each pulse, and overall coke yields of 5-10 weight percent (See Table II under Results Discussion). There is some evidence of absorption of water and light aromatics when vapor first contacts the catalyst, so that the reported yields of liquid products are probably conservative. We plan to insert wood dowels in a continuous manner to verify the behavior under steady state of wood addition. 

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