Influences of different co-solvents in simultaneous supercritical extraction and transesterification of Jatropha curcas L. seeds for the production of biodiesel

Simultaneous supercritical extraction and transesterification (SET) process is a novel biodiesel production process for oil seeds in which the solid oil-bearing material is used as the primary reactant together with short-chain alcohol directly in supercritical condition. In this experimental work, SET process with methanol was carried out in a high-pressure batch reactor to produce fatty acid methyl esters (FAME) from Jatropha curcas L. seeds (15.0 g feed, 300 °C, 5.0 ml/g methanol to solid ratio and 30 min). Different types of co-solvents (pentane, heptane, toluene, tetrahydrofuran, nitrogen and carbon dioxide) with varying amount (1.0–5.0 ml/g for liquid and 10–50 bar for gas) were added into the process to study their influences towards the extraction efficiency, Ey and FAME yield, Fy. It was found that pentane and CO2 provided higher responses (Ey: 102.6% and 107.0%, Fy: 100.4% and 102.3%) at concentration of 1.0 ml/g and 50 bar respectively. Addition of pentane and CO2 was also discovered to lower the critical conditions of the reactant mixture and could achieve near optimum product yield at lower temperature (280 °C) and lower methanol to solid ratio (4.0 ml/g). Addition of appropriate co-solvents could increase the extraction rate (solid–liquid) and enhance methanol–oil inter-phase miscibility during the reaction phase. This proved that SET process can be rather promising as another alternative route for biodiesel production.

► Different types of co-solvents have different ± effects on SET process.
► Longer carbon chain of heptane can increase extraction but reduce process conversion.
► High concentration of co-solvent will compete with reaction and dilute reactants.
► Co-solvent acts as extraction reagent before turning into reaction promoter.
► Optimum biodiesel yield can be achieved at lower process severity with CO2 and pentane.