(560t) Hydrothermal Carbonization of Microalgae for Hydrochar Production

Microalgae are viewed as a potentially sustainable source of chemicals, biologicals, and fuels that can help chemical manufacturing lower its greenhouse gas emissions and thus combat climate change. The fast growth rate of photosynthetic microalgae and their ability to utilize low-grade water and nutrients could help improve the cost competitiveness of renewable products compared to their fossil counterparts. Using hydrothermal carbonization (HTC), algal biomass can be thermochemically converted to hydrochar, a solid product that can be used in a variety of environmental and energy applications, such as solid nutrient amendment, water retention, solid fuel, capacitors, low cost adsorbents, and conversion into industrial chemicals. The process takes place at temperatures lower than those of fast pyrolysis and hence is less energy intensive, while yielding a product highly enriched in carbon. In this project, we focus our attention on the production of high-value hydrochar and testing it for application in industry. The microalga Nannochloropsis oculata was cultivated in photobioreactors, harvested, and dried to a certain moisture content. The algal biomass was then heated in batch mode in a stainless steel Parr reactor to a final temperature in the 180-240^oC range over various residence times in the absence and presence of catalysts to determine the effect of conditions and catalyst on the yield and quality of the hydrochar. This product was analyzed for carbon content, porosity, surface area, and structure and its properties were compared to those reported in the literature. Activation steps to further improve key properties of the hydrochar are under investigation in an effort to meet the carbon black specifications required for high-value industrial applications.