# Microwave Pyrolysis of Biomass: The Influence of Surface Area and Structure of a Layer
## 4 Results and Discussion
### Surface Structure  
This section details the effect of artificial modification of the biomass layer on the composition of the pyrolysis gas. Figure 12a,b shows the surface structure of the biomass. The artificial pores were small round voids in the surface layer of the biomass (Figure 12a). The channels were narrow, long, hollow spaces separating the biomass layer. Figure 13 shows the trends for the individual components of the gas mixture formed during the pyrolysis of sawdust with varying surface structure of the sample. The release of CO, CH\({}_{4}\) and H\({}_{2}\) started faster when the biomass was distributed in an even layer. In addition, in this case, emission lasted the longest (Figure 13c). In the presence of channels and pores in the biomass structure, the start time and duration of gas release were almost identical (Figure 13a,b). During the pyrolysis of biomass with artificial channels in the structure, there were two peaks at which the maximum concentrations of CO, CO\({}_{2}\), CH\({}_{4}\) and H\({}_{2}\) gases were reached: 13%, 36%, 21% and 3.5% (first peak) and 13.8%, 34%, 17% and 2.8% (second peak). During the pyrolysis of a sample with artificial pores, one peak of CO and CO\({}_{2}\) concentrations was observed--52.5% and 18%, respectively. With the distribution of biomass in an even layer, we recorded a gradual increase and then a decrease in CO\({}_{2}\) concentrations with a maximum of 17%. The concentrations of CO, CH \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Experiment**} & \multirow{2}{*}{**Gas**} & **Average** & **Average** & **Average** & **Total Amount of** \\  & & **Concentrations** & **Concentrations** & **concentrations** & **Pyrolysis Gas** \\  & & **(\%)** & **(ppm)** & **(mg/M\({}^{3}\))** & **(mg/m\({}^{3}\))** \\ \hline \multirow{8}{*}{Biomass is distributed into large fragments} & CO & 8.72 & 87,200 & 101,535.88 & 203,070,000 \\  & CO\({}_{2}\) & 5.27 & 52,700 & 96,416.63 & 123,198,144 \\ \cline{1-1}  & CH\({}_{4}\) & 3.2 & 32,000 & 21,337.54 & 25,455,041 \\ \cline{1-1}  & H\({}_{2}\) & 1.47 & 14,700 & 2681.29 & 5,372,724 \\ \cline{1-1}  & H\({}_{2}\)S & 0.004743 & 47.43 & 67.20 & 77,750 \\ \cline{1-1}  & SO\({}_{2}\) & 0.00209 & 20.9 & 55.66 & 19,792 \\ \cline{1-1}  & NO & 0.00182 & 18.2 & 22.71 & 45,510 \\ \hline \multirow{8}{*}{Biomass is divided into small fragments} & CO & 10.52 & 105,200 & 122,495.12 & 153,853,720 \\ \cline{1-1}  & CO\({}_{2}\) & 6.55 & 65,500 & 119,834.71 & 105,693,588 \\ \cline{1-1}  & CH\({}_{4}\) & 3.67 & 36,700 & 24,471.49 & 28,117,179 \\ \cline{1-1}  & H\({}_{2}\) & 1.08 & 10,800 & 904.94 & 1,237,576 \\ \cline{1-1}  & H\({}_{2}\)S & 0.009053 & 90.53 & 128.26 & 172,288 \\ \cline{1-1}  & SO\({}_{2}\) & 0.00285 & 28.5 & 75.90 & 30,056 \\ \cline{1-1}  & NO & 0.002863 & 28.63 & 35.72 & 48,936 \\ \hline \multirow{8}{*}{Biomass is distributed over a half of the crucible bottom} & CO & 15.5 & 155,000 & 180,482.36 & 465,102,114 \\ \cline{1-1}  & CO\({}_{2}\) & 7.01 & 70,100 & 128,250.58 & 138,382,375 \\ \cline{1-1}  & CH\({}_{4}\) & 2.88 & 28,800 & 19,203.78 & 45,319,080 \\ \cline{1-1}  & H\({}_{2}\) & 0.88 & 8800 & 737.36 & 22,739,200 \\ \cline{1-1}  & H\({}_{2}\)S & 0.003759 & 37.59 & 53.26 & 50,104.47 \\ \cline{1-1}  & SO\({}_{2}\) & 0.00165 & 16.5 & 43.94 & 18,298.5 \\ \cline{1-1}  & NO & 0.00123 & 12.3 & 15.34 & 31,783.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: The yield of the main gases. and H\({}_{2}\) have two peaks: 25%, 3% and 2.5% (first peak), and 46%, 11% and 2.6% (second peak), respectively. Figure 14 shows the average and maximum concentrations of the gas mixture components. Figure 12: Structure of the biomass surface with artificial pores (**a**) and channels (**b**); 1—crucible; 2—biomass; 3—artificial pores; 4—artificial channels. Figure 13: _Cont._  
The results showed that the creation of artificial pores on the surface of the biomass makes it possible to increase the CO yield by 18% and 32% compared to artificial channels and an even layer, respectively.