Cyclic pressurization assisted extraction of lipids from microalgae for biodiesel production: Non-equilibrium and equilibrium data

• Cyclically pressurized extraction of lipids from microalgae was investigated.
• Alkyl esters were produced from the extracted lipids.
• Equilibrium data were obtained from kinetic curves.
• The yield of lipids by cyclic pressurization extraction was up to 53% higher than that at atmospheric pressure.
• The yield of ester was ≈89% from lipids extracted with ethanol at atmospheric pressure and under cyclic pressurization.

The extraction of lipids from a microalgae (Chlorella pyrenoidosa) was experimentally investigated at a constant temperature of 30 °C with ethanol. The experiments involved a bed of dry solids loaded in a cylindrical vessel with approximately 23.5 × 10−3 kg of solvent. At the top of the cylinder there was a moving piston to allow extraction at cyclic or constant pressurization. A set of 10 kinetic extraction experiments was performed by varying the solid–liquid feed ratio at 5 levels under atmospheric pressure (91.4 kPa) and cyclic pressurization (300 s at 91.4 kPa + 300 s at 200 kPa per cycle) for 25,200 s (51 × 21 = 10). At p ⩽ 0.1 a significant statistical effect of cyclic pressurization and solid–solvent ratio on mass fraction of extracted lipid at equilibrium (yAe) was observed, while the influence of pressure at cyclic pressurization on the same response was negligible. yAe was a parameter of a reliable first-order kinetic model tuned on different extraction curves involving a full set of almost 500 experimental kinetic data. Based on these equilibrium data, the highest yield and efficiency of lipid extraction were 11.3% d.b. and 72%, respectively. The slopes of tie lines in rectangular equilibrium diagrams of Ponchon–Savarit for extraction at atmospheric pressure and cyclic pressurization confirm that lipids in microalgae are not easily removed from the insoluble solid. The fraction of microalgae lipids converted to biodiesel by an esterification reaction based on the method of Hartman and Lago was approximately 89 ± 7%.