Biopetróleo a partir da biomassa de microalgas via liquefação hidrotermal: uma avaliação energética e ambiental

Abstract

The transition to a more sustainable energy matrix with less impact is a global objective, and bioenergies play a significant role in this transition. Finding opportunities for improvements in the production and consumption of energy resources supports increased energy efficiency and lessens its impact on the environment. This study carried out a Life Cycle Assessment (LCA) to identify the energy demand and carbon footprint in the production of biopetroleum by hydrothermal liquefaction (HTL). The species Scenedesmus acutus (SC),Chlorella vulgaris (CV) and Nannochloropsis granulata (NG) were considered for the comparison of three microalgae biomass production scenarios: high protein content (HP), high carbohydrate (HC) and high lipid (HL). The reference flow was 1 kg of microalgae biomass in total processed solids in HTL. The ecoinvent™ 3.6 database and assessment methods for cumulative energy demand (CED) in megajoules (MJ) and global warming potential (IPCC-2021 – 100-year GWP) in kilograms of carbon dioxide equivalent (kg CO2eq ) were used in openLCA® 1.11.0. The most favorable scenario was the NG-HL, which presented the lowest energy demand and carbon footprint, 19.1 MJ kg−1 and 0.85 kg CO2eq /kg of biopetroleum, respectively. NG-HL achieved the highest biopetroleum yield 68.3%m/m with 42.1 MJ kg−1 HHV. In addition, two sensitivity analyzes were developed, the first to obtain more realistic values from the literature regarding the cultivation time before harvesting and the second aimed at understanding the influence of heat demand on the HTL. The return on energy investment (EROI) ranged from 0.8 to 2.4 in the evaluated scenarios. The late harvest time considered in the sensitivity analysis increased the energy demand by 84% and the carbon footprint by 70% in NG-HL. In addition, the heat demand in the HTL is a key parameter in the energy and environmental performance of the biopetroleum, which ranged from -19–30% in the sensitivity analysis of the evaluated categories when changing from 5.9 MJ kg−1 in HTL for 3 –10 MJ kg−1. It has been shown that microalgae biomass for bioepetroleum production using waste heat sources can reduce energy demand and carbon footprint. The approach proposed in this study supports decision-making in HTL based on biomass composition, growing time before harvest and heat demand in HTL to reduce the energy demand and carbon footprint of microalgae bioproducts. Due to the need to optimize technical parameters, such as production efficiency and operating costs, the implementation of biopetroleum from microalgae in the supply chain faces challenges on a commercial scale, which reflects the need for further studies.