Sustainability and circularity assessment of the potential of a biofuel produced from black liquor as a substitute for conventional fuels

The European Bioeconomy Strategy aims to accelerate the deployment of a sustainable European bioeconomy to maximize its contribution to the 2030 Agenda and its Sustainable Development Goals (SDGs), as well as to the Paris Agreement on climate change. In this context, transport is considered as a key sector, with aviation and shipping playing an important role due to the need to meet its huge demand. In order to reduce potential emissions from the transport sector, the use of biofuels could be considered as a solution. However, with the aim of using biofuels to replace conventional fuels, it is important to assess their cost-effectiveness and feasibility, and in this aspect the valorization of waste streams for their production could help to meet this challenge. This is the framework of this research report, which is based on the use of black liquor (BL) from pulp and paper production to produce biofuel through a hydrothermal liquefaction (HTL) unit. Three technological designs and production capacities were considered: full extraction of the oil phase and its upgrading by catalytic hydrothermal deoxygenation (Scenario 1, S1), partial extraction of the oil phase (Scenario 2, S2) and full extraction but without upgrading (Scenario 3, S3). Low (100 t/d), medium (300 t/d) and high (600 t/d) production capacities were regarded. From the modelling data, a life cycle perspective was adopted, taking into account both the environmental analysis (LCA) and the life cycle costs (LCC), as well as the circular potential using different performance, resource-flow circularity and economic indicators. In addition, a composite indicator, CI LCA- LCC-CA,- CA , has been proposed to obtain a single score taking into account the three assessments: environmental, cost and circularity. The results obtained show that S3, with a production of 300 t/d, has the lowest environmental impact and the highest profitability corresponds to a capacity of 600 t/d. In terms of circularity, S3 also shows the best performance, mainly due to its higher resource productivity and lower energy intensity. These results are in line with those obtained for the composite indicator, and also show that higher production capacities and a simple but efficient process technology, such as S3, is the alternative with the highest potential for both sustainability and circularity.