Sustainable Aviation Fuel from Kraft Lignin - Life Cycle Assessment in Early Stage Research and Development

Abstract

Sustainable aviation fuels (SAF) are of key importance to reduce greenhouse gas emissions, especially for long distance transport, where no other viable alternative is currently available. The EU-project ABC-Salt investigated a novel production route for jet fuel from lignocellulosic waste streams, in particular Kraft pulp mill lignin. However, potential production cost and benefits in terms of environmental impacts are hard to quantify for a process at lab-scale development stage. Therefore, chemical engineering know-how was applied to scale up the process to a commercial production scale and use the resulting process simulation as a basis for a life cycle assessment (LCA). DLR's in-house tool TEPET+ semi-automates the process simulation based LCA of chemical processes and technologies by enabling the user to link Aspen Plus® process simulation information to background data from LCA databases like ecoinvent. The thereby generated life cycle inventories are then automatically transferred to Brightway2 for the life cycle impact assessment. By linking LCA to process simulation data the investigated process can firstly be assessed at commercial scale and secondly process parameter studies can be easily performed. The environmental impact breakdown reveals Kraft pulp mill lignin as the main contributor to almost all categories of the Environmental Footprint method. When different allocation approaches are compared for the multi-output pulp mill process, a significant range (11 and 26 gCO2-eq./MJ) of global warming potentials (GWP) is found for the SAF. Overall, many impacts are increased compared to fossil jet fuel, suggesting that the applicability of other lignin or biomass sources should be emphasised in future research as the conversion efficiency is already quite high. A parameter study on the recovery rate of unreacted hydrogen shows that the GWP can be reduced for higher recovery rates because the hydrogen supply decreases although the membrane area for the hydrogen separation increases exponentially. Utilising chemical engineering knowledge to create process simulations provides a great basis for the LCA of processes in its up-scaled version. You not only obtain a more realistic view of the potential environmental impacts of the process but parameter studies can also provide indicators for process improvement. The ABC-Salt process could become a promising SAF production route if the impacts related to lignin can be reduced.