# Microwave Pyrolysis of Biomass: The Influence of Surface Area and Structure of a Layer
## 4 Results and Discussion
### Influence of Biomass Particle Size
The experimental results are in good agreement with the data obtained in [60]. [PERSON] et al. [60] studied the effect of biomass particle size (0.3 to 1.0 mm) on the yield of gasification products such as gas, tar and char. The temperature in the reactor varied from 700 \({}^{\circ}\)C to 1000 \({}^{\circ}\)C. The results showed that smaller biomass particles produced more H\({}_{2}\), CO and CH\({}_{4}\) than larger particles. In particular, feedstock particles with a size of 0.3-0.5 mm provided a higher H\({}_{2}\) yield (33.93 vol.%), which is 1.5 times higher compared to particles with a size of 0.5-1.0 mm. The influence of the biomass particle size on the yield and composition of the pyrolysis gas was also studied in [61], where palm oil waste with particle sizes of 0.15-1.0, 1.0-2.0 and 2.0-5.0 mm was used as a fuel. The H\({}_{2}\) yield increased \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}{*}{140 \(\mu\)m} & CO & 17.38 & 173,800 & 202,373 & 135,792,283 \\  & CO\({}_{2}\) & 6.91 & 69,100 & 126,421 & 86,851,227 \\  & CH\({}_{4}\) & 7.1 & 71,000 & 47,342 & 31,766,482 \\  & H\({}_{2}\) & 1.09 & 10,900 & 913 & 1,291,895 \\  & H\({}_{2}\)S & 0.0106 & 106 & 150 & 106,650 \\  & SO\({}_{2}\) & 0.0045049 & 45.05 & 120 & 32,160 \\  & NO & 0.00425 & 42.5 & 53 & 37,365 \\ \hline \multirow{8}{*}{250 \(\mu\)m} & CO & 15.5 & 155,000 & 179,800 & 233,740,000 \\  & CO\({}_{2}\) & 7.01 & 700,100 & 1,281,183 & 1,076,193,720 \\  & CH\({}_{4}\) & 5.01 & 50,100 & 33,406 & 47,269,490 \\ \cline{1-1}  & H\({}_{2}\) & 0.88 & 8800 & 913 & 1,291,895 \\ \cline{1-1}  & H\({}_{2}\)S & 0.006342 & 63.4 & 89.85 & 125,935 \\ \cline{1-1}  & SO\({}_{2}\) & 0.0018449 & 18.45 & 49.13 & 22,649 \\ \cline{1-1}  & NO & 0.00008 & 0.08 & 0.10 & 0.8 \\ \hline \multirow{8}{*}{2000 \(\mu\)m} & CO & 10.2 & 102,000 & 118,319.9 & 165,648,000 \\ \cline{1-1}  & CO\({}_{2}\) & 8.07 & 807,000 & 1,476,810 & 2,658,258,000 \\ \cline{1-1}  & CH\({}_{4}\) & 2.88 & 28,800 & 19,203.78 & 45,319,080 \\ \cline{1-1}  & H\({}_{2}\) & 0.62 & 6200 & 523 & 1,113,000 \\ \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 7: The yield of the main gases. Figure 17: Average (**a**) and maximum (**b**) concentrations of the gas mixture components when varying the average size of biomass particles. by 5% as the particle size decreased from 5 to 0.15 mm. In the present study, the minimum concentration of CO of 10.2% was recorded for particles with a size of 250 \(\upmu\)m.  
The established trends are due to the fact that raw materials of finer grinding have a larger total surface area of the particles. As a consequence, such fuel warms up better, and higher reaction rates can be achieved during pyrolysis. This contributes to the production of a larger amount of light gases and a smaller amount of coke and condensate [61; 62]. With a larger particle size, the temperature gradient inside it increases. At the same moment of time, the temperature inside the particle is lower than on its surface, which leads to an increase in the yield of semi-coke and resins and, accordingly, the gas yield decreases [63]. Figure 18 shows the trends of changes in the individual components of the gas mixture formed during the pyrolysis of sawdust with varying particle sizes.