The role of pressure and steam on pyrolysis of biogenic waste: value-added commodity products

• An increase in steam-to-biomass ratio improves liquid yield with a reduction in gas and solid yield. • An increase in pressure increases char yield with a reduction in gas and liquid yield. • Pressurized steam pyrolysis facilitates superior product properties and favours the production of value-added chemicals. • Utilization of products in various applications is briefly discussed. • Conceptual process design to utilize waste heat recovery from a nuclear power plant. The global concerns regarding climate change and the steep increase in greenhouse gas emissions, driving the society to transform biogenic waste into renewable value-added products. Thermal depolymerization of biomass is regarded as the most promising thermochemical conversion technology to produce bio-oil, biochar and syngas. To date, previously published review articles revolve around various biomass pyrolysis aspects, such as the chemistry of biomass, application of pyrolysis products, effects of pyrolysis parameters and kinetics, effect of various catalysts on product yield, upgradation strategies, and process technologies. The commercialization of conventional pyrolysis technology is challenging due to the inferior oil properties (oxygenates nearly 40 wt%), agglomeration, feeding constraints, ash content in the biomass, heat and mass transfer limitations, pressure build-up due to tar formation and thermal distribution across the reactor. Pressurized steam pyrolysis of biomass improves the product quality (oil, char and gas) with a production of value-added chemicals. Despite this, studies regarding the combined effect of steam and pressure on product quality from pyrolysis technology are not available in the literature. This study offers a comprehensive overview of the state-of-the-art on the effect of pressure and steam on biogenic pyrolysis. Additionally, the study also explains how pressure and steam can be utilized to improve the properties of the pyrolysis products. The review examine the fundamentals of biomass conversion, the effect of pressure and steam, with interlaid mechanisms on biomass conversion and challenges with pressurized steam pyrolysis. Finally, the benefits of products in various applications and a conceptual process perspective of pressurized steam pyrolysis are briefly outlined.