Pyrolysis of Red Eucalyptus, Camelina Straw, and Wheat Straw in an Ablative Reactor

Abstract

The purpose of this study is to produce and characterize biomass pyrolysis liquids obtained in an ablative bed reactor at laboratory scale. The feedstocks selected include eucalyptus (Eucalyptus tereticornis) chips, camelina (Camelina sativa) straw pellets, and wheat (Triticum aestivum) straw pellets. Pyrolysis experiments were carried out at 550 °C and atmospheric pressure with a nitrogen flow rate of 2.24 N L/min and an average solids feeding rate of 2.5 g/min, yielding 42.4, 48.8, and 41.0 wt % liquids for eucalyptus, camelina straw pellets, and wheat straw pellets, respectively. Such liquids, also known as bio-oils, were characterized using gas chromatography–mass spectrometry and complemented with water content, pH measurements, higher heating values, viscosity, and proximate, and ultimate analyses. The distribution of products and their properties were influenced by both the raw materials characteristics (chemical composition and structure) and the operating conditions used in the experimental setup. With regard to raw material characteristics, features such as fixed carbon content in raw biomass seemed to impact the amount of solid products obtained as in the case of eucalyptus chips, which was the sample with higher fixed carbon content and the one that yielded a greater amount of solids. On the other hand, the experimental setup conditioned the results in the sense of how devolatilization of the materials took place, which in turn influenced the yield to liquid products obtained from the process. Wheat straw yielded a bio-oil with a significant number of unknown molecules in the organic phase (∼32.8 wt %), most likely produced from the protein fraction of this biomass. On the other hand, eucalyptus resulted in a larger fraction of carbonaceous residues (∼37.1 wt %), while wheat and camelina straw produced around 28.1 and 25.5 wt %, respectively. Finally, camelina presented interesting characteristics as feedstock for pyrolysis due to its low nitrogen content (0.4–0.5 wt %) and lower char yields (∼25.5 wt %).