Investigation and Optimization of Relationship Among Hydrothermal Liquefaction Condition, Biocrude Yields/Properties, and Its Wastewater’s Characteristics

Hydrothermal liquefaction (HTL) can be one of the potential thermochemical approaches to produce biofuels and bioproducts because it does not require dewatering or drying and is able to use a wide variety of organic materials as feedstocks. In addition to biocrude and biochar, HTL also generates wastewater which may include toxic compounds. Therefore, we not only aim at the production of high quality cost-effective biocrude but also consider the HTL wastewater biodegradability. Biological treatment can be a less expensive option than other approaches, such as activated carbon and chemical treatment. The current research includes two objectives: 1) investigate the relationship among HTL operating conditions, the biocrude yields/properties and the characteristics of HTL wastewater to predict the wastewater biodegradability by using statistical analysis; and 2) optimize the biocrude yields/properties and HTL wastewater biodegradability. In the experiments, corn stover was used as biomass. Corn stover and water were put into the pressure vessel and the vessel closed was heated under high-pressure and high-temperature condition for a predetermined residence time. Then, mixture was collected and separated into hydrochar, heavy bio-oil, light bio-oil, and HTL wastewater (HTL-WW). Those samples were weighed and analyzed with CHNS and TOC/TN. Ash contents were measured for the samples as well. It was found that there were relationships between HTL operating condition and acquired biocrude’s yield/performance. As a part of results of this study, low temperature and short residence time led to high yield of hydrochar whereas high temperature and short residence time led to high yield of heavy bio-oil.