*3.3. Product Distribution and Yields*

As a result of the study of the pyrolysis process at a temperature of 550 ◦C, three products were obtained: gas, bio-oil, and biochar (Table 4). Generally, the yields of liquid, solid and gaseous products are 50–70 wt%, 13–25 wt%, and 12–15 wt%, respectively [59]. A similar trend is typical for the results obtained. For all samples, the mass fraction of bio-oil among the pyrolysis products was the largest. In a number of studies, it has already been shown that the pyrolysis temperature from 450 to 550 ◦C contributes to the production of liquid products [35,60]. The yield of pyrolysis products when using AR leaves is similar to pine, AR inflorescences are comparable to *Acacia cincinnata* trunk, and AR stems are similar to agricultural biomass residues [61].


**Table 4.** Distribution of product pyrolysis yields and uncertainty analysis.

The results obtained in this study were compared with experimental data on the pyrolysis of plant biomass. Table 5 presents data on the products of thermal decomposition obtained during the pyrolysis of various biomass, its parts, and the plant as a whole. Experiments in which the process temperature was 500–600 ◦C and the heating rate varied from 5 to 50 ◦C/min were considered as pyrolysis conditions.


**Table 5.** Distribution of pyrolysis products obtained from various raw materials.

A large yield of pyrolysis liquid was observed during pyrolysis of *Alternanthera philoxeroides* biomass [15]. The authors of [15] conclude that with an increase in temperature from 350 ◦C to 450 ◦C, the bio-oil yield and the yield of gas increase while the yield of biochar decreases. An increase in temperature leads to an increase in the gas yield and a decrease in the yield of pyrolysis liquid, which is associated with the secondary cracking of pyrolysis vapors at a higher pyrolysis temperature. During the pyrolysis of the banana pseudo-stem, a high mass yield of biochar was observed [21]. During the thermochemical conversion of the mixture of discarded vegetables and fruits at 500 ◦C, the maximum yield of bio-oil was observed, with an increase in temperature, its yield decreased [20]. During catalytic pyrolysis, there was a tendency to increase the yield of pyrolysis liquid and pyrolysis gases [14,19,20].

The heating rate during pyrolysis also affects the product yield. With fast pyrolysis, the yield of liquid products is higher, as this technology is characterized by high heating rates [17,20]. The analysis of studies showed that the temperature of 600 ◦C turned out to be optimal for further research on optimization due to its highest yields [15,17,20,27]. A comparative analysis showed that the results obtained in this work are comparable with the values obtained by other authors. The difference in values is explained by the composition of the feedstock, the influence of the parameters of the pyrolysis process and the influence of catalysts.

#### *3.4. Composition of Bio-Oils*

The composition of pyrolysis products is dominated by bio-oil or pyrolysis liquid, which is associated with the rich chemical composition of AR biomass. It contains at least 15 substances of phenolic nature, pectin substances, organic acids, tannins, amino acids, flavonoids, and other chemical components [62]. Furthermore, a significant content of

hemicellulose can contribute to a higher yield of pyrolysis liquid [63]. Bio-oil consists of an aqueous fraction and an oil fraction (Figure 4). The highest yield of the aqueous fraction was obtained during the pyrolysis of AR stems, which may be due to the high content of holocellulose in them. The high content of the aqueous fraction in all bio-oil samples is due to lignin oligomers present in biomass due to the presence of hydrophilic polar functional groups [64].

**Figure 4.** The content of the fractions in the pyrolysis liquid.

The oil fraction can be used as a fuel directly or converted into a high-quality fuel or chemical material. While the aqueous phase cannot be used directly as a fuel. As a result of the GC–MS analysis of the oil fractions of the pyrolysis liquid, their chemical composition was determined. It varies significantly depending on the part of the plant and is a complex mixture of organic compounds that contains hundreds of chemicals in total [65].

In the oil fraction from AR leaves, mass spectra of 72 substances of organic nature were determined, which were combined into four groups (Figure 5).

**Figure 5.** Chemical composition of the oil fraction from leaves.

In total, 33.8% of the total composition of the oil fraction was identified. The majority of all identified compounds are aliphatic hydrocarbons (15.5%), of which 11.8% are paraffinic hydrocarbons (C11–C31) and 3.7 % are olefinic hydrocarbons (C12–C23). This carbon distribution is consistent with some bio-oils that can be used as liquid fuels in terms of carbon distribution [66,67]. A small part (4.23%) consists of cyclic hydrocarbons. The group of oxygen-containing components includes alcohols (0.79%), aldehydes (0.91%), ketones (1.58%), ethers (1.02%), and phenols (1.64%). Nitrogen-containing compounds account for 8.2%, more than half of which (4.34%) are heterocyclic in nature. The slight presence of seeds in the samples can lead to an increase in the content of hydrocarbons in bio-oil [68].

A GC–MS analysis of the oil fraction from AR inflorescences was also carried out, as a result of which the mass spectra of 80 organic substances were obtained (Figure 6). In total, 38.8% of the total composition of the liquid was identified.

**Figure 6.** Chemical composition of the oil fraction from inflorescences.

There were marked changes in the composition of the oil fraction obtained from inflorescences relative to the composition of the oil fraction obtained from leaves. The main mass fraction of all identified compounds here is represented by an oxygen-containing group of substances (17%): alcohols (3.12%), ketones (3.94%), ethers (3.17%), and phenols (6.77%). At the same time, the proportion of phenols increased markedly. The content of aliphatic hydrocarbons decreased to 9.88%, mainly due to a decrease in the content of paraffinic hydrocarbons to 4.84%. The fractions of hydrocarbons also changed: paraffinic (C16–C44) and olefinic (C14–C30), respectively. Cyclic hydrocarbons make up 3.44%. Nitrogen-containing compounds account for 8.43%, of which less than half are heterocycles (3.48%).

The chemical composition of the pyrolysis liquid from the AR stems is mainly relatively simple and is represented by phenolic compounds (Figure 7). The data obtained are consistent with [4]. Phenolic compounds in bio-oil are a typical conversion product of lignocellulosic biomass, obtained mainly from the decomposition of lignin [69].

**Figure 7.** Chemical composition of the oil fraction of the stems.

Mass spectra of 12 organic substances were obtained. Phenolic compounds from AR stems have great potential to produce valuable chemical compounds.
