3.1. Squalene/FFA fractionation from neutralized model mixture Due to their inherent economical value and to the reported dif- ficulties in their fractionation [1,4–6], the two main compounds in the OODD mixture that require more intensive fractionation studies are squalene and FFA. Thus, fractionation experiments were firstly carried out using a model mixture of 50% (w/w) of squalene and oleic acid. This mixture was subjected to a reaction with choline hydrogen carbonate for 1–1.5 h at 323 K, as previously described. Gas liberation was observed immediately, confirming that neutralization of FFA was effectively taking place, since carbon dioxide is one of the by-products formed during this reaction (Fig. 1). This also allowed us to monitor the evolution of the reaction given that when it is completed the liberation of carbon dioxide would cease. The separation of squalene from the formed choline carboxylates was subsequently carried out in the extraction apparatus described before. All experiments were carried out at 313 K and pressures between 12 and 20 MPa and CO2 flow rates of 2–4 ml min1 .