A cellulose monolithic stir bar for sorptive extraction of glycerol from biodiesel

Abstract

This work presents an eco-friendly approach for determining free glycerol in biodiesel samples, using a cellulose monolith stir bar in the sorptive extraction method with analysis by high-performance liquid chromatography and a refractive index detector. The cellulose monolith was produced from cellulose acetate by non-solvent-induced phase separation and subsequent alkaline deacetylation. The cellulose monolith presented a hierarchically porous structure, with 68% porosity and almost total deacetylation, with morphological and polarity characteristics that favor an efficient extraction of free glycerol from biodiesel. The sorptive extraction method using a cellulose monolith stir bar was optimized, obtaining a total extraction time of 30 min at 70 °C, using ultrapure water as the desorption solvent, and extraction of free glycerol of 93.6 ± 2.3%. The proposed method showed selectivity in free glycerol extraction, with limits of detection and quantification of 6.60 × 10⁻⁵% w/w and 2.18 × 10⁻⁴% w/w, respectively. Compared with the official reference method, the proposed one presented similar precision and accuracy, with few manipulations and any reagent/solvents. Furthermore, it is compatible with the principles of green chemistry and can be considered an eco-friendly method for determining free glycerol in biodiesel.