*3.5. Thermodynamic Analysis*

To design, optimize, and scale the parameters of the pyrolysis reactor, it is also necessary to know the thermodynamic properties of the feedstock used. Thermodynamic parameters were determined for a heating rate of 10 ◦C/min (Figure 7). In biomass pyrolysis, Δ*H* is the total energy required for biomass decomposition into solid, liquid, and gaseous products [45,89,90]. The Δ*H* values for the studied AIW sample were in the range of 152.28–287.03 kJ/mol according to the Friedman method, 151.86–260.34 kJ/mol according to the KAS method, and 152.05–260.52 kJ/mol according to the FWO method. Positive values of Δ*H* indicate the endothermic nature of biomass pyrolysis, which implies the need for energy from an external heat source [6]. The difference between the average values of *Eα* and Δ*H* is insignificant, approximately 5 kJ/mol (for all methods), which indicates that the studied AIW sample is suitable for pyrolysis [43,87,88,90–94].

**Figure 7.** *Cont.*

**Figure 7.** (**a**) Δ*H*, (**b**) Δ*G*, and (**c**) Δ*S* of the pyrolysis of AIW.

The change in Δ*G* makes it possible to judge the energy available in biomass [6,49,95,96]. The Δ*G* values for the studied AIW sample ranged from 147.90 to 150.78 kJ/mol by the Friedman method, 148.38–150.19 kJ/mol by the KAS method, and 148.38–150.18 kJ/mol by the OFW method. For most known biomasses and their mixtures, the Δ*G* values are positive [87,90,95–98]. The resulting average value of Δ*G* is 149.61 kJ/mol of the AIW sample. It is comparable to the Δ*G* values for pseudo-hemicelluloses of cocoa shell (143.19 kJ/mol) [99], torrefied biomass of *Acacia nilotica* T-250 (159.97 kJ/mol) [100], and red macroalgae *Gelidium floridanum* for stage 1 (147.25 kJ/mol) [44], but higher than mustard stalk (128 kJ/mol) [78]. The data obtained indicate the high energy potential of AIW.

Entropy is a function of the state of a thermodynamic system, which characterizes the direction of spontaneous processes and is a measure of their irreversibility. The change in Δ*S* serves as a measure of the change in the order of a thermodynamic system. The entropy of the system is the higher the greater the degree of disorder of the system. Thus, if the process goes in the direction of increasing the disorder of the system, then Δ*S* is a positive value. To increase the degree of order in the system, it is necessary to expend energy [90,93]. The Δ*S* values of amaranth samples range from 2.15 to 235.45 J/mol·K by the Friedman method and 1.42-189.78 J/mol·K by the KAS and OFW methods. Throughout the conversion process, the Δ*S* values were positive for the three model-free methods, indicating a high reactivity of the biomass and a rapid formation of the activated complex. It should be noted that the degree of disorder in the resulting products was quite high, and this is typical of the pyrolysis process [48,100]. The mean Δ*S* of the AIW sample was 105.41 J/mol·K by the Friedman method, 91.15 J/mol·K by the KAS method, and 91.46 J/mol·K by the OFW method. The Δ*S* value is comparable with the values obtained for mixtures of sugarcane bagasse, water hyacinth *Eichhornia crassipes* and yellow oleander *Thevetia Peruviana* [101].

#### **4. Conclusions**

In this work, a study was made of the pyrolysis of a new type of plant waste using TGA and experiments in a laboratory installation for thermochemical processing. The physicochemical parameters of the studied raw materials correspond to the range of values typical for commercial biomass fuels. The test sample has a high content of volatile substances and high reactivity. The maximum specific gravity in the pyrolysis products of 37.1% corresponds to the pyrolysis liquid. The maximum mass fraction in the pyrolysis products of 37.1 wt.% corresponds to the pyrolysis liquid. At the same time, the oil fraction contains 41.8% hydrocarbons, which characterizes it as a high-quality fuel. Analysis of the features of thermal decomposition of waste was determined at heating rates of 10, 15, and 20 ◦C/min in an inert atmosphere. The main stage of thermochemical degradation is devolatilization. The kinetic parameters for this stage were determined using the model-free methods of Friedman, OFW, and KAS. The one-dimensional diffusion model (D1), then random nucleation with two nuclei in the individual particle (F1), and random

nucleation with two nuclei on the individual particle (F2) were recommended to describe the mechanism of AIW thermal destruction. The average activation energy values are in the range of 208.44–216.17 kJ/mol, and they were used to calculate the thermodynamic parameters. The results indicate that the pyrolysis application will allow the efficient conversion of AIW into value-added products.

**Author Contributions:** Conceptualization, J.K.; methodology, J.K.; software, S.T. and V.P.; validation, V.B. and V.P.; formal analysis, S.I. and F.A.; investigation, S.T., S.I., K.B. and F.A.; resources, J.K., V.B. and V.P.; data curation, J.K., S.T., V.B. and V.P.; writing—original draft preparation, S.T., S.I., K.B. and F.A.; writing—review and editing, J.K. and V.B.; visualization, S.T.; supervision, V.B. and V.P.; project administration, J.K.; funding acquisition, V.B. and V.P;. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.
