Novel Process for Valuable By-Products Recovery from Hot-Liquid Water Pretreatment of Biomass

Hot-liquid water pretreatment of lignocellulosic biomass is an environmentally friendly method with relatively mild process conditions and low costs. However, the value of the liquid remaining after the pretreatment is usually underestimated. The novelty of this research is an enhancement of the biomass pretreatment step through recovery of valuable by-products (acetic acid, formic acid, furfural and 5-hydroxymethyl furfural (HMF)) from this liquid, which would otherwise be waste stream.

Different methods are reported for recovery of mentioned components from aqueous solutions, but yields are often insufficiently high, downstream processing is complex due to the usage of additional chemicals and research is done only on a lab-level, without scaling-up. Therefore, distillation is used as the main separation method in this work. The main challenge is highly diluted feed stream (>96wt% water) and thermodynamic constraints due to the formation of three azeotropes (water-furfural, water-acetic acid-formic acid and water-formic acid), together with the tangent pinch in water-acetic acid mixtures. Aspen Plus was effectively used to develop rigorous simulations for the full process operation.

About 78.8% of acetic acid from initial liquid is obtained as a high-purity product (99.8wt%), while the rest is recycled, together with most of the water, to the biomass pretreatment step. Recoveries of formic acid, furfural and HMF are higher than 99.5% and product purities satisfy market requirements (73.6wt% formic acid, 97.9wt% furfural and 100wt%HMF). Mechanical vapor recompression and heat integration are implemented to decrease energy use. This results in 88.0% reduction in primary energy requirements (from 75.13 to 8.99 kWh/kg_product), 76.6% reduction in total annual costs (from 2.41 to 0.56 $/kg_product) and 99.7% reduction in CO₂ emission (from 10.84 to 0.03 kg_CO2/kg_product). In conclusion, the original contribution of this work is an optimal waste-to-value process which can enhance economic viability and competitiveness of biorefineries compared to fossil-based fuel production alternatives.