Conversion of sunflower seed hulls, waste from edible oil production, into valuable products

Sunflower seed hulls are an abundant waste produced by the edible oil industry. Pyrolysis was assessed as a way of turning this material into a liquid rich in valuable products, as well as leading to densification of this voluminous waste. In pursuing this, raw and pre-treated hulls were subjected to fast pyrolysis in a vertical reactor, at 450 degrees C under 200 ml.min-1 of N2. Pre-treatments of sunflower seed hulls consist in washing the material with 15% m/v phosphoric, sulfuric acid solution and 15% m/v sodium hydroxide solution. Then the material undergoes a hydrothermal treatment at 180 degrees C. Raw and pre-treated hulls were characterized prior to pyrolysis by using Proximate and Ultimate Analysis and by TGA/DTG. Pre-treatments lead to substantial modifications in the characteristics of waste hulls producing different bio-oils with diverse compositions. A kinetic study of these pyrolysis reactions was performed in order to determine Ea and rate constants for biomass waste conversion. Hydrothermal pre-treatment leads to selective extraction of hemicellulose, which results in a bio-oil that is highly rich in levoglucosan. Sulfuric and phosphoric acid washing produce lower liquid yields when compared to raw hulls. The bio-oil from phosphoric acid pre-treatment shows a notably high concentration of furfural. NaOH pre-treatment results in an unstable bio-oil, which is rich in tar precursors.