Understanding the Miscibility and Co-feeding Potential of Hydrothermal Liquefaction Biocrude in Refinery Streams: Role of Hydrodeoxygenation

Co-processing of hydrothermal liquefaction bio-crudes in existing refineries is attracting tremendous attention for large-scale commercialization of sustainable biofuels. As a result of the higher oxygen content, these biocrudes are not compatible with refinery streams; therefore, co-processing requires an essential (stand-alone) prior mild hydrotreating step. Therefore, Spirulina biocrude and mild hydrotreated samples (200, 250, 300, and 340 degrees C) were comprehensively investigated for their compatibility and solubility behavior with straight-run gas oil (SRGO) and rapeseed oil (RO). In total, 245 solubility tests were performed in 35 different solvents, and these tests provide the basis for theoretical predictions made by Hansen solubility parameters (HSPs) and three-dimensional Hansen double-sphere solubility plots. The compatibility of biocrude samples with SRGO and RO was verified by the overlapping area in their Hansen double-sphere plots and center-to-center distances (Dcc). All of these values were found to be in direct relation with the degree of hydrodeoxygenation (HDO), meaning that higher compatibility is strongly dependent upon higher oxygen removal. Experimental miscibility studies confirmed the theoretical predictions and exhibited that severe HDO (93.4%) is needed to achieve the complete miscibility of the biocrude sample (mildly hydrotreated at 340 degrees C) in SRGO and RO. 13C nuclear magnetic resonance spectroscopy was used to effectively study the functional groups, and the obtained spectra corroborated with the results obtained from theoretical and experimental studies. The finding that HSPs can predict compatibilities of complex biocrudes very close to experimental results and a severe HDO (>90%) is essential to enhance solubility will pave a way in assessing the co -processing scenario.