Life Cycle Assessment of Biomass Pyrolysis

Biomass is a renewable source of bioenergy, making it a promising solution for reducing greenhouse gas (GHG) emissions. Biomass is converted into bioenergy by the thermochemical and biological routes. Among all thermochemical conversion processes, pyrolysis is the most popular due to its ease of operation. Temperature, gas residence time, particle size, and heating rate are important operating parameters in pyrolysis. Bio-oil, biochar, and syngas are the main products from pyrolysis, and by giving suitable upgrading treatment, these products are converted into value-added products. The impact of pyrolysis on the environment is assessed using the life cycle assessment (LCA) tool. This review critically examines the reported literature for the goal and scope of the study, and boundaries are chosen, the process including pretreatment and product upgrading. Most researchers have recommended using biomass for bioenergy production instead of fossil fuel to reduce the impact. The most commonly used software is SimaPro, followed by GaBi, while the commonly chosen boundary is cradle-to-grave, and global warming potential is the most studied impact category. The life cycle impacts due to pyrolysis and pretreatment have been evaluated in this study. Impact variations due to alteration in energy (electricity) sources have also been gauged by undertaking different scenarios. The pyrolysis unit and bio-oil combustion unit are the main contributors (> 30%) of GHG emissions. The topics that were not covered in previous reviews, like environmental impact due to pretreatment and product upgrading, are deliberated in detail in this paper. The potential of biochar as a negative emission technology has also been discussed. Based on the reported work, the gaps are identified, and future research opportunities are presented.