Biorefinery of Safflower Seeds in a Sequential Process for Effective Use of the Substrate for Biofuel Production

Biofuels are a promising alternative to fossil fuels that addresses the associated environmental concerns and satisfies growing global energy demand. In this study, safflower seeds were used to produce multiple biofuels with an integrated biorefinery perspective. The safflower oil was used for biodiesel production while the resultant seed cake was employed in subsequent ethanol production. Pretreatment of the residual solid is necessary in order to improve the ethanol production yield. Contrasting costly chemical pretreatments, the seed cake was instead pretreated using incomplete anaerobic digestion to remove hemicellulose, increase cellulose accessibility for fermentation, and produce methane. The seed cake produced 124.8 ml/g-VS of methane after 20 days of anaerobic digestion. The digestate (biologically pretreated seed cake) produced 92 g ethanol/kg solid, in stark contrast to 42 g ethanol/kg solid from untreated seed cake. This ethanol was later utilized in biodiesel production. The safflower oil produced 85.9% biodiesel via ethanolic transesterification at optimum conditions. From the integrated biorefinery perspective, the seed cake from 1 kg of safflower seeds produced 70 l of methane at NTP and 51.0 g of ethanol—surpassing the 47.6 g of ethanol stoichiometrically necessary to complete transesterification of safflower oil. Thus, this ethanol could be recycled, largely decreasing the need for an external stream of ethanol for biodiesel production. The incomplete anaerobic digestion is an effective and environmentally friendly way to improve the ethanol production from the safflower seed cake with biomethane as an additional valuable byproduct.