Supercritical extraction of lignin oxidation products in a microfluidic device

• Extraction of lignin oxidation products from the reaction mixture with scCO2.
• Microfluidic device for continuous supercritical extraction at high pressures.
• Process for separation and purification of monomeric aromatic chemicals from lignin.
• Distribution ratios of the main monomers at different pressures and temperatures.

Lignin represents a promising renewable source of chemicals. Valuable aromatic monomers, such as vanillin and methyl vanillate, can be obtained through its acidic oxidation and subsequently have to be separated and purified for further usage. Extraction directly from the aqueous reaction mixture using supercritical carbon dioxide as solvent was evaluated as a possible separation step. Fast screening of different extraction conditions up to pressures of 121 bar at temperatures from 39.8 to 59.3 °C was enabled using a continuous microfluidic device. Distribution ratios of the main five monomeric products were calculated from concentration measurements. With increasing pressure and decreasing temperature higher quantities of monomers were extracted, thereby decreasing selectivity. Overall, selectivity towards specific monomers was high, especially at conditions close to the critical point of supercritical carbon dioxide, confirming the potential of this green and cheap purification method.