Techno-economic assessment of rice straw biorefineries to produce ethanol with co-production of xylitol and phenolic acids
Rafael Cunha de Assis Castro, Camilo E. Cabrera Camacho, Inês C. Roberto, Solange I. Mussatto
Abstract
Rice straw is one of the most abundant agricultural residues globally. Its large availability makes it a promising feedstock for biorefineries, offering a renewable and sustainable resource for producing bio-based products. In this study, different strategies for converting rice straw into ethanol and co-products were assessed to provide recommendations for industrial implementation of a rice straw biorefinery. Three scenarios (Sc) were evaluated, all considering glucose conversion to ethanol through simultaneous saccharification and fermentation, and lignin as a source of phenolic acids. The scenarios differed in the utilization of the pentose fraction: Sc.1- no use of xylose; Sc.2- xylose conversion into ethanol; and Sc.3- xylose conversion into xylitol. Net Revenue (NR) was chosen as the economic indicator to evaluate the processes. The assessment revealed that the pretreatment step (using dilute acid) had the highest impact on operating costs, followed by raw materials and ethanol distillation. Using xylose for xylitol production gave a better payback compared to its conversion into ethanol. However, none of the scenarios was profitable at current prices, with NR values of −539.4, −640.5, and −508.2 thousand USD/y for Sc.1 , Sc.2 and Sc.3 , respectively. To achieve a process with a positive economic margin, a low price of natural gas is essential. Producing valuable chemicals from sugar fractions, instead of just ethanol, supports the process's economy. Exploring the potential of lignin streams is also crucial to have a positive revenue. These results highlight critical aspects to be addressed to enhance the economic viability and potential implementation of rice straw biorefineries. • Techno-economic feasibility of 2G ethanol production from rice straw was assessed. • Dilute acid pretreatment had the highest impact on operating costs. • Producing xylitol from xylose and ethanol from glucose improved revenues. • Lignin conversion into high-value chemicals was crucial for profitability. • Low price for natural gas is essential for the process economy.