Instant Controlled Pressure-Drop (DIC) for Volatile Compound Extraction and Bioethanol Production from Empty Aleppo Pinecones and Eucalyptus Chips: Process Optimization and Statistical Modeling

Several plant species contain volatile compounds extracted as “essential oils” through different technologies. After essential oil extraction, the residual solid is a lignocellulosic solid waste. This work proposes the instant controlled pressure-drop (DIC) technology to autovaporize volatile compounds and modify the lignocellulosic matrix. Indeed, DIC technology is a thermomechanical process based on short-time/high-temperature and pressure pretreatment. It enhances the saccharification and fermentation process (SSF) for bioethanol production. A 3-variable design of experiments optimized the DIC processing parameters to reach 100% efficiency (EE) of volatile compound extraction using response surface methodology (RSM). Eucalyptus chips presented 50 volatile identified compounds after 7 min of DIC treatment. 1,8-Cineole, β-phellandrene, aromadendrene, eudesmol, and spathulenol are the most important volatile compounds. The empty Aleppo pinecones delivered 32 volatile compounds in 5 min of DIC treatment, the most important of which were caryophyllene, nortricyclene, verbenol, and camphor. After the autovaporization extraction stage, solid fraction residues were hydrolyzed and fermented in the same stirred bioreactor, using SSF strategy for 72 h at 37 °C. The highest bioethanol yields reached 73.9% and 54.82% (g per 100 g DM) from eucalyptus chip and empty Aleppo pinecone, respectively.