This study aims to conduct a techno-economic analysis (TEA) of renewable diesel production through autothermal pyrolysis of hot water-extracted willow biomass. Autothermal pyrolysis provides a self-sustaining process by harnessing exothermic reactions to minimize external energy input, rendering it an attractive pathway for large-scale biomass valorization. This study investigates the incorporation of hot water extraction (HWE) as a pretreatment step in biorefinery processing willow biomass. A process model for a 2000-ton/day facility integrating hot water extraction, autothermal pyrolysis, and bio-oil hydroprocessing was developed using Aspen Plus. HWE pretreatment facilitates the recovery of xylose from hemicellulose and enhances sugar yields during subsequent pyrolysis. Following pretreatment, the biomass undergoes drying and autothermal pyrolysis, yielding char and pyrolysis vapors. The vapors condensed into light and heavy fractions, primarily composed of sugars and phenolic compounds. Cellulosic sugars are extracted, while the phenolic-rich fraction, derived from lignin, is stabilized through hydrogenation and subsequently upgraded via hydroprocessing to produce renewable diesel. Simulation results indicate that hot water-extracted biomass generates 18.9% heavy ends, 33.2% light ends, 19.5% char, and 25.4% non-condensable gases. The energy demand for drying and pyrolysis can be met through the combustion of char and non-condensable gases, with residual energy remaining. Additionally, hydrogen required for hydroprocessing can be sourced from light-end hydrogen production. Preliminary results suggest that the process has the potential to produce approximately 511.11, 97.76, and 151.02 tons/day of xylose, anhydrosugars, and renewable diesel, respectively, along with co-product hydrogen yields of around 47.47 tons/day. These values are subject to refinement as investigations continue. Economic feasibility will be assessed using Aspen Process Economic Analyzer (APEA) for equipment sizing and cost estimation. A discounted cash flow analysis will be conducted for an nth-plant scenario, assuming a 20-year operational period with a 10% annual discount rate. The internal rate of return (IRR) will be assessed based on feedstock costs, fixed capital investment (FCI), catalyst expenses, and facility revenue.
Keywords: Techno-economic analysis, Autothermal pyrolysis, Anhydrosugars production, Hot water extraction, Woody biomass conversion, Renewable Diesel
