A review on the catalytic upgradation of vegetable/pyrolysis bio-oil from renewable sources: kinetic studies and environmental impact assessment

Abstract

This study examines several aspects of bio-oil upgrading from vegetable oil (triglyceride-based) and pyrolysis oil through various catalysts, process conditions, and kinetic analyses of the thermochemical conversion processes for three distinct species: terrestrial biomass, macroalgae, and microalgae. Additionally, the overall environmental impact of the bio-oil production process is evaluated. Several fundamental physico-chemical characteristics of vegetable oil and pyrolysis oil are briefly discussed. Based on a review of the literature, it is determined that the primary issue is the oxygen content in vegetable or pyrolysis oil, which significantly lowers the oil's calorific value. This study further elaborates on various catalytic upgradation processes that have been reported in the literature. In addition, the catalysts' mechanisms are explained, and they are specifically classified as zeolites, metal sulfides, and non-sulfides. A total of 255 research publications pertinent to this topic have been reviewed to support this research article. In total, 241 articles have been surveyed, excluding books, chapters, theses, and technical reports. Furthermore, 185 catalytic upgrading research articles of vegetable oils or pyrolysis oils are considered in this study, including 41 pyrolysis process kinetics studies, 11 environmental effect assessments, and 18 other articles. A comparison of terrestrial biomass, microalgae, and macroalgae has been conducted using kinetics analysis, considering kinetic models such as KAS, FWO, Friedman, single-step, and global reaction models. To establish a sustainable pathway, waste-derived catalysts from renewable sources, such as biochar or other waste materials, have been incorporated. In addition, this study focuses on cost-effective processes and industrial applications. Lastly, catalyst regeneration and the energy and mass balance of a typical slow pyrolysis process are also considered in this work.