Prospective life cycle assessment: Identifying the most promising methods for sustainable cellulose nanocrystal production

Abstract

Concerted endeavors are presently in progress to discern eco-friendlier methods for cellulose nanocrystals (CNC) production, negating the conventional reliance on hazardous concentrated sulfuric acids. Despite the proliferation of methods purported to be environmentally sound, their assertions often lack rigorous scrutiny, relying on theoretical postulations. This study presents the first prospective glimpse into their environmental performance utilizing a life cycle assessment (LCA) methodology from cradle-to-gate. The results transpired that many of the vaunted environmentally-friendly methods resulted in higher environmental loads compared to the traditional method, due to lower conversion rates and higher reaction energy demand. Notably, only specific methods demonstrate lower endpoint impact scores, including deep eutectic solvent extraction (−48 %), ammonium persulfate-assisted oxidation (−62 %), sulfuric acid hydrolysis in glycerol medium (−56 %), and enzymatic hydrolysis (−40 %). Their primary green attributes associate with the utilization of solvents carrying lower climate impact and toxicity level. The reaction stage carries the heaviest burden due to the increased energy required to counteract modest reactivities of the milder solvents. As mitigation strategies, heat integration and by-product recovery for energy generation were explored, resulting in emission reductions of 11–26 % and 41–68 %, respectively, across the proven eco-friendlier methods. This study comprehensively validated a roster of genuinely green candidates, offering a more sustainable prospect than traditional methods and paving the way for large-scale green CNC production.