Modelagem em Aspen Plus da produção de biocombustíveis a partir de biomassa de microalgas com liquefação hidrotérmica - HTI

Abstract

The search for sustainable routes for fuel production has intensified due to the need to reduce emissions associated with the use of fossil fuels. Among the alternatives under development, the production of liquid biofuels from the hydrothermal liquefaction (HTL) of microalgae stands out. Microalgae biomass can be cultivated using CO₂ from industrial processes, enabling the development of systems with the potential for carbon-neutral operation. However, the absence of commercial biorefineries that integrate CO₂ capture with the conversion of microalgae through HTL limits the availability of operational data at an industrial scale, hindering comprehensive assessments of process performance. In this context, process modeling emerges as a relevant tool to estimate HTL behavior, predict product distribution, and provide support for technical, energetic, and environmental feasibility analyses. Thus, the main objective of this study was to develop and implement a detailed kinetic model for the HTL process of microalgae using the Aspen Plus simulator. The model was structured based on kinetic parameters, such as pre-exponential factors and activation energies associated with a reaction network representing biomass decomposition into the main products of interest. These parameters were derived from literature sources and fully implemented within the simulator environment in a plug flow reactor (PFR), without the use of external scripts, which are often reported as necessary to overcome convergence issues in simulations. The developed model was able to represent the formation of the oil, aqueous, gaseous, and solid phases, as well as the main chemical species associated with each phase. The system configuration considered the adaptation of the process to a PFR with a volume of 0.69 m³ and included typical industrial process equipment such as pumps, heaters, coolers, filters, and three-phase separators. Simulations were conducted at 250 bar and temperatures ranging from 250 °C to 400 °C, considering different biomass compositions and five microalgae species (Chlorella sp., Isochrysis sp., Spirulina sp., Nannochloropsis sp., and Pavlova sp.). The average crude bio-oil yields on a dry basis were 31.59%, 38.35%, 29.46%, 43.83%, and 34.66%, respectively, highlighting the higher potential of Nannochloropsis sp. for oil phase production. The analysis of biomass concentration in the feed indicated that increasing the solids content from 15% to 25% leads to higher bio-oil yields due to the lower dilution of organic matter in the reaction medium. Additionally, an energy analysis of the process was carried out for Nannochloropsis sp., indicating that increasing reactor temperature is associated with higher energy consumption per kilogram of bio-oil produced, mainly due to the higher thermal demand required for heating the feed stream.