Liquefaction and chemical composition of walnut shells

Abstract The cultivation of walnut ( Juglans regia L.) for the exploitation of the fruit has been increasingly recognized worldwide; therefore, it is important to valorize a large amount of biomass from walnut shells (WS), where liquefaction may play an important role. This work intends to contribute to an improved understanding of the best uses for this material. The assays were made with a binary mixture of ethylene glycol and glycerol (1:1 v/v) as solvents, catalyzed by sulfuric acid. The tested parameters were as follows: particle size >0.420–0.177 mm, temperature 140–200°C, and reaction time between 15 and 60 min. The initial dried material, the liquefied material, and the resulting solid residue were analyzed by FTIR-ATR for polyol characterization. The results showed that WS are mostly composed of lignin with 35.0% and polysaccharides, 30.0% cellulose and 24.9% hemicelluloses. High-lignin content indicated that WS might be used as a bio-fuel or adhesives. Extractives represent 10.2% with almost half (4.6%) of polar extractives. The best conditions to attain the optimal liquefaction yield were 160°C, 30 min, and 0.420–0.250 mm particle size, for the tested parameters. FTIR spectrum of the liquefied material is very different from the original material, and solid residue spectra seem to indicate that there is higher liquefaction of polysaccharides when compared with lignin since there is a higher absorption at 1,600 cm −1 and lower absorption at 1,040 cm −1 and that liquefied compounds are probably in smaller molecules.