(202d) Renewable Transportation Biofuel Converted from Wet Biowaste Via Hydrothermal Liquefaction

Authors: 
Chen, W. T., University of Illinois
Zhang, Y., University of Illinois
Wu, Z., University of Illinois
Sharma, B. K., University of Illinois at Urbana-Champaign
This study demonstrates a proof-of-concept in the production of high quality renewable biofuel from wet biowaste via hydrothermal liquefaction (HTL). Distillation was employed to effectively separate the biocrude oil converted from swine manure (SW), food processing waste (FPW), and Spirulina platensis (SP) via HTL into different fractions. Distillation curves of different types of HTL biocrude oil were reported. Physicochemical characterizations, including viscosity, elemental test, chemical compositions, and acidity, were conducted on distillates separated from different feedstocks. SW-, FPW-, and SP-derived biocrude respectively contains 15 wt.% , 56 wt.%, and 15 wt.% distillates with heating values of 43-46 MJ/kg and alkanes with carbon numbers ranging from C8 to C18. Compared to the distillates from SW- and SP-derived biocrude oil, the distillates from FPW-derived biocrude demonstrate the closest energy content to petroleum diesel, though this type of distillates contained an excessively high acidity that need to be reduced from 35.3 mg KOH/g to ≤ 3 mg/g (the requirements suggested by the ASTM standard). An orthogonal array design of esterification experiment was performed to optimize the reaction temperature (50-70°C), reaction time (0.5h-6h), catalysts concentration (0.5 wt.%-2 wt.%), and the molar ratio of FPW-distillates to methanol (1:5-1:15), for achieving the lowest acidity. Compared to other available methods to upgrade HTL biocrude oil, the integrative upgrading approach proposed by this study (distillation plus esterification) demonstrates a competitive energy consumption ratio (0.03-0.06) to zeolite cracking (0.07), supercritical fluid (SCF) treatment (0.17), and hydrotreating (0.24). Moreover, the reaction severity (Ro) of the upgrading approach used in this study (with log Ro of 5.9-9.5) is much lower than those of zeolite cracking (with log Ro of 11.0), SCF treatment (with log Ro of 10.6), and hydrotreating (with log Ro of 11.3). Finally, the fuel specification analysis and engine test were conducted with the drop-in biodiesel, which was prepared with 10 vol.% (HTL10) and 20 vol.% (HTL20) upgraded distillates and 80-90 vol.% petroleum diesel. HTL10 and HTL20 exhibited a qualified Cetane number (>40 min), lubricity (<520 µm), and oxidation stability (>6 hr), as well as a comparable viscosity (0.2%-19% lower) and net heat of combustion (3%-4% lower) to those of petroleum diesel. Further, diesel engine tests demonstrated that HTL10 can lead to a superior power output (8% higher) and lower emissions of NOx (3-7%), CO (1-44%), CO2 (1-4%), and unburned hydrocarbons (10-21%). The present study showcases an energy-efficient and technically cohesive approach to produce renewable high-quality drop-in biofuels for demanding transport applications.