Effect of Various Green Carbon Tracking Methods on Life Cycle Assessment Results for Fluid Catalytic Cracker Co-processing of Fast Pyrolysis Bio-oil

Co-processing fast pyrolysis bio-oil (FPBO) in conventional oil refineries and, specifically, in fluid catalytic cracker (FCC) units is one of the most cost-effective and least capex-intensive routes to produce advanced biofuels. It provides a direct way to replace fossil feedstocks, meaning that less crude oil is needed to meet the demand for transportation fuels and more oil reserves can stay untouched. Tracking biogenic carbon through a refinery is important for the legislative aspects of co-processing and, therefore, also for the process economics. Two types of methods exist for tracing biogenic carbon: analytical and bookkeeping methods. Choosing a certain method may influence the outcome of life cycle assessments (LCAs) that calculate the environmental impact of the advanced biofuels produced in this way, because different methods may provide a different result for the calculated volumes of bio-based products that come from co-processing. The goal of this article was to assess the various methods that exist in the literature to determine the biogenic content of products that are derived from the FCC co-processing of FPBO. Six methods were described here and used to calculate the yield of biogenic products from the co-processing of 5 wt % FPBO. These outcomes were used as input for a comparative greenhouse gas (GHG) LCA case study, which analyzed a hypothetical value chain based on a fast pyrolysis plant in Finland that produces FPBO and a petroleum refinery in western Europe where the FPBO is co-processed in the FCC. The biogasoline yields that were obtained from co-processing FPBO ranged between 27 and 94% on an energy basis, depending upon which method was selected. However, the range of differences between the resulting GHG emissions for the entire supply chain from forestry to biogasoline production was a lot narrower than the range in biogasoline yield differences, namely, between 87 and 94% GHG savings. Therefore, it can be concluded that, despite the differences between the calculation methods, all of them lead to a qualification of the biogasoline as an advanced biofuel with a high potential for GHG emission reduction.