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

Abstract

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 °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 °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.