Life cycle assessment of the production of gasoline and diesel from forest residues using integrated hydropyrolysis and hydroconversion

Purpose Renewable gasoline and diesel can be produced through integrated hydropyrolysis and hydroconversion (IH2) using renewable feedstocks such as woody biomass from logging residues. This study assesses the potential environmental impacts of IH2 process fuels manufactured in Ontonagon, Michigan, to determine their environmental impacts and if these manufactured fuels will meet Renewable Fuel Standards (RFS) requirements. The energy return on investment (EROI) is also calculated for comparison to other renewable fuels. Methods A cradle-to-grave life cycle assessment was conducted using regional forestry, timber harvest, and transportation data from the region. Regional geographic data was used to determine service areas that may provide woody biomass. The service areas were then developed into inventory data based upon the type and distribution of potential woody biomass feedstocks. Survey data from loggers in the region were used to ensure that harvest types were allocated in accordance with regional activity. Remaining inventory items were derived from existing data in the literature or existing life cycle inventory databases. This study uses a functional unit of one megajoule of gasoline or diesel produced using the IH2 process and assessed several environmental indicators as well as EROI. Results and discussion Fuels produced generate approximately 88% less greenhouse gas (GHG) emissions compared to petroleum fuels given RFS assumptions. Manufacturing and transportation of feedstocks accounts for 92.19% of energy used in production giving a calculated EROI of 4.19 and 4.31 per kilogram of diesel and gasoline, respectively. Pessimistic estimates of soil organic carbon (SOC) loss result in GHG emissions that are approximately 83% lower. If a 1:0.5 displacement ratio of IH2 fuels is considered, the GHG emissions are about 76% lower without SOC loss and 66% lower with. This study demonstrates that while environmental impacts and EROI are sensitive to site selection and SOC estimates, there is a sufficient GHG emission reduction such that IH2 fuels are capable of meeting regulatory requirements. Conclusions Fuels produced at the facility result in a reduction in GHG emissions, but better site selection may result in less fuel being used in transportation. Reducing the quantity of electricity needed in n-th-generation facilities would also reduce environmental impacts while improving the EROI. The energy mix used to supply IH2 facilities should also be considered during the planning process. Finally, future research may be needed to ensure feedstocks recovered from logging operations match expectations.