## 3 Results and Discussion
The minimum total time of pyrolysis was recorded at 2200 W (1890 \(\pm\) 40 s). The pyrolysis process was the longest (3948 \(\pm\) 55 s) when using the minimum power of microwave processing of biomass. The increase in power contributed to a decrease in the duration of the inert period, i.e., the time when pyrolysis gas is not yet released. Increasing the microwave power from 840 W to 2200 W reduced the delay time of pyrolysis gas yield by about 20 times. According to Figure 4b, approximate formulas (Equations (6)-(8)) for the characteristic times of microwave pyrolysis of woody biomass are determined:  
\[t_{0}=-0.5586P+1309.7 \tag{6}\]  
\[t_{1}=-0.9627P+3904.3 \tag{7}\]  
\[\sum=-1.5213P+5214 \tag{8}\]  
Figure 5 illustrates typical time trends in the concentrations of gaseous products from the pyrolysis of sawdust. The curves have some fluctuations as well as several extremes. The non-monotonicity of gas release is explained by the fact that the temperature in the layer increases during microwave pyrolysis. Therefore, the released gases enter into secondary reactions with the pyrolysis liquid and the resulting biochar at higher temperatures. Experiments have shown that microwave power is an important factor influencing the dynamics of pyrolysis gas formation. For example, at low microwave power, methane evolution was characterized by a single-peak mode, in which the maximum possible concentrations are released for a rather short time relative to the total pyrolysis time. For other components, a similar trend was observed--with an increase in power, both the maximum yield of combustible gases increased, and the conditional \"density\" of this yield increased, i.e., a large proportion of the total pyrolysis time included the useful time for the release of gases. Figure 6 shows that with increasing microwave power, the relative yield of solid and liquid products decreased. The largest masses of solid and liquid products (6.4 \(\pm\) 0.2 g and 5.5 \(\pm\) 0.2 g, respectively) were recorded at 840 W, and the smallest (1.2 \(\pm\) 0.1 g and 2.0 \(\pm\) 0.1 g) were recorded at a power of 2200 W. The decrease in liquid yield is due to secondary cracking reactions at a high energy level. The yield of biochar decreased with increasing power since the decomposition of biomass into volatile substances was promoted by high temperature and energy supply, which inhibited the carbonization process. The decrease in the mass of solid and liquid residues with increasing power is due to more intense degassing of hemicellulose and lignin during wood pyrolysis. With intense exposure to microwaves and the corresponding self-heating of the biomass layer, side-chain cleavage reactions of hemicellulose and lignin occur, such as deacetylation and demethylation [39]. With an increase in temperature, the processes of depolymerization of hemicellulose and lignin are intensified [39], which leads to a decrease in the mass of solid and liquid residues and an increase in gas formation. According to the results obtained, an increase in the power of microwaves contributed to a decrease in the mass of the solid residue by 5.3 times. The mass of the liquid product decreased by 2.7 times. Based on experimental data, ap  
proximation formulas were obtained to predict the percentage yield of solid and liquid products obtained during microwave pyrolysis (relative to the initial dry weight of raw materials):  
\[\text{O}_{2}=-0.0012P+17.547 \tag{1}\]0 \[\text{O}_{2}=-0.0012P+17.547 \tag{1}\]1  
\[\text{O}_{2}=-0.0012P+17.547 \tag{1}\]2 Time trends in the concentrations of pyrolysis gas components with varying microwave power: (**a**) 840 \(W\); (**b**) 1760 \(W\); (**c**) 2200 W.  
The integral efficiency of wood pyrolysis at various powers of the microwave reactor can be estimated through a set of indicators. Multiple-criteria decision analysis [40] has been developed for such problems. In particular, the weighted sum method [41] can be used.