Comparative analysis of sulfuric acid and free cellulase hydrolysis for waste-paper-to-glucose conversion:...

The approach of converting waste paper (WP) to glucose via hydrolysis reaction is a promising alternative to current disposal methods. Glucose is a key intermediate in the production of various chemicals. In this study, we first characterize WP by several analytical tools and then compare the WP-to-glucose conversion via sulfuric acid (SA)- and free cellulase enzyme (FE)-catalysed reactions, primarily focusing on experimental and techno-economic evaluation. WP contains loosely connected fibres with inorganic filler elements (Ca, Si and Al) distributed on their surfaces. SA-hydrolysis completely hydrolyses WP to glucose in just 2 h; however, the use of H₂SO₄ and CaCO₃, the production of CO₂ and CaSO₄ by-products, as well as the complex procedure significantly increase the projected operating costs, leading to substantial profit loss. Similarly, FE-hydrolysis converts all cellulose in WP into 100% glucose, as other components (hemicellulose, lignin and inorganic fillers) appear not to impede cellulose-enzyme binding, while loosely cross-linked fibres further enhance enzyme interaction. With water as the waste, FE-hydrolysis is projected to have much lower operating costs, contributing to ca 400 times lower profit loss compared with SA-hydrolysis. However, the 72 h hydrolysis period and the difficulty in separating cellulase enzyme from glucose solution present significant challenges, necessitating further process improvements.