Gasification versus fast pyrolysis bio-oil production: A life cycle assessment

A life cycle assessment was performed to compare the sustainability of gasification and fast pyrolysis processes for producing bio-oil using agricultural wastes from biomass. The objective was to carry out the environmental analysis associated with the production of 1 MJ bio-oil using different agricultural wastes biomasses for both thermochemical processes to determine which process is more respectful with the environment. The life cycle assessment revealed that gasification was more detrimental to the environment for all agricultural biomasses under study. In addition, greenhouse gas emissions over a 100-year time horizon were calculated, thereby demonstrating that CO2 yield emissions were higher than those for CH4 and N2O in both thermochemical processes. Furthermore, to gain a comprehensive overview, both thermochemical processes were divided into different equipment blocks to evaluate their individual impacts. Almond shell, pistachio shell and olive stone were identified as the biomasses for which minor amount of feed was needed to produce 1 MJ bio-oil. This assessment determined that the gasification stage of the gasification process and the separation stage for fast pyrolysis, were the main contributors to all mid-point impact categories. Finally, fast pyrolysis was the most environmentally friendly option for producing 1 MJ bio-oil.