*Article* **Exploring the Prospective of Weed** *Amaranthus retroflexus* **for Biofuel Production through Pyrolysis**

**Julia Karaeva 1,\*, Svetlana Timofeeva 1, Marat Gilfanov 1, Marina Slobozhaninova 1, Olga Sidorkina 1, Ekaterina Luchkina 1, Vladimir Panchenko <sup>2</sup> and Vadim Bolshev 3,\***


**Abstract:** *Amaranthus retroflexus* or redroot pigweed is a second generation lignocellulosic fuel. Each biomass sample (leaves, inflorescences and stems) was pyrolyzed in a lab-scale furnace, in a nitrogen atmosphere under non-isothermal conditions at heating rates of 10 ◦C/min until the furnace temperature reached 550 ◦C. The pyrolysis characteristics of the three major components were also studied through thermogravimetric analysis. The thermal decomposition of the biomass samples is similar to the process of pyrolysis of lignocellulosic materials and proceeds in three main stages: dehydration, devolatilization, and carbonation. The highest bio-oil yield was obtained for inflorescences (55%) and leaves (45%). Gas chromatography—mass spectrometry analysis was carried out for oil fractions of the pyrolysis liquid from *Amaranthus retroflexus*. The composition of the pyrolysis oil fraction from the leaves had an overbearing aliphatic hydrocarbon nature whereas the oil fraction from inflorescences and stems was composed mainly of oxygen-containing components. The use of *Amaranthus retroflexus* biochars can lead to slag formation in power equipment, so it is advisable to use them to produce composite fuel, for example, mixed with coal. The results would help to better understand the thermal behavior of *Amaranthus retroflexus* biomass and its utilization for fuels or chemicals.

**Keywords:** biomass; *Amaranthus retroflexus*; pyrolysis; thermogravimetric analysis; bio-oil; biochar
