## 2 Materials, Experimental Setup, and Procedures  
Pine sawdust was used as raw material. For the experiments, sawdust of one tree species (Pinus sibirica) was used. Sawdust came from one of the local woodworking enterprises. The woody biomass was clean (no oil, paint, glue, or other contaminants). Unlike conventional thermal pyrolysis, microwave pyrolysis is based on the principle of interaction of electromagnetic waves with matter. Therefore, this type of conversion does not require external drying of the fuel. Microwave pyrolysis provides fairly fast volumetric heating, when, in fact, there is a conversion of electrical energy into thermal energy. The efficiency of microwave pyrolysis depends on the dielectric properties of the raw material. Water is a special substance characterized by an extremely high permittivity. Therefore, in microwave pyrolysis, for efficient energy conversion, it is expedient to use moistened raw materials in order to improve the absorption of microwaves. Water provides rapid heating of the raw material layer due to the very high dielectric constant. Upon reaching the boiling point, water turns into water vapor. The permittivity of water vapor is many times lower than that of water: at a temperature of 373 K in the state of saturation, water vapor has a permittivity of 1.006, and water has a permittivity of about 55. However, water molecules not only receive energy from an external source, but also transfer molecules of the pyrolyzed raw material throughout its volume. Thus, more efficient heat transfer is achieved in the first conversion stage. [PERSON] et al. [22] showed that a liquid can be effectively used to \"pump\" energy into a material during microwave pyrolysis. But, of course, the role of water can be ambiguous at subsequent stages, when water vapor can participate in the reactions. During pyrolysis, moisture in the biomass contributes to the formation of a vapor-air mixture in the reaction zone. A high steam concentration promotes pyrolysis towards the generation of more H\({}_{2}\) and CO\({}_{2}\)[23]: CO + H\({}_{2}\)O \(\rightarrow\) CO\({}_{2}\) + H\({}_{2}\). In [2], a more humid fraction gave a higher quality gas product in terms of the yield of carbon monoxide and hydrogen. However, many studies on steam gasification (for example, [24; 25]) indicate that an excess amount of water vapor can worsen the reactions, lower the temperature, and, as a result, worsen the composition of the synthesis gas. In the present study, the wood raw material was mixed with water to provide microwave volumetric heating. The composition 60% sawdust-40% water was prepared. Pine sawdust absorbs and retains water very well. Therefore, in the mixture used, the proportion of water was large enough (40 wt%) to ensure uniform saturation of sawdust with water throughout the volume. In addition, experiments with a gas analyzer were performed to assess the influence of the moisture factor on the composition of the conversion products (the procedure is described below). Experiments were carried out with sawdust with a water content of 20%, 40%, and 60%. The results showed that the best composition of the pyrolysis gas was obtained when the mixture \"60% sawdust, 40% water\" was used (Figure 1). For these reasons, this ratio was used for further experiments. A typical industrial microwave installation consists of three main components: a microwave generator (magnetron), guiding systems (waveguide), and a resonator. In industry, microwave generators with operating frequencies of 433, 915, and 2375 MHz are most often used [26]. Household microwave devices use an operating frequency of 2375 MHz, which corresponds to an electromagnetic wavelength of 12.2 cm. Below is a brief overview of the reactors used in microwave pyrolysis research. In [27], microwave pyrolysis of corn cobs was carried out using a microwave installation, consisting of a modified household microwave oven, a condenser tube, and a quartz flask.