**1. Introduction**

Amaranth is of great importance for world food security, especially for developing countries in Africa and Asia [1,2]. These plants are pseudocereals that were very important for ancient civilizations [3]. Currently, interest in this culture is growing for a number of reasons. First, amaranth can grow in a wide range of weather conditions and is droughttolerant. Secondly, the growing demand for a healthy diet encourages the use of this plant. Amaranth is recognized as a rich and inexpensive source of dietary fiber, minerals, vitamins, proteins, and antioxidants [2,4]. One of the most common cereal species is Amaranthus cruentus [5]. After the grain is extracted, waste in the form of inflorescences remains, which can be used to obtain useful new products.

Pyrolysis is a technology widely used for waste disposal [6–8]. The uniqueness of this process lies in the simultaneous production of gaseous, liquid and solid products. The sphere of use of these products is quite wide, including the chemical industry [9], energy [10,11], and agro-industrial complex [12,13]. The process of biomass pyrolysis can be carried out in a decentralized manner, which is especially important for agriculture [14]. It is necessary to assess the energy potential of the resulting pyrolysis products in order

**Citation:** Karaeva, J.; Timofeeva, S.; Islamova, S.; Bulygina, K.; Aliev, F.; Panchenko, V.; Bolshev, V. Pyrolysis of Amaranth Inflorescence Wastes: Bioenergy Potential, Biochar and Hydrocarbon Rich Bio-Oil Production. *Agriculture* **2023**, *13*, 260. https://doi.org/10.3390/ agriculture13020260

Academic Editor: Giorgio Testa

Received: 22 December 2022 Revised: 13 January 2023 Accepted: 18 January 2023 Published: 20 January 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

to assess the possibility of creating a local non-volatile enterprise. It should be noted that biooil is of particular interest since its composition is very complex and largely depends on the feedstock [15]. It is important to find such a source of biomass, which initially, without the use of catalysts during thermochemical conversion and joint pyrolysis with polymers, contains a significant amount of hydrocarbons.

Currently, thermogravimetric analysis (TGA) is used for a detailed assessment of the pyrolysis process [16–18]. TGA data are used to study the kinetics of the thermochemical conversion. This allows a comprehensive study of pyrolysis reactions, revealing the characteristic mechanism and predicting the degree of complexity of the reaction, which is necessary for designing pyrolysis apparatuses and evaluating the possibilities of using products [19]. The kinetics of the amaranth inflorescence wastes (AIW) pyrolysis process was studied using the model-free methods of Friedman, OFW (Ozawa-Flynn-Wall) and KAS (Kissinger-Akahira-Sunose), since they have shown themselves to be effective in assessing the kinetics of biomass pyrolysis reactions [6,20–26]. Currently, numerous studies are being carried out on the use of biomass as a raw material for thermal decomposition [27,28]; however, there are few works on the pyrolysis of amaranth [8,29–31], and no study has yet been reported on the thermal decomposition characteristics of the inflorescences of this plant.

This study is aimed at solving the following problems: (a) determining the material balance of the pyrolysis process of a new type of plant waste; (b) study of the composition and quality of the resulting pyrolysis products to assess their subsequent use; (c) analysis of the features of thermal decomposition of waste according to TGA data at heating rates of 10, 15 and 20 ◦C/min in an inert atmosphere; (d) determination of kinetic triplets for the main stage of pyrolysis—isolation of volatile components using model-free methods; and (e) determination of thermodynamic functions for subsequent design, optimization and scaling of the parameters of the pyrolysis reactor. Thus, the cultivation of amaranth and the subsequent pyrolysis of the remaining waste will improve not only food, but also energy security, which is especially important for countries with adverse climatic conditions.

#### **2. Materials and Methods**

#### *2.1. Amaranth Inflorescence Wastes*

AIW samples were taken from a farm after harvest (Russia). Inflorescences were dried at room temperature. All samples of AIW were manually cut into small pieces with the help of blades and then finely powdered using a mixer-cum-grinder. All powdered samples were kept in airtight containers for use in further experiments.
