Bench-Scale Second-Generation Bioethanol Production from Bleached Pinus taeda Kraft Pulp

Abstract

The production of second-generation bioethanol from lignocellulosic biomass requires efficient enzymatic hydrolysis and fermentation processes that remain effective at industrially relevant solids loadings. In this study, bleached Pinus taeda kraft pulp was evaluated as a model substrate for bioethanol production at bench scale (4 L reactor) under high-consistency conditions (12.5–13.9% solids). Three process configurations were compared: separate hydrolysis and fermentation (SHF), simultaneous saccharification and fermentation (SSF), and pre-hydrolysis followed by simultaneous saccharification and fermentation (pSSF). Enzymatic hydrolysis in the SHF and SSF configurations stabilized between 54% and 58%, indicating that hydrolysis was the main process bottleneck under the evaluated conditions. In contrast, Saccharomyces cerevisiae efficiently fermented the available glucose, achieving nearly complete conversion of glucose. Among the evaluated strategies, pSSF showed the highest ethanol yield and volumetric productivity, achieving an ethanol yield of 61.8% and a productivity of 0.61 g L−1 h−1. While laboratory-scale SSF experiments conducted at 2% solids achieved complete conversion, the ethanol yield decreased to approximately 58% at the bench scale, highlighting the impact of high-solids operation on process performance. The lower performance observed at high solids may be associated with factors commonly reported during scale-up, including increased slurry viscosity, reduced mixing efficiency, limited enzyme accessibility, and mass-transfer constraints. Overall, the results manifest the need to enhance hydrolysis performance through improved reactor design, more effective mixing strategies, and optimized high-solids processing to facilitate the scale-up of lignocellulosic bioethanol production.