Production of Nanocellulose Using Citric Acid in a Biorefinery Concept: Effect of the Hydrolysis Reaction Time and Techno-Economic Analysis

Nanocellulosic materials, either as cellulose nanofibrils (CNF) or cellulose nanocrystals (CNC), have a wide range of potential applications in different industrial sectors, due to their renewable nature and remarkable properties. Here, a sustainable and environmentally friendly method to obtain nanocellulose was evaluated using hydrolysis with citric acid, an organic acid that can be obtained as a biorefinery product. This approach resulted in a single-step extraction of nanocellulose, with carboxyl functionalization of the surface varying according to hydrolysis reaction times from 1.5 to 6 h, at 120 °C, as evidenced using NMR to measure the degree of substitution. The charged surface groups of CNC and CNF resulted in improved colloidal stability, with ζ-potential values from −36 to −48 mV. Both CNC and CNF extracted using different reaction times were thermally stable, but the increase of carboxyl groups reduced the degradation temperature. Techno-economic analysis (TEA) showed that the cost of citric acid had the greatest influence on the minimum product selling price (MPSP) of the nanocellulose, indicating that the production of citric acid within the biorefinery could be an interesting way to make this approach feasible.