Selective extraction of waxes from bioethanol production side-stream via supercritical carbon dioxide: Thermal characterization and modeling

Bioethanol production relies heavily on agricultural products, with 95% of ethanol being produced from corn, sorghum, and other starch-rich grains. However, converting grains into ethanol generates a lipid-rich slurry that is wasted. This slurry is rich in high melting point waxes, oils, and phytochemicals. Although there are efforts to extract/purify waxes from this slurry, the purification of waxes is challenging due to (i) the presence of high amounts of lipids with similar solubilities, (ii) cloggings in membrane filtrations, and (iii) use of toxic organic solvents, resulting in underutilization of the slurry. Therefore, the objective was to develop a green process based on supercritical carbon dioxide (SC-CO₂) to selectively fractionate lipids present in the lipid slurry side stream to purify high-melting point waxes.

A three-factor response surface design was employed to optimize the SC-CO₂ processing conditions (i.e., the pressure (8-40 MPa), temperature (35-75 °C), and time (2-6 h)) for selective separation of the waxes. Extracted oils and waxes were characterized through GC and DSC analyses. The melting profiles of the waxes were analyzed using the JMP_Pro_17.0 software - Functional Data Explorer platform to match the melting profiles of the industrial waxes.

At the optimized conditions (40 MPa, 75 °C, and 6 h), 92% (w/w) of crude oil was extracted, leaving behind high-purity wax powders. Functional principal component analyses indicate that the DSC curve of high-purity wax was classified with the commercial carnauba and candelilla waxes, while under other conditions, the waxes melted similarly to beeswax and paraffin waxes.