Understanding the nature of bio-asphaltenes produced during hydrothermal liquefaction

Abstract Asphaltenes, the heaviest and most polar components of crudes, are generally associated with considerable operational issues in refineries. In order to understand potential operational issues during upgrading/processing of bio-crudes, structural and thermal behaviour of asphaltenes derived from bio-crude (bio-asphaltenes) from hydrothermal liquefaction of food-waste and wood residues were compared with petroleum derived asphaltenes derived from bitumen. Structural analysis using nuclear magnetic resonance and elemental analysis revealed 7 aromatic rings per unit structure for bitumen asphaltenes, 4 for food-waste asphaltenes, and 3 for wood asphaltenes. The calculated molecular weight per unit structure followed the order: bitumen asphaltenes (589-636 g mol-1) > food-waste derived asphaltenes (338-358 g mol-1)> wood residue derived asphaltenes (268-274 g mol-1). The carbon residues using thermal gravimetric analysis (bitumen asphaltenes= 40 percent, bio-asphaltenes=19-25 percent) and glass transition temperature (bitumen asphaltenes= 80 °C, bio-asphaltenes= 4-64 °C) followed the same order. These results indicate a very different structural and thermal behaviour for petroleum and bio-asphaltenes.